JP2023074702A - Negative electrode, non-aqueous electrolyte storage element, and method for manufacturing negative electrode - Google Patents

Abstract

To provide a negative electrode capable of reducing manufacturing costs while having an insulating layer composed of insulating particles.SOLUTION: A negative electrode according to an embodiment of the present invention includes a negative electrode base material, a negative electrode active material layer directly or indirectly laminated on the surface of the negative electrode substrate, and an insulating layer directly or indirectly laminated on the surface of the negative electrode active material layer, and the insulating layer includes insulating particles and a binder, and the insulating particles are coated with the binder.SELECTED DRAWING: None

Description

The present invention relates to a negative electrode, a non-aqueous electrolyte storage element, and a method for manufacturing a negative electrode.

In Patent Document 1, an electrode mixture layer formed of electrode mixture particles obtained by granulating an electrode active material and a binder is provided on at least one current collector of a positive electrode and a negative electrode. describes a lithium ion secondary battery having a separator particle layer formed by separator particles formed by granulating polyolefin particles between. According to this aspect, the electrode mixture layer as the active material layer and the separator particle layer as the separator are formed in powder form.

JP 2014-41793 A

SUMMARY OF THE INVENTION An object of the present invention is to provide a negative electrode having an insulating layer composed of insulating particles and capable of reducing manufacturing costs.

A negative electrode according to an aspect of the present invention includes a negative electrode substrate, a negative electrode active material layer directly or indirectly laminated on the surface of the negative electrode substrate, and a negative electrode active material layer directly or indirectly laminated on the surface of the negative electrode active material layer. an insulating layer, the insulating layer containing insulating particles and a binder, and the insulating particles being coated with the binder.

A non-aqueous electrolyte energy storage element according to another aspect of the present invention includes a positive electrode and a negative electrode, and the negative electrode is a negative electrode substrate and a negative electrode active material laminated directly or indirectly on the surface of the negative electrode substrate. and an insulating layer laminated directly or indirectly on the surface of the negative electrode active material layer, the insulating layer containing insulating particles and a binder, and the insulating particles being coated with the binder.

A method for manufacturing a negative electrode according to still another aspect of the present invention includes: laminating a negative electrode active material layer directly or indirectly on a surface of a negative electrode substrate; and heating the adhering mixture.

According to the negative electrode, the non-aqueous electrolyte storage element, and the negative electrode manufacturing method of the present invention, the manufacturing cost of the negative electrode provided with the insulating layer composed of the insulating particles can be reduced.

FIG. 1 is an external perspective view showing one embodiment of the non-aqueous electrolyte storage element of the present invention. FIG. 2 is a schematic diagram showing a power storage device configured by assembling a plurality of non-aqueous electrolyte power storage elements according to an embodiment of the present invention.

First, an overview of the negative electrode, the non-aqueous electrolyte storage element, and the method for manufacturing the negative electrode disclosed by the present specification will be described.

A negative electrode according to an aspect of the present invention includes a negative electrode substrate, a negative electrode active material layer directly or indirectly laminated on the surface of the negative electrode substrate, and a negative electrode active material layer directly or indirectly laminated on the surface of the negative electrode active material layer. an insulating layer, the insulating layer containing insulating particles and a binder, and the insulating particles being coated with the binder.

According to this negative electrode, insulating particles coated with a binder are used. Therefore, a binder exists between the surface of the negative electrode active material layer and the insulating particles. Therefore, even if the heating temperature is low when manufacturing the negative electrode, the binder allows the surface of the negative electrode active material layer and the insulating particles to adhere to each other. On the other hand, when the insulating particles are not coated with a binder, the binder must be melted to increase the fluidity in order to increase the adhesion between the two. and the heating temperature must be increased. That is, according to this negative electrode, by using the insulating particles coated with the binder, the insulating layer can be brought into close contact with the surface of the negative electrode active material layer even if the heating temperature is low when manufacturing the negative electrode. Therefore, since the energy required for heating can be reduced when manufacturing the negative electrode, the manufacturing cost of the negative electrode can be reduced.

Here, the negative electrode active material layer may contain graphite.

Graphite has high thermal conductivity. By including graphite in the negative electrode active material layer in this way, it becomes easier to heat when forming the insulating layer, and as a result, the heating temperature can be further lowered. Therefore, the manufacturing cost of the negative electrode can be further reduced.

Moreover, the binder may contain a fluororesin.

The binder is required to have a performance that does not dissolve into the non-aqueous electrolyte. The fluororesin has a high performance of not eluting into the non-aqueous electrolyte even without cross-linking. Also, by not cross-linking the fluororesin, the heating temperature for obtaining adhesion can be lowered. In other words, by including the fluororesin in the binder in this way, it is possible to achieve both the performance of not eluting into the non-aqueous electrolyte and the adhesion even when the heating temperature is low.

A non-aqueous electrolyte energy storage element according to another aspect of the present invention includes a positive electrode and a negative electrode, and the negative electrode is a negative electrode substrate and a negative electrode active material laminated directly or indirectly on the surface of the negative electrode substrate. and an insulating layer laminated directly or indirectly on the surface of the negative electrode active material layer, the insulating layer containing insulating particles and a binder, and the insulating particles being coated with the binder.

According to this non-aqueous electrolyte power storage element, the negative electrode has the insulating layer, the insulating layer contains the insulating particles and the binder, and the insulating particles are coated with the binder. According to the above negative electrode, by using the insulating particles coated with the binder, the insulating layer can be brought into close contact with the surface of the negative electrode active material layer even if the heating temperature is low when manufacturing the negative electrode. Therefore, the energy required for heating when manufacturing the negative electrode can be reduced, so that the manufacturing cost of the non-aqueous electrolyte storage element can be reduced.

A method for manufacturing a negative electrode according to still another aspect of the present invention includes: laminating a negative electrode active material layer directly or indirectly on a surface of a negative electrode substrate; and heating the adhering mixture.

According to the negative electrode manufacturing method, the insulating particles coated with the binder are formed by heating the mixture of the insulating particles and the binder particles. Therefore, the insulating particles coated with the binder can adhere the insulating layer to the surface of the negative electrode active material layer even at a low heating temperature. Therefore, since the energy required for heating can be reduced, the production cost of the negative electrode production method can be reduced.

Here, it is preferable to use infrared heating when heating the mixture directly or indirectly attached to the surface of the negative electrode active material layer. By using infrared heating in this way, the binder particles are efficiently heated, so that the energy required for heating during manufacturing of the negative electrode can be further reduced, and the manufacturing cost can be further reduced.

A negative electrode, a non-aqueous electrolyte storage element, a method for manufacturing a negative electrode, and other embodiments according to one embodiment of the present invention will be described in detail. Note that the name of each component (each component) used in each embodiment may be different from the name of each component (each component) used in the background art.

A non-aqueous electrolyte storage element (hereinafter also simply referred to as "storage element") according to one embodiment of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. A non-aqueous electrolyte secondary battery (hereinafter also simply referred to as a “secondary battery”) will be described as an example of the storage element.

(negative electrode)
The negative electrode has a negative electrode substrate, a negative electrode active material layer directly or indirectly laminated on the surface of the negative electrode substrate, and an insulating layer directly or indirectly laminated on the surface of the negative electrode active material layer.

A negative electrode base material has electroconductivity. Whether or not the material has "conductivity" is determined using a volume resistivity of 10 ⁷ Ω·cm or less measured according to JIS-H-0505 (1975) as a threshold.

As the material of the negative electrode base material, metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys thereof are used. Among these, copper or a copper alloy is preferred. Examples of negative electrode substrates include foils and vapor deposition films, and foils are preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferable as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

The average thickness of the negative electrode substrate is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, even more preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode substrate within the above range, the energy density per volume of the secondary battery can be increased while increasing the strength of the negative electrode substrate. "Average thickness" refers to a value obtained by dividing the punched mass when a substrate having a predetermined area is punched out by the true density and the punched area of the substrate. The same definition applies when using the "average thickness" for the positive electrode substrate.

When the negative electrode active material layer is indirectly laminated on the surface of the negative electrode substrate, the negative electrode has an intermediate layer arranged between the negative electrode substrate and the negative electrode active material layer. This intermediate layer reduces the contact resistance between the negative electrode substrate and the negative electrode active material layer by containing conductive particles such as carbon particles. The composition of the intermediate layer is not particularly limited, and includes, for example, a binder and a conductive agent.

The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, a filler, etc., as required.

The negative electrode active material layer contains typical nonmetallic elements such as B, N, P, F, Cl, Br, and I; typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, and Ge; , Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, Sn, Sr, Ba, W, etc. are used as negative electrode active materials, conductive agents, binders, and thickeners. You may contain as a component other than a sticky agent and a filler.

The negative electrode active material can be appropriately selected from known negative electrode active materials. Materials capable of intercalating and deintercalating lithium ions are usually used as negative electrode active materials for lithium ion secondary batteries. Examples of the negative electrode active material include metal Li; metals or metalloids such as Si and Sn; metal oxides and metalloid oxides such as Si oxide, Ti oxide and Sn oxide; Li ₄ Ti ₅ O ₁₂ ; Titanium-containing oxides such as LiTiO _{2 and} TiNb ₂ O ₇ ; polyphosphate compounds; silicon carbide; carbon materials such as graphite and non-graphitizable carbon (easily graphitizable carbon or non-graphitizable carbon) be done. Among these materials, graphite is preferred. By including graphite in the negative electrode active material layer in this way, it becomes easier to heat when forming the insulating layer, and as a result, the heating temperature can be further lowered. Therefore, the manufacturing cost of the negative electrode can be further reduced. In addition, in the negative electrode active material layer, one of these materials may be used alone, or two or more of them may be used in combination.

“Non-graphitic carbon” means a carbon material having an average lattice spacing (d ₀₀₂ ) of the (002) plane determined by X-ray diffraction before charging/discharging or in a discharged state of 0.34 nm or more and 0.42 nm or less. say. Non-graphitizable carbon includes non-graphitizable carbon and graphitizable carbon. Examples of non-graphitic carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

Here, the term “discharged state” means a state in which the carbon material, which is the negative electrode active material, is discharged such that lithium ions that can be intercalated and deintercalated are sufficiently released during charging and discharging. For example, in a half-cell using a negative electrode containing a carbon material as a negative electrode active material as a working electrode and metal Li as a counter electrode, the open circuit voltage is 0.7 V or higher.

The term “non-graphitizable carbon” refers to a carbon material having a d ₀₀₂ of 0.36 nm or more and 0.42 nm or less.

“Graphitizable carbon” refers to a carbon material having a d ₀₀₂ of 0.34 nm or more and less than 0.36 nm.

The average particle size of the negative electrode active material can be, for example, 1 μm or more and 100 μm or less. By making the average particle size of the negative electrode active material equal to or greater than the above lower limit, the production or handling of the negative electrode active material is facilitated. By making the average particle size of the negative electrode active material equal to or less than the above upper limit, the electron conductivity of the negative electrode active material layer is improved. Note that when a mixture of the negative electrode active material and other materials is used, the average particle size of the mixture is taken as the average particle size of the negative electrode active material. "Average particle size" is based on JIS-Z-8825 (2013), based on the particle size distribution measured by a laser diffraction / scattering method for a diluted solution in which particles are diluted with a solvent, JIS-Z-8819 -2 (2001) means a value at which the volume-based integrated distribution calculated according to 50%.

A pulverizer, a classifier, or the like is used to obtain powder having a predetermined particle size. Pulverization methods include, for example, methods using a mortar, ball mill, sand mill, vibrating ball mill, planetary ball mill, jet mill, counter jet mill, whirling jet mill, or sieve. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane is allowed to coexist can also be used. As a classification method, a sieve, an air classifier, or the like is used as necessary, both dry and wet.

The content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass or more and 99% by mass or less, more preferably 90% by mass or more and 98% by mass or less. By setting the content of the negative electrode active material within the above range, it is possible to achieve both high energy density and manufacturability of the negative electrode active material layer.

The conductive agent is not particularly limited as long as it is a conductive material. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Carbonaceous materials include graphite, non-graphitic carbon, graphene-based carbon, and the like. Examples of non-graphitic carbon include carbon nanofiber, pitch-based carbon fiber, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Graphene-based carbon includes graphene, carbon nanotube (CNT), fullerene, and the like. The shape of the conductive agent may be powdery, fibrous, or the like. As the conductive agent, one type of these materials may be used alone, or two or more types may be mixed and used. Also, these materials may be combined for use. For example, a composite material of carbon black and CNT may be used. Among these, carbon black is preferable from the viewpoint of electron conductivity and coatability, and acetylene black is particularly preferable.

The content of the conductive agent in the negative electrode active material layer is preferably 1% by mass or more and 10% by mass or less, more preferably 3% by mass or more and 9% by mass or less. By setting the content of the conductive agent within the above range, the energy density of the secondary battery can be increased.

Binders include, for example, fluorine resins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, polyacryl, and polyimide; ethylene-propylene-diene rubber (EPDM), sulfone Elastomers such as modified EPDM, styrene-butadiene rubber (SBR) and fluororubber; polysaccharide polymers and the like.

The content of the binder in the negative electrode active material layer is preferably 1% by mass or more and 10% by mass or less, more preferably 3% by mass or more and 9% by mass or less. By setting the content of the binder within the above range, the active material can be stably retained.

Examples of thickeners include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. When the thickener has a functional group that reacts with lithium or the like, the functional group may be previously deactivated by methylation or the like.

A filler is not specifically limited. Fillers include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide and aluminosilicate, magnesium hydroxide, calcium hydroxide, hydroxide Hydroxides such as aluminum, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, talc, montmorillonite, boehmite, zeolite, Mineral resource-derived substances such as apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof may be used.

(insulating layer)
The insulating layer has insulating properties. That the insulating layer has “insulating properties” means that the conductivity is lower than that of the negative electrode substrate and the negative electrode active material layer. Specifically, the insulating layer has "insulating properties" means that the two-point probe of Mitsubishi Chemical Analytic Tech's low resistivity meter "Loresta EP MCP T360" is an insulating layer or a negative electrode active material without an insulating layer. It means that the surface resistance of the insulating layer measured by pressing against the layer is 50 times or more the surface resistance of the negative electrode active material layer without the insulating layer.

A part of the insulating layer may also be laminated on the surface of the negative electrode substrate that is not covered with the negative electrode active material layer.

The insulating layer contains insulating particles and a binder (second binder). Thereby, insulation can be exhibited. The insulating layer may contain components other than the insulating particles and the binder.

The insulating particles are coated with a binder. The binder binds the insulating particles and the negative electrode active material layer in addition to the insulating particles. Moreover, the binder is not included in the negative electrode active material layer.

This insulating layer is preferably formed by dry coating as a dry coating. Dry coating refers to a coating method that does not use a solvent. In wet coating, a powder and a solvent are mixed to form a paste, which is then applied. In dry coating, a powder is applied without making a paste. The insulating layer is preferably a cured powder coating. To improve the high-rate discharge performance of a storage element using a negative electrode in which an insulating layer is laminated directly or indirectly on the surface of a negative electrode active material layer by forming the insulating layer by dry coating, more preferably powder coating. can be done.

The insulating particles are particles having insulating properties, and may be either inorganic particles or organic particles, but inorganic particles are preferable from the viewpoint of heat resistance. Examples of inorganic particles include inorganic oxides such as silica, alumina, titania, zirconia, magnesia, ceria, yttria, zinc oxide and iron oxide; inorganic nitrides such as silicon nitride, titanium nitride and boron nitride; silicon carbide; Lithium carbonate, aluminum sulfate, aluminum hydroxide, potassium titanate, talc, kaolin clay, kaolinite, boehmite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, aluminosilicate, calcium silicate , magnesium silicate, diatomaceous earth, silica sand, glass, and the like. Among these, inorganic oxides are preferred, and alumina is more preferred.

In the insulating layer, the insulating particles are preferably laminated in layers. The term “insulating particles are laminated in layers” means that, in a cross-sectional view, each insulating particle is linearly arranged, and there is one or more layers formed with a thickness of one particle. Whether or not the insulating particles are laminated in layers can be determined by observing the cross section of the insulating layer with an electron microscope. By laminating the insulating particles in layers, an insulating layer having excellent homogeneity can be formed, and the insulating properties can be ensured even if the thickness of the insulating layer is thin.

The insulating particles are preferably monodisperse particles. This makes it possible to relatively easily form an insulating layer in which insulating particles are laminated in layers. The variation coefficient of the particle size of the insulating particles is preferably 0.2 or less, more preferably 0.12 or less. Note that the variation coefficient of the particle size of the insulating particles is calculated from the particle sizes of 20 arbitrary insulating particles that can be confirmed from the electron microscope image of the cross section of the insulating layer. In addition, the particle size of the insulating particles is the average value of the major axis and the minor axis (diameter orthogonal to the major axis). The lower limit of the coefficient of variation is not particularly limited and may be 0, but is usually 0.01 or more.

The average particle size of the insulating particles is preferably 0.5 μm or more and 10 μm or less, more preferably 1 μm or more and 5 μm or less. By setting the average particle diameter of the insulating particles within the above range, it is possible to further increase the non-aqueous electrolyte permeability while maintaining sufficient insulating properties. The average particle size of the insulating particles is the average value of the particle sizes of 20 insulating particles used for calculating the coefficient of variation of the particle size of the insulating particles.

As the binder (second binder), a binder that can fix insulating particles and the like and that is electrochemically stable within the range of use is usually used. As the binder, the same binders as those exemplified as the binder contained in the negative electrode active material layer can be used. Among these, from the viewpoint of heat resistance, etc., it is preferable to contain a fluororesin, and it is more preferable to contain PVDF. By including the fluororesin in the binder in this way, it is possible to improve the performance of not eluting into the non-aqueous electrolyte without cross-linking. Furthermore, the negative electrode can achieve both the performance of preventing elution into the non-aqueous electrolyte and adhesion even when the heating temperature for forming the insulating layer is low. The binder (first binder) in the negative electrode active material layer and the binder (second binder) in the insulating layer may be of the same type or different types.

The content of the binder in the insulating layer is preferably 5% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 40% by mass or less, and even more preferably 12% by mass or more and 35% by mass or less. By setting the content of the binder in the insulating layer within the above range, it is possible to secure appropriate voids between the insulating particles while maintaining the adhesiveness of the insulating layer.

Considering the adhesion of the insulating layer, the preferable content of the binder in the insulating layer can be appropriately selected according to the type and average particle size of the insulating particles in the insulating layer. For example, when the insulating particles are alumina, the binder content is preferably 5% by mass or more and 25% by mass or less, more preferably 8% by mass or more and 15% by mass or less. As the above alumina, one having an average particle size of 2 μm or more and 4 μm or less can be preferably used. When the insulating particles are boehmite, the binder content is preferably 20% by mass or more and 40% by mass or less, more preferably 25% by mass or more and 35% by mass or less. Boehmite having an average particle size of 1 μm or more and 3 μm or less can be preferably used as the boehmite.

The content of the binder (second binder) in the insulating layer is preferably higher than the content of the binder (first binder) in the negative electrode active material layer. The difference in content is preferably 1% by mass or more and 50% by mass or less, more preferably 2% by mass or more and 20% by mass or less, further preferably 3% by mass or more and 10% by mass or less, and 4% by mass or more and 6% by mass or less. is particularly preferred. By setting the content rate difference within the above range, a good porous state of the negative electrode active material layer and, in turn, good non-aqueous electrolyte permeability can be ensured, and the high-rate discharge performance of the electric storage element can be enhanced.

The average thickness of the insulating layer is preferably 3 μm or more and 30 μm or less, more preferably 6 μm or more and 20 μm or less, and even more preferably 7 μm or more and 16 μm or less. By setting the average thickness of the insulating layer within the above range, it is possible to reduce the thickness of the electric storage element, improve the energy density, etc. while maintaining the insulating properties.

The porosity of the insulating layer is preferably 5% to 70% by volume, preferably 10% to 65% by volume, and more preferably 15% to 35% by volume. By setting the porosity of the insulating layer within the above range, the non-aqueous electrolyte permeability can be ensured while maintaining the adhesion of the insulating layer, and the high-rate discharge performance of the electric storage element can be enhanced. Here, the porosity of the insulating layer is a value obtained by the following formula.
Porosity (%) = (void volume of insulating layer/volume of insulating layer) x 100
The pore volume of the insulating layer is measured by a mercury intrusion method using a mercury porosimeter.

The insulating particles and the binder may form a composite. The composite has a so-called core-shell structure, and includes a core composed of insulating particles and a shell composed of a binder covering the core. That is, the insulating layer may be configured in a state in which the composite is bound.

When the insulating particles and the binder constitute a composite, the average coating thickness of the shell portion composed of the binder is preferably 0.4 μm or more and 1 μm or less. By setting the average coating thickness of the shell portion within the above range, it is possible to maintain sufficient insulation while suppressing detachment of the insulating particles. The average coating thickness of the shell portion can be measured by the following procedure. First, an element distribution analysis image (magnification: 8000 times, analysis range: 30 μm × 30 μm) of a cross section near the outer surface of the insulating layer was obtained by an electron probe microanalyzer (EPMA). The regions of the core portion (insulating particles) and the shell portion (binder) of the composite are determined from . Next, five composites are selected in descending order of particle size from the composites present on the outermost side of the insulating layer in the image. The thickness of the shell portion on the outer surface of the insulating layer of the above five composites is measured, and the average value is taken as the average coating thickness of the shell portion.

In the composite, the variation coefficient of the average coating thickness of the shell portion is preferably 0.35 or less, more preferably 0.30 or less. By setting the coefficient of variation of the average coating thickness of the shell portion to the above upper limit or less, it is possible to form an insulating layer that is excellent in insulating properties and in which detachment of insulating particles is suppressed. The lower limit of the coefficient of variation is not particularly limited and may be 0, but is usually 0.01 or more.

The coverage of the surface of the core portion by the shell portion in the composite is preferably 80 area % or more, more preferably 90 area % or more, and even more preferably 95 area % or more. Detachment of the insulating particles can be suppressed by setting the coverage of the surface of the core portion by the shell portion to be equal to or higher than the lower limit. The upper limit of the coverage rate is not particularly limited, and may be 100 area %.

The ratio of the thickness of the shell portion to the average particle size of the core portion in the composite (thickness of shell portion/average particle size of core portion) is preferably 0.05 or more and 0.4 or less, and 0.08 or more. 0.25 or less is more preferable. By setting the above ratio within the above range, it is possible to prevent the insulating particles from being detached while preventing the insulating layer from becoming too thick.

(Manufacturing method of negative electrode)
The negative electrode can be manufactured by the following manufacturing method. That is, the method for manufacturing a negative electrode according to an embodiment of the present invention comprises: directly or indirectly laminating a negative electrode active material layer on the surface of a negative electrode base material (negative electrode active material layer laminating step); The method includes directly or indirectly attaching the mixture to the surface of the negative electrode active material layer (adhering step) and heating the attached mixture (heating step).

In the negative electrode active material layer laminating step, the negative electrode active material layer is laminated directly or indirectly on the surface of the negative electrode substrate. A negative electrode active material layer can be formed by a known method. For example, the negative electrode active material layer can be formed by applying a negative electrode mixture paste in which components constituting the negative electrode active material layer are dispersed in water or an organic solvent, and drying the paste.

In the manufacturing method of the negative electrode, the insulating layer is laminated by the adhesion process and the heating process. Lamination of this insulating layer is preferably carried out by dry coating.

In the adhering step, a mixture of insulating particles and binder particles is directly or indirectly adhered to the surface of the negative electrode active material layer.

As the mixture, in addition to a simple mixture of the insulating particles and the binder particles, a composite particle formed by attaching the insulating particles and the binder particles around the insulating particles, a core composed of the insulating particles, Core-shell particles including a shell portion composed of binder particles can be used. Among these, it is preferable to use composite particles or core-shell particles, and it is more preferable to use composite particles. By using composite particles or core-shell particles, the binder can be more reliably present between the surface of the negative electrode active material layer and the insulating particles. Easy to adhere to the surface of the layer. In addition, by using composite particles in which binder particles are selectively present on the surfaces of the insulating particles, the amount of binder existing in the gaps between the insulating particles can be reduced, and the spaces between the insulating particles can be secured. Better non-aqueous electrolyte permeability in the layer.

The composite particles can be obtained, for example, by putting insulating particles and binder particles into a stirrer equipped with rotating blades and stirring and mixing these particles. In this method, triboelectrification occurs between the insulating particles and the binder particles, and composite particles in which the binder particles are arranged on the surfaces of the insulating particles are obtained. When the composite particles are used, a composite having a core-shell structure in which the insulating particles are coated with the binder is formed by heating in the heating step described later.

For the adhesion of the mixture to the surface of the negative electrode active material layer, a method of spraying (dispersing) the mixture onto the surface of the negative electrode active material layer using various feeders such as an air flow feeder and a vibration feeder can be used. In addition, an electrostatic coating method can be employed in which the mixture is charged with static electricity during spraying. By using the electrostatic coating method, it is possible to efficiently form an insulating layer in which insulating particles are laminated in layers with higher uniformity, and a stable insulating layer with a small coefficient of variation in the thickness of the insulating layer can be obtained. can be formed.

In the heating step, the mixture directly or indirectly attached to the surface of the negative electrode active material layer is heated. This heating step may be performed after the deposition step, or may be performed simultaneously with the deposition step.

This heating melts the binder particles to obtain binder-coated insulating particles. In addition, the fusion of the binder particles binds the insulating particles and the negative electrode active material layer in addition to the adjacent insulating particles, forming an insulating layer directly or indirectly laminated on the surface of the negative electrode active material layer. .

The heating temperature in the heating step is preferably 150° C. or higher and 250° C. or lower, more preferably 150° C. or higher and 225° C. or lower. By setting the heating temperature within the above range, the energy required for heating in manufacturing the negative electrode can be reduced, and the manufacturing cost of the negative electrode can be reduced.

Moreover, when heating the adhering mixture, it is preferable to use infrared heating. By using infrared heating in this way, the binder particles are efficiently heated, so that the energy required for heating during manufacturing of the negative electrode can be further reduced, and the manufacturing cost can be further reduced.

The laminated insulating layer may be molded to a predetermined thickness by pressing with a press or rollers. Note that this pressing step may be omitted if the thickness of the insulating layer can be sufficiently set during coating.

(positive electrode)
The positive electrode has a positive electrode base material and a positive electrode active material layer disposed directly on the positive electrode base material or via an intermediate layer. The structure of the intermediate layer is not particularly limited, and can be selected from, for example, the structures exemplified for the negative electrode.

A positive electrode base material has electroconductivity.

As the material for the positive electrode substrate, metals such as aluminum, titanium, tantalum and stainless steel, or alloys thereof are used. Among these, aluminum or an aluminum alloy is preferable from the viewpoint of potential resistance, high conductivity, and cost. Examples of positive electrode substrates include foils and deposited films, and foils are preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferable as the positive electrode substrate. Examples of aluminum or aluminum alloy include A1085 and A3003 defined in JIS-H-4000 (2014).

The average thickness of the positive electrode substrate is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, even more preferably 8 μm or more and 30 μm or less, and particularly preferably 10 μm or more and 25 μm or less. By setting the average thickness of the positive electrode substrate within the above range, the energy density per volume of the secondary battery can be increased while increasing the strength of the positive electrode substrate.

The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, a filler, etc., as required. Optional components such as a conductive agent, a binder, a thickener, and a filler can be selected from the materials exemplified for the negative electrode.

The positive electrode active material can be appropriately selected from known positive electrode active materials. As a positive electrode active material for lithium ion secondary batteries, a material capable of intercalating and deintercalating lithium ions is usually used. Examples of positive electrode active materials include lithium-transition metal composite oxides having an α-NaFeO ₂ type crystal structure, lithium-transition metal composite oxides having a spinel-type crystal structure, polyanion compounds, chalcogen compounds, and sulfur. Li[Li _x Ni _{1 -x} ]O ₂ (0≦x<0.5), Li[Li _x Ni _γ Co _{(1− x−γ)} ]O ₂ (0≦x<0.5, 0<γ<1), Li[Li _x Co _(1−x) ]O ₂ (0≦x<0.5), Li[Li _x Ni _γ Mn _(1-x-γ) ]O ₂ (0≦x<0.5, 0<γ<1), Li[Li _x Ni _γ Mn _β Co _(1-x-γ-β ]O ₂ ( 0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1), Li[Li _x Ni _γ Co _β Al _(1-x-γ-β ]O ₂ (0≦x< 0.5, 0<γ, 0<β, 0.5<γ+β<1), etc. Examples of lithium transition metal composite oxides having a spinel crystal structure include Li _x Mn ₂ O ₄ and Li _x Ni _γ. Mn _(2-γ) O ₄ etc. Polyanion compounds include LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F etc. Chalcogen compounds include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc. Atoms or polyanions in these materials are partially substituted with atoms or anion species of other elements. The surface of these materials may be coated with another material.In the positive electrode active material layer, one of these materials may be used alone, or two or more of these materials may be used in combination. good.

The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By making the average particle size of the positive electrode active material equal to or more than the above lower limit, manufacturing or handling of the positive electrode active material becomes easy. By setting the average particle size of the positive electrode active material to the above upper limit or less, the electron conductivity of the positive electrode active material layer is improved. A pulverizer, a classifier, or the like is used to obtain powder having a predetermined particle size. The pulverization method and the powder class method can be selected from, for example, the methods exemplified for the negative electrode.

The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass or more and 99% by mass or less, more preferably 70% by mass or more and 98% by mass or less, and even more preferably 80% by mass or more and 95% by mass or less. By setting the content of the positive electrode active material within the above range, it is possible to achieve both high energy density and manufacturability of the positive electrode active material layer.

The positive electrode active material layer contains typical nonmetallic elements such as B, N, P, F, Cl, Br, and I; typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, and Ge; , Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, Sn, Sr, Ba, W, etc. are used as positive electrode active materials, conductive agents, binders, thickeners, fillers. It may be contained as a component other than

(Non-aqueous electrolyte)
The non-aqueous electrolyte can be appropriately selected from known non-aqueous electrolytes. A non-aqueous electrolyte may be used as the non-aqueous electrolyte. The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent.

The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Non-aqueous solvents include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphoric acid esters, sulfonic acid esters, ethers, amides, nitriles and the like. As the non-aqueous solvent, those in which some of the hydrogen atoms contained in these compounds are substituted with halogens may be used.

Cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), and difluoroethylene carbonate. (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate and the like. Among these, EC is preferred.

Chain carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diphenyl carbonate, trifluoroethylmethyl carbonate, bis(trifluoroethyl) carbonate and the like. Among these, EMC is preferred.

As the non-aqueous solvent, it is preferable to use a cyclic carbonate or a chain carbonate, and it is more preferable to use a combination of a cyclic carbonate and a chain carbonate. By using a cyclic carbonate, it is possible to promote the dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. By using a chain carbonate, the viscosity of the non-aqueous electrolyte can be kept low. When a cyclic carbonate and a chain carbonate are used together, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

The electrolyte salt can be appropriately selected from known electrolyte salts. Examples of electrolyte salts include lithium salts, sodium salts, potassium salts, magnesium salts, onium salts and the like. Among these, lithium salts are preferred.

Lithium salts include inorganic lithium salts such as LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ and LiN(SO ₂ F) ₂ , LiSO ₃ CF ₃ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO _{2 C2F5} ) ₂ , LiN( _{SO2CF3 )} ( _SO2C4F9 ) _{, LiC} ( _SO2CF3 ) ₃ , _{LiC ( SO2C2F5 ) 3} and other halogenated _hydrocarbon groups and lithium salts having Among these, inorganic lithium salts are preferred, and _LiPF6 is more preferred.

The content of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol/dm ³ or more and 2.5 mol/dm ³ or less, more preferably 0.3 mol/dm ³ or more and 2.0 mol/dm ³ or less, and 0.5 mol /dm ³ or more and 1.7 mol/dm ³ or less is more preferable, and 0.7 mol/dm ³ or more and 1.5 mol/dm ^{3 or} less is particularly preferable. By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

The non-aqueous electrolyte may contain additives. Examples of the above additives include halogenated carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), lithium bis( Oxalates such as difluorophosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butyl aromatic compounds such as benzene, t-amylbenzene, diphenyl ether, dibenzofuran; partial halides of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene; 2,4-difluoroanisole, Halogenated anisole compounds such as 2,5-difluoroanisole, 2,6-difluoroanisole and 3,5-difluoroanisole; vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, propanesultone, propenesultone, butanesultone, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate ethylene sulfate, sulfolane, dimethylsulfone, diethylsulfone, dimethylsulfoxide, diethylsulfoxide, tetramethylenesulfoxide, diphenylsulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane, 4-methylsulfonyloxy methyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate , lithium difluorophosphate, etc. These additives may be used singly or in combination of two or more.

The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 7% by mass or less with respect to the total mass of the non-aqueous electrolyte. , more preferably 0.2% by mass or more and 5% by mass or less, and particularly preferably 0.3% by mass or more and 3% by mass or less. By setting the content of the additive within the above range, it is possible to improve capacity retention performance or cycle performance after high-temperature storage, or to further improve safety.

A solid electrolyte may be used as the non-aqueous electrolyte, or a non-aqueous electrolyte and a solid electrolyte may be used in combination.

The solid electrolyte can be selected from any materials such as lithium, sodium, calcium, etc., which have ion conductivity and are solid at room temperature (for example, 15° C. or higher and 25° C. or lower). Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, and polymer solid electrolytes.

Examples of sulfide solid electrolytes for lithium ion secondary batteries include Li ₂ SP ₂ S ₅ system and the like. Examples of sulfide solid electrolytes include Li ₂ SP ₂ S ₅ , LiI—Li ₂ SP ₂ S ₅ , Li ₁₀ Ge—P ₂ S ₁₂ , and the like.

The shape of the electric storage element of the present embodiment is not particularly limited, and examples thereof include cylindrical batteries, square batteries, flat batteries, coin batteries, button batteries, and the like.

FIG. 1 shows a non-aqueous electrolyte storage element 1 as an example of a square battery. In addition, the same figure is taken as the figure which saw through the inside of a container. In the non-aqueous electrolyte storage element 1 , an electrode body 2 having a wound positive electrode and a negative electrode is housed in a rectangular container 3 . The positive electrode is electrically connected to the positive electrode terminal 4 via a positive electrode lead 41 . The negative electrode is electrically connected to the negative terminal 5 via a negative lead 51 .

The positive and negative electrodes of the electrode assembly 2 may be wound with a separator interposed therebetween. The separator is not particularly limited, and known separators for electric storage elements can be used. As for the shape of the separator, 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 from the viewpoint of strength. Polyolefins such as polyethylene and polypropylene are preferable as the material of the separator from the viewpoint of the shutdown function. Also, a resin obtained by combining these resins with a resin such as aramid or polyimide may be used. A separator containing an inorganic filler or a separator in which an inorganic layer is laminated on a porous resin film can also be used.

<Configuration of power storage device>
The power storage device of the present embodiment is a power source for automobiles such as electric vehicles (EV), hybrid vehicles (HEV), and plug-in hybrid vehicles (PHEV), power sources for electronic devices such as personal computers and communication terminals, or power sources for power storage. For example, it can be mounted as a power storage unit (battery module) configured by assembling a plurality of non-aqueous electrolyte power storage elements. In this case, the technology of the present invention may be applied to at least one non-aqueous electrolyte storage element included in the storage unit.

FIG. 2 shows an example of a power storage device 30 in which a power storage unit 20 in which two or more electrically connected non-aqueous electrolyte power storage elements 10 are assembled is further assembled. The power storage device 30 may include a bus bar (not shown) electrically connecting two or more non-aqueous electrolyte power storage elements 10 and a bus bar (not shown) electrically connecting two or more power storage units 20. good. The power storage unit 20 or the power storage device 30 may include a state monitoring device (not shown) that monitors the state of one or more non-aqueous electrolyte power storage elements.

<Method for producing non-aqueous electrolyte storage element>
The method for manufacturing the non-aqueous electrolyte storage element of the present embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, a step of preparing an electrode body, a step of preparing a non-aqueous electrolyte, and a step of accommodating the electrode body and the non-aqueous electrolyte in a container. The step of preparing the electrode body includes a step of preparing a positive electrode and a negative electrode, and a step of laminating or winding the positive electrode and the negative electrode to form the electrode body.

The step of accommodating the non-aqueous electrolyte in the container can be appropriately selected from known methods. For example, when a non-aqueous electrolytic solution is used as the non-aqueous electrolyte, the non-aqueous electrolytic solution may be injected from an inlet formed in the container, and then the inlet may be sealed.

<Other embodiments>
The present invention is not limited to the above embodiments, and various modifications may be made without departing from the gist of the present invention. For example, part of the configuration of an embodiment can be deleted. Also, well-known techniques can be added to the configuration of a certain embodiment.

In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable/dischargeable nonaqueous electrolyte secondary battery (for example, a lithium ion secondary battery). The capacity and the like are arbitrary. The present invention can also be applied to capacitors such as various secondary batteries, electric double layer capacitors, and lithium ion capacitors.

1 Nonaqueous electrolyte storage element 2 Electrode body 3 Container 4 Positive electrode terminal 41 Positive electrode lead 5 Negative electrode terminal 51 Negative electrode lead 10 Nonaqueous electrolyte storage element 20 Storage unit 30 Storage device

Claims (6)

a negative electrode base material;
a negative electrode active material layer directly or indirectly laminated on the surface of the negative electrode substrate;
and an insulating layer directly or indirectly laminated on the surface of the negative electrode active material layer,
The insulating layer contains insulating particles and a binder,
A negative electrode in which the insulating particles are coated with the binder. The negative electrode according to claim 1, wherein the negative electrode active material layer contains graphite. 3. The negative electrode according to claim 1, wherein the binder contains a fluororesin. a positive electrode;
with a negative electrode and
The negative electrode is
a negative electrode base material;
a negative electrode active material layer directly or indirectly laminated on the surface of the negative electrode substrate;
and an insulating layer directly or indirectly laminated on the surface of the negative electrode active material layer,
The insulating layer contains insulating particles and a binder,
A non-aqueous electrolyte storage element, wherein the insulating particles are coated with the binder. Laminating a negative electrode active material layer directly or indirectly on the surface of the negative electrode substrate;
Directly or indirectly attaching a mixture of insulating particles and binder particles to the surface of the negative electrode active material layer;
A method of manufacturing a negative electrode, comprising: heating the deposited mixture. 6. The method for producing a negative electrode according to claim 5, wherein infrared heating is used when heating the adhering mixture.

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