JP7431192B2 - Control method for alkaline secondary batteries - Google Patents

Description

The present invention relates to a method of controlling an alkaline secondary battery, and more particularly, to a method of controlling an alkaline secondary battery that extends the battery life when the electrolyte decreases.

A hybrid vehicle or the like equipped with a motor generator uses electric power stored in a secondary battery to drive the vehicle using the motor generator as an electric motor. Furthermore, when the electric power stored in the secondary battery is insufficient, the internal combustion engine mounted on the vehicle is driven to generate electricity using the motor generator as a generator, and the electric power is stored in the secondary battery. In addition, regenerative braking is a unique feature of such electric vehicles. Regenerative braking involves converting the kinetic energy of the vehicle into electrical energy and performing braking by making the electric motor function as a generator when braking the vehicle. In addition, the obtained electrical energy is charged into a secondary battery and reused when accelerating the vehicle. Among such secondary batteries, alkaline secondary batteries such as nickel-hydrogen storage batteries are widely used in vehicles because they are capable of charging and discharging large currents.

In a nickel-metal hydride storage battery installed in such a vehicle, as the voltage increases during charging, gas is generated as a side reaction of charging, and the internal pressure of the secondary battery increases. Oxygen gas is generated mainly at the positive electrode, which may increase internal pressure. When the internal pressure rises above a certain level due to the generated gas, the exhaust valve may open to discharge the gas. When the gas exhaust valve operates, the electrolyte is ejected along with gases such as oxygen and hydrogen to the outside of the battery system. This causes depletion of the electrolyte in the separator (separator dryout), increases internal resistance, and reduces capacity. Therefore, in order to improve battery life, it is necessary to secure a sufficient amount of electrolyte.

Therefore, in the invention disclosed in Patent Document 1, an invention is disclosed in which side reactions (gas generation) and electrochemical deterioration due to overvoltage accompanying charging are suppressed by intervening a standing period during charging, thereby suppressing the decrease in electrolyte solution. ing.

Furthermore, the invention disclosed in Patent Document 2 proposes a control method for suppressing valve opening by estimating the battery internal pressure from the amount of gas generated by side reactions.

Japanese Patent Application Publication No. 2001-45674 Japanese Patent Application Publication No. 2011-239573

The inventions described in Patent Document 1 and Patent Document 2 prevent depletion of the electrolyte in the separator (separator dryout) by suppressing electrochemical deterioration and avoiding valve opening. This is a preventive invention.

However, the electrolyte may actually decrease over time due to the valve opening, pinholes or cracks in the battery case, defective welds, or moisture permeation through the resin battery case. .

The control method for an alkaline secondary battery of the present invention can prevent the electrolyte from decreasing over time due to actual valve opening or moisture permeation through the resin battery case. The challenge is to extend battery life.

In order to solve the above-mentioned problems, the present invention provides a method for controlling an alkaline secondary battery that charges and discharges an alkaline secondary battery having a positive electrode containing an active material mainly composed of nickel hydroxide and an electrolyte consisting of an alkaline aqueous solution. In the high SOC charging in the high SOC state where the SOC is set, intermittent discharging is performed in which discharging is performed intermittently.

The high SOC charging is preferably performed in a range where the SOC is 40% or more, and the high SOC charging is preferably performed in a range where the SOC is 100% or less.
The intermittent discharge is characterized in that it is performed so that a certain polarization state remains, and at the same time, it creates unevenness in the potential state of the particle surface of the active material of the positive electrode and locally generates oxygen.

After the high SOC charging, it is also preferable to perform rapid discharging in which the battery is rapidly discharged with a current larger than the charging rate of the high SOC charging. It is preferable that the rapid discharge has a discharge rate of 1C or more.

It is preferable that the intermittent discharge is performed at a rate of 2 times or less at regular intervals while charging SOC 3%, and the intermittent discharge is performed once at regular intervals while charging SOC 3%. It is also preferable to perform the discharge at a rate of at least 3 times. It is also preferable that the intermittent discharge has a discharge rate of 15 to 25C.

Preferably, the high SOC charging is performed when the amount of the electrolytic solution becomes less than a preset threshold.
The alkaline secondary battery control method is a control method performed on an alkaline secondary battery mounted on a vehicle for driving, and is based on the relationship between the voltage drop amount at the time of output and the amount of electrolyte solution set in advance. Based on this, when the amount of voltage drop at the time of output is equal to or higher than a threshold value V1, it is determined that the amount of the electrolytic solution has become less than a preset threshold value, and the high SOC charging is performed. do. The vehicle can be suitably implemented as a hybrid vehicle. Further, the alkaline secondary battery can be suitably implemented as a nickel-metal hydride storage battery.

According to the alkaline secondary battery control method of the present invention, even if the valve actually opens or the electrolyte decreases over time due to moisture permeation from the resin battery case, the battery life can be extended.

FIG. 2 is a block diagram of a control device for a nickel-metal hydride storage battery of a hybrid vehicle according to the present embodiment. (a) is a schematic diagram showing oxygen in a reaction during charging on the particle surface of an active material of a positive electrode of a nickel-hydrogen storage battery. (b) is a reaction equation showing the main reaction of the normal positive electrode during discharge and the side reactions when oxygen is generated and local liquid depletion occurs. A time chart showing the SOC of a preliminary charging PC, a high SOC charging HC including an intermittent discharge ID, and a rapid discharge QD. Graph showing the relationship between the number of intermittent discharges per 3% SOC and the amount of oxygen generated [g] in high SOC charging. FIG. 2 is a cross-sectional view of a part of the battery module of the nickel-metal hydride storage battery according to the present embodiment. 1 is a flowchart showing the procedure of a method for controlling a nickel-metal hydride storage battery according to the present embodiment. 5 is a flowchart of a subroutine showing a procedure of charging/discharging control including a high SOC charge HC including an intermittent discharge ID and a rapid discharge QD procedure according to the present embodiment. , a map obtained by experiment of the relationship between "voltage drop amount [ΔV] during output" and "electrolyte amount [g]" when outputting for a short time of 0.1 seconds. A graph showing the relationship between the "total amount of discharged electricity [Ah]" and the amount of electrolyte solution [g].

Hereinafter, the method for controlling an alkaline secondary battery of the present invention will be explained using an embodiment of the method for controlling a nickel-metal hydride storage battery with reference to FIGS. 1 to 9.
<Vehicle configuration of hybrid vehicle>
FIG. 1 is a block diagram of a control device for a hybrid vehicle that implements the method for controlling a nickel-metal hydride storage battery according to the present embodiment.

A hybrid vehicle equipped with the battery module 90 of the nickel-metal hydride storage battery of this embodiment is equipped with a motor generator 17 that has both the functions of a driving motor and a generator. The motor generator 17 receives power from the battery module 90 and serves as a motor to drive the vehicle. Furthermore, when braking the vehicle, regenerative braking is performed and mechanical energy is converted into electrical energy by the motor generator 17. The battery module 90 stores the regenerated electrical energy. Further, an internal combustion engine 18 consisting of a gasoline engine rotationally drives a motor generator 17 to generate electricity. Inverter 20 inputs and outputs current from motor generator 17 . Further, the inverter 20 charges and discharges the battery module 90. It also supplies power to loads such as air conditioners and lighting. This inverter 20 functions not only as an inverter but also as a converter, and optimizes input and output electricity.

<Issues of this embodiment>
Such hybrid vehicles are widely used around the world due to their energy saving, environmental protection, economic efficiency, power performance, and durability. Hybrid vehicles are used in various regions. For example, it may be used in hot and humid tropical rainforests. It may also be used in deserts that are dry and have large daily temperature differences. Furthermore, it may be used in mountainous areas with rough roads and low temperatures and low atmospheric pressure. Such a harsh environment is also a harsh environment for in-vehicle nickel-metal hydride storage batteries. Therefore, gas may be generated inside and the valve may actually open. In addition, severe vibrations and temperature differences tend to cause pinholes and cracks in the battery case, as well as defects in the welded parts. Furthermore, in environments that are hot and dry, or where there are drastic changes in atmospheric pressure, the electrolyte tends to decrease due to moisture permeation through the resin battery case.

Furthermore, rapid discharge due to rapid acceleration, rapid charging from a low SOC, rapid charging in a low-temperature environment, over-discharging, etc. may progress the deterioration of the nickel-metal hydride storage battery, leading to a decrease in the amount of electrolyte. In particular, when the internal pressure of the battery increases and the valve opens, gas is released and the electrolyte is lost due to the ejection of the electrolyte.

Therefore, in the nickel-metal hydride storage battery control method of this embodiment, a charging/discharging method is adopted that can cope with such a decrease in electrolyte solution.
<Principle of this embodiment>
<Generation of oxygen>
When the potential of the positive electrode increases to a predetermined potential, the potential for water electrolysis is reached, and water electrolysis occurs as a side reaction. In water electrolysis, O ₂ is generated at the positive electrode by a reaction expressed by the following equation (1).

4OH ^- → O ₂ + 2H ₂ O + 4e ^- ... (1)
<Surface of particles of positive electrode active material>
FIG. 2(a) is a schematic diagram showing oxygen in a reaction during charging on the particle surface of the active material of the positive electrode of a nickel-metal hydride storage battery. The particles of the active material of the positive electrode change between Ni(OH) ₂ and β-NiOOH upon charging and discharging. As shown in Figure 2(a), when the surface of Ni(OH) ₂ /β-NiOOH, which is the active material of the positive electrode, reaches a high potential due to charging, a side reaction occurs as shown in equation (1) above. , O ₂ bubbles B are generated on the particle surface of the positive electrode active material. When O ₂ is generated at the positive electrode during charging, oxygen bubbles B directly adhere to the particle interface of the active material of the positive electrode. The O ₂ bubbles attached to the particle interface of the positive electrode active material physically eliminate H ₂ O and OH ⁻ at the positive electrode active material interface, causing local "liquid drying up" in that area. Become. Neither H ₂ O nor OH ^- physically exists here.

As time passes, the O ₂ bubbles B separate from the particle surface of the positive electrode active material like the bubbles A.
<Reaction at the positive electrode during discharge>
FIG. 2(b) is a reaction equation showing a normal main reaction of the positive electrode during discharge and an abnormal side reaction when oxygen is generated and local liquid depletion occurs.

In the normal main reaction during discharge of a nickel-metal hydride storage battery, Ni(OH) ₂ and OH ^- are generated from β-NiOOH on the premise of the presence of H ₂ O, as shown in equation (2) below. In this case, H ₂ O in the electrolyte will be consumed and reduced. OH ⁻ acts as an alkali ion in the electrolyte.

β-NiOOH+H ₂ O+e ^- →Ni(OH) ₂ +OH ^- ...(2)
Normally, there is sufficient H ₂ O in the electrolyte, so this is a normal reaction without any problems.
On the other hand, when the positive electrode is at a high potential and electrolysis of H ₂ O occurs, O ₂ is generated by the reaction as shown in equation (1) above. When O ₂ is generated at the positive electrode during charging, oxygen bubbles B first adhere to the particle interface of the active material of the positive electrode. In this case, a local "liquid dry up" state as described above occurs, and H ₂ O is not supplied. In this case, the reaction as shown in the above formula (1) does not occur.

In the case of this "liquid drying up", an abnormal side reaction occurs during discharging of the nickel-metal hydride storage battery, resulting in a reaction as shown in equation (3) below.
16β-NiOOH+4e ^- →8Ni ₂ O ₃ H+H ₂ O+O ₂ +4OH ^- ......(3)
That is, the reaction occurs without using H ₂ O, and on the contrary, H ₂ O is produced. Ni ₂ O ₃ H, O ₂ and OH ^- are produced as other products. Of these, O ₂ is smoothly absorbed at the negative electrode (recombination reaction) through the separator as shown in equation (4) below as time passes, maintaining a closed system.

4MH+ _O2 →4M+ _2H2O ......(4)
Here, Ni ₂ O ₃ H is an electrochemically inert product, and when Ni ₂ O ₃ H is generated, it is considered a problem that it causes an increase in battery resistance and a decrease in battery capacity. . Therefore, the generation of Ni ₂ O ₃ H is considered undesirable and is normally suppressed.

However, when comparing the advantages and disadvantages of depletion of H ₂ O and generation of Ni ₂ O ₃ H, depletion of H ₂ O immediately impairs the main reaction of the battery, increases battery resistance, and leads to a decrease in output. . On the other hand, although the generation of Ni ₂ O ₃ H causes an increase in battery resistance and a decrease in battery capacity, the amount of decrease is small compared to depletion of H ₂ O, and the severity of the problem for the operation of hybrid vehicles is considered to be small. I can say that.

In other words, the nickel-metal hydride storage battery control method of this embodiment prevents the generation of Ni ₂ O ₃ H, which is less serious, as an emergency evacuation, in order to avoid depletion of H ₂ O, which is more serious for the operation of a hybrid vehicle. This is an invention that we dare to allow.

<Summary of the procedure of this embodiment>
FIG. 3 is a time chart showing the SOC of the preliminary charging PC, the high SOC charging HC including the intermittent discharge ID, and the rapid discharging QD.

The starting SOC in FIG. 3 is, for example, 40% or more. This state of SOC of 40% or more is referred to as a "high SOC state" in this application. Further, in this application, charging that starts from this high SOC state is referred to as "high SOC charging H." The charging rate of the high SOC charging HC is, for example, 2C or more.

High SOC charging HC is basically not performed when the SOC exceeds 100%. However, if it is determined that the level of urgency is high, the battery may be placed in an overcharged state. High SOC charging HC is performed up to a target SOC, for example, SOC 100%.

Intermittent discharge ID is basically discharge that is performed at constant intervals t2 during high SOC charging HC. The intermittent discharge ID is performed so that a certain polarization state remains, and at the same time, unevenness is formed in the charged state on the surface of the Ni(OH) ₂ particles and oxygen is locally generated. Therefore, in order to ensure that a sufficient polarized state remains, a lower limit is set for the interval t2. On the other hand, if the interval is too long, unevenness in the potential of the positive electrode becomes less likely to occur. Therefore, it is optimized depending on the configuration of the nickel-metal hydride storage battery and various conditions. In the intermittent discharge ID of this embodiment, intermittent discharge ID is performed once or more and twice or less at regular intervals during charging to SOC 3%.

The discharge rate of the intermittent discharge ID can be set to 1C or more, more preferably 15C or more. If it is 15C or more, potential unevenness can be suitably caused. Further, from the viewpoint of causing potential unevenness, this rate is preferably higher, and specifically, it can be increased to the upper limit of the vehicle system (specifically, about 25C).

Further, when the SOC of the nickel metal hydride storage battery reaches the target SOC, for example 100%, by the high SOC charging HC, the high SOC charging HC is ended. Then, rapid discharge QD is immediately performed. A fast discharge QD rapidly discharges after a high SOC charge HC at a current greater than the charging rate of a high SOC charge HD due to the production of H ₂ O. In this embodiment, the rapid discharge QD has a discharge rate of 1C or more.

(Action of this embodiment)
<Generation of _O2 due to high SOC charging>
The purpose of high SOC charging HC is to form O ₂ bubbles, like bubbles B in FIG. 2(a), on the particle surface of the active material of the positive electrode. Therefore, the high SOC charging HC causes unevenness in the charging state on the surface of the particles of the active material of the positive electrode. In order to form an uneven state of charge on the surface of particles of the active material of the positive electrode, the current is rapidly reversed during high SOC charging HC to eliminate polarization caused by charging the positive electrode. That is, for example, high rate intermittent discharge ID of 25C is performed. By rapidly reversing the current, the state of charge on the surface of the active material particles in the positive electrode becomes uneven. If the number of intermittent discharge IDs is greater than a predetermined number of times, uneven charging will occur, but polarization will be eliminated. When polarization is eliminated, the potential of the positive electrode decreases. When the potential of the positive electrode decreases, it becomes lower than the potential for electrolysis of H ₂ O, and the amount of oxygen generated decreases.

On the other hand, if the number of intermittent discharges is less than the predetermined number, the particle surface will be in a highly charged state on average and the potential will increase. However, since the surface of the particles of the positive electrode active material is charged uniformly and local potential unevenness is eliminated, oxygen is no longer generated locally.

FIG. 4 is a graph showing the relationship between the number of intermittent discharges ID per 3% SOC and the amount of oxygen generated [g] in high SOC charging HC. Looking at the relationship between the number of intermittent discharge IDs per 3% SOC and the amount of oxygen generated [g] in high SOC charging HC, the amount of oxygen generated [g] when the number of intermittent discharge IDs is approximately 1 time/3% SOC ] was the peak _OP . Further, the amount of oxygen generated [g] when the number of intermittent discharge IDs was approximately "2 times/SOC 3%" was a high concentration _OH . Further, the amount of oxygen generated [g] when the number of intermittent discharge IDs was "0 times/SOC3%" was a concentration O ₀ . From the viewpoint of the amount of oxygen generated, it can be determined that sufficient oxygen is generated when the intermittent discharge ID is "0 to 2 times/SOC 3%".

On the other hand, in the present embodiment, the purpose is to locally generate O ₂ due to local potential unevenness on the surface of the particles of the active material of the positive electrode, and to generate Ni ₂ O ₃ H in this state. If the duration of high SOC charging HC is too long, the potential of the positive electrode will be averaged. Therefore, in order to ensure the effect, it is desirable that the intermittent discharge ID be greater than "1 time/SOC 3%".

From the above points, it is desirable that the number of intermittent discharge IDs is "1 to 2 times/SOC3%".
In this embodiment, high SOC charging HC is performed in a high SOC state, for example, at a high rate of 2C or more from 40% or higher. In the intermittent discharge ID of this embodiment, during this high SOC charging HC, intermittent discharge ID is performed at a high rate of 25C at regular intervals, once or more and twice or less, while charging SOC 3%. . With this setting, basically polarization of the positive electrode occurs due to high SOC charging HC. At the same time, due to the intermittent discharge ID performed at intervals of time t2, local potential unevenness occurs on the surface of the particles of the positive electrode active material, causing localized unevenness in the potential, such as the O ₂ bubbles B in FIG. 2(a). O ₂ bubbles are generated on the surface of the particles of the positive electrode active material.

<Generation of H ₂ O due to intermittent discharge ID>
Here, intermittent discharge ID will be explained with reference to FIGS. 2(a) and 2(b).
When high SOC charging HC is not performed as in this embodiment, that is, when charging is performed in a low SOC state with a low SOC of less than 40%, almost no O ₂ is generated. Furthermore, at charging rates below 2C, relatively little O ₂ is produced as well.

On the other hand, in the high SOC charging HC of this embodiment, the starting SOC shown in FIG. 3 is set to 40% or more, and charging continues in the high SOC state after that. Furthermore, in the case of this embodiment, the high SOC charging HC charges at a high rate of 2C or more. Therefore, not only the positive electrode potential is high but also strong polarization occurs. Due to this high potential, a large amount of O ₂ is generated.

As shown in Fig. 2(a), when intermittent discharge ID is performed at a high rate of 25C from such a state, O ₂ generated on the surface of the particles of the positive electrode active material becomes active in the positive electrode like bubbles B. It remains on the surface of the particle of matter.

Then, during intermittent discharge ID, if O ₂ bubbles are attached to the particle surface of the positive electrode active material, the electrolyte in that area is locally depleted, and H ₂ O and OH ⁻ are not present.
Then, β-NiOOH reacts without H ₂ O, resulting in an abnormal side reaction as shown in equation (4) below, and Ni ₂ O ₃ H is irreversibly produced.

16β-NiOOH+4e ^- →8Ni ₂ O ₃ H + 2H ₂ O+O ₂ +4OH ^-... (4)
On the other hand, in this side reaction, H ₂ O is not consumed in the first place. Therefore, even in a state where the electrolyte decreases and is likely to cause depletion of the electrolyte in the separator (separator dryout), this reaction can be performed without any problem.

Next, in this side reaction, H ₂ O is produced conversely. Therefore, the electrolyte can be replenished with H ₂ O in a situation where the electrolyte in the separator is likely to be depleted. As a result, depletion of the electrolyte in the separator can be effectively avoided.

Note that the generation of Ni ₂ O ₃ H is certainly not desirable. However, depletion of the electrolyte in the separator immediately causes a rapid decrease in battery capacity, which seriously affects the operation of the hybrid vehicle. If this influence and profit are balanced, the increase in battery resistance and decrease in battery capacity due to the generation of Ni ₂ O ₃ H will not seriously affect the operation of the hybrid vehicle if it is only temporary. Therefore, as a control method for a nickel-metal hydride storage battery for emergency evacuation, this method is extremely effective in practice.

<Generation of H ₂ O by rapid discharge QD>
As shown in FIG. 3, in this embodiment, when the SOC of the battery reaches the target SOC (for example, 100%) at time t3 by high SOC charging HC while intermittent discharge ID is in between, rapid discharge QD is performed from time t3.

As shown in FIG. 2(a), immediately after high SOC charging HC, O ₂ bubbles B are attached to the surface of the particles of the positive electrode active material. This O ₂ bubble B prevents the reaction with H ₂ O and OH ⁻ on the surface of the active material particles of the positive electrode. However, the O ₂ bubbles B, like the bubbles A, separate from the surface of the particles of the positive electrode active material over time. As a result, a main reaction that consumes H ₂ O as shown in A of FIG. 2(b) occurs, and a side reaction that produces Ni ₂ O ₃ H as shown in the formula B does not occur.

Therefore, by performing rapid discharge QD in the state of bubbles B before they separate from the surface of the particles of the positive electrode active material like bubbles A, a side reaction that generates Ni ₂ O ₃ H is caused. Thereby, H ₂ O in the electrolytic solution is not consumed, and H ₂ O can be generated to replenish the H ₂ O in the electrolytic solution. As a result, depletion of the electrolyte in the separator (separator dryout) can be effectively avoided.

(Configuration of this embodiment)
The configuration for implementing the control method of this embodiment will be described in detail below.
<Nickel-metal hydride storage battery>
FIG. 5 shows a cross-sectional view of a portion of the battery module 90 of the nickel-metal hydride storage battery of this embodiment. As shown in FIG. 5, the nickel-metal hydride storage battery is a sealed battery that is used as a power source for vehicles such as electric cars and hybrid cars. As a nickel-metal hydride storage battery installed in a vehicle, a rectangular sealed secondary battery consisting of a battery module 90 configured by electrically connecting a plurality of single cells 110 in series is known to obtain the required power capacity. ing.

The battery module 90 has a rectangular parallelepiped-shaped case 300 that includes an integrated battery case 100 that can accommodate a plurality of single cells 110 and a lid 200 that seals the integrated battery case 100. Note that this square case 300 may be made of resin.

The integrated battery case 100 that constitutes the square case 300 is made of a synthetic resin material that is resistant to alkaline electrolyte, such as polypropylene or polyethylene. A partition wall 120 is formed inside the integrated battery case 100 to partition a plurality of cells 110, and the portion partitioned by the partition wall 120 becomes a cell case 130 for each cell cell 110. The integrated battery case 100 has, for example, six battery cases 130, and FIG. 1 shows four of them.

In the battery case 130 thus partitioned, an electrode plate group 140, a positive electrode current collector plate 150 and a negative electrode current collector plate 160 joined to both sides of the electrode plate group 140 are housed together with an electrolyte.
The electrode plate group 140 is configured by laminating a rectangular positive electrode plate 141 and a negative electrode plate 142 with a separator 143 in between. At this time, the direction in which the positive electrode plate 141, the negative electrode plate 142, and the separator 143 are laminated (the direction perpendicular to the plane of the paper) is the lamination direction. The positive electrode plate 141 and the negative electrode plate 142 of the electrode plate group 140 are protruded from the sides opposite to each other in the direction of the plate surface (direction along the plane of the paper), so that the lead portion 141a of the positive electrode plate 141 and the negative electrode plate 142 A lead portion 142a is configured. Current collector plates 150 and 160 are joined to the side edges of these lead portions 141a and 142a, respectively.

Further, a through hole 170 used for connecting each battery case 130 is formed in the upper part of the partition wall 120. The through hole 170 has two connecting protrusions 151 and 161, a connecting protrusion 151 protruding from the upper part of the current collecting plate 150 and a connecting protruding part 161 protruding from the upper part of the current collecting plate 160. The welding connection is made through the through hole 170. This electrically connects the electrode plate groups 140 of adjacent battery cases 130 in series. Among the through-holes 170, the through-holes 170 located on the outside of each of the battery cases 130 at both ends are fitted with positive electrode connection terminals 152 or negative electrode connection terminals 153 (not shown) above the end side walls of the integrated battery case 100. . The positive electrode connection terminal 152 is connected to the connection protrusion 151 of the current collector plate 150 by welding. The negative electrode connection terminal 153 is connected to the connection protrusion 161 of the current collector plate 160 by welding. In this way, the total output of the series-connected electrode plate group 140, that is, the plurality of cells 110, is taken out from the positive electrode connection terminal 152 and the negative electrode connection terminal 153.

On the other hand, the lid body 200 constituting the square case 300 has an exhaust valve 210 for reducing the internal pressure of the square case 300 below the opening pressure, and a sensor mounting hole for mounting a sensor for detecting the temperature of the electrode plate group 140. 220 is provided. The sensor mounting hole 220 is a hole that extends inside the battery case 130 to the vicinity of the electrode plate group 140, making it possible to measure the temperature of the electrode plate group 140.

The exhaust valve 210 is for maintaining the internal pressure within the integrated battery case 100 below an allowable threshold value, and when the internal pressure value exceeds the valve opening pressure exceeding the allowable threshold value, When the valve is opened, the gas generated inside the integrated battery case 100 is discharged. The internal pressure of the integrated battery case 100 is made uniform in all the battery cases 130 by a communication hole (not shown) formed in the partition wall 120. Thereby, the integrated battery case 100 discharges gas until the internal pressure equalized in all the battery cases 130 becomes less than the valve opening pressure, and the internal pressure is maintained below the allowable valve opening pressure. It becomes like this.

<Configuration of electrode plate group 140>
<Positive electrode plate 141>
The positive electrode plate 141 is made of nickel hydroxide and cobalt as active materials. In detail, first make a paste by adding an appropriate amount of a conductive agent such as cobalt hydroxide or metallic cobalt powder to nickel hydroxide, and if necessary, a thickener such as carboxymethyl cellulose or a binder such as polytetrafluoroethylene. Process. Thereafter, the paste-like processed product is applied or filled into a core material such as a three-dimensional porous nickel foam, and then dried, rolled, and cut to form a plate-shaped positive electrode plate 141. Note that the three-dimensional porous nickel foam material used is one obtained by applying nickel plating to the surface of the urethane skeleton of urethane foam and then burning off the urethane foam.

<Negative electrode plate 142>
The negative electrode plate 142 is configured, for example, as an active material of misch metal, which is a mixture of rare earth elements such as lanthanum, cerium, and neodymium, and a hydrogen storage alloy whose constituent elements are nickel, aluminum, cobalt, and manganese. In detail, this hydrogen storage alloy is first made into a paste by adding a conductive agent such as carbon black, and if necessary, a thickener such as carboxymethyl cellulose and a binder such as styrene-butadiene copolymer. Process. Thereafter, the hydrogen storage alloy processed into a paste is coated or filled into a core material such as a punching metal (active material support), and then dried, rolled, and cut to form a negative electrode plate 14 in the same plate shape. form.

<Separator 143>
As the separator 143, a nonwoven fabric made of olefin resin such as polypropylene, or a fabric subjected to a hydrophilic treatment such as sulfonation as necessary can be used.

<Assembling the nickel metal hydride storage battery>
The positive electrode plate 141, the negative electrode plate 142, and the separator 143 are constructed by alternately stacking the positive electrode plate 141 and the negative electrode plate 142 with the separator 143 interposed in such a manner that the positive electrode plate 141 and the negative electrode plate 142 protrude in opposite directions. Configure. Then, the outer edge of the lead portion 141a of each positive electrode plate 141 stacked so as to protrude on one side and the current collector plate 150 are joined by spot welding or the like, and the lead portion 142a of each negative electrode plate 142 stacked so as to protrude on the other side is joined to the current collecting plate 150. The outer edge of the current collector plate 160 is joined by spot welding or the like.

The welded electrode plate group 140 of the current collector plates 150 and 160 is housed in each battery case 130 within the rectangular case 300. The positive current collector plate 150 and the negative current collector plate 160 of the adjacent electrode plate group 140 are connected to each other by spot welding or the like using connection protrusions 151 and 161 provided above them. Therefore, adjacent electrode plate groups 140 are electrically connected in series.

A predetermined amount of an alkaline aqueous solution (electrolyte) containing potassium hydroxide as a main component is injected into each battery case 130, and the opening of the integrated battery case 100 is sealed with the lid body 200. As a result, a battery module 90 having a rated capacity of "6.5 Ah", for example, is constituted by a plurality of single cells 110 (nickel metal hydride storage batteries). Such battery modules 90 are further combined, housed in a resin case, and equipped with a control device, various sensors, etc., and installed as an on-vehicle battery pack 24 (see FIG. 1) as a battery for driving a vehicle.

<Nickel-metal hydride storage battery control device 10>
The control device 10 will be described with reference to a block diagram of the control device 10 for a nickel-metal hydride storage battery shown in FIG. Here, a case will be described in which the nickel-metal hydride storage battery is controlled in the state of the battery pack 24 containing the battery module 90.

<Vehicle configuration of hybrid vehicle>
A hybrid vehicle equipped with the battery module 90 of the nickel-metal hydride storage battery of this embodiment includes a motor generator 17 that has both the functions of a motor and a generator. The motor generator 17 receives power from the battery module 90 and serves as a motor to drive the vehicle. Furthermore, when braking the vehicle, regenerative braking is performed and mechanical energy is converted into electrical energy by the motor generator 17. The battery module 90 stores the regenerated electrical energy. Further, an internal combustion engine 18 consisting of a gasoline engine rotationally drives a motor generator 17 to generate electricity. Inverter 20 inputs and outputs current from motor generator 17 . Further, the inverter 20 charges and discharges the battery module 90. It also supplies power to loads such as air conditioners and lighting. This inverter 20 functions not only as an inverter but also as a converter, and optimizes input and output electricity.

<Control device 10>
The control device 10 is mounted on a vehicle (onboard) and can control the battery module 90 of the vehicle in real time or based on accumulated data.

The control device 10 controls and charges the inverter 20 as a charging device that charges the battery module 90 with a current from the motor generator 17 as a generator. Further, the control device 10 controls the inverter 20 as a power supply device to discharge the current from the battery module 90 to the motor generator 17 as a drive motor serving as a load.

The control device 10 includes a current detector 21 that measures the current of the battery module 90, a voltage detector 22 that measures the voltage between the terminals of the battery module 90, and a temperature detector 23 that measures the temperature of the battery module 90. ing.

The temperature detector 23 includes a temperature sensor placed in a sensor mounting hole 220 shown in FIG. The temperature sensor measures the temperature near the electrode plate group 140 of the corresponding cell 110 of the battery module 90 and outputs the measured temperature value to the control device 10 as an electrical signal.

<Control unit 11>
The control unit 11 of the control device 10 is configured as a computer including a CPU, RAM, ROM, and an interface that controls the entire control device 10. This can be implemented using a well-known ECU (Electronic Control Unit).

<Storage unit 12>
The storage unit 12 includes a storage medium in which a program for the control device 10 and necessary data for implementing the control method of this embodiment are stored. The program includes a program that executes the steps of controlling the charging and discharging of the nickel-metal hydride storage battery of this embodiment, a program that calculates the SOC, and the like.

<Information acquisition unit 13>
The information acquisition unit 13 sequentially acquires the charging current value from the current detector 21, acquires the voltage value from the voltage detector 22, and acquires and stores the battery temperature from the temperature detector 23.

<SOC calculation unit 14>
The SOC calculation unit 14 estimates the SOC of the battery module 90 from the voltage measured by the voltage detector 22 and the like. Furthermore, the positive electrode SOC, negative electrode SOC, etc. are estimated from here with reference to a map or the like.

<Charge/discharge control section 15>
The charging/discharging control unit 16 monitors the voltage of the battery module 90 and, if the SOC is lower than a threshold value, generates power using the motor generator 17 and charges the battery module 90 via the inverter 20 . On the other hand, when the vehicle is braked, the battery module 90 is charged with regenerative current from the motor generator 17 via the inverter 20. In this case, if there is excessive current or the SOC of the battery module 90 is too high, charging is restricted. The threshold value and the like at this time are stored in the storage unit 12.

On the other hand, when the vehicle is being driven, a necessary current is supplied from the battery module 90 to the motor generator 17 via the inverter 20 in response to a command from the control unit 11 .
<Control method of nickel metal hydride storage battery>
FIG. 6 is a flowchart showing the procedure of the nickel-metal hydride storage battery control method of this embodiment. Hereinafter, the procedure of the control method for the nickel-metal hydride storage battery of this embodiment will be explained along FIG. 6.

<Start>
When the power of the hybrid vehicle is turned on, the control device 10 is turned on. When the control device 10 is turned on, the information acquisition unit 13 constantly monitors the battery current, battery voltage, and battery temperature from the battery module 90 using the current detector 21, voltage detector 22, and temperature detector 23.

<Voltage measurement at output (S1)>
From the collected current and voltage of the battery module 90, the control unit 11 determines the amount of voltage drop when the battery module 90 outputs power, such as when the vehicle is turned on, when the accelerator is operated while driving, when the vehicle is idling, etc. Measure [ΔV].

<Voltage drop amount ≧ threshold value V1? (S2)>
Here, FIG. 8 is a map obtained experimentally showing the relationship between the "voltage drop amount [ΔV] during output" and the "electrolyte amount [g]" when outputting for a short time of 0.1 seconds. It is. This map is stored in the storage unit 12. Therefore, the control unit 11 determines the voltage drop amount [ΔV ] The amount of electrolyte [g] can be estimated. That is, when the "voltage drop amount [ΔV] during output" when outputting for a short time of 0.1 seconds exceeds the threshold value V1, it is determined that the amount of electrolyte is insufficient.

Moreover, FIG. 9 is a graph showing the relationship between the "total amount of discharged electricity [Ah]" and the amount of electrolyte solution [g]. When the total amount of discharged electricity [Ah] increases and the estimated amount of electrolyte [g] becomes less than the threshold, the high SOC charging HC of this embodiment replenishes the electrolyte with H ₂ O. Implement control methods for nickel-metal hydride storage batteries, including rapid discharge. As a result, when the total amount of discharged electricity [Ah] increases thereafter, the amount [g] of the electrolytic solution is restored.

<Charge/discharge control not executed (S3)>
If the voltage drop amount is less than the threshold value V1 (S2: NO), the control unit 11 determines that there is sufficient electrolyte. In particular, it is determined that replenishment of electrolyte is not necessary for the battery module 90, and the nickel-metal hydride storage battery control method including high SOC charging HC and rapid discharge of the present embodiment is not executed (S3), and the process proceeds to S5. move on.

<Charge/discharge control (S4)>
On the other hand, if the voltage drop amount is equal to or greater than the threshold value V1 (S2: YES), the control unit 11 determines that the electrolyte is insufficient. Then, it is determined that electrolyte replenishment is particularly necessary for the battery module 90, and the nickel-metal hydride storage battery control method including high SOC charging HC and rapid discharging of the present embodiment is executed (S4).

Details of the charge/discharge control (S4) will be described later.
<Operation ended>
If the charging/discharging control is not executed (S3), or if the charging/discharging control (S4) procedure is completed and the vehicle power is turned off (S5: YES), the control method for the nickel-metal hydride storage battery is changed. To end (end). Otherwise (S5: NO), the process returns to S1 again and the control is continued.

<Charge/discharge control (S4) subroutine>
FIG. 7 is a flowchart of a subroutine showing the procedure of the charge/discharge control (S4) of FIG. 6 including the high SOC charge HC including the intermittent discharge ID and the rapid discharge QD procedure of the present embodiment. Hereinafter, the procedure of charge/discharge control (S4) will be explained in detail with reference to FIG.

<Start>
If the voltage drop amount is equal to or higher than the threshold value V1 (S2: YES), the control unit 11 determines that the electrolyte is insufficient, and performs high SOC charging HC including the intermittent discharge ID of this embodiment and rapid charging. Start charge/discharge control including discharge QD procedure.

<High SOC state? (S41)>
When charging/discharging control is started, it is first determined whether or not the state is a high SOC (S41). Here, it is determined whether the state is a high SOC state, which is a prerequisite for high SOC charging HC. In this embodiment, the "high SOC state" refers to a state where the SOC is 40% or more. Therefore, the starting SOC shown in FIG. 3 is set to 40% OC. If the current state is not a high SOC state, that is, the SOC is less than 40% (S41: NO), pre-charging PC is performed (S42).

<Preliminary charging (S42)>
The preliminary charging PC is charged under the same conditions except that high SOC charging HC and intermittent discharge ID are not included, and the charging rate is the same as that of high SOC charging HC, for example, at 2C or more. Charging is continued unless the SOC is in a high SOC state, that is, the SOC is not 40% or more (S41: NO→S42).

<High SOC charging HC (S43)>
If the battery is already in a high SOC state or becomes a high SOC state (S41: YES), high SOC charging HC (S43) is started. The control unit 11 counts the elapsed time with this point as time t0. High SOC charging is performed at a high rate of 2C or more, for example.

< Has the specified interval passed? (S44)>
If a preset time t2 has not elapsed from time t0 when high SOC charging HC was started, high SOC charging HC is continued (S44: NO→S43). When time t2 has elapsed from time t0, high SOC charging HC (S43) ends, and it is determined whether the SOC is at the upper limit (S45).

<Less than upper limit SOC (S45: NO)>
When the high SOC charging HC (S43) ends, the control unit 11 calculates the SOC of the battery module 90 using the SOC calculation unit 14, and determines whether the SOC exceeds the upper limit SOC (S47). This upper limit SOC is the same as the target SOC shown in FIG. 3, and is set to 100% SOC in this embodiment. If the SOC does not exceed the upper limit SOC (S45: NO), high SOC charging HC is ended and intermittent discharge ID (S46) is started.

<Intermittent discharge ID (S46)>
In this embodiment, the intermittent discharge ID is performed at a high discharge rate of 25C.
< Has the specified time passed? (S47)>
When the intermittent discharge ID is started, the control unit 11 counts the elapsed time. For example, if the elapsed time (here, 1 second) has not elapsed (S47: NO), the intermittent discharge is continued, and when 1 second has elapsed (S47: YES) End the intermittent discharge ID. After completing the intermittent discharge ID, high SOC charging is performed again (S41).

<Upper limit SOC (S45: YES)>
When the high SOC charge HC (S43) is finished and the SOC exceeds the upper limit SOC (S45: YES), the high SOC charge HC is finished and the rapid discharge QD (S48) is started.

<Rapid discharge QD (S48)>
The higher the discharge rate of the rapid discharge QD (S48), the more desirable it is, and in this embodiment, discharge is performed at 1C or more.

<Discharge finished? (S49)>
Rapid discharge QDs only need to complete the side reaction in which H ₂ O is produced. Therefore, in this embodiment, assuming that the side reaction is completed within 1 second from time t3, it is determined that the discharge is not terminated before 1 second has elapsed (S49: NO). Further, after one second has elapsed from time t3, discharging is terminated (S49: YES), and the procedure of charge/discharge control (S4) is terminated (end).

(Effects of embodiment)
Since the method for controlling a nickel-metal hydride storage battery according to the present embodiment has the above-described configuration, the following effects can be achieved.

(1) The control method for a nickel-metal hydride storage battery according to the present embodiment can be used even if the valve actually opens or the electrolyte decreases over time due to moisture permeation through the resin battery case. Battery life can be extended after the fact.

(2) In particular, even when there is a shortage of electrolyte and the operation of the vehicle is likely to become difficult, the control device 10 autonomously makes a judgment and performs the charging/discharging control of this embodiment to remove H ₂ O. By generating electrolyte and replenishing the electrolyte, it is possible to continue the operation of the vehicle.

(3) Since the high SOC charging HC of this embodiment performs high rate charging in a high SOC state, it can promote oxygen generation and efficiently generate H ₂ O.
(4) Since the SOC is controlled within a range that does not exceed 100%, battery deterioration due to overcharging can be avoided.

(5) Intermittent discharge ID is a high-rate discharge that rapidly changes the direction of current when polarization occurs due to constant charging of the positive electrode at sufficient intervals. This causes unevenness. Therefore, by locally raising the potential, it is possible to generate O ₂ bubbles and make them adhere to the surface of the particles of the positive electrode active material.

(6) If the intermittent discharge ID interval is too long, the surface of the particles of the positive electrode active material will be charged uniformly. Therefore, local potential unevenness is eliminated and oxygen is no longer generated locally, so the interval is set so as not to become too long.

(7) In addition, intermittent discharge ID is a state of local "liquid depletion" caused by O ₂ bubbles attached to the surface of the particles of the active material of the positive electrode, which causes a side reaction of discharge and generates H ₂ O. and replenish the electrolyte.

(8) The nickel-metal hydride storage battery control device of this embodiment is installed in a hybrid vehicle, and the control device 10 constantly monitors electrolyte shortage. When it is detected that the electrolytic solution is insufficient, the charging/discharging control of this embodiment can be performed autonomously to generate H ₂ O and replenish the electrolytic solution.

(9) Insufficiency of the electrolyte can be detected based on the relationship between the voltage drop at the time of output set in advance and the amount of the electrolyte, so accurate determination can be made using a simple method.
(10) In this embodiment, a nickel-metal hydride storage battery is used as the alkaline secondary battery, and the effects of the present invention are suitably exhibited.

(Modified example)
The above embodiment can also be implemented as follows.
The time chart shown in FIG. 3 is an example showing the principle of the invention, and the number of intermittent discharge IDs, time, and SOC are not limited to this time chart.

○ In this embodiment, an example is shown in which the intermittent discharge ID is performed at equal intervals of a fixed time t2, but it is not necessarily necessary to do it at equal intervals. For example, the time t2 may be changed depending on the state of polarization, etc. can be converted into

In this embodiment, the duration t1 of the intermittent discharge ID itself does not need to be constant, and can be optimized, for example, by changing it depending on the SOC.
- In this embodiment, the electrolyte shortage is estimated based on the relationship between the amount of voltage drop during output and the amount of electrolyte, but the method is not limited to this, and various methods such as changes in internal resistance can be used. It can be estimated by

In the present embodiment, intermittent discharge ID is not performed while the pre-charging PC is in a low SOC state, but intermittent discharge ID can be performed also in the pre-charging PC.
In this embodiment, rapid discharge QD is performed immediately after high SOC charging, but this can be omitted.

In this embodiment S49, the end of the rapid discharge QD is determined based on the elapsed time, but the present invention is not limited to this, and may be determined based on the current [Ah] or the like.
Although the present embodiment has been described using a hybrid vehicle as an example, the present invention can also be implemented in a fuel cell vehicle that generates power using a fuel cell and stores the generated power in an alkaline secondary battery.

Furthermore, in an EV where the alkaline secondary battery has developed a memory effect, it can also be applied to control when charging power at a power station when the SOC has decreased.
○ Furthermore, it can also be applied to the control of storage batteries in houses equipped with power generation equipment such as solar power generation systems and wind power generation systems.

Although the nickel-metal hydride storage battery of the present embodiment is an assembled battery including a vehicle-mounted battery module 90, its purpose is not limited to vehicle-mounted use. Further, the shape is not limited, such as a cylindrical shape.

In addition, the nickel-metal hydride storage battery to be controlled is not limited to the battery module 90, and may be a single battery.
In this embodiment, a nickel-metal hydride storage battery is used as an example of an alkaline secondary battery, but the present invention can also be implemented with an alkaline battery such as a nickel-cadmium storage battery that uses NiOOH for the positive electrode and is composed of an alkaline electrolyte.

○ In this embodiment, the explanation about γ-NiOOH is omitted, and the reaction formula during discharge is explained using β-NiOOH as an example, but it is not limited to β-NiOOH, and the same reaction can be performed for γ-NiOOH. arise.

〇 The SOC value [%], charge/discharge rate [C], current value [A], voltage value [V], time [s], etc. illustrated in this embodiment are merely examples and are applicable. Optimized by a person skilled in the art according to the characteristics of the battery. The threshold value is similarly optimized.

The flowcharts shown in FIGS. 6 and 7 are just examples, and those skilled in the art can change the order of the steps, add steps, or omit them.
It goes without saying that those skilled in the art can add, delete, and change configurations without departing from the scope of the claims.

10...Nickel-metal hydride storage battery control device 11...Control unit 12...Storage unit (program)
13...Information acquisition unit (map/battery usage history)
14...SOC calculation unit 15...Charging control unit 16...Load (air conditioner, etc.)
17...Motor generator 18...Internal combustion engine 20...Inverter 21...Current detector 22...Voltage detector 23...Temperature detector 24...Battery pack 90...Battery module (nickel metal hydride storage battery)
DESCRIPTION OF SYMBOLS 100... Integral battery case 110... Cell 120... Partition wall 130... Battery case 140... Electrode plate group 141... Positive electrode plate 141a... Lead part 142... Negative electrode plate 142a... Lead part 143... Separator 150... Current collector plate 151... Connection protrusion 152...Connection terminal 153...Connection terminal 160...Current collector plate 161...Connection protrusion 170...Through hole 200...Lid body 210...Exhaust valve 220...Sensor mounting hole 300...Square case A, B...O ₂ air bubbles HC...High SOC charging ID...intermittent discharge QD...rapid discharge t0-t4...time

Claims (8)

A method for controlling an alkaline secondary battery that charges and discharges an alkaline secondary battery having a positive electrode containing an active material containing nickel hydroxide as a main component and an electrolyte consisting of an alkaline aqueous solution, the method comprising:
In charging performed when the amount of the electrolytic solution becomes less than a preset threshold in a state where the SOC is in a range of 40% or more and 100% or less ,
Intermittent discharge is performed intermittently at a discharge rate of 15C or higher, so that a certain polarization state remains and the potential state of the particle surface of the positive electrode active material is uneven and oxygen is generated locally. A method for controlling an alkaline secondary battery, characterized in that: 2. The method of controlling an alkaline secondary battery according to claim 1 , wherein after said charging , rapid discharging is performed in which the battery is rapidly discharged with a current larger than the charging rate of said charging . 3. The method of controlling an alkaline secondary battery according to claim 1, wherein the intermittent discharge is performed at regular intervals and twice or less during charging to an SOC of 3%. 4. The method of controlling an alkaline secondary battery according to claim 3 , wherein the intermittent discharge is performed at regular intervals at least once during charging to an SOC of 3%. 5. The method for controlling an alkaline secondary battery according to claim 1, wherein the intermittent discharge has a discharge rate of 25C or less. The alkaline secondary battery control method is a control method performed on an alkaline secondary battery mounted on a vehicle for driving,
Based on the relationship between the preset voltage drop amount at the time of output and the amount of the electrolyte solution, when the voltage drop amount at the time of output is equal to or greater than the threshold value V1, the amount of the electrolyte solution is less than the preset threshold value. 2. The method of controlling an alkaline secondary battery according to claim 1 , wherein the charging is performed after determining that the battery has become charged. 7. The method of controlling an alkaline secondary battery according to claim 6 , wherein the vehicle is a hybrid vehicle. The method for controlling an alkaline secondary battery according to any one of claims 1 to 7, wherein the alkaline secondary battery is a nickel-metal hydride storage battery.