JP2017199577A - Manufacturing method of secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of secondary battery which allows for accurate detection of a battery that has short-circuited in the manufacturing process.SOLUTION: A manufacturing method of secondary battery includes multiple voltage drop amount acquisition steps S4, S5, S6 of performing a voltage drop amount acquisition step of acquiring a voltage drop amount ΔV1, and the like, by leaving a secondary battery 1 in terminal open state under a predetermined temperature over a predetermined time Da, under temperatures T1, and the like, different from each other, a coefficient acquisition step S7 of acquiring the coefficient b of an exponential approximation curve ΔV=aeof the left temperature T and voltage drop amount ΔV1, based on the multiple voltage drop amounts ΔV1, and a short circuit determination step S8 of determining that internal short circuit has occurred in secondary battery 1, when the coefficient b is smaller than a reference coefficient B.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for manufacturing a secondary battery including a short-circuit determination step for determining the presence or absence of an internal short circuit of a secondary battery.

  It is known that in the process of manufacturing a secondary battery such as a lithium ion secondary battery (hereinafter also simply referred to as a battery), a short circuit inspection is performed to determine whether or not an internal short circuit (hereinafter also simply referred to as a short circuit) has occurred in the battery. ing. Specifically, the battery is self-discharged for a predetermined leaving time under a predetermined leaving temperature (discharged with the terminal open), and the voltage drop amount ΔV due to self-discharge is calculated from the battery voltage measured before and after the self-discharging. Ask. When the voltage drop amount ΔV is larger than the reference voltage drop amount ΔVr (ΔV> ΔVr), it is determined that a short circuit has occurred in the battery.

  Furthermore, in order to improve the accuracy of this short-circuit inspection, the batteries are finely classified based on the battery production lot, other production conditions, and inspection conditions, and the reference voltage drop amount ΔVr is set for each of these inspection lots to short-circuit. It is also known to perform inspections. For example, Patent Document 1 describes that a battery short-circuit inspection is performed for each inspection lot in which the batteries are finely classified as described above (see the claims of Patent Document 1).

JP 2013-165029 A

  However, if the batteries are further classified to improve the accuracy of the short circuit inspection, the number of batteries belonging to the same inspection lot may be reduced. Then, in an inspection lot with a small number of batteries, it is difficult to set the reference voltage drop amount ΔVr appropriately, and thus there may be a case where the short-circuit inspection cannot be performed with high accuracy. Thus, conventionally, it has been difficult to perform a short-circuit inspection with high accuracy for all assembled batteries.

  This invention is made | formed in view of this present condition, Comprising: It aims at providing the manufacturing method of the secondary battery which can detect the battery which has produced the short circuit in the manufacture process accurately.

One aspect of the present invention for solving the above problem is that a secondary battery is left for a predetermined leaving time at a predetermined leaving temperature and a terminal is opened, and a voltage drop amount of the battery voltage before and after the leaving is obtained. The voltage drop amount acquisition step is performed at a plurality of voltage drop amount acquisition steps performed at different stand-by temperatures, and the stand-off temperature T and the voltage drop amount ΔV are determined based on the obtained plurality of voltage drop amounts. Exponential approximation curve ΔV = ae ^bT (a and b are coefficients, where a> 0, b> 0), a coefficient acquisition step of acquiring the coefficient b, and the obtained coefficient b is smaller than the reference coefficient B (b <B) In the case, a secondary battery manufacturing method comprising: a short circuit determination step for determining that an internal short circuit has occurred in the secondary battery.

  The voltage drop amount ΔV when self-discharged for a predetermined standing time at a predetermined standing temperature is a voltage drop amount ΔVa caused by a chemical reaction (such as a reaction in which a film grows on the particle surface of the negative electrode active material particles). , A voltage drop amount ΔVb caused by a physical reaction (internal short circuit) is included (ΔV = ΔVa + ΔVb). The voltage drop amount ΔVa due to the chemical reaction increases as the battery temperature increases, while the voltage drop amount ΔVb due to the internal short circuit does not depend on the battery temperature and is substantially constant. For this reason, it can be seen that a normal battery (with no internal short circuit) has a large temperature dependency of the voltage drop ΔV, whereas a battery with an internal short circuit has a small temperature dependency of the voltage drop ΔV. I came.

In the above-described secondary battery manufacturing method, the leaving temperature T and the voltage drop amount ΔV are based on a plurality of voltage drop amounts ΔV (ΔV1, ΔV2,...) Obtained at different leave temperatures T (T1, T2,...). When the coefficient b of the exponential approximation curve ΔV = ae ^bT is acquired and the obtained coefficient b is smaller than the reference coefficient B (b <B), it is determined that a short circuit has occurred in the battery. As described above, since the battery in which the short circuit occurs has a smaller temperature dependency of the voltage drop ΔV than the normal battery, the coefficient b of the exponential approximation curve obtained in the battery in which the short circuit occurs is normal. This is smaller than the coefficient b of the exponential approximation curve obtained with a simple battery. In addition, there is almost no difference between the normal battery and the short-circuited battery in the voltage drop amount ΔV obtained at a certain standing temperature T. Even when these cannot be discriminated, the coefficient b of the exponential approximation curve is seen. It has been found that there is a large difference between a normal battery and a battery in which a short circuit occurs. For this reason, by comparing the coefficient b of the acquired exponential approximation curve with the reference coefficient B, it is possible to accurately detect a battery in which a short circuit has occurred.

The “standing temperature” T is preferably T = 0 ° C. or higher. By setting the standing temperature T to 0 ° C. or higher, the equipment for leaving the battery while cooling can be simplified or eliminated, and the production cost can be suppressed. Further, the leaving temperature T is preferably T = 30 ° C. or less, as will be described later.
The “leaving time” Da is preferably within a range of Da = 1.0 to 7.0 days. By setting the leaving time Da to 1.0 day or longer, the voltage drop amount ΔV before and after being left can be increased. On the other hand, by setting the leaving time Da to 7.0 days or less, the time required for the voltage drop amount acquisition step can be suppressed, and the productivity of battery manufacturing can be improved.

  Furthermore, in the method for manufacturing a secondary battery described above, it is preferable that each of the plurality of voltage drop amount acquisition steps is a method for manufacturing a secondary battery in which the standing temperature is 30 ° C. or less.

  If the standing temperature T is too high, specifically, if the standing temperature T is higher than 30 ° C., the ratio of the voltage drop ΔVa due to the chemical reaction in the voltage drop ΔV due to self-discharge is caused by the internal short circuit. It is too large compared to the resulting voltage drop amount ΔVb. For this reason, when the voltage drop amount acquisition step is performed with the standing temperature T set to 30 ° C. or higher, the voltage drop amount ΔVb included in the measured voltage drop amount ΔV becomes relatively small. This makes it difficult to determine the magnitude of the voltage drop amount ΔVb.

  On the other hand, in any of the above-described secondary battery manufacturing methods, since any voltage drop amount acquisition step sets the standing temperature T to 30 ° C. or less, each voltage drop amount ΔV is caused by a chemical reaction. The ratio of the voltage drop amount ΔVa does not become too large compared to the voltage drop amount ΔVb caused by the internal short circuit. For this reason, the difference between the coefficient b of the exponential approximate curve obtained with a battery in which an internal short circuit has occurred and the coefficient b of the exponential approximate curve obtained with a normal battery become clear. Therefore, a battery in which an internal short circuit has occurred can be detected with higher accuracy in the short circuit determination step.

According to another aspect, a voltage reduction amount acquisition step is performed in which the secondary battery is left for a predetermined leaving time at a predetermined leaving temperature and a terminal is opened, and the voltage drop amount of the battery voltage before and after the leaving is acquired. A plurality of voltage drop amount acquisition steps performed at the different standing temperatures, and an exponential approximation curve ΔV = ae ^bT for the standing temperature T and the voltage drop amount ΔV based on the obtained plurality of voltage drop amounts. (A, b are coefficients, where a> 0, b> 0) and a coefficient acquisition step of acquiring the coefficient b, and when the obtained coefficient b is smaller than the reference coefficient B (b <B), And a short circuit determination step for determining that an internal short circuit has occurred in the secondary battery.

In the secondary battery inspection method described above, the coefficient b of the exponential approximation curve ΔV = ae ^{bT for} the leaving temperature T and the voltage drop amount ΔV is obtained based on a plurality of voltage drop amounts ΔV obtained at different standing temperatures T. When the obtained coefficient b is smaller than the reference coefficient B (b <B), it is determined that a short circuit has occurred in the battery. By doing in this way, the battery in which the short circuit has arisen can be detected accurately.

1 is a perspective view of a secondary battery according to an embodiment. It is a longitudinal cross-sectional view of the secondary battery which concerns on embodiment. It is a flowchart which shows the manufacturing process of the secondary battery which concerns on embodiment. It is a graph which shows the relationship between the leaving temperature T and the voltage drop amount ratio ΔVh.

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are a perspective view and a longitudinal sectional view of a secondary battery (hereinafter also simply referred to as “battery”) 1 according to the present embodiment. In the following description, the battery thickness direction BH, the battery lateral direction CH, and the battery vertical direction DH of the battery 1 are defined as the directions shown in FIGS. 1 and 2.
The battery 1 is a rectangular and sealed lithium ion secondary battery mounted on a vehicle such as a hybrid car, a plug-in hybrid car, or an electric car. The battery 1 includes a battery case 10, an electrode body 20 accommodated therein, a positive terminal member 50 and a negative terminal member 60 supported by the battery case 10, and the like. In addition, a non-aqueous electrolyte 19 is accommodated in the battery case 10, and a part thereof is impregnated in the electrode body 20.

  Among these, the battery case 10 has a rectangular parallelepiped box shape and is made of metal (in this embodiment, aluminum). The battery case 10 is composed of a bottomed rectangular tube-shaped case main body member 11 that is open only on the upper side, and a rectangular plate-shaped case lid member 13 that is welded in a form that closes the opening of the case main body member 11. The A positive terminal member 50 made of aluminum is fixed to the case lid member 13 while being insulated from the case lid member 13. The positive electrode terminal member 50 is connected to the positive electrode plate 21 of the electrode body 20 in the battery case 10 to be conductive, and extends through the case lid member 13 to the outside of the battery. Further, a negative electrode terminal member 60 made of copper is fixed to the case lid member 13 while being insulated from the case lid member 13. The negative electrode terminal member 60 is connected to and conductive with the negative electrode plate 31 of the electrode body 20 in the battery case 10, and extends through the case lid member 13 to the outside of the battery.

  The electrode body 20 has a flat shape and is accommodated in the battery case 10 in a laid-down state. Between the electrode body 20 and the battery case 10, a bag-shaped insulating film enclosure 17 made of an insulating film is disposed. The electrode body 20 is formed by laminating a belt-like positive electrode plate 21 and a belt-like negative electrode plate 31 with a pair of strip-like separators 41 and 41 wound around each other and compressed in a flat shape. The positive electrode plate 21 is provided with a positive electrode active material layer in a band shape at predetermined positions on both main surfaces of a positive electrode current collector foil made of a band-shaped aluminum foil. Moreover, the negative electrode plate 31 is provided with a negative electrode active material layer at a predetermined position on both main surfaces of a negative electrode current collector foil made of a strip-shaped copper foil. The separator 41 is a porous film made of a resin and has a strip shape and a film shape.

  Next, a method for manufacturing the battery 1 will be described (see FIG. 3). First, in the “assembly process S1”, the battery 1 is assembled. Specifically, the positive electrode plate 21 and the negative electrode plate 31 are overlapped with each other via a pair of separators 41 and 41 and wound into a flat shape to form the electrode body 20. Next, the case lid member 13 is prepared, and the positive electrode terminal member 50 and the negative electrode terminal member 60 are fixed thereto (see FIGS. 1 and 2). Thereafter, the positive electrode terminal member 50 and the negative electrode terminal member 60 are welded to the positive electrode plate 21 and the negative electrode plate 31 of the electrode body 20, respectively. Next, the electrode body 20 is covered with the insulating film enclosure 17 and inserted into the case main body member 11, and the opening of the case main body member 11 is closed with the case lid member 13. The case body member 11 and the case lid member 13 are welded to form the battery case 10. Thereafter, the nonaqueous electrolytic solution 19 is injected into the battery case 10 through the injection hole 13 h and impregnated in the electrode body 20. Thereafter, the liquid injection hole 13h is sealed.

  Next, the battery 1 is restrained prior to performing the initial charging step S2. Specifically, the wide side surface of the battery case 10 is sandwiched in the battery thickness direction BH by a pair of plate-shaped pressing jigs, and the battery 1 is restrained while being pressed in the battery thickness direction BH. In the present embodiment, the process from the “initial charging step S2” to the “internal resistance value acquisition / determination step S10” described below is performed in a state where the battery 1 is restrained as described above.

  After the battery 1 is restrained, the battery 1 is initially charged in the “initial charging step S2”. Specifically, the battery 1 is initially charged to SOC 100% by constant current constant voltage charging (CCCV charging) at room temperature (25 ± 5 ° C.). The initial charging step S2 can also be performed at a temperature other than room temperature. However, if it is performed at room temperature, the battery 1 does not have to be heated or cooled, so that the production cost can be reduced.

  Next, in the “aging step S3”, the battery 1 is left to age. Specifically, the battery 1 after initial charging is left to age for 20 hours with the terminals open at a temperature of 60 ° C.

  Next, in the “first voltage decrease amount acquisition step S4”, the first voltage decrease amount ΔV1 due to self-discharge is acquired. Specifically, the battery 1 is left for a predetermined leaving time Da (Da in this embodiment) in a state where the terminal is opened in an environment of a first leaving temperature T1 (T1 = 30 ° C. in this embodiment) of 30 ° C. or less. = 3.0 days) Leave (self-discharge). The battery voltage Vc (Vc1s, Vc1e) before and after this discharge is measured to obtain the first voltage drop amount ΔV1 (ΔV1 = Vc1s−Vc1e).

  Next, in the “second voltage drop amount acquisition step S5”, the second voltage drop amount ΔV2 due to self-discharge is acquired. Specifically, the battery 1 is left in a predetermined leaving state with the terminals open in an environment of a second leaving temperature T2 (T2 = 15 ° C. in the present embodiment) different from the first leaving temperature T1 of 30 ° C. or less. Leave for time Da (Da = 3.0 days). The battery voltage Vc (Vc2s, Vc2e) before and after this discharge is measured to obtain the second voltage drop amount ΔV2 (ΔV2 = Vc2s−Vc2e).

  Next, in the “third voltage decrease amount acquisition step S6”, a third voltage decrease amount ΔV3 due to self-discharge is acquired. Specifically, the terminal of the battery 1 is opened under an environment of a third standing temperature T3 (T3 = 0 ° C. in the present embodiment) that is 30 ° C. or less and different from the first and second standing temperatures T1 and T2. In this state, it is left for a predetermined leaving time Da (Da = 3.0 days). The battery voltage Vc (Vc3s, Vc3e) before and after the discharge is measured to obtain a third voltage drop amount ΔV3 (ΔV3 = Vc3s−Vc3e).

Next, in the “coefficient acquisition step S7”, the coefficient b of the exponential approximate curve for the battery 1 is acquired. More specifically, based on the obtained plural (three in this embodiment) voltage drop amounts ΔV (first to third voltage drop amounts ΔV1, ΔV2, ΔV3), the standing temperature T and the voltage drop amount ΔV. The exponent approximate curve ΔV = ae ^bT (where a and b are coefficients, where a> 0, b> 0), and the coefficient b is obtained.

However, when a graph of an exponential approximate curve is drawn using a plurality of voltage drop amounts ΔV, there is a difference between the coefficient a and the coefficient b between a normal battery and a battery in which an internal short circuit occurs. Differences due to b become difficult to understand. Therefore, in this embodiment, in order to make it easy to understand the difference between the two coefficients b, as described below, the first to third are based on the third voltage drop amount ΔV3 at the third leaving temperature T3 = 0 ° C. An exponential approximation curve of ^ΔVh = e ^bT (b is a coefficient, where b> 0) with respect to the voltage drop amount ratios ΔVh1, ΔVh2, ΔVh3 (= 1.0) obtained by standardizing the voltage drop amounts ΔV1, ΔV2, ΔV3, respectively. The coefficient b was obtained. In this case, ΔVh = 1 is passed at T = 0 ° C. in any case.

On the other hand, the coefficient b of the exponential approximate curve of ^ΔVh = ^ebT obtained using the voltage drop ratios ΔVh1, ΔVh2, ΔVh3 as in the present embodiment and the first to third voltage drop amounts ΔV1, ΔV2, ΔV3 are directly calculated. The coefficient b obtained by ^calculating the exponential approximation curve (ΔV = ae ^bT ) is almost the same value.
Therefore, even when the exponential approximate curve (ΔV = ae ^bT ) is obtained by directly using the first to third voltage drop amounts ΔV1, ΔV2, and ΔV3, the coefficient b is compared with the reference coefficient B of the reference exponent curve. It can be seen that whether or not a short circuit has occurred in the battery 1 can be determined.

Specifically, first, the first voltage drop amount ratio ΔVh1 = ΔV1 / ΔV3 of the first voltage drop amount ΔV1 is calculated with the third voltage drop amount ΔV3 as a reference.
Further, the second voltage drop amount ratio ΔVh2 = ΔV2 / ΔV3 of the second voltage drop amount ΔV2 is calculated with the third voltage drop amount ΔV3 as a reference.
The third voltage drop amount ratio ΔVh3 of the third voltage drop amount ΔV3 with respect to the third voltage drop amount ΔV3 is ΔVh3 = ΔV3 / ΔV3 = 1.00.

Next, based on the obtained voltage drop amount ratio ΔVh (first and second voltage drop amount ratios ΔVh1, ΔVh2), the coefficient a = 1.00 in the exponential approximation curve ΔV = ae ^bT described above is used, and the standing temperature T and the voltage An exponential approximation curve ^ΔVh = e ^bT (b is a coefficient, where b> 0) is obtained for the decrease amount ratio ^ΔVh , and a coefficient b is obtained.
The coefficient a = 1.00 is, as described above, because the third voltage drop amount ratio ΔVh3 = 1.00 of the third voltage drop amount ΔV3 at the third leaving temperature T3 = 0 ° C. This is because a = 1.00 can be obtained by substituting = 0 and ΔVh = 1.00 into ^ΔVh = ae ^bT .

Here, FIG. 4 shows a graph of the exponential approximation curve ^ΔVh = ^ebT . From the average voltage drop amount ratio ΔVh (first and second voltage drop amount ratios ΔVh1, ΔVh2) of the normal battery 1 (in which no internal short circuit has occurred), an exponential approximation curve (coefficient) shown by a thin solid line in FIG. b = 0.075). On the other hand, in the battery 1 in which a short circuit has occurred, for example, an exponential approximation curve (coefficient b = 0.040) indicated by a broken line as a defective product 1 in FIG. 4 or an index indicated by a one-dot chain line as a defective product 2 in FIG. An approximate curve (coefficient b = 0.020), an exponential approximate curve (coefficient b = 0.007) indicated by a two-dot chain line in FIG.

  As is clear from these graphs, the value of the coefficient b of the obtained exponential approximate curve is clearly smaller in each battery 1 in which a short circuit occurs than in the normal battery 1. Therefore, a reference index curve for distinguishing between the battery 1 in which a short circuit has occurred and the normal battery 1 is set (in this embodiment, the coefficient b = B = 0.060). Then, by comparing the magnitude of the coefficient b of the exponential approximate curve obtained with the inspected battery 1 and the reference coefficient B (= 0.060) of the reference index curve, whether or not the battery 1 is short-circuited is determined. Determine whether.

  Specifically, in the “short circuit determination step S8”, the obtained coefficient b is compared with a predetermined reference coefficient B (= 0.060). When the obtained coefficient b is smaller than the reference coefficient B (b <B), it is determined that an internal short circuit has occurred in the battery 1 (defective product), and the battery 1 is removed. On the other hand, when the obtained coefficient b is larger than the reference coefficient B (b ≧ B), it is determined that the battery 1 is normal (non-defective product in which no internal short circuit occurs).

  Next, “discharge electric quantity acquisition / determination step S9” is performed. That is, for the battery 1 determined to be normal in the short-circuit determination step S8, a charge / discharge device is connected to forcibly discharge to SOC 30%. Further, during this discharge period, the amount of discharged electricity Qa discharged from SOC 70% to SOC 30% is measured. Then, this discharge electricity quantity Qa is compared with the reference discharge electricity quantity Qk, and when the discharge electricity quantity Qa is smaller than the reference discharge electricity quantity Qk (Qa <Qk), the battery 1 is determined as a defective product, and the battery 1 is removed. On the other hand, when the obtained discharge electricity quantity Qa is larger than the reference discharge electricity quantity Qk (Qa ≧ Qk), the battery 1 is determined to be normal (good product).

  Next, “internal resistance value acquisition / determination step S10” is performed. That is, the internal resistance value (IV resistance value) Ra of the battery 1 determined to be normal in the discharge electricity quantity acquisition / determination step S9 is measured. Specifically, the battery 1 is charged to SOC 40%. Thereafter, the battery 1 is discharged at a constant current of 4 C for 4 seconds, and the battery voltage Vc before and after the discharge is measured. Thereafter, the change amount ΔVf of the battery voltage Vc changed by the discharge is divided by the discharge current value (4C) to obtain the IV resistance value (internal resistance value) Ra. Then, when the obtained internal resistance value Ra is out of the predetermined reference range, the battery 1 is determined as a defective product, and the battery 1 is removed. On the other hand, when the obtained internal resistance value Ra is within the reference range, the battery 1 is determined to be normal (good product).

  After finishing the internal resistance value acquisition / determination step S10, the restraining jig restraining the battery 1 is removed, and the restraining body of the battery 1 is released. Thus, the battery 1 is completed.

As described above, in the manufacturing method of the battery 1, based on the plurality of voltage drop amounts ΔV1, ΔV2, and ΔV3 obtained at different leave temperatures T1, T2, and T3, the stand temperature T and the voltage drop amount ΔV are determined. The coefficient b of the exponential approximation curve ΔV = ae ^bT is acquired. More specifically, in the present embodiment, the coefficient b of the exponential approximate curve ^ΔVh = ^ebT with respect to the voltage drop amount ratio ^{ΔVh based on} the standing temperature T and 0 ° C. is acquired. When the obtained coefficient b is smaller than the reference coefficient B (b <B), it is determined that a short circuit has occurred in the battery 1. As described above, since the battery 1 in which the short circuit has occurred has less temperature dependency of the voltage drop ΔV than the normal battery 1, the coefficient b of the exponential approximation curve acquired in the battery 1 in which the short circuit has occurred. Is smaller than the coefficient b of the exponential approximation curve obtained with the normal battery 1. In addition, there is almost no difference between the normal battery 1 and the short-circuited battery 1 in the voltage drop amount ΔV obtained at a certain standing temperature T, and even when these cannot be distinguished, the coefficient b of the exponential approximation curve As for, there is a large difference between the normal battery 1 and the battery 1 in which a short circuit occurs. For this reason, by comparing the coefficient b of the acquired exponential approximation curve with the reference coefficient B, it is possible to accurately detect the battery 1 in which a short circuit has occurred.

  Furthermore, in this embodiment, since any of the first to second voltage drop amount acquisition steps S4, S5, and S6 has the leaving temperatures T1, T2, and T3 of 30 ° C. or less, the respective voltage drop amounts ΔV1, ΔV2 , ΔV3, the ratio of the voltage drop amount ΔVa caused by the chemical reaction does not become too large compared to the voltage drop amount ΔVb caused by the internal short circuit. For this reason, the difference between the coefficient b of the exponential approximate curve acquired with the battery 1 in which an internal short circuit has occurred and the coefficient b of the exponential approximate curve acquired with the normal battery 1 becomes clear. Therefore, the battery 1 in which an internal short circuit has occurred can be detected with higher accuracy in the short circuit determination step S8.

In the above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof.
For example, in the embodiment, the first neglecting temperature T is set as the first neglecting temperature T1 = 30 ° C., the second neglecting temperature T2 = 15 ° C., and the third neglecting temperature T3 = 0 ° C. Although S5 and S6 were performed, each leaving temperature T can be appropriately changed, and the standing temperature T may not include 0 ° C.
In the embodiment, the voltage decrease amount acquisition process is performed three times (first voltage decrease amount acquisition step S4, second voltage decrease amount acquisition step S5, and third voltage decrease amount acquisition step S6). A process can also be made into 2 times or 4 times or more.

In the coefficient acquisition step S7 of the embodiment, the first voltage drop amount ratio ΔVh1 (= ΔV1 / ΔV3) and the second voltage drop amount ratio ΔVh2 (= ΔV2 / ΔV3) once based on the third voltage drop amount ΔV3. ) Was calculated. Then, an exponential approximate curve ^ΔVh = ^ebT with a coefficient a = 1.00 for the standing temperature T and the voltage drop amount ratio ^ΔVh was obtained, and the coefficient b was obtained. However, the exponential approximate curve ΔV = ae ^bT is obtained directly using the first to third voltage drop amounts ΔV1, ΔV2, and ΔV3 obtained in the first to third voltage drop amount acquisition steps S4 to ^S6 , and the coefficient a , B may be acquired.

In the embodiment, the initial charging step S2 to the internal resistance value acquisition / determination step S10 are performed in a state where the battery 1 is restrained. However, these steps S2 to S10 may be performed without restraining the battery 1. it can.
In the embodiment, the battery 1 is charged to 100% SOC in the initial charging step S2. However, for example, the value of the SOC to be initially charged can be changed as appropriate, such as charging to SOC 80%.
In the embodiment, the aging step S3 is performed in a state where the terminal of the battery 1 is opened. However, the aging step S3 may be performed in a state where a power source is connected to the battery 1 and maintained at a constant voltage.

  In the embodiment, in the manufacturing process of the battery 1, the first voltage drop amount acquisition process S <b> 4 to the short circuit determination process S <b> 8 are performed to check whether an internal short circuit has occurred in the battery 1. The battery 1 can be inspected for internal short circuits. That is, the battery 1 after being shipped from the factory can be inspected for the presence of an internal short circuit by performing the first voltage drop amount acquisition step S4 to the short circuit determination step S8. Also in this case, the battery 1 in which an internal short circuit has occurred can be detected with high accuracy.

DESCRIPTION OF SYMBOLS 1 Battery 10 Battery case 20 Electrode body 50 Positive electrode terminal member 60 Negative electrode terminal member S1 Assembly process S2 Initial charge process S3 Aging process S4 1st voltage fall amount acquisition process S5 2nd voltage fall amount acquisition process S6 3rd voltage fall amount acquisition process S7 Coefficient acquisition step S8 Short circuit determination step T Left temperature T1 First left temperature T2 Second left temperature T3 Third left temperature Da Left time Vc, Vc1s, Vc1e, Vc2s, Vc2e, Vc3s, Vc3e Battery voltage ΔV Voltage drop ΔV1 First 1 Voltage drop amount ΔV2 Second voltage drop amount ΔV3 Third voltage drop amount a, b Coefficient B Reference coefficient

Claims (1)

The voltage reduction amount acquisition step of acquiring the voltage drop amount of the battery voltage before and after the storage is left under a predetermined storage temperature and with the terminal open for a predetermined storage time. A plurality of voltage drop amount acquisition steps performed in
Based on the obtained plurality of voltage drop amounts, an exponential approximation curve ΔV = ae ^bT (where a, b are coefficients, where a> 0, b> 0) with respect to the standing temperature T and the voltage drop amount ΔV. A coefficient acquisition step of acquiring the coefficient b;
And a short-circuit determining step for determining that an internal short circuit has occurred in the secondary battery when the obtained coefficient b is smaller than the reference coefficient B (b <B).

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