Zinc battery control method and power supply system

Abstract

In this control method for a zinc battery, when the zinc battery is charged, the charge is finished once the charging current falls below a first threshold. Then, even when the charging current does not fall below the first threshold, the charge is finished once the amount of electric charge in the zinc battery exceeds a second threshold. The power supply system comprises the zinc battery and a control unit that controls the charge and discharge of the zinc battery. When the zinc battery is charged, the control unit finishes the charge once the charging current falls below the first threshold. Even when the charging current does not fall below the first threshold, the control unit finishes the charge once the amount of electric charge in the zinc battery exceeds the second threshold.

Description

[Technical Field]

[0001] The present disclosure relates to a zinc battery control method and a power supply system. This application claims priority to Japanese Patent Application No. 2021-014855 filed on February 2, 2021, and incorporates by reference all of the contents of said Japanese application. [Background technology]

[0002] Patent Document 1 discloses a method for keeping a zinc battery on standby in a charged state. In the method described in this document, a charging step for charging the zinc battery and a discharging step for forcibly discharging the zinc battery are continuously and alternately repeated. Patent Document 2 discloses a method for charging a non-aqueous secondary battery. In the method described in this document, after starting charging the secondary battery, charging is stopped before the capacity charged to the secondary battery reaches the rated capacity of the secondary battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-182284 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-30750 Summary of the Invention [Problem to be solved by the invention]

[0004] Zinc batteries have been attracting attention as secondary batteries for use in power supply systems. For example, nickel-zinc batteries are aqueous batteries that use an aqueous electrolyte such as a potassium hydroxide solution, and therefore offer high safety. In addition, nickel-zinc batteries have a high electromotive force for aqueous batteries due to the combination of zinc electrodes and nickel electrodes. Furthermore, nickel-zinc batteries have the advantages of low cost in addition to excellent input / output performance. Zinc batteries can be used, for example, as auxiliary batteries, or auxiliary machinery, in electric vehicles or hybrid vehicles.

[0005] In a power supply system equipped with a secondary battery, after discharging the secondary battery, the charge amount or state of charge (SOC) is restored by charging in preparation for the next discharge. Normally, repeated discharge and charge of the secondary battery gradually deteriorates, and the discharge capacity decreases.

[0006] The present disclosure aims to provide a zinc battery control method and a power supply system equipped with a zinc battery that can suppress deterioration of the zinc battery and extend the battery life. [Means for solving the problem]

[0007] In the zinc battery control method according to the present disclosure, when charging a zinc battery, the charging is terminated when the charging current falls below a first threshold, and even if the charging current does not fall below the first threshold, the charging is terminated when the amount of charge of the zinc battery exceeds a second threshold.

[0008] The power supply system according to the present disclosure includes a zinc battery and a control unit that controls charging and discharging of the zinc battery. The control unit terminates charging of the zinc battery when the charging current falls below a first threshold. The control unit terminates charging of the zinc battery when the charge amount of the zinc battery exceeds a second threshold, even if the charging current does not fall below the first threshold.

[0009] When charging a secondary battery, the charging current decreases as the SOC approaches 100%. Therefore, the criterion for stopping charging can be determined when the charging current falls below a certain threshold. However, according to the inventor's research, in the case of zinc batteries, the charging current may not decrease sufficiently even when the SOC significantly exceeds 100%, especially in the early stages of operation. In such cases, overcharging of the zinc battery occurs significantly, and repeated overcharging accelerates deterioration of the zinc battery, i.e., a decrease in discharge capacity. In the above control method and power supply system, when charging a zinc battery, even if the charging current does not decrease sufficiently, charging is terminated when the charging charge of the zinc battery exceeds a second threshold. This prevents overcharging of the zinc battery, suppresses deterioration of the zinc battery, and extends battery life.

[0010] When charging a zinc battery, there are cases where the charging current does not fall below the first threshold and the amount of charge does not exceed the second threshold. Even in such cases, the charging may be terminated when the elapsed time from the start of the charging exceeds the third threshold. In this case, the charging operation can be terminated more reliably.

[0011] The first threshold may be in the range of 0.01 C to 0.1 C. In this case, the charging operation of the zinc battery can be terminated at an appropriate timing.

[0012] The second threshold value may be a value that results in an SOC in the range of 90% to 110%. For example, by setting the second threshold value to a value in this range, overcharging of the zinc battery can be appropriately prevented and deterioration of the zinc battery can be more effectively suppressed. [Effects of the Invention]

[0013] According to the present disclosure, it is possible to provide a zinc battery control method and a power supply system that can suppress deterioration of zinc batteries and extend battery life. [Brief explanation of the drawings]

[0014] [Figure 1]FIG. 1 is a circuit diagram showing an example of the configuration of a power supply system. [Figure 2] FIG. 2 is a diagram illustrating an example of a hardware configuration of a computer. [Figure 3] FIG. 3 is a flowchart showing a method for controlling a zinc battery. [Figure 4] FIG. 4 is a diagram conceptually showing conditions for terminating charging. [Figure 5] FIG. 5 is a graph plotting the relationship between the number of cycles and the discharge capacity retention rate of the nickel-zinc battery obtained by the cycle test. [Figure 6] FIG. 6 is a graph showing the plot of the relationship between coulombic efficiency and the number of cycles in a cycle test of a nickel-zinc battery. [Figure 7] FIG. 7 is a graph showing the initial charge / discharge curves in a cycle test in which the end of charging was determined only by the charging current and charging time. [Figure 8] FIG. 8 is a graph showing the initial charge-discharge curves when the end of charging is determined based on the charging current, charging time, and charging charge amount in a cycle test. [Figure 9] FIG. 9 is a graph showing the initial charge-discharge curves when the end of charging was determined based on the charging current, charging time, and charging charge amount in a cycle test. [Figure 10] FIG. 10 is a graph plotting the relationship between the number of cycles in the cycle test and the capacity retention rate. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of a zinc battery control method and a power supply system according to the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicated explanations will be omitted. In the following description, the zinc battery is a concept of a battery that uses zinc in the negative electrode, such as a nickel-zinc battery, an air-zinc battery, or a silver-zinc battery.

[0016] FIG. 1 is a circuit diagram showing an example of the configuration of a power supply system 1 according to an embodiment of the present disclosure. The power supply system 1 is used, for example, as an auxiliary battery, i.e., an auxiliary device, for an electric vehicle or a hybrid vehicle. The application of the power supply system 1 is not limited to mobile objects, but the power supply system 1 can also be applied to fixed objects. As an example of application to fixed objects, the power supply system 1 can be used as an uninterruptible power supply (UPS) in various places such as homes, offices, factories, and farms.

[0017] As shown in Fig. 1, the power supply system 1 includes a zinc battery 2, a control unit 3, a charge / discharge control circuit 4, a current sensor 5, and a thermistor 6. The zinc battery 2 has a positive terminal 2a and a negative terminal 2b. The zinc battery 2 may be configured to include multiple cells connected in series between the positive terminal 2a and the negative terminal 2b. The negative terminal 2b is connected to the ground wiring of the power supply system 1.

[0018] The charge / discharge control circuit 4 has a charge control circuit 41 and a discharge control circuit 42. The input terminal of the charge control circuit 41 is electrically connected to an external power source of the power supply system 1 via the power supply wiring, and receives power supply power Pin from the power supply wiring. The power supply power Pin is, for example, +12 V. The output terminal of the charge control circuit 41 is electrically connected to the positive terminal 2a of the zinc battery 2 via a current sensor 5. When the charge control circuit 41 receives a charging instruction from the control unit 3, it applies a charging voltage to the positive terminal 2a of the zinc battery 2 and supplies a charging current Jc.

[0019] The input terminal of the discharge control circuit 42 is electrically connected to the positive terminal 2a of the zinc battery 2 via the current sensor 5. The output terminal of the discharge control circuit 42 is electrically connected to a power load such as an in-vehicle device outside the power supply system 1. When the discharge control circuit 42 receives a discharge instruction from the control unit 3, it receives a discharge current Jd from the positive terminal 2a of the zinc battery 2 and supplies this discharge current Jd to the power load as output power Pout.

[0020] 1, the current sensor 5 serves both as a current sensor between the charge control circuit 41 and the zinc battery 2, and as a current sensor between the discharge control circuit 42 and the zinc battery 2. These current sensors may be provided separately.

[0021] The control unit 3 has a computer 31, a power supply unit 32, a communication circuit 33, a voltage dividing unit 34, an oscillation circuit 35, a reference voltage generating circuit 36, and a sensor power supply unit 37. The control unit 3 is configured by housing these components in a single package. The control unit 3 has a plurality of terminals 3a to 3n in the package for inputting and outputting signals to and from the outside of the control unit 3.

[0022] The computer 31 is a computer that controls the charging and discharging of the zinc battery 2, and is, for example, a microcomputer. FIG. 2 is a diagram showing an example of the hardware configuration of the computer 31. As shown in this diagram, the computer 31 has a processor 311, a memory 312, and an analog-to-digital (A / D) conversion circuit 313. The processor 311, the memory 312, and the A / D conversion circuit 313 are connected to each other via a data bus 314. The processor 311 is, for example, a CPU, and the memory 312 is, for example, a flash memory. Each function of the computer 31 is realized by the processor 311 executing a program stored in the memory 312. For example, the processor 311 performs a predetermined calculation on data read from the memory 312 or data received via a communication terminal. The processor 311 controls another device by outputting the calculation results to the other device. Alternatively, the processor 311 stores the received data or the calculation results in the memory 312. The computer 31 may be configured as a single computer or as a collection of multiple computers, i.e., a distributed system. The hardware configuration of the control unit 3 is not limited to a computer, and may be any circuit having similar functions.

[0023] Referring again to Figure 1, the computer 31 has first and second signal input / output terminals, in other words, I / O ports. The first signal input / output terminal is electrically connected to a control terminal of the charge control circuit 41 via a terminal 3a of the control unit 3. The second signal input / output terminal is electrically connected to a control terminal of the discharge control circuit 42 via a terminal 3b of the control unit 3. The computer 31 controls the operations of the charge control circuit 41 and the discharge control circuit 42 by outputting control signals from these signal input / output terminals.

[0024] The power supply unit 32 is electrically connected to the positive terminal 2a of the zinc battery 2 via terminal 3c of the control unit 3. The power supply unit 32 receives the terminal voltage Vb of the zinc battery 2 as a power supply voltage for driving the control unit 3. The power supply unit 32 receives an activation signal S1 from outside the power supply system 1 via terminal 3d of the control unit 3. The power supply unit 32 starts voltage conversion depending on the state of the activation signal S1. The power supply unit 32 converts the terminal voltage Vb of the zinc battery 2 into a power supply voltage Vs1 and supplies it to the sensor power supply unit 37. The sensor power supply unit 37 generates a constant voltage Vs2 from this power supply voltage Vs1. The sensor power supply unit 37 supplies the constant voltage Vs2 to the current sensor 5 via terminal 3e of the control unit 3. The power supply unit 32 converts the terminal voltage Vb of the zinc battery 2 into a power supply terminal of the computer 31 and also supplies it to the thermistor 6 via a resistor 38. The ground terminal of the computer 31 is electrically connected to the negative terminal 2b of the zinc battery 2 via the terminal 3f of the control unit 3. As a result, the ground terminal of the computer 31 is at the same potential as the negative terminal 2b of the zinc battery 2, i.e., at ground potential.

[0025] The communication circuit 33 is provided for communication between the computer 31 and the outside of the power supply system 1. The communication circuit 33 is an interface circuit for serial communication, such as a CAN (Controller Area Network). The communication circuit 33 has a differential input / output terminal and an opposite differential input / output terminal. One differential input / output terminal of the communication circuit 33 is electrically connected to a communication terminal of the computer 31 via wiring within the package. The other differential input / output terminal of the communication circuit 33 is electrically connected to an electronic device outside the power supply system 1 via a pair of terminals 3g, 3h of the control unit 3. The computer 31 transmits and receives a communication signal S2 to and from the outside of the power supply system 1 via the communication circuit 33.

[0026] The voltage divider 34 is provided to divide the terminal voltage Vb of the zinc battery 2. The voltage divider 34 has resistors 341 and 342 connected in series. One end of the series circuit consisting of the resistors 341 and 342 is electrically connected to the positive terminal 2a of the zinc battery 2 via terminal 3c. The other end of the series circuit is electrically connected to the negative terminal 2b of the zinc battery 2 via terminal 3f of the control unit 3. Therefore, a voltage signal Sd is generated at the node between the resistors 341 and 342, by dividing the terminal voltage Vb according to the resistance ratio of the resistors 341 and 342. The voltage signal Sd is input to the analog input terminal of the computer 31. The voltage signal Sd is converted into a digital signal by an A / D conversion circuit 313 built into the computer 31. The computer 31 can determine the magnitude of the terminal voltage Vb based on the magnitude of this voltage signal Sd.

[0027] The oscillator circuit 35 is connected to a clock terminal of the computer 31. The oscillator circuit 35 provides a periodic clock signal to the computer 31. The oscillator circuit 35 can be configured by, for example, a quartz oscillator.

[0028] The reference voltage generation circuit 36 ​​is a reference voltage source IC that generates a reference voltage Vref. The reference voltage Vref generated by the reference voltage generation circuit 36 ​​is input to an analog input terminal of the computer 31 and converted into a digital signal by an A / D conversion circuit 313 built into the computer 31. This digital signal is used as a reference voltage for the analog signals input to the computer 31, i.e., the aforementioned voltage signal Sd, and the voltage signals Sa and Sb and temperature signal Sc, which will be described later.

[0029] The current sensor 5 detects the magnitude of the charging current Jc and the discharging current Jd. The current sensor 5 has four terminals. One terminal of the current sensor 5 receives a constant voltage Vs2 from the sensor power supply unit 37 via terminal 3e of the control unit 3. The other terminal of the current sensor 5 is connected to the ground potential of the control unit 3 via terminal 3i of the control unit 3. The remaining two terminals of the current sensor 5 output voltage signals Sa and Sb indicating the magnitude of the charging current Jc or the discharging current Jd, respectively. The voltage signals Sa and Sb are input to the control unit 3 via terminals 3j and 3k of the control unit 3, respectively, and then input to an analog input terminal of the computer 31. The voltage signals Sa and Sb are converted into digital signals by an A / D conversion circuit 313 built into the computer 31. The computer 31 can determine the magnitude of the charging current Jc or the discharging current Jd based on the differential voltage between the voltage signals Sa and Sb.

[0030] The thermistor 6 is located near the zinc battery 2 to detect the temperature of the zinc battery 2. The thermistor 6 has a pair of terminals, each connected to terminals 3m and 3n of the control unit 3. Terminal 3m is connected to an analog input terminal of the computer 31 via wiring provided inside the package of the control unit 3 and is also connected to the power supply unit 32 via resistor 38 as described above. Terminal 3n is connected to the ground wiring inside the control unit 3. In this configuration, the power supply voltage Vs1 from the power supply unit 32 is divided by the resistance of the thermistor 6 and resistor 38, and the divided voltage is input to the analog input terminal of the computer 31 as a temperature signal Sc. The resistance value of the thermistor 6 varies depending on the temperature of the zinc battery 2. Therefore, the magnitude of the temperature signal Sc varies depending on the temperature of the zinc battery 2. The computer 31 can determine the temperature of the zinc battery 2 based on the magnitude of the temperature signal Sc.

[0031] The operation of the power supply system 1 of this embodiment having the above configuration will be described. At the same time, a method for controlling the zinc battery according to this embodiment will be described. Fig. 3 is a flowchart showing the method for controlling the zinc battery according to this embodiment.

[0032] First, when the power supply unit 32 receives an activation signal S1 from outside the power supply system 1, the power supply unit 32 starts generating a power supply voltage Vs1. This enables current detection by the current sensor 5 and temperature detection by the thermistor 6. In addition, the computer 31 starts operating (step ST1). At this time, the computer 31 starts measuring the charge amount of the zinc battery 2. The charge amount is the amount of charge stored in the zinc battery 2. The ratio of the charge amount to the discharge capacity of the zinc battery 2 is called the SOC. The charge amount of the zinc battery 2 is obtained by continuously integrating the amounts of the charge current Jc and discharge current Jd obtained based on the magnitudes of the voltage signals Sa and Sb from the current sensor 5 over time, and subtracting the time integral value of the discharge current Jd from the time integral value of the charge current Jc.

[0033] Next, when the computer 31 receives a signal indicating a charging instruction from outside the power supply system 1 via the communication circuit 33, the computer 31 sends a control signal to the charging control circuit 41, causing the charging control circuit 41 to start charging (step ST2). For example, the computer 31 first controls the charging control circuit 41 to perform constant current charging. Then, when the terminal voltage Vb of the zinc battery 2 reaches a predetermined voltage, the computer 31 controls the charging control circuit 41 to switch to constant voltage charging at that predetermined voltage. The current value in constant current charging is, for example, in the range of 0.1 C to 10 C, and in one embodiment, is 0.3 C. In this specification, the magnitude of the current that completely discharges the theoretical capacity of the battery in one hour is defined as 1 C. The voltage value in constant voltage charging is, for example, in the range of 1.75 V to 1.95 V, and in one embodiment, is 1.9 V.

[0034] Once the charging operation is started, the computer 31 repeatedly determines whether to terminate charging. FIG. 4 is a diagram conceptually illustrating conditions for terminating charging. First, the computer 31 determines whether the amount of charging current Jc has fallen below a first threshold based on the magnitude of the voltage signals Sa and Sb from the current sensor 5 (step ST3). This condition is indicated as termination condition A in FIG. 4. When the charging voltage is constant, the magnitude of the charging current Jc flowing through the zinc battery 2 gradually decreases as the amount of charge increases, in other words, as the SOC approaches 100%. Therefore, the magnitude of the charging current Jc has a close correlation with the amount of charge charged in the zinc battery 2. The first threshold is, for example, within a range of 0.01 C to 0.1 C, and is 0.05 C in one embodiment. When the amount of charging current Jc has fallen below the first threshold (step ST3: YES), the computer 31 terminates the charging operation of the charging control circuit 41 (step ST6). If the amount of charge of the zinc battery 2 is not below the first threshold (step ST3: NO), the computer 31 determines whether the amount of charge of the zinc battery 2 has exceeded a second threshold (step ST4). This condition is shown as termination condition B in FIG. 4. The second threshold is a value at which the SOC is within a range of, for example, 90% to 110%, preferably a value within a range of 90% to 100%. In one embodiment, the second threshold is a value at which the SOC is 100%. If the amount of charge of the zinc battery 2 exceeds the second threshold (step ST4: YES), the computer 31 terminates the charging operation of the charging control circuit 41 (step ST6). If the amount of charge of the zinc battery 2 is not above the second threshold (step ST4: NO), the computer 31 determines whether the elapsed time since the start of the charging operation of the charging control circuit 41 has exceeded a third threshold (step ST5). This condition is shown as termination condition C in FIG. 4. The third threshold is, for example, within a range of 1 hour to 20 hours, and in one embodiment, is 5 hours. The third threshold is set according to the magnitude of the charging current Jc. If the elapsed time exceeds the third threshold (step ST5: YES), the computer 31 ends the charging operation of the charging control circuit 41 (step ST6).If the elapsed time does not exceed the third threshold value (step ST5: NO), the computer 31 continues the charging operation of the charge control circuit 41. Thereafter, steps ST3 to ST5 are repeated until the charging operation of the charge control circuit 41 ends in step ST6.

[0035] After step ST6, when the computer 31 receives a signal indicating a discharge instruction from outside the power supply system 1 through the communication circuit 33, the computer 31 transmits a control signal to the discharge control circuit 42, causing the discharge control circuit 42 to perform a discharge operation (step ST7). Thereafter, steps ST2 to ST7 are repeated until the operation of the power supply system 1 is completed (step ST8).

[0036] The effects achieved by the power supply system 1 and the control method for the zinc battery 2 according to the present embodiment, which are configured as described above, will now be described. In this embodiment, when charging the zinc battery 2, charging is terminated when the charging current Jc falls below a first threshold. Even if the charging current Jc does not fall below the first threshold, charging is terminated when the charge amount of the zinc battery 2 exceeds a second threshold. Generally, when charging a secondary battery such as a zinc battery 2, the charging current gradually decreases as the SOC approaches 100%. Therefore, the criterion for stopping charging can be determined when the charging current falls below a certain threshold. However, according to research by the inventors, in the case of zinc batteries, the charging current may not decrease sufficiently even when the SOC significantly exceeds 100%, particularly in the early stages of operation. In such cases, overcharging of the zinc battery 2 occurs significantly, and repeated overcharging accelerates deterioration of the zinc battery 2, i.e., a decrease in discharge capacity. In this embodiment, when charging the zinc battery 2, charging is terminated when the charge amount of the zinc battery 2 exceeds a predetermined second threshold, even if the charging current does not decrease sufficiently. This prevents overcharging of the zinc battery 2, suppresses deterioration of the zinc battery 2, and extends the battery life.

[0037] When charging the zinc battery 2, there are cases where the charging current Jc does not fall below the first threshold and the charging charge does not exceed the second threshold. Even in such cases, as in this embodiment, the charging may be terminated when the elapsed time from the start of the charging exceeds the third threshold. In this case, the charging operation can be terminated more reliably.

[0038] As in this embodiment, the first threshold may be in the range of 0.01 C to 0.1 C. In this case, the charging operation of the zinc battery 2 can be terminated at an appropriate timing.

[0039] As in this embodiment, the second threshold value may be a value that results in an SOC in the range of 90% to 110%. For example, by setting the second threshold value to a value within this range, overcharging of the zinc battery 2 can be appropriately prevented and deterioration of the zinc battery 2 can be more effectively suppressed. The second threshold value may be a value that results in an SOC in the range of 90% to 100%. Alternatively, as shown in the following examples, the second threshold value may be a value that results in an SOC greater than 100% and equal to or less than 110%. Even in this case, deterioration of the zinc battery 2 can be suppressed.

[0040] The effects of the present embodiment will now be described in more detail. FIG. 5 is a graph plotting the relationship between the number of cycles and the discharge capacity retention rate (%) of a nickel-zinc battery obtained through a cycle test. The discharge capacity retention rate is the ratio of the discharge capacity at each time point to the initial discharge capacity. In FIG. 5, plots P11 and P12 are graphs for two nickel-zinc batteries, respectively, at a battery temperature of 40°C. Plots P13 and P14 are graphs for two nickel-zinc batteries, respectively, at a battery temperature of 60°C. In this cycle test, the current value during the constant current charging period was 0.33 C, and the voltage value during the constant voltage charging period was 1.9 V. In FIG. 5, the vertical axis represents the discharge capacity retention rate, and the horizontal axis represents the number of cycles. Referring to FIG. 5, it can be seen that, at any battery temperature, the discharge capacity retention rate decreases as the number of cycles increases. A decrease in the discharge capacity retention rate indicates deterioration of the nickel-zinc battery. Referring to FIG. 5, it can be seen that the higher the battery temperature, the more rapidly the discharge capacity retention rate decreases, i.e., the zinc battery deteriorates.

[0041] The inventors investigated the causes of nickel-zinc battery degradation as the battery temperature increases and solutions to this problem. Figure 6 shows plots of the relationship between Coulombic efficiency and the number of cycles in a cycle test of a nickel-zinc battery. Coulombic efficiency is the ratio of the discharge capacity during discharge to the charge capacity during charge, expressed as a percentage. In other words, Coulombic efficiency indicates the degree of overcharge of a nickel-zinc battery, with a lower Coulombic efficiency indicating a greater degree of overcharge. In this cycle test, the battery temperature was 60°C, the charge current during the constant-current charging period was 0.33 C, the charge voltage during the constant-voltage charging period was 1.9 V, the discharge current was 0.3 C, and the threshold voltage for determining the end of discharge was 1.1 V. The termination conditions for the charging operation were different for each of the three nickel-zinc batteries. In Figure 6, plot P21 shows the Coulombic efficiency of a nickel-zinc battery in which charging was terminated only by termination conditions A and C in Figure 4. However, the first threshold for the charge current under termination condition A is 0.05 C, and the third threshold for the charge time under termination condition C is 5 hours. Plots P22 and P23 show the coulombic efficiency of a nickel-zinc battery set to terminate charging according to termination conditions A, B, and C in Figure 4. Plot P22 shows the case where the second threshold for the charge amount under termination condition B is 8.8 Ah. The charge amount at 8.8 Ah is equivalent to 110% SOC. Plot P23 shows the case where the second threshold for the charge amount under termination condition B is 8.3 Ah. The charge amount at 8.3 Ah is equivalent to 100% SOC. In plots P22 and P23, the first threshold under termination condition A and the third threshold under termination condition C are the same as those in plot P21.

[0042] Referring to plot P21 in Figure 6, when the end of charging is determined solely by the charging current and charging time, the coulombic efficiency significantly decreases, especially in the early stages of the cycles, i.e., from the first cycle to the eighth cycle. Figure 7 is a graph showing the charge / discharge curves for the first cycle corresponding to plot P21. In Figure 7, curve G31 represents the charge curve, and curve G32 represents the discharge curve. The vertical axis represents the terminal voltage (V) of the nickel-zinc battery, and the horizontal axis represents the charge or discharge charge (Ah). Referring to charge curve G31 in Figure 7, it can be seen that the terminal voltage gradually increases as the charge increases. Furthermore, charging continues even after reaching a predetermined terminal voltage (1.9 V in this case), and the charge ultimately reaches nearly 12 Ah. On the other hand, referring to discharge curve G32 in Figure 7, it can be seen that the terminal voltage gradually decreases as the discharged charge increases. The discharged charge ultimately reaches only approximately 8.3 Ah. These results show that the charging current does not decrease sufficiently in the early stages of the cycle, and overcharging proceeds without satisfying termination condition A. When the temperature of a nickel-zinc battery rises, the decomposition voltage of the electrolyte decreases. As a result, the charging reaction and the decomposition reaction of the electrolyte occur in concert, and the current value does not converge even when the charging voltage is reached. This is thought to be the reason why the charging current does not decrease sufficiently.

[0043] In contrast, referring to plots P22 and P23 in Figure 6, when the end of charging is determined based on the charge amount in addition to the charge current and charge time, the decrease in coulombic efficiency is reduced throughout all cycles, including the initial cycle. Figure 8 is a graph showing the initial charge-discharge curve corresponding to plot P22. Figure 9 is a graph showing the initial charge-discharge curve corresponding to plot P23. In Figures 8 and 9, curves G41 and G51 represent charge curves, and curves G42 and G52 represent discharge curves. The vertical axis represents the terminal voltage (V) of the nickel-zinc battery. The horizontal axis represents the charge amount or discharge amount (Ah). Referring to charge curve G41 in Figure 8, charging ended when the charge amount reached 8.8 Ah. 8.8 Ah is the second threshold in this test. On the other hand, referring to discharge curve G42, the discharge amount eventually reached approximately 8.1 Ah, indicating an improvement in coulombic efficiency compared to Figure 7. Similarly, referring to the charge curve G51 in Figure 9, charging ended when the charge amount reached 8.3 Ah, which is the second threshold value in this test. In contrast, referring to the discharge curve G52, the discharge amount eventually reached approximately 8.0 Ah, indicating a further improvement in coulomb efficiency compared to Figure 8.

[0044] In this way, by determining the end of charge using the charge charge, overcharging in the early stages of cycling can be suppressed. Figure 10 is a graph plotting the relationship between the number of cycles and the discharge capacity retention rate in the above-mentioned cycle test. Plot P61 corresponds to plot P21 in Figure 6. Plot P62 corresponds to plot P22 in Figure 6. Plot P63 corresponds to plot P23 in Figure 6. Referring to Figure 10, it can be seen that, compared to plot P21, i.e., when the end of charge is determined based only on the charge current and charge time, plots P22 and P23, i.e., when the end of charge is determined based on the charge charge in addition to the charge current and charge time, the degree of decline in the discharge capacity retention rate is smaller; in other words, deterioration of the nickel-zinc battery is suppressed. Furthermore, comparing plots P22 and P23, it can be seen that the smaller the second threshold value of the charge charge, the smaller the degree of decline in the discharge capacity retention rate; in other words, deterioration of the nickel-zinc battery is suppressed.

[0045] The zinc battery control method and power supply system according to the present invention are not limited to the above-described exemplary embodiments, but are defined by the claims, and are intended to include all modifications within the meaning and scope of the claims.

[0046] In the above-described embodiment, charging is terminated when the charge amount of the zinc battery 2 exceeds the second threshold, regardless of the temperature of the zinc battery 2. However, this is not limited to this; charging may be terminated when the charge amount of the zinc battery 2 exceeds the second threshold only when the temperature of the zinc battery 2 exceeds a predetermined threshold. This is because, as shown in FIG. 5, the problem to be solved by the above-described embodiment is more pronounced when the zinc battery is at a high temperature. In this case, the computer 31 of the control unit 3 can know the temperature of the zinc battery 2 based on the temperature signal Sc from the thermistor 6. [Explanation of symbols]

[0047] 1...power supply system, 2...zinc battery, 2a...positive terminal, 2b...negative terminal, 3...control unit, 3a to 3n...terminals, 4...charge and discharge control circuit, 5...current sensor, 6...thermistor, 31...computer, 32...power supply unit, 33...communication circuit, 34...voltage divider unit, 35...oscillator circuit, 36...reference voltage generation circuit, 37...sensor power supply unit, 38...resistor, 41...charge control circuit, 42...discharge control circuit, 311...processor, 312...memory, 341, 342...resistor, Jc...charge current, Jd...discharge current, Pin...power supply power, Pout...output power, S1...startup signal, S2...communication signal, Sa, Sb...voltage signal, Sc...temperature signal, Sd...voltage signal, Vb...terminal voltage, Vref...reference voltage, Vs1...power supply voltage, Vs2...constant voltage.

Claims

1. 1. A method of controlling a zinc battery, comprising: A constant current charge is performed, and after the terminal voltage of the zinc battery reaches a predetermined voltage during the constant current charge, a constant voltage charge is performed. When charging the zinc battery in the constant voltage charging, the charging is terminated when the charging current falls below a first threshold value; A method for controlling a zinc battery, in which charging is terminated when the charging charge of the zinc battery exceeds a second threshold, even if the charging current during constant voltage charging does not fall below the first threshold.

2. A control method for a zinc battery as described in claim 1, wherein when charging the zinc battery during constant voltage charging, even if the charging current does not fall below the first threshold and the charging charge amount does not exceed the second threshold, the charging is terminated if the elapsed time from the start of charging exceeds a third threshold.

3. The zinc battery control method according to claim 1 or 2, wherein the first threshold value is in the range of 0.01C to 0.1C.

4. The zinc battery control method according to any one of claims 1 to 3, wherein the second threshold value is a value within the range of 90% to 110% of SOC.

5. A method for controlling a zinc battery described in any one of claims 1 to 4, wherein when the charging charge of the zinc battery exceeds the second threshold, charging is terminated only when the temperature of the zinc battery exceeds a predetermined temperature threshold.

6. A zinc battery, A control unit that controls charging and discharging of the zinc battery; Equipped with The control unit performs constant current charging, and performs constant voltage charging after the terminal voltage of the zinc battery reaches a predetermined voltage during the constant current charging, and when charging the zinc battery during the constant voltage charging, terminates the charging if the charging current falls below a first threshold, and terminates the charging if the charged charge of the zinc battery exceeds a second threshold even if the charging current does not fall below the first threshold during the constant voltage charging.

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