JP2022129020A - Nonaqueous electrolyte power storage device, and manufacturing method thereof - Google Patents

Abstract

To provide a nonaqueous electrolyte power storage device which can reduce an initial DC resistance at a low temperature, and suppress the worsening of a capacity-keeping rate after having gone through a charge-discharge cycle.SOLUTION: A nonaqueous electrolyte power storage device according to an aspect of the present invention comprises: a positive electrode; a negative electrode; a separator interposed between the positive and negative electrodes; and a nonaqueous electrolyte. The separator has a porosity of 44 vol.% or more. The nonaqueous electrolyte contains a compound represented by the formula (1). In the formula (1), R1 and R2 independently represent a hydrogen atom or a fluorine atom.SELECTED DRAWING: None

Description

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

Non-aqueous electrolyte secondary batteries, typified by lithium ion secondary batteries, are widely used in electronic devices such as personal computers, communication terminals, and automobiles because of their high energy density. The non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes, and transfers ions between the electrodes. It is configured to be charged and discharged by 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.

Generally, the non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent, and other components are added as necessary. For example, a non-aqueous electrolyte for a secondary battery has been proposed in which a fluorinated carboxylic acid ester and a specific film-forming compound are contained in a non-aqueous solvent (see Patent Document 1).

JP 2009-289414 A

The use of a non-aqueous electrolyte containing a fluorinated carboxylic acid ester or the like tends to improve the charge-discharge cycle performance. However, when a non-aqueous electrolyte containing a fluorinated carboxylic acid ester or the like is used, the initial DC resistance of a non-aqueous electrolyte storage element such as a non-aqueous electrolyte secondary battery may be high at low temperatures.

The present invention has been made based on the above circumstances, and its object is to provide a non-aqueous electrolyte that can reduce the initial DC resistance at low temperatures and suppress the decrease in the capacity retention rate after charge-discharge cycles. It is to provide an electric storage element.

A non-aqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, and the separator has a porosity of 44 volumes. % or more, and the non-aqueous electrolyte contains a compound represented by the following formula (1).

式（１）中、Ｒ^１及びＲ^２は、それぞれ独立して、水素原子又はフッ素原子である。

In formula (1), R ¹ and R ² are each independently a hydrogen atom or a fluorine atom.

A method for manufacturing a non-aqueous electrolyte storage element according to another aspect of the present invention comprises preparing a separator having a porosity of 44% by volume or more, and providing a water electrolyte.

式（１）中、Ｒ^１及びＲ^２は、それぞれ独立して、水素原子又はフッ素原子である。

In formula (1), R ¹ and R ² are each independently a hydrogen atom or a fluorine atom.

The non-aqueous electrolyte storage device according to one aspect of the present invention can reduce the initial direct current resistance at low temperatures and suppress the decrease in the capacity retention rate after charge-discharge cycles.

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 positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, and the separator has a porosity of 44 volumes. % or more, and the non-aqueous electrolyte contains a compound represented by the following formula (1).

式（１）中、Ｒ^１及びＲ^２は、それぞれ独立して、水素原子又はフッ素原子である。

In formula (1), R ¹ and R ² are each independently a hydrogen atom or a fluorine atom.

According to the non-aqueous electrolyte storage element, the porosity of the separator is 44% by volume or more, and the non-aqueous electrolyte contains the compound represented by the above formula (1), so that the initial DC resistance at low temperature is can be reduced, and a decrease in the capacity retention rate after charge-discharge cycles can be suppressed. Although the reason for this is not clear, the following reasons are presumed, for example. One factor that reduces the life performance of the battery is that the decomposition products of the non-aqueous electrolyte decomposed on the negative electrode reach the positive electrode and deteriorate the positive electrode. However, the compound represented by the above formula (1) is reductively decomposed to form a good film on the negative electrode, thereby protecting the negative electrode and suppressing the decomposition of the non-aqueous electrolyte. is expected to improve. Further, in the non-aqueous electrolyte storage element, the porosity of the separator is 44% by volume or more, so that the effect of reducing the initial DC resistance of the non-aqueous electrolyte storage element at low temperatures can be obtained, and the above formula ( The compound represented by 1) can further improve the effect of suppressing the decrease in capacity retention rate after charge-discharge cycles. In the non-aqueous electrolyte storage element, in addition to the effect of improving charge-discharge cycle performance due to the above compound, the increase in resistance is small, so the charge-discharge reaction of the positive and negative electrodes proceeds deeper, and the reductive decomposition reaction of the compound is promoted. It is thought that the effect of improving the charge-discharge cycle performance is specifically increased due to the synergistic effect of the above. On the other hand, when a large amount of additive is added to the non-aqueous electrolyte, the initial resistance tends to increase, and the charge-discharge cycle performance tends to decrease due to oxidative decomposition and thermal decomposition of the remaining additive. Further, when the porosity of the separator is high, residual additives and reductive decomposition products of the non-aqueous electrolyte are likely to be transported from the negative electrode to the positive electrode, possibly deteriorating the charge-discharge cycle performance. On the other hand, the above compound is reductively decomposed to form a good film on the negative electrode, which sufficiently protects the negative electrode and does not adversely affect the positive electrode. It is considered that the charge-discharge cycle performance does not deteriorate even if the Therefore, the non-aqueous electrolyte storage element can reduce the initial direct current resistance at low temperatures and suppress the decrease in the capacity retention rate after charge-discharge cycles.

The content of the compound in the non-aqueous electrolyte is preferably 0.7% by mass or more and 5.0% by mass or less. When the content of the compound is 0.7% by mass or more and 5.0% by mass or less, an increase in initial resistance can be suppressed.

A method for manufacturing a non-aqueous electrolyte storage element according to another aspect of the present invention comprises preparing a separator having a porosity of 44% by volume or more, and providing a water electrolyte.

式（１）中、Ｒ^１及びＲ^２は、それぞれ独立して、水素原子又はフッ素原子である。

In formula (1), R ¹ and R ² are each independently a hydrogen atom or a fluorine atom.

According to the manufacturing method of the non-aqueous electrolyte storage element, it is possible to manufacture a non-aqueous electrolyte storage element that can reduce the initial DC resistance at low temperature and suppress the decrease in the capacity retention rate after charge-discharge cycles.

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.

<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.

(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.

A positive 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 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 intermediate layer is a layer arranged between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The composition of the intermediate layer is not particularly limited, and includes, for example, a binder and a conductive agent.

The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer contains arbitrary components such as a conductive agent, a binder (binding agent), 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. "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, sieve, and the like. 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 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 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 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 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 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.

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.

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

(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. The structure of the intermediate layer is not particularly limited, and can be selected from, for example, the structures exemplified for the positive electrode.

A negative electrode base material has electroconductivity. As materials for the negative electrode substrate, metals such as copper, nickel, stainless steel, nickel-plated steel, aluminum, 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 negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer contains arbitrary components such as a conductive agent, a binder, a thickener, a filler, etc., as required. Optional components such as conductive agents, binders, thickeners, and fillers can be selected from the materials exemplified for the positive electrode.

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, Typical metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W, etc. are used as negative electrode active materials, conductive agents, binders, You may contain as a component other than a thickener 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 and non-graphitic carbon are preferred. In the negative electrode active material layer, one type of these materials may be used alone, or two or more types may be mixed and used.

“Graphite” refers to a carbon material having an average lattice spacing (d002) of the (002) plane of 0.33 nm or more and less than 0.34 nm as determined by X-ray diffraction before charging/discharging or in a discharged state. Graphite includes natural graphite and artificial graphite. Artificial graphite is preferable from the viewpoint that a material with stable physical properties can be obtained.

“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 single electrode battery 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 more.

The term "non-graphitizable carbon" refers to a carbon material having d002 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 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 size of the negative electrode active material to the above upper limit or less, the electron conductivity of the 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 positive electrode. When the negative electrode active material is metal such as metal Li, the negative electrode active material may be foil-shaped.

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.

(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 lower limit of the porosity of the separator is 44% by volume, preferably 50% by volume. When the porosity of the separator is equal to or higher than the above lower limit, the effect of reducing the initial direct current resistance of the non-aqueous electrolyte storage element at low temperature is obtained, and after charge-discharge cycles by the compound represented by the above formula (1). It is possible to improve the effect of suppressing the decrease in the capacity retention rate of On the other hand, the upper limit of the porosity is preferably 70% by volume, more preferably 60% by volume. When the porosity of the separator is equal to or less than the above upper limit, the strength of the separator can be improved.

The porosity [%] of the separator is calculated from the following formula.
Porosity (%) = 100 - (W / (ρ x t) x 100)
W: Mass per unit area [g cm ^-2 ]
ρ: True density of constituent material [g cm ⁻³ ]
t: thickness [cm]

The upper limit of the air permeability of the separator is preferably 150 seconds/100 cm ³ , more preferably 120 seconds/100 cm ³ . When the air permeability of the separator is equal to or less than the above upper limit, the initial DC resistance of the non-aqueous electrolyte storage element at low temperatures can be reduced. On the other hand, the lower limit of the air permeability of the separator is preferably 50 seconds/100 cm ³ and more preferably 60 seconds/100 cm ³ from the viewpoint of maintaining the strength of the separator. The air permeability of the above separator, also called Gurley value, indicates the number of seconds for a constant volume of air to pass through a constant area of the separator under a constant pressure difference, and is measured in accordance with JIS-P8117 (2009). value.

The lower limit of the average thickness of the separator is preferably 14 μm, more preferably 16 μm. The upper limit of the average thickness is preferably 25 μm, more preferably 22 μm. By making the average thickness of the separator equal to or greater than the lower limit, it is possible to prevent deterioration in the safety of the non-aqueous electrolyte storage element. Further, by setting the average thickness of the separator to the above upper limit or less, the initial DC resistance at low temperatures can be reduced.

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 contains a compound represented by the following formula (1). A non-aqueous electrolyte may be used as the non-aqueous electrolyte. The non-aqueous electrolyte contains a non-aqueous solvent, an electrolyte salt dissolved in this non-aqueous solvent, and a compound represented by the following formula (1).

The non-aqueous electrolyte contains a compound represented by the following formula (1) as an additive. When the non-aqueous electrolyte contains the compound represented by the above formula (1), the compound is reductively decomposed to form a good-quality coating on the negative electrode. As a result, in the non-aqueous electrolyte storage element, the negative electrode is protected, and the capacity retention rate is considered to be improved.

In formula (1), R ¹ and R ² are each independently a hydrogen atom or a fluorine atom. When R ¹ and R ² are fluorine atoms, it is believed that the oxidation resistance of the compound represented by formula (1) can be further improved.

Examples of the above compounds include compounds represented by the following formulas (1-1) to (1-3).

The lower limit of the content of the above compound in the non-aqueous electrolyte is preferably 0.7% by mass, more preferably 0.8% by mass, and even more preferably 1.0% by mass. When the content of the compound is equal to or higher than the lower limit, it is possible to reduce the initial direct current resistance at low temperature and to suppress the decrease in the capacity retention rate after charge-discharge cycles. On the other hand, the upper limit of the content of the compound is preferably 5.0% by mass, more preferably 4.0% by mass. When the content of the compound is equal to or less than the upper limit, an increase in initial resistance can be suppressed.

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 non-aqueous electrolyte may contain additives other than the compound represented by the formula (1) as long as they do not inhibit the effects of the present invention. Examples of the above-mentioned other additives include various additives contained in general non-aqueous electrolytes. Examples of the other additives include halogenated carbonate esters such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), lithium Oxalates such as bis(oxalate) difluorophosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t -aromatic compounds such as butylbenzene, t-amylbenzene, diphenyl ether and dibenzofuran; partial halides of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene and p-cyclohexylfluorobenzene; 2,4-difluoro Halogenated anisole compounds such as anisole, 2,5-difluoroanisole, 2,6-difluoroanisole, 3,5-difluoroanisole; vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride Acid, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, propanesultone, propenesultone, butanesultone, methyl methanesulfonate, busulfan, methyl toluenesulfonate, sulfuric acid dimethyl, 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-butene sultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate, lithium difluorophosphate and the like. These additives may be used singly or in combination of two or more.

The content of other additives contained in the non-aqueous electrolyte is preferably 0.2% by mass or more and 3.0% by mass or less, based on the total mass of the non-aqueous electrolyte, and is 0.5% by mass or more. It is more preferably 2.0% by mass or less. By setting the content of the other additives within the above range, it is possible to improve capacity retention performance or cycle performance after high-temperature storage, and to further improve safety.

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.

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. to 25° C.). 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 , 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 power source for storage or the like as a power storage unit (battery module) configured by collecting a plurality of non-aqueous electrolyte power storage elements 1 . 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.

<Method for producing non-aqueous electrolyte storage element>
The method for manufacturing a non-aqueous electrolyte storage element of the present embodiment comprises preparing a separator having a porosity of 44% by volume or more, and preparing a non-aqueous electrolyte containing a compound represented by the following formula (1). Be prepared.

式（１）中、Ｒ^１及びＲ^２は、それぞれ独立して、水素原子又はフッ素原子である。

In formula (1), R ¹ and R ² are each independently a hydrogen atom or a fluorine atom.

The manufacturing method includes, as other steps, for example, preparing an electrode body 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 an electrode body by laminating or winding the positive electrode and the negative electrode with the separator interposed therebetween. The specific configurations of the separator and the non-aqueous electrolyte are as described above.

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.

According to the manufacturing method of the non-aqueous electrolyte storage element, it is possible to manufacture a non-aqueous electrolyte storage element that can reduce the initial DC resistance at low temperature and 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.

[Examples 1 to 3 and Comparative Examples 1 to 10]
(Preparation of positive electrode)
A lithium transition metal composite oxide represented by LiNi _1/2 Co _1/5 Mn _3/10 O ₂ was used as a positive electrode active material.

A positive electrode paste was prepared using N-methylpyrrolidone (NMP) as a dispersion medium and containing the positive electrode active material, acetylene black as a conductive agent, and PVdF as a binder in a mass ratio of 93:4:3. This positive electrode mixture paste is applied to both surfaces of an aluminum foil having an average thickness of 15 μm, which is a positive electrode substrate, leaving an uncoated portion (positive electrode mixture layer non-forming region), and dried to form a positive electrode mixture layer. made. After that, roll pressing was performed to produce a positive electrode. The thickness of the positive electrode was 135 μm.

(Preparation of negative electrode)
Graphite was used as the negative electrode active material. A negative electrode mixture paste containing water as a dispersion medium, the negative electrode active material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener at a mass ratio of 96:2:2. made. This negative electrode mixture paste is applied to both surfaces of a copper foil having an average thickness of 10 μm, which is the negative electrode substrate, leaving an uncoated portion (negative electrode mixture layer non-forming region), and dried to form a negative electrode mixture layer. made. After that, roll pressing was performed to produce a negative electrode. The thickness of the negative electrode was 148 μm.

(Preparation of non-aqueous electrolyte)
Additives listed in Tables 1 and 2 and LiPF ₆ at a concentration of 1.0 mol/dm ³ are dissolved in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 30:70. to form a non-aqueous electrolyte. In Comparative Examples 1 to 3, only LiPF ₆ was dissolved in the mixed solvent.

(separator)
A polypropylene microporous membrane having an average thickness of 20 μm was used as the separator. Tables 1 and 2 show the porosity and air permeability of the separators of Examples 1 to 3 and Comparative Examples 1 to 10.

(Preparation of non-aqueous electrolyte storage element)
The positive electrode and the negative electrode were layered and wound with the separator interposed therebetween. After that, the positive electrode mixture layer non-formed region of the positive electrode and the negative electrode mixture layer non-formed region of the negative electrode are welded to the positive electrode lead and the negative electrode lead, respectively, and sealed in a container. was injected and sealed to obtain non-aqueous electrolyte storage elements of Examples 1 to 3 and Comparative Examples 1 to 10.

(initial charge/discharge)
Initial charge/discharge was performed on each obtained non-aqueous electrolyte storage element under the following conditions. At 25° C., constant-current and constant-voltage charging was performed with a charging current of 1.0 C and a charge termination voltage of 4.25 V. The end condition of charging was until the charging time reached 3 hours. A rest period of 10 minutes was then provided. Thereafter, constant current discharge was performed with a discharge current of 1.0 C and a discharge final voltage of 2.75 V, followed by a rest period of 10 minutes. Two cycles of this charging and discharging were performed.

(Charge-discharge cycle test)
Next, the following charge/discharge cycle test was performed. Each non-aqueous electrolyte storage element was stored in a constant temperature bath at 45° C. for 3 hours, then charged at a constant current of 1 C to 4.25 V, and then charged at a constant voltage of 4.25 V until the charging time was 3 hours. did. After that, constant current discharge was performed at a current of 1.0 C to 2.75 V, followed by a rest period of 10 minutes. These charging and discharging steps were regarded as one cycle, and this cycle was repeated 300 cycles. Both charging, discharging and resting were performed in a constant temperature bath at 45°C.

(Capacity retention rate after charge-discharge cycle test)
For each non-aqueous electrolyte storage element after the charge-discharge cycle test, the discharge capacity at 45° C. in the 300th cycle with respect to the discharge capacity at 45° C. in the 1st cycle was obtained as a capacity retention rate [%].

(initial DC resistance at low temperature)
The initial direct current resistance of each non-aqueous electrolyte storage element was evaluated at low temperatures. Each non-aqueous electrolyte storage element after the initial charge/discharge was constant-current charged at a current of 1.0 C in a constant temperature bath at 25° C. to make the SOC (State of Charge) 50%. Each non-aqueous electrolyte storage element was stored in a constant temperature bath at -10°C for 4 hours, and then discharged at currents of 0.1C, 0.2C and 0.3C for 30 seconds. After completion of each discharge, constant current charging was performed at a current of 0.05 C to bring the SOC to 50%. The voltage 10 seconds after the start of discharge was plotted on the vertical axis, and the discharge current was plotted on the horizontal axis.

The evaluation results are shown in Tables 1 and 2 below.

As shown in Tables 1 and 2, the porosity of the separator is 44% by volume or more, and the non-aqueous electrolyte of Examples 1 to 3 containing the compound represented by the above formula (1) In the water electrolyte storage device, the initial direct current resistance at low temperature was reduced, and the decrease in the capacity retention rate after charge-discharge cycles was sufficiently suppressed.

Further, as shown in Table 1, in Comparative Examples 2 and 3 in which the non-aqueous electrolyte does not contain an additive, and in Comparative Example 5 in which the non-aqueous electrolyte contains vinylene carbonate, the porosity of the separator was 44. When the volume % or more was used, the capacity retention rate after charge-discharge cycles was rather lowered. On the other hand, in Examples 1 and 2 in which the non-aqueous electrolyte contained the compound represented by the above formula (1), the porosity of the separator was set to 44% by volume or more, so that the capacity after charge-discharge cycles was It can be seen that the effect of suppressing a decrease in retention rate is enhanced. Therefore, by combining the compound represented by the above formula (1) and a separator having a porosity of 44% by volume or more, it is possible to obtain an unexpected effect that a decrease in the capacity retention rate after charge-discharge cycles can be suppressed. I understand.

Furthermore, as shown in Table 2, in Comparative Examples 9 and 10, even if the compound represented by the above formula (1) has a dimer structure similar to that of the compound represented by the above formula (1), In the case where it is not a dimer structure of ethylene carbonate like the compound represented, even if the porosity of the separator is 44% by volume or more, the capacity retention rate after charge-discharge cycles is lower than that of Comparative Example 7 containing no additive. Was. In addition, in Comparative Example 7, since the non-aqueous electrolyte contained vinylene carbonate, the initial direct current resistance at low temperatures was increased as compared with Comparative Example 7 containing no additive. On the other hand, as shown in Example 3, the non-aqueous electrolyte contains the compound represented by the above formula (1), thereby reducing the initial DC resistance at low temperatures and improving the capacity retention rate after charge-discharge cycles. It can be seen that the effect of suppressing the decrease is high.

As a result, it was shown that the non-aqueous electrolyte storage device can reduce the initial direct current resistance at low temperature and can suppress the decrease in the capacity retention rate after charge-discharge cycles.

INDUSTRIAL APPLICABILITY The present invention can be applied to non-aqueous electrolyte storage elements used as power sources for electronic devices such as personal computers and communication terminals, and automobiles.

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 (3)

a positive electrode;
a negative electrode;
a separator interposed between the positive electrode and the negative electrode;
with a non-aqueous electrolyte and
The separator has a porosity of 44% by volume or more,
A non-aqueous electrolyte storage element, wherein the non-aqueous electrolyte contains a compound represented by the following formula (1).

In formula (1), R ¹ and R ² are each independently a hydrogen atom or a fluorine atom. 2. The non-aqueous electrolyte storage element according to claim 1, wherein the content of said compound in said non-aqueous electrolyte is 0.7% by mass or more and 5.0% by mass or less. Preparing a separator having a porosity of 44% by volume or more;
A method for producing a non-aqueous electrolyte storage element, comprising: preparing a non-aqueous electrolyte containing a compound represented by the following formula (1).

In formula (1), R ¹ and R ² are each independently a hydrogen atom or a fluorine atom.

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