JP2018186033A - Manufacturing method of electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of electrode using a wet granule molding method, capable of improving end precision of an electrode mixture material layer, while restraining occurrence of surface collapse of the electrode mixture material layer degrading battery performance.SOLUTION: A manufacturing method of electrode includes a step of preparing a wet granule agent containing an electrode active material, a binder and a solvent, a molding step of forming an electrode mixture material layer by supplying the wet granule agent to a gap between a pair of rollers, and compression molding the wet granule agent, and a step of placing the electrode mixture material layer on an electrode collector. The wet granule agent contains a first wet granule agent, and a second wet granule agent having malleability lower than that of the first wet granule agent. The pair of rollers have revolving shafts in parallel with each other, and rotary driven in the directions opposite to each other, and in the gap between the pair of rollers, the second wet granule agent is supplied to the end in the direction of the revolving shaft, and the first wet granule agent is supplied to the central part in the direction of the revolving shaft.SELECTED DRAWING: Figure 5

Description

  The present disclosure relates to a method for manufacturing an electrode.

  Japanese Patent Laid-Open No. 03-263757 (Patent Document 1) discloses a mixture (wet granule) of a wet granulation (wet granule) containing an electrode active material and the like together with a conductive substrate (electrode current collector). A method of manufacturing a sheet-like battery electrode plate (electrode) by rolling between a pair of rolls (hereinafter referred to as “wet granule forming method”) is disclosed.

Japanese Patent Laid-Open No. 03-263757

  However, the wet granule protrudes outside the end shape of the desired electrode mixture layer at the end of the pair of rolls in the direction of the rotation axis (the width direction of the sheet-like electrode). As a result, the edge accuracy (the linearity of the edge shape) of the electrode mixture layer may be deteriorated.

  In addition, it is considered that by reducing the malleability of the wet granule, an excessive spread when the wet granule is rolled is suppressed, and end creaking is reduced. However, in this case, due to the low malleability of the wet granule, the surface of the electrode composite layer may be crushed (surface collapse) due to cracking or deformation of the wet granule, or the wet granule may have poor elongation. Therefore, there is a possibility that the electrode mixture layer is not formed in a desired range, and the battery performance may be deteriorated.

  Therefore, the present disclosure is directed to manufacturing an electrode using a wet granule molding method that can increase the edge accuracy of the electrode mixture layer while suppressing the occurrence of surface crushing of the electrode mixture layer that degrades battery performance. It aims to provide a method.

[1] A method of manufacturing an electrode according to the present disclosure includes:
Preparing a wet granule comprising an electrode active material, a binder and a solvent;
A forming step of forming an electrode mixture layer by supplying wet granules to a gap between a pair of rolls and compressing the wet granules,
Arranging an electrode mixture layer on the electrode current collector.
The wet granule includes a first wet granule and a second wet granule that is less malleable than the first wet granule,
The pair of rolls have rotation axes parallel to each other and are driven to rotate in directions opposite to each other,
In the gap between the pair of rolls, the second wet granule is supplied to the end in the direction of the rotation axis, and the first wet granule is supplied to the center in the direction of the rotation axis.

  According to the method for producing an electrode of [1], in the forming step, the second wet granule supplied to the end in the rotation axis direction of the roll is low in the gap between the pair of rolls. It is possible to reduce squeezing and to increase the end accuracy of the electrode mixture layer. Moreover, since the malleability of the 1st wet granule supplied to a center part (parts other than an edge part) is high, generation | occurrence | production of the surface crushing of the electrode compound-material layer etc. which reduce battery performance can be suppressed.

  Therefore, there is provided an electrode manufacturing method using a wet granule molding method that can improve the edge accuracy of the electrode mixture layer while suppressing the occurrence of surface crushing of the electrode mixture layer that degrades battery performance. The

[2] The second wet granule preferably has a smaller average particle size than the first wet granule.
In this case, the malleability of the second wet granule is lower than that of the first wet granule. For this reason, the effect of this indication that the edge part precision of an electrode compound-material layer can be improved can be produced | generated, suppressing generation | occurrence | production of the surface crushing etc. of the electrode compound-material layer which reduces battery performance.
[3] The second wet granule preferably has an average particle size of 0.3 mm to 1.0 mm. In this case, the effect of the present disclosure can be obtained more reliably.

  [4] The second wet granule preferably has a higher nonvolatile content than the first wet granule. In this case, the malleability of the second wet granule is lower than that of the first wet granule. For this reason, the effect of this indication that the edge part precision of an electrode compound-material layer can be improved can be produced | generated, suppressing generation | occurrence | production of the surface crushing etc. of the electrode compound-material layer which reduces battery performance.

  [5] The second wet granule preferably has a nonvolatile fraction of 79% by mass or more and 80% by mass or less. In this case, the effect of the present disclosure can be obtained more reliably.

3 is a flowchart illustrating an outline of a method for manufacturing an electrode according to the first embodiment. It is a schematic sectional drawing which shows the electrode manufacturing apparatus used for the manufacturing method of the electrode of Embodiment 1. It is a schematic perspective view which shows the electrode manufacturing apparatus used for the manufacturing method of the conventional electrode. It is a schematic diagram for demonstrating the formation process in the manufacturing method of the conventional electrode. It is a schematic perspective view which shows the electrode manufacturing apparatus used for the manufacturing method of the electrode of Embodiment 1. 6 is a schematic diagram for explaining a forming step in the electrode manufacturing method of Embodiment 1. FIG. It is a graph which shows the largest uneven | corrugated difference of the edge part of an electrode compound-material layer about the electrode obtained in Examples 1-3 and Comparative Example 1. FIG. It is a photograph which shows the state of the edge part of an electrode compound-material layer about the electrode obtained by the comparative example 1 (conventional) and Example 2 (Embodiment 1 of this indication). FIG. 10 is a schematic diagram for explaining a forming step in the electrode manufacturing method of Embodiment 2. It is a graph which shows the relationship between the non-volatile fraction of a wet granule, and spreadability. It is a graph which shows the relationship between the non-volatile fraction of a 2nd wet granule, and the largest uneven | corrugated difference of the width direction edge part of an electrode compound-material layer about the electrode obtained in Examples 4-7. It is a photograph which shows the state of the edge part of an electrode compound-material layer about the electrode obtained by the comparative example 1 (conventional) and Example 5 (Embodiment 2 of this indication). It is a reference photograph which shows the surface crushing of an electrode compound-material layer.

  Hereinafter, an embodiment of the present disclosure will be described. However, the present disclosure is not limited to these.

  In the drawings, the same reference numerals represent the same or corresponding parts. In addition, dimensional relationships such as length, width, thickness, and height are changed as appropriate for clarity and simplification of the drawings, and do not represent actual dimensional relationships.

  In this specification, “positive electrode” and “negative electrode” are collectively referred to as “electrode”. The “electrode mixture layer” indicates at least one of the “positive electrode mixture layer” and the “negative electrode mixture layer”, and the “electrode active material” indicates at least one of the “positive electrode active material” and the “negative electrode active material”. “Electrode current collector” indicates at least one of “positive electrode current collector” and “negative electrode current collector”.

<Wet granule>
In the present specification, the “wet granule” means a wet granule (that is, a granule containing a solvent) obtained by a granulation operation or the like. The “wet granule” means a mixture (aggregate) of a plurality of wet granules. A wet granule contains the structural component of electrode compound-material layers, such as an electrode active material and a binder, and a solvent. In addition, each of the wet granules constituting the wet granule usually contains an electrode active material, a component of the electrode mixture layer such as a binder, and a solvent, but each of the wet granules does not necessarily have to be an electrode active material. It is not necessary to include all the components of the electrode mixture layer such as the binder and the solvent.

(Electrode active material)
The electrode active material may be a positive electrode active material or a negative electrode active material.

Examples of the positive electrode active material include lithium-containing metal oxides and lithium-containing phosphates. Examples of the lithium-containing metal oxide are LiCoO ₂ , LiNiO ₂ , and general formula LiNi _a Co _b O ₂ (where a + b = 1, 0 <a <1, 0 <b <1). Compound, LiMnO ₂ , LiMn ₂ O ₄ , general formula LiNi _a Co _b Mn _c O ₂ (where a + b + c = 1, 0 <a <1, 0 <b <1, 0 <c <1 .)), LiFePO _{4 and the} like. Here, examples of the compound represented by the general formula LiNi _a Co _b Mn _c O ₂ include LiNi _1/3 Co _1/3 Mn _1/3 O ₂ . Examples of the lithium-containing phosphate include LiFePO _{4 and the} like. The crystal structure of the lithium-containing metal oxide should not be particularly limited. The lithium-containing metal oxide can be, for example, a layered rock salt type oxide, a spinel type oxide, an olivine type oxide, or the like. The average particle diameter of the positive electrode active material may be about 1 to 25 μm, for example.

  In the present specification, the “average particle diameter” is also referred to as a 50% cumulative particle diameter (“D50” or “median diameter”) from the fine particle side in the volume-based particle size distribution measured by the laser diffraction scattering method. Means).

  Examples of the negative electrode active material include carbon-based negative electrode active materials such as graphite, graphitizable carbon, and non-graphitizable carbon, and alloy-based negative electrode active materials containing silicon (Si), tin (Sn), and the like. Can be mentioned. The average particle diameter of the negative electrode active material may be, for example, about 1 to 25 μm.

  The mixing ratio of the electrode active material to the total amount of nonvolatile components (components other than the solvent) in the wet granule (that is, the content of the electrode active material in the electrode mixture layer) is, for example, about 90 to 99% by mass. .

(Binder)
Examples of the binder include carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), and the like. A binder may be used individually by 1 type and may be used in combination of 2 or more type.

  The blending ratio of the binder to the total amount of nonvolatile components in the wet granule (that is, the binder content in the electrode mixture layer) is, for example, about 1 to 10% by mass.

(Other ingredients)
As a constituent component of the electrode mixture layer, components other than those described above may be included. For example, a conductive material may be included. Examples of the conductive material include carbon black such as acetylene black (AB), thermal black, and furnace black. The conductive material is expected to improve electronic conductivity.

(solvent)
Examples of the solvent include an organic solvent and an aqueous solvent. The aqueous solvent means water or a mixed solvent containing water and a polar organic solvent.

  Examples of the organic solvent include N-methyl-2-pyrrolidone (NMP). In addition, an organic solvent can be used suitably as a solvent for positive electrode manufacture.

  As the aqueous solvent, water can be preferably used from the viewpoint of easy handling. Examples of the polar organic solvent that can be used for the mixed solvent include alcohols such as methanol, ethanol, and isopropyl alcohol, ketones such as acetone, and ethers such as tetrahydrofuran. In addition, an aqueous solvent can be used suitably as a solvent for negative electrode manufacture.

  The amount of the solvent used is preferably adjusted so that the non-volatile fraction of the wet granules (first wet granule and second wet granule) is 70% by mass or more and less than 100% by mass. The “nonvolatile fraction” means the mass ratio of components (nonvolatile components) other than the solvent to the total mass of all raw materials including the solvent.

  In this case, it is easy to prepare wet granules (wet granules) by a granulating operation or the like in the wet granule preparation process. In addition, when the non-volatile fraction in the material mixed by granulation operation etc. is less than 70 mass%, the mixture obtained becomes paste-like or clay-like, and there is a tendency that it becomes difficult to obtain wet granules (granulated body). is there. Moreover, when a non-volatile fraction is 100 mass%, it is a case where a solvent is not used and a wet granule cannot be obtained.

<Method for producing electrode>
Embodiment 1
FIG. 1 is a flowchart showing an outline of a method for manufacturing an electrode according to the present embodiment. As shown in FIG. 1, the electrode manufacturing method of this embodiment includes at least the following wet granule preparation step (S10), a molding step (S20), and an arrangement step (S30) in this order.

<< wet granule preparation process (S10) >>
In the wet granule preparation step, the above wet granule containing an electrode active material, a binder and a solvent is prepared. The wet granule includes a first wet granule and a second wet granule. The second wet granule has a smaller average particle size than the first wet granule. Thereby, the second wet granule is less malleable than the first wet granule.

  In addition, malleability means the easiness to extend with respect to a compressive force. However, in this specification, the term “extensibility” may include the meaning of ductility, which is the ease of extension against tensile force.

(First wet granule)
The first wet granule can be prepared, for example, by mixing (granulating) an electrode active material, a binder, a solvent, and the like. Examples of various granulation operations used for preparing the first wet granule include stirring granulation, fluidized bed granulation, rolling granulation and the like. For these granulating operations, various granulating apparatuses such as a stirring and mixing apparatus can be used. When the stirring and mixing device has a stirring blade (rotor blade), the rotation speed of the stirring blade is, for example, about 200 to 5000 rpm.

  The average particle diameter of the first wet granule is preferably 0.3 mm or more and 4 mm or less, and more preferably 0.3 mm or more and 1.0 mm or less. In this case, the effect of the present disclosure can be obtained more reliably.

  The average particle size of the first wet granule can be adjusted by changing various known conditions in the granulation operation. For example, the average particle diameter of the obtained wet granule can be adjusted by changing the average particle diameter of the electrode active material, the type of binder, the blending amount of the electrode active material and the binder, the amount of solvent used, and the like. In addition, the average particle size of the resulting wet granule can be adjusted by changing the type of granulator used in the granulation operation, the rotational speed of the stirring blade, the time of the granulation operation (mixing time), etc. it can.

(Second wet granule)
Similar to the first wet granule, the second wet granule can be prepared, for example, by mixing (granulating) an electrode active material, a binder, a solvent, and the like.
The average particle size of the second wet granule can be prepared in the same manner as the first wet granule. However, in this embodiment, the second wet granule has an average particle size smaller than that of the first wet granule. That is, in this embodiment, in order to make the malleability of the second wet granule lower than that of the first wet granule, the average particle diameter of the second wet granule is made smaller than that of the first wet granule. .

  The average particle size of the second wet granule is preferably 0.3 mm or greater and 1.0 mm or less, and more preferably 0.3 mm or greater and 0.5 mm or less. In this case, the effect of the present disclosure can be obtained more reliably.

  The second wet granule can be prepared, for example, by classifying particles having a small particle size from the first wet granule using a sieve having a predetermined opening. However, it is not always necessary to use a sieve. In the granulation operation, the second wet granule having an average particle size smaller than that of the first wet granule is used in the same manner as the adjustment of the average particle size of the first wet granule. It may be prepared.

<< Molding process (S20) >>
In the molding step, wet granules (first wet granule and second wet granule prepared in the wet granule preparation step (S10)) are supplied to the gap between the pair of rolls, and the wet granule is compression-molded. By doing so, a sheet-like electrode mixture layer is formed.

  In this step, an electrode manufacturing apparatus 3 as shown in FIGS. 2 and 5 is used. The electrode manufacturing apparatus 3 includes four rolls (A roll 31, B roll 32, C roll 33, and D roll 34).

  2 and 5, the wet granule 10 (the first wet granule 101 and the second wet granule 102) is supplied to the gap between the pair of rolls (A roll 31 and B roll 32) and compression-molded. (The electrode mixture layer 12 is formed).

  Referring to FIG. 5, in the upper vicinity between the pair of rolls (A roll 31 and B roll 32), a pair of side plates 21 that regulate the end face (width dimension) of the electrode mixture layer 12, and those Two partition walls 22 are provided between them. Then, the first wet granule 101 is placed between the two partition walls 22 from above by a feeder (not shown) or the like disposed immediately above the gap between the pair of rolls (A roll 31 and B roll 32). The second wet granule 102 is supplied between the side plate 21 and the partition wall 22. Accordingly, in the gap between the pair of rolls, the second wet granule 102 is supplied to the end portion in the direction of the rotation axis of the roll, and the first wet granule 101 is supplied to the center portion in the direction of the rotation axis of the roll. .

  In FIG. 5, for simplification, the particle diameter of the wet granule is drawn in the same way, but in practice, the first wet granule 101 at the center and the second wet granule at the end are used. The particle size is different from that of 102.

  On the other hand, conventionally, an electrode has been manufactured using an apparatus as shown in FIGS. FIG. 4 is a conceptual diagram for explaining a conventional electrode manufacturing method (wet granule forming method). Conventionally, the wet granule supplied to the gap between the pair of rolls has the malleability (average particle size or non-volatile fraction) of the wet granule 10 at the center and the end in the rotation axis direction of the roll. There was no difference (see 23a before spreading in FIG. 4). For this reason, application of wet granules may occur at the end in the rotational axis direction of the roll (see 23b after spreading in FIG. 4).

  On the other hand, in the manufacturing method of the electrode of this embodiment, as described above, an apparatus as shown in FIG. 2 and FIG. 5 is used, and at the central part and the end part in the rotation axis direction of the roll, There is a difference in the average particle size (extensibility) of the wet granules (see 23a before spreading in FIG. 6). Thereby, the edge part precision of an electrode compound-material layer can be improved, suppressing generation | occurrence | production of the surface crushing etc. of the electrode compound-material layer which reduces battery performance (refer 23b after extending of FIG. 6).

  The ratio of the distance between the side plate 21 and the partition wall 22 to the distance between the pair of side plates 21 (the width of the electrode mixture layer), that is, the total length of the central portion and the end portion in the rotation axis direction of the roll ( The ratio of the length of each end to the width of the electrode mixture layer is, for example, about 5 to 40%. In the case of such a ratio, the effect of the present disclosure that achieves both the effect of suppressing the occurrence of surface crushing of the electrode mixture layer and the effect of increasing the edge accuracy of the electrode mixture layer can be more reliably obtained. Can do. That is, when this ratio is too small, the supply amount of the second wet granule is insufficient, and it is difficult to obtain the effect of improving the edge accuracy of the electrode mixture layer. Moreover, there is a possibility that the second wet granule cannot be supplied smoothly. On the other hand, when this ratio is too large, the amount of the second wet granule having low malleability is increased, and the surface of the electrode mixture layer is likely to be crushed.

  The ratio of the supply amount per unit time of the second wet granule to the total supply amount (supply rate) of the wet granule (first wet granule and second wet granule) per unit time is, for example, 5 to It is about 40% by mass. For the same reason as the above-mentioned distance ratio, in such a ratio, both the effect of suppressing the occurrence of surface crushing of the electrode mixture layer and the effect of increasing the edge accuracy of the electrode mixture layer are compatible. The effect of the present disclosure can be obtained more reliably.

  In addition, as for the A roll 31 and the B roll 32, those rotating shafts are hold | maintained so that the distance between them may be maintained constant. The B roll 32 and the C roll 33 also hold their rotation axes so that the distance between them is maintained constant. The distance between the A roll 31 and the B roll 32 (the shortest linear distance connecting the surfaces of the pair of rolls) and the distance between the B roll 32 and the C roll 33 are, for example, about 50 μm to 10 mm, preferably 100 μm. About 1 mm. In the conventional method for manufacturing an electrode, the edge portion of the electrode mixture layer is likely to occur in such a case, and thus the effect of the present disclosure is particularly useful. The basis weight (mass per unit area) of the electrode mixture layer 12 can be adjusted by the distance between the pair of rolls.

  Moreover, the diameter of each of A roll 31, B roll 32, and C roll 33 is about 20-25 cm, for example. The diameters of the A roll 31, the B roll 32, and the C roll 33 may be the same or different. When the diameters are different, the ratio of the diameters of the pair of rolls (for example, A roll 31 and B roll 32) is about 1: 2 to 2: 1. The material of each roll is not particularly limited, and various known materials can be used. For example, stainless steel (SUS) can be used.

  The A roll 31 and the B roll 32 (a pair of rolls) have rotation axes (center axes) parallel to each other, and are driven to rotate in directions opposite to each other. The B roll 32 and the C roll 33 also have rotational axes parallel to each other and are driven to rotate in opposite directions. The C roll 33 and the D roll 34 also have rotation axes parallel to each other and are driven to rotate in opposite directions. 2, 3, and 5, arc-shaped arrows drawn on each roll indicate the rotation direction of each roll.

  The peripheral speed of the B roll 32 is preferably faster than the peripheral speed of the A roll 31. The peripheral speed of the B roll 32 is about 3 to 5 times the peripheral speed of the A roll 31. By making the peripheral speed of the B roll 32 faster than the peripheral speed of the A roll 31, the wet granule is stretched more on the surface of the B roll 32 than on the surface of the A roll 31. For this reason, the area where the liquid crosslinking (solvent) portion of the wet granule is in contact with the surface of the B roll 32 is larger than the area of contact with the surface of the A roll 31. Thereby, the wet granule (electrode mixture layer 12) after rolling sticks to the B roll 32 side and is conveyed by the B roll 32. Here, the peripheral speed of the roll is the moving speed of the roll surface.

  Similarly, the peripheral speed of the C roll 33 is preferably faster than the peripheral speed of the B roll 32. For example, the peripheral speed of the C roll 33 is about 3 to 5 times the peripheral speed of the B roll 32.

  In the present embodiment, it is desirable to improve the linearity (end portion accuracy) of the shape at both ends of the electrode mixture layer by supplying the second wet granule to both ends in the rotation axis direction of the pair of rolls. . However, if the second wet granule is supplied to at least one end, it is possible to obtain the effect of the present disclosure, which improves the end accuracy of the electrode mixture layer when an electrode is produced by the wet granulation method. Is possible.

<< Arrangement Step (S30) >>
In the arranging step, the electrode mixture layer 12 is arranged on the electrode current collector 13. The electrode current collector 13 is not particularly limited. For example, various known metal foils for electrodes can be used. As the positive electrode current collector, for example, an aluminum foil can be used. As the negative electrode current collector, for example, a copper foil (rolled copper foil, electrolytic copper foil, etc.) can be used. Although the thickness of an electrode electrical power collector is not specifically limited, For example, it is about 5-20 micrometers.

  Specifically, the electrode mixture layer 12 is disposed on the electrode current collector 13 by transferring the sheet-like electrode mixture layer 12 produced in the forming step (S <b> 20) to the electrode current collector 13.

  Specifically, with reference to FIGS. 2 and 5, the electrode current collector 13 is conveyed on the C roll 33 and supplied to the gap between the B roll 32 and the C roll 33. After leaving the gap between the A roll 31 and the B roll 32, the electrode mixture layer 12 is conveyed on the B roll 32 and supplied to the gap between the B roll 32 and the C roll 33.

  In the gap between the B roll 32 and the C roll 33, the electrode mixture layer 12 is pressed against the electrode current collector 13, and the electrode mixture layer 12 is separated from the B roll 32 and is crimped to the electrode current collector 13. The That is, the electrode mixture layer 12 is transferred from the B roll 32 to the electrode current collector 13. In this way, the sheet-like electrode mixture layer 12 is disposed at a predetermined position on the electrode current collector.

  An exposed portion where the electrode mixture layer 12 is not disposed can be provided at both ends of the electrode current collector 13 in the width direction. The exposed portion can be connected to a current collecting terminal of the battery.

  After the electrode mixture layer 12 is dried, the electrode current collector 13 and the electrode mixture layer 12 (electrode 11 in FIGS. 2 and 5) are cut into a predetermined size (length) using, for example, a slitter or the like. By doing so, a sheet-like electrode (electrode sheet) can be manufactured.

  In the above description, the arrangement step (S30) is performed after the molding step (S20). However, in the electrode manufacturing method of the present disclosure, the molding step (S20) and the arrangement step (S30) are performed simultaneously. It is also possible to implement.

  Specifically, for example, as shown in FIGS. 2 and 5, using only the A roll 31 and the B roll 32, the electrode current collector 13 is conveyed onto the surface of the B roll 32, and the A roll 31. In the same manner as in the molding step (S20), wet granules (first wet granules and second wet granules) are supplied to the gap between the B roll 32 and the B roll 32. Thereby, in the gap, the wet granule is compression-molded to form the electrode mixture layer 12, and at the same time, the electrode mixture layer 12 is pressed against the electrode current collector 13. In this manner, the forming step (S20) and the arranging step (S30) are performed at the same time, and the sheet-like electrode mixture layer 12 can be arranged on the electrode current collector 13.

[Embodiment 2]
In this embodiment, in order to make the malleability of the second wet granule lower than that of the first wet granule, the non-volatile fraction (NV ratio) of the second wet granule is made larger than that of the first wet granule. This is different from the first embodiment. The other points of this embodiment are basically the same as those of the first embodiment.

  In the electrode manufacturing method of the present embodiment, an apparatus as shown in FIGS. 2 and 5 is used, and there is a difference in the NV ratio of the wet granule between the center portion and the end portion in the rotation axis direction of the roll. (See 23a before spreading in FIG. 9). That is, in this embodiment, the non-volatile fraction of the second wet granule is larger than that of the first wet granule, so that the malleability of the second wet granule is lower than the malleability of the first wet granule. Become. Thereby, the edge part precision of an electrode compound material layer can be improved, suppressing generation | occurrence | production of the surface crushing etc. of the electrode compound material layer which reduces battery performance (refer 23b after extending of FIG. 9).

  The second wet granule preferably has a nonvolatile fraction of 79% by mass to 80% by mass. In this case, the effect of the present disclosure can be obtained more reliably. Moreover, the non-volatile fraction of the first wet granule is preferably 78% by mass or less, and more preferably 75 to 78% by mass.

  In addition, in the manufacturing method of the electrode of this indication, the malleability of the 2nd wet granule should just be lower than the 1st wet granule, and is not restricted to an aspect like Embodiment 1 and Embodiment 2.

  The electrode obtained by the manufacturing method of the above-described embodiment can be used, for example, as an electrode of a lithium ion secondary battery (nonaqueous electrolyte secondary battery). The lithium ion secondary battery can be used, for example, as a power source for a hybrid vehicle (HV), an electric vehicle (EV), a plug-in hybrid vehicle (PHV), or the like. However, the electrode obtained by the manufacturing method of the present disclosure is not limited to such a use, and can be applied to any use.

  Hereinafter, although this embodiment is described using an example, this embodiment is not limited to these.

<Manufacture of electrodes>
[Examples 1-3]
The electrodes (positive electrode sheets for lithium ion secondary batteries) of Examples 1 to 3 were manufactured as follows.

<< wet granule preparation process >>
First, the following positive electrode materials were prepared.
Positive electrode active material: LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (average particle size: 5 μm)
Binder: PVDF
Conductive material: AB
Solvent: NMP

(Preparation of first wet granule)
A positive electrode active material (94.5 parts by mass) and a conductive material (4 parts by mass) were charged into a stirring tank of a tabletop granulator (stirring granulator), and the stirring blade was rotated at 4500 rpm and mixed for 20 seconds. . Thereafter, while continuing the same mixing, the mixture was sprayed (20 seconds) with a 5.0% by weight binder solution (containing 1.5 parts by weight of the binder, the solvent being NMP) to obtain a wet body. It was. The obtained wet body was further refined with a stirring blade to prepare a first wet granule. The amount of the solvent used was adjusted so that the non-volatile fraction (NV ratio) of the first wet granule was 70% by mass. It was 2.0 mm when the average particle diameter of the 1st wet granule was measured. In addition, as described in the first embodiment, as the average particle size, in the volume-based particle size distribution measured by the laser diffraction scattering method, a particle size (D50) of 50% cumulative from the fine particle side was measured.

(Preparation of second wet granule)
A part of the prepared first wet granule was classified using a predetermined sieve, and the second wet granule was collected.

  Here, the average particle size of the second wet granule was measured. As a result of measuring the particle size distribution, the average particle sizes of the second wet granules in Examples 1 to 3 were 1.0 mm, 0.5 mm, and 0.3 mm.

<Molding process>
In the same manner as in the above-described embodiment, the wet granule (first wet granule and second wet granule) obtained in the wet granule preparation step using the electrode manufacturing apparatus 3 as shown in FIGS. 2 and 5 From this, a sheet-like electrode mixture layer 12 (positive electrode mixture layer) was formed.

  The distance between the side plate 21 and the partition wall 22 was about 3 mm, and the distance between the partition wall 22 and the partition wall 22 was about 114 mm. The supply amount of the 2 wet granules was 5% by mass to 10% by mass with respect to the total amount of the first wet granules and the second wet granules.

《Arrangement process》
The electrode mixture layer formed as described above is formed on the electrode current collector 13 (positive electrode current collector) using the electrode manufacturing apparatus 3 shown in FIGS. 2 and 5 in the same manner as in the above embodiment. Arranged. As the positive electrode current collector, an aluminum foil (thickness: 15 μm) was used.

  After the electrode mixture layer was dried, the electrode current collector and the electrode mixture layer were cut into a predetermined size using a slitter to produce a sheet-like electrode 11 (positive electrode sheet). Thus, the electrodes of Examples 1 to 3 were manufactured.

  In the electrode manufacturing apparatus 3, the peripheral speeds of the C roll 33 and the D roll 34 were set so that the positive electrode sheet was manufactured at a speed of 30 m / min. The peripheral speed of the B roll 32 was set to be slower than the peripheral speed of the C roll 33, and the peripheral speed of the A roll 31 was set to be slower than the peripheral speed of the B roll 32. In addition, the space | interval of A roll 31 and B roll 32 was 50 micrometers, and the space | interval of B roll 32 and C roll 33 was 65 micrometers. The diameters of the A roll 31, the B roll 32, and the C roll 33 were all 25 cm.

[Comparative Example 1]
In Comparative Example 1, the electrode mixture layer was formed by compression molding only one kind of wet granule 10 (first wet granule) with an apparatus without the partition wall 22 as shown in FIG. This is different from the first embodiment. Otherwise in the same manner as in Example 1, an electrode (positive electrode sheet) of Comparative Example 1 was produced.

(Evaluation 1)
About Examples 1-3 and Comparative Example 1, the maximum unevenness | corrugation difference of the width direction edge part of an electrode compound material layer was measured as a parameter | index of the edge part precision of an electrode (electrode compound material layer). The measurement results are shown in Table 1 and FIG. Moreover, the photograph of the edge part of the electrode compound-material layer in Example 2 and Comparative Example 1 is shown to Fig.8 (a) and (b). In addition, “the unevenness difference at the end in the width direction of the electrode mixture layer” means the width direction of the electrode mixture layer in a plan view when the sheet-like electrode mixture layer is viewed from the direction perpendicular to the main surface. It is the maximum value of the unevenness difference for the two-dimensional shape of the end. Here, the “concavo-convex difference” means a difference in height between adjacent concave and convex portions (a difference in position in the width direction of the sheet-shaped electrode composite layer). Note that such unevenness can be measured with a microscope.

  Moreover, the presence or absence of surface crushing (see FIG. 13) of the electrode mixture layer (active material) was determined by visually observing a SEM photograph of the surface of the electrode mixture layer. As a result, in all of Examples 1 to 3 and Comparative Example 1, surface crushing of the electrode mixture layer was not observed.

From the results shown in Table 1, FIG. 7 and FIG. 8, the average particle size of the second wet granule supplied to the end of the roll in the rotation axis direction is the first supplied to the center of the roll in the rotation axis direction. It turns out that the edge part precision of an electrode compound-material layer can be raised by making it smaller than 1 wet granule. Further, in all of Examples 1 to 3 and Comparative Example 1, surface crushing of the electrode mixture layer was not observed. This is because the malleability of the second wet granule supplied to the end of the roll in the rotation axis direction is low, and the malleability of the first wet granule supplied to the center of the roll in the rotation axis direction is high. It is considered to be an effect.
Such an effect is considered to be obtained more reliably when the average particle size of the second wet granule is 0.3 mm or more and 1.0 mm or less. Further, for example, when the target value of the maximum unevenness difference is set to 0.7 mm or less, the target value can be achieved when the average particle size of the second wet granule is 0.3 mm or more and 0.5 mm or less. You can see (see Figure 7).

[Examples 4 to 7]
In Examples 4 to 7, the second wet granule having a higher NV ratio than the first wet granule was prepared by changing the concentration of the binder solution sprayed in the preparation of the second wet granule. This is different from the first embodiment. Other than that was carried out similarly to Example 1, and manufactured the electrode (positive electrode sheet) of Examples 4-7. In Examples 4 to 7, the NV ratio of the second wet granule is 78% by mass, 79% by mass, 80% by mass, and 81% by mass of the solvent used for the sprayed binder solution. The amount of was adjusted. The NV ratio of the first wet granule is 70% by mass as in Example 1. The average particle size of the second wet granule is the same as that of the first wet granule.

(Evaluation 2)
About Examples 4-7, it carried out similarly to Examples 1-3 and the comparative example 1, and measured the largest uneven | corrugated difference. The measurement results are shown in Table 2. FIG. 11 is a graph showing the relationship between the non-volatile fraction of the second wet granule and the maximum unevenness of the end portion in the width direction of the electrode mixture layer. In addition, the photograph of the edge part of the electrode compound-material layer in Example 5 and Comparative Example 1 is shown to Fig.12 (a) and (b).

  Moreover, the presence or absence of surface crushing (see FIG. 13) of the electrode mixture layer (active material) was determined by visually observing a SEM photograph of the surface of the electrode mixture layer. The results are also shown in Table 2.

  From the results of Table 2, the NV ratio of the second wet granule is made higher than that of the first wet granule particles, thereby suppressing the occurrence of surface crushing of the electrode mixture layer that reduces the battery performance, and the electrode combination. It turns out that the edge part precision of a material layer can be improved.

  FIG. 10 is a graph showing the relationship between the nonvolatile fraction of wet granules and malleability. The compressive force on the vertical axis in the figure is the compressive force (kN) required to spread the sample per unit to a predetermined area, and is measured by a spreadability evaluation apparatus. As shown in FIG. 10, the malleability increases as the non-volatile fraction of the wet granule increases. From this, in Examples 4-7, the malleability of the 2nd wet granule supplied to the edge part of the rotating shaft direction of a roll is low, and the 2nd wet granule supplied to the center part of the rotating shaft direction of a roll is low. It is considered that the end accuracy of the electrode mixture layer was improved while suppressing the occurrence of surface crushing of the electrode mixture layer which deteriorates the battery performance.

  Moreover, it is thought that the effect of this indication can be acquired more reliably when the non-volatile fraction of a 2nd wet granule is 79 to 80 mass%.

  The NV rate shown in Table 2 is a ratio calculated based on the amount of solvent used in the sprayed binder solution (mass ratio of components other than the solvent to the total mass of all raw materials including the solvent). In the wet granule actually supplied between a pair of rolls, the ratio of the non-volatile component may be slightly higher than this value due to volatilization of the solvent and the like.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present disclosure is defined by the scope of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the scope of the claims.

  10 wet granules, 101 first wet granules, 102 second wet granules, 11 electrodes, 12 electrode composite layers, 13 electrode current collectors, 21 side plates, 22 partition walls, 23a before spreading, 23b after spreading, 3 Electrode manufacturing apparatus, 31 A roll, 32 B roll, 33 C roll, 34 D roll.

Claims (5)

Preparing a wet granule comprising an electrode active material, a binder and a solvent;
A forming step of forming an electrode mixture layer by supplying the wet granule to a gap between a pair of rolls and compressing the wet granule,
Arranging the electrode mixture layer on an electrode current collector, and a method for producing an electrode,
The wet granule includes a first wet granule and a second wet granule that is less malleable than the first wet granule,
The pair of rolls have rotation axes parallel to each other and are driven to rotate in directions opposite to each other,
In the gap between the pair of rolls, the second wet granule is supplied to an end portion in the direction of the rotary shaft, and the first wet granule is supplied to a central portion in the direction of the rotary shaft. Method.   The method for producing an electrode according to claim 1, wherein the second wet granule has an average particle size smaller than that of the first wet granule.   The method for producing an electrode according to claim 2, wherein the second wet granule has an average particle size of 0.3 mm or more and 1.0 mm or less.   The method for producing an electrode according to claim 1, wherein the second wet granule has a non-volatile fraction larger than that of the first wet granule.   The method for producing an electrode according to claim 4, wherein the second wet granule has a nonvolatile fraction of 79% by mass or more and 80% by mass or less.