Battery pack state determination device, and battery pack inspection method

Abstract

To provide a state determination device that can obtain accurate information on the minimum value of the amount of reserve in negative electrodes of a plurality of battery cells that form a battery pack.SOLUTION: A PU measures impedances Z1, Z2 in frequencies f1, f2 (S20, S22). The PU calculates a limit capacity C by using imaginary number values of the impedances Z1, Z2 (S24). The PU selects a battery pack having the limit capacity C equal to or more than a predetermined value Cth, and subsequently determines whether a reactance component Z1i that is the imaginary number value of the impedance Z1 of the selected battery pack is larger than a threshold Zith (S28). The PU determines the battery pack having the reactance component Z1i larger than the threshold Zith as being deteriorated.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a battery pack state determination device and a battery pack inspection method. [Background technology]

[0002] As described in Patent Document 1 below, it is well known that in nickel-metal hydride secondary batteries, a discharge reserve is provided in the negative electrode so that the battery capacity is not limited by the negative electrode during discharge. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2013 / 115038 Summary of the Invention [Problem to be solved by the invention]

[0004] It is desirable to collect used secondary batteries and inspect whether they can be reused. In this case, it is desirable to know the minimum discharge reserve of the battery cells that make up a battery pack in which multiple battery cells are connected in series. [Means for solving the problem]

[0005] Means for solving the above problems and their effects will be described below. 1. A battery pack state determination device that determines the state of an assembled battery which is a series connection of multiple battery cells, the device being configured to execute an impedance calculation process, a variation variable acquisition process, a variation determination process, and an information output process, wherein the impedance calculation process receives as input a response signal when an AC signal of a predetermined frequency or less is input to the assembled battery, and calculates the impedance of the assembled battery, the variation variable acquisition process receives as input a variation variable, the variation variable being a variable correlated with the degree of variation in capacity between the battery cells that constitute the assembled battery, the variation determination process determines whether the degree of variation indicated by the value of the variation variable is equal to or less than a predetermined amount, and the information output process is a process selectively executed on the assembled battery that is determined to be equal to or less than the predetermined amount, and wherein an imaginary value of the impedance is input, and information relating to a minimum reserve value of the negative electrodes of the multiple battery cells that constitute the assembled battery is output.

[0006] The imaginary value of the impedance calculated from the response signal of the AC signal at or below a certain frequency has a negative correlation with the minimum reserve amount of each of the negative electrodes of the multiple battery cells constituting the battery pack. However, if the capacity of the battery cells varies greatly, the imaginary value may become large due to the large variation.

[0007] Therefore, in the above configuration, for those whose degree of variation is equal to or less than a predetermined amount, information on the minimum reserve amount is output based on the imaginary value, thereby making it possible to obtain accurate information on the minimum reserve amount of each negative electrode of the multiple battery cells that make up the battery pack.

[0008] 2. The battery pack state determination device according to claim 1, wherein the variation variable acquisition process includes a process of acquiring a calculation result of the impedance by the impedance calculation process. The variation in capacity has a negative correlation with the capacity of the battery pack. Meanwhile, the impedance calculated based on the response signal to the AC signal having a frequency equal to or lower than a predetermined frequency contains information about the capacity of the battery pack. Therefore, in the above configuration, the variation variable acquisition process includes a process for acquiring the impedance calculation result. This makes it possible to acquire the value of the variation variable by using the calculation result.

[0009] 3. The device for determining the state of a battery pack as described in claim 2, wherein the variation variable acquisition process is a process in which an imaginary value of the impedance calculated by the impedance calculation process when the frequency of the AC signal is set to each of two or more different values ​​is an input, and a limit capacity of the battery pack is an output.

[0010] In the above configuration, the correlation between the imaginary value of the impedance and the limit capacity is utilized to calculate the limit capacity that is correlated with the capacity variation. In particular, when the frequency of the AC signal is low, the influence of components other than the capacitive reactance component on the difference between the imaginary values ​​of the impedance at different frequencies is small. Therefore, the limit capacity can be calculated with high accuracy.

[0011] 4. The battery pack state determination device described in any one of 1 to 3 above, wherein the information output process is a process of outputting information indicating that the negative electrode reserve minimum value falls outside the allowable range when the imaginary value of the impedance is equal to or greater than a threshold value.

[0012] With the above configuration, it is possible to obtain information as to whether or not there is any battery cell in the plurality of battery cells constituting the battery pack whose negative electrode reserve amount is below the allowable range. 5. A method for inspecting the condition of a used battery pack, comprising a simple diagnosis process and a precise sorting process, wherein the simple diagnosis process is a process for executing each of the processes by the battery pack condition determination device described in 4 above, and the precise sorting process is a process for inspecting the battery pack that takes a longer time than the simple diagnosis process and is a process for determining whether the battery pack is reusable or not, and wherein a battery pack determined by the information output process to have a minimum reserve value of the negative electrode that is outside the allowable range is excluded from the precise sorting process.

[0013] In the above method, a battery pack for which the simplified diagnosis step outputs information indicating that the negative electrode minimum reserve value is outside the allowable range is excluded from the precision sorting step, thereby reducing the number of steps required to determine whether the battery pack can be reused. [Brief description of the drawings]

[0014] [Figure 1] 1 is a diagram illustrating a battery pack and a state determination device according to an embodiment; [Diagram 2] 4 is a flowchart showing an inspection process of the battery pack according to the embodiment. [Diagram 3] FIG. 2 is a diagram showing the positive electrode capacity and the negative electrode capacity of a battery cell. [Figure 4] 4 is a flowchart showing a procedure of a process executed by the state determination device according to the embodiment. [Diagram 5] FIG. 4 is a diagram showing the complex impedance of a battery pack. [Figure 6] FIG. 13 is a plot of the relationship between capacity variation and limit capacity. [Figure 7] FIG. 13 is a plot of the relationship between the reactance component of impedance and the minimum value of the negative electrode reserve of a battery cell. [Figure 8] FIG. 13 is a plot of the relationship between the reactance component of impedance and the minimum value of the negative electrode reserve of a battery cell. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment will be described with reference to the drawings. System Configuration FIG. 1 shows the configuration of a system for simply diagnosing the state of a battery pack 10. As shown in FIG.

[0016] The battery pack 10 shown in Fig. 1 is collected after use. The battery pack 10 may be collected after being mounted on a moving object such as a vehicle and used. Alternatively, the battery pack 10 may be collected after being placed in a house and used.

[0017] The battery pack 10 includes a plurality of battery cells 12. As an example, the battery pack 10 includes six battery cells 12. The battery cells 12 are nickel-metal hydride secondary batteries. The battery pack 10 is a sealed battery with a rectangular plate-like appearance. The battery pack 10 includes a battery case 14 capable of housing the plurality of battery cells 12, and a lid 16 that seals the opening of the battery case 14. The battery case 14 houses the plurality of battery cells 12 that are electrically connected in series. Two ends of the battery cells 12 that are connected in series to each other are connected to a positive terminal 18 and a negative terminal 19 provided on the battery case 14.

[0018] The charge / discharge circuit 20 is a circuit for charging and discharging the battery pack 10. The charge / discharge circuit 20 is particularly capable of passing an AC current through the battery pack 10. The state determination device 30 includes a PU 32 and a storage device 34. The PU 32 is a software processing device such as a CPU, a GPU, or a TPU. The storage device 34 may be an electrically non-rewritable non-volatile memory. The storage device 34 may also be an electrically rewritable non-volatile memory or a storage medium such as a disk medium. The state determination device 30 executes a process of determining the state of the battery pack 10 by the PU 32 executing a program stored in the storage device 34.

[0019] The state determination device 30 refers to the current I of the battery pack 10 detected by the current sensor 40 in order to determine the state of the battery pack 10. The current I is the flow rate of charge moving from the positive terminal 18 to the negative terminal 19. The state determination device 30 refers to the voltage V detected by the voltage sensor 42 in order to determine the state of the battery pack 10. The voltage V is the potential difference between the positive terminal 18 and the negative terminal 19.

[0020] "Summary of evaluation of the condition of battery pack 10" The collected battery pack 10 is evaluated as to whether it can be reused. The process for the above evaluation is shown in Figure 2. In the following, each step is numbered with a number preceded by the letter "S."

[0021] In the series of steps shown in Fig. 2, first, a simple diagnosis step is performed on the battery pack 10 (S10). The simple diagnosis step is a step executed by the state determination device 30 shown in Fig. 1. The simple diagnosis step is a step of simply diagnosing whether or not the battery cells 12 constituting the battery pack 10 include any deteriorated cells whose negative electrode discharge reserve is not guaranteed.

[0022] FIG. 3 shows the positive and negative electrode capacities of a normal battery cell 12 and a deteriorated battery cell 12. When the battery cell 12 is first used, the battery capacity of the negative electrode is set to be larger than the battery capacity of the positive electrode, so that the battery cell 12 is limited by the positive electrode. This excess capacity of the negative electrode, which is larger than the positive electrode, is called the negative electrode discharge reserve R [Ah]. This makes it possible to use 100% of the positive electrode capacity. The normal state of the battery cell 12 shown on the left side of FIG. 3 is a state in which the negative electrode discharge reserve R is secured.

[0023] On the other hand, the right side of FIG. 3 shows a state where the negative electrode capacity is reduced due to the deterioration of the battery cell 12. When the hydrogen storage alloy MH is used, it gradually collapses due to expansion and contraction caused by charging and discharging, and the amount of hydrogen ions that can be absorbed decreases. In addition, the battery capacity of the positive electrode may also decrease for other reasons. If the capacity of the negative electrode is not deteriorated, hydrogen ions can be released at the limit of the capacity of the positive electrode during discharge. However, the capacity of the negative electrode may decrease. In this case, even if the capacity of the positive electrode remains, hydrogen ions that move from the negative electrode to the positive electrode during discharge are depleted, and discharging does not occur. In other words, the initial setting, which was a state of positive electrode regulation, becomes a state of negative electrode regulation, and as a result, the capacity of the entire battery pack 10 decreases. In addition, in such a state, the internal resistance of the battery pack 10 becomes extremely large.

[0024] Returning to FIG. 2, when the simple diagnosis step is completed, it is determined whether or not a deterioration judgment has been made in the simple diagnosis step (S12). If it is determined that the battery pack 10 to be diagnosed includes a deteriorated battery pack 10 in which the discharge reserve of the negative electrode is not guaranteed, this means that a deterioration judgment has been made in the simple diagnosis. If the battery pack 10 has not been judged to be deteriorated in the simple diagnosis (S12: NO), a precision sorting step is executed for the battery pack 10 (S14). The precision sorting step is a step of precisely inspecting whether or not the battery pack 10 can be reused. The precision sorting step is a step that requires more steps and a longer time than the simple diagnosis step. The precision sorting step may include, for example, a step of measuring a fully charged charge amount. The precision sorting step may include a step of measuring a direct current resistance. The precision sorting step may include a step of inspecting an appearance. The precision sorting step may include a step of measuring an open circuit voltage.

[0025] When the precision sorting process is completed, it is determined whether the deterioration degree of the battery pack 10 is within an allowable range through the precision sorting process (S16). If it is determined that the deterioration degree is within an allowable range (S16: NO), the battery pack 10 is determined to be usable (S18).

[0026] It should be noted that the series of steps shown in FIG. 2 is temporarily terminated when the step of S18 is completed, when a positive determination is made in the step of S12, or when a negative determination is made in the step of S16.

[0027] "Determination of negative electrode capacity deterioration" The procedure of the simple diagnosis process is shown in Fig. 4. The series of processes shown in Fig. 4 is realized by the PU 32 repeatedly executing a program stored in the storage device 34, for example, at a predetermined interval.

[0028] In the series of processes shown in Fig. 4, the PU 32 first measures the impedance Z1 when the charge / discharge circuit 20 is operated to pass an AC current of frequency f1 through the battery pack 10 (S20). That is, the PU 32 operates the charge / discharge circuit 20 by a feedback control operation amount in which the current I detected by the current sensor 40 is a controlled variable and a current command value that periodically changes at frequency f1 is a target value of the controlled variable. The PU 32 then calculates the impedance Z1 from the relationship between the voltage V detected by the voltage sensor 42 and the current I. The process of measuring the impedance Z1 includes a process in which the PU 32 calculates a resistance component Z1r, which is a real axis component of the impedance Z1, and a reactance component Z1i, which is an imaginary axis component of the impedance. The voltage V and current I, which are inputs to the process of S20, are time-series data.

[0029] The frequency f1 belongs to the diffused resistor region. The diffused resistor region will now be described with reference to FIG. 5 shows the results of measuring impedance when the frequency of the AC current flowing through the battery pack 10 is changed. In detail, the horizontal axis represents the resistance component Zr, which is the real axis component of the impedance, and the vertical axis represents the reactance component Zi, which is the imaginary axis component of the impedance.

[0030] In FIG. 5, "area a" is a circuit resistance area corresponding to the circuit resistance and a solution resistance area corresponding to the solution resistance. "Area b" is a reaction resistance area caused by reaction resistance. "Area c" is a area where the reactance component Zi changes approximately linearly with respect to the change in the resistance component Zr. Area c is a diffusion resistance area corresponding to diffusion resistance. By changing the frequency of the above AC current from high frequency to low frequency, the impedance value changes from area a through area b to the value of area c. Area c appears when the frequency is equal to or lower than a specified value. Here, the specified value is, for example, "1 Hz."

[0031] Note that, when detecting the maximum frequency at which the frequency of the AC current falls within the diffusion resistance region while lowering the frequency of the AC current for a plurality of battery assemblies 10, the detected frequency varies due to individual differences between the battery assemblies 10. The frequency f1 is preset to a value that is considered to be surely within the diffusion resistance region while taking into consideration individual differences, etc. The frequency f1 can be set, for example, by detecting the upper limit of the frequency at which the frequency of the AC current falls within the diffusion resistance region for a plurality of battery assemblies 10 while lowering the frequency of the AC current.

[0032] Returning to FIG. 4, the PU 32 measures the impedance Z2 when the charge / discharge circuit 20 is operated to pass an AC current of frequency f2 through the battery pack 10 (S22). The frequency f2 belongs to the diffused resistance region. It is desirable that the difference between the frequency f2 and the frequency f1 is equal to or less than a specified amount. Here, the specified amount may be, for example, "0.1 Hz." The process of measuring the impedance Z2 described above includes a process in which the PU 32 calculates a resistance component Z2r, which is the real axis component of the impedance Z2, and a reactance component Z2i, which is the imaginary axis component of the impedance. The voltage V and current I, which are inputs to the process of S22, are time-series data.

[0033] Next, the PU32 calculates the limit capacity C from the relationship between the difference between the frequencies f1 and f2 and the difference between the impedances Z1 and Z2 (S24). That is, the PU32 substitutes "2π(f1-f2)" for the angular velocity change amount Δω. The PU32 also substitutes "Z1i-Z2i" for the reactance change amount ΔZi. Here, the reactance components Z1i and Z2i are the reactance components of the impedances Z1 and Z2, respectively. The PU32 then substitutes a value obtained by dividing the inverse of the angular velocity change amount Δω by the reactance change amount ΔZi for the limit capacity C.

[0034] Next, the PU 32 judges whether the limit capacity C is equal to or greater than a predetermined value Cth (S26). The process of S26 is a process for judging whether the variation in the positive electrode capacity of the six battery cells 12 constituting the battery pack 10 is equal to or less than a predetermined amount Δth. This process is provided in consideration of the fact that when the variation in the positive electrode capacity is greater than the predetermined amount Δth, the discharge reserve of the negative electrode cannot be detected with high accuracy by the process described later.

[0035] Here, the battery pack 10 according to this embodiment cannot individually detect the positive electrode capacity of each of the six battery cells 12. Therefore, the process of S26 utilizes the property that the variation in the positive electrode capacity of the six battery cells 12 is correlated with the limit capacity C.

[0036] FIG. 6 shows the relationship between the limit capacity C and the variation between the positive electrode capacities of the six battery cells 12. Each point shown in FIG. 6 was obtained by measuring the limit capacity C and the variation between the positive electrode capacities of the six battery cells 12 for a plurality of assembled batteries 10. Here, the variation between the positive electrode capacities of the six battery cells 12 was measured by disassembling the assembled battery 10 after measuring the limit capacity C and detecting the positive electrode capacity of each battery cell 12. As shown in FIG. 6, there is a negative correlation between the limit capacity C and the variation between the positive electrode capacities of the six battery cells 12. Therefore, in the process of S26, by determining whether the limit capacity C is equal to or greater than a predetermined value Cth, it is possible to determine whether the variation between the positive electrode capacities of the six battery cells 12 is equal to or less than a predetermined amount Δth. The variation between the positive electrode capacities of the battery cells 12 is the difference between the maximum and minimum values ​​of the positive electrode capacities.

[0037] 4, when the PU 32 determines that the limit capacity C is equal to or greater than the predetermined value Cth (S26: YES), the PU 32 determines whether or not the reactance component Z1i of the impedance Z1 is greater than a threshold value Zith (S28). This process is to determine whether or not the minimum value of the discharge reserve of the negative electrodes of the six battery cells 12 constituting the battery pack 10 is less than a specified amount.

[0038] FIG. 7 shows the relationship between the reactance component Z1i of the battery pack 10 and the minimum value of the discharge reserve of the negative electrode of the six battery cells 12 constituting the battery pack 10. Each point shown in FIG. 7 is a measurement point obtained by measuring the impedance Z1 of the battery pack 10, disassembling the battery pack 10 into six battery cells 12, and measuring the discharge reserve of each battery cell 12. As shown in FIG. 7, the minimum value of the discharge reserve of the negative electrode of the six battery cells 12 constituting the battery pack 10 has a negative correlation with the reactance component Z1i. This correlation in the diffusion resistance region is caused by the fact that the electromigration resistance increases as the negative electrode capacity decreases. That is, in the diffusion resistance region, the impedance of the positive electrode changes significantly, but the change in the impedance of the negative electrode tends to be small. However, the increase in electromigration resistance caused by the decrease in the negative electrode capacity affects the diffusion resistance region. Therefore, when the negative electrode capacity decreases, the reactance component Z1i increases due to the increase in the impedance of the negative electrode.

[0039] The straight line f shown in Fig. 7 indicates a regression equation obtained by, for example, the least squares method using the above-mentioned multiple measurement points. Fig. 7 shows an example in which the value of the reactance component when the minimum value of the discharge reserve is "0" in the regression equation is the threshold value Zith.

[0040] 4, when the PU 32 determines that the reactance component Z1i is greater than the threshold value Zith (S28: YES), it performs a degradation determination (S30) of the battery pack 10. That is, in the simplified diagnosis process, the battery pack 10 that has been subjected to the process of S30 is excluded from the subsequent inspection of whether it is usable or not, because a positive determination is made in the process of S12 in FIG.

[0041] When the process of S30 is completed or when the determination is affirmative in the processes of S26 and S28, the PU 32 temporarily ends the series of processes shown in FIG. "Actions and Effects of the Present Embodiment" A used battery pack 10 is inspected to determine whether it can be reused. This inspection includes a simple diagnosis process and a precision sorting process. In the simple diagnosis process, the PU 32 determines whether the minimum discharge reserve of the multiple battery cells 12 that make up the battery pack 10 is less than a specified amount.

[0042] Here, the PU 32 grasps the minimum value of the discharge reserve of the plurality of battery cells 12 by using the reactance component Z1i of the impedance Z1 in the diffusion resistance region. Fig. 8 shows the relationship between the reactance component Z1i of the battery pack 10 and the minimum value of the discharge reserve of the negative electrodes of the six battery cells 12 that make up the battery pack 10. The points shown in Fig. 8 are measurement points obtained by measuring the impedance Z1 of the battery pack 10, disassembling the battery pack 10 into the six battery cells 12, and measuring the discharge reserve of each battery cell 12.

[0043] The measurement points shown in FIG. 7 are the measurement points shown in FIG. 8 excluding the measurement points of the assembled battery 10 where the variation between the positive electrode capacities is greater than a predetermined amount Δth. The measurement points of the assembled battery 10 where the variation between the positive electrode capacities is greater than a predetermined amount Δth are mainly within area A in FIGS. 7 and 8. When the variation in the positive electrode capacities is greater than a predetermined amount Δth, the reactance component Z1i of the assembled battery 10 becomes large due to the variation in the positive electrode capacities. Therefore, when the assembled battery 10 includes the variation in the positive electrode capacities that is greater than or equal to the predetermined amount Δth, the minimum value of the discharge reserve cannot be grasped by the reactance component Z1i.

[0044] In response to this, the PU 32 determines whether the minimum value of the discharge reserve is less than the specified amount based on the reactance component Z1i of the battery pack 10 only when the process of S26 makes a positive determination. This makes it possible to quickly find battery packs 10 whose minimum value of the discharge reserve is less than the specified amount. Furthermore, battery packs 10 whose minimum value of the discharge reserve is less than the specified amount are not subject to the precision sorting process, so that the number of inspection steps for the battery packs 10 can be reduced.

[0045] The battery pack 10 for which a negative determination is made in the process of S26 is subjected to a precision sorting process. According to the present embodiment described above, the following actions and effects can be obtained.

[0046] (1) PU32 calculated the limit capacity C using the reactance change ΔZi. In the low frequency range, the effect of components other than capacitive reactance on the reactance change ΔZi is small. Therefore, by using the reactance change ΔZi, the limit capacity C can be calculated with higher accuracy than when the limit capacity C is calculated as "1 / (2·π·f1·Z1i)".

[0047] (2) The battery pack 10 whose limit capacity C is less than a predetermined value Cth is subjected to a precision sorting process. Therefore, even for the battery pack 10 whose minimum discharge reserve cannot be accurately determined from the reactance component Z1i, the possibility of reuse can be determined.

[0048] <Correspondence> The correspondence between the matters in the above embodiment and the matters described in the above "Means for solving the problem" column is as follows. In the following, the correspondence is shown for each number of the means for solving the problem described in the "Means for solving the problem" column. [1,4] The AC signal corresponds to the AC current. The response signal corresponds to the voltage V. The impedance calculation process corresponds to the process of S20. The variation variable acquisition process corresponds to the process of S24. The variation variable corresponds to the limit capacity C. The variation determination process corresponds to the process of S26. The information output process corresponds to the process of S28. The "information regarding the minimum value of the negative electrode reserve" is binary information indicating whether the minimum value of the negative electrode reserve is less than a specified amount. [2,3] The impedance Z1 calculated by the process of S20 is included in the input of the process of S24. [5] The simple diagnosis process corresponds to the process of S10. The precision selection process corresponds to the process of S14.

[0049] <Other embodiments> This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0050] "Calculating impedance" The input for the impedance calculation process is not limited to the voltage V and the current I as a response signal when an AC current is applied to the battery pack 10. When feedback control is performed using the current as a controlled variable, a current command value may be input instead of the current I.

[0051] The input for the impedance calculation process is not limited to the voltage V as a response signal when an AC current is applied to the battery pack 10. For example, the input for the impedance calculation process may be the current I as a response signal when an AC voltage is applied to the battery pack 10. In that case, the input for the impedance calculation process further includes a voltage command value or the voltage V.

[0052] The process of calculating the impedance Z1 in the diffused resistance region is not limited to the process in which the PU 32 calculates the impedance Z1 at a predetermined frequency f1. For example, the process may include the process in which the PU 32 calculates the impedance Z while gradually lowering the frequency of the AC signal. In this case, the PU 32 may determine that the region in which the change in the reactance component Zi of the impedance Z is proportional to the change in the resistance component Zr of the impedance Z is the diffused resistance region.

[0053] "About the variability variable acquisition process" · As a process of obtaining the limit capacitance C by the ratio of the reciprocal of the angular velocity change amount Δω to the reactance change amount ΔZi, it is not limited to a process in which the reactance components in AC signals of two different frequencies are input. For example, the process of obtaining this limit capacitance C may be a process in which the reactance components in AC signals of three or more different frequencies are input. For example, a process in which the reactance components in AC signals of frequency f1, frequency f2, and frequency f3 are input may be executed as follows. However, "f1 < f2 < f3". That is, the PU32 calculates a first limit capacitance using the reactance components measured at frequencies f1 and f2. Further, the PU32 calculates a second limit capacitance using the reactance components measured at frequencies f2 and f3. Then, the PU32 substitutes the average value of the first limit capacitance and the second limit capacitance into the final limit capacitance C.

[0054] · As a process in which the reactance is input and the limit capacitance C is output, it is not limited to a process in which the reactance components at two or more different frequencies are input. For example, the PU32 may substitute "1 / (2·π·f1·Z1i)" or "1 / (2·π·f2·Z2i)" into the limit capacitance C.

[0055] Note that the variation variable may be the reactance component Z1i or the reactance component Z2i instead of the limit capacitance C. In that case, the process of S26 becomes a process of determining whether the reactance component is less than or equal to the threshold value.

[0056] The variation variable does not necessarily have to be the limit capacity C or the reactance component. For example, it may be a relaxation rate constant by a current interrupter method. The relaxation rate constant may be calculated by the PU 32, for example, as follows. The PU 32 first charges or discharges the battery pack 10, and then stops charging and discharging the battery pack 10. The PU 32 then calculates a relaxation rate, which is a rate of change in the terminal voltage of the battery pack 10 after a predetermined time has elapsed since the charging and discharging were stopped. Here, the predetermined time is a time required from the change in the terminal voltage until the effect of the reaction resistance can be ignored. The predetermined time may be set to, for example, 10 seconds or more. Next, the PU 32 multiplies the relaxation rate by the square root of the predetermined time and assigns the value to the relaxation rate constant. The relaxation rate constant calculated in this manner has a positive correlation with the variation in the positive electrode capacity of the multiple battery cells constituting the battery pack 10.

[0057] The variation variable acquisition process may be, for example, a process of acquiring a relationship between the charged charge and the open circuit voltage immediately before the battery pack 10 is collected. Here, the charged charge and the open circuit voltage constitute a capacity variable. In this case, the PU 32 may execute the process of S28 when a value obtained by dividing the charged charge by the open circuit voltage is equal to or greater than a threshold value.

[0058] "About information output processing" The information output process is not limited to a process of outputting information regarding whether the minimum value of the discharge reserve of the battery cells constituting the assembled battery 10 is within an allowable range. For example, it may be a process of outputting the value of a variable indicating the minimum value of the discharge reserve of the battery cells constituting the assembled battery 10. This may include, for example, a process in which the PU 32 determines the minimum reserve amount corresponding to the value of the reactance component Z1i of the straight line f shown in Fig. 7. However, the value of the variable indicating the minimum value of the discharge reserve may be the reactance component Z1i itself.

[0059] "About the status determination device" The condition determination device does not have to be a device intended to automatically perform a simple diagnostic process.

[0060] The state determination device is not limited to a device that executes software processing. For example, a dedicated hardware circuit such as an ASIC that executes at least a part of the processing executed in the above embodiment may be included. That is, the state determination device may include a processing circuit having any of the following configurations (a) to (c). (a) A processing circuit including a processing device that executes all of the above processing according to a program, and a program storage device such as a storage device that stores the program. (b) A processing circuit including a processing device and a program storage device that executes part of the above processing according to a program, and a dedicated hardware circuit that executes the remaining processing. (c) A processing circuit including a dedicated hardware circuit that executes all of the above processing. Here, there may be multiple software execution devices including a processing device and a program storage device. Also, there may be multiple dedicated hardware circuits.

[0061] "About assembled batteries" The number of battery cells 12 constituting the assembled battery 10 is not limited to six. The number of battery cells 12 constituting the assembled battery 10 may be, for example, two to five. Furthermore, for example, the number of battery cells 12 constituting the assembled battery 10 may be seven or more.

[0062] The battery cells 12 that make up the battery pack 10 do not necessarily have to be nickel-metal hydride secondary batteries. [Explanation of symbols]

[0063] 10. Battery pack 12…Battery cell 14…Battery case 16…Lid body 18…Positive terminal 19...Negative terminal 30...Status determination device 40...Current sensor

Claims

1. A battery state determination device that determines a state of a battery assembly that is a series connection of a plurality of battery cells, comprising: The impedance calculation process, the variation variable acquisition process, the variation determination process, and the information output process are configured to be executed; the impedance calculation process is a process in which a response signal is input when an AC signal having a frequency equal to or lower than a predetermined frequency is input to the battery pack, and an impedance of the battery pack is calculated; the variance variable acquisition process is a process of acquiring a variance variable, the variation variable is a variable correlated with a degree of variation in capacity between battery cells constituting the assembled battery, the variation determination process is a process of determining whether or not a degree of variation indicated by a value of the variation variable is equal to or less than a predetermined amount, The information output process is a process that is selectively executed on the battery pack that is determined to be below the predetermined amount, and the imaginary value of the impedance is an input and information regarding the minimum reserve value of the negative electrodes of the multiple battery cells that constitute the battery pack is an output.

2. The battery pack state determination device according to claim 1 , wherein the variation variable acquisition process includes a process of acquiring a calculation result of the impedance by the impedance calculation process.

3. 3. The device for determining a state of a battery pack according to claim 2, wherein the variation variable acquisition process is a process in which an imaginary value of the impedance calculated by the impedance calculation process when the frequency of the AC signal is set to each of two or more different values ​​is an input, and a limit capacity of the battery pack is an output.

4. 2. The battery pack state determination device according to claim 1, wherein the information output process outputs information indicating that the negative electrode reserve minimum value is out of an allowable range when the imaginary value of the impedance is equal to or greater than a threshold value.

5. A method for inspecting a state of a used battery pack, comprising the steps of: The method includes a simple diagnosis step and a precise selection step, The simplified diagnosis step is a step of executing each of the processes by the battery pack state determination device according to claim 4, the precise sorting step is a step of inspecting the battery pack that takes a longer time than the simple diagnosis step and is a step for determining whether the battery pack can be reused; a battery pack inspection method in which a battery pack determined by the information output process to have a minimum reserve value of the negative electrode that is outside an allowable range is excluded from the precision sorting process.

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