JP2023137939A - Recovery method and recovery device of nickel hydride storage battery - Google Patents

Abstract

To recover deterioration of a capacitance of a nickel hydride storage battery in which a memory effect is generated.SOLUTION: A recovery method of a nickel hydride storage battery measures a complex impedance of the nickel hydride storage battery that previously becomes a recovery object, and acquires an accuracy full capacity on the basis of a measurement result. On the basis of this full capacity, a voltage PV[V] of the current at first is acquired (S35) if a charging for acquiring an OCV-SOC curve (S31) is required (S34: YES), and a charging is performed by 3[C] of a high rate as a first charging rate (S37) in the case where it is a SOC lower than a high SOC region (S35: NO). If it is determined that it is the high SOC region (S38:YES), a charging is performed by 1/3[C] of a low rate as a second charging rate (S39). A charging is terminated immediately (S40) when the charging reaches an upper limit voltage (S38:NO).SELECTED DRAWING: Figure 13

Description

The present invention relates to a recovery method and device for a nickel-metal hydride storage battery, and more particularly to a recovery method and device for a nickel-metal hydride battery that can effectively eliminate memory effects.

In recent years, nickel-metal hydride storage batteries are safe and can input and output large amounts of current, so they have been used in a variety of applications such as electric vehicles, notebook PCs, and for storing late-night electricity or solar-generated electricity in homes and factories. ing.

Such nickel-metal hydride storage batteries can be used in various ways. For example, depending on the charging and discharging conditions, repeated charging and discharging may generate electrochemically inert nickel oxide (Ni ₂ O ₃ H), which may cause an increase in battery resistance or a decrease in battery capacity. There is.

Therefore, the invention disclosed in Patent Document 1 has a state of charge (SOC) of 20 to 80% at a current density of 100 [A/m ² ]. A battery has been proposed in which Ni ₂ O ₃ H becomes less than a specified amount when charging and discharging a total amount of electricity of 10 [kAh] within the range.

Japanese Patent Application Publication No. 2011-233423

However, the present inventors discovered that even when a nickel-metal hydride storage battery is repeatedly partially charged and discharged in an intermediate SOC range such as SOC 20 to 80 [%] as disclosed in Patent Document 1, the battery capacity may decrease. I found a problem. The cause of this is thought to be the so-called memory effect of the nickel-metal hydride storage battery.

One of the causes of the memory effect is thought to be variations in the charging of nickel hydroxide, the positive electrode active material. In such cases, there is a so-called battery refresh method that eliminates the memory effect and restores battery capacity. In the conventional battery refresh method, once the battery is completely discharged to SOC 0 [%], the charged nickel hydroxide is used up. It is common knowledge among those skilled in the art to eliminate the memory effect by charging at a low rate so that variations in charging of nickel hydroxide do not occur in this state.

However, according to the experimental analysis conducted by the present inventors, it has been found that even with the conventional battery refresh method as described above, which was said to restore the battery capacity, the capacity of the nickel-metal hydride storage battery actually decreases.

The problem to be solved by the nickel hydride storage battery recovery method and recovery device of the present invention is to effectively eliminate the memory effect of nickel hydride storage batteries.

In order to solve the above problems, in the nickel hydride storage battery recovery method of the present invention, the nickel hydride storage battery used is charged in advance, and the state where uncharged nickel hydroxide is gone is SOC100 [%] In this case, the nickel-metal hydride storage battery is characterized in that SOC 100 [%] is set as the upper limit SOC, and the nickel-metal hydride storage battery is charged at a set charging rate up to a range including the upper limit SOC.

In addition, obtaining the full capacity of SOC100 [%] of the used nickel metal hydride storage battery is as follows:
an impedance measurement step of measuring the complex impedance of a secondary battery to be measured based on application of AC power for measurement; and two steps of measuring the complex impedance of a secondary battery that is within a diffusion region and has a different measured angular velocity among the measured complex impedances. a parameter calculation step of calculating a parameter consisting of a ratio between the difference in measured angular velocity of the two complex impedances and the difference in imaginary components of the two complex impedances; It is also preferable to include a capacity calculation step of calculating the capacity of the secondary battery based on information indicating a relationship with the parameters and the parameters calculated in the parameter calculation step.

Further, when the SOC 100 [%] of the nickel metal hydride storage battery is set as the upper limit SOC, and the SOC [%] lower than the upper limit SOC by a set value is set as the reference SOC, in the low SOC region that is the region below the reference SOC. , while charging to a preset first charging rate as an upper limit, and in a high SOC region exceeding the reference SOC and below the upper limit SOC, charging to a second charging rate lower than the first charging rate as an upper limit. It is also preferable to charge the battery.

Further, it is also preferable to set the reference SOC to 70 to 90 [%].
Further, it is also preferable that the charging rate or the second charging rate is 1/3 [C] or less.

In addition, the recovery method for a nickel-metal hydride storage battery is based on the assumption that the SOC is 100[%] when the battery capacity [Ah] of the used nickel-metal hydride battery is 100[%], and the battery voltage OCV [V] at SOC 100[%] is the upper limit. When the voltage UL [V] and the battery voltage OCV [V] at SOC [%] lower than SOC 100 [%] by a set value are set as the reference voltage RV [V], the voltage below the reference voltage RV [V] is In the low SOC region, charging is performed to the upper limit of the first charging rate set in advance, and in the high SOC region, which is the region exceeding the reference voltage RV [V] and below the upper limit voltage UL [V], Charging can be performed up to a second charging rate lower than the first charging rate.

Further, the recovery device for a nickel-hydrogen storage battery of the present invention includes a charging/discharging control device for a nickel-hydrogen storage battery, and the charging/discharging control device is configured to control when the battery capacity [Ah] of the used nickel-hydrogen storage battery is 100 [%]. is SOC100[%], and the battery voltage OCV[V] at SOC100[%] is the upper limit voltage UL[V], and the battery voltage OCV[V] at SOC[%] is lower than SOC100[%] by a set value. When is the reference voltage RV [V],
In the low SOC region, which is the region below the reference voltage RV [V], charging is performed to the upper limit at the first charging rate set in advance, and at the same time, the charge exceeds the reference voltage RV [V] and is below the upper limit voltage UL [V]. In the high SOC region, which is the region, charging is performed using a second charging rate lower than the first charging rate as an upper limit.

According to the nickel-hydrogen storage battery recovery method and recovery device of the present invention, the memory effect of the nickel-hydrogen storage battery can be effectively eliminated.

It is an OCV-SOC curve showing the relationship between the open cell voltage OCV and SOC of a nickel metal hydride storage battery without capacity deterioration. It is an OCV-SOC curve showing the relationship between OCV and SOC of a nickel-metal hydride storage battery whose capacity has decreased. 2 is a graph showing an OCV-SOC curve V ₁ in a nickel-metal hydride storage battery with a reduced capacity to be controlled, and the relationship between SOC and charging rate. It is an OCV-SOC curve showing the relationship between open cell voltage OCV and SOC during charging and discharging. FIG. 2 is a block diagram of a control device for a nickel-metal hydride storage battery. 1 is a flowchart showing a procedure for controlling the nickel-metal hydride storage battery 10 according to the present embodiment. It is a graph showing the relationship between the total amount of discharged electricity [Ah] in Experimental Examples 1 to 7 and the chargeable battery capacity [Ah] of the nickel-metal hydride storage battery at that time when the SOC conditions for charging and discharging are changed. FIG. 2 is a block diagram showing the configuration of a measuring device that measures the battery electric capacity and capacity retention rate of a nickel-metal hydride storage battery. FIG. 3 is a graph showing an example of a Nyquist diagram created from AC impedance measured for a secondary battery in the present embodiment. FIG. 7 is a graph showing an example of the relationship between the reciprocal of the measured angular velocity of AC impedance and the imaginary component in the present embodiment. In the present embodiment, it is a graph showing the relationship between a parameter consisting of the ratio of the measured angular velocity of AC impedance and the imaginary component and battery capacitance. It is a figure which shows an example of the Nyquist diagram created from the alternating current impedance measured about a battery. It is a flowchart which shows the procedure of charge/discharge control (S4) of the nickel metal hydride storage battery 10 by the nickel metal hydride storage battery control device 1 of this embodiment. 7 is a graph illustrating a comparison of battery capacity recovery due to refresh between the present embodiment and the prior art.

The recovery method and recovery device for a nickel-hydrogen storage battery of the present invention will be described below with reference to FIGS. 1 to 13 using a recovery method using a control device 1 for a nickel-hydrogen storage battery 10, which is an embodiment. The use of the nickel-metal hydride storage battery 10 of this embodiment is not limited to a wide range of uses, but for ease of explanation, for example, a usage mode in which the nickel-metal hydride storage battery 10 is charged to SOC 100 [%] at a specific time will be exemplified. . For example, there is a case where a household charges electric power from a power line late at night and uses this electric power during the day. Further, it is assumed that there are no other charging/discharging operations, and the description thereof will be omitted.

<Technical background of this embodiment>
As described in the related art, when Ni ₂ O ₃ H is generated, the battery capacity of the nickel-metal hydride storage battery 10 decreases. Therefore, in the invention disclosed in Patent Document 1, when charging and discharging with a total electricity amount of 10 [kAh] within the range of SOC 20 to 80 [%] at a current density of 100 [A/m ² ], Ni A battery in which ₂ O ₃ H is below a specified amount has been proposed.

However, as described above, even if the nickel-metal hydride storage battery 10 is repeatedly partially charged and discharged in an intermediate SOC region such as SOC 20 to 80 [%] as described above, the battery capacity may decrease due to the memory effect.

When the memory effect occurs and the full capacity of the nickel-metal hydride storage battery 10 decreases, the corresponding SOC [%] will differ even if the OCV [V] is the same. However, in order to appropriately control charging and discharging, it is necessary to accurately estimate SOC [%].

Here, FIG. 1 is an OCV-SOC curve V ₀ showing the relationship between the open cell voltage OCV (hereinafter sometimes simply abbreviated as "OCV") and SOC of a nickel-metal hydride storage battery without capacity deterioration. As shown in FIG. 1, if the relationship between OCV and SOC of the target nickel-metal hydride storage battery is obtained as an OCV-SOC curve _V0 , the SOC can be estimated from the OCV. In FIG. 1, OCV [V] when the SOC is 100 [%] indicates V ₁₀₀ [V]. Further, when the OCV is V ₈₀ [V], it can be estimated that the SOC is 80 [%].

FIG. 2 is an OCV-SOC curve _V1 showing the relationship between OCV and SOC of a nickel-metal hydride storage battery with reduced capacity. In a nickel-metal hydride storage battery, the battery capacity may be reduced by repeatedly performing partial charging and discharging in an intermediate SOC region such as the above-mentioned SOC of 20 to 80 [%]. When the battery capacity decreases, as shown in FIG. 2, even with the same OCV, the SOC may actually become higher than the initial OCV-SOC curve V ₀ . In FIG. 1, the OCV [V] when the SOC is 80 [%] is OCV=V ₈₀ . However, when the capacity of the nickel metal hydride storage battery decreases, as shown in the OCV-SOC curve _V1 shown in Figure 2, when OCV=V ₈₀ [V], the SOC actually exceeds 80 [%]. value.

Therefore, when OCV=V80[V], if we estimate that the SOC at that time is 80[%], this nickel-metal hydride storage battery is actually controlled at an SOC[%] higher than SOC=80[%]. It turns out. If an error occurs in SOC estimation in this way, it may be used in a high SOC region where the SOC exceeds 80 [%], which may lead to overcharging in some cases, and may also become a factor in the formation of Ni ₂ O ₃ H. It may be stored away. In such a case, if even a small amount of Ni ₂ O ₃ H is generated, the capacity of the battery will decrease, so if the battery is continued to be used assuming the specified capacity (Ah), the error in estimating the SOC will substantially increase. However, this leads to further formation of Ni ₂ O ₃ H. As a result, it may even become impossible to use the battery repeatedly. In order to accurately estimate the SOC in this way, it is necessary to eliminate the memory effect and recover the reduced capacity of the nickel-metal hydride storage battery.

<Method for refreshing the nickel-metal hydride storage battery of this embodiment>
In view of this background, the present inventors have developed a new method for restoring the nickel-metal hydride battery 10 (so-called "refresh method") in which the capacity of the nickel-metal hydride battery is less likely to decrease. This method suppresses a decrease in the capacity of the nickel-metal hydride storage battery 10. By keeping the capacity of the nickel-metal hydride storage battery constant, the SOC can be estimated accurately. As a result, it is possible to perform appropriate control according to the accurate SOC at that time, so that it is possible to continuously suppress a decrease in capacity.

<Estimation of SOC of this embodiment>
As a premise of the nickel-metal hydride storage battery control method of this embodiment, it is necessary to accurately estimate the deterioration of the SOC [%] of the nickel-metal hydride battery that has a history of use and is subject to control.

For exact measurement of SOC [%], for example, X-ray photoelectron spectroscopy (XPS) is used to detect the chemical bonds of nickel hydroxide, which is the positive electrode active material, existing on the surface of the positive electrode plate (at a depth of several nanometers). It can be estimated by clarifying the state. However, it is not easy to analyze because it requires a dedicated measuring device or a destructive inspection.

A simple method is to estimate by integrating the battery current [Ah] or to analyze the change in OCV [V]. These methods allow non-destructive inspection by measuring current and voltage. In particular, in order to estimate the SOC from the battery voltage OCV, the SOC can be easily estimated by using the above-mentioned OCV-SOC curve, so there is also a method of obtaining the voltage of SOC 100 [%] from the OCV-SOC curve. However, the method of obtaining the battery voltage OCV at SOC 100 [%] from the OCV-SOC curve takes time to obtain. Furthermore, there is a problem in that the accuracy of the obtained battery voltage OCV at SOC 100 [%] is relatively low. In this embodiment, effective control can be achieved by accurately obtaining the capacity at SOC 100 [%], so it is desired to obtain the battery capacity more quickly and accurately.

Therefore, the present inventors have invented a technique for estimating capacitance using a Nyquist diagram created based on measurement of complex impedance, as disclosed in Japanese Patent Application Publication No. 2018-040629. By using this method in the present invention, accurate battery capacity can be determined non-destructively and quickly. Details will be described later.

<Characteristics of the recovery method of this embodiment>
In the recovery method of the nickel-metal hydride storage battery 10 of this embodiment, a usage mode is exemplified in which the battery is discharged arbitrarily and then charged to SOC 100 [%] at a certain time.

Figure 3 shows an OCV-SOC curve _V1 showing the relationship between the "upper limit voltage UL [V]" corresponding to the "upper limit SOC [%]" in a nickel metal hydride storage battery with reduced capacity, and the SOC [%] and charging rate [ C] is a graph showing the relationship.

In the present embodiment shown in FIG. 3, when the battery capacity of the nickel-metal hydride storage battery 10 is 100 [%], the SOC is set to 100 [%] and is defined as the "upper limit SOC." Further, the OCV at the upper limit SOC is defined as the upper limit voltage UL [V]. At the same time, the SOC (that is, SOC 80 [%]) that is lower by a set value (for example, 20 [%]) than the "upper limit SOC" is set as the "reference SOC". Further, the OCV at the reference SOC is defined as the reference voltage RV [V]. The "standard SOC" is preferably 70[%] or more and 90[%] or less. If the reference SOC is too low, the overall charging efficiency will decrease. On the other hand, if the reference SOC is too high, the charging of the positive electrode active material will not be uniform enough. Therefore, the "standard SOC" is preferably 70 [%] or more and 90 [%] or less, although it is not limited thereto.

In the "low SOC region" which is the region below the "reference SOC", charging is performed up to the preset "first charging rate C ₁ ". The “first charging rate C ₁ ” is, for example, a high rate of 3 [C]. Note that if the first charging rate _C1 is less than 1 [C], the overall charging efficiency deteriorates. Moreover, if it exceeds 3 [C], local overcharging is likely to occur. Therefore, although not limited thereto, it is desirable that the first charging rate _C1 is 1 [C] or more and 3 [C] or less.

On the other hand, in a "high SOC region" which is a region exceeding the "reference SOC" and below the "upper limit SOC", charging is performed to the upper limit of the "second charging rate C ₂ " which is lower than the "first charging rate C ₁ ". The “second charging rate C ₂ ” is, for example, a low rate of 1/3 [C]. If the second charging rate _C2 is low, it is preferable for uniformity of the positive electrode active material, but in consideration of charging efficiency, it is preferable that the charging rate is high to some extent. Therefore, although not limited to this, in this embodiment, it is set to 1/3 [C].

Furthermore, in the present embodiment, charging and discharging of the nickel-metal hydride storage battery 10 is performed within a charging and discharging range that does not fall below the "lower limit SOC", which is the SOC set to exceed SOC0 [%], even if it is not at a predetermined time. Let's do it. The "lower limit SOC" is, for example, SOC20 [%]. If the lower limit SOC is too low, it will not be possible to prepare for sudden discharge, and there is a risk that overdischarge will occur. On the other hand, if it is too high, the capacity of the nickel metal hydride battery cannot be fully utilized. Therefore, in this embodiment, the lower limit SOC is set to 20[%], although it is not limited thereto.

<Charging in low SOC region>
In the "low SOC region" which is the region below the "reference SOC", charging is performed up to the preset "first charging rate C ₁ ". This embodiment is characterized in that all the positive electrode active materials are uniformly charged when the SOC is 100%. On the other hand, in this low SOC region, there is no need for the positive electrode active material to be uniformly charged. Therefore, a high charging rate with high charging efficiency can be allowed. Therefore, in the low SOC region of this embodiment, charging at a high rate of 3 [C] is allowed.

<Charging in high SOC area>
On the other hand, the nickel-metal hydride storage battery 10 is charged and discharged with SOC 100 [%] as the upper limit SOC, and is performed within a charging and discharging range that includes this upper limit SOC. However, do not charge the battery above SOC 100%. This is because overcharging to an SOC exceeding 100% increases the possibility of oxygen generation and the possibility of Ni ₂ O ₃ H being generated.

Charging in this "high SOC region" changes the positive electrode active material, Ni(OH) ₂ , into nickel oxyhydroxide (NiOOH). At this time, for example, 1/3 [C ] Charge slowly at a low rate below. By slowly charging at such a low rate, all the positive electrode active materials are uniformly charged just at the upper limit SOC of 100 [%] while suppressing the occurrence of local overcharging within the positive electrode.

In other words, in this embodiment, "SOC 100 [%]" is a state in which all the positive electrode active materials are uniformly charged in this way, and there is no uncharged nickel hydroxide in the positive electrode. That is, charging is completed immediately at this point. If the battery is charged more than this, it becomes overcharged and oxygen (O ₂ ) is likely to be generated at the positive electrode. When oxygen (O ₂ ) is easily generated, Ni ₂ O ₃ H is easily generated. Therefore, it is necessary to accurately grasp the point in time when the SOC reaches 100%.

<Two-step charging reaction of nickel metal hydride storage battery>
Here, charging of a nickel-metal hydride storage battery will be described with reference to FIG. 1. As shown in FIG. 1, the OCV-SOC curve V ₀ generally consists of regions St1 to St4.

In region St1, uncharged nickel hydroxide is gradually charged at a low SOC, and as the capacity increases, OCV [V] also increases. Here, since there is a large amount of uncharged nickel hydroxide, the OCV increases rapidly at the start of charging. After that, the rate of increase in OCV gradually slows down.

In region St2, the potential changes most easily from nickel hydroxide (Ni(OH) ₂ ) to nickel oxyhydroxide (NiOOH). Therefore, since the electrical energy for charging is spent on the energy for chemical change, the battery capacity [Ah] increases, but the OCV [V] does not easily rise, resulting in a nearly horizontal graph.

In region St3, uncharged nickel hydroxide decreases, and battery voltage OCV increases as capacity increases. At this time, the battery voltage OCV when the SOC is 80 [%] is V ₈₀ [V]. Further, the right end of the region St3 is exactly at the SOC of 100 [%], and at this time, uncharged nickel hydroxide disappears. The battery voltage OCV [V] at this time indicates V ₁₀₀ [V].

In region St4, an overcharge state occurs, and the charging current is not used to charge nickel hydroxide, but becomes energy for oxygen generation. Therefore, even if the battery is charged, the battery voltage OCV does not increase, and the graph becomes horizontal again.

If the battery capacity of the nickel-metal hydride storage battery has not decreased, an OCV-SOC curve V ₀ as shown in Figure 1 can be obtained, so SOC [%] can be easily estimated by measuring OCV [V]. .

<About the generation of Ni ₂ O ₃ H at low SOC>
<Condition 1 for Ni ₂ O ₃ H generation>
Here, FIG. 4 is an OCV-SOC curve showing the relationship between the open cell voltage OCV and SOC during charging and discharging.

The first condition for producing Ni ₂ O ₃ H is as follows. As shown in FIG. 4, repeated charging and discharging at a low SOC causes a memory effect. In this case, the OCV-SOC curve Lc of the nickel-metal hydride storage battery during charging shifts to the noble side (higher potential), resulting in a system in which oxygen O ₂ is more likely to be generated during charging.

On the other hand, since the OCV-SOC curve Ld during discharge shifts to the base side (low potential), the system is used at a low positive electrode potential during discharge. When oxygen is generated at the nickel hydroxide interface of the positive electrode, the oxygen causes a local depletion state at the nickel hydroxide particle interface. When discharging is performed in a state where this water is insufficient, the discharge voltage shifts to a base value, and thus stays at a positive electrode potential lower than usual, approaching the Ni ₂ O ₃ H generation potential.

<Condition 2 for Ni ₂ O ₃ H generation>
The second condition for the production of Ni ₂ O ₃ H is as follows. The generation of oxygen attempts to compensate for the locally insufficient water, thereby promoting a reaction in which H ₂ O and Ni ₂ O ₃ H are simultaneously produced from βNiOOH.

<Ni ₂ O ₃ H generation>
Conditions 1 and 2 above overlap, and Ni ₂ O ₃ H is generated at an accelerated rate. As a result, a decrease in capacity is caused.

<Method for restoring the capacity of the nickel-metal hydride storage battery 10 of this embodiment>
FIG. 2 is an OCV-SOC curve _V1 showing the relationship between the open cell voltage OCV and SOC of a nickel-metal hydride storage battery whose capacity has decreased due to the occurrence of a memory effect.

Based on the mechanism in which Ni ₂ O ₃ H is generated at an accelerated rate as described above, initial local charging and discharging is the main factor (starting point) for the formation of Ni ₂ O ₃ H. Therefore, it is necessary to prevent this. At the charging voltage at the start of the two-stage charging reaction (≈oxygen generation voltage), there are almost no uncharged Ni(OH) ₂ particles. That is, by stopping charging when the SOC reaches 100%, all Ni(OH) ₂ particles are charged and the positive electrode active material is in a uniform state. If the battery is discharged from this state, non-uniformity of the positive electrode active material, which is a cause of the memory effect, can be eliminated, and refreshing of the nickel-metal hydride storage battery 10 is completed.

As a result, deviations in the initial OCV-SOC curve can be suppressed.
<About capacity recovery in conventional area St4>
It has been explained that the range indicated by region St4 in FIG. 1 is overcharged. Conventionally, there has been a method of deliberately overcharging a nickel-metal hydride storage battery to restore its capacity (for example, Japanese Patent Application Laid-Open No. 2018-14270).

The method for restoring the capacity is based on the premise that hydrogen H ₂ in the nickel-metal hydride storage battery leaks to the outside, disrupting the balance of the hydrogen partial pressure inside the battery case.
In order to maintain this equilibrium, hydrogen is released from the metal hydride (MH) of the negative electrode in accordance with the amount of hydrogen leakage. When hydrogen is discharged to the outside of the battery module in this manner, the discharge capacity decreases because the discharge reserve of the negative electrode decreases.

Therefore, in order to increase the discharge reserve, the battery module is overcharged. In overcharging, since charging continues even after the uncharged portion of the positive electrode is exhausted, hydroxyl groups in the electrolytic solution are decomposed and oxygen is generated, as shown in the following half-reaction formula (1). At the negative electrode, a reaction proceeds in which hydrogen is stored in the uncharged portion of the negative electrode active material, that is, in the hydrogen storage alloy, as shown in the following half-reaction formula (2). In addition, as shown in the half-reaction equation (3) below, at the same time as the reaction of storing hydrogen in the hydrogen storage alloy, the metal hydride and oxygen react in the charged part, that is, the hydrogen storage alloy that has stored hydrogen, A reaction occurs in which water is produced. At this time, the metal hydride (MH) returns to the hydrogen storage alloy (M). That is, when the safety valve is not open during overcharging, a reaction in which the uncharged portion is charged and a reaction in which the charged portion returns to the uncharged portion occur simultaneously at the negative electrode.

(Positive electrode) OH ^- → 1/4O ₂ + 1/2H ₂ O+e ^-... (1)
(Negative electrode) M+H ₂ O+e ⁻ →MH+OH ⁻ …(2)
MH+1/ _4O2 →M+1/ _2H2O ...(3)
On the other hand, when oxygen is generated from the positive electrode and the internal pressure rises, and the internal pressure exceeds the valve opening pressure, the safety valve opens and oxygen gas is discharged to the outside. When oxygen gas is discharged, the reaction represented by half-reaction formula (3), that is, the reaction in which the charged portion returns to the uncharged portion, is suppressed. Therefore, the hydrogen storage alloy that has stored hydrogen is maintained in a hydrogen storage state, and if there is an uncharged portion of the negative electrode, the reaction shown by the half-reaction formula (2) proceeds and the discharge reserve is secured. .

<Control in area St4 in this embodiment>
In this embodiment, there is no assumption that hydrogen H ₂ in the nickel-metal hydride storage battery leaks to the outside and the hydrogen partial pressure in the battery case becomes imbalanced.

Therefore, when oxygen is generated from the positive electrode and the internal pressure rises, and the internal pressure exceeds the valve opening pressure, the safety valve opens and oxygen gas is discharged to the outside. There are also major disadvantages, such as a decrease in volume.

Further, the present inventors have confirmed through experiments that oxygen O ₂ is generated at the positive electrode due to overcharging, and Ni ₂ O ₃ H is generated due to the generation of oxygen.
For this reason, in this embodiment, charging is immediately stopped in the region St4 where the SOC exceeds 100%.

<Nickel-metal hydride storage battery control device 1>
FIG. 5 is a block diagram of the control device 1 for the nickel-hydrogen storage battery 10. The solid line shown in FIG. 5 indicates electrical connection. Furthermore, broken lines indicate connections of control signals. The nickel-metal hydride storage battery 10 illustrated in this embodiment is a stationary battery for household use. For example, we envisage a system that would be fully charged using low-cost late-night power from a power line, and then discharged during the day to supply power to necessary lighting, air conditioning, home appliances, etc.

Of course, the nickel-metal hydride storage battery of this embodiment can be used in vehicles such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHVs). In addition, it can be used in homes and factories that generate small-scale power generation such as solar power generation and wind power generation. Its use is not limited. Here, since the charging/discharging operation is simple and the explanation of the basic control method of the nickel-metal hydride storage battery of this embodiment is easy to understand, a household stationary battery will be explained as an example. Here, only the common basic configuration is shown.

The control device 1 includes a charge/discharge control device 2, a power supply device 3, a voltage measurement device 4, a current measurement device 5, a switch 6, and a load 7.
<Charge/discharge control device 2>
The charge/discharge control device 2 exchanges signals with a power supply device 3, a voltage measurement device 4, a current measurement device 5, a switch 6, and a load 7. Data on the OCV [V] and battery current [A] of the nickel-metal hydride storage battery 10 is received from the voltage measuring device 4 and the current measuring device 5 . Based on these, the control method for the nickel-metal hydride storage battery 10 of this embodiment is executed by transmitting the amount of power supplied from the power supply device 3 and a control signal for supplying the power to be supplied to the load 7 .

The charge/discharge control device 2 includes a CPU (Central Processing Unit) 11, a RAM (Random Access Memory) 12, and a ROM (Read Only Memory) 13. Further, the computer is configured to include a storage device 14 made of, for example, a PROM (Programmable ROM). The ROM 13 and the storage device 14 store a program for a method of controlling the nickel-metal hydride storage battery 10 of this embodiment.

In addition, it is equipped with a well-known computer configuration such as a power supply, an interface, and a timer.
<Power supply device 3>
The power supply device 3 is a device that can supply power to the nickel-metal hydride storage battery 10. This embodiment corresponds to a late-night power supply device via a power line. Further, the supplied power is, for example, in an electric vehicle (EV) or the like, power supplied from a charger using a power line or regenerated power. In addition, in a hybrid vehicle (HV), etc., the electric power generated by the prime mover and the regenerated electric power correspond to the electric power generated by the prime mover. In addition, for homes and factories that use solar power generation, wind power generation, and small-scale hydroelectric power generation, the electricity is generated by power generation facilities including solar panels.

The power supply device 3 includes a switch (not shown), a voltage regulator, a current regulator, an inverter, etc., which ensure that the supplied power is appropriate, and is controlled by the control device 1.
<Voltage measuring device 4>
The voltage measuring device 4 measures the open cell voltage OCV [V] of the nickel-metal hydride storage battery 10 . Actually, the power supply device 3 and the load 7 are connected, but the method is not limited as long as the OCV can be actually measured or estimated.

<Current measuring device 5>
The current measuring device 5 measures the battery current [A] of the nickel-metal hydride storage battery 10 . Actually, the power supply device 3 and the load 7 are connected, but the method is not limited as long as the battery current [A] can be actually measured or estimated.

<Load 7>
The load 7 in this embodiment corresponds to equipment that consumes power in the home, such as lighting, air conditioning, and home appliances. In the case of electric vehicles and hybrid vehicles, this includes equipment such as a drive motor generator and air conditioner. In addition, for households and factories that generate solar power, electricity transmission through electricity sales is also equivalent. It also includes one in which the SOC of the nickel-metal hydride storage battery 10 is adjusted by simply discharging it.

In addition, although the switch 6 provided in the load 7 is not shown, it includes not only a switching means but also a switch (not shown), a voltage regulator, a current regulator, an inverter, etc., to ensure that the supplied power is appropriate. This is controlled by the charge/discharge control device 2.

<Procedure for recovering the nickel-metal hydride storage battery of this embodiment>
FIG. 6 is a flowchart showing the recovery procedure of the nickel-metal hydride storage battery 10 of this embodiment.

As described above, the control device 1, which is a recovery device for the nickel-metal hydride storage battery 10 of this embodiment, is designed to store late-night power at a certain time in the night at home and consume it during the day, for the sake of simplicity. I gave an example. Therefore, in reality, exceptional charging/discharging procedures may be performed, but these are omitted in this flowchart. Hereinafter, a method for recovering the nickel-hydrogen storage battery 10 of this embodiment using the control device 1 for the nickel-hydrogen storage battery 10 of this embodiment will be described. Note that the application is not limited to electric vehicles (EV), hybrid vehicles, and stationary use in homes and factories equipped with power generation equipment such as solar power generation and wind power generation. Furthermore, it goes without saying that the control procedure varies depending on the application, and is not limited to this embodiment.

As shown in FIG. 6, when the recovery procedure of the nickel-metal hydride storage battery 10 of this embodiment is started, first, in the "complex impedance measurement (S1)" procedure, the nickel-metal hydride to be controlled is measured by measuring the complex impedance. A Nyquist diagram of the storage battery 10 is obtained.

Next, based on the acquired Nyquist diagram, the battery capacity when fully charged at SOC 100 [%] is estimated and acquired (S2).
FIG. 3 is a graph showing the OCV-SOC curve V ₁ of a nickel-metal hydride storage battery with a reduced capacity to be controlled, and the relationship between SOC [%] and charging rate [C].

Next, from the obtained battery capacity at full charge, the upper limit voltage UL [V] corresponding to the upper limit SOC=100 [%] is specified using the OCV-SOC curve _V1 shown in FIG. Similarly, the reference voltage RV[V] corresponding to the reference SOC=80[%] is specified. Further, the lower limit voltage LL [V] corresponding to the lower limit SOC=20 [%] is specified.

Then, "upper limit voltage UL [V]" corresponding to "upper limit SOC [%]", "reference voltage RV [V]" corresponding to "reference SOC", "lower limit voltage LL [V]" corresponding to "lower limit SOC" ]" Charge/discharge control of the nickel-metal hydride storage battery 10 is performed (S3).

<Measurement of complex impedance (S1)>
The measurement of complex impedance (S1) will be described in detail below. Here, estimation of the capacity by measuring the complex impedance of the nickel-metal hydride storage battery 10 to be controlled will be described. Generally, nickel-metal hydride secondary batteries are adjusted so that the electrical capacity, which is the amount of electricity that can be charged to the negative electrode, is greater than the electrical capacity, which is the amount of electricity that can be charged to the positive electrode, to meet the so-called positive electrode regulation. . Therefore, unless a capacity shift occurs, the battery electric capacity, which is the amount of electricity that can be charged to the battery, is usually equal to the positive electrode electric capacity. In addition, in the nickel-metal hydride storage battery 10, the battery electric capacity in the after-use state, which is the state after the start of use, tends to decrease due to deterioration, compared to the battery electric capacity in the initial state, which is the state at the time of starting use. . The ratio of the battery capacity in the used state to the battery capacity in the initial state is the "capacity retention rate." When the battery capacitance of the nickel-metal hydride storage battery 10 is measured, the capacity maintenance rate is calculated based on the measured battery capacitance. For example, the capacity retention rate can be used to calculate the state of charge (SOC) of the nickel-metal hydride storage battery 10, to determine deterioration, or to control charging and discharging of the battery.

<Measuring device 30>
FIG. 8 is a block diagram showing the configuration of a measuring device 30 that measures the battery electric capacity [Ah] and capacity retention rate [%] of the nickel-metal hydride storage battery 10.

As shown in FIG. 8, a nickel-metal hydride storage battery 10, whose battery capacity is to be measured, is connected to a load, a charger, etc. via a switch (not shown) or the like. The nickel-metal hydride storage battery 10 is charged and discharged by closing the switch and connecting it to a load, etc., and the amount of charge is changed. On the other hand, when the complex impedance of the nickel-hydrogen storage battery 10 is measured, the switch is opened and the nickel-metal hydride storage battery 10 is disconnected from the load and the like.

A measurement power source 20 that supplies alternating current as alternating current power to the nickel-metal hydride battery 10 is connected between the electrodes of the nickel-metal hydride battery 10 . Further, a voltage measuring device 21 that measures the voltage between the electrodes of the nickel-hydrogen storage battery 10 and a current measuring device 22 that measures the current flowing between the measurement power source 20 and the nickel-hydrogen storage battery 10 are connected.

The measurement power supply 20 generates an alternating current with a predetermined measurement frequency, and outputs the generated alternating current between the electrodes of the nickel-metal hydride storage battery 10 . Further, the measurement power source 20 can change the measurement frequency of the alternating current. The measurement power supply 20 has an output current and a frequency range of a measurement frequency set, and outputs an alternating current of the set output current as a measurement frequency that changes within the same set frequency range. The frequency range to be set is, for example, from 100 [kHz] as a high frequency side to 1 [mHz] as a low frequency side. However, the present invention is not limited to this, and the high frequency side may be higher than 100 [kHz], and the lower frequency side may be lower than 1 [mHz].

<Nyquist diagram>
FIG. 12 is a diagram showing an example of a Nyquist diagram created from the AC impedance measured for the nickel-hydrogen storage battery 10. Even if it outputs a frequency range aimed at the "straight line area da" of the "diffusion area d" shown in FIG. 12, for example, the range from 0.1 [Hz] to 0.01 [Hz]. good. Further, two or more different frequencies in the "diffusion region d", for example, frequencies between 0.1 [Hz] and 0.01 [Hz] may be output. Note that, as stated above, it is clear that the relationship between angular velocity and frequency is "angular velocity = 2π x frequency," so for convenience of explanation, both angular velocity and frequency will be used in the explanation.

The measurement power supply 20 outputs each signal related to the set value of the output alternating current and the set value of the measurement frequency to the measuring device 30. Further, the measurement power source 20 switches between outputting and stopping the alternating current in response to an output start signal and an output stop signal input from the measuring device 30.

<Voltage measuring device 21>
The voltage measuring device 21 outputs a voltage signal corresponding to the voltage measured between the electrodes of the nickel-metal hydride storage battery 10 to the measuring device 30.

<Current measuring device 22>
The current measuring device 22 outputs a current signal corresponding to the current measured between the measuring power source 20 and the nickel metal hydride storage battery 10 to the measuring device 30.

<Measuring device 30>
The measuring device 30 measures the battery electric capacity and battery capacity maintenance rate of the nickel-metal hydride storage battery 10. The measuring device 30 may display the measured battery electric capacity and battery capacity maintenance rate of the nickel-metal hydride storage battery 10, or output it to the outside. For example, an external battery control device (not shown) may perform charge/discharge control on the nickel-hydrogen storage battery 10 according to the battery capacity of the nickel-hydrogen storage battery 10 output from the measuring device 30.

The measuring device 30 inputs a voltage signal from the voltage measuring device 21, obtains the voltage between the terminals of the nickel metal hydride storage battery 10 from the input voltage signal, inputs a current signal from the current measuring device 22, and obtains the voltage between the terminals of the nickel metal hydride storage battery 10 from the inputted voltage signal. The current flowing between the measurement power source and the nickel metal hydride storage battery 10 is acquired. The measurement device 30 acquires the output setting of the alternating current and the output measurement frequency from the signal input from the measurement power supply 20.

The measuring device 30 also includes a processing unit 40 that performs calculation processing related to measurement of the current battery capacitance of the nickel-metal hydride storage battery 10, and a storage unit 50 that holds information used in the calculation process of the battery capacitance of the nickel-metal hydride storage battery 10. Equipped with.

<Storage unit 50>
The storage unit 50 is a nonvolatile storage device such as a hard disk or flash memory, and holds various data. In the present embodiment, the storage unit 50 stores correlation data 51 between parameters and capacity required for calculating battery electric capacity, and calculation data 52. As the calculation data 52, the battery electric capacity of the nickel-metal hydride storage battery 10 in its initial state is set.

<Processing unit 40>
The processing unit 40 includes a microcomputer including a CPU, ROM, RAM, and the like. The processing unit 40 executes various processes in the processing unit 40 by, for example, executing various programs stored in a ROM or RAM on a CPU. In this embodiment, the processing unit 40 performs processing for calculating battery electric capacity and processing for calculating battery capacity maintenance rate. Further, the processing unit 40 can utilize the voltage, current, measurement frequency, etc. acquired by the measuring device 30. Further, the processing unit 40 can exchange data with the storage unit 50.

The processing unit 40 includes an impedance measurement unit 41 that measures complex impedance Z, a Nyquist diagram creation unit 43 that creates a Nyquist diagram, a parameter calculation unit 44 that calculates parameters, and a battery electric capacity and battery capacity maintenance rate. It also includes a capacity calculation unit 45 that calculates the capacity.

<Impedance measuring section 41>
In the impedance measurement unit 41, a process (impedance measurement process) of measuring the complex impedance Z of the nickel-metal hydride storage battery 10 is performed. The impedance measurement section 41 instructs the measurement power source 20 to start or end measurement. The impedance measurement unit 41 measures the complex impedance Z of the nickel-metal hydride storage battery 10 based on the voltage and current acquired from the start to the end of the measurement. The unit of complex impedance Z is [Ω] (ohm). The complex impedance Z is expressed by a real component Zr [Ω] and an imaginary component Zi [Ω], which are vector components, as shown in equation (1). Note that "j" is an imaginary unit. Hereinafter, the unit [Ω] will be omitted.

<Nyquist diagram creation unit 43>
The Nyquist diagram creation unit 43 creates a Nyquist diagram from the real component Zr and the imaginary component Zi, which are vector components, based on the complex impedance Z at a plurality of measurement frequencies.

FIG. 9 is a graph showing an example of a Nyquist diagram created from AC impedance measured for a secondary battery in this embodiment. For example, as shown in FIG. 9, the Nyquist diagram creation unit 43 creates an impedance curve L21 and an impedance curve L22 as a Nyquist diagram on a complex plane in which the horizontal axis is the real axis and the vertical axis is the imaginary axis. Note that the impedance curve L21 is an example of a Nyquist diagram corresponding to the nickel-hydrogen storage battery 10 in an initial state, and the impedance curve L22 is an example of a Nyquist diagram corresponding to the nickel-hydrogen storage battery 10 in a used state. In each of the impedance curves L21 and L22, the magnitudes of the real component Zr and the imaginary component Zi of the complex impedance Z are plotted on a complex plane. The impedance curves L21 and L22 are based on the complex impedance Z measured by changing the measurement frequency of the alternating current supplied from the measurement power source 20 to the nickel-hydrogen storage battery 10.

<Impedance curves L21, L22>
In FIG. 9, dots and circles in the impedance curves L21 and L22 indicate one measurement frequency. Regarding the measurement frequencies, in FIG. 2, the lower side is the high frequency side, and the upper side is the low frequency side. The impedance curves L21 and L22 change depending on the SOC of the nickel-hydrogen storage battery 10 and the battery temperature. It also changes depending on the battery type, such as a nickel-metal hydride secondary battery or a lithium-ion secondary battery. Furthermore, even if the battery type is the same, the number of cells, capacity, etc. will change if they differ.

Here, each impedance curve L21, L22 of the nickel-metal hydride storage battery 10 will be described in detail with reference to FIGS. 9 and 12.
<About areas a to d>
As shown in FIG. 9, each impedance curve L21, L22 of the nickel-hydrogen storage battery 10 is divided into a plurality of regions corresponding to the characteristics of the nickel-hydrogen storage battery 10. The plurality of regions are divided into "region a", "region b", "region c", and "diffusion region d" from the high frequency side to the low frequency side of the measurement frequency. "Area a" is a circuit resistance region corresponding to the circuit resistance. "Region b" is a solution resistance region corresponding to solution resistance. “Region c” is a reaction resistance region corresponding to complex impedance caused by reaction resistance. The "diffusion region d" is a region corresponding to a substantially linear diffused resistance. The circuit resistance is the impedance of wiring, etc. made of active materials, contact resistance within the current collector, and the like. Solution resistance is electron movement resistance such as resistance when ions in the electrolyte in the separator move. The reaction resistance is the resistance of charge transfer during electrode reaction. Diffusion resistance is impedance related to material diffusion.

Note that since each resistance influences each other, it is difficult to divide each region a, b, c, and d into only parts affected only by each resistance. However, at least in each of the regions a, b, c, and d of the impedance curves L21 and L22, the rough behavior of the curve is determined by the resistance component that is most affected. For example, "region c" is greatly influenced by the aspect of the negative electrode, and "diffusion region d" is greatly influenced by the aspect of the positive electrode.

<Analysis of impedance curve>
Roughly speaking, the impedance curves L21 and L22 of the nickel-metal hydride storage battery 10 are curves obtained by combining the impedance of the positive electrode and the impedance of the negative electrode. For example, in the frequency range corresponding to the "diffusion region d", the impedance of the positive electrode changes greatly, while the change of impedance of the negative electrode is small. In other words, it can be said that the "diffusion region d" of the impedance curves L21 and L22 is a region greatly affected by the impedance of the positive electrode, and reflects the state of the positive electrode. On the other hand, in the frequency range corresponding to "region c", the impedance of the negative electrode changes greatly, while the change of impedance of the positive electrode is small. In other words, "region c" of the impedance curves L21 and L22 is a region where the impedance of the negative electrode has a large influence, and it can be said that the state of the negative electrode is reflected.

According to the impedance curves L21 and L22, the frequency range corresponding to the "diffusion region d" is 0.1 [Hz] or less, and FIG. 2 shows up to 0.01 [Hz]. Further, the frequency range corresponding to "region c" is greater than 0.1 [Hz] and less than or equal to 100 [Hz]. Incidentally, the frequency range corresponding to "region b" is 100 [Hz] and its vicinity, and the frequency range corresponding to "region a" is higher than 100 [Hz]. Note that the "diffusion region d" may be larger or smaller than 0.1 [Hz] as long as it is in a lower frequency range than the "region c".

<Diffusion area d>
Further, as shown in FIG. 12, the "diffusion region d" includes a "straight region da," a "vertical region dc," and a "region db." The "linear area da" is an area where the ratio of the amount of change in the imaginary component to the amount of change in the real component is within a predetermined value range close to "1". That is, in the figure, it is a range close to an angle of 45°, in other words, a range in which the absolute value of the rate of change of the imaginary component with respect to the real component of the complex impedance is 0.5 or more and 2 or less. Therefore, in the "straight line area da", there is a correlation between the imaginary number component and the real number component. The "vertical region dc" is a region where the graph changes substantially vertically in the figure because only the imaginary component changes significantly relative to the real component. That is, in the figure, the range is close to an angle of 90°. The "area db" is the boundary and the area surrounding the boundary where the "linear area da" changes to the "vertical area dc."

By the way, in the nickel-metal hydride storage battery 10, due to the characteristics of the nickel-metal hydride secondary battery and the practicality of the measured value, the measurement of complex impedance generally ends in the "linear region da." In addition, in nickel-metal hydride secondary batteries, the measurement frequency at which the "vertical region dc" occurs tends to be lower than the frequency at which the "vertical region dc" occurs in lithium ion secondary batteries. In addition, in order to more reliably measure the "vertical area dc" of the nickel-metal hydride storage battery 10, it is necessary to prepare the measurement environment by increasing the temperature of the battery, and to set the measurement frequency to a frequency lower than 0.01 [Hz]. Therefore, it is necessary to select a frequency that requires time to measure. Furthermore, since the measurement frequency at which the "vertical region dc" occurs cannot be known in advance, the dead time required for measurement may become long. When attempting to measure the value of the "vertical area dc", it is difficult to estimate the time required for measurement. is considered unrealistic.

<Parameter calculation unit 44>
The parameter calculation unit 44 shown in FIG. 8 calculates the ratio between the difference in measured acceleration of two complex impedances that are within the "diffusion region d" and have different measurement frequencies, and the difference in imaginary components of the two complex impedances. (parameter calculation step). Here, the two complex impedances are "Z1" and "Z2", the imaginary component of the complex impedance "Z1" is "Zi1", the measurement frequency is "f1", the imaginary component of the complex impedance "Z2" is "Zi2", Let the measurement frequency be "f2".

More specifically, the parameter calculation unit 44 calculates the difference between two values. One is the difference (change amount) between the measured angular velocities of the two complex impedances "Z1" and "Z2" of the nickel-metal hydride storage battery 10, "Δω=2π×(f1-f2)". be. The other is the difference (amount of change) between the imaginary components of the two complex impedances, “ΔZi=Zi1−Zi2”.

FIG. 10 is a graph showing an example of the relationship between the reciprocal of the measured angular velocity of AC impedance and the imaginary component in this embodiment. As shown in FIG. 10, the parameter “Q _D ” is calculated based on the difference “Δ(ω ⁻¹ )” between the reciprocals of the measured angular velocities of the two complex impedances and the difference “ΔZi” between the imaginary components of the two complex impedances. Calculate. Logically, the parameter "Q _D " is determined as shown in equation (2). In other words, equation (2) indicates that the reciprocal of the ratio of "ΔZi" to "Δ(ω ⁻¹ )" is the parameter "Q _D ". Note that since it is preferable to calculate the parameter “Q _D ” as a positive value, “Δ(ω ⁻¹ )” and “ΔZi” may be taken as absolute values, if necessary.

As described above, the parameter "Q _D " can be calculated theoretically from equation (2), but it can also be calculated based on equation (3), which is a modified version of equation (2). For example, the parameter calculation unit 44 is set to calculate parameters using the equation shown on the right side of equation (3). In other words, equation (3) shows that the ratio of the difference "Δ(ω ^-1 )" between the reciprocals of the measured angular velocities of two complex impedances with different measurement frequencies to the difference "ΔZi" between the imaginary components of the two complex impedances is the parameter " Q _D ".

The capacity calculation unit 45 calculates the capacity of the nickel-metal hydride storage battery 10 based on correlation data 51 between parameters and capacity, which is information preset in the storage unit 50, and the parameter “Q _D ” calculated by the parameter calculation unit 44. Calculate battery electric capacity (capacity calculation step).

<Correlation data 51 between parameters and capacity>
FIG. 11 is a graph showing the relationship between a parameter consisting of the ratio of the measured angular velocity of the AC impedance to the imaginary component and the battery capacitance in this embodiment. With reference to FIG. 11, correlation data 51 between parameters and capacity will be described. The parameter-capacity correlation data 51 is information indicating the relationship between the parameter “Q _D ” within the “diffusion region d” regarding the complex impedance Z of the nickel-metal hydride battery 10 and the battery electric capacity of the nickel-metal hydride battery 10.

FIG. 11 shows a graph L41 as a calibration curve, which is an example of correlation data 51 between parameters and capacity. Specifically, the graph L41 shows the relationship between the parameter “Q _D ” (=(ΔZi/Δ(ω ⁻¹ )) ⁻¹ ) and the battery electric capacity [Ah] of the nickel-hydrogen storage battery 10. Graph L41 was created based on the complex impedance obtained by pre-measurement of the nickel-metal hydride battery 10 manufactured with the same specifications as the nickel-metal hydride battery 10 to be measured, and the battery electric capacity at that time. . Note that the graph L41 may be created from measured values, may be created by combining measured values with theory and experience, or may be information created based on theory and experience. good. Further, since the graph L41 changes depending on the temperature, it may be set for each predetermined temperature. By having a different graph L41 for each predetermined temperature, the capacity of the secondary battery can be more suitably calculated and measured.

In other words, the parameter-capacity correlation data 51 held in the storage unit 50 in FIG. 8 is information set in the storage unit 50 in advance. This is information indicating the relationship between the parameter "Q _D " related to the complex impedance Z in the "diffusion region d" of the complex impedance of the nickel-metal hydride battery 10 and the battery electric capacity of the nickel-metal hydride battery 10.

<Reason why battery electric capacity can be calculated>
With reference to FIGS. 9 to 11, the reason why the battery capacitance can be calculated from the parameter “Q _D ” related to the complex impedance in the “diffusion region d” of the complex impedance of the nickel-metal hydride storage battery 10 in this embodiment will be explained.

When using the nickel-metal hydride storage battery 10 as a power source, it is necessary to accurately calculate its SOC, but it is better to calculate it in consideration of the influence of deterioration of the nickel-metal hydride storage battery 10. Therefore, in the conventional technique, the degree of deterioration of the secondary battery is measured in the "diffusion region d" based on the value of the imaginary component in the "vertical region dc" on the lower frequency side. At this time, a "vertical region dc" is created by controlling the temperature of the battery so that it is between 40 [℃] and 70 [℃], but such temperature control is performed on the battery in use. That is difficult. Further, in the conventional technology, it is necessary to set the measurement frequency to less than 10 [mHz], preferably less than 3 [mHz]. At such measurement frequencies, it takes about 1.7 [minutes] at 10 [mHz] and about 5.6 [minutes] at 3 [mHz], so the measurement time is It was not suitable for measurement.

Therefore, the inventors conducted extensive research on a method for calculating battery capacitance that is less affected by battery temperature, and discovered the technology shown in this embodiment. According to this technique, the influence of battery temperature can be suppressed by using the difference between two complex impedances. Additionally, this technology eliminates the need to create a "vertical region dc," which is difficult to create in lithium-ion secondary batteries and even more difficult to create in nickel-metal hydride secondary batteries, for calculating the capacity retention rate. . As a result, the time required for measurement could be made shorter than a practical length, for example, "about 1.7 minutes."

As described above, FIG. 9 shows an example of the Nyquist diagram of the impedance curve L21 corresponding to the nickel-hydrogen storage battery 10 in the initial state, and the Nyquist diagram of the impedance curve L22 corresponding to the nickel-hydrogen storage battery 10 in the used state. An example is shown. For example, the state after use is the state after 1000 cycles of charging and discharging the nickel-metal hydride storage battery 10 in its initial state in an environment of 45°C within the range of SOC 40% to 80%. .

Here, when comparing the impedance curve L21 and the impedance curve L22, the impedance curve L22 has a smaller amount of change in the imaginary component Zi with respect to the real component Zr in the "diffusion region d" than the impedance curve L21, and the slope of the graph is smaller. is small.

FIG. 10 shows graphs L31 and L32 showing the relationship between the reciprocal of the measured angular velocity “ω ⁻¹ ” in the “diffusion region d” and the imaginary component “Zi” of the complex impedance. Graph L31 is a graph corresponding to the nickel-hydrogen storage battery 10 in an initial state, and graph L32 is a graph corresponding to the nickel-hydrogen storage battery 10 in a used state. At this time, in the graph L32, the amount of change "ΔZr/Δ(ω ^-1 )" of the imaginary component Zi with respect to the reciprocal number "ω ^-1 " of the measured angular velocity is large compared to the graph L31, and the slope of the graph is large. Therefore, the parameter “Q _D ” obtained as the reciprocal of the amount of change “ΔZr/Δ(ω ⁻¹ )” is smaller in graph L32 than in graph L31. In other words, the parameter “Q _D ” is smaller in the state after use than in the initial state of the nickel-metal hydride storage battery 10.

As shown in FIG. 11, a graph L41 shows the relationship between the complex impedance and the battery capacitance, and the relationship between the parameter “Q _D ” (=(ΔZi/Δ(ω ⁻¹ )) ⁻¹ ) and the battery of the nickel-metal hydride storage battery 10. It is expressed in relation to electric capacity.

<Capacity maintenance rate calculation process>
The calculation process of the capacity maintenance rate of the measuring device 30 of this embodiment will be explained together with its operation.

First, information corresponding to the graph L41 shown in FIG. 11 is stored in advance in the storage unit 50 as correlation data 51 between parameters and capacity.
Then, the measuring device 30 measures the complex impedance of the nickel-metal hydride storage battery 10 using the impedance measuring section 41 . At this time, the measurement frequency range is set so that a "diffusion region d" appears in the Nyquist diagram. For example, assume that the two measurement frequencies f1 and f2 are two points between 0.1 Hz and 0.01 Hz. For example, assume that measurement frequency f1>measurement frequency f2.

<Nyquist diagram creation unit 43>
The Nyquist diagram creation section 43 creates a Nyquist diagram based on the complex impedance measured by the impedance measurement section 41 and the measurement frequency at that time. In addition, the Nyquist diagram creation unit 43 identifies a "diffusion region d" from the created Nyquist diagram, and corresponds to the two measurement frequencies "f1" and "f2" included in the specified "diffusion region d", respectively. Obtain the imaginary components "Zi1" and "Zi2" of the complex impedance.

The parameter calculation unit 44 obtains two measurement frequencies “f1” and “f2” and the corresponding imaginary components “Zi1” and “Zi2” of the complex impedance from the Nyquist diagram creation unit 43. Then, the difference between the measured angular velocities "Δω=2π×(f1-f2)" and the difference between the imaginary components "ΔZi=Zi1-Zi2" are calculated. Then, the parameter “Q _D ” is calculated by applying the calculated reciprocal of the difference in measured angular velocity “Δ(ω ⁻¹ )” and the difference in imaginary component “ΔZi” to equation (2) or equation (3).

The capacity calculation unit 45 acquires the parameter “Q _D ” calculated by the parameter calculation unit 44, and also uses the acquired parameter “Q _D ” in a graph L41 (related to correlation data 51 between parameters and capacity) held in the storage unit 50. information) to obtain the battery electric capacity. If the parameter "Q _D " is large, the battery capacitance is large, and if the parameter "Q _D " is small, the battery capacitance is small. In this way, the measuring device 30 measures the battery capacity of the nickel-metal hydride storage battery 10.

In addition, the capacity calculation unit 45 compares the obtained battery electric capacity with the initial state battery electric capacity of the nickel-metal hydride storage battery 10 set in the calculation data 52, and calculates the capacity retention rate with respect to the initial state battery electric capacity. Calculate. For example, the capacity calculation unit 45 calculates "(obtained battery electric capacity/initial state battery electric capacity) x 100" [%] as the capacity maintenance rate. In this way, the measuring device 30 measures the battery capacity of the nickel-metal hydride storage battery 10.

In "Estimating Full Charge Capacity (S2)", the full charge capacity [Ah] is accurately estimated using the procedure described above.
<Charge/discharge control (S3) procedure>
FIG. 13 is a flowchart showing the procedure for charge/discharge control (S3) of the nickel-hydrogen storage battery 10 by the nickel-hydrogen storage battery control device 1 of this embodiment. After accurately estimating the full charge capacity [Ah] in the procedure of "Estimating Full Charge Capacity (S2)", the procedure of charging and discharging control of the nickel-metal hydride storage battery 10 (S3) is carried out.

The procedure of charge/discharge control (S3) of the nickel-metal hydride storage battery 10 is performed by the control device 1 of the nickel-metal hydride battery 10 as shown in the flowchart shown in FIG. Hereinafter, the procedure for charge/discharge control (S3) of the nickel-metal hydride storage battery 10 of this embodiment will be described with reference to FIG. 13.

<OCV-SOC curve acquisition (S31)>
After accurately estimating the full charge capacity [Ah] in "Estimate full charge capacity (S2)", next, obtain the OCV-SOC curve V ₁ (see FIG. 3). This is the "upper limit voltage UL [V]" corresponding to the "upper limit SOC [%]", the "reference voltage RV [V]" corresponding to the "reference SOC", and the "lower limit voltage LL [V]" corresponding to the "lower limit SOC". This is to obtain information such as "V]".

The control device 1 obtains the OCV-SOC curve V ₁ of the nickel-metal hydride storage battery 10 to be controlled. The OCV-SOC curve _V1 is calculated by charging at a low rate of 1/3 or less from a fully discharged state of SOC 0 [%], integrating the charging current, and estimating the SOC from the full charge capacity [Ah]. Record the OCV at the time. In this OCV-SOC curve _V1 , the OCV when the SOC is 100 [%] when the full charge capacity [Ah] is charged is read, and this is stored as the "upper limit voltage UL [V]". Further, in this OCV-SOC curve, "reference voltage RV [V]" corresponding to "reference SOC", "lower limit voltage LL [V]" corresponding to "lower limit SOC", etc. are acquired and stored.

<Set OCV of SOC100 [%] as upper limit voltage UL [V] (S32)>
Then, the nickel-metal hydride storage battery control device 1 sets the OCV at SOC 100 [%] obtained in the procedure of "OCV-SOC curve acquisition (S31)" as the "upper limit voltage UL [V]." Similarly, "reference voltage RV [V]" and "lower limit voltage LL [V]" are set.

<Start of control of nickel metal hydride storage battery (S33)>
When the above preparation steps are completed, the control device 1 of the nickel-metal hydride storage battery 10 performs charging and discharging control (S33).

<Charging? (S34)>
The control device 1 of the nickel-metal hydride storage battery 10 determines whether or not it should be charged (S34). This embodiment exemplifies a mode in which charging is performed at a constant time every day. Therefore, it is determined whether or not it is time to charge. If charging is not to be performed (S34: NO), a waiting loop is entered until it is time to charge. Then, when the time to charge comes (S34: YES), the current voltage PV [V] is acquired (S35).

<Acquisition of current voltage PV [V] (S35)>
The control device 1 of the nickel-hydrogen storage battery 10 acquires the current OCV of the nickel-hydrogen storage battery 10 using the voltage measurement device 4 (FIG. 5) (S35). Then, the CPU 11 estimates the current SOC [%] of the nickel-hydrogen storage battery 10 based on the OCV-SOC curve V ₁ from the voltage PV [V] which is the current OCV of the nickel-hydrogen storage battery 10 .

<Low SOC area? (S36)>
Compare the current voltage PE[V] and the reference voltage RV[V]. If the current voltage PE [V] is lower than the reference voltage RV [V], it can be seen that the current SOC is 80 [%] or less and is in the low SOC region (S36: YES).

<Charging at 3 [C] (S37)>
When the current SOC is 80 [%] or less and is in the low SOC region (S36: YES), since the current SOC is in the low SOC region, charging is performed at the first charging rate of 3 [C] which is a high rate (S37).

Is <PV≦upper limit voltage UL [V]? (S38)>
Compare the current voltage PE[V] and the reference voltage RV[V]. If the current voltage PE [V] is higher than the reference voltage RV [V], it can be seen that the current SOC is in a high SOC region exceeding 80 [%]. In other words, it can be seen that it is not a low SOC region (S36: NO).

Next, if the voltage PV [V] does not exceed the upper limit voltage UL [V] (S38: YES), charging is continued at the second charging rate 1/3 [C] which is a low rate (S39).
<Charging end (S40)>
If the voltage PV[V] exceeds the upper limit voltage UL[V] (S38: NO), the SOC will exceed 100%, so charging is immediately terminated (S40). Note that the recovery method for a nickel-metal hydride storage battery according to the present embodiment is completed when charging is completed (S40).

<Discharge allowed below 3 [C] (S41)>
When charging is completed (S40), discharging is allowed at 3 [C] or less (S41). Note that this flowchart only explains the basic operation. For example, although emergency charging due to a sudden drop in OCV and charging other than normal charging are not explained, it goes without saying that such procedures may be included.

<Is it finished? (S42)>
Except when the operation of the nickel-metal hydride storage battery itself ends (S42: YES → end), if the operation of the nickel-hydrogen storage battery does not end (S42: NO), the process returns to the standby state for charging at S34, and the steps from S35 to S42 are performed. is repeated.

<Recovery of battery capacity by refreshing in this embodiment>
FIG. 14 is a graph showing a comparison of battery capacity recovery due to refresh between this embodiment and the prior art. This graph shows the battery capacity ratio CR [%] of the nickel-metal hydride storage battery 10 before refreshing. Furthermore, the battery capacity ratio CR [%] of the nickel-metal hydride battery 10 that has been refreshed using the recovery method for the nickel-metal hydride battery 10 of this embodiment is shown. Then, the battery capacity ratio CR [%] of the nickel-metal hydride storage battery 10 that has been refreshed using the conventional method is shown.

Here, in this application, "battery capacity ratio CR [%]" means the battery capacity [Ah] of the nickel-hydrogen storage battery 10 to be measured, when the battery capacity [Ah] of the unused nickel-hydrogen storage battery 10 is 100 [%]. The ratio [%] of Ah] is shown. Therefore, it is a different concept from SOC [%], which is the relative charging rate of the nickel-metal hydride storage battery 10 at that point in time when it is fully charged. “Battery capacity ratio CR [%]” is defined below. In other words, the ratio of the absolute value of the fully charged battery capacity [Ah] of the nickel hydride storage battery 10 to be measured to the absolute value of the fully charged battery capacity [Ah] of the standard unused nickel hydride storage battery 10. is the value of

First, in the nickel-metal hydride storage battery 10 that has a history of use, the battery capacity ratio CR [%] has decreased to 70 [%] compared to the unused nickel-metal hydride battery 10 due to use without any usage conditions. Here, it is estimated that a memory effect occurs and the battery capacity ratio CR [%] decreases.

Next, the nickel-metal hydride storage battery 10 with such a usage history is completely discharged at a low discharge rate of 1/3C to SOC 0 [%], and the nickel-metal hydride storage battery after the conventional technology refresh is performed only once. Indicates the battery capacity [%]. As shown in the graph, the battery capacity ratio CR [%] was recovered to 80 [%] by refreshing using this conventional refresh method.

Then, the battery capacity ratio CR [%] of the nickel-metal hydride storage battery after refreshing of this embodiment is shown. Here, as described above, a nickel-metal hydride battery whose battery capacity ratio CR [%] has decreased to 70 [%] compared to 10 unused nickel-metal hydride batteries is refreshed according to the flowchart shown in FIG. I did it only once. Specifically, the battery is charged at 1C until the SOC reaches 80%, and charged at a low rate of 1/3C until the SOC reaches 100%, and then the charging is completed. As shown in the graph shown in FIG. 14, the battery capacity ratio CR [%] is recovered to 85 [%] by refreshing using this conventional refresh method. In this embodiment, charging is performed at a low rate of 1/3C until the SOC reaches 100%, and then charging is completed.

As described above, it was demonstrated through experiments that the refresh method of this embodiment can effectively recover the nickel-metal hydride storage battery 10 whose battery capacity has decreased.
(Experiment example of this embodiment)
FIG. 7 shows the relationship between the total amount of discharged electricity [Ah] in Experimental Examples 1 to 7 and the chargeable battery capacity [Ah] of the nickel-metal hydride storage battery 10 at that time when the SOC conditions for charging and discharging were changed. This is a graph showing. In the experiment, charging and discharging were repeatedly performed at a charging and discharging rate of 1/3 [C] within a specified SOC range.

<Experiment example 1>
Experimental example 1 shown in FIG. 7 shows the relationship between the total amount of discharged electricity [Ah] and the battery capacity [Ah] of the present embodiment described above. As shown here, the charging/discharging SOC range was set to 100 to 20[%], and the range was set to ΔSOC=80[%]. Here, "ΔSOC" represents the difference between the maximum value and the minimum value of SOC [%]. Then, during charging, the battery was charged to the upper limit voltage UL [V] to ensure that the SOC was 100 [%]. In this case, it was found that the initial battery capacity of approximately 5.2 [Ah] did not decrease even if the total amount of discharged electricity [Ah] increased.

<Experiment example 2>
Next, in Experimental Example 2, the SOC range for charging and discharging is set to 100 to 40 [%]. If the range is reduced to ΔSOC=60[%], similarly, the SOC is always set to 100[%] during charging. In such a case, it was found that the initial battery capacity of approximately 3.9 [Ah] did not decrease even if the total amount of discharged electricity [Ah] increased.

<Experiment example 3>
Furthermore, in Experimental Example 3, the SOC range for charging and discharging is set to 100 to 60 [%], and is further reduced to ΔSOC=40 [%]. Even in such a case, if the SOC is always set to 100 [%] when charging, the initial battery capacity of approximately 2.6 [Ah] will increase even if the total discharged electricity [Ah] increases. It was found that the capacity [Ah] did not decrease.

<Experiment example 4>
In Experimental Example 4, as in Experimental Example 1, ΔSOC was set to 80[%], but the upper limit was set to SOC90[%], and the lower limit was set to SOC10[%]. Then, during charging, the battery was charged so that the SOC was always 90%. In this case, the battery capacity [Ah] at the time of manufacture was approximately 5.2 [Ah], but as the total amount of discharged electricity [Ah] increased, the battery capacity [Ah] decreased. As shown in FIG. 7, the charging capacity of the battery, which was initially about 5.2 [Ah], decreased to about 4.8 [Ah] when the total amount of discharged electricity [Ah] reached 2000 [Ah]. Furthermore, the total amount of discharged electricity [Ah] decreased to about 4.2 [Ah] when it reached 4000 [Ah]. Furthermore, the total amount of discharged electricity [Ah] decreased to 6000 [Ah] and approximately 3.5 [Ah]. Then, the total amount of discharged electricity [Ah] decreased to about 3.2 [Ah] to 8000 [Ah]. From this, it was confirmed that the battery capacity [Ah] decreases with use in charging and discharging that does not include charging up to SOC 100 [%].

<Experiment example 5>
In Experimental Example 5, as in Experimental Example 1, ΔSOC was set to 80 [%], but the upper limit was set to SOC80 [%], and the lower limit was set to SOC0 [%]. Then, during charging, the battery was charged so that the SOC was always 80%. In this case, the battery capacity [Ah] at the time of manufacture was approximately 5.2 [Ah], but as the total amount of discharged electricity [Ah] increased, the battery capacity [Ah] decreased. As shown in Figure 7, the charging capacity of the battery, which was initially approximately 5.2 [Ah], suddenly decreased to approximately 2.6 [Ah] when the total amount of discharged electricity [Ah] reached 2000 [Ah]. . From this, it was confirmed that the battery capacity [Ah] decreases with use in charging and discharging that does not include charging up to SOC 100 [%]. In particular, even when compared with Experimental Example 4, the battery capacity decreased significantly.

The present inventors particularly focused on the fact that in Experimental Example 5, charging and discharging were performed in a range including SOC0 [%]. Conventionally, it has been thought that refreshing the nickel-metal hydride storage battery 10 can be done by completely discharging it to a SOC of 0% and then slowly charging it at a low charging rate.

However, as described above and shown in FIG. 7, the present inventors have discovered that the battery capacity decreases significantly even through SOC0 [%], which was thought to be effective in eliminating the memory effect by those skilled in the art. I found it.

<Experiment example 6>
In Experimental Example 6, as in Experimental Example 2, ΔSOC was set to 60 [%], but the upper limit was set to SOC 70 [%] and the lower limit was set to SOC 10 [%]. Then, when charging, the battery was charged so that the SOC was always 70%. In this case, the battery capacity [Ah] at the time of manufacture was approximately 3.8 [Ah], but as the total amount of discharged electricity [Ah] increased, the battery capacity [Ah] decreased. As shown in FIG. 7, the charging capacity of the battery, which was initially about 3.8 [Ah], decreased to about 4.8 [Ah] when the total amount of discharged electricity [Ah] reached 2000 [Ah].

<Experiment Example 7>
In Experimental Example 7, as in Experimental Example 3, ΔSOC was set to 40 [%], but the upper limit was set to SOC 50 [%] and the lower limit was set to SOC 10 [%]. Then, when charging, the battery was always charged at an SOC of 50%. In this case, the battery capacity [Ah] at the time of manufacture was approximately 2.6 [Ah], but as the total amount of discharged electricity [Ah] increased, the battery capacity [Ah] decreased. As shown in FIG. 7, the charging capacity of the battery, which was initially about 2.6 [Ah], decreased to about 1.1 [Ah] when the total amount of discharged electricity [Ah] reached 2000 [Ah].

<Summary of the experiment>
(a) As derived from Experimental Examples 1, 2, and 3, if the charging and discharging range has an upper limit of SOC 100 [%] and the charge is always made until the SOC reaches 100 [%], the charging range ΔSOC It differs from 80 to 40 [%]. Despite this, no deterioration of battery capacity [Ah] occurred in any case. In other words, at least the so-called memory effect does not occur. In other words, a refreshing effect is observed.

Furthermore, it can be seen that Ni ₂ O ₃ H was not generated at the same time. That is, in this experiment, charging was always stopped and discharging started at the moment the SOC reached 100%. Therefore, it can be estimated that Ni ₂ O ₃ H was not generated by avoiding the overcharge state where oxygen is likely to be generated.

(b) On the other hand, as derived from Experimental Examples 4, 6, and 7, in the charging/discharging range where the upper limit is SOC lower than SOC100[%], the battery capacity [Ah] deteriorates regardless of the charging range ΔSOC. occurred.

In this case, the SOC does not exceed 100% where oxygen is generated.
Further, the charge/discharge rate is 1/3 [C] in both cases, and high rate charge/discharge is not performed at a low SOC of 10 [%]. Therefore, it is difficult to think that the deterioration of the battery capacity [Ah] is caused by the generation of Ni ₂ O ₃ H.

Therefore, it can be estimated that the refreshing effect proposed by the present inventors by always reaching SOC 100 [%] during charging could not be achieved.
(c) Furthermore, as derived from Experimental Example 5, at least under the conditions of this experiment, even if the SOC is completely discharged to 0 [%] and then slowly charged at a low charging rate of 1/3 [C], Deterioration of battery capacity [Ah] has occurred. That is, conventionally, the battery is completely discharged to a SOC of 0% to bring the nickel hydroxide, which is the positive electrode active material, into a completely uncharged state, thereby eliminating variations among the positive electrode active materials. Although it was thought to be common knowledge among those skilled in the art that it is possible to perform refresh to eliminate the memory effect by subsequently charging at a low charging rate, it was discovered that this does not necessarily hold true, and we obtained groundbreaking results. was completed.

(Action of this embodiment)
The recovery method for the nickel-hydrogen storage battery 10 of this embodiment has the following effects.
- In the recovery method of the nickel-metal hydride storage battery 10 of this embodiment, the nickel-metal hydride storage battery 10 is charged and discharged with SOC 100 [%] as the upper limit SOC, and is performed in a charging and discharging range that includes this upper limit SOC. However, do not charge the battery above SOC 100%. Overcharging to an SOC of over 100% has the effect of suppressing the possibility that Ni ₂ O ₃ H will be generated due to the generation of oxygen.

・Charging in this "high SOC region" changes the positive electrode active material, Ni(OH) ₂ , into nickel oxyhydroxide (NiOOH), but at this time, in order to avoid variations, for example, 1/3 [C] or less Charge slowly at a low rate. By slowly charging at such a low rate, all positive electrode active materials are uniformly charged at exactly the upper limit SOC of 100 [%] while suppressing the occurrence of local overcharging within the positive electrode. There is this effect. In other words, it has the effect of refreshing the nickel-metal hydride storage battery 10.

- In the "low SOC region" which is the region below the "reference SOC", charging is performed with the "first charging rate C ₁ " set to 3 [C], for example, as the upper limit. Therefore, there is an effect that charging can be performed quickly.

- Also, in order to manage charging and discharging within a range that does not fall below the lower limit SOC, over-discharge and extremely low SOC conditions are avoided.
・By measuring complex impedance, the full capacity of the nickel-metal hydride storage battery, which is a prerequisite for control, can be obtained quickly and accurately in a non-destructive manner, allowing for accurate control.

- Accurate control can suppress a decrease in the capacity of the nickel-metal hydride storage battery 10.
- Since a decrease in the capacity of the nickel-metal hydride storage battery 10 can be suppressed, accurate SOC estimation becomes possible.

- Therefore, accurate control based on the accurate full capacity of the nickel metal hydride storage battery can be continuously performed.
(Effects of this embodiment)
(1) According to the recovery method and recovery device for the nickel-metal hydride storage battery 10 of the present embodiment, there is an effect that a decrease in the capacity of the nickel-metal hydride battery 10 can be effectively recovered.

(2) In the present embodiment, in the low SOC region, charging is performed using the high-rate first charging rate _C1 as the upper limit, which has the effect of quickly charging the battery.
(3) On the other hand, in the high SOC region, since charging is performed up to the upper limit SOC using the low second charging rate _C2 as the upper limit, the state of charge of the positive electrode active material becomes uniform. By making the state of charge of the positive electrode active material uniform, the nickel-metal hydride storage battery 10 is refreshed and a decrease in capacity can be effectively recovered.

(4) Do not charge beyond the upper limit SOC, that is, SOC 100 [%]. Therefore, it is possible to avoid charging in a region where Ni ₂ O ₃ H is likely to be generated due to overcharging.

(5) The charging and discharging of the nickel-metal hydride storage battery 10 is controlled within a charging and discharging range that does not fall below the lower limit SOC, which is SOC [%] set to exceed SOC0 [%]. Therefore, over-discharge and extremely low SOC can be avoided, and the nickel-metal hydride storage battery can be smoothly controlled.

(6) The standard SOC was set at 70 to 90 [%]. Therefore, the positive electrode active material can be sufficiently uniformized in the high SOC region where low rate charging is performed. Furthermore, by providing a sufficient low SOC region for high-rate charging, there is an effect that charging efficiency can be improved.

(7) The second charging rate _C2 was set to 1/3 [C] or less. Therefore, there is an effect that the positive electrode active material can be sufficiently uniformized in the high SOC region.
(6) Since the full capacity of the nickel-hydrogen storage battery 10 is accurately estimated in advance based on the measurement of complex impedance, there is an effect that the characteristics of the nickel-hydrogen storage battery 10 to be controlled can be accurately specified.

(7) Since the OCV-SOC curve is obtained based on the full capacity of the nickel-metal hydride storage battery 10 obtained based on the measurement of complex impedance, there is an effect that an accurate OCV-SOC curve can be obtained.

(8) There is an effect that the SOC can be accurately estimated from the measured OCV based on an accurate OCV-SOC curve.
(9) There is an effect that accurate control can be performed based on the accurately acquired SOC.

(10) By performing accurate control based on the accurately acquired SOC, the capacity of the nickel-metal hydride storage battery 10 can be recovered.
(11) By restoring the capacity of the nickel-metal hydride storage battery 10, accurate control can be continuously performed based on accurate battery capacity.

(Another example)
The present invention is not limited to the embodiments and can be implemented as follows.
The procedure shown in the flowchart of FIG. 13 does not need to be performed all the time; for example, charging and discharging are normally performed at SOC of 40 to 80%, and the procedure shown in the flowchart of FIG. 13 may be performed arbitrarily. Alternatively, it may be performed when there is charging that satisfies certain criteria. Furthermore, it may be implemented periodically.

○ In this embodiment, control is performed according to OCV [V], but it may be controlled depending on other parameters such as estimated SOC [%], current [A] and its integrated value [Ah], temperature [℃], These can also be referenced and controlled.

In the present embodiment, a recovery method for a stationary nickel-metal hydride storage battery 10 in a home that is charged at night using late-night power is exemplified, but this example is provided to simplify the explanation since the operation is simple. In the present invention, the use of the nickel-metal hydride storage battery 10 is not limited to the embodiments. For example, it can be applied as a battery for driving vehicles such as electric vehicles (EV), plug-in hybrids (PHV), and hybrids (HV). Of course, it can also be applied to aircraft and ships. It can also be used as a stationary battery for homes and factories equipped with solar power generation facilities, wind power generation facilities, and small-scale hydroelectric power generation facilities. Furthermore, it can also be implemented for the purpose of refreshing the nickel-metal hydride storage battery 10 in a power source for a computer or audio equipment.

In this embodiment, the battery is divided into a low SOC region of SOC 80 or less and a high SOC region of more than SOC 80 [%], and is charged at a first charging rate C ₁ and a second charging rate C _{2 ,} respectively. However, the present invention is not limited to this, and for example, the SOC of more than 80% and less than 90% is defined as a "medium SOC region." In addition, the area exceeding SOC 90 [%] and up to SOC 100 [%] is defined as a high SOC region. In the medium SOC region, a medium charging rate, for example 1 [C], may be controlled in three stages.

○Charging is not limited to a fixed charging rate, and for example, charging down time may be provided intermittently to ensure uniform charging of the positive electrode active material.
○Also, the charging rate [C] may be gradually lowered continuously as the SOC approaches 100 [%].

In this embodiment, discharge at a uniform discharge rate of 3 [C] is allowed in a low SOC region of SOC 80 [%] or less. However, in a low SOC region of 20 to 50 [%], for example, a memory effect is likely to occur, so the discharge rate can be controlled to be limited to 1 [C] or less, for example.

○Also, as in the conventional technology, once the SOC is completely discharged to 0% at a low rate discharge rate of, for example, 1/3 [C], and then slowly charged at a low rate charge rate of, for example, 1/3 [C]. This does not preclude the implementation of conventional refresh methods such as

○The method for actually measuring and estimating SOC [%] during charging and discharging is not limited to acquisition using an OCV-SOC curve, and any method that can actually measure and estimate SOC [%] may be used.
The OCV-SOC curves shown in FIGS. 1 to 4 and the graph of capacity deterioration shown in FIG. 7 in the embodiment are merely examples, and vary depending on the characteristics of the target nickel-metal hydride storage battery 10.

The full capacity of the nickel-metal hydride storage battery 10 of this embodiment was estimated by measuring the complex impedance and analyzing the result using a Nyquist diagram, but this does not preclude estimation of the full capacity by actual measurement of OCV-SOC. .

The lower limit SOC [%], lower limit voltage LL [V], reference voltage RV [V], charging rate [C], first or second discharge rate [C], etc. in the embodiment are examples. Therefore, the values are not limited to these values, and can be appropriately optimized according to the characteristics of the nickel-metal hydride storage battery 10 by those skilled in the art.

The block diagrams shown in FIGS. 5 and 8 are diagrams for explaining the present embodiment, and the present invention can use a control device 1 having a different configuration to control the nickel-metal hydride storage battery 10.
The flowcharts shown in FIGS. 6 and 13 show examples of control procedures, and the procedures can be added, deleted, or modified.

It goes without saying that the present invention can be implemented by adding, deleting, or changing other configurations by those skilled in the art without departing from the scope of the claims.

DESCRIPTION OF SYMBOLS 1... Nickel metal hydride storage battery control device 2... Charge/discharge control device 3... Power supply device 4... Voltage measuring device 5... Current measuring device 6... Switch 7... Load 10... Nickel metal hydride storage battery 11... CPU
12...RAM
13...ROM
14... Storage device 20... Power supply for measurement 21... Voltage measuring device 22... Current measuring device 30... Measuring device 40... Processing section 41... Impedance measuring section 43... Nyquist diagram creating section 44... Parameter calculating section 45... Capacity calculating section 50 ...Storage part 51...Correlation data 52...Data for calculation a, b, c, d...Region Z...Complex impedance f1, f2...Measurement frequency L21, L22, L51...Impedance curve L31, L32, L41...Graph V ₀ , V ₁ ...OCV-SOC curve OCV...Battery voltage UL...Upper limit voltage [V]
LL...lower limit voltage [V]
RV...Reference voltage [V]
PV…Current voltage [V]
C ₁ ...First charging rate [C]
C ₂ ...Second charging rate [C]

Claims (7)

In the nickel metal hydride storage battery used,
When the nickel-metal hydride storage battery is charged in advance and the state in which there is no uncharged nickel hydroxide is taken as SOC 100 [%],
A recovery method for a nickel-hydrogen storage battery, characterized in that the nickel-hydrogen storage battery is charged at a charging rate set to a range including the upper limit SOC, with an SOC of 100 [%] as the upper limit SOC. Obtaining the full capacity of SOC100 [%] of the used nickel metal hydride storage battery is as follows:
an impedance measurement step of measuring the complex impedance of a secondary battery to be measured based on application of AC power for measurement;
Among the measured complex impedances, a parameter is calculated from the ratio of the difference in measured angular velocity of two complex impedances that are in a diffusion region and have different measured angular velocities and the difference in imaginary components of the two complex impedances. Parameter calculation process,
a capacity calculation step of calculating the capacity of the secondary battery based on preset information indicating a relationship between the capacity of the secondary battery and the parameter and the parameter calculated in the parameter calculation step; The method for recovering a nickel-metal hydride storage battery according to claim 1, comprising: The SOC 100 [%] of the nickel metal hydride storage battery is set as the upper limit SOC, and
When the SOC [%] lower than the upper limit SOC by the set value is set as the reference SOC,
In a low SOC region that is a region below the reference SOC, charging is performed at a preset first charging rate as an upper limit, and
3. In a high SOC region that is a region exceeding the reference SOC and below the upper limit SOC, charging is performed using a second charging rate lower than the first charging rate as the upper limit. How to recover a nickel metal hydride storage battery. The method for recovering a nickel-metal hydride storage battery according to claim 3, wherein the reference SOC is set to 70 to 90%. The method for recovering a nickel-metal hydride storage battery according to any one of claims 1 to 4, wherein the charging rate or the second charging rate is 1/3 [C] or less. When the battery capacity [Ah] of the used nickel-metal hydride storage battery is 100 [%], the SOC is 100 [%], and the battery voltage OCV [V] at SOC 100 [%] is the upper limit voltage UL [V],
When the battery voltage OCV [V] at SOC [%] lower than SOC 100 [%] by the set value is the reference voltage RV [V],
In a low SOC region that is a region below the reference voltage RV [V], charging is performed at a preset first charging rate as an upper limit, and
In a high SOC region that is a region exceeding the reference voltage RV [V] and below the upper limit voltage UL [V], charging is performed with a second charging rate lower than the first charging rate as the upper limit. How to recover a nickel metal hydride storage battery. Equipped with a charge/discharge control device for nickel-metal hydride storage batteries,
The charge/discharge control device sets SOC 100 [%] when the battery capacity [Ah] of the nickel-metal hydride storage battery used is 100 [%], and sets the battery voltage OCV [V] at SOC 100 [%] to the upper limit voltage UL [V]. ], and
When the battery voltage OCV [V] at SOC [%] lower than SOC 100 [%] by the set value is the reference voltage RV [V],
In a low SOC region that is a region below the reference voltage RV [V], charging is performed at a preset first charging rate as an upper limit, and
In a high SOC region that is a region exceeding the reference voltage RV [V] and below the upper limit voltage UL [V], charging is performed with a second charging rate lower than the first charging rate as the upper limit. Recovery device for nickel metal hydride storage batteries.

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