JP2014002122A - Method of estimating total battery capacity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a total battery capacity estimation method configured to reduce the time required for acquiring the total battery capacity.SOLUTION: A total battery capacity estimation method includes: a measurement step S2 that discharges a battery 100 in a range smaller than the total range from SOC 0% to SOC 100% to measure a sectional discharge amount Qa discharged at that time; and a total capacity estimation step S3 that estimates a total battery capacity Cb of the battery 100 from the sectional discharge amount Qa.

Description

  The present invention relates to a total battery capacity estimation method for estimating a total battery capacity of a battery.

  Conventionally, as a method of measuring the total battery capacity, after charging the battery until the state of charge (SOC) of the battery reaches 100% SOC, from 100% SOC to 0% SOC (for example, 4 for a lithium ion secondary battery). .1V to 3.0V), and the amount of discharged electricity discharged at that time is the total battery capacity (discharge capacity). In addition, as a related prior art, patent document 1 is mentioned, for example.

JP 2002-352864 A

  However, in order to accurately measure the discharge capacity, when discharging the battery from SOC 100% to SOC 0%, the discharge current is set to a low current of, for example, about 0.3 C. It takes a lot of time.

  The present invention has been made in view of the present situation, and provides a total battery capacity estimation method capable of shortening the time taken to acquire the total battery capacity.

  One aspect of the present invention for solving the above problems is a measurement step in which a battery is discharged in a section narrower than the entire section from SOC 0% to SOC 100%, and the section discharge electricity quantity Qa discharged at that time is measured. And a total capacity estimating step of estimating the total battery capacity Cb of the battery from the section discharge electricity quantity Qa.

  In this total battery capacity estimation method, the discharge of the battery performed to estimate the total battery capacity Cb is a section narrower than the entire section from SOC 100% to SOC 0%, for example, the section from SOC 70% to SOC 20%. For this reason, the discharge time is shortened, and the time required for obtaining the total battery capacity Cb can be shortened.

  Furthermore, in the total battery capacity estimation method described above, before the measurement step, the battery in which the open circuit voltage is in the first charging state with the first terminal voltage V1 is discharged at a constant current value Ia. A voltage drop amount obtaining step for obtaining a voltage drop amount α which is a difference (V1−V2) between the second terminal voltage V2 immediately after the start of discharge and the first terminal voltage V1, and the state of charge is SOC100. In the second charging state smaller than%, the open circuit voltage of the battery is the third inter-terminal voltage V3, the fourth inter-terminal voltage V4 is V4 = V3-α, and the third charging state is greater than SOC 0%. When the open circuit voltage of the battery at 5 is the fifth inter-terminal voltage V5 (where V5 <V3) and the sixth inter-terminal voltage V6 is V6 = V5-α, the measuring step includes at least the battery Fourth terminal voltage V4 From the fourth inter-terminal voltage V4 to the sixth inter-terminal voltage V6, the interval discharge electricity quantity Qa discharged from the fourth inter-terminal voltage V4 to the sixth inter-terminal voltage V6. The total battery capacity estimation method which is a step of measuring

  In the measurement step, for example, if the battery is discharged with a relatively large current of 0.7 C or more, the discharge time is shortened, so that the time required for obtaining the total battery capacity Cb can be further shortened. However, if the battery is discharged with such a relatively large current, a voltage drop due to the internal resistance of the battery is large, so that the total battery capacity cannot be measured accurately. That is, if the apparent terminal voltage drops by 0.1 V due to the voltage drop, for example, even if the discharge current is measured in the voltage section from 4.1 V to 3.0 V, for example, it is actually 0.1 V higher than that. Since the discharge current was measured in the voltage interval up to 3.1 V, the total battery capacity cannot be obtained accurately. In addition, since the magnitude of the battery internal resistance varies from battery to battery, the amount of voltage drop also varies from battery to battery, so it is difficult to predetermine a voltage interval to be measured in consideration of the amount of voltage drop.

  On the other hand, in this total battery capacity estimation method, taking into account the voltage drop amount α generated when the battery in measurement is discharged at the constant current value Ia, at least the voltage between the fourth terminal V4 and the sixth terminal. The battery is discharged at a constant current value Ia up to a voltage V6. Then, the section discharge electricity quantity Qa from the fourth terminal voltage V4 to the sixth terminal voltage V6 is measured, and the total battery capacity Cb is estimated from the section discharge electricity quantity Qa. As a result, the influence of the voltage drop due to the battery internal resistance that differs for each battery can be eliminated, so that the total battery capacity Cb can be accurately estimated regardless of the magnitude of the constant current value Ia.

Note that the voltage drop amount acquisition step for acquiring the voltage drop amount α may be performed away from the measurement step for measuring the section discharge electricity quantity Qa, or may be performed immediately before the measurement step to continue the measurement step. You may make it perform.
Further, the first charge state can be selected as appropriate, a charge state in which the SOC is larger than the SOC in the second charge state, a charge state in which the SOC and SOC in the second charge state are equal (first charge state = second charge) State), a charging state in which the SOC is smaller than the SOC in the second charging state and the SOC is larger than that in the third charging state, and a charging state in which the SOC and SOC in the third charging state are equal (first charging state = third charging) State) or a state of charge having a smaller SOC than that of the third state of charge.

  Furthermore, in the total battery capacity estimation method described above, the third charge state may be a total battery capacity estimation method in which the SOC is 20% or less.

In the battery, the total battery capacity Cb varies from battery to battery depending on the amount of the positive electrode active material in the positive electrode plate and the basis weight of the negative electrode active material in the negative electrode plate. The variation in the total battery capacity Cb is greatly different within a region where the SOC is 20% or less in a discharge curve in which the horizontal axis is SOC (%) and the vertical axis is the open-circuit voltage (V) between terminals. It tends to appear. Therefore, by setting the third state of charge to SOC 20% or less so that the area in which the section discharge electricity amount Qa is measured includes this SOC 20% or less region, the section discharge electricity amount Qa (section battery capacity Ca) for each battery is set. ) Is easily clarified. Thereby, the total battery capacity Cb of each battery can be estimated more accurately.
It is more preferable that the third state of charge is a state of charge of SOC 15% or less.

  Furthermore, the total battery capacity estimation method according to any one of the above, wherein the second charge state is a total battery capacity estimation method in which the SOC is 70% or more.

By making the second state of charge in this way, the correlation between the section discharge electricity quantity Qa measured in the measurement step and the total battery capacity Cb estimated in the total capacity estimation step can be made higher, so that the total battery capacity Cb is further increased. It can be estimated with high accuracy.
It is more preferable that the second state of charge is a state of charge of SOC 75% or more.

  Furthermore, the total battery capacity estimation method according to any one of the above, wherein the constant current value Ia is preferably a total battery capacity estimation method of 0.7 C or more.

  By increasing the constant current value Ia in this way, the battery discharge time can be shortened. Therefore, the time required for estimating the total battery capacity Cb can be further shortened.

Furthermore, in the total battery capacity estimation method according to any one of the above, the second charging state is a charging state of SOC 95% or less, and the third charging state is a charging state of SOC 5% or more. The battery capacity estimation method is preferred.
By making the second charge state and the third charge state in this way, the voltage interval (V4 → V6) for actually discharging the battery is reduced, and the discharge time can be shortened. Therefore, the time required for estimating the total battery capacity Cb can be further shortened.

1 is a perspective view of a lithium ion secondary battery according to Embodiments 1 and 2. FIG. It is explanatory drawing which concerns on Embodiment 1 and shows the total battery capacity estimation method. 6 is a graph illustrating a relationship between the SOC and a voltage between terminals according to the first and second embodiments. It is a graph which concerns on Embodiment 1, 2, and shows the relationship between the total battery capacity Cb and the section battery capacity Ca.

(Embodiment 1)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a lithium ion secondary battery 100 (hereinafter also simply referred to as battery 100) used in the first embodiment. The battery 100 is a rectangular sealed battery that is mounted on a vehicle such as a hybrid vehicle or an electric vehicle, or a battery-powered device such as a hammer drill. The battery 100 includes a rectangular parallelepiped battery case 110, a flat wound electrode body 120 accommodated in the battery case 110, a positive terminal 150 and a negative terminal 160 supported by the battery case 110, and the like. Has been. In addition, a non-aqueous electrolyte solution 117 is held in the battery case 110.

Next, a total battery capacity estimation method for estimating the total battery capacity Cb of the battery 100 according to the first embodiment will be described (see FIGS. 2 and 3).
First, a battery 100 that is in a first charge state in which the state of charge is SOC 95% and the open circuit voltage is the first terminal voltage V1 (4.00 V in the first embodiment) is prepared. Then, in the voltage drop amount acquisition step S1, the battery 100 is discharged at a constant current value Ia of 0.7 C or more (Ia = 0.8 C in the first embodiment). A voltage V2 between the second terminals is measured immediately after the start of discharge (specifically, after 10 seconds), and a voltage drop amount which is a difference (V1−V2) between the voltage V2 between the second terminals and the voltage V1 between the first terminals. α (V) is calculated. In the first embodiment, since the first terminal voltage V1 is 4.00V as described above, assuming that the second terminal voltage V2 of the battery 100 to be measured is, for example, 3.90V, the voltage drop amount α Is α = V1-V2 = 4.00-3.90 = 0.10 (V).

  Thereafter, the battery 100 is discharged, and the state of charge is less than SOC 100%, further SOC 95% or less, and SOC 70% or more (SOC 90% in the first embodiment), and the open circuit voltage is the third terminal voltage V3 ( In the first embodiment, the second charging state is 3.90 V). Further, the voltage V4 between the fourth terminals is set to V4 = V3−α. As described above, when the voltage drop amount α is 0.10 V, the voltage V4 between the fourth terminals is V4 = V3−α = 3.90−0.10 = 3.80 (V).

  Further, when the SOC is larger than 0%, further SOC is 5% or more and SOC is 20% or less (SOC 10% in the first embodiment), the open circuit voltage is the fifth terminal voltage V5 (3.40 V in the first embodiment). The state of the battery 100 is defined as the third charging state. Further, the sixth inter-terminal voltage V6 is set to V6 = V5-α. As described above, when the voltage drop amount α is 0.10 V, the voltage V6 between the sixth terminals is V6 = V5−α = 3.40−0.10 = 3.30 (V).

  In the measurement step S2, the constant current value Ia (specifically described above) is obtained from the fourth terminal voltage V4 (specifically 3.80 V) to the sixth terminal voltage V6 (specifically 3.30 V). Specifically, the battery 100 is discharged at 0.8 C). In addition, the section discharge electricity quantity Qa (Ah) discharged during that period (discharged from the fourth inter-terminal voltage V4 to the sixth inter-terminal voltage V6) is measured.

  Next, in the total capacity estimation step S3, the total battery capacity Cb (Ah) from the above-described section discharge electricity quantity Qa (Ah), that is, the section battery capacity Ca (Ah) from the second charge state to the third charge state. Is estimated. Specifically, the relationship between the section battery capacity Ca and the total battery capacity Cb is obtained in advance through experiments or the like. In the first embodiment, as can be seen from the relationship between the total battery capacity Cb and the section battery capacity Ca shown by a solid line in FIG. 4 (shown as Example 1), the total battery capacity Cb and the section battery capacity Ca are Cb = A The relationship of × Ca + B is satisfied. A and B are coefficients, respectively, and are determined by the magnitudes of the fourth terminal voltage V4 and the sixth terminal voltage V6. Substituting the section battery capacity Ca (Ah) into this equation, the total battery capacity Cb (Ah) is obtained. Thus, the total battery capacity Cb of the battery 100 related to the measurement can be estimated in a short time.

(Embodiment 2)
Next, a second embodiment will be described. The total battery capacity estimation method according to the second embodiment is different from the first embodiment in that the voltage drop amount acquisition step S1 is not performed and the measurement step S2 is performed without considering the voltage drop amount α (V). Other than that, the second embodiment is the same as the first embodiment, and the description of the same parts as the first embodiment is omitted or simplified.

  First, the battery 100 in which the open circuit voltage is in the second charging state with the third terminal voltage V3 (3.90 V in the second embodiment) is prepared. Then, in the measurement step S2, the battery 100 is set at the constant current value Ia (specifically 0.8C) until the terminal voltage during discharging reaches the fifth terminal voltage V5 (specifically 3.40V). Discharge. Moreover, the section discharge electricity quantity Qa (Ah) discharged in the period is measured.

  Next, in the total capacity estimation step S3, the total battery capacity Cb (Ah) is estimated from the measured section discharge electricity quantity Qa (section battery capacity Ca). The relationship between the section battery capacity Ca and the total battery capacity Cb is obtained in advance through experiments or the like. In the second embodiment, as can be seen from the relationship between the total battery capacity Cb indicated by a broken line in FIG. 4 (shown as Example 2) and the section battery capacity Ca, the total battery capacity Cb and the section battery capacity Ca are Cb = E. XCa + F relationship is satisfied. E and F are coefficients. Substituting the section battery capacity Ca (Ah) into this equation, the total battery capacity Cb (Ah) is obtained. Thus, the total battery capacity Cb of the battery 100 related to the measurement can be estimated in a short time.

(Examples and Comparative Examples)
Next, the results of tests performed to verify the effects of the total battery capacity estimation methods according to Embodiments 1 and 2 will be described. As Example 1, the total battery capacity Cb (Ah) of the battery 100 was estimated by the total battery capacity estimation method according to the first embodiment. In this total battery capacity estimation method, as described above, the voltage drop amount acquisition step S1, the measurement step S2, and the total capacity estimation step S3 are performed, thereby taking into account the voltage drop amount α for each battery 100, and the interval battery capacity Ca. And the total battery capacity Cb was estimated from the section battery capacity Ca. “Measurement method” in Table 1 indicates “measurement of interval battery capacity Ca + correction of voltage drop amount α”. Further, the total time taken to obtain the total battery capacity Cb (shown as “measurement time” in Table 1) was approximately equal to the discharge time taken for the measurement step S2, which was about 1 hour.

Prior to the first embodiment, for a number of batteries 100, the section battery capacity Ca (section discharge electricity quantity Qa obtained in measurement step S2) is measured, while the total battery capacity Cb is measured for the battery 100, The relationship between the section battery capacity Ca and the total battery capacity Cb was investigated (indicated by ♦ in FIG. 4). In FIG. 4, the nominal capacity Co (Ah) of the battery 100 is set to “1”, and the size of the section battery capacity Ca and the total battery capacity Cb is shown in a ratio to the nominal capacity Co.
Further, when a linear regression line was obtained and a correlation coefficient R (determination coefficient R ² ) with each measurement point was obtained, R ² = 0.99. The total battery capacity Cb is the amount of discharged electricity that is discharged when the battery 100 charged to SOC 100% is discharged to SOC 0% with a small constant current value (specifically, I = 0.3C). . The results are shown in Table 1.

  Further, as Example 2, the total battery capacity Cb (Ah) of the battery 100 was estimated by the total battery capacity estimation method according to the second embodiment. In this total battery capacity estimation method, as described above, the voltage drop amount α for each battery 100 is not taken into consideration by performing the measurement step S2 and the total capacity estimation step S3 without performing the voltage drop amount acquisition step S1. Then, the battery capacity Ca was measured, and the total battery capacity Cb was estimated from the battery capacity Ca. The “measurement method” in Table 1 indicates “measurement of interval battery capacity Ca”. Further, the total time required to obtain the total battery capacity Cb (approximately equal to the discharge time) was about 1 hour as in Example 1.

In addition, for a large number of batteries 100, the section battery capacity Ca (section discharge electricity quantity Qa) is measured in the same manner as in Example 2, while the total battery capacity Cb is measured for the battery 100 to determine the section battery capacity Ca and the total battery. The relationship with the capacity Cb was investigated (indicated by ▲ in FIG. 4). Furthermore, when a linear regression line was obtained and a correlation coefficient R (determination coefficient R ² ) with each measurement point was obtained, it was R ² = 0.90 although it was lower than that in Example 1. These results are also shown in Table 1.

On the other hand, in the comparative example, the battery 100 charged to SOC 100% is discharged to SOC 0% at a constant current value (specifically, I = 0.3C), and the amount of discharged electricity discharged at that time is measured. This was defined as the total battery capacity Cb. “Measurement method” in Table 1 indicates “measurement of total battery capacity Cb”. Further, the total time required to obtain the total battery capacity Cb was about 3 hours. In this comparative example, since the total battery capacity Cb is actually measured, the correlation coefficient R (determination coefficient R ² ) in Table 1 is shown as R ² = 1.0.

  In Table 1, first, the measurement time (time taken to obtain the total battery capacity Cb) was about 3 hours in the comparative example, but about 1 hour in Example 1 and Example 2. You can see that This is because in Example 1 and Example 2, the current value at the time of discharge was set to Ia = 0.8C, which was larger than that in the comparative example (I = 0.3C). In addition, in the comparative example, the battery 100 is discharged over the entire region from SOC 100% to SOC 0%, whereas in Example 1 and Example 2, the battery 100 is only in the section region from SOC 90% to SOC 10%. This is because the was discharged.

Next, regarding the correlation coefficient R (determination coefficient R ² ), in Example 2, the correlation coefficient R (determination coefficient R ² ) is R ² = 0.90, and the estimation accuracy of the total battery capacity Cb is high. On the other hand, in Example 1, the correlation coefficient R (determination coefficient R ² ) is R ² = 0.99, and it can be seen that the estimation accuracy of the total battery capacity Cb is extremely high. As described above, in the comparative example, since the total battery capacity Cb itself is actually measured, the correlation coefficient R (determination coefficient R ² ) is R ² = 1.0.

The reason why the correlation coefficient R (determination coefficient R ² ) was relatively small in Example 2 was that discharging was performed at a large current value (Ia = 0.8 C), and a large voltage drop due to battery internal resistance occurred. Nevertheless, the voltage drop amount α in each battery 100 is not considered. That is, from the second charging state to the third charging state (for example, if the voltage drop amount α = 0.10V, the voltage between the sixth terminals V6 = 3.30V) is actually discharged. Without considering the magnitude of the voltage drop amount α of 100, discharging was performed until the inter-terminal voltage reached 3.40V. For this reason, variation occurs in the SOC at the end of discharge, and the section discharge electricity quantity Qa from the second charge state to the third charge state cannot be measured accurately.

On the other hand, the correlation coefficient R (determination coefficient R ² ) in Example 1 is extremely large, and the reason for the particularly good correlation is that the voltage drop amount α due to the battery internal resistance of each battery 100 is taken into consideration. The battery was accurately discharged from the second charge state to the third charge state (for example, if the voltage drop amount α = 0.10V, the voltage between the terminals becomes the sixth inter-terminal voltage V6 = 3.30V, for example, the voltage If the drop amount α = 0.05V, the terminal voltage was discharged until the sixth terminal voltage V6 = 3.35V). For this reason, it is because the section discharge electricity quantity Qa from the 2nd charge state to the 3rd charge state was measured correctly.

As described above, in the total battery capacity estimation methods of the first and second embodiments, the battery discharge performed for estimating the total battery capacity Cb is a section narrower than the entire section from SOC 100% to SOC 0%. For this reason, the discharge time is shortened, and the time required for obtaining the total battery capacity Cb can be shortened.
Furthermore, in the total battery capacity estimation method according to the first embodiment, the voltage drop amount α generated when the battery 100 to be measured is discharged at the constant current value Ia is taken into consideration and the fourth terminal voltage V4 to the sixth terminal. The battery 100 is discharged at a constant current value Ia up to the voltage V6. Then, the section discharge electricity quantity Qa (from the fourth terminal voltage V4 to the sixth terminal voltage V6) of that period is measured, and the total battery capacity Cb is calculated from this section discharge electricity quantity Qa (section battery capacity Ca). presume. Thereby, since the influence of the voltage drop by the battery internal resistance which changes for every battery 100 can be excluded, the total battery capacity Cb can be estimated with high accuracy.

  Furthermore, in the battery 100, the total battery capacity Cb varies from battery 100 to battery 100 depending on the amount of the positive electrode active material in the positive electrode plate and the negative electrode active material in the negative electrode plate. The variation in the total battery capacity Cb is greatly different within a region where the SOC is 20% or less in a discharge curve in which the horizontal axis is SOC (%) and the vertical axis is the open-circuit voltage (V) between terminals. appear. Therefore, by setting the third state of charge to SOC 20% or less so that the area where the SOC is 20% or less is included in the area where the section discharge electricity amount Qa (section battery capacity Ca) is measured, the discharge electricity amount for each battery 100 is set. The difference in (interval battery capacity Ca) becomes clear. Thereby, the total battery capacity Cb of each battery 100 can be estimated more accurately.

Further, by setting the second state of charge to SOC 70% or more, the correlation between the section discharge electricity quantity Qa (section battery capacity Ca) measured in the measurement step S2 and the total battery capacity Cb estimated in the total capacity estimation step S3 is obtained. Since it can be made higher, the total battery capacity Cb can be estimated with higher accuracy.
Moreover, the discharge time of the battery 100 can be shortened by increasing the constant current value Ia to 0.7 C or more. Therefore, the time required for estimating the total battery capacity Cb can be further shortened.
Further, by setting the second charged state to SOC 95% or lower and the third charged state to SOC 5% or higher, the voltage interval (V4 → V6) for actually discharging the battery 100 is reduced, and the discharge time can be shortened. Therefore, the time required for estimating the total battery capacity Cb can be further shortened.

  In the above, the present invention has been described with reference to the first and second embodiments. However, the present invention is not limited to the above-described first and second embodiments, and can be appropriately modified and applied without departing from the gist thereof. Needless to say, you can.

100 Lithium ion secondary battery (battery)
110 Battery Case 120 Electrode Body 150 Positive Terminal 160 Negative Terminal

Claims (5)

A measurement step of discharging the battery in a section narrower than the entire section from SOC 0% to SOC 100% and measuring the section discharge electricity quantity Qa discharged at that time;
A total capacity estimating step of estimating a total battery capacity Cb of the battery from the section discharge electricity quantity Qa. The total battery capacity estimation method according to claim 1,
Prior to the measuring step, the battery in the first charging state with the open circuit voltage of the first inter-terminal voltage V1 is discharged at a constant current value Ia, and the second inter-terminal voltage V2 immediately after starting the discharge. And a voltage drop amount acquisition step of acquiring a voltage drop amount α that is a difference (V1−V2) between the first terminal voltage V1 and
The open circuit voltage of the battery in the second charging state in which the charging state is smaller than SOC 100% is the third terminal voltage V3, the fourth terminal voltage V4 is V4 = V3-α,
When the open circuit voltage of the battery in the third charging state where the charging state is greater than SOC 0% is the fifth inter-terminal voltage V5 (where V5 <V3), and the sixth inter-terminal voltage V6 is V6 = V5-α. ,
The measuring step includes
The battery is discharged at the constant current value Ia at least from the fourth inter-terminal voltage V4 to the sixth inter-terminal voltage V6 to change from the fourth inter-terminal voltage V4 to the sixth inter-terminal voltage V6. A method for estimating the total battery capacity, which is a step of measuring the section discharge electricity quantity Qa discharged until now. The total battery capacity estimation method according to claim 2,
The method for estimating the total battery capacity, wherein the third state of charge is a state of charge of SOC 20% or less. A total battery capacity estimation method according to claim 2 or claim 3, wherein
The second battery state is a total battery capacity estimating method in which the SOC is 70% or more. A total battery capacity estimation method according to any one of claims 2 to 4,
The method for estimating the total battery capacity, wherein the constant current value Ia is 0.7 C or more.

Images