JP2017003325A - Secondary battery inspection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery inspection method capable of quickly and accurately inspecting whether minute short-circuiting occurs in a secondary battery.SOLUTION: In a first step, a magnetic field intensity of a secondary battery 701 is calculated when a voltage of the secondary battery 701 is a first voltage V1. In a second step, the voltage of the secondary battery 701 is changed to a second voltage V2 different from the first voltage V1. In a third step, the magnetic field intensity of the secondary battery 701 is calculated when the voltage of the secondary battery 701 is the second voltage V2. In a fourth step, it is determined whether short-circuiting occurs in the secondary battery 701 or not on the basis of the difference between the magnetic field intensity (first magnetic field intensity B1) of the secondary battery 701 calculated in the first step and the magnetic field intensity (second magnetic field intensity B2) of the second battery calculated in the third step.SELECTED DRAWING: Figure 4

Description

  The present invention particularly relates to an inspection method for eliminating defects resulting from a minute short circuit of a secondary battery.

  If a conductive foreign matter enters inside the secondary battery and the foreign matter penetrates the separator inside the secondary battery, a short circuit between the positive electrode and the negative electrode may occur inside the secondary battery. When a short circuit occurs between the positive electrode and the negative electrode inside the secondary battery due to such a thing, a current of a value obtained by dividing the electromotive force of the secondary battery by the internal resistance of the short-circuit portion flows into the secondary battery. Voltage drops. For this reason, the secondary battery in which the short circuit between the positive electrode and the negative electrode has occurred needs to be excluded by inspection before shipment.

  In Patent Document 1, the secondary battery is aged before shipment, the amount of change in terminal voltage (terminal voltage difference) before and after aging is calculated, and this terminal voltage difference is compared with a predetermined threshold value. A secondary battery inspection method for determining the presence or absence of a short circuit between the positive electrode and the negative electrode inside the secondary battery is described.

Japanese Patent Laid-Open No. 2004-13276

  However, the secondary battery inspection method described in Patent Document 1 has a problem that it takes time for inspection because it takes several days for aging.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a secondary battery inspection method capable of quickly and accurately inspecting the presence or absence of a micro short circuit in a secondary battery.

  The present invention is a method for inspecting a secondary battery, the first step of calculating the magnetic field strength of the secondary battery when the voltage of the secondary battery is the first voltage, and the voltage of the secondary battery A second step of changing the second battery voltage to a second voltage different from the first voltage, and a third step of calculating the magnetic field strength of the secondary battery when the voltage of the secondary battery is the second voltage. And a short circuit inside the secondary battery based on the difference between the magnetic field intensity of the secondary battery calculated in the first process and the magnetic field intensity of the secondary battery calculated in the third process. A fourth step of determining whether or not there is, the first step and the third step are arranged around the secondary battery, and the positive electrode and the negative electrode of the secondary battery are Reading data obtained by continuously reading detection data detected via a magnetic sensor that detects the magnetic field strength in an open state Divide the group evenly with a certain section width, calculate the average value for each data group included in the section in each section, and the reference value for which the dispersion of multiple average values obtained for each section is predetermined A first step of determining whether or not the difference exceeds the reference value when the variation in the plurality of average values is determined to exceed the reference value in the first step; If necessary, the range of the read data group is expanded and the first step is performed again, and the variation of the plurality of average values in the first step is less than or equal to the reference value. And a third step of calculating the magnetic strength of the secondary battery based on the read data group when determined to be present.

  ADVANTAGE OF THE INVENTION According to this invention, the inspection method of a secondary battery which can test | inspect the presence or absence of the micro short circuit of a secondary battery rapidly and accurately can be provided.

1 is a diagram illustrating a schematic configuration of an inspection apparatus used in a secondary battery inspection method according to a first embodiment; It is a figure which shows the state inside a secondary battery when the secondary battery concerning Embodiment 1 does not have a short circuit. It is a figure which shows the state inside a secondary battery in case the secondary battery concerning Embodiment 1 has a short circuit. 3 is a flowchart of a process for determining whether or not there is a micro short circuit in the secondary battery according to the first embodiment; In the inspection method of the secondary battery concerning Embodiment 1, it is a figure explaining change of variation of an average value group before and after changing section width. 3 is a flowchart of a process for calculating the magnetic field strength of the secondary battery according to the first embodiment.

Embodiments of the present invention will be described below with reference to the drawings.
First, an inspection apparatus used for a method for inspecting the presence or absence of a short circuit inside a secondary battery, which is an inspection method for a secondary battery according to this embodiment, will be described.

  The inspection apparatus 100 inspects the presence or absence of a short circuit inside the secondary battery 701 due to the conductive foreign material 702 or the like by calculating the strength of the magnetic field 703 of the secondary battery 701 (hereinafter also referred to as magnetic field strength). As shown in FIG. 1, the inspection apparatus 100 of the secondary battery inspection method according to the present embodiment includes a magnetic sensor 101 that detects a magnetic field, a magnetic field calculation unit 102, a pass / fail determination unit 103, and a storage unit 104. The charging / discharging device 110 is provided. The secondary battery 701 to be inspected by the secondary battery inspection method according to the present embodiment is, for example, a lithium ion secondary battery, a nickel hydride secondary battery, or the like. The secondary battery to be inspected may be any secondary battery that generates a magnetic field when short-circuited.

  The magnetic sensor 101 is disposed around the secondary battery 701 and detects a magnetic field 703 generated by the secondary battery 701. As the magnetic sensor 101, for example, a SQUID (Superconducting Quantum Interference Device) sensor or an MI (Magneto-Impedance) sensor is used. The sensitivity of the magnetic sensor 101 depends on the distance from a location where a current is generated (in other words, a location where a magnetic field is generated). For this reason, it is preferable to arrange the magnetic sensor 101 as close to the secondary battery 701 as possible. In particular, if the magnetic sensor 101 is disposed so as to be in contact with the surface of the secondary battery 701, the sensitivity of the magnetic sensor 101 can be further improved.

  By disposing a plurality of magnetic sensors 101 around the secondary battery 701, detection accuracy can be improved and detection time can be shortened. For example, a plurality of magnetic sensors 101 may be arranged in a grid on the same plane so that the magnetic field distribution on the upper surface of the secondary battery 701 can be detected at a time. Further, the magnetic sensor 101 may be provided on each plane around the secondary battery 701. For example, you may provide the magnetic sensor 101 in the upper surface and lower surface of the secondary battery 701, respectively. Further, the magnetic sensor 101 may be provided with emphasis at a location where a short circuit is likely to occur.

  The magnetic field calculation unit 102 calculates the magnetic field strength of the secondary battery 701 based on the detection data detected via the magnetic sensor 101. The magnetic field strength of the secondary battery 701 calculated by the magnetic field calculation unit 102 is stored in the storage unit 104.

  The pass / fail determination unit 103 determines whether the positive electrode and the negative electrode of the secondary battery 701 are short-circuited based on the calculation result of the magnetic field by the magnetic field calculation unit 102. A specific determination method for determining whether the positive electrode and the negative electrode of the secondary battery 701 are short-circuited will be described later.

  The charging / discharging device 110 changes the voltage of the secondary battery 701. By connecting the terminal of the charging / discharging device 110 to the positive electrode and the negative electrode of the secondary battery 701 to charge / discharge the secondary battery 701, the voltage of the secondary battery 701 can be changed. The secondary battery 701 generally includes a positive electrode material carrying a positive electrode active material, a negative electrode material carrying a negative electrode active material, a separator interposed between the positive electrode material and the negative electrode material, a non-aqueous electrolyte, and the like. . For example, in the lithium ion secondary battery, the terminal of the charging / discharging device 110 is connected to the positive electrode and the negative electrode of the lithium ion secondary battery, and the lithium ions contained in the non-aqueous electrolyte are moved between the positive electrode and the negative electrode. As a result, the lithium ion secondary battery is charged and discharged.

Next, the reason why a magnetic field is generated around the secondary battery 701 when a short circuit between the positive electrode and the negative electrode occurs in the secondary battery 701 will be described below.
As shown in FIGS. 2 and 3, the secondary battery 701 includes a positive electrode material 201, a negative electrode material 202, a separator 203 sandwiched between the positive electrode material 201 and the negative electrode material 202, and the like. Since the positive electrode material 201 and the negative electrode material 202 are insulated by the separator 203, as shown in FIG. 2, when there is no short circuit between the positive electrode and the negative electrode inside the secondary battery 701, the positive electrode No current flows between the material 201 and the negative electrode material 202.

On the other hand, as shown in FIG. 3, when a short circuit between the positive electrode and the negative electrode occurs due to the conductive foreign matter 702 inside the secondary battery 701, a current flows through the short circuit portion. When the electromotive force of the secondary battery 701 is V and the electrical resistance of the short-circuit portion is R, the electromotive force V is divided by the electrical resistance R between the positive electrode material 201 and the negative electrode material 202 according to Ohm's law. A current I (I = V / R) flows. Although the short-circuit current that flows depends on the degree of short-circuit between the positive electrode and the negative electrode, in the case of the above-described lithium ion secondary battery, for example, even with a short circuit current of about several hundred μA, a location that is several [cm] away from the short-circuit portion Generates a magnetic field of about 10 ⁻¹² [T].

Here, an outline of a method for determining whether or not a short circuit between the positive electrode and the negative electrode has occurred inside the secondary battery 701 will be described below.
The secondary battery 701 itself has a unique residual magnetism. This residual magnetism remains constant even when the voltage of the secondary battery 701 is changed. For this reason, unless the short circuit between the positive electrode and the negative electrode occurs in the secondary battery 701, the magnetic field strength of the secondary battery 701 is kept constant. On the other hand, when a short circuit between the positive electrode and the negative electrode occurs in the secondary battery 701, the amount of current flowing through the short circuit location depends on the voltage of the secondary battery 701. Along with this, the magnetic field strength of the secondary battery 701 also changes. Whether or not a short circuit between the positive electrode and the negative electrode occurs in the secondary battery by determining whether or not the magnetic field strength of the secondary battery 701 is equal before and after the voltage of the secondary battery 701 is changed. Can be determined.

Next, a processing flow for determining whether or not a short circuit between the positive electrode and the negative electrode has occurred inside the secondary battery 701 will be described below.
As shown in FIG. 4, first, the secondary battery 701 to be inspected is placed in the secondary battery inspection apparatus 100 (step S601). Subsequently, the magnetic field strength of the secondary battery 701 (referred to as “first magnetic field strength B1”) is calculated in a state where the positive electrode and the negative electrode of the secondary battery 701 are opened (step S602). The calculation of the first magnetic field strength B1 is performed based on a read data group obtained by continuously reading magnetic field strength detection data detected via the magnetic sensor 101. The voltage of the secondary battery 701 at the time of calculating the first magnetic field strength B1 is defined as “first voltage V1”. During detection of magnetic field strength detection data, the voltage value of the secondary battery 701 is kept constant. Details of the processing flow for calculating the magnetic field strength B1 will be described later.

  Following step S602, with the positional relationship between the secondary battery 701 and the magnetic sensor fixed, the charging / discharging device 110 is connected to the positive electrode and the negative electrode of the secondary battery 701, and the voltage of the secondary battery 701 is changed to the first voltage. The voltage is changed to a voltage different from the first voltage V1 (referred to as “second voltage V2”) (step S603). Subsequently, the magnetic field strength (referred to as “second magnetic field strength B2”) of the secondary battery 701 is calculated in a state where the positive electrode and the negative electrode of the secondary battery 701 are opened (step S604). The calculation of the second magnetic field intensity B2 is performed based on the read data group obtained by continuously reading the magnetic intensity detection data detected via the magnetic sensor 101, as in the case of the calculation of the first magnetic field intensity B1. During detection of magnetic field strength detection data, the voltage value of the secondary battery 701 is kept constant. Details of the processing flow for calculating the magnetic field strength B2 will be described later.

  The second voltage V2 may be larger or smaller than the first voltage V1. The first voltage V <b> 1 can be the lower limit voltage for use of the secondary battery 701, and the second voltage V <b> 2 can be the upper limit voltage for use of the secondary battery 701. When a short circuit between the positive electrode and the negative electrode occurs in the secondary battery 701, increasing the difference between the first voltage V1 and the second voltage V2 increases the difference in the short circuit current before and after the voltage change. For this reason, the difference between the magnetic field strength of the secondary battery 701 when the voltage of the secondary battery 701 is the first voltage V1 and the magnetic field strength of the secondary battery 701 when the voltage is the second voltage V2 becomes large. The detection sensitivity of the short circuit between the positive electrode and the negative electrode inside the secondary battery 701 is improved. Moreover, in order to improve the detection sensitivity of a short circuit, you may use a voltage larger than a use upper limit voltage or a voltage smaller than a use lower limit voltage only at the time of a test | inspection.

  Following step S604, the pass / fail judgment unit 103 determines whether or not the first magnetic field strength B1 calculated in step S602 is equal to the second magnetic field strength B2 calculated in step S604 (B1≈B2). Determination is made (step S605). Here, the fact that the first magnetic field strength B1 and the second magnetic field strength B2 are equal means that the absolute value of the difference between the first magnetic field strength B1 and the second magnetic field strength B2 is not more than a predetermined reference value. Means that.

  When it is determined in step S605 that the first magnetic field strength B1 and the second magnetic field strength B2 are equal, it is determined that the secondary battery 701 to be inspected is a non-defective product, and this secondary battery 701 is sent to the next process. (Step S606). On the other hand, if it is determined in step S605 that the first magnetic field strength B1 and the second magnetic field strength B2 are not equal, the secondary battery 701 to be inspected is determined to be a defective product having a short-circuited portion inside. (Step S607). The secondary battery 701 determined to be defective is not sent to the next process.

Here, the number of detection data necessary for leveling the influence of the change in disturbance in the calculation of the first magnetic field strength B1 and the second magnetic field strength B2 will be described below.
Disturbances such as environmental magnetic fields change from moment to moment. For this reason, the magnitudes of the disturbance components included in the detection data detected at different times via the magnetic sensor 101 are different. In the read data group in which the detection data detected via the magnetic sensor 101 is continuously read, the influence of changes in disturbance can be leveled by increasing the number of detection data and averaging them. However, the number of detected data in the read data group cannot be increased without limit. As the number of detection data increases, the time required for the inspection of the presence or absence of a short circuit in the secondary battery 701 becomes longer. For this reason, a criterion for determining how much the number of detected data can be increased to equalize the influence of changes in disturbance is necessary.

  In the calculation of the first magnetic field strength B1 and the second magnetic field strength B2, the detection data group detected via the magnetic sensor 101 is evenly divided by a certain section width (the section width is defined by a time width or the number of data points). The average value is calculated for each data group included in the section. Assuming that the number of detected data included in one section is sufficient to equalize the influence of changes in disturbance, the variation in the average values obtained for each section (hereinafter referred to as “average value group Variation ”) is small enough to be ignored. On the other hand, if the number of detected data included in one section is smaller than the number of detected data sufficient to equalize the influence of changes in disturbance, the variation of the average value group does not become so small that it can be ignored. That is, by determining the magnitude of variation in the average value group, it can be determined whether or not the influence of the change in disturbance is sufficiently leveled.

  FIG. 5A shows a case where a certain read data group is equally divided by the section width Wa, and FIG. 5B shows a case where the read data group is equally divided by the section width Wb. 5 (a) and 5 (b), the average values of the data groups included in the sections in the sections are calculated as average values Lan (n = 1, 2,..., 10), respectively. The average value is Lbn (n = 1, 2).

  The section width Wb shown in FIG. 5B is wider than the section width Wa shown in FIG. In other words, when the section width is increased, the number of detection data included in one section increases, so that the influence of a change in disturbance on the calculated average value of the section becomes smaller. For this reason, the variation of the average value group (Lb1, Lb2) in FIG. 5B is smaller than the variation of the average value group (La1, La2,..., La10) of FIG.

  When the interval width is gradually increased and the variation in the average value group falls below a predetermined reference value, the number of detected data included in the interval width at that time is sufficient to smooth out the influence of the change in disturbance. It can be determined that the number of detected data is large.

Next, a processing flow for calculating the first magnetic field strength B1 and the second magnetic field strength B2 will be described below. Note that the processing flow for calculating the first magnetic field strength B1 and the second magnetic field strength B2 is the same.
As shown in FIG. 6, the initial values are respectively set for the width of the read data group for continuously reading the detection data detected via the magnetic sensor 101 and the section width for equally dividing the read data group. Is set (step S701). The width and interval width of the read data group are defined by the time width or the number of data points. In setting the initial values of the read data group width and section width, the sampling rate and the like are also taken into consideration. Subsequently, the detection data is read by the width of the read data group (step S702). In reading detection data, data that has been detected in advance may be read, or data that is currently being detected may be read.

  Subsequent to step S702, an average value for each data group included in each section is calculated in each section, and the average value group obtained by the calculation varies (hereinafter referred to as "average value group variation"). Is calculated (step S703). For example, “standard deviation” or “difference between maximum value and minimum value” can be used as an index of variation. Subsequently, it is determined whether or not the variation of the average value group calculated in step S703 is within a predetermined reference value (step S704).

  If it is determined in step S704 that the variation of the average value group is within a predetermined reference value, the magnetic field strength of the secondary battery 701 is calculated (step S705). Specifically, an average value of all detection data included in the read data group is calculated, and this is used as the magnetic field strength around the secondary battery 701. After step S705, the process ends.

  If it is determined in step S704 that the variation in the average value group exceeds a predetermined reference value, a new section width is obtained by expanding the section width by a predetermined width (step S706). . Subsequently, it is determined whether or not the number of samples in the average value group (the number of average values to be obtained) is equal to or greater than a predetermined required number of samples (step S707). When the width and interval width of the read data group are defined by the time width, the number of samples in the average value group is a quotient obtained by dividing the time width of the read data group by the time width of one interval. When the width and interval width of the read data group are defined by the number of data points, the number of samples of the average value group is a quotient obtained by dividing all the detected data points included in the read data group by the data points of one interval. The necessary number of samples means the minimum number of samples necessary for appropriately determining the magnitude of variation in the average value group. The required number of samples is 2 or more. The required number of samples is preferably determined from a statistical point of view.

If it is determined in step S707 that the number of samples in the average value group is equal to or greater than the required number of samples, the process returns to step S703. On the other hand, if it is determined in step S707 that the number of samples in the average value group is less than the required number of samples, the width of the read data group is increased by a predetermined width (step S708), and the process returns to step S702. When reading the detection data, when reading the detection data currently being detected, all the data detected up to the time of determination in step S707 may be read.
According to the processing flow for calculating the first magnetic field strength B1 and the second magnetic field strength B2 described above, the magnetic strength of the secondary battery 701 can be accurately calculated regardless of the influence of disturbance such as an environmental magnetic field. it can.

  According to the inspection method of the secondary battery according to the present invention described above, it is possible to quickly and accurately inspect the presence or absence of the micro short circuit of the secondary battery.

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention. In the present embodiment, in the calculation of the magnetic field strength (first magnetic field strength B1 and second magnetic field strength B2) of the secondary battery, an average value of all detection data included in the read data group is calculated and this is calculated. Although it is set as the magnetic field intensity of a secondary battery, it is not restricted to this. For example, an average value of detection data included in the first section of the read data group may be used as the magnetic field strength of the secondary battery. Alternatively, the average value of the detection data included in a certain section of the read data group may be used as the magnetic field strength of the secondary battery.

DESCRIPTION OF SYMBOLS 100 Inspection apparatus 101 Magnetic sensor 102 Magnetic field calculation part 103 Pass / fail judgment part 104 Storage part 110 Charging / discharging apparatus 120 Magnetic shield box 201 Positive electrode material 202 Negative electrode material 203 Separator 701 Secondary battery 702 Conductive foreign material 703 Magnetic field

Claims (1)

A first step of calculating the magnetic field strength of the secondary battery when the voltage of the secondary battery is the first voltage;
A second step of changing the voltage of the secondary battery to a second voltage different from the first voltage;
A third step of calculating the magnetic field strength of the secondary battery when the voltage of the secondary battery is the second voltage;
Whether there is a short circuit inside the secondary battery based on the difference between the magnetic field strength of the secondary battery calculated in the first step and the magnetic field strength of the secondary battery calculated in the third step. A fourth step of determining whether or not
The first step and the third step are:
A section width of a read data group that is continuously read from detection data detected through a magnetic sensor that is arranged around the secondary battery and detects a magnetic field intensity in a state where the positive electrode and the negative electrode of the secondary battery are opened. Is divided evenly, and the average value for each data group included in the section is calculated for each section, and whether or not the variation of the plurality of average values obtained for each section exceeds a predetermined reference value The first step of determining whether
When it is determined that the variation of the plurality of average values exceeds the reference value in the first step, the width of the certain section is increased, and the range of the read data group is expanded as necessary. Again, a second step of performing the first step;
A third step of calculating the magnetic strength of the secondary battery based on the read data group when it is determined in the first step that the variation of the plurality of average values is equal to or less than the reference value; Secondary battery inspection method comprising:

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