JP2017059378A - Electrode, power storage element, and method for manufacturing electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode in which conductive particles are dramatically improved in fixing strength and uniformity relative to a conductor layer, a manufacturing method thereof, and a power storage element in which the electrode is used.SOLUTION: An electrode of the present invention includes: a conductor layer for a current collector; an intermediate layer covering at least a part of a surface of the conductor layer; and an active material layer laminated on an intermediate layer side of the laminate that includes the conductor layer and the intermediate layer. The intermediate layer contains a conductive particle and a non-conductive inorganic particle, the outer surface of the conductive particle being covered with the non-conductive inorganic particle.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrode, a power storage device using the electrode, and a method for manufacturing the electrode.

  Nonaqueous electrolyte batteries represented by lithium ion secondary batteries are frequently used in electronic devices such as personal computers and communication terminals, automobiles and the like because of their high energy density.

  The nonaqueous electrolyte battery generally has a pair of electrodes in which an active material layer is laminated on a conductor layer such as a metal foil, and these are electrically separated by a separator, and ions are transferred between the negative electrode and the positive electrode. It is configured to charge and discharge by performing.

  When a metal foil is used as the conductor layer, some metal foils, such as aluminum foil, have an oxide film formed on the surface. Such an oxide film may increase the contact resistance at the interface between the active material layer and the metal foil.

  On the other hand, a method of reducing the contact resistance between the metal foil and the active material layer by forming an intermediate layer by coating conductive particles such as carbon particles on the surface of the metal foil using a resin binder Proposed by However, in this method, the resin binder is swollen by the electrolytic solution after coating, and an increase in resistance between the metal foil and the active material layer can occur.

  Thus, a method has been proposed in which carbon particles are pressure-bonded to the surface of the conductor layer without using a resin binder (see, for example, JP 2011-98472 A). However, with this method, it is difficult to ensure the fixing strength of the carbon particles and to uniformly coat the surface of the conductor layer with the carbon particles.

JP 2011-98472 A

  The present invention has been made based on the above-described circumstances, and an electrode in which the strength and uniformity of fixing conductive particles to a conductor layer are remarkably improved, a method for manufacturing the same, and a storage element using the electrode The purpose is to provide.

  The invention made in order to solve the above problems includes a conductor layer, an active material layer, and an intermediate layer formed between the conductor layer and the active material layer and covering at least a part of the surface of the conductor layer. And the intermediate layer includes conductive particles and non-conductive inorganic particles, and an outer surface of the conductive particles is coated with the non-conductive inorganic particles.

  Still another invention made in order to solve the above-mentioned problems is a conductor layer, an active material layer, and formed between the conductor layer and the active material layer, covering at least a part of the surface of the conductor layer. A method for producing an electrode comprising an intermediate layer, comprising a step of rubbing conductive particles and non-conductive inorganic particles on at least a part of the surface of the conductor layer, wherein an outer surface of the conductive particles is the non-conductive inorganic layer It is characterized by being coated with particles.

  Here, “conductive” means that the volume resistivity measured in accordance with JIS-H-0505 (1975) is 107 Ω · cm or less, and “nonconductive” It means that the volume resistivity is over 107 Ω · cm. “Arithmetic mean roughness Ra” means arithmetic mean roughness measured in accordance with JIS-B-0601 (2001) with a cutoff value (λc) of 0.25 mm and an evaluation length (l) of 150 μm. To do.

  In the electrode of the present invention, the fixing strength and uniformity of the conductive particles to the conductor layer are remarkably improved. In addition, the electrode manufacturing method of the present invention can provide an electrode in which the fixing strength and uniformity of the conductive particles to the conductor layer are remarkably improved. Furthermore, the electricity storage device of the present invention can reduce the contact resistance at the interface between the conductor layer and the active material layer.

FIG. 1 is a schematic cross-sectional view showing an electrode in one embodiment of the present invention. FIG. 2 is a schematic partial enlarged view of FIG. FIG. 3 is a schematic view for explaining the contact angle of the conductive particles. FIG. 4 is a schematic perspective view showing one step of the electrode manufacturing method according to one embodiment of the present invention. FIG. 5 is a schematic cross-sectional view showing a power storage element according to an embodiment of the present invention.

  Hereinafter, embodiments of an electrode according to the present invention, a method for manufacturing the electrode, and a storage element using the electrode will be described in detail with reference to the drawings.

[electrode]
FIG. 1 shows the lowest structural unit of an electrode. An electrode 1 shown in FIG. 1 includes a current collecting conductor layer 2, an intermediate layer 3 covering at least a part of the surface of the conductor layer 2, and an intermediate layer of a laminate including the conductor layer 2 and the intermediate layer 3. And an active material layer 4 laminated on the 3 side. The conductor layer 2 and the intermediate layer 3 constitute a so-called current collector.

<Conductor layer>
The conductor layer 2 is a conductive layer. As a material of the conductor layer 2, a metal such as aluminum, copper, iron, nickel, or an alloy thereof is used. Among these, aluminum, an aluminum alloy, copper, and a copper alloy are preferable from the balance between high conductivity and cost. Moreover, as a formation form of the conductor layer 2, foil, a vapor deposition film, etc. are mentioned, A foil is preferable from the surface of cost. That is, the conductor layer 2 is preferably an aluminum foil or a copper foil.

  Aluminum or an aluminum alloy can be suitably used when the electrode 1 is used as a positive electrode or a negative electrode of a power storage element or a capacitor electrode, and copper or a copper alloy is suitable when the electrode 1 is used as a negative electrode of a power storage element. Can be used for Examples of aluminum or aluminum alloy include A1085P and A3003P defined in JIS-H-4000 (2014). Examples of the copper foil include rolled copper foil and electrolytic copper foil.

  The lower limit of the average thickness of the conductor layer 2 is preferably 5 μm and more preferably 10 μm. On the other hand, the upper limit of the average thickness of the conductor layer 2 is preferably 50 μm, and more preferably 40 μm. When the average thickness of the conductor layer 2 is smaller than the above lower limit, the strength of the conductor layer 2 is insufficient, and it may be difficult to form the electrode 1. On the other hand, when the average thickness of the conductor layer 2 exceeds the above upper limit, the thickness of the other constituent elements may be insufficient to keep the thickness of the power storage element constant.

  The “average thickness” means an average value of thicknesses measured at arbitrary ten points. In the following description, the term “average thickness” is defined similarly for other members.

  The conductor layer 2 preferably has a roughened surface as shown in FIG. Specifically, the lower limit of the arithmetic average roughness Ra on the surface of the conductor layer 2 covered by the intermediate layer 3 is preferably 0.05 μm, more preferably 0.1 μm, and even more preferably 0.8 μm. On the other hand, the upper limit of the arithmetic average roughness Ra is preferably 4 μm, and more preferably 2 μm. By setting the arithmetic average roughness Ra of the conductor layer 2 within the above range, the conductor layer 2 can be easily attached by rubbing or the like, and thus the intermediate layer 3 can be uniformly formed. When the arithmetic average roughness Ra is smaller than the lower limit, the conductive particles 6 are hardly supported on the surface of the conductor layer 2, and the fixing strength of the conductive particles 6 on the surface of the conductor layer 2 may be reduced. On the other hand, when the arithmetic average roughness Ra exceeds the upper limit, the conductive particles 6 may not be able to uniformly fill the unevenness of the surface of the conductor layer 2, and the homogeneous intermediate layer 3 may not be formed. In the case of a rolled foil, the arithmetic average roughness Ra can be adjusted to the above range depending on the rolling conditions without performing a separate roughening treatment.

  Moreover, as a minimum of the average diameter of the hollow 8 of the depth of 1 micrometer or more in the conductor layer 2 surface, 3 micrometers is preferable and 5 micrometers is more preferable. On the other hand, the upper limit of the average diameter of the recess 8 is preferably 18 μm, and more preferably 15 μm. When the average diameter of the recess 8 is smaller than the lower limit, the conductive particles 6 may be difficult to be supported on the surface of the conductor layer 2. On the other hand, when the average diameter of the recess 8 exceeds the upper limit, the homogeneous intermediate layer 3 may not be formed. Here, the “average diameter of the recesses 8 having a depth of 1 μm or more on the surface of the conductor layer” means that five recesses having a depth of 1 μm or more are extracted and the diameters of round circles (such as etc.) observed by an electron microscope of these recesses are extracted. It means the average value of the diameter of the area circle.

  In order to improve the adhesion between the intermediate layer 3 and the active material layer 4, a surface treatment such as application of a coupling agent may be performed on the surface of the conductor layer 2.

<Intermediate layer>
The intermediate layer 3 is a coating layer on the surface of the conductor layer 2 and contains conductive particles 6 and nonconductive inorganic particles 7. From the viewpoint of suppressing an increase in resistance due to swelling of the resin binder, it is preferable that the intermediate layer 3 does not substantially contain a resin binder. The “resin binder” means a binder mainly composed of a resin. Here, the “main component” means a component contained in an amount of 50% by mass or more, more preferably a component contained in an amount of 90% by mass or more.

(Conductive particles)
As shown in FIG. 2, the conductive particles 6 cover the conductor layer 2 so as to fill the depressions 8 on the surface of the conductor layer 2. The conductive particles 6 are preferably highly conductive particles. The volume resistivity of the conductive particles 6 is 107 Ω · cm or less, preferably 10 −1 Ω · cm or less. As the conductive particles 6, particles mainly composed of a metal such as nickel, silver, and gold, particles mainly composed of carbon, and the like can be used. Among these, the conductive particles 6 are preferably carbon particles mainly composed of carbon. Specific examples of the carbon particles include natural or artificial graphite, carbon black such as furnace black, acetylene black, and ketjen black. The conductive particles 6 may be used in combination of two or more.

  Moreover, it is preferable that the electroconductive particle 6 is flaky. Here, the “flaky shape” is a concept including a shape called a plate shape, a sheet shape, a flake shape, or a scale shape, and means a shape having a relatively large ratio of width and length to thickness.

  The lower limit of the average major axis of the conductive particles 6 is preferably 2.5 μm and more preferably 5 μm. On the other hand, the upper limit of the average major axis of the conductive particles 6 is preferably 15 μm and more preferably 10 μm. When the average major axis of the conductive particles 6 is smaller than the lower limit, it may be difficult to cover the conductor layer 2. On the other hand, when the average major axis of the conductive particles 6 exceeds the upper limit, it may be difficult to form the homogeneous intermediate layer 3. Here, the “average major axis of the conductive particles” means a value obtained by the following procedure. First, for example, a cross section of the intermediate layer is observed using an SEM image having a magnification of 2000 to 10,000, and five conductive particles having a conductor layer and a contact point are selected. Next, for the selected conductive particles, the length of the portion near the maximum width is measured five times, and the deviation of these measured values (the difference between the average value of the five measured values and each measured value) is the average value. Repeat the measurement until it is within 10%. This operation is performed for every five conductive particles, and the average of the measured values of the five finally obtained conductive particles is taken as the average major axis of the conductive particles.

  The lower limit of the average contact angle of the conductive particles 6 with the conductor layer 2 is usually 0 °. On the other hand, the upper limit of the average contact angle of the conductive particles 6 with the conductor layer 2 is preferably 50 ° and more preferably 30 °. When the average contact angle of the conductive particles 6 with the conductor layer 2 exceeds the upper limit, the conductor layer 2 may not be uniformly coated. Here, “the average contact angle of the conductive particles with the conductor layer” means a value obtained by the following procedure. First, for example, a cross section of the intermediate layer is observed using an SEM image having a magnification of 2000 to 10,000, and five conductive particles having a conductor layer and a contact point are selected. Next, for each selected conductive particle, the vicinity of an arbitrary contact P between the conductive particle 6 and the conductor layer 2 is enlarged as shown in FIG. 3, and the tangent L of the surface of the conductor layer 2 in the vicinity of the contact P is obtained. And the angle (acute angle) formed by the center line M in the major axis direction of the conductive particles 6 is measured five times, and the deviation of these measured values (the difference between the average value of the five measured values and each measured value) is the average. Repeat the measurement until it is within 10% of the value. This operation is performed for every five conductive particles, and the average of the measured values of the finally obtained five conductive particles is defined as the average contact angle with the conductive layer of the conductive particles.

  In the case where the conductive particles 6 are in the form of flakes, it is preferable that the long side surface is disposed along the surface of the conductor layer 2. Thereby, the reduction effect of contact resistance can be promoted. The “long side surface” means a surface having a length in a direction orthogonal to the thickness direction that is longer than the other surfaces among the surfaces extending in the thickness direction of the conductive particles 6.

  As a minimum of the aspect-ratio of the electroconductive particle 6, 1 is preferable and 2 is more preferable. On the other hand, the upper limit of the aspect ratio of the conductive particles 6 is preferably 100 and more preferably 80. When the aspect ratio of the conductive particles 6 is smaller than the lower limit, it may be difficult to uniformly coat the conductor layer 2. On the other hand, when the aspect ratio of the conductive particles 6 exceeds the above upper limit, the conductive particles 6 become fragile, so that they are divided during the formation of the intermediate layer 3 and it is difficult to uniformly coat the conductor layer 2. Here, the “aspect ratio of conductive particles” means an average value of values obtained by dividing the major axis of five conductive particles having a conductor layer and a contact point by the minor axis, and “minor axis” means the conductive axis. It means a value calculated in the same procedure as the major axis for the length in the direction perpendicular to the major axis direction of the particles.

  As a minimum of content of electroconductive particle 6 in middle class 3, 55 mass% is preferred, 60 mass% is more preferred, and 65 mass% is still more preferred. On the other hand, as an upper limit of content of the electroconductive particle 6, 98 mass% is preferable, 90 mass% is more preferable, and 80 mass% is further more preferable. By making the content of the conductive particles 6 in the intermediate layer 3 in the above range, the effect of reducing the contact resistance at the interface between the conductor layer 2 and the active material layer 4 and the effect of improving the fixing strength of the conductive particles 6 are facilitated. And can be demonstrated reliably. When content of the electroconductive particle 6 is smaller than the said minimum, there exists a possibility that the reduction effect of the contact resistance of the conductor layer 2 and the active material layer 4 may become inadequate. On the other hand, when the content of the conductive particles 6 exceeds the above upper limit, the content of the nonconductive inorganic particles 7 is decreased, so that the fixing strength of the conductive particles 6 may be insufficient.

(Non-conductive inorganic particles)
The nonconductive inorganic particles 7 contained in the intermediate layer 3 serve to fix the conductive particles 6 to the conductor layer 2. The non-conductive inorganic particles 7 are preferably inorganic particles that have as little conductivity as possible. The volume resistivity of the non-conductive inorganic particles 7 is over 107 Ω · cm, preferably over 1010 Ω · cm. Moreover, as the nonelectroconductive inorganic particle 7, what does not decompose | disassemble in the range of room temperature (20 degreeC) or more and 150 degrees C or less is preferable.

  Examples of the non-conductive inorganic particles 7 include metal oxides, nitrides, halides, inorganic acid salts, organic acid salts, and minerals. Specifically, metal oxides such as zirconia, magnesia, alumina, ceria, yttria, silica, zinc oxide, iron oxide, titanium oxide, calcium oxide, lanthanum oxide, and manganese oxide; zirconium oxychloride, hydroxyzirconium chloride, zirconium nitrate Zirconium compounds such as zirconium sulfate, zirconium acetate, ammonium zirconium carbonate and zirconium propionate; titanium compounds such as titanium nitride and potassium titanate; aluminum compounds such as aluminum sulfate; ores of silicon carbide, silicon nitride, alkoxysilane and alkoxysilane Examples thereof include partial hydrolysis products with acids, silicon compounds such as diatomaceous earth, silica sand, and glass; silicate minerals and the like. Of these, silicate minerals are preferred.

  Further, from the viewpoint of increasing the fixing strength of the conductive particles 6, the nonconductive inorganic particles 7 are preferably layered. Examples of the layered silicate mineral include kaolinite, halloysite, bentonite, and montmorillonite. Thus, by using a layered silicate mineral as the non-conductive inorganic particles 7, the effect of improving the fixing strength of the conductive particles 6 can be easily and reliably promoted.

  The lower limit of the average particle diameter of the non-conductive inorganic particles 7 is preferably 0.001 μm, more preferably 0.01 μm, and further preferably 0.1 μm. On the other hand, the upper limit of the average particle size of the non-conductive inorganic particles 7 is preferably 10 μm, more preferably 5 μm, and even more preferably 2 μm. When the average particle size of the non-conductive inorganic particles 7 is smaller than the lower limit, the contact between the conductive particles 6 is reduced, and the effect of reducing the contact resistance between the conductor layer 2 and the active material layer 4 may be insufficient. . On the other hand, when the average particle diameter of the nonconductive inorganic particles 7 exceeds the above upper limit, there is a possibility that improvement of the fixing strength of the conductive particles 6 by the coating of the nonconductive inorganic particles 7 may be insufficient. Here, the “average particle diameter” is based on JIS-Z-8815 (2013), based on the particle size distribution measured by a laser diffraction / scattering method with respect to a diluted solution obtained by diluting particles with a solvent. It means a value at which the volume-based cumulative distribution calculated according to Z-8819-2 (2001) is 50%.

  The outer surface of the conductive particles 6 is covered with non-conductive inorganic particles 7. By covering the conductive particles 6 with the non-conductive inorganic particles 7 in this way, the fixing strength and uniformity of the conductive particles 6 on the surface of the conductor layer 2 can be significantly improved. Moreover, since the non-conductive inorganic particles 7 are used to secure the adhesion between the conductive particles 6, the resin binder is not contained or the amount of the resin binder can be reduced as much as possible. The resistance can be reduced. Note that the coated form includes a form in which a part of the non-conductive inorganic particles 7 is buried in the surface of the conductive particles 6. Moreover, the form in which the nonconductive inorganic particles 7 form a layer and the conductive particles 6 are dispersed inside the layer is the form in which the outer surface of the conductive particles 6 is covered with the nonconductive inorganic particles 7. include.

The area ratio (coverage) that the non-conductive inorganic particles 7 cover the surfaces of the conductive particles 6 is preferably 30% or more, and more preferably 70% or more. When the coverage is 70% or more, the adhesion between the conductive particles 6 and the adhesion between the conductive particles 6 and the conductive layer 2 can be ensured.
On the other hand, from the viewpoint of reducing the contact resistance, the surface of the conductive particles 6 is preferably not completely covered with the non-conductive inorganic particles 7 but has a contact point with other conductive particles 6, and the coverage is 90%. The following is preferred.

  The lower limit of the content of the nonconductive inorganic particles 7 in the intermediate layer 3 is preferably 1% by mass, more preferably 3% by mass, and still more preferably 5% by mass. On the other hand, as an upper limit of content of the nonelectroconductive inorganic particle 7, 40 mass% is preferable, 35 mass% is more preferable, and 30 mass% is further more preferable. By making the content of the non-conductive inorganic particles 7 in the intermediate layer 3 within the above range, the contact resistance at the interface between the conductor layer 2 and the active material layer 4 is reduced, and the fixing strength of the conductive particles 6 is improved. Can be demonstrated easily and reliably. When content of the nonelectroconductive inorganic particle 7 is smaller than the said minimum, there exists a possibility that the fixed strength of the electroconductive particle 6 may become inadequate. On the other hand, when the content of the non-conductive inorganic particles 7 exceeds the above upper limit, the content of the conductive particles 6 decreases, so that the effect of reducing the contact resistance between the conductor layer 2 and the active material layer 4 becomes insufficient. There is a fear.

(Middle layer structure)
The lower limit of the total content of the conductive particles 6 and the nonconductive inorganic particles 7 in the intermediate layer 3 is preferably 60% by mass, more preferably 70% by mass, further preferably 80% by mass, and particularly preferably 90% by mass. .

  The lower limit of the mass ratio of the content of the nonconductive inorganic particles 7 to the content of the conductive particles 6 in the intermediate layer 3 is preferably 1%, more preferably 3%, and even more preferably 5%. On the other hand, the upper limit of the mass ratio is preferably 70%, more preferably 60%, and even more preferably 50%. When the said mass ratio is smaller than the said minimum, there exists a possibility that the fixed strength of the electroconductive particle 6 may become inadequate. Conversely, when the mass ratio exceeds the upper limit, the effect of reducing the contact resistance between the conductor layer 2 and the active material layer 4 may be insufficient.

  In the case where the conductive particles 6 are carbon particles and the non-conductive inorganic particles 7 are silicate minerals, the element C in the presence region of the conductive particles 6 in the intermediate layer 3 is analyzed by EPMA (electron beam microanalyzer). It is preferable that Si is detected at a position where the intensity is maximum. That is, it is preferable that the non-conductive inorganic particles 7 are detected at positions where the conductive particles 6 exist. Thereby, it is ensured that the conductive particles 6 are covered with the non-conductive inorganic particles 7 and fixed to the conductor layer 2. Note that EPMA analysis means measuring the intensity of each element by irradiating the cross section of the electrode 1 with an electron beam.

  Further, the lower limit of the C element strength ratio with respect to Si at the position where the C element strength is maximum is preferably 10, and more preferably 40. On the other hand, the upper limit of the element strength ratio is preferably 800, and more preferably 500. When the element strength ratio is smaller than the lower limit, the existence ratio of the conductive particles 6 is smaller than the non-conductive inorganic particles 7, and the effect of reducing the contact resistance between the conductor layer 2 and the active material layer 4 is insufficient. There is a risk. On the contrary, when the element strength ratio exceeds the upper limit, the abundance ratio of the non-conductive inorganic particles 7 is small with respect to the conductive particles 6 and the fixing strength of the conductive particles 6 may be insufficient.

  Further, the lower limit of the elemental strength ratio of O to Si at the position where the elemental strength of C is maximum is preferably 0.04 and more preferably 1. On the other hand, the upper limit of the element strength ratio is preferably 100 and more preferably 10. When the element strength ratio is smaller than the lower limit or exceeds the upper limit, the ratio of impurities other than the conductive particles 6 and the non-conductive inorganic particles 7 may increase, and the fixing strength of the conductive particles 6 may be insufficient. In addition, the effect of reducing the contact resistance between the conductor layer 2 and the active material layer 4 may be insufficient.

  As a minimum of the coverage of intermediate layer 3 to conductor layer 2, 1% is preferred, 30% is more preferred, and 50% is still more preferred. On the other hand, the upper limit of the coverage is preferably 95%, more preferably 90%, and even more preferably 80%. When the said coverage is smaller than the said minimum, there exists a possibility that the reduction effect of the contact resistance of the conductor layer 2 and the active material layer 4 may become inadequate. On the contrary, when the said coverage exceeds the said upper limit, there exists a possibility of causing the fall of manufacturing efficiency and the thickness increase of the said electrode 1. Here, the “coverage ratio of the intermediate layer to the conductor layer” means the area ratio of the surface of the conductor layer covered by the intermediate layer to the entire surface of the conductor layer. When it is coated, it means the value on one surface.

  The lower limit of the weight per unit area (coating amount) of the intermediate layer 3 is preferably 0.1 g / m2, and more preferably 0.5 g / m2. On the other hand, the upper limit of the basis weight of the intermediate layer 3 is preferably 2 g / m2, and more preferably 1.2 g / m2. When the basis weight of the intermediate layer 3 is smaller than the lower limit, the contact resistance reducing effect of the intermediate layer 3 may be insufficient. On the other hand, when the weight per unit area of the intermediate layer 3 exceeds the upper limit, there is a risk that the manufacturing efficiency is lowered and the thickness of the electrode 1 is increased.

  The lower limit of the average thickness of the intermediate layer 3 is preferably 0.1 μm, more preferably 0.5 μm, and even more preferably 0.8 μm. On the other hand, the upper limit of the average thickness of the intermediate layer 3 is preferably 10 μm and more preferably 5 μm. When the average thickness of the intermediate layer 3 is smaller than the lower limit, the effect of reducing the contact resistance by the intermediate layer 3 may be insufficient. On the other hand, when the average thickness of the intermediate layer 3 exceeds the above upper limit, the production efficiency may be reduced.

<Active material layer>
The active material layer 4 is formed of a so-called composite material containing active material particles. Moreover, the composite material which forms the active material layer 4 contains arbitrary components, such as a electrically conductive agent, a binder, and a thickener, as needed.

(Active material particles)
As the active material particles contained in the active material layer 4, known particles that are usually used for power storage elements can be used. When the electrode 1 is used for a positive electrode of a lithium ion secondary battery, an active material powder capable of inserting and extracting lithium ions is used as the active material particles. As a specific active material, general formula Li1-aM1O2 (0 ≦ a ≦ 1, M1 is Ni, Mn, Ti, Cr, Fe, Co, Cu, Zn, Al, Ge, Sn, Mg, Mo, or Zr) A compound represented by the general formula Li1-aNixM2yM3zO2 (0 ≦ a ≦ 1, M2, M3 are Mn, Ti, Cr, Fe, Co, Cu, Zn, Al, Ge, Sn, Mg, Mo or Zr, and M2 ≠ M3, x + y + z = 1, 0 <x ≦ 1, 0 ≦ y <1, 0 ≦ z <1), a compound represented by the general formula LiM4PO4 (M4 is Mn, Fe or Co), a general formula LibM52O4 (M5) Are transition metals, compounds represented by 0 ≦ b ≦ 2), and the like. Of the compounds represented by the general formula Li1-aNixM2yM3zO2, compounds represented by LiNixMnyCozO2 (x + y + z = 1, 0 <x <1, 0 <y <1, 0 <z <1) are more preferable.

  Specific examples of the compound represented by the above general formula include, for example, lithium cobaltate (LiCoO2), lithium manganate (LiMn2O4), lithium nickelate (LiNiO2), and Co—Mn—Ni ternary lithium compound (LiNixMnyCozO2). And olivine-based lithium compound (LiFePO4).

  Moreover, as an active material in the case of using for the positive electrode of an electrical storage element, in addition to MnO2, FeO2, TiO2, etc., metal chalcogenides such as V2O5, V6O13, TiS2, etc. other than the compounds represented by the above general formula, A composite oxide or the like can also be used.

  The active material particles used for the positive electrode of the energy storage device preferably have a hollow structure or a layered structure.

  On the other hand, when the electrode 1 is used for a negative electrode of a lithium ion secondary battery, an active material powder capable of inserting and extracting lithium ions is used as the active material particles. Specific examples of the active material include metals such as lithium and lithium alloys (lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, etc.), metal oxides, polyphosphate compounds, and graphite. And carbon materials such as amorphous carbon.

  Furthermore, when the electrode 1 is used for a capacitor electrode, examples of the active material constituting the active material particles include carbon materials such as metal oxide, graphite, and amorphous carbon.

  Note that the active material particles used for the positive electrode or the negative electrode of the power storage element may be used in a mixture of two or more kinds described above.

  The lower limit of the average particle diameter of the active material particles is preferably 0.1 μm, and more preferably 1 μm. On the other hand, the upper limit of the average particle diameter of the active material particles is preferably 10 μm, and more preferably 5 μm. When the average particle diameter of the active material particles is smaller than the above lower limit, the production and handling of the active material particles may be difficult. Conversely, when the average particle diameter of the active material particles exceeds the upper limit, the electronic conductivity of the active material layer 4 may be reduced.

  The average particle diameter of the active material particles is preferably smaller than the average major axis of the conductive particles 6. Specifically, the lower limit of the ratio of the average particle diameter of the active material particles to the average major axis of the conductive particles 6 is preferably 0.01, and more preferably 0.1. On the other hand, the upper limit of the ratio is preferably 2.0 and more preferably 1.6. When the ratio is smaller than the lower limit, it may be difficult to produce and handle the active material particles, or the conductive particles 6 may be coarsened. On the contrary, when the ratio exceeds the upper limit, the contact between the conductive particles 6 and the active material particles decreases, and the effect of reducing the contact resistance between the conductor layer 2 and the active material layer 4 may be insufficient. .

  As a minimum of content of active material particles in active material layer 4, 50 mass% is preferred and 80 mass% is more preferred. On the other hand, the upper limit of the content of the active material particles is preferably 99% by mass. By setting the content of the active material particles in the above range, the electric capacity of the battery using the electrode 1 can be increased.

(Optional component)
The conductive agent is not particularly limited as long as it is a conductive material that does not adversely affect battery performance. Examples of such a conductive material include natural or artificial graphite, carbon black such as furnace black, acetylene black, and ketjen black, metals, and conductive ceramics. Examples of the shape of the conductive agent include powder and fiber.

  As the binder, thermoplastic resins such as fluororesin (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene; ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), elastomers such as fluororubber; polysaccharide polymers and the like.

  Examples of the thickener include polysaccharide polymers such as carboxymethylcellulose and methylcellulose. When the electrode 1 is used for a lithium ion secondary battery, when the thickener has a functional group that reacts with lithium, it is preferable to deactivate the functional group in advance by methylation or the like.

  Note that when the active material layer 4 is formed on the surface of the intermediate layer 3, the binder contained in the active material layer 4 may flow into the voids present in the intermediate layer 3. In this case, the binder flowing into the intermediate layer 3 from the active material layer 4 is a component of the active material layer 4, and is not regarded as a component of the intermediate layer 3.

<Advantages>
Since the electrode 1 includes non-conductive inorganic particles 7 that cover the outer surface of the conductive particles 6 together with the conductive particles 6, the electrode 1 is covered with the non-conductive inorganic particles 7. 6 is carried on the conductor layer 2. Therefore, the electrode 1 has a relatively high fixed strength and the conductive particles 6 are uniformly coated on the surface of the conductor layer 2 and can easily and reliably reduce the contact resistance at the interface between the conductor layer 2 and the active material layer 4. . Furthermore, since the electrode 1 can form an intermediate layer without using a resinous binder, the material cost of the resinous binder can be reduced as compared with the conventional electrode in which the intermediate layer 3 is formed by coating the resinous binder. Since the intermediate layer 3 can be formed by rubbing the paint or the like, the manufacturing cost can also be reduced.

[Electrode manufacturing method]
The method for producing the electrode includes a step of forming an intermediate layer by rubbing a fired product of slurry containing conductive particles and non-conductive inorganic particles on at least a part of the surface of the conductor layer, and a step of drying the intermediate layer And a step of forming an active material layer on the intermediate layer side of the laminate including the conductor layer and the intermediate layer.

<Rubbing process>
In this step, first, a fired product of slurry containing conductive particles and non-conductive inorganic particles is obtained. This slurry is obtained by adding a solvent to conductive particles and non-conductive inorganic particles and kneading them. The solvent is not particularly limited as long as it does not react with conductive particles and non-conductive inorganic particles, and for example, an organic solvent or water can be used. Moreover, additives other than electroconductive particle and nonelectroconductive inorganic particle may be contained in a slurry. The kneading is preferably performed while heating.

  The fired product may be a commercially available product, or a commercially available kneaded product (slurry) may be prepared and fired. In addition, the fired product may include, for example, fats and oils for facilitating rubbing described later.

  The specific procedure for firing the slurry is as follows. First, the slurry is dried in air at, for example, 100 ° C. or more and 150 ° C. or less for 10 hours or more and 30 hours or less, and the solvent is evaporated. Next, the dried slurry is heated and fired in a nitrogen atmosphere. Then, fats and oils are added by immersing a baked product in fats and oils, such as lard, as needed.

  As a minimum of the calcination temperature in the above-mentioned calcination process, 1000 ° C is preferred and 1100 ° C is more preferred. On the other hand, as an upper limit of a calcination temperature, 1400 degreeC is preferable and 1300 degreeC is more preferable. When the firing temperature is lower than the lower limit, firing is insufficient and the strength of the fired product may be reduced. Conversely, when the firing temperature exceeds the above upper limit, the conductive particles and the like may be deteriorated or damaged.

  The firing time at the firing temperature is preferably from 30 minutes to 2 hours. Further, the rate of temperature rise up to the firing temperature is preferably 100 ° C./hour or more and 200 ° C./hour or less.

  The shape of the fired product is preferably a columnar shape as shown in FIG. Specifically, a cylindrical fired product is obtained by extruding the slurry into a cylindrical shape and firing the slurry. In this fired product, non-conductive inorganic particles are disposed so as to cover the outer surfaces of the conductive particles.

  In this step, the intermediate layer is then formed by rubbing the fired product of the slurry as a solid paint onto at least a part of the surface of the conductor layer. Specifically, as shown in FIG. 4, while the conductor layer 2 is fed by a roller R, the fired product B is pressed against the surface and slid. At this time, when using a rolled foil as the conductor layer 2, the fired product B is arranged so that the rolling direction of the metal foil is the feeding direction of the conductor layer 2, and the axial direction is perpendicular to the feeding direction, and a constant pressure is applied. However, it is preferable to reciprocate the fired product B in the axial direction. By moving the fired product B in this way, the conductive particles can be disposed so that the conductive particles are caught by the rolling marks and the long side faces the surface of the conductor layer 2. Thereby, the electroconductivity of an intermediate | middle layer can be improved. In addition, when using metal foil as a conductor layer, it is preferable to dry before rubbing. Moreover, when obtaining the electrode provided with an intermediate | middle layer on both surfaces of a conductor layer, the baking products B are rubbed on both surfaces of a conductor layer.

  The lower limit of the rubbing pressure is preferably 0.1 N / cm2, more preferably 0.2 N / cm2. On the other hand, the upper limit of the rubbing pressure is preferably 1 N / cm 2 and more preferably 0.5 N / cm 2. When the rubbing pressure is smaller than the above lower limit, the adhesion of conductive particles or the like to the surface of the conductor layer may be insufficient. Conversely, when the rubbing pressure exceeds the above upper limit, the conductor layer, conductive particles, etc. may be deformed.

  Although it does not specifically limit as the frequency | count of rubbing, For example, it can be 1 time or more and 10 times or less. The basis weight of the intermediate layer 3 can be adjusted by the number of times of rubbing.

<Drying process>
In this step, the intermediate layer obtained in the rubbing step is dried. As a result, the solvent and oil remaining in the intermediate layer are removed, and the adhesion between the intermediate layer and the conductor layer is improved.

  As a minimum of drying temperature, 60 ° C is preferred and 70 ° C is more preferred. On the other hand, as an upper limit of drying temperature, 200 degreeC is preferable and 180 degreeC is more preferable. When the drying temperature is lower than the above lower limit, the drying becomes insufficient and the solvent or the like may remain. Conversely, when the drying temperature exceeds the upper limit, the conductive particles and the like may be deteriorated or damaged.

  As a minimum of drying time, 30 minutes are preferred and 40 minutes are more preferred. On the other hand, the upper limit of the drying time is preferably 60 minutes, and more preferably 50 minutes. When the drying time is smaller than the above lower limit, the drying becomes insufficient and the solvent or the like may remain. Conversely, when the drying time exceeds the above upper limit, the conductive particles and the like may be deteriorated or damaged.

<Active material layer forming step>
In this step, an active material layer is formed on the intermediate layer side of the laminate including the conductor layer and the intermediate layer obtained in the rubbing step. Specifically, the active material layer is formed by coating the active material layer forming material on the intermediate layer side of the laminate and heat treatment.

  The active material layer forming material is a mixed solution in which the above-described active material particles and optional components are mixed with a solvent. As this solvent, for example, an organic solvent such as N-methylpyrrolidone or toluene can be used.

  The heat treatment temperature can be, for example, 50 ° C. or higher and 150 ° C. or lower. Moreover, as heat processing time, it can be 10 minutes or more and 3 hours or less, for example.

  In addition, it is preferable to press the laminated body which laminated | stacked the active material layer with the roll etc. after the said heat processing. Further, the drying step can be omitted.

<Advantages>
In the method for producing the electrode, an intermediate layer is formed by rubbing at least a part of the surface of the conductor layer with a fired product containing conductive particles and non-conductive inorganic particles covering the outer surface of the conductive particles, The electrode described above is obtained. The manufacturing method of the electrode can reduce the material cost of the resin binder, and can reduce the coating cost because steps such as drying and baking can be omitted by the step of rubbing the fired product.

[Storage element]
The power storage element shown in FIG. 5 mainly includes a pair of positive electrodes 1a and negative electrodes 1b and a separator 5 disposed between these electrodes. FIG. 5 shows the lowest structural unit of the electricity storage element. In the electric storage element, positive electrodes 1 a and negative electrodes 1 b are alternately stacked via separators 5. Further, the power storage element is filled with a nonaqueous electrolyte (electrolytic solution) containing ethylene carbonate, diethyl carbonate, or the like in which lithium hexafluorophosphate (LiPF6) or the like is dissolved in a case.

<Electrode>
The positive electrode 1a and the negative electrode 1b have the same configuration as the electrode 1 described above. The positive electrode 1a and the negative electrode 1b can have the same configuration except that the active material particles contained in the active material layers 4a and 4b are selected according to the positive and negative as described above. The conductor layer 2, the intermediate layer 3, and the active material layers 4a and 4b are as described in the electrode of the embodiment of FIG.

<Separator>
As a material of the separator 5, for example, a woven fabric, a nonwoven fabric, a porous resin film, or the like is used. Among these, a porous resin film is preferable. The main component of the porous resin film is preferably a polyolefin such as polyethylene or polypropylene from the viewpoint of strength. Moreover, you may use the porous resin film which compounded these resins and resin, such as an aramid and a polyimide.

[Other Embodiments]
The electrode of the present invention, the method for producing the same, and the electricity storage device of the present invention are not limited to the above embodiment. For example, the power storage element can include a pair of positive and negative electrodes. In this case, in each electrode, the intermediate layer is laminated only on one surface of the conductor layer, and the active material layer is laminated only on the intermediate layer side of the laminate including the conductor layer and the intermediate layer. In addition, the power storage element may be configured to include an intermediate layer on either the positive electrode or the negative electrode.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

[Example 1]
First, 70 parts by mass of scale-like natural graphite (average major axis: 8 μm) as conductive particles, 5 parts by mass of kaolinite and 5 parts by mass of halloysite as non-conductive inorganic particles, and 30 parts by mass of water were used with a Henschel mixer. A slurry was obtained by kneading. In addition, the resin binder is not added to this slurry. Next, this slurry was heated and kneaded until water became about 20 parts by mass. Thereafter, this mixture was extruded into a linear body using an extrusion die. Further, the molded product was heat treated in air at 120 ° C. for 20 hours to remove moisture, then heated to 1200 ° C. in 10 hours in a nitrogen atmosphere, and then fired at 1200 ° C. for 1 hour. After firing, the fired product was immersed in lard.
The mass ratio of the fired product after being immersed in lard was 70 parts by mass of natural graphite, 10 parts by mass of non-conductive inorganic particles (kaolinite and halloysite), and 20 parts by mass of oil (lard).

  The fired product is rubbed at a basis weight of 1.0 g / m2 onto the surface of an aluminum foil (A1085P, arithmetic average roughness Ra: 0.07 μm, average thickness: 15 μm) as a conductor layer, and dried at 150 ° C. A layer was formed. Further, an active material layer in which the mass ratio of LiNi1 / 3Mn1 / 3Co1 / 3O2: acetylene black: polyvinylidene fluoride was 90: 5: 5 was laminated on the surface of the intermediate layer, whereby the electrode of Example 1 was obtained. Note that pressing is not performed after the lamination of the active material layers. Arithmetic mean roughness Ra is 2,000 times magnification, measuring range 150 μm × 110 μm equivalent (exactly 16683 μm2), height using Keyence laser microscope “VK-8500” and analysis software “VK-H1W” Height data was measured under conditions of a direction measurement range of 8 μm and a measurement pitch of 0.1 μm, a height data reference plane was obtained by the least square method, and the height data was calculated from the difference between the reference plane and the height data of each point. This calculation condition is based on JIS-B-0601 (2001), and can be regarded as equivalent to the arithmetic average roughness Ra measured with a cutoff value (λc) of 0.25 mm and an evaluation length (l) of 150 μm.

[Examples 2 to 6]
The electrodes of Examples 2 to 6 were obtained in the same manner as in Example 1 except that the arithmetic average roughness Ra of the used aluminum foil or the basis weight of the intermediate layer was changed to the values shown in Table 1.

[Comparative Example 1]
The same active material layer as in Example 1 was directly laminated without forming an intermediate layer on the surface of the aluminum foil used in Example 1, and the electrode of Comparative Example 1 was obtained.

[Comparative Example 2]
Comparative Example as in Example 1 except that as the slurry, an intermediate layer was formed by applying a coating liquid in which 30 parts by mass of acetylene black and 70 parts by mass of a resin binder (polyvinylidene fluoride) were applied. 2 electrodes were obtained.

[Evaluation]
The electrodes of Examples 1 to 6 and Comparative Examples 1 and 2 were evaluated by the following method. First, each electrode was punched into a 2 cm square, and a resistivity meter (“Lorester EP MCP-T360” manufactured by Mitsubishi Chemical Analytech Co., Ltd.) was used to push the two terminals against the surface of the active material layer of the sample The resistance value of the sample was measured. The measurement was performed 10 times, and the average value was defined as the resistance value a. This was performed for three samples, and an average resistance value A, which is an average value of the resistance values a of each material, was calculated.

  Next, these samples were immersed in an electrolytic solution having a volume ratio of ethylene carbonate: diethyl carbonate of 3: 7 at 65 ° C. and left for 50 hours. After immersion, the sample was taken out, washed with dimethyl carbonate and vacuum-dried, and then the above-described resistance value was measured again to calculate the average resistance value B of the three samples.

  Using the average resistance value A and the average resistance value B, the resistance increase rate was calculated by (B / A) × 100-100. The results are shown in Table 1.

  Moreover, when the micrographs of the cross sections of the electrodes of Examples 1 to 6 were observed, the conductive particles whose outer surfaces were coated with the nonconductive inorganic particles were arranged so that the long side faces the surface in the recesses of the aluminum foil. It was set up.

  As shown in Table 1, the electrodes of Examples 1 to 6 have a smaller resistance value B after being immersed in the electrolytic solution than the electrodes of Comparative Examples 1 and 2, and the resistance increase rate is kept low. Recognize. This is considered to be because the conductive particles are coated on the surface of the conductor layer with relatively high fixing strength and uniformity. Moreover, it is thought that the decrease in the resistance increase rate is due to the fact that swelling due to the resin binder does not occur.

  As described above, in the electrode of the present invention, the fixing strength and uniformity of the conductive particles to the conductor layer are remarkably improved. In addition, the electrode manufacturing method of the present invention can provide an electrode in which the fixing strength and uniformity of the conductive particles to the conductor layer are remarkably improved. Furthermore, since the electrical storage element of this invention can reduce the contact resistance in the interface of a conductor layer and an active material layer easily and reliably, it is used suitably, for example as a lithium ion secondary battery.

1, 1a, 1b Electrode 2 Conductor layer 3 Intermediate layer 4, 4a, 4b Active material layer 5 Separator 6 Conductive particle 7 Non-conductive inorganic particle 8 Dimple B Firing product R Roller

Claims (6)

A conductor layer, an active material layer, an intermediate layer formed between the conductor layer and the active material layer and covering at least a part of the surface of the conductor layer;
The intermediate layer includes conductive particles and non-conductive inorganic particles, and an outer surface of the conductive particles is covered with the non-conductive inorganic particles.   The electrode according to claim 1, wherein the non-conductive inorganic particles are layered silicate minerals.   The content of the conductive particles in the intermediate layer is 55% by mass or more and 98% by mass or less, and the content of the non-conductive inorganic particles is 1% by mass or more and 40% by mass or less. Electrodes.   The electrode according to any one of claims 1 to 3, wherein an arithmetic average roughness Ra of the conductor layer is 0.05 µm or more and 4 µm or less.   A power storage element using the electrode according to any one of claims 1 to 4. A method for producing an electrode comprising a conductor layer, an active material layer, and an intermediate layer formed between the conductor layer and the active material layer and covering at least part of the surface of the conductor layer,
An electrode comprising: a step of rubbing conductive particles and non-conductive inorganic particles on at least a part of a surface of the conductor layer, wherein an outer surface of the conductive particles is coated with the non-conductive inorganic particles. Production method.

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