JP2014089819A - Magnetic field measuring device, and battery deterioration inspecting method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide technology for spacially evaluating capacity deterioration of a lithium ion battery with high accuracy to contribute it to designing a highly reliable battery hard to deteriorate, and to apply it to the inspection process in battery manufacturing by enabling detection of capacity deterioration of the lithium ion battery in a short time.SOLUTION: A magnetic field measuring device includes: a magnetic field detection part for detecting a magnetic field generated from the battery; and an arithmetic processing part for calculating a magnetic field distribution in the battery based on the detected magnetic field. The magnetic field detection part detects first and second magnetic fields generated from the battery when charging and discharging the battery using a first applied current and a second applied current having a current amount different from that of the first applied current to the battery in a prescribed charged state, and the arithmetic processing part calculates first and second magnetic field distributions based on the first and second magnetic fields and evaluates the deterioration state of the battery based on a difference between the first and second magnetic fields or the ratio of the first magnetic field distribution to the second magnetic field distribution.

Description

  The present invention relates to a magnetic field measurement device and a battery deterioration inspection method using the same, and measures, for example, a magnetic field generated from a lithium ion battery being charged / discharged using a magnetic sensor and evaluates a deterioration state of the lithium ion battery. The present invention relates to a battery deterioration inspection apparatus and method using a measurement apparatus.

In recent years, there has been a social interest in power storage technologies such as secondary batteries. For example, the core technologies of energy storage systems for renewable energy such as solar power generation and wind power generation that do not generate CO ₂ , home energy storage systems that use nighttime power, electric vehicles, hybrid vehicles, and plug-in hybrid vehicles The government and companies are actively working on the development and popularization of energy storage systems.

  As described above, lithium-ion batteries have begun to be widely used as storage batteries for power storage systems that are attracting a lot of social interest (about 1.2 billion in 2010). A lithium ion battery can obtain a high voltage (3.7 V) and has a high energy density. For this reason, lithium-ion batteries can achieve high voltage despite being lightweight and compact, so they will be used as batteries for mobile phones and laptop computers, and for electric and hybrid vehicles. Is expected to increase. In addition, recently, by adopting a laminate structure for a lithium ion battery, it is possible to realize a thin and large capacity, and its mounting on electric vehicles and household power storage systems is rapidly expanding.

  As demand for lithium-ion batteries is expected to increase, evaluating the performance of lithium-ion batteries and ensuring their quality is one of the important efforts. The battery capacity of a lithium ion battery is reduced by repeating charge and discharge. This phenomenon is called capacity deterioration. When this capacity deterioration occurs, the operation time of a device using a battery is shortened or suddenly becomes unusable.

  As a method for evaluating the capacity deterioration of the lithium ion battery, in the performance evaluation in the battery design and the inspection process of the battery manufacture (see FIG. 11), the battery voltage is measured when charging / discharging is repeated, or the AC impedance (internal resistance). The measurement etc. are implemented (nonpatent literature 1).

  However, these measurements measure the voltage between the terminals of the battery, and it is possible to evaluate the deterioration of the entire battery, but it is difficult to evaluate the local voltage and impedance in the battery. Therefore, in order to investigate in detail the cause of battery capacity degradation, a method for inspecting a local site inside the battery with high spatial resolution has been desired.

  On the other hand, as a device for evaluating the performance of a fuel cell or a solar cell, a device that measures a magnetic field generated from a battery and visualizes a current distribution in the battery from the measured magnetic field signal has been developed (Patent Documents 1-3). . For example, in Patent Document 1, a magnetic sensor is optimally arranged around the battery, the geomagnetism is removed, and the current distribution in the battery is visualized by calculation processing from the recorded magnetic field signal. In Patent Document 2, a triaxial magnetic sensor is arranged in parallel with the light receiving surface and the back surface of the solar cell, and at least one of the magnetic sensor and the battery is moved to visualize the distribution of magnetic fields on the light receiving surface and the back surface of the battery. doing. In Patent Document 3, a magnetic sensor is installed at the end of the fuel cell stack in the thickness direction, a magnetic field generated when electricity flows through the current collecting member is measured by the magnetic sensor, and the fuel cell is measured from the measured magnetic field. The current distribution of the cell stack is measured, and the power generation state of the fuel cell is evaluated based on the current distribution.

JP-T-2004-500689 JP 2010-171065 A JP 2005-183040 A

Kazuhiko Takeno, Tomomi Soda, “Capacity degradation characteristics of lithium-ion batteries for mobile terminals”, NTT CDoCoMo Technical Journal, Vol. 13, no. 4, pp. 62-65, 2006 BJ Roth, NG Sepulveda, and JP Wikswo Jr, “Using a magnetometer to image a two-dimensional current distribution”, vol. 65, no. 1, pp. 361-372, 1989

  As described above, in the prior art, the magnetic field generated from the battery is measured, the current distribution is calculated from the magnetic field signal data obtained by the measurement, and the power generation state is evaluated from the way of the current distribution (Patent Documents 1 to 3). 3).

  However, in lithium ion batteries, the current distribution of normal and deteriorated products measured under the same conditions tends to show similar current patterns, and it is not possible to evaluate the deterioration of lithium ion batteries from the current distribution. It was often difficult.

  Accordingly, an object of the present invention is to provide a technique for evaluating the capacity deterioration of a lithium ion battery with high spatial accuracy. In addition, based on the evaluation, it is to provide a highly reliable battery design that is unlikely to deteriorate by grasping a spatial region where the capacity is likely to deteriorate.

  Furthermore, the capacity deterioration of the lithium ion battery can be detected in a short time and applied to the inspection process of battery manufacture.

  The main embodiment of the present invention for solving the above-mentioned problems is as follows.

  The magnetic field measurement apparatus includes a magnetic field detection unit that detects a magnetic field generated from the battery, and an arithmetic processing unit that calculates a magnetic field distribution in the battery based on the detected magnetic field. When a battery is charged and discharged using a first applied current and a second applied current having a current amount different from that of the first applied current, a first magnetic field and a second magnetic field generated from the battery are detected. Then, the first magnetic field distribution based on the first and second magnetic fields and the second magnetic field distribution are calculated by the arithmetic processing unit, and the difference or ratio between the first magnetic field distribution and the second magnetic field distribution is calculated. Based on the above, the deterioration state of the battery is evaluated.

  In a battery deterioration inspection method, magnetic field detection is performed using a magnetic field measurement device including a magnetic field detection unit that detects a magnetic field generated from a battery and an arithmetic processing unit that calculates a magnetic field distribution in the battery based on the detected magnetic field. The first applied current to the battery in a predetermined charged state and a second applied current having a current amount different from that of the first applied current. The first and second magnetic fields are detected, and the arithmetic processing unit calculates the first magnetic field distribution and the second magnetic field distribution based on the first and second magnetic fields, and the first magnetic field distribution and the second magnetic field distribution. The deterioration state of the battery is evaluated based on the difference or ratio with the magnetic field distribution.

  According to the present invention, capacity degradation of a lithium ion battery can be evaluated with high spatial accuracy. In addition, based on the evaluation, it is possible to design a highly reliable battery that is unlikely to deteriorate by grasping a spatial region where the capacity is likely to deteriorate. Furthermore, capacity deterioration of the lithium ion battery can be detected in a short time, and can be applied to a battery manufacturing inspection process.

It is a figure which shows the structural example of the magnetic field measuring apparatus of the battery which concerns on this embodiment. It is a figure which shows an example of the high resolution magnetic field measurement system which concerns on this embodiment. It is a flowchart which shows the magnetic field measurement procedure at the time of discharge. It is a flowchart which shows another procedure of the magnetic field measurement at the time of discharge. It is a flowchart which shows the analysis procedure using a measurement magnetic field distribution. It is a flowchart which shows the analysis procedure using the electric current distribution computed from the measurement magnetic field distribution. It is a figure which shows the difference magnetic field distribution (in the case of a normal product) obtained from the magnetic field distribution measured at the time of 1C discharge and 2C discharge. It is a figure which shows the difference electric current distribution (in the case of a normal product) obtained from the difference magnetic field distribution shown in FIG. It is a figure which shows the difference magnetic field distribution (in the case of a deteriorated product) obtained from the magnetic field distribution measured at the time of 1C discharge and 2C discharge. It is a figure which shows the difference electric current distribution (in the case of a degradation product) obtained from the difference magnetic field distribution shown in FIG. It is a figure which shows an example of a lithium ion battery manufacturing process flow.

  Hereinafter, modes for carrying out the present invention (hereinafter referred to as “embodiments”) will be described in detail with reference to the drawings as appropriate.

Embodiment 1
FIG. 1 is a schematic diagram illustrating a configuration example of a magnetic field measurement apparatus for a battery according to the present embodiment.

  In this apparatus, the magnetic sensors 2 are arranged in a plane in a matrix at predetermined intervals as shown in the figure. The magnetic sensors 2 arranged in a matrix are arranged on the surface of the lithium ion battery 11 and spatially detect a magnetic field generated from the battery.

  First, in the first embodiment, an apparatus configuration and method for measuring a magnetic field with high accuracy by reducing magnetic field noise generated during magnetic field measurement will be mainly described. The magnetic field noise canceling means used in the first embodiment is also applied to the second embodiment described later.

As shown in FIG. 1, when the lithium ion battery 11 is arranged on a plane determined by the xy axis, the components of the magnetic field measuring apparatus 1 of the lithium ion battery are as follows. That is, a plurality of magnetic sensors 2 that measure a magnetic field signal B _z in a direction perpendicular to the electrode surface of the lithium ion battery 11 (z direction), a drive circuit 3 that drives the magnetic sensor, and an output from the drive circuit 3 are amplified. The amplifier filter unit 4 that filters the signal, the AD converter 5 that converts the output from the amplifier filter unit 4 into a digital signal, and the output signal from the AD converter 5 are collected, and the collected data (hereinafter “ A control arithmetic unit 6 that controls each part of the magnetic field measuring device 1 of the battery, and a display device 7 that displays the analysis result analyzed by the control arithmetic unit 6. ing. Around the magnetic sensor 2, a cancel coil 8 is disposed that generates a magnetic field having an opposite phase for canceling magnetic field noise in the z direction measured by each magnetic sensor 2.

  The magnitude of the current applied to the cancel coil 8 is determined by the control arithmetic device 6. A digital signal for generating the current value is output from the arithmetic unit 6 and converted into an analog signal by the DA converter 9. An appropriate current is applied to the cancel coil 8 by the signal converted to analog by the DA converter 9, and a magnetic field is generated in the cancel coil 8.

Incidentally, the magnetic field measurement apparatus 1 of the battery of the present embodiment, the magnetic measuring the magnetic field signal B _y in the y direction perpendicular to the magnetic field signal B _x and the x-direction parallel x-direction with respect to the electrode surface of the lithium-ion battery Sensors can also be applied. At this time, the cancel coil 8 is arranged so as to generate a magnetic field for canceling the magnetic field noise in the x direction and the magnetic field noise in the y direction.

  The battery magnetic field measuring apparatus 1 of the present embodiment is an apparatus for measuring the magnetic field of a lithium ion battery during charging / discharging. In particular, magnetic field cancellation by the cancel coil 8 and magnetic field data recorded before charging / discharging (for correction) It is characterized by magnetic field cancellation by the arithmetic unit 6 using magnetic field data). Therefore, regardless of the shape of the lithium ion battery, the configuration and operation of the magnetic field measuring apparatus 1 of the present invention can be applied as appropriate to any of, for example, a rectangular, cylindrical, or laminated lithium ion battery.

  Further, as the magnetic sensor 2 of the battery magnetic field measurement device 1 of the present embodiment, for example, any of a magnetic sensor such as a Hall element, a Magnetic Impedance (MI) sensor, a Magnetic Resistance (MR) sensor, a flux gate, The configuration and operation of the magnetic field measurement apparatus 1 of the present invention can be applied as appropriate.

  The magnetic sensor described in the first embodiment is fixed to a holding base (not shown). Therefore, since the magnetic field generated from the lithium ion battery 11 is detected only in the vicinity of the magnetic sensor 2, the magnetic field detection accuracy, that is, the spatial resolution is determined by the interval of the magnetic sensor 2. In order to increase the detection accuracy, it is preferable to reduce the distance between the magnetic sensors 2, further reduce the width of the magnetic sensor 2 as much as possible in terms of manufacturing, and reduce the distance.

  Although this embodiment is limited by the magnetic sensor interval in terms of detection accuracy, it does not use the precision XY stage shown in the second embodiment to be described later, and therefore has a feature that the apparatus configuration can be simple and inexpensive.

  Using the magnetic field measurement device 1 described above, the state of battery deterioration can be evaluated by measuring the magnetic field from the battery during discharging or charging. The magnetic field measurement procedure and the analysis procedure can be processed in the same manner as in the second embodiment described below, and are therefore omitted in the first embodiment.

<< Embodiment 2 >>
FIG. 2 shows a magnetic field measurement system using an MR (Magnetic Resistance) sensor according to this embodiment. In the first embodiment, the configuration in which the magnetic sensor for detecting the magnetic field is fixedly arranged in a matrix is shown. However, this magnetic field measurement system is an example of a device configuration for measuring the magnetic field distribution generated from the lithium ion battery with high resolution. It is.

FIG. 2 shows a high-resolution magnetic field measurement system configured by combining a 128-channel magnetic field measurement system and a precision XY stage 35 in order to measure a magnetic field distribution generated from a lithium ion battery with high resolution.
First, the high-resolution magnetic field measurement system includes a 128-channel magnetic field measurement system including a magnetic field measurement system sensor unit 34, a magnetic field measurement system control unit 36, and a magnetic field measurement system PC 37, a precision XY stage 35, a battery holder 32, a magnetic field. The shield box 30 is used.
The lithium ion battery 31 was placed on a battery holder 32, and a magnetic field measurement system sensor unit 34 fixed to the precision XY stage 35 was installed directly below the lithium ion battery 31.

On the upper surface of the magnetic field measurement system sensor unit 34, the magnetic sensors 2 shown in FIG. 1 are arranged at a predetermined interval. In the present embodiment, the MR sensor 33 is used as the magnetic sensor.
The high-resolution magnetic field measurement system was installed in a magnetic field shield box 30 that can shield ambient magnetic field noise.
The precision XY stage 35 is movable in the X direction or the Y direction, and the movement step is set so that the movement can be performed at a distance sufficiently smaller than a predetermined interval in which the MR sensors 33 are arranged. Yes.

Therefore, the magnetic field measurement system sensor unit 34 can be arranged at an arbitrary position of the lithium ion battery 31 with this configuration, and the magnetic field distribution can be measured at an interval sufficiently smaller than the predetermined interval. Can be obtained.
Note that the description of the arrangement of the cancel coil 8 and the like described in FIG. 1 of the first embodiment is omitted, but in order to obtain an accurate magnetic field distribution in the system of FIG. Apply as appropriate.

<Procedure for magnetic field measurement during discharge-1>
FIG. 3 is a flowchart showing a procedure for measuring the magnetic field from the lithium ion battery during discharge with high resolution using the above-described high-resolution magnetic field measurement system.

  First, the lithium ion battery 31 is set in a state where it can be discharged to the battery holder 32 of the high resolution magnetic field measurement system (step 40).

  While the lithium ion battery 31 is not discharged, the magnetic field measurement is performed by moving the magnetic field measurement system sensor unit 34 to the first designated measurement position using the XY stage 35. The magnetic field measurement system sensor unit 34 is moved to the next measurement position to perform magnetic field measurement. The same thing is repeated, the XY stage 35 is moved to N measurement positions, and the magnetic field measurement is repeatedly performed on the XY plane, thereby performing the offset magnetic field measurement process based on the obtained magnetic data. Perform (step 41).

Subsequently, 1C discharge is started, and a magnetic field is measured at N measurement positions in a state where current flows in the lithium ion battery, and magnetic field measurement processing during 1C discharge is performed (step 42).
Here, 1C indicates a current value that can charge or discharge the battery in one hour.

  Further, 2C discharge of the lithium ion battery is started, and a magnetic field is measured at N measurement positions in a state where current flows in the lithium ion battery, and magnetic field measurement processing during 2C discharge is performed (step 43).

  Here, 2C indicates a current value at which the battery can be charged or discharged in 0.5 hours.

  The discharge start and the magnetic field measurement in steps 42 and 43 are executed based on command control from the magnetic field measurement system control unit 36.

  In addition, when measuring the magnetic field of the lithium ion battery at the time of discharge of 1C and 2C, it is necessary to make a lithium ion battery into the same charge state. That is, in this embodiment, a 25% charged state is adopted as will be described later.

<Procedure 2 for magnetic field measurement during discharge>
In the second embodiment, the high-resolution magnetic field measurement system shown in FIG. 2 is used. However, when the magnetic sensors 2 shown in FIG. 1 are arranged at a high density, that is, the magnetism is obtained at the above-mentioned predetermined interval or less. When the sensor 2 can be arranged, it is not necessary to move the magnetic field measurement system sensor unit 34 to N measurement positions, and magnetic field measurement processing having desired accuracy can be performed with the apparatus configuration shown in FIG. .

The measurement procedure in that case is shown in the flowchart of FIG.
First, the lithium ion battery 11 is set in a state where it can be discharged to the magnetic field measuring apparatus 1 shown in FIG. 1 (step 50).

  By performing magnetic field measurement at measurement positions corresponding to the plurality of magnetic sensors 2 in a state where the lithium ion battery 11 is not discharged, offset magnetic field measurement processing is performed based on the obtained magnetic data (step 51). .

  Subsequently, 1C discharge is started, and a magnetic field is measured at a measurement position corresponding to the plurality of magnetic sensors 2 in a state where current flows in the lithium ion battery 11, and magnetic field measurement processing during 1C discharge is performed (step). 52). Here, the definition of 1C is the same as the above-described <magnetic field measurement procedure-1>.

Furthermore, 2C discharge of the lithium ion battery 11 is started, and a magnetic field is measured at a measurement position corresponding to the plurality of magnetic sensors 2 in a state where current flows in the lithium ion battery 11, and magnetic field measurement processing during 2C discharge is performed. (Step 53). Here, the definition of 2C is the same as the above-described <magnetic field measurement procedure-1>.
The discharge start and magnetic field measurement from steps 51 to 53 are executed based on a command from the control arithmetic device 6.

  In the first and second embodiments, as described above, the magnetic field measurement at the time of discharging has been described, but the magnetic field measurement at the time of charging can also be performed by the same procedure.

<Analysis procedure-1>
The analysis procedure based on the magnetic field measurement result at the time of discharging will be described below, but the analysis procedure at the time of charging can take the same procedure.

  FIG. 5 is a flowchart showing an analysis procedure using the measured magnetic field distribution.

  First, an addition average process of the offset magnetic field signal obtained as a result of the offset magnetic field measurement process shown in the above-described <magnetic field measurement procedure-1> is performed to obtain an offset addition average magnetic field (step 60).

  The purpose of this step 60 is to calculate an additive average magnetic field for noise removal from the offset magnetic field signal measured before discharging.

  Next, it is determined whether the discharge current is 1C or 2C (step 61).

  In the case of 1C, the addition average process of the magnetic field signal at the time of 1C discharge is performed to obtain the addition average magnetic field (step 611). Subsequently, the offset addition average magnetic field is removed from the addition average magnetic field during 1C discharge (step 612).

  In step 61, when branching to 2C, the same procedure as in the case of 1C is performed. That is, in the case of 2C, an addition average process of magnetic field signals at the time of 2C discharge is performed to obtain an addition average magnetic field (step 613). Subsequently, the offset addition average magnetic field is removed from the addition average magnetic field during 2C discharge (step 614).

  Next, it is determined whether the analysis method is a difference or a ratio (increase rate) is adopted (step 62).

When the difference is selected, the difference is calculated by removing the addition average magnetic field at 1C discharge doubled from the addition average magnetic field at 2C discharge (step 621).
The difference in the magnetic field distribution obtained in step 621 is hereinafter referred to as “difference magnetic field distribution”.

When the ratio is selected in step 62, the rate of increase of the additional average magnetic field during 2C discharge is calculated based on the additional average magnetic field during 1C discharge (step 622).
The ratio of the magnetic field distribution obtained in step 622 is hereinafter referred to as “ratio magnetic field distribution”. However, unless otherwise specified, the term “difference magnetic field distribution” includes “ratio magnetic field distribution”.

  Although the analysis procedure 1 has been described based on the above-described <magnetic field measurement procedure-1>, the analysis procedure 1 can be performed in the same manner also in the case of the above-described <magnetic field measurement procedure-2>.

<Analysis procedure-2>
FIG. 6 is a flowchart showing the analysis procedure using the current distribution calculated from the measured magnetic field distribution.

  The difference between the analysis procedure 2 and the analysis procedure 1 is whether the deterioration evaluation of the battery performance is performed using the differential magnetic field distribution or the differential current distribution is used.

  First, an addition average process of the offset magnetic field signal obtained as a result of the offset magnetic field measurement process shown in the above-described <magnetic field measurement procedure-1> is performed to obtain an offset addition average magnetic field (step 70).

  The purpose of this step 70 is to calculate an additive average magnetic field for noise removal from the offset magnetic field signal measured before discharging.

  Next, it is determined whether the discharge current is 1C or 2C (step 71).

  In the case of 1C, the addition average process of the magnetic field signal at the time of 1C discharge is performed to obtain the addition average magnetic field (step 711). Subsequently, the offset addition average magnetic field is removed from the addition average magnetic field during 1C discharge (step 712).

  Next, a current distribution is calculated from the addition average magnetic field during 1C discharge (step 713).

  In step 71, when branching to 2C, the same procedure as in the case of 1C is performed. That is, in the case of 2C, the addition average process of the magnetic field signal at the time of 2C discharge is performed to obtain the addition average magnetic field (step 714). Subsequently, the offset addition average magnetic field is removed from the addition average magnetic field during 2C discharge (step 715).

  Subsequently, the current distribution is calculated from the addition average magnetic field during 2C discharge (step 716).

  Next, it is determined whether the analysis method is a difference or a ratio is taken (step 72).

If the difference is selected, the difference between the current distribution during 2C discharge and the current distribution during 1C discharge multiplied by 2 is calculated (step 721).
The difference in current distribution obtained in step 721 is hereinafter referred to as “differential current distribution”.

If the ratio is selected in step 72, the rate of increase in current distribution during 2C discharge is calculated based on the current distribution during 1C discharge (step 722).
The ratio of the current distribution obtained in step 722 is hereinafter referred to as “ratio current distribution”. However, unless otherwise specified, the term “difference current distribution” includes “ratio current distribution”.

  In Steps 713 and 716, the Fourier kernel method (Non-patent Document 2), which is a known method for obtaining a two-dimensional current distribution, was used as a method for calculating a current distribution from an addition average magnetic field during discharge of a lithium ion battery.

  Although the analysis procedure 2 has been described based on the above-described <magnetic field measurement procedure-1>, the analysis procedure 2 can be performed in the same manner also in the case of the above-described <magnetic field measurement procedure-2>.

<Measurement results>
7 and 8 show measurement results for normal products.

  First, FIG. 7 is a diagram showing a differential magnetic field distribution (in the case of a normal product) obtained from the magnetic field distribution measured during 1C discharge and 2C discharge.

  The battery to be measured here is a normal product with a 25% charge state, and the magnetic field distribution obtained by obtaining the difference between the magnetic field distribution at the time of 2C discharge and the magnetic field distribution at the time of 1C discharge doubled, that is, “difference magnetic field”. Distribution ".

  FIGS. 7A, 7B, and 7C correspond to the differential magnetic fields of the x component, the y component, and the z component, respectively. The dotted line in FIG. 7 represents the battery electrode, and the differential magnetic field outside the electrode area of the battery was zero. Here, the illustrated electrode is illustrated by overlapping a negative electrode and a positive electrode, and the lead-out from each electrode is connected to the positive electrode tab and the negative electrode tab.

  At the right end of FIG. 7, a gradation scale showing the magnetic field strength [μT] is shown. This scale is applied to any of the x component, the y component, and the z component.

  7A and 7B, the negative peak of the differential magnetic field distribution of the x component was about −3.0 μT, and the negative peak of the differential magnetic field distribution of the y component was about −1.8. Therefore, the negative peak of the differential magnetic field distribution in the xy component is in the range of about −1.8 to −3.0 μT. Moreover, from FIG.7 (c), the negative peak of the difference magnetic field distribution of z component was about -26 microT.

  Next, FIG. 8 is a diagram showing a differential current distribution (in the case of a normal product) obtained from the differential magnetic field distribution shown in FIG.

  The battery to be measured here is a normal product in a 25% charged state, and the current distribution obtained by calculating the difference between the current distribution at the time of 2C discharge and the current distribution at the time of 1C discharge doubled, that is, “difference current”. Distribution ".

The plan view of FIG. 8 is the same as that shown in FIG. 7, and the illustrated electrodes are shown by overlapping the negative electrode and the positive electrode, and the lead-out from each electrode is connected to the positive electrode tab and the negative electrode tab. Yes. On the right end of FIG. 8, a gradation scale showing the current value [A / m ² ] is shown.

As shown in FIG. 8, a region having a strong differential current was recognized in the range of 10 to 20 mm from the positive electrode / negative electrode tab side. The peak (maximum current) of the differential current distribution was about 1.6 × 10 ³ A / m ² , and the total current was 1.1 × 10 ⁵ A / m ² .

  Next, FIG. 9 and FIG. 10 show the measurement results for the deteriorated product.

  First, FIG. 9 is a diagram showing a differential magnetic field distribution (in the case of a deteriorated product) obtained from the magnetic field distribution measured during 1C discharge and 2C discharge.

  The battery to be measured here is a deteriorated product in a 25% charged state, and the magnetic field distribution obtained by obtaining the difference between the magnetic field distribution at the time of 2C discharge and the magnetic field distribution at the time of 1C discharge doubled, that is, “difference magnetic field”. Distribution ".

  9A, 9B, and 9C correspond to the differential magnetic fields of the x component, the y component, and the z component, respectively. The gradation scale displayed on the right end of FIG. 9 is the same gradation scale as the normal product of FIG. The dotted line in FIG. 9 represents the battery electrode, and the differential magnetic field outside the battery electrode region was zero. Here, the illustrated electrode is illustrated by overlapping a negative electrode and a positive electrode, and the lead-out from each electrode is connected to the positive electrode tab and the negative electrode tab.

  9A and 9B, the negative peak of the differential magnetic field distribution of the x component is about −9.8 μT, and the negative peak of the differential magnetic field distribution of the y component is about −9.3. Therefore, since the negative peak of the differential magnetic field distribution in the xy component is in the range of about −9.3 to −9.8 μT, the value is stronger than that of the normal product.

  Moreover, from FIG.9 (c), the negative peak of the difference magnetic field distribution of z component is about -39.7 microT, and the negative peak of z component also showed the strong value compared with the normal product. Further, from FIGS. 9A to 9C, the positive peak and the negative peak of each component were recognized in the vicinity of the tab.

  Next, FIG. 10 is a diagram showing a differential current distribution (in the case of a deteriorated product) obtained from the differential magnetic field distribution shown in FIG.

  The battery to be measured here is a deteriorated product of 25% charge state, and the current distribution obtained by obtaining the difference between the current distribution at the time of 2C discharge and the current distribution at the time of 1C discharge doubled, that is, “difference current”. Distribution ".

The plan view of FIG. 10 is the same as that shown in FIG. 8, and the illustrated electrodes are shown by overlapping the negative electrode and the positive electrode, and the lead-out from each electrode is connected to the positive electrode tab and the negative electrode tab. Yes. On the right end of FIG. 10, a gradation scale indicating the current value [A / m ² ] is shown.

As shown in FIG. 10, a region having a strong differential current is recognized in the range of 50 to 60 mm from the positive electrode / negative electrode tab side, and it can be seen that this region is wider than a normal product. Moreover, the peak (maximum current) of the differential current distribution is about 6.7 × 10 ³ A / m ² , and the total current is about 3.0 × 10 ⁵ A / m ^2, which is a stronger value than that of a normal product. showed that.

  7 to 10, the magnetic field distribution or the current distribution measured at the time of 1C discharge and 2C discharge has been described. However, it is not necessary to limit at the time of 1C discharge and 2C discharge, at the time of 1C discharge, at the time of 2C discharge, ..NC (n ≧ 2) may be discharged. As described above, the purpose of using different current values is to give a condition that the current is different from 1C and the load is increased on the battery, in other words, the stress is increased on the battery. In this way, by applying a larger stress, a normal product does not show any deterioration with respect to the stress, but a battery that easily deteriorates shows a deterioration state with respect to the stress.

  In the above description, the magnetic field distribution measured at the time of discharging is used, but the magnetic field distribution measured at the time of charging may be used. Although the absolute value of the numerical value itself is different between the data at the time of discharging and the data at the time of charging, either data may be used for the purpose of evaluating the deterioration state of the battery according to the present invention.

<Evaluation of battery deterioration state>
From the results shown in FIGS. 7 to 10, it is clear that the difference magnetic field distribution and the difference current distribution are different between the normal product and the deteriorated product when discharged at 1C and 2C.

  Here, since the data of normal products can be prepared in advance, a determination value or a threshold value is set as a reference for determining how much the deviation is compared with that of a normal product. This makes it possible to determine whether the product is normal or deteriorated.

  Therefore, since the amount of magnetic field change and the amount of current change are different at different currents for normal products and deteriorated products, the deterioration state of the lithium ion battery can be evaluated by using the judgment values for the magnetic field change amount and the current change amount. Indicated.

  In the deteriorated product, the magnetic field change amount and current change amount in the left end region (near the positive electrode / negative electrode tab) of the battery were strong, indicating the possibility of reflecting deterioration around the tab. It also suggests that it is possible to identify places where deterioration is likely to occur. Therefore, it can be applied at the development / design stage to improve a place that is likely to deteriorate.

  Further, since the time required for evaluating the deterioration state of the battery is about several minutes to several tens of minutes, the state of the battery can be inspected in a short time.

  Although it has been shown that the deterioration state of the battery can be evaluated based on the measurement result at the time of discharging, it is obvious that the deterioration state of the battery can be similarly evaluated from the above-described embodiment even if the measurement result at the time of charging is used. .

<< Embodiment 3 >>
As described above, the deterioration state of the battery can be evaluated based on the difference magnetic field distribution calculated from the magnetic field distribution measured when the battery to be inspected is discharged or the difference current distribution calculated based on the difference magnetic field distribution. . According to the present invention, since it is possible to specify a place where deterioration is likely to occur, it is easy to deal with the structure of the battery and the place of deterioration, and it is easy to analyze the cause of deterioration. ing. In particular, if the differential current distribution is used, it is easy to visually grasp the physical phenomenon occurring inside the actual battery, and the effect can be exhibited at the development / design stage.

  Furthermore, the present invention can be effectively applied to a battery manufacturing process.

  FIG. 11 shows a lithium ion battery manufacturing process flow. First, in the positive electrode / negative electrode manufacturing process, a positive electrode and a negative electrode are prepared (step 20). Next, a cell is assembled using a separator and an electrolyte for the produced positive electrode and negative electrode (step 21). In the inspection process, the completed battery cell is inspected for performance and safety (step 22).

  In this inspection step, the deterioration state of the battery can be evaluated based on the difference magnetic field distribution calculated from the magnetic field distribution at the time of discharging the completed battery or the difference current distribution calculated based on the difference magnetic field distribution. At that time, it is possible to determine whether the product is a normal product or a deteriorated product as compared with a preset determination value (threshold value). According to the evaluation method of the present invention, since the deterioration state of the battery can be grasped in a short time (several minutes to several tens of minutes) and by nondestructive inspection, it can be applied to the inspection process in the battery manufacturing process.

  In this inspection process, unlike the application at the development / design stage described above, determination can be made by numerical data processing, and visual data need not be provided, so it is appropriate to use the differential magnetic field distribution. . In addition, since the time required for the calculation process is shorter than the calculation of the differential current distribution, it can be said that the inspection process is more effective.

  In addition, although the said description described the case based on the difference magnetic field distribution at the time of discharge, or a difference electric current distribution, it cannot be overemphasized that it is applicable also when based on the difference magnetic field distribution at the time of charge, or a difference electric current distribution.

1: Magnetic field measuring device,
2: Magnetic sensor,
3: Drive circuit,
4: Amplifier filter unit,
5: AD converter,
6: Control arithmetic unit,
7: Display device,
8: Cancel coil,
9: DA converter,
10: MR sensor,
11: Lithium ion battery
12: + terminal,
13:-terminal,
20: positive electrode / negative electrode manufacturing process,
21: Cell assembly process,
22: Inspection process (performance / safety),
30: Magnetic field shield box,
31: Lithium ion battery
32: Battery holder
33: MR sensor,
34: Magnetic field measurement system sensor unit,
35: XY stage
36: Magnetic field measurement system control unit,
37: Magnetic field measurement system PC.

Claims (14)

A magnetic field measuring device for evaluating a deterioration state of a battery,
Means for calculating two types of magnetic field distributions based on the magnetic fields generated from the respective applied currents when at least two types of applied currents having different current amounts are passed through the battery in a predetermined charging state; ,
Means for calculating two types of current distribution corresponding to each applied current from the two types of calculated magnetic field distributions;
A magnetic field measuring apparatus comprising: means for evaluating a deterioration state of the battery based on the two kinds of magnetic field distributions or the two kinds of current distributions. A magnetic field detector for detecting the magnetic field generated from the battery;
An arithmetic processing unit that calculates a magnetic field distribution in the battery based on the detected magnetic field,
When the magnetic field detection unit charges and discharges the battery using a first applied current and a second applied current having a current amount different from that of the first applied current to the battery in a predetermined charged state. Detecting first and second magnetic fields respectively generated from
The arithmetic processing unit calculates a first magnetic field distribution based on the first and second magnetic fields, and a second magnetic field distribution, and a difference between the first magnetic field distribution and the second magnetic field distribution, Alternatively, a magnetic field measurement apparatus that evaluates a deterioration state of the battery based on a ratio.   The magnetic field measurement apparatus according to claim 2, wherein the predetermined state of charge is 25% of a fully charged state. The first applied current is a 1C charge / discharge current that is a current value that can be charged / discharged in one hour,
The magnetic field measurement apparatus according to claim 2, wherein the second applied current is a 2C charge / discharge current having a current value that can be charged / discharged in 0.5 hours.   The difference or ratio is the subtraction or division of the magnetic field of the second magnetic field distribution obtained from the 2C charge / discharge current and the value obtained by doubling the magnetic field of the first magnetic field distribution obtained from the 1C charge / discharge current. The magnetic field measurement apparatus according to claim 2, wherein the magnetic field measurement apparatus is obtained by:   The magnetic field measurement apparatus according to claim 2, wherein the deterioration state of the battery is evaluated based on a determination value in which the difference or the ratio is set in advance.   The magnetic field detection unit is mounted on a holding table movable in a plane direction, and adjusts a moving pitch interval of the holding table according to required accuracy of a magnetic field distribution generated from the battery. 2. The magnetic field measuring apparatus according to 2. The magnetic field detection unit includes a magnetic sensor that detects a magnetic field generated from the battery,
A cancellation coil arranged to surround the magnetic sensor and canceling magnetic field noise detected by the magnetic sensor;
Recording means for recording a magnetic field detected by the magnetic sensor when no current or voltage is applied to the terminal of the battery as a correction magnetic field;
Differential processing means for calculating a correction difference between the magnetic field generated from the battery when a current and voltage are applied to the terminal of the battery and the correction magnetic field recorded in the recording means;
The magnetic field measurement apparatus according to claim 2, wherein a magnetic field noise is removed by adjusting a correction difference from the first and second magnetic fields detected by the magnetic field detection unit. Using a magnetic field measurement device including a magnetic field detection unit that detects a magnetic field generated from a battery, and an arithmetic processing unit that calculates a magnetic field distribution in the battery based on the detected magnetic field,
When the magnetic field detection unit charges and discharges the battery using a first applied current and a second applied current having a current amount different from that of the first applied current to the battery in a predetermined charged state. Detecting first and second magnetic fields respectively generated from
The arithmetic processing unit calculates a first magnetic field distribution based on the first and second magnetic fields, and a second magnetic field distribution, and a difference between the first magnetic field distribution and the second magnetic field distribution, Alternatively, a battery deterioration inspection method characterized by evaluating a deterioration state of the battery based on a ratio.   The first and second current distributions are calculated from the first and second magnetic field distributions, respectively, and the deterioration state of the battery is evaluated from the difference or ratio between the first and second current distributions. The battery deterioration inspection method according to claim 9. The first applied current is a 1C charge / discharge current that is a current value that can be charged / discharged in one hour,
The battery deterioration inspection method according to claim 9, wherein the second applied current is a 2C charge / discharge current that is a current value that can be charged / discharged in 0.5 hours.   The difference or ratio is obtained by subtracting or dividing the magnetic field of the second magnetic field distribution obtained from the 2C charge / discharge current from the value obtained by doubling the magnetic field of the first magnetic field distribution obtained from the 1C charge / discharge current. The battery deterioration inspection method according to claim 9, wherein the battery deterioration inspection method is obtained.   The battery deterioration inspection method according to claim 9, wherein the deterioration state of the battery is evaluated based on a determination value in which the difference or ratio is set in advance.   A battery deterioration inspection method, comprising: inspecting a deterioration state of the battery using the magnetic field measuring device according to claim 2 in an inspection step of battery manufacture.

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