JP2023128834A - Secondary cell self-discharge inspection method and self-discharge inspection device - Google Patents

Abstract

To appropriately determine good and defective secondary cells in a manufacturing process.SOLUTION: A secondary cell self-discharge inspection device performs self-discharge inspection in a process to successively manufacture a plurality of secondary cells, and comprises a charge-discharge device, a voltage measurement device, and a control device that includes a computing device. The control device individually acquires a voltage difference ΔV that represents a change of secondary cell voltage before and after an aging step, calculates the moving average MA of a plurality of secondary cells including the relevant secondary cell whose voltage difference ΔV has been acquired and the voltage difference ΔV of other secondary cells that have been manufactured adjacent to the relevant secondary cell, calculates a difference DA between the moving average MA and the voltage difference ΔV of the relevant secondary cell, and compares the difference DA with a preset threshold Ta to determine whether being defective or not.SELECTED DRAWING: Figure 2

Description

The present invention relates to a self-discharge testing method and a self-discharge testing device for a secondary battery, and more particularly to a self-discharging testing method and a self-discharge testing device for a secondary battery that appropriately determine whether a secondary battery is good or defective in a manufacturing process.

Conventionally, when manufacturing secondary batteries, finished products are inspected, one of which is a self-discharge inspection in the aging process to determine whether self-discharge is within an allowable range. In the aging process, a method may be used in which the battery is charged to a certain value and then maintained at a high temperature without any load. At this time, it eliminates minute short circuits within the secondary battery and stabilizes the electrodes. After the aging step is completed, the voltage difference ΔV [V] between the voltages of the secondary battery is measured. At this time, if the voltage difference ΔV [V] is larger than the set design value, it is assumed that self-discharge is large and the test is failed, and the product is not shipped as a defective product and is subject to disposal in principle.

FIG. 13 is a graph showing a method of determining the voltage difference ΔV [V] in absolute value from a common threshold value T based on conventional design values. The vertical axis indicates the voltage difference ΔV [V]. The horizontal axis indicates individual secondary batteries included in each lot.

In such voltage difference ΔV [V] inspection, the voltage difference ΔV [V] is due to secondary factors such as variations in solid solution elements in the positive electrode active material, variations in additives in the electrolyte, and temperature variations inside the battery. There are many factors that cause variations in self-discharge that are unique to batteries.

Taking these variations into consideration, the threshold for determining whether a secondary battery is a good product or a defective product, the voltage difference ΔV [V], is set to over-detect (excessively reject a good product) in order to prevent failure to detect a defective product. It is necessary to decide on a threshold value with a margin for erroneously detecting a non-defective product. As a result, some secondary batteries are judged to be defective from a safety standpoint, even though they are actually good. For this reason, there has been a problem in that losses in the manufacturing process of the secondary battery increase.

Therefore, the invention disclosed in Patent Document 1 discloses the following invention. Here, the terminal voltage in the aging process is taken as the potential in the discharge state, and the standard assumes the amount of terminal voltage drop of a defective battery with a minute internal short circuit with respect to the average value ΔVA of ΔV [V] that varies for each inspection lot. Set the value ΔVB as an absolute value. Further, an inspection method is disclosed in which a battery having a ΔV [V] smaller than the value of ΔVA-ΔVB is determined to be a defective product.

If such an inspection method is based on an absolute value based on the average value of the entire lot, depending on the variation of the secondary batteries to be inspected, the influence of the voltage difference ΔV [V] of some secondary batteries may still be affected. The average value changes and the threshold value is affected. Then, there is a possibility that the threshold value has a margin on the side of overdetection.

FIG. 14(a) is a graph showing the voltage difference ΔV [V] between secondary batteries consisting of material lot 1 and material lot 2 to be inspected. The vertical axis indicates the voltage difference ΔV [V]. The horizontal axis indicates individual secondary batteries included in each lot. FIG. 14(b) is a graph showing a method of determining the voltage difference ΔV [V] using a relative value. The vertical axis shows the probability, and the horizontal axis shows the standard deviation σ of the voltage difference ΔV [V]. The threshold value Tr is set to an arbitrary standard deviation σ (for example, “+3σ”).

In the absolute value determination described above, the threshold value may have a margin on the side of overdetection depending on variations in the secondary battery to be inspected. Here, each of the secondary batteries shown in FIG. 14(a), including each secondary battery included in material lot 1 and each secondary battery included in material lot 2, are good products with no problem with self-discharge. Suppose there is. Next, as shown in FIG. 14(b), the average μ of these secondary batteries is determined, the variance σ ² is determined, and a probability distribution graph L1 is created. Here, an arbitrary threshold value (for example, +3σ) is set as the threshold value Tr, and a secondary battery with a standard deviation σ exceeding the threshold value Tr is detected as an abnormal value and a defective product. However, as described in the premise shown in FIG. 14(a), all the products are good products G, and no defective products NG are included. However, regardless of the setting of the threshold value Tr in FIG. 14(b), a secondary battery exceeding the threshold value Tr will be detected as a defective product.

Japanese Patent Application Publication No. 2013-190292

As described above, conventionally, even a secondary battery that should originally be determined to be a good product may be over-detected as a defective product. For this reason, there has been a problem in that even if a non-defective secondary battery is produced in the manufacturing process, it is determined to be a defective product.

The problem to be solved by the secondary battery self-discharge testing method and self-discharge testing device of the present invention is to appropriately determine whether a secondary battery is good or defective in the manufacturing process.

In order to solve the above problems, the self-discharge testing method for a secondary battery of the present invention is a self-discharge testing method for a secondary battery in the process of continuously manufacturing a plurality of secondary batteries. a ΔV acquisition step of individually acquiring a voltage difference ΔV, which is a change in voltage of the secondary battery before and after the process; and a target secondary battery, which is the secondary battery from which the voltage difference ΔV was acquired in the ΔV acquisition step; a moving average calculation step of calculating a moving average MA of the voltage difference ΔV of the comparison secondary battery manufactured adjacent to the target secondary battery; the moving average MA calculated in the moving average calculation step; A difference calculation step of calculating the difference DA with the target secondary battery from which the voltage difference ΔV was obtained in the ΔV acquisition step, and a difference DA calculated in the difference calculation step is compared with a preset threshold Ta. A difference determination step for determining whether the product is good or not.

Further, the standard deviation of the voltage difference ΔV of each of the secondary batteries included in the material lot is calculated based on the variance when the voltage difference ΔV of the secondary batteries included in the material lot is taken as a population. a step of calculating a relative value; and a step of relative determination, comparing the standard deviation of the secondary battery calculated in the step of calculating the relative value with a preset threshold Tr to determine whether it is a defective product. It is preferable that the method further includes a final determination step of determining, as a defective product, the secondary battery that was determined to be a defective product in both the step of the difference determination and the step of the relative determination.

Further, the comparison secondary batteries manufactured adjacently in the step of calculating the moving average may be secondary batteries manufactured before and after the target secondary battery from which the voltage difference V was acquired in the step of acquiring ΔV.

It is desirable that the step of calculating the moving average is performed continuously across different material lots. It is preferable that the variance is a population variance σ ² based on all the secondary batteries in the material lot. The no-load discharge process can be an aging process.

This can be suitably carried out when the secondary battery is a nickel-metal hydride storage battery.
Further, the self-discharge testing device for secondary batteries of the present invention is a self-discharging testing device for secondary batteries that performs self-discharging testing of secondary batteries in the process of continuously manufacturing a plurality of secondary batteries for each material lot. The control device includes a voltage measuring device that measures the voltage of the secondary battery and a control device including an arithmetic device, and the control device measures changes in the voltage of the secondary battery before and after the aging process using the voltage measuring device. A target secondary battery, which is a secondary battery from which the voltage difference ΔV was individually acquired, and the voltage difference ΔV was acquired by the arithmetic device, and a comparison secondary battery manufactured adjacent to the target secondary battery. A moving average MA of a plurality of secondary batteries including a voltage difference ΔV is calculated, a difference DA between the moving average MA and a voltage difference ΔV of the target secondary battery is calculated, and the difference DA and a preset threshold value are calculated. It is characterized by comparing it with Ta to determine whether it is a defective product or not.

Further, the control device further controls the voltage of each of the secondary batteries included in the material lot based on the variance when the voltage difference ΔV of the secondary batteries included in the material lot is taken as a population. A standard deviation σ of the difference ΔV is calculated, and the standard deviation σ is compared with a preset threshold Tr to determine whether the product is defective or not. It is desirable that the secondary battery is finally determined to be a defective product when it is determined to be a defective product in comparison with the Tr.

According to the self-discharge testing method and self-discharge testing device for a secondary battery of the present invention, it is possible to appropriately determine whether a secondary battery is good or defective in the manufacturing process.

FIG. 1 is a block diagram showing a secondary battery manufacturing apparatus according to the present embodiment. 3 is a flowchart showing the procedure of a self-discharge testing method for a secondary battery according to the present embodiment. It is a figure showing acquisition of moving average MA of ΔV [V] in difference judgment. It is a figure showing acquisition of moving average MA of ΔV [V] in difference judgment. FIG. 3 is a diagram showing a moving average MA of ΔV[V] of each of the secondary batteries B1 to B11 obtained in the differential determination and ΔV[V] of the secondary battery. FIG. 6 is a diagram showing the difference between the moving average MA of ΔV of each secondary battery B obtained in the difference determination and ΔV[V] of that secondary battery B. FIG. FIG. 6 is a diagram illustrating the necessity of cross-checking with relative determination when there is a possibility of excessive detection at a material lot switching section. This is a formula for calculating the population variance σ ² . FIG. 2 is a schematic diagram of defective product detection in a conventional self-discharge test. FIG. 3 is a schematic diagram of defective product detection in a self-discharge test based on a difference determination according to the present embodiment. It is a graph showing the ratio of over-detected non-defective products. It is a graph showing the detection of defective products when the conventional method is set as an index of 100. 12 is a graph showing a method of determining a voltage difference ΔV [V] using an absolute value from a common threshold value T based on a conventional design value. FIG. 14(a) is a graph showing the voltage difference ΔV [V] between the secondary batteries of material lot 1 and material lot 2 to be inspected. FIG. 14(b) is a graph showing a method of determining the voltage difference ΔV [V] using a relative value.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The self-discharge testing method and self-discharge testing device for secondary batteries of the present invention will be described below with reference to FIGS.

<Configuration of secondary battery of this embodiment>
The secondary battery B of this embodiment is a nickel-metal hydride storage battery that is an on-vehicle battery for driving an electric vehicle or a hybrid vehicle, but is not limited thereto. In a nickel-metal hydride storage battery, for example, the positive electrode plate has a positive electrode substrate made of a porous nickel foam and filled with a positive electrode composite layer using nickel hydroxide or the like as a positive electrode active material. On the other hand, in the negative electrode plate, a negative electrode composite layer is formed using a hydrogen storage alloy as a negative electrode active material on a negative electrode substrate made of a punched plate made of nickel. These positive electrode plates and negative electrode plates are laminated with a separator in between to form an electrode group. The electrode groups are housed in a plurality of battery containers provided in the battery case, and are connected in series and connected to external connection terminals. An alkaline electrolyte such as an aqueous potassium hydroxide solution is injected here, and the assembly of the battery module is completed by attaching the lid to the battery case.

Such a nickel-metal hydride storage battery is not yet completed as a battery even after the assembly of battery elements is completed, and after initial charging and conditioning, the battery is tested for capacity, voltage, internal resistance, etc. Further, aging is performed in which the battery charged to a predetermined voltage is placed in a high temperature and no-load state. Aging eliminates shortness and chemically stabilizes the electrode. Generally, this aging process is used to test for self-discharge.

Nickel-metal hydride storage batteries are prone to variations such as self-decomposition of the positive electrode due to variations in the characteristics of material lots. For this reason, it is difficult to distinguish between self-discharge caused by variations in the characteristics of material lots and self-discharge caused by slight shortening in such nickel-metal hydride storage batteries (see FIG. 10). Therefore, the self-discharge testing method for a secondary battery according to the present embodiment can be suitably carried out for a nickel-metal hydride storage battery.

Note that although a nickel-metal hydride battery is used as an example of the secondary battery, it is not intended to be limited to a nickel-metal hydride battery, and it goes without saying that other secondary batteries such as a lithium-ion secondary battery can be used as long as the present invention can be practiced.

<Secondary battery self-discharge testing device>
FIG. 1 is a block diagram showing a secondary battery manufacturing apparatus of this embodiment. In the secondary battery manufacturing apparatus 1 of this embodiment, a plurality of secondary batteries B are successively assembled for each material lot by an assembly apparatus 2. The charging/discharging device 5 charges and discharges the secondary battery B that has been assembled in the assembly device 2 of the secondary battery manufacturing device 1 . The charging/discharging device 5 includes sensors such as a voltmeter and an ammeter (not shown). This charging/discharging device 5 is controlled by a control device 4. The self-discharge test device 3 of this embodiment performs a self-discharge test on a secondary battery that is controlled to a constant state of charge by the charging/discharging device 5. Note that the purpose of the aging step (S1 in FIG. 2) of this embodiment is to test self-discharge, so if the charging rate is relatively low (for example, SOC 10 [%] or less), the voltage difference ΔV due to self-discharge will be large. Therefore, it is preferable.

The secondary battery self-discharge testing device 3 of this embodiment includes a voltage measuring device 6 that measures the battery voltage of the secondary battery B, and a control device 4 that includes a calculation device. This control device 4 is shared with the charge/discharge device 5.

Although not shown in the drawings, the assembled secondary battery B is subjected to initial charging, conditioning, and various inspections. The test measures things like battery voltage and internal resistance.
For the secondary battery whose assembly has been completed, the step of the aging process is started by the charging/discharging device 5 controlled by the control device 4 (FIG. 2: S1). In the step of the aging process, after the controller 4 charges the secondary battery B to a certain value using the charging/discharging device 5, the secondary battery B is raised to a predetermined temperature using a heating device (not shown) as a preparatory step. Then, an aging step is performed in which the device is left unloaded for a certain period of time. In this aging process, minute short circuits caused by, for example, minute metal powder are eliminated. Moreover, the inside of the battery becomes chemically stable. In this embodiment, one of the purposes is to inspect self-discharge. Since there is no load during this aging process, there is no external discharge of power. However, micro short circuits and discharge via the electrolyte occur, resulting in a voltage drop due to "self-discharge." If the self-discharge is large, the voltage will drop quickly even when not in use, and the performance of the battery will deteriorate. Therefore, when the assembly of the secondary battery B is completed, first, the charging/discharging device 5 charges it to the set charging rate, and then the self-discharge testing device 3 performs the step (S1) of the aging process as a self-discharge test. It will be done.

In the control device 4, in the step of preliminary battery voltage V measurement (S2) and the step of post-measurement of battery voltage V (S3), the voltages of the individual secondary batteries B1 to B9... are acquired by the voltage measurement device 6, be remembered.

The control device 4 includes a computer including a CPU, RAM, ROM, and storage means. The control device 4 controls the charging/discharging device 5 and the self-discharge testing device 3. Then, the battery voltage of each secondary battery B is measured in the step of preliminary battery voltage V measurement (S2) and the step of post-measurement of battery voltage V (S3). The measured results are stored in the storage means, and the voltage difference ΔV [V] is stored. The stored ΔV [V] is calculated according to the procedure described later, and the self-discharge of each secondary battery is inspected by performing differential judgment and relative judgment to determine whether the secondary battery is a good product or a defective product.

(Procedures of this embodiment)
As described above, in the conventional absolute value determination, there is a possibility that even if the product is good in both the relative determination and the relative determination, it may be over-detected as a defective product. For this reason, there has been a problem of overdetection in that even if a good secondary battery is produced in the manufacturing process, it is determined to be a defective product.

On the other hand, when relative determination is used alone, there is a problem due to overdetection. Here, in this embodiment, the concepts of absolute value determination and relative determination are combined. However, simply combining absolute value determination and relative determination does not solve either of the problems.

Therefore, the present inventors have discovered a unique method to take advantage of the characteristics of absolute value determination and relative determination.
(Self-discharge testing method for secondary batteries of this embodiment)
FIG. 2 is a flowchart showing the procedure of the self-discharge testing method for a secondary battery according to this embodiment. Hereinafter, the procedure of the self-discharge testing method for a secondary battery according to the present embodiment will be explained with reference to a flowchart.

<Acquisition of ΔV[V]>
In this method, first, the control device 4 starts the procedure of step (S1) of the aging process using the self-discharge testing device 3. Note that the step (S1) of the aging process is continued until the measurement of the battery voltage V of the secondary battery B is completed by the voltage measuring device 6 in the "step of post-measurement of the battery voltage V (S3)". When step (S1) of the aging process is started, first, secondary battery B that has been charged to a predetermined charging rate (for example, SOC 10%) is heated to a predetermined temperature. After raising the temperature of the secondary battery B to a predetermined temperature, the temperature of the secondary battery B is maintained constant thereafter.

When the temperature of the secondary battery B rises to a predetermined temperature, the control device 4 measures the battery voltage V of the secondary battery B with the voltage measuring device 6 in the "preliminary battery voltage V measurement step (S2)". Thereafter, a constant temperature aging step is performed, and after the set time has elapsed, the control device 4 measures the battery voltage V of the secondary battery B with the voltage measuring device 6 in the "post-measurement step (S3) of battery voltage V." Measure. Then, the procedure of “ΔV acquisition step (S4)” is executed. In the "step of acquiring ΔV (S4)", the voltage difference ΔV between the voltage measured in the "step of preliminary battery voltage V measurement (S2)" and the voltage measured in the "step of post-measurement of battery voltage V (S3)" is determined. Get [V]. The voltage difference ΔV is obtained for each secondary battery B1, B2, . . . . In this embodiment, the secondary battery B to be inspected for which the voltage difference ΔV [V] has been acquired in this "ΔV acquisition step (S4)" is referred to as the "target secondary battery".

<Calculation of moving average MA>
In the subsequent "moving average calculation step (S5)", a moving average MA of the voltage difference ΔV [V] between the "target secondary battery" and a "comparative secondary battery" for comparison manufactured adjacently is calculated.

In the secondary battery manufacturing process, secondary batteries B are successively produced one after another on a manufacturing line. Here, the "adjacent secondary battery" includes at least the secondary battery before the "target secondary battery" or after the "target secondary battery". Furthermore, the moving average of a total of five secondary batteries, two before and after, or two before and after, may be obtained.

Note that at the start of production, there is no "previously adjacent secondary battery," but in that case, a moving average may be taken using only the data that can be obtained, or the data that cannot be obtained may be replaced with other data. For example, in principle, the moving average MA is taken for a total of three secondary batteries, including two "comparison secondary batteries" adjacent to the "target secondary battery" before and after the "target secondary battery". However, if the first secondary battery to be manufactured is the target secondary battery, the moving average MA may be taken for the "target secondary battery" and the "comparison secondary battery" adjacent to the back. Alternatively, the moving average MA may be taken by doubling the ΔV[V] of the "target secondary battery" and the "comparison secondary battery" adjacent to the back, and using three ΔV[V].

Such handling can be similarly applied to the case where the last secondary battery to be produced is the "target secondary battery".
<Specific example of moving average MA>
FIG. 3 is a diagram showing acquisition of the moving average MA of ΔV[V] in difference determination. Here, the secondary battery B2 to be measured is the target secondary battery, and the preceding secondary battery B1 and the following secondary battery B3 are the comparative secondary batteries and form the group G1. A moving average MA of the group G1 consisting of these three secondary batteries B1 to B3 is calculated. The calculation is performed by dividing the sum of three voltage differences ΔV [V] by the number of secondary batteries B using a simple average. The moving average MA calculated in this way becomes the moving average of the secondary battery B2.

FIG. 4 is a diagram showing the acquisition of the moving average MA of ΔV[V] in the difference determination. Here, the secondary battery B3 to be measured is defined as a target secondary battery, and the preceding secondary battery B2 and the following secondary battery B4 are defined as comparison secondary batteries in group G2. A moving average MA of group G2 consisting of these three secondary batteries B2 to B4 is calculated. The calculation is performed by dividing the sum of three voltage differences ΔV [V] by the number of secondary batteries B using a simple average. The moving average MA calculated in this way becomes the moving average of the secondary battery B3.

<Difference DA calculation>
FIG. 5 is a diagram showing the moving average MA of ΔV[V] of each of the secondary batteries B1 to B11 obtained in the difference determination and the ΔV[V] of the secondary battery. Using the method shown in FIGS. 3 and 4, a graph of the moving average MA is shown using the secondary batteries B1 to B11 as target secondary batteries and the comparison secondary batteries before and after the target secondary batteries. Note that for the secondary battery B1, the secondary battery B2 was the only comparison secondary battery. In addition, for the secondary battery B11, the only comparison secondary battery was the secondary battery B10.

In the "step of calculating the difference (S6)", the moving average MA calculated in the "step of calculating the moving average (S5)" and the "target secondary battery ” Calculate the difference DA.

<Difference judgment>
FIG. 6 is a diagram showing the difference between the moving average MA of ΔV of each secondary battery B obtained in the difference determination and ΔV [V] of that secondary battery B. The difference DA is expressed as the difference obtained by subtracting the moving average MA from ΔV [V] of the secondary battery B. For example, in the case of the secondary battery B1, as shown in FIG. 5, ΔV [V] is larger than the moving average MA, so it becomes a positive number. Next, in the secondary battery B2, as shown in FIG. 5, ΔV [V] is smaller than the moving average MA, so it becomes a negative number. In the secondary battery B7, ΔV [V] is extremely large, so the difference DA becomes a large positive number. Similarly, the difference DA of the secondary battery B11 is a large positive number.

It can be estimated that a plurality of adjacent secondary batteries (here, comparison secondary batteries with respect to the target secondary battery) have substantially the same characteristics such as their materials. If there is a large difference between ΔV [V] of the moving average MA and ΔV [V] of the "target secondary battery", the cause is not due to characteristics such as variations in the material of the material lot, but is due to the inherent characteristics of the "target secondary battery". This shows that there are differences in the characteristics of In that sense, this "difference DA" performs relative evaluation within a narrow range. Conventional relative evaluation involves comparison with the entire product or material lot. However, the difference DA in this embodiment is a relative evaluation within a narrow range, so by comparing a plurality of adjacent secondary batteries that can be estimated to have almost the same characteristics such as materials, Accuracy can be increased.

Here, the threshold value Ta is a reference value for determining the difference DA. That is, the fact that the difference DA is large means that ΔV [V] is extremely large with respect to the moving average MA. That is, since the target secondary battery exhibits greater self-discharge than the comparative secondary battery, it can be determined that the target secondary battery has a problem with self-discharge. If this threshold value Ta exceeds the range expected from variations in the materials of manufactured secondary batteries, it can be determined that self-discharge is increasing due to a problem with the "target secondary battery" itself. Since the variations in the materials of the manufactured secondary batteries are thought to be smaller in a narrow range, this threshold value Ta can also be set with higher accuracy.

Therefore, in the "difference determination step (S7)", it is possible to compare the difference DA calculated in the "difference calculation step (S6)" with a preset threshold value Ta to determine whether the product is good or defective. can. The determination result here is stored in the storage means of the control device 4.

<Moving average MA between different material lots>
FIG. 7 is a diagram showing the necessity of cross-checking with relative judgment when there is a possibility of excessive detection at the material lot switching section.

In this embodiment, secondary batteries B of different material lots (production lots using different raw materials) are also manufactured continuously. In this case, it can be assumed that there are relatively few variations in materials within the same material lot. On the other hand, it can be assumed that there is a relatively large variation in materials between different material lots. For this reason, when the moving average MA is calculated across different material lots, the variation in ΔV [V] of the comparative secondary batteries becomes larger than the moving average MA within the same material lot. Therefore, the difference DA also tends to increase. As a result, if the threshold value Ta is the same, there is a high possibility that over-detection will occur in which a non-defective product is determined to be a defective product.

Target secondary battery B5 is a secondary battery using material lot 2. As shown in FIG. 7, in material lot 1, ΔV[V] is higher than that in material lot 2, with an average value of A1. On the other hand, in material lot 2, ΔV[V] is lower than that in material lot 1, with an average of A2. Note that since the secondary battery B7 and the secondary battery B11 are defective products, their influence will be ignored. Then, there is an average difference ΔA between the average A1 of material lot 1 and the average A2 of material lot 2. Then, the moving average MA becomes lower due to the influence of material lot 2, and therefore the difference DA of the secondary battery B4, which is the target secondary battery, becomes larger. For these reasons, in the case of moving average MA across material lots, there is a high possibility of overdetection.

<Relative judgment>
Therefore, in such a case, a "step of relative value calculation (S8)" and a "step of relative determination (S9)" are performed.

In the "relative value calculation step (S8)", such overdetection is suppressed by performing relative determination within the same material lot. In the relative determination, the population variance is determined when the population is the voltage difference ΔV [V] of the secondary batteries B included in one material lot. Next, the population standard deviation σ of the voltage difference ΔV [V] of each secondary battery B included in the material lot is calculated.

In the "relative determination step (S9)", the calculated population standard deviation σ of each secondary battery B is compared with a preset threshold value Tr to determine whether or not it is a defective product.
In this embodiment, the total number of ΔV[V] of each lot is totaled.

FIG. 8 is a formula for calculating the population variance σ ² . Specifically, the population variance is equal to the average of the squares of the deviations from the mean. The population variance “σ ² ” of a population of data x ₁ , x ₂ , ..., x _n whose size is “n” is the population mean value for “x ₁ , x ₂ , ..., x _n ” When expressed by "μ", it can be expressed by the formula shown in FIG. Here, "σ ² " is the population variance, and "σ" is the population standard deviation.

Note that when the population of material lots is large, the "variance s ² " of samples may be determined instead of counting the total number of target secondary batteries. When the "population standard deviation σ" is not known, the "standard deviation s" may be used instead of the population standard deviation σ.

Furthermore, when the "population standard deviation σ" is not known, the unbiased deviation of the sample can be used as an estimate of the standard deviation of the population.
Note that when this relative determination is used alone, over-detection cannot be prevented as described in the prior art. In other words, secondary battery B, which was determined to be a defective product due to over-detection based on the moving average MA across different material lots, is determined to be a non-defective product based on the relative determination based on over-detection. It is something to do. The determination results for each secondary battery B here are stored in the storage means of the control device 4.

<Final judgment>
In the "final determination step (S10)," the secondary battery that was determined to be defective in both the differential determination step (S7) and the relative determination step (S9) is determined to be a defective product. In the final determination step (S10), first, in the differential determination step (S7), whether or not the secondary battery B to be inspected is a good product is read from the storage means of the control device 4. If it is determined that the product is non-defective, the product is directly determined to be non-defective (S11), and the process ends.

On the other hand, in the step of determining the difference (S7), whether or not the secondary battery B to be inspected is a good product is read from the storage means of the control device 4. If the product is determined to be defective here, the storage means of the control device 4 reads out whether or not the product is determined to be non-defective in the relative determination step (S9). If the product is determined to be non-defective in the step of relative determination (S9), the product is directly determined to be non-defective (S11), and the process ends.

On the other hand, in the relative judgment step (S9), if the product is read out from the storage means of the control device 4 and determined to be defective, it has already been determined to be defective in the difference judgment step (S7). Therefore, as a final determination, it is determined that the product is defective (S12) and the process ends.

(Action of this embodiment)
<Effect of difference judgment>
FIG. 9 is a schematic diagram of defective product detection in conventional self-discharge testing. As shown in FIG. 9, self-discharge in the aging process is caused by micro short circuits specific to the secondary battery. On the other hand, there is self-discharge due to self-decomposition of the positive electrode due to variations in raw materials in material lots. These cannot be distinguished only by detecting ΔV [V]. Self-discharge due to self-decomposition of the positive electrode due to variations in raw materials in material lots can be said to be a characteristic of the secondary battery, and cannot be immediately determined to be a defective product. However, in the past, since it was not possible to distinguish only by detecting ΔV [V], there was a possibility that a secondary battery belonging to material lot 1, which was a good product, would also be over-detected as a defective product.

FIG. 10 is a schematic diagram of defective product detection in the self-discharge test based on the difference determination according to the present embodiment. In this embodiment, by using the moving average MA, by canceling out ΔV [V] caused by self-decomposition of the positive electrode caused by variations in the raw materials of common material lots in the same material lot, microscopic Self-discharge caused by short circuits can be detected. Then, in the step (S7) of determining the difference in the present embodiment, the threshold value Ta for detecting self-discharge caused by a micro-short circuit, etc., specific to the secondary battery is used to more accurately detect self-discharge caused by a micro-short circuit, etc. The generated secondary battery can be appropriately detected.

<Suppression of over-detection>
FIG. 11 is a graph showing the ratio of over-detected non-defective products. Here, "overdetection" refers to erroneously detecting an excessive number of good products as defective products. In a comparative example using conventional absolute value determination, the ratio of over-detected non-defective products was approximately 2,100 per million, or 0.21%. On the other hand, according to the self-discharge testing method of this embodiment, the ratio of over-detected non-defective products was dramatically reduced to 0.02%. Therefore, it was possible to significantly reduce losses in the manufacturing process of the secondary battery.

<Reducing failure to detect defective products>
FIG. 12 is a graph showing detection of defective products when the conventional method is set as an index of 100. In contrast to the comparative example in which the detection of defective products by conventional absolute value determination was set to an index of 100, the index was set to 101 according to the example using the self-discharge testing method of the present embodiment. That is, it means that a potentially defective product that was determined to be non-defective in the comparative example was correctly identified as a defective product in the example.

According to the example of the self-discharge testing method of this embodiment, there is an effect that both non-defective products and defective products can be detected correctly in this way.
(Effects of this embodiment)
(1) According to the self-discharge testing method for secondary battery B and the self-discharge testing device 3 of this embodiment, it is possible to appropriately determine whether a secondary battery is good or defective in the manufacturing process.

(2) In this embodiment, the voltage difference ΔV of the secondary battery B is acquired in the ΔV acquisition step (S4). Then, in a moving average calculation step (S5), a moving average MA of the voltage difference ΔV between the target secondary battery Bo and the comparison secondary battery Bc manufactured adjacently is calculated. Therefore, it is possible to perform a relative evaluation with secondary batteries made from the same material lot and having similar characteristics.

(3) In the step of calculating the difference (S6), the calculated moving average MA is compared with the threshold value Ta to calculate the difference DA. Then, in the step of determining the difference (S7), by comparing the difference DA with the threshold value Ta, it is possible to easily and accurately detect a defective product NG that exhibits self-discharge characteristic of the target secondary battery Bo.

(4) Similarly, by comparing the difference DA with the threshold value Ta, it is possible to easily and accurately detect failure to detect the target secondary battery Bo, which is a defective product NG, as a good product G.
(5) Furthermore, when the moving average MA crosses different material lots, a good product G may be detected as a defective product NG in the step of determining the difference (S7). In this case, in the step of relative value calculation (S8) and the step of relative judgment (S9), if there is no problem in the relative judgment within the same material lot, the product is judged as good in the final judgment step, suppressing over-detection. can do.

(6) Therefore, secondary batteries B using different material lots can also be manufactured continuously, so production efficiency can be improved.
(7) Relative judgment is performed using the mean value μ, population variance σ ² , and population standard deviation σ with all secondary batteries B belonging to the material lot as a population, so accurate judgment cannot be made. can.

(8) In this embodiment, step (S1) of the aging process is used as the discharge process under no load. Therefore, the normal production process of secondary battery B is not hindered, and production efficiency is not reduced.

(9) The secondary battery in this embodiment is a nickel-hydrogen storage battery. Since nickel-metal hydride storage batteries have a large change in ΔV due to self-discharge caused by variations in materials, testing using the secondary battery self-discharge testing method of this embodiment also has the effect of enabling more appropriate testing.

(10) The secondary battery self-discharge testing device 3 of this embodiment allows the secondary battery self-discharge testing method of this embodiment to be executed by the control device 4, thereby making it easy to carry out the present embodiment. can. Therefore, it can be carried out using existing equipment without requiring any special equipment.

(Another example)
○ In this embodiment, the secondary battery B is a battery module of a nickel-metal hydride storage battery for use in a vehicle. However, the target secondary battery may be a self-contained battery such as a lithium ion secondary battery, a nickel cadmium battery, or an all-solid-state battery. It can be applied to a wide range of secondary batteries that require discharge inspection.

Further, the use of the secondary battery B is not limited to use in vehicles, and may be used as a power source for computers, etc., or in power storage equipment in homes and factories.
In this embodiment, it is assumed that continuous production is performed across different material lots, but it is also possible to manufacture only a single material lot. In that case, the step of relative value calculation (S8), the step of relative determination (S9), and the step of final determination (S10) may be omitted. In this case, a good product G or a defective product NG is determined by the determination in step (S7) of difference determination.

In the present embodiment, the moving average MA is calculated using three comparison secondary batteries Bc, which are the secondary batteries that are adjacent before and after the target secondary battery Bo that is the object of the test. However, as described above, the comparison secondary battery Bc can also be a moving average of two secondary batteries B, which are adjacent to either the front or rear of the target secondary battery Bo. Furthermore, the moving average MA may be calculated using five comparative secondary batteries Bc, two each adjacent to the front and rear of the target secondary battery Bo.

○Furthermore, although the modified examples of how to obtain the moving average for different material lots at the start of production and at the end of production are described above, those skilled in the art can further adopt an appropriate method.
○Also, in the relative value calculation step (S8), the mean value μ, population variance σ ² , etc. were calculated from the total number of secondary batteries B included in the same material lot serving as the population, but as mentioned above, the sample You can also extract it. A method for this determination can be appropriately selected by those skilled in the art.

In addition, although the case where the no-load discharge process of this embodiment is an aging process has been described, it is not limited to an aging process as long as the voltage drop due to self-discharge can be appropriately measured.

The secondary battery manufacturing apparatus 1 of this embodiment shown in FIG. 1 is a schematic block diagram showing the minimum configuration as a premise, and the secondary battery manufacturing apparatus 1 and self-discharge testing apparatus 3 are as follows: It is not limited to this embodiment.

The numerical values, ranges, materials, etc. described in this specification are merely examples, and can be appropriately optimized and implemented by those skilled in the art.
The flowchart shown in FIG. 2 is an example of a procedure, and those skilled in the art can add, delete, or change the procedure, or change the order of the procedure.

The present invention is not limited to the embodiments, and can be implemented by those skilled in the art by adding, deleting, or changing the configuration without departing from the scope of the claims.

1... Secondary battery manufacturing device 2... Assembly device 3... Self-discharge testing device 4... Control device (equipped with an arithmetic device) 5... Charging/discharging device 6... Voltage measuring device B (B1, B2...)... Secondary battery Bo...Target secondary battery Bc...Comparison secondary battery ΔV...Voltage difference MA...Moving average DA...Difference Ta...Threshold value μ...Population mean value σ ² ...Population variance σ...Population standard deviation Tr...Threshold value NG...Defective product G... Good product E... Over-detected secondary battery

Claims (9)

A self-discharge testing method for secondary batteries in a process of continuously manufacturing a plurality of secondary batteries, the method comprising:
a step of acquiring ΔV, which individually acquires a voltage difference ΔV, which is a change in voltage of the secondary battery before and after a discharge process with no load;
Calculate the moving average MA of the voltage difference ΔV between the target secondary battery, which is the secondary battery from which the voltage difference ΔV was acquired in the ΔV acquisition step, and a comparison secondary battery manufactured adjacent to the target secondary battery. A step of calculating a moving average,
a difference calculation step of calculating a difference DA between the moving average MA calculated in the moving average calculation step and the target secondary battery whose voltage difference ΔV was obtained in the ΔV acquisition step;
a step of determining a difference by comparing the difference DA calculated in the step of calculating the difference with a preset threshold value Ta to determine whether the product is defective;
Self-discharge testing method for secondary batteries equipped with A relative that calculates the standard deviation of the voltage difference ΔV of each of the secondary batteries included in the material lot based on the variance when the voltage difference ΔV of the secondary batteries included in the material lot is taken as a population. Step of value calculation,
a relative determination step of comparing the standard deviation of the secondary battery calculated in the relative value calculation step with a preset threshold Tr to determine whether it is a defective product;
Claim further comprising: a final determination step of determining, as a defective product, the secondary battery that was determined to be a defective product in both the differential determination step and the relative determination step. 1. The self-discharge testing method for a secondary battery according to 1. The comparative secondary batteries manufactured adjacently in the step of calculating the moving average are the secondary batteries manufactured before and after the target secondary battery from which the voltage difference V was acquired in the step of acquiring ΔV. The self-discharge testing method for a secondary battery according to claim 1 or 2. 3. The self-discharge testing method for a secondary battery according to claim 2, wherein the step of calculating the moving average is performed continuously across different material lots. The self-discharge testing method for secondary batteries according to claim 2 or 4, wherein the variance is a population variance σ ² based on the total number of secondary batteries in the material lot. The self-discharge testing method for a secondary battery according to claim 1, wherein the discharge step under no load is an aging step. 7. The self-discharge testing method for a secondary battery according to claim 1, wherein the secondary battery is a nickel-metal hydride storage battery. A secondary battery self-discharge inspection device that performs a self-discharge inspection of a secondary battery in a process of continuously manufacturing a plurality of secondary batteries for each material lot, comprising:
a voltage measuring device that measures the voltage of the secondary battery;
Equipped with a control device equipped with a calculation device,
The control device includes:
The voltage difference ΔV, which is the change in voltage of the secondary battery before and after the aging process, is individually acquired by the voltage measuring device,
A plurality of secondary batteries including a voltage difference ΔV between a target secondary battery, which is a secondary battery that has obtained the voltage difference ΔV by the calculation device, and a comparison secondary battery manufactured adjacent to the target secondary battery. Calculate the moving average MA,
Calculating the difference DA between the moving average MA and the voltage difference ΔV of the target secondary battery,
A self-discharge testing device for a secondary battery, characterized in that the difference DA is compared with a preset threshold value Ta to determine whether or not the product is defective. The control device includes:
Calculate the standard deviation σ of the voltage difference ΔV of each of the secondary batteries included in the material lot based on the variance when the voltage difference ΔV of the secondary batteries included in the material lot is taken as a population. death,
Comparing the standard deviation σ with a preset threshold Tr to determine whether the product is defective;
9. The secondary battery is finally determined to be a defective product when it is determined to be a defective product by comparison with the threshold value Ta and is determined to be a defective product by comparison with the threshold value Tr. self-discharge testing device for secondary batteries.

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