JP2013197014A - Electrode and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To finely form an active material on an electric body and efficiently secure an electronic conduction path between the active materials or the active material and a collector.SOLUTION: After ink 10 including an electrode material is coated on one surface in a thickness direction of a collector 11, centrifugal force in a direction from the one surface in the thickness direction toward the other surface is applied to the collector 11 to which the ink 10 has been coated. At this time, electrode active materials having the largest density and particle diameter in the ink 10 are preferentially deposited finely on the collector, thereby improving contact between the active materials and contact between the active material and the collector 11. Also, a binding material melts in a solvent and enters a gap between the finely deposited active materials, thereby improving adhesion between the active materials and adhesion between the active material and the collector 11 without damaging the contact between the active materials or the active material and the collector 11. Therefore, it is possible to provide an electrode of a battery with fewer energy loss.

Description

  The present invention relates to an electrode and a manufacturing method thereof.

  Lithium-ion secondary batteries are superior in light weight and small footprint due to their high energy density, and have the advantage of less memory effect than nickel-cadmium batteries and nickel-hydrogen batteries. Widely used in portable devices such as phones and notebook computers. Moreover, in recent years, it has been increasingly used as a power source to replace fossil fuels such as oil that have been used in automobiles because of its environmental impact. In addition, recently, there is a high expectation for stationary storage batteries that bear a part of power supply.

Commonly used components of lithium ion secondary batteries consist of electrodes, electrolytes, separators, current collectors, and exterior bodies, and the electrodes are positive electrode active materials or negative electrode active materials, conductive aids, binders. It is composed of materials. Hereinafter, a mixture of these constituent materials at a predetermined mixing ratio is collectively referred to as a positive electrode material and a negative electrode material, and a positive electrode material and a negative electrode material are collectively referred to as an electrode material. The active material is a material that can insert and desorb lithium ions in the positive electrode and the negative electrode of the lithium ion secondary battery, and plays a role of flowing current by accompanying the exchange of electrons at the time of insertion and desorption. The positive electrode active material layer compound such as LiCoO _2, LiNiO _2, spinel structure compounds represented by LiMn ₂ O _4, and the like olivine compound represented by LiFePO _4. On the other hand, representative examples of the negative electrode active material include carbon-based materials such as spherical graphite, flaky graphite, and hard carbon, silicon-based materials, and titanium oxide-based materials such as Li ₄ Ti ₅ O ₁₂ . The conductive auxiliary material is disposed inside the electrode in order to smoothly move electrons between the active material and the active material and between the active material and the current collector. Examples of the conductive aid include conductive carbon-based materials. The binder is disposed inside the electrode in order to enhance the adhesion between the active material, the conductive additive and the current collector. The types of binders are broadly divided into those using an aqueous solvent and those using a non-aqueous solvent, and typical examples thereof include styrene butadiene rubber and polyvinylidene fluoride.

  The current collector plays a role in generating an electric current in the circuit by giving and receiving the movement of electrons accompanying insertion and desorption of lithium ions to and from the active material to the active material or the conductive assistant.

  As the exterior body, two types of a metal can and an aluminum laminate film are mainly used for the purpose of preventing electrolyte leakage and protecting a lithium ion secondary battery that is sensitive to moisture from the outside air. In particular, an aluminum laminate film having good heat dissipation and a high degree of freedom in shape is advantageous.

  The separator is disposed between the positive electrode and the negative electrode for the purpose of preventing the battery from being short-circuited due to the contact between the positive electrode and the negative electrode, and the porous material is formed so that the electrolytic solution is held therein and allows lithium ions to pass therethrough. It is used. Generally, the material has a porosity of about 30% to 50%. Furthermore, it must be formed of a material that is resistant to the electrolyte. As such a separator material, a polyolefin-based material such as polyethylene or polypropylene is used.

  Among the constituent members of the battery described above, a factor affecting the charge / discharge characteristics of the battery is a filling state of the electrode material formed on the current collector. In general, the active material, the conductive additive, and the binder in the electrode material are uniformly mixed in a desired ratio and formed on the current collector using a technique such as a printing method. As the binder used, an insulator material as described in [0003] is used. Therefore, if the uniformity of the kneading of the electrode material is too high, a binder that is an insulator is disposed uniformly around the particles of the active material and the conductive additive, and between the active material, the conductive additive, and the current collector. Since the movement of electrons is hindered, when the electrode material is formed on a current collector and used as a battery electrode, desired charge / discharge characteristics cannot be obtained. Therefore, after forming the electrode material on the current collector, it is common to add a step of improving the contact between the active material, the conductive auxiliary material, and the current collector by pressing the electrode material. In particular, when an active material with poor conductivity is handled, improving the contact property between the active material and the conductive aid greatly affects the charge / discharge characteristics of the battery by performing the above pressing step.

  On the other hand, when the active material itself has high conductivity, the active material itself may be densely formed on the current collector, and the gap may be filled with a binder. The contact effect is small compared to the case of using an active material with poor conductivity as described in [0007].

  In any case, ensuring the contact between the active materials and the contact between the active material and the current collector, that is, ensuring the electron conduction path, is very important in obtaining battery characteristics. As a means for efficiently ensuring an electron conduction path, for example, a method of forming a colloidal graphite-based conductive additive around an active material has been proposed. (Patent Document 1) According to this method, if the active materials are in contact with each other or between the active material and the current collector, the electron conduction path is strongly secured, which is effective. If the binder is uniformly deposited between the current collectors, the electron conduction path is lost.

  In addition, a method of improving the contact between the active material and the current collector by forming a hollow or protruding metal layer on the current collector has been proposed. (Patent Document 2) According to this method, since the surface area of the current collector is improved, it is effective in improving the contact property between the active material and the current collector. Alternatively, when the binder is uniformly attached between the active material and the current collector, the electron conduction path is lost. In addition, it is difficult to uniformly apply an ink containing an active material in a gap between fine metal layers.

  A method of improving the binding between the electrode material and the current collector by improving the binding material has also been proposed. (Patent Document 3) According to this method, the binding force between the active materials or between the active material and the current collector is improved, but the binding material between the active materials or between the active material and the current collector as in [0009]. If the film is uniformly deposited, the electron conduction path is lost.

JP-A-6-013081 Patent No. 3221306 JP 11-067215

  Therefore, the present invention has been made to solve the above-mentioned problems, and kneaded electrode materials utilizing the difference in the density of the material constituting the electrode (showing true density here) and the particle diameter. After the ink containing the ink is coated on the current collector, the active material is densely formed on the current collector by applying centrifugal force to the current collector coated with the ink before the step of drying the solvent. With the goal.

  The present invention described in claim 1 includes a step of dispersing an electrode material obtained by mixing a material containing an electrode active material, a conductive additive, and a binder in a solvent to produce ink, and a thickness direction of the current collector Applying the ink to one surface of the ink, applying a centrifugal force in a direction from one surface of the thickness direction to the other surface of the current collector coated with the ink, And a step of drying the current collector coated with the ink after the step of applying a centrifugal force is completed.

  The present invention according to claim 2 is the electrode manufacturing method according to claim 1, wherein the step of applying the centrifugal force has an inner peripheral surface centered on the rotation axis and is rotatable around the rotation axis. And the other surface located on the opposite side to the one surface with the one surface of the current collector coated with the ink facing the rotation shaft. It is an electrode manufacturing method characterized in that it is made by rotating the rotating body around the rotation axis in a state of being attached to a surface.

  According to a third aspect of the present invention, in the electrode manufacturing method according to the second aspect, in the step of applying the centrifugal force, the rotational speed of the rotating body is 100 to 10,000 rpm (round / min). An electrode manufacturing method characterized by the above.

  According to a fourth aspect of the present invention, there is provided an electrode manufactured using the method for manufacturing an electrode according to the first or second aspect.

  A fifth aspect of the present invention is the electrode according to the fourth aspect, wherein the electrode active material has a gradation structure in which the concentration of the electrode active material increases stepwise from the electrode surface toward the current collector side. To do.

  A sixth aspect of the present invention is a battery manufactured using the electrode according to the fourth or fifth aspect.

  A seventh aspect of the present invention is an apparatus that operates using the battery according to the fifth aspect as a power source or a power source.

  The method for producing an electrode according to the present invention comprises: applying an ink containing an electrode material to one surface in the thickness direction of the current collector; and then applying the ink before the step of drying the solvent. The centrifugal force can be applied to the ink containing the electrode material by applying a centrifugal force in a direction from one surface in the thickness direction to the other surface. At this time, the electrode active material having the largest density and particle diameter is preferentially deposited densely on the current collector, and the contact between the active materials and the contact between the active material and the current collector can be easily improved. Is possible. In addition, since the binder is dissolved in the solvent, the binder enters the gap between the densely deposited active materials, and when the solvent is volatilized by the drying process, the binder is contacted between the active materials or between the active material and the current collector. It is possible to improve the adhesion between the active materials and between the active material and the current collector without impairing the resistance. For this reason, it is possible to provide a battery electrode with less energy loss.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic sectional drawing for demonstrating the manufacturing process of the electrode of this invention, (a) is a figure which shows the state in which the ink was applied to one surface of the thickness direction of a collector, (b) is ink. It is a figure which shows the state which applies centrifugal force to the apply | coated electrical power collector.

  Hereinafter, an embodiment of the present invention will be described with reference to FIG.

First, an electrode material is dispersed in a solvent to prepare an ink. The electrode material is not particularly limited. For example, in the case of a positive electrode material, lithium that includes LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFePO _4, V ₂ O ₅ , TiO ₂ or the like as an active material may be inserted and released. It has a high electronic conductivity such as spherical carbon represented by acetylene black and ketjen black, and fibrous carbon fiber represented by carbon nanofiber. , One that does not contribute to the charge / discharge reaction and is composed of an electrochemically stable material or a combination thereof, and the binder is polyethylene, polyvinylidene fluoride, styrene butadiene rubber, ethylene butadiene rubber, polytetrafluoroethylene, Appropriately selected from the materials listed in the epoxy resin, etc. according to the solvent type when mixing the electrode material Those having a desired mixing ratio for obtaining battery characteristics can be used, but in particular, if the amount of the binder is large, an insulating layer is easily formed, and the battery characteristics deteriorate. The binder is preferably within 10 wt%. On the other hand, regarding the negative electrode material, for example, a material capable of inserting and desorbing lithium including hard carbon, amorphous carbon, graphite, Li ₄ Ti ₅ O ₁₂ , silicon, SiO _2, TiO ₂ or the like as an active material, or a combination thereof The conductive auxiliary material and the binder include those composed of the same exemplary materials as the positive electrode material or combinations thereof, and those composed of a desired mixing ratio that provides battery characteristics. As with the positive electrode material, the binder is preferably within 10 wt%. Further, the solvent for dispersing the electrode material is not particularly limited, and examples thereof include water, water appropriately mixed with carboxymethylcellulose as a thickener, n-methyl-2-pyrrolidone, acetonitrile, and the like. It can be selected appropriately according to the situation.

The present invention is characterized by preferentially depositing the electrode active material preferentially on the current collector by utilizing the difference in density and particle diameter of the electrode material, so that the active material, the conductive auxiliary agent, the binder The relationship between the density and the particle diameter is important. The particle diameter of a general active material is often formed in a range of 1 μm to 50 μm in order to accelerate ion diffusion in the active material as much as possible. On the other hand, the conductive auxiliary agent needs to connect the gaps between the active material particles finely to form a path for electrons, and therefore, in general, a conductive auxiliary agent of several tens to several μm is often used. Since the binder is completely dissolved in the solvent, the binder is disposed so as to fill a gap between the active material and the conductive additive. The density varies depending on the positive electrode material and the negative electrode material. For example, LiCoO ₂ is 5.1 g / cc and LiMn ₂ O ₄ is 4.2 g / cc as commonly used positive electrode active materials. As the negative electrode active material, graphite is from 2.2 g / cc to 2.3 g / cc, whereas the carbon-based material that is a conductive aid is from 1.8 g / cc to 2 g / cc. In most cases, the density is higher than that of the conductive assistant. For this reason, when a centrifugal force is applied, the active material always preferentially deposits densely on the current collector side.

  The method for dispersing the electrode material in the solvent is not particularly limited. For example, a planetary mixer, a bead mill, a ball mill, an ultrasonic disperser, a disper, or the like may be used.

  Next, the ink 10 is applied to one surface in the thickness direction of the current collector 11 (FIG. 1A). The material of the current collector 11 can be appropriately selected depending on the electrode material used. For example, it is preferable to use a material containing aluminum for the current collector 11 on the positive electrode side and a material containing copper or nickel for the current collector layer on the negative electrode side. Aluminum is a material that can withstand the potential of the positive electrode, and is used as a positive electrode material for an inexpensive and general lithium ion secondary battery. On the other hand, copper or nickel is a material that can withstand the potential of the negative electrode and does not form an alloy with lithium. Therefore, copper or nickel is used as a general negative electrode material for lithium ion secondary batteries in the same manner as the positive electrode. Further, the current collector 11 is not necessarily formed of a metal material, and a metal foil formed on a base material such as plastic may be used. By using plastic as the base material, the weight of the current collector 11 is reduced, and the energy per unit weight of the battery can be efficiently extracted.

  In addition, the method of applying the ink 10 to the current collector 11 can be selected as appropriate in accordance with the desired shape and dimensions. Examples thereof include an ink jet method, a die coating method, and a screen printing method.

Next, a centrifugal force (centrifugal acceleration) in a direction from one surface in the thickness direction to the other surface is applied to the current collector 11 coated with the ink 10. Thereby, a centrifugal force is applied to the ink 10 containing the electrode material. In the present embodiment, the current collector 11 coated with the ink 10 is applied to the inner wall of the rotator 12 having a hollow inside and rotated (FIG. 1B).
More specifically, the rotating body 12 having an inner peripheral surface 1204 around the rotating shaft 1202 and configured to be rotatable around the rotating shaft is prepared. The rotating body 12 is rotated in a state where one surface of the current collector 11 coated with the ink 10 is directed to the rotation shaft 1202 and the other surface located opposite to the one surface is attached to the inner peripheral surface 1204. Rotate around the axis.
In general, the sedimentation speed of particles in a solvent is determined by the diameter and density of the particles, the density of the solution, the viscosity of the solution, and the centrifugal acceleration, which is defined by the radius of rotation and the rotational speed (number of rotations per minute). And is calculated by equation (1). For this reason, it is necessary to appropriately select the rotation speed depending on the electrode material. Further, in the formula (1), it is the particle diameter and the rotation speed indicated by the square term that have a great influence on the sedimentation speed. For example, as described above, the particle diameter of a general active material is: In order to accelerate ion diffusion in the active material as much as possible, many are formed in the range of 1 μm to 50 μm. Further, although the film thickness of the electrode varies depending on the positive electrode material and the negative electrode material, it is generally formed with a thickness of about several tens to 100 μm. On the other hand, it is more advantageous in terms of manufacturing cost to shorten the time required for manufacturing the electrode, and it is desirable that the time for settling the particles is within several minutes. From these facts, a rotational speed of at least 1000 rpm is required in order to allow the active material having the smallest diameter (for example, 1 μm) to settle within a few minutes from the surface side of the formed electrode to the current collector side. Become. On the other hand, at a speed of 10,000 rpm or more for similar particles, the speed until the particles settle is within several seconds and hardly affects the production time. In addition, in order to settle an active material (for example, 50 μm) having the largest diameter from the surface side of the formed electrode to the current collector side within a few minutes, a rotational speed of at least 100 rpm is required. On the other hand, at 1000 rpm or more for similar particles, the speed until the particles settle is within a few seconds and hardly affects the production time. From these facts, it is reasonable that the rotation speed is in the range of about 100 rpm to 10,000 rpm.

v: particle sedimentation rate (cm / sec), d: particle diameter (cm), σ: particle density (g / cc), ρ: solution density (g / cc), η: solution viscosity (g · Cm ^-1 · sec ^-1 ), r: rotational radius (cm), N: rotational speed (number of revolutions per minute) (rpm)

  Next, the current collector 11 coated with the ink 10 is dried. The drying method can be appropriately selected from hot air drying, vacuum drying, infrared drying and the like.

  As mentioned above, the manufacturing method of the electrode of this invention can be implemented. In addition, the manufacturing method of the electrode of this invention is not limited to the said embodiment, The other well-known method which can be estimated in each process shall also be included.

First, the electrode material is a mesocarbon microbead having a density of 2.2 g / cc as an active material and a particle diameter of 20 μm, an acetylene black having a density of 1.8 g / cc and a particle diameter of 100 nm as a conductive material, and a binder. As a solvent, styrene butadiene rubber was used at a ratio of 90: 2: 8, and water and carboxymethyl cellulose were mixed at a ratio of 98: 2. The amount of the electrode material mixed with the solvent was adjusted so that the solid content ratio in the solvent was 50%. These materials were stirred for 3 hours using a disper at a rotation speed of 1000 rpm to carry out a dispersion treatment, and ink 10 having a viscosity of 50 g · cm ⁻¹ · sec ⁻¹ was produced.

  Next, the ink 10 was applied to one surface in the thickness direction of the current collector 11 using a die coating method. For the current collector 11, a copper foil having a thickness of 20 μm was prepared. The coating thickness of the ink 10 was about 70 μm.

  Next, the other surface of the current collector 11 coated with the ink 10 was attached to the inner peripheral surface 1204 of the rotating body 12 having an inner diameter of 150 cm and rotated. The rotation speed was 500 rpm and the rotation process was performed for 10 seconds.

  Next, the solvent was removed from the coated ink 10 by hot air drying. The drying condition was 80 ° C. for 3 hours.

  From the above, it was possible to produce a negative electrode having a gradation structure in which the active material was densely deposited on the current collector 11 side and the concentration of the active material gradually increased from the electrode surface to the current collector side.

The electrode material is LiCoO ₂ having a density of 5.1 g / cc as an active material and a particle diameter of 10 μm, acetylene black having a density of 1.8 g / cc and a particle diameter of 100 nm as a conductive additive, and polyvinylidene fluoride as a binder. Were used in a ratio of 95: 2: 3, respectively, and n-methyl-2-pyrrolidone was selected as the solvent. The amount of the electrode material mixed with the solvent was adjusted so that the solid content ratio in the solvent was 65%. These materials were stirred for 5 hours using a planetary mixer to perform a dispersion treatment, and an ink 10 of 70 g · cm ⁻¹ · sec ⁻¹ was produced.

  Next, the ink 10 was applied to one surface in the thickness direction of the current collector 11 using a die coating method. The current collector 11 was prepared with an aluminum foil having a thickness of 15 μm. The coating thickness of the ink 10 was about 110 μm.

  Next, the other surface of the current collector 11 coated with the ink 10 was attached to the inner peripheral surface 1204 of the rotating body 12 having an inner diameter of 150 cm and rotated. The rotation speed was 500 rpm and the rotation process was performed for 60 seconds.

  Next, the solvent was removed from the coated ink 10 by hot air drying. The drying condition was 80 ° C. for 3 hours.

As described above, a positive electrode having a gradation structure in which the active material is densely deposited on the current collector 11 side and the concentration of the active material gradually increases from the electrode surface to the current collector side can be produced.
[Comparative Example 1]

As in the paragraph [0039], the electrode material is LiCoO ₂ having a density of 5.1 g / cc as an active material and a particle diameter of 10 μm, and acetylene black having a density of 1.8 g / cc and a particle diameter of 100 nm as a conductive additive. Polyvinylidene fluoride was used as the binder at a ratio of 95: 2 to 3, respectively, and n-methyl-2-pyrrolidone was selected as the solvent. The amount of the electrode material mixed with the solvent was adjusted so that the solid content ratio in the solvent was 65%. These materials were stirred for 5 hours using a planetary mixer to carry out a dispersion treatment to produce an ink of 70 g · cm ⁻¹ · sec ⁻¹ , using a die coating method as described in [0040]. Ink was applied on the current collector. An aluminum foil having a thickness of 15 μm was prepared as a current collector. The ink coating thickness was about 110 μm.

  Next, the current collector coated with ink was applied to the inner wall of a rotating body having an inner diameter of 150 cm and rotated. The rotational speed was 10 rpm, and a rotation process was performed for 60 seconds, and the solvent was removed from the coated ink by hot air drying in the same manner as in [0042]. The drying condition was 80 ° C. for 3 hours.

The positive electrode produced by the above steps had an almost uniform composition from the electrode surface to the current collector side without the active material being densely deposited on the current collector side.
[Comparative Example 2]

As in the paragraph [0039], the electrode material is LiCoO ₂ having a density of 5.1 g / cc as an active material and a particle diameter of 10 μm, and acetylene black having a density of 1.8 g / cc and a particle diameter of 100 nm as a conductive additive. Polyvinylidene fluoride was used as the binder at a ratio of 95: 2: 3, respectively, and n-methyl-2-pyrrolidone was selected as the solvent. The amount of the electrode material mixed with the solvent was adjusted so that the solid content ratio in the solvent was 65%. These materials were stirred for 5 hours using a planetary mixer to carry out a dispersion treatment to produce an ink of 70 g · cm ⁻¹ · sec ⁻¹ , using a die coating method as described in [0040]. Ink was applied on the current collector. An aluminum foil having a thickness of 15 μm was prepared as a current collector. The ink coating thickness was about 110 μm.

  Next, the current collector coated with ink was applied to the inner wall of a rotating body having an inner diameter of 150 cm and rotated. The rotational speed was set at 10,000 rpm, and a rotation process was carried out for 60 seconds, and the solvent was removed from the coated ink by hot air drying in the same manner as in [0042]. The drying condition was 80 ° C. for 3 hours.

  The positive electrode produced by the above process has a gradation structure in which the active material is densely deposited on the current collector side and the concentration of the active material is gradually increased from the electrode surface to the current collector side, as in [0046]. .

The battery manufacturing method of the present invention can be applied not only to the field of lithium ion secondary batteries, but also to all fields that require a mechanism for preventing contact between two types of electrodes, for example, for fuel cells and solar cells. It can also be applied to fields.
In the embodiment, the case where the inner peripheral surface 1204 of the rotator 12 is a cylindrical surface has been described. However, the cross section of the rotator 12 may be a regular polygon and may be an inner peripheral surface 1204 composed of a plurality of planes. In this case, each plane constituting the inner peripheral surface 1204 may be set to a size that allows the current collector 11 to be attached.

10 ... Ink 11 ... Current collector 12 ... Rotating body

Claims (7)

A step of preparing an ink by dispersing an electrode material obtained by mixing an electrode active material, a conductive additive, and a material containing a binder in a solvent;
Applying the ink to one surface in the thickness direction of the current collector;
Applying a centrifugal force in a direction from one surface in the thickness direction to the other surface of the current collector coated with the ink;
After the step of applying the centrifugal force is completed, drying the current collector coated with the ink;
The manufacturing method of the electrode characterized by including. A method for producing an electrode according to claim 1,
The step of applying the centrifugal force includes preparing a rotating body having an inner peripheral surface around the rotating shaft and configured to be rotatable around the rotating shaft, and applying the ink to the one of the current collectors It is made by rotating the rotating body around the rotation axis in a state where the other surface located on the opposite side to the one surface is attached to the inner peripheral surface with the surface facing the rotation axis.
An electrode manufacturing method characterized by the above.   The electrode manufacturing method according to claim 2, wherein in the step of applying the centrifugal force, a rotation speed of the rotating body is 100 to 10,000 rpm (round / min).   It manufactures using the manufacturing method of the electrode as described in any one of Claims 1-3, The electrode characterized by the above-mentioned.   5. The electrode according to claim 4, wherein the electrode has a gradation structure in which the concentration of the electrode active material increases stepwise from the electrode surface toward the current collector side.   A battery manufactured using the electrode according to claim 4.   A device that operates using the battery according to claim 6 as a power source or a power source.

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