JP2022160120A - Method for manufacturing electrode for secondary battery - Google Patents

Abstract

To provide a method for manufacturing an electrode for a secondary battery, which is high in a capacity-keeping rate.SOLUTION: A method for manufacturing an electrode for a secondary battery comprises the steps of: rolling an argillaceous granulated material produced by mixing at least an active substance and a solvent by passing the argillaceous granulated material through between a pair of rolls, transferring the rolled granulated material to a surface of a collector foil 11 to form a granulated material film 21 on the surface of the collector foil 11; concavely providing, in the granulated material film 21, a hole part 22 extending from the surface of the granulated material film 21 in a thickness direction to form a hole part-formed film 23; applying liquid slurry obtained by mixing at least the active substance and solvent to the surface of the hole part-formed film 23 to form a slurry film 41; and drying the hole part-formed film 23 and the slurry film 41 to form a mixture material layer 50.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing an electrode for a secondary battery.

Electrodes used in secondary batteries such as lithium ion secondary batteries include a conductive current collector (collector foil) and a composite layer containing an active material and the like held on the current collector. ing. A lithium-ion secondary battery is a non-aqueous secondary battery that can be charged and discharged by moving lithium ions in an electrolytic solution between a positive electrode and a negative electrode that absorb and release lithium ions.

For the purpose of increasing the capacity and output of such a secondary battery, the composite material layer may be subjected to microfabrication. For example, there is known a technique for improving the utilization efficiency of the electrolytic solution by providing fine holes extending in the thickness direction in the composite material layer.

In Patent Document 1, a mixture layer containing an active material is provided on at least one side of a current collector. In the thickness direction of the mixture layer, a large number of micropores having openings with a pore diameter of 0.3 to 150 μm are formed on the surface opposite to the current collector. and a non-aqueous secondary battery having the electrode.

JP 2012-190625 A

The non-aqueous secondary battery described in Patent Document 1 is characterized by a large capacity during high-power discharge and excellent load characteristics even when the mixture layer (mixture layer) of the electrode is thick. However, in the technique described in Patent Document 1, micropores are formed by pressing after drying a coating film in which an electrode material and a solvent are mixed. In the composite material layer of the electrode manufactured in this way, the active material in the processed portion where the fine holes are formed may be damaged by pressing. In this case, when charging and discharging are repeated during use of the secondary battery, there is a problem that a substance derived from the charge carrier is deposited and the battery capacity is lowered.

The present invention has been made to solve such problems, and an object of the present invention is to provide a method for manufacturing a secondary battery electrode having a high capacity retention rate.

A method for manufacturing a secondary battery electrode according to one embodiment includes rolling a clay-like granule obtained by mixing at least an active material and a solvent, and rolling the granule by passing it between a pair of rolls. is transferred to the surface of the current collector foil to form a granule film on the surface of the current collector foil; applying a liquid slurry obtained by mixing at least an active material and a solvent on the surface of the hole forming film to form a slurry film; and drying the formed film and the slurry film to form a composite layer.

The present invention can provide a method for manufacturing a secondary battery electrode having a high capacity retention rate.

4 is a flow chart showing a method for manufacturing a secondary battery electrode according to Embodiment 1. FIG. FIG. 2 is a partial cross-sectional view showing step S1 in the flow chart shown in FIG. 1; 2 is a partial cross-sectional view showing step S2 in the flow chart shown in FIG. 1; FIG. 2 is a partial cross-sectional view showing step S3 in the flowchart shown in FIG. 1; FIG. 2 is a partial cross-sectional view showing step S4 in the flow chart shown in FIG. 1; FIG. 4 is a table showing electrode manufacturing conditions and characteristic evaluation results.

Embodiment 1
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments. Also, for clarity of explanation, the following description and drawings are simplified as appropriate. What is shown in the drawing is a part of the whole, and actually includes many other configurations not shown. Furthermore, in the following description, the same or equivalent elements are denoted by the same reference numerals, and overlapping descriptions are omitted.

Hereinafter, as one preferred embodiment of the secondary battery electrode manufacturing method according to the present embodiment, a method for manufacturing a lithium ion secondary battery electrode will be specifically described. Lithium-ion secondary batteries use lithium ions as charge carriers, and charge and discharge are realized by the transfer of charge between the positive electrode (positive electrode plate) and the negative electrode (negative electrode plate), which are electrodes (electrode plates). Battery.

First, the outline of the electrode plate 100 manufactured by the manufacturing method of the secondary battery electrode according to the present embodiment will be described. The electrode plate 100 has a collector foil 11 and a composite material layer 50 formed on the surface of the collector foil 11 (see FIG. 5).

The current collector foil 11 is formed in a plate-like or foil-like shape and is made of a highly conductive metal. In the case of the positive electrode plate, examples of the metal forming the current collector foil 11 include aluminum, aluminum alloys, nickel, titanium, and stainless steel. In the case of the negative electrode plate, examples of the metal forming the collector foil 11 include copper, copper alloys, nickel, titanium, and stainless steel.

The composite material layer 50 is formed on at least one surface of the current collector foil 11 except for an edge portion along one edge in the width direction. In addition, the electrode plate 100 has an exposed portion where the collector foil 11 is exposed without forming the composite material layer 50 at the edge of the collector foil 11 . The composite material layer 50 contains at least an active material and is held by the current collector foil 11 . The composite material layer 50 may contain additives such as a conductive material, a binder, and a thickener as necessary, in addition to the active material.

(active material)
The active material used for the positive electrode plate is a material capable of intercalating and deintercalating lithium ions, and any active material that can be used for lithium ion secondary batteries can be used without particular limitation. Active materials include, for example, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium iron phosphate (LiFePO ₄ ), lithium nickel cobalt aluminum oxide (NCA), Nickel cobalt lithium manganate (NCM) and the like can be used alone or in combination. In addition, other metal elements may be added to the active material.

The active material used for the negative electrode plate is a material capable of intercalating and deintercalating lithium ions, and for example, carbon materials such as natural graphite, artificial graphite, hard carbon, soft carbon, and activated carbon can be used.

The primary particles of the active material are particulate. The average particle size (D50) of the active material (primary particles) is, for example, 0.1 μm to 50 μm, preferably 1 μm to 20 μm from the viewpoint of fluidity during granulation. The average particle size (D50) of the active material can be determined, for example, from the results of particle size distribution measurement by a laser diffraction scattering method.

(Conductive material)
The conductive material has a function of transmitting electricity generated by the active material to the collector foil 11 . Examples of conductive materials that can be used include carbon materials such as various carbon blacks (eg, acetylene black), activated carbon, graphite, and carbon fibers.

(Binder)
The binder binds the electrode materials forming the mixture layer 50 to each other to form the mixture layer 50 , and binds the formed mixture layer 50 to the surface of the current collector foil 11 . . The binder having such a function is not particularly limited as long as it is a material that dissolves or disperses in the solvent described below. Examples of binders that can be used include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyethylene oxide (PEO), styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC).

(Mixed material layer)
From the viewpoint of achieving high energy density, the proportion of the active material in the entire composite material layer 50 is, for example, 70% by mass to 99% by mass, preferably 85% by mass to 95% by mass. In addition, the proportion of the conductive material in the entire mixture layer 50 is, for example, 0.5% by mass to 20% by mass, preferably 2% by mass, from the viewpoint of achieving both output characteristics and energy density at a high level. % to 10% by mass.

The proportion of the binder in the entire composite material layer 50 is, for example, 0.5% by mass to 10% by mass, preferably 1% by mass to 5% by mass, from the viewpoint of peel strength and film-forming properties. If the ratio of the binder is too small, the amount of binder near the current collector foil 11 is insufficient, and the peel strength between the composite material layer 50 and the current collector foil 11 tends to decrease. In addition, the film-forming properties of the composite material layer 50 are deteriorated, resulting in the formation of voids and streaks, which may lead to the deterioration of the battery performance, for example, the deposition of lithium during charging and discharging. On the other hand, if the proportion of the binder is too high, the binder may cover the surface of the positive electrode active material, hindering the movement of lithium ions, and tending to increase the internal resistance of the battery.

The composite material layer 50 has a large number of micropores 51 extending in the thickness direction from the surface of the composite material layer 50 . The shape of the fine holes 51 is exemplified by a conical shape that tapers from the surface of the composite material layer 50 toward the collector foil 11, but is not limited to this.

At least part of the micropores 51 preferably has a depth of 50% or more of the thickness of the composite material layer 50 . The ratio of the total area of the openings of the micropores 51 to the surface area of the composite material layer 50 is preferably 1% to 10%, for example. The distance between the centers of micropores 51 adjacent to each other is preferably 0.5 to 500 μm. In the electrode plate 100 provided with the micropores 51, the electrolytic solution penetrates deep into the electrode plate 100, so that the active material and the lithium ions as charge carriers come into contact with each other more often, and the electrolytic solution is utilized more efficiently. improves. As a result, an effect of suppressing an increase in diffusion resistance and improving output performance can be obtained.

Furthermore, the composite material layer 50 includes the first composite material layer 24 formed on the surface of the current collector foil 11 and the second composite material layer 42 formed on the surface of the first composite material layer 24. , has In this embodiment, the first composite material layer 24 is formed using clay-like granules having a relatively high solid content. Also, the second composite material layer 42 is formed using a liquid slurry having a relatively low solid content. Both the granules and the slurry are composite material layer forming compositions for forming the composite material layer 50 .

The thickness of the composite material layer 50 is, for example, 70 to 400 μm. The density of the composite material layer 50 is, for example, 0.9 g/cm ³ to 1.5 g/cm ³ . Among the composite material layers 50, the density of the first composite material layer 24 is, for example, 1.0 g/cm ³ to 1.8 g/cm ³ . Further, the density of the second composite material layer 42 in the composite material layer 50 is, for example, 0.8 g/cm ³ to 1.2 g/cm ³ . The density of the second mixture layer 42 is preferably lower than the density of the first mixture layer 24 .

Next, a method for manufacturing a secondary battery electrode according to this embodiment will be described with reference to FIG. FIG. 1 is a flowchart showing a method for manufacturing a secondary battery electrode according to Embodiment 1. FIG. The manufacturing method of the secondary battery electrode according to the present embodiment can be applied to both the positive electrode plate and the negative electrode plate 100 .

As shown in FIG. 1, the method for manufacturing a secondary battery electrode according to this embodiment includes steps S1 to S4. In step S1, clay-like granules obtained by mixing at least an active material and a solvent are passed between a pair of rolls and rolled, and the rolled granules are transferred to the surface of current collector foil 11 and collected. A granule film 21 is formed on the surface of the electric foil 11 . In step S<b>2 , holes 22 extending in the thickness direction from the surface of the granule film 21 are recessed in the granule film 21 to form the hole forming film 23 . In step S3, a slurry film 41 is formed by applying a liquid slurry obtained by mixing at least the active material and the solvent on the surface of the hole forming film 23. As shown in FIG. In step S<b>4 , the hole forming film 23 and the slurry film 41 are dried to form the composite material layer 50 .

Each of the above steps will be described in detail with reference to FIGS. 2 to 5. FIG. FIG. 2 is a partial cross-sectional view showing step S1 in the flow chart shown in FIG. FIG. 3 is a partial cross-sectional view showing step S2 of the flow chart shown in FIG. FIG. 4 is a partial cross-sectional view showing step S3 of the flow chart shown in FIG. FIG. 5 is a partial cross-sectional view showing step S4 in the flow chart shown in FIG. 2 to 5 show part of a cross section taken along a direction perpendicular to the surface of the current collector foil 11. As shown in FIG.

As shown in FIG. 1, in step S1, a granule film 21 is formed on the surface of current collector foil 11 . In this embodiment, the granules in a wet state are passed between a pair of rolls and rolled, and the rolled granules are transferred to the surface of the substrate (here, the current collector foil 11) to form a film. A granule membrane 21 is formed using a method. The granules contain an electrode material and a solvent for forming the composite material layer 50 (first composite material layer 24), and are in the form of clay having a relatively high solid content and viscosity.

The granules, which are the material of the granule film 21, are prepared by adding a small amount of solvent to a powder containing an active material and, if necessary, other solid components such as a conductive material, a binder, and a thickener. It is prepared by moistening and granulating it. For example, a stirring granulator such as a planetary mixer can be used to prepare the granules. The granules thus obtained are spherical secondary particles in which the solvent is wet between the particles of the conductive material and the active material, and the particles are bound and bonded to each other.

For example, a roll coater having three rolls can be used as a coating device for coating the granules. The three rolls are a first roll, a second roll, and a third roll. A predetermined gap is formed between a pair of horizontally adjacent first and second rolls. The outer peripheral surface of the first roll and the outer peripheral surface of the second roll face each other. The first roll and the second roll rotate in opposite directions. A third roll that conveys the current collector foil 11 is arranged next to the second roll. The outer peripheral surface of the second roll and the outer peripheral surface of the third roll face each other. The second and third rolls rotate in opposite directions. The position of the third roll may be any position as long as the molded body can be transferred to the surface of the current collector foil 11 .

In addition, partition walls are provided at both ends in the width direction of the first roll and the second roll. The partition walls hold the powder of the granules on the first roll and the second roll, and the width of the granule film 21 formed on the surface of the current collector foil 11 is defined by the distance between the partition walls. have a function.

In coating the granules on the surface of the current collector foil 11, first, the granules are supplied between the first roll and the second roll. In this state, when the first, second, and third rolls are rotated in opposite directions, the granules are sent to the gap and compressed between the first and second rolls to form a sheet. is molded into That is, the granules are rolled by the first roll and the second roll to form a sheet-like formed body (rolled granules).

At this time, if the peripheral speed of the second roll is higher than the peripheral speed of the first roll, and the peripheral speed of the third roll is higher than that of the second roll, the compact will remain attached to the surface of the second roll, Conveyed up to 3 rolls. The compact transported to the third roll is continuously transferred to the surface of the current collector foil 11 while being compressed between the second and third rolls. Thereby, the first laminate L1 having the granule film 21 formed on the surface of the current collector foil 11 can be formed. In addition, it is preferable to adjust the thickness of the molded body to an appropriate thickness so as not to generate scales and cracks.

Here, the density of the first composite material layer 24 can also be adjusted by the thickness of the compact and the degree of compression of the granule. The degree of compression of the granules is adjusted by the gap between the first roll and the second roll. As the gap is made smaller, the thickness of the compact becomes thinner, and the first composite material layer 24 can be formed with a higher density. On the other hand, if the density of the entire composite material layer 50 is too high, the voids in the composite material layer 50 are reduced, making it difficult for the composite material layer 50 to permeate and retain the electrolytic solution. If the amount of electrolyte retained in the composite material layer 50 is reduced, the capacity retention rate may decrease, which is not preferable. It is preferable to adjust the coating amount of the granules so that the basis weight is, for example, 5.0 mg/cm ² to 20.0 mg/cm ² per side of the current collector foil 11 .

The granules have, for example, an average particle size (D50) of 100 μm to 4 mm, preferably 200 μm to 1 mm. The average particle size (D50) of the granules can be adjusted according to the conditions during granulation. The average particle size (D50) of the granules can be obtained from the results of particle size distribution measurement by a laser diffraction scattering method, for example. Further, the solid content of the granules obtained by removing the solvent from the entire granules is, from the viewpoint of film-forming properties, for example, 60% by mass to 95% by mass, preferably 70% by mass to 80% by mass. be. The solid content of the granules can be adjusted by adjusting the blending amounts of the active material, other solid components, and solvent.

Non-aqueous solvents and aqueous solvents can be used without particular limitation as long as they can uniformly dissolve or disperse the binder. A solvent is appropriately selected according to the binder to be used. Examples of the solvent include N-methyl-2-pyrrolidone (NMP), methyl ethyl ketone (MEK), dimethylformamide (DMF), non-aqueous solvents such as toluene, mixed solvents combining non-aqueous solvents, water, and mainly water. Aqueous solvents such as mixed solvents can be used.

The ratio of the solvent to the whole granules is adjusted so that the solid content of the granules falls within the above range. If the proportion of the solvent is too low or too high, the film formability will deteriorate. If the proportion of the solvent is too high, the drying time for drying the granule membrane 21 will be lengthened, resulting in a decrease in productivity.

Subsequently, as shown in FIG. 3, in step S2, holes 22 are recessed in the granule film 21 formed in step S1. For recessing the holes 22 , for example, a mold 30 having a rectangular base 31 and a large number of protrusions 32 protruding from the surface of the base 31 can be used. The metal mold 30 is flat on the surface on which the protrusions 32 are provided, except for the protrusions 32 . The shape of the convex portion 32 is appropriately designed according to the desired shape of the fine hole 51, and has, for example, a conical shape that tapers toward the tip.

The mold 30 is arranged so that the tip of the projection 32 faces the surface of the first laminate L1 (the surface of the granule film 21). Then, the mold 30 is lowered toward the first laminate L1 to insert the protrusions 32 into the granule film 21 . At this time, it is preferable to press the surface of the granule film 21 using the mold 30 . Since the granules are clay-like with a high solid content, when the projections 32 of the mold 30 are inserted into the granule film 21 , the granule film 21 is deformed. Further, even after the convex portion 32 of the mold 30 is removed from the granule film 21, the given deformation can be maintained. Therefore, the granule membrane 21 can be formed into a desired shape.

Thus, the granules (the granule film 21) have, for example, the above-described value of the solid content, so that the shape retention is better than that of the liquid slurry. Further, by adjusting the thickness of the granule film 21 as the metal mold 30 presses, the first composite material layer 24 can be consolidated.

After pressing is performed until the first laminate L<b>1 has a desired thickness, the mold 30 is raised to remove the protrusions 32 from the granule film 21 . In this manner, the second laminate L2 having the collector foil 11 and the hole forming film 23 can be formed. The hole forming film 23 is provided with holes 22 extending in the thickness direction from the surface.

Granules in a wet state have a certain degree of flexibility. Therefore, when the granule membrane 21 in a wet state is pressed, the stress acting on the electrode material is reduced and the electrode material is not damaged as compared with, for example, the case where the granule membrane 21 is dried and then pressed. Hard to accept.

Therefore, by pressing the granule film 21 composed of the granules in a wet state for the purpose of forming the holes 22 and consolidating the granules, damage to the active material can be suppressed. Laser processing can be used as another method for recessing the holes 22 in the granule film 21, but the method using the mold 30 is more preferable because the processing and pressing of the holes 22 can be performed at the same time. preferable.

Subsequently, as shown in FIG. 4, in step S3, a slurry film 41 is formed using a slurry method. The slurry method is, for example, a coating method in which slurry is discharged from a die head of a die coater to apply the slurry onto the surface of the substrate (here, the second laminate L2). The slurry is a liquid mixture layer-forming composition having a relatively low solids content and viscosity and containing an electrode material and a solvent for forming the mixture layer 50 (second mixture layer 42).

The slurry, which is the material of the slurry film 41, is prepared by adding a solvent to powder containing other solid components such as an active material and, if necessary, a conductive material, a binder, a thickener, etc., and kneading the mixture. Prepare. The slurry may be prepared by adding a solvent to the granules granulated in step S1. For example, a kneader such as a planetary mixer can be used to prepare the slurry.

In addition to the die coater described above, a slit coater, comma coater, gravure coater, blade coater, or the like can be used for coating the slurry. A die coater is preferably used because it can form a uniform coating film with high accuracy.

The die coater mainly has a die head that discharges slurry toward the opposing base material (here, the second laminate L2) through a predetermined gap and coats the surface of the base material with the slurry. The second laminate L2 as a base material is attached to a conveying roller and conveyed by the rotation of the conveying roller. The second laminate L2 and the die head are arranged such that the hole forming film 23 of the second laminate L2 faces the ejection port of the die head.

When applying the slurry onto the surface of the second laminate L2 (on the surface of the hole forming film 23), the slurry is applied from the ejection port of the die head to the second laminate L2 conveyed by the conveying roller. A slurry film 41 is applied on the surface of the hole forming film 23 by discharging the slurry film 41 . It is preferable to adjust the coating amount of the slurry so that the basis weight of the slurry is, for example, 2.0 mg/cm ² to 5.0 mg/cm ² per side of the current collector foil 11 .

Since the liquid slurry has fluidity, it can also enter inside the holes 22 . Therefore, the slurry film 41 is formed following the surface shape of the hole forming film 23 . In this manner, the third laminate L3 having the collector foil 11, the hole forming film 23, and the slurry film 41 can be formed.

From the viewpoint of drying efficiency, the solid content of the slurry is preferably, for example, 40% by mass or more, and more preferably 50% by mass or more. By increasing the solid content of the slurry, the drying time for drying the slurry film 41 is shortened. From the viewpoint of productivity, the solid content of the slurry is preferably 70% by mass or less, more preferably 60% by mass or less.

Moreover, it is preferable that the viscosity of the slurry is as high as possible within a range that does not impair the coatability. With such a configuration, the slurry film 41 is uniformly held on the surface of the hole forming film 23, and a reaction interface that contributes to the battery chemical reaction between the composite material layer 50 and the electrolytic solution is easily formed.

The viscosity of the slurry is, for example, preferably 3000 mPa·s or more, more preferably 5000 mPa·s or more. On the other hand, if the viscosity is too high, the coatability is impaired, and streaks and thickness unevenness may occur in the slurry film 41, which is not preferable. Therefore, the viscosity of the slurry is, for example, preferably 20000 mPa·s or less, more preferably 17000 mPa·s or less. The solid content and viscosity of the slurry can be adjusted by adjusting the blending amounts of the active material, other solid components, and solvent. The ratio of the solvent to the entire slurry is appropriately adjusted so that the solid content or viscosity of the slurry is within the above range.

Subsequently, as shown in FIG. 5, in step S4, the third laminate L3 formed in step S3 is dried. A drying furnace that generates hot air can be used for drying the third laminate L3. In addition, the drying method is not limited to this.

The third laminate L3 is placed in a drying oven and dried with hot air to remove the solvent contained in the hole forming film 23 and the slurry film 41, thereby drying them. The hole forming film 23 is dried to form the first mixture layer 24 of the mixture layer 50 , and the slurry film 41 is dried to form the second mixture layer 42 of the mixture layer 50 . In this way, the composite material layer 50 provided with a large number of fine holes 51 is formed.

By the manufacturing method described above, the electrode plate 100 having the configuration in which the composite material layer 50 is held on the surface of the current collector foil 11 can be manufactured. Furthermore, after drying, the thickness of the entire electrode plate 100 may be adjusted by pressing using a flat plate press or the like.

Examples and comparative examples will be described below with reference to FIG. In addition, an Example does not limit this invention. FIG. 6 is a table showing electrode manufacturing conditions and characteristic evaluation results. Negative plates of Examples 1 to 3 and Comparative Examples 1 to 6 were manufactured under the manufacturing conditions shown in FIG. Then, evaluation lithium ion secondary batteries (evaluation batteries) were constructed using each of the manufactured negative electrode plates, and battery characteristics (cost, lithium deposition resistance) were evaluated.

In the following description, among the composite material layers obtained under the manufacturing conditions of each example, the one arranged on the surface of the current collector foil is referred to as the first layer, and the one arranged on the surface of the first layer will be referred to as the second layer. The operation of drying the first layer will be referred to as intermediate drying, the operation of pressing using a mold will be referred to as intermediate pressing, and the operation of pressing using a plate press will be referred to as final pressing.

[Negative electrode]
Natural graphite (C, average particle size 8 μm) was used as the negative electrode active material. CMC was used as a thickener. SBR was used as a binder. Ion-exchanged water was used as the solvent. A copper foil (thickness: 10 μm) was used as the current collector foil.

The mass ratio of the negative electrode active material, the thickener, and the binder in the total solid content was weighed so that C:CMC:SBR=98:1:1, and a required amount of solvent was added to these electrode materials. They were added and mixed to prepare granules and/or slurry. The thickness of the entire negative electrode plate manufactured using the prepared granules and/or slurry was approximately 150 μm. The granules and slurries used in the examples and comparative examples described below contain a mixture of a negative electrode active material, a thickener, and a binder in a predetermined ratio. are both adjusted by the solvent content.

(Example 1)
A negative electrode plate 100 (electrode plate 100) according to Example 1 was manufactured according to the flow shown in FIG. In step S1, a negative electrode active material, a thickener, a binder, and a solvent are put into a stirring granulator and mixed and granulated to obtain granules having a solid content of 80% by mass. body was prepared. Next, using a roll coater having three rolls as a coating device, the rolled granules were transferred to the surface of the current collector foil 11 to form the first layer on the surface of the current collector foil 11 . A particle film 21 was formed to obtain a first laminate L1. Then, the first laminated body L1 was cut out into approximately 30 cm squares. The coating amount of the granules was adjusted so that the basis weight was 15 mg/cm ² on one side of the current collector foil 11 and 30 mg/cm ² on both sides.

Subsequently, in step S2, a conical hole 22 was recessed using a die 30 in the granule film 21 of the cut first laminate L1. At this time, intermediate pressing was performed to adjust the thickness of the granule film 21 by pressing the surface of the granule film 21 using the mold 30 . As a result, a second laminate L2 in which the first hole forming film 23 was formed on the surface of the current collector foil 11 was obtained. In the second laminate L2, a plurality of holes 22 are arranged in a grid pattern along the longitudinal direction and the width direction. The depth of the holes 22 was 50 μm, and the diameter of the openings of the holes 22 on the surface was 25 μm. Moreover, the center interval between the holes 22 adjacent to each other in the same direction was 100 μm.

Subsequently, in step S3, a negative electrode active material, a thickener, a binder, and a required amount of solvent are put into a kneader and kneaded to obtain a viscosity of 15000 mPa s. A slurry was obtained. The slurry was applied to the surface of the hole forming film 23 using a die coater. As a result, a second slurry film 41 was formed on the surface of the hole forming film 23 to obtain a third laminate L3. The coating amount of the slurry was adjusted so that the basis weight was 2 mg/cm ² on one side of the current collector foil 11 and 4 mg/cm ² on both sides.

Subsequently, in step S4, the third laminate L3 was placed in a drying oven and dried with hot air (90° C., 5 minutes) for final drying to obtain the negative electrode mixture layer 50 . As a result, the negative electrode plate 100 having the negative electrode mixture layers 50 held on both sides of the current collector foil 11 was manufactured.

The negative electrode plate 100 manufactured under the manufacturing conditions of Example 1 includes a negative electrode mixture layer 50 having a first layer formed using granules and a second layer formed using slurry. The negative electrode mixture layer 50 is provided with micropores 51 . Further, the processing and pressing of the holes 22 are performed in a wet state before drying the applied mixture layer-forming composition (granules).

(Example 2)
In step S2, the intermediate press was omitted. Further, in step S4, final pressing was performed. In Example 2, the negative electrode plate 100 was manufactured in the same manner as in Example 1 except for these.

The negative electrode plate 100 manufactured under the manufacturing conditions of Example 2 includes a negative electrode mixture layer 50 having a first layer formed using granules and a second layer formed using slurry. The negative electrode mixture layer 50 is provided with micropores 51 . Further, the processing of the holes 22 is performed in a wet state before drying the applied mixture layer-forming composition (granules). On the other hand, the pressing is performed after drying the coated mixture layer-forming composition (granules and slurry).

(Example 3)
In step S2, the intermediate press was omitted. Further, in step S3, a slurry having a viscosity of 5000 mPa·s was used to form the second slurry film 41 . Further, in step S4, final pressing was performed. In Example 3, the negative electrode plate 100 was manufactured in the same manner as in Example 1 except for these.

The negative electrode plate 100 manufactured under the manufacturing conditions of Example 3 includes a negative electrode mixture layer 50 having a first layer formed using granules and a second layer formed using slurry. The negative electrode mixture layer 50 is provided with micropores 51 . Further, the processing of the holes 22 is performed in a wet state before drying the applied mixture layer-forming composition (granules). On the other hand, the pressing is performed after drying the coated mixture layer-forming composition (granules and slurry). The second layer is formed using low-viscosity slurry.

(Comparative example 1)
A negative electrode active material, a thickener, a binder, and a solvent were put into a kneader and kneaded to obtain a slurry having a viscosity of 3000 mPa·s. Next, a coating film was formed on the surface of the current collector foil by applying the slurry to the surface of the current collector foil using a die coater. This was placed in a drying oven and dried with hot air (80° C., 10 minutes) for final drying. The coating amount of the slurry was adjusted so that the basis weight was 17 mg/cm ² on one side of the current collector foil and 34 mg/cm ² on both sides.

The negative electrode plate manufactured under the manufacturing conditions of Comparative Example 1 includes a negative electrode mixture layer having only the first layer formed using slurry, and the negative electrode mixture layer is not provided with micropores. . Further, the pressing is performed after drying the coated mixture layer-forming composition (slurry).

(Comparative example 2)
A slurry having a viscosity of 3000 mPa·s was obtained in the same manner as in Comparative Example 1. Next, a coating film was formed on the surface of the current collector foil by applying the slurry to the surface of the current collector foil using a die coater. The mold was lowered toward the coating film on the surface of the current collector foil, and after inserting the projections of the mold into the coating film, the projections of the mold were removed. However, it was not possible to confirm the formation of pores in the coating film. The basis weight of the slurry is the same as in Comparative Example 1.

As shown in Comparative Example 2, since the liquid slurry contains a large amount of solvent and has a low solid content, it is difficult to process the holes. For example, even if the coating film is deformed by inserting the projections of the mold into the slurry coating film, the coating film cannot maintain the deformation after the projections of the mold are removed. Therefore, the slurry is considered to have low shape retention. Therefore, under the manufacturing conditions of Comparative Example 2, a negative electrode plate could not be manufactured.

(Comparative Example 3)
A slurry having a viscosity of 3000 mPa·s was obtained in the same manner as in Comparative Example 1. Next, a die coater was used to apply the slurry to the surface of the current collector foil, thereby forming a first coating film on the surface of the current collector foil. This was placed in a drying oven and dried with hot air (80° C., 10 minutes) for intermediate drying to obtain a dried slurry.

For the coating film in the dry state of the slurry dried body cut out to about 30 cm square, after forming holes using a mold, the intermediate press is omitted, and the slurry for the second layer is the same as in Example 1. A laminate was obtained by forming a film. Then, a negative electrode plate was manufactured by applying a final press to the laminate. The coating weight of the slurry for the first layer was adjusted to 15 mg/cm 2 on one side of the current collector foil and 30 mg/cm ² on both sides, and the basis weight of the second layer was adjusted to 15 mg/cm 2 on one side of the current collector foil and 30 mg/cm ² on both sides. Same as 1.

The negative electrode plate manufactured under the manufacturing conditions of Comparative Example 3 includes a negative electrode mixture layer having first and second layers formed using slurry, and the negative electrode mixture layer has micropores. is provided. However, the pressing is performed after drying the applied mixture layer-forming composition (slurry).

(Comparative Example 4)
A negative electrode plate was manufactured in the same manner as in Comparative Example 3, except that the processing of the holes was omitted. The negative electrode plate manufactured under the manufacturing conditions of Comparative Example 4 includes a negative electrode mixture layer having first and second layers formed using slurry, and the negative electrode mixture layer has micropores. Not provided. Further, the pressing is performed after drying the coated mixture layer-forming composition (slurry).

(Comparative Example 5)
Steps S2 and S3 in the flowchart of FIG. 1 are omitted, and after forming a granule film dried with hot air (80° C., 5 minutes) on the surface of the current collector foil according to steps S1 and S4, a final press is performed. Approximately 30 cm square was cut into a negative electrode plate. The coating amount of the granules was adjusted so that the basis weight was 17 mg/cm ² on one side of the current collector foil and 34 mg/cm ² on both sides.

The negative electrode plate manufactured under the manufacturing conditions of Comparative Example 5 includes a negative electrode mixture layer having only the first layer formed using granules, and the negative electrode mixture layer is provided with micropores. not Further, the pressing is performed after drying the applied mixture layer-forming composition (granules).

(Comparative Example 6)
After forming the granule film on the surface of the current collector foil according to step S1 in the flow chart of FIG. was performed to obtain a dried product. After forming holes using a mold in the granule film that is in a dry state from the dried body cut into a square of about 30 cm, a slurry having a viscosity of 15000 mPa s is used to form a second slurry film. A laminate was obtained by forming. At this time, the intermediate press was omitted. Then, a negative electrode plate was manufactured by applying a final press to the laminate. The weight per unit area of the granules and the slurry was the same as in Example 1.

The negative electrode plate manufactured under the manufacturing conditions of Comparative Example 6 includes a negative electrode mixture layer having a first layer formed using granules and a second layer formed using slurry. , the negative electrode mixture layer is provided with micropores. However, the pressing is performed after drying the applied mixture layer-forming composition (granules and slurry).

[Positive electrode]
NCM powder (average particle size: 5 μm) was used as the positive electrode active material. Acetylene black (AB) powder was used as the conductive material. PVdF was used as the binder. NMP was used as the solvent. An aluminum foil (thickness: 15 μm) was used as the current collector foil. No micropores were provided in the positive electrode mixture layer of the positive electrode plate.

The weight ratio of the positive electrode active material, the conductive material, and the binder in the total solid content is respectively weighed so that NCM:AB:PVdF=95:4:1, and a solvent is added to these electrode materials and kneaded. Thus, a positive electrode slurry was produced. Then, using a die coater, the positive electrode slurry is applied to both sides of the current collector foil, placed in a drying oven and dried with hot air (120 ° C., 10 minutes), and the thickness of the entire positive electrode plate is about 160 μm. It was pressed so that In this manner, a positive electrode plate having positive electrode mixture layers on both sides of the current collector foil was produced. The coating amount of the positive electrode slurry was adjusted so that the basis weight was 19 mg/cm ² on one side of the current collector foil and 38 mg/cm ² on both sides.

[evaluation]
Each of the negative electrode plates, the positive electrode plate, and the separator, which is a polyolefin resin sheet, were laminated in an insulated state to form an electrode assembly. Furthermore, each battery for evaluation was constructed by housing the electrode body and the non-aqueous electrolyte in a battery case as an exterior body. For each constructed battery for evaluation, relative evaluation of cost and evaluation of lithium deposition resistance (Li deposition resistance) based on the measurement result of capacity retention rate were performed.

(cost)
The evaluation of the cost was comprehensively evaluated based on the amount of material used, the number of manufacturing processes, and the increase or decrease in cost required for manufacturing time. The results are shown in the column of cost in the table of FIG. As shown in FIG. 6, in the column of cost, the battery for evaluation manufactured under the manufacturing conditions of Comparative Example 1 is used as a standard, and the overall cost is lower than that of Comparative Example 1. "X" indicates that the overall cost increased compared to Comparative Example 1.

For example, when the cost reduction rate was quantified, the reduction rate was higher in the order of Example 1, Example 2, Example 3, Comparative Example 5, Comparative Example 1, Comparative Example 4, Comparative Example 6, and Comparative Example 3. . Comparative Example 2 was not evaluated because a negative electrode plate could not be produced.

(lithium deposition resistance)
By measuring the capacity retention rate, the presence or absence of lithium deposition (whether the resistance to lithium deposition is good or bad) can be evaluated. The capacity retention rate was measured as follows. Note that "C" is a unit of current value, and "1C" means a current value at which the rated capacity of the battery can be discharged in one hour.

First, in a temperature environment of 25° C., the initial capacity of each battery for evaluation was measured after one cycle of charge and discharge was performed under the condition of 1C. After that, in a temperature environment of 0° C., 50 cycles of repeated charging and discharging were sequentially performed under each condition of 5C, 6C, 7C, 8C, 9C, and 10C, and then the capacity of each battery for evaluation was measured. Then, the capacity retention rate was obtained using the following formula.

Capacity retention rate (%) = (capacity of battery for evaluation after repeated charging/discharging/initial capacity of battery for evaluation) x 100

Then, based on the evaluation battery manufactured under the manufacturing conditions of Comparative Example 1, the relative percentage of each example when the capacity retention rate of Comparative Example 1 is 100% is calculated, and the lithium deposition resistance is evaluated. value. In the column of lithium deposition resistance (%) in FIG. .

Specific numerical values of evaluation values of resistance to lithium deposition are as follows.
Comparative Example 1: 100 (%)
Comparative Example 2: N/A
Comparative Example 3: 102 (%)
Comparative Example 4: 102 (%)
Comparative Example 5: 90 (%)
Comparative Example 6: 95 (%)
Example 1: 112 (%)
Example 2: 108 (%)
Example 3: 105 (%)

In the evaluation values shown here, the larger the value, the smaller the capacity deterioration of the battery after charge-discharge cycles at a large current, and the better the lithium deposition resistance.

As is clear from the results of FIG. 6, Examples 1 to 3 were evaluated as “○” for both cost and lithium deposition resistance, and Comparative Examples 1 to 6 were evaluated for at least one of cost and lithium deposition resistance. was "x". Compared with Comparative Examples 1 to 6, Examples 1 to 3 had a large cost reduction effect and good resistance to lithium deposition. That is, compared to the evaluation batteries manufactured under the manufacturing conditions of Comparative Examples 1-6, the evaluation batteries manufactured under the manufacturing conditions of Examples 1-3 are superior in battery characteristics. The reason for such results is considered as follows.

First, when compared from the viewpoint of cost, in Comparative Examples 1 to 4, the first layer, which is the main component of the negative electrode mixture layer, is formed of slurry. On the other hand, in Examples 1 to 3, the first layer, which is the main component of the negative electrode mixture layer 50, is formed of granules. Since the granules can be produced with a smaller amount of solvent than slurries, the amount of materials used can be reduced. Also, the drying time for removing the solvent can be shortened.

Furthermore, as is clear from Comparative Examples 2 and 3, intermediate drying is necessary when the first layer in which the holes are processed is made of slurry. That is, since the slurry is liquid and has low shape retention, it is necessary to process the holes after drying. On the other hand, in Examples 1 to 3, since the first layer in which the holes 22 are processed is composed of the granules, intermediate drying can be omitted. That is, since the granules are clay-like with a high solid content and have good shape retention, the holes 22 can be processed in a wet state containing a solvent. In Comparative Example 6, although the first layer is formed of granules, intermediate drying is performed, so the number of manufacturing steps increases, resulting in an increase in cost.

For these reasons, when forming a mixture layer provided with fine holes, granules are used rather than slurry as the composition for forming the mixture layer of the first layer in which the holes 22 are processed. This reduces costs and improves productivity. In particular, in Examples 1 and 2, the solid content (viscosity) of the slurry used for the second layer is higher than that in Example 3, so that the amount of material used is further reduced and the effect of shortening the drying time is high. Therefore, by using granules for the first layer and slurry having a high solid content (viscosity) for the second layer, it is possible to more effectively reduce costs and improve productivity.

Next, a comparative study will be made from the viewpoint of battery performance. In the evaluation batteries manufactured under the manufacturing conditions of Comparative Example 1, the negative electrode mixture layer was formed using only slurry with a low solid content (viscosity). It has a negative electrode mixture layer with a lower density than the conventional one. In the low-density negative electrode mixture layer, the electrolyte solution is easily discharged from the negative electrode mixture layer as the negative electrode mixture layer expands and contracts due to repeated charging and discharging during use of the battery. When the amount of electrolyte retained in the negative electrode mixture layer decreases due to accelerated discharge of the electrolyte, the lithium deposition resistance deteriorates and the capacity retention ratio decreases.

On the other hand, in Comparative Examples 3 and 4, a high-density layer exists on the surface layer of the negative electrode mixture layer by providing the second layer formed of a slurry having a high solid content (viscosity). It is believed that this suppresses the discharge of the electrolytic solution from the negative electrode mixture layer caused by the expansion and contraction of the negative electrode mixture layer, thereby slightly improving the capacity retention ratio (lithium deposition resistance).

Subsequently, Examples 1 to 3 and Comparative Examples 5 and 6 in which the first layer is formed using granules having a higher solid content than the slurry will be compared. Among them, in Comparative Examples 5 and 6, lithium deposition resistance was poor.

In Comparative Example 5, the negative electrode mixture layer was composed of only the granules of the first layer, and the surface of the negative electrode mixture layer, which was the processed portion, was crushed due to the pressing in the wet state. In this case, the reaction interface that contributes to the battery chemical reaction is reduced at the interface between the negative electrode mixture layer and the electrolytic solution, which may hinder the movement of lithium ions. Lithium ions whose movement is hindered are deposited on the surface of the negative electrode mixture layer. Therefore, in Comparative Example 5, it is considered that the capacity retention rate decreased.

On the other hand, in order to prevent crushing of the mixture layer surface by pressing, it is conceivable to increase the solid content of the granules. If it becomes too large, the amount of electrolyte retained in the composite material layer is reduced, so there is a risk that the capacity retention rate will be reduced.

Since Comparative Example 6 has fine pores, the utilization efficiency of the electrolytic solution is improved. It is considered that the electrode material was damaged due to the stress caused by the processing in the vicinity of the processed portion. In particular, when the active material is damaged, the reaction area of the active material increases and the decomposition reaction of the electrolyte occurs, thereby generating decomposed products of the electrolyte and gas. Therefore, if the active material is damaged, the movement of lithium ions is hindered and the battery expands. In Comparative Example 6, it is considered that the deterioration of the resistance to lithium deposition due to the damage to the active material had a large effect, and the capacity retention ratio decreased.

On the other hand, in Examples 1 to 3, the hole 22 can be processed in a wet state because the first layer for processing the hole 22 is formed of a granule having good shape retention. . Therefore, damage to the active material caused by processing the hole 22 is suppressed. Furthermore, compared with Examples 2 and 3, which were pressed in a dry state, damage to the active material caused by pressing is suppressed in Example 1, which was pressed in a wet state. In addition, in Example 1, since the machining and pressing of the hole 22 are performed simultaneously using one die 30, the productivity is high.

Further, in Examples 1 to 3, a second layer formed of slurry was applied. With such a configuration, the first layer, the surface of which is crushed by pressing in a wet state, is coated with a fluid slurry. Since the second layer formed of the slurry is arranged on the surface layer of the negative electrode mixture layer 50, the negative electrode plate 100 having such a structure sufficiently provides a reaction interface between the negative electrode mixture layer 50 and the electrolyte. can be formed into By increasing the viscosity of the slurry used for the second layer, the slurry film 41 is uniformly held on the surface of the granule film 21, increasing the reaction interface.

Furthermore, the second layer formed of slurry is preferably pressed at a pressure as low as possible, and more preferably not pressed. According to such a configuration, unevenness at the interface between the negative electrode mixture layer 50 and the electrolytic solution caused by pressing and damage to the active material are further suppressed. For example, in Example 1 in which the second layer is not pressed, compared with Examples 2 and 3, unevenness at the interface and damage to the active material caused by pressing are further suppressed, and the capacity retention rate is improved.

In the negative electrode plate 100 manufactured under the manufacturing conditions of Examples 1 to 3, the micropores 51 are provided in the negative electrode mixture layer 50 . Therefore, in a secondary battery including such a negative electrode plate 100, the electrolytic solution penetrates deep into the negative electrode mixture layer 50, so that the utilization efficiency of the electrolytic solution is improved. Furthermore, in the negative electrode plate 100 manufactured in this way, damage to the electrode material (especially the active material) caused by forming the micropores is suppressed, as in Patent Document 1, for example. 51 works better.

For these reasons, in the evaluation secondary batteries of Examples 1 to 3, deposition of lithium is suppressed, and as a result, the capacity retention rate is improved.

As described above, according to the method for manufacturing a secondary battery electrode according to the present embodiment, it is possible to manufacture a secondary battery electrode having a high capacity retention rate while ensuring productivity.

It should be noted that the present invention is not limited to the above embodiments, and can be modified as appropriate without departing from the scope of the invention. For example, the shape, size, material (material), etc. of each member described in the above embodiment, or the manufacturing method are not limited to those exemplified. Any method can be used as long as the electrode can be manufactured.

11 current collector foil 21 granule film 22 hole 23 hole forming film 24 first mixture layer 30 mold 31 base 32 convex portion 41 slurry film 42 second mixture layer 50 mixture layer 51 micropores 100 Electrode plate L1 First laminate L2 Second laminate L3 Third laminate

Claims (3)

A clay-like granule obtained by mixing at least an active material and a solvent is passed between a pair of rolls and rolled, and the rolled granule is transferred to the surface of a current collector foil to form a surface of the current collector foil. depositing a granule film thereon;
forming a hole-forming film by recessing a hole extending in the thickness direction from the surface of the granule film in the granule film;
applying a liquid slurry obtained by mixing at least an active material and a solvent onto the surface of the hole forming film to form a slurry film;
a step of drying the hole forming film and the slurry film to form a mixture layer;
A method for manufacturing a secondary battery electrode having The hole is formed in the granule film by pressing the surface of the granule film with a mold provided with a convex portion corresponding to the shape of the hole,
The thickness of the granule film is adjusted as the surface of the granule film is pressed.
A manufacturing method of the secondary battery electrode according to claim 1 . The viscosity of the slurry is 15000 mPa s or more,
3. A method for manufacturing the secondary battery electrode according to claim 1 or 2.

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