JP6935722B2 - Electrodes, electrode manufacturing methods and power storage elements - Google Patents

Description

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

In a non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery, a method of coating an electrode constituting the non-aqueous electrolyte secondary battery with an insulating layer may be used as a method for enhancing the safety thereof. By providing the insulating layer, the insulating property between the positive and negative electrodes is ensured even when the separator shrinks or breaks. More specifically, for an electrode having a current collector foil and a mixture layer provided on the current collector foil, the surface of the mixture layer is coated with an insulating layer in order to prevent a short circuit between the positive and negative electrodes. A method of (overcoating) is known.

Republished Patent WO2010 / 116533 Gazette Japanese Unexamined Patent Publication No. 2016-225077

In the insulating layer, insulating particles composed of an inorganic substance are often used as an insulator. However, when the insulating layer is formed by the insulating particles, the hardness of the insulating particles is high. Therefore, when the insulating particles are formed or the electrode is manufactured, the manufacturing apparatus on the pass line (for example, a roll press machine or a winding machine) is used. Etc.) may damage the roll etc.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an electrode which is provided with an insulating layer composed of insulating particles but which is unlikely to damage a manufacturing apparatus. be.

The electrode of the present invention includes a mixture layer and an insulating layer arranged on the surface of the mixture layer, the insulating layer contains insulating particles and a binder, and the insulating particles are coated on the binder. The thickness of the binder is 0.4 μm or more.

According to the present invention, by using the insulating particles coated on the binder having a specific thickness, it is possible to provide an electrode having an insulating layer composed of the insulating particles but hardly damaging the manufacturing apparatus. .. Further, according to the present invention, the presence of more binders certain thickness on the surface of the insulating particles, it is possible to secure a binding property between the insulating particles to suppress the detachment or the like of the insulating particles Can be done.

It is the schematic sectional drawing of the electrode by one Embodiment of this invention. It is a schematic partial cross-sectional view which shows the outer surface of the insulating layer of the electrode by one Embodiment of this invention. It is a partially cutaway perspective view which shows the schematic structure of the non-aqueous electrolyte secondary battery by one Embodiment of this invention. It is a cross-sectional analysis image by the electron probe microanalyzer (EPMA) of the positive electrode mixture layer and the insulating layer in the Example of this invention.

A. Outline of Electrode FIG. 1 is a schematic cross-sectional view of an electrode according to one embodiment of the present invention. The electrode 101 includes a mixture layer 10 and an insulating layer 20 arranged on the surface of the mixture layer 10. Practically, the electrode 101 may further include a current collecting foil 30 on the side of the mixture layer 10 opposite to the insulating layer 20. Although not shown, an insulating layer may be formed on the current collector foil in addition to the mixture layer.

The insulating layer 20 includes insulating particles 21a and a binder 21b. FIG. 2 is a schematic partial cross-sectional view showing the outer surface of the insulating layer of the electrode according to one embodiment of the present invention. The insulating particles 21a are coated on the binder 21b. The binder 21b coats the insulating particles 21a at least on the outer surface of the insulating layer 20. The thickness of the binder 21b is 0.4 μm or more (details will be described later).

If the non-aqueous electrolyte secondary battery is constructed using the electrodes of the present invention provided with an insulating layer, the insulating property between the positive and negative electrodes can be ensured even when the separator shrinks or breaks. In the present invention, by forming an insulating layer using insulating particles coated with a binder having a thickness of 0.4 μm or more, an electrode that does not easily damage the roll or the like of the manufacturing apparatus on the pass line in the battery manufacturing process. Can be obtained. The present invention is particularly useful when high hardness particles (eg, inorganic particles) are used as insulating particles. Further, since the insulating particles are covered with a thick binder, the contact area between the composites composed of the insulating particles and the binder and the contact area between the composite and the mixture layer become large in the insulating layer. As a result, the detachment of the insulating particles is suppressed.

The electrode of the present invention is used as a positive electrode or a negative electrode of a non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery. In one embodiment, the electrodes of the present invention are used as the positive electrode of a non-aqueous electrolyte secondary battery. If a positive electrode having an insulating layer formed is used, contact between the separator and the positive electrode mixture layer can be avoided, and oxidation of the separator can be prevented.

B. Insulation layer As described above, the insulation layer is composed of insulating particles and a binder, and the insulating particles are coated with the binder. More specifically, the insulating particles and the binder form a complex, and the complex has a so-called core-shell structure, and includes a core portion composed of the insulating particles and a shell portion composed of the binder. The binder has a function of binding the insulating particles to each other and the insulating particles and the mixture layer.

The thickness of the binder is 0.4 μm or more, more preferably 0.5 μm to 1.0 μm. In the battery manufacturing process, it is possible to obtain an electrode that does not easily damage the roll or the like of the manufacturing apparatus on the pass line. Further, within such a range, the detachment of the insulating particles can be prevented. The insulating layer composed of the insulating particles coated with the thick binder as described above can be formed by a dry coating method (electrostatic coating) described later. The "binder thickness" is measured by the following procedure.
(I) A cross-sectional analysis image (magnification: 8000 times, analysis range: length 30 μm × depth about 30 μm) obtained by an electron probe microanalyzer (EPMA) near the outer surface of the randomly selected portion of the insulating layer was acquired. , The core particle (insulating particle) / shell part (binder) of the complex is discriminated from the image;
(Ii) From the insulating particles existing on the outermost side of the insulating layer in the above image, the top five insulating particles having a large particle size are selected;
(Iii) The thickness of the binder on the outer surface of the insulating layer of the selected insulating particles is measured;
(Iv) The thicknesses of the binders at five points measured in (iii) are averaged, and the obtained average value is defined as the "binder thickness".
In FIG. 2, the portion surrounded by the broken line indicates the range of the cross-sectional analysis image, and the arrow indicates the thickness of the binder on the outer surface of the insulating layer of the upper five insulating particles having a large particle size.

The CV value (coefficient of variation) of the thickness of the binder is preferably 0.35 or less, and more preferably 0.3 or less. The insulating layer composed of insulating particles having a uniform binder thickness has excellent insulating properties and the detachment of the insulating particles is suppressed. The smaller the CV value is, the more preferable it is, but the lower limit value thereof is, for example, 0.05 (preferably 0.01). The "CV value of the binder thickness" can be calculated from the measured value obtained by the above-mentioned measurement procedure of the "binder thickness".

It is preferable that 80 area% or more of the surface of the insulating particles is covered with a binder, 90 area% or more is more preferably covered with a binder, and 95 area% or more is covered with a binder. More preferred. Since 80 area% or more of the surface of the insulating particles is covered with a binder, the probability that the insulating particles are exposed on the surface of the insulating layer can be reduced, so that the manufacturing apparatus on the pass line is scratched in the battery manufacturing process. It is possible to obtain electrodes that are difficult to attach.

The average particle size of the insulating particles is preferably 1 μm or more, more preferably 1.2 μm to 5.0 μm , and further preferably 1.8 μm to 3.5 μm. In the present specification, the "average particle size" refers to the particle size distribution measured by the laser diffraction / scattering method with respect to a diluted solution obtained by diluting the particles with a solvent in accordance with JIS-Z-8815 (2013). Based on this, it means a value at which the volume-based integrated distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50%.

The ratio of the thickness of the binder to the average particle size of the insulating particles (thickness of the binder / average particle size of the insulating particles) is preferably 0.05 or more, more preferably 0.08 or more. Within such a range, the thickness of the binder is sufficient, and the detachment of the insulating particles can be prevented. Further, in the battery manufacturing process, it is possible to obtain an electrode that does not easily damage the manufacturing apparatus on the pass line. The upper limit of the ratio of the thickness of the binder to the average particle size of the insulating particles (thickness of the binder / average particle size of the insulating particles) is preferably 0.4, more preferably 0.25. Within such a range, it is possible to prevent the insulating layer from becoming too thick.

As the material of the insulating particles, any suitable material can be used as long as it has insulating properties. Insulating inorganic substances can be used as the material constituting the particles. If insulating particles composed of inorganic substances are used, an insulating layer having excellent heat resistance can be formed. Examples of the insulating inorganic substance include metal oxides such as alumina, boehmite, aluminum hydroxide, silica, zirconia, and magnesia. Further, a silicate such as silicon carbide, a nitride such as aluminum nitride, or the like may be used. The shape is not particularly limited, but a spherical shape or a lump shape is preferable from the viewpoint of coatability. Spherical or massive refers to a shape having an aspect ratio of 1.5 or less.

As the material constituting the binder, a material made of resin or rubber is preferable. Since the binder made of resin or rubber has a low hardness, the effect of the present invention can be easily obtained. Examples of the material constituting the binder include fluororesins such as polyvinylidene fluoride, polytetrafluoroethylene and fluororubber, polyolefin resins such as polypropylene and polyethylene, polyacrylic acid resins such as polymethylmethacrylate, polyimides and polyamides. Examples thereof include imide-based resins such as imide and rubbers such as styrene-butadiene rubber (SBR).

The average particle size of the binder particles (the average particle size before heating) is preferably 0.1 to 0.5 μm, and more preferably 0.15 to 0.3 μm. Within such a range, when forming a complex of the insulating particles and the binder particles, the layer thickness of the binder particles before heating can be adjusted, so that the insulating particles coated with the binder having an appropriate thickness Can be obtained. If the binder particles are likely to aggregate, the average particle size can be measured by SEM observation. Specifically, 10 particles are arbitrarily selected in the SEM image, their particle diameters are measured (when the particle shape is not spherical, the average of the longest diameter and the shortest diameter is taken as the particle diameter), and they are used. Let the average particle size be the average particle size.

The thickness of the insulating layer is preferably 2 μm to 15 μm, more preferably 3 μm to 10 μm.

The area of the insulating layer is preferably 80% or more, more preferably 90% or more, still more preferably 95% or more, and particularly preferably 95% or more, based on the total area of the flat surface portion of the mixture layer. It is 100%. Within such a range, an insulating layer having a small adverse effect on battery performance and excellent insulating properties can be formed.

The porosity of the insulating layer is preferably 10% to 50%, more preferably 15% to 35%. Within such a range, an insulating layer having a small adverse effect on battery performance and excellent insulating properties can be formed.

C. Mixture layer In one embodiment, when the electrode is configured as a negative electrode, the mixture layer contains a negative electrode active material capable of occluding and releasing lithium ions. Examples of the negative electrode active material include carbon materials such as graphite (scaly graphite, scaly graphite, earthy graphite, artificial graphite), acetylene black, carbon black, coke, activated carbon, fullerene, carbon nanotubes, aluminum, silicon, and lead. , Alloy of tin, zinc, cadmium, etc. and lithium, lithium _{nitride such as Li 5} (Li ₃ N), metallic lithium, _{metal oxides such as LiFe 2} O ₃ , WO ₂ , MoO ₂ , SiO, CuO, etc. Be done. The negative electrode active material may be used alone or in combination of two or more.

In another embodiment, when the electrode is configured as a positive electrode, the mixture layer contains a positive electrode active material capable of occluding and releasing lithium ions. As the positive electrode active material, the composite _{oxide represented by the composition formulas Li x} MO ₂ and Li _y M ₂ O ₄ (where M is one or more kinds of transition metals, 0 ≦ x ≦ 1, 0 ≦ y ≦ 2). , Tunnel-structured or layered-structured metal chalcogenides, metal oxides, and other transition metal oxides that occlude and release lithium can be used. Specific examples thereof include LiCoO ₂ , LiNiO ₂ , LiNi _1/2 Mn _1/2 O ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiCo _x Ni _1-x O ₂ , and LiMn ₂ O. ₄ , Li ₂ Mn ₂ O _{4 and the} like can be mentioned.

The mixture layer may further contain additives such as binders, conductive agents, thickeners, fillers and the like. Examples of the binder include polyvinylidene fluoride, styrene butadiene rubber, carboxymethyl cellulose, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylonitrile, ethylene-propylene-dienter polymer (EPDM), sulfonated EPDM, fluororubber, and the like. Examples thereof include a vinylidene fluoride-hexafluoropropylene copolymer. Examples of the conductive agent include conductive inorganic compounds such as metals and conductive ceramics, and conductive organic compounds such as conductive polymers.

D. Current collector foil As the current collector foil, any suitable current collector foil commonly used for non-aqueous electrolyte secondary batteries can be used. When the electrode is configured as a negative electrode, a metal foil such as a copper foil is used as the current collecting foil. When the electrode is configured as a positive electrode, a metal foil such as an aluminum foil is used as the current collecting foil.

E. Method of manufacturing an electrode The electrode can be manufactured by applying an insulating layer forming material on a mixture layer of a laminate composed of a current collector foil and a mixture layer. A part of the insulating layer forming material may be applied to the current collecting foil to form an insulating layer on the current collecting foil. For example, if the insulating layer forming material is applied so that the insulating layer is formed on the current collecting foil near the end of the mixture layer, the insulating layer can also be formed on the surface of the current collecting foil.

In one embodiment, the insulating layer is formed by a solvent-free dry coating method. As a method for manufacturing an electrode by a dry coating method, a composite of insulating particles and particulate binders (hereinafter, also referred to as binder particles) is attached to a mixture layer (and, if necessary, the surface of a current collector foil) for insulation. There is a manufacturing method for forming layers. More specifically, (i) a step of mixing the insulating particles and the binder particles to obtain a composite in which the surface of the insulating particles is coated with the binder particles, and (ii) the above-mentioned composite is applied to a mixture layer (i). An insulating layer containing the insulating particles and the binder is formed through a step of adhering to the surface of the current collecting foil, if necessary, and a step of (iii) heating the complex to melt the binder particles. As a result of the above manufacturing method, a form in which the binder covers the surface of the insulating particles is obtained.

If a dry coating method that does not use a solvent is used, the binder does not invade the mixture layer together with the solvent. As a result, the binder can be held on the surface of the insulating particles, so that the insulating particles coated with a thick binder can be obtained. Further, since the binder does not invade the mixture layer and block the gaps between the active material particles with the binder, it is possible to obtain a mixture layer having excellent permeability of the electrolytic solution, and as a result, high rate discharge characteristics. It is possible to obtain an excellent non-aqueous electrolyte secondary battery. On the other hand, in wet coating using a solvent, since the binder flows into the synthetic layer together with the solvent, it is difficult to form a binder having a certain thickness on the surface of the insulating particles. In order to form a binder having a certain thickness or more on the surface of the insulating particles by wet coating, it is necessary to increase the mass of the binder of the insulating layer, and the gap between the insulating particles may be blocked by the binder. ..

Any suitable method is adopted as the mixing method of the insulating particles and the binder particles. For example, by putting the insulating particles and the binder particles into a stirrer provided with rotating blades and stirring and mixing these particles, a composite in which the binder particles are arranged on the surface of the insulating particles can be obtained. Stirring conditions are set so that sufficient frictional and electrical resistance is generated between the insulating particles and the binder particles.

Electrostatic coating is mentioned as one of the dry coating methods, and as the electrostatic coating, for example, an electrostatic flow immersion method, an electrostatic powder spray method, or the like can be adopted. In one embodiment, in a coating booth provided with an electrode for electrostatic coating, a laminate composed of the current collector foil and a mixture layer and a composite composed of insulating particles and binder particles. Is charged, the composite is charged, and the composite is adhered to the mixture layer (and, if necessary, the surface of the current collecting foil) by electrostatic attraction.
After electrostatic coating, the composite is heated to melt the binder particles to obtain binder-coated insulating particles. By fusing the binder particles, adjacent insulating particles and the insulating particles and the mixture layer are bonded to each other. The heating temperature can be any suitable temperature depending on the type of binder particles. Examples of the heating method include a method of putting the laminate to which the complex is attached into a heating furnace, a method of heating the laminate to which the complex is attached while pressing it using a heating roll, and the like.

The thickness of the binder can be adjusted by the mass ratio of the insulating particles and the binder. That is, the thickness of the binder after heating can be adjusted by the amount of the binder particles adhering to the surface of the insulating particles in the mixing of the insulating particles and the binder particles. The content of the binder is preferably 10 parts by mass to 40 parts by mass, and more preferably 15 parts by mass to 30 parts by mass with respect to the total mass of the insulating particles and the binder.

According to the above electrode manufacturing method, the surface of the insulating particles can be coated with a binder having a predetermined thickness. By arranging such insulating particles on the outermost surface of the insulating layer, it is possible to prevent the insulating particles from damaging the manufacturing apparatus such as a pass line or a press machine.

F. Non-aqueous electrolyte secondary battery FIG. 3 is a partially cutaway perspective view showing a schematic configuration of a non-aqueous electrolyte secondary battery according to one embodiment of the present invention. The non-aqueous electrolyte secondary battery 110 includes a positive electrode 100 having a current collector foil and a positive electrode mixture layer, and a negative electrode 200 having a current collector foil and a negative electrode mixture layer. Typically, as shown in FIG. 3, the non-aqueous electrolyte secondary battery 110 includes a power generation element 111 in which a positive electrode 100 and a negative electrode 200 are wound around the separator 300. The power generation element 111 is housed in the battery case 112 in a state where the separator 300 is impregnated with a non-aqueous electrolyte. The battery case 112 is, for example, a substantially box type having an opening on the upper surface side. The opening is closed by a plate-shaped battery lid 113. The battery lid 113 is provided with a positive electrode terminal 114 and a negative electrode terminal 115. The positive electrode terminal 114 is electrically connected to the positive electrode 100 via the positive electrode lead 116, and the negative electrode terminal 115 is electrically connected to the negative electrode 200 via the negative electrode lead 117. It is connected.

The above electrodes are used as the negative electrode and / or the positive electrode. Preferably, as described above, the non-aqueous electrolyte secondary battery uses the above electrode as the positive electrode.

As the non-aqueous electrolyte, any suitable non-aqueous electrolyte is used. Non-aqueous electrolytes include non-aqueous solvents and electrolyte salts. Examples of the non-aqueous solvent include chain carbonates such as ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and diphenyl carbonate; ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, styrene carbonate, and the like. And so on. These non-aqueous solvents may be used alone or in combination of two or more. Examples of the electrolyte salt include ionic compounds such as LiPF6, LiPF2 (C2O4) 2, LiPF3 (CF2CF3) 3, LiPF4 (C2O4) , LiClO4, LiBF4, and LiAsF6.

As the separator, for example, a microporous membrane containing a polyolefin resin such as polyethylene or polypropylene as a main component is used. The microporous membrane may be used alone as a monolayer membrane, or a plurality of microporous membranes may be used as a composite membrane in combination. Further, the microporous membrane may contain an appropriate amount of additives such as various plasticizers, antioxidants and flame retardants.

Hereinafter, the present invention will be described based on examples, but the present invention is not limited thereto.
(Positive electrode mixture layer)
A lithium transition metal composite oxide (LiNi1 / 3Co1 / 3Mn1 / 3O2) having an average particle diameter (D50) of 5 μm and a lithium transition metal composite oxide (LiMn2O4) having an average particle diameter (D50) of 20 μm, which are positive electrode active materials. A positive electrode slurry was prepared using acetylene black as a conductive agent, vinylidene fluoride (PVDF) as a binder, and N-methylpyrrolidone (NMP) as a non-aqueous solvent. The mass ratio of the positive electrode active material, the binder and the conductive agent was 93: 4: 3 (in terms of solid content). This positive electrode slurry was applied to a 15 μm aluminum foil, dried, and rolled pressed to prepare a positive electrode mixture layer.

(Insulation layer)
Alumina with an average particle diameter (D50) of 3 μm, which is an insulating particle, and polyvinylidene fluoride (PVDF), which is a binder particle with an average particle diameter (measured by SEM observation) of 0.2 μm, are used at a mass ratio of 85:15. By mixing with mechanofusion, a composite in which PVDF particles were attached to the surface of the alumina particles was prepared. After charging this complex, it was sprayed onto the above-mentioned positive electrode mixture layer and heated to form an insulating layer by dry coating.

FIG. 4 shows a cross-sectional analysis image (magnification: 8000 times, analysis range: length 30 μm × depth about 30 μm) of the positive electrode mixture layer and the insulating layer prepared above by an electron probe microanalyzer (EPMA). As can be seen from FIG. 4, a binder layer having a certain thickness is formed on the outer surface of the insulating layer, and the presence of the binder layer having a certain thickness allows the insulating particles having high hardness to be produced in the battery manufacturing process. It is possible to prevent the roll and the like of the manufacturing apparatus from being damaged. On the other hand, when the insulating layer is formed by wet coating using a solvent, a phenomenon is observed in which the slurry containing the binder flows into the positive electrode active material layer, and the outer surface of the insulating layer has a constant (0.4 μm) thickness. The existence of the binder layer having it could not be confirmed.

In this embodiment, the insulating layer is formed on the positive electrode mixture layer, but the insulating layer may be formed on the negative electrode mixture layer.

10 Mixture layer 20 Insulation layer 21 Composite 21a Insulation particles 21b Binder 30 Current collector foil
101 electrode

Claims (5)

A mixture layer and an insulating layer arranged on the surface of the mixture layer are provided.
The insulating layer contains insulating particles and a binder, and the insulating layer contains insulating particles and a binder.
The insulating particles are coated with the binder and
An electrode having a binder thickness of 0.4 μm or more. The electrode according to claim 1, wherein 80 area% or more of the surface of the insulating particles is covered with the binder. The electrode according to any one of claims 1 or 2, wherein the ratio of the thickness of the binder to the average particle size of the insulating particles (thickness of the binder / average particle size of the insulating particles) is 0.05 or more. The method for manufacturing an electrode according to any one of claims 1 to 3.
A method for manufacturing an electrode, which comprises forming the insulating layer by a dry coating method. A power storage element comprising the electrode according to any one of claims 1 to 3.

Images