JP7175372B1 - Low Co hydrogen storage alloy - Google Patents
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- 229910045601 alloy Inorganic materials 0.000 title claims abstract description 147
- 239000000956 alloy Substances 0.000 title claims abstract description 147
- 239000001257 hydrogen Substances 0.000 title claims abstract description 129
- 229910052739 hydrogen Inorganic materials 0.000 title claims abstract description 129
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 title claims abstract description 121
- 238000003860 storage Methods 0.000 title claims abstract description 87
- 239000013078 crystal Substances 0.000 claims abstract description 55
- 238000004458 analytical method Methods 0.000 claims abstract description 23
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 23
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 18
- 229910052746 lanthanum Inorganic materials 0.000 claims abstract description 13
- 229910004247 CaCu Inorganic materials 0.000 claims abstract description 12
- 229910001122 Mischmetal Inorganic materials 0.000 claims abstract description 10
- 238000010298 pulverizing process Methods 0.000 claims description 33
- 239000000843 powder Substances 0.000 claims description 28
- 229910052684 Cerium Inorganic materials 0.000 claims description 8
- 239000007773 negative electrode material Substances 0.000 claims description 5
- 239000002994 raw material Substances 0.000 abstract description 14
- 239000011159 matrix material Substances 0.000 abstract description 11
- 229910052987 metal hydride Inorganic materials 0.000 abstract description 11
- 238000005204 segregation Methods 0.000 description 62
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- 239000011149 active material Substances 0.000 description 2
- 229910000905 alloy phase Inorganic materials 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 229910052804 chromium Inorganic materials 0.000 description 2
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- 229910052802 copper Inorganic materials 0.000 description 2
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 1
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- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
【課題】ニッケル水素電池の負極として用いられるＣｏ含有ＣａＣｕ５型水素吸蔵合金について、Ｃｏ含有量低減による原料コスト抑制と、負極の寿命特性とを両立させることを課題とする。
【解決手段】水素吸蔵合金は、ＣａＣｕ５型結晶構造の母相を有する。この母相は、ＭｍＮｉａＭｎｂＡｌｃＣｏｄ（式中、Ｍｍはミッシュメタルであり、４．３０≦ａ≦４．７５、０．２５≦ｂ≦０．４５、０．３５≦ｃ≦０．４５、０≦ｄ≦０．１２、５．２０≦ａ＋ｂ＋ｃ＋ｄ≦５．５５）で表される。そして、この水素吸蔵合金では、エネルギー分散型X線分析装置（ＥＤＳ）で相分析したときに検出されるＬａ及びＮｉからなる第１相が面積比で９７．５％以上１００％未満であり、Ｎｉ、Ｍｎを主として含む第２相が面積比で０％を超えて１．５％以下である。
【選択図】図７
A Co-containing CaCu5-type hydrogen-absorbing alloy used as a negative electrode of a nickel-metal hydride battery is to achieve both cost reduction of raw materials by reducing the Co content and longevity of the negative electrode.
A hydrogen storage alloy has a matrix of CaCu type 5 crystal structure. This parent phase is MmNiaMnbAlcCod (wherein Mm is a misch metal, 4.30 ≤ a ≤ 4.75, 0.25 ≤ b ≤ 0.45, 0.35 ≤ c ≤ 0.45, 0 ≤ d ≤0.12, 5.20≤a+b+c+d≤5.55). In this hydrogen-absorbing alloy, the first phase composed of La and Ni detected by phase analysis with an energy dispersive X-ray spectrometer (EDS) has an area ratio of 97.5% or more and less than 100%, The area ratio of the second phase mainly containing Ni and Mn exceeds 0% and is 1.5% or less.
[Selection drawing] Fig. 7
Description
本発明は、ニッケル水素電池の負極として用いられるＣａＣｕ５型の結晶構造を有するＣｏ含有量の少ない水素吸蔵合金に関する。更に本発明は、この水素吸蔵合金を用いた負極およびこの負極を使用した電池に関する。 TECHNICAL FIELD The present invention relates to a hydrogen storage alloy having a CaCu 5 -type crystal structure and a low Co content, which is used as a negative electrode of a nickel-metal hydride battery. Further, the present invention relates to a negative electrode using this hydrogen storage alloy and a battery using this negative electrode.
負極に水素吸蔵合金を用いたニッケル水素電池は、１９９０年代前半に商品化され、その後、広く普及している。 Nickel-metal hydride batteries using a hydrogen storage alloy for the negative electrode were commercialized in the first half of the 1990s and have been widely used since then.
ニッケル水素電池は、商品化当初は携帯電話やノートパソコンの電源として活躍していたが、その後は、徐々に小型で軽量なリチウムイオン電池へと置き換えられ、現在では、低廉さと安全性の高さ、及び、体積当りのエネルギー密度とのバランスの良さなどから、玩具、小型機器、更にはハイブリッド自動車などに用いられている。 When nickel-metal hydride batteries were first commercialized, they were used as power sources for mobile phones and notebook computers, but since then they have gradually been replaced by smaller, lighter lithium-ion batteries. , and because of its well-balanced energy density per volume, it is used in toys, small devices, and even hybrid cars.
このようなニッケル水素電池に用いられる水素吸蔵合金は、水素と反応して金属水素化物となる合金である。この水素吸蔵合金は、室温付近で多量の水素を可逆的に吸蔵・放出することができる。 A hydrogen storage alloy used in such a nickel-metal hydride battery is an alloy that reacts with hydrogen to form a metal hydride. This hydrogen storage alloy can reversibly store and release a large amount of hydrogen at around room temperature.
水素吸蔵合金としては、ＬａＮｉ５に代表されるＡＢ５型合金、ＺｒＶ０．４Ｎｉ１．５に代表されるＡＢ２型合金のほか、ＡＢ型、Ａ２Ｂ型、ＡＢ３型などの様々なタイプの合金が知られている。これらの合金は、水素との親和性が高く水素吸蔵量を高める役割を果たす元素グループ（希土類元素，Ｃａ，Ｍｇ，Ｔｉ，Ｚｒ，Ｖ，Ｎｂ，Ｐｔ，Ｐｄ等）と、水素との親和性が比較的低く吸蔵量は少ないが、水素化反応が促進して反応温度を低くする役割を果たす元素グループ（Ｎｉ，Ｍｎ，Ｃｏ，Ａｌ等）との組合せで構成されている。 Hydrogen storage alloys include AB 5 type alloys typified by LaNi 5 , AB 2 type alloys typified by ZrV 0.4 Ni 1.5 , AB type, A 2 B type, and AB 3 type alloys. types of alloys are known. These alloys have a high affinity with hydrogen and a group of elements (rare earth elements, Ca, Mg, Ti, Zr, V, Nb, Pt, Pd, etc.) that play a role in increasing the hydrogen storage capacity and affinity with hydrogen. is relatively low and the amount of storage is small, but it is composed of a combination with an element group (Ni, Mn, Co, Al, etc.) that promotes the hydrogenation reaction and lowers the reaction temperature.
これらの中で、ＣａＣｕ５型結晶構造を有するＡＢ５型水素吸蔵合金、例えば、Ａサイトに希土類系の混合物であるミッシュメタル（以下「Ｍｍ」という。）を用い、ＢサイトにＮｉ，Ｍｎ，Ｃｏ，Ａｌ等の元素を用いた合金は、他の組成の合金に比べて、比較的安価な材料で負極を形成することができる。 Among these, AB5 -type hydrogen storage alloys having a CaCu5 -type crystal structure, for example, misch metal (hereinafter referred to as "Mm"), which is a mixture of rare earth elements, is used for the A site, and Ni, Mn, Alloys using elements such as Co and Al can form the negative electrode with relatively inexpensive materials compared to alloys with other compositions.
ＡＢ５型水素吸蔵合金では、Ａサイト原子量に対するＢサイト原子量の割合（ＡＢ比）、及びＮｉの一部をＣｏ、Ｍｎ、Ａｌ等の置換量を調整することにより、それを用いた負極の充放電容量、入出力特性、サイクル寿命などの様々な特性を調整することができる。そのような特徴をもつＡＢ５型水素吸蔵合金は、様々な用途に応じたニッケル水素蓄電池を造り分けすることを可能としている。 In the AB 5 -type hydrogen storage alloy, by adjusting the ratio of the B site atomic weight to the A site atomic weight (AB ratio) and the amount of substitution of a part of Ni with Co, Mn, Al, etc., it is possible to charge the negative electrode using it. Various characteristics such as discharge capacity, input/output characteristics, and cycle life can be adjusted. The AB5 -type hydrogen storage alloy with such characteristics makes it possible to produce different nickel-metal hydride storage batteries according to various uses.
ハイブリッド自動車を普及拡大させるためには、ニッケル水素電池の製造コストを低く抑え、負極の寿命特性および入出力特性をさらに向上させる必要がある。この目的を達成するために、ＡＢ５型水素吸蔵合金の研究開発が活発に行なわれている。特に高価なレアメタルであるＣｏの使用量を可能な限り低減したＡＢ５型水素吸蔵合金にて、寿命特性の維持向上を目的として、合金中の「偏析相」に着目した検討が行われている。 In order to popularize and expand hybrid vehicles, it is necessary to keep down the production cost of nickel-metal hydride batteries and further improve the life characteristics and input/output characteristics of the negative electrode. In order to achieve this purpose, research and development of AB5 -type hydrogen storage alloys are actively carried out. In particular, AB5 -type hydrogen storage alloys, in which the amount of Co, which is an expensive rare metal, is reduced as much as possible, are being studied with a focus on the "segregation phase" in the alloy for the purpose of maintaining and improving the life characteristics. .
例えば、特許文献１において、水素吸蔵合金電極の活物質として、ＣａＣｕ５型の結晶構造を有し、ＭｍＭｇＮｉＣｏＭｎＡｌからなる水素吸蔵合金粉末であって、少なくとも水素吸蔵合金粉末の内部にＭｇＮｉＣｏＭｎＡｌ合金相からなる微細な偏析相が分散して存在している水素吸蔵合金粉末を適用する。また、好ましくは、前記水素吸蔵合金粉末の表面に、ＮｉとＣｏの合金からなる表面層を備えた水素吸蔵合金粉末を適用することが提案されている。このようにすることで、水素吸蔵合金粉末の微細化が抑制されるとしている。 For example, in Patent Document 1, a hydrogen storage alloy powder having a CaCu 5 -type crystal structure and made of MmMgNiCoMnAl is used as an active material for a hydrogen storage alloy electrode, and at least the inside of the hydrogen storage alloy powder consists of an MgNiCoMnAl alloy phase. A hydrogen-absorbing alloy powder in which fine segregation phases are dispersed is applied. It is also proposed to preferably apply a hydrogen-absorbing alloy powder having a surface layer made of an alloy of Ni and Co on the surface of the hydrogen-absorbing alloy powder. It is stated that by doing so, the refinement of the hydrogen-absorbing alloy powder is suppressed.
また特許文献２において、Ｌａ量が６０～９０ｗｔ％のミッシュメタル、Ｍｇ、Ｎｉ、Ｃｏ、Ｍｎ及びＡｌを含み、ミッシュメタルとＭｇの合計量を基準として、Ｍｇ量が２～６原子％である水素吸蔵合金であって、母相中に少なくとも一相の偏析相が存在し、該偏析相中のＭｇ濃度が母相中のＭｇ濃度より高いことを特徴とする希土類系水素吸蔵合金が提案されている。このようにすることで、電池活性化時に合金中の偏析相が選択的に腐食されて、偏析相付近から表面積が増大し、早期に合金が活性化されるとしている。 Further, in Patent Document 2, the amount of La is 60 to 90 wt%, misch metal, Mg, Ni, Co, Mn and Al are included, and the amount of Mg is 2 to 6 atomic % based on the total amount of misch metal and Mg. There has been proposed a rare earth hydrogen storage alloy which is a hydrogen storage alloy, characterized in that at least one segregation phase exists in the matrix phase and the Mg concentration in the segregation phase is higher than the Mg concentration in the matrix phase. ing. By doing so, the segregation phase in the alloy is selectively corroded during battery activation, the surface area increases from the vicinity of the segregation phase, and the alloy is activated early.
また特許文献３において、負極活物質として、Ｍｍ（Ｍｍは３０重量％以上のＬａを含む２種類以上の希土類元素の混合物を表す）と、少なくともＮｉ、Ｃｏ、Ｍｎ及びＡｌを構成元素とする水素吸蔵合金であって、上記水素吸蔵合金中にＮｉを主体とする偏析相を有し、かつ合金断面の任意の１５μｍ平方の領域に露出する偏析相の数（ただし、偏析相に最小直径で外接する円の直径が０．０５μｍ以上の偏析相の数）が１～４０である水素吸蔵合金を用いることが提案されている。このようにすることによって、高容量で、低温での高率放電が可能であり、かつ高温貯蔵特性が優れるとしている。 Further, in Patent Document 3, Mm (Mm represents a mixture of two or more rare earth elements containing 30% by weight or more of La) and hydrogen containing at least Ni, Co, Mn and Al as constituent elements of the negative electrode active material The hydrogen storage alloy, which has a segregation phase mainly composed of Ni in the hydrogen storage alloy, and the number of segregation phases exposed in an arbitrary 15 μm square area of the cross section of the alloy (however, the number of segregation phases circumscribed by the minimum diameter It has been proposed to use a hydrogen storage alloy having a number of segregation phases with a diameter of 0.05 μm or more) of 1 to 40. By doing so, it is possible to achieve high capacity, high rate discharge at low temperatures, and excellent high temperature storage characteristics.
そして特許文献４において、ＣａＣｕ５型結晶構造の母相を有する水素吸蔵合金であって、エネルギー分散型Ｘ線分析装置（ＥＤＸ）で点分析した時の母相のＦｅピーク強度に対する、偏析相のＦｅピーク強度の比率であるＦｅピーク強度比［{（偏析のＦｅピーク強度）／（母相のＦｅピーク強度）}×１００（％）］と、母相のＭｎピーク強度に対する、偏析相のＭｎピーク強度の比率であるＭｎピーク強度比［{（偏析相のＭｎピーク強度）／（母相のＭｎピーク強度）}×１００（％）］との比率であるＦｅ／Ｍｎピーク比［Ｆｅ／Ｍｎ比］が、０．１２＜［Ｆｅ／Ｍｎ比］＜０．３７であることを特徴とする水素吸蔵合金が提案されている。このようにすることで、優れたサイクル特性を得るとしている。該偏析相が、母相の水素吸蔵・放出に伴う格子の膨張・収縮による歪みを緩和する役割（クッションの役割）を果たしているとしている。 And in Patent Document 4, a hydrogen storage alloy having a CaCu 5 -type crystal structure parent phase, and the segregation phase relative to the Fe peak intensity of the parent phase when point analysis is performed with an energy dispersive X-ray spectrometer (EDX). Fe peak intensity ratio [{(Segregation Fe peak intensity) / (Mother phase Fe peak intensity)} × 100 (%)], which is the ratio of Fe peak intensity, and Mn of the segregation phase with respect to Mn peak intensity of the mother phase Fe/Mn peak ratio [Fe/Mn ratio] is 0.12<[Fe/Mn ratio]<0.37. By doing so, excellent cycle characteristics are obtained. It is said that the segregation phase plays a role (cushion role) of alleviating strain due to expansion/contraction of the lattice associated with hydrogen absorption/desorption of the matrix phase.
さらに特許文献５において、一般式ＭｍＮｉx Ｍy（Ｍｍはミッシュメタルまたは希土類元素の混合物、ＭはＡｌ、Ｍｎ、Ｃｏ、Ｃｕ、Ｆｅ、Ｃｒ、ＴｉおよびＶよりなる群から選択される少なくとも１種の元素であり、５.０≦ｘ＋ｙ≦５.５）で表され、その合金組織が、ＣａＣｕ５型の結晶構造を有し水素を可逆的に吸蔵放出する相と、Ｍｍ以外の元素を主成分とし水素を吸蔵しない１種または複数の相からなり、後者の相が前者の相中に島状に分散している水素吸蔵合金が提案されている。そのようにすることで、多量のＣｏを含まなくとも長寿命と優れた高率放電特性を兼ね備えるとしている。水素を吸蔵しない相が、水素を吸蔵する相自体を応力に強い構造にするとしている。 Furthermore, in Patent Document 5, the general formula MmNix My (Mm is a mixture of misch metals or rare earth elements, M is at least one element selected from the group consisting of Al, Mn, Co, Cu, Fe, Cr, Ti and V 5.0 ≤ x + y ≤ 5.5), and the alloy structure has a CaCu 5 -type crystal structure, a phase that reversibly absorbs and releases hydrogen, and elements other than Mm as main components. A hydrogen storage alloy has been proposed which consists of one or more phases which do not store hydrogen, the latter phase being dispersed in the former phase in the form of islands. By doing so, it is possible to achieve both long life and excellent high-rate discharge characteristics without containing a large amount of Co. It is said that the phase that does not absorb hydrogen makes the phase itself that absorbs hydrogen a stress-resistant structure.
上記の通り、これまでにも検討がなされてきているが、近年レアメタルであるＣｏの取引価格が高騰するなか、Ｃｏを含有するＡＢ５型水素吸蔵合金の原料コストを維持あるいは低減するためには、Ｃｏの含有率を可能な限り低減する必要がある。しかし、ＡＢ５型水素吸蔵合金のＣｏ含有率を低減すると、水素の吸蔵放出が繰り返されることによる合金の微粉化が促進し、負極の寿命特性が低下する傾向がある。Ｃｏ含有量の低減と、負極の寿命特性を両立させるための有効な課題解決策は見つかっていない。 As described above, investigations have been made so far, but in recent years, as the transaction price of Co, a rare metal, has soared, in order to maintain or reduce the raw material cost of AB 5 type hydrogen storage alloys containing Co, , Co content should be reduced as much as possible. However, when the Co content of the AB 5 type hydrogen storage alloy is reduced, the repeated hydrogen absorption/desorption promotes pulverization of the alloy, which tends to reduce the life characteristics of the negative electrode. No effective solution has been found for achieving both the reduction of the Co content and the longevity characteristics of the negative electrode.
特許文献１には、水素吸蔵合金電極の活物質として、ＣａＣｕ５型の結晶構造を有し、ＭｍＭｇＮｉＣｏＭｎＡｌからなる水素吸蔵合金粉末であって、少なくとも水素吸蔵合金粉末の内部にＭｇＮｉＣｏＭｎＡｌ合金相からなる微細な偏析相が分散して存在し、前記ＭｇＮｉＣｏＭｎＡｌからなる偏析相の比率が０．５～１．５ｗｔ％が好ましいとしている。しかし、この水素吸蔵合金のＣｏ含有量は０．２～１．０モルとしており、実施例でのＣｏ含有量は０．７５モルの場合だけと、Ｃｏ量が多すぎる課題がある。即ち、Ｃｏ量が少ない組成域でかつＭｇが存在しない組成域で、偏析相の効果を有するということは記載も示唆もない。 Patent Document 1 discloses a hydrogen-absorbing alloy powder having a CaCu 5 -type crystal structure and composed of MmMgNiCoMnAl as an active material for a hydrogen-absorbing alloy electrode. A segregation phase is dispersedly present, and the ratio of the segregation phase composed of MgNiCoMnAl is preferably 0.5 to 1.5 wt%. However, the Co content of this hydrogen-absorbing alloy is 0.2 to 1.0 mol, and the Co content in the examples is only 0.75 mol. In other words, there is neither description nor suggestion that a composition region with a small amount of Co and no Mg content has the effect of a segregation phase.
特許文献２では、Ｌａ量が６０～９０ｗｔ％のミッシュメタル、Ｍｇ、Ｎｉ，Ｃｏ、Ｍｎ及びＡｌを含み、ミッシュメタルとＭｇの合計量を基準として、Ｍｇ量が２～６原子％である水素吸蔵合金であって、母相中に少なくとも一相の偏析相が存在し、該偏析相中のＭｇ濃度が母相中のＭｇ濃度より高いことを特徴としている。しかし、この水素吸蔵合金のＣｏ含有量は０．２モル以上０．７モル以下としており、実施例でのＣｏ含有量も０．３モルの場合だけと、Ｃｏ含有量が多い課題がある。同様に、Ｃｏ量が少ない組成域でかつＭｇが存在しない組成域で、偏析相の効果を有するということは記載も示唆もない。 In Patent Document 2, the amount of La is 60 to 90 wt% misch metal, Mg, Ni, Co, Mn and Al, based on the total amount of misch metal and Mg, based on the total amount of Mg hydrogen The storage alloy is characterized in that at least one segregation phase exists in the matrix phase, and the Mg concentration in the segregation phase is higher than the Mg concentration in the matrix phase. However, the Co content of this hydrogen storage alloy is 0.2 mol or more and 0.7 mol or less, and the Co content in the examples is only 0.3 mol, so there is a problem that the Co content is large. Similarly, there is neither description nor suggestion that a composition region with a small amount of Co and no Mg has the effect of a segregation phase.
特許文献３には、Ｍｍ（Ｍｍは３０重量％以上のＬａを含む２種類以上の希土類元素の混合物を表す）と、少なくともＮｉ、Ｃｏ、ＭｎおよびＡｌを構成元素とする水素吸蔵合金であって、上記水素吸蔵合金中にＮｉを主体とする偏析相を有し、かつ合金断面の任意の１５μｍ平方の領域に露出する偏析相の数（ただし、偏析相に最小直径で外接する円の直径が０．０５μｍ以上の偏析相の数）が１～４０である水素吸蔵合金を用いることを特徴としている。しかし、この水素吸蔵合金のＣｏ含有量は０．２モル以上０．７モル以下と多く、比較例で示すようにＣｏ含有量０．２５モルでは偏析相が多く劣化が進むという課題がある。即ち、Ｃｏ量が少ない組成域で、偏析相の効果を有するということは記載も示唆もない。また、１５μｍ平方に露出する偏析相、即ちｍ１５μｍ平方に偏析相が存在することを必須としているので、更に広間隔で点在する偏析相の分散では効果が得られないことを意味する。 Patent Document 3 discloses a hydrogen storage alloy containing Mm (Mm is a mixture of two or more rare earth elements containing 30% by weight or more of La) and at least Ni, Co, Mn and Al as constituent elements, , the number of segregation phases having a segregation phase mainly composed of Ni in the hydrogen storage alloy and exposed in an arbitrary 15 μm square region of the cross section of the alloy (however, the diameter of the circle circumscribing the segregation phase at the minimum diameter is The number of segregation phases of 0.05 μm or more) is characterized by using a hydrogen storage alloy of 1 to 40. However, the Co content of this hydrogen-absorbing alloy is as large as 0.2 mol or more and 0.7 mol or less. In other words, there is neither description nor suggestion that the segregation phase has an effect in a composition range where the amount of Co is small. In addition, since it is essential that the segregation phase is exposed in a square of 15 μm, that is, the segregation phase exists in a square of 15 μm, it means that the dispersion of the segregation phase scattered at wider intervals cannot obtain the effect.
特許文献４には、ＣａＣｕ５型結晶構造の母相を有する水素吸蔵合金であって、エネルギー分散型Ｘ線分析装置（ＥＤＸ）で点分析した時の母相のＦｅピーク強度に対する、偏析相のＦｅピーク強度の比率であるＦｅピーク強度比［{（偏析相のＦｅピーク強度）／（母相のＦｅピーク強度）}×１００（％）］と、母相のＭｎピーク強度に対する、偏析相のＭｎピーク強度の比率であるＭｎピーク強度比［{（偏析相のＭｎピーク強度）／（母相のＭｎピーク強度）}×１００（％）］との比率であるＦｅ／Ｍｎピーク比［Ｆｅ／Ｍｎ比］が、０．１２＜［Ｆｅ／Ｍｎ比］＜０．３７であることを特徴としている。Ｃｏ含有量は０．３５モル以下に設定し、Ｃｏに代わってＦｅで加えることで微粉化特性（すなわち寿命特性）を提案したものであるが、充放電容量に相当する水素吸蔵量（Ｈ／Ｍ）等の記載はなく、この文献に示した結果だけでは、Ｃｏ含有量の低減と負極の寿命特性を両立しているとはいえない。また、Ｆｅを含む組成を必須としているので、Ｆｅを含まない組成における微粉化特性に関する記載や示唆はない。 Patent Document 4 describes a hydrogen storage alloy having a matrix of CaCu type 5 crystal structure, and the segregation phase relative to the Fe peak intensity of the matrix when point analysis is performed with an energy dispersive X-ray spectrometer (EDX). Fe peak intensity ratio [{(Fe peak intensity of segregation phase) / (Fe peak intensity of mother phase)} × 100 (%)], which is the ratio of Fe peak intensity, and segregation phase relative to Mn peak intensity of mother phase Fe/Mn peak ratio [Fe/ Mn ratio] is 0.12<[Fe/Mn ratio]<0.37. The Co content is set to 0.35 mol or less, and by adding Fe instead of Co, it is proposed to improve the pulverization characteristics (that is, life characteristics). M) etc. are not described, and it cannot be said that the reduction of the Co content and the life characteristics of the negative electrode are compatible only with the results shown in this document. In addition, since the composition containing Fe is essential, there is no description or suggestion regarding the pulverization characteristics of the composition containing no Fe.
特許文献５には、多量のＣｏを含まなくとも長寿命と優れた高率放電特性を兼ね備え、低コストの水素吸蔵合金を提供することを目的に、合金組織がＣａＣｕ５型の結晶構造を有し水素を可逆的に吸蔵放出する相と、Ｍｍ以外の元素を主成分とし水素を吸蔵しない１種または複数の相からなり、後者の相が前者の相中に島状に分散している水素吸蔵合金が提案されているが、Ｃｏ含有量が０．３モル以下であるものの、Ｃｏに代わる元素として、Ｃｕ、Ｆｅ、Ｃｒ、Ｙによる置換も行っていることからＡＢ比が大きく、概ね初期容量が低下する問題がある。 In Patent Document 5, the alloy structure has a CaCu 5 -type crystal structure for the purpose of providing a low-cost hydrogen storage alloy that has a long life and excellent high-rate discharge characteristics without containing a large amount of Co. It consists of a phase that reversibly absorbs and releases hydrogen and one or more phases that contain elements other than Mm as main components and do not absorb hydrogen, and the latter phase is dispersed in the former phase in the form of islands. Storage alloys have been proposed, but although the Co content is 0.3 mol or less, substitution with Cu, Fe, Cr, and Y is also performed as an element to replace Co, so the AB ratio is large. There is a problem of reduced capacity.
本発明は、上記問題点に鑑みてなされたものであり、Ｃｏを含有するＡＢ５型水素吸蔵合金について、Ｃｏ含有量の低減により原料コストを抑制したうえで、水素の繰返し吸蔵放出による合金の微粉化を抑制することで、負極活物質に用いたときの寿命特性を維持することができる水素吸蔵合金および水素吸蔵合金を用いた負極、電池を提供することを課題としている。 The present invention has been made in view of the above problems, and for AB 5 type hydrogen storage alloys containing Co, the raw material cost is suppressed by reducing the Co content, and the alloy is improved by repeated hydrogen absorption and desorption. An object of the present invention is to provide a hydrogen-absorbing alloy and a negative electrode and a battery using the hydrogen-absorbing alloy that can maintain life characteristics when used as a negative-electrode active material by suppressing pulverization.
本発明者は、上記課題を解決すべく、鋭意研究し、ＡＢ５型水素吸蔵合金において、Ｃｏ含有量の低減により原料コストを抑制したうえで、Ｃｏによる微粉化抑制効果を代替する方法を検討した結果、先行技術文献にあるような偏析相が水素吸蔵相の歪みを緩和する役割となるのではく、寧ろ水素吸蔵によって体積変化する相と体積変化しない相が混在すると割れが発生しやすい（微粉化しやすい）ことが分かり、寧ろ、水素吸蔵相の大きな結晶粒の間に少量適度に偏析相が存在する水素吸蔵合金とすることでニッケル水素電池の負極とするために粉砕した際に偏析相を起点に割れるので負極とする水素吸蔵合金相に歪みを与えず微粉化し難くなることを見出し、その結果、合金の水素吸蔵量の低下がなく、水素の繰返し吸蔵放出による合金の微粉化を抑制でき、負極活物質に用いたときの寿命特性が維持されることになり、本発明を完成させた。 In order to solve the above problems, the present inventors have made intensive research, and in the AB 5 type hydrogen storage alloy, after suppressing the raw material cost by reducing the Co content, consider a method to replace the pulverization suppressing effect of Co. As a result, the segregation phase does not play the role of relaxing the distortion of the hydrogen absorption phase as in the prior art literature, but rather, cracks are likely to occur if the phase that changes volume due to hydrogen absorption and the phase that does not change volume are mixed ( On the contrary, by making a hydrogen-absorbing alloy in which a small amount of moderately segregated phase exists between large crystal grains of the hydrogen-absorbing phase, the segregation phase when pulverized for use as a negative electrode of a nickel-metal hydride battery It was found that the hydrogen storage alloy phase used as the negative electrode is not distorted and becomes difficult to pulverize because it cracks from the starting point. Thus, the life characteristics when used as a negative electrode active material can be maintained, and the present invention has been completed.
本発明の要旨は、次の通りである。 The gist of the present invention is as follows.
（１）一般式ＭｍＮｉａＭｎｂＡｌｃＣｏｄ（式中、Ｍｍはミッシュメタルであり、４．３０≦ａ≦４．７５、０．２５≦ｂ≦０．４５、０．３５≦ｃ≦０．４５、０≦ｄ≦０．１２、５．２０≦ａ＋ｂ＋ｃ＋ｄ≦５．５５）で表され、ＣａＣｕ５型結晶構造を有し、前記Ｍｍは、ＬａおよびＣｅの割合が全Ｍｍに対して９０質量％以上１００質量％以下の範囲内であり、
エネルギー分散型X線分析装置（ＥＤＳ）で相分析したときに検出されるＬａとＮｉを含む第１相が面積比で９７．５％以上１００％未満であると共に、Ｎｉ、Ｍｎを主として含む第２相が面積比で０％を超え１．５％以下であり、かつ前記第１相が３００μｍ以上のサイズの結晶を含むことを特徴とする水素吸蔵合金のインゴット。
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（２）０≦ｄ≦０．０５であることを特徴とする（１）記載の水素吸蔵合金のインゴット。
（３）前記第２相の円相当直径の平均が１０μｍ以上８０μｍ以下であることを特徴とする（１）又は（２）記載の水素吸蔵合金のインゴット。
（４）前記第１相の結晶の平均サイズは１６０μｍ以上であることを特徴とする（１）～（３）のいずれかに記載の水素吸蔵合金のインゴット。
（５）（１）～（４）のいずれかに記載の水素吸蔵合金のインゴットを粉砕した水素吸蔵合金粉末を負極活物質としたことを特徴とする負極。
（６）（５）に記載の負極を用いたことを特徴とする電池。
(1) General formula MmNiaMnbAlcCod (wherein Mm is a misch metal, 4.30 ≤ a ≤ 4.75, 0.25 ≤ b ≤ 0.45, 0.35 ≤ c ≤ 0.45, 0 ≤ d ≤ 0.12, 5.20 ≤ a + b + c + d ≤ 5.55), has a CaCu type 5 crystal structure, and the Mm has a La and Ce ratio of 90% by mass or more and 100% by mass with respect to the total Mm within the following range ,
The first phase containing La and Ni detected by phase analysis with an energy dispersive X-ray spectrometer (EDS) has an area ratio of 97.5% or more and less than 100%, and the second phase mainly containing Ni and Mn A hydrogen-absorbing alloy ingot , characterized in that two phases have an area ratio of more than 0% to 1.5% or less, and the first phase contains crystals having a size of 300 μm or more.
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(2) The hydrogen storage alloy ingot according to (1), wherein 0≤d≤0.05.
(3) The hydrogen storage alloy ingot according to (1) or (2), wherein the second phase has an average equivalent circle diameter of 10 μm or more and 80 μm or less.
(4) The hydrogen storage alloy ingot according to any one of (1) to (3), wherein the average crystal size of the first phase is 160 μm or more.
(5) A negative electrode characterized by using a hydrogen-absorbing alloy powder obtained by pulverizing an ingot of the hydrogen-absorbing alloy according to any one of (1) to (4) as a negative electrode active material.
(6) A battery using the negative electrode described in (5).
本発明により、Ｃｏ含有量の低減により原料コストを抑制したうえで、水素の繰返し吸蔵放出による合金の微粉化を抑制したＡＢ５型水素吸蔵合金を提供することができ、負極や電池に有効に用いることができる。 INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an AB5 -type hydrogen storage alloy that suppresses the pulverization of the alloy due to repeated absorption and release of hydrogen, while suppressing the raw material cost by reducing the Co content, and is effective for negative electrodes and batteries. can be used.
以下に本発明を詳細に説明する。 The present invention will be described in detail below.
本発明者は、Ｃｏ含有量の少ないＡＢ５型水素吸蔵合金において、水素吸蔵・放出に伴う微粉化と偏析相の関係について詳細に検討した結果、次のような結論に達した。先行技術文献のように水素吸蔵・放出に伴う体積変化する水素吸蔵相と水素吸蔵・放出しない偏析相が共存していると、体積変化する相と体積変化しない相の界面で亀裂が発生して微粉化が進む、即ち、偏析相が存在しない方がよいということが分かった。よって、偏析相は電池の負極として使用されているときには無い方が良いということである。しかしながら、発明者らは、更に深く検討した結果、水素吸蔵相の結晶を大きく成長させてその結晶粒界面に偏析相を僅かに存在させることで、電池の負極とするために水素吸蔵合金を粉砕する際に偏析相を起点に亀裂が入って該合金が割れることにより水素吸蔵相の結晶内部に歪みや残留応力が発生し難くなることを見出した。このような歪みや残留応力の少ない結晶相でできた水素吸蔵合金では、水素吸蔵・放出の繰り返しがなされても微粉化が進み難く、その結果耐久性に優れ長寿命の電池とすることができた。 The present inventors have made detailed studies on the relationship between pulverization and segregation phases accompanying hydrogen absorption/desorption in AB 5 -type hydrogen storage alloys with a low Co content, and have reached the following conclusions. If a hydrogen absorption phase whose volume changes due to hydrogen absorption /desorption and a segregation phase which does not absorb/desorb hydrogen coexist as in prior art documents, cracks occur at the interface between the volume-changing phase and the non-volume-changing phase. It has been found that it is better if the pulverization is advanced, ie no segregation phase is present. Therefore, the segregation phase should be absent when used as the negative electrode of the battery. However, as a result of more in-depth studies, the inventors found that by growing large crystals of the hydrogen-absorbing phase and allowing a slight segregation phase to exist at the grain boundaries, the hydrogen-absorbing alloy was pulverized for use as the negative electrode of the battery. It has been found that when the alloy is cracked, cracks start from the segregation phase and the alloy cracks, thereby making it difficult for strain and residual stress to occur inside the crystals of the hydrogen storage phase. In such a hydrogen storage alloy made of a crystalline phase with little strain and residual stress, pulverization is difficult to progress even if hydrogen absorption and desorption are repeated, and as a result, a battery with excellent durability and long life can be obtained. rice field.
以上のことを踏まえて具体的に水素吸蔵合金を開発した結果、本発明の水素吸蔵合金は、一般式ＭｍＮｉａＭｎｂＡｌｃＣｏｄ（式中、Ｍｍはミッシュメタルであり、４．３０≦ａ≦４．７５、０．２５≦ｂ≦０．４５、０．３５≦ｃ≦０．４５、０≦ｄ≦０．１２、５．２０≦ａ＋ｂ＋ｃ＋ｄ≦５．５５）で表され、ＣａＣｕ５型結晶構造を有し、前記Ｍｍは、ＬａおよびＣｅの割合が全Ｍｍに対して９０質量％以上１００質量％以下の範囲内であり、エネルギー分散型X線分析装置（ＥＤＳ、Energy dispersive X-ray spectroscopy）で相分析したときに検出されるＬａとＮｉを含む第１相が面積比で９７．５％以上１００％未満であり、かつ前記第１相が３００μｍ以上のサイズの結晶を含み、Ｎｉ、Ｍｎを主として含む第２相が、面積比で０％以上１．５％以下とするものである。
上記のような組織は、どのような方法によって形成させても本発明の効果が得られるものであるが、１つの例として次のようの考え方で本発明の組織を形成させることができる。
As a result of specifically developing a hydrogen storage alloy based on the above, the hydrogen storage alloy of the present invention has the general formula MmNiaMnbAlcCod (wherein Mm is a misch metal, 4.30 ≤ a ≤ 4.75, 0 .25 ≤ b ≤ 0.45, 0.35 ≤ c ≤ 0.45, 0 ≤ d ≤ 0.12, 5.20 ≤ a + b + c + d ≤ 5.55) and has a CaCu type 5 crystal structure, The Mm has a ratio of La and Ce in the range of 90% by mass or more and 100% by mass or less with respect to the total Mm, and phase analysis is performed with an energy dispersive X-ray spectroscopy (EDS). The first phase containing La and Ni detected at times has an area ratio of 97.5% or more and less than 100%, and the first phase contains crystals with a size of 300 μm or more, and Ni and Mn. The area ratio of two phases is 0% or more and 1.5% or less.
Although the structure described above can be formed by any method, the effect of the present invention can be obtained. As an example, the structure of the present invention can be formed based on the following concept.
水素吸蔵合金の製造工程において、溶融金属の鋳型面で不均一核発生をさせ、発生した結晶核を成長させるように凝固させるという方法に注目し、そのような凝固を起こすために溶湯を鋳型で冷却する工程で、熱伝導率の高い鋳型を用いて鋳型面で溶湯から核発生を起こし該結晶核を成長させるように凝固させることにより、柱状の大きな結晶が成長するので偏析相の生成を抑制できる。このようにして得られた組織から熱処理によって結晶成長させると、水素吸蔵相が大きな結晶となり、僅かに形成される偏析相の該大きな結晶の結晶粒界に位置しやすくなる。その結果、上述のように、Ｃｏ含有量が少なくても、微粉化難度が低下せず、負極に用いたときに寿命特性が維持されるＡＢ５型水素吸蔵合金を製造できる。 In the process of manufacturing hydrogen storage alloys, we focused on the method of generating heterogeneous nuclei on the mold surface of the molten metal and solidifying the generated crystal nuclei to grow. In the cooling step, a mold with high thermal conductivity is used to generate nuclei from the molten metal on the mold surface, and solidification is performed so that the crystal nuclei grow, so that large columnar crystals grow, suppressing the generation of segregation phases. can. When crystals are grown from the structure thus obtained by heat treatment, the hydrogen-absorbing phase becomes large crystals, and the slightly formed segregation phase tends to be located at the grain boundaries of the large crystals. As a result, as described above, even if the Co content is small, it is possible to manufacture an AB 5 -type hydrogen-absorbing alloy that does not reduce the difficulty of pulverization and maintains the life characteristics when used for a negative electrode.
本発明の組織にすることで微粉化し難くなる主な理由は、上述したが、次のような要因もあると考えている。
（１）一方向性凝固させることで、即ち、六方晶であるＣａＣｕ５型結晶構造をもつＡＢ５型水素吸蔵合金が、結晶成長する方向が揃った状態で凝固させることにより、集合組織、合金組成の均一性が向上し、偏析相の生成が抑制される。
（２）偏析相が低減したことにより、偏析相を含む水素吸蔵相の粒子が殆どなくなり、水素吸蔵放出に伴う結晶格子の膨張収縮が粒子全体に均一に進むために（膨張収縮しない偏析相が存在しないので偏析相との間で発生する応力がない）、粒子全体に均一に歪む。
（３）偏析相では水素吸蔵量が少なく或いは水素吸蔵しなく、水素吸蔵に伴う結晶格子の膨張が小さい或いは膨張しない。そのため、水素吸蔵放出によって膨張収縮して歪む周囲の水素吸蔵相の結晶との間に応力が発生し、その応力が割れの起因となっていたが、その偏析相が電池に組み込んだ際に殆どなくなっている。
As described above, the main reason why the structure of the present invention makes it difficult to pulverize is considered to be the following factors.
(1) By unidirectionally solidifying, that is, by solidifying the AB 5 -type hydrogen storage alloy having a hexagonal CaCu 5 -type crystal structure in a state in which the crystal growth direction is aligned, the texture, the alloy The uniformity of composition is improved, and the formation of segregation phases is suppressed.
(2) Since the segregation phase is reduced, the particles of the hydrogen absorption phase including the segregation phase are almost eliminated, and the expansion and contraction of the crystal lattice due to hydrogen absorption and desorption proceeds uniformly throughout the particles (the segregation phase that does not expand and contract is There is no stress generated between the segregation phases), and the grains are uniformly strained.
(3) The segregation phase has little or no hydrogen absorption, and little or no expansion of the crystal lattice accompanying hydrogen absorption. Therefore, stress is generated between the surrounding crystals of the hydrogen absorption phase, which expands and shrinks due to hydrogen absorption and desorption, and is distorted, and this stress causes cracking. Gone.
本発明のＡＢ５型水素吸蔵合金において、まずＡサイトを構成する金属について説明する。本発明では、Ａサイトを構成する金属として、ＬａまたはＬａの一部もしくは全部が希土類金属混合物であるミッシュメタル（Ｍｍ）を用いる。Ｍｍでは、ＬａおよびＣｅが、Ｍｍ全質量に対して９０質量％以上１００質量％以下の範囲内の割合を占めている、より好ましくは、Ｌａが７０～９６質量％、Ｃｅが４～３０質量％の範囲であり、更に好ましくは、Ｌａが７４～９４質量％、Ｃｅが６～２６質量％の範囲である。 In the AB 5 -type hydrogen storage alloy of the present invention, metals constituting the A site will be described first. In the present invention, La or a misch metal (Mm) in which La or part or all of La is a mixture of rare earth metals is used as the metal constituting the A site. In Mm, La and Ce occupy a ratio within the range of 90% by mass or more and 100% by mass or less with respect to the total mass of Mm, more preferably 70 to 96% by mass of La and 4 to 30% by mass of Ce. %, more preferably 74 to 94% by mass of La and 6 to 26% by mass of Ce.
次にＢサイトを構成する金属について説明する。本発明では、Ｂサイトを構成する金属として、Ｎｉ、Ｍｎ、Ａｌ、及びＣｏを用いる。これら金属のモル比は以下の条件を満たすものである。
Ｎｉモル比（ａ） ４．３０≦ ａ≦４．７５
Ｍｎモル比（ｂ） ０．２５≦ ｂ≦０．４５
Ａｌモル比（ｃ） ０．３５≦ ｃ≦０．４５
Ｃｏモル比（ｄ） ０≦ ｄ ≦０．１２
ＡＢ比 ５．２０≦（ａ+ b + c + d ） ≦５．５５
好ましい条件は、次の通りである。
Ｎｉモル比（ａ） ４．４０≦ ａ≦４．７０
Ｍｎモル比（ｂ） ０．２５≦ ｂ≦０．４１
Ａｌモル比（ｃ） ０．３８≦ ｃ≦０．４２
Ｃｏモル比（ｄ） ０≦ ｄ ≦０．０５
ＡＢ比 ５．２５≦（ａ+ b + c + d ） ≦５．４６
Ｃｏのモル比ｄは、原料コスト低減のため、なるべく少ない方が好ましく、０≦ｄ≦０．１２としている。ｄを０より大きく、０．１２以下とすることにより、即ち、Ｃｏ置換することにより、水素の吸蔵放出が繰り返されても微粉化し難くなり、置換量が増加するとその傾向が著しくなる。しかし、ｄ＝０、即ち、Ｃｏ置換しなくても、本発明のＡＢ５型水素吸蔵合金にすることにより、水素の吸蔵放出が繰り返されても微粉化し難くさせることができる。そのため、Ｃｏモル比（ｄ）は０≦ｄ≦０．１２であり、好ましくは０≦ｄ≦０．０５である。なお、ｄが０．１２を超えると、原料コスト低減につながらない。
Next, metals forming the B site will be described. In the present invention, Ni, Mn, Al, and Co are used as metals forming the B site. The molar ratio of these metals satisfies the following conditions.
Ni molar ratio (a) 4.30 ≤ a ≤ 4.75
Mn molar ratio (b) 0.25 ≤ b ≤ 0.45
Al molar ratio (c) 0.35 ≤ c ≤ 0.45
Co molar ratio (d) 0 ≤ d ≤ 0.12
AB ratio 5.20 ≤ (a + b + c + d) ≤ 5.55
Preferred conditions are as follows.
Ni molar ratio (a) 4.40 ≤ a ≤ 4.70
Mn molar ratio (b) 0.25 ≤ b ≤ 0.41
Al molar ratio (c) 0.38 ≤ c ≤ 0.42
Co molar ratio (d) 0 ≤ d ≤ 0.05
AB ratio 5.25≦(a+b+c+d)≦5.46
The molar ratio d of Co is preferably as small as possible in order to reduce raw material costs, and is 0≦d≦0.12. By setting d to be greater than 0 and 0.12 or less, that is, by substituting with Co, it becomes difficult to pulverize even if hydrogen absorption/desorption is repeated, and this tendency becomes more pronounced as the amount of substitution increases. However, even if d=0, that is, without Co substitution, the AB 5 -type hydrogen storage alloy of the present invention can be made difficult to pulverize even if hydrogen absorption and desorption are repeated. Therefore, the Co molar ratio (d) is 0≤d≤0.12, preferably 0≤d≤0.05. In addition, when d exceeds 0.12, it does not lead to reduction in raw material cost.
ＭｍのＬａ、Ｃｅの比率、Ｎｉ、Ｍｎ、Ａｌのモル比を上記の通りに設定した理由としては、ＡＢ５型水素吸蔵合金の水素吸蔵量（Ｈ／Ｍ）が、０．８５～１．００とすることにより充放電容量を確保すること、平衡圧を０．０４～０．０７ＭＰａとして初期活性化しやすくすること、ＰＣＴ曲線におけるプラトー域をなるべく広くすることを考慮したためである。
Ｍｍでは、ＬａおよびＣｅが、ＭｍのＭｍ全質量に対して９０質量％以上１００質量％以下の範囲内とすることで、水素吸蔵量（Ｈ／Ｍ）を０．８５～１．００として充放電容量を確保することができるためである。Ｎｉの割合（ａ）は、上述の通り、４．３０以上４．７５以下の範囲内であるが、水素吸蔵合金粉末を活物質として負極を作製した際、その出力特性を維持し易く、しかもその寿命特性を格別に悪化させることもない。Ｍｎの割合（ｂ）は、上述の通り、０．２５以上０．４５以下の範囲内であるが、この範囲内であれば、水素吸蔵合金粉末の微粉化難度を維持し易くすることができる。Ａｌの割合（ｃ）は、上述の通り、０．３５以上０．４５以下の範囲内であるが、この範囲内であれば、ＰＣＴ特性におけるヒステリシスが小さく水素吸蔵合金粉末の充放電効率の悪化を抑えることでき、かつ水素吸蔵合金粉末の水素吸蔵量の低下を抑えることができる。
The reason why the ratios of La and Ce in Mm and the molar ratios of Ni, Mn and Al are set as described above is that the hydrogen storage capacity (H/M) of the AB 5 type hydrogen storage alloy is 0.85 to 1.0. 00 to secure the charge/discharge capacity, to facilitate the initial activation by setting the equilibrium pressure to 0.04 to 0.07 MPa, and to widen the plateau region in the PCT curve as much as possible.
In Mm, La and Ce are in the range of 90% by mass or more and 100% by mass or less with respect to the total mass of Mm, so that the hydrogen storage capacity (H / M) is 0.85 to 1.00. This is because the discharge capacity can be secured. As described above, the ratio (a) of Ni is in the range of 4.30 or more and 4.75 or less. The life characteristics are not particularly deteriorated. As described above, the ratio (b) of Mn is in the range of 0.25 or more and 0.45 or less, and within this range, it is possible to easily maintain the difficulty of pulverization of the hydrogen-absorbing alloy powder. . As described above, the Al ratio (c) is within the range of 0.35 or more and 0.45 or less, but within this range, the hysteresis in the PCT characteristics is small, and the charge and discharge efficiency of the hydrogen storage alloy powder is deteriorated. can be suppressed, and a decrease in the hydrogen storage capacity of the hydrogen storage alloy powder can be suppressed.
前記、水素吸蔵合金において、エネルギー分散型X線分析装置（ＥＤＳ）で相分析したときに検出されるＬａ及びＮｉを含む第１相が面積比で９７．５％以上１００％未満であり、Ｎｉ、Ｍｎを主として含む第２相が、面積比で０％を超え１．５％以下、さらには１．２％以下であることが好ましい。より好ましくは、第１相が面積比で９８．５％以上１００％未満であり、更に好ましくは、第２相が面積比で０％を超え１．０％以下である。第１相と第２相がこの範囲をとることで、Ｃｏ含有量が少ない水素吸蔵合金においても、微粉化難度を０．４８～０．６０の範囲とすることが可能になる。なお、水素吸蔵合金の第１相と第２相を合計しても、１００％にならない場合があるが、これは、後記するように、合金を大気雰囲気下で研磨して観察するために一部が酸化してしまうこと、研磨材由来の不純物等が残存するためである。また、Ｎｉ、Ｍｎを主として含む第２相とは、後述するように、ＥＤＳによる相のマップ分析において、Ｎｉ元素とＭｎ元素とが重なって位置する部分の相を意味するものであり、例えば、Ｎｉ元素とＭｎ元素とが重なる位置にＬａ元素が少量存在するような場合を含むものとする。つまり、Ｎｉ、Ｍｎを主として含むとは、第２相を構成する元素の６０％以上がＮｉ元素とＭｎ元素からなることを意味する。 In the hydrogen storage alloy, the first phase containing La and Ni detected when phase analysis is performed with an energy dispersive X-ray spectrometer (EDS) has an area ratio of 97.5% or more and less than 100%, and Ni , and Mn in an area ratio of more than 0% to 1.5% or less, more preferably 1.2% or less. More preferably, the area ratio of the first phase is 98.5% or more and less than 100%, and more preferably the area ratio of the second phase is more than 0% and 1.0% or less. By setting the first phase and the second phase in this range, even in a hydrogen storage alloy with a small Co content, it is possible to set the pulverization difficulty within the range of 0.48 to 0.60. The sum of the first and second phases of the hydrogen-absorbing alloy may not be 100%. This is because the portion is oxidized and impurities derived from the abrasive remain. Further, the second phase mainly containing Ni and Mn means the phase in the portion where the Ni element and the Mn element are overlapped in the map analysis of the phase by EDS, as described later. This includes the case where a small amount of La element is present at the position where the Ni element and the Mn element overlap. In other words, "mainly containing Ni and Mn" means that 60% or more of the elements constituting the second phase are composed of Ni elements and Mn elements.
前記水素吸蔵合金において、水素吸蔵量（Ｈ／Ｍ）が０．８５～１．００であり、かつ微粉化難度が０．４８～０．６０、プラトー圧力が０．０４～０．０７ＭＰａであることで、水素吸蔵合金粉末を負極としたときに、充放電容量が大きく、寿命特性が長く、及び初期活性化がしやすい負極となる。
ここで、微粉化難度とは、「保持温度４５℃および水素圧力調整１．８２ＭＰａの環境下における水素の吸蔵放出サイクル１０回後の水素吸蔵合金粉末の粒度」を「水素吸蔵合金粉末の初期粒度」で除した値である。また、プラトー圧力は、測定温度４５℃水素放出側のＨ／Ｍ＝０．５における平衡水素圧力（ＭＰａ）のことである。
The hydrogen storage alloy has a hydrogen storage capacity (H/M) of 0.85 to 1.00, a pulverization difficulty of 0.48 to 0.60, and a plateau pressure of 0.04 to 0.07 MPa. As a result, when the hydrogen-absorbing alloy powder is used as a negative electrode, the negative electrode has a large charge/discharge capacity, a long life characteristic, and is easily activated at the initial stage.
Here, the degree of pulverization difficulty is defined as "the particle size of the hydrogen-absorbing alloy powder after 10 hydrogen absorption/desorption cycles in an environment where the holding temperature is 45°C and the hydrogen pressure is adjusted to 1.82 MPa", and the "initial particle size of the hydrogen-absorbing alloy powder". is the value divided by . The plateau pressure is the equilibrium hydrogen pressure (MPa) at H/M=0.5 on the hydrogen release side at a measurement temperature of 45°C.
微粉化難度を０．４８～０．６０とした理由は、高すぎると初期活性化し難く、かつ、電池の入出力特性が低下するためであり、反対に低すぎると、電池の寿命特性が確保されないためである。微粉化難度は水素吸蔵量（Ｈ／Ｍ）と相関があり、Ｈ／Ｍが多いほど微粉化難度は低め、Ｈ／Ｍが少ないほど微粉化難度は高めになる傾向があるため、Ｈ／Ｍと組み合わせて考慮する必要がある。Ｈ／Ｍを０．８５～１．００とした理由は、ニッケル水素電池用負極を作製したときに、目標の充放電容量を確保するためである。 The reason why the pulverization difficulty is set to 0.48 to 0.60 is that if it is too high, it will be difficult to activate in the initial stage and the input/output characteristics of the battery will decrease. because it is not The difficulty of pulverization is correlated with the amount of hydrogen storage (H / M). should be considered in combination with The reason why H/M is set to 0.85 to 1.00 is to secure the target charge/discharge capacity when producing a negative electrode for a nickel-metal hydride battery.
本発明の水素吸蔵合金では、前記第１相が３００μｍ以上のサイズの結晶を含むものである。前記第１相が３００μｍ以上のサイズの結晶を含まないような小さな結晶相から形成された組織であると、電池とするために該合金を粉砕した際に１つの粒子内に結晶粒界が含まれた粒子が多くなったり、粒子内に第２相を含んだ粒子が多くなったりする。これらが要因で微粉化が進みやすくなる。１つの粒子内に結晶粒界が存在すると水素を吸蔵放出による変形度合いが1つの粒子内で異なるので結晶粒界に応力が発生して割れやすくなる。また、１つの粒子内に第２相が存在すると、上述のように、水素の吸蔵放出で変形する相と殆ど変形しない相が共存するのでそれらの界面に応力が発生してクラックが生じやすくなる。
よって、前記第１相の結晶の平均サイズは、１６０μｍ以上であるのがよりこのましい。前記第１相は、大きな結晶であるほど前記理由で好ましいが、現実的な製造条件で得られる最大の平均サイズは、８００μｍ程度である。
尚、前記第１相の結晶のサイズは、電子線後方散乱回析法（ＥＢＳＤ）によって決めるものである。水素吸蔵合金のインゴットにおいて、冷却面付近より数ｍｍ四方程度の欠片をサンプリングし、走査型電子顕微鏡（ＳＥＭ）の観察用に直径１インチの樹脂に包埋、鏡面研磨し、最終仕上げとして粒径６０ｎｍのコロイダルシリカを用いて研磨を行う。ＳＥＭにて１００から３００倍程度の倍率で、二次電子像を観察する。任意の面において、菊池パターンと呼ばれる電子線回折パターンが明確に観察できる視野にて、結晶型にＬａＮｉ５を選定してＥＢＳＤマップ分析を行い、結晶相を色分けして表示させる。このとき結晶粒界を区別する角度は５°とする。その後、結晶粒（グレイン）の解析を行い、検出された各結晶粒の面積から、結晶粒サイズを円相当径で計測することができ、その際に３００μｍ以上のサイズを有する結晶の存在が確認される。また、本発明でいう第１相の結晶の平均サイズは、１０視野を観察してそれぞれ前記計測にて求めた平均値とする。
In the hydrogen storage alloy of the present invention, the first phase contains crystals with a size of 300 μm or more. If the first phase has a structure formed from small crystal phases that do not contain crystals with a size of 300 μm or more, then when the alloy is pulverized to make a battery, a grain boundary will be included in one grain. In this case, the number of grains containing the second phase is increased, or the number of grains containing the second phase is increased. These factors facilitate the progress of pulverization. If a grain boundary exists in one grain, the degree of deformation due to absorption and desorption of hydrogen differs within one grain, so stress is generated at the grain boundary and cracking is likely to occur. In addition, when a second phase exists in one particle, as described above, a phase that deforms due to the absorption and desorption of hydrogen and a phase that hardly deforms coexist, so stress is generated at the interface between them, and cracks are likely to occur. .
Therefore, it is more preferable that the average size of the crystals of the first phase is 160 μm or more. For the above reason, the larger the crystals of the first phase, the better, but the maximum average size obtained under realistic production conditions is about 800 μm.
The crystal size of the first phase is determined by electron beam backscatter diffraction (EBSD). In the ingot of the hydrogen storage alloy, a fragment of about several mm square is sampled from the vicinity of the cooling surface, embedded in a resin with a diameter of 1 inch for observation with a scanning electron microscope (SEM), mirror-polished, and grain size as a final finish. Polishing is performed using 60 nm colloidal silica. A secondary electron image is observed with a SEM at a magnification of about 100 to 300 times. LaNi 5 is selected as the crystal type, EBSD map analysis is performed, and the crystal phases are color-coded and displayed in a field of view where an electron beam diffraction pattern called a Kikuchi pattern can be clearly observed on an arbitrary surface. At this time, the angle for discriminating the grain boundaries is set to 5°. After that, crystal grains (grains) are analyzed, and from the area of each detected crystal grain, the crystal grain size can be measured in equivalent circle diameter. be done. In addition, the average size of the crystals of the first phase referred to in the present invention is the average value obtained by observing 10 fields of view and measuring each of them.
本発明の水素吸蔵合金では、更に、前記第２相の円相当直径の平均が１０μｍ以上８０μｍ以下であると本発明の作用効果をより好適に得られるので好ましい。上述のように、第２相の役割は、水素吸蔵合金を電池に用いるために粉砕する過程において第１相の結晶粒界に存在する第２相が起点になって割れることで第１相に残留応力や結晶歪みを生じさせないようにできること、また、このような割れ方をすることで第２相が粒子表面に存在させるようにできること（粒子内部に第２相を存在させないようにすること）で、微粉化が進み難くなる。したがって、第２相が１０μｍ未満で小さく分散していると、粒子内部に閉じ込める確率が高くなって前記効果が望めなくなる場合があったり、粉砕の際に第２相を起点に割れが生じなくなる場合があったりする。第２相が８０μｍを超えるようになると第２相の分散数が少なくなり過ぎて本発明の効果が得られなくなる場合がある。第２相は、エネルギー分散型X線分析装置（ＥＤＳ）で面分析して検出される第２相の形態から円相当直径を求める。１０個の第２相を測定して平均したものを前記第２相の円相当直径の平均とする。 In the hydrogen-absorbing alloy of the present invention, it is preferable that the second phase has an average equivalent circle diameter of 10 μm or more and 80 μm or less, since the effects of the present invention can be obtained more preferably. As described above, the role of the second phase is that in the process of pulverizing the hydrogen storage alloy for use in batteries, the second phase existing at the crystal grain boundary of the first phase cracks as a starting point, so that the first phase is formed. It is possible to prevent residual stress and crystal strain from being generated, and to allow the second phase to exist on the grain surface by such a method of cracking (prevent the presence of the second phase inside the grain). This makes it difficult to advance the pulverization. Therefore, if the second phase is less than 10 μm and is dispersed in a small size, the probability of confinement inside the particles increases and the above effect may not be expected, or cracks may not occur starting from the second phase during pulverization. Sometimes there is When the second phase exceeds 80 µm, the number of dispersed second phases becomes too small, and the effect of the present invention may not be obtained. For the second phase, the equivalent circle diameter is obtained from the form of the second phase detected by surface analysis using an energy dispersive X-ray spectrometer (EDS). An average of 10 second phase measurements is taken as the average equivalent circle diameter of the second phase.
本発明の水素吸蔵合金は、本発明の要件を満たす組織にできれば、どのような方法で製造しても本発明の作用効果を奏するものである。以下に、本発明の水素吸蔵合金の製造方法の１つの例を示す。
水素吸蔵合金は、秤量工程、混合工程、鋳造工程、熱処理工程で製造できる電池に使用するには、このようにして製造した水素吸蔵合金を粉砕して使用される（粉砕工程を経て使用される）。秤量工程では、所望の合金組成となるように水素吸蔵合金の各原料が秤量される。混合工程では、秤量された複数種類の原料が混合される。鋳造工程において、高周波加熱溶解炉に混合原料を投入し、混合原料を溶解させて溶湯となし、この溶湯を例えば鋳型に流し込んで１１５０℃～１５５０℃の範囲の温度（鋳造温度＝鋳造開始時の坩堝内溶湯温度）で鋳造する。鋳造温度が高いほど凝固した組織が第１相の結晶が大きく成長する。第１相の結晶の成長は、鋳造温度だけでなく、鋳型抜熱度合いとの関係が影響する。鋳型抜熱が急速に効果的起こし鋳型側から凝固が進むような鋳造温度と鋳型抜熱の関係にするのが好ましい。即ち、鋳造温度が低いとより鋳型抜熱度合いを大きくすることになるし、鋳造温度が高いと鋳型抜熱度合いが大きくなくてもよい。このようなことを考慮して、鋳造の際に第１相を出来るだけ規則的に大きく結晶を成長させる方が本発明の好ましい組織を形成しやすい。ここで、鋳型による冷却（鋳型抜熱）においては、上述のように、溶融金属が急速凝固して（鋳型面で不均一核発生して）柱状の結晶に成長しやすい条件とすることで、偏析相の生成を抑制できる。そのためには、例えば、２０℃における熱伝導率が４３Ｗ/（ｍ・℃）以上の鋳型を用いることが好ましい。更に好ましくは、２０℃における熱伝導率が５２Ｗ/（ｍ・℃）以上の鋳型を用いることである。
The hydrogen-absorbing alloy of the present invention can produce the effects of the present invention by any method as long as it has a structure that satisfies the requirements of the present invention. One example of the method for producing the hydrogen storage alloy of the present invention is shown below.
The hydrogen-absorbing alloy is used in a battery that can be manufactured in a weighing process, a mixing process, a casting process, and a heat treatment process. ). In the weighing step, each raw material of the hydrogen storage alloy is weighed so as to obtain a desired alloy composition. In the mixing step, the weighed plural kinds of raw materials are mixed. In the casting process, the mixed raw material is put into a high-frequency heating melting furnace, and the mixed raw material is melted to form a molten metal. The temperature of the molten metal in the crucible). The higher the casting temperature, the larger the crystals of the first phase in the solidified structure grow. The growth of the crystals of the first phase is affected not only by the casting temperature but also by the degree of heat removal from the mold. It is preferable to set the relationship between the casting temperature and the heat removal from the mold such that the heat removal from the mold is rapidly and effectively caused and solidification proceeds from the mold side. That is, when the casting temperature is low, the degree of heat removal from the mold is increased, and when the casting temperature is high, the degree of heat removal from the mold does not have to be large. Taking this into account, it is easier to form the preferred structure of the present invention if the crystals of the first phase are grown as large as possible as regularly as possible during casting. Here, in the cooling by the mold (mold heat removal), as described above, the molten metal is rapidly solidified (heterogeneous nuclei are generated on the mold surface) and columnar crystals are easily grown. It can suppress the generation of segregation phase. For that purpose, for example, it is preferable to use a mold having a thermal conductivity of 43 W/(m·°C) or more at 20°C. More preferably, a mold having a thermal conductivity of 52 W/(m·°C) or more at 20°C is used.
鋳造後の合金は、熱処理工程において非酸化雰囲気下で９５０℃～１２５０℃の温度で熱処理される。また、熱処理時間は、鋳造後のインゴット（水素吸蔵合金片）の大きさにもよるが、例えば、５時間以上から１８時間以下である。インゴットの中心部まで所定温度になって、所望の結晶サイズに粒成長するように時間設定すれば良い。
鋳造した合金の結晶サイズが小さい場合には、熱処理工程の条件を高温長時間にすることで大きな結晶サイズにすることになる。鋳造した合金の結晶サイズが大きい場合には、熱処理工程の条件を高温長時間にしなくても十分大きな結晶サイズにすることができるが、もちろん、ここで熱処理工程の条件を高温長時間にするとより大きな結晶サイズにすることができる。このような過程で小さな偏析相が集まって大きな偏析相を形成することになる。
電池に使用するには、このようにして製造した水素吸蔵合金を粉砕して使用される。この粉砕工程では、粗粉砕、微粉砕により必要な粒度の水素吸蔵合金粉末にする。例えば、インゴットを５００μｍの篩目を通過するサイズまで粉砕して水素吸蔵合金粉末とする。
The cast alloy is heat treated at a temperature of 950° C. to 1250° C. in a non-oxidizing atmosphere in a heat treatment step. The heat treatment time is, for example, 5 hours or more and 18 hours or less, depending on the size of the ingot (hydrogen-absorbing alloy piece) after casting. The time may be set so that the central portion of the ingot reaches a predetermined temperature and grains grow to a desired crystal size.
When the crystal size of the cast alloy is small, the crystal size is increased by setting the conditions of the heat treatment process to a high temperature and a long time. When the crystal size of the cast alloy is large, it is possible to obtain a sufficiently large crystal size without setting the conditions of the heat treatment process to a high temperature for a long time. Large crystal size can be obtained. In this process, small segregation phases gather to form large segregation phases.
For use in batteries, the hydrogen storage alloy thus produced is pulverized and used. In this pulverization step, the hydrogen-absorbing alloy powder having a required particle size is obtained by coarse pulverization and fine pulverization. For example, an ingot is pulverized to a size that can pass through a sieve mesh of 500 μm to obtain a hydrogen-absorbing alloy powder.
このようにして得られた水素吸蔵合金粉末は、ＰＣＴ（水素圧-組成-等温線図）特性評価装置によって、水素吸蔵量（Ｈ／Ｍ）、プラトー圧力を測定する。 The hydrogen storage alloy powder thus obtained is measured for hydrogen storage capacity (H/M) and plateau pressure by a PCT (hydrogen pressure-composition-isothermal diagram) characteristic evaluation device.
本発明におけるエネルギー分散型X線分析装置（ＥＤＳ）による相分析について説明する。水素吸蔵合金のインゴットより、数ｍｍ四方程度の欠片をサンプリングし、走査型電子顕微鏡（ＳＥＭ）の観察用に直径１インチの樹脂に包埋、鏡面研磨する。ＳＥＭにて数百倍程度の低倍率で、エネルギー分散型X線分析装置（ＥＤＳ）で含有する元素（Ｌａ、Ｃｅ、Ｎｉ、Ｍｎ、Ａｌ、Ｃｏ）についての面分析を行う。任意の面において、各元素の含有率を定量した後に、相の分析を行い、偏析（二次電子像で濃淡の異なる部分）の有無と、その面積比、母相と偏析相がどのような元素で構成されているか確認することができる。相の分析において、Ｎｉ元素とＬａ元素が重なって存在する領域を母相（第１相）として特定し、一方、Ｌａ元素が検出されずＮｉ元素とＭｎ元素が重なって存在する領域あるいはＮｉ元素とＭｎ元素及び僅かなＬａ元素が重なって存在する相を偏析相（第２相）として特定し（具体的には、Ｌａ元素がＮｉ元素やＭｎ元素よりも少なくＮｉ元素とＭｎ元素の合計が６０％以上である領域とした。）、観察範囲における第１相(母相）と第２相（偏析相）の面積を測定する。このとき、研磨材由来の元素（Ｓｉ）を含む不純物相や、母相の一部が酸化した不純物相（酸素（Ｏ）を含む相）、特定できない相（Unassigned pixels）は、第１相（母相）、第２相（偏析相）とは見なさい。 Phase analysis by an energy dispersive X-ray spectrometer (EDS) in the present invention will be described. A piece about several millimeters square is sampled from an ingot of a hydrogen-absorbing alloy, embedded in a resin having a diameter of 1 inch and mirror-polished for observation with a scanning electron microscope (SEM). Plane analysis of the contained elements (La, Ce, Ni, Mn, Al, Co) is performed with an energy dispersive X-ray spectrometer (EDS) at a low magnification of about several hundred by SEM. After quantifying the content of each element on an arbitrary surface, the phase is analyzed to determine the presence or absence of segregation (parts with different densities in the secondary electron image), their area ratio, and what the matrix and segregation phases are. You can check if it is composed of elements. In the phase analysis, the region where the Ni element and the La element overlap is specified as the matrix phase (first phase), while the La element is not detected and the Ni element and the Mn element overlap, or the Ni element and Mn element and a small amount of La element are overlapped to identify the phase as a segregation phase (second phase) (specifically, the La element is less than the Ni element and the Mn element, and the total of the Ni element and the Mn element is 60% or more), and the areas of the first phase (mother phase) and the second phase (segregation phase) in the observation range are measured. At this time, the impurity phase containing the element (Si) derived from the abrasive, the impurity phase (phase containing oxygen (O)) in which a part of the matrix phase is oxidized, and the unspecified phase (Unassigned pixels) are the first phase ( mother phase) and second phase (segregation phase).
本発明における微粉化難度の測定方法について説明する。
ＰＣＴ（水素圧-組成-等温線図）特性評価装置を用いて、「保持温度４５℃および水素圧力調整１．８２ＭＰａの環境下における水素の吸蔵放出サイクル１０回後の水素吸蔵合金粉末の粒度」を「水素吸蔵合金粉末の初期粒度」で除した値を、微粉化難度として指標化した。すなわち、微粉化難度は、１に近いほど水素吸蔵合金粉末が微粉化しにくいことを示し、０に近いほど水素吸蔵合金粉末が微粉化しやすいことを示す。微粉化難度を求めるに当たり、「水素吸蔵合金粉末の初期粒度」とは、リーズアンドノースラップ社製の粒度分布測定装置７９９７ＳＲＡを用いて測定した平均粒径Ｄ５０のことである。「保持温度４５℃および水素圧力調整１．８２ＭＰａの環境下における水素の吸蔵放出サイクル１０回後の水素吸蔵合金粉末の粒度」とは、株式会社鈴木商館製の全自動ＰＣＴ測定装置（１／２インチ直管サンプルセル，試料量３ｇ）を用いて保持温度４５℃および水素圧力調整１．８２ＭＰａの環境下で水素の吸蔵放出サイクルを１０回行った後に、リーズアンドノースラップ社製の粒度分布測定装置７９９７ＳＲＡを用いて測定した平均粒径Ｄ５０のことである。なお、全自動ＰＣＴ測定装置における水素吸蔵合金粉末の活性化処理は、活性化温度８０℃および水素圧力１．８２ＭＰａの環境下で行ない、同装置における水素吸蔵合金粉末の水素吸蔵放出サイクルは、保持温度４５℃、水素吸蔵圧力１．８２ＭＰａおよび水素放出圧力０ＭＰａの環境下で行った。
A method for measuring the difficulty of pulverization in the present invention will be described.
Using a PCT (hydrogen pressure-composition-isothermal diagram) characteristic evaluation device, "particle size of hydrogen storage alloy powder after 10 hydrogen storage and release cycles in an environment with a holding temperature of 45 ° C and a hydrogen pressure adjustment of 1.82 MPa" is divided by the "initial particle size of the hydrogen-absorbing alloy powder", and the value is indexed as the degree of pulverization difficulty. That is, the closer the pulverization difficulty is to 1, the harder it is to pulverize the hydrogen-absorbing alloy powder, and the closer it is to 0, the easier it is to pulverize the hydrogen-absorbing alloy powder. In determining the degree of difficulty of pulverization, the "initial particle size of the hydrogen-absorbing alloy powder" is the average particle size D50 measured using a particle size distribution analyzer 7997SRA manufactured by Leeds & Northrup. "Particle size of hydrogen-absorbing alloy powder after 10 hydrogen absorption-desorption cycles in an environment with a holding temperature of 45 ° C. and a hydrogen pressure adjustment of 1.82 MPa" is a fully automatic PCT measuring device manufactured by Suzuki Shokan Co., Ltd. (1/2 Using an inch straight tube sample cell, sample amount 3 g), hydrogen absorption and desorption cycles were performed 10 times in an environment with a holding temperature of 45 ° C. and a hydrogen pressure adjustment of 1.82 MPa. It refers to the average particle size D50 measured using the instrument 7997SRA. The activation treatment of the hydrogen-absorbing alloy powder in the fully automatic PCT measuring device was performed in an environment with an activation temperature of 80°C and a hydrogen pressure of 1.82 MPa. It was carried out under an environment of a temperature of 45° C., a hydrogen absorption pressure of 1.82 MPa, and a hydrogen release pressure of 0 MPa.
以下、本発明の実施例に基づいて説明する。なお、本発明は実施例に限定されるものはない。 Examples of the present invention will be described below. In addition, the present invention is not limited to the examples.
［実施例１～１２、比較例１～５］
Ｎｉ、Ｍｎ、Ａｌ、Ｃｏ、及びＭｍとしてＬａとＣｅの各金属原料を、表１に示した合金組成となるように秤量した。それらの原料を溶解炉内のルツボに入れて真空排気した後、アルゴンガス雰囲気とした。次いで高周波加熱装置で加熱溶解し、溶湯を鋳型に流し込んで鋳造を行い、不活性雰囲気下で熱処理を行って合金インゴット（水素吸蔵合金）を得た。得られた合金インゴットは、不活性雰囲気下でクラッシャーにより粗粉砕し、続いて、不活性雰囲気下でカッティングミルを用いて粉砕し、続いて篩目５００μｍを通過する粒子サイズ（５００μｍ以下）の水素吸蔵合金粉末とした。
[Examples 1 to 12, Comparative Examples 1 to 5]
Metal raw materials of Ni, Mn, Al, Co, and La and Ce as Mm were weighed so as to obtain the alloy compositions shown in Table 1. After putting these raw materials into a crucible in a melting furnace and evacuating, an argon gas atmosphere was created. Then, the alloy was melted by heating with a high-frequency heating device, poured into a mold for casting, and heat-treated in an inert atmosphere to obtain an alloy ingot (hydrogen storage alloy). The obtained alloy ingot is coarsely pulverized by a crusher under an inert atmosphere, then pulverized using a cutting mill under an inert atmosphere, and then hydrogen powder having a particle size (500 μm or less) passing through a sieve mesh of 500 μm. A storage alloy powder was used.
（ＰＣＴ特性の測定）
得られた水素吸蔵合金粉末について、ＰＣＴ特性評価装置により、水素吸蔵量（Ｈ／Ｍ）、プラトー圧力を測定した。
(Measurement of PCT characteristics)
The obtained hydrogen storage alloy powder was measured for hydrogen storage capacity (H/M) and plateau pressure using a PCT characteristic evaluation device.
（微粉化難度の測定）
粒度分布測定装置及びＰＣＴ特性評価装置を用いて、微粉化難度を測定した。
(Measurement of micronization difficulty)
Micronization difficulty was measured using a particle size distribution analyzer and a PCT characterizer.
（偏析相の測定）
熱処理後の合金インゴットの自由冷却面付近より、数ｍｍ四方程度の欠片をサンプリングし樹脂包埋、鏡面研磨後に、走査型電子顕微鏡（日本電子株式会社製、ＪＳＭ－７９００Ｆ）に付帯しているエネルギー分散型X線分析装置（ＥＤＳ）を用いて、水素吸蔵合金に含まれる元素について面分析を行った。このときの二次電子像の観察倍率は３００倍とした。またＥＤＳの解析ソフトは、オックスフォード・インストゥルメンツ株式会社のＡＺｔｅｃを使用した。面分析の後に「相の分析」を実施し、偏析相の構成元素、面積比を調査した。ただし、面積比については、複数個所の観察領域で測定して得た値の平均値を面積比として算出した。相分析を行った組織写真を、図１～図３、図６に示し、組織写真から測定・算出した第１相（母相)、第２相（偏析相）の面積比の値を表２に示し、また、不純物相を含めた各相の面積比率を表３に示す。
なお、第１相（母相)、第２相（偏析相）及び不純物相の面積比率の測定・算出は、電子顕微鏡の画像処理の機能を用い、偏析して色味が違ったピクセル数をカウントし、全体のピクセル数に対する割合を求めることによって、観察領域における各相の面積比率を算出することができる。また、第１相及び第２相の特定は前述のとおりとして、相の分析でＮｉ元素とＬａ元素が重なって存在する領域を母相（第１相）とし、Ｌａ元素が検出されずＮｉ元素とＭｎ元素が重なって存在する領域、あるいは、Ｎｉ元素とＭｎ元素及び僅かなＬａ元素が重なって存在するがＬａ元素がＮｉ元素やＭｎ元素よりも少なくＮｉ元素とＭｎ元素の合計が６０％以上である領域を偏析相（第２相）とした。
(Measurement of segregation phase)
From the vicinity of the free cooling surface of the alloy ingot after heat treatment, sample a piece of about several mm square, embed it in resin, mirror-polish, and scan electron microscope (manufactured by JEOL Ltd., JSM-7900F) Energy incidental Using a dispersive X-ray spectrometer (EDS), surface analysis was performed on the elements contained in the hydrogen storage alloy. The observation magnification of the secondary electron image at this time was 300 times. AZtec of Oxford Instruments Co., Ltd. was used as EDS analysis software. After the area analysis, "phase analysis" was performed to investigate the constituent elements of the segregation phase and the area ratio. However, with respect to the area ratio, the average value of the values obtained by measuring the observation regions at a plurality of locations was calculated as the area ratio. Figures 1 to 3 and 6 show the photographs of the structures subjected to phase analysis. and Table 3 shows the area ratio of each phase including the impurity phase.
The area ratios of the first phase (mother phase), the second phase (segregation phase) and the impurity phase were measured and calculated using the image processing function of the electron microscope, and the number of pixels with different colors due to segregation was counted. By counting and calculating the ratio to the total number of pixels, the area ratio of each phase in the observation area can be calculated. In addition, the identification of the first phase and the second phase is as described above. and Mn elements overlap, or Ni elements and Mn elements and a small amount of La elements overlap, but La elements are less than Ni elements and Mn elements, and the total of Ni elements and Mn elements is 60% or more A region was defined as a segregation phase (second phase).
図１～図３には、実施例の代表的な相分析の組織写真（実施例１、実施例１０、実施例１２）と、図４～図６には、比較例の代表的なの相分析の組織写真（比較例１、比較例２、比較例３）を示す。
また、図７として、縦軸に微粉化難度、横軸に第１相の割合をプロットしたグラフを示し、更には、図８として、縦軸に微粉化難度、横軸に第２相（偏析相）の割合をプロットしたものを示す。
FIGS. 1 to 3 show structural photographs of representative phase analyzes of Examples (Example 1, Example 10, and Example 12), and FIGS. 4 to 6 show representative phase analyzes of Comparative Examples. (Comparative Example 1, Comparative Example 2, Comparative Example 3).
Further, FIG. 7 shows a graph plotting the degree of difficulty in pulverization on the vertical axis and the ratio of the first phase on the horizontal axis, and FIG. phase) is plotted.
表２、図１～６、及び図７～８より、本発明の水素吸蔵合金(実施例１～１２)は、第２相（偏析相）が少なくかつ微粉化難度が高い結果を示した。更に、Ｈ／Ｍが、０．９０以上と高く、プラトー圧力も低めであることが確認できた。これに対して、比較例１～５は、Ｈ／Ｍ、プラトー圧力については本発明とほぼ同等であったが、第２相（偏析相）の生成を十分に抑制することができず、本発明の実施例１～１２に匹敵する微粉化難度を得ることができなかった。このことから、本発明の水素吸蔵合金は、Ｃｏ含有量が少なく原料コストが低く、初期特性、寿命特性に優れ、ニッケル水素電池用負極に好適な合金であることが確認できた。
From Table 2, FIGS. 1 to 6, and FIGS. 7 to 8, the hydrogen storage alloys of the present invention (Examples 1 to 12) showed less second phase (segregation phase) and high pulverization difficulty. Furthermore, it was confirmed that H/M was as high as 0.90 or more and the plateau pressure was rather low. On the other hand, in Comparative Examples 1 to 5, the H/M and plateau pressure were almost the same as those of the present invention, but the formation of the second phase (segregation phase) could not be sufficiently suppressed. A micronization difficulty comparable to Inventive Examples 1-12 could not be obtained. From this, it was confirmed that the hydrogen storage alloy of the present invention has a low Co content, a low raw material cost, excellent initial characteristics and life characteristics, and is suitable for a negative electrode for a nickel-metal hydride battery.
Claims (6)
エネルギー分散型X線分析装置（ＥＤＳ）で相分析したときに検出されるＬａとＮｉを含む第１相が面積比で９７．５％以上１００％未満であると共に、Ｎｉ、Ｍｎを主として含む第２相が面積比で０％を超え１．５％以下であり、かつ前記第１相が３００μｍ以上のサイズの結晶を含むことを特徴とする水素吸蔵合金のインゴット。 General formula MmNiaMnbAlcCod (wherein Mm is a misch metal, 4.30≤a≤4.75, 0.25≤b≤0.45, 0.35≤c≤0.45, 0≤d≤0. 12, 5.20 ≤ a + b + c + d ≤ 5.55), has a CaCu type 5 crystal structure, and the Mm has a ratio of La and Ce in the range of 90% by mass to 100% by mass with respect to the total Mm is within
The first phase containing La and Ni detected when phase analysis is performed with an energy dispersive X-ray spectrometer (EDS) has an area ratio of 97.5% or more and less than 100%, and the second phase mainly containing Ni and Mn A hydrogen-absorbing alloy ingot , characterized in that two phases have an area ratio of more than 0% to 1.5% or less, and the first phase contains crystals having a size of 300 µm or more.
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| WO2005014871A1 (en) | 2003-08-08 | 2005-02-17 | Mitsui Mining & Smelting Co., Ltd. | LOW Co HYDROGEN OCCLUSION ALLOY |
| JP2010255104A (en) | 2009-03-31 | 2010-11-11 | Mitsui Mining & Smelting Co Ltd | Method for producing hydrogen storage alloy powder |
| WO2015147044A1 (en) | 2014-03-26 | 2015-10-01 | 三井金属鉱業株式会社 | Hydrogen storage alloy |
| WO2018123752A1 (en) | 2016-12-26 | 2018-07-05 | 三井金属鉱業株式会社 | Hydrogen storage alloy |
| JP6608558B1 (en) | 2019-06-18 | 2019-11-20 | 新日本電工株式会社 | Nickel metal hydride secondary battery negative electrode active material and nickel metal hydride secondary battery that do not require surface treatment |
| JP6934097B1 (en) | 2020-08-18 | 2021-09-08 | 新日本電工株式会社 | Hydrogen storage alloy |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| WO2005014871A1 (en) | 2003-08-08 | 2005-02-17 | Mitsui Mining & Smelting Co., Ltd. | LOW Co HYDROGEN OCCLUSION ALLOY |
| JP2010255104A (en) | 2009-03-31 | 2010-11-11 | Mitsui Mining & Smelting Co Ltd | Method for producing hydrogen storage alloy powder |
| WO2015147044A1 (en) | 2014-03-26 | 2015-10-01 | 三井金属鉱業株式会社 | Hydrogen storage alloy |
| WO2018123752A1 (en) | 2016-12-26 | 2018-07-05 | 三井金属鉱業株式会社 | Hydrogen storage alloy |
| JP6608558B1 (en) | 2019-06-18 | 2019-11-20 | 新日本電工株式会社 | Nickel metal hydride secondary battery negative electrode active material and nickel metal hydride secondary battery that do not require surface treatment |
| JP6934097B1 (en) | 2020-08-18 | 2021-09-08 | 新日本電工株式会社 | Hydrogen storage alloy |
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