JP2013096790A - Method for detecting deterioration in lithium ion capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a deterioration detection method capable of quickly detecting deterioration compared with a method for detecting deterioration caused by high-rate discharge, on the basis of a change in a resistance value of a lithium ion capacitor.SOLUTION: The deterioration detection method includes steps of: calculating as a capacitance rate a ratio of an in-use capacitance value to an initial capacitance value in each of a first voltage area where a cell voltage of the lithium ion capacitor becomes 3 V or more during using the lithium ion capacitor and a second voltage area where the cell voltage of the lithium ion capacitor becomes less than 3 V; and comparing a difference value between the capacitance rate in the first voltage area and the capacitance rate in the second voltage area, with a preset threshold and detecting a timing when the deterioration of the lithium ion capacitor occurs.

Description

  The present invention relates to a deterioration detection method for a lithium ion capacitor, and more particularly, to a deterioration detection method for detecting deterioration caused by high-rate discharge of a lithium ion capacitor.

  While environmental issues are being highlighted, hybrid vehicles and fuel cell vehicles are being actively developed, and along with this development, development of lithium-ion batteries to be used as the main power supply or auxiliary power supply for these vehicles is also underway. Has been done.

  Lithium-ion batteries are subject to deterioration when the so-called high-rate discharge, which is caused by flowing a relatively large current with respect to the capacity of the battery, is repeated. Is required. Therefore, for example, as a device that suppresses deterioration, the charging current value to the battery and the discharging current value from the battery are detected and stored, and an evaluation value of deterioration caused by high-rate discharge is calculated based on the stored result. And the apparatus which controls the value of discharge electric power based on this calculated result is known (refer to patent documents 1).

JP 2010-60408 A

  In recent years, research and development of lithium ion capacitors have started to be performed because of their low internal resistance and superior output characteristics compared to lithium ion batteries. In general, a lithium ion capacitor uses activated carbon as a positive electrode active material and a carbon material capable of occluding or releasing lithium ions as a negative electrode active material. The positive and negative electrodes are arranged through a separator, and an electrolyte containing a lithium salt. An infiltrated configuration is adopted.

  When high-rate discharge is repeatedly performed on a lithium ion capacitor having such a configuration, ions in the electrolytic solution move from one electrode to the other electrode, resulting in a bias in ion concentration in the electrolytic solution, and in the electrolytic solution. The balance of salt concentration is lost. When the balance of the salt concentration in the electrolytic solution is lost, the conductivity in the electrolytic solution is reduced, so that ions in the electrolytic solution are difficult to diffuse, and as a result, the resistance value of the lithium ion capacitor is increased.

  When the resistance value increases, the voltage of the lithium ion capacitor is likely to reach the oxidation / reduction decomposition region of the electrolytic solution or the oxidation / reduction decomposition region of the binder for the electrode, so that the progress of deterioration accelerates. . In addition, if the ions in the electrolytic solution are difficult to diffuse, the ions cannot reach the surface of the electrode, causing a decrease in capacitance.

  As described above, since the life of the lithium ion capacitor is shortened due to the deterioration caused by the high rate discharge, it is necessary to take some measures. As in the conventional technique described above, it is also possible to detect deterioration based on the degree of voltage drop, in other words, resistance rise. However, in the case of a lithium ion capacitor in which a sudden increase in resistance occurs, it is required to detect more quickly rather than detecting deterioration after the increase in resistance occurs.

  Accordingly, the present invention provides a method for detecting deterioration of a lithium ion capacitor that can quickly detect deterioration as compared to a method for detecting deterioration caused by high-rate discharge based on a change in resistance value of the lithium ion capacitor. For the purpose.

  In order to solve the above-described problems, a lithium ion capacitor deterioration detection method according to the present invention includes a first voltage region in which a cell voltage of the lithium ion capacitor is 3 V or more while the lithium ion capacitor is in use, In each of the second voltage regions in which the voltage is less than 3 V, a step of calculating the in-use capacitance value of the lithium ion capacitor in time series, and before using the lithium ion capacitor, the first voltage region and the second voltage region Obtaining a capacitance of the lithium ion capacitor as an initial capacitance value in each of the voltage regions, and in-use electrostatic capacity with respect to the initial capacitance value in each of the first voltage region and the second voltage region. A step of calculating a ratio of capacitance values as a capacitance ratio; and a capacitance ratio in the first voltage region and a second voltage region A difference value between the capacitance ratio, compared with the predetermined threshold value, characterized in that it and a step of detecting a timing at which the deterioration of the lithium ion capacitor is generated.

  Since the lithium ion capacitor has a first voltage region in which the cell voltage of the lithium ion capacitor is 3 V or more and a second voltage region in which the cell voltage of the lithium ion capacitor is less than 3 V, ion exchange occurs at the positive electrode. The ion concentration in the electrolytic solution is biased and the deterioration proceeds. Therefore, the method for detecting deterioration of a lithium ion capacitor according to the present invention is a static ion that decreases with an uneven ion concentration in the electrolyte at the cell voltage of 3 V of the lithium ion capacitor as a boundary while using the lithium ion capacitor. Paying attention to the capacitance value, in the first voltage region and the second voltage region, the capacitance ratio during use of the lithium ion capacitor is calculated, the difference value thereof is compared with a predetermined threshold value, and the lithium ion It is possible to detect the timing at which deterioration of the capacitor occurs. It has been found that the deterioration detection method based on the difference value can detect the deterioration at a relatively early stage of the use time of the lithium ion capacitor as compared with the deterioration detection method based on the change in the resistance value of the lithium ion capacitor. As a result, the deterioration detection method according to the present invention can detect the deterioration more quickly than the deterioration detection method based on the change in the resistance value of the lithium ion capacitor.

  According to the present invention, it is possible to quickly detect deterioration as compared with a method of detecting deterioration caused by high-rate discharge based on a change in resistance value of a lithium ion capacitor.

It is a schematic diagram which shows the external appearance of the single cell of the lithium ion capacitor which is one Embodiment of this invention. It is explanatory drawing for calculating an electrostatic capacitance value and a cell resistance value in the cycle test time which repeatedly discharges / charges. It is a graph which shows the relationship between a capacitance rate and cell use time. It is a graph which shows the relationship between the difference value of an electrostatic capacitance rate, and cell use time. It is a graph which shows the relationship between a cell resistance increase rate and cell use time. It is the graph which compared the graph based on the difference value of an electrostatic capacitance rate, and the graph based on a cell resistance value.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In order to facilitate the understanding of the description, the same constituent elements in the drawings will be denoted by the same reference numerals as much as possible, and redundant description will be omitted.

  FIG. 1 is a schematic diagram showing an appearance of a single cell 2 of a lithium ion capacitor 1 according to an embodiment of the present invention. A single cell (hereinafter simply referred to as a cell) 2 constituting the lithium ion capacitor 1 of the present embodiment is formed of an external extraction electrode 3 and a main body 4. The main body 4 is composed of a positive electrode, a negative electrode, a separator, and an electrolytic solution (not shown). The lithium ion capacitor 1 used in the present embodiment has a square cell having a width W of 100 mm, a length of 100 mm, and a depth of 5 mm, a laminate-type electrode structure, and a capacitance of 100F. The lithium ion capacitor 1 of the present embodiment uses activated carbon for the positive electrode, a carbon material pre-doped with lithium ions for the negative electrode, and an organic electrolytic solution in which a lithium salt is dissolved in an organic solvent. .

  Here, in the lithium ion capacitor 1, two types of ions are used on the positive electrode side with the cell voltage V being 3V as a boundary. In the region A1 (shown in FIG. 2) where the cell voltage V is 3V or more, anions are used at the positive electrode, and in the region A2 (shown in FIG. 2) where the cell voltage V is less than 3V, lithium ions are used at the positive electrode. Thus, in the lithium ion capacitor 1, since the exchange of ions occurs at the positive electrode with the cell voltage V of 3V as a boundary, the ion concentration in the electrolytic solution is biased and the deterioration proceeds.

  Therefore, in the method for detecting deterioration of the lithium ion capacitor 1 according to the present embodiment, while the lithium ion capacitor 1 is being used, the cell voltage V decreases with the deviation of the ion concentration in the electrolyte at 3V. Focusing on the capacitance value, the capacitance ratio during use is calculated in time series in the region around 3V, and the deterioration is detected based on the difference value between them. While using the lithium ion capacitor 1, based on the capacitance value C1 and its capacitance ratio R1 in the region of 3V or more, and the capacitance value C2 and its capacitance rate R2 in the region of less than 3V, Detect the timing of deterioration.

  Specifically, first, a charge / discharge cycle test is performed using the lithium ion capacitor 1 of the present embodiment, and the electrostatic capacity in the region A1 of 3 V or more during use of the lithium ion capacitor 1 during the cycle test. A value C1 and a capacitance value C2 in the region A2 of less than 3V are calculated.

The capacitance value C1 in the region A1 where the cell voltage V is 3V or more, and the capacitance value C2 in the region A2 where the cell voltage V is less than 3V are respectively expressed by the following equations.
C1 = (Δt1 / ΔV1) × A ′
C2 = (Δt2 / ΔV2) × A ′
As shown in FIG. 2, Δt1 and Δt2 are the usage time during which the cell is used, ΔV1 is a voltage drop value at Δt1 time, ΔV2 is a voltage drop value at Δt2 time, and A ′ is an average current flowing through the cell. .

Next, the capacitance ratio R1 in the region A1 of 3V or more and the capacitance ratio R2 in the region A2 of less than 3V are obtained from the following equations, respectively. The capacitance ratios R1 and R2 in each of the areas A1 and A2 indicate how much the capacitance values C1 and C2 in use are maintained with respect to the acquired initial capacitance values C10 and C20. It shows the index of whether or not. Therefore, when these capacitance ratios R1 and R2 are low, the degree of deterioration is high.
R1 = C1 / C10
R2 = C2 / C20
C10 is an initial capacitance value in the region A1 of 3V or more, and C20 is an initial capacitance value in the region A2 of less than 3V.

  FIG. 3 shows graphs G1 and G2 showing the relationship between the capacitance ratios R1 and R2 thus determined and the cell usage time t. The graph G1 shows the relationship between the capacitance rate R1 and the cell usage time t, and the graph G2 shows the relationship between the capacitance rate R2 and the cell usage time t. It is shown that the capacitance ratios R1 and R2 decrease as the cell use time t elapses. Therefore, in each of the regions A1 of 3 V or more and the regions A2 of less than 3 V, the respective electrostatic capacitances R1 and R2 are reduced. It can be confirmed that the capacity is decreasing.

  Next, the difference between the capacitance rate R1 in the region A1 of 3V or more and the capacitance rate R2 in the region A2 of less than 3V is calculated. FIG. 4 shows a graph G3 showing the relationship between the absolute value D (D = | R1-R2 |, hereinafter simply referred to as difference value D) and the cell usage time t based on the calculated difference.

  According to this graph G3, when the cell use time t is 60 hours or more, since the difference value D is rapidly increased, it can be confirmed that a large deviation in the ion concentration in the electrolytic solution has begun to occur. . As a result, the difference value D when the cell usage time t has passed 60 hours can be set as the threshold value T.

  When the difference value D between the capacitance ratio R1 in the region A1 of 3V or more and the capacitance ratio R2 in the region A2 of less than 3V exceeds the threshold T (| R1-R2 |> T). Therefore, it can be detected that deterioration due to high-rate discharge of the lithium ion capacitor has occurred.

  Such a detection method of deterioration can detect the timing at which the deterioration of the lithium ion capacitor occurs earlier than detecting the deterioration by increasing the cell resistance.

Here, as shown in FIG. 2, the cell resistance value R can be calculated by the following equation.
R = ΔVr / A
ΔVr is a voltage drop value obtained by subtracting the measured value Vx of the upper limit voltage of the cell from the initial value Vmax of the upper limit voltage of the cell 2, and A is the current value flowing through the cell 2.

  The cell resistance value R is appropriately calculated according to the passage of the cell usage time t, and the rate of increase r with respect to the initial value of the cell resistance is calculated. FIG. 5 shows a graph G4 showing the relationship between the cell resistance increase rate r thus calculated and the cell usage time t.

  According to this graph G4, when the cell usage time t has passed 85 hours or more, the cell resistance increase rate r has increased rapidly, so that a large deviation in ion concentration in the electrolytic solution has begun to occur. Can be confirmed.

  As shown in FIG. 6, the graph showing the relationship between the difference value D and the cell usage time t and the graph showing the relationship between the cell resistance increase rate r and the cell usage time t are superimposed, In comparison, it can be confirmed that the detection of the deterioration based on the difference value D can detect the deterioration before the detection of the deterioration based on the change in the increase rate of the cell resistance.

DESCRIPTION OF SYMBOLS 1 Lithium ion capacitor 2 Cell 3 Extraction electrode 4 Main body A1 3V or more area | region (1st voltage area)
A2 Area below 3V (second voltage area)
C1 In-use capacitance value in the region of 3V or more C10 Initial capacitance value in the region of 3V or more C2 In-use capacitance value in the region of less than 3V C20 Initial capacitance value in the region of less than 3V R1 Capacitance rate in the region of 3V or more R2 Capacitance rate in the region of less than 3V G1 Graph based on the capacitance rate R1 G2 Graph based on the capacitance rate R2 G3 Graph based on the difference value G4 Increase rate of the cell resistance Graph based on D D Difference value (absolute value of difference)
T threshold V cell voltage

Claims (1)

A deterioration detection method for detecting deterioration of a lithium ion capacitor,
While using the lithium ion capacitor, in each of the first voltage region in which the cell voltage of the lithium ion capacitor is 3 V or more and the second voltage region in which the cell voltage of the lithium ion capacitor is less than 3 V, Calculating the capacitance value of the ion capacitor during use in time series;
Obtaining a capacitance value of the lithium ion capacitor as an initial capacitance value in each of the first voltage region and the second voltage region before using the lithium ion capacitor;
Calculating a ratio of the in-use capacitance value to the initial capacitance value as a capacitance ratio in each of the first voltage region and the second voltage region;
The difference value between the capacitance ratio in the first voltage region and the capacitance ratio in the second voltage region is compared with a predetermined threshold, and the timing at which the deterioration of the lithium ion capacitor occurs is determined. Detecting process;
A method for detecting deterioration of a lithium ion capacitor.

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