Nickel-metal hydride battery control method and control device

Abstract

To suppress a decrease in the capacity of a nickel-metal hydride storage battery.SOLUTION: A nickel-metal hydride storage battery is charged and discharged with SOC 100 [%] as the upper limit SOC, and is performed within a charge and discharge range that includes this upper limit SOC (S5). During charging, Ni(OH)2, which is a positive electrode active material, changes to nickel oxyhydroxide (NiOOH), but to avoid variations at this time, charge at a slow charging rate of 1 / 3C or less (S7) is performed. By slowly charging at such a low rate, the positive electrode active material can be uniformly charged while suppressing the occurrence of local overcharging within the positive electrode. As a result, the nickel-metal hydride storage battery can be refreshed.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a control method and control device for a nickel-metal hydride battery, and more particularly to a control method and control device for a nickel-metal hydride battery that can suppress errors in estimating SOC. [Background technology]

[0002] In recent years, nickel-metal hydride batteries have been used in electric vehicles, laptop computers, and homes and factories to store late-night electricity and solar-generated electricity because they are safe and can input and output large amounts of current.

[0003] Such nickel-metal hydride batteries can be used in a variety of ways. In this case, depending on the charge / discharge conditions, repeated charge / discharge may result in the generation of electrochemically inactive nickel oxide (Ni2O3H), which may cause an increase in battery resistance and a decrease in battery capacity. For this reason, the invention disclosed in Patent Document 1 uses a current density of 100 A / m 2 A battery has been proposed that will keep Ni2O3H below a specified amount when charging and discharging a total amount of electricity of 10 kAh within a charging rate SOC (State Of Charge, hereafter sometimes abbreviated as "SOC") range of 20 to 80%. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-233423 Summary of the Invention [Problem to be solved by the invention]

[0005] However, for such control, it is necessary to accurately estimate the SOC. Figure 1 shows an OCV-SOC curve that shows the relationship between the open cell voltage OCV (hereinafter sometimes abbreviated simply as "OCV") and 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 an OCV-SOC curve, the SOC can be estimated from the OCV. In Figure 1, the OCV [V] at SOC 100 [%] is V 100 [V]. Also, the OCV is V 80 When [V], the SOC can be estimated to be 80[%].

[0006] Figure 2 shows the OCV-SOC curve that shows the relationship between the OCV and SOC of a nickel-metal hydride battery with reduced capacity. In nickel-metal hydride batteries, the battery capacity may decrease due to repeated partial charging and discharging in the intermediate SOC region, such as SOC 20-80% as mentioned above. When the battery capacity decreases, as shown in Figure 2, even with the same OCV, the SOC may actually be higher than the initial OCV-SOC curve. In Figure 1, the OCV [V] at SOC 80 [%] is OCV = V 80 However, when the capacity of a nickel-metal hydride battery decreases, the OCV becomes equal to V, as shown in the OCV-SOC curve in Figure 2. 80 At [V], the SOC actually exceeds 80%.

[0007] Therefore, if the SOC is estimated to be 80% when the OCV is 80V, the nickel-metal hydride battery is actually being controlled at a higher SOC than 80%. Such errors in the SOC estimation can lead to the battery being used in a high SOC range exceeding 80%, potentially resulting in overcharging and the formation of Ni2O3H. In such cases, even a small amount of Ni2O3H formation reduces the battery's capacity. Therefore, continued use based on the specified capacity (Ah) effectively increases the SOC estimation error, leading to further Ni2O3H formation. This can even render the battery unusable. To accurately estimate the SOC, it is necessary to suppress the decline in the nickel-metal hydride battery's capacity.

[0008] The problem to be solved by the nickel-metal hydride battery control method and control device of the present invention is to suppress the decrease in capacity of the nickel-metal hydride battery. [Means for solving the problem]

[0009] In order to solve the above problems, in the control method for a nickel-metal hydride storage battery of the present invention, when a nickel-metal hydride storage battery is pre-charged and the state in which uncharged nickel hydroxide has disappeared is defined as SOC100[%], the nickel-metal hydride storage battery is charged and discharged within a charge and discharge range that includes SOC100[%] as the upper limit SOC.

[0010] The nickel-metal hydride storage battery may be discharged in advance, and when the state in which the charged nickel hydroxide is gone is defined as SOC0 [%], the nickel-metal hydride storage battery may be charged and discharged within a charge and discharge range in which a lower limit SOC is set to be greater than SOC0 [%].

[0011] The lower limit SOC may be set to 20 to 40%. The nickel-metal hydride storage battery can be charged and discharged within a range of the battery voltage OCV that includes the upper limit voltage UL [V], which is the battery voltage OCV at SOC 100 [%].

[0012] The nickel-metal hydride battery may be charged and discharged within a range of a battery voltage OCV whose lower limit is a lower limit voltage LL [V], which is a battery voltage set so that the charging and discharging of the nickel-metal hydride battery exceeds SOC 0 [%].

[0013] It is preferable that the charge rate of the charge / discharge is limited to 1 / 3 C or less, and it is also preferable that the discharge rate of the charge / discharge is limited to 1 C or less. It is controlled to be switchable between normal mode and refresh mode, In the normal mode, a reference SOC of less than SOC 100 [%] is set, and charging and discharging are performed within a charge / discharge range with the reference SOC as the upper limit, and in the refresh mode, charging and discharging are performed within a charge / discharge range with the upper limit SOC as the upper limit and including an upper limit voltage UL [V].

[0014] The device is controlled to be switchable between normal mode and refresh mode, and in the normal mode, the OCV has a reference voltage RV [V] of less than SOC 100 [%], and charging and discharging are performed within a charge and discharge range with the reference voltage RV [V] as the upper limit, and in the refresh mode, charging and discharging can be performed at a set timing within a charge and discharge range that includes the upper limit voltage UL [V] as the upper limit.

[0015] A charging width may be set in the normal mode, and the refresh mode may be executed when the number of times charging has been performed at or above the set charging width reaches or exceeds a preset number.

[0016] The nickel-metal hydride battery control device of the present invention is a nickel-metal hydride battery control device that controls a charging / discharging device that charges and discharges a nickel-metal hydride battery, and stores an upper limit voltage UL [V], which is the battery voltage at SOC 100 [%] of the nickel-metal hydride battery, and can charge and discharge within a charge / discharge range that has the upper limit voltage UL [V] as an upper limit and always includes the upper limit voltage UL [V].

[0017] A lower limit voltage LL [V], which is a battery voltage set to exceed the SOC 0 [%] of the nickel-metal hydride storage battery, is stored, and charging and discharging can be performed within the charge and discharge range of the battery voltage OCV, with the lower limit voltage LL [V] as the lower limit. [Effects of the Invention]

[0018] According to the control method and control device for a nickel-metal hydride storage battery of the present invention, it is possible to suppress a decrease in the capacity of the nickel-metal hydride storage battery. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is an OCV-SOC curve showing the relationship between the open cell voltage OCV and SOC of a nickel-metal hydride storage battery without capacity degradation. [Figure 2] 1 is an OCV-SOC curve showing the relationship between the open cell voltage OCV and SOC of a nickel-metal hydride storage battery with reduced capacity. [Figure 3] 4 is an OCV-SOC curve showing the relationship between open cell voltage OCV and SOC, illustrating the control method for the nickel-metal hydride storage battery of the present embodiment. [Figure 4] 1 is an OCV-SOC curve showing the relationship between open cell voltage OCV and SOC during charging and discharging. [Figure 5] FIG. 1 is a block diagram of a control device 1 for a nickel-metal hydride storage battery. [Figure 6] 3 is a flowchart showing a procedure for controlling the nickel-metal hydride storage battery 10 of the present embodiment. [Figure 7]1 is a graph showing the relationship between the total discharged amount of electricity [Ah] and the chargeable battery capacity [Ah] of the nickel-metal hydride storage battery at that time in Experimental Examples 1 to 7 when the condition of SOC for charging and discharging is changed. [Figure 8] 6 is a flowchart showing the procedure of a main routine of a control method for a nickel-metal hydride storage battery according to a second embodiment. [Figure 9] 10 is a flowchart showing the procedure of a subroutine for controlling the nickel-metal hydride storage battery in a normal mode. [Figure 10] 1 is a graph showing the change in OCV [V] over time of a nickel-metal hydride storage battery in normal mode. [Figure 11] 10 is a flowchart showing the procedure of a subroutine for controlling the nickel-metal hydride storage battery in a refresh mode. [Figure 12] 10 is a graph showing the relationship between the total discharged amount of electricity [Ah] and the chargeable battery capacity [Ah] of the nickel-metal hydride storage battery at that time in Experimental Examples 1, 8, and 9 when the conditions of SOC for charging and discharging are changed. DETAILED DESCRIPTION OF THE INVENTION

[0020] A control method and control device for a nickel-metal hydride battery according to the present invention will be described below using a control device 1 for a nickel-metal hydride battery 10 as one embodiment, with reference to FIGS. (First embodiment) <Technical Background of the Present Embodiment> As described in the prior art, when Ni2O3H is produced, the battery capacity of the nickel-metal hydride storage battery 10 decreases. Therefore, the invention disclosed in Patent Document 1 proposes a battery in which the amount of Ni2O3H is kept below a specified amount when charging and discharging is performed with a total amount of electricity of 10 kAh at a current density of 100 A / m2 and an SOC (State Of Charge) in the range of 20 to 80%.

[0021] The present inventors have also confirmed through experiments that when a battery is charged in a state of high SOC, such as when it is overcharged, oxygen is generated at the positive electrode, and Ni2O3H is generated as a result of this oxygen generation. <Memory effect and conventional refresh methods> However, even when the nickel-metal hydride battery 10 is repeatedly partially charged and discharged in an intermediate SOC range such as SOC 20 to 80% as described above, the battery capacity may decrease due to factors other than the generation of Ni2O3H at high SOC. One of the causes of this is the so-called memory effect of the nickel-metal hydride battery 10.

[0022] One of the causes of the memory effect is thought to be variations in the charge of nickel hydroxide, the positive electrode active material. In such cases, the conventional method of eliminating the memory effect, known as battery refresh, involves first completely discharging the battery to SOC 0% to remove the charged nickel hydroxide. From that state, the battery is then charged at a low rate to prevent variations in the charge of the nickel hydroxide, eliminating the memory effect, a common technical knowledge held by those skilled in the art.

[0023] However, according to the analysis of the present inventors, it was found that the capacity of a nickel-metal hydride storage battery also decreases when the battery is completely discharged to an SOC of 0% to remove the charged nickel hydroxide, and then the battery is charged at a low rate.

[0024] <Method for refreshing a nickel-metal hydride battery according to the present embodiment> In light of this background, the present inventors have discovered a new method for controlling a nickel-metal hydride battery that is less likely to cause a decrease in capacity. This method suppresses the decrease in capacity of the nickel-metal hydride battery. It is possible to accurately estimate the SOC while the capacity of the nickel-metal hydride battery remains constant. As a result, it is possible to perform appropriate control according to the accurate SOC at that time.

[0025] In the control method of the nickel-hydrogen storage battery 10 of this embodiment, the nickel-hydrogen storage battery 10 is fully discharged in advance, then charged at a low rate, and the state where uncharged nickel hydroxide has disappeared is set as SOC 100 [%]. Then, the charge and discharge of the nickel-hydrogen storage battery 10 are carried out within a charge and discharge range with SOC 100 [%] as the upper limit SOC and including this upper limit SOC. However, charging beyond SOC 100 [%] is not performed.

[0026] Upon charging, Ni(OH)2, which is the positive electrode active material, changes to nickel oxyhydroxide (NiOOH). At this time, in order to have no variation, it is charged slowly, for example, at a low rate of 1C or less. It is more preferable that it is 1 / 3C or less. By charging slowly at such a low rate, while suppressing the occurrence of local overcharging in the positive electrode, uniform charging is performed on the positive electrode active material.

[0027] Such charging is performed, and the state where uncharged nickel hydroxide has disappeared in the positive electrode is set as "SOC 100 [%]". That is, charging is completed at this point. If charging is continued further, overcharging will occur and oxygen (O2) will easily be generated in the positive electrode. When oxygen (O2) is easily generated, a state where Ni2O3H is easily generated will occur. Therefore, it is necessary to accurately grasp this point of SOC 100 [%].

[0028] <Estimation of SOC> For a precise measurement of SOC [%], it can be estimated by clarifying the chemical bonding state of nickel hydroxide, which is the positive electrode active material, present on the surface of the positive electrode plate (depth of several nm) using X-ray photoelectron spectroscopy (XPS) or the like. However, because a dedicated measuring device or the like is required and a destructive inspection is required, it cannot be easily analyzed.

[0029] Simple methods include estimating the SOC by integrating the battery current [Ah] or analyzing changes in the OCV [V]. These methods allow non-destructive testing by measuring the current and voltage. In particular, to estimate the SOC from the battery voltage (OCV), the SOC can be easily estimated using the OCV-SOC curve described above. Therefore, in this embodiment, the SOC is calculated from the OCV-SOC curve.

[0030] <Two-stage charging reaction of nickel-metal hydride batteries> Here, charging of a nickel-metal hydride storage battery will be described with reference to Fig. 1. As shown in Fig. 1, the OCV-SOC curve is generally made up of regions St1 to St4.

[0031] In region St1, at low SOC, the uncharged nickel hydroxide is gradually charged, and as the capacity increases, the OCV [V] also rises. Here, because there is a large amount of uncharged nickel hydroxide, the OCV rises quickly at the start of charging. After that, the rate of OCV rise gradually slows down.

[0032] In region St2, the potential is such that nickel hydroxide (Ni(OH)2) changes most easily to nickel oxyhydroxide (NiOOH). Therefore, the electrical energy of charging is consumed for the energy of the chemical change, so although the battery capacity [Ah] increases, the OCV [V] does not increase easily, and the graph is nearly horizontal.

[0033] In region St3, the amount of 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 The right end of the region St3 is exactly SOC 100 [%], and at this point the uncharged nickel hydroxide is gone. The battery voltage OCV [V] at this time is V 100 Indicates [V].

[0034] In region St4, the battery is overcharged, and the charging current is not used to charge the nickel hydroxide, but is used to generate oxygen. Therefore, the battery voltage OCV does not increase even when the battery is charged, and the graph becomes horizontal again.

[0035] If the battery capacity of the nickel-hydrogen storage battery has not decreased, an OCV-SOC curve as shown in FIG. 1 can be obtained, so the SOC [%] can be easily estimated by measuring the OCV [V].

[0036] <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.

[0037] [[ID=!4]] The first condition for the generation of Ni2O3H is as follows. As shown in FIG. 4, when charging and discharging are repeated at 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 oxygen O2 is likely to be generated during charging.

[0038] On the other hand, the OCV-SOC curve Ld during discharging shifts to the base side (lower potential), so that the system is used at a low positive electrode potential during discharging. 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 discharging voltage shifts to the base side, and staying at a lower positive electrode potential than normal approaches the Ni2O3H generation potential.

[0039] <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.

[0040] <Ni2O3H generation> The above conditions 1 and 2 overlap, and Ni2O3H is generated acceleratively. As a result, the capacity is reduced.

[0041] <Control Method of This Embodiment> FIG. 2 is an OCV-SOC curve showing the relationship between the open cell voltage (OCV) and SOC of a nickel-metal hydride battery in which the capacity has decreased due to the memory effect.

[0042] Therefore, based on the mechanism by which these Ni2O3H are generated at an accelerated rate, the initial partial charge / discharge is the main cause (starting point). For this reason, it is necessary to prevent this. Since there are almost no uncharged Ni(OH)2 particles at the charge voltage at the start of the two-stage charge reaction (≒ oxygen generation voltage), starting charge / discharge from this point will prevent the generation of particles in the uncharged area, which is the cause of the memory effect.

[0043] As a result, deviations in the initial OCV-SOC curve can be suppressed. <Capacity recovery in conventional region St4> It has been explained that the range indicated by region St4 in Figure 1 is overcharged. Conventionally, there has been a method of intentionally putting a nickel-metal hydride storage battery into an overcharged state to recover capacity (for example, JP 2018-4270 A).

[0044] The method for restoring capacity is based on the premise that hydrogen (H2) inside the nickel-metal hydride battery has leaked to the outside, causing an imbalance in the hydrogen partial pressure inside the battery case. To maintain this balance, hydrogen is released from the metal hydride (MH) in the negative electrode according to the amount of hydrogen leakage. When hydrogen is released outside the battery module in this way, the discharge reserve of the negative electrode decreases, and therefore the discharge capacity decreases.

[0045] Therefore, to increase the discharge reserve, the battery module is overcharged. During overcharge, charging continues even after the uncharged portion of the positive electrode is depleted, resulting in the decomposition of hydroxyl groups in the electrolyte, generating oxygen, as shown in half-reaction (1) below. At the negative electrode, a reaction occurs in which hydrogen is absorbed into the uncharged portion of the negative electrode active material, i.e., the hydrogen storage alloy, as shown in half-reaction (2) below. Furthermore, as shown in half-reaction (3) below, simultaneously with the hydrogen absorption reaction in the hydrogen storage alloy, a reaction occurs in the charged portion, i.e., the hydrogen storage alloy that has absorbed hydrogen, whereby metal hydride reacts with oxygen to generate water. At this time, the metal hydride (MH) returns to the hydrogen storage alloy (M). In other words, during overcharge, when the safety valve is not open, the reaction in which the uncharged portion is charged and the charged portion returns to the uncharged portion simultaneously occur at the negative electrode.

[0046] (Positive electrode) OH - →1 / 4O2+1 / 2H2O+e - … (1) (Negative electrode)M+H2O+e - →MH+OH - …(2) MH+1 / 4O2 → M+1 / 2H2O…(3) Meanwhile, 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 releases oxygen gas to the outside. When oxygen gas is released, the reaction shown in half-reaction (3), in which the charged portion returns to the uncharged portion, is suppressed. Therefore, the hydrogen storage alloy that has absorbed hydrogen maintains its hydrogen-absorbed state, and if there is an uncharged portion of the negative electrode, the reaction shown in half-reaction (2) proceeds, ensuring a discharge reserve.

[0047] <Control in region St4 in this embodiment> In this embodiment, there is no assumption that hydrogen H2 in the nickel-metal hydride storage battery leaks to the outside and the balance of the hydrogen partial pressure in the battery case is disrupted.

[0048] For this reason, 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 also has significant disadvantages, such as a decrease in the absolute amount of electrolyte.

[0049] Furthermore, the inventors have confirmed through experiments that oxygen O2 is generated at the positive electrode due to overcharging, and Ni2O3H is generated as a result of this oxygen generation. For this reason, in this embodiment, the nickel-metal hydride battery is not used in the region St4 where the SOC exceeds 100%.

[0050] <Nickel-metal hydride battery control device 1> Figure 5 is a block diagram of a control device 1 for a nickel-metal hydride storage battery 10. Solid lines in Figure 5 indicate electrical connections, and dashed lines indicate connections for control signals. The control device 1 for a nickel-metal hydride storage battery 10 of this embodiment is intended for a stationary battery for home use, and is intended to be fully charged using low-cost electricity during the night, for example, and to supply power to necessary lighting, air conditioning, home appliances, etc. during the day.

[0051] Of course, the nickel-metal hydride storage battery of this embodiment can be used in vehicles such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHVs). It can also be used in homes and factories that generate small amounts of electricity, such as solar power or wind power. Furthermore, its applications are not limited. Here, a stationary battery for home use will be used as an example, since the charging and discharging operations are simple and the control method for the nickel-metal hydride storage battery of this embodiment is easy to understand. Here, only the basic configuration common to both is shown.

[0052] The control device 1 includes 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 exchanges signals with the power supply device 3, voltage measurement device 4, current measurement device 5, switch 6, and load 7. It receives data on the OCV [V] and battery current [A] of the nickel-metal hydride storage battery 10 from the voltage measurement device 4 and current measurement device 5. Based on this data, it transmits control signals for the amount of power supplied from the power supply device 3 and the power to be supplied to the load 7, thereby implementing the method for controlling the nickel-metal hydride storage battery 10 of this embodiment.

[0053] The charge / discharge control device 2 includes a CPU (Central Processing Unit) 21, a RAM (Random Access Memory) 22, and a ROM (Read Only Memory) 23. It is also configured as a computer including a storage device 24 such as a PROM (Programmable ROM). The ROM 23 and the storage device 24 store a program for the method of controlling the nickel-metal hydride storage battery 10 of this embodiment.

[0054] In addition, it is equipped with well-known computer components such as a power supply, an interface, and a timer. <Power supply device 3> The power supply device 3 is a device capable of supplying power to the nickel-metal hydride storage battery 10. In this embodiment, this corresponds to a device that supplies late-night power via a power line. The supplied power is, for example, in an electric vehicle (EV), power supplied from a charger via a power line or regenerated power. In a hybrid vehicle (HV), this corresponds to power generated by a prime mover or regenerated power. In homes or factories that use solar power generation, wind power generation, or small-scale hydroelectric power generation, this corresponds to power generated by power generation facilities including solar panels.

[0055] The power supply device 3 has a switch, a voltage regulator, a current regulator, an inverter, and the like (not shown) for adjusting the supplied power, and is controlled by the control device 1. <Voltage measuring device 4> The voltage measuring device 4 measures the OCV [V], which is the open cell voltage of the nickel-metal hydride storage battery 10. In practice, the power supply device 3 and the load 7 are connected, but the method for measuring or estimating the OCV is not limited as long as it can be done.

[0056] <Current measuring device 5> The current measuring device 5 measures the battery current [A] of the nickel-metal hydride storage battery 10. In practice, the power supply device 3 and the load 7 are connected, but the method for measuring or estimating the battery current [A] is not limited as long as it can be measured or estimated.

[0057] <Load 7> The load 7 in this embodiment corresponds to household power consuming devices such as lighting, air conditioning, and home appliances. In the case of an electric vehicle or hybrid vehicle, this corresponds to devices such as a drive motor generator and an air conditioner. In homes and factories that generate solar power, this also corresponds to power transmission for selling electricity. It also includes devices that adjust the SOC of the nickel-metal hydride storage battery 10 by simply discharging.

[0058] The switch 6 provided in the load 7 is also not shown in the figure, but it has not only an opening / closing means but also switches, voltage regulators, current regulators, inverters, etc. (not shown) that ensure the appropriate amount of power is supplied, and is controlled by the charge / discharge control device 2.

[0059] <Control procedure for nickel-metal hydride storage battery according to this embodiment> FIG. 6 is a flowchart showing the control procedure for the nickel-metal hydride storage battery 10 of this embodiment.

[0060] As mentioned above, for the sake of simplicity, the control device 1 for the nickel-metal hydride battery 10 of this embodiment is illustrated as a device that stores late-night power at night and consumes it during the day in a home. Therefore, while exceptional charging and discharging procedures may be performed in practice, they are not shown in this flowchart. Below, a control method for the nickel-metal hydride battery 10 of this embodiment using the control device 1 for the nickel-metal hydride battery 10 of this embodiment will be described. It should be noted that the battery may also be used for electric vehicles (EVs), hybrid vehicles, or stationary use in homes or factories equipped with power generation facilities such as solar power generation or wind power generation, and is not limited to this embodiment. Needless to say, the control procedures will differ depending on the application, and the present embodiment is not intended to limit the scope of the present invention.

[0061] <Preparation stage> When the nickel-metal hydride storage battery 10 is first used (start), the "OCV-SOC curve" is first obtained (S1). Here, the nickel-metal hydride storage battery 10 is fully discharged by the charge / discharge control device 2, and while charging at a low charge rate of 1 / 3C, the relationship between the integrated value of the charging current [Ah] and the OCV is recorded.

[0062] Next, the OCV at SOC 100 [%] is set as the upper limit voltage UL [V] (S2). Here, the moment when the OCV-SOC curve becomes smaller than the set slope at the boundary between region St3 and region St4 shown in FIG. 1 is regarded as the charge capacity [Ah] at which SOC becomes 100 [%] as shown in FIG. 3, and this is stored in the storage device 24 as the "upper limit voltage UL [V]." Note that the "upper limit voltage UL [V]" may also be determined by measuring "dQ / dV," which is the change dQ in capacity [Ah] relative to the change dV in OCV [V], and determining the peak value. This completes the preparation stage.

[0063] <Start of nickel-metal hydride battery control (S3)> Once the preparation stage is complete, the charge / discharge control device 2 starts control as the nickel-metal hydride storage battery 10. In the case of this embodiment, the battery is operated in the SOC range of 20 to 100%.

[0064] <Principle Control> In principle, the nickel-metal hydride battery 10 is controlled so that it is charged to an upper limit voltage UL [V] using, for example, overnight power from the power line, so that the nickel-metal hydride battery 10 reaches an SOC of 100 [%]. In this case, the charging rate is 1 / 3C. Charging is stopped when the nickel-metal hydride battery 10 reaches an SOC of 100 [%]. During the day, depending on the load, the battery is discharged at a maximum rate of 1C until it reaches a lower limit voltage LL [V]. Note that while charging is always performed up to the upper limit voltage UL [V], it is not necessary to discharge to the lower limit voltage LL [V], and charging can be performed as needed.

[0065] <Exceptional Control> As an exceptional case, for example, in a home with solar panels, high-rate charging may be permitted in cases where charging is performed using solar power. Also, when battery capacity is reduced due to the use of an air conditioner in extreme heat, high-rate charging may be permitted to maintain a minimum capacity.

[0066] On the other hand, the discharge rate is basically limited to 1 C or less. In this embodiment, if the SOC falls below 20%, discharge is limited. Even in this case, high-rate discharge is permitted when necessary, such as when using an air conditioner in extreme heat.

[0067] These exceptional controls are not essential to the present embodiment, and so are not described in detail in the flowchart, but are always performed. Furthermore, if the purpose is different, it goes without saying that a person skilled in the art can perform controls that suit the purpose and the usage environment as appropriate.

[0068] <Getting the current voltage PV [V] (S4)> The charge / discharge control device 2 acquires and monitors the voltage PV [V], which is the current OCV, measured by the voltage measurement device 4.

[0069] <Control of upper limit voltage UL [V]> The charge / discharge control device 2 compares the acquired voltage PV [V] with the upper limit voltage UL [V]. If "PV>Upper limit voltage UL" is not true, that is, if the voltage PV [V] is equal to or lower than the upper limit voltage UL [V] (S5: NO), charging at a charge rate of 1 / 3C is permitted (S7). In this case, the SOC [%] is equal to or lower than 100 [%].

[0070] On the other hand, if charging continues at 1 / 3C and the voltage PV exceeds the upper limit voltage UL (S5: NO), that is, if the voltage PV [V] exceeds the upper limit voltage UL [V], charging is immediately terminated (S6). In this case, the SOC [%] exceeds 100 [%], which is the overcharge range, and charging is immediately stopped.

[0071] In the flowchart of this embodiment, once charging is completed (S6), the subsequent determination in S5 is not made, and in principle, no further charging is performed. Basically, the refreshing effect can be achieved once charging is completed.

[0072] <Control of the lower limit voltage LL [V]> When charging is completed (S6), the charge / discharge control device 2 compares the acquired voltage PV [V] with the lower limit voltage LL [V]. If "PV<lower limit voltage LL" is not true, that is, if the voltage PV [V] is equal to or greater than the lower limit voltage LL [V] (S8: NO), discharge at a charge rate of 1C or less is permitted (S9). In this embodiment, this is the case when the SOC [%] is 20 [%] or greater.

[0073] On the other hand, if "PV<lower limit voltage LL", that is, if the voltage PV [V] is lower than the lower limit voltage LL [V] (S8: NO), discharge is limited (S10). In this case, the SOC [%] falls below 20 [%], so discharge is stopped. If charging other than the procedure of "charging at 1 / 3C or less" shown in S7 is performed in a manner not described in this flowchart, and the condition "PV<lower limit voltage LL" is not met, then "discharge allowed at 1C or less (S10)" will be entered again.

[0074] <End of control, continue> For example, if the control is to be ended (S11: YES), the control is ended (END). In such a case, for example, when charging is to be performed again, the control returns to "START" again. If not (S11: NO), the process returns to obtaining the current voltage PV [V] (S4) and repeats the steps of S8 to S11.

[0075] The above description is simplified to facilitate understanding of the present embodiment, and only describes the main steps. Procedures for cases where exceptionally large charging and discharging have occurred are omitted. As mentioned above, it goes without saying that those skilled in the art will perform processes not described in this flowchart depending on the purpose for which the present embodiment is applied.

[0076] (Experimental example of the first embodiment) 7 is a graph showing the relationship between the total discharged amount of electricity [Ah] in Experimental Examples 1 to 7 when the charge / discharge SOC conditions were changed and the chargeable battery capacity [Ah] of the nickel-metal hydride storage battery 10 at that time. In the experiments, charge / discharge was repeatedly performed at a charge / discharge rate of 1 / 3C within the specified SOC range.

[0077] <Experimental Example 1> Experimental Example 1 shown in Figure 7 shows the relationship between the total discharged amount of electricity [Ah] and the battery capacity [Ah] of this embodiment. As shown here, the range of SOC during charging and discharging was set to 100-20% and this range was set to ΔSOC = 80%. Here, "ΔSOC" represents the difference between the maximum and minimum SOC [%]. During charging, the battery was charged up to an upper limit voltage UL [V] to ensure an SOC of 100%. In this case, it was found that the battery capacity [Ah] at the time of manufacture, approximately 5.2 [Ah], did not decrease even when the total discharged amount of electricity [Ah] increased.

[0078] <Experimental Example 2> Next, in Experimental Example 2, the range of SOC during charging and discharging was set to 100-40%. When this range was narrowed to ΔSOC = 60%, the SOC was set to 100% during charging. In this case, it was found that the battery capacity (Ah) at the time of manufacture, approximately 3.9Ah, did not decrease even if the total discharged amount of electricity (Ah) increased.

[0079] <Experimental Example 3> Furthermore, in Experimental Example 3, the range of SOC during charging and discharging is set to 100-60% and ΔSOC is further reduced to 40%. Even in this case, if the SOC is always set to 100% during charging, it was found that the battery capacity [Ah] at the time of manufacture, which was approximately 2.6 [Ah], does not decrease even if the total discharged amount of electricity [Ah] increases.

[0080] <Experimental Example 4> In Experimental Example 4, similar to Experimental Example 1, ΔSOC was set to 80%. However, SOC 90% was set as the upper limit and SOC 10% as the lower limit. The battery was always charged to an SOC of 90%. In this case, the battery capacity (Ah) at the time of manufacture was approximately 5.2 Ah, but as the total discharged amount of electricity (Ah) increased, the battery capacity (Ah) decreased. As shown in Figure 7, the battery's charge capacity, which was initially approximately 5.2 Ah, decreased to approximately 4.8 Ah when the total discharged amount of electricity (Ah) reached 2000 Ah. It further decreased to approximately 4.2 Ah when the total discharged amount of electricity (Ah) reached 4000 Ah. It further decreased to approximately 3.5 Ah when the total discharged amount of electricity (Ah) reached 6000 Ah. When the total discharged electricity amount [Ah] reached 8000 [Ah], it decreased to approximately 3.2 [Ah]. This confirmed that the battery capacity [Ah] decreased with use when charging and discharging without charging up to SOC 100 [%].

[0081] <Experimental Example 5> In Experimental Example 5, similar to Experimental Example 1, ΔSOC was set to 80%. However, SOC 80% was set as the upper limit and SOC 0% as the lower limit. The battery was always charged to an SOC of 80%. In this case, the battery capacity (Ah) at the time of manufacture was approximately 5.2 Ah, but as the total discharged amount of electricity (Ah) increased, the battery capacity (Ah) decreased. As shown in Figure 7, the battery's charge capacity, which was initially approximately 5.2 Ah, suddenly dropped to approximately 2.6 Ah when the total discharged amount of electricity (Ah) reached 2000 Ah. This confirmed that the battery capacity (Ah) decreased with use when charging and discharging without charging to an SOC of 100%. In particular, the battery capacity decreased significantly compared to Experimental Example 4.

[0082] What particularly caught the attention of the inventors was that charging and discharging was performed within a range including SOC 0 [%] in Experimental Example 5. Conventionally, it was thought that refreshing a nickel-metal hydride storage battery 10 could be achieved by fully discharging it to SOC 0 [%] and then slowly charging it at a low charge rate.

[0083] However, as shown in FIG. 7, the inventors have found that the battery capacity decreases significantly even when passing through SOC0 [%], which is believed by those skilled in the art to be effective in eliminating the memory effect.

[0084] <Experimental Example 6> In Experimental Example 6, as in Experimental Example 2, ΔSOC was set to 60%; however, SOC 70% was set as the upper limit and SOC 10% as the lower limit. The battery was always charged to an SOC of 70%. In this case, the battery capacity (Ah) at the time of manufacture was approximately 3.8 Ah, but decreased as the total discharged amount of electricity (Ah) increased. As shown in Figure 7, the battery's charge capacity, which was initially approximately 3.8 Ah, decreased to approximately 4.8 Ah when the total discharged amount of electricity (Ah) reached 2000 Ah.

[0085] <Experimental Example 7> In Experimental Example 7, as in Experimental Example 3, ΔSOC was set to 40%. However, SOC 50% was set as the upper limit and SOC 10% as the lower limit. The battery was always charged to an SOC of 50%. In this case, the battery capacity (Ah) at the time of manufacture was approximately 2.6 Ah, but decreased as the total discharged amount of electricity (Ah) increased. As shown in Figure 7, the battery's charge capacity, which was initially approximately 2.6 Ah, decreased to approximately 1.1 Ah when the total discharged amount of electricity (Ah) reached 2000 Ah.

[0086] <Summary of the experiment> (a) As can be seen from Experimental Examples 1, 2, and 3, when charging is performed within a charge / discharge range with an upper limit of SOC 100% and the battery is always charged to SOC 100%, the ΔSOC range is different, ranging from 80 to 40%. Despite this, no deterioration in battery capacity [Ah] occurred in any of the cases. In other words, at least, the so-called memory effect did not occur. In other words, a refresh effect was observed.

[0087] It can also be seen that Ni2O3H was not generated at the same time. In other words, in this experiment, charging was stopped and discharging started the moment SOC reached 100% during charging. This avoided the overcharge state that is prone to oxygen generation, and it can be assumed that Ni2O3H was not generated.

[0088] (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 SOC 100 [%], the battery capacity [Ah] deteriorated regardless of ΔSOC, which is the charge range.

[0089] In this case, the SOC is not such that oxygen is generated at an SOC of 100% or more. In addition, the charge / discharge rate was 1 / 3C in both cases, and high-rate charge / discharge was not performed at a low SOC of 10%. Therefore, it is unlikely that the deterioration in battery capacity [Ah] is due to the formation of Ni2O3H.

[0090] For this reason, it can be assumed that the refreshing effect proposed by the present inventors, which is achieved by 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 if the battery was fully discharged to SOC 0 [%] and then slowly charged at a low charge rate of 1 / 3C, the battery capacity [Ah] still deteriorated. In other words, the conventional method of fully discharging the battery to SOC 0 [%] puts the positive electrode active material, nickel hydroxide, into a completely uncharged state, eliminating the variation between positive electrode active materials. It was previously thought to be common knowledge among those skilled in the art that refreshing the battery to eliminate the memory effect by subsequently charging at a low charge rate does not necessarily hold true, and this led to groundbreaking results.

[0091] (Operation of the first embodiment) In the control 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 SOC range of, for example, SOC 20% with an upper SOC limit of 100%. The positive electrode active material, Ni(OH)2, changes to nickel oxyhydroxide (NiOOH) during charging, and to prevent variations in this process, the battery is slowly charged at a low rate, for example, 1 / 3C or less. By slowly charging to SOC 100% at such a low rate, the positive electrode active material is uniformly charged while preventing local overcharging within the positive electrode. Charging is completed exactly when SOC 100% is reached.

[0092] If the battery is charged any further than this, it will become overcharged and oxygen (O2) will be more likely to be generated at the positive electrode. This is because when oxygen (O2) is more likely to be generated, it becomes easier for Ni2O3H to be generated. The control method for the nickel-metal hydride storage battery 10 of this embodiment has the effect of suppressing the decrease in battery capacity by refreshing the decrease in battery capacity due to the memory effect.

[0093] In addition, by not charging the battery beyond SOC 100% it is possible to suppress the generation of Ni2O3H. In addition, since the battery capacity is not reduced, the OCV-SOC curve does not change, so once the OCV-SOC curve is obtained, the SOC can be easily and accurately estimated from the OCV [V].

[0094] Furthermore, based on the SOC thus accurately estimated, control according to the SOC [%] at that time becomes possible, which has the effect of further suppressing the deterioration of the battery capacity.

[0095] (Effects of the first embodiment) (1-1) In the control method for the nickel-metal hydride battery 10 of this embodiment, the nickel-metal hydride battery 10 is charged and discharged within a charge / discharge range that includes SOC 100 [%] as the upper limit SOC. This makes it possible to suppress capacity degradation of the nickel-metal hydride battery 10.

[0096] (1-2) The nickel-metal hydride storage battery 10 to be controlled is actually charged in advance, and the state in which there is no uncharged nickel hydroxide is set to SOC 100 [%], so that control can be performed based on an accurate SOC [%].

[0097] (1-3) When the nickel-metal hydride battery 10 is previously discharged and the state in which the charged nickel hydroxide is gone is defined as SOC 0 [%], the nickel-metal hydride battery 10 is charged and discharged within a charge and discharge range with a lower limit SOC set to exceed SOC 0 [%]. Even within this range, refreshing can be performed by setting the SOC to 100 [%]. This has the effect of preventing the nickel-metal hydride battery 10 from being fully discharged and over-discharging.

[0098] (1-4) Furthermore, since the nickel-metal hydride storage battery 10 is not brought into a fully discharged state, there is an advantage that a surplus of power supply can always be maintained. Also, the nickel-metal hydride storage battery 10 is not brought into an over-discharge state. (1-5) In this embodiment, since the OCV-SOC curve is acquired, the SOC [%] can be easily and accurately estimated from the OCV [V].

[0099] (1-6) Furthermore, the control method for the nickel-metal hydride storage battery 10 of this embodiment does not cause deterioration of the battery capacity, so that the SOC [%] can always be easily and accurately estimated from the OCV-SOC curve.

[0100] (1-7) Since the SOC [%] can be accurately estimated at all times, appropriate control according to the SOC [%] can be performed to further effectively suppress the deterioration of the nickel-metal hydride storage battery.

[0101] (1-8) The charge rate is low, 1 / 3 C, so that the positive electrode active material can be charged evenly without causing local overcharging at the positive electrode. (Second embodiment) In the second embodiment of the present invention, in principle, charging is always performed up to SOC 100[%], with some exceptions, as in the first embodiment. On the other hand, in the second embodiment, control is performed to switch between "normal mode" and "refresh mode." In "normal mode," the OCV has a reference voltage RV[V] corresponding to an SOC of less than 100[%] (for example, SOC 80[%]), and charging and discharging are performed within a charge / discharge range with the reference voltage RV[V] as the upper limit.

[0102] On the other hand, in "refresh mode", charging and discharging are performed at the set timing within a charging and discharging range that includes the upper limit voltage UL [V] corresponding to SOC 100 [%], as in the first embodiment.

[0103] The set timing may be, for example, a method in which the refresh mode is executed when the OCV reaches the reference voltage RV [V] a set number of times (for example, five times) set in the normal mode.

[0104] (Procedure of the control method for the nickel-metal hydride battery according to the second embodiment) FIG. 8 is a flowchart showing the procedure of a main routine of the control method for the nickel-metal hydride storage battery according to the second embodiment.

[0105] First, the preparatory steps S101 and S102 are the same as the steps S1 and S2 in the first embodiment shown in FIG. 6, and therefore a description thereof will be omitted. <Start of nickel-metal hydride battery control (S103)> Once the preparation stages (S101, S102) are complete, the process moves to the start of control of the nickel-metal hydride battery (S103). Here, similar to step S3 in the first embodiment, basic control of the nickel-metal hydride battery 10 and exceptional control of the nickel-metal hydride battery 10 are performed. These controls are performed at all times. What differs from the first embodiment is that the basic control of the nickel-metal hydride battery 10 is characterized by switching between two modes, a "normal mode" and a "refresh mode."

[0106] <Normal mode (S104)> FIG. 9 is a flowchart showing the procedure of a subroutine for controlling the nickel-metal hydride storage battery 10 in the normal mode (S104).

[0107] When the normal mode (S104) is started (S1041), the following control is performed. <Principle Control> In principle, the nickel-metal hydride battery 10 is charged not only with late-night power but also with external power, such as solar power generation during the day, with a reference voltage RV [V] as the upper limit. In this case, the charge rate is 1C. This is because normal mode does not particularly aim to refresh the nickel-metal hydride battery 10. Charging stops when the nickel-metal hydride battery 10 reaches the reference voltage RV [V]. Furthermore, the battery is discharged at a discharge rate of 1C with a lower limit voltage LL [V] as the lower limit. This is repeated randomly.

[0108] Unlike the first embodiment, it is not necessarily required to charge to the reference voltage RV [V], and it is not necessarily required to discharge to the lower limit voltage LL [V]. That is, in normal mode, charging and discharging are performed according to the operation of the nickel-metal hydride storage battery 10, except that the reference voltage RV [V] is set as the upper limit and the lower limit voltage LL [V] is set as the lower limit. Unlike the refresh mode (S105), control is not performed to always set the upper limit voltage UL [V]. This allows for efficient use of the nickel-metal hydride storage battery 10.

[0109] On the other hand, depending on the environment in which the nickel-metal hydride battery 10 is placed, random and drastic fluctuations in SOC [%] may occur. For example, high-rate charging and discharging at low SOC [%] may be permitted. As a result, there are concerns about the occurrence of memory effects and the generation of Ni2O3H.

[0110] Therefore, it is desirable to eliminate the memory effect at a certain rate by using the refresh mode (S105). <Exceptional Control> As an exceptional control, the same exceptional control as that performed in the first embodiment is performed, but the description thereof will be omitted here.

[0111] <Transition to refresh mode> As shown in Fig. 9, after the normal mode control (S1041) is started, it is determined whether or not the number of charges has reached five (S1402), and the normal mode control is performed until the number of charges reaches five (S1042: NO). Then, when the number of charges reaches five (S1042: YES), the subroutine for the normal mode control (S104) ends, and the process returns to the main routine shown in Fig. 8, and the refresh mode control (S105) is performed.

[0112] 10 is a graph showing an example of the change in OCV [V] over time for the nickel-metal hydride battery 10 in normal mode. In normal mode, charging and discharging are performed with the reference voltage RV [V] as the upper limit and the lower limit voltage LL [V] as the lower limit. Here, charging and discharging are performed in accordance with the operation of the nickel-metal hydride battery 10, except that the reference voltage RV [V] is the upper limit and the lower limit voltage LL [V] is the lower limit. Unlike the refresh mode (S105), control is not performed to ensure that the upper limit voltage UL [V] is reached.

[0113] Therefore, the normal mode (104) is ended and the process returns to the main routine shown in FIG. 8 in the following procedure. As shown in Figure 10, when the refresh mode ends, charging and discharging in normal mode starts from the upper limit voltage UL [V], and then charging and discharging is performed freely according to the operation of the nickel-metal hydride battery in normal mode. At this time, a predetermined charging width is set as a reference. The charging width may be the difference in OCV [V], but it is preferable to convert a fixed difference in SOC [%] (e.g., 40 [%]) into a difference in OCV [V].

[0114] In the OCV [V] fluctuations shown in Figure 10, when the previous refresh mode ends, discharging is performed first, and when the lower limit voltage LL [V] is reached, charging is performed up to the reference voltage RV [V]. At this time, if the lower limit voltage LL [V] corresponds to an SOC of 20 [%] and the reference voltage RV [V] corresponds to an SOC of 80 [%], the charging range corresponds to 60 [%]. Therefore, since it exceeds the set charging range of SOC of 40 [%], this charging is counted as the "first time."

[0115] Similarly, the second and third charges also exceed the charging range of SOC 40% and are therefore counted as "one charge." On the other hand, in the next charge, if the charge width is approximately SOC 10[%], it is smaller than the set charge width of SOC 40[%], so this charge will not be counted as "one charge" in normal mode.

[0116] When charging is performed in this manner, the charging width is determined to determine whether or not to count it as "one charge" in the normal mode. The number of times that it is counted as "one charge" in the normal mode is accumulated in the RAM 22 or the storage device 24 of the charge / discharge control device 2.

[0117] The final charge shown in Figure 10 exceeds the set charge range of SOC 40[%], so this charge is counted as "one charge" and is determined to be the "fifth charge." In the normal mode, a charging width is set, and when the number of times charging is performed at or above the set charging width reaches a preset number (here, five times) or more, the refresh mode is executed.

[0118] Therefore, as shown in FIG. 10, if it is determined that charging has reached five times (FIG. 9: S1042: YES), the process returns to the main routine shown in FIG. 8 and transitions to control in refresh mode (S105).

[0119] <Refresh mode (S105)> FIG. 11 is a flowchart showing the procedure of a subroutine for controlling the nickel-metal hydride storage battery 10 in the refresh mode.

[0120] The steps S1051 to S1059 of the control of the refresh mode are basically the same as the steps S3 to S11 of the flowchart of the control of the nickel-metal hydride storage battery of the first embodiment shown in Fig. 6. The difference is that step S1059 of the refresh mode (S105) is the end of a subroutine rather than the end of the entire control, so the procedure returns to the main routine shown in Fig. 8.

[0121] (Experimental example of the second embodiment) FIG. 12 is a graph showing the relationship between the total discharged amount of electricity [Ah] in Experimental Examples 1, 4, and 9 when the charge / discharge SOC conditions are changed and the chargeable battery capacity [Ah] of the nickel-metal hydride storage battery 10 at that time.

[0122] <Experimental Example 1> Experimental Example 1 shown in Figure 12 shows the relationship between the total discharged amount of electricity [Ah] and the battery capacity [Ah] of this embodiment. As shown here, the range of SOC during charging and discharging was set to 100-20 [%], and this range was set to ΔSOC = 80 [%]. Here, "ΔSOC" represents the difference between the maximum and minimum SOC [%]. During charging, the battery was charged at a charge rate of 1 / 3C up to the upper limit voltage UL [V], ensuring that the SOC was 100 [%].

[0123] In this case, it was found that the battery capacity at the time of manufacture, which was approximately 5.2 [Ah], did not decrease even if the total discharged amount of electricity [Ah] increased. <Experimental Example 4> In Experimental Example 4, ΔSOC was set to 80% as in Experimental Example 1, but the upper limit was set to SOC 90% and the lower limit was set to SOC 10%. During charging, the battery was charged at a charge rate of 1 / 3C to ensure that the SOC was always 90%.

[0124] In this case, the battery capacity at the time of manufacture was approximately 5.2 [Ah], but as the total discharged amount of electricity [Ah] increased, the battery capacity [Ah] decreased. As shown in Figure 7, the battery's charge capacity, which was initially approximately 5.2 [Ah], decreased to approximately 4.8 [Ah] when the total discharged amount of electricity [Ah] was 2000 [Ah]. It further decreased to approximately 4.2 [Ah] when the total discharged amount of electricity [Ah] was 4000 [Ah]. It further decreased to approximately 3.5 [Ah] when the total discharged amount of electricity [Ah] was 6000 [Ah]. It further decreased to approximately 3.2 [Ah] when the total discharged amount of electricity [Ah] was 8000 [Ah]. This confirmed that battery capacity [Ah] decreases with use when charging and discharging, excluding charging up to SOC 100 [%].

[0125] <Experimental Example 8> In Experimental Example 8, as shown in the second embodiment, the battery was charged in normal mode at a charge rate of 1 / 3C until the SOC reached 80% and then discharged at a discharge rate of 1C until the SOC reached 20%. This was repeated five times, and then the battery was charged in refresh mode at a charge rate of 1 / 3C until the upper limit voltage UL [V] was reached, ensuring that the SOC reached 100%. The battery was then discharged at a discharge rate of 1C until the SOC reached 20%. This set was repeated.

[0126] In this case, the battery capacity at the time of manufacture was approximately 5.2 [Ah], but as the total discharged amount of electricity [Ah] increased, the battery capacity [Ah] decreased. As shown in Figure 12, the battery's charge capacity, which was initially approximately 5.2 [Ah], did not change when the total discharged amount of electricity [Ah] was 2000 [Ah]. Furthermore, when the total discharged amount of electricity [Ah] was 4000 [Ah], it decreased to approximately 5.0 [Ah]. Furthermore, when the total discharged amount of electricity [Ah] was 6000 [Ah], it decreased to approximately 4.7 [Ah]. Finally, when the total discharged amount of electricity [Ah] was 8000 [Ah], it decreased to approximately 4.5 [Ah].

[0127] <Summary of the experiment> In Experimental Example 8, charging and discharging were performed five times in normal mode and one time in refresh mode. This is approximately equivalent to Experimental Example 1, in which charging and discharging were performed only in refresh mode in the second embodiment. Furthermore, Experimental Example 4 is approximately equivalent to Experimental Example 4, in which charging and discharging were performed only in normal mode in the second embodiment. In contrast, Experimental Example 8 can be said to be a combination of these conditions, as shown in the second embodiment. Therefore, the degradation in Experimental Example 8 can be expected to be about 5 / 6 of that in Experimental Example 4, since only one out of six cycles was in refresh mode. However, the degradation in Experimental Example 8 was roughly 1 / 3 of that in Experimental Example 4.

[0128] This result shows that deterioration is suppressed by charging and discharging in refresh mode. (Operation of the second embodiment) In the second embodiment, charging and discharging are performed five times in normal mode and one time in refresh mode. Therefore, by slowly charging at a charge rate of 1 / 3 in refresh mode up to SOC 100[%], the same refresh action as in the first embodiment is achieved.

[0129] In addition, the deterioration in the normal mode can be recovered in the refresh mode. (Effects of the second embodiment) (2-1) Even if deterioration occurs due to unlimited charging and discharging in the normal mode, the nickel-metal hydride storage battery 10 can be restored by charging and discharging in the refresh mode.

[0130] (2-2) Therefore, the nickel-metal hydride storage battery 10 can be used with greater flexibility, making it possible to fully utilize the battery's capabilities and suppressing a decrease in the capacity of the nickel-metal hydride storage battery 10. (Another example) The present invention is not limited to the embodiments and can be implemented as follows.

[0131] In this embodiment, a stationary nickel-metal hydride storage battery 10 for use at home that is charged overnight using late-night power has been illustrated, but this is an example given for the sake of simplicity of explanation because its operation is simple. The present invention does not limit the uses of nickel-metal hydride storage battery 10. For example, it can be used as a battery for driving vehicles such as electric vehicles (EVs), plug-in hybrids (PHVs), and hybrids (HVs). It can also be used as a stationary battery in homes or factories equipped with solar power generation facilities, wind power generation facilities, or small-scale hydroelectric power generation facilities. Furthermore, it can also be used for refreshing nickel-metal hydride storage battery 10 in the power sources of computers and audio equipment.

[0132] The method for measuring and estimating the SOC [%] during charging and discharging is not limited to obtaining it using the OCV-SOC curve, and any method that can measure and estimate the SOC [%] may be used. The OCV-SOC curves shown in FIGS. 1 to 4 and the capacity deterioration graphs shown in FIGS. 7 and 12 in the embodiments are examples, and will vary depending on the characteristics of the nickel-metal hydride storage battery 10 in question.

[0133] The lower limit SOC [%], lower limit voltage LL [V], reference voltage RV [V], charge rate [C], discharge rate [C], etc. in the embodiments are merely examples and are not limited to these numerical values, and may be optimized as appropriate by a person skilled in the art.

[0134] The block diagram shown in FIG. 5 is a diagram for explaining this embodiment, and the present invention can use a control device 1 with a different configuration to control the nickel-metal hydride storage battery 10. The flowcharts shown in Figures 6, 8, 9, and 11 show examples of control procedures, and the procedures can be added, deleted, or modified in order to implement the present invention.

[0135] In addition, it goes without saying that those skilled in the art can add, delete, or modify the configuration of the present invention without departing from the scope of the claims. [Explanation of symbols]

[0136] 1... Nickel-metal hydride battery control device 2...Charge / discharge control device 3…Power supply device 4...Voltage measuring device 5...Current measuring device 6...Switch 7. Load 10... Nickel-metal hydride battery 21...CPU 22...RAM 23...ROM 24…Storage device OCV: Battery voltage UL: Upper limit voltage [V] LL: Lower limit voltage [V] RV: Reference voltage [V] PV: Current voltage [V]

Claims

1. A fully discharged nickel-metal hydride storage battery to be controlled is charged at a charge rate of 1 / 3C or less to obtain an OCV-SOC curve, and the moment when the OCV-SOC curve becomes smaller than a set slope is deemed to be the SOC of 100 [%], which is a state in which uncharged nickel hydroxide has run out, and charging of the nickel-metal hydride storage battery is performed with the SOC of 100 [%] as the upper limit SOC, When the nickel-metal hydride storage battery is completely discharged and the charged nickel hydroxide disappears, the SOC is set to 0 [%], and the nickel-metal hydride storage battery is charged and discharged within a charge and discharge range having a lower limit SOC of an SOC set to exceed the SOC 0 [%], A method for controlling a nickel-metal hydride storage battery, characterized in that the charge rate of the charge and discharge is limited to 1 / 3 C or less, and the discharge rate of the charge and discharge is limited to 1 C or less.

2. A control method for a nickel-metal hydride storage battery as described in claim 1, characterized in that the lower limit SOC exceeding the SOC 0 [%] is set to 20 to 40 [%].

3. A control method for a nickel-metal hydride storage battery as described in claim 1, wherein charging and discharging of the nickel-metal hydride storage battery is performed within a charging and discharging range of the battery voltage OCV that includes an upper limit voltage UL [V], which is the battery voltage OCV at the SOC of 100 [%].

4. A control method for a nickel-metal hydride storage battery as described in claim 3, in which charging and discharging of the nickel-metal hydride storage battery is performed within a charging and discharging range of a battery voltage OCV having a lower limit voltage LL [V], which is a battery voltage set so as to exceed the SOC 0 [%].

5. It is controlled to be switchable between normal mode and refresh mode, In the normal mode, a reference SOC of less than 100% is set, and charging and discharging are performed within a charging and discharging range with the reference SOC as an upper limit. A charging width in the normal mode is set, and when the number of times that the OCV reaches a reference voltage RV [V] by charging at or above the set charging width is equal to or greater than a preset number of times, the mode is switched to the refresh mode, 2. The method for controlling a nickel-metal hydride battery according to claim 1, wherein in the refresh mode, charging and discharging are performed within a charging and discharging range that includes the upper limit SOC and has the upper limit SOC as an upper limit.

6. It is controlled to be switchable between normal mode and refresh mode, In the normal mode, the battery has a reference voltage RV [V] of an OCV that is less than 100% of the SOC, and charging and discharging are performed within a charging and discharging range with the reference voltage RV [V] as an upper limit. A charging width is set in the normal mode, and when the number of times that the OCV reaches a reference voltage RV [V] by charging at or above the set charging width is equal to or greater than a preset number of times, the mode is switched to the refresh mode, 5. The control method for a nickel-metal hydride storage battery according to claim 3, wherein in the refresh mode, charging and discharging are performed at a set timing within a charging and discharging range that includes an upper limit voltage UL [V], which is the battery voltage OCV at the SOC of 100 [%].

7. A control device for a nickel-metal hydride storage battery that controls a charge / discharge device that charges and discharges a nickel-metal hydride storage battery, A control device for a nickel-metal hydride storage battery, which acquires an OCV-SOC curve by charging a fully discharged nickel-metal hydride storage battery to be controlled at a charge rate of 1 / 3C or less, and when the instant when the OCV-SOC curve becomes smaller than a set slope is regarded as an SOC of 100[%], a state in which uncharged nickel hydroxide has been depleted, stores an upper limit voltage UL[V], which is the battery voltage of the nickel-metal hydride storage battery at SOC of 100[%], and performs charging and discharging within a charge and discharge range which has as an upper limit the upper limit voltage UL[V] and which always includes the upper limit voltage UL[V].

8. A control device for a nickel-metal hydride storage battery as described in claim 7, which stores a lower limit voltage LL [V], which is a battery voltage set to exceed the SOC0 [%] of the nickel-metal hydride storage battery when the nickel-metal hydride storage battery is fully discharged and the charged nickel hydroxide is gone, and performs charging and discharging within a charging and discharging range of the battery voltage OCV, with the lower limit being the lower limit of the lower limit voltage LL [V].

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