Manufacturing method for energy storage devices

Abstract

The present invention provides a method for manufacturing an energy storage device that can suppress the warping of electrodes caused by the pressing process. [Solution] The method for manufacturing an energy storage device according to the present disclosure comprises a first pressing step of pressurizing an electrode 14 on which an active material layer 16 and an active material layer 17 are formed on an electrode plate 15 to increase the density of the active material layer 16 and the active material layer 17, and a second pressing step of pressurizing the electrode 14 with a straightening mold T having a curved pressing surface to straighten the electrode 14 into a shape including a curved portion C.

Description

Technical Field

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

Background Art

[0002] For example, as disclosed in Patent Document 1, a monopolar electrode or a bipolar electrode constituting a power storage device is manufactured by forming an active material layer on the surface of an electrode plate.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Regarding the method for manufacturing a power storage device disclosed in Patent Document 1, the inventors have found the following problems. The electrode with the active material layer formed on the electrode plate is pressed with a predetermined pressure in order to increase the density of the active material layer. Here, due to the difference between the elongation rate of the active material layer and the elongation rate of the electrode plate, warpage may occur in the pressed electrode. If a power storage module in which a plurality of warped electrodes are stacked is used in a power storage device, the battery capacity of the power storage device may decrease.

[0005] The present invention has been made to solve such problems, and an object thereof is to provide a method for manufacturing a power storage device capable of suppressing warpage of an electrode in a pressing process.

Means for Solving the Problems

[0006] The method for manufacturing an energy storage device according to this disclosure comprises a first pressing step of pressurizing an electrode having an active material layer formed on an electrode plate to increase the density of the active material layer, and a second pressing step of pressurizing the electrode with a straightening die having a curved pressing surface to straighten the electrode into a shape including a curved portion. By deliberately straightening the electrode to be curved, the warping of the electrode that occurred in the first pressing step is suppressed.

[0007] The electrode plate has a coated portion on which the active material layer is formed and an uncoated portion on which the active material layer is not formed, and the curved portion may be provided in multiple locations on the coated portion.

[0008] The pressure applied in the second pressing step may be less than the pressure applied in the first pressing step.

[0009] The second pressing step may involve pressurizing the electrode laminate in which the plurality of electrodes are stacked.

[0010] The process may further include an injection step in which, after the second pressing step, the electrode laminate is held in place by the straightening die, and an electrolyte solution is injected into the interior of the electrode laminate. [Effects of the Invention]

[0011] The present invention provides a method for manufacturing an energy storage device that can suppress the warping of electrodes caused by the pressing process. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic cross-sectional view showing the internal configuration of the energy storage module according to Embodiment 1. [Figure 2] Figure 2 shows the configuration of the electrode after the active material layer has been formed on the electrode plate, according to Embodiment 1. [Figure 3] Figure 3 is a flowchart of the manufacturing method for the energy storage device according to Embodiment 1. [Figure 4] Figure 4 is a cross-sectional view showing the electrodes before and after the second pressing process according to Embodiment 1. [Figure 5] Figure 5 is a cross-sectional view of the electrode and straightening die in the second pressing process according to Embodiment 1. [Figure 6] Figure 6 shows an example of the lower die of the straightening die in the second pressing process according to Embodiment 1. [Modes for carrying out the invention]

[0013] The following describes specific embodiments of this disclosure in detail with reference to the drawings. However, this disclosure is not limited to the following embodiments. Also, for clarity, the following descriptions and drawings have been simplified as appropriate.

[0014] (Embodiment 1) <Configuration of the energy storage device> The energy storage device comprises one or more energy storage modules. The energy storage modules are plate-shaped, non-aqueous batteries, such as bipolar batteries with bipolar electrodes or monopolar batteries with monopolar electrodes. The following example describes a bipolar battery with bipolar electrodes.

[0015] Referring to Figure 1, the energy storage module included in the energy storage device according to this embodiment 1 will be described. Figure 1 is a schematic cross-sectional view showing the internal configuration of the energy storage module according to embodiment 1. The energy storage module 1 comprises an electrode stack 11 including a plurality of electrodes 14 and a sealant 12 that seals the electrode stack 11.

[0016] Within the electrode stack 11, multiple electrodes 14 are stacked with separators 13 in between. Each electrode 14 is a bipolar electrode comprising an electrode plate 15, a positive electrode layer 16, and a negative electrode layer 17.

[0017] The electrode plate 15 is a sheet-like conductive material and is substantially rectangular in shape. The electrode plate 15 has a structure in which multiple metal foils, each containing different types of metals, are integrated. The multiple metal foils are joined together. Each metal foil is, for example, copper foil, aluminum foil, titanium foil, or nickel foil.

[0018] The positive electrode layer 16 is formed by applying a positive electrode layer material onto the surface of the electrode plate 15 and then drying it. The positive electrode layer material includes a positive electrode active material, a conductive assistant, and a binder. The negative electrode layer 17 is formed by applying a negative electrode layer material onto the surface of the electrode plate 15 opposite to the surface where the positive electrode layer 16 is formed and then drying it. The negative electrode layer material includes a negative electrode active material, a conductive assistant, and a binder. The positive electrode layer 16 and the negative electrode layer 17 are referred to as active material layers.

[0019] FIG. 2 is a diagram showing the configuration of an electrode after forming an active material layer on an electrode plate according to Embodiment 1. The upper diagram of FIG. 2 is a plan view of the electrode 14, and the lower diagram of FIG. 2 is a cross-sectional view of the electrode 14. The electrode 14 has a coated portion P1 where an active material layer is formed on the electrode plate 15 and an uncoated portion P2 where an active material layer is not formed on the electrode plate 15.

[0020] Returning to the description of FIG. 1, a negative electrode layer terminal electrode 18 is disposed at the first end of the electrode laminate 11, and a positive electrode layer terminal electrode 19 is disposed at the second end of the electrode laminate 11 opposite to the first end. The negative electrode layer terminal electrode 18 is an electrode including the electrode plate 15 and the negative electrode layer 17. The positive electrode layer terminal electrode 19 is an electrode including the electrode plate 15 and the positive electrode layer 16. The plurality of electrodes 14 are disposed between the negative electrode layer terminal electrode 18 and the positive electrode layer terminal electrode 19 in the stacking direction.

[0021] The sealing body 12 is provided so as to surround the side surface of the electrode laminate 11. Examples of the material used for the sealing body 12 include polypropylene, polyphenylene sulfide, or modified polyphenylene ether. Further, the sealing body 12 has a through-hole (not shown) for supplying an electrolytic solution into the electrode laminate 11.

[0022] <Manufacturing Method of the Power Storage Device> Subsequently, the manufacturing method of the power storage device according to Embodiment 1 will be described. FIG. 3 is a flowchart of the manufacturing method of the power storage device according to Embodiment 1.

[0023] First, a coating process is performed in which the positive electrode layer material is applied to one side of the electrode plate 15 and the negative electrode layer material is applied to the other side (step S101). Next, a drying process is performed to dry the positive electrode layer material and the negative electrode layer material applied to the electrode plate 15 (step S102). By removing the solvent from the positive electrode layer material and the negative electrode layer material through drying, the positive electrode layer 16 and the negative electrode layer 17 are formed.

[0024] Note that the formation of the positive electrode layer 16 and the negative electrode layer 17 by the coating process (step S101) and the drying process (step S102) does not have to be simultaneous. In other words, for example, the positive electrode layer 16 may be formed first by the coating process (step S101) and the drying process (step S102), and then the negative electrode layer 17 may be formed again by the coating process (step S101) and the drying process (step S102).

[0025] Next, a first pressing step is performed (step S103) in which the electrode 14 is pressurized to increase the density of the positive electrode layer 16 and the negative electrode layer 17. By pressurizing, the thickness of the positive electrode layer 16 and the negative electrode layer 17 is reduced, thereby increasing the density of the active material in the positive electrode layer 16 and the negative electrode layer 17. In the first pressing step, the electrode 14 is pressurized while being transported, for example, by the rotation of a pair of press rolls. Note that the electrode 14 may be pressurized by a pair of molds, not limited to a pair of press rolls.

[0026] Next, a cutting process is performed to divide the electrode 14 into multiple parts (step S104). The electrode 14 is cut to a predetermined length using, for example, a cutting device having a blade.

[0027] Next, a second pressing step is performed (step S105) in which the electrode 14 is pressed by a straightening mold T having a curved pressure surface, and the electrode 14 is straightened into a shape including the curved portion C. The second pressing step (step S105) will be explained in detail later.

[0028] Next, a lamination process is performed to form an electrode stack 11 by stacking multiple electrodes 14 via a separator 13 (step S106). After that, a sealant 12 is formed on the electrode stack 11.

[0029] Next, an electrolyte injection process is performed (step S107) in which the electrolyte is injected into the interior of the electrode stack 11. First, the electrode stack 11 and the sealant 12 are held in the stacking direction by a restraining plate. Then, the electrode stack 11 and the sealant 12 are restrained with a predetermined pressure. While maintaining the restraint, the electrolyte is injected into the interior of the electrode stack 11 through a through hole (not shown) provided in the sealant 12. The injected electrolyte impregnates the separator 13, the positive electrode layer 16, and the negative electrode layer 17, respectively. The energy storage module 1 is thus obtained. The method of injecting the electrolyte is not particularly limited, and for example, a known method using an injection device can be used. As the electrolyte, for example, a known organic electrolyte used in lithium-ion secondary batteries can be used as appropriate.

[0030] Next, an activation process is performed to activate the energy storage module 1 as a battery (step S108). In the activation process (step S108), the energy storage module 1 is activated by sequentially performing, for example, an initial charging process, a high-temperature aging process, and a self-discharge test.

[0031] Finally, a sealing process is performed to seal the energy storage module 1 under reduced pressure (step S109). First, the energy storage module 1 is placed in a chamber and the chamber is evacuated. Then, the through-holes (not shown) provided in the sealing body 12 are sealed. This allows the energy storage module 1 to be sealed under reduced pressure.

[0032] <Second pressing process> The second pressing process (step S105) will be explained in detail. Figure 4 is a cross-sectional view showing the electrodes before and after the second pressing process according to Embodiment 1. The upper part of Figure 4 is a cross-sectional view of the electrode 14 before the second pressing process (step S105), and the lower part of Figure 4 is a cross-sectional view of the electrode 14 after the second pressing process (step S105).

[0033] Because the elongation rates of the electrode plate 15, the positive electrode layer 16, and the negative electrode layer 17 are different, the electrode 14 warps after the first pressing process (step S103), as shown in the upper part of Figure 4. If a power storage module 1 in which multiple warped electrodes 14 are stacked is used in a power storage device, the battery capacity of the power storage device may decrease. Therefore, a second pressing process (step S105) is performed to suppress the warping caused by the first pressing process (step S103).

[0034] In the second pressing step (step S105), the electrode 14 is straightened into a shape that includes a curved portion C, as shown in the lower part of Figure 4. By deliberately straightening the electrode 14 in this curved shape, the warping caused by the first pressing step (step S103) is suppressed.

[0035] Figure 5 is a cross-sectional view of the electrode and straightening die in the second pressing process according to Embodiment 1. As shown in Figure 5, the electrode 14 is pressed by a pair of straightening dies T having curved pressing surfaces. The straightening dies T may also be press rolls. When the straightening dies T are press rolls, the electrode 14 is pressed while being transported by the rotation of the pair of press rolls. Alternatively, one of the pair of straightening dies T may be a die with a curved pressing surface, and the other may be a die made of an elastic material with a flat processing surface.

[0036] The number and shape of the curved portions C of the electrode 14 are determined based on the number and shape of the irregularities provided on the processing surface of the straightening die T. Figure 6 shows an example of the lower die of the straightening die in the second pressing process according to Embodiment 1. In the electrode 14 manufactured using the lower die of the straightening die T shown in Figure 6, for example, the number of curved portions C is 1 in Embodiment 1, the number of curved portions C is 16 in Embodiment 5, and the number of curved portions C is 8 in Embodiment 6. As shown in Figure 6, the curved portions C of the electrode 14 may be arranged alternately with upwardly convex curved portions C and downwardly convex curved portions C. Also, the shape of the curved portions C may be elliptical, as in Embodiments 3 and 6.

[0037] The greater the number of curved portions C on the electrode 14, the greater the warping suppression effect. As shown in Figure 6, the number of irregularities on the processed surface of the straightening mold T is greatest in Example 5. And, in the examples shown in Figure 6, the electrode 14 pressed by the straightening mold T of Example 5 showed the greatest warping suppression effect.

[0038] Furthermore, it is preferable that the pressure applied in the second pressing step (step S105) is smaller than the pressure applied in the first pressing step (step S103). This suppresses the localized load applied to the curved portion C of the electrode 14, which is generated by the pressure applied by the straightening mold T. This suppresses the occurrence of damage to the positive electrode layer 16 and the negative electrode layer 17.

[0039] Since the electrode 14 has creep properties, warping can be more effectively suppressed by appropriately optimizing the pressure applied, room temperature, and pressurizing time in the second pressing process (step S105). For example, the pressure is preferably 40 to 80 kPa, and the temperature is preferably 80°C or higher. However, the optimal values ​​for the pressure applied, room temperature, and pressurizing time are not limited to the above values, as they vary depending on the material and dimensions of the electrode 14.

[0040] A busbar is provided in the uncoated portion P2 of the electrode 14. Therefore, it is preferable that the curved portion C of the electrode 14 is provided in the coated portion P1 rather than in the uncoated portion P2.

[0041] The method for manufacturing the energy storage device according to this embodiment 1 has been described above, but the order of the steps is not limited to this and may be rearranged as appropriate. For example, the second pressing step (step S105) may be performed after the lamination step (step S106). In this case, the second pressing step (step S105) applies pressure to the electrode laminate 11 with a straightening mold T to straighten the electrode laminate 11 into a shape that includes a plurality of curved portions C.

[0042] Then, in the subsequent liquid injection step (step S107), the electrolyte may be injected into the inside of the electrode stack 11 while the electrode stack 11 and the sealant 12 are still held between the straightening mold T. This reduces the effort required to move the electrode stack 11 and the sealant 12 from the straightening mold T to the restraining plate. [Explanation of symbols]

[0043] 1. Energy storage module 11 Electrode Stack 12 Sealing body 13 Separator 14 electrodes 15 Electrode plate 16. Positive electrode layer 17. Negative electrode layer 18 Negative layer terminal electrode 19 Positive layer terminal electrode C Curved section P1 Coated area P2 Unpainted area T orthodontic type

Claims

1. A first pressing step involves pressurizing an electrode plate on which an active material layer has been formed to increase the density of the active material layer, The device comprises a second pressing step of applying pressure to the electrode with a straightening mold having a curved pressure surface, thereby straightening the electrode into a shape that includes the curved portion. A method for manufacturing an energy storage device.

2. The electrode plate has a coated portion on which the active material layer is formed and an uncoated portion on which the active material layer is not formed. The curved portion is provided in multiple locations in the coated portion. A method for manufacturing an energy storage device according to claim 1.

3. The pressure applied in the second pressing step is less than the pressure applied in the first pressing step. A method for manufacturing an energy storage device according to claim 1 or 2.

4. The second pressing step involves applying pressure to the electrode laminate in which the plurality of electrodes are stacked. A method for manufacturing an energy storage device according to claim 1 or 2.

5. The second pressing step is followed by an injection step in which an electrolyte solution is injected into the interior of the electrode laminate while the electrode laminate is still held in place by the straightening die. A method for manufacturing an energy storage device according to claim 4.

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