JP4601754B2 - Hydrogen storage alloy electrode and manufacturing method thereof - Google Patents

Description

【００４０】
【表２】

【００４１】
表１および２から明らかなように、比較例は、最大放電容量が小さく、容量劣化も激しい。一方、実施例は、いずれも４５０ｍＡｈ／ｇ以上の高い放電容量を有し、容量劣化率も１０％以内であり、優れた特性を有している。
【００４２】
《実施例１》
本実施例ではＦｅおよびＳｉの添加が電池の高温保存特性に与える影響を検討した。
表３に示した組成の合金粉末を上述の（１）の方法で製造した。
次に、《参考例１》と同様の方法で前記合金粉末粒子の表層部にＴｉ−Ｎｉ系合金相を形成し、粒子状活物質とした。
得られた粒子状活物質を用いて上述の（５）に基づいて密閉電池を作製し、上述の（６）に基づいて高温保存後の容量維持率を求めた。結果を表３に示す。
【００４３】
【表３】

【００４４】
表３から明らかなように、ＦｅおよびＳｉを添加した合金からなる試料（２−４）〜（２−６）を用いた電池の容量維持率が高く、高温保存特性が優れている。また、Ｆｅの量が増加すると容量維持率は上昇しているが、Ｓｉの添加がない場合には逆に低下している。
なお、ＦｅとＳｉの合計量が０．２を超えると、ＴｉＦｅ系の第２相の析出が始まり、０．３を超えると容量の低下が顕著であった。以上の結果から、合金にＦｅおよびＳｉを少量含有させることにより、高温保存特性を改善できることがわかる。
【００４５】
《参考例２》
本参考例では、Ｔｉ−Ｎｉ系合金相を有する表層部の形成方法を検討した。
上述の（１）の方法で製造したＴｉ_0.5Ｍｏ_0.05Ｎｂ_0.05Ｃｒ_0.39Ｌａ_0.01で示される組成の合金粉末粒子の表層部にＴｉ−Ｎｉ系合金相を形成し、粒子状活物質とした。
【００４６】
Ｔｉ−Ｎｉ系合金相の形成に用いた方法は以下の通りである。
試料（３−１）〜（３−５）：上述の（３）の方法１に基づいてＴｉ−Ｎｉ系合金相を形成した。ただし、試料（３−１）はＮｉメッキ後の熱処理を行わず、試料（３−２）〜（３−５）は、減圧雰囲気で表４にそれぞれ示した所定の温度で所定の時間熱処理した。
試料（３−６）および（３−７）：上述の（３）の方法２に基づいてＴｉ−Ｎｉ系合金相を形成した。ただし、試料（３−６）は合金粒子の表面にＮｉ粉末を被着させた後の熱処理を行わず、試料（３−７）のみ減圧雰囲気で６００℃で６時間熱処理を行った。
試料（３−８）：上述の（３）の方法３に基づいてＴｉ−Ｎｉ系合金相を形成した。
試料（３−９）〜（３−１４）：上述の（３）の方法４に基づいてＴｉ−Ｎｉ系合金相を形成した。ただし、試料（３−９）については、ニッケルカルボニル６０％および一酸化炭素４０％からなるガスを熱分解させた。また、試料（３−１０）〜（３−１４）については、ニッケルカルボニル５０％、一酸化炭素４５％および鉄カルボニル、クロムカルボニル、モリブデンカルボニルまたはタングステンカルボニル５％からなるガスを、それぞれ同条件で熱分解させた。また、試料（３−１４）については、先にモリブデンカルボニル６０％および一酸化炭素４０％からなるガスを熱分解させて合金粒子の表面にＭｏを被着させた後に、ニッケルカルボニル６０％および一酸化炭素４０％からなるガスを熱分解させた。ここで、ニッケル以外の金属元素はＮｉに対して１０重量％被着させた。
【００４７】
得られた粒子状活物質の電極特性を上述の（４）に基づいて測定した。電極の最大放電容量および充放電５０サイクル後の容量劣化率を表４に示す。
【００４８】
【表４】

【００４９】
表４から明らかなように、表面にＮｉを付与したのみの試料（３−１）および（３−６）は、合金粒子の表層部にＴｉ−Ｎｉ系合金相が形成されていないため、高い放電容量が得られていない。一方、これらの試料に熱処理（試料（３−２）〜（３−５）、（３−７））や機械的な力を加える処理（試料（３−８））を行った場合、合金粒子の表層部にＴｉ−Ｎｉ系合金相が形成されるため、高い放電容量が得られており、容量劣化率も低くなっている。
【００５０】
例えば試料（３−３）と（３−７）の比較からは、方法１が方法２よりも優れていることがわかる。これは、メッキ法を用いる方法１では、Ｎｉが合金粒子の表面を緻密に覆うためと考えられる。ニッケルカルボニルの熱分解によりＮｉを被着させた試料（３−９）や（３−１４）も優れた特性を示している。特に、Ｆｅ、Ｃｒ、ＭｏまたはＷをＮｉとともに被着した試料はさらに容量劣化率が改善されている。
【００５１】
試料（３−２）〜（３−５）の比較からは、Ｎｉメッキ後の熱処理温度を５００〜１０００℃とすることが好ましいことがわかる。熱処理温度が５００℃未満である試料（３−２）および１０００℃を超える試料（３−５）は、放電容量が不充分である。これは、加熱温度が５００℃より低くなると、Ｎｉの拡散が不充分となり、１０００℃を超えると、加熱時間を短くしたとしてもＮｉの拡散が進みすぎ、Ｔｉ−Ｎｉ系合金相におけるＴｉ₂Ｎｉの比率が増大するためと考えられる。
なお、熱処理後の試料のＸ線回折を調べたところ、Ｔｉ−Ｎｉ系合金相中のＴｉＮｉのメインピーク比が７０％以下になる、すなわちＴｉ−Ｎｉ系合金相中のＴｉＮｉが７０体積％以下になると、放電容量が減少し、容量劣化率が高くなることがわかった。
【００５２】
試料（３−３）、（３−４）および（３−７）〜（３−１４）の粒子状活物質の断面をＳＥＭおよびＥＰＭＡにより観察した。その結果、Ｎｉの濃度は表面から内部に向かって徐々に減少していることがわかった。また、全てのＮｉの９０％が粒子表面から深さ２μｍまでに存在していることがわかった。
【００５３】
《参考例３》
本参考例では、Ｔｉ−Ｎｉ系合金相を形成する前の熱処理の効果を検討した。
上述の（１）の方法でＴｉ_0.5Ｍｏ_0.05Ｎｂ_0.05Ｃｒ_0.39Ｌａ_0.01で示される組成の合金粉末を製造し、試料（４−１）以外は表５に示した所定の温度で２時間熱処理した。その他は試料（３−３）と同様にして粒子状活物質を得、同様に評価した。結果を表５に示す。
【００５４】
【表５】

【００５５】
表５から明らかなように、Ｎｉを拡散させる前に熱処理を行った試料（４−２）および（４−３）は、熱処理を行わなかった試料（４−１）に比べて放電容量が高くなっている。また、１３００℃で熱処理した試料（４−３）が最も高い放電容量を示している。熱処理温度が１５００℃になると、合金が一部溶解するという問題が生じた。
各試料のＸ線回折を調べたところ、試料（４−１）や熱処理温度が低かった試料（４−２）には偏析相のピークが見られるのに対し、試料（４−３）では組織が均質化していることが確認できた。そのため、水素吸蔵量が増大し、放電容量が増加したと考えられる。
したがって、１３００℃を中心とする１２００〜１４００℃で熱処理を行うことが高い放電容量を得るうえで好ましいことがわかる。
【００５６】
《参考例４》
本参考例では、電極を作製する際の合金粒子の粒径の検討を行った。
上述の（１）の方法でＴｉ_0.5Ｍｏ_0.05Ｎｂ_0.05Ｃｒ_0.39Ｌａ_0.01で示される組成の合金粉末を製造した。本参考例では、それぞれ７５μｍ、４０μｍおよび１５μｍのメッシュサイズで分級した合金粉末を用いた。その他は試料（３−３）と同様にして粒子状活物質を得、同様に評価した。結果を表６に示す。
【００５７】
【表６】

【００５８】
表６から明らかなように、４０μｍを超える粒径の合金粒子を含有する合金粉末を用いた試料（５−２）は、放電容量がやや低く、容量劣化率がやや高くなっている。一方、粒径が４０μｍ以下の合金粉末を用いた試料（５−１）および（５−３）は、優れた特性を示している。これは、粒径が４０μｍを超えると、Ｎｉで覆われる面積が小さくなるうえに、充放電中に大きな粒子の微粉化が進み、Ｎｉで覆われていない面が発生するからと考えられる。粒径が４０μｍ以下の合金粉末であれば、ほぼ同等の特性が得られると考えられる。しかし、粒径が１５μｍ未満になると、比表面積が大きくなり、酸化の影響を受けて放電容量が低下し、Ｎｉの拡散層が薄くなって耐食性も低下する。そのため試料（５−３）は若干特性が低下したものと考えられる。
【００５９】
【発明の効果】
本発明によれば、従来に比べ、高い放電容量と優れたサイクル特性を有する水素吸蔵合金電極を得ることができる。したがって、この電極を用いれば、従来に比べて高容量なニッケル水素蓄電池を得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydrogen storage alloy electrode using a hydrogen storage alloy capable of reversibly storing and releasing electrochemical hydrogen as an active material, and a method for producing the same.
[0002]
[Prior art]
An electrode using a hydrogen storage alloy capable of reversibly absorbing and releasing hydrogen as an active material has a theoretical capacity density larger than that of a cadmium electrode, and deformation and dendrite formation unlike a zinc electrode do not occur. Therefore, future development is expected as a negative electrode for alkaline storage batteries having a long life and no pollution, and having a high energy density.
[0003]
An alloy used for the hydrogen storage alloy electrode is usually manufactured by an arc melting method, a high frequency induction heating melting method, or the like. At present, the hydrogen storage alloy in practical use as an electrode is a La (or Mm: mixture of rare earth elements (Misch metal))-Ni-based multi-component alloy. This is AB_FiveType (A: element having high affinity with hydrogen such as La, Zr and Ti, B: element having low affinity with hydrogen such as transition elements such as Ni, Mn and Cr).
[0004]
Also AB_FiveAs an alloy having a larger hydrogen storage capacity than the type, there is a Ti-V-based hydrogen storage alloy. For example, Ti_xV_yNi_zA hydrogen storage alloy electrode using an alloy has been proposed in JP-A-6-228699, JP-A-7-268513, JP-A-7-268514, and the like.
[0005]
[Problems to be solved by the invention]
However, La (or Mm) -Ni based multi-component alloys almost use the theoretical capacity, and no significant increase in capacity in the future can be expected.
Further, when a Ti-V-based hydrogen storage alloy is used for the electrode, the discharge capacity is higher than that of a La (or Mm) -Ni-based multi-component alloy, but the discharge capacity is lower than its theoretical discharge capacity. There is a problem. Furthermore, there are problems of improvement in cycle characteristics and cost reduction.
[0006]
[Means for Solving the Problems]
  The present invention relates to the general formula Ti_aM¹ _bCr_cM² _dL_e Fe _f Si _g (M¹Is at least one element selected from the group consisting of Nb and Mo, M²Is Mn, Co, Cu, Zn, Zr, Ag, Hf, Ta, W, Al, C, N, P and B, at least one element selected from the group consisting of N, P and B, L is at least one element selected from the group consisting of rare earth elements and Y, 0.2 ≦ a ≦ 0.7, 01 ≦ b ≦ 0.4, 0.1 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.3, 0 ≦ e ≦ 0.03,0.003 ≦ f <0.2, 0 <g ≦ 0.1, d + f + g ≦ 0.2,a + b + c + d + e+ F + g= 1.0), which is a hydrogen storage alloy having a body-centered cubic or body-centered tetragonal crystal structure, and has a Ti—Ni alloy phase in the surface layer portion.70% by volume or more of the Ti—Ni alloy phase has a TiNi body-centered cubic crystal structure.The present invention relates to a hydrogen storage alloy electrode made of a particulate active material.
[0007]
  Preferred among the hydrogen storage alloys are 0.4 ≦ a ≦ 0.64, 0.05 ≦ b ≦ 0.2, 0.3 ≦ c ≦ 0.4, 0 ≦ d ≦ 0.2, 0 ≦ e ≦ 0.03Fulfill.
[0008]
  here,in frontIt is preferable that the Ni concentration of the particulate active material is gradually decreased from the particle surface toward the inside. The particle active material preferably has a particle size of 40 μm or less.
[0009]
  In addition, the present invention provides (A) a step of plating Ni on the surface of the hydrogen storage alloy powder, a step of depositing Ni powder, or a mixture of the hydrogen storage alloy powder with a nickel carbonyl-containing gas and thermally decomposing the gas to form an alloy. A method for producing a hydrogen storage alloy electrode comprising the steps of depositing Ni on the surface of the powder, and (B) thereafter heating the alloy powder at 500 to 1000 ° C. in an inert gas, hydrogen gas or a reduced pressure atmosphere. The hydrogen storage alloy as a raw material is represented by the general formula Ti_aM¹ _bCr_cM² _dL_e Fe _f Si _g (M¹Is at least one element selected from the group consisting of Nb and Mo, M²Is Mn, Co, Cu, Zn, Zr, Ag, Hf, Ta, W, Al, C, N, P and B, at least one element selected from the group consisting of N, P and B, L is at least one element selected from the group consisting of rare earth elements and Y, 0.2 ≦ a ≦ 0.7, 01 ≦ b ≦ 0.4, 0.1 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.3, 0 ≦ e ≦ 0.03,0.003 ≦ f <0.2, 0 <g ≦ 0.1, d + f + g ≦ 0.2,a + b + c + d + e+ F + g= 1.0) and has a body-centered cubic or body-centered tetragonal crystal structure.
[0010]
The nickel carbonyl-containing gas is preferably composed of 20 to 90% nickel carbonyl and 10 to 80% carbon monoxide by volume percentage. Alternatively, the nickel carbonyl-containing gas may be, by volume percentage, nickel carbonyl 20 to 85%, carbon monoxide 10 to 75%, and at least one selected from the group consisting of iron carbonyl, chromium carbonyl, molybdenum carbonyl, and tungsten carbonyl 5 to 5%. It is preferable to contain 50%.
Further, before the step (A), (X) the hydrogen storage alloy powder is at least one selected from the group consisting of iron carbonyl, chromium carbonyl, molybdenum carbonyl and tungsten carbonyl in a volume percentage of 20 to 90%. And a step of adhering at least one selected from the group consisting of iron, chromium, molybdenum and tungsten on the surface of the alloy powder by mixing with a source gas composed of 10 to 80% carbon monoxide and thermally decomposing the gas. Preferably it is done.
Moreover, it is preferable to perform the said process (A) or (X) after heating the said hydrogen storage alloy powder by 1200-1400 degreeC by inert gas, hydrogen gas, or pressure reduction atmosphere previously.
[0011]
  The present invention further relates to a method for producing a hydrogen storage alloy electrode comprising a step of performing a mechanochemical reaction between a hydrogen storage alloy powder and Ni, wherein the hydrogen storage alloy is represented by the general formula Ti._aM¹ _bCr_cM² _dL_e Fe _f Si _g (M¹Is at least one element selected from the group consisting of Nb and Mo, M²Is Mn, Co, Cu, Zn, Zr, Ag, Hf, Ta, W, Al, C, N, P and B, at least one element selected from the group consisting of N, P and B, L is at least one element selected from the group consisting of rare earth elements and Y, 0.2 ≦ a ≦ 0.7, 01 ≦ b ≦ 0.4, 0.1 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.3, 0 ≦ e ≦ 0.03,0.003 ≦ f <0.2, 0 <g ≦ 0.1, d + f + g ≦ 0.2,a + b + c + d + e+ F + g= 1.0) and has a body-centered cubic or body-centered tetragonal crystal structure.
  The hydrogen storage alloy powder is also preferably subjected to a mechanochemical reaction after heating at 1200 to 1400 ° C. in an inert gas, hydrogen gas or a reduced pressure atmosphere in advance.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The particulate active material according to the present invention is an improvement of a conventional hydrogen storage alloy powder having a body-centered cubic crystal structure. That is, a Ti—Ni-based alloy phase is formed on the surface layer portion of hydrogen storage alloy particles having a body-centered cubic or body-centered tetragonal crystal structure that does not contain Ni. When the particulate matter having such a structure is used, the hydrogen storage amount and the discharge capacity are increased, the corrosion resistance of the alloy is improved, and a long-life electrode can be obtained.
[0013]
(1) First, the composition of the hydrogen storage alloy before the Ti—Ni alloy phase is formed on the surface layer will be described.
  The hydrogen storage alloy has the general formula Ti_aM¹ _bCr_cM² _dL_e Fe _f Si _g (M¹Is at least one element selected from the group consisting of Nb and Mo, M²Is Mn, Co, Cu, Zn, Zr, Ag, Hf, Ta, W, Al, C, N, P and B, at least one element selected from the group consisting of N, P and B, L is at least one element selected from the group consisting of rare earth elements and Y, 0.2 ≦ a ≦ 0.7, 01 ≦ b ≦ 0.4, 0.1 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.3, 0 ≦ e ≦ 0.03,0.003 ≦ f <0.2, 0 <g ≦ 0.1, d + f + g ≦ 0.2,a + b + c + d + e+ F + g= 1.0).
[0014]
The reason why the hydrogen storage alloy does not contain Ni is that when Ni is dissolved at the same time, a segregation phase containing Ni with a small amount of hydrogen storage is formed in the entire alloy, and the hydrogen storage amount decreases. At this time, a small amount of Ni is dissolved in the main phase, leading to an increase in plateau pressure (hydrogen equilibrium pressure) and a decrease in hydrogen storage amount. Therefore, the amount of hydrogen occlusion increases by removing Ni from the basic composition. Note that the Ti-Ni alloy phase formed by diffusing Ni into the surface layer portion by a method described later does not form the segregation phase, and only the effect of improving the corrosion resistance and electrode characteristics of the surface layer portion is considered to be obtained. It is done.
[0015]
The hydrogen storage alloy contains Ti because Ti has a large atomic radius, the lattice size of the alloy increases, the plateau pressure decreases, and the hydrogen storage amount increases. In addition, when Ti is present, the reaction easily proceeds at a lower temperature even when Ni is diffused from the surface of the alloy particles to form a Ti—Ni alloy phase. When the amount of Ti in the alloy, that is, a in the above general formula becomes 0.2 or more, the increase in the hydrogen storage amount is significant. On the other hand, when a exceeds 0.7, hydrogen is stabilized in the alloy and is not easily released, and the occlusion amount is reduced. However, it is desirable to satisfy 0.4 ≦ a ≦ 0.64 in order to keep the plateau pressure at 0.01 to 0.1 MPa, which is considered optimal for battery applications. When the plateau pressure is less than 0.01 MPa, the output characteristics of the battery tend to decrease, and when it exceeds 0.1 MPa, the rapid charge characteristics tend to decrease.
[0016]
M¹That is, Mo and Nb also have a large atomic radius like Ti, which contributes to an increase in the lattice size of the alloy. Moreover, these elements have an effect of improving the cycle life of the electrode. This is presumably because Ti passivation is suppressed. The effects of both elements are almost the same. In order to obtain the effect of the present invention, b in the above general formula should be 0.01 ≦ b ≦ 0.4, but in order to keep the plateau pressure in the optimum range for the battery application, 0.05 ≦ b ≦ 0.2 is desirable.
[0017]
The reason why the alloy contains Cr is to facilitate activation of the alloy and to provide corrosion resistance in an alkaline electrolyte. In order to obtain these effects, the amount of Cr, that is, c in the above general formula needs to be 0.1 or more. However, Cr also has the effect of increasing the plateau pressure of the alloy and reducing the hydrogen storage capacity. Therefore, c needs to be 0.7 or less. Further, in order to keep the plateau pressure in the optimum range for the battery application, 0.3 ≦ c ≦ 0.4 is desirable.
[0018]
The reason why the alloy contains a small amount of rare earth elements such as La and Ce or Y is because the hydrogen storage amount further increases. This is presumably because these elements serve as oxygen scavengers to remove impurity oxygen from the alloy. Since these elements precipitate as the second phase and are hardly contained in the matrix phase, they hardly affect the composition of the matrix phase, and can increase only the hydrogen storage amount without changing the plateau pressure or the like. Even if the amount of the element L exceeds 3 atomic% in the alloy, no further improvement in the effect is recognized. Therefore, e in the general formula is 0 ≦ e ≦ 0.03.
[0019]
  In addition to the above elements, the alloy includes Mn, Co, Cu, Zn, Zr, Ag, Hf, Ta, W, Al, C, N, P or B can be included as required. By including one or more of these elements, the lattice size of the alloy can be changed according to the atomic radius, the plateau pressure can be controlled, and the hydrogen storage amount can be increased. In particular, Mn, Ta, and Al have an effect of increasing the hydrogen storage amount, and Fe, Co, Cu, Zn, Zr, Ag, Hf, W, Si, N, P, and B increase the electrode activity and discharge. It has the effect of improving capacity and cycle life. Element M², I.e., d in the above general formula must be 0.3 or less. The reason is that when it exceeds 0.3, phases other than the body-centered cubic crystal structure are precipitated, and conversely, the hydrogen storage amount decreases. Moreover, it is preferable that 0 ≦ d ≦ 0.2.
[0020]
FWhen both e and Si are included, that is, the alloy has the general formula Ti_aM¹ _bCr_cM² _dL_eFe_fSi_gIn this case, a battery having excellent high-temperature storage characteristics can be obtained. This is presumably because the pulverization of the alloy is suppressed or the oxide film containing Fe and Si formed on the alloy surface suppresses the dissolution of the alloy during high temperature storage.
  Here, in order to sufficiently improve the high temperature storage characteristics of the battery, it is desirable to satisfy 0.003 ≦ f <0.2, 0 <g ≦ 0.1, d + f + g ≦ 0.2, and a + b + c + d + e + f + g = 1.0. .
[0021]
(2) Next, formation of the Ti—Ni alloy phase will be described.
In the present invention, from the viewpoint of giving the hydrogen storage alloy particularly excellent hydrogen storage ability and catalytic ability for electrochemically storing and releasing hydrogen, a Ti—Ni alloy phase is formed on the surface layer portion of the alloy particles. Form. At that time, Ni atoms are diffused from the surface of the alloy particles to form a Ti—Ni-based alloy phase in the surface layer portion. Note that simply depositing Ni on the surface of the alloy particles reduces the capacity and the hydrogen diffusion rate.
[0022]
  The Ti—Ni alloy phase is, for example, Ti₂Ni, TiNi, TiNi_ThreeEtc. In addition, the Ti-Ni alloy phase has a structure in which alloy constituent elements such as Cr and Mo are incorporated in addition to Ti, so that a good balance of catalytic ability, corrosion resistance, and hydrogen storage capacity is obtained, and an excellent electrode is obtained. It is done. Among these, an alloy phase having the same body-centered cubic crystal structure as TiNi is preferable in terms of a good balance of electrode activity, corrosion resistance, and hydrogen storage characteristics. Therefore, 70 volume% or more of the Ti—Ni alloy phase has the same body-centered cubic crystal structure as TiNi.TheThe content of the same body-centered cubic crystal structure as TiNi can be determined by, for example, X-ray diffraction.
[0023]
The amount of Ni to be added is preferably 5 to 15% by weight with respect to the hydrogen storage alloy because the balance of catalytic ability, corrosion resistance, and hydrogen storage amount is good. In addition, it is preferable that the concentration of Ni is gradually decreased from the surface of the alloy particle toward the inside from the viewpoint that the familiarity between the surface layer portion and the inside is good, and it becomes an active material having high resistance to the charge / discharge cycle. . Furthermore, it is preferable that 90% or more of all Ni is present at a depth of 0.5 to 3 μm, more preferably 1 to 2 μm from the surface of the alloy particles. As a method for obtaining such a structure, (A) a step of plating Ni on the surface of the hydrogen storage alloy powder (plating method), a step of depositing Ni powder (powder method), or a hydrogen storage alloy powder containing nickel carbonyl Mixing with gas, thermally decomposing the gas to deposit Ni on the surface of the alloy powder (vapor phase method), and (B) thereafter heating the alloy powder in an inert gas, hydrogen gas or a reduced pressure atmosphere Is suitable. In the gas phase method, the gas may be thermally decomposed at a temperature of about 300 ° C., for example.
Further, a method of physically diffusing Ni may be used, for example, mechanical alloying using a planetary ball mill or the like, for example, a step of performing a mechanochemical reaction between the hydrogen storage alloy powder and Ni.
[0024]
The heating temperature in the heating step (B) is preferably 500 to 1000 ° C, more preferably 550 to 700 ° C. When the heating temperature is lower than 500 ° C., Ni diffusion does not proceed. On the other hand, when it exceeds 1000 ° C., Ni diffuses further to the inside, and the hydrogen storage amount decreases, and Ti in the surface layer portion is reduced.₂The amount of Ni increases and the electrode characteristics deteriorate. Moreover, although heating time changes with heating temperature, it is about 3 to 48 hours. For example, when nickel is deposited by a plating method, it is preferably heated at 600 to 700 ° C. for 3 to 24 hours.
[0025]
When nickel is deposited by the vapor phase method, the nickel carbonyl-containing gas is preferably composed of 20 to 90% nickel carbonyl and 10 to 80% carbon monoxide by volume percentage.
Further, before the step (A), (X) at least one selected from the group consisting of iron carbonyl, chromium carbonyl, molybdenum carbonyl and tungsten carbonyl, 20% to 90%, and (X) the hydrogen storage alloy powder and It may be mixed with a source gas composed of 10 to 80% carbon monoxide, and the gas may be thermally decomposed to deposit at least one selected from the group consisting of iron, chromium, molybdenum and tungsten on the surface of the alloy powder. . By depositing these metals in advance and then depositing Ni thereon, the Ni concentration on the particle surface can be increased, and the electrode characteristics can be further improved. The amount of these elements is preferably 5 to 50% in the total of the number of moles of these elements and the number of moles of Ni.
[0026]
Alternatively, a gas containing, by volume percentage, nickel carbonyl 20 to 85%, carbon monoxide 10 to 75%, and at least one selected from the group consisting of iron carbonyl, chromium carbonyl, molybdenum carbonyl and tungsten carbonyl 5 to 50%. It may be used. In this case, iron, chromium, molybdenum or tungsten is deposited on the surface of the alloy particles simultaneously with Ni. In this way, iron, chromium, molybdenum or tungsten is taken into the TiNi phase, and further excellent characteristics can be obtained.
[0027]
The hydrogen storage alloy powder is heated in advance at 1200 to 1400 ° C. for 2 to 12 hours in an inert gas, hydrogen gas or reduced pressure atmosphere before forming the Ti—Ni-based alloy phase in the surface layer portion, ) Or (X) or a mechanochemical reaction is preferably performed. This is because if this pretreatment is performed, it becomes easier to obtain a single-phase alloy having a body-centered cubic crystal structure, and a higher discharge capacity can be obtained.
[0028]
The particle size of the active material completed by forming a Ti—Ni-based alloy phase in the surface layer is preferably 40 μm or less, and more preferably 30 μm or less. When the particle diameter exceeds 40 μm, pulverization proceeds in the process of occlusion / release of hydrogen, the ratio of the surface provided with the Ni diffusion layer decreases, and the electrode characteristics deteriorate.
[0029]
In addition, in an alloy containing Fe, by using an Fe—Mo alloy as a raw material, the melting temperature can be reduced, and a homogeneous alloy is easily obtained.
[0030]
【Example】
Next, the present invention will be described in more detail based on examples.
[0031]
(1) Production of hydrogen storage alloy
The hydrogen storage alloy was manufactured by an arc melting method using commercially available raw materials. The obtained alloy was depressurized at 200 ° C. for 1 hour, and then hydrogen pulverized by applying 50 atm hydrogen to occlude hydrogen, and further repeating the cycle of releasing hydrogen under reduced pressure for 5 hours three times. Thereafter, mechanical pulverization was further performed to classify to a desired particle size. The alloy powder used below has a particle size of 40 μm or less unless otherwise specified.
[0032]
(2) Characteristics of hydrogen storage alloy
The hydrogen storage characteristics of the alloy powder were measured using a Siebelz apparatus. The measurement was performed at 25 ° C., and the hydrogen equilibrium pressure (plateau pressure) of the plateau portion during hydrogen storage was determined.
[0033]
(3) Formation of Ti-Ni alloy phase
A Ti—Ni-based alloy phase was formed on the surface layer portion of the alloy particles by the following method to obtain a particulate active material. Here, 10% by weight of Ni was diffused with respect to the hydrogen storage alloy.
Method 1
The surface of the alloy powder particles was cleaned with 2% hydrofluoric acid, placed in an electroless plating bath, and allowed to stand for 30 minutes with stirring at 50 ° C. Here, a commercially available Ni electroless plating solution (Schumer S-780 (trade name) manufactured by Nippon Kanisen Co., Ltd.) was used. Thereafter, predetermined heat treatment was performed.
Method 2
The alloy powder and Ni powder having an average particle size of 0.03 μm were mixed to deposit Ni powder on the surface of the alloy powder, and then a predetermined heat treatment was performed.
Method 3
A mechanical alloying method was performed. That is, the alloy powder and Ni powder having an average particle size of 0.03 μm were mixed for 3 hours using a ball mill (P-5 (planetary ball mill) manufactured by Fritsch) to perform a mechanochemical reaction.
Method 4
The alloy powder was mixed with a nickel carbonyl-containing gas, the gas was pyrolyzed at 200 ° C. to deposit Ni on the surface of the powder particles, and then heat-treated at 600 ° C. for 6 hours in a reduced pressure atmosphere.
[0034]
(4) Preparation and evaluation of hydrogen storage alloy electrodes
A hydrogen storage alloy electrode was prepared by mixing 0.1 g of the obtained particulate active material and 0.4 g of Cu powder and pressing the mixture into a pellet. A Ni mesh was pressure-bonded thereto, and a Ni ribbon was welded to obtain a current collector. Using the electrode as a negative electrode, a nickel hydroxide electrode having an excessive electric capacity as a counter electrode, and using a potassium hydroxide aqueous solution with a specific gravity of 1.30 as the electrolyte, the capacity is regulated by the negative electrode under conditions where the electrolyte is abundant. The open system was charged and discharged.
Charging was performed at 100 mA per gram of the hydrogen storage alloy for 12 hours in the first cycle and 6 hours after the second cycle, and discharging was performed at 50 mA per gram of the alloy until the terminal voltage reached 1.0 V, and the charge / discharge cycle was repeated. The capacity deterioration rate was calculated from the following calculation formula.
Capacity degradation rate (%) = {(Amount of decrease in discharge capacity after 50 cycles) / (Maximum discharge capacity)} × 100
[0035]
(5) Fabrication of sealed battery
The particulate active material was mixed and stirred with a dilute aqueous solution of carboxymethylcellulose (CMC) to form a paste, and filled into a foamed nickel sheet having a porosity of 95% and a thickness of 0.8 mm. This was dried at 120 ° C., stretched with a roller press, and further coated with fluororesin powder on the surface to obtain a hydrogen storage alloy electrode.
The electrode was adjusted to have a width of 3.9 cm, a length of 10.5 cm, and a thickness of 0.40 mm. The positive electrode and the separator were layered into three layers, which were spirally stored in an AA size battery case. Lead plates were attached to the positive electrode and the negative electrode, and these were welded to the positive electrode terminal and the negative electrode terminal, respectively. Here, as the positive electrode, a known foamed nickel electrode was used by cutting to a width of 3.9 cm, a length of 70 cm, and a thickness of 0.075 cm. In addition, a nonwoven fabric made of polypropylene with hydrophilicity is used for the separator, and the electrolyte is a solution in which lithium hydroxide is dissolved in a potassium hydroxide aqueous solution having a specific gravity of 1.30 to a concentration of 30 g / L. Using. Then, the battery case was sealed to obtain a sealed battery. The capacity of the battery is regulated by the positive electrode, and the nominal capacity is 1.3 Ah.
[0036]
(6) High temperature storage test
As the initial charge / discharge of the sealed battery, the battery was charged at 25 ° C. and 0.1 C for 15 hours, discharged at 0.2 C, and then left at 50 ° C. for 2 days. Thereafter, charge / discharge was repeated for 5 cycles under the same conditions as the initial charge / discharge, and the capacity was confirmed. The battery after capacity | capacitance confirmation was preserve | saved at 80 degreeC for 3 months, charging / discharging was repeated on the same conditions after that, and the discharge capacity before and behind preservation | save was compared. Specifically, the capacity retention rate of the sealed battery after high temperature storage was calculated from the following formula.
Capacity retention rate (%) = {(discharge capacity after storage) / (discharge capacity before storage)} × 100
[0037]
《referenceExample 1
  In this example, the composition of the hydrogen storage alloy was examined.
  Alloy powders having the compositions shown in Tables 1 and 2 were produced by the method (1) described above. Here, the samples (1-1) to (1-30) are of the present invention.referenceCorresponding to the example, samples (1-31) to (1-36) correspond to comparative examples. As the element L constituting the alloy, La was used unless another element was indicated in the table. Mm represents Misch metal. The plateau pressure of the obtained alloy powder was measured based on the above (2). The results are shown in Tables 1 and 2.
[0038]
Next, a Ti—Ni-based alloy phase was formed on the surface layer portion of the alloy powder particles based on the method 1 of (3) described above to obtain a particulate active material. Here, the heat treatment after Ni plating was performed by heating at 625 ° C. for 6 hours in a reduced pressure atmosphere. The electrode characteristics of the obtained particulate active material were measured based on the above (4). Tables 1 and 2 show the maximum discharge capacity of the electrode and the capacity deterioration rate after 50 cycles of charge and discharge.
[0039]
[Table 1]

[0040]
[Table 2]

[0041]
As is clear from Tables 1 and 2, the comparative example has a small maximum discharge capacity and severe capacity deterioration. On the other hand, each of the examples has a high discharge capacity of 450 mAh / g or more, a capacity deterioration rate of 10% or less, and has excellent characteristics.
[0042]
"Example1》
  In this example, the effect of addition of Fe and Si on the high-temperature storage characteristics of the battery was examined.
  Alloy powders having the compositions shown in Table 3 were produced by the method (1) described above.
  next,"referenceIn the same manner as in Example 1, a Ti—Ni-based alloy phase was formed on the surface layer of the alloy powder particles to obtain a particulate active material.
  Using the obtained particulate active material, a sealed battery was prepared based on the above (5), and the capacity retention rate after high-temperature storage was determined based on the above (6). The results are shown in Table 3.
[0043]
[Table 3]

[0044]
As is apparent from Table 3, the capacity retention rate of the battery using the samples (2-4) to (2-6) made of the alloy added with Fe and Si is high, and the high-temperature storage characteristics are excellent. In addition, the capacity retention rate increases as the amount of Fe increases, but decreases in the absence of Si addition.
In addition, when the total amount of Fe and Si exceeded 0.2, precipitation of the TiFe-based second phase started, and when it exceeded 0.3, the capacity was significantly reduced. From the above results, it can be seen that the high temperature storage characteristics can be improved by adding a small amount of Fe and Si to the alloy.
[0045]
《referenceExample2》
  BookreferenceIn the example, a method for forming a surface layer portion having a Ti—Ni alloy phase was examined.
  Ti produced by the method (1) above_0.5Mo_0.05Nb_0.05Cr_0.39La_0.01A Ti—Ni-based alloy phase was formed on the surface layer portion of the alloy powder particles having the composition shown in FIG.
[0046]
The method used for forming the Ti—Ni alloy phase is as follows.
Samples (3-1) to (3-5): Ti—Ni-based alloy phases were formed based on the method 1 of (3) described above. However, the sample (3-1) was not heat-treated after Ni plating, and the samples (3-2) to (3-5) were heat-treated at a predetermined temperature shown in Table 4 for a predetermined time in a reduced pressure atmosphere. .
Samples (3-6) and (3-7): Ti—Ni-based alloy phases were formed based on the method 2 of (3) described above. However, sample (3-6) was not heat-treated after Ni powder was deposited on the surface of the alloy particles, and only sample (3-7) was heat-treated at 600 ° C. for 6 hours in a reduced-pressure atmosphere.
Sample (3-8): A Ti—Ni-based alloy phase was formed based on Method 3 of (3) above.
Samples (3-9) to (3-14): Ti—Ni-based alloy phases were formed based on the method 4 of (3) described above. However, for sample (3-9), a gas composed of 60% nickel carbonyl and 40% carbon monoxide was thermally decomposed. For samples (3-10) to (3-14), a gas composed of 50% nickel carbonyl, 45% carbon monoxide and 5% iron carbonyl, chromium carbonyl, molybdenum carbonyl or tungsten carbonyl was used under the same conditions. Thermally decomposed. For sample (3-14), a gas composed of 60% molybdenum carbonyl and 40% carbon monoxide was first pyrolyzed to deposit Mo on the surface of the alloy particles, and then 60% nickel carbonyl and one carbon monoxide were deposited. A gas composed of 40% carbon oxide was pyrolyzed. Here, the metal elements other than nickel were deposited at 10% by weight with respect to Ni.
[0047]
The electrode characteristics of the obtained particulate active material were measured based on the above (4). Table 4 shows the maximum discharge capacity of the electrode and the capacity deterioration rate after 50 cycles of charge and discharge.
[0048]
[Table 4]

[0049]
As is clear from Table 4, the samples (3-1) and (3-6) in which Ni was applied to the surface were high because no Ti—Ni-based alloy phase was formed on the surface layer portion of the alloy particles. Discharge capacity is not obtained. On the other hand, when these samples were subjected to heat treatment (samples (3-2) to (3-5), (3-7)) or mechanical force treatment (sample (3-8)), alloy particles Since the Ti—Ni-based alloy phase is formed in the surface layer portion, a high discharge capacity is obtained and the capacity deterioration rate is low.
[0050]
For example, from comparison between samples (3-3) and (3-7), it can be seen that Method 1 is superior to Method 2. This is considered to be because in Method 1 using the plating method, Ni densely covers the surface of the alloy particles. Samples (3-9) and (3-14) coated with Ni by thermal decomposition of nickel carbonyl also show excellent characteristics. In particular, the capacity deterioration rate of the sample in which Fe, Cr, Mo, or W is deposited together with Ni is further improved.
[0051]
From the comparison of samples (3-2) to (3-5), it can be seen that the heat treatment temperature after Ni plating is preferably 500 to 1000 ° C. The sample (3-2) having a heat treatment temperature of less than 500 ° C and the sample (3-5) having a heat treatment temperature exceeding 1000 ° C have insufficient discharge capacity. This is because when the heating temperature is lower than 500 ° C., the diffusion of Ni becomes insufficient, and when it exceeds 1000 ° C., the diffusion of Ni proceeds excessively even if the heating time is shortened, and Ti in the Ti—Ni-based alloy phase₂This is probably because the Ni ratio increases.
When the X-ray diffraction of the heat-treated sample was examined, the main peak ratio of TiNi in the Ti—Ni alloy phase was 70% or less, that is, TiNi in the Ti—Ni alloy phase was 70% by volume or less. It was found that the discharge capacity decreased and the capacity deterioration rate increased.
[0052]
Cross sections of the particulate active materials of Samples (3-3), (3-4), and (3-7) to (3-14) were observed by SEM and EPMA. As a result, it was found that the Ni concentration gradually decreased from the surface toward the inside. It was also found that 90% of all Ni was present from the particle surface to a depth of 2 μm.
[0053]
《referenceExample3》
  BookreferenceIn the example, the effect of heat treatment before forming the Ti—Ni alloy phase was examined.
  Ti by the above method (1)_0.5Mo_0.05Nb_0.05Cr_0.39La_0.01An alloy powder having the composition shown in FIG. 6 was manufactured, and heat treatment was performed for 2 hours at a predetermined temperature shown in Table 5 except for the sample (4-1). Otherwise, a particulate active material was obtained in the same manner as in Sample (3-3) and evaluated in the same manner. The results are shown in Table 5.
[0054]
[Table 5]

[0055]
As is clear from Table 5, the samples (4-2) and (4-3) that were heat-treated before Ni was diffused had a higher discharge capacity than the sample (4-1) that was not heat-treated. It has become. Sample (4-3) heat-treated at 1300 ° C. has the highest discharge capacity. When the heat treatment temperature reached 1500 ° C., there was a problem that the alloy was partially dissolved.
When the X-ray diffraction of each sample was examined, the sample (4-1) and the sample (4-2) having a low heat treatment temperature showed segregation phase peaks, whereas the sample (4-3) had a texture. Was confirmed to be homogenized. Therefore, it is considered that the hydrogen storage amount increased and the discharge capacity increased.
Therefore, it can be seen that heat treatment at 1200 to 1400 ° C. centered at 1300 ° C. is preferable for obtaining a high discharge capacity.
[0056]
《referenceExample4》
  BookreferenceIn the example, the particle size of the alloy particles when producing the electrode was examined.
  Ti by the above method (1)_0.5Mo_0.05Nb_0.05Cr_0.39La_0.01An alloy powder having the composition shown in FIG. BookreferenceIn the examples, alloy powders classified with mesh sizes of 75 μm, 40 μm and 15 μm were used. Otherwise, a particulate active material was obtained in the same manner as in Sample (3-3) and evaluated in the same manner. The results are shown in Table 6.
[0057]
[Table 6]

[0058]
As is clear from Table 6, the sample (5-2) using the alloy powder containing alloy particles having a particle diameter exceeding 40 μm has a slightly low discharge capacity and a slightly high capacity deterioration rate. On the other hand, Samples (5-1) and (5-3) using alloy powder having a particle size of 40 μm or less show excellent characteristics. This is presumably because when the particle size exceeds 40 μm, the area covered with Ni becomes small, and the pulverization of large particles progresses during charging and discharging, and a surface not covered with Ni is generated. It is considered that almost the same characteristics can be obtained if the alloy powder has a particle size of 40 μm or less. However, when the particle size is less than 15 μm, the specific surface area increases, the discharge capacity decreases due to the influence of oxidation, the Ni diffusion layer becomes thin, and the corrosion resistance also decreases. Therefore, it is considered that the characteristics of the sample (5-3) are slightly deteriorated.
[0059]
【The invention's effect】
According to the present invention, it is possible to obtain a hydrogen storage alloy electrode having a high discharge capacity and excellent cycle characteristics as compared with the prior art. Therefore, if this electrode is used, it is possible to obtain a nickel-metal hydride storage battery having a higher capacity than conventional ones.

Claims (10)

Formula ^{_{Ti a M 1 b Cr c M}} 2 d L e Fe f Si g ( M ¹ is at least one element selected from the group consisting of Nb and Mo, M ² is Mn, C o, Cu, Zn , At least one element selected from the group consisting of Zr, Ag, Hf, Ta, W, Al 2 , C 3 , N, P and B, and L is at least one element selected from the group consisting of rare earth elements and Y 0.2 ≦ a ≦ 0.7, 0.01 ≦ b ≦ 0.4, 0.1 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.3, 0 ≦ e ≦ 0.03, 0.003 ≦ f <0.2, 0 <g ≦ 0.1, d + f + g ≦ 0.2, a + b + c + d + e + f + g = 1.0) and a hydrogen storage alloy having a body-centered cubic or body-centered tetragonal crystal structure, and have a Ti-Ni system alloy phase in the surface portion,
Hydrogen storage alloy electrode more than 70% by volume of the TiNi system alloy phase consists particulate active material have a body-centered cubic crystal structure of TiNi. The composition of the hydrogen storage alloy is 0.4 ≦ a ≦ 0.64, 0.05 ≦ b ≦ 0.2, 0.3 ≦ c ≦ 0.4, 0 ≦ d ≦ 0.2, 0 ≦ e ≦ 0. The hydrogen storage alloy electrode according to claim 1, wherein 0.03 is satisfied. The hydrogen storage alloy electrode according to claim 1 or 2 , wherein the Ni concentration of the particulate active material is gradually decreased from the particle surface toward the inside. Hydrogen storage alloy electrode according to any of claims 1 to 3 particle size of the particulate active material is 40μm or less. (A) The step of plating Ni on the surface of the hydrogen storage alloy powder or the step of depositing the Ni powder or the hydrogen storage alloy powder is mixed with a nickel carbonyl-containing gas, and the gas is thermally decomposed to form Ni on the surface of the alloy powder. A method for producing a hydrogen-absorbing alloy electrode, comprising: depositing; and (B) heating the alloy powder at 500 to 1000 ° C. in an inert gas, hydrogen gas or a reduced pressure atmosphere,
At least one element the hydrogen storage alloy as a raw material formula ^{_{Ti a M 1 b Cr c M}} 2 d L e Fe f Si g (M 1 is selected from the group consisting of Nb and Mo, M ² is Mn , Co, Cu, Zn, Zr, Ag, Hf, Ta, W, Al 2 , C 3 , N, P and B, at least one element selected from the group consisting of rare earth elements and Y At least one selected element, 0.2 ≦ a ≦ 0.7, 0.01 ≦ b ≦ 0.4, 0.1 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.3, 0 ≦ e ≦ 0.03, 0.003 ≦ f <0.2, 0 <g ≦ 0.1, d + f + g ≦ 0.2, a + b + c + d + e + f + g = 1.0), and a body-centered cubic or body-centered tetragonal crystal structure A method for producing a hydrogen storage alloy electrode, comprising: The method for producing a hydrogen storage alloy electrode according to claim 5 , wherein the nickel carbonyl-containing gas is composed of 20 to 90% nickel carbonyl and 10 to 80% carbon monoxide by volume percentage. The nickel carbonyl-containing gas is, by volume percentage, nickel carbonyl 20 to 85%, carbon monoxide 10 to 75%, and at least one selected from the group consisting of iron carbonyl, chromium carbonyl, molybdenum carbonyl and tungsten carbonyl 5 to 50%. The method for producing a hydrogen storage alloy electrode according to claim 5, comprising: Prior to the step (A), (X) 20 to 90% of at least one selected from the group consisting of iron carbonyl, chromium carbonyl, molybdenum carbonyl and tungsten carbonyl and carbon monoxide in volume percentage. mixed with a raw material gas consisting of 10% to 80%, claim performing gas is thermally decomposed iron on the surface of the alloy powder, chromium, a step of depositing at least one selected from the group consisting of molybdenum and tungsten 5 The manufacturing method of the hydrogen storage alloy electrode of description. A method of manufacturing a hydrogen-absorbing alloy electrode including a step of performing mechanochemical reaction between hydrogen storage alloy powder and Ni, the general formula Ti _a M ¹ a hydrogen storage alloy ^{_{b Cr c M 2 d L e}} Fe f Si g (M ¹ is at least one element selected from the group consisting of Nb and Mo, M ² is Mn, Co, Cu , Zn, Zr, Ag, Hf, Ta, W, Al, C, N, P and At least one element selected from the group consisting of B, L is at least one element selected from the group consisting of rare earth elements and Y, 0.2 ≦ a ≦ 0.7, 0.01 ≦ b ≦ 0 .4, 0.1 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.3, 0 ≦ e ≦ 0.03, 0.003 ≦ f <0.2, 0 <g ≦ 0.1, d + f + g ≦ 0 .2, a + b + c + d + e + f + g = 1.0), and has a body-centered cubic or body-centered tetragonal crystal structure. A method of manufacturing a hydrogen storage alloy electrode. Advance the hydrogen-absorbing alloy powder, an inert gas, after heating at 1200 to 1400 ° C. in a hydrogen gas or a vacuum atmosphere, wherein step (A) or (X) or claim 5 for mechanochemical reaction, 8 or according 9 Manufacturing method of hydrogen storage alloy electrode.