JP2004119271A - Nickel-hydrogen storage battery - Google Patents
Nickel-hydrogen storage battery Download PDFInfo
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- JP2004119271A JP2004119271A JP2002283383A JP2002283383A JP2004119271A JP 2004119271 A JP2004119271 A JP 2004119271A JP 2002283383 A JP2002283383 A JP 2002283383A JP 2002283383 A JP2002283383 A JP 2002283383A JP 2004119271 A JP2004119271 A JP 2004119271A
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- 238000003860 storage Methods 0.000 title claims abstract description 142
- 239000001257 hydrogen Substances 0.000 title claims abstract description 140
- 229910052739 hydrogen Inorganic materials 0.000 title claims abstract description 140
- 229910045601 alloy Inorganic materials 0.000 claims abstract description 120
- 239000000956 alloy Substances 0.000 claims abstract description 120
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims abstract description 116
- BFDHFSHZJLFAMC-UHFFFAOYSA-L nickel(ii) hydroxide Chemical compound [OH-].[OH-].[Ni+2] BFDHFSHZJLFAMC-UHFFFAOYSA-L 0.000 claims abstract description 71
- 239000011777 magnesium Substances 0.000 claims description 101
- 239000011572 manganese Substances 0.000 claims description 69
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 31
- 239000006104 solid solution Substances 0.000 claims description 25
- 239000007774 positive electrode material Substances 0.000 claims description 24
- 239000011701 zinc Substances 0.000 claims description 24
- 239000000203 mixture Substances 0.000 claims description 22
- 150000001869 cobalt compounds Chemical class 0.000 claims description 19
- 229910018007 MmNi Inorganic materials 0.000 claims description 18
- 229910052749 magnesium Inorganic materials 0.000 claims description 15
- 229910052759 nickel Inorganic materials 0.000 claims description 15
- 239000003513 alkali Substances 0.000 claims description 11
- 229910052748 manganese Inorganic materials 0.000 claims description 11
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims description 10
- 229910004247 CaCu Inorganic materials 0.000 claims description 8
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims description 6
- 229910052725 zinc Inorganic materials 0.000 claims description 6
- 150000001768 cations Chemical class 0.000 claims description 5
- 239000003792 electrolyte Substances 0.000 claims description 5
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims description 4
- 229910052782 aluminium Inorganic materials 0.000 claims description 3
- 238000010828 elution Methods 0.000 abstract description 16
- 150000001875 compounds Chemical class 0.000 abstract description 6
- 230000015572 biosynthetic process Effects 0.000 abstract description 5
- 230000015556 catabolic process Effects 0.000 abstract 2
- 238000006731 degradation reaction Methods 0.000 abstract 2
- 239000000843 powder Substances 0.000 description 20
- 239000011149 active material Substances 0.000 description 16
- 230000014759 maintenance of location Effects 0.000 description 15
- 230000000694 effects Effects 0.000 description 13
- 239000008151 electrolyte solution Substances 0.000 description 11
- 238000000034 method Methods 0.000 description 11
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 9
- 239000002131 composite material Substances 0.000 description 7
- 230000007423 decrease Effects 0.000 description 7
- 238000007599 discharging Methods 0.000 description 7
- 229910052751 metal Inorganic materials 0.000 description 7
- 239000002184 metal Substances 0.000 description 7
- 239000000243 solution Substances 0.000 description 7
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 6
- 230000006378 damage Effects 0.000 description 6
- 238000010438 heat treatment Methods 0.000 description 6
- 239000002245 particle Substances 0.000 description 6
- 239000007864 aqueous solution Substances 0.000 description 5
- 239000010410 layer Substances 0.000 description 5
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 4
- 229910017052 cobalt Inorganic materials 0.000 description 4
- 239000010941 cobalt Substances 0.000 description 4
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 4
- 238000010586 diagram Methods 0.000 description 4
- 238000003487 electrochemical reaction Methods 0.000 description 4
- -1 hydroxyl propyl Chemical group 0.000 description 4
- 239000001301 oxygen Substances 0.000 description 4
- 229910052760 oxygen Inorganic materials 0.000 description 4
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 229910052987 metal hydride Inorganic materials 0.000 description 3
- 238000002360 preparation method Methods 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 229910021503 Cobalt(II) hydroxide Inorganic materials 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- CSNNHWWHGAXBCP-UHFFFAOYSA-L Magnesium sulfate Chemical compound [Mg+2].[O-][S+2]([O-])([O-])[O-] CSNNHWWHGAXBCP-UHFFFAOYSA-L 0.000 description 2
- 229920003171 Poly (ethylene oxide) Polymers 0.000 description 2
- 239000011230 binding agent Substances 0.000 description 2
- 229920002678 cellulose Polymers 0.000 description 2
- 239000001913 cellulose Substances 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 229910000361 cobalt sulfate Inorganic materials 0.000 description 2
- 229940044175 cobalt sulfate Drugs 0.000 description 2
- KTVIXTQDYHMGHF-UHFFFAOYSA-L cobalt(2+) sulfate Chemical compound [Co+2].[O-]S([O-])(=O)=O KTVIXTQDYHMGHF-UHFFFAOYSA-L 0.000 description 2
- ASKVAEGIVYSGNY-UHFFFAOYSA-L cobalt(ii) hydroxide Chemical compound [OH-].[OH-].[Co+2] ASKVAEGIVYSGNY-UHFFFAOYSA-L 0.000 description 2
- 239000006258 conductive agent Substances 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000007773 negative electrode material Substances 0.000 description 2
- 229910000480 nickel oxide Inorganic materials 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- GNRSAWUEBMWBQH-UHFFFAOYSA-N oxonickel Chemical compound [Ni]=O GNRSAWUEBMWBQH-UHFFFAOYSA-N 0.000 description 2
- 238000010298 pulverizing process Methods 0.000 description 2
- 238000007789 sealing Methods 0.000 description 2
- 239000002002 slurry Substances 0.000 description 2
- 238000010301 surface-oxidation reaction Methods 0.000 description 2
- JBQYATWDVHIOAR-UHFFFAOYSA-N tellanylidenegermanium Chemical compound [Te]=[Ge] JBQYATWDVHIOAR-UHFFFAOYSA-N 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 229910052727 yttrium Inorganic materials 0.000 description 2
- 229910052691 Erbium Inorganic materials 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- 229910001122 Mischmetal Inorganic materials 0.000 description 1
- 239000004743 Polypropylene Substances 0.000 description 1
- 229910052769 Ytterbium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 239000011247 coating layer Substances 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- UYAHIZSMUZPPFV-UHFFFAOYSA-N erbium Chemical compound [Er] UYAHIZSMUZPPFV-UHFFFAOYSA-N 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- 150000004679 hydroxides Chemical class 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910052943 magnesium sulfate Inorganic materials 0.000 description 1
- 229960003390 magnesium sulfate Drugs 0.000 description 1
- 235000019341 magnesium sulphate Nutrition 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- LGQLOGILCSXPEA-UHFFFAOYSA-L nickel sulfate Chemical compound [Ni+2].[O-]S([O-])(=O)=O LGQLOGILCSXPEA-UHFFFAOYSA-L 0.000 description 1
- 229940053662 nickel sulfate Drugs 0.000 description 1
- 229910000363 nickel(II) sulfate Inorganic materials 0.000 description 1
- 239000004745 nonwoven fabric Substances 0.000 description 1
- 238000012856 packing Methods 0.000 description 1
- 229920001155 polypropylene Polymers 0.000 description 1
- 238000004080 punching Methods 0.000 description 1
- 229910001404 rare earth metal oxide Inorganic materials 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- NAWDYIZEMPQZHO-UHFFFAOYSA-N ytterbium Chemical compound [Yb] NAWDYIZEMPQZHO-UHFFFAOYSA-N 0.000 description 1
- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 description 1
- NWONKYPBYAMBJT-UHFFFAOYSA-L zinc sulfate Chemical compound [Zn+2].[O-]S([O-])(=O)=O NWONKYPBYAMBJT-UHFFFAOYSA-L 0.000 description 1
- 229910000368 zinc sulfate Inorganic materials 0.000 description 1
- 229960001763 zinc sulfate Drugs 0.000 description 1
Images
Classifications
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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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- Secondary Cells (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は水酸化ニッケルを主成分とする正極活物質を含有した正極と、水素吸蔵合金を主成分とする負極活物質を含有した負極と、アルカリ電解液とを備えたニッケル−水素蓄電池に関するものである。
【０００２】
【従来の技術】
近年、小型携帯機器の増加に伴い、充放電が可能な二次電池（蓄電池）の需要が高まっており、特に、機器の小型化、薄型化、スペース効率化に伴い、大容量が得られるニッケル−水素蓄電池の需要が急速に高まった。この種のニッケル−水素蓄電池は、正極活物質に水酸化ニッケルを使用する正極と、負極活物質に水素吸蔵合金を使用する負極とをセパレータを介して渦巻状に巻回して渦巻状電極群とし、この渦巻状電極群をアルカリ電解液とともに金属製外装缶（電池ケース）内に収納し、金属製外装缶を密封することにより製造される。
【０００３】
現在においては、この種のニッケル−水素蓄電池の需要がさらに高まり、小型の機器のみならず、電動工具、アシスト自転車、電気自動車などの大電流用途にも需要が拡大するようになった。これに伴い、より大きな電流値を取り出すことができるように、正極および負極の両面から改良が進められている。例えば、正極面からの改良としては、水酸化ニッケルを主成分とする正極活物質に、導電剤助剤として少量のコバルト化合物を添加することが一般に行われている。
【０００４】
しかしながら、導電剤助剤としてコバルト化合物を添加するだけでは、高容量で高性能なニッケル−水素蓄電池が得られないため、水酸化ニッケルの表面にコバルト化合物の被覆を施した後、アルカリおよび酸素の共存下で加熱するアルカリ熱処理法が、特許文献１（特許第２５８９１２３号公報）にて提案されるようになった。この特許第２５８９１２３号公報にて提案されたアルカリ熱処理法によれば、コバルト化合物をアルカリおよび酸素の共存下で加熱することにより、導電性が高い高次コバルト化合物を生成させて、活物質の利用率が向上し、高容量化が達成できるようになる。
【０００５】
ところが、特許第２５８９１２３号公報にて提案されるように、活物質（水酸化ニッケル）の表面に導電性が高い高次コバルト化合物を生成させると、反応に関与しないコバルト化合物が水酸化ニッケルの表面に均一に存在するようになる。このため、水酸化ニッケルと電解液との接触が阻害されるようになって、高率放電特性が低下するという問題を生じた。この問題に対処するため、水酸化ニッケルの表面の一部にアルカリカチオンを含む高次コバルト化合物を被覆する方法が提案されるようになった。この方法によれば、良好な導電ネットワークが形成されるとともに、電解液が直接水酸化ニッケルに接触するようになるため、活物質利用率と高率放電特性の向上を達成できるようになる。
【０００６】
一方、負極面からの改良としては、水素吸蔵合金の粒子間の導電性を低下させる表面酸化物被膜を除去する方法が、特許文献２（特開平５−２２５９７５号公報）にて提案されるようになった。この特開平５−２２５９７５号公報にて提案された方法においては、水素吸蔵合金粉末を塩酸に浸漬して、表面酸化物被膜を構成する希土類酸化物を除去することには有効であるが、ニッケルの水酸化物および酸化物の除去にはあまり有効でなく、ニッケルの水酸化物が新たに形成されるという問題が生じた。また、導電性をさらに向上させる手段として、ニッケルの酸化物あるいは水酸化物をニッケル金属に還元させる方法、即ち、水素を吸蔵しない温度、圧力の水素雰囲気中で合金表面を還元する方法が特許文献３（特開平９−２３７６２８号公報）にて提案されるようになった。
【特許文献１】
特許第２５８９１２３号公報
【特許文献２】
特開平５−２２５９７５号公報
【特許文献３】
特開平９−２３７６２８号公報
【０００７】
【発明が解決しようとする課題】
しかしながら、上述のように正極及び負極に改良を施しても、充放電を繰り返すに伴って、高率放電容量が低下するという問題を生じた。この理由としては、以下のようなことが考えられる。即ち、負極に用いる水素吸蔵合金を上述した特開平５−２２５９７５号公報あるいは特開平９−２３７６２８号公報に記載されるような方法で表面酸化物を除去しておいても、充放電を繰り返すに伴って水素吸蔵合金の微粉化が進行して、電解液および正極から発生する酸素等で、再度、表面が酸化されて表面の活性度が低下する。これにより、負極の高率放電特性は低下することとなる。
【０００８】
また、充放電を繰り返すにつれて、水素吸蔵合金中のマンガン（Ｍｎ）が電解液中に溶解して、この溶解したＭｎが電解液を介して正極に達するようになる。すると、正極活物質表面を被覆するコバルト化合物層の偏析部分からＭｎが侵入して、良好な導電ネットワークを破壊するため、正極の高率放電特性も低下することとなる。さらに、充放電を繰り返すに伴って、正極活物質（水酸化ニッケル）中に固溶した亜鉛（Ｚｎ）も電解液中に溶出するため、負極から溶出したＭｎと反応してセパレータ内にＭｎ−Ｚｎ複合酸化物を形成する。このＭｎ−Ｚｎ複合酸化物は電気化学的な抵抗成分となるため、充放電サイクル経過後の高率放電特性は低下するようになる。
【０００９】
上述したような理由により、充放電を繰り返すにつれて、負極の水素吸蔵合金の表面酸化、正極の水酸化ニッケル表面のコバルト被覆層による導電ネットワークの破壊、Ｍｎ−Ｚｎ複合酸化物のセパレータ内への形成等に起因して、充放電サイクル経過後の高率放電特性が低下すると推定されている。そこで、負極の水素吸蔵合金にＭｎを添加しないようにするとともに、正極の水酸化ニッケルにＺｎを添加しないようにすれば、水素吸蔵合金の表面酸化や導電ネットワークの破壊が防止でき、Ｍｎ−Ｚｎ複合酸化物も形成されなくなって、充放電サイクル経過後の高率放電特性の低下を防止できるようになると考えられる。
【００１０】
ところが、負極の水素吸蔵合金にＭｎを添加しない場合には、電池容量が低下するという新たな問題が生じた。また、正極の水酸化ニッケルにＺｎを添加しない場合には、充放電サイクルが繰り返されるに伴って正極が膨化するという新たな問題が生じた。このため、負極の水素吸蔵合金へのＭｎの添加および正極の水酸化ニッケルへのＺｎの添加は必須の条件となる。
そこで、本発明はこのような条件を満たしても、即ち、水素吸蔵合金へＭｎを添加しても、水酸化ニッケルへＺｎを添加しても、充放電サイクル経過後の高率放電特性が低下しないニッケル−水素蓄電池を提供することを目的とするものである。
【００１１】
【課題を解決するための手段】
上記目的を達成するため、本発明のニッケル−水素蓄電池は、亜鉛が固溶添加された水酸化ニッケルを主成分とする正極活物質を含有した正極と、マンガンを含む水素吸蔵合金を含有した負極と、アルカリ電解液とを備えるとともに、正極及び負極にはマグネシウムが添加されていることを特徴とする。好ましくは、正極に用いられる水酸化ニッケルは亜鉛とマグネシウムが固溶されているとともに、負極に用いられる水素吸蔵合金はマンガンとマグネシウムが固溶されている。
【００１２】
このように、正極の水酸化ニッケル中にＭｇを固溶させ、負極の水素吸蔵合金中にもＭｇを含有させると、充放電サイクルの経過に伴う正極の水酸化ニッケルからのＺｎの溶出、負極の水素吸蔵合金からのＭｎの溶出を最低限に抑制することが可能となる。これにより、セパレータ内で電気化学的な抵抗成分となるＭｎ−Ｚｎ複合酸化物の形成を最低限に抑制することが可能となる。この結果、水素吸蔵合金にＭｎを添加した負極と、水酸化ニッケルにＺｎを添加した正極を用いても、充放電サイクル経過後の高率放電特性が低下しないニッケル−水素蓄電池を提供できるようになる。
【００１３】
ここで、正極に用いられる水酸化ニッケルにマグネシウムを固溶させると、正極から溶出したＭｇは電解液を介して負極の水素吸蔵合金表面に到達し、水素吸蔵合金表面でＭｇ水酸化物として存在する。このＭｇ水酸化物は、電解液および充放電サイクルに伴う正極からの酸素発生による水素吸蔵合金の酸化を抑制するため、充放電サイクル経過後の高率放電特性が向上する。また、負極に用いられる水素吸蔵合金にマグネシウムを固溶させると、水素吸蔵合金に微粉化が生じても、微粉化により生じた新生面からＭｇが溶出するようになって、電解液を介して正極の水酸化ニッケルの表面に存在するようになる。
【００１４】
この正極の水酸化ニッケルの表面に存在するＭｇにより、正極活物質表面を被覆するコバルト化合物層の偏析部分からＭｎが侵入して、良好な導電ネットワークが破壊されるのを抑制する。更に、正・負極から溶出したＭｇは、微量に溶け出したＺｎとＭｎがセパレータ内で電気化学的な抵抗成分となるＭｎ−Ｚｎ複合酸化物の形成を抑制する効果も有する。これらの効果により、充放電サイクルを経過しても電気化学的な導電性を良好に保つことが可能となり、充放電サイクル経過後の高率放電特性が向上する。
【００１５】
この場合、水酸化ニッケル中のＭｇ固溶量が０．１０質量％（水酸化ニッケルの質量に対して；以下では同様である）よりも少なくなると、Ｚｎの溶出を抑制する効果が発揮できなくなるとともに、水酸化ニッケル表面を被覆する導電ネットワークの破壊抑制効果も発揮できなることが明らかになった。また、水酸化ニッケル中のＭｇ固溶量が０．４５質量％よりも多くなると、Ｍｇの溶出量が過多となるため、正極及び負極の表面にＭｇ水酸化物が過多に生成されて、逆に電気化学的反応を阻害するようになる。このことから、水酸化ニッケル活物質中に固溶されるＭｇの固溶量は０．１０質量％以上で、０．４５質量％以下であるのが望ましい。
【００１６】
ここで、水素吸蔵合金の組成式がＭｍＮｉａＣｏｂＡｌｃＭｎｄＭｇｅで表されるＣａＣｕ５型の水素吸蔵合金であり、かつ、ＮｉとＣｏとＡｌとＭｎとＭｇの組成比の和が４．４以上で５．４以下（４．４≦ａ＋ｂ＋ｃ＋ｄ＋ｅ≦５．４）である水素吸蔵合金を用いた場合、水素吸蔵合金中のＭｎ添加モル比が０．５０よりも大きくなると、Ｍｎの溶出が過多となって、Ｍｇを含有させてもその溶出抑制効果を充分に発揮できなくなる。また、水素吸蔵合金中のＭｎの添加モル比が０．２０よりも小さくなると初期放電容量が低下する。このことから、水素吸蔵合金中のＭｎの添加モル比は０．２０以上で０．５０以下（０．２０≦ｄ≦０．５０）に規定するのが望ましい。
【００１７】
また、水素吸蔵合金中のＭｇの添加モル比が０．０３より少なくなると、水素吸蔵合金が微粉化するのを抑制することができなくなるとともに、Ｍｎの溶出抑制効果が発揮できなくなる。また、水素吸蔵合金中のＭｇの添加モル比が０．２０よりも大きくなると、Ｍｎの代わりにＭｇが溶出過多となって、Ｍｇ水酸化物が過多に生成されるようになって、逆に電気化学的反応を阻害するようになる。このことから、水素吸蔵合金中のＭｇの添加モル比は０．０３以上で０．２０以下（０．０３≦ｅ≦０．２０）に規定するのが望ましい。
【００１８】
なお、正極の水酸化ニッケルの表面をコバルト化合物で被覆した正極活物質を用いると、正極活物質間が被覆されたコバルト化合物で導電ネットワークが形成されるようになって活物質利用率が向上するので望ましい。この場合、コバルト化合物がアルカリカチオンを含有する高次コバルト化合物（コバルトの平均価数が２を超えるコバルト化合物）であると、このアルカリカチオンを含有する高次コバルト化合物はさらに導電性が優れているため、活物質利用率がさらに向上するので好ましい。
【００１９】
【発明の実施の形態】
以下に、本発明の実施の形態を詳細に説明するが、本発明はこれに限定されるものでなく、その要旨を変更しない範囲で適宜変更して実施することができる。
１．ニッケル正極
（１）正極活物質の調製
Ｎｉ、Ｚｎ、Ｃｏ、Ｍｇが所定のモル比になるように硫酸ニッケル、硫酸亜鉛、硫酸コバルト、硫酸マグネシウムの混合水溶液を調整した。この後、混合水溶液を攪拌しながら水酸化ナトリウム水溶液を徐々に添加し、反応溶液中のｐＨが１３〜１４になるように維持させて、所定量のＭｇが固溶した水酸化ニッケルを析出させた。この水酸化ニッケルが析出した溶液に対して、硫酸コバルト水溶液を添加し、この反応溶液中のｐＨが９〜１０になるように維持させて、主成分が水酸化ニッケルである水酸化物粒子を結晶核として、この結晶核の表面に水酸化コバルトを析出させた。
【００２０】
このようにして表面に水酸化コバルトが析出した水酸化ニッケルを熱気流中でアルカリ溶液を噴霧するアルカリ熱処理を行った。なお、このアルカリ熱処理において、水酸化ニッケル粒子の温度が６０℃になるように温度調節し、コバルト量に対して５倍量の３５質量％のアルカリ溶液（水酸化ナトリウム水溶液）を噴霧した。この後、水酸化ニッケル粒子の温度が９０℃に達するまで昇温した。ついで、これを水洗した後、６０℃で乾燥させて、水酸化ニッケル粒子の表面にナトリウム（アルカリカチオン）含有コバルト化合物の高導電性被膜が形成された水酸化ニッケル粉末（正極活物質）を得た。
【００２１】
ここで、Ｍｇの固溶量が水酸化ニッケルの質量に対して０．１０質量％になるように調整して得られた水酸化ニッケルを正極活物質α１とした。また、Ｍｇの固溶量が水酸化ニッケルの質量に対して０．３０質量％になるように調整して得られた水酸化ニッケルを正極活物質α２とし、Ｍｇの固溶量が水酸化ニッケルの質量に対して０．４５質量％になるように調整して得られた水酸化ニッケルを正極活物質α３とし、Ｍｇの固溶量が水酸化ニッケルの質量に対して０．５０質量％になるように調整して得られた水酸化ニッケルを正極活物質α４とした。さらに、Ｍｇが無添加（Ｍｇの固溶量が０）になるように調整して得られた水酸化ニッケルを正極活物質α５とした。
【００２２】
（２）ニッケル正極の作製
ついで、上述のように調製した各正極活物質α１〜α５を用い、これらの各正極活物質５００ｇに対して０．２５質量％のＨＰＣ（ヒドロキシルプロピルセルロース）ディスパージョン液を２００ｇ混合して活物質スラリーをそれぞれ作製した。ついで、上述のように作製した活物質スラリーを厚みが１．７ｍｍの発泡ニッケルからなる電極基板に所定の充填密度となるようにそれぞれ充填した。この後、乾燥させて、厚みが０．７５ｍｍになるまで圧延し、所定の寸法に切断して非焼結式ニッケル正極ａ１〜ａ４およびｘをそれぞれ作製した。なお、正極活物質α１を用いた非焼結式ニッケル正極を正極ａ１とした。同様に、正極活物質α２を用いたものを正極ａ２とし、正極活物質α３を用いたものを正極ａ３し、正極活物質α４を用いたものを正極ａ４とした。さらに、正極活物質α５を用いたものを正極ｘとした。
【００２３】
２．水素吸蔵合金負極
（１）水素吸蔵合金の調製
ミッシュメタル（Ｍｍ）、ニッケル（Ｎｉ：純度９９．９％）、コバルト（Ｃｏ）、アルミニウム（Ａｌ）、マンガン（Ｍｎ）およびマグネシウム（Ｍｇ）のモル比が、Ｍｍ：Ｎｉ：Ｃｏ：Ａｌ：Ｍｎ：Ｍｇ＝１．０：３．９０：０．５０：０．２０：０．３０：０．１０となるになるように混合して混合物とした。この後、この混合物をアルゴンガス雰囲気の高周波誘導炉で誘導加熱して合金溶湯とした。この合金溶湯を公知の方法で鋳型に流し込み、冷却して、組成式がＭｍＮｉ３．９０Ｃｏ０．５０Ａｌ０．２０Ｍｎ０．３０Ｍｇ０．１０で表されるＣａＣｕ５型の水素吸蔵合金のインゴットを作製した。この水素吸蔵合金インゴットを機械的粉砕法により、平均粒子径が約６０μｍになるまで粉砕してＣａＣｕ５型の水素吸蔵合金粉末を得た。
【００２４】
（２）水素吸蔵合金負極の作製
ついで、この水素吸蔵合金粉末１００質量部に対して、結着剤としての５質量％のポリエチレンオキサイド（ＰＥＯ）の水溶液を２０質量部を混合して水素吸蔵合金ペーストを作製した。この水素吸蔵合金ペーストをパンチングメタルからなる芯体の両面に塗布し、室温で乾燥させた後、所定の厚みに圧延し、所定の寸法に切断して水素吸蔵合金負極を作製した。
【００２５】
３．ニッケル−水素蓄電池
（１）ニッケル−水素蓄電池の作製
上述のように作製した非焼結式ニッケル正極ａ１〜ａ４およびｘと水素吸蔵合金負極をそれぞれ用い、これらの間にポリプロピレン製不織布からなるセパレータを介在させ、これらをスパイラル状に巻回して電極群をそれぞれ作製した。ついで、各電極群を外装缶に挿入した後、各電極群の負極から延出する負極リードを外装缶に接続するとともに、正極から延出する正極リードを封口体に設けられた正極蓋に接続した。この後、外装缶内に電解液（例えば、３０質量％の水酸化カリウム水溶液）を注入し、更に外装缶の開口部を封口体により封止して、公称容量１２５０ｍＡｈのＡＡサイズのニッケル−水素蓄電池Ａ１，Ａ２，Ａ３，Ａ４，Ｘをそれぞれ作製した。ここで、正極ａ１を用いたものを電池Ａ１とし、正極ａ２を用いたものを電池Ａ２とし、正極ａ３を用いたものを電池Ａ３とし、正極ａ４を用いたものを電池Ａ４とした。また、正極ｘを用いたものを電池Ｘとした。
【００２６】
（２）放電容量の測定
ついで、上述のように作製した電池Ａ１〜Ａ４およびＸを用いて、これらの各電池を２５℃の温度条件で、１２５ｍＡの充電電流で１６時間充電した後、２５０ｍＡの放電電流で、電池電圧が１．０Ｖになるまで放電させて、放電時間から初期放電容量（ｍＡｈ）を求めると、下記の表１に示すような結果となった。更に、５０００ｍＡの充電電流で１６時間再度充電した後、５００ｍＡの放電電流で、電池電圧が０．６Ｖになるまで放電させて、放電時間から初期高率放電容量（ｍＡｈ）を求めると、下記の表１に示すような結果となった。
【００２７】
その後、これらの各電池を室温（約２５℃）で、それぞれ１２５０ｍＡの充電電流で充電し、電池電圧が最大値を示してから１０ｍＶ低下（−ΔＶ＝１０ｍＶ）した時点で充電を１時間休止させた。その後、１２５０ｍＡの放電電流で電池電圧が１．０Ｖになるまで放電させるサイクルを５００サイクル繰り返して行い、５００サイクル終了後に、１２５ｍＡの充電電流で１６時間再度充電した後、５０００ｍＡの放電電流で、電池電圧が０．６Ｖになるまで放電させて、放電時間から５００サイクル後の高率放電容量（ｍＡｈ）を求めると、下記の表１に示すような結果となった。
【００２８】
また、求めた初期高率放電容量に対する５００サイクル後の高率放電容量の比率を容量維持率（％）として算出すると、下記の表１に示すような結果となった。そして、表１の結果から、水酸化ニッケル活物質中に固溶されたＭｇの固溶量（質量％）を横軸にプロットし、５００サイクル後の高率放電容量（ｍＡｈ）を縦軸にプロットすると、図１（ａ）に示すような結果となった。また、水酸化ニッケル活物質中に固溶されたＭｇの固溶量（質量％）を横軸にプロットし、容量維持率（％）を縦軸にプロットすると、図１（ｂ）に示すような結果となった。
【００２９】
【表１】
上記表１および図１（ａ），（ｂ）の結果から明らかなように、水酸化ニッケル活物質中に固溶されたＭｇの固溶量がいずれであっても、初期放電容量（ｍＡｈ）および初期高率放電容量（ｍＡｈ）はそれほど変わらないが、Ｍｇの固溶量が０．１０質量％（水酸化ニッケル活物質の質量に対する）よりも少なくなったり、０．４５質量％よりも多くなると、５００サイクル後の高率放電容量（図１（ａ）参照）および５００サイクル後の容量維持率（図１（ｂ）参照）が減少することが分かる。一方、水酸化ニッケル活物質中に固溶されたＭｇの固溶量が０．１０質量％以上で、０．４５質量％以下であると、５００サイクル後の高率放電容量（図１（ａ）参照）および５００サイクル後の容量維持率（図１（ｂ）参照）が向上することが分かる。
【００３１】
これは、水酸化ニッケル中のＭｇの固溶量が０．１０質量％よりも少なくなると、Ｚｎの溶出を抑制する効果が発揮できなくなるとともに、水酸化ニッケル表面を被覆するＣｏ化合物層による導電ネットワークの破壊抑制効果が発揮できなくなる。また、水酸化ニッケル中のＭｇの固溶量が０．４５質量％よりも多くなると、Ｍｇの溶出量が過多となる。このため、正極及び負極の表面にＭｇ水酸化物が過多に生成されて、逆に電気化学的反応を阻害するためと考えられる。
【００３２】
これに対して、水酸化ニッケル活物質中に固溶されるＭｇの固溶量が０．１０質量％以上で、０．４５質量％以下であると、Ｚｎの溶出が抑制されるとともに、水酸化ニッケル表面を被覆するＣｏ化合物層による導電ネットワークが保護されるようになる。また、正極から溶出したＭｇは電解液を介して負極の水素吸蔵合金表面に到達し、水素吸蔵合金表面でＭｇ水酸化物として存在し、酸素発生による水素吸蔵合金の酸化を抑制するために、５００サイクル後の高率放電容量および容量維持率が向上したと考えられる。
これらのことから、水酸化ニッケル活物質中に固溶されるＭｇの固溶量は０．１０質量％以上で、０．４５質量％以下であるのが望ましいということができる。
【００３３】
４．水素吸蔵合金に添加されるＭｇ量の検討
ついで、水素吸蔵合金に添加されるＭｇ量（水素吸蔵合金中のＭｇの添加モル比）について検討した。
そこで、Ｍｍ：Ｎｉ：Ｃｏ：Ａｌ：Ｍｎ：Ｍｇ＝１．０：３．９７：０．５０：０．２０：０．３０：０．０３となるになるように各金属を混合して、上述と同様に組成式がＭｍＮｉ３．９７Ｃｏ０．５０Ａｌ０．２０Ｍｎ０．３０Ｍｇ０．０３（ｄ＝０．３０，ｅ＝０．０３）で表されるＣａＣｕ５型の水素吸蔵合金粉末を得た。得られた水素吸蔵合金粉末を用いて、上述と同様に水素吸蔵合金負極を作製し、これを負極ｂ１とした。同様に、組成式がＭｍＮｉ３．９５Ｃｏ０．５０Ａｌ０．２０Ｍｎ０．３０Ｍｇ０．０５（ｄ＝０．３０，ｅ＝０．０５）で表される水素吸蔵合金粉末を得た後、水素吸蔵合金負極を作製して負極ｂ２とした。
【００３４】
同様に、組成式がＭｍＮｉ３．９０Ｃｏ０．５０Ａｌ０．２０Ｍｎ０．３０Ｍｇ０．１０（ｄ＝０．３０，ｅ＝０．１０）で表される水素吸蔵合金粉末を得た後、水素吸蔵合金負極を作製して負極ｂ３とし、組成式がＭｍＮｉ３．８５Ｃｏ０．５０Ａｌ０．２０Ｍｎ０．３０Ｍｇ０．１５（ｄ＝０．３０，ｅ＝０．１５）で表される水素吸蔵合金粉末を得た後、水素吸蔵合金負極を作製して負極ｂ４とし、組成式がＭｍＮｉ３．８０Ｃｏ０．５０Ａｌ０．２０Ｍｎ０．３０Ｍｇ０．２０（ｄ＝０．３０，ｅ＝０．２０）で表される水素吸蔵合金粉末を得た後、水素吸蔵合金負極を作製して負極ｂ５とし、組成式がＭｍＮｉ３．７５Ｃｏ０．５０Ａｌ０．２０Ｍｎ０．３０Ｍｇ０．２５（ｄ＝０．３０，ｅ＝０．２５）で表される水素吸蔵合金粉末を得た後、水素吸蔵合金負極を作製して負極ｂ６とした。また、Ｍｇが無添加の組成式がＭｍＮｉ４．００Ｃｏ０．５０Ａｌ０．２０Ｍｎ０．３０（ｄ＝０．３０，ｅ＝０）で表される水素吸蔵合金粉末を得た後、水素吸蔵合金負極を作製して負極ｙとした。
【００３５】
ついで、上述のように作製した水素吸蔵合金負極ｂ１〜ｂ６およびｙと、上述した非焼結式ニッケル正極ａ２（水酸化ニッケル中のＭｇ固溶量が０．３０質量％のもの）とをそれぞれ用い、上述と同様に公称容量１２５０ｍＡｈのＡＡサイズのニッケル−水素蓄電池Ｂ１〜Ｂ６，Ｙをそれぞれ作製した。ここで、負極ｂ１を用いたものを電池Ｂ１とし、負極ｂ２を用いたものを電池Ｂ２とし、負極ｂ３を用いたものを電池Ｂ３とし、負極ｂ４を用いたものを電池Ｂ４とし、負極ｂ５を用いたものを電池Ｂ５とし、負極ｂ６を用いたものを電池Ｂ６とした。また、負極ｙを用いたものを電池Ｙとした。
【００３６】
ついで、上述と同様に充放電を行って、初期放電容量（ｍＡｈ）、初期高率放電容量（ｍＡｈ）、５００サイクル後の高率放電容量（ｍＡｈ）および５００サイクル後の容量維持率を求めると、下記の表２に示すような結果となった。そして、表２の結果から、水素吸蔵合金に添加されるＭｇ量（水素吸蔵合金中のＭｇの添加モル比）を横軸にプロットし、５００サイクル後の高率放電容量（ｍＡｈ）を縦軸にプロットすると、図２（ａ）に示すような結果となった。また、水素吸蔵合金に添加されるＭｇ量（水素吸蔵合金中のＭｇの添加モル比）を横軸にプロットし、容量維持率（％）を縦軸にプロットすると、図２（ｂ）に示すような結果となった。
【００３７】
【表２】
上記表２および図２（ａ），（ｂ）の結果から明らかなように、水素吸蔵合金中のＭｇの添加モル比がいずれであっも、初期放電容量（ｍＡｈ）および初期高率放電容量（ｍＡｈ）はそれほど変わらないが、Ｍｇの添加モル比が０．０３よりも小さくなったり、０．２０よりも大きくなると、５００サイクル後の高率放電容量（図２（ａ）参照）および５００サイクル後の容量維持率（図２（ｂ）参照）が減少することが分かる。一方、水素吸蔵合金中のＭｇの添加モル比が０．０３以上で、０．２０以下であると、５００サイクル後の高率放電容量（図２（ａ）参照）および５００サイクル後の容量維持率（図２（ｂ）参照）が向上することが分かる。
【００３９】
これは、水素吸蔵合金中にＭｇが添加されていないか、添加モル比が０．０３より少なくなると、水素吸蔵合金が微粉化するのを抑制することができなくなるとともに、Ｍｎの溶出抑制効果が発揮できなくなる。また、水素吸蔵合金中のＭｇの添加モル比が０．２０よりも大きくなると、Ｍｎの代わりにＭｇが溶出過多となって、Ｍｇ水酸化物が過多に生成されるようになって、逆に電気化学的反応を阻害するようになる。
【００４０】
これに対して、水素吸蔵合金中のＭｇの添加モル比を０．０３以上で０．２０以下（０．０３≦ｅ≦０．２０）であると、水素吸蔵合金に微粉化が生じても、微粉化により生じた新生面からＭｇが溶出するようになって、電解液を介して正極の水酸化ニッケルの表面を被覆しているＣｏ化合物層に存在するようになる。これにより、水酸化ニッケルの表面のＣｏ化合物による導電ネットワークの破壊抑制効果が発揮されるようになる。
これらのことから、水素吸蔵合金中のＭｇの添加モル比を０．０３以上で０．２０以下（０．０３≦ｅ≦０．２０）に規定するのが望ましいということができる。
【００４１】
５．水素吸蔵合金に添加されるＭｎ量の検討
ついで、水素吸蔵合金に添加されるＭｎ量（水素吸蔵合金中のＭｎ添加モル比）について検討した。
そこで、Ｍｍ：Ｎｉ：Ｃｏ：Ａｌ：Ｍｎ：Ｍｇ＝１．０：４．１０：０．５０：０．２０：０．１０：０．１０となるになるように各金属を混合して、上述と同様に組成式がＭｍＮｉ４．１０Ｃｏ０．５０Ａｌ０．２０Ｍｎ０．１０Ｍｇ０．１０（ｄ＝０．１０，ｅ＝０．１０）で表されるＣａＣｕ５型の水素吸蔵合金粉末を得た。得られた水素吸蔵合金粉末を用いて、上述と同様に水素吸蔵合金負極を作製し、これを負極ｃ１とした。同様に、組成式がＭｍＮｉ４．００Ｃｏ０．５０Ａｌ０．２０Ｍｎ０．２０Ｍｇ０．１０（ｄ＝０．２０，ｅ＝０．１０）で表される水素吸蔵合金粉末を得た後、水素吸蔵合金負極を作製して負極ｃ２とした。
【００４２】
同様に、組成式がＭｍＮｉ３．９０Ｃｏ０．５０Ａｌ０．２０Ｍｎ０．３０Ｍｇ０．１０（ｄ＝０．３０，ｅ＝０．１０）で表される水素吸蔵合金粉末を得た後、水素吸蔵合金負極を作製して負極ｃ３とし、組成式がＭｍＮｉ３．８０Ｃｏ０．５０Ａｌ０．２０Ｍｎ０．４０Ｍｇ０．１０（ｄ＝０．４０，ｅ＝０．１０）で表される水素吸蔵合金粉末を得た後、水素吸蔵合金負極を作製して負極ｃ４とし、組成式がＭｍＮｉ３．７０Ｃｏ０．５０Ａｌ０．２０Ｍｎ０．５０Ｍｇ０．１０（ｄ＝０．５０，ｅ＝０．１０）で表される水素吸蔵合金粉末を得た後、水素吸蔵合金負極を作製して負極ｃ５とし、組成式がＭｍＮｉ３．６０Ｃｏ０．５０Ａｌ０．２０Ｍｎ０．６０Ｍｇ０．１０（ｄ＝０．６０，ｅ＝０．１０）で表される水素吸蔵合金粉末を得た後、水素吸蔵合金負極を作製して負極ｂ６とした。
【００４３】
ついで、上述のように作製した水素吸蔵合金負極ｃ１〜ｃ６と、上述した非焼結式ニッケル正極ａ２（水酸化ニッケル中のＭｇ固溶量が０．３０質量％のもの）とをそれぞれ用い、上述と同様に公称容量１２５０ｍＡｈのＡＡサイズのニッケル−水素蓄電池Ｃ１〜Ｃ６をそれぞれ作製した。ここで、負極ｃ１を用いたものを電池Ｃ１とし、負極ｃ２を用いたものを電池Ｃ２とし、負極ｃ３を用いたものを電池Ｃ３とし、負極ｃ４を用いたものを電池Ｃ４とし、負極ｃ５を用いたものを電池Ｃ５とし、負極ｃ６を用いたものを電池Ｃ６とした。
【００４４】
ついで、上述と同様に充放電を行って、初期放電容量（ｍＡｈ）、初期高率放電容量（ｍＡｈ）、５００サイクル後の高率放電容量（ｍＡｈ）および５００サイクル後の容量維持率を求めると、下記の表３に示すような結果となった。そして、表３の結果から、水素吸蔵合金に添加されるＭｎ量（水素吸蔵合金中のＭｎの添加モル比）を横軸にプロットし、５００サイクル後の高率放電容量（ｍＡｈ）を縦軸にプロットすると、図３（ａ）に示すような結果となった。また、水素吸蔵合金に添加されるＭｎ量（水素吸蔵合金中のＭｎの添加モル比）を横軸にプロットし、容量維持率（％）を縦軸にプロットすると、図３（ｂ）に示すような結果となった。
【００４５】
【表３】
上記表３および図３（ａ），（ｂ）の結果から明らかなように、水素吸蔵合金中のＭｎの添加モル比が０．２０よりも小さくなると初期放電容量（ｍＡｈ）および初期高率放電容量（ｍＡｈ）が低下し、Ｍｎの添加モル比が０．５０よりも大きくなると、５００サイクル後の高率放電容量（図３（ａ）参照）および５００サイクル後の容量維持率（図３（ｂ）参照）が減少することが分かる。一方、水素吸蔵合金中のＭｎの添加モル比が０．２０以上で、０．５０以下であると、初期放電容量（ｍＡｈ）および初期高率放電容量（ｍＡｈ）が良好であるとともに、５００サイクル後の高率放電容量（図３（ａ）参照）および５００サイクル後の容量維持率（図３（ｂ）参照）が向上することが分かる。
【００４７】
これは、水素吸蔵合金中のＭｎの添加モル比が０．５０よりも大きくなると、Ｍｎの溶出が過多となって、Ｍｇを含有させてもその溶出抑制効果を充分に発揮できなくなるためである。そして、水素吸蔵合金中のＭｎの添加モル比が０．２０よりも小さくなると初期放電容量（ｍＡｈ）および初期高率放電容量（ｍＡｈ）が低下することから、水素吸蔵合金中のＭｎの添加モル比は０．２０以上で０．５０以下（０．２０≦ｄ≦０．５０）に規定するのが望ましいということができる。
【００４８】
【発明の効果】
上述したように、本発明においては、正極の水酸化ニッケル中にＭｇを固溶させているとともに、負極の水素吸蔵合金中にもＭｇを含有させているため、充放電サイクルの経過に伴う正極の水酸化ニッケルからのＺｎの溶出、負極の水素吸蔵合金からのＭｎの溶出を最低限に抑制することが可能となる。これにより、セパレータ内でのＭｎ−Ｚｎ複合酸化物の形成を最低限に抑制することが可能となる。この結果、水素吸蔵合金にＭｎを添加した負極と、水酸化ニッケルにＺｎを添加した正極を用いても、高率放電特性が低下しないニッケル−水素蓄電池を提供できるようになる。
【００４９】
なお、上述した実施の形態においては、ニッケル正極中に結着剤としてのＨＰＣ（ヒドロキシルプロピルセルロース）のみを添加した例について説明したが、ニッケル正極中に、イットリウム（Ｙ）、イッテルビウム（Ｙｂ）、エルビウム（Ｅｒ）、亜鉛（Ｚｎ）から選択される１種の元素またはその化合物の粉末を添加すると、正極内により良好な導電ネットワークが形成されて、さらに活物質利用率が向上して、高容量の蓄電池が得られるようになる。この場合、イットリウム化合物としてＹ２Ｏ３を用いるのが特に好ましい。
【図面の簡単な説明】
【図１】正極の水酸化ニッケル中のＭｇの固溶量と放電特性との関係を示す図であり、図１（ａ）はＭｇの固溶量と５００サイクル後の高率放電容量との関係を示す図であり、図１（ｂ）はＭｇの固溶量と５００サイクル後の容量維持率との関係を示す図である。
【図２】負極の水素吸蔵合金中のＭｇの添加モル比と放電特性との関係を示す図であり、図２（ａ）はＭｇの添加モル比と５００サイクル後の高率放電容量との関係を示す図であり、図２（ｂ）はＭｇの添加モル比と５００サイクル後の容量維持率との関係を示す図である。
【図３】負極の水素吸蔵合金中のＭｎの添加モル比と放電特性との関係を示す図であり、図３（ａ）はＭｎの添加モル比と５００サイクル後の高率放電容量との関係を示す図であり、図３（ｂ）はＭｎの添加モル比と５００サイクル後の容量維持率との関係を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a nickel-hydrogen storage battery including a positive electrode containing a positive electrode active material containing nickel hydroxide as a main component, a negative electrode containing a negative electrode active material containing a hydrogen storage alloy as a main component, and an alkaline electrolyte. It is.
[0002]
[Prior art]
In recent years, demand for secondary batteries (storage batteries) that can be charged and discharged has been increasing along with the increase in small portable devices. In particular, with the miniaturization, thinning, and space efficiency of devices, nickel, which has a large capacity, can be obtained. -Demand for hydrogen storage batteries has increased rapidly. In this type of nickel-hydrogen storage battery, a positive electrode using nickel hydroxide as a positive electrode active material and a negative electrode using a hydrogen storage alloy as a negative electrode active material are spirally wound through a separator to form a spiral electrode group. The spirally wound electrode group is housed in a metal outer can (battery case) together with an alkaline electrolyte, and the metal outer can is sealed.
[0003]
At present, the demand for this type of nickel-metal hydride storage battery has been further increased, and the demand has been expanding not only for small-sized devices but also for high-current applications such as electric tools, assisted bicycles, and electric vehicles. Accordingly, improvements have been made on both the positive electrode and the negative electrode so that a larger current value can be obtained. For example, as an improvement from the positive electrode surface, it is common practice to add a small amount of a cobalt compound as a conductive agent auxiliary to a positive electrode active material mainly containing nickel hydroxide.
[0004]
However, simply adding a cobalt compound as a conductive agent assistant does not provide a high-capacity, high-performance nickel-hydrogen storage battery. An alkali heat treatment method of heating in the coexistence has been proposed in Patent Document 1 (Japanese Patent No. 2589123). According to the alkali heat treatment method proposed in Japanese Patent No. 2589123, by heating a cobalt compound in the coexistence of alkali and oxygen, a high-order cobalt compound having high conductivity is generated, and the active material is used. The rate is improved, and a higher capacity can be achieved.
[0005]
However, as proposed in Japanese Patent No. 2589123, when a high-order cobalt compound having high conductivity is generated on the surface of the active material (nickel hydroxide), the cobalt compound which does not participate in the reaction becomes a surface of the nickel hydroxide. To be uniformly present. For this reason, the contact between nickel hydroxide and the electrolytic solution is hindered, causing a problem that the high-rate discharge characteristics are reduced. In order to address this problem, a method of coating a part of the surface of nickel hydroxide with a higher cobalt compound containing an alkali cation has been proposed. According to this method, a good conductive network is formed, and the electrolytic solution comes into direct contact with the nickel hydroxide, so that the active material utilization and the high rate discharge characteristics can be improved.
[0006]
On the other hand, as an improvement from the negative electrode surface, a method of removing a surface oxide film that lowers the conductivity between particles of the hydrogen storage alloy is proposed in Patent Document 2 (Japanese Patent Application Laid-Open No. 5-225975). Became. The method proposed in Japanese Patent Application Laid-Open No. 5-225975 is effective for immersing a hydrogen storage alloy powder in hydrochloric acid to remove rare earth oxides constituting a surface oxide film. This is not very effective in removing hydroxides and oxides, and a new nickel hydroxide is formed. As a means for further improving conductivity, a method of reducing nickel oxide or hydroxide to nickel metal, that is, a method of reducing an alloy surface in a hydrogen atmosphere at a temperature and a pressure at which hydrogen is not absorbed is disclosed in Patent Document 1. 3 (JP-A-9-237628).
[Patent Document 1]
Japanese Patent No. 2589123
[Patent Document 2]
JP-A-5-225975
[Patent Document 3]
JP-A-9-237628
[0007]
[Problems to be solved by the invention]
However, even when the positive electrode and the negative electrode are improved as described above, there has been a problem that the high-rate discharge capacity decreases as charging and discharging are repeated. The reason may be as follows. That is, even if the surface oxide is removed from the hydrogen storage alloy used for the negative electrode by the method described in JP-A-5-225975 or JP-A-9-237628 described above, charging and discharging are repeated. As a result, the hydrogen storage alloy is pulverized, and the surface is oxidized again by oxygen and the like generated from the electrolytic solution and the positive electrode, and the surface activity is reduced. As a result, the high-rate discharge characteristics of the negative electrode decrease.
[0008]
Further, as charging and discharging are repeated, manganese (Mn) in the hydrogen storage alloy dissolves in the electrolytic solution, and the dissolved Mn reaches the positive electrode via the electrolytic solution. Then, Mn invades from the segregated portion of the cobalt compound layer covering the surface of the positive electrode active material and breaks a good conductive network, so that the high-rate discharge characteristics of the positive electrode also deteriorate. Further, as charge and discharge are repeated, zinc (Zn) dissolved in the positive electrode active material (nickel hydroxide) also elutes into the electrolytic solution, and thus reacts with Mn eluted from the negative electrode to form Mn- in the separator. A Zn composite oxide is formed. Since this Mn-Zn composite oxide becomes an electrochemical resistance component, the high-rate discharge characteristics after the passage of charge / discharge cycles deteriorate.
[0009]
For the reasons described above, as charge and discharge are repeated, the surface oxidation of the hydrogen storage alloy of the negative electrode, the destruction of the conductive network by the cobalt coating layer on the nickel hydroxide surface of the positive electrode, and the formation of a Mn-Zn composite oxide in the separator It is presumed that the high-rate discharge characteristics after the charge / discharge cycle have been reduced due to the above factors. Therefore, by not adding Mn to the hydrogen storage alloy of the negative electrode and not adding Zn to nickel hydroxide of the positive electrode, surface oxidation of the hydrogen storage alloy and destruction of the conductive network can be prevented, and Mn-Zn It is considered that the composite oxide is no longer formed, so that it is possible to prevent the high-rate discharge characteristics from being lowered after the charge / discharge cycle.
[0010]
However, when Mn is not added to the hydrogen storage alloy of the negative electrode, there is a new problem that the battery capacity is reduced. Further, when Zn is not added to nickel hydroxide of the positive electrode, a new problem arises in that the positive electrode expands as the charge / discharge cycle is repeated. Therefore, the addition of Mn to the hydrogen storage alloy of the negative electrode and the addition of Zn to nickel hydroxide of the positive electrode are essential conditions.
Therefore, the present invention, even if such a condition is satisfied, that is, even if Mn is added to the hydrogen storage alloy or Zn is added to nickel hydroxide, the high-rate discharge characteristics after the charge / discharge cycle has passed are deteriorated. It is an object of the present invention to provide a nickel-metal hydride storage battery that does not use such a battery.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a nickel-hydrogen storage battery of the present invention includes a positive electrode containing a positive electrode active material mainly containing nickel hydroxide to which zinc is added as a solid solution, and a negative electrode containing a hydrogen storage alloy containing manganese. And an alkaline electrolyte, and magnesium is added to the positive electrode and the negative electrode. Preferably, the nickel hydroxide used for the positive electrode has a solid solution of zinc and magnesium, and the hydrogen storage alloy used for the negative electrode has a solid solution of manganese and magnesium.
[0012]
As described above, when Mg is dissolved in the nickel hydroxide of the positive electrode and Mg is also contained in the hydrogen storage alloy of the negative electrode, elution of Zn from the nickel hydroxide of the positive electrode with the progress of the charge / discharge cycle, Elution of Mn from the hydrogen storage alloy can be minimized. This makes it possible to minimize the formation of the Mn—Zn composite oxide that becomes an electrochemical resistance component in the separator. As a result, even if a negative electrode in which Mn is added to a hydrogen storage alloy and a positive electrode in which Zn is added to nickel hydroxide are used, it is possible to provide a nickel-hydrogen storage battery in which high-rate discharge characteristics after charge / discharge cycles have not been reduced. Become.
[0013]
Here, when magnesium is dissolved in nickel hydroxide used for the positive electrode, Mg eluted from the positive electrode reaches the surface of the hydrogen storage alloy of the negative electrode via the electrolytic solution, and exists as Mg hydroxide on the surface of the hydrogen storage alloy. I do. The Mg hydroxide suppresses the oxidation of the hydrogen storage alloy due to the generation of oxygen from the electrolyte and the positive electrode during the charge / discharge cycle, thereby improving the high-rate discharge characteristics after the charge / discharge cycle. Also, when magnesium is dissolved in the hydrogen storage alloy used for the negative electrode, even if the hydrogen storage alloy is finely divided, Mg is eluted from the newly formed surface caused by the finely divided metal, and the positive electrode is formed through the electrolytic solution. On the surface of nickel hydroxide.
[0014]
The Mg present on the surface of the nickel hydroxide of the positive electrode suppresses the intrusion of Mn from the segregated portion of the cobalt compound layer covering the surface of the positive electrode active material, thereby suppressing the destruction of a good conductive network. Further, Mg eluted from the positive and negative electrodes also has an effect of suppressing the formation of a Mn-Zn composite oxide in which a minute amount of dissolved Zn and Mn becomes an electrochemical resistance component in the separator. Due to these effects, it is possible to maintain good electrochemical conductivity even after the charge and discharge cycle, and to improve the high rate discharge characteristics after the charge and discharge cycle.
[0015]
In this case, when the amount of Mg solid solution in nickel hydroxide is less than 0.10% by mass (based on the mass of nickel hydroxide; the same applies hereinafter), the effect of suppressing the elution of Zn cannot be exhibited. At the same time, it became clear that the effect of suppressing the destruction of the conductive network covering the nickel hydroxide surface could be exhibited. If the amount of Mg dissolved in nickel hydroxide is more than 0.45% by mass, the amount of Mg eluted is too large, so that Mg hydroxide is excessively generated on the surfaces of the positive electrode and the negative electrode, and conversely. In addition, the electrochemical reaction is inhibited. For this reason, the amount of solid solution of Mg dissolved in the nickel hydroxide active material is preferably 0.10% by mass or more and 0.45% by mass or less.
[0016]
Here, the composition formula of the hydrogen storage alloy is MmNi a Co b Al c Mn d Mg e CaCu represented by 5 Alloy having a composition ratio of Ni, Co, Al, Mn and Mg of 4.4 or more and 5.4 or less (4.4 ≦ a + b + c + d + e ≦ 5.4) In the case where is used, if the molar ratio of Mn addition in the hydrogen storage alloy is larger than 0.50, the elution of Mn becomes excessive, and even if Mg is contained, the elution suppressing effect cannot be sufficiently exhibited. When the molar ratio of Mn in the hydrogen storage alloy is smaller than 0.20, the initial discharge capacity decreases. For this reason, it is desirable that the molar ratio of Mn added to the hydrogen storage alloy be 0.20 or more and 0.50 or less (0.20 ≦ d ≦ 0.50).
[0017]
On the other hand, when the molar ratio of Mg in the hydrogen storage alloy is less than 0.03, it is not possible to prevent the hydrogen storage alloy from being pulverized, and it is impossible to exert the effect of suppressing the elution of Mn. When the molar ratio of Mg in the hydrogen storage alloy is larger than 0.20, Mg is excessively eluted instead of Mn, and Mg hydroxide is generated excessively. Inhibits electrochemical reactions. From this, it is desirable that the molar ratio of addition of Mg in the hydrogen storage alloy be 0.03 or more and 0.20 or less (0.03 ≦ e ≦ 0.20).
[0018]
When a positive electrode active material in which the surface of nickel hydroxide of the positive electrode is coated with a cobalt compound is used, a conductive network is formed with the cobalt compound coated between the positive electrode active materials, and the active material utilization rate is improved. So desirable. In this case, when the cobalt compound is a higher-order cobalt compound containing an alkali cation (a cobalt compound having an average valence of cobalt of more than 2), the higher-order cobalt compound containing the alkali cation has more excellent conductivity. Therefore, the utilization rate of the active material is further improved, which is preferable.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to these embodiments, and can be implemented with appropriate modifications without departing from the spirit of the present invention.
1. Nickel positive electrode
(1) Preparation of positive electrode active material
A mixed aqueous solution of nickel sulfate, zinc sulfate, cobalt sulfate, and magnesium sulfate was adjusted so that Ni, Zn, Co, and Mg had a predetermined molar ratio. Thereafter, an aqueous sodium hydroxide solution was gradually added while stirring the mixed aqueous solution, and the pH in the reaction solution was maintained at 13 to 14 to precipitate a predetermined amount of nickel hydroxide in which Mg was dissolved. Was. An aqueous solution of cobalt sulfate was added to the solution in which the nickel hydroxide was precipitated, and the pH of the reaction solution was maintained at 9 to 10 to reduce hydroxide particles whose main component was nickel hydroxide. As a crystal nucleus, cobalt hydroxide was deposited on the surface of the crystal nucleus.
[0020]
The nickel hydroxide having cobalt hydroxide deposited on the surface in this manner was subjected to an alkali heat treatment of spraying an alkali solution in a hot air stream. In this alkaline heat treatment, the temperature of the nickel hydroxide particles was adjusted to 60 ° C., and a 35 mass% alkali solution (aqueous sodium hydroxide solution) was sprayed five times the amount of cobalt. Thereafter, the temperature was raised until the temperature of the nickel hydroxide particles reached 90 ° C. Then, after washing with water, it is dried at 60 ° C. to obtain a nickel hydroxide powder (a positive electrode active material) in which a highly conductive film of a cobalt compound containing sodium (alkali cation) is formed on the surface of the nickel hydroxide particles. Was.
[0021]
Here, nickel hydroxide obtained by adjusting the solid solution amount of Mg to be 0.10% by mass with respect to the mass of nickel hydroxide was used as the positive electrode active material α1. Nickel hydroxide obtained by adjusting the amount of Mg to be 0.30% by mass with respect to the mass of the nickel hydroxide was used as the positive electrode active material α2. The nickel hydroxide obtained by adjusting so as to be 0.45% by mass with respect to the mass of the positive electrode was used as the positive electrode active material α3. The obtained nickel hydroxide was adjusted to be the positive electrode active material α4. Further, nickel hydroxide obtained by adjusting so that Mg was not added (the solid solution amount of Mg was 0) was used as positive electrode active material α5.
[0022]
(2) Preparation of nickel positive electrode
Then, using each of the positive electrode active materials α1 to α5 prepared as described above, 200 g of a 0.25% by mass HPC (hydroxyl propyl cellulose) dispersion liquid was mixed with 500 g of each of the positive electrode active materials to prepare an active material. Each slurry was prepared. Next, the active material slurry prepared as described above was filled into an electrode substrate made of foamed nickel having a thickness of 1.7 mm so as to have a predetermined packing density. Thereafter, it was dried, rolled to a thickness of 0.75 mm, and cut to a predetermined size to produce non-sintered nickel positive electrodes a1 to a4 and x, respectively. The non-sintered nickel positive electrode using the positive electrode active material α1 was referred to as a positive electrode a1. Similarly, the positive electrode a2 was formed using the positive electrode active material α2, the positive electrode a3 was formed using the positive electrode active material α3, and the positive electrode a4 was formed using the positive electrode active material α4. Further, the positive electrode x using the positive electrode active material α5 was used.
[0023]
2. Hydrogen storage alloy negative electrode
(1) Preparation of hydrogen storage alloy
The molar ratio of misch metal (Mm), nickel (Ni: 99.9% purity), cobalt (Co), aluminum (Al), manganese (Mn) and magnesium (Mg) is Mm: Ni: Co: Al: Mn. : Mg = 1.0: 3.90: 0.50: 0.20: 0.30: 0.10 to obtain a mixture. Thereafter, the mixture was induction-heated in a high-frequency induction furnace in an argon gas atmosphere to obtain a molten alloy. This alloy melt is poured into a mold by a known method, cooled, and the composition formula is MmNi. 3.90 Co 0.50 Al 0.20 Mn 0.30 Mg 0.10 CaCu represented by 5 A hydrogen storage alloy ingot of a mold type was produced. This hydrogen storage alloy ingot is pulverized by a mechanical pulverization method until the average particle size becomes about 60 μm, and CaCu is added. 5 A hydrogen storage alloy powder of a mold was obtained.
[0024]
(2) Production of hydrogen storage alloy negative electrode
Next, a hydrogen storage alloy paste was prepared by mixing 20 parts by weight of a 5 mass% aqueous solution of polyethylene oxide (PEO) as a binder with 100 parts by mass of the hydrogen storage alloy powder. This hydrogen-absorbing alloy paste was applied to both surfaces of a core made of punching metal, dried at room temperature, rolled to a predetermined thickness, and cut to a predetermined size to produce a hydrogen-absorbing alloy negative electrode.
[0025]
3. Nickel-hydrogen storage battery
(1) Production of nickel-hydrogen storage battery
Using the non-sintered nickel positive electrodes a1 to a4 and x and the hydrogen storage alloy negative electrode produced as described above, a separator made of a nonwoven fabric made of polypropylene is interposed therebetween, and these are spirally wound to form an electrode group. Were prepared respectively. Then, after inserting each electrode group into the outer can, the negative electrode lead extending from the negative electrode of each electrode group is connected to the outer can, and the positive electrode lead extending from the positive electrode is connected to the positive electrode lid provided on the sealing body. did. Thereafter, an electrolytic solution (for example, a 30% by mass aqueous solution of potassium hydroxide) is injected into the outer can, and the opening of the outer can is sealed with a sealing body to obtain an AA-size nickel-hydrogen having a nominal capacity of 1250 mAh. Storage batteries A1, A2, A3, A4, and X were produced, respectively. Here, the battery using the positive electrode a1 was referred to as a battery A1, the battery using the positive electrode a2 was referred to as a battery A2, the battery using the positive electrode a3 was referred to as a battery A3, and the battery using the positive electrode a4 was referred to as a battery A4. A battery using the positive electrode x was referred to as a battery X.
[0026]
(2) Measurement of discharge capacity
Next, using the batteries A1 to A4 and X manufactured as described above, each of these batteries was charged at a temperature of 25 ° C. with a charging current of 125 mA for 16 hours, and then at a discharging current of 250 mA, the battery voltage was increased. When the battery was discharged to 1.0 V and the initial discharge capacity (mAh) was determined from the discharge time, the results shown in Table 1 below were obtained. Further, after recharging for 16 hours with a charging current of 5000 mA, the battery was discharged with a discharging current of 500 mA until the battery voltage became 0.6 V, and the initial high rate discharge capacity (mAh) was obtained from the discharging time. The results are as shown in Table 1.
[0027]
Thereafter, each of these batteries was charged at room temperature (about 25 ° C.) with a charging current of 1250 mA. When the battery voltage showed a maximum value and dropped by 10 mV (−ΔV = 10 mV), charging was suspended for 1 hour. Was. Thereafter, a cycle of discharging with a discharge current of 1250 mA until the battery voltage becomes 1.0 V was repeated 500 times, and after 500 cycles, the battery was recharged with a charging current of 125 mA for 16 hours and then discharged with a discharge current of 5000 mA. The battery was discharged until the voltage reached 0.6 V, and the high-rate discharge capacity (mAh) after 500 cycles from the discharge time was determined. The results were as shown in Table 1 below.
[0028]
When the ratio of the high-rate discharge capacity after 500 cycles to the obtained initial high-rate discharge capacity was calculated as a capacity retention ratio (%), the results shown in Table 1 below were obtained. From the results in Table 1, the solid solution amount (% by mass) of Mg dissolved in the nickel hydroxide active material is plotted on the horizontal axis, and the high-rate discharge capacity (mAh) after 500 cycles is plotted on the vertical axis. When plotted, the result was as shown in FIG. Also, when the solid solution amount (% by mass) of Mg dissolved in the nickel hydroxide active material is plotted on the horizontal axis, and the capacity retention (%) is plotted on the vertical axis, as shown in FIG. Results.
[0029]
[Table 1]
As is clear from the results of Table 1 and FIGS. 1A and 1B, the initial discharge capacity (mAh) was obtained regardless of the solid solution amount of Mg dissolved in the nickel hydroxide active material. And the initial high rate discharge capacity (mAh) is not so different, but the solid solution amount of Mg is less than 0.10% by mass (based on the mass of the nickel hydroxide active material) or more than 0.45% by mass. It can be seen that the high rate discharge capacity after 500 cycles (see FIG. 1A) and the capacity retention rate after 500 cycles (see FIG. 1B) decrease. On the other hand, when the amount of solid solution of Mg dissolved in the nickel hydroxide active material is 0.10% by mass or more and 0.45% by mass or less, the high rate discharge capacity after 500 cycles (FIG. )) And the capacity retention rate after 500 cycles (see FIG. 1B) is improved.
[0031]
This is because when the solid solution amount of Mg in nickel hydroxide is less than 0.10% by mass, the effect of suppressing the elution of Zn cannot be exhibited, and the conductive network formed by the Co compound layer covering the nickel hydroxide surface. The effect of suppressing the destruction cannot be exhibited. On the other hand, if the solid solution amount of Mg in nickel hydroxide is more than 0.45% by mass, the elution amount of Mg becomes excessive. For this reason, it is considered that Mg hydroxide is excessively generated on the surfaces of the positive electrode and the negative electrode, and conversely inhibits the electrochemical reaction.
[0032]
On the other hand, when the solid solution amount of Mg dissolved in the nickel hydroxide active material is 0.10% by mass or more and 0.45% by mass or less, elution of Zn is suppressed and water is dissolved. The conductive network is protected by the Co compound layer covering the nickel oxide surface. In addition, Mg eluted from the positive electrode reaches the hydrogen storage alloy surface of the negative electrode via the electrolytic solution, exists as Mg hydroxide on the surface of the hydrogen storage alloy, and suppresses oxidation of the hydrogen storage alloy due to oxygen generation. It is considered that the high rate discharge capacity and the capacity retention rate after 500 cycles were improved.
From these facts, it can be said that the solid solution amount of Mg dissolved in the nickel hydroxide active material is preferably 0.10% by mass or more and 0.45% by mass or less.
[0033]
4. Examination of the amount of Mg added to hydrogen storage alloy
Next, the amount of Mg added to the hydrogen storage alloy (the molar ratio of Mg added to the hydrogen storage alloy) was examined.
Therefore, each metal is mixed so that Mm: Ni: Co: Al: Mn: Mg = 1.0: 3.97: 0.50: 0.20: 0.30: 0.03, and As described above, the composition formula is MmNi 3.97 Co 0.50 Al 0.20 Mn 0.30 Mg 0.03 CaCu represented by (d = 0.30, e = 0.03) 5 A hydrogen storage alloy powder of a mold was obtained. Using the obtained hydrogen storage alloy powder, a hydrogen storage alloy negative electrode was prepared in the same manner as described above, and this was used as a negative electrode b1. Similarly, the composition formula is MmNi 3.95 Co 0.50 Al 0.20 Mn 0.30 Mg 0.05 After obtaining a hydrogen storage alloy powder represented by (d = 0.30, e = 0.05), a hydrogen storage alloy negative electrode was prepared and used as a negative electrode b2.
[0034]
Similarly, the composition formula is MmNi 3.90 Co 0.50 Al 0.20 Mn 0.30 Mg 0.10 After obtaining a hydrogen storage alloy powder represented by (d = 0.30, e = 0.10), a hydrogen storage alloy negative electrode was prepared and used as a negative electrode b3, and the composition formula was MmNi 3.85 Co 0.50 Al 0.20 Mn 0.30 Mg 0.15 After obtaining a hydrogen storage alloy powder represented by (d = 0.30, e = 0.15), a hydrogen storage alloy negative electrode was prepared and used as a negative electrode b4, and the composition formula was MmNi. 3.80 Co 0.50 Al 0.20 Mn 0.30 Mg 0.20 After obtaining a hydrogen storage alloy powder represented by (d = 0.30, e = 0.20), a hydrogen storage alloy negative electrode was prepared and used as a negative electrode b5, and the composition formula was MmNi. 3.75 Co 0.50 Al 0.20 Mn 0.30 Mg 0.25 After obtaining a hydrogen storage alloy powder represented by (d = 0.30, e = 0.25), a hydrogen storage alloy negative electrode was prepared to obtain a negative electrode b6. Further, the composition formula without Mg is MmNi. 4.00 Co 0.50 Al 0.20 Mn 0.30 After obtaining a hydrogen storage alloy powder represented by (d = 0.30, e = 0), a hydrogen storage alloy negative electrode was prepared and used as a negative electrode y.
[0035]
Next, the hydrogen storage alloy negative electrodes b1 to b6 and y produced as described above, and the above-described non-sintered nickel positive electrode a2 (having a Mg solid solution amount of 0.30% by mass in nickel hydroxide) were respectively used. AA size nickel-hydrogen storage batteries B1 to B6 and Y with a nominal capacity of 1250 mAh were produced in the same manner as described above. Here, the battery using the negative electrode b1 is referred to as a battery B1, the battery using the negative electrode b2 is referred to as a battery B2, the battery using the negative electrode b3 as a battery B3, the battery using the negative electrode b4 as a battery B4, and the negative electrode b5 as a battery. The battery used was used as battery B5, and the battery using negative electrode b6 was used as battery B6. A battery using the negative electrode y was referred to as a battery Y.
[0036]
Next, charge and discharge are performed in the same manner as described above, and the initial discharge capacity (mAh), the initial high rate discharge capacity (mAh), the high rate discharge capacity (mAh) after 500 cycles, and the capacity retention rate after 500 cycles are obtained. The results were as shown in Table 2 below. From the results in Table 2, the abscissa plots the amount of Mg added to the hydrogen storage alloy (the molar ratio of Mg added in the hydrogen storage alloy), and the high-rate discharge capacity (mAh) after 500 cycles is plotted on the ordinate. Plotted in FIG. 2 resulted in the results shown in FIG. FIG. 2B shows the amount of Mg added to the hydrogen storage alloy (molar ratio of Mg in the hydrogen storage alloy) plotted on the horizontal axis and the capacity retention (%) plotted on the vertical axis. The result was as follows.
[0037]
[Table 2]
As is clear from the results of Table 2 and FIGS. 2A and 2B, the initial discharge capacity (mAh) and the initial high-rate discharge capacity (mAh) were obtained regardless of the molar ratio of Mg in the hydrogen storage alloy. mAh) does not change much, but when the molar ratio of Mg is smaller than 0.03 or larger than 0.20, the high rate discharge capacity after 500 cycles (see FIG. 2A) and 500 cycles It can be seen that the later capacity retention ratio (see FIG. 2B) decreases. On the other hand, when the molar ratio of Mg added to the hydrogen storage alloy is 0.03 or more and 0.20 or less, the high-rate discharge capacity after 500 cycles (see FIG. 2A) and the capacity maintenance after 500 cycles It can be seen that the rate (see FIG. 2B) is improved.
[0039]
This is because if Mg is not added to the hydrogen storage alloy or the addition molar ratio is less than 0.03, it becomes impossible to suppress the hydrogen storage alloy from being pulverized, and the effect of suppressing the elution of Mn is reduced. You can not demonstrate. When the molar ratio of Mg in the hydrogen storage alloy is larger than 0.20, Mg is excessively eluted instead of Mn, and Mg hydroxide is generated excessively. Inhibits electrochemical reactions.
[0040]
On the other hand, when the molar ratio of Mg in the hydrogen storage alloy is 0.03 or more and 0.20 or less (0.03 ≦ e ≦ 0.20), even if the hydrogen storage alloy is finely divided, Then, Mg elutes from the new surface generated by the pulverization, and becomes present in the Co compound layer coating the surface of the nickel hydroxide of the positive electrode via the electrolytic solution. Thereby, the effect of suppressing the destruction of the conductive network by the Co compound on the surface of the nickel hydroxide is exhibited.
From these facts, it can be said that it is desirable to define the molar ratio of Mg added to the hydrogen storage alloy to be 0.03 or more and 0.20 or less (0.03 ≦ e ≦ 0.20).
[0041]
5. Examination of the amount of Mn added to hydrogen storage alloy
Next, the amount of Mn added to the hydrogen storage alloy (Mn addition molar ratio in the hydrogen storage alloy) was examined.
Therefore, each metal is mixed so that Mm: Ni: Co: Al: Mn: Mg = 1.0: 4.10: 0.50: 0.20: 0.10: 0.10. As described above, the composition formula is MmNi 4.10 Co 0.50 Al 0.20 Mn 0.10 Mg 0.10 CaCu represented by (d = 0.10, e = 0.10) 5 A hydrogen storage alloy powder of a mold was obtained. Using the obtained hydrogen storage alloy powder, a hydrogen storage alloy negative electrode was prepared in the same manner as described above, and this was used as a negative electrode c1. Similarly, the composition formula is MmNi 4.00 Co 0.50 Al 0.20 Mn 0.20 Mg 0.10 After obtaining a hydrogen storage alloy powder represented by (d = 0.20, e = 0.10), a hydrogen storage alloy negative electrode was prepared and used as a negative electrode c2.
[0042]
Similarly, the composition formula is MmNi 3.90 Co 0.50 Al 0.20 Mn 0.30 Mg 0.10 After obtaining a hydrogen storage alloy powder represented by (d = 0.30, e = 0.10), a hydrogen storage alloy negative electrode was prepared and used as a negative electrode c3, and the composition formula was MmNi 3.80 Co 0.50 Al 0.20 Mn 0.40 Mg 0.10 After obtaining a hydrogen storage alloy powder represented by (d = 0.40, e = 0.10), a hydrogen storage alloy negative electrode was prepared and used as a negative electrode c4, and the composition formula was MmNi. 3.70 Co 0.50 Al 0.20 Mn 0.50 Mg 0.10 After obtaining a hydrogen storage alloy powder represented by (d = 0.50, e = 0.10), a hydrogen storage alloy negative electrode was prepared and used as a negative electrode c5, and the composition formula was MmNi. 3.60 Co 0.50 Al 0.20 Mn 0.60 Mg 0.10 After obtaining a hydrogen storage alloy powder represented by (d = 0.60, e = 0.10), a hydrogen storage alloy negative electrode was prepared to obtain a negative electrode b6.
[0043]
Next, the hydrogen storage alloy negative electrodes c1 to c6 prepared as described above and the above-described non-sintered nickel positive electrode a2 (the amount of Mg solid solution in nickel hydroxide was 0.30% by mass) were used, respectively. In the same manner as above, nickel-metal hydride storage batteries C1 to C6 of AA size having a nominal capacity of 1250 mAh were respectively manufactured. Here, a battery using the negative electrode c1 is referred to as a battery C1, a battery using the negative electrode c2 is referred to as a battery C2, a battery using the negative electrode c3 as a battery C3, a battery using the negative electrode c4 as a battery C4, and a negative electrode c5 as a battery C4. The battery used was called Battery C5, and the battery using negative electrode c6 was called Battery C6.
[0044]
Next, charge and discharge are performed in the same manner as described above, and the initial discharge capacity (mAh), the initial high rate discharge capacity (mAh), the high rate discharge capacity (mAh) after 500 cycles, and the capacity retention rate after 500 cycles are obtained. The results were as shown in Table 3 below. From the results in Table 3, the amount of Mn added to the hydrogen storage alloy (the molar ratio of Mn added to the hydrogen storage alloy) is plotted on the horizontal axis, and the high-rate discharge capacity (mAh) after 500 cycles is plotted on the vertical axis. When plotted in FIG. 3, the result as shown in FIG. FIG. 3B shows a plot of the amount of Mn added to the hydrogen storage alloy (the molar ratio of Mn added to the hydrogen storage alloy) on the horizontal axis and the capacity retention (%) on the vertical axis. The result was as follows.
[0045]
[Table 3]
As is clear from the results of Table 3 and FIGS. 3 (a) and 3 (b), when the molar ratio of added Mn in the hydrogen storage alloy is smaller than 0.20, the initial discharge capacity (mAh) and the initial high-rate discharge are reduced. When the capacity (mAh) decreases and the molar ratio of Mn added becomes larger than 0.50, the high-rate discharge capacity after 500 cycles (see FIG. 3A) and the capacity retention rate after 500 cycles (FIG. b)). On the other hand, when the molar ratio of Mn added to the hydrogen storage alloy is 0.20 or more and 0.50 or less, the initial discharge capacity (mAh) and the initial high-rate discharge capacity (mAh) are good, and 500 cycles. It can be seen that the high rate discharge capacity (see FIG. 3A) after and the capacity retention rate after 500 cycles (see FIG. 3B) are improved.
[0047]
This is because if the molar ratio of Mn added in the hydrogen storage alloy is larger than 0.50, the elution of Mn becomes excessive, and even if Mg is contained, the elution suppressing effect cannot be sufficiently exerted. . When the molar ratio of Mn in the hydrogen storage alloy is smaller than 0.20, the initial discharge capacity (mAh) and the initial high-rate discharge capacity (mAh) decrease. It can be said that the ratio is desirably set to 0.20 or more and 0.50 or less (0.20 ≦ d ≦ 0.50).
[0048]
【The invention's effect】
As described above, in the present invention, Mg is dissolved in nickel hydroxide of the positive electrode and Mg is also contained in the hydrogen storage alloy of the negative electrode. Elution of Zn from nickel hydroxide, and elution of Mn from the hydrogen storage alloy of the negative electrode can be minimized. This makes it possible to minimize the formation of the Mn-Zn composite oxide in the separator. As a result, even if a negative electrode in which Mn is added to a hydrogen storage alloy and a positive electrode in which Zn is added to nickel hydroxide are used, a nickel-hydrogen storage battery in which high-rate discharge characteristics do not deteriorate can be provided.
[0049]
In the above-described embodiment, an example was described in which only HPC (hydroxyl propyl cellulose) as a binder was added to the nickel positive electrode. However, yttrium (Y), ytterbium (Yb), When a powder of one element selected from erbium (Er) and zinc (Zn) or a compound thereof is added, a better conductive network is formed in the positive electrode, the active material utilization rate is further improved, and a high capacity is obtained. Storage battery can be obtained. In this case, Y as a yttrium compound 2 O 3 It is particularly preferred to use
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the solid solution amount of Mg in nickel hydroxide of a positive electrode and discharge characteristics. FIG. 1 (a) shows the relationship between the solid solution amount of Mg and the high-rate discharge capacity after 500 cycles. FIG. 1B is a diagram showing the relationship between the solid solution amount of Mg and the capacity retention after 500 cycles.
FIG. 2 is a diagram showing the relationship between the addition molar ratio of Mg in the hydrogen storage alloy of the negative electrode and discharge characteristics. FIG. 2 (a) shows the relationship between the addition molar ratio of Mg and the high-rate discharge capacity after 500 cycles. FIG. 2B is a diagram showing the relationship between the molar ratio of Mg added and the capacity retention after 500 cycles.
FIG. 3 is a graph showing the relationship between the molar ratio of Mn in the hydrogen storage alloy of the negative electrode and the discharge characteristics. FIG. 3 (a) shows the relationship between the molar ratio of Mn and the high-rate discharge capacity after 500 cycles. FIG. 3B is a diagram showing the relationship between the molar ratio of Mn added and the capacity retention after 500 cycles.
Claims (8)
前記正極及び負極にはマグネシウムが添加されていることを特徴とするニッケル−水素蓄電池。A nickel-hydrogen storage battery comprising: a positive electrode containing a positive electrode active material mainly containing nickel hydroxide to which zinc is added as a solid solution; a negative electrode containing a hydrogen storage alloy containing manganese; and an alkaline electrolyte. ,
A nickel-hydrogen storage battery, wherein magnesium is added to the positive electrode and the negative electrode.
前記負極に用いられる前記水素吸蔵合金はマンガンとマグネシウムが固溶されていることを特徴とする請求項１に記載のニッケル−水素蓄電池。The nickel hydroxide used for the positive electrode has a solid solution of zinc and magnesium,
2. The nickel-hydrogen storage battery according to claim 1, wherein the hydrogen storage alloy used for the negative electrode contains manganese and magnesium in a solid solution.
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| JP2008053223A (en) * | 2006-07-25 | 2008-03-06 | Matsushita Electric Ind Co Ltd | Negative electrode active material for nickel metal hydride battery, nickel metal hydride battery, and method for treating negative electrode active material for nickel metal hydride battery |
| JP2008153097A (en) * | 2006-12-19 | 2008-07-03 | Matsushita Electric Ind Co Ltd | Alkaline storage battery |
| WO2009013848A1 (en) | 2007-07-24 | 2009-01-29 | Panasonic Corporation | Negative-electrode material for nickel hydrogen battery, method of treating the same, and nickel hydrogen battery |
| JP2010182684A (en) * | 2006-07-25 | 2010-08-19 | Panasonic Corp | Processing method of anode active material for nickel hydrogen battery, anode active material for nickel hydrogen battery, and nickel hydrogen battery |
| DE102015120719A1 (en) | 2014-12-01 | 2016-06-02 | Toyota Jidosha Kabushiki Kaisha | hybrid vehicle |
| WO2019225461A1 (en) * | 2018-05-21 | 2019-11-28 | トヨタ自動車株式会社 | Positive electrode active material, positive electrode, alkaline battery, and method for producing positive electrode active material |
-
2002
- 2002-09-27 JP JP2002283383A patent/JP2004119271A/en not_active Withdrawn
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| JP2008053223A (en) * | 2006-07-25 | 2008-03-06 | Matsushita Electric Ind Co Ltd | Negative electrode active material for nickel metal hydride battery, nickel metal hydride battery, and method for treating negative electrode active material for nickel metal hydride battery |
| JP2010182684A (en) * | 2006-07-25 | 2010-08-19 | Panasonic Corp | Processing method of anode active material for nickel hydrogen battery, anode active material for nickel hydrogen battery, and nickel hydrogen battery |
| JP2008153097A (en) * | 2006-12-19 | 2008-07-03 | Matsushita Electric Ind Co Ltd | Alkaline storage battery |
| WO2009013848A1 (en) | 2007-07-24 | 2009-01-29 | Panasonic Corporation | Negative-electrode material for nickel hydrogen battery, method of treating the same, and nickel hydrogen battery |
| US8202650B2 (en) | 2007-07-24 | 2012-06-19 | Panasonic Corporation | Negative electrode material for nickel-metal hydride battery and treatment method thereof, and nickel-metal hydride battery |
| DE102015120719A1 (en) | 2014-12-01 | 2016-06-02 | Toyota Jidosha Kabushiki Kaisha | hybrid vehicle |
| US9758154B2 (en) | 2014-12-01 | 2017-09-12 | Toyota Jidosha Kabushiki Kaisha | Hybrid vehicle |
| WO2019225461A1 (en) * | 2018-05-21 | 2019-11-28 | トヨタ自動車株式会社 | Positive electrode active material, positive electrode, alkaline battery, and method for producing positive electrode active material |
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