Method for determining the state of a nickel-metal hydride secondary battery and apparatus for determining the state of a nickel-metal hydride secondary battery

Abstract

This invention provides a method for determining the state of a nickel-metal hydride secondary battery that allows for the determination of the degree of corrosion of the negative electrode without the need for constant fitting. [Solution] PU32 measures the impedance based on the voltage V as a response signal and the current I when multiple AC currents of multiple frequencies f in a predetermined frequency range are passed through the battery pack 10. PU32 determines that the amount of corrosion on the negative electrode is large if the slopes of the multiple impedances are less than a predetermined value. Here, the impedance slope is the ratio of the difference between the resistance components and the difference between the reactance components of the impedance at different frequencies.

Claims

1. This includes the execution of periodic signal output processing, impedance measurement processing, angle variable calculation processing, and judgment processing. The aforementioned periodic signal output processing is a process in which the input device inputs periodic signals of two or more frequencies, each including the frequencies at both ends of a predetermined frequency range, to the nickel-metal hydride secondary battery that is the subject of the determination. The impedance measurement process is a process of measuring the impedance of the nickel-metal hydride secondary battery based on the detected value of the response signal of the nickel-metal hydride secondary battery to two or more periodic signals detected by a detection device. The angle variable calculation process is a process in which a processing circuit calculates the value of an angle variable. The angle variable is a variable that indicates the slope, which is the ratio of the change in the imaginary axis component to the change in the real axis component of the impedance in the predetermined frequency domain. The aforementioned determination process is a process in which the processing circuit determines the degree of corrosion of the negative electrode of the nickel-metal hydride secondary battery based on the inclination indicated by the angle variable. The frequency at the lower-frequency end of the predetermined frequency range is set to be less than or equal to the lower-frequency range in the arc region. A method for determining the state of a nickel-metal hydride secondary battery, wherein the arc region is a frequency region in which the Nyquist plot of the impedance with respect to the periodic signal takes an arc shape when the nickel-metal hydride secondary battery is not degraded.

2. The method for determining the state of a nickel-metal hydride secondary battery according to claim 1, wherein the frequency at the lower-frequency end of the predetermined frequency range is set to be less than or equal to the frequency corresponding to the average value of the logarithmic values ​​of the respective frequencies at both ends of the arc region.

3. The method for determining the state of a nickel-metal hydride secondary battery according to claim 1, wherein the impedance measurement process is performed on the nickel-metal hydride secondary battery having a charge level of 20 to 80%.

4. The method for determining the state of a nickel-metal hydride secondary battery according to claim 1, wherein the predetermined frequency range is greater than 0.1 Hz and less than or equal to 10 Hz.

5. It is configured to perform periodic signal output processing, impedance measurement processing, angle variable calculation processing, and judgment processing. The aforementioned periodic signal output process involves inputting periodic signals of two or more frequencies, each including the frequencies at both ends of a predetermined frequency range, to the nickel-metal hydride secondary battery that is the subject of the determination. The impedance measurement process is a process of measuring the impedance of the nickel-metal hydride secondary battery based on the detected value of the response signal of the nickel-metal hydride secondary battery to two or more periodic signals detected by a detection device. The angle variable calculation process is a process for calculating the value of the angle variable, The angle variable is a variable that indicates the slope, which is the ratio of the change in the imaginary axis component to the change in the real axis component of the impedance in the predetermined frequency domain. The aforementioned determination process is a process that determines the degree of corrosion of the negative electrode of the nickel-metal hydride secondary battery based on the inclination indicated by the angle variable. The frequency at the lower-frequency end of the predetermined frequency range is set to be less than or equal to the lower-frequency range in the arc region. The aforementioned arc region is a frequency region in which the Nyquist plot of the impedance for the periodic signal when the nickel-metal hydride secondary battery is not degraded takes on an arc shape, in a nickel-metal hydride secondary battery state determination device.

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