JP2023057353A - Non-aqueous electrolyte storage element - Google Patents

Abstract

To provide a non-aqueous electrolyte storage element capable of reducing the initial DC resistance and suppressing the deterioration of the capacity retention rate after charge/discharge cycles even when using a negative electrode active material with a high proportion of artificial graphite.SOLUTION: A non-aqueous electrolyte storage element includes a negative electrode active material layer including a negative electrode active material and an acrylic resin, and the negative electrode active material contains artificial graphite and natural graphite, the content of the artificial graphite with respect to the total content of the artificial graphite and the natural graphite is 50% by mass or more and 90% by mass or less, and the acrylic resin does not have a structural unit derived from butadiene.SELECTED DRAWING: None

Description

The present invention relates to a non-aqueous electrolyte storage element.

Non-aqueous electrolyte secondary batteries, typified by lithium ion non-aqueous electrolyte secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, automobiles, and the like because of their high energy density. The non-aqueous electrolyte secondary battery generally comprises an electrode body having a pair of electrodes electrically isolated by a separator, and a non-aqueous electrolyte interposed between the electrodes, wherein charge-transporting ions are generated between the electrodes. It is configured to charge and discharge by performing delivery. Capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte storage elements other than non-aqueous electrolyte secondary batteries.

For the purpose of improving the energy density of such non-aqueous electrolyte storage elements, a carbon material such as graphite is used as the negative electrode active material of the non-aqueous electrolyte storage elements (see Patent Document 1).

JP-A-2005-222933

On the other hand, styrene-butadiene rubber, which can be used in a relatively small amount, is widely used as a binder for negative electrodes used in non-aqueous electrolyte storage elements. However, when the styrene-butadiene rubber and the negative electrode active material with a high proportion of artificial graphite were used, it was observed that the initial DC resistance increased. In addition, the non-aqueous electrolyte storage element is required to further improve the capacity retention rate after charging/discharging cycles as a power source for the above-mentioned automobiles and the like.

An object of the present invention is to provide a non-aqueous electrolyte storage element that can reduce the initial DC resistance and suppress the decrease in the capacity retention rate after charge-discharge cycles even when a negative electrode active material with a high proportion of artificial graphite is used. to provide.

A non-aqueous electrolyte storage element according to one aspect of the present invention includes a negative electrode having a negative electrode active material layer, the negative electrode active material layer containing a negative electrode active material and an acrylic resin, and the negative electrode active material containing artificial graphite. and natural graphite, the content of the artificial graphite with respect to the total content of the artificial graphite and the natural graphite is 50% by mass or more and 90% by mass or less, and the acrylic resin has a structural unit derived from butadiene. do not have.

The non-aqueous electrolyte storage element according to one aspect of the present invention can reduce the initial DC resistance and prevent the decrease in the capacity retention rate after charge-discharge cycles even when a negative electrode active material with a high proportion of artificial graphite is used. can be suppressed.

FIG. 1 is a see-through perspective view showing one embodiment of a non-aqueous electrolyte storage element. FIG. 2 is a schematic diagram showing an embodiment of a power storage device configured by assembling a plurality of non-aqueous electrolyte power storage elements.

First, an outline of the non-aqueous electrolyte storage element disclosed by the present specification will be described.

A non-aqueous electrolyte storage element according to one aspect of the present invention includes a negative electrode having a negative electrode active material layer, the negative electrode active material layer containing a negative electrode active material and an acrylic resin, and the negative electrode active material containing artificial graphite. and natural graphite, the content of the artificial graphite with respect to the total content of the artificial graphite and the natural graphite is 50% by mass or more and 90% by mass or less, and the acrylic resin has a structural unit derived from butadiene. do not have.

The present inventors have found that the negative electrode active material layer of the non-aqueous electrolyte storage element contains artificial graphite and natural graphite as negative electrode active materials and an acrylic resin as a binder, so that the negative electrode active material has a high proportion of artificial graphite. It was found that the initial direct current resistance can be reduced and the decrease in the capacity retention rate after charge-discharge cycles can be suppressed even when using . Although the reason for this is not clear, it is considered as follows. When a negative electrode active material with a high proportion of artificial graphite is used and a polymer having a structural unit derived from butadiene such as styrene-butadiene rubber is used as the binder for the negative electrode active material layer, the binder aggregates on the surface of the artificial graphite particles. Therefore, it is considered that the reaction active sites for insertion and desorption of charge transport ions such as lithium ions decrease, and the initial DC resistance increases. On the other hand, when an acrylic resin is used as the binder, the binder does not agglomerate only on the surfaces of the artificial graphite particles, but rather disperses throughout the negative electrode active material layer. Since the decrease is suppressed, it is thought that the DC resistance in the initial stage is reduced and the decrease in the capacity retention rate after charge-discharge cycles is suppressed. In addition, since the acrylic resin does not have a structural unit derived from butadiene, the aggregation of the acrylic resin on the surface of the artificial graphite particles can be further suppressed, so that the initial DC resistance can be reduced, and the charge / discharge cycle A subsequent decrease in the capacity retention rate can be further suppressed. Therefore, even when a negative electrode active material containing a high proportion of artificial graphite is used, it is possible to reduce the initial DC resistance and suppress the decrease in the capacity retention rate after charge-discharge cycles. On the other hand, natural graphite has a larger BET specific surface area than artificial graphite, and there are many reaction active sites for insertion and desorption of charge transport ions. It is considered that there is little difference between the case of using rubber and the case of using acrylic resin.

At least part of the surface of the artificial graphite is preferably coated with a carbon material. Since at least part of the surface of the artificial graphite is coated with a carbon material, the interaction between the carbon material and the acrylic resin improves the dispersion state of the binder in the negative electrode active material layer. It is thought that it is possible to further suppress the decrease in the capacity retention rate of

A configuration of a non-aqueous electrolyte storage element, a configuration of a power storage device, a method for manufacturing a non-aqueous electrolyte storage element, 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.

<Structure of non-aqueous electrolyte storage element>
A non-aqueous electrolyte storage element according to one embodiment of the present invention (hereinafter also simply referred to as "storage element") includes an electrode body having a positive electrode, a negative electrode and a separator, a non-aqueous electrolyte, the electrode body and the non-aqueous electrolyte and a container that houses the The electrode body is usually a laminated type in which a plurality of positive electrodes and a plurality of negative electrodes are laminated with separators interposed therebetween, or a wound type in which positive electrodes and negative electrodes are laminated with separators interposed and wound. The non-aqueous electrolyte exists in a state contained in the positive electrode, the negative electrode and the separator. As an example of the non-aqueous electrolyte storage element, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as "secondary battery") will be described.

(negative electrode)
The negative electrode has a negative electrode base material and a negative electrode active material layer disposed directly on the negative electrode base material or via an intermediate layer.

A negative electrode base material has electroconductivity. Whether or not a material has "conductivity" is determined using a volume resistivity of 10 ⁷ Ω·cm as a threshold measured according to JIS-H-0505 (1975). As materials for the negative electrode substrate, metals such as copper, nickel, stainless steel, nickel-plated steel, alloys thereof, carbonaceous materials, and the like are used. Among these, copper or a copper alloy is preferred. Examples of the negative electrode substrate include foil, deposited film, mesh, porous material, and the like, and foil is preferable 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.

The intermediate layer is a layer arranged between the negative electrode substrate and the negative electrode active material layer. The intermediate layer reduces the contact resistance between the negative electrode substrate and the negative electrode active material layer by containing a conductive agent 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 includes a negative electrode active material and an acrylic resin.

The negative electrode active material layer contains typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, and the like. and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W are used as negative electrode active materials, acrylic resins, and conductive agents. , a thickener, and a component other than a filler.

The non-aqueous electrolyte storage element contains natural graphite and artificial graphite as a negative electrode active material. By including natural graphite and artificial graphite as the negative electrode active material, it is possible to reduce the initial direct current resistance and to suppress the decrease in the capacity retention rate after charge-discharge cycles. Here, artificial graphite is a general term for artificially produced graphite, and natural graphite is a general term for graphite obtained from natural minerals. Specific examples of natural graphite include flaky graphite, massive graphite (flaky graphite), earthy graphite, and the like.

The content ratio of the artificial graphite with respect to the total content of the artificial graphite and the natural graphite is 50% by mass or more and 90% by mass or less. The lower limit of the content ratio of the artificial graphite to the total content of the artificial graphite and the natural graphite is 50% by mass, may be 55% by mass, and may be preferably 60% by mass or 70% by mass. The upper limit of the content of the artificial graphite with respect to the total content of the artificial graphite and the natural graphite is 90% by mass, preferably 85% by mass, more preferably 80% by mass, and preferably 70% by mass or 60% by mass. In some cases. When the content ratio of the artificial graphite to the total content of the artificial graphite and the natural graphite is within the above range, the initial DC resistance can be further reduced, and the decrease in the capacity retention rate after charge-discharge cycles can be further suppressed. . The content ratio of the artificial graphite to the total content of the artificial graphite and the natural graphite can be measured by thermogravimetric differential thermal analysis (TG/DTA) in a water vapor atmosphere.

“Graphite” refers to 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 0.33 nm or more and less than 0.34 nm. The natural graphite may have four peaks in the diffraction angle 2θ range of 40° to 50° in an X-ray diffraction pattern using CuKα rays measured before charging/discharging or in a discharged state. These four peaks are said to be two peaks derived from the hexagonal structure and two peaks derived from the rhombohedral structure. On the other hand, artificial graphite has two peaks derived from a hexagonal structure in the X-ray diffraction pattern using CuKα rays measured before charging and discharging or in a discharged state, with a diffraction angle 2θ in the range of 40 ° to 50 °. may appear only.

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.

At least part of the surface of the artificial graphite is preferably coated with a carbon material. Since at least part of the surface of the artificial graphite is coated with a carbon material, the interaction between the carbon material and the acrylic resin improves the dispersion state of the binder in the negative electrode active material layer. It is possible to further suppress the decrease in the capacity retention rate of As the carbon material used as the coating material (coating material), non-graphitizable carbon (easily graphitizable carbon or non-graphitizable carbon) is preferred.

“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.

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 content of the carbon material coated on the surface of the artificial graphite is 0.1% by mass or more and 20% by mass with respect to the artificial graphite coated with the carbon material (hereinafter also referred to as "carbon material-coated artificial graphite"). % or less is preferable. By setting the content of the carbon material with which the surface of the artificial graphite is coated within the above range, the effect of suppressing a decrease in the capacity retention rate after charge-discharge cycles can be further enhanced. The content of the carbon material coated on the surface of the artificial graphite can be measured, for example, by TG/DTA analysis under a water vapor atmosphere.

The negative electrode active material of the non-aqueous electrolyte storage element may contain a negative electrode active material other than artificial graphite and natural graphite. The other negative electrode active materials 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 other negative electrode active materials include metal Li; metals or semimetals _such as Si and Sn; metal oxides and semimetal oxides such as Si oxide, _Ti oxide and Sn oxide; Titanium-containing oxides such as O ₁₂ , LiTiO _{2 and} TiNb ₂ O ₇ ; polyphosphate compounds; silicon carbide; and carbon materials such as non-graphitic carbon. Among these materials, non-graphitic carbon is preferable as the other negative electrode active material.

The negative electrode active material is usually particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. When the negative electrode active material is a carbon material, a titanium-containing oxide or a polyphosphate compound, the average particle size may be 1 μm or more and 100 μm or less. When the negative electrode active material is Si, Sn, Si oxide, Sn oxide, or the like, the average particle size may be 1 nm or more and 1 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 setting the average particle diameter of the negative electrode active material to the above upper limit or less, the electron conductivity of the negative electrode active material layer is improved. "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 lower limit of the total content of artificial graphite and natural graphite in the negative electrode active material is preferably 60% by mass, more preferably 70% by mass, and even more preferably 80% by mass. On the other hand, the upper limit of this content may be 90% by mass or 95% by mass, but substantially 100% by mass is preferable.

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 negative electrode active material layer of the non-aqueous electrolyte storage element contains an acrylic resin as a binder. "Acrylic resin" does not include polyacrylic acid, which is a homopolymer of monomers having acryloyl groups. Examples of acrylic resins include polymers containing monomers having groups other than acryloyl groups, such as acrylic acid esters, methacrylic acid or methacrylic acid ester polymers, and polyacrylamides. Moreover, the acrylic resin does not have a structural unit derived from butadiene. Since the acrylic resin does not have a structural unit derived from butadiene, it is possible to reduce the initial DC resistance and further suppress the decrease in the capacity retention rate after charge-discharge cycles.

The acrylic resin content in the binder is preferably 99% by mass or more, and may be 100% by mass.

The lower limit of the binder content in the negative electrode active material layer is preferably 0.2% by mass, more preferably 0.5% by mass, and even more preferably 1% by mass. On the other hand, the upper limit of this content is preferably 10% by mass, more preferably 5% by mass.

The negative electrode active material layer contains arbitrary components such as a conductive agent, a thickening agent, a filler, etc., if necessary.

The conductive agent is not particularly limited as long as it is a conductive material. Carbon materials such as the artificial graphite, the natural graphite, and the non-graphitic carbon, which are used as the negative electrode active material, also have conductivity, but are not included in the conductive agent in the negative electrode active material layer. Examples of conductive agents other than the above carbon materials include other carbonaceous materials, metals, and conductive ceramics. Other carbonaceous materials include 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.

When the negative electrode active material layer contains a conductive agent, the content of the conductive agent in the negative electrode active material layer is preferably 1% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 10% 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.

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.

(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 the positive electrode substrate include foil, deposited film, mesh, porous material, and the like, and foil is preferable from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferable as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, A1N30, etc. defined in JIS-H-4000 (2014) or JIS-H4160 (2006).

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.

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. Examples of lithium transition metal composite oxides having an α-NaFeO ₂ type crystal structure include 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) and the like. 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 . Examples of polyanion compounds include _{LiFePO4 , LiMnPO4} , LiNiPO4 _{, LiCoPO4 , Li3V2} ( _PO4 ) ₃ , _{Li2MnSiO4 , Li2CoPO4F} and the like. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. The atoms or polyanions in these materials may be partially substituted with atoms or anionic species of other elements. These materials may be coated with other materials on their surfaces. In the positive electrode active material layer, one kind of these materials may be used alone, or two or more kinds may be mixed and used.

The positive electrode active material is usually particles (powder). 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. Note that when a composite of a positive electrode active material and another material is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material.

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.

Examples of the binder in the positive electrode active material layer include fluorine resins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, polyacryl, and polyimide; ethylene-propylene-diene rubber. (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber and other elastomers; polysaccharide polymers and the like.

The content of the binder in the positive 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.

Optional components such as a conductive agent, a thickener, and a filler can be selected from the materials exemplified for the negative electrode. In addition, in the positive electrode active material layer, carbon materials such as graphite and non-graphitic carbon are also included in the conductive agent.

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

(separator)
The separator can be appropriately selected from known separators. As the separator, for example, a separator consisting of only a substrate layer, a separator having a heat-resistant layer containing heat-resistant particles and a binder formed on one or both surfaces of a substrate layer, or the like can be used. Examples of the form of the base material layer of the separator include woven fabric, non-woven fabric, porous resin film, and the like. Among these forms, a porous resin film is preferred from the viewpoint of strength, and a non-woven fabric is preferred from the viewpoint of non-aqueous electrolyte retention. As the material for the base layer of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of shutdown function, and polyimide, aramid, and the like are preferable from the viewpoint of oxidative decomposition resistance. A material obtained by combining these resins may be used as the base material layer of the separator.

The heat-resistant particles contained in the heat-resistant layer preferably have a mass loss of 5% or less when the temperature is raised from room temperature to 500 ° C. in an air atmosphere of 1 atm, and the mass loss when the temperature is raised from room temperature to 800 ° C. is more preferably 5% or less. An inorganic compound can be mentioned as a material whose mass reduction is less than or equal to a predetermined value. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate; nitrides such as aluminum nitride and silicon nitride. carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalent crystals such as silicon and diamond; Mineral resource-derived substances such as zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. As the inorganic compound, a single substance or a composite of these substances may be used alone, or two or more of them may be mixed and used. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferable from the viewpoint of the safety of the electric storage device.

The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and preferably 20% by volume or more from the viewpoint of discharge performance. Here, the "porosity" is a volume-based value and means a value measured with a mercury porosimeter.

A polymer gel composed of a polymer and a non-aqueous electrolyte may be used as the separator. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyvinylidene fluoride, and the like. The use of polymer gel has the effect of suppressing liquid leakage. As the separator, a polymer gel may be used in combination with the porous resin film or non-woven fabric as described above.

(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 , lithium bis(oxalate) borate (LiBOB), lithium difluorooxalate borate (LiFOB). , lithium oxalate salts _such as lithium bis ₍ oxalate) difluorophosphate (LiFOP), _LiSO3CF3 , LiN( _SO2CF3 ) _{2 ,} LiN _{( SO2C2F5 ) 2} , LiN( _SO2CF3 ) (SO ₂ C ₄ F ₉ ), LiC(SO ₂ CF ₃ ) ₃ , LiC(SO ₂ C ₂ F ₅ ) ₃ and other lithium salts having a halogenated hydrocarbon group. 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/dm3 ^or more and 2.5 mol/dm3 or less, and 0.3 mol/ ^{dm3 or} more and 2.0 mol/dm3 or less at 20°C and 1 atm. It is more preferably ³ or less, more preferably 0.5 mol/dm ³ or more and 1.7 mol/dm ³ or less, and particularly preferably 0.7 mol/dm ³ or more and 1.5 mol/dm ³ or less. 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 in addition to the non-aqueous solvent and electrolyte salt. Examples of additives include oxalates such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), lithium bis(oxalate)difluorophosphate (LiFOP); lithium bis(fluorosulfonyl)imide ( LiFSI) and other imide salts; biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran and other aromatic compounds; 2-fluorobiphenyl, Partial halides of the above aromatic compounds such as o-cyclohexylfluorobenzene and p-cyclohexylfluorobenzene; 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, 3,5-difluoroanisole, etc. Halogenated anisole compounds of: 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, 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-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1, 3-propenesultone, 1,3-propanesultone, 1,4-butanesultone, 1,4-butenesultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate, difluoro Lithium phosphate etc. are mentioned. 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, and 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, it is 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 arbitrary materials such as lithium, sodium, calcium, etc., which have ion conductivity and are solid at room temperature (for example, 15° C. to 25° C.). Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, polymer solid electrolytes, gel polymer electrolytes, and the like.

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

<Configuration of power storage device>
The shape of the non-aqueous electrolyte storage element of the present embodiment is not particularly limited, and examples thereof include cylindrical batteries, rectangular 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. An electrode body 2 having a positive electrode and a negative electrode wound with a separator sandwiched therebetween 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 non-aqueous electrolyte storage element 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 electric power It can be installed in a storage power source or the like 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 1 are assembled is further assembled. The power storage device 30 includes a bus bar (not shown) electrically connecting two or more non-aqueous electrolyte power storage elements 1, a bus bar (not shown) electrically connecting two or more power storage units 20, and the like. good too. 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 1 .

<Method for producing non-aqueous electrolyte storage element>
A 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, preparing an electrode body, preparing a non-aqueous electrolyte, and housing the electrode body and the non-aqueous electrolyte in a container. Preparing the electrode body includes preparing a positive electrode and a negative electrode, and forming the electrode body by laminating or winding the positive electrode and the negative electrode with a separator interposed therebetween. The positive electrode can be obtained by laminating the positive electrode active material layer directly or via an intermediate layer on a positive electrode substrate. Lamination of the positive electrode active material layer can be performed by applying a positive electrode material mixture paste containing the positive electrode active material to the positive electrode substrate. Moreover, the negative electrode can be obtained by laminating the negative electrode active material layer directly or via an intermediate layer on a negative electrode substrate, like the positive electrode. Lamination of the negative electrode active material layer can be performed by applying a negative electrode mixture paste containing artificial graphite, natural graphite, and an acrylic resin to the negative electrode substrate. The positive electrode mixture paste and the negative electrode mixture paste may contain a dispersion medium. As the dispersion medium, for example, an aqueous solvent such as water or a mixed solvent mainly containing water; or an organic solvent such as N-methylpyrrolidone or toluene can be used.

A suitable method for containing the non-aqueous electrolyte in the container can be selected from known methods. For example, when a non-aqueous electrolyte is used as the non-aqueous electrolyte, the non-aqueous electrolyte may be injected through an inlet formed in the container, and then the inlet may be sealed. The details of each element constituting the non-aqueous electrolyte storage element obtained by the above manufacturing method are as described above.

According to the non-aqueous electrolyte power storage element, even when a negative electrode active material with a high proportion of artificial graphite is used, it is possible to reduce the initial direct current resistance and to suppress the decrease in the capacity retention rate after charge-discharge cycles.

<Other embodiments>
It should be noted that the non-aqueous electrolyte storage device of 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, the configuration of another embodiment can be added to the configuration of one embodiment, and part of the configuration of one embodiment can be replaced with the configuration of another embodiment or a known technique. Furthermore, some of the configurations of certain embodiments 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.

In the above embodiments, the electrode body in which the positive electrode and the negative electrode are laminated with the separator interposed therebetween has been described, but the electrode body may not include the separator. For example, the positive electrode and the negative electrode may be in direct contact with each other in a state in which a layer having no conductivity is formed on the active material layer of the positive electrode or the negative electrode.

EXAMPLES The present invention will be described in more detail below with reference to examples. The invention is not limited to the following examples.

[Example 1]
(negative electrode)
An acrylic resin was used as a binder for the negative electrode active material layer. A negative electrode mixture paste containing artificial graphite and natural graphite as negative electrode active materials, a binder, and CMC as a thickener, and using water as a dispersion medium was prepared. The artificial graphite content was 70% by mass and the natural graphite content was 30% by mass with respect to the total content of artificial graphite and natural graphite in the negative electrode active material layer. The mixing ratio of the negative electrode active material, the binder, and the thickener was 98:1:1 (converted to solid content) by mass. The negative electrode mixture paste is applied to one side of a negative electrode substrate made of copper foil with a thickness of 10 μm at a coating weight of 14 mg/cm ² (in terms of solid content), dried to form a negative electrode active material layer, and then pressed. Then, the negative electrode of Example 1 was obtained.
(Non-aqueous electrolyte)
A non-aqueous electrolyte was prepared by dissolving LiPF ₆ at a concentration of 1 mol/dm ³ in a non-aqueous solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 30:70.
(positive electrode)
LiNi _0.5 Co _0.2 Mn _0.3 O ₂ having an α-NaFeO ₂ type crystal structure was used as a positive electrode active material. A positive electrode mixture paste containing the positive electrode active material, polyvinylidene fluoride (PVDF) as a binder, acetylene black as a conductive agent, and using N-methyl-2-pyrrolidone (NMP) as a dispersion medium was prepared. . The mixing ratio of the positive electrode active material, the binder, and the conductive agent was 93:4:3 (in terms of solid content) in terms of mass ratio. The positive electrode mixture paste is applied to one side of a positive electrode substrate made of aluminum foil with a thickness of 15 μm at a coating mass of 25 mg/cm ² (in terms of solid content), dried to form a positive electrode active material layer, and then pressed. Then, a positive electrode was obtained.

(Preparation of non-aqueous electrolyte storage element)
As the separator, a separator having a microporous base layer made of polyethylene was used. The positive electrode and the negative electrode were laminated with the separator interposed therebetween to produce an electrode assembly. This electrode assembly was housed in a container, and a positive electrode terminal and a negative electrode terminal were attached. After injecting the non-aqueous electrolyte into the container, the container was sealed to obtain a non-aqueous electrolyte storage element of Example 1.

[Example 2, Example 3 and Comparative Examples 1 to 5]
In the same manner as in Example 1, except that the type of binder in the negative electrode active material layer and the content ratio of artificial graphite and natural graphite with respect to the total content of artificial graphite and natural graphite in the negative electrode active material were as shown in Table 1. Non-aqueous electrolyte storage elements of Examples 2 and 3 and Comparative Examples 1 to 5 were produced.

[Example 4]
A non-aqueous electrolyte storage element of Example 4 was produced in the same manner as in Example 1, except that artificial graphite coated with a carbon material (amorphous carbon) was used as the artificial graphite in the negative electrode active material.

[evaluation]
(Initial capacity confirmation test)
Each obtained non-aqueous electrolyte storage element was charged at 25° C. with a constant current of 0.2 C to 4.25 V, and then charged with a constant voltage of 4.25 V. The charging termination condition was until the charging current reached 0.01C. After a rest period of 10 minutes was provided after charging, the battery was discharged at a constant current of 0.2C to 2.75V at 25°C. The discharge capacity obtained in this test was defined as "initial capacity".

(Measurement of initial DC resistance)
After the initial capacity confirmation test, each of the non-aqueous electrolyte storage elements of Examples 1 to 3 and Comparative Examples 1 to 5 was charged to 50% of the initial capacity, thereby reducing the state of charge (SOC) of the battery to 50%. and held at -10 ° C. for 3 hours, then the voltage (E1) when discharged for 10 seconds at a current of 0.1 C, the voltage (E2) when discharged for 10 seconds at a current of 0.2 C, and A voltage (E3) was measured when discharging at a current of 0.3 C for 10 seconds. After completion of each discharge, constant current charging was performed at a current of 0.05 C to bring the SOC to 50%. Direct current resistance was calculated using these measured values (E1, E2, E3). Specifically, the measured values E1, E2, and E3 are plotted on a graph in which the horizontal axis is current and the vertical axis is voltage, and these three points are approximated by a regression line (approximate line) by the least squares method, The slope of the straight line was determined and used as the initial DC resistance. Table 1 shows the initial DC resistance of each non-aqueous electrolyte storage element obtained.

(Charge-discharge cycle test (1))
After the initial capacity confirmation test, the non-aqueous electrolyte storage elements of Example 1 and Comparative Example 2 were subjected to the following charge-discharge cycle test. At 45.degree. The charging termination condition was until the charging current reached 0.01C. A rest period of 10 minutes was then provided. Thereafter, constant current discharge was performed at a discharge current of 1.0 C to 2.75 V, followed by a rest period of 10 minutes. 700 cycles were carried out with these charging and discharging as one cycle.
Thereafter, a discharge capacity confirmation test after the charge/discharge cycle test was performed in the same manner as the initial capacity confirmation test. The discharge capacity obtained in this test was defined as the discharge capacity after 700 cycles at 45°C. The percentage of the discharge capacity after the charge-discharge cycle test of 45°C, 700 cycles to the initial capacity was defined as the "capacity retention rate after 45°C, 700 cycles". Table 2 shows the capacity retention rate after 700 cycles at 45°C.

(Charge-discharge cycle test (2))
After the initial capacity confirmation test, Examples 1 to 4 were subjected to the following charge-discharge cycle test. At 60.degree. The charging termination condition was until the charging current reached 0.01C. A rest period of 10 minutes was then provided. Thereafter, constant current discharge was performed at a discharge current of 1.0 C to 2.75 V, followed by a rest period of 10 minutes. 300 cycles were carried out with these charging and discharging as one cycle.
Thereafter, a discharge capacity confirmation test after the charge/discharge cycle test was performed in the same manner as the initial capacity confirmation test. The discharge capacity obtained in this test was defined as the discharge capacity after 300 cycles at 60°C. The percentage of the discharge capacity after 300 cycles at 60°C to the initial capacity was defined as the "capacity retention rate after 300 cycles at 60°C". Table 3 shows the capacity retention rate after 300 cycles at 60°C. In addition, "-" in Table 3 indicates that the corresponding component is not contained.

As shown in Table 1, the negative electrode active material layer includes a negative electrode active material having a content ratio of artificial graphite of 50% by mass or more and 90% by mass or less with respect to the total content of artificial graphite and natural graphite, and an acrylic resin. In Examples 1 to 3, the effect of reducing the initial DC resistance was good. On the other hand, in Comparative Examples 1, 3, 4 and 5 in which the negative electrode active material layer contains a styrene-butadiene copolymer, and the content ratio of artificial graphite to the total content of artificial graphite and natural graphite is Comparative Example 2 using 100% by mass of the negative electrode active material had a large initial DC resistance. Furthermore, as shown in Table 2, when comparing the capacity retention rate after 700 cycles at 45°C in Example 1 and Comparative Example 2, the content of artificial graphite with respect to the total content of artificial graphite and natural graphite was 100%. Comparative Example 2 using a negative electrode active material of 45% by mass is 45 ° C. , the capacity retention rate after 700 cycles decreased. For these reasons, in the negative electrode active material layer, a negative electrode active material in which the content of artificial graphite relative to the total content of artificial graphite and natural graphite is 50% by mass or more and 90% by mass or less is used in combination with an acrylic resin. , even when graphite with a high ratio of artificial graphite is used as the negative electrode active material of the non-aqueous electrolyte storage element, the initial DC resistance can be reduced and the decrease in the capacity retention rate after charge-discharge cycles can be suppressed. .

Further, as shown in Table 3, in Example 4 using artificial graphite whose surface is coated with a carbon material as artificial graphite, it is possible to charge the non-aqueous electrolyte storage element by using it in combination with an acrylic resin. It can be seen that the effect of suppressing a decrease in capacity retention rate after discharge cycles can be further improved.

As described above, the non-aqueous electrolyte storage element can reduce the initial DC resistance even when graphite with a high proportion of artificial graphite is used as the negative electrode active material, and the capacity retention rate after charge-discharge cycles decreases. can be suppressed.

INDUSTRIAL APPLICABILITY The present invention is suitably used as a non-aqueous electrolyte storage element including a non-aqueous electrolyte secondary battery used as a power source for electronic equipment such as personal computers and communication terminals, and automobiles such as EV, HEV and PHEV.

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

Claims (2)

A negative electrode having a negative electrode active material layer,
The negative electrode active material layer contains a negative electrode active material and an acrylic resin,
The negative electrode active material contains artificial graphite and natural graphite,
A content ratio of the artificial graphite with respect to the total content of the artificial graphite and the natural graphite is 50% by mass or more and 90% by mass or less,
A non-aqueous electrolyte storage element in which the acrylic resin does not have a structural unit derived from butadiene. 2. The non-aqueous electrolyte storage element according to claim 1, wherein at least part of the surface of said artificial graphite is coated with a carbon material.

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