Deterioration state estimation device and deterioration state estimation method

Abstract

A deterioration state estimation device (1) that estimates a deterioration state of a secondary battery comprises: a storage unit that stores initial data of an initial state of a secondary battery; an acquisition unit (11) that acquires an electric current and a voltage of the secondary battery; and a deterioration state estimation unit (13) that estimates a deterioration state of the secondary battery. The initial data includes data of initial battery characteristics indicating a relationship between an electric current integrated value and a positive electrode OCP of the secondary battery in an initial state. The deterioration state estimation unit (13) calculates the electric current integrated value and the positive electrode OCP of the secondary battery after deterioration on the basis of the electric current and the voltage of the secondary battery acquired by the acquisition unit (11), and estimates a positive electrode deterioration degree of the secondary battery on the basis of the difference between the initial battery characteristics and post-deterioration battery characteristics indicating the relationship between the electric current integrated value and the positive electrode OCP of the secondary battery after deterioration.

Description

Deterioration state estimation device and deterioration state estimation method

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

[0002] Battery diagnostic systems that predict and diagnose the predicted degradation state of a secondary battery have been known. For example, a battery diagnostic system described in Patent Document 1 includes a load history acquisition unit, an interpolation processing unit, a degradation estimation unit, a degradation prediction unit, and an output unit. The load history acquisition unit acquires a battery load history of a used secondary battery. If part of the configuration data in the battery load history is missing, the interpolation processing unit estimates and interpolates the missing part of the configuration data using the remaining part of the configuration data. The degradation estimation unit estimates the current degradation state of the secondary battery and the degradation factors that caused the degradation state based on the battery load history. The degradation prediction unit predicts and diagnoses the predicted degradation state of the secondary battery that will occur in the future if used in a certain manner, using the predicted battery load and the current degradation state and degradation factors of the secondary battery estimated by the degradation estimation unit.

[0003] International Publication No. 2022-109367

[0004] However, the above-described battery diagnostic system has a problem in that it requires the load history of the battery to estimate the deterioration state.

[0005] The problem to be solved by the present invention is to provide a degradation state estimation device and a degradation state estimation method that can estimate the degree of degradation of a positive electrode based on the current state of a secondary battery.

[0006] The present invention solves the above problem by calculating the current integration value and positive electrode OCP of a deteriorated secondary battery, and estimating the degree of deterioration of the positive electrode of the secondary battery based on the difference between the deteriorated battery characteristics, which indicate the relationship between the current integration value and positive electrode OCP of the deteriorated secondary battery, and the initial battery characteristics, which indicate the relationship between the current integration value and positive electrode OCP of the secondary battery in its initial state.

[0007] According to the present invention, the degree of deterioration of the positive electrode of a secondary battery can be estimated.

[0008] FIG. 1 is a block diagram of a degradation state estimation device, a battery, a charging device, and a load according to an embodiment of the present invention. FIG. 2 is a graph showing the OCV and OCP curves of the positive and negative electrodes of a battery cell before and after degradation. FIG. 3 is a table for explaining the change in the valence of a transition metal (Ni) during charge and discharge of an initial product and a degraded product. FIG. 4 is a graph showing the characteristics of the positive electrode OCP of a battery cell 20. FIG. 5 is a flowchart showing the control procedure of the degradation state estimation method according to this embodiment.

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

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

[0011] The memory 14 stores initial data indicating battery characteristics of the battery cell 20 in an initial state. The initial data includes data related to the full charge capacity of the battery cell 20, upper and lower limit voltages of the battery cell 20, an initial OCV curve of the battery cell 20, and an initial OCP (open circuit potential) curve (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 (integrated current value) and OCV (open circuit voltage) of the battery cell 20 in the initial state. The initial OCP curve (positive electrode, negative electrode) is a battery characteristic indicated by the relationship between the battery capacity (integrated current value) and OCP of the battery cell 20 in the initial state at each of 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 degradation data or the like that indicates the battery characteristics of the battery cell 20 during charging or discharging. The degradation data is data that indicates the battery characteristics after the battery cell 20 has been used, and includes data on the voltage, current, and temperature of the battery cell 20 during charging or discharging, and data on the voltage, current, and temperature of the battery cell 20 before or after charging or discharging is started or finished.

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

[0014] The SOC-internal resistance characteristics also vary depending on the battery temperature, charge / discharge time, degree of deterioration, and charge / discharge C rate. For example, assuming the SOC is the same, the corresponding internal resistance on the SOC-internal resistance characteristics increases as the battery temperature decreases. Similarly, the longer the charge / discharge time, the higher the internal resistance, and the greater the degree of deterioration. Similarly, with respect to the charge / discharge C rate, in an SOC range above a predetermined value, the higher the charge / discharge C rate, the higher the internal resistance. 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 parallel. The battery cells 20 are, for example, lithium-ion secondary batteries. One example of the battery cells 20 is a flat laminate film lithium-ion secondary battery, which has a power generating element formed by laminating electrode layers (positive electrode layer and negative electrode layer) and separators and filling them with an electrolyte, 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 includes a current collector plate made of 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 additive, a binder, an electrolyte, etc. As the positive electrode active material, a composite oxide of a transition metal and lithium can be used. Specific examples include Li-Co composite oxides, Li-Ni composite oxides, and Li-Mn composite oxides.

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

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

[0019] In this embodiment, the charge / discharge characteristics of the battery cell 20 in its initial state (before deterioration) are as follows: The maximum OCV is approximately 4.2 V. Furthermore, as the battery cell 20 is charged and discharged, the positive electrode OCP varies in the range of approximately 3.0 V to approximately 4.2 V, and the negative electrode OCP varies in the range with a lower limit voltage of 0 V and an upper limit voltage of 1.1 to 1.3 V. If the battery cell 20 deteriorates (if the degree of deterioration is greater than or equal to a predetermined level), the above charge / 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 also installed. The voltage sensor 21 detects the voltage of each of the multiple battery cells 20. Note that in FIG. 1 , the voltage sensor 21 is illustrated as being connected to both ends of a battery group in which multiple battery cells are connected, but the voltage sensor 21 may detect the cell voltage of each battery cell 20 by, for example, connecting voltage detection resistors in parallel to each of the multiple battery cells 20 and detecting the voltage applied to each resistor.

[0021] The current sensor 22 detects the charge / discharge current flowing through the battery cell 20. The temperature sensor 23 detects the cell temperature of the battery cell 20. The detected 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 degradation state estimating device 1 is provided in a vehicle, the charging device 3 corresponds to a charging facility outside the vehicle, and the load 4 corresponds to an inverter, a motor, etc.

[0023] Next, the functions 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 detected 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 voltage of each of multiple battery cells, which is the charge voltage and / or discharge voltage. The acquisition unit 11 does not need to acquire the current, etc. in real time during charging / discharging of the battery 2. For example, if battery data during charging / discharging of the battery cell 20 is stored in a database (not shown), the controller 10 may access the database, and the acquisition unit 11 may acquire the charge / discharge current, charge / discharge voltage, and cell temperature from the stored battery data. The acquisition unit 11 also acquires 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. When charging the battery 2, the charge / discharge control unit 12 controls the charging device 3, and when discharging the battery 2, the charge / discharge control unit 12 controls a switch etc. included in the load 4 to control the discharge current.

[0025] The degradation state estimation unit 13 estimates the degradation state of the battery 2. The degradation state estimation unit 13 estimates the degradation state (degradation level) of the battery 2 using Charge Curve Analysis (CCA). The degradation state of the battery 2 is useful information for managing the state of the battery 2 and for reusing the battery 2. The degradation state of the battery 2 does not necessarily progress at the same rate in the positive electrode and the negative electrode. For example, when reusing the battery 2 by separating the positive electrode and the negative electrode, the overall degradation level of the battery 2 may be low, but the degradation of the positive electrode may not be very advanced. Therefore, in order to determine the degradation state of the battery 2, it is necessary to understand the degradation levels of the positive electrode capacity and the negative electrode capacity in addition to the overall degradation level.

[0026] In the charge curve analysis method, a fitting calculation is performed on the charge / discharge curve of the battery cell 20 using the OCP curves of the positive and negative electrode active materials as a reference, with the positive electrode capacity degradation coefficient α, the negative electrode capacity degradation coefficient β, and the capacity deviation 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 γ indicates the deviation between the positive and negative electrode capacities. In the following description, the coefficients (α, β) indicate the degrees of degradation of the positive electrode capacity and the negative electrode capacity of the battery cell 20, and the coefficient (γ) indicates the deviation between the positive and negative electrode capacities of the battery cell 20.

[0027] The coefficients (α, β, γ) using CCA are calculated using an initial OCV curve and a post-deterioration OCV curve. The degradation state estimation unit 13 acquires initial OCV curves (positive electrode, negative electrode) from the initial data stored in the memory 14. The initial OCV curve corresponds to the difference between the initial positive electrode OCP curve and the initial negative electrode OCP curve. The degradation state estimation unit 13 also obtains a post-deterioration OCV curve through calculation processing. A method for calculating the post-deterioration OCV curve will be described below.

[0028] The degradation state estimation unit 13 calculates a 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 (current integrated value) and 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 while the battery cell 20 is being charged or discharged. Note that in the following description, the battery capacity may be replaced with the current integrated value. The degradation state estimation unit 13 acquires, from the acquisition unit 11, the voltage of the battery cell 20 corresponding to the current integration timing from the start to the end of charging / discharging 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 element 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 / discharge time of the battery cell 20, and the degree of deterioration of the battery cell 20. The degradation state estimation unit 13 refers to data stored in the memory 14 that indicates a correlation between the internal resistance of the battery cell 20 and battery parameters. The degradation state estimation unit 13 acquires, for example, data that indicates a correlation between the SOC, cell temperature, and internal resistance of the battery cell 20 from the memory 14. The degradation state estimation unit 13 acquires the cell temperature from the acquisition unit 11 and calculates the SOC from the current integrated value calculated above. Then, the degradation state estimation unit 13 calculates, based on the acquired data, a resistance value corresponding to the cell temperature and SOC as the internal resistance of the battery cell 20. Note that the battery parameters used to calculate the internal resistance may be multiple elements. The degradation state estimation unit 13 may also calculate the internal resistance of the battery cell 20 from the slope of the IV characteristics (current-voltage characteristics) of the battery cell 20 .

[0030] The degradation state estimation unit 13 calculates the OCV by subtracting (using the charging voltage) or adding (using the discharging voltage) the value obtained by multiplying the charging / discharging current and 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 of charging / discharging to the end of charging / discharging. As a result, the degradation state estimation unit 13 can estimate the OCV of the battery cell 20 (estimated OCV value) based on the voltage (cell voltage) acquired by the acquisition unit 11, the current (charging / discharging current) acquired by the acquisition unit 11, and the internal resistance of the battery cell 20. Then, the degradation state estimation unit 13 calculates a post-degradation OCV curve based on the estimated OCV value and the battery capacity (integrated current value). Note that the OCV is not limited to an estimated value calculated by calculation, and may be a measured OCV value. For example, the battery cell 20 is charged / discharged off-board, and the OCV of the battery cell 20 is measured. The OCV measurement value is calculated using a map from the detected voltage of the voltage sensor 21. Then, the measurement data of the OCV measurement value is stored in the memory 14. The acquisition unit 11 acquires the data of the OCV measurement value from the memory 14 and calculates a post-degradation OCV curve based on the battery capacity based on the OCV measurement value. That is, the degradation state estimation unit 13 calculates the post-degradation OCV curve based on the OCV of either the OCV measurement value or the OCV estimated value.

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

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

[0033] Next, the degradation state estimation unit 13 calculates the post-degradation OCV curve (OCV ｄｅｇ，ｅｘｐ The method for calculating the post-deterioration OCV curve is as described above.

[0034] The degradation state estimation unit 13 calculates the initial positive electrode OCP curve (OCP Ｃａ，ｉｎｉ ) and the initial negative electrode OCP curve (OCP Ａｎ，ｉｎｉ ) is contracted and moved horizontally to obtain the OCV curve after deterioration (OCV ｄｅｇ，ｅｘｐ ) and the OCV curve (OCV ｄｅｇ，ｃａｌ Specifically, the OCV curve (OCV ｄｅｇ，ｃａｌ ) is the initial positive electrode OCP curve (OCP Ｃａ，ｉｎｉ ), the entire battery capacity axis is multiplied by a coefficient (α) to obtain the initial negative electrode OCP curve (OCP Ａｎ，ｉｎｉ ), the entire battery capacity axis is multiplied by a coefficient (β) to obtain the initial negative electrode OCP curve (OCP Ａｎ，ｉｎｉ ) is calculated by shifting the battery capacity axis horizontally by the coefficient (γ).

[0035] OCV curve (OCV ｄｅｇ，ｃａｌ ) is expressed by the following formula (2) using coefficients (α, β, γ). In addition, capacity Ａｎ，ｉｎｉ is the initial negative electrode capacity, and the coefficients satisfy the conditions (0<α, β<1, γ<initial battery capacity).

[0036] In this way, the degradation state estimation unit 13 calculates the post-degradation OCV curve (OCV ｄｅｇ，ｅｘｐ ) and OCV curve (OCV ｄｅｇ，ｃａｌThe 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) that minimize the difference between the initial OCV curve and the post-degradation OCV curve. In the regression calculations, for example, the average value of the sum of squares of the OCV differences may be calculated. 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, we will explain the deterioration phenomenon specific to the positive electrode. As the deterioration of the positive electrode progresses, it manifests itself as a change in the surface structure of the positive electrode active material. The surface structure of the positive electrode active material before deterioration is layered, but as deterioration progresses, part of the surface structure changes to a rock salt structure. This change in surface structure is a deterioration phenomenon specific to the positive electrode, and occurs due to changes in the internal state of the positive electrode (cracks, changes in crystal structure, splits, etc.). The change in the surface structure of the positive electrode active material reduces the amount of effective active material in the positive electrode, which manifests as the degree of positive electrode deterioration. Below, with reference to Figure 3, we will explain the change in the valence of the transition metal (Ni) during charge and discharge of an initial product and a deteriorated product.

[0038] Assume that the positive electrode battery capacity of the initial product is "1" and the positive electrode capacity of the deteriorated product is "0.9". In other words, the positive electrode battery capacity of the deteriorated battery cell 20 is 90% of the positive electrode battery capacity of the battery cell 20 before deterioration. The positive electrode active material is Li(NiMnCo)O ２ The change in valence before and after charging in the initial product and the deteriorated product is as shown in Figure 3. The valence of the positive electrode transition metal (Ni) increases by charging, and as shown in the example of Figure 3, the change in Ni valence before and after charging in the initial product is as follows: ２＋ increased by 0.2, and Ni ３＋ In the deteriorated battery, the valence of Ni before charging (Ni ０．５ ) Among them, Ni ２＋ ０．０６ has a rock salt structure, and the valence of Ni with a layered structure is Ni ２＋ ０．１１ and Ni ３＋ ０．３３ In other words, the 10% deterioration of the positive electrode capacity is reflected in the valence of Ni with a rock salt structure. ２＋ ０．０６Therefore, the Ni valence change before and after charging in a deteriorated product is ２＋ increased by 0.11, and Ni ３＋ increases by 0.43, resulting in a total increase of 0.54. In other words, the rate of Ni valence change during charging changes due to deterioration of the positive electrode. This valence change is reflected in the shape of the positive electrode OCP characteristics. Note that while the example in Figure 3 describes the valence change during charging, valence change also occurs during discharge.

[0039] 4 is a graph showing the characteristics of the positive electrode OCP of the battery cell 20. Graph a shows the characteristics of the positive electrode OCP of an initial product, and graph b shows the characteristics of the positive electrode OCP of a degraded product. As shown in FIG. 4 , when the battery cell 20 degrades, the positive electrode OCP decreases in a region where the positive electrode capacity maintenance rate is equal to or greater than a predetermined value (e.g., 0.5), and the difference (OCP difference) between the positive electrode OCP of the initial product and the positive electrode OCP of the degraded product increases.

[0040] The degree of deterioration inside the positive electrode is estimated from the difference in shape of the positive electrode OCP before and after deterioration. Furthermore, for example, the greater the proportion of cracks that have occurred in the positive electrode or the greater the proportion of structural changes from a layered structure to a rock salt structure, the greater the difference in positive electrode OCP and / or the integrated value of the difference in positive electrode OCP. Therefore, the controller 10 of the deterioration state estimation device 1 identifies the difference in shape of the positive electrode OCP before and after deterioration from the difference in positive electrode OCP and / or the integrated value of the difference in positive electrode OCP, and estimates the degree of deterioration of the positive electrode of the battery cell 20 based on the difference in positive electrode OCP and / or the integrated value of the difference in positive electrode OCP.

[0041] In order to identify the difference in the shape of the positive electrode OCP before and after deterioration, the degradation state estimation unit 13 calculates post-deterioration battery characteristics that indicate the relationship between the current integration value of the battery cell 20 after deterioration and the positive electrode OCP. The degradation state estimation unit 13 calculates the positive electrode OCP (OCP Ｃａ，ｄｅｇ ) is calculated.

[0042] This allows the degradation state estimation unit 13 to estimate the positive electrode OCP of the battery cell 20 after degradation. The degradation state estimation unit 13 estimates the positive electrode OCP (OCP Ｃａ，ｄｅｇThe degradation state estimation unit 13 calculates the positive electrode OCP (OCP Ｃａ，ｄｅｇ The post-deterioration battery characteristics, which indicate the relationship between the post-deterioration current integrated value of the battery cell 20 and the positive electrode OCP (OCP), are calculated from the estimated value of the post-deterioration current integrated value and the current integrated value. The post-deterioration battery characteristics are calculated as the relationship between the post-deterioration current integrated value of the battery cell 20 and the positive electrode OCP (OCP Ｃａ，ｄｅｇ ) characteristics.

[0043] The degradation state estimation unit 13 may calculate the degraded battery characteristics based on the positive electrode OCP measurement value. The positive electrode OCP measurement value is a measurement value of the positive electrode OCP of the degraded battery cell 20, and can be measured using, for example, a half cell. The degradation state estimation unit 13 may then calculate the degraded battery characteristics by matching the battery capacity (integrated current value) with the positive electrode OCP measurement value. That is, the degradation state estimation unit 13 calculates the degraded battery characteristics based on the OCP of either the positive electrode OCP measurement value or the positive electrode OCP estimated value.

[0044] The degradation state estimation unit 13 identifies an initial OCP curve (positive electrode) from the initial data. The initial OCP curve (positive electrode) corresponds to the initial battery characteristics that indicate the relationship between the current integration value and the positive electrode OCP of the battery cell 20 in the initial state. The degradation state estimation unit 13 estimates the degree of positive electrode deterioration of the battery cell 20 based on the difference between the degraded battery characteristics and the initial battery characteristics. Specifically, the degradation state estimation unit 13 converts the current integration values ​​of the degraded battery characteristics and the initial battery characteristics into the SOC of the battery cell 20. In other words, the degradation state estimation unit 13 converts the initial battery characteristics and the degraded battery characteristics into characteristics that indicate the relationship between the SOC and the positive electrode OCP. After converting the current integration value into the SOC, the degradation state estimation unit 13 calculates the difference between the initial battery characteristics and the degraded battery characteristics and calculates the integrated value of the difference. The degradation state estimation unit 13 then estimates the degree of positive electrode deterioration based on the integrated value of the calculated difference. For example, the degradation state estimating unit 13 may estimate the degree of positive electrode degradation so that the greater the maximum difference or the integrated value of the differences in the positive electrode OCP, the higher the degree of positive electrode degradation.

[0045] Next, a process flow for estimating the degradation state of the battery cell 20 by the controller 10 will be described with reference to Fig. 5. Fig. 5 is a flowchart showing the control procedure of the degradation state estimation method executed by the controller 10. The controller 10 may store the calculation results calculated in the following control flow in the memory 14 as calculation data.

[0046] In step S1, the acquisition unit 11 acquires initial data of the battery cell 20 from the memory 14. The initial data includes data on an initial OCV curve, an initial OCP (positive electrode, negative electrode) curve, etc. The initial OCV curve may be represented by an OCV characteristic relative to the battery capacity, the current integrated value, or the SOC, and the OCP (positive electrode, negative electrode) curve may be represented by an OCP (positive electrode, negative electrode) characteristic relative to the battery capacity, the current integrated value, or the SOC.

[0047] In step S2, the acquisition unit 11 acquires deterioration data of the battery cell 20 from the memory 14. The deterioration data includes the OCV at the start of charging / discharging, the voltage and current of the battery cell 20 for charging / discharging current, the battery temperature, etc. 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.

[0048] In step S4, the degradation state estimation unit 13 calculates a post-degradation OCV curve by integrating the current values ​​acquired by the acquisition unit 11 and correlating the battery integrated value with the OCV calculated in the control flow of step S3. Note that if the OCV estimated value of the battery cell 20 is insufficient and cannot be compared with the initial OCV curve, the degradation state estimation unit 13 may apply a linear storage value to compensate for the shortage in the OCV estimated value.

[0049] In step S5, the degradation state estimation unit 13 calculates coefficients (α, β, γ) based on the difference between the initial OCV curve and the post-deterioration OCV curve through the CCA calculation process. In step S6, the degradation state estimation unit 13 calculates the estimated OCV value (OCV ｄｅｇ，ｅｘｐ ), coefficients (β, γ), initial negative electrode OCP (OCPAn,ini) shown in the initial OCP curve, and initial negative electrode capacity (capacity Ａｎ，ｉｎｉ) and calculates the positive electrode OCP of the battery cell 20 after deterioration. ｄｅｇ，ｅｘｐ ) is estimated based on the battery integrated value during charging and discharging of the battery cell 20. The initial OCP curve is represented by the characteristics of the integrated current value and OCP. Therefore, the positive electrode OCP of the battery cell 20 after deterioration is calculated as an estimated value based on the integrated current value. In step S7, the degradation state estimation unit 13 calculates the post-deterioration battery characteristics from the calculated positive electrode OCP and the integrated current value.

[0050] In step S8, the degradation state estimation unit 13 converts the initial battery characteristics and the degraded battery characteristics corresponding to the initial OCP curve into characteristics that indicate the relationship between the SOC and the positive electrode OCP. That is, the degradation state estimation unit 13 aligns the capacity axes (axis of integrated current) of the initial battery characteristics and the degraded battery characteristics with the SOC so that the characteristics can be compared. Then, the degradation state estimation unit 13 calculates the difference between the initial battery characteristics and the degraded battery characteristics and calculates an integrated value of the difference. As a result, the degradation state estimation unit 13 calculates an integrated value of the difference in the positive electrode OCP at each SOC. In step S9, the degradation state estimation unit 13 estimates the degree of degradation of the positive electrode based on the calculated integrated value.

[0051] As described above, the degradation state estimation device 1 in this embodiment includes the memory 14 that stores initial data on the initial state of the battery cell 20, the acquisition unit 11 that acquires the current and voltage of the battery cell 20, and the degradation state estimation unit 13 that estimates the degradation state of the battery cell 20. The degradation state estimation unit 13 calculates the integrated current value and positive electrode OCP of the battery cell 20 after degradation based on the current and voltage of the battery cell 20 acquired by the acquisition unit 11, and estimates the degree of positive electrode degradation of the battery cell 20 based on the difference between the post-degradation battery characteristics that indicate the relationship between the integrated current value and positive electrode OCP of the battery cell 20 after degradation and the initial battery characteristics that indicate the relationship between the integrated current value and positive electrode OCP of the battery cell 20 in an initial state. In this way, the degree of positive electrode degradation of the battery cell 20 can be estimated.

[0052] Furthermore, in this embodiment, the degradation state estimation unit 13 calculates an integrated value of the difference in positive electrode OCP at each SOC of the battery cell 20 based on the difference between the degraded battery characteristics and the initial battery characteristics, and estimates the degree of positive electrode degradation based on the integrated value. As a result, the difference in positive electrode OCP before and after degradation is taken as the integrated value of the difference in positive electrode OCP, making it possible to quantitatively calculate the degree of positive electrode degradation.

[0053] In this embodiment, the degradation state estimation unit 13 calculates the battery resistance of the battery cell 20 based on at least elements of the battery temperature, SOC, C rate, charge / discharge duration, and battery degradation level, calculates an estimated OCV value of the battery cell 20 based on the voltage, current, and calculated battery resistance acquired by the acquisition unit 11, and calculates post-degradation battery characteristics based on either the measured OCV value of the battery cell 20 or the calculated estimated OCV value. That is, in this embodiment, when the battery capacity (integrated current value) and the measured OCV value can be acquired, the post-degradation battery characteristics can be calculated based on the measured OCV value. Furthermore, the estimated OCV value can be estimated from the measured values ​​(voltage, current) and internal resistance of the battery cell 20, and the post-degradation battery characteristics can be acquired from the estimated OCV value. This improves the accuracy of estimating the positive electrode degradation level.

[0054] In this embodiment, the degradation state estimation unit 13 calculates a post-degradation OCV curve based on the current and voltage of the battery cell 20 acquired by the acquisition unit 11, and calculates coefficients (α, β, γ) based on the difference between the initial OCV curve and the post-degradation OCV curve. This makes it possible to estimate the degradation state of the positive electrode of the battery cell 20 with high accuracy.

[0055] In this embodiment, the degradation state estimation unit 13 calculates an estimated positive electrode OCP value of the battery cell 20 based on the initial OCV curve, the post-degradation OCV curve, the negative electrode capacity degradation coefficient β, and the capacity deviation amount γ, and calculates post-degradation battery characteristics based on either the measured positive electrode OCP value or the estimated positive electrode OCP value. This makes it possible to estimate the degree of positive electrode degradation of the battery cell 20. Furthermore, the positive electrode OCP of a degraded cell can be calculated using a measured OCV curve or an OCV curve estimated from an initial charge / discharge curve, without measuring the positive electrode OCP.

[0056] As a modified example of this embodiment, the degradation state estimation unit 13 may calculate the integrated current value acquired by the acquisition unit 11 when the OCV at the start and end of charging / discharging is within the upper and lower limit voltage ranges of the battery cell 20, calculate the positive electrode OCP by multiplying the initial positive electrode capacity by the positive electrode capacity degradation coefficient α, and calculate the post-degradation battery characteristics based on the integrated current value and the positive electrode OCP. The initial positive electrode capacity indicates the positive electrode capacity of the battery cell 20 in its initial state, and data on the initial positive electrode capacity is stored in the memory 14. The upper and lower limit voltages of the battery cell 20 are thresholds experimentally determined depending on the materials contained in the battery cell 20, and for example, the upper and lower limits of the operating voltage range of the battery cell 20 may be used as the upper and lower limit voltages of the battery cell 20. The fully charged battery capacity (degraded battery capacity) of the battery cell 20 at the degradation level is lower than the fully charged battery capacity (initial battery capacity) of the battery cell 20 in its initial state. Therefore, the relationship between the battery capacity (integrated value) and SOC of the deteriorated battery cell 20 is defined by calculating the OCV while limiting the calculation of the current integrated value of the battery cell 20 to the range of the upper and lower limit voltages of the battery cell 20. The current integrated values ​​of the deteriorated battery characteristics and the initial battery characteristics can be converted into the SOC of the battery cell 20, respectively, to obtain SOC-OCP curves before and after deterioration, thereby improving the accuracy of comparing the SOC-OCP curves before and after deterioration.

[0057] In addition, since the positive electrode capacity deterioration coefficient α can be calculated by CCA, when the initial data stored in the memory 14 includes data on the initial positive electrode capacity, the value obtained by multiplying the initial positive electrode capacity by the positive electrode capacity deterioration coefficient α is calculated as the positive electrode OCP (OCP Ｃａ，ｄｅｇ That is, the degradation state estimation unit 13 may calculate the positive electrode OCP (OCP Ｃａ，ｄｅｇ This improves the accuracy of OCV comparison and improves the accuracy of estimating the positive electrode capacity degradation.

[0058] As a modification of this embodiment, the degradation state estimation unit 13 may estimate the degree of positive electrode degradation based on the difference between the post-degradation battery characteristics and the initial battery characteristics, within a range in which the difference between the positive electrode OCP in the initial state and the post-degradation positive electrode OCP at each SOC is equal to or greater than a predetermined SOC threshold. As shown in FIG. 4 , the difference between the positive electrode OCP before and after degradation increases in a region in which the positive electrode capacity maintenance ratio is equal to or greater than a predetermined value (e.g., 0.5). For example, if a large amount of data (calculation results) with low positive electrode OCP differences is collected, integrating the positive electrode OCP differences in the control flow of step S8 may result in values ​​with low correlation with the estimation of the positive electrode degradation level, potentially reducing the accuracy of the estimation of the positive electrode degradation level. Therefore, in this modification, a threshold value is set for the OCP so that only calculation results with high correlation are obtained. This improves the correlation between the integrated value of the OCP differences before and after degradation and the positive electrode degradation level.

[0059] In this embodiment, the battery cell 20 corresponds to the "secondary battery" of the present invention, and the memory 14 corresponds to the "storage unit" of the present invention. In this embodiment, the execution order of the control flows shown in FIG. 5 is not limited to the order shown in the figure. In the control flow shown in FIG. 5, if data on the positive electrode capacity of the deteriorated battery cell 20 is stored in the memory 14, the controller 10 may proceed to step S8 after the control flow of step S1 without executing steps S2 to S7. Furthermore, the controller 10 may store the calculation results obtained by executing the control flow from steps S2 to S7 in the memory 14 as data. For example, the controller 10 may store the positive electrode OCP, which is the calculation result of the control flow of step S6, or the post-deterioration battery characteristics, which are the calculation result of the control flow of step S6, in the memory 14 as positive electrode capacity data.

[0060] Although the embodiments of the present invention have been described above, these embodiments are described to facilitate understanding of the present invention and are not described to limit the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

[0061] REFERENCE SIGNS LIST 1 Degradation state estimation device 2 Battery 3 Charging device 4 Load 10 Controller 11 Acquisition unit 12 Charging / discharging control unit 13 Degradation state estimation unit 14 Memory 20 Battery cell 21 Voltage sensor 22 Current sensor 23 Temperature sensor

Claims

A degradation state estimation device that estimates a degradation state of a secondary battery, a storage unit that stores initial data of an initial state of the secondary battery; an acquisition unit that acquires a current and a voltage of the secondary battery; a degradation state estimation unit that estimates a degradation state of the secondary battery, the initial data includes data of initial battery characteristics indicating a relationship between an integrated current value of the secondary battery in an initial state and a positive electrode OCP, The degradation state estimation unit calculating an integrated current value and a positive electrode OCP of the secondary battery after deterioration based on the current and voltage of the secondary battery acquired by the acquisition unit; A degradation state estimation device that estimates a degree of positive electrode degradation of the secondary battery based on a difference between post-degradation battery characteristics indicating the relationship between the current integrated value and the positive electrode OCP of the secondary battery after the degradation and the initial battery characteristics.

2. The degradation state estimating device according to claim 1, The degradation state estimation unit calculating an integrated value of the difference in the positive electrode OCP at each SOC of the secondary battery based on a difference between the post-degradation battery characteristics and the initial battery characteristics; A degradation state estimation device that estimates the degree of degradation of the positive electrode based on the integrated value.

3. The degradation state estimating device according to claim 1 or 2, The degradation state estimation unit calculating a battery resistance of the secondary battery based on at least elements of a battery temperature, an SOC, a C rate, a charge / discharge duration, and a degree of battery deterioration; calculating an estimated OCV value of the secondary battery based on the voltage, the current, and the battery resistance acquired by the acquisition unit; The degradation state estimation device calculates the post-degradation battery characteristics based on either the measured OCV value of the secondary battery or the estimated OCV value. 　 The degradation state estimating device according to any one of claims 1 to 3, the initial data includes data of an initial OCV curve that indicates a relationship between a battery capacity and an OCV of the secondary battery in the initial state, The degradation state estimation unit calculating a post-deterioration OCV curve indicated by the relationship between the current integrated value and OCV of the secondary battery after deterioration based on the current and voltage of the secondary battery acquired by the acquisition unit; a positive electrode capacity deterioration coefficient α indicating a degree of deterioration of a positive electrode capacity of the secondary battery, a negative electrode capacity deterioration coefficient β indicating a degree of deterioration of a negative electrode capacity, and a capacity deviation amount γ indicating a deviation amount between the positive and negative electrode capacities, based on a difference between the initial OCV curve and the OCV curve after deterioration.

5. The degradation state estimating device according to claim 4, The degradation state estimation unit calculating an estimated positive electrode OCP value of the secondary battery based on the initial OCV curve, the post-degradation OCV curve, the negative electrode capacity degradation coefficient β, and the capacity deviation amount γ; The degradation state estimation device calculates the post-degradation battery characteristics based on either one of the measured positive electrode OCP value of the secondary battery and the estimated positive electrode OCP value.

6. The degradation state estimating device according to claim 4 or 5, the initial data includes data on an initial positive electrode capacity indicating a positive electrode capacity of the secondary battery in an initial state of the secondary battery, The degradation state estimation unit an OCV at the start and end of charging / discharging is within a range of an upper and lower limit voltage of the secondary battery, and an integrated value of the current acquired by the acquisition unit is calculated as the integrated current value; The positive electrode OCP is calculated as a value obtained by multiplying the initial positive electrode capacity by the positive electrode capacity deterioration coefficient α, The degradation state estimation device calculates the post-degradation battery characteristics based on the current integration value and the positive electrode OCP. 　 The degradation state estimating device according to any one of claims 1 to 6, The degradation state estimation unit a degradation state estimation device that estimates a degree of degradation of the positive electrode based on a difference between the post-degradation battery characteristics and the initial battery characteristics within a range in which a difference between the positive electrode OCP in the initial state and the positive electrode OCP after the degradation at each SOC is equal to or greater than a predetermined OCP threshold. 　 A degradation state estimation method for estimating a degradation state of a secondary battery, executed by a processor, comprising: The processor: Acquire the current and voltage of the secondary battery; calculating an integrated current value and a positive electrode OCP of the secondary battery after deterioration based on the current and voltage of the secondary battery; A degradation state estimation method for estimating a degree of positive electrode degradation of the secondary battery based on a difference between post-degradation battery characteristics indicating the relationship between the current integrated value and the positive electrode OCP of the secondary battery after the degradation and initial battery characteristics indicating the relationship between the current integrated value and the positive electrode OCP of the secondary battery in an initial state.

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