Battery module

Abstract

To provide a battery module 1 for detecting 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 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 BMS 4 for performing equalization processing on charging depths of the plurality of battery cells 30, a measurement circuit 5 for measuring a first impedance characteristic of the assembled battery 3 before the equalization processing and a second reference impedance characteristic of a reference battery cell 32 after the equalization processing, and a processor which uses the first impedance characteristic and the second reference impedance characteristic 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

[Technical Field]

[0001] An embodiment of the present invention relates to a battery module including a battery pack in which a plurality of battery cells are connected in series. [Background technology]

[0002] 2. Description of the Related Art Battery modules including rechargeable secondary batteries are used in portable devices, power tools, electric vehicles, etc. Small, large-capacity lithium-ion batteries and the like have attracted attention as secondary batteries.

[0003] A battery module is a battery assembly in which multiple battery cells are connected in series to obtain a desired output voltage. Furthermore, a desired current capacity is obtained by connecting battery assemblies that provide a predetermined output voltage in parallel. There are also battery assemblies in which a desired output voltage is obtained by connecting battery sets, each of which has multiple battery cells connected in parallel to obtain a desired current capacity, in series.

[0004] The multiple battery cells that make up a battery pack deteriorate over time and with repeated charging and discharging, but the state of health (SOH), which indicates the degree of deterioration of each battery cell, is not the same. When charging a battery pack, a battery cell with a low SOH (high degree of deterioration) will have a higher SOC (Stake of Charge) faster than the other battery cells, and may be overcharged.

[0005] For this reason, battery packs are used that include a balancer that measures the SOC of each of a plurality of battery cells and equalizes the SOC of the plurality of battery cells by, for example, discharging the charge of a battery cell with a large SOC.

[0006] Here, the reason why a certain battery cell has a higher SOC than other battery cells may not only be due to its high level of degradation, but also due to other factors. For this reason, it is important to detect abnormal degradation of battery cells with a high SOC.

[0007] Japanese Patent Application Laid-Open Publication No. 2013-29411 discloses a measuring device in which each battery cell is connected to a respective impedance calculation unit in order to evaluate the degree of deterioration of a plurality of battery cells of a battery pack.

[0008] However, a measuring device equipped with a plurality of impedance calculation units corresponding to a plurality of battery cells respectively has a complex configuration and is therefore expensive. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-29411 Summary of the Invention [Problem to be solved by the invention]

[0010] An embodiment of the present invention aims to provide a battery module with a simple configuration that detects whether a battery cell with a greater depth of charge than other battery cells has a greater degree of deterioration than the other battery cells in a battery pack including multiple battery cells. [Means for solving the problem]

[0011] A battery module according to an embodiment of the present invention includes: an assembled battery system including an assembled battery in which a plurality of battery cells are connected in series; and a balancer that equalizes the depths of charge of the plurality of battery cells; a measurement circuit for measuring a first impedance characteristic of the assembled battery before the equalization process or a second impedance characteristic of the assembled battery after the equalization process, and a first reference impedance characteristic of a reference battery cell that is one of the battery cells of the assembled battery before the equalization process or a second reference impedance characteristic of the reference battery cell after the equalization process; and a processor that uses the first impedance characteristic or the second impedance characteristic and the first reference impedance characteristic or the second reference impedance characteristic to detect that a first battery cell among the plurality of battery cells, which has a greater depth of charge than other battery cells, is more deteriorated than the other battery cells. [Effects of the Invention]

[0012] According to an embodiment of the present invention, a battery module with a simple configuration can be provided that can detect whether a battery cell with a higher depth of charge than other battery cells in a battery pack including multiple battery cells has a higher degree of deterioration than the other battery cells. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a configuration diagram of a battery module according to a first embodiment. [Figure 2] 1 is an example of a Nyquist plot of a battery. [Figure 3] 3 is a flowchart of a method for evaluating a battery module according to the first embodiment. [Figure 4] 3 is an example of a Nyquist plot of the battery module of the first embodiment. [Figure 5] 3 is an example of a Nyquist plot of the battery module of the first embodiment. [Figure 6] 4 is an example of a rate of change in impedance characteristics of the battery module of the first embodiment. [Figure 7]4 is an example of a rate of change in impedance characteristics of the battery module of the first embodiment. [Figure 8] 3 is an example of a Nyquist plot of the battery module of the first embodiment. [Figure 9] 3 is an example of a Nyquist plot of the battery module of the first embodiment. [Figure 10] 1 is an example of a rate of change in impedance characteristics of a battery module according to a first embodiment; [Figure 11] 10 is a flowchart of a method for evaluating a battery module according to Modification 1 of the first embodiment. [Figure 12] 10 is a flowchart of a method for evaluating a battery module according to a second modification of the first embodiment. [Figure 13] 10 is an example of a Nyquist plot of a battery module according to Modification 2 of the first embodiment; [Figure 14] 10 is an example of a Nyquist plot of a battery module according to Modification 2 of the first embodiment; [Figure 15] FIG. 10 is a configuration diagram of a battery module according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] First Embodiment <Battery module configuration> 1, a battery module 1 of this embodiment includes a battery pack 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.

[0015] In the following description, the drawings based on each embodiment are schematic and may omit illustration of components. For example, some of the internal wiring of the battery pack system 2 and the measurement circuit 5 is not shown.

[0016] The PCS 7 supplies 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.

[0017] The battery pack system 2 includes a battery pack 3 and a BMS (battery management system) 4 that includes a balancer. The battery pack 3 is configured by connecting four battery cells 31 to 34 in series. Hereinafter, each of the battery cells 31 to 34 will be referred to as a battery cell 30. The battery cell 30 is a lithium-ion battery cell and includes a positive electrode that absorbs / desorbs lithium ions, an electrolyte, a separator, and a negative electrode that absorbs / desorbs lithium ions.

[0018] The balancer of the BMS 4 measures the state of charge of each of the multiple battery cells 30 and performs an equalization process for the state of charge (SOC) of the multiple battery cells 30. The balancer has a voltmeter 41 that measures the voltage of each battery cell 30, a resistor 42 for discharging the charge of each battery cell 30, and a discharge switch 43. A processor of the BMS 4 (not shown) also controls the equalization process. A general resistor or an electronic load device is used for the resistor 42.

[0019] The measurement circuit 5 is used to measure the impedance characteristics of the assembled battery 3 and the impedance characteristics of a battery cell 32, which is one of the multiple battery cells 30. Hereinafter, the battery cell whose impedance is measured will be referred to as the reference battery cell. The reference battery cell may be any of the battery cells 31 to 34. The measurement circuit 5 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, a voltmeter 53 that measures the voltage applied to the battery cell 32, and an ammeter 52 that measures the current. The voltmeters 51 and 53 used to measure the impedance characteristics are more accurate than the voltmeter 41 that measures the voltage used to obtain the state of charge. 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 not necessary. The BMS 4 may also perform some of the control functions performed by the EMS 6. Conversely, the EMS 6 may also perform at least some of the control functions performed by the BMS.

[0020] <Impedance measurement> The impedance characteristics are measured, for example, by an AC impedance method. In the AC impedance method, for example, a signal in which a small AC voltage signal (measurement signal) is superimposed on a DC voltage is applied to the battery cell 30, and the impedance characteristics are measured from the response signal. Because the AC impedance measurement method applies a small signal voltage, it is possible to measure the impedance characteristics without changing the state of the battery cell 30 (battery pack 3) being measured.

[0021] The DC voltage component is set to approximately the voltage of the battery cell 30 to be measured. The AC voltage component to be superimposed is set to a voltage that does not affect the characteristics of the battery cell 30. Note that the AC voltage component to be superimposed may be an AC current that is set to a voltage that does not affect the characteristics of the battery cell 30.

[0022] 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 battery cell 30 are measured at each frequency at predetermined frequency intervals.

[0023] For example, the impedance characteristics are measured under the following conditions: The bias voltage is the voltage of the assembled battery 3. That is, the AC impedance of the battery module 1 can be measured even when the assembled battery system 2 is in use.

[0024] Frequency measurement range: 0.01Hz to 100kHz Voltage amplitude: 5mV Bias voltage: 12V Temperature: 25℃

[0025] Figure 2 shows an example of impedance characteristics of a battery measured by the frequency sweep method. The measured impedance is shown as a Nyquist plot (Cole-Cole plot) displayed on a complex plane with the real axis (Z') representing inductance (resistance component) and the imaginary axis (Z'') representing reactance (usually capacitive). As shown in Figure 2, when the measurement frequency is changed from high to low frequencies, a Nyquist plot is obtained, which is the locus of impedance (Z', Z'') that includes a semicircle in the clockwise direction.

[0026] The Nyquist plot is divided into an inductance region (region A), a charge transfer reaction region (region B) where two semicircles overlap, and an ion diffusion region (region C). The inductance region (region A) is a high-frequency region, for example, above 100 kHz.

[0027] The method for measuring impedance characteristics is not limited to the frequency sweep method. For example, impedance characteristics at multiple frequencies (f1, 2f1, 3f1, ...) may be measured by using a rectangular wave with a fundamental frequency f1 as the measurement signal and performing a Fourier transform on a response signal containing harmonic components (2f1, 3f1, ...). Alternatively, impedance characteristics may be measured using a measurement signal in which signals of multiple frequencies are superimposed. Of course, impedance characteristics may also be measured using multiple measurement signals with different frequencies.

[0028] <Battery module evaluation method> Next, a method for evaluating the battery module 1 will be described in detail with reference to the flowchart shown in Fig. 3. Note that a battery cell that has a higher SOC than the other battery cells and is the target for discharge in the equalization process is referred to as a first battery cell.

[0029] Below, we will explain battery packs A and B, in which the battery cell other than the reference battery cell is the first battery cell, and battery packs C and D, in which the reference battery cell is the first battery cell. In battery packs A and C, the SOH of all battery cells is 100%. In battery packs B and D, the SOH of the first battery cell is 80%, and the SOH of the other battery cells is 100%.

[0030] <Batteries A, B> First, battery packs A and B will be described.

[0031] <Step S110> SOC measurement step Under the control of the EMS 6, power is output from the PCS 7, thereby charging the battery pack 3. During charging or after charging is completed, the BMS 4 measures the SOC of the multiple battery cells 30. The SOC of the battery cells 30 is measured using a voltmeter 41.

[0032] <Step S120> SOC variation determination step The BMS 4 determines whether the variation in SOC of the multiple battery cells 30 exceeds a predetermined range. For example, if the SOC of battery cell 31 is 100%, the SOC of battery cells 32, 33, and 34 is 80%, and the predetermined range is 15%, the BMS 4 determines that there is variation (YES). Then, battery cell 32 becomes the first battery cell.

[0033] If the variation is within the predetermined range (NO), the battery pack 3 goes into a normal discharge process.

[0034] <Step S130> First impedance measurement step The high-frequency power supply 59 of the measurement circuit 5 applies a measurement signal of a predetermined frequency, for example, a sine wave of 100 kHz to 0.01 Hz, to the battery pack 3 to acquire the impedance characteristics (first impedance characteristics). The impedance characteristics are measured using the voltmeter 51 and ammeter 52 of the measurement circuit 5. The first impedance characteristics are the impedance characteristics of the battery pack before equalization processing.

[0035] Because the impedance characteristics are significantly affected by temperature, it is preferable that the measurement circuit 5 also acquires the measured temperature using a temperature sensor (not shown) disposed in the battery pack 3. Then, it is preferable that the EMS 6, which is a processor that processes the data from the measurement circuit 5, corrects the impedance characteristics depending on the temperature.

[0036] <Step S140> Equalization processing step The BMS 4 equalizes the SOCs of the plurality of battery cells 30 by discharging the charge of the battery cell 31 (SOC 100%), which is the first battery cell.

[0037] The BMS 4 turns on (conducts) the switch 43 connected to the battery cell 31, causing a current to flow from the battery cell 32 to the resistor 42. The charge in the battery cell 31 is converted into thermal energy in the resistor 42. The charge in the battery cell 31 is discharged until the SOC of the battery cell 31 becomes the same as the SOC of the other battery cells 32, 33, and 34 (80%).

[0038] <Step S150> Second reference (2nd ref.) impedance measurement step The high-frequency power supply 59 of the measurement circuit 5 applies a measurement signal to the battery cell 32, which is the reference battery cell, and the EMS 6 acquires the impedance characteristics (second reference impedance characteristics). The second reference impedance characteristics are the impedance characteristics of the reference battery cell after equalization processing. <Step S60> Impedance characteristic change detection step

[0039] FIG. 4 shows a Nyquist plot (first impedance characteristic) of battery pack A and a Nyquist plot obtained by multiplying the second reference impedance characteristic of the reference battery cell (battery cell 31) by four.

[0040] There is no significant difference between the first impedance characteristic and (second reference impedance characteristic x 4).

[0041] Next, FIG. 5 shows a Nyquist plot (first impedance characteristic) of the battery pack 3B and a Nyquist plot obtained by multiplying the second reference impedance characteristic of the reference battery cell (battery cell 31) by four.

[0042] The first impedance characteristic and (second reference impedance characteristic x 4) are significantly different at frequencies of 10 Hz or less.

[0043] As is clear from Figures 4 and 5, by comparing the first impedance characteristic with the second reference impedance characteristic, it is possible to detect whether the first battery cell (battery cell 31) whose SOC was 100% also has a lower SOH (greater degree of deterioration) than the other battery cells 32, 33, and 34.

[0044] For example, the EMS 6 may perform machine learning on the AI ​​using past history data of a plurality of assembled batteries, each of which includes the first impedance characteristic, the second reference impedance characteristic, and SOH data, to make an AI determination.

[0045] The EMS6 uses big data of multiple battery packs, each of which includes the first impedance characteristic, the second reference impedance characteristic, and SOH data, to perform deep learning using a neural network in the AI ​​and make an AI judgment.

[0046] For easier quantitative detection than AI determination, it is preferable to obtain the impedance characteristic change rate, for example, the difference rate of the second reference impedance characteristic from the first impedance characteristic. Of course, the difference rate of the first impedance characteristic from the second reference impedance characteristic may also be obtained.

[0047] When reactance Z is used as the impedance characteristic, the reactance difference rate is obtained using, for example, the following formula. The reactance of the battery pack before equalization is the first reactance, and the reactance of the reference battery cell after equalization is the second reference reactance. ABS indicates the absolute value.

[0048] Reactance difference rate (%) = ABS((first reactance - second reference reactance x 4) / first reactance) x 100

[0049] Figure 6 shows the reactance difference rate between battery packs A and B before and after equalization.

[0050] Unlike battery pack A, battery pack B has a large peak in the reactance difference rate at a frequency of 10 Hz, which is the charge transfer region.

[0051] <Steps S70, S80> SOH determination step, warning step The EMS 6 determines whether the difference in impedance characteristics is equal to or greater than a predetermined range. In battery pack B, the SOH of the first battery cell (battery cell 32) was 80%, so the reactance difference rate M in the charge transfer region (10 Hz) was 500% or more of the reactance difference rate D in the ion diffusion region (0.1 Hz).

[0052] For example, when the reactance difference rate M is 200% or more of the reactance difference rate D, the EMS 6 issues a warning that the deterioration level of the first battery cell (battery cell 32) is greater than the deterioration levels of the other battery cells 31, 33, and 24. The warning is given by sound, display, or lighting of a lamp, etc.

[0053] When warning by lighting a lamp, the color of the lamp may be changed based on the ratio between the reactance difference rate M and the reactance difference rate D. For example, if the deterioration level of the first battery cell (battery cell 32) is at a level that does not pose a problem for use, a green lamp may be lit, if slight deterioration of the first battery cell is confirmed, a yellow lamp may be lit, and if the first battery cell is at a level that requires replacement, a red lamp may be lit.

[0054] For example, the EMS 6 may send a warning signal to the BMS, and a warning may be displayed on the battery pack system 2.

[0055] The impedance characteristics include at least one of a real component (resistance) Z', an imaginary component (reactance) Z'', a phase angle θ, and an impedance absolute value |Z|.

[0056] When using a phase angle (argument angle) θ as the impedance characteristic, the phase angle change rate is obtained using, for example, the following formula. The phase angle of the battery pack before equalization is the first phase angle, and the phase angle of the reference battery cell after equalization is the second reference phase angle. ABS indicates the absolute value.

[0057] Phase angle change rate (%) = ABS((first phase angle - second reference phase angle) / first phase angle) x 100

[0058] As shown in FIG. 7, unlike battery pack A, battery pack B has a large peak in the rate of change of the phase angle in the charge transfer frequency range of 1 Hz or more and 10 Hz or less.

[0059] <Assembled battery C, assembled battery D> Next, battery packs C and D in which the reference battery cell 32 is a first battery cell having a higher SOC than the other battery cells 31, 33, and 34 will be described.

[0060] The battery packs C and D were evaluated using the same method as the battery packs A and B.

[0061] The two Nyquist plots of battery pack C shown in FIG. 8 are more different than the two Nyquist plots of battery pack D shown in FIG.

[0062] As shown in FIG. 10, even when the detection method using the reactance difference rate is used, the difference between the assembled batteries C and D is significant.

[0063] In the battery packs C and D, by using the same method as in the battery packs A and B, it can be detected that the deterioration level of the first battery cell (battery cell 32) is greater than the deterioration levels of the other battery cells 31, 33, and 24.

[0064] As explained above, in the evaluation method using the Nyquist plot, the impedance characteristics are resistance Z' and reactance Z''. In the evaluation method using the reactance change rate, the impedance characteristics are the reactance corresponding to the measurement frequency. Three or more impedance characteristics may be combined. Of course, two or more evaluation methods may also be combined. Evaluation may also be performed using admittance, which is the reciprocal of impedance.

[0065] The balancer may operate not only in a passive manner in which the charge of the battery cell 30 with a high SOC is discharged by the resistor 42, but also in an active manner in which the charge of the battery cell 30 with a high SOC is regenerated to the battery cell with a low SOC.

[0066] Alternatively, only the impedance characteristics at one first measurement frequency in the charge transfer region and one second measurement frequency in the ion diffusion region may be measured. For example, even if only the impedance characteristics at a frequency of 5 Hz in the charge transfer region and the impedance characteristics at a frequency of 0.1 Hz in the ion diffusion region are used, it is possible to detect whether the first battery cell (battery cell 32) that had a higher SOH than the other battery cells also has a lower SOH (is more deteriorated) than the other battery cells 31, 33, and 34.

[0067] <Modification 1 of the First Embodiment> 11 is a flowchart of the battery module evaluation method of this modification. Explanation of steps (for example, S210) that are the same as those in the flowchart of FIG.

[0068] In the battery module of this modification, the EMS 6 measures the second impedance characteristic and the first reference (1st ref.) impedance characteristic using the measurement circuit 5. The first reference impedance characteristic measured in step S230 is the impedance characteristic of the reference battery cell before the equalization process (S240). The second impedance characteristic measured in step S250 is the impedance characteristic of the battery pack after the equalization process.

[0069] In step S260, the EMS 6, which is a processor, uses the second impedance characteristic and the first reference impedance characteristic to detect that the deterioration level of the battery cell having a higher SOC than the other battery cells is higher than that of the other battery cells.

[0070] It goes without saying that the battery module of Modification 1 can detect that the degree of deterioration of the first battery cell is greater than the degrees of deterioration of the other battery cells by using the same method as the battery module of the first embodiment.

[0071] <Modification 2 of the First Embodiment> 12 is a flowchart of the battery module evaluation method of this modification. Explanation of steps (for example, S310) that are the same as those in the flowchart of FIG.

[0072] In the battery module of this modification, the EMS 6 measures the second impedance characteristic and the second reference impedance characteristic using the measurement circuit 5. The second reference impedance characteristic measured in step S340 is the impedance characteristic of the reference battery cell after the equalization process (step S330). The second impedance characteristic measured in step S350 is the impedance characteristic of the battery pack after the equalization process. The order of steps S340 and S350 may be reversed.

[0073] In step S360, the EMS 6, which is a processor, uses the second impedance characteristic and the second reference impedance characteristic to detect that the deterioration level of the battery cell having a higher SOC than the other battery cells is higher than that of the other battery cells.

[0074] FIG. 13 is a Cole-Cole plot of battery pack A, and FIG. 14 is a Cole-Cole plot of battery pack B.

[0075] The battery module of Modification 2 can detect that the degree of deterioration of the first battery cell is greater than the degrees of deterioration of the other battery cells by using the same method as the battery module of the first embodiment.

[0076] Second Embodiment FIG. 15 is a configuration diagram of a battery module 1A of this embodiment.

[0077] In the battery module 1A, the reference battery cell is battery cell 35 included in the measurement circuit 5A. Battery cell 35 has substantially the same configuration as battery cells 31 to 34. Because battery cell 35 is connected in series with battery cells 31 to 34, the battery cells 31 to 34 and 35 can be considered as a single assembled battery in the battery module 1A. In other words, the reference battery cell 35 is a separate, detachable unit from the battery cells 31 to 34 other than the reference battery cell 35 of the assembled battery.

[0078] The battery module 1A is configured by connecting a measurement circuit 5A, an EMS 6, and a PCS 7 to a general-purpose battery pack system 2 without changing the configuration of the battery pack system 2.

[0079] Although not shown, the battery cells 35 also have resistors for discharging electric charge under the control of the EMS 6. In the battery module 1A, the equalization process is performed by cooperative control between the EMS 6 and the BMS 4.

[0080] Furthermore, when comparing the reactance of the battery pack with that of the reference battery cell, for example, it goes without saying that the reactance of the battery pack is compared with (the reactance of the reference battery cell×5).

[0081] The battery module of the embodiment includes a battery pack in which four or five battery cells are connected in series. However, the number of battery cells 30 included in the battery pack may be two or more, with the upper limit being, for example, 50.

[0082] In the battery module of the embodiment, even if multiple battery cells have a higher SOC than other battery cells and the charges of the multiple battery cells are discharged during the equalization process, it is possible to detect that the degree of deterioration of at least one of the battery cells is greater than that of the other battery cells.

[0083] Each battery cell 30 may be configured by connecting multiple battery cells in parallel. In this configuration, the impedance characteristics and the like are measured as the average value of the parallel-connected battery cells. Alternatively, each battery cell 30 may be configured by connecting multiple battery cells in series. In this case, the impedance characteristics and the like are measured as the sum of the impedance characteristics of the series-connected battery cells.

[0084] The voltmeter 41 does not have to be connected to all battery cells. In that case, it is possible to measure only the voltage of each voltmeter.

[0085] 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.

[0086] The battery cells of the battery module of the embodiment are not limited to lithium-ion battery cells due to their operating principle, but may be other secondary battery cells, such as lithium polymer battery cells or lithium-sulfur battery cells, or all-solid-state battery cells having a solid electrolyte. Furthermore, the battery pack may be a bipolar battery in which adjacent battery cells share a common current collector for the positive and negative electrodes, or a bipolar all-solid-state battery.

[0087] The structure of the battery pack may be any of a stacked type, a wound type, a coin type, and a laminate type.

[0088] The present invention is not limited to the above-described embodiments, and various changes and modifications, for example, combinations of components of the embodiments, are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0089] 1, 1A...Battery module 2. Battery pack system 3. Battery pack 5, 5A…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

1. a battery pack system including a battery pack in which a plurality of battery cells are connected in series, and a balancer that equalizes the depth of charge of the plurality of battery cells; a measurement circuit for measuring a first impedance characteristic of the assembled battery before the equalization process and a second reference impedance characteristic of a reference battery cell that is one of the battery cells of the assembled battery after the equalization process; a processor that uses the first impedance characteristic and the second reference impedance characteristic to detect that a degree of deterioration of a first battery cell among the plurality of battery cells, the first battery cell having a greater depth of charge than other battery cells, is greater than the degrees of deterioration of the other battery cells.

2. a battery pack system including a battery pack in which a plurality of battery cells are connected in series, and a balancer that equalizes the depth of charge of the plurality of battery cells; a measurement circuit for measuring a second impedance characteristic of the assembled battery after the equalization process and a first reference impedance characteristic of a reference battery cell that is one of the battery cells of the assembled battery before the equalization process; a processor that uses the second impedance characteristic and the first reference impedance characteristic to detect that a degree of deterioration of a first battery cell among the plurality of battery cells, the first battery cell having a greater depth of charge than other battery cells, is greater than the degrees of deterioration of the other battery cells.

3. a battery pack system including a battery pack in which a plurality of battery cells are connected in series, and a balancer that equalizes the depth of charge of the plurality of battery cells; a measurement circuit for measuring a second impedance characteristic of the assembled battery after the equalization process and a second reference impedance characteristic of a reference battery cell that is one of the battery cells of the assembled battery after the equalization process; a processor that uses the second impedance characteristic and the second reference impedance characteristic to detect that a degree of deterioration of a first battery cell among the plurality of battery cells, the first battery cell having a greater depth of charge than other battery cells, is greater than the degrees of deterioration of the other battery cells.

4. 4. The battery module according to claim 1, wherein the reference battery cell is a separate, detachable body from battery cells other than the reference battery cell of the assembled battery.

5. 2. The battery module according to claim 1, wherein the first impedance characteristic is at least one of resistance, reactance, impedance absolute value, and phase angle.

6. A battery module as described in claim 1, characterized in that the second reference impedance characteristic is at least one of resistance, reactance, impedance absolute value and phase angle.

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