Battery manufacturing method
A two-step inspection process for batteries, including voltage convergence and self-discharge testing, addresses the challenge of accurately identifying short circuits, enhancing battery manufacturing precision.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- TOYOTA JIDOSHA KK
- Filing Date
- 2024-11-05
- Publication Date
- 2026-05-19
AI Technical Summary
Existing methods struggle to accurately determine the presence or absence of short circuits in various types of batteries due to variations in battery voltage drops after electrolyte injection, which can be misleading.
A two-step inspection process involving a first inspection to check for voltage convergence between electrodes post-electrolyte injection and a second self-discharge test for batteries not initially detected as short-circuited, utilizing the characteristic voltage convergence and self-discharge rates to confirm short circuits accurately.
Enables precise determination of short circuits in batteries with high accuracy, reducing false positives and minimizing unnecessary inspections while ensuring high-quality battery production.
Smart Images
Figure 2026081565000001_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to a method for manufacturing a battery.
Background Art
[0002] Japanese Unexamined Patent Application Publication No. 2019-075302 (Patent Document 1) discloses a technique for determining that a short circuit has occurred in an uncharged secondary battery when the amount of decrease in the cell voltage per unit time exceeds a threshold value after injecting an electrolytic solution into the case (accommodating portion) of the uncharged secondary battery.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] In the method described in Patent Document 1 above, if the amount of decrease in the cell voltage (battery voltage) per unit time after injection is large, it is determined that a short circuit has occurred in the battery. However, the amount of decrease in the battery voltage per unit time after injection does not necessarily indicate the degree of short circuit of the battery. Depending on the type of battery, there are batteries in which the battery voltage drops significantly immediately after injection, regardless of whether there is a short circuit. Therefore, it is difficult to accurately determine the presence or absence of a short circuit in various types of batteries using the method described in Patent Document 1 above.
[0005] The present disclosure has been made to solve the above problems, and an object thereof is to accurately determine the presence or absence of a short circuit in various types of batteries.
Means for Solving the Problems
[0006] A method for manufacturing a battery according to one embodiment of the present disclosure includes a forming process for forming a positive electrode and a negative electrode of a battery and a housing portion for housing the positive electrode and the negative electrode; an electrolyte injection process for pouring an electrolyte into the formed housing portion; a first inspection process for determining that a short circuit exists between the positive electrode and the negative electrode when the voltage between the positive electrode and the negative electrode converges to a predetermined range as a result of the electrolyte injection process; and a second inspection process for performing a self-discharge test on a battery that has been determined not to be short-circuited by the first inspection process.
[0007] In many batteries, if there is a short circuit between the positive and negative electrodes, the voltage between the positive and negative electrodes will converge to a predetermined range (for example, around 0V) after the electrolyte injection process. The first inspection process described above utilizes this characteristic (i.e., a characteristic common to many batteries) to determine whether or not there is a short circuit between the positive and negative electrodes. Furthermore, in the above method, batteries determined not to be short-circuited by the first inspection process undergo a self-discharge test in the second inspection process. Batteries with a short circuit tend to have a higher self-discharge rate. By performing multiple types of tests as described above, it becomes possible to determine the presence or absence of short circuits in various types of batteries with high accuracy. [Effects of the Invention]
[0008] According to this disclosure, it will be possible to determine with high accuracy whether or not there is a short circuit in various types of batteries. [Brief explanation of the drawing]
[0009] [Figure 1] This is a flowchart showing a method for manufacturing a battery according to an embodiment of the present disclosure. [Figure 2] This is a cross-sectional view showing the structure of the laminate formed by the process shown in Figure 1. [Figure 3] This is a diagram illustrating the inspection process according to this embodiment. [Modes for carrying out the invention]
[0010] Embodiments of this disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their descriptions will not be repeated. In the drawings used below, of the mutually orthogonal X, Y, and Z axes, the Z axis indicates the thickness direction of the battery. Hereinafter, the direction indicated by the arrows on the X, Y, and Z axes will be denoted by "+", and the opposite direction by "-".
[0011] Figure 1 is a flowchart showing a method for manufacturing a battery according to this embodiment. In this method, first, in step S10, a laminate 10 shown in Figure 2 is formed. Figure 2 is a cross-sectional view showing the structure of the laminate formed in step S10 of Figure 1. Referring to Figure 2, the laminate 10 comprises an energy storage section 10a and a sealing section 3 that seals the energy storage section 10a. The Z direction corresponds to the stacking direction. The energy storage section 10a includes a plurality of cells C (unit batteries) arranged in the Z direction. Each of the plurality of cells C comprises 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 store energy. Each of the multiple cells C functions as a secondary battery. The negative electrode active material layer 12A functions as the negative electrode of cell C, and the positive electrode active material layer 12B functions as the positive electrode of cell C. In this embodiment, the energy 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 energy storage unit 10a may be 3 or more but less than 50, or 50 or more. The sealing unit 3 is formed to surround the energy storage unit 10a.
[0013] The laminate 10 includes a plurality of electrodes (one negative terminal electrode 2A, a plurality of bipolar electrodes 1, and one positive terminal electrode 2B) stacked along the Z direction. Separators 13 are placed between the electrodes. The bipolar electrode 1 includes a current collector 11, a negative electrode active material layer 12A provided on the +Z side of the current collector 11, and a positive electrode active material layer 12B provided on the -Z side of the current collector 11. The negative terminal electrode 2A has a configuration in which the positive electrode active material layer 12B is removed from the bipolar electrode 1. An insulating layer 19A covering the periphery of the current collector 11 is formed on the -Z side of the current collector 11 that constitutes the negative terminal electrode 2A. The positive terminal electrode 2B has a configuration in which the negative electrode active material layer 12A is removed from the bipolar electrode 1. An insulating layer 19B is formed on the +Z side surface of the current collector 11 that constitutes the positive terminal electrode 2B, covering the peripheral edge of the current collector 11.
[0014] In this embodiment, a metal foil (e.g., aluminum foil) is used as the current collector 11 for each electrode. Surface treatment (e.g., plating) may be applied to one or both sides of the metal foil. A voltage detection terminal 20 is connected to the current collector 11 of each electrode. In this embodiment, the voltage detection terminal 20 includes 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 contains the negative electrode active material. The positive electrode active material layer 12B contains the positive electrode active material. In one example, the positive electrode active material is olivine-type lithium iron phosphate (LiFePO4), and the negative electrode active material is a carbon-based material. However, other examples of negative electrode active materials include silicon and tin.
[0016] In the laminate 10, cells C are formed between the multiple stacked current collectors 11. Specifically, a cell C is formed between a 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 also formed between the 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 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 multiple cells C contained in the laminate 10, and the aforementioned insulating layers 19A and 19B. Any sealing material can be used as the material for the sealing portion 3.
[0017] The laminate 10 functions as a bipolar secondary battery. Each of the multiple cells C contained in the laminate 10 (particularly the energy storage section 10a) functions as, for example, an LFP battery (a lithium-ion secondary battery containing lithium iron phosphate as the positive electrode active material). Hereinafter, the first, second, third, ... cells C from the positive electrode side (+Z side) of the laminate 10 may be denoted as cell C-1, cell C-2, cell C-3, ... (see Figure 3). In the laminate 10, multiple cells are stacked in the Z direction. Adjacent cells have common electrodes. Specifically, the current collector 11 and voltage detection terminal 20 located between adjacent cells function as common electrodes for those two adjacent cells.
[0018] The manufacturing system according to this embodiment forms a laminate 10 (Figure 2) to which the aforementioned voltage detection terminal 20 is connected, through various processes such as coating, pressing, seal welding, separator welding, cutting, terminal (voltage detection terminal) welding, end face welding, and liquid injection port welding. The manufacturing system according to this embodiment includes a system for preparing the laminate 10 (a system including equipment corresponding to each process for forming the laminate 10) and an inspection system that performs liquid injection, a first inspection process (short circuit inspection after liquid injection), restraint, charging, aging, and a second inspection process (self-discharge inspection) on the laminate 10. However, it is not essential that the manufacturing (including inspection) of the energy storage device be performed automatically (i.e., that the equipment performs all processes related to manufacturing), and a person (worker) may perform some of the processes.
[0019] Referring to FIG. 1 together with FIG. 2, in S10, a laminate 10 having the above structure is formed. In this embodiment, S10 corresponds to an example of the "forming process" according to the present disclosure. Note that the structure of the laminate 10 is not limited to the structure shown in FIG. 2 and can be changed as appropriate.
[0020] In the subsequent S11, the inspection system pours an electrolytic solution into a storage portion (the power storage portion 10a surrounded by the sealing portion 3) that houses a plurality of cells C. As a result, the space surrounded by the sealing portion 3 is filled with the electrolytic solution. The electrolytic solution is impregnated into the separator 13. The electrolytic solution is, for example, a non-aqueous electrolytic solution. In this embodiment, S11 corresponds to an example of the "electrolytic solution pouring process" according to the present disclosure. Note that the electrolytic solution is optional and may be an aqueous electrolytic solution.
[0021] Subsequently, in S12, the inspection system determines, for each of the plurality of cells C included in the laminate 10, whether or not the voltage between the positive electrode and the negative electrode converges within a predetermined range (hereinafter referred to as the "short-circuit range"). The short-circuit range may be set within a range of -0.01 V or more and 0.01 V or less. In this embodiment, a range of -0.005 V or more and 0.005 V or less is set as the short-circuit range. Hereinafter, the voltage between the positive electrode (positive electrode active material layer 12B) and the negative electrode (negative electrode active material layer 12A) of the cell C is referred to as the "cell voltage". The inspection system may detect the cell voltage using the voltage detection terminal 20 shown in FIG. 2.
[0022] If the cell voltage of any of the cells C does not converge within the short-circuit range (NO in S-12), the process proceeds to S13. In S13, the inspection system determines whether or not a predetermined period (hereinafter referred to as the "determination period") has elapsed. The determination period is, for example, a period from the time when the electrolytic solution pouring process (S11) is completed until a predetermined time has elapsed. The predetermined time in the determination period may be set within a range of 10 hours or more and 50 hours or less. In this embodiment, the period from the time when the electrolytic solution pouring process is completed until 20 hours have elapsed is set as the determination period. While the determination period has not elapsed (NO in S13), the determination in S12 is repeatedly executed.
[0023] FIG. 3 is a diagram for explaining the inspection process according to this embodiment. In this embodiment, S12 and S13 correspond to an example of the "first inspection process" according to the present disclosure. Hereinafter, the first inspection process will be described with reference to FIG. 3.
[0024] In FIG. 3, the data D11, D12, D21, and D22 show the results of measuring the change in the cell voltage after liquid injection for each of the four cells C included in the laminate 10.
[0025] In each of the data D11 and D12, the cell voltage (voltage between the positive and negative electrodes) decreased due to the liquid injection process. In data D11, the cell voltage converged immediately after the liquid injection. In data D12, the cell voltage converged at the timing when about 15 hours had elapsed since the liquid injection. In both D11 and D12, the cell voltage converged within the short-circuit range R during the determination period.
[0026] On the other hand, in each of the data D21 and D22, the cell voltage also decreased due to the liquid injection process. However, in D21 and D22, a natural potential (inherent voltage due to the material) was generated between the positive and negative electrodes of the cell C due to the liquid injection process, and the cell voltage did not converge within the determination period.
[0027] Referring to FIG. 1 again, in the first inspection process, when it is determined that the cell voltage has converged within the short-circuit range for at least one cell C included in the laminate 10, it is determined as YES in S12, and the process proceeds to S14. The inspection system may determine that the cell voltage has converged, for example, when the change rate of the cell voltage (the amount of change in the cell voltage per unit time) becomes less than or equal to a predetermined value. If the converged cell voltage is within the short-circuit range during the determination period, it is determined as YES in S12. For example, when the data D11 or D12 shown in FIG. 3 is measured for at least one cell C included in the laminate 10, it is determined as YES in S12. Note that the method for determining convergence is not limited to the above and is arbitrary.
[0028] In S14, the inspection system determines that a short circuit has occurred in the laminate 10 and reports and / or records the determination result. In the following S15, the inspection system estimates the electrical resistance value between the positive and negative electrodes (hereinafter referred to as "short-circuit resistance") for each of the one or more cells C whose cell voltage was determined to have converged to the short-circuit range in S12. The inspection system may estimate the short-circuit resistance based on the magnitude of the cell voltage that has converged to the short-circuit range (convergence value). The inspection system may estimate that the closer the converged value is to a predetermined reference value, the smaller the short-circuit resistance. In the example shown in Figure 3, the converged value of data D11 is closer to the reference value (0V) than the converged value of data D12. Therefore, the inspection system estimates the short-circuit resistance of cell C related to data D11 as, for example, "100Ω", and the short-circuit resistance of cell C related to data D12 as, for example, "1kΩ". The short-circuit resistance for each cell C estimated in S15 is stored linked to the identification information (cell ID) of cell C. This data may be used to improve manufacturing conditions. Once process S15 is executed, the processing flow shown in Figure 1 will terminate.
[0029] On the other hand, if the judgment period elapses before a YES is determined in S12 (YES in S13), the process proceeds to S21. However, for data D21 and D22 shown in Figure 3, it is also possible to determine that the cell voltage has not converged to the short-circuit range before the judgment period elapses, i.e., when the cell voltage falls below -0.005V (the lower limit of the short-circuit range).
[0030] In S21, the inspection system restrains the laminate 10 with a restraining jig. The inspection system may also sandwich the laminate 10 between a pair of end plates (restraining plates). Subsequently, in S22, the inspection system performs the initial charging of the laminate 10. Initial charging is the first time the formed laminate 10 is charged. For example, the inspection system applies a voltage between the positive and negative terminals of the laminate 10 (for example, the current collectors 11 located at both ends in the Z direction as shown in Figure 2). This charges all the cells C connected in series.
[0031] Next, in S23, the inspection system raises the temperature of the laminate 10 to an aging temperature higher than room temperature. The aging temperature may be between 50°C and 85°C. Next, in S24, the inspection system performs high-temperature aging of the laminate 10. The inspection system maintains the temperature of the laminate 10 at the above aging temperature until a predetermined time (hereinafter referred to as "aging time") has elapsed. The aging time can be set arbitrarily. Once high-temperature aging is complete, in S25, the inspection system cools the laminate 10 to room temperature (for example, around 25°C).
[0032] After the laminate 10 has cooled, the inspection system performs a self-discharge test on the laminate 10 in S26. In this embodiment, S26 corresponds to an example of the "second inspection process" according to this disclosure. The second inspection process will be described below with reference to Figure 3.
[0033] In the second inspection process (self-discharge test), an inspection circuit (inspection circuits Ch1, Ch2, ... shown in Figure 3) containing a DC power supply is connected to each of the multiple cells C (cells C-1, C-2, ... shown in Figure 3) contained in the laminate 10. Then, a power supply voltage (VS) is applied to cell C with the same magnitude as the cell voltage at the start of the test but in the reverse direction. The power supply voltage (VS) corresponds to the output voltage of the DC power supply. VS is kept constant during the test. This makes the equation "IB = (VS - VB) / Rext" true. In the equation, "Rext" represents the resistance value of the inspection circuit. Rext 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. In the equation, "VB" represents the voltage of cell C. In the equation, "IB" represents the current value flowing through cell C and the inspection circuit.
[0034] At the start of the test, VB and VS are equal, so IB is zero. Subsequently, as VB decreases due to the self-discharge of cell C, IB increases. When IB increases to equal the self-discharge current, the decrease in VB stops. At the same time, the increase in IB also stops, and IB converges. This converged value of IB represents the self-discharge current.
[0035] In Figure 3, data D31 and D32, respectively, show the changes in IB measured during the self-discharge test. The inspection system determines cells with a self-discharge current of 10 or more that exceed a predetermined reference value (hereinafter referred to as "Is") as short-circuited cells (defective products). The inspection system also determines cells with a self-discharge current of less than Is as good cells. In data D31, the converged value of IB was less than Is. Therefore, cell C related to data D31 is determined to be a good cell. On the other hand, in data D32, the converged value of IB was 10 or more that exceeded Is. Therefore, cell C related to data D32 is determined to be a short-circuited cell. The inspection system determines that the laminate 10 is a defective product if it contains at least one short-circuited cell. Note that it is not essential to keep the power supply voltage (VS) constant during the self-discharge test. The power supply voltage may be feedback controlled.
[0036] As described above, the battery manufacturing method according to this embodiment includes the processes shown in Figure 1. In this method, the first inspection process (S12, S13) is performed before the second inspection process (S26). According to the first inspection process, it is possible to determine whether or not there is a short circuit in cell C without charging or discharging cell C. According to the first inspection process, there is a low possibility of incorrectly determining that cell C is short-circuited when it is not. Furthermore, for batteries (laminated 10) that are determined to be short-circuited in the first inspection process, the processes from S21 onwards are not performed. This reduces inspection costs. On the other hand, for batteries (laminated 10) that are determined not to be short-circuited by the first inspection process, the second inspection process (self-discharge test) is performed. The second inspection process takes longer than the first inspection process, but it can determine whether or not there is a short circuit in cell C with high accuracy. According to the first and second inspection processes described above, it becomes possible to determine whether or not there is a short circuit in various types of batteries with high accuracy.
[0037] A laminate 10 that is judged to be a good product by the above inspection can function as a bipolar secondary battery on its own. However, a bipolar secondary battery may also be manufactured by combining multiple modules of the laminate 10 as one module. The manufactured bipolar secondary battery may be mounted on a mobile device. Examples of mobile devices include automobiles (electric vehicles, hybrid vehicles, etc.), vehicles other than automobiles, and mobile machinery (agricultural machinery, construction machinery, etc.). However, the application of the battery is arbitrary, and a stationary battery may also be manufactured by the above method.
[0038] The processing flow shown in Figure 1 can be modified as needed. For example, the order of processing may be changed, or the content of any of the processing steps may be changed, depending on the purpose.
[0039] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]
[0040] 10 Laminate, 10a Energy storage section, 11 Current collector, 12A Negative electrode active material layer, 12B Positive electrode active material layer, 20 Voltage detection terminal, C Cell.
Claims
[Claim 1] A forming process for forming the positive electrode and negative electrode of a battery, and a housing portion for housing the positive electrode and the negative electrode, An electrolyte solution is poured into the formed containment, A first inspection process determines that a short circuit exists between the positive electrode and the negative electrode when the voltage between the positive electrode and the negative electrode converges to a predetermined range as a result of the liquid injection process. A second inspection process is performed to perform a self-discharge test on the battery that has been determined not to be short-circuited by the first inspection process, A method for manufacturing batteries, including the invention of a battery.