JP2018018680A - Method for manufacturing electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an electrode capable of suppressing a swelling of an edge of a coating part and generation of density unevenness in the coating part.SOLUTION: A die head 31 comprises a first applying part 32 including a first discharge port 32c arranged so as to face a portion serving as a first edge 16a of a coating part 16, a second applying part 33 including a second discharge port 33c arranged so as to face a portion serving as a second edge 16b of the coating part 16, and a third applying part 34 including a third discharge port 34c arranged so as to face a portion serving as a central part 16c of the coating part 16. The first applying part 32 and the second applying part 33 are supplied with a low solid content active material mixture, and the third applying part 34 is supplied with a high solid content active material mixture. The first discharge port 32c and the second discharge port 33c form the first edge 16a and the second edge 16b of the coating part 16 by discharging the low solid content active material mixture onto a strip-like collector 15. The third discharge port 34c forms the central part 16c of the coating part 16 by discharging the high solid content active material mixture onto the strip-like collector 15.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an electrode manufacturing method.

  2. Description of the Related Art Conventionally, a method for manufacturing an electrode used in a power storage device is a coating process in which an active material mixture containing an active material, a solvent, a thickener, a conductive assistant, a binder, and the like is applied on the surface of a metal foil made of aluminum or the like And a drying step of drying the coated part of the active material mixture. Furthermore, the manufacturing method of an electrode includes the rolling process which presses a coating part as needed, and the punching process which punches a metal foil and a coating part in the shape of an electrode. By the way, after drying a coating part by a drying process, the problem that the edge part of a coating part will rise may arise. When the edge of the coating part is raised, there is a possibility that wrinkles or foil tears may be generated due to the raised part of the edge when winding the metal foil in a reel shape.

  For example, in Patent Document 1, when applying a coating solution for forming a coating portion on a glass substrate, only the outer peripheral edge portion of the coating portion is applied as a technique for suppressing the rising of the edge portion of the coating portion. The viscosity of the liquid is relatively low. By lowering the viscosity of the outer peripheral edge of the coating part, the rise of the edge of the coating part due to surface tension can be suppressed.

JP 2001-351845 A

  However, even if the viscosity of the outer peripheral edge of the coated part is lowered, the edge of the coated part has a specific surface area (unit mass or surface area per unit volume) as compared to the part other than the edge of the coated part. Large and the evaporation rate of the solvent in the coating solution is fast. Then, convection occurs during the drying of the coated part, and a migration phenomenon occurs in which solid contents such as a thickener and a binder move to the edge in the coated part. Therefore, density unevenness occurs in the coated part obtained after drying, and if an electrode manufactured from a metal foil with density unevenness in the coated part is used, battery performance may be reduced.

  The present invention has been made paying attention to such problems existing in the prior art, and its purpose is to suppress the bulge of the edge of the coating part and to prevent density unevenness of the coating part. It is providing the manufacturing method of the electrode which can suppress generation | occurrence | production.

  An electrode manufacturing method for solving the above-described problem is an electrode manufacturing method including an active material layer containing an active material on the surface of a current collector, and includes an active material mixture containing a solvent, the active material, and a solid content. An agent is applied on a long current collector, and includes a coating step for forming a coating portion to be a precursor of the active material layer, the coating step being an edge of the coating portion, The amount of the solid content in the edge portion of the long current collector extending in the longitudinal direction is less than the amount of the solid content in the coating portion excluding the edge portion. It is characterized by applying a material mixture.

  According to this, in the edge part of the coating part, the edge part formed in a state extending in the longitudinal direction of the current collector has a larger amount of the solvent than the part excluding the edge part, so that the migration phenomenon occurs. It is hard to generate | occur | produce and it is hard to produce the movement to this edge part of solid content in a coating part. Therefore, the rise of the edge part formed in the state extended in the longitudinal direction of a collector among the edge parts of a coating part can be suppressed, and generation | occurrence | production of the density | concentration nonuniformity of a coating part can be suppressed.

  In the electrode manufacturing method, the solid content in the edge portion may be 95% or less with respect to the solid content in the coating portion excluding the edge portion. When the solid content is more than 95%, the viscosity of the active material mixture is high. Therefore, in the coating process of applying the active material mixture on the long current collector, The thickness may be non-uniform. Therefore, by setting the amount of solid content to 95% or less, the thickness of the coating portion layer is unlikely to be uneven.

  In the electrode manufacturing method, the solid content in the edge portion is 50% or more and 90% or less with respect to the solid content in the portion excluding the edge portion in the coating portion. Also good. When the solid content is less than 50%, the active material mixture has a low viscosity. Therefore, in the coating step of applying the active material mixture onto the long current collector, the active material mixture is applied. At the same time, there is a possibility that the active material mixture is not held on the surface of the current collector and hangs down due to gravity, making it impossible to form a layer. On the contrary, when the amount of solid content is more than 90%, there is a possibility that the concentration unevenness of the active material mixture may occur in the coating part in the coating process. Therefore, by setting the amount of solid content to 50% or more and 90% or less, density unevenness can be suppressed while forming the layer of the coating part in the coating process.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the electrode which can suppress the swelling of the edge part of a coating part and can suppress the density | concentration nonuniformity of a coating part can be provided.

The perspective view of the electrode manufactured by the manufacturing method of an embodiment. Schematic of the manufacturing method of the electrode which concerns on embodiment. The top view which shows the die head used for the manufacturing method of embodiment. FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. Sectional drawing of the coating part after the drying which concerns on embodiment. Sectional drawing of the coating part after drying which shows the comparative example with embodiment.

Hereinafter, an embodiment in which a method for manufacturing an electrode is embodied in a method for manufacturing an electrode for a power storage device will be described with reference to FIGS.
Although not shown, the secondary battery as a power storage device using the electrode manufactured by the manufacturing method of this embodiment is a rectangular battery having a rectangular external appearance, and is a lithium ion secondary battery. This secondary battery includes an electrode assembly in a case. The electrode assembly includes a plurality of positive electrodes and a plurality of negative electrodes. The electrode assembly is configured by alternately laminating positive electrodes and negative electrodes in a state where they are insulated by a separator.

  As shown in FIG. 1, an electrode 10 as a power storage device electrode used in the secondary battery includes a metal foil 11 as a current collector and an active material layer 12 present on the surface (both sides) of the metal foil 11. Is provided. The electrode 10 has an uncoated portion 13 where the metal foil 11 is exposed along one side thereof. The electrode 10 has a current collecting tab 14 having a shape protruding from a part of the uncoated portion 13. The active material layer 12 has an edge portion 12a on the uncoated portion 13 side and an edge portion 12b located on the opposite side of the edge portion 12a on the uncoated portion 13 side.

Next, the manufacturing process of the electrode 10 will be described.
As shown in FIG. 2, the manufacturing process includes a coating process. In the coating step, an active material mixture is applied onto the belt-like current collector 15 while conveying the belt-like current collector 15 as a long current collector, and a coating part that becomes a precursor of the active material layer 12 16 is a step of forming 16. Further, the manufacturing process includes a drying process for drying the coating part 16. 2 shows a state in which the coating portion 16 has already been formed on one side (lower surface) of the strip-shaped current collector 15, and the active material mixture has been applied to the remaining one side (upper surface). .

  The transport device 21 that transports the strip-shaped current collector 15 includes a supply reel 22 around which the strip-shaped current collector 15 is wound, a plurality of guide rolls 23, and a take-up reel 24 that winds the strip-shaped current collector 15. Prepare. The strip-shaped current collector 15 is supplied from the supply reel 22, is wound around the take-up reel 24, is transported in the transport direction, is transported toward the coating device 30 via the guide roll 23.

  The coating device 30 that performs the coating process includes a die head 31, a back roller 35 that faces the die head 31 and the belt-like current collector 15 therebetween, and a kneading device (not shown) that kneads the active material mixture. .

  As shown in FIG. 3, the die head 31 includes a first application unit 32, a second application unit 33, and a third application unit 34. The first application part 32, the third application part 34, and the second application part 33 are arranged side by side along the short direction of the strip-shaped current collector 15. The first application part 32 is disposed opposite to a part that becomes the first edge part 16 a in a state extending in the longitudinal direction of the belt-like current collector 15 in the region that becomes the coating part 16 of the belt-like current collector 15. The second application portion 33 is disposed opposite to a portion that becomes the second edge portion 16 b in a state extending in the longitudinal direction of the strip-shaped current collector 15 in the region that becomes the coating portion 16 of the strip-shaped current collector 15. The second edge portion 16b is located on the opposite side of the first edge portion 16a. The 3rd application part 34 is arranged opposite to the part used as the central part 16c which is the part except the 1st and 2nd edge parts 16a and 16b in the field used as application part 16 of beltlike current collection object 15. .

  The die head 31 forms the coating portion 16 on the strip-shaped current collector 15 by applying an active material mixture from the respective coating portions 32, 33, and 34 to the region to be the coating portion 16 of the strip-shaped current collector 15. To do. The first application part 32 forms the first edge 16 a of the application part 16 on the strip-shaped current collector 15. The second application part 33 forms the second edge 16 b of the application part 16 on the strip-shaped current collector 15. The third application part 34 forms the central part 16 c of the coating part 16 on the strip-shaped current collector 15.

  The kneading apparatus is an apparatus that generates an active material mixture to be supplied to the first application unit 32, the second application unit 33, and the third application unit 34. The kneading apparatus kneads and disperses an active material, a conductive additive as a solid content, a binder, and a solvent (solvent). In the kneading apparatus, two types of active material mixtures having different solid contents are generated. One active material mixture has a lower solid content than the other active material mixture. As the amount of solid content, the amount of solid content of one active material mixture is preferably 95% or less with respect to the amount of solid content of the other active material mixture, and the solid content of the other active material mixture More preferably, the solid content of one active material mixture is 50% or more and 90% or less with respect to the amount of minutes.

  In the coating step of applying the active material mixture to the strip-shaped current collector 15, simultaneously with the application of the active material mixture, the active material mixture is not held on the surface of the strip-shaped current collector 15 and droops due to gravity. In order to suppress this, the solid content in one active material mixture is preferably set to 50% or more with respect to the solid content in the other active material mixture. In addition, in the coating process, in order to suppress the occurrence of uneven concentration of the active material mixture in the obtained coating part 16, the amount of the solid content of one active material mixture is the solid content of the other active material mixture. It is preferable to make it 90% or less with respect to the amount of minutes. The active material mixture with a small amount of solid content (hereinafter referred to as “low solid content”) is supplied to the first coating unit 32 and the second coating unit 33 and has a large amount of solid content (hereinafter referred to as high solid content, The active material mixture is supplied to the third application unit 34.

  Examples of the positive electrode active material for the positive electrode include composite oxide, metallic lithium, sulfur and the like. The composite oxide includes at least one of manganese, nickel, cobalt, and aluminum and lithium.

  The negative electrode active material for the negative electrode includes, for example, carbon such as graphite, highly oriented graphite, mesocarbon microbeads, hard carbon and soft carbon, alkali metals such as lithium and sodium, metal compounds, SiOx (0.5 ≦ x ≦ 1.5) and the like, and boron-added carbon.

The conductive auxiliary agent is a carbon-based substance containing carbon (C), and examples thereof include carbon black, graphite, acetylene black, and ketjen black.
Examples of the binder include thermoplastic resins such as polyimide amide and polyimide, and polymer resins having an imide bond in the main chain.

Examples of the solvent (solvent) include organic solvents such as NMP (N-methylpyrrolidone), methanol, and methyl isobutyl ketone, and water.
The first application unit 32 includes a first manifold 32a, a first supply nozzle 32b that connects the first manifold 32a and the kneading device, and a first edge 16a of the application unit 16 in a region to be the application unit 16. And a first discharge port 32c that discharges the active material mixture. The low solid content active material mixture generated by the kneading apparatus is supplied to the first manifold 32a via the first supply nozzle 32b. The supplied low solid content active material mixture temporarily accumulates in the first manifold 32a and is pushed out from the first manifold 32a to the first discharge port 32c. The first application part 32 has a low solid content active material mixture in a part that becomes the first edge 16a of the coating part 16 in a region that becomes the coating part 16 of the strip-shaped current collector 15 from the first discharge port 32c. The agent is discharged to form the first edge portion 16 a of the coating portion 16 on the strip-shaped current collector 15.

  The second application unit 33 includes a second manifold 33a, a second supply nozzle 33b that connects the second manifold 33a and the kneading device, and a second edge 16b of the application unit 16 in the region to be the application unit 16. And a second discharge port 33c that discharges the active material mixture. The low solid content active material mixture generated by the kneading apparatus is supplied to the second manifold 33a via the second supply nozzle 33b. The supplied low solid content active material mixture temporarily accumulates in the second manifold 33a and is pushed out from the second manifold 33a to the second discharge port 33c. The second application part 33 has a low solid content active material mixture in a part that becomes the second edge 16b of the coating part 16 in the area that becomes the coating part 16 of the strip-shaped current collector 15 from the second discharge port 33c. The second edge portion 16b of the coating portion 16 is formed on the strip-shaped current collector 15 by discharging the agent.

  The third application part 34 is provided in a portion that becomes the central part 16c of the coating part 16 in a region that becomes the coating part 16 and a third supply nozzle 34b that connects the third manifold 34a, the third manifold 34a and the kneading device. And a third discharge port 34c that is disposed so as to discharge the active material mixture. The tip of the third discharge port 34c is disposed so as to contact the tip of the first discharge port 32c and the tip of the second discharge port 33c. The high solid content active material mixture generated by the kneading apparatus is supplied to the third manifold 34a via the third supply nozzle 34b. The supplied high solid content active material mixture temporarily accumulates in the third manifold 34a and is pushed out from the third manifold 34a to the third discharge port 34c. The 3rd application part 34 discharges the active material mixture of high solid content to the part used as the center part 16c of the coating part 16 in the area | region used as the coating part 16 of the strip | belt-shaped collector 15 from the 3rd discharge outlet 34c. Then, the central portion 16 c of the coating portion 16 is formed on the strip-shaped current collector 15.

  The strip-shaped current collector 15 that has undergone the coating process includes a coating portion 16 and an exposed portion 17 where the coating portion 16 is not formed and the metal foil 11 is exposed. The coating part 16 and the exposed part 17 are arranged in the short direction of the strip-shaped current collector 15 and are continuously formed in the longitudinal direction. The first and second edge portions 16a and 16b of the coating portion 16 have a smaller amount of solids and a larger amount of solvent than the central portion 16c. The widths of the first and second edge portions 16 a and 16 b are not particularly limited, but are preferably 0.5 to 1.5% with respect to the entire width of the coating portion 16. The exposed portion 17 includes a first exposed portion 17a on the first edge portion 16a side of the coating portion 16 and a second exposed portion 17b on the second edge portion 16b side. An electrode material 18 is formed from the strip-shaped current collector 15, the coating portion 16, and the exposed portion 17.

  The electrode material 18 is conveyed toward the drying device 26 through the guide roll 23. As shown in FIG. 4, the coating portion 16 of the electrode material 18 before passing through the drying process has a gentle surface shape in which the first and second edge portions 16a and 16b do not rise compared to the central portion 16c. Have.

  After passing through the drying process, as shown in FIG. 5, the electrode material 18 has a thickness such that the first edge portion 16a and the second edge portion 16b face the first exposed portion 17a and the second exposed portion 17b, respectively. Has a reduced taper shape.

  For example, when the coating process is performed with the solid content of the first and second edge portions 16a and 16b equal to the solid content of the central portion 16c, the electrode material 18 that has undergone the drying process is shown in FIG. As shown in FIG. 6, the first and second edges 16a and 16b are raised. When the amount of solid content of the first and second edge portions 16a and 16b is equal to the amount of solid content of the central portion 16c, the amount of the solvent contained in the first and second edge portions 16a and 16b and the central portion 16c. The amount is equal. In this case, when the coating portion 16 is dried, the first and second edge portions 16a and 16b have a larger specific surface area than the central portion 16c, and thus the solvent evaporation rate is high. Then, due to the migration phenomenon, solid contents such as the conductive assistant and the binder in the coating part 16 are easily moved to the first and second edge parts 16a and 16b. As a result, when the solid content of the first and second edge portions 16a and 16b is equal to the solid content of the central portion 16c, the first and second edge portions 16a and 16b rise. Will occur.

  As shown in FIG. 2, the electrode material 18 dried by the coating unit 16 through the drying process is taken up by the take-up reel 24 through the guide roll 23. The wound electrode material 18 is then subjected to a rolling process (not shown). In the rolling process, the coating material 16 is rolled by passing the electrode material 18 between a pair of rolling rolls.

  The electrode material 18 that has undergone the rolling process undergoes a punching process (not shown). As shown in FIG. 3, the electrode material 18 is punched along a two-dot chain line 19 by a punching process. Then, the uncoated part 13 and the current collection tab 14 are formed from the 1st exposed part 17a. The active material layer 12 of the electrode 10 is formed by punching the coating portion 16 of the electrode material 18. An edge portion 12a on the uncoated portion 13 side of the active material layer 12 is formed from the first edge portion 16a of the coated portion 16, and an edge portion 12b that is opposite to the edge portion 12a on the uncoated portion 13 side is the first edge portion 12a. 2 is formed from a part of the edge 16b.

According to the embodiment described in detail above, the following excellent effects are obtained.
(1) The first and second application portions 32 and 33 of the die head 31 apply a low solid content active material mixture to the portions to be the first and second edge portions 16a and 16b of the coating portion 16, First and second edge portions 16 a and 16 b of the coating portion 16 are formed on the strip-shaped current collector 15. Further, the third application part 34 of the die head 31 applies an active material mixture having a high solid content to a part that becomes the central part 16 c of the coating part 16, and the central part of the coating part 16 on the strip-shaped current collector 15. 16c is formed. Since the first and second edge portions 16a and 16b have a larger amount of solvent than the central portion 16c, the migration phenomenon hardly occurs during the drying of the coating portion 16, and the solid content in the coating portion 16 is the first. It is difficult to move to the first and second edges 16a and 16b. As a result, in the electrode material 18 after passing through the drying step, the swell of the first and second edge portions 16a and 16b can be suppressed, and each edge portion 12a and 12b of the active material layer 12 formed from the coating portion 16 is suppressed. Can suppress the excitement. Therefore, when the electrode material 18 is taken up by the take-up reel 24, it is possible to suppress the occurrence of wrinkles and foil breakage of the electrode material 18 due to the swells of the edges 16a and 16b of the coating part 16. Furthermore, when the positive electrode and the negative electrode are alternately laminated with the separators interposed between the positive electrodes and the negative electrodes, it is possible to suppress breakage of the separator due to the rise of the active material layer 12.

Moreover, generation | occurrence | production of the density | concentration nonuniformity of the coating part 16 can be suppressed, and generation | occurrence | production of the density | concentration nonuniformity of the active material layer 12 formed from the coating part 16 can be suppressed.
(2) The tip of the third discharge port 34c is disposed so as to contact the tip of the first discharge port 32c and the tip of the second discharge port 33c. As a result, each active material mixture discharged from each discharge port 32c, 33c, 34c is applied to the strip-shaped current collector 15 in contact with each other. Therefore, in the coating part 16, the boundary part of the 1st edge part 16a and the center part 16c and the 2nd edge part 16b and the center part 16c can be made smooth.

  (3) In the low solid content active material mixture, the solid content was 95% or less of the solid content of the high solid content active material mixture. For this reason, the viscosity of the active material mixture with a low solid content does not become too high, and it is possible to suppress the layer thickness of the coating portion 16 from becoming uneven in the coating process.

  (4) In the low solid content active material mixture, the solid content was 50% or more and 90% or less of the solid content of the high solid content active material mixture. For this reason, the density unevenness of the coating part 16 can be suppressed while suppressing the layer of the coating part 16 from sagging in the coating process.

In addition, you may change said embodiment as follows.
○ The low solid content active material mixture applied from the first and second application portions 32 and 33 may be only the solvent contained in the high solid content active material mixture applied from the third application portion 34. . In this case, the process of manufacturing the active material mixture having a low solid content can be omitted.

  In the embodiment, the die head 31 includes first and second application units 32 and 33 that apply a low solid content active material mixture, and a third application unit 34 that applies a high solid content active material mixture. However, the second application unit 33 may not be provided, and only the first and third application units 32 and 34 may be provided. In this case, by punching out the second edge portion 16b of the coating portion 16 by the punching process, the electrode 10 having no swell is produced on each of the edge portions 12a and 12b of the active material layer 12.

  ○ Two kinds of active material mixtures having different solid contents may have the same viscosity. In this case, the discharge pressure when the active material mixture is discharged from the first and second application portions 32 and 33 and the third application portion 34 is equal, and the discharge pressure can be easily controlled.

  (Circle) the electrode material 18 may give vibrations, such as a mechanical vibration and an ultrasonic vibration, before passing through a drying process. In this case, the first edge portion 16a and the center portion 16c of the coating portion 16 and the boundary portion between the second edge portion 16b and the center portion 16c can be made gentler.

The power storage device may be another power storage device such as an electric double layer capacitor.
In the embodiment, the secondary battery is a lithium ion secondary battery, but is not limited to this, and may be another secondary battery such as nickel metal hydride.

Next, the technical idea that can be grasped from the above embodiment and other examples will be described below.
(1) A power storage device including a plurality of electrodes including an active material layer containing an active material on a surface of a current collector, the power storage device including the electrode according to any one of claims 1 to 3.

  (2) The power storage device is a secondary battery.

  DESCRIPTION OF SYMBOLS 10 ... Electrode, 11 ... Metal foil as a collector, 12 ... Active material layer, 15 ... Strip | belt-shaped collector as an elongate collector, 16 ... Coating part, 16a ... 1st edge part, 16b ... 2nd edge part, 16c ... Center part as a part except an edge part.

Claims (3)

An electrode manufacturing method comprising an active material layer containing an active material on the surface of a current collector,
An application step of applying a solvent, an active material mixture containing the active material and a solid content on a long current collector, and forming a coating portion to be a precursor of the active material layer,
In the coating step, the amount of the solid content in the edge portion of the coating portion that extends in the longitudinal direction of the elongated current collector is excluded from the edge portion in the coating portion. A method for producing an electrode, wherein the active material mixture is applied so as to be less than the amount of the solid content in the portion.   2. The electrode according to claim 1, wherein, in the coating portion, the amount of the solid content in the edge portion is 95% or less with respect to the amount of the solid content in a portion excluding the edge portion. Production method.   The amount of the solid content in the edge portion is 50% or more and 90% or less with respect to the solid content amount in a portion excluding the edge portion in the coating portion. Of manufacturing the electrode.

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