JP5171123B2 - Alkaline secondary battery - Google Patents

Alkaline secondary battery Download PDF

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JP5171123B2
JP5171123B2 JP2007165192A JP2007165192A JP5171123B2 JP 5171123 B2 JP5171123 B2 JP 5171123B2 JP 2007165192 A JP2007165192 A JP 2007165192A JP 2007165192 A JP2007165192 A JP 2007165192A JP 5171123 B2 JP5171123 B2 JP 5171123B2
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hydrogen storage
storage alloy
hydrogen
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alloy
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JP2009004255A (en
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賢大 遠藤
勝 木原
明 佐口
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Sanyo Electric Co Ltd
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    • YGENERAL 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
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    • Y02E60/10Energy storage using batteries

Description

本発明はアルカリ二次電池に関する。   The present invention relates to an alkaline secondary battery.

アルカリ二次電池としてニッケル水素二次電池の負極に用いられる水素吸蔵合金としては、例えば、MmNi系水素吸蔵合金(Mmはミッシュメタル)が既に実用化されている。MmNi系水素吸蔵合金は、CaCu型結晶構造を主結晶相とし、MmNiのNiの一部を、Co,Mn,AIなどの元素で置換したものである。
また、アルカリ二次電池の負極用の水素吸蔵合金として、希土類-Mg-Ni系水素吸蔵合金が知られている。希土類-Mg-Ni系水素吸蔵合金は、MmNi系水素吸蔵合金よりも常温下において多量の水素を吸蔵可能である(特許文献1)。
As a hydrogen storage alloy used for the negative electrode of a nickel metal hydride secondary battery as an alkaline secondary battery, for example, an MmNi 5- based hydrogen storage alloy (Mm is Misch metal) has already been put into practical use. The MmNi 5 series hydrogen storage alloy has a CaCu 5 type crystal structure as a main crystal phase, and a part of Ni in MmNi 5 is substituted with an element such as Co, Mn, or AI.
Further, rare earth-Mg—Ni-based hydrogen storage alloys are known as hydrogen storage alloys for negative electrodes of alkaline secondary batteries. The rare earth-Mg-Ni-based hydrogen storage alloy can store a larger amount of hydrogen at room temperature than the MmNi 5- based hydrogen storage alloy (Patent Document 1).

ところで、アルカリ二次電池は、例えばデジタルスチルカメラ等の電子・電気機器の電源として用いられるが、これらの電子・電気機器にあっては、使用者の利便性を考慮し、電池残量を表示することが一般に行われている。
電池残量を判定する際には、DOD(放電深度:Depth of Discharge)とOCV(開路電圧:Open Circuit Voltage)の関係が用いられる。例えば、DODを0%〜4O%、40%〜80%、80%〜100%の3段階で判定する場合には、DODが40%のときのOCVの基準値V1、及び、DODが80%のときのOCVの基準値V2を予め設定しておき、検出したOCVと基準値V1及びV2とを比較する。
特開2002-164045号公報
By the way, the alkaline secondary battery is used as a power source for electronic / electric equipment such as a digital still camera. For these electronic / electric equipment, the remaining battery capacity is displayed in consideration of user convenience. It is generally done.
When determining the remaining battery level, the relationship between DOD (Depth of Discharge) and OCV (Open Circuit Voltage) is used. For example, when the DOD is judged in three stages of 0% to 40%, 40% to 80%, 80% to 100%, the OCV reference value V1 when the DOD is 40% and the DOD is 80% The OCV reference value V2 at this time is set in advance, and the detected OCV is compared with the reference values V1 and V2.
Japanese Patent Laid-Open No. 2002-164045

アルカリ二次電池にあっては、そのサイクル寿命を延ばす取り組みがなされている。
具体的には、負極にMmNi系水素吸蔵合金を用いる場合には、MmNi系水素吸蔵合金に比較的多くのCoを含有させ、充放電サイクルに伴うMmNi系水素吸蔵合金の微粉化を抑制している。しかしながら、MmNi系水素吸蔵合金に多くのCoを含有させた場合、電池の貯蔵特性が、特に高温で貯蔵した場合に低下する。すなわち、貯蔵中に、負極のMmNi系水素吸蔵合金から溶出したCoが正極を還元したり、セパレータに析出することで、電池容量の低下や自己放電特性の低下が生じる。
For alkaline secondary batteries, efforts are made to extend their cycle life.
Specifically, in the case of using the negative electrode MmNi 5 system hydrogen absorbing alloy, is contained a relatively large amount of Co in the MmNi 5 system hydrogen absorbing alloy, the pulverization of the MmNi 5 system hydrogen absorbing alloy caused by charging and discharging cycle Suppressed. However, when a large amount of Co is contained in the MmNi 5- based hydrogen storage alloy, the storage characteristics of the battery are deteriorated particularly when stored at a high temperature. That is, during storage, Co eluted from the MmNi 5- based hydrogen storage alloy of the negative electrode reduces the positive electrode or deposits on the separator, resulting in a decrease in battery capacity and a decrease in self-discharge characteristics.

希土類-Mg-Ni系水素吸蔵合金については、特許文献1が、組成を限定することによりサイクル寿命・放電特性を向上させることを開示している。しかしながら、特許文献1が開示する希土類-Mg-Ni系水素吸蔵合金にあっても、十分な特性改善がなされていない。
一方、検出したOCVに基づいて電池残量を判定する場合、基準値V1と基準値V2の差が大きいことが必要になる。
Regarding rare earth-Mg-Ni-based hydrogen storage alloys, Patent Document 1 discloses that cycle life and discharge characteristics are improved by limiting the composition. However, even in the rare earth-Mg—Ni-based hydrogen storage alloy disclosed in Patent Document 1, sufficient characteristics have not been improved.
On the other hand, when the remaining battery level is determined based on the detected OCV, the difference between the reference value V1 and the reference value V2 needs to be large.

しかしながら、負極が一種類のMmNi系水素吸蔵合金のみを含む場合、基準値V1と基準値V2の差が小さく、検出したOCVに基づいて電池残量を判定することが困難であった。
これに対し、希土類-Mg-Ni系水素吸蔵合金を用いたアルカリ二次電池では、MmNi系水素吸蔵合金を用いた場合に比べて、DODが40%から80%に変化するときのOCVの変化の割合が大きいという特徴がある。つまり、DODに対するOCVの変化を示す放電曲線の傾きが大きく、これは、希土類-Mg-Ni系水素吸蔵合金と水素ガスとの気固系反応のPCT特性(圧力組成等温線)では、プラトー性が低い傾向にあるためである。このため、希土類-Mg-Ni系水素吸蔵合金を用いたアルカリ二次電池では、検出したOCVに基づいて、電池残量を高精度にて容易に判定可能である。
However, when the negative electrode contains only one type of MmNi 5 hydrogen storage alloy, the difference between the reference value V1 and the reference value V2 is small, and it is difficult to determine the remaining battery level based on the detected OCV.
On the other hand, in the alkaline secondary battery using rare earth-Mg-Ni hydrogen storage alloy, the OCV of DOD changes from 40% to 80% compared to the case using MmNi 5 system hydrogen storage alloy. It is characterized by a high rate of change. In other words, the slope of the discharge curve showing the change in OCV with respect to DOD is large. This is a plateau in the PCT characteristics (pressure composition isotherm) of the gas-solid reaction between rare earth-Mg-Ni hydrogen storage alloy and hydrogen gas. This is because of a low tendency. For this reason, in an alkaline secondary battery using a rare earth-Mg—Ni-based hydrogen storage alloy, the remaining battery level can be easily determined with high accuracy based on the detected OCV.

しかしながら、PCT特性のプラ卜ー性が顕著に低い希土類-Mg-Ni系水素吸蔵合金を負極に用いた場合、電池のサイクル寿命が短くなる傾向がある。
かくして従来のアルカリ二次電池にあっては、サイクル寿命と電池残量の判定のし易さとが両立しなかった。
本発明は、上述した事情に基づいてなされたものであって、その目的とするところは、電池残量をOCV若しくはCCV(閉回路電圧:Closed Circuit Voltage)によって高精度にて判定し易く、且つ、寿命特性に優れるアルカリ二次電池を提供することにある。
However, when a rare earth-Mg-Ni hydrogen storage alloy having a remarkably low PCT characteristic plasticity is used for the negative electrode, the cycle life of the battery tends to be shortened.
Thus, in the conventional alkaline secondary battery, the cycle life and the ease of determination of the remaining battery capacity are not compatible.
The present invention has been made based on the above-described circumstances, and its object is to easily determine the remaining battery level with high accuracy by OCV or CCV (Closed Circuit Voltage), and An object of the present invention is to provide an alkaline secondary battery having excellent life characteristics.

上記した目的を達成するため、本発明者らは種々の検討を重ね、本発明に想到した。本発明によれば、正極、希土類-Mg-Ni系水素吸蔵合金を含む負極、セパレータ及び電解液を備えるアルカリ二次電池において、前記負極は、前記希土類-Mg-Ni系水素吸蔵合金として、互いに水素平衡圧の異なる第1の水素吸蔵合金及び第2の水素吸蔵合金を少なくとも含み、前記負極に含まれる希土類-Mg-Ni水素吸蔵合金の全質量に占める前記第1の水素吸蔵合金の質量の比率は50%以上90%以下であり且つ前記第2の水素吸蔵合金の質量の比率は10%以上50%以下であり、前記第1の水素吸蔵合金は、
一般式:((Pr,Nd,Sm)αLn1―α)1−βMgβNiγ−δ―εAlδTε
(式中、Lnは、La,Ce,Pm,Eu,Gd,Tb,Dy,Ho,Er,Tm,Yb,Lu,Ca,Sr,Sc,Y,Ti,Zr及びHfよりなる群から選ばれる少なくとも1種を表し、TはV,Nb,Ta,Cr,Mo,Mn,Fe,Co,Zn,Ga,Sn,In,Cu,Si,P及びBよりなる群から選ばれる少なくとも1種を表し、添字α,β,γ,δ,εは、それぞれ、0.7<α,0.05<β<0.15,3.0≦γ≦4.2,0.15≦δ≦0.30,0≦ε≦0.50を満たす数を表す)で示される組成を有し、前記第1の水素吸蔵合金の水素平衡圧をP1とし、前記第2の水素吸蔵金の水素平衡圧をP2とし、水素平衡圧差ΔPをΔP=log(P1/P2)としたときに、P1>P2且つΔP≧0.3であることを特徴とするアルカリ二次電池が提供される(請求項1)。
In order to achieve the above-mentioned object, the present inventors have made various studies and arrived at the present invention. According to the present invention, in an alkaline secondary battery comprising a positive electrode, a negative electrode containing a rare earth-Mg-Ni-based hydrogen storage alloy, a separator, and an electrolyte, the negative electrodes are mutually connected as the rare-earth-Mg-Ni-based hydrogen storage alloy. Including at least a first hydrogen storage alloy and a second hydrogen storage alloy having different hydrogen equilibrium pressures, the mass of the first hydrogen storage alloy occupying the total mass of the rare earth-Mg—Ni hydrogen storage alloy included in the negative electrode The ratio is not less than 50% and not more than 90%, and the mass ratio of the second hydrogen storage alloy is not less than 10% and not more than 50%.
General formula: ((Pr, Nd, Sm) α Ln 1-α ) 1-β Mg β Ni γ-δ-ε Al δ T ε
(Wherein Ln is selected from the group consisting of La, Ce, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ca, Sr, Sc, Y, Ti, Zr and Hf. T represents at least one selected from the group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Zn, Ga, Sn, In, Cu, Si, P and B. Subscripts α, β, γ, δ, and ε represent numbers satisfying 0.7 <α, 0.05 <β <0.15, 3.0 ≦ γ ≦ 4.2, 0.15 ≦ δ ≦ 0.30, and 0 ≦ ε ≦ 0.50, respectively. The hydrogen equilibrium pressure of the first hydrogen storage alloy is P1, the hydrogen equilibrium pressure of the second hydrogen storage gold is P2, and the hydrogen equilibrium pressure difference ΔP is ΔP = log (P1 / P2) Then, an alkaline secondary battery characterized in that P1> P2 and ΔP ≧ 0.3 is provided (claim 1).

本発明の請求項1のアルカリ二次電池にあっては、負極に含まれる水素吸蔵合金の全質量に占める第1の水素吸蔵合金及び第2の水素吸蔵合金の質量の比率が所定の範囲にあり、第1の水素吸蔵合金の水素平衡圧P1が第2の水素吸蔵合金の水素平衡圧P2よりも大きく、水素平衡圧差ΔPが0.3以上であり、第1の水素吸蔵合金が所定の組成を有することにより、寿命特性が優れているとともに、OCV又はCCVにより電池残量が高精度にて容易に判定される。   In the alkaline secondary battery according to claim 1 of the present invention, the ratio of the mass of the first hydrogen storage alloy and the second hydrogen storage alloy in the total mass of the hydrogen storage alloy contained in the negative electrode is within a predetermined range. Yes, the hydrogen equilibrium pressure P1 of the first hydrogen storage alloy is larger than the hydrogen equilibrium pressure P2 of the second hydrogen storage alloy, the hydrogen equilibrium pressure difference ΔP is 0.3 or more, and the first hydrogen storage alloy has a predetermined composition. By having it, the life characteristics are excellent, and the remaining battery level is easily determined with high accuracy by OCV or CCV.

図1は、本発明の一実施形態のアルカリ二次電池として、ニッケル水素蓄電池を示す。
このニッケル水素蓄電池は、有底円筒形状の導電性を有する外装缶1を備え、外装缶1の中に電極群2が収容されている。電極群2は、正極3及び負極4を、セパレータ5を介して渦巻状に巻回してなる積層体であり、電極群2の最外周には、その渦巻き方向でみて負極4の外端側の部位が配置され、負極4が外装缶1の内周壁と電気的に接続されている。また、外装缶1の中には、図示しないアルカリ電解液が収容されている。
FIG. 1 shows a nickel metal hydride storage battery as an alkaline secondary battery according to an embodiment of the present invention.
The nickel metal hydride storage battery includes a bottomed cylindrical conductive outer can 1, and an electrode group 2 is accommodated in the outer can 1. The electrode group 2 is a laminate in which the positive electrode 3 and the negative electrode 4 are spirally wound via the separator 5, and the outermost periphery of the electrode group 2 is on the outer end side of the negative electrode 4 as viewed in the spiral direction. The part is disposed, and the negative electrode 4 is electrically connected to the inner peripheral wall of the outer can 1. The outer can 1 contains an alkaline electrolyte (not shown).

なお、アルカリ電解液としては、例えば水酸化カリウム水溶液と、これに水酸化ナトリウム水溶液、水酸化リチウム水溶液などを混合したものが使用される。
外装缶1の開口端には、中央にガス抜き孔6を有する円形の封ロ板7が配置されている。具体的には、封ロ板7の外周縁と外装缶1の開口端縁との間にはリング状の絶縁性ガスケット8が配置されている。そして、外装缶1の開口端縁を径方向内側に縮径するかしめ加工を行うことにより、外装缶1の開口端にガスケット8を介して封ロ板7が気密に固定されている。
In addition, as alkaline electrolyte, what mixed potassium hydroxide aqueous solution and sodium hydroxide aqueous solution, lithium hydroxide aqueous solution, etc. to this is used, for example.
A circular sealing plate 7 having a gas vent hole 6 in the center is disposed at the open end of the outer can 1. Specifically, a ring-shaped insulating gasket 8 is disposed between the outer peripheral edge of the sealing plate 7 and the opening edge of the outer can 1. The sealing plate 7 is airtightly fixed to the opening end of the outer can 1 through the gasket 8 by performing caulking processing to reduce the opening edge of the outer can 1 inward in the radial direction.

電極群2と封口板7との間には正極リード9が配置されている。正極リード9の一端は、電極群2中の正極3に接続され、正極リード9の他端は封ロ板7の内面に接続されている。封口板7の外面上には、ガス抜き孔6を閉塞するようにゴム製の弁体10が配置され、更に、弁体10を囲むようにフランジ付きの円筒形状の正極端子11が取り付けられている。
また、外装缶1の開口端縁上には環状の押さえ板12が配置され、正極端子11の円筒部は押さえ板12の中央孔を貫通して突出している。符号13は、外装チューブに付されており、外装チューブ13は押さえ板12の外周縁、外装缶1の外周面及び底壁外周縁を被覆している。
A positive electrode lead 9 is disposed between the electrode group 2 and the sealing plate 7. One end of the positive electrode lead 9 is connected to the positive electrode 3 in the electrode group 2, and the other end of the positive electrode lead 9 is connected to the inner surface of the sealing plate 7. A rubber valve body 10 is arranged on the outer surface of the sealing plate 7 so as to close the gas vent hole 6, and a cylindrical positive electrode terminal 11 with a flange is attached so as to surround the valve body 10. Yes.
An annular pressing plate 12 is disposed on the opening edge of the outer can 1, and the cylindrical portion of the positive terminal 11 protrudes through the central hole of the pressing plate 12. Reference numeral 13 is attached to the outer tube, and the outer tube 13 covers the outer peripheral edge of the pressing plate 12, the outer peripheral surface of the outer can 1 and the outer peripheral edge of the bottom wall.

正極3は、導電性の正極基板と、正極基板に保持された正極合剤とから構成されている。正極基板としては、例えば、ニッケルめっきが施された網状、スポンジ状、繊維状、フエルト状の金属多孔体を用いることができる。
正極合剤は、正極活物質としての水酸化ニッケルを主成分とする粉末(水酸化ニッケル粉末)、導電剤及び結着剤を含むが、水酸化ニッケル粉末としては、ニッケルの平均価数が2価よりも大きく且つ各粒子の表面の少なくとも一部若しくは全部がコバルト化合物で被覆されている粉末を用いるのが好ましい。また、水酸化ニッケル粉末は、コバルト及び亜鉛が固溶していてもよい。
The positive electrode 3 is composed of a conductive positive electrode substrate and a positive electrode mixture held on the positive electrode substrate. As the positive electrode substrate, for example, a net-like, sponge-like, fiber-like, or felt-like metal porous body plated with nickel can be used.
The positive electrode mixture includes a powder mainly composed of nickel hydroxide as a positive electrode active material (nickel hydroxide powder), a conductive agent, and a binder. As the nickel hydroxide powder, the average valence of nickel is 2 It is preferable to use a powder having a particle size greater than the value and at least part or all of the surface of each particle coated with a cobalt compound. Moreover, cobalt hydroxide and zinc may be dissolved in the nickel hydroxide powder.

導電剤としては、例えば、コバルト酸化物、コバルト水酸化物、金属コバルトなどの粉末を用いることができる。また結着剤としては、例えば、カルボキシメチルセルロース、メチルセルロース、PTFEディスパージョン、HPCディスパージョンなどを用いることができる。
上記した正極3は、例えば、水酸化ニッケル粉末、導電剤、結着剤、及び水を混練して正極用スラリを調製し、この正極用スラリが塗着・充填された正極基板を、正極用スラリの乾燥を経てから圧延・裁断して作製することができる。
As the conductive agent, for example, powders of cobalt oxide, cobalt hydroxide, metallic cobalt and the like can be used. As the binder, for example, carboxymethylcellulose, methylcellulose, PTFE dispersion, HPC dispersion, and the like can be used.
The positive electrode 3 is prepared by, for example, preparing a positive electrode slurry by kneading nickel hydroxide powder, a conductive agent, a binder, and water, and using the positive electrode substrate coated and filled with the positive electrode slurry as a positive electrode It can be produced by rolling and cutting after slurry drying.

負極4は、導電性の負極基板と負極基板に保持された負極合剤とから構成される。負極基板としては例えば、ニッケルめっきされたパンチングメタルを用いることができる。
負極合剤は、図1の円内に概略的に示したように、複数の第1の水素吸蔵合金粒子14、複数の第2の水素吸蔵合金粒子16、結着剤18、及び必要に応じて導電剤から構成される。結着剤18としては、正極合剤と同じ結着剤の外に、更に例えばポリアクリル酸ナトリウムなどを併用してもよい。また、導電剤としては、例えばカーボン粉末などを用いることができる。なお図1の円内には、第1の水素吸蔵合金粒子14、第2の水素吸蔵合金粒子16及び結着剤18のみを概略的に示し、負極基板及び導電剤を省略した。
The negative electrode 4 includes a conductive negative electrode substrate and a negative electrode mixture held on the negative electrode substrate. As the negative electrode substrate, for example, a punching metal plated with nickel can be used.
As schematically shown in the circle of FIG. 1, the negative electrode mixture is composed of a plurality of first hydrogen storage alloy particles 14, a plurality of second hydrogen storage alloy particles 16, a binder 18, and as necessary. And composed of a conductive agent. As the binder 18, in addition to the same binder as the positive electrode mixture, for example, sodium polyacrylate may be used in combination. In addition, as the conductive agent, for example, carbon powder can be used. In FIG. 1, only the first hydrogen storage alloy particles 14, the second hydrogen storage alloy particles 16 and the binder 18 are schematically shown, and the negative electrode substrate and the conductive agent are omitted.

第1の水素吸蔵合金粒子14及び第2の水素吸蔵合金粒子16は、それぞれ希土類-Mg-Ni系水素吸蔵合金(希土類-Mg-Ni系合金)からなり、結晶構造がCaCu(AB)型ではなく、CeNi型若しくはCeNi型に類似した結晶構造を有する。CeNi型は、AB型とAB型とをあわせたような超格子構造である。
AB3.5型(CeNi型)に類似する結晶構造の希土類-Mg-Ni系水素吸蔵合金としては、AB3.8型(CeCo19型)、AB3.8型(PrCo19型)又はAB3.0型(PuNi型)のものを用いることができる。
The first hydrogen storage alloy particles 14 and the second hydrogen storage alloy particles 16 are each made of a rare earth-Mg-Ni hydrogen storage alloy (rare earth-Mg-Ni alloy), and the crystal structure is CaCu 5 (AB 5 ). It is not a mold but has a crystal structure similar to Ce 2 Ni 7 type or Ce 2 Ni 7 type. The Ce 2 Ni 7 type has a superlattice structure that combines the AB 5 type and the AB 2 type.
AB 3.8 type (Ce 5 Co 19 type), AB 3.8 type (Pr) as rare earth-Mg-Ni hydrogen storage alloys having a crystal structure similar to AB 3.5 type (Ce 2 Ni 7 type) 5 Co 19 type) or AB 3.0 type (PuNi 3 type) can be used.

第1の水素吸蔵合金粒子14と第2の水素吸蔵合金粒子16とでは、互いに水素吸蔵合金の組成が異なり、第1の水素吸蔵合金粒子14における組成は、
一般式(I):((Pr,Nd,Sm)αLn1―α)1−βMgβNiγ−δ―εAlδTε
で示される。ただし式(I)中、Lnは、La,Ce,Pm,Eu,Gd,Tb,Dy,Ho,Er,Tm,Yb,Lu,Ca,Sr,Sc,Y,Ti,Zr及びHfよりなる群から選ばれる少なくとも1種を表し、TはV,Nb,Ta,Cr,Mo,Mn,Fe,Co,Zn,Ga,Sn,In,Cu,Si,P及びBよりなる群から選ばれる少なくとも1種を表し、添字α,β,γ,δ,εは、それぞれ、0.7<α,0.05<β<0.15,3.0≦γ≦4.2,0.15≦δ≦0.30,0≦ε≦0.50を満たす数を表す。
The first hydrogen storage alloy particles 14 and the second hydrogen storage alloy particles 16 have different compositions of the hydrogen storage alloy, and the composition of the first hydrogen storage alloy particles 14 is:
Formula (I): ((Pr, Nd, Sm) α Ln 1-α ) 1-β Mg β Ni γ-δ-ε Al δ T ε
Indicated by In the formula (I), Ln is a group consisting of La, Ce, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ca, Sr, Sc, Y, Ti, Zr, and Hf. T represents at least one selected from the group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Zn, Ga, Sn, In, Cu, Si, P, and B. Represents the seed, and the subscripts α, β, γ, δ, and ε represent numbers satisfying 0.7 <α, 0.05 <β <0.15, 3.0 ≦ γ ≦ 4.2, 0.15 ≦ δ ≦ 0.30, and 0 ≦ ε ≦ 0.50, respectively. .

第1の水素吸蔵合金粒子14と第2の水素吸蔵合金粒子16とでは、水素平衡圧が異なり、第1の水素吸蔵合金粒子14の水素平衡圧をP1とし、第2の水素吸蔵金16の水素平衡圧をP2とし、水素平衡圧差ΔPをΔP=log10(P1/P2)と定義したときに、P1>P2且つΔP≧0.3である。つまり、第1の水素吸蔵合金粒子14の水素平衡圧P1は、第2の水素吸蔵金粒子16の水素平衡圧P2よりも大きく、水素平衡圧差ΔPは0.3以上であり、好ましくは、0.5以上である。 The first hydrogen storage alloy particles 14 and the second hydrogen storage alloy particles 16 have different hydrogen equilibrium pressures. The hydrogen equilibrium pressure of the first hydrogen storage alloy particles 14 is P1, and the second hydrogen storage alloy particles 16 When the hydrogen equilibrium pressure is P2, and the hydrogen equilibrium pressure difference ΔP is defined as ΔP = log 10 (P1 / P2), P1> P2 and ΔP ≧ 0.3. That is, the hydrogen equilibrium pressure P1 of the first hydrogen storage alloy particles 14 is larger than the hydrogen equilibrium pressure P2 of the second hydrogen storage gold particles 16, and the hydrogen equilibrium pressure difference ΔP is 0.3 or more, preferably 0.5 or more. is there.

なお、水素平衡圧P1、P2は、温度80℃、H/M=0.4での水素平衡圧である。
負極4は、第1の水素吸蔵合金粒子14及び第2の水素吸蔵合金粒子16以外の希土類-Mg-Ni系水素吸蔵合金を含んでいてもよいが、負極4に含まれる水素吸蔵合金の全質量に占める、第1の水素吸蔵合金粒子14の質量の比率は50%以上90%以下であり、好ましくは60%以上80%以下である。
The hydrogen equilibrium pressures P1 and P2 are hydrogen equilibrium pressures at a temperature of 80 ° C. and H / M = 0.4.
The negative electrode 4 may contain a rare earth-Mg—Ni-based hydrogen storage alloy other than the first hydrogen storage alloy particles 14 and the second hydrogen storage alloy particles 16, but all of the hydrogen storage alloys contained in the negative electrode 4. The ratio of the mass of the first hydrogen storage alloy particles 14 to the mass is 50% or more and 90% or less, preferably 60% or more and 80% or less.

第2の水素吸蔵合金粒子16は、希土類-Mg-Ni系水素吸蔵合金であれば、その組成は特に限定されない。負極4に含まれる水素吸蔵合金の全質量に占める第2の水素吸蔵合金粒子16の比率は10%以上50%以下であり、好ましくは20%以上40%以下である。
負極4は、第1の水素吸蔵合金粒子14、第2の水素吸蔵合金粒子16、結着剤及び必要に応じて導電剤を混練して負極用スラリを調製し、調製した負極用スラリを塗着した負極基板を、負極用スラリの乾燥を経てから圧延・裁断して作製することができる。
第1の水素吸蔵合金粒子14及び第2の水素吸蔵合金粒子16は、例えば以下のようにして得られる。
The composition of the second hydrogen storage alloy particle 16 is not particularly limited as long as it is a rare earth-Mg—Ni-based hydrogen storage alloy. The ratio of the second hydrogen storage alloy particles 16 to the total mass of the hydrogen storage alloy contained in the negative electrode 4 is 10% or more and 50% or less, preferably 20% or more and 40% or less.
The negative electrode 4 is prepared by mixing the first hydrogen storage alloy particles 14, the second hydrogen storage alloy particles 16, a binder and, if necessary, a conductive agent to prepare a negative electrode slurry, and applying the prepared negative electrode slurry. The attached negative electrode substrate can be produced by rolling and cutting after drying the negative electrode slurry.
The first hydrogen storage alloy particles 14 and the second hydrogen storage alloy particles 16 are obtained, for example, as follows.

まず、所定の組成となるよう金属原材料を秤量して混合し、この混合物を例えば高周波溶解炉で溶解してインゴットにする。得られたインゴットに、900〜1200℃の温度の不活性ガス雰囲気下にて5〜24時間加熱する熱処理を施し、インゴットの金属組織をCeNi型若しくはこれに類似した結晶構造にする。この後、インゴットを粉砕し、篩分けにより所望粒径に分級して、第1の水素吸蔵合金粒子14又は第2の水素吸蔵合金粒子16が得られる。 First, metal raw materials are weighed and mixed so as to have a predetermined composition, and this mixture is melted in, for example, a high-frequency melting furnace to form an ingot. The obtained ingot is subjected to heat treatment in an inert gas atmosphere at a temperature of 900 to 1200 ° C. for 5 to 24 hours, so that the metal structure of the ingot has a Ce 2 Ni 7 type or a similar crystal structure. Thereafter, the ingot is pulverized and classified to a desired particle size by sieving to obtain the first hydrogen storage alloy particles 14 or the second hydrogen storage alloy particles 16.

上述したニッケル水素蓄電池では、負極4に含まれる希土類-Mg-Ni系水素吸蔵合金の全質量に占める第1の水素吸蔵合金粒子14の質量の比率が50%以上90%以下であり且つ第2の水素吸蔵合金の比率が10%以上50%以下であり、第1の水素吸蔵合金粒子14の水素平衡圧P1が第2の水素吸蔵合金粒子16の水素平衡圧P2よりも大きく、水素平衡圧差ΔPが0.3以上であり、第1の水素吸蔵合金粒子14が所定の組成を有することにより、寿命特性が優れているとともに、OCV又はCCVにより電池残量が高精度にて容易に判定される。   In the above-described nickel-metal hydride storage battery, the ratio of the mass of the first hydrogen storage alloy particles 14 to the total mass of the rare earth-Mg—Ni-based hydrogen storage alloy contained in the negative electrode 4 is 50% to 90% and the second The ratio of the hydrogen storage alloy is 10% to 50%, the hydrogen equilibrium pressure P1 of the first hydrogen storage alloy particles 14 is greater than the hydrogen equilibrium pressure P2 of the second hydrogen storage alloy particles 16, and the hydrogen equilibrium pressure difference Since ΔP is 0.3 or more and the first hydrogen storage alloy particles 14 have a predetermined composition, the life characteristics are excellent, and the remaining battery level is easily determined with high accuracy by OCV or CCV.

なお、上述したニッケル水素蓄電池においては、一般式中αが0.7よりも大に設定されることにより、合金構造の安定化を図ることができる。また後述するAl量を所定量まで増やせる効果がある。更に水素平衡圧を高められ、P1値を高くすることができる。なお、αの上限は1である。
一般式(I)中、添字βが0.15未満に設定されることにより、Mgを主成分とする不所望の相の析出が防止され、この点からも、電池の寿命特性が向上する。すなわち、添字βが0.15未満であることにより、充放電サイクルに伴う第1の水素吸蔵合金粒子14の微粒子化が抑制され、もって、寿命特性が向上する。一方、添字βが0.05よりも大きく設定されることにより、第1の水素吸蔵合金粒子14は多量の水素を吸蔵可能である。
In the nickel-metal hydride storage battery described above, the alloy structure can be stabilized by setting α in the general formula to be larger than 0.7. In addition, there is an effect that the amount of Al described later can be increased to a predetermined amount. Furthermore, the hydrogen equilibrium pressure can be increased and the P1 value can be increased. The upper limit of α is 1.
In the general formula (I), by setting the subscript β to less than 0.15, precipitation of an undesired phase containing Mg as a main component is prevented, and the life characteristics of the battery are also improved in this respect. That is, when the subscript β is less than 0.15, the formation of fine particles of the first hydrogen storage alloy particles 14 accompanying the charge / discharge cycle is suppressed, thereby improving the life characteristics. On the other hand, when the subscript β is set to be larger than 0.05, the first hydrogen storage alloy particles 14 can store a large amount of hydrogen.

一般式(I)において、添字γが小さくなりすぎると、第1の水素吸蔵合金粒子14内における水素の吸蔵安定性が高くなるため、水素放出能が劣化し、また添字γが大きくなりすぎると、今度は、水素吸蔵合金における水素の吸蔵サイトが減少して、水素吸蔵能の劣化が起こりはじめる。それ故、添字γは、3.0≦γ≦4.2を満たすように設定される。
一般式(I)において、添字δはNiのAlによる置換量を示すが、0.15>δの場合、合金構造が不安定になり、合金容量が小さくなる。若しくは、サイクル進行に伴い構造が不安定化し合金容量が大きく低下する。一方δ>0.30の場合、Alを主成分とする不所望の相が析出し、合金容量の低下や耐食性が低下することで寿命特性が低下する。それ故、添字δは、0.15≦δ≦0.30を満たすように設定される。
In the general formula (I), if the subscript γ is too small, the hydrogen storage stability in the first hydrogen storage alloy particles 14 is increased, so that the hydrogen releasing ability is deteriorated and the subscript γ is too large. This time, the hydrogen storage sites in the hydrogen storage alloy decrease and the hydrogen storage capacity begins to deteriorate. Therefore, the subscript γ is set so as to satisfy 3.0 ≦ γ ≦ 4.2.
In the general formula (I), the subscript δ indicates the amount of substitution of Ni by Al. When 0.15> δ, the alloy structure becomes unstable and the alloy capacity becomes small. Or, as the cycle progresses, the structure becomes unstable and the alloy capacity greatly decreases. On the other hand, in the case of δ> 0.30, an undesired phase containing Al as a main component is precipitated, and the life characteristics are deteriorated due to a decrease in alloy capacity and a decrease in corrosion resistance. Therefore, the subscript δ is set so as to satisfy 0.15 ≦ δ ≦ 0.30.

一般式(I)において、添字εはNiの置換元素Tによる置換量を示すが、添字εが大きくなりすぎると、水素吸蔵合金はその結晶構造が変化して水素の吸蔵・放出能を喪失しはじめるとともに、アルカリ電解液への置換元素Tの溶出が起こりはじめ、その複合物がセパレータに析出して電池の長期貯蔵性が低下する。それ故、添字εは、0≦ε≦0.50を満たすように設定される。   In the general formula (I), the subscript ε indicates the amount of substitution of Ni by the substituting element T, but if the subscript ε becomes too large, the hydrogen storage alloy changes its crystal structure and loses the ability to store and release hydrogen. At the same time, elution of the substitution element T into the alkaline electrolyte begins to occur, and the composite precipitates on the separator, thereby reducing the long-term storage property of the battery. Therefore, the subscript ε is set so as to satisfy 0 ≦ ε ≦ 0.50.

1.正極の作製
各粒子の全部若しくは一部がコバルト化合物で被覆された水酸化ニッケル粉末を用意し、この水酸化ニッケル粉末100質量部に対し、濃度が40質量%のHPCディスパージョンを混合して正極用スラリを調製した。この正極用スラリが塗着・充填されたシート状のニッケル多孔体を、乾燥を経てから、圧延・裁断して正極を作製した。
2.負極の作製
原材料として、組成が異なる4種類の水素吸蔵合金の粉末A,B,C,Dを用意した。これら合金粉末A,B,C,Dの組成及び水素平衡圧を表1に示す。なお、JIS H7201に準じて、温度80℃及びH/Mが0.4のときの水素平衡圧を測定した。
1. Preparation of positive electrode Nickel hydroxide powder in which all or a part of each particle is coated with a cobalt compound is prepared, and 100% by mass of this nickel hydroxide powder is mixed with an HPC dispersion having a concentration of 40% by mass. A slurry was prepared. The sheet-like nickel porous body coated and filled with this positive electrode slurry was dried and then rolled and cut to produce a positive electrode.
2. Production of negative electrode Four kinds of hydrogen storage alloy powders A, B, C and D with different compositions were prepared as raw materials. Table 1 shows the compositions and hydrogen equilibrium pressures of these alloy powders A, B, C, and D. In addition, according to JIS H7201, the hydrogen equilibrium pressure when the temperature was 80 ° C. and H / M was 0.4 was measured.

具体的には、表1に示した組成となるように、各元素を含む原材料を秤量し、その混合物を高周波溶解炉で溶解したのちインゴットを製造した。熱処理を施した後、各インゴットを平均粒径D50が50μmになるように粉砕、分級し、合金粉末A,B,C,Dを作製した。
なお、平均粒径D50は、各合金粉末A,B,C,Dについてレーザ回折・散乱式粒度分布測定装置(HORIBA製LA-300)を用いて測定した粒度分布において、重量積分50%にあたる粒径である。
Specifically, raw materials containing each element were weighed so as to have the composition shown in Table 1, and the mixture was melted in a high-frequency melting furnace, and then an ingot was manufactured. After heat treatment, each ingot was pulverized and classified so that the average particle size D50 was 50 μm, and alloy powders A, B, C, and D were produced.
The average particle size D50 is the particle size distribution measured for each alloy powder A, B, C, D using a laser diffraction / scattering type particle size distribution analyzer (LA-300 manufactured by HORIBA), which corresponds to 50% weight integral. Is the diameter.

合金粉末A,B,Cの結晶構造をX線粉末回折法により解析したところ、合金粉末A,B,Cの主相の結晶構造は、CeNi型若しくはそれに酷似する結晶構造であることが確認された。同じく合金粉末Dの主相の結晶構造は、CaCu型であることが確認された。
得られた合金粉末A,B,C,Dを表2に示す混合比率にて混合したもの100質量部に対し、ポリアクリル酸ナトリウム0.5質量部、カルボキシメチルセルロース0.12質量部、PTFEディスバージョン(比重1.5、固形分60質量%)1.0質量部(固形分換算)、カーボンブラック1.0質量部、および水30質量部を混練して負極用スラリを調製した。調製した負極用スラリを塗着したパンチングメタルを、負極用スラリの乾燥を経てからロール圧延・裁断して、負極を作製した。
When the crystal structures of alloy powders A, B, and C are analyzed by X-ray powder diffraction, the crystal structure of the main phase of alloy powders A, B, and C is a Ce 2 Ni 7 type or a crystal structure that is very similar to it. Was confirmed. Similarly, the crystal structure of the main phase of the alloy powder D was confirmed to be CaCu 5 type.
100 parts by mass of the obtained alloy powders A, B, C, and D mixed at the mixing ratio shown in Table 2, 0.5 parts by mass of sodium polyacrylate, 0.12 parts by mass of carboxymethylcellulose, PTFE dispersion (specific gravity 1.5 The slurry for negative electrode was prepared by kneading 1.0 part by mass (in terms of solids), 1.0 part by mass of carbon black, and 30 parts by mass of water. The punched metal coated with the prepared negative electrode slurry was roll-rolled and cut after the negative electrode slurry was dried to prepare a negative electrode.

3.ニッケル水素蓄電池の組立て
作製した正極と負極とを、これらの間にポリプ口ピレン繊維製不織布から成る厚み0.10mm(目付量50g/m)のセパレータを介装しながら渦巻状に巻回して電極群を作製した。この電極群を有底円筒形状の外装缶に収納し、同時に、7Nの水酸化カリウム水溶液と1Nの水酸化リチウム水溶液とから成るアルカリ電解液を注液し、封ロして、定格容量2000mAhのAAサイズ密閉円筒形ニッケル水素蓄電池を組み立てた。
3. Assembling the nickel-metal hydride storage battery The positive electrode and negative electrode thus produced were wound in a spiral shape with a separator having a thickness of 0.10 mm (weight per unit area: 50 g / m 2 ) made of a nonwoven fabric made of polypyrene fiber between them. Groups were made. This electrode group is housed in a cylindrical can with a bottom, and at the same time, an alkaline electrolyte composed of a 7N potassium hydroxide aqueous solution and a 1N lithium hydroxide aqueous solution is injected, sealed, and sealed with a rated capacity of 2000 mAh. AA size sealed cylindrical nickel metal hydride storage battery was assembled.

4.ニッケル水素蓄電池の評価
(1)電池活性化
各ニッケル水素蓄電池につき、温度25℃において、0.1C相当の電流で15時間充電してから、0.2C相当の電流で終止電圧1.0Vまで放電させる初期活性化処理を施した。
(2)放電曲線の測定
初期活性化処理を施した各ニッケル水素蓄電池につき、1C相当の電流でdV制御の充電を行ってから、20%ずつ放電させた。この際、各DODにて、放電から60分の休止時間をおいてOCVを測定し、OCVの測定が終わってから次のDODまで放電させた。実施例1及び比較例1〜3,5の結果を図2に示すとともに、実施例1〜4及び比較例1〜5について、DODが40%のときのOCVとDODが80%のときのOCVとの差ΔVを表2に示す。
4). Evaluation of Nickel Metal Hydride Battery (1) Battery activation Initial activity for each nickel metal hydride battery to be charged at a temperature equivalent to 0.1C for 15 hours at a temperature of 25 ° C and then discharged to a final voltage of 1.0V at a current equivalent to 0.2C. Was applied.
(2) Measurement of discharge curve Each nickel metal hydride storage battery subjected to the initial activation treatment was charged by dV control at a current equivalent to 1 C and then discharged by 20%. At this time, at each DOD, OCV was measured after a 60-minute rest period from the discharge, and after the OCV measurement was completed, the discharge was performed until the next DOD. The results of Example 1 and Comparative Examples 1 to 3 and 5 are shown in FIG. 2, and for Examples 1 to 4 and Comparative Examples 1 to 5, OCV when DOD is 40% and OCV when DOD is 80%. The difference ΔV is shown in Table 2.

(3)寿命特性
初期活性化処理を施した各ニッケル水素蓄電池につき、温度25℃にて、1C相当の電流でdV制御の充電後、1C相当の電流で終止電圧1.0Vまで放電させる充放電サイクルを反復し、1サイクル目の放電容量に対する容量維持率が60%に到達するまでのサイクル数を寿命特性として数えた。この結果を比較例1のサイクル数を1とする比(サイクル数比)にして表2に示す。
(3) Life characteristics Charging / discharging cycle for each nickel-metal hydride storage battery that has been subjected to initial activation treatment, at a temperature of 25 ° C, after charging with dV control at a current equivalent to 1C, and then discharging to a final voltage of 1.0V at a current equivalent to 1C. Was repeated, and the number of cycles until the capacity maintenance ratio with respect to the discharge capacity at the first cycle reached 60% was counted as a life characteristic. The results are shown in Table 2 as a ratio (cycle number ratio) where the cycle number of Comparative Example 1 is 1.

(4)評価結果
表1、表2及び図2から次のことが明らかである。
(i)比較例2のOCVは、比較例1のOCVと比較して、DODの浅い領域から深い領域に亘り全体的に低下している。これは、合金粉末A,Bの水素平衡圧の差に依存していると考えられる。
(ii)組成が一般式(I)から外れている合金粉末Bを用いた比較例2においては、寿命特性が大きく低下している。寿命特性評価後のニッケル水素蓄電池を分解して合金粉末Bの劣化調査をした結果、合金粉末Bの腐食量は、比較例1の合金粉末Aよりも増加していることが確認された。
(4) Evaluation Results From Tables 1 and 2 and FIG.
(I) Compared with the OCV of Comparative Example 1, the OCV of Comparative Example 2 generally decreases from a shallow region to a deep region of DOD. This is considered to depend on the difference in hydrogen equilibrium pressure between the alloy powders A and B.
(Ii) In Comparative Example 2 using the alloy powder B whose composition deviates from the general formula (I), the life characteristics are greatly deteriorated. As a result of decomposing the nickel-metal hydride storage battery after evaluating the life characteristics and investigating the deterioration of the alloy powder B, it was confirmed that the corrosion amount of the alloy powder B was higher than that of the alloy powder A of Comparative Example 1.

(iii)水素平衡圧の異なる合金粉末A,Bを混合して用いた実施例1のOCVは、DODが浅い領域では、水素平衡圧の高い合金粉末Aのみを用いた比較例1のOCVをトレースし、DODが深い領域では、水素平衡圧の低い合金粉末Bのみを用いた比較例2のOCVをトレースしている。この結果として、実施例1では、DODが40%のときのOCVとDODが80%のときのOCVとの差△Vが、比較例1及び比較例2に比べて広くなっており、残容量の検出がし易い。実施例2、3についても本発明の範囲内において同様な結果である。また合金粉末Cを用いた場合も、実施例4において同様な効果が得られた。 (Iii) The OCV of Example 1 using a mixture of alloy powders A and B having different hydrogen equilibrium pressures is the OCV of Comparative Example 1 using only the alloy powder A having a high hydrogen equilibrium pressure in the region where the DOD is shallow. In the region where the DOD is deep, the OCV of Comparative Example 2 using only the alloy powder B having a low hydrogen equilibrium pressure is traced. As a result, in Example 1, the difference ΔV between the OCV when the DOD is 40% and the OCV when the DOD is 80% is wider than that in Comparative Examples 1 and 2, and the remaining capacity is large. Is easy to detect. Examples 2 and 3 have similar results within the scope of the present invention. Further, when the alloy powder C was used, the same effect was obtained in Example 4.

(iv)水素平衡圧の異なる合金粉末A,Bを混合して用いているものの、合金粉末Aの混合比率が50%より少ない比較例3では、実施例1に比べて、寿命特性が低下した。また合金粉末Cを用いた場合も、同様に比較例4において寿命特性が低下した。
(v)MmNi5系水素吸蔵合金である合金粉末Dを用いた比較例5では、合金粉末DのPCT特性におけるプラトー性が良い為、△Vが小さく残容量を検出するのが困難である。また、寿命特性も低下している。
(Iv) Although alloy powders A and B having different hydrogen equilibrium pressures are mixed and used, in Comparative Example 3 in which the mixing ratio of alloy powder A is less than 50%, the life characteristics are deteriorated as compared with Example 1. . Similarly, when alloy powder C was used, the life characteristics in Comparative Example 4 also decreased.
(V) In Comparative Example 5 using the alloy powder D, which is an MmNi5-based hydrogen storage alloy, the plateau property in the PCT characteristic of the alloy powder D is good, so ΔV is small and it is difficult to detect the remaining capacity. In addition, the life characteristics are deteriorated.

本発明は上記した一実施形態及び実施例に限定されることはなく、種々変形が可能である。例えば、一実施形態の二次電池は円筒形であったけれども、角形であってもよいのは勿論である。また、電池の形状及び寸法、安全弁の仕組み、及び、電極板と電極端子との間の接続方法等も上述の記載に限定されることはない。   The present invention is not limited to the above-described embodiment and examples, and various modifications can be made. For example, although the secondary battery of one embodiment has a cylindrical shape, it may be a square shape. Further, the shape and dimensions of the battery, the mechanism of the safety valve, the connection method between the electrode plate and the electrode terminal, and the like are not limited to the above description.

Figure 0005171123
Figure 0005171123

Figure 0005171123
Figure 0005171123

一実施形態のニッケル水素二次電池の1例を示す部分切欠斜視図であり、円内に負極の一部を拡大して概略的に示した。1 is a partially cutaway perspective view showing an example of a nickel metal hydride secondary battery according to an embodiment, and schematically shows an enlarged part of a negative electrode in a circle. 実施例1及び比較例1,2,5のニッケル水素蓄電池におけるDOD(放電深度)とOCV(開路電圧)の関係を示すグラフである。It is a graph which shows the relationship between DOD (discharge depth) and OCV (open circuit voltage) in the nickel hydride storage battery of Example 1 and Comparative Examples 1, 2, and 5.

符号の説明Explanation of symbols

1 外装缶
2 電極群
3 正極
4 負極板
5 セパレータ
14 第1の水素吸蔵合金粒子
16 第2の水素吸蔵合金粒子
18 結着剤
1 Exterior can
2 Electrode group
3 Positive electrode
4 Negative electrode plate
5 Separator
14 First hydrogen storage alloy particles
16 Second hydrogen storage alloy particles
18 Binder

Claims (1)

正極、希土類-Mg-Ni系水素吸蔵合金を含む負極、セパレータ及び電解液を備えるアルカリ二次電池において、
前記負極は、前記希土類-Mg-Ni系水素吸蔵合金として、互いに水素平衡圧の異なる第1の水素吸蔵合金及び第2の水素吸蔵合金を少なくとも含み、
前記負極に含まれる希土類-Mg-Ni水素吸蔵合金の全質量に占める前記第1の水素吸蔵合金の質量の比率は50%以上90%以下であり且つ前記第2の水素吸蔵合金の質量の比率は10%以上50%以下であり、
前記第1の水素吸蔵合金は、一般式:
((Pr,Nd,Sm)αLn1―α)1−βMgβNiγ−δ―εAlδTε
(式中、Lnは、La,Ce,Pm,Eu,Gd,Tb,Dy,Ho,Er,Tm,Yb,Lu,Ca,Sr,Sc,Y,Ti,Zr及びHfよりなる群から選ばれる少なくとも1種を表し、TはV,Nb,Ta,Cr,Mo,Mn,Fe,Co,Zn,Ga,Sn,In,Cu,Si,P及びBよりなる群から選ばれる少なくとも1種を表し、添字α,β,γ,δ,εは、それぞれ、0.7<α,0.05<β<0.15,3.0≦γ≦4.2,0.15≦δ≦0.30,0≦ε≦0.50を満たす数を表す)で示される組成を有し、
前記第1の水素吸蔵合金の水素平衡圧をP1とし、前記第2の水素吸蔵金の水素平衡圧をP2とし、水素平衡圧差ΔPをΔP=log10(P1/P2)としたときに、P1>P2且つΔP≧0.3である
ことを特徴とするアルカリ二次電池。
In an alkaline secondary battery including a positive electrode, a negative electrode including a rare earth-Mg-Ni-based hydrogen storage alloy, a separator, and an electrolyte solution,
The negative electrode includes at least a first hydrogen storage alloy and a second hydrogen storage alloy having different hydrogen equilibrium pressures as the rare earth-Mg—Ni-based hydrogen storage alloy,
The ratio of the mass of the first hydrogen storage alloy to the total mass of the rare earth-Mg—Ni hydrogen storage alloy contained in the negative electrode is 50% or more and 90% or less, and the ratio of the mass of the second hydrogen storage alloy Is 10% or more and 50% or less,
The first hydrogen storage alloy has the general formula:
((Pr, Nd, Sm) α Ln 1-α ) 1-β Mg β Ni γ-δ-ε Al δ T ε
(Wherein Ln is selected from the group consisting of La, Ce, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ca, Sr, Sc, Y, Ti, Zr and Hf. T represents at least one selected from the group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Zn, Ga, Sn, In, Cu, Si, P and B. Subscripts α, β, γ, δ, and ε represent numbers satisfying 0.7 <α, 0.05 <β <0.15, 3.0 ≦ γ ≦ 4.2, 0.15 ≦ δ ≦ 0.30, and 0 ≦ ε ≦ 0.50, respectively. Having a composition
When the hydrogen equilibrium pressure of the first hydrogen storage alloy is P1, the hydrogen equilibrium pressure of the second hydrogen storage gold is P2, and the hydrogen equilibrium pressure difference ΔP is ΔP = log 10 (P1 / P2), P1 > Alkaline secondary battery, wherein P2 and ΔP ≧ 0.3.
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