JP6123637B2 - Manufacturing method of secondary battery - Google Patents

Description

  The present invention relates to a method for manufacturing a secondary battery.

  As a method for determining the quality of a secondary battery, a method is known that uses a voltage drop amount of a battery voltage before and after aging.

  For example, Patent Document 1 discloses a quality determination method using a voltage drop amount of a battery. In Patent Document 1, an inspection lot (inspection group) to be a pass / fail determination target is formed. At that time, each battery is stratified by production lot and inspected with batteries that are the same production lot (several products manufactured in the same production line at the same production time using the same lot of raw materials) Form a group.

JP 2011-18482 A

  However, as in the technique disclosed in Patent Document 1, batteries of the same production lot (the same lot of battery assembly conditions such as electrode lot raw materials, production time, production line, and combination of positive and negative electrode lots) Even if an inspection group is formed by collecting data, if the conditions of the subsequent manufacturing process (temperature, aging time, temperature history, etc.) are different, the voltage drop amount of some inspection groups is different from that of other inspection groups. May be off. In this case, there is a problem that some of the inspection groups whose voltage drop amounts are shifted are treated as defective because they are abnormal compared to other inspection groups even though they are actually good products.

  On the other hand, if only the batteries having the same manufacturing process conditions such as temperature are collected to form the inspection group, the number of the inspection group population is reduced as compared to the inspection group collecting the batteries of the same manufacturing lot. For this reason, when determining pass / fail by using a deviation (standard deviation) from the median value of the voltage drop amount of the inspection group, there is a possibility that the determination accuracy is lowered. Therefore, an object of the present invention is to provide an inspection method with improved determination accuracy.

  A method for manufacturing a secondary battery according to one embodiment of the present invention includes a small group including a plurality of battery cells having the same conditions for the first aging process and the cooling process, and the first aging process and the cooling process. A large group obtained by combining a plurality of the small groups with different conditions, and a measurement result of a voltage drop amount of the battery cell in a second aging step for one of the small group and the large group The first determination criterion is set using the first determination criterion, the quality of the battery cells included in the one group is determined based on the first determination criterion, and the one group is not determined as a non-defective product When the battery cell is included, the voltage of the battery cell in the second aging step for the other group including the battery cell that has not been determined to be non-defective. Set the second criterion using the measurement result of the lower amount, based on the second criterion, and performs quality determination of the battery cells included in the other group. Thereby, it is possible to re-determine that the battery cells determined as defective in the quality determination in the large group are good in the small group due to the influence of the difference in the manufacturing process conditions. As a result, the accuracy of pass / fail determination can be improved.

  In addition, when the battery cell that is not determined as good in the quality determination based on the first determination criterion is not determined as good in the quality determination based on the second determination criterion, the battery cell is defective. You may determine that there is.

  In addition, a median value of the voltage drop amounts of the plurality of battery cells in the large group is calculated, and the quality determination of the battery cells included in the large group is performed based on the median value. When the battery cell that has not been determined to be included is included, the median value is calculated for each small group that includes the battery cell that has not been determined to be non-defective, and the median value is included in the small group. You may determine the quality of a battery cell.

  In addition, a median value of the voltage drop amounts of the plurality of battery cells in the small group is calculated, and the quality determination of the battery cells included in the small group is performed based on the median value. When the battery cells that are not determined to be included are included, the small group and the battery cells that are not determined to be non-defective and other small groups that include the battery cells that have the same battery cell assembly process conditions, In addition, the large group may be formed, the median value in the large group may be calculated, and the quality of the battery cells included in the large group may be determined based on the median value.

  In addition, when the battery cell that is not determined to be non-defective based on the median value is not included in the one group, the standard deviation of the voltage drop amounts of the plurality of battery cells included in the one group is determined. And determining whether the battery cells included in the one group are acceptable or not. In the quality determination based on the standard deviation, when the battery cells that are not determined as non-defective are included in the one group, Based on the median value in the group, the quality determination of the battery cells included in the other group may be performed.

  In addition, when the battery cell that is not determined to be non-defective based on the median value is not included in the other group, the standard deviation of the voltage drop amount of the plurality of battery cells included in the other group is determined. Based on whether the battery cell included in the other group includes a battery cell that is not determined to be non-defective in the other group in the quality determination based on the standard deviation. The battery cells included in the group may be determined as defective products.

  The large group may include at least one of the small groups including the battery cells having different battery cell assembly process conditions.

  According to the present invention, an inspection method with improved determination accuracy can be provided.

3 is a flowchart showing a battery manufacturing process according to the first embodiment; 3 is a flowchart showing pass / fail determination according to the first exemplary embodiment. 3 is a graph for explaining variation in the amount of voltage drop according to the first embodiment; FIG. 3 is a diagram for explaining grouping according to the first exemplary embodiment; 6 is a graph for explaining grouping according to the first exemplary embodiment; 10 is a flowchart showing pass / fail determination according to the second exemplary embodiment. 10 is a graph for explaining grouping according to the second exemplary embodiment;

<Embodiment 1>
Embodiment 1 of the present invention will be described below with reference to the drawings. First, an outline of a method for producing a nonaqueous electrolyte secondary battery (for example, a lithium ion secondary battery) will be described with reference to the flowchart shown in FIG. In addition, since this invention has the characteristics in the quality determination of the secondary battery after an aging process, description of the manufacturing process before a battery assembly process is abbreviate | omitted. In the following description, the secondary battery may be simply referred to as a battery.

<Outline of manufacturing process>
First, a process for assembling a battery is performed (step S101). A wound body obtained by winding a laminate of the positive electrode and the negative electrode is assembled to the battery case. Then, a nonaqueous electrolyte is injected into the battery case. The wound body absorbs the nonaqueous electrolyte, so that the positive electrode and the negative electrode are in contact with the nonaqueous electrolyte. Thereby, a battery element is assembled as a battery and can be charged.

  Next, a battery charging step is performed (step S102). In this charging step, the battery is charged for the first time (initial charge). In the charging step, the battery is charged to a predetermined capacity. Charging can be performed using, for example, constant current and constant voltage charging.

  Next, a first aging process is performed (step S103). As the aging process, it is preferable to leave the battery in a state where the positive electrode and the negative electrode are opened (open circuit) for a predetermined time. The first aging is performed by storing the battery for a certain period at a predetermined environmental temperature (40 to 80 ° C.).

  Next, a cooling process is performed (step S104). In the battery cooling process, the battery is held within a predetermined temperature range. In order to stably perform self-discharge, the predetermined temperature range is preferably higher than the freezing point of the electrolytic solution. By providing the cooling step, the battery is maintained at a constant specified temperature in the following steps.

  In addition, said 1st aging process (step S103) and cooling process (step S104) are performed per pallet. The pallet (small group) includes a plurality of batteries (for example, about 20 to 30). That is, all the batteries included in one pallet go through the first aging process and the cooling process under the same conditions (temperature, aging time, temperature history, etc.).

  Next, a second aging process is performed (step S105). The second aging is a self-discharge process, and the battery is self-discharged by storing the battery in an open circuit for a predetermined period at a predetermined environmental temperature (0 to 30 ° C.). Before the start of the second aging step, the voltage of the battery that has reached the specified temperature in the cooling step is measured to obtain the value of the battery voltage (potential difference between the positive electrode and the negative electrode) before aging. After voltage measurement, the positive and negative terminals are opened and stored (aged) for a predetermined period. The predetermined period is preferably several days to several weeks. By setting it as such a period, the self-discharge by mixing of a foreign material becomes obvious and can be detected as a voltage drop. Then, the voltage of the self-discharged battery is measured for a predetermined period, and the value of the battery voltage after aging is obtained.

  Finally, a quality determination process is performed (step S106). In the pass / fail judgment step, the presence or absence of a short circuit of the battery is inspected. Specifically, in the pass / fail determination step, a voltage drop amount (self-discharge amount) in the second aging step is calculated. The amount of voltage drop can be obtained by calculating the difference between the battery voltage before aging and the battery voltage after aging. Then, the calculated voltage drop amount is compared with the median value of the voltage drop amounts of a plurality of batteries included in the inspection lot. Based on the comparison result, it is determined whether the battery is a good product or a defective product. The pass / fail determination process will be described in detail below.

<Details of pass / fail judgment>
Next, details of the pass / fail determination will be described. FIG. 2 shows a flowchart for explaining the pass / fail judgment step. In addition, each process of the flowchart demonstrated below is performed by the control part (illustration omitted) containing CPU (Central Processing Unit) according to the program set beforehand.

  First, the control unit forms a large group as an inspection lot (step S201). Here, the large group is formed by combining a plurality of pallets (small groups) having different conditions (temperature, aging time, temperature history, etc.) in the first aging process and the cooling process. At this time, it is not necessary that the pallets included in the large group have different conditions, as long as pallets that have undergone at least two different manufacturing processes (first aging process and cooling process) are included. As an example, in the present embodiment, 25 battery cells are included in the small group, and 6 small groups (25 × 6 = 150 battery cells) are included in the large group.

  Next, the control unit determines whether or not the number of battery cells included in the large group is greater than or equal to a predetermined value (step S202). That is, the control unit determines whether or not a population for obtaining a reliable result as a quality determination test is available. Here, the predetermined value is, for example, about 10.

  When the number of battery cells included in the large group is less than the predetermined value (step S202: No), it is determined that the inspection result of the large group has low reliability. That is, it is determined that the large group has low inspection capability. Therefore, all the battery cells included in the large group are regarded as defective products (step S211).

  On the other hand, when the number of battery cells included in the large group is equal to or greater than a predetermined value (step S202: Yes), the control unit determines the voltage drop amount and the voltage drop amount in the second aging process of the battery cells included in the large group. The difference from the median is calculated. At this time, the median value of voltage drop means the median value of all the battery cells included in the large group. And a control part determines whether a difference is below a predetermined value (step S203).

  When the difference between the voltage drop amount and the median value of the battery cells included in the large group is larger than the predetermined value (step S203: No), the control unit determines that these battery cells have an abnormal voltage drop amount, Not determined as a battery cell. Thereafter, the control unit forms a small group including battery cells that are not determined to be non-defective (step S205). The control unit stores the determination result in a memory or the like (not shown).

  On the other hand, when the difference between the voltage drop amount of the battery cells included in the large group and the median value is equal to or smaller than the predetermined value (step S203: Yes), the control unit sets the standard of the voltage drop amount of the battery cells included in the large group. It is determined whether or not the deviation is equal to or less than a predetermined value (step S204). That is, the control unit confirms that non-defective products are collected to such an extent that a reliable result can be obtained as a pass / fail determination test by looking at variations in the voltage drop amount of the large group. Thereby, the inspection result of the large group containing many defective products can be rejected. Note that the predetermined value in step S204 and the predetermined value in step S203 are different values.

  When the standard deviation is equal to or less than the predetermined value (step S204: Yes), it is determined that all the battery cells included in the large group are non-defective (step S210).

  On the other hand, when the standard deviation is larger than the predetermined value (step S204: No), the control unit does not determine all the battery cells included in the large group as non-defective products, assuming that the inspection result in the large group cannot be adopted. That is, the control unit determines that all battery cells included in the large group are not good products. And a control part forms a small group using a one part pallet of a large group (step S205).

  Here, an example of a state in which the standard deviation is larger than a predetermined value is shown in the graph of FIG. The graph of FIG. 3 is a diagram showing the voltage drop amount (self-discharge amount) of the battery cells included in the first to sixth pallets for each pallet. The horizontal axis in FIG. 3 indicates the pallet number (first to sixth), and the vertical axis indicates the self-discharge amount of each battery cell. Further, the measurement conditions in FIG. 3 are as follows: the positive electrode is a three-dimensional active material, the negative electrode is carbon, the electrolyte is LiPF6 (lithium hexafluorophosphate), and the electrolyte is EC (ethylene carbonate), DMC ( This is a Li2.0 prismatic battery that is dimethyl carbonate) or DME (dimethoxyethane).

  As shown in FIG. 3, only the first pallet has a smaller self-discharge amount than the other pallets (second to fifth pallets). Therefore, the standard deviation of the self-discharge amount (voltage drop amount) as a whole large group becomes larger than a predetermined value. For this reason, the entire battery cells included in the large group (first to sixth pallets) are not determined as non-defective products. That is, the control unit determines that all battery cells included in the large group are not good products.

  As described above, when the difference between the voltage drop amount of the battery cell and the median value is larger than the predetermined value (step S203: No), or when the standard deviation is larger than the predetermined value (step S204: No), the control unit A small group is formed by using some battery cells of the large group. As shown in FIG. 4, in the present embodiment, the control unit forms a small group 200 from one large pallet from the large group 100 formed using six pallets. The pallet extracted at this time is a pallet including battery cells that are not determined to be non-defective in step S203 or S204. When the small group is formed, the control unit resets the quality determination of the battery cells included in the small group (step S206). Then, the pass / fail determination is performed on the small group in the same manner as in steps S202 to S204 described above. In addition, the measurement result of the voltage drop amount used for the quality determination of the small group shown below does not need to be measured again, and the measurement result used for the quality determination of the large group can be used. The measurement results of the battery cells are stored in advance in a list format in a memory (not shown), for example.

  First, the control unit determines whether or not the number of battery cells included in the small group is greater than or equal to a predetermined value (step S207). That is, the control unit determines whether or not a population for obtaining a reliable result as a quality determination test is available. The predetermined value at this time is also the same value as in step S202, for example, about 10.

  When the number of battery cells included in the small group is less than the predetermined value (step S207: No), it is determined that the inspection result of the small group has low reliability. That is, it is determined that the small group has low inspection capability. Therefore, all the battery cells included in the small group are regarded as defective products (step S211).

  On the other hand, when the number of battery cells included in the small group is equal to or larger than the predetermined value (step S207: Yes), the control unit determines the voltage drop amount and the voltage drop amount in the second aging process of the battery cells included in the small group. The difference from the median is calculated. At this time, the median voltage drop amount means the median value of all the battery cells included in the small group to be inspected. And a control part determines whether a difference is below a predetermined value (step S208). Note that the predetermined value at this time is the same value as the predetermined value in step S203.

  When the difference between the voltage drop amount and the median value of the battery cells included in the small group is larger than the predetermined value (step S208: No), these battery cells are determined as defective products because the voltage drop amount is abnormal. (Step S211).

  On the other hand, when the difference between the voltage drop amount of the battery cells included in the small group and the median value is equal to or less than the predetermined value (step S208: Yes), the control unit sets the standard of the voltage drop amount of the battery cells included in the small group. It is determined whether or not the deviation is equal to or less than a predetermined value (step S209). That is, the control unit confirms that the non-defective products are collected to such an extent that a reliable result can be obtained as a quality determination test by looking at variations in the voltage drop amount of the small group. Thereby, the inspection result of the small group containing many defective products can be rejected. The predetermined value in step S209 is the same value as in step S204.

  When the standard deviation is equal to or less than the predetermined value (step S209: Yes), it is determined that all the battery cells included in the small group are non-defective (step S210).

  On the other hand, when the standard deviation is larger than the predetermined value (step S209: No), it is determined that all the battery cells included in the small group are defective, because the inspection result in the small group cannot be adopted.

  As described above, in the manufacturing method according to the present embodiment, the control unit first determines the quality of the large group. When there is a battery cell that has not been determined to be non-defective, the control unit forms a small group including the battery cells that have not been determined to be non-defective, and performs pass / fail determination again for each small group.

(Comparative example)
Here, the manufacturing method concerning a comparative example is demonstrated. The manufacturing method according to the comparative example performs pass / fail judgment using only the large group. That is, the pass / fail determination is completed by the processing from step S201 to step S204 in FIG.

  For example, consider a state in which the measured values of the self-discharge amount (voltage drop amount) of the battery cells of each pallet are shown in FIG. Note that the vertical and horizontal axes in FIG. 5 are the same as those in the graph shown in FIG. In FIG. 5, the three small groups 200 of the first to third pallets are combined to form the large group 100. Although the self-discharge amount is small only in the first pallet due to the difference in the conditions of the first aging process and the cooling process, all the battery cells included in the first pallet to the third pallet are actually all. It shall be a good product.

  In addition, in the graph of FIG. 5, the battery cells in the Δ plot and the battery cells in the x plot are different conditions (part number such as electrodes, part raw materials, part production line, part production time, part combination, etc. Assume that the assembling process is performed in the battery assembling conditions including the above. However, Δ plots are battery cells manufactured in the assembly process under the same conditions, and x plots are battery cells manufactured in the assembly process under the same conditions.

  In the graph of FIG. 5, in the second palette, Δ plots and x plots are mixed. For example, if up to 25 batteries can be stored in one pallet and there are 30 battery cells manufactured by the assembly process under the same conditions, the first pallet (first pallet) has 25 batteries. The cell is stored. However, in the next pallet (second pallet), five battery cells manufactured by the assembly process under the same conditions and 20 battery cells manufactured by the assembly process under different conditions are stored. This is because it is not desired to create a gap in the pallet storage space. For these reasons, battery cells with different assembly processes may be stored in the same pallet.

  First, in the manufacturing method according to the comparative example, the control unit determines whether or not the number of battery cells is equal to or greater than a predetermined value. For convenience of explanation, it is assumed that the number of battery cells included in the large group is equal to or greater than a predetermined value and satisfies the above condition.

  Next, the control unit calculates a median value of the voltage drop amounts of the battery cells included in the large group, and calculates a difference between the voltage drop amount and the median value of each battery cell. And a control part determines whether the said difference is below a predetermined value. As is clear from FIG. 5, the first pallet has a smaller self-discharge amount as a whole than the second pallet and the third pallet. Therefore, among the battery cells included in the first pallet, the battery cells in the Δ plot surrounded by the broken-line circle are treated as defective products.

  In addition, even if a defective product is not found in the comparison between the self-discharge amount of each battery cell and the median value, the standard deviation of the self-discharge amount of the entire large group of battery cells is larger than a predetermined value. there is a possibility. As a result, the entire large group is treated as a defective product.

  At this time, there are two possible causes for the difference between the voltage drop amount of the large group and the median value being greater than or equal to a predetermined value, or the standard deviation being greater than the predetermined value. The first is a case where defective battery cells are included in the first place. The second is a case where the voltage drop amount in the large group appears to vary because the manufacturing conditions of the battery cells are different. However, the battery cell determined to be defective for the second reason is actually a good product. For this reason, in the comparative example, a non-defective product is erroneously determined as a defective product.

  On the other hand, in the manufacturing method according to the present embodiment, when a battery cell that has not been determined to be non-defective in the large group pass / fail determination occurs, the control unit includes a pallet that includes the battery cell that has not been determined to be non-defective. Is judged again as a small group.

  Specifically, the control unit forms a small group using a first pallet including battery cells that are not determined to be non-defective (Δ plots surrounded by broken-line circles). First, the control unit determines whether or not the number of battery cells included in the small group is greater than or equal to a predetermined value. For convenience of explanation, it is assumed that the number of battery cells included in the small group is equal to or greater than a predetermined value and satisfies the above condition.

  Next, the control unit calculates a median value of the voltage drop amounts of the battery cells included in the small group (first pallet), and calculates a difference between the voltage drop amount of each battery cell and the median value. And it is determined whether the said difference is below a predetermined value. As described above, all of the first pallets are Δ plots, and are composed of battery cells manufactured in the assembly process under the same conditions. Moreover, since it is the same pallet, the battery cells in the first pallet have the same conditions for the first aging process and the cooling process. Therefore, on the assumption that all the battery cells are non-defective, the difference between the voltage drop amount of the battery cell included in the first pallet and the median value in the first pallet is all equal to or less than a predetermined value.

  Finally, the control unit determines whether the standard deviation of the self-discharge amount of the battery cells included in the small group is equal to or less than a predetermined value. As described above, the battery cells of the first pallet are all battery cells manufactured in the assembly process, the first aging process, and the cooling process under the same conditions. For this reason, as shown in FIG. 5, there is little variation in the amount of self-discharge. Therefore, the standard deviation falls below a predetermined value. As a result, battery cells that are not determined to be non-defective in the large group determination (Δ plots surrounded by broken-line circles) are all determined to be non-defective in the small group (first pallet). . As described above, by performing the pass / fail determination again using the measurement value of the voltage drop amount in units of small groups (pallets), it is possible to perform the pass / fail determination in consideration of the manufacturing conditions unique to the pallet.

  As described above, according to the configuration of the method for manufacturing a secondary battery according to the present embodiment, a large group is formed by combining a plurality of small groups (pallets) having different conditions for the first aging process and the cooling process. . For the large group, a median value (first determination criterion) is set using the measurement result of the voltage drop amount of the battery cell in the second aging process. And the quality determination of the battery cell contained in a large group is performed based on the comparison result of the said median and the amount of voltage drops of each battery cell. At this time, when battery cells that have not been determined to be non-defective are included in the large group, the voltage drop amount of the battery cells in the second aging process is measured for a small group (pallet) that includes the battery cells that have not been determined to be non-defective. A median (second criterion) is set using the result. And the quality determination of the battery cell contained in a small group is performed based on the comparison result of the said median and the voltage drop amount of each battery cell.

  Thereby, about the battery cell which was not determined to be non-defective in the quality determination in the large group, it can be determined as non-defective in the small group. Therefore, even if a battery cell that is a non-defective product is not erroneously determined to be a non-defective product due to a difference in conditions between the first aging process and the cooling process, it can be re-determined as a non-defective product by a small group quality determination. it can. That is, the accuracy of pass / fail judgment can be improved.

  Furthermore, for example, suppose that 10 pallets containing battery cells that were not determined to be non-defective products were found as a result of performing an inspection at a time with 50 pallets as a large group. In this case, since each of these 10 pallets is inspected again as a small group, the inspection is performed 11 times in total, once for the large group and 10 times for the small group. On the other hand, when inspection is performed for each pallet from the beginning, 50 inspections are required. Thus, according to the manufacturing method of this Embodiment, compared with the case where it test | inspects for every pallet, the frequency | count of an inspection can be reduced.

  In addition, for the large group, a standard deviation (first determination criterion) is set using the measurement result of the voltage drop amount of the battery cell in the second aging process, and pass / fail determination is performed using the standard deviation. In the pass / fail determination using the standard deviation of the large group, if the product is not determined to be a non-defective product, the standard deviation (the second deviation) is measured for the small group using the measurement result of the voltage drop amount of the battery cell in the second aging process. Judgment criteria) is set, and pass / fail judgment is performed using the standard deviation. As a result, even when the voltage drop amount varies in units of pallets in the large group inspection, the variation can be suppressed by performing the inspection again in the small group. As a result, a pallet that is not determined to be non-defective in the quality determination in the large group can be determined as non-defective in the quality determination in the small group.

<Embodiment 2>
A second embodiment according to the present invention will be described. The outline of the manufacturing method is the same as that described in FIG. Below, the detail of the quality determination concerning this Embodiment is demonstrated.

  In the quality determination according to the present embodiment, the control unit first forms a small group and performs quality determination in the small group. And when the battery cell which was not determined to be non-defective in the pass / fail determination in the small group is found, the control unit forms a large group including the battery cells not determined to be non-defective, and performs the pass / fail determination in the large group. Do. FIG. 6 shows a flowchart for explaining the pass / fail judgment step.

  First, the control unit forms a small group as an inspection lot (step S301). That is, a plurality of battery cells having the same conditions for the first aging process and the cooling process are collected to form a small group. For example, one pallet is a small group.

  Next, the control unit determines whether or not the number of battery cells included in the small group is greater than or equal to a predetermined value (step S302).

  When the number of battery cells included in the small group is less than the predetermined value (step S302: No), it is determined that the inspection result of the small group has low reliability. Therefore, all the battery cells included in the small group are regarded as defective products (step S311).

  On the other hand, when the number of battery cells included in the small group is equal to or larger than the predetermined value (step S302: Yes), the control unit determines the voltage drop amount and the voltage drop amount in the second aging process of the battery cells included in the small group. The difference from the median is calculated. The median voltage drop amount means the median value of all the battery cells included in the small group to be inspected. And a control part determines whether a difference is below a predetermined value (step S303).

  When the difference between the voltage drop amount and the median value of the battery cells included in the small group is larger than the predetermined value (step S303: No), the control unit determines that these battery cells have an abnormal voltage drop amount, Do not judge. Thereafter, the control unit forms a large group using a pallet including battery cells that are not determined to be non-defective and another pallet (step S305).

  On the other hand, when the difference between the voltage drop amount of the battery cells included in the small group and the median value is equal to or less than the predetermined value (step S303: Yes), the control unit sets the standard of the voltage drop amount of the battery cells included in the small group. It is determined whether or not the deviation is equal to or less than a predetermined value (step S304). That is, the control unit confirms that the non-defective products are collected to such an extent that a reliable result can be obtained as a quality determination test by looking at variations in the voltage drop amount of the small group. Thereby, the inspection result of the small group containing many defective products can be rejected. Note that the predetermined value in step S304 is different from the predetermined value in step S303.

  When the standard deviation is equal to or less than the predetermined value (step S304: Yes), it is determined that all the battery cells included in the small group are non-defective (step S310).

  On the other hand, when the standard deviation is larger than the predetermined value (step S304: No), the control unit determines that the inspection result in the small group cannot be adopted, and does not determine that all the battery cells included in the small group are non-defective products. That is, the control unit determines that all battery cells included in the small group are not good products. Then, the control unit forms a large group including a pallet that has not been determined to be non-defective and another pallet (step S305).

  As described above, when the difference between the voltage drop amount of the battery cell and the median value is larger than the predetermined value (step S303: No), or when the standard deviation is larger than the predetermined value (step S304: No), the small group is selected. A large group is formed. At this time, the control unit matches the other small groups (pallets) including the battery cells that have undergone the assembly process under the same conditions as the small group of battery cells to the small groups inspected in steps S302 to S304, and sets the large group. Form. In addition, the other small group matched with the small group used as the test object may be one, and plural may be sufficient as it.

  When the large group is formed, the control unit resets the quality determination of the battery cells included in the large group (step S306). Then, the pass / fail determination is performed on the large group in the same manner as steps S302 to S304 described above.

  First, the control unit determines whether or not the number of battery cells included in the large group is greater than or equal to a predetermined value (step S307). The predetermined value at this time is also the same value as in step S302.

  When the number of battery cells included in the large group is less than the predetermined value (step S307: No), it is determined that the inspection result of the large group has low reliability. Therefore, all the battery cells included in the large group are regarded as defective products (step S311).

  On the other hand, when the number of battery cells included in the large group is greater than or equal to a predetermined value (step S307: Yes), the control unit determines the amount of voltage drop and the amount of voltage drop in the second aging process of the battery cells included in the large group. The difference from the median is calculated. The median voltage drop means the median value of all the battery cells included in the large group. And a control part determines whether a difference is below a predetermined value (step S308). Note that the predetermined value in step S308 is the same value as the predetermined value in step S303.

  When the difference between the voltage drop amount and the median value of the battery cells included in the large group is larger than the predetermined value (step S308: No), these battery cells are determined as defective products because the voltage drop amount is abnormal. (Step S311).

  On the other hand, when the difference between the voltage drop amount of the battery cells included in the large group and the median value is equal to or less than the predetermined value (step S308: Yes), the control unit sets the standard of the voltage drop amount of the battery cells included in the large group. It is determined whether the deviation is equal to or less than a predetermined value (step S309). That is, the control unit confirms that non-defective products are collected to such an extent that a reliable result can be obtained as a pass / fail determination test by looking at variations in the voltage drop amount of the large group. Thereby, the inspection result of the large group containing many defective products can be rejected. Note that the predetermined value in step S309 is the same value as the predetermined value in step S304.

  When the standard deviation is equal to or smaller than the predetermined value (step S309: Yes), it is determined that all the battery cells included in the large group are non-defective (step S210).

  On the other hand, when the standard deviation is larger than the predetermined value (step S309: No), it is determined that all the battery cells included in the large group are defective, because the inspection result in the large group cannot be adopted.

  Thus, in the manufacturing method according to the present embodiment, the control unit performs the pass / fail determination of the small group, and when there is a battery cell that has not been determined to be non-defective, the small group and the other small groups Are combined to form a large group, and pass / fail judgment is again performed on the large group.

(Comparative example)
Here, the manufacturing method concerning a comparative example is demonstrated. The manufacturing method according to the comparative example performs pass / fail judgment using only a small group. That is, the pass / fail judgment is completed by the processing from step S301 to S304 in FIG.

  For example, consider a state where the measured values of the self-discharge amount (voltage drop amount) of the battery cells of each pallet are shown in FIG. Note that the vertical and horizontal axes in FIG. 7 are the same as those in the graph shown in FIG. In FIG. 7, the first to third pallets each constitute a small group 200. The battery cells included in the first pallet to the third pallet are actually all non-defective products.

  Similarly to the graph of FIG. 5, in the graph of FIG. 7, the battery cells in the Δ plot and the battery cells in the x plot are assumed to be assembled under different conditions. However, Δ plots are battery cells manufactured in the assembly process under the same conditions, and x plots are battery cells manufactured in the assembly process under the same conditions.

  First, in the manufacturing method according to the comparative example, the control unit determines whether or not the number of battery cells is equal to or greater than a predetermined value. For convenience of explanation, it is assumed that the number of battery cells included in the small group is equal to or greater than a predetermined value and satisfies the above condition.

  Next, the control unit calculates a median value of the voltage drop amounts of the battery cells included in the small group, and calculates a difference between the voltage drop amount and the median value of each battery cell. And it is determined whether the said difference is below a predetermined value. As is apparent from FIG. 7, when attention is paid to the second pallet, the Δ plot surrounded by a broken-line circle has a difference in the self-discharge amount from the x plot of the second pallet. Therefore, the difference between the self-discharge amount of these Δ plots and the median value becomes larger than a predetermined value. Therefore, among the battery cells included in the second pallet, the battery cells in the Δ plot surrounded by the broken-line circle are treated as defective products.

  In addition, even if no defective product is found in the comparison between the self-discharge amount of each battery cell and the median value, the standard deviation of the self-discharge amount of all the battery cells in the small group (second pallet) May be larger than a predetermined value. As a result, the entire small group is treated as a defective product.

  At this time, there are two possible causes for the difference between the voltage drop amount of the small group and the median value being greater than or equal to a predetermined value, or the standard deviation being greater than the predetermined value. The first is a case where defective battery cells are included in the first place. The second is a case where the voltage drop amount in the small group appears to vary because the battery cell manufacturing conditions are different. However, the battery cell determined to be defective for the second reason is actually a good product. For this reason, in the comparative example, a non-defective product is erroneously determined as a defective product.

  On the other hand, in the manufacturing method according to the present embodiment, the control unit combines the pallet and another pallet (small group) when the small group is not determined to be non-defective in the pass / fail determination of the small group. A large group is formed and a pass / fail judgment is made again.

  Specifically, the control unit includes the second pallet including battery cells that are not determined to be non-defective (Δ plots surrounded by broken-line circles) and the same assembly process as the battery cells that are not determined to be non-defective. Together with the first pallet including the manufactured battery cells, a large group is formed.

  First, the control unit determines whether or not the number of battery cells included in the large group is greater than or equal to a predetermined value. For convenience of explanation, it is assumed that the number of battery cells included in the large group is equal to or greater than a predetermined value and satisfies the above condition.

  Next, the control unit calculates the median voltage drop amount of the battery cells included in the large group (the first pallet and the second pallet), and calculates the difference between the voltage drop amount and the median value of each battery cell. calculate. Then, it is determined whether or not the difference is within a predetermined value. As shown in FIG. 7, since the first pallet is a Δ plot, the battery cells in the Δ plot of the second pallet that were not determined to be non-defective are combined with the battery cells manufactured in the same assembly process. It is possible to perform pass / fail judgment. Therefore, the difference between the voltage drop amount of the battery cells included in the large group 100 (first pallet and second pallet) and the median value in the large group 100 (first pallet and second pallet) are all predetermined. Below the value.

  Finally, the control unit determines whether the standard deviation of the self-discharge amount of the battery cells included in the large group is equal to or less than a predetermined value. As described above, since the battery cell of the first pallet is manufactured in the assembly process under the same conditions as the battery cell of the Δ plot of the second pallet, only a small group (second pallet) is used. The standard deviation calculated using the large group (the first pallet and the second pallet) is smaller than the standard deviation calculated in this way. For this reason, the standard deviation falls within a predetermined value. Therefore, battery cells that are not determined to be non-defective in the small group determination are all determined to be non-defective in the large group (first pallet and second pallet).

  As described above, according to the method for manufacturing a secondary battery according to the present embodiment, small groups (pallets) having the same conditions for the first aging process and the cooling process are formed. For the small group, a median value (first determination criterion) is set using the measurement result of the voltage drop amount of the battery cell in the second aging process. And the quality determination of the battery cell contained in a small group is performed based on the comparison result of the said median and the voltage drop amount of each battery cell. At this time, when the small group includes battery cells that are not determined to be non-defective, the small group and other small cells including battery cells that are manufactured in the assembly process under the same conditions as the battery cells that are not determined to be non-defective. Together with the group (pallet), a large group is formed. And about a large group, a median value (2nd criterion) is set using the measurement result of the voltage drop amount of the battery cell in a 2nd aging process. And the quality determination of the battery cell contained in a large group is performed based on the comparison result of the said median and the amount of voltage drops of each battery cell.

  Thereby, about the battery cell which was not determined to be non-defective in the quality determination in the small group, it can be determined as non-defective in the large group. Therefore, even if a battery cell that is a non-defective product is erroneously determined not to be a non-defective product due to a difference in assembly process conditions, it can be determined as a non-defective product by a large group quality determination. In other words, the battery cells manufactured by the assembly process under the same conditions for the battery cells that are not determined to be non-defective due to the fact that the conditions of the assembly process are the same but are divided into a plurality of pallets. Form a large group and inspect again. Thus, the inspection can be performed while excluding the voltage drop caused by the difference in the conditions of the assembly process. That is, the accuracy of pass / fail judgment can be improved.

  In addition, for the small group, a standard deviation (first determination criterion) is set using the measurement result of the voltage drop amount of the battery cell in the second aging process, and pass / fail determination is performed using the standard deviation. And in the quality determination using the standard deviation of a small group, when it is not determined to be a non-defective product, the standard deviation (the second deviation) is measured for the large group using the measurement result of the voltage drop amount of the battery cell in the second aging process. Judgment criteria) is set, and pass / fail judgment is performed using the standard deviation. As a result, even when the voltage drop amount varies in the small group inspection, the variation in the voltage drop amount in the large group is suppressed by combining with other small groups including battery cells in the same condition in the assembly process. Can do. As a result, a pallet that is not determined to be non-defective in the quality determination in the small group can be determined as non-defective in the quality determination in the large group.

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention. For example, in the above embodiment, the small group is described using one pallet, but the present invention is not limited to this. If the conditions of the first aging process and the cooling process are the same, a plurality of pallets may be made into a small group. The smallest structural unit of the small group is a pallet. For example, the small group is not formed by combining one pallet and one battery cell.

  In the above embodiment, the median value of the voltage drop amount and the standard deviation of the voltage drop amount are used as the first determination criterion and the second determination criterion. However, the present invention is not limited to this. Any value that changes by changing the grouping and that indicates the distribution (variation) of the voltage drop in the group may be used. For example, the first determination criterion and the second determination criterion may be an average value or variance of the voltage drop amount, or a value derived using a scatter diagram or histogram of the measured voltage drop amount. It may be.

  Furthermore, after the inspection in the large group, the small group inspection may be performed, and then the large group inspection may be performed again. Similarly, in the reverse case, after the inspection in the small group, the inspection in the large group may be performed, and then the inspection in the small group may be performed again. That is, the first determination criterion set using the measurement result of the voltage drop amount in the large group (small group) and the second determination criterion set using the measurement result of the voltage drop amount in the small group (large group). What is necessary is just to perform the quality determination of a battery cell using determination criteria.

  Moreover, the arbitrary processes included in the flowcharts of FIGS. 2 and 6 described above can be realized by causing a CPU (Central Processing Unit) to execute a computer program. Specifically, if the data of the measurement result of the voltage drop amount of each of the plurality of battery cells to be inspected can be acquired, the CPU forms a group and the batteries in the group based on a program stored in advance in a memory (not shown). The number of cells can be determined, the median can be calculated, the difference from the median can be calculated, the standard deviation can be calculated, and the quality can be determined. In addition, in the process of forming a group, information regarding the manufacturing process conditions of each battery cell is required, and these pieces of information are assumed to be associated with each battery cell in advance in the pass / fail judgment stage. More specifically, information on manufacturing process conditions (manufacturing lot, manufacturing location, temperature of the first aging process, time and date / time, temperature of cooling process, time and date / time, etc.) includes the voltage drop amount of each battery cell in advance. Assume that they are stored in a memory (not shown) in association with the measurement results. Furthermore, not only when the functions of the above-described embodiment are realized by executing a program that realizes the above-described processing by the computer, but this program is not limited to an OS (Operating System) or a computer running on the computer. A case where the above-described processing is realized in cooperation with application software is also included in the embodiment of the present invention.

100 large group 200 small group

Claims (7)

A small group including a plurality of battery cells in which the conditions of the first aging step and the cooling step are the same, and a large group of the plurality of small groups having different conditions of the first aging step and the cooling step; Form the
For one of the small group and the large group, a first determination criterion is set using a value indicating a distribution of the voltage drop amount of the battery cell in a second aging step, and the first determination Based on the criteria, the quality determination of the battery cells included in the one group,
When the battery cell that is not determined to be non-defective is included in the one group, the voltage drop amount of the battery cell in the second aging step is determined for the other group that includes the battery cell that is not determined to be non-defective. A method for manufacturing a secondary battery, wherein a second determination criterion is set using a value indicating a distribution, and the quality of the battery cell included in the other group is determined based on the second determination criterion.   When the battery cell that is not determined to be non-defective in the pass / fail determination based on the first determination criterion is not determined to be non-defective in the pass / fail determination based on the second determination criterion, the battery cell is determined to be defective. The manufacturing method of the secondary battery of Claim 1 to determine. Calculating a median value of the voltage drops of the plurality of battery cells in the large group;
Based on the median, perform a pass / fail determination of the battery cells included in the large group,
When the battery cell that is not determined to be non-defective is included in the large group, the median value is calculated for each of the small groups including the battery cell that is not determined to be non-defective, and the small value is calculated based on the median value. The method for manufacturing a secondary battery according to claim 1, wherein the quality of the battery cells included in the group is determined. Calculating a median value of the voltage drops of the plurality of battery cells in the small group;
Based on the median, perform a pass / fail determination of the battery cells included in the small group,
When the battery cells that are not determined to be non-defective items are included in the small group, the battery cells that are not determined to be non-defective products and the battery cells that have the same conditions for the battery cell assembly process are included. Together with a small group to form the large group,
The method for manufacturing a secondary battery according to claim 1, wherein the median value in the large group is calculated, and the quality of the battery cells included in the large group is determined based on the median value. When the battery cell that is not determined to be non-defective based on the median value is not included in the one group, based on a standard deviation of the voltage drop amounts of the plurality of battery cells included in the one group. , Perform pass / fail judgment of the battery cells included in the one group,
In the quality determination based on the standard deviation, when the battery cell that is not determined to be non-defective is included in the one group, the battery cell included in the other group based on the median value in the other group The manufacturing method of the secondary battery of Claim 3 or 4 which performs quality determination. When the battery cell that is not determined to be non-defective based on the median value is not included in the other group, based on a standard deviation of the voltage drop amounts of the plurality of battery cells included in the other group. , Perform pass / fail judgment of the battery cells included in the other group,
6. In the quality determination based on the standard deviation, when the battery cell that is not determined as a non-defective product is included in the other group, the battery cell included in the other group is determined as a defective product. A method for manufacturing a secondary battery.   The said large group is a manufacturing method of the secondary battery as described in any one of Claims 1-6 containing at least 1 the said small group in which the said battery cell from which the conditions of a battery cell assembly process differ is contained.

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