JP5445958B2 - Battery evaluation apparatus and battery evaluation method - Google Patents

Description

  The present invention relates to a battery evaluation apparatus for evaluating battery characteristics based on electrochemical measurements, and more particularly to a battery evaluation apparatus for evaluating battery frequency characteristics.

  Conventionally, as a method for displaying the impedance characteristics of a battery, there is a Cole-Cole plot or Nyquist diagram that represents changes in resistance component (Z ′) and reactance component (Z ″) due to changes in the frequency of a given signal in two dimensions. It is used.

  For example, FIG. 5 shows two-dimensional changes in the resistance component (Z ′) and reactance component (Z ″) with respect to a frequency change of 0.01 kHz to 10 kHz for two types of batteries A and B having different conditions. It is. In FIG. 5, the solid line is the data for battery A, and the broken line is the data for battery B. The absolute value of impedance shows a minimum value at a high frequency, and the absolute value of impedance increases as the frequency becomes low, and extends to the upper right in the figure. As described above, the battery generally has an impedance characteristic that the absolute value of the impedance increases as the frequency decreases.

  According to the two-dimensional plot of the resistance component (Z ′) and the reactance component (Z ″) as shown in FIG. 5, the difference in the response to the frequency change is visually caused by the increase or decrease of the semicircular response peak. There is an advantage that it is easy to understand. For this reason, it is useful to find a characteristic frequency response and analyze the chemical reaction by parameter fitting based on the corresponding electric circuit model.

JP 2007-265894 A

`` Investigation of solid electrolyte interfacial layer development during continuous cycling using ac impedance spectra and micro-structural analysis '' P. L. Moss, G. Au, E. J. Plichta, J. P. Zheng Journal of Power Sources 189 (2009) 66-71

  However, in the conventional technology as described above, when comparing the data of the battery A and the battery B, it is difficult to distinguish which battery data is in the portion where the graphs are close to each other. In addition, at high frequencies, data points are generally crowded, so details cannot be expressed and are difficult to read. In addition, it is difficult to visually match the input frequency, and it is difficult to compare characteristics between points corresponding to the same frequency. For example, even if both plots overlap, it cannot be determined that both exhibit the same frequency characteristic. This is because the overlapping plots may correspond to different frequencies.

  An object of the present invention is to provide a battery evaluation apparatus and a battery evaluation method capable of clearly expressing a difference in characteristics when comparing frequency characteristics of batteries and easily comparing points corresponding to the same frequency. Is to provide.

The battery evaluation apparatus of the present invention is a battery evaluation apparatus that evaluates the frequency characteristics of the battery by separating the frequency characteristics into a real component and an imaginary component, and the first frequency characteristic and the second frequency characteristic are each expressed as a function of frequency. The acquisition means for acquiring the sum of the real number component and the imaginary number component, the comparison component for each frequency of the first frequency characteristic and the second frequency characteristic, the real number component that is a function value at the frequency, and the Based on the imaginary number component, the calculation means for calculating the sum of the real number component and the imaginary number component as a function value of the frequency, and the real number component and the imaginary number component as the comparison component calculated by the calculation means correspond to the frequency And presenting means for presenting the information.
According to this battery evaluation apparatus, the frequency characteristics of the batteries to be compared are acquired as a real number component and an imaginary number component as a function of frequency. Then, a comparison component composed of a real component and an imaginary component is calculated and presented in association with the frequency. For this reason, it is possible to clearly express the difference in frequency characteristics and easily compare points corresponding to the same frequency.

  The calculation unit may calculate a ratio of the second frequency characteristic to the first frequency characteristic as the comparison component.

  The calculation means may calculate a value obtained by subtracting the first frequency characteristic from the second frequency characteristic as the comparison component.

  The presenting means may present the real number component, the imaginary number component, and the frequency by a display associated with each other.

  The presenting means may present a three-dimensional display with the real component, the imaginary component, and the frequency as axes, or a display obtained by projecting the three-dimensional display onto a two-dimensional plane.

The battery evaluation method of the present invention is a battery evaluation method in which the frequency characteristics of the battery are evaluated by separating them into a real component and an imaginary component, and the first frequency characteristic and the second frequency characteristic are each expressed as a function of frequency. An acquisition step of acquiring as a sum of a real number component and an imaginary number component, and a comparison component for each frequency of the first frequency characteristic and the second frequency characteristic, the real number component that is a function value at the frequency and the Based on the imaginary component, a calculation step of calculating the sum of the real component and the imaginary component as a function value of the frequency, and the real component and the imaginary component as the comparison component calculated by the calculation step correspond to the frequency And a presentation step to be presented.
According to this battery evaluation method, the frequency characteristics of the batteries to be compared are acquired as a real number component and an imaginary number component as a function of frequency. Then, a comparison component composed of a real component and an imaginary component is calculated and presented in association with the frequency. For this reason, it is possible to clearly express the difference in frequency characteristics and easily compare points corresponding to the same frequency.

  According to the battery evaluation apparatus of the present invention, the frequency characteristics of the batteries to be compared are acquired as a real number component and an imaginary number component as a function of frequency. Then, a comparison component composed of a real component and an imaginary component is calculated and presented in association with the frequency. For this reason, it is possible to clearly express the difference in frequency characteristics and easily compare points corresponding to the same frequency.

  According to the battery evaluation method of the present invention, the frequency characteristics of the batteries to be compared are acquired as a real number component and an imaginary number component as a function of frequency. Then, a comparison component composed of a real component and an imaginary component is calculated and presented in association with the frequency. For this reason, it is possible to clearly express the difference in frequency characteristics and easily compare points corresponding to the same frequency.

It is a figure which shows the impedance measurement evaluation apparatus of one Embodiment, FIG. 1 (a) is a figure which shows the cross section of the fuel cell at the time of impedance measurement, and the connection method at the time of measurement, FIG.1 (b) shows the structure of an evaluation apparatus. Functional block diagram. The figure which shows the real component K (real) and the imaginary component K (imag) of the comparison component K (f) with respect to a frequency change. The figure which shows the example which displayed the value of the frequency. The figure which takes a frequency axis as a 3rd axis | shaft and presents the comparative characteristic of a battery by a three-dimensional display. The figure which shows the two-dimensional display example of the change of the resistance component (Z ') and the reactance component (Z ") with respect to the frequency change of 0.01 kHz-10 kHz about two types of batteries A and B from which conditions differ.

  Hereinafter, an embodiment of a battery evaluation apparatus according to the present invention will be described. This embodiment shows an example of comparing impedance frequency characteristics, and hereinafter, the present invention is applied to an impedance measurement evaluation apparatus that measures the impedance of a battery while changing the measurement frequency, and compares and presents the impedance characteristics. An example will be described.

  FIG. 1 is a diagram showing an impedance measurement and evaluation apparatus, FIG. 1 (a) is a diagram showing a cross section of a fuel cell at the time of impedance measurement and a connection method at the time of measurement, and FIG. 1 (b) is a configuration of the evaluation apparatus. It is a block diagram functionally shown.

  As shown in FIG. 1A, the fuel cell 10 includes a solid polymer membrane 1, a cathode electrode 2 electrically insulated from the solid polymer membrane 1, and a solid polymer membrane 1 similar to the cathode electrode 2. And an anode electrode 3 opposed to the cathode electrode 2 with the solid polymer film 1 interposed therebetween.

  The cathode electrode 2 is formed by sequentially stacking a catalyst layer, a diffusion layer, and a separator (not shown) from the solid polymer membrane 1 side to the outside. Similarly, the anode electrode 3 is configured by sequentially stacking a catalyst layer, a diffusion layer, and a separator (not shown) from the solid polymer membrane 1 side to the outside. In the separators constituting the cathode electrode 2 and the anode electrode 3, gas flow paths for supplying fuel gas are formed.

  The load circuit of the fuel cell 10 includes a voltage measurement module 501 that measures the voltage between the cathode electrode 2 and the anode electrode 3 (fuel cell voltage Vfc), and a current (load current I) that flows through the electronic load device 4. A current measurement module 502 to be measured is connected. The measurement results by the voltage measurement module 501 and the current measurement module 502 are given to the impedance measurement evaluation device 5.

  As shown in FIGS. 1A and 1B, the impedance measurement evaluation device 5 is a load control unit 51 that controls the current value of the electronic load device 4 connected between the cathode electrode 2 and the anode electrode 3. Based on the voltage value (fuel cell voltage Vfc) and the current value (load current I) that change according to the current of the electronic load device 4, the frequency characteristic of the impedance of the fuel cell as a function of frequency And a measurement unit 52 as an acquisition unit that calculates the sum of the imaginary number component, a calculation unit 53 that calculates a comparison component based on a real number component and an imaginary number component of the frequency characteristic obtained by the measurement unit 52, and a calculation by the calculation unit 53 And a display means 54 such as a monitor for comparing and presenting the impedance characteristics of the batteries based on the results.

Next, an impedance measurement procedure will be described.
The load control unit 51 of the evaluation device 5 sets a frequency for performing impedance measurement, a direct current value, and a superimposed alternating current amplitude for the electronic load device 4 to control the current load on the battery. The waveform of the fuel cell voltage Vfc is measured by the voltage module 501 with respect to the current load on which the AC component is superimposed, and the measurement unit 52 determines the gain and phase of the AC component of the voltage (fuel cell voltage Vfc) with respect to the AC current load ( Impedance Z is obtained based on (phase). Here, the impedance Z corresponds to the internal impedance of the battery. The impedance of the battery is obtained by sequentially measuring the impedance by changing the frequency of the superimposed alternating current amplitude.

  The measuring unit 52 of the evaluation device 5 performs impedance measurement for each of the two batteries A, B, or measurement conditions A, and measurement conditions B to be compared. The impedance ZA of the battery A or the measurement condition A and the battery B or the measurement conditions are measured. The impedance ZB of B is acquired as the sum of the real component and the imaginary component, respectively. The acquired impedances ZA and ZB are given to the calculation unit 53, and the calculation unit 53 calculates a comparison component of the impedances ZA and ZB based on the impedances ZA and ZB. The comparison component is composed of a real component and an imaginary component as frequency function values. The calculation result is given to the presenting means 54 such as a monitor, and the presenting means 54 presents the real number component and the imaginary number component as the comparison component in association with the frequency.

  When expressing the fluctuation of the impedance ZB of the battery B with the impedance ZA of the battery A as a reference, the comparison component K (f) (K (f) = ZB (f) / ZA ( f)) is defined. Since the impedances ZA and ZB are complex numbers, the comparison component K (f), which is the ratio thereof, is also generally complex. The calculation means 53 represents the comparison component K (f) by decomposing it into a real component and an imaginary component.

  FIG. 2 shows an example in which the presentation means 54 presents the real component K (real) and the imaginary component K (imag) of the comparison component K (f) with respect to the frequency change (0.01 kHz ≦ f ≦ 10 kHz). The coordinates of each point correspond to the real component K (real) and the imaginary component K (imag) of the comparison component K (f) calculated by the impedance ZA (f) and the impedance ZB (f) at the frequency f. .

  Thus, in the battery evaluation apparatus according to the present embodiment, the comparison component K (f) at the frequency f is calculated based on the impedance ZA (f) and the impedance ZB (f) at the same frequency f. For this reason, by confirming the state of the comparison component K (f), it is possible to directly grasp the difference in impedance at the same frequency.

  Further, FIG. 3 shows an example in which frequency values (f = 1 Hz, 100 Hz, 1 kHz) are additionally displayed on the plot of FIG. In this case, the relationship between the frequency and the difference in impedance can be recognized more clearly.

  In the example of FIGS. 2 and 3, the absolute value of the comparison component K (f) gradually increases from about 10 kHz to 100 Hz, and then decreases again as the frequency becomes lower. It can be clearly seen that the phase difference and the phase difference change during that time. Further, since it is approximately constant at a low frequency of 1 Hz or less, it can be understood that the impedance ZB shows a change of almost real number in this region. This display method can visually express information that contributes to analysis in this way.

  FIG. 4 shows an example in which the frequency axis is taken as the third axis and the comparative evaluation characteristics of the battery are presented in a three-dimensional display. In this example, the comparison component K (f) is three-dimensionally displayed by the real component K (real), the imaginary component K (imag), and the frequency. Actually, since it is necessary to reduce to a two-dimensional display on a monitor screen or the like, the display is performed by projecting the three-dimensional display onto a two-dimensional plane. The real number component K (real) and the imaginary number component K (imag) are indicated by the points pointed by the arrows. According to this presentation method, the corresponding frequency can be intuitively grasped.

By the way, considering the case where the impedance Z is applied in parallel to the reference impedance ZA, the combined resistance ZB is calculated according to the equation (1).
ZB = {Z / (ZA + Z)} · ZA (1) That is, the expressions of FIGS. 2, 3 and 4 are particularly suitable for expressing the case where the impedance is applied in parallel.

Furthermore, when the impedance ZA is expressed as, for example, the expression (2), the comparison component K can be defined according to the expression (3).
ZA = | ZA | · exp (jθ_A) (2) Equation K = | ZB | / | ZA | · exp {j (θ_B−θ_A)} (3) Equation

  That is, the magnitude of the comparison component K is the ratio of the magnitudes of the impedance ZA and the impedance ZB, and the phase of the comparison component K represents the phase difference between the impedance ZA and the impedance ZB. Therefore, for example, when the impedance ZB matches the reference impedance ZA, the comparison component K = 1. This indicates that when the comparison component K is in the vicinity of 1.0 on the real component K (real) axis, the impedance ZA and the impedance ZB are in a similar state. On the other hand, the fact that the comparison component K has an imaginary component indicates that there is a phase difference between the impedance ZA and the impedance ZB.

  On the other hand, as another method for expressing the fluctuation of the impedance ZB with the impedance ZA as a reference, the impedance ZA is subtracted from the impedance ZB, and the comparison component T (f) (T (f) = ZB (f) −ZA ( f)) may be defined. The calculation means 53 calculates the comparison component T (f) as the sum of the real number component and the imaginary number component, and the real number component and the imaginary number component are presented by the presentation means 54. The expression method is the same as in the case of FIG. 2, FIG. 3, and FIG. This method is suitable for expressing the change when impedance is added in series and ZB = ZA + T.

  In the battery evaluation apparatus of the above embodiment, not only the comparison component K or the comparison component T but also the impedance ZA and the impedance ZB may be displayed. For example, the comparison component K or the comparison component T and the impedance ZA and the impedance ZB can be switched, or the impedance ZA and the impedance ZB may be displayed side by side with the comparison component K or the comparison component T on the same screen. In this case, the display forms shown in FIGS. 2, 3, and 4 can be applied as display forms of the impedance ZA and the impedance ZB.

  As described above, according to the battery evaluation apparatus of this embodiment, the impedance, which is the frequency characteristic of the battery to be compared, is acquired as a real component and an imaginary component as a function of frequency. Then, a comparison component composed of a real component and an imaginary component is calculated and presented in association with the frequency. For this reason, the difference in impedance characteristics can be clearly expressed, and the points corresponding to the same frequency can be easily compared.

  Further, according to the battery evaluation apparatus of the present embodiment, since the ratio of the impedance ZB to the impedance ZA is calculated as the comparison component K, an appropriate expression can be made when the impedance is added in parallel.

  Furthermore, according to the battery evaluation apparatus of the present embodiment, since the value obtained by subtracting the impedance ZA from the impedance ZB is calculated as the comparison component T, an appropriate expression can be made when the impedance is added in series.

  Further, according to the present invention, influences such as differences in battery configuration and battery operating conditions can be extracted as comparative components. Differences in the configuration of the battery include, for example, differences in the structure and shape of the polymer film and the structure and shape of the electrode. Further, the difference in battery operating conditions includes, for example, gas composition, gas flow rate, gas temperature, gas humidity, magnitude of DC current load, battery usage history, and the like.

  The scope of application of the present invention is not limited to the above embodiment. The present invention can be widely applied to battery evaluation devices that compare and evaluate battery characteristics based on electrochemical measurements. Further, the present invention is not limited to application to a fuel cell, and the frequency characteristics in the present invention are not limited to impedance characteristics.

10 Fuel cell (battery)
52 Measurement unit (acquisition means)
53 Calculation means 54 Presentation means

Claims (6)

In a battery evaluation device that evaluates the frequency characteristics of a battery by separating it into a real component and an imaginary component,
Obtaining means for obtaining the first frequency characteristic and the second frequency characteristic as a sum of a real component and an imaginary component, respectively, as a function of frequency;
The comparison component for each frequency of the first frequency characteristic and the second frequency characteristic is based on the real component and the imaginary component that are function values at the frequency, and a real component as a function value of the frequency and Calculating means for calculating the sum of imaginary components;
Presenting means for presenting the real component and the imaginary component as the comparison components calculated by the calculating means in association with frequencies;
A battery evaluation apparatus comprising: The battery evaluation apparatus according to claim 1, wherein the calculation unit calculates a ratio of the second frequency characteristic to the first frequency characteristic as the comparison component. The battery evaluation apparatus according to claim 1, wherein the calculating unit calculates a value obtained by subtracting the first frequency characteristic from the second frequency characteristic as the comparison component. 4. The battery evaluation apparatus according to claim 1, wherein the presenting unit presents the real number component, the imaginary number component, and the frequency by display associated with each other. 5. The presenting means presents the three-dimensional display with the real number component, the imaginary number component, and the frequency as axes, or a display obtained by projecting the three-dimensional display onto a two-dimensional plane. Battery evaluation equipment. In a battery evaluation method for evaluating the frequency characteristics of a battery by separating it into a real component and an imaginary component,
Obtaining a first frequency characteristic and a second frequency characteristic as a sum of a real component and an imaginary component, respectively, as a function of frequency;
The comparison component for each frequency of the first frequency characteristic and the second frequency characteristic is based on the real component and the imaginary component that are function values at the frequency, and a real component as a function value of the frequency and A calculation step for calculating the sum of imaginary components;
A presenting step of presenting the real component and the imaginary component as the comparison component calculated by the calculating step in association with a frequency;
A battery evaluation method comprising: