JPH0440831B2

JPH0440831B2 -

Info

Publication number: JPH0440831B2
Application number: JP60030866A
Authority: JP
Inventors: Takahisa Awaja; Hideki Matsui
Original assignee: Sanyo Electric Co Ltd
Current assignee: Sanyo Electric Co Ltd
Priority date: 1985-02-19
Filing date: 1985-02-19
Publication date: 1992-07-06
Also published as: JPS61190860A

Description

[Detailed description of the invention]

(イ) 産業上の利用分野本発明はアルカリ蓄電池用の焼結式カドミウム
陰極板の製造方法にかかり、特に極板中に残留す
る硝酸根の除去と充放電効率の向上に関するもの
である。 (ロ) 従来の技術焼結式カドミウム陰極板は一般に多孔性ニツケ
ル焼結基板に硝酸カドミウム溶液を含浸した後、
水酸化ナトリウム等のアルカリ溶液中で硝酸カド
ミウムを水酸化カドミウムに転化させ、基板中に
所望量の活物質を充填して作製されている。この
極板の製造方法では極板中に硝酸根が残留し、こ
の硝酸根は電池中に持ち込まれた場合に著しく保
存特性を低下させることが知られており、電池を
構成する以前に必ず除去する必要がある。しかし
ながら、この硝酸根は極板を長時間水洗すること
によつても除去することはできない。こうして作製されたカドミウム陰極板から硝酸
根を除去する方法として従来から行なわれている
ものに、電気化学的処理、即ち比較的低電流で充
放電を１〜数回行なう化成処理及び特開昭54−
148235号公報に於いて提案されるような焼成処理
がある。ところが、１〜数回の充放電を行なう方法では
化成の目的である活物質の活性化（特に硝酸根）
の除去は達成されるが、化成のための大幅な工数
が必要であるため作業性が悪く、処理時間も長い
ため極板の連続処理には不向きである。また焼成
処理を行なう方法では硝酸根の除去は容易に達成
できるが、特開昭54−148235号公報に示される
ように空気中で焼成処理を行なうと、焼成時にニ
ツケル焼結基板の表面が酸化されて絶縁性の酸化
ニツケルに変化するため、基板と活物質の導電性
が低下し、充放電効率が低下する現象が現われ
る。また種々の雰囲気中で焼成実験を行なつた結
果、窒素雰囲気中で焼成する場合は、焼成炉内
に極板を導入する際に、極板中に吸着等により内
蔵される微量の空気によつて、ニツケル焼結基板
の表面が酸化される。これを防止するためには、
焼成炉導入前に基板を脱気する等の複雑な操作を
必要とする。水素雰囲気中で焼成する場合は、
基板の酸化は防止できるが、この焼成により生成
する金属カドミウムが非常に反応性に富むため、
焼成後に酸化防止処理が必要となる。また水素を
使つた場合に生じる最大の問題は爆発の問題であ
る。水素は４％以上の濃度で爆発下限界を越える
ので、水素雰囲気中での焼成では常に爆発の危険
性があるため、装置設計上あるいは安全対策の面
から大きな制約を受ける。 (ハ) 発明が解決しようとする問題点本発明は活物質充填後のカドミウム陰極板の硝
酸根の除去及び活物質の活性化を行なうときに必
要な化成処理による大幅な工数増加や処理時間の
増大と、焼成処理に於ける焼結基板表面の酸化に
よる充放電効率の低下及び爆発の危険性の問題を
解消しようとするものである。 (ニ) 問題点を解決するための手段本発明は活物質充填後のカドミウム陰極板を、
不活性ガスと爆発下限界以下の水素との混合雰囲
気で焼成するものである。 (ホ) 作用硝酸カドミウムを出発物質として多孔性金属基
板内に活物質を充填してなるカドミウム陰極板を
焼成処理すると、基板内の水酸化カドミウムは酸
化カドミウムに転化し、同時に活物質中に残存し
ている硝酸塩が反応して硝酸根が遊離する。この
焼成の際、焼成温度は210℃未満では水酸化カド
ミウムの酸化カドミウムへの反応速度が遅くなる
ため実用上適さず、また310℃を越えるとカドミ
ウムの溶融、揮発等の問題が生じる。したがつて
焼成温度は210℃〜310℃の範囲内で行なう必要が
ある。尚、焼成により遊離した硝酸根は水洗や短
時間の充電または放電により容易に除去すること
が可能である。上記焼成時の雰囲気をアルゴンや窒素などの不
活性ガスと爆発下限界以下の水素との混合雰囲気
にすると、焼結基板の酸化による導電性低下を防
止できると共に活物質の活性化を行なうことがで
きる。更に焼成時に爆発が生じることがなく、ま
た、金属カドミウムの生成量を低く抑えることが
できるため焼成後に酸化防止処理を施す必要がな
い。 (ヘ) 実施例多孔度約80％のニツケル焼結基板に硝酸カドミ
ウム水溶液を含浸し、アルカリにより前記硝酸カ
ドミウムを水酸化カドミウムに転化する通常の活
物質充填操作を行なうことによつて水酸化カドミ
ウム極板を作製した。該極板をH₂2vol％、
N₂98vol％の雰囲気中で300℃で10分間焼成し本
発明極板とする。他に比較として前記水酸化カド
ミウム極板を空気中及びN₂中で同一温度、同一
時間焼成して比較極板を得る。これら各種雰囲気中で焼成した極板を30分間水
洗した後30分間乾燥し、しかる後極板２ｇ中の残
存硝酸根量及び酸化ニツケル量を測定した。次表
にその結果を示す。尚、酸化ニツケル量は極板重
量に対する重量％で示した。 (a) Industrial Application Field The present invention relates to a method for manufacturing a sintered cadmium cathode plate for an alkaline storage battery, and particularly relates to the removal of nitrate radicals remaining in the electrode plate and the improvement of charging and discharging efficiency. (b) Conventional technology A sintered cadmium cathode plate is generally produced by impregnating a porous sintered nickel substrate with a cadmium nitrate solution.
It is manufactured by converting cadmium nitrate into cadmium hydroxide in an alkaline solution such as sodium hydroxide, and filling the substrate with a desired amount of active material. This method of manufacturing electrode plates leaves nitrate radicals in the electrode plates, and it is known that if these nitrate radicals are brought into the battery, they will significantly reduce the storage characteristics, so they must be removed before constructing the battery. There is a need to. However, these nitrate radicals cannot be removed even by washing the electrode plate with water for a long time. Conventional methods for removing nitrate radicals from the cadmium cathode plate produced in this way include electrochemical treatment, that is, chemical conversion treatment in which charging and discharging are performed one to several times at a relatively low current, and JP-A-54 −
There is a firing process as proposed in Japanese Patent No. 148235. However, in the method of charging and discharging one to several times, the purpose of chemical formation is to activate the active material (especially nitrate radicals).
However, it requires a large number of man-hours for chemical formation, resulting in poor workability and long processing time, making it unsuitable for continuous processing of electrode plates. In addition, the removal of nitrate radicals can be easily achieved using a firing treatment method, but when firing treatment is performed in air as shown in JP-A-54-148235, the surface of the nickel sintered substrate becomes oxidized during firing. This causes the conductivity of the substrate and the active material to decrease, resulting in a decrease in charging and discharging efficiency. In addition, as a result of firing experiments in various atmospheres, we found that when firing in a nitrogen atmosphere, when introducing the electrode plate into the firing furnace, a small amount of air that is absorbed into the electrode plate due to adsorption etc. Then, the surface of the nickel sintered substrate is oxidized. To prevent this,
It requires complicated operations such as deaerating the substrate before introducing it into the firing furnace. When firing in a hydrogen atmosphere,
Oxidation of the substrate can be prevented, but the metal cadmium produced by this firing is highly reactive, so
Anti-oxidation treatment is required after firing. The biggest problem that arises when using hydrogen is explosion. Since hydrogen exceeds the lower explosive limit at a concentration of 4% or more, there is always a risk of explosion when firing in a hydrogen atmosphere, which imposes major restrictions in terms of equipment design and safety measures. (c) Problems to be Solved by the Invention The present invention solves the problem of significantly increasing the number of man-hours and processing time due to the chemical conversion treatment required to remove nitrate radicals from the cadmium cathode plate after filling the active material and to activate the active material. This is an attempt to solve the problem of a decrease in charging/discharging efficiency and a risk of explosion due to oxidation of the sintered substrate surface during the firing process. (d) Means for solving the problems The present invention provides a cadmium cathode plate filled with an active material,
It is fired in a mixed atmosphere of inert gas and hydrogen below the lower explosive limit. (e) Action When a cadmium cathode plate made of cadmium nitrate as a starting material and a porous metal substrate filled with active material is fired, cadmium hydroxide in the substrate is converted to cadmium oxide, and at the same time remains in the active material. The nitrates react and nitrate radicals are liberated. During this calcination, if the calcination temperature is less than 210°C, the reaction rate of cadmium hydroxide to cadmium oxide will be slow, which is not practical, and if it exceeds 310°C, problems such as melting and volatilization of cadmium will occur. Therefore, the firing temperature must be within the range of 210°C to 310°C. Note that the nitrate radicals liberated by firing can be easily removed by washing with water or by charging or discharging for a short time. If the atmosphere during the above firing is a mixed atmosphere of an inert gas such as argon or nitrogen and hydrogen below the lower explosive limit, it is possible to prevent conductivity from decreasing due to oxidation of the sintered substrate and to activate the active material. can. Furthermore, no explosion occurs during firing, and the amount of metal cadmium produced can be kept low, so there is no need to perform oxidation prevention treatment after firing. (f) Example A nickel sintered substrate with a porosity of approximately 80% is impregnated with an aqueous cadmium nitrate solution, and cadmium hydroxide is produced by carrying out the usual active material filling operation of converting the cadmium nitrate into cadmium hydroxide with an alkali. An electrode plate was produced. The electrode plate was heated with H ₂ 2vol%,
The electrode plate of the present invention is obtained by firing at 300° C. for 10 minutes in an atmosphere containing 98 vol% N ₂ . In addition, for comparison, the cadmium hydroxide electrode plate was fired in air and N ₂ at the same temperature and for the same time to obtain a comparative electrode plate. The electrode plates fired in these various atmospheres were washed with water for 30 minutes and then dried for 30 minutes, and then the amount of residual nitrate radicals and the amount of nickel oxide in 2 g of the electrode plates was measured. The results are shown in the table below. Incidentally, the amount of nickel oxide is expressed in weight % with respect to the weight of the electrode plate.

【表】表から明らかなように、本発明極板及び比較極
板り、焼成時の雰囲気の影響は見られない。酸化
ニツケル量は空気中及びN₂中で焼成した比較極
板で増加し、逆に本発明極板では若干減少してい
る。次いでこれら極板の充電効率の測定結果を図面
に示す。測定は試料極板を85mm×41mmの大きさに
切断し、これを20％水酸化カリウム水溶液中で
50mA×10Hrsの充電を行なつた後50mAで放電
することによつて行なつた。尚、前記切断によつ
て得られた極板の容量は約1000mAHである。図
面に於いて縦軸は酸化水銀参照電極に対する極板
の電位、横軸は放電量を夫々示しており、充電効
率は例えば0Vを基準にとれば、本発明極板が84
％（420mAH／500mAH）、N₂中で焼成した比較
極板が71％（355mAH／500mAH）となる。図
面からわかるように空気中及びN₂中で焼成した
比較電極は、焼成前の極板に比べかなり充電効率
が低下している。また、これら比較電極は放電末
期に電位がなだらかに落ちている。これらの現象
は酸化ニツケルの増加による焼結体と活物質間の
導電性の低下が原因となつていると考えられる。
一方本発明極板は充電効率が焼成前に比べて上昇
しており、放電末期の電位低下もシヤープであ
る。この充電効率の向上の原因を推察するに、本
発明極板は焼成後直ちに放電しても放電量は極板
容量全体の１％程度と極僅かであり、充電効率の
上昇量より遥かに少ない。また、酸化ニツケル量
も焼成前に比べ僅かに減少しているだけであるの
で酸化ニツケルによる要因とも考え難い。したが
つて、如何なる作用によるかは不明であるが、
H₂により活物質が活性化され充電効率の上昇を
もたらしたのではないか考えられる。 (ト) 発明の効果本発明のカドミウム陰極板の製造方法は、多孔
性金属基板に硝酸カドミウムを含浸し、次いで該
硝酸カドミウムを水酸化カドミウムに転化させる
操作によつて前記基板中に所望量の活物質を充填
した後、前記基板を不活性ガスと爆発下限界以下
の水素の混合雰囲気で焼成するものであるから、
活物質含浸後のカドミウム陰極板から容易に硝酸
根を除去することができる。また、焼成の際に生
じる焼結基板表面の酸化による充電効率の低下を
防止でき、水素雰囲気中での焼成の際に酸化防止
処理を行なう必要がなくなると共に、爆発の危険
性がなくなるので装置設計及び安全対策上のメリ
ツトが大きく、同時に活物質の活性化をも行うこ
とが可能である。[Table] As is clear from the table, no influence of the atmosphere during firing was observed in the electrode plates of the present invention and the comparative electrode plates. The amount of nickel oxide increases in the comparative plates fired in air and _N2 , and on the contrary, it slightly decreases in the plates of the present invention. Next, the results of measuring the charging efficiency of these electrode plates are shown in the drawings. For measurement, the sample electrode plate was cut into a size of 85 mm x 41 mm, and this was placed in a 20% potassium hydroxide aqueous solution.
This was done by charging at 50 mA x 10 hours and then discharging at 50 mA. Incidentally, the capacity of the electrode plate obtained by the above-mentioned cutting is about 1000 mAH. In the drawing, the vertical axis shows the potential of the electrode plate with respect to the mercury oxide reference electrode, and the horizontal axis shows the discharge amount.If the charging efficiency is taken as a reference, for example, 0V, the electrode plate of the present invention has an electric potential of 84
% (420mAH/500mAH), and the comparative electrode plate fired in _N2 is 71% (355mAH/500mAH). As can be seen from the drawing, the charging efficiency of the comparison electrode fired in air and N ₂ was considerably lower than that of the electrode plate before firing. Furthermore, the potential of these comparison electrodes drops gradually at the end of discharge. These phenomena are thought to be caused by a decrease in conductivity between the sintered body and the active material due to an increase in nickel oxide.
On the other hand, the charging efficiency of the electrode plate of the present invention is higher than that before firing, and the potential drop at the end of discharge is also sharp. Inferring the cause of this improvement in charging efficiency, even if the electrode plate of the present invention is discharged immediately after firing, the amount of discharge is extremely small, about 1% of the total plate capacity, which is far less than the increase in charging efficiency. . Furthermore, since the amount of nickel oxide was only slightly reduced compared to before firing, it is difficult to think that nickel oxide was the cause. Therefore, although it is unclear what kind of effect it has,
It is thought that the active material was activated by H ₂ , resulting in an increase in charging efficiency. (G) Effects of the Invention The method for producing a cadmium cathode plate of the present invention includes impregnating a porous metal substrate with cadmium nitrate, and then converting the cadmium nitrate into cadmium hydroxide to inject a desired amount into the substrate. After filling the active material, the substrate is fired in a mixed atmosphere of inert gas and hydrogen below the lower explosive limit.
Nitrate radicals can be easily removed from the cadmium cathode plate after impregnation with the active material. In addition, it is possible to prevent a decrease in charging efficiency due to oxidation of the surface of the sintered substrate that occurs during firing, eliminating the need for oxidation prevention treatment when firing in a hydrogen atmosphere, and eliminating the risk of explosion. This has great advantages in terms of safety measures, and it is also possible to activate the active material at the same time.

[Brief explanation of drawings]

図面は本発明極板と比較極板の充電効率を示す
図面である。 The drawing shows the charging efficiency of the electrode plate of the present invention and the comparative electrode plate.

Claims

[Claims] 1. Impregnating a porous metal substrate with cadmium nitrate,
Then, after filling the substrate with a desired amount of active material by converting the cadmium nitrate into cadmium hydroxide, the substrate is fired in a mixed atmosphere containing an inert gas and hydrogen below the lower explosive limit. A method for producing a cadmium cathode plate characterized by: 2. The method for manufacturing a cadmium cathode plate according to claim 1, wherein the firing temperature is 210°C to 310°C.