Method and device for calculating DC resistance of battery

Abstract

In the present invention, when calculating the DC resistance of a lithium secondary battery (20) by linear regression on the basis of currents and voltages measured at a plurality of measurement points of the lithium secondary battery in which a positive electrode layer, an electrolyte layer containing a solid electrolyte, and a negative electrode layer are laminated in this order, the quantity of change in the DC resistance corresponding to the change in pressure applied to the lithium secondary battery (20) between the plurality of measurement points is estimated, and correction using the quantity of change in the DC resistance is performed in the calculation of the DC resistance by linear regression.

Description

Battery DC resistance calculation method and calculation device

[0001] The present invention relates to a method and device for calculating the DC resistance of a battery.

[0002] A deterioration level estimation device is known that calculates the final remaining capacity of a battery from a first remaining capacity based on an integrated value of charge / discharge current and a second remaining capacity based on open-circuit voltage, determines the timing to acquire voltage and current data using at least one of a hysteresis function that represents the degree of fluctuation in open-circuit voltage and the deviation between the final remaining capacity and the second remaining capacity, calculates the internal resistance of the battery from the acquired voltage and current data, and estimates the deterioration level of the battery from the rate of increase in the internal resistance (Patent Document 1).

[0003] Patent No. 4638195

[0004] In a lithium secondary battery in which a positive electrode layer, an electrolyte layer containing a solid electrolyte, and an anode layer are stacked in this order, pressure is applied in the stacking direction of the battery cell to ensure close contact between the electrolyte layer and the positive electrode layer and the negative electrode layer. The above-mentioned conventional technology has a problem in that it is not possible to accurately calculate the DC resistance of the lithium secondary battery when this pressure changes.

[0005] The problem to be solved by the present invention is to provide a calculation method and a calculation device that can accurately determine the DC resistance of a lithium secondary battery.

[0006] The present invention solves the above problem by estimating the amount of change in DC resistance corresponding to a change in pressure applied to the lithium secondary battery between the multiple measurement points when calculating the DC resistance of the lithium secondary battery by linear regression based on the current and voltage measured at multiple measurement points of the lithium secondary battery in which a positive electrode layer, an electrolyte layer containing a solid electrolyte, and a negative electrode layer are laminated in this order, and performing correction using the amount of change in DC resistance in the calculation of the DC resistance by linear regression.

[0007] According to the present invention, the DC resistance of a lithium secondary battery can be accurately determined.

[0008] 4 is a block diagram showing an example of an embodiment of a battery control system according to the present invention. FIG. 4 is a diagram showing an example of calculation of open-circuit voltage and DC resistance by linear regression. FIG. 5 is a diagram showing an example of the relationship between the charging rate and DC resistance when the pressure applied to the lithium secondary battery of FIG. 1 is constant. FIG. 6 is a diagram showing an example of the relationship between the pressure applied to the lithium secondary battery of FIG. 1 and DC resistance. FIG. 7 is a diagram showing an example of pressure control by the pressure mechanism and actuator of FIG. 1. FIG. 8 is a diagram showing an example of pressure change and the amount of change in DC resistance in the relationship between pressure and DC resistance of FIG. 4. FIG. 9 is a flowchart showing an example of a processing procedure in the battery control system of FIG. 1. FIG. 10 is a flowchart showing another example of the processing procedure for pressure change calculation of the present embodiment. FIG. 11 is a flowchart showing yet another example of the processing procedure for pressure change calculation of the present embodiment. FIG. 12 is a flowchart showing yet another example of the processing procedure for pressure change calculation of the present embodiment. FIG. 13 is a flowchart showing an example of a range in which correction of the present embodiment is performed. FIG. 14 is a diagram showing another example of a range in which correction of the present embodiment is performed. FIG. 15 is a diagram showing an example of a first predetermined pressure of the present embodiment. FIG. 16 is a diagram showing another example of the first predetermined pressure of the present embodiment. FIG. 17 is a diagram showing yet another example of a range in which correction of the present embodiment is performed.

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] [Configuration of Battery Control System] Fig. 1 is a block diagram showing an example of an embodiment of a battery control system according to the present invention. The battery control system is a group of devices that estimate the state of charge (hereinafter also referred to as SOC) and state of health (hereinafter also referred to as SOH) of a battery (e.g., a lithium secondary battery including an all-solid-state battery) and appropriately manage the battery. The state of charge is also referred to as the state of charge, and the state of health is also referred to as the health level or capacity maintenance rate. The capacity maintenance rate is the ratio of the current battery capacity to the battery capacity in the initial state.

[0011] 1, the battery control system 10 includes a voltage sensor 11, a current sensor 12, an inverter 13, a computing device 14, and a lithium secondary battery 20. The lithium secondary battery 20 includes a battery cell 21, a pressure sensor 22, a pressurizing mechanism 23, and an actuator 24. The actuator 24 is an example of a pressure control device of this embodiment.

[0012] The voltage sensor 11 detects the voltage between the terminals of the lithium secondary battery 20. The voltage sensor 11 is connected between the wiring that is connected to the positive and negative electrodes of the lithium secondary battery 20.

[0013] The current sensor 12 detects the input / output current of the lithium secondary battery 20. The input / output current is at least one of the current flowing into the lithium secondary battery 20 and the current flowing out of the lithium secondary battery 20. The current sensor 12 is connected to a wiring connected to the positive electrode or the negative electrode of the lithium secondary battery 20.

[0014] Inverter 13 adjusts the input / output current and the voltage between the terminals of lithium secondary battery 20 when charging lithium secondary battery 20 or when discharging lithium secondary battery 20. Inverter 13 includes a circuit for adjusting the current and voltage, and performs the adjustment based on a command from computing device 14. For example, inverter 13 is provided on the wiring connecting the positive electrode of lithium secondary battery 20 and current sensor 12, and smoothes the current flowing into current sensor 12.

[0015] The arithmetic device 14 is a device that controls and cooperates with the devices that make up the battery control system 10 and manages the state of the lithium secondary battery 20. The arithmetic device 14 is, for example, a computer, and includes a CPU (Central Processing Unit) that is a processor, a ROM (Read Only Memory) that stores programs, and a RAM (Random Access Memory) that functions as an accessible storage device. The CPU is an operating circuit that executes the programs stored in the ROM and realizes the functions of the arithmetic device 14.

[0016] The lithium secondary battery 20 is a battery module formed by stacking multiple battery cells 21, and is electrically connected to a load (not shown) such as a motor. The load is a device that operates using the power from the lithium secondary battery 20, such as a motor that drives a vehicle, and auxiliary equipment such as an air conditioner and lights. The computing device 14 controls the discharge of the lithium secondary battery 20 in response to requests from external devices, etc.

[0017] The battery cell 21 has at least a positive electrode layer, a negative electrode layer, and an electrolyte layer. The positive electrode layer contains a positive electrode active material that releases and stores alkali metals such as lithium (Li), sodium (Na), and potassium (K). The positive electrode layer contains a positive electrode active material, a conductive additive, and a binder. The positive electrode active material is LiMn ２ O ４ Examples of the conductive additive include lithium-transition metal composite oxides such as those mentioned above, which may contain sulfur. Examples of the conductive additive include acetylene black, carbon black, and graphite. Examples of the binder include polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), and polyimide. The positive electrode layer is produced, for example, by applying a mixture of a positive electrode active material, a conductive additive, a binder, and the like to a current collector, followed by drying and rolling.

[0018] The negative electrode layer includes a negative electrode active material, a conductive additive, a binder, and the like. Examples of the negative electrode active material include graphite-based carbon materials (graphite-based), hard carbon (non-graphitizable carbon materials), and lithium-transition metal composite oxides. The negative electrode active material may be, for example, any material containing lithium, and may also contain lithium metal or a lithium alloy. The conductive additive and binder are the same as those for the positive electrode layer. The negative electrode layer, like the positive electrode layer, is produced by applying a mixture of a negative electrode active material, a conductive additive, a binder, and the like to a current collector, followed by drying and rolling.

[0019] The electrolyte layer is a layer in which an electrolyte is held in a separator (not shown). It is disposed between the positive electrode layer and the negative electrode layer and prevents direct contact between them. The separator has the function of holding the electrolyte to ensure ionic conductivity between the positive electrode layer and the negative electrode layer and the function of acting as a partition wall between the positive electrode layer and the negative electrode layer. Examples of the separator include a porous sheet separator made of a polymer or fiber that absorbs and holds the electrolyte, and a nonwoven fabric separator. The electrolyte is not particularly limited, and examples include an electrolytic solution or a gel polymer electrolyte. The electrolyte may also include a solid electrolyte such as a sulfide solid electrolyte or an oxide solid electrolyte.

[0020] In the battery cell 21, a positive electrode layer, an electrolyte layer, and a negative electrode layer are stacked in this order. That is, in the battery cell 21, the electrolyte layer is disposed between the positive electrode layer and the negative electrode layer, and the positive electrode layer and the negative electrode layer sandwich the electrolyte layer. For example, the positive electrode layers and the negative electrode layers are stacked alternately with the electrolyte layer interposed therebetween, and further, the electrolyte layer is stacked on the top and bottom layers, respectively.

[0021] The battery cells 21 have a flat shape and are sealed with an exterior member with tabs connected to a laminate including a positive electrode layer, a negative electrode layer, and an electrolyte layer. The stacked battery cells 21 are connected to each other by bus bars (not shown). In the lithium secondary battery 20 shown in FIG. 1 , the battery cells 21 are stacked along the x-axis direction, and the surface along the yz plane is the main surface of the battery cell 21. Hereinafter, the direction in which the battery cells 21 are stacked (the x-axis direction in FIG. 1 ) is also referred to as the stacking direction.

[0022] The pressure sensor 22 is provided along the main surface of the battery cell 21 and measures the pressure on the main surface. The pressure sensor 22 may measure the pressure on the entire main surface of the battery cell 21, or may measure the pressure at at least one measurement point on the main surface. The computing device 14 acquires pressure information from the pressure sensor 22 at predetermined time intervals (for example, every 0.1 to 1 millisecond).

[0023] The pressure mechanism 23 presses the multiple battery cells 21 in the stacking direction with the end plates 23a, applying pressure to the lithium secondary battery 20. The position of the end plates 23a in the x-axis direction is controlled by the actuator 24. That is, the computing device 14 operates the actuator 24 to control the pressure (hereinafter simply referred to as pressure) applied to the lithium secondary battery 20 (battery cells 21) in the stacking direction. Examples of the actuator 24 include a servo motor, a hydraulic motor, and a hydraulic cylinder.

[0024] The pressure mechanism 23 is not limited to the one shown in Fig. 1. For example, the pressure mechanism 23 may not have the actuator 24, but may instead restrain the multiple battery cells 21 using the elastic force of an elastic body such as rubber. Also, a jack may be used instead of the actuator 24, and a plate that moves using a feed screw may be used instead of the end plate 23a.

[0025] [Function of Calculation Device] A program for managing the lithium secondary battery 20 is stored in the ROM of the calculation device 14, and the CPU of the calculation device 14 executes the program to perform processing related to management of the lithium secondary battery 20. As part of this processing, the calculation device 14 estimates the direct current resistance (hereinafter also referred to as DCR) of the lithium secondary battery 20 in order to estimate the degradation state of the lithium secondary battery 20.

[0026] The calculation device 14 calculates the DC resistance by at least one of map calculation using a map showing the relationship between DC resistance, state of charge, and temperature, and extrapolation by linear regression. An example of calculation of the DC resistance of the lithium secondary battery 20 by linear regression is shown in Figure 2. The DC resistance is also called the internal resistance of the battery.

[0027] In the example shown in FIG. 2, the current value I １ is acquired, and the voltage value V １ At the second measurement point M2, the current value I １ Larger current value I ２ is acquired, and the voltage value V １The smaller voltage value V ２ In this case, the DC resistance of the lithium secondary battery 20 is assumed to be R Ｂ The electromotive forces of the lithium secondary battery 20 at the first measurement point M1 and the second measurement point M2 are respectively defined as E １ and E ２ Then, the following equations (1) and (2) hold at each measurement point.

[0028] V １ = E １ -I １ ×R Ｂ ... (1) V ２ = E ２ -I ２ ×R Ｂ ... (2)

[0029] Electromotive force E １ , E ２ is equal to the open circuit voltage (hereinafter also referred to as OCV) of the lithium secondary battery 20, the formulas (1) and (2) can be rewritten as the following formulas (3) and (4).

[0030] V １ =OCV-I １ ×R Ｂ ... (3) V ２ =OCV-I ２ ×R Ｂ ... (4)

[0031] By subtracting both sides of equation (3) and equation (4), the following equation (5) is obtained.

[0032] V １ -V ２ = (I ２ -I １ ) x R Ｂ ... (5)

[0033] That is, the DC resistance of the lithium secondary battery 20 is R Ｂ corresponds to the slope of the line L1 shown in FIG. 2, and the open-circuit voltage of the lithium secondary battery 20 is the intercept of the vertical axis of the line L1 (V ０ )

[0034] The DC resistance of the lithium secondary battery 20 depends on the temperature and charging rate of the lithium secondary battery 20. Figure 3 is a graph showing an example of the relationship between the charging rate and DC resistance when a constant pressure is applied to the lithium secondary battery 20. Figure 3 shows lines L2 to L6 that indicate the relationship between the charging rate and DC resistance at five different temperatures. As shown in Figure 3, when the pressure is constant, the lower the charging rate, the higher the DC resistance value.

[0035] Furthermore, the DC resistance value increases as the temperature decreases. Among lines L2 to L6 shown in Figure 3, line L2 shows the relationship between the charging rate and DC resistance at the highest temperature, and line L6 shows the relationship between the charging rate and DC resistance at the lowest temperature. In other words, as the temperature decreases, the DC resistance value shifts in the direction of arrow A1.

[0036] Furthermore, in the lithium secondary battery 20, the value of DC resistance changes depending on the pressure state of the pressure mechanism 23 (the pressure applied in the stacking direction of the lithium secondary battery 20). Fig. 4 is a graph showing an example of the relationship between the pressure applied to the lithium secondary battery 20 and the DC resistance. Fig. 3 shows lines L7 to L10 that indicate the relationship between the pressure and the DC resistance at four different charging rates (or temperatures). As shown in Fig. 4, when the charging rate (or temperature) is constant, the lower the pressure, the higher the DC resistance.

[0037] Furthermore, the DC resistance value increases as the temperature decreases and as the charging rate decreases. Therefore, among lines L7 to L10 shown in Figure 4, line L7 shows the relationship between pressure and DC resistance at the highest charging rate (or temperature), and line L10 shows the relationship between pressure and DC resistance at the lowest charging rate (or temperature). In other words, as at least one of the charging rate and temperature decreases, the DC resistance value shifts in the direction of arrow A2.

[0038] In the linear regression calculation shown in Figure 2, if the pressure changes between the first measurement point M1 and the second measurement point M2, the DC resistance (= the slope of the line L1) at each measurement point changes, and the DC resistance cannot be determined by linear regression. Furthermore, due to the structure of the lithium secondary battery 20, it is often difficult to install a pressure sensor 22 on the lithium secondary battery 20, and the displacement of the battery cell 21 itself is small, making it difficult to accurately estimate pressure changes from the displacement of the lithium secondary battery 20 (battery cell 21). Furthermore, there are various configurations of the pressure mechanism 23 and the actuator 24, and the pressure change characteristics differ depending on the configuration.

[0039] Fig. 5 is a diagram showing an example of pressure control by the pressure mechanism 23 and the actuator 24. For example, if the lithium secondary battery 20 does not have the actuator 24 and the multiple battery cells 21 are constrained by the elastic force of the elastic body (pressure mechanism 23), the higher the charge rate, the thicker the negative electrode becomes and the higher the pressure becomes, so that the pressure increases as the charge rate increases, as shown by line L11 in Fig. 5. In this case, the amount of change in surface pressure can be estimated from the charge / discharge amount of the lithium secondary battery 20, so the pressure change is estimated from the change in the integrated current value or the charge rate.

[0040] On the other hand, if the lithium secondary battery 20 has an actuator 24, the pressure change can be controlled by the amount of operation of the actuator 24. In this case, it is possible to control the pressure so that it increases as the charging rate increases (line L12), to control the pressure so that it remains constant regardless of the charging rate (line L13), or to control the pressure so that it decreases as the charging rate increases (line L14).

[0041] As described above, it is necessary to correct the DC resistance according to the pressurized state of the lithium secondary battery 20. Furthermore, a method for correcting the DC resistance when pressure changes cannot be detected accurately and a correction method according to the configurations of the pressurizing mechanism 23 and the actuator 24 are also required. Therefore, when calculating the DC resistance of the lithium secondary battery 20 by linear regression based on the current and voltage of the lithium secondary battery 20 measured at multiple measurement points, the calculation device 14 of this embodiment actually measures or estimates the pressure change between the multiple measurement points. Then, it estimates the amount of change in DC resistance according to the pressure change, and performs correction using the amount of change in DC resistance in the calculation of the DC resistance by linear regression.

[0042] A measurement point is a point corresponding to a pair of a voltage value measured by voltage sensor 11 and a current value measured by current sensor 12, and is a point on a coordinate system (e.g., a Cartesian coordinate system) in which the horizontal axis represents the current value and the vertical axis represents the voltage value. Calculation device 14 measures the voltage value and current value of lithium secondary battery 20 at least twice to generate at least two measurement points. That is, calculation device 14 executes the process of acquiring the voltage value from voltage sensor 11 and the current value from current sensor 12 multiple times.

[0043] When calculating the DC resistance of the lithium secondary battery 20 using linear regression, the calculation device 14 determines an approximate line that shows the relationship between current and voltage, with the current as the independent variable and the voltage as the dependent variable. The slope of this approximate line corresponds to the DC resistance, and the intercept on the vertical axis corresponds to the open-circuit voltage. In the example shown in Figure 2, the DC resistance was calculated using only two points, the first measurement point M1 and the second measurement point M2. However, the number of measurement points is not particularly limited as long as it is two or more, and may be three or more.

[0044] When calculating the DC resistance of the lithium secondary battery 20 using linear regression, the calculation device 14 measures or estimates the pressure change between multiple measurement points. When actually measuring the pressure change, the calculation device 14 calculates the pressure change based on the pressure acquired from the pressure sensor 22. For example, the calculation device 14 calculates the pressure change by comparing the pressure value when a measurement corresponding to one measurement point is performed with the pressure value when a measurement corresponding to another measurement point is performed. On the other hand, when estimating the pressure change, the calculation device 14 estimates the pressure change from the amount of movement of the end plate 23a, the amount of operation of the actuator 24, the amount of displacement of the battery cell 21, etc.

[0045] When two measurement points are generated, the calculation device 14 uses one of the measurement points as a reference and calculates the pressure change from when a measurement corresponding to one measurement point is performed until when a measurement corresponding to the other measurement point is performed. When three or more measurement points are generated, one measurement point is set as a reference and the calculation device 14 calculates the pressure change from when a measurement corresponding to one measurement point is performed until when a measurement corresponding to any of the other measurement points is performed.

[0046] When estimating the change in DC resistance in response to a pressure change, the calculation device 14 uses a previously determined relationship between the pressure change and the change in DC resistance. For example, the calculation device 14 estimates the change in DC resistance from the pressure change using information such as a graph showing the characteristics of DC resistance as shown in FIG. 4 and a map used in the map calculation of DC resistance. The calculation device 14 then uses the change in DC resistance to perform correction when calculating the DC resistance by linear regression. That is, the calculation device 14 corrects the DC resistance calculated by linear regression using information about the DC resistance characteristics of the lithium secondary battery 20.

[0047] 6 is a diagram showing an example of a change in pressure applied to the lithium secondary battery 20 and a change in DC resistance. In the example shown in FIG. 6, it is assumed that the pressure applied to the lithium secondary battery 20 changes from pressure Pa to pressure Pb between the first measurement point M1 and the second measurement point M2 in FIG. 2. In this case, the pressure change ΔP is Pb−Pa. Furthermore, since the DC resistance at the first measurement point M1 is Ra and the DC resistance at the second measurement point M2 is Rb, the change ΔR in DC resistance corresponding to the pressure change ΔP is Rb−Ra.

[0048] A positive value of the pressure change ΔP indicates an increase in pressure between the two measurement points, and a negative value of the pressure change ΔP indicates a decrease in pressure between the two measurement points. Also, a positive value of the change in DC resistance ΔR indicates an increase in DC resistance between the two measurement points, and a negative value of the change in DC resistance ΔR indicates a decrease in DC resistance between the two measurement points.

[0049] As shown in the example of Figure 6, when linear regression is calculated at two measurement points, if the pressure changes between the measurement points, a term corresponding to the change in DC resistance is added to equation (5) for calculating the DC resistance, and the DC resistance is corrected. Ｂ１ The DC resistance between the first measurement point M1 and the second measurement point M2 is ΔR １２ , the equations (3) and (4) can be rewritten as follows:

[0050] V１ =OCV-I １ ×R Ｂ１ ... (6) V ２ =OCV-I ２ × (R Ｂ１ +ΔR １２ ) ... (7)

[0051] By subtracting both sides of equation (6) and equation (7), the following equation (8) is obtained.

[0052] V １ -V ２ = (I ２ -I １ ) x R Ｂ１ +I ２ ×ΔR １２ ... (8)

[0053] Formula (8) "I ２ ×ΔR １２ " is a correction term for the DC resistance, and when correcting the DC resistance, the calculation device 14 corrects the calculated DC resistance R Ｂ１ From "(I ２ ×ΔR １２ ) / (I ２ -I １ This allows the change in DC resistance with respect to the pressure change between the measurement points to be calculated based on the relationship between pressure and DC resistance (characteristics of DC resistance).

[0054] 7 is a flowchart showing an example of a processing procedure executed in the battery control system 10. The processing described below is executed by a processor (CPU) included in the arithmetic device 14 at predetermined time intervals (for example, every 0.1 to 1 millisecond).

[0055] First, in step S1, the arithmetic device 14 determines whether or not to perform linear regression based on the current value and temperature of the lithium secondary battery 20. If it is determined that linear regression is to be performed, the process proceeds to step S2, where the arithmetic device 14 measures the voltage value using the voltage sensor 11, the current value using the current sensor 12, and the pressure using the pressure sensor 22. On the other hand, if it is determined that linear regression is not to be performed, the process proceeds to step S3.

[0056] In step S3, the calculation device 14 determines whether or not to perform correction based on the measured pressure. If it is determined that correction is not to be performed, the process ends. On the other hand, if it is determined that correction is to be performed, the process proceeds to step S4. In step S4, the calculation device 14 obtains the pressure change between the two measurement points from the pressure measured by the pressure sensor 22. Alternatively, the calculation device 14 estimates the pressure change due to a change in thickness of the lithium secondary battery 20 (battery cell 21) based on the charge / discharge amount between the two measurement points.

[0057] In the next step S5, the calculation device 14 calculates the amount of change in DC resistance in response to the pressure change, and in step S6, calculates a correction amount (for example, "(I ２ ×ΔR １２ ) / (I ２ -I １ Then, in step S7, the calculation device 14 performs correction using the correction amount to calculate the DC resistance. Thereafter, the process ends. [Other Embodiments]

[0058] When estimating the pressure change, the calculation device 14 may estimate the pressure change based on the charge / discharge amount between two of the multiple measurement points. By estimating the pressure change according to the change in thickness of the lithium secondary battery 20 (battery cell 21) due to the charge / discharge amount, the pressure change can be estimated with high accuracy even when the pressure sensor 22 cannot detect the pressure change with high accuracy.

[0059] 8 is a flowchart showing an example of a procedure for calculating pressure changes executed in the battery control system 10. The process described below is executed by a processor (CPU) included in the calculation device 14 at predetermined time intervals (for example, every 0.1 to 1 millisecond).

[0060] First, in step S11 of FIG. 8 , the calculation device 14 determines whether or not a linear regression calculation is being performed. If it is determined that a linear regression calculation is being performed, the process proceeds to step S12, where the integration of the charge / discharge current is started. If it is determined that a linear regression calculation is not being performed, the process proceeds to step S13, where the integration of the charge / discharge current is ended. That is, the calculation device 14 starts the integration of the charge / discharge current in the first measurement, and ends the integration and resets the integrated value in the second measurement. In step S14, the calculation device 14 calculates (estimates) the pressure change due to the charge / discharge amount. Characteristic data for the change in thickness of the lithium secondary battery 20 due to the charge / discharge amount can be obtained experimentally in advance.

[0061] 9 is a flowchart showing another example of the procedure for calculating pressure changes executed in the battery control system 10. Note that explanations of steps that overlap with those in the flowchart shown in FIG.

[0062] If it is determined in step S11 that a linear regression calculation is being performed, the process proceeds to step S21. In step S21, the calculation device 14 acquires from the voltage sensor 11 the voltage at the start of the linear regression calculation, and in the subsequent step S22, calculates (estimates) the charging rate at the start of the linear regression calculation. On the other hand, if it is determined in step S11 that a linear regression calculation is not being performed, the process proceeds to step S23. In step S23, the calculation device 14 acquires from the voltage sensor 11 the voltage at the end of the linear regression calculation, and in the subsequent step S24, calculates (estimates) the charging rate at the end of the linear regression calculation.

[0063] The characteristic data of the voltage and charging rate of the lithium secondary battery 20 is experimentally obtained in advance. In steps S21 to S24, the charging rate at the first measurement point is calculated in the first measurement, and the charging rate at the second measurement point is calculated in the second measurement, and the charge / discharge amount is calculated from the change in the charging rate between the two measurement points.

[0064] When estimating a pressure change, the calculation device 14 may estimate the pressure change from the operation amount of the actuator 24 (pressure control device) that controls the pressure. This makes it possible to accurately estimate the pressure change between measurement points when the pressure change cannot be accurately detected by the pressure sensor 22. Examples of the operation amount of the actuator 24 include the rotation amount of the motor, the rotation amount of the feed screw, and the change in length of the hydraulic cylinder.

[0065] 10 is a flowchart showing another example of the procedure for calculating pressure changes executed in the battery control system 10. Note that explanations of steps that overlap with the flowcharts shown in FIGS.

[0066] After step S12, in step S31, the calculation device 14 acquires the movement amount of the actuator 24 at the start of the linear regression calculation, and proceeds to step S 14. On the other hand, after step S13, in step S32, the calculation device 14 acquires the movement amount of the actuator 24 at the end of the linear regression calculation, and proceeds to step S 14. Also, after step S14, in step S33, the calculation device 14 calculates (estimates) the pressure change caused by the pressurizing mechanism 23.

[0067] The pressure mechanism 23 is composed of a hydraulic pump, a screw feed mechanism using a stepping motor, etc. For example, since the pressure changes depending on the step position of the stepping motor, the pressure change caused by the pressure mechanism 23 can be estimated from the change in step position between measurement points. Furthermore, characteristic data on the change in pressure depending on the step position can be obtained in advance.

[0068] Figure 11 is a flowchart showing yet another example of the processing procedure for calculating pressure changes executed in the battery control system 10. In the flowchart shown in Figure 11, step S31 is provided between step S22 and step S14 in the flowchart shown in Figure 9, step S32 is provided between step S24 and step S14, and step S33 is provided after step S14. The steps in the flowchart shown in Figure 11 overlap with those in the flowcharts shown in Figures 8 to 10, and similar processing is performed, so a description of the processing in each step will be omitted.

[0069] The calculation device 14 may perform correction when the pressure is equal to or lower than a first predetermined pressure. That is, the calculation device 14 corrects the DC resistance in a pressure range where the change in DC resistance is large. Figure 12 is a diagram showing an example of the first predetermined pressure P1, in which no correction is performed in the range to the right of the first predetermined pressure P1, and correction is performed in the range to the left of the first predetermined pressure P1. The first predetermined pressure P1 can be set to an appropriate value within a range in which the DC resistance can be appropriately corrected, for example, 2 MPa.

[0070] The first predetermined pressure may be higher as the charging rate of the lithium secondary battery 20 is lower and as the temperature of the lithium secondary battery 20 is lower. This is to correct the DC resistance when the change in DC resistance increases due to a low charging rate and a low temperature. FIG. 13 shows the relationship between the first predetermined pressure P1 and the charging rate. Lines L16 to L18, which show the characteristics of the first predetermined pressure P1, indicate that the lower the charging rate, the higher the first predetermined pressure P1, and the higher the charging rate, the lower the first predetermined pressure P1. Furthermore, because the lower the temperature of the lithium secondary battery 20, the lower the first predetermined surface pressure P1 is set, the lower the first predetermined surface pressure P1 shifts from line L16 to line L18 (in the direction of arrow A5) as the temperature decreases.

[0071] For example, when the first predetermined surface pressure P1 indicated by the line L16 is plotted on the graph shown in Fig. 13, the first predetermined surface pressure P1 is represented by a straight line Lp shown in Fig. 14. No correction is made in the range to the right of the line Lp (the side of the arrow A3), but correction is made in the range to the left of the line Lp (the side of the arrow A4).

[0072] Furthermore, the first predetermined pressure may be higher as the charge rate of the lithium secondary battery 20 decreases when the charge rate is less than 50%, and may be higher as the charge rate increases when the charge rate is 50% or higher. FIG. 15 is a graph showing an example of a first predetermined pressure whose characteristics change at a charge rate of 50%. Lines L19 to L21 showing the characteristics of the first predetermined pressure P1 have a downwardly convex shape with an inflection point at the 50% charge rate, allowing DC resistance correction even for a lithium secondary battery 20 whose characteristics change depending on the charge rate. Furthermore, since the first predetermined pressure P1 is set higher as the temperature of the lithium secondary battery 20 decreases, the first predetermined surface pressure P1 shifts from line L19 to line L21 (in the direction of arrows A6 and A7) as the temperature decreases.

[0073] When the pressure is equal to or lower than the first predetermined pressure, the calculation device 14 may decrease the current measured at the measurement point as the pressure decreases. The smaller the current, the smaller the charge / discharge amount and the less the thickness of the battery cell 21 changes, thereby reducing errors in the DC resistance.

[0074] When the pressure is equal to or lower than the first predetermined pressure, the calculation device 14 may shorten the interval at which the current and voltage are measured as the pressure decreases. By shortening the time interval between measurements between measurement points, changes in the pressure and temperature of the lithium secondary battery 20 can be suppressed, and errors in the DC resistance can be suppressed.

[0075] When the pressure is equal to or lower than a first predetermined pressure, the calculation device 14 may reduce the amount of movement of the actuator 24 (pressure control device) that controls the pressure while measuring the current and voltage, as the pressure decreases. By reducing the pressure change, errors in the DC resistance can be suppressed.

[0076] The calculation device 14 does not need to perform correction when the pressure is equal to or lower than a second predetermined pressure P2, which is lower than the first predetermined pressure P1. This is because the error in linear regression calculation increases in the low pressure range where the change in DC resistance increases. FIG. 16 shows an example of the second predetermined pressure, and correction is not performed in the range to the left of the second predetermined pressure P2. In this range, for example, DC resistance is calculated using map calculation instead of linear regression calculation. In FIG. 17, correction in linear regression calculation is performed in the range to the right of the second predetermined pressure P2 and to the left of the line Lp (arrow A4 side). The second predetermined pressure P2 can be set to an appropriate value within a range in which DC resistance correction can be appropriately performed, such as 0.5 MPa.

[0077] According to the present embodiment, there is provided a method for calculating the DC resistance of a lithium secondary battery 20, which is formed by stacking a positive electrode layer, an electrolyte layer containing a solid electrolyte, and an anode layer in this order, and which is executed by a computing device 14 that calculates the DC resistance of the lithium secondary battery 20 by linear regression based on currents and voltages measured at a plurality of measurement points of the lithium secondary battery 20, wherein the computing device 14 actually measures or estimates changes in pressure applied to the lithium secondary battery 20 between the plurality of measurement points, estimates an amount of change in the DC resistance corresponding to the pressure change, and performs correction using the amount of change in the calculation of the DC resistance by linear regression. This allows the DC resistance of the lithium secondary battery 20 to be accurately determined.

[0078] In the calculation method of this embodiment, the calculation device 14 estimates the pressure change based on the charge / discharge amount between two of the plurality of measurement points, thereby enabling the pressure change to be estimated with high accuracy.

[0079] In the calculation method of this embodiment, the calculation device 14 estimates the pressure change from the operation amount of a pressure control device that controls the pressure, thereby enabling the pressure change to be estimated with high accuracy.

[0080] In the calculation method of this embodiment, the correction is performed when the pressure is equal to or lower than a first predetermined pressure, thereby making it possible to perform correction within a pressure range in which the amount of change in DC resistance is large.

[0081] In the calculation method of this embodiment, the first predetermined pressure is higher as the charging rate of the lithium secondary battery 20 is lower and as the temperature of the lithium secondary battery 20 is lower. This allows correction when the amount of change in DC resistance is large due to a low charging rate and a low temperature.

[0082] In the calculation method of this embodiment, when the state of charge of the lithium secondary battery 20 is less than 50%, the lower the state of charge, the higher the first predetermined pressure, and when the state of charge is 50% or higher, the higher the state of charge, the higher the first predetermined pressure. This makes it possible to correct the DC resistance even for lithium secondary batteries 20 whose characteristics change depending on the state of charge.

[0083] In the calculation method of this embodiment, when the pressure is equal to or lower than the first predetermined pressure, the current measured at the measurement point is made smaller as the pressure becomes lower, thereby reducing errors in the calculation of the DC resistance.

[0084] In the calculation method of this embodiment, when the pressure is equal to or lower than the first predetermined pressure, the interval at which the current and the voltage are measured is shortened as the pressure decreases, thereby reducing errors in the calculation of the DC resistance.

[0085] In the calculation method of this embodiment, when the pressure is equal to or lower than the first predetermined pressure, the amount of operation of the pressure control device that controls the pressure while the current and the voltage are measured is reduced as the pressure becomes lower, thereby suppressing errors that occur in the calculation of the DC resistance.

[0086] In the calculation method of this embodiment, the correction is not performed when the pressure is equal to or lower than a second predetermined pressure that is lower than the first predetermined pressure, thereby making it possible to accurately determine the DC resistance of the lithium secondary battery 20.

[0087] Furthermore, according to the present embodiment, there is provided a battery DC resistance calculation device 14 that calculates the DC resistance of a lithium secondary battery 20 by linear regression based on currents and voltages measured at a plurality of measurement points of the lithium secondary battery 20, which is made up of a positive electrode layer, an electrolyte layer containing a solid electrolyte, and a negative electrode layer stacked in this order, the calculation device 14 actually measuring or estimating changes in pressure applied to the lithium secondary battery 20 between the plurality of measurement points, estimating the amount of change in the DC resistance corresponding to the pressure change, and performing correction using the amount of change in the calculation of the DC resistance by linear regression. This allows the DC resistance of the lithium secondary battery 20 to be accurately determined.

[0088] 10... Battery control system, 11... Voltage sensor, 12... Current sensor, 13... Inverter, 14... Calculation device, 20... Lithium secondary battery, 21... Battery cell, 22... Pressure sensor, 23... Pressurization mechanism, 23a... End plate, 24... Actuator (pressure control device), A1, A2, A3, A4, A5, A6, A7, A8, A9, A10... Arrows, I １ , I ２ ...current value, L1, Lp...lines, L2, L3, L4, L5, L6, L7, L8, L9, L10, L11, L12, L13, L14, L15, L16, L17, L18, L19, L20, L21...lines, M1...first measurement point, M2...second measurement point, Pa, Pb...pressure, P1...first predetermined pressure, P2...second predetermined pressure, R Ｂ , R Ｂ１ , Ra, Rb...DC resistance, V ０ …open circuit voltage (OCV), V １ , V ２ ...voltage value, ΔP...pressure change, ΔR, ΔR １２ …Change in DC resistance

Claims

1. A method for calculating the DC resistance of a lithium secondary battery, which is made by linear regression based on the current and voltage measured at multiple measurement points of the lithium secondary battery, which is made up of a positive electrode layer, an electrolyte layer containing a solid electrolyte, and a negative electrode layer stacked in this order, the method comprising: actually measuring or estimating changes in pressure applied to the lithium secondary battery between the multiple measurement points; estimating the amount of change in the DC resistance corresponding to the pressure change; and performing correction using the amount of change in the calculation of the DC resistance by linear regression.

2. The calculation method according to claim 1, wherein the pressure change is estimated based on the amount of charge and discharge between two of the plurality of measurement points.

3. The calculation method according to claim 1 or 2, wherein the pressure change is estimated from the operating amount of a pressure control device that controls the pressure.

4. The calculation method according to any one of claims 1 to 3, wherein the correction is performed when the pressure is equal to or lower than a first predetermined pressure.

5. The calculation method according to claim 4, wherein the first predetermined pressure is higher as the charging rate of the lithium secondary battery is lower and as the temperature of the lithium secondary battery is lower.

6. The calculation method according to claim 4, wherein the first predetermined pressure is higher the lower the charging rate of the lithium secondary battery is when the charging rate is less than 50%, and higher the higher the charging rate is when the charging rate is 50% or higher.

7. A calculation method according to any one of claims 4 to 6, wherein, when the pressure is equal to or lower than the first predetermined pressure, the current measured at the measurement point is made smaller as the pressure becomes lower.

8. A calculation method according to any one of claims 4 to 7, wherein, when the pressure is equal to or lower than the first predetermined pressure, the interval at which the current and the voltage are measured is shortened as the pressure becomes lower.

9. A calculation method according to any one of claims 4 to 8, wherein, when the pressure is equal to or lower than the first predetermined pressure, the lower the pressure, the smaller the amount of operation of a pressure control device that controls the pressure while the current and the voltage are measured.

10. A calculation method according to any one of claims 1 to 9, wherein the correction is not performed when the pressure is equal to or lower than a second predetermined pressure that is lower than the first predetermined pressure.

11. A battery DC resistance calculation device that calculates the DC resistance of a lithium secondary battery by linear regression based on the current and voltage measured at multiple measurement points of the lithium secondary battery, which is made up of a positive electrode layer, an electrolyte layer containing a solid electrolyte, and a negative electrode layer stacked in this order, the calculation device measuring or estimating pressure changes applied to the lithium secondary battery between the multiple measurement points, estimating the amount of change in the DC resistance corresponding to the pressure change, and performing correction using the amount of change in the calculation of the DC resistance by linear regression.

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