Manufacturing method of secondary batteries

Abstract

To provide a manufacturing method of a non-aqueous electrolyte secondary battery capable of manufacturing a high-performance non-aqueous electrolyte secondary battery.SOLUTION: A manufacturing method of a secondary battery is provided for implementing aging in a state where a load is applied to an electrode body. The manufacturing method of the secondary battery includes: measuring a spring constant of the electrode body prior to the aging; calculating an upper limit value of the load, which is applied to the electrode body during the aging, on the basis of the measured spring constant of the electrode body and a predetermined displacement amount upper limit value of the electrode body; and implementing the aging in a state where a load equal to or less than the calculated upper limit value of the load is applied to the electrode body.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a secondary battery.

Background Art

[0002] Patent Document 1 describes a method for manufacturing a secondary battery. The secondary battery is mounted on vehicles such as electric vehicles and hybrid vehicles, for example. An in-vehicle battery pack is constituted by stacking a plurality of secondary batteries in one direction, that is, stacking them.

[0003] In the method for manufacturing a secondary battery described in Patent Document 1, a load is applied to an electrode body included in the secondary battery during aging. By applying a load during aging, gas generated in the secondary battery is discharged. By discharging gas from the secondary battery, the risk of deterioration in the performance of the secondary battery is reduced.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In such a method for manufacturing a secondary battery, if the load applied to the electrode body during aging is large, the electrode body may be deformed so as to be crushed. In this case, the spring constant of the electrode body may increase. When the spring constant of the electrode body increases, the stacking property of the secondary battery deteriorates. [[ID=四十一]]

Means for Solving the Problems

[0006] A method for manufacturing a secondary battery that solves the above problems is a method for manufacturing a secondary battery in which aging is performed with a load applied to an electrode body, and includes measuring the spring constant of the electrode body before aging, calculating an upper limit of the load to be applied to the electrode body during aging based on the measured spring constant of the electrode body and a predetermined upper limit of the displacement of the electrode body, and performing aging with a load of less than or equal to the calculated upper limit of the load applied to the electrode body.

[0007] By multiplying the displacement of the electrode body by the spring constant, the load required to displace it by that amount can be calculated. In other words, by multiplying the spring constant by the upper limit of the displacement, the upper limit of the load applied to the electrode body during aging can be determined. Therefore, according to the above method, a secondary battery with good performance can be manufactured.

[0008] In the above-described method for manufacturing secondary batteries, the upper limit of the displacement may be a value predetermined based on the spring constants of multiple secondary batteries, measured under conditions where each battery is displaced by a different amount of displacement by applying different loads during aging.

[0009] By measuring the spring constant of multiple secondary batteries that have been displaced by different loads during aging, the relationship between the spring constant and the displacement can be determined. The displacement at which the spring constant increases represents the displacement at which the electrode body deforms, i.e., the load. Therefore, the displacement just before the spring constant increases is the upper limit of the displacement. Using the above method with this defined upper limit of displacement, it is possible to manufacture secondary batteries with good performance.

[0010] In the above-described method for manufacturing secondary batteries, the upper limit of the displacement may be a value predetermined based on a range set with reference to the spring constant of a secondary battery whose displacement is 0, among the plurality of secondary batteries which are displaced by different amounts of displacement by applying different loads to each of them during aging.

[0011] The upper limit of the displacement is determined based on the spring constant of a secondary battery with zero displacement. Therefore, for example, if the measured spring constant of a secondary battery exceeds a predetermined range that includes the spring constant of a secondary battery with zero displacement among several secondary batteries, it can be considered that the measured spring constant has increased. By using the above method with the upper limit of the displacement determined in this way, it is possible to manufacture secondary batteries with good performance.

[0012] The above method for manufacturing a secondary battery may include calculating a lower limit of the load to be applied to the electrode body during aging based on the measured spring constant of the electrode body and a predetermined lower limit of the displacement of the electrode body, and performing aging while applying a load to the electrode body that is less than or equal to the calculated upper limit of the load and greater than or equal to the calculated lower limit of the load.

[0013] If the load applied to the electrode during aging is too small, there is a risk that the gas will not be sufficiently discharged. The lower limit of the load applied to the electrode during aging can be calculated by multiplying the spring constant by the lower limit of the displacement. Therefore, according to the above method, a secondary battery with good performance can be manufactured.

[0014] In the above-described method for manufacturing secondary batteries, the lower limit of the displacement may be a predetermined value based on the residual amount of gas measured when each of the multiple secondary batteries is displaced by a different amount of displacement by applying different loads during aging.

[0015] The amount of residual gas in a secondary battery can be determined, for example, from a CT scan of the secondary battery. Therefore, for example, a lower limit of displacement can be determined based on the amount of residual gas from a CT scan of a secondary battery. By using the above method with the lower limit of displacement determined in this way, a secondary battery with good performance can be manufactured.

[0016] In the method for manufacturing the secondary battery, before aging, the spring constant may be measured based on the difference between the displacement amount when a first load is applied to the electrode body and the displacement amount when a second load smaller than the first load is applied to the electrode body. According to the above method, the spring constant of the secondary battery can be measured more accurately than when applying a single load.

[0017] In the method for manufacturing the secondary battery, the upper limit value of the displacement amount may be 0.024 mm, and the lower limit value of the displacement amount may be 0.008 mm. According to the above method, a secondary battery with good performance can be manufactured.

Effect of the Invention

[0018] According to the present invention, a secondary battery with good performance can be manufactured.

Brief Description of the Drawings

[0019] [Figure 1] It is a perspective view of a secondary battery. [Figure 2] It is a view showing a part of the electrode body developed. [Figure 3] It is a flowchart showing the manufacturing process of the secondary battery. [Figure 4] It is a flowchart showing the load determination process. <* [Figure 5] It is a graph showing the relationship between the load and the displacement amount in the electrode body. [Figure 6] It is a graph showing the upper limit value and the lower limit value of the displacement amount in the first example. [Figure 7] It is a CT image of a secondary battery with a displacement amount of 0.000 mm. [Figure 8] It is an image of the electrode plate of a secondary battery with a displacement amount of 0.000 mm. [Figure 9] It is a CT image of a secondary battery with a displacement amount of 0.008 mm or more. [Figure 10] It is a graph showing the upper limit value and the lower limit value of the displacement amount in the second example.

Mode for Carrying Out the Invention

[0020] The manufacturing method of secondary batteries will be explained with reference to the diagram. First, the structure of secondary batteries will be explained. A secondary battery is, for example, a non-aqueous secondary battery, specifically a lithium-ion secondary battery. A secondary battery is, for example, a cell battery. Multiple secondary batteries are stacked in one direction, so-called stacks, to form a battery pack for use in vehicles.

[0021] <Configuration of a secondary battery> As shown in Figure 1, the secondary battery 10 comprises a case 11 and a lid 12. The lid 12 is attached to the case 11 so as to close the opening of the case 11. An electrolyte injection hole 13 is provided in the lid 12. Electrolyte is injected into the case 11 through the electrolyte injection hole 13. After the electrolyte is injected, the electrolyte injection hole 13 is sealed, for example, by welding. An exhaust port 14 is provided in the lid 12. Gas inside the case 11 is discharged through the exhaust port 14.

[0022] The secondary battery 10 is equipped with an exhaust valve 15. The exhaust valve 15 is a valve that discharges gas generated inside the case 11. The exhaust valve 15 is attached to the lid 12. The exhaust valve 15 closes the exhaust port 14. Gas is discharged from inside the case 11 through the exhaust valve 15 and the exhaust port 14.

[0023] The electrolyte is, for example, a composition containing a supporting salt in a non-aqueous solvent. As the non-aqueous solvent, one or more materials selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, etc. can be used. As the supporting salt, one or more lithium compounds, i.e., lithium salts, selected from LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiI, etc. can be used.

[0024] The secondary battery 10 has two external terminals. The secondary battery 10 has a positive external terminal 16 and a negative external terminal 17. The positive external terminal 16 and the negative external terminal 17 extend, for example, from the lid 12 outwards from the case 11.

[0025] The secondary battery 10 comprises two current collectors. The secondary battery 10 comprises a positive electrode current collector 18 and a negative electrode current collector 19. The positive electrode current collector 18 and the negative electrode current collector 19 extend, for example, from the lid 12 into the case 11. The positive electrode current collector 18 is electrically connected to the positive electrode external terminal 16. The negative electrode current collector 19 is electrically connected to the negative electrode external terminal 17.

[0026] The secondary battery 10 includes an electrode body 20. The electrode body 20 is located inside the case 11. The electrode body 20 is housed in the case 11 together with the electrolyte. The electrode body 20 is connected to a positive electrode current collector 18 and a negative electrode current collector 19. That is, the electrode body 20 is connected to a positive electrode external terminal 16 and a negative electrode external terminal 17.

[0027] As shown in Figure 2, the electrode body 20 includes two electrode plates. The electrode body 20 includes a positive electrode plate 21 and a negative electrode plate 22. The electrode body 20 further includes a separator 23 and a separator 24. The electrode body 20 is a laminate formed by stacking the positive electrode plate 21, the negative electrode plate 22, the separator 23, and the separator 24. The positive electrode plate 21, the separator 23, the negative electrode plate 22, and the separator 24 are stacked in this order.

[0028] The electrode body 20 is constructed, for example, by winding together a positive electrode plate 21, a separator 23, a negative electrode plate 22, and a separator 24 in this order. The electrode body 20 may also be constructed, for example, by stacking a positive electrode plate 21, a separator 23, a negative electrode plate 22, and a separator 24, each of which is a single sheet, in this order.

[0029] The positive electrode plate 21 includes a positive electrode current collector 25 and a positive electrode active material layer 26. The positive electrode current collector 25 is, for example, a metal foil. The positive electrode current collector 25 is made of a material including, for example, aluminum.

[0030] The positive electrode current collector 25 has a connection portion 27. The connection portion 27 is the part that is electrically connected to the positive electrode current collector member 18. The connection portion 27 is located at the end of the positive electrode current collector 25. The connection portion 27 is the part of the positive electrode current collector 25 where the positive electrode active material layer 26 is not located.

[0031] The positive electrode active material layer 26 is located on the positive electrode current collector 25. The positive electrode active material layer 26 extends along the entire length of the positive electrode current collector 25. The width of the positive electrode active material layer 26 is smaller than the width of the positive electrode current collector 25. This ensures a connection portion 27.

[0032] The positive electrode active material layer 26 is located, for example, on one side of the positive electrode current collector 25. The positive electrode active material layer 26 may be located on both sides of the positive electrode current collector 25. The positive electrode active material layer 26 contains positive electrode active material. The positive electrode active material layer 26 is formed by applying a paste-like positive electrode mixture containing positive electrode active material to the positive electrode current collector 25.

[0033] The positive electrode active material is, for example, a material capable of intercalating and releasing lithium. The positive electrode active material is, for example, a lithium-containing composite oxide. A lithium-containing composite oxide is an oxide containing lithium and other metallic elements. Examples of positive electrode active materials include lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), and lithium nickel oxide (LiNiO2). Alternatively, the positive electrode active material may be composed of a mixture of these materials in any proportion.

[0034] The positive electrode composite material is prepared by kneading the positive electrode active material. In addition to the positive electrode active material, the positive electrode composite material may also be prepared by kneading together a conductive agent, a positive electrode solvent, a positive electrode binder, a thickener, etc. The conductive agent is, for example, carbon black such as acetylene black or Ketjen black, or graphite. The positive electrode solvent is, for example, an NMP (N-methyl-2-pyrrolidone) solution. The positive electrode binder is, for example, polyvinylidene fluoride, polytetrafluoroethylene, or carboxymethylcellulose (CMC).

[0035] The negative electrode plate 22 includes a negative electrode current collector 28 and a negative electrode active material layer 29. The negative electrode current collector 28 is, for example, a metal foil. The negative electrode current collector 28 is composed of, for example, a material containing copper. The negative electrode current collector 28 has a connection portion 30. The connection portion 30 is the part that is electrically connected to the negative electrode current collector member 19. The connection portion 30 is located at the end of the negative electrode current collector 28. The connection portion 30 is the part of the negative electrode current collector 28 where the negative electrode active material layer 29 is not located.

[0036] The negative electrode active material layer 29 is located on the negative electrode current collector 28. The negative electrode active material layer 29 extends along the entire length of the negative electrode current collector 28. The width of the negative electrode active material layer 29 is smaller than the width of the negative electrode current collector 28. This ensures a connection portion 30.

[0037] The negative electrode active material layer 29 is located, for example, on one side of the negative electrode current collector 28. The negative electrode active material layer 29 may be located on both sides of the negative electrode current collector 28. The negative electrode active material layer 29 contains negative electrode active material. The negative electrode active material layer 29 is formed by applying a paste-like negative electrode mixture containing negative electrode active material to the negative electrode current collector 28.

[0038] The negative electrode active material is, for example, a material capable of intercalating and releasing lithium. The negative electrode active material is, for example, a carbon material. The negative electrode active material is, for example, graphite such as natural graphite or artificial graphite.

[0039] The negative electrode composite is prepared by kneading the negative electrode active material. In addition to the negative electrode active material, the negative electrode composite may also be prepared by kneading together a dispersant, a negative electrode solvent, a negative electrode binder, a thickener, etc. The dispersant is, for example, carboxymethylcellulose (CMC). The negative electrode solvent is, for example, water. The negative electrode binder is, for example, styrene-butadiene rubber (SBR).

[0040] Separators 23 and 24 are, for example, nonwoven fabrics made of resin. For example, porous polymer membranes such as porous polyethylene membranes, porous polyolefin membranes, and porous polyvinyl chloride membranes, and ion-conductive polymer electrolyte membranes can be used as separators 23 and 24.

[0041] <Manufacturing process for secondary batteries> Next, we will explain the manufacturing method of the secondary battery 10, which is carried out in the manufacturing process. As shown in Figure 3, the manufacturing process includes each of the steps shown from step S11 to step S17.

[0042] In step S11, the source process is carried out. In the source process, the positive electrode plate 21 and the negative electrode plate 22 are manufactured. Specifically, the electrode plates are manufactured by applying the composite material onto the current collector and then pressing the composite material.

[0043] In step S12, the assembly process is carried out. In the assembly process, the secondary battery 10 is assembled using the manufactured electrode plates. In the assembly process, first, the electrode body 20 is manufactured from the positive electrode plate 21 and the negative electrode plate 22. Specifically, the electrode body 20 is manufactured by stacking the positive electrode plate 21, the negative electrode plate 22, the separator 23, and the separator 24, and then pressing them to make them flat. Next, the electrode body 20 is connected to the positive electrode current collector 18 and the negative electrode current collector 19. Next, the electrode body 20 is housed in the case 11. At this time, the lid 12 is welded to the case 11. Next, electrolyte is injected into the case 11 through the electrolyte injection hole 13. After that, the electrolyte injection hole 13 is welded.

[0044] In step S13, the initial charging process is performed. During the initial charging process, the assembled secondary battery 10 is charged. At this time, a film is formed on the surface of the active material layer. For example, an SEI film is formed on the surface of the negative electrode active material layer 29. This improves the performance of the secondary battery 10.

[0045] During the initial charging process, the secondary battery 10 is charged under load. During the initial charging process, a film is formed on the surface of the active material, while gas is generated inside the case 11. By charging the secondary battery 10 while applying a load, the gas generated on the electrodes is discharged outside the electrode body 20 instead of remaining inside it. For example, a load is applied to the secondary battery 10 by clamping the case 11 with a press device or press jig. A load is applied to the secondary battery 10 in the direction in which multiple secondary batteries 10 are stacked, i.e., in the stacking direction. This compresses the electrode body 20. In this way, the secondary battery 10 is initially charged under load, i.e., under constraint.

[0046] In step S14, a load determination process is performed. In the load determination process, the load to be applied to the secondary battery 10 in the subsequent aging process is determined. The load determination process will be explained later.

[0047] In step S15, an aging process is performed. During the aging process, the secondary battery 10 is stored in a predetermined environment for a predetermined period of time. This allows the secondary battery 10 to become chemically stable. The aging process is performed at high temperatures. Specifically, the aging process is performed at a temperature of 60 degrees Celsius or higher.

[0048] During the aging process, the secondary battery 10 is stored under load. In the aging process, gas is generated inside the case 11, similar to the initial charging process. By performing the aging process while applying load to the secondary battery 10, the gas generated on the electrodes is discharged outside the electrode body 20 instead of remaining inside it.

[0049] During the aging process, if the load is large, the secondary battery 10 may deform and collapse. This is because the secondary battery 10 is subjected to a load at high temperatures during the aging process. At high temperatures in particular, the separators 23 and 24 are prone to collapse due to the applied load. When the separators 23 and 24 collapse, i.e., when the electrode body 20 collapses, the secondary battery 10 may deform irreversibly. In this case, the spring constant of the electrode body 20, i.e., the spring constant of the secondary battery 10, increases. When the spring constant of the secondary battery 10 increases, its stackability decreases. Stackability refers to the ease of assembly when stacking multiple secondary batteries 10 in one direction. When multiple secondary batteries 10 are stacked, they are usually housed in a frame. At this time, if the spring constant of the secondary battery 10 is large, i.e., the secondary battery 10 is stiff, it becomes difficult to house multiple secondary batteries 10 in the frame.

[0050] During the aging process, if the load is small, there is a risk that the amount of residual gas in the secondary battery 10 will increase. If the amount of residual gas increases, there is a risk that the inter-electrode distance will increase. The inter-electrode distance is the distance between the electrode plates. For example, the inter-electrode distance is the distance between the positive electrode plate 21 and the negative electrode plate 22. When the inter-electrode distance increases, metal deposition becomes easier. In lithium-ion secondary batteries, for example, lithium is more likely to be deposited. If metal deposition occurs, the performance of the secondary battery 10 may deteriorate.

[0051] As described above, in the aging process, appropriately controlling the load applied to the secondary battery 10 is crucial for manufacturing a high-performance secondary battery 10. In other words, to manufacture a high-performance secondary battery 10, it is necessary to perform aging while applying a load in such a way that the spring constant of the electrode body 20 does not increase. Preferably, it is desirable to perform aging while applying a load in such a way that the spring constant of the electrode body 20 does not increase and the amount of residual gas is reduced. In the load determination process, a load that satisfies these conditions is determined. In the aging process, the load determined in the load determination process is applied to the secondary battery 10. This results in the manufacture of a secondary battery 10 with good stackability and gas discharge properties, i.e., a high-performance secondary battery 10.

[0052] In step S16, a self-discharge test is performed. In the self-discharge test, the quality of the secondary battery 10 is inspected by measuring the voltage drop per unit time in the secondary battery 10. The self-discharge test is performed, for example, under load. The self-discharge test is performed, for example, based on the voltage drop that occurred during the storage period in the aging process.

[0053] In step S17, a shipping inspection is performed. During the shipping inspection, the quality of the secondary battery 10 is checked by examining its appearance, leakage, voltage, internal resistance, etc. After the shipping inspection, the secondary battery 10 is stacked.

[0054] <Load determination process> Next, we will explain the method for determining the load used in the load determination process. The load applied to the secondary battery 10 is expressed by the displacement of the secondary battery 10, i.e., the displacement of the electrode body 20, and the spring constant of the electrode body 20. Specifically, the load applied to the secondary battery 10 is the product of the displacement of the electrode body 20 and the spring constant of the electrode body 20. Therefore, the load applied during aging can be expressed by the displacement during aging.

[0055] When a load is applied to the secondary battery 10, the electrode body 20 is compressed and displaced. As the amount of displacement of the electrode body 20 increases, the spring constant of the electrode body 20 increases as it collapses. In this specification, the upper limit of the amount of displacement at which the spring constant of the electrode body 20 does not increase is referred to as the upper limit of displacement XU. In this specification, the lower limit of the amount of displacement at which the residual amount of gas falls below a predetermined amount is referred to as the lower limit of displacement XL. The predetermined amount represents a residual amount of gas that does not adversely affect the performance of the secondary battery 10. In the load determination step, a load is determined at which the amount of displacement of the electrode body 20 is less than or equal to the upper limit of displacement XU. Preferably, in the load determination step, a load is determined at which the amount of displacement of the electrode body 20 is less than or equal to the upper limit of displacement XU and greater than or equal to the lower limit of displacement XL.

[0056] As shown in Figure 4, the loading process includes each of the steps indicated by steps S21 to S24. In step S21, the spring constant of the electrode body 20 before aging is measured.

[0057] As shown in Figure 5, the spring constant of the electrode body 20 is measured by applying a first load F1 and a second load F2, which is different from the first load F1, to the secondary battery 10. The spring constant of the electrode body 20 is measured based on the difference between the displacement of the electrode body 20 when the first load F1 is applied to the secondary battery 10 and the displacement of the electrode body 20 when the second load F2 is applied to the secondary battery 10.

[0058] The first load F1 is greater than the second load F2. Therefore, the displacement of the electrode body 20 due to the first load F1 is greater than the displacement of the electrode body 20 due to the second load F2. The displacement due to the first load F1 is the first displacement X1. The displacement due to the second load F2 is the second displacement X2.

[0059] The spring constant of the electrode body 20 is measured by dividing the difference between the first load F1 and the second load F2 by the difference between the first displacement X1 and the second displacement X2. That is, the spring constant of the electrode body 20 is expressed as {(F1-F2) / (X1-X2)}. The first load F1 is, for example, 3.7 [kN]. The second load F2 is, for example, 0.2 [kN]. By applying loads of different magnitudes, the measurement accuracy of the spring constant is improved compared to applying a single load.

[0060] As shown in Figure 4, in step S22, the upper limit of the load is calculated. Specifically, the upper limit of the load is calculated by multiplying the displacement limit XU by the measured spring constant. In this specification, the upper limit of the load is referred to as the load limit FU. Therefore, the load limit FU is calculated based on the displacement limit XU. The displacement limit XU is a predetermined value. The displacement limit XU will be explained later.

[0061] In step S23, the lower limit of the load may be calculated. For example, the lower limit of the load can be calculated by multiplying the displacement lower limit XL by the measured spring constant. In this specification, the lower limit of the load is referred to as the load lower limit FL. Therefore, the load lower limit FL is calculated based on the displacement lower limit XL. The displacement lower limit XL is a predetermined value. The displacement lower limit XL will be explained later.

[0062] In step S24, the load applied during aging is determined. That is, the load applied during aging is determined to be less than or equal to the upper load limit FU. Preferably, the load applied during aging is determined to be less than or equal to the upper load limit FU and greater than or equal to the lower load limit FL. In this case, the load applied during aging is determined to be within the range defined by the upper load limit FU and the lower load limit FL.

[0063] As described above, the method for manufacturing the secondary battery 10 includes measuring the spring constant of the electrode body 20, calculating the upper load limit FU, and performing aging while applying a load less than or equal to the upper load limit FU. Preferably, the method for manufacturing the secondary battery 10 includes calculating the lower load limit FL, and performing aging while applying a load greater than or equal to the lower load limit FL. That is, it is preferable that the method for manufacturing the secondary battery 10 performs aging while applying a load that is less than or equal to the upper load limit FU and greater than or equal to the lower load limit FL.

[0064] <Method for determining the upper and lower limits of displacement> Next, the method for determining the upper limit XU and lower limit XL of the displacement amount will be described. In this specification, the method for determining the upper limit XU and lower limit XL of the displacement amount will be described using two types of electrode bodies 20 with different spring constants. The spring constant of the electrode body 20 is determined by, for example, the thickness of the electrode plate and the thickness of the active material. In the first example, the spring constant of the electrode body 20 is 44.0 [kN / mm]. In the second example, the spring constant of the electrode body 20 is 31.0 [kN / mm].

[0065] First, let's explain using the first example. The manufacturer prepares multiple rechargeable batteries 10. For example, multiple rechargeable batteries 10 manufactured within the same lot will exhibit the same spring constant.

[0066] As shown in Figure 6, the manufacturer performs aging on multiple secondary batteries 10 while applying different loads to each. More specifically, the manufacturer performs aging on multiple secondary batteries 10 while applying loads such that each receives a different displacement. For example, the manufacturer performs aging on multiple secondary batteries 10 while applying different loads between 0.0 [kN] and 3.0 [kN].

[0067] The manufacturer measures the spring constant of each of the multiple secondary batteries 10. At this time, the manufacturer measures the spring constant by applying a first load F1 and a second load F2 to the secondary battery 10. This spring constant is measured during aging. That is, the manufacturer measures the spring constant of the secondary battery 10 in a constrained state. The first load F1 is, for example, 1000 [kgf]. The second load F2 is, for example, 1500 [kgf]. The method for measuring the spring constant is the same as the method shown in the load determination process.

[0068] The manufacturer determines the upper limit of displacement XU from each spring constant. For example, the manufacturer determines the upper limit of displacement XU based on the spring constant of the secondary battery 10 when the displacement is 0. More specifically, the manufacturer determines the upper limit of displacement XU based on a range set using the spring constant of the secondary battery 10 when the displacement is 0 as a reference.

[0069] The manufacturer determines the displacement limit XU as the displacement amount just before the spring constant exceeds a range set based on the spring constant exhibited by the secondary battery 10 with a displacement of 0. For example, the manufacturer determines that the spring constant has increased if it exceeds a range that takes into account the error of the spring constant exhibited by the secondary battery 10 with a displacement of 0. The manufacturer may also determine that the spring constant has increased if it exceeds a range that takes into account a predetermined value, not limited to the error. In the first example, the manufacturer determines that the spring constant has increased when the displacement exceeds 0.024 [mm], based on the spring constant exhibited by the secondary battery 10 with a displacement of 0.000 [mm]. Therefore, in the first example, the displacement limit XU is set to 0.024 [mm]. Thus, the upper limit of displacement XU is a predetermined value based on the spring constants of multiple secondary batteries 10, which were measured under conditions where different loads were applied to each battery during aging, resulting in different displacement amounts.

[0070] The manufacturer inspects the amount of residual gas in multiple aged secondary batteries 10. The manufacturer can inspect the amount of residual gas, for example, by looking at CT images of multiple secondary batteries 10. Based on the amount of residual gas, the manufacturer determines the lower limit value XL of the displacement.

[0071] As shown in Figure 7, the CT image of secondary battery 10 with a displacement of 0.000 [mm] shows that there is a large amount of residual gas. As shown in Figure 8, when the electrode plate of the secondary battery 10 with a displacement of 0.000 [mm] was examined after the lithium deposition test, lithium deposition was confirmed. Therefore, a displacement of 0.000 [mm] may adversely affect the performance of the secondary battery 10.

[0072] As shown in Figure 9, the CT image of secondary battery 10 with a displacement of 0.008 [mm] shows that the amount of residual gas is small. Specifically, no residual gas was detected in the CT image of secondary battery 10 with a displacement of 0.008 [mm]. In other words, if the displacement is 0.008 [mm] or greater, the amount of residual gas will be small. Therefore, in the first example, the lower limit of the displacement value XL is set to 0.008 [mm]. Thus, the lower limit of the displacement value XL is a value predetermined based on the amount of residual gas.

[0073] In the first example, a high-performance secondary battery 10 is manufactured by performing aging while applying a load such that the displacement is 0.024 [mm] or less and 0.008 [mm] or more. In the first example, 1.06 [kN / mm] is calculated as the upper limit load value FU by multiplying 44.0 [kN] by 0.024 [mm]. 0.35 [kN / mm] is calculated as the lower limit load value FL by multiplying 44.0 [kN] by 0.008 [mm]. Therefore, in the first example, a high-performance secondary battery 10 is manufactured by performing aging while applying a load of 1.06 [kN / mm] or less and 0.35 [kN / mm] or more to the secondary battery 10.

[0074] Next, we will explain using the second example. Parts that overlap with the first example will be omitted. As shown in Figure 10, in the second example, the manufacturer determines that the spring constant is large when the displacement exceeds 0.024 mm, based on the spring constant of the secondary battery 10 with a displacement of 0.000 mm. Therefore, in the second example, the upper limit of the displacement XU is set to 0.024 mm.

[0075] In the second example, CT images similar to those in the first example were obtained for secondary battery 10 with a displacement of 0.000 [mm] and secondary battery 10 with a displacement of 0.008 [mm]. Therefore, in the second example, as in the first example, the lower limit of the displacement XL is determined to be 0.008 [mm].

[0076] In the second example, a high-performance secondary battery 10 is manufactured by performing aging while applying a load such that the displacement is 0.024 [mm] or less and 0.008 [mm] or more. In the second example, 0.75 [kN / mm] is calculated as the upper limit load value FU by multiplying 31.0 [kN] by 0.024 [mm]. 0.35 [kN / mm] is calculated as the lower limit load value FL by multiplying 31.0 [kN] by 0.008 [mm]. Therefore, in the second example, a high-performance secondary battery 10 is manufactured by performing aging while applying a load of 0.75 [kN / mm] or less and 0.25 [kN / mm] or more to the secondary battery 10.

[0077] <Effects of the manufacturing method> Next, the effects of the above embodiment will be described. (1) The method for manufacturing the secondary battery 10 includes measuring the spring constant of the electrode body 20 before aging. The method for manufacturing the secondary battery 10 includes calculating the upper limit of the load to be applied to the electrode body 20 during aging based on the measured spring constant of the electrode body 20 and a predetermined upper limit XU of the displacement amount of the electrode body 20. The method for manufacturing the secondary battery 10 includes performing aging with a load of less than or equal to the calculated upper limit applied to the electrode body 20.

[0078] By multiplying the displacement of the electrode body 20 by the spring constant of the electrode body 20, the load required to displace it by that amount is calculated. That is, by multiplying the spring constant by the upper limit of the displacement XU, the upper limit of the load applied to the electrode body 20 during aging can be determined. Therefore, according to the above method, a secondary battery 10 with good performance can be manufactured.

[0079] (2) The upper limit of displacement XU is a predetermined value based on the spring constants of each secondary battery 10, which were measured under conditions where different loads were applied to each of them during aging, resulting in different displacement amounts.

[0080] By measuring the spring constant of multiple secondary batteries 10 that have been displaced by different amounts by applying different loads during aging, the change in the spring constant relative to the amount of displacement can be determined. The amount of displacement at which the spring constant increases indicates the amount of displacement that causes the electrode body 20 to deform, i.e., the load. Therefore, the amount of displacement just before the spring constant increases is the upper limit of the displacement XU. By using the above method with the upper limit of the displacement XU determined in this way, a secondary battery 10 with good performance can be manufactured.

[0081] (3) The upper limit of displacement XU is a value predetermined based on a range set using the spring constant of the secondary battery 10 whose displacement is 0 as a reference, among several secondary batteries 10 which are displaced by different amounts by applying different loads during aging.

[0082] The displacement limit XU is determined based on the spring constant of the secondary battery 10 with a displacement of 0. Therefore, for example, if the measured spring constant of the secondary battery 10 exceeds a predetermined range that includes the spring constant of the secondary battery 10 with a displacement of 0 among multiple secondary batteries 10, it can be considered that the measured spring constant has increased. By using the above method with the displacement limit XU determined in this way, a secondary battery 10 with good performance can be manufactured.

[0083] (4) The method for manufacturing the secondary battery 10 includes calculating the lower limit of the load to be applied to the electrode body 20 during aging based on the measured spring constant of the electrode body 20 and a predetermined lower limit XL of the displacement of the electrode body 20. The method for manufacturing the secondary battery 10 also includes performing aging with a load applied to the electrode body 20 that is less than or equal to the calculated upper limit of the load and greater than or equal to the calculated lower limit of the load.

[0084] If the load applied to the electrode body 20 during aging is too small, there is a risk that the gas will not be sufficiently discharged. The lower limit of the load applied to the electrode body 20 during aging can be calculated by multiplying the spring constant by the lower limit of the displacement XL. Therefore, a secondary battery 10 with good performance can be manufactured using the above method.

[0085] (5) The lower limit of displacement XL is a predetermined value based on the residual amount of gas measured for multiple secondary batteries 10 under conditions where different loads were applied to each battery during aging, resulting in different displacement amounts for each battery.

[0086] The amount of residual gas in the secondary battery 10 can be determined, for example, from a CT scan of the secondary battery 10. Therefore, for example, the lower limit of the displacement XL can be determined based on the amount of residual gas from the CT scan of the secondary battery 10. By using the above method with the lower limit of the displacement XL determined in this way, a secondary battery 10 with good performance can be manufactured.

[0087] (6) Before aging, the spring constant is measured based on the difference between the displacement when a first load F1 is applied to the electrode body 20 and the displacement when a second load F2, which is smaller than the first load F1, is applied to the electrode body 20. According to the above method, the spring constant of the secondary battery 10 can be measured with greater accuracy compared to when only one load is applied.

[0088] (7) The upper limit of the displacement XU is 0.024 mm. The lower limit of the displacement XL is 0.008 mm. According to the above method, a secondary battery 10 with good performance can be manufactured. [Explanation of Symbols]

[0089] 10…Secondary battery 11… Case 12…Lid 13…Injection hole 14… Exhaust vent 15… Exhaust valve 16…Positive external terminal 17... Negative external terminal 18…Positive electrode current collector 19... Negative electrode current collector 20...Electrode body 21…Positive plate 22... Negative plate 23... Separator 24... Separator 25...Positive electrode current collector 26...Cathode active material layer 27...Connection part 28...Negative electrode current collector 29...Negative electrode active material layer 30...Connection part

Claims

1. A method for manufacturing a secondary battery, in which aging is performed with a load applied to the electrode body, The spring constant of the electrode body is measured before aging, Based on the measured spring constant of the electrode body and a predetermined upper limit of the displacement of the electrode body, the upper limit of the load applied to the electrode body during aging is calculated. A method for manufacturing a secondary battery, comprising performing aging while applying a load to the electrode body that is less than or equal to the upper limit of the calculated load.

2. The method for manufacturing a secondary battery according to claim 1, wherein the upper limit of the displacement is a predetermined value based on the respective spring constants measured for each of the multiple secondary batteries when they are displaced by different amounts by applying different loads to each of them during aging.

3. The method for manufacturing a secondary battery according to claim 2, wherein the upper limit of the displacement is a value predetermined based on a range set with reference to the spring constant of a secondary battery whose displacement is 0, among the plurality of secondary batteries which are displaced by different amounts of displacement by applying different loads to each of them during aging.

4. Based on the measured spring constant of the electrode body and a predetermined lower limit of the displacement of the electrode body, the lower limit of the load to be applied to the electrode body during aging is calculated. A method for manufacturing a secondary battery according to claim 1, comprising performing aging while applying a load to the electrode body such that the load is less than or equal to the upper limit of the calculated load and greater than or equal to the lower limit of the calculated load.

5. The method for manufacturing a secondary battery according to claim 4, wherein the lower limit of the displacement is a predetermined value based on the residual amount of gas measured when each of the multiple secondary batteries is displaced by a different amount of displacement by applying different loads to each of them during aging.

6. A method for manufacturing a secondary battery according to claim 1, wherein, before aging, the spring constant is measured based on the difference between the amount of displacement when a first load is applied to the electrode body and the amount of displacement when a second load smaller than the first load is applied to the electrode body.

7. The upper limit of the displacement is 0.024 mm. The method for manufacturing a secondary battery according to claim 4 or claim 5, wherein the lower limit of the displacement is 0.008 mm.

Images