JP2006047283A - Determination method for degradation in capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance power saving performance and accuracy, in the measurement for determination method of degradation in a capacitor with electrolytic solution arranged in between electrode objects. <P>SOLUTION: In the method, a capacitor is provided with a pair of electrode objects and electrolytic solution arranged in between the electrode objects. An AC voltage is applied to this capacitor to measure impedance characteristics, based on the frequency of the AC voltage and then determine degradation in the capacitor, where an inflection point, appearing in the impedance characteristic by degradation in the electrolytic solution, is calculated in advance, so as to compare the impedance value of a domain of frequency lower than that of this inflection point, for determination of degradation in the capacitor. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for determining deterioration of a capacitor in which an electrolytic solution is disposed between electrode bodies.

  A general capacitor uses an activated carbon that has a large specific surface area of electrode material and is electrochemically inert, and uses a large electric double layer capacity in combination with an electrolyte. It can be rapidly charged / discharged with a large current without being accompanied by a large current density, and its output density is higher than that of a chemical battery. It can be applied to large current generation circuits, instantaneous compensation power supplies, load leveling circuits, etc. Is expected.

  The electric double layer capacitor has a coin type for memory backup and a cylindrical type for power. In the coin type, a disk-shaped lower electrode, separator, and upper electrode are sequentially laminated on a low-profile cylindrical metal case with an open upper end, and an electrolyte is injected into the inside. A gasket for insulation and sealing is housed in the peripheral portion, a metal lid is covered on the upper surface, and the metal case and the metal lid are not crimped directly so as to have a caulking process.

  Moreover, as shown in FIG. 6 for the configuration of the cylindrical electric double layer capacitor, the capacitor element 20 has a strip-shaped metal foil, a punching metal, an expanded metal or the like as a current collector, and both or one side of the current collector. In addition, a polarizing electrode made of activated carbon, carbon and a binder is applied, and two of them are prepared. Between these current collectors, a strip for insulating and holding an electrolyte solution is interposed in the same manner. Each current collector is connected to one electrode terminal 21 one by one, wound in a spiral shape, and finally fixed with an adhesive tape 22. The electrode terminal 21 of the capacitor element 20 is connected to a fitting 27 of a sealing body 24, has a bottomed cylindrical shape, and a lead terminal 26 protrudes to the outside in a metal case 23 in which a concave groove 25 is formed near the upper end. The electric double layer capacitor is configured by storing an electrolyte solution (not shown) and bending the upper end portion of the metal case 23 inward and sealing.

  In such an electric double layer capacitor, deterioration of the dry-up mode in which the internal electrolytic solution evaporates and the internal resistance increases and the electrostatic capacity decreases due to long-term use proceeds and eventually reaches the end of its life.

  As a method of measuring this lifetime, a technique of adding a low-frequency square wave signal as a measurement signal, integrating a predetermined portion of the response signal, and detecting a characteristic change of the electric double layer capacitor based on the integrated value ( For example, refer to Patent Document 1), when energization control of the electric double layer capacitor is performed, and the voltage between the terminals of the electric double layer capacitor reaches the deterioration technology voltage within a predetermined time from the time when the voltage between the terminals reaches a predetermined value. And a technique for determining that the surface temperature of the electric double layer capacitor is increased (for example, see Patent Document 3).

Non-patent document 1 also describes a technique related to impedance characteristics of the electric double layer capacitor.
Japanese Patent Application Laid-Open No. 06-342042 Japanese Patent Laid-Open No. 2001-297554 JP 2001-085283 A Brian E.M. Conway, “Electrochemical Capacitors Fundamentals, Materials, Applications” published by NTS, Inc., June 5, 2001, p. 393-401

  However, the conventional method for measuring deterioration of an electric double layer capacitor requires signal processing by a measurement signal source, a circuit unit such as an A / D converter, and a CPU, and the measurement device becomes expensive and the method of detecting deterioration is complicated. In the technique of measuring the surface temperature of the electric double layer capacitor, there is a problem in measurement accuracy.

  Further, even in the electrolytic capacitor degradation measurement technique, there is a problem that the accumulation of measured data becomes enormous, and the circuit device for judging degradation based on the data becomes expensive and complicated.

  Furthermore, when performing deterioration determination of a capacitor in which an electrolyte is disposed between electrode bodies such as an electric double layer capacitor, its capacitance component and DC capacitor resistance (hereinafter referred to as DCR) component are measured, and the measurement results are used as a basis. However, when measuring the capacitance component and the DCR component, the DC voltage method for measuring the capacitance component and the DCR component based on the behavior of the DC voltage when charging and discharging the capacitor, and the AC There is an AC impedance method in which voltage is applied and derived from the impedance value. When the former DC voltage method is used, accurate measurement results can be obtained because direct measurement is performed from the DC voltage in charge / discharge, but for charge / discharge. In addition, since most of the charge in the capacitor is used, a large amount of power is consumed for the deterioration determination.

  In the AC impedance method, which is the latter, the power consumption can be reduced because the frequency characteristics of the AC voltage are used. However, in the state in which the capacitor has deteriorated, the value becomes smaller than the value obtained by the DC voltage method. It has been determined that it has not deteriorated, and its reliability is low.

  An object of the present invention is to solve such a conventional problem and to improve the measurement accuracy of the AC impedance method with low power consumption when determining deterioration of a capacitor.

  In order to solve the above-mentioned problems, the present invention applies an AC voltage to a capacitor including a pair of electrode bodies and an electrolytic solution disposed between the electrode bodies, and measures impedance characteristics depending on the frequency of the AC voltage. In this method, the inflection point that appears in the impedance characteristics due to the deterioration of the electrolyte solution is obtained in advance, and the impedance value in a frequency region lower than the inflection point is compared to determine the deterioration. This is a method for determining the deterioration of

  With this deterioration determination method, the measurement accuracy in determining the deterioration of the capacitor can be increased, and the power consumption required for the determination can be suppressed.

(Embodiment 1)
Hereinafter, Embodiment 1 of the present invention will be described with reference to the drawings.

  FIG. 1 is a basic circuit diagram using an electric double layer capacitor. The figure shows that the load unit is operated by applying voltage from the input power supply unit, part of which charges the electric double layer capacitor and the input power supply unit becomes abnormal or requires high power In such a case, electric power is supplied from the electric double layer capacitor. And since the electric double layer capacitor deteriorates due to long-term use or usage environment, the deterioration is determined by the deterioration measuring unit, and when it is determined to be deteriorated, it can be detected by an alarm or display on the abnormality display unit. Is.

  As shown in FIG. 2, the electric double layer capacitor includes a pair of electrode bodies 1 and an electrolyte solution 3 disposed between the electrode bodies 1, and a housing filled with the electrolyte solution 3. 4 includes a pair of electrode bodies 1, a separator 2 disposed between the electrode bodies 1, a lead terminal 5 connected to each electrode body 1, and a sealing body 6 that seals the housing 4. . The electrode body 1 is formed by covering the surface of a current collector 1a made of a metal such as aluminum with activated carbon 1b. Further, the separator 2 can be removed by using a highly viscous electrolyte solution 3 such as a gel.

  The deterioration determination of the electric double layer capacitor is performed by measuring by an AC impedance method using a deterioration measuring unit, and this AC impedance method can perform a very power-saving measurement. It is important to improve the credibility of

  When an AC voltage is applied to the electric double layer capacitor and impedance characteristics according to the frequency of the AC voltage are measured, the result is as shown in FIG. In the figure, the vertical axis represents the impedance value, and the horizontal axis represents the frequency when a constant AC voltage is applied. The impedance characteristic of the initial electric double layer capacitor is as shown by locus 7, and the resistance component of the electrolytic solution 3, the activated carbon 1b, and the current collector 1a constituting the electric double layer capacitor, so-called equivalent series resistance (ESR). As 9 is used, it increases to become locus 8.

  As the electric double layer capacitor is further used, its equivalent series resistance (ESR) further increases, and a deteriorated product of the electrolytic solution 3 appears in the electrolytic solution 3, and the deteriorated product appears on the surface of the activated carbon 1 b and the separator. 2, a resistance component against movement of ions, a so-called diffusion resistance component 10, is formed, and a locus 11 having an inflection point 12 generated by deterioration of the electrolytic solution is formed.

  Based on the presence of the inflection point 12, the present invention obtains a highly accurate result that substantially matches the measurement result derived from the DC voltage method by making a determination based on the impedance value in the frequency region 13 lower than the inflection point 12. It is possible to realize power saving measurement which is an advantage of the AC impedance method.

  More specifically, FIG. 4 shows a flowchart of a method for determining the deterioration of the electric double layer capacitor by the deterioration measuring unit in FIG.

  First, the deterioration characteristics of the electric double layer capacitor used are examined. As for the deterioration characteristics of the electric double layer capacitor, a load (2.0 to 2.5 V) is applied at a temperature of 50 ° C., and the impedance characteristics after 10,000 to 15000 hours are measured. This deterioration characteristic can be shortened by further increasing the temperature.

  The inflection point 12 generated by the deterioration of the electrolytic solution is obtained from the impedance characteristics at the time of deterioration, a frequency lower than the inflection point 12 is determined as a measurement frequency, and the frequency and the impedance value are stored in the deterioration measurement unit. Remember. Further, the deterioration limit impedance value of the electric double layer capacitor is determined from the product design of the circuit incorporating the electric double layer capacitor, and stored in the deterioration measuring unit.

  And by operating the circuit incorporating the electric double layer capacitor, the electric double layer capacitor gradually deteriorates. An AC voltage is applied at predetermined intervals during the operation of this circuit, and the impedance value is measured at a preset frequency.

  The measured impedance value is compared with the impedance value of the preset deterioration limit, and if it is less than that, it is determined that there is no abnormality, and the electric double layer capacitor can be used continuously. If the measured impedance value exceeds the deterioration limit impedance value, it is determined that there is an abnormality and displayed by a warning lamp or the like.

  Thus, by determining the deterioration of the electric double layer capacitor based on the impedance value in the frequency region 13 lower than the inflection point 12 of the impedance characteristic, the deterioration of the capacitor can be accurately determined, and the power used for the measurement Can also save power.

  In addition, if the deterioration determination of the electric double layer capacitor is measured and determined at a frequency higher than the inflection point 12 of the AC impedance characteristic, the impedance value shows a low value even if the capacitor is deteriorated. A large error occurs, and the accuracy of the deterioration determination deteriorates.

  The circuit diagram using the electric double layer capacitor is a basic circuit to the last, and the present invention is not limited to this circuit diagram.

(Embodiment 2)
In the first embodiment, first, the DCR of the degradation characteristics of the electric double layer capacitor is measured by the DC voltage method. Next, the AC impedance characteristic is measured in the same manner as in the first embodiment. Next, a correlation between the DCR and the AC impedance characteristic is obtained. The correlation at this time is shown in FIG.

  From FIG. 5, the deterioration measuring unit stores the AC impedance value (hereinafter referred to as Z) having a frequency lower than the inflection point 15 when the electric double layer capacitor is deteriorated and the DCR / Z ratio. Then, the electric double layer capacitor is gradually deteriorated by operating the circuit incorporating the electric double layer capacitor as in the first embodiment. During the operation of this circuit, an AC voltage is applied at predetermined time intervals, Z at a preset frequency is measured, DCR is measured at the same time, and the DCR / Z ratio is set to the preset degradation limit DCR. The / Z ratio is compared, and if it is less than that, it is determined that there is no abnormality, and the electric double layer capacitor can be used continuously. If the measured DCR / Z ratio exceeds the degradation limit DCR / Z ratio, it is determined that there is an abnormality and a warning lamp or the like is displayed.

  By measuring by such an AC impedance method, it is possible to more accurately determine the deterioration of the electric double layer capacitor.

(Embodiment 3)
In the first embodiment, the low frequency region 14 in which the impedance value suddenly decreases from the frequency 0 of the result of measuring the impedance characteristics of the electric double layer capacitor (FIG. 3) is the power gradient accompanying the self-discharge of the electric double layer capacitor. The capacitance component is shown, and it is possible to determine the deterioration of the electric double layer capacitor from the low frequency region 14.

  Thus, by using self-discharge, it is possible to suppress power consumption required for determining the deterioration of the electric double layer capacitor.

  When measuring impedance values using the AC impedance method or measuring capacitance components using capacitor self-discharge, it is necessary to measure when not using a capacitor with little voltage fluctuation in order to further improve the accuracy. desirable.

  In addition, it has been proposed to use this electric double layer capacitor as an on-vehicle power source for fuel cell vehicles, etc., which has been recently proposed. In fields where suppression is desired as much as possible, measurement of impedance values using the AC impedance method described above and measurement of capacitance components using capacitor self-discharge are effective. Further, in order to further improve the accuracy of the deterioration determination, it is desirable to perform measurement when the on-vehicle power source with little voltage fluctuation is not used.

  Furthermore, although the electric double layer capacitor has been described in the present embodiment, the present invention is not limited to this embodiment, and a pair of electrode bodies 1 and a separator 2 disposed between the electrode bodies 1. In addition, examples of the capacitor provided with the electrolytic solution 3 include a redox capacitor and the like, and have the same effect.

  The method for determining deterioration of a capacitor in which an electrolytic solution is disposed between electrode bodies according to the present invention has an effect that power can be saved, and is particularly useful in an in-vehicle application in which miniaturization is required.

Basic circuit diagram using electric double layer capacitor in Embodiment 1 of the present invention Sectional view showing the same electric double layer capacitor Same impedance characteristics Flow chart of the same deterioration judgment method Characteristic diagram of DCR / Z ratio after deterioration in the second embodiment Sectional view showing a conventional electric double layer capacitor

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrode body 1a Current collector 1b Activated carbon 2 Separator 3 Electrolytic solution 4 Housing 5 Lead terminal 6 Sealing body

Claims (4)

A method for determining deterioration by applying an AC voltage to a capacitor including a pair of electrode bodies and an electrolyte disposed between the electrode bodies and measuring impedance characteristics depending on the frequency of the AC voltage,
A capacitor deterioration determination method in which an inflection point that appears in impedance characteristics due to deterioration of the electrolytic solution is obtained in advance, and deterioration determination is performed by comparing impedance values in a frequency region lower than the inflection point. The capacitor deterioration determination method according to claim 1, wherein the deterioration determination comparison is made with an impedance value obtained by deterioration in advance. 2. The method of determining deterioration of a capacitor according to claim 1, wherein the comparison of the deterioration determination is made by comparing a value obtained by correlation between an impedance value obtained by deterioration in advance and a series capacitor resistance. The method for determining deterioration of a capacitor according to claim 1, wherein the comparison of the deterioration determination is performed using a capacitance component whose voltage changes due to self-discharge of the capacitor.

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