Method for manufacturing bipolar secondary battery

Abstract

To appropriately perform self-discharge inspection of each power storage cell included in a bipolar secondary battery.SOLUTION: A method for manufacturing a bipolar secondary cell includes connecting a power source to each of a plurality of electric storage cells included in the bipolar secondary cell to form an inspection circuit for each electric storage cell such that inspection circuits of adjacent electric storage cells have a common wire portion (S101), and performing a self-discharge inspection of each electric storage cell while canceling out a current flowing through each inspection circuit of the adjacent electric storage cells at the common wire portion by feedback control of the power source connected to each electric storage cell (S111 to S116).SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Japanese Patent Application Laid-Open No. 2019-113450 (Patent Document 1) discloses a technique for connecting a power source to a secondary battery to form a circuit, and using the power source to pass a current through the circuit to perform a self-discharge test on the secondary battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-113450 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, Patent Document 1 does not fully consider a method for efficiently conducting self-discharge testing of multiple secondary batteries. When the technology described in Patent Document 1 is used to test the self-discharge of a bipolar secondary battery having multiple storage cells, there is a risk that the testing time will be long and the testing accuracy will be reduced.

[0005] The present disclosure has been made to solve the above-mentioned problems, and its purpose is to appropriately perform a self-discharge test on each storage cell included in a bipolar secondary battery. [Means for solving the problem]

[0006] According to one aspect of the present disclosure, there is provided a method for manufacturing a bipolar secondary battery including a plurality of storage cells, the method including: connecting a power supply to each of the plurality of storage cells to form an inspection circuit for each storage cell such that the inspection circuits of adjacent storage cells have a common wiring portion; and conducting a self-discharge inspection of each storage cell while canceling out currents flowing through the inspection circuits of adjacent storage cells at the common wiring portion through feedback control of the power supply connected to each storage cell. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to appropriately perform a self-discharge test on each storage cell included in a bipolar secondary battery. [Brief explanation of the drawings]

[0008] [Figure 1] 10 is a flowchart showing a procedure for a self-discharge inspection according to the present embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing the configuration of a laminate included in an inspection object. [Figure 3] FIG. 2 is a diagram for explaining a test circuit according to the present embodiment. [Figure 4] 10A and 10B are diagrams for explaining a self-discharge inspection according to the present embodiment; [Figure 5] 5A to 5C are diagrams for explaining the operation and effect of the method for manufacturing a bipolar secondary battery according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, identical or corresponding parts are designated by the same reference numerals, and their description will not be repeated. In each of the drawings used below, the X-axis, Y-axis, and Z-axis are perpendicular to each other, and the Z-axis indicates the thickness direction of the battery. Hereinafter, the directions indicated by the arrows of the X-axis, Y-axis, and Z-axis will be indicated with a "+" and the opposite directions will be indicated with a "-".

[0010] 1 is a flowchart showing the procedure for a self-discharge inspection according to this embodiment. In the method for manufacturing a bipolar secondary battery according to this embodiment, first, an object to be inspected is prepared. Then, a self-discharge inspection is performed on the object to be inspected according to the process flow shown in FIG.

[0011] The test object according to this embodiment includes a laminate 10 shown in FIG. 2. FIG. 2 is a cross-sectional view showing the configuration of the laminate included in the test object. Referring to FIG. 2, the laminate 10 includes a power storage unit 10a and a sealing unit 3 that seals the power storage unit 10a. The Z direction corresponds to the stacking direction. The power storage unit 10a includes a plurality of cells C (unit batteries) lined up in the Z direction. Each of the plurality of cells C includes a negative electrode active material layer 12A, a positive electrode active material layer 12B, and a separator 13.

[0012] Each of the multiple cells C is configured to be able to store electricity. Each of the multiple cells C functions as a secondary battery. Each of the multiple cells C corresponds to an example of a "storage cell" according to the present disclosure. In this embodiment, the power storage unit 10a includes 10 or more cells C. However, the number of cells C can be set as desired. The number of cells C included in the power storage unit 10a may be 3 or more but less than 50, or may be 50 or more. The sealing unit 3 is formed to surround the power storage unit 10a. The space surrounded by the sealing unit 3 is filled with an electrolyte. The electrolyte is impregnated into the separator 13.

[0013] The laminate 10 includes multiple electrodes (one negative terminal electrode 2A, multiple bipolar electrodes 1, and one positive terminal electrode 2B) stacked along the Z direction. A separator 13 is disposed between the electrodes. The bipolar electrode 1 includes a current collector 11, a negative electrode active material layer 12A provided on the +Z side surface of the current collector 11, and a positive electrode active material layer 12B provided on the -Z side surface of the current collector 11. The negative electrode terminal electrode 2A has a configuration in which the positive electrode active material layer 12B has been removed from the bipolar electrode 1. An insulating layer 19A covering the periphery of the current collector 11 is formed on the -Z side surface of the current collector 11 constituting the negative electrode terminal electrode 2A. The positive electrode terminal electrode 2B has a configuration in which the negative electrode active material layer 12A has been removed from the bipolar electrode 1. An insulating layer 19B covering the periphery of current collector 11 is formed on the +Z side surface of current collector 11 that constitutes positive terminal electrode 2B.

[0014] In this embodiment, a metal foil (e.g., aluminum foil) is used as the current collector 11 of each electrode. One or both sides of the metal foil may be subjected to a surface treatment (e.g., plating treatment). A voltage detection terminal 20 is connected to the current collector 11 of each electrode. In this embodiment, the voltage detection terminal 20 comprises stainless steel (e.g., SUS304). Stainless steel has excellent corrosion resistance, heat resistance, and workability. However, the material of the voltage detection terminal 20 can be changed as appropriate. Other metals (e.g., copper) may be used instead of stainless steel.

[0015] The negative electrode active material layer 12A includes a negative electrode active material. The positive electrode active material layer 12B includes a positive electrode active material. In one example, the positive electrode active material is olivine-type lithium iron phosphate (LiFePO4), the negative electrode active material is a carbon-based material, and the electrolyte is a non-aqueous electrolyte. However, other examples of the negative electrode active material include silicon and tin. The electrolyte may be an aqueous electrolyte. Alternatively, a gel or solid electrolyte may be used instead of the electrolyte.

[0016] In the laminate 10, cells C are formed between the stacked current collectors 11. Specifically, a cell C is formed between a certain current collector 11 (first current collector) and a current collector 11 (second current collector) adjacent to the first current collector. Furthermore, a cell C is formed between a second current collector and a current collector 11 (third current collector) adjacent to the second current collector. In this way, the current collectors 11 and the cells C are arranged alternately in the stacking direction of the laminate 10. The sealing portion 3 includes seal layers 14 and 15 arranged around each of the plurality of cells C included in the laminate 10, and the aforementioned insulating layers 19A and 19B. Any sealing material can be used as the material of the sealing portion 3.

[0017] The laminate 10 functions as a bipolar secondary battery. Each of the multiple cells C included in the laminate 10 (particularly, the power storage unit 10a) functions as, for example, an LFP battery (a lithium-ion secondary battery containing lithium iron phosphate as a positive electrode active material). Hereinafter, the first, second, third, fourth, fifth, and so on cells C from the positive electrode side (+Z side) end of the laminate 10 may be referred to as cell C-1, cell C-2, cell C-3, cell C-4, cell C-5, and so on, respectively (see FIG. 4, which will be described later). In the laminate 10, multiple cells are stacked in the Z direction. Adjacent cells have a common electrode. Specifically, the current collector 11 and the voltage detection terminal 20 located between adjacent cells function as a common electrode. This common electrode functions as a common wiring, which will be described later (see FIG. 3).

[0018] For example, the manufacturing system may perform various processes such as coating, pressing, seal welding, separator welding, cutting, terminal (voltage detection terminal) welding, end face welding, injection molding, liquid injection, and temporary sealing to form the laminate 10 ( FIG. 2 ) to which the voltage detection terminal 20 is connected. The laminate 10 may then be restrained by a restraining jig. The laminate 10 may also be sandwiched and pressed between a pair of end plates (restraint plates). After restraint, the manufacturing system charges and ages the laminate 10. Charging is performed before and / or during aging. Aging may be performed at a temperature higher than room temperature (high-temperature aging), for example. The high-temperature aging temperature may be 50°C or higher and 85°C or lower.

[0019] Charging after the constraint may include initial charging and individual charging. Initial charging is the first charging of the formed laminate 10. For example, the manufacturing system applies a voltage between the positive and negative terminals of the laminate 10 (e.g., the current collectors 11 located at both ends in the Z direction shown in FIG. 2). This charges all of the cells C connected in series. After the initial charging, the manufacturing system may connect a power source to the voltage detection terminal 20 to perform individual charging. The manufacturing system may individually charge each cell using power supplied from a power source to each cell through the voltage detection terminal 20 for each cell. The manufacturing system may perform individual charging of one of the odd-numbered cells and the even-numbered cells, and then perform individual charging of the other. The odd-numbered cells are the odd-numbered cells C from the positive electrode end of the laminate 10. The even-numbered cells are the even-numbered cells C from the positive electrode end of the laminate 10. High-temperature aging may be started during individual charging. The manufacturing system may perform individual charging while performing high-temperature aging on the laminate 10. After high-temperature aging, the manufacturing system may cool the laminate 10 to room temperature (for example, about 25° C.).

[0020] Referring again to Fig. 1, in this embodiment, an object to be inspected (e.g., the laminate 10 in a constrained state) is prepared through the formation of the laminate 10, restraint, initial charging, individual charging, high-temperature aging, and cooling. Then, when the object to be inspected is handed over to an inspection device (e.g., the inspection device 100 shown in Fig. 4, which will be described later), the inspection device automatically executes the processing flow shown in Fig. 1 for the object to be inspected. Note that "S" in the flowchart denotes a step.

[0021] In S101, the inspection device forms an inspection circuit by connecting the inspection object to the power supply unit of the inspection device. In the following S102, the inspection device measures the circuit resistance (e.g., wiring resistance and contact resistance) of the formed inspection circuit. Thereafter, the inspection device performs a self-discharge inspection of the inspection object by processing from S111 onwards. The self-discharge inspection will be described later.

[0022] The manufacturing system includes devices (devices corresponding to each process) that prepare the test object and a test device that performs a self-discharge test on the test object. However, it is not necessary that the manufacturing of the power storage device (including the self-discharge test) be performed automatically (i.e., that all processes related to the manufacturing be performed by the device), and some processes may be performed by a person (operator). Furthermore, restraint, individual charging, aging, and cooling are not required, and at least one of these processes may be omitted. Furthermore, the test object can be changed as appropriate. The structure of the test object is not limited to the structure shown in FIG. 2. The type of battery is not limited to an LFP battery, and may be another secondary battery (for example, a ternary lithium-ion secondary battery or a nickel-metal hydride secondary battery).

[0023] Fig. 3 is a diagram for explaining the test circuit. Circuit 400 shown in Fig. 3 corresponds to the test circuit according to this embodiment. However, before explaining circuit 400, circuits 300 and 300A formed for one cell will be explained.

[0024] The circuit 300 shown in FIG. 3 includes a battery circuit 310 and a power supply circuit 320. The battery circuit 310 corresponds to an equivalent circuit model of one cell. Between terminals B1 and B2 of the battery circuit 310, there are an electromotive element 311, a short-circuit resistor 312 connected in parallel to the electromotive element 311, and an internal resistor 313 connected in series to the electromotive element 311. The electromotive force of the electromotive element 311 (hereinafter referred to as "Vcell") decreases due to self-discharge of the cell. The self-discharge current of the cell (hereinafter referred to as "Icell") flows through the short-circuit resistor 312. The smaller the resistance value (hereinafter referred to as "Rp") of the short-circuit resistor 312, the larger Icell. The terminal voltage of the battery circuit 310 (hereinafter referred to as "VB") corresponds to the potential difference (cell voltage) between the positive and negative electrodes of the cell. The power supply circuit 320 includes a DC power supply 321 and a circuit resistor 322. The DC power supply 321 outputs a voltage (hereinafter referred to as "VS"). The resistance value (hereinafter referred to as "Rext") of the circuit resistor 322 is, for example, the total value of parasitic resistance present in the entire circuit. Parasitic resistance includes wiring resistance (electrical resistance of each conductor that makes up the circuit) as well as contact resistance. Hereinafter, the current that flows through the circuit 300 due to VS will be referred to as "IB". When the output voltage (VS) of the DC power supply 321 is constant, the following equation (1) holds.

[0025] IB = (VS - VB) / Rext (1)

[0026] When VB decreases due to cell self-discharge, IB increases. When IB increases and becomes equal to the self-discharge current (Icell), VB stops decreasing and the cell voltage becomes constant. At this time, IB represents the self-discharge current.

[0027] On the other hand, by increasing the output voltage (VS) of the DC power supply 321, IB increases faster than when VS is constant. This shortens the time it takes for IB to become equal to the self-discharge current. However, in order to suppress overshoot, it is desirable to introduce the concept of virtual resistance and consider the circuit 300 as being replaced with circuit 300A. The virtual resistance reduces Rext in an artificial manner. As Rext decreases, IB increases accordingly. Note that virtual resistance is an imaginary electrical resistance that does not actually exist.

[0028] Circuit 300A has basically the same configuration as circuit 300, but includes power supply circuit 320A instead of power supply circuit 320. In power supply circuit 320A, virtual resistor 323 is inserted in series with circuit resistor 322. The resistance value of virtual resistor 323 (hereinafter referred to as "Rim") is a negative value or zero. Hereinafter, the sum of Rext and Rim will be referred to as "Rext'". In this case, the following equation (2) holds.

[0029] IB=(VS-VB) / Rext' …(2)

[0030] In equation (2), Rext' must be a positive value. Reducing Rim (making it more negative) also reduces Rext'. By reducing Rim while keeping VS constant in circuit 300A, it is possible to virtually create the same situation as when VS is increased in circuit 300. For example, if Rext is 5 Ω and Rim is -4 Ω, Rext' becomes 1 Ω. Reducing Rim from 0 Ω to -4 Ω increases IB by five times. The closer Rext' is to zero, the larger IB becomes.

[0031] Next, a circuit 400 formed for a series of multiple cells C under test will be described. The circuit 400 includes a battery circuit 410 and a power supply circuit 420. The battery circuit 410 is configured by the test object. The test object according to this embodiment has more than three cells, but FIG. 3 shows three representative cells (cells C-1 to C-3). Each of the cells C-1 to C-3 is represented by the same equivalent circuit model as the battery circuit 310 described above.

[0032] The power supply circuit 420 is configured, for example, by a power supply unit 110 and a connection unit 120 (see FIG. 4) of the inspection device 100, which will be described later. The power supply circuit 420 has a plurality of channels (hereinafter referred to as "Ch") for self-discharge inspection. Each Ch has a DC power supply 41, an ammeter 42, a voltmeter 43, a terminal T1 (positive terminal), and a terminal T2 (negative terminal). The output voltage of the DC power supply 41 is variable. The DC power supply 41 is controlled by a control device 150 (see FIG. 4), which will be described later. The ammeter 42 is connected in series to the DC power supply 41, and the voltmeter 43 is connected in parallel to the DC power supply 41. The ammeter 42 detects the current flowing through the cell connected to this Ch. The voltmeter 43 detects the voltage between terminals T1 and T2.

[0033] In the circuit 400, each cell included in the battery circuit 410 is individually connected to a channel (Ch). Hereinafter, the channels to which cells C-1, C-2, and C-3 are connected will be referred to as "Ch1," "Ch2," and "Ch3," respectively. A first terminal B11 (e.g., a positive terminal) of cell C-1, which is located at the farthest end of the test object, is connected to the positive terminal of Ch1 via a wire W1. Furthermore, a second terminal B12 (e.g., a negative terminal) of cell C-1 and a first terminal B21 (e.g., a positive terminal) of cell C-2 are connected to the negative terminal of Ch1 and the positive terminal of Ch2 via a common wire W2. The test circuit for cell C-1 is a closed circuit including cell C-1, wires W1 and W2, and Ch1.

[0034] The wiring W2 has a branched portion, and one of the two branched ends is connected to the negative terminal of Ch1 and the other is connected to the positive terminal of Ch2. Furthermore, the second terminal B22 (e.g., the negative terminal) of cell C-2 and the first terminal B31 (e.g., the positive terminal) of cell C-3 are connected to the negative terminal of Ch2 and the positive terminal of Ch3 via a common wiring W3. The wiring W3 has a branched portion, and one of the two branched ends is connected to the negative terminal of Ch2 and the positive terminal of Ch3. The inspection circuit for cell C-2 is a closed circuit including cell C-2, wiring W2, W3, and Ch2.

[0035] Wiring W1 is an independent wiring for one cell (a wiring not shared by multiple cells). Wirings W2 and W3 are each common wiring shared by multiple cells. Although not shown in FIG. 3, a cell located at the opposite end from cell C-1 is also connected to Ch via a common wiring, similar to cell C-1, with its first terminal (e.g., positive terminal) connected to Ch via a common wiring and its second terminal (e.g., negative terminal) connected to Ch via an independent wiring. Hereinafter, the resistances of wiring W1, W2, and W3 will be referred to as "R1," "R12," and "R23," respectively. The currents flowing through the inspection circuits of cells C-1, C-2, and C-3 will be referred to as "I1," "I2," and "I3," respectively. The output voltages of the DC power supply 41 at Ch1 and Ch2 will be referred to as "VS1" and "VS2," respectively. The voltages of cells C-1 and C-2 will be referred to as "VB1" and "VB2," respectively.

[0036] Although not shown, the circuit 400 also has the aforementioned Rext (circuit resistance). Hereinafter, the total number of cells will be represented by "N." The Rext of the test circuits of the first, second, third, ..., and Nth cells C from the positive electrode end of the laminate 10 may be represented as "Rext(1)," "Rext(2)," "Rext(3)," ..., and "Rext(N)," respectively. Each of these Rext corresponds to the parasitic resistance of the test circuit of the cell identified by the number in parentheses, excluding the common wiring portion. The parasitic resistance of the test circuit of cell C-1 is, for example, the sum of Rext(1) and R12. The parasitic resistance of the test circuit of cell C-2 is, for example, the sum of Rext(2), R12, and R23. Similarly to the above Rext, Rext' and Rim may also be represented by identifying the cell (test circuit) using the number in parentheses. For example, for cells C-1 and C-2, "Rext'(1) = Rext(1) + Rim(1)" and "Rext'(2) = Rext(2) + Rim(2)" respectively hold. For I1 and I2, the following equations (3) and (4) hold.

[0037] I1={VS1-VB1+(I2-I1)×R12} / Rext'(1) …(3) I2={VS2-VB2-(I2-I1)×R12-(I2-I3)×R23} / Rext'(2) …(4)

[0038] As mentioned above, two adjacent cells share a single wiring (common wiring). The currents flowing through the test circuits of two adjacent cells flow in opposite directions through the common wiring. Therefore, if there is a difference in the current values ​​between the two adjacent cells, a potential difference (voltage) corresponding to the difference in the current values ​​is generated. For example, according to equation (3), the value obtained by multiplying the difference in the current values ​​of cells C-1 and C-2 (I2 - I1) by the common wiring resistance (R12) is added to the power supply voltage (VS1). Also, according to equation (4), the value obtained by multiplying the difference in the current values ​​of cells C-2 and C-1 (I2 - I1) by the common wiring resistance (R12) is subtracted from the power supply voltage (VS2). Furthermore, the value obtained by multiplying the difference in the current values ​​of cells C-2 and C-3 (I2 - I3) by the common wiring resistance (R23) is also subtracted from the power supply voltage (VS2). In this way, when current is simultaneously applied to the test circuits of the cells C-1 to C-3, the voltage applied to each cell is affected by the current of the adjacent cell.

[0039] Therefore, in the battery manufacturing method according to this embodiment, the self-discharge test for each cell is performed by using feedback control of the power supply (DC power supply 41) connected to each cell to cancel out the current flowing through each test circuit of adjacent cells C at the common wiring portion. This prevents the voltage applied to each cell from being affected by the current of the adjacent cell (i.e., the effect of the common wiring resistance). Eliminating the effect of the common wiring resistance makes it possible to perform the test based on the above-mentioned equation (2). Transforming equation (2) yields equation (5) shown below.

[0040] VS=VB+IB×Rext' …(5)

[0041] In Rext' (=Rext+Rim), Rim is the resistance value of the virtual resistor. Therefore, the inspection device makes equation (5) valid by increasing VS. The processing flow shown in Figure 1 will be explained below with reference to Figure 4.

[0042] FIG. 4 is a diagram for explaining a self-discharge inspection. As shown in FIG. 4, the inspection target according to this embodiment includes a laminate 10 (see FIG. 2) and a connector 30. The connector 30 is provided for a plurality of voltage detection terminals 20 (see FIG. 2) connected to the laminate 10. The voltage detection terminals 20 are welded to the +X-side end of the current collector 11, for example. Examples of welding methods include ultrasonic welding and laser welding. The connector 30 includes a resin part 31 and a housing 32. For example, the resin part 31 connecting the +X-side end face of the laminate 10 to the housing 32 is formed by injection molding, with the housing 32 aligning the voltage detection terminals 20 attached to the tip of the voltage detection terminals 20. This forms the connector 30 joined to the laminate 10. The plurality of voltage detection terminals 20 are configured to be connectable to an external power source (e.g., a DC power source 41). Each of the plurality of voltage detection terminals 20 functions as a pin of the connector 30. The connector 30 is a male connector configured to be able to accommodate a female connector (e.g., a socket).

[0043] The inspection device 100 includes a power supply unit 110, a connection unit 120, and a control device 150. The control device 150 includes a processor and a storage device. In this embodiment, the processor executes a program stored in the storage device to perform the self-discharge inspection. However, each process related to the self-discharge inspection may be performed only by hardware (electronic circuits) without using software.

[0044] The power supply unit 110 includes the above-mentioned multiple Ch (see FIG. 3). The connection unit 120 functions as a female connector that can be attached to the connector 30. The connection unit 120 also includes a branch portion of the above-mentioned common wiring (see FIG. 3). In the example shown in FIG. 4, a branch portion is also formed in the independent wiring, but the independent wiring does not have to be branched. The branch portion may also be formed in the object to be inspected (for example, the connector 30) rather than in the inspection device 100.

[0045] 1, in S101, the inspection device 100 connects the connection unit 120 of the inspection device 100 to the connector 30 of the inspection target. The inspection device 100 may include a robot that connects connectors. By connecting the corresponding terminals (e.g., female terminals) of the connection unit 120 to the terminals (e.g., male terminals) of the connector 30, each cell included in the inspection target is connected to the power supply unit 110 of the inspection device 100. Cells C-1, C-2, C-3, C-4, C-5, and C-6 are connected to Ch1, Ch2, Ch3, Ch4, Ch5, and Ch6, respectively. This forms the aforementioned inspection circuit (see FIG. 3) for each cell included in the inspection target. In this way, in S101 of FIG. 1, an inspection circuit is formed for each cell C (storage cell) of the inspection target (bipolar secondary battery) so that the inspection circuits of adjacent cells C have a common wiring portion. As shown in FIG. 3, each inspection circuit is a closed circuit.

[0046] Next, in S102, the inspection device 100 measures the circuit resistance of the inspection circuit of each formed cell. For the inspection circuit of each cell, the inspection device 100 calculates Rext (parasitic resistance of portions other than the common wiring portion) and the electrical resistance of the common wiring portion. Rext is calculated for each cell (in other words, for each inspection circuit). The electrical resistance of the common wiring portion is calculated for each common wiring. For example, the inspection device 100 may control the DC power supply 41 of each channel to a predetermined state and obtain Rext(1) to (N) based on the current and voltage detection results obtained by the ammeter 42 and voltmeter 43 of each channel. The inspection device 100 may separately measure the circuit resistance when a voltage is applied only to Ch1 and the circuit resistance when a voltage is applied to Ch1 and Ch2, and calculate the resistance value of the common wiring portion shared by cells C-1 and C-2 based on a comparison of the two measurements. Then, the inspection device 100 performs the self-discharge inspection for each cell through the subsequent processes of S111 to S116.

[0047] In S111, the inspection device 100 measures the voltage of each cell under inspection (each cell included in the stack 10). The inspection device 100 may acquire the cell voltage based on the voltage detection result of the voltmeter 43 shown in FIG. 3. In the following S112, the inspection device 100 sets an initial power supply voltage for each cell under inspection and starts a self-discharge inspection. Specifically, for each cell, the inspection device 100 sets a voltage equal to but opposite in direction to the cell voltage measured in S111 as the initial voltage value of the DC power supply 41 for the corresponding channel. This causes the power supply unit 110 of the inspection device 100 to apply a voltage to each cell. However, in the inspection circuit, if the cell voltage (VB) and the power supply voltage (VS) match, the circuit current (IB) becomes zero according to equation (2). Thereafter, if VB decreases due to cell self-discharge, a circuit current is generated.

[0048] When a predetermined time (hereinafter referred to as "dT1") has elapsed since the initial application of the power supply voltage (S112), the inspection device 100 measures the current (circuit current) flowing through the inspection circuit for each cell under inspection in S113. Note that for cells C-1, C-2, and C-3, I1, I2, and I3 shown in FIG. 3 correspond to the circuit currents, respectively. dT1 is, for example, 1 second. However, it is not limited to this, and dT1 can be set arbitrarily or may be variable.

[0049] In the next step S114, it is determined whether or not it is possible to determine the quality of the cell with respect to self-discharge. The inspection device 100 may determine whether or not it is possible to determine the quality of the cell with respect to self-discharge based on whether or not the circuit current of each cell under inspection has converged. The inspection device 100 may determine that the circuit current has converged, for example, when the amount of change in the circuit current per unit time is equal to or less than a predetermined value. However, the method of determining convergence is not limited to this, and any method may be used.

[0050] If the circuit current of any of the cells under test has not converged, a NO determination is made in S114, and the process proceeds to S115. In S115, the inspection device 100 performs feedback control of the DC power supply 41 connected to each cell. Specifically, the inspection device 100 determines Rim based on Rext measured in S102 and the electrical resistance of the common wiring portion. Rim is determined for each cell (in other words, for each inspection circuit). Then, the inspection device 100 changes the power supply voltage based on the following equation (6).

[0051] VS y =VS x +(Rext(M)-Rext'(M))×I M +(I M+1 -I M )×r M -(I M -I M-1 )×r M-1 …(6)

[0052] In equation (6), for the Mth cell C from the positive electrode end of the stack 10, the power supply voltage before the change is "VS x ", and the changed power supply voltage is "VS y ", and the current flowing through the test circuit is "I M ”, and the electrical resistance of the common wiring part between the inspection circuit of the Mth cell C and the inspection circuit of the adjacent (M+1)th cell C is “r M ". That is, "r M-1 " means the electrical resistance of the common wiring portion between the inspection circuit of the (M-1)th cell C and the inspection circuit of the Mth cell C. M+1 -I M " and "I M -I M-1 Each of the r corresponds to the difference in current flowing through each test circuit of adjacent cells. M and r M-1 Each of these corresponds to the electrical resistance of the common wiring portion. When the total number of cells is represented by "N", M is an integer between 2 and "N-1".

[0053] According to equation (6), for example, the power supply voltage of cell C-2 (the second cell C from the end on the positive electrode side of the stack 10) is feedback controlled in accordance with equation (7) shown below.

[0054] VS2=VS2+(Rext(2)-Rext'(2))×I2+(I3-I2)×R23-(I2-I1)×R12 …(7)

[0055] In equation (7), "VS2" on the right side is the power supply voltage before the change, and "VS2" on the left side is the power supply voltage after the change. As can be seen from equations (4) and (7), the following equation (8) holds for cell C-2.

[0056] I2=(VS2-VB2) / Rext'(2) …(8)

[0057] In this way, the DC power supply 41 of each Ch is feedback controlled according to equation (6), so that the currents flowing through the test circuits of adjacent cells C are cancelled out at the common wiring portion.

[0058] The inspection device 100 changes the power supply voltage for the first and Nth cells C from the end of the positive electrode side of the laminate 10 based on the following equations (9) and (10), respectively.

[0059] VS1=VS1+(Rext(1)-Rext'(1))×I1+(I2-I1)×R12…(9)

[0060] VS N =VS N +(Rext(N)-Rext'(N))×I N -(I N -I N-1 )×r N-1 …(10)

[0061] In equations (9) and (10), the right-hand sides of "VS1" and "VS N " is the power supply voltage before the change, and "VS1" and "VS N " is the power supply voltage after the change.

[0062] By the process of S115, the changed power supply voltage is calculated for each cell (in other words, for each test circuit) according to the formulas (6), (9), and (10). Then, the power supply voltage of each test target cell is calculated as VS x From VS y The inspection device 100 determines the amount of increase in the power supply voltage (voltage increase amount) according to the formulas (6), (9), and (10) at a predetermined cycle, and increases the power supply voltage by the determined amount of increase. This causes the current flowing through the inspection circuit to approach the self-discharge current of the corresponding cell. For example, in formula (6), "(Rext(M)-Rext'(M))×I M " is "I M ×(-Rim(M))" Rim(M) is a function of Rext(M) and r M ,r M-1 The test device 100 determines Rim(M) so that Rext'(M) is a positive value. The test device 100 determines the amount of voltage increase using the parasitic resistance of the test circuit of the cell being tested other than the common wiring portion, the difference between the current flowing in the test circuit of the cell and the current flowing in the test circuit of the adjacent cell, and the electrical resistance of the common wiring portion of the test circuits of those adjacent cells. This method makes it easier to determine an appropriate amount of voltage increase in feedback control of the power supply voltage.

[0063] When a predetermined time (hereinafter, referred to as "dT2") has elapsed since the change in power supply voltage (S115), the process returns to S113. Then, the circuit current is measured (S113) and a convergence determination is performed (S114). dT2 is, for example, 1 second. However, dT2 is not limited to this and can be set arbitrarily and may be variable. During the period in which a NO determination is made in S114, the inspection device 100 performs feedback control of the power supply voltage at a predetermined cycle so that the current (circuit current) flowing through the inspection circuit of the cell being inspected approaches the self-discharge current of the cell. The DC power supply 41 connected to each cell under inspection applies a power supply voltage to the inspection circuit of the corresponding cell, thereby supplying current to the corresponding cell through the voltage detection terminal 20. This allows current to be supplied to all cells under inspection simultaneously and individually. Increasing the power supply voltage through the feedback control allows the circuit current to converge quickly, thereby shortening the inspection time. Furthermore, using the voltage detection terminal 20 allows power (current) to be supplied individually to each cell.

[0064] When the circuit currents of all the cells under test have converged (YES in S114), the inspection device 100 judges the quality of each cell under test in S116. In the self-discharge test according to this embodiment, a cell whose self-discharge current is equal to or greater than a predetermined reference value (hereinafter referred to as "Is") is judged to be a short-circuited cell (defective product). The converged circuit current is considered to correspond to the self-discharge current of the cell. In this embodiment, when the current flowing through the test circuit of the cell under test has converged, the inspection device 100 measures the self-discharge current of the cell based on the current value. Furthermore, for each cell under test, the inspection device 100 judges whether the cell is a good product (good cell) or a defective product (short-circuited cell) based on the converged circuit current of the cell.

[0065] The inspection apparatus 100 may determine that the test object is defective if it contains at least one shorted cell. If the circuit current measured in S113 for at least one cell included in the test object reaches Is, the inspection apparatus 100 may determine YES in S114 even if the circuit currents of all cells have not converged. The inspection apparatus 100 may then determine that the test object is defective in S116. In this way, by determining that a cell is defective when the current flowing through the test circuit of the cell being tested exceeds a predetermined reference value, shorted cells (defective products) can be found early. Furthermore, by ending the test once the pass / fail determination result for a test object is known and moving on to the next test object, the efficiency of the test can be improved.

[0066] FIG. 5 is a diagram for explaining the function and effect of the manufacturing method of a bipolar secondary battery according to this embodiment. In each graph shown in FIG. 5, the horizontal axis represents the elapsed time from the start of the test. Each of lines L11 and L12 is data relating to the self-discharge test according to the example. In the self-discharge test according to the example, as described above, the power supply connected to each cell under test was feedback-controlled in accordance with equations (6), (9), and (10), thereby simultaneously conducting self-discharge tests on all cells under test while canceling out the currents flowing through the test circuits of adjacent cells in the common wiring portion (see FIG. 1). On the other hand, each of lines L21 and L22 is data relating to the self-discharge test according to the comparative example. In the self-discharge test according to the comparative example, the equation "VS y =VS x +(Rext(M)-Rext'(M))×I M " Self-discharge tests were performed simultaneously on all cells under test while feedback-controlling the power supplies connected to each cell under test according to the "Test Method for Cells C-1 and C-2." When cell C-1 is a good product and cell C-2 is a defective product, lines L11 and L21 each show the transition of the current (circuit current) flowing through the test circuit of cell C-2 (the short-circuited cell), and lines L12 and L22 each show the transition of the current (circuit current) flowing through the test circuit of cell C-1 (the good cell).

[0067] In the self-discharge test according to the comparative example, as shown in the above-mentioned formula (3), the voltage applied to each cell is affected by the current of the adjacent cell. If only cell C-2 of adjacent cells C-1 and C-2 is a short-circuited cell, a large current flows through the common wiring of cells C-1 and C-2 (for example, wiring W2 shown in FIG. 3). As a result, the power supply voltage appears to decrease in the test circuit of cell C-2. This slows down the rise in the circuit current (line L21) of the short-circuited cell. On the other hand, the power supply voltage appears to increase in the test circuit of cell C-1. This makes it easier for the circuit current (line L22) of the non-defective cell to rise.

[0068] In contrast, in the self-discharge test according to the embodiment, currents are canceled out at the common wiring, so the voltage applied to each cell is not affected by the current of the adjacent cell. Specifically, according to the power supply feedback control according to Equations (6), (9), and (10), if only one of adjacent storage cells is a short-circuited cell, the power supply voltage of the test circuit of the other storage cell increases, and the currents flowing through the test circuits of the adjacent storage cells are canceled out at the common wiring. Therefore, the circuit current of the short-circuited cell (line L11) increases quickly, while the circuit current of the good cells (line L12) converges with almost no increase. According to the self-discharge test according to the embodiment, good cells and short-circuited cells can be easily distinguished based on the circuit current of each cell. For example, even if the boundary value (Is) for distinguishing good cells from short-circuited cells is set low, good cells can be distinguished from short-circuited cells with high accuracy. The lower the I, the easier it is to find defective cells earlier.

[0069] As described above, the method for manufacturing a bipolar secondary battery according to this embodiment includes the steps shown in FIG. 1. In S101, a power supply is connected to each of a plurality of storage cells, and an inspection circuit is formed for each storage cell so that the inspection circuits of adjacent storage cells have a common wiring portion. In S111 to S116, a self-discharge inspection is performed on each storage cell while canceling out the current flowing through each inspection circuit of adjacent storage cells at the common wiring portion through feedback control of the power supply connected to each storage cell. This method makes it possible to appropriately inspect the self-discharge of each cell included in the bipolar secondary battery. This also facilitates efficient manufacturing of high-quality bipolar secondary batteries.

[0070] The laminate 10 determined to be a non-defective product by the above inspection can function as a bipolar secondary battery by itself. However, a bipolar secondary battery may be manufactured by combining a plurality of modules, each of which is the laminate 10. The manufactured bipolar secondary battery may be mounted on a mobile object. Examples of mobile objects include automobiles (electric vehicles, hybrid vehicles, etc.), vehicles other than automobiles, and mobile machinery (agricultural machinery, construction machinery, etc.). However, the battery may be used for any purpose, and a stationary battery may be manufactured by the above method.

[0071] The processing flow shown in Fig. 1 can be modified as needed. For example, the order of processing may be changed or the content of any of the processing may be changed depending on the purpose.

[0072] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0073] 1 bipolar electrode, 10 laminate, 11 current collector, 20 voltage detection terminal, 30 connector, 41 DC power supply, 42 ammeter, 43 voltmeter, 100 inspection device, 110 power supply unit, 120 connection unit, 150 control device, C cell, W1 to W3 wiring.

Claims

1. A method for manufacturing a bipolar secondary battery including a plurality of storage cells, comprising: The method comprises: connecting a power source to each of the plurality of storage cells, and forming an inspection circuit for each storage cell such that inspection circuits of adjacent storage cells have a common wiring portion; conducting a self-discharge test for each storage cell while canceling out currents flowing through the test circuits of adjacent storage cells at the common wiring portion by feedback control of the power supplies connected to each storage cell; A method for manufacturing a bipolar secondary battery, comprising:

2. 2. The method for manufacturing a bipolar secondary battery according to claim 1, wherein, in the self-discharge test, a current flowing in the test circuit approaches a self-discharge current of the storage cell being tested by feedback control of the power supply, and when the current flowing in the test circuit reaches or exceeds a predetermined reference value, the storage cell is determined to be defective, and when the current flowing in the test circuit converges, the self-discharge current of the storage cell is measured based on the current value.

3. 3. The method for manufacturing a bipolar secondary battery according to claim 1, wherein, in the feedback control of the power supply, when only one of adjacent storage cells is a short-circuited cell, the power supply voltage in the inspection circuit of the other storage cell is increased so that the currents flowing through the inspection circuits of the adjacent storage cells are canceled out by the common wiring portion.

4. In the feedback control of the power supply, a voltage increase amount of the power supply is determined at a predetermined cycle, and the power supply is feedback-controlled based on the determined voltage increase amount; 3. The method for manufacturing a bipolar secondary battery according to claim 1, wherein the feedback control of the power supply determines an amount of voltage increase of the power supply using a parasitic resistance other than the common wiring portion of the inspection circuit of the storage cell to be inspected, a difference between a current flowing in the inspection circuit of the storage cell and a current flowing in the inspection circuit of an adjacent storage cell, and an electrical resistance of the common wiring portion of the inspection circuits of the adjacent storage cells.

5. Each of the plurality of storage cells has a voltage detection terminal configured to be connectable to an external power supply, an inspection circuit for each of the storage cells is formed by connecting the power supply to the voltage detection terminal of each of the plurality of storage cells; 3. The method for manufacturing a bipolar secondary battery according to claim 1, wherein in the self-discharge test, the power source connected to each of the plurality of storage cells supplies a current to the corresponding storage cell through the voltage detection terminal.

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