Electrode manufacturing method

Abstract

To provide a manufacturing method for an electrode, in which the excess drying at an end part of a coating part can be suppressed.SOLUTION: A manufacturing method for an electrode in the present disclosure includes: a preparing step of preparing a coating sheet including a current collector sheet with a longitudinal direction and a coating part disposed on a first surface of the current collector sheet; and a drying step of drying the coating part by irradiation with a laser emitted from a plurality of laser heads disposed in the longitudinal direction while conveying the coating sheet in the longitudinal direction. The coating part contains an electrode material including at least an active material. The drying step includes a calculating process of calculating the moisture content of the coating part using a radiation pyrometer, and a drying process of performing the drying by adjusting the laser irradiation width for each of the laser heads on the basis of the moisture content. In the drying process, the drying is performed by adjusting the laser irradiation width according to predetermined (i) and (ii).SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing an electrode. [Background technology]

[0002] A known technique for manufacturing an electrode sheet used in the manufacture of batteries such as lithium-ion secondary batteries is to apply an electrode material to a conveyed current collector sheet to form a coated portion, and then dry the coated portion to obtain an electrode layer.

[0003] For example, Patent Document 1 discloses a method for manufacturing an electrode, which is characterized by including: a coating process in which an active material mixture is applied to a long metal foil being transported to form a coated portion of the active material mixture; a first irradiation process that is performed before the coating process and in which a laser is irradiated to an irradiation position on the long metal foil that is located upstream in the transport direction of the long metal foil from both ends of the mixture application location along the short side of the long metal foil; a second irradiation process that is performed after the first irradiation process and in which a laser is irradiated to both short side edges of the coated portion formed by the coating process; and a drying process that is performed after the second irradiation process and in which the coated portion is dried. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-029256 Summary of the Invention [Problem to be solved by the invention]

[0005] In a coated sheet, the edges of the coated portion, which include the main surface and side surfaces, have a larger surface area than the central portion, which includes the main surface. It is also expected that the edges will have a smaller basis weight than the central portion. Therefore, the edges of the coated portion are more likely to dry, and if the edges of the coated portion are dried in the same way as the central portion, they may become overdried. Overdried edges may have a reduced peel strength, which may result in peeling in the resulting electrode.

[0006] The present disclosure has been made in consideration of the above-described circumstances, and a main object of the present disclosure is to provide a method for manufacturing an electrode that can suppress over-drying at the end of a coated portion. [Means for solving the problem]

[0007] [1] a drying step of drying the coated portion with lasers irradiated from a plurality of laser heads arranged in the longitudinal direction while conveying the coated sheet in the longitudinal direction, wherein the coated portion contains an electrode material including at least an active material; and a drying step of calculating a moisture content of the coated portion using a radiation thermometer; and a drying step of adjusting an irradiation width of the laser for each of the plurality of laser heads based on the moisture content to perform the drying, wherein the adjustment of the irradiation width of the laser in the drying step is performed in accordance with the following (i) and (ii): (i) If the moisture content is equal to or greater than the threshold value, the irradiation width of the laser is set to be the same as the width of the coated portion. (ii) If the moisture content is less than the threshold value, the irradiation width of the laser is made narrower than the width of the coated portion.

[0008] [2] The method for producing an electrode according to [1], wherein the threshold value is 20% or more and 40% or less.

[0009] [3] The method for manufacturing an electrode according to [1] or [2], wherein in (ii) above, the irradiation width of the laser is set to a length that satisfies the following formula (1): Laser irradiation width = Pe (Q(100-R)) +Width of coating area (1) (In formula (1), P is a number that satisfies -0.03≦P≦-0.01, Q is a number that satisfies 0.06≦Q≦0.08, R means the moisture content (%) in the coated area, and e means the Napier's number.) [Effects of the Invention]

[0010] The present disclosure has the effect of making it possible to manufacture an electrode while preventing excessive drying of the coated portion at the end. [Brief explanation of the drawings]

[0011] [Figure 1] 1A and 1B are a schematic plan view and a schematic cross-sectional view illustrating a coated sheet according to the present disclosure. [Figure 2] FIG. 2 is a schematic side view illustrating a drying process in the present disclosure. [Figure 3] FIG. 2 is a schematic plan view illustrating a drying step in the present disclosure. [Figure 4] FIG. 10 is a schematic plan view illustrating the measurement position of the moisture content in the drying process. [Figure 5] 1 is a schematic cross-sectional view illustrating an electrode according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0012] The electrode manufacturing method according to the present disclosure will be described in detail below with reference to the drawings. The drawings are schematic, and the size and shape of each part are appropriately exaggerated for ease of understanding. In addition, in this disclosure, "width" refers to the length in the short direction perpendicular to the longitudinal direction.

[0013] Fig. 1(a) is a schematic plan view illustrating a coated sheet prepared in the preparation step, and Fig. 1(b) is a cross-sectional view taken along line AA in Fig. 1(a). Figs. 2(a) to 2(c) are schematic side views showing the drying step as viewed from the short side. Figs. 3(a) to 3(c) are schematic plan views showing the coated sheet in the drying step as viewed from the coated section side. Figs. 3(a) to 3(c) correspond to Figs. 2(a) to 2(c), respectively.

[0014] As shown in FIGS. 1(a) and 1(b), the electrode manufacturing method of the present disclosure first prepares a coated sheet 10 having a current collector sheet 1 with a longitudinal direction D1 and a coated portion 2 disposed on a first surface S1 of the current collector sheet 1 (preparation step). The coated portion 2 contains an electrode material including at least an active material. Next, as shown in FIGS. 2(a) to 2(c), while the coated sheet 10 is conveyed in the longitudinal direction D1, the coated portion 2 is dried using lasers L (L1 to L3) irradiated from multiple laser heads 20 (20A to 20C) arranged in the longitudinal direction D1 (drying step). The drying step also includes a calculation step in which the moisture content of the coated portion 2 is calculated using a radiation thermometer 30 (30A to 30C). Furthermore, as shown in FIGS. 3(a) to 3(c), the drying step further includes a drying step in which the irradiation width of the laser L is adjusted for each of the multiple laser heads 20 according to predetermined conditions based on the moisture content.

[0015] According to the present disclosure, the laser irradiation width is adjusted based on the moisture content of the coated portion to dry the coated portion, thereby preventing the edges of the coated portion from drying excessively.

[0016] For example, if the laser irradiation width is constant on the upstream side (early drying period) and downstream side (late drying period) of multiple laser heads, the entire coated portion will be dried uniformly during the drying process. However, as mentioned above, the edges of the coated portion are more easily dried than the center in terms of surface area and coating weight, which may result in over-drying of the edges. In contrast, the electrode manufacturing method of the present disclosure adjusts the laser irradiation width based on the moisture content of the coated portion. In other words, the laser can be preferentially irradiated to areas that are not yet sufficiently dried and have a high moisture content, such as the center of the coated portion, while laser irradiation of areas that are sufficiently dried and have a low moisture content, such as the edges of the coated portion, can be suppressed. As a result, over-drying of the edges can be suppressed. Furthermore, because the electrode manufacturing method of the present disclosure can suppress over-drying, the amount of binder added to suppress electrode peeling can be reduced. As a result, the electrode manufacturing method of the present disclosure also has the advantage of allowing for a larger amount of active material in the electrode.

[0017] 1. Preparation process The preparation step in the present disclosure is a step of preparing a coated sheet having a longitudinal current collecting sheet and a coated portion disposed on a first surface of the current collecting sheet.

[0018] As shown in FIG. 1(a), the current collector sheet 1 has a longitudinal direction D1. Furthermore, the current collector sheet 1 typically has a lateral direction D2. Furthermore, as shown in FIG. 1(b), the current collector sheet 1 has a first surface S1, which is one surface in the thickness direction, and typically has a second surface S2, which is the reverse side of the first surface S1. The current collector sheet is preferably made of a material used as a current collector, such as a negative electrode current collector, a positive electrode current collector, or a bipolar current collector. Examples of materials for the current collector sheet include metals such as aluminum, copper, SUS, and nickel. The thickness of the current collector sheet is, for example, 0.1 μm or more and 100 μm or less.

[0019] The coated portion is disposed on the first surface of the current collecting sheet and contains an electrode material including at least an active material. The coated portion is the portion that will become the electrode layer after the drying process described below. The coated portion may be disposed only on the first surface of the current collecting sheet, or may be disposed on both the first and second surfaces of the current collecting sheet.

[0020] The coated portions are preferably arranged along the longitudinal direction of the current collecting sheet. Alternatively, the coated portions may be arranged intermittently along the longitudinal direction D1 of the current collecting sheet 1, as shown in Fig. 1(a). Alternatively, although not specifically shown, the coated portions may be arranged continuously along the longitudinal direction of the current collecting sheet.

[0021] The width of the coated portion is, for example, 300 mm or more and 1500 mm or less.

[0022] The coated portion contains an electrode material containing at least an active material. The electrode material may also contain at least one of an electrolyte, a conductive material, and a binder, as needed.

[0023] The active material may be a positive electrode active material. Examples of the positive electrode active material include oxide active materials. Examples of oxide active materials include LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc., rock salt layered active materials, LiMn2O4, Li(Ni 0.5 Mn 1.5 )O4, and olivine type active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCuPO4.

[0024] The active material may be a negative electrode active material. Examples of the negative electrode active material include carbon active materials, oxide active materials, and metal active materials. Examples of the carbon active material include mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. Examples of the oxide active material include Nb2O5, Li4Ti5O 12and SiO. Examples of metal active materials include In, Al, Si, and Sn.

[0025] Examples of the electrolyte include inorganic solid electrolytes such as sulfide solid electrolytes and oxide solid electrolytes. Examples of the sulfide solid electrolyte include solid electrolytes containing Li, X (where X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. The sulfide solid electrolyte may further contain at least one of O and a halogen element. Examples of the halogen element include F, Cl, Br, and I.

[0026] Examples of oxide solid electrolytes include Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, and Li 1.3 Al 0.3 Ti 0.7 (PO4)3, Li5La3Ta2O 12 , Li7La3Zr2O 12 , Li6BaLa2Ta2O 12 , Li 3.6 Si 0.6 P 0.4 O4, Li4SiO4, Li3PO4, Li3PO 4-3 / 2x N x (x≦1).

[0027] Examples of conductive materials include carbon materials, metal particles, and conductive polymers. Examples of carbon materials include particulate carbon materials such as acetylene black (AB) and ketjen black (KB); and fibrous carbon materials such as carbon fiber, carbon nanotubes (CNT), and carbon nanofibers (CNF). Examples of binders include fluorine-containing binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), rubber-based binders such as butadiene rubber, and acrylic binders.

[0028] Furthermore, the coated sheet typically has an uncoated portion that is disposed on the first surface of the current collecting sheet and does not contain an electrode material. The uncoated portion can be understood as a portion of the coated sheet where the current collecting sheet is exposed. As shown in FIG. 1(a), the uncoated portion 3 is disposed at the ends (both ends) of the coated portion 2 in the short-side direction D2 of the current collecting sheet 1. When the coated portions 2 are disposed intermittently in the longitudinal direction D1, as shown in FIGS. 1(a) and 1(b), the uncoated portion 3 is also disposed at the ends (both ends) of the coated portion 2 in the longitudinal direction D1. In other words, the uncoated portion 3 is disposed around the entire outer edge of the coated portion 2.

[0029] The coated sheet can be prepared by mixing the above-mentioned electrode material with a solvent such as water to prepare an electrode slurry, and applying the slurry to the first surface of the current collector sheet.

[0030] 2.Drying process The drying process according to the present disclosure is a process of drying the coated portion of the coated sheet with lasers irradiated from a plurality of laser heads arranged in the longitudinal direction while the coated sheet is being conveyed in the longitudinal direction. The drying process according to the present disclosure also includes a predetermined calculation process and a drying process.

[0031] The number of laser heads is two or more, may be three or more, or may be five or more. As shown in FIGS. 2(a) to 2(c), the laser heads typically include a first laser head 20A located at the most upstream position in the longitudinal direction D1 and a second laser head 20B located at the most downstream position. The laser heads may also include a third laser head 20C disposed between the first laser head 20A and the second laser head 20B in the longitudinal direction D1. The number of third laser heads is not particularly limited and may be one, two or more.

[0032] Furthermore, although not particularly shown, a hot air device for blowing hot air to the coating section may be provided between the plurality of laser heads in the longitudinal direction.

[0033] (1) Calculation process In the calculation process, the moisture content of the coated portion is calculated using a radiation thermometer. Here, "moisture content of the coated portion" means the moisture content of the portion of the coated portion corresponding to each of the multiple laser heads, i.e., the moisture content of the portion of the coated portion irradiated with laser light by each of the multiple laser heads.

[0034] The moisture content of the coated area can be calculated, for example, based on a map created from a preliminary experiment and the temperature of the coated area surface measured with a radiation thermometer. First, the drying temperature in the drying process generally has a preheating section, a constant rate section, and a decreasing rate section. The evaporation rate of moisture is determined by the electrode temperature in the constant rate section, where the latent heat of evaporation and sensible heat are balanced. Therefore, a preliminary experiment is conducted in advance to map the relationship between the electrode temperature and the evaporation rate. Then, during the actual drying process, the temperature of the electrode surface is measured with a radiation thermometer, and the time (seconds) that this temperature is maintained is measured. These data can then be applied to the map to determine the moisture content of the coated area.

[0035] As shown in FIGS. 2(a) to 2(c), radiation thermometers 30A to 30C may be provided corresponding to the multiple laser heads 20A to 20C, respectively. This allows the moisture content of the coated portion passing through the multiple laser heads to be directly determined. Alternatively, although not shown, a single radiation thermometer may be used. In this case, the single radiation thermometer is provided corresponding to the most upstream laser head (first laser head). Based on the moisture content calculated by the radiation thermometer provided corresponding to the first laser head, the moisture content of the coated portion passing through the downstream laser heads (second laser head and third laser head) can be indirectly determined. For example, the downstream moisture content may be calculated from the moisture content calculated upstream based on drying conditions such as laser energy density and conveying speed.

[0036] The measurement position of the radiation thermometer is not particularly limited. For example, as shown in Fig. 4, if the width of the coated section 2 is Wa and the shortest length in the short side direction from the end E to the measurement position P is Wb, the measurement position P is a position where Wb / Wa is, for example, 0.07 or more and 0.3 or less. Wb is, for example, 50 mm or more and 150 mm or less.

[0037] (2) Drying process In the drying process, the laser irradiation width is adjusted according to predetermined conditions for each of the multiple laser heads based on the moisture content, and the drying is performed. Here, the "laser irradiation width" refers to the width of the area (shaded area) of the coated part irradiated with the laser, as shown in Figure 4.

[0038] The irradiation width of the laser is adjusted according to the following (i). (i) If the moisture content is equal to or greater than the threshold value, the irradiation width of the laser is set to be the same as the width of the coated portion.

[0039] The threshold value for moisture content can be set appropriately. The range of the threshold value is, for example, 20% or more, or may be 30% or more. On the other hand, the range of the threshold value is, for example, 40% or less.

[0040] 3 and 4, for example, the moisture content calculated using radiation thermometer 30A was equal to or greater than the threshold, so the irradiation width of laser L1 from first laser head 20A was adjusted to be the same as the width of the coated portion. Also, the moisture content calculated using radiation thermometers 30B and 30C was less than the threshold, so the irradiation width of laser L2 from second laser head 20B and the irradiation width of laser L3 from third laser head 20C were adjusted to be narrower than the width of the coated portion.

[0041] The irradiation width of the laser is adjusted according to the following (ii). (ii) If the moisture content is less than the threshold value, the irradiation width of the laser is made narrower than the width of the coated portion.

[0042] In the case of (ii) above, it is preferable that the region of the coated portion irradiated with the laser does not include both ends of the coated portion in the lateral direction, as shown in Figures 3 and 4. This is because over-drying can be prevented at both ends of the coated portion. On the other hand, although not specifically shown, the region of the coated portion irradiated with the laser may include one end of the coated portion in the lateral direction.

[0043] In the case of (ii) above, it is preferable that the laser irradiation width is set to a length that satisfies the following formula (1). Laser irradiation width = Pe (Q(100-R)) +Width of coating area (1) In formula (1), P is a number that satisfies −0.03≦P≦−0.01, Q is a number that satisfies 0.06≦Q≦0.08, R means the moisture content (%) in the coated area, and e means the Napier's number. P may be -0.025 or greater, or may be -0.020 or greater. On the other hand, P may be -0.015 or less. Q may be 0.065 or greater, or may be 0.070 or greater. On the other hand, Q may be 0.075 or less.

[0044] According to the above formula (1), the lower the moisture content, the narrower the laser irradiation width can be adjusted, so that excessive drying of the edge portions can be further suppressed.

[0045] Here, the relationship between the laser irradiation widths adjusted according to (i) and (ii) above will be described. For example, if the number of laser heads is N (N≧3), the laser irradiation width of the Mth (2≦M≦N) laser head from the upstream may be different from or the same as the irradiation width of the (M−1)th laser head. In other words, the laser irradiation width may narrow continuously or intermittently from upstream to downstream. For example, in FIG. 2(c), the laser irradiation width narrows continuously from the first laser head (first laser head 20A) from upstream to the most downstream laser head (second laser head 20B). Note that if the laser irradiation width of the third laser head 20C is equal to the laser irradiation width of either the first laser head 20A or the second laser head 20B, the laser irradiation width is considered to be intermittently narrowed.

[0046] The energy density of the laser is not particularly limited and can be adjusted as appropriate. For example, the energy density of the laser is 0.1 W / cm. 2 More than 1.0W / cm 2 The conveying speed of the coated sheet in the drying step is not particularly limited and can be adjusted as appropriate.

[0047] 3. Electrode Fig. 5 is a schematic cross-sectional view showing an example of an electrode manufactured in the present disclosure. As shown in Fig. 5, the electrode has a current collecting sheet 101 and an electrode layer 102 formed on a first surface S1 of the current collecting sheet 101. In Fig. 5, the electrode layer 102 is formed intermittently. Although not specifically shown, the electrode layer 102 may be formed on both the first surface S1 and the second surface S2 of the current collecting sheet. Furthermore, the electrode is usually in the form of a sheet having a longitudinal direction and a lateral direction.

[0048] Such electrodes (electrode sheets) are typically used in the manufacture of batteries. The electrode sheet may be a positive electrode sheet or a negative electrode sheet. When the electrode sheet in the present disclosure is a positive electrode sheet, it is combined with a negative electrode sheet and a separator to form an electrode body. Similarly, when the electrode sheet in the present disclosure is a negative electrode sheet, it is combined with a positive electrode sheet and a separator to form an electrode body. Furthermore, the electrode layer 102 shown in FIG. 5 may be a positive electrode active material layer or a negative electrode active material layer.

[0049] The electrode layer contains either a positive electrode active material or a negative electrode active material. The electrode layer may further contain at least one of an electrolyte, a conductive material, and a binder. These materials are as described above.

[0050] The type of battery in which the electrode is used is not particularly limited, and examples thereof include lithium-ion secondary batteries. Examples of uses of the battery include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, the battery is preferably used as a driving power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). The battery may also be used as a power source for mobile objects other than vehicles (for example, trains, ships, and aircraft), or as a power source for electrical appliances such as information processing devices.

[0051] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0052] [Example 1] The negative electrode active material (artificial graphite), thickener (carboxymethyl cellulose: CMC), and binder (styrene butadiene rubber: SBR) were mixed with water to obtain a negative electrode slurry. The resulting negative electrode slurry was applied to a current collector sheet (copper foil) to obtain a coated sheet with a current collector sheet and a coated area. The width of the coated area was 500 mm.

[0053] The moisture content of the resulting coated sheet was calculated using multiple radiation thermometers, as shown in Figures 2(a) to 2(c). The coated area was dried by adjusting the laser irradiation width based on the moisture content according to (i) and (ii) above. Specifically, the moisture content threshold was set to 30%, and when the moisture content was 30% or higher, the laser irradiation width was set to the same width as the coated area (500 mm). When the moisture content was less than 30%, the laser irradiation width was set to a length that satisfied the above formula (1). Four laser heads and four radiation thermometers were used. The measurement positions of the radiation thermometers were each 100 mm inward from the edge of the coated area. In formula (1), P = -0.02 and Q = 0.07.

[0054] [Comparative Examples 1 and 2] A coated sheet was prepared and dried in the same manner as in Example 1, except that the width of the coated portion was changed and the adjustment of the laser irradiation width was not in accordance with (i) and (ii) above.

[0055] [evaluation] The drying condition of the coated edge after drying was checked visually, and the results are shown in Table 1.

[0056] [Table 1]

[0057] As shown in Table 1, by adjusting the laser irradiation width according to the specified (i) and (ii) based on the moisture content, it was possible to prevent excessive drying of the edges of the coated area and achieve sufficient drying. [Explanation of symbols]

[0058] 1... Current collecting sheet 2... Coating department 3...Uncoated area 10...Coated sheet 20...Laser head 30...Radiation thermometer 40...Drying oven L...Laser

Claims

1. a preparation step of preparing a coated sheet having a current collecting sheet with a longitudinal direction and a coated portion disposed on a first surface of the current collecting sheet; a drying step of drying the coated portion by lasers irradiated from a plurality of laser heads arranged in the longitudinal direction while conveying the coated sheet in the longitudinal direction, the coated portion contains an electrode material including at least an active material, The drying step includes: a calculation process of calculating the moisture content of the coated portion using a radiation thermometer; and a drying process for performing the drying by adjusting the laser irradiation width for each of the plurality of laser heads based on the moisture content according to the following (i) and (ii). (i) When the moisture content is equal to or greater than the threshold value, the laser irradiation width is set to be the same as the width of the coated portion. (ii) If the moisture content is less than the threshold value, the laser irradiation width is made narrower than the width of the coated portion.

2. The method for manufacturing an electrode according to claim 1 , wherein the threshold value is 20% or more and 40% or less.

3. 3. The method for manufacturing an electrode according to claim 1, wherein in the step (ii), the irradiation width of the laser is set to a length that satisfies the following formula (1): Laser irradiation width = Pe （Ｑ（１００－Ｒ）） + Width of coated area... (1) (In formula (1), P is a number that satisfies −0.03≦P≦−0.01, Q is a number that satisfies 0.06≦Q≦0.08, R represents the moisture content (%) in the coated portion, and e represents the Napier's number.)

Images