Diagnostic apparatus, diagnostic method, and non-transitory computer-readable recording medium storing diagnostic instructions

Abstract

The present disclosure provides a diagnostic device including a calculator that calculates a value related to a capacity of a battery cell based on a comparison result between a measured Q-V curve and a reference Q-V curve, the measured Q-V curve indicating a relationship between a voltage and an integrated current amount obtained from measured data of the battery cell. The calculator also calculates an amount of capacity degradation caused by a voltage difference between the measured Q-V curve and the reference Q-V curve by multiplying a slope of the measured Q-V curve by the voltage difference, and calculates a temporary maximum capacity after a capacity degradation caused by a change in the slope of the measured Q-V curve with respect to a slope of the reference Q-V curve.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Japanese Patent Application No. 2021-161867, filed on September 30, 2021, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to a diagnostic device, a diagnostic method, and a non-transitory computer-readable recording medium for storing diagnostic instructions. Background Technology

[0004] Various methods have been proposed for diagnosing the capacity of battery cells (see, for example, JP2016-145795A).

[0005] Methods for indicating battery cell characteristics include the QV curve, which indicates the relationship between voltage and integral current. There is still room for exploring methods to diagnose battery cell capacity based on the QV curve. Summary of the Invention

[0006] One or more embodiments of the present invention can diagnose the capacity of a battery cell based on the QV curve.

[0007] According to one or more embodiments of the present invention, a diagnostic device includes a calculator that calculates a value related to the capacity of a battery cell based on a comparison between a measured QV curve and a reference QV curve, the measured QV curve indicating the relationship between voltage and integral current obtained from measurement data of the battery cell, wherein the calculator includes at least one of the following: a first calculator that calculates the amount of capacity degradation caused by the voltage difference between the measured QV curve and the reference QV curve 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 calculator that calculates the temporary maximum capacity after capacity degradation caused by the change in the slope of the measured QV curve relative to the slope of the reference QV curve by multiplying the ratio between the slope of the measured QV curve and the slope of the reference QV curve by a reference maximum capacity.

[0008] According to one or more embodiments of the present invention, a diagnostic device includes a calculator that calculates a value related to the capacity of a battery cell using a function model of a QV curve that approximately indicates the relationship between the voltage and integral current of the battery cell. The calculator includes: a function model generator that generates a function model fitted to a reference QV curve; a fitting unit that fits the function model generated by the function model generator to measurement data of the battery cell; and a maximum capacity calculator that calculates the maximum capacity of the battery cell using the function model fitted by the fitting unit.

[0009] According to one or more embodiments of the present invention, a diagnostic method includes calculating a value related to the capacity of a battery cell based on a comparison between a measured QV curve and a reference QV curve, the measured QV curve indicating the relationship between voltage and integral current obtained from measurement data of the battery cell, wherein the calculation includes at least one of: calculating a capacity degradation amount caused by the voltage difference between the measured QV curve and the reference QV curve by multiplying the slope of the measured QV curve by the voltage difference between the measured QV curve and the reference QV curve; and calculating a temporary maximum capacity after capacity degradation caused by a change in the slope of the measured QV curve relative to the slope of the reference QV curve by multiplying the ratio between the slope of the measured QV curve and the slope of the reference QV curve by a reference maximum capacity.

[0010] According to one or more embodiments of the present invention, a diagnostic method includes calculating a value related to the capacity of a battery cell by using a function model of a QV curve that approximately indicates the relationship between the voltage and integral current of the battery cell, wherein the calculation includes: generating a function model fitted to a reference QV curve; fitting the generated function model to measurement data of the battery cell; and calculating the maximum capacity of the battery cell using the fitted function model.

[0011] According to one or more embodiments of the present invention, a non-transitory computer-readable recording medium stores diagnostic instructions therein, the diagnostic instructions causing a computer to perform processing to calculate a value related to the capacity of a battery cell based on a comparison between a measured QV curve and a reference QV curve, the measured QV curve indicating the relationship between voltage and integral current obtained from measurement data of the battery cell, wherein the calculation processing includes at least one of the following processes: calculating the amount of capacity degradation caused by the voltage difference between the measured QV curve and the reference QV curve by multiplying the slope of the measured QV curve by the voltage difference between the measured QV curve and the reference QV curve; and calculating the temporary maximum capacity after capacity degradation caused by the change in the slope of the measured QV curve relative to the slope of the reference QV curve by multiplying the ratio between the slope of the measured QV curve and the slope of the reference QV curve by a reference maximum capacity.

[0012] According to one or more embodiments of the present invention, a non-transitory computer-readable recording medium stores diagnostic instructions therein, the diagnostic instructions causing a computer to perform a process of calculating a value related to the capacity of a battery cell by using a function model of a QV curve that approximates the relationship between the voltage and integral current of the battery cell, wherein the calculation process includes the following steps: 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 fitted function model. Attached Figure Description

[0013] Figure 1 The voltage and current of the battery cell are schematically shown;

[0014] Figure 2 An example of a QV curve is shown;

[0015] Figure 3 An example of the relationship between capacity decay and the QV curve is shown;

[0016] Figure 4 An example of a differential curve is shown;

[0017] Figure 5 An example of a schematic configuration of a diagnostic device according to one or more embodiments is shown;

[0018] Figure 6 An example of a schematic configuration of a calculator according to one or more embodiments is shown;

[0019] Figure 7 Examples of a reference QV curve and a measured QV curve are shown;

[0020] Figure 8 An example of a differential curve is shown;

[0021] Figure 9 An example of a reference QV curve and a measured QV curve for another type of battery cell is shown;

[0022] Figure 10 An example of a differential curve is shown;

[0023] Figure 11 Another example of a differential curve is shown;

[0024] Figure 12 Another example of a schematic configuration of a calculator according to one or more embodiments is shown;

[0025] Figure 13 Another calculation method is shown; and

[0026] Figure 14 An example of a schematic configuration of a diagnostic device according to one or more embodiments is shown. Detailed Implementation

[0027] The embodiments will now be described with reference to the accompanying drawings. The same elements are denoted by the same reference numerals, and redundant descriptions will be omitted where appropriate.

[0028] Introduction

[0029] The disclosed technology relates to the diagnosis of capacity degradation in batteries (e.g., lithium-ion batteries), and more specifically, to the diagnosis of capacity degradation in battery cells and battery systems. A battery cell represents the smallest unit of a tractable battery. A battery cell can also be simply referred to as a battery, and may be appropriately understood as such unless there is a contradiction. A battery system has a configuration in which multiple battery cells are connected in parallel or series.

[0030] Figure 1 The voltage and current of the battery cell are schematically shown. The voltage of the battery cell is called the battery voltage V and is shown. The current of the battery cell is called the battery current I and is shown. The characteristics of the battery cell are represented, for example, by the QV curve (QV characteristic). The QV curve shows the relationship between the battery voltage V and the integral current. The integral current corresponds to the capacity (Q) measured in coulombs, with units of Ah.

[0031] Figure 2 An example of a QV curve is shown. The horizontal axis in the graph represents the integral current (Ah), and the vertical axis represents the voltage (V). As shown by the solid line in the graph, the battery voltage V varies with charging and discharging (i.e., the integral current). The battery cell is used within a predetermined range of battery voltage V. The minimum voltage within this range is called the lower limit voltage V. LLAnd it is shown. The maximum voltage is called the upper limit voltage V. UL , and is shown.

[0032] When the battery voltage V is the lower limit voltage V LL At this time, the battery cell's state of charge (SOC) is 0% (fully discharged). When the battery voltage V is at its upper limit voltage V... UL At that time, the SOC is 100% (fully charged state). The maximum capacity of the battery cell DUT corresponds to the capacity of the battery cell when it is charged from the upper limit voltage V. UL Discharge to the lower limit voltage V LL When or when the battery cell drops from the lower limit voltage V LL Charge to the upper limit voltage V UL The integral current at any given time. The battery voltage V at any point in time is called the battery voltage V0. C And it is shown. Battery voltage V C The remaining capacity corresponds to the capacity of the battery cell when it drops from the lower limit voltage V. LL Charge to battery voltage V C When or when the battery cell draws from the battery voltage V C Discharge to the lower limit voltage V LL The integral current at that time.

[0033] Figure 3 An example of the relationship between capacity degradation and QV curves is shown. Seven QV curves with different capacity degradation progression states are shown as curves C1 to C7. The capacity degradation of the battery cell progresses in the order of curves C1 to C7. As understood, the capacity degradation of the battery cell is caused, in particular, by the battery voltage V reaching the upper limit voltage Vmax. UL This is caused by the decrease in the integral current. In the comparison between curves C1 and C7, the maximum capacity in curve C1 corresponds to the maximum capacity before the decay, and the maximum capacity in curve C7 corresponds to the maximum capacity after the decay.

[0034] The differential curve of the QV curve also indicates the characteristics of the battery cell. The differential curve indicates the curve obtained by differentiating the integral current with respect to the battery voltage V (dQ / dV) or by differentiating the battery voltage V with respect to the integral current (dV / dQ).

[0035] Figure 4 An example of a differential curve is shown. In this example, the horizontal axis represents voltage (V), and the vertical axis represents (dQ / dV). Curves C1 to C7 correspond to those described above. Figure 3The differential curves are curves C1 to C7 in the diagram. These differential curves have several characteristic points. Examples of characteristic points include extrema (local maxima and local minima). In the following text, unless otherwise specified, a characteristic point is a local maximum that first appears in the differential curve within the range of the battery cell's usage.

[0036] When battery cells are used for extended periods, capacity degradation occurs, and the reduction in maximum capacity becomes significant, necessitating capacity diagnostics for each cell. This also applies to battery systems comprising multiple battery cells. For example, a battery system with multiple battery cells connected in series works fine when the remaining and maximum capacities of the cells are equal (balanced state). However, if this balance is lost, the usable capacity of the battery system (i.e., the overall capacity of the battery system) decreases. For instance, consider a battery system where... Figure 2 The solid lines represent the cell voltage V and the dashed lines represent the cell voltage Vc. X The battery cells are connected in series. The remaining capacities of the two battery cells are different, resulting in an imbalance. A battery storage system is used to ensure that the voltage of each of the two battery cells falls below the lower limit voltage V. LL Up to the upper limit voltage V UL Within this range. In this case, battery cells with a battery voltage of V cannot be used up to the lower limit voltage V. LL Battery voltage V X The battery cells cannot be used until the upper limit voltage V. UL The application range of battery cells is narrowed, and the overall capacity of the battery system is reduced.

[0037] Depending on the constituent materials, batteries exhibit varying initial charge / discharge characteristics and changes in characteristics during capacity decay. For example, lithium-ion batteries using Ni-Mn-Co oxides (known as ternary systems) as the positive electrode material have different charge / discharge characteristics depending on the mixing ratio of the three elements and the substances added. Furthermore, since the battery voltage V is output as the potential difference between the negative and positive electrode characteristics, the negative electrode characteristics also alter the aforementioned properties.

[0038] For battery cells, which have various properties depending on the constituent materials as described above, developing algorithms to understand the characteristics of battery cells corresponding to each constituent material from each manufacturer requires a significant amount of time. According to the disclosed technology, it is possible to diagnose the capacity of battery cells with lower material dependence. Taking lithium-ion batteries as an example, the capacity degradation of battery cells is assessed from two factors. These two factors include: (1) the deviation of the positive and negative electrode potentials from the initial design values ​​caused by degradation due to charge / discharge operations and the immobilization of Li in the negative electrode due to being left in a charging state; and (2) the capacity reduction due to deactivation factors such as the immobilization of active materials. Diagnosis can also be performed without requiring complete charge / discharge, which reduces the diagnostic time. For example, the diagnostic time can be shortened. Based on the diagnostic time, after using the battery cell or battery system in electric vehicles, hybrid vehicles, etc., the performance of the battery cell or battery system is evaluated, and it is determined whether the battery cell or battery system will be reused or recycled to recover materials.

[0039] Example

[0040] Figure 5 An example of a schematic configuration of a diagnostic device according to one or more embodiments is shown. The battery cell to be diagnosed by the diagnostic device 1 is referred to as the battery cell DUT and is shown. 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, for example, at a desired charge / discharge rate. According to the principles described later, it is sufficient to perform charge / discharge only for a portion of the voltage range (the range of the integrated current and the range of the state of charge).

[0041] Diagnostic device 1 includes a voltage detector 2, a current detector 3, a memory 4, a calculator 5, and an output unit 6. Voltage detector 2 detects the battery voltage V of the battery cell DUT. For example, voltage detector 2 acquires the measurement result of a voltmeter (not shown). Voltage detector 2 may include a voltmeter. Memory 4 stores the detection result of voltage detector 2. Current detector 3 detects the battery current I of the battery cell DUT. For example, current detector 3 acquires the measurement result of an ammeter (not shown). Current detector 3 may include an ammeter. Memory 4 stores the detection result of current detector 3.

[0042] The memory 4 stores various information required for the processing performed in the diagnostic device 1. Examples of the stored information include reference data 41, measurement data 42, and diagnostic procedures (diagnostic instructions) 43.

[0043] Reference data 41 serves as a standard (for comparison) for the capacity degradation of the battery cell DUT and includes, for example, data corresponding to the QV curve. Reference data 41 may be based on actual measurements of the battery cell DUT before capacity degradation progresses, or it may be based on design and simulated values ​​of the battery cell DUT. Reference data 41 may be measurement data at a predetermined temperature or charge / discharge rate.

[0044] Measurement data 42 corresponds to at least a portion of the QV curve of the battery cell DUT. Measurement data 42 is based on the detection results of the voltage detector 2 and current detector 3 described above. Measurement data 42 can be measurement data at substantially the same temperature or charge / discharge rate as the reference data 41 described above. Note that, for example, a temperature sensor (not shown) detects and monitors the temperature. The integrated current in the QV curve of the battery cell DUT is obtained by integrating the battery current I detected by the current detector 3.

[0045] The diagnostic program 43 causes the computer to perform the processing of the diagnostic device 1, such as the processing performed by the calculator 5 and output unit 6 described later (e.g., calculation processing and output processing). For example, at least a portion of the functionality of the diagnostic device 1 is implemented by running a general-purpose computer according to the diagnostic program 43. The computer includes, for example, communication devices, display devices, storage devices, memory, and a processor interconnected via a bus. The processor reads the diagnostic program 43 from the storage device, etc., and expands the diagnostic program 43 in memory, thereby enabling the computer to function as the diagnostic device 1. Note that the diagnostic program 43 can be distributed via a network (e.g., the Internet). The diagnostic program 43 can be recorded on a computer-readable recording medium such as a hard disk, floppy disk (FD), CD-ROM, magneto-optical (MO) disk, and digital multifunction disk (DVD). Note that, of course, dedicated hardware running according to the diagnostic program 43 can be used instead of the general-purpose computer.

[0046] Calculator 5 calculates values ​​related to the capacity of the battery cell DUT. In one or more embodiments, calculator 5 calculates the values ​​related to the capacity of the battery cell DUT based on a comparison between the QV curve obtained from measurement data 42 and the QV curve obtained from reference data 41. The QV curve obtained from measurement data 42 is also referred to as the "measured QV curve". The measured QV curve can also be referred to as the QV curve after capacity degradation. The QV curve obtained from reference data 41 is also referred to as the "reference QV curve". The reference QV curve can also be referred to as the QV curve before capacity degradation.

[0047] Figure 6 An example of a schematic configuration of a calculator is shown. Calculator 5 includes a first calculator 51, a second calculator 52, and a maximum capacity calculator 53 as functional blocks. (Refer to...) Figure 7 and Figure 8 Describe the specific calculation method.

[0048] Figure 7 Examples of a reference QV curve and a measured QV curve are shown. Curve C ref This represents the reference QV curve. Curve C DUT This indicates the measurement of the QV curve. Lower limit voltage V LL For example, approximately 2.8V, upper limit voltage V UL For example, approximately 4.2V. When curve C... ref With curve C DUT When making comparisons, the factors contributing to the capacity degradation of the battery cell DUT can be described by dividing this factor into two components.

[0049] The first factor is the magnitude of the battery voltage V (the deviation of the battery voltage V along the vertical axis). A larger battery voltage V will accelerate the reaching of the upper limit voltage Vmax. UL This reduces the maximum capacity. For example, in the case of lithium-ion batteries, the deviation of the positive and negative electrode potentials from the initial design values ​​manifests as a shift in the battery voltage V. This deviation is caused by degradation due to factors such as the immobilization of Li in the negative electrode. Immobilization occurs due to the charging and discharging operations of the battery cell and the battery cell being kept in a charged state.

[0050] The second factor is the slope of the battery voltage V. A steeper slope will accelerate the reaching of the upper limit voltage V. UL This reduces the maximum capacity. Capacity reduction due to deactivation factors such as the immobilization of active materials manifests as a change in the slope of the battery voltage V. Similarly, as... Figure 7 As shown, in the case of battery cells using a combination of materials with multiple capacity-holding potentials (e.g., ternary systems), the battery voltage V increases relatively monotonically with increasing integrated current. When a battery cell with this characteristic becomes inactive or experiences capacity degradation due to partial damage to the electrode structure, the rate of increase in battery voltage V relative to integrated current (i.e., the slope) increases. Even with a small integrated current, the battery voltage V changes significantly.

[0051] The first calculator 51 calculates the first factor described above (potential deviation between positive and negative electrodes) (i.e., measures the QV curve (curve C)). DUT ) and reference QV curve (curve C) ref The capacity degradation caused by the voltage difference between the measured QV curve and the reference QV curve is called the "capacity degradation ΔQ". The voltage difference is called the "voltage difference ΔV". For example, the first calculator 51 calculates the difference between the voltages at characteristic points on the differential curves of the measured QV curve and the reference QV curve as the voltage difference ΔV.

[0052] Figure 8An example of a differential curve is shown. Curve C ref And curve C DUT Corresponding to Figure 7 Curve C in ref And curve C DUT The differential curves. In this example, the difference between the voltages where a local maximum first appears in the two differential curves is calculated as the voltage difference ΔV. Note that a local maximum can be interpreted as including the maximum.

[0053] The first calculator 51 calculates the 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 relative to the battery voltage V (dQ / dV)) by the voltage difference ΔV. For example, it uses the following equation (1). The slope (dQ / dV) used for multiplication here can be the slope when the battery voltage V is equal to or greater than the voltage at the characteristic point. It can be used close to the upper limit voltage V. UL The slope in the region. For example, when the upper limit voltage V UL When the voltage is 4.2V and the voltage difference ΔV is 0.05V, the average slope from 4.15V to 4.2V can be used.

[0054]

[0055] The second calculator 52 calculates the maximum capacity after capacity decay caused by the second factor (inactivation) described above (i.e., the change in the slope of the measured QV curve relative to the slope of the reference QV curve). This maximum capacity is a temporary maximum capacity considering only the second factor, and is therefore referred to as the "temporary maximum capacity Q". DUT ".

[0056] Specifically, refer to again Figure 7 The second calculator 52 is designed for the reference QV curve (curve C). ref ) and measuring the QV curve (curve C) DUT Each of the calculations in the table represents the slope (dV / dQ) of the battery voltage V relative to the integrated current. The slope calculated here can be the slope when the battery voltage V is equal to or greater than the voltage at the characteristic point. The slope (dV / dQ) can be calculated over a voltage range with a relatively high SOC (e.g., approximately 3.8V to 4.0V). This is because, for example, when the negative electrode is made of graphite, the region of the negative electrode with excellent capacity retention (also referred to as stage 1, stage 2, etc.) contributes to the formation of a high SOC side, and it is believed that the deactivation of the positive electrode active material is more pronounced during degradation on the high SOC side.

[0057] exist Figure 7 In it, there is a calculated reference QV curve (curve C). refThe slope of the straight line is represented by the dashed line as (dV / dQ). ref It has the calculated measurement QV curve (curve C). DUT The slope of the straight line is represented by the dashed line as (dV / dQ). DUT .

[0058] The second calculator 52 calculates the ratio between the slope of the measured QV curve and the slope of the calculated reference QV curve by multiplying the ratio by the reference maximum capacity Q. ref To calculate the temporary maximum capacity Q DUT For example, use equation (2) below. Refer to the maximum capacity Q. ref It is the maximum capacity obtained from the reference QV curve, and corresponds to the maximum capacity of the battery cell DUT before degradation.

[0059]

[0060] Maximum capacity calculator 53 uses the temporary maximum capacity Q calculated by second calculator 52. DUT The maximum capacity Q of the battery cell DUT is calculated by subtracting the capacity degradation ΔQ calculated by the first calculator 51. DUTMAX For example, using equation (3) below. The maximum capacity Q calculated in this way DUTMAX It is the maximum capacity that takes into account both the first factor (potential deviation between positive and negative electrodes) and the second factor (deactivation) described above.

[0061] Q DUTMAX =Q DUT -ΔQ (3)

[0062] A portion of the QV curve data from the battery cell DUT is sufficient to satisfy the measurement data 42 required for calculations by the first calculator 51, the second calculator 52, and the maximum capacity calculator 53. In the example described above, the voltage range near the feature point (e.g., 3.4V to 3.6V) and the upper limit voltage V UL Measurement data within a nearby voltage range (e.g., 4.15V to 4.2V) allows for the calculation of capacity degradation ΔQ and temporary maximum capacity Q. DUT and maximum capacity Q DUTMAX By taking measurements outside of these ranges, diagnostic time can be reduced.

[0063] Back Figure 5 Output unit 6 outputs the calculation result from calculator 5 as a diagnostic result of the battery cell DUT's capacity. Examples of output include presentation to the user (e.g., display) and data transmission to an external server device (not shown). For example, output unit 6 outputs the maximum capacity Q of the battery cell DUT calculated by maximum capacity calculator 53.DUTMAX It can output from the reference maximum capacity Q. ref The reduction (Q) ref -Q DUTMAX It can output the remaining capacity calculated based on the battery voltage V of the battery cell DUT at the end of the diagnostic process.

[0064] In addition, output unit 6 can output the capacity decay amount ΔQ calculated by the first calculator 51a and the temporary maximum capacity Q calculated by the second calculator 52. DUT For example, the capacity degradation ΔQ can be displayed together with a notification that the capacity degradation ΔQ is caused by a first factor (potential deviation between the positive and negative electrodes). Temporary maximum capacity Q DUT Can be used with temporary maximum capacity Q DUT It is displayed together with the notification of temporary capacity decline that only considers capacity decline caused by the second factor (inactivation). This helps in understanding the decline factors.

[0065] For example, as described above, the capacity of the battery cell DUT can be diagnosed. Note that in some battery cells, the battery voltage V increases significantly at the end of charging. The calculation method described above can even be applied to this type of battery cell. This will refer to... Figure 9 and Figure 10 Describe it.

[0066] Figure 9 An example of a reference QV curve and a measured QV curve for another type of battery cell is shown. Figure 10 An example of a differential curve is shown. The battery voltage V is at its upper limit voltage Vmax. UL The capacity decreases significantly near the end of charging. Similarly, in this case, as described so far, the capacity degradation ΔQ can be calculated by multiplying the slope (dQ / dV) of the integral current relative to the battery voltage V by the voltage difference ΔV. Temporary maximum capacity Q DUT The slope (dV / dQ) of the QV curve can be measured. DUT The slope (dV / dQ) of the reference QV curve. ref The ratio between them multiplied by the reference maximum capacity Q ref To calculate. The maximum capacity Q can also be calculated. DUTMAX .

[0067] Note that the description above illustrates an example where the differential curve is obtained by differentiating the integral current with respect to the battery voltage V (dQ / dV). However, note that, as described above, the differential curve can also be obtained by differentiating the battery voltage V with respect to the integral current (dV / dQ).

[0068] Figure 11 Another example of a differential curve is shown. The differential curve shown is obtained by differentiating the battery voltage V with respect to the integral current (dV / dQ). Five differential curves with different capacity degradation progression states are shown as curves C11 to C15. The capacity degradation of the battery cell progresses in the order of curves C11 to C15. Such differential curves also have characteristic points (e.g., the first occurrence of a local maximum). Therefore, the voltage difference ΔV can be calculated.

[0069] Reference Figure 12 and Figure 13 This describes a calculation method used by calculator 5 that differs from the calculation method described above. Figure 12 Another example of a schematic configuration of the calculator is shown. The calculator 5A shown calculates values ​​related to the capacity of the battery cell DUT by using a function model that approximates the QV curve of the battery cell DUT. Calculator 5A includes a function model generator 54, a fitting unit 55, and a maximum capacity calculator 56 as its functional blocks.

[0070] Figure 13 Another calculation method is shown. For example... Figure 13 As shown in (A), the function model generator 54 generates a function model V that is fitted to the reference QV curve. ref Functional model V ref A portion of the QV curve can be approximated. In this example, the function model V... ref This approximates the portion of the reference QV curve corresponding to the linear region indicated by arrow AR1 and the nonlinear region indicated by arrow AR2. Note that the curve outside the approximate range is indicated by a dotted line. Within the linear region, the battery voltage V can vary substantially linearly with respect to the integral current. The linear region can have a voltage equal to or greater than the voltage at the characteristic point. Within the nonlinear region, the battery voltage V varies nonlinearly with respect to the integral current. Compared to the linear region, the nonlinear region is located on the high-voltage side (high SOC side). The battery voltage V at the boundary between the linear and nonlinear regions is called the threshold voltage V0. ref_th And it is shown. Function model V ref It can also be described as the voltage at or above the characteristic point (threshold voltage V). ref_th The function model at the voltage of ).

[0071] Determine the function model V shown. ref This ensures that V satisfies the condition within the linear region. ref =f ref (I ref ), satisfying V in the nonlinear region ref =f ref (Iref )+g ref (I ref ). I ref yes Figure 13 The integrated current quantity in graph (A). Function f ref (I ref For example, using the integral current I ref A linear function of variables. The function g ref (I ref For example, using the integral current I ref An exponential or multi-order function of variables. Adjustment function f ref (I ref ) and function g ref (I ref The parameters (e.g., coefficients) are used to approximate the reference QV curve (curve C). ref The corresponding part of ). For approximate adjustments, common methods such as least squares can be used.

[0072] Fitting unit 55 will use the function model V generated by function model generator 54. ref Fit the measured data 42. Adjust the function model V. ref The parameters are used to approximate the measurement data 42. Figure 13 (B) and (C) show the fitting of the function model V DUT The subsequent function model V ref Functional model V DUT The QV curve of the approximate battery cell DUT. Note that the curve outside the approximate range is indicated by a dashed line. Figure 13 (B) diagram is drawn in a way that is easy to understand and Figure 13 The positions of the relationships between the horizontal axes in graph (A). Figure 13 The (C) diagram is drawn in a way that is easy to understand and Figure 13 The position of the relationship between the vertical axes of graph (A). In the function model V DUT The battery voltage V at the boundary between the linear and nonlinear regions in the circuit is called the threshold voltage V. DUT_th And it is shown. Function model V DUT It can also be said that it is equal to or greater than the threshold voltage V DUT_th The function model at the voltage.

[0073] In this example, by using the function f DUT (I DUT ) and function g DUT (I DUT ) represents the functional model V DUT I DUT yes Figure 13The integral current quantities in graphs (B) and (C). Function f DUT (I DUT By adjusting the function f described above DUT (I DUT The parameter is obtained from the function g. DUT (I DUT By adjusting the function g described above ref (I ref The parameters are obtained from the parameters.

[0074] A portion of the QV curve data of the battery cell DUT is sufficient to satisfy the measurement data 42 required for fitting cell 55. Figure 13 (B) shows the ranges R1 and R2 as the necessary measurement data 42. Range R1 includes the feature point and its surroundings. Range R2 includes the boundary between the linear and nonlinear regions and its surroundings. The measurement data in these ranges R1 and R2 make it possible to fit a function f corresponding to the linear and nonlinear regions. DUT (I C ) and function g DUT (I C ).

[0075] The maximum capacity calculator 56 uses the fitted function model V through fitting unit 55. ref (i.e., function model V) DUT Calculate the maximum capacity Q of the battery cell DUT. DUTMAX In the function model V DUT The indicated battery voltage V is the upper limit voltage V. UL Integral current I under the condition C This could be the maximum capacity you want to obtain. However, note that, as from... Figure 13 The functional model V as understood in (A) and (C) ref The horizontal axis and the function model V DUT The horizontal axis is inconsistent. Maximum capacity Q DUTMAX It can be calculated by correcting for the deviation between the horizontal axes (by aligning the horizontal axes).

[0076] Here, since the remaining capacity (Ah) at characteristic points in the low SOC region is the first response accompanying battery energy absorption during charging, it is approximately assumed (assuming) that battery cells before and after capacity degradation have the same amount. In this case, the function model V needs to be modified. DUT The position of this feature point in the differential curve is related to the function model V. ref The position of the feature point in the differential curve is aligned.

[0077] Functional model V refThe integral current at the characteristic point is called the integral current I1 and is shown. For example, the integral current I1 is calculated as the integral current corresponding to the voltage at the characteristic point of the differential curve (dQ / dV) calculated based on the measurement data in the range R1 of reference data 41. Function model V DUT The integral current at the characteristic point is called the integral current I2 and is shown. For example, the integral current I2 is calculated as the integral current corresponding to the voltage at the characteristic point in the differential curve (dQ / dV) calculated based on the measurement data in the range R1 of the measurement data 42. When the function model V ref The horizontal axis and the function model V DUT When the difference between the horizontal axes is defined as ΔI, then ΔI = I2 - I1 is established. In the function model V... DUT In the middle, it can be obtained from the integral current I DUT The horizontal axis is corrected by subtracting ΔI from the middle.

[0078] The calculations performed by the maximum capacity calculator 56 include corrections to the function model V. ref sum function model V DUT The positions of feature points in the differential curve are aligned. Specifically, the maximum capacity calculator 56 calculates the function model V in the nonlinear region. DUT (i.e. f) DUT (I DUT )+g DUT (I DUT )) equals the upper limit voltage V UL Integral current I DUT Furthermore, the value corrected by ΔI (I) is calculated. DUT -ΔI) as the maximum capacity Q DUTMAX As a result, the appropriate maximum capacity was calculated, taking into account the deviation between the horizontal axes.

[0079] By not only using the maximum capacity Q DUTMAX It also uses the function model V DUT With its differential curve, the maximum capacity calculator 56 can calculate various values ​​related to capacity. For example, since it can be used as... Figure 13 The voltage difference ΔV is calculated as shown in (C), so the capacity decay ΔQ caused by the first factor (potential deviation between the positive and negative electrodes) can be calculated. The temporary maximum capacity Q after capacity decay caused by the second factor (deactivation) can also be calculated. DUT Similar to the calculation results of calculator 5 described above, output unit 6 can output the calculation results of calculator 5A.

[0080] The example of diagnosing the capacity of a battery cell DUT connected to the charging / discharging device 8 has been described above. In this case, it is necessary to suspend 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 battery cell DUTs that are integrated into and used in the battery system (during operation).

[0081] For various reasons, it is difficult to practically measure the maximum capacity of a typical battery system. For example, to allow for a margin of safety or extend lifespan, actual battery systems are not used within the 0-100% SOC range. Battery systems typically used for system stabilization, for example, rarely have a period of complete charge-discharge. A complete charge-discharge requires 2 hours at a 1C rate and 10 hours at a 0.2C rate. In battery systems with multiple cells connected in series, if battery balance is lost, each cell cannot be fully charged and discharged, making it impossible to practically measure the maximum capacity of each cell.

[0082] As described above, in practical battery systems, maximum capacity is displayed through the following methods. For example, there is a method that statistically reduces the maximum capacity based on conditions (e.g., operating time and number of charge-discharge cycles). Unfortunately, in this method, the displayed maximum capacity does not match the actual maximum capacity when unexpected battery cells are used. There is also a method that pre-sets a maximum capacity with a margin. Unfortunately, in this method, the battery cells are not being used effectively. While a method could be used that periodically performs full charge-discharge cycles and actually measures and reflects the maximum capacity, this method might not be suitable for battery systems. It fails to account for the reduction in effective capacity due to variations in individual battery cells.

[0083] Figure 14 An example of a schematic configuration of a diagnostic device is shown. The diagnostic device 1A shown diagnoses the capacity of the battery system 9 by diagnosing the capacity of multiple battery cell DUTs in the battery system 9. In this example, the battery system 9 includes multiple battery cell DUTs connected in series. The battery system 9 is also referred to as an assembled battery, an energy storage system (ESS), etc. The battery system 9 may also include a voltage detector 2A and a current detector 3.

[0084] Diagnostic device 1A includes a voltage detector 2A, a current detector 3, a memory 4A, a calculator 5, an output unit 6A, and a supplementary unit 7. If voltage detector 2A and current detector 3 are components of the battery system 9 and diagnostic device 1A uses voltage detector 2A and current detector 3, then diagnostic device 1A itself does not need to include voltage detector 2A and current detector 3. Note that calculator 5 can also be calculator 5A.

[0085] Voltage detector 2A detects the battery voltage V of each of the multiple battery cell DUTs. Current detector 3 detects the battery current I. Since the battery cell DUTs are connected in series, the battery current I is common to all battery cell DUTs. The battery voltage V and battery current I detected by voltage detector 2A and current detector 3 are the battery voltage V and battery current I during operation.

[0086] Memory 4A stores various information required for the processing performed in diagnostic device 1A. Examples of the stored information include reference data 41, measurement data 42A, and diagnostic program 43A. Since reference data 41 has been described above, its description will not be repeated. Measurement data 42A relates to the QV characteristics of each of the plurality of battery cell DUTs, for example, corresponding to at least a portion of the QV curve. Diagnostic program 43A causes a computer to perform the processing of diagnostic device 1A.

[0087] First, the supplementary unit 7 will be described. The supplementary unit 7 supplements the measurement data 42A as needed. Since the measurement data 42A is limited to the detection results of the battery voltage V and battery current I during operation, the measurement data required for the calculations performed by the calculator 5 may be insufficient. In this case, the supplementary unit 7 performs the supplementation. Although there are no particular limitations on the supplementation method, for example, linear interpolation or supplementation using multi-order expressions can be employed. Note that the measurement data 42A supplemented by the data supplementary unit 7 is also referred to as measurement data 42A.

[0088] Calculator 5 calculates values ​​related to the capacity of each of the multiple battery cell DUTs using reference data 41 and measurement data 42A stored in memory 4A. The same applies to calculator 5A. Since the details have already been described above, they will not be repeated.

[0089] Output unit 6A outputs (e.g., displays) the calculation results of calculator 5 (or calculator 5A) as a diagnostic result of the capacity of battery system 9. For example, output unit 6A outputs the maximum capacity of all multiple battery cell DUTs (i.e., the capacity of battery system 9), or outputs the balance state of each battery cell DUT in battery system 9. Similar to the output unit 6 described above... Figure 5 The output unit 6A can output the maximum capacity Q of each battery cell DUT. DUTMAX Capacity reduction (Q) ref -Q DUTMAX (e.g., remaining capacity, capacity decay).

[0090] Some embodiments of the disclosed technology have been described above. The disclosed technology is not limited to the embodiments described above. For example, in the embodiments described above, calculator 5 has been described ( Figure 5 and Figure 6 The example includes three functional blocks: a first calculator 51, a second calculator 52, and a maximum capacity calculator 53. However, note that calculator 5 does not need to include all of these functional blocks. For example, calculator 5 only needs to include at least one of the first calculator 51 and the second calculator 52. The capacity of the battery cell can be diagnosed using only the first calculator 51 to calculate the capacity degradation ΔQ. The temporary maximum capacity Q can be calculated using only the second calculator 52. DUT This allows for the diagnosis of the battery cell capacity.

[0091] In the above description, the embodiments have been described primarily in terms of the form of the device (e.g., diagnostic device 1) and the procedures (instructions, such as diagnostic procedure 43). However, it should be noted that various processes (i.e., diagnostic methods implemented by the device and the procedures (instructions) are also possible in one or more embodiments.

[0092] For example, the technology described above is detailed below. One disclosed technology is a diagnostic device. (See reference...) Figures 5 to 11 As described above, diagnostic device 1 calculates a value related to the capacity of the battery cell DUT based on a comparison between the measured QV curve and a reference QV curve. The measured QV curve indicates the relationship between the voltage (battery voltage V) obtained from the measured data 42 of the battery cell DUT and the integrated current. Calculator 5 includes at least one of a first calculator 51 and a second calculator 52. The first calculator 51 calculates the capacity degradation 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. The second calculator 52 calculates the capacity degradation ΔQ caused by the voltage difference ΔV by multiplying the slope (dV / dQ) of the measured QV curve. DUT The slope (dV / dQ) of the reference QV curve. ref The ratio between them multiplied by the reference maximum capacity Q ref Calculate the temporary maximum capacity Q after capacity decay caused by the change in the slope of the measured QV curve relative to the slope of the reference QV curve. DUT .

[0093] According to the diagnostic device 1 described above, the capacity of the battery cell DUT can be diagnosed based on the QV curve. For example, by calculating the capacity degradation amount ΔQ, it is possible to diagnose capacity degradation caused by the potential difference between the positive and negative electrodes (the first factor). The temporary maximum capacity Q can be calculated... DUTThis method can diagnose capacity degradation caused by deactivation (the second factor). It is not a material-specific algorithm, but rather a universally applicable algorithm for battery cells that have different initial charge-discharge characteristics depending on the constituent materials, and different characteristic changes during capacity degradation. It allows for the rapid development of an algorithm to understand the characteristics of battery cells corresponding to each constituent material from each battery manufacturer, and also reduces the development budget for such an algorithm.

[0094] In addition, as mentioned above Figure 7 and Figure 8 As described, a portion of the QV curve data from the battery cell DUT is sufficient to calculate the required measurement data 42, enabling a reduction in diagnostic time. For example, diagnostic time can be shortened. Based on the diagnostic time, after using the battery cell or battery system in electric vehicles, hybrid vehicles, etc., the performance of the battery cell or battery system is evaluated, and it is determined whether the battery cell or battery system will be reused or recycled to recover materials.

[0095] Calculator 5 may include a maximum capacity calculator 53, which calculates a temporary maximum capacity Q from the temporary maximum capacity Q calculated by the second calculator 52. DUT The maximum capacity Q of the battery cell DUT is calculated by subtracting the capacity degradation ΔQ calculated by the first calculator 51. DUTMAX In this way, the maximum capacity Q can be appropriately calculated by taking into account both the potential difference between the positive and negative electrodes and deactivation. DUTMAX In other words, the maximum capacity of the battery cell DUT can be properly diagnosed.

[0096] The voltage difference ΔV can be the voltage difference between characteristic points on the differential curves of the measured QV curve and the reference QV curve. For example, the voltage difference ΔV can be calculated in this way.

[0097] A characteristic point is a local maximum that first appears in a differential curve. The slope described above can be the slope at a voltage equal to or greater than the voltage at the characteristic point. For example, the capacity decay ΔQ and the temporary maximum capacity Q can be calculated based on such a characteristic point and slope. DUT and maximum capacity Q DUTMAX .

[0098] For reference Figure 12 and Figure 13 As described above, in another calculation method, calculator 5A uses a function model V that approximates the QV curve. DUTCalculate values ​​related to the capacity of the battery cell DUT. Calculator 5A includes a function model generator 54, a fitting unit 55, and a maximum capacity calculator 56. The function model generator 54 generates a function model V fitted to a reference QV curve. ref The fitting unit 55 will use the function model V generated by the function model generator 54. ref The measurement data 42 of the battery cell DUT is fitted. The maximum capacity calculator 56 uses the fitting unit 55 to fit the function model V. DUT Calculate the maximum capacity Q of the battery cell DUT. DUTMAX The Calculator 5A also achieves similar effects to the Calculator 5 described above.

[0099] The calculations performed by the maximum capacity calculator 56 may include performing the function model V before and after fitting on the fitting unit 55. ref sum function model V DUT Align the positions of feature points in the differential curve. In the function model V ref sum function model V DUT Once the axes are aligned, the appropriate maximum capacity Q can be calculated. DUTMAX .

[0100] A characteristic point is a local maximum that first appears in a differential curve. Function model V ref sum function model V DUT This can be a function model at a voltage equal to or greater than the voltage at the characteristic point. For example, the maximum capacity Q can be calculated based on such a characteristic point and function model. DUTMAX .

[0101] The method for diagnosing battery cells and battery systems using diagnostic device 1 is also one of the techniques disclosed herein. The diagnostic method includes calculating a value related to the capacity of the battery cell DUT based on a comparison between a measured QV curve and a reference QV curve. The measured QV curve indicates the relationship between the voltage (battery voltage V) and the integrated current obtained from the measured data 42 of the battery cell DUT. The calculation includes at least one of the following: calculating the capacity degradation 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 calculating the capacity degradation ΔQ caused by the voltage difference ΔV by multiplying the slope (dV / dQ) of the measured QV curve by... DUT Slope of the reference QV curve (dV / dQ) ref The ratio between them multiplied by the reference maximum capacity Q ref To calculate the temporary maximum capacity Q after capacity decay caused by the change in the slope of the measured QV curve relative to the slope of the reference QV curve. DUT It achieves similar results to the diagnostic device 1 described above.

[0102] The method of diagnosing battery cells and battery systems using diagnostic equipment 1A is also one of the techniques disclosed in this paper. The diagnostic method includes using a function model V... DUT To calculate values ​​related to the capacity of the battery cell DUT, the function model V DUT A QV curve approximating the relationship between the voltage (battery voltage V) of a battery cell DUT and the integral current. The calculation includes: generating a function model V fitted to a reference QV curve. ref The generated function model V ref The measurement data 42 of the battery cell DUT were fitted; the fitted function model V was then used. DUT Calculate the maximum capacity Q of the battery cell DUT. DUTMAX It achieves similar results to the diagnostic device 1A described above.

[0103] Reference Figure 5 The diagnostic procedure 43 described herein is also one of the techniques disclosed herein. Diagnostic procedure 43 enables a computer to perform processing to calculate values ​​related to the capacity of the battery cell DUT based on a comparison between the measured QV curve and a reference QV curve. The measured QV curve indicates the relationship between the voltage (battery voltage V) and the integrated current obtained from the measured data 42 of the battery cell DUT. The calculation processing includes at least one of the following: calculating the capacity degradation 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 calculating the capacity degradation ΔQ caused by the voltage difference ΔV by multiplying the slope (dV / dQ) of the measured QV curve by... DUT Slope of the reference QV curve (dV / dQ) ref The ratio between them multiplied by the reference maximum capacity Q ref To calculate the temporary maximum capacity Q after capacity decay caused by the change in the slope of the measured QV curve relative to the slope of the reference QV curve. DUT Alternatively, diagnostic procedure 43 causes the computer to execute using function model V. DUT The processing of values ​​related to the capacity of the battery cell DUT is performed using the function model V. DUT A QV curve approximating the relationship between the voltage (battery voltage V) of a battery cell DUT and the integral current. The computational process includes generating a function model V fitted to a reference QV curve. ref The generated function model V ref The measurement data 42 of the battery cell DUT were fitted; the fitted function model V was then used. DUT Calculate the maximum capacity Q of the battery cell DUT. DUTMAXIt achieves effects similar to those of diagnostic device 1 or diagnostic device 1A described above.

[0104] Although this disclosure has been described with respect to only a limited number of embodiments, those skilled in the art will understand, upon benefiting from this disclosure, that various other embodiments can be devised without departing from the scope of the invention. Therefore, the scope of the invention should be defined only by the appended claims.

Claims

1. A diagnostic device, comprising: Calculator, this calculator: Based on a function model of the QV curve, which approximates the relationship between the voltage of a battery cell and the integral current of the battery cell, values ​​related to the capacity of the battery cell are calculated. Generate a function model that fits to the reference QV curve. The generated function model is fitted to the measurement data of the battery cell, and Based on the fitted function model, the maximum capacity of the battery cell is calculated. Specifically, the calculator aligns the positions of feature points in the differential curve of the function model before fitting with the positions of another feature point in another differential curve of the function model after fitting. The feature point is the first local maximum value to appear in the differential curve. The other feature point is the local maximum value that first appears in the other differential curve. The function model before fitting is a function model under a voltage equal to or greater than the voltage at the feature point, and The fitted function model is a function model under a voltage equal to or greater than the voltage of the other feature point.

2. The diagnostic device according to claim 1, wherein, The calculator also performs the following functions: Calculate the integral current corresponding to the characteristic points in the differential curves of both the function model before and after fitting; and The integral current of the fitted function model is corrected based on the difference between the calculated integral currents.

3. A diagnostic method, comprising: Based on a function model of the QV curve, which approximates the relationship between the voltage of a battery cell and the integral current of the battery cell, values ​​related to the capacity of the battery cell are calculated. Generate a function model that fits to the reference QV curve; The generated function model is fitted to the measurement data of the battery cell; and Based on the fitted function model, the maximum capacity of the battery cell is calculated. The method further includes aligning the positions of feature points in the differential curve of the function model before fitting with the positions of another feature point in another differential curve of the function model after fitting. The feature point is the first local maximum value to appear in the differential curve. The other feature point is the local maximum value that first appears in the other differential curve. The function model before fitting is a function model under a voltage equal to or greater than the voltage at the feature point, and The fitted function model is a function model under a voltage equal to or greater than the voltage of the other feature point.

4. A non-transitory computer-readable recording medium storing diagnostic instructions that cause a computer to perform: Based on a function model of the QV curve, which approximates the relationship between the voltage and integral current of a battery cell, values ​​related to the capacity of the battery cell are calculated. Generate a function model that fits to the reference QV curve; The generated function model is fitted to the measurement data of the battery cell; and Based on the fitted function model, the maximum capacity of the battery cell is calculated. in, The diagnostic command also instructs the computer to align the positions of feature points in the differential curve of the function model before fitting with the positions of another feature point in another differential curve of the function model after fitting. The feature point is the first local maximum value to appear in the differential curve. The other feature point is the local maximum value that first appears in the other differential curve. The function model before fitting is a function model under a voltage equal to or greater than the voltage at the feature point, and The fitted function model is a function model under a voltage equal to or greater than the voltage of the other feature point.

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