JP2023027792A - Hydrogen storage alloy - Google Patents
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- 229910045601 alloy Inorganic materials 0.000 title claims abstract description 134
- 239000000956 alloy Substances 0.000 title claims abstract description 134
- 239000001257 hydrogen Substances 0.000 title claims abstract description 110
- 229910052739 hydrogen Inorganic materials 0.000 title claims abstract description 110
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 title claims abstract description 107
- 238000003860 storage Methods 0.000 title claims abstract description 84
- 239000013078 crystal Substances 0.000 claims abstract description 126
- 229910001122 Mischmetal Inorganic materials 0.000 claims abstract description 10
- 238000005204 segregation Methods 0.000 claims description 27
- 238000010894 electron beam technology Methods 0.000 claims description 16
- 229910004247 CaCu Inorganic materials 0.000 claims description 7
- 238000002050 diffraction method Methods 0.000 claims description 6
- 239000007773 negative electrode material Substances 0.000 claims description 6
- 239000002994 raw material Substances 0.000 abstract description 16
- 238000004458 analytical method Methods 0.000 abstract description 5
- 238000001887 electron backscatter diffraction Methods 0.000 abstract 1
- 235000013339 cereals Nutrition 0.000 description 48
- 238000010298 pulverizing process Methods 0.000 description 34
- 229910052751 metal Inorganic materials 0.000 description 23
- 239000002184 metal Substances 0.000 description 23
- 239000000843 powder Substances 0.000 description 21
- 238000010438 heat treatment Methods 0.000 description 16
- 238000000034 method Methods 0.000 description 15
- 239000000203 mixture Substances 0.000 description 15
- 239000002245 particle Substances 0.000 description 13
- 238000005266 casting Methods 0.000 description 12
- 229910052987 metal hydride Inorganic materials 0.000 description 12
- 238000007711 solidification Methods 0.000 description 11
- 230000008023 solidification Effects 0.000 description 11
- 238000010521 absorption reaction Methods 0.000 description 10
- 238000001816 cooling Methods 0.000 description 9
- 238000003795 desorption Methods 0.000 description 9
- 229910052782 aluminium Inorganic materials 0.000 description 8
- 229910052746 lanthanum Inorganic materials 0.000 description 8
- 238000002844 melting Methods 0.000 description 8
- 230000008018 melting Effects 0.000 description 8
- 230000000052 comparative effect Effects 0.000 description 7
- 238000005259 measurement Methods 0.000 description 7
- 229910052759 nickel Inorganic materials 0.000 description 7
- 229910052684 Cerium Inorganic materials 0.000 description 6
- 229910052748 manganese Inorganic materials 0.000 description 6
- 150000002739 metals Chemical class 0.000 description 6
- 238000002149 energy-dispersive X-ray emission spectroscopy Methods 0.000 description 5
- 229910052761 rare earth metal Inorganic materials 0.000 description 5
- 230000004913 activation Effects 0.000 description 4
- 238000010586 diagram Methods 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 229910002335 LaNi5 Inorganic materials 0.000 description 3
- 229910017052 cobalt Inorganic materials 0.000 description 3
- 239000010941 cobalt Substances 0.000 description 3
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 3
- 238000005520 cutting process Methods 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
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- 238000004519 manufacturing process Methods 0.000 description 3
- 229910052758 niobium Inorganic materials 0.000 description 3
- 238000005498 polishing Methods 0.000 description 3
- 238000010791 quenching Methods 0.000 description 3
- 230000000171 quenching effect Effects 0.000 description 3
- 229910052719 titanium Inorganic materials 0.000 description 3
- 229910052720 vanadium Inorganic materials 0.000 description 3
- 238000005303 weighing Methods 0.000 description 3
- 229910052726 zirconium Inorganic materials 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 229910052804 chromium Inorganic materials 0.000 description 2
- 239000008119 colloidal silica Substances 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 229910052735 hafnium Inorganic materials 0.000 description 2
- 150000002431 hydrogen Chemical class 0.000 description 2
- 229910052738 indium Inorganic materials 0.000 description 2
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 description 2
- 238000002156 mixing Methods 0.000 description 2
- 229910052750 molybdenum Inorganic materials 0.000 description 2
- 239000011347 resin Substances 0.000 description 2
- 229920005989 resin Polymers 0.000 description 2
- 229910052715 tantalum Inorganic materials 0.000 description 2
- 229910052721 tungsten Inorganic materials 0.000 description 2
- 229910052727 yttrium Inorganic materials 0.000 description 2
- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 description 2
- 229910052725 zinc Inorganic materials 0.000 description 2
- 229910004269 CaCu5 Inorganic materials 0.000 description 1
- 229910000878 H alloy Inorganic materials 0.000 description 1
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 1
- 240000007594 Oryza sativa Species 0.000 description 1
- 235000007164 Oryza sativa Nutrition 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000008602 contraction Effects 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 239000012634 fragment Substances 0.000 description 1
- 229910052733 gallium Inorganic materials 0.000 description 1
- 238000007429 general method Methods 0.000 description 1
- 238000005984 hydrogenation reaction Methods 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 229910001416 lithium ion Inorganic materials 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 150000004681 metal hydrides Chemical class 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 150000002910 rare earth metals Chemical class 0.000 description 1
- 238000011160 research Methods 0.000 description 1
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- 238000001308 synthesis method Methods 0.000 description 1
- 229910052718 tin Inorganic materials 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
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Abstract
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及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, which is used as a negative electrode of a nickel-metal hydride battery. Furthermore, 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、負極の寿命特性及び入出力特性を更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ＡＢ５型水素吸蔵合金にて、寿命特性の維持向上などを目的として、合金中の「柱状結晶」に注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, AB 5 -type hydrogen storage alloys have been studied with a focus on "columnar crystals" in the alloys for the purpose of maintaining and improving life characteristics.
例えば、特許文献１において、ミッシュメタルＭｍ、Ｎｉ、Ｃｏ、及びＡｌ金属を融解し、柱状結晶を形成するように冷却して水素吸蔵合金を製造し、その平均結晶粒径が１０ミクロン以下の微粒とすることが提案されている。 For example, in Patent Document 1, misch metal Mm, Ni, Co, and Al metals are melted and cooled to form columnar crystals to produce a hydrogen storage alloy, and the average crystal grain size is 10 microns or less. It is proposed that
また特許文献２において、表面がエピタキシャルな結晶成長を促進する材質からなるロール上に水素吸蔵合金の溶湯を噴出させるロール急冷装置により、９割以上が柱状晶である水素吸蔵合金粉末から構成される水素吸蔵合金電極が提案されている。 In addition, in Patent Document 2, a roll quenching device that spouts a molten hydrogen-absorbing alloy onto a roll whose surface is made of a material that promotes epitaxial crystal growth is used. Hydrogen storage alloy electrodes have been proposed.
更に、特許文献３において、一般式Ａ Ｎｉa Ｍｎb Ａｌc Ｃｏd Ｍe （但し、ＡはＹ（イットリウム）を含む希土類元素より選択される少なくとも１種の元素、ＭはＷ，Ｔａ，Ｍｏ，Ｎｂ，Ｉｎ，Ｇａ，Ｓｎ，Ｚｎ，Ｃｒ，Ｖ，Ｔｉ，Ｚｒ及びＨｆの中から選択される少なくとも１種の元素、３．５≦ａ≦５，０．１≦ｂ≦１，０≦ｃ≦１，０．１≦ｄ≦１，０＜ｅ≦０．６，４．５≦ａ＋ｂ＋ｃ＋ｄ＋ｅ≦６）で表わされる組成を有する合金から成り、この合金が少なくとも一部に柱状晶組織を有し、この柱状晶の平均短径が５～３０μｍであり柱状晶の割合が面積比で７０％以上である水素吸蔵合金が提案されている。 Furthermore, in Patent Document 3, the general formula A Nia Mnb Alc Cod Me (where A is at least one element selected from rare earth elements including Y (yttrium), M is W, Ta, Mo, Nb, In, at least one element selected from Ga, Sn, Zn, Cr, V, Ti, Zr and Hf, 3.5≤a≤5, 0.1≤b≤1,0≤c≤1,0 .1 ≤ d ≤ 1, 0 < e ≤ 0.6, 4.5 ≤ a + b + c + d + e ≤ 6), the alloy having a columnar crystal structure at least in part, and the columnar crystal A hydrogen-absorbing alloy has been proposed in which the average short axis is 5 to 30 μm and the proportion of columnar crystals is 70% or more in area ratio.
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に、柱状結晶に注目した検討がされてきたが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. In order to achieve both the reduction of the Co content and the longevity characteristics of the negative electrode, studies have been made focusing on columnar crystals, but no effective solution to the problem has been found.
特許文献１には、ミッシュメタルＭｍ、Ｎｉ、Ｃｏ、及びＡｌ金属を融解し、柱状結晶を形成するように冷却して水素吸蔵合金を製造し、その平均結晶粒径が１０ミクロン以下とすることが提案されているが、水素吸蔵合金のＣｏ含有量が０．４～１．４と、まだ多すぎる課題がある。 In Patent Document 1, misch metal Mm, Ni, Co, and Al metals are melted and cooled to form columnar crystals to produce a hydrogen storage alloy, and the average crystal grain size is 10 microns or less. However, the Co content of the hydrogen storage alloy is 0.4 to 1.4, which is still too many problems.
特許文献２では、表面がエピタキシャルな結晶成長を促進する材質からなるロール上に水素吸蔵合金の溶湯を噴出させるロール急冷装置により、９割以上が柱状晶である水素吸蔵合金粉末から構成される水素吸蔵合金電極が提案されているが、ロール急冷法では生産性が低いこと、柱状晶比率については顕微鏡で調べるという記述しかなく、具体的にどのような結晶粒をしているかの開示も示唆もない。 In Patent Document 2, a roll quenching device for ejecting molten metal of a hydrogen-absorbing alloy onto a roll made of a material that promotes epitaxial crystal growth is used to remove hydrogen composed of a hydrogen-absorbing alloy powder whose 90% or more is columnar crystals. A storage alloy electrode has been proposed, but there is only a description that the productivity of the roll quenching method is low and that the ratio of columnar crystals is examined with a microscope. do not have.
特許文献３には、一般式Ａ Ｎｉa Ｍｎb Ａｌc Ｃｏd Ｍe （但し、ＡはＹ（イットリウム）を含む希土類元素より選択される少なくとも１種の元素、ＭはＷ，Ｔａ，Ｍｏ，Ｎｂ，Ｉｎ，Ｇａ，Ｓｎ，Ｚｎ，Ｃｒ，Ｖ，Ｔｉ，ＺｒおよびＨｆの中から選択される少なくとも１種の元素、３．５≦ａ≦５，０．１≦ｂ≦１，０≦ｃ≦１，０．１≦ｄ≦１，０＜ｅ≦０．６，４．５≦ａ＋ｂ＋ｃ＋ｄ＋ｅ≦６）で表わされる組成を有する合金から成り、この合金が少なくとも一部に柱状晶組織を有し、この柱状晶の平均短径が５～３０μｍであり柱状晶の割合が面積比で７０％以上である水素吸蔵合金が提案されているものの、製法がロール急冷法であり生産性に課題があること、さらに、柱状晶組織の観察は、ニッケル水素電池を組立て１０サイクル充放電した後に、電池を分解して負極を取り出して走査型電子顕微鏡で観察したものであり、水素吸蔵合金製造後の組織を観察したものではない。 In Patent Document 3, the general formula A Nia Mnb Alc Cod Me (where A is at least one element selected from rare earth elements including Y (yttrium), M is W, Ta, Mo, Nb, In, Ga , Sn, Zn, Cr, V, Ti, Zr and Hf, 3.5≤a≤5, 0.1≤b≤1,0≤c≤1,0. 1 ≤ d ≤ 1, 0 < e ≤ 0.6, 4.5 ≤ a + b + c + d + e ≤ 6), the alloy has a columnar crystal structure at least in part, and the columnar crystals A hydrogen-absorbing alloy having an average short diameter of 5 to 30 μm and a ratio of columnar crystals of 70% or more in area ratio has been proposed. The crystal structure was observed by assembling the nickel-metal hydride battery, charging and discharging it for 10 cycles, disassembling the battery, taking out the negative electrode, and observing it with a scanning electron microscope. do not have.
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、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を課題としている。 The present invention has been made in view of the above problems, and in the AB 5 type hydrogen storage alloy containing Co, the raw material cost is suppressed by reducing the Co content, and the alloy is improved by repeatedly absorbing and desorbing hydrogen. An object of the present invention is to 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、Ｃｏを含有する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、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ためには、これまで以上の大きな結晶粒にした合金から負極活物質を調製することで達成できることを見出し、本発明を完成させた。 In order to solve the above problems, the present inventors have made intensive research, and have found that the Co-containing AB 5 type hydrogen storage alloy can reduce the raw material cost by reducing the Co content, and the alloy can be produced by repeatedly absorbing and desorbing hydrogen. In order to suppress pulverization and maintain the life characteristics when used as a negative electrode active material, it was found that it can be achieved by preparing a negative electrode active material from an alloy with larger crystal grains than ever before. 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≦４．７０、０．２５≦ｂ≦０．４５、０．２５≦ｃ≦０．４５、０≦ｄ≦０．１４、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及びＣｅの割合の合計が全Ｍｍに対して９０質量％以上１００質量％以下の範囲内であり、
電子線後方散乱回析法により測定される平均結晶粒サイズが、円相当直径で１８０μｍ以上であることを特徴とする水素吸蔵合金。
（２）結晶成長方向と平行面の合金を電子線後方散乱回析法により測定される結晶粒の長径／短径の比が、１．２以上であることを特徴とする（１）記載の水素吸蔵合金。
（３）結晶成長方向と直角面の合金を電子線後方散乱回析法により測定される結晶粒の長径／短径の比が、２．０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。
（４）Ｌａを含まない偏析相が存在し、該偏析相の平均サイズが円相当直径で前記平均結晶粒サイズの０．２倍以下であり、かつ、該偏析相は前記結晶粒の粒界に点在す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。
（５）（１）～（４）のいずれかに記載の水素吸蔵合金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 ≤ 4.70, 0.25 ≤ b ≤ 0.45, 0.25 ≤ c ≤ 0.45, 0 ≤ d ≤ 0.14, 5.20 ≤ a + b + c + d ≤ 5.55), has a CaCu type 5 crystal structure, and the Mm is 90% by mass or more of the total Mm and the total ratio of La and Ce is 100 Within the range of % by mass or less,
A hydrogen storage alloy characterized by having an average grain size of 180 μm or more in equivalent circle diameter as measured by an electron beam backscattering diffraction method.
(2) The ratio of the major axis/minor axis of the crystal grains measured by electron beam backscattering diffraction of the alloy in a plane parallel to the crystal growth direction is 1.2 or more according to (1). Hydrogen storage alloy.
(3) The ratio of the major axis/minor axis of the crystal grain measured by the electron beam backscattering diffraction method of the alloy in the plane perpendicular to the crystal growth direction is 2.0 or less (1) or ( 2) The hydrogen storage alloy described.
(4) A segregation phase containing no La is present, and the average size of the segregation phase is 0.2 times or less of the average grain size in equivalent circle diameter, and the segregation phase is the grain boundary of the grain. The hydrogen storage alloy according to any one of (1) to (3), characterized in that it is scattered in.
(5) A negative electrode characterized by using the hydrogen storage 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、これまで以上の大きな結晶粒にした合金とすることで、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型水素吸蔵合金を得ることができる。 According to the present invention, the raw material cost is suppressed by reducing the Co content, and the alloy is made into larger crystal grains than ever before, thereby suppressing the pulverization of the alloy due to repeated absorption and release of hydrogen AB 5 type hydrogen A storage alloy can be obtained.
以下に本発明を詳細に説明する。 The present invention will be described in detail below.
本発明者らは、Ｃｏ含有量の少ないＡＢ５型水素吸蔵合金において、水素吸蔵量を低下させることなく、微粉化難度を維持する方法について鋭意検討した。その結果、これまで以上の大きな結晶粒にすることで、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ことを見出した。具体的には、電子線後方散乱回析法（ＥＢＳＤ）により測定される平均結晶粒サイズが、円相当径で１８０μｍ以上であると、前記効果が得られる。 The present inventors diligently studied a method for maintaining the difficulty of pulverization without reducing the hydrogen storage capacity of an AB5 type hydrogen storage alloy with a low Co content. As a result, they found that by making the crystal grains larger than before, the difficulty of pulverization does not decrease even if the Co content is small, and the life characteristics are maintained when used for the negative electrode. Specifically, the above effects can be obtained when the average grain size measured by electron beam backscatter diffraction (EBSD) is 180 μm or more in equivalent circle diameter.
その理由は推測に留まるが、次のように考えている。
（１）結晶粒サイズを大きくすることで、六方晶であるＣａＣｕ５型結晶構造をもつＡＢ５型水素吸蔵合金の合金組織ならびに合金組成の均一性が向上したこと。
（２）微粉化抑制に効果があるＣｏ含有量を低減したにも関わらず、微粉化難度が保持された理由としては、組成の均一化向上により、水素吸蔵放出に伴う結晶格子の膨張収縮が、より均一に進むために、各結晶に発生する応力が緩和されたこと。
（３）大きな結晶粒に成長したことで、水素を吸蔵放出しにくい偏析相が減少及び偏在化したためと考えられる。
The reason for this is speculation, but I think it is as follows.
(1) By increasing the grain size, the homogeneity of the alloy structure and the alloy composition of the AB5-type hydrogen storage alloy having the hexagonal CaCu5- type crystal structure was improved.
(2) Although the Co content, which is effective in suppressing pulverization, was reduced, the difficulty of pulverization was maintained. , that the stress generated in each crystal was relaxed in order to proceed more uniformly.
(3) It is believed that the growth of large crystal grains reduced and unevenly distributed the segregation phase, which is difficult to store and release hydrogen.
本発明のＡＢ５型水素吸蔵合金は、ＣａＣｕ５型結晶構造の母相を有する。ＣａＣｕ５型結晶構造の母相は、一般式ＭｍＮｉａＭｎｂＡｌｃＣｏｄ（Ｍｍはミッシュメタルであり、４．３０≦ａ≦４．７０、０．２５≦ｂ≦０．４５、０．２５≦ｃ≦０．４５、０≦ｄ≦０．１４、５．２０≦ａ＋ｂ＋ｃ＋ｄ≦５．５５）で表される。 The AB 5 -type hydrogen storage alloy of the present invention has a matrix of CaCu 5 -type crystal structure. The parent phase of the CaCu type 5 crystal structure has the general formula MmNiaMnbAlcCod (Mm is a misch metal, 4.30 ≤ a ≤ 4.70, 0.25 ≤ b ≤ 0.45, 0.25 ≤ c ≤ 0.45 , 0≤d≤0.14, 5.20≤a+b+c+d≤5.55).
ＡＢ５型水素吸蔵合金において、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又はＬａの一部若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及び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ことが好ましく、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。 Metals forming the A site in the AB type 5 hydrogen storage alloy will be described. 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 preferably occupy a proportion 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 La is 70 to 96% by mass, Ce is 4 30 mass %, more preferably 74 to 94 mass % for La and 6 to 26 mass % for 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ことが好ましい。
Ｎｉモル比（ａ） ４．３０≦ａ≦４．７０
Ｍｎモル比（ｂ） ０．２５≦ｂ≦０．４５
Ａｌモル比（ｃ） ０．２５≦ｃ≦０．４５
Ｃｏモル比（ｄ） ０≦ｄ≦０．１４
ＡＢ比 ５．２０≦（ａ＋ｂ＋ｃ＋ｄ）≦５．５５
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 preferably satisfies the following conditions.
Ni molar ratio (a) 4.30 ≤ a ≤ 4.70
Mn molar ratio (b) 0.25 ≤ b ≤ 0.45
Al molar ratio (c) 0.25 ≤ c ≤ 0.45
Co molar ratio (d) 0 ≤ d ≤ 0.14
AB ratio 5.20 ≤ (a + b + c + d) ≤ 5.55
本発明の水素吸蔵合金において、電子線後方散乱回析法（ＥＢＳＤ）のグレイン解析により計測される平均結晶粒サイズが、円相当直径で１８０μｍ以上である。更に好ましくは、平均結晶粒サイズが円相当直径で２５０μｍ以上である。ここで、平均結晶粒サイズは、一定以上に成長していればよく、結晶粒の形状も問わないが、その上限は、電子顕微鏡で観察可能な最大視野で１つの結晶粒しか観察されない場合となり、例えば、倍率１００倍という低倍率で観察した場合（後述の実施例参照）には、結晶粒サイズの最大径は１０００μｍということになる。 In the hydrogen-absorbing alloy of the present invention, the average grain size measured by grain analysis by electron beam backscattering diffraction (EBSD) is 180 μm or more in equivalent circle diameter. More preferably, the average grain size is 250 μm or more in equivalent circle diameter. Here, the average crystal grain size may grow to a certain size or more, and the shape of the crystal grains does not matter. For example, when observed at a low magnification of 100 times (see Examples described later), the maximum diameter of the crystal grain size is 1000 μm.
また、本発明においては、結晶成長方向と平行面の合金を電子線後方散乱回析法により測定される結晶粒の長径／短径の比が、１．２以上であるのがより好ましい。長径／短径＝１、即ち、円状（球状）結晶で形成された合金で相互の結晶成長による発生する応力によって結晶歪が生じ易い。その結果、上述のように結晶粒が大きくなると組成の均一性が向上して水素吸蔵放出に伴う結晶格子の膨張収縮によって結晶が割れやすくなる傾向がある。しかしながら、長径／短径＞１の結晶で形成された合金では上記に比べて相互の結晶成長による発生する応力によって生じる結晶歪がより小さくなる。これにより、水素吸蔵放出に伴う結晶格子の膨張収縮が起こっても結晶が割れ難い。この効果が顕著に現れるのが、長径／短径の比が１．２以上である。更に好ましくは１．４以上である。 In the present invention, it is more preferable that the ratio of major axis/minor axis of crystal grains measured by electron beam backscattering diffraction of the alloy in a plane parallel to the crystal growth direction is 1.2 or more. Major axis/minor axis=1, that is, in an alloy formed of circular (spherical) crystals, crystal strain is likely to occur due to stress generated by mutual crystal growth. As a result, as described above, as the crystal grains become larger, the uniformity of the composition improves and the crystal tends to crack due to expansion and contraction of the crystal lattice accompanying hydrogen absorption and desorption. However, in alloys formed of crystals with major axis/minor axis>1, crystal strain caused by stress generated by mutual crystal growth is smaller than in the above case. As a result, the crystal is less likely to crack even when the crystal lattice expands and contracts due to hydrogen absorption and desorption. This effect remarkably appears when the ratio of major axis/minor axis is 1.2 or more. More preferably, it is 1.4 or more.
更に、結晶成長方向と直角面の合金を電子線後方散乱回析法により測定される結晶粒の長径／短径の比が、２．０以下であるのがより好ましい。結晶粒が大きくて前記長径／短径の比が小さいということは、鋳型面で均一（等間隔で偏りなく）に核発生して成長していることを意味しており、結晶成長によって発生する結晶粒同士間の応力が最小限になる。その結果、結晶成長による発生する応力によって生じる結晶歪がより小さくなる。これにより、水素吸蔵放出に伴う結晶格子の膨張収縮が起こっても結晶が割れ難い。よって、前記の長径／短径の比が１．５以下であるのがより好ましく、理想的には、前記の長径／短径＝１である。 Furthermore, it is more preferable that the ratio of the major axis/minor axis of the crystal grain measured by the electron beam backscattering diffraction method of the alloy in the plane perpendicular to the crystal growth direction is 2.0 or less. The fact that the crystal grains are large and the ratio of the major axis/minor axis is small means that the nuclei are generated and grown uniformly (equally spaced and without bias) on the mold surface, and are generated by crystal growth. The stress between grains is minimized. As a result, crystal strain caused by stress generated by crystal growth becomes smaller. As a result, the crystal is less likely to crack even when the crystal lattice expands and contracts due to hydrogen absorption and desorption. Therefore, it is more preferable that the ratio of the major axis/minor axis is 1.5 or less, and ideally, the major axis/minor axis=1.
また、ランタン（La）を含まない偏析相が存在し、該偏析相の平均サイズが円相当直径で水素吸蔵合金の前記平均結晶粒サイズの１／５以下であり、前記結晶粒の粒界に点在するのが好ましい。偏析相が少ない方が好ましいが、実質的にはゼロにできない。しかしながら、偏析相の存在状態を最適にすれば、微粒化が抑制できる。前記偏析相の点在する間隔の平均距離は、水素吸蔵合金の前記平均結晶粒サイズ１／３以上１／１以下であるのが好ましい。 In addition, there is a segregation phase that does not contain lanthanum (La), the average size of the segregation phase is 1/5 or less of the average crystal grain size of the hydrogen storage alloy in equivalent circle diameter, and the grain boundary of the crystal grain Dotted is preferred. It is preferable that the segregation phase is small, but it cannot be substantially zero. However, by optimizing the existence state of the segregation phase, the grain size reduction can be suppressed. It is preferable that the average distance between the interspersed intervals of the segregation phase is 1/3 or more and 1/1 or less of the average crystal grain size of the hydrogen storage alloy.
本発明の水素吸蔵合金は、水素吸蔵量（Ｈ／Ｍ）が０．８５～１．００であるのがよく、微粉化難度が０．４６～０．６０であるのがよく、プラトー圧力が０．０４～０．０７ＭＰａであるのがよい。ここで、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。プラトー圧力をこの範囲とすることで、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。また、本発明の水素吸蔵合金の作用効果は、水素の繰返し吸蔵放出による合金の微粉化を抑制であるが、これは微粒化難度で判断する。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。微粉化難度を上記範囲にした理由は、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。更には、微粉化難度は水素吸蔵量（Ｈ／Ｍ）と相間があり、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。なお、後述するように、水素吸蔵量（Ｈ／Ｍ）とプラトー圧力は、ＰＣＴ（水素圧－組成－等温線図）特性評価装置によって測定することができる。 The hydrogen storage alloy of the present invention preferably has a hydrogen storage capacity (H/M) of 0.85 to 1.00, a pulverization difficulty of 0.46 to 0.60, and a plateau pressure of It is preferably 0.04 to 0.07 MPa. Here, 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. By setting the plateau pressure within this range, 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. The effect of the hydrogen storage alloy of the present invention is to suppress the pulverization of the alloy due to repeated hydrogen absorption and desorption, and this is judged by the degree of difficulty of pulverization. The degree of pulverization difficulty is obtained by dividing the “particle size of the 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” by the “initial particle size of the hydrogen-absorbing alloy powder”. is the value The reason why the difficulty of pulverization is set in the above range is that if it is too high, the initial activation is difficult and the input/output characteristics of the battery deteriorate, and if it is too low, the life characteristics of the battery cannot be ensured. Furthermore, the difficulty of pulverization has a correlation with the amount of hydrogen storage (H/M). It must be considered in combination with H/M. 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. As will be described later, the hydrogen storage capacity (H/M) and the plateau pressure can be measured by a PCT (hydrogen pressure-composition-isothermal diagram) characteristic evaluation device.
前記水素吸蔵合金の製造方法としては、本発明の結晶サイズ及びその他の必要要件を満たすことができれば、どのような製造方法でも構わない。例えば、例えば、真空溶融炉や大気溶融炉による溶解法、気相合成法、アーク溶融法、プラズマ溶解法等で製造することができ、得られたものを再度熱処理するようにしてもよい。また、得られた水素吸蔵合金は、ニッケル水素電池の負極等に用いるために、所定の粒度に粉砕して水素吸蔵合金粉末として使用するようにしてもよい。 Any method for producing the hydrogen storage alloy may be used as long as it satisfies the crystal size and other requirements of the present invention. For example, it can be produced by a melting method using a vacuum melting furnace or an air melting furnace, a gas phase synthesis method, an arc melting method, a plasma melting method, or the like, and the obtained product may be heat-treated again. Further, the obtained hydrogen-absorbing alloy may be pulverized to a predetermined particle size and used as a hydrogen-absorbing alloy powder for use as a negative electrode of a nickel-metal hydride battery.
前記製造方法の一例を次に示す。所定量を秤量後混合された各金属原料を、高周波加熱方式で溶解し、鋳型に流し込んで冷却して固化してインゴットを得る。更に、前記インゴットをそのまま或いは適度に分割した後、熱処理してもよい。本発明の大きな結晶サイズを得るためには、組成にもよるが、鋳型に流し込んで結晶を形成させる際にできるだけ結晶成長（粒成長）させる条件が好ましい。例えば、鋳型側から凝固させて結晶成長させる（一方向性凝固）ことが好ましい。その為には、鋳型側からの抜熱を効率良くすることが必要であり、例えば、鋳型との反対側の抜熱をおさせて凝固を遅らせるようにしたり、鋳型を水冷したり、鋳型の熱容量を大きくしたり、鋳型の熱伝導率を大きくしたり、これらを適宜組み合わせて鋳型の側面からの抜熱の効率を上げるなどして、一方向性凝固を実現させる。 An example of the manufacturing method is shown below. Each metal raw material mixed after weighing a predetermined amount is melted by a high-frequency heating method, poured into a mold, cooled and solidified to obtain an ingot. Further, the ingot may be heat-treated as it is or after being divided appropriately. In order to obtain the large crystal size of the present invention, although it depends on the composition, it is preferable to use conditions that allow crystal growth (grain growth) as much as possible when the material is poured into a mold to form crystals. For example, it is preferable to solidify from the mold side to grow crystals (unidirectional solidification). For that purpose, it is necessary to efficiently extract heat from the mold side. Unidirectional solidification is achieved by increasing the heat capacity, increasing the thermal conductivity of the mold, or combining them appropriately to increase the efficiency of heat removal from the sides of the mold.
このうち、鋳型の熱伝導率に関しては、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。また、凝固後に熱処理すると更に結晶成長させることができる。凝固後の結晶サイズが不十分であっても熱処理によって十分なサイズの結晶に成長させることができる。凝固後の結晶組織が規則的配列になっている方が、その後の熱処理によって結晶成長させやすい。更には、合金組成によって、結晶成長のし易さが異なるので、大きな結晶を得るためには上記手段を適宜用いて所望の合金を作製する。
よって、本発明の水素吸蔵合金は、組成、溶湯温度や凝固方法等の鋳造条件、熱処理条件を適宜選択して組合わせることによって目的の結晶粒、結晶形態、偏析相を形成させることができる。
Regarding the thermal conductivity of the mold, 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. Also, if heat treatment is performed after solidification, further crystal growth can be achieved. Even if the crystal size after solidification is insufficient, the crystal can be grown to a sufficient size by heat treatment. If the crystal structure after solidification is in a regular arrangement, it is easier to grow crystals by subsequent heat treatment. Furthermore, since the easiness of crystal growth differs depending on the alloy composition, a desired alloy is produced by appropriately using the above means in order to obtain a large crystal.
Therefore, the hydrogen storage alloy of the present invention can form desired crystal grains, crystal morphology, and segregation phase by appropriately selecting and combining composition, casting conditions such as molten metal temperature and solidification method, and heat treatment conditions.
本発明の水素吸蔵合金を得るにあたっては、上述した以外には一般的な方法と同様に、秤量工程、混合工程、鋳造工程、熱処理工程、冷却工程、及び粉砕工程を経て製造される。秤量工程では、所定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。ここで鋳造温度は、１２００℃～１４５０℃の範囲が好ましく、１３００℃～１４００℃がより好ましく、１３４０℃～１３６０℃の範囲であることが更に好ましい。ここで、鋳型による冷却においては、溶融金属が鋳型面側で不均一核発生して急速凝固し、前記核から結晶が成長しやすい条件とすることが望ましい。そのためには、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。 In obtaining the hydrogen-absorbing alloy of the present invention, it is manufactured through the weighing process, the mixing process, the casting process, the heat treatment process, the cooling process, and the pulverizing process in the same manner as in the general method except for the above-described steps. In the weighing step, each raw material of the hydrogen storage alloy is weighed so as to obtain a predetermined 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). Here, the casting temperature is preferably in the range of 1200°C to 1450°C, more preferably 1300°C to 1400°C, even more preferably 1340°C to 1360°C. Here, in the cooling by the mold, it is desirable that the molten metal generates heterogeneous nuclei on the mold surface side, rapidly solidifies, and crystals easily grow from the nuclei. For this purpose, 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℃～１２００℃の温度で熱処理される。本実施の形態にかかる水素吸蔵合金において、熱処理温度は１０００℃～１１５０℃が好ましい。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、数時間から十数時間が一般的であり、インゴットの中心部まで所定温度になるように時間設定すれば良い。冷却工程では熱処理された鋳造物が冷却される。冷却方法は、放冷でも空冷であってもよい。冷却速度も特に問わない。粉砕工程では、このようにして得られたインゴットが、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ことができる。 The alloy after casting is heat treated at a temperature of 950° C. to 1200° C. in a non-oxidizing atmosphere in a heat treatment step. In the hydrogen storage alloy according to this embodiment, the heat treatment temperature is preferably 1000.degree. C. to 1150.degree. The heat treatment time depends on the size of the ingot (hydrogen-absorbing alloy piece) after casting, but it is generally from several hours to ten and several hours. good. The cooling step cools the heat-treated casting. The cooling method may be natural cooling or air cooling. There is no particular limitation on the cooling rate. In the pulverization step, the ingot thus obtained is coarsely pulverized and finely pulverized into hydrogen-absorbing alloy powder having a required particle size. For example, an ingot can be pulverized to a size that can pass through a 500 μm sieve to obtain a hydrogen-absorbing alloy powder.
本発明におけるＡＢ５型水素吸蔵合金は、ＣａＣｕ５型結晶構造を有し、一般式ＭｍＮｉａＭｎｂＡｌｃＣｏｄ（Ｍｍはミッシュメタルであり、４．３０≦ａ≦４．７０、０．２５≦ｂ≦０．４５、０．２５≦ｃ≦０．４５、０．０≦ｄ≦０．１４、５．２０≦ａ＋ｂ＋ｃ＋ｄ≦５．５５）で表され、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≦０．１４としている。一般に、Ｃｏ含有量が０では、通常十分な微粉化難度が得られないが、本発明の要件を満たせば十分な微粉化難度が得られる。一方、０．１４超では十分な微粉化難度は得られるが原料コスト低減につながらない。なお、本発明においてはＣｏを含有してもよく、好ましくは０．０１≦ｄ≦０．１０、更に好ましくは０．０１≦ｄ≦０．０５であるのがよい。 The AB 5 -type hydrogen storage alloy in the present invention has a CaCu 5 -type crystal structure and has the general formula MmNiaMnbAlcCod (Mm is a misch metal, 4.30 ≤ a ≤ 4.70, 0.25 ≤ b ≤ 0.45 , 0.25 ≤ c ≤ 0.45, 0.0 ≤ d ≤ 0.14, 5.20 ≤ a + b + c + d ≤ 5.55), and the molar ratio d of Co is as small as possible to reduce raw material costs. 0≦d≦0.14. In general, when the Co content is 0, a sufficient degree of difficulty in pulverization cannot be obtained, but a sufficient degree of difficulty in pulverization can be obtained if the requirements of the present invention are satisfied. On the other hand, if it exceeds 0.14, a sufficient degree of difficulty in pulverization can be obtained, but this does not lead to a reduction in raw material costs. In the present invention, Co may be contained, preferably 0.01≤d≤0.10, more preferably 0.01≤d≤0.05.
ＭｍのＬａ、Ｃｅの比率、Ｎｉ、Ｍｎ、Ａｌのモル比を前述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、プラトー圧力を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及びＣｅの合計が、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４．７０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、０．２５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 ratio of La and Ce in Mm and the molar ratio 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 plateau pressure to 0.04 to 0.07 MPa, and to widen the plateau region in the PCT curve as much as possible. In Mm, the sum of La and Ce is within 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 4.70 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 in the range of 0.25 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.
本発明における電子線後方散乱回析法（ＥＢＳＤ）による結晶粒サイズの測定方法について説明する。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。このとき巣や欠落箇所の無い平坦な面を選択して観察することが望ましい。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る。本発明の平均結晶粒サイズは、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。
結晶成長方向と平行にカットして上述と同様に観察した各結晶の長径と短径を測定し、長径／短径の比を求め、平均値としたものが本発明の結晶成長方向と平行面の結晶粒の長径／短径の比である。また、結晶成長方向に対して直角（垂直）にカットして上述と同様に観察した各結晶の長径と短径を測定し、長径／短径の比を求め、平均値としたものが本発明の結晶成長方向と直角面の結晶粒の長径／短径の比である。
A method for measuring the crystal grain size by electron beam backscatter diffraction (EBSD) in the present invention will be described. 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. At this time, it is desirable to select and observe a flat surface with no cavities or gaps. 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, the crystal grains (grains) are analyzed, and from the detected area of each crystal grain, the crystal grain size can be measured in equivalent circle diameter. The average crystal grain size of the present invention is the average value obtained by observing 10 fields of view and obtaining the respective measurements.
The major axis and minor axis of each crystal observed in the same manner as described above were measured by cutting in parallel with the crystal growth direction, and the ratio of major axis/minor axis was obtained. is the ratio of the major axis/minor axis of the crystal grains. In addition, the long axis and short axis of each crystal observed in the same manner as described above were measured by cutting at right angles (perpendicular) to the crystal growth direction, and the ratio of the long axis/minor axis was obtained, and the average value was taken as the present invention. It is the ratio of the major axis/minor axis of the crystal grain in the plane perpendicular to the crystal growth direction.
また、偏析相については、ランタンＬａを含まない、即ち、ＬａＮｉ５結晶相ではない相であり、ＥＢＳＤ解析でＬａＮｉ５結晶でない部分或いはＥＤＳ分析でＬａが含まれない部分として主相ＬａＮｉ５相と区別できる。そのうち、偏析相のサイズは、エネルギー分散型Ｘ線分光法（ＥＤＳ、Energy dispersive X-ray spectroscopy）で面分析することで偏析相の分布（存在状態）や個々の形態が認識できるので、その形態（面積）から円相当径で偏析相のサイズを算出する。 In addition, the segregation phase does not contain lanthanum La, that is, it is a phase that is not a LaNi5 crystal phase, and is distinguished from the main phase LaNi5 phase as a portion that is not a LaNi5 crystal in EBSD analysis or a portion that does not contain La in EDS analysis. can. Of these, the size of the segregation phase can be determined by surface analysis using energy dispersive X-ray spectroscopy (EDS), which allows the distribution (existence state) and individual morphology of the segregation phase to be recognized. From (area), the size of the segregation phase is calculated from the equivalent circle diameter.
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（下記実施例ではこの方法に従った）。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 (this method was followed in the following examples). Using a PCT (hydrogen pressure-composition-isothermal diagram) characteristic evaluation device, ``particle size of hydrogen storage alloy powder after 10 hydrogen absorption and desorption 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 more difficult 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.) The "initial particle size of the storage 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１～１０、比較例１～３）
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、表１の温度の溶湯を表１の熱伝導率の鋳型に流し込んで鋳造を行い、不活性雰囲気下で表１の温度と時間で熱処理を行って水素吸蔵合金を作製した。鋳造においては、溶湯が凝固に対して鋳型の熱容量を過剰として鋳型による抜熱を効果的に行うと結晶成長が促進させた。反対に、例えば、鋳造において、溶湯の凝固に対する鋳型の熱容量を小さくし、かつ、熱伝導率も小さくすると、溶湯中のあらゆるところから核発生が生じて大きな結晶成長せずに凝固させた。もちろん、その後の熱処理によって結晶成長するが、温度と時間によって該結晶成長程度が変わってくる。
(Examples 1 to 10, Comparative Examples 1 to 3)
Metal raw materials of La and Ce as Ni, Mn, Al, Co, and 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. Next, it is heated and melted with a high-frequency heating device, and the molten metal at the temperature shown in Table 1 is poured into a mold with the thermal conductivity shown in Table 1 for casting, and heat-treated at the temperature and time shown in Table 1 in an inert atmosphere to produce a hydrogen storage alloy. was made. In casting, crystal growth was promoted when the heat capacity of the mold was excessive for solidification of the molten metal and the heat was effectively removed by the mold. On the contrary, for example, in casting, if the heat capacity of the mold for solidification of the molten metal is reduced and the thermal conductivity is also reduced, nuclei are generated from all places in the molten metal and the molten metal is solidified without large crystal growth. Of course, the subsequent heat treatment causes crystal growth, but the degree of crystal growth varies depending on temperature and time.
詳しくは、実施例１～４では、コバルトＣｏが含有されている組成であるので、比較的粒成長する傾向でありが、更に、鋳込み溶湯温度を高くして鋳込み、鋳型の熱伝導率を大きくすることで、鋳型からの抜熱が良くなり不均一核発生しやすくしている。溶湯温度が高いので、鋳型とは反対側（自由面側）の凝固が直ぐに起こらず核発生した鋳型面側から凝固が進み粒成長する。即ち、鋳込みにおいて既に大きな結晶粒が形成できている。更に、熱処理条件で高い温度で長時間にすると結晶粒を大きくできている。
また、実施例５～１０では、コバルトＣｏが含有されていない組成であるがＡＢ比を大きくすることで比較的粒成長する傾向にしている。鋳型の熱伝導率が低い実施例５～８に比べて鋳型の熱伝導率が高いかつ溶融の温度が高い実施例９～１０は上述の理由で大きな結晶粒が形成できている。実施例５～８においても熱処理条件の温度が高く時間が長い条件では粒成長できている。
一方、比較例１～２では、比較的粒成長し易い組成であるが、鋳型の熱伝導率が低い鋳型で溶湯温度が低いので、凝固の際均一核発生が起こり粒成長しづらくなった。その後の熱処理も比較的低温短時間としているので粒成長が起こっていない。比較例３は、コバルトＣｏが含有されずＡＢ比も小さい組成なので粒成長しづらいので、熱伝導率の大きな鋳型を使っても大きな結晶粒が得られなかった。その後の熱処理も低温短時間としているので粒成長が起こっていない。
このようにして、実施例１～１０、比較例１～３に係る水素吸蔵合金（インゴット）を得た。
Specifically, in Examples 1 to 4, since the composition contains cobalt Co, grains tend to grow relatively, but the temperature of the molten metal for casting is increased to increase the thermal conductivity of the mold. By doing so, heat removal from the mold is improved, making it easier to generate heterogeneous nuclei. Since the temperature of the molten metal is high, solidification of the side opposite to the mold (free surface) does not occur immediately, and solidification proceeds from the side of the mold where nuclei are generated, resulting in grain growth. That is, large crystal grains have already been formed during casting. Furthermore, the crystal grains can be made large when the heat treatment is performed at a high temperature for a long time.
Further, in Examples 5 to 10, although the composition does not contain cobalt Co, the grains tend to grow relatively by increasing the AB ratio. Large crystal grains can be formed in Examples 9-10 in which the thermal conductivity of the mold is high and the melting temperature is high compared to Examples 5-8 in which the thermal conductivity of the mold is low, for the reasons described above. In Examples 5 to 8 as well, grain growth was achieved under the heat treatment conditions of high temperature and long time.
On the other hand, in Comparative Examples 1 and 2, although the composition is relatively easy to grow grains, since the mold has a low thermal conductivity and the temperature of the molten metal is low, uniform nucleation occurs during solidification, making grain growth difficult. Since subsequent heat treatment is also performed at a relatively low temperature for a short time, grain growth does not occur. In Comparative Example 3, since cobalt Co was not contained and the AB ratio was small, it was difficult to grow grains, so large crystal grains could not be obtained even if a mold with high thermal conductivity was used. Since the subsequent heat treatment is also performed at a low temperature for a short period of time, grain growth does not occur.
Thus, hydrogen storage alloys (ingots) according to Examples 1 to 10 and Comparative Examples 1 to 3 were obtained.
また、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て、ＰＣＴ特性及び微粉化難度を測定した。なお、得られた各水素合金粉末を分析して求めた合金組成は、表１の組成と一致している。 In addition, 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 has a particle size (500 μm or less) that passes through a sieve mesh of 500 μm. PCT properties and pulverization difficulty were measured as a hydrogen storage alloy powder. The alloy composition obtained by analyzing each of the obtained hydrogen alloy powders matches the composition shown in Table 1.
（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。詳細は前述のとおりであり、結果を表２にまとめて示す。
(Measurement of micronization difficulty)
Micronization difficulty was measured using a particle size distribution analyzer and a PCT characterizer. The details are as described above, and the results are summarized in Table 2.
（平均結晶粒サイズ等の測定）
水素吸蔵合金（インゴット）の冷却面側より、数ｍｍ四方程度の欠片をサンプリングし、結晶成長方向と平行面及び直角面が観察できるようにそれぞれ樹脂包埋、鏡面研磨、コロイダルシリカによる研磨後に、走査型電子顕微鏡（日本電子株式会社製、JSM-7900F）に付帯しているオックスフォード・インスツルメント株式会社製の電子線後方散乱回析分析装置（EBSD）を用いて、水素吸蔵合金の平均結晶粒サイズの測定を行った。このときの二次電子像の観察倍率は１００倍とした。また、ＥＢＳＤ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。そして、表２には、実施例１～１０、比較例１～３で得られた各水素吸蔵合金のグレイン解析による平均結晶粒サイズと、結晶成長方向と平行面の場合及び直角面の場合における結晶粒の長径／短径の比とをまとめて示す。
(Measurement of average crystal grain size, etc.)
From the cooling surface side of the hydrogen storage alloy (ingot), a piece of about several mm square is sampled, and the surface parallel and perpendicular to the crystal growth direction can be observed. After embedding in resin, mirror polishing, and polishing with colloidal silica, Using an electron beam backscattering diffraction analyzer (EBSD) manufactured by Oxford Instruments Co., Ltd. attached to a scanning electron microscope (manufactured by JEOL Ltd., JSM-7900F), the average crystallinity of the hydrogen storage alloy Particle size measurements were made. The observation magnification of the secondary electron image at this time was 100 times. AZtec of Oxford Instruments Co., Ltd. was used as EBSD analysis software. Table 2 shows the average grain size obtained by grain analysis of each hydrogen storage alloy obtained in Examples 1 to 10 and Comparative Examples 1 to 3, and in the case of a plane parallel to the crystal growth direction and in the case of a plane perpendicular to the crystal growth direction. The ratio of major axis/minor axis of crystal grains is shown together.
（偏析相のサイズ等の測定）
偏析相は、上述のようにして確認し、走査型電子顕微鏡（日本電子株式会社製、JSM-7900F）に付帯しているオックスフォード・インスツルメント株式会社製のエネルギー分散型Ｘ線分光装置（ＥＤＳ、Energy dispersive X-ray spectroscopy）で、偏析相の形態を観察してそのサイズを計測し、Ｌａを含まない偏析相の円相当直径での平均サイズと各水素吸蔵合金の平均結晶粒サイズとの比を求めた。結果を表２に示す。なお、実施例１～１０、比較例１～３に係る各水素吸蔵合金では、いずれもＬａを含まない偏析相は各水素吸蔵合金における結晶粒の粒界に点在していることが確認された。
(Measurement of segregation phase size, etc.)
The segregation phase is confirmed as described above, and an energy dispersive X-ray spectrometer (EDS , Energy dispersive X-ray spectroscopy) to observe the morphology of the segregation phase and measure its size. I asked for a ratio. Table 2 shows the results. In addition, in each of the hydrogen storage alloys according to Examples 1 to 10 and Comparative Examples 1 to 3, it was confirmed that the segregation phase containing no La was scattered at the grain boundaries of the crystal grains in each hydrogen storage alloy. rice field.
表２に示されるとおり、実施例では平均結晶粒サイズが比較例と比べて大きく、微粉化難度が高い。詳しくは、図１に示したように、平均結晶粒サイズが大きくなるにつれて微粉化難度が高くなる傾向を示しており、比較例においては、本発明の実施例に匹敵する微粉化難度を得ることができなかった。また、結晶成長方向と平行面における結晶の長径／短径の比が大きくなると微粉化難度が高くなる傾向である。結晶成長方向と直角面における結晶の長径／短径の比が小さくなると微粉化難度が高くなる傾向である。更には、偏析相に関して、図２に示したように、偏析相サイズ／本結晶（母結晶）サイズの比が小さいほど微粉化難度が高くなる傾向である。 As shown in Table 2, the average crystal grain size is larger in the example than in the comparative example, and the difficulty of pulverization is high. Specifically, as shown in FIG. 1, the difficulty of pulverization tends to increase as the average grain size increases. I couldn't do it. Further, when the ratio of the major axis/minor axis of the crystal in the plane parallel to the crystal growth direction increases, the difficulty of pulverization tends to increase. As the ratio of the major axis/minor axis of the crystal in the plane perpendicular to the crystal growth direction decreases, the difficulty of pulverization tends to increase. Furthermore, regarding the segregation phase, as shown in FIG. 2, the smaller the ratio of segregation phase size/main crystal (mother crystal) size, the higher the difficulty of pulverization.
以上のとおり、本発明によれば、結晶粒のサイズを大きくした上で、それが所定の形状を有した水素吸蔵合金にすることで、Ｃｏ含有量の低減により原料コストを抑制しながら、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型水素吸蔵合金を得ることができる。そのため、ニッケル水素電池の負極に利用したときに、寿命特性や入出力特性を向上させることが可能になる。 As described above, according to the present invention, by increasing the size of the crystal grain and making it a hydrogen-absorbing alloy having a predetermined shape, the Co content is reduced and the raw material cost is suppressed, while hydrogen It is possible to obtain an AB5 type hydrogen storage alloy that suppresses pulverization of the alloy due to repeated storage and release of . Therefore, when used for the negative electrode of a nickel-metal hydride battery, it is possible to improve life characteristics and input/output characteristics.
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。 INDUSTRIAL APPLICABILITY 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.
（１）一般式ＭｍＮｉａＭｎｂＡｌｃＣｏｄ（式中、Ｍｍはミッシュメタルであり、４．３０≦ａ≦４．７０、０．２５≦ｂ≦０．４５、０．２５≦ｃ≦０．４５、０≦ｄ≦０．１４、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の割合の合計が全Ｍｍに対して９０質量％以上１００質量％以下の範囲内であり、
電子線後方散乱回析法により測定されるインゴットの状態での平均結晶粒サイズが、円相当直径で１８０μｍ以上であることを特徴とする水素吸蔵合金。
（２）結晶成長方向と平行面の合金を電子線後方散乱回析法により測定される結晶粒の長径／短径の比が、１．２以上であることを特徴とする（１）記載の水素吸蔵合金。
（３）結晶成長方向と直角面の合金を電子線後方散乱回析法により測定される結晶粒の長径／短径の比が、２．０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。
（４）Ｌａを含まない偏析相が存在し、該偏析相の平均サイズが円相当直径で前記平均結晶粒サイズの０．２倍以下であり、かつ、該偏析相は前記結晶粒の粒界に点在す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。
（５）篩目５００μｍを通過するサイズに粉砕した際の微粉化難度が０．４６～０．６０である（１）～（４）のいずれかに記載の水素吸蔵合金。
（６）（１）～（５）のいずれかに記載の水素吸蔵合金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。
（７）（６）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 ≤ 4.70, 0.25 ≤ b ≤ 0.45, 0.25 ≤ c ≤ 0.45, 0 ≤ d ≤ 0.14, 5.20 ≤ a + b + c + d ≤ 5.55), has a CaCu type 5 crystal structure, and the Mm is 90 mass% or more of the total Mm and the total ratio of La and Ce is 100 Within the range of % by mass or less,
A hydrogen storage alloy characterized by having an average grain size in an ingot state of 180 μm or more in equivalent circle diameter as measured by an electron beam backscattering diffraction method.
(2) The ratio of the major axis/minor axis of the crystal grains measured by electron beam backscattering diffraction of the alloy in a plane parallel to the crystal growth direction is 1.2 or more according to (1). Hydrogen storage alloy.
(3) The ratio of the major axis/minor axis of the crystal grain measured by the electron beam backscattering diffraction method of the alloy in the plane perpendicular to the crystal growth direction is 2.0 or less (1) or ( 2) The hydrogen storage alloy described.
(4) A segregation phase containing no La is present, and the average size of the segregation phase is 0.2 times or less of the average grain size in equivalent circle diameter, and the segregation phase is the grain boundary of the grain. The hydrogen storage alloy according to any one of (1) to (3), characterized in that it is scattered in.
(5) The hydrogen storage alloy according to any one of (1) to (4), which has a pulverization difficulty of 0.46 to 0.60 when pulverized to a size passing through a sieve mesh of 500 μm.
( 6 ) A negative electrode characterized by using a hydrogen-absorbing alloy powder obtained by pulverizing the hydrogen-absorbing alloy according to any one of (1) to ( 5 ) as a negative electrode active material.
( 7 ) A battery using the negative electrode according to ( 6 ).
Claims (6)
電子線後方散乱回析法により測定される平均結晶粒サイズが、円相当直径で１８０μｍ以上であることを特徴とする水素吸蔵合金。 general formula MmNiaMnbAlcCod (wherein Mm is a misch metal, 4.30≤a≤4.70, 0.25≤b≤0.45, 0.25≤c≤0.45, 0≤d≤0. 14, 5.20 ≤ a + b + c + d ≤ 5.55), has a CaCu type 5 crystal structure, and the Mm is 90% by mass or more and 100% by mass or less with respect to the total Mm. is within the range of
A hydrogen storage alloy characterized by having an average grain size of 180 μm or more in equivalent circle diameter as measured by an electron beam backscattering diffraction method.
A battery comprising the negative electrode according to claim 5 .
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| JPH10237569A (en) * | 1997-02-26 | 1998-09-08 | Toshiba Corp | Hydrogen storate alloy for battery, its production and nickel-hydrogen secondary battery |
| JP3301792B2 (en) * | 1992-11-19 | 2002-07-15 | 三洋電機株式会社 | Hydrogen storage alloy electrode |
| 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 |
| JP6948441B1 (en) * | 2020-07-21 | 2021-10-13 | 新日本電工株式会社 | Low Co hydrogen storage alloy powder |
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| JP3301792B2 (en) * | 1992-11-19 | 2002-07-15 | 三洋電機株式会社 | Hydrogen storage alloy electrode |
| JPH10237569A (en) * | 1997-02-26 | 1998-09-08 | Toshiba Corp | Hydrogen storate alloy for battery, its production and nickel-hydrogen secondary battery |
| 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 |
| JP6948441B1 (en) * | 2020-07-21 | 2021-10-13 | 新日本電工株式会社 | Low Co hydrogen storage alloy powder |
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