Deterioration state estimation device and deterioration state estimation method

Abstract

To provide a deterioration state estimation device and a deterioration state estimation method with improved estimation accuracy of a deterioration degree.SOLUTION: A deterioration state estimation device 1 for estimating a deterioration state of a secondary battery includes a storage part for storing initial data of an initial state of the secondary battery, an acquisition part 11 for acquiring a current and a voltage of the secondary battery, and a deterioration state estimation part 13 for estimating the deterioration state of the secondary battery. The initial data includes data of an initial OCV curve represented by a relationship between the battery capacity and the OCV of the secondary battery in the initial state. The deterioration state estimation unit 13 calculates a post-deterioration OCV curve indicated by a relationship between the battery capacity and the OCV of the secondary battery after deterioration based on the current and the voltage of the secondary battery acquired by the acquisition unit 11, and calculates a positive electrode capacity deterioration coefficient α indicating a deterioration degree of the positive electrode capacity of the secondary battery, a negative electrode capacity deterioration coefficient β indicating a deterioration degree of the negative electrode capacity, and a capacity deviation amount γ indicating a deviation amount of the positive and negative electrode capacities based on a difference between the initial OCV curve and the post-deterioration OCV curve.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a deterioration state estimation device and a deterioration state estimation method for estimating the deterioration state of a secondary battery.

Background Art

[0002] Conventionally, a battery state estimation device for estimating the degree of deterioration of a secondary battery has been known. For example, the battery state estimation device described in Patent Document 1 calculates a positive electrode capacity deterioration coefficient α indicating the degree of deterioration of the positive electrode capacity, an OCP shift amount β indicating the amount of shift in the open circuit potential of the positive electrode accompanying the valence change of the positive electrode transition metal, and a capacity shift amount δ indicating the amount of shift in capacity between the positive electrode OCP characteristic and the negative electrode OCP characteristic in the deteriorated secondary battery based on the estimated current integrated value and the measured current integrated value. From the integration start point when the open circuit voltage is acquired to the integration end point when the open circuit voltage is acquired again, an estimated value of the current integrated value flowing during this period is expressed using α, β, and δ, and deterioration characteristic data is estimated based on the calculated α, β, and δ and the initial characteristic data stored in the storage unit.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the above battery state estimation device has a problem in that the estimation accuracy of the degree of deterioration is low because the OCP shift amount β is added at the same value over the entire battery capacity to obtain the deterioration characteristic data.

[0005] The problem to be solved by the present invention is to provide a deterioration state estimation device and a deterioration state estimation method with improved estimation accuracy of the degree of deterioration.

Means for Solving the Problems

[0006] Based on the current and voltage of the battery cell, the present invention calculates the OCV curve after degradation, and based on the difference between the initial OCV curve and the OCV curve after degradation, calculates the positive electrode capacity degradation coefficient α, the negative electrode capacity degradation coefficient β, and the capacity deviation amount γ of the battery cell 20, and sets the range of the OCV curve used for the calculation of the positive electrode capacity degradation coefficient α to a range where the positive electrode OCP difference (open circuit potential difference) is ±12 mV or less and / or a range where the positive electrode OCP is 3.75 V or more, thereby solving the above problems.

Effects of the Invention

[0007] According to the present invention, the estimation accuracy of the degree of degradation can be improved.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

BEST MODE FOR CARRYING OUT THE INVENTION

[0009] An embodiment of a deterioration state estimation apparatus and a deterioration state estimation method according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a deterioration state estimation apparatus 1, a battery 2, a charging apparatus 3, and a load 4. The deterioration state estimation apparatus 1 is a system that estimates the deterioration state (degree of deterioration) of a battery 2 mounted on a vehicle. The deterioration state estimation apparatus 1 connects a battery taken out from a device such as a vehicle and estimates the deterioration state of the battery. The deterioration state estimation apparatus 1 may be mounted on a device equipped with a battery such as a vehicle, and may estimate the deterioration state of a battery mounted on a vehicle.

[0010] The deterioration state estimation apparatus 1 includes a controller 10 and a memory 14. The controller 10 is a processor, and includes a ROM (Read Only Memory) in which a program is stored, a CPU (Central Processing Unit) that executes the program stored in the ROM, and a RAM (Random Access Memory) that functions as an accessible storage device. The controller 10 has an acquisition unit 11, a deterioration state estimation unit 13, and a charge / discharge control unit 12. The controller 10 executes the functions of the acquisition unit 11, the charge / discharge control unit 12, and the deterioration state estimation unit 13 by executing the program stored in the ROM by the CPU. Details of each functional block such as the acquisition unit 11 will be described later. Note that the controller 10 does not necessarily have the charge / discharge control unit 12.

[0011] The memory 14 stores initial data indicating the initial battery characteristics of the battery cell 20. The initial data includes data regarding the full charge capacity of the battery cell 20, the upper and lower limit voltages of the battery cell 20, the initial OCV curve of the battery cell 20, and the initial OCP (open circuit potential) curves (positive electrode, negative electrode) of the battery cell 20. The initial OCV curve is a battery characteristic indicated by the relationship between the battery capacity and the OCV (open circuit voltage) of the battery cell 20 in the initial state. The initial OCP curves (positive electrode, negative electrode) are battery characteristics indicating the relationship between the battery capacity and the OCP of the battery cell 20 in the initial state, respectively, with the positive electrode potential and the negative electrode potential. The initial data may include, for example, data indicating the correlation between OCV and SOC.

[0012] The memory 14 may store deterioration data and the like indicating the battery characteristics of the state of the battery cell 20 during charge and discharge. The deterioration data is data indicating the battery characteristics after using the battery cell 20, and includes data on the voltage, current, and temperature of the battery cell 20 during charge and discharge, and data on the voltage, current, and temperature of the battery cell 20 before the start or after the end of charge and discharge.

[0013] The memory 14 may store data indicating the correlation between the internal resistance of the battery cell 20 and the battery parameters. The OCV of the battery cell 20 is calculated by subtracting (charging) or adding (discharging) the value obtained by multiplying the charging and discharging current by the internal resistance from the voltage of the battery cell 20 during charge and discharge. However, the internal resistance has a dependency on the battery parameters. The battery parameters having a dependency on the internal resistance are, for example, the temperature of the battery cell 20, SOC, current (charge and discharge C rate), charge and discharge time, degree of deterioration, and the like. Since the internal resistance changes according to the current SOC, data on the correlation between SOC and the internal resistance (hereinafter also referred to as SOC-internal resistance characteristics) obtained from the experimental data of the battery cell 20 may be stored in the memory 14.

[0014] Also, the SOC-internal resistance characteristics change depending on the battery temperature, charge / discharge time, degree of degradation, and charge / discharge C-rate. For example, with the same SOC value, the corresponding internal resistance on the SOC-internal resistance characteristics increases as the battery temperature decreases. Similarly, the internal resistance increases as the charge / discharge time lengthens, and also increases as the degree of degradation increases. Also, regarding the charge / discharge C-rate, in the SOC region above a predetermined value, the internal resistance increases as the charge / discharge C-rate increases. The memory 14 may store battery data indicating these relationships.

[0015] The battery 2 is a battery cell or a battery module formed by connecting a plurality of battery cells 20 in series or in parallel. The battery cell 20 is, for example, a lithium-ion secondary battery. As an example of the battery cell 20, a flat laminate film lithium-ion secondary battery has a power generation element in which an electrode layer (a positive electrode layer and a negative electrode layer) and a separator are laminated and filled with an electrolytic solution, a positive electrode tab connected to the positive electrode layer, a negative electrode tab connected to the negative electrode layer, and an exterior member that houses and seals these.

[0016] The positive electrode layer has a current collector plate made of a metal foil and a positive electrode active material layer containing a positive electrode active material. The positive electrode active material may contain, in addition to the positive electrode active material, a conductive assistant, a binder, an electrolyte, etc. As the positive electrode active material, a composite oxide of a transition metal and lithium can be used. Specifically, Li·Co-based composite oxides, Li·Ni-based composite oxides, Li·Mn-based composite oxides, etc. can be mentioned.

[0017] The negative electrode layer has a current collector plate made of a metal foil and a negative electrode active material layer containing a negative electrode active material that occludes and releases lithium ions. As the negative electrode active material, a graphite-based active material containing a graphite structure is suitable as an active material having a plurality of charge / discharge regions in which the charge / discharge voltage changes stepwise as lithium ions are inserted / extracted.

[0018] The electrolytic solution is a liquid electrolyte in which a lithium salt such as lithium perchlorate, lithium borofluoride, or lithium hexafluorophosphate is used as a solute in an organic liquid solvent.

[0019] In this embodiment, the charge and discharge characteristics of the battery cell 20 in the initial state (before deterioration) are as follows. The maximum value of the OCV is approximately 4.2 V. Also, due to the charge and discharge of the battery cell 20, the positive electrode OCP changes in the range from approximately 3.0 V to approximately 4.2 V, and the negative electrode OCP changes within the range with 0 V as the lower limit voltage and 1.1 to 1.3 (V) as the upper limit voltage. When the battery cell 20 deteriorates (when the degree of deterioration is equal to or greater than a predetermined level), the above charge and discharge characteristics change, and the full charge capacity decreases.

[0020] A voltage sensor 21 and a current sensor 22 are connected to the battery 2, and a temperature sensor 23 is installed. The voltage sensor 21 detects the voltage of each of the plurality of battery cells 20. In FIG. 1, the voltage sensor 21 is illustrated as being connected to both ends of a battery pack in which a plurality of battery cells are connected. However, the voltage sensor 21 may detect the cell voltage of the battery cell 20, for example, by connecting resistors for voltage detection in parallel to each of the plurality of battery cells 20 and detecting the voltage applied to each resistor.

[0021] The current sensor 22 detects the charge and discharge current flowing through the battery cell 20. The temperature sensor 23 detects the cell temperature of the battery cell 20. The detection values of the voltage sensor 21, the current sensor 22, and the temperature sensor 23 are output to the controller 10.

[0022] The charging device 3 is connected to the battery 2 and supplies a charging current to the battery 2 to charge the battery 2. The load 4 is connected to the battery 2 and consumes the power of the battery 2. When the deterioration state estimation device 1 is provided in a vehicle, the charging device 3 corresponds to an external charging facility, and the load 4 corresponds to an inverter, a motor, or the like.

[0023] Next, each function of the functional blocks included in the controller 10 will be described. The acquisition unit 11 acquires the current, voltage, and cell temperature of the battery cell 20 from the detection values of various sensors such as the voltage sensor 21. The current (charge / discharge current) of the battery cell 20 is the charge current and / or discharge current of the battery cell 20. The voltage of the battery 2 is the cell voltage or the voltages of a plurality of battery cells, and is the charge voltage and / or discharge voltage. The acquisition unit 11 does not necessarily have to acquire the current etc. in real time during the charge / discharge of the battery 2. For example, when the battery data during the charge / discharge of the battery cell 20 is stored in a database (not shown), the controller 10 accesses that database, and the acquisition unit 11 may acquire the charge / discharge current, charge / discharge voltage, and cell temperature from the stored battery data. Also, the acquisition unit 11 acquires the initial data of the battery cell 20 from the memory 14.

[0024] The charge / discharge control unit 12 manages the state of charge (SOC) of the battery 2 based on the voltage etc. acquired by the acquisition unit 11, and controls the charge / discharge current of the battery 2. During charging of the battery 2, the charge / discharge control unit 12 controls the charging device 3, and during discharging of the battery 2, it controls switches etc. included in the load 4 to control the discharge current.

[0025] The deterioration state estimation unit 13 estimates the deterioration state of the battery. The deterioration state estimation unit 13 estimates the deterioration state (degree of deterioration) of the battery 2 by the charge curve analysis method (CCA). The deterioration state of the battery 2 is useful information for the state management of the battery 2 and for the reuse of the battery 2. The deterioration state of the battery 2 does not necessarily progress at the same rate for the positive electrode and the negative electrode. For example, when reusing the battery 2 by separating the positive electrode and the negative electrode, there are cases where the overall degree of deterioration of the battery 2 is low, but the deterioration of the positive electrode has not progressed so much. Therefore, it is required to grasp the degree of deterioration of the positive electrode capacity and the degree of deterioration of the negative electrode capacity in addition to the overall degree of deterioration of the battery 2 for the deterioration state of the battery 2.

[0026] In the charge curve analysis method, based on the OCP curves of the active materials of the positive and negative electrodes, fitting calculations are performed on the charge and discharge curves of the battery cell 20 with the positive electrode capacity degradation coefficient α, the negative electrode capacity degradation coefficient β, and the capacity deviation amount γ as variables to determine the values of each variable. The positive electrode capacity degradation coefficient α indicates the degree of degradation of the positive electrode capacity of the battery cell 20, the negative electrode capacity degradation coefficient β indicates the degree of degradation of the negative electrode capacity of the battery cell 20, and the capacity deviation amount γ indicates the deviation amount between the positive and negative electrode capacities. In the following description, the coefficients (α, β) indicate the degree of degradation of the positive and negative electrode capacities of the battery cell 20, and the coefficient (γ) indicates the deviation amount between the positive and negative electrode capacities of the battery cell 20.

[0027] For the calculation of the coefficients (α, β, γ) using CCA, the initial OCV curve and the post-degradation OCV curve are used. The degradation state estimation unit 13 acquires the initial OCP curves (positive electrode, negative electrode) from the initial data stored in the memory 14. Note that the initial OCV curve corresponds to the difference between the initial positive electrode OCP curve and the initial negative electrode OCP curve. Also, the degradation state estimation unit 13 obtains the post-degradation OCV curve through arithmetic processing. The following describes the arithmetic method of the post-degradation OCV curve.

[0028] The degradation state estimation unit 13 calculates the post-degradation OCV curve based on the current and voltage of the battery cell 20 acquired by the acquisition unit 11. The post-degradation OCV curve is a characteristic indicated by the relationship between the battery capacity and the OCV of the battery cell 20 after degradation. The degradation state estimation unit 13 calculates the post-degradation battery capacity by integrating the current acquired by the acquisition unit 11 during charging or discharging of the battery cell 20. The degradation state estimation unit 13 acquires the voltage of the battery cell 20 from the acquisition unit 11 corresponding to the current integration timing from the start to the end of charge and discharge of the battery cell 20.

[0029] The degradation state estimation unit 13 may calculate the internal resistance of the battery cell 20 based on at least one of the cell temperature of the battery cell 20, the SOC of the battery cell 20, the current of the battery cell 20, the charge and discharge time of the battery cell 20, and the degree of degradation of the battery cell 20. The degradation state estimation unit 13 refers to data stored in the memory 14 that shows the correlation between the internal resistance of the battery cell 20 and the battery parameters. The degradation state estimation unit 13 obtains, for example, data showing the correlation between the SOC, cell temperature, and internal resistance of the battery cell 20 from the memory 14. The degradation state estimation unit 13 obtains the cell temperature from the acquisition unit 11 and calculates the SOC from the current integration value calculated above. Then, the degradation state estimation unit 13 calculates the resistance value corresponding to the cell temperature and SOC as the internal resistance of the battery cell 20 based on the acquired data. Note that the battery parameters used in the calculation of the internal resistance may be multiple elements. Further, the degradation state estimation unit 13 may calculate the internal resistance of the battery cell 20 from the slope of the IV characteristic (current-voltage characteristic) of the battery cell 20.

[0030] The degradation state estimation unit 13 calculates the OCV by subtracting (using the charge voltage) or adding (using the discharge voltage) the value obtained by multiplying the charge and discharge current by the internal resistance from the acquired voltage. The degradation state estimation unit 13 calculates the OCV of the battery cell 20 corresponding to the current integration timing from the start to the end of charge and discharge. Thereby, the degradation state estimation unit 13 calculates the post-degradation OCV curve based on the voltage (cell voltage) acquired by the acquisition unit 11, the current (charge and discharge current) acquired by the acquisition unit 11, the internal resistance of the battery cell 20, and the battery capacity (current integration value of the battery cell 20).

[0031] FIG. 2 is a graph showing the OCV before and after degradation of the battery cell 20 and the OCP curves of the positive and negative electrodes. With reference to FIG. 2, a method (CCA calculation process) for calculating coefficients (α, β, γ) by CCA will be described. In FIG. 2, OCV ini shows the initial OCV curve, and OCP Ca,ini shows the initial positive electrode OCP curve, and OCP An,ini shows the initial negative electrode OCP curve. Also, OCV deg,exp shows the post-degradation OCV curve (calculated value), and OCPCa,deg shows the positive electrode OCP curve after deterioration, and OCP An,deg shows the negative electrode OCP curve after deterioration. OCV deg,cal is the initial positive electrode OCP curve (OCP Ca,ini ) and the OCV curve after regression calculation for the initial negative electrode OCP curve (OCP An,ini ). The horizontal axis represents the battery capacity, and the vertical axis represents OCP and OCV.

[0032] The deterioration state estimation unit 13 obtains OCP Ca,ini and OCP An,ini from the initial data in the memory 14. The initial OCV curve (OCV ini ) is represented by the following formula (1).

Equation

[0033] Next, the deterioration state estimation unit 13 calculates the OCV curve after deterioration (OCV deg,exp ).

[0034] The deterioration state estimation unit 13 shrinks and horizontally moves the initial positive electrode OCP curve (OCP Ca,ini ) and the initial negative electrode OCP curve (OCP An,ini ) to calculate an OCV curve (OCV deg,exp ) such that the difference from the OCV curve after deterioration (OCV deg,cal ) is minimized. Specifically, the OCV curve (OCV deg,cal ) is obtained by multiplying the entire battery capacity axis by a coefficient (α) for the initial positive electrode OCP curve (OCP Ca,ini ), multiplying the entire battery capacity axis by a coefficient (β) for the initial negative electrode OCP curve (OCP An,ini ), and horizontally moving the battery capacity axis by a coefficient (γ) for the initial negative electrode OCP curve (OCP An,ini ).

[0035] The OCV curve (OCV deg,cal ) is represented by the following formula (2) using the coefficients (α, β, γ).

Equation

[0036] In this way, the degradation state estimation unit 13 calculates the degree of degradation of the positive electrode / negative electrode of the battery cell 20 and the overall degree of degradation of the battery cell 20 by performing regression calculations on the coefficients (α, β, γ) such that the difference between the post-degradation OCV curve (OCV deg,exp ) and the OCV curve (OCV deg,cal ) is minimized. In the regression calculation, for example, the mean square value of the difference in OCV may be obtained. That is, the degradation state estimation unit 13 calculates the coefficients (α, β, γ) based on the difference between the initial OCV curve and the post-degradation OCV curve.

[0037] Next, the degradation phenomenon specific to the transition metal contained in the positive electrode of the battery cell 20 will be described. Since the transition metal contained in the positive electrode has a specific degradation phenomenon due to metal elution, crystal structure change, etc., as the degradation of the battery cell 20 progresses, the positive electrode OCP curve changes in a specific region.

[0038] FIG. 3 is a graph showing the relationship between the degree of degradation of the positive electrode of the battery cell 20 and the positive electrode OCP, and a graph showing the relationship between the degree of degradation of the positive electrode and the difference in OCP before and after degradation. In FIG. 3, OCP Ca,ini represents the initial positive electrode OCP curve, OCP ’ Ca,ini represents a graph obtained by multiplying the coefficient (α) by the initial positive electrode OCP curve (hereinafter referred to as the corrected OCP curve), OCP Ca,deg represents the post-degradation positive electrode OCP curve, and Δ(OCP ’ Ca,ini -OCP Ca,deg) shows the OCP difference between the corrected OCP curve and the post-deterioration positive electrode OCP curve. The horizontal axis represents the positive electrode capacity retention rate, and the vertical axis represents the positive electrode OCP and the OCP difference, respectively. Note that the OCP difference is the difference between the positive electrode OCP of the battery cell 20 in the initial state with respect to a predetermined positive electrode capacity and the positive electrode OCP of the battery cell 20 after deterioration with respect to the same predetermined positive electrode capacity. In other words, the OCP difference is the difference between the positive electrode OCP in the initial state with respect to the positive electrode capacity and the positive electrode OCP after deterioration when the positive electrode capacity is set to the same value.

[0039] The battery cell 20 after deterioration shown in FIG. 3 is a battery after charge and discharge cycles with the cell temperature set to 45°C. Also, after charge and discharge cycles, the positive electrode capacity retention rate decreases to 0.85 with respect to the initial state (1.0). Note that the correction of multiplying the coefficient (α) to the initial positive electrode OCP curve (OCP Ca,ini ) corresponds to the calculation of the positive electrode OCP curve in the calculation of CCA.

[0040] The post-deterioration positive electrode OCP curve (OCP Ca,deg ) does not match the corrected OCP curve (OCP ’ Ca,ini ), and a deviation occurs. The deviation of the OCP curve becomes larger in the region where the positive electrode OCP is less than 3.75 V, or in the region where the OCP difference is greater than 12 mV. That is, the region with a small deviation is the region where the positive electrode OCP is 3.75 V or more, or the region where the OCP difference is 12 mV or less. And when the deterioration state estimation unit 13 calculates the coefficient (α) by CCP using the OCP curve in the region where the OCP deviation is small before and after deterioration, the degree of deterioration of the positive electrode can be obtained with high accuracy. On the other hand, when the OCP curve used in the calculation process of CCP includes a region with a large OCP deviation before and after deterioration, the estimation accuracy of the degree of deterioration of the positive electrode becomes low.

[0041] Referring to FIGS. 4 and 5, the estimation accuracy of the degree of deterioration of the positive electrode with respect to the deviation of the OCP curve will be described. FIG. 4 is a graph showing the lower limit value of the OCP curve used in the CCP arithmetic processing and the calculation result of the positive electrode capacity retention rate. The positive electrode OCP shown on the horizontal axis of FIG. 4 represents the lower limit value of the OCP curve used in the CCP arithmetic processing. For example, in the case of the positive electrode OCP (3.75V), it indicates that the battery cell 20 is charged or discharged so that the positive electrode OCP changes between 3.75V and the upper limit voltage, and the OCP curve of the positive electrode after deterioration is obtained.

[0042] FIG. 5 is a graph showing the difference between the OCPs before and after deterioration and the calculation result of the positive electrode capacity retention rate, which are used in the CCP arithmetic processing. The OCP difference shown on the horizontal axis of FIG. 5 represents the upper limit value of the difference (potential) between the initial positive electrode OCP curve and the positive electrode OCP curve after deterioration, which is used in the CCP arithmetic processing.

[0043] Also, the dotted lines (positive electrode capacity retention rate = approximately 85.5%) in FIGS. 4 and 5 show the experimental results of the battery cell 20. The positive electrode capacity retention rate corresponds to the coefficient (α) calculated in the CCA arithmetic processing. And the closer the positive electrode capacity retention rate obtained by the CCP arithmetic processing is to the positive electrode capacity retention rate (approximately 85.5%) obtained by the experimental results, the higher the estimation accuracy. When the lower limit value of the OCP curve used in the CCP arithmetic processing is 3.75V or more (corresponding to the part of region а in FIG. 3), the positive electrode capacity retention rate obtained by the CCP arithmetic processing is close to the experimental result (positive electrode capacity retention rate = approximately 85.5%). On the other hand, when the lower limit value of the OCP curve used in the CCP arithmetic processing is less than 3.75V, the positive electrode capacity retention rate obtained by the CCP arithmetic processing is significantly different from the experimental result. That is, when the lower limit value of the OCP curve is less than 3.75V, the estimation accuracy suddenly deteriorates.

[0044] As shown in Fig. 5, when the upper limit value of the difference in the OCP curve used in the CCP arithmetic processing is 12 mV or less (corresponding to the part of region b in Fig. 3), the positive electrode capacity retention rate obtained by the CCP arithmetic processing is close to the experimental result (positive electrode capacity retention rate = about 85.5%). On the other hand, when the upper limit value of the difference in the OCP curve used in the CCP arithmetic processing is greater than 12 mV, the positive electrode capacity retention rate obtained by the CCP arithmetic processing is significantly different from the experimental result. That is, when the upper limit value of the difference in the OCP curve is greater than 12 mV, the estimation accuracy suddenly deteriorates.

[0045] Next, the changes in the positive electrode OCP, negative electrode OCP, and OCV before and after degradation will be described. Fig. 6 is a graph showing the OCV before degradation of the battery cell 20 and the OCP curves of the positive and negative electrodes, and the OCV curve after degradation. The horizontal axis represents the discharge capacity, the vertical axis (left side) represents the OCV of the cell and the OCP of the positive electrode, and the vertical axis (right side) represents the OCP of the negative electrode. The graph in Fig. 6 is a graph in which the OCV, the OCP of the positive electrode, and the OCP of the negative electrode are represented on the left and right vertical axes respectively with respect to the graph in Fig. 2. Fig. 7 shows the difference in the positive electrode OCP before and after degradation with respect to the battery capacity axis, and Fig. 8 shows the difference in the negative electrode OCP before and after degradation with respect to the battery capacity axis. Before degradation, it corresponds to the initial state, and after degradation, it corresponds to the state in which the positive and negative electrode capacity retention rates have degraded in 5% increments from 95% to 80%. Figs. 7 and 8 show the characteristics when the positive and negative electrode capacity retention rates decrease in 5% increments from 95% to 80%.

[0046] When the battery cell 20 is discharged from the fully charged state, the difference in the positive electrode OCP before and after degradation gradually increases until a certain point of discharge capacity (the capacity at the time of positive electrode OCP 3.75 V), but when it exceeds a certain point (the capacity at the time of positive electrode OCP 3.75 V), the difference in the positive electrode OCP before and after degradation becomes smaller (see Fig. 7). Also, as shown in Fig. 8, the difference in the negative electrode OCP before and after degradation is small until a certain point of discharge capacity (the capacity at the time of positive electrode OCP 3.75 V), but when the discharge capacity exceeds a certain point (the capacity at the time of positive electrode OCP 3.75 V), the difference in the negative electrode OCP before and after degradation becomes larger.

[0047] In the charge-discharge curve shown in FIG. 6, after dividing the region of the OCP curve used in the CCP arithmetic processing at a certain battery capacity as a boundary, the influence on the arithmetic result of the deterioration state will be described. In the positive electrode OCP curve, the battery capacity serving as the boundary corresponds to the positive electrode OCP (3.75 V). In region X, the difference in the positive electrode OCP is large, the difference in the negative electrode OCP is small, and the change in the shape of the positive electrode OCP before and after deterioration is small. In region Y, the difference in the positive electrode OCP is small, the difference in the negative electrode OCP is large, and the change in the shape of the positive electrode OCP before and after deterioration is large. When calculating the deterioration state by CCP using the OCP curve included in region X where the change in the shape of the positive electrode OCP before and after deterioration is small, the accuracy of the fitting calculation is high. On the other hand, when calculating the deterioration state by CCP using the OCP curve included in region Y where the change in the shape of the positive electrode OCP before and after deterioration is large, the accuracy is lower than when calculating using region X. Also, in region Y, since arithmetic processing is performed to adjust with the large difference in the negative electrode OCP with a large OCP difference, the deterioration of the positive electrode is no longer reflected. Since the fitting calculation by CCP performs arithmetic processing to minimize the difference, the deterioration with the larger OCP difference affects the arithmetic result. When calculating the coefficients (α, β, γ) by CCP using the OCP curve included in region X, since the OCP difference caused by deterioration is reflected in the coefficient (α), the error between the actual value of the positive electrode deterioration and the calculation result of the fitting calculation can be reduced. On the other hand, when calculating the coefficients (α, β, γ) by CCP using the OCP curve included in region Y, since the OCP difference caused by deterioration is reflected in the coefficient (β or γ) rather than the coefficient (α), the negative electrode deterioration is overestimated and the deterioration of the positive electrode is underestimated.

[0048] Therefore, the deterioration state estimation unit 13 sets the range (comparison range) of the OCV curve used for calculating the coefficient (α) to a range where the positive electrode OCP difference (open circuit potential difference) is ±12 mV or less and / or a range where the positive electrode OCP is 3.75 V or more, and estimates the deterioration state of the battery cell 20 using the OCV curve included in this range. Thereby, the degree of deterioration of the positive electrode can be estimated with high accuracy. Note that, taking the absolute value of the positive electrode OCP difference, the positive electrode OCP difference is in the range of 12 mV or less.

[0049] Next, with reference to FIG. 9, a processing flow for estimating the deterioration state of the battery cell 20 by the controller 10 will be described. FIG. 9 is a flowchart showing the control procedure of the deterioration state estimation method executed by the controller 10.

[0050] In step S1, the acquisition unit 11 acquires the initial data of the battery cell 20 from the memory 14. The initial data includes data such as the data of the initial OCV curve. In step S2, the acquisition unit 11 acquires the deterioration data of the battery cell 20 from the memory 14. The deterioration data includes the voltage, current, etc. of the battery cell 20 of the charge and discharge current. In step S3, the deterioration state estimation unit 13 calculates the OCV of the battery cell 20 based on the voltage and current of the battery cell 20 acquired by the acquisition unit 11. Note that the memory 14 stores a map showing the correlation between the battery parameters and the internal resistance, and the deterioration state estimation unit 13 may calculate the OCV with reference to this map. At this time, the deterioration state estimation unit 13 may correct the value of the map according to the degree of deterioration (previous calculation value) of the battery cell 20. Note that the deterioration state estimation unit 13 may apply a linearly stored value when there is a shortage in the calculated value of the OCV to be compared with the initial OCV curve.

[0051] In step S4, the deterioration state estimation unit 13 calculates the battery capacity by integrating the current value acquired by the acquisition unit 11, and then calculates the post-deterioration OCV curve by associating the battery capacity with the OCV. In step S5, the deterioration state estimation unit 13 designates a comparison region to be processed in the CCA calculation process. The comparison region is a range where the positive electrode OCP difference (open circuit potential difference) is ±12 mV or less, and / or a range where the positive electrode OCP is 3.75 V or more. In step S6, the deterioration state estimation unit 13 calculates coefficients (α, β, γ) based on the difference between the initial OCV curve and the post-deterioration OCV curve included in the comparison region.

[0052] As described above, the degradation state estimation device 1 according to the present embodiment includes a memory 14 that stores initial data of the initial state of the battery cell 20, an acquisition unit 11 that acquires the current and voltage of the battery cell 20, and a degradation state estimation unit 13 that estimates the degradation state of the battery cell 20. The degradation state estimation unit 13 calculates a post-degradation OCV curve based on the current and voltage of the battery cell 20, and calculates a positive electrode capacity degradation coefficient α, a negative electrode capacity degradation coefficient β, and a capacity deviation amount γ of the battery cell 20 based on the difference between the initial OCV curve and the post-degradation OCV curve. The range of the OCV curve used for calculating the positive electrode capacity degradation coefficient α is a range where the positive electrode OCP difference (open circuit potential difference) is ±12 mV or less and / or a range where the positive electrode OCP is 3.75 V or more. Thereby, the degradation state (degradation state of the positive electrode) of the battery cell 20 can be estimated with high accuracy.

[0053] Also, in the present embodiment, the degradation state estimation unit 13 calculates an OCV curve corresponding to the coefficients (α, β, γ) from the positive / negative electrode OCP curves and the OCV curve of the battery cell 20 in the initial state. Then, the degradation state estimation unit 13 extracts the initial OCV curve and the post-degradation OCV curve included in the comparison region, and obtains a regression value of the coefficients (α, β, γ) at which the difference in OCV is minimized, and calculates the positive electrode capacity degradation coefficient α. Thereby, the degradation state of the positive electrode of the battery cell 20 can be estimated with high accuracy.

[0054] Also, in the present embodiment, the degradation state estimation unit 13 calculates the post-degradation battery capacity by integrating the current acquired by the acquisition unit 11 during charging and discharging of the battery cell 20, and calculates the internal resistance of the battery cell 20 based on at least one of the cell temperature, SOC, current, charge / discharge time, and degree of degradation, and calculates a post-degradation OCV curve based on the voltage, current, calculated internal resistance, and degree of degradation acquired by the acquisition unit 11. Thereby, the calculation accuracy of the post-degradation OCV is improved, and the estimation accuracy of the degradation state of the positive electrode can be enhanced.

[0055] As a modification of this embodiment, the acquisition unit 11 acquires the start voltage which is the voltage of the battery cell 20 at the start of charge and discharge, the end voltage which is the voltage of the battery cell 20 at the end of charge and discharge, and the current during charge and discharge. The deterioration state estimation unit 13 may calculate the battery capacity after deterioration by integrating the current from the start of charge and discharge to the end of charge and discharge, and calculate the OCV curve after deterioration based on the OCV corresponding to the start voltage, the OCV for the end voltage, and the battery capacity after deterioration.

[0056] The OVC curve included in the initial data is the OCV curve from the lower limit value to the upper limit value of the battery capacity of the battery cell 20. On the other hand, the deterioration data stored in the memory 14, or the battery data acquired by the acquisition unit 11 during the charge and discharge current of the battery cell 20 is not necessarily the data when the battery cell 20 is charged and discharged from the lower limit value to the upper limit value of the battery capacity. That is, if the battery data obtained by charging and discharging from the lower limit value to the upper limit value is defined as full charge and discharge data, the data acquired by the acquisition unit 11 may be partial charge and discharge data. In the modification, when partial charge and discharge data is acquired, the deterioration state estimation unit 13 determines whether the start voltage and the end voltage are included in the comparison region. When the start voltage and the end voltage are included in the comparison region, the deterioration state estimation unit 13 calculates the positive electrode capacity deterioration coefficient α by arithmetic processing using CCP. Thereby, the degree of deterioration of the positive electrode can be estimated from the partial charge and discharge data.

[0057] Also, as a modification of this embodiment, the start voltage may be one of the upper limit voltage and the lower limit voltage of the battery cell 20, and the end voltage may be the other of the upper limit voltage and the lower limit voltage of the battery cell 20. The upper limit voltage is a voltage for protecting the battery cell 20 from overcharge, and the lower limit voltage is a voltage for protecting from over-discharge, and is preset according to the performance of the battery cell 20 and the like. In the modification, for example, the charge and discharge control unit 12 charges the battery cell 20 to full charge before estimating the deterioration state, and discharges the battery cell 20 from the full charge state to the lower limit value of the battery capacity. Then, the acquisition unit 11 acquires the battery data during discharge. Thereby, the acquisition unit 11 can acquire full charge and discharge data. Thereby, the OCV comparison accuracy is improved, and the estimation accuracy of the degree of deterioration of the positive electrode can be enhanced.

[0058] As a modification of this embodiment, the degradation state estimation unit 13 may calculate an SOC curve represented by the relationship between the battery capacity and the SOC of the degraded battery cell 20 based on the OCV corresponding to the start voltage, the OCV for the end voltage, and the battery capacity after degradation. Thereby, the estimation accuracy of the SOC can be improved.

[0059] Note that the control flow of FIG. 9 is premised on off-board (acquiring battery data after the charge and discharge of the battery cell 20 are completed), but this embodiment may be on-board (acquiring battery data during the charge and discharge of the battery cell 20). Referring to FIG. 10, the processing flow of estimating the degradation state assuming on-board will be described. It is assumed that the battery 2 is being charged as a premise for executing the following flow.

[0060] The acquisition unit 11 acquires the voltage of the battery cell 20 from the voltage sensor 21 and determines whether or not the acquired voltage is equal to or higher than a voltage threshold value. The voltage threshold value corresponds to a voltage value obtained by converting the OCV (3.75 V) into the terminal voltage of the battery cell 20. Note that since the terminal voltage changes depending on the internal resistance and the charge and discharge current of the battery cell 20, the voltage threshold value may be obtained by calculation. When the voltage of the battery cell 20 is equal to or higher than the voltage threshold value, in step S12, the acquisition unit 11 acquires detection values from the current sensor 22 and the temperature sensor 23. The detection values correspond to the degradation data of the battery cell 20. In step S13, the charge and discharge control unit 12 determines whether or not the charging of the battery cell 20 has ended. If the charging has not ended, the controller 10 executes the control flow of step S11. That is, by executing the control flow of steps S11 to S13, battery data (partial charge and discharge data) included in the comparison region can be acquired. If the charging has ended, the controller 10 executes the control flow of steps S14 to S18. Since the control flow of steps S14 to S18 is the same as the control flow of steps S1, S3 to S6 shown in FIG. 9, the description thereof is omitted.

[0061] The battery cell 20 in this embodiment corresponds to the "secondary battery" of the present invention, and the memory 14 corresponds to the "memory unit" of the present invention. In addition, in this embodiment, the execution order of each control flow shown in FIG. 9 or FIG. 10 is not limited to the order shown in the figure.

[0062] As described above, the embodiments of the present invention have been described. However, these embodiments are described for facilitating the understanding of the present invention and are not described for limiting the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

Explanation of Reference Numerals

[0063] 1 Degradation state estimation device 2 Battery 3 Charging device 4 Load 10 Controller 11 Acquisition unit 12 Charge and discharge control unit 13 Degradation state estimation unit 14 Memory 20 Battery cell 21 Voltage sensor 22 Current sensor 23 Temperature sensor

Claims

1. A state-of-deterioration estimation device for estimating the state of deterioration of a secondary battery, comprising: a storage unit that stores initial data of the initial state of the secondary battery; an acquisition unit that acquires the current and voltage of the secondary battery; a state-of-deterioration estimation unit that estimates the state of deterioration of the secondary battery, wherein the initial data includes data of an initial OCV curve represented by the relationship between the battery capacity and OCV of the secondary battery in the initial state; the state-of-deterioration estimation unit calculates a post-deterioration OCV curve represented by the relationship between the battery capacity and OCV of the post-deterioration secondary battery based on the current and voltage of the secondary battery acquired by the acquisition unit; calculates a positive electrode capacity deterioration coefficient α indicating the degree of deterioration of the positive electrode capacity, a negative electrode capacity deterioration coefficient β indicating the degree of deterioration of the negative electrode capacity, and a capacity deviation amount γ indicating the deviation amount between the positive and negative electrode capacities based on the difference between the initial OCV curve and the post-deterioration OCV curve; the range of the OCV curve used for calculating the positive electrode capacity deterioration coefficient α is a range where the positive electrode open-circuit potential difference is ±12 mV or less and / or a range where the positive electrode open-circuit potential is 3.75 V or more; the positive electrode open-circuit potential difference is the difference between the positive electrode open-circuit potential in the initial state with respect to a predetermined positive electrode capacity and the positive electrode open-circuit potential after deterioration with respect to the predetermined positive electrode capacity, and the state-of-deterioration estimation device.

2. The state-of-deterioration estimation device according to Claim 1, wherein the acquisition unit acquires the temperature of the secondary battery, and the state-of-deterioration estimation unit calculates the post-deterioration battery capacity by integrating the current acquired by the acquisition unit during charging and discharging of the secondary battery; calculates the internal resistance of the secondary battery based on at least one of the temperature, the SOC of the secondary battery, the current, the charging and discharging time of the secondary battery, and the degree of deterioration of the secondary battery; calculates the post-deterioration OCV curve based on the voltage acquired by the acquisition unit, the current acquired by the acquisition unit, the calculated internal resistance, and the degree of deterioration.

3. The state-of-deterioration estimation device according to Claim 1 or 2, wherein the acquisition unit acquires a start voltage that is the voltage of the secondary battery at the start of charging and discharging, an end voltage that is the voltage of the secondary battery at the end of charging and discharging, and a current during charging and discharging; and the state-of-deterioration estimation unit calculates the post-deterioration battery capacity by integrating the current from the start of charging and discharging to the end of charging and discharging. A state-of-deterioration estimation device that calculates the post-deterioration OCV curve based on the OCV corresponding to the start voltage, the OCV for the end voltage, and the battery capacity after deterioration.

4. The state-of-deterioration estimation device according to claim 3, wherein the start voltage is one of the upper limit voltage and the lower limit voltage of the secondary battery, and the end voltage is the other of the upper limit voltage and the lower limit voltage of the secondary battery.

5. The state-of-deterioration estimation device according to claim 3, wherein the state-of-deterioration estimation unit calculates an SOC curve represented by the relationship between the battery capacity and the SOC of the secondary battery after deterioration based on the OCV corresponding to the start voltage, the OCV for the end voltage, and the battery capacity after deterioration.

6. A state-of-deterioration estimation method for estimating the state of deterioration of a secondary battery, which is executed by a processor, wherein the processor obtains data of an initial OCV curve represented by the relationship between the battery capacity and the OCV of the secondary battery in the initial state from a storage unit, obtains the current and voltage of the secondary battery, calculates a post-deterioration OCV curve represented by the relationship between the battery capacity and the OCV of the secondary battery after deterioration based on the current and voltage of the secondary battery, calculates a positive electrode capacity deterioration coefficient α indicating the degree of deterioration of the positive electrode capacity, a negative electrode capacity deterioration coefficient β indicating the degree of deterioration of the negative electrode capacity, and a capacity deviation amount γ indicating the deviation amount between the positive and negative electrode capacities based on the difference between the initial OCV curve and the post-deterioration OCV curve, the range of the OCV curve used for the calculation of the positive electrode capacity deterioration coefficient α is a range where the positive electrode open circuit potential difference is ±12 mV or less and / or a range where the positive electrode open circuit potential is 3.75 V or more, and the positive electrode open circuit potential difference is the difference between the positive electrode open circuit potential in the initial state for a predetermined positive electrode capacity ratio and the positive electrode open circuit potential after deterioration for the predetermined positive electrode capacity ratio.

Images