Method of manufacturing bipolar battery

Abstract

To provide a method of manufacturing a bipolar secondary battery that can reduce high-temperature aging time in a high-temperature aging step.SOLUTION: A method of manufacturing a bipolar secondary battery, includes: an initial charging step of charging a first cell group having a plurality of cells that are adjacent in every other position in a stacking direction, and a second cell group having a plurality of cells that are adjacent to the cells contained in the first cell group to a defined voltage; a high-temperature aging step of performing aging at a temperature higher than a normal temperature; and an aging charing step of alternately charging the first cell group and the second cell group to the defined voltage in the high temperature aging step. In the aging charging step, a charging completion condition for at least one of the first cell group and the second cell group is determined on the basis of a dissolution rate calculated on the basis of a type of a metal abnormality and a positive electrode potential, a voltage of each cell in the aging charging step, and aging time.SELECTED DRAWING: Figure 4

Description

[Technical field]

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

[0002] Conventionally, in the manufacturing method of secondary batteries such as lithium-ion secondary batteries, a technique is known that includes a high-temperature aging process in which assembled cells are kept at high temperatures for a long time to facilitate the impregnation of the electrolyte into the electrode layer and the progress of irreversible side reactions other than the battery reaction, thereby uniforming the quality of the cells. Patent Document 1 discloses a technique that, if the temperature or time in high-temperature aging is outside the standard range, adjusts the subsequent aging conditions, thereby enabling quality assurance while maintaining the battery capacity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-122160 A Summary of the Invention [Problem to be solved by the invention]

[0004] On the other hand, in a bipolar battery having a bipolar structure, since charging is performed using terminals shared by adjacent cells in the stacking direction, it is necessary to charge the even-numbered cells and the odd-numbered cells separately in the stacking direction, which may result in a long time being required for the high-temperature aging process in which charging is performed to smoothly dissolve foreign matter.

[0005] In consideration of the above, an object of the present invention is to provide a method for producing a bipolar secondary battery capable of shortening the high-temperature aging time in the high-temperature aging step. [Means for solving the problem]

[0006] The method for producing a bipolar secondary battery according to the present invention as set forth in claim 1 includes an initial charging step of charging a first cell group having a plurality of cells adjacent to every other cell in a stacking direction and a second cell group having a plurality of cells adjacent to a cell included in the first cell group, to a specified voltage, a high-temperature aging step of aging at a high temperature higher than room temperature, and an aging charging step of alternately charging the first cell group and the second cell group until the voltage reaches a specified voltage during the high-temperature aging step, and in the aging charging step, a completion condition for charging at least one of the first cell group and the second cell group is determined based on a dissolution rate calculated based on the type of metallic foreign matter and the positive electrode potential, and on the voltage and aging time of each of the cells in the aging charging step.

[0007] The method for manufacturing a bipolar secondary battery according to the present invention described in claim 1 includes an aging charging step in which a first cell group having a plurality of cells adjacent to every other cell in the stacking direction and a second cell group having a plurality of cells adjacent to a cell included in the first cell group are alternately charged until a specified voltage is reached during the high-temperature aging step. In the aging charging step, the completion condition of at least one of the first cell group and the second cell group is determined based on a dissolution rate calculated based on the type of metallic foreign matter and the positive electrode potential, and the voltage and aging time of each cell in the aging charging step. In this way, the completion condition of the charge is determined based on the dissolution rate calculated based on the type of metallic foreign matter and the positive electrode potential, and the voltage and aging time of each cell in the aging charging step. Therefore, the time required to complete the charge in the high-temperature aging step can be shortened compared to the case where the charge is completed under the completion condition set for the lowest voltage cell without considering the dissolution rate of the foreign matter as in the conventional technology, and therefore the high-temperature aging time can be shortened.

[0008] In addition, the manufacturing method of a bipolar secondary battery according to the present invention described in claim 2 has the configuration described in claim 1, in which a switching charge capacity or a switching charge time is set as a switching determination condition for switching the charging of the cell to be charged in the aging charging process, and the switching charge capacity is a value smaller than the charging capacity at the previous charging, and the switching charge time is a time shorter than the charging time at the previous charging.

[0009] As an example, after the first charging of the first cell group is completed, while the first charging of the second cell group is being performed, the charge may be lost in each cell of the first cell group. Therefore, when the first cell group is charged for the second or subsequent times, the charge that was lost during the waiting period is replenished, so the charge capacity gradually decreases compared to the first charging. In other words, the more times the cells are charged, the closer they are to full charge, and the smaller the charge capacity becomes.

[0010] Therefore, in the method for producing a bipolar secondary battery according to the present invention as set forth in claim 2, the conditions for determining whether to switch charging the cell to be charged are that the switching charge capacity is set to a value smaller than the charge capacity at the previous charge, and the switching charge time is set to a time shorter than the charge time at the previous charge. As a result, in the aging charging step, the cell to be charged is charged at a charge capacity or charge time according to the number of times it has been charged. This makes it possible to prevent unnecessary charging and shorten the time required to complete charging.

[0011] In addition, in the manufacturing method of a bipolar secondary battery according to the present invention described in claim 3, in the configuration described in claim 1 or claim 2, the abnormality determination condition for determining that the cell to be charged in the aging charging process is abnormal is a case in which at least one of the amount of change in voltage with respect to time and the amount of change in battery capacity with respect to the voltage change falls outside a predetermined error range of the amount of change.

[0012] For example, if there is an extreme change in the charging conditions, the amount of change in voltage or the amount of change in battery capacity will deviate from the normal range. For example, if a short circuit occurs in a cell, the voltage will not increase and the amount of change in voltage will be small. Therefore, in the manufacturing method of a bipolar secondary battery according to the present invention described in claim 3, the abnormality determination condition for determining that a cell to be charged is abnormal in the aging charging step is when at least one of the amount of change in voltage with respect to time change and the amount of change in battery capacity with respect to voltage change falls outside a predetermined error range of the amount of change. As a result, if the amount of change in voltage or the amount of change in battery capacity falls outside the predetermined error range of the amount of change, it is determined to be abnormal, so that defective products can be detected in the aging charging step without going to the inspection step.

[0013] In addition, the manufacturing method of a bipolar secondary battery according to the present invention described in claim 4, in the configuration described in any one of claims 1 to 3, is such that the abnormality determination condition during the suspension of charging of the cell to be charged in the aging charging process is a case in which the voltage after a predetermined specified time has elapsed since charging was suspended is equal to or lower than a specified voltage value previously set for each number of charging attempts.

[0014] For example, as the number of charging times increases, the voltage drop during charging pauses tends to stop as the cell approaches full charge, so in the manufacturing method for a bipolar secondary battery according to the present invention described in claim 4, the condition for determining an abnormality during charging pauses for the cell to be charged is when the voltage after a preset specified time has elapsed since charging was paused is equal to or lower than a preset voltage value preset for each charging time. This allows a cell to be determined to be abnormal when the voltage during charging pauses is equal to or lower than a preset voltage value preset for each charging time, making it possible to detect defective products during the aging charging process without going to an inspection process.

[0015] In addition, the method for producing a bipolar secondary battery according to the present invention described in claim 5 has the configuration described in any one of claims 1 to 4, wherein the positive electrode uses lithium iron phosphate as a positive electrode active material.

[0016] In the method for producing a bipolar secondary battery according to the present invention, as described in claim 5, the positive electrode uses lithium iron phosphate as the positive electrode active material, so that the voltage drop near the dissolution potential of the foreign matter is steeper, and therefore the effects of the present invention can be more easily obtained. Effect of the Invention

[0017] As described above, the method for manufacturing a bipolar secondary battery according to the present invention has the excellent effect of being able to shorten the high-temperature aging time in the high-temperature aging step. [Brief description of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view of an electrode body according to one embodiment of the present invention. [Diagram 2] 1 is a cross-sectional view showing a schematic configuration of a two-dimensional battery according to an embodiment of the present invention. [Diagram 3] 1 is a graph showing the dissolution rate of SUS foreign matter depending on the electric potential. [Figure 4] FIG. 11 is a diagram showing the relationship between voltage and the dissolved size of SUS foreign matter over time in an odd-numbered cell according to the first embodiment of the present invention. [Diagram 5] FIG. 11 is a diagram showing the relationship between voltage and the dissolved size of SUS foreign matter over time in an odd-numbered cell according to the second embodiment of the present invention. [Figure 6] FIG. 11 is a diagram showing the relationship between voltage and the dissolved size of SUS foreign matter over time in an odd-numbered cell according to the third embodiment of the present invention. [Figure 7] FIG. 13 is a diagram showing a condition for determining whether to switch charge capacity with respect to the number of times of charging in an odd-numbered cell. [Figure 8] FIG. 13 is a diagram showing a switching determination condition for the charging time with respect to the number of charging times for odd-numbered cells. [Figure 9] 1 is a graph of a charging curve showing the relationship between voltage and charging time. [Figure 10]FIG. 1A is a graph showing the amount of change in voltage with respect to time, and FIG. 1B is a graph showing the amount of change in voltage with respect to voltage. [Figure 11] FIG. 4 is a graph showing the amount of change in battery capacity relative to voltage. [Figure 12] FIG. 11 is a diagram showing the relationship between the charging pause elapsed time and the voltage for each number of charging operations. [Figure 13] FIG. 13 is a graph showing the relationship between the number of charging times and the voltage two hours after charging was suspended. [Figure 14] FIG. 13 is a graph showing the relationship between the number of charging times and the voltage 10 hours after charging was suspended. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] A method for manufacturing a secondary battery according to an embodiment of the present invention will be described below with reference to the accompanying drawings. The secondary battery 100 of this embodiment is used, for example, as a lithium ion secondary battery or a nickel hydrogen secondary battery, which are examples of non-aqueous electrolyte secondary batteries. The non-aqueous electrolyte secondary battery is used, for example, as a battery for various vehicles such as a forklift, a hybrid vehicle, and an electric vehicle. The non-aqueous electrolyte secondary battery is, for example, a flat laminated battery, and specifically, is configured by laminating a plurality of bipolar electrodes 10 described later.

[0020] As shown in Fig. 1, the bipolar electrode 10 has a current collector 12 including one surface 12a and another surface 12b provided on the opposite side of the one surface 12a, a positive electrode mixture layer 14 as a positive electrode provided on the one surface 12a, and a negative electrode mixture layer 16 as a negative electrode provided on the other surface 12b. The bipolar electrode 10 can be easily obtained by coating the current collector 12 with one of the negative electrode mixture or the positive electrode mixture and drying it, and then coating the other in the same manner and drying it. The bipolar electrode 10 may be pressed and cut as necessary.

[0021] The current collector 12 is formed of a rectangular metal plate made of a metal such as aluminum, stainless steel, nickel, or copper. Alternatively, the current collector 12 may be a foil whose metal surface is coated with aluminum, copper, or the like. An edge portion 12c of the current collector 12 is formed into a rectangular frame shape, and serves as an uncoated region where the positive electrode mixture layer 14 and the negative electrode mixture layer 16 are not coated. The metal member constituting the current collector 12 may be appropriately selected from one or more metal members depending on the purpose.

[0022] The positive electrode mixture layer 14 includes a positive electrode active material, a conductive agent, and a binder. Examples of the positive electrode active material include lithium composite oxides. Examples of the lithium composite oxides include lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium iron phosphate (LFP), LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 The lithium composite oxide may contain at least one selected from the group consisting of F, Cl, N, S, Br and I. The shape of the positive electrode active material is not particularly limited. For example, it may be spherical (e.g., spherical, elliptical, etc.), fibrous, etc.

[0023] Examples of the conductive agent include carbon materials such as acetylene black, ketjen black, vapor grown carbon fiber (VGCF (registered trademark)), carbon nanotubes (CNT), etc. The content of the conductive agent is, for example, 3% by mass to 5% by mass with respect to the negative electrode active material.

[0024] Examples of the binder include polyvinylidene fluoride (PVDF) / NMP-based, styrene butadiene rubber (SBR) / water-based, polytetrafluoroethylene (PTFE) / water-based binders, etc. The content of the binder is, for example, 3% by mass to 5% by mass with respect to the negative electrode active material.

[0025] The negative electrode mixture layer 16 includes a negative electrode active material, a conductive agent, and a binder. Examples of the negative electrode active material include a Li-based active material such as metallic lithium, a carbon-based active material such as graphite, and lithium titanate (for example, Li 4 Ti5 O 12 Examples of the active material include oxide-based active materials such as SiO2, and Si-based active materials such as simple Si. The shape of the negative electrode active material is not particularly limited. For example, it may be spherical (e.g., spherical, elliptical, etc.), fibrous, etc.

[0026] The conductive agent may be, for example, a carbon material such as acetylene black, ketjen black, vapor grown carbon fiber (VGCF (registered trademark)), or carbon nanotube (CNT), similarly to the positive electrode mixture layer 14. The content of the conductive agent is, for example, 3% by mass to 5% by mass with respect to the negative electrode active material.

[0027] Examples of the binder include polyvinylidene fluoride (PVDF) / NMP-based, styrene butadiene rubber (SBR) / water-based, and polytetrafluoroethylene (PTFE) / water-based binders, similar to those of the positive electrode mixture layer 14. The content of the binder is, for example, 3% by mass to 5% by mass with respect to the negative electrode active material.

[0028] The bipolar electrodes 10 constructed as described above are alternately stacked with electrolyte layers 18 interposed therebetween to form a bipolar secondary battery 100, as shown in FIG.

[0029] In this embodiment, the electrolyte layer 18 may include a solid electrolyte layer or a separator and an electrolyte solution.

[0030] When the electrolyte layer 18 is a solid electrolyte layer, examples of the solid electrolyte include lithium lanthanum zirconate, LiPON, Li 1+X Al X Ge 2-X (PO4) 3 , Li-SiO-based glass, Li-Al-SO-based glass, and other oxide solid electrolytes; Li 2 SP 2 S 5 , Li 2 S-SiS 2 , LiI-Li 2 S-SiS 2 , LiI-Si 2 SP 2 S5 , Li 2 SP 2 S 5 -LiI-LiBr, LiI-Li 2 SP 2 S 5 , LiI-Li 2 SP 2 O 5 , LiI-Li 3 PO 4 -P 2 S 5 , Li 2 SP 2 S 5 -GeS 2 The solid electrolyte layer can be obtained by pressing the solid electrolyte.

[0031] When the electrolyte layer 18 is composed of a separator and an electrolytic solution, the separator may be, for example, a resin sheet such as polyethylene (PE) or polypropylene (PP). The electrolytic solution contains a predetermined electrolyte and a solvent. The predetermined electrolyte may be LiPF 6 , LiBF 4 , LiAsF 6 , Li(CF 3 SO 2 ) 2 N, Li(C 2 F 5 SO 2 ) 2 N, LiTaF 6 , LiClO 4 , LiCF 3 SO 3 etc.

[0032] Examples of the solvent include cyclic carbonate solvents such as ethylene carbonate (EC) and propylene carbonate (PC), and chain carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), etc. The concentration of the electrolyte is, for example, 0.1 to 1 mol / L.

[0033] In the manufacturing method of the secondary battery 100 of this embodiment, after the manufacturing of the secondary battery 100 is completed, an initial charging process and a high-temperature aging process of the secondary battery 100 are performed. The initial charging process is performed at a relatively low charging rate, and the temperature rise of the secondary battery 100 is suppressed. In this embodiment, CCCV charging is adopted as an example. CCCV charging is a method in which charging is first performed at a constant current (CC: Constant Current), and when the battery voltage reaches a specified value, control is switched to a constant voltage (CV: Constant Voltage) to continue charging, and charging is performed until full charging while avoiding an overvoltage charging state. In the charging process, full charging is performed to a SOC (State Of Charge) of 100%, but it may be, for example, SOC 90%. In this embodiment, the charging process is performed at room temperature, for example, about 20°C.

[0034] Here, the secondary battery 100 of this embodiment is a bipolar type secondary battery in which a plurality of bipolar electrodes 10 are stacked with electrolyte layers 18 interposed therebetween. As shown in Fig. 1, in this embodiment, a positive electrode mixture layer 14, an electrolyte layer 18, and a negative electrode mixture layer 16 provided between adjacent current collectors 12 in the stacking direction D are regarded as one cell 20. In the bipolar type secondary battery 100, when each cell 20 is charged, a terminal 32 connected to the current collector 12 located between the adjacent cells 20 is used, so that the adjacent cells 20 cannot be charged simultaneously.

[0035] Therefore, in this embodiment, every other adjacent cell in the stacking direction D is charged alternately. As shown in FIG. 2, every other adjacent cell from the top to the bottom in the stacking direction D is an odd-numbered cell 20A, and a cell adjacent to the odd-numbered cell 20A in the stacking direction D is an even-numbered cell 20B. In addition, a plurality of odd-numbered cells 20A are grouped together as an odd-numbered cell group 30A as a first cell group, and a plurality of even-numbered cells 20B are grouped together as an even-numbered cell group 30B as a second cell group. In this embodiment, the odd-numbered cell group 30A and the even-numbered cell group 30B are charged alternately. In FIG. 2, the colored cells 20 indicate cells 20 being charged.

[0036] After the charging process is completed, a high-temperature aging process is performed. The high-temperature aging process is a process in which the secondary battery 100 charged in the charging process is stored in a high-temperature environment. In the high-temperature aging process, the secondary battery 100 is chemically stabilized and activated. That is, if there is a minute short circuit caused by a foreign metal object mixed into the cell 20 from the manufacturing process or materials, the high temperature is used to accelerate the dissolution and precipitation (chemical reaction) of the foreign metal object, and detect the short circuit. For this reason, the high-temperature aging process is performed by keeping the temperature higher than room temperature, for example, at a high temperature of about 60°C in this embodiment.

[0037] However, for example, when the secondary battery 100 is a lithium ion secondary battery, the voltage (positive electrode potential) drops immediately when the initial charging is suspended. As described above, in this embodiment, since the odd-numbered cell group 30A and the even-numbered cell group 30B are charged alternately, it is difficult to maintain all the cells 20 at a specified voltage during series charging. In addition, when the metallic foreign matter that may be mixed in is, for example, SUS304, the necessary conditions for dissolving SUS304 are 62.5°C or higher and 3.60V or higher, so charging is required during the high-temperature aging process.

[0038] Therefore, in this embodiment, the high-temperature aging step includes an aging charging step in which the odd-numbered cell group 30A and the even-numbered cell group 30B are alternately charged. In this aging charging step, the condition for completing charging of at least one of the odd-numbered cell group 30A and the even-numbered cell group 30B is determined based on the dissolution rate calculated based on the type of metallic foreign matter and the positive electrode potential, and the voltage and aging time of each cell 20 in the aging charging step.

[0039] For example, when the possible foreign matter is a SUS foreign matter, the dissolution rate differs depending on the positive electrode potential as shown in FIG. 3. Specifically, the higher the positive electrode potential, the faster the dissolution rate. As an example, it can be assumed that the SUS foreign matter is to be dissolved until the outer diameter size (hereinafter referred to as the dissolution size) becomes 200 μm or less. In this case, based on the dissolution rate according to the positive electrode potential of the SUS foreign matter (see FIG. 3), the voltage and time conditions required to make the dissolution size of the SUS foreign matter 200 μm or less in each cell 20 are set in advance, and charging is determined to be completed when the set conditions are satisfied. Specifically, as an example, the time t is calculated so as to satisfy the following formula (1). Here, t indicates time (h) and x indicates the dissolution rate (μm / h).

[0040] [Table 1]

[0041] 200≦x 3.67~3.75 ×t 3.67~3.75 +x 3.62~3.67 ×t 3.62~3.67 +x 3.53~3.62 ×t 3.53~3.62 (1)

[0042] FIG. 4 is a diagram showing the relationship between the voltage and the dissolution size of SUS foreign matter with respect to the passage of time t in the odd-numbered cell 20A according to the first embodiment of the present invention. In FIG. 4, the solid line is a graph of the odd-numbered cell 20A, and the dotted line is a graph of the even-numbered cell 20B. As shown in FIG. 4, in the first embodiment, as an example, the charging of the odd-numbered cell 20A is started, the voltage of the odd-numbered cell 20A is kept at 3.75 (v), and the charging of the odd-numbered cell 20A is completed after 28 to 29 hours, which is the time t when the dissolution size of the SUS foreign matter reaches 200 μm. Then, after the charging of the odd-numbered cell 20A is completed, the charging of the even-numbered cell 20B is started next. Specifically, in Table 1 above, the dissolution speed x when the battery voltage is 3.75 (v) is 6.592 (μm / h), and this value is applied to the above formula (1) to calculate the time t.

[0043] Then, similarly to the odd-numbered cell 20A, charging of the even-numbered cell 20B is started and the voltage of the even-numbered cell 20B is maintained at 3.75 (v), and charging of the even-numbered cell 20B is completed after 58 hours, which is the time t when the dissolved size of the SUS foreign matter reaches 200 μm. That is, the SUS foreign matter is dissolved in the odd-numbered cell 20A and the even-numbered cell 20B (the odd-numbered cell group 30A and the even-numbered cell group 30B) in 58 hours.

[0044] Fig. 5 is a diagram showing the relationship between the voltage and the dissolved size of SUS foreign matter over time t in the odd-numbered cell 20A according to the second embodiment of the present invention. As shown in Fig. 5, in the second embodiment, as an example, charging of the odd-numbered cell 20A is started, the voltage of the odd-numbered cell 20A is maintained at 3.75 (v), and charging of the odd-numbered cell 20A is completed after 24 hours, which is the time t that allows the dissolved size of SUS foreign matter to reach 200 μm under normal conditions. Then, when charging of the odd-numbered cell 20A is completed, charging of the even-numbered cell 20B is started next.

[0045] That is, in each cell 20, in addition to dissolving SUS foreign matter during charging (while the voltage is held at the specified voltage), dissolution of SUS foreign matter also occurs during rest after charging (while the voltage drops from the specified voltage). Therefore, by obtaining the voltage value over time in advance, the time at which the dissolution size of the SUS foreign matter can reach 200 μm under normal conditions can be obtained based on the above formula (1).

[0046] As shown in Figure 5, in odd-numbered cell 20A, the dissolved size of the SUS foreign matter reaches 200 μm 33 hours after the start of charging. In other words, dissolution proceeds normally for 9 hours after charging is completed.

[0047] Then, similarly to the odd-numbered cell 20A, charging of the even-numbered cell 20B is started and the voltage of the even-numbered cell 20B is maintained at 3.75 (v), and charging of the even-numbered cell 20B is completed after 48 hours, which is the time t that allows the dissolution size of the SUS foreign matter to reach 200 μm under normal conditions. Then, dissolution under normal conditions is performed over a period of 9 hours after the completion of charging of the even-numbered cell 20B. That is, in the odd-numbered cell 20A and the even-numbered cell 20B (the odd-numbered cell group 30A and the even-numbered cell group 30B), the SUS foreign matter is dissolved in 57 hours, which is one hour shorter than the time required to dissolve the SUS foreign matter compared to the first embodiment described above.

[0048] Fig. 6 is a diagram showing the relationship between the voltage and the dissolved size of SUS foreign matter over time t in the odd-numbered cell 20A according to the third embodiment of the present invention. As shown in Fig. 6, in the third embodiment, as an example, the charging of the odd-numbered cell 20A is started, the voltage of the odd-numbered cell 20A is held at 3.75 (v) for 10 hours, and then the first charging is completed. Then, after the first charging of the odd-numbered cell 20A is completed, the first charging of the even-numbered cell 20B is started. In the odd-numbered cell 20A, dissolution continues normally even after the first charging is completed.

[0049] As with the odd-numbered cell 20A, charging of the even-numbered cell 20B is started, and the voltage of the even-numbered cell 20B is maintained at 3.75 (v) for 10 hours, after which the first charging is completed. Then, when the first charging of the even-numbered cell 20B is completed, the second charging of the odd-numbered cell 20A is started. After the first charging is completed, dissolution of the even-numbered cell 20B is also performed normally.

[0050] The second charge of the odd-numbered cell 20A is started, and the voltage of the odd-numbered cell 20A is maintained at 3.75 (v) for 2.5 hours, after which the second charge is completed. Then, when the second charge of the odd-numbered cell 20A is completed, the second charge of the even-numbered cell 20B is started. In the odd-numbered cell 20A, dissolution is continued normally even after the second charge is completed.

[0051] In the even-numbered cell 20B, similarly to the odd-numbered cell 20A, the second charge of the even-numbered cell 20B is started, and the voltage of the even-numbered cell 20B is maintained at 3.75 (v) for 2.5 hours, after which the second charge is completed. Then, in the even-numbered cell 20B, dissolution is performed normally after the second charge is completed.

[0052] In the third embodiment, unlike the first and second embodiments described above, charging is performed twice in the odd-numbered cells 20A and the even-numbered cells 20B. That is, the time for dissolving the SUS foreign matter in the normal manner is increased. As a result, the SUS foreign matter is dissolved in the odd-numbered cells 20A and the even-numbered cells 20B (the odd-numbered cell group 30A and the even-numbered cell group 30B) in 50 hours, which is 8 hours shorter than the first embodiment described above and 7 hours shorter than the second embodiment described above.

[0053] Next, the effects of the manufacturing method of the bipolar secondary battery 100 in the first to third embodiments will be described.

[0054] The manufacturing method of the bipolar secondary battery 100 in the first to third embodiments includes an aging charging step in which, during the high-temperature aging step, an odd-numbered cell group 30A having a plurality of odd-numbered cells 20A adjacent to every other cell in the stacking direction and an even-numbered cell group 30B having a plurality of even-numbered cells 20B adjacent to the odd-numbered cells 20A included in the odd-numbered cell group 30A are alternately charged until a specified voltage is reached. In the aging charging step, the conditions for completing charging of the odd-numbered cell group 30A and the even-numbered cell group 30B are determined based on the dissolution rate x calculated based on the type of metallic foreign matter and the positive electrode potential, and the voltage V and aging time t of each cell 20 in the aging charging step.

[0055] In this way, the charge completion condition is determined based on the dissolution rate x calculated based on the type of metallic foreign matter and the positive electrode potential, and on the voltage V and aging time t of each cell 20 in the aging charging process. Therefore, in the high-temperature aging process, the time required to complete charging can be shortened compared to the conventional technology in which charging is completed based on the completion condition set for the cell 20 with the lowest voltage without taking into account the dissolution rate x of the foreign matter, and therefore the high-temperature aging time can be shortened.

[0056] In addition, by taking into consideration the natural dissolution like in the manufacturing method of the bipolar secondary battery 100 in the second embodiment, the time required to complete charging can be shortened more than in the first embodiment in which the natural dissolution is not taken into consideration, and therefore the high-temperature aging time can be shortened more.

[0057] Furthermore, by performing charging in multiple steps as in the manufacturing method of the bipolar secondary battery 100 in the third embodiment, the time required to complete charging can be further shortened compared to the first and second embodiments in which charging is performed in a single step, and therefore the high-temperature aging time can be further shortened.

[0058] Next, a method for manufacturing the bipolar secondary battery 100 according to the fourth embodiment will be described below. In this embodiment, in the above-mentioned aging charging step, the cell 20 to be charged is charged multiple times. In this case, a switching charge capacity is set as a switching judgment condition for switching between charges, and the switching charge capacity is a value smaller than the charge capacity at the previous charge. FIG. 7 is a diagram showing a switching judgment condition for the charge capacity (mAh) versus the number of charges for the odd-numbered cell 20A. The value of the charge capacity is set each time charging is performed, and a value according to the number of charges is set.

[0059] Here, as an example, cell 20 has positive electrode composite layer 14 made of LFP and negative electrode composite layer 16 made of graphite. The initial charging conditions in the initial charging step are 25° C., 3.75 V-CC charging, and a charging rate of 0.06 C. The charging conditions in the aging charging step are 65° C., 3.75 V-CC charging (SOC 100%), and a charging rate of 0.0017 C, the charging pause conditions are 65° C., 10 hours, and the number of repeated charging times is 20.

[0060] As shown in FIG. 7, for example, in the odd-numbered cell 20A, if the switching judgment condition at the first charging is when the charge capacity of the cell becomes 0.5 (mAh), the switching judgment condition at the second charging is set to when the charge capacity of the cell becomes 0.1 (mAh), which is smaller than the charge capacity at the first charging. That is, at the second charging, when the charge capacity is 0.1 mAh, the charging is switched from the odd-numbered cell 20A to the even-numbered cell 20B. Similarly, from the third charging onwards, a value smaller than the charge capacity at the previous charging is set as the switching judgment condition. That is, as shown in FIG. 7, the more times the charging is performed, the smaller the value of the charge capacity that is the switching judgment condition is set. Here, in FIG. 7, when the value of the charge capacity becomes larger than the value shown by the solid line, the charging is switched from the odd-numbered cell 20A to the even-numbered cell 20B, or from the even-numbered cell 20B to the odd-numbered cell 20A. In other words, when the value of the charge capacity is smaller than the value shown by the solid line in FIG. 7, charging is performed until the value of the charge capacity becomes larger.

[0061] Next, the effects of the method for manufacturing the bipolar secondary battery 100 in the fourth embodiment will be described.

[0062] In a bipolar secondary battery 100, the charging of the cell 20 other than the cell 20 to be charged is suspended while the cell 20 to be charged is being charged, and the charge may be lost during the suspension of charging. Therefore, when charging for the second or subsequent times, the charge that was lost during standby is replenished, so the charge capacity gradually decreases compared to the first charging. In other words, the more times the battery is charged, the closer it gets to full charge, and the smaller the charge capacity becomes.

[0063] In the manufacturing method of the bipolar secondary battery 100 in the above four embodiments, a switching charge capacity is set as a switching determination condition for switching the charging of the cell 20 to be charged, and the switching charge capacity is a value smaller than the charge capacity at the previous charge. Therefore, in the aging charging step, the cell 20 to be charged is charged at a charge capacity according to the number of times it has been charged. This makes it possible to prevent unnecessary charging and shorten the time required to complete charging.

[0064] In the fourth embodiment, as shown in Fig. 7, the value of the charge capacity is set according to the number of charging times, but the present invention is not limited to this. Instead of the charge capacity, a value of ΔSOC (%) may be set. Here, ΔSOC (%) is a set value expressed as charge capacity (Ah) / cell capacity (Ah).

[0065] Next, a method for manufacturing the bipolar secondary battery 100 according to the fifth embodiment will be described below. In the fourth embodiment, a switching charge capacity is set as a switching judgment condition for switching the charge, and the switching charge capacity is set to a value smaller than the charging capacity at the previous charge. In contrast, in this embodiment, a switching charge time is set as a switching judgment condition for switching the charge, and the switching charge time is set to a time shorter than the charging time at the previous charge. FIG. 8 is a diagram showing a switching judgment condition for the charge time (hr) to 3.75V versus the number of charges in the odd-numbered cell 20A. The value of the charge time is set every time charging, and a value according to the number of charges is set. The cell 20 of this embodiment has the same configuration as the cell 20 of the fourth embodiment.

[0066] As shown in FIG. 8, for example, in the odd-numbered cell 20A, if the first charging switching judgment condition is when the charging time of the cell reaches 3.75V after 5 hours, the second charging switching judgment condition is set to when the charging time of the cell reaches 3 hours, which is shorter than the charging time of the first charging. That is, when the charging time reaches 3 hours after the second charging, the charging is switched from the odd-numbered cell 20A to the even-numbered cell 20B. Similarly, the charging time shorter than the charging time of the previous charging is set as the switching judgment condition from the third charging onwards. That is, as shown in FIG. 8, the more times the charging is performed, the smaller the value of the charging time that is the switching judgment condition is set. Here, in FIG. 8, when the charging time becomes longer than the value shown by the solid line, the charging is switched from the odd-numbered cell 20A to the even-numbered cell 20B, or from the even-numbered cell 20B to the odd-numbered cell 20A. In other words, when the charging time is shorter than the value shown by the solid line in FIG. 7, the charging is performed until the charging time becomes longer.

[0067] Next, the effects of the method for manufacturing the bipolar secondary battery 100 in the fifth embodiment will be described.

[0068] In a bipolar secondary battery 100, the charging of the cell 20 other than the cell 20 to be charged is suspended while the cell 20 to be charged is being charged, and the charge may be lost during the suspension of charging. Therefore, when charging for the second or subsequent times, the charge that was lost during the standby period is replenished, so the charge capacity gradually decreases and the charging time gradually shortens compared to the first charging. In other words, the more times the battery is charged, the closer it gets to full charge, and the shorter the charging time becomes.

[0069] In the manufacturing method of the bipolar secondary battery 100 in the fifth embodiment, a switching charge time is set as a switching determination condition for switching the charging of the cell 20 to be charged, and the switching charge time is a time shorter than the charging time of the previous charge. Therefore, in the aging charging step, the cell 20 to be charged is charged for a charging time according to the number of times it has been charged. This makes it possible to prevent unnecessary charging and shorten the time required to complete charging.

[0070] In the fifth embodiment, as shown in Fig. 8, the value of the charging time up to 3.75V is set according to the number of charging times, but the present invention is not limited to this. Instead of the charging time, the value of the charging time (h) at 1C rate may be set. Here, the charging time (h) at 1C rate is a set value expressed by the charging time (hr) up to 3.75V x 0.0017.

[0071] Next, a method for manufacturing a bipolar secondary battery 100 according to the sixth embodiment will be described below. In this embodiment, an abnormality determination condition is set for determining that the cell 20 to be charged is abnormal in the above-mentioned aging charging process. The abnormality determination condition is a case where the amount of change in voltage over time falls outside a predetermined error range of the amount of change. Here, the "error range" indicates a range of values ​​from a lower limit to an upper limit that can be considered as an error for the value of the amount of change in voltage over time. FIG. 9 is a graph of a charging curve showing the relationship between voltage and charging time, FIG. 10(A) is a diagram showing the amount of change in voltage over time, and FIG. 10(B) is a diagram showing the amount of change in voltage over voltage. The cell 20 of this embodiment has the same configuration as the cell 20 of the fourth embodiment.

[0072] Normally, when charging the cell 20, the voltage value increases at a substantially constant rate over time, as shown in Fig. 9. However, for example, if there is an extreme change in the charging conditions, the voltage change may deviate from the normal range. For example, if a short circuit occurs in the cell 20, the voltage does not increase, and the voltage change becomes small.

[0073] Therefore, in this embodiment, the condition for determining an abnormality in the cell 20 to be charged during the aging charging process is when at least one of the changes in voltage with respect to time or the changes in voltage with respect to voltage falls outside a predetermined error range for that change.

[0074] For example, when the first charge is performed at 0.0017 C, charging is performed with the voltage change over time shown by the dotted line as shown in Fig. 10(A). In this case, in this embodiment, if the voltage change is outside the error range of the value shown by the dotted line, i.e., outside the vicinity of the solid line, it is determined that an abnormality has occurred.

[0075] Also, for example, when the first charge is performed at 0.0017 C, as shown in Fig. 10(B), charging is performed with the voltage change amount shown by the dotted line relative to the voltage. In this case, in this embodiment, if the voltage change amount is outside the error range of the value shown by the dotted line, i.e., outside the vicinity of the solid line, it is determined that an abnormality has occurred.

[0076] Next, the effects of the method for manufacturing the bipolar secondary battery 100 in the sixth embodiment will be described.

[0077] In the manufacturing method of the bipolar secondary battery 100 in the sixth embodiment, the abnormality determination condition for the cell 20 to be charged in the aging charging step is when at least one of the amount of change in voltage with respect to time and the amount of change in voltage with respect to voltage falls outside a predetermined error range for the amount of change. This makes it possible to detect defective products in the aging charging step without going to an inspection step, since an abnormality is determined when the amount of change in voltage falls outside the predetermined error range for the amount of change.

[0078] In the sixth embodiment, as shown in Fig. 10, the value of the voltage change is set with respect to time or voltage, but the present invention is not limited to this. Instead of the value of the voltage change, the value of the voltage change at 1C rate may be set. Here, the voltage change at 1C rate is a set value expressed by the voltage change (V / sec)÷0.0017.

[0079] Next, a method for manufacturing a bipolar secondary battery 100 according to the seventh embodiment will be described below. In the sixth embodiment described above, the abnormality determination condition is when the amount of change in voltage with respect to time and the amount of change in voltage with respect to voltage are outside of a predetermined error range of the amount of change, whereas in this embodiment, the abnormality determination condition is when the amount of change in battery capacity with respect to voltage is outside of a predetermined error range of the amount of change. Fig. 11 is a diagram showing the amount of change in battery capacity with respect to voltage. The cell 20 of this embodiment has the same configuration as the cell 20 of the fourth embodiment.

[0080] Normally, when charging cell 20, the voltage value increases at a substantially constant rate over time, as shown in Fig. 9. However, for example, if there is an extreme change in the charging conditions, the amount of change in voltage deviates from the normal range, and therefore the amount of change in battery capacity also deviates from the normal range.

[0081] Therefore, in this embodiment, the abnormality determination condition for the cell 20 to be charged in the aging charging step is when the amount of change in battery capacity relative to voltage falls outside a predetermined error range for that amount of change.

[0082] For example, when the first charge is performed at 0.0017 C, charging is performed with the amount of change in battery capacity versus voltage shown by the solid line, as shown in Fig. 11. In this case, in this embodiment, if the amount of change in battery capacity is outside the error range of the value shown by the solid line, i.e., outside the vicinity of the solid line, it is determined that an abnormality has occurred.

[0083] Next, the effects of the method for manufacturing the bipolar secondary battery 100 in the seventh embodiment will be described.

[0084] In the manufacturing method of the bipolar secondary battery 100 in the seventh embodiment, the abnormality determination condition for the cell 20 to be charged in the aging charging step is when the amount of change in battery capacity relative to the voltage falls outside a predetermined error range of the amount of change. This allows the cell to be determined as abnormal when the amount of change in battery capacity falls outside the predetermined error range of the amount of change, making it possible to detect defective products in the aging charging step without going to an inspection step.

[0085] In the seventh embodiment, as shown in FIG. 11, the value of the change in battery capacity is set with respect to the voltage, but the present invention is not limited to this. Instead of the value of the change in battery capacity, the value of the change in battery capacity at 1 Ah of battery capacity may be set. Here, the change in battery capacity at 1 Ah of battery capacity is a set value indicated by the change in battery capacity at 1 mAh of battery capacity (mAh / V)÷56. Furthermore, instead of the value of the change in battery capacity at 1 Ah of battery capacity, the value of the change in SOC may be set. Here, the change in SOC (%) is a set value obtained by converting the battery capacity (Ah) at 1 Ah of battery capacity into SOC (%).

[0086] Next, a method for manufacturing the bipolar secondary battery 100 according to the eighth embodiment will be described below. Fig. 12 is a diagram showing the relationship between the charging pause time and the voltage for each number of charging times, Fig. 13 is a diagram showing the relationship between the number of charging times and the voltage two hours after charging is paused, and Fig. 14 is a diagram showing the relationship between the number of charging times and the voltage ten hours after charging is paused. The cell 20 of this embodiment has the same configuration as the cell 20 of the fourth embodiment.

[0087] 12, for example, when the odd-numbered cell 20A is paused while the even-numbered cell 20B is being charged, the voltage of the odd-numbered cell 20A drops as the time of the pause in charging of the odd-numbered cell 20A passes. In this case, the odd-numbered cell 20A that has been charged ten times is closer to being fully charged than the odd-numbered cell 20A that has been charged only once, so the voltage drop is more stable.

[0088] Therefore, in this embodiment, the condition for determining an abnormality during the aging charging process for the cell 20 to be charged while charging is suspended is when the voltage after a predetermined specified time has elapsed since charging was suspended is equal to or lower than a specified voltage value that is previously set for each number of charging attempts.

[0089] That is, for each number of charging times, the voltage after 2 hours, as an example, is specified as shown by the solid line in Fig. 13. Similarly, for each number of charging times, the voltage after 10 hours, as an example, is specified as shown by the solid line in Fig. 14. The specified value is set taking into consideration variations. Then, for each number of charging times, at least one of the voltages, as an example, after 2 hours and 10 hours, is measured, and if the voltage is lower than the specified voltage value set for each number of charging times, it is determined that the voltage has dropped too much and is therefore abnormal.

[0090] Next, the effects of the method for manufacturing the bipolar secondary battery 100 in the eighth embodiment will be described.

[0091] In the manufacturing method of the bipolar secondary battery 100 in the eighth embodiment, the condition for determining an abnormality during a charging pause of the cell 20 to be charged is that the voltage after a preset specified time has elapsed since charging was paused is equal to or lower than a preset voltage value preset for each charging count. This allows detection of defective products in the aging charging process without going to an inspection process, since an abnormality is determined when the voltage during charging pause is equal to or lower than a preset voltage value preset for each charging count.

[0092] [remarks] In the above-described embodiment, the charging completion condition is determined for both the odd cell 20A (i.e., odd cell group 30A) and the even cell 20B (i.e., even cell group 30B), but the present invention is not limited to this, and the effects of the present invention can be obtained by determining the charging completion condition for only one of them.

[0093] In the present invention, the positive electrode active material used in the positive electrode mixture layer 14 as the positive electrode is not limited, but it is preferable to use lithium iron phosphate ions. Since lithium iron phosphate has a steeper voltage drop near the dissolution potential of foreign matter, the effect of the present invention can be more easily obtained.

[0094] In the above embodiment, SUS such as SUS304 is used as an example of a possible foreign object, but the present invention is not limited to this. For example, copper contained in the current collector 12 may also be used as a possible foreign object.

[0095] Furthermore, the configuration of the present disclosure is not limited to the above-described embodiment, and the configuration can be modified as appropriate as long as the problem can be solved. [Explanation of symbols]

[0096] 12 current collector, 14 positive electrode mixture layer (positive electrode), 16 negative electrode mixture layer (negative electrode), 18 electrolyte layer, 20 cells, 20A odd cells, 20B even cells, 30A odd cell group (first cell group), 30B even cell group (second cell group), 100 Bipolar secondary battery

Claims

1. In a bipolar secondary battery in which a plurality of cells each including a positive electrode, a negative electrode, and an electrolyte layer are stacked, an initial charging step of charging a first cell group having a plurality of cells adjacent to every other cell in the stacking direction and a second cell group having a plurality of cells adjacent to the cells included in the first cell group to a specified voltage; A high-temperature aging process in which aging is performed at a temperature higher than room temperature; and an aging charging step of alternately charging the first cell group and the second cell group until a specified voltage is reached during the high-temperature aging step, a dissolution rate of the first cell group and the second cell group calculated based on a type of metallic foreign matter and a positive electrode potential, and a voltage and an aging time of the first cell group and the positive electrode potential.

2. In the aging charging step, a switching charge capacity or a switching charge time is set as a switching determination condition for switching the charging of the cell to be charged, The switching charge capacity is a value smaller than the charge capacity at the time of the previous charge, 2. The method for manufacturing a bipolar secondary battery according to claim 1, wherein the switching charge time is shorter than the charge time of the previous charge.

3. 2. The method for manufacturing a bipolar secondary battery according to claim 1, wherein the abnormality determination condition for determining that the cell to be charged in the aging charging process is abnormal is a case in which at least one of the amount of change in voltage with respect to time and the amount of change in battery capacity with respect to the voltage change falls outside a predetermined error range of the amount of change.

4. 2. The method for manufacturing a bipolar secondary battery according to claim 1, wherein in the aging charging process, a condition for determining an abnormality during a charging pause of the cell to be charged is a case in which the voltage after a predetermined specified time has elapsed since charging was paused is equal to or lower than a specified voltage value that is preset for each number of charging attempts.

5. 2. The method for producing a bipolar secondary battery according to claim 1, wherein the positive electrode uses lithium iron phosphate as a positive electrode active material.

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