JP3744642B2 - Nickel-metal hydride storage battery and method for manufacturing the same - Google Patents

Nickel-metal hydride storage battery and method for manufacturing the same Download PDF

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JP3744642B2
JP3744642B2 JP07381697A JP7381697A JP3744642B2 JP 3744642 B2 JP3744642 B2 JP 3744642B2 JP 07381697 A JP07381697 A JP 07381697A JP 7381697 A JP7381697 A JP 7381697A JP 3744642 B2 JP3744642 B2 JP 3744642B2
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nickel
capacity
negative electrode
metal hydride
battery
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JPH103940A (en
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正夫 武江
幹朗 田所
忠司 伊勢
章史 山脇
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Sanyo Electric Co Ltd
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Sanyo Electric Co Ltd
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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    • Y02E60/10Energy storage using batteries

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Description

【0001】
【発明の属する技術分野】
本発明はニッケル−金属水素化物蓄電池に関し、詳しくは表面がコバルト化合物で被覆された水酸化ニッケル活物質を含む正極を備えたニッケル−金属水素化物蓄電池及びそのような蓄電池の製造方法に関する。
【0002】
【従来の技術】
ニッケル−金属水素化物蓄電池に用いられるニッケル正極の製法には、ニッケル粉末を焼結した焼結式基体に活物質を充填するいわゆる焼結式と、ニッケル繊維焼結多孔体や発泡ニッケル多孔体などの高多孔度のニッケル基体にペースト状の活物質を充填するいわゆる非焼結式(ペースト式)とがある。
【0003】
焼結式は、活物質の充填作業が煩雑であり、また基板の高多孔度化に限界があるため、電極の高エネルギー密度化を図り難いという欠点がある。これに対し、ペースト式は、充填作業性がよく、高密度充填が可能であるという特徴を有するので、電池の高エネルギー密度化、低価格化の要請の高まりとともに、焼結式に代えて非焼結式のニッケル正極が主流になりつつある。
【0004】
しかし、高多孔度のニッケル基体を用いるペースト式は、高密度充填が可能である反面、基体の細孔径が大きいので、活物質と基体との電気的接触が不充分となる。よって、電極の集電効率が悪い。このため、高密度に充填された活物質の発電能力を十分に引出し得ないという欠点がある。
【0005】
そこで、このようなペースト式の欠点を改善することを目的とし、従来より、▲1▼水酸化ニッケルと水酸化カドミウム又は水酸化コバルトを含む固溶体活物質粉末の表面に水酸化コバルトの被覆層を形成する技術(特開昭62−222566号公報)や、▲2▼水酸化ニッケルの表面部に水酸化ニッケルと水酸化コバルトの固溶体を形成する技術(特開平3−62457号公報)、更には前記特開昭62−222566号公報に記載の技術を一層改良した技術として▲3▼水酸化ニッケル表面に形成されたコバルト化合物を含む被覆層の上に親水性有機物膜を施す技術(特開平5ー151962号公報)などが提案されている。
【0006】
これらの技術によると、活物粒子相互間の導電性が向上し、活物質利用率が高まるので、ニッケル正極の電極容量が向上する。しかし、ニッケル正極の容量の向上が直ちにアルカリニッケル蓄電池の性能向上に直結するものではない。
【0007】
なぜなら、活物質利用率が高まると、正極の実働電極容量が大きくなるが、この正極に対し従来の負極をそのまま使用した場合、正極の実働電極容量が大きくなった分、負極の余裕容量(充電リザーブ)が縮小する。したがって、充電時に負極より解離する水素の量が多くなり、電池内圧が高まる。また、充放電サイクルの進行により負極性能が劣化すると、容易に正極規制が崩れる。解離水素の増加や正極規制の崩壊は、安全弁の作動による電解液の電池外への放出を結果し、蓄電池のサイクル寿命を低下させる。
【0008】
よって、ニッケル正極の電極容量の向上をアルカリニッケル蓄電池の性能向上に繋げるためには、当該ニッケル正極の性能に適合する負極を用い、かつ正負両電極の電極容量を適正にバランスさせる必要がある。
【0009】
【発明が解決しようとする課題】
本発明は、活物質利用率の高いニッケル正極と、低温放電特性に優れた水素吸蔵合金負極を用い、両電極のバランスを好適に規定して、実働電池容量が大きく、かつ充電時の電池内圧の上昇が少ない、低温放電特性やサイクル特性に優れたニッケル−金属水素化物蓄電池を提供することを目的とする。
【0010】
【課題を解決するための手段】
上記目的を達成するために、一群の発明は次のように構成されている。 1の発明は、水酸化ニッケル又は主成分が水酸化ニッケルである母粒子の表面に、コバルト化合物層が形成されてなる被覆Ni活物質を含む非焼結ニッケル電極と、水素を吸蔵放出することのできる水素吸蔵合金を含む金属水素化物電極と、アルカリ電解液とで構成されるニッケル−金属水素化物蓄電池であって、下記数2で表される初期充放電後における負極充電深度が、80%以下に規制されたニッケル−金属水素化物蓄電池である。
【数2】

Figure 0003744642
【0011】
第2の発明は、水酸化ニッケル又は主成分が水酸化ニッケルである母粒子の表面に、コバルト化合物層が形成されてなる被覆Ni活物質を含む非焼結ニッケル電極と、水素を吸蔵放出することのできる水素吸蔵合金を含む金属水素化物電極と、アルカリ電解液とで構成されるニッケル−金属水素化物蓄電池であって、下記数1で表される初期充放電後における正極未反応容量率が16%以下であり、かつ下記数2で表される初期充放電後における負極充電深度が80%以下に規制されたニッケル−金属水素化物蓄電池である。
【0012】
【数1】
Figure 0003744642
【0013】
【数2】
Figure 0003744642
【0014】
第3の発明は、上記第1または第2の発明にかかるニッケル−金属水素化物蓄電池において、前記コバルト化合物層のコバルト化合物の平均価数が、2価よりも大きいことを特徴とする 。
【0015】
第4の発明は、上記第1乃至第3の発明にかかるニッケル−金属水素化物蓄電池において、前記数2における負極残存容量が、電池実働容量の40%以下であり、かつ前記水素吸蔵合金が、酸性水溶液により表面処理した水素吸蔵合金であることを特徴とする。
【0016】
第5の発明は、上記第4の発明にかかるニッケル−金属水素化物蓄電池において、前記表面処理した水素吸蔵合金が、pHが0.5以上、3.5以下の酸性水溶液で洗浄して表面処理したものであることを特徴とする。
【0017】
第6の発明は、水酸化ニッケル又は主成分が水酸化ニッケルである母粒子を、コバルト化合物を含有する溶液に分散し、この分散液にアルカリ溶液を注加して分散液pHを調整することによりコバルト化合物を析出させ、前記母粒子をコバルト化合物で被覆して被覆粒子となす第1の工程と、上記被覆粒子にアルカリ金属溶液を含浸し、酸素存在下で加熱処理して被覆Ni活物質となす第2の工程と、第2の工程で加熱処理した被覆Ni活物質を用いて、下記数1で表される正極未反応容量率が16%以下の非焼結ニッケル正極を作製する第3の工程と、上記非焼結ニッケル正極と、水素吸蔵合金の充填された金属水素化物負極と、アルカリ電解液とを用いて、下記数2で表される初期充放電後における負極充電深度が、80%以下に規制されたニッケル−金属水素化物蓄電池を作製する第4の工程を備えるニッケル−金属水素化物蓄電池の製造方法である。
【0018】
【数1】
Figure 0003744642
【0019】
【数2】
Figure 0003744642
【0020】
第7の発明は、上記第6の発明にかかるニッケル−金属水素化物蓄電池の製造方法において、前記第2の工程の加熱処理が、コバルト化合物層を形成するコバルト化合物の平均価数を2価よりも大きくすることを内容とする。
【0021】
第8の発明は、上記第6または第7の発明にかかるニッケル−金属水素化物蓄電池の製造方法において、前記第2の工程におけるアルカリ金属溶液のアルカリ濃度を15〜40wt%とすることを特徴とする。
【0022】
第9の発明は、上記第6乃至第8の発明にかかるニッケル−金属水素化物蓄電池の製造方法において、前記第2の工程における加熱処理温度を50〜150℃とすることを特徴とする。
【0023】
第10の発明は、上記第6乃至第9の発明にかかるニッケル−金属水素化物蓄電池の製造方法において、前記数2における負極残存容量が、電池実働容量の40%以下である場合においては、前記水素吸蔵合金として、酸性水溶液により表面処理した水素吸蔵合金を使用することを特徴とする。
【0024】
第11の発明は、上記第10の発明にかかるニッケル−金属水素化物蓄電池の製造方法において、前記酸性水溶液のpH値を0.5〜3.5とすることを特徴とする。
【0025】
【発明の実施の形態】
本発明の実施の形態を製造方法に基づいて説明する。本発明ニッケル−金属水素化物蓄電池は、第1の工程から第4の工程を備える下記製造方法により製造できる。即ち、第1の工程においては、水酸化ニッケル又は主成分が水酸化ニッケルである母粒子を、コバルト化合物を溶解した溶液に分散し、この分散液にアルカリ溶液を注加して分散液pHを所定値に調整する。これにより分散液中のコバルト化合物が析出し、母粒子の表面がコバルト化合物で被覆される。このようにして被覆粒子を作製する。
【0026】
第2の工程においては、第1の工程で作製した被覆粒子にアルカリ金属溶液を含浸させて、酸素の存在下で加熱処理する。この加熱処理により、母粒子表面のコバルト化合物層(被覆層)の結晶構造を乱れさせることができる。また、コバルト化合物層のコバルトの酸化数を高次化できる。これにより、コバルト化合物層の電解液浸透性が良くなると共に導電性が高まり、その結果としてニッケル活物質の電気化学的反応性が顕著に向上する。
【0027】
上記加熱処理においては、好ましくはコバルト化合物層のコバルト化合物の平均価数を2価よりも大にする。平均価数が2価よりも大のコバルト化合物は、導電性が高いので、活物質粒子の利用率が確実に向上する。また、平均価数が2価よりも大のコバルト化合物は、充電電気量を消費する程度が小さいので、電極の充電効率が向上する。なお、平均価数の小さいコバルト化合物は、より多くの充電容量(酸化容量)を有するが、放電には直接寄与しない。よって、充電容量が大きい分、無用に充電電気量が消費されることになる。
【0028】
上記加熱処理においては、前記アルカリ金属溶液のアルカリ濃度を好ましくは15〜40wt%とする。この濃度であると、アルカリ強度の面から好適であると共に、適度な粘性を有するアルカリ水溶液となるので、アルカリ液がCo被覆粒子中に好適に浸透する。よって、被覆層中のコバルト化合物をムラなく2価を超えるコバルトの化合物に変化させることができる。
【0029】
また、上記加熱処理においては、加熱処理温度を好ましくは50〜150℃とする。この温度であると、酸素とアルカリの共存下で被覆層のコバルト化合物の平均価数を確実に2価以上の高次コバルト化合物に変化させることができ、かつ被覆層を形成する水酸化ニッケルの結晶構造を好適な状態に変化させることができるので、被覆Ni活物質の電気化学活性を顕著に向上させることができる。
【0030】
上記第2の工程に続く、第3の工程においては、前記被覆Ni活物質を用いて、下記数1で定義される正極の未反応容量率が16%以下の非焼結ニッケル正極を作製する。正極の未反応容量率が16%以下の活物質利用率の高い非焼結ニッケル正極を用いると、ニッケル−金属水素化物蓄電池の性能を顕著に高めることができる。ここで、未反応容量率が16%以下の高性能正極は、第2の工程で作製した導電性及び電解液浸透性に優れ電気化学的活性の高い被覆Ni活物質粒子を用い、この活物質粒子をペースト状とし高多孔度の非焼結式基体に充填することにより実現できる。
【0031】
なお、この第3の工程における「正極未反応容量率が16%以下」の要件は、本発明において常に必要不可欠な要件ではない。なぜなら、コバルト化合物被覆層を有しない従来のニッケル活物質を用いた正極の未反応容量率はおよそ19%以上であり、このことからして、Co被覆層を有する被覆Ni活物質を用い、未反応容量率が19%未満の正極と成せば、本発明独自の効果がそれなりに得られるからである。
【0032】
第4の工程においては、上記非焼結ニッケル正極に、水素吸蔵合金電極(金属水素化物負極)と、アルカリ電解液とを組み合わせて、下記数2で表される負極充電深度が80%以下に規制されるニッケル−金属水素化物蓄電池を作製する。
【0033】
【数1】
Figure 0003744642
【0034】
【数2】
Figure 0003744642
【0035】
上記数1における電池実働容量は、正極支配の電池系で測定した値である。また、正極理論容量は、水酸化ニッケルの充放電反応における価数変化が2価←→3価とした場合における単位重量当たりの電気容量289mAh/gを用い、数3によって算出した値である。
【0036】
【数3】
Figure 0003744642
【0037】
以上のようにして作製される本発明にかかるニッケル−金属水素化物蓄電池の特性について更に説明する。
【0038】
上記構成では、未反応容量率が16%以下の高性能なニッケル正極に対し、負極充電深度を80%以下に規制できる水素吸蔵合金電極を組み合わせた。負極充電深度を80%以下に規制した場合、負極余裕容量が十分に確保されているので、充電時において負極から解離する水素ガスを少なくできる。よって、水素ガス圧によって安全弁が作動することがないので、電解液の減少に起因する電池性能の低下(サイクル特性の低下)を生じない。つまり、上記構成によれば、電池実働容量を十分に大きくし、かつ負極からの水素ガスの発生を適正に抑制することができる。よって、高容量でサイクル寿命の長い電池が得られる。
【0039】
このような本発明構成の意義を、第1図に基づいて詳細に説明する。
第1図は、蓄電池の容量構成を示す概念図である。第1図において、正極の理論容量は、水酸化ニッケル未充放電容量(a)と電池実働容量(b)と水酸化ニッケル未放電容量(c)とを合算したもので表される。また、負極全容量は、負極余裕容量(x)と電池実働容量(b)と負極残存容量(y)とを合算したもので表される。負極全容量のうち負極残存容量(y)は、水酸化ニッケル未放電容量(c)及びコバルト化合物未放電容量(d)に対応する負極残存容量分y1 と、例えばセパレータの酸化などの正極反応以外の酸化反応分y2 からなる。
【0040】
水酸化ニッケル未充放電容量(a)は、充電も放電もされない未活用部分であり、水酸化ニッケル未放電容量(c)及びコバルト化合物未放電容量(d)は、充電されるが放電されない部分である。但し、コバルト化合物未放電容量(d)は、活物質利用率を高める目的で配合されたコバルト化合物の充電容量(酸化容量)を示すものであり、放電に寄与し得ないものであるので、正極理論容量の算出対象外としてある。
【0041】
ここで、本発明にかかる被覆Ni活物質の被覆層は、アルカリ加熱処理によってコバルトを高次化してあるので、充電に際し充電電気量の消費が少ない。また、高次のコバルト化合物からなる被覆層は、導電性に優れ、かつ結晶構造が乱れているので、電解液に対する濡れ性がよい。したがって、この被覆Ni活物質は利用率が高いので、このような被覆Ni活物質を充填してなるニッケル正極は未反応容量率が小さい。つまり、本発明によれば、第1図のa、c、dを縮小させ、bを大きくできる。より具体的には、本発明によれば、前記数1で定義される未反応容量率を16%以下とでき、このようなニッケル正極は優れて高い電極容量を有する。
【0042】
なお、本発明者らは、水酸化ニッケルに対しコバルト化合物粉末を添加し単に混合してなる活物質を充填した従来の非焼結式ニッケル正極では、未反応容量率が19.0%以上であることを確認している。
【0043】
ところで、未反応容量率16%以下の高性能なニッケル正極を、従来の負極と組み合わせて電池を構成した場合、水酸化ニッケル未充放電容量(a)と水酸化ニッケル未放電容量(c)とコバルト化合物未放電容量(d)とが縮小して正極の実働容量(b)が増加するが、その分、負極余裕容量xや負極残存容量yが縮小することになる。そして、このこと自体は、負極性能を最大限に引き出す方向に作用するので本来的に好ましいことである。しかし、本発明にかかる高性能なニッケル正極と、従来の負極とをそのまま組み合わせた場合、正極容量と負極容量が接近するため、充電時に負極から解離する水素の増加を招き、更には負極の僅かな劣化によっても電池の正極支配が崩れる。よって、ニッケル正極の性能の向上が電池性能の向上に結びつかない。
【0044】
ここにおいて、本発明では、上記数2で表される負極充電深度を80%以下となるように規制した。負極充電深度を80%以下に規制すると、負極余裕容量xが十分に確保されているので、充電時に安全弁が作動する程に負極から大量の水素が解離することがない。また、負極劣化が直ちに電池の正極支配の崩壊に繋がらない。よって、安全弁の作動に起因するサイクル特性の低下が防止でき、高容量でサイクル寿命に優れたニッケル−金属水素化物蓄電池となすことができる。
【0045】
このような本発明ニッケル−金属水素化物蓄電池においては、更に次のような構成を採用することができる。
第3の工程における負極未放電容量としては、好ましくは電池実働容量の40%以下とし、この場合においては負極活物質として酸性水溶液で表面処理した水素吸蔵合金を用いる。この構成によると、低温放電特性の低下が抑制できる。その理由は次のようである。
【0046】
上述したように、コバルト化合物の平均価数が2価より大であると、コバルトの充電電気量の消費量が減少すると共に、被覆Ni活物質の導電性が向上する結果、正極における水酸化ニッケル未放電容量c及びコバルト化合物未放電容量dが減少し、これに対応して負極残存容量yも減少する。そして、十分な実働放電容量を取り出すためには、負極残存容量は小さい程好ましい。ところが、負極活物質である水素吸蔵合金は、低温での電気化学的反応性が正極のニッケル活物質よりも低下し易い。したがって、負極残存容量を小さくし過ぎると、低温環境下での放電に際し電池が負極支配型となり、十分な放電容量が取り出せない(ニッケル正極の性能を十分に引き出せない)という問題が生じる。
【0047】
本発明者らが調べたところ、この種の従来電池の負極残存容量は、電池実働容量に対し約42%であり、負極残存容量が電池実働容量に対して40%以下である場合において、低温放電特性に問題が生じることが判った。このことを踏まえ、本発明者らは、水素吸蔵合金電極の低温放電特性を高める手段を種々検討した。その結果、前記被覆Ni活物質を充填してなる高性能ニッケル正極に対しては、酸性水溶液で表面処理した水素吸蔵合金を充填してなる水素吸蔵合金電極を組み合わせるのが好ましく、この組み合わせであると負極残存容量yを電池実働容量bに対し40%以下とした場合であっても、優れた低温放電特性が保持できる。
【0048】
具体的には、水素吸蔵合金を酸性水溶液、より好ましくはpH0.5〜3.5の酸性水溶液で洗浄し表面処理すると、水素吸蔵合金の電気化学的活性が高まる。この活性の高い水素吸蔵合金を用い構成した負極を用いると、電池実働容量bに対する負極残存容量yが40%以下であっても、低温放電特性が著しく低下しないニッケル−金属水素化物蓄電池とできる。つまり、低温放電特性を犠牲にすることなく、高容量の電池とできる。
【0049】
なお、酸性水溶液での処理によって、低温放電特性が高まるのは、粉砕工程等において水素吸蔵合金表面に形成された酸化物層が、酸性水溶液での洗浄により除去され、合金表面に触媒活性な金属単離層(Niリッチ層)が形成されるためと考えられる。
【0050】
ところで、上記アルカリ金属としては、例えば水酸化ナトリウム、水酸化カリウム、水酸化リチウムなどが例示できる。また、酸性水溶液としては、塩酸、硝酸、フッソ酸、リン酸などの水溶液が例示できる。更に、上記水素吸蔵合金としては、希土類系、ジルコニウム系、マグネシウム系等の水素吸蔵合金が例示できる。
【0051】
【実施例】
本発明の具体的内容を実験(図2〜図7)に基づいて説明する。
(正極の作製)
▲1▼コバルト化合物が加熱処理されていない正極
硫酸ニッケル水溶液に、この硫酸ニッケルに対して2モル%の硫酸亜鉛水溶液と、水酸化ナトリウム水溶液とを、アンモニア水でpHを調整しながら徐々に加えて、固溶状態の亜鉛が2モル%添加された水酸化ニッケル粉末を析出させた。
次に、この固溶状態の亜鉛が添加された水酸化ニッケル粉末に、硫酸コバルト水溶液と水酸化ナトリウム水溶液とを添加し、その添加量を調整しつつ、pH10で反応させた。これにより、前記水酸化ニッケル粉末の粒子表面に、コバルト化合物層が析出する。この際、水酸化ニッケルに対するコバルト化合物の割合は10モル%とした。その後、水洗、乾燥工程を経てコバルト化合物が被覆された活物質(被覆粒子)を作製した。
【0052】
次いで、上記活物質100重量部と、0.2重量部のヒドロキシプロピルセルロースを溶解させた水溶液50重量部とを混合して活物質スラリーを調製した。この後、このスラリーを多孔度95%の発泡体ニッケル(厚み1.6mm)に充填し、乾燥した後、これを圧延して、6種のニッケル電極(厚み0.6〜0.7mm)を作製した。これら6個のニッケル電極は、それぞれ活物質の充填量が異なっている。
このようにして作製したニッケル電極を、以下、それぞれ正極p1〜p6と称する。
【0053】
▲2▼コバルト化合物が空気中で加熱処理された正極
コバルト化合物が被覆された上記活物質(被覆粒子)を、空気中で100℃にて加熱処理した。この加熱処理した活物質を用いて活物質スラリーを調整したこと以外は、上記▲1▼の方法と同様にしてニッケル電極を作製した。
このようにして作製したニッケル電極を、以下、正極p7と称する。
【0054】
▲3▼コバルト化合物が酸素とアルカリの共存下で加熱処理された正極
コバルト化合物が被覆された上記活物質(被覆粒子)に対し、種々濃度の水酸化ナトリウム水溶液を添加し、しかる後、酸素ガスの存在下で種々温度にて30分間加熱処理し、更に水洗、乾燥を行って加熱処理済活物質粒子(被覆Ni活物質)を得た。この被覆Ni活物質を用いて活物質スラリーを調整したこと以外は、上記▲1▼の方法と同様にして9種のニッケル電極を作製した。
このようにして作製したニッケル電極を、以下、それぞれ正極p8〜p16と称する。
【0055】
▲4▼コバルト化合物粉末が単に混合された正極
固溶状態の亜鉛が2モル%添加された上記水酸化ニッケル粉末90重量部に、水酸化コバルト粉末10重量部を添加して両者を混合して、ニッケル活物質となしたこと以外は、上記▲1▼の方法と同様にしてニッケル正極(比較正極)を作製した。
このようにして作製したニッケル電極を、以下、正極p17と称する。
【0056】
下記表1に、上記正極p1〜p16における熱処理条件を示す。また、表2に、上記正極p1〜p6における単位重量当たりの容量及び正極容量を示す。各正極の容量(極板容量)は、正極とニッケル板からなる対極と、30重量%のKOH水溶液とで構成した試験セルに対し、電流120mAで24時間充電した後、1時間休止し、再び電流400mAhで放電終止電圧が−0.8V(v.s.ニッケル極)となるまで放電し、この時の放電容量を測定して、これを正極容量とした。正極の単位重量当たりの容量は、上記正極容量を正極活物質量で割った値である。
【0057】
【表1】
Figure 0003744642
【0058】
【表2】
Figure 0003744642
【0059】
(負極の作製)
▲1▼酸処理しない負極
先ず、市販のミッシュメタル(Mm;La,Ce,Nd,Pr等の希土類元素の混合物)、ニッケル(Ni)、コバルト(Co)、アルミニウム(Al)、マンガン(Mn)を原料とし、これらが元素比で1:3.4 :0.8 :0.2 :0.6 の割合となるように秤量し、高周波溶解炉を用い1000℃で10時間加熱して、組成式MmNi3.4 Co0.8 Al0.2 Mn0.6 の水素吸蔵合金鋳塊を作製した。
【0060】
次に、この合金鋳塊を窒素ガス雰囲気中で機械的に粉砕して合金粉末とし、この合金粉末を100メッシュ(目開き:150μm)及び500メッシュ(目開き:25μm)のフルイを使用して分級し、100メッシュから500メッシュの間に分級される合金粉末を得た。
【0061】
次いで、上記の各種合金粉末に、ポリテトラフルオロエチレン等の結着剤と、適量の水とを加えて混合し、水素吸蔵合金ペーストを調製した。この後、水素吸蔵合金ペーストの量を種々調整しつつ、これをパンチングメタルの両面に塗布した後、プレスした。このようにして電極容量の異なる6種の水素吸蔵合金電極(厚み0.4〜0.5mm)を作製した。
これらの水素吸蔵合金電極を、以下、それぞれ負極n1〜n6と称する。
下記表3に各負極の単位重量当たりの容量と負極容量とを示す。
【0062】
【表3】
Figure 0003744642
【0063】
▲2▼酸処理された負極
水素吸蔵合金粉末に下記に示すような酸処理を施したこと以外は、上記▲1▼と同様にして水素吸蔵合金電極を作製した。
先ず、前記合金粉末を種々pHの酸(合金粉末に対する割合:100wt%)に浸漬し、pHが7に達するまで攪拌型混合機で反応させた。次に、上記溶液を捨てた後、純水を合金重量当たり100wt%添加し、更に10分間攪拌型混合機で洗浄した後、この洗浄液を捨てた。しかる後、真空乾燥することにより、6通りの酸処理がなされた合金粉末を得た。
このようにして作製した6通りの水素吸蔵合金電極を、以下、それぞれ負極n8〜n13と称する。
下記表4に6通りの負極の酸処理時のpHを示す。
【0064】
【表4】
Figure 0003744642
【0065】
(電池の作製)
上記正極p1〜p16と負極n1〜n6、n8〜n13とを用い、下記に示す方法により電池を作製した。
先ず、正極と、負極と、ポリオレフィン樹脂繊維から成る不織布を主体とするセパレータとをそれぞれ所定寸法に切断した後、正極と負極とをセパレータを介して巻回し、渦巻型の電極体を得た。次に、この電極体を外装缶に挿入した後、アルカリ電解液を注液した後、外装缶を密閉した。このようにして、各種の円筒型ニッケル−水素化物蓄電池を作製した。
尚、各電池に何れの正負極を用いたかを判り易くするため、後記各実験結果を示す表に電池の種類と電極の種類とが併記してある。
【0066】
(実験1)
種々の容量を有する正極p1〜p6及びp17と、種々の容量を有する負極n1〜n6とを用いて本発明電池A1〜A3及び比較電池X1〜X4を作製し、各電池について、正極未反応容量率、負極充電深度、電池実働容量、電池内圧を調べた。その結果を下記表5及び図2に示す。 負極充電深度、充電時の電池内圧、及び電池実働容量の算出、測定方法については、以下の通りである。
【0067】
(1) 電池実働容量
各電池について、電流120mAで16時間充電した後、1時間休止し、電流240mAで放電終止電圧1.0Vになるまで放電した後、1時間休止するというサイクルを3サイクル行い、電池を活性化した。そして、3サイクル目の放電容量を実測し、これを電池実働容量(電池の初期容量)とした。
【0068】
(2) 正極未反応容量率
下記数1に従って算出した。
【0069】
Figure 0003744642
【0070】
ここで、電池実働容量は上記(1) で測定した値であり、正極理論容量は、活物質である水酸化ニッケルの充放電反応における価数変化が2価←→3価であるとし、この時の単位重量当たりの電気容量を289mAh/gとして下記数3から算出したものである。
【0071】
正極理論容量=289mAh/g×(正極中の水酸化ニッケル量g)…数3
【0072】
(3) 負極充電深度
負極充電深度は、下記数2に従って算出した。
Figure 0003744642
【0073】
ここで、負極全容量は、次のようにして測定した。先ず、水素吸蔵合金粉末1gに、導電剤としてカルボニルニッケル1.2gと結着剤としてポリテトラフルオロエチレン粉末0.2gとを加え、混練して合金ペーストを調製し、この合金ペーストをニッケルメッシュに包みプレス加工して容量測定用電極を作製した。この電極と、この電極より十分大きな容量を持つ非焼結式ニッケル電極を密閉容器に配置し、電解液として30重量%のKOHを過剰量入れて、容量測定用電池となした。
【0074】
次に、この容量測定用電池に対し、電流50mAh/gで8時間充電を行った後、1時間休止し、再び電流50mAh/gで放電終止電圧が1.0Vとなるまで放電するという条件で充放電して放電容量を測定した。そして、この放電容量から合金の単位重量当たり容量を算出し、この単位重量当たり容量を用いて、n1〜n6、n10〜n13の水素吸蔵合金電極の全容量を算出した。
【0075】
他方、負極残存容量は、次のようにして測定した。前記(1) 電池実働容量の測定に示したと同様の条件で電池を活性化した後、30%のKOH水溶液中で正負極を過放電させ、この時の負極残存容量を測定した。過放電条件としては、電流120mAで放電終止負極電位が−0.3V(v.s.水銀/酸化水銀電極)まで放電するという条件を採用した。
【0076】
(4) 充電時の電池内圧
前記(1) 電池実働容量の測定で示したのと同様の条件で活性化した電池に対し、電流1200mAで1時間の充電を行った後に、電池内圧を測定した。
【0077】
【表5】
Figure 0003744642
【0078】
上記表5及び図2から、正極未反応容量率が14.8〜15.4%であり、かつ負極充電深度が80%以下の本発明電池A1〜A3では、電池実働容量が若干小さくなったものの、電池内圧が低かった。これに対し、本発明電池A1〜A3とほぼ同様の正極未反応容量率を有し、かつ負極充電深度が80%を超える比較電池X1〜X3では、電池内圧が高く、特に負極充電深度が84%を超える比較電池X2、X3では、電池内圧が高かった。
【0079】
これは、本発明電池A1〜A3では、負極充電深度が80%以下に規制されているため、負極からの解離水素が少ないのに対し、比較電池X1〜X3では負極充電深度が高いため多量の解離水素が発生するためと考えられる。
他方、上記A1〜A3及びX1〜X3に比べ、正極未反応容量率の高い比較電池X4(未反応容量率19.0%)では、電池内圧が本発明電池A1〜A3よりも高かった。また、負極充電深度及び電池内圧についてはX1とほぼ同等であったが、電池実働容量についてはX1よりも小さかった。
【0080】
この比較電池X4は、コバルト化合物粉末を単に混合してなるニッケル活物質を用いたものである。このX4において、X1と同等の電池実働容量を確保しようとすると、正極活物質量を増量しなければならない。なぜなら、X4はX1に比較し正極未反容量率が大きいからである。ここで、同一サイズ(同一容積)の電池であれば、正極活物質量を増量した分、負極活物質量を削減しなければならなくなるが、このように改変した電池X4では、当然に元の電池X4よりも負極充電深度が大きくなる。したがって、電池内圧が大幅に上昇する。つまり、正極未反応容量率が19.0%の正極(p17)用いたのでは、本発明電池A3の如くに電池実働容量に優れ、且つ電池内圧の上昇の少ない電池が得られ難い。
【0081】
以上から、電池内圧を低い水準に保ち、且つ電池実働容量の大きい電池となすためには、正極未反応容量率が19.0%未満、好ましくは16%以下のニッケル正極を用い、かつこのニッケル正極を、負極充電深度が80%以下となるような水素吸蔵合金負極と組み合わせる必要がある。
【0082】
(実験2)
加熱処理を行っていない正極p4、アルカリを用いないで空気中で加熱処理した正極p7、及び酸素とアルカリとの共存下で加熱処理(アルカリ加熱処理)した正極p10について、活物質の単位重量当たりの容量を測定したので、その結果を下記表6に示す。
【0083】
単位重量当たりの容量の測定方法は、前記した方法と同様である。すなわち、各正極とニッケル板と、30重量%のKOH水溶液とで構成した試験セルに対し、電流120mAで24時間充電した後、1時間休止し、再び電流400mAhで放電終止電圧が−0.8V(v.s.ニッケル極)となるまで放電し、この時の放電容量を測定し、この放電容量を正極活物質量で割った値を単位重量当たりの容量とした。
【0084】
【表6】
Figure 0003744642
【0085】
上記表6から明らかなように、空気中でアルカリを共存させず加熱処理を行った正極p7は単位重量当たりの容量が178mAh/gと大きく低下していることが認められた。また、加熱処理を行っていない正極p4では単位重量当たりの容量が226mAh/gであった。これに対し、酸素とアルカリとの共存下でアルカリ加熱処理を行った正極p10では単位重量当たりの容量が243mAh/gと大きく向上していた。
【0086】
この結果から、アルカリ加熱処理により、正極の水酸化ニッケル未充放電容量a、水酸化ニッケル未放電容量c(第1図参照)を縮小させることが確認できた。そして、上記a、cの縮小は負極残存容量の縮小に連動するので、電池実働容量が高まり、その結果として高容量の二次電池を得ることができる。
【0087】
なお、表6の結果は、次のように考察できる。加熱処理を行っていない正極p4では、正極活物質の主成分である水酸化ニッケルが、初期の充放電反応において完全に放電できず、また正極活物質の利用率を改善するために添加しているコバルト化合物が放電に寄与しないため、それに対応する電気量が負極に蓄積される。
これに対し、アルカリ加熱処理を行った正極p10では、このアルカリ加熱処理によって化学的に水酸化ニッケル及びコバルト化合物が酸化(充電と等価)されるので、その分、初期充放電において充電電気量の損失が緩和される。更に、このアルカリ加熱処理によりコバルト化合物が高次化し、Co被覆層の導電性が高まるので、正極活物質(被覆Ni活物質)の利用率が向上する。つまり、正極p10は、充放電効率が高いので、その分単位重量当たりの容量が大きくなる。
【0088】
その一方、アルカリを共存させず加熱処理を行った正極p7において、単位重量当たりの容量が大きく低下したのは、アルカリの存在がないと、結晶性の高いコバルト化合物が生成し、このようなコバルト化合物は結晶性の乱れたコバルト化合物に比べ導電性が低いためではないかと考えられる。したがって、加熱処理は酸素とアルカリとの共存下で行うアルカリ加熱処理とするのが好ましい。
【0089】
(実験3)
上記実験2で示したことを確認すべく、正極p4及びp10を用いた電池A4及びA9(負極はn4共通)について電池実働容量及び負極残存容量を測定した。尚、測定は、上記実験1で示した方法と同様の方法にて行った。
その結果、電池実働容量は、電池A4が1266mAhであるのに対し、電池A9では1327mAhであり、電池A9において電池実働容量が大幅に向上していた。また、負極残存容量は、電池A4が533mAhであるのに対し、電池A9では320mAhであり、電池A9において負極残存容量が大幅に低減していた(表8参照)。
【0090】
この結果からも、上記実験2で示したように、酸素とアルカリとの共存下で加熱処理を行えば、負極残存容量を低下させることができ、その結果として電池の高容量化が達成できることが確認できた。
【0091】
(実験4)
正極p4及びp10で用いた水酸化ニッケルについて、コバルト化合物の結晶性の違いを調べた。その結果を、図3に示す。
結晶性の違いは、加熱処理を行わないコバルト化合物(p4)と、酸素とアルカリとの共存下で加熱処理したアルカリ加熱処理済のコバルト化合物(p10)をX線回折分析法で比較する方法によった。尚、X線回折分析法における諸条件は、以下の通りである。
【0092】
対陰極:Cukα
管電圧:40kV
走査速度:2.00°/分
管電流:30mA
【0093】
図3から明らかなように、加熱処理をしないコバルトでは高い結晶性が見られたのに対し(図中a参照)、アルカリ加熱処理を行ったコバルトでは結晶性が殆ど見られなかった(図中b参照)。
【0094】
(実験5)
次に、加熱処理をしない正極p4及び酸素とアルカリとの共存下で加熱処理した正極p10に用いた活物質の被覆層(水酸化ニッケル表面のコバルト化合物)の平均価数を原子吸光法にて測定した。その結果を下記表7に示す。
平均価数の具体的測定方法は、次の通りである。
【0095】
先ず、試料を一定量秤量し、濃塩酸に溶かし、溶液中のコバルト量を原子吸光法にて定量する。この際、すべてのコバルト(2価コバルト及び3価コバルト)は塩酸に溶けるため、この時定量されるコバルト量は被覆層中に含まれる全コバルト量(2価コバルト及び3価コバルトの総量)となる。この量をAとする。次に、別途同じ試料を先と同じ量を秤量し、濃硝酸に溶かし、溶液を濾過した後、濾液中のコバルト量を原子吸光法にて定量する。この際、2価のコバルトは硝酸に溶けるが、3価コバルトは硝酸に溶けないため、濾過により2価コバルトのみ含む濾液が得られる。よって、この時定量されるコバルト量は被覆層中に含まれる2価コバルト量のみとなる。この量をBとする。そして、各試料の平均価数を下記数4により算出する。
【0096】
コバルト平均価数=(3A−B)/A …数4
【0097】
【表7】
Figure 0003744642
【0098】
上記表7から明らかなように、加熱処理をしない正極p4ではコバルトの価数が2.0であったのに対し、酸素とアルカリとの共存下で加熱処理した正極p10ではコバルトの価数2.9であり、大きく高次化していることが認められた。本実験5および前記実験4の結果からして、アルカリ加熱処理した場合、被覆層のコバルト化合物が化学的に酸化されて、平均価数が2価より大になると共に、コバルト化合物の結晶性に乱れが生じる。そして、コバルト化合物のこのような変化に起因して、前記表8の電池A9に示すような高い電池実働容量が得られたものと考えられる。
【0099】
(実験6)
酸素とアルカリとの共存下で加熱処理する際のアルカリ濃度が異なる電池A7〜A11を用いて、アルカリ濃度と電池実働容量及び負極残存容量との関係を調べた。その結果を下記表8及び図4に示す。
尚、電池実働容量及び負極残存容量の測定は上記実験1に示す方法と同様の方法で行った。
【0100】
【表8】
Figure 0003744642
【0101】
表8及び図4から明らかなように、アルカリ濃度が15〜40重量%のときに負極残存容量が小さくなって、電池実働容量が大きくなっていることが認められた。したがって、酸素とアルカリとの共存下で加熱処理する際のアルカリ濃度は、15〜40重量%であるのが望ましい。
【0102】
(実験7)
酸素とアルカリとの共存下で加熱処理する際の温度が異なる電池A9及びA12〜A15を用いて、処理温度と電池実働容量及び負極残存容量との関係を調べた。その結果を下記表9及び図5に示す。
尚、電池実働容量及び負極残存容量の測定は上記実験1に示す方法と同様の方法で行った。
【0103】
【表9】
Figure 0003744642
【0104】
上記表9及び図5から明らかなように、処理温度が50〜150℃のときに負極残存容量が小さくなって、電池実働容量が大きくなっていることが認められた。この結果からして、酸素とアルカリとの共存下で加熱処理する際の処理温度は、50〜150℃であるのが望ましい。
【0105】
(実験8)
電池実働容量に対する負極残存容量の比率が異なる電池A9及びA12〜A15を用いて、電池実働容量に対する負極残存容量の比率(以下、負極残存容量率と称する)と低温における放電率(以下、低温放電率と称する)との関係を調べた。その結果を下記表10及び図6(図中●で示している)に示す。
低温放電率の算出は、以下のようにして行った。
先ず、前記▲1▼電池実働容量の測定で示す条件で電池を活性化する。次に、電流120mAで16時間充電した後、−10℃で1時間休止し、更に電流1200mAで放電終止電圧1.0Vまで放電する。そして、この放電時の放電容量の、電池初期容量に対する比率(百分率)を低温放電率%とした。
【0106】
【表10】
Figure 0003744642
【0107】
上記表10及び図6から明らかなように、負極残存容量率が40%以下の電池A9、A13及びA14では、低温放電率が大きく低下した。よって、負極充電深度を低く規定して負極残存容量率を40%以下にしたのでは、常温におけるサイクル特性等は向上するが、低温放電特性が低下するという問題が生じる。
そこで、低温放電特性をも改善すべく、下記実験9を行った。
【0108】
(実験9)
電池A16〜A20(水素吸蔵合金を酸性水溶液により表面処理した電池)を用いて、負極残存容量率と低温放電率との関係を調べたので、その結果を下記表11及び図6(図中▲で示している)に示す。
尚、低温放電率の算出は、上記実験8と同様にして行った。
【0109】
【表11】
Figure 0003744642
【0110】
上記表11及び図6から明らかなように、酸処理しない水素吸蔵合金負極を用いた電池(●)では、負極残存容量率が低下すると、低温放電率が顕著に低下した。これに対し、酸性水溶液により表面処理した負極を用いた電池(▲)では、負極残存容量率が40%以下となっても、低温放電率の低下が少なかった。このことから、負極残存容量率を40%以下とし、かつ酸処理した水素吸蔵合金を用いることにより、常温におけるサイクル特性等の向上と共に、低温放電特性をも向上させることができることが判る。
【0111】
水素吸蔵合金を酸性水溶液により表面処理することにより、サイクル特性や低温放電特性を向上させることができるのは、酸処理により合金表面の活性面が十分に露出し、その結果として、負極の反応性が高まるからであると考えられる。
【0112】
(実験10)
種々のpHで酸処理した水素吸蔵合金を使用した電池A10及びA22〜A26(前記表4及び下記表12参照)を用いて、酸処理時のpHと低温放電率との関係を調べた。その結果を下記表12及び図7に示す。
尚、低温放電率の算出は、上記実験8と同様にして行った。
【0113】
【表12】
Figure 0003744642
【0114】
上記表12及び図7から明らかなように、酸性水溶液のpHが0.5〜3.5の場合に、高い低温放電率が得られることが認められた。
【0115】
【発明の効果】
以上説明したように、表面にCo被覆層が形成された水酸化ニッケルを用いた高性能な非焼結式ニッケル正極(未反応容量率が16%以下)に対し、負極充電深度が80%以下になる容量を有する水素吸蔵合金電極とを組み合わせる本発明構成によると、電池実働容量が大きくかつ電池内圧の上昇の少ないニッケル−金属水素化物蓄電池が得られる。
【0116】
特に、上記Co被覆層を組成するコバルト化合物の平均価数を2価よりも大にし、負極活物質である水素吸蔵合金を酸性水溶液で表面処理し、更に負極残存容量を電池実働容量の40%以下とする本発明構成によると、電池実働容量、サイクル特性に優れ、更に低温放電特性にも優れたニッケル−金属水素化物蓄電池が提供できる。
【図面の簡単な説明】
【図1】電池の容量構成を示す説明図である。
【図2】負極充電深度と電池内圧及び電池実働容量との関係を示すグラフである。
【図3】正極p4及びp10に用いたコバルト化合物のX線チャート図である。
【図4】アルカリ加熱処理時のアルカリ濃度と電池実働容量及び負極残存容量との関係を示すグラフである。
【図5】アルカリ加熱処理時の処理温度と電池実働容量及び負極残存容量との関係を示すグラフである。
【図6】負極残存容量率と低温放電率との関係を示すグラフである。
【図7】酸処理時のpHと低温放電率との関係を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a nickel-metal hydride storage battery, and more particularly to a nickel-metal hydride storage battery having a positive electrode containing a nickel hydroxide active material whose surface is coated with a cobalt compound and a method for manufacturing such a storage battery.
[0002]
[Prior art]
The nickel positive electrode used in nickel-metal hydride storage batteries includes a so-called sintered type in which a sintered base in which nickel powder is sintered is filled with an active material, a nickel fiber sintered porous body, a foamed nickel porous body, etc. There is a so-called non-sintered type (paste type) in which a pasty active material is filled in a highly porous nickel base.
[0003]
The sintering method has a drawback that it is difficult to increase the energy density of the electrode because the filling operation of the active material is complicated and there is a limit to increasing the porosity of the substrate. On the other hand, the paste type has the characteristics that the filling workability is good and high density filling is possible. Therefore, with the increasing demand for higher energy density and lower price of the battery, the paste type is replaced with a non-sintering type. Sintered nickel positive electrodes are becoming mainstream.
[0004]
However, the paste type using a highly porous nickel substrate is capable of high-density filling, but has a large pore diameter of the substrate, resulting in insufficient electrical contact between the active material and the substrate. Therefore, the current collection efficiency of the electrode is poor. For this reason, there exists a fault that the electric power generation capability of the active material filled with high density cannot be pulled out sufficiently.
[0005]
Therefore, in order to improve the disadvantages of the paste type, a coating layer of cobalt hydroxide is conventionally formed on the surface of the solid solution active material powder containing (1) nickel hydroxide and cadmium hydroxide or cobalt hydroxide. Forming technology (Japanese Patent Laid-Open No. 62-222656), (2) technology for forming a solid solution of nickel hydroxide and cobalt hydroxide on the surface of nickel hydroxide (Japanese Patent Laid-Open No. 3-62457), and (3) Technology for applying a hydrophilic organic film on a coating layer containing a cobalt compound formed on a nickel hydroxide surface as a technology that further improves the technology described in the above-mentioned JP-A-62-222566. No. 151962) has been proposed.
[0006]
According to these techniques, the electrical conductivity between the active material particles is improved and the active material utilization rate is increased, so that the electrode capacity of the nickel positive electrode is improved. However, the improvement in the capacity of the nickel positive electrode does not immediately lead to the improvement in the performance of the alkaline nickel storage battery.
[0007]
This is because when the active material utilization rate increases, the working electrode capacity of the positive electrode increases, but when the conventional negative electrode is used as it is, the capacity of the negative electrode (charge) (Reserve) is reduced. Therefore, the amount of hydrogen dissociated from the negative electrode during charging increases, and the battery internal pressure increases. Further, when the negative electrode performance deteriorates due to the progress of the charge / discharge cycle, the positive electrode regulation is easily broken. The increase in dissociated hydrogen and the collapse of the positive electrode regulation result in the release of the electrolyte from the battery due to the operation of the safety valve, thereby reducing the cycle life of the storage battery.
[0008]
Therefore, in order to improve the electrode capacity of the nickel positive electrode to improve the performance of the alkaline nickel storage battery, it is necessary to use a negative electrode suitable for the performance of the nickel positive electrode and to properly balance the electrode capacity of the positive and negative electrodes.
[0009]
[Problems to be solved by the invention]
The present invention uses a nickel positive electrode with a high active material utilization rate and a hydrogen storage alloy negative electrode with excellent low-temperature discharge characteristics, suitably defines the balance between both electrodes, has a large working battery capacity, and a battery internal pressure during charging. An object of the present invention is to provide a nickel-metal hydride storage battery that is excellent in low-temperature discharge characteristics and cycle characteristics.
[0010]
[Means for Solving the Problems]
  To achieve the above objectives,DepartureMing is organized as follows.First 1According to the present invention, a non-sintered nickel electrode including a coated Ni active material in which a cobalt compound layer is formed on the surface of nickel hydroxide or a mother particle whose main component is nickel hydroxide, and occlusion and release of hydrogen. A nickel-metal hydride storage battery comprising a metal hydride electrode containing a hydrogen storage alloy and an alkaline electrolyte, and the negative electrode charge depth after initial charge / discharge represented by the following formula 2 is 80% or less Is a nickel-metal hydride storage battery regulated by
[Expression 2]
Figure 0003744642
[0011]
  SecondAccording to the present invention, a non-sintered nickel electrode including a coated Ni active material in which a cobalt compound layer is formed on the surface of nickel hydroxide or a mother particle whose main component is nickel hydroxide, and occlusion and release of hydrogen. A nickel-metal hydride storage battery comprising a metal hydride electrode containing a hydrogen storage alloy and an alkaline electrolyte, and the positive electrode unreacted capacity ratio after initial charge / discharge represented by the following formula 1 is 16% This is a nickel-metal hydride storage battery in which the negative electrode charge depth after the initial charge / discharge represented by the following formula 2 is regulated to 80% or less.
[0012]
[Expression 1]
Figure 0003744642
[0013]
[Expression 2]
Figure 0003744642
[0014]
  ThirdThe invention ofAccording to the first or second inventionThe nickel-metal hydride storage battery is characterized in that an average valence of the cobalt compound in the cobalt compound layer is greater than 2.
[0015]
  4thThe invention ofThe firstThruConcerning the third inventionIn the nickel-metal hydride storage battery, the remaining capacity of the negative electrode in Formula 2 is 40% or less of the battery working capacity, and the hydrogen storage alloy is a hydrogen storage alloy surface-treated with an acidic aqueous solution. .
[0016]
  5thThe invention ofAccording to the fourth inventionThe nickel-metal hydride storage battery is characterized in that the surface-treated hydrogen storage alloy is a surface treatment by washing with an acidic aqueous solution having a pH of 0.5 or more and 3.5 or less.
[0017]
  6thIn this invention, nickel hydroxide or mother particles whose main component is nickel hydroxide is dispersed in a solution containing a cobalt compound, and an alkaline solution is poured into this dispersion to adjust the pH of the dispersion. A first step of depositing a compound and coating the base particles with a cobalt compound to form coated particles; and impregnating the coated particles with an alkali metal solution and heat-treating in the presence of oxygen to form a coated Ni active material. Using the second step and the coated Ni active material heat-treated in the second step, a third non-sintered nickel positive electrode having a positive electrode unreacted capacity ratio represented by the following formula 1 of 16% or less is prepared. Using the step, the non-sintered nickel positive electrode, the metal hydride negative electrode filled with the hydrogen storage alloy, and the alkaline electrolyte, the negative electrode charge depth after the initial charge / discharge represented by the following formula 2 is 80 % Regulated Nickel - nickel comprising a fourth step of preparing a metal hydride storage batteries - a method for producing a metal hydride storage battery.
[0018]
[Expression 1]
Figure 0003744642
[0019]
[Expression 2]
Figure 0003744642
[0020]
  7thThe invention ofAccording to the sixth inventionIn the method for manufacturing a nickel-metal hydride storage battery, the heat treatment in the second step is to make the average valence of the cobalt compound forming the cobalt compound layer larger than divalent.
[0021]
  8thThe invention ofAccording to the sixth or seventh inventionIn the method for manufacturing a nickel-metal hydride storage battery, the alkali concentration of the alkali metal solution in the second step is 15 to 40 wt%.
[0022]
  9thThe invention ofAccording to the sixth to eighth inventionsIn the method for producing a nickel-metal hydride storage battery, the heat treatment temperature in the second step is 50 to 150 ° C.
[0023]
  10thThe invention ofAccording to the sixth to ninth inventionsIn the method for producing a nickel-metal hydride storage battery, when the remaining capacity of the negative electrode in Equation 2 is 40% or less of the battery working capacity, a hydrogen storage alloy surface-treated with an acidic aqueous solution is used as the hydrogen storage alloy. It is characterized by doing.
[0024]
  11thThe invention ofAccording to the tenth aspect of the inventionIn the method for producing a nickel-metal hydride storage battery, the acidic aqueous solution has a pH value of 0.5 to 3.5.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described based on a manufacturing method. This invention nickel-metal hydride storage battery can be manufactured with the following manufacturing method provided with a 4th process from a 1st process. That is, in the first step, nickel hydroxide or mother particles whose main component is nickel hydroxide is dispersed in a solution in which a cobalt compound is dissolved, and an alkaline solution is poured into this dispersion to adjust the dispersion pH. Adjust to a predetermined value. As a result, the cobalt compound in the dispersion is precipitated, and the surface of the mother particle is coated with the cobalt compound. In this way, coated particles are produced.
[0026]
In the second step, the coated particles produced in the first step are impregnated with an alkali metal solution and heat-treated in the presence of oxygen. By this heat treatment, the crystal structure of the cobalt compound layer (coating layer) on the surface of the mother particles can be disturbed. Further, the oxidation number of cobalt in the cobalt compound layer can be increased. Thereby, the electrolytic solution permeability of the cobalt compound layer is improved and the conductivity is increased. As a result, the electrochemical reactivity of the nickel active material is remarkably improved.
[0027]
In the heat treatment, the average valence of the cobalt compound in the cobalt compound layer is preferably set to be greater than 2. Since the cobalt compound having an average valence larger than divalent has high conductivity, the utilization factor of the active material particles is reliably improved. In addition, since the cobalt compound having an average valence larger than divalent has a small degree of consumption of charge electricity, the charging efficiency of the electrode is improved. A cobalt compound having a small average valence has more charge capacity (oxidation capacity), but does not directly contribute to discharge. Therefore, the amount of charge electricity is consumed unnecessarily due to the large charge capacity.
[0028]
In the heat treatment, the alkali concentration of the alkali metal solution is preferably 15 to 40 wt%. This concentration is suitable from the viewpoint of alkali strength and becomes an alkaline aqueous solution having an appropriate viscosity, so that the alkaline liquid suitably penetrates into the Co-coated particles. Therefore, the cobalt compound in the coating layer can be changed to a cobalt compound exceeding divalent without any unevenness.
[0029]
In the heat treatment, the heat treatment temperature is preferably 50 to 150 ° C. At this temperature, the average valence of the cobalt compound in the coating layer can be reliably changed to a higher-order cobalt compound having a valence of 2 or more in the presence of oxygen and alkali, and the nickel hydroxide that forms the coating layer can be used. Since the crystal structure can be changed to a suitable state, the electrochemical activity of the coated Ni active material can be significantly improved.
[0030]
In the third step subsequent to the second step, a non-sintered nickel positive electrode in which the unreacted capacity rate of the positive electrode defined by the following formula 1 is 16% or less is produced using the coated Ni active material. . When a non-sintered nickel positive electrode having a high active material utilization rate with an unreacted capacity ratio of the positive electrode of 16% or less is used, the performance of the nickel-metal hydride storage battery can be remarkably improved. Here, the high-performance positive electrode having an unreacted capacity ratio of 16% or less uses the coated Ni active material particles having excellent electroconductivity and electrolyte permeability and high electrochemical activity produced in the second step. This can be realized by making the particles into a paste and filling a highly porous non-sintered substrate.
[0031]
Note that the requirement that the positive electrode unreacted capacity ratio is 16% or less in the third step is not always indispensable in the present invention. This is because the unreacted capacity ratio of the positive electrode using the conventional nickel active material having no cobalt compound coating layer is about 19% or more, and therefore, using the coated Ni active material having the Co coating layer, This is because if the positive electrode has a reaction capacity ratio of less than 19%, the effect unique to the present invention can be obtained.
[0032]
In the fourth step, the non-sintered nickel positive electrode is combined with a hydrogen storage alloy electrode (metal hydride negative electrode) and an alkaline electrolyte, and the negative electrode charging depth represented by the following formula 2 is reduced to 80% or less. A regulated nickel-metal hydride battery is made.
[0033]
[Expression 1]
Figure 0003744642
[0034]
[Expression 2]
Figure 0003744642
[0035]
The battery working capacity in Equation 1 is a value measured in a positive electrode-dominated battery system. The theoretical capacity of the positive electrode is a value calculated by Equation 3 using the electric capacity 289 mAh / g per unit weight when the valence change in the charge / discharge reaction of nickel hydroxide is divalent ← → trivalent.
[0036]
[Equation 3]
Figure 0003744642
[0037]
The characteristics of the nickel-metal hydride storage battery according to the present invention produced as described above will be further described.
[0038]
In the above configuration, a hydrogen storage alloy electrode capable of regulating the negative electrode charging depth to 80% or less is combined with a high performance nickel positive electrode having an unreacted capacity ratio of 16% or less. When the negative electrode charging depth is regulated to 80% or less, a sufficient negative electrode capacity is secured, so that hydrogen gas dissociated from the negative electrode during charging can be reduced. Therefore, since the safety valve is not operated by the hydrogen gas pressure, the battery performance is not deteriorated (the cycle characteristics are not deteriorated) due to the decrease in the electrolyte. That is, according to the above configuration, it is possible to sufficiently increase the battery working capacity and appropriately suppress the generation of hydrogen gas from the negative electrode. Therefore, a battery having a high capacity and a long cycle life can be obtained.
[0039]
The significance of the configuration of the present invention will be described in detail with reference to FIG.
FIG. 1 is a conceptual diagram showing a capacity configuration of a storage battery. In FIG. 1, the theoretical capacity of the positive electrode is represented by the sum of nickel hydroxide uncharged and discharged capacity (a), battery actual capacity (b), and nickel hydroxide undischarged capacity (c). The total negative electrode capacity is represented by the sum of the negative electrode surplus capacity (x), the battery working capacity (b), and the negative electrode remaining capacity (y). Of the total capacity of the negative electrode, the negative electrode remaining capacity (y) is the negative electrode remaining capacity y corresponding to the nickel hydroxide undischarge capacity (c) and the cobalt compound undischarge capacity (d).1And, for example, an oxidation reaction component y other than the positive electrode reaction such as oxidation of the separator2Consists of.
[0040]
The nickel hydroxide uncharged / discharged capacity (a) is an unused part that is neither charged nor discharged, and the nickel hydroxide undischarged capacity (c) and the cobalt compound undischarged capacity (d) are parts that are charged but not discharged. It is. However, the cobalt compound non-discharge capacity (d) indicates the charge capacity (oxidation capacity) of the cobalt compound blended for the purpose of increasing the active material utilization rate and cannot contribute to the discharge. Not subject to calculation of theoretical capacity.
[0041]
Here, since the coating layer of the coated Ni active material according to the present invention has higher-order cobalt by alkaline heat treatment, the amount of charged electricity is less during charging. In addition, the coating layer made of a higher-order cobalt compound is excellent in conductivity and has a disordered crystal structure, and therefore has good wettability with respect to the electrolytic solution. Therefore, since this coated Ni active material has a high utilization factor, the nickel positive electrode formed by filling such a coated Ni active material has a small unreacted capacity ratio. That is, according to the present invention, a, c and d in FIG. 1 can be reduced and b can be increased. More specifically, according to the present invention, the unreacted capacity ratio defined by Equation 1 can be 16% or less, and such a nickel positive electrode has an excellent high electrode capacity.
[0042]
In the conventional non-sintered nickel positive electrode filled with an active material obtained by simply adding a cobalt compound powder to nickel hydroxide and mixing them, the unreacted capacity ratio is 19.0% or more. Confirm that there is.
[0043]
By the way, when a battery is constructed by combining a high-performance nickel positive electrode with an unreacted capacity ratio of 16% or less with a conventional negative electrode, nickel hydroxide uncharged discharge capacity (a) and nickel hydroxide undischarge capacity (c) The cobalt compound undischarged capacity (d) is reduced and the positive working capacity (b) is increased, but the negative electrode surplus capacity x and the negative electrode remaining capacity y are reduced accordingly. This is inherently preferable because it acts in the direction of maximizing the negative electrode performance. However, when the high-performance nickel positive electrode according to the present invention is combined with the conventional negative electrode as it is, the positive electrode capacity and the negative electrode capacity are close to each other. Even if the battery deteriorates, the control of the positive electrode of the battery is lost. Therefore, the improvement of the performance of the nickel positive electrode does not lead to the improvement of the battery performance.
[0044]
Here, in this invention, it controlled so that the negative electrode charge depth represented by the said Formula 2 might be 80% or less. If the negative electrode charging depth is regulated to 80% or less, the negative electrode surplus capacity x is sufficiently secured, so that a large amount of hydrogen is not dissociated from the negative electrode to the extent that the safety valve is activated during charging. Also, the negative electrode deterioration does not immediately lead to the collapse of the positive electrode control of the battery. Therefore, it is possible to prevent a decrease in cycle characteristics due to the operation of the safety valve, and to obtain a nickel-metal hydride storage battery having a high capacity and excellent cycle life.
[0045]
In such a nickel-metal hydride storage battery of the present invention, the following configuration can be further adopted.
The negative electrode undischarge capacity in the third step is preferably 40% or less of the battery working capacity. In this case, a hydrogen storage alloy surface-treated with an acidic aqueous solution is used as the negative electrode active material. According to this configuration, it is possible to suppress a decrease in low-temperature discharge characteristics. The reason is as follows.
[0046]
As described above, if the average valence of the cobalt compound is greater than 2, the consumption amount of the charged electricity of cobalt is reduced and the conductivity of the coated Ni active material is improved. As a result, nickel hydroxide in the positive electrode The undischarge capacity c and the cobalt compound undischarge capacity d decrease, and the negative electrode remaining capacity y decreases correspondingly. And in order to take out sufficient working discharge capacity, a negative electrode residual capacity is so preferable that it is small. However, the hydrogen storage alloy, which is a negative electrode active material, has a lower electrochemical reactivity at low temperatures than the nickel active material of the positive electrode. Therefore, if the remaining capacity of the negative electrode is made too small, the battery becomes the negative electrode dominant type during discharge in a low temperature environment, and there arises a problem that a sufficient discharge capacity cannot be taken out (the performance of the nickel positive electrode cannot be fully taken out).
[0047]
When the present inventors investigated, the negative electrode remaining capacity of this type of conventional battery was about 42% with respect to the battery working capacity, and when the negative electrode remaining capacity was 40% or less with respect to the battery working capacity, the low temperature was low. It was found that there was a problem with the discharge characteristics. Based on this, the present inventors have studied various means for improving the low temperature discharge characteristics of the hydrogen storage alloy electrode. As a result, for the high-performance nickel positive electrode filled with the coated Ni active material, it is preferable to combine a hydrogen storage alloy electrode filled with a hydrogen storage alloy surface-treated with an acidic aqueous solution, and this combination Even when the negative electrode remaining capacity y is 40% or less of the battery working capacity b, excellent low temperature discharge characteristics can be maintained.
[0048]
Specifically, when the hydrogen storage alloy is washed with an acidic aqueous solution, more preferably with an acidic aqueous solution having a pH of 0.5 to 3.5, and the surface treatment is performed, the electrochemical activity of the hydrogen storage alloy is increased. When a negative electrode composed of this highly active hydrogen storage alloy is used, even if the negative electrode remaining capacity y with respect to the battery working capacity b is 40% or less, a nickel-metal hydride storage battery in which the low-temperature discharge characteristics are not significantly reduced can be obtained. That is, the battery can have a high capacity without sacrificing the low-temperature discharge characteristics.
[0049]
The low-temperature discharge characteristics are enhanced by the treatment with the acidic aqueous solution because the oxide layer formed on the surface of the hydrogen storage alloy in the pulverization process or the like is removed by washing with the acidic aqueous solution, and a catalytically active metal is formed on the alloy surface. This is probably because an isolated layer (Ni-rich layer) is formed.
[0050]
By the way, examples of the alkali metal include sodium hydroxide, potassium hydroxide, and lithium hydroxide. Examples of the acidic aqueous solution include aqueous solutions of hydrochloric acid, nitric acid, hydrofluoric acid, phosphoric acid, and the like. Furthermore, examples of the hydrogen storage alloy include rare earth-based, zirconium-based, and magnesium-based hydrogen storage alloys.
[0051]
【Example】
Specific contents of the present invention will be described based on experiments (FIGS. 2 to 7).
(Preparation of positive electrode)
(1) Positive electrode without cobalt compound heat treatment
A 2 mol% zinc sulfate aqueous solution and a sodium hydroxide aqueous solution are gradually added to the nickel sulfate aqueous solution while adjusting the pH with aqueous ammonia, and 2 mol% of solid solution zinc is added. The prepared nickel hydroxide powder was deposited.
Next, a cobalt sulfate aqueous solution and a sodium hydroxide aqueous solution were added to the nickel hydroxide powder to which zinc in a solid solution state was added, and the reaction was performed at pH 10 while adjusting the addition amount. Thereby, a cobalt compound layer is deposited on the particle surface of the nickel hydroxide powder. At this time, the ratio of the cobalt compound to nickel hydroxide was 10 mol%. Thereafter, an active material (coated particles) coated with a cobalt compound was produced through a washing step and a drying step.
[0052]
Next, 100 parts by weight of the active material and 50 parts by weight of an aqueous solution in which 0.2 part by weight of hydroxypropylcellulose was dissolved were mixed to prepare an active material slurry. Thereafter, this slurry was filled in foam nickel (thickness 1.6 mm) having a porosity of 95%, dried, and then rolled to obtain six kinds of nickel electrodes (thickness 0.6 to 0.7 mm). Produced. Each of these six nickel electrodes has a different filling amount of the active material.
The nickel electrodes thus fabricated are hereinafter referred to as positive electrodes p1 to p6, respectively.
[0053]
(2) Positive electrode with cobalt compound heat-treated in air
The active material (coated particles) coated with the cobalt compound was heat-treated at 100 ° C. in air. A nickel electrode was produced in the same manner as in the above method (1) except that the active material slurry was prepared using the heat-treated active material.
The nickel electrode thus produced is hereinafter referred to as positive electrode p7.
[0054]
(3) Positive electrode in which cobalt compound is heat-treated in the presence of oxygen and alkali
Various concentrations of aqueous sodium hydroxide solution are added to the active material (coated particles) coated with the cobalt compound, and then heat-treated at various temperatures for 30 minutes in the presence of oxygen gas, followed by washing with water and drying. To obtain heat-treated active material particles (coated Ni active material). Nine kinds of nickel electrodes were produced in the same manner as in the above method (1) except that the active material slurry was prepared using this coated Ni active material.
The nickel electrodes thus fabricated are hereinafter referred to as positive electrodes p8 to p16, respectively.
[0055]
(4) Positive electrode in which cobalt compound powder is simply mixed
The above except that 10 parts by weight of cobalt hydroxide powder was added to 90 parts by weight of the above nickel hydroxide powder to which 2 mol% of solid solution zinc was added, and both were mixed to form a nickel active material. A nickel positive electrode (comparative positive electrode) was produced in the same manner as in method (1).
The nickel electrode thus produced is hereinafter referred to as positive electrode p17.
[0056]
Table 1 below shows the heat treatment conditions for the positive electrodes p1 to p16. Table 2 shows the capacity per unit weight and the positive electrode capacity in the positive electrodes p1 to p6. The capacity of each positive electrode (electrode plate capacity) was charged for 24 hours at a current of 120 mA to a test cell composed of a counter electrode composed of a positive electrode and a nickel plate and a 30 wt% KOH aqueous solution, then rested for 1 hour, and again The battery was discharged at a current of 400 mAh until the end-of-discharge voltage was −0.8 V (vs. nickel electrode), and the discharge capacity at this time was measured and used as the positive electrode capacity. The capacity per unit weight of the positive electrode is a value obtained by dividing the positive electrode capacity by the positive electrode active material amount.
[0057]
[Table 1]
Figure 0003744642
[0058]
[Table 2]
Figure 0003744642
[0059]
(Preparation of negative electrode)
(1) Negative electrode without acid treatment
First, commercially available misch metal (Mm; a mixture of rare earth elements such as La, Ce, Nd, and Pr), nickel (Ni), cobalt (Co), aluminum (Al), and manganese (Mn) are used as raw materials. Weigh it so that the ratio is 1: 3.4: 0.8: 0.2: 0.6, and heat it at 1000 ° C. for 10 hours using a high-frequency melting furnace.3.4Co0.8Al0.2Mn0.6A hydrogen storage alloy ingot was prepared.
[0060]
Next, the alloy ingot is mechanically pulverized into an alloy powder in a nitrogen gas atmosphere, and the alloy powder is obtained using 100 mesh (aperture: 150 μm) and 500 mesh (aperture: 25 μm) sieves. Classification was performed to obtain an alloy powder classified between 100 mesh and 500 mesh.
[0061]
Subsequently, a binder such as polytetrafluoroethylene and an appropriate amount of water were added to and mixed with the various alloy powders described above to prepare a hydrogen storage alloy paste. Thereafter, while applying various amounts of the hydrogen storage alloy paste, it was applied to both sides of the punching metal and then pressed. In this way, six types of hydrogen storage alloy electrodes (thickness 0.4 to 0.5 mm) having different electrode capacities were produced.
These hydrogen storage alloy electrodes are hereinafter referred to as negative electrodes n1 to n6, respectively.
Table 3 below shows the capacity per unit weight and the negative electrode capacity of each negative electrode.
[0062]
[Table 3]
Figure 0003744642
[0063]
(2) Acid-treated negative electrode
A hydrogen storage alloy electrode was produced in the same manner as in the above (1) except that the hydrogen storage alloy powder was subjected to an acid treatment as shown below.
First, the alloy powder was immersed in acids of various pH (ratio to the alloy powder: 100 wt%) and reacted with a stirring mixer until the pH reached 7. Next, after discarding the above solution, 100 wt% of pure water was added per alloy weight, and after further washing with a stirring mixer for 10 minutes, this washing solution was discarded. Thereafter, vacuum drying was performed to obtain an alloy powder subjected to six acid treatments.
The six hydrogen storage alloy electrodes thus prepared are hereinafter referred to as negative electrodes n8 to n13, respectively.
Table 4 below shows the pH during acid treatment of the six negative electrodes.
[0064]
[Table 4]
Figure 0003744642
[0065]
(Production of battery)
Using the positive electrodes p1 to p16 and the negative electrodes n1 to n6 and n8 to n13, batteries were produced by the method described below.
First, a positive electrode, a negative electrode, and a separator mainly composed of a nonwoven fabric made of polyolefin resin fibers were cut into predetermined dimensions, and then the positive electrode and the negative electrode were wound through the separator to obtain a spiral electrode body. Next, this electrode body was inserted into an outer can, and then an alkaline electrolyte was injected, and then the outer can was sealed. In this manner, various cylindrical nickel-hydride storage batteries were produced.
In addition, in order to make it easy to understand which positive and negative electrodes were used for each battery, the types of batteries and the types of electrodes are shown together in a table showing the results of each experiment described later.
[0066]
(Experiment 1)
Invention batteries A1 to A3 and comparative batteries X1 to X4 are prepared using positive electrodes p1 to p6 and p17 having various capacities and negative electrodes n1 to n6 having various capacities. The rate, the negative electrode charging depth, the battery working capacity, and the battery internal pressure were examined. The results are shown in Table 5 below and FIG. The method for calculating and measuring the negative electrode charging depth, the battery internal pressure during charging, and the battery working capacity is as follows.
[0067]
(1) Battery working capacity
Each battery was charged for 16 hours at a current of 120 mA, paused for 1 hour, discharged to a final discharge voltage of 1.0 V at a current of 240 mA, and then paused for 3 hours to activate the battery. . And the discharge capacity of the 3rd cycle was measured, and this was made into the battery working capacity (battery initial capacity).
[0068]
(2) Positive electrode unreacted capacity ratio
It calculated according to the following number 1.
[0069]
Figure 0003744642
[0070]
Here, the battery actual capacity is the value measured in the above (1), and the positive electrode theoretical capacity is assumed that the valence change in the charge / discharge reaction of nickel hydroxide as an active material is divalent ← → trivalent. The electric capacity per unit weight at the time is 289 mAh / g and calculated from the following formula 3.
[0071]
Positive electrode theoretical capacity = 289 mAh / g × (amount of nickel hydroxide in positive electrode g)
[0072]
(3) Negative electrode charging depth
The negative electrode charging depth was calculated according to the following formula 2.
Figure 0003744642
[0073]
Here, the total capacity of the negative electrode was measured as follows. First, 1.2 g of carbonyl nickel as a conductive agent and 0.2 g of polytetrafluoroethylene powder as a binder are added to 1 g of hydrogen storage alloy powder and kneaded to prepare an alloy paste. The electrode for capacity measurement was produced by wrapping and pressing. This electrode and a non-sintered nickel electrode having a capacity sufficiently larger than this electrode were placed in a hermetically sealed container, and an excess amount of 30 wt% KOH was added as an electrolytic solution to obtain a capacity measuring battery.
[0074]
Next, the capacity measurement battery was charged for 8 hours at a current of 50 mAh / g, then rested for 1 hour, and discharged again at a current of 50 mAh / g until the discharge end voltage reached 1.0 V. The discharge capacity was measured by charging and discharging. And the capacity | capacitance per unit weight of an alloy was computed from this discharge capacity, and the total capacity | capacitance of the hydrogen storage alloy electrode of n1-n6 and n10-n13 was computed using the capacity | capacitance per unit weight.
[0075]
On the other hand, the negative electrode remaining capacity was measured as follows. After activating the battery under the same conditions as described in (1) Measurement of battery working capacity, the positive and negative electrodes were overdischarged in a 30% KOH aqueous solution, and the negative electrode remaining capacity at this time was measured. As the overdischarge condition, a condition was adopted in which the discharge end negative electrode potential was discharged to −0.3 V (vs. mercury / mercury oxide electrode) at a current of 120 mA.
[0076]
(4) Battery internal pressure during charging
A battery activated under the same conditions as described in the above (1) measurement of battery working capacity was charged at a current of 1200 mA for 1 hour, and then the internal pressure of the battery was measured.
[0077]
[Table 5]
Figure 0003744642
[0078]
From the above Table 5 and FIG. 2, in the present invention batteries A1 to A3 in which the positive electrode unreacted capacity ratio was 14.8 to 15.4% and the negative electrode charge depth was 80% or less, the battery working capacity was slightly reduced. However, the battery internal pressure was low. On the other hand, in the comparative batteries X1 to X3 having the positive electrode unreacted capacity ratio substantially the same as the batteries A1 to A3 of the present invention and the negative electrode charging depth exceeding 80%, the battery internal pressure is high, in particular, the negative electrode charging depth is 84. In the comparative batteries X2 and X3 exceeding%, the battery internal pressure was high.
[0079]
In the present invention batteries A1 to A3, since the negative electrode charging depth is regulated to 80% or less, the dissociated hydrogen from the negative electrode is small, whereas in the comparative batteries X1 to X3, the negative electrode charging depth is high, so that a large amount This is probably because dissociated hydrogen is generated.
On the other hand, in the comparative battery X4 (unreacted capacity ratio 19.0%) having a higher positive electrode unreacted capacity ratio than the above-described A1 to A3 and X1 to X3, the battery internal pressure was higher than that of the batteries A1 to A3 of the present invention. Moreover, although the negative electrode charge depth and the battery internal pressure were almost the same as X1, the battery working capacity was smaller than X1.
[0080]
This comparative battery X4 uses a nickel active material obtained by simply mixing cobalt compound powder. In X4, in order to secure a battery working capacity equivalent to X1, the amount of the positive electrode active material must be increased. This is because X4 has a larger positive electrode non-reverse capacity ratio than X1. Here, if batteries of the same size (same volume) are used, the amount of the negative electrode active material must be reduced by the amount of increase in the amount of the positive electrode active material. The negative electrode charging depth is larger than that of the battery X4. Therefore, the battery internal pressure increases significantly. That is, when the positive electrode (p17) having a positive electrode unreacted capacity ratio of 19.0% is used, it is difficult to obtain a battery having excellent battery working capacity and little increase in battery internal pressure, as in the battery A3 of the present invention.
[0081]
From the above, in order to keep the battery internal pressure at a low level and obtain a battery having a large battery working capacity, a nickel positive electrode having a positive electrode unreacted capacity ratio of less than 19.0%, preferably 16% or less, is used. It is necessary to combine the positive electrode with a hydrogen storage alloy negative electrode in which the negative electrode charging depth is 80% or less.
[0082]
(Experiment 2)
Per unit weight of active material for positive electrode p4 not subjected to heat treatment, positive electrode p7 heat-treated in air without using alkali, and positive electrode p10 heat-treated in the coexistence of oxygen and alkali (alkali heat treatment) The capacity was measured, and the results are shown in Table 6 below.
[0083]
The method for measuring the capacity per unit weight is the same as described above. That is, a test cell composed of each positive electrode, a nickel plate, and a 30 wt% KOH aqueous solution was charged at a current of 120 mA for 24 hours, then rested for 1 hour, and again at a current of 400 mAh, the discharge end voltage was -0.8 V. The discharge capacity at this time was measured, and the value obtained by dividing the discharge capacity by the amount of the positive electrode active material was defined as the capacity per unit weight.
[0084]
[Table 6]
Figure 0003744642
[0085]
As is apparent from Table 6 above, it was confirmed that the capacity per unit weight of the positive electrode p7 which was heat-treated without coexisting alkali in the air was greatly reduced to 178 mAh / g. Moreover, in the positive electrode p4 which was not heat-processed, the capacity | capacitance per unit weight was 226 mAh / g. On the other hand, the capacity per unit weight was greatly improved to 243 mAh / g in the positive electrode p10 subjected to the alkali heat treatment in the coexistence of oxygen and alkali.
[0086]
From this result, it was confirmed that the nickel hydroxide uncharged / discharge capacity a and the nickel hydroxide undischarge capacity c (see FIG. 1) of the positive electrode were reduced by the alkali heat treatment. Since the reduction of a and c is linked to the reduction of the negative electrode remaining capacity, the battery working capacity is increased, and as a result, a high-capacity secondary battery can be obtained.
[0087]
The results in Table 6 can be considered as follows. In the positive electrode p4 not subjected to the heat treatment, nickel hydroxide, which is the main component of the positive electrode active material, cannot be completely discharged in the initial charge / discharge reaction, and is added to improve the utilization rate of the positive electrode active material. Since the cobalt compound does not contribute to the discharge, the corresponding amount of electricity is accumulated in the negative electrode.
On the other hand, in the positive electrode p10 that has been subjected to the alkali heat treatment, the nickel hydroxide and the cobalt compound are chemically oxidized (equivalent to charge) by the alkali heat treatment. Loss is mitigated. Furthermore, this alkali heat treatment increases the cobalt compound and increases the conductivity of the Co coating layer, thereby improving the utilization factor of the positive electrode active material (coated Ni active material). That is, since the positive electrode p10 has high charge / discharge efficiency, the capacity per unit weight increases accordingly.
[0088]
On the other hand, in the positive electrode p7 that was heat-treated without coexisting alkali, the capacity per unit weight was greatly reduced in the absence of alkali to produce a highly crystalline cobalt compound. The compound is thought to be because of its low conductivity compared to a cobalt compound with disordered crystallinity. Therefore, the heat treatment is preferably an alkali heat treatment performed in the presence of oxygen and alkali.
[0089]
(Experiment 3)
In order to confirm that it was shown in the experiment 2, the battery working capacity and the negative electrode remaining capacity were measured for the batteries A4 and A9 (the negative electrode is common to n4) using the positive electrodes p4 and p10. In addition, the measurement was performed by the method similar to the method shown in the experiment 1 above.
As a result, the battery working capacity was 1266 mAh in the battery A4, whereas it was 1327 mAh in the battery A9, and the battery working capacity was significantly improved in the battery A9. The remaining capacity of the negative electrode was 533 mAh in the battery A4, but 320 mAh in the battery A9, and the remaining capacity of the negative electrode was significantly reduced in the battery A9 (see Table 8).
[0090]
Also from this result, as shown in the experiment 2, if the heat treatment is performed in the coexistence of oxygen and alkali, the remaining capacity of the negative electrode can be reduced, and as a result, the battery can be increased in capacity. It could be confirmed.
[0091]
(Experiment 4)
Regarding the nickel hydroxide used in the positive electrodes p4 and p10, the difference in crystallinity of the cobalt compound was examined. The result is shown in FIG.
The difference in crystallinity is in the method of comparing the cobalt compound (p4) not subjected to heat treatment with the cobalt compound (p10) subjected to heat treatment in the coexistence of oxygen and alkali by X-ray diffraction analysis. I did. Various conditions in the X-ray diffraction analysis method are as follows.
[0092]
Counter cathode: Cuka
Tube voltage: 40 kV
Scanning speed: 2.00 ° / min
Tube current: 30 mA
[0093]
As is clear from FIG. 3, high crystallinity was observed with cobalt without heat treatment (see a in the figure), whereas almost no crystallinity was observed with cobalt that had been subjected to alkali heat treatment (in the figure). b).
[0094]
(Experiment 5)
Next, the average valence of the active material coating layer (cobalt compound on the nickel hydroxide surface) used for the positive electrode p4 not subjected to heat treatment and the positive electrode p10 heat-treated in the coexistence of oxygen and alkali was determined by atomic absorption spectrometry. It was measured. The results are shown in Table 7 below.
A specific method for measuring the average valence is as follows.
[0095]
First, a certain amount of sample is weighed and dissolved in concentrated hydrochloric acid, and the amount of cobalt in the solution is quantified by atomic absorption spectrometry. At this time, since all cobalt (divalent cobalt and trivalent cobalt) is dissolved in hydrochloric acid, the amount of cobalt quantified at this time is the total amount of cobalt contained in the coating layer (total amount of divalent cobalt and trivalent cobalt). Become. Let this amount be A. Next, separately the same amount of the same sample as above is weighed, dissolved in concentrated nitric acid, the solution is filtered, and then the amount of cobalt in the filtrate is quantified by atomic absorption spectrometry. At this time, divalent cobalt dissolves in nitric acid, but trivalent cobalt does not dissolve in nitric acid, and thus a filtrate containing only divalent cobalt is obtained by filtration. Therefore, the amount of cobalt determined at this time is only the amount of divalent cobalt contained in the coating layer. Let this amount be B. Then, the average valence of each sample is calculated by the following formula 4.
[0096]
Cobalt average valence = (3A-B) / A ... number 4
[0097]
[Table 7]
Figure 0003744642
[0098]
As apparent from Table 7 above, the valence of cobalt was 2.0 in the positive electrode p4 that was not heat-treated, whereas the valence of cobalt was 2 in the positive electrode p10 that was heat-treated in the presence of oxygen and alkali. .9, and it was confirmed that the order was greatly increased. Based on the results of Experiment 5 and Experiment 4, when the alkali heat treatment is performed, the cobalt compound in the coating layer is chemically oxidized, the average valence becomes larger than two, and the crystallinity of the cobalt compound is increased. Disturbance occurs. It is considered that a high battery working capacity as shown in the battery A9 in Table 8 was obtained due to such a change in the cobalt compound.
[0099]
(Experiment 6)
Using batteries A7 to A11 having different alkali concentrations when heat-treated in the presence of oxygen and alkali, the relationship between the alkali concentration, the battery working capacity, and the negative electrode remaining capacity was examined. The results are shown in Table 8 below and FIG.
The battery working capacity and the negative electrode remaining capacity were measured by the same method as shown in Experiment 1 above.
[0100]
[Table 8]
Figure 0003744642
[0101]
As apparent from Table 8 and FIG. 4, it was recognized that when the alkali concentration was 15 to 40% by weight, the negative electrode remaining capacity was reduced and the battery working capacity was increased. Therefore, it is desirable that the alkali concentration in the heat treatment in the coexistence of oxygen and alkali is 15 to 40% by weight.
[0102]
(Experiment 7)
Using batteries A9 and A12 to A15 having different temperatures at the time of heat treatment in the coexistence of oxygen and alkali, the relationship between the treatment temperature, the battery working capacity, and the negative electrode remaining capacity was examined. The results are shown in Table 9 below and FIG.
The battery working capacity and the negative electrode remaining capacity were measured by the same method as shown in Experiment 1 above.
[0103]
[Table 9]
Figure 0003744642
[0104]
As apparent from Table 9 and FIG. 5, it was recognized that the remaining capacity of the negative electrode was reduced and the battery working capacity was increased when the treatment temperature was 50 to 150 ° C. From this result, it is desirable that the treatment temperature in the heat treatment in the coexistence of oxygen and alkali is 50 to 150 ° C.
[0105]
(Experiment 8)
Using batteries A9 and A12 to A15 having different ratios of the negative electrode remaining capacity to the battery working capacity, the ratio of the negative electrode remaining capacity to the battery working capacity (hereinafter referred to as negative electrode remaining capacity ratio) and the discharge rate at low temperature (hereinafter referred to as low temperature discharge). (Referred to as a rate). The results are shown in Table 10 below and FIG. 6 (indicated by ● in the figure).
Calculation of the low temperature discharge rate was performed as follows.
First, the battery is activated under the conditions indicated by the measurement of the battery working capacity. Next, after charging for 16 hours at a current of 120 mA, the battery is rested at −10 ° C. for 1 hour, and further discharged to a discharge end voltage of 1.0 V at a current of 1200 mA. The ratio (percentage) of the discharge capacity at the time of discharge to the initial battery capacity was defined as the low temperature discharge rate%.
[0106]
[Table 10]
Figure 0003744642
[0107]
As can be seen from Table 10 and FIG. 6, the low-temperature discharge rate greatly decreased in the batteries A9, A13, and A14 having a negative electrode remaining capacity ratio of 40% or less. Therefore, if the negative electrode charging depth is specified to be low and the negative electrode remaining capacity ratio is set to 40% or less, the cycle characteristics at room temperature are improved, but the problem of low temperature discharge characteristics is lowered.
Therefore, the following experiment 9 was conducted in order to improve the low temperature discharge characteristics.
[0108]
(Experiment 9)
Since the relationship between the negative electrode remaining capacity rate and the low-temperature discharge rate was examined using the batteries A16 to A20 (battery whose surface was treated with an acidic aqueous solution of a hydrogen storage alloy), the results are shown in Table 11 and FIG. Is shown).
The low temperature discharge rate was calculated in the same manner as in Experiment 8 above.
[0109]
[Table 11]
Figure 0003744642
[0110]
As is clear from Table 11 and FIG. 6, in the battery (●) using the hydrogen storage alloy negative electrode that was not acid-treated, the low-temperature discharge rate was significantly reduced when the negative electrode residual capacity rate was reduced. On the other hand, in the battery (▲) using the negative electrode surface-treated with an acidic aqueous solution, the low-temperature discharge rate decreased little even when the negative electrode residual capacity ratio was 40% or less. From this, it can be seen that by using a hydrogen storage alloy having a negative electrode residual capacity ratio of 40% or less and an acid treatment, it is possible to improve not only cycle characteristics at room temperature but also low-temperature discharge characteristics.
[0111]
The surface treatment of the hydrogen storage alloy with an acidic aqueous solution can improve cycle characteristics and low-temperature discharge characteristics because the active surface of the alloy surface is sufficiently exposed by the acid treatment, and as a result, the reactivity of the negative electrode It is thought that this is because of the increase.
[0112]
(Experiment 10)
Using batteries A10 and A22 to A26 (see Table 4 and Table 12 below) using hydrogen storage alloys acid-treated at various pHs, the relationship between pH during acid treatment and low-temperature discharge rate was examined. The results are shown in Table 12 below and FIG.
The low temperature discharge rate was calculated in the same manner as in Experiment 8 above.
[0113]
[Table 12]
Figure 0003744642
[0114]
As apparent from Table 12 and FIG. 7, it was confirmed that a high low-temperature discharge rate was obtained when the pH of the acidic aqueous solution was 0.5 to 3.5.
[0115]
【The invention's effect】
As described above, the charge depth of the negative electrode is 80% or less with respect to the high-performance non-sintered nickel positive electrode using nickel hydroxide having a Co coating layer formed on the surface (the unreacted capacity ratio is 16% or less). According to the configuration of the present invention in combination with the hydrogen storage alloy electrode having the capacity to be obtained, a nickel-metal hydride storage battery having a large battery working capacity and a small increase in battery internal pressure can be obtained.
[0116]
In particular, the average valence of the cobalt compound constituting the Co coating layer is made larger than 2, the hydrogen storage alloy as the negative electrode active material is surface-treated with an acidic aqueous solution, and the negative electrode remaining capacity is 40% of the battery working capacity. According to the configuration of the present invention described below, a nickel-metal hydride storage battery having excellent battery working capacity and cycle characteristics and excellent low-temperature discharge characteristics can be provided.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a capacity configuration of a battery.
FIG. 2 is a graph showing the relationship between negative electrode charging depth, battery internal pressure, and battery working capacity.
FIG. 3 is an X-ray chart of a cobalt compound used for positive electrodes p4 and p10.
FIG. 4 is a graph showing the relationship between alkali concentration, battery working capacity and negative electrode remaining capacity during alkali heat treatment.
FIG. 5 is a graph showing the relationship between the treatment temperature during alkaline heat treatment, the battery working capacity, and the negative electrode remaining capacity.
FIG. 6 is a graph showing the relationship between the negative electrode remaining capacity rate and the low-temperature discharge rate.
FIG. 7 is a graph showing the relationship between pH during acid treatment and low-temperature discharge rate.

Claims (8)

水酸化ニッケル又は主成分が水酸化ニッケルである母粒子の表面に、コバルト化合物層が形成されてなる被覆Ni活物質を含む非焼結ニッケル電極と、水素を吸蔵放出することのできる水素吸蔵合金を含む金属水素化物電極と、アルカリ電解液とで構成されるニッケル−金属水素化物蓄電池であって、
下記数2で表される初期充放電後における負極充電深度が、80%以下に規制され
下記数2における負極残存容量が、電池実働容量の40%以下であり、かつ前記水素吸蔵合金が、酸性水溶液により表面処理されてなる水素吸蔵合金である、
ことを特徴とするニッケル−金属水素化物蓄電池。
Figure 0003744642
Non-sintered nickel electrode containing a coated Ni active material in which a cobalt compound layer is formed on the surface of nickel hydroxide or a mother particle whose main component is nickel hydroxide, and a hydrogen storage alloy capable of occluding and releasing hydrogen A nickel-metal hydride storage battery composed of a metal hydride electrode containing and an alkaline electrolyte,
The negative electrode charge depth after the initial charge / discharge represented by the following formula 2 is regulated to 80% or less ,
The remaining capacity of the negative electrode in the following equation 2 is 40% or less of the battery working capacity, and the hydrogen storage alloy is a hydrogen storage alloy that is surface-treated with an acidic aqueous solution.
Nickel-metal hydride storage battery characterized by the above.
Figure 0003744642
水酸化ニッケル又は主成分が水酸化ニッケルである母粒子の表面に、コバルト化合物層が形成されてなる被覆Ni活物質を含む非焼結ニッケル電極と、水素を吸蔵放出することのできる水素吸蔵合金を含む金属水素化物電極と、アルカリ電解液とで構成されるニッケル−金属水素化物蓄電池であって、
下記数1で表される初期充放電後における正極未反応容量率が16%以下に規制され、かつ下記数2で表される初期充放電後における負極充電深度が80%以下に規制され
更に前記数2における負極残存容量が、電池実働容量の40%以下であり、前記水素吸蔵合金が、酸性水溶液により表面処理されてなる水素吸蔵合金である、
ことを特徴とするニッケル−金属水素化物蓄電池。
Figure 0003744642
Figure 0003744642
Non-sintered nickel electrode containing a coated Ni active material in which a cobalt compound layer is formed on the surface of nickel hydroxide or a mother particle whose main component is nickel hydroxide, and a hydrogen storage alloy capable of occluding and releasing hydrogen A nickel-metal hydride storage battery composed of a metal hydride electrode containing and an alkaline electrolyte,
The positive electrode unreacted capacity ratio after the initial charge / discharge represented by the following formula 1 is regulated to 16% or less , and the negative electrode charge depth after the initial charge / discharge represented by the following formula 2 is regulated to 80% or less ,
Furthermore, the negative electrode remaining capacity in the formula 2 is 40% or less of the battery working capacity, and the hydrogen storage alloy is a hydrogen storage alloy that is surface-treated with an acidic aqueous solution.
Nickel-metal hydride storage battery characterized by the above.
Figure 0003744642
Figure 0003744642
前記コバルト化合物層のコバルト化合物の平均価数が、2価よりも大きいことを特徴とする請求項1または2記載のニッケル−金属水素化物蓄電池。 3. The nickel-metal hydride storage battery according to claim 1, wherein an average valence of the cobalt compound in the cobalt compound layer is greater than 2. 水酸化ニッケル又は主成分が水酸化ニッケルである母粒子を、コバルト化合物を含有する溶液に分散し、この分散液にアルカリ溶液を注加して分散液pHを調整することによりコバルト化合物を析出させ、前記母粒子をコバルト化合物で被覆して被覆粒子となす第1の工程と、
上記被覆粒子にアルカリ金属溶液を含浸し、酸素存在下で加熱処理して被覆Ni活物質となす第2の工程と、
第2の工程で加熱処理した被覆Ni活物質を用いて、下記数1で表される正極未反応容量率が16%以下の非焼結ニッケル正極を作製する第3の工程と、
上記非焼結ニッケル正極と、酸性水溶液により表面処理されてなる水素吸蔵合金の充填された金属水素化物負極と、アルカリ電解液とを用いて、下記数2で表される初期充放電後における負極充電深度が80%以下で、かつ負極残存容量が電池実働容量の40%以下に規制されたニッケル−金属水素化物蓄電池を作製する第4の工程と、
を備えるニッケル−金属水素化物蓄電池の製造方法。
Figure 0003744642
Figure 0003744642
Nickel hydroxide or mother particles whose main component is nickel hydroxide is dispersed in a solution containing a cobalt compound, and an alkaline solution is added to the dispersion to adjust the pH of the dispersion to precipitate the cobalt compound. A first step of coating the base particles with a cobalt compound to form coated particles;
A second step of impregnating the coated particles with an alkali metal solution and heat-treating in the presence of oxygen to form a coated Ni active material;
A third step of producing a non-sintered nickel positive electrode having a positive electrode unreacted capacity ratio of 16% or less represented by the following formula 1, using the coated Ni active material heat-treated in the second step;
Using the non-sintered nickel positive electrode, a metal hydride negative electrode filled with a hydrogen storage alloy that has been surface-treated with an acidic aqueous solution , and an alkaline electrolyte, the negative electrode after the initial charge / discharge represented by Equation 2 below A fourth step of producing a nickel-metal hydride storage battery in which the charging depth is 80% or less and the negative electrode remaining capacity is regulated to 40% or less of the battery working capacity ;
A method for producing a nickel-metal hydride storage battery.
Figure 0003744642
Figure 0003744642
前記第2の工程の加熱処理が、コバルト化合物層を形成するコバルト化合物の平均価数を2価よりも大きくすることを内容とする、請求項4記載のニッケル−金属水素化物蓄電池の製造方法。The method for producing a nickel-metal hydride storage battery according to claim 4 , wherein the heat treatment in the second step makes the average valence of the cobalt compound forming the cobalt compound layer larger than divalent. 前記第2の工程におけるアルカリ金属溶液のアルカリ濃度が、15〜40wt%である、請求項4または5記載のニッケル−金属水素化物蓄電池の製造方法。The method for producing a nickel-metal hydride storage battery according to claim 4 or 5 , wherein the alkali concentration of the alkali metal solution in the second step is 15 to 40 wt%. 前記第2の工程における加熱処理温度が、50〜150℃である、請求項4乃至6記載のニッケル−金属水素化物蓄電池の製造方法。The manufacturing method of the nickel metal hydride storage battery of Claim 4 thru | or 6 whose heat processing temperature in a said 2nd process is 50-150 degreeC. 前記酸性水溶液のpH値が、0.5〜3.5である、請求項7記載のニッケル−金属水素化物蓄電池の製造方法。The manufacturing method of the nickel metal hydride storage battery of Claim 7 whose pH value of the said acidic aqueous solution is 0.5-3.5.
JP07381697A 1996-03-27 1997-03-26 Nickel-metal hydride storage battery and method for manufacturing the same Expired - Lifetime JP3744642B2 (en)

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