JP2021015745A - Method for manufacturing secondary battery - Google Patents

Abstract

To provide a method for manufacturing a secondary battery which includes an inspection step, but has a short required time and a small energy loss.SOLUTION: A secondary battery is manufactured by performing an assembly step of assembling the secondary battery, a charging step of charging the assembled secondary battery, and an inspection step of inspecting the battery capacity of the charged secondary battery. Here, the inspection step performs a circuit configuration step of configuring a closed circuit with a secondary battery and an external power supply, a current value acquiring step of acquiring a current value of the closed circuit while a voltage is applied to the closed circuit by the secondary battery and an external power supply, and a determination step of determining whether a change amount per unit time of the acquired current value is within a predetermined appropriate range.SELECTED DRAWING: Figure 3

Description

The present invention relates to a method for manufacturing a secondary battery. More specifically, the present invention relates to a method for manufacturing a secondary battery in which the battery capacity of the assembled secondary battery is also inspected.

The battery capacity of a secondary battery such as a lithium ion secondary battery is a main index for evaluating its performance. For this reason, there is an example in which the battery capacity is also inspected when manufacturing a secondary battery. Patent Document 1 describes an example of a technique that can be used as an inspection process for that purpose. In the inspection technology of the same document, the discharge process of discharging the secondary battery from the initial voltage to the discharge end voltage is performed. The battery capacity is calculated from the discharge current and discharge time at that time, and the quality of the secondary battery is judged based on this.

Japanese Unexamined Patent Publication No. 2014-185927

However, the above-mentioned conventional technique has the following problems. The time required for the inspection process and the energy loss are large. The reason is that the discharge time is one of the parameters for calculating the battery capacity. This is because the calculation accuracy will be low unless the discharge time is long to some extent. Therefore, it is difficult to shorten the required time. Discharging is equivalent to discarding the energy input to the secondary battery in the initial charge. Therefore, the energy loss is also large.

The present invention has been made to solve the problems of the above-mentioned conventional techniques. That is, the problem is to provide a method for manufacturing a secondary battery, which includes an inspection process but has a short required time and a small energy loss.

The method for manufacturing a secondary battery according to one aspect of the present invention includes an assembly step of assembling the secondary battery, a charging step of charging the assembled secondary battery, and an inspection step of inspecting the battery capacity of the charged secondary battery. It is a method of manufacturing a secondary battery by performing. Here, in the inspection process, a circuit configuration step of forming a closed circuit with a secondary battery and an external power supply, and a current for acquiring the current value of the closed circuit with a voltage applied to the closed circuit with the secondary battery and an external power supply. A value acquisition step and a determination step of determining whether or not the amount of change in the acquired current value per hour is within a predetermined appropriate range are performed.

In the method for manufacturing a secondary battery in the above aspect, an inspection step of inspecting the pass / fail of the battery capacity is performed on the assembled and charged secondary battery. In the inspection process, the current value of the closed circuit composed of the secondary battery to be inspected and another external power supply is acquired. Judgment is made based on the amount of change in the current value per hour. Since the circuit current is acquired while the voltage is applied to the secondary battery by an external power supply, the discharge of the secondary battery is suppressed and the amount of change in the current value is stable. Therefore, energy loss is suppressed and judgment can be made in a short time. Since the secondary battery whose battery capacity is determined to be out of specification may be excluded, only a non-defective secondary battery can be manufactured.

According to this configuration, a method for manufacturing a secondary battery, which includes an inspection step but has a short required time and a small energy loss, is provided.

It is sectional drawing which shows the internal structure of the battery manufactured by embodiment. It is a flowchart which shows the manufacturing method of the battery which concerns on embodiment. It is a flowchart which shows the content of the capacity inspection process. It is a circuit diagram which shows the circuit used in the capacity inspection process which concerns on embodiment. It is a graph which shows the transition of the amount of change of a current value per time.

Hereinafter, embodiments embodying the present invention will be described in detail with reference to the accompanying drawings. This embodiment embodies the present invention as a method for manufacturing the battery 1 shown in FIG. The battery 1 in FIG. 1 is a flat-angle battery case 10 in which an electrode winding body 20 is housed. The electrode winding body 20 includes a central power generation unit 41, positive electrode connection portions 21 on both sides thereof, and negative electrode connection portions 31. In addition to the electrode winding body 20, the electrolytic solution 19 is also housed in the battery case 10. A part of the stored electrolytic solution 19 is impregnated in the electrode winding body 20. A positive electrode terminal 51 and a negative electrode terminal 61 are provided on the lid portion 13 of the battery case 10. Inside the battery case 10, the positive electrode terminal 51 and the positive electrode connecting portion 21 are connected by the positive electrode current collecting member 50, and the negative electrode terminal 61 and the negative electrode connecting portion 31 are connected by the negative electrode current collecting member 60.

The battery 1 is a lithium ion secondary battery or other secondary battery. In this embodiment, the battery 1 is manufactured by the procedure shown in FIG. The procedure of FIG. 2 includes each step of an assembly step, an initial charging step, a high temperature aging step, a cooling step, a short circuit inspection step, and a capacity inspection step. Of these, the high-temperature aging step, the cooling step, and the short-circuit inspection step are more preferably carried out than not carried out, but are not essential embodiments of the present invention.

The assembling step is a step of producing the above-mentioned electrode winding body 20 and storing it in the battery case 10 to form the battery 1. The attachment of the positive electrode terminal 51, the negative electrode terminal 61, and the injection of the electrolytic solution 19 are also included in this step. The initial charging step is a step of charging the assembled battery 1 for the first time. The high temperature aging step is a step of maintaining the battery 1 after the initial charging at a high temperature (about 50 to 100 ° C.) for a predetermined time (about 10 to 30 hours). The high temperature aging process is performed to improve the accuracy of inspection by clarifying the defect rate due to internal short circuit. The cooling step is a step of lowering the temperature of the battery 1 after the high temperature aging step to room temperature. The short-circuit inspection step is a step of detecting and eliminating a battery 1 having an internal short-circuit defect. The short-circuit inspection step can be carried out, for example, by the method described in [0034] of JP-A-2019-21510.

The capacity inspection process will be described. In this step, it is individually determined whether or not the battery capacity of the battery 1 is within the appropriate range, and if there is a defective battery 1 that is not within the appropriate range, it is eliminated. This step is carried out by the procedure shown in FIG. As shown in FIG. 3, in the capacitance inspection process, the current value is acquired and the determination is performed for both the circuit configuration.

In the circuit configuration process, the circuit shown in FIG. 4 is configured. The circuit of FIG. 4 has a power supply device 2, a resistor 3, a resistor 4, and an ammeter 5 in addition to the battery 1. The power supply device 2 in FIG. 4 plays a role of applying a voltage to the battery 1 from the outside. In FIG. 4, the positive terminal of the power supply device 2 is connected to the positive electrode terminal 51 of the battery 1, and the negative terminal of the power supply device 2 is connected to the negative electrode terminal 61 of the battery 1. As a result, the power supply device 2 applies an external voltage in the opposite direction to the battery 1.

A resistor 3 and an ammeter 5 are arranged on the wiring connecting the battery 1 and the power supply device 2. The ammeter 5 measures the circuit current flowing through the closed circuit composed of the battery 1 and the power supply device 2. A resistor 4 is arranged between the positive electrode terminal 51 and the negative electrode terminal 61 separately from the ammeter 5 and the resistor 3. In the circuit of FIG. 4, the resistance value R3 of the resistor 3 is set to be larger than the resistance value R4 of the resistor 4.

In FIG. 4, the battery 1 is represented by a model based on the internal capacity CI, the internal resistance RI, and the short-circuit resistance RS. The internal resistance RI is arranged in series and the short-circuit resistance RS is arranged in parallel with respect to the internal capacitance CI. The internal capacity CI is a model in which the battery capacity is expressed as a capacitance. The internal resistance RI is a model showing the loss due to the battery 1 itself due to charging / discharging. The short-circuit resistor RS is a model representing the self-discharge of the battery 1. The short-circuit inspection step described above is an inspection for eliminating the battery 1 having an excessive short-circuit resistance RS as a defective product.

After building the circuit shown in FIG. 4, the current value is acquired. Of course, the current value to be acquired is the reading value of the ammeter 5. The output voltage of the power supply device 2 when acquiring the circuit current value is approximately the same as the open circuit voltage of the battery 1. In this embodiment, the current value is acquired repeatedly for about 1 minute.

The battery capacity is determined based on the acquired current value. The index of judgment is not the current value itself but the amount of change. This is because the amount of change in the circuit current, particularly the amount of change per hour, appropriately reflects the battery capacity of the battery 1. In the state where the circuit of FIG. 4 is assembled, the battery 1 is in a state of being slowly discharged (or charged). Therefore, the battery voltage gradually changes, which appears as a change in the circuit current. The change in the current value is faster as the battery capacity is smaller, and slower as the battery capacity is larger. Therefore, an appropriate range should be set for the amount of change in the current value. If the amount of change in the acquired current value is within the appropriate range, it can be determined that the battery capacity of the battery 1 is within the standard, and if it is outside the appropriate range, it can be determined that the battery capacity of the battery 1 is out of the standard. Therefore, it is sufficient to determine whether or not the amount of change in the current value is within the appropriate range.

This determination will be further described with reference to the graph of FIG. The vertical axis of the graph in FIG. 5 is the amount of change [μA / sec] of the current value per hour. The horizontal axis is the elapsed time [seconds] from the start of acquisition of the current value. The graph of FIG. 5 shows the non-defective battery 1 (the battery capacity is as rated) and the defective battery 1 (the battery capacity is out of the rating) under the following conditions.

[About battery 1]
Battery type: Lithium ion secondary battery Positive electrode Active material: Three-way lithium salt Negative electrode Active material: Carbon electrolyte 19 Electrolyte: Lithium hexafluorophosphate Solvent 19 solvent: Mixed solvent (ethylene carbonate, dimethyl carbonate, ethyl Methyl carbonate)
Rated battery capacity: 3.8Ah (ampere hour)
Battery voltage: 3.9V (at the start of current value acquisition)

[About the circuit]
Resistance value R3: 1kΩ
Resistance value R4: 10Ω

Under the above conditions, when the measurement was started with the output voltage of the power supply device 2 in the circuit of FIG. 4 set to 3.95 V, the reading value of the ammeter 5 was about 30 mA, and then gradually increased. The acquisition interval of the current value was 10 seconds.

As can be seen from FIG. 5, each of the non-defective product and the defective product shows a substantially constant amount of change per hour from the initial stage of current value acquisition. However, there is a significant difference of about 4 μA / sec between the amount of change per hour of good products and the amount of change per hour of defective products. Therefore, a good product and a defective product can be clearly distinguished. The defective product in the example of FIG. 5 shows a lower amount of change per hour than the non-defective product. This means that the battery capacity of the defective product is excessive with respect to the rating. If the product is defective such that the battery capacity is too small, the amount of change per hour will be higher than that of the non-defective product. Of course, this is also clearly distinguishable as in the defective product shown in FIG. 5 in which the battery capacity is excessive.

The fact that the values of both the non-defective product and the defective product are stable in FIG. 5 means that it is not necessary to spend a particularly long time for the determination. Therefore, although the amount of change in the elapsed time of about 4 minutes is plotted in FIG. 5, about 1 minute is actually sufficient. After that, the acquisition of the current value may be stopped. Therefore, the discharge amount of the battery 1 in the capacity inspection step remains at about 1.5 μAh. This means that the time and energy saving can be significantly reduced as compared with the conventional technique in which the inspection is performed while discharging several Ah over a period of several tens of minutes.

Here, the resistor 3 plays a role of mitigating the influence of variation in the output voltage of the power supply device 2 and reducing inspection noise. When the circuit current is represented by Ic, the output voltage of the power supply device 2 is represented by Vm, and the voltage of the battery 1 is represented by Vcell, the circuit current Ic is given by the following equation (1). From this, the larger the resistance value R3, the smaller the variation in the circuit current Ic due to the fluctuation of the voltage Vm, that is, the inspection noise. The setting of the resistance value R3 described above is determined from this viewpoint.
Ic = (Vm-Vcell) / R3 …… (1)

In principle, the determination of the battery capacity based on the amount of change in the circuit current as described above in the present embodiment is possible only with the battery 1, the ammeter 5, and the resistor 3 among those shown in FIG. However, with that alone, it is not possible to obtain high determination accuracy while obtaining the short required time and high energy saving as described above. In the case of only these three, the circuit current is measured while simply discharging the battery 1. In this case, since the discharge amount is suppressed only by the resistor 3, it is difficult to achieve both shortening of the determination time and energy saving and determination accuracy. In this embodiment, the power supply device 2 measures the current value while applying a voltage to the battery 1, so that both are possible.

In this embodiment, the inspection time is also shortened by providing the resistor 4. In this embodiment, since the determination is made based on the amount of change in the circuit current as described above, it is advantageous that the amount of change appears to some extent for quick determination. The change in the circuit current is caused by the change (decrease) in the battery voltage Vcell after the start of the inspection. When the amount of change in the circuit current is represented by ΔIc and the amount of change in the battery voltage is represented by ΔVcell, the amount of change in the circuit current ΔIc is given by the following equation (2).
ΔIc = (Vm−ΔVcell) / R3 …… (2)

Here, the resistance value R3 is a fixed value, and the output voltage Vm is substantially equal to the initial value of the battery voltage Vcell, so that the current change amount ΔIc is substantially proportional to the battery voltage change amount ΔVcell. The larger the voltage change amount ΔVcell, the larger the current change amount ΔIc, which is advantageous for quick determination. In order to increase the voltage change amount ΔVcell, the battery 1 may be discharged to some extent by using a resistor 4 having a small resistance value. Therefore, the resistance value R4 should be small. In particular, it is desirable that the resistance value R4 is smaller than the resistance value R3. The setting of the resistance value R4 described above is determined from this viewpoint. The small resistance value R4 is a factor in increasing the discharge amount of the battery 1 at the time of inspection, that is, the energy loss. However, since the inspection time is short as described above, the actual energy loss does not increase so much.

As described in detail above, according to the present embodiment, the capacity inspection process is performed on the assembled and charged battery 1 by forming a closed circuit together with the power supply device 2 which is an external power source. In the capacity inspection step, the battery capacity of the battery 1 is determined using the amount of change in the current value acquired while applying a voltage to the battery 1 as a determination index. Thus, a method for manufacturing a secondary battery, which includes an inspection process but has a short required time and a small energy loss, has been realized.

It should be noted that the present embodiment is merely an example and does not limit the present invention in any way. Therefore, as a matter of course, the present invention can be improved and modified in various ways without departing from the gist thereof. For example, the target type of the secondary battery is not limited to the lithium ion secondary battery mentioned in the explanation of the graph of FIG. 5, and may be another type. Further, a resistance element arranged in parallel with the power supply device 2 as viewed from the battery 1 is not an essential item between the resistors 4 in the circuit of FIG. 4, that is, the bipolar terminals of the battery 1. Further, the resistance element arranged on the closed circuit including the resistor 3, that is, the battery 1 and the power supply device 2 can be omitted. When the resistor 3 is omitted, the output voltage of the power supply device 2 may be controlled with extremely high accuracy.

1 Battery 2 Power supply 5 Ammeter

Claims (1)

The assembly process for assembling the secondary battery and
The charging process to charge the assembled rechargeable battery,
A secondary battery is manufactured by performing an inspection process that inspects the battery capacity of a charged secondary battery, and at the same time.
In the inspection process,
A circuit configuration process that constitutes a closed circuit with the secondary battery and an external power supply, and
A current value acquisition step of acquiring the current value of the closed circuit in a state where a voltage is applied to the closed circuit by the secondary battery and the external power source, and
A method for manufacturing a secondary battery, which comprises a determination step of determining whether or not the amount of change in the acquired current value per hour is within a predetermined appropriate range.

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