JP2022080182A - Battery module - Google Patents

Abstract

To provide a battery module 1 for detecting that the degree of deterioration of a battery cell having a charging depth larger than that of another battery cell 30 is larger than that of the other battery cell in an assembled battery including a plurality of battery cells 30.SOLUTION: The battery module 1 includes an assembled battery system 2 including an assembled battery 3 in which a plurality of battery cells 30 are connected in series, and a balancer for performing equalization processing on charging depths of the plurality of battery cells 30, a measurement circuit 5 for measuring the impedance characteristic before and after the equalization processing of the assembled battery 3, and a processor 6 which uses the impedance characteristic before and after the first equalization processing to detect that a first battery cell having a charging depth larger than that of another battery cell has a higher degree of deterioration than the other battery cell.SELECTED DRAWING: Figure 1

Description

An embodiment of the present invention relates to a battery module including an assembled battery in which a plurality of battery cells are connected in series.

Battery modules including rechargeable and dischargeable secondary batteries are used in portable devices, electric tools, electric vehicles, and the like. As a secondary battery, a small-sized and large-capacity lithium-ion battery and the like are attracting attention.

The battery module is an assembled battery in which a plurality of battery cells are connected in series to obtain a desired output voltage. Further, a desired current capacity is obtained by connecting assembled batteries capable of obtaining a predetermined output voltage in parallel. Further, there is also an assembled battery in which a battery set in which a plurality of battery cells are connected in parallel so as to obtain a desired current capacity is connected in series to obtain a desired output voltage.

A plurality of battery cells constituting an assembled battery deteriorate with the passage of time and repeated charging and discharging, but the capacity retention rate (SOH: State Of Health) indicating the degree of deterioration of each battery cell is not the same. When charging an assembled battery, a battery cell with a large degree of deterioration, that is, a battery cell with a small SOH, may be overcharged because the charging depth (SOC: Stake Of Charge) is larger than that of other battery cells. ..

Therefore, a combined battery including a balancer that measures the SOC of each of a plurality of battery cells and discharges the charge of the battery cell having a large SOC to equalize the SOC of the plurality of battery cells is used. There is.

Here, the reason why the SOC of a certain battery cell is larger than that of another battery cell is considered not only to have a large degree of deterioration but also to other factors. Therefore, it is important to detect SOH abnormalities in battery cells with a large SOC.

Japanese Unexamined Patent Publication No. 2013-29411 discloses a measuring device in which each battery cell is connected to each impedance calculation unit in order to evaluate the SOH of a plurality of battery cells of the assembled battery.

However, a measuring device provided with a plurality of impedance calculation units corresponding to each of the plurality of battery cells is expensive due to the complicated configuration.

Japanese Unexamined Patent Publication No. 2013-29411

An embodiment of the present invention is a battery module having a simple configuration for detecting that, in an assembled battery including a plurality of battery cells, the degree of deterioration of the battery cell having a charging depth larger than that of other battery cells is larger than that of other battery cells. The purpose is to provide.

The battery module of the embodiment of the present invention includes an assembled battery system in which a plurality of battery cells are connected in series, a balancer for equalizing the charging depth of the plurality of battery cells, and an equalizing process. A measurement circuit for measuring the first impedance characteristic of the previous assembled battery and the second impedance characteristic of the assembled battery after the equalization treatment, and a battery cell having a charging depth higher than that of the other battery cell among the plurality of battery cells. The first battery cell, which is also large, comprises a processor that detects that the degree of deterioration of the first battery cell is larger than that of the other battery cells by using the first impedance characteristic and the second impedance characteristic.

According to the embodiment of the present invention, in an assembled battery including a plurality of battery cells, a battery cell having a charging depth larger than that of other battery cells has a simple configuration for detecting that the degree of deterioration of the battery cell is larger than that of other battery cells. Battery modules can be provided.

It is a block diagram of the battery module of an embodiment. This is an example of the Nyquist plot of a battery. It is a flowchart of the evaluation method of the battery module of an embodiment. It is an example of the Nyquist plot of the battery module of the embodiment. It is an example of the Nyquist plot of the battery module of the embodiment. This is an example of the impedance characteristic change rate of the battery module of the embodiment. This is an example of the impedance characteristic change rate of the battery module of the embodiment.

<Battery module configuration>
As shown in FIG. 1, the battery module 1 of the embodiment includes an assembled battery system 2, a measurement circuit 5, a PCS (power conditioning system) 7, and an EMS (energy management system) 6. The battery module 1 is connected to a load (not shown), for example, a drive circuit of an electric vehicle, and outputs drive power.

In the following description, the drawings based on the respective embodiments are schematic, and the illustration of the components may be omitted. For example, a part of the internal wiring of the assembled battery system 2 and the measuring circuit 5 is not shown.

The PCS 7 supplies electric power to the assembled battery system 2. The EMS 6 is a processor that controls the battery module 1. The BMS 4 controls the assembled battery system 2.

For example, the battery module 1 is configured by connecting the measurement circuits 5, EMS6, and PCS7 to the assembled battery system 2 without changing the configuration of the general-purpose assembled battery system 2.

The assembled battery system 2 has a assembled battery 3 and a BMS (battery management system) 4 including a balancer. The assembled battery 3 is configured by connecting four battery cells 31 to 34 in series. Hereinafter, each of the plurality of battery cells 31 to 34 is referred to as a battery cell 30. The battery cell 30 is a lithium ion battery cell and has a positive electrode for storing / releasing lithium ions, an electrolyte, a separator, and a negative electrode for storing / releasing lithium ions.

The balancer of the BMS 4 measures the charging depth of each of the plurality of battery cells 30, and equalizes the charging depth SOC of the plurality of battery cells 30. The balancer has a voltmeter 41 for measuring the voltage of each battery cell 30, a resistance 42 for discharging the charge of each battery cell 30, and a discharge switch 43. For the resistor 42, a general resistor or an electronic load device is used. The BMS4 processor (not shown) controls the equalization process.

The measuring circuit 5 for measuring the impedance characteristics of the assembled battery 3 includes a high frequency power supply 59 that outputs an AC voltage signal, a voltmeter 51 that measures the voltage applied to the assembled battery 3, and a current meter 52 that measures the current. And, including. The voltmeter 51 for measuring impedance characteristics is more accurate than the voltmeter 41 for measuring voltage for acquiring SOC. If the PCS 7 can output a high frequency current that can be used to measure the impedance characteristics, the high frequency power supply 59 is unnecessary. Further, the BMS 4 may perform a part of the control performed by the EMS 6. On the contrary, the EMS 6 may perform at least a part of the control performed by the BMS.

<Impedance measurement>
Impedance characteristics are measured, for example, by the AC impedance method. In the AC impedance method, a signal obtained by superimposing a minute AC voltage signal (measurement signal) on a DC voltage is applied to the assembled battery 3, and the impedance characteristics are measured from the response signal. In the AC impedance measurement method, since the applied signal voltage is small, the impedance characteristics can be measured without changing the state of the assembled battery 3 to be measured.

The DC voltage component is set to about the voltage of the battery cell 30 to be measured. Further, the superimposed AC voltage component is set to a voltage that does not affect the characteristics of the battery cell 30. As the superimposed AC voltage component, an AC current set to a voltage that does not affect the characteristics of the battery cell 30 may be used.

In the frequency sweep method, the frequency of the measurement signal is swept from a high frequency to a low frequency, and the impedance characteristics of the assembled battery 3 at each frequency are measured at predetermined frequency intervals.

For example, the impedance characteristic is measured under the following conditions. The bias voltage is the voltage of the assembled battery 3. That is, the battery module 1 can measure the AC impedance even when the assembled battery system 2 is used.

Frequency measurement range: 0.01Hz-100kHz
Voltage amplitude: 5 mV
Bias voltage: 12V
Temperature: 25 ° C

FIG. 2 shows an example of the frequency characteristics of the impedance characteristics by the frequency sweep method of the battery. The frequency characteristics of the measured impedance characteristics are the Nyquist plot (call) displayed in a complex plan view with the real axis (Z') as the inductance (resistance component) and the imaginary axis (Z'') as the reactance (usually capacitive). Call plot). As shown in FIG. 2, when the measurement frequency is changed from high frequency to low frequency, a call call plot which is a locus of impedance (Z ′, Z ″) including a semicircle is obtained in a clockwise direction.

The Nyquist plot is divided into an inductance region (region A), a charge transfer reaction region (region B) on which two semicircles are superimposed, and an ion diffusion region (region C). The inductance region (region A) is, for example, a high frequency region of 100 kHz or higher.

The method for measuring the impedance characteristic is not limited to the frequency sweep method. For example, by using a square wave having a fundamental frequency f1 as a measurement signal and Fourier transforming a response signal containing harmonic components (2f1, 3f1, ...), a plurality of frequencies (f1, 2f1, 3f1, ...) ,) May be measured. Alternatively, the impedance characteristics may be measured using a measurement signal on which signals of a plurality of frequencies are superimposed. Of course, the impedance characteristics may be measured using a plurality of measurement signals having different frequencies.

<Evaluation method of battery module>
Next, the evaluation method of the battery module 1 will be described in detail with reference to the flowchart shown in FIG. A battery cell that has a larger SOC than other battery cells and is a target of discharge in the equalization process is called a first battery cell. Further, the description will be made using an assembled battery A in which the SOH of all the battery cells is 100% and an assembled battery B in which the SOH of any of the battery cells is 80%.

<Step S10> SOC measurement step The assembled battery 3 is charged by outputting electric power from the PCS 7 under the control of the EMS 6. During or after charging, the BMS 4 measures the SOCs of the plurality of battery cells 30. The SOC of the battery cell 30 is measured using a voltmeter 41.

<Step S20> SOC variation determination step The BMS 4 determines whether the SOC variation of the plurality of battery cells 30 exceeds a predetermined range. For example, if the SOC of the battery cell 32 is 100%, the SOC of the battery cells 31, 33, 34 is 80%, and the predetermined range is 15%, the BMS 4 is "variable (YES)". judge. Then, the battery cell 32 becomes the first battery cell.

When the variation is within a predetermined range (NO), the assembled battery 3 shifts to the normal discharge process.

<Step S30> First Impedance Measurement Step The high frequency power supply 59 of the measurement circuit 5 applies a measurement signal of a sine wave having a predetermined frequency, for example, 100 kHz to 0.01 Hz, to the assembled battery 3, and impedance characteristics (first). Impedance characteristics) is acquired. The impedance characteristic is performed by using the voltmeter 51 and the ammeter 52 of the measurement circuit 5. The first impedance characteristic is the impedance characteristic of the assembled battery before the equalization process.

Since the impedance characteristic is greatly affected by the temperature, it is preferable that the measuring circuit 5 also acquires the measured temperature by the temperature sensor (not shown) provided in the assembled battery 3. The EMS6, which is a processor that processes the data of the measurement circuit 5, preferably corrects the impedance characteristics according to the temperature.

<Step S40> Equalization processing step BMS4 equalizes the SOCs of a plurality of battery cells 31 to 34 by discharging the electric charge of the battery cell 32 (SOC 100%) which is the first battery cell.

The BMS 4 turns on (conducts) the switch 43 connected to the battery cell 32, and causes a current to flow from the battery cell 32 to the resistance 42. The charge of the battery cell 32 is converted into the thermal energy of the resistor 42. The charge of the battery cell 32 is discharged until the SOC of the battery cell 32 becomes the same (80%) as the SOC of the other battery cells 31, 33, 34.

<Step S50> Second Impedance Measurement Step The high-frequency power supply 59 of the measurement circuit 5 applies a measurement signal to the assembled battery 3 to acquire impedance characteristics (second impedance characteristics). The second impedance characteristic is the impedance characteristic of the assembled battery after the equalization process.
<Step S60> Change detection step of impedance characteristics

FIG. 4 shows a Nyquist plot when the SOH of the battery cells 31 to 34 is 100% (assembled battery A). Due to the equalization process, the impedance curve is changed in the ion diffusion region having a frequency of 0.1 Hz or less.

On the other hand, in FIG. 5, among the plurality of battery cells 30, the SOH of the first battery cell 32 is 80%, and the SOH of the other battery cells 31, 32, 34 is 100%. The Nyquist plot of (assembled battery B) is shown. Due to the equalization process, the impedance curve is changed in the charge transfer region having a frequency of 1 Hz or more and 10 Hz or less.

As is clear from FIGS. 4 and 5, by comparing the Nyquist plots before and after the equalization process, the first battery cell (battery cell 32) having a higher SOC than the other battery cells became the other battery cell. Whether or not the SOH is smaller than 31, 33, and 34 (whether the degree of deterioration is large) can be detected.

For example, EMS 6 compares the change in the ion diffusion region having a frequency of 0.1 Hz or less with the change in the charge transfer region having a frequency of 1 Hz or more and 10 Hz or less in the Nyquist plot before and after the equalization process.

The EMS 6 may perform machine learning on AI using the impedance characteristics before and after the equalization process and the past history data of a plurality of assembled batteries including SOH data, and perform AI determination.

For example, the EMS 6 may perform deep learning by a neural network on AI using big data of a plurality of assembled batteries including impedance characteristics before and after equalization processing and SOH data, and perform AI determination. good.

In order to detect the impedance characteristic more easily and quantitatively than the AI determination, it is preferable to acquire the impedance characteristic change rate, for example, the change rate of the second impedance characteristic with respect to the first impedance characteristic. Of course, the rate of change of the first impedance characteristic with respect to the second impedance characteristic may be acquired.

For example, when reactance Z ″ is used as the impedance characteristic, the reactance change rate is obtained by using the following equation. The reactance before the equalization treatment is the first reactance, and the reactance after the equalization treatment is the second reactance. ABS indicates an absolute value.

Reactance change rate (%) = ABS ((first reactance-second reactance) / first reactance) × 100

FIG. 6 shows the reactance change rates of the assembled battery A and the assembled battery B before and after the equalization treatment.

Compared with the assembled battery A, the assembled battery B has a large peak in the reactance change rate in the charge transfer region having a frequency of 1 Hz or more and 10 Hz or less.

<Steps S70 and S80> The SOH determination step and the warning step EMS6 determine whether or not the change in impedance characteristics is within a predetermined range. Since the SOH of the first battery cell (battery cell 32) of the assembled battery B was 80%, the peak intensity P of the reactance change rate in the charge transfer region having a frequency of 1 Hz or more and 10 Hz or less had a frequency of 0.01 Hz or more and 0. It was 150% or more of the average value A of the reactance change rate in the ion diffusion region of 1 Hz or less.

For example, in EMS6, when the peak intensity P is 125% or more of the average value A, the SOH of the first battery cell (battery cell 32) is larger than the SOH of the other battery cells 31, 33, 24. To warn you. The warning is given by sound, display, lighting of a lamp, or the like.

When warning by lighting the lamp, the color of the lamp may be changed based on the ratio of the peak intensity P to the average value A. For example, when the SOH of the first battery cell (battery cell 32) is at a level that does not cause any problem in use, the green lamp is turned on, and when a slight deterioration of the first battery cell is confirmed. Turn on the yellow lamp and turn on the red lamp if the first battery cell needs to be replaced.

For example, the EMS 6 may send a warning signal to the BMS 4 to display a warning on the assembled battery system 2.

The impedance characteristic is at least one of a real number component (resistance) Z ′, an imaginary number component (reactance) Z ″, a phase angle θ, and an absolute value | Z |.

When the phase angle (argument angle) θ is used as the impedance characteristic, for example, the phase angle change rate is acquired by using the following equation. The phase angle before the equalization process is the first phase angle, and the phase angle after the equalization process is the second phase angle. ABS indicates an absolute value.

Phase angle change rate (%) = ABS ((first phase angle-second phase angle) / first phase angle) x 100

As shown in FIG. 7, the assembled battery B has a peak in the phase angle change rate in the charge transfer region having a frequency of 1 Hz or more and 10 Hz or less as compared with the assembled battery A.

As described above, in the evaluation method by Nyquist plot, the impedance characteristics are resistance Z ′ and reactance Z ″. In the evaluation method based on the reactance rate of change, the impedance characteristic is the reactance corresponding to the measured frequency. Three or more impedance characteristics may be combined. Of course, two or more evaluation methods may be combined. It may be evaluated using admittance, which is the reciprocal of impedance.

The battery module 1 includes an assembled battery system 2 in which four battery cells 31 to 34 are connected in series. However, the number of battery cells 30 included in the assembled battery is 2 or more, but the upper limit is, for example, 50.

In the battery module of the embodiment, even if the plurality of battery cells have a larger SOC than the other battery cells and the charges of the plurality of battery cells are discharged in the equalization process, at least one of the batteries is used. It can be detected that the SOH of a cell is smaller than the SOH of another battery cell (the degree of deterioration is large).

The operation of the balancer may be not only a passive method in which the charge of the battery cell 30 having a large SOC is discharged by the resistance 42, but also an active method in which the charge of the battery cell 30 having a large SOC is regenerated to the battery cell having a small SOC.

In the case of a battery module in which a plurality of assembled batteries are connected in parallel, it is preferable to have a circuit changeover switch for measuring the impedance characteristics of each assembled battery.

The battery cell of the battery module of the embodiment is not limited to the lithium ion battery cell from the principle thereof, and may be another secondary battery cell, for example, a lithium polymer battery cell, a lithium sulfur battery cell, or a solid electrolyte. It may be an all-solid-state battery cell having. Further, the assembled battery may be a bipolar battery in which adjacent battery cells have a common current collector for the positive electrode and the negative electrode, or may be a bipolar all-solid-state battery.

Further, the structure of the assembled battery may be any of a laminated type, a wound type, a coin type, and a laminated type.

Each battery cell 30 may be configured by connecting a plurality of battery cells in parallel. In this configuration, the impedance characteristics and the like are measured as the average value of the battery cells connected in parallel. Further, each battery cell 30 may be configured by connecting a plurality of battery cells in series. In this case, the impedance characteristics and the like are measured as the sum of the battery cells connected in series.

The voltmeter 41 may not be connected to all battery cells. In that case, only the voltage of each voltmeter can be measured.

The present invention is not limited to the above-described embodiment, and various changes and modifications, for example, combinations of components of the embodiment are possible without changing the gist of the present invention.

1 ... Battery module 2 ... Assembled battery system 3 ... Assembled battery 5 ... Measurement circuit 6 ... Processor (EMS)
30 (31-34) ... Battery cell 40 ... BMS
41 ... Voltmeter 42 ... Resistance 43 ... Switch 51 ... Voltmeter 52 ... Ammeter 59 ... High frequency power supply

Claims (4)

An assembled battery system including an assembled battery in which a plurality of battery cells are connected in series and a balancer for equalizing the charging depth of the plurality of battery cells.
A measurement circuit for measuring the first impedance characteristic of the assembled battery before the equalization treatment and the second impedance characteristic of the assembled battery after the equalization treatment.
The first impedance characteristic and the first item indicate that the degree of deterioration of the first battery cell having a charging depth larger than that of the other battery cells among the plurality of battery cells is larger than the degree of deterioration of the other battery cells. A battery module comprising: a processor that detects using the impedance characteristic of 2. In the processor, the degree of deterioration of the first battery cell is the deterioration of the other battery cell based on the change of the first impedance characteristic and the second impedance characteristic in the charge transfer region and the ion diffusion region of the Nyquist plot. The battery module according to claim 1, wherein the battery module is detected to be larger than the degree. The processor determines that the degree of deterioration of the first battery cell is greater than the degree of deterioration of the other battery cells based on the change in the second impedance characteristic with respect to the first impedance characteristic in the charge transfer region. The battery module according to claim 1, wherein the battery module is detected. One of claims 1 to 3, wherein the first impedance characteristic and the second impedance characteristic are at least one of resistance, reactance, absolute impedance value, and phase angle, respectively. Battery module described in.

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