JP2011141259A - Device for sorting lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device that sorts the quality of a lithium ion secondary battery in a short time automatically. <P>SOLUTION: The amplitude of a current which flows instantaneously through electrodes by a micro-short circuit of the lithium ion secondary battery, or the frequency distribution of the duration thereof, is calculated, and the quality is sorted automatically, according to a prescribed standard set beforehand. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an apparatus for detecting a micro-short generated in a lithium ion secondary battery and selecting a lithium ion secondary battery.

  In the inspection in the manufacturing process of the lithium ion secondary battery, selection of non-defective product and defective product is judged by the amount of leakage current. The leakage current of a lithium ion secondary battery becomes a problem particularly when a plurality of batteries are used in combination in series connection. Lithium ion secondary batteries require a protection circuit against overcharge and overdischarge in consideration of safety, so batteries that have a large leakage current when left unattended for a long time are overdischarge protection circuits earlier than other batteries. Will stop working before the remaining battery capacity of the other combined batteries is used up. When recharging is performed in such a state, when the overcharge protection circuit for a battery that does not use up its battery capacity is activated, the battery having a large leakage current is not yet fully charged. If charging / discharging is repeated in this manner, this combination battery falls into a state where it cannot be charged or discharged.

  Currently, battery manufacturers measure the difference between the voltage after initial charging and the voltage after standing for several weeks, and inspect lithium ion secondary batteries manufactured by a method that excludes those whose voltage drops below the reference value. Is going. Although this inspection method is reliable, it takes a long time to detect a defect, and this is an obstacle to improving the productivity of the lithium ion secondary battery. Therefore, an apparatus capable of inspecting in a shorter time is desired.

  The problem to be solved by the present invention is to provide an apparatus capable of selecting the quality of a lithium ion secondary battery in a short time.

In the present invention, the above-described problems are solved by the following means.
An electronic circuit that measures the magnitude or duration of a current that instantaneously flows between the electrodes of the lithium ion secondary battery by a micro short circuit generated inside the lithium ion secondary battery, and the magnitude or duration of the current A lithium ion secondary battery sorting device that automatically calculates the frequency distribution of time, determines the calculation result based on a predetermined criterion set in advance, and automatically sorts the quality of the lithium ion secondary battery. .

  A typical waveform that is pre-registered by converting the waveform of the current that instantaneously flows between the electrodes of the lithium ion secondary battery to digital data by an A / D converter due to a micro short circuit generated inside the lithium ion secondary battery There may be a lithium ion secondary battery sorting device that counts only when it is determined that the current waveform data due to micro short circuit and the data obtained by the A / D converter are approximate.

  The present invention statistically measures the amount and duration of instantaneous current caused by a micro short measured using a circuit that detects the instantaneous current generated by the micro short that is the cause of leakage current of a lithium ion secondary battery. By classifying by a method, an apparatus for determining the quality of a lithium ion secondary battery is provided, and the production efficiency of the lithium ion secondary battery is improved.

  When a micro short circuit (minute short circuit) occurs inside the lithium ion secondary battery, a current flows instantaneously between the positive and negative electrodes. The current waveform output from the circuit for detecting this current typically shows a change as shown in FIG. According to the inventor's verification, several other types of waveforms have been confirmed, all of which have a single impulse shape. The period during which current flows (duration tw) is often about 10 nanoseconds to several tens of nanoseconds. When this current waveform is observed for a large number of lithium ion secondary batteries, variations in amplitude and duration are observed, and the frequency of occurrence within a certain time varies depending on the battery. In the present invention, the quality of the lithium ion secondary battery is judged from the correlation between the current amplitude and duration frequency distribution due to the micro short circuit and the leakage current.

  An embodiment of the present invention is shown in FIG. The amplitude of the output waveform of the circuit 3 for detecting the instantaneous current due to the micro short circuit generated in the lithium ion secondary battery 1 is compared by a plurality of comparators 4 having different reference voltages 5, and the output of the comparator 4 is compared by the microprocessor 6. By performing counting within a certain period, a frequency distribution indicating the frequency of occurrence for each amplitude is obtained. The microprocessor 6 stores in advance the characteristics of the frequency distribution of the non-defective product and the defective product, and performs a statistical process such as correlation and deviation with the measured result to determine pass / fail.

  FIG. 3 shows an embodiment in which similar processing is performed using an A / D converter 7 instead of a comparator. The micro short detection circuit may detect noise that wraps around from the surrounding radio wave or the power supply of the measuring device in order to detect a minute current. If such noise is counted incorrectly, the accuracy of the pass / fail judgment is reduced. In this embodiment, the current waveform is converted into digital data by using the high-speed A / D converter 7, and the current waveform caused by micro short circuit and the waveform caused by noise can be distinguished and counted, thereby improving the determination accuracy. . As shown in FIG. 2, the waveform a due to micro short is a single impulse, whereas the waveform b due to noise shows a damped oscillation of about t = several hundred nanoseconds, and there is a clear difference, but only the amplitude comparison by the comparator. So I don't know the difference.

  In the embodiment shown in FIG. 3, not only the amplitude of the current waveform due to the micro short circuit but also the frequency distribution of the duration can be obtained. By analyzing the frequency distribution three-dimensionally with two elements of amplitude and duration, a more accurate pass / fail judgment can be made. It is also possible to use a time interval meter 8 shown in FIG. 4 for measuring the duration. Here, the time interval meter 8 is a circuit that outputs a voltage proportional to the pulse width corresponding to the duration of the current obtained at the output of the comparator 4. The output voltage of the time interval meter 8 is converted into digital data by the A / D converter 7, and the time width is determined by the microprocessor 6.

  The embodiment shown in FIG. 5 is a combination of amplitude measurement by the comparator 4 and duration measurement by the time interval meter 8. Since the output signal of the time interval meter 8 can be measured with a relatively low-speed A / D converter, the A / D converter 7 incorporated in the microprocessor 6 is used in this embodiment. The circuit is simplified.

  The embodiment described with reference to FIGS. 1, 3, 4, and 5 includes a charge / discharge terminal 2. This is because the state of occurrence of micro short circuit changes depending on the state (charging or discharging) of the lithium ion secondary battery, the amount of charging current, and the amount of discharging current.

  Embodiment of the sorting apparatus according to the present invention   Micro short waveform and noise waveform   Example of sorting device for determining waveform   Example of sorting device for measuring time span   Example of sorting device for measuring amplitude and time width

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 2 Charging / discharging terminal 3 The circuit which detects the electric current by micro short circuit 4 Comparator 5 Reference voltage 6 Microprocessor 7 A / D converter 8 Time interval meter

Claims (2)

  An electronic circuit that measures the magnitude or duration of a current that instantaneously flows between the electrodes of the lithium ion secondary battery by a micro short circuit generated inside the lithium ion secondary battery, and the magnitude or duration of the current A lithium ion secondary battery, wherein a frequency distribution of time is automatically calculated, the calculation result is determined based on a predetermined criterion set in advance, and the quality of the lithium ion secondary battery is automatically selected. Sorting device.   Microwaves that are instantaneously flowing between the electrodes of a lithium ion secondary battery due to microshorts generated inside the lithium ion secondary battery are converted into digital data by an A / D converter, and pre-registered microshorts 2. The lithium ion secondary battery sorting apparatus according to claim 1, wherein the counting is performed only when it is determined that the current waveform data obtained by the above and the data obtained by the A / D converter are approximate.

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