JP2025016810A - Electronic device and analysis method - Google Patents

Abstract

To provide an electronic apparatus and an analysis method that can perform analysis of deterioration in various deterioration modes.SOLUTION: An electronic apparatus according to an aspect of the present technique comprises a measurement unit, a storage unit, a calculation unit, and an analysis unit. The measurement unit measures, during and after charging or discharging of a battery pack formed by including a plurality of electric cells, the voltage and current of the plurality of electric cells included in the battery pack. The storage unit stores a voltage value and a current value obtained through the measurement performed by the measurement unit. The calculation unit calculates, for each of the electric cells, two or more circuit constants of an equivalent circuit of the electric cell, by using the voltage value and the current value stored in the storage unit. The analysis unit performs multivariate analysis by using information on the distribution of the two or more circuit constants in the plurality of electric cells or information on the distribution of two or more circuit constants in a plurality of normal batteries.SELECTED DRAWING: Figure 1

Description

This technology relates to electronic devices and analysis methods.

In recent years, the use of secondary batteries has expanded to larger-scale devices, such as electric vehicles and energy storage systems. The larger the device, the greater the damage that may occur if it catches fire, so the importance of developing technology to improve safety is growing. In addition, it is important to properly understand any abnormal behavior or deterioration of secondary batteries during use.

In Patent Document 1, the internal resistance is focused on as a circuit constant used to determine the deterioration of a secondary battery. In Patent Document 1, coulomb counting is performed during CV charging in CCCV charging, and the internal resistance is calculated with high accuracy based on the amount of charged electricity.

JP 2004-152755 A

However, the method described in Patent Document 1 requires only one circuit constant, the internal resistance, and is insufficient as a method for determining the deterioration of a secondary battery, since it is unable to express the deterioration phenomenon of the secondary battery from multiple perspectives. Therefore, it is desirable to provide an electronic device and an analysis method that can handle multiple circuit constants and can analyze deterioration due to various deterioration modes.

The electronic device according to the first aspect of the present technology includes a measurement unit, a storage unit, a calculation unit, and an analysis unit. The measurement unit measures the voltage and current of the cells included in the battery pack during and after charging or discharging the battery pack including the cells. The storage unit stores the voltage and current values obtained by the measurement in the measurement unit. The calculation unit calculates two or more circuit constants of the equivalent circuit of the cells for each cell using the voltage and current values stored in the storage unit. The analysis unit performs multivariate analysis using distribution information of the two or more circuit constants in the cells or distribution information of the two or more circuit constants in the normal cells.

The electronic device according to the second aspect of the present technology includes a measurement unit, a memory unit, a calculation unit, and an analysis unit. The measurement unit measures the voltage and current of the cell during and after charging or discharging the cell. The memory unit stores the voltage and current values obtained by the measurement in the measurement unit. The calculation unit calculates two or more circuit constants of the equivalent circuit of the cell using the voltage and current values stored in the memory unit. The analysis unit performs multivariate analysis using distribution information of two or more circuit constants in a plurality of normal batteries.

The analysis method according to the third aspect of the present technology includes the following four steps.
(A) a measurement step of measuring the voltage and current of a plurality of cells included in a battery pack during and after charging or discharging the battery pack including a plurality of cells; (B) a storage step of storing the voltage and current values obtained in the measurement step; (C) a calculation step of calculating two or more circuit constants of an equivalent circuit of the cells for each cell using the voltage and current values stored in the storage step; (D) a solution step of performing a multivariate analysis using distribution information of two or more circuit constants in the plurality of cells or distribution information of two or more circuit constants in a plurality of normal batteries.

The analysis method according to the fourth aspect of the present technology includes the following four steps.
(A) a measurement step of measuring the voltage and current of a single cell during and after charging or discharging the single cell; (B) a storage step of storing the voltage and current values obtained in the measurement step; (C) a calculation step of calculating two or more circuit constants of an equivalent circuit of the single cell using the voltage and current values stored in the storage step; and (D) a solution step of performing a multivariate analysis using distribution information of two or more circuit constants in a plurality of normal batteries.

According to the electronic device according to the first aspect of the present technology and the analysis method according to the third aspect of the present technology, a multivariate analysis is performed using distribution information of two or more circuit constants in a plurality of single cells, or distribution information of two or more circuit constants in a plurality of normal batteries, so that it is possible to analyze the deterioration of a secondary battery due to various deterioration modes.

According to the electronic device according to the second aspect of the present technology and the analysis method according to the fourth aspect of the present technology, a multivariate analysis is performed using distribution information of two or more circuit constants in a plurality of normal batteries, so that it is possible to analyze the deterioration of a secondary battery due to various deterioration modes.

Note that the effects of this technology are not necessarily limited to the effects described here, but may be any of a series of effects related to this technology described below.

FIG. 2 is a diagram illustrating an example of a functional block of an analysis device according to an embodiment of the present technology. FIG. 2 is a diagram showing an equivalent circuit of a secondary battery that is the subject of analysis by the analysis device of FIG. 1 . 2 is a diagram showing an example of an analysis procedure in the analysis device of FIG. 1 . 2 is a diagram showing an example of an analysis result in the analysis device of FIG. 1 . 2 is a diagram showing an example of an analysis result in the analysis device of FIG. 1 . 2 is a diagram showing an example of an analysis result in the analysis device of FIG. 1 . 2 is a diagram showing an example of an analysis result in the analysis device of FIG. 1 . 2 is a diagram showing an example of an analysis result in the analysis device of FIG. 1 . 2 is a diagram showing an example of an analysis result in the analysis device of FIG. 1 . 2 is a diagram showing an example of an analysis result in the analysis device of FIG. 1 . 2 is a diagram showing an example of an analysis result in the analysis device of FIG. 1 . 2 is a diagram showing an example of an analysis result in the analysis device of FIG. 1 . FIG. 13 is a diagram illustrating a modified example of a functional block of an analysis device according to an embodiment of the present technology. FIG. 13 is a diagram illustrating a modified example of a functional block of an analysis device according to an embodiment of the present technology.

Below, the form for implementing this technology will be explained in detail with reference to the drawings.

1. Embodiment
[composition]
A configuration of an analysis device 10 according to an embodiment of the present technology will be described. The analysis device 10 is a device that analyzes the deterioration state of a secondary battery. In the present embodiment, a secondary battery that is an analysis target of the analysis device 10 is an assembled battery 20. The assembled battery 20 is, for example, a lithium ion secondary battery. The assembled battery 20 is configured to include a plurality of single cells 21. Each single cell 21 may be a unit cell, or may be a battery block in which a plurality of unit cells are connected. In each single cell 21, a plurality of secondary batteries may be connected in series, or a plurality of secondary batteries may be connected in parallel.

As shown in FIG. 1, the analysis device 10 includes, for example, a charge/discharge unit 11, a voltage measurement unit 12, a current measurement unit 13, a temporary storage unit 14, a circuit constant calculation unit 15, and a multivariate analysis unit 16.

The charging/discharging unit 11 is a device that discharges and charges the assembled battery 20 installed in the analysis device 10. The charging/discharging unit 11 is capable of, for example, CCCV charging as a charging method. The charging/discharging unit 11 has a charging circuit that includes, for example, a generator and a converter. This charging circuit controls the voltage for charging the assembled battery 20.

The voltage measurement unit 12 has a measurement circuit that measures the voltage of each cell 21 included in the battery pack 20. Note that FIG. 1 illustrates a configuration in which wiring is connected to the positive and negative electrodes of each cell 21, and the voltage of each cell 21 is measured by measuring the voltage obtained through the wiring, but the method of measuring the voltage of each cell 21 is not limited to this method. The voltage measurement unit 12 stores data (voltage value) on the voltage measured by the measurement circuit in the temporary storage unit 14. The voltage measurement unit 12 measures the voltage of each cell 21 during and after charging or discharging the battery pack 20 (steps S102 and S106 in FIG. 3).

The current measurement unit 13 has a measurement circuit that measures the current of each cell 21 included in the battery pack 20. Note that FIG. 1 illustrates a configuration in which wiring is connected to the positive and negative electrodes of the battery pack 20, and the current of each cell 21 is measured by measuring the current obtained through the wiring, but the method of measuring the current of each cell 21 is not limited to this method. The current measurement unit 13 stores data (current value) on the current measured by the measurement circuit in the temporary storage unit 14. The current measurement unit 13 measures the current of each cell 21 (i.e., the current of the battery pack 20) during and after charging or discharging the battery pack 20 (steps S102 and S106 in FIG. 3).

The temporary storage unit 14 is configured to include, for example, a volatile memory or a non-volatile memory. The temporary storage unit 14 stores the voltage value of each cell 21 measured by the voltage measurement unit 12 and the current value of each cell 21 measured by the current measurement unit 13. The temporary storage unit 14 stores the voltage value and current value measured during and after charging or discharging the battery pack 20 (steps S103 and S107 in FIG. 3).

The circuit constant calculation unit 15 calculates two or more circuit constants of the equivalent circuit of each cell 21 using the voltage and current values during and after charging or discharging for each cell 21 stored in the temporary storage unit 14 (step S109 in FIG. 3).

Figure 2 shows the equivalent circuit of each cell 21. As shown in Figure 2, each cell 21 is represented by an equivalent circuit consisting of six elements: inductance L, solution resistance Rs, charge transfer resistance Rct, Warburg impedance σ, constant phase element CPE related to electric double layer capacitance Cdl, and differential capacitance C'. The following eight circuit constants of these six elements are calculated by curve fitting.

(8 circuit constants)
Inductance L
Solution resistance Rs
・Charge transfer resistance Rct
・Warburg impedance σ
Parameters p and T for describing the constant phase element CPE (hereinafter referred to as CPE(p) and CPE(T) respectively)
Differential capacitance C'
Electric double layer capacitance Cdl

The inductance L, solution resistance Rs, charge transfer resistance Rct, Warburg impedance σ, parameter CPE(p), parameter CPE(T) and differential capacitance C′ can be obtained, for example, as the output of analysis software EIS manufactured by Hokuto Denko Corp. The electric double layer capacitance Cdl is calculated by the following formula described in "Electrochemical Impedance Method" by Masayuki Itagaki, Maruzen Publishing (p. 84).
Cdl=CPE(T) ^(1/CPE(p))・Rct ^{((1-CPE(p))/CPE(p))}

The multivariate analysis unit 16 derives distribution information of two or more circuit constants in the multiple single cells 21, and performs multivariate analysis using the distribution information thus obtained (step S110 in FIG. 3). The multivariate analysis unit 16 uses, for example, the Mahalanobis-Taguchi method or the one-class support vector machine method as a method of multivariate analysis. Multivariate analysis using the Mahalanobis-Taguchi method is described in detail below. The multivariate analysis unit 16 derives the degree of anomaly ai for each single cell 21, for example, by performing the following multivariate analysis.

(Preparation of sample lithium-ion battery)
Thirteen commercially available lithium-ion batteries US18650FTC1 (rated capacity 1.05 Ah) whose main positive electrode active material is lithium iron phosphate (LiFePO4, LFP) and whose main negative electrode active material is graphite were prepared. All of these were from the same manufacturing lot. Ten of these batteries were first discharged at a constant current equivalent to a 0.2 hour rate until the voltage fell below 2.0 V (the rated capacity was 1.05 Ah, and the current value It at the 1 hour rate was 1.05 A, so the current value I at the 0.2 hour rate was 0.2I = 210 mA), and then immediately charged at a set current of 1.05 A (= 1 It) and a set voltage of 3.6 V (a two-step charge in which constant current charging at a set current value is performed until the set voltage is reached, and constant voltage charging is performed when the set voltage is reached), and this was stopped 2.5 h after the start of charging. While maintaining the 10 lithium-ion batteries in a fully charged state, each one was placed in a thermostatic chamber set to a total of 10 different temperatures: 45°C, 50°C, ..., 90°C, and left there for 25 days to deteriorate.

(AC impedance measurement)
To measure the circuit constant of the battery, the charging state was adjusted first. The battery was placed in a thermostatic bath at 23°C and CCCV charging was performed with a set current of 1.05A (=1It) and a set voltage of 3.6V. This CCCV charging was stopped when the current value during constant voltage charging fell below 105mA (=0.1It). After that, the battery was left in an open state for 1h, and AC impedance measurement was performed. SP-240 manufactured by Bio-Logic was used for AC impedance measurement. Regarding the measurement conditions, first, the control was set to a potentiostatic mode regulated by voltage, and the effective value of the amplitude was set to 5mV. In addition, the center voltage and the open circuit voltage were made to match so that no bias current would flow during the measurement. The frequency sweep range was from 10kHz to 1mHz, and a logarithmic sweep was performed with five measurement points per digit of frequency. In addition, measurements were performed twice for each frequency to reduce random noise. Of the 13 lithium-ion batteries prepared, the AC impedance was measured four times for each of the three lithium-ion batteries that had not undergone the above-mentioned deterioration process, and the AC impedance was measured only once for the ten lithium-ion batteries that had undergone the above-mentioned deterioration process.

(Multivariate analysis)
For three lithium-ion batteries that had not undergone the above-mentioned deterioration process, AC impedance measurements were performed four times for each battery. The obtained data (each set of data including eight circuit constants) were defined as twelve vectors x (where i is an integer from 1 to 12) as shown in the following formula (1).

Next, the average value vector μ of the 12 sets of data for each circuit constant and the variance-covariance matrix Σ were calculated using equations (2) and (3), respectively.

Next, 10 sets of data (each also including 8 circuit constants) obtained from 10 lithium-ion batteries that had undergone the above-mentioned degradation process were defined as 10 additional vectors x, as shown in formula (4) (i is an integer between 13 and 22). Then, the degree of anomaly a was calculated for all 22 vectors in total according to formula (5).

For comparison, we also calculated the degree of abnormality using only one circuit constant rather than multiple variables (Figures 4 to 11). In addition, for all results, we calculated thresholds for determining whether or not there was an abnormality from the 95th and 99th percentiles in the F-distribution table.

Figure 12 shows the results of the abnormality calculation using all eight circuit constants. In both figures, "A" to "L" on the horizontal axis are data obtained from batteries that have not undergone the above-mentioned deterioration process, which corresponds to i = 1, 2, ..., 12 in formula (5). Also, "M" to "V" on the horizontal axis are data obtained from batteries that have undergone the above-mentioned deterioration process, which corresponds to i = 13, 14, ..., 22 in formula (5). Since "A" to "L" have not undergone the above-mentioned deterioration process, in the following discussion, these are considered to be data obtained from good batteries (normal batteries). On the other hand, "M" to "V" are data obtained from batteries stored at storage temperatures of 45°C, 50°C, ..., 90°C, respectively, and are considered to be data obtained from defective batteries, with the degree of deterioration increasing as the value approaches Z.

Figures 4 and 5 show that there is no clear difference in the degree of abnormality between the "A" to "L" batteries that were deemed to be good products and the "M" to "V" batteries that were deemed to be bad products. In other words, it was found that it is not possible to determine whether a product is good or bad using only one of the impedance L and the solution resistance Rs.

Figures 6, 7 and 10 show that there is a tendency for the defective batteries to have a higher degree of abnormality than the "A" to "L" batteries that were deemed to be good products, and the "M" to "V" batteries that were deemed to be defective products. However, there is no clear difference between the two, which means that it is difficult to determine whether a product is good or defective using only one of the parameters CPE(p), CPE(T) and differential capacity C'.

Figures 8 and 9 show a clear tendency for the defective batteries to have a higher degree of abnormality than the "A" to "L" batteries, which were deemed to be good products, and the "M" to "V" batteries, which were deemed to be defective products. In other words, it was suggested that the charge transfer resistance Rct and the Warburg impedance σ can be used to determine whether a product is good or defective even when only one circuit constant is used. On the other hand, regardless of which circuit constant is used, when the degree of deterioration is small, such as "M" and "N", the degree of abnormality falls below the 95% threshold, making it difficult to find a significant difference from a good product, and therefore it was found that there is a slight problem in terms of sensitivity.

Figure 11 shows a clear tendency for the defective batteries to have higher abnormalities than the "A" to "L" batteries, which were deemed to be good products, and the "M" to "V" batteries, which were deemed to be defective products. Even "M" and "N" batteries had abnormalities that exceeded the 99% threshold. In other words, it was found that the electric double layer capacitance Cdl can be used to determine whether a product is good or defective even when only one circuit constant is used.

Figure 12 shows a clear tendency for the degree of abnormality to be higher for defective batteries, between "A" through "L" batteries considered to be good and "M" through "V" batteries considered to be defective. Comparing Figures 11 and 12, in Figure 11, even among "A" through "L" batteries considered to be good, some have an abnormality level close to the 95% threshold. On the other hand, in Figure 12, the abnormality levels for "A" through "L" are all very small, which means that by using all eight circuit constants using the Mahalanobis-Taguchi method, it is possible to judge whether a product is good or defective with greater sensitivity.

For the above reasons, the multivariate analysis unit 16 selects two or more circuit constants in the plurality of single cells 21 in the multivariate analysis, which include at least a circuit constant related to a physical phenomenon that causes a transient response. Such circuit constants include at least the electric double layer capacitance Cdl or the charge transfer resistance Rct.

The two or more circuit constants in the plurality of single cells 21 selected in the multivariate analysis include, for example, the electric double layer capacitance Cdl and at least one of the inductance L, the solution resistance Rs, the charge transfer resistance Rct, the Warburg impedance σ, the parameter CPE(p), the parameter CPE(T), and the differential capacitance C'. The two or more circuit constants in the plurality of single cells 21 selected in the multivariate analysis include, for example, the charge transfer resistance Rct and at least one of the inductance L, the solution resistance Rs, the Warburg impedance σ, the parameter CPE(p), the parameter CPE(T), and the differential capacitance C'.

[effect]
Next, the effects of the analysis device 10 will be described.

In recent years, the use of secondary batteries has expanded to larger-scale devices, such as electric vehicles and energy storage systems. The larger the device, the greater the damage that may occur if it catches fire, so the importance of developing technology to improve safety is growing. In addition, it is important to properly understand any abnormal behavior or deterioration of secondary batteries during use.

In Patent Document 1, attention is focused on the internal resistance as a circuit constant used to determine the deterioration of a secondary battery. In Patent Document 1, coulomb counting is performed during CV charging in CCCV charging, and the internal resistance is calculated with high precision based on the amount of charged electricity. However, the method described in Patent Document 1 cannot express the transient response of a secondary battery, so it cannot analyze deterioration from multiple angles, and is therefore insufficient as a method for determining the deterioration of a secondary battery.

In contrast, in this embodiment, a multivariate analysis is performed using distribution information of two or more circuit constants in multiple single cells 21, or distribution information of two or more circuit constants in multiple normal batteries, making it possible to perform a multifaceted analysis, including degradation modes caused by the transient response of the secondary battery.

In this embodiment, the multivariate analysis unit 16 may perform multivariate analysis using distribution information stored in the memory unit 17 instead of distribution information of two or more circuit constants in a plurality of single cells 21, as shown in FIG. 13, for example. The distribution information stored in the memory unit 17 is distribution information of two or more circuit constants in a plurality of normal batteries.

In this case, the two or more circuit constants in the multiple normal batteries selected in the multivariate analysis include, for example, electric double layer capacitance Cdl and at least one of inductance L, solution resistance Rs, charge transfer resistance Rct, Warburg impedance σ, parameter CPE(p), parameter CPE(T), and differential capacitance C'. Also, the two or more circuit constants in the multiple normal batteries selected in the multivariate analysis include, for example, charge transfer resistance Rct and at least one of inductance L, solution resistance Rs, Warburg impedance σ, parameter CPE(p), parameter CPE(T), and differential capacitance C'.

In this embodiment, the secondary battery to be analyzed by the analysis device 10 may be, for example, a single battery 30 as shown in FIG. 14. In this case, the single battery 30 may be a unit cell or a battery block in which a plurality of unit cells are connected. In the single battery 30, a plurality of secondary batteries may be connected in series, or a plurality of secondary batteries may be connected in parallel. In this case, the multivariate analysis unit 16 may perform multivariate analysis using distribution information stored in the memory unit 17 instead of distribution information of two or more circuit constants in a plurality of single batteries 21 as shown in FIG. 14. The distribution information stored in the memory unit 17 is distribution information of two or more circuit constants in a plurality of normal batteries.

10...analysis device, 11...charging/discharging unit, 12...voltage measurement unit, 13...current measurement unit, 14...temporary storage unit, 15...circuit constant calculation unit, 16...multivariate analysis unit, 17...storage unit, 20...battery pack, 21...single cell, 30...single cell.

Claims (12)

a measurement unit that measures a voltage and a current of a plurality of single cells included in a battery pack configured to include a plurality of single cells during and after charging or discharging the battery pack;
a storage unit that stores the voltage value and the current value obtained by the measurement by the measurement unit;
a calculation unit that calculates two or more circuit constants of an equivalent circuit of the battery cell for each battery cell by using the voltage value and the current value stored in the storage unit;
and an analysis unit that performs multivariate analysis using distribution information of the two or more circuit constants in the plurality of single cells or distribution information of the two or more circuit constants in a plurality of normal batteries. A measurement unit that measures the voltage and current of the battery cell during and after charging or discharging the battery cell;
a storage unit that stores the voltage value and the current value obtained by the measurement by the measurement unit;
a calculation unit that calculates two or more circuit constants of an equivalent circuit of the battery cell using the voltage value and the current value stored in the storage unit;
and an analysis unit that performs multivariate analysis using distribution information of the two or more circuit constants in a plurality of normal batteries. The electronic device according to claim 1 , wherein the multivariate analysis method is a Mahalanobis-Taguchi method. The electronic device according to claim 1 , wherein the multivariate analysis method is a one-class support vector machine method. The electronic device according to claim 1 , wherein the two or more circuit constants include an electric double layer capacitance. The electronic device according to claim 1 , wherein the two or more circuit constants include a charge transfer resistance. a measuring step of measuring a voltage and a current of a plurality of single cells included in a battery pack during and after charging or discharging the battery pack including the plurality of single cells;
a storage step of storing the voltage value and the current value obtained in the measurement step;
a calculation step of calculating, for each of the unit cells, two or more circuit constants of an equivalent circuit of the unit cells using the voltage value and the current value stored in the storage step;
and performing a multivariate analysis using distribution information of the two or more circuit constants in the plurality of unit cells or distribution information of the two or more circuit constants in a plurality of normal batteries. measuring the voltage and current of the cell during and after charging or discharging the cell;
a storage step of storing the voltage value and the current value obtained in the measurement step;
a calculation step of calculating two or more circuit constants of an equivalent circuit of the battery cell using the voltage value and the current value stored in the storage step;
and a solution step of performing a multivariate analysis using distribution information of the two or more circuit constants in a plurality of normal batteries. The analysis method according to claim 7 or 8, wherein the multivariate analysis is performed using a Mahalanobis-Taguchi method. The analysis method according to claim 7 or 8, wherein the multivariate analysis method is a one-class support vector machine method. The analysis method according to claim 7 , wherein the two or more circuit constants include an electric double layer capacitance. The analysis method according to claim 7 , wherein the two or more circuit constants include a charge transfer resistance.

Images