Measuring device and measuring method

Abstract

This measurement device (10) measures a secondary battery (20). The measurement device (10) comprises a voltage application unit (140), a switching unit (120), a measurement unit (160), and a processing unit (180). The voltage application unit (140) applies, to the secondary battery (20), a prescribed voltage that is derived on the basis of the open voltage of the secondary battery (20). The switching unit (120) switches between a first state in which the prescribed voltage is applied to the secondary battery (20) and a second state in which the secondary battery is opened. The measurement unit (160) measures a transient response of an external magnetic field of the secondary battery, the transient response occurring at the instance of switching from the first state to the second state. The processing unit (180) generates information relating to the interior of the secondary battery (20) by using the result of measurement by the measurement unit (160).

Description

[Technical field]

[0001] The present invention relates to a measurement device and a measurement method. [Background technology]

[0002] As the use of rechargeable secondary batteries becomes more widespread, non-destructive inspection techniques are becoming increasingly important.

[0003] Patent Document 1 describes measuring the magnetic field around a battery while a current is flowing, and deriving the electrical conductivity distribution within the battery.

[0004] Patent Document 2 describes that while an external voltage superimposed with an AC voltage is applied to a battery, the magnetic field outside the battery is measured, and the magnetic field distribution or current distribution inside the battery is derived. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2015 / 136931 [Patent Document 2] International Publication No. 2015 / 136930 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the technology of Patent Document 1 has a problem in that the internal state of the battery changes because charging or discharging proceeds during measurement, and the technology of Patent Document 2 has a problem in that it is difficult to detect minute defects in the battery.

[0007] In view of the above problems, the present invention provides a new technique for measuring a secondary battery. [Means for solving the problem]

[0008] According to one aspect of the present invention, the following measurement device and measurement method are provided.

[0009] 1. A measuring device for measuring a secondary battery, a voltage application unit that applies a predetermined voltage to the secondary battery, the voltage being determined based on an open circuit voltage of the secondary battery; a switching unit that switches between a first state in which the predetermined voltage is applied to the secondary battery and a second state in which the secondary battery is open; a measurement unit that measures a transient response of a magnetic field outside the secondary battery when the secondary battery is switched from the first state to the second state; a processing unit that generates information regarding the inside of the secondary battery using a measurement result by the measurement unit. Measuring equipment. 2. In the measuring device according to 1., A control unit that controls the voltage application unit and the measurement unit, The measurement unit includes a sensor unit and a sensor driving unit, The control unit controls the voltage application unit and the measurement unit so that a determination step of determining a fixed input value to the sensor unit for canceling at least a part of a noise magnetic field and a measurement step of measuring the transient response in a state in which the fixed input value is input to the sensor unit are performed in that order. Measuring equipment. 3. In the measuring device according to 2., In the specifying step, the sensor driving unit feedback controls an input value to the sensor unit so that the output of the sensor unit approaches a reference level in a state where a voltage corresponding to an open circuit voltage is applied to the secondary battery, and the control unit controls the voltage application unit and the measurement unit so that the fixed input value is specified. Measuring equipment. 4. The measuring device according to 2. or 3., The secondary battery includes a ferromagnetic material. Measuring equipment. 5. In the measuring device according to any one of 1. to 4., the measurement unit measures the transient response at a plurality of positions in one or more planes outside the secondary battery; The processing unit generates a map indicating information about the inside of the secondary battery. Measuring equipment. 6. The measuring device according to 5., The measurement unit includes a plurality of sensor elements arranged in a matrix. Measuring equipment. 7. The measuring device according to any one of 1. to 6., The processing unit includes: Using the measurement result by the measurement unit, it is determined whether or not there is an abnormality in the measured secondary battery; If it is determined that the secondary battery is abnormal, a notification is output. Measuring equipment. 8. The measuring device according to any one of 1. to 7., the voltage application unit applies the predetermined voltage to the secondary battery in response to a periodic signal; The switching unit switches between the first state and the second state in response to a periodic signal having a frequency that is an integer multiple of the frequency of the periodic signal. Measuring equipment. 9. The measuring device according to any one of 1. to 8., The measurement unit measures magnetic field components in two directions perpendicular to each other as the transient response, The processing unit generates a conductivity distribution inside the secondary battery by using the magnetic field components in the two directions. Measuring equipment. 10. A method for measuring a secondary battery, comprising: switching between a first state in which a predetermined voltage determined based on an open circuit voltage of the secondary battery is applied to the secondary battery and a second state in which the secondary battery is open circuit; measuring a transient response of a magnetic field external to the secondary battery when the secondary battery switches from the first state to the second state; Generate information about the inside of the secondary battery using the measurement result of the transient response Measurement method. Effect of the Invention

[0010] According to the present invention, a new technique for measuring a secondary battery can be provided. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a diagram illustrating an example of a functional configuration of a measurement device according to a first embodiment. [Diagram 2] 1 is a cross-sectional view illustrating a structure of a secondary battery. [Diagram 3] 1 is a schematic diagram illustrating a state in which a secondary battery is measured by a measuring device; [Figure 4] FIG. 13 is a diagram showing a modified example of the sensor unit. [Diagram 5] 4 is a diagram for explaining a voltage applied to a secondary battery by a measuring device. FIG. [Figure 6] 4 is a diagram for explaining a voltage applied to a secondary battery by a measuring device. FIG. [Figure 7] FIG. 13 is a diagram illustrating a computer for implementing the measurement device. [Figure 8] 13 is a diagram illustrating the configuration of a switching section and a voltage application section included in a measurement device according to a second embodiment. FIG. [Figure 9] 10A to 10C are diagrams for explaining the operation of the measurement device according to the second embodiment. [Figure 10] 13(a) to 13(g) are diagrams illustrating an example in which the frequency of a periodic signal output by a multiplier is changed. [Figure 11] 13 is a diagram illustrating an example of a signal flow in a measurement section according to the third embodiment. FIG. [Figure 12] FIG. 13 is a diagram illustrating an example of a hardware configuration of a measurement unit according to a third embodiment. [Figure 13] FIG. 13 is a diagram illustrating the configuration of a measurement device according to a third embodiment. [Figure 14] FIG. 2 is a schematic cross-sectional view showing the structure of a secondary battery to be measured. [Figure 15] FIG. 13 is a diagram showing measurement areas and defect positions in a photograph of a secondary battery. [Figure 16]FIG. 13 shows a map generated using measurements of the transient response of a magnetic field. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In all drawings, the same components are denoted by the same reference numerals, and the description will be omitted as appropriate. In the following description, unless otherwise specified, each component of each device is shown as a functional block, not a hardware configuration.

[0013] (First embodiment) FIG. 1 is a diagram illustrating a functional configuration of a measuring device 10 according to a first embodiment. The measuring device 10 according to this embodiment is a device that measures a secondary battery 20. The measuring device 10 includes a voltage application unit 140, a switching unit 120, a measuring unit 160, and a processing unit 180. The voltage application unit 140 applies a predetermined voltage to the secondary battery 20, the voltage being determined based on the open circuit voltage (OCV) of the secondary battery 20. The switching unit 120 switches between a first state in which a predetermined voltage is applied to the secondary battery 20 and a second state in which the secondary battery is open. The measuring unit 160 measures a transient response of a magnetic field outside the secondary battery 20 when the state is switched from the first state to the second state. The processing unit 180 generates information about the inside of the secondary battery 20 using the measurement result by the measuring unit 160. This will be described in detail below.

[0014] In the example shown in the figure, the measurement device 10 further includes a control unit 190. In the example shown in the figure, the control unit 190 controls the switching unit 120, the voltage application unit 140, and the measurement unit 160.

[0015] FIG. 2 is a cross-sectional view illustrating the structure of a secondary battery 20. The measurement target of the measuring device 10 is the secondary battery 20, and by using the measuring device 10, for example, defects such as short circuits in the secondary battery 20 can be detected. The secondary battery 20 is not particularly limited, but may be, for example, a lead-acid battery, a nickel-cadmium battery, a lithium-ion battery, or a sodium-ion battery. The secondary battery 20 includes a positive electrode 211, a negative electrode 212, an electrolyte 230, a package 240, a positive electrode terminal 221, and a negative electrode terminal 222. The positive electrode 211 and the negative electrode 212 are each a plate-shaped, film-shaped, or layer-shaped electrode, and are parallel to each other. The secondary battery 20 may include a plurality of positive electrodes 211 and a plurality of negative electrodes 212. The electrolyte 230 is located between the positive electrode 211 and the negative electrode 212. The electrolyte 230 may be a liquid, a solid, or a gel. Furthermore, a separator may be further provided between the positive electrode 211 and the negative electrode 212. The positive electrode 211, the negative electrode 212, and the electrolyte 230 are covered and sealed in a package 240. The package 240 is, for example, a metal package.

[0016] One end of the positive electrode terminal 221 is electrically connected to the positive electrode 211 inside the package 240, and the other end of the positive electrode terminal 221 is located outside the package 240. When the secondary battery 20 has a plurality of positive electrodes 211, the positive electrode terminal 221 is electrically connected to the plurality of positive electrodes 211. One end of the negative electrode terminal 222 is electrically connected to the negative electrode 212 inside the package 240, and the other end of the negative electrode terminal 222 is located outside the package 240. When the secondary battery 20 has a plurality of negative electrodes 212, the negative electrode terminal 222 is electrically connected to the plurality of negative electrodes 212. The positive electrode terminal 221 and the negative electrode terminal 222 are, for example, tabs. Applying a voltage to the secondary battery 20 means applying a voltage between the positive electrode terminal 221 and the negative electrode terminal 222.

[0017] The measuring unit 160 of the measuring device 10 is configured to measure a magnetic field in a plane 201 outside the secondary battery 20, for example. The plane 201 is a plane parallel to the main surfaces of the positive electrode 211 and the negative electrode 212. The distance between the outermost surface of the secondary battery 20 and the plane 201 is not particularly limited, but is, for example, 0.01 mm or more and 100 mm or less. If the distance is within this range, the magnetic field from the secondary battery 20 can be measured with high accuracy, and the measurement can be performed stably while avoiding contact between the sensor unit 161 described later and the secondary battery 20. Hereinafter, the stacking direction of the positive electrode terminal 221 and the negative electrode 212 is referred to as the z direction, and the two directions that are both perpendicular to the z direction and perpendicular to each other are referred to as the x direction and the y direction.

[0018] 3 is a schematic diagram illustrating a state in which the secondary battery 20 is measured by the measuring device 10. During measurement by the measuring device 10, at least one of the positive electrode terminal 221 and the negative electrode terminal 222 of the secondary battery 20 is connected to the voltage application unit 140 via the switching unit 120. This allows a voltage to be applied between the positive electrode terminal 221 and the negative electrode terminal 222, i.e., to the secondary battery 20. One of the positive electrode terminal 221 and the negative electrode terminal 222 may be grounded.

[0019] The measuring unit 160 preferably measures the magnetic field at a plurality of positions. The measuring unit 160 includes a sensor unit 161, and measures the magnetic field (e.g., magnetic flux density) at the position of the sensor unit 161. The sensor unit 161 includes any magnetic sensor, such as a coil, a Hall element, an optical pumping magnetic sensor, a diamond magnetic sensor, a magnetic impedance sensor, or a magnetoresistance effect element.

[0020] In the example of this figure, the measurement unit 160 scans the outside of the secondary battery 20 one-dimensionally or two-dimensionally with the sensor unit 161 included in the measurement unit 160. In this way, the measurement unit 160 measures the magnetic field at a plurality of measurement positions in the plane 201, i.e., at a plurality of points (x, y). The plurality of measurement positions are preferably distributed two-dimensionally in the plane 201. In the example of this figure, the secondary battery 20 is placed on the stage 150. The stage 150 can drive the secondary battery 20 in the x direction and the y direction. Alternatively, the stage 150 may be capable of driving the secondary battery 20 in the x direction, the y direction, and the z direction. The stage 150 drives the secondary battery 20, so that the sensor unit 161 can sequentially perform measurements at a plurality of positions. However, the stage 150 may be configured to drive the sensor unit 161 instead of driving the secondary battery 20. The control unit 190 can further control the stage 150 so that the measurement unit 160 measures the transient response of the magnetic field at a plurality of positions in the plane 201.

[0021] FIG. 4 is a diagram showing a modified example of the sensor unit 161. In the example of this figure, the measurement unit 160 includes a plurality of sensor elements 165 arranged in a matrix in the sensor unit 161. The sensor elements 165 may be any magnetic sensor such as a coil, a Hall element, an optical pumping magnetic sensor, a diamond magnetic sensor, a magnetic impedance sensor, or a magnetoresistance effect element. The plurality of sensor elements 165 are integrated. According to this modified example, instead of measuring at a plurality of positions by scanning with the sensor unit 161 as shown in FIG. 3, measurements at a plurality of positions can be performed simultaneously by the plurality of sensor elements 165. Therefore, the measurement time can be significantly reduced. In the example of this figure, the plurality of sensor elements 165 are arranged in a two-dimensional matrix. Therefore, data of measurement points arranged two-dimensionally in the plane 201 is obtained. However, the plurality of sensor elements 165 may be arranged in a one-dimensional line. In that case, the plurality of sensor elements 165 may be moved in a direction perpendicular to the direction in which the plurality of sensor elements 165 are arranged to perform measurements. By this method, data at measurement points (measurement positions) arranged two-dimensionally in the plane 201 can also be obtained.

[0022] Returning to FIG. 1, each functional component of the measuring device 10 will be described. The direction of the magnetic field measured by the measuring unit 160 may be one direction, two directions, or three directions. For example, the measuring unit 160 measures the magnetic field components in one or more directions of the x direction, y direction, and z direction. In particular, it is preferable that the measuring unit 160 measures at least one of the x direction component and the y direction component of the magnetic field vector. When the sensor unit 161 includes a coil, the measuring unit 160 can measure the axial component of the coil, and can measure the magnetic field components in multiple directions by changing the orientation of the coil or using multiple coils.

[0023] The voltage application unit 140 includes at least a DC voltage source. The switching unit 120 switches whether or not the output voltage of the voltage application unit 140 is applied to the secondary battery 20. The switching unit 120 is, for example, a switch or a transistor.

[0024] 5 and 6 are diagrams for explaining the voltage applied to the secondary battery 20 by the measuring device 10. In each of Fig. 5 and Fig. 6, the upper part shows the applied voltage V B The waveform of the magnetic flux leaking out of the secondary battery 20 is shown in the lower part.

[0025] For example, in the example of FIG. 5, the voltage application unit 140 outputs a predetermined voltage V1. The predetermined voltage V1 is a voltage determined based on the open circuit voltage. For example, ΔV1, which is the difference between the open circuit voltage and the output voltage of the voltage application unit 140, is determined in advance, and the voltage V1 for the secondary battery 20 is determined by adding ΔV1 to the open circuit voltage of the secondary battery 20 to be measured. The open circuit voltage of the secondary battery 20 can be confirmed by a separate measurement prior to the measurement. When the switching unit 120 is in the ON state, the output voltage of the voltage application unit 140 is applied to the secondary battery 20. That is, when the switching unit 120 is in the ON state, the first state is reached. In the example of this figure, the secondary battery 20 is charged in the first state. On the other hand, when the switching unit 120 is in the OFF state, the output voltage of the voltage application unit 140 is not applied to the secondary battery 20. At this time, the positive terminal 221 and the negative terminal 222 of the secondary battery 20 are in an open state (floating state). That is, the second state is when the switching unit 120 is in the OFF state. In the second state, no charge flows in or out of the positive terminal 221 and the negative terminal 222.

[0026] In the example of FIG. 6, the voltage application unit 140 outputs a predetermined voltage V2. The predetermined voltage V2 is a voltage determined based on the open circuit voltage. For example, ΔV2, which is the difference between the open circuit voltage and the output voltage of the voltage application unit 140, is determined in advance, and the voltage V2 for the secondary battery 20 is determined by subtracting ΔV2 from the open circuit voltage of the secondary battery 20 to be measured. When the switching unit 120 is in the ON state, the output voltage of the voltage application unit 140 is applied to the secondary battery 20. That is, when the switching unit 120 is in the ON state, the first state is reached. In the example of this figure, the secondary battery 20 is discharged in the first state. On the other hand, when the switching unit 120 is in the OFF state, the output voltage of the voltage application unit 140 is not applied to the secondary battery 20. At this time, the positive terminal 221 and the negative terminal 222 of the secondary battery 20 are in an open state (floating state). That is, when the switching unit 120 is in the OFF state, the second state is reached. In the second state, no charge flows in or out of the positive terminal 221 and the negative terminal 222.

[0027] In the first state caused by the measurement device 10, the secondary battery 20 may be charged as shown in FIG. 5, or the secondary battery 20 may be discharged as shown in FIG.

[0028] The measuring unit 160 of the measuring device 10 measures the magnetic field leaking out of the secondary battery 20 in the second state. For example, the measuring unit 160 generates time-series data of the magnetic field in the second state as a measurement result. In the second state, the strength of the magnetic field measured by the measuring unit 160 approaches zero over time from the time when the state is switched from the first state to the second state. The measuring unit 160 measures this transient response. In the second state following the first state, the positive electrode terminal 221 and the negative electrode terminal 222 of the secondary battery 20 are in an open state, so that no charge flows in or out of the secondary battery 20. In such a second state, the charge distribution is relaxed inside the secondary battery 20. In the process of this relaxation, the charge moves, generating a magnetic field, and the magnetic field also leaks out to the outside of the secondary battery 20. The measuring unit 160 measures this leaked magnetic field. Here, how the charge distribution is relaxed depends on the distribution of electrical characteristics (such as impedance) inside the secondary battery 20. Therefore, it can be said that the magnetic field measured by the measuring unit 160 contains information on the distribution of electrical characteristics inside the secondary battery 20.

[0029] According to the measuring device 10 of this embodiment, the secondary battery 20 is neither charged nor discharged in the second state. That is, the measurement is performed with the current flowing through the positive terminal 221 and the negative terminal 222 cut off. The effect of this will be further explained. If the magnetic field is measured with a current flowing through the electrodes of the secondary battery 20, current concentration occurs near the positive terminal 221 and the negative terminal 222, and the measurement is performed with a strong magnetic field occurring near these terminals. In order to measure such a strong magnetic field, it is necessary to make the measurement range of the magnetic field by the sensor large. On the other hand, with a large measurement range, it becomes difficult to measure in detail a weak magnetic field at a position away from the positive terminal 221 and the negative terminal 222. In contrast, in the measuring device 10 of this embodiment, the magnetic field is measured with no current flowing through the positive terminal 221 and the negative terminal 222. Therefore, no current concentration or strong magnetic field occurs near the positive terminal 221 and the negative terminal 222, and the magnetic field becomes uniform overall compared to when a current flows through the terminals. As a result, magnetic field measurements can be performed in a good measurement range throughout the entire secondary battery 20, and even weak magnetic fields can be measured with high accuracy.

[0030] The processing unit 180 processes the transient response measured by the measurement unit 160 to calculate the feature amount of the transient response. For example, the processing unit 180 calculates the time average of the magnetic field measured by the measurement unit 160 as the feature amount. Alternatively, the processing unit 180 may calculate the time constant of the transient response measured by the measurement unit 160 as the feature amount. The feature amount is not limited to these values, and various statistical values ​​can be used as the feature amount. As described above, when the measurement unit 160 measures the transient response at multiple positions in one or more planes 201 outside the secondary battery 20, the processing unit 180 can generate a map showing information about the inside of the secondary battery 20. The processing unit 180 generates a map showing the distribution of the calculated feature amount. The map generated by the processing unit 180 can be output as an image. According to such an image, a contrast occurs between defective parts and normal parts inside the secondary battery 20. Therefore, a user who checks the image can understand the presence or absence of defective parts and their positions.

[0031] Furthermore, the processing unit 180 may determine whether or not there is an abnormality in the secondary battery 20 using the measurement result by the measurement unit 160. Then, the processing unit 180 may output a notification when it is determined that there is an abnormality in the secondary battery 20.

[0032] For example, when measuring a plurality of secondary batteries 20 manufactured by the same method, it is assumed that there is not much individual difference between the secondary batteries 20. Therefore, a predetermined normal range is compared with the calculated feature amount, and whether or not there is an abnormality in the secondary battery 20 can be determined based on the comparison result. That is, if the feature amount is within the normal range, the processing unit 180 determines that there is no abnormality in the secondary battery 20. If the feature amount is not within the normal range, the processing unit 180 determines that there is an abnormality in the secondary battery 20. The normal range can be determined by a prior test or the like. The processing unit 180 can read information indicating the normal range stored in a storage unit accessible from the processing unit 180 and use it for the determination. The information indicating the normal range can be one or more threshold values ​​indicating the ends of the normal range.

[0033] When the processing unit 180 calculates the feature amounts for a plurality of measurement positions within the plane 201, if at least one of the plurality of feature amounts is not within the normal range, the processing unit 180 determines that the secondary battery 20 has an abnormality.

[0034] As another example, the processing unit 180 may determine whether or not there is an abnormality in the secondary battery 20 based on the variation (e.g., variance) of multiple feature amounts calculated for multiple measurement positions. That is, if the variation in the feature amounts is equal to or less than a predetermined threshold, the processing unit 180 determines that there is no abnormality in the secondary battery 20. If the variation in the feature amounts is greater than the threshold, the processing unit 180 determines that there is an abnormality in the secondary battery 20. The threshold can be determined by a prior test or the like. The processing unit 180 can read information indicating the threshold amount stored in a storage unit accessible from the processing unit 180 and use the information for the determination.

[0035] The processing unit 180 can output the generated map or a notification indicating the determination result as output information, for example, by displaying it on a display provided in the processing unit 180. As another example, the processing unit 180 may output the output information to a device external to the measuring device 10, or may store the output information in a storage device accessible from the processing unit 180. When it is determined that there is an abnormality, the processing unit 180 may display a message indicating that there is an abnormality on a display as a notification, may output a message indicating that there is an abnormality by voice, may output a predetermined sound, or may turn on or blink a predetermined lamp. Furthermore, when it is determined that there is no abnormality, the processing unit 180 may output a notification different from that when it is determined that there is an abnormality.

[0036] The measuring unit 160 may measure multiple transient responses (i.e., multiple transient responses) at each measurement position. For example, the first state and the second state may be alternately and repeatedly realized by the switching unit 120 and the voltage application unit 140, and the measuring unit 160 may measure the transient response of the magnetic field in each second state. Here, in the multiple first states, it is preferable that charging and discharging are alternately performed. In other words, it is preferable that the first state in which the secondary battery 20 is charged and the first state in which the secondary battery 20 is discharged are alternately realized. That is, the voltage V as shown in FIG. B and the voltage V as shown in Figure 6 B and are applied alternately. As a result, the first state and the second state in which the secondary battery 20 is charged, and the first state and the second state in which the secondary battery 20 is discharged are repeatedly realized in this order. This makes it possible to repeatedly measure the secondary battery 20 in approximately the same charge state without charging or discharging proceeding unilaterally. The S / N ratio can be improved by accumulating or averaging the multiple measurement results obtained. As a result, an abnormality in the secondary battery 20 can be detected with high accuracy.

[0037] It is preferable that the first state is repeated a number of times to maintain a balance between the charge amount and the discharge amount. The charge amount is determined by the time length t c The product of V1 and the difference between V1 and the open circuit voltage ΔV1, tc × ΔV1. On the other hand, the discharge amount is quantified by the length of time t d The product of V2 and the difference between V2 and the open circuit voltage ΔV2, t d ×ΔV2. Therefore, t c ×ΔV1=t d It is preferable that the first state and the second state are alternately repeated in a state where ×ΔV2 holds. The length of the first state may be the same or different from each other. In addition, the difference between the voltage applied to the secondary battery 20 and the open circuit voltage in the first state may be the same or different from each other. c and t d are, for example, 0.1 seconds or more and 10 seconds or less. ΔV1 and ΔV2 are, for example, 0.01 V or more and 4 V or less. ΔV1 and ΔV2 may be the same as each other or may be different. For example, one of ΔV1 and ΔV2 may be a value obtained by adding a compensation value for compensating for the asymmetry between the positive electrode and the negative electrode of the secondary battery 20 to the other of ΔV1 and ΔV2.

[0038] Furthermore, when the first state in which the secondary battery 20 is charged, the second state, the first state in which the secondary battery 20 is discharged, and the second state are repeatedly realized in this order as described above, the measurement unit 160 may measure both the transient response when the secondary battery 20 is switched from the first state in which the secondary battery 20 is charged to the second state (hereinafter referred to as the post-charge transient response) and the transient response when the secondary battery 20 is switched from the first state in which the secondary battery 20 is discharged to the second state (hereinafter referred to as the post-discharge transient response), or may measure only one of them.

[0039] When the measuring unit 160 measures a plurality of transient responses at each measurement position, the processing unit 180 calculates, for example, a feature amount of the transient response for each measurement position. Examples of the feature amount include an average value of the time average of the magnetic field in the plurality of transient responses, or an average value of the time constants of the plurality of transient responses. The processing unit 180 can generate a map showing the distribution of the calculated feature amount. The processing unit 180 can also compare the calculated feature amount with a predetermined normal range to determine whether or not there is an abnormality in the secondary battery 20. In addition, in the calculation of the feature amount, data of the post-charge transient response and data of the post-discharge transient response may or may not be distinguished. In the case where these data are distinguished, feature amounts can be calculated for each of the data of the post-charge transient response and the data of the post-discharge transient response. In the case where the data of the post-charge transient response and the data of the post-discharge transient response are not distinguished, for example, in the calculation of the time average of the magnetic field, the strength of the magnetic field, i.e., the absolute value, is used.

[0040] The hardware configuration of the measurement device 10 will be described. The switching unit 120, the voltage application unit 140, the processing unit 180, and the control unit 190 of the measurement device 10 may be realized by hardware (e.g., electronic circuits, etc.) that realizes the switching unit 120, the voltage application unit 140, the processing unit 180, and the control unit 190, or may be realized by using a combination of hardware and software (e.g., a combination of an electronic circuit and a program that controls the electronic circuit). Below, a further description will be given of a case where the switching unit 120, the voltage application unit 140, the processing unit 180, and the control unit 190 of the measurement device 10 are realized by using a combination of hardware and software.

[0041] FIG. 7 is a diagram illustrating a computer 1000 for implementing the measurement device 10. The computer 1000 is any computer. For example, the computer 1000 is a system on chip (SoC), a personal computer (PC), a server machine, a tablet terminal, or a smartphone. The computer 1000 may be a dedicated computer designed for implementing the measurement device 10, or may be a general-purpose computer. The measurement device 10 may be implemented using one computer 1000, or may be implemented using a combination of multiple computers 1000.

[0042] The computer 1000 includes a bus 1020, a processor 1040, a memory 1060, a storage device 1080, an input / output interface 1100, and a network interface 1120. The bus 1020 is a data transmission path for the processor 1040, the memory 1060, the storage device 1080, the input / output interface 1100, and the network interface 1120 to transmit and receive data to and from each other. However, the method of connecting the processor 1040 and the like to each other is not limited to bus connection. The processor 1040 is various processors such as a central processing unit (CPU), a graphics processing unit (GPU), or a field-programmable gate array (FPGA). The memory 1060 is a main storage device realized using a random access memory (RAM) or the like. The storage device 1080 is an auxiliary storage device realized using a hard disk, a solid state drive (SSD), a memory card, or a read only memory (ROM) or the like.

[0043] The input / output interface 1100 is an interface for connecting the computer 1000 and an input / output device. For example, an input device such as a keyboard and an output device such as a display are connected to the input / output interface 1100. The input / output interface 1100 may be connected to the input device or the output device by wireless connection or by wired connection.

[0044] The network interface 1120 is an interface for connecting the computer 1000 to a network. This communication network is, for example, a LAN (Local Area Network) or a WAN (Wide Area Network). The method for connecting the network interface 1120 to the network may be a wireless connection or a wired connection.

[0045] The storage device 1080 stores program modules for implementing each functional component of the measurement device 10. The processor 1040 reads each of these program modules into the memory 1060 and executes them to implement the function corresponding to each program module.

[0046] A measurement method according to this embodiment will be described. The measurement method according to this embodiment is a method for measuring the secondary battery 20. In this measurement method, the secondary battery 20 is switched between a first state in which a predetermined voltage determined based on the open circuit voltage of the secondary battery 20 is applied, and a second state in which the secondary battery 20 is open. In addition, a transient response of the magnetic field outside the secondary battery 20 is measured when switching from the first state to the second state. Then, information about the inside of the secondary battery 20 is generated using the measurement result of the transient response.

[0047] The measurement method according to this embodiment is realized by the measurement device 10 according to this embodiment.

[0048] According to this embodiment, by measuring the transient response of the magnetic field outside the secondary battery when it switches from the first state to the second state, stable measurement can be performed when charging or discharging is not in progress, and information about the inside of the secondary battery can be obtained. In addition, magnetic field measurement can be performed in a good measurement range throughout the secondary battery 20, and even weak magnetic fields can be measured with high accuracy.

[0049] Second embodiment Fig. 8 is a diagram illustrating the configuration of the switching section 120 and the voltage application section 140 included in the measurement device 10 according to the second embodiment. Fig. 9 is a diagram for explaining the operation of the measurement device 10 according to the present embodiment. The measurement device 10 and the measurement method according to the present embodiment are the same as the measurement device 10 and the measurement method according to the first embodiment, except for the points described below.

[0050] In the measuring device 10 according to this embodiment, the voltage application section 140 applies a predetermined voltage to the secondary battery 20 by a periodic signal. Then, the switching section 120 switches between a first state and a second state by a periodic signal having a frequency that is an integer multiple of the frequency of the periodic signal. This will be described in detail below.

[0051] 8, voltage application section 140 includes DC voltage source 141 and oscillator 142. DC voltage source 141 is set to output a DC voltage having the same voltage value as the open-circuit voltage of secondary battery 20. The open-circuit voltage of secondary battery 20 can be measured separately prior to measurement by measurement device 10. Then, prior to measurement by measurement device 10, a user of measurement device 10 sets the output voltage value of DC voltage source 141.

[0052] Oscillator 142 outputs a voltage signal, for example, a square wave. The signal output by oscillator 142 is also referred to as a reference signal below. DC voltage source 141 and oscillator 142 are connected in series, and voltage application unit 140 outputs a voltage V A In the first state, the output voltage V Ais applied between the positive terminal 221 and the negative terminal 222 of the secondary battery 20, a predetermined voltage determined based on the open circuit voltage of the secondary battery 20 is applied to the secondary battery 20.

[0053] The upper part of FIG. 9 shows the output voltage V A The waveform of the voltage V A The waveform of is a square wave centered on the open circuit voltage. In other words, the voltage V A The waveform of the reference signal is obtained by adding a DC offset of the open circuit voltage to the reference waveform. The frequency of the reference signal can be set arbitrarily depending on the characteristics of the secondary battery 20, and is, for example, 0.1 Hz to 100 kHz. The amplitude of the reference signal is, for example, 0.02 V. p-p More than 8V p-p The voltage V A The voltages V1 and V2, which are the peak values ​​of the above voltages, are the voltages applied to the secondary battery 20 in the first state. When the voltage V1, which is higher than the open-circuit voltage, is applied, the secondary battery 20 is charged. When the voltage V2, which is lower than the open-circuit voltage, is applied, the secondary battery 20 is discharged.

[0054] 8, the switching unit 120 includes a MOSFET 121, a multiplier 122, and an AND gate 123. An output signal of the AND gate 123 is input to the gate of the MOSFET 121. One of the source and drain of the MOSFET 121 is connected to one output terminal of the voltage application unit 140. The other of the source and drain of the MOSFET 121 is connected to one of the positive terminal 221 and the negative terminal 222 of the secondary battery 20. The other output terminal of the voltage application unit 140 is connected to the other of the positive terminal 221 and the negative terminal 222 of the secondary battery 20. The output terminal of the voltage application unit 140 refers to a terminal that outputs a voltage V A This means the terminal that outputs

[0055] In the example shown in the figure, the MOSFET 121 is a p-channel MOSFET, but the MOSFET 121 is not limited to this example and may be an n-channel MOSFET or another switching element. A control signal from the control unit 190 and an output signal of the multiplier 122 are input to two input terminals of the AND gate 123.

[0056] The control unit 190 continues to input a "1" level signal as a control signal to the AND gate 123 while the first state or the second state is being maintained (for example, during a measurement step described later in the third embodiment). On the other hand, the control unit 190 continues to input a "0" level signal as a control signal to the AND gate 123 while the state is other than the first state or the second state (for example, during a specifying step described later in the third embodiment). In this example, the "1" level signal is a negative voltage, and the "0" level signal is 0V.

[0057] A reference signal output from oscillator 142 is input to multiplier 122. This reference signal is a periodic signal having the same frequency as the reference signal. Multiplier 122 outputs a periodic signal (e.g., a square wave) having a frequency that is an integer multiple of the frequency of the reference signal.

[0058] FIG. 9 shows an example in which the multiplier 122 outputs a periodic signal having a frequency twice that of the reference signal. Also, in this figure, an example in which the control unit 190 continues to input a signal of level "1" to the AND gate 123 as a control signal. That is, when the output of the multiplier 122 is at level "1", the output of the AND gate 123 is at level "1", and otherwise, the output of the AND gate 123 is at level "0". As a result, the output of the AND gate 123 becomes a signal that switches between level "1" and level "0" at a frequency twice that of the reference signal, that is, twice that of the reference signal. The MOSFET 121 is in an ON state when the input to the gate is at level "1", and in an OFF state when the input to the gate is at level "0". In the example of this figure, when the input to the gate of the MOSFET 121 is at level "1", the gate potential is negative.

[0059] As a result of these operations, the voltage V A The application of the reference signal is turned on / off at twice the frequency of the reference signal. The period during which the MOSFET 121 is in the ON state corresponds to the period of the first state, and the period during which the MOSFET 121 is in the OFF state corresponds to the period of the second state. As shown in the middle part of the figure, the first state and the second state are repeated at twice the frequency of the reference signal. The lower part of the figure shows an example of a waveform assumed to be the magnetic flux density outside the secondary battery 20.

[0060] According to the measuring device 10 of this embodiment, the first state in which the secondary battery 20 is charged, the second state, the first state in which the secondary battery 20 is discharged, and the second state are repeatedly realized in this order. c ×ΔV1=t d ×ΔV2 is established. As described above in the first embodiment, the measurement unit 160 according to this embodiment can repeatedly measure the transient response of the secondary battery 20 in approximately the same charged state. The processing unit 180 can obtain information with a high S / N ratio by using a plurality of measured transient responses. As a result, an abnormality in the secondary battery 20 can be detected with high accuracy.

[0061] However, the hardware configuration of the switching section 120 and the voltage application section 140 included in the measurement device 10 according to this embodiment is not limited to the example in FIG.

[0062] 10(a) to 10(g) are diagrams showing an example in which the frequency of the periodic signal output by the multiplier 122 is changed. FIG. 10(a) shows the waveform of a reference signal. FIG. 10(b) and FIG. 10(c) show the voltage V B 10(d) and 10(e) respectively show examples of the output waveform of the measurement unit 160. The voltage V B10(f) and 10(g) respectively show examples of the output waveform of the measurement unit 160. The voltage V B and show examples of assumed output waveforms of the measuring unit 160. In the dashed line parts of Figures 10(b), 10(d), and 10(f), the secondary battery 20 is in an open state. V0 in Figures 10(c), 10(e), and 10(g) is the sensor output value when the magnetic flux density is zero.

[0063] In this way, the multiplier 122 outputs a periodic signal having a frequency that is an even multiple of the frequency of the reference signal, so that a set of the first state and the second state in which the secondary battery 20 is charged continues N times, and then a set of the first state and the second state in which the secondary battery 20 is discharged continues N times. That is, the number of times the first state in which the secondary battery 20 is charged is equal to the number of times the first state in which the secondary battery 20 is discharged. Therefore, the measurement of the transient response can be repeatedly performed while maintaining a balance between the charge amount and the discharge amount. Here, N is an integer equal to or greater than 1.

[0064] (Third embodiment) Fig. 11 is a diagram illustrating a signal flow in the measurement section 160 according to the third embodiment. Fig. 12 is a diagram illustrating a hardware configuration of the measurement section 160 according to the present embodiment. The measurement device 10 according to the present embodiment is the same as the measurement device 10 according to the first or second embodiment except for the points described below. The measurement method according to the present embodiment is the same as the measurement method according to the first or second embodiment except for the points described below.

[0065] The measurement device 10 according to this embodiment includes a control unit 190 that controls the voltage application unit 140 and the measurement unit 160. The measurement unit 160 includes a sensor unit 161 and a sensor driving unit 162. The control unit 190 controls the voltage application unit 140 and the measurement unit 160 so that the identification step and the measurement step are performed in that order. In the identification step, a fixed input value to the sensor unit 161 for canceling at least a part of the noise magnetic field is identified. In the measurement step, a transient response is measured with the fixed input value being input to the sensor unit 161.

[0066] More specifically, in the identification process, when a voltage equivalent to the open circuit voltage is applied to the secondary battery 20, the control unit 190 controls the voltage application unit 140 and the measurement unit 160 so that the sensor driving unit 162 feedback controls the input value to the sensor unit 161 so that the output of the sensor unit 161 approaches a reference level, thereby identifying a fixed input value.

[0067] The secondary battery 20 may contain a ferromagnetic material, for example as an electrode material. Examples of the ferromagnetic material contained in the secondary battery 20 include nickel, cobalt, and iron. Due to this ferromagnetic material, the secondary battery 20 may generate a magnetic field regardless of the relaxation of the charge. Such a magnetic field acts as noise in the measurement. In addition, there may also be a noise magnetic field due to the geomagnetism or a magnetic material near the measurement position.

[0068] In this embodiment, the sensor unit 161 may include any magnetic sensor such as a coil, a Hall element, an optical pumping magnetic sensor, a diamond magnetic sensor, a magnetic impedance sensor, or a magnetoresistance effect element. The sensor unit 161 may have, for example, a core and one or more coils wound around the core. In the example of FIG. 11, the sensor unit 161 receives an input signal S FB The coil 166 of the sensor unit 161 receives an input signal S FB A current flows according to the input signal S, generating a magnetic field. FB By appropriately setting, the generated magnetic field can cancel out the noise magnetic field.

[0069] The sensor unit 161 receives an input signal S FB The monitor signal S indicates the level m The sensor unit 161 also outputs an output signal S indicating the measured magnetic flux density. out Output.

[0070] The sensor driver 162 receives the output signal S from the sensor unit 161. out A predetermined target value is subtracted from the signal, and the resulting signal is added to the monitor signal S. m The sensor driving unit 162 may further amplify the signal after the addition. The target value is the output signal S of the sensor unit 161 when the measured magnetic flux density is zero. out This target value is set as the reference level. Such a sensor driving section 162 enables feedback control to cancel out the noise magnetic field measured by the sensor section 161.

[0071] The hardware configuration of the measurement unit 160 will be described with reference to Fig. 12. The sensor driving unit 162 includes a D / A converter 164 and an A / D converter 163. The sensor driving unit 162 is realized by using a computer 1000. out and monitor signal S m is input to the computer 1000 via the A / D converter 163. FB is output from the computer 1000 and input to the sensor unit 161 via the D / A converter 164. The hardware configuration of the computer 1000 for implementing the sensor driving unit 162 is shown in, for example, FIG. 7, similar to the control unit 190 and the like. However, a program module for implementing the function of the sensor driving unit 162 is further stored in the storage device 1080 of the computer 1000 for implementing the sensor driving unit 162.

[0072] 13 is a diagram illustrating the configuration of the measurement device 10 according to this embodiment. In this diagram, an example is shown in which the switching section 120 and the voltage application section 140 have the configurations of the switching section 120 and the voltage application section 140 of the measurement device 10 according to the second embodiment, respectively, but the configurations of the switching section 120 and the voltage application section 140 are not limited to this example.

[0073] As described above, the measuring device 10 according to this embodiment performs the specifying step and the measuring step in this order. Specifically, at each measurement position, the specifying step is performed once prior to the measuring step.

[0074] In the identification step, a voltage equivalent to the open circuit voltage is applied between the positive terminal 221 and the negative terminal 222 of the secondary battery 20 by the voltage application unit 140. The voltage application unit 140 includes, for example, a switch 143 that can be switched under the control of the control unit 190. By switching this switch 143, a state in which a voltage equivalent to the open circuit voltage is applied to the secondary battery 20 from the DC voltage source 141 and a state for the measurement step that realizes the first state and the second state are switched. The control unit 190 can control the switching of the switch 143.

[0075] In the identification process, feedback control by the sensor driving unit 162 is started in a state where a voltage equivalent to the open circuit voltage is applied to the secondary battery 20 from the DC voltage source 141. In a state where a voltage equivalent to the open circuit voltage is applied to the secondary battery 20, the secondary battery 20 is neither charged nor discharged, and therefore only the noise magnetic field is measured. Then, the output signal S of the sensor unit 161 is out The control loop is repeated at a predetermined period until the noise magnetic field is cancelled by the reference level. Then, the sensor driver 162 outputs the output signal S out The feedback control is terminated when the input signal (feedback signal) S at the time of the termination of the feedback control is reached. FBis set as a fixed input value. This fixed input value can be said to be a set value that can adequately cancel out the noise magnetic field at the measurement position. In the measurement process that is performed next, the sensor driving unit 162 drives the input signal S FB is fixed to a fixed input value. The control unit 190 controls the sensor driving unit 162 so that such operations are performed in the identification process and the measurement process.

[0076] In the measurement step, as described in the first and second embodiments, the first and second states are realized, and the transient response of the magnetic field in the second state is measured by the measuring unit 160.

[0077] In the example shown in the figure, the switching unit 120 is controlled by a control signal from a computer 1000 having the functions of a control unit 190. The control unit 190 inputs a control signal of level "0" to the AND gate 123 during the identification step, as explained in the second embodiment, for example. Also, during the measurement step, it inputs a control signal of level "1" to the AND gate 123. The control unit 190 also monitors the output signal of the AND gate 123 to monitor the switching state of the switching unit 120. Then, the control unit 190 identifies the period of the second state based on the monitored switching state, and during the period of the second state, outputs the output signal S of the sensor unit 161. out Get the.

[0078] In this embodiment, the same actions and effects as those of the first embodiment can be obtained. In addition, it is possible to perform measurements with reduced influence of noise magnetic fields.

[0079] (Fourth embodiment) The measurement device 10 according to the fourth embodiment is the same as the measurement device 10 according to at least one of the first to third embodiments, except for the points described below. The measurement method according to this embodiment is the same as the measurement method according to at least one of the first to third embodiments, except for the points described below.

[0080] The measuring unit 160 of the measuring device 10 according to this embodiment measures magnetic field components in two mutually orthogonal directions as a transient response. Then, the processing unit 180 uses the magnetic field components in the two directions to generate a conductivity distribution inside the secondary battery 20. This will be described in detail below.

[0081] Specifically, the measuring unit 160 measures the x-direction magnetic field component and the y-direction magnetic field component for a plurality of measuring points (x, y) in a plane 201 parallel to the main surfaces of the positive electrode 211 and the negative electrode 212. The x-direction magnetic field component means the x-direction component of the magnetic flux density, and the y-direction magnetic field component means the y-direction component of the magnetic flux density.

[0082] For example, the processing unit 180 calculates the time average of each transient response of the magnetic field component in each direction. Then, the average value of the time average is calculated as the feature value for each measurement position. In this way, for each measurement point (x, y), the feature value of the magnetic field component in the x direction (hereinafter referred to as the x component) and the feature value of the magnetic field component in the y direction (hereinafter referred to as the y component) are obtained.

[0083] The processing unit 180 further uses these feature amounts to generate a conductivity distribution inside the secondary battery 20. As a method for generating a conductivity distribution inside the secondary battery 20, for example, the method described in Patent Document 1 can be used.

[0084] Specifically, the processing unit 180 derives the conductivity distribution of a predetermined plane in the secondary battery 20 that satisfies a plurality of relational expressions for the obtained x component and y component. Note that the predetermined plane is a plane parallel to the xy plane.

[0085] More specifically, the processing unit 180 derives the conductivity distribution represented by σ based on the following formulas (1) to (3).

[0086]

number

number

number

[0087] In the formulas (1) to (3), the coordinate in the x direction is represented by x, the coordinate in the y direction is represented by y, the coordinate in the z direction is represented by z, the coordinate in the z direction of the first electrode (positive electrode 211 or negative electrode 212) closest to the plane 201 is represented by z0, and the x component is H x and the y component is H y The thickness of the first electrode in the z-direction is represented by h, and the distance between a pair of electrodes including the first electrode is represented by h T The conductivity of the first electrode is expressed as σ0, and the potential distribution is

number

[0088] The processing unit 180 can derive the electrical conductivity distribution using various formulas derived from formulas (1) to (3).

[0089] The processing unit 180 can output the derived conductivity distribution, for example, as an image. The processing unit 180 can output the generated image as output information, for example, by displaying it on a display provided in the processing unit 180. As another example, the processing unit 180 may output the output information to a device external to the measuring device 10, or may store the output information in a storage device accessible from the processing unit 180.

[0090] In this embodiment, the same actions and effects as those of the first embodiment can be obtained. In addition, the conductivity distribution in the secondary battery 20 can be grasped. EXAMPLES

[0091] The present embodiment will be described in detail below with reference to examples. However, the present embodiment is not limited to the description of these examples.

[0092] FIG. 14 is a schematic cross-sectional view showing the structure of a secondary battery 90 to be measured. The secondary battery 90 was measured by the method described in the third embodiment. The secondary battery 90 includes a laminate of a negative electrode 91, a separator 92, and a positive electrode 93, and the laminate was covered with a package. Note that the package is omitted in this figure. As shown in this figure, a hole was made in the separator 92 as a defect 94, and the secondary battery 90 to be measured was used. By making a hole in the separator 92, the positive electrode 93 and the negative electrode 91 were brought into physical contact at the defect 94, causing a short circuit.

[0093] FIG. 15 is a diagram showing the positions of a measurement area 95 and a defect 94 in a photograph of a secondary battery 90. The measurement area was 120 mm×100 mm, and a map of 16×12 pixels was obtained. The integration time at each measurement position was 200 sec. The frequency of the reference signal was 4 Hz, and the current flowing through the secondary battery 90 during charging and discharging in the measurement process was 500 mA. p-p The amount of voltage drop due to natural discharge of the secondary battery 90 was 1.5 mV / day (from a fully charged state of 3.67 V).

[0094] FIG. 16 is a diagram showing a map generated using the measurement results of the transient response of the magnetic field. In generating this map, the absolute value of the time average of the magnetic flux density of the measured transient response was calculated for each measurement position. Then, the average value of the absolute values ​​calculated for multiple transient responses (referred to as the average magnetic flux density in FIG. 16 and below) was calculated. The distribution of the calculated average magnetic flux density is shown in the map. In generating this map, the average value was calculated using data on the transient response after charging and data on the transient response after discharging without distinguishing between them. In this figure, the map is shown superimposed on a photograph of the secondary battery 90 at the corresponding positions.

[0095] As shown in the figure, a different level of average magnetic flux density was measured near the defect 94 compared to other areas. More specifically, the average magnetic flux density was higher near the defect 94 than in other areas. From this result, it was confirmed that this measurement method can obtain information inside the secondary battery 90 and detect defects.

[0096] Although the embodiments of the present invention have been described above with reference to the drawings, these are merely examples of the present invention, and various configurations other than those described above may also be adopted. Furthermore, the above-described embodiments may be combined within a range in which the contents are not contradictory.

[0097] This application claims priority based on Japanese Patent Application No. 2022-109689, filed on July 7, 2022, the disclosure of which is incorporated herein in its entirety. [Explanation of symbols]

[0098] 10. Measuring Equipment 20 Secondary battery 120 Switching section 121 MOSFET 122 Multiplier 123 AND Gate 140 Voltage application section 141 DC voltage source 142 Oscillator 143 Switch 150 Stages 160 Measuring section 161 Sensor section 162 Sensor drive unit 180 Processing section 190 Control section 211 Positive electrode 212 Negative electrode 221 Positive terminal 222 Negative terminal 230 Electrolytes 240 packages 1000 calculator

Claims

1. A measurement device for measuring a secondary battery, a voltage application unit that applies a predetermined voltage to the secondary battery, the voltage being determined based on an open circuit voltage of the secondary battery; a switching unit that switches between a first state in which the predetermined voltage is applied to the secondary battery and a second state in which the secondary battery is open; a measurement unit that measures a transient response of a magnetic field outside the secondary battery when the secondary battery is switched from the first state to the second state; a processing unit that generates information regarding the inside of the secondary battery using a measurement result by the measurement unit. Measuring equipment.

2. 2. The measuring device according to claim 1, A control unit that controls the voltage application unit and the measurement unit, The measurement unit includes a sensor unit and a sensor driving unit, The control unit controls the voltage application unit and the measurement unit so that a determination step of determining a fixed input value to the sensor unit for canceling at least a part of a noise magnetic field and a measurement step of measuring the transient response in a state in which the fixed input value is input to the sensor unit are performed in that order. Measuring equipment.

3. 3. The measuring device according to claim 2, In the specifying step, the sensor driving unit feedback-controls an input value to the sensor unit so that the output of the sensor unit approaches a reference level in a state where a voltage corresponding to an open circuit voltage is applied to the secondary battery, and the control unit controls the voltage application unit and the measurement unit so that the fixed input value is specified. Measuring equipment.

4. 4. The measuring device according to claim 2, The secondary battery includes a ferromagnetic material. Measuring equipment.

5. The measuring device according to any one of claims 1 to 3, the measurement unit measures the transient response at a plurality of positions in one or more planes outside the secondary battery; The processing unit generates a map indicating information about the inside of the secondary battery. Measuring equipment.

6. 6. The measuring device according to claim 5, The measurement unit includes a plurality of sensor elements arranged in a matrix. Measuring equipment.

7. The measuring device according to any one of claims 1 to 3, The processing unit includes: Using the measurement result by the measurement unit, it is determined whether or not there is an abnormality in the measured secondary battery; If it is determined that the secondary battery is abnormal, a notification is output. Measuring equipment.

8. The measuring device according to any one of claims 1 to 3, the voltage application unit applies the predetermined voltage to the secondary battery in response to a periodic signal; The switching unit switches between the first state and the second state in response to a periodic signal having a frequency that is an integer multiple of the frequency of the periodic signal. Measuring equipment.

9. The measuring device according to any one of claims 1 to 3, The measurement unit measures magnetic field components in two directions perpendicular to each other as the transient response, The processing unit generates a conductivity distribution inside the secondary battery by using the magnetic field components in the two directions. Measuring equipment.

10. A method for measuring a secondary battery, comprising: switching between a first state in which a predetermined voltage determined based on an open circuit voltage of the secondary battery is applied to the secondary battery and a second state in which the secondary battery is open circuit; measuring a transient response of a magnetic field external to the secondary battery when the secondary battery is switched from the first state to the second state; Generate information about the inside of the secondary battery using the measurement result of the transient response Measurement method.

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