Manufacturing method for power storage device

Abstract

To provide a manufacturing method for a power storage device that can suppress deterioration in accuracy of self-discharge testing caused by detection errors of the charge storage amount of a secondary battery or variations in the charge storage amount between unit batteries.SOLUTION: A manufacturing method for a power storage device includes forming a secondary battery containing lithium iron phosphate as a positive electrode active material (S101), and conducting a self-discharge test of the secondary battery while charging the secondary battery into a state of charge SOC where dV / dQ, which is a ratio of a change dV in the voltage V of the secondary battery to a change dQ in the amount of stored charge Q of the secondary battery, is less than 0.0003 V / mAh (S13).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a power storage device.

Background Art

[0002] Japanese Unexamined Patent Application Publication No. 2015-106475 (Patent Document 1) discloses a method for determining the quality of a plurality of unit cells in a self-discharge inspection of a secondary battery including the plurality of unit cells, based on the voltage drop amounts of the plurality of unit cells before and after aging. In this method, when the difference between the voltage drop amounts of the plurality of unit cells before and after aging and the non-defective product reference value is larger than the threshold value, the plurality of unit cells are determined to be defective products. Note that the threshold value is set to decrease as the voltage drop amount increases.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As described above, when performing a self-discharge inspection on a plurality of unit cells collectively, the stored power amounts in the plurality of unit cells do not necessarily become uniform. And the dV / dQ of a secondary battery changes depending on the stored power amount. dV / dQ is the ratio of the change amount (dV) of the voltage of a secondary battery to the change amount (dQ) of the stored power amount of the secondary battery. If there are variations in the stored power amounts among the unit cells, dV / dQ and even the non-defective product reference value are likely to vary among the unit cells. As a result, the accuracy of determining the quality of a secondary battery regarding self-discharge is likely to decrease.

[0005] In addition, when performing a self-discharge test on a single secondary battery, the same problems as described above may occur due to the detection error of the stored charge amount of the secondary battery. When the detection error of the stored charge amount increases, the determination accuracy may decrease because the pass / fail determination is made based on an incorrect acceptable standard value. For example, in an inspection system that estimates the state of a secondary battery without directly detecting it, there is a risk that the detection error (estimation error) of the stored charge amount of the secondary battery will increase.

[0006] The present disclosure has been made to solve the above problems, and an object thereof is to provide a method for manufacturing a power storage device that can suppress a decrease in the accuracy of a self-discharge test caused by a detection error of the stored charge amount of a secondary battery or a variation in the stored charge amount between unit batteries.

Means for Solving the Problems

[0007] According to one aspect of the present disclosure, there is provided a method for manufacturing a power storage device including a secondary battery. The secondary battery contains lithium iron phosphate as a positive electrode active material. The method for manufacturing the power storage device includes forming the secondary battery, and performing a self-discharge test on the secondary battery in a state where the secondary battery is charged to a state of charge (SOC) at which dV / dQ, which is the ratio of the change amount dV of the voltage V of the secondary battery to the change amount dQ of the stored charge amount Q of the secondary battery, is less than 0.0003 V / mAh.

Effects of the Invention

[0008] According to the present disclosure, it becomes possible to provide a method for manufacturing a power storage device that can suppress a decrease in the accuracy of a self-discharge test caused by a detection error of the stored charge amount of a secondary battery or a variation in the stored charge amount between unit batteries.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0010] Embodiments of the present 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 description will not be repeated. In each of the drawings used below, among the X-axis, Y-axis, and Z-axis that are orthogonal to each other, the X-axis represents the in-plane direction of the first surface of the battery (for example, the width direction), the Y-axis represents the in-plane direction of the second surface of the battery (for example, the length direction), and the Z-axis represents the thickness direction of the battery. Hereinafter, “+” is attached to the direction indicated by the arrows of the X-axis, Y-axis, and Z-axis, and “-” is attached to the opposite direction.

[0011] FIG. 1 is a diagram for explaining an outline of a method for manufacturing a power storage device according to this embodiment. Referring to FIG. 1, the method for manufacturing a power storage device according to this embodiment includes a processing flow F0. The power storage device to be manufactured includes a lithium ion secondary battery. In the flowchart, “S” means step. Hereinafter, the processing flow F0 will be described. In S101, the manufacturing system forms, for example, the laminate 10 shown in FIG. 2.

[0012] FIG. 2 is a cross-sectional view showing the configuration of the laminate 10. 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 arbitrarily set. The number of cells C included in the power storage unit 10a may be 3 or more and less than 50, or 50 or more. The sealing unit 3 is formed so as to surround the power storage unit 10a. The space surrounded by the sealing unit 3 (the space between the cell C and the sealing unit 3) is filled with an electrolytic solution. The electrolytic solution is impregnated into the separator 13. The separator 13 may be a porous sheet.

[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) laminated along the Z direction. A separator 13 is disposed between the electrodes. The laminate 10 includes a plurality of separators 13. The bipolar electrode 1 includes a current collector 11, a negative electrode active material layer 12A provided on one surface (+Z side surface) of the current collector 11, and a positive electrode active material layer 12B provided on the other surface (-Z side surface) 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 is formed on the -Z side surface of the current collector 11 constituting the negative terminal electrode 2A. The insulating layer 19A covers the peripheral portion of the negative terminal electrode 2A and exposes the central portion of the negative terminal electrode 2A (the current collector 11 located at the -Z side end of the power storage unit 10a). 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 constituting the positive terminal electrode 2B. The insulating layer 19B covers the peripheral portion of the positive terminal electrode 2B and exposes the central portion of the positive terminal electrode 2B (the current collector 11 located at the +Z side end of the power storage unit 10a).

[0014] In this embodiment, a metal foil (for example, aluminum foil) is employed as the current collector 11 of each electrode. Surface treatment (for example, plating treatment) may be applied to one side or both sides of the metal foil. A voltage detection terminal 20 is connected to the current collector 11 of each electrode. The voltage detection terminal 20 is welded, for example, to the end portion on the +X side of the current collector 11. Examples of welding methods include ultrasonic welding or laser welding. A connector (including an alignment housing) (not shown) may be provided for the plurality of voltage detection terminals 20 connected to the laminate 10. Further, a liquid injection port for the electrolytic solution may be provided at the end face of the laminate 10.

[0015] The negative electrode active material layer 12A contains a negative electrode active material. The positive electrode active material layer 12B contains 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 (for example, graphite), and the electrolytic solution is a non-aqueous electrolytic solution (for example, an ester-based electrolytic solution). However, other examples of the negative electrode active material include silicon and tin. The electrolytic solution may be an aqueous electrolytic solution. Further, a gel-like or solid electrolyte may be employed instead of the electrolytic solution. Examples of materials constituting the separator 13 include polypropylene, polyethylene, polyester, and cellulose. The structure of the separator 13 may be a single-layer structure or a multi-layer structure. The separator 13 may include, for example, a base material layer and a pair of adhesive layers, and may be adhered to the negative electrode active material layer 12A and the positive electrode active material layer 12B by the pair of adhesive layers.

[0016] In the laminate 10, a cell C is formed between the plurality of stacked current collectors 11. Specifically, a cell C is formed between a certain current collector 11 (the first current collector) and the current collector 11 (the second current collector) adjacent to the first current collector. Further, a cell C is also formed between the second current collector and the current collector 11 (the third current collector) adjacent to the second current collector. Thus, the current collector 11 and the cell C are alternately arranged in the stacking direction of the laminate 10.

[0017] The sealing portion 3 includes the seal layers 14 and 15 disposed around each of the plurality of cells C included in the laminate 10, and the insulating layers 19A and 19B described above. Any sealing material can be adopted as the material constituting the sealing portion 3. Examples of the sealing material include resin materials such as polyethylene, polypropylene, acid-modified polyethylene, or acid-modified polypropylene. The structure of the sealing portion 3 between the current collectors 11 is not limited to a two-layer structure (seal layers 14 and 15), and may be a three-layer structure. The sealing portion 3 may include a spacer.

[0018] Referring again to FIG. 1, in S101, the manufacturing system forms the laminate 10 (FIG. 2) to which the voltage detection terminal 20 described above is connected through various processes such as, for example, coating, pressing, seal welding, separator welding, cutting, terminal (voltage detection terminal) welding, end face welding, injection molding, liquid injection, and temporary sealing. The laminate 10 may be sandwiched between a pair of end plates (constraint plates). The pair of end plates may be fastened so as to apply a constraint load from the outside to the inside in the stacking direction with respect to the laminate 10. The manufacturing system includes devices corresponding to each process.

[0019] In S102, the manufacturing system ages the laminate 10 formed in S101. Charging and / or discharging of the laminate 10 may be performed before or during aging. Aging may include at least one of aging at room temperature (low-temperature aging) and aging at a temperature higher than room temperature (high-temperature aging). The temperature of the high-temperature aging may be 50°C or higher and 85°C or lower, for example, 65°C. The temperature adjustment of the laminate 10 may be performed by a temperature adjustment device 200 (FIG. 3) described later.

[0020] After aging, the manufacturing system performs a self-discharge inspection of the laminate 10 in S103. FIG. 3 is a diagram for explaining the self-discharge inspection. Referring to FIG. 3, the manufacturing system according to this embodiment includes a control device 100, a temperature adjustment device 200, a charging device 300, and a notification device 500. Various devices included in the manufacturing system (including the temperature adjustment device 200, the charging device 300, and the notification device 500) are controlled by the control device 100. The control device 100 includes one or more processors 110 and one or more storage devices 120. The storage device 120 is configured to be able to store the stored information. In addition to the program, information used in the program (for example, maps and various parameters) is stored in the storage device 120. In this embodiment, by the one or more processors 110 executing the program stored in the one or more storage devices 120, the processing flows F0 and F1 shown in the flowchart in FIG. 1 are executed. However, these processes may be executed only by hardware (electronic circuits) without using software.

[0021] Prior to the self-discharge inspection (S103 in FIG. 1), the laminate 10 is attached to the temperature adjustment device 200 and the charging device 300. The temperature adjustment device 200 is configured to be able to adjust the temperature of the laminate 10. The temperature adjustment device 200 may have a thermostatic chamber whose temperature can be controlled. The control device 100 adjusts the temperature of the laminate 10 by controlling the temperature adjustment device 200 according to the conditions of the self-discharge inspection. In addition, the charging device 300 includes a power supply 310, a charging circuit 320, and a detector 330. The power supply 310 is connected to the positive electrode terminal (the current collector 11 of the positive terminal electrode 2B shown in FIG. 2) and the negative electrode terminal (the current collector 11 of the negative terminal electrode 2A shown in FIG. 2) of the laminate 10 via the charging circuit 320. The detector 330 detects the current (supply current) supplied from the power supply 310 to the laminate 10 and the state of charge (SOC) of each of the plurality of cells C included in the laminate 10, and outputs the detection result to the control device 100.

[0022] Each of the plurality of cells C included in the laminate 10 (power storage unit 10a) is positioned between a plurality of stacked current collectors 11 and functions as an LFP battery (a battery containing lithium iron phosphate as a positive electrode active material). Lithium iron phosphate corresponds to a positive electrode active material having a normal operating potential of 4 V or less with respect to lithium metal. The normal operating potential is represented by a catalog value, an average operating potential, a nominal voltage, or the like of the material. Line L10 indicates the charging characteristics of cell C. The measurement conditions of the data are an environmental temperature of "25°C (constant)", a charging rate (C rate) of "0.05C", and a voltage range of 3.00 V to 3.75 V. The SOC (State Of Charge) on the horizontal axis of the graph indicates the stored charge amount, and represents, for example, the ratio of the current stored charge amount to the stored charge amount in a fully charged state as 0 to 100%. As shown by line L10, in the LFP battery, in each of the SOC ranges "0 to 5%" and "98 to 100%", dV / dQ (the ratio of the change amount dV of the battery voltage to the change amount dQ of the stored charge amount) rapidly increases.

[0023] Referring to FIG. 1 again, processing flow F1 shows the details of S103 of processing flow F0. In S11, the control device 100 acquires one or more specific SOC regions of cell C based on the dV / dQ information of cell C. The specific SOC region is an SOC region where the dV / dQ of cell C is less than 0.0003 V / mAh. The dV / dQ information corresponds to information indicating the relationship between SOC (stored charge amount) and dV / dQ for cell C (LFP battery) formed in S101. The dV / dQ information indicates one or more specific SOC regions. The dV / dQ information is, for example, measured in advance and stored in the storage device 120. FIG. 4 is a diagram showing an example of the dV / dQ information.

[0024] Referring to FIG. 4, line L20 indicates the dV / dQ information of cell C. The measurement conditions for line L20 are an environmental temperature of "25°C (constant)", a charging rate (C-rate) of "0.05C", and a voltage range of 3.00V to 3.75V. The dV / dQ information indicates the first SOC region R1 and the second SOC region R2. Each of the first SOC region R1 and the second SOC region R2 corresponds to a specific SOC region. The first SOC region R1 corresponds to an SOC range of 31% or more and 44% or less, and its SOC width is 13%. The second SOC region R2 corresponds to an SOC range of 68% or more and 75% or less, and its SOC width is 7% (see the enlarged view on the right side of line L20).

[0025] Referring again to FIG. 1, in S12, the control device 100 uses the specific SOC region obtained in S11 to adjust the SOC (state of charge) of each of the plurality of cells C included in the laminate 10 (power storage unit 10a) so that the dV / dQ of each of the plurality of cells C becomes less than 0.0003 V / mAh. Specifically, the control device 100 charges the laminate 10 by the charging device 300 shown in FIG. 2 so that the SOC of all the cells C included in the laminate 10 falls within the first SOC region R1 or the second SOC region R2. The charging conditions are an environmental temperature of "25°C (constant)" and a charging rate (C-rate) of "0.05C". The power supply 310 applies a voltage between the positive and negative terminals of the laminate 10 via the charging circuit 320. Due to the power supplied from the power supply 310 to the laminate 10, a charging current flows through the entire laminate 10 in the Z direction (lamination direction). As a result, all the cells C included in the laminate 10 are charged. The power supply 310 and the charging circuit 320 function as a precision power supply capable of precisely adjusting the current. The charging circuit 320 controls the power (current and voltage) supplied from the power supply 310 to the laminate 10 according to a control command from the control device 100. The detector 330 may detect the voltage of the cell C using the voltage detection terminal 20 and obtain the SOC of the cell C based on the voltage of the cell C. The detector 330 may also detect the voltage of the cell C based on the potential difference between the two current collectors 11 sandwiching the cell C.

[0026] When the charging device 300 performs charging on a plurality of cells C (a plurality of batteries) collectively as described above, the SOC (state of charge) in the plurality of cells C does not necessarily become uniform. For example, in the formation of the laminate 10 (S101 in FIG. 1), it is difficult to form the laminate 10 such that all the cells C have the same capacity, and there is a tendency for a capacity variation of about several percent to occur between cells. Due to the influence of such capacity variations and the like, the SOC of the plurality of cells C included in the laminate 10 tends to become non-uniform. In S12, the control device 100 may charge the laminate 10 until the highest SOC value among the SOC values of those cells C reaches the SOC upper limit value of the specific SOC region ("75%" in the second SOC region R2) in order to bring the SOC of all the cells C into the specific SOC region. By doing so, it becomes easier for the SOC of all the cells C to enter the specific SOC region. Also, even if the SOC of the cell C decreases during the self-discharge inspection, it becomes easier for the SOC of all the cells C to continue to be included within the specific SOC region.

[0027] In subsequent S13, the control device 100 measures the self-discharge amount of the laminate 10. For example, the open-circuit voltage of the charged battery is acquired, and a voltage equal to the open-circuit voltage is continuously applied to the battery. Then, a state is reached where the power supply current and the self-discharge current are balanced. The power supply current at that time is detected as the self-discharge current. The self-discharge current is detected based on the power ( = current value) required to maintain the SOC of the charged battery.

[0028] In one example, the self-discharge amount of the laminate 10 is measured in a state where the SOC of each of the plurality of cells C included in the laminate 10 is within a specific SOC region, that is, a state where dV / dQ of each of these cells C is less than 0.0003 V / mAh. Specifically, the control device 100 controls the voltage applied by the power supply 310 to the laminate 10 so that the self-discharge amount (leakage current from the laminate 10) of the laminate 10 and the current (supply current) supplied by the power supply 310 to the laminate 10 are balanced. In the self-discharge inspection according to this embodiment, charging is performed using the individual voltage detection terminals 20 (voltage detection lines). Since the leakage current is minute, charging can be performed using the voltage detection terminals 20. The control device 100 cannot directly measure the self-discharge amount of the laminate 10. The control device 100 may determine whether the self-discharge amount of the laminate 10 and the supply current are balanced based on the change in the SOC of each of the plurality of cells C included in the laminate 10. The control device 100 may determine that the self-discharge amount of the laminate 10 and the supply current are balanced when the amount of change in the SOC becomes equal to or less than a predetermined value during the current supply from the power supply 310 to the laminate 10. The control device 100 may regard the supply current when it is determined that they are balanced as the self-discharge amount of the laminate 10. During the measurement of the self-discharge amount, current is supplied from the power supply 310 to the laminate 10 under the condition of an environmental temperature of "25°C (constant)". The control device 100 may control the supply current so that the SOC of all the cells C is continuously included within the specific SOC region (dV / dQ becomes less than 0.0003 V / mAh) during the measurement of the self-discharge amount. When it is determined that the self-discharge amount of the laminate 10 and the supply current are balanced, the control device 100 acquires the self-discharge amount and stops the current supply from the power supply 310 to the laminate 10. Thereby, the measurement of the self-discharge amount is completed.

[0029] In subsequent S14, the control device 100 determines whether the self-discharge amount measured in S13 is greater than a predetermined threshold value. The storage device 120 may store in advance a first threshold value for the first SOC region R1 and a second threshold value for the second SOC region R2. When the self-discharge amount of the laminate 10 in the first SOC region R1 is measured in S13, the control device 100 may use the first threshold value in S14. When the self-discharge amount of the laminate 10 in the second SOC region R2 is measured in S13, the control device 100 may use the second threshold value in S14. When the self-discharge amount is equal to or less than the threshold value (NO in S14), the control device 100 determines in S15 that the laminate 10 is a non-defective product. In this case, the laminate 10 is sent to a subsequent process (for example, appearance inspection). When the self-discharge amount is greater than the threshold value (YES in S14), the control device 100 determines in S16 that the laminate 10 is a defective product. Subsequently, the control device 100 controls the notification device 500 in S17 so that the user is notified that the laminate 10 has been determined to be defective in the self-discharge inspection. The notification device 500 includes, for example, at least one of a display device, a lamp, a speaker, and a buzzer. In this case, the processing flow F1 ends without the laminate 10 being sent to a subsequent process. The control device 100 may record the result of the pass / fail determination in the storage device 120. Note that the control device 100 may perform a pass / fail determination of the laminate 10 in the self-discharge inspection based on the difference between the self-discharge amount and the non-defective product reference value in S14.

[0030] Referring to FIG. 4, lines L1 to L4 are graphs showing the relationship between the self-discharge amount (vertical axis) and time (horizontal axis) for cells C in different states. The method for measuring the self-discharge amount is the same as that of S13 described above. Line L1 shows the result of measuring the self-discharge amount for a normal cell C (first cell: good product) with an SOC of "70%" and a dV / dQ of "0.000178 V / mAh". Line L2 shows the result of measuring the self-discharge amount for a normal cell C (second cell: good product) with an SOC of "75%" and a dV / dQ of "0.000266 V / mAh". The self-discharge amount of each of the first cell and the second cell corresponds to the good product reference value and is less than 10 μA. Specifically, as shown by lines L1 and L2, the good product reference value is about 3 μA. Each of the first cell and the second cell has an SOC (70% or 75%) within the second SOC region R2. As shown by lines L1 and L2, the good product reference value in a specific SOC region hardly changes even when the power storage amount of cell C changes. Line L3 shows the result of measuring the self-discharge amount for an abnormal cell C (third cell: defective product) with an SOC of "75%" and a dV / dQ of "0.000266 V / mAh". As shown by line L3, the self-discharge amount of the third cell is about 20 μA. Therefore, by setting the second threshold value described above to a value of 5 μA or more and 15 μA or less (for example, 10 μA), the control device 100 can appropriately determine whether the laminate 10 includes defective products (for example, short-circuited products) based on whether the self-discharge amount of the laminate 10 is greater than the second threshold value.

[0031] On the one hand, line L4 shows the result of measuring the self-discharge amount of a normal cell C (the fourth cell: a good product) with an SOC of "92%" and a dV / dQ of "0.00111 V / mAh". The SOC (92%) of the fourth cell is included in the general plateau region but not in the specific SOC region. As shown by line L4, the self-discharge amount of the fourth cell is greater than 20 μA. Even if all the cells C included in the laminate 10 are normal, when the laminate 10 includes the fourth cell, there is a possibility that the laminate 10 may be erroneously determined to include a defective product (abnormal cell C). In this regard, in the manufacturing method of the power storage device according to this embodiment, the self-discharge amount of the laminate 10 is measured in a state where the dV / dQ of all the cells C included in the laminate 10 is less than 0.0003 V / mAh, that is, in a state where the SOC of each of these cells C is within the specific SOC region. According to such a method, it is possible to suppress a decrease in the accuracy of the self-discharge inspection caused by variations in the stored power amount between cells and the like.

[0032] The manufacturing method of the power storage device according to this embodiment includes forming a laminate 10 including a plurality of cells C (S101 in FIG. 1), and performing a self-discharge inspection of the laminate 10 in a state where dV / dQ of each of the plurality of cells C is less than 0.0003 V / mAh (S13 in FIG. 1). The inventor of the present application focused on the fact that when an LFP battery (a battery containing lithium iron phosphate as a positive electrode active material) is charged, there is a specific SOC region (an SOC region where dV / dQ becomes less than 0.0003 V / mAh), and found that by using such a specific SOC region, a self-discharge inspection of the LFP battery can be performed with high accuracy. The self-discharge amount (good product reference value) of a normal battery in the specific SOC region hardly changes even if the power storage amount of the battery changes. That is, even if the recognized power storage amount deviates from the true value due to a detection error of the power storage amount or a variation in the power storage amount, the good product reference value in the specific SOC region is hardly affected by this. Thus, according to the above method, it is possible to suppress a decrease in the accuracy of the self-discharge inspection caused by a detection error of the power storage amount of the battery or a variation in the power storage amount between batteries. In addition, a step of equalizing the power storage amount of each cell before the self-discharge inspection can be omitted. In the experiments of the inventor of the present application, for batteries other than the LFP battery (for example, a ternary battery containing a positive electrode active material mainly composed of NCM (nickel-cobalt-manganese)), a specific SOC region that can be used in the self-discharge inspection could not be confirmed.

[0033] In the above embodiment, both the first SOC region R1 and the second SOC region R2 (FIG. 4) correspond to SOC regions with an SOC width of 5% or more. This makes it easier to adjust the SOC of all the cells C included in the laminate 10 within the specific SOC region. FIG. 4 shows an example of performing a self-discharge inspection of the laminate 10 in a state where the SOC of all the cells C of the laminate 10 is within the second SOC region R2, but the self-discharge inspection of the laminate 10 may be performed in a state where the SOC of each cell is adjusted within the first SOC region R1. Also, it is not essential that a threshold value is set for each specific SOC region. A threshold value common to a plurality of specific SOC regions may be used in S14.

[0034] The laminate 10 inspected as described above can function as a power storage device alone. However, the laminate 10 may be used as one module, and a plurality of modules may be combined to manufacture a power storage device. For example, a plurality of modules may be stacked such that the plurality of modules are electrically connected in series, and the stacked plurality of modules may be stored in a case together with other components (such as a cooler) to complete a battery pack (power storage device). The manufactured power storage device may be mounted on a moving body, for example. Examples of the moving body include automobiles (electric vehicles, hybrid vehicles, etc.), vehicles other than automobiles (ships, airplanes, etc.), mobile machines (agricultural machines, construction machines, etc.), and unmanned moving bodies (automated guided vehicles, robots, etc.). However, the use of the manufactured battery is arbitrary, and a stationary battery may be manufactured by the above method.

[0035] The processing flows F0 and F1 shown in FIG. 1 can be changed as appropriate. For example, instead of the processing flow F1, the control device 100 may execute the processing flow F2 shown in FIG. 5. FIG. 5 is a flowchart showing a modified example of the self-discharge inspection shown in FIG. 1. The processing flow F2 is the same as the processing flow F1 except that S11A to S11C are adopted instead of S11 (FIG. 1), and S12A, S13A, and S14A are added.

[0036] Referring to FIG. 5, in S11A, the control device 100 acquires one or more specific SOC regions of the cell C and one or more steep regions of the cell C based on the dV / dQ information of the cell C. The steep region is an SOC region where dV / dQ is 0.01 V / mAh or more. The dV / dQ information (line L20) shown in FIG. 4 shows a first steep region represented by the SOC range "0 to 5%" and a second steep region represented by the SOC range "98 to 100%".

[0037] In subsequent S11B, the control device 100 acquires the degree of variation in the stored power amounts among the plurality of cells C included in the laminate 10. For example, the control device 100 acquires the SOC of each of those cells C and acquires the degree of variation in the SOC among those cells C. The degree of variation may be represented by the standard deviation or variance, which are well-known indices. Further, the control device 100 may acquire the degree of variation in the SOC among those cells C based on the difference between the maximum value and the minimum value of the SOC among the plurality of cells C included in the laminate 10.

[0038] In subsequent S11C, the control device 100 determines whether or not the degree of variation in the SOC acquired in S11B is greater than a predetermined reference value. If the degree of variation in the SOC is greater than the reference value (YES in S11C), the process proceeds to S12. Thereby, the processes of S12 to S14 described above are executed.

[0039] On the other hand, if the degree of variation in the SOC is less than or equal to the reference value (NO in S11C), the process proceeds to S12A. Note that, for example, in a monopolar battery, unlike a bipolar battery, since the cells can be charged individually, it is easy to equalize the SOC. In a pattern with small SOC variation, the self-discharge amount variation is small and the possibility of misjudgment is also small, so appropriate inspection can be performed even outside the specified SOC range (specific SOC region).

[0040] In S12A, the control device 100 adjusts the SOC (state of charge) of each of the plurality of cells C included in the laminate 10 (power storage unit 10a) so that dV / dQ of each of the plurality of cells C becomes 0.01 V / mAh or more. Specifically, the control device 100 charges the laminate 10 by the charging device 300 shown in FIG. 2 so that the SOC of all the cells C included in the laminate 10 enters the first steep region or the second steep region. The charging conditions are an environmental temperature of "25°C (constant)" and a charging rate (C rate) of "0.05C". When the adjustment of the SOC (state of charge) is completed, the control device 100 stops charging. Subsequently, in S13A, the control device 100 measures the self-discharge amount of the laminate 10 based on the voltage drop amount of the laminate 10 over time. Specifically, the control device 100 sequentially measures the average voltage value of all the cells C included in the laminate 10 (hereinafter referred to as "average cell voltage"), and subtracts the average cell voltage at a point in time from the average cell voltage when a predetermined time has elapsed from that point in time to calculate the voltage drop amount of the laminate 10. Line L30 shows the result of measuring the voltage transition of a normal cell C (fifth cell: good product) having an SOC within the second steep region. As shown by line L30, when the cell C is left without power being supplied, the voltage of the cell C decreases over time. The larger the self-discharge amount of the cell C, the larger the voltage drop amount of the cell C.

[0041] In subsequent S14A, the control device 100 determines whether or not the self-discharge amount corresponding to the voltage drop measured in S13A is greater than a predetermined threshold value. The storage device 120 may store in advance a third threshold value for the first steep region and a fourth threshold value for the second steep region. When the voltage drop (self-discharge amount) of the laminate 10 in the first steep region is measured in S13A, the control device 100 may use the third threshold value in S14A. When the voltage drop (self-discharge amount) of the laminate 10 in the second steep region is measured in S13A, the control device 100 may use the fourth threshold value in S14A. If the self-discharge amount is equal to or less than the threshold value (NO in S14A), it is determined in S15 that the laminate 10 is a non-defective product, and the laminate 10 is sent to the subsequent process. On the other hand, if the self-discharge amount is greater than the threshold value (YES in S14A), it is determined in S16 that the laminate 10 is a defective product, and notification processing is executed in S17. Then, without the laminate 10 being sent to the subsequent process, the processing flow F2 ends. Note that the control device 100 may determine the pass / fail of the laminate 10 in the self-discharge inspection based on the difference between the self-discharge amount and the non-defective product reference value in S14A.

[0042] In the method according to the above-described modified example, the control device 100 obtains the degree of variation in the stored power in the plurality of cells C included in the laminate 10, and based on the degree of variation in the stored power, determines whether to perform the self-discharge inspection in the specific SOC region / steep region. According to such a method, it becomes possible to change the method of the self-discharge inspection according to the degree of variation in the stored power. Specifically, when the degree of variation in the stored power is greater than the reference value, the self-discharge inspection of the laminate 10 is performed in a state where dV / dQ of all the cells C included in the laminate 10 is less than 0.0003 V / mAh. Thereby, a decrease in the accuracy of the self-discharge inspection due to variations in the stored power between cells is suppressed. Further, when the degree of variation in the stored power is less than the reference value, the self-discharge inspection of the laminate 10 is performed in a state where dV / dQ of all the cells C included in the laminate 10 is 0.01 V / mAh or more. In a state where dV / dQ is large, while a decrease in the accuracy of the self-discharge inspection due to variations in the stored power between cells is likely to occur, it becomes easier to detect the self-discharge amount with high sensitivity. If the degree of variation in the stored power is sufficiently small, it is considered that almost no decrease in the accuracy of the self-discharge inspection due to variations in the stored power occurs. Therefore, in the above method, when the degree of variation in the stored power in the plurality of cells C included in the laminate 10 is less than the reference value, the self-discharge inspection of the laminate 10 is performed in a state where dV / dQ of each of these cells C is 0.01 V / mAh or more. Thereby, it becomes possible to detect the self-discharge amount of the laminate 10 with high sensitivity.

[0043] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is shown not by the description of the above-described embodiments but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Explanation of Reference Numerals

[0044] 1 bipolar electrode, 10 laminate, 11 current collector, 12A negative electrode active material layer, 12B positive electrode active material layer, 13 separator, 100 control device, C cell.

Claims

1. A method for manufacturing an energy storage device including a secondary battery, wherein the secondary battery contains lithium iron phosphate as a positive electrode active material, and the method for manufacturing the energy storage device includes: forming the secondary battery; performing a self-discharge inspection on the secondary battery in a charged state where a ratio dV / dQ of a change amount dV of the voltage V of the secondary battery to a change amount dQ of the stored charge Q of the secondary battery is less than 0.0003 V / mAh; A method for manufacturing an energy storage device, including the above steps.

2. The secondary battery includes a laminate including a plurality of bipolar electrodes and a plurality of separators, each of the plurality of bipolar electrodes having a current collector, a positive electrode active material layer provided on one surface of the current collector, and a negative electrode active material layer provided on the other surface of the current collector, a plurality of unit cells are formed in the laminate, each of the plurality of unit cells being located between the current collectors adjacent to each other in the stacking direction and including the positive electrode active material layer, the separator, and the negative electrode active material layer, the positive electrode active material layer of each of the plurality of unit cells containing lithium iron phosphate as the positive electrode active material, in the formation of the secondary battery, the laminate is formed, in the self-discharge inspection, the self-discharge amount of each of the plurality of unit cells is measured in a state where each of the plurality of unit cells is charged to a state of charge SOC at which dV / dQ is less than 0.0003 V / mAh. The method for manufacturing an energy storage device according to claim 1.

3. The method for manufacturing the energy storage device further includes: acquiring a degree of variation in the stored charge in the plurality of unit cells prior to the self-discharge inspection; when the degree of variation is greater than a reference value, adjusting the stored charge of each of the plurality of unit cells so that dV / dQ of each of the plurality of unit cells is less than 0.0003 V / mAh; The self-discharge inspection is performed when the degree of variation is greater than the reference value. The method for manufacturing an energy storage device according to claim 2.

4. when the degree of variation is less than the reference value, adjusting the stored charge of each of the plurality of unit cells so that dV / dQ of each of the plurality of unit cells is 0.01 V / mAh or more; when the degree of variation is less than the reference value, measuring the self-discharge amount of the laminate in a state where dV / dQ of each of the plurality of unit cells is 0.01 V / mAh or more. ​ The method for manufacturing an electric storage device according to claim 3, further comprising

5. The method for manufacturing the electric storage device obtains one or more SOC regions where the dV / dQ of the secondary battery becomes less than 0.0003 V / mAh, based on information indicating the relationship between the SOC (State Of Charge) indicating the stored charge amount with respect to the secondary battery and the dV / dQ further comprising The method for manufacturing an electric storage device according to any one of claims 1 to 4, wherein the one or more SOC regions include an SOC region having an SOC width of 5% or more.

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