JP7193420B2 - Nickel-metal hydride secondary battery manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a nickel-metal hydride secondary battery.

In general, nickel-metal hydride secondary batteries, which are secondary batteries with high energy density and excellent reliability, are widely used as power sources for portable devices, mobile devices, and the like, and as power sources for electric vehicles and hybrid vehicles. A nickel-hydrogen secondary battery is composed of a positive electrode whose main component is nickel hydroxide, a negative electrode whose main component is a hydrogen storage alloy, and an alkaline electrolyte.

In such a nickel-metal hydride secondary battery, the activity of the hydrogen storage alloy immediately after battery assembly is low, and the initial output tends to decrease. Therefore, a technique for activating the hydrogen storage alloy has been proposed (see, for example, Patent Document 1).

The technique described in Patent Document 1 activates a positive electrode active material including activation of nickel hydroxide in the positive electrode of a nickel-hydrogen secondary battery, and charges and discharges the positive electrode activated secondary battery one or more times. The execution of the cycle activates the hydrogen storage alloy, which is the active material of the negative electrode. When activating the hydrogen-absorbing alloy, charging is performed until the state of charge of the secondary battery reaches an overcharged state for at least one of one or more charge-discharge cycles.

JP 2010-153261 A

In the technique described in Patent Literature 1, a hydrogen storage alloy, which is the active material of the negative electrode, is activated by current flowing in one or more charge-discharge cycles.
By the way, since the nickel-metal hydride secondary battery deteriorates in battery performance as the temperature rises, there is a possibility that it may not be properly activated.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method of manufacturing a nickel-metal hydride secondary battery that enables the activation of the battery in a favorable manner.

In a method for manufacturing a nickel-metal hydride secondary battery that solves the above problems, an electrode plate group and an alkaline electrolyte are accommodated in a battery case of the nickel-hydrogen secondary battery, and then the active material of the electrode plate group is activated by charging and discharging. the activation step includes an activation charging step having at least one charging rest period before the start of charging or during charging, and the upper limit of the charging rate of the activation charging step The value is set to a charging rate at which the pressure of gas generated by overcharging does not cause the exhaust valve of the battery case to open, and the total length of the at least one charging pause period is the charging rate of the activation charging step. is set to a period in which the temperature of the nickel-metal hydride secondary battery falls below a predetermined temperature when is in the high charging range.

According to this method, the temperature of the nickel-metal hydride secondary battery decreases during the charging suspension period, so even when the secondary battery is charged to the upper limit value in the activation charging process, the temperature of the nickel-metal hydride secondary battery is reduced. Keeps the maximum temperature low. In nickel-metal hydride secondary batteries, the lower the battery temperature, the better the charge acceptance of the electrode plate group. of “γ-NiOOH” is likely to be generated. When the ratio of 3.5-valent "γ-NiOOH" increases, the voltage between the terminals of the electrode plate group with respect to the charge amount shifts to the base, so the charge amount required for the voltage between the terminals to reach the oxygen generation potential increases. Become. Along with this, the generation of "O ₂ ", which is a side reaction corresponding to the large amount of charge, is suppressed. Therefore, even if the amount of charge increases, the promotion of the main reaction associated with charging is maintained, and the battery capacity increases. In other words, the activation of the battery is favorably performed.

Further, charging up to the upper limit charging rate causes more cracks on the surface of the hydrogen-absorbing alloy, pulverizes the surface of the hydrogen-absorbing alloy, and expands the reaction area. Thereby, the internal resistance can be further reduced in the activation of the negative electrode.

As a preferred method, the upper limit value of the charging rate in the activation charging step is larger than the maximum value of the appropriate usage range for the nickel-metal hydride secondary battery.
According to this method, the negative electrode and the positive electrode are activated in a region where the charging rate of the nickel-metal hydride secondary battery is higher than the maximum charging rate of the usage range, and the utilization rate of the active material is increased. The life of the nickel-metal hydride secondary battery can be extended.

For example, if the charging rate is low, the amount of active material that remains unused and not activated increases, but the amount of active material that is activated when the charging rate is higher than the maximum value of the usage range. can be increased.

As a preferred method, the predetermined temperature is 50° C. or less when the charging rate of the activation charging step is greater than the maximum value of the proper use range.
According to such a method, for a nickel-metal hydride secondary battery whose charging efficiency decreases when the temperature exceeds 50° C., it is possible to suppress the decrease in charging efficiency by keeping the maximum temperature reached by charging low.

As a preferred method, the predetermined temperature is a temperature at which the charging efficiency is maintained at 98% or more when the charging efficiency at 20° C. of the nickel-hydrogen secondary battery is used as a reference.
According to this method, since the charging efficiency in the activation charging process is maintained at 98% or more, the amount of activated active material can be increased.

As a preferred method, the activation step includes performing one or more charge-discharge cycles in which the charging rate of the nickel-metal hydride secondary battery reciprocates between the lower limit value and the upper limit value once or more, and the charge-discharge cycle is performed one or more times. is the activation charging step.

According to such a method, an activation charging step can be included in the charge/discharge cycle.
As a preferred method, among the charge/discharge cycles, the charge/discharge cycle in which charging is not the activation charging process is defined as a first charge/discharge cycle, and the charge/discharge cycle in which charging is the activation charging process is defined as a second charge/discharge cycle. When the charge-discharge cycle is defined as the first charge-discharge cycle, the first charge-discharge cycle is continuously charged from the time the discharge ends immediately before the start of the first charge-discharge cycle until the charge of the first charge-discharge cycle is completed. is done.

According to such a method, in the charge/discharge cycle, the second charge/discharge cycle having a charge rest period and the first charge/discharge cycle in which charging is continuously performed can be combined.
As a preferred method, the upper limit of the charging rate of the second charging/discharging cycle is higher than the upper limit of the charging rate of the first charging/discharging cycle.

According to such a method, the charge/discharge ranges of the second charge/discharge cycle and the first charge/discharge cycle can be made different according to the purpose.

ADVANTAGE OF THE INVENTION According to this invention, it can enable it to perform activation of a battery suitably.

1 is a perspective view including a partial cross-sectional structure of an embodiment of a nickel-metal hydride secondary battery manufactured by a nickel-hydrogen secondary battery manufacturing method; FIG. 4 is a flow chart showing the steps of a method for manufacturing a secondary battery according to the same embodiment; 4 is a flow chart showing the procedure of an activation step in the same embodiment; Explanatory drawing which shows the range of the charging rate in the same embodiment. The figure which shows each charging/discharging cycle, the 1st charging/discharging cycle, and the 2nd charging/discharging cycle, and corresponding relationship in the same embodiment. 4 is a graph showing the relationship between battery temperature and charging efficiency in the same embodiment. 4 is a graph showing the relationship between the rest time of the activation process and the battery temperature; A graph showing the relationship between the upper limit of the charging rate in the activation process and the 25° C. DC-IR reduction rate. 4 is a graph showing the relationship between the upper limit of the charging rate in the activation process and the capacity improvement rate;

An embodiment of a nickel-metal hydride secondary battery manufactured by a nickel-hydrogen secondary battery manufacturing method will be described with reference to FIGS. 1 to 9. FIG.
As shown in FIG. 1, the nickel-metal hydride secondary battery is a sealed battery used as a power source for vehicles such as electric vehicles and hybrid vehicles. As a nickel-metal hydride secondary battery mounted on a vehicle, there is a prismatic sealed secondary battery composed of a battery module 11 configured by electrically connecting a plurality of single cells 30 in series in order to obtain a required power capacity. Are known.

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 lid body 14 is provided with an exhaust valve 141 for reducing the internal pressure of the integrated battery case 10 to the valve opening pressure or lower, and a sensor mounting hole 142 for mounting a sensor for detecting the temperature of the electrode plate group 20 . ing. The exhaust valve 141 is opened when the internal pressure of the integrated battery case 10, which is communicated with a communication hole (not shown) in the upper portion of the partition wall 18, exceeds the allowable threshold value and is equal to or higher than the valve opening pressure. Thus, the gas generated inside the integrated battery case 10 is discharged.

(Structure of electrode plate group)
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. A hydrogen storage alloy is applied to the electrode core material.
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 .
(battery module)
The charging rate of the manufactured battery module 11 is indicated by SOC (State Of Charge) [%]. The SOC is calculated as a percentage of the battery module 11 fully charged. The SOC is the ratio of the amount of electricity actually charged in the battery module 11 to the rated capacity. The SOC can be calculated based on the charge/discharge history of the battery module 11, and can also be calculated by a well-known method such as estimating the inter-terminal voltage (OCV, etc.) between released terminals, impedance, and electromotive voltage. .

In addition, the charging reaction at the positive electrode and the negative electrode of the nickel-hydrogen secondary battery is as shown in half-reaction formulas (1) and (3) for the reaction of the active material, and as shown in half-reaction formulas (2) and (4) for the electrolysis of water. )become that way. During discharge, the reaction proceeds in the opposite direction. At the negative electrode, the hydrogen-absorbing alloy is hydrogenated during charging and dehydrogenated during discharging.

・Positive electrode Ni(OH) ₂ +OH ⁻ →NiOOH+H ₂ O+e ⁻ (1)
OH ⁻ →1/4O ₂ +1/2H ₂ O+e ⁻ (2)
・Negative electrode M+H ₂ O+e ⁻ →MH+OH ⁻ (3)
H ₂ O+e ⁻ →1/2H ₂ +OH ⁻ (4)
Combining half-reaction formulas (2) and (4), as shown in reaction formula (5), oxygen gas (oxygen molecule: O ₂ ) and hydrogen gas (hydrogen molecule: H ₂ ) are produced by electrolysis of water. reaction that occurs. At this time, the gas ratio, which is the ratio of oxygen gas to hydrogen gas (H ₂ /O ₂ ratio), is “2”.

2H ₂ O→2H ₂ +O ₂ (5)
By the way, the inventors have found that the lower the battery temperature, the better the charge acceptability of the electrode plate assembly in the nickel-metal hydride secondary battery. It was found that the generation of “O ₂ ”, which is a side reaction, is suppressed and the battery capacity is improved. More specifically, NiOOH (nickel oxyhydroxide) includes trivalent "β-NiOOH" and 3.5-valent "γ-NiOOH", which is higher in valence than "β-NiOOH". When the battery module 11 was charged when the battery temperature was low, more 3.5-valence “γ-NiOOH” was produced than when the battery temperature was high. In a nickel-metal hydride secondary battery in which a large amount of 3.5-valence "γ-NiOOH" is generated, the voltage between terminals of the electrode plate group with respect to the amount of charge shifts to the base, resulting in a drop in voltage between terminals. The amount of charge required for the terminal voltage to reach the oxygen evolution potential increases. As a result, it has been found that the risk of oxygen generation is reduced, enabling more charging. In addition, the increase in the amount of charge required for the terminal voltage to reach the oxygen generation potential due to the presence of a large amount of 3.5-valent "γ-NiOOH" causes the generation of "O ₂ ", which is a side reaction of charging at the oxygen generation potential. In addition, the promotion of the main reaction accompanying charging is maintained even if the amount of charge increases, so that the battery capacity is improved.

(Manufacturing method of battery module 11)
A method for manufacturing the battery module 11 will be described with reference to FIGS.
The method for manufacturing the battery module 11 includes a battery module assembly process (step S10 in FIG. 2), an activation process (step S11 in FIG. 2), a defective product determination process (step S12 in FIG. 2), and an assembled battery assembly process. (Step S13 in FIG. 2).

First, in the battery module assembly process (step S10 in FIG. 2), the battery module 11 is assembled by sealing the opening 16 of the rectangular case 13 containing the electrode plate group 20 and the electrolytic solution with the lid 14. be done.

More specifically, the electrode plate group 20 includes the positive electrode plate 21, the negative electrode plate 22, and the separator 23 alternately via the separator 23 in such a manner that the lead portion of the positive electrode plate 21 and the lead portion of the negative electrode plate 22 protrude in opposite directions. It is configured in a rectangular parallelepiped shape by stacking

The electrode plate group 20 to which the two current collector plates 24 and 25 are welded is housed in each container 15 in the rectangular case 13 so that the positive current collector plate 24 and the negative current collector of the adjacent electrode plate group 20 are connected. By connecting the plates 25 with the connection protrusions protruding from their upper portions, the adjacent electrode plate groups 20 are electrically connected in series.

Each container 15 is filled with a predetermined amount of alkaline electrolyte, and the opening 16 of the rectangular case 13 is sealed with the lid 14 to provide a plurality of single cells 30, for example, a rated capacity. 6.5 Ah" battery module 11 is configured (assembled).

Next, in the activation step (step S11 in FIG. 2), the positive and negative electrodes are activated.
After that, in the defective product determination step (step S12 in FIG. 2), initial failure of the battery module 11 is determined. Defect determination of secondary batteries is performed based on, for example, an OCV inspection or a current interrupter method.

Then, in the assembled battery assembly process (step S13 in FIG. 2), 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 is configured by electrically connecting a plurality of non-defective, activated battery modules 11 in series or parallel and mechanically fixing and connecting them.

This completes the manufacture of the battery module 11 .
(Activation step)
First, the premise of the activation process will be described with reference to FIG.

In the activation process, the battery module 11 is subjected to one or more charge/discharge cycles. In the charging/discharging cycle, the battery module 11 is charged/discharged so that the charging rate is reciprocated once between the lower limit value and the upper limit value. The charge/discharge cycle includes a first charge/discharge cycle C1 and a second charge/discharge cycle C2. The first charge/discharge cycle C1 is a charge/discharge cycle in which the lower limit value C11 of the charging rate is set to SOC "0%" and the first upper limit value C12 of the charging rate is set to the upper limit value R42. The second charge-discharge cycle C2 is a charge-discharge cycle in which the lower limit value C21 of the charging rate is set to SOC "0%" and the upper limit value of the charging rate is set to a second upper limit value C22 higher than the first upper limit value C12. . Also, the charging in the second charging/discharging cycle C2 constitutes the activation charging step.

The SOC range for the battery module 11 is divided into a normal use range R1, a second charge/discharge range R2 as a high charge range, a valve opening range R3, and a first charge/discharge range R4. The first charge/discharge cycle C1 is a charge/discharge cycle in which charge/discharge is performed between the lower limit value R41 and the upper limit value R42 of the first charge/discharge range R4. The second charge/discharge cycle C2 is a charge/discharge cycle in which charge/discharge is performed between the lower limit value R41 of the first charge/discharge range R4 and the upper limit value R22 of the second charge/discharge range R2.

The normal use range R1 is the use range in the intended use of the battery module 11 . The SOC of the normal range R1 is a value included in the range defined by the lower limit value R11 and the upper limit value R12. Here, the battery module 11 is used as a power source mounted on a vehicle, and the SOC corresponding to the lower limit value R11 of the normal use range R1 is "30%", and the SOC corresponding to the upper limit value R12 is "80%". ” is set to the following values:

The valve opening range R3 is a range in which the gas pressure in the battery case of the battery module 11 reaches the gas pressure that causes the exhaust valve 141 to open. The SOC of the valve opening range R3 is a value included in a range larger than the lower limit value R31. Here, in the battery module 11 mounted on the vehicle, the SOC, which is the lower limit value R31 of the valve opening range R3, is a value higher than "140%".

The second charge/discharge range R2 is defined between the normal range R1 and the valve opening range R3. The second charge/discharge range R2 is a range that is larger than the upper limit value R12 of the normal use range R1 and equal to or lower than the lower limit value R31 of the valve opening range R3, and part or all of it is included in the second charge/discharge cycle C2. Range. A second upper limit value C22, which is the SOC in the second charge/discharge range R2, is a value included in the range defined by the upper limit value R12 and the lower limit value R31. The SOC, which is the lower limit R21 of the second charge/discharge range R2, is set to the upper limit R12 (80%) of the normal range R1 (R21=R12). Also, the SOC, which is the upper limit value R22 of the second charge/discharge range R2, is set to the value of the lower limit value R31 (140%) of the valve opening range R3 (R22=R31).

The first charge/discharge range R4 is defined between the SOC "0%" and the second charge/discharge range R2. The first charge/discharge range R4 is a range included in the first charge/discharge cycle C1 and the second charge/discharge cycle C2. In the first charge/discharge range R4, the SOC that becomes the lower limit value R41 is "0%" and the SOC that becomes the upper limit value R42 is "80%". In this embodiment, the upper limit value R42 of the first charge/discharge range R4 and the upper limit value R12 of the normal range R1 are the same value, but these values may be different values.

Next, details of the activation step (step S11 in FIG. 2) will be described.
In activating the positive electrode, charge and discharge are performed to activate the positive electrode active material including activation of nickel hydroxide in the positive electrode. This forms a conductive network of electrochemically active cobalt on the surface of the foamed nickel substrate. For example, the battery module 11 is charged with a current within the range of "0.05C to 0.2C (1C=rated battery capacity/1 hour)" until the SOC reaches "10% to 30%".

In the activation of the negative electrode, the battery module 11 with the activated positive electrode is charged and discharged to activate the negative electrode active material, thereby expanding the reaction area of the hydrogen absorbing alloy in the negative electrode. As the negative electrode is charged and discharged, so-called cracks occur on the surface of the hydrogen-absorbing alloy, and the surface is gradually pulverized. As a result, the surface area of the hydrogen storage alloy expands the reaction area as an electrode material.

Also, a positive electrode active material is used in the activation process. That is, since the current path inside the battery is determined by the positive electrode active material used for the current flowing when the positive and negative electrodes are activated, the range including the second charge/discharge range R2 is used so that more of the positive electrode active material is used. is preferably charged and discharged to a higher charge rate.

When the charging rate is low, the amount of unused active material that remains without being activated increases, but by setting the charging rate to the second charging/discharging range R2, the amount of activated active material increases. be able to. Therefore, the negative electrode and the positive electrode are activated to increase the utilization rate of the active material, thereby extending the life of the nickel-metal hydride secondary battery.

As shown in FIG. 3, the activation step includes determining whether or not to execute the second charge/discharge cycle C2 (step S20 in FIG. 3), and setting the charging rate for the second charge/discharge cycle (step S21 in FIG. 3). ), charging suspension processing (step S22 in FIG. 3), and charging rate setting for the first charge/discharge cycle (step S23 in FIG. 3). The activation process includes charging (step S24 in FIG. 3), discharging (step S25 in FIG. 3), and determining whether or not to end the activation process (step S26 in FIG. 3).

First, it is determined whether or not to execute the second charge/discharge cycle C2 (step S20 in FIG. 3). In this determination, it is determined to perform the second charge/discharge cycle C2 based on the fact that the current number of charge/discharge cycles matches the specified number of times to perform the second charge/discharge cycle C2. In the activation process, the number of charging/discharging cycles is specified for the battery module 11, and whether each charging/discharging cycle is the first charging/discharging cycle C1 or the second charging/discharging cycle C2 is determined. stipulated. In the present embodiment, at least one charge/discharge cycle out of one or more charge/discharge cycles is specified as the second charge/discharge cycle C2, and the other charge/discharge cycles are specified as the first charge/discharge cycle C1. It is

For example, as shown in FIG. 5, the number of charging/discharging cycles of the battery module 11 is regulated to 10 times. At this time, the 1st to 5th and 7th to 10th cycles are defined as the first charge/discharge cycle C1, and the 6th cycle is defined as the second charge/discharge cycle C2.

When it is determined to execute the second charge/discharge cycle C2 (YES in step S20 of FIG. 3), the lower limit value of the charge/discharge cycle C21 is the lower limit value of the charge/discharge cycle, and the upper limit value is the second charge/discharge cycle C2. is set (step S21 in FIG. 3). For example, the lower limit value C21 is "0%", and the second upper limit value C22 is the upper limit value R22 of the values included in the second charge/discharge range R2.

When the battery module 11 is charged to the second upper limit value C22, which is larger than the first upper limit value C12, cracks occur on the surface of the hydrogen-absorbing alloy as compared with charging at the first upper limit value C12, and hydrogen The surface of the storage alloy is pulverized to expand the reaction area. Therefore, the internal resistance can be further reduced in the activation of the negative electrode. Further, by charging up to the second upper limit value C22, the usage rate of the positive electrode active material increases, and more current paths are determined inside the battery, which also reduces the internal resistance.

Then, charging/discharging is suspended for a predetermined period before charging is started in the second charging/discharging cycle C2 (step S22 in FIG. 3). For example, after the fifth first charging/discharging cycle C1 ends, when the sixth second charging/discharging cycle C2 is started, only a rest period (charging rest period) for resting charging set under predetermined conditions Charging is started after charging/discharging is suspended. Here, when the SOC is "0%", charging and discharging of the battery module 11 is suspended during the suspension period.

The idle period is a period during which the temperature of the battery module 11 is set to a predetermined temperature (eg, 50° C.) or lower. At this time, the predetermined temperature is the temperature at which the charging rate is higher than the upper limit value R12 of the normal use range R1 in the second charge/discharge cycle C2. The predetermined temperature may be the temperature when the charging rate is equal to or lower than the upper limit value R12 of the normal use range R1 in the second charging/discharging cycle C2, but the predetermined temperature when the charging rate is in the second charging/discharging range R2 Since it is necessary to set it to the following value, it is better to set it to a value that takes into account the temperature rise.

For example, the battery modules 11 whose temperature has risen in the first to fifth first charge/discharge cycles C1 are naturally or forcedly cooled during the pause period. Then, the battery temperature of the battery module 11 is prevented from becoming high in the sixth second charge/discharge cycle C2. That is, in the second charge/discharge cycle C2, in which the charge amount and the charge time are longer than those in the first charge/discharge cycle C1, and the temperature continues to rise, the battery temperature rises in the second charge/discharge range R2 region of the charging rate. Fear is suppressed. In addition, since the battery temperature is kept low, a decrease in charging efficiency due to a temperature rise is suppressed, and the second charging/discharging cycle C2 of the battery module 11 can be performed with little decrease in charging efficiency.

On the other hand, when it is determined not to execute the second charge/discharge cycle C2 (NO in step S20 of FIG. 3), the lower limit value C11 of the first charge/discharge cycle C1 is set as the lower limit value of the charge/discharge cycle, and the upper limit value A first upper limit value C12 for the first charge/discharge cycle C1 is set (step S23 in FIG. 3). For example, the lower limit value C11 is "0%", and the first upper limit value C12 is the upper limit value R42 of the values included in the first charge/discharge range R4.

By charging the battery module 11 to the first upper limit value C12, the hydrogen storage alloy is activated, the degree of activation of the negative electrode increases, and the internal resistance decreases.
In the charging process (step S24 in FIG. 3), the battery module 11 is charged up to the set upper limit of the charge/discharge cycle. The upper limit value is the first upper limit value C12 for the first charge/discharge cycle C1, and the second upper limit value C22 for the second charge/discharge cycle C2. For example, the charging current amount from the SOC "0%" to the first upper limit value C12 is "2C to 5C", and the charging current amount from the first upper limit value C12 to the second upper limit value C22 is "0.2C to 2C". is.

In the discharging process (step S25 in FIG. 3), the battery module 11 is discharged to the set lower limit of the charging/discharging cycle. The lower limit value is the lower limit value C11 for the first charge/discharge cycle C1, and the lower limit value C21 for the second charge/discharge cycle C2. For example, the discharge current amount from the second upper limit value C22 to the first upper limit value C12 is "0.2C to 2C", and the discharge current amount from the first upper limit value C12 to the SOC "0%" is "2C to 5C ”.

In the termination determination of activation (step S26 in FIG. 3), it is determined whether or not to terminate the activation process based on a comparison between the number of charge/discharge cycles performed and a predetermined number of charge/discharge cycles. It should be noted that other termination conditions may be determined based on measurement results of the voltage, current, temperature, etc., of the battery module 11 .

When it is determined that the number of charging/discharging cycles is equal to or greater than the predetermined number of charging/discharging cycles (YES in step S26 of FIG. 3), the activation process is terminated.
On the other hand, if it is determined that the number of charge/discharge cycles performed is less than the predetermined number of charge/discharge cycles (NO in step S26 of FIG. 3), the process returns to step S20, and the activation process after step S20. is executed.

(Action by Activation Step)
The action of the activation process will be described with reference to FIGS. 6 to 9. FIG.
The inventors have found that the charging efficiency of the nickel-hydrogen secondary battery changes with the battery temperature, as shown in the graph L61 of FIG. Specifically, it was found that the charging efficiency of the nickel-metal hydride secondary battery is lowered in a high-temperature environment. In other words, the inventors found that the degree of activation of the nickel-metal hydride secondary battery is lowered due to a decrease in charging efficiency that occurs in response to a temperature rise that accompanies a charge-discharge cycle that activates the negative electrode.

For example, if the battery temperature is 50°C or lower, the charging efficiency is maintained at 98% or higher, but if the battery temperature exceeds 50°C, the charging efficiency drops sharply. Therefore, in the first charge-discharge cycle C1 and the second charge-discharge cycle C2, by maintaining the battery temperature at 50 ° C. or less, activation according to the charging current is expected, but the battery temperature exceeds 50 ° C. , activation according to the charging current cannot be expected. Therefore, it is desirable that the battery temperature be maintained at 50° C. or less in the second charge/discharge cycle C2.

The effect of the idle period will be described with reference to FIG.
A graph B71 shows the battery temperature when the rest period is 0 minutes and the charging rate is the lower limit value R21 (before overcharging) in the second charge/discharge cycle C2. That is, the lower limit value R21 of the second charge/discharge cycle C2, in other words, the battery temperature at the upper limit value R12 of the first charge/discharge cycle C1 and the pause period of "0 minutes" is 51 to 52° C. (graph B71). In the case of the first charge/discharge cycle C1, the first charge/discharge cycle C1 ends with a sufficiently long period of high charging efficiency. Further, graph B72 shows that the battery temperature during the second charge/discharge cycle C2 is 49 to 48° C. when the charging rate is at the lower limit value R21 (before overcharging) and the rest period is 10 minutes. ing. Further, graph B73 shows that the battery temperature during the second charge/discharge cycle C2 is 43 to 42° C. when the charging rate is at the lower limit value R21 (before overcharging) and the rest period is 30 minutes. ing.

Therefore, the charging current can be set so that the battery temperature immediately after the end of each charge/discharge cycle is 50° C. or less for the continuous first charge/discharge cycle C1.
On the other hand, in the second charge/discharge cycle C2, charging is performed in the same manner as in the first charge/discharge cycle C1 up to the first upper limit C12, and from the first upper limit C12 to the second upper limit C22, the first charge/discharge Charging similar to cycle C1 or otherwise specified charging is performed. Then, when the second charging/discharging cycle C2 is executed, it is inevitable that the battery temperature rises to nearly 50° C. by charging in the first charging/discharging range R4 (up to the first upper limit value C12). However, the battery temperature may greatly exceed 50° C. during charging in the second charging/discharging range R2. For example, as shown in the graph L61 of FIG. 6, when the battery temperature exceeds 50° C., the charging efficiency may drop rapidly. A decrease in charging efficiency reduces the activation degree of the positive electrode and the negative electrode. Therefore, in the case of charging without considering the battery temperature, the activation in the second charging/discharging cycle C2 is suppressed particularly in the charging rate range of the second charging/discharging range R2.

Therefore, in the activation step of the present embodiment, the battery temperature of the battery module 11 is lowered by providing a pause period before the start of charging in the second charge/discharge cycle C2 or during charging. If the battery temperature is lowered in consideration of the temperature rise in the second charge/discharge cycle C2, the battery temperature can be kept below 50° C. at least in the high charge range. Therefore, in the second charging/discharging cycle C2, charging in the first charging/discharging range R4 is performed in the same manner as in the first charging/discharging cycle C1, and the battery temperature is 50° C. or less with a charging rest period interposed. In this manner, charging in the second charging/discharging range R2 can be performed. As a result, even when the second charge-discharge cycle C2 is performed, the same execution result as when the first charge-discharge cycle C1 is performed and the charging efficiency is maintained high and the second charge-discharge with a high degree of activation is maintained. Execution result of cycle C2 is obtained.

FIG. 8 shows the rate of reduction of the 25° C. DC-IR (direct current internal resistance) of the battery module 11 as a result of executing charge-discharge cycles.
A graph B81 shows the internal resistance value of the battery module 11 when all the charging/discharging cycles are performed in the first charging/discharging cycle C1, which is defined as "100%". On the other hand, the graph B82 shows that the internal resistance value is "99% ” (become better). Graph B83 shows that when the second charge/discharge cycle C2 with a pause period is executed in the sixth charge/discharge cycle, and the first charge/discharge cycle C1 is executed otherwise, the internal resistance value decreases to "98%". It shows that it will (become better).

In other words, in the activation process including the second charge-discharge cycle C2 in the charge-discharge cycle, the internal resistance value decreases to about "99%" when there is no rest period, and the internal resistance value decreases to "99%" by providing the rest period. 98%”. That is, the battery performance of the battery module 11 is improved and the battery life is extended.

FIG. 9 shows the capacity improvement rate of the battery module 11 as a result of executing charge-discharge cycles.
A graph B91 is the capacity improvement rate of the battery module 11 when all the charge/discharge cycles are executed as the first charge/discharge cycle, and is set to "100%." On the other hand, graph B92 shows that when the sixth charge/discharge cycle is the second charge/discharge cycle C2 with no rest period, and the other charge/discharge cycles are the first charge/discharge cycles C1, the capacity improvement rate is "100. 4%” (become better). Graph B93 shows that the capacity improvement rate is "100.8%" when the second charge-discharge cycle C2 with a pause period is executed for the sixth charge-discharge cycle, and the first charge-discharge cycle C1 is executed otherwise. It shows that it rises (becomes better) to some extent.

That is, in the activation process including the second charge-discharge cycle C2 in the charge-discharge cycle, the capacity improvement rate is increased by about "0.4%" when there is no rest period, and by providing the rest period, the capacity improvement rate " 0.8%”. That is, the battery capacity of the battery module 11 increases.

According to this embodiment, the following effects are obtained.
(1) Since the temperature of the battery module 11 drops during the charging suspension period, the battery module 11 is charged from the first upper limit value C12 to the second upper limit value C22 by charging in the second charge/discharge cycle C2. Also, the maximum temperature of the battery module 11 can be kept low. In the battery module 11, the lower the battery temperature, the better the charge acceptance of the electrode plate group 20. Therefore, 3.5-valence "γ-NiOOH", which has a higher valence than trivalence "β-NiOOH", is used. easier to generate. When the proportion of 3.5-valent "γ-NiOOH" increases, the voltage across the terminals of the electrode plate group 20 with respect to the charged amount shifts to the base, so the charged amount required for the voltage across the terminals to reach the oxygen evolution potential increases. growing. Along with this, the generation of "O ₂ ", which is a side reaction corresponding to the large amount of charge, is suppressed. Therefore, even if the amount of charge increases, the promotion of the main reaction associated with charging is maintained, and the battery capacity increases. In other words, the activation of the battery is favorably performed.

In addition, charging up to the second upper limit C22 causes more cracks on the surface of the hydrogen-absorbing alloy than charging up to the first upper limit C12, pulverizes the surface of the hydrogen-absorbing alloy, and expands the reaction area. . Thereby, the internal resistance can be further reduced in the activation of the negative electrode.

(2) In a region where the charging rate of the battery module 11 is higher than the charging rate of the upper limit value R12, which is the maximum value of the normal use range R1 as the usage range, the negative electrode and the positive electrode are activated to increase the utilization rate of the active material. Thereby, the life of the battery module 11 can be extended.

For example, if the charging rate is low, the amount of active material that remains unused and not activated increases, but the amount of active material that is activated when the charging rate is higher than the maximum value of the usage range. can be increased.

(3) For the battery module 11 whose charging efficiency drops when the battery temperature exceeds 50° C., the maximum temperature reached by charging can be kept low, and the drop in charging efficiency can be suppressed.
(4) Since the charging efficiency in the activation charging step is maintained at 98% or more, the amount of activated active material can be increased.

(5) Since the charge/discharge cycle includes the first charge/discharge cycle C1 and the second charge/discharge cycle, the charge/discharge cycle can include the activation charging step.
(6) In charge/discharge cycles, a second charge/discharge cycle C2 having a charge rest period and a first charge/discharge cycle C1 in which charging is continuously performed can be combined.

(7) Since the second upper limit value C22 of the second charge/discharge cycle C2 and the first upper limit value C12 of the first charge/discharge cycle C1 are different, the charge between the second charge/discharge cycle C2 and the first charge/discharge cycle C1 The discharge range can be varied according to purpose.

The above embodiment can be implemented with the following modifications. The above embodiments and the following modifications can be combined with each other within a technically consistent range.
- In the above embodiment, the case where the defective product determination is performed by the OCV inspection or the current interrupter method is exemplified. , or other determination methods. At this time, defective products may be determined based on the state in which the secondary battery is in the second charging/discharging range or the state in which the charging rate is in the process of decreasing from the second charging/discharging range.

- In the above embodiment, the second upper limit C22 of the second charge/discharge cycle C2 is greater than the first upper limit C12 of the first charge/discharge cycle C1. However, without being limited to this, in the high charge range, the second upper limit value and the first upper limit value may be the same, or the first upper limit value may be greater than the second upper limit value. Even if the charging rate of the second charging/discharging cycle and the charging rate of the first charging/discharging cycle are both in the high charging range, the battery temperature in the second charging/discharging cycle is higher than that in the first charging/discharging cycle. Since the temperature is lower than the battery temperature, the portion that is not activated in the first charge/discharge cycle is activated in the second charge/discharge cycle.

- In the above-described embodiment, the first charge/discharge cycle C1 is continuously charged from after the discharge completed immediately before the start of the first charge/discharge cycle C1 until the charge of the first charge/discharge cycle C1 is completed. The case where it is done is illustrated. However, the present invention is not limited to this, and in the first charge/discharge cycle, charging may be temporarily stopped for a period during which the battery temperature does not drop significantly.

- In the above embodiment, the case where the number of charge/discharge cycles is 10 was exemplified.

- In the above embodiment, the case where one of the ten charge-discharge cycles is the second charge-discharge cycle C2 is exemplified, but not limited to this, even if the second charge-discharge cycle is two or more times good. Also, the number of second charge/discharge cycles may be less than 10% of all charge/discharge cycles, or may be more than 10%.

- In the above-described embodiment, the case where the SOC of the lower limit value R21 of the second charge/discharge range R2 is 80% or more has been exemplified. However, not limited to this, the SOC of the lower limit value R21 may be higher than "100%". For example, when the upper limit value of the usage range is SOC "100%", the lower limit value of the second charge/discharge range may be set to a value higher than SOC "100%", the so-called overcharge range.

- In the above embodiment, the case where the lower limit of the second charge/discharge range R2 is SOC "80%" was exemplified. %”, it may be greater than the upper limit of the appropriate usage range for that application. For example, it may be greater than SOC "80%" or less than SOC "80%". If the upper limit of the appropriate usage range for the application is SOC "90%", the lower limit of the second charge/discharge range can be changed to SOC "90%".

- In the above embodiment, the second upper limit value C22 is the upper limit value R22 (140%) of the values included in the second charge/discharge range R2. It may be a value higher than the lower limit and lower than the upper limit of the values included in the second charge/discharge range.

- In the above embodiment, the upper limit value of the second charge/discharge range R2 was illustrated as SOC "140%", but the present invention is not limited to this. , it should be lower than the lower limit of the charging rate at which the exhaust valve of the battery case is opened. For example, it may be higher than SOC "140%" or may be lower than SOC "140%".

- In the above embodiment, the case where the predetermined temperature is 50°C or less was exemplified. good too. In any case, by providing an idle period and lowering the temperature of the battery module, it becomes possible to execute charge/discharge cycles with relatively high charging efficiency.

- In the above embodiment, the charging efficiency is 98% or higher, but the charging efficiency may be lower than 98%, or may be higher than 98%. Even if the rest period is long or short, by providing the rest period and lowering the temperature of the battery module, it is possible to execute the charge/discharge cycle with relatively high charging efficiency.

- The temperature that serves as a reference for charging efficiency may be higher or lower than 20°C as long as it can be used as a reference.
- The lower limit value may be higher than 0% as long as it is possible to ensure a charge-discharge cycle that allows activation.

- The upper limit value may be a value different from the maximum value of the appropriate usage range in the application of the nickel-metal hydride secondary battery, as long as the SOC is suitable for activation.
- In the above embodiment, the case of providing a rest period before charging in the second charge/discharge cycle was exemplified, but this is not limiting, and a rest period may be provided before the start of the second charge/discharge range or during charging. . Also, a rest period may be provided when the SOC is within the first charge/discharge range in the second charge/discharge cycle.

- In the above-described embodiment, the case where the second charge/discharge cycle has one rest period was exemplified. When the rest period is a plurality of times, the temperature of the battery reaches a predetermined value when the total length of the period obtained by adding all the rest periods is in a high charging range in which the charging rate exceeds the first upper limit value of the first charge-discharge cycle. , the temperature (for example, 50° C.) or less.

- In the above-described embodiment, the case where the electrode plate group 20 is the laminated type is exemplified. However, the electrode plate assembly is not limited to this, and may have a non-laminated shape such as a wound type in which a long positive electrode plate and a long negative electrode plate are flatly wound with a long separator interposed therebetween. .

- In the above-described embodiment, the case where the battery module 11 is composed of a plurality of cells has been exemplified. However, the battery is not limited to this, and may be a single battery.
- In the above-described embodiment, the case where the nickel-metal hydride secondary battery is used as a power source for a vehicle such as an electric vehicle or a hybrid vehicle has been exemplified. However, the nickel-hydrogen secondary battery is not limited to this, and may be applied as a power supply for other devices.

DESCRIPTION OF SYMBOLS 10... Integrated battery case 11... Battery module 13... Rectangular case 14... Lid body 15... Battery case 16... Opening part 18... Partition wall 20... Electrode plate group 21... Positive electrode plate 22... Negative electrode plate , 23... separator, 24... collector plate, 25... collector plate, 29a... connection terminal, 30... cell, 32... through hole, 141... exhaust valve, 142... sensor mounting hole.

Claims (5)

an activation step of activating the active material of the electrode plate group by charging and discharging after housing the electrode plate group and the alkaline electrolyte in the battery case of the nickel-metal hydride secondary battery;
The activation step includes an activation charging step having at least one charging rest period during charging,
The upper limit of the charging rate in the activation charging step is set to a charging rate at which the pressure of gas generated by overcharging does not cause the exhaust valve of the battery case to open,
At least one of the charging pause periods is such that the total length of the period is such that the state of charge (SOC) of the activation charging step is in a high charging range greater than 80% , and the temperature of the nickel-metal hydride secondary battery is 50°C. A method for manufacturing a nickel-metal hydride secondary battery, which is set for a period of 30 minutes or less. The temperature is a temperature at which the charging efficiency is maintained at 98% or more when the charging efficiency of the nickel-metal hydride secondary battery at 20° C. is used as a reference.
A method for manufacturing a nickel-metal hydride secondary battery according to claim 1 . In the activation step, the charging/discharging cycle of reciprocating between the lower limit value and the upper limit value of the charging rate of the nickel-metal hydride secondary battery is performed one or more times,
Charging in at least one of the one or more charge-discharge cycles is the activation charge step.
3. The method of manufacturing the nickel-hydrogen secondary battery according to claim 1 or 2 . Among the charge/discharge cycles, the charge/discharge cycle in which the charge is not the activation charge process is defined as a first charge/discharge cycle, and the charge/discharge cycle in which the charge is the activation charge process is defined as a second charge/discharge cycle. and when,
In the first charge/discharge cycle, charging is continuously performed from after the discharge completed immediately before the start of the first charge/discharge cycle until the charge in the first charge/discharge cycle is completed.
4. The method of manufacturing the nickel-hydrogen secondary battery according to claim 3 . The upper limit of the charging rate of the second charging/discharging cycle is higher than the upper limit of the charging rate of the first charging/discharging cycle
5. The method of manufacturing the nickel-hydrogen secondary battery according to claim 4 .

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