Electrode manufacturing method

Abstract

To provide an electrode manufacturing method that can suppress deterioration of an active material mixture while drying the active material mixture by suppressing absorption of moisture into the active material mixture when winding up a metal foil coated with the active material mixture that constitutes an electrode.SOLUTION: An electrode manufacturing method includes a primary drying step of drying an active material mixture coated on the surface of a metal foil in a drying furnace, and a winding step of winding up the metal foil coated with the active material mixture using a winding roll, and the winding step includes a secondary drying step of heating the end faces of the metal foil that has been wound into a cylindrical shape with exhaust from the drying furnace.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] This application relates to a method for manufacturing a battery electrode. [Background technology]

[0002] Patent Document 1 discloses a method including a primary drying step in which a metal foil coated with an active material mixture is placed in a drying oven to dry the active material mixture, and a secondary drying step in which the active material mixture is dried after the exit of the drying oven while the metal foil is being wound up by a winding roll. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-017158 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses that in the secondary drying step, the active material mixture is heated and dried using a winding roll so as to heat the mixture at a temperature that causes almost no thermal expansion or contraction of the active material mixture. However, prolonged heating may cause deterioration of the binder (binding agent) contained in the active material mixture.

[0005] The present disclosure aims to provide a method for manufacturing an electrode that can suppress deterioration of an active material mixture while drying the metal foil coated with the active material mixture that constitutes the electrode by suppressing absorption of moisture into the active material mixture when the metal foil is wound up. [Means for solving the problem]

[0006] The present application discloses a method for manufacturing an electrode, which includes a primary drying step of drying an active material mixture coated on the surface of a metal foil in a drying furnace, and a winding step of winding up the metal foil coated with the active material mixture using a winding roll, wherein the winding step includes a secondary drying step of heating the end faces of the cylindrical metal foil that has been wound into a cylindrical shape with exhaust from the drying furnace. [Effects of the Invention]

[0007] A metal foil coated with an active material composite (hereinafter sometimes referred to as a "composite-laminated metal foil") has an active material composite laminated in a strip shape on the surface of the strip-shaped metal foil, but because the width of the strip (the size in the direction perpendicular to the longitudinal direction) of the metal foil is larger than that of the active material composite, portions (uncoated portions) where no active material composite is disposed are formed at the widthwise ends of the metal foil. Therefore, when the composite-laminated metal foil is wound up on a winding roll, the uncoated portions where no active material composite is disposed overlap the cylindrical end faces of the composite-laminated metal foil that has become a cylindrical roll. While such a composite-laminated metal foil is being wound up on a take-up roll, moisture is absorbed into the active material composite from the end face of the roll. In response to this problem, the electrode manufacturing method disclosed herein heats the end face using only convection heat, thereby heating the uncoated portion and preventing moisture from reaching the coated active material composite, thereby suppressing moisture absorption. Furthermore, because the convection heat acts on the uncoated portion, the thermal effect on the active material composite can be reduced, making it possible to suppress deterioration of the active material composite. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating a composite laminated metal foil 10. As shown in FIG. [Figure 2] FIG. 2 is a diagram illustrating drying. [Figure 3] FIG. 3 is a diagram illustrating the secondary drying process. DETAILED DESCRIPTION OF THE INVENTION

[0009] 1. Electrodes, composite laminated metal foil First, a composite laminated metal foil, which is an electrode for a battery and an intermediate member for the electrode, will be described. The composite laminated metal foil is the target for winding in the present disclosure. The battery has a positive electrode made of a positive electrode composite and a metal foil on which the positive electrode composite is laminated, and a negative electrode made of a negative electrode composite and a metal foil on which the negative electrode composite is laminated, and these are laminated together. This laminate is used as a single unit to form a cell, and a battery may be formed by stacking multiple single cells. Alternatively, the positive electrode composite may be laminated on one side of a single metal foil and the negative electrode composite on the other side (e.g., a bipolar electrode). The positive electrode mixture contains a positive electrode active material, and optionally a conductive additive, a binder, and an electrolyte, while the negative electrode mixture contains a negative electrode active material, and optionally a conductive additive, a binder, and an electrolyte. Since the present disclosure is applicable to both positive electrodes and negative electrodes, in order to describe the present disclosure without making any particular distinction between positive electrodes and negative electrodes, the term "electrode" will be used to mean either a positive electrode or a negative electrode, the term "active material composite" will be used to mean either a positive electrode composite or a negative electrode composite, and both the metal foil of a positive electrode and the metal foil of a negative electrode will be referred to as "metal foil."

[0010] The composite laminated metal foil is a component that becomes an electrode, and is a component in the form of a continuous strip. Therefore, the composite laminated metal foil can be cut to a predetermined length to become an electrode. Figure 1 is a plan view of a portion of the composite laminated metal foil 10, showing the strip-shaped composite laminated metal foil 10 as viewed from the side where the active material composite 12 is laminated. The composite-laminated metal foil 10 is formed by laminating a strip of active material composite 12 on one surface of a strip of metal foil 11. Here, the width B of the active material composite 12 is arranged to be smaller than the width A of the metal foil 11. Therefore, uncoated portions 11a where no active material composite 12 is arranged are formed at both ends in the width direction of the metal foil 11. The size ((AB) / 2) of the uncoated portions 11a is not particularly limited, but is 5 mm to 10 mm. Note that the uncoated portion 11a may not have anything disposed on the surface of the metal foil 11, but may have a coating agent such as carbon, boehmite, or alumina laminated thereon. In this case, however, the thickness of the coating agent is made thinner than the thickness of the active material mixture 12. This makes it possible to fill in part of the step between the active material mixture 12 and the metal foil 11, thereby making it possible to prevent moisture from penetrating into the active material mixture 12 in that area.

[0011] 2. Manufacturing of composite laminated metal foil and electrodes The alloy-laminated metal foil 10 is produced, for example, as follows: Figs. 2 and 3 show explanatory diagrams. First, an active material mixture 12 is laminated on one surface of a metal foil 11. The lamination method is not particularly limited, and conventionally known methods such as roll coating, die coating, dip coating, doctor blade coating, spray coating, and curtain coating can be used. Specifically, materials constituting the active material are mixed with a solvent to produce a slurry composition, and the composition is then applied to the surface of the metal foil 11. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. This is then wound up to form a pre-drying roll 15.

[0012] Next, as shown in FIG. 2 , the pre-dried composite laminated metal foil 10 is sequentially placed into the furnace body 21 of the drying furnace 20 while the pre-dried roll body 15 is unwound. The conveying speed of the composite laminated metal foil 10 is not particularly limited, but is typically about 30 m / min. The drying furnace 20 performs a primary drying process. In this embodiment, heated dry air is delivered from a dry air generator and heater 22 through an air supply duct 23 to the furnace body 21 of the drying furnace 20, drying the active material composite 12 of the composite laminated metal foil 10 moving within the furnace body 21. In this embodiment, the furnace body 21 has a first chamber 21a on the upstream side and a second chamber 21c on the downstream side, along which the composite laminated metal foil 10 is delivered. The first chamber 21a is equipped with an exhaust duct 21b, and the second chamber 21c is equipped with an exhaust duct 21d. In this embodiment, a laser dryer 24 that irradiates the composite laminated metal foil 10 with a laser is also provided in the first chamber 21a. The temperature inside the furnace body 21 (temperature of the supply air) is not particularly limited, but is typically about 200°C.

[0013] After the primary drying in the drying furnace 20, the composite laminated metal foil 10 leaves the furnace body 21 and undergoes a winding process in which it is wound around a winding roll to form a dried roll 30. In the present disclosure, a secondary drying process is carried out while the dried roll 30 is being formed. In the secondary drying process, the end faces of the cylinder of the composite laminated metal foil 10 are heated by exhaust gas from the drying furnace 20 as it is wound into a cylindrical roll. This is described in more detail below.

[0014] As shown in Figure 3, during the winding process of the composite laminated metal foil 10 that has completed primary drying, the composite laminated metal foil 10 takes on a cylindrical shape and gradually increases in diameter, during which heated air is supplied from an air supply cover 40 toward the end face of the cylinder. The air supply cover 40 has a surface 40a that faces the end face of the cylinder of the alloy laminated metal foil 10 at a predetermined distance, and surface 40a has a plurality of holes (not shown) through which the heated air is supplied. The temperature of the supply air is not particularly limited, but is preferably 100°C or higher.

[0015] In this embodiment, an exhaust duct 21d from the second chamber 21c of the drying furnace 20 is connected to the air intake cover 40, and the exhaust air is supplied through the air intake cover 40. This makes it possible to utilize the exhaust heat of the drying furnace 20. Furthermore, the second chamber 21c is the region of the drying furnace 20 where drying is progressing, and has a lower humidity than the exhaust air from the first chamber 21a, so dry, heated air can be sent to the air intake cover 40.

[0016] The supplied air heats the end face of the cylinder around which the composite laminated metal foil 10 is wound, and then flows radially outward from the cylinder and is exhausted through the exhaust duct 41.

[0017] This results in a dried roll 30 of composite laminated metal foil 10 that has been subjected to secondary drying. Thereafter, composite laminated metal foil 10 can be unwound from dried roll 30 and cut to a predetermined size to obtain an electrode.

[0018] 3. Effects etc. According to the present disclosure, the following effects can be achieved, particularly by secondary drying. Because the composite laminated metal foil 10 has uncoated portions 11a, when the composite laminated metal foil 10 is wound around a take-up roll, the end faces of the cylindrical roll of composite laminated metal foil are overlapped with the uncoated portions 11a where no active material mixture 12 is disposed. With such a composite laminated metal foil 10, moisture is absorbed into the active material mixture 12 from the end faces of the roll while the composite laminated metal foil 10 is being wound around the take-up roll. In contrast, according to the electrode manufacturing method of the present disclosure, particularly the secondary drying step, the space between the end faces of the roll and the air intake cover 40 is heated, and the end faces of the roll are heated only by convection heat, thereby heating only the portions of the metal foil 11 (uncoated portions 11a) and preventing moisture from reaching the coated active material mixture 12, thereby suppressing moisture absorption. As described above, the end surface of the roll body has uncoated portion 11a, and therefore the thermal influence on active material mixture 12 is small, so that deterioration of the active material mixture can be further suppressed. In addition, in this embodiment, the exhaust air from the drying furnace 20 is used to supply air to the end surface of the roll body, so that the thermal efficiency can be improved.

[0019] The inventors conducted the following test to confirm the effect. A strip of composite-laminated metal foil was prepared by laminating an active material composite (a composite containing a positive electrode active material, 300 mm wide and 350 μm thick) on one side of an aluminum metal foil (400 mm wide and 10 μm thick). The composite-laminated metal foil was then wound 10 times around a roll 100 mm in diameter and 500 mm long (the ends were secured with heat-resistant tape). Two such rolls were prepared, and both were dried in a vacuum drying oven at 100°C and -100 KPa for 6 hours. Immediately after drying, samples were taken in a dry box with a dew point of -60°C and an atmosphere of 25°C. The moisture content of the samples was measured using a Karl Fischer moisture meter (80°C), and both rolls were found to be 50 ppm.

[0020] The first roll was left in a dry box with a dew point of -30°C and an atmosphere of 25°C for 5 hours, and then sampled. The moisture content of the sample was measured using a Karl Fischer moisture meter (temperature of the Karl Fischer moisture meter: 80°C), and it was found to be 575 ppm. This shows that the moisture content increases when the sample is left in the roll form.

[0021] The second roll was left in a dry box with a dew point of -30°C for 5 hours while supplying air at 100°C to the end surface of the roll, and then sampled. The moisture content of the sample was measured using a Karl Fischer moisture meter (temperature of the Karl Fischer moisture meter: 80°C), and it was found to be 50 ppm. In other words, the moisture content did not increase when heated air was supplied to the end surface of the roll. [Explanation of symbols]

[0022] 10... alloy laminated metal foil, 11... metal foil, 12... active material mixture, 15... roll body before drying, 20... drying furnace, 21... furnace body, 21a... first chamber, 21b... exhaust duct, 21c... second chamber, 21d... exhaust duct, 30... roll body after drying, 40... air intake cover, 41... exhaust duct

Claims

[Claim 1] A method for manufacturing an electrode, comprising: a primary drying step of drying an active material mixture coated on a surface of a metal foil in a drying furnace; and a winding step of winding up the metal foil coated with the active material mixture using a winding roll, The winding step includes a secondary drying step of heating an end surface of the cylindrical metal foil wound into a cylindrical shape with exhaust gas from the drying furnace. Electrode manufacturing method.

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