Diagnostic device, diagnostic method, and diagnostic program

Abstract

To diagnose the capacity of battery cells from a QV curve.SOLUTION: A diagnosis device according to the present invention includes a calculation unit for calculating a value that pertains to the capacity of battery cells on the basis of the result of comparison, with a reference QV curve, of a measured QV curve that indicates the relationship of a voltage and an integral current value obtained from the measured data of battery cells. The calculation unit includes a first calculation unit for multiplying a voltage difference between the measured QV curve and the reference QV curve to the inclination of the measured QV curve and thereby calculating a capacity degradation amount attributable to the voltage difference and / or a second calculation unit for multiplying a maximum reference capacity to the ratio of the inclination of the measured QV curve to the reference QV curve and thereby calculating a temporal maximum capacity after a capacity degradation attributable to a change of inclination of the measured QV curve relative to the inclination of the reference QV curve.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a diagnostic apparatus, a diagnostic method, and a diagnostic program.

Background Art

[0002] Various methods for diagnosing the capacity of a battery cell have been proposed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As an indication of the characteristics of a battery cell, there is a QV curve showing the relationship between voltage and integrated current. There is room for improvement in the method of diagnosing the capacity of a battery cell from the QV curve.

[0005] An object of the present invention is to diagnose the capacity of a battery cell from a QV curve.

Means for Solving the Problems

[0006] A diagnostic apparatus according to one aspect includes a calculation unit that calculates a value related to the capacity of a battery cell based on a comparison result between a measured QV curve showing the relationship between the voltage and the integrated current obtained from the measurement data of the battery cell and a reference QV curve. The calculation unit includes at least one of a first calculation unit that calculates a capacity degradation amount due to a voltage difference by multiplying the slope of the measured QV curve by the voltage difference between the measured QV curve and the reference QV curve, and a second calculation unit that calculates a provisional maximum capacity after capacity degradation due to a change in the slope of the measured QV curve with respect to the slope of the reference QV curve by multiplying the ratio of the slope of the measured QV curve to the slope of the reference QV curve by the reference maximum capacity.

[0007] The diagnostic device according to one aspect includes a calculation unit that calculates a value related to the capacity of a battery cell using a function model that approximates a QV curve showing the relationship between the voltage and the integrated current amount of the battery cell. The calculation unit includes a function model generation unit that generates a function model fitted to a reference QV curve, a fitting unit that fits the function model generated by the function model generation unit to the measurement data of the battery cell, and a maximum capacity calculation unit that calculates the maximum capacity of the battery cell using the function model after fitting by the fitting unit.

[0008] The diagnostic method according to one aspect includes calculating a value related to the capacity of a battery cell based on a comparison result between a measurement QV curve showing the relationship between the voltage and the integrated current amount obtained from the measurement data of the battery cell and a reference QV curve. The calculating includes calculating a capacity degradation amount caused by the voltage difference by multiplying the slope of the measurement QV curve by the voltage difference between the measurement QV curve and the reference QV curve, and calculating a provisional maximum capacity after capacity degradation caused by a change in the slope of the measurement QV curve with respect to the slope of the reference QV curve by multiplying the ratio of the slope of the measurement QV curve to the slope of the reference QV curve by the reference maximum capacity, including at least one of these.

[0009] The diagnostic method according to one aspect includes calculating a value related to the capacity of a battery cell using a function model that approximates a QV curve showing the relationship between the voltage and the integrated current amount of the battery cell. The calculating includes generating a function model fitted to a reference QV curve, fitting the generated function model to the measurement data of the battery cell, and calculating the maximum capacity of the battery cell using the function model after fitting.

[0010] The diagnostic program according to one aspect causes a computer to execute a process of calculating a value related to the capacity of a battery cell based on a comparison result between a measurement QV curve showing the relationship between the voltage and the integrated current amount obtained from the measurement data of the battery cell and a reference QV curve. The calculating process includes at least one of a process of calculating the amount of capacity deterioration caused by the voltage difference by multiplying the slope of the measurement QV curve by the voltage difference between the measurement QV curve and the reference QV curve, and a process of calculating the provisional maximum capacity after capacity deterioration caused by the change in the slope of the measurement QV curve with respect to the slope of the reference QV curve by multiplying the ratio of the slope of the measurement QV curve to the slope of the reference QV curve by the reference maximum capacity.

[0011] The diagnostic program according to one aspect causes a computer to execute a process of calculating a value related to the capacity of a battery cell by using a function model that approximates a QV curve showing the relationship between the voltage and the integrated current amount of the battery cell. The calculating process includes a process of generating a function model fitted to the reference QV curve, a process of fitting the generated function model to the measurement data of the battery cell, and a process of calculating the maximum capacity of the battery cell by using the function model after fitting.

Advantages of the Invention

[0012] According to the present invention, it becomes possible to diagnose the capacity of a battery cell from a QV curve.

Brief Description of the Drawings

[0013]

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Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments will be described with reference to the drawings. The same elements are denoted by the same reference numerals, and redundant descriptions will be omitted as appropriate.

[0015] <Preface> The disclosed technology relates to the diagnosis of capacity degradation of storage batteries such as lithium-ion batteries, more specifically, battery cells and battery systems. A battery cell represents the smallest unit of a storage battery that can be handled. A battery cell can also be simply referred to as a storage battery and may be appropriately read as such within a non-contradictory range. A battery system has a configuration in which a plurality of battery cells are connected in parallel or in series.

[0016] FIG. 1 is a diagram schematically showing the voltage and current of a battery cell. The voltage of the battery cell is denoted as battery voltage V and illustrated. The current of the battery cell is denoted as battery current I and illustrated. The characteristics of the battery cell are represented by, for example, a QV curve (QV characteristic). The QV curve is a curve showing the relationship between the battery voltage V and the integrated current amount. The integrated current amount corresponds to the capacity (Q) by Coulomb counting and has the unit of Ah.

[0017] FIG. 2 is a diagram showing an example of a QV curve. The horizontal axis of the graph indicates the integrated current amount (Ah), and the vertical axis indicates the voltage (V). As shown by the solid line graph line, the battery voltage V changes according to charging and discharging, that is, according to the integrated current amount. The battery cell is used at a battery voltage V within a defined range. The minimum voltage within that range is denoted as the lower limit voltage V LL and is illustrated. The maximum voltage is denoted as the upper limit voltage V UL and is illustrated.

[0018] When the battery voltage V is the lower limit voltage V LL , the state of charge (SOC) of the battery cell is 0% (fully discharged state). When the battery voltage V is the upper limit voltage V UL , the SOC is 100% (fully charged state). The maximum capacity of the battery cell DUT corresponds to the integrated current amount when the battery cell is discharged from the upper limit voltage V UL to the lower limit voltage V LL , or when the battery cell is charged from the lower limit voltage V LL to the upper limit voltage V UL . The battery voltage V at an arbitrary point in time is denoted as the battery voltage V C and is illustrated. The remaining capacity at the battery voltage V C corresponds to the integrated current amount when the battery cell is charged from the lower limit voltage V LL to the battery voltage V C , or when the battery cell is discharged from the battery voltage V C to the lower limit voltage V LL .

[0019] FIG. 3 is a diagram showing an example of the relationship between capacity degradation and the QV curve. Seven QV curves with different progress states of capacity degradation are illustrated as graph lines C1 to C7. In the order of graph line C1 to graph line C7, the capacity degradation of the battery cell progresses. As can be understood, the capacity degradation of the battery cell occurs particularly when the integrated current amount when the battery voltage V reaches the upper limit voltage V UL becomes small. In terms of the comparison between graph line C1 and graph line C7, the maximum capacity corresponding to graph line C1 is the maximum capacity before degradation, and the maximum capacity corresponding to graph line C7 is the maximum capacity after degradation.

[0020] The differential curve of the Q-V curve also indicates the characteristics of the battery cell. The differential curve refers to the curve obtained by differentiating the integrated current amount with respect to the battery voltage V (dQ / dV), or the curve obtained by differentiating the battery voltage V with respect to the integrated current amount (dV / dQ).

[0021] FIG. 4 is a diagram showing an example of a differential curve. In this example, the horizontal axis of the graph indicates the voltage (V), and the vertical axis indicates (dQ / dV). Graph lines C1 to C7 correspond to the differential curves of graph lines C1 to C7 in FIG. 3 described above. There are several characteristic points on the differential curve. An example of a characteristic point is an extreme value (maximum value, minimum value). Hereinafter, unless otherwise specifically described, the characteristic point shall be the maximum value that first appears in the differential curve within the usage range of the battery cell.

[0022] When a battery cell is used for a long period of time, capacity degradation progresses and the decrease in the maximum capacity becomes apparent, so it is necessary to diagnose the capacity of the battery cell. The same applies to a battery storage system including a plurality of battery cells. For example, in a battery storage system in which a plurality of battery cells are connected in series, there is no problem if the remaining capacity and the maximum capacity of each individual battery cell match (balanced state). However, if the balanced state is disrupted, the effective capacity that can be utilized as the battery storage system, that is, the capacity of the entire battery storage system, will decrease. For example, consider a battery storage system in which a battery cell with a battery voltage V represented by a solid graph line in FIG. 2 and a battery cell with a battery voltage V X represented by a dashed graph line are connected in series. The remaining capacities of the two battery cells are different and the balance is disrupted. The battery storage system is used such that the voltage of each of the two battery cells is within the range of the lower limit voltage V LL to the upper limit voltage V UL . In this case, the battery cell with the battery voltage V cannot be used until the lower limit voltage V LL , and the battery cell with the battery voltage V X cannot be used until the upper limit voltage V UL . The usage range of the battery cell becomes narrow, and the capacity of the entire battery storage system decreases.

[0023] Batteries have differences in their initial charge-discharge characteristics and characteristic changes during capacity degradation depending on their constituent materials. For example, lithium-ion batteries using Ni-Mn-Co oxides, known as ternary systems, as the cathode material exhibit differences in charge-discharge characteristics depending on the mixing ratio of the three elements and the substances added. Also, since the battery voltage V is the output of the potential difference between the anode and cathode characteristics, the characteristics also change due to differences in anode characteristics.

[0024] For battery cells with various characteristics depending on the constituent materials in this way, it takes a huge amount of time to develop an algorithm for grasping the battery cell characteristics corresponding to each constituent material of each manufacturer. According to the disclosed technology, taking a lithium-ion battery as an example, the capacity degradation of a battery cell is caused by (1) the deviation of the initial design values of the cathode potential and the anode potential from the degradation resulting from the immobilization of Li in the anode due to charge-discharge operations and standing in the charged state, etc., and (2) the capacity reduction of the inactivation factors due to the immobilization of the active material, etc. It is possible to grasp from these two factors and enable the diagnosis of the capacity of a battery cell with less material dependence. Diagnosis without requiring full charge-discharge is also possible, leading to a reduction in the diagnosis time. For example, it is possible to shorten the diagnosis time, which is the basis for judgments such as whether to reuse or recycle the materials after performance evaluation of battery cells and battery systems used in electric vehicles, hybrid vehicles, etc.

[0025] <Embodiment> FIG. 5 is a diagram showing an example of the schematic configuration of a diagnostic device according to an embodiment. The battery cell to be diagnosed by the diagnostic device 1 is illustrated and referred to as the battery cell DUT. In this example, the battery cell DUT is connected to a charge-discharge device 8. The charge-discharge device 8 charges and discharges the battery cell DUT at a desired charge-discharge rate, for example. According to the principle described later, charge-discharge only requires a partial voltage range (range of integrated current amount, range of SOC).

[0026] The diagnostic device 1 includes a voltage detection unit 2, a current detection unit 3, a memory unit 4, a calculation unit 5, and an output unit 6. The voltage detection unit 2 detects the battery voltage V of the battery cell DUT. The voltage detection unit 2 is configured to obtain, for example, the measurement result of a voltmeter (not shown). The voltmeter may be included in the voltage detection unit 2. The detection result of the voltage detection unit 2 is stored in the memory unit 4. The current detection unit 3 detects the battery current I of the battery cell DUT. The current detection unit 3 is configured to obtain, for example, the measurement result of an ammeter (not shown). The ammeter may be included in the current detection unit 3. The detection result of the current detection unit 3 is stored in the memory unit 4.

[0027] The memory unit 4 stores various information necessary for the processes executed in the diagnostic device 1. Examples of the stored information include reference data 41, measurement data 42, and a diagnostic program 43.

[0028] The reference data 41 is data that serves as a standard (a comparison target) for the capacity degradation of the battery cell DUT and includes, for example, data corresponding to a QV curve. The reference data 41 may be data based on the actual measurement values of the battery cell DUT before the capacity degradation progresses, or may be data based on the design values or simulation values of the battery cell DUT. The reference data 41 may be measurement data at a predetermined temperature and charge-discharge rate.

[0029] The measurement data 42 is data corresponding to at least a part of the QV curve of the battery cell DUT. The measurement data 42 is data based on the detection results of the above-described voltage detection unit 2 and current detection unit 3. The measurement data 42 may be measurement data at substantially the same temperature and charge-discharge rate as the above-described reference data 41. Note that the temperature is detected and grasped by, for example, a temperature sensor (not shown). The integrated current amount in the QV curve of the battery cell DUT is obtained by integrating the battery current I detected by the current detection unit 3.

[0030] The diagnostic program 43 is a program that causes a computer to execute the processes of the diagnostic device 1, such as the processes (calculation process, output process, etc.) by the calculation unit 5 and the output unit 6 described later. At least some of the functions of the diagnostic device 1 are realized, for example, by operating a general-purpose computer according to the diagnostic program 43. The computer is configured to include, for example, a communication device, a display device, a storage device, a memory, a processor, etc. that are interconnected by a bus or the like. The processor reads the diagnostic program 43 from a storage device or the like and expands it into the memory, thereby causing the computer to function as the diagnostic device 1. Note that the diagnostic program 43 may be distributed via a network such as the Internet. The diagnostic program 43 may be recorded on a computer-readable recording medium such as a hard disk, a flexible disk (FD), a CD-ROM, a MO (Magneto-Optical disk), a DVD (Digital Versatile Disc). Of course, dedicated hardware that operates according to the diagnostic program 43 may be used instead of a general-purpose computer.

[0031] The calculation unit 5 calculates a value related to the capacity of the battery cell DUT. In one embodiment, the calculation unit 5 calculates a value related to the capacity of the battery cell DUT based on the comparison result between the QV curve obtained from the measurement data 42 and the QV curve obtained from the reference data 41. The QV curve obtained from the measurement data 42 is also referred to as the "measured QV curve". The measured QV curve can also be said to be the QV curve after capacity degradation. The QV curve obtained from the reference data 41 is also referred to as the "reference QV curve". The reference QV curve can also be said to be the QV curve before capacity degradation.

[0032] FIG. 6 is a diagram showing an example of the schematic configuration of the calculation unit. The calculation unit 5 includes, as functional blocks, a first calculation unit 51, a second calculation unit 52, and a maximum capacity calculation unit 53. A specific calculation method will be described with reference to FIGS. 7 and 8.

[0033] FIG. 7 is a diagram showing examples of the reference QV curve and the measured QV curve. The graph line C ref shows the reference QV curve. The graph line C DUTshows the measured QV curve. The lower limit voltage V LL is, for example, about 2.8 V, and the upper limit voltage V UL is, for example, about 4.2 V. Comparing graph line C ref with graph line C DUT it can be explained separately in two ways what are the factors for the capacity degradation of the battery cell DUT.

[0034] The first factor is the change in the magnitude of the battery voltage V (shift of the battery voltage V in the vertical axis direction). As the battery voltage V increases, the reaching of the upper limit voltage V UL is accelerated and the maximum capacity decreases. For example, in the case of a lithium-ion battery, the deviation from the initial design values of the positive electrode potential and the negative electrode potential caused by degradation due to the charge-discharge operation of the battery cell and the immobilization of Li in the negative electrode during storage in the charged state appears as a shift of the battery voltage V.

[0035] The second factor is the change in the slope of the battery voltage V. As the slope increases, the reaching of the upper limit voltage V UL is accelerated and the maximum capacity decreases. The capacity decrease due to deactivation factors such as active material immobilization appears as a change in the slope of the battery voltage V. As also shown in FIG. 7, in the case of a battery cell using a plurality of materials having capacity retention potentials such as a ternary system in combination, the battery voltage V increases relatively monotonically as the integrated current amount increases. When a battery cell with such characteristics deteriorates in capacity due to deactivation or partial destruction of the electrode structure, the degree of increase of the battery voltage V with respect to the integrated current amount, that is, the slope, becomes large. The battery voltage V changes greatly even with a small integrated current amount.

[0036] The first calculation unit 51 calculates the amount of capacity degradation caused by the above-described first factor (positive and negative electrode potential deviation), that is, the measured QV curve (graph line C DUT ) and the reference QV curve (graph line C ref ). This amount of capacity degradation is referred to as "capacity degradation amount ΔQ". The voltage difference is referred to as "voltage difference ΔV". For example, the first calculation unit 51 calculates the difference between the voltages of the characteristic points of the differential curves of the measured QV curve and the reference QV curve as the voltage difference ΔV.

[0037] FIG. 8 is a diagram showing an example of a differential curve. Graph line C ref and graph line C DUT correspond to the differential curves of graph line C ref and graph line C DUT in FIG. 7. In this example, the difference between the voltages of the maximum values that first appear in the two differential curves is calculated as the voltage difference ΔV. Note that the maximum value may be interpreted to include the maximum value.

[0038] The first calculation unit 51 calculates the amount of capacity degradation ΔQ caused by the voltage difference ΔV by multiplying the slope of the QV curve, more specifically, the slope of the integrated current amount with respect to the battery voltage V (dQ / dV), by the voltage difference ΔV. For example, the following formula (1) is used. The slope (dQ / dV) used for multiplication here may be the slope at a voltage where the battery voltage V is equal to or higher than the voltage of the characteristic point. The slope in the region near the upper limit voltage V UL may be used. For example, if the upper limit voltage V UL is 4.2V and the voltage difference ΔV is 0.05V, the average slope between 4.15V and 4.2V may be used.

Equation

[0039] The second calculation unit 52 calculates the maximum capacity after capacity degradation caused by the change in the slope of the measured QV curve with respect to the slope of the reference QV curve, that is, the above-described second factor (deactivation). Since the maximum capacity here is a provisional maximum capacity considering only the second factor, it is referred to as "provisional maximum capacity Q DUT ".

[0040] Specifically, referring to FIG. 7 again, the second calculation unit 52 includes a reference QV curve (graph line C ref ) and a measured QV curve (graph line C DUT)For each, calculate the slope (dV / dQ) of the battery voltage V with respect to the integrated current. The slope calculated here may be the slope at a voltage where the battery voltage V is equal to or higher than the voltage at the characteristic point. The slope (dV / dQ) may be calculated in a voltage range where the SOC is relatively high (for example, about 3.8 V to about 4.0 V). This is because, for example, when the negative electrode is graphite, a region with excellent capacity retention ability of the negative electrode (a region also called stage 1, stage 2, etc.) contributes to the high SOC side, and deactivation of the positive electrode active material is likely to be seen in the degradation on the high SOC side.

[0041] In FIG. 7, a straight line having the slope of the calculated reference QV curve (graph line C ref ) is indicated by a broken line as (dV / dQ) ref . A straight line having the slope of the calculated measured QV curve (graph line C DUT ) is indicated by a broken line as (dV / dQ) DUT .

[0042] The second calculation unit 52 multiplies the ratio of the slope of the calculated measured QV curve to the slope of the reference QV curve by the reference maximum capacity Q ref to calculate the provisional maximum capacity Q DUT . For example, the following formula (2) is used. The reference maximum capacity Q ref is the maximum capacity obtained from the reference QV curve and corresponds to the maximum capacity of the battery cell DUT before degradation.

Equation

[0043] The maximum capacity calculation unit 53 subtracts the capacity degradation amount ΔQ calculated by the first calculation unit 51 from the provisional maximum capacity Q DUT calculated by the second calculation unit 52 to calculate the maximum capacity Q DUTMAX of the battery cell DUT. For example, the following formula (3) is used. The maximum capacity Q DUTMAX calculated in this way is the maximum capacity considering both the above-mentioned first factor (positive and negative electrode potential shift) and the second factor (deactivation).

Equation

[0044] The measurement data 42 necessary for the calculations by the first calculation unit 51, the second calculation unit 52, and the maximum capacity calculation unit 53 is sufficient with the data of a part of the QV curve of the battery cell DUT. In the above example, with the measurement data of the voltage range near the characteristic point (for example, 3.4V to 3.6V, etc.) and the voltage range near the upper limit voltage V UL if there is measurement data in the voltage range near (for example, 4.15V to 4.2V, etc.), the capacity degradation amount ΔQ, the temporary maximum capacity Q DUT and the maximum capacity Q DUTMAX can be calculated. By not performing measurements outside those ranges, the diagnosis time can be shortened.

[0045] Returning to FIG. 5, the output unit 6 outputs the calculation result of the calculation unit 5 as a diagnosis result of the capacity of the battery cell DUT. Examples of the output are presentation (display, etc.) to the user, data transmission to an external server device (not shown), etc. For example, the output unit 6 outputs the maximum capacity Q DUTMAX of the battery cell DUT calculated by the maximum capacity calculation unit 53. The decrease amount (Qref - Q ref DUTMAX ) from the reference maximum capacity Qmay be output. The remaining capacity calculated from the battery voltage V of the battery cell DUT at the end of the diagnosis may be output.

[0046] Also, the output unit 6 may output the capacity degradation amount ΔQ calculated by the first calculation unit 51 and the temporary maximum capacity Q DUT calculated by the second calculation unit 52. The capacity degradation amount ΔQ may be displayed, etc., together with the fact that it is the capacity degradation amount due to the first factor (positive and negative electrode potential shift). The temporary maximum capacity QDUT may be displayed together with the fact that it is a temporary capacity degradation amount considering only the capacity degradation due to the second factor (deactivation). It can contribute to understanding the degradation factor.

[0047] For example, as described above, the capacity of the battery cell DUT can be diagnosed. Note that there are also battery cells in which the battery voltage V increases significantly at the end of charging. Even for such types of battery cells, the above-described calculation method is applicable. This will be described with reference to FIGS. 9 and 10.

[0048] FIG. 9 is a diagram showing an example of a reference QV curve and a measured QV curve of another type of battery cell. FIG. 10 is a diagram showing an example of a differential curve. The upper limit voltage V UL nearby, that is, at the end of charging, the battery voltage V increases significantly. Even in this case, in the same manner as the method described so far, the amount of capacity degradation ΔQ can be calculated by multiplying the voltage difference ΔV by the slope (dQ / dV) of the integrated current amount with respect to the battery voltage V. The slope (dV / dQ) of the measured QV curve DUT and the slope (dV / dQ) of the reference QV curve ref to the ratio of, the reference maximum capacity Q ref is multiplied to calculate the provisional maximum capacity Q DUT . The maximum capacity Q DUTMAX can also be calculated.

[0049] Note that in the above, an example in which the differential curve is a curve (dQ / dV) obtained by differentiating the integrated current amount with respect to the battery voltage V has been described. However, as described above, the differential curve may be a curve (dV / dQ) obtained by differentiating the battery voltage V with respect to the integrated current amount.

[0050] FIG. 11 is a diagram showing another example of a differential curve. The illustrated differential curve is a curve (dV / dQ) obtained by differentiating the battery voltage V with respect to the integrated current amount. Five differential curves with different progress states of capacity degradation are illustrated as graph lines C11 to C15. In the order of graph line C11 to graph line C15, the capacity degradation of the battery cell is progressing. Such a differential curve also has a characteristic point (for example, the first maximum value that appears). Therefore, the voltage difference ΔV can be calculated.

[0051] Another calculation method different from the calculation method by the above-described calculation unit 5 will be described with reference to FIGS. 12 and 13. FIG. 12 is a diagram showing another example of the schematic configuration of the calculation unit. The illustrated calculation unit 5A calculates a value related to the capacity of the battery cell DUT using a function model that approximates the QV curve of the battery cell DUT. As functional blocks therefor, the calculation unit 5A includes a function model generation unit 54, a fitting unit 55, and a maximum capacity calculation unit 56.

[0052] FIG. 13 is a diagram for explaining another calculation method. As shown in FIG. 13(A), the function model generation unit 54 generates a function model V ref that is fitted to the reference QV curve. The function model V ref may be a function model that approximates a part of the reference QV curve. In this example, the function model V ref approximates the portions corresponding to the linear region indicated by the arrow AR1 and the non-linear region indicated by the arrow AR2 in the reference QV curve. Note that the graph lines of the regions outside the approximation range are shown by dashed lines. The linear region is a region where the battery voltage V changes substantially linearly with respect to the integrated current amount, and may be a region of a voltage equal to or higher than the voltage of the characteristic point. The non-linear region is a region where the battery voltage V changes non-linearly with respect to the integrated current amount, and is a region on the higher voltage side (higher SOC side) than the linear region. The battery voltage V at the boundary between the linear region and the non-linear region is referred to as the threshold voltage V ref_th and is shown in the figure. The function model V ref can also be said to be a function model at a voltage equal to or higher than the voltage of the characteristic point (threshold voltage V ref_th ).

[0053] The illustrated function model V ref is defined such that in the linear region, V ref = f ref (I ref ), and in the non-linear region, V ref = f ref (I ref ) + g ref (I ref ). I ref is the integrated current amount in the graph of FIG. 13(A). The function f ref (I ref) is, for example, a linear function with the integrated current I ref as a variable. The function g ref (I ref ) is, for example, an exponential function or a polynomial function with the integrated current I ref as a variable. The parameters (such as coefficients) of the functions f ref (I ref ) and the function g ref (I ref ) are adjusted so as to approximate the corresponding part of the reference QV curve (graph line C ref ). General methods such as the least squares method may be used for the approximation adjustment.

[0054] The fitting unit 55 fits the function model V ref generated by the function model generation unit 54 to the measurement data 42. The parameters of the function model V ref are adjusted so as to approximate the measurement data 42. In FIGS. 13(B) and 13(C), the function model V ref after fitting is shown as the function model V DUT . The function model V DUT is a function model that approximates the QV curve of the battery cell DUT . Note that the graph line in the region outside the approximation range is shown by a dashed line. The graph in FIG. 13(B) is drawn at a position where it is easy to grasp the relationship of the horizontal axis with the graph in FIG. 13(A). The graph in FIG. 13(C) is drawn at a position where it is easy to grasp the relationship of the vertical axis with the graph in FIG. 13(A). The battery voltage V at the boundary between the linear region and the non-linear region in the function model V DUT is referred to as the threshold voltage V DUT_th and is illustrated. The function model V DUT can also be said to be a function model at voltages of the threshold voltage V DUT_th or higher.

[0055] In this example, the function model V DUT is represented using the functions f DUT (I DUT ) and the function g DUT (I DUT ). I DUT is the integrated current in the graphs of FIGS. 13(B) and 13(C). The function fDUT (I DUT ) is a function obtained by adjusting the parameters of the above-mentioned function f ref (I ref ). The function g DUT (I DUT ) is a function obtained by adjusting the parameters of the above-mentioned function g ref (I ref ).

[0056] The measurement data 42 necessary for fitting by the fitting unit 55 can be the data of a part of the QV curve of the battery cell DUT. In (B) of FIG. 13, as the range of the necessary measurement data 42, a range R1 and a range R2 are exemplified. The range R1 is a range including the feature point and its periphery. The range R2 is a range including the boundary between the linear region and the non-linear region and its periphery. If there is measurement data for these ranges R1 and R2, the functions f DUT (I C ) and the function g DUT (I C ) corresponding to the linear region and the non-linear region can be fitted.

[0057] The maximum capacity calculation unit 56 calculates the maximum capacity Q ref of the battery cell DUT, that is, the function model V DUT , using the function model V DUTMAX after fitting by the fitting unit 55. The integrated current I DUT when the battery voltage V shown in the function model V UL becomes the upper limit voltage V C can be the maximum capacity to be obtained. However, as understood from (A) and (C) of FIG. 13, the horizontal axis of the function model V ref does not coincide with the horizontal axis of the function model V DUT . By correcting this shift of the horizontal axis (by aligning the horizontal axes), the maximum capacity Q DUTMAX can be calculated.

[0058] Here, the remaining capacity (Ah) at the characteristic point in the low SOC region is approximated (assumed) to be the same for the battery cell before the capacity degradation progresses and the battery cell after the progress because it is the first reaction accompanying the absorption of battery energy during charging. In this case, the position of the characteristic point of the differential curve of the function model V DUT may be aligned with the position of the characteristic point of the differential curve of the function model V ref .

[0059] The integrated current amount at the characteristic point of the function model V ref is referred to as the integrated current amount I1 and illustrated. The integrated current amount I1 is calculated as the integrated current amount corresponding to the voltage at the characteristic point of the differential curve (dQ / dV) calculated from the measurement data in the range R1 of, for example, the reference data 41. The integrated current amount at the characteristic point of the function model V DUT is referred to as the integrated current amount I2 and illustrated. The integrated current amount I2 is calculated as the integrated current amount corresponding to the voltage at the characteristic point of the differential curve (dQ / dV) calculated from the measurement data in the range R1 of, for example, the measurement data 42. If the difference between the horizontal axis of the function model V ref and the horizontal axis of the function model V DUT is ΔI, then ΔI = I2 - I1. By subtracting ΔI from the integrated current amount I DUT in the function model V DUT , the horizontal axis can be corrected.

[0060] The calculation by the maximum capacity calculation unit 56 includes correcting so that the positions of the characteristic points of the differential curves of the function model V ref and the function model V DUT are aligned. Specifically, the maximum capacity calculation unit 56 calculates the integrated current amount I DUT in the non-linear region, that is, f DUT (I DUT ) + g DUT (I DUT ) becomes equal to the upper limit voltage V UL , and further calculates the value (I DUT -ΔI) corrected by ΔI as the maximum capacity Q DUT DUTMAX . Thereby, an appropriate maximum capacity considering the shift of the horizontal axis is calculated.

[0061] ​ The maximum capacity calculation unit 56 calculates the maximum capacity Q DUTMAX Regardless, various values related to the capacity may be calculated using the function model V DUT or its differential curve. For example, as shown in (C) of FIG. 13, the voltage difference ΔV can be calculated, so the capacity degradation amount ΔQ due to the first factor (potential shift between the positive and negative electrodes) can be calculated. The provisional maximum capacity Q after capacity degradation due to the second factor (deactivation) can also be calculated. The calculation result of the calculation unit 5A may also be output by the output unit 6 in the same manner as the calculation result of the calculation unit 5 described above. DUT

[0062] So far, an example in which the capacity of the battery cell DUT connected to the charge / discharge device 8 is diagnosed has been described. In this case, it is necessary to interrupt the use of the battery cell DUT to be diagnosed. From a more practical point of view, it is desirable to be able to diagnose the capacity of the battery cell DUT (during operation) incorporated in and used in the battery storage system.

[0063] It is difficult to actually measure the maximum capacity in a general battery storage system for various reasons. For example, in an actual battery storage system, in order to have a margin or extend the life, it is not used in the range of SOC from 0 to 100%. In a battery storage system that is constantly used for system stabilization, etc., it is difficult to provide a period for full charge and discharge. It takes 2 hours at a charge / discharge rate of 1C and 10 hours at a charge / discharge rate of 0.2C to perform full charge and discharge. In a battery storage system in which a plurality of battery cells are connected in series, if the balance of the battery cells is lost, each battery cell cannot be fully charged and discharged, so the maximum capacity of each individual battery cell cannot be actually measured.

[0064] ​From the above, in an actual battery system, the maximum capacity is displayed by the following methods, but each has its own problems. For example, there is a method of statistically attenuating according to conditions such as operation time and number of charge-discharge cycles, but it does not match the actual situation when there are unexpected battery cells. There is a method of setting the maximum capacity in advance with a margin, but the battery cells are not used effectively. There is a method that may be used to perform full charge and discharge regularly and measure and reflect the maximum capacity, but there are cases where the battery system cannot be used. The factor of reduction in the execution capacity due to the variation of individual battery cells cannot be taken into account.

[0065] FIG. 14 is a diagram showing an example of the schematic configuration of a diagnostic device. The illustrated diagnostic device 1A diagnoses the capacity of the battery system 9 by diagnosing the capacities of a plurality of battery cells DUT included in the battery system 9. In this example, the battery system 9 includes a plurality of battery cells DUT connected in series. The battery system 9 is also referred to as a battery pack, an ESS (energy storage system), etc. The battery system 9 may also include a voltage detection unit 2A and a current detection unit 3.

[0066] The diagnostic device 1A includes a voltage detection unit 2A, a current detection unit 3, a storage unit 4A, a calculation unit 5, an output unit 6A, and a complement unit 7. When the voltage detection unit 2A and the current detection unit 3 are components of the battery system 9 and the diagnostic device 1A uses them, the diagnostic device 1A itself does not need to include the voltage detection unit 2A and the current detection unit 3. Note that the calculation unit 5 may be a calculation unit 5A.

[0067] The voltage detection unit 2A detects the battery voltage V of each of the plurality of battery cells DUT. The current detection unit 3 detects the battery current I. Since the battery cells DUT are connected in series, the battery current I is a current common to each battery cell DUT. The battery voltage V and the battery current I detected by the voltage detection unit 2A and the current detection unit 3 are the battery voltage V and the battery current I during operation.

[0068] The storage unit 4A stores various information necessary for the processes executed in the diagnostic device 1A. Examples of the information stored include reference data 41, measurement data 42A, and a diagnostic program 43A. Since the reference data 41 has been described above, the description will not be repeated. The measurement data 42A is data regarding the QV characteristics of each of a plurality of battery cells DUT, for example, data corresponding to at least a part of the QV curve. The diagnostic program 43A is a program that causes a computer to execute the processes of the diagnostic device 1A.

[0069] The complementing unit 7 will be described first. The complementing unit 7 complements the measurement data 42A as necessary. Since the measurement data 42A is limited to the detection results of the battery voltage V and the battery current I during operation, there may be a shortage of measurement data necessary for the calculation by the calculation unit 5. In such a case, complementing by the complementing unit 7 is performed. The method of complementing is not particularly limited, and for example, linear interpolation, complementing using a polynomial, etc. may be used. Note that the measurement data 42A after being complemented by the complementing unit 7 is also continuously referred to as the measurement data 42A.

[0070] The calculation unit 5 calculates values related to the capacity of each of a plurality of battery cells DUT using the reference data 41 and the measurement data 42A stored in the storage unit 4A. The same applies to the case of the calculation unit 5A. Since it has been described in detail above, the description will not be repeated.

[0071] The output unit 6A outputs (displays, etc.) the calculation result of the calculation unit 5 (or the calculation unit 5A) as a diagnostic result of the capacity of the battery storage system 9. For example, the output unit 6A outputs the maximum capacity of the entire plurality of battery cells DUT, that is, the capacity of the battery storage system 9, or outputs the balance state of each battery cell DUT in the battery storage system 9. Similar to the output unit 6 (FIG. 5) described above, the maximum capacity Q of each battery cell DUT DUTMAX , the amount of decrease in capacity (Q ref - Q DUTMAX ), the remaining capacity, the amount of capacity degradation ΔQ, etc. can also be output.

[0072] Some embodiments of the disclosed technology have been described above. The disclosed technology is not limited to the above embodiments. For example, in the above embodiments, an example has been described in which the calculation unit 5 (Figs. 5 and 6) includes three functional blocks: a first calculation unit 51, a second calculation unit 52, and a maximum capacity calculation unit 53. However, not all of these functional blocks need to be included in the calculation unit 5. For example, the calculation unit 5 may include only at least one of the first calculation unit 51 and the second calculation unit 52. Even if only the first calculation unit 51 calculates the capacity degradation amount ΔQ, it can lead to the diagnosis of the capacity of the battery cell. Even if only the second calculation unit 52 calculates the temporary maximum capacity Q DUT it can lead to the diagnosis of the capacity of the battery cell.

[0073] In the above, the embodiments have been mainly described from the aspects of the form of devices such as the diagnostic device 1 and the programs such as the diagnostic program 43. However, various processes realized by the devices and programs, that is, the diagnostic methods, are also one of the embodiments.

[0074] The technology described above is specified as follows, for example. One of the disclosed technologies is a diagnostic device. As described with reference to Figs. 5 to 11 etc., the diagnostic device 1 calculates a value related to the capacity of the battery cell DUT based on the comparison result between the measurement QV curve showing the relationship between the voltage (battery voltage V) and the integrated current amount obtained from the measurement data 42 of the battery cell DUT and the reference QV curve. The calculation unit 5 includes at least one of the first calculation unit 51 and the second calculation unit 52. The first calculation unit 51 calculates the capacity degradation amount ΔQ caused by the voltage difference ΔV by multiplying the slope (dQ / dV) of the measurement QV curve by the voltage difference ΔV between the measurement QV curve and the reference QV curve. The second calculation unit 52 is the slope (dV / dQ) of the measurement QV curve DUT and the slope (dV / dQ) of the reference QV curve ref and multiplying the ratio by the reference maximum capacity Q ref to calculate the temporary maximum capacity Q DUT after capacity degradation caused by the change in the slope of the measurement QV curve with respect to the slope of the reference QV curve.

[0075] According to the above diagnostic device 1, the capacity of the battery cell DUT can be diagnosed from the QV curve. For example, by calculating the capacity degradation amount ΔQ, it is possible to diagnose the capacity degradation caused by the potential shift between the positive and negative electrodes (the first factor). Hypothetical maximum capacity Q DUT By calculating, it is possible to diagnose the capacity degradation caused by deactivation (the second factor). Such a calculation method is not an algorithm specialized for each type of material, but an algorithm that can be generally applied to battery cells with different initial charge / discharge characteristics and characteristic changes during capacity degradation depending on the constituent materials. It is possible to develop an algorithm for grasping the battery cell characteristics corresponding to each constituent material of each battery manufacturer in a short period of time, and the development budget for this can also be reduced.

[0076] In addition, as described above with reference to FIGS. 7 and 8, since the measurement data 42 required for the calculation is only a part of the data of the QV curve of the battery cell DUT, the diagnostic time can be shortened. For example, it is possible to shorten the diagnostic time that serves as a basis for determining whether to reuse a battery cell or a battery storage system after use in an electric vehicle, a hybrid vehicle, etc., or to recycle the extracted materials.

[0077] The calculation unit 5 may include a maximum capacity calculation unit 53 that calculates the maximum capacity Q of the battery cell DUT by subtracting the capacity degradation amount ΔQ calculated by the first calculation unit 51 from the hypothetical maximum capacity Q DUT calculated by the second calculation unit 52. In this way, an appropriate maximum capacity Q DUTMAX taking into account the two factors of the potential shift between the positive and negative electrodes and deactivation can be calculated, that is, the maximum capacity of the battery cell DUT can be appropriately diagnosed. DUTMAX

[0078] The voltage difference ΔV may be the voltage difference between the characteristic points of the differential curves of the measured QV curve and the reference QV curve respectively. For example, the voltage difference ΔV can be calculated in this way.

[0079] The feature point is the maximum value that first appears on the differential curve, and the above-mentioned slope may be the slope at a voltage equal to or higher than the voltage of the feature point. For example, based on such a feature point and slope, the amount of capacitance degradation ΔQ and the provisional maximum capacitance Q DUT , and further the maximum capacitance Q DUTMAX can be calculated.

[0080] As described with reference to FIGS. 12 and 13, etc., in another calculation method, the calculation unit 5A calculates a value related to the capacitance of the battery cell DUT using a function model V DUT that approximates the QV curve. The calculation unit 5A includes a function model generation unit 54, a fitting unit 55, and a maximum capacitance calculation unit 56. The function model generation unit 54 generates a function model V ref fitted to the reference QV curve. The fitting unit 55 fits the function model V ref generated by the function model generation unit 54 to the measurement data 42 of the battery cell DUT. The maximum capacitance calculation unit 56 calculates the maximum capacitance Q DUT of the battery cell DUT using the function model V DUTMAX after fitting by the fitting unit 55. The calculation unit 5A also achieves the same effect as that of the above-mentioned calculation unit 5.

[0081] The calculation by the maximum capacitance calculation unit 56 may include aligning the positions of the feature points of the differential curves of the function model V ref and the function model V DUT respectively. After aligning the axes of the function model V ref and the function model V DUT , an appropriate maximum capacitance Q DUTMAX can be calculated.

[0082] The feature point is the maximum value that first appears on the differential curve, and the function model V ref and the function model V DUT may be function models at voltages equal to or higher than the voltage of the feature point. For example, based on such a feature point and function model, the maximum capacitance Q DUTMAX can be calculated.

[0083] A diagnostic method for a battery cell or a battery system by the diagnostic device 1 is also one of the disclosed technologies. The diagnostic method includes calculating a value related to the capacity of the battery cell DUT based on a comparison result between a measurement QV curve showing the relationship between the voltage (battery voltage V) and the integrated current amount obtained from the measurement data 42 of the battery cell DUT and a reference QV curve. The calculating includes calculating a capacity degradation amount ΔQ caused by the voltage difference ΔV by multiplying the slope (dQ / dV) of the measurement QV curve by the voltage difference ΔV between the measurement QV curve and the reference QV curve, and the slope (dV / dQ) of the measurement QV curve DUT and the slope (dV / dQ) of the reference QV curve ref and multiplying the ratio by the reference maximum capacity Q ref to calculate a provisional maximum capacity Q after capacity degradation caused by a change in the slope of the measurement QV curve with respect to the slope of the reference QV curve DUT including at least one of. The same effect as that of the above-described diagnostic device 1 is achieved

[0084] A diagnostic method for a battery or a battery system by the diagnostic device 1A is also one of the disclosed technologies. The diagnostic method includes calculating a value related to the capacity of the battery cell DUT by using a function model V that approximates a QV curve showing the relationship between the voltage (battery voltage V) and the integrated current amount of the battery cell DUT. The calculating includes generating a function model V fitted to the reference QV curve, fitting the generated function model V to the measurement data 42 of the battery cell DUT, and using the fitted function model V DUT to calculate the maximum capacity Q of the battery cell DUT ref including generating, ref fitting the generated function model V to the measurement data 42 of the battery cell DUT, and DUT using the fitted function model V DUTMAX to calculate the maximum capacity Q of the battery cell DUT. The same effect as that of the above-described diagnostic device 1A is achieved

[0085] The diagnostic program 43 described with reference to FIG. 5 and the like is also one of the disclosed technologies. The diagnostic program 43 causes a computer to execute a process of calculating a value related to the capacity of the battery cell DUT based on the comparison result between the measured QV curve showing the relationship between the voltage (battery voltage V) and the integrated current amount obtained from the measurement data 42 of the battery cell DUT and the reference QV curve. The calculation process includes at least one of: a process of calculating the capacity degradation amount ΔQ caused by the voltage difference ΔV by multiplying the slope (dQ / dV) of the measured QV curve by the voltage difference ΔV between the measured QV curve and the reference QV curve; and a process of calculating the provisional maximum capacity Q after capacity degradation caused by the change in the slope of the measured QV curve with respect to the slope of the reference QV curve by multiplying the ratio of the slope of the measured QV curve to the slope of the reference QV curve by the reference maximum capacity Qref. Alternatively, the diagnostic program 43 causes a computer to execute a process of calculating a value related to the capacity of the battery cell DUT using the function model V that approximates the QV curve showing the relationship between the voltage (battery voltage V) and the integrated current amount of the battery cell DUT. The calculation process includes: a process of generating the function model V fitted to the reference QV curve; a process of fitting the generated function model V to the measurement data 42 of the battery cell DUT; and a process of calculating the maximum capacity Q of the battery cell DUT using the function model V after fitting. The same effects as those of the above-described diagnostic device 1 or diagnostic device 1A are achieved. DUT and the reference QV curve (dV / dQ) ref by multiplying the ratio of the slope of the measured QV curve to the slope of the reference QV curve by the reference maximum capacity Qref, the provisional maximum capacity Q after capacity degradation caused by the change in the slope of the measured QV curve with respect to the slope of the reference QV curve DUT is calculated. Or, the diagnostic program 43 causes a computer to execute a process of calculating a value related to the capacity of the battery cell DUT using the function model V that approximates the QV curve showing the relationship between the voltage (battery voltage V) and the integrated current amount of the battery cell DUT. DUT using ref a function model V fitted to the reference QV curve ref is generated, the generated function model V DUT is fitted to the measurement data 42 of the battery cell DUT, and using the function model V after fitting, the maximum capacity Q DUTMAX of the battery cell DUT is calculated. The same effects as those of the above-described diagnostic device 1 or diagnostic device 1A are achieved.

Description of Reference Numerals

[0086] 1 Diagnostic device 2 Voltage detection unit 3 Current detection unit 4 Storage unit 5 Calculation unit 6 Output unit 7 Completion unit 8 Charge / discharge device 9 Battery system 41 Reference data 42 Measurement data 43 Diagnostic program 51 First calculation unit 52 Second calculation unit 53 Maximum capacity calculation unit 54 Function model generation unit 55 Fitting unit 56 Maximum capacity calculation unit

Claims

1. a calculation unit that calculates a value related to a capacity of the battery cell by using a function model that approximates a QV curve that indicates a relationship between a voltage of the battery cell and an integrated current amount, The calculation unit is a function model generating unit that generates a function model that is fitted to a reference QV curve and includes a linear region and a nonlinear region on a higher voltage side than the linear region; a fitting unit that fits the function model generated by the function model generation unit to first measurement data in a first range including characteristic points of a differential curve and second measurement data in a second range including a boundary between the linear region and the nonlinear region, using the function model generated by the function model generation unit as measurement data of the battery cell; a maximum capacity calculation unit that calculates a maximum capacity of the battery cell using the function model after fitting by the fitting unit; Including, Diagnostic equipment.

2. the calculation by the maximum capacity calculation unit includes aligning positions of the feature points of the function models before and after fitting by the fitting unit; The diagnostic device of claim 1 .

3. the characteristic point is a maximum value that first appears on the differential curve, The function model is a function model at a voltage equal to or higher than the voltage of the characteristic point. The diagnostic device of claim 2.

4. calculating a value relating to the capacity of the battery cell using a function model that approximates a QV curve that indicates the relationship between the voltage and the integrated current of the battery cell; A diagnostic method comprising: The calculating step comprises: generating a function model fitted to the reference QV curve, the function model including a linear region and a portion corresponding to a nonlinear region on a higher voltage side than the linear region; Fitting the generated function model to first measurement data in a first range including a characteristic point of the differential curve and second measurement data in a second range including a boundary between the linear region and the nonlinear region, using the measurement data of the battery cell as the measurement data; Calculating a maximum capacity of the battery cell using the fitted function model; Including, Diagnostic methods.

5. On the computer, Calculating a value related to the capacity of the battery cell using a function model that approximates a QV curve that indicates the relationship between the voltage and the integrated current of the battery cell; A diagnostic program for executing a process, The calculation process includes: A process of generating a function model fitted to a reference QV curve, the function model including a linear region and a portion corresponding to a nonlinear region on a higher voltage side than the linear region; A process of fitting the generated function model to first measurement data in a first range including characteristic points of the differential curve and second measurement data in a second range including a boundary between the linear region and the nonlinear region, using the measurement data of the battery cell as the measurement data; Calculating a maximum capacity of the battery cell using the fitted function model; Including, Diagnostic program.

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