Manufacturing method for electrode

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] 2. Description of the Related Art Known technology relating to a manufacturing method of an electrode sheet used in manufacturing batteries such as lithium-ion secondary batteries is a method in which an electrode material is applied to a conveyed current collector sheet to form a coated portion, and the coated portion is dried to obtain an electrode layer.

[0003] For example, Patent Document 1 discloses a method for manufacturing an electrode, which includes a coating step 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 step that is performed prior to the coating step 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 step that is performed after the first irradiation step and in which a laser is irradiated to both edges in the short side of the coated portion formed by the coating step; and a drying step that is performed after the second irradiation step and in which the coated portion is dried. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-029256 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the coated sheet, the end of the coated part, which is a part including the main surface part and the side surface part, has a larger surface area than the central part, which is a part including the main surface part. In addition, it is expected that the end will have a smaller basis weight than the central part. Therefore, the end of the coated part is more likely to dry, and if the end of the coated part is dried in the same way as the central part, the end may become overdried. The overdried end may have a reduced peel strength, and peeling may occur in the manufactured electrode.

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

[0007] [1] A method for manufacturing an electrode, comprising: a preparation step of preparing a coated sheet having a current collecting sheet having a longitudinal direction and a coated portion arranged on a first surface of the current collecting sheet; and a drying step of drying the coated portion with laser 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, the drying step comprising: a calculation 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 in the drying step, the adjustment of the irradiation width of the laser is performed in accordance with the following (i) and (ii) to perform the drying. (i) When the moisture content is equal to or greater than a 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 the above (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 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.) Effect of the Invention

[0010] The present disclosure has an effect of enabling the production of an electrode while preventing the end of the coated portion from being over-dried. [Brief description 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. [Diagram 2] FIG. 2 is a schematic side view illustrating a drying process in the present disclosure. [Diagram 3] FIG. 2 is a schematic plan view illustrating a drying step in the present disclosure. [Figure 4] FIG. 4 is a schematic plan view illustrating a measurement position of the moisture content in a drying process. [Diagram 5] 1 is a schematic cross-sectional view illustrating an electrode according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The manufacturing method of the electrode in the present disclosure will be described in detail below with reference to the drawings. Each of the drawings shown below is a schematic illustration, and the size and shape of each part are appropriately exaggerated for easy understanding. In addition, in the present disclosure, "width" refers to the length in the short direction perpendicular to the long 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 of Fig. 1(a). Figs. 2(a)-(c) are schematic side views showing the drying step as viewed from the short side. Figs. 3(a)-(c) are schematic plan views showing the coated sheet in the drying step as viewed from the coating section side. Figs. 3(a)-(c) correspond to Figs. 2(a)-(c), respectively.

[0014] As shown in Figs. 1(a) and (b), in the manufacturing method of an electrode in the present disclosure, first, a coated sheet 10 having a current collecting sheet 1 having a longitudinal direction D1 and a coated portion 2 arranged on a first surface S1 of the current collecting sheet 1 is prepared (preparation step). The coated portion 2 contains an electrode material including at least an active material. Next, as shown in Figs. 2(a) to (c), while the coated sheet 10 is conveyed in the longitudinal direction D1, the coated portion 2 is dried by lasers L (L1 to L3) irradiated from a plurality of laser heads 20 (20A to 20C) arranged in the longitudinal direction D1 (drying step). The drying step also includes a calculation process for calculating the moisture content of the coated portion 2 using a radiation thermometer 30 (30A to 30C). Furthermore, as shown in Figs. 3(a) to (c), the drying step also includes a drying process for performing the drying by adjusting the irradiation width of the laser L for each of the plurality of 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 being over-dried.

[0016] For example, when the laser irradiation width is constant on the upstream side (early drying) and downstream side (late drying) of the multiple laser heads, the entire coated part is dried uniformly in the drying process. On the other hand, as described above, the ends of the coated part are more likely to dry than the center in terms of surface area and basis weight, so there is a risk that the ends will become overdried. In contrast, in the manufacturing method of the electrode in the present disclosure, the irradiation width of the laser is adjusted based on the moisture content of the coated part. In other words, the laser can be preferentially irradiated to the part that is still insufficiently dried and has a high moisture content, such as the center part of the coated part, and the laser irradiation of the part that is sufficiently dried and has a low moisture content, such as the end of the coated part, can be suppressed. As a result, the end can be suppressed from becoming overdried. In addition, with the manufacturing method of the electrode in the present disclosure, since overdrying can be suppressed, the amount of binder added to suppress electrode peeling can be reduced. As a result, the manufacturing method of the electrode in the present disclosure also has the advantage of being able to increase the amount of active material in the electrode.

[0017] 1.Preparation process The preparing 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. The current collector sheet 1 usually has a lateral direction D2. 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 usually has a second surface S2 which is the reverse side of the first surface S1. The material of the current collector sheet is preferably 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 the material of 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 a portion that becomes an electrode layer after a drying process described later. The coated portion may be disposed only on the first surface of the current collecting sheet, or may be disposed on both the first surface and the second surface 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 particularly shown, the coated portions may be arranged continuously along the longitudinal direction of the current collecting sheet.

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

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

[0023] The active material may be a positive electrode active material. Examples of the positive electrode active material include oxide active materials. Examples of the oxide active material 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 the like; 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. Metal active materials include, for example, 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 (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 halogen elements. Examples of the halogen elements include F, Cl, Br, and I.

[0026] Examples of oxide solid electrolytes include Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, Li 1.3 Al 0.3 Ti 0.7 (PO4)3, Li5La3Ta2O 12 , Li7La3Zr2O 12 , Li6BaLa2Ta2O 12 , Li 3.6 S 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] Moreover, the coated sheet usually 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 regarded 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 direction D2 of the current collecting sheet 1. As shown in FIGS. 1(a) and 1(b), when the coated portion 2 is disposed intermittently in the longitudinal direction D1, 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 materials together with a solvent such as water to prepare an electrode slurry, and applying the electrode slurry to the first surface of a current collector sheet.

[0030] 2.Drying process The drying process in the present disclosure is a process 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 drying process in the present disclosure also includes a predetermined calculation process and a drying process.

[0031] The number of laser heads is 2 or more, may be 3 or more, or may be 5 or more. As shown in Fig. 2(a) to (c), the laser heads usually 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 the third laser heads is not particularly limited and may be 1, 2 or more.

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

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

[0034] The moisture content of the coated part can be calculated based on, for example, a map created from a preliminary experiment and the temperature of the surface of the coated part measured by a radiation thermometer. First, the drying temperature in the drying process generally includes 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, which is a section where the latent heat of evaporation and the sensible heat are balanced, so a preliminary experiment is conducted in advance to map the relationship between the electrode temperature and the evaporation rate. Then, in 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, and the moisture content of the coated part can be calculated by applying these to the map.

[0035] As shown in Fig. 2(a) to (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 coating portion passing through the multiple laser heads to be directly calculated. On the other hand, although not shown, one radiation thermometer may be used. In this case, one 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 coating portion passing through the downstream laser heads (second laser head and third laser head) can be indirectly calculated. For example, the downstream moisture content may be calculated from the moisture content calculated upstream based on drying conditions such as the laser energy density and the 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 part 2 is Wa and the shortest length in the short 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 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 FIG.

[0038] The irradiation width of the laser is adjusted according to the following (i). (i) When the moisture content is equal to or greater than a 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 of the moisture content can be set appropriately. The range of the threshold value is, for example, 20% or more, and 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 the radiation thermometer 30A was equal to or greater than the threshold, so the irradiation width of the laser L1 from the first laser head 20A was adjusted to be the same as the width of the coated portion. Also, the moisture content calculated using the radiation thermometers 30B and 30C was less than the threshold, so the irradiation width of the laser L2 from the second laser head 20B and the irradiation width of the laser L3 from the 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 short side direction, as shown in Figures 3 and 4. This is because over-drying can be suppressed at both ends of the coated portion. On the other hand, although not particularly shown, the region of the coated portion irradiated with the laser may include one end of the coated portion in the short side direction.

[0043] In the above case (ii), 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 represents the moisture content (%) in the coated portion, and e represents the Napier's number. P may be -0.025 or more, or may be -0.020 or more. Meanwhile, P may be -0.015 or less. Q may be 0.065 or more, or may be 0.070 or more. Meanwhile, 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 irradiation widths of the lasers adjusted according to (i) and (ii) above will be described. For example, when the number of laser heads is N (N≧3), the irradiation width of the laser in the Mth (2≦M≦N) laser head from the upstream may be different from or the same as the irradiation width of the M-1th laser head. In other words, the laser irradiation width may be narrowed continuously or intermittently from the upstream to the downstream. For example, in FIG. 2(c), the laser irradiation width is narrowed continuously from the first laser head (first laser head 20A) from the upstream to the most downstream laser head (second laser head 20B). Note that when the laser irradiation width in the third laser head 20C is equal to the laser irradiation width in either the first laser head 20A or the second laser head 20B, the laser irradiation width is considered to be narrowed intermittently.

[0046] The energy density of the laser is not particularly limited and can be adjusted appropriately. The energy density of the laser is, for example, 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 appropriately.

[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 particularly shown, the electrode layer 102 may be formed on the first surface S1 and the second surface S2 of the current collecting sheet. In addition, the shape of the electrode is usually a sheet having a longitudinal direction and a lateral direction.

[0048] Such an electrode (electrode sheet) is usually used in the manufacture of a battery. 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. Also, 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 one of a positive electrode active material and 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 may be, for example, a lithium ion secondary battery. 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 automobiles, and diesel automobiles. 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 moving objects other than vehicles (for example, railways, ships, and aircraft), and may also be used as a power source for electrical appliances such as information processing devices.

[0051] The present disclosure is not limited to the above-described embodiment. The above-described embodiment is merely an example, and any configuration that is substantially the same as the technical idea described in the claims of the present disclosure and that exhibits similar effects is included in the technical scope of the present disclosure. EXAMPLES

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

[0053] The moisture content of the obtained coated sheet was calculated using multiple radiation thermometers as shown in Figures 2(a) to (c). Based on the moisture content, the laser irradiation width was adjusted according to (i) and (ii) above to dry the coated part. Specifically, the moisture content threshold was set to 30%, and when the moisture content was 30% or more, the laser irradiation width was set to the same width (500 mm) of the coated part, and 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 set to positions 100 mm inward from the ends of the coated part. 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 made in accordance with the above (i) and (ii).

[0055] [evaluation] The drying condition of the coated edge after drying was visually checked, 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, over-drying of the edges of the coated area could be suppressed and the coated area could be dried sufficiently. [Explanation of symbols]

[0058] 1...Current collecting sheet 2 … Coating section 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 having 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 in accordance with the following (i) and (ii). (i) When the moisture content is equal to or greater than a threshold value, the irradiation width of the laser is set to be the same as the width of the coated portion. (ii) When 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.

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), an 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 satisfying -0.03≦P≦-0.01, Q is a number satisfying 0.06≦Q≦0.08, R means the moisture content (%) in the coated portion, and e means the Napier's number.)

Images