JP2022115311A - Manufacturing method of alkaline secondary battery - Google Patents

Abstract

To improve output characteristics of an alkaline secondary battery by efficient positive electrode activation.SOLUTION: A control device of a manufacturing device of a nickel-metal hydride storage battery controls a charging current so as to maintain a cell voltage at 0.2 [V] in a section from t1 to t2 by first-stage charging (S2). When a current value falls below a threshold Aend1 (S3: YES), the charging current is controlled so as to maintain the cell voltage at 1.0 [V] in a section from t2 to t3 by second-stage charging (S4). When the current value falls below a threshold Aend2 (S5: YES), a Co charging process ends. The efficient Co charging process can improve a conductive Co network by CoOOH of a positive electrode and improve output characteristics.SELECTED DRAWING: Figure 4

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing an alkaline secondary battery, and more particularly to a method for manufacturing an alkaline secondary battery in which the cobalt of the positive electrode is more preferably activated.

For alkaline secondary batteries, a paste containing nickel hydroxide powder and a powder of a cobalt compound, such as metallic cobalt (Co) or cobalt monoxide (CoO), is prepared. Then, there is a method of manufacturing a non-sintered paste-type nickel positive electrode by filling a net made of nickel as a current collector with this paste. In such an alkaline secondary battery, the activity of the cobalt compound and the like is poor immediately after assembly, and the initial DC internal resistance value (DC-IR) is large. Therefore, the battery is activated by charging and discharging the battery in a cobalt charging process under predetermined conditions.

For example, a nickel-cadmium secondary battery, which is an example of an alkaline secondary battery described in Patent Document 1, is manufactured by the following method. First, a paste containing nickel hydroxide powder and cobalt compound powder such as cobalt monoxide (CoO) is prepared. Then, a paste-type nickel positive electrode is produced by filling a net made of nickel as a current collector. Subsequently, an electrode group is produced by interposing a separator between the positive electrode and the negative electrode. This electrode group is housed in a container together with an alkaline electrolyte, and the container is sealed. Then, initial charging and discharging are performed to activate the secondary battery.

As shown in FIG. 14, the initial charging process is performed with a constant current. First, cobalt monoxide (CoO), which has a low oxidation potential, is oxidized at the positive electrode and changed to cobalt oxyhydroxide (CoOOH). This oxidation reaction increases the voltage of the secondary battery. Then, nickel hydroxide (Ni(OH)2) having a higher oxidation potential is oxidized. Cobalt oxyhydroxide has high electrical conductivity, so that it improves electrical conductivity between nickel hydroxide and the current collector, thereby improving the utilization rate of the positive electrode.

With such an invention, the secondary battery could be activated more efficiently.

JP-A-7-211353

However, when the initial charge is performed at a constant current in this way, it takes a long time of 10 hours or more to oxidize all the cobalt monoxide, and there is a problem that mass productivity is inferior.
The problem to be solved by the manufacturing method of the alkaline secondary battery of the present invention is to improve the output characteristics of the alkaline secondary battery by efficiently activating the positive electrode.

In order to solve the above problems, the method for producing an alkaline secondary battery of the present invention includes a positive electrode containing nickel hydroxide as an active material and metallic cobalt or a cobalt compound, a negative electrode, a separator, and an alkaline electrolyte. In the method for producing an alkaline secondary battery, the initial charging step includes a first step of charging at a potential that changes from metallic cobalt or a cobalt compound to HCoO ₂ ⁻ at the positive electrode potential, and charging from a high rate to a gradually low rate. , at the positive electrode potential, a second stage of charging at a potential that changes from HCoO ₂ ⁻ to CoOOH at a rate higher than that of the first stage and at a rate that is progressively lower.

In the first stage and the second stage, as the resistance value of the positive electrode increases, the charging current may be decreased so that the positive electrode potential remains constant at the set potential. In this case, in the first stage and the second stage, the current to be applied is determined by recording the experimental result of the relationship between the cell voltage and the applied current in advance so that the positive electrode potential is constant, and measuring the cell voltage. However, the applied current may be controlled so that the positive electrode potential is constant based on data based on the experimental results.

In addition, in the first stage and the second stage, the charging current may be decreased so that the cell voltage is kept constant at the set potential as the resistance value of the positive electrode increases. In this case, the cell voltage in the first stage is in the range of 0.1 to 0.4 V, and charging is started at a predetermined rate. Charging may be started at a higher charging rate than the charging rate at which charging is started in the first stage.

The first step may be performed until the current value is equal to or less than a preset threshold value, and the second step may be performed until the current value is equal to or less than the preset threshold value. may

In the first stage, a preliminary application of gradually increasing the current value may be performed at the start of charging.
It can be suitably applied when the alkaline secondary battery is a nickel-hydrogen storage battery.

The method for producing an alkaline secondary battery according to the present invention can improve the output characteristics of the alkaline secondary battery by efficiently activating the positive electrode.

The perspective view which shows the structure of the nickel-hydrogen storage battery of this embodiment. Sectional drawing of the laminated body provided in the nickel-hydrogen storage battery of this embodiment. FIG. 2 is a schematic diagram showing a nickel-metal hydride storage battery manufacturing apparatus according to the present embodiment. 4 is a flow chart showing the procedure of the cobalt charging process of the present embodiment. 4 is a graph showing the relationship between time and cell voltage in the cobalt charging process of this embodiment. 4 is a graph showing the relationship between charging time and current value in the cobalt charging step of the present embodiment. 4 is a graph showing the relationship between the positive electrode potential and the response current, which shows the reaction in the cobalt charging step of the present embodiment. 5 is a graph showing the relationship between the capacity and voltage of a nickel-metal hydride storage battery compared with the conventional technology of the present embodiment; 5 is a graph showing the DC-IR improvement at 60% SOC with a cobalt charging process compared to the prior art of the present embodiment; 4 is a graph showing the DC-IR improvement at 20% SOC with the cobalt charging process compared to the prior art of the present embodiment; 5 is a graph showing the improvement in Co network content due to the cobalt charging process compared to the prior art of the present embodiment; 5 is a graph showing the time and potential control method of the positive electrode potential in the cobalt charging process of the first embodiment. 7 is a graph showing the time and potential control method of the positive electrode potential in the cobalt charging process of the second embodiment. 1 is a graph of time versus cell voltage for a prior art cobalt charging process;

Hereinafter, the method for manufacturing an alkaline secondary battery of the present invention will be described as follows: a positive electrode using nickel hydroxide (Ni(OH) ₂ ) as a positive electrode active material; a negative electrode using a hydrogen storage alloy as a negative electrode active material; An embodiment of a method for manufacturing a hydrogen storage battery will now be described with reference to FIGS.

<Outline of this embodiment>
In the method of manufacturing the nickel-metal hydride storage battery 11 of this embodiment, the initial charging process includes a first stage and a second stage. The first step is to charge at a potential that changes from metallic cobalt or a cobalt compound to HCoO ₂ ⁻ at the positive electrode potential, charging from a high rate to a progressively lower rate. In the second stage, the potential changes from HCoO ₂ ⁻ to CoOOH at the positive electrode potential, and the charging rate is charged at a rate higher than that in the first stage and then gradually lower.

<Principle of this embodiment>
The reaction in the cobalt charging process of this embodiment is divided into two stages. That is, the added metallic cobalt or cobalt compound changes to divalent Co(II), and then from divalent Co(II) to trivalent Co(III). change from metallic cobalt or cobalt compounds to HCoO ₂ ^- and from HCoO ₂ ^- to CoOOH. Ultimately, a sufficient amount of CoOOH dominates the discharge performance of the positive electrode.

Comparing the potential at which metallic cobalt or a cobalt compound changes to HCoO ₂ ^— and the potential at which HCoO ₂ ^— changes to CoOOH, the potential at which metallic cobalt or a cobalt compound changes to HCoO ₂ ^— is lower. The present inventor believes that if the potential of the positive electrode is focused only on the reaction in which HCoO ₂ ⁻ changes to CoOOH as in the prior art, metallic cobalt or a cobalt compound cannot be sufficiently changed to HCoO ₂ ⁻ . We obtained knowledge that there is room for improvement in activation.

As described above, when the initial charge is performed with a constant current, the voltage applied to the secondary battery varies depending on the battery because the internal resistance of the secondary battery varies depending on the manufacturing conditions. As a result, depending on the internal resistance of the secondary battery, the voltage applied to the secondary battery may be higher than the oxidation potential of the metallic cobalt or cobalt compound. There was a problem that the rate decreased.

In the invention described in Patent Document 1, the initial charging process is performed by two or more stages of constant voltage charging, and the two or more stages of constant voltage charging are such that the voltage increases stepwise within a range of 1.3 V or less. is set to The reason why the voltage is set in the range of 1.3 V or less is that when the set voltage exceeds 1.3 V, the oxidation reaction of the nickel hydroxide powder proceeds at the same time, so the cobalt compound remains without being oxidized, and the use of the positive electrode is reduced. This is because the rate will decrease. However, in the invention described in Patent Document 1, the set voltage is at least 1.1 V or more, and at this voltage, CoO cannot be dissolved in the alkaline electrolyte to sufficiently generate HCoO ₂ ⁻ . There was a problem.

The inventors of the present invention have conducted experiments with respect to this problem, and have found that it is important to dissolve CoO, which is the premise, in an alkaline electrolyte to sufficiently generate HCoO ₂ ⁻ in order to sufficiently generate CoOOH. I got it. As a result, the inventors have arrived at the configuration of the present invention.

As a result, in order to maintain a potential at which metallic cobalt or a cobalt compound is converted to HCoO ₂ ⁻ , the current rate during the initial charge is reduced stepwise at least twice, thereby increasing the conductivity of CoOOH at the positive electrode. It is a charging method that strengthens the sexual network. As a result, the high-rate discharge performance can be improved, resulting in improved output characteristics. In particular, the improvement in DC-IR in the low SOC region is remarkable.

<Structure of Nickel Metal Hydride Battery 11>
FIG. 1 is a perspective view showing the structure of a nickel-metal hydride storage battery 11 of this embodiment. FIG. 2 is a cross-sectional view of a stack of battery cells 12 provided in the nickel-metal hydride storage battery 11 of this embodiment. First, the nickel-metal hydride storage battery 11 according to the method for manufacturing the nickel-metal hydride storage battery 11 of this embodiment will be described.

<Battery module>
As shown in FIG. 1 , the nickel-metal hydride storage battery 11 is configured as a battery module having a plurality of battery cells 12 . The nickel-metal hydride storage battery 11 is a rectangular plate-shaped sealed battery. It has an integrated battery case 13 capable of accommodating a plurality of (six in this case) battery cells 12 and a lid 14 that seals the opening of the integrated battery case 13 . The integrated battery case 13 and the lid 14 are made of, for example, a resin material. The integrated battery case 13 accommodates six battery cells 12 electrically connected in series. Electric power of these battery cells 12 is taken out from a positive electrode terminal 13 a and a negative electrode terminal 13 b provided in the integrated battery case 13 .

<Battery cell 12>
As shown in FIG. 2 , the battery cell 12 includes a plate group 20 in which a plate-shaped positive plate 15 and a plate-shaped negative plate 16 are stacked with a separator 17 interposed therebetween. It also has a laminate composed of current collector plates 21 and 22 and an electrolytic solution accommodated in integrated battery container 13 together with the laminate. The end portion 15a of the positive electrode plate 15 is joined to the joint surface of the current collector plate 21 of the positive electrode. An end portion 16 a of the negative electrode plate 16 is bonded to the bonding surface of the current collector plate 22 of the negative electrode.

<Negative plate 16>
Next, the negative plate 16 will be described. The negative electrode plate 16 includes a core material and a hydrogen storage alloy carried on the core material. The type of hydrogen storage alloy is not particularly limited, but for example, an alloy of nickel and misch metal, which is a mixture of rare earth elements, and a part of the alloy replaced with a metal such as aluminum, cobalt, manganese. This negative electrode plate 16 is made by adding a thickener such as carbon black and a binder such as styrene-butadiene copolymer to a hydrogen storage alloy and processing it into a paste. It is manufactured by filling, drying, rolling and cutting.

<Electrolyte>
Next, the electrolytic solution will be explained. The electrolyte is held in the separator 17 and conducts ions between the positive plate 15 and the negative plate 16 .

The electrolytic solution is an alkaline aqueous solution containing potassium hydroxide (KOH) as the main component of the solute.
<Positive plate 15>
Next, the positive electrode plate 15 will be described. The positive electrode plate 15 has a base material made of a three-dimensional porous body made of nickel, and a positive electrode mixture supported by the base material. The base material has a function of a carrier that supports a filler and a function of a current collector. The positive electrode mixture paste contains positive electrode active material particles containing nickel hydroxide as a main component, cobalt (Co), which is a metal that functions as a conductive material, a thickener, a binder, and the like. In this embodiment, metallic cobalt (Co) is exemplified, but cobalt oxide such as cobalt monoxide (CoO), cobalt compounds, and the like may be contained.

The positive electrode active material particles of the product have a coating layer provided on the surface of the nickel hydroxide particles. This coating layer is mainly composed of cobalt oxyhydroxide (CoOOH). In the step of producing the positive electrode plate 15, the positive electrode plate 15 is produced using CoOOH having a β-type crystal structure. When the nickel-metal hydride storage battery using this positive electrode plate 15 is charged (initial charge) for the first time after being assembled, the resistance of β-type CoOOH decreases due to the change in crystallinity.

Co contained in the positive electrode mixture is electrochemically oxidized and deposited as CoOOH through CoO and HCoO ₂ ^— when the nickel-metal hydride storage battery is initially charged (sometimes simply referred to as charging). At this time, CoOOH generated by oxidation of cobalt is deposited between the positive electrode active material particles, between the positive electrode active material and the base material, etc., so that the gap between the positive electrode active material particles, the positive electrode active material and the base material You can fill the gaps between Therefore, the coating layer containing CoOOH and cobalt-derived CoOOH, which constitutes the coating layer before the initial charge, becomes a high-density layer with reduced gaps provided between the positive electrode active material particles. Even this CoOOH alone forms a conductive network in the positive electrode that connects the nickel hydroxide particles, the nickel hydroxide particles and the substrate, and the like.

By forming a conductive network by CoOOH, the utilization rate of the positive electrode active material can be improved. The utilization rate of the positive electrode active material is calculated as the ratio of the discharged capacity to the theoretical capacity obtained by multiplying the weight of the positive electrode active material by the theoretical capacity of the active material. Since CoOOH is stable within the operating voltage range of the nickel-metal hydride storage battery, CoOOH will not be reduced to cobalt or the like as long as the nickel-metal hydride storage battery operates within the operating voltage range.

<Nickel-metal hydride storage battery manufacturing device 30>
FIG. 3 is a schematic diagram showing a partial configuration of an example of the manufacturing apparatus 30 for the nickel-metal hydride storage battery 11. As shown in FIG. As shown in FIG. 3, the manufacturing apparatus 30 for the nickel-metal hydride storage battery 11 has a charging/discharging device 32 capable of charging/discharging the nickel-metal hydride storage battery 11 and a control device for controlling the charging/discharging device 32, as shown in FIG. 31. The control device 31 has a computer and controls the charging/discharging device 32 with a control signal. The charging/discharging device 32 charges or discharges the nickel-metal hydride storage battery 11 based on signal control from the control device 31 . The control device 31 controls charging and discharging of the nickel-hydrogen storage battery 11 at a predetermined voltage or current based on a stored program. Control is performed based on the results of measurement by a voltmeter 34 that measures the cell voltage of the nickel-metal hydride storage battery 11 and an ammeter 33 that measures the current flowing through the nickel-metal hydride storage battery 11 . The voltmeter 34 can measure the voltage of each battery cell 12 individually. Using the functions of the manufacturing apparatus 30 for the nickel-metal hydride storage battery 11, the cobalt charging process and the like are performed.

<Manufacturing Method of Nickel Metal Hydride Battery 11>
Next, a method for manufacturing the nickel-metal hydride storage battery 11 will be described. The method for manufacturing the nickel-metal hydride storage battery 11 includes a positive electrode manufacturing process, a negative electrode manufacturing process, an assembling process, a cobalt charging process, and a post-process.

<Positive electrode manufacturing process>
In the positive electrode preparation step, a predetermined amount of cobalt, a thickening agent and the like are added to the positive electrode active material particles having a coating layer, and the mixture is kneaded to form a paste. Then, this paste is filled into a base material made of foamed three-dimensional nickel porous material. After drying, the positive electrode plate 15 is produced by pressure molding and cutting into a predetermined size.

<Negative Electrode Manufacturing Process>
In the negative electrode preparation step, the hydrogen-absorbing alloy powder is immersed in an alkaline aqueous solution and stirred, then washed with water and dried. Further, a binder and the like are added to the dried hydrogen-absorbing alloy powder and kneaded to prepare an active material paste. Then, this active material paste is applied to a core material such as a punching metal, dried, rolled and cut to fabricate the negative electrode plate 16 .

<Assembly process>
In the assembly process, the positive electrode plate 15 and the negative electrode plate 16 are laminated with a separator 17 made of non-woven fabric of an alkali-resistant resin interposed therebetween. Also, the end portion 15a of the positive electrode plate 15 is joined to the current collector plate 21 by welding or the like, and the end portion 16a of the negative electrode plate 16 is joined to the current collector plate 22 by welding or the like to produce a laminate. Further, the laminate is housed in an integrated battery case 13 together with an electrolytic solution containing potassium hydroxide as a main component of the solute, and sealed.

<Cobalt charging process>
The cobalt charging step is a step of electrochemically oxidizing Co contained in the positive electrode mixture and depositing it as CoOOH by charging the nickel-hydrogen storage battery 11 at a predetermined voltage.

FIG. 4 is a flow chart showing the procedure of the cobalt charging process of this embodiment. FIG. 5 is a graph showing the relationship between the time [seconds] and the cell voltage [V] in the cobalt charging process of this embodiment, and FIG. 6 shows the charging time [seconds] and It is a graph which shows a relationship with a current value [A]. Hereinafter, the cobalt charging process will be described along the flowchart of FIG.

<First Stage Preliminary Charge (S1)>
When the cobalt charging process is started (start), the control device 31 (see FIG. 3) performs the first stage of preliminary charging (S1). In the preliminary charging from t0 to t1 shown in FIG. 6, the charging current [A] is applied so as to gradually increase the current value from zero to increase the cell voltage [V]. As shown in FIG. 5, when the cell voltage [V] reaches a target voltage (for example, 0.2 [V]), the charging proceeds to the first stage.

<First Stage Charging (S2)>
When the cell voltage reaches 0.2 [V] due to the first-stage preliminary charging, the control device 31 controls the charging current so as to maintain the voltage in the section from t1 to t2. At the beginning of the reaction, the amount of unreacted Co is large and the reaction resistance is relatively small, so the current for maintaining the voltage is relatively large and the charging is performed at a high charging rate. After that, when the battery is charged with the same current for a certain period of time, as the charging progresses, unreacted Co decreases and the reaction resistance increases. Therefore, the charging current for maintaining the same voltage is relatively small, resulting in charging at a relatively low charging rate.

In this embodiment, the cell voltage is maintained near 0.2 [V]. Therefore, for example, 0.3 [V] higher than 0.2 [V] is set as the upper limit threshold Vmax1. When this cell voltage exceeds the threshold Vmax1, the controller 31 reduces the applied current [A] by a certain width. This reduction width is set to a predetermined value. The amount of reduction is set so as not to fall below the lower limit threshold Vmin1 (for example, 0.1 [V]) of the cell voltage. Therefore, the control device 31 controls that the cell voltage [V] in the section from t1 to t2 shown in FIG. The charging current [A] is decreased stepwise as shown in FIG. 6 so as to be constant at 2 [V].

When the charging current is greater than the predetermined end current Aend1 (S3: NO), the control device 31 continues the first stage charging (S2), and when the charging current becomes equal to or less than the predetermined end current Aend1 (S3 : YES), the charging of the first stage is terminated and the charging is shifted to the charging of the second stage (S4).

<Second Stage Charging (S4)>
In the second stage of charging, the charging current is controlled so as to maintain the voltage in the interval from t2 to t3 shown in FIG. At the beginning of the reaction, there is a large amount of unreacted HCoO ₂ ⁻ and the reaction resistance is relatively small, so the current for maintaining the voltage is relatively large and charging is performed at a high charging rate. After that, when the battery is charged with the same current for a certain period of time, as the charging progresses, unreacted HCoO ₂ ⁻ decreases and the reaction resistance increases. Therefore, the charging current for maintaining the same voltage is relatively small, resulting in charging at a relatively low charging rate.

In this embodiment, the cell voltage is maintained at 1.0 [V], but the upper limit threshold value Vmax2 is set at 1.2 [V], which is higher than 1.0 [V], for example. When this cell voltage exceeds the threshold Vmax2, the controller 31 reduces the applied current [A] by a certain width. This reduction width is set to a predetermined value. This decrease is set so as not to fall below the lower limit threshold Vmin2 (for example, 0.8 [V]) of the cell voltage. Therefore, the control device 31 controls the cell voltage [V] in the interval from t2 to t3 shown in FIG. The charging current [A] is decreased stepwise as shown in FIG. 6 so as to be constant at 0 [V].

When the charging current is greater than the predetermined end current Aend2 (S5: NO), the control device 31 continues the second stage charging (S4), and when the charging current becomes equal to or less than the predetermined end current Aend2 (S5 : YES), and terminate the charging of the second stage (end).

(Action of the first embodiment)
<Positive electrode potential [V] and response current [A]>
FIG. 7 is a graph showing the relationship between the positive electrode potential [V] and the response current [A] showing the reaction in the cobalt charging step of this embodiment. The positive electrode potential [V] is a potential relative to a mercury oxide reference electrode (Hg/HgO).

As shown in FIG. 7, when the cell voltage is maintained at approximately 0.2 [V], the positive electrode potential [V] at this time is approximately -0.65 [V]. At this positive electrode potential [V], Co becomes HCoO ₂ ⁻ and cobalt dissolves in the electrolytic solution. On the other hand, at this positive electrode potential [V], HCoO ₂ ^- becomes CoOOH and Ni(OH) ₂ becomes NiOOH, so that current is not consumed and Co is converted to HCoO ₂ ^- without waste. be able to.

Further, when the cell voltage is maintained at approximately 1.0 [V], the positive electrode potential [V] at this time is approximately 0.15 [V]. At this positive electrode potential [V], HCoO ₂ ⁻ becomes CoOOH, and CoOOH on the positive electrode can be produced without waste. Since Co has already become HCoO ₂ ⁻ without waste, the generation of HCoO ₂ ⁻ is not hindered by this positive electrode potential [V]. In addition, since the positive electrode potential [V] is too low for Ni(OH) ₂ to become NiOOH, CoOOH can be efficiently produced without interfering with the production of CoOOH.

Therefore, when charging is performed at a high rate after the cobalt charging step and the positive electrode potential [V] reaches approximately 0.2 to 0.5 [V], Ni(OH) ₂ becomes NiOOH, so the positive electrode is activated. . At this time as well, Co has already converted to CoOOH through HCoO ₂ ⁻ without waste, so there is no problem in setting the positive electrode potential [V] to about 0.2 to 0.5 [V].

<Increased battery capacity>
FIG. 8 is a graph showing the relationship between the capacity and voltage of the nickel-hydrogen storage battery of this embodiment. In the conventional cobalt charging process indicated by the dotted line in FIG. 8, the amount of CoOOH generated is small because the first stage of charging is not performed. In the cobalt charging process of the present embodiment, CoOOH is efficiently generated from Co without waste, so the battery capacity is larger than in the conventional case.

As a result, the amount of CoOOH produced in the positive electrode can be increased, and the conductive network can be strengthened.
<Improvement of DC-IR>
FIG. 9 is a graph showing the improvement in DC-IR at 60% SOC due to the cobalt charging process compared to the prior art in this embodiment. As shown in FIG. 9, in this embodiment, the amount of CoOOH generated in the positive electrode is increased, and the conductive network is strengthened. It can be seen that the improvement is

FIG. 10 is a graph showing the DC-IR improvement at 20% SOC with the cobalt charging process compared to the prior art of the present embodiment. As shown in FIG. 10, in the present embodiment, the amount of CoOOH generated in the positive electrode is increased and the conductive network is strengthened, so the DC-IR is reduced by 3% compared to the conventional cobalt charging process. It can be seen that the improvement is

Thus, the nickel-metal hydride storage battery 11 subjected to the cobalt charging process of the present embodiment has a stronger conductive network and lower DC-IR than the nickel-metal hydride storage battery subjected to the conventional cobalt charging process. In particular, a significant effect was confirmed at SOC 20%.

<Co network amount>
FIG. 11 is a graph showing the improvement in Co network content due to the cobalt charging process compared to the prior art of this embodiment.

“dQ/dV” is the ratio of the rate of change dQ/dt of the discharge capacity (amount of discharged electricity) to the rate of change dV/dt of the positive electrode potential. “dQ/dV” indicates a change in discharge capacity per unit voltage, and is used to determine deterioration of each battery cell 12 . "Co network volume" is the indexed dQ/dV value. As shown in FIG. 11, when the amount of Co network in the conventional cobalt charging process is 100, the amount of Co network in the cobalt charging process of this embodiment is 138, which is very large. That is, it is confirmed that the nickel-metal hydride storage battery 11 subjected to the cobalt charging process of the present embodiment has a strong conductive network.

(Effect of the first embodiment)
(1) The amount of cobalt oxyhydroxide CoOOH produced at the positive electrode can be increased.
(2) In addition to the second-stage charging as in the prior art, the first-stage charging is performed in advance in the present embodiment, so that the charging efficiency of the Co charging can be improved.

(3) The amount of conductive Co network increases as the charging efficiency improves.
(4) DC-IR decreases as the amount of Co network increases. For example, an improvement can be seen even at an intermediate SOC of about 60%, but a remarkable effect is obtained especially at a low SOC such as an SOC of 20%.

(5) Since the DC-IR is lowered and the battery capacity is increased, the output characteristics can be improved.
(6) Since the charging efficiency of Co charging can be improved, the cobalt charging process can be performed in a short time.

(7) The termination of the first stage charging and the termination of the second stage charging can be easily determined using the cell voltage. Therefore, it is possible to simplify the configuration of the nickel-metal hydride storage battery manufacturing apparatus that performs the Co charging step.

(8) The termination of the first stage charging and the termination of the second stage charging can be easily determined using the cell voltage. Therefore, the control of the control device 31 can be simplified.
(Second embodiment)
In the first embodiment, the charging in the first stage and the charging in the second stage are terminated when the charging current is lower than the predetermined termination currents Aend1 and Aend2. In place of this, in time management, the first stage charging section t1 to t2 and the second stage charging section t2 to t3 are set to a constant time in accordance with the takt time of the battery manufacturing line. You may try to manage your time as follows. For this purpose, the time from t1 to t2 and the time from t2 to t3 are stored in advance in the control device 31 by managing the current value as in the first embodiment using the same type of battery.

(Action and effect of the second embodiment)
(9) By managing the time in this way, it is possible to match the takt time of the battery manufacturing line and improve the production efficiency.

(Third embodiment)
In the first embodiment, the control device 31 controls the cell voltage [V] to be approximately constant in the first stage charging and the second stage charging. In the second embodiment, the positive electrode potential [V] is controlled so as to be substantially constant in order to improve the accuracy of the cobalt charging process.

FIG. 12 is a graph showing the time and potential control method of the positive electrode potential in the cobalt charging step of the first embodiment. FIG. 13 is a graph showing the time and potential control method of the positive electrode potential in the cobalt charging step of the second embodiment.

In the first embodiment, the cell voltage [V] of the voltmeter 34 is referred to as shown in FIG. ). In the first embodiment, the positive electrode potential [V] and the cell voltage [V] are strongly correlated. ”, the cell voltage [V] was maintained around 0.2 [V]. In addition, in the second-stage charging, the cell voltage [V] is maintained around 1.0 [V] in order to set the positive electrode potential [V] to "0.15 [V]". rice field.

However, as shown in FIG. 12, even if the cell voltage [V] is kept constant, the positive electrode potential [V] increases as the charging time elapses. This is because the cell voltage [V] is obtained from the difference between the positive electrode potential [V] and the negative electrode potential [V]. This is because the positive electrode potential [V] increases as the negative electrode potential [V] decreases even if the potential is kept constant.

Therefore, in the third embodiment, as shown in FIG. 13, the control device 31 controls to keep the positive electrode potential [V] constant. In this case, the manufacturing apparatus 30 for the nickel-metal hydride storage battery 11 shown in FIG. 3 cannot detect the positive electrode potential [V]. Therefore, the charging current [A] to be applied in advance in the first stage charging and the second stage charging is determined in advance in the relationship between the cell voltage [V] and the applied current [A] so that the positive electrode potential is constant. The experimental results are recorded in the storage means of the controller 31 as a "reference table (or map)" showing the relationship between the cell voltage [V] and the positive electrode potential [V] at the time of predetermined charging. Then, while measuring the cell voltage [V] while referring to the “reference table” with the target positive electrode potential [V] as an argument, the positive electrode potential [V] is kept constant based on the data based on the experimental results. Controls the charging current [A] applied to

(Action and effect of the third embodiment)
(10) at a positive electrode potential [V] suitable for the change from metallic cobalt or cobalt compounds to HCoO ₂ ⁻ exactly in the first stage of charging and from HCoO ₂ ⁻ to CoOOH in the second stage of charging; can be charged.

(11) By recording the relationship between the cell voltage [V] and the positive electrode potential [V] at the time of predetermined charging as a "reference table (or map)", a simple manufacturing apparatus as shown in FIG. A suitable cobalt charging process can be implemented.

(Modification)
The present invention is not limited to the above embodiments, and can be implemented as follows.
As for cobalt, metallic cobalt (Co) was exemplified in the embodiment, but cobalt oxide such as cobalt monoxide (CoO), a cobalt compound, or a mixture thereof can be used.

* In the embodiment, the control of the charging current [A] according to the cell voltage [V] is performed in a stepwise manner in the graph shown in FIG. The width of this current drop can be adjusted as appropriate. Further, the control is not limited to this example, and may be controlled continuously in real time so as to form a continuous curve in the graph shown in FIG.

* Numerical values shown in the embodiment are examples, and can be appropriately changed for optimal implementation of the present invention in accordance with the structure of the alkaline secondary battery.
○ The battery module described as an example is just an example, and it can be implemented by changing it according to the purpose, etc., or by changing it to a new material or configuration. For example, the battery case may be made of metal instead of resin.

In the present embodiment, the nickel-metal hydride storage battery 11 having a plate-like appearance and six battery cells 12 has been described as an example. Doesn't have to be a module.

〇 Alkaline secondary batteries are not limited to nickel-metal hydride batteries, but can also be applied to nickel-cadmium batteries, nickel-zinc batteries, and the like.
o The positive electrode, the negative electrode, the separator, the electrolytic solution, and the like are not limited to the configurations described in the embodiments.

〇The flow chart is an example, and steps can be added, deleted, or replaced.
○ It is needless to say that a person skilled in the art can add, delete, and change the configuration without departing from the scope of the claims.

DESCRIPTION OF SYMBOLS 11... Nickel metal hydride storage battery 12... Battery cell 13... Integrated battery case 13a... Positive electrode terminal 13b... Negative electrode terminal 14... Cover body 15... Positive electrode plate 15a, 16a... End 16... Negative electrode plate 17... Separator 20... Electrode plate group 21, DESCRIPTION OF SYMBOLS 22... Current collector 30... Manufacturing apparatus (of a nickel metal hydride storage battery) 31... Control apparatus 32... Charge/discharge apparatus 33... Ammeter 34... Voltmeter

Claims (9)

A method for producing an alkaline secondary battery comprising a positive electrode containing nickel hydroxide as an active material and metallic cobalt or a cobalt compound, a negative electrode, a separator, and an alkaline electrolyte,
The initial charging process is
a first step of charging at a high to progressively lower charging rate at a potential changing from metallic cobalt or a cobalt compound to HCoO ₂ ⁻ at the positive electrode potential;
and a second step of charging at a potential that changes from HCoO ₂ ⁻ to CoOOH at the positive electrode potential at a charging rate that is higher than that in the first step and then gradually lower. 2. The method according to claim 1, wherein in the first stage and the second stage, as the resistance of the positive electrode increases, the charging current is decreased so that the potential of the positive electrode remains constant at a set potential. A method for manufacturing an alkaline secondary battery. In the first stage and the second stage, the current to be applied is such that the experimental result of the relationship between the cell voltage and the applied current is recorded in advance so that the positive electrode potential is constant, and the cell voltage is measured while performing the experiment. 3. The method of manufacturing an alkaline secondary battery according to claim 2, wherein the applied current is controlled based on data based on the results so that the positive electrode potential is constant. 2. The method according to claim 1, wherein in the first stage and the second stage, as the positive electrode resistance increases, the charging current is decreased so that the cell voltage is kept constant at a set voltage. A method for manufacturing an alkaline secondary battery. Start charging at a predetermined rate with the first stage cell voltage in the range of 0.1 to 0.4 V,
5. The method according to claim 4, wherein in the second stage, charging is started at a cell voltage in the range of 0.8 to 1.2V and at a charging rate higher than the charging rate at which charging is started in the first stage. A method for manufacturing an alkaline secondary battery. 6. The method of manufacturing an alkaline secondary battery according to claim 1, wherein the first step is performed until the current value becomes equal to or less than a preset threshold value. The method for manufacturing an alkaline secondary battery according to any one of claims 1 to 6, wherein the second step is performed until the current value becomes equal to or less than a preset threshold value. 8. The method of manufacturing an alkaline secondary battery according to any one of claims 1 to 7, wherein in the first step, preliminary application of a gradual increase in current value is performed at the start of charging. The method for producing an alkaline secondary battery according to any one of claims 1 to 8, wherein the alkaline secondary battery is a nickel-metal hydride storage battery.

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