JP3934800B2 - Hydrogen storage alloy and secondary battery - Google Patents
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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
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Description
【０００１】
【発明の属する技術分野】
本発明は、水素吸蔵合金およびこの水素吸蔵合金を負極に用いた二次電池に関する。
【０００２】
【従来の技術】
水素吸蔵合金は、安全、かつ容易に水素を吸蔵できることから、新しいエネルギー変換材料およびエネルギー貯蔵材料として注目されている。すなわち、水素吸蔵合金は、1)水素の貯蔵・輸送、熱の貯蔵・輸送、2)熱−機械エネルギーの変換、3)水素の分離・精製、4)水素同位体の分離、5)水素を活物質とする電池、6)合成化学における触媒、7)温度センサなど、機能性新素材として広範囲に亘る応用が進められている。
【０００３】
たとえば、水素吸蔵合金を負極材料に使用したニッケル水素二次電池は、 (a)高容量であること、 (b)過充電・過放電に強いこと、 (c)高率充放電が可能であること、 (d)クリーンであること、 (e)ニッケルカドミウム電池と互換性があること、などの特長を持つため次世代の民生用電池として注目され、また、その応用・実用化が活発に行われている。このように、水素吸蔵合金は、機械的、物理的、化学的に様々な応用の可能性を秘めているので、将来の産業におけるキー材料の一つとして挙げられる。
【０００４】
ところで、水素を吸蔵する金属としては、水素と安定な化合物を形成し得る金属、たとえばPd、Ti、Zr、 V、希土類金属元素、アルカリ土類元素などの単体、あるいはこれらの金属元素と他の金属元素との合金が挙げられる。特に、合金型の場合は、▲１▼金属−水素間の結合力を適度に弱めて、水素の吸蔵反応だけでなく離脱反応も比較的容易に行えること、▲２▼反応に必要な平衡水素圧（プラトー圧）の大きさ、平衡領域（プラトー領域）の広さ、水素を吸蔵する過程での平衡圧の変化（平坦性）など、吸蔵・放出反応が改善されること、▲３▼化学的、物理的安定性が高いことなどの特長を有する。
【０００５】
そして、このような水素吸蔵合金としては、下記のような水素吸蔵合金系が知られている。また、一応用例である電池の電極材としては、一般的に、LaNi5 もしくはMmNi5 などで示される希土類系合金が使用されている。しかし、その放電容量は理論容量の80％を超えているとはいえ、高容量化に限界がある。
【０００６】
(1 )希土類系（LaNi5 ，MmNi5 など）、
(2) ラーベス系（ ZrV2 ，ZrMn2 など）、
(3) チタン系（TiNi，TiFeなど）、
(4) マグネシウム系（Mg2 Ni，MgNi2 など）、
(5) その他（クラスター合金など）。
【０００７】
【発明が解決しようとする課題】
マグネシウム元素でランタン元素成分の一部を置換したマグネシウム−希土類系合金は、水素ガスを多量に吸蔵できるという特長を有するが、たとえばLa1-x Mgx Ni2 は、水素との結合の安定性が高く水素放出速度が遅いので、水素電極としての機能に問題がある。すなわち、マグネシウム−希土類系合金の場合は、理論的な気相中での水素吸蔵量は多いものの水素放出性が劣っているため、常温時において、アルカリ電解液中で電池電極としてほとんど作用しないので、水素負極の構成に使用できない。
【０００８】
また、最近、PuNi3 型を有するMg2 LaNi9 で表されるマグネシウム−希土類系合金も報告されているが、その水素吸・脱蔵特性は著しく低いものである。
【０００９】
本発明は、上記事情に対処してなされたもので、マグネシウム−希土類系の水素吸蔵合金において、多量の水素吸蔵能力を有する一方、吸蔵した水素の離脱性ないし放出性を大幅に改善した水素吸蔵合金の提供を目的とする。
【００１０】
また、この水素吸蔵・放出性のすぐれた水素吸蔵合金を負極に応用することにより、高容量で充放電サイクルのすぐれた金属酸化物・水素二次電池を提供することを目的とする。
【００１１】
【課題を解決するための手段】
請求項１の発明は、一般式Ｍｇa Ｒ1-a-b Ｔb （Ｎｉ1-x Ｍx ）z
（式中、ＲはＹを含む希土類元素から選ばれた少なくとも１種の元素、ＴはＣａ、Ｔｉ、ＺｒおよびＨｆから選ばれた少なくとも１種の元素、ＭはＣｏ、Ｍｎ、Ｆｅ、Ａｌ、Ｇａ、Ｚｎ、Ｃ、Ｓｎ、Ｃｕ、Ｓｉ、Ｂ、Ｎｂ、Ｗ、Ｍｏ、Ｖ、Ｃｒ、Ｔａ、ＰおよびＳから選ばれた少なくとも１種の元素、０．２≦ａ≦０．３５、０≦ｂ≦０．３、０＜ｘ≦０．６、３≦ｚ≦３．８）で表される組成（原子比）を有し、かつラーベス相をＡ、ＣａＣｕ ５ 型構造をＢとするＡおよびＢサブセルの積み重ねによって構成されているユニットセル層が、２種以上の周期構造で平行連晶構造を形成しており、この周期構造を示す積層部分が５ｎｍ〜１μｍのユニット層から形成されている前記平行連晶構造を含有する結晶粒が存在していることを特徴とする水素吸蔵合金である。
【００１４】
請求項１の発明において、一般式Ｍｇａ Ｒ１−ａ−ｂＴｂ（Ｎｉ１−ｘＭｘ）ｚで表される組成において、Mgの組成比 (a)、(Mg+R+T)と(Ni+M)との比 (z)は、上記範囲内で選ばれる必要がある。すなわち、Mgの組成比 (a)、(Mg+R+T)と(Ni+M)との比 (z)を上記範囲内に選択することにより、合金主相中に平行連晶が形成され、この平行連晶の形成に伴って高い水素吸蔵量を有しつつ、一方では水素を放出し易くなり、大きな放電容量を有する金属酸化物・水素二次電池を実現できる水素吸蔵合金が得られるからである。
【００１５】
また、Ｒで表される Yを含む希土類元素から選ばれた少なくとも１種の元素は、水素吸蔵合金の低コスト化を考慮すると、好ましくはLa、Ce、Pr、Ndおよび Yであり、より好ましくは希土類元素の混合系であるミッシュメタルで、CeがリッチなミッシュメタルやLaがリッチなミッシュメタルを使用することもできる。
【００１６】
さらに、Ｔで表されるＣａ、Ｔｉ、ＺｒおよびＨｆから選ばれた少なくとも１種の元素は、いわゆる置換成分であり、この置換成分によって水素吸蔵量を低減させずに、水素の放出性の改善・向上や水素の放出に伴う合金の微細化を抑制するための成分である。ここで、置換量（ｂ）が０．３を超えると、水素の放出性の改善・向上および水素の放出に伴う合金の微細化抑制が図られないので、０．３以下に限定される。そして、この置換量（ｂ）の少ない方が、長いサイクル寿命化を得られる傾向にあるので０．２以下が好ましい。
【００１７】
さらにまた、Ｍで表されるCo、Mn、Fe、Al、Ga、Zn、 C、Sn、Cu、Si、 B、Nb、 W、Mo、 V、Cr、Ta、 Pおよび Sから選ばれた少なくとも１種の元素も、Ni成分に対する置換成分であり、この置換成分は水素の吸蔵・放出特性の向上に寄与する。ここで、Ｍで表される置換成分による置換で、合金内に侵入する水素の拡散や、水素の吸蔵・放出が容易になるものと推定され、二次電池の負極材に使用した場合は、飛躍的にすぐれた充放電サイクル特性を呈する。なお、その置換量 (x)が 0.6を超えると放電容量の低下を招来するので、常に、 0.6以下の範囲内、好ましくは0.02〜 0.3の範囲内で選ばれる。
【００１８】
請求項１の発明に係る水素吸蔵合金は、たとえば N、 O、 Fなどの不純物を水素吸蔵合金の特性を損なわない範囲、たとえば重量比でそれぞれ1％以下の範囲で含有していてもよい。
【００１９】
請求項１の発明に係る水素吸蔵合金は、たとえば次のようにして製造できる。すなわち、各原料元素成分を秤量し、アルゴンガスなどの不活性雰囲気下で、単ロール法もしくは双ロール法などの溶湯急冷法により、所要の水素吸蔵合金を製造できる。ここで、溶湯の急冷速度（冷却速度）は1000℃／s 未満、好ましくは 800℃／s 未満、より好ましくは 700℃／s 未満である。
【００２０】
なお、上記溶湯急冷法の代りに、不活性雰囲気下で秤量した各原料元素成分を高周波誘導溶解した後、金型などに鋳造して合金インゴットを得、これを急冷する方式を採ってもよい。または、 RNi5 系、 R2 Ni7 系、 RNi3 系、 RNi2 系、Ni2 Mg系、MgNi2 系などの母合金を高周波誘導溶解にて製造した後、これらの母合金を所要の組成となるように秤量し、再び高周波誘導溶解後、鋳造して合金インゴットを得、これを急冷する方式を採ってもよい。
【００２１】
次いで、前記製造した合金を真空中もしくは不活性雰囲気中、３００℃以上８５０℃未満の温度、好ましくは４００℃以上８００℃未満の温度で、５０〜８００時間、さらに好ましくは２００〜６００時間の比較的長時間の熱処理を施すことにより、水素吸蔵・放出速度などの特性がすぐれた水素吸蔵合金を得ることができる。なお、熱処理温度が８５０℃を超えると、水素吸蔵特性の低下を招来する恐れがある。
【００２２】
請求項１の発明において、合金中の“平行連晶”とは、六方晶のａ軸の長さがほぼ同じで、ｃ軸の長さが異なるような２種類以上のユニットセル層の積み重ね（積層）で形成されたものである。すなわち、この発明に係る水素吸蔵合金系におけるユニットセル層は、ラーベス相をＡ、CaCu5 型構造をＢとすると、ＡおよびＢサブセルの積み重ね（Ａm Ｂn ：m ，n は１以上の整数）によって構成されている。
【００２３】
したがって、たとえばLa2 Ni7 型（ABB)の周期構造を示す積層（ユニットセル層）部分中に、長さが10nm以内であるLaNi3 型(AB)もしくはLa5 Ni19(ABBB)などのユニットセル層の積層から成る周期構造を含む平行連晶を形成することが可能である。そして、前記平行連晶の形成により、水素吸蔵・放出に対する合金自体の耐久性が向上し、二次電池の電極材としたときには、サイクル特性が向上する。 なお、合金中の“平行連晶”は、透過型電子顕微鏡を用いて倍率１万〜50万倍で、結晶粒の（1,1,0)面における透過電子顕微鏡像を撮影することにより観察できる。
【００２４】
また、周期構造を示す積層部分の平均長さが 5nm〜 1μm の場合、水素の吸蔵・放出特性が改善され、放電容量の大きい金属酸化物・水素二次電池の提供に寄与する。ここで、水素吸蔵合金の組成系によって差異もあるが、一般的に、周期構造を示す積層部分の平均長さは、好ましくは10nm〜 500nm、より好ましくは20nm〜 200nmの場合、水素の吸蔵・放出特性がさらに改善され、放電容量およびサイクル特性のすぐれた金属酸化物・水素二次電池の提供が可能になる。
【００２５】
なお、周期構造の積層部分の平均長さは、透過型電子顕微鏡を用い倍率40万倍で、結晶粒の（1,1,0)面 100nm× 100nmの透過電子顕微鏡像を計20か所撮影し、周期構造を形成する積層部分の長の平均値である。
【００２６】
請求項２の発明は、水素吸蔵合金を主成分として成る水素負極と、正極と、水素負極および正極を隔絶するセパレータと、アルカリ性電解液とを有する二次電池であって、水素負極が請求項１に記載された水素吸蔵合金を含有していることを特徴とする二次電池である。
【００２７】
すなわち、請求項２の発明は、上記請求項１の発明に係る水素吸蔵合金が、水素吸蔵・放出特性にすぐれていること、充放電サイクル特性も改善・向上していることに着目したものである。そして、水素負極の構成材に、前記水素吸蔵合金を使用することにより、大きな放電容量を有するとともに、サイクル特性のすぐれた金属酸化物・水素二次電池を提供することを骨子としている。
【００２８】
【発明の実施の形態】
以下に実施例を説明する。
【００２９】
【表１】
【００３０】
前記各合金薄片に、アルゴンガス雰囲気下で 700℃， 200時間それぞれ熱処理を施して、対応する水素吸蔵合金を製造した。なお、表１中、LmはLa＝90重量％，Ce＝ 2重量％，Pr＝ 5重量％，Nd＝ 3重量％から成るミッシュメタルであり、また、MmはLa＝35重量％，Ce＝50.3重量％，Pr＝ 5.5重量％，Nd＝ 9重量％，Sm＝ 0.2重量％から成るミッシュメタルである。
【００３１】
また、比較例として、表１に示す水素吸蔵合金の組成を成すように各元素成分をそれぞれ秤量し、アルゴンガス雰囲気下で高周波溶解した後、1000℃／s の急冷速度（比較例１，２）もしくは3000℃／s （比較例３，４，５）で、それぞれ銅製単ロールの表面に滴下・冷却して合金薄片を作製した。次いで、各合金薄片に、アルゴンガス雰囲気下で 950℃， 3時間（比較例１，２）もしくは 850℃， 4時間（比較例３，４，５）それぞれ熱処理を施して、対応する５種類の水素吸蔵合金を製造した。
【００３２】
上記水素吸蔵合金について、透過型電子顕微鏡を用い40万倍の倍率で、結晶粒の (1,0,0)面の透過型電子顕微鏡像を20か所撮像し、周期構造を有する積層部分の長さの平均値、すなわち、La2 Ni7 型を有する領域の厚さを平均した値を表１に併せて示す。
【００３３】
上記で得た実施例および比較例に係る各水素吸蔵合金をそれぞれ粉砕し、粒度 100μm 以下の水素吸蔵合金粉末を作製した。これら各水素吸蔵合金粉末と電解銅粉とを重量比 1： 2の割合でそれぞれ混合し、この混合体 1 gを10 ton／cm2 の圧力で 5分間加圧して、直径10mmのペレットをそれぞれ作製した。これらペレットをニッケルメッシュでそれぞれ挟み込み、周縁部をスポット溶接して圧接し、さらに、ニッケルリード線をスポット溶接して、水素吸蔵合金電極（負極）をそれぞれ作製した。
【００３４】
上記作製した負極を焼結式ニッケル電極（正極）とともに、それぞれ濃度 8規定の水酸化カリウム水溶液に浸漬・配置し、35℃の温度下で充放電サイクル試験を行った。すなわち、負極中の水素吸蔵合金 1 g当たり 100mAの電流で 5時間充電した後、10分間休止、負極中の水素吸蔵合金 1 g当たり 100mAの電流で酸化水銀電極に対して−0.75 Vに成るまで放電を行うサイクルを繰り返し、最大放電容量およびサイクル寿命（放電容量が最大放電容量の80％まで低下したときのサイクル数）をそれぞれ測定した。この測定結果を表２にそれぞれ示す。
【００３５】
【表２】
【００３６】
【発明の効果】
請求項１の発明によれば、従来のマグネシウム−希土類系水素吸蔵合金に比べて、高い水素吸蔵容量性を損なわずに、吸蔵・放出特性の向上されたマグネシウム−希土類系水素吸蔵合金を提供できる。したがって、たとえば水素の貯蔵・輸送、熱の貯蔵・輸送、熱−機械エネルギーの変換、水素の分離・精製、水素同位体の分離、水素を活物質とする電池、合成化学における触媒、温度センサなど、水素吸蔵合金の応用分野の拡充、さらには、新規な応用分野の開拓も図られる。
【００３７】
請求項２の発明によれば、高い水素吸蔵容量性および吸蔵・放出特性を兼ね備えた水素吸蔵合金を利用（応用）したことにより、放電容量が大きくてサイクル特性もすぐれた金属酸化物・水素二次電池が提供される。
【００３８】[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydrogen storage alloy and a secondary battery using the hydrogen storage alloy for a negative electrode.
[0002]
[Prior art]
Hydrogen storage alloys are attracting attention as new energy conversion materials and energy storage materials because they can store hydrogen safely and easily. That is, hydrogen storage alloys are: 1) hydrogen storage / transport, heat storage / transport, 2) thermal-mechanical energy conversion, 3) hydrogen separation / purification, 4) hydrogen isotope separation, 5) hydrogen A wide range of applications such as batteries as active materials, 6) catalysts in synthetic chemistry, and 7) temperature sensors are being developed as functional new materials.
[0003]
For example, a nickel metal hydride secondary battery using a hydrogen storage alloy as a negative electrode material can be (a) high capacity, (b) strong against overcharge / overdischarge, and (c) high rate charge / discharge. (D) cleanliness, (e) compatibility with nickel cadmium batteries, and so on, and has attracted attention as a next-generation consumer battery. It has been broken. As described above, the hydrogen storage alloy has a variety of mechanical, physical, and chemical applications, and is therefore one of key materials in future industries.
[0004]
By the way, as a metal that absorbs hydrogen, a metal that can form a stable compound with hydrogen, for example, Pd, Ti, Zr, V, a rare earth metal element, an alkaline earth element or the like, or these metal elements and other metals. Examples include alloys with metal elements. In particular, in the case of the alloy type, (1) the ability to moderately weaken the bonding force between metal and hydrogen and perform not only the hydrogen occlusion reaction but also the separation reaction, and (2) the equilibrium hydrogen required for the reaction. The occlusion / release reaction is improved, such as the size of the pressure (plateau pressure), the width of the equilibrium region (plateau region), and the change in equilibrium pressure (flatness) during the process of occluding hydrogen, (3) chemistry Features such as high mechanical and physical stability.
[0005]
The following hydrogen storage alloy systems are known as such hydrogen storage alloys. Further, as an electrode material of a battery which is an application example, a rare earth alloy represented by LaNi 5 or MmNi 5 is generally used. However, although the discharge capacity exceeds 80% of the theoretical capacity, there is a limit to increasing the capacity.
[0006]
(1) Rare earths (LaNi 5 , MmNi 5 etc.),
(2) Laves system (ZrV 2 , ZrMn 2 etc.),
(3) Titanium (TiNi, TiFe, etc.),
(4) Magnesium (Mg 2 Ni, MgNi 2 etc.),
(5) Others (such as cluster alloys).
[0007]
[Problems to be solved by the invention]
Magnesium-rare earth alloys in which a part of the lanthanum element component is replaced with magnesium element have the feature that a large amount of hydrogen gas can be occluded. For example, La 1-x Mg x Ni 2 is stable in hydrogen bonding. Is high and the hydrogen release rate is slow, there is a problem in the function as a hydrogen electrode. That is, in the case of a magnesium-rare earth alloy, the hydrogen storage capacity in the gas phase is large, but the hydrogen releasing property is inferior, so that it hardly acts as a battery electrode in an alkaline electrolyte at room temperature. It cannot be used for the construction of a hydrogen negative electrode.
[0008]
Recently, a magnesium-rare earth alloy represented by Mg 2 LaNi 9 having PuNi 3 type has also been reported, but its hydrogen absorption / desorption characteristics are extremely low.
[0009]
The present invention has been made in view of the above circumstances, and in a magnesium-rare earth-based hydrogen storage alloy, it has a large amount of hydrogen storage capability, while significantly improving the ability to desorb or release stored hydrogen. The purpose is to provide alloys.
[0010]
Another object of the present invention is to provide a metal oxide / hydrogen secondary battery having a high capacity and an excellent charge / discharge cycle by applying the hydrogen storage alloy having excellent hydrogen storage / release properties to the negative electrode.
[0011]
[Means for Solving the Problems]
The invention of claim 1 has the general formula Mg a R 1-ab T b (Ni 1-x M x ) z
(Wherein R is at least one element selected from rare earth elements including Y, T is at least one element selected from Ca, Ti, Zr and Hf, M is Co, Mn, Fe, Al, At least one element selected from Ga, Zn, C, Sn, Cu, Si, B, Nb, W, Mo, V, Cr, Ta, P and S, 0.2 ≦ a ≦ 0.35, 0 ≦ b ≦ 0.3, 0 <has a composition represented by x ≦ 0.6,3 ≦ z ≦ 3.8) ( atomic ratio), and the Laves phase a, the CaCu 5 type structure B The unit cell layer formed by stacking the A and B subcells forms a parallel continuous crystal structure with two or more types of periodic structures, and the laminated portion showing this periodic structure is formed from a unit layer of 5 nm to 1 μm. and wherein the crystal grains are present containing said parallel intergrowth structure has It is that the hydrogen-absorbing alloy.
[0014]
In the invention of claim 1 , the general formula Mg a In the composition represented by R 1-a-b T b (Ni 1-x M x) z, the composition ratio of Mg (a), the ratio of (Mg + R + T) and the (Ni + M) (z ) Must be selected within the above range. That is, by selecting the Mg composition ratio (a) and the ratio (z) of (Mg + R + T) and (Ni + M) within the above range, parallel intergrowth is formed in the alloy main phase. As a result of the formation of the parallel intergrowth, a hydrogen storage alloy that has a high hydrogen storage capacity and on the other hand, easily releases hydrogen and can realize a metal oxide / hydrogen secondary battery having a large discharge capacity can be obtained. Because.
[0015]
In addition, the at least one element selected from rare earth elements including Y represented by R is preferably La, Ce, Pr, Nd and Y, more preferably considering the cost reduction of the hydrogen storage alloy. Is a misch metal that is a mixed system of rare earth elements, and it is also possible to use a misch metal rich in Ce or a misch metal rich in La.
[0016]
Furthermore, at least one element selected from Ca, Ti, Zr and Hf represented by T is a so-called substitution component, and the hydrogen release performance is improved without reducing the hydrogen storage amount by this substitution component. -It is a component for suppressing refinement of the alloy due to improvement and release of hydrogen. Here, if the substitution amount (b) exceeds 0.3, the improvement and improvement of hydrogen release properties and the suppression of the refinement of the alloy accompanying the hydrogen release cannot be achieved, so the amount is limited to 0.3 or less. And since the one where this substitution amount (b) is small tends to obtain a long cycle life, 0.2 or less is preferable.
[0017]
Furthermore, at least selected from Co, Mn, Fe, Al, Ga, Zn, C, Sn, Cu, Si, B, Nb, W, Mo, V, Cr, Ta, P and S represented by M One kind of element is also a substitute component for the Ni component, and this substitute component contributes to the improvement of the hydrogen storage / release characteristics. Here, it is presumed that the substitution with the substitution component represented by M facilitates the diffusion of hydrogen that penetrates into the alloy and the storage and release of hydrogen, and when used for the negative electrode material of a secondary battery, It exhibits dramatically improved charge / discharge cycle characteristics. Note that, when the substitution amount (x) exceeds 0.6, the discharge capacity is reduced, so that it is always selected within the range of 0.6 or less, preferably within the range of 0.02 to 0.3.
[0018]
The hydrogen storage alloy according to the invention of claim 1 may contain impurities such as N, O, and F in a range that does not impair the characteristics of the hydrogen storage alloy, for example, in a range of 1% or less by weight.
[0019]
The hydrogen storage alloy according to the invention of claim 1 can be manufactured, for example, as follows. That is, a required hydrogen storage alloy can be manufactured by weighing each raw material element component and performing a molten metal quenching method such as a single roll method or a twin roll method in an inert atmosphere such as argon gas. Here, the rapid cooling rate (cooling rate) of the molten metal is less than 1000 ° C./s, preferably less than 800 ° C./s, more preferably less than 700 ° C./s.
[0020]
Instead of the molten metal quenching method, each raw material element component weighed in an inert atmosphere may be induction-melted at high frequency, and then cast into a mold or the like to obtain an alloy ingot, which may be rapidly cooled. . Or, RNi 5 system, R 2 Ni 7 type, RNi 3 system, RNi 2 system, Ni 2 Mg system, after the production of the master alloy in an induction dissolution of such MgNi 2 system, the composition of these mother alloys of the required It is possible to adopt a method of weighing so as to be, and after high frequency induction melting again, casting to obtain an alloy ingot and rapidly cooling it.
[0021]
Next, the produced alloy is heated in a vacuum or in an inert atmosphere at a temperature of 300 ° C. or higher and lower than 850 ° C., preferably 400 ° C. or higher and lower than 800 ° C., for 50 to 800 hours, more preferably 200 to 600 hours. By performing heat treatment for a relatively long time, a hydrogen storage alloy having excellent characteristics such as hydrogen storage / release rate can be obtained. In addition, when heat processing temperature exceeds 850 degreeC, there exists a possibility of causing the fall of a hydrogen storage characteristic.
[0022]
In the invention of claim 1 , the “parallel intergrowth” in the alloy is a stack of two or more unit cell layers in which hexagonal a-axis lengths are substantially the same and c-axis lengths are different ( Layered). That is, the unit cell layer in the hydrogen storage alloy system according to the present invention is formed by stacking A and B subcells (Am Bn: m, n is an integer of 1 or more), where the Laves phase is A and the CaCu 5 type structure is B. It is configured.
[0023]
Therefore, for example, a unit such as LaNi 3 type (AB) or La 5 Ni 19 (ABBB) having a length of 10 nm or less in a laminated (unit cell layer) portion showing a periodic structure of La 2 Ni 7 type (ABB) It is possible to form a parallel continuous crystal including a periodic structure including a stack of cell layers. The formation of the parallel continuous crystals improves the durability of the alloy itself against hydrogen storage / release, and improves the cycle characteristics when used as an electrode material for a secondary battery. In addition, "parallel intergrowth" in the alloy is observed by taking a transmission electron microscope image on the (1,1,0) plane of the crystal grain at a magnification of 10,000 to 500,000 times using a transmission electron microscope. it can.
[0024]
In addition, when the average length of the laminated portion having a periodic structure is 5 nm to 1 μm, the hydrogen storage / release characteristics are improved, which contributes to the provision of a metal oxide / hydrogen secondary battery having a large discharge capacity. Here, although there is a difference depending on the composition system of the hydrogen storage alloy, generally, the average length of the laminated portion showing the periodic structure is preferably 10 nm to 500 nm, more preferably 20 nm to 200 nm. The emission characteristics are further improved, and a metal oxide / hydrogen secondary battery with excellent discharge capacity and cycle characteristics can be provided.
[0025]
The average length of the layered portion of the periodic structure was measured with a transmission electron microscope at a magnification of 400,000, and a total of 20 transmission electron microscope images (100 nm x 100 nm) of the (1,1,0) plane of the crystal grains were taken. And the average value of the lengths of the laminated portions forming the periodic structure.
[0026]
The invention of claim 2 is a secondary battery comprising a hydrogen negative electrode composed mainly of a hydrogen storage alloy, a positive electrode, a separator separating the hydrogen negative electrode and the positive electrode, and an alkaline electrolyte, wherein the hydrogen negative electrode is claimed. 1. A secondary battery comprising the hydrogen storage alloy according to 1 .
[0027]
That is, the invention of claim 2 pays attention to the fact that the hydrogen storage alloy according to the invention of claim 1 is excellent in hydrogen storage / release characteristics and has improved / improved charge / discharge cycle characteristics. is there. The main point is to provide a metal oxide / hydrogen secondary battery having a large discharge capacity and excellent cycle characteristics by using the hydrogen storage alloy as a constituent material of the hydrogen negative electrode.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Examples will be described below.
[0029]
[Table 1]
[0030]
Each alloy flake was heat-treated at 700 ° C. for 200 hours in an argon gas atmosphere to produce a corresponding hydrogen storage alloy. In Table 1, Lm is a misch metal composed of La = 90 wt%, Ce = 2 wt%, Pr = 5 wt%, Nd = 3 wt%, and Mm is La = 35 wt%, Ce = It is a misch metal consisting of 50.3 wt%, Pr = 5.5 wt%, Nd = 9 wt%, Sm = 0.2 wt%.
[0031]
As a comparative example, each elemental component was weighed so as to form the composition of the hydrogen storage alloy shown in Table 1, and after high-frequency dissolution in an argon gas atmosphere, a rapid cooling rate of 1000 ° C./s (Comparative Examples 1 and 2) ) Or 3000 ° C./s (Comparative Examples 3, 4, and 5), each was dropped and cooled on the surface of a single copper roll to produce alloy flakes. Each alloy flake was then heat-treated in an argon gas atmosphere at 950 ° C. for 3 hours (Comparative Examples 1 and 2) or 850 ° C. for 4 hours (Comparative Examples 3, 4, and 5), respectively. A hydrogen storage alloy was produced.
[0032]
About the hydrogen storage alloy, 20 transmission electron microscope images of the (1,0,0) plane of the crystal grains were taken at a magnification of 400,000 using a transmission electron microscope, and the laminated part having the periodic structure was imaged. Table 1 also shows average values of the lengths, that is, values obtained by averaging the thicknesses of the regions having the La 2 Ni 7 type.
[0033]
Each of the hydrogen storage alloys according to Examples and Comparative Examples obtained above was pulverized to produce hydrogen storage alloy powder having a particle size of 100 μm or less. Each of these hydrogen storage alloy powders and electrolytic copper powders were mixed at a weight ratio of 1: 2, and 1 g of this mixture was pressed at a pressure of 10 ton / cm 2 for 5 minutes to obtain 10 mm diameter pellets. Produced. Each of these pellets was sandwiched between nickel meshes, spot welded at the peripheral edge, and further spot welded with nickel lead wires to prepare hydrogen storage alloy electrodes (negative electrodes).
[0034]
The prepared negative electrode was immersed and placed in a potassium hydroxide aqueous solution having a concentration of 8 N together with a sintered nickel electrode (positive electrode), and a charge / discharge cycle test was conducted at a temperature of 35 ° C. That is, after charging for 5 hours at a current of 100 mA per gram of hydrogen storage alloy in the negative electrode, pause for 10 minutes, until it reaches −0.75 V against the mercury oxide electrode at a current of 100 mA per gram of hydrogen storage alloy in the negative electrode. The discharge cycle was repeated, and the maximum discharge capacity and cycle life (number of cycles when the discharge capacity was reduced to 80% of the maximum discharge capacity) were measured. The measurement results are shown in Table 2, respectively.
[0035]
[Table 2]
[0036]
【The invention's effect】
According to the invention of claim 1 , it is possible to provide a magnesium-rare earth hydrogen storage alloy having improved storage / release characteristics without impairing high hydrogen storage capacity as compared with the conventional magnesium-rare earth hydrogen storage alloy. . Thus, for example, hydrogen storage / transport, heat storage / transport, thermal-mechanical energy conversion, hydrogen separation / purification, hydrogen isotope separation, hydrogen-based batteries, catalysts in synthetic chemistry, temperature sensors, etc. In addition, the application fields of hydrogen storage alloys will be expanded and new application fields will be developed.
[0037]
According to the invention of claim 2 , by using (applying) a hydrogen storage alloy having high hydrogen storage capacity and storage / release characteristics, the metal oxide / hydrogen dioxide having a large discharge capacity and excellent cycle characteristics. A secondary battery is provided.
[0038]
Claims (2)
ＭｇａＲ１−ａ−ｂＴｂ（Ｎｉ１−ｘＭｘ）ｚ
（式中、ＲはＹを含む希土類元素から選ばれた少なくとも１種の元素、ＴはＣａ、Ｔｉ、ＺｒおよびＨｆから選ばれた少なくとも１種の元素、ＭはＣｏ、Ｍｎ、Ｆｅ、Ａｌ、Ｇａ、Ｚｎ、Ｃ、Ｓｎ、Ｃｕ、Ｓｉ、Ｂ、Ｎｂ、Ｗ、Ｍｏ、Ｖ、Ｃｒ、Ｔａ、ＰおよびＳから選ばれた少なくとも１種の元素、０．２≦ａ≦０．３５、０≦ｂ≦０．３、０＜ｘ≦０．６、３≦ｚ≦３．８）で表される組成（原子比）を有し、かつラーベス相をＡ、ＣａＣｕ ５ 型構造をＢとするＡおよびＢサブセルの積み重ねによって構成されているユニットセル層が、２種以上の周期構造で平行連晶構造を形成しており、この周期構造を示す積層部分が５ｎｍ〜１μｍのユニット層から形成されている前記平行連晶構造を含有する結晶粒が存在していることを特徴とする水素吸蔵合金。General formula Mg a R 1-ab Tb (Ni 1-x M x ) z
(Wherein R is at least one element selected from rare earth elements including Y, T is at least one element selected from Ca, Ti, Zr and Hf, M is Co, Mn, Fe, Al, At least one element selected from Ga, Zn, C, Sn, Cu, Si, B, Nb, W, Mo, V, Cr, Ta, P and S, 0.2 ≦ a ≦ 0.35, 0 ≦ b ≦ 0.3, 0 <has a composition represented by x ≦ 0.6,3 ≦ z ≦ 3.8) ( atomic ratio), and the Laves phase a, the CaCu 5 type structure B The unit cell layer formed by stacking the A and B subcells forms a parallel continuous crystal structure with two or more types of periodic structures, and the laminated portion showing this periodic structure is formed from a unit layer of 5 nm to 1 μm. and wherein the crystal grains are present containing said parallel intergrowth structure has That the hydrogen-absorbing alloy.
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| JP23917998A JP3934800B2 (en) | 1998-08-25 | 1998-08-25 | Hydrogen storage alloy and secondary battery |
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| JP23917998A JP3934800B2 (en) | 1998-08-25 | 1998-08-25 | Hydrogen storage alloy and secondary battery |
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| JP3934800B2 true JP3934800B2 (en) | 2007-06-20 |
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| KR100496316B1 (en) * | 1999-12-27 | 2005-06-20 | 가부시끼가이샤 도시바 | Alloy for hydrogen storage, secondary battery, hybrid car and electric vehicle |
| JP2001291511A (en) * | 2000-04-07 | 2001-10-19 | Toshiba Corp | Hydrogen storage alloy electrode, secondary battery, hybrid car and electric vehicle |
| JP2001307720A (en) * | 2000-04-21 | 2001-11-02 | Toshiba Corp | Hydrogen storage alloy electrode, secondary battery, hybrid car, and electric vehicle |
| JP2004319429A (en) * | 2003-03-31 | 2004-11-11 | Sanyo Electric Co Ltd | Nickel-hydrogen storage battery |
| JP4587734B2 (en) | 2004-07-30 | 2010-11-24 | 三洋電機株式会社 | Hydrogen storage alloy electrode and secondary battery using the electrode |
| JP4566025B2 (en) | 2005-02-28 | 2010-10-20 | 三洋電機株式会社 | Alkaline storage battery |
| JP2006278189A (en) * | 2005-03-30 | 2006-10-12 | Sanyo Electric Co Ltd | Hydrogen storage alloy for alkaline storage battery and nickel hydrogen battery |
| JP2007254782A (en) * | 2006-03-22 | 2007-10-04 | Sanyo Electric Co Ltd | Hydrogen storage alloy for alkaline storage battery, and alkaline storage battery |
| CN101501896B (en) | 2006-08-09 | 2011-05-04 | 株式会社杰士汤浅国际 | Hydrogen storage alloy, hydrogen storage alloy electrode, secondary battery, and method for producing hydrogen storage alloy |
| JP2008218070A (en) * | 2007-03-01 | 2008-09-18 | Sanyo Electric Co Ltd | Hydrogen storage alloy for alkaline storage battery and alkaline storage battery |
| JP5481803B2 (en) * | 2008-05-02 | 2014-04-23 | 株式会社Ｇｓユアサ | Nickel metal hydride storage battery |
| JP2011127177A (en) * | 2009-12-17 | 2011-06-30 | Sanyo Electric Co Ltd | Hydrogen storage alloy, method for producing the same, and alkali storage battery |
| US9972837B2 (en) * | 2014-05-14 | 2018-05-15 | Basf Corporation | Hydrogen storage multi-phase alloys |
| CN105220015A (en) * | 2015-09-16 | 2016-01-06 | 江西稀有稀土金属钨业集团有限公司 | A kind of heavy body is containing magnesium rare earth hydrogen storage alloy and preparation method thereof |
| CN114672740B (en) * | 2022-03-31 | 2023-06-02 | 包头稀土研究院 | Yttrium-iron-based hydrogen storage alloy, battery and preparation method |
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