JP2000195565A - Inspection method of secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply discriminate a good battery from a potentially shorted battery by applying a voltage between electrodes before filling an electrolyte and detecting a current causing electric breakdown between electrodes. SOLUTION: Output voltage of a constant voltage power source 2 of a breakdown voltage test device 1 is set to a voltage which does not cause electric breakdown to a good battery but causes electric breakdown to a potentially shorted battery, for example, set to 100-400 V in the inspection of a Ni-hydrogen battery. In the inspection, since the good battery does not cause electric breakdown, voltage is made equal to electric breakdown voltage of the potentially shorted battery, and a current becomes a leak current, and very small. The potentially shorted battery causes electric breakdown, voltage can not rise to electric breakdown voltage of the potentially shorted battery and very high current flows. The good battery and the potentially shorted battery can be discriminated by detecting the current flowing between electrodes 4 with a current detecting circuit 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of inspecting a secondary battery for determining a potential short-circuited battery which is not short-circuited in a manufactured state but short-circuited in the future.

[0002]

2. Description of the Related Art A secondary battery in which an electrode body in which a positive electrode and a negative electrode are laminated with a separator interposed therebetween is placed in an outer can, is contacted with the electrode when foreign matter such as fragments of the electrode is mixed between the positive and negative electrodes. , Short. A battery with an internal short circuit is excluded by measuring and determining a resistance and a voltage in a battery assembling process.

A method for inspecting the assembled secondary battery is described in, for example, Japanese Patent Application Laid-Open No. SHO 51-16439. The inspection method described in this publication is 1000-3000V
And an extremely high voltage is applied as a pulse voltage for 10 to 20 μsec to detect an internal short circuit between the electrodes. In a secondary battery in which the positive electrode and the negative electrode are in contact with each other and short-circuited internally, a short-circuit current flows in a pulse shape when a pulse voltage is applied. Therefore, the internal short-circuit of the secondary battery can be detected by detecting the current. In this method, there is an oxide film or the like on the surface of the positive electrode or the negative electrode, and although the positive electrode and the negative electrode are actually in contact,
In order to eliminate the adverse effect that short current does not flow, 100
A high voltage of 0 V to 3000 V is applied.

[0004]

The internal short circuit of the secondary battery can be determined by the inspection method described in the above publication.
However, the method described in this publication cannot identify a potential short-circuit battery in which the positive electrode and the negative electrode are not in contact with each other when inspected, but the electrodes will come into contact and cause an internal short-circuit in the future. This is because a secondary battery assembled by attaching small foreign matter or the like between the electrodes may not be short-circuited when assembled. However, repeated charging and discharging may cause the electrodes to come into contact and cause a short circuit. The latent short battery in such a state cannot be identified as a good battery by inspection at the time of assembly. In particular, secondary batteries in which an aqueous electrolyte solution is injected have high conductivity after the injection, regardless of the presence or absence of foreign matter that may cause a short circuit in the electrode after injection. Due to the extremely low resistance, the method of measuring voltage and current makes it difficult to identify a potential short battery. In addition, even before the injection, since the resistance between the electrodes is extremely large, there is no difference between the latent short battery and the non-defective battery, and the latent short battery cannot be identified.

[0005] Identifying and removing potential short batteries is extremely important in the manufacture of secondary batteries.
This is because, when a plurality of secondary batteries are used in series, such as a battery pack, the life of one battery determines the lifetime of the whole battery pack. For example, when 10 secondary batteries are connected in series and used, only 1
If the secondary batteries become defective, the entire battery cannot be used even if the remaining nine secondary batteries can be used normally. Therefore, when a large number of secondary batteries are connected in series and used, it is extremely important to remove the potential short-circuit batteries. However, the potential short-circuited battery has the same electrical characteristics as a good battery immediately after being manufactured, so that it is extremely difficult to identify it. For this reason,
Potential short batteries are shipped together with non-defective batteries, and short-circuiting of one secondary battery prevents many normal secondary batteries used with the potential short battery from being used effectively. Is the actual situation. In order to solve this problem, it is necessary to reliably identify and remove the potential short battery. Furthermore, since the ratio of the potential short-circuit batteries included in the manufactured secondary batteries is small, even if the potential short-circuit batteries are removed, the number of manufactured secondary batteries hardly decreases.

SUMMARY OF THE INVENTION The present invention has been developed for the purpose of accurately identifying a potential short-circuited battery. The present invention is directed to an inspection of a secondary battery capable of identifying a potential short-circuited battery having a short cycle life by an extremely simple method. It is to provide a method.

[0007]

SUMMARY OF THE INVENTION The present invention is a method for inspecting a secondary battery which is assembled by putting an electrode body in which a positive electrode and a negative electrode are wound or laminated with a separator interposed therebetween in an outer can. In the inspection method for a secondary battery according to the first aspect of the present invention, a voltage is applied between the electrodes in a state where the electrolyte is not injected, a current that causes a dielectric breakdown between the electrodes is detected, and the non-defective battery and the latent short-circuit battery are separated. Identify. In the method of measuring the dielectric breakdown voltage by placing the electrode body in an outer can, the dielectric breakdown voltage between the electrodes is measured in a state where the electrolytic solution is not injected into the outer can containing the electrode body. In a state where the electrode body is not put in the outer can, a potential short-circuit battery can be identified by detecting a dielectric breakdown current.

[0008] The voltage at which a potential short-circuit battery breaks down is:
It changes depending on the distance between the positive electrode and the negative electrode. An electrode body in which the positive electrode and the negative electrode are close to each other has a low voltage causing dielectric breakdown. This is because the voltage causing dielectric breakdown between the positive electrode and the negative electrode is inversely proportional to the distance between the electrodes. In the inspection method of the present invention, a voltage is applied between the positive electrode and the negative electrode in a state where the electrolytic solution is not injected, a current between the electrodes at the time of dielectric breakdown is detected, and the non-defective battery and the potential short-circuit battery are separated. Identify.

In a state where the electrolyte is not filled, air exists between the positive electrode and the negative electrode. The voltage at which the opposing electrodes cause dielectric breakdown in air is about 1500 V / mm.
Therefore, if the interval between the positive electrode and the negative electrode is 0.3 mm,
The voltage at which dielectric breakdown occurs between the positive electrode and the negative electrode of a good battery is about 450 V. In a latent short battery in which a positive electrode and a negative electrode are close to each other due to the adhesion of foreign matter between the electrodes, the voltage causing dielectric breakdown is lower than 450V. For example, if the distance between the positive electrode and the negative electrode is reduced by half, the voltage causing dielectric breakdown is also reduced to approximately 450 V.

The voltage applied between the electrodes is set lower than the voltage at which the non-defective battery causes the dielectric breakdown, and higher than the voltage at which the latent short battery causes the dielectric breakdown.

When the voltage applied between the electrodes is set lower than the voltage at which the non-defective battery causes dielectric breakdown, the potential short-circuit battery can be identified without causing the non-defective battery to undergo dielectric breakdown. In a latent short battery, a foreign substance is interposed between the positive electrode and the negative electrode, and the distance between the positive electrode and the negative electrode is reduced due to the foreign substance. As a result, the voltage causing dielectric breakdown is lower than that of a non-defective battery.

According to the method for inspecting a secondary battery of the present invention described in claim 2 of the present invention, in a state in which the electrode body is not brought into contact with the electrolytic solution, no dielectric breakdown occurs in a good battery, but in a latent short battery, A voltage causing dielectric breakdown is applied between the electrodes, and the current between the electrodes is detected. In this state, a secondary battery whose detected current is larger than the set current is determined as a potential short-circuited battery that will be short-circuited in the future, and a secondary battery whose detected current is smaller than the set current is determined as a non-defective battery.

The secondary battery is laminated with a separator sandwiched between a positive electrode and a negative electrode. The thickness of the separator determines the distance between the positive and negative electrodes. The separator is designed to be as thin as possible without contact between the positive electrode and the negative electrode. Since most potential short-circuit batteries have a voltage that causes dielectric breakdown of about 100 to 400 V, as described in claim 3, a battery that causes dielectric breakdown at this voltage can be identified as a potential short-circuit battery.

Further, the inspection method according to claim 4 of the present invention,
A potential short-circuited battery such as a nickel-hydrogen battery or a nickel-cadmium battery is identified. A battery with a large current flow is a latent short battery, and a battery with a smaller current is identified as a good battery.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. However, the following examples illustrate a method of inspecting a secondary battery for embodying the technical idea of the present invention, and the present invention does not specify a method of inspecting a secondary battery below.

Further, in this specification, in order to make it easier to understand the claims, the numbers corresponding to the members shown in the embodiments will be referred to as "claims" and "claims". In the column of “means”.
However, the members described in the claims are not limited to the members of the embodiments.

The principle of the secondary battery inspection method of the present invention for distinguishing a non-defective battery from a potential short-circuited battery will be described with reference to FIG. INDUSTRIAL APPLICABILITY The present invention is most suitable for inspection of a battery using an aqueous electrolyte, such as a nickel-hydrogen battery and a nickel-cadmium battery. However, it can also be used for inspection of secondary batteries other than these batteries, for example, lithium ion secondary batteries. Since the lithium ion secondary battery has a narrower electrode interval than a nickel-hydrogen battery or a nickel-cadmium battery, the potential breakdown voltage of a potential short battery supplied to the battery during inspection is set low.

According to the present invention, a latent short battery and a non-defective battery are distinguished in a state where an electrode body is put in an outer can and the electrolyte is not filled. The electrode body is obtained by winding or laminating a positive electrode and a negative electrode via a separator. In the state where the electrolyte is filled in the outer can containing the electrode body, the conductivity of the electrolyte is high, and it becomes impossible to detect the dielectric breakdown between the electrodes. Therefore, the latent short battery is identified without the electrolyte. . FIG. 1 shows the current-voltage characteristics of a non-defective battery, a latent short-circuited battery, and a battery already short-circuited internally in a state where an electrode body is placed in an outer can.

In this figure, the solid line G shows the current-voltage characteristics of a good battery, the solid line B shows the current-voltage characteristics of a latent short-circuited battery, and the solid line NG shows the current-voltage characteristics of a battery already short-circuited internally. Further, a dashed line G 'shows the characteristics of a good battery at high humidity, and a dashed line B' shows the characteristics of a latent short battery at high humidity. As shown in this figure, the battery with an internal short circuit has a current-voltage characteristic with a slope of
Unlike a good battery and a potential short-circuit battery, a large current flows in a state where the applied voltage is low, so that it can be identified from the current-voltage characteristics. However, the non-defective battery and the latent short battery have extremely similar current-voltage characteristics in a region where the current between the electrodes is small. For this reason, a good battery and a latent short battery cannot be distinguished from the current-voltage characteristics.

However, as shown by solid lines G and B,
The voltage of the non-defective battery and the potential short-circuit battery are constant without increasing the voltage even if the current is increased above a certain voltage. This state is a state in which dielectric breakdown has occurred. The limit voltage at which the voltage is constant, that is, the breakdown voltage, is determined by the distance between the positive electrode and the negative electrode, and the type and shape of the foreign matter attached to the electrode. A latent short battery in which a foreign substance exists between the electrodes can be identified as a good battery by detecting a decrease in dielectric breakdown voltage.

Specifically, for example, the maximum value of the output voltage and the output current of the constant voltage / constant current circuit is set at point A1 in the figure, that is, the dielectric breakdown voltage and the maximum current of the latent short-circuit battery are set at point A1. When the voltage is set to the voltage and the current, and the electrode body is not in contact with the electrolyte, that is, when applied between the positive electrode and the negative electrode of the secondary battery before the injection, a small leakage current flows in the non-defective battery. On the other hand, a latent short-circuit battery causes a dielectric breakdown at this voltage and a large current flows. Therefore,
By comparing the magnitude of the current, a good battery and a potential short battery can be distinguished.

However, even in the battery before the injection, if moisture is adsorbed on the separator, for example, due to high humidity, the detection accuracy may be reduced due to the influence of the resistance value. In the high humidity state, the relationship between the current and the voltage changes as shown by chain lines G ′ and B ′. In this state, for example, when a voltage is applied in a state where the breakdown voltage and the maximum current of the latent short battery are set to the point A2 in the figure, the non-defective battery and the latent short battery both exceed the set value and cannot be determined. This is because, in this state, the leakage current of the non-defective battery increases even if the dielectric breakdown does not occur. This problem can be solved by increasing the detection current to point A1.

In the above-described method, a voltage is applied between the electrodes in a state in which the latent short battery causes the dielectric breakdown, but the non-defective battery does not cause the dielectric breakdown. The inspection method of the present invention can also identify a potential short-circuit battery by causing a dielectric breakdown in both the non-defective battery and the potential short-circuit battery.

FIG. 2 is a circuit diagram of an inspection apparatus used in the method according to the embodiment of the present invention. The inspection apparatus shown in FIG. 1 is a withstand voltage test apparatus 1 and includes a constant voltage power supply 2 and a current detection circuit 3.

The constant voltage power supply 2 converts AC commercial power into DC or AC constant voltage and supplies it to the electrode body. The output voltage of the constant voltage power supply 2 is preferably such that a non-defective battery does not cause a dielectric breakdown, but a latent short battery has a voltage that causes a dielectric breakdown, such as a nickel-hydrogen battery or a nickel-hydrogen battery.
In the inspection of the cadmium battery, the voltage is set to 100 to 400V. The voltage at which the potential short-circuit battery causes dielectric breakdown is determined to be an optimum value depending on the distance between the positive electrode and the negative electrode of the battery to be inspected. For a battery with a large distance between the positive electrode and the negative electrode, the dielectric breakdown voltage of a potential short-circuited battery is set high, and for a narrow battery, the voltage is set low. The closer the breakdown voltage of a potential short battery is to the breakdown voltage of a good battery, the more accurately the potential short battery can be identified.

When a current equal to or greater than the set current value flows between the electrodes of the battery, the current detection circuit 3 displays the current using a buzzer, a lamp, or the like, and cuts off the current. The set values of the output voltage and the detection current are set in a region where a non-defective battery does not cause a dielectric breakdown and a potential short-circuit battery causes a dielectric breakdown, as indicated by a point A3 in FIG. 3, and a region indicated by hatching in FIG. You. In the constant voltage power supply 2, the set current indicating the output characteristic indicated by the solid line D in FIG. 3 is set to 5 mA or more, preferably 10 mA or more.

When a secondary battery is connected to this inspection device and inspected, a non-defective battery does not cause dielectric breakdown, so that it becomes equal to the dielectric breakdown voltage of the latent short battery, and becomes a voltage at point a1 or b1. Becomes extremely small as a leakage current. The latent short battery causes a dielectric breakdown, and the voltage cannot rise to the dielectric breakdown voltage of the latent short battery, so that a very large current flows. Therefore,
The good battery and the potential short battery can be distinguished into a good battery and a potential short battery by detecting the current between the electrodes.

[0028]

EXAMPLE In the following steps, an electrode assembly was actually manufactured and a latent short battery was inspected. [Preparation of Electrode Body] A negative electrode prepared by applying a hydrogen storage alloy to a punching metal and a positive electrode which is a sintered nickel electrode were wound through a nonwoven fabric separator to prepare an electrode body. The electrode body was provided with an uncoated portion where the active material was not applied along one side edge for electrical connection. When winding the positive electrode and the negative electrode, the positive electrode and the negative electrode were slightly shifted so that the uncoated portion protruded from both ends of the electrode body.

Further, in order to perform a discrimination test between a good battery and a potential short battery, an electrode body of a potential short battery into which a piece of an electrode is intentionally mixed and an electrode body which is a non-defective battery in which no piece of an electrode is mixed. Was prototyped. After winding, the resistance value of each electrode body was measured, and it was confirmed that no internal short circuit occurred.

[Preliminary Inspection of Judgment of Latent Short Battery] For the inspection, a withstand voltage test device (TOS5051 manufactured by Kikusui Electronics) having the circuit shown in FIG. 2 was used. The applied current was an alternating current (commercial waveform).

On the upper and lower uncoated portions of the wound electrode body,
The output terminals of the inspection device were closely connected and electrically connected. The set current value is set to 1 mA, and the applied voltage is gradually increased until a current equal to or higher than the set current is detected.
I asked. The same operation is performed for 2, 3, 4, 5, 10, 20,
30, 40, 50, 60, 70, and 100 mA were similarly obtained. Next, the same operation was performed with the battery kept in a high humidity state (80% humidity). The above inspection was performed on the electrode bodies of the non-defective battery and the latent short battery, and the relationship between the current and the voltage was obtained.

[Inspection Results] The measurement results are shown in Table 1 and FIG. In FIG. 4, solid lines G and G ′ indicate the current-voltage characteristics of the non-defective battery, and solid line B indicates the current-voltage characteristics of the latent short-circuited battery. This table and figure show that the electrode body of the non-defective battery has a dielectric breakdown voltage of 450 V, and the electrode body of the latent short battery has a dielectric breakdown voltage of 100 V. At the time of high humidity, as shown by the solid line G ', the current causing dielectric breakdown is as large as about 5 mA or more, but the voltage causing dielectric breakdown does not change. For this reason, it turned out that the electrode body of a latent short battery can be identified stably by setting the set value of the current to 5 mA or more.

[0033]

[Table 1]

When the set value of the current is 50 mA or more,
When the voltage was increased, the voltage fluctuated momentarily. This is considered to be due to the fact that the set current value was too large, and even if the dielectric breakdown occurred, the phenomenon was not detected. From this, the current value for identifying the potential short-circuit battery is preferably 5 to 50 mA. The breakdown voltage for distinguishing a good battery from a potential short battery is 1
00 to 400V.

In the above inspection, the electrolyte was injected into an outer can containing the electrode body determined to be a good battery and a potential short-circuited battery, and then sealed to assemble the battery. The battery was subjected to repeated charge / discharge cycles. The cycle life was measured. A battery determined as a good battery had a cycle life of 1,000 cycles. On the other hand, those that were determined to be latent short-circuit batteries had a cycle life of less than half.

[Identification Test of Latent Short Battery] When about 1,000 solid batteries were fabricated and the rate of short-circuiting after 500 cycles of charge and discharge was measured, the short-circuit rate was 1.0% as shown in Test Example 17 in Table 2. became. Therefore, the potential short-circuit rate is considered to be 1.0%.

[0037]

[Table 2]

An inspection apparatus shown in FIG. 2 was used to create this table. In Test Examples 1 to 12, the potential short-circuit battery was identified and removed by setting the set voltage of the constant voltage circuit to 100 to 400 V and setting the current to 5 to 50 mA. In the set from which the latent short-circuited battery was removed in this test example, there was no battery that short-circuited when charged and discharged for 500 cycles, and the ratio of the short-circuited battery to the entire battery, that is, the short-circuit rate was 0%. . In the inspection example 13, the set voltage is set to 90
Due to the low setting of V, all potential short batteries could not be identified, and only some potential short batteries were identified.
The set of batteries excluding the potential short battery in Test Example 14 is:
Although the short-circuit rate at the time of 500 charge / discharges was 0%, since the set voltage was as high as 450 V, a non-defective battery was also identified as a potential short-circuit battery, and the detection rate was 40%. In Test Example 15, since the detected current value was low, a part of the non-defective batteries caused a current to flow due to the influence of humidity or the like, and was detected as a potential short-circuited battery. For this reason, the detection rate was increased. In the test example 16, since the detected current value was high, a battery that was not detected occurred despite the occurrence of the dielectric breakdown.
The detection rate of the latent short battery was 0.3%. From the above inspection results, when detecting a potential short-circuited battery of a nickel-hydrogen battery, the voltage was set to 100 to 400 V and the current was set to 5
Optimally, it is set to ５０50 mA. From the above test results, the detection rate of the potential short-circuit batteries was 1.0%, and all the potential short-circuit batteries were detected by this test. The method of the present invention ensures that all potential short batteries are identified by setting the voltage and current to values appropriate for each battery.

In this embodiment, the inspection is performed in the state of the electrode body. However, the same effect can be obtained even when the electrode body is put in the outer can and the electrolytic solution is not injected. In this embodiment, an AC voltage is applied. However, a similar effect can be obtained by applying a DC voltage.

[0040]

The inspection method according to the first aspect of the present invention has a feature that a latent short battery having a short cycle life can be reliably specified and identified by an extremely simple method. That is, in the state where the inspection method of the present invention does not contact the electrode body with the electrolyte,
This is because a voltage is applied between the electrodes to detect a dielectric breakdown between the electrodes, and a potential short-circuit battery and a non-defective battery that may be short-circuited in the future are identified.

The inspection method of the present invention has a feature that a potential short battery can be effectively identified without giving an electric shock to a good battery. This is because a potential short-circuited battery can be identified by causing a dielectric breakdown only between the electrodes of the potential short-circuited battery without causing the dielectric breakdown between the electrodes of the non-defective battery.

Further, the inspection method according to claims 3 to 5 of the present invention is characterized in that a latent short-circuit battery can be identified very accurately in a nickel-hydrogen battery manufacturing process.

[Brief description of the drawings]

FIG. 1 is a graph showing the principle of operation of a method for testing a secondary battery according to the present invention.

FIG. 2 is a block diagram showing an inspection apparatus used in an embodiment of the present invention.

3 is a graph showing voltage-current characteristics of the inspection device shown in FIG.

FIG. 4 is a graph showing voltage-current characteristics of a non-defective battery and a potential short-circuited battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Withstand voltage test device 2 ... Constant voltage power supply 3 ... Current detection circuit 4 ... Electrode

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G016 CA00 CB05 CC01 CC06 CE01 5G003 BA01 EA09 5H028 AA01 BB12 CC12 HH10 5H030 AA09 AS18 FF42 FF43

Claims (5)

[Claims] In a method for inspecting a secondary battery assembled by putting an electrolyte and an electrolyte in which a positive electrode and a negative electrode are wound or laminated via a separator in an outer can, a state in which the electrode is not brought into contact with the electrolyte A method for inspecting a secondary battery, characterized in that a voltage is applied between the electrodes to detect a current that causes a dielectric breakdown between the electrodes, and a potential short-circuited battery and a non-defective battery that may be short-circuited in the future are identified. 2. A method for inspecting a secondary battery in which an electrode body in which a positive electrode and a negative electrode are wound or laminated with a separator interposed therebetween and an electrolyte solution placed in an outer can is assembled, wherein the electrode body is not brought into contact with the electrolyte solution. A voltage between the electrodes that is lower than the voltage at which a non-defective battery causes dielectric breakdown and higher than the voltage at which the potential short-circuit battery causes dielectric breakdown is applied, and the current between the electrodes is detected. 2. The secondary battery according to claim 1, wherein a secondary battery whose current is larger than the set current is determined as a potential short-circuit battery, and a secondary battery whose detected current is smaller than the set current is determined as a non-defective battery. Inspection method. 3. The voltage applied between the electrodes is 100 to 400 V
The inspection method for a secondary battery according to claim 1. 4. The method for inspecting a secondary battery according to claim 1, wherein the secondary battery is a nickel-metal hydride battery. 5. The method for inspecting a secondary battery according to claim 3, wherein a set current for distinguishing the potential short-circuited battery from the non-defective battery is 5 mA or more.