Battery manufacturing method and battery inspection method

Abstract

Improved accuracy in detecting battery defects. [Solution] The battery manufacturing method includes the steps of performing an aging process on multiple batteries, obtaining the terminal voltages of the multiple batteries before the aging process, obtaining the terminal voltages of the multiple batteries after the aging process, and determining whether each of the multiple batteries is defective or not. In the determination step, a threshold is set by subtracting at least one terminal voltage difference from the terminal voltage difference before and after the aging process for each of the multiple batteries.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a battery and a method for inspecting a battery.

Background Art

[0002] Japanese Unexamined Patent Application Publication No. 2006-253027 discloses a method for manufacturing a secondary battery, which includes determining a defect of a secondary battery and re-determining a defect of other secondary batteries excluding the secondary battery determined to be defective.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When manufacturing a battery, a defect of the battery may be determined based on the electrical characteristics of a plurality of batteries.

Means for Solving the Problems

[0005] The battery manufacturing method disclosed herein includes a step of performing an aging process on a plurality of batteries, a step of obtaining the inter-terminal voltage of the plurality of batteries before the aging process, a step of obtaining the inter-terminal voltage of the plurality of batteries after the aging process, and a step of determining whether each of the plurality of batteries is defective. In the determination step, a threshold value is set by excluding at least one inter-terminal voltage difference from the inter-terminal voltage differences before and after the aging process of each of the plurality of batteries. According to such a battery manufacturing method, the accuracy in determining a defect of the battery is improved.

Brief Description of the Drawings

[0007] Hereinafter, an embodiment of the technology disclosed herein will be described with reference to the drawings. The embodiment described herein is, of course, not intended to particularly limit the present invention. Each drawing is schematic and does not necessarily reflect the actual object. Furthermore, components and parts that perform the same function are appropriately denoted by the same reference numerals, and redundant descriptions are omitted as appropriate. In this specification, notations such as "X~Y" indicating a numerical range mean "X or greater and Y or less" unless otherwise specified.

[0008] Figure 1 is a flowchart of a battery manufacturing method. As shown in Figure 1, the battery manufacturing method includes a step S10 for preparing multiple batteries and a step S20 for determining battery defects. The battery manufacturing method may include other steps. The battery manufacturing method will be explained below using a lithium-ion secondary battery as an example. Note that the technology disclosed herein is not limited to the manufacturing method of lithium-ion secondary batteries, but is also applicable to other known batteries (e.g., sodium-ion secondary batteries).

[0009] <Step S10: Preparing multiple batteries> In step S10, which involves preparing multiple batteries, multiple batteries 1 are prepared according to a known method. As shown in Figure 1, step S10, which involves preparing multiple batteries, includes a battery assembly preparation step S11 and an initial charging step S12.

[0010] <Battery assembly preparation process S11> In the battery assembly preparation step S11, the battery assembly 1 is prepared before initial charging. Figure 2 is a schematic cross-sectional view showing the internal structure of the battery 1. Figure 3 is a schematic diagram of the electrode body 20. In the battery assembly preparation step S11, the case 10, the electrode body 20, and the non-aqueous electrolyte (not shown) are prepared.

[0011] As shown in Figure 2, the case 10 is a rectangular container. The case 10 is made of a metal material with a certain strength (aluminum, aluminum alloy, etc.). The case 10 comprises a case body 12 having an opening at the top and a lid 14 that closes the opening. The case 10 contains an electrode body 20 and an electrolyte. The lid 14 is provided with an injection port 15 into which the electrolyte is poured. The lid 14 is provided with a gas discharge valve 19. The positive electrode terminal 16 and the negative electrode terminal 18 are attached to the lid 14 via insulating members 16a and 18a. The positive electrode terminal 16 and the negative electrode terminal 18 are connected to the electrode body 20 via current collectors 26 and 28 provided inside the case 10, respectively. Aluminum, aluminum alloy, etc. may be used for the positive electrode terminal 16. Copper, copper alloy, etc. may be used for the negative electrode terminal 18.

[0012] The electrode body 20 is the power generation element of the battery 1. As shown in Figure 3, the electrode body 20 comprises a positive electrode plate 30, a negative electrode plate 40, and a separator 50. In this embodiment, the electrode body 20 is a wound electrode body. The wound electrode body is manufactured by stacking the positive electrode plate 30, the negative electrode plate 40, and the separator 50 and winding them together. The structure of the electrode body 20 is not particularly limited and may be other conventionally known structures (such as a laminated electrode body).

[0013] The positive electrode plate 30 includes a positive electrode core 32 which is a conductive metal foil, and a positive electrode active material layer 34 formed on the surface of the positive electrode core 32. Aluminum or the like is used for the positive electrode core 32. The positive electrode active material layer 34 contains a positive electrode active material, a conductive material, a binder, and the like. As the positive electrode active material, for example, a lithium transition metal composite oxide can be used. As the conductive material, carbon materials such as acetylene black and graphite can be used. As the binder, resin materials such as polyvinylidene fluoride (PVdF) can be used.

[0014] The negative electrode plate 40 includes a negative electrode core 42 which is a conductive metal foil, and a negative electrode active material layer 44 provided on the surface of the negative electrode core 42. Copper or the like is used for the negative electrode core 42. Further, the negative electrode active material layer 44 contains a negative electrode active material, a binder, a thickener, and the like. As the negative electrode active material, carbon materials such as graphite, hard carbon, and soft carbon can be used. As the binder, resin materials such as styrene butadiene rubber (SBR) can be used. As the thickener, resin materials such as carboxymethyl cellulose (CMC) can be used.

[0015] The separator 50 is an insulating sheet interposed between the positive electrode plate 30 and the negative electrode plate 40. As the separator 50, for example, resin materials such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide can be used. A heat-resistant layer containing an inorganic filler may be formed on the surface of the separator 50.

[0016] The electrolytic solution contains a non-aqueous solvent and a supporting salt. As the non-aqueous solvent, for example, ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), etc. can be used. As the supporting salt, various lithium salts can be used, for example, LiPF6 etc. can be used.

[0017] In the battery assembly preparation step S11, the electrode body 20 is accommodated in the prepared case 10, and the battery assembly 1 is prepared by injecting an electrolytic solution (see FIG. 2). After injecting the electrolytic solution, the injection port 15 is sealed by a sealing member 15a. In the battery assembly preparation step S11, a plurality of battery assemblies 1 are prepared.

[0018] 〈Initial charging step S12〉 In the initial charging step S12, initial charging is performed on a plurality of battery assemblies 1. In the initial charging step S12, the battery assembly 1 is charged under predetermined conditions until it reaches a predetermined voltage value. The initial charging can be performed by a known method. Although not particularly limited, the voltage value can be selected to be about 10% to 90% with respect to the SOC (State of Charge) at full charge. Although not particularly limited, the initial charging can be performed, for example, at a charging rate of about 0.05C to 10C in a normal temperature environment of about 25°C (for example, about 20°C to 30°C). Note that the voltage value, charging conditions, etc. of the initial charging are set according to the type of battery, etc. In the initial charging step S12, initial charging is performed individually on each of the plurality of battery assemblies 1.

[0019] By initially charging a plurality of battery assemblies 1, a plurality of batteries 1 are prepared. When a plurality of batteries 1 are prepared, subsequently, it is determined whether any of the plurality of batteries 1 has a defect. Note that the initial charging step S12 may include a step of repeatedly charging and discharging the battery 1 under predetermined conditions. By such an initial charging step S12, the battery 1 is activated.

[0020] 〈Step S20 for determining battery defects〉 The step S20 for determining battery defects is performed based on the inter-terminal voltage of the battery 1 before and after aging. As shown in FIG. 1, the step S20 for determining battery defects includes a first inter-terminal voltage acquisition step S21, an aging treatment step S22, a second inter-terminal voltage acquisition step S23, and a determination step S30.

[0021] 〈First inter-terminal voltage acquisition step S21〉 In the first terminal voltage acquisition step S21, the terminal voltages (first terminal voltages) V1 of multiple batteries 1 before aging treatment are acquired. At this time, the multiple batteries 1 are charged to a predetermined voltage (or a voltage equivalent to a predetermined SOC). The voltage and SOC of the batteries 1 in the first terminal voltage acquisition step S21 are not particularly limited. The batteries 1 may be charged to a predetermined voltage in the initial charging step S12. The voltage of the batteries 1 may be adjusted to a predetermined voltage after the initial charging step S12.

[0022] The first terminal voltage V1 can be measured by a voltage measuring device (not shown). The positive terminal 16 and negative terminal 18 of the battery 1 are connected to the positive and negative terminals of the voltage measuring device, respectively, and the first terminal voltage V1 can be measured. If, in the first terminal voltage acquisition step S21, any battery has a first terminal voltage V1 that falls outside a predetermined range, that battery may be excluded as defective. The excluded battery 1 will also be excluded from subsequent steps. After the first terminal voltage acquisition step S21, the multiple batteries 1 are subjected to aging treatment.

[0023] <Aging process S22> In aging process S22, aging is performed on multiple batteries 1. In aging process S22, multiple batteries 1 are housed in an aging device (not shown) and placed in an environment with a predetermined temperature for a predetermined period of time. Multiple batteries 1 may be aged in one aging device or in different aging devices. The aging conditions are set according to the type of battery, etc., and are not particularly limited. The aging temperature may be set to a constant temperature selected from approximately 20°C to 75°C. The aging period may be set to approximately 5 to 15 days. After the aging process, the terminal voltage of the batteries 1 is obtained again.

[0024] <Second terminal voltage acquisition process S23> In the second terminal voltage acquisition step S23, the terminal voltage (second terminal voltage) V2 of multiple batteries 1 after aging treatment is acquired. The method for acquiring the second terminal voltage V2 may be the same as the method for acquiring the first terminal voltage V1. If, in the second terminal voltage acquisition step S23, any battery has a second terminal voltage V2 that falls outside a predetermined range, that battery may be excluded as defective. The excluded battery 1 will also be excluded from subsequent steps.

[0025] After the aging process, the terminal voltages of multiple batteries 1 are lower than the terminal voltages before the aging process. In other words, the second terminal voltage V2 is lower than the first terminal voltage V1. Based on the first terminal voltage V1 and the second terminal voltage V2, it is determined whether each of the multiple batteries 1 is defective or not.

[0026] <Judgment step S30> In the determination step S30, it is determined whether each of the multiple batteries 1 is defective based on the terminal voltage difference V1-V2(ΔV) before and after the aging process for each of the multiple batteries 1. Figure 4 is a flowchart of the determination step S30. As shown in Figure 4, the determination step S30 includes a step S31 to calculate the terminal voltage difference for the multiple batteries, a step S32 to remove at least one terminal voltage difference, a step S33 to calculate the average value of the terminal voltage differences, a step S34 to calculate the standard deviation of the terminal voltage differences, a step S35 to determine if a battery is defective based on a threshold, a step S36 to remove the battery determined to be defective, and a step S37 to determine if the defect determination has been repeated a predetermined number of times. Here, N batteries 1 are the targets of determination step S30. Here, N is an integer. The number of batteries to be determined is not particularly limited.

[0027] Figures 5 and 6 are graphs showing the terminal voltage difference ΔV after aging. In Figures 5 and 6, the open circuit voltage (OCV) and terminal voltage difference ΔV after aging are shown for each battery 1 for which the terminal voltage difference ΔV was calculated. In Figure 5, all terminal voltage differences ΔV for multiple batteries 1 are shown as circles. Figures 7 and 8 are graphs showing the terminal voltage difference ΔV after excluding defective batteries 1. Figure 7 shows the graph showing the terminal voltage difference ΔV after the first exclusion of defective batteries 1. Figure 8 shows the graph showing the terminal voltage difference ΔV after the second exclusion of defective batteries 1. In Figures 5-8, the average value ΔVa of the terminal voltage difference ΔV is shown as a dashed line, and the threshold Th based on the average value ΔVa is shown as a dashed line. In Figures 6 to 8, among the terminal voltage differences ΔV of multiple batteries 1, the terminal voltage differences ΔV that are excluded in step S32 are shown as triangles, and the terminal voltage differences ΔV that are not excluded in step S32 are shown as circles.

[0028] <Step S31: Calculate the voltage difference between terminals for battery 1> In step S31, which calculates the terminal voltage difference for battery 1, the terminal voltage difference ΔV is calculated from the difference between the first terminal voltage V1 and the second terminal voltage V2. Here, the terminal voltage difference ΔV is calculated for each of the multiple batteries 1. In this embodiment, the terminal voltage difference ΔV is calculated for N batteries 1 (see Figure 5). The terminal voltage difference ΔV is the value obtained by dividing the difference between the first terminal voltage V1 and the second terminal voltage V2 by the aging period (number of days). However, the terminal voltage difference ΔV is not necessarily limited to this calculation method. For example, the terminal voltage difference ΔV may be the difference between the first terminal voltage V1 and the second terminal voltage V2, rather than the value obtained by dividing by the aging period.

[0029] <Step S32: Remove the voltage difference between at least one terminal> In step S32, which excludes at least one terminal voltage difference, at least one terminal voltage difference ΔV calculated for each of the multiple (in this embodiment, N) batteries 1 that are subject to evaluation is excluded from subsequent calculations (in this embodiment, calculation of the mean (S33) and calculation of the standard deviation (S34)).

[0030] In the embodiment shown in Figure 5, the average value of the terminal voltage difference ΔV (mV / Day) of the multiple batteries 1 is 0.0272, and the standard deviation is 0.0390. As shown in Figure 6, the maximum value ΔVmax and minimum value ΔVmin are excluded from the terminal voltage difference ΔV of the multiple batteries 1. Here, the maximum and minimum terminal voltage differences ΔV of the N batteries 1 are excluded. A threshold Th for determining whether a battery 1 is defective is set based on the terminal voltage differences ΔV of the remaining N-2 batteries 1.

[0031] <Step S33: Calculation of the average value of the voltage difference between terminals> In step S33, which calculates the average value of the terminal voltage difference, the average value ΔV of the terminal voltage difference ΔV of battery 1 is calculated. Here, the average value of the terminal voltage difference ΔV of N-2 batteries 1, excluding the maximum value ΔVmax and the minimum value ΔVmin, is calculated. In this embodiment, the average value ΔVa is 0.0224.

[0032] <Step S34: Calculation of the standard deviation of the voltage difference between terminals> In step S34, which calculates the standard deviation of the terminal voltage difference, the standard deviation σ of the terminal voltage difference ΔV of battery 1 is calculated. Here, similar to step S33, which calculates the average value, the standard deviation σ of the terminal voltage difference ΔV of N-2 batteries 1, excluding the maximum value ΔVmax and the minimum value ΔVmin, is calculated. In this embodiment, the standard deviation σ is 0.0257.

[0033] <Step S35 to determine if battery 1 is defective based on a threshold> In step S35, which determines whether a battery 1 is defective based on a threshold, it is determined whether a battery 1 is defective based on a preset threshold Th. In this embodiment, the threshold Th is set excluding at least one terminal voltage difference ΔV (maximum value ΔVmax and minimum value ΔVmin). Here, it is determined whether all N batteries 1 to be evaluated are defective or not.

[0034] The threshold Th is set based on the standard deviation σ calculated in step S34, which calculates the standard deviation. The threshold Th can be set to a value (nσ) obtained by multiplying the standard deviation σ by a predetermined value n. The value n can be predetermined by mass production tests or the like, depending on the type of battery. In this embodiment, the threshold Th is set to three times the standard deviation σ (3σ). However, the threshold Th is not limited to this value.

[0035] Based on the threshold Th, it is determined whether all N batteries 1 are defective or not. Here, for each battery 1, it is determined whether the difference between the terminal voltage difference ΔV and the average value ΔVa calculated in step S33 is less than or equal to the threshold Th. As shown in Figure 6, for N-2 of the N batteries 1, the difference between the terminal voltage difference ΔV and the average value ΔVa is less than or equal to the threshold Th. For the battery 1 with the highest terminal voltage difference ΔV and the battery 1 with the second highest terminal voltage difference ΔV, the difference between the terminal voltage difference ΔV and the average value ΔVa is greater than the threshold Th. The battery 1 with the highest terminal voltage difference ΔV and the battery 1 with the second highest terminal voltage difference ΔV are determined to be defective. If it is determined that there are defective batteries 1 (NO), the process proceeds to step S36.

[0036] <Process S36: Removal of batteries determined to be defective> In step S36, which involves removing batteries that have been determined to be defective, two batteries 1 that have been determined to be defective are removed from the evaluation target out of the N batteries 1 that are being evaluated. After removing these two batteries 1 from the evaluation target, the process returns to step S32, which involves removing at least one terminal voltage difference.

[0037] <Step S32: Remove the voltage difference between at least one terminal> In step S32, which removes at least one terminal voltage difference for the second time, at least one terminal voltage difference ΔV calculated for each of the multiple batteries 1 is excluded from subsequent calculations, similar to the first step S32. In step S36, two batteries 1 are excluded from the judgment. Here, the maximum and minimum terminal voltage differences ΔV are excluded from the N-2 terminal voltage differences ΔV, similar to the first step S32. A threshold Th for determining whether a battery 1 is defective is set based on the terminal voltage differences ΔV of the remaining N-4 batteries 1.

[0038] As shown in Figure 7, the maximum value ΔVmax and minimum value ΔVmin are excluded from the terminal voltage difference ΔV of the multiple batteries 1. Here, the maximum and minimum terminal voltage differences ΔV of the N-2 batteries 1 are excluded. Based on the terminal voltage differences ΔV of the remaining N-4 batteries 1, the threshold Th for determining the defects of the batteries 1 is set again. Note that the minimum value ΔVmin is the same as the one excluded in the first step S32.

[0039] <Step S33: Calculation of the average value of the voltage difference between terminals> In step S33, which calculates the average value of the second terminal voltage difference, the average value of the terminal voltage difference ΔV of N-4 batteries 1, excluding the maximum value ΔVmax and minimum value ΔVmin, is calculated. In this embodiment, the average value ΔVa is 0.0171.

[0040] <Step S34: Calculation of the standard deviation of the voltage difference between terminals> In the second step, S34, which calculates the standard deviation of the terminal voltage difference, the standard deviation σ of the terminal voltage difference ΔV of N-4 batteries 1, excluding the maximum value ΔVmax and minimum value ΔVmin, is calculated, similar to the step S33 which calculates the average value. In this embodiment, the standard deviation σ is 0.0060.

[0041] <Step S35 to determine if battery 1 is defective based on a threshold> In step S35, where the defect of battery 1 is determined based on the second threshold, the maximum value ΔVmax and minimum value ΔVmin are excluded from the setting, similar to the first step S35. Here, the defect status of N-2 batteries 1 is determined, excluding the two batteries that were determined to be defective in the first step S35.

[0042] The threshold Th is set based on the standard deviation σ calculated in step S34, the same as in the first step S35. The threshold Th is set to three times the standard deviation σ (3σ), the same as in the first step S35. The threshold Th is not limited to this value.

[0043] Based on the threshold Th, it is determined whether or not each of the N-2 batteries 1 is defective. As shown in Figure 7, for N-3 of the N-2 batteries 1, the difference between the terminal voltage difference ΔV and the average value ΔVa is less than or equal to the threshold Th. For the battery 1 with the highest terminal voltage difference ΔV, the difference between the terminal voltage difference ΔV and the average value ΔVa is greater than the threshold Th. The battery 1 with the highest terminal voltage difference ΔV is determined to be defective. If it is determined that there is a defective battery 1 (NO), the process proceeds back to step S36.

[0044] <Process S36: Removal of batteries determined to be defective> In step S36, which involves removing batteries that have been determined to be defective, one more battery 1 that has been determined to be defective is removed from the evaluation process from the N-2 batteries 1 remaining after removing the two batteries that have already been removed. With one battery 1 removed, the remaining N-3 batteries 1 are subject to evaluation. The process then returns to step S32, which involves removing at least one terminal voltage difference.

[0045] <Step S32: Remove the voltage difference between at least one terminal> In the third step S32, the same processing as in the first and second steps S32 is performed. Of the N-3 terminal voltage differences ΔV, the maximum and minimum terminal voltage differences ΔV are removed. Based on the remaining N-5 terminal voltage differences ΔV of the batteries 1, a threshold Th for determining the defects of batteries 1 is set. As shown in Figure 8, of the terminal voltage differences ΔV of the multiple batteries 1, the maximum value ΔVmax and minimum value ΔVmin are removed. Here, of the N-3 terminal voltage differences ΔV of the batteries 1, the maximum and minimum terminal voltage differences ΔV are removed. Based on the remaining N-5 terminal voltage differences ΔV of the batteries 1, a threshold Th for determining the defects of batteries 1 is set again. Note that the minimum value ΔVmin is the same as the one removed in the first step S32.

[0046] <Step S33 to calculate the average value of the voltage difference between terminals, Step S34 to calculate the standard deviation of the voltage difference between terminals> In step S33, the third step in calculating the average value of the terminal voltage difference, the average value of the terminal voltage difference ΔV of N-5 batteries 1, excluding the maximum value ΔVmax and minimum value ΔVmin, is calculated. In this embodiment, the average value ΔVa is 0.0167. In step S34, the third step in calculating the standard deviation of the terminal voltage difference, the standard deviation σ of the terminal voltage difference ΔV of N-5 batteries 1, excluding the maximum value ΔVmax and minimum value ΔVmin, is calculated, similar to step S33 in calculating the average value. In this embodiment, the standard deviation σ is 0.0055.

[0047] <Step S35 to determine if battery 1 is defective based on a threshold> In step S35, which determines whether battery 1 is defective based on the third threshold, the maximum value ΔVmax and minimum value ΔVmin are excluded from the setting, similar to the first and second steps S35. Here, the defect status of N-3 batteries 1 is determined, excluding the one battery that was determined to be defective in the second step S35. The threshold Th is set to three times the standard deviation σ (3σ), similar to the first and second steps S35.

[0048] Based on the threshold Th, it is determined whether or not each of the N-3 batteries 1 is defective. As shown in Figure 8, for all N-3 batteries 1 being evaluated, the difference between the terminal voltage difference ΔV and the average value ΔVa was less than or equal to the threshold Th. If it is determined that there are no defective batteries 1 (YES), the process proceeds to step S37.

[0049] <Step S37: Determining whether the defect determination has been repeated a predetermined number of times> In step S37, which determines whether the defect determination has been repeated a predetermined number of times, it is determined whether the determination in step S35 has reached the predetermined number of times. Although not particularly limited, the number of determinations in step S35 can be set to around 5 to 10 times. In this case, the number of determinations in step S35 is 3, so it is determined that the predetermined number has not been reached (NO), and the process returns to step S32.

[0050] The above-described steps S32 to S37 are repeated, and in step S37, if it is determined that the number of times a defect has been determined has reached a predetermined number (YES), the determination step S30 ends. In other words, the determination of whether each of the multiple batteries 1 is defective or not is completed based on the voltage difference ΔV between the terminals of each of the multiple batteries 1 before and after the aging process. In the determination step S30, out of the N batteries 1 to be determined, 3 batteries 1 were determined to be defective.

[0051] The following describes a case where step S32, which removes at least one terminal voltage difference from the judgment step S30 described above, is not performed. Figure 9 is a graph showing the terminal voltage difference ΔV after the removal of the defective battery 1, according to another embodiment.

[0052] As described above, in the embodiment shown in Figure 5, the average value ΔVa of the terminal voltage difference ΔV of the N batteries 1 is 0.0272, and the standard deviation σ is 0.0390. If step S32 is not performed, as shown in Figure 5, the battery 1 with the highest terminal voltage difference ΔV and the battery 1 with the second highest terminal voltage difference ΔV among the N batteries 1 to be evaluated are determined to be defective. The two batteries 1 determined to be defective are excluded from the evaluation.

[0053] The average value ΔVa of the terminal voltage difference ΔV for the remaining N-2 batteries 1 is 0.0175, and the standard deviation σ is 0.0073. If step S32 is not performed, as shown in Figure 9, the difference between the terminal voltage difference ΔV and the average value ΔVa was less than or equal to the threshold Th for all N-2 batteries 1 to be judged. If it is determined that there are no defective batteries 1 and the number of judgments reaches a predetermined number, the judgment process ends.

[0054] In the embodiment shown in Figure 9, the terminal voltage difference ΔV (shown as a square in Figure 9) of one of the N-2 batteries 1 being evaluated is significantly larger than the terminal voltage differences ΔV of the other N-3 batteries 1. The terminal voltage difference ΔV of this battery 1 is 2.91 times higher than the average value by a standard deviation. The terminal voltage difference ΔV of this battery 1 is an extremely large value (a so-called outlier) compared to the terminal voltage differences ΔV of the other N-4 batteries 1. In the inventor's knowledge, if the deviation is large compared to the terminal voltage differences ΔV of the other batteries 1, there is a possibility that the battery 1 has a defect such as a minute short circuit. If the terminal voltage difference ΔV of an outlier that may have a defect is included in the calculation of the threshold Th, it will be difficult to set the threshold Th appropriately due to the outlier terminal voltage difference ΔV. For example, if the defect of a battery 1 is determined based on the average value ΔVa and standard deviation σ of the terminal voltage differences ΔV of multiple batteries 1, the standard deviation σ will be large, and the threshold Th may be set to be wide. In this case, during the battery failure detection process (step S35 in this embodiment), it becomes less likely that a battery 1 that may have a defect will be judged as defective. In order to judge such a battery 1 as defective, it may be considered to set the threshold Th strictly. For example, when setting the threshold Th by multiplying the standard deviation σ by the value n, a small value for n may be selected. However, if the threshold Th is set strictly, there is a concern that even batteries 1 that do not have a defect will be judged as defective.

[0055] In the embodiment described above, the battery manufacturing method includes the steps of: obtaining the terminal voltage V1 of multiple batteries 1 before aging treatment (step S21); performing aging treatment on multiple batteries 1 (step S22); obtaining the terminal voltage V2 of multiple batteries 1 after aging treatment (step S23); and determining whether each of the multiple batteries 1 is defective or not (step S30). In the step of determining whether each of the multiple batteries 1 is defective or not, a threshold Th is set by excluding at least one terminal voltage difference ΔV from the terminal voltage difference ΔV of each of the multiple batteries 1 before and after aging treatment. In this manufacturing method, when setting the threshold Th, it is possible to set the threshold Th while excluding terminal voltage differences ΔV that have a large deviation compared to the terminal voltage differences ΔV of other batteries 1. This prevents the threshold Th (standard deviation σ in this embodiment) from being set too broadly by terminal voltage differences ΔV with a large deviation. As a result, the threshold Th is more likely to be set appropriately. By appropriately setting the threshold Th, batteries 1 with outlier terminal voltage differences ΔV compared to other batteries 1 (batteries 1 that may have defects such as minute short circuits) are more easily identified as defective. As a result, the accuracy of identifying defective batteries 1 is improved.

[0056] In the embodiment described above, at least one terminal voltage difference ΔV is the maximum value ΔVmax and minimum value ΔVmin among the terminal voltage differences ΔV of the multiple batteries 1. When the maximum value ΔVmax and minimum value ΔVmin are excluded from the terminal voltage differences ΔV, terminal voltage differences ΔV with large deviations are more likely to be excluded when setting the threshold Th. Also, when a battery 1 with an extremely large terminal voltage difference ΔV is included compared to other batteries 1, or when a battery 1 with an extremely small terminal voltage difference ΔV is included, terminal voltage differences ΔV with large deviations are more likely to be excluded. As a result, the threshold Th is more likely to be set appropriately.

[0057] In the embodiment described above, the maximum value ΔVmax and minimum value ΔVmin of the terminal voltage difference ΔV are excluded. However, the terminal voltage differences ΔV of multiple batteries 1 may be excluded so that the maximum value ΔVmax and minimum value ΔVmin are included in ΔV. For example, the maximum value ΔVmax and the second highest value may be excluded from the multiple terminal voltage differences ΔV. The minimum value ΔVmin and the second lowest value may also be excluded from the multiple terminal voltage differences ΔV. Three or more terminal voltage differences ΔV may be excluded.

[0058] If the failure rate of battery 1 is known in advance, the number of terminal voltage differences ΔV to be excluded may be determined based on that rate (failure rate). This makes it easier to appropriately exclude terminal voltage differences ΔV with large deviations, and makes it easier to set the threshold Th appropriately. The number of terminal voltage differences ΔV to be excluded may be set to, for example, the number of batteries 1 to be judged multiplied by the failure rate. The failure rate may be obtained, for example, from mass production tests, mass production results, etc.

[0059] In the embodiment described above, step S20 for determining a battery defect includes excluding the battery 1 determined to be defective from the plurality of batteries 1 (step S36). Furthermore, step S20 for determining a battery defect includes setting a threshold Th based on the standard deviation σ calculated by further excluding at least one terminal voltage difference ΔV from the terminal voltage difference ΔV of the plurality of batteries 1 excluding the battery 1 determined to be defective, and repeating the process of determining which battery is defective (steps S35, S36). Since the threshold Th is set again with the battery 1 determined to be defective excluded in advance, the threshold Th is more likely to be set appropriately in stages. As a result, the threshold Th is more likely to be set appropriately.

[0060] In the embodiment described above, there are N batteries 1 to be judged. Preferably, the number of batteries 1 to be judged is 7 or more. This makes it easier to appropriately set the threshold Th for determining the defect of a battery 1 using the method described above. Note that the number of batteries 1 to be judged is not limited to the number described above.

[0061] In the embodiments described above, the threshold Th is set based on the standard deviation σ. However, the embodiment is not limited to this form, and the threshold Th may be a value predetermined by mass production tests, mass production results, or the degree of minor short circuits that should be judged as defects.

[0062] The battery manufacturing method described above is applicable to battery testing methods when the terminal voltages before and after aging treatment are obtained in advance. This testing method improves the accuracy of identifying defective batteries.

[0063] The technologies disclosed herein have been described in detail above. Unless otherwise specified, the embodiments and other details mentioned herein do not limit the present invention. Furthermore, the technologies disclosed herein can be modified in various ways, and each component and each process mentioned herein may be omitted or combined as appropriate, unless no particular problems arise. This specification also includes the disclosures described in the following sections.

[0064] Section 1: A process of performing aging treatment on multiple batteries, A step of obtaining the terminal voltages of the plurality of batteries before the aging process, A step of obtaining the terminal voltages of the plurality of batteries after the aging process, A step of setting a threshold by subtracting at least one terminal voltage difference from the terminal voltage difference before and after the aging process for each of the plurality of batteries, and determining whether each of the plurality of batteries is defective or not. including, Battery manufacturing method.

[0065] Section 2: In the aforementioned determination process, The batteries that have been determined to be defective are excluded from the aforementioned group of batteries, A threshold is set based on the standard deviation calculated by subtracting at least one more terminal voltage difference from the terminal voltage differences of multiple batteries excluding the battery that was determined to be defective, and this process of determining which batteries are defective is repeated a predetermined number of times. A method for manufacturing a battery as described in item 1, further comprising:

[0066] Section 3: A method for manufacturing a battery according to item 1 or 2, wherein the at least one terminal voltage difference includes the maximum and minimum values ​​of the terminal voltage differences of the plurality of batteries.

[0067] Section 4: A method for manufacturing batteries according to any one of items 1 to 3, wherein the plurality of batteries are seven or more.

[0068] Section 5: A method for manufacturing a battery as described in any one of items 1 to 4, wherein the rate at which defects occur in the aforementioned battery is obtained in advance, and the number of terminal voltage differences to be excluded is determined based on the aforementioned rate.

[0069] Item 6: A process to obtain the terminal voltage of multiple batteries before aging treatment, A step of obtaining the terminal voltages of the plurality of batteries after the aging process, A step of setting a threshold by subtracting at least one terminal voltage difference from the terminal voltage difference before and after the aging process for each of the plurality of batteries, and determining whether each of the plurality of batteries is defective or not. including, Battery testing methods.

[0070] Section 7: In the aforementioned determination process, The batteries that have been determined to be defective are excluded from the aforementioned group of batteries, A threshold is set based on the standard deviation calculated by subtracting at least one more terminal voltage difference from the terminal voltage differences of multiple batteries excluding the battery that was determined to be defective, and this process of determining which batteries are defective is repeated a predetermined number of times. The battery testing method described in item 6, further including the following.

[0071] Section 8: The battery inspection method described in item 6 or 7, wherein the voltage difference between at least one terminal includes the maximum and minimum values ​​of the voltage differences between the terminals of the plurality of batteries.

[0072] Section 9: The method for testing batteries as described in any one of items 6 to 8, wherein the plurality of batteries is seven or more.

[0073] Section 10: A battery inspection method described in any one of items 6 to 9, wherein the rate at which defects occur in the aforementioned battery is obtained in advance, and the number of terminal voltage differences to be excluded is determined based on the aforementioned rate. [Explanation of Symbols]

[0074] 1 battery (battery assembly) 10 cases 12 Case body 14 Lid 15 Inlet 15a Sealing member 16 Positive terminal 16a, 18a Insulating material 18 Negative terminal 19 Gas discharge valve 20 Electrode body 26,28 Current collector 30 Positive plate 32 Positive electrode core 34 Cathode active material layer 40 Negative plate 42 Negative electrode core 44 Negative electrode active material layer 50 Separators

Claims

1. A process of performing aging treatment on multiple batteries, A step of obtaining the terminal voltages of the plurality of batteries before the aging process, A step of obtaining the terminal voltages of the plurality of batteries after the aging process, A step of setting a threshold by subtracting at least one terminal voltage difference from the terminal voltage difference before and after the aging process for each of the plurality of batteries, and determining whether each of the plurality of batteries is defective or not. including, Battery manufacturing method.

2. In the aforementioned determination process, The batteries that have been determined to be defective are excluded from the aforementioned group of batteries, A threshold is set based on the standard deviation calculated by subtracting at least one more terminal voltage difference from the terminal voltage differences of the remaining batteries, excluding the battery that was determined to be defective, and this process of determining which batteries are defective is repeated a predetermined number of times. A method for manufacturing a battery according to claim 1, further comprising:

3. A method for manufacturing a battery according to claim 1 or 2, wherein the at least one terminal voltage difference includes the maximum and minimum values ​​of the terminal voltage differences of the plurality of batteries.

4. The method for manufacturing a battery according to claim 1 or 2, wherein the plurality of batteries are seven or more.

5. A method for manufacturing a battery according to claim 1 or 2, wherein the rate at which defects occur in the aforementioned battery is obtained in advance, and the number of terminal voltage differences to be excluded is determined based on the rate.

6. A process to obtain the terminal voltage of multiple batteries before aging treatment, A step of obtaining the terminal voltages of the plurality of batteries after the aging process, A step of setting a threshold by subtracting at least one terminal voltage difference from the terminal voltage difference before and after the aging process for each of the plurality of batteries, and determining whether each of the plurality of batteries is defective or not. including, Battery testing methods.

7. In the aforementioned determination process, The batteries that have been determined to be defective are excluded from the aforementioned group of batteries, A threshold is set based on the standard deviation calculated by subtracting at least one more terminal voltage difference from the terminal voltage differences of the remaining batteries, excluding the battery that was determined to be defective, and this process of determining which batteries are defective is repeated a predetermined number of times. A battery inspection method according to claim 6, further comprising:

8. The battery inspection method according to claim 6 or 7, wherein the at least one terminal voltage difference includes the maximum and minimum values ​​of the terminal voltage differences of the plurality of batteries.

9. The battery inspection method according to claim 6 or 7, wherein the plurality of batteries are seven or more.

10. A battery inspection method according to claim 6 or 7, wherein the percentage of batteries in which defects occur is obtained in advance, and the number of terminal voltage differences to be excluded is determined based on the percentage.

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