JP4432285B2 - Nickel electrode active material for alkaline storage battery, nickel electrode for alkaline storage battery and alkaline storage battery - Google Patents

Description

【００１７】
式（ｉ）中、ＸＦｅは硫酸第一鉄アンモニウムの秤量量（ｇ）、Ｖは過マンガン酸カリウム溶液の滴定量（ｍｌ）、ｆは過マンガン酸カリウム溶液のファクター、Ｘｓｐは試料粉末の秤量量（ｇ）である。
【００１８】
次に、試料粉末中に含まれるニッケル量（重量％）を、ＩＣＰ発光分析法や原原子吸光分析法などの方法により定量分析し、次の式（ｉｉ）から水酸化ニッケル中のニッケルの酸化数を算出する。
【００１９】
【数２】

【００２０】
本発明で用いられるコバルト化合物は、それを構成するコバルトの酸化数が２価より大きなものであり、例えばオキシ水酸化コバルトである。このようなコバルト化合物は、コバルト、またはアルカリ蓄電池の電解液として用いられるアルカリ溶液中においてコバルトイオンを溶出可能なコバルト化合物、例えばα型水酸化コバルト、β型水酸化コバルト若しくは一酸化コバルト（以下、便宜上、コバルト化合物前駆体という）を酸化処理すると調製することができる。
【００２１】
ここでの酸化処理は、通常、先ずアルカリ水溶液を調製し、このアルカリ水溶液中にコバルト化合物前駆体を投入する。ここで利用可能なアルカリ水溶液は、特に限定されるものではないが、通常は水酸化カリウムおよび水酸化ナトリウムのうちの少なくとも１つを含むものであり、酸化処理を促進する観点から、温度が６０℃以上に設定されているのが好ましい。
【００２２】
次に、上述のアルカリ水溶液中に酸化剤を添加し、当該水溶液中に含まれるコバルト化合物前駆体を酸化処理する。これにより、コバルト化合物前駆体は、コバルトの酸化数が２価より大きなコバルト化合物（例えば、オキシ水酸化コバルト）に転換される。
【００２３】
なお、ここで用いられる酸化剤は、特に限定されるものではなく、公知の各種のものであるが、酸化力が大きく、コバルト化合物前駆体を効率的に酸化処理することができる点で、ペルオキソ二硫酸カリウム（Ｋ₂Ｓ₂Ｏ₈）、ペルオキソ二硫酸ナトリム（Ｎａ₂Ｓ₂Ｏ₈）、ペルオキソ二硫酸アンモニウム（（ＮＨ₄）₂Ｓ₂Ｏ₈）および次亜塩素酸ナトリウム（ＮａＣｌＯ）からなる群から選択された少なくとも１つを用いるのが好ましい。
【００２４】
なお、酸化剤の添加量は、酸化剤の種類により変化するため一概に特定できるものではないが、コバルト化合物前駆体を所要のコバルト化合物に転換するための十分な量に設定するのが好ましい。
【００２５】
本発明のアルカリ蓄電池用ニッケル電極活物質において、上述のコバルト化合物は、上述の水酸化ニッケル粒子の表面を被覆した状態で含まれていてもよい。このようなコバルト化合物が被覆された水酸化ニッケルは、例えば、公知の方法（例えば、特開昭６２−２３４８６７号公報参照）によりコバルト化合物前駆体が被覆された水酸化ニッケル粒子の群（以下、便宜上、コバルト被覆水酸化ニッケルという）を製造し、このコバルト被覆水酸化ニッケルを酸化処理すると製造することができる。
【００２６】
ここで、コバルト被覆水酸化ニッケルの酸化処理は、通常、上述のコバルト化合物前駆体の酸化処理と同じく、コバルト被覆水酸化ニッケルをアルカリ水溶液中において酸化剤を用いて処理すると実施することができる。すなわち、先ず、アルカリ水溶液を調製し、このアルカリ水溶液中にコバルト被覆水酸化ニッケルを投入する。ここで利用可能なアルカリ水溶液は、特に限定されるものではないが、通常は水酸化カリウムおよび水酸化ナトリウムのうちの少なくとも１つを含むものである。特に、水酸化ナトリウム水溶液を用いた場合は、酸化処理工程において、コバルト被覆水酸化ニッケルの芯層側の水酸化ニッケルがγ―ＮｉＯＯＨに変換するのを抑制することができる。また、アルカリ水溶液は、酸化処理を促進する観点から、温度が６０℃以上に設定されているのが好ましい。
【００２７】
次に、上述のアルカリ水溶液中に酸化剤を添加し、当該水溶液中に含まれるコバルト被覆水酸化ニッケルを酸化処理する。これにより、上記コバルト被覆水酸化ニッケルにおいて芯層の水酸化ニッケルを被覆するコバルト化合物前駆体（表面層）が酸化され、このコバルト化合物前駆体はコバルトの酸化数が２価より大きなコバルト化合物（例えば、オキシ水酸化コバルト）に転換される。
【００２８】
なお、ここで用いられる酸化剤は、上述のものと同様である。また、酸化剤の添加量は、酸化剤の種類により変化するため一概に特定できるものではないが、コバルト被覆水酸化ニッケルの表面層、すなわちコバルト化合物前駆体が所要のコバルト化合物に転換され、しかも芯層側の水酸化ニッケルの酸化数が上述の範囲に止まる範囲に設定するのが好ましい。
【００２９】
本発明で用いられる希土類元素化合物は、イッテルビウム、エルビウム、ルテチウムおよびツリウムからなる元素群から選ばれた少なくとも１つの元素を含み、コバルトのＫα線によるＸ線回折図においてｄ＝０．８８５±０．００８ｎｍ、ｄ＝０．８３８±０．０１ｎｍおよびｄ＝０．７５９±０．００７ｎｍに回折ピークを有するものであり、通常、そのような化合物の粉末である。一例として、イッテルビウムを含む希土類元素化合物のＸ線回折図を図１に示す。なお、この希土類元素化合物は、Ｌｎ（ＯＨ）₃・Ｈ₂ＯまたはＬｎＯＯＨ・２Ｈ₂Ｏで示される結晶水を含む化合物と推定される（化学式中、Ｌｎは希土類元素を示す）。
【００３０】
このような希土類元素化合物は、例えば、イッテルビウム、エルビウム、ルテチウムおよびツリウムからなる元素群から選択された少なくとも１つの元素を含む化合物（原料化合物）を酸化処理すると得られる。
【００３１】
ここで用いられる原料化合物は、通常、上記元素群から選ばれた少なくとも１つの元素を含む酸化物や水酸化物である。すなわち、原料化合物は、通常、上記元素群から選ばれた１つの元素の酸化物や水酸化物、または上記元素群から選ばれた２つ以上の元素の複合酸化物や複合水酸化物である。なお、このような原料化合物は、２種以上のものが適宜併用されてもよい。
【００３２】
目的とする希土類元素化合物は、上述の原料化合物を酸化処理すると得られる。ここで、原料化合物が上述の酸化物若しくは水酸化物の場合、酸化処理は、通常、原料化合物をアルカリ金属水酸化物水溶液中、例えば、水酸化ナトリウムや水酸化カリウムの水溶液中に浸漬して放置すると達成することができる。アルカリ金属水酸化物水溶液の濃度は、通常、２５重量％〜４０重量％に設定するのが好ましい。この酸化処理において、アルカリ金属水酸化物水溶液は、酸化処理を促進するために、適宜加熱してもよい。例えば、６０℃に加熱された６．８規定の水酸化カリウム水溶液中に上述の酸化物や水酸化物を浸漬して放置すると、通常、数時間から数日で目的とする希土類元素化合物が得られる。
【００３３】
上述のような酸化処理方法において、アルカリ金属水酸化物の水溶液中には、例えば、次亜塩素酸ナトリウム（ＮａＣｌＯ）のような酸化剤を添加したり、空気（酸素）を吹き込んでもよい。この場合、原料化合物の酸化処理が促進され、目的とする酸化処理化合物をより速やかに調製することができる。
【００３４】
因みに、イッテルビウム、エルビウム、ルテチウムおよびツリウム以外の希土類元素の酸化物や水酸化物について上述のような酸化処理を施した場合、Ｌｎ（ＯＨ）_３に相当する六方晶（Ｐ６₃／ｍ）の結晶構造を有する水酸化物が得られるが、この水酸化物は上述のような回折ピークを示さない。
【００３５】
なお、上述の希土類元素化合物は、２種以上のものが適宜併用されてもよい。
【００３６】
また、本発明のアルカリ蓄電池用ニッケル電極活物質は、上述の希土類元素化合物に替えて、または上述の希土類元素化合物と共に、ストロンチウム化合物、ビスマス化合物およびイットリウム化合物のうちの少なくとも１つ（以下、便宜上、添加材化合物という）を含んでいてもよい。
【００３７】
ここで用いられるストロンチウム化合物は、コバルトのＫα線によるＸ線回折図の２θ＝５〜８５°の範囲において、ｄ＝０．３５４±０．００２ｎｍおよびｄ＝０．２４８±０．００１ｎｍにそれぞれ第１強度の回折ピークおよび第２強度の回折ピークを有するものである。例えば、図２に示すように、このストロンチウム化合物は、水酸化ストロンチウムのＸ線回折図において特有のｄ＝０．５８５ｎｍ（２θ＝１７．６°）の回折ピークが消失し、ｄ＝０．３５４ｎｍ（２θ＝２９．３°）およびｄ＝０．２４８ｎｍ（２θ＝４２．３°）にそれぞれ第１強度の回折ピークおよび第２強度の回折ピークを有している。
【００３８】
また、ここで用いられるビスマス化合物は、コバルトのＫα線によるＸ線回折図の２θ＝５〜８５°の範囲において、ｄ＝０．３２６±０．００２ｎｍ、ｄ＝０．２６９±０．００１ｎｍおよびｄ＝０．２５６±０．００１ｎｍにそれぞれ第１強度の回折ピーク、第２強度の回折ピークおよび第３強度の回折ピークを有し、ｄ＝０．２６９±０．００１ｎｍの第２強度の回折ピークがｄ＝０．３２６±０．００２ｎｍの第１強度の回折ピークの１／２以上の強度のものである。例えば、図３に示すように、このビスマス化合物は、酸化ビスマスのＸ線回折図において特有のｄ＝０．２９５ｎｍ（２θ＝３５．３°）の回折ピークが消失し、ｄ＝０．３２６ｎｍ（２θ＝３１．９°）、ｄ＝０．２６９ｎｍ（２θ＝３８．８°）およびｄ＝０．２５６ｎｍ（２θ＝４０．９°）にそれぞれ第１強度の回折ピーク、第２強度の回折ピークおよび第３強度の回折ピークを有し、ｄ＝０．２６９ｎｍの第２強度の回折ピークがｄ＝０．３２６ｎｍの第１強度の回折ピークの１／２以上の強度である。
【００３９】
さらに、ここで用いられるイットリウム化合物は、コバルトのＫα線によるＸ線回折図の２θ＝５〜８５°の範囲において、ｄ＝０．５４４±０．００６ｎｍおよびｄ＝０．３１３±０．００２ｎｍに回折ピークを有しており、ｄ＝０．５４４±０．００６ｎｍの回折ピークが当該範囲における最強ピークのものである。例えば、図４に示すように、このイットリウム化合物は、酸化イットリウムや水酸化イットリウムのＸ線回折図において見られないｄ＝０．５４４ｎｍ（２θ＝１８．９°）およびｄ＝０．３１３ｎｍ（２θ＝３３．２°）に回折ピークを有しており、２θ＝５〜８５°の範囲において、ｄ＝０．５４４ｎｍの回折ピークが最強ピークである。
【００４０】
なお、上述の添加材化合物は、上述の希土類元素化合物の場合と同様にして調製することができる。すなわち、これらの化合物は、ストロンチウム、ビスマスまたはイットリウムを含む原料化合物（例えば酸化物や水酸化物）を上述のような方法で酸化処理すると調製することができる。
【００４１】
本発明のニッケル電極活物質は、上述の水酸化ニッケル、コバルト化合物および希土類化合物を混合すると調製することができる。ここで、コバルト化合物の含有量は、通常、水酸化ニッケルの２〜１０重量％に設定されているのが好ましく、３〜７重量％に設定されているのがより好ましい。この含有量が２重量％未満の場合は、水酸化ニッケルに対して所要の導電性ネットワークが形成されにくくなり、アルカリ蓄電池の放電特性、特に高率放電特性が低下する可能性がある。逆に、この含有量が１０重量％を超える場合は、活物質中の水酸化ニッケル量が相対的に少なくなるため、アルカリ蓄電池の小型化を維持しつつ、その容量を高めるのが困難になる。
【００４２】
また、希土類元素化合物の含有量は、通常、水酸化ニッケルの０．５〜８重量％に設定するのが好ましく、２〜８重量％に設定するのがより好ましい。この含有量が０．５重量％未満の場合は、ニッケル電極の酸素発生電位を貴な方向にシフトさせる効果が乏しく、高温環境下におけるアルカリ蓄電池の充電効率を高めるのが困難になる可能性がある。逆に、この含有量が８重量％を超える場合は、それに比例した効果を達成できず不経済であるばかりか、ニッケル電極活物質中における水酸化ニッケル量が相対的に少なくなるため、アルカリ蓄電池の小型化を維持しつつ、その容量を高めるのが困難になる。
【００４３】
なお、本発明の活物質において、上述の希土類元素化合物に替えて上述の添加材化合物を用いる場合、本発明の活物質中におけるその含有量は、希土類元素化合物の場合と同様に設定するのが好ましい。また、本発明の活物質において、上述の希土類元素化合物と共に、上述の添加材化合物を用いる場合、添加材化合物の含有量は、希土類元素化合物との合計量が希土類元素化合物に関する上述の含有量の範囲になるよう設定するのが好ましい。
【００４４】
本発明のアルカリ蓄電池用ニッケル電極は、集電体と、この集電体に配置されれた本発明のニッケル電極活物質とを備えている。このニッケル電極に用いられる集電体は、アルカリ蓄電池用のニッケル電極において利用可能なものであれば特に限定されるものではないが、例えば、穿孔鋼板や発泡基板などである。
【００４５】
このニッケル電極を製造する場合は、先ず、本発明に係る上述の活物質を調製する。そして、この活物質にカルボキシメチルセルロース等のバインダーを加えてスラリーまたはペーストを調製し、このスラリーまたはペーストを集電体に対して塗布または充填することにより配置する。
【００４６】
本発明のアルカリ蓄電池は、電槽と、当該電槽内に収容された上述のようなニッケル電極、すなわち正極、負極および正極と負極との間に配置されたセパレータと、電槽内に注入された電解液とを主に備えている。
【００４７】
ここで用いられる負極は、ニッケル電極を正極とするアルカリ蓄電池において用いられるものであれば特に限定されるものではなく、通常、水素吸蔵合金電極、カドミウム電極または亜鉛電極である。因みに、負極として水素吸蔵合金電極を用いる場合、水素吸蔵合金としてはＣａＣｕ₅型構造を有するＭｍＮｉ_3.55Ｃｏ_0.75Ｍｎ_0.4Ａｌ_0.3の組成で示される合金、ＭｍＮｉ_５合金のニッケルの一部をアルミニウム、マンガン、コバルト、チタン、銅および亜鉛のうちの少なくとも１つで置換した多元素系合金、ＴｉＮｉ系合金およびＴｉＦｅ系合金等を用いることができる。なお、Ｍｍは希土類元素の混合物（通常はランタン、セリウム、プラセオジムおよびネオジウムの混合物）を意味している。
【００４８】
セパレータは、正極と負極との短絡を防止すると共に電解液を保持するためのものであり、アルカリ蓄電池において利用可能なものであれば特に限定されるものではないが、例えば、ポリプロピレン樹脂繊維などのポリオレフィン樹脂繊維またはポリアミド樹脂繊維を用いて形成された不織布である。なお、このような不織布を形成するためのポリオレフィン樹脂繊維やポリアミド樹脂繊維には、必要に応じてスルホン化処理やアクリル酸などをグラフト重合して親水性が付与されていてもよい。
【００４９】
電解液は、同じくアルカリ蓄電池において用いられるものであれば特に限定されるものではなく、例えば、水酸化カリウム水溶液、水酸化ナトリウム水溶液または水酸化リチウム水溶液などのアルカリ金属水酸化物水溶液である。アルカリ金属水酸化物水溶液は、２種以上のものが混合して用いられてもよい。
【００５０】
本発明のアルカリ蓄電池の正極に用いられるニッケル電極は、本発明のニッケル電極、すなわち、本発明のニッケル電極活物質を用いたものであるため、初期充電工程において負極に形成される放電リザーブを削減することができる。つまり、ここで用いられるニッケル電極活物質に含まれるコバルト化合物は、初期充電工程においてニッケル電極活物質に対して導電性ネットワークを付与可能な導電性コバルト化合物に転換するものではなく、コバルトの酸化数が２価より大きなコバルト化合物であって初期充電工程前より導電性を有し、それが初期充電工程前からニッケル電極活物質に対して導電性ネットワークを付与しているため、初期充電工程において負極に放電リザーブを形成しにくい。このため、このようなニッケル電極活物質を用いた本発明のアルカリ蓄電池は、負極の容量を増加させずに正極の容量を高めることができるので、小型化を図りながら高容量化を達成することができる。
【００５１】
また、このアルカリ蓄電池は、正極のニッケル電極活物質において、上述のように初期充電工程前からコバルト化合物による導電性ネットワークが形成されているため、高率放電特性が良好である。さらに、ニッケル電極活物質は、上述のような希土類元素化合物を含んでいるため、高温下での充電時において正極の酸素発生電位を貴にシフトさせることができる。このため、このアルカリ蓄電池は、高温環境下で充電した場合、正極において水酸化ニッケルの酸化電位と酸素発生電位との差が大きくなり、高温下での充電効率が高まる。この点、ニッケル電極活物質が上述のような添加材化合物を含んでいる場合も同様である。
【００５２】
【実施例】
製造例１
６０℃に設定された４０重量％水酸化カリウム水溶液中に酸化イッテルビウム（Ｙｂ₂Ｏ₃）を投入し、７２時間放置した。これにより、酸化イッテルビウムを酸化処理し、希土類元素化合物を得た。この希土類元素化合物について、コバルトのＫα線によるＸ線回折を実施したところ、ｄ＝０．８８５ｎｍ（２θ＝１１．６°）、ｄ＝０．８３６ｎｍ（２θ＝１２．３°）およびｄ＝０．７５８ｎｍ（２θ＝１３．６°）に回折ピークを有する図１のＸ線回折図が得られた。
【００５３】
製造例２
酸化イッテルビウムに替えて酸化エルビウム（Ｅｒ₂Ｏ₃）を用いた点を除いて製造例１の場合と同様に操作し、コバルトのＫα線によるＸ線回折を実施した場合に製造例１の希土類元素化合物と同様の３つの回折ピークを有する希土類元素化合物を得た。
【００５４】
製造例３
酸化イッテルビウムに替えて酸化ツリウム（Ｔｍ₂Ｏ₃）を用いた点を除いて製造例１の場合と同様に操作し、コバルトのＫα線によるＸ線回折を実施した場合に製造例１の希土類元素化合物と同様の３つの回折ピークを有する希土類元素化合物を得た。
【００５５】
製造例４
酸化イッテルビウムに替えて酸化ルテチウム（Ｌｕ₂Ｏ₃）を用いた点を除いて製造例１の場合と同様に操作し、コバルトのＫα線によるＸ線回折を実施した場合に製造例１の希土類元素化合物と同様の３つの回折ピークを有する希土類元素化合物を得た。
【００５６】
製造例５
酸化イッテルビウムに替えて、酸化ツリウム（Ｔｍ₂Ｏ₃）２５重量％、酸化イッテルビウム（Ｙｂ₂Ｏ₃）５０重量％および酸化ルテチウム（Ｌｕ₂Ｏ₃）２５重量％を含む混合物を用いた点を除いて製造例１の場合と同様に操作し、コバルトのＫα線によるＸ線回折を実施した場合に製造例１の希土類元素化合物と同様の３つの回折ピークを有する希土類元素化合物を得た。
【００５７】
製造例６
酸化イッテルビウムに替えて、ツリウムを１．０ａｔｍ．％、イッテルビウムを９０．０ａｔｍ．％およびルテチウムを９．０ａｔｍ．％含む複合酸化物を用いた点を除いて製造例１の場合と同様に操作し、コバルトのＫα線によるＸ線回折を実施した場合に製造例１の希土類元素化合物と同様の３つの回折ピークを有する希土類元素化合物を得た。
【００５８】
実施例１〜６
硫酸ニッケル、硫酸亜鉛および硫酸コバルトを所定比で溶解した水溶液に硫酸アンモニウムと水酸化ナトリウム水溶液とを添加してアンミン錯体を生成させた。そして、この反応系を激しく攪拌しながら水酸化ナトリウム水溶液をさらに滴下し、反応系のｐＨを１０から１３の範囲に制御した。これにより、球状の高密度水酸化ニッケル粒子の群を得た。
【００５９】
次に、得られた高密度水酸化ニッケル粒子の群を、水酸化ナトリウムでｐＨを１０から１３に制御したアルカリ水溶液中に投入した。そして、この溶液を攪拌しながら、所定濃度の硫酸コバルトおよびアンモニアを含む水溶液を滴下した。この間、水酸化ナトリウム水溶液を適宜滴下して反応系のｐＨを１０から１３の範囲に約１時間保持した。これにより、コバルト水酸化物（コバルト化合物前駆体）からなる表面層が形成された高密度水酸化ニッケル粒子（コバルト被覆水酸化ニッケル）の群が得られた。この高密度水酸化ニッケル粒子において、表面層の割合は、芯層を構成する高密度水酸化ニッケルの８．２重量％であった。
【００６０】
得られたコバルト被覆水酸化ニッケル５０ｇを１１０℃の３０重量％水酸化ナトリウム水溶液中に投入し、十分に攪拌した。続いて、コバルト被覆水酸化ニッケルの表面層を形成しているコバルト化合物前駆体の当量に対して過剰の酸化剤（Ｋ₂Ｓ₂Ｏ₈）を水酸化ナトリウム水溶液中に添加した。そして、コバルト被覆水酸化ニッケルの表面から酸素ガスが発生するのを確認した後、コバルト被覆水酸化ニッケルを濾過して水洗し、乾燥した。このようにして酸化処理されたコバルト被覆水酸化ニッケルは、表面層を形成しているコバルト化合物前駆体が酸化されてコバルトの酸化数が２価より大きなコバルト化合物（オキシ水酸化コバルト）に転換されていた。また、芯層の水酸化ニッケルの酸化数は２．０５であり、芯層のニッケルと表面層のコバルトとの平均酸化値は２．１５であった。
【００６１】
上述のようにして酸化処理されたコバルト被覆水酸化ニッケルに対して製造例１〜６で得られた希土類元素化合物の一つを５重量％添加して混合し、さらにカルボキシメチルセルロースの水溶液を加えてペーストを調製した。このペーストの所定量を面密度が４５０ｇ／ｍ²、多孔度が約９５％のニッケル金属多孔板に均一に充填し、ペーストを乾燥した後に加圧してニッケル電極（正極）を作成した。このニッケル電極の容量は１，６００ｍＡｈであった。
【００６２】
実施例７〜１２
実施例１〜６の場合と同様にして、酸化処理されたコバルト被覆水酸化ニッケルを製造した。これに対し、製造例１で得られた希土類元素化合物を、表面層を除いた高密度水酸化ニッケル量の０．２重量％（実施例７）、０．５重量％（実施例８）、２重量％（実施例９）、８重量％（実施例１０）、１５重量％（実施例１１）および２０重量％（実施例１２）添加して混合し、さらにカルボキシメチルセルロースの水溶液を加えてペーストを調製した。そして、このペーストを用い、実施例１〜６と同様のニッケル電極（正極：容量＝１，６００ｍＡｈ）を作成した。
【００６３】
比較例１
実施例１〜６で得られた酸化処理前のコバルト被覆水酸化ニッケルにカルボキシメチルセルロースの水溶液を加え、ペーストを調製した。そして、このペーストを用い、実施例１〜６と同様のニッケル電極（正極：容量＝１，６００ｍＡｈ）を作成した。
【００６４】
比較例２
実施例１〜６で得られた酸化処理前のコバルト被覆水酸化ニッケルに製造例１で得られた希土類元素化合物を５重量％添加して混合し、さらにカルボキシメチルセルロースの水溶液を加えてペーストを調製した。そして、このペーストを用い、実施例１〜６と同様のニッケル電極（正極：容量＝１，６００ｍＡｈ）を作成した。
【００６５】
比較例３
実施例１〜６の場合と同様にして、酸化処理されたコバルト被覆水酸化ニッケルを製造した。そして、これに対してカルボキシメチルセルロースの水溶液を加え、ペーストを調製した。このペーストを用い、実施例１〜６と同様のニッケル電極（正極：容量＝１，６００ｍＡｈ）を作成した。
【００６６】
評価
ＣａＣｕ₅型構造を有するＭｍＮｉ_3.55Ｃｏ_0.75Ｍｎ_0.4Ａｌ_0.3の組成で示される水素吸蔵合金（Ｍｍはランタン４５％、セリウム３０％、プラセオジム３％およびネオジム２２％の混合物）の粉末に増粘剤を加えてペーストを調製し、このペーストを穿孔鋼板に塗布して乾燥した。そして、これを加圧した後に切断し、水素吸蔵合金電極（負極：容量＝２，６４０ｍＡｈ）を作成した。
【００６７】
実施例１〜１２および比較例１〜３で得られたニッケル電極（正極）と上述の水素吸蔵合金電極（負極）とを、アクリル酸をグラフト重合したポリプロピレン樹脂繊維からなる不織布を挟んで円筒状に巻き込み、電極群を作成した。そして、この電極群を円筒状のケース（電槽）内に収容し、また、ケース内に６．８規定の水酸化カリウム水溶液からなる電解液を１．９ｍＬ注入して密閉した。これにより、容量が１，６００ｍＡｈ、Ｎ／Ｐ比が１．６５の円筒型ＡＡサイズの密閉型アルカリ蓄電池を得た。得られたアルカリ蓄電池を、電解液を注入して密閉した後に２時間放置し、その後、０．１ＣｍＡで１５時間定電流充電（初期充電）し、また、０．２ＣｍＡで１．０Ｖまで定電流放電（初期放電）した。放電容量が安定した後、次の各試験を実施した。
【００６８】
（充電効率の評価試験）
実施例１〜６および比較例１〜３の正極を用いたアルカリ蓄電池の温度を２０℃、４０℃、５０℃および６０℃に設定し、上述の初期充電および初期放電と同じ条件で、放電容量が一定になるまで充放電を繰り返した。そして、２０℃において０．２ＣｍＡで放電した場合の放電容量を１００％とし、各アルカリ蓄電池について各温度での放電容量比（充電効率）を求めた。結果を表１に示す。
【００６９】
【表１】

【００７０】
表１から、実施例１〜６の正極を用いたアルカリ蓄電池は、正極に希土類元素化合物を含まない比較例１および３のアルカリ蓄電池に比べ、高温においても高い充電効率を示すことがわかる。これは、実施例１〜６の正極を用いたアルカリ蓄電池は、正極が希土類元素化合物を含んでいるため、充電末期に生じる酸素ガスの発生が抑制され、充電受け入れ性が改善されたためと考えられる。
【００７１】
また、実施例１、実施例７〜１２および比較例３の正極を用いたアルカリ蓄電池について、電池温度を５０℃に設定し、上述と同様の方法で充電効率を求めた結果を図５に示す。図５から、正極に希土類元素化合物を含まない比較例３のアルカリ蓄電池に比べ、実施例１および実施例７〜１２の正極を用いたアルカリ蓄電池は充電効率が向上していることがわかる。但し、図５によると、正極における希土類元素化合物の含有量が８重量％を超えても充電効率について顕著な改善効果は見られない。これより、正極のニッケル電極活物質における希土類元素化合物の含有量は、少なくとも０．５重量％（好ましくは２重量％）に設定するのが好ましく、上限を８重量％以下に設定するのが好ましいことがわかる。
【００７２】
（放電リザーブの評価試験）
実施例１および比較例１，２の正極を用いたアルカリ蓄電池について、２０℃で１０サイクルの充放電を繰り返した後、放電末期の状態で解体して負極を取り出し、負極に含まれる水素ガス量を測定した。ここでは、先ず、蒸留水で満たした三角フラスコ内に負極を入れ、シリコンゴム製の栓で三角フラスコを密栓した。そして、栓の中央に管を通し、この管を通じて負極から発生する水素ガスを水上置換法によりメスシリンダーで捕集した。この際、三角フラスコを加熱し、負極中に含まれる水素ガスを完全に放出させた。
【００７３】
メスシリンダーで捕集された水素ガス量を測定し、それに基づいて負極の放電リザーブを評価した。ここでは、下記の反応式に従って水素ガス１モル（２２．４Ｌ）あたり、２電子（すなわち２クーロン）消費されるものと考え、下記の式（iii）に従って捕集した水素ガス量を電気化学容量に換算し、放電リザーブの目安を求めた。
【００７４】
【化１】

【００７５】
【数３】

【００７６】
結果を図６に示す。図６では、水素ガスの発生量から求めた放電リザーブ量（Ａｈ）を負極全体の理論容量（２．６４Ａｈ）に対する比率（（放電リザーブ量／負極全体の理論容量）×１００）で示しており、これを放電リザーブ率とする。図６によると、実施例１の正極を用いたアルカリ蓄電池は、放電リザーブ率が１０％以下であり、比較例１，２の正極を用いたアルカリ蓄電池に比べて放電リザーブが削減されていることがわかる。したがって、実施例１の正極を用いたアルカリ蓄電池は、小型化を維持しつつ容量を高めることができる。
【００７７】
（高率放電特性の評価試験）
実施例１の正極を用いたアルカリ蓄電池と、比較例２の正極を用いたアルカリ蓄電池とを、２０℃において、０．２〜３ＣｍＡの放電レートで放電した。この際、充電条件は、上述の初期充電と同じに設定した。結果を図７に示す。図７から明らかなように、実施例１の正極を用いたアルカリ蓄電池は、比較例２の正極を用いたアルカリ蓄電池に比べて高率放電時の容量が大きい。これは、実施例１の正極において、コバルト化合物による導電性ネットワークが初期充電前より形成されているためと考えられる。
【００７８】
【発明の効果】
本発明のアルカリ蓄電池用ニッケル電極活物質は、水酸化ニッケルと、コバルトの酸化数が２価より大きなコバルト化合物と、Ｘ線回折図において特有の回折ピークを示す希土類元素化合物とを含んでいるため、アルカリ蓄電池について、高率放電特性と高温下での充電効率とを同時に高め、さらに小型化を図りながら高容量化を達成することができる。
【００７９】
また、本発明のアルカリ蓄電池用ニッケル電極は、本発明のニッケル電極活物質を備えているため、アルカリ蓄電池について、高率放電特性と高温下での充電効率とを同時に高め、さらに小型化を図りながら高容量化を達成することができる。
【００８０】
さらに、本発明のアルカリ蓄電池は、本発明のニッケル電極を備えているため、高率放電特性と高温下での充電効率とが同時に高められ、さらに小型化を図りながら高容量化することができる。
【図面の簡単な説明】
【図１】イッテルビウムを含む希土類元素化合物のＸ線回折図。
【図２】ストロンチウムを含む添加材化合物のＸ線回折図。
【図３】ビスマスを含む添加材化合物のＸ線回折図。
【図４】イットリウムを含む添加材化合物のＸ線回折図。
【図５】実施例における充電効率の評価試験結果を示す図。
【図６】実施例における放電リザーブ率の評価試験結果を示す図。
【図７】実施例における高率放電特性の評価試験結果を示す図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a nickel electrode active material, a nickel electrode, and a storage battery, and more particularly to a nickel electrode active material for an alkaline storage battery, a nickel electrode for an alkaline storage battery, and an alkaline storage battery.
[0002]
[Prior art and its problems]
Alkaline storage batteries such as nickel metal hydride storage batteries, nickel cadmium storage batteries, and nickel zinc storage batteries are used as power sources for charging and discharging used in devices that require large currents such as power tools and hybrid electric vehicles (HEV). Is growing rapidly.
[0003]
A nickel electrode is used for the positive electrode of such an alkaline storage battery. As a nickel electrode, a sintered electrode in which nickel hydroxide is deposited on an electrode plate obtained by sintering a powder such as nickel has been mainly used so far. Due to the rapid increase in demand below, recently, it is easier to increase the capacity and easier to manufacture compared to sintered electrodes, so thickeners etc. are added to high-density spherical nickel hydroxide powder (active material) A non-sintered electrode in which a slurry prepared by mixing an agent is applied to or filled in an electrode such as a perforated steel plate or a foamed substrate has been increasingly used.
[0004]
However, the non-sintered electrode has a large distance between the electrode and the active material, and since the contact between the active materials is insufficient, the conductivity is small and the high rate discharge characteristic is inferior to the sintered electrode. . For this reason, various active materials for non-sintered electrodes in which cobalt or a cobalt compound is added to nickel hydroxide have been proposed (for example, Japanese Patent Laid-Open No. 62-256366). In the non-sintered electrode using such an active material, cobalt ions are eluted from the cobalt or cobalt compound into the alkaline electrolyte in the alkaline electrolyte, and the cobalt ions are precipitated as cobalt hydroxide. The cobalt hydroxide is oxidized during initial charging to become cobalt oxyhydroxide, which forms a dense network that increases the conductivity between the nickel hydroxide powder particles, thereby increasing the conductivity of the electrode. As a result, the high rate discharge characteristics of the non-sintered electrode are enhanced to the same extent as the sintered electrode.
[0005]
By the way, when the non-sintered electrode as described above is used for a nickel metal hydride storage battery, the reaction that cobalt oxyhydroxide is generated from cobalt or a cobalt compound is an irreversible reaction. Therefore, it is stored on the negative electrode side as a potential amount of discharge electricity (discharge reserve). Moreover, when such a nickel metal hydride storage battery is overcharged, oxygen gas is generated on the positive electrode side. This oxygen gas may increase the internal pressure of the nickel-metal hydride storage battery, causing liquid leakage and shortening the battery life. Therefore, in a nickel metal hydride storage battery, a chargeable capacity (charging reserve) that does not participate in actual charging / discharging is provided on the negative electrode side, and oxygen gas generated on the positive electrode side is absorbed or consumed by the negative electrode charging reserve and converted to water. The rise of internal pressure is suppressed. Under such circumstances, the nickel-metal hydride storage battery is set such that the capacity of the negative electrode is set larger than the capacity of the positive electrode, and the charge / discharge capacity is regulated by the capacity of the positive electrode. Therefore, in order to increase the capacity of the nickel metal hydride storage battery, it is necessary to increase the capacity of the positive electrode and also increase the capacity of the negative electrode in consideration of the accompanying charge reserve and discharge reserve. In other words, it is difficult for the nickel metal hydride storage battery to achieve a high capacity while achieving a reduction in size.
[0006]
Also, alkaline storage batteries equipped with non-sintered electrodes increase the battery temperature during charging / discharging. Especially, when charging / discharging is repeated with a large current, the next charging / discharging process is performed with insufficient cooling. In many cases, it must be migrated. That is, the alkaline storage battery is frequently used in a high temperature environment. However, when the alkaline storage battery is charged in a high temperature environment, the difference between the oxidation potential of nickel hydroxide and the oxygen generation potential at the end of charging becomes small, so the oxidation reaction and the oxygen generation reaction compete and the charging efficiency decreases. To do. In particular, in the case of an apparatus using an assembled battery combined with an alkaline storage battery, such as a hybrid electric vehicle, the temperature of each alkaline storage battery becomes difficult to be constant, and the charging efficiency is likely to decrease. In order to improve this point, in addition to the above-described cobalt or cobalt compound, an element compound having an effect of preciously shifting the oxygen generation potential at the end of charging of the positive electrode at a high temperature, relative to the active material for the non-sintered electrode Has been proposed (see, for example, JP-A-5-28992, JP-A-6-150925, JP-A-8-195198, and JP-A-9-92279).
[0007]
However, among the elements that have the effect of preciously shifting the oxygen generation potential of the positive electrode, the precipitation of the cobalt hydroxide in the alkaline electrolyte is prevented, resulting in the formation of a conductive network by the cobalt oxyhydroxide. There is something to prevent. For this reason, although the electrode containing such an element increases the charging efficiency at high temperatures, the high-rate discharge characteristics are extremely reduced. In order to solve this, it is conceivable to increase the amount of cobalt or cobalt compound contained in the active material so that a conductive network between nickel hydroxides can be easily formed, but in this case, the discharge reserve increases. Therefore, it becomes more difficult to achieve a high capacity while reducing the size of the alkaline storage battery.
[0008]
An object of the present invention is to achieve a high capacity for an alkaline storage battery while simultaneously improving a high rate discharge characteristic and a charging efficiency at a high temperature and further reducing the size.
[0009]
[Means for Solving the Problems]
The nickel electrode active material for an alkaline storage battery of the present invention comprises at least one element selected from the group consisting of nickel hydroxide, a cobalt compound in which the oxidation number of cobalt is greater than divalent, and ytterbium, erbium, lutetium, and thulium. A rare earth element compound having diffraction peaks at d = 0.85 ± 0.008 nm, d = 0.838 ± 0.01 nm, and d = 0.759 ± 0.007 nm in an X-ray diffraction pattern of cobalt and containing Kα rays Is included.
[0010]
Here, nickel hydroxide has an oxidation number of 2.04 to 2.40, for example. Moreover, this nickel electrode active material for alkaline storage batteries contains, for example, a rare earth element compound in an amount of 0.5 to 8% by weight of nickel hydroxide.
[0011]
The nickel electrode for alkaline storage batteries of the present invention comprises a current collector and an active material disposed on the current collector. The active material contains at least one element selected from the group consisting of nickel hydroxide, a cobalt compound having an oxidation number greater than 2 and ytterbium, erbium, lutetium, and thulium, and X-ray diffraction by cobalt Kα rays In the figure, a rare earth element compound having diffraction peaks at d = 0.85 ± 0.008 nm, d = 0.828 ± 0.01 nm, and d = 0.759 ± 0.007 nm is included.
[0012]
The alkaline storage battery of the present invention includes a positive electrode, a negative electrode, and an alkaline electrolyte disposed between the positive electrode and the negative electrode. The positive electrode includes nickel hydroxide, a cobalt compound having an oxidation number greater than 2 and ytterbium. And at least one element selected from the group consisting of erbium, lutetium, and thulium, and d = 0.85 ± 0.008 nm and d = 0.848 ± 0.01 nm in an X-ray diffraction pattern by cobalt Kα ray And a rare earth element compound having a diffraction peak at d = 0.759 ± 0.007 nm.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The nickel electrode active material for alkaline storage batteries of the present invention contains nickel hydroxide, a cobalt compound, and a rare earth element compound.
The nickel hydroxide used in the present invention is usually in the form of fine particles and is not particularly limited as long as it is used as an active material for a nickel electrode of an alkaline storage battery. Nickel oxide. This nickel hydroxide is a group 2A element such as magnesium and calcium, and a group 2B element such as zinc and cadmium in order to suppress the formation of γ-type nickel oxyhydroxide, which causes a decrease in the charge / discharge cycle life of the alkaline storage battery. And at least one element of cobalt may be contained in a solid solution state. That is, in this nickel hydroxide, a part of the nickel element may be substituted with at least one element selected from the group 2A element, group 2B element and cobalt.
[0014]
Moreover, it is preferable that a part of nickel which is the constituent element of this nickel hydroxide is oxidized. Such nickel hydroxide can be prepared, for example, by appropriately oxidizing nickel hydroxide. In this case, it is preferable that the oxidation number of nickel hydroxide is set to 2.04 to 2.40. When the oxidation number is less than 2.04, in the negative electrode of the alkaline storage battery using the nickel electrode active material of the present invention, it becomes difficult to reduce discharge reserve, and as a result, it is difficult to ensure sufficient charge reserve. There is a possibility. As a result, when the alkaline storage battery is overcharged, it is difficult to absorb oxygen gas generated on the nickel electrode side at the charge reserve portion, and it may be difficult to suppress an increase in the internal pressure of the alkaline storage battery. . On the other hand, when the oxidation number exceeds 2.40, in the same alkaline storage battery, there is a possibility that the battery capacity becomes negative electrode regulation and the discharge capacity decreases, and as a result, the cycle life of the alkaline storage battery may be impaired. There is sex.
[0015]
The above oxidation number is a value measured by the ferrous sulfate method. Specifically, first, the amount of active oxygen contained in nickel hydroxide is determined. Here, 0.1 g of nickel hydroxide powder (sample powder) and 1 g of ferrous ammonium sulfate are weighed and added to a 20% by volume aqueous acetic acid solution set at 5 ° C. Then, after stirring for about 3 to 10 hours to completely dissolve the solution, the solution was titrated with a 1/10 N (0.02 mol / l) potassium permanganate solution, from the following formula (i) The amount of active oxygen is calculated.
[0016]
[Expression 1]

[0017]
In formula (i), XFe is a weighed amount of ferrous ammonium sulfate (g), V is a titration amount (ml) of potassium permanganate solution, f is a factor of potassium permanganate solution, and Xsp is a weighed sample powder. Amount (g).
[0018]
Next, the amount (% by weight) of nickel contained in the sample powder is quantitatively analyzed by a method such as ICP emission analysis or original atomic absorption spectrometry, and oxidation of nickel in nickel hydroxide is calculated from the following formula (ii). Calculate the number.
[0019]
[Expression 2]

[0020]
The cobalt compound used in the present invention has a cobalt oxidation number larger than divalent, for example, cobalt oxyhydroxide. Such a cobalt compound is cobalt or a cobalt compound that can elute cobalt ions in an alkaline solution used as an electrolyte of an alkaline storage battery, such as α-type cobalt hydroxide, β-type cobalt hydroxide, or cobalt monoxide (hereinafter, For convenience, it can be prepared by oxidizing a cobalt compound precursor).
[0021]
In this oxidation treatment, usually, an alkaline aqueous solution is first prepared, and a cobalt compound precursor is introduced into the alkaline aqueous solution. The alkaline aqueous solution usable here is not particularly limited, but usually contains at least one of potassium hydroxide and sodium hydroxide, and the temperature is 60 from the viewpoint of promoting the oxidation treatment. It is preferable that the temperature is set to be equal to or higher than ° C.
[0022]
Next, an oxidizing agent is added to the above-mentioned alkaline aqueous solution, and the cobalt compound precursor contained in the aqueous solution is oxidized. Thereby, a cobalt compound precursor is converted into a cobalt compound (for example, cobalt oxyhydroxide) in which the oxidation number of cobalt is larger than divalent.
[0023]
The oxidizing agent used here is not particularly limited, and is a variety of known ones. However, it has a high oxidizing power and can efficiently oxidize a cobalt compound precursor. Potassium disulfate (K₂S₂O₈), Sodium peroxodisulfate (Na₂S₂O₈), Ammonium peroxodisulfate ((NH_Four)₂S₂O₈And at least one selected from the group consisting of sodium hypochlorite (NaClO).
[0024]
In addition, since the addition amount of an oxidizing agent changes with kinds of oxidizing agent, it cannot be specified unconditionally, However, It is preferable to set to a sufficient quantity for converting a cobalt compound precursor into a required cobalt compound.
[0025]
In the nickel electrode active material for an alkaline storage battery of the present invention, the cobalt compound may be contained in a state where the surface of the nickel hydroxide particles is covered. The nickel hydroxide coated with such a cobalt compound is, for example, a group of nickel hydroxide particles coated with a cobalt compound precursor by a known method (for example, see JP-A-62-234867) (hereinafter, referred to as JP-A-62-234867). For convenience, it can be produced by producing cobalt-coated nickel hydroxide) and oxidizing the cobalt-coated nickel hydroxide.
[0026]
Here, the oxidation treatment of cobalt-coated nickel hydroxide can be usually carried out by treating the cobalt-coated nickel hydroxide with an oxidizing agent in an alkaline aqueous solution in the same manner as the oxidation treatment of the cobalt compound precursor described above. That is, first, an alkaline aqueous solution is prepared, and cobalt-coated nickel hydroxide is introduced into the alkaline aqueous solution. The alkaline aqueous solution that can be used here is not particularly limited, but usually contains at least one of potassium hydroxide and sodium hydroxide. In particular, when an aqueous sodium hydroxide solution is used, it is possible to suppress the conversion of nickel hydroxide on the core layer side of cobalt-coated nickel hydroxide into γ-NiOOH in the oxidation treatment step. Moreover, it is preferable that the temperature of the alkaline aqueous solution is set to 60 ° C. or higher from the viewpoint of promoting the oxidation treatment.
[0027]
Next, an oxidizing agent is added to the above-mentioned alkaline aqueous solution, and the cobalt-coated nickel hydroxide contained in the aqueous solution is oxidized. As a result, a cobalt compound precursor (surface layer) that coats the nickel hydroxide of the core layer is oxidized in the cobalt-coated nickel hydroxide, and the cobalt compound precursor is a cobalt compound having a cobalt oxidation number greater than 2 (for example, To cobalt oxyhydroxide).
[0028]
The oxidizing agent used here is the same as that described above. In addition, the amount of oxidizer added varies depending on the type of oxidizer and cannot be specified in general. However, the surface layer of cobalt-coated nickel hydroxide, that is, the cobalt compound precursor is converted into the required cobalt compound, and It is preferable to set the oxidation number of nickel hydroxide on the core layer side within the above range.
[0029]
The rare earth element compound used in the present invention contains at least one element selected from the group consisting of ytterbium, erbium, lutetium and thulium, and d = 0.85 ± 0. It has a diffraction peak at 008 nm, d = 0.838 ± 0.01 nm and d = 0.759 ± 0.007 nm, and is usually a powder of such a compound. As an example, an X-ray diffraction pattern of a rare earth element compound containing ytterbium is shown in FIG. This rare earth element compound is Ln (OH)_Three・ H₂O or LnOOH · 2H₂Presumed to be a compound containing water of crystallization represented by O (in the chemical formula, Ln represents a rare earth element).
[0030]
Such a rare earth element compound can be obtained, for example, by oxidizing a compound (raw material compound) containing at least one element selected from the element group consisting of ytterbium, erbium, lutetium, and thulium.
[0031]
The raw material compound used here is usually an oxide or hydroxide containing at least one element selected from the above element group. That is, the raw material compound is usually an oxide or hydroxide of one element selected from the above element group, or a composite oxide or composite hydroxide of two or more elements selected from the above element group. . Two or more kinds of such raw material compounds may be used in combination as appropriate.
[0032]
The target rare earth element compound can be obtained by oxidizing the above-mentioned raw material compound. Here, when the raw material compound is the above-mentioned oxide or hydroxide, the oxidation treatment is usually performed by immersing the raw material compound in an aqueous alkali metal hydroxide solution, for example, an aqueous solution of sodium hydroxide or potassium hydroxide. This can be achieved if left unattended. The concentration of the aqueous alkali metal hydroxide solution is usually preferably set to 25 wt% to 40 wt%. In this oxidation treatment, the aqueous alkali metal hydroxide solution may be appropriately heated to accelerate the oxidation treatment. For example, if the above-mentioned oxide or hydroxide is immersed in a 6.8 N aqueous potassium hydroxide solution heated to 60 ° C. and left to stand, the desired rare earth element compound is usually obtained in several hours to several days. It is done.
[0033]
In the oxidation treatment method as described above, an oxidizing agent such as sodium hypochlorite (NaClO) may be added or air (oxygen) may be blown into the aqueous alkali metal hydroxide solution. In this case, the oxidation treatment of the raw material compound is promoted, and the target oxidation treatment compound can be prepared more quickly.
[0034]
Incidentally, when the above-described oxidation treatment is performed on oxides or hydroxides of rare earth elements other than ytterbium, erbium, lutetium and thulium, Ln (OH)₃Hexagonal crystal (P6_ThreeA hydroxide having a crystal structure of / m) is obtained, but this hydroxide does not show the diffraction peak as described above.
[0035]
Note that two or more of the rare earth element compounds described above may be used in combination as appropriate.
[0036]
In addition, the nickel electrode active material for alkaline storage batteries of the present invention is at least one of a strontium compound, a bismuth compound and an yttrium compound instead of the above rare earth element compound or together with the above rare earth element compound (hereinafter, for convenience, It may contain an additive compound).
[0037]
The strontium compound used here has d = 0.354 ± 0.002 nm and d = 0.248 ± 0.001 nm in the range of 2θ = 5 to 85 ° in the X-ray diffraction pattern of cobalt Kα ray. It has a diffraction peak of 1 intensity and a diffraction peak of 2nd intensity. For example, as shown in FIG. 2, this strontium compound has a diffraction peak of d = 0.585 nm (2θ = 17.6 °) peculiar to the X-ray diffraction pattern of strontium hydroxide, and d = 0.354 nm. (2θ = 29.3 °) and d = 0.248 nm (2θ = 42.3 °) have a first intensity diffraction peak and a second intensity diffraction peak, respectively.
[0038]
Further, the bismuth compound used here is d = 0.326 ± 0.002 nm, d = 0.269 ± 0.001 nm in the range of 2θ = 5 to 85 ° of the X-ray diffraction diagram of cobalt by Kα ray d = 0.256 ± 0.001 nm having a first intensity diffraction peak, a second intensity diffraction peak, and a third intensity diffraction peak, respectively, and d = 0.269 ± 0.001 nm second intensity diffraction. The peak has an intensity of ½ or more of the first intensity diffraction peak of d = 0.326 ± 0.002 nm. For example, as shown in FIG. 3, in this bismuth compound, the diffraction peak of d = 0.295 nm (2θ = 35.3 °) peculiar to the X-ray diffraction pattern of bismuth oxide disappears, and d = 0.326 nm ( 2θ = 31.9 °), d = 0.269 nm (2θ = 38.8 °) and d = 0.256 nm (2θ = 40.9 °), respectively, the first intensity diffraction peak and the second intensity diffraction peak And a diffraction peak having a third intensity and a diffraction peak having a second intensity of d = 0.269 nm are at least half the intensity of the diffraction peak of the first intensity having d = 0.326 nm.
[0039]
Further, the yttrium compound used here has d = 0.544 ± 0.006 nm and d = 0.313 ± 0.002 nm in the range of 2θ = 5 to 85 ° in the X-ray diffraction diagram of cobalt Kα ray. It has a diffraction peak, and the diffraction peak of d = 0.544 ± 0.006 nm is the strongest peak in the range. For example, as shown in FIG. 4, this yttrium compound has d = 0.544 nm (2θ = 18.9 °) and d = 0.313 nm (2θ which are not found in the X-ray diffraction pattern of yttrium oxide or yttrium hydroxide. = 33.2 °), and the diffraction peak at d = 0.544 nm is the strongest peak in the range of 2θ = 5 to 85 °.
[0040]
The additive compound described above can be prepared in the same manner as in the case of the rare earth element compound described above. That is, these compounds can be prepared by oxidizing a raw material compound (for example, oxide or hydroxide) containing strontium, bismuth or yttrium by the method as described above.
[0041]
The nickel electrode active material of the present invention can be prepared by mixing the above-described nickel hydroxide, cobalt compound and rare earth compound. Here, the content of the cobalt compound is usually preferably set to 2 to 10% by weight of nickel hydroxide, and more preferably set to 3 to 7% by weight. When this content is less than 2% by weight, it becomes difficult to form a required conductive network with respect to nickel hydroxide, and the discharge characteristics, particularly the high rate discharge characteristics, of the alkaline storage battery may be deteriorated. On the contrary, when the content exceeds 10% by weight, the amount of nickel hydroxide in the active material becomes relatively small, so that it is difficult to increase the capacity while maintaining the miniaturization of the alkaline storage battery. .
[0042]
Further, the content of the rare earth element compound is usually preferably set to 0.5 to 8% by weight of nickel hydroxide, and more preferably set to 2 to 8% by weight. When this content is less than 0.5% by weight, the effect of shifting the oxygen generation potential of the nickel electrode in a noble direction is poor, and it may be difficult to increase the charging efficiency of the alkaline storage battery in a high temperature environment. is there. On the other hand, when the content exceeds 8% by weight, not only is it impossible to achieve a proportional effect, but it is not economical, and the amount of nickel hydroxide in the nickel electrode active material is relatively small. It is difficult to increase the capacity while maintaining the miniaturization of the device.
[0043]
In the active material of the present invention, when the above-described additive compound is used instead of the above-mentioned rare earth element compound, the content in the active material of the present invention is set similarly to the case of the rare earth element compound. preferable. Moreover, in the active material of the present invention, when the above-mentioned additive compound is used together with the above-mentioned rare earth element compound, the content of the additive compound is such that the total amount with the rare earth element compound is the above-mentioned content related to the rare earth element compound. It is preferable to set the range.
[0044]
The nickel electrode for alkaline storage batteries of the present invention includes a current collector and the nickel electrode active material of the present invention disposed on the current collector. The current collector used for the nickel electrode is not particularly limited as long as it can be used in the nickel electrode for an alkaline storage battery, and is, for example, a perforated steel plate or a foamed substrate.
[0045]
When manufacturing this nickel electrode, first, the above-mentioned active material according to the present invention is prepared. Then, a slurry or paste is prepared by adding a binder such as carboxymethylcellulose to the active material, and the slurry or paste is disposed on the current collector by coating or filling.
[0046]
The alkaline storage battery of the present invention is injected into a battery case, a nickel electrode as described above housed in the battery case, that is, a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and the battery case. Main electrolyte.
[0047]
The negative electrode used here is not particularly limited as long as it is used in an alkaline storage battery having a nickel electrode as a positive electrode, and is usually a hydrogen storage alloy electrode, a cadmium electrode, or a zinc electrode. Incidentally, when a hydrogen storage alloy electrode is used as the negative electrode, the hydrogen storage alloy is CaCu._FiveMmNi with mold structure_3.55Co_0.75Mn_0.4Al_0.3An alloy represented by the composition: MmNi₅A multielement alloy, a TiNi alloy, a TiFe alloy, or the like in which a part of nickel in the alloy is replaced with at least one of aluminum, manganese, cobalt, titanium, copper, and zinc can be used. Mm means a mixture of rare earth elements (usually a mixture of lanthanum, cerium, praseodymium and neodymium).
[0048]
The separator is used for preventing a short circuit between the positive electrode and the negative electrode and holding the electrolytic solution, and is not particularly limited as long as it can be used in an alkaline storage battery. A nonwoven fabric formed using polyolefin resin fibers or polyamide resin fibers. It should be noted that the polyolefin resin fibers and polyamide resin fibers for forming such a nonwoven fabric may be imparted with hydrophilicity by graft polymerization of sulfonation treatment or acrylic acid, if necessary.
[0049]
The electrolytic solution is not particularly limited as long as it is also used in an alkaline storage battery, and is, for example, an alkali metal hydroxide aqueous solution such as a potassium hydroxide aqueous solution, a sodium hydroxide aqueous solution, or a lithium hydroxide aqueous solution. Two or more alkali metal hydroxide aqueous solutions may be mixed and used.
[0050]
Since the nickel electrode used for the positive electrode of the alkaline storage battery of the present invention uses the nickel electrode of the present invention, that is, the nickel electrode active material of the present invention, the discharge reserve formed on the negative electrode in the initial charging step is reduced. can do. That is, the cobalt compound contained in the nickel electrode active material used here is not converted into a conductive cobalt compound capable of imparting a conductive network to the nickel electrode active material in the initial charging step, but the oxidation number of cobalt. Is a cobalt compound larger than divalent, and has conductivity before the initial charging step, and imparts a conductive network to the nickel electrode active material before the initial charging step. It is difficult to form a discharge reserve. For this reason, the alkaline storage battery of the present invention using such a nickel electrode active material can increase the capacity of the positive electrode without increasing the capacity of the negative electrode. Can do.
[0051]
Further, this alkaline storage battery has a high rate discharge characteristic because a conductive network made of a cobalt compound is formed in the positive electrode nickel electrode active material before the initial charging step as described above. Furthermore, since the nickel electrode active material contains the rare earth element compound as described above, the oxygen generation potential of the positive electrode can be shifted preciously during charging at a high temperature. For this reason, when this alkaline storage battery is charged under a high temperature environment, the difference between the oxidation potential of nickel hydroxide and the oxygen generation potential is increased at the positive electrode, and the charging efficiency at a high temperature is increased. The same applies to the case where the nickel electrode active material contains the additive compound as described above.
[0052]
【Example】
Production Example 1
Ytterbium oxide (Yb) in a 40 wt% aqueous potassium hydroxide solution set at 60 ° C.₂O_Three) And left for 72 hours. As a result, ytterbium oxide was oxidized to obtain a rare earth element compound. When this rare earth element compound was subjected to X-ray diffraction of cobalt by Kα ray, d = 0.855 nm (2θ = 11.6 °), d = 0.835 nm (2θ = 12.3 °), and d = 0. The X-ray diffraction pattern of FIG. 1 having a diffraction peak at .758 nm (2θ = 13.6 °) was obtained.
[0053]
Production Example 2
Erbium oxide instead of ytterbium oxide (Er₂O_ThreeThe rare earth element having the same three diffraction peaks as those of the rare earth element compound of Production Example 1 when X-ray diffraction by cobalt Kα rays was performed. A compound was obtained.
[0054]
Production Example 3
Thulium oxide (Tm instead of ytterbium oxide)₂O_ThreeThe rare earth element having the same three diffraction peaks as those of the rare earth element compound of Production Example 1 when X-ray diffraction by cobalt Kα rays was performed. A compound was obtained.
[0055]
Production Example 4
Instead of ytterbium oxide, lutetium oxide (Lu₂O_ThreeThe rare earth element having the same three diffraction peaks as those of the rare earth element compound of Production Example 1 when X-ray diffraction by cobalt Kα rays was performed. A compound was obtained.
[0056]
Production Example 5
Instead of ytterbium oxide, thulium oxide (Tm₂O_Three) 25% by weight, ytterbium oxide (Yb₂O_Three50% by weight and lutetium oxide (Lu)₂O_Three3) The same operation as in Production Example 1 except that a mixture containing 25% by weight was used, and when X-ray diffraction by cobalt Kα ray was performed, the same three rare earth element compounds as in Production Example 1 A rare earth element compound having a diffraction peak was obtained.
[0057]
Production Example 6
Instead of ytterbium oxide, thulium was added at 1.0 atm. %, Ytterbium 90.0 atm. % And lutetium at 9.0 atm. The same three diffraction peaks as those of the rare earth element compound of Production Example 1 when the X-ray diffraction by cobalt Kα ray was performed in the same manner as in Production Example 1 except that the composite oxide containing 1% was used. A rare earth element compound having was obtained.
[0058]
Examples 1-6
An ammonium complex and an aqueous sodium hydroxide solution were added to an aqueous solution in which nickel sulfate, zinc sulfate and cobalt sulfate were dissolved in a predetermined ratio to form an ammine complex. Then, while stirring the reaction system vigorously, an aqueous sodium hydroxide solution was further added dropwise to control the pH of the reaction system in the range of 10 to 13. Thereby, a group of spherical high density nickel hydroxide particles was obtained.
[0059]
Next, the obtained group of high-density nickel hydroxide particles was put into an alkaline aqueous solution whose pH was controlled from 10 to 13 with sodium hydroxide. Then, an aqueous solution containing cobalt sulfate and ammonia having a predetermined concentration was dropped while stirring the solution. During this time, an aqueous sodium hydroxide solution was appropriately added dropwise to maintain the pH of the reaction system in the range of 10 to 13 for about 1 hour. Thereby, a group of high-density nickel hydroxide particles (cobalt-coated nickel hydroxide) in which a surface layer made of cobalt hydroxide (cobalt compound precursor) was formed was obtained. In the high density nickel hydroxide particles, the proportion of the surface layer was 8.2% by weight of the high density nickel hydroxide constituting the core layer.
[0060]
50 g of the obtained cobalt-coated nickel hydroxide was put into a 30 wt% sodium hydroxide aqueous solution at 110 ° C. and sufficiently stirred. Subsequently, an excess of oxidizing agent (K) relative to the equivalent of the cobalt compound precursor forming the surface layer of cobalt-coated nickel hydroxide.₂S₂O₈) Was added into an aqueous sodium hydroxide solution. And after confirming that oxygen gas was generated from the surface of cobalt covering nickel hydroxide, cobalt covering nickel hydroxide was filtered, washed with water, and dried. The cobalt-coated nickel hydroxide thus oxidized is converted to a cobalt compound (cobalt oxyhydroxide) in which the cobalt compound precursor forming the surface layer is oxidized and the oxidation number of cobalt is larger than divalent. It was. The oxidation number of nickel hydroxide in the core layer was 2.05, and the average oxidation value of nickel in the core layer and cobalt in the surface layer was 2.15.
[0061]
One of the rare earth element compounds obtained in Production Examples 1 to 6 was added to and mixed with the cobalt-coated nickel hydroxide oxidized as described above, and an aqueous solution of carboxymethylcellulose was further added. A paste was prepared. A predetermined amount of this paste has an area density of 450 g / m.²A nickel metal porous plate having a porosity of about 95% was uniformly filled, and the paste was dried and then pressed to prepare a nickel electrode (positive electrode). The capacity of this nickel electrode was 1,600 mAh.
[0062]
Examples 7-12
In the same manner as in Examples 1 to 6, oxidized cobalt-coated nickel hydroxide was produced. On the other hand, the rare earth element compound obtained in Production Example 1 was 0.2% by weight (Example 7), 0.5% by weight (Example 8) of the amount of high-density nickel hydroxide excluding the surface layer, 2% by weight (Example 9), 8% by weight (Example 10), 15% by weight (Example 11) and 20% by weight (Example 12) are added and mixed, and an aqueous solution of carboxymethyl cellulose is further added to the paste. Was prepared. And the nickel electrode (positive electrode: capacity | capacitance = 1,600mAh) similar to Examples 1-6 was created using this paste.
[0063]
Comparative Example 1
An aqueous solution of carboxymethyl cellulose was added to the cobalt-coated nickel hydroxide before oxidation treatment obtained in Examples 1 to 6 to prepare a paste. And the nickel electrode (positive electrode: capacity | capacitance = 1,600mAh) similar to Examples 1-6 was created using this paste.
[0064]
Comparative Example 2
5% by weight of the rare earth element compound obtained in Production Example 1 was added to and mixed with the cobalt-coated nickel hydroxide before oxidation treatment obtained in Examples 1 to 6, and an aqueous solution of carboxymethyl cellulose was further added to prepare a paste. did. And the nickel electrode (positive electrode: capacity | capacitance = 1,600mAh) similar to Examples 1-6 was created using this paste.
[0065]
Comparative Example 3
In the same manner as in Examples 1 to 6, oxidized cobalt-coated nickel hydroxide was produced. And the aqueous solution of carboxymethylcellulose was added with respect to this, and the paste was prepared. Using this paste, the same nickel electrode (positive electrode: capacity = 1,600 mAh) as in Examples 1 to 6 was prepared.
[0066]
Evaluation
CaCu_FiveMmNi with mold structure_3.55Co_0.75Mn_0.4Al_0.3A paste was prepared by adding a thickener to the powder of a hydrogen storage alloy (Mm is a mixture of 45% lanthanum, 30% cerium, 3% praseodymium and 22% neodymium), and this paste was applied to a perforated steel sheet. And dried. Then, this was pressurized and then cut to prepare a hydrogen storage alloy electrode (negative electrode: capacity = 2,640 mAh).
[0067]
The nickel electrode (positive electrode) obtained in Examples 1 to 12 and Comparative Examples 1 to 3 and the hydrogen storage alloy electrode (negative electrode) described above are cylindrical with a nonwoven fabric made of polypropylene resin fiber grafted with acrylic acid interposed therebetween. The electrode group was created. And this electrode group was accommodated in the cylindrical case (battery case), and 1.9 mL of electrolyte solution which consists of 6.8 normal potassium hydroxide aqueous solution was inject | poured in the case, and it sealed. As a result, a cylindrical alkaline AA battery having a capacity of 1,600 mAh and an N / P ratio of 1.65 was obtained. The obtained alkaline storage battery was sealed for 2 hours after injecting an electrolyte solution, and then charged with constant current (initial charge) at 0.1 CmA for 15 hours, and further at constant current up to 1.0 V at 0.2 CmA. Discharge (initial discharge). After the discharge capacity was stabilized, the following tests were performed.
[0068]
(Evaluation test of charging efficiency)
The temperature of the alkaline storage battery using the positive electrodes of Examples 1 to 6 and Comparative Examples 1 to 3 was set to 20 ° C., 40 ° C., 50 ° C. and 60 ° C., and the discharge capacity was the same as the above initial charge and initial discharge. The charge and discharge were repeated until became constant. And the discharge capacity at the time of discharging at 0.2 CmA at 20 degreeC was made into 100%, and the discharge capacity ratio (charge efficiency) in each temperature was calculated | required about each alkaline storage battery. The results are shown in Table 1.
[0069]
[Table 1]

[0070]
From Table 1, it can be seen that the alkaline storage batteries using the positive electrodes of Examples 1 to 6 show higher charging efficiency even at higher temperatures than the alkaline storage batteries of Comparative Examples 1 and 3 in which the positive electrode does not contain a rare earth element compound. This is thought to be because the alkaline storage batteries using the positive electrodes of Examples 1 to 6 are improved in charge acceptability by suppressing the generation of oxygen gas generated at the end of charge because the positive electrode contains a rare earth element compound. .
[0071]
Moreover, about the alkaline storage battery using the positive electrode of Example 1, Examples 7-12, and the comparative example 3, the battery temperature was set to 50 degreeC, and the result of having calculated | required charging efficiency by the method similar to the above is shown in FIG. . FIG. 5 shows that the alkaline storage batteries using the positive electrodes of Example 1 and Examples 7 to 12 have improved charging efficiency as compared with the alkaline storage battery of Comparative Example 3 in which the positive electrode does not contain a rare earth element compound. However, according to FIG. 5, even if the content of the rare earth element compound in the positive electrode exceeds 8% by weight, no significant improvement effect on the charging efficiency is observed. Accordingly, the content of the rare earth element compound in the positive electrode nickel electrode active material is preferably set to at least 0.5 wt% (preferably 2 wt%), and the upper limit is preferably set to 8 wt% or less. I understand that.
[0072]
(Evaluation test of discharge reserve)
About the alkaline storage battery using the positive electrode of Example 1 and Comparative Examples 1 and 2, after 10 cycles of charging / discharging at 20 ° C., the battery was disassembled at the end of discharge and the negative electrode was taken out, and the amount of hydrogen gas contained in the negative electrode Was measured. Here, first, the negative electrode was placed in an Erlenmeyer flask filled with distilled water, and the Erlenmeyer flask was sealed with a silicone rubber stopper. Then, a tube was passed through the center of the stopper, and hydrogen gas generated from the negative electrode through this tube was collected with a graduated cylinder by a water displacement method. At this time, the Erlenmeyer flask was heated to completely release the hydrogen gas contained in the negative electrode.
[0073]
The amount of hydrogen gas collected by the graduated cylinder was measured, and the discharge reserve of the negative electrode was evaluated based on the measured amount. Here, it is assumed that 2 electrons (that is, 2 coulombs) are consumed per 1 mol (22.4 L) of hydrogen gas according to the following reaction formula, and the amount of hydrogen gas collected according to the following formula (iii) is represented by the electrochemical capacity. To obtain a guide for the discharge reserve.
[0074]
[Chemical 1]

[0075]
[Equation 3]

[0076]
The results are shown in FIG. In FIG. 6, the discharge reserve amount (Ah) obtained from the amount of hydrogen gas generated is shown as a ratio ((discharge reserve amount / theoretical capacity of the entire negative electrode) × 100) to the theoretical capacity (2.64 Ah) of the entire negative electrode. This is the discharge reserve rate. According to FIG. 6, the alkaline storage battery using the positive electrode of Example 1 has a discharge reserve rate of 10% or less, and the discharge reserve is reduced compared to the alkaline storage battery using the positive electrode of Comparative Examples 1 and 2. I understand. Therefore, the alkaline storage battery using the positive electrode of Example 1 can increase the capacity while maintaining miniaturization.
[0077]
(Evaluation test of high rate discharge characteristics)
The alkaline storage battery using the positive electrode of Example 1 and the alkaline storage battery using the positive electrode of Comparative Example 2 were discharged at a discharge rate of 0.2 to 3 CmA at 20 ° C. At this time, the charging conditions were set to be the same as the initial charging described above. The results are shown in FIG. As is clear from FIG. 7, the alkaline storage battery using the positive electrode of Example 1 has a higher capacity during high rate discharge than the alkaline storage battery using the positive electrode of Comparative Example 2. This is presumably because in the positive electrode of Example 1, a conductive network made of a cobalt compound was formed before the initial charge.
[0078]
【The invention's effect】
The nickel electrode active material for an alkaline storage battery of the present invention contains nickel hydroxide, a cobalt compound in which the oxidation number of cobalt is larger than two valences, and a rare earth element compound showing a specific diffraction peak in an X-ray diffraction diagram. As for alkaline storage batteries, it is possible to simultaneously increase the high-rate discharge characteristics and the charging efficiency at high temperatures, and achieve higher capacity while further reducing the size.
[0079]
In addition, since the nickel electrode for alkaline storage battery of the present invention includes the nickel electrode active material of the present invention, the alkaline storage battery is simultaneously improved in high rate discharge characteristics and charging efficiency at high temperature, and further miniaturized. High capacity can be achieved.
[0080]
Furthermore, since the alkaline storage battery of the present invention includes the nickel electrode of the present invention, the high rate discharge characteristics and the charging efficiency at high temperature can be improved at the same time, and the capacity can be increased while further downsizing. .
[Brief description of the drawings]
FIG. 1 is an X-ray diffraction pattern of a rare earth element compound containing ytterbium.
FIG. 2 is an X-ray diffraction pattern of an additive compound containing strontium.
FIG. 3 is an X-ray diffraction pattern of an additive compound containing bismuth.
FIG. 4 is an X-ray diffraction pattern of an additive compound containing yttrium.
FIG. 5 is a diagram showing the evaluation test results of charging efficiency in Examples.
FIG. 6 is a diagram showing an evaluation test result of a discharge reserve rate in Examples.
FIG. 7 is a graph showing evaluation test results of high rate discharge characteristics in Examples.

Claims (5)

Nickel hydroxide,
A cobalt compound in which the oxidation number of cobalt is greater than 2;
It contains at least one element selected from the element group consisting of ytterbium, erbium, lutetium and thulium, and d = 0.85 ± 0.008 nm and d = 0.848 ± 0. A rare earth element compound having a diffraction peak at 01 nm and d = 0.759 ± 0.007 nm;
A nickel electrode active material for alkaline storage batteries. The nickel hydroxide active material for an alkaline storage battery according to claim 1, wherein the nickel hydroxide has an oxidation number of 2.04 to 2.40. The nickel electrode active material for alkaline storage batteries according to claim 1 or 2, wherein the rare earth element compound is contained in an amount of 0.5 to 8% by weight of the nickel hydroxide. A current collector,
An active material disposed on the current collector,
The active material contains nickel hydroxide, a cobalt compound in which the oxidation number of cobalt is greater than divalent, and at least one element selected from the group consisting of ytterbium, erbium, lutetium, and thulium, and is based on cobalt Kα rays. A rare earth element compound having diffraction peaks at x = 0.85 ± 0.008 nm, d = 0.828 ± 0.01 nm, and d = 0.759 ± 0.007 nm in the X-ray diffraction diagram,
Nickel electrode for alkaline storage battery. In an X-ray diffraction diagram of cobalt by Kα ray, including nickel hydroxide, a cobalt compound in which the oxidation number of cobalt is greater than divalent, and at least one element selected from the group consisting of ytterbium, erbium, lutetium and thulium a positive electrode having an active material including a rare earth element compound having diffraction peaks at d = 0.85 ± 0.008 nm, d = 0.838 ± 0.01 nm, and d = 0.759 ± 0.007 nm;
A negative electrode,
An alkaline electrolyte disposed between the positive electrode and the negative electrode;
Alkaline storage battery.

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