JP6788800B2 - Inspection method for non-aqueous electrolyte secondary batteries - Google Patents

Description

The present invention relates to a method for inspecting a non-aqueous electrolyte secondary battery.

In Japanese Patent Application Laid-Open No. 2014-17056, in the initial discharge stage of first discharging after the production of the lithium ion secondary battery, the additional charging stage of charging the lithium ion secondary battery discharged in the initial discharging stage, and the additional charging stage An inspection method having an additional discharge step of discharging a charged lithium ion secondary battery and a voltage measurement step of measuring the voltage of the lithium ion secondary battery after the additional discharge step has been proposed. In the same publication, by such additional charging / discharging, the variation in the battery voltage is reduced by activating both electrodes by the transfer of lithium ions in each electrode and reducing the variation in the in-plane distribution of lithium ions. It is said that this can improve the accuracy of determining the quality of the battery and shorten the battery standing time required for measuring the amount of voltage fluctuation.

Japanese Unexamined Patent Publication No. 2014-17506

By the way, when inspecting the capacity value and the battery resistance value as the parameters of the initial inspection of the battery, it is desired to shorten the inspection time and inspect accurately.
The capacity value is obtained, for example, based on the discharge capacity value when the battery is discharged from a predetermined voltage to a predetermined voltage. The battery resistance value is determined based on the voltage drop during which the battery is adjusted to a predetermined voltage after discharging to obtain the capacity value, and then discharged at a predetermined discharge rate for a predetermined time. It is good to get the battery resistance value. In this case, if the discharge current is small when acquiring the capacitance value, the inspection takes time. On the other hand, in order to shorten the inspection time, it is preferable to increase the discharge current when acquiring the capacitance value, but there are cases where an accurate resistance value cannot be obtained by measuring the resistance value.

The non-aqueous electrolyte secondary battery inspection method proposed here includes a short-circuit inspection step, a step of measuring the section capacity, a pause step, and a step of obtaining a battery resistance value.
Here, the short-circuit inspection step includes an aging process in which the assembled non-aqueous electrolyte secondary battery is charged to a predetermined voltage and left to stand.
In the step of measuring the section capacity, after the short-circuit inspection step, the section capacity is measured by discharging the non-aqueous electrolyte secondary battery at a predetermined discharge rate.
In the resting step, the non-aqueous electrolyte secondary battery is left for a predetermined time after the step of measuring the section capacity.
In the step of obtaining the battery resistance value, after the pause process, the non-aqueous electrolyte secondary battery is charged, adjusted to a predetermined voltage, and then subjected to a predetermined discharge treatment to perform the battery resistance of the non-aqueous electrolyte secondary battery. The value is obtained.
According to such an inspection method, both the reduction of the inspection time as a whole and the accuracy of the battery resistance value are compatible.

FIG. 1 is a graph showing the relationship between the discharge rate and time when measuring the section capacitance. FIG. 2 is a graph showing the relationship between the discharge rate in the step of measuring the section capacity and the measured battery resistance value. FIG. 3 is a flowchart showing a process up to battery resistance measurement in the inspection method proposed here. FIG. 4 is a graph showing the relationship between the discharge rate and the battery resistance value in the step of measuring the section capacity. FIG. 5 is a graph schematically showing the transition of the voltage when the discharge rate in the step of measuring the section capacitance is 1.5C. FIG. 6 is a graph schematically showing the transition of the voltage when the discharge rate in the step of measuring the section capacitance is 5C.

Hereinafter, an embodiment of the inspection method for the non-aqueous electrolyte secondary battery proposed here will be described. The embodiments described herein are, of course, not intended to specifically limit the present invention. The present invention is not limited to the embodiments described herein, unless otherwise specified.

The non-aqueous electrolyte secondary battery inspection method proposed here includes a short-circuit inspection step, a step of measuring the section capacity, a pause step, and a step of obtaining the battery resistance value of the non-aqueous electrolyte secondary battery. There is.

Here, the short-circuit inspection step includes an aging process in which the assembled non-aqueous electrolyte secondary battery is charged to a predetermined voltage and left to stand. In such a short-circuit inspection step, for example, an assembled non-aqueous electrolyte secondary battery is prepared, and initial charging, high-temperature aging, and self-discharge are performed in order.

Here, the assembled non-aqueous electrolyte secondary battery includes a battery case, an electrode body housed in the battery case, and an electrolyte (electrolyte solution).
Here, the electrode body may be a wound electrode body in which a positive electrode sheet and a negative electrode sheet are laminated with a separator made of a resin-made porous film interposed therebetween and wound. Further, the electrode body may be a laminated electrode body in which a positive electrode sheet and a negative electrode sheet are laminated with a separator made of a resin porous film interposed therebetween.

The positive electrode sheet is, for example, a sheet in which a positive electrode active material layer containing a positive electrode active material is formed on a current collector foil. The negative electrode sheet is, for example, a sheet in which a negative electrode active material layer containing a negative electrode active material is formed on a current collector foil. The separator is, for example, a porous resin sheet through which an electrolyte having a required heat resistance can pass. As the electrolyte, for example, an electrolytic solution in which a lithium salt is dissolved in an organic solvent is used.

The positive electrode active material is, for example, a material that can release lithium ions during charging and absorb lithium ions during discharging, such as a lithium transition metal composite material in a lithium ion secondary battery. Various positive electrode active materials have been proposed in addition to the lithium transition metal composite material, and are not particularly limited.
The negative electrode active material is, for example, in a lithium ion secondary battery, a material that can store lithium ions during charging and release the stored lithium ions during charging, such as natural graphite. Various negative electrode active materials have been proposed other than natural graphite, and are not particularly limited.
Examples of the electrolytic solution include a non-aqueous electrolytic solution in which LiPF ₆ is contained in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC).

As the battery case, for example, a so-called square battery case can be adopted, which is composed of a flat square case body having an open upper surface and a lid body that closes the upper surface of the case body. Various non-aqueous electrolyte secondary batteries have been proposed, and the structure of the battery is not limited unless otherwise specified.

In the initial charge, the battery is charged under predetermined conditions. For example, in an environment of 25 ° C., charge with a constant current of 1 / 3C (CC charge) until the voltage between the positive and negative terminals reaches 4.0 V, and then until the total charging time reaches 1.5 hours. Charge at a constant voltage (CV charging).

In the high-temperature aging step, the non-aqueous electrolyte secondary battery charged by the initial charge is left in a constant temperature bath at a predetermined temperature for a predetermined time. Further, in the self-discharge step, it is left in a room temperature environment for a predetermined time. For example, in the high temperature aging step, the non-aqueous electrolyte secondary battery charged by the initial charge is placed in a constant temperature bath at 60 ° C. for 20 hours. Further, in the self-discharge step, the self-discharge step is left in a room temperature environment of 20 ° C. to 25 ° C. for 3 days. In these steps, when a foreign substance is mixed in the non-aqueous electrolyte secondary battery, a short circuit occurs in the non-aqueous electrolyte secondary battery. In such a short-circuit inspection, a non-aqueous electrolyte secondary battery whose voltage is not maintained is excluded as a defective product. The non-aqueous electrolyte secondary battery that has passed these inspection steps is charged by the initial charge, and then is maintained in a state of being charged through a high temperature aging step and a self-discharge step.

Next, in the step of measuring the section capacitance, after the above-mentioned short-circuit inspection step, the battery is discharged at a predetermined discharge rate until a predetermined voltage is reached. For example, a non-aqueous electrolyte secondary battery is discharged at a predetermined discharge rate after a short circuit inspection until the voltage between the positive and negative terminals reaches 3.0 V. Then, the section capacity is measured based on the discharge capacity at this time. It takes time to measure the section capacitance because the voltage range is wide.

In the measurement of the section capacity, the time is shortened by increasing the current value when discharging the non-aqueous electrolyte secondary battery. FIG. 1 is a graph showing the relationship between the discharge rate (current value at the time of discharging) when measuring the section capacitance and the time. In the example shown in FIG. 1, when the discharge rate is 1.5C, it takes about 37 minutes, but when the discharge rate is 5C, it takes about 10 minutes. As described above, the higher the discharge rate, the shorter the time required to measure the section capacitance.

After the section capacitance is measured, the voltage is adjusted, discharged at a predetermined discharge rate for a predetermined time, and the battery resistance value is measured. For example, after the voltage between the positive and negative terminals is adjusted to a predetermined voltage, the voltage is left for a certain period of time, discharged with a predetermined current value for a predetermined time, and the resistance value is based on the voltage drop at that time. Is measured. For example, the resistance value is measured by charging the CCCV so that the voltage between the positive and negative terminals becomes 3.4 V, leaving it for 1 hour, and discharging it at 20 A for 4 seconds.

According to the findings of the present inventor, in the step of measuring the section capacitance, when the discharge rate is high, the resistance tends to be low. FIG. 2 is a graph showing the relationship between the discharge rate and the battery resistance value in the step of measuring the section capacity. FIG. 2 shows a graph in the case where the voltage is adjusted immediately after the discharge in the step of measuring the section capacity and the battery resistance value is measured. As shown in FIG. 2, in the step of measuring the section capacity, when the discharge rate is as small as, for example, about 1.5C, the voltage is adjusted to measure the battery resistance value immediately after the discharge. However, the resistance value is measured properly. However, the measured resistance value tends to decrease as the discharge rate increases.

The present inventor considers this tendency to be caused by a large voltage return after discharge when discharged at a high discharge rate. That is, in the case of being discharged at a high discharge rate, if the voltage is adjusted immediately after the discharge, charging is started in the middle of the voltage return. In this case, if the voltage is adjusted immediately after discharging, the voltage is further adjusted and then returned. Therefore, the voltage when measuring the resistance value becomes high. As a result, it is considered that the measured resistance value tends to be small.

Based on these findings, the present inventor considered providing an appropriate rest period after the step of measuring the section capacitance before adjusting the voltage. FIG. 3 is a flowchart showing a process up to battery resistance measurement in the inspection method proposed here.

As shown in FIG. 3, in the inspection method proposed here, the assembled non-aqueous electrolyte secondary battery is subjected to initial charging (S1), high temperature aging (S2), and self-discharge (S3) in this order. After that, it is discharged for section capacitance measurement (S4). In the inspection method proposed here, a rest period is provided after the discharge for measuring the section capacitance (S5). After such a pause period is provided, voltage adjustment (charging) for measuring the battery resistance value is performed (S6), and the resistance value is measured (S7). Since a pause period (S5) is provided after the discharge for section capacitance measurement, even if the discharge (S4) is performed at a high discharge rate for section capacitance measurement, the voltage is appropriately applied during the pause period. Returns. Then, since the voltage adjustment (S6) for measuring the battery resistance value is appropriately performed, an appropriate battery resistance value is measured (S7).

FIG. 4 is a graph showing the relationship between the discharge rate and the battery resistance value in the step of measuring the section capacity. In FIG. 4, the graph of A shows a case where the voltage is adjusted immediately after the discharge in the step of measuring the section capacitance. The graph of B shows the case where the voltage is adjusted with a rest period of 1 minute after the discharge in the step of measuring the section capacitance. The graph of C shows the case where the voltage is adjusted with a pause of 10 minutes after the discharge in the step of measuring the section capacitance. After discharging in the process of measuring the section capacity, a rest period of about 1 to 10 minutes is provided to adjust the voltage, so that the battery resistance value is measured to the same extent as when the discharge rate is small, which is appropriate. The battery resistance value is measured.
As described above, the rest period after discharge in the step of measuring the section capacitance may be about 1 minute to 10 minutes.

FIG. 5 is a graph schematically showing the transition of the voltage when the discharge rate in the step of measuring the section capacitance is 1.5C. In FIG. 5, the graph of D shows a case where the voltage is adjusted without providing a rest period after the discharge in the step of measuring the section capacitance. The graph of E shows a case where a rest period is provided and the voltage is adjusted after the discharge in the step of measuring the section capacitance.

Here, D1 indicates a step of measuring the section capacity. The step D1 for measuring the section capacity is common to the graph D and the graph E. D2 indicates a step in which the voltage is adjusted without providing a pause period. D3 is a subsequent rest period, and D4 is a step of measuring the resistance value. The rest period D3 is set to stabilize the temperature of the non-aqueous electrolyte secondary battery after being charged in the process of adjusting the voltage. During this period, the non-aqueous electrolyte secondary battery is left for a predetermined time. E1 is a pause period, and E2 is a step in which the voltage is adjusted after the pause period (E1). E3 is the subsequent rest period. E4 is a step of measuring the resistance value.

As shown in FIG. 5, when the discharge rate in the step of measuring the section capacitance is as small as about 1.5C, the voltage return is small after the discharge in the step of measuring the section capacitance. Therefore, as shown in Graph D and Graph E, an appropriate battery resistance value is measured with or without a pause period. That is, the measured battery resistance values are about the same when the voltage is adjusted by providing a pause period after discharging in the process of measuring the section capacity and when the voltage is adjusted by providing a pause period. is there.

FIG. 6 is a graph schematically showing the transition of the voltage when the discharge rate in the step of measuring the section capacitance is 5C. In FIG. 6, the graph of F shows a case where the voltage is adjusted without providing a rest period after the discharge in the step of measuring the section capacitance. The graph of G shows a case where a rest period is provided and the voltage is adjusted after the discharge in the step of measuring the section capacitance.

Here, F1 indicates a step of measuring the section capacity. The step F1 for measuring the section capacity is common to the graph F and the graph G. F2 indicates a step in which the voltage is adjusted without providing a pause period. F3 is a subsequent rest period, and F4 is a step of measuring the resistance value. G1 is a pause period, and G2 is a step in which the voltage is adjusted after the pause period G1. G3 is a subsequent rest period, and G4 is a step of measuring the resistance value.

As shown in FIG. 6, when the discharge rate in the step of measuring the section capacitance is as large as about 5C, the return of the voltage after discharging in the step of measuring the section capacitance is large. Therefore, as shown in the graph F, when the pause period is not provided, the voltage rise in the pause period F3 after the step F2 in which the voltage is adjusted is large. Therefore, in the step F4 for measuring the resistance value, the initial voltage is high and the battery resistance value is low. On the other hand, as shown in the graph G, when the rest period G1 is provided after the step F1 for measuring the section capacitance, the voltage is sufficiently returned in the rest period G1. Therefore, the voltage rise in the rest period G3 after being charged in the subsequent step G2 in which the voltage is adjusted is small. Therefore, in the step G4 for measuring the resistance value, the initial voltage is suppressed to a low level, and a more appropriate battery resistance value is measured.

When the discharge rate in the step of measuring the section capacitance is large in this way, the return of the voltage after discharging in the step of measuring the section capacitance is large. Therefore, as shown in Graph F, the battery resistance value is not accurately measured when the rest period is not provided. That is, the time reduction in the process of measuring the section capacity and the accuracy of the battery resistance value are not compatible. On the other hand, when the rest period G1 is provided after the step of measuring the section capacity as in the graph G, the accuracy of the battery resistance value is improved. That is, in the graph G, the rest period G1 is provided after the step F1 for measuring the section capacitance, but the time can be shortened as a whole by increasing the discharge rate in the step F1 for measuring the section capacitance. As described above, according to the inspection method proposed here, both the reduction of the inspection time as a whole and the accuracy of the battery resistance value are compatible.

As described above, the inspection method for the non-aqueous electrolyte secondary battery proposed here includes a short-circuit inspection step, a step of measuring the section capacity, a pause step, and a step of obtaining the battery resistance value.
Here, the short-circuit inspection step includes an aging process in which the assembled non-aqueous electrolyte secondary battery is charged to a predetermined voltage and left to stand.
In the step (F1) of measuring the section capacity, the section capacity is measured by discharging the non-aqueous electrolyte secondary battery at a predetermined discharge rate after the short-circuit inspection step.
In the resting step (G1), the non-aqueous electrolyte secondary battery is left for a predetermined time after the step F1 for measuring the section capacity.
In the step of obtaining the battery resistance value (G2 to G4), after the pause step (G1), the non-aqueous electrolyte secondary battery is charged, adjusted to a predetermined voltage, and then a predetermined discharge process is performed. The battery resistance value of the non-aqueous electrolyte secondary battery can be obtained.
According to such an inspection method, after the step of measuring the section capacity (F1), there is a resting step (G1) in which the non-aqueous electrolyte secondary battery is left for a predetermined time, so that the inspection time as a whole is shortened. And the accuracy of the battery resistance value are compatible. Here, in parentheses, the corresponding reference numerals in the graph illustrated in FIG. 6 are shown for each step of the inspection method.

Here, the step of measuring the section capacitance can be carried out, for example, at a discharge rate of 3C or more and 10C or less. In the step of measuring the section capacitance, since the voltage section to be discharged is large, for example, 4.1 V to 3.0 V, the effect of shortening the time is great by increasing the discharge rate. In addition, the rest period in the subsequent rest process may be, for example, about 1 to 10 minutes. If the pause period is too short, it becomes difficult to obtain the effect of improving the accuracy of the battery resistance value. On the other hand, if the rest period is too long, the effect of shortening the time by increasing the discharge rate in the step of measuring the section capacitance is canceled out.

In the above, various inspection methods for the non-aqueous electrolyte secondary battery proposed here have been described. Unless otherwise specified, the embodiments of the inspection method for the non-aqueous electrolyte secondary battery mentioned here do not limit the present invention.

F1 Step of measuring the section capacitance G1 Resting period G2 Step of adjusting the voltage G3 Resting period G4 Step of measuring the resistance value

Claims (1)

A short-circuit inspection process including an aging process in which the assembled non-aqueous electrolyte secondary battery is charged to a predetermined voltage and left to stand.
After the short-circuit inspection step, the non-aqueous electrolyte secondary battery is discharged at a predetermined discharge rate of 3C or more and 10C or less, and the section capacity is measured.
After the step of measuring the section capacity, a pause step of leaving the non-aqueous electrolyte secondary battery for a predetermined time of 1 minute or more and 10 minutes or less ,
After the resting step, the non-aqueous electrolyte secondary battery is charged, adjusted to a predetermined voltage, and then subjected to a predetermined discharge treatment to obtain a battery resistance value of the non-aqueous electrolyte secondary battery. including,
Inspection method for non-aqueous electrolyte secondary batteries.

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