Method for manufacturing bipolar secondary battery

Abstract

To appropriately perform self-discharge inspection of each unit cell included in a bipolar secondary battery.SOLUTION: The plurality of unit cells in the bipolar secondary battery are classified into first unit cells and second unit cells that are alternately arranged. The method includes forming a test circuit of each of the first unit cells by connecting a power source to each of the first unit cells (S100), performing a self-discharge test of each of the first unit cells by applying a current to the test circuit of each of the first unit cells by the power source connected to each of the first unit cells (S111 to S116), forming a test circuit of each of the second unit cells by connecting a power source to each of the second unit cells (S100), and performing a self-discharge test of each of the second unit cells by applying a current to the test circuit of each of the second unit cells (S121 to S126). The self-discharge inspection of each first unit cell and the self-discharge inspection of each second unit cell are performed separately.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 a self-discharge test on multiple secondary batteries. When the technique described in Patent Document 1 is used to conduct a self-discharge test on a bipolar secondary battery including multiple unit batteries, there is a risk that the test time will be long and the test 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 unit battery 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 unit batteries. The plurality of unit batteries are classified into first unit batteries and second unit batteries arranged alternately. The method includes connecting a power source to each of the first unit batteries to form a test circuit for each of the first unit batteries, conducting a self-discharge test for each of the first unit batteries by passing a current through the test circuit for each of the first unit batteries using the power source connected to each of the first unit batteries, connecting a power source to each of the second unit batteries to form a test circuit for each of the second unit batteries, and conducting a self-discharge test for each of the second unit batteries by passing a current through the test circuit for each of the second unit batteries using the power source connected to each of the second unit batteries. The self-discharge test for each of the first unit batteries and the self-discharge test for each of the second unit batteries are performed separately. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to appropriately perform a self-discharge test on each unit battery 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. [Figure 6] FIG. 5 is a diagram showing a modified example of the inspection device shown in FIG. 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 arranged 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. In this embodiment, the power storage unit 10a includes 10 or more cells C. However, the number of cells C can be set arbitrarily. The number of cells C included in the power storage unit 10a may be 3 or more and 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 separator 13 is impregnated with the electrolyte.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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 end of the positive electrode side (+Z side) 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 addition, odd-numbered cells C from the end of the positive electrode side of the laminate 10 may be collectively referred to as "odd cells," and even-numbered cells C from the end of the positive electrode side of the laminate 10 may be collectively referred to as "even cells." In the laminate 10, odd-numbered cells and even-numbered cells are alternately arranged in the Z direction (stacking direction). Adjacent odd-numbered cells and even-numbered cells have common electrodes. 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).

[0017] 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 restraining, 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.

[0018] 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 described below, and then perform individual charging of the other. 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 (e.g., about 25°C).

[0019] 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.

[0020] In S100, the inspection device forms an inspection circuit by connecting the inspection target to the power supply unit of the inspection device. After that, the inspection device performs a self-discharge inspection of the inspection target by processing from S111 onwards. The self-discharge inspection will be described later.

[0021] 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).

[0022] 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.

[0023] 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.

[0024] IB = (VS - VB) / Rext (1)

[0025] 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.

[0026] 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.

[0027] 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.

[0028] IB=(VS-VB) / Rext' …(2)

[0029] 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.

[0030] 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.

[0031] The power supply circuit 420 is configured by, for example, 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 includes 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.

[0032] 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 includes cell C-1, wires W1 and W2, and Ch1.

[0033] 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 includes cell C-2, wiring W2, W3, and Ch2.

[0034] 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.

[0035] Although not shown, the aforementioned Rext (circuit resistance) also exists in the circuit 400. When the aforementioned virtual resistances (Rim) and Rext' (=Rext+Rim) are introduced, the following equations (3) and (4) hold for I1 and I2.

[0036] I1={VS1-VB1+(I2-I1)×R12} / Rext' …(3) I2={VS2-VB2-(I2-I1)×R12-(I2-I3)×R23} / Rext' …(4)

[0037] 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-1 and C-2 (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.

[0038] Therefore, in the battery manufacturing method according to this embodiment, a test circuit for each unit battery is used to perform a self-discharge test separately for odd-numbered cells and even-numbered cells (S111 to S116 and S121 to S126 in FIG. 1). Specifically, currents are passed through the test circuits for odd-numbered cells and even-numbered cells separately, and the self-discharge test for odd-numbered cells is performed using the current flowing through the test circuit for odd-numbered cells, and the self-discharge test for even-numbered cells is performed using the current flowing through the test circuit for even-numbered cells. By performing the self-discharge test separately for odd-numbered cells and even-numbered cells, currents do not flow simultaneously through the test circuits of two adjacent cells. This prevents the power supply voltage of 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 enables testing based on the aforementioned equation (2). By modifying equation (2), the following equation (5) is obtained.

[0039] VS=VB+IB×Rext' …(5)

[0040] 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.

[0041] 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).

[0042] The cells C included in the laminate 10 are odd-numbered cells C arranged alternately. A and even cell C B Odd cell C A is the (2N-1)th cell C from the end of the positive electrode side (+Z side) of the laminate 10, the even-numbered cell C B corresponds to the (2N)th cell C from the end of the positive electrode side (+Z side) of the laminate 10. N is an integer ranging from 1 to the total number of cells.

[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 S100, the inspection device 100 connects the connection unit 120 of the inspection device 100 to the connector 30 under inspection. The inspection device 100 may include a robot for connecting 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 S100 of FIG. 1, an inspection circuit is formed for each cell C (unit battery) under inspection (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. Then, the inspection device 100 performs the subsequent steps S111 to S116 to check the odd-numbered cell C A In steps S111 to S116, the inspection device 100 inspects the even-numbered cells C B Set the power supply voltage of the corresponding Ch (Ch2, Ch4, Ch6, ...) to zero.

[0046] In S111, the inspection device 100 A Measure the circuit resistance (for example, the aforementioned Rext) for the test circuit of odd cell C A Specifically, the inspection device 100 measures the voltage of each cell included in the odd-numbered cell C AAlternatively, the DC power supply 41 of each channel connected to the test circuit may be controlled to a predetermined state, and Rext may be obtained based on the current and voltage detection results obtained by the ammeter 42 and voltmeter 43 of each channel. Also, the test device 100 may obtain the cell voltage based on the voltage detection results obtained by the voltmeter 43 shown in FIG. 3.

[0047] In the next step S112, the inspection device 100 A Specifically, the test device 100 sets an initial power supply voltage for odd-numbered cells C and starts a self-discharge test. A For each cell included in the odd-numbered cells C, a voltage having the same magnitude as the cell voltage measured in S111 but in the opposite direction is set as the initial voltage value (VS) of the DC power supply 41 of the corresponding Ch. As a result, the power supply unit 110 (more specifically, Ch1, Ch3, Ch5, ...) of the inspection device 100 supplies the odd-numbered cells C A However, if the cell voltage (VB) and the power supply voltage (VS) match in the test circuit, the circuit current (IB) becomes zero according to equation (2). After that, if VB decreases due to self-discharge of the cell, a circuit current will occur.

[0048] When a predetermined time (hereinafter referred to as "dT1") has elapsed since the initial application of the power supply voltage (S112), the testing device 100 performs S113 to check the odd-numbered cell C A For each cell included in the test circuit, the current (IB) flowing through the test circuit is measured. For cells C-1 and C-3, I1 and I3 shown in FIG. 3 correspond to the circuit current (IB). dT1 is, for example, 1 second. However, this is not limited to this, and dT1 can be set arbitrarily or may be variable.

[0049] In the next step S114, odd cell C A The inspection device 100 determines whether it is possible to judge whether the odd-numbered cell C is good or bad with respect to self-discharge. A Based on whether the circuit current (IB) of each cell included in has converged, the odd cell C AThe inspection device 100 may determine whether or not it is possible to determine whether the self-discharge of the battery is good or bad. For example, the inspection device 100 may determine that the IB has converged when the amount of change in IB per unit time becomes equal to or less than a predetermined value. However, the invention is not limited to this, and any method for determining convergence may be used.

[0050] Odd cell C A If the circuit current (IB) of any cell included in has not converged, a NO determination is made in S114, and the process proceeds to S115. In S115, the inspection device 100 performs power supply feedback control. Specifically, the inspection device 100 determines Rim based on Rext measured in S111. Then, the inspection device 100 calculates Rim based on the odd-numbered cell C in accordance with the following equation (6): A Increases the VS of each cell contained in

[0051] VS=VS+IB×(Rext-Rext') …(6)

[0052] In equation (6), "VS" on the right side is the power supply voltage before the change, and "VS" on the left side is the power supply voltage after the change. The power supply voltage after the change is calculated for each cell. By the process of S115, odd-numbered cell C A The power supply voltage of each cell included in is changed from "VS" on the right side to "VS" on the left side. The inspection device 100 periodically determines the amount of increase in the power supply voltage according to equation (6) and increases the power supply voltage by the determined amount. This causes IB to approach the self-discharge current. In equation (6), "IB × (Rext - Rext')" corresponds to the increase in VS and can be rewritten as "IB × (-Rim)." The absolute value of Rim is the value obtained by dividing the increase in VS by IB. Rim is determined based on Rext, as described above. That is, the inspection device 100 determines the amount of increase in the power supply voltage based on the parasitic resistance of the inspection circuit of the cell being inspected and the current flowing through the inspection circuit. The inspection device 100 may determine Rim so that Rext' becomes a positive value close to zero. However, this is not limited to this, and the inspection device 100 can arbitrarily set Rext' and Rim.

[0053] 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, IB measurement (S113) and IB convergence determination (S114) are performed. dT2 is, for example, 1 second. However, it is not limited to this, and dT2 can be set arbitrarily and may be variable. During the period in which the determination in S114 is NO, the inspection device 100 performs feedback control of the power supply voltage (VS) at a predetermined cycle so that the current (IB) flowing through the inspection circuit of the cell being inspected approaches the self-discharge current of the cell. Odd-numbered cell C A The DC power supply 41 connected to each cell included in the battery applies VS to the test circuit of the corresponding cell, thereby supplying current to the corresponding cell through the voltage detection terminal 20. By increasing VS through the feedback control, it becomes possible to quickly converge IB, thereby shortening the test time. Furthermore, by using the voltage detection terminal 20, it becomes possible to supply power (current) to each cell individually.

[0054] Odd cell C A When the circuit currents (IB) of all the cells included in the odd-numbered cell C converge (YES in S114), the inspection device 100 performs S116. A It is determined whether or not any defective product is included in the cell. 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 determined to be a short-circuited cell (defective product). The circuit current (IB) of a cell that has converged 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 being tested has converged, the test device 100 measures the self-discharge current of the cell based on the current value. In addition, the test device 100 also measures the self-discharge current of odd-numbered cells C A For each cell included in the table, it is determined whether the cell is a good product (good cell) or a bad product (short-circuited cell) based on the converged circuit current (IB) of the cell.

[0055] Odd cell C A When the self-discharge inspection is completed, the inspection device 100 performs the subsequent processes of S121 to S126 to inspect the even-numbered cells C BIn steps S121 to S126, the cells to be inspected are odd-numbered cells C. A From even cell C B The power supply used is changed to even cell C B Then, in steps S121 to S126, the inspection device 100 determines whether the odd-numbered cell C A The power supply voltages of the Chs (Ch1, Ch3, Ch5, . . . ) corresponding to these are set to zero. However, the processes of S121 to S126 are basically the same as the processes of S111 to S116 described above, respectively, and therefore will not be described repeatedly.

[0056] The inspection apparatus 100 may determine that the test object is defective if the test object includes at least one short-circuited cell. A If the circuit current (IB) measured in S113 reaches Is for at least one cell included in odd-numbered cell C, the inspection apparatus 100 may determine YES in S114 even if the IBs of all cells have not converged. A Even cell C may be judged as defective. B The same can be said for the inspections (S123, S124, S126). In this way, if the current flowing through the inspection circuit of the cell being inspected exceeds a predetermined reference value, the cell is determined to be defective, thereby making it possible to find shorted cells (defective products) early.

[0057] In addition, in S116, odd cell C A If it is determined that the even-numbered cell C includes at least one short-circuited cell, the inspection apparatus 100 B The self-discharge test (the process after S121) does not need to be performed. The efficiency of the test can be improved by ending the test when the pass / fail judgment result for a test object is known and moving on to the test of the next test object.

[0058] FIG. 5 is a diagram for explaining the operation 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 represents data relating to the self-discharge test according to the example. In the self-discharge test according to the example, the self-discharge test was performed separately for odd-numbered cells and even-numbered cells as described above (see FIG. 1). On the other hand, each of lines L21 and L22 represents data relating to the self-discharge test according to the comparative example. In the self-discharge test according to the comparative example, the self-discharge test was performed on all cells simultaneously while current was passed through all of the cells to be tested using all channels of the test device 100. In the case where cell C-1 is a good product and cell C-2 is a defective product, lines L11 and L21 show the transition of the current (IB) flowing through the test circuit of cell C-2 (short-circuited cell), and lines L12 and L22 show the transition of the current (IB) flowing through the test circuit of cell C-1 (good cell). In both self-discharge tests, feedback control of the power supply voltage (VS) was performed at a predetermined cycle so that IB approached the self-discharge current for each cell.

[0059] 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 (e.g., wiring W2 shown in FIG. 3) of cells C-1 and C-2. As a result, the power supply voltage appears to decrease in the test circuit of cell C-2. This slows down the rise in IB (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 IB (line L22) of good cells to rise.

[0060] In contrast, in the self-discharge test according to the embodiment, the self-discharge test is performed separately for odd-numbered cells and even-numbered cells, so the voltage applied to each cell is not affected by the current of the adjacent cell. As a result, the IB (line L11) of the shorted cells increases early, while the IB (line L12) of the good cells converges with almost no increase. The self-discharge test according to the embodiment makes it easier to distinguish good cells from shorted cells based on the IB of each cell. For example, even if the boundary value (Is) for distinguishing good cells from shorted cells is set low, it is possible to distinguish good cells from shorted cells with high accuracy. The lower the Is, the easier it is to find defective cells earlier.

[0061] As described above, the manufacturing method of the bipolar secondary battery according to this embodiment includes the steps shown in FIG. 1. Hereinafter, each of the cells classified as odd-numbered cells (cells C-1, C-3, C-5, ...) will be referred to as a "first unit battery." Also, each of the cells classified as even-numbered cells (cells C-2, C-4, C-6, ...) will be referred to as a "second unit battery." In S100, a power supply is connected to each of the first unit batteries to form an inspection circuit for each of the first unit batteries. In S100, a power supply is connected to each of the second unit batteries to further form an inspection circuit for each of the second unit batteries. In S111 to S116, a current is passed through the inspection circuit for each of the first unit batteries by the power supplies (DC power supplies 41 of Ch1, Ch3, Ch5, ...) connected to each of the first unit batteries, thereby inspecting the self-discharge of each of the first unit batteries. In S121 to S126, a current is passed through the inspection circuit of each second unit battery by the power supply (DC power supply 41 of Ch2, Ch4, Ch6, ...) connected to each second unit battery, thereby conducting a self-discharge inspection of each second unit battery. As shown in FIG. 1, the self-discharge inspection of each first unit battery (S111 to S116) and the self-discharge inspection of each second unit battery (S121 to S126) are carried out separately. This method makes it possible to properly inspect the self-discharge of each unit battery included in a bipolar secondary battery. This also facilitates the efficient manufacture of high-quality bipolar secondary batteries.

[0062] The stack 10 inspected as described above 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 stack 10 as one module. 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 (ships, airplanes, etc.), and mobile machines (agricultural machines, construction machines, etc.). However, the battery may be used for any purpose, and a stationary battery may be manufactured by the above method.

[0063] The process flow shown in Figure 1 can be modified as needed. For example, the order of the processes may be changed, or the content of any of the processes may be changed, depending on the purpose. For example, the measurement order may be reversed, and the self-discharge test for even-numbered cells may be performed before the self-discharge test for odd-numbered cells.

[0064] The power supply unit 110 of the inspection device 100 shown in FIG. 4 includes the same number of channels as the number of cells included in the test object. However, this is not limited to this, and the configuration of the power supply unit 110 can be modified as appropriate. FIG. 6 is a diagram showing a modified example of the inspection device shown in FIG. 4. Referring to FIG. 6, the inspection device 100A includes a power supply unit 110A, a connection unit 120, a switching circuit 130, and a control device 150A. The power supply unit 110A includes half the number of channels (Ch1, Ch2, Ch3, ...) of the cells included in the test object. The switching circuit 130 is located between the power supply unit 110A and the connection unit 120 and is configured to switch the connection state between the power supply unit 110A and the connection unit 120. The control device 150A controls each of the power supply unit 110A and the switching circuit 130. Before starting a self-discharge test on the odd-numbered cells to be tested, the control device 150A controls the switching circuit 130 so that the DC power supplies 41 (FIG. 3) for each channel included in the power supply unit 110A are connected to the wiring corresponding to the odd-numbered cells included in the connection unit 120. This forms a test circuit for the odd-numbered cells. Furthermore, before starting a self-discharge test on the even-numbered cells to be tested, the control device 150A controls the switching circuit 130 so that the DC power supplies 41 (FIG. 3) for each channel included in the power supply unit 110A are connected to the wiring corresponding to the even-numbered cells included in the connection unit 120. This forms a test circuit for the even-numbered cells. This test device 100A can also perform self-discharge tests on odd-numbered cells and even-numbered cells separately.

[0065] 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]

[0066] 1 Bipolar electrode, 10 Laminate, 11 Current collector, 20 Voltage detection terminal, 30 Connector, 41 DC power supply, 42 Ammeter, 43 Voltmeter, 100, 100A Inspection device, 110, 110A Power supply unit, 120 Connection unit, 130 Switching circuit, 150, 150A Control device, C Cell, CA Odd cells, C B Even cells, W1~W3 wiring.

Claims

1. A method for manufacturing a bipolar secondary battery including a plurality of unit batteries, comprising: the plurality of unit batteries are classified into first unit batteries and second unit batteries that are arranged alternately; The method comprises: connecting a power source to each of the first unit batteries to form a test circuit for each of the first unit batteries; conducting a self-discharge test for each of the first unit batteries by causing a current to flow through the test circuit of each of the first unit batteries using the power supply connected to each of the first unit batteries; connecting a power source to each second unit battery to form a test circuit for each second unit battery; conducting a self-discharge test for each second unit battery by causing a current to flow through a test circuit for each second unit battery using the power supply connected to each second unit battery; Including, A method for manufacturing a bipolar secondary battery, wherein a self-discharge test for each first unit battery and a self-discharge test for each second unit battery are carried out separately.

2. 2. The method for manufacturing a bipolar secondary battery according to claim 1, wherein in the self-discharge test of each first unit battery and the self-discharge test of each second unit battery, feedback control of the power supply voltage of the test circuit of the unit battery being tested is performed so that the current flowing in the test circuit approaches the self-discharge current of the unit battery, and when the current flowing in the test circuit becomes equal to or greater than a predetermined reference value, the unit battery is determined to be defective.

3. 2. The method for manufacturing a bipolar secondary battery according to claim 1, wherein in the self-discharge test of each first unit battery and the self-discharge test of each second unit battery, feedback control of the power supply voltage of the test circuit of the unit battery being tested is performed so that the current flowing in the test circuit approaches the self-discharge current of the unit battery, and when the current flowing in the test circuit has converged, the self-discharge current of the unit battery is measured based on that current value.

4. In the feedback control of the power supply voltage, an increase amount of the power supply voltage is determined at a predetermined cycle, and the power supply voltage is increased by the determined increase amount; 4. The method for manufacturing a bipolar secondary battery according to claim 2, wherein the feedback control of the power supply voltage determines an amount of increase in the power supply voltage based on a parasitic resistance of the inspection circuit of the unit battery being tested and a current flowing through the inspection circuit.

5. each of the plurality of unit batteries has a voltage detection terminal configured to be connectable to an external power supply; A power supply is connected to the voltage detection terminal of each first unit battery to form an inspection circuit for each first unit battery; a power supply is connected to the voltage detection terminal of each second unit battery to form an inspection circuit for each second unit battery; In the self-discharge test of each first unit battery, the power source connected to each first unit battery supplies a current to the corresponding first unit battery through the voltage detection terminal; 2. The method for manufacturing a bipolar secondary battery according to claim 1, wherein in the self-discharge test of each second unit battery, the power source connected to each second unit battery supplies a current to the corresponding second unit battery through the voltage detection terminal.

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