JPH0963581A - Surface treatment method for hydrogen storage alloy powder and alkaline secondary battery obtained by applying this method - Google Patents

Surface treatment method for hydrogen storage alloy powder and alkaline secondary battery obtained by applying this method

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Publication number
JPH0963581A
JPH0963581A JP7222115A JP22211595A JPH0963581A JP H0963581 A JPH0963581 A JP H0963581A JP 7222115 A JP7222115 A JP 7222115A JP 22211595 A JP22211595 A JP 22211595A JP H0963581 A JPH0963581 A JP H0963581A
Authority
JP
Japan
Prior art keywords
alloy powder
hydrogen storage
storage alloy
aqueous solution
hydrogen
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
JP7222115A
Other languages
Japanese (ja)
Other versions
JP2978094B2 (en
Inventor
Takeshi Nishimura
健 西村
Haruo Sawa
春夫 澤
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Furukawa Electric Co Ltd
Furukawa Battery Co Ltd
Original Assignee
Furukawa Electric Co Ltd
Furukawa Battery Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Furukawa Electric Co Ltd, Furukawa Battery Co Ltd filed Critical Furukawa Electric Co Ltd
Priority to JP7222115A priority Critical patent/JP2978094B2/en
Publication of JPH0963581A publication Critical patent/JPH0963581A/en
Application granted granted Critical
Publication of JP2978094B2 publication Critical patent/JP2978094B2/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • 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

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  • Secondary Cells (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

PROBLEM TO BE SOLVED: To provide a surface treatment method capable of enhancing corrosion resistance to high concentration alkaline electrolyte for hydrogen storage alloy powder which is a negative electrode material of a nickel - hydrogen secondary battery, and provide an alkaline secondary battery with excellent high rate discharge characteristics at low temperature and long cycle life by applying this method. SOLUTION: A surface treatment method is that hydrogen storage alloy powder containing a rear earth element or a hydrogen storage alloy electrode supporting this hydrogen storage alloy powder as the main component is brought into contact with alkaline aqueous solution to increase the specific surface area of the hydrogen storage alloy powder, then brought into contact with acidic aqueous solution having a pH of 3-6 and containing fluorine ions to perform fluoridation treatment on the surface of the hydrogen storage alloy powder whose specific surface area is increased. An alkaline secondary battery using the hydrogen storage alloy electrode manufactured by applying this method as a negative electrode is obtained.

Description

【発明の詳細な説明】Detailed Description of the Invention

【０００１】[0001]

【発明の属する技術分野】本発明は水素吸蔵合金粉末の
比表面積を増加させ、かつ耐食性を高めることができる
表面処理方法と、その方法を適用して製造された水素吸
蔵合金電極が負極として組み込まれているアルカリ二次
電池に関し、更に詳しくは、処理後の水素吸蔵合金粉末
が担持されている電極を負極として組み込んでニッケル
・水素二次電池のようなアルカリ二次電池を組み立てた
ときに、当該電池の低温下における高率放電特性とサイ
クル寿命特性を向上させることができる水素吸蔵合金粉
末の表面処理方法と得られた合金粉末を用いて製造され
たアルカリ二次電池に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method capable of increasing the specific surface area of hydrogen storage alloy powder and enhancing corrosion resistance, and a hydrogen storage alloy electrode manufactured by applying the method as a negative electrode. With regard to the alkaline secondary battery, more specifically, when an electrode carrying the treated hydrogen storage alloy powder is incorporated as a negative electrode and an alkaline secondary battery such as a nickel-hydrogen secondary battery is assembled, The present invention relates to a surface treatment method of a hydrogen storage alloy powder capable of improving high rate discharge characteristics and cycle life characteristics of the battery at low temperature, and an alkaline secondary battery manufactured using the obtained alloy powder.

【０００２】[0002]

【従来の技術】最近、高容量のアルカリ二次電池とし
て、ニッケル・水素二次電池が注目を集めている。この
ニッケル・水素二次電池は水素を負極活物質として作動
するものであり、充放電動作に伴っ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の粉末を集電体
に担持して成る負極（水素吸蔵合金電極）と、正極活物
質として動作する水酸化ニッケルの粉末を同じく集電体
に担持して成る正極（ニッケル極）と、電気絶縁性でか
つ通液性を備えたセパレータとを重ね合わせて発電要素
を形成し、この発電要素を導電性の缶体の中に収容し、
更に缶体の中に所定のアルカリ電解液を注液したのち全
体を密封構造にして組み立てられる。2. Description of the Related Art Recently, nickel-hydrogen secondary batteries have been attracting attention as high-capacity alkaline secondary batteries. This nickel-hydrogen secondary battery operates by using hydrogen as a negative electrode active material, and has a current collector carrying powder of a hydrogen storage alloy capable of reversibly storing and releasing hydrogen during charge / discharge operation. And a negative electrode (hydrogen storage alloy electrode) that is formed of, and a positive electrode (nickel electrode) that also supports nickel hydroxide powder that operates as a positive electrode active material on a current collector, and is electrically insulating and liquid-permeable. A power generating element is formed by stacking it with a separator, and the power generating element is housed in a conductive can body.
Further, after pouring a predetermined alkaline electrolyte into the can body, the whole body is assembled into a hermetically sealed structure.

【０００３】この電池で使用される上記した水素吸蔵合
金電極は、通常、次のようにして製造されている。ま
ず、所定粒径の水素吸蔵合金粉末と、例えばカーボニル
ニッケル粉末のような所定粒径の導電材粉末と、例えば
ポリテトラフルオロエチレン粉末のような結着材粉末と
を、それぞれ所定の重量割合で混合して混合粉末にす
る。The above-mentioned hydrogen storage alloy electrode used in this battery is usually manufactured as follows. First, a hydrogen storage alloy powder having a predetermined particle size, a conductive material powder having a predetermined particle size such as carbonyl nickel powder, and a binder powder such as polytetrafluoroethylene powder are mixed at predetermined weight ratios. Mix to a mixed powder.

【０００４】ついで、この混合粉末と、水に例えばカル
ボキシメチルセルロースなどの増粘剤を所定量溶解して
成る増粘剤水溶液の所定量とを混合して粘稠で流動性を
備えた活物質合剤スラリーを調製する。そして、この活
物質合剤スラリーを、例えばパンチングメタル（鉄にニ
ッケルめっき）シート，ニッケルネット，３次元網状構
造のニッケル発泡体のような集電体に塗布または充填し
たのち乾燥し、ついで全体に圧延処理を施すことによ
り、当該活物質合剤を集電体に担持させて目的とする水
素吸蔵合金電極にする。Then, the mixed powder is mixed with a predetermined amount of a thickener aqueous solution obtained by dissolving a predetermined amount of a thickener such as carboxymethyl cellulose in water to obtain a viscous and fluid active material mixture. Prepare the agent slurry. Then, this active material mixture slurry is applied to or filled in a current collector such as a punching metal (iron plated with nickel) sheet, a nickel net, or a nickel foam having a three-dimensional net structure, and then dried, and then the whole is dried. By carrying out the rolling treatment, the active material mixture is supported on the current collector to obtain the intended hydrogen storage alloy electrode.

【０００５】このような水素吸蔵合金電極を負極とする
電池では、前記した活物質合剤の主成分である水素吸蔵
合金粉末とアルカリ電解液との接触界面で電気化学反応
が生起して電池反応が進行する。すなわち、充電時に
は、水素吸蔵合金粉末の表面で還元反応が起こり、水の
電気分解によって生成した水素が水素吸蔵合金の結晶格
子内に進入して吸蔵され、また放電時には、酸化反応が
起こって水素吸蔵合金内に吸蔵されていた水素が合金粉
末の表面で水酸化イオンと反応して水に戻る。In a battery using such a hydrogen storage alloy electrode as a negative electrode, an electrochemical reaction occurs at the contact interface between the hydrogen storage alloy powder, which is the main component of the active material mixture, and the alkaline electrolyte to cause a battery reaction. Progresses. That is, at the time of charging, a reduction reaction occurs on the surface of the hydrogen storage alloy powder, hydrogen generated by the electrolysis of water enters and is stored in the crystal lattice of the hydrogen storage alloy, and at the time of discharge, an oxidation reaction occurs to generate hydrogen. The hydrogen stored in the storage alloy reacts with hydroxide ions on the surface of the alloy powder and returns to water.

【０００６】このような働きをする水素吸蔵合金として
は、従来から、主として、ＬａＮｉ 5 ，ＺｒＶ2 ，Ｚｒ
ＭｎＮｉ系合金のようなものが研究されていたが、電池
のサイクル寿命特性を向上させるということから、最近
では、Ｎｉの一部をＣｏ，Ａｌ，Ｍｎなどで置換して多
元化したものが使用されはじめている。また、経済的な
観点から、Ｌａを、Ｌａ，Ｃｅ，Ｐｒ，Ｎｄ，Ｙなど希
土類元素の混合物であるミッシュメタル（Ｍｍ）で置換
した合金が多用されている。As a hydrogen storage alloy having such a function
Has traditionally been mainly LaNi Five , ZrV2, Zr
Although MnNi-based alloys have been studied, batteries
From the fact that it improves the cycle life characteristics of
Then, some of Ni is replaced by Co, Al, Mn, etc.
The original version is being used. Also economical
From the viewpoint, La is rarely used as La, Ce, Pr, Nd, Y or the like.
Replaced by misch metal (Mm), a mixture of earth elements
The alloys used are often used.

【０００７】ところで、水素吸蔵合金電極を構成する水
素吸蔵合金粉末は、電池内で高濃度のアルカリ電解液に
接触すると、ある合金成分がアルカリ電解液に溶出した
り、水酸化物を生成したりして合金の腐食が進行する。
このような腐食現象はアルカリ電解液中の水を消費する
化学反応である。そのため、セパレータに保持されてい
るアルカリ電解液の量的なバランスが崩れたり、水素吸
蔵合金粉末の表面状態の変化に伴い濡れ性に影響を及ぼ
すことがある。By the way, when the hydrogen storage alloy powder constituting the hydrogen storage alloy electrode comes into contact with a high-concentration alkaline electrolyte in the battery, a certain alloy component elutes in the alkaline electrolyte or forms a hydroxide. Then, the corrosion of the alloy proceeds.
Such a corrosion phenomenon is a chemical reaction that consumes water in the alkaline electrolyte. Therefore, the quantitative balance of the alkaline electrolyte retained in the separator may be lost, and the wettability may be affected by the change in the surface state of the hydrogen storage alloy powder.

【０００８】このような事態が起こると、電池の内部抵
抗は上昇し、その結果として、高率放電特性、とりわけ
低温下における高率放電特性の低下、ひいてはサイクル
寿命特性の低下が引き起こされるようになる。また、こ
のニッケル・水素二次電池の場合、充電末期から過充電
時に、正極から酸素ガスが発生し、この酸素ガスは電池
内に拡散し、セパレータを通過して水素吸蔵合金電極
（負極）にまで到達する。水素吸蔵合金電極の表面で水
素の酸化反応が適正に起こらない場合には、拡散してき
た酸素ガスは水に復元しなくなって電池内圧の上昇を招
き、同時に、担持されている水素吸蔵合金粉末の表面が
酸化されて不動態皮膜を形成し、水素吸蔵合金粉末の水
素吸蔵能は阻害され、ますます電池内圧の上昇が引き起
こされる。When such a situation occurs, the internal resistance of the battery rises, and as a result, the high rate discharge characteristics, especially the high rate discharge characteristics at low temperature, and the cycle life characteristics are deteriorated. Become. In addition, in the case of this nickel-hydrogen secondary battery, oxygen gas is generated from the positive electrode from the end of charge to overcharge, and this oxygen gas diffuses into the battery and passes through the separator to the hydrogen storage alloy electrode (negative electrode). Reach up to. When the hydrogen oxidation reaction does not occur properly on the surface of the hydrogen storage alloy electrode, the diffused oxygen gas is not restored to water and causes an increase in the battery internal pressure, and at the same time, the supported hydrogen storage alloy powder The surface is oxidized to form a passive film, and the hydrogen storage capacity of the hydrogen storage alloy powder is hindered, and the internal pressure of the battery is further increased.

【０００９】水素吸蔵合金電極の上記したような問題を
解消するために、従来から、各種の方法が提案されてい
る。例えば、特開昭６１−１７６０６３号公報，特開昭
６１−２８５６５８号公報，特開昭６３−１７５３４０
号公報などには、使用する水素吸蔵合金粉末やそれを主
成分として製造した水素吸蔵合金電極を７Ｎ−ＫＯＨ水
溶液単独、または、ＫＯＨ，ＮａＯＨ，ＬｉＯＨの混液
のようなアルカリ水溶液に浸漬することにより、水素吸
蔵合金粉末の不均質成分の金属を溶解させたり、また表
面に金属層を形成する方法が開示されている。In order to solve the above problems of the hydrogen storage alloy electrode, various methods have been conventionally proposed. For example, JP-A-61-176063, JP-A-61-285658, and JP-A-63-175340.
In Japanese Patent Laid-Open Publication No. 2003-242, the hydrogen storage alloy powder to be used and the hydrogen storage alloy electrode produced by using it as a main component are dipped in an aqueous 7N-KOH solution alone or in an alkaline aqueous solution such as a mixed solution of KOH, NaOH and LiOH. , A method of dissolving a metal of a heterogeneous component of a hydrogen storage alloy powder or forming a metal layer on the surface is disclosed.

【００１０】しかしながら、この表面処理が施された水
素吸蔵合金粉末は、電池に組み込まれたときに、合金に
含有されているＡｌ，Ｃｏ，Ｍｎなどの成分の一部が電
池のアルカリ電解液に溶出してしまい、合金粉末の耐食
性は必ずしも向上していない。また、特開昭６１−２３
３９６７号公報には、電池へ組み込む前の段階で、水素
吸蔵合金電極に対し酸素発生が確認できるまで電解酸化
を行う方法が開示されている。However, when the surface-treated hydrogen-absorbing alloy powder is incorporated into a battery, some of the components such as Al, Co and Mn contained in the alloy are contained in the alkaline electrolyte of the battery. It is eluted, and the corrosion resistance of the alloy powder is not necessarily improved. Also, JP-A-61-23
Japanese Patent No. 3967 discloses a method of electrolytically oxidizing a hydrogen storage alloy electrode until the generation of oxygen can be confirmed before the battery is incorporated into a battery.

【００１１】しかしながら、この方法は、設備コストが
高くなり、処理工程も煩雑であって、実用的であるとは
いいがたい。特開平５−２１３６０１号公報には、Ｋ3
ＡｌＦ6 やＫ3 ＴｉＦ6 のようなフッ化金属化合物で水
素吸蔵合金粉末を処理して、当該水素吸蔵合金粉末の表
面を高活性にする方法が開示されている。However, this method cannot be said to be practical because the equipment cost is high and the processing steps are complicated. Japanese Patent Application Laid-Open No. 5-213601 discloses K 3
A method of treating a hydrogen storage alloy powder with a metal fluoride compound such as AlF 6 or K 3 TiF 6 to make the surface of the hydrogen storage alloy powder highly active is disclosed.

【００１２】しかしながら、この方法で表面処理された
水素吸蔵合金粉末を用いて電極を製造すると、そのイン
ピーダンスは高くなり、得られた電池の充放電特性の低
下が引き起こされる。更に、特開平６−２７５２６２号
公報には、Ｌａを含む水素吸蔵合金粉末をＫＯＨやＮａ
ＯＨのようなアルカリ水溶液で処理して外殻部のＬａを
除去し、代わってＣｅ，Ｐｒ，Ｎｄなどで置換する方法
が開示されている。However, when an electrode is manufactured using the hydrogen storage alloy powder surface-treated by this method, its impedance becomes high and the charge / discharge characteristics of the obtained battery are deteriorated. Further, in Japanese Patent Laid-Open No. 6-275262, a hydrogen storage alloy powder containing La is added to KOH or Na.
A method is disclosed in which La in the outer shell is removed by treatment with an alkaline aqueous solution such as OH and replaced with Ce, Pr, Nd or the like.

【００１３】しかしながら、この方法で得られた水素吸
蔵合金粉末も、前記したアルカリ処理後の合金粉末の場
合と同じように、Ａｌ，Ｃｏ，Ｍｎなどの一部が溶出
し、耐食性は必ずしも充分とはいえない。However, in the hydrogen storage alloy powder obtained by this method, as in the case of the alloy powder after the alkali treatment described above, a part of Al, Co, Mn, etc. is eluted, and the corrosion resistance is not always sufficient. I can't say.

【００１４】[0014]

【発明が解決しようとする課題】本発明は、水素吸蔵合
金粉末の表面処理に関する前記各先行技術の上記した問
題を解決し、処理後の水素吸蔵合金粉末のアルカリ電解
液に対する耐食性を向上させ、組み立てたニッケル・水
素二次電池の内部抵抗の上昇を抑制し、もってそのニッ
ケル・水素二次電池の高率放電特性とサイクル寿命特性
の向上を実現することができる水素吸蔵合金粉末の表面
処理方法と、得られた水素吸蔵合金粉末を用いた負極が
組み込まれているアルカリ二次電池の提供を目的とす
る。DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the above-mentioned respective prior arts regarding the surface treatment of hydrogen storage alloy powder, and improves the corrosion resistance of the hydrogen storage alloy powder after treatment to an alkaline electrolyte, Surface treatment method of hydrogen storage alloy powder that can suppress increase in internal resistance of assembled nickel-hydrogen secondary battery and realize high rate discharge characteristics and improvement of cycle life characteristics of the nickel-hydrogen secondary battery Another object of the present invention is to provide an alkaline secondary battery in which a negative electrode using the obtained hydrogen storage alloy powder is incorporated.

【００１５】[0015]

【課題を解決するための手段】上記した目的を達成する
ために、本発明においては、希土類元素を含む水素吸蔵
合金粉末またはそれを主成分として担持する水素吸蔵合
金電極をアルカリ性水溶液と接触させて前記水素吸蔵合
金粉末の比表面積を増加させ、ついで、フッ素イオンを
含むｐＨ３〜６の酸性水溶液と接触させて前記比表面積
が増加した水素吸蔵合金粉末の表面にフッ化処理を施す
ことを特徴とする水素吸蔵合金粉末の表面処理方法が提
供される。In order to achieve the above object, in the present invention, a hydrogen storage alloy powder containing a rare earth element or a hydrogen storage alloy electrode carrying the same as a main component is brought into contact with an alkaline aqueous solution. The specific surface area of the hydrogen storage alloy powder is increased, and then the surface of the hydrogen storage alloy powder having the increased specific surface area is subjected to a fluorination treatment by contacting it with an acidic aqueous solution containing fluorine ions having a pH of 3 to 6. A method for treating the surface of a hydrogen storage alloy powder is provided.

【００１６】また、本発明においては、上記した方法で
得られた水素吸蔵合金粉末を用いて製造された負極が組
み込まれているアルカリ二次電池が提供される。The present invention also provides an alkaline secondary battery incorporating a negative electrode manufactured using the hydrogen storage alloy powder obtained by the above method.

【００１７】[0017]

【発明の実施の形態】まず、本発明方法は、水素吸蔵合
金電極を製造する前の素材である水素吸蔵合金粉末、ま
た、既に製造が終了している水素吸蔵合金電極のいずれ
に対しても適用することができる。後者の場合、集電体
に担持されている活物質合剤において、その主成分であ
る水素吸蔵合金粉末は、後述するアルカリ性水溶液と酸
性水溶液に接触することができ、そのことによって本発
明方法の作用効果が発揮されるからである。BEST MODE FOR CARRYING OUT THE INVENTION First, the method of the present invention is applied to both hydrogen storage alloy powder, which is a raw material before manufacturing hydrogen storage alloy electrodes, and hydrogen storage alloy electrodes which have already been manufactured. Can be applied. In the latter case, in the active material mixture carried on the current collector, the hydrogen-absorbing alloy powder as the main component can be brought into contact with the alkaline aqueous solution and the acidic aqueous solution described later, whereby the method of the present invention This is because the action effect is exhibited.

【００１８】本発明方法で、処理対象となる水素吸蔵合
金粉末は、希土類元素を含むものである。具体的には、
Ｌａ，Ｃｅ，Ｎｄ，Ｐｒ，Ｙの少なくとも１種またはこ
れらの混合物であるミッシュメタルを含むものをあげる
ことができ、とりわけＣｅが含まれているものを好適と
する。また、これら希土類元素とともに、例えば、Ａ
ｌ，Ｃｏ，Ｍｎ，Ｃａを含むもの、とりわけＡｌを含む
ものは処理対象として有用である。In the method of the present invention, the hydrogen storage alloy powder to be treated contains a rare earth element. In particular,
Examples thereof include those containing misch metal which is at least one kind of La, Ce, Nd, Pr, Y or a mixture thereof, and those containing Ce are particularly preferable. In addition to these rare earth elements, for example, A
Those containing l, Co, Mn, and Ca, especially those containing Al, are useful as a processing target.

【００１９】本発明では、まず、上記した水素吸蔵合金
粉末がアルカリ性水溶液と接触させられる（以下、第１
工程という）。この処理によって、水素吸蔵合金粉末の
比表面積が増加する。例えば、希土類元素の代表として
Ｃｅを選び、そのＣｅを含む水素吸蔵合金粉末の場合で
説明すると、その合金粉末がアルカリ性水溶液に接触し
たとき、その接触界面では、含有されていたＣｅの一部
は溶出してそのイオンにより、次式： Ｃｅ3+＋３ＯＨ- ＝Ｃｅ（ＯＨ)3 …(1) または、次式：In the present invention, first, the above hydrogen storage alloy powder is brought into contact with an alkaline aqueous solution (hereinafter, referred to as the first
Process). This treatment increases the specific surface area of the hydrogen storage alloy powder. For example, when Ce is selected as a representative of rare earth elements and the hydrogen storage alloy powder containing the Ce is described, when the alloy powder comes into contact with an alkaline aqueous solution, a part of Ce contained at the contact interface is By elution and the ions, the following formula: Ce 3+ + 3OH − = Ce (OH) 3 (1) or the following formula:

【００２０】[0020]

【数１】 [Equation 1]

【００２１】で示される水酸化物生成反応が生起する。
このＣｅ（ＯＨ)3は、アルカリ性水溶液に不溶であり、
合金粉末の表面に沈着して無数の針状突起を形成する。
反応条件にもよるが、個々の針状突起は、概ね、幅２０
０ｎｍ程度、長さ６００ｎｍ程度の大きさである。この
ように、針状突起が析出している合金粉末は、したがっ
て、その表面積は大きくなりその比表面積が増大してい
る。A hydroxide-forming reaction represented by the following occurs.
This Ce (OH) 3 is insoluble in alkaline aqueous solution,
It deposits on the surface of the alloy powder to form innumerable needle-shaped protrusions.
Depending on the reaction conditions, the individual needle-shaped protrusions generally have a width of 20
The size is about 0 nm and the length is about 600 nm. Thus, the alloy powder in which the needle-shaped protrusions are deposited has a large surface area and an increased specific surface area.

【００２２】また、このときの反応条件、処理対象の合
金粉末の組成や結晶構造などによって様々に変化する
が、処理後の合金粉末の表層部には、多数の微細クラッ
クが発生したり、微小な燐片形状をした小片が複雑に多
数重なり合っている層構造が形成されたり、３次元網状
構造の薄い多孔組織が形成されたり、溶出成分の影響と
思われる無数の微小痕跡から成るクレータ状の粗面が形
成されたりする。Further, although it varies variously depending on the reaction conditions at this time, the composition and the crystal structure of the alloy powder to be treated, many fine cracks are generated in the surface layer of the alloy powder after the treatment, and minute cracks are generated. A layer structure is formed in which a large number of small pieces in the form of different scales are complicatedly overlapped, a thin porous structure with a three-dimensional network structure is formed, and a crater-like structure composed of innumerable minute traces that is thought to be due to the elution component. A rough surface may be formed.

【００２３】その結果、処理後の合金粉末の表層部に
は、全体として、無数の微小凹凸と微小空隙が複合して
成る多孔面組織が薄く形成され、合金粉末は処理前の合
金粉末の場合に比べて、その比表面積が増大する。ま
た、例えばＡｌを含む水素吸蔵合金粉末の場合は、この
合金粉末がアルカリ性水溶液に接触すると、その接触界
面では、次式： Ａｌ2 Ｏ3 ＋Ｈ2 Ｏ＝２ＡｌＯ2 - ＋２Ｈ+ …(2)As a result, in the surface layer portion of the treated alloy powder, a porous surface structure composed of innumerable minute irregularities and minute voids is thinly formed as a whole, and when the alloy powder is the untreated alloy powder. Its specific surface area is larger than that of. Further, for example, in the case of a hydrogen-absorbing alloy powder containing Al, when the alloy powder comes into contact with an alkaline aqueous solution, at the contact interface, the following formula: Al 2 O 3 + H 2 O = 2AlO 2 − + 2H + (2)

【００２４】[0024]

【数２】 [Equation 2]

【００２５】に基づく反応が生起して、含有されていた
Ａｌが当該合金粉末から溶出する。その結果、合金粉末
の表層部には、これら溶出Ａｌの残痕がクレータ状に形
成され、また、前記したように、様々な形態をした多孔
面組織が形成されて、処理前に比べてその比表面積は増
大する。このようにして、合金粉末の表層部に上記多孔
面組織を形成することによって合金粉末の比表面積を増
大させたのち、後述するフッ化処理によってこの多孔面
組織に存在する希土類元素をフッ化して成る合金粉末を
担持した電極は、電池のアルカリ電解液と接触しても希
土類元素のフッ化物の働きで耐食性が向上するととも
に、電池反応時の電極反応における反応面積が大きくな
って、電池特性の向上がもたらされる。The reaction based on (3) occurs, and the contained Al is eluted from the alloy powder. As a result, in the surface layer portion of the alloy powder, the residual traces of these eluted Al are formed in a crater shape, and as described above, the porous surface structures having various shapes are formed, which are different from those before the treatment. The specific surface area increases. In this way, after increasing the specific surface area of the alloy powder by forming the porous surface structure in the surface layer portion of the alloy powder, the rare earth elements present in this porous surface structure are fluorinated by the fluorination treatment described later. The electrode supporting the alloy powder consisting of the alloy has improved corrosion resistance due to the action of the fluoride of the rare earth element even when contacted with the alkaline electrolyte of the battery, and at the same time, the reaction area in the electrode reaction during the battery reaction increases and Improvement is brought about.

【００２６】ところで、(1) 式，(1)'式，(2) 式，(3)
式で示した反応は、いずれも、用いるアルカリ性水溶液
の種類とは関係なく、その濃度が高くなるほど、平衡関
係は各式の右側にずれる。すなわち、用いるアルカリ性
水溶液の濃度を高くすればするほど、処理後の合金粉末
の表層部における多孔面組織の組織形態、その広さや厚
みなどが複雑化してその比表面積は増加する傾向があ
る。By the way, equation (1), equation (1) ', equation (2), (3)
In any of the reactions shown in the equations, the equilibrium relationship shifts to the right side of each equation as the concentration increases, regardless of the type of alkaline aqueous solution used. That is, the higher the concentration of the alkaline aqueous solution used, the more complicated the structure morphology of the porous surface structure in the surface layer portion of the treated alloy powder, its width and thickness, and the more its specific surface area tends to increase.

【００２７】しかし、その濃度をあまり高くすると、Ａ
ｌなどが過剰に溶出して原料ロスが無視できなくなった
り、過飽和による沈澱物の発生などの問題が生じ始めて
不都合であり、しかも、処理後における洗浄等のハンド
リングが煩雑になるので、比重が1.２５〜1.４ｇ／ｃｍ
3 のアルカリ電解液をそのまま用いることで充分であ
る。However, if the concentration is too high, A
1 and the like are excessively eluted and the raw material loss cannot be ignored, and problems such as the occurrence of precipitates due to oversaturation start to occur, which is inconvenient, and since the handling such as washing after the treatment becomes complicated, the specific gravity is 1 .25 to 1.4 g / cm
It is sufficient to use the alkaline electrolyte of 3 as it is.

【００２８】この第１工程において、処理後の比表面積
を処理前の比表面積に比べて過度に増大させるような処
理を行うと、処理後の合金粉末は表層部だけではなく内
部まで前記したような多孔面組織になって当該合金粉末
の活性低下が起こり、また、あまり比表面積を増大させ
ないような処理の場合には、得られた合金粉末の電極反
応に寄与する反応面積が小さくなって水素吸蔵合金電極
の特性向上に貢献しなくなる。In the first step, when the treatment is carried out so that the specific surface area after the treatment is excessively increased as compared with the specific surface area before the treatment, the alloy powder after the treatment is not limited to the surface layer portion but to the inside as described above. In the case of a treatment in which the activity of the alloy powder is reduced due to the formation of a porous surface structure and the specific surface area is not increased so much, the reaction area of the obtained alloy powder that contributes to the electrode reaction is reduced and hydrogen is reduced. It does not contribute to the improvement of the characteristics of the storage alloy electrode.

【００２９】このようなことから、この第１工程では、
処理後の比表面積が処理前の比表面積の1.４〜４倍にな
るように条件設定することが好ましい。その場合、(1)
式、(1)'式の反応で生起する水酸化物（針状突起）の長
さが３００ｎｍ以上となるように条件を設定し、また
(2) 式，(3) 式の反応で溶出するＡｌの溶出量が合金粉
末の重量に対し0.０２〜2.０重量％程度となるように条
件設定することが好ましい。Therefore, in this first step,
It is preferable to set the conditions such that the specific surface area after the treatment is 1.4 to 4 times the specific surface area before the treatment. In that case, (1)
The conditions are set so that the length of the hydroxides (needle-shaped protrusions) generated by the reaction of the equation (1) 'is 300 nm or more, and
It is preferable to set the conditions so that the amount of Al eluted in the reactions of the expressions (2) and (3) is about 0.02 to 2.0% by weight based on the weight of the alloy powder.

【００３０】この処理過程で用いるアルカリ性水溶液と
しては、前記したように、その種類を問うものではない
が、例えば、ＫＯＨ水溶液、ＮａＯＨ水溶液、ＬｉＯＨ
水溶液、およびこれらの混合液などをあげることができ
る。また、それらの濃度は、６〜８Ｎであることが好ま
しい。このような第１工程を終了した水素吸蔵合金粉末
に対しては、つぎにフッ化処理が施される（以下、第２
工程という）。As described above, the alkaline aqueous solution used in this treatment step may be of any kind, but may be, for example, KOH aqueous solution, NaOH aqueous solution or LiOH.
Examples thereof include an aqueous solution and a mixed solution thereof. Further, their concentration is preferably 6 to 8N. The hydrogen storage alloy powder that has undergone the first step is then subjected to a fluorination treatment (hereinafter referred to as the second step).
Process).

【００３１】この第２工程では、第１工程で比表面積が
大きくなった合金粉末の表層部をフッ素イオンが含まれ
ている酸性水溶液に接触させることにより、その表層部
に形成されている前記多孔面組織に、電池のアルカリ電
解液に難溶性の希土類フッ化物を生成させ、もって合金
粉末の耐食性を高める。例えば、Ｃｅを含む水素吸蔵合
金粉末の場合、フッ素イオンを含む酸性水溶液に接触す
ると、その接触界面では、含有されているＣｅが酸性水
溶液に溶出してイオン化し、次式： Ｃｅ3+＋３Ｆ- ＝ＣｅＦ3 …(4) で示される反応に基づいて、フッ化セリウムが生成し、
これが当該合金粉末の表面を被覆したり、また沈着した
りする。In the second step, the surface layer portion of the alloy powder having a large specific surface area in the first step is brought into contact with an acidic aqueous solution containing fluorine ions, so that the porosity formed in the surface layer portion. Rare-earth fluoride, which is hardly soluble in the alkaline electrolyte of the battery, is generated in the surface structure, thereby enhancing the corrosion resistance of the alloy powder. For example, in the case of a hydrogen storage alloy powder containing Ce, when it comes into contact with an acidic aqueous solution containing fluorine ions, Ce contained therein is eluted into the acidic aqueous solution and ionized, and the following formula: Ce 3+ + 3F − = CeF 3 (4), cerium fluoride is produced based on the reaction represented by
This coats or deposits on the surface of the alloy powder.

【００３２】その場合、第１工程が終了した時点で、合
金粉末の表層部は前記した多孔面組織になっているの
で、この多孔面組織の微小空隙や微小凹凸がこの希土類
フッ化物で満たされたり被覆されたりする。このＣｅＦ
3 のような希土類フッ化物は化学的に安定であり、高濃
度のアルカリ性水溶液にも難溶性である。In this case, since the surface layer portion of the alloy powder has the above-mentioned porous surface structure at the time when the first step is completed, the minute voids and minute irregularities of this porous surface structure are filled with this rare earth fluoride. Or covered. This CeF
Rare earth fluorides such as 3 are chemically stable and hardly soluble in high-concentration alkaline aqueous solutions.

【００３３】したがって、この第２工程の終了後にあっ
ては、合金粉末の表層部は、例えば水素が通過でき、し
かも電池のアルカリ電解液にも難溶な状態を呈し、合金
粉末の内部にまでアルカリ電解液による腐食が進行する
ことを防止できる状態になっている。また、このように
して形成された表層部は、電池の充電末期から過充電時
に正極から発生する酸素ガスによって合金粉末が酸化さ
れることを防止することができる保護膜的な働きをす
る。Therefore, after the completion of the second step, the surface layer portion of the alloy powder can pass hydrogen, for example, and is hardly soluble in the alkaline electrolyte of the battery, even inside the alloy powder. It is in a state where it is possible to prevent the corrosion due to the alkaline electrolyte from proceeding. Further, the surface layer portion thus formed acts as a protective film capable of preventing the alloy powder from being oxidized by the oxygen gas generated from the positive electrode during the overcharge from the end of charging of the battery.

【００３４】ところで、(4) 式が成立する前提は、合金
粉末中のＣｅが用いた酸性水溶液に溶出してイオン化す
ることである。したがって、仮に用いる酸性水溶液が極
端に弱い酸である場合には、合金粉末のＣｅの溶出が充
分に進行しないので、(4) 式に基づくＣｅＦ3 の生成は
起こらず、合金粉末の表層部には耐食性が付与されなく
なる。また、用いる酸性水溶液が強酸である場合には、
(1) 式，(1)'式，(2) 式，(3) 式に基づいて形成された
表層部の多孔面組織が溶解して消失するとともに、更に
は合金粉末それ自体も溶解してしまうという不都合が発
生する。By the way, the premise of the expression (4) is that Ce in the alloy powder is eluted into the acidic aqueous solution used and ionized. Therefore, if the acidic aqueous solution used is an extremely weak acid, since the elution of Ce from the alloy powder does not proceed sufficiently, the formation of CeF 3 based on the equation (4) does not occur and the surface layer of the alloy powder does not form. Has no corrosion resistance. When the acidic aqueous solution used is a strong acid,
The porous surface structure of the surface layer formed based on Eqs. (1), (1) ', (2), and (3) dissolves and disappears, and the alloy powder itself also dissolves. The inconvenience occurs.

【００３５】このようなことから、第１工程で形成した
表層部の多孔面組織をそのまま残置させ、同時に、そこ
に(4) 式で示した反応を実現させ、難溶性の希土類フッ
化物を生成させるためには、用いる酸性水溶液は、ｐＨ
３〜６の範囲に位置するものであることが必要である。
なお、この工程で用いる酸性水溶液としては格別限定さ
れるものではないが、上記したｐＨ値を満足するもので
あれば何であってもよく、例えばフタル酸水素カリウム
−塩酸溶液、酢酸−酢酸ナトリウム、リン酸水素カリウ
ム−リン酸水素ナトリウム緩衝溶液などをあげることが
できる。From the above, the porous surface structure of the surface layer portion formed in the first step is left as it is, and at the same time, the reaction represented by the formula (4) is realized to form a hardly soluble rare earth fluoride. In order to do so, the acidic aqueous solution used must have a pH
It is necessary to be located in the range of 3 to 6.
The acidic aqueous solution used in this step is not particularly limited, but may be anything as long as it satisfies the above-mentioned pH value, for example, potassium hydrogen phthalate-hydrochloric acid solution, acetic acid-sodium acetate, Examples thereof include potassium hydrogen phosphate-sodium hydrogen phosphate buffer solution.

【００３６】この第２工程で用いる酸性水溶液には、フ
ッ素イオン（Ｆ- ）が含まれている。その場合、(4) 式
から明らかなように、フッ素イオンの濃度が高いほどフ
ッ化物の生成は促進されて、第１工程で形成した多孔面
組織になっている表層部の耐食性を高めることができ
る。そのようなことから、フッ素イオンの供給源として
は、例えば、ＬｉＦ，ＮａＦ，ＫＦ，ＲｂＦ，ＣｓＦの
ような塩またはそれらの水素塩を好適なのものとしてあ
げることができる。水素塩としては、例えば塩がＫＦで
ある場合には、ＫＦ・２ＨＦ，ＫＦ・３ＨＦ，ＫＦ・４
ＨＦ，ＫＦ・５ＨＦなどをあげることができる。The acidic aqueous solution used in the second step contains fluorine ions (F − ). In that case, as is clear from the equation (4), the higher the concentration of the fluorine ions, the more the formation of the fluoride is promoted, and the corrosion resistance of the surface layer portion having the porous surface structure formed in the first step can be enhanced. it can. Therefore, as a source of fluorine ions, for example, salts such as LiF, NaF, KF, RbF, and CsF or hydrogen salts thereof can be cited as preferable ones. As the hydrogen salt, for example, when the salt is KF, KF · 2HF, KF · 3HF, KF · 4
HF, KF, 5HF, etc. can be mentioned.

【００３７】これらの塩と水素塩は、いずれも、水に対
する溶解度が大きく、しかも水溶液中での解離度も大き
く、フッ素イオン濃度を高めることができるからであ
る。酸性水溶液中のフッ素イオンの濃度は、第１工程で
形成した表層部の多孔面組織の粗面化状態または微小空
隙の多寡をベースにし、また合金粉末の組成や用いる酸
性水溶液のｐＨ値などによって適宜に決定すればよい。This is because both of these salts and hydrogen salts have a high solubility in water, a high dissociation degree in an aqueous solution, and a high fluorine ion concentration. The concentration of fluorine ions in the acidic aqueous solution is based on the roughened state of the surface texture of the surface layer formed in the first step or the amount of microvoids, and also depends on the composition of the alloy powder and the pH value of the acidic aqueous solution used. It may be determined appropriately.

【００３８】本発明の表面処理方法は、その粒径が１５
〜３５μｍ程度である合金粉末に適用することが好まし
い。その理由は以下のとおりである。一般に、水素吸蔵
合金は、水素の吸蔵と放出を反復する過程で微粉化して
いく。しかし、この微粉化の現象は無限に進行するわけ
ではなく、合金の組成や製法によっても異なるが、５０
０サイクル程度の水素の吸蔵・放出（充放電）の後にお
いては、合金の粒径は１５〜３５μｍで安定化する。The surface treatment method of the present invention has a particle size of 15
It is preferably applied to alloy powder having a size of about 35 μm. The reason is as follows. Generally, a hydrogen storage alloy is pulverized in the process of repeating storage and release of hydrogen. However, this phenomenon of pulverization does not progress indefinitely, but it depends on the composition of the alloy and the manufacturing method.
After hydrogen storage / release (charge / discharge) for about 0 cycles, the grain size of the alloy stabilizes at 15 to 35 μm.

【００３９】したがって、本発明の表面処理を粒径が３
５μｍよりも大きい合金粉末に適用すると、処理後の合
金粉末が使用されている水素吸蔵合金電極は、反復する
充放電の過程で微粉化が進み未処理の新生面を表出させ
るようになり、その新生面での腐食現象が進行するから
である。また、あまり微細な合金粉末の場合には、濾過
に長時間を要したり、水洗時の流出により歩留りが低下
する。更に、第１工程のアルカリ処理時に、当該合金粉
末の表層部の組成が変質し、水素吸蔵量が減少してしま
うような事態が起こることがある。Therefore, the surface treatment of the present invention has a particle size of 3
When applied to an alloy powder having a size of more than 5 μm, the hydrogen-absorbing alloy electrode in which the treated alloy powder is used becomes finely pulverized during repeated charging / discharging processes to expose an untreated new surface. This is because the corrosion phenomenon on the new surface progresses. Further, if the alloy powder is too fine, the filtration will take a long time, and the yield will decrease due to the outflow during washing with water. Furthermore, during the alkali treatment in the first step, the composition of the surface layer portion of the alloy powder may be altered and the hydrogen storage amount may decrease.

【００４０】[0040]

【発明の実施例】Examples of the invention

実施例１〜４，比較例１〜５ 組成：ＭｍＮｉ3.5 Ｃｏ0.8 Ｍｎ0.4 Ａｌ0.3 （ただ
し、Ｍｍは、組成：Ｌａ 0.26Ｃｅ0.49Ｐｒ0.06Ｎｄ0.4
のミッシュメタル）の水素吸蔵合金を粉砕したのち、４
００メッシュ（タイラー篩）下の合金粉末とした。この
合金粉末の平均粒径は２６μｍであり、また比表面積
（Ｓ0)は0.１３ｍ2 ／ｇであった。 Examples 1-4, Comparative Examples 1-5 Composition: MmNi3.5Co0.8Mn0.4Al0.3(However
Mm is the composition: La 0.26Ce0.49Pr0.06Nd0.4
After crushing the hydrogen storage alloy of (Misch metal), 4
The alloy powder under 00 mesh (Tyler sieve) was used. this
The average particle size of the alloy powder is 26 μm, and the specific surface area is
(S0) Is 0.13m2/ G.

【００４１】つぎに、ＫＯＨ水溶液（濃度７Ｎ）を調製
し、このＫＯＨ水溶液１００重量部に対し前記した合金
粉末２５重量部を投入して、全体を室温下で１２時間撹
拌して第１工程を行った。合金粉末を濾取・水洗したの
ち、乾燥してその比表面積（Ｓ1 ）を測定した。あわせ
て、誘導プラズマ発光分光分析により濾液の化学分析を
行って溶出したＡｌ成分を定量し、処理前の合金粉末に
対する重量割合を算出した。その結果を表１に示した。Next, an aqueous KOH solution (concentration 7N) was prepared, 25 parts by weight of the above-mentioned alloy powder was added to 100 parts by weight of this KOH aqueous solution, and the whole was stirred at room temperature for 12 hours to carry out the first step. went. The alloy powder was filtered, washed with water, and then dried to measure its specific surface area (S 1 ). At the same time, chemical analysis of the filtrate was conducted by induction plasma emission spectroscopy to quantify the eluted Al component, and the weight ratio to the alloy powder before treatment was calculated. The results are shown in Table 1.

【００４２】ついで、酸として0.０２Ｎの塩酸を用意
し、緩衝溶液として0.１Ｎの酢酸−酢酸ナトリウムまた
はホウ酸−酸化ホウ素を用意し、これらを適当量混合し
て表１に示したｐＨ値の酸性水溶液を調製し、ここに、
ＫＦを濃度0.１ ｍｏｌ／ｍ3となるように溶解させた。
これらの酸性水溶液に、上記した合金粉末１０００ｇを
投入したのち全体を室温下で所定の時間撹拌して第２工
程を行った。Next, 0.02N hydrochloric acid was prepared as an acid, and 0.1N acetic acid-sodium acetate or boric acid-boron oxide was prepared as a buffer solution. These were mixed in appropriate amounts and the pH shown in Table 1 was obtained. Value of acidic aqueous solution is prepared and
KF was dissolved at a concentration of 0.1 mol / m 3 .
1000 g of the alloy powder described above was added to these acidic aqueous solutions, and the whole was stirred at room temperature for a predetermined time to perform the second step.

【００４３】合金粉末をブフナーロートで濾別し、水洗
したのち乾燥し、その重量（Ｗ）を測定した。そして、
（１０００−Ｗ）×（１００／１０００）の計算式に基
づいて重量変化率を算出すると同時に、その表面を走査
電顕で観察した。その結果を表１に示した。得られた各
合金粉末を用いて常法により水素吸蔵合金電極を製造
し、また常法によりＮｉ（ＯＨ)2を活物質とするニッケ
ル極を製造したのち、ＫＯＨ３０重量％とＬｉＯＨ１重
量％を含むアルカリ電解液を用いて、定格容量１１００
ｍＡｈのＡＡ型のニッケル・水素二次電池を組み立て
た。The alloy powder was filtered with a Buchner funnel, washed with water and dried, and the weight (W) was measured. And
The weight change rate was calculated based on the calculation formula of (1000-W) × (100/1000), and at the same time, the surface was observed with a scanning electron microscope. The results are shown in Table 1. A hydrogen storage alloy electrode is manufactured by a conventional method using each of the obtained alloy powders, and a nickel electrode having Ni (OH) 2 as an active material is manufactured by a conventional method, and then 30% by weight of KOH and 1% by weight of LiOH are contained. Rated capacity of 1100 using alkaline electrolyte
A mAh AA type nickel-hydrogen secondary battery was assembled.

【００４４】これらの電池につき、下記の仕様で率別放
電試験とサイクル寿命試験を行った。 率別放電試験：温度２０℃において0.２Ｃで１５０％の
過充電を行い、ついで、温度０℃において、0.２Ｃ，1.
０Ｃ，3.０Ｃで電池電圧が1.０Ｖになるまで放電し、そ
のときの放電容量を測定。このときの放電容量が大きい
ものほど低温下における放電特性に優れている。A rate-dependent discharge test and a cycle life test were carried out on these batteries with the following specifications. Rate discharge test: 150% overcharge at 0.2C at 20 ° C, then 0.2C, 1. at 0 ° C.
Discharge until the battery voltage reaches 1.0V at 0C and 3.0C, and measure the discharge capacity at that time. The larger the discharge capacity at this time, the better the discharge characteristics at low temperature.

【００４５】サイクル寿命試験：温度２０℃において、
定電流法により１Ｃ，−ΔＶ（−１０ｍＶ）制御で充電
し、同じく定電流法により１Ｃで電池電圧が1.０Ｖにな
るまで放電する充放電サイクルを５００回反復し、その
ときの放電容量を測定して初回容量に対する維持率
（％）を算出。この維持率が高いほど、サイクル寿命特
性は優れている。Cycle life test: at a temperature of 20 ° C.
Charge and discharge cycle is repeated 500 times to charge by 1C, -ΔV (-10 mV) control by constant current method, and also discharge by 1C by constant current method until the battery voltage becomes 1.0V. Measure and calculate the retention rate (%) for the initial capacity. The higher the maintenance rate, the better the cycle life characteristics.

【００４６】以上の結果を一括して表１に示した。な
お、比較例１は、第１工程と第２工程を行うことなく、
粉砕して得られた合金粉末をそのまま使用した場合であ
り、比較例２は第１工程のみを行った場合を示し、更に
比較例３は第１工程を行わず、第２工程は実施例２の条
件で行った場合を示す。The above results are collectively shown in Table 1. In Comparative Example 1, without performing the first step and the second step,
It is a case where the alloy powder obtained by pulverization is used as it is, Comparative Example 2 shows a case where only the first step is carried out, further Comparative Example 3 does not carry out the first step, and the second step does the Example 2. The following shows the case of performing under the conditions.

【００４７】[0047]

【表１】 [Table 1]

【００４８】表１から明らかなように、実施例２と比較
例３における3.０Ｃの放電特性を比較すると、実施例２
の場合は比較例３の場合よりも約２０％放電容量が増大
しており、低温（０℃）下における放電特性が優れてい
る。また、第１工程を経たのちの合金粉末は、その表面
からＡｌの溶出が進んでおり、そしてその表面が複雑な
多孔面組織になっていて、結果として、その比表面積Ｓ
1 は0.４６ｍ2 ／ｇに増大し、処理前の比表面積Ｓ0 の
約３倍の値になっている。実施例２と比較例２を比べて
明らかなように、第１工程を行っても第２工程を行わな
い場合は、率別放電試験結果とサイク寿命試験結果のい
ずれもが劣っている。これは、合金粉末の比表面積を大
きくしてもそこにフッ化処理を行わなかったからであ
る。また、実施例２と比較例３を比べて明らかなよう
に、第２工程を行っても第１工程を行わず、合金粉末の
比表面積を増大させていない場合も上記した電池の試験
結果は劣っている。As is clear from Table 1, when the discharge characteristics of 3.0 C in Example 2 and Comparative Example 3 are compared, Example 2
In the case of, the discharge capacity is increased by about 20% as compared with the case of Comparative Example 3, and the discharge characteristics at low temperature (0 ° C.) are excellent. Further, in the alloy powder after the first step, the elution of Al is progressing from the surface, and the surface has a complicated porous surface structure, and as a result, the specific surface area S
1 increased to 0.46 m 2 / g, which is about 3 times the specific surface area S 0 before treatment. As is clear from comparison between Example 2 and Comparative Example 2, both the rate-based discharge test result and the cycle life test result are inferior when the first step is performed and the second step is not performed. This is because even if the specific surface area of the alloy powder was increased, the fluorination treatment was not performed there. Further, as is clear from comparison between Example 2 and Comparative Example 3, even when the second step is performed, the first step is not performed, and the specific surface area of the alloy powder is not increased. Inferior

【００４９】また、第２工程で用いる酸性水溶液がｐＨ
２の場合（比較例４）には、処理後の重量変化率および
走査電顕による表面観察からも明らかなように、酸によ
る溶解が進んで原料ロスが大きい。しかし、ｐＨ値が６
より高くなると（比較例５の場合）、走査電顕の表面観
察で示されているように、希土類のフッ化物（網目状生
成物）は生成しておらず、その結果、電池内で合金の腐
食が進行して電池特性の低下が引き起こされている。The pH of the acidic aqueous solution used in the second step is
In the case of No. 2 (Comparative Example 4), as is clear from the rate of change in weight after the treatment and the surface observation by scanning electron microscopy, the dissolution by acid progresses and the raw material loss is large. However, the pH value is 6
At higher values (in the case of Comparative Example 5), as shown in the surface observation of the scanning electron microscope, the rare earth fluoride (mesh product) was not formed, and as a result, the alloy of the alloy was formed in the battery. Corrosion progresses, causing deterioration of battery characteristics.

【００５０】なお、前記した(1) 式、(1)'式、(2) 式、
(3) 式で示される反応はアルカリ性水溶液の濃度が高い
ほど促進されるが、そのときの反応速度は反応温度や撹
拌速度に大きく依存する。処理工程における生産性の問
題を考慮すると、アルカリ電解液の濃度（通常、６〜８
Ｎ）と同一で充分である。処理対象の水素吸蔵合金粉末
とアルカリ性水溶液との接触は、温度と時間の組み合わ
せで決定することが好ましい。温度は室温から９０℃程
度でよく、室温の場合には１２時間以上接触させること
が必要となり、９０℃の場合には少なくとも３０分の接
触で充分である。The above formula (1), formula (1) ′, formula (2),
The reaction represented by the formula (3) is promoted as the concentration of the alkaline aqueous solution increases, but the reaction rate at that time largely depends on the reaction temperature and the stirring rate. Considering the productivity problem in the treatment process, the concentration of the alkaline electrolyte (usually 6-8
The same as N) is sufficient. The contact between the hydrogen storage alloy powder to be treated and the alkaline aqueous solution is preferably determined by a combination of temperature and time. The temperature may be from room temperature to about 90 ° C., and at room temperature it is necessary to contact for 12 hours or more, and at 90 ° C., contact for at least 30 minutes is sufficient.

【００５１】アルカリ性水溶液との接触により、水素吸
蔵合金粉末の比表面積が増加するが、その場合、比表面
積を接触前の比表面積に対し1.４倍より小さい場合には
処理後の比表面積が充分に増加していないため、低温下
における率別特性の改善が不充分となる。また、４倍よ
り大きくなると、水素吸蔵合金の腐食が過剰になるため
放電容量の低下減少が生ずる。The contact with the alkaline aqueous solution increases the specific surface area of the hydrogen storage alloy powder. In that case, if the specific surface area is less than 1.4 times the specific surface area before contact, the specific surface area after treatment is Since the amount is not sufficiently increased, the improvement of the rate characteristic at a low temperature becomes insufficient. On the other hand, if it exceeds 4 times, the corrosion of the hydrogen storage alloy becomes excessive, so that the discharge capacity decreases.

【００５２】実施例５〜８、比較例６、７ 実施例２において、第２工程で用いる酸性水溶液に溶解
させたＫＦを変化させることにより、フッ素イオン濃度
を表２で示したように変化させ、他の条件は実施例２と
同じに設定して合金粉末の表面処理を行った。得られた
合金粉末を用いて実施例２と同じニッケル・水素二次電
池を組立て、それら電池の特性を測定した。その結果を
表２に示した。Examples 5 to 8 and Comparative Examples 6 and 7 In Example 2, the fluorine ion concentration was changed as shown in Table 2 by changing the KF dissolved in the acidic aqueous solution used in the second step. The other conditions were set to be the same as in Example 2, and the surface treatment of the alloy powder was performed. Using the obtained alloy powder, the same nickel-hydrogen secondary batteries as in Example 2 were assembled and the characteristics of those batteries were measured. The results are shown in Table 2.

【００５３】[0053]

【表２】 [Table 2]

【００５４】表２から明らかなように、フッ素イオン濃
度を１００〜５０００ ｍｏｌ／ｍ3 の範囲に設定する
と、電池の率別放電特性とサイクル寿命特性（維持率）
は向上している。 実施例９〜１３、比較例８、９ 組成は実施例１で用いた水素吸蔵合金と同じであるが、
平均粒径を表３で示したように変化させた合金粉末を用
いて、実施例２と同じ条件で第１工程と第２工程を行っ
た。As is clear from Table 2, the fluorine ion concentration
100 to 5000 mol / mThree Set to the range of
And discharge characteristics and cycle life characteristics (maintenance rate) of each battery
Is improving. Examples 9 to 13 and Comparative Examples 8 and 9 have the same composition as the hydrogen storage alloy used in Example 1,
Use alloy powders whose average particle size is changed as shown in Table 3.
Then, the first step and the second step are performed under the same conditions as in the second embodiment.
Was.

【００５５】得られた合金粉末を用いて、実施例１ と
同じニッケル・水素二次電池を組立て、その電池特性を
測定した。その結果を表３に示した。Using the obtained alloy powder, the same nickel-hydrogen secondary battery as in Example 1 was assembled and the battery characteristics were measured. Table 3 shows the results.

【００５６】[0056]

【表３】 [Table 3]

【００５７】表３から明らかなように、合金粉末の粒径
が４５μｍより大きくなると、電池特性の低下が認めら
れる。そして、粒径４５μｍの合金粉末を用いた電池に
つき、初期活性化処理後の時点で水素吸蔵合金電極を取
り出してその表面を観察したところ、合金粉末は微細化
し、その半分以下は、新生面の非処理面になっていた。As is clear from Table 3, when the particle size of the alloy powder is larger than 45 μm, deterioration of battery characteristics is recognized. Then, for the battery using the alloy powder having a particle diameter of 45 μm, the hydrogen storage alloy electrode was taken out at the time point after the initial activation treatment and the surface thereof was observed. It was on the processing side.

【００５８】また、平均粒径が１０μｍのものは、凝集
が起こりやすく、酸化しやすいことから、その取り扱い
が困難であることがわかった。このようなことから、と
くに平均粒径が１５〜３５μｍの合金粉末に対して本発
明の表面処理は有効であることがわかる。なお、本発明
方法が対象とする水素吸蔵合金は、Ｃｏまたは希土類金
属のＡＢ 5 型のものに限定されるものではなく、ＡＢ2
型のラーベス相合金やＭｇを主体とする金属などにも適
用することができる。If the average particle size is 10 μm, the particles are aggregated.
Is likely to occur and is easily oxidized, so handle it
Turned out to be difficult. Because of this,
Mainly for alloy powders with an average particle size of 15 to 35 μm
It can be seen that the bright surface treatment is effective. The present invention
The hydrogen storage alloy targeted by the method is Co or rare earth gold.
Genus AB FiveThe type is not limited to AB2
Type Laves phase alloy and Mg-based metals
Can be used.

【００５９】[0059]

【発明の効果】以上の説明で明らかなように、本発明方
法によれば、処理後の水素吸蔵合金粉末の比表面積は増
大し、しかもその部分の高濃度アルカリ電解液に対する
耐食性が向上する。したがって、その合金粉末を用いた
水素吸蔵合金電極が組み込まれているニッケル・水素二
次電池は、率別放電容量、とりわけ低温下における率別
放電容量が大きく、しかもサイクル寿命特性が優れた電
池になっている。As is apparent from the above description, according to the method of the present invention, the specific surface area of the hydrogen-absorbing alloy powder after treatment is increased, and the corrosion resistance of the portion to the high-concentration alkaline electrolyte is improved. Therefore, the nickel-hydrogen secondary battery in which the hydrogen storage alloy electrode using the alloy powder is incorporated has a large discharge capacity by rate, especially a discharge capacity by rate at low temperature, and has excellent cycle life characteristics. Has become.

【００６０】本発明の表面処理方法は、水素吸蔵合金粉
末または水素吸蔵合金電極を、最初、アルカリ性水溶液
に浸漬し、ついでフッ素イオンを含むｐＨ３〜６の酸性
水溶液に浸漬するという簡単な工程だけで成立するの
で、その工業的価値は大である。The surface treatment method of the present invention comprises the simple steps of first immersing the hydrogen storage alloy powder or the hydrogen storage alloy electrode in an alkaline aqueous solution, and then in an acidic aqueous solution containing fluorine ions and having a pH of 3 to 6. Since it is approved, its industrial value is great.

Claims (4)

【特許請求の範囲】[Claims] 【請求項１】 希土類元素を含む水素吸蔵合金粉末また
はそれを主成分として担持する水素吸蔵合金電極をアル
カリ性水溶液と接触させて前記水素吸蔵合金粉末の比表
面積を増加させ、ついで、フッ素イオンを含むｐＨ３〜
６の酸性水溶液と接触させて前記比表面積が増加した水
素吸蔵合金粉末の表面にフッ化処理を施すことを特徴と
する水素吸蔵合金粉末の表面処理方法。1. A hydrogen storage alloy powder containing a rare earth element or a hydrogen storage alloy electrode supporting the hydrogen storage alloy powder as a main component is contacted with an alkaline aqueous solution to increase the specific surface area of the hydrogen storage alloy powder, and then contains a fluorine ion. pH 3 ~
7. A method for treating the surface of a hydrogen storage alloy powder, wherein the surface of the hydrogen storage alloy powder having an increased specific surface area is subjected to a fluorination treatment by being brought into contact with the acidic aqueous solution of 6. 【請求項２】 前記水素吸蔵合金粉末には、更にアルミ
ニウムが含有されている請求項１の水素吸蔵合金粉末の
表面処理方法。2. The surface treatment method for a hydrogen storage alloy powder according to claim 1, wherein the hydrogen storage alloy powder further contains aluminum. 【請求項３】 前記水素吸蔵合金粉末の比表面積を、ア
ルカリ性水溶液との接触で1.４〜４倍に増大させる請求
項１または２の水素吸蔵合金粉末の表面処理方法。3. The surface treatment method for a hydrogen storage alloy powder according to claim 1, wherein the specific surface area of the hydrogen storage alloy powder is increased by 1.4 to 4 times by contact with an alkaline aqueous solution. 【請求項４】 請求項１、請求項２または請求項３の表
面処理方法を適用して製造した水素吸蔵合金電極が負極
として組み込まれていることを特徴とするアルカリ二次
電池。4. An alkaline secondary battery in which a hydrogen storage alloy electrode manufactured by applying the surface treatment method according to claim 1, 2 or 3 is incorporated as a negative electrode.
JP7222115A 1995-08-30 1995-08-30 Surface treatment method of hydrogen storage alloy powder and alkaline secondary battery obtained by applying the method Expired - Lifetime JP2978094B2 (en)

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JP2000294235A (en) * 1999-04-09 2000-10-20 Santoku Corp Hydrogen storage alloy powder for battery and manufacture of the same
US6322925B1 (en) 1997-08-28 2001-11-27 Sanyo Electric Co., Ltd. Metal hydride alkaline storage cell
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Publication number Priority date Publication date Assignee Title
US5932034A (en) * 1996-10-16 1999-08-03 Shin-Etsu Chemical Co., Ltd. Method of producing hydrogen absorbing alloy powder, and electrode using hydrogen absorbing alloy powder produced by said method
EP0837515A1 (en) * 1996-10-16 1998-04-22 Shin-Etsu Chemical Co., Ltd. Method of surface treating of a hydrogen absorbing alloy powder, and electrode using hydrogen absorbing alloy powder produced by said method
US6322925B1 (en) 1997-08-28 2001-11-27 Sanyo Electric Co., Ltd. Metal hydride alkaline storage cell
US6852447B2 (en) 1997-08-28 2005-02-08 Sanyo Electric Co., Ltd. Metal hydride alkaline storage cell and manufacturing method thereof
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US9738952B2 (en) 2014-03-26 2017-08-22 Mitsui Mining & Smelting Co., Ltd. Hydrogen storing alloy
JP2016012443A (en) * 2014-06-27 2016-01-21 Fdk株式会社 Nickel-hydrogen secondary battery
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JP2016149299A (en) * 2015-02-13 2016-08-18 Fdk株式会社 Nickel hydrogen secondary battery
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