JP2016081712A - Inspection method for battery stack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve inspection accuracy even if a plurality of cells of which the inspection conditions are different from each other are included within the same battery stack.SOLUTION: An inspection method for the battery stack includes the steps of: applying high-temperature aging processing S10; applying low-temperature aging processing S20; inspecting performances of the cells S30; regulating voltages of the cells S40; forming the stack S50 after execution of S10 to S40; leaving the stack for a standing term S60; measuring a cell voltage V1 after the lapse of the standing term S70; measuring a cell voltage V2 after the lapse of a predetermined term from the measurement of the cell voltage V1 S90; and discriminating the presence/absence of abnormality in the stack by calculating a voltage drop amount from the cell voltage V1 to the cell voltage V2 for each of the cells and comparing the voltage drop amounts between the plurality of cells S100. The standing term is determined based on a high-temperature aging term T1, a low-temperature aging term T2 and a voltage regulation term T3 from the end of capacity inspection to start of voltage regulation.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a method for inspecting a battery stack, and more particularly to a method for inspecting an abnormality of a battery stack formed using a plurality of cells.

  A power storage device mounted on an electric vehicle or the like includes a battery stack (hereinafter sometimes abbreviated as a stack) in which a plurality of cells are assembled. In such a stack, in general, a short circuit inspection of each cell is first performed in a single cell state. As a result of the inspection, cells determined to be defective are excluded, and a stack is formed by assembling only the cells determined to be non-defective. Since a short circuit may occur when the stack is formed, the short circuit inspection is performed again for each cell constituting the stack. This short circuit inspection is performed by measuring the self-discharge amount of each cell and comparing the measurement results between the cells.

  Various techniques have been proposed to improve the accuracy of short circuit inspection. For example, in the inspection method disclosed in Japanese Patent Application Laid-Open No. 2013-165029 (Patent Document 1), not all cells belonging to the same production lot are subjected to short-circuit inspection comparison, but the production lot is set as a manufacturing condition and an inspection condition. Based on the subdivision, an inspection lot is formed. By performing a short circuit inspection for each inspection lot, it is possible to accurately discriminate between good and defective cells (see paragraphs [0010] and [0011] of Patent Document 1).

JP 2013-165029 A JP 2013-84508 A JP 2012-221648 A

  In the inspection process of a single cell, an abnormality may occur in the facility, or the factory operation may be suspended due to a long vacation. If the inspection process is interrupted for a long period of time, there may be a difference in the inspection conditions between a cell in which processing has been started before the interruption and a cell in which processing has been newly started after resumption. For example, inspection conditions such as an aging period may differ between a cell in which aging processing has been started before interruption and a cell in which aging processing has been newly started after restart. When a plurality of cells having different inspection conditions are mixed in the same stack as described above, the self-discharge amount differs among the cells. As a result, the accuracy of the short circuit inspection becomes lower than the case where the inspection conditions of all the cells in the stack are equal, and the possibility of erroneous determination is increased.

  The present invention has been made to solve the above-mentioned problems, and its object is to form a battery stack using a plurality of cells and inspect the same battery stack in an inspection method for inspecting abnormality of the battery stack. Even when a plurality of cells having different conditions are included, the inspection accuracy is improved.

  A battery stack inspection method according to an aspect of the present invention is an inspection method for inspecting a battery stack formed using a plurality of cells. The inspection method includes a step of performing a high temperature aging process on each of the plurality of cells, a step of performing a low temperature aging process on each of the plurality of cells, a step of inspecting the capacity of each of the plurality of cells, A battery stack is formed using a plurality of cells after performing the steps of adjusting each voltage, performing the high-temperature aging process, performing the low-temperature aging process, testing the capacity, and adjusting the voltage. A step of leaving the battery stack during the leaving period, a step of measuring an initial voltage for each of a plurality of cells constituting the battery stack after the leaving period, and a predetermined period from the measurement of the initial voltage After the elapse of time, for each of a plurality of cells constituting the battery stack, a step of measuring a voltage after being left, Calculating a voltage drop amount from the initial voltage to the after-stand voltage for each of a plurality of cells constituting the battery and comparing the voltage drop amount between the plurality of cells to determine whether there is an abnormality in the battery stack. With. The neglect period is based on the required period of the step for performing the high temperature aging process, the required period of the step for performing the low temperature aging process, and the required period from the end of the step of inspecting the capacity to the start of the step of adjusting the voltage. It is determined.

  According to the above method, the step of leaving the entire battery stack during the leaving period is provided prior to the measurement of the initial voltage. As will be described in detail later, the inventor starts the step of adjusting the voltage from the time required for the step for performing the high-temperature aging process, the time required for the step for performing the low-temperature aging process, and the step of inspecting the capacity. By setting an appropriate leaving period according to the required period up to the time, the amount of reduction (decrease rate) per unit time of the voltage drop amount of each cell in the same battery stack is equal to each other after the leaving period has elapsed. I found out that Therefore, by making the time interval between the step of measuring the initial voltage and the step of measuring the voltage after standing for all the cells in the battery stack in common, the voltage drop amounts can be made equal to each other. Thereby, even when the battery stack includes a plurality of cells having different inspection conditions, the inspection accuracy can be improved.

  According to the present invention, in the inspection method for forming a battery stack using a plurality of cells and inspecting the abnormality of the battery stack, a plurality of cells having different inspection conditions are included in the same battery stack. Even if it exists, inspection accuracy can be improved.

FIG. 3 is a diagram schematically showing a stack that is an object of the inspection method according to the first embodiment. It is a flowchart for demonstrating the inspection method of the stack | stuck which concerns on a comparative example. It is a figure for demonstrating the method of forming a stack from several cells. 4 is a flowchart for explaining a stack inspection method according to the first embodiment; It is a figure for demonstrating the flow of the information in the test | inspection method shown in FIG. It is a figure for demonstrating the difference in the behavior of the voltage fall amount of the cell according to a low temperature aging period. It is a figure for demonstrating the difference in the behavior of the voltage fall amount of the cell according to a high temperature aging period. It is a figure for demonstrating the difference in the behavior of the voltage fall amount of the cell according to a voltage adjustment period. 5 is a flowchart for explaining the grouping process shown in FIG. 4. 10 is a flowchart for explaining group number determination processing shown in FIG. 9. It is a figure for demonstrating the leaving period defined according to a stack number. It is a figure which shows an example of the determination method of a stack number. 10 is a flowchart for explaining processing according to a modification of the first embodiment. 10 is a flowchart for explaining a stack inspection method according to the second embodiment. It is a figure for demonstrating the flow of the information in the test | inspection method shown in FIG. It is a flowchart for demonstrating the grouping process shown in FIG. It is a flowchart for demonstrating the group number determination process shown in FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

[Embodiment 1]
<Stack configuration>
FIG. 1 is a diagram schematically showing a stack that is an object of the inspection method according to the first embodiment. Referring to FIG. 1, stack 100 includes a plurality of cells 1 arranged. The cell 1 is a power storage element configured to be rechargeable. Although the kind of cell 1 is not specifically limited, In this Embodiment, the example in which a lithium ion secondary battery is employ | adopted is demonstrated. In addition, since the structure of the cell 1 is equivalent to the structure of a typical lithium ion secondary battery, detailed description is not repeated here. In the present embodiment, the case where the number of cells constituting the stack 100 is n = n1 will be described as an example. Generally, a power storage device mounted on an electric vehicle uses a stack including about several tens to 100 cells. However, the number n of cells is not particularly limited as long as the number n is two or more.

<Outline of stack inspection method>
Hereinafter, the stack inspection method according to the comparative example will be described first, and then, in comparison, the stack 100 inspection method according to the first embodiment will be described. The configuration of the stack according to the comparative example is the same as the configuration of stack 100 according to Embodiment 1 (see FIG. 1), and thus detailed description will not be repeated.

  FIG. 2 is a flowchart for explaining a stack inspection method according to a comparative example. This flowchart and the flowchart shown in FIG. 4 described later are executed after the initial charging of the cell before being assembled in the stack is completed.

  Referring to FIG. 2, in step (hereinafter abbreviated as S) 10, each cell is placed in an atmosphere maintained at a temperature higher than room temperature (for example, 40 ° C. to 80 ° C.), and high temperature aging treatment is performed. The Further, in S20, each cell is placed in an atmosphere maintained at a lower temperature (for example, 20 ° C. to 30 ° C.) than the atmospheric temperature of the high temperature aging treatment, and the low temperature aging treatment is performed.

  In S30, for each cell, the capacity and internal resistance of each cell are measured as the battery performance in a single cell state. For each cell after the measurement of the capacity and the internal resistance, the voltage is adjusted so that the SOC (State Of Charge) is within a predetermined range (S40). Hereinafter, the period from the end of capacitance measurement to the start of voltage adjustment is referred to as voltage adjustment period T3. In addition, information on the high temperature aging period T1, the low temperature aging period T2, and the voltage adjustment period T3 may be referred to as “time history” (inspection conditions).

  In S50, a stack is formed by assembling cells by a predetermined number n (in this embodiment, n1). When forming the stack, for example, a metal foreign substance may be mixed between the positive electrode and the negative electrode of the cell to cause a short circuit. Therefore, each cell in the stack is short-circuited again as shown in S60 to S100 below. Inspection is carried out.

  The voltage of each cell constituting the stack decreases relatively rapidly after voltage adjustment. Therefore, the stack is left for a predetermined period until the behavior of the voltage drop amount of each cell is stabilized to some extent (S60). The behavior of the voltage drop amount during the leaving period varies depending on the time history.

  The cell voltage V1 (initial voltage) is measured for each cell constituting the stack after being left (S70). Thereafter, a voltage drop due to self-discharge occurs in each cell (S80). After a predetermined period from the measurement of the cell voltage V1, the cell voltage V2 (post-discharge voltage) is measured for each cell after self-discharge (S90).

  In S100, the presence or absence of abnormality is determined for each cell in the stack based on the cell voltages V1 and V2. More specifically, the voltage drop amount ΔV (k) from the cell voltage V1 to the cell voltage V2 is calculated for each cell. However, k is a natural number representing the number of the cell, and is any natural number from 1 to 28 in the present embodiment (see the following formula (1)).

ΔV (k) = V1−V2 (k = 1, 2,... 28) (1)
Next, the average value ΔVave of the voltage drop amount is calculated by dividing the sum of the voltage drop amounts ΔV (k) of all the cells by the number of cells n (see the following formula (2)).

ΔVave = ΣΔV (k) / n (2)
Then, for each cell, the presence / absence of an abnormality is determined based on the voltage drop amount ΔV (k) and the average value ΔVave. Specifically, when the absolute value of the difference between the voltage drop amount ΔV (k) and the average value ΔVave is less than a predetermined reference value P (see the following formula (3)), the cell is determined to be normal. When the absolute value is equal to or greater than the reference value P (see the following formula (4)), the cell is determined to be abnormal.

| ΔV (k) −ΔVave | <P (determined as normal) (3)
| ΔV (k) −ΔVave | ≧ P (determined as abnormal) (4)
When all the cells in the stack are determined to be normal, the stack is determined to be normal. On the other hand, if even one cell determined to be abnormal is included in the stack, the stack is determined to be abnormal. In this case, the entire stack may be discarded, or the abnormal cell may be replaced with another cell and the short circuit inspection may be performed again.

<Suspension of cell inspection process>
The cell inspection process (a series of steps shown in Fig. 2) is temporarily suspended or left for reasons such as when power outages occur in the facility or the factory operation is suspended due to long vacations. There is a case. FIG. 3 is a diagram for explaining a method of forming a stack from a plurality of cells. FIG. 3A shows a state during normal operation, and FIG. 3B shows a state when an interruption occurs.

  Referring to FIG. 3A, generally, a cell is manufactured for each predetermined unit (so-called manufacturing lot). In the example shown in FIG. 3, each of the production lots A to C includes n2 cells. Since the number of cells n2 in each production lot is not a multiple of the number of cells n1 constituting the stack, it is necessary to combine the cells between the production lots to form a stack. During normal operation, the time histories between the production lots are almost equal, so it is possible to form a stack by combining cells between the production lots.

  Next, a case where the stack inspection process is interrupted will be described with reference to FIG. As an example, it is assumed that the factory operation is suspended after the low-temperature aging process (S20 in FIG. 2) of the production lots A and B is started. Since the ambient temperature (for example, 20 ° C. to 30 ° C.) during the low temperature aging treatment is approximately equal to room temperature, the low temperature aging treatment can proceed even during the interruption period. For this reason, the low temperature aging period T2 of the production lots A and B is expressed as the sum of the period implemented before the interruption and the interruption period. As a result, when the interruption period is long, the low temperature aging period T2 can be significantly longer than that during normal operation. On the other hand, since the low temperature aging period T2 of the production lot C in which the low temperature aging process is newly started after the restart is relatively short, the low temperature aging period T2 is different between the production lots A and B and the production lot C. .

  In such a case, if a stack is formed using cells from production lots A and B and cells from production lot C, the stack includes a plurality of cells having different low-temperature aging periods T2. become. However, as described above, the self-discharge amount may be different between cells having different time histories (high temperature aging period T1, low temperature aging period T2, and voltage adjustment period T3). The determination of the presence / absence of abnormality is performed by comparing the voltage drop amount ΔV (k) of each cell with the average value ΔVave of the voltage drop amount of all cells, as described in the above formulas (1) to (4). Therefore, when cells having different time histories are mixed in the same stack, the inspection accuracy of the short-circuit inspection becomes lower than when the time histories of all the cells in the stack are equal. As a result, the possibility of misjudgment increases.

  Or, from the opposite viewpoint, in order to improve the inspection accuracy, it is necessary to prevent a plurality of cells having different time histories from being mixed in the same stack. However, in this case, the fractional cells generated before and after the interruption must be discarded, which reduces the yield and increases the manufacturing cost.

  Therefore, according to the present embodiment, after assembling the stack 100, information on the time history is acquired, and the cells 1 in the stack 100 are divided into several groups based on the time history of each cell 1 ( Grouping process). Cells 1 belonging to the same group are assigned the same group number. Then, the leaving period of the entire stack 100 is determined according to the group numbers of all the cells 1 in the stack 100.

  As will be described in detail later, the present inventor sets an appropriate leaving period according to the time history, thereby reducing the amount of voltage drop per unit time (decreasing speed) of each cell 1 after the leaving period has elapsed. ) Are equal to each other. That is, after the leaving period has elapsed, the time interval between the step of measuring the cell voltage V1 (S70) and the step of measuring the cell voltage V2 (S90) (that is, the required period of S80) is set to all cells in the stack 100. By making common for 1, voltage drop amounts can be made equal to each other. Thereby, even if the stack 100 includes a plurality of cells 1 having different time histories, the inspection accuracy can be improved.

  FIG. 4 is a flowchart for explaining the stack 100 inspection method according to the first embodiment. This flowchart differs from the flowchart according to the comparative example (see FIG. 2) in that it further includes a grouping process (S55). Referring to FIG. 4, when stack 100 is formed from n1 cells (S50), a group number is assigned to each cell 1 in stack 100 in S55. Then, the leaving period of the entire stack 100 is determined according to the group numbers of all the cells 1 in the stack 100 (S60). Details of the leaving period determination method (S55, S60) based on the grouping process will be described later with reference to FIGS. Since other processes are equivalent to the corresponding processes of the flowchart according to the comparative example, detailed description will not be repeated.

  FIG. 5 is a diagram for explaining the flow of information in the inspection method shown in FIG. Referring to FIG. 4 and FIG. 5, cell 1 in which all of high temperature aging processing (S10), low temperature aging processing (S20), performance inspection (capacity inspection) processing (S30), and voltage adjustment processing (S40) have been completed. When the stack 100 is assembled (S50), the group number is determined for each of the cells 1 constituting the stack 100 based on the information (time history) regarding the high temperature aging period T1, the low temperature aging period T2, and the voltage adjustment period T3. It is determined. Furthermore, the leaving period of the entire stack 100 is determined according to the group number of each cell 1. When the cell voltages V1 and V2 are measured before and after the leaving period (S70 and S90), even if a plurality of cells 1 having different time histories are mixed in the same stack 100, It is experimentally determined in advance so that the decrease rate of the decrease amount is approximately equal between the cells 1. The reason for determining the leaving period in this way will be described in detail below with reference to FIGS. By appropriately setting the leaving period, the inspection accuracy can be improved even when the same stack 100 includes a plurality of cells 1 having different time histories.

<Influence of time history>
The reason why the leaving period is determined based on the time history will be described in detail below in the order of the low temperature aging period T2, the high temperature aging period T1, and the voltage adjustment period T3.

  FIG. 6 is a diagram for explaining a difference in behavior of the voltage drop amount of the cell 1 according to the low temperature aging period T2. 6 and FIG. 7 and FIG. 8 described later, the horizontal axis represents the elapsed time, and the vertical axis represents the voltage drop amount of the cell 1. Each curve represents the behavior of the voltage drop amount of the different cells 1 from each other.

  Referring to FIG. 6, each of the curves C1 shows the behavior of the voltage drop amount of each cell 1 when the low temperature aging period T2 is less than the boundary value. Each of the curves C2 shows the behavior of the voltage drop amount of each cell 1 when the low temperature aging period T2 is equal to or greater than the boundary value. The boundary value is determined according to the configuration of the cell 1, conditions of the low temperature aging process, and the like, but is Ta (unit: time) in the present embodiment.

  The curve C1 in which the low temperature aging period T2 is less than Ta corresponds to the low temperature aging process during normal operation, and the curve C2 in which the low temperature aging period T2 is greater than or equal to Ta corresponds to the low temperature aging process when the interruption occurs. it can. Hereinafter, the cell 1 having a low temperature aging period T2 of less than Ta is abbreviated as “a cell having a low temperature aging period T2 is short”, and the cell 1 having a low temperature aging period T2 of not less than Ta is abbreviated as a “cell having a long low temperature aging period T2”.

  When the voltage adjustment process (S30 in FIG. 4) ends at time t0, the voltage drop amount of each cell 1 rapidly decreases after time t0. Thereafter, as shown by the curve C1, the voltage drop amounts of the cells having a short low-temperature aging period T2 are similar to each other in that the rate of reduction of the voltage drop amount is relatively large (in other words, the voltage drop amount tends to be small). Show the behavior. On the other hand, as shown by the curve C2, the voltage decrease amount of the cell having a long low temperature aging period T2 is smaller than the voltage decrease amount of the cell having a short low temperature aging period T2 ( In other words, there is a tendency that the amount of voltage drop is not easily reduced.

  From another viewpoint, the voltage drop amount ΔV (k) (see Expression (1)) is larger in a cell having a short low-temperature aging period T2 than in a cell having a short low-temperature aging period T2. On the other hand, in a cell having a long low temperature aging period T2, the voltage drop amount ΔV (k) is relatively small.

  When a small number of cells having a long low temperature aging period T2 coexist in the stack 100 in which the majority of the cells have a short low temperature aging period T2, the average value ΔVave of the voltage drop amount becomes relatively large. In this case, when the voltage drop amount ΔV (k) and the average value ΔVave of the voltage drop amount are compared according to the above formulas (3) and (4) for the cell having a long low temperature aging period T2, it is actually abnormal (short circuit). In spite of not having occurred, possibility that it will determine with abnormality will become high. Therefore, all the cells in the same stack need to be configured only with cells having a short low-temperature aging period T2 (only cells during normal operation).

  FIG. 7 is a diagram for explaining the difference in the behavior of the voltage drop amount of the cell 1 according to the high temperature aging period T1. FIG. 7A shows an example of the behavior of the voltage drop amount of the cell 1 when the high-temperature aging period T1 is less than Tb (unit: time) (Ta> Tb) (see the curve C3). FIG. 7B shows an example of the behavior of the voltage drop amount of the cell 1 when the high temperature aging period T1 is equal to or greater than Tb (see the curve C4). Between the curve C3 and the curve C4, the inspection conditions (such as the low temperature aging period T2) other than the high temperature aging period T1 are equal to each other.

  Hereinafter, a cell 1 having a high temperature aging period T1 of less than Tb is abbreviated as “a cell having a short high temperature aging period T1”, and a cell 1 having a high temperature aging period T1 of Tb or more is abbreviated as a “cell having a high temperature aging period T1”. However, “Tb” is determined according to the configuration of the cell 1, the conditions of the high temperature aging process, and the like, similarly to the boundary value “Ta” of the low temperature aging period T 2 described above.

  Referring to FIG. 7A, when the voltage adjustment process (S30 in FIG. 4) ends at time t0, the voltage decrease amount rapidly decreases after time t0. However, in a cell with a short high-temperature aging period T1, the rate of decrease in the voltage drop amount (the slope of the tangent line Ct3 of the curve C3) becomes substantially constant after time t11. The shortest period (the period from time t0 to time t11) required for the rate of decrease in the voltage drop amount to become substantially constant after the voltage adjustment processing is completed is referred to as a “shortest neglected period”.

  On the other hand, referring to FIG. 7B, in the cell having a long high-temperature aging period T1, the decrease rate of the voltage decrease amount is not constant at time t11, and the decrease rate of the voltage decrease amount after time t12 (in curve C4). The slope of the tangent line Ct4) is substantially constant. That is, in a cell having a long high temperature aging period T1, the shortest standing period tends to be longer than in a cell having a short high temperature aging period T1.

  The present inventors have found that the slope of the tangent line Ct3 and the slope of the tangent line Ct4 are almost equal regardless of the length of the high temperature aging period T1. By utilizing this characteristic, even when a cell having a long high temperature aging period T1 and a short cell coexist in the stack 100, after the voltage adjustment process is completed, the shortest standing period of the cell having a long high temperature aging period T1 ( By leaving the stack 100 for a period equal to or longer than the shortest standing period of the curve C4, the rate of decrease in the voltage drop amount of all the cells 1 in the stack 100 becomes equal to each other. Therefore, in the example shown in FIG. 7, the cell voltage V1 is measured at time t13 and the cell voltage V2 is measured at time t14, whereby the voltage drop amount ΔV (= V1−) of the cell having a long high temperature aging period T1 and the short cell. V2) becomes equal.

  As described above, if the leaving period in S50 of FIG. 4 is set to be sufficiently long in accordance with a cell having a long high temperature aging period T1, the voltage drops regardless of the length of the high temperature aging period T1 of each cell 1 in the stack 100. The quantity ΔV can be made equal. As a result, even when a plurality of cells having different high-temperature aging periods T1 are included in the same stack, the short-circuit inspection can be performed with higher accuracy than in the comparative example.

  FIG. 8 is a diagram for explaining a difference in behavior of the voltage drop amount of the cell 1 according to the voltage adjustment period T3. 8A to 8C, the curve L1 corresponds to the voltage adjustment period T3 = Tg, and the curve L2 corresponds to the voltage adjustment period T3 = Tf. To do. Curve L3 corresponds to voltage adjustment period T3 = Te, and curve L4 corresponds to voltage adjustment period T3 = Td. Curve L5 corresponds to voltage adjustment period T3 = Tc, and curve L2 corresponds to voltage adjustment period T3> Tc. However, Tc> Td> Te> Tf> Tg (unit: time).

  Referring to FIG. 8A, when the voltage adjustment period T3 = Tg, as shown by the curve L1, the decrease rate of the voltage drop amount (the slope of the tangent Lt1 of the curve Lt) is substantially constant after time t31. Become. That is, when the voltage adjustment period T3 = Tg, if the leaving period of the stack 100 is equal to or longer than the shortest leaving period (a period between time t0 and time t31), the slope of the tangent Lt1 becomes substantially constant.

  Similarly, when the voltage adjustment period T3 = Tf, as shown by the curve L2, the decrease rate of the voltage drop amount (the slope of the tangent Lt2 of the curve L2) becomes substantially constant after time t32. That is, when the voltage adjustment period T3 = Tf, the slope of the tangent line Lt2 is almost constant if the leaving period of the stack 100 is equal to or longer than the shortest leaving period (a period between time t0 and time t32). Since the other curves L3 to L6 shown in FIG. 8B or FIG. 8C are the same, detailed description will not be repeated.

  The present inventors have found that the slopes of the tangents Lt1 to Lt6 are substantially equal to each other as in the case of the high temperature aging treatment (see FIG. 7). By utilizing this characteristic, the cell voltage V1, V2 is measured after the elapse of the longest period among the shortest neglected periods of the plurality of cells constituting the stack 100, thereby increasing or decreasing the voltage adjustment period T3. Regardless, the voltage drop amounts ΔV can be made equal to each other.

  For example, when a cell with a voltage adjustment period T3 = Tg, a cell with a voltage adjustment period T3 = Tf, and a cell with a voltage adjustment period T3 = Te are included in the same stack, the shortest cell in the voltage adjustment period T3 = Te By setting the leaving period of the entire stack 100 to be longer than the leaving period (the shortest leaving period of the curve L3), the voltage drop amount ΔV of all the cells 1 of the stack 100 can be made substantially equal. Therefore, even when a plurality of cells having different voltage adjustment periods T3 are included in the same stack, the short circuit inspection can be performed with higher accuracy than in the comparative example.

  As described above with reference to FIG. 6, the short-circuit inspection can be performed with high accuracy only for the cells whose low-temperature aging period T2 is less than Ta (cells during normal operation). In addition, about the cell (cell at the time of interruption occurrence) whose low temperature aging period T2 is more than Ta, when the number is insufficient with respect to the number required to form a stack, you may discard. Alternatively, when there are more cells at the time of occurrence of interruptions than the number of stacks that can be formed, the stack may be formed using a method as described later in the second embodiment.

  Further, as described with reference to FIGS. 7 and 8, by setting the leaving period to the longest of the shortest leaving of each cell in the stack, regardless of the high temperature aging period T1 and the voltage adjustment period T3, Short circuit inspection can be performed with high accuracy. Therefore, grouping (grouping processing) is performed for each cell in the stack 100 according to the high temperature aging period T1, the low temperature aging period T2, and the voltage adjustment period T3.

<Grouping process>
FIG. 9 is a flowchart for explaining the grouping process (S55) shown in FIG. Each step of the flowchart shown in FIG. 9 and FIG. 10 described later is realized by software processing by a control device (for example, a microcomputer) (not shown) after the cell assembling step (S50 in FIG. 4) is completed. However, the configuration of the control device is not particularly limited, and may be realized by dedicated hardware (electronic circuit). Referring to FIG. 9, in S200, a group number is determined for each cell 1 in stack 100.

  FIG. 10 is a flowchart for explaining the group number determination process (S200) shown in FIG. Each process described below is performed on all the cells 1 in the stack 100, but may be performed on all the cells 1 simultaneously or sequentially.

  Referring to FIG. 10, in S210, information regarding a time history of a certain cell 1 in stack 100, that is, a high temperature aging period T1, a low temperature aging period T2, and a voltage adjustment period T3 is acquired.

  In S220, it is determined whether or not the low temperature aging period T2 of the cell 1 is less than Ta. When the low temperature aging period T2 is equal to or longer than Ta (NO in S220), as described with reference to FIG. 6, the behavior of the voltage drop amount after the end of the voltage adjustment may be different from the case where the low temperature aging period T2 is less than Ta. Therefore, the group number is determined to be “0”, assuming that the short circuit inspection cannot be accurately performed for the cell 1 (S225). On the other hand, when low temperature aging period T2 is less than Ta (YES in S210), the process proceeds to S230.

  In S230, it is determined whether or not the high temperature aging period T1 of the cell 1 is less than Tb. When the high temperature aging period is equal to or longer than Tb (NO in S230), the group number of the cell 1 is determined to be “6” (S235). On the other hand, when the high temperature aging period is less than Tb (YES in S230), the process proceeds to S240.

  In S240, it is determined whether or not the voltage adjustment period T3 of the cell 1 is less than Tc. When voltage adjustment period T3 is equal to or longer than Tc (NO in S240), the group number of cell 1 is determined to be “5” (S245). On the other hand, when voltage adjustment period T3 is less than Tc (YES in S240), the process proceeds to S250.

  In S250, it is determined whether or not the voltage adjustment period T3 of the cell 1 is less than Td. When voltage adjustment period T3 is equal to or greater than Td and less than Tc (NO in S250), the group number of cell 1 is determined to be “4” (S255). On the other hand, when voltage adjustment period T3 is less than Td (YES in S250), the process proceeds to S260.

  In S260, it is determined whether or not the voltage adjustment period T3 of the cell 1 is less than Te. When voltage adjustment period T3 is equal to or greater than Te and less than Td (NO in S260), the group number of cell 1 is determined to be “3” (S265). On the other hand, when voltage adjustment period T3 is less than Te (YES in S260), the process proceeds to S270.

  In S270, it is determined whether or not the voltage adjustment period T3 of the cell 1 is less than Tf. When voltage adjustment period T3 is equal to or greater than Tf and less than Te (NO in S270), the group number of cell 1 is determined to be “2” (S275). On the other hand, when voltage adjustment period T3 is less than Tf (YES in S270), the group number of the cell is determined to be “1” (S280). When the group numbers are determined for all the cells 1 in the stack 100 as described above, the process returns to the flowchart shown in FIG.

  Referring again to FIG. 9, when group number “0” is assigned to at least one cell 1 in stack 100 because the short-circuit inspection cannot be performed with high accuracy in S225 of FIG. 10 (YES in S290). For the stack 100, the series of processing is terminated without performing the short circuit inspection (S295).

  On the other hand, if cell 1 with group number “0” is not included in stack 100 (NO in S290), whether or not the group numbers of all cells 1 in stack 100 are the same. It is determined (S300). When the group numbers of all the cells 1 are the same (YES in S300), the group number is determined as the number of the stack 100 (hereinafter referred to as “stack number”) (S310).

  On the other hand, when a plurality of cells 1 having different group numbers are mixed in the stack 100 (NO in S300), the largest group number is determined as the stack number (S320). Thereafter, the leaving period is calculated according to the stack number determined in S310 or S320 (S330).

  FIG. 11 is a diagram for explaining a leaving period determined according to the stack number. Referring to FIG. 11, when the stack number is “1”, the leaving period is the shortest, and is determined to be, for example, D1 (unit: day). As the stack number increases, the leaving period becomes longer. When the stack number is “6”, the leaving period is the longest and is determined to be D6 (unit: day). That is, D1 <D2 <D3 <D4 <D5 <D6. Note that D6 = Ta may be set.

  FIG. 12 is a diagram illustrating an example of a stack number determination method. Referring to FIG. 12, among n1 cells 1 constituting stack 100, na cell 1 has a group number “1”, and nb cell 1 has a group number “5”. A case where the group number of nc cells 1 is “3” will be described (na + nb + nc = n1). In this case, the stack number of the stack 100 is “5” which is the largest among the group numbers 1, 3, and 5 (see S320 of FIG. 9), and the leaving period of the entire stack 100 is determined as D5 from FIG.

  Thus, according to Embodiment 1, when a plurality of cells having different time histories are included in the stack, the leaving period of the entire stack is determined based on the time history of each cell. More specifically, the neglect period is a period (shortest time) required for the rate of decrease in the voltage drop amount (the slope of each tangent line shown in FIGS. 7 and 8) to be substantially constant among all the cells in the stack. (Leave period) is determined according to the longest cell. By doing so, as described with reference to FIGS. 7 and 8, the rate of decrease in the voltage drop amount of all the cells in the stack can be made equal. Therefore, even when a plurality of cells having different time histories are included in the stack, the inspection accuracy can be improved.

  Furthermore, according to the first embodiment, when the interruption period as described in FIG. 3B occurs, a stack is formed including a plurality of cells having different high-temperature aging periods T1 or voltage adjustment periods T3. It becomes possible to do. Therefore, since the cell yield is improved, the manufacturing cost can be reduced.

[Modification]
In the first embodiment, the configuration for determining the leaving period in units of stacks has been described. However, in the stack inspection process, a storage shelf for managing and storing a plurality of stacks at once is provided, and short-circuit inspection is performed in units of storage shelves. May be implemented. In the modification of the first embodiment, a configuration will be described in which after determining the stack number, a storage shelf number (storage shelf number) is further determined based on the stack number.

  FIG. 13 is a flowchart for explaining processing according to the modification of the first embodiment. Referring to FIG. 13, this flowchart differs from the flowchart shown in FIG. 9 in that it includes the processes of S340 to S370 instead of S330.

  In S310 or S320, stack numbers are determined for all stacks 100 installed on a certain storage shelf. Thereafter, in S340, it is determined whether or not the stack number is the same between the stacks. If all stacks 100 have the same stack number (YES in S340), the stack number is determined as a storage shelf number (S350). On the other hand, when a plurality of stacks 100 having different stack numbers are mixed in the storage shelf (NO in S340), the largest stack number is determined as the storage shelf number (S360). Thereafter, the leaving period is calculated according to the stack number determined in S350 or S360 (S370). The method for calculating the leaving period is the same as that shown in FIG. 11 if “stack number” is replaced with “storage shelf number”, and therefore detailed description will not be repeated.

  According to this modification, by determining the leaving period in units of storage shelves, it becomes possible to manage whether or not the leaving period elapses in units of storage shelves. Compared with the first mode 1), it is possible to prevent management from becoming complicated.

[Embodiment 2]
In the first embodiment and the modification thereof, it has been described that the presence / absence of abnormality cannot be determined with high accuracy for a stack in which a cell having a long low temperature aging period T2 and a short cell are mixed (see S295 in FIG. 9). According to the second embodiment, a configuration for enabling determination of the presence / absence of an abnormality in the stack will be described.

  Referring to FIG. 6 again, as described above, the behavior of the voltage drop amount of the cell having the long low temperature aging period T2 (curve C2) is the same as the behavior of the voltage drop amount of the cell having the short low temperature aging period T2 (curve C1). Different. However, when attention is paid only to the cell having a long low-temperature aging period T2, it can be seen that the behavior of the voltage drop amount is similar. Therefore, if cells having a long low-temperature aging period T2 are not mixed in the same stack 100, cells having a long low-temperature aging period T2 are abnormal. It is possible to determine whether or not there is. Therefore, in the second embodiment, the reordering process of the cells 1 is performed according to the low temperature aging period T2 so as to avoid a state in which cells having a long low temperature aging period T2 and short cells are mixed in the same stack 100. Is done.

  FIG. 14 is a flowchart for explaining an inspection method for stack 100 according to the second embodiment. Referring to FIG. 14, this flowchart is a flowchart according to the first embodiment in that it includes S55A in place of the grouping process (S55) shown in FIG. 4 and a rearrangement process (S45). 4). Since the other processes are equivalent to the corresponding processes in the flowchart shown in FIG. 4, detailed description will not be repeated.

  FIG. 15 is a diagram for explaining the flow of information in the inspection method shown in FIG. Referring to FIGS. 14 and 15, the cell 1 rearrangement process (S45) is performed based on the information of the low temperature aging period T2 at the stage of the single cell before being assembled into the stack 100. More specifically, for example, among n1 cells to be assembled into the stack 100, nd cells have a long low temperature aging period T2, and the remaining ne cells have a short low temperature aging period T2, The nd cells are replaced by cells having a short low temperature aging period T2. As a result, the stack 100 is configured to include only cells having a short low-temperature aging period T2. Or conversely, the stack 100 may include only cells having a long low-temperature aging period T2. Thus, according to the second embodiment, the cell 1 rearrangement process is performed so that the stack 100 is configured by only one of the long cell and the short cell having the low temperature aging period T2.

  In the grouping process in the second embodiment, the information on the low temperature aging period T2 may not be used. That is, since the low temperature aging period T2 is common to all the cells 1 in the stack 100 after the rearrangement process is performed, the grouping process substantially includes the information of the high temperature aging period T1 and the voltage adjustment period T3. Based on.

  FIG. 16 is a flowchart for explaining the grouping process (S55A) shown in FIG. Referring to FIG. 16, this flowchart replaces the group number determination process (S200) shown in FIG. 10 and includes a process including S201, and a process for determining the presence or absence of cell 1 having a group number of “0” (FIG. 9). (S290, S295) is different from the flowchart according to the first embodiment (see FIG. 9). Since other processes are equivalent to the corresponding processes in the flowchart shown in FIG. 9, detailed description will not be repeated.

  FIG. 17 is a flowchart for explaining the group number determination process (S201) shown in FIG. This flowchart differs from the flowchart according to the first embodiment (see FIG. 10) in that it does not include the process (S220, S225 in FIG. 10) for assigning the group number “0” based on the low temperature aging period T2. Referring to FIG. 14, FIG. 16, and FIG. 17, in S210, when information on the high temperature aging period T1, the low temperature aging period T2, and the voltage adjustment period T3 is acquired, the group number of each cell 1 is obtained after S230. It is determined. Since each process of S230-S280 is equivalent to each process (refer FIG. 10) demonstrated in Embodiment 1, detailed description is not repeated.

  Thus, according to the second embodiment, based on the information on the low temperature aging period T2, so that only one of the long cell and the short cell is included in the same stack, Rearrange the cells before being assembled into the stack. As a result, the behavior of the voltage drop amount of all the cells in the stack becomes substantially equal, so that it is possible to accurately determine whether there is an abnormality in each cell regardless of the length of the low temperature aging period T2. As a result, since the number of cells that can be assembled in the stack is increased and the yield is further improved as compared with the first embodiment, the manufacturing cost can be further reduced.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 cell, 100 stacks.

Claims (1)

An inspection method for inspecting abnormality of a battery stack formed using a plurality of cells,
Applying a high temperature aging treatment to each of the plurality of cells;
Applying a low temperature aging treatment to each of the plurality of cells;
Inspecting the capacity of each of the plurality of cells;
Adjusting the voltage of each of the plurality of cells;
Forming the battery stack using the plurality of cells after performing the high temperature aging process, performing the low temperature aging process, inspecting the capacity, and adjusting the voltage;
Leaving the battery stack for a period of time;
Measuring an initial voltage for each of the plurality of cells constituting the battery stack after elapse of the leaving period;
Measuring a voltage after being left for each of the plurality of cells constituting the battery stack after a predetermined period of time has elapsed since the measurement of the initial voltage;
By calculating a voltage drop amount from the initial voltage to the after-stand voltage for each of the plurality of cells constituting the battery stack, and comparing the voltage drop amount between the plurality of cells, Determining whether there is an abnormality,
The neglect period is a required period of the step of performing the high temperature aging process, a required period of the step of performing the low temperature aging process, and a period from the end of the step of inspecting the capacity to the start of the step of adjusting the voltage. A method for inspecting a battery stack, which is determined based on a period.

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