JP5399285B2 - Manufacturing method of nickel metal hydride storage battery - Google Patents

Description

The present invention includes a positive electrode having an active material powder obtained by oxidizing a nickel hydroxide powder provided with a surface layer containing a cobalt compound using an oxidizing agent, and a negative electrode having an active material powder made of a hydrogen storage alloy. The present invention relates to a method for manufacturing a nickel metal hydride storage battery .

Nickel metal hydride storage batteries have higher energy density than nickel cadmium storage batteries, which are one of the same alkaline storage batteries, and do not contain harmful cadmium, so there is less risk of environmental pollution. It is widely used as a power source for portable small electronic devices such as computers, and the demand has increased dramatically with the spread of these small electronic devices. Advances in miniaturization and weight reduction have greatly restricted the installation space for power supplies, and on the other hand, power consumption has increased with the increase in functionality. For this reason, in a nickel metal hydride storage battery used for such small electronic devices, it is necessary to simultaneously achieve the contradictory problems of miniaturization and high capacity.

By the way, nickel-metal hydride storage batteries are generally composed of a positive electrode including an active material mainly composed of nickel hydroxide and a negative electrode including a hydrogen storage alloy. In a nickel metal hydride storage battery, the utilization factor of the positive electrode is higher than that of the negative electrode, particularly in large current discharge. Therefore, an excessive capacity (discharge reserve) is provided in the negative electrode so that the discharge does not end while the positive electrode has an undischarged capacity during discharge.

In addition, the nickel metal hydride storage battery generates oxygen gas on the positive electrode side during overcharge. This oxygen gas causes an increase in internal pressure in a sealed storage battery, and as a result, there is a risk of shortening the battery life due to liquid leakage. Therefore, in the nickel-metal hydride storage battery, in order to absorb the oxygen gas generated at the positive electrode by the hydrogen storage alloy of the negative electrode, a capacity (charge reserve) that can be overcharged is provided on the negative electrode side.

From the above circumstances, in the nickel-metal hydride storage battery, the capacity of the negative electrode is set larger than the capacity of the positive electrode, and the charge / discharge capacity is regulated by the capacity of the positive electrode (positive electrode regulation method).

Therefore, the improvement of the discharge capacity of the nickel metal hydride storage battery can be achieved by increasing the capacity of the positive electrode. However, when the capacity of the positive electrode is increased, the amount of discharge reserve and charge reserve increases accordingly. Therefore, it is necessary to simultaneously increase the capacity of the negative electrode that does not contribute to the improvement of the battery discharge capacity. For this reason, there is a limitation in improving the discharge capacity of the battery by increasing the capacity of the positive electrode.

In order to solve these problems, for example, Japanese Patent Application No. 2000-307130 discloses that a powder comprising a core layer containing nickel hydroxide and a surface layer containing a cobalt compound and covering the core layer is oxidized before battery assembly. A method has been proposed in which the reserve amount of the negative electrode is reduced by pre-oxidation using an agent to increase the capacity of the battery.

By using such a positive electrode to which an active material that has been previously oxidized is used, a cobalt compound that is a precursor of a conductive agent is converted into a highly conductive high-order cobalt compound (cobalt with trivalent oxidation number) before battery assembly. This is also converted to cobalt oxyhydroxide), and at the same time, a part of nickel hydroxide is oxidized and converted to a higher nickel compound (trivalent nickel compound, also called nickel oxyhydroxide). Therefore, it is possible to reduce the generation of negative electrode reserve formed in the process of initial charging after battery assembly.

However, a battery that has achieved a high capacity using the above-described means has various problems described below. First, as a result of reducing the discharge reserve, the ratio between the negative electrode capacity and the positive electrode capacity (negative electrode capacity / positive electrode capacity) is reduced. When such a nickel metal hydride storage battery is subjected to a large current discharge such as a 1 hour rate [current 1 It (A)] or a 1/3 hour rate [current 3 It (A)], the negative electrode capacity is restricted. For this reason, the discharge ends with the undischarged capacity remaining on the positive electrode. If the battery is used repeatedly in such a state, an undischarged portion is accumulated on the positive electrode, resulting in an overcharged state, leading to a shortened battery life.

In addition, since the conductive function between the active material particles of the positive electrode is only due to the physical contact of the higher cobalt compound formed on the particle surface by oxidizing the active material particles, the conductive function is inferior, particularly during high current discharge. There was a risk of voltage drop.

Furthermore, in the case of a negative electrode made of a hydrogen storage alloy, an oxide or hydroxide film of an alloy constituent component is formed on the alloy surface during the production of the alloy and during the subsequent storage and electrode production process. During the discharge operation, this film has a drawback of acting as a large reaction resistance.

For this reason, in the conventional battery, since the overvoltage at the time of charging is large, there is a problem that hydrogen is not occluded in the alloy and the activity of the negative electrode is not sufficiently increased. To solve this problem, it is possible to reduce the overvoltage by sufficiently reducing the charging current during the initial activation process, but 10 to 30 hours are required for one charge. Furthermore, it is necessary to repeat the charge / discharge operation for initial activation many times, and the production efficiency is greatly reduced.

Japanese Patent Application No. 2000-307130

The object of the present invention has been made in view of the problems of the conventional battery described above, and is a nickel-metal hydride storage battery having a high capacity and excellent cycle characteristics, and realizing a nickel-metal hydride storage battery excellent in high-rate discharge characteristics. Therefore, it is to realize a manufacturing method for initial activation of the nickel-metal hydride storage battery in a short time.

The method for producing a nickel metal hydride storage battery according to the present invention comprises a core layer mainly composed of nickel hydroxide and a surface layer mainly composed of a higher cobalt compound, wherein the nickel hydroxide is partially oxidized. A porous metal substrate is filled with a substance powder, and a positive electrode formed by bonding the active material powders together with a higher cobalt compound is provided, and a negative electrode comprising a hydrogen storage alloy electrode is provided, and the active material of the hydrogen storage alloy electrode A method for producing a nickel metal hydride storage battery having a filling capacity of 1.5 times or less of the nickel hydroxide active material filling capacity, wherein a surface layer of a cobalt compound is provided on the surface of a core layer mainly composed of nickel hydroxide. and the powder, the step of performing chemical oxidation treatment using an oxidizing agent, in the course of initial activation activated by applying charge and discharge operations to the battery, at least one over-discharge operation during the operation real To the reduction of the part of the higher order cobalt compound, characterized in that a step of generating a number divalent cobalt compound oxide.

The cobalt hydroxide generated by the overdischarge repeats dissolution in an alkaline electrolyte and precipitation from the electrolyte. In this process, adjacent active material powders are bonded with cobalt hydroxide. In the subsequent charging process, the cobalt hydroxide is oxidized and converted into a conductive higher-order cobalt compound. The produced higher-order cobalt compound binds adjacent active material powders like the precursor cobalt hydroxide. Higher order cobalt compounds formed by oxidation treatment are combined with the higher order cobalt compounds on the surface of each active material powder and the higher order cobalt compounds newly formed by the over-discharge operation and the subsequent charging operation. A conductive network of compounds is formed.

FIG. 1 is a view schematically showing a state of contact between adjacent active material powders in a positive electrode of a nickel metal hydride storage battery according to the present invention. In FIG. 1, 1 is a core layer mainly composed of nickel hydroxide, 2 is a surface layer made of a higher cobalt compound formed by oxidizing the active material powder using an oxidizing agent, It is a high-order cobalt compound newly formed by discharge treatment and subsequent charging. FIG. 2 is a view schematically showing a state of contact between adjacent active material powders in a positive electrode of a conventional battery. As shown in FIG. 2, in the positive electrode of the conventional battery, adjacent active material powders are merely in physical contact with each other, but in the case of the battery according to the present invention, adjacent active material powders are new. Since it is bonded by the high-order cobalt compound formed in, it has a high conductive function.

In addition, the active material powder for nickel electrodes having a higher order cobalt compound as a surface layer is obtained by depositing cobalt hydroxide on the surface of the nickel hydroxide powder and then using an oxidizing agent such as hypochlorite in an alkaline aqueous solution. Can be synthesized by chemical oxidation treatment.

The overdischarge operation in the present invention refers to an operation for further discharging after the terminal voltage of the battery has dropped to 1.0 V, which is a final voltage in normal discharge. In the present invention, it is desirable that the amount of overdischarge in the overdischarge operation is 2 to 10% of the rated capacity of the battery. By performing overdischarge at a constant current and defining the time, the amount of overdischarge electricity can be controlled.

In the initial activation treatment of the nickel-metal hydride storage battery according to the present invention, prior to the overdischarge operation, the battery is discharged in a temperature range of 40 to 80 ° C. after the end of normal discharge (discharge with a discharge end voltage of 1.0 V), It is desirable to leave for 5 to 24 hours. By standing at the high temperature, the oxide oxide or hydroxide coating on the surface of the hydrogen storage alloy can be removed.

The nickel metal hydride storage battery according to the present invention is a battery having a large discharge capacity and excellent cycle performance, and is also excellent in high rate discharge characteristics.

ADVANTAGE OF THE INVENTION According to this invention, the nickel-metal hydride battery excellent in the high rate discharge characteristic can be provided, preventing the increase in discharge reserve production | generation of a nickel-metal hydride storage battery. Moreover, the initial activation of the nickel metal hydride storage battery can be accelerated.

According to the present invention, it is possible to enhance the effect of suppressing the increase in discharge reserve generation.

ADVANTAGE OF THE INVENTION According to this invention, the improvement effect of a high rate discharge characteristic can be improved further, and the fall of charging / discharging cycling characteristics can be suppressed.

According to the present invention, the effect of improving the high rate discharge characteristics is remarkable.

It is a schematic diagram which shows the state of the contact of the active material powder which adjoins the positive electrode in the Example battery which concerns on this invention. It is a schematic diagram which shows the state of the contact of the active material powder which adjoins the positive electrode in a conventional battery. It is a graph which shows transition of the discharge capacity in the initial stage activation process of the Example battery which concerns on this invention, and a comparative example battery. It is a graph which shows transition of the discharge capacity in the initial stage activation process of the Example battery which concerns on this invention, and a comparison battery. It is a graph which shows transition of the discharge capacity in the initial stage activation process of the Example battery which concerns on this invention, and a comparison battery. It is a graph which shows the charging / discharging cycling characteristics of the Example battery and comparative example battery which concern on this invention.

The active material powder used for the positive electrode of the nickel metal hydride storage battery according to the present invention is a powder in which a surface layer of a cobalt compound such as cobalt hydroxide is provided on the surface of a core layer mainly composed of nickel hydroxide using an oxidizing agent. By applying a chemical oxidation treatment, cobalt contained in the powder is made a high-order cobalt compound. Further, at the same time as the oxidation of the cobalt compound, one part of nickel hydroxide constituting the core layer can be oxidized to form a higher order nickel compound.

The positive electrode of the nickel metal hydride storage battery according to the present invention is obtained by filling the active material powder in a porous metal substrate such as foamed nickel, and the active material powders are bonded to each other by a high-order Koval compound.

The method for producing a nickel-metal hydride storage battery according to the present invention is for producing a high-capacity nickel-metal hydride battery excellent in high-rate discharge characteristics, and can be produced through the following steps. An overdischarge operation is carried out at least once in the process of initial activation of a nickel metal hydride storage battery having a hydrogen storage alloy electrode on the positive electrode and the negative electrode. A part of the higher cobalt compound is reduced to cobalt hydroxide by the overdischarge operation. Cobalt hydroxide is changed to a higher cobalt compound by charging after overdischarge. In this process, the active material powders are bonded to each other with a high-order cobalt compound, and a conductive network made of the high-order cobalt compound is formed in the positive electrode.

A method of producing a higher-order cobalt compound that has been generally adopted conventionally is that a nickel electrode to which an active material powder containing a cobalt compound such as cobalt hydroxide is applied is incorporated in a battery, and then the cobalt hydroxide is charged by charging. It is a method of oxidizing to a higher cobalt compound. In the case of this method, an amount of discharge reserve corresponding to the amount of charged electricity consumed for the oxidation reaction is generated in the negative electrode. On the other hand, if the nickel electrode active material powder is oxidized in advance using an oxidizing agent, the amount of discharge reserve generated can be reduced because the oxidation of cobalt hydroxide by charging is unnecessary.

In addition, as a result of reducing the discharge reserve of the negative electrode, it is possible to allocate the reduced amount to the charge reserve of the negative electrode. Therefore, the nickel metal hydride storage battery using this positive electrode can effectively absorb the gas (oxygen gas, etc.) generated during overcharge by the charge reserve of the negative electrode, so that it is difficult for the internal pressure to rise, resulting in charge and discharge. Cycle life can be improved.

In the case of a positive electrode to which an active material powder in which a high-order cobalt compound is formed on the surface by oxidation treatment is applied, as shown in FIG. 2, adjacent active material powders for nickel electrodes adjacent to each other before the overdischarge operation is performed. Are simply in physical contact. For this reason, the current collecting function of the nickel electrode is inferior, and the discharge characteristics in large current discharge are inferior. On the other hand, in the nickel metal hydride storage battery according to the present invention, the active material powders of the positive electrodes are bonded together by a high-order cobalt compound, and a conductive network is formed in the positive electrode. A battery having excellent rate discharge characteristics can be obtained.

The amount of overdischarge electricity in the overdischarge operation may be an amount sufficient to reduce a part of the higher order cobalt compound and form a conductive network of the higher order cobalt compound in the nickel electrode by subsequent charging. If the amount of overdischarge electricity in one overdischarge operation is large, the hydrogen storage alloy is reduced to the irreversible region, and the battery capacity is reduced. In addition, there is a risk of adverse effects such as impairing the conductive function of the positive electrode and increasing the discharge reserve as described later. Therefore, the amount of overdischarge electricity in one overdischarge operation is an amount sufficient to form a conductive network and should be as small as possible.

The proportion of the cobalt compound in the nickel electrode active material powder is at most 25% by weight, usually 5 to 10% by weight. In the present invention, the rated capacity of the nickel-metal hydride storage battery, in which about 1/4 to 1/2 of the higher-order cobalt compound only needs to be reduced, is defined by the filling amount of nickel hydroxide. Therefore, the range of the amount of the higher cobalt compound contained in the nickel electrode is determined by the rated capacity of the battery. For these reasons, in the present invention, it is preferable that the amount of overdischarge electricity in one overdischarge operation is 2 to 10%.

In the present invention, in order to enhance the effect of the overdischarge operation, it is desirable to leave the battery at a high temperature prior to the overdischarge operation. By performing the leaving operation, in addition to reducing the oxide or hydroxide of the hydrogen storage alloy existing as a film on the surface of the hydrogen storage alloy to a metal, the alloy surface is etched.

In the etching, rare earth elements on the alloy surface are preferentially eluted, and a rare layer of rare earth elements is formed on the surface. When the overdischarge operation is performed without performing the high temperature leaving operation, a nonconductive rare earth element hydroxide is generated on the surface of the hydrogen storage alloy. According to the present invention, since a poor layer of rare earth elements is generated on the surface of the hydrogen alloy powder prior to the overdischarge operation, generation of the rare earth element hydroxide is suppressed even when the overdischarge operation is performed, Therefore, the conductivity of the hydrogen storage alloy electrode can be maintained.

The lower limit of the standing temperature is determined from the viewpoint of the temperature at which the oxide or hydroxide film of the hydrogen storage alloy is removed and the surface of the hydrogen storage alloy can be etched. From this point, it is preferable to set the lower limit of the standing temperature to 40 ° C.

The upper limit of the standing temperature is desirably a temperature that the binder forming the positive electrode and the negative electrode can withstand. The binder is generally CMC (carboxymethylcellulose), PTFE (polytetrafluoroethylene), PVA (polyvinyl alcohol), PNVA (poly N vinylacetamide), natural polymer thickener (xanthan gum), etc. Use. In order to avoid deterioration of these polymer materials at high temperatures, it is desirable that the standing temperature is 80 ° C. or lower. Furthermore, the binding force of the polymer material may decrease when left at a temperature exceeding 65 ° C. for a long time. When the binding force of the binder is significantly reduced, the hydrogen storage alloy powder or nickel hydroxide powder may fall off the base, resulting in a decrease in capacity and further a slight short circuit. Therefore, the upper limit of the standing temperature is more preferably 65 ° C. or less.

The standing time in the high temperature standing is also selected on the condition that the oxide or hydroxide film of the hydrogen storage alloy, which is the same viewpoint as the temperature selection, can be removed and that the binding power of the binder is not significantly reduced. . From such a viewpoint, it is desirable to set the leaving time to 5 to 24 hours.

Since the hydrogen storage alloy hydroxide elutes into the electrolyte by being left at a high temperature prior to the overdischarge, the surface of the hydrogen storage alloy powder can be further cleaned to enhance the activity of the negative electrode.

In the present invention, the next charge after the overdischarge operation is performed at the rate of 20 hours rate {current is 1/20 It (A)} or less, and 5 to 30% of the rated capacity of the battery is charged in the first stage. Then, charging at a rate of 10 hour rate [current is 1/10 It (A)] to 1 hour rate [current is 1 It (A)] to 105 to 170% of the rated capacity of the battery is performed together with the first stage charging. Perform staged charging.

In the next charging operation after the overdischarge operation, the first stage charging is performed at a low rate of 20 hours or less. When the charging is performed at a high rate, the positive electrode potential suddenly rises and Ni2 + is changed to Ni3 +. This is because the oxidation reaction from Co2 + to Co3 +, which proceeds at a lower potential than the oxidation reaction, does not proceed sufficiently. In the first-stage charging operation, the cobalt compound once reduced is oxidized, and a dense conductive network made of a higher cobalt compound is formed in the nickel electrode as the positive electrode.

Since this multistage charging is intended to shorten the time of the activation cycle, it is preferable that the rate of the charging current after the second stage is about 1 hour {current is 1 It (A)}. When charging at a higher rate than this, the inactive positive and negative electrodes do not accept the charge sufficiently, and as a result, the activation may be insufficient or the number of activation cycles may be increased. .

In the charging operation after overdischarge, if the total amount of charged electricity is less than 105% of the rated capacity of the battery, charging is insufficient and activation is difficult to proceed. In addition, if the total amount of electricity charged exceeds 170% of the rated capacity of the battery, γ-NiOOH may be generated in the positive electrode, or corrosion may occur in the hydrogen storage alloy of the negative electrode, which may reduce battery performance. This is not preferable.

Below, the suitable aspect of this invention is demonstrated based on an Example. In addition, the manufacturing method of the nickel metal hydride storage battery according to the present invention includes a positive electrode having an active material powder which is provided with a core layer mainly composed of nickel hydroxide and a surface layer containing a cobalt compound and is oxidized using an oxidizing agent. The activation method is applicable to all nickel-metal hydride storage batteries having a negative electrode having an active material powder made of a hydrogen storage alloy, and the details of the constituent materials of the electrode are limited to the contents described in the following examples. It is not a thing.

(Preparation of nickel electrode active material powder)
Cobalt hydroxide coating layer on the surface with high-density nickel hydroxide containing cobalt and zinc in the form of 1 wt% and 5 wt% (2.5 wt%) in terms of hydroxide, respectively, in accordance with the usual method A nickel hydroxide-based nickel electrode active material powder having an average particle diameter of 8 μm was prepared. In this nickel hydroxide-based material powder, the amount of the cobalt hydroxide coating layer was 10% by weight.

Further, the nickel hydroxide-based material powder is put into a sodium hydroxide aqueous solution having a temperature of 50 ° C. (85 ° C.) and a concentration of 15% by weight, and slowly stirred, while the hypoxia having a concentration of 5% as an oxidizing agent is added. An aqueous sodium chlorate solution was added dropwise to carry out the oxidation treatment. The ratio of the oxidant addition amount to the input amount of the nickel hydroxide material powder was adjusted so that the average oxidation number of cobalt and nickel contained in the material powder after the oxidation treatment was 2.15.

The average oxidation number of the positive electrode active material obtained by the ferrous sulfate method was measured, and as a result, the average oxidation number of cobalt and nickel contained in the material powder after the oxidation treatment was 2.14. An active material powder for a nickel electrode was obtained. The nickel electrode active material powder contains two kinds of transition metal elements, nickel and cobalt, but cobalt + / Co3 + has a lower redox potential than Ni2 + / Ni3 +, so cobalt. Is preferentially oxidized. Therefore, the obtained active material powder is a powder mainly composed of nickel hydroxide, the surface of which is coated with a higher-order compound of cobalt and a part of nickel hydroxide in the core layer is oxidized.

(Production of nickel electrode)
A nickel electrode active material paste was prepared by adding and kneading a CMC aqueous solution having a concentration of 0.7% by weight to 100 parts by weight of the obtained nickel electrode active material powder. The paste was filled in a foamed nickel porous substrate having a thickness of 1.4 mm, dried, and then pressed to adjust the thickness to 0.6 mm to obtain a long strip-shaped original plate for nickel electrode. The original plate was cut into a predetermined size to obtain a nickel electrode.

The active material filling capacity of the nickel electrode is calculated to be 456.47 mAh per 1 g of Ni element in the active material filled in the nickel electrode based on the following formula assuming the following one-electron reaction of Ni2 + → Ni3 +. did. The active material filling capacity of the nickel electrode determined from the calculated amount was 1650 mAh.

On the other hand, a hydrogen storage alloy powder having a particle size of 50 μm or less, which is represented by a composition of MmNiAlCoMn (Mm is a misch metal and is a mixture of rare earth elements composed of La, Ce, Pr, and Nd), is prepared. A paste was prepared by adding an aqueous solution of CMC as a thickener and an aqueous dispersion of polytetrafluoroethylene as a binder to the alloy powder. This paste was applied to both sides of the punching metal and dried, and then pressed to adjust the thickness to 0.6 mm, to obtain a long belt-shaped raw material for a hydrogen storage alloy electrode. The original plate was cut into a predetermined size to obtain a hydrogen storage alloy electrode. The active material filling capacity of the hydrogen storage alloy electrode was 2475 mAh, 1.5 times the nickel electrode active material filling capacity.

(Production of nickel metal hydride storage battery)
The nickel electrode and the hydrogen storage alloy electrode were wound up in a spiral shape with a separator having a thickness of 0.15 mm made of a nonwoven fabric of polyolefin resin fibers to produce an electrode group. The electrode group was housed in a cylindrical metal case, and a predetermined amount of an electrolytic solution composed of a 7 mol / dm 3 potassium hydroxide aqueous solution and a 1 mol / dm 3 lithium hydroxide aqueous solution was injected. Next, the metal case was sealed using a metal lid provided with a safety valve to obtain an AA size cylindrical nickel-metal hydride storage battery with a rated capacity of 1650 mAh.

The obtained nickel metal hydride storage battery was subjected to an evaluation test under the conditions described below.
(Initial activation)
(First charge, first discharge)
The prototype battery was subjected to initial charging at a temperature of 20 ° C. In the first charge, the charging current for the first stage is 82.5 mA {1/20 It (A)} for 6 hours, and the charging current for the second stage is 330 mA [1/5 It (A)] for 4 hours, the first stage. And the second stage, 110% of the rated capacity was charged (130 mA, 16 hours). The battery after the initial charge was discharged under normal conditions. Discharging was carried out at a constant current of 165 mA {1/10 It (A)} (260 mA), and ended when the terminal voltage fell below 1.0V.

(High temperature storage)
The battery in which one cycle of the first charge / discharge operation was performed was left under the following conditions. The standing temperature was left for 12 hours under the conditions of four levels of 25 ° C., 40 ° C., 60 ° C. and 80 ° C. Also, a battery was prepared that was immediately charged for the second time without being left unattended.

Furthermore, regarding the standing temperature of 6O ° C., the standing time was set to 12 hours, and the four conditions of 1 hour, 5 hours, 24 hours, and 36 hours were added and left standing.

(2nd cycle charge, 2nd cycle discharge and overdischarge operation)
After the batteries 1 to 21 were charged, the battery 5 and the battery 20 were subjected to a discharging operation, and the other batteries except this were subjected to a discharging and overdischarging operation. Charging was performed at a charging current of 330 mA [1/5 It (A)], and 110% of the rated capacity of the battery was charged. The discharge operation was performed at a constant current of a discharge current of 165 mA {1/10 It (A)}, and ended when the terminal voltage fell below 1.0V. The overdischarge operation was continued with the same current as the discharge operation, and was terminated by a timer when the overdischarge electricity amount reached a predetermined value. (130 mA, 0-24 hours)

The amount of overdischarge electricity was 5% of the rated capacity. The batteries left for 12 hours at a temperature of 60 ° C. were classified into 5 levels of 1%, 2%, 5%, 10%, and 15%, and the batteries were designated as Battery 6, Battery 7, Battery 13, Battery 15, and Battery, respectively. 16

(3rd cycle charging operation)
A battery that had been charged in one stage and a battery that had been charged in two stages were prepared. One type (Battery 8 in Table 1) out of those that did not perform overdischarge operation (Battery 5 and Battery 20 in Table 1 below) and those that performed overdischarge operation was regarded as one-stage charging. In the first stage charging, the charging current was set to 165 mA [1/10 It (A)], and 110% of the rated capacity of the battery was charged. In the second stage charging, the charging current of the first stage charging was fixed to 82.5 mA {1/20 It (A)}, and the second stage charging current was fixed to 165 mA {1/10 It (A)}. In addition, for a battery that was overdischarged 5% after being left at 60 ° C. for 12 hours, the first stage discharge current was 33 mA {1/50 It (A)}, 82.5 mA {1/20 It (A)}, and 132 mA. Five levels of {1 / 12.5It (A)} were used. In addition, a 165 mA {1/10 It (A)} one-stage charge was also prepared. The amount of charged electricity at the first stage was 30% of the rated capacity, the amount of charged electricity at the second stage was 80% of the rated capacity, and the combined charge of the first and second stages was 110%. Furthermore, for the case where the first stage charging was performed at a charging current of 82.5 mA {1/20 It (A)}, the ratio of the amount of charged electricity to the rated capacity was set to three levels of 2%, 5% and 10%. Additional charging was performed.

(Discharge operation in the third cycle)
Constant current discharge was performed with a current of 165 mA {1/10 It (A)] and a final voltage of 1.0 V.

(4th and 5th cycle charge / discharge operations)
Next, these batteries were charged at a constant current of 110% at 330 mA {1/5 It (A)} and then discharged at a constant current of 165 mA [1/10 It (A)]. The charge / discharge cycle was defined as 1 cycle, and the 2nd cycle charge / discharge operation of the 4th and 5th cycles was repeated. Initial activation was completed with the charge / discharge operation in the fifth cycle. The main steps of the initial activation described above are summarized in Table 1.

(Changes in discharge capacity during initial activation)
FIG. 3 shows the transition of the discharge capacity (expressed as a ratio (%) to the rated capacity) in the initial charge / discharge cycle of the battery 5, battery 8, battery 13, battery 20, and battery 21. As shown in FIG. 3, the rise of the discharge capacity after the third cycle of the battery 13 and the battery 21 which are the example batteries according to the present invention is large. This is due to the effect of the overdischarge operation performed in the second cycle. Further, when the battery 13 and the battery 21 are compared, the battery 13 has a larger discharge capacity rise. This is due to the effect of the neglect operation performed prior to the overdischarge operation. In the case of the battery 8, the rise of the discharge capacity after the third cycle is inferior to that of the battery 13. The battery 8 is also overdischarged in the same manner as the battery 13, but the charge after the overdischarge is 10 hour rate [charging current 165 mA [1/10 It (A)]] and the 20 hour rate of the battery 13 [charging current 82. 5 mA [1/20 It (A)]], which was carried out at a higher rate, and therefore, after a portion of the higher cobalt oxide was reduced by overdischarge, the formation of a conductive network by charging was insufficient. it is conceivable that. For this reason, it is desirable to perform charging after the overdischarge operation at a low rate of 20 hours rate [current 1/20 It (A)] or less.

FIG. 4 shows the transition of the discharge capacity in the initial charge / discharge cycle of the battery 1, the battery 2, the battery 13, the battery 19 and the battery 21. As shown in FIG. 4, compared to the battery 1 and the battery 21, the discharge capacity rises after the third cycle of the battery 2, the battery 13, and the battery 19. This is due to the effect of leaving the battery 13 at a high temperature prior to the overdischarge operation. In the case of the battery 1, since the aging temperature was low, it is considered that the rise of the discharge capacity is inferior.

FIG. 5 shows the transition of the discharge capacity in the initial charge / discharge cycle of the battery 3, the battery 4, the battery 13, the battery 17 and the battery 18. As shown in FIG. 5, compared to the battery 3, the discharge capacities of the battery 4, the battery 13, the battery 17, and the battery 18 are large after the third cycle. This result indicates that it is desirable to leave the battery for 5 hours or more in the leaving operation. In addition, there is no difference in the rise effect of the discharge capacity when left for 24 hours and 36 hours. If the standing time at a high temperature is prolonged, there is a risk of adverse effects such as the corrosion of the hydrogen storage alloy. Therefore, it is desirable that the standing time is 5 to 24 hours.

(Room temperature high rate discharge test)
Battery 5, Battery 6, Battery 7, Battery 15 and Battery 16 that have passed the initial five cycles are charged with a constant current of 110% at 330 mA {1/5 It (A)} and then at 4950 mA {3 It (A)} at a temperature of 20 ° C. The battery was discharged at a final voltage of 1.0V. Table 2 shows the discharge capacity and the discharge capacity ratio (%) at 330 mA {1/5 It (A)} and the final voltage of 1.0 V for each battery.

As shown in Table 2, the battery 6, battery 7, and battery 15, which are the example batteries according to the present invention, have excellent high rate discharge characteristics. This is due to the effect of performing the overdischarge operation. In contrast to the example battery according to the present invention, a part of the high-order cobalt compound generated by the oxidation treatment by the overdischarge operation is reduced, whereas in the case of the battery 16, the overdischarge electricity amount is too large. It is considered that the conductive function of the nickel electrode was lowered because almost all of the higher-order cobalt compound had been reduced.

After charging the battery 9, battery 10, battery 11, battery 12, battery 13 and battery 14 after 110 cycles of constant current at 330 mA {1/5 It (A)} and 4950 mA {3 It (A )} At a final voltage of 1.0V. Table 3 shows the discharge capacity ratio of each battery in the discharge and the discharge capacity ratio in the discharge of 330 mA {1/5 It (A)} and the final voltage of 1.0 V.

As shown in Table 3, the high rate discharge characteristics of the battery 10 and the battery 14 are lower than the high rate discharge characteristics of other batteries. When the charge rate after the overdischarge operation is high, it is difficult to form the conductive network by reprecipitation of the higher cobalt compound in the nickel electrode. In the case of the battery 10, the amount of electricity charged by the first-stage low rate charging is insufficient. In the case of the battery 14, the first stage charging rate is high. For this reason, in the battery 10 and the battery 14, since the said electroconductive network formation is inadequate, it is thought that a high rate discharge characteristic is inferior. From this result, it is desirable to set the charge rate of the first stage after the overdischarge operation to 1/20 hour rate or less, and it is desirable to set the amount of charged electricity to 5% or more with respect to the rated capacity.

(Low temperature high rate discharge test)
Example battery 13, battery 21 and comparative battery 5 and battery 20 of the present invention after the initial 5 cycles were charged at 110 mA constant current at 330 mA {1/5 It (A)}, and then 4950 mA at a temperature of -20 ° C. The battery was discharged at a final voltage of 1.0 V at {3 It (A)}. Table 4 shows the ratio of the discharge capacity of each battery to the discharge capacity at 330 mA {1/5 It (A)} and the discharge voltage at a final voltage of 1.0 V.

The battery 13 and the battery 21 which are the examples according to the present invention show a higher discharge capacity than the battery 5 and the battery 20 which are the comparative example batteries. In the case of the example battery, it is considered that the effect of the overdischarge operation is exerted. Moreover, the battery 13 which performed the high temperature leaving operation also in the Example battery has shown especially high discharge capacity.

(Charge / discharge cycle test)
After initial activation of the example battery 13, the example battery 15, the example battery 18 and the comparative example battery 16, at a temperature of 20 ° C., a current of 1650 mA {1 It (A)} is charged at 105% of the rated capacity. At 1650 mA {1 It (A)}, a final voltage 1.0 V discharge was taken as one cycle and subjected to a charge / discharge cycle test.

The result is shown in FIG. The comparative example battery 16 is inferior in charge / discharge cycle performance as compared with the example batteries 13 and 15. In the case of the comparative battery 16, since the amount of overdischarge electricity was excessive in the overdischarge operation, almost all cobalt higher-order compounds were reduced in the overdischarge operation, and this increased the amount of discharge reserve generated. There is a fear. For this reason, it is thought that it led to the fall of charging / discharging cycle performance. As can be seen from this, the amount of overdischarge electricity needs to be limited to an amount that reduces a part of the higher cobalt compound contained in the nickel electrode active material.

In addition, the example battery 18 is slightly inferior in cycle performance to the other example batteries, and at the same time has a high internal impedance. This is presumably because the hydrogen storage alloy corrodes when left at high temperatures for a long period of time, so that the increase in the discharge reserve of the negative electrode and the decrease in the charge reserve have advanced, and the internal pressure of the battery has increased.

DESCRIPTION OF SYMBOLS 1 Core layer 2 Surface layer 3 Higher order cobalt compound which couple | bonds active material powders

Claims (3)

A core layer mainly composed of nickel hydroxide and a surface layer mainly composed of a higher-order cobalt compound are provided, and a porous metal substrate is filled with an active material powder in which a part of the nickel hydroxide is oxidized. A positive electrode formed by bonding the active material powders with a high-order cobalt compound, a negative electrode comprising a hydrogen storage alloy electrode, and the active material filling capacity of the hydrogen storage alloy electrode being the active material filling capacity of the nickel hydroxide Is a method for producing a nickel-metal hydride storage battery that is 1.5 times or less of the above, and a powder in which a cobalt compound surface layer is provided on the surface of a core layer mainly composed of nickel hydroxide is chemically oxidized using an oxidizing agent. In the process of performing the treatment and in the process of initial activation that is activated by performing a charge / discharge operation on the battery, an overdischarge operation is performed at least once during the operation to reduce a part of the higher-order cobalt compound. And The manufacturing method of the nickel hydride storage battery characterized by providing the process of producing | generating a bivalent oxidation cobalt compound. 2. The method for producing a nickel-metal hydride storage battery according to claim 1 , wherein the battery after discharge is left in a temperature range of 40 to 80 [deg.] C. before performing the overdischarge operation. 3. The method for producing a nickel-metal hydride storage battery according to claim 2 , wherein the battery is allowed to stand in a temperature range of 40 to 80 [deg.] C. after discharge is 5 to 24 hours.

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