JP7271488B2 - Method for manufacturing nickel-metal hydride storage battery - Google Patents

Description

The present invention relates to a method for manufacturing a nickel-metal hydride storage battery, and more particularly, to a method for manufacturing a nickel-metal hydride storage battery including activation charge/discharge of the nickel-metal hydride storage battery for reducing internal resistance.

2. Description of the Related Art In recent years, alkaline storage batteries have been attracting attention as power sources for portable devices and mobile devices, and as power sources for electric vehicles and hybrid vehicles. In particular, the nickel-metal hydride storage battery is a secondary battery comprising a positive electrode made of an active material mainly composed of nickel hydroxide and a negative electrode made mainly of a hydrogen-absorbing alloy, and has high energy density and excellent reliability. It is widely used as a power source for those applications.

Such a nickel-metal hydride storage battery has the property that the activity of the hydrogen storage alloy immediately after battery assembly is low, resulting in a decrease in initial output. Therefore, proposals have been made to activate such hydrogen storage alloys.

Conventionally, as indicated by the dotted line in FIG. 7(b), it was the common general knowledge of those skilled in the art to try to rapidly activate the hydrogen storage alloy by first making the negative electrode SOC high.
In particular, in the method for manufacturing a nickel-metal hydride storage battery described in Patent Document 1, after cobalt charging, overcharging (SOC 100 to 130%) is first performed during multiple cycles of active charging and discharging for activating the negative electrode. is proposed. By performing such overcharging, the hydrogen storage alloy can be rapidly activated.

JP 2010-153261 A

However, since the activity of the negative electrode has not sufficiently progressed in the first cycle, the charge acceptability is poor, and gas is generated when the battery is overcharged as in Patent Document 1 from the first cycle, which may lead to an increase in the internal pressure of the battery. be. If the valve is opened due to this pressure increase, there is a problem that the battery deteriorates. Also, it is possible to avoid opening the valve by using a back pressure device, but there is a problem that it leads to an increase in manufacturing cost.

The problem to be solved by the present invention is to effectively increase the activity of a hydrogen storage alloy while suppressing excessive gas generation during activation charging and discharging after battery assembly in a method for manufacturing a nickel-metal hydride storage battery.

In order to solve the above-mentioned problems, a method for manufacturing a nickel-metal hydride storage battery of the present invention comprises a positive electrode using nickel hydroxide as an active material and a negative electrode using a hydrogen-absorbing alloy as an active material. An assembly process of assembling a battery by enclosing an electrode plate group formed by laminating with a separator interposed in a case together with an electrolytic solution, and performing a plurality of charge-discharge cycles, and performing a plurality of charge-discharge cycles. and an activation charging/discharging step of performing charging/discharging so as to increase the negative electrode SOC stepwise in accordance with the measured charging efficiency of the negative electrode.

Each charge/discharge cycle in the activation charge/discharge step may be charged at a negative electrode SOC that is less than 100% of the charge efficiency.
Further, in each charging/discharging cycle in the activation charging/discharging step, charging may be performed at a negative electrode SOC exceeding 70% of the charging efficiency.

In each charge/discharge cycle in the activation charge/discharge step, it is desirable to charge at a negative electrode SOC equal to the charge efficiency. Here, "equal" includes not only the error range but also the range in which the gas generation can be sufficiently suppressed to the extent that the risk of opening the valve can be avoided.

The method for manufacturing a nickel-metal hydride storage battery according to the present invention can effectively enhance the activity of the hydrogen storage alloy while suppressing excessive generation of gas during activation charging and discharging after battery assembly.

Schematic diagram showing the alloy crystal structure during charging after discharging. 1 is a block diagram of a manufacturing apparatus for a nickel-metal hydride storage battery according to the present embodiment; FIG. 4 is a flow chart showing the steps of a method for manufacturing a nickel-metal hydride storage battery according to the present embodiment. FIG. 2 is a perspective view including a partial cross-sectional structure of a battery module 11 of a nickel-metal hydride storage battery manufactured by a method for manufacturing a nickel-metal hydride storage battery. 4 is a flow chart showing the procedure of negative electrode activation charge/discharge in the present embodiment. 4 is a graph showing the PCT curve of the nickel-metal hydride storage battery of the present embodiment; (a) is a graph showing the relationship between the negative electrode SOC [%] and the charging efficiency [%] of the negative electrode in each charging/discharging cycle in the procedure of the activation step measured in advance. (b) is a graph showing the relationship of the negative electrode SOC [%] for each charge/discharge cycle in the procedure of the activation process. 5 is a graph showing the charge efficiency and the negative electrode SOC of the negative electrode in the first to tenth charge/discharge cycles of the present embodiment. 4 is a graph comparing the direct current resistance DC-IR of the conventional nickel-metal hydride battery manufacturing method and the direct current resistance DC-IR of the nickel-metal hydride battery manufacturing method of the present embodiment. 10 is a graph showing a Nyquist plot of the conventional nickel-metal hydride storage battery and the nickel-metal hydride storage battery of the present embodiment by the AC impedance method;

An embodiment of a method for manufacturing a nickel-metal hydride storage battery according to the present invention will be described below.
<Overview of Embodiment>
<Battery capacity of nickel metal hydride storage battery>
The capacity of the negative electrode of a nickel-metal hydride storage battery is theoretically determined and designed according to the capacity defined by the limit amount of hydrogen that can be absorbed by the hydrogen storage alloy of the negative electrode. The capacity required here is called "design capacity". However, since the hydrogen-absorbing alloy is not sufficiently activated in the initial charge, the theoretical negative electrode capacity cannot be satisfied. Here, the negative electrode SOC [%] (State Of Charge/depth of charge) representing the charging rate or state of charge of the negative electrode is calculated by “remaining capacity/fully charged capacity × 100”, and the theoretical fully charged state is negative electrode SOC 100. %, and the fully discharged state is defined as negative electrode SOC 0%. Here, the "full charge capacity" is the "design capacity" and is a theoretical value. The capacity to be applied is limited, and the negative electrode SOC does not reach 100%.

Next, in the present embodiment, "charging efficiency (%)" means that, when the design capacity of the negative electrode is 100%, the negative electrode potential reaches −0.7 V/cell after being fully charged at 0.3 C. and use the obtained capacity ratio. In this case, the charging efficiency in the first charging/discharging is the lowest, and as the charging/discharging cycle is repeated, the hydrogen storage alloy is activated, so the charging efficiency gradually increases. Note that the -0.7 V/cell is a voltage corresponding to a negative electrode capacity of 0% in the battery of the present embodiment, and is a different value depending on the battery.

<Principle of Activation of Hydrogen Storage Alloy>
Next, the activation mechanism of the hydrogen storage alloy will be described. FIG. 1 is a schematic diagram showing the alloy crystal structure during charging after discharging. As shown in FIG. 1, at the start of charging, the negative electrode SOC is the lowest, hydrogen H is absorbed by the alloy lattice of the hydrogen absorbing alloy containing Mn and Ni, the hydrogen equilibrium pressure of the negative electrode increases, and the alloy lattice expands. state. The hydrogen storage alloy has a high hydrogen equilibrium pressure at a high SOC in which a large amount of hydrogen H is stored.

After the charging is finished, it shifts to discharging. When discharge starts, hydrogen H is released, the negative electrode SOC gradually decreases from the maximum value, and the negative electrode SOC becomes 0% at the end of discharge. That is, hydrogen H is released from the negative electrode, the hydrogen equilibrium pressure of the negative electrode drops, and the alloy lattice of the hydrogen-absorbing alloy shrinks. When the hydrogen equilibrium pressure is high, cracking of the hydrogen-absorbing alloy is accelerated. IR) can be reduced.

As a result, the contact area with the electrolytic solution, that is, the reaction area (active point) as the electrode material can be increased. In other words, the reaction surface area of the alloy can be increased, and the direct current resistance DC-IR reduction effect can be sufficiently obtained.

<Characteristics of this embodiment>
In this embodiment, the activation charge/discharge process is performed after the battery assembly process. At this time, a plurality of charge/discharge cycles are performed, and in at least part of each charge/discharge cycle, charge/discharge is performed so as to increase the negative electrode SOC stepwise in accordance with the charge efficiency of the negative electrode measured in advance.

Prior to this activation charge/discharge step, the characteristics of the manufactured battery are tested and data are collected. In this test, charging/discharging cycles are repeated to determine the "charging efficiency" in each charging/discharging cycle.

Next, in each charge/discharge cycle in the activation charge/discharge process, the battery is charged at an SOC exceeding 70% of the charging efficiency and charged at an SOC not exceeding 100% of the charging efficiency. By charging at an SOC exceeding 70% of the charging efficiency, pulverization of the hydrogen storage alloy is effectively advanced. On the other hand, by charging at an SOC that does not exceed 100% of the charging efficiency, it is possible to suppress the generation of gas in the battery, which reduces the risk of valve opening and eliminates the need for equipment such as a back pressure device. In this embodiment, charging is performed such that the negative electrode SOC is equal to the charging efficiency.

The present embodiment will be described in detail below.
<Manufacturing equipment for nickel-metal hydride storage batteries>
FIG. 2 is a block diagram of a manufacturing apparatus for a nickel-metal hydride storage battery according to this embodiment. A nickel-metal hydride storage battery 1 is connected to a nickel-metal hydride storage battery manufacturing apparatus 2 . A nickel-metal hydride battery manufacturing apparatus 2 includes a charging/discharging device 3 , a voltage measuring device 4 , a current measuring device 5 , a thermometer 6 , and a heat insulating cooling device 7 , each of which is connected to the nickel-metal hydride storage battery 1 . The charging/discharging device 3 charges and discharges the nickel-metal hydride storage battery 1 at a predetermined charging/discharging rate. A voltage measuring device 4 measures the cell voltage of the nickel-hydrogen storage battery 1 . A current measuring device 5 measures the current of the nickel-hydrogen storage battery 1 . Thermometer 6 measures battery temperature T of nickel-metal hydride storage battery 1 . The heat-retaining cooling device 7 heats or cools the nickel-metal hydride storage battery 1 to adjust the battery temperature T. As shown in FIG. The control device 8 is configured as a well-known computer having a CPU 81 and a memory 82 such as a ROM/RAM, and based on the data from the voltage measuring device 4, the current measuring device 5, and the thermometer 6, the charging/discharging device 3 , controls the heat-retaining cooling device 7 .

<Manufacturing method of nickel-metal hydride storage battery>
FIG. 3 is a flow chart showing the steps of the method for manufacturing a nickel-metal hydride storage battery according to this embodiment.

In the method of manufacturing the nickel-metal hydride storage battery 1, first, a battery module assembly step (S1) is performed. Here, first, cell batteries (not shown) are assembled, and a plurality of cell batteries are connected to assemble the battery module 11 (FIG. 4).

Next, an activation step (S2) is performed. Here, charging and discharging are repeated by the charging and discharging device 3 under predetermined conditions to activate the electrodes.
Next, a defective product determination step (S3) is performed to eliminate defective products. Finally, in the assembled battery assembly step (S4), a battery pack, which is an assembled battery as a product, is completed.

<Battery Module Assembly Step (S1)>
<Nickel metal hydride storage battery>
FIG. 4 is a perspective view including a partial cross-sectional structure of the battery module 11 of the nickel-metal hydride storage battery manufactured by the nickel-metal hydride storage battery manufacturing method. As shown in FIG. 4, the nickel-metal hydride storage battery of this embodiment is a sealed battery that is used as a power source for vehicles such as electric vehicles and hybrid vehicles. As a nickel-metal hydride storage battery mounted on a vehicle, there is known a prismatic sealed storage battery comprising a battery module 11 configured by electrically connecting a plurality of single cells 30 in series in order to obtain a required power capacity. .

The battery module 11 includes an integrated battery case 10 as a rectangular parallelepiped battery case composed of a rectangular case 13 capable of accommodating a plurality of cells 30 and a lid 14 sealing an opening 16 of the rectangular case 13 . have. In addition, a plurality of irregularities (not shown) are formed on the surface of the rectangular case 13 to enhance heat dissipation during battery use.

The rectangular case 13 and lid 14 that constitute the integrated battery container 10 are made of polypropylene (PP) and polyphenylene ether (PPE), which are resin materials resistant to alkaline electrolytes. A partition wall 18 is formed inside the integrated battery case 10 to partition the plurality of cells 30 . In the integrated battery case 10 , for example, each of the six battery cases 15 constitutes a single battery 30 .

In the battery container 15 thus partitioned, the electrode plate group 20 and the positive electrode current collector plate 24 and the negative electrode current collector plate 25 joined to both sides of the electrode plate group 20 contain an aqueous solution containing potassium hydroxide (KOH) as a main component. It is housed together with an alkaline electrolyte, which is an electrolyte.

The electrode plate group 20 is configured by stacking a rectangular positive electrode plate 21 and a rectangular negative electrode plate 22 with a separator 23 interposed therebetween. At this time, the direction in which the positive electrode plate 21, the negative electrode plate 22 and the separator 23 are stacked is the stacking direction. The positive electrode plate 21 and the negative electrode plate 22 of the electrode plate group 20 are current-collected at the side edges of the lead portions of the positive electrode plate 21 which are formed by protruding from the side portions opposite to each other in the plane direction of the electrode plates. The plate 24 is joined by spot welding or the like, and the collector plate 25 is joined to the side edge of the lead portion of the negative electrode plate 22 by spot welding or the like.

Further, through holes 32 used for connecting the battery containers 15 are formed in the upper part of the partition wall 18 . The through hole 32 is formed by two connecting projections, one projecting from the upper part of the current collector plate 24 and the other projecting from the upper part of the current collecting plate 25 . The electrode plate groups 20 of the battery cases 15 adjacent to each other are electrically connected in series by welding and connecting by spot welding or the like. Of the through-holes 32 , the through-holes 32 positioned outside the battery containers 15 at both ends are fitted with the positive electrode connection terminal 29 a or the negative electrode connection terminal (not shown) above the end sidewalls of the integrated battery container 10 . The positive electrode connection terminal 29 a is welded to the connection protrusion of the current collector plate 24 . The negative electrode connection terminal is welded to the connection protrusion of the current collector plate 25 . The electrode plate group 20 connected in series in this manner, that is, the total output of the plurality of cells 30 is taken out from the positive connection terminal 29a and the negative connection terminal.

On the other hand, the cover 14 is provided with an exhaust valve 33 for reducing the internal pressure of the integrated battery case 10 to the valve opening pressure or less, and a sensor mounting hole 34 for mounting a sensor for detecting the temperature of the electrode plate group 20 . ing. The exhaust valve 33 is opened when the internal pressure of the integrated battery case 10, which is communicated through a communication hole (not shown) in the upper portion of the partition wall 18, exceeds the valve opening pressure that exceeds the permissible threshold. Thus, the gas generated inside the integrated battery case 10 is discharged. It should be noted that once the valve is opened, the generated gas is released and the electrolytic solution is lost, which is not preferable. A back pressure device can also be used to avoid an increase in the pressure inside the module, but this is not preferable because it requires an additional device for the manufacturing device and the battery, which increases the production cost.

<Structure of Electrode Plate Group 20>
The positive electrode plate 21 includes a foamed nickel substrate that is a metal porous body, a positive electrode active material mainly composed of nickel oxide such as nickel hydroxide and nickel oxyhydroxide filled in the foamed nickel substrate, and additives (such as a conductive agent). ). The conductive agent is a metal compound, here a cobalt compound such as cobalt oxyhydroxide (CoOOH), which coats the surface of the nickel oxide.

Highly conductive cobalt oxyhydroxide forms a conductive network in the positive electrode and increases the utilization rate of the positive electrode (percentage of "discharge capacity/theoretical capacity").
The negative electrode plate 22 has an electrode core made of punching metal or the like, and a hydrogen storage alloy (MH) applied to the electrode core.

The separator 23 is a non-woven fabric made of olefinic resin such as polypropylene, or a non-woven fabric which is subjected to a hydrophilic treatment such as sulfonation as necessary.
The battery module 11 is manufactured using the positive electrode plate 21 , the negative electrode plate 22 and the separator 23 .

<Activation step (S2)>
The activation step (S2) is performed by the CPU 81 of the control device 8 of the nickel-hydrogen storage battery manufacturing apparatus 2 shown in FIG. 2, and consists of a positive electrode activation step and a negative electrode activation step.

<Positive electrode activation step>
The positive electrode activation step is a step of electrochemically oxidizing cobalt contained in the positive electrode mixture by charging the nickel-metal hydride storage battery, depositing it as cobalt oxyhydroxide, and increasing conductivity. In the positive electrode activation step, it is preferable to charge the assembled nickel-hydrogen storage battery before charging at a constant current of 0.1 A or more and 2.0 A or less for 1 hour or more and 5 hours or less. By charging the nickel-metal hydride storage battery under this condition, it is possible to achieve both the resistance reduction of the β-type cobalt oxyhydroxide and the deposition of cobalt.

<Negative electrode activation step>
Next, a negative electrode activation process is performed. Here, "activation charge/discharge" is performed. FIG. 5 is a flow chart showing the procedure of activation charging and discharging of the negative electrode of this embodiment.

<Relationship between negative electrode SOC and activation>
FIG. 6 is a graph showing the PCT curve of the nickel-metal hydride storage battery of this embodiment. In the negative electrode activation charging/discharging step of the present embodiment, the negative electrode alloy is pulverized by charging and discharging, and the reaction surface area increases, so the charging efficiency (hydrogen storage amount) of the negative electrode improves as the negative electrode is activated. . The internal pressure associated with the hydrogen storage capacity of the negative electrode is from about 70% or more of the negative electrode SOC to the internal pressure on the PCT curve (P: pressure, C: hydrogen storage capacity, T: temperature) that represents the equilibrium characteristics of the reaction between the hydrogen storage alloy and hydrogen. becomes higher. Therefore, the stress applied to the hydrogen-absorbing alloy is increased, and this is the region where the negative electrode is pulverized, and the negative electrode is charged in which a large resistance reduction effect can be obtained. In the present embodiment, the negative electrode SOC is set to about 70% or more in each charge/discharge cycle, which promotes pulverization of the negative electrode.

<Measurement of charging efficiency (S10)>
FIG. 7(a) is a graph showing the relationship between the negative electrode SOC [%] and the negative electrode charging efficiency [%] in each charging/discharging cycle in the procedure of the activation step measured in advance. FIG. 7(b) is a graph showing the relationship of the negative electrode SOC [%] in each charge/discharge cycle in the procedure of the activation process. Hereinafter, the activation charging/discharging procedure will be described along the flowchart of FIG. 5 with reference to FIGS. 7(a) and 7(b).

As shown in FIG. 5, in the negative electrode activation charging/discharging step, the charging efficiency is measured (S10) prior to the charging step (S11). In the charging efficiency measurement (S10), the CPU 81 of the control device 8 of the nickel-metal hydride battery manufacturing apparatus 2 shown in FIG.

In the charging efficiency measurement (S10), the nickel-metal hydride storage battery to be measured is assembled into a battery module in the same manner as in the normal battery module assembly process (S1), and the positive electrodes are activated.

Next, charge/discharge of the first charge/discharge cycle is performed. Here, since the charging efficiency of the negative electrode is unknown, the charging current is set to 0.3 C, for example, and charging is performed for a sufficient time so as to approach 100% of the design capacity. When the charging is completed, discharge is started while measuring the discharge current until the negative electrode potential reaches -0.7 V/cell. The discharge capacity obtained at this time is divided by the design capacity to obtain a capacity ratio. This value is the charging efficiency. Here, for example, assume that it is 50%.

In the second charging/discharging cycle, charging is performed at a current value such that the negative electrode SOC (for example, 80%) is within a range not exceeding 100% of the negative electrode SOC and exceeding the initial capacity ratio. Then, the battery is discharged in this state and the discharge capacity is measured. For example, assume that the charging efficiency here is 75%.

After the third charge/discharge cycle, the charging efficiency in each charge/discharge cycle is obtained by repeating this process. Here, it is assumed that the charging efficiency in the charging/discharging of the third cycle is 80% and the charging efficiency in the charging/discharging of the fourth cycle is 90%. Thus, the charging efficiency in each charging/discharging cycle can be obtained.

However, it is desirable to set the negative electrode SOC according to the charging efficiency based on the result of one measurement, and repeat the measurement with a different, newly manufactured nickel-metal hydride storage battery. For example, in the above example, in the first charge/discharge cycle, charging is performed with a current value that makes the negative electrode SOC 70% to 100% of the previously measured charging efficiency, that is, 35% or more and 50% or less. Then, the charging efficiency of the first charging/discharging cycle is calculated. Similarly, in the second charging/discharging cycle, the battery is charged with a current value such that the negative electrode SOC is 70 to 100% of the previously measured charging efficiency, that is, 53.9% or more and 75% or less.

Since the charging efficiency is unknown at the first measurement, it is necessary to charge with a current that greatly exceeds the charging efficiency. However, when charging with a current value that exceeds the charging efficiency, it is considered that pulverization of the hydrogen-absorbing alloy progresses more than when charging with a current value that does not exceed the charging efficiency. Then, in the second charging/discharging cycle, the charging efficiency becomes different from that in the actual production process. Therefore, by repeatedly adjusting and measuring the target negative electrode SOC for charging in a new battery, it is possible to achieve higher accuracy.

Repeat the measurement under these conditions, measure the DC resistance DC-IR [%] for each charge-discharge cycle, and determine the number of charge-discharge cycles until the required DC resistance DC-IR [%] is reached. . In this embodiment, for example, 10 cycles are used.

In this way, data on the charging efficiency characteristics of the nickel-metal hydride storage battery to be manufactured is collected.
<Setting of Negative SOC>
Assuming that the target negative electrode SOC is, for example, the charge efficiency in the first charge/discharge cycle is 50%. If the charging efficiency of the stored first charge/discharge cycle is 50%, the target negative electrode SOC is 70% to 100%, that is, a negative electrode SOC of 35% or more and 50% or less. The battery is charged with a current value such that the efficiency is 40% of 90%.

Similarly, if the charge efficiency of the second charge-discharge cycle in which the second charge-discharge cycle is also stored is 75%, the negative electrode SOC is 70 to 100%, that is, 53.9% or more and 75% or less. Charge with a current value similar to The negative electrode SOC for each charge/discharge cycle determined based on this data is stored in advance in the memory 82 of the controller 8 of the nickel-metal hydride storage battery manufacturing apparatus 2 shown in FIG.

FIG. 8 is a graph showing the charge efficiency of the negative electrode and the negative electrode SOC in the first to tenth charge/discharge cycles of this embodiment. By repeatedly collecting data as described above, the charging efficiency of the negative electrode can be accurately measured in the end, so charging is performed at the negative electrode SOC equal to the charging efficiency of the negative electrode. By setting in this way, the most efficient negative electrode activation can be performed while suppressing gas generation within a range in which the negative electrode can accept charging. Here, "equal" includes not only the error range but also the range in which the gas generation can be sufficiently suppressed to the extent that the risk of opening the valve can be avoided. For example, an excess of about 10 to 20% is within the "equal" range.

Also, the charge/discharge cycle is 10 times. The setting of the number of times is determined according to the case where the DC resistance DC-IR becomes the required value or the DC resistance DC-IR does not improve even after repeating the charging/discharging cycle.

<Charging step (S11)>
Next, a charging step (S11) is performed. In the charging step (S11), charging is performed at a low rate current of 0.3 C, for example, in the first charge/discharge cycle. By performing at such a low rate, activation can be performed while suppressing gas generation.

In this charging step, the battery is charged to the negative SOC [%] shown in FIG. 8, which is stored in advance in the memory 82 of the control device 8 of the nickel-metal hydride storage battery manufacturing apparatus 2 shown in FIG.
The negative electrode SOC is estimated, for example, from a map (not shown) that determines the negative electrode potential from the relationship between the battery open-circuit voltage OCV and the negative electrode potential. Alternatively, the SOC may be estimated by a current integration method of estimating the SOC by integrating the current flowing through the battery, and detected by the current measuring device 5 .

<Judgment of Completion of Charging (S12)>
Here, the CPU 81 of the control device 8 of the nickel-metal hydride battery manufacturing apparatus 2 shown in FIG. When the negative electrode SOC is estimated to be the target negative electrode SOC, it is determined that charging is completed (S12: YES), charging is stopped, and the discharging step (S13) is performed.

<Discharge step (S13)>
In the discharge step (S13), the discharge current is adjusted by a predetermined load resistance, and the CPU 81 of the control device 8 of the nickel-metal hydride battery manufacturing apparatus 2 shown in FIG. Monitor to estimate negative electrode potential.

<Determination of discharge completion (S14)>
Discharge is continued until the negative electrode potential reaches a negative electrode potential of −0.7 V/cell at which the negative electrode SOC is estimated to be 0%. When the CPU 81 of the control device 8 of the nickel-metal hydride battery manufacturing apparatus 2 monitors the battery open-circuit voltage OCV of the nickel-metal hydride battery with the voltage measuring device 4 and estimates that the negative electrode potential has reached −0.7 V/cell, the discharge step ( S13) is completed (S14: YES).

<Determination of Completion of Charging and Discharging of Specified Cycle (S15)>
The CPU 81 of the control device 8 of the nickel-metal hydride storage battery manufacturing apparatus 2 determines whether or not the predetermined number of charging/discharging cycles has been reached. When it is determined that the number of charge/discharge cycles performed has not reached the prescribed number (S15: NO), the process returns to the charging step (S11) for the next charge/discharge cycle. When it is determined that the number of charge-discharge cycles performed has reached the prescribed number (S15: YES), the negative electrode activation step is terminated.

<Defective Product Judgment Step (S3)>
Next, returning to FIG. 3, the description of the procedure of the method for manufacturing the nickel-metal hydride storage battery is continued. After the activation step (S2) ends, a defective product determination step is performed (S3).

After that, in the defective product determination step (S3), the initial failure of the battery module 11 is determined. Defective storage battery determination is performed based on, for example, an OCV inspection or a current interrupter method.

<Battery Assembling Step (S4)>
Then, in an assembled battery assembly step (S4), an assembled battery (not shown) is assembled from the plurality of battery modules 11 thus manufactured. The assembled battery constitutes a battery pack installed in a vehicle or the like where it is used. The assembled battery includes a plurality of non-defective, activated battery modules 11 electrically connected in series or parallel, stacked and mechanically fixed, and further equipped with a control device, a measurement device, and the like. Configured.

This completes the nickel-metal hydride storage battery as a product.
(Action of this embodiment)
A characteristic of nickel-metal hydride storage batteries is that if the activation of the negative electrode is not progressing, the charging efficiency is low. Even if a current exceeding the charging efficiency is applied, the activation does not proceed, and instead gas is generated, increasing the risk of valve opening. , you need equipment to process the gas. In the charging/discharging cycle of this embodiment, the charging efficiency of the nickel-metal hydride storage battery is measured in advance, and charging is managed so that the negative SOC does not exceed the charging efficiency in each charging/discharging cycle. Therefore, even if there is no device for processing the gas, the risk of opening the valve due to the generation of gas does not increase. Within this range, the most efficient activation of the negative electrode is performed.

(Effect of this embodiment)
(1) According to the method for manufacturing a nickel-metal hydride storage battery of the present embodiment, the negative electrode can be more preferably activated, and the DC resistance DC-IR can be efficiently reduced.

FIG. 9 is a graph comparing the direct current resistance DC-IR of the conventional nickel-metal hydride battery manufacturing method and the direct current resistance DC-IR of the nickel-metal hydride battery manufacturing method of the present embodiment. When the direct current resistance DC-IR of the conventional nickel-metal hydride battery manufacturing method is 100%, the direct current resistance DC-IR of the nickel-metal hydride battery manufacturing method of the present embodiment is 98%, and the effect is significantly confirmed. rice field.

FIG. 10 is a graph showing a Nyquist plot of the conventional nickel-metal hydride storage battery and the nickel-metal hydride storage battery of the present embodiment by the AC impedance method. Compared to the conventional nickel-metal hydride storage battery indicated by the dashed line, the zero cross of the nickel-metal hydride battery of the present embodiment indicated by the solid line is shifted to the left and the radius of the arc portion is reduced. This indicates that the resistance of the electrolyte, the poles, the current collector plate, etc., when the electrons move, is reduced. In other words, it is supported that the negative electrode is being pulverized.

(2) Since the DC resistance DC-IR can be efficiently reduced, the performance of the nickel-metal hydride storage battery can be improved.
(3) In the nickel-metal hydride battery manufacturing method of the present embodiment, the charge efficiency characteristics of the nickel-metal hydride storage battery to be manufactured are measured in advance, and negative electrode activation charging/discharging suitable for the characteristics is performed. Therefore, negative electrode activation charging/discharging can be performed in advance under conditions most suitable for the nickel-hydrogen storage battery to be manufactured.

(4) The method of manufacturing a nickel-metal hydride storage battery according to the present embodiment can be applied without modification of a general nickel-metal hydride storage battery, and thus has versatility and can reduce production costs.
(5) The method of manufacturing a nickel-metal hydride storage battery according to the present embodiment can be implemented only by controlling the charging current, and can be implemented without the need for a special device such as a back pressure device, so production costs can be suppressed.

(6) In the method of manufacturing the nickel-metal hydride storage battery of the present embodiment, the method can be automatically performed only by controlling the charging current.
(Another example)
The above embodiment can also be implemented as follows.
Wear.

The flowcharts shown in FIGS. 3 and 5 are examples, and a person skilled in the art can change the order of these procedures, add procedures, or omit them.
○ Further, it goes without saying 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 1... Nickel-metal hydride storage battery 2... Nickel-metal hydride storage battery manufacturing apparatus 3... Charging/discharging apparatus 4... Voltage measuring device 5... Current measuring device 6... Thermometer 7... Thermal insulation cooling device 8... Control device 81... CPU
82 Memory 11 Battery module 13 Rectangular case 20 Electrode plate group 21 Positive electrode plate 22 Negative electrode plate 23 Separator 33 Exhaust valve DC-IR Direct current resistance (internal resistance)

Claims (4)

A method for manufacturing a nickel-metal hydride storage battery comprising a positive electrode using nickel hydroxide as an active material and a negative electrode using a hydrogen storage alloy as an active material,
an assembling step of assembling a battery by encapsulating an electrode plate group formed by stacking the positive electrode and the negative electrode with a separator interposed therebetween in a case together with an electrolytic solution;
an activation charge/discharge step having a positive electrode activation step performed after the assembly step and a negative electrode activation step performed subsequent to the positive electrode activation step;
A charge efficiency measurement step performed prior to the negative electrode activation step,
In the negative electrode activation step, a plurality of charge/discharge cycles are performed, and the negative electrode SOC is increased stepwise from the first charge/discharge cycle according to the charge efficiency of the negative electrode previously measured in the charge efficiency measurement step. A method for manufacturing a nickel-metal hydride storage battery, comprising charging and discharging. 2. The method of manufacturing a nickel-metal hydride storage battery according to claim 1, wherein in each charge-discharge cycle in said activation charge-discharge step, charging is performed at a negative electrode SOC of less than 100% of said charge efficiency. 3. The method of manufacturing a nickel-metal hydride storage battery according to claim 1, wherein each charge-discharge cycle in the activation charge-discharge step is charged at a negative electrode SOC exceeding 70% of the charge efficiency. 2. The method of manufacturing a nickel-hydrogen storage battery according to claim 1, wherein in each charge-discharge cycle in said activation charge-discharge step, charging is performed at a negative electrode SOC equal to said charge efficiency.

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