JP3568355B2 - Hydrogen storage alloy for alkaline storage batteries - Google Patents
Hydrogen storage alloy for alkaline storage batteries Download PDFInfo
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- JP3568355B2 JP3568355B2 JP09967797A JP9967797A JP3568355B2 JP 3568355 B2 JP3568355 B2 JP 3568355B2 JP 09967797 A JP09967797 A JP 09967797A JP 9967797 A JP9967797 A JP 9967797A JP 3568355 B2 JP3568355 B2 JP 3568355B2
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- 229910045601 alloy Inorganic materials 0.000 title claims description 80
- 239000000956 alloy Substances 0.000 title claims description 80
- 238000003860 storage Methods 0.000 title claims description 68
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 title claims description 54
- 239000001257 hydrogen Substances 0.000 title claims description 54
- 229910052739 hydrogen Inorganic materials 0.000 title claims description 54
- 239000002245 particle Substances 0.000 claims description 60
- 229910052761 rare earth metal Inorganic materials 0.000 claims description 41
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims description 22
- 239000007864 aqueous solution Substances 0.000 claims description 16
- 239000000203 mixture Substances 0.000 claims description 13
- 229910017052 cobalt Inorganic materials 0.000 claims description 11
- 239000010941 cobalt Substances 0.000 claims description 11
- 239000000843 powder Substances 0.000 claims description 11
- 229910052782 aluminium Inorganic materials 0.000 claims description 10
- 229910001122 Mischmetal Inorganic materials 0.000 claims description 9
- 239000002253 acid Substances 0.000 claims description 9
- AZDRQVAHHNSJOQ-UHFFFAOYSA-N alumane Chemical group [AlH3] AZDRQVAHHNSJOQ-UHFFFAOYSA-N 0.000 claims description 8
- 229910052759 nickel Inorganic materials 0.000 claims description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 8
- 238000010306 acid treatment Methods 0.000 claims description 6
- -1 rare earth hydroxide Chemical class 0.000 claims description 6
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 5
- 229910052748 manganese Inorganic materials 0.000 claims description 5
- 238000010521 absorption reaction Methods 0.000 claims description 4
- 229910052804 chromium Inorganic materials 0.000 claims description 4
- 229910052802 copper Inorganic materials 0.000 claims description 4
- 229910052733 gallium Inorganic materials 0.000 claims description 4
- 229910052738 indium Inorganic materials 0.000 claims description 4
- 229910052742 iron Inorganic materials 0.000 claims description 4
- 229910052750 molybdenum Inorganic materials 0.000 claims description 4
- 229910052710 silicon Inorganic materials 0.000 claims description 4
- 239000000243 solution Substances 0.000 claims description 4
- 229910052718 tin Inorganic materials 0.000 claims description 4
- 229910052721 tungsten Inorganic materials 0.000 claims description 4
- 229910052725 zinc Inorganic materials 0.000 claims description 4
- 229910021503 Cobalt(II) hydroxide Inorganic materials 0.000 claims description 3
- ASKVAEGIVYSGNY-UHFFFAOYSA-L cobalt(ii) hydroxide Chemical compound [OH-].[OH-].[Co+2] ASKVAEGIVYSGNY-UHFFFAOYSA-L 0.000 claims description 3
- 150000002910 rare earth metals Chemical class 0.000 claims description 3
- WNROFYMDJYEPJX-UHFFFAOYSA-K aluminium hydroxide Chemical compound [OH-].[OH-].[OH-].[Al+3] WNROFYMDJYEPJX-UHFFFAOYSA-K 0.000 claims description 2
- 229910000428 cobalt oxide Inorganic materials 0.000 claims 1
- IVMYJDGYRUAWML-UHFFFAOYSA-N cobalt(ii) oxide Chemical compound [Co]=O IVMYJDGYRUAWML-UHFFFAOYSA-N 0.000 claims 1
- 238000000151 deposition Methods 0.000 claims 1
- 238000001035 drying Methods 0.000 claims 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 16
- 239000001301 oxygen Substances 0.000 description 16
- 229910052760 oxygen Inorganic materials 0.000 description 16
- 239000003513 alkali Substances 0.000 description 13
- 230000000694 effects Effects 0.000 description 12
- 230000004913 activation Effects 0.000 description 11
- 238000003411 electrode reaction Methods 0.000 description 10
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 9
- 238000002474 experimental method Methods 0.000 description 9
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 9
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 8
- 238000007254 oxidation reaction Methods 0.000 description 5
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 4
- VSCWAEJMTAWNJL-UHFFFAOYSA-K aluminium trichloride Chemical compound Cl[Al](Cl)Cl VSCWAEJMTAWNJL-UHFFFAOYSA-K 0.000 description 4
- GVPFVAHMJGGAJG-UHFFFAOYSA-L cobalt dichloride Chemical compound [Cl-].[Cl-].[Co+2] GVPFVAHMJGGAJG-UHFFFAOYSA-L 0.000 description 4
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 description 4
- ICAKDTKJOYSXGC-UHFFFAOYSA-K lanthanum(iii) chloride Chemical compound Cl[La](Cl)Cl ICAKDTKJOYSXGC-UHFFFAOYSA-K 0.000 description 4
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 description 3
- 229910018007 MmNi Inorganic materials 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 239000003792 electrolyte Substances 0.000 description 3
- 229910052746 lanthanum Inorganic materials 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- BFDHFSHZJLFAMC-UHFFFAOYSA-L nickel(ii) hydroxide Chemical compound [OH-].[OH-].[Ni+2] BFDHFSHZJLFAMC-UHFFFAOYSA-L 0.000 description 3
- 230000003647 oxidation Effects 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 150000003839 salts Chemical class 0.000 description 3
- 238000004381 surface treatment Methods 0.000 description 3
- CPELXLSAUQHCOX-UHFFFAOYSA-M Bromide Chemical compound [Br-] CPELXLSAUQHCOX-UHFFFAOYSA-M 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- 229910052786 argon Inorganic materials 0.000 description 2
- 239000011230 binding agent Substances 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 239000012266 salt solution Substances 0.000 description 2
- 239000002002 slurry Substances 0.000 description 2
- 229920003171 Poly (ethylene oxide) Polymers 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 150000004679 hydroxides Chemical class 0.000 description 1
- 238000004898 kneading Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 1
- 239000004810 polytetrafluoroethylene Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000004080 punching Methods 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 238000004611 spectroscopical analysis Methods 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Landscapes
- Powder Metallurgy (AREA)
- Battery Electrode And Active Subsutance (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は、アルカリ蓄電池の負極に使用される水素吸蔵合金に関する。
【０００２】
【従来の技術及び発明が解決しようとする課題】
アルカリ蓄電池の負極に使用される水素吸蔵合金としては、組成式ＡＢ５ 〔Ａは希土類元素（水素吸収時発熱型元素）であり、ＢはＮｉ、Ｃｏ（水素吸収時吸熱型元素）などである〕で表されるものがよく知られている。しかし、この種の水素吸蔵合金の粒子表面から２ｎｍ以下の距離に位置する粒子表面部には、自然酸化によりコバルトを含まない酸化物層又は水酸化物層が形成されており、このような粒子表面部にコバルトが全く存在しない水素吸蔵合金は、電極反応における活性が低く、これを使用しても、比容量の大きい水素吸蔵合金電極は得られない。
【０００３】
電極反応における活性を高めるべく、水素吸蔵合金を酸性水溶液に浸漬して酸化物層又は水酸化物層を除去することが提案されている（特開平４−１７９０５５号公報参照）。
【０００４】
しかしながら、上記の表面処理を行うと、電極反応における活性は高められるものの、アルカリの攻撃から合金を保護する働きをする易溶解性の希土類元素の酸化物層及び水酸化物層が表面処理時に溶出してしまうために、水素吸蔵合金の耐アルカリ性が低下して、電解液（アルカリ）により酸化され易くなる。
【０００５】
本発明は、以上の事情に鑑みなされたものであって、電極反応における活性が高く、しかも耐アルカリ性の良いアルカリ蓄電池用水素吸蔵合金を提供することを目的とする。
【０００６】
【課題を解決するための手段】
請求項１記載の発明に係るアルカリ蓄電池用水素吸蔵合金は、水素吸蔵合金粉末を酸溶液に浸漬して酸処理し、この酸処理した水素吸蔵合金粉末を希土類とコバルトとを含む水溶液に浸漬し、アルカリ水溶液を添加して粒子表面に希土類水酸化物及び水酸化コバルトを析出させ、乾燥して得られる組成式ＡＢx （式中、４．４≦ｘ≦５．５、Ａは一種又は二種以上の希土類元素、Ｂは少なくともＮｉ及びＣｏを含み、Ｃｕ、Ｆｅ、Ｓｎ、Ｓｉ、Ａｌ、Ｗ、Ｍｎ、Ｚｎ、Ｃｒ、Ｍｏ、Ｉｎ及びＧａよりなる群から選ばれた少なくとも一種の水素吸収時吸熱型元素をさらに含んでいてもよい）で表され、粒子表面から１０ｎｍ以上の粒子内部における単位面積当たりの希土類元素数（但し、ミッシュメタルについては１式量を希土類元素１原子と数える）に対する粒子表面から２ｎｍ以下の粒子表面部における単位面積当たりの希土類元素数（但し、ミッシュメタルについては１式量を希土類元素１原子と数える）の比の値が０．３〜２．０であり、且つ前記粒子内部における単位面積当たりのコバルト原子数に対する前記粒子表面部における単位面積当たりのコバルト原子数の比の値が、０．８〜３．０である合金である。
【０００７】
また、請求項２記載の発明に係るアルカリ蓄電池用水素吸蔵合金は、水素吸蔵合金粉末を酸溶液に浸漬して酸処理し、この酸処理した水素吸蔵合金粉末を希土類とコバルトとアルミニウムとを含む水溶液に浸漬し、アルカリ水溶液を添加して粒子表面に希土類水酸化物、水酸化コバルト及び水酸化アルミニウムを析出させ、乾燥して得られる組成式ＡＢx （式中、４．４≦ｘ≦５．５、Ａは一種又は二種以上の希土類元素、Ｂは少なくともＮｉ、Ｃｏ及びＡｌを含み、Ｃｕ、Ｆｅ、Ｓｎ、Ｓｉ、Ｗ、Ｍｎ、Ｚｎ、Ｃｒ、Ｍｏ、Ｉｎ及びＧａよりなる群から選ばれた少なくとも一種の水素吸収時吸熱型元素をさらに含んでいてもよい）で表され、粒子表面から１０ｎｍ以上の粒子内部における単位面積当たりの希土類元素数（但し、ミッシュメタルについては１式量を希土類元素１原子と数える）に対する粒子表面から２ｎｍ以下の粒子表面部における単位面積当たりの希土類元素数（但し、ミッシュメタルについては１式量を希土類元素１原子と数える）の比の値が、０．３〜２．０であり、前記粒子内部における単位面積当たりのコバルト原子数に対する前記粒子表面部における単位面積当たりのコバルト原子数の比の値が、０．８〜３．０であり、且つ前記粒子内部における単位面積当たりのアルミニウム原子数に対する前記粒子表面部における単位面積当たりのアルミニウム原子数の比の値が、０．２〜３．０である合金である。
【０００８】
請求項１記載の発明に係るアルカリ蓄電池用水素吸蔵合金における希土類元素及びＮｉは、電池作動時の温度及び圧力において水素を電気化学的に吸蔵及び放出することが可能な合金結晶格子を形成するために必要な成分であり、Ｃｏは、電極反応における活性を高めるために必要な成分である。また、請求項２記載の発明に係るアルカリ蓄電池用水素吸蔵合金において、Ａｌは、耐アルカリ性（耐酸化性）を高めるために有用な成分である。
【０００９】
請求項１記載の発明に係るアルカリ蓄電池用水素吸蔵合金は、希土類元素及びコバルトが粒子中に適度に分布しているので、電極反応における活性が高く、しかも耐アルカリ性が良い。また、請求項２記載の発明に係るアルカリ蓄電池用水素吸蔵合金は、希土類元素及びコバルトが粒子中に適度に分布していることに加えて、さらにアルミニウムも粒子中に適度に分布しているので、電極反応における活性が高く、しかも耐アルカリ性が極めて良い。
【００１０】
【実施例】
以下、本発明を実施例に基づいてさらに詳細に説明するが、本発明は下記実施例に何ら限定されるものではなく、その要旨を変更しない範囲において適宜変更して実施することが可能なものである。
【００１１】
（実験１）
（水素吸蔵合金の作製）
Ｍｍ（ミッシュメタル；希土類元素の混合物）、Ｎｉ、Ｃｏ、Ａｌ及びＭｎを所定の割合で混合した混合物を、アルゴンガス雰囲気下のアーク溶解炉内で加熱溶融させて溶湯とした後、冷却して、組成式ＭｍＮｉ３．６ Ｃｏ０．６ Ａｌ０．２ Ｍｎ０．６ で表される水素吸蔵合金塊を得た。次いで、これをアルゴンガス雰囲気下にて平均粒径６０μｍに粉砕して粉末とし、得られた粉末１００ｇを、ｐＨ＝１．０の塩酸水溶液１００ｇに浸漬し、１０分間攪拌して、酸処理（表面処理）した後、濾別し、水洗した。この酸処理後の水素吸蔵合金粉末を、塩化ランタンと塩化コバルトとを水に所定量溶かした塩水溶液に１０分間浸漬し、水酸化カリウム水溶液を添加して水溶液のｐＨを１２に高めて、合金の粒子表面にランタンとコバルトとを水酸化物として析出させた後、濾別し、水洗し、乾燥して、アルカリ蓄電池用水素吸蔵合金Ａ１〜Ａ８（本発明合金），Ｘ１〜Ｘ７（比較合金）を得た。各アルカリ蓄電池用水素吸蔵合金を作製する際に使用した塩水溶液の塩化ランタン濃度（モル／リットル）及び塩化コバルト濃度（モル／リットル）を表１に示す。
【００１２】
【表１】
上記の各アルカリ蓄電池用水素吸蔵合金について、粒子内部（粒子表面から１０ｎｍ以上のところ）における単位面積当たりの希土類元素数（但し、ミッシュメタル１式量を希土類元素１原子と数える）に対する粒子表面部における単位面積当たりのランタン原子数の比の値Ｒ１及び粒子内部における単位面積当たりのコバルト原子数に対する粒子表面部における単位面積当たりのコバルト原子数の比の値Ｒ２を求めた。Ｒ１及びＲ２は、ＸＰＳ（Ｘ−ｒａｙ ｐｈｏｔｏｎ Ｓｐｅｃｔｒｏｓｃｏｐｙ）により得たスペクトルの該当ピークの面積比として求めた。なお、粒子内部における希土類元素数及びコバルト原子数は、水素吸蔵合金をＸＰＳに付属の装置でイオンエッチングし、組成が変化しなくなったところ（元の粒子表面から１０ｎｍ以上のところ）での測定値である。各アルカリ蓄電池用水素吸蔵合金のＲ１及びＲ２を表２に示す。
【００１４】
（試験電極の作製）
上記の各アルカリ蓄電池用水素吸蔵合金１００重量部と、結着剤としてのポリテトラフルオロエチレン５重量部と、水とを混練してペーストを調製し、このペーストを板状に圧延し、所定の寸法の円盤状に切断し、ニッケルメッシュで包み込み、加圧成形して、試験電極を作製した。
【００１５】
（単極試験セルの組立）
上記の各試験電極（作用極）と従来公知の焼結式ニッケル極（対極）と半分充電した焼結式水酸化ニッケル極（参照極）とを用いて、単極試験セルを組み立てた。
【００１６】
（活性化率）
上記の各単極試験セルを、２００ｍＡ／ｇで充電した後、２００ｍＡ／ｇで終止電圧−０．９５Ｖ（ｖｓ．半分充電した焼結式水酸化ニッケル極の電位）まで放電して放電容量Ｃ１を求め、３０分間休止した後、５０ｍＡ／ｇで終止電圧−０．９５Ｖ（ｖｓ．半分充電した焼結式水酸化ニッケル極の電位）まで放電して放電容量Ｃ２を求めた。放電容量Ｃ１及び放電容量Ｃ２から、下式で定義される水素吸蔵合金の活性化率Ｐ（％）を求めた。活性化率Ｐが大きいものほど、電極反応における活性が高い水素吸蔵合金である。結果を表２に示す。
【００１７】
活性化率Ｐ（％）＝｛Ｃ１／（Ｃ１＋Ｃ２）｝×１００
【００１８】
（酸素濃度上昇度）
上記の各水素吸蔵合金１００重量部と、結着剤としてのポリエチレンオキサイド０．５重量部と、水とを混練してスラリーを調製し、このスラリーを集電体としてのパンチングメタルに塗着し、所定の寸法の円盤状に切断して、水素吸蔵合金電極を作製した。この電極から合金を少量剥離し、その合金の酸素濃度Ｄ１を、酸素濃度分析装置（レコ（ＬＥＣＯ）社製、商品コード「ＲＱ−４１６ＤＲ」）にて測定した。次いで、これらの各水素吸蔵合金電極を６０°Ｃに加温した３０重量％水酸化カリウム水溶液に２週間浸漬し、電極から合金を少量剥離し、水洗し、乾燥して、その合金の酸素濃度Ｄ２を、先と同じ装置にて測定した。酸素濃度Ｄ１及び酸素濃度Ｄ２から、下式で定義される酸素濃度上昇度Ｑを求めた。酸素濃度上昇度Ｑが小さいものほど、アルカリ電解液中で酸化され難い、耐アルカリ性の良い水素吸蔵合金である。結果を表２に示す。
【００１９】
酸素濃度上昇度Ｑ＝Ｄ２／Ｄ１
【００２０】
【表２】
合金Ａ１〜Ａ８は、合金Ｘ１〜Ｘ７に比べて、活性化率Ｐが大きく、しかも酸素濃度上昇度Ｑが小さい。合金Ｘ１（未処理の従来合金）の活性化率Ｐが極めて小さいのは、粒子表面部にＣｏが全く存在しないからである。また、合金Ｘ１の酸素濃度上昇度Ｑがそれほど大きくないのは、活性化率Ｐが極めて小さいために、合金の酸化が起こりにくいからである。合金Ｘ２（酸処理した従来合金）の酸素濃度上昇度Ｑが大きいのは、電解液（アルカリ）の攻撃から合金を保護する粒子表面部の希土類元素が少ないために、耐アルカリ性が良くないからである。また、合金Ｘ２の活性化率Ｐが小さいのは、Ｃｏは存在するもののポーラスな希土類元素の酸化物層又は水酸化物層が少ないために、反応面積（合金と電解液との接触部の面積）が小さいからである。合金Ｘ３，Ｘ４の活性化率Ｐが小さいのは、粒子表面部の希土類元素の酸化物又は水酸化物の量が多過ぎるからである。合金Ｘ３，Ｘ４の酸素濃度上昇度Ｑが極めて大きいのは、希土類元素とＣｏとが共存する活性の高い部分が粒子表面に少ないために、合金の酸化反応が促進されたためである。合金Ｘ５，Ｘ６の活性化率Ｐが小さいのは、粒子表面部のＣｏが少な過ぎるからである。合金Ｘ７の酸素濃度上昇度Ｑが大きいのは、粒子表面部のＣｏが多過ぎるために、電極反応における活性が低下して、合金の酸化反応が促進されたためである。
【００２２】
（実験２）
電池用水素吸蔵合金を作製する際に塩化ランタンと塩化コバルトと塩化アルミニウムを水に所定量溶かした塩水溶液を使用し、この塩水溶液の塩化ランタン濃度（モル／リットル）、塩化コバルト濃度（モル／リットル）及び塩化アルミニウム濃度（モル／リットル）を表３に示すごとく変えたこと以外は実験１と同様にして、水素吸蔵合金Ａ９〜Ａ１５を得た。これらの各水素吸蔵合金について、実験１と同様にして、Ｒ１、Ｒ２、粒子内部における単位面積当たりのアルミニウム原子数に対する粒子表面部における単位面積当たりのアルミニウム原子数の比の値Ｒ３、活性化率Ｐ及び酸素濃度上昇度Ｑを求めた。結果を表４に示す。
【００２３】
【表３】
【表４】
表４より、粒子内部における単位面積当たりのアルミニウム原子数に対する粒子表面部における単位面積当たりのアルミニウム原子数の比の値が、０．２〜３．０である水素吸蔵合金Ａ１１〜Ａ１４が、酸素濃度上昇度が小さく、耐アルカリ性に優れていることが分かる。
【００２６】
実験１では、粒子内部の組成が式ＭｍＮｉ３．６ Ｃｏ０．６ Ａｌ０．２ Ｍｎ０．６ で表されるアルカリ蓄電池用水素吸蔵合金について調べたが、粒子内部の組成が式ＬａＮｉ４．５ Ｃｏ０．５ で表される水素吸蔵合金についても実験１と同様の結果が得られることを別途確認した。
【００２７】
実験２では、粒子内部の組成が式ＭｍＮｉ３．６ Ｃｏ０．６ Ａｌ０．２ Ｍｎ０．６ で表されるアルカリ蓄電池用水素吸蔵合金について調べたが、粒子内部の組成が式Ｍｍ（Ｎｉ３．６ Ｃｏ０．６ Ａｌ０．２ Ｍｎ０．６ ）ｘ （ｘ＝０．８８、０．９２、０．９５、１．００、１．０２、１．０５又は１．１０）で表される水素吸蔵合金についても実験２と同様の結果が得られることを別途確認した。
【００２８】
なお、実験１及び実験２におけるランタン原料及びコバルト原料として、塩化物に代えて、臭化物又は水酸化物を使用してもよい。また、実験２におけるアルミニウム原料についても、塩化物に代えて、臭化物又は水酸化物を使用してもよい。また、塩水溶液からランタン、コバルト及びアルミニウムの各水酸化物を合金の粒子表面に析出させる際に添加するアルカリ剤として、水酸化カリウムに代えて、例えば、水酸化ナトリウム又は水酸化リチウムを使用してもよい。
【００２９】
【発明の効果】
本発明により、電極反応における活性が高く、しかも耐アルカリ性の良いアルカリ蓄電池用水素吸蔵合金が提供される。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hydrogen storage alloy used for a negative electrode of an alkaline storage battery.
[0002]
Problems to be solved by the prior art and the invention
As the hydrogen storage alloy used for the negative electrode of the alkaline storage battery, the composition formula AB 5 [A is a rare earth element (element generating heat when absorbing hydrogen), B is Ni, Co (element absorbing heat when absorbing hydrogen), and the like. ] Are well known. However, an oxide layer or a hydroxide layer containing no cobalt is formed by natural oxidation on the particle surface located at a distance of 2 nm or less from the particle surface of this type of hydrogen storage alloy. A hydrogen storage alloy having no cobalt on its surface has a low activity in an electrode reaction, and a hydrogen storage alloy electrode having a large specific capacity cannot be obtained by using this.
[0003]
In order to enhance the activity in the electrode reaction, it has been proposed to remove the oxide layer or the hydroxide layer by immersing the hydrogen storage alloy in an acidic aqueous solution (see Japanese Patent Application Laid-Open No. Hei 4-17955).
[0004]
However, when the above-described surface treatment is performed, although the activity in the electrode reaction is enhanced, the readily soluble rare earth element oxide layer and hydroxide layer which function to protect the alloy from alkali attack are eluted during the surface treatment. Therefore, the alkali resistance of the hydrogen storage alloy is reduced, and the hydrogen storage alloy is easily oxidized by the electrolyte (alkali).
[0005]
The present invention has been made in view of the above circumstances, and has as its object to provide a hydrogen storage alloy for an alkaline storage battery having high activity in an electrode reaction and good alkali resistance.
[0006]
[Means for Solving the Problems]
In the hydrogen storage alloy for an alkaline storage battery according to the first aspect of the invention, the hydrogen storage alloy powder is immersed in an acid solution for acid treatment, and the acid-treated hydrogen storage alloy powder is immersed in an aqueous solution containing rare earth and cobalt. An alkaline aqueous solution is added to precipitate a rare earth hydroxide and cobalt hydroxide on the particle surface and then dried to obtain a composition formula AB x (where 4.4 ≦ x ≦ 5.5, where A is one or two At least one kind of rare earth element, B contains at least Ni and Co, and at least one kind of hydrogen absorption selected from the group consisting of Cu, Fe, Sn, Si, Al, W, Mn, Zn, Cr, Mo, In and Ga (Which may further include an endothermic element), and the number of rare earth elements per unit area within the particle of 10 nm or more from the particle surface (however, for misch metal, one formula amount is defined as one atom of the rare earth element). The ratio of the number of rare earth elements per unit area in the particle surface portion of 2 nm or less from the particle surface to the particle surface (however, for misch metal, one formula amount is counted as one atom of the rare earth element) is 0.3 to 2.0. Wherein the ratio of the number of cobalt atoms per unit area on the particle surface to the number of cobalt atoms per unit area inside the particle is 0.8 to 3.0.
[0007]
Further, the hydrogen storage alloy for an alkaline storage battery according to the second aspect of the present invention includes immersing the hydrogen storage alloy powder in an acid solution to perform an acid treatment, and the acid-treated hydrogen storage alloy powder contains a rare earth element, cobalt, and aluminum. The composition is immersed in an aqueous solution, and an alkaline aqueous solution is added to precipitate rare earth hydroxide, cobalt hydroxide and aluminum hydroxide on the particle surface, and dried to obtain a composition formula AB x (where 4.4 ≦ x ≦ 5 .5, A is one or more rare earth elements, B contains at least Ni, Co and Al, and is selected from the group consisting of Cu, Fe, Sn, Si, W, Mn, Zn, Cr, Mo, In and Ga. At least one selected endothermic element at the time of hydrogen absorption may be included), and the number of rare earth elements per unit area within the particle of 10 nm or more from the particle surface (however, The number of rare earth elements per unit area in the particle surface area of 2 nm or less from the particle surface to the amount of one formula is counted as one atom of rare earth element for the metal (however, for misch metal, the amount of one formula is counted as one atom of rare earth element) The ratio of the number of cobalt atoms per unit area on the surface of the particle to the number of cobalt atoms per unit area inside the particle is from 0.8 to 2.0. An alloy wherein the ratio of the number of aluminum atoms per unit area on the particle surface to the number of aluminum atoms per unit area inside the particle is 0.2 to 3.0.
[0008]
The rare earth element and Ni in the hydrogen storage alloy for an alkaline storage battery according to the first aspect of the invention form an alloy crystal lattice capable of electrochemically storing and releasing hydrogen at the temperature and pressure during battery operation. Is a component necessary for increasing the activity in the electrode reaction. In the hydrogen storage alloy for an alkaline storage battery according to the second aspect of the present invention, Al is a component useful for improving alkali resistance (oxidation resistance).
[0009]
The hydrogen storage alloy for an alkaline storage battery according to the first aspect of the invention has a high activity in an electrode reaction and a good alkali resistance because the rare earth element and cobalt are appropriately distributed in the particles. In the hydrogen storage alloy for an alkaline storage battery according to the second aspect of the present invention, the rare earth element and cobalt are appropriately distributed in the particles, and aluminum is also appropriately distributed in the particles. It has a high activity in the electrode reaction and has extremely good alkali resistance.
[0010]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and can be implemented by appropriately changing the scope without changing the gist thereof. It is.
[0011]
(Experiment 1)
(Production of hydrogen storage alloy)
A mixture obtained by mixing Mm (Misch metal; a mixture of rare earth elements), Ni, Co, Al and Mn at a predetermined ratio is heated and melted in an arc melting furnace under an argon gas atmosphere to form a molten metal, and then cooled. Thus, a hydrogen storage alloy lump represented by a composition formula of MmNi 3.6 Co 0.6 Al 0.2 Mn 0.6 was obtained. Next, this was pulverized in an argon gas atmosphere to an average particle diameter of 60 μm to obtain a powder. 100 g of the obtained powder was immersed in 100 g of a hydrochloric acid aqueous solution having a pH of 1.0, and stirred for 10 minutes to perform acid treatment ( After surface treatment, the mixture was filtered and washed with water. The hydrogen-absorbing alloy powder after the acid treatment is immersed for 10 minutes in a salt solution obtained by dissolving a predetermined amount of lanthanum chloride and cobalt chloride in water, and an aqueous solution of potassium hydroxide is added to increase the pH of the aqueous solution to 12. Lanthanum and cobalt are precipitated as hydroxides on the particle surfaces of, and then separated by filtration, washed with water and dried, and hydrogen storage alloys A1 to A8 for alkaline storage batteries (alloys of the present invention) and X1 to X7 (comparative alloys) ) Got. Table 1 shows the concentration of lanthanum chloride (mol / liter) and the concentration of cobalt chloride (mol / liter) in the aqueous salt solution used for producing each hydrogen storage alloy for alkaline storage batteries.
[0012]
[Table 1]
For each of the above-mentioned hydrogen storage alloys for alkaline storage batteries, the particle surface portion relative to the number of rare earth elements per unit area (where the amount of one misch metal is counted as one atom of the rare earth element) inside the particle (at least 10 nm from the particle surface). The value R1 of the ratio of the number of lanthanum atoms per unit area in R1 and the value R2 of the ratio of the number of cobalt atoms per unit area on the particle surface to the number of cobalt atoms per unit area inside the particle were determined. R1 and R2 were determined as the area ratio of the corresponding peak in the spectrum obtained by XPS (X-ray photon Spectroscopy). In addition, the number of rare earth elements and the number of cobalt atoms in the particles are measured at a point where the composition does not change (at least 10 nm from the original particle surface) when the hydrogen storage alloy is ion-etched by an apparatus attached to XPS. It is. Table 2 shows R1 and R2 of each hydrogen storage alloy for alkaline storage batteries.
[0014]
(Preparation of test electrode)
A paste is prepared by kneading 100 parts by weight of the above-mentioned hydrogen storage alloy for each alkaline storage battery, 5 parts by weight of polytetrafluoroethylene as a binder, and water, and rolling the paste into a plate shape. It was cut into a disk having the same dimensions, wrapped with a nickel mesh, and pressed to form a test electrode.
[0015]
(Assembly of monopolar test cell)
A monopolar test cell was assembled using each of the test electrodes (working electrode), a conventionally known sintered nickel electrode (counter electrode), and a half-charged sintered nickel hydroxide electrode (reference electrode).
[0016]
(Activation rate)
After charging each of the monopolar test cells at 200 mA / g, the cells were discharged at 200 mA / g to a final voltage of -0.95 V (vs. the potential of a half-charged sintered nickel hydroxide electrode) to discharge capacity C1. After suspending for 30 minutes, the battery was discharged at 50 mA / g to a final voltage of -0.95 V (vs. the potential of a half-charged sintered nickel hydroxide electrode) to obtain a discharge capacity C2. From the discharge capacity C1 and the discharge capacity C2, the activation rate P (%) of the hydrogen storage alloy defined by the following equation was determined. A hydrogen storage alloy having a higher activation rate P has a higher activity in the electrode reaction. Table 2 shows the results.
[0017]
Activation rate P (%) = {C1 / (C1 + C2)} × 100
[0018]
(Oxygen concentration increase)
100 parts by weight of each of the above hydrogen storage alloys, 0.5 part by weight of polyethylene oxide as a binder, and water are kneaded to prepare a slurry, and this slurry is applied to a punching metal as a current collector. Then, the electrode was cut into a disk having a predetermined size to produce a hydrogen storage alloy electrode. A small amount of the alloy was peeled off from this electrode, and the oxygen concentration D1 of the alloy was measured with an oxygen concentration analyzer (manufactured by LECO, product code "RQ-416DR"). Next, each of these hydrogen storage alloy electrodes was immersed in a 30% by weight aqueous solution of potassium hydroxide heated to 60 ° C. for 2 weeks, a small amount of the alloy was peeled off from the electrode, washed with water and dried, and the oxygen concentration of the alloy was measured. D2 was measured with the same device as above. From the oxygen concentration D1 and the oxygen concentration D2, an oxygen concentration increase Q defined by the following equation was obtained. The smaller the degree of increase in the oxygen concentration Q, the less likely it is to be oxidized in the alkaline electrolyte, and the better the alkali resistance of the hydrogen storage alloy. Table 2 shows the results.
[0019]
Oxygen concentration increase Q = D2 / D1
[0020]
[Table 2]
Alloys A1 to A8 have a higher activation rate P and a smaller oxygen concentration increase Q than alloys X1 to X7. The activation rate P of the alloy X1 (untreated conventional alloy) is extremely small because no Co is present on the particle surface. Further, the reason why the oxygen concentration increase Q of the alloy X1 is not so large is that the activation rate P is extremely small, so that oxidation of the alloy hardly occurs. The reason why the oxygen concentration increase Q of the alloy X2 (acid-treated conventional alloy) is large is that the alkali resistance is not good because there are few rare earth elements on the surface of the particles that protect the alloy from attack by the electrolyte (alkali). is there. Also, the activation rate P of the alloy X2 is small because the presence of Co but a small number of porous rare earth element oxide layers or hydroxide layers make the reaction area (the area of the contact portion between the alloy and the electrolyte solution) small. ) Is small. The activation rate P of the alloys X3 and X4 is small because the amount of the oxide or hydroxide of the rare earth element on the particle surface is too large. The reason why the oxygen concentration increase Q of the alloys X3 and X4 is extremely large is that the oxidation reaction of the alloy is promoted because the high activity portion where the rare earth element and Co coexist is small on the particle surface. The activation rate P of the alloys X5 and X6 is small because the Co on the particle surface is too small. The reason why the oxygen concentration increase degree Q of the alloy X7 is large is that the amount of Co in the particle surface portion is too large, the activity in the electrode reaction is reduced, and the oxidation reaction of the alloy is promoted.
[0022]
(Experiment 2)
When producing a hydrogen storage alloy for a battery, a salt aqueous solution obtained by dissolving predetermined amounts of lanthanum chloride, cobalt chloride and aluminum chloride in water is used. The lanthanum chloride concentration (mol / liter) and the cobalt chloride concentration (mol / liter) of this salt aqueous solution are used. Liter) and the concentration of aluminum chloride (mol / liter) were changed as shown in Table 3, and hydrogen absorbing alloys A9 to A15 were obtained in the same manner as in Experiment 1. For each of these hydrogen storage alloys, R1, R2, the ratio of the number of aluminum atoms per unit area at the particle surface to the number of aluminum atoms per unit area inside the particle, R3, activation rate P and the oxygen concentration increase Q were determined. Table 4 shows the results.
[0023]
[Table 3]
[Table 4]
According to Table 4, the hydrogen storage alloys A11 to A14 in which the ratio of the number of aluminum atoms per unit area on the particle surface to the number of aluminum atoms per unit area inside the particle is 0.2 to 3.0 are oxygen-containing alloys. It can be seen that the degree of concentration increase is small and the alkali resistance is excellent.
[0026]
In Experiment 1, the composition of the inside of the particles was examined for a hydrogen storage alloy for an alkaline storage battery represented by the formula MmNi 3.6 Co 0.6 Al 0.2 Mn 0.6 . for hydrogen storage alloy represented by the 5 Co 0.5 were also separately confirmed that the obtained similar results as in experiment 1.
[0027]
In Experiment 2, the composition of the inside of the particles was examined for a hydrogen storage alloy for an alkaline storage battery represented by the formula MmNi 3.6 Co 0.6 Al 0.2 Mn 0.6. 3.6 Co 0.6 Al 0.2 Mn 0.6 ) x (x = 0.88, 0.92, 0.95, 1.00, 1.02, 1.05 or 1.10) It was separately confirmed that the same results as in Experiment 2 were obtained for the hydrogen storage alloy to be used.
[0028]
In addition, as a lanthanum raw material and a cobalt raw material in Experiments 1 and 2, bromide or hydroxide may be used instead of chloride. Further, as for the aluminum raw material in Experiment 2, bromide or hydroxide may be used instead of chloride. In addition, as an alkali agent added when each hydroxide of lanthanum, cobalt and aluminum is precipitated from the salt aqueous solution on the surface of the alloy particles, for example, sodium hydroxide or lithium hydroxide is used instead of potassium hydroxide. You may.
[0029]
【The invention's effect】
According to the present invention, a hydrogen storage alloy for an alkaline storage battery having high activity in an electrode reaction and good alkali resistance is provided.
Claims (2)
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| JP09967797A JP3568355B2 (en) | 1997-04-02 | 1997-04-02 | Hydrogen storage alloy for alkaline storage batteries |
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| JP09967797A JP3568355B2 (en) | 1997-04-02 | 1997-04-02 | Hydrogen storage alloy for alkaline storage batteries |
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| JP3568355B2 true JP3568355B2 (en) | 2004-09-22 |
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