Method and apparatus for restoring nickel-metal hydride batteries

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

[Technical Field]

[0001] This invention relates to a method and apparatus for restoring nickel-metal hydride batteries, and more specifically, to a method and apparatus for restoring nickel-metal hydride batteries that can effectively eliminate the memory effect. [Background technology]

[0002] In recent years, nickel-metal hydride batteries have been widely used in electric vehicles, laptop computers, and homes and factories for storing electricity from off-peak hours or solar power, due to their safe operation and ability to input and output large amounts of current.

[0003] Nickel-metal hydride batteries have various applications. For example, depending on the charge and discharge conditions, repeated charging and discharging can generate electrochemically inert nickel oxide (Ni2O3H), which can lead to increased battery resistance and decreased battery capacity.

[0004] Therefore, in the invention disclosed in Patent Document 1, the current density is 100 [A / m]. 2 A battery has been proposed in which, when charging and discharging a total electrical charge of 10 kAh is performed within the charge rate (SOC, State of Charge, hereinafter sometimes simply abbreviated as "SOC") range of 20 to 80%, the amount of Ni2O3H remains below a specified level. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2011-233423 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, the inventors have found problems in the method of repeatedly performing partial charge and discharge in the intermediate SOC range such as SOC 20 to 80 [%] as disclosed in Patent Document 1 for nickel - hydrogen storage batteries, where the battery capacity may decrease. As such a cause, it is considered that the so - called memory effect of nickel - hydrogen storage batteries has occurred.

[0007] The memory effect is considered to be caused by variations in the charging of nickel hydroxide which is the positive electrode active material. In such a case, there is a so - called battery refresh method to eliminate the memory effect and restore the battery capacity. The conventional battery refresh method once completely discharges to SOC 0 [%] so that there is no nickel hydroxide that has been charged. And then, from that state, it is common technical knowledge for those skilled in the art to eliminate the memory effect by charging at a low rate so that variations in the charging of nickel hydroxide do not occur.

[0008] However, according to the analysis by the inventors' experiments, it has been found that even in the above - mentioned conventional battery refresh method which is said to restore the battery capacity, in fact, the capacity of nickel - hydrogen storage batteries decreases.

[0009] The problem to be solved by the recovery method and recovery device of the nickel - hydrogen storage battery of the present invention is to effectively eliminate the memory effect of the nickel - hydrogen storage battery.

Means for Solving the Problem

[0010] To solve the above problem, in the recovery method of the nickel - hydrogen storage battery of the present invention, in the used nickel - hydrogen storage battery, when the nickel - hydrogen storage battery is pre - charged and the state where there is no uncharged nickel hydroxide is set as SOC 100 [%], the nickel - hydrogen storage battery is charged at a charging rate set to a range including the upper limit SOC with the upper limit SOC being SOC 100 [%].

[0011] Also, the acquisition of the full capacity of SOC 100 [%] of the used nickel - hydrogen storage battery is An impedance measurement step of measuring the complex impedance of a secondary battery to be measured based on the application of alternating current power for measurement, and, among the measured complex impedances, a parameter consisting of the ratio of the difference in the measurement angular velocity between two complex impedances within the diffusion region and having different measurement angular velocities and the difference in the imaginary components of the two complex impedances. A parameter calculation step of calculating the parameter, and information set in advance, information indicating the relationship between the capacity of the secondary battery and the parameter, and a capacity calculation step of calculating the capacity of the secondary battery based on the parameter calculated in the parameter calculation step. It is also preferable to include.

[0012] Also, when the SOC of the nickel-hydrogen storage battery is set to 100 [%] as the upper limit SOC, and the SOC [%] that is lower than the upper limit SOC by a set value is set as the reference SOC, in the low SOC region, which is the region below the reference SOC, charging is performed with a preset first charging rate as the upper limit. It is also preferable to charge with a second charging rate lower than the first charging rate as the upper limit in the high SOC region, which is the region exceeding the reference SOC and below the upper limit SOC.

[0013] Also, it is preferable to set the reference SOC to 70 to 90 [%]. Also, it is preferable that the charging rate or the second charging rate is 1 / 3 [C] or less.

[0014] Also, in the method for recovering a nickel-hydrogen storage battery, when 100 [%] of the battery capacity [Ah] of the used nickel-hydrogen storage battery is set as SOC100 [%], and the battery voltage OCV [V] at SOC100 [%] is set as the upper limit voltage UL [V], and the battery voltage OCV [V] at SOC [%] that is lower than SOC100 [%] by a set value is set as the reference voltage RV [V], in the low SOC region, which is the region below the reference voltage RV [V], charging is performed with a preset first charging rate as the upper limit. 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 with a second charging rate lower than the first charging rate as the upper limit.

[0015] Furthermore, the nickel-metal hydride battery recovery device of the present invention includes a charge / discharge control device for the nickel-metal hydride battery, and the charge / discharge control device defines the state of emergency (SOC) as 100% when the battery capacity [Ah] of the used nickel-metal hydride battery is 100% [Ah], sets the battery voltage OCV [V] at SOC 100% [Ah] as the upper limit voltage UL [V], and sets the battery voltage OCV [V] at an SOC [Ah] that is a set value lower than SOC 100% [Ah] as the reference voltage RV [V], In the low SOC region, which is below the reference voltage RV[V], charging is performed up to a preset first charging rate, and in the high SOC region, which is above the reference voltage RV[V] and below the upper limit voltage UL[V], charging is performed up to a second charging rate lower than the first charging rate. [Effects of the Invention]

[0016] According to the nickel-metal hydride battery recovery method and recovery device of the present invention, the memory effect of the nickel-metal hydride battery can be effectively eliminated. [Brief explanation of the drawing]

[0017] [Figure 1] This is an OCV-SOC curve showing the relationship between the open-circuit battery voltage (OCV) and state of charge (SOC) of a nickel-metal hydride battery without capacity degradation. [Figure 2] This is an OCV-SOC curve showing the relationship between OCV and SOC for a nickel-metal hydride battery with reduced capacity. [Figure 3] This graph shows the OCV-SOC curve V1 for a nickel-metal hydride battery with reduced capacity, and the relationship between SOC and charge rate. [Figure 4] This is an OCV-SOC curve showing the relationship between the open-circuit battery voltage (OCV) and the state of charge (SOC) during charging and discharging. [Figure 5] This is a block diagram of the control device for a nickel-metal hydride battery. [Figure 6] This flowchart shows the control procedure for the nickel-metal hydride battery 10 of this embodiment. [Figure 7] This graph shows the relationship between the total discharged electricity [Ah] and the rechargeable battery capacity [Ah] of the nickel-metal hydride battery at that time, when the charge / discharge state of charge (SOC) conditions were changed in experimental examples 1-7. [Figure 8] This is a block diagram showing the configuration of a measuring device for measuring the battery electrical capacity and capacity retention rate of nickel-metal hydride batteries. [Figure 9] In this embodiment, the figure shows an example of a Nyquist plot created from the AC impedance measured for a secondary battery. [Figure 10] In this embodiment, the figure shows an example of the relationship between the reciprocal of the measured angular velocity of the AC impedance and its imaginary component in a graph. [Figure 11] This embodiment shows a graph illustrating the relationship between a parameter consisting of the ratio of the measured angular velocity and imaginary component of the AC impedance and the battery capacity. [Figure 12] This figure shows an example of a Nyquist plot created from the AC impedance measured for a battery. [Figure 13] This flowchart shows the procedure for charge and discharge control (S4) of the nickel-metal hydride battery 10 by the control device 1 of this embodiment. [Figure 14] This graph shows a comparison of battery capacity recovery by refreshing in this embodiment and the conventional technology. [Modes for carrying out the invention]

[0018] The recovery method and recovery device for the nickel-metal hydride battery of the present invention will be described below with reference to Figures 1 to 13, using a recovery method by a control device 1 for the nickel-metal hydride battery 10, which is one embodiment. The nickel-metal hydride battery 10 of this embodiment has a wide range of applications and is not limited, but for the sake of simplicity of explanation, we will illustrate a usage scenario in which the battery is charged to 100% of its State of Charge (SOC) at a specific time. For example, this could be the case in a home where the battery is charged using nighttime electricity from the power line and this electricity is used during the day. Furthermore, we will omit explanations of other charge and discharge scenarios, assuming that they do not exist.

[0019] <Technical background of this embodiment> As described in the prior art section, the generation of Ni2O3H reduces the battery capacity of the nickel-metal hydride battery 10. For this reason, in the invention disclosed in Patent Document 1, the current density is 100 [A / m]. 2 A battery has been proposed in which, when charging and discharging a total charge of 10 kAh is performed within the range of SOC 20-80%, the amount of Ni2O3H remains below a specified level.

[0020] However, as mentioned above, even if the nickel-metal hydride battery 10 is repeatedly partially charged and discharged in an intermediate SOC region such as 20-80%, the battery capacity may decrease due to the memory effect.

[0021] When the memory effect occurs and the full capacity of the nickel-metal hydride battery 10 decreases, the corresponding state of charge (SOC) will differ even if the OCV [V] remains the same. However, accurate estimation of the SOC [%] is necessary for proper charge and discharge control.

[0022] Here, Figure 1 is the OCV-SOC curve V0, which shows the relationship between the open-circuit battery voltage OCV (hereinafter sometimes simply abbreviated as "OCV") and the state of charge (SOC) of a nickel-metal hydride battery without capacity degradation. As shown in Figure 1, if the relationship between the OCV and SOC of the target nickel-metal hydride battery is obtained as the OCV-SOC curve V0, the SOC can be estimated from the OCV. In Figure 1, the OCV [V] when the SOC is 100[%] is V 100 It indicates [V]. Also, OCV is V 80 When [V] is true, the SOC can be estimated to be 80%.

[0023] Figure 2 shows the OCV-SOC curve V1, which illustrates the relationship between OCV and SOC for a nickel-metal hydride battery with reduced capacity. In nickel-metal hydride batteries, repeated partial charging and discharging in the intermediate SOC region, such as 20-80%, can reduce battery capacity. As battery capacity decreases, even with the same OCV, the actual SOC may be higher than the initial OCV-SOC curve V0, as shown in Figure 2. In Figure 1, the OCV[V] when the SOC is 80% is OCV=V 80 However, if the capacity of the nickel-metal hydride battery decreases, OCV = V, as shown in the OCV-SOC curve V1 in Figure 2. 80 When [V] is true, the SOC is actually a value exceeding 80[%].

[0024] Therefore, if we estimate the SOC to be 80% when OCV = V80[V], it means that the nickel-metal hydride battery is actually being controlled at a higher SOC[%] than 80%. When errors occur in SOC estimation in this way, the battery may be used in a high SOC region exceeding 80%, which can lead to overcharging and, in some cases, to the generation of Ni2O3H. In such cases, even a small amount of Ni2O3H generated will reduce the battery's capacity, and if the battery is continuously used based on the specified capacity (Ah), the error in SOC estimation will effectively increase, leading to further Ni2O3H generation. As a result, it may even become impossible to reuse the battery repeatedly. Thus, in order to accurately estimate SOC, it is necessary to eliminate the memory effect and recover from the decrease in nickel-metal hydride battery capacity.

[0025] <Method for refreshing a nickel-metal hydride battery according to this embodiment> Therefore, in light of this background, the inventors have developed a new method for restoring nickel-metal hydride batteries 10 (a so-called "refresh method") that is less prone to capacity degradation. This method suppresses the degradation of the nickel-metal hydride battery 10's capacity. By keeping the nickel-metal hydride battery's capacity constant, the State of Charge (SOC) can be estimated accurately. As a result, appropriate control can be performed according to the accurate SOC at that time, thus continuously suppressing capacity degradation.

[0026] <Estimation of SOC in this embodiment> As a prerequisite for the nickel-metal hydride battery control method of this embodiment, it is necessary to accurately estimate the degradation of the State of Charge (SOC) [%] of the nickel-metal hydride battery with a usage history that is to be controlled.

[0027] For precise measurement of SOC[%], it is possible to estimate it by revealing the chemical bonding state of nickel hydroxide, the positive electrode active material present on the positive electrode plate surface (to a depth of several nanometers), using methods such as X-ray photoelectron spectroscopy (XPS). However, this method requires specialized measuring equipment or destructive testing, making it not easily performed.

[0028] Simple methods include estimating the battery current [Ah] by integrating it, or analyzing changes in OCV [V]. These methods allow for non-destructive testing by measuring current and voltage. In particular, to estimate the state of charge (SOC) from the battery voltage OCV, the aforementioned OCV-SOC curve can be used to easily estimate the SOC, so there is also a method of obtaining the voltage at 100% SOC from the OCV-SOC curve. However, obtaining the battery voltage OCV at 100% SOC from the OCV-SOC curve is time-consuming. Furthermore, the accuracy of the obtained battery voltage OCV at 100% SOC is relatively low. In this embodiment, since effective control is possible by accurately obtaining the capacity at 100% SOC, a faster and more accurate acquisition of battery capacity is desired.

[0029] Therefore, the present inventors have invented a technique for estimating capacity using a Nyquist diagram created based on the measurement of complex impedance, as disclosed in Japanese Patent Application Publication No. 2018-040629. By using this method in the present invention, the battery capacity can be determined non-destructively, quickly, and accurately. Details will be described later.

[0030] <Features of the recovery method in this embodiment> In the recovery method for the nickel-metal hydride battery 10 of this embodiment, an example of use is provided in which the battery is discharged as needed and then charged to a state of charge (SOC) of 100% at a certain time.

[0031] Figure 3 shows the OCV-SOC curve V1, which illustrates the relationship between the "upper limit voltage UL [V]" and the "upper limit SOC [%]" in a nickel-metal hydride battery with reduced capacity, and a graph showing the relationship between SOC [%] and the charge rate [C].

[0032] In this embodiment shown in Figure 3, the state of charge (SOC) at 100% of the nickel-metal hydride battery 10 is defined as the "upper limit SOC" (SOC100%). The overvoltage (OCV) at the upper limit SOC is defined as the upper limit voltage (UL) [V]. In addition, an SOC that is lower than the "upper limit SOC" by a set value (e.g., 20%) (i.e., SOC80%) is defined as the "reference SOC" (reference voltage). The OCV at the reference SOC is defined as the reference voltage (RV) [V]. The "reference SOC" is preferably between 70% and 90%. 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 uniformity of charging of the positive electrode active material will not be sufficient. Therefore, although the "reference SOC" is not limited to this, it is desirable to have a value between 70% and 90%.

[0033] In the "low SOC region," which is below the "reference SOC," charging is limited to a predetermined "first charging rate C1." The "first charging rate C1" is, for example, a high rate of 3[C]. If the first charging rate C1 is less than 1[C], the overall charging efficiency will be poor. If it exceeds 3[C], localized overcharging is more likely to occur. Therefore, although not limited to this, the first charging rate C1 is preferably between 1[C] and 3[C].

[0034] On the other hand, in the "high SOC region," which is above the "reference SOC" and below the "upper limit SOC," charging is performed with a "second charging rate C2" lower than the "first charging rate C1" as the upper limit. The "second charging rate C2" is, for example, a low rate of 1 / 3[C]. While a lower second charging rate C2 is preferable for homogenizing the positive electrode active material, a somewhat higher charging rate is preferable when considering charging efficiency. Therefore, although not limited to this, in this embodiment it is set to 1 / 3[C].

[0035] Furthermore, in this embodiment, charging and discharging of the nickel-metal hydride battery 10 is performed within a charging and discharging range that does not fall below a "lower limit SOC," which is an SOC set to exceed 0% even outside of predetermined times. The "lower limit SOC" is, for example, 20%. If the lower limit SOC is too low, it may not be able to prepare for sudden discharges, and there is a risk of over-discharge. 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, although not limited to this, 20% is set as the lower limit SOC.

[0036] <Charging in the low SOC range> In the "low SOC region," which is below the "reference SOC," charging is performed up to a preset "first charging rate C1." A key feature of this embodiment is that when the SOC is 100%, all positive electrode active materials are uniformly charged. On the other hand, in this low SOC region, it is not necessary for the positive electrode active materials to be uniformly charged. Therefore, a high-rate charging rate with high charging efficiency can be permitted. For this reason, in the low SOC region of this embodiment, charging at a high rate of 3[C] is permitted.

[0037] <Charging in the high SOC range> On the other hand, charging and discharging of the nickel-metal hydride battery 10 is performed within a charge / discharge range that includes the upper limit of SOC (State of Charge) of 100%. However, charging beyond 100% SOC is not performed. This is because overcharging beyond 100% SOC increases the likelihood of oxygen generation and thus the likelihood of Ni2O3H formation.

[0038] During charging in this "high SOC region," the positive electrode active material Ni(OH)2 is converted to nickel oxyhydroxide (NiOOH). To prevent localized variations during this process, charging is performed slowly at a low rate, for example, 1 / 3[C] or less. By charging slowly at such a low rate, localized overcharging within the positive electrode is suppressed, and all positive electrode active materials are uniformly charged precisely at the upper limit of SOC, which is 100[%].

[0039] In other words, in this embodiment, "SOC 100%" means that all positive electrode active material has been uniformly charged, and there is no uncharged nickel hydroxide left in the positive electrode. That is, charging should be completed immediately at this point. If charging continues, it will result in overcharging, making it easier for oxygen (O2) to be generated in the positive electrode. When oxygen (O2) is easily generated, conditions are more likely to form Ni2O3H. Therefore, it is necessary to accurately determine the point at which SOC reaches 100%.

[0040] <Two-stage charging reaction of nickel-metal hydride batteries> Here, the charging of a nickel-hydrogen storage battery will be described with reference to FIG. 1. As shown in FIG. 1, the OCV-SOC curve V0 generally consists of portions in regions St1 to St4.

[0041] In region St1, uncharged nickel hydroxide is gradually charged at low SOC, the capacity increases, and the OCV [V] also rises. Here, since there is a large amount of uncharged nickel hydroxide, the OCV rises rapidly at the start of charging. Subsequently, the rate of increase of the OCV gradually decreases.

[0042] In region St2, it becomes the potential at which nickel hydroxide (Ni(OH)2) most easily changes to nickel oxyhydroxide (NiOOH). Therefore, since the electrical energy of charging is consumed for the energy of chemical change, the battery capacity [Ah] increases, but the OCV [V] hardly rises and becomes a graph close to horizontal.

[0043] In region St3, the uncharged nickel hydroxide decreases, and the battery voltage OCV rises as the capacity increases. At this time, the battery voltage OCV at SOC 80 [%] is V 80 [V] is shown. Also, the right end of region St3 is exactly at SOC 100 [%], and at this time, the uncharged nickel hydroxide disappears. The battery voltage OCV [V] at this time is V 100 [V] is shown.

[0044] In region St4, it is in an overcharged state, and the charging current is not used for charging nickel hydroxide but becomes the energy for oxygen generation. Therefore, even if it is charged, the battery voltage OCV does not rise, so it becomes a horizontal graph again.

[0045] If the battery capacity of the nickel-hydrogen storage battery has not decreased, an OCV-SOC curve V0 as shown in FIG. 1 can be obtained, and thus the SOC [%] can be easily estimated by measuring the OCV [V].

[0046] <Regarding the generation of Ni2O3H at low SOC> <Condition 1 for Ni2O3H generation> Here, FIG. 4 is an OCV-SOC curve showing the relationship between the open-circuit battery voltage OCV and the SOC during charging and discharging.

[0047] The first condition for the generation of Ni2O3H is as follows. As shown in FIG. 4, when repeatedly charging and discharging at a low SOC, a memory effect occurs. Then, the OCV-SOC curve Lc of the nickel-hydrogen storage battery during charging shifts to the noble side (higher potential), so that during charging, a system in which oxygen O2 is likely to be generated is formed.

[0048] On the other hand, the OCV-SOC curve Ld during discharge shifts to the base side (lower potential), so that during discharge, a system in which it is used at a low positive electrode potential is formed. When oxygen is generated at the nickel hydroxide interface of the positive electrode, a local liquid depletion state occurs at the nickel hydroxide particle interface due to the oxygen. When discharging in this state where water is insufficient, the discharge voltage shifts to the base side, and by staying at a lower positive electrode potential than normal, it approaches the Ni2O3H generation potential.

[0049] <Condition 2 for Ni2O3H generation> The second condition for the generation of Ni2O3H is as follows. In order to supplement the locally insufficient water due to the generation of oxygen, the reaction in which H2O and Ni2O3H are simultaneously generated from βNiOOH is promoted.

[0050] <Ni2O3H generation> The above conditions 1 and 2 overlap, and Ni2O3H is generated acceleratively. As a result, the capacity is reduced.

[0051] <Method for recovering the capacity of the nickel-hydrogen storage battery 10 of the present embodiment> FIG. 2 is an OCV-SOC curve V1 showing the relationship between the open-circuit battery voltage OCV and the SOC of a nickel-hydrogen storage battery in which a memory effect has occurred and the capacity has decreased.

[0052] Based on the mechanism by which Ni2O3H is rapidly generated as described above, initial localized charging and discharging is the main cause (starting point) of Ni2O3H generation. Therefore, it is necessary to prevent this. At the start of the two-stage charging reaction (≒oxygen generation voltage), there are almost no uncharged Ni(OH)2 particles. In other words, by stopping charging when the state of charge (SOC) reaches 100%, all Ni(OH)2 particles are charged, and the positive electrode active material becomes uniform. Then, by discharging from this state, the non-uniformity of the positive electrode active material, which is the cause of the memory effect, can be eliminated, and the nickel-metal hydride battery 10 is refreshed.

[0053] As a result, the initial deviation of the OCV-SOC curve can be suppressed. <Regarding capacity recovery in conventional region St4> In Figure 1, the area indicated by region St4 represents overcharging. Conventionally, there have been methods to recover the capacity of nickel-metal hydride batteries by deliberately putting them into an overcharged state (for example, Japanese Patent Publication No. 2018-14270).

[0054] The method for restoring that capacity is based on the premise that hydrogen (H2) inside the nickel-metal hydride battery has leaked out, disrupting the equilibrium of hydrogen partial pressure within the battery case. To maintain this equilibrium, hydrogen is released from the metal hydride (MH) of the negative electrode in proportion to the amount of hydrogen leakage. When hydrogen is released to the outside of the battery module in this way, the discharge capacity decreases because the discharge reserve of the negative electrode decreases.

[0055] Therefore, overcharging of the battery module is performed to increase the discharge reserve. During overcharging, since charging continues even after the uncharged portion of the positive electrode disappears, as shown in the following half-reaction formula (1), the hydroxyl group of the electrolyte is decomposed to generate oxygen. At the negative electrode, as shown in the following half-reaction formula (2), the reaction in which hydrogen is occluded in the uncharged portion of the negative electrode active material, that is, the hydrogen storage alloy, proceeds. Further, as shown in the following half-reaction formula (3), simultaneously with the reaction in which hydrogen is occluded in the hydrogen storage alloy, a reaction occurs in which metal hydride and oxygen react to generate water in the charged portion, that is, the hydrogen storage alloy that has occluded hydrogen. At this time, the metal hydride (MH) returns to the hydrogen storage alloy (M). That is, when overcharging occurs and the safety valve is not open, at the negative electrode, the reaction in which the uncharged portion is charged and the reaction in which the charged portion returns to the uncharged portion occur simultaneously.

[0056] (Positive electrode) OH - →1 / 4O2 + 1 / 2H2O + e - …(1) (Negative electrode) M + H2O + e - →MH + OH - …(2) MH + 1 / 4O2 → M + 1 / 2H2O…(3) On the other hand, oxygen is generated from the positive electrode and the internal pressure rises. When the internal pressure becomes equal to or higher than the valve opening pressure, the safety valve opens and oxygen gas is discharged to the outside. When the oxygen gas is discharged, the reaction shown in the 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 occluded hydrogen maintains the state of occluding hydrogen, and when there is an uncharged portion of the negative electrode, the reaction shown in the half-reaction formula (2) proceeds to secure the discharge reserve.

[0057] <Control in Region St4 in the Present Embodiment> In the present embodiment, there is no premise that hydrogen H2 in the nickel-hydrogen storage battery leaks to the outside and the balance of the hydrogen partial pressure in the battery case is disrupted.

[0058] Therefore, oxygen is generated from the positive electrode, causing the internal pressure to rise. When the internal pressure exceeds the valve opening pressure, the safety valve opens and oxygen gas is released to the outside. However, opening the valve has significant disadvantages, such as a decrease in the absolute amount of electrolyte.

[0059] Furthermore, the inventors have experimentally confirmed that overcharging generates oxygen (O2) at the positive electrode, and that this oxygen generation leads to the formation of Ni2O3H. For these reasons, in this embodiment, charging is immediately stopped in region St4 where the SOC exceeds 100%.

[0060] <Control device 1 for nickel-metal hydride storage batteries> Figure 5 is a block diagram of the control device 1 for the nickel-metal hydride battery 10. The solid lines in Figure 5 indicate electrical connections. The dashed lines indicate connections for control signals. The nickel-metal hydride battery 10 exemplified in this embodiment is a stationary battery for household use. For example, it is assumed to be fully charged using inexpensive nighttime electricity from the power line and discharged during the day to supply power to necessary lighting, heating and cooling, and home appliances.

[0061] Of course, the nickel-metal hydride battery of this embodiment can be used in vehicles such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHVs). It can also be used in homes and factories that perform small-scale power generation, such as solar power and wind power. Its applications are not limited. Here, we will explain using a stationary battery for home use as an example, as the charging and discharging operations are simple and the basic control method of the nickel-metal hydride battery of this embodiment is easy to understand. Here, only the common basic configuration is shown.

[0062] The control device 1 comprises a charge / discharge control device 2, a power supply device 3, a voltage measuring device 4, a current measuring device 5, a switch 6, and a load 7. <Charge / Discharge Control Device 2> The charge / discharge control device 2 communicates signals with the power supply unit 3, voltage measuring device 4, current measuring device 5, switch 6, and load 7. The voltage measuring device 4 and current measuring device 5 receive data on the OCV [V] and battery current [A] of the nickel-metal hydride battery 10. Based on this, the device transmits control signals to supply power from the power supply unit 3 and to supply power to the load 7, thereby executing the control method for the nickel-metal hydride battery 10 of this embodiment.

[0063] The charge / discharge control device 2 comprises a CPU (Central Processing Unit) 11, RAM (Random Access Memory) 12, and ROM (Read Only Memory) 13. Furthermore, it is configured as a computer equipped with a storage device 14, such as a PROM (Programmable ROM). The ROM 13 and storage device 14 store a program for the control method of the nickel-metal hydride battery 10 of this embodiment.

[0064] In addition, it is equipped with other components that are standard for a computer, such as a power supply, interface, and timer. <Power supply device 3> Power supply device 3 is a device capable of supplying power to nickel-metal hydride battery 10. In this embodiment, it corresponds to a power supply device for off-peak electricity via the power lines. The supplied power is, for example, power supplied from a charger via the power lines or regenerative power in electric vehicles (EVs). In hybrid vehicles (HVs), it corresponds to power generated by the prime mover or regenerative power. In homes and factories that use solar power generation, wind power generation, or small-scale hydroelectric power generation, it is power generated by power generation facilities including solar panels.

[0065] The power supply unit 3 has switches, voltage regulators, current regulators, inverters, etc. (not shown in the diagram) that ensure the power supplied is appropriate, and is controlled by the control device 1. <Voltage measuring device 4> The voltage measuring device 4 measures the open-circuit battery voltage (OCV) [V] of the nickel-metal hydride battery 10. In practice, a power supply 3 and a load 7 are connected, but the method is not limited as long as the OCV can be measured or estimated.

[0066] <Current measuring device 5> The current measuring device 5 measures the battery current [A] of the nickel-metal hydride battery 10. In practice, a power supply unit 3 and a load 7 are connected, but the method is not limited as long as the battery current [A] can be measured or estimated.

[0067] <Load 7> In this embodiment, load 7 corresponds to household appliances that consume electricity, such as lighting, heating and cooling systems, and home appliances. In the case of electric vehicles or hybrid vehicles, it corresponds to the motor generator for propulsion and equipment such as air conditioners. In households or factories that generate solar power, it also corresponds to the transmission of electricity sold back to the grid. Furthermore, it also includes simply discharging the nickel-metal hydride battery 10 to adjust its State of Charge (SOC).

[0068] Furthermore, although not shown in the illustration, the switch 6 provided on the load 7 also includes not only switching means but also switches, voltage regulators, current regulators, inverters, etc., which are not shown in the illustration, to ensure that the supplied power is appropriate, and is controlled by the charge / discharge control device 2.

[0069] <Procedure for restoring the nickel-metal hydride battery of this embodiment> Figure 6 is a flowchart showing the recovery procedure for the nickel-metal hydride battery 10 in this embodiment.

[0070] As mentioned above, for the sake of simplicity, the control device 1, which is the recovery device for the nickel-metal hydride battery 10 in this embodiment, is illustrated as an example of a system that stores nighttime electricity at a certain time in a home and consumes it during the day. Therefore, although exceptional charging and discharging procedures may actually be performed, these are omitted from this flowchart. The following describes the recovery method of the nickel-metal hydride battery 10 of this embodiment using the control device 1 of the nickel-metal hydride battery 10 of this embodiment. It should be noted that its use is not limited to electric vehicles (EVs), hybrid vehicles, or stationary use in homes and factories equipped with power generation facilities such as solar power generation and wind power generation. Furthermore, it goes without saying that the control procedure will differ depending on the application, and is not limited to this embodiment.

[0071] As shown in Figure 6, when the recovery procedure for the nickel-metal hydride battery 10 of this embodiment is initiated, the first step is the "complex impedance measurement (S1)" procedure, in which the complex impedance is measured to obtain the Nyquist plot of the nickel-metal hydride battery 10 to be controlled.

[0072] Next, the battery capacity at full charge (SOC 100%) is estimated and obtained based on the acquired Nyquist plot (S2). Figure 3 shows the OCV-SOC curve V1 for a nickel-metal hydride battery with reduced capacity, and a graph illustrating the relationship between SOC [%] and charge rate [C].

[0073] Next, using the battery capacity obtained when fully charged, the upper limit voltage UL [V] corresponding to the upper limit SOC = 100[%] is determined using the OCV-SOC curve V1 shown in Figure 3. Similarly, the reference voltage RV [V] corresponding to the reference SOC = 80[%] is determined. Furthermore, the lower limit voltage LL [V] corresponding to the lower limit SOC = 20[%] is determined.

[0074] Then, charging and discharging control of the nickel-metal hydride battery 10 is performed based on the "upper voltage UL [V]" corresponding to the "upper SOC [%]", the "reference voltage RV [V]" corresponding to the "reference SOC", and the "lower voltage LL [V]" corresponding to the "lower SOC" (S3).

[0075] <Measurement of complex impedance (S1)> The following describes in detail the measurement of complex impedance (S1). Here, we will explain the estimation of capacity by measuring the complex impedance of the nickel-metal hydride battery 10 that is the target of control. In general, 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, thereby achieving what is known as positive electrode regulation. Therefore, unless there is a capacity difference, the battery electrical capacity, which is the amount of electricity that can be charged to the battery, is usually equal to the positive electrode electrical capacity. In addition, the battery electrical capacity of the nickel-metal hydride battery 10 tends to decrease due to degradation from the battery electrical capacity in the initial state, which is the state at the start of use. The ratio of the battery electrical capacity in the post-use state to the battery electrical capacity in the initial state is called the "capacity retention rate". The capacity retention rate is calculated based on the measured battery electrical capacity when the battery electrical capacity of the nickel-metal hydride battery 10 is measured. For example, the capacity retention rate can be used to calculate the State of Charge (SOC) of the nickel-metal hydride battery 10, to determine degradation, or to control the charging and discharging of the battery.

[0076] <Measuring device 30> Figure 8 is a block diagram showing the configuration of a measuring device 30 for measuring the battery electrical capacity [Ah] and capacity retention rate [%] of a nickel-metal hydride battery 10.

[0077] As shown in Figure 8, the nickel-metal hydride battery 10, which is the target of battery capacity measurement, is connected to a load or charger via a switch (not shown). The nickel-metal hydride battery 10 is charged and discharged when the switch is closed and connected to the load, etc., and the charge level is changed. On the other hand, when the complex impedance of the nickel-metal hydride battery 10 is measured, the switch is opened and the battery is disconnected from the load, etc.

[0078] A measuring power supply 20 is connected between the electrodes of the nickel-metal hydride battery 10 to supply alternating current as AC power to the nickel-metal hydride battery 10. A voltage measuring instrument 21 is also connected to measure the voltage between the electrodes of the nickel-metal hydride battery 10, and a current measuring instrument 22 is connected to measure the current flowing between the measuring power supply 20 and the nickel-metal hydride battery 10.

[0079] The measuring power supply 20 generates an alternating current at a predetermined measurement frequency and outputs this generated alternating current between the electrodes of the nickel-metal hydride battery 10. The measuring power supply 20 is also capable of changing the measurement frequency of the alternating current. The measuring power supply 20 has a set output current and a frequency range for the measurement frequency, and outputs an alternating current of this set output current as a measurement frequency that changes within the same set frequency range. The set frequency range is, for example, from 100 kHz on the high frequency side to 1 mHz on the low frequency side. However, it is not limited to this, and the high frequency side may be higher than 100 kHz, and the low frequency side may be lower than 1 mHz.

[0080] <Nyquist diagram> Figure 12 shows an example of a Nyquist plot created from the AC impedance measured for the nickel-metal hydride battery 10. The "linear region da" within the "diffusion region d" shown in Figure 12 may be the target frequency range, for example, from 0.1 [Hz] to 0.01 [Hz]. Alternatively, two or more different frequencies within the "diffusion region d" may be output, for example, a frequency between 0.1 [Hz] and 0.01 [Hz]. As mentioned above, it is clear that angular velocity and frequency have the relationship "angular velocity = 2π × frequency," so for the sake of explanation, both angular velocity and frequency will be used in the explanation.

[0081] The measuring power supply 20 outputs signals to the measuring device 30 regarding the set value of the output AC current and the set value of the measurement frequency. The measuring power supply 20 also switches the output and stop of the AC current in response to the output start signal and output stop signal input from the measuring device 30.

[0082] <Voltage Measuring Instrument 21> The voltage measuring instrument 21 outputs a voltage signal corresponding to the voltage measured between the electrodes of the nickel-metal hydride battery 10 to the measuring device 30.

[0083] <Current measuring device 22> The current measuring instrument 22 outputs a current signal to the measuring device 30 that corresponds to the current measured between the measuring power supply 20 and the nickel-metal hydride battery 10.

[0084] <Measuring device 30> The measuring device 30 measures the battery capacity and battery capacity retention rate of the nickel-metal hydride battery 10. The measuring device 30 may also display or output the measured battery capacity and battery capacity retention rate of the nickel-metal hydride battery 10 to an external source. For example, an external battery control device (not shown) may perform charge and discharge control on the nickel-metal hydride battery 10 according to the battery capacity output from the measuring device 30.

[0085] The measuring device 30 receives a voltage signal from the voltage meter 21, obtains the voltage between the terminals of the nickel-metal hydride battery 10 from the input voltage signal, receives a current signal from the current meter 22, and obtains the current flowing between the measuring power supply and the nickel-metal hydride battery 10 from the input current signal. The measuring device 30 obtains the AC current output setting and the output measurement frequency from the signal input from the measuring power supply 20.

[0086] Furthermore, the measuring device 30 includes a processing unit 40 that performs calculation processing related to measuring the current battery capacity of the nickel-metal hydride battery 10, and a storage unit 50 that holds information used in the calculation process of the battery capacity of the nickel-metal hydride battery 10.

[0087] <Storage section 50> The storage unit 50 is a non-volatile storage device such as a hard disk or flash memory, and holds various types of data. In this embodiment, the storage unit 50 holds correlation data 51 between parameters and capacity required to calculate the battery electrical capacity, and calculation data 52. The calculation data 52 includes the initial state of the nickel-metal hydride battery 10, etc.

[0088] <Processing section 40> The processing unit 40 includes a microcomputer composed of a CPU, ROM, RAM, etc. The processing unit 40 performs various processes by, for example, executing various programs stored in ROM and RAM using the CPU. In this embodiment, the processing unit 40 performs processes to calculate the battery electrical capacity and the battery capacity retention rate. The processing unit 40 can also utilize the voltage, current, measurement frequency, etc., acquired by the measuring device 30. Furthermore, the processing unit 40 can exchange data with the storage unit 50.

[0089] The processing unit 40 includes an impedance measurement unit 41 for measuring the complex impedance Z, a Nyquist plot creation unit 43 for creating a Nyquist plot, a parameter calculation unit 44 for calculating parameters, and a capacity calculation unit 45 for calculating the battery electrical capacity and battery capacity maintenance rate.

[0090] <Impedance measurement section 41> The impedance measurement unit 41 performs a process (impedance measurement step) to measure the complex impedance Z of the nickel-metal hydride battery 10. The impedance measurement unit 41 instructs the measurement power supply 20 to start and end the measurement. The impedance measurement unit 41 measures the complex impedance Z of the nickel-metal hydride battery 10 based on the voltage and current acquired between the start and end of the measurement. The unit of complex impedance Z is [Ω] (ohm). The complex impedance Z is expressed by equation (1) using its vector components, the real component Zr [Ω] and the imaginary component Zi [Ω]. Note that "j" is the imaginary unit. Hereafter, the unit [Ω] will be omitted.

[0091]

number

[0092] <Nyquist diagram creation section 43> The Nyquist plot generation unit 43 generates a Nyquist plot based on the complex impedance Z at multiple measurement frequencies, using the vector components, which are the real component Zr and the imaginary component Zi.

[0093] Figure 9 is a graph showing an example of a Nyquist plot created from the AC impedance measured for a secondary battery in this embodiment. For example, as shown in Figure 9, the Nyquist plot creation unit 43 creates impedance curves L21 and L22 as Nyquist plots on a complex plane where the horizontal axis is the real axis and the vertical axis is the imaginary axis. Impedance curve L21 is an example of a Nyquist plot corresponding to the nickel-metal hydride battery 10 in its initial state, and impedance curve L22 is an example of a Nyquist plot corresponding to the nickel-metal hydride battery 10 in its used state. Each impedance curve L21 and L22 plots the magnitudes of the real component Zr and the imaginary component Zi of the complex impedance Z on the complex plane. These impedance curves L21 and L22 are based on the complex impedance Z measured by changing the measurement frequency of the AC current supplied from the measuring power supply 20 to the nickel-metal hydride battery 10.

[0094] <Impedance curves L21, L22> In Figure 9, the dots and circles in the impedance curves L21 and L22 represent a single measurement frequency. In Figure 2, the lower side represents the high frequency side, and the upper side represents the low frequency side. The impedance curves L21 and L22 change depending on the state of charge (SOC) and battery temperature of the nickel-metal hydride battery 10. They also change depending on the type of battery, such as nickel-metal hydride secondary batteries and lithium-ion secondary batteries. Furthermore, even within the same battery type, they change if the number of cells, capacity, etc., differ.

[0095] Here, with reference to Figures 9 and 12, the impedance curves L21 and L22 of the nickel-metal hydride battery 10 will be described in detail. <Regarding areas a-d> As shown in Figure 9, the impedance curves L21 and L22 of the nickel-metal hydride battery 10 are divided into multiple regions corresponding to the characteristics of the nickel-metal hydride battery 10. These multiple 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. "Region a" is the circuit resistance region corresponding to the circuit resistance. "Region b" is the solution resistance region corresponding to the solution resistance. "Region c" is the reaction resistance region corresponding to the complex impedance caused by the reaction resistance. "Diffusion region d" is the region corresponding to the approximately linear diffusion resistance. Circuit resistance is the impedance of wiring, etc., consisting of contact resistance in the active material and current collector. Solution resistance is the resistance of electron movement, such as the resistance when ions move in the electrolyte in the separator. Reaction resistance is the resistance of charge transfer in electrode reactions. Diffusion resistance is the impedance involving material diffusion.

[0096] Furthermore, since each resistor influences the others, it is difficult to divide each region a, b, c, and d into parts influenced only by each resistor. However, at least the general behavior of each region a, b, c, and d of the impedance curves L21 and L22 is determined by the resistance component that has the greatest influence on each region. For example, "region c" is greatly influenced by the characteristics of the negative electrode, and "diffusion region d" is greatly influenced by the characteristics of the positive electrode.

[0097] <Analysis of Impedance Curves> In simple terms, the impedance curves L21 and L22 of the nickel-metal hydride 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 "diffusion region d", the impedance of the positive electrode changes significantly, while the change in the impedance of the negative electrode is small. In other words, "diffusion region d" of the impedance curves L21 and L22 is a region where the influence of the impedance of the positive electrode is large, and it can be said that the state of the positive electrode is reflected. In contrast, in the frequency range corresponding to "region c", the impedance of the negative electrode changes significantly, while the change in the impedance of the positive electrode is small. In other words, "region c" of the impedance curves L21 and L22 is a region where the influence of the impedance of the negative electrode is large, and it can be said that the state of the negative electrode is reflected.

[0098] According to impedance curves L21 and L22, the frequency range corresponding to "diffusion region d" is 0.1 Hz or less, and Figure 2 shows it down to 0.01 Hz. 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 "diffusion region d" can be greater or less than 0.1 Hz, as long as it is in a frequency range lower than "region c".

[0099] <Diffusion area d> Furthermore, as shown in Figure 12, the "diffusion region d" includes the "linear region da," the "vertical region dc," and the "region db." The "linear region da" is the region where the ratio of the change in the imaginary component to the change in the real component is within a predetermined range close to "1." In other words, it is the range close to an angle of 45° in the figure, or to put it another way, the range where the absolute value of the rate of change of the imaginary component relative to the real component of the complex impedance is 0.5 or greater and 2 or less. Therefore, there is a correlation between the imaginary and real components in the "linear region da." The "vertical region dc" is the region where only the imaginary component changes significantly relative to the real component, so the graph changes almost vertically in the figure. In other words, it is the range close to an angle of 90° in the figure. The "region db" is the boundary and surrounding region where the transition occurs from the "linear region da" to the "vertical region dc."

[0100] Incidentally, due to the characteristics of nickel-metal hydride batteries and the practicality of the measured values, the measurement of the complex impedance of nickel-metal hydride batteries 10 is generally completed in the "linear region da". Furthermore, the measurement frequency at which the "vertical region dc" occurs in nickel-metal hydride batteries tends to be lower than the measurement frequency at which the "vertical region dc" occurs in lithium-ion batteries. In addition, in order to measure the "vertical region dc" of nickel-metal hydride batteries 10 more reliably, it is necessary to prepare the measurement environment, such as raising the battery temperature, and to set the measurement frequency to a frequency much lower than 0.01 Hz, which requires more time for measurement. Moreover, since the measurement frequency at which the "vertical region dc" occurs cannot be known in advance, the time wasted during measurement can be long. And the difficulty in estimating the time required for measurement when attempting to measure the value of the "vertical region dc" makes it impractical to measure the value of the "vertical region dc" of nickel-metal hydride batteries 10 while they are in use.

[0101] <Parameter calculation unit 44> As shown in Figure 8, the parameter calculation unit 44 is located within the "diffusion region d" and calculates the ratio of the difference in the measured acceleration of two complex impedances with different measurement frequencies to the difference in the imaginary components of the two complex impedances (parameter calculation step). Here, the two complex impedances are "Z1" and "Z2", the imaginary component of complex impedance "Z1" is "Zi1", the measurement frequency is "f1", the imaginary component of complex impedance "Z2" is "Zi2", and the measurement frequency is "f2".

[0102] More specifically, the parameter calculation unit 44 calculates the difference between two values. One is the difference (change) in the measured angular velocity of the two complex impedances "Z1" and "Z2" of the nickel-metal hydride battery 10 when they are measured, "Δω = 2π × (f1 - f2)". The other is the difference (change) in the imaginary components of the two complex impedances, "ΔZi = Zi1 - Zi2".

[0103] Figure 10 is a graph showing an example of the relationship between the reciprocal of the measured angular velocity of the AC impedance and the imaginary component in this embodiment. As shown in Figure 10, the difference between the reciprocals of the measured angular velocities of the two complex impedances "Δ(ω) -1 ) and the difference between the imaginary components of the two complex impedances is "ΔZi", and the parameter "Q" is based on this. D The parameter "Q" is calculated. Logically, the parameter "Q" is used to calculate the value of "Q". D " can be found as shown in equation (2). In other words, equation (2) is "Δ(ω -1 The reciprocal of the ratio of "ΔZi" to ")" is the parameter "Q" D This indicates that the parameter "Q" is true. D Since it is preferable to calculate " as a positive value, if necessary, "Δ(ω -1 You can also use ")" or "ΔZi" as absolute values.

[0104]

number

[0105] As mentioned above, the parameter "Q D" can theoretically be calculated 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 the parameter using the equation shown on the right side of equation (3). In other words, equation (3) is the difference between the reciprocals of the measured angular velocities of two complex impedances with different measurement frequencies "Δ(ω -1 The parameter "Q" is the ratio of the difference "ΔZi" between the imaginary components of the two complex impedances. D This indicates that it is ".

[0106]

number

[0107] The capacity calculation unit 45 uses the correlation data 51 between parameters and capacity, which is information pre-set in the storage unit 50, and the parameter "Q" calculated by the parameter calculation unit 44. D Based on this, the battery capacity of the nickel-metal hydride battery 10 is calculated (capacity calculation step).

[0108] <Correlation data between parameters and capacity 51> Figure 11 is a graph showing the relationship between the parameter, which consists of the ratio of the measured angular velocity and imaginary component of the AC impedance, and the battery capacity in this embodiment. The correlation data 51 between the parameter and capacity will be explained with reference to Figure 11. The correlation data 51 between the parameter and capacity is the complex impedance Z of the nickel-metal hydride battery 10 within the "diffusion region d" of the parameter "Q D This information shows the relationship between this and the battery capacity of the nickel-metal hydride battery 10.

[0109] Figure 11 shows graph L41 as a calibration curve, which is an example of correlation data 51 between parameters and capacity. Specifically, graph L41 shows the parameter "Q D )=(ΔZi / Δ(ω -1 )) -1This graph shows the relationship between the complex impedance and the battery capacity [Ah] of the nickel-metal hydride battery 10. Graph L41 was created based on the complex impedance and battery capacity obtained in advance from a nickel-metal hydride battery 10 manufactured to the same specifications as the nickel-metal hydride battery 10 being measured. Note that graph L41 may be created from measured values, or from a combination of measured values, theory, and experience, or from information created based on theory and experience. Furthermore, since graph L41 changes with temperature, it may be set for predetermined temperature intervals. By having different graphs L41 for predetermined temperature intervals, the capacity of the secondary battery can be calculated and measured more appropriately.

[0110] In other words, the correlation data 51 between parameters and capacity held in the memory unit 50 in Figure 8 is information pre-set in the memory unit 50. This is related to the parameter "Q" in the complex impedance Z within the "diffusion region d" of the nickel-metal hydride battery 10. D This information shows the relationship between this and the battery capacity of the nickel-metal hydride battery 10.

[0111] <Reasons why battery capacity can be calculated> Referring to Figures 9 to 11, the parameter "Q" relating to the complex impedance within the "diffusion region d" of the nickel-metal hydride battery 10 in this embodiment. D This explains why the battery capacity can be calculated from this.

[0112] When using a nickel-metal hydride battery 10 as a power source, it is necessary to accurately calculate its State of Charge (SOC), and it is better to calculate it while considering the effects of SOC degradation of the nickel-metal hydride battery 10. Therefore, conventional technology measures the degree of degradation of a secondary battery based on the value of the imaginary component in the lower frequency "vertical region dc" within the "diffusion region d". In this case, the "vertical region dc" is created by controlling the temperature so that the battery temperature is between 40°C and 70°C, but such temperature control is difficult to perform on a battery in use. Furthermore, conventional technology requires the measurement frequency to be less than 10 mHz, preferably less than 3 mHz. At such measurement frequencies, measurement takes approximately 1.7 minutes at 10 mHz and approximately 5.6 minutes at 3 mHz, so it was not suitable for measuring a nickel-metal hydride battery 10 in use, whose SOC changes.

[0113] Therefore, the inventors diligently researched methods for calculating battery capacity that are less affected by battery temperature, and discovered the technology shown in this embodiment. This technology makes it possible to suppress the effect of battery temperature by using the difference between two complex impedances. Furthermore, this technology eliminates the need to use the "vertical region dc" for calculating the capacity retention rate, which is less likely to occur in lithium-ion secondary batteries and even less likely in nickel-metal hydride secondary batteries. As a result, the time required for measurement can be shortened to a practical length, for example, "about 1.7 minutes".

[0114] Figure 9 shows, as described above, an example of a Nyquist plot of the impedance curve L21 corresponding to the nickel-metal hydride battery 10 in its initial state, and an example of a Nyquist plot of the impedance curve L22 corresponding to the nickel-metal hydride battery 10 in its post-use state. Here, for example, the post-use state is the state after the nickel-metal hydride battery 10 in its initial state has undergone 1000 charge-discharge cycles in a 45°C environment with a SOC of 40% to 80%.

[0115] Comparing impedance curves L21 and L22, we see that in the "diffusion region d", impedance curve L22 has a smaller change in the imaginary component Zi relative to the real component Zr, resulting in a smaller slope of the graph compared to impedance curve L21.

[0116] Figure 10 shows the reciprocal of the measured angular velocity in the "diffusion region d", "ω -1 Graphs L31 and L32 are shown, illustrating the relationship between the complex impedance and the imaginary component "Zi". Graph L31 corresponds to the nickel-metal hydride battery 10 in its initial state, and graph L32 corresponds to the nickel-metal hydride battery 10 in its used state. In this case, graph L32 is the reciprocal of the measured angular velocity "ω" for graph L31. -1 The change in the imaginary component Zi for "" is "ΔZr / Δ(ω -1 The value of ) is large, and the slope of the graph is steep. Therefore, the change "ΔZr / Δ(ω -1 The parameter "Q" is obtained as the reciprocal of ")". D "This means that graph L32 is smaller than graph L31. In other words, the parameter "Q" D "The state after use is smaller compared to the initial state of the nickel-metal hydride battery 10."

[0117] Then, as shown in Figure 11, graph L41 shows the relationship between complex impedance and battery capacitance, with parameter "Q" D )=(ΔZi / Δ(ω -1 )) -1 The relationship between this and the battery capacity of the nickel-metal hydride battery 10 will be shown.

[0118] <Calculation process for capacity retention rate> The calculation process for the capacity retention rate of the measuring device 30 in this embodiment will be described along with its operation.

[0119] First, the storage unit 50 pre-stores information corresponding to graph L41 shown in Figure 11 as correlation data 51 between parameters and capacity. Next, the measuring device 30 measures the complex impedance of the nickel-metal hydride battery 10 using the impedance measuring unit 41. At this time, the range of the measurement frequency is set so that a "diffusion region d" appears in the Nyquist diagram. For example, two measurement frequencies f1 and f2 are set to two points between 0.1 Hz and 0.01 Hz. For example, it is assumed that measurement frequency f1 > measurement frequency f2.

[0120] <Nyquist diagram creation section 43> The Nyquist plot generation unit 43 creates a Nyquist plot based on the complex impedance measured by the impedance measurement unit 41 and the measurement frequency at that time. The Nyquist plot generation unit 43 also identifies a "diffusion region d" from the created Nyquist plot and obtains the imaginary components "Zi1" and "Zi2" of the complex impedance corresponding to the two measurement frequencies "f1" and "f2" included in the identified "diffusion region d".

[0121] The parameter calculation unit 44 obtains two measurement frequencies "f1" and "f2" and the corresponding imaginary components of the complex impedance "Zi1" and "Zi2" from the Nyquist plot creation unit 43. Then it calculates the difference in measured angular velocity "Δω = 2π × (f1 - f2)" and the difference in the imaginary components "ΔZi = Zi1 - Zi2". Then it calculates the reciprocal of the calculated difference in measured angular velocity "Δ(ω -1 Apply the difference between the imaginary component "ΔZi" and "Q" to equation (2) or equation (3) to obtain the parameter "Q D Calculate ".

[0122] The capacity calculation unit 45 calculates the parameter "Q" calculated by the parameter calculation unit 44. D The acquired parameter "Q" is obtained along with the acquired parameter "Q D The parameter "Q" is applied to graph L41 (information on the correlation data 51 between parameters and capacity) stored in memory unit 50 to obtain the battery electrical capacity. D The larger the value of "Q", the larger the battery capacity. D If the value is small, the battery capacity is small. In this way, the battery capacity of the nickel-metal hydride battery 10 is measured by the measuring device 30.

[0123] Further, the capacity calculation unit 45 compares the acquired battery electrical capacity with the initial-state battery electrical capacity of the nickel-hydrogen storage battery 10 set in the calculation data 52, and calculates a capacity maintenance rate with respect to the initial-state battery electrical capacity. For example, the capacity calculation unit 45 calculates "[(acquired battery electrical capacity / initial-state battery electrical capacity) × 100]" [%] as the capacity maintenance rate. In this way, the battery capacity of the nickel-hydrogen storage battery 10 is measured by the measuring device 30.

[0124] In "Estimate full charge capacity (S2)", the full charge capacity [Ah] is accurately estimated by the above procedure. <Procedure of charge / discharge control (S3)> FIG. 13 is a flowchart showing the procedure of charge / discharge control (S3) of the nickel-hydrogen storage battery 10 by the control device 1 of the nickel-hydrogen storage battery according to the present embodiment. After accurately estimating the full charge capacity [Ah] in the procedure of "Estimate full charge capacity (S2)", the procedure of charge / discharge control (S3) of the nickel-hydrogen storage battery 10 is performed.

[0125] The procedure of charge / discharge control (S3) of the nickel-hydrogen storage battery 10 is performed by the control device 1 of the nickel-hydrogen storage battery 10 according to the procedure of the flowchart shown in FIG. 13. Hereinafter, the procedure of charge / discharge control (S3) of the nickel-hydrogen storage battery 10 according to the present embodiment will be described with reference to FIG. 13.

[0126] <Obtain OCV-SOC curve (S31)> After accurately estimating the full charge capacity [Ah] in "Estimate full charge capacity (S2)", next, the OCV-SOC curve V1 (see FIG. 3) is obtained. This is to obtain the "upper limit voltage UL [V]" corresponding to the "upper limit SOC [%]", the "reference voltage RV [V]" corresponding to the "reference SOC", the "lower limit voltage LL [V]" corresponding to the "lower limit SOC", and the like.

[0127] The control device 1 acquires the OCV-SOC curve V1 of the nickel-metal hydride battery 10 to be controlled. The OCV-SOC curve V1 is obtained by charging from the fully discharged state of SOC0 [%] at a low rate of 1 / 3 or less, integrating the charging current, estimating the SOC from the full charge capacity [Ah], and recording the OCV at that time. In this OCV-SOC curve V1, the OCV at the time of SOC100 [%] when the full charge capacity [Ah] is charged is read and stored as the "upper limit voltage UL [V]". Also, in this OCV-SOC curve, the "reference voltage RV [V]" corresponding to the "reference SOC", the "lower limit voltage LL [V]" corresponding to the "lower limit SOC", etc. are acquired and stored.

[0128] <Set the OCV at SOC100 [%] as the upper limit voltage UL [V] (S32)> Then, the control device 1 of the nickel-metal hydride battery sets the OCV at the time of SOC100 [%] acquired in the procedure of "acquisition of OCV-SOC curve (S31)" as the "upper limit voltage UL [V]". Similarly, the "reference voltage RV [V]" and the "lower limit voltage LL [V]" are set.

[0129] <Start control of nickel-metal hydride battery (S33)> When the above preparation stage is completed, the control device 1 of the nickel-metal hydride battery 10 performs charge-discharge control (S33).

[0130] <Should it be charged? (S34)> The control device 1 of the nickel-metal hydride battery 10 determines whether or not to charge (S34). What is illustrated in this embodiment is a mode of charging at a fixed time every day. Therefore, it is determined whether or not it is the time to charge. If it is not time to charge (S34: NO), it becomes a standby loop until it is time to charge. Then, when it is time to charge (S34: YES), the current voltage PV [V] is acquired (S35).

[0131] <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 by the voltage measurement device 4 (Fig. 5) (S35). Then, the CPU 11 estimates the SOC [%] of the current nickel-hydrogen storage battery 10 from the voltage PV [V], which is the current OCV of the nickel-hydrogen storage battery 10, by the OCV-SOC curve V1.

[0132] <Is it the low SOC region? (S36)> Compare the current voltage PE [V] with 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 it is the low SOC region (S36: YES).

[0133] <Charge at 3 [C] (S37)> When the current SOC is 80 [%] or less and it is the low SOC region (S36: YES), since it is the low SOC region, charge at the first charge rate 3 [C], which is the high rate (S37).

[0134] <Is PV ≤ upper limit voltage UL [V]? (S38)> Compare the current voltage PE [V] with 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 exceeds 80 [%], that is, it is not the low SOC region (S36: NO).

[0135] Next, if the voltage PV [V] does not exceed the upper limit voltage UL [V] (S38: YES), continue charging at the second charge rate 1 / 3 [C], which is the low rate (S39). <Charging completed (S40)> When the voltage PV [V] exceeds the upper limit voltage UL [V] (S38: NO), since the SOC will exceed 100%, immediately stop charging (S40). Note that the recovery method of the nickel-hydrogen storage battery in this embodiment is completed when the charging is completed (S40).

[0136] <Discharge is allowed at 3 [C] or less (S41)> Once charging is complete (S40), discharge is permitted at 3[C] or less (S41). Note that this flowchart only explains the general operation. For example, it does not explain emergency charging due to a sudden drop in OCV or charging other than normal charging, but it goes without saying that such procedures may be included.

[0137] <Is it over? (S42)> Unless the operation of the nickel-metal hydride battery itself is terminated (S42: YES → Termination), if the operation of the nickel-metal hydride battery is not terminated (S42: NO), the system returns to the charging standby state in S34, and the procedures from S35 to S42 are repeated.

[0138] <Battery capacity is restored by refreshing in this embodiment> Figure 14 is a graph comparing the battery capacity recovery by refreshing using this embodiment and the conventional technology. This graph shows the battery capacity percentage CR[%] of the nickel-metal hydride battery 10 before refreshing. It also shows the battery capacity percentage CR[%] of the nickel-metal hydride battery 10 after refreshing using the recovery method of this embodiment. And it shows the battery capacity percentage CR[%] of the nickel-metal hydride battery 10 after refreshing using the conventional method.

[0139] Here, in this application, "battery capacity ratio CR[%]" refers to the ratio [%] of the battery capacity [Ah] of the nickel-metal hydride battery 10 being measured, when the battery capacity [Ah] of an unused nickel-metal hydride battery 10 is set to 100[%]. Therefore, it is a different concept from SOC[%], which is the relative charge rate of the nickel-metal hydride battery 10 at that point in time relative to a full charge. "Battery capacity ratio CR[%]" is defined as follows: It is the ratio value obtained by comparing the absolute value of the fully charged battery capacity [Ah] of the nickel-metal hydride battery 10 to be measured with the absolute value of the fully charged battery capacity [Ah] of a reference unused nickel-metal hydride battery 10.

[0140] First, in the nickel-metal hydride battery 10 with a usage history, the battery capacity ratio CR[%] decreased to 70[%] compared to the unused nickel-metal hydride battery 10 due to use without any specified usage conditions. Here, it is presumed that the memory effect occurred, causing the battery capacity ratio CR[%] to decrease.

[0141] Next, the battery capacity [%] of the nickel-metal hydride battery 10 with such a usage history is shown after being completely discharged to SOC 0[%] at a low discharge rate of 1 / 3C and performing a single conventional refresh. As shown in the graph, the battery capacity ratio CR[%] recovered to 80[%] after this conventional refresh method.

[0142] Next, the battery capacity ratio CR[%] of the nickel-metal hydride battery after refreshing in this embodiment is shown. Here, as described above, a nickel-metal hydride battery whose battery capacity ratio CR[%] has decreased to 70[%] of the unused nickel-metal hydride battery 10 was refreshed only once according to the flowchart shown in Figure 13. Specifically, it was charged at 1C until the SOC reached 80[%], then charged at a low rate of 1 / 3C until the SOC reached 100[%], and then the charging was terminated. As shown in the graph in Figure 14, the battery capacity ratio CR[%] recovered to 85[%] by refreshing using this conventional refresh method. In this embodiment, charging was terminated at a low rate of 1 / 3C until the SOC reached 100[%].

[0143] Thus, through experiments, we were able to demonstrate that the refresh method of this embodiment can effectively restore the capacity of a nickel-metal hydride battery 10 that has deteriorated. (Experimental example of this embodiment) Figure 7 is a graph showing the relationship between the total discharged electricity [Ah] and the rechargeable battery capacity [Ah] of the nickel-metal hydride battery 10 at that time, when the state of charge (SOC) conditions for charging and discharging are changed in experimental examples 1 to 7. In the experiment, charging and discharging were repeatedly performed at a charge / discharge rate of 1 / 3 [C] within the specified SOC range.

[0144] <Experimental Example 1> Experimental Example 1, shown in Figure 7, illustrates the relationship between the total discharge amount [Ah] and the battery capacity [Ah] in this embodiment described above. As shown here, the charge / discharge state of charge (SOC) range was set to 100-20% and the range was set to ΔSOC = 80%. Here, "ΔSOC" represents the difference between the maximum and minimum values ​​of SOC [%]. During charging, the battery was charged up to the upper limit voltage UL [V], ensuring that the SOC always reached 100%. In this case, it was found that the battery capacity [Ah], which was approximately 5.2 [Ah] at the time of manufacture, did not decrease even when the total discharge amount [Ah] increased.

[0145] <Experimental Example 2> Next, in Experimental Example 2, the charge-discharge State of Charge (SOC) range is set to 100-40%. Then, when this range is reduced to ΔSOC = 60%, the SOC is always set to 100% during charging. In this case, it was found that the battery capacity [Ah] does not decrease even when the total discharge amount [Ah] increases, even though the initial battery capacity is approximately 3.9 [Ah].

[0146] <Experimental Example 3> Furthermore, in Experimental Example 3, the charge-discharge SOC range was set to 100-60%, and ΔSOC was further reduced to 40%. Even in this case, if the SOC was always set to 100% during charging, it was found that the battery capacity [Ah] did not decrease even as the total discharge amount [Ah] increased, maintaining the initial battery capacity of approximately 2.6 [Ah].

[0147] <Experimental Example 4> In Experimental Example 4, as in Experimental Example 1, ΔSOC = 80[%] was set, but with an upper limit of SOC 90[%] and a lower limit of SOC 10[%]. During charging, the battery was always charged to achieve an SOC of 90[%]. In this case, the battery capacity [Ah], which was approximately 5.2[Ah] at the time of manufacture, decreased as the total discharge amount [Ah] increased. As shown in Figure 7, the charging capacity of the battery, which was initially approximately 5.2[Ah], decreased to approximately 4.8[Ah] when the total discharge amount [Ah] reached 2000[Ah]. Furthermore, it decreased to approximately 4.2[Ah] when the total discharge amount [Ah] reached 4000[Ah]. Furthermore, it decreased to approximately 3.5[Ah] when the total discharge amount [Ah] reached 6000[Ah]. Furthermore, the total discharged electrical charge [Ah] decreased to approximately 3.2 [Ah] when the total discharged electrical charge [Ah] reached 8000 [Ah]. From this, it was confirmed that charging and discharging without charging to SOC 100 [%] results in a decrease in battery capacity [Ah] with use.

[0148] <Experimental Example 5> In Experimental Example 5, as in Experimental Example 1, ΔSOC = 80[%] was set, but with SOC 80[%] as the upper limit and SOC 0[%] as the lower limit. During charging, the battery was always charged to reach SOC 80[%]. In this case, the battery capacity [Ah], which was approximately 5.2[Ah] at the time of manufacture, decreased as the total discharge amount [Ah] increased. As shown in Figure 7, the charging capacity of the battery, which was initially approximately 5.2[Ah], dropped sharply to approximately 2.6[Ah] when the total discharge amount [Ah] reached 2000[Ah]. From this, it was confirmed that charging and discharging without charging up to SOC 100[%] results in a decrease in battery capacity [Ah] with use. In particular, the battery capacity decreased significantly compared to Experimental Example 4.

[0149] The inventors of this invention particularly focused on the fact that in Experimental Example 5, charging and discharging are performed within a range that includes SOC 0%. Conventionally, it was thought that refreshing a nickel-metal hydride battery 10 could be done by completely discharging it to SOC 0% and then slowly charging it at a low charge rate.

[0150] However, as described above and shown in Figure 7, the inventors have found that even when passing through SOC0[%], which was considered effective in eliminating the memory effect by those skilled in the art, the battery capacity decreases significantly.

[0151] <Experimental Example 6> In Experimental Example 6, as in Experimental Example 2, ΔSOC = 60[%] was set, but with an upper limit of SOC 70[%] and a lower limit of SOC 10[%]. During charging, the battery was always charged to achieve an SOC of 70[%]. In this case, the battery capacity [Ah], which was approximately 3.8[Ah] at the time of manufacture, decreased as the total discharge amount [Ah] increased. As shown in Figure 7, the charging capacity of the battery, which was initially approximately 3.8[Ah], decreased to approximately 4.8[Ah] when the total discharge amount [Ah] reached 2000[Ah].

[0152] <Experimental Example 7> In Experimental Example 7, as in Experimental Example 3, ΔSOC = 40[%] was set, but with an upper limit of SOC 50[%] and a lower limit of SOC 10[%]. During charging, the battery was always charged to achieve an SOC of 50[%]. In this case, the battery capacity [Ah], which was approximately 2.6[Ah] at the time of manufacture, decreased as the total discharge amount [Ah] increased. As shown in Figure 7, the charging capacity of the battery, which was initially approximately 2.6[Ah], decreased to approximately 1.1[Ah] when the total discharge amount [Ah] reached 2000[Ah].

[0153] <Summary of the experiment> (a) As can be seen from Experimental Examples 1, 2, and 3, within the charge / discharge range with an upper limit of 100% SOC, if the battery is always charged until it reaches 100% SOC during charging, the charging range ΔSOC is different, ranging from 80% to 40%. Nevertheless, no degradation of battery capacity [Ah] occurred in any of these cases. In other words, at least the so-called memory effect did not occur. That is, a refresh effect was observed.

[0154] Furthermore, it was found that Ni2O3H was not generated at the same time. In other words, in this experiment, charging was stopped and discharging started the moment the SOC reached 100%. By doing so, it can be inferred that Ni2O3H was not generated because the overcharging condition, which is prone to oxygen generation, was avoided.

[0155] (b) On the other hand, as can be seen from experimental examples 4, 6, and 7, in the charge / discharge range with an upper limit of SOC lower than 100% SOC, degradation of battery capacity [Ah] occurred regardless of the charge range ΔSOC.

[0156] In this case, the SOC is not such that it exceeds 100% (SOC) at which oxygen is generated. Furthermore, the charge / discharge rates were both 1 / 3[C], and high-rate charging and discharging were not being performed at a low SOC of 10[%]. Therefore, it is unlikely that the degradation of battery capacity[Ah] is due to the formation of Ni2O3H.

[0157] Therefore, it can be inferred that the refresh effect proposed by the present inventors, which involves always reaching SOC 100% during charging, was not achieved. (c) Furthermore, as can be seen from Experimental Example 5, at least under the conditions of this experiment, even when the battery is completely discharged to SOC 0[%] and then slowly charged at a low charge rate of 1 / 3[C], degradation of the battery capacity [Ah] occurs. In other words, it was previously considered common technical knowledge among those skilled in the art that by completely discharging to SOC 0[%] to make the nickel hydroxide, which is the positive electrode active material, completely uncharged, and eliminating variations between the positive electrode active materials, and then charging at a low charge rate, a refresh that eliminates the memory effect can be performed. However, it has been found that this is not necessarily true, and we have obtained a groundbreaking result.

[0158] (Operation of this embodiment) The recovery method for the nickel-metal hydride battery 10 in this embodiment has the following effects. In the recovery method for the nickel-metal hydride battery 10 of this embodiment, charging and discharging of the nickel-metal hydride battery 10 is performed within a charge / discharge range that includes the upper limit of SOC (State of Charge) of 100%. However, charging beyond 100% SOC is not performed. Overcharging beyond 100% SOC has the effect of suppressing the possibility of Ni2O3H being generated due to oxygen generation.

[0159] • During charging in this "high SOC region," the positive electrode active material Ni(OH)2 changes to nickel oxyhydroxide (NiOOH). To ensure uniformity during this process, charging is performed slowly at a low rate, for example, 1 / 3[C] or less. This slow charging at a low rate suppresses localized overcharging within the positive electrode while uniformly charging all positive electrode active materials at the upper limit of SOC, which is 100%. In other words, it refreshes the nickel-metal hydride battery 10.

[0160] In the "low SOC region," which is below the "reference SOC," charging is limited to the "first charging rate C1," which is set to, for example, 3[C]. This has the effect of enabling rapid charging.

[0161] Furthermore, to manage charging and discharging within a range that does not fall below the lower limit of SOC, over-discharging and extremely low SOC conditions are avoided. Furthermore, by measuring complex impedance, the full capacity of the nickel-metal hydride battery, which is a prerequisite for control, can be obtained non-destructively, quickly, and accurately, thus enabling precise control.

[0162] By implementing precise control, the decrease in capacity of the nickel-metal hydride battery 10 can be suppressed. • This suppresses the decrease in capacity of the nickel-metal hydride battery 10, enabling accurate estimation of the State of Charge (SOC).

[0163] Therefore, precise control can be continuously performed based on the full capacity of the nickel-metal hydride battery. (Effects of this embodiment) (1) The method and device for restoring the nickel-metal hydride battery 10 of this embodiment have the effect of effectively restoring the reduced capacity of the nickel-metal hydride battery 10.

[0164] (2) In this embodiment, in the low SOC region, charging is limited to the first high-rate charge rate C1, which has the effect of enabling rapid charging. (3) On the other hand, in the high SOC region, charging is performed up to the upper limit of the second low-rate charge rate C2, so the charge state of the positive electrode active material becomes uniform. This uniform charge state of the positive electrode active material has the effect of refreshing the nickel-metal hydride battery 10 and effectively recovering the decrease in capacity.

[0165] (4) Do not charge above the upper limit of SOC, i.e., SOC 100%. This has the effect of avoiding charging in the region where Ni2O3H is likely to be generated due to overcharging.

[0166] (5) The charging and discharging of the nickel-metal hydride battery 10 is controlled within a charging and discharging range that does not fall below the lower limit SOC, which is set to be above SOC 0[%]. This has the effect of preventing over-discharging and extremely low SOC, and enabling smooth control of the nickel-metal hydride battery.

[0167] (6) The standard SOC was set to 70-90%. This allows for sufficient homogenization of the positive electrode active material in the high SOC region where low-rate charging is performed. In addition, by providing a sufficient low SOC region where high-rate charging is performed, the charging efficiency can be improved.

[0168] (7) The second charge rate C2 was set to 1 / 3 [C] or less. This has the effect of allowing sufficient homogenization of the positive electrode active material in the high SOC region. (6) Because the full capacity of the nickel-metal hydride battery 10 is accurately estimated in advance based on the measurement of complex impedance, there is an effect in that the characteristics of the nickel-metal hydride battery 10 to be controlled can be accurately identified.

[0169] (7) Since the OCV-SOC curve is obtained based on the full capacity of the nickel-metal hydride battery 10, which is obtained based on the measurement of complex impedance, there is an effect that an accurate OCV-SOC curve can be obtained.

[0170] (8) Based on an accurate OCV-SOC curve, it is possible to accurately estimate SOC from the measured OCV. (9) This has the effect of enabling precise control based on the accurately acquired SOC.

[0171] (10) By performing precise control based on the accurately acquired SOC, the capacity of the nickel-metal hydride battery 10 can be restored. (11) By restoring the capacity of the nickel-metal hydride battery 10, accurate control can be continued based on the accurate battery capacity.

[0172] (Another example) The present invention is not limited to the embodiments and can be implemented as follows. ○The procedure shown in the flowchart of Figure 13 does not need to be performed at all times. For example, charging and discharging are normally performed at a SOC of 40-80%, and the procedure shown in the flowchart of Figure 13 may be performed as needed. Alternatively, it may be performed when a charge that meets certain criteria is reached. Furthermore, it may be performed periodically.

[0173] ○In this embodiment, control is performed according to OCV [V], but control can also be performed using, or by referring to, other parameters such as estimated SOC [%], current [A] and its integrated value [Ah], and temperature [°C].

[0174] ○In this embodiment, a method for restoring a stationary nickel-metal hydride battery 10 in a home that is charged at night using off-peak electricity is illustrated, but this is only an example for the sake of simplicity of explanation due to the simplicity of the operation.In the present invention, the applications of the nickel-metal hydride battery 10 are not limited to the embodiment.For example, it can be applied as a battery for driving vehicles such as electric vehicles (EVs), plug-in hybrids (PHVs), and hybrid vehicles (HVs).Of course, it can also be applied to aircraft and ships.It can also be applied as a stationary battery in homes and factories equipped with solar power generation facilities, wind power generation facilities, and small-scale hydroelectric power generation facilities.Furthermore, it can be implemented for the purpose of refreshing the nickel-metal hydride battery 10 in power supplies for computers and audio equipment.

[0175] ○In this embodiment, the system is divided into a low SOC region of 80% or less and a high SOC region of 80% or more, and is charged at a first charge rate C1 and a second charge rate C2, respectively. However, it is not limited to this, for example, the region exceeding 80% but less than 90% is defined as the "medium SOC region". Also, the region exceeding 90% but up to 100% is defined as the high SOC region. Furthermore, in the medium SOC region, it is also possible to control it in three stages using a medium charge rate, for example, 1C.

[0176] ○Charging is not limited to a constant charging rate; for example, intermittent charging pauses may be introduced to ensure uniform charging of the positive electrode active material. ○Also, the charging rate [C] may be continuously reduced as the SOC approaches 100%.

[0177] ○In this embodiment, in the low SOC region of 80% or less, discharge at a uniform discharge rate of 3[C] is permitted. However, in the low SOC region, for example, 20-50%, the memory effect is more likely to occur, so the discharge rate can be controlled to be limited to 1[C] or less.

[0178] ○Furthermore, this does not prevent the implementation of conventional refresh methods, such as completely discharging the battery to a state of charge (SOC) of 0% at a low discharge rate of, for example, 1 / 3[C], and then slowly charging it at a low charge rate of, for example, 1 / 3[C], as is done in conventional technology.

[0179] ○The method for measuring and estimating SOC[%] during charging and discharging is not limited to obtaining it using the OCV-SOC curve; any method that allows for the measurement and estimation of SOC[%] is acceptable. ○The OCV-SOC curves shown in Figures 1-4 and the capacity degradation graph shown in Figure 7 in the embodiment are illustrative examples and will vary depending on the characteristics of the nickel-metal hydride battery 10 in question.

[0180] ○In this embodiment, the full capacity of the nickel-metal hydride battery 10 was estimated by measuring the complex impedance and analyzing the results using a Nyquist plot, but this does not preclude determining it by actual measurement of OCV-SOC.

[0181] ○The lower limit SOC[%], lower limit voltage LL[V], reference voltage RV[V], charge rate[C], first or second discharge rate[C], etc., in the embodiment are examples only. Therefore, these values ​​are not limited to those shown, and can be appropriately optimized by those skilled in the art to match the characteristics of the nickel-metal hydride battery 10.

[0182] The block diagrams shown in Figures 5 and 8 are for illustrative purposes of this embodiment, and the present invention allows the use of control devices 1 with different configurations to control the nickel-metal hydride battery 10. The flowcharts shown in Figures 6 and 13 illustrate an example of the control procedure, and can be implemented by adding, deleting, or modifying these steps.

[0183] It goes without saying that, within the scope of the claims, the present invention can be implemented by those skilled in the art by adding, deleting, or modifying its configuration. [Explanation of Symbols]

[0184] 1…Control device for nickel-metal hydride batteries 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 battery 11…CPU 12...RAM 13…ROM 14...Storage device 20…Measurement power supply 21…Voltage measuring instrument 22…Current measuring device 30… Measuring device 40… Processing Unit 41...Impedance measurement section 43...Nyquist Diagram Creation Department 44...Parameter calculation unit 45...Capacity calculation section 50...Storage section 51…Correlation data 52...Calculation data a,b,c,d…area Z...complex impedance f1,f2…Measurement frequency L21, L22, L51... Impedance curves L31, L32, L41... Graph V0, V1…OCV-SOC curve OCV…Battery Voltage UL…Maximum voltage [V] LL...Lower voltage limit [V] RV…Reference voltage [V] PV…Current voltage [V] C1…First charging rate [C] C2…Second charging rate [C]

Claims

1. A method for restoring a used nickel-metal hydride battery, An impedance measurement step of measuring the complex impedance of the nickel-metal hydride battery to be measured based on the application of AC power for measurement, A parameter calculation step is to calculate a parameter consisting of the ratio of the difference in the measured angular velocity of two complex impedances that are within the diffusion region and have different measured angular velocities, and the difference in the imaginary components of the two complex impedances. The process for obtaining the full capacity of the nickel-metal hydride storage battery at SOC 100% includes a capacity calculation step which calculates the capacity of the secondary battery based on pre-set information that shows the relationship between the capacity of the secondary battery and the parameters, and the parameters calculated in the parameter calculation step, The SOC of the nickel-metal hydride battery is set to 100% as the upper limit of SOC, When the SOC [%] set to 70-90 [%] of the aforementioned upper limit SOC is used as the reference SOC, In the low SOC region, which is below the aforementioned standard SOC, charging is performed up to a predetermined first charging rate, In the high SOC region, which is the region exceeding the reference SOC and below the upper limit SOC, charging is performed with a second charging rate of 1 / 3 [C] or less, which is lower than the first charging rate, as the upper limit. Charging is completed when the SOC exceeds 100%. A method for restoring a nickel-metal hydride battery, characterized by the features described above.

2. Equipped with a charge / discharge control device for nickel-metal hydride batteries, The charge / discharge control device sets the battery voltage OCV [V] at SOC 100 [%] as the upper limit voltage UL [V], When the battery voltage OCV [V] at an SOC [%] set to 70-90% of SOC 100 [%] is used as the reference voltage RV [V], In the low SOC region, which is below the aforementioned reference voltage RV [V], charging is performed up to a preset first charging rate, In the high SOC region, which is the region where the reference voltage RV [V] is exceeded and the upper limit voltage UL [V] is not exceeded, charging is performed with a second charging rate of 1 / 3 [C] or less, which is lower than the first charging rate, as the upper limit, and charging is completed when the SOC exceeds 100 [%]. A recovery device for nickel-metal hydride batteries, characterized by the following features.

Images