JP2000028689A - Estimation method for discharge capacity of - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an estimation method, for the discharge capacity of a secondary battery, in which the discharge capacity of a fuel cell can be estimated with a short- time measurement. SOLUTION: A plurality of secondary batteries are used as samples. Their terminal voltage is measure data time when they are charged with a set current for a fixed time. After that, they are charged up to nearly 100%. Then, the ratio of a charging capacity at a time when the respective batteries are charged for a set time to a charging capacity at nearly 100% is found. The characteristic (1) of the terminal voltage with reference to the ratio is found in advance. An actual discharge capacity when the sample batteries are discharged by a prescribed discharge current is measured. The characteristic (2) of the discharge current with respect to the charging capacity at nearly 100% of the respective sample batteries is found in advance. On the basis of the result by measuring the terminal voltage at a time when the sample batteries are charged with the set current for a set time, the charging capacity at nearly 100% of the sample batteries is computed and estimated on the basis of the characteristic (1). A discharge capacity when the sample batteries are discharged at a prescribed discharge current is estimated, on the basis of its estimated result and on the basis of the characteristic (2).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for estimating a discharge capacity when a secondary battery is discharged at a predetermined discharge current value.

[0002]

2. Description of the Related Art Secondary batteries have large variations in their individual capacities. At the end of the manufacturing process, each finished product is actually subjected to a charge / discharge test, and the respective discharge capacities are measured to determine the stratification of each battery. Work needs to be done. FIG. 6 shows an example of such a conventional charge / discharge test method. For example, when a sample battery such as a lithium secondary battery is discharged from 0 V to a current of 1 C (a current at which the battery is completely discharged in one hour, for example, a nominal capacity of 1000
The battery is charged at a constant current of, for example, 1000 mA for a mAh battery.

When the terminal voltage of the battery gradually rises and reaches a maximum voltage Vmax (for example, 4.2 V), the charging current gradually decreases from 1 C so that the terminal voltage maintains the maximum voltage. Then, constant voltage charging is performed. Then, the charging is terminated when the amount of the charging current becomes substantially zero.

After an interval (rest) of about 10 minutes, the charged battery is discharged at a constant current of, for example, 1 C. Then, the terminal voltage of the battery gradually decreases. Then, the terminal voltage becomes the minimum voltage Vmin from the start of discharge.
(For example, 3.0 V), the discharge capacity of the sample battery is determined by measuring the time until the discharge ends. That is, the discharge capacity of the sample battery when the minimum voltage Vmin is reached after one hour with a discharge current of 1000 mA is 1000 mAh.

[0005]

However, in such a charge / discharge test method, for example, 2.5 hours for charging,
If it takes about one hour for discharging, about four hours are required for one sample battery including the preceding and following processes. Therefore, in order to secure a certain number of products in a mass production line or the like, it is necessary to increase the number of facilities for the charge / discharge test and perform the tests in parallel, which raises the problem of increasing the production cost.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for estimating a discharge capacity of a secondary battery, which can estimate a discharge capacity of a sample battery by a short-time measurement. It is in.

[0007]

According to the method for estimating the discharge capacity of a secondary battery according to the present invention, when a plurality of secondary batteries are used as a sample and the sample battery is charged at a constant current for a predetermined time, the terminal voltage is reduced. Is measured, and then the sample battery is
Charge to 00%. Then, for each of the sample batteries, the ratio of the charge capacity at the time of charging for a certain period of time to the charge capacity of approximately 100% is determined, and the characteristics of the terminal voltage with respect to the ratio are defined as characteristics. Further, the actual discharge capacity when the sample batteries are discharged at a predetermined discharge current is measured, and the characteristics of the discharge capacity with respect to the charge capacity of approximately 100% of each sample battery are defined as characteristics.

[0008] By obtaining these characteristics in advance, the terminal voltage of the sample battery measured when the sample battery is charged with the constant current for the predetermined time is measured. A charge capacity of approximately 100% of the battery is estimated by calculation, and a discharge capacity when the sample battery is discharged at the predetermined discharge current is estimated based on the estimation result and characteristics.

That is, in order to measure the discharge capacity by the conventional method, the sample battery is charged to approximately 100% and then actually discharged until the terminal voltage reaches the minimum voltage (discharge end voltage). However, according to the method of the present invention, the measurement actually performed on the sample battery is only in the middle of charging, and thereafter, the discharge capacity can be estimated based on the characteristics. Therefore, the time required for the measurement can be significantly reduced as compared with the related art, so that the discharge capacity of many batteries can be estimated without the need for a large number of equipment such as a charger used for the measurement. Cost can be reduced.

According to the method for estimating the discharge capacity of a secondary battery according to the present invention, the characteristics are determined by measuring the actual discharge capacity for each of a plurality of batteries discharged at a plurality of predetermined discharge currents. By obtaining the values, it is possible to estimate the discharge capacity at a plurality of stages of the predetermined discharge current by performing only one measurement on the sample battery.

According to the method for estimating the discharge capacity of a secondary battery according to the third aspect of the present invention, the fixed time for charging the sample battery is made the same as the fixed time for obtaining the characteristics.
The accuracy of estimating the discharge capacity can be further improved.

According to the method for estimating the discharge capacity of a secondary battery according to the present invention, the predetermined time is set near the time required for the terminal voltage of the sample battery to exceed the lower limit of the usable voltage range. In addition, the time for actually performing measurement on the sample battery can be substantially minimized. According to the method for estimating the discharge capacity of a secondary battery according to the fifth aspect, when estimating the discharge capacity of a lithium battery, the time required for measurement can be reduced.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. (1) Derivation of characteristics First, a plurality of samples of the same type of secondary battery, for example, a battery composed of a lithium ion secondary battery and having the same specification (immediately after completion and never charged) are prepared as samples. , By the same charging method as before, the charging capacities MA, MB, Mc,... Of the entire usable voltage range (that is, approximately 100% charging capacity, hereinafter referred to as 100% capacity).
Ask for ...

The charging capacity is (charging current) × (charging time)
Is required. Note that when the mode shifts to constant voltage charging, the charging current value gradually decreases from the initial value. However, since the charging current value is controlled by a charger (not shown), the charging capacity for each charging current value that changes in a stepwise manner. Is integrated over time to determine the total charge capacity.

Here, the "total usable voltage range" will be described. For example, the nominal working voltage range (Vma
Even if x-Vmin) is 4.2V-3.0V, in practice, after a certain time has passed after charging the battery to 4.2V, the terminal voltage of the battery slightly decreases from 4.2V. {(4.2-α) V}.

Also, when the battery is discharged to 3.0 V, after a certain period of time has elapsed, the terminal voltage of the battery slightly increases from 3.0 VＶ (3.0 + β).
V｝. Therefore, the whole usable voltage range here is a voltage range that can be actually used (4.2−α) V〜.
(3.0 + β) V.

In the process of obtaining the 100% capacity, as shown in FIG. 3, after a lapse of a fixed time (for example, 30 minutes) from the start of constant current charging, the terminal voltage VT (VA, VB, VC ...) is measured. In this case, the terminal voltage VT is (3.0 + β) <VT <(4.2−α) That is, the terminal voltage VT is measured within the usable voltage range. At this time, the charge capacity of each sample battery is, for example, 1000 if the charge current value is 1000 mA.
It is calculated as mA × 0.5h = 500 mAh.

After the measurement of the 100% capacity, the percentage of the charged capacity of each sample battery relative to the 100% capacity after a lapse of a predetermined time from the start of charging (hereinafter referred to as capacity%) is calculated. (A%, B%, C%,
…). For example, the charging capacity after a certain time has passed is 500 mA.
h, the 100% capacity of the sample battery is 880 mAh, the capacity% is about 500/880 = 57
(%).

Thus, the inventors of the present invention indicate the corresponding terminal voltages VA, VB, VC,... On the abscissa axis, which is the determined capacity% of each sample battery, A%, B%, C%,. When the measurement results are plotted with the vertical axis as, as shown in FIG. 1, it has been experimentally revealed that batteries of the same type and of the same standard can obtain substantially constant characteristics.

(2) Derivation of Characteristics Next, each of the sample batteries whose 100% capacity has been measured is actually discharged at a plurality of predetermined discharge current values, and the discharge capacity for each discharge current value is measured. FIG. 2 shows the results of measurements performed by the inventor, where the number of samples N = 100. As shown in FIG. 2, for 0.2 C, 0.6 C, and 1 C having relatively low discharge current values, the discharge capacity is approximately proportional to the 100% capacity of each sample battery.

The discharge current value is relatively high at 1.5 C,
2C does not show a certain tendency. However, when the secondary battery is actually used, it is hardly assumed that the discharge current is set to such a high value and the battery is continuously used. It is sufficient if the discharge capacity of the above is obtained.

As described above, characteristics and characteristics of sample batteries of the same type and of the same standard are determined in advance, and the discharge capacity of each sample battery with respect to each discharge current value is estimated as follows.

(3) Measurement of Sample Battery and Estimation of Discharge Capacity a) First, as shown in FIG. 4, the sample battery was subjected to the same constant current (for example, 1) as the constant current and the fixed time in (1).
000 mA) and for a fixed time (for example, 30 minutes), and the terminal voltage VX at that time is measured. b) When the terminal voltage VX is obtained, the capacity% of the sample battery at that time is obtained depending on the characteristics. For example, when the terminal voltage VX is 3.95 V, the capacity% of the sample battery is about 57%.

C) Then, since the charging capacity of the sample battery at that time is 500 mAh, the 100% capacity is
It is estimated by calculation as about (500 mAh) /0.57=877 mAh. d) Then, since the 100% capacity of the sample battery is estimated, the discharge capacity for each discharge current value of the sample battery can be estimated from the characteristics. For example, 100
If the% capacity is 877 mAh, the discharge capacity of the sample battery can be estimated as follows: discharge current value: 0.2 C → discharge capacity: 850 mAh: 0.6 C →: 820 mAh: 1.0 C →: 790 mAh.

As described above, according to the present embodiment, the time required for the measurement actually performed to obtain the discharge capacity for each discharge current value of the sample battery by obtaining the characteristics and the characteristics in advance is (3) Only 30 minutes in (a). On the other hand, in the conventional test method, it takes about 3.6 hours to calculate the discharge capacity for one discharge current value (see FIG. 5), and the discharge capacity is also required for other discharge current values. It took twice or three times as long to find.

That is, according to the test method of this embodiment, even if charging is stopped halfway without charging the sample battery to approximately 100%, it is possible to estimate a 100% charge capacity by utilizing the characteristics, Further, by utilizing the characteristics, it is possible to estimate a discharge capacity corresponding to each discharge current value without actually performing a discharge test.

Therefore, the time required for the actual measurement can be greatly reduced, so that the equipment required for the test can be reduced, and the manufacturing cost of the battery can be reduced.

The present invention is not limited to the embodiment described above and shown in the drawings, and the following modifications or extensions are possible. It is preferable to set the charging time to a time near the time required for the terminal voltage of the sample battery to exceed the lower limit (3.0 + β) V of the usable voltage range. In such a case, it is possible to substantially minimize the time for actually measuring the sample battery. The charging time for charging the sample battery does not necessarily need to be the same as the charging current value and charging time for obtaining the characteristics. Although the same accuracy as in the embodiment can improve the estimation accuracy of 100% capacity, for example, when time is more important than accuracy, the charging time may be shortened.

For example, when only one kind of discharge current value is assumed when the battery is actually used, the discharge capacity may be obtained for only one discharge current value. The 100% charge capacity of the sample battery may be obtained using a method similar to the conventional method, and the discharge capacity for a predetermined discharge current may be estimated using only the characteristics. Rechargeable batteries are not limited to lithium-ion batteries.
Other lithium secondary batteries such as lithium, manganese lithium and lithium polymer, or nickel-cadmium batteries or nickel-metal hydride batteries may be used.

[Brief description of the drawings]

FIG. 1 is a diagram showing a characteristic which is a relationship between a ratio of a charging capacity of a secondary battery and a terminal voltage in one embodiment of the present invention.

FIG. 2 is a diagram showing characteristics representing a relationship between a 100% charge capacity of a secondary battery and a discharge capacity for each discharge current value.

FIG. 3 is a diagram showing a relationship between a charging time of a sample battery and a terminal voltage when characteristics are obtained.

FIG. 4 is a diagram showing a relationship between a charging time of a sample battery and a terminal voltage.

5A and 5B are diagrams comparing the time required for a charge test and the time required for a conventional charge / discharge test, wherein FIG. 5A shows a change in terminal voltage of the secondary battery with respect to time, and FIG. 5B shows a charge current value with respect to time. Show changes in

6A and 6B are diagrams illustrating an example of a charge / discharge test according to the related art, in which FIG. 6A illustrates a change in terminal voltage of a secondary battery with respect to time, and FIG. 6B illustrates a change in a charge current value with respect to time.

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Claims (5)

[Claims] In a battery of the same type comprising a secondary battery, when a plurality of batteries are charged at a constant current for a fixed time, a terminal voltage indicated by each battery is measured, and then a voltage of about 100% of each battery is measured. % Of the charge capacity, and from the measurement result, a ratio of the charge capacity of each of the batteries at the time of performing the charging for the predetermined time with respect to the charge capacity of approximately 100% is obtained. The characteristics of the terminal voltage indicated by each of the batteries are obtained as characteristics in advance, and the actual discharge capacities when the plurality of batteries are discharged at a predetermined discharge current are measured. The characteristics of the discharge capacity with respect to the charge capacity of 100% are obtained in advance as characteristics, and when the sample battery is charged with the constant current for a certain period of time, the terminal voltage indicated by the sample battery is measured. Estimating a charge capacity of about 100% of the sample battery based on the calculation, and estimating a discharge capacity when the sample battery is discharged at the predetermined discharge current based on the estimation result and the characteristics. Characteristic method of estimating discharge capacity of secondary battery. 2. The method according to claim 1, wherein the characteristic is obtained by measuring an actual discharge capacity for each of the cases where the plurality of batteries are discharged by a plurality of predetermined discharge currents. Method for estimating the discharge capacity of the secondary battery. 3. The method for estimating the discharge capacity of a secondary battery according to claim 1, wherein a certain time when charging the sample battery is the same as a certain time when obtaining the characteristics. 4. The apparatus according to claim 1, wherein the predetermined time is set near a time required for a terminal voltage of the sample battery to exceed a lower limit of a usable voltage range. 3. The method for estimating the discharge capacity of a secondary battery according to item 1. 5. The method for estimating a discharge capacity of a secondary battery according to claim 1, wherein the battery is a lithium battery.