Method for manufacturing electrochemical cells

Abstract

This invention provides a method for manufacturing an electrochemical cell that can form a thin separator. [Solution] A method for manufacturing a battery comprising a positive electrode body 5 containing a positive electrode active material, a negative electrode body containing a negative electrode active material, and a separator 6 interposed between the positive electrode body 5 and the negative electrode body, the method comprising a separator forming step in which a paint with a viscosity of 1 Pa·s or more and 7 Pa·s or less is sprayed onto the outer surface of the positive electrode body 5 and dried to form the separator 6.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an electrochemical cell.

Background Art

[0002] Conventionally, electrochemical cells such as lithium-ion secondary batteries and electric double layer capacitors have been widely used as power sources for small devices such as smartphones, wearable devices, and hearing aids. An electrochemical cell has a configuration in which a positive electrode body and a negative electrode body facing each other through a separator are provided inside an exterior body. For example, as described in Patent Document 1, an electrode in which a plurality of electrode bodies are connected in a带状 shape via an electrode connection portion to form an electrode structure, and an electrode terminal is formed on the electrode body on one end side, and the electrode structure has a laminated structure having a current collector layer, an active material layer formed on both surfaces thereof, and a separator layer. An electrochemical cell is disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in an electrochemical cell, from the viewpoint of increasing the charge capacity, charge current, and discharge current, it is desired to form the separator thinly.

[0005] Therefore, the present invention provides a method for manufacturing an electrochemical cell capable of forming a thin separator.

Means for Solving the Problems

[0006] A method for manufacturing an electrochemical cell according to a first aspect of the present invention is a method for manufacturing an electrochemical cell comprising a positive electrode body containing a positive electrode active material, a negative electrode body containing a negative electrode active material, and a separator interposed between the positive electrode body and the negative electrode body, the method comprising a separator forming step of forming the separator by spraying a paint having a viscosity of 1 Pa·s or more and 7 Pa·s or less onto the outer surface of one of the electrode bodies, the positive electrode body and the negative electrode body, and drying it.

[0007] According to the first embodiment, it was confirmed that by setting the paint to the viscosity described above, the paint can be easily and evenly applied to the electrode body by spraying. As a result, a thin layer of paint can be applied to the electrode body, making it possible to form a thin separator. Furthermore, in a configuration where separators are formed on both sides of the electrode body, when applying the paint raw material for the separator using the doctor blade method, it is necessary to apply the paint to both sides of the electrode body separately. In this case, when applying the paint to the second main surface of the electrode body in the second application, the paint may spread to the first main surface of the electrode body, and the solvent in the spread-over paint may dissolve the separator formed on the first main surface of the electrode body in the first application, potentially causing the micropores of the separator to disappear. According to the first embodiment, by applying the paint by spray atomization, the amount of paint applied per application can be reduced, so even when the paint is applied to the electrode body in multiple applications, the amount of solvent contained in the paint per application is also reduced, and the dissolution of the underlying separator by the applied paint can be suppressed. As a result, even when paint is applied to both sides of the electrode body, defects in the formation of the separator are less likely to occur. Therefore, this can be a suitable manufacturing method when forming separators on both sides of an electrode body. Furthermore, when paint is dropped onto pellet-shaped electrode bodies to form a separator, there is a limit to how small the droplet size can be, resulting in a relatively large amount of paint being dropped. In this case, the solvent contained in the dropped paint may seep into the electrode body, causing it to swell. According to the first embodiment, it is possible to apply a thin layer of paint to the electrode body, thus reducing the amount of solvent contained in the paint applied to the electrode body. This suppresses swelling of the electrode body when paint is applied to pellet-shaped electrode bodies, and consequently suppresses the occurrence of manufacturing defects in electrochemical cells.

[0008] A second aspect of the present invention relates to a method for manufacturing an electrochemical cell, in which the thickness of the separator may be 5 μm or more and 15 μm or less, in the method for manufacturing an electrochemical cell according to the first aspect described above.

[0009] According to the second aspect, it was confirmed that the separator functions normally in the electrochemical cell cycle evaluation as long as the separator thickness is at least within the above range.

[0010] A third aspect of the present invention relates to a method for manufacturing an electrochemical cell, which further comprises a viscosity adjustment step in which the paint before viscosity adjustment is diluted with a solvent to produce a paint with a viscosity of 1 Pa·s or more and 7 Pa·s or less, in the method for manufacturing an electrochemical cell according to the first or second aspect of the present invention.

[0011] Even if paint with a viscosity of 7 Pa·s or higher is sprayed directly, it is difficult to apply the paint uniformly. According to the third embodiment, by including a viscosity adjustment step, it is possible to use paint with a viscosity of 7 Pa·s or higher to form a separator.

[0012] A method for manufacturing an electrochemical cell according to a fourth aspect of the present invention is a method for manufacturing an electrochemical cell according to any of the first to third aspects described above, wherein the separator formation step may include: a first spraying step of spraying the paint onto one electrode body to form a first coating layer formed by the paint; a first drying step of drying the first coating layer to form a first separator layer; a second spraying step of spraying the paint onto the first separator layer to form a second coating layer formed by the paint; and a second drying step of drying the second coating layer to form a second separator layer.

[0013] In the formation of a separator by a single spray application, even if the paint is applied evenly, minute areas may occur in the separator after drying where the paint is not sufficiently thick. This is likely to occur when the amount of paint applied is small in order to form a thin separator. According to the fourth embodiment, the first separator layer formed by the first spraying step and the first drying step is covered with paint in the second spraying step, so that minute irregularities in the first separator layer are filled in by the second coating layer. Therefore, the total film thickness of the first separator layer and the second separator layer laminated after the second drying step becomes more uniform. Thus, a more uniform separator can be formed.

[0014] A fifth aspect of the present invention relates to a method for manufacturing an electrochemical cell, in which, in the method for manufacturing an electrochemical cell according to any of the first to fourth aspects described above, the coating may be a varnish containing a polyimide resin and N-methyl-2-pyrrolidone.

[0015] According to the fifth aspect, a paint suitable for achieving the above-mentioned effects can be used.

[0016] A sixth aspect of the present invention relates to a method for manufacturing an electrochemical cell, in which, in a method for manufacturing an electrochemical cell according to any of the first to fifth aspects described above, one electrode body may be formed by cutting a sheet body having an electrode layer containing an active material on a sheet-shaped current collector.

[0017] According to the sixth embodiment, the electrode body is formed by cutting the sheet body, such as by punching, so that the current collector is exposed at the end face. In the separator formation process, paint can be applied thinly and reliably to the end face of the electrode body. This allows a separator to be formed on the end face of the electrode body, thereby suppressing internal short circuits in the electrochemical cell.

[0018] A method for manufacturing an electrochemical cell according to a seventh aspect of the present invention is the method for manufacturing an electrochemical cell according to the sixth aspect described above, wherein in the separator forming step, the paint may be sprayed onto the first main surface and the second main surface of the one electrode body, respectively.

[0019] According to the seventh embodiment, by applying the paint by spraying, the amount of paint applied per application can be reduced, thus reducing the amount of solvent contained in the paint per application, and suppressing the dissolution of the underlying separator by the applied paint. As a result, even if paint is applied to both sides of the electrode body, defects in the formation of the separator are less likely to occur. Therefore, this can be a suitable manufacturing method when forming separators on both sides of the electrode body.

[0020] The eighth aspect of the present invention relates to a method for manufacturing an electrochemical cell, in which, in the separator forming step, the paint may also be applied to the end face of one of the electrode bodies.

[0021] According to the eighth aspect, by spraying paint toward the main surface of the electrode body, the paint is also applied to the end surface of the electrode body by wrapping around it. Therefore, a separator can be formed on the end surface of the electrode body without adding the step of spraying paint toward the end surface of the electrode body.

[0022] The method for manufacturing an electrochemical cell according to the ninth aspect of the present invention is the method for manufacturing an electrochemical cell according to any one of the first to fifth aspects, wherein the electrochemical cell further includes a battery can that houses the positive electrode body, the negative electrode body, and the separator, one of the electrode bodies is in the form of a pellet containing a binder and is connected inside the battery can, and in the separator forming step, the paint may be applied by spray coating onto the opposing surface of the one electrode body facing the other electrode body among the positive electrode body and the negative electrode body.

[0023] According to the ninth aspect, it is possible to thinly apply the paint to the electrode body, so that the amount of the solvent contained in the paint applied to the electrode body can also be reduced. As a result, it is possible to suppress the swelling of the electrode body due to the application of the paint to the pellet-shaped electrode body, and thus suppress the occurrence of manufacturing defects in the electrochemical cell.

Advantages of the Invention

[0024] According to the method for manufacturing an electrochemical cell of the present invention, a separator can be formed thinly.

Brief Description of the Drawings

[0025] [Figure 1] It is a plan view of a battery according to the first embodiment. [Figure 2] It is a cross-sectional view taken along line II-II of FIG. 1. [Figure 3] It is a perspective view of an electrode structure according to the first embodiment. [Figure 4] It is a plan view of an electrode structure according to the first embodiment. [Figure 5] It is a developed view of a positive electrode structure including a positive electrode body according to the first embodiment. [Figure 6] It is a flowchart showing a method for manufacturing a positive electrode structure according to the first embodiment. [Figure 7] It is a plan view showing a state where a positive electrode active material layer is formed on a current collector sheet in the method for manufacturing a positive electrode structure according to the first embodiment. [Figure 8]This is a plan view showing a state in which a punched portion is formed on a current collector sheet on which a positive electrode active material layer is formed, in the manufacturing method of the positive electrode structure of the first embodiment. [Figure 9] This figure shows the step of forming a separator on a current collector sheet on which a positive electrode active material layer is formed, in the manufacturing method of the positive electrode structure of the first embodiment. [Figure 10] This figure shows the step of forming a separator on a current collector sheet on which a positive electrode active material layer is formed, in the manufacturing method of the positive electrode structure of the first embodiment. [Figure 11] This is a plan view showing the state in which a separator has been formed on the current collector sheet in the manufacturing method of the positive electrode structure of the first embodiment. [Figure 12] This is a cross-sectional view of a battery according to the second embodiment, and corresponds to Figure 2. [Figure 13] This figure shows the step of forming a separator on the positive electrode body in the manufacturing method of the positive electrode structure of the second embodiment. [Modes for carrying out the invention]

[0026] Embodiments of the present invention will be described below with reference to the drawings. In the following description, components having the same or similar functions will be denoted by the same reference numerals. Duplication of these components may be omitted.

[0027] [First Embodiment] Figure 1 is a plan view of a battery according to the first embodiment. Figure 2 is a cross-sectional view taken along line II-II in Figure 1. Battery 1 is a lithium-ion secondary battery and is an example of an electrochemical cell. As shown in Figures 1 and 2, Battery 1 is a coin-type battery having a circular planar shape. Note that the planar shape of Battery 1 does not have to be circular, and various shapes such as elliptical, square, or polygonal shapes can be used, but in this embodiment, for the sake of simplicity of explanation, a coin-type battery with a circular planar shape will be used as an example. Battery 1 comprises an electrode structure 2 of a power generation element having a positive electrode active material and a negative electrode active material, an electrolyte (not shown) impregnated into the electrode structure 2, and an outer casing 10 that houses the electrode structure 2.

[0028] Figure 3 is a perspective view of the electrode structure of the first embodiment. Figure 4 is a plan view of the electrode structure of the first embodiment. Note that in Figures 3 to 5, the thickness of the separator 6 is exaggerated. As shown in Figures 3 and 4, the electrode structure 2 comprises a negative electrode 3 folded in a zigzag shape, a positive electrode 5 folded in a zigzag shape in a direction intersecting the negative electrode 3 so as to be stacked alternately with the negative electrode 3, and a separator 6 interposed between the negative electrode 3 and the positive electrode 5.

[0029] As shown in Figure 2, the negative electrode 3 comprises a negative electrode current collector 20 and a negative electrode active material layer 22 formed on both sides of the negative electrode current collector 20. For example, the negative electrode current collector 20 is made of a metallic material such as copper, nickel, or stainless steel. The negative electrode active material layer 22 contains a negative electrode active material, a conductive additive, a binder, and a thickener. For example, the negative electrode active material layer 22 is made of a carbon material such as graphite. For example, conductive additives include carbon blacks, carbon materials, and metal powders. For example, binders include resin materials such as polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), and polytetrafluoroethylene (PTFE). For example, thickeners include resin materials such as carboxymethylcellulose (CMC).

[0030] As shown in Figures 3 and 4, the negative electrode body 3 is strip-shaped when unfolded from its zigzag state. The negative electrode body 3 comprises a plurality of negative electrode connection portions 3a and a plurality of substantially circular negative electrode bodies 3b. An extension portion 21 of the negative electrode current collector 20, which serves as the terminal of the negative electrode body 3, is formed at one end of the negative electrode body 3. The extension portion 21 is the part of the negative electrode current collector 20 that extends outward from the negative electrode body 3b in the longitudinal direction of the negative electrode body 3.

[0031] As shown in Figure 2, the positive electrode body 5 comprises a strip-shaped positive electrode current collector 30 and a positive electrode active material layer 32 formed on both sides of the positive electrode current collector 30. For example, the positive electrode current collector 30 is made of a metallic material such as aluminum, an aluminum alloy, or stainless steel. The positive electrode active material layer 32 contains a positive electrode active material, a conductive additive, a binder, and a thickener. For example, the positive electrode active material layer 32 is made of a composite metal oxide such as lithium cobaltate or lithium nickelate. For example, conductive additives include carbon blacks, carbon materials, and metal powders. For example, binders include resin materials such as polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), and polytetrafluoroethylene (PTFE). For example, thickeners include resin materials such as carboxymethylcellulose (CMC).

[0032] Figure 5 is an exploded view of the positive electrode structure including the positive electrode body of the first embodiment. As shown in Figures 3 to 5, the positive electrode body 5 is strip-shaped when unfolded from its zigzag state. The general shape of the positive electrode body 5 is substantially the same as that of the negative electrode body 3. The positive electrode body 5 comprises a plurality of positive electrode connection portions 5a and a plurality of substantially circular positive electrode bodies 5b. Hereinafter, the direction perpendicular to the longitudinal direction of the strip-shaped positive electrode body 5 may be referred to as the "width direction of the positive electrode body 5". The positive electrode connection portions 5a are recessed inward in the width direction of the positive electrode body 5. An extension portion 31 of the positive electrode current collector 30, which serves as the terminal of the positive electrode body 5, is formed at one end of the positive electrode body 5. The extension portion 31 is the part of the positive electrode current collector 30 that extends outward from the positive electrode body 5b in the longitudinal direction of the positive electrode body 5.

[0033] As shown in Figure 5, when the positive electrode body 5 is unfolded, the positive electrode body 5b is positioned adjacent to the positive electrode connection portion 5a in the longitudinal direction of the positive electrode body 5. The positive electrode body 5b extends outward in an arc shape beyond the positive electrode connection portion 5a in the width direction of the positive electrode body 5. In this embodiment, the unfolded positive electrode body 5b is substantially circular in shape and is connected linearly to the four positive electrode connection portions 5a.

[0034] As shown in Figure 3, in the zigzag structure of the positive electrode body 5, each positive electrode body 5b is stacked substantially parallel to one another. The positive electrode connection portion 5a is connected to the edge of each positive electrode body 5b in the longitudinal direction of the positive electrode body 5. That is, the positive electrode connection portion 5a connects two adjacent positive electrode bodies 5b in series.

[0035] As shown in Figures 3 and 4, the outer shape of the positive electrode 5 (outer contour when viewed in plan along the stacking direction) is slightly smaller than the outer shape of the negative electrode 3 (outer contour when viewed in plan along the stacking direction). In other words, the outer shapes of the positive electrode connection portion 5a and the positive electrode body 5b of the positive electrode 5 are slightly smaller than the outer shapes of the negative electrode connection portion 3a and the negative electrode body 3b of the negative electrode 3.

[0036] As shown in Figure 5, the separator 6 covers almost the entire portion of the positive electrode body 5, excluding the tip of the extension portion 31. The film thickness of the separator 6 is 5 μm to 15 μm on the main surface of the positive electrode body 5. However, the film thickness of the separator 6 is not particularly limited on the end face of the positive electrode body 5. The separator 6 is integrated with the positive electrode body 5 to form the positive electrode structure 4. The manufacturing method of the positive electrode structure 4 will be described later. The positive electrode body 5 has an unformed portion 5e on its outer surface at the end opposite the extension portion 31 that is not covered by the separator 6. The unformed portion 5e is covered by an insulating layer 6f made of insulating tape.

[0037] As shown in Figures 1 and 2, the outer casing 10 is a battery can comprising a positive electrode can 11, a negative electrode can 12, and a gasket 13 that electrically insulates the positive electrode can 11 and the negative electrode can 12 from each other.

[0038] The positive electrode can 11 and the negative electrode can 12 are flattened, bottomed cylindrical shapes. The inner diameter of the positive electrode can 11 is slightly larger than the outer diameter of the negative electrode can 12. With the cylindrical portion of the negative electrode can 12 inserted into the positive electrode can 11, the electrode structure 2 is sandwiched between the bottom surface of the negative electrode can 12 and the bottom surface of the positive electrode can 11. The gasket 13 is positioned between the outer circumferential surface of the cylindrical portion of the negative electrode can 12 and the inner circumferential surface of the cylindrical portion of the positive electrode can 11. The gasket 13 seals the electrode structure 2 to the outer casing 10.

[0039] As shown in Figures 2 and 3, the positive electrode can 11 is connected to the extension 31 of the positive electrode current collector 30 inside the outer casing 10 and functions as a positive electrode. On the other hand, the negative electrode can 12 is connected to the extension 21 of the negative electrode current collector 20 inside the outer casing 10 and functions as a negative electrode terminal. Note that the extensions 21 and 31 are not shown in Figure 2.

[0040] Although the example of enclosing the electrode structure 2 in an outer casing 10 to form a coin shape was used for explanation, this embodiment is not limited to this structure. A structure in which the electrode structure 2 is enclosed in a laminate pack made of laminate film, and lead wires electrically connected to the electrode structure protrude from the laminate pack to the outside, may also be adopted. In the case of a laminate pack made of laminate film, the sealing performance is superior to that of a can structure, and therefore the battery 1 has the advantage of superior long-term reliability.

[0041] In addition to the structure in which a strip-shaped negative electrode 3 and a strip-shaped positive electrode 5 are folded in the aforementioned zigzag shape, the electrode structure may also be in a shape in which the strip-shaped negative electrode and the strip-shaped positive electrode are wound around a separator. In an electrode structure formed by winding, the strip-shaped negative electrode and the strip-shaped positive electrode may be rectangular (strip-shaped) in which the main body and the connecting part are formed to the same width, in addition to the shapes described above.

[0042] Below, an example of a method for manufacturing the positive electrode structure 4 will be described as part of the manufacturing method for the battery 1 of the first embodiment. Figure 6 is a flowchart showing the manufacturing method of the positive electrode structure according to the first embodiment. As shown in Figure 6, the manufacturing method of the positive electrode structure 4 of this embodiment comprises a positive electrode body formation step S10, a viscosity adjustment step S20, and a separator formation step S30.

[0043] First, the positive electrode formation process S10 is performed. First, a coating solution (slurry) containing the constituent materials for forming the positive electrode active material layer 32 is prepared. Hereinafter, the coating solution containing the constituent materials for forming the positive electrode active material layer 32 will be referred to as the "positive electrode slurry." The positive electrode slurry contains the positive electrode active material, conductive additive, binder, and thickener mentioned above. The solvent for the slurry can be any solvent that dissolves the binder and thickener and disperses the active material and conductive additive.

[0044] Next, a current collector sheet 50 is prepared, which is rectangular in shape in plan view and has a greater vertical and horizontal width than the positive electrode body 5 in its unfolded state. The current collector sheet 50 in this embodiment is large enough to align multiple positive electrode bodies 5 in the horizontal direction. Since the current collector sheet 50 will become the positive electrode current collector 30 after processing, it is made of a metal sheet such as aluminum, an aluminum alloy, or stainless steel, as described above. As an example, its thickness is about 10-something micrometers.

[0045] For the sake of simplicity, this explanation assumes the simultaneous manufacture of two positive electrode bodies 5 and describes an example where the width of the current collector sheet 50 is set to approximately 3 to 4 times the width of the positive electrode body 5. Since there is no particular limit to the number of positive electrode bodies 5 formed on a single current collector sheet 50, a current collector sheet 50 with an even larger width, as shown in Figure 7, can be used. In this case, even more positive electrode bodies 5 can be produced simultaneously by punching.

[0046] Figure 7 is a plan view showing the state in which a positive electrode active material layer has been formed on the current collector sheet in the manufacturing method of the positive electrode structure of the first embodiment. Next, as shown in Figure 7, the positive electrode slurry is applied to the front and back surfaces of the current collector sheet 50, which is a vertically elongated rectangular shape in plan view, excluding a predetermined width strip-shaped (rectangular) area (uncoated portion) 50a at the top of the front and back surfaces of the current collector sheet 50. The slurry is then dried and hardened to form a positive electrode active material layer 51 (electrode layer). The vertical width a of the uncoated portion 50a shown in Figure 7 is formed to be slightly larger than the extension portion 31 of the positive electrode body 5 to be manufactured, and the vertical width b of the area where the positive electrode active material layer 51 is formed is formed to be slightly larger than the overall length of the positive electrode structure 4 shown in Figure 5.

[0047] Figure 8 is a plan view showing the state in which a punched portion is formed on a current collector sheet on which a positive electrode active material layer is formed, in the manufacturing method of the positive electrode structure of the first embodiment. Next, as shown in Figure 8, the current collector sheet 50 on which the positive electrode active material layer 51 is formed is punched out to form two outlines of positive electrode bodies 5 of the desired size, arranged side by side on the current collector sheet 50. In the state shown in Figure 8, punched-out portions 52, 53, and 54 are formed on the current collector sheet 50, and both ends of the two positive electrode bodies 5 are supported by the rectangular frame of the current collector sheet 50 so that the extended portion 31 is continuous with the uncoated portion 50a.

[0048] Next, viscosity adjustment process S20 is performed. First, the viscosity of the paint containing the constituent materials of the separator 6 is adjusted. Before viscosity adjustment, the paint is a solution obtained by dissolving a polymer resin that can withstand an electrolyte, such as a polyimide resin, in a solvent. A polyimide resin is a polymer compound containing imide bonds, such as polyimide or polyamideimide. In this embodiment, the paint before viscosity adjustment is a varnish containing polyamideimide and N-methyl-2-pyrrolidone as a solvent. However, the polymer resin contained in the paint before viscosity adjustment is not limited to polyamideimide. The viscosity of the paint before viscosity adjustment is greater than 7 Pa·s. In viscosity adjustment step S20, the paint before viscosity adjustment is diluted with a solvent to produce a paint with a viscosity of 1 Pa·s or more and 7 Pa·s or less. The solvent used for dilution is not particularly limited, but for example, the same solvent contained in the paint before viscosity adjustment can be used.

[0049] Next, the separator formation process S30 is performed. In the separator formation process S30, the paint generated in the viscosity adjustment process S20 is sprayed onto the outer surface of the positive electrode 5 and dried to form a separator 6. In this case, the paint is sprayed toward both main surfaces of the positive electrode 5. That is, in the separator formation process S30, the paint is sprayed toward the first main surface 5c of the positive electrode 5 to form a separator 6 on the first main surface 5c, and the paint is sprayed toward the second main surface 5d of the positive electrode 5 to form a separator 6 on the second main surface 5d.

[0050] Figures 9 and 10 show the process of forming a separator on a current collector sheet on which a positive electrode active material layer is formed, in the manufacturing method of the positive electrode structure of the first embodiment. First, as shown in Figure 9, a separator 6 is formed on the first main surface 5c of the positive electrode body 5. In this embodiment, the positive electrode body 5 is processed together with the current collector sheet 50 on which it is formed. The process of forming the separator 6 on the first main surface 5c of the positive electrode body 5 comprises a first spraying step S31, a first drying step S32, a second spraying step S33, and a second drying step S34 (see Figure 6). In the first spraying step S31, paint is sprayed onto the positive electrode body 5 to form a first coating layer formed by the paint. The first coating layer is formed to cover the entire positive electrode active material layer 51 on the first main surface 5c of the positive electrode body 5. Furthermore, the first coating layer is formed from the first main surface 5c to the end face of the positive electrode body 5 by the wrapping of the sprayed paint. Next, in the first drying step S32, the first coating layer is dried to volatilize the solvent contained in the first coating layer and form the first separator layer. The first coating layer may be dried naturally or by heat drying. By drying the first coating layer, a first separator layer made of high-molecular-weight resin contained in the paint is formed.

[0051] Next, in the second spraying step S33, paint is sprayed onto the first separator layer again to form a second coating layer made of paint. For example, the second coating layer is laminated over the entire first separator layer. Next, in the second drying step S34, the second coating layer is dried to volatilize the solvent contained in the second coating layer and form a second separator layer. The drying of the second coating layer may be done by natural drying or by heat drying. By drying the second coating layer, a second separator layer made of polymer resin contained in the paint is formed. As a result, a separator 6 is formed on the first main surface 5c of the positive electrode body 5 by laminating the first separator layer and the second separator layer. The solvent contained in the second coating layer may melt a part of the first separator layer, causing the second separator layer to become integrated with the first separator layer. In this case, a boundary between the first separator layer and the second separator layer does not need to be formed on the separator 6.

[0052] Next, as shown in Figure 10, a separator 6 is formed on the second main surface 5d of the positive electrode body 5. The step of forming the separator 6 on the second main surface 5d of the positive electrode body 5 is the same as the step of forming the separator 6 on the first main surface 5c of the positive electrode body 5. As a result, the separator 6 is formed on the outer surface of the positive electrode body 5, including the end face.

[0053] Figure 11 is a plan view showing the state in which a separator has been formed on the current collector sheet in the manufacturing method of the positive electrode structure of the first embodiment. Then, as shown in Figure 11, by cutting the positive electrode body 5 from the current collector sheet 50, a positive electrode structure 4 can be obtained in which a separator 6 is integrally formed on the positive electrode body 5. In the obtained positive electrode structure 4, substantially the entire outer surface of the positive electrode body 5, excluding the cut surfaces and extensions 31 at both ends, is covered by the separator 6. At the end of the positive electrode body 5 opposite the extension 31, a cut surface is formed in which the positive electrode current collector 30 is exposed. The cut surface in which the positive electrode current collector 30 is exposed corresponds to the aforementioned unformed portion 5e and is covered by an insulating layer 6f separate from the separator 6 (see Figure 5).

[0054] As described above, the manufacturing method of the battery 1 of this embodiment includes a separator forming step S30 in which a paint with a viscosity of 1 Pa·s to 7 Pa·s is sprayed onto the outer surface of the positive electrode 5 and dried to form a separator 6. With this manufacturing method, it has been confirmed that by setting the paint to the above viscosity, the paint can be easily and evenly applied to the positive electrode 5 by spraying. As a result, the paint can be applied thinly to the positive electrode 5, and a thin separator 6 can be formed.

[0055] Furthermore, it was confirmed that the separator 6 functions normally in the cycle evaluation of battery 1 as long as the thickness of separator 6 is within the range of at least 5 μm to 15 μm.

[0056] In this case, it is difficult to apply paint uniformly by simply spraying paint with a viscosity of 7 Pa·s or higher. The manufacturing method of the battery 1 in this embodiment further includes a viscosity adjustment step S20 in which the paint before viscosity adjustment is diluted with a solvent to produce paint with a viscosity of 1 Pa·s or more and 7 Pa·s or less. According to this manufacturing method, the separator 6 can be formed by using paint with a viscosity of 7 Pa·s or higher.

[0057] The separator formation process S30 includes a first spraying step S31 in which paint is sprayed onto the positive electrode body 5 to form a first coating layer formed by the paint, a first drying step S32 in which the first coating layer is dried to form a first separator layer, a second spraying step S33 in which paint is sprayed onto the first separator layer to form a second coating layer formed by the paint, and a second drying step S34 in which the second coating layer is dried to form a second separator layer.

[0058] In the case of separator formation by a single spray application, even if the paint is applied evenly, minute areas may occur in the separator after drying where the paint is not sufficiently thick. This is likely to occur when the amount of paint applied is small in order to form a thin separator. According to this embodiment, the first separator layer formed by the first spraying step S31 and the first drying step S32 is covered with paint in the second spraying step S33, so that minute irregularities in the first separator layer are filled in by the second coating layer. Therefore, the total film thickness of the first separator layer and the second separator layer laminated after the second drying step S34 becomes more uniform. Thus, the separator 6 can be formed more uniformly.

[0059] The coating is a varnish containing a polyimide resin and N-methyl-2-pyrrolidone. This manufacturing method allows for the use of a coating suitable for achieving the above-mentioned effects.

[0060] In the manufacturing method of the battery 1 of this embodiment, a sheet body having a positive electrode active material layer 51 containing an active material is punched out on a current collector sheet 50 to form a positive electrode body 5. In this case, the positive electrode body 5 is formed such that the current collector sheet 50 is exposed at the end face when the sheet body is punched out, and in the separator formation step S30, a thin and reliable coating can be applied to the end face of the positive electrode body 5. As a result, a separator 6 can be formed on the end face of the positive electrode body 5, and internal short circuits in the battery 1 can be suppressed.

[0061] In this configuration, where separators are formed on both sides of the positive electrode, if the paint material for the separator is applied using the doctor blade method, the paint must be applied to both sides of the positive electrode separately. In this case, when applying the paint to the second main surface of the positive electrode during the second application, the paint may spread to the first main surface of the positive electrode, and the solvent in the spreading paint may dissolve the separator formed on the first main surface of the positive electrode during the first application, potentially causing the micropores of the separator to disappear.

[0062] In this embodiment, during the separator formation step S30, paint is sprayed onto the first main surface 5c and the second main surface 5d of the positive electrode body 5. This manufacturing method allows for a reduction in the amount of paint applied per application by spraying, thus reducing the amount of solvent contained in the paint per application and preventing the applied paint from dissolving the underlying separator. As a result, even when paint is applied to both sides of the positive electrode body 5, defects in the formation of the separator 6 are less likely to occur. Therefore, this method is suitable for forming separators 6 on both sides of the positive electrode body 5.

[0063] Furthermore, in this embodiment, paint is also applied to the end face of the positive electrode 5 in the separator formation step S30. According to this manufacturing method, by spraying paint toward the first main surface 5c or the second main surface 5d of the positive electrode 5, the paint is also applied to the end face of the positive electrode 5 by wrapping around. Therefore, a separator 6 can be formed on the end face of the positive electrode 5 without adding a step of spraying paint toward the end face of the positive electrode 5.

[0064] In the above embodiment, the separator 6 is formed with both ends of the positive electrode 5 supported by the current collector sheet 50, but the configuration is not limited to this. For example, the separator 6 may be formed on the positive electrode 5 which has been completely punched out from the current collector sheet 50. In this case, it is preferable because there is no cut surface (unformed portion 5e) where the positive electrode current collector 30 is exposed, which occurs when the positive electrode 5 is cut from the current collector sheet 50 after the separator formation step S30.

[0065] In the above embodiment, in the positive electrode body formation step S10, punched-out portions are formed by punching out the current collector sheet 50 on which the positive electrode active material layer 51 is formed. However, if the positive electrode body is rectangular in shape, for example, the positive electrode body may be manufactured by cutting the current collector sheet 50 using a cutter such as a slitter instead of punching out.

[0066] In the above embodiment, the separator 6 is formed on the first main surface 5c of the positive electrode body 5, and then on the second main surface 5d of the positive electrode body 5, but the embodiment is not limited to this. For example, the separator 6 may be formed on the second main surface 5d during the process of forming the separator 6 on the first main surface 5c (for example, immediately before the second spraying step).

[0067] In the above embodiment, the separator 6 is formed on each main surface of the positive electrode 5 through multiple drying steps, but the configuration is not limited to this. That is, the separator 6 may be formed through one spraying step and drying step on each main surface of the positive electrode 5. Alternatively, the spraying step on both main surfaces of the positive electrode 5 may be performed continuously by circulating a sprayer that sprays paint around the positive electrode 5.

[0068] [Second Embodiment] Next, a second embodiment will be described. The second embodiment differs from the first embodiment in that the positive electrode body 105 is formed in a pellet shape. Other than what is described below, the configuration is the same as that of the first embodiment.

[0069] Figure 12 is a cross-sectional view of a battery according to the second embodiment, and corresponds to Figure 2. Battery 101 is an example of an electrochemical cell. As shown in Figure 12, battery 101 comprises an outer casing 10, a positive electrode 105, a negative electrode 103, and a separator 106 housed within the outer casing 10, and an electrolyte 108 filled within the outer casing 10. The outer casing 10 has the same configuration as in the first embodiment.

[0070] The positive electrode body 105 and the negative electrode body 103 are arranged facing each other via a separator 106. The positive electrode body 105 comprises a pellet-shaped positive electrode mixture 130 and a positive electrode current collector 131 connected to the inner surface of the positive electrode can 11. The positive electrode mixture 130 is formed in a flat cylindrical shape. The positive electrode mixture 130 is electrically connected to the positive electrode can 11 via the positive electrode current collector 131. The negative electrode body 103 comprises a pellet-shaped negative electrode mixture 120, a negative electrode current collector 121 connected to the inner surface of the negative electrode can 12, and a lithium foil 122. The negative electrode mixture 120 is formed in a flat cylindrical shape. The negative electrode mixture 120 is electrically connected to the negative electrode can 12 via the negative electrode current collector 121. Alternatively, the positive electrode mixture 130 may be directly connected to the positive electrode can 11 to give the positive electrode can 11 the function of a current collector. Alternatively, the negative electrode mixture 120 may be directly connected to the negative electrode container 12 to give the negative electrode container 12 the function of a current collector.

[0071] In the positive electrode mixture 130, the type of positive electrode active material is not particularly limited, but it is preferable to use one containing lithium manganese oxide as the positive electrode active material. The content of the positive electrode active material in the positive electrode mixture 130 is determined considering the discharge capacity required for the battery 101, and can be in the range of 50 to 95% by mass. If the content of the positive electrode active material is above the lower limit of the above preferred range, a sufficient discharge capacity is easily obtained, and if it is below the preferred upper limit, the positive electrode mixture 130 is easy to mold.

[0072] The positive electrode mixture 130 may contain a conductive additive (hereinafter, the conductive additive used in the positive electrode mixture 130 may be referred to as the "positive electrode conductive additive"). Examples of positive electrode conductive additives include carbonaceous materials such as furnace black, Ketjen black, acetylene black, and graphite. One of the above positive electrode conductive additives may be used alone, or two or more may be used in combination.

[0073] The positive electrode mixture 130 contains a binder. Hereinafter, the binder used in the positive electrode mixture 130 will be referred to as the "positive electrode binder." As the positive electrode binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyacrylic acid (PA), carboxymethylcellulose (CMC), polyvinyl alcohol (PVA), etc. may be selected. Furthermore, one of the above types of positive electrode binder may be used alone, or two or more types may be used in combination. The content of the positive electrode binder in the positive electrode mixture 130 can be, for example, 1 to 20% by mass. As the positive electrode current collector 131, a conductive resin adhesive with carbon as a conductive filler can be used.

[0074] Furthermore, in this embodiment, in addition to the lithium manganese oxide described above, the positive electrode active material may also contain other positive electrode active materials. For example, it may contain one or more other oxides such as molybdenum oxide, lithium iron phosphate compounds, lithium cobalt oxide, lithium nickel oxide, vanadium oxide, etc.

[0075] In the negative electrode mixture 120, the type of negative electrode active material is not particularly limited, but for example, it is preferable to include silicon oxide as the negative electrode active material. Furthermore, in the negative electrode mixture 120, it is preferable that the negative electrode active material consists of silicon oxide represented by SiOx (0≦x<2).

[0076] Furthermore, the negative electrode mixture 120 may contain other negative electrode active materials in addition to the above-mentioned SiOx (0≦x<2) as the negative electrode active material, such as Si or C. When granular SiOx (0≦x<2) is used as the negative electrode active material, the particle size (D50) is not particularly limited, and for example, a range of 0.1 to 30 μm can be selected, or a range of 1 to 10 μm can be selected. If the particle size (D50) of SiOx is below the lower limit of the above range, the reactivity may increase when the battery 101 is stored and used in a harsh high-temperature and high-humidity environment, or when reflow processing is performed, which may impair the battery characteristics. If it exceeds the upper limit, the discharge rate may decrease.

[0077] The content of the negative electrode active material, i.e., SiOx (0 ≤ x < 2), in the negative electrode mixture 120 is determined considering the required discharge capacity of the battery 101, and a range of 50% by mass or more can be selected, and a range of 60 to 80% by mass can be selected. If the content of the negative electrode active material consisting of the above elements in the negative electrode mixture 120 is above the lower limit of the above range, a sufficient discharge capacity is easily obtained, and if it is below the upper limit, the negative electrode mixture 120 is easy to mold.

[0078] The negative electrode mixture 120 may contain a conductive additive (hereinafter, the conductive additive used in the negative electrode mixture 120 may be referred to as the "negative electrode conductive additive"). The negative electrode conductive additive is the same as the positive electrode conductive additive.

[0079] The negative electrode mixture 120 contains a binder. Hereinafter, the binder used in the negative electrode mixture 120 will be referred to as the "negative electrode binder." As the negative electrode binder, polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyacrylic acid (PA), carboxymethylcellulose (CMC), polyimide (PI), polyamide-imide (PAI), etc., can be selected.

[0080] Furthermore, the negative electrode binder may be one of the above types used alone, or two or more types may be used in combination. When polyacrylic acid is used as the negative electrode binder, the polyacrylic acid can be pre-adjusted to a pH of 3 to 10. For pH adjustment in this case, for example, alkali metal hydroxides such as lithium hydroxide or alkaline earth metal hydroxides such as magnesium hydroxide can be used. The content of the negative electrode binder in the negative electrode mixture 120 is, for example, in the range of 1 to 20% by mass.

[0081] The separator 106 is interposed between the positive electrode body 105 and the negative electrode body 103. The separator 106 is positioned between the positive electrode mixture 130 and the lithium foil 122. The separator 106 extends over the entire surface of one end face 130a of the positive electrode mixture 130 that faces the negative electrode body 103. The external shape of the separator 106 substantially matches the external shape of one end face 130a of the positive electrode mixture 130. The film thickness of the separator 106 on one end face 130a of the positive electrode mixture 130 is 5 μm or more and 15 μm or less. The separator 106 integrates with the positive electrode body 105 to form the positive electrode structure 104. The manufacturing method of the positive electrode structure 104 will be described later.

[0082] The electrolyte 108 is impregnated into the positive electrode 105, negative electrode 103, and separator 106 within the outer casing 10. The electrolyte 108 is typically prepared by dissolving a support salt in a non-aqueous solvent. In this embodiment, the non-aqueous solvent of the electrolyte 108 is primarily composed of tetraglyme (TEG), with diethoxyethane (DEE) as a secondary solvent, and further containing ethylene carbonate (EC) and vinylene carbonate (VC) as additives. The non-aqueous solvent is usually determined considering the heat resistance and viscosity required for the electrolyte 108. In addition to tetraglyme, triglyme, pentaglyme, diglyme, etc., can be used as the primary solvent for the glyme-based solvent.

[0083] The electrolyte 108 in this embodiment uses a non-aqueous solvent containing ethylene carbonate (EC), tetraglyme (TEG), and diethoxyethane (DEE). By adopting this configuration, DEE and TEG solvate the Li ions that form the supporting salt. At this time, since DEE has a higher donor number than TEG, DEE selectively solvates with the Li ions. In this way, DEE and TEG solvate the Li ions that form the supporting salt, protecting the Li ions. As a result, even if moisture enters the inside of the non-aqueous electrolyte secondary battery in a high-temperature, high-humidity environment, the reaction between the moisture and Li can be prevented, thereby suppressing a decrease in discharge capacity and improving storage characteristics.

[0084] The ratio of each solvent in the non-aqueous solvent in electrolyte 108 is not particularly limited, but for example, a range of TEG: 30% to 48.5% by mass, DEE: 30% to 48.5% by mass, EC: 0.5% to 10% by mass, and VC: 2% to 13% by mass (total 100%) can be selected. When the ratios of TEG, DEE, and EC contained in the non-aqueous solvent are within the above range, the effect described above, in which the Li ions are protected by the solvation of DEE with Li ions, is obtained.

[0085] Even within the ranges described above, the VC content is preferably in the range of 2.5% to 10% by mass, and more preferably in the range of 5.0% to 7.5% by mass. The upper limit for the TEG and DEE content is preferably 48.25% by mass or less, and more preferably 48% by mass or less. When the VC content is in the range of 2% to 13% by mass, even when heated during reflow soldering, the change in thickness of the casing 10, which consists of the positive electrode can 11 and the negative electrode can 12, is small, and the increase in internal resistance can also be reduced. Furthermore, when the VC content is in the range of 2.5% to 10.0% by mass, even when heated during reflow soldering, the change in thickness of the casing 10 can be reduced even further, and the increase in internal resistance can also be reduced even further. Even within these ranges, the VC content is most preferably in the range of 5.0% to 7.5% by mass.

[0086] Examples of supporting salts include lithium salts such as lithium organic acids (LiCH3SO3, LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiC(CF3SO2)3, LiN(CF3SO3)2, LiN(FSO2)2, and lithium inorganic acids (LiPF6, LiBF4, LiB(C6H5)4, LiCl, LiBr). Among these, it is preferable to use a lithium salt that is a lithium ion conductive compound as the supporting salt, and it is more preferable to use LiN(CF3SO2)2, LiN(FSO2)2, or LiBF4. In particular, LiN(CF3SO2)2 is preferred as a supporting salt from the viewpoint of low heat resistance and reactivity with moisture, and being able to fully exhibit storage characteristics. The supporting salt may be one of the above types used alone, or two or more types may be used in combination.

[0087] The amount of supporting salt in the electrolyte 108 can be determined by considering the type of supporting salt, etc. For example, the amount of supporting salt in the electrolyte 108 is preferably 0.1 to 3.5 mol / L, more preferably 0.5 to 3 mol / L, and particularly preferably 1 to 2.5 mol / L. If the concentration of supporting salt in the electrolyte 108 is too high or too low, a decrease in conductivity may occur, which may adversely affect the battery characteristics.

[0088] Below, as part of the manufacturing method for the battery 101 of the second embodiment, an example of a manufacturing method for the positive electrode structure 104 will be described. The manufacturing method for the positive electrode structure 104 of this embodiment comprises a viscosity adjustment step and a separator formation step. The viscosity adjustment step is the same as in the first embodiment.

[0089] Following the viscosity adjustment step, a separator formation step is performed. In the separator formation step, the paint generated in the viscosity adjustment step is sprayed onto the outer surface of the pellet-shaped positive electrode body 105 and dried to form a separator 106. In this case, the paint is sprayed toward the surface of the positive electrode body 105 that faces the negative electrode body 103. The separator formation step in this embodiment comprises a spraying step and a drying step.

[0090] Figure 13 shows the process of forming a separator on the positive electrode body in the manufacturing method of the positive electrode structure of the second embodiment. As shown in Figure 13, in the spraying step, paint is sprayed onto the positive electrode body 105 to form a coating layer 161 made of paint. The coating layer 161 is formed to cover the entire flat end face 130a on the negative electrode body 103 side of the positive electrode mixture 130. The coating layer 161 may also be formed from the end face 130a to the outer surface of the positive electrode mixture 130 by the wrapping of the sprayed paint. Next, in the drying step, the separator 106 is formed by drying the coating layer 161. The drying of the coating layer 161 may be done by natural drying or by heat drying. By drying the coating layer 161, a separator 106 made of polymer resin contained in the paint is formed. In this way, the separator 106 of this embodiment is formed in a single spraying step.

[0091] This embodiment provides the same effects as the first embodiment. In addition, this embodiment provides the following effects. In this embodiment, a separator 106 is formed on a pellet-shaped positive electrode mixture 130. When forming a separator by dropping paint onto a pellet-shaped positive electrode, there is a limit to how small the droplet size can be, so the amount of paint dropped is relatively large. In this case, the solvent contained in the dropped paint may seep into the positive electrode, causing it to swell. According to this embodiment, it is possible to apply a thin layer of paint to the positive electrode 105, so the amount of solvent contained in the paint applied to the positive electrode 105 can also be reduced. As a result, swelling of the positive electrode mixture 130 by applying paint to the pellet-shaped positive electrode mixture 130 can be suppressed, and consequently, the occurrence of manufacturing defects in the battery 101 can be suppressed.

[0092] It should be noted that the present invention is not limited to the embodiments described above with reference to the drawings, and various modifications are conceivable within its technical scope. For example, in the above embodiment, a lithium-ion secondary battery was used as an example of an electrochemical cell, but the above configuration may be applied to other types of secondary batteries, electric double-layer capacitors, primary batteries, etc. When applying the above configuration to an electric double-layer capacitor, although the electric double-layer capacitor has a pair of electrodes that do not have a distinction between positive and negative in terms of function, one electrode can be considered as the negative electrode and the other electrode as the positive electrode.

[0093] In the above embodiment, a separator is formed on the outer surface of the positive electrode body, but this is not limited to this. That is, a separator may be formed on the outer surface of the negative electrode body.

[0094] Furthermore, it is possible to replace the components in the above-described embodiments with well-known components as appropriate, without departing from the spirit of the present invention. [Explanation of Symbols]

[0095] 1,101…Battery (electrochemical cell) 3,103…Negative electrode 5,105…Positive electrode (one electrode) 5c…First main surface 5d…Second main surface 6,106…Separator S20…Viscosity adjustment process S30…Separator formation process S31…First spraying process S32…First drying process S33…Second spraying process S34…Second drying process

Claims

1. A positive electrode body containing positive electrode active material, A negative electrode body containing a negative electrode active material, A separator interposed between the positive electrode and the negative electrode, A method for manufacturing an electrochemical cell comprising: The method includes a separator forming step in which a paint with a viscosity of 1 Pa·s or more and 7 Pa·s or less is sprayed onto the outer surface of one of the electrode bodies, the positive electrode and the negative electrode, and dried to form the separator. A method for manufacturing electrochemical cells.

2. The thickness of the separator is set to be 5 μm or more and 15 μm or less. A method for producing an electrochemical cell according to claim 1.

3. The method further includes a viscosity adjustment step of diluting the paint before viscosity adjustment with a solvent to produce the paint with a viscosity of 1 Pa·s or more and 7 Pa·s or less. A method for producing an electrochemical cell according to claim 1.

4. The separator formation step is as follows: A first spraying step involves spraying the paint onto one of the electrodes to form a first coating layer made of the paint, A first drying step in which the first coating layer is dried to form a first separator layer, A second spraying step involves spraying the paint onto the first separator layer to form a second coating layer made of the paint, A second drying step in which the second coating layer is dried to form a second separator layer, Equipped with, A method for producing an electrochemical cell according to claim 1.

5. The aforementioned coating is a varnish containing a polyimide resin and N-methyl-2-pyrrolidone. A method for producing an electrochemical cell according to any one of claims 1 to 4.

6. One of the electrode bodies is formed by cutting a sheet body having an electrode layer containing an active material on a sheet-shaped current collector. A method for producing an electrochemical cell according to any one of claims 1 to 4.

7. In the separator forming step, the paint is sprayed onto the first main surface and the second main surface of the one electrode body, respectively. A method for producing an electrochemical cell according to claim 6.

8. In the separator forming step, the paint is also applied to the end face of one of the electrode bodies. A method for producing an electrochemical cell according to claim 7.

9. The electrochemical cell further comprises a battery container housing the positive electrode, the negative electrode, and the separator. The aforementioned electrode body is in the form of a pellet containing a binder and is connected to the inside of the battery can. In the separator forming step, the paint is applied by spray spraying to the opposing surfaces of the positive electrode and the negative electrode of one electrode body that face the other electrode body. A method for producing an electrochemical cell according to any one of claims 1 to 4.

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