Method for manufacturing secondary battery

Abstract

To provide a method for manufacturing a secondary battery which can suppress variation of voltage drop amounts in a plurality of secondary batteries.SOLUTION: A method for manufacturing a secondary battery 1 includes: a first aging treatment step S2 of performing first aging treatment on the secondary battery 1 which has been subjected to initial charging; a voltage measurement step S4 of measuring a voltage of the secondary battery 1 which has been subjected to the first aging treatment; and a second aging treatment step S5 of performing second aging treatment on the secondary battery 1 which has been subjected to the first aging treatment, at a temperature corresponding to the measured voltage of the secondary battery 1, which has been obtained in the voltage measurement step S4. The secondary batteries 1 are classified into a plurality of groups on the basis of a magnitude of the measured voltage. In the second aging treatment step S5, the second aging treatment is performed on the secondary batteries 1 of each group at different temperatures so that the temperature of the second aging treatment becomes higher as the measured voltage becomes lower.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing a secondary battery. [Background technology]

[0002] Currently, secondary batteries such as lithium-ion batteries are used in electric vehicles, hybrid vehicles, plug-in hybrid vehicles, etc. Various techniques have been proposed to adjust the amount of voltage drop due to self-discharge of such secondary batteries.

[0003] As an example of a technique for adjusting the amount of voltage drop in a secondary battery, Patent Document 1 discloses a SOC (State Of Charge) adjustment process in which an initially charged and activated secondary battery is discharged and the SOC value is adjusted to a value such that the slope of the discharge curve of the secondary battery divided by the battery capacity is 0.05 or greater. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2014-134395 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the aging process performed on the initially charged secondary batteries, multiple secondary batteries are placed in a predetermined temperature environment, but the temperature of each secondary battery may vary depending on the local environment of each secondary battery. This temperature variation may affect the amount of voltage drop of the secondary batteries. However, the voltage adjustment method disclosed in Patent Document 1 has a problem in that it does not take into account the effect of such temperature variation.

[0006] The present disclosure is intended to solve such problems, and aims to provide a method for manufacturing a secondary battery that is capable of suppressing variation in the amount of voltage drop among multiple secondary batteries, taking into account the effects of temperature variation in individual secondary batteries during aging treatment. [Means for solving the problem]

[0007] A method for producing a secondary battery according to an embodiment includes the steps of: a first aging treatment step of performing a first aging treatment on the secondary battery after the initial charge; a voltage measuring step of measuring a voltage of the secondary battery that has been subjected to the first aging treatment; a second aging treatment step of performing a second aging treatment on the secondary battery that has been subjected to the first aging treatment at a temperature corresponding to the measured voltage of the secondary battery obtained in the voltage measurement step; Secondary batteries are classified into several groups based on the magnitude of the measured voltage, In the second aging treatment step, the second aging treatment is performed at different temperatures for the secondary batteries of each group such that the lower the measured voltage, the higher the temperature of the second aging treatment; The different temperatures include temperatures equal to or greater than the predetermined temperature.

[0008] In addition, the secondary batteries can be classified into a first group whose measured voltage is equal to or lower than a predetermined reference voltage and a second group whose measured voltage is higher than the predetermined reference voltage; In the second aging treatment step, performing a second aging treatment on the secondary batteries belonging to the first group at a temperature equal to or higher than a predetermined temperature; The secondary batteries belonging to the second group can be subjected to the second aging treatment at a temperature lower than the predetermined temperature.

[0009] Further, the secondary batteries can be classified into a first group, a second group, and a third group, the first group is a group including secondary batteries whose measured voltage is equal to or lower than a first boundary voltage that is lower than a predetermined reference voltage; the second group is a group including secondary batteries whose measured voltage is greater than the first boundary voltage and less than a second boundary voltage that is greater than the reference voltage; the third group is a group including secondary batteries whose measured voltage is equal to or higher than the second boundary voltage; In the second aging treatment step, performing a second aging treatment on the secondary batteries belonging to the first group at a temperature lower than a predetermined temperature; performing a second aging treatment on the secondary batteries belonging to the second group at a first temperature that is equal to or higher than a predetermined temperature; The secondary batteries belonging to the third group can be subjected to a second aging treatment at a second temperature that is equal to or higher than the first temperature.

[0010] Furthermore, the method for producing a secondary battery includes the steps of: a first aging treatment step of performing a first aging treatment on the secondary battery after the initial charge; a voltage measuring step of measuring a voltage of the secondary battery that has been subjected to the first aging treatment; a second aging treatment step of performing a second aging treatment on the secondary battery that has been subjected to the first aging treatment at a temperature corresponding to the measured voltage of the secondary battery obtained in the voltage measurement step; In the second aging treatment step, performing a second aging process at a temperature equal to or higher than a predetermined temperature on a secondary battery whose measured voltage is equal to or lower than a predetermined reference voltage; A secondary battery whose measured voltage is greater than a predetermined reference voltage can be subjected to a second aging treatment at a temperature lower than the predetermined temperature.

[0011] The predetermined temperature may be a temperature corresponding to a change point in the relationship between the temperature of the second aging treatment and the amount of voltage drop due to self-discharge of the secondary battery after the second aging treatment. Effect of the Invention

[0012] The present disclosure makes it possible to provide a method for manufacturing a secondary battery that is capable of suppressing variation in the amount of voltage drop among a plurality of secondary batteries by taking into account the effect of temperature variation among the individual secondary batteries during aging treatment. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram illustrating an example of a secondary battery according to the present disclosure. [Diagram 2] 4 is a flowchart showing a method for manufacturing a secondary battery according to the present disclosure. [Diagram 3] FIG. 11 is a diagram showing an example of measured voltages V1 for a plurality of secondary batteries. [Figure 4] 1 is a diagram showing the relationship between the measured voltage V1 for a plurality of secondary batteries and the voltage difference ΔV between these secondary batteries. [Diagram 5] FIG. 11 is a diagram showing the relationship between the temperature in the second aging treatment and the voltage difference ΔV. [Figure 6] FIG. 11 is a diagram showing the relationship between the temperature in a second aging treatment and the voltage difference ΔV of a secondary battery that has been subjected to the second aging treatment. [Figure 7] FIG. 11 is a diagram showing a change over time in the voltage difference ΔV of a secondary battery. [Figure 8] 11 is a diagram showing a change in voltage difference ΔV of a secondary battery in which a measured voltage V1 is equal to or lower than a reference voltage. [Figure 9] FIG. 13 is a diagram showing another example of the measured voltage V1 for a plurality of secondary batteries. [Figure 10] FIG. 11 is a diagram showing the relationship between the temperature in the second aging treatment and the voltage difference ΔV. [Figure 11] FIG. 13 is a diagram showing the relationship between the number of self-discharge days and the voltage difference ΔV in the self-discharge process of a secondary battery that has not been subjected to a second aging treatment. [Figure 12] FIG. 13 is a diagram showing the relationship between the number of self-discharge days and the voltage difference ΔV in the self-discharge process of a secondary battery that has been subjected to a second aging treatment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] <First embodiment> Hereinafter, an embodiment according to the present disclosure will be described with reference to the drawings. Fig. 1 is a diagram showing an example of a secondary battery 1 manufactured by a method for manufacturing a secondary battery 1 according to the present disclosure. The secondary battery 1 includes a battery case 2 and an electrode assembly housed in the battery case 2.

[0015] 2 is a diagram showing a method for manufacturing the secondary battery 1 according to the present disclosure. The method for manufacturing the secondary battery 1 includes an initial charging step S1, a first aging treatment step S2, a first forced cooling step S3, a first voltage measurement step S4, a second aging treatment step S5, a second forced cooling step S6, a second voltage measurement step S7, a self-discharge step S8, a third voltage measurement step S9, and a self-discharge determination step S10.

[0016] The initial charging step S1 is a step of initially charging the secondary battery 1. Specifically, the secondary battery 1 is charged to a predetermined voltage value at room temperature (e.g., 5 to 35°C). The predetermined voltage value is preferably a voltage value when the SOC of the secondary battery 1 is 80% or more of the fully charged state.

[0017] The first aging treatment step S2 is a step of performing a first aging treatment on the secondary battery 1 that has been initially charged. For example, in the first aging treatment, the secondary battery 1 is placed in a space at a predetermined room temperature (e.g., 60°C) for a predetermined time (e.g., about 24 hours). In the aging treatment, multiple secondary batteries 1 are placed in a predetermined temperature environment, but the temperature of each secondary battery 1 may vary depending on the local environment of each secondary battery.

[0018] The first forced cooling step S3 is a step of cooling the secondary battery 1 after the first aging treatment is completed. For example, the secondary battery 1 is cooled using a fan or the like in a room temperature environment.

[0019] The first voltage measurement step S4 is a step of measuring the voltage V1 of the secondary batteries 1 after the first forced cooling step S3 is completed. The measured voltage V1 may be affected by temperature variations of the secondary batteries 1 during the first aging treatment.

[0020] The second aging treatment step S5 is a step of performing a second aging treatment on the secondary battery 1 cooled in the first forced cooling step S3 at a temperature corresponding to the measured voltage V1 of the secondary battery. Specifically, in the second aging treatment, the secondary battery 1 is placed in a space at room temperature, which is the temperature corresponding to the measured voltage V1, for a predetermined time (for example, 24 hours or less).

[0021] FIG. 3 is a diagram showing the measured voltage V1 for multiple secondary batteries 1. As shown in FIG. 3, the multiple secondary batteries 1 can be classified into those whose measured voltage V1 is greater than a reference voltage and those whose measured voltage V1 is equal to or less than the reference voltage. The reference voltage can be a value such as the median or average value of the measured voltages V1 for the multiple secondary batteries 1. Note that secondary batteries 1 that exceed the rated upper limit voltage and secondary batteries 1 that are less than the rated lower limit voltage are excluded. The rated upper limit voltage is the upper limit value of the allowable measured voltage V1. The rated lower limit voltage is the lower limit value of the allowable measured voltage V1.

[0022] In this embodiment, in the second aging treatment step, the secondary battery 1 whose measured voltage V1 is equal to or lower than the reference voltage is subjected to the second aging treatment at a temperature equal to or higher than a specific temperature (X°C). On the other hand, the secondary battery 1 whose measured voltage V1 is higher than the reference voltage is subjected to the second aging treatment at a temperature lower than the specific temperature (X°C).

[0023] The second forced cooling step S6 is a step of cooling the secondary battery 1 after the completion of the second aging treatment. In the second forced cooling step S6, similar to the first forced cooling step S3, the secondary battery 1 is cooled in a room temperature environment using a fan or the like.

[0024] The second voltage measurement step S7 is a step of measuring the voltage of the secondary battery 1 after the second forced cooling step S6 is completed.

[0025] The self-discharge step S8 is a step of discharging the secondary battery 1 after the second voltage measurement step S7. In the self-discharge step S8, the secondary battery 1 is placed in a room temperature environment for a predetermined number of days (for example, several days).

[0026] The third voltage measurement step S9 is a step of measuring the voltage of the secondary battery 1 after the self-discharge step S8 ends.

[0027] The self-discharge determination process S10 is a process for determining the amount of self-discharge of the secondary battery 1, which corresponds to the difference between the measured voltage V2 obtained in the second voltage measurement process S7 and the measured voltage V3 obtained in the third voltage measurement process S9, based on these measured voltages.

[0028] As described above, the method for manufacturing the secondary battery 1 according to the first embodiment includes a first aging treatment step S2, a first voltage measurement step S4, and a second aging treatment step S5. In the first aging treatment step S2, a first aging treatment is performed on the secondary battery 1 after initial charging. In the first voltage measurement step S4, a voltage V1 of the secondary battery 1 that has been subjected to the first aging treatment is measured. In the second aging treatment step S5, a second aging treatment is performed on the secondary battery 1 that has been subjected to the first aging treatment at a temperature corresponding to the measured voltage V1 of the secondary battery 1 obtained in the first voltage measurement step S4.

[0029] The secondary batteries 1 are classified into a plurality of groups based on the magnitude of the measured voltage V1. In the second aging treatment step S5, the secondary batteries 1 in each group are subjected to the second aging treatment at different temperatures such that the temperature of the second aging treatment is higher as the measured voltage V1 is lower. The different temperatures include temperatures equal to or higher than a specific temperature (X°C).

[0030] More specifically, the secondary batteries 1 are classified into a first group whose measured voltage V1 is equal to or lower than a predetermined reference voltage, and a second group whose measured voltage V1 is higher than the predetermined reference voltage. In the second aging treatment step S5, the secondary batteries 1 belonging to the first group are subjected to a second aging treatment at a specific temperature (X°C) or higher. In other words, in the second aging treatment step S5, the secondary batteries 1 whose measured voltage V1 is equal to or lower than the predetermined reference voltage are subjected to the second aging treatment at a specific temperature (X°C) or higher.

[0031] On the other hand, the second aging process is performed on the secondary batteries 1 belonging to the second group at a temperature below a specific temperature (X° C.). In other words, the second aging process is performed on the secondary batteries 1 whose measured voltage V1 is greater than the predetermined reference voltage at a temperature below the specific temperature (X° C.).

[0032] 4 is a diagram showing the relationship between the measured voltage V1 for multiple secondary batteries 1 and the voltage difference ΔV between these secondary batteries 1. The horizontal axis of FIG. 4 represents the measured voltage V1. The vertical axis of FIG. 4 represents the voltage difference ΔV, which is the difference between the measured voltage V3 and the measured voltage V2. The voltage difference ΔV is defined by Equation 1.

number

[0033] FIG. 5 is a diagram showing the effect of the temperature of the second aging treatment on the voltage difference ΔV. The horizontal axis of FIG. 5 represents the number of days of self-discharge, which is the number of days in the self-discharge step S8. The vertical axis of FIG. 5 represents the voltage difference ΔV. The graph of FIG. 5 shows the results when the second aging treatment was performed on the secondary battery 1 at 25° C. and 35° C. From this result, it was found that the higher the temperature of the second aging treatment, the greater the degree of reduction in the voltage difference ΔV.

[0034] Fig. 6 is a diagram showing the relationship between the temperature of the second aging treatment and the slope of the voltage difference ΔV of the secondary battery 1 that has been subjected to the second aging treatment. The horizontal axis of Fig. 6 represents the temperature of the second aging treatment. The vertical axis of Fig. 6 represents the absolute value of the slope of the voltage difference ΔV. The slope of the voltage difference ΔV represents the slope of the straight line portion (the dashed line portion of Fig. 7) of the graph of Fig. 7 showing the change over time in the voltage difference ΔV of the secondary battery 1.

[0035] The results shown in FIG. 6 were obtained by subjecting the secondary battery 1 to the second aging treatment at various temperatures. From these results, it was found that when the temperature of the second aging treatment is equal to or higher than a specific temperature (X°C), the amount of voltage drop increases according to the temperature of the second aging treatment. On the other hand, when the temperature of the second aging treatment is lower than the specific temperature (X°C), the amount of voltage drop is substantially constant. The specific temperature (X°C) is a temperature corresponding to a change point in the relationship between the temperature of the second aging treatment and the amount of voltage drop due to self-discharge of the secondary battery 1 after the second aging treatment. The specific temperature (X°C) corresponds to a predetermined temperature. It is assumed that this specific temperature varies depending on the design conditions of the secondary battery 1, such as the type and amount of active material, the restraining pressure of the secondary battery 1, and the form of the electrodes, such as stacking or winding.

[0036] In the first embodiment, in the second aging process, the second aging process is performed at a temperature equal to or higher than a specific temperature (X°C) for secondary batteries 1 whose measured voltage V1 is equal to or lower than a predetermined reference voltage, that is, for secondary batteries 1 whose measured voltage V1 exceeds the predetermined reference voltage and whose voltage drop is assumed to be smaller than that of secondary batteries 1 whose measured voltage V1 exceeds the predetermined reference voltage. This makes it possible to make the voltage difference ΔV of secondary batteries whose measured voltage V1 is equal to or lower than the predetermined reference voltage a desired voltage difference ΔV, as shown in FIG. 8. In other words, it is possible to increase the voltage drop of secondary batteries 1 whose voltage drop is assumed to be smaller. By adopting this method, it is possible to suppress the variation in the voltage drop of multiple secondary batteries 1, taking into consideration the effect of the variation in temperature of each secondary battery 1 in the first aging process, which affects the measured voltage V1.

[0037] As a result, in the first aging treatment step S2, it is possible to omit the task of changing the position of the secondary battery 1 in order to suppress the variation in the amount of voltage drop of the secondary battery 1. Furthermore, by suppressing the variation in the amount of voltage drop, it is possible to shorten the number of days of self-discharge required to suppress the variation in the amount of voltage drop of the secondary battery 1, and thus to shorten the lead time.

[0038] <Second embodiment> The second embodiment will be described below, focusing on the differences from the first embodiment. In the second embodiment, the secondary batteries 1 are classified into three groups, a first group, a second group, and a third group, based on the measured voltage V1.

[0039] Specifically, as shown in FIG. 9, the first group is a group to which secondary batteries 1 whose measured voltage V1 is equal to or lower than a first boundary voltage belong. The first boundary voltage is a voltage lower than the reference voltage and equal to or higher than the rated lower limit voltage. The second group is a group to which secondary batteries 1 whose measured voltage V1 is greater than the first boundary voltage and less than a second boundary voltage belong. The second boundary voltage is a voltage higher than the reference voltage and equal to or lower than the rated upper limit voltage. The third group is a group to which secondary batteries 1 whose measured voltage V1 is equal to or higher than the second boundary voltage belong.

[0040] In the second aging treatment step S5, the secondary batteries 1 belonging to the first group are subjected to a second aging treatment at temperature A which is less than a specific temperature (X°C), as shown in FIG. 10. Also, in the second aging treatment step S5, the secondary batteries 1 belonging to the second group are subjected to a second aging treatment at temperature B which is equal to or higher than a specific temperature (X°C). Temperature B corresponds to the first temperature. Furthermore, in the second aging treatment step S5, the secondary batteries 1 belonging to the third group are subjected to a second aging treatment at temperature C which is equal to or higher than temperature B. Temperature C corresponds to the second temperature.

[0041] FIG. 11 is a diagram showing the relationship between the number of days of self-discharge and the voltage difference ΔV when the second aging process is not performed for the secondary battery 1 whose measured voltage V1 is the lower limit of the standard, the first boundary voltage, the second boundary voltage, and the upper limit of the standard. Here, the slope of the line representing the voltage difference ΔV of the secondary battery 1 whose measured voltage V1 is the lower limit of the standard is a (a<0). The slope of the line representing the voltage difference ΔV of the secondary battery 1 whose measured voltage V1 is the first boundary voltage is 2a. The slope of the line representing the voltage difference ΔV of the secondary battery 1 whose measured voltage V1 is the second boundary voltage is 3a. The slope of the line representing the voltage difference ΔV of the secondary battery 1 whose measured voltage V1 is the upper limit of the standard is 4a. In this case, the variation Va of the voltage difference ΔV when the second aging process is not performed can be expressed as 3a × the number of days of self-discharge.

[0042] 12 is a diagram showing the relationship between the number of days of self-discharge and the voltage difference ΔV when the second aging process is performed at temperatures A, B, and C shown in FIG. 10 for the secondary battery 1 with the measurement voltage V1 at the lower limit of the standard, the first boundary voltage, the second boundary voltage, and the upper limit of the standard. As shown in FIG. 10, if the difference in the absolute value of the slope of the voltage difference ΔV is a, the variation Vb of the voltage difference ΔV when the second aging process is performed can be expressed as a × the number of days of self-discharge. Therefore, the variation of the voltage difference ΔV can be reduced by performing the second aging process at temperatures A, B, and C for the secondary battery 1 belonging to the first group, the secondary battery 1 belonging to the second group, and the secondary battery 1 belonging to the third group.

[0043] In another embodiment, the secondary batteries 1 may be classified into four or more groups based on the magnitude of the measured voltage V1. In this case, three or more boundary voltages can be defined to classify the secondary batteries 1 into four or more groups. In this embodiment, similar to the first and second embodiments, in the second aging treatment step S5, the second aging treatment is performed on the secondary batteries 1 of each group at different temperatures so that the lower the measured voltage V1, the higher the temperature of the second aging treatment.

[0044] The present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0045] 1 Secondary battery 2 battery case S1 Initial charging process S2 First aging treatment step S3 First forced cooling process S4 First voltage measurement process S5 Second aging process S6 Second forced cooling process S7 Second voltage measurement process S8 Self-discharge process S9 Third voltage measurement process S10 Self-discharge judgment process

Claims

1. A method for manufacturing a secondary battery, comprising: a first aging treatment step of performing a first aging treatment on the secondary battery after the initial charge; a voltage measuring step of measuring a voltage of the secondary battery that has been subjected to the first aging treatment; a second aging treatment step of performing a second aging treatment on the secondary battery that has been subjected to the first aging treatment at a temperature corresponding to the measured voltage of the secondary battery obtained in the voltage measurement step, The secondary batteries are classified into a plurality of groups based on the magnitude of the measured voltage, In the second aging treatment step, the second aging treatment is performed on the secondary batteries of each group at different temperatures such that the temperature of the second aging treatment is higher as the measured voltage is smaller; The different temperatures include a temperature equal to or greater than a predetermined temperature. A method for manufacturing a secondary battery.

2. The secondary batteries are classified into a first group whose measured voltage is equal to or lower than a predetermined reference voltage and a second group whose measured voltage is higher than the predetermined reference voltage; In the second aging treatment step, performing the second aging treatment on the secondary batteries belonging to the first group at a temperature equal to or higher than the predetermined temperature; performing the second aging treatment on the secondary batteries belonging to the second group at a temperature lower than the predetermined temperature; The method for producing the secondary battery according to claim 1 .

3. The secondary batteries are classified into a first group, a second group, and a third group; the first group is a group to which the secondary batteries belong, the measured voltage of which is equal to or lower than a first boundary voltage that is lower than a predetermined reference voltage; the second group is a group including the secondary batteries whose measured voltage is greater than the first boundary voltage and less than a second boundary voltage that is greater than the reference voltage; the third group is a group to which the secondary batteries whose measured voltage is equal to or higher than the second boundary voltage belong; In the second aging treatment step, performing the second aging treatment on the secondary batteries belonging to the first group at a temperature lower than the predetermined temperature; performing the second aging treatment on the secondary batteries belonging to the second group at a first temperature that is equal to or higher than the predetermined temperature; performing the second aging treatment on the secondary batteries belonging to the third group at a second temperature that is equal to or higher than the first temperature; The method for producing the secondary battery according to claim 1 .

4. A method for manufacturing a secondary battery, comprising: a first aging treatment step of performing a first aging treatment on the secondary battery after the initial charge; a voltage measuring step of measuring a voltage of the secondary battery that has been subjected to the first aging treatment; a second aging treatment step of performing a second aging treatment on the secondary battery that has been subjected to the first aging treatment at a temperature corresponding to the measured voltage of the secondary battery obtained in the voltage measurement step, In the second aging treatment step, performing the second aging treatment at a temperature equal to or higher than a predetermined temperature on a secondary battery whose measured voltage is equal to or lower than a predetermined reference voltage; performing the second aging treatment at a temperature lower than the predetermined temperature for a secondary battery having a measured voltage higher than the predetermined reference voltage; A method for manufacturing a secondary battery.

5. 5. The method for manufacturing a secondary battery according to claim 1, wherein the predetermined temperature is a temperature corresponding to a change point in a relationship between a temperature of the second aging treatment and an amount of voltage drop due to self-discharge of the secondary battery after the second aging treatment.

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