JP7831324B2 - Non-aqueous electrolyte energy storage element and energy storage device - Google Patents

Description

This invention relates to a non-aqueous electrolyte energy storage element and an energy storage device.

Non-aqueous electrolyte secondary batteries, such as lithium-ion batteries, are widely used in electronic devices like personal computers and communication terminals, as well as automobiles, due to their high energy density. Generally, these non-aqueous electrolyte secondary batteries consist of a pair of electrodes electrically isolated by a separator, and a non-aqueous electrolyte interposed between these electrodes. They are configured to charge and discharge by transferring ions between the two electrodes. In addition to non-aqueous electrolyte secondary batteries, capacitors such as lithium-ion capacitors and electric double-layer capacitors are also widely used as non-aqueous electrolyte energy storage elements.

As an example of a non-aqueous electrolyte energy storage element, Patent Document 1 discloses a lithium secondary battery using lithium metal foil as the negative electrode.

Re-table No. 2017-047019

However, while lithium secondary batteries using lithium metal as the negative electrode as shown in the above-mentioned patent document have high energy density, their internal resistance may increase with charge-discharge cycles, and lithium metal may deposit in a dendritic pattern on the negative electrode surface during charging (hereinafter, lithium metal in a dendritic form will be referred to as "dendrites"), which may cause internal short circuits.

The object of the present invention is to provide a non-aqueous electrolyte energy storage element and energy storage device that have high energy density, can suppress the increase in internal resistance associated with charge-discharge cycles, and can delay the occurrence of internal short circuits.

A non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a positive electrode having a positive electrode mixture containing a phosphorus element, a negative electrode containing a lithium metal, and a non-aqueous electrolyte containing compound a, wherein compound a contains oxygen, fluorine, phosphorus, and boron.

Another aspect of the present invention is an energy storage device comprising two or more non-aqueous electrolyte energy storage elements, and further comprising one or more non-aqueous electrolyte energy storage elements according to the other aspect of the present invention.

One aspect of the present invention relates to a non-aqueous electrolyte energy storage element and energy storage device, which have high energy density, can suppress the increase in internal resistance associated with charge-discharge cycles, and can delay the occurrence of internal short circuits.

Figure 1 is a perspective view showing one embodiment of a non-aqueous electrolyte energy storage element. Figure 2 is a schematic diagram showing one embodiment of an energy storage device constructed by assembling multiple non-aqueous electrolyte energy storage elements.

First, an overview of the non-aqueous electrolyte energy storage elements and energy storage devices disclosed herein will be provided.

A non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a positive electrode having a positive electrode mixture containing a phosphorus element, a negative electrode containing a lithium metal, and a non-aqueous electrolyte containing compound a, wherein compound a contains oxygen, fluorine, phosphorus, and boron.

The non-aqueous electrolyte energy storage element has a high energy density, can suppress the increase in internal resistance associated with charge-discharge cycles, and can delay the occurrence of internal short circuits. The following reasons are presumed to be for this: The non-aqueous electrolyte energy storage element has a high energy density because it is equipped with a negative electrode containing lithium metal. In conventional non-aqueous electrolyte energy storage elements equipped with a negative electrode containing lithium metal, the decomposition of the non-aqueous electrolyte is significantly accelerated on the negative electrode surface, so the ionic conductivity of the non-aqueous electrolyte is greatly reduced. Furthermore, the film formed on the negative electrode surface tends to increase in thickness due to the above decomposition, and the ionic conductivity of the negative electrode surface decreases. As a result, internal resistance tends to increase. In addition, because the above film is formed unevenly, localized current concentration occurs at the negative electrode, which makes it easier for dendrite deposition of lithium metal to progress on the negative electrode surface during charging, and as a result, internal short circuits are likely to occur. In contrast, in the non-aqueous electrolyte energy storage element, compound a contained in the non-aqueous electrolyte reacts with the lithium metal of the negative electrode preferentially over other components of the non-aqueous electrolyte, forming a film derived from compound a on the negative electrode surface. The film derived from compound a at the negative electrode can suppress the decomposition of other components of the non-aqueous electrolyte. Furthermore, because the film derived from compound a has the above-described composition, it has relatively high ionic conductivity. Moreover, the film derived from compound a is easily formed uniformly, which can suppress localized current concentration at the negative electrode. On the other hand, the positive electrode of the non-aqueous electrolyte energy storage element has a positive electrode mixture containing phosphorus, and at this positive electrode, the film derived from phosphorus is formed by the reaction between the positive electrode mixture and the non-aqueous electrolyte. The film derived from phosphorus at the positive electrode suppresses the decomposition of the non-aqueous electrolyte on the positive electrode surface, while contributing to the selective reaction of compound a contained in the non-aqueous electrolyte at the negative electrode surface. Therefore, the presence of the phosphorus-derived film at the positive electrode makes it easier for the film derived from compound a at the negative electrode to be formed more uniformly and well. For the reasons stated above, in this non-aqueous electrolyte energy storage element, even though the negative electrode containing lithium metal exhibits high reactivity, the interaction between the phosphorus element contained in the positive electrode mixture and compound a contained in the non-aqueous electrolyte results in the formation of good coatings on both the positive and negative electrodes. As a result, it is believed that dendrite deposition, which causes an increase in internal resistance and internal short circuits, is effectively reduced.

Here, compound a may be lithium difluorophosphate (LiDFP) or lithium difluorooxalate borate (LiDFOB). If compound a is lithium difluorophosphate (LiDFP) or lithium difluorooxalate borate (LiDFOB), the coating derived from compound a on the negative electrode is more easily formed uniformly and effectively.

Here, in the spectrum of the positive electrode mixture obtained by X-ray photoelectron spectroscopy, the peak position of P2p may be 135 eV or lower. The P2p peak appearing below 135 eV in the above spectrum is a peak of phosphorus atoms derived from phosphorus oxoacids such as phosphonic acid. That is, it indicates that phosphorus atoms derived from phosphorus oxoacids are present on the surface of the positive electrode mixture, and that a film containing the above phosphorus atoms is formed on the positive electrode surface. When a film containing the above phosphorus atoms is formed on the positive electrode surface in this way, the decomposition of the non-aqueous electrolyte on the positive electrode surface is further suppressed. In addition, because the formation of the film containing the above phosphorus atoms on the positive electrode makes the above compound a react more selectively on the negative electrode surface than on the positive electrode surface, the film derived from the above compound a on the negative electrode is more likely to be formed more uniformly and well.

The sample used for measuring the spectrum of the positive electrode mixture by X-ray photoelectron spectroscopy (XPS) is prepared by the following method: The non-aqueous electrolyte energy storage element is discharged with a current of 0.1 C to the discharge termination voltage for normal use, thereby bringing it into a discharged state. Here, "normal use" refers to the case where the non-aqueous electrolyte energy storage element is used under the discharge conditions recommended or specified for the element. The discharged non-aqueous electrolyte energy storage element is disassembled, the positive electrode is removed, the positive electrode is thoroughly washed with dimethyl carbonate, and then dried under reduced pressure at room temperature. The dried positive electrode is cut to a predetermined size (e.g., 2 × 2 ^cm² ) and used as the sample for spectral measurement by XPS. The work from disassembling the non-aqueous electrolyte energy storage element to preparing the sample for spectral measurement by XPS is carried out in an argon atmosphere with a dew point of -60°C or lower, and the sample is sealed in a transfer vessel and subjected to spectral measurement by XPS without exposure to air. The equipment and measurement conditions used for spectral measurement of the cathode mixture by XPS are as follows:
Equipment: KRATOS ANALYTICAL's "AXIS NOVA"
X-ray source: Monochromatic AlKα
Tube voltage: 15kV
Tube current: 10mA
Neutralizing gun: ON
Analysis area: 700μm x 300μm
Measurement range: P2p = 142 to 125 eV, C1s = 300 to 272 eV
Measurement interval: 0.1 eV
Dwell Time: P2p = 426 milliseconds, C1s = 250 milliseconds. Number of cumulative cycles: P2p = 15, C1s = 8.

Furthermore, the peak position of P2p in the above spectrum is determined as follows: First, the bond energy of the sp2 carbon peak in C1s is set to 284.8 eV, and all obtained spectra are corrected. Next, each spectrum is leveled by removing the background using the linear method. In the spectrum after leveling, the bond energy showing the highest peak intensity in the range of 130 to 138 eV is taken as the peak position of P2p.

This document details the configuration of a non-aqueous electrolyte energy storage element, the configuration of an energy storage device, a method for manufacturing the non-aqueous electrolyte energy storage element, and other embodiments according to one embodiment of the present invention. Note that the names of the components (parts) used in each embodiment may differ from the names of the components (parts) used in the background art.

<Configuration of a non-aqueous electrolyte energy storage element>
A non-aqueous electrolyte energy storage element (hereinafter also simply referred to as "energy storage element") according to one embodiment of the present invention comprises an electrode body having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container for housing the electrode body and the non-aqueous electrolyte. The electrode body is usually a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked with a separator in between, or a wound type in which the positive electrode and negative electrode are wound in a stacked state with a separator in between. The non-aqueous electrolyte exists contained within the positive electrode, negative electrode, and separator. As an example of a non-aqueous electrolyte energy storage element, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as "secondary battery") will be described.

[Positive electrode]
The above-mentioned positive electrode comprises a positive electrode substrate and a positive electrode mixture layer disposed directly on the positive electrode substrate or via an intermediate layer.

(Positive electrode substrate)
The positive electrode substrate is conductive. Whether or not it is conductive is determined by a volume resistivity of ^10⁷ Ω·cm, measured in accordance with JIS-H-0505 (1975), with a threshold value of 10⁷ Ω·cm. As the material of the positive electrode substrate, metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof, are used. Among these, aluminum or aluminum alloys are preferred from the viewpoint of potential resistance, high conductivity, and cost. Examples of positive electrode substrates include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30 as specified in JIS-H-4000 (2014) or JIS-H4160 (2006).

The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, it is possible to increase the strength of the positive electrode substrate while increasing the energy density per unit volume of the secondary battery.

(Middle class)
The intermediate layer is a layer placed between the positive electrode substrate and the positive electrode mixture 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 mixture layer. The composition of the intermediate layer is not particularly limited and may include, for example, a binder and a conductive agent.

(Positive electrode mixture layer)
The positive electrode mixture layer is a layer formed by the positive electrode mixture. This positive electrode mixture contains phosphorus. The positive electrode mixture further contains a positive electrode active material and, as necessary, other optional components such as conductive agents, binders, thickeners, and fillers. The positive electrode mixture layer is usually formed on the surface of the positive electrode substrate by coating and drying the positive electrode mixture paste.

The positive electrode active material can be appropriately selected from known positive electrode active materials. Examples of positive electrode active materials for lithium secondary batteries include lithium transition metal composite oxides having an α- _NaFeO2 crystal structure, lithium transition metal composite oxides having a spinel crystal structure, polyanion compounds, chalcogen compounds, sulfur, and the like. Examples of lithium transition metal composite oxides having 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 Examples include _γ Co _β Al _(1-x-γ-β) ]O ₂ (0 ≤ x < 0.5, 0 < γ, 0 < β, 0.5 < γ + β < 1). Examples of lithium transition metal composite oxides having a spinel-type crystal structure include Li _x Mn ₂ O ₄ and Li _x Ni _γ Mn _(2-γ) O _4. Examples of polyanion compounds include LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , and Li ₂ CoPO ₄ F. 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 anions of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode mixture layer, one of these materials may be used alone, or two or more may be used in mixture form.

The positive electrode active material is usually in the form of 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. Setting the average particle size of the positive electrode active material above the lower limit makes it easier to manufacture or handle. Setting the average particle size of the positive electrode active material below the upper limit improves the electronic conductivity of the positive electrode composite layer. When a composite of the positive electrode active material and other materials is used, the average particle size of the composite is considered the average particle size of the positive electrode active material. "Average particle size" refers to the value at which the volume-based integrated distribution, calculated according to JIS-Z-8819-2 (2001), is 50%, based on the particle size distribution measured by laser diffraction/scattering on a dilution obtained by diluting particles with a solvent, in accordance with JIS-Z-8825 (2013).

To obtain powder with a predetermined particle size, grinders and classifiers are used. Grinding methods include, for example, using mortars, ball mills, sand mills, vibrating ball mills, planetary ball mills, jet mills, counter-jet mills, swirling airflow jet mills, or sieves. Wet grinding, using water or organic solvents such as hexane, can also be employed during grinding. For classification, sieves and air-powered classifiers are used as needed, both dry and wet.

The content of the positive electrode active material in the positive electrode mixture layer is preferably 50% to 99% by mass, more preferably 70% to 98% by mass, and even more preferably 80% to 95% by mass. 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 in the positive electrode mixture layer.

The phosphorus element contained in the positive electrode mixture is preferably present in the positive electrode mixture in the form of phosphorus oxoacid or a derivative obtained from the above phosphorus oxoacid. That is, it is preferable that the positive electrode mixture contains phosphorus oxoacid or a derivative thereof. The above phosphorus oxoacid refers to a compound having a structure in which a hydroxyl group (-OH) and an oxy group ₍ =O) are bonded to a phosphorus atom. Examples of the above phosphorus oxoacid include phosphoric acid ( _H3PO4 ), phosphonic acid ( _H3PO3 ), phosphinic acid ( _{H3PO2 )} , pyrophosphate ( _H4P2O7 ), _{polyphosphate , etc.} , with phosphonic acid being more preferred among these. Examples of derivatives obtained from the above phosphorus oxoacid include phosphorus oxoates and phosphorus oxoacid esters. In this way, by containing phosphorus oxoacid or a derivative thereof in the positive electrode mixture, a good film containing phosphorus atoms is easily formed on the positive electrode surface. Furthermore, the formation of a film containing the above-mentioned phosphorus atoms on the positive electrode surface promotes the formation of a uniform and good film derived from compound a on the negative electrode.

In the spectrum of the positive electrode mixture layer (positive electrode mixture) obtained by the above-mentioned X-ray photoelectron spectroscopy, the P2p peak position is preferably 135 eV or lower. Furthermore, this peak position is preferably 131 eV or higher, more preferably 132 eV or higher, and even more preferably 133 eV or higher.

The P2p peaks appearing in the above range are peaks of phosphorus atoms derived from phosphorus oxoacids such as phosphonic acid. In other words, the above P2p peaks indicate that phosphorus atoms derived from phosphorus oxoacids are present on the surface of the positive electrode mixture, and that these phosphorus atoms form a film on the positive electrode surface. The formation of this film containing phosphorus atoms on the positive electrode surface further suppresses the decomposition of the non-aqueous electrolyte on the positive electrode surface. Furthermore, the formation of such a film promotes the formation of a uniform and good film on the negative electrode. Note that there may be P2p peaks outside the above range in the above spectrum. P2p peaks appearing in the range where the binding energy is 135 eV or higher are, for example, peaks of phosphorus atoms derived from phosphorus fluoride.

The conductive agent is not particularly limited as long as it is a material that has electrical conductivity. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and Ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. The conductive agent can take the form of powder or fiber. One of these materials may be used alone as the conductive agent, or two or more may be used in mixture form. These materials may also be used in composite form. For example, a composite material of carbon black and CNTs may be used. Among these, carbon black is preferred from the viewpoint of electronic conductivity and coating properties, and acetylene black is particularly preferred.

The content of the conductive agent in the positive electrode mixture layer is preferably 1% by mass or more and 10% by mass or less, and 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.

Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

The binder content in the positive electrode mixture layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By keeping the binder content within the above range, the positive electrode active material can be stably maintained.

Examples of thickening agents include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. If the thickening agent has a functional group that reacts with lithium, etc., this functional group may be deactivated beforehand by methylation or the like.

The filler is not particularly limited. Examples of 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 aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, 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, mineral resource-derived materials such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof.

The positive electrode mixture layer may contain typical nonmetallic elements such as B, N, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, phosphorus elements (e.g., phosphorus oxoacid or its derivatives), conductive agents, binders, thickeners, and fillers.

[Negative electrode]
The negative electrode has a negative electrode active material layer. The negative electrode may further have a negative electrode substrate and an intermediate layer disposed between the negative electrode substrate and the negative electrode active material layer. The configuration of the intermediate layer is not particularly limited and can be selected from, for example, the configurations exemplified in the positive electrode above.

The negative electrode substrate is electrically conductive. Suitable materials for the negative electrode substrate include metals such as copper, nickel, stainless steel, nickel-plated steel, or their alloys, as well as carbonaceous materials. Among these, stainless steel, copper, or copper alloys are preferred. Examples of negative electrode substrates include foil, vapor-deposited film, mesh, and porous materials, with foil being preferred from a cost perspective. Therefore, stainless steel foil, copper foil, or copper alloy foil are preferred 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 to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, it is possible to increase the strength of the negative electrode substrate while increasing the energy density per unit volume of the secondary battery.

The negative electrode active material layer contains lithium metal. Lithium metal is a component that functions as the negative electrode active material. Lithium metal may exist as pure lithium metal consisting substantially only of lithium elements, or as a lithium alloy containing other metallic elements. These are collectively referred to as "lithium metal." Examples of lithium alloys include lithium gold alloy, lithium tin alloy, lithium silver alloy, lithium zinc alloy, lithium calcium alloy, lithium aluminum alloy, lithium magnesium alloy, and lithium indium alloy. Lithium alloys may also contain multiple metallic elements other than lithium.

The negative electrode active material layer may be a layer consisting substantially only of lithium metal. The lithium metal content in the negative electrode active material layer may be 90% by mass or more, 99% by mass or more, or 100% by mass. A lithium metal content in the negative electrode active material layer above the above lower limit can further increase the energy density of the secondary battery.

The negative electrode active material layer may be a lithium metal foil (including lithium alloy foil). The negative electrode active material layer may also be a non-porous layer (solid layer). The average thickness of the negative electrode active material layer is preferably 5 μm to 600 μm, more preferably 10 μm to 400 μm, and even more preferably 30 μm to 200 μm. By setting the average thickness of the negative electrode active material layer within the above range, both high energy density and manufacturability of the negative electrode active material layer can be achieved.

[Separator]
The separator can be appropriately selected from known separators. Examples of separators include a separator consisting only of a base layer, or a separator in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both sides of the base layer. Examples of the base layer shape of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of liquid retention of non-aqueous electrolytes. As for the material of the base layer of the separator, polyolefins such as polyethylene and polypropylene are preferred from the viewpoint of shutdown function, and polyimide and aramid are preferred from the viewpoint of oxidative degradation resistance. A composite material of these resins may also be used as the base layer of the separator.

The heat-resistant particles contained in the heat-resistant layer preferably have a mass reduction of 5% or less when heated from room temperature to 500°C in an air atmosphere of 1 atmosphere, and more preferably have a mass reduction of 5% or less when heated from room temperature to 800°C. Inorganic compounds are examples of materials with a mass reduction of less than the predetermined amount. 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 aluminosilicates; 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 materials such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. These inorganic compounds may be used individually or in combination, or two or more may be used in mixture form. Among these inorganic compounds, silicon dioxide, aluminum oxide, or aluminosilicates are preferred from the viewpoint of safety for energy storage elements.

The porosity of the separator is preferably 80 volume% or less from the viewpoint of strength, and preferably 20 volume% or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value and means the measurement value obtained using a mercury porosimeter.

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

[Non-aqueous electrolytes]
The non-aqueous electrolyte contains compound a. A non-aqueous electrolyte solution may be used as the non-aqueous electrolyte. The non-aqueous electrolyte solution contains a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent. In addition to the non-aqueous solvent and the electrolyte salt, the non-aqueous electrolyte solution may contain additives. Compound a may be included in the non-aqueous electrolyte as an electrolyte salt or as an additive. Compound a is included in at least one of the electrolyte salt and the additive.

As the non-aqueous solvent, it can be appropriately selected from known non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonates, linear carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, and nitriles. As the non-aqueous solvent, compounds in which some of the hydrogen atoms contained in these compounds are substituted with halogens may also be used.

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

Examples of linear carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate (TFEMC), and bis(trifluoroethyl) carbonate. Among these, DMC and TFEMC are preferred.

It is preferable to use a cyclic carbonate or a linear carbonate as the non-aqueous solvent, and it is more preferable to use a cyclic carbonate and a linear carbonate in combination. Using a cyclic carbonate can promote the dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. Using a linear carbonate can keep the viscosity of the non-aqueous electrolyte low. When using a cyclic carbonate and a linear carbonate in combination, the volume ratio of the cyclic carbonate to the linear carbonate (cyclic carbonate: linear carbonate) is preferably in the range of 5:95 to 50:50, for example.

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

Lithium salts include inorganic lithium salts such as _LiPF₂₆ , lithium difluorophosphate (LiDFP), lithium monofluorophosphate, _LiBF₄ , _LiClO₄ , and LiN( _SO₂F ) _₂ ; lithium oxalate salts such as lithium bis(oxalate) borate (LiBOB), lithium difluorooxalate borate (LiDFOB), lithium difluorobis(oxalate) phosphate (LiFOP), and lithium tetrafluorooxalate phosphate; and _LiSO₃CF₃ , LiN( _SO₂CF₃ ) _₂ , LiN( _{SO₂C₂F₅} ) _{₂ ,} LiN( _SO₂CF₃ ) _{( SO₂C₄F ₹ )} , LiC( _{SO₂CF₃ ) ₃ , and} LiC _{( SO₂C₂F₅ ) .} Examples include lithium salts having halogenated hydrocarbon groups of _{the third} order. Among these, inorganic lithium salts are preferred, and _LiPF6 is more preferred. The above-mentioned lithium difluorophosphate (LiDFP), lithium monofluorophosphate, lithium difluorooxalate borate (LiDFOB), lithium difluorobis(oxalate) phosphate (LiFOP), and lithium tetrafluorooxalate phosphate are compound a as electrolyte salts. Thus, compound a may be used as an electrolyte salt.

The electrolyte salt content in the non-aqueous electrolyte is preferably 0.1 mol/dm³ to ^2.5 mol/dm³ at 20°C and ¹ atm, more preferably 0.3 mol/dm³ to ^2.0 mol/dm³, even more preferably 0.5 mol/ ^dm³ to ^1.7 mol/ ^dm³ , and particularly preferably 0.7 mol/dm³ to 1.5 mol/dm³ at 20°C and ^{1 atm} . By setting the electrolyte salt content within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

Compound a may be used as an electrolyte salt as described above, or as an additive. Compound a as an additive contains oxygen, fluorine, and at least one of phosphorus and boron. Preferred compounds a include lithium phosphate containing lithium, oxygen, and fluorine, lithium oxalate containing lithium, boron, and fluorine, and lithium oxalate containing lithium, phosphorus, and fluorine. Among these, lithium difluorophosphate (LiDFP), lithium monofluorophosphate, lithium difluorooxalate borate (LiDFOB), lithium difluorobis(oxalate) phosphate (LiFOP), and lithium tetrafluorooxalate phosphate are more preferred, with lithium difluorophosphate (LiDFP) or lithium difluorooxalate borate (LiDFOB) being even more preferred. Among compound a, lithium phosphate containing lithium, oxygen, and fluorine is preferred because it delays the occurrence of internal short circuits. In this way, because the non-aqueous electrolyte contains the above compound a, a good film derived from the above compound a is easily formed on the surface of the negative electrode.

The non-aqueous electrolyte may contain other additives in addition to compound a above. Examples of these other additives include halogenated carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); oxalates such as lithium bis(oxalate)borate (LiBOB); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partially halogenated compounds of the aforementioned aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, succinic anhydride, and anhydride. Glutaric acid, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic acid anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2- Examples of additives include dioxo-1,3,2-dioxathiolane, 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propensultone, 1,3-propanesultone, 1,4-butanesultone, 1,4-butensultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, and tetrakithtrimethylsilyl titanate. These additives may be used individually or in combination of two or more.

The content of compound a in the non-aqueous electrolyte is preferably 0.01% to 10% by mass, more preferably 0.1% to 7% by mass, even more preferably 0.2% to 6% by mass, and particularly preferably 0.3% to 5% by mass, relative to the total mass of the non-aqueous electrolyte. By setting the content of the compound in the non-aqueous electrolyte within the above range, a coating derived from compound a on the negative electrode is more easily formed uniformly and well.

The total content of compound a and the other additives in the non-aqueous electrolyte is preferably 0.01% to 10% by mass, more preferably 0.1% to 9% by mass, even more preferably 0.2% to 8% by mass, and particularly preferably 0.3% to 7% by mass, relative to the total mass of the non-aqueous electrolyte. By setting the total content of compound a and the other additives within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and to further improve safety.

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

The solid electrolyte can be selected from any material that has ionic conductivity, such as lithium, sodium, and calcium, and is solid at room temperature (e.g., 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 secondary batteries include _Li₂S - _P₂S₅ , LiI- _Li₂S - _{P₂S₅ , and Li₁₀Ge} - _P₂S₁₂ .

The shape of the non-aqueous electrolyte energy storage element in this embodiment is not particularly limited, and examples include cylindrical batteries, prismatic batteries, flat batteries, coin-type batteries, button-type batteries, and the like.
Figure 1 shows a non-aqueous electrolyte energy storage element 1 as an example of a rectangular battery. Note that the figure is a transparent view of the inside of the container. An electrode body 2 having a positive electrode and a negative electrode wound around a separator 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 electrode terminal 5 via a negative electrode lead 51.

<Configuration of the energy storage device>
The non-aqueous electrolyte energy storage element of this embodiment can be mounted as an energy storage unit (battery module) composed of multiple non-aqueous electrolyte energy storage elements 1 in power supplies for automobiles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), power supplies for electronic devices such as personal computers and communication terminals, or power storage power supplies. In this case, it is sufficient that the technology of the present invention is applied to at least one of the non-aqueous electrolyte energy storage elements included in the energy storage unit.
An energy storage device according to one embodiment of the present invention comprises two or more non-aqueous electrolyte energy storage elements and one or more non-aqueous electrolyte energy storage elements according to the above embodiment (hereinafter referred to as the "second embodiment"). In the energy storage device according to the second embodiment, the technology according to one embodiment of the present invention may be applied to at least one non-aqueous electrolyte energy storage element included in the energy storage device according to the above embodiment of the present invention, and it may comprise one non-aqueous electrolyte energy storage element according to the above embodiment of the present invention and one or more non-aqueous electrolyte energy storage elements not relating to the above embodiment of the present invention, or it may comprise two or more non-aqueous electrolyte energy storage elements according to the above embodiment of the present invention. Figure 2 shows an example of an energy storage device 30 according to the second embodiment, which further comprises energy storage units 20, each comprising two or more electrically connected non-aqueous electrolyte energy storage elements 1. The energy storage device 30 may include busbars (not shown) for electrically connecting two or more non-aqueous electrolyte energy storage elements 1, busbars (not shown) for electrically connecting two or more energy storage units 20, etc. The energy storage unit 20 or the energy storage device 30 may include a condition monitoring device (not shown) for monitoring the state of one or more non-aqueous electrolyte energy storage elements.

<Manufacturing method for non-aqueous electrolyte energy storage elements>
The method for manufacturing the non-aqueous electrolyte energy storage element of this embodiment can be appropriately selected from known methods. This manufacturing method, for example, comprises preparing a positive electrode having a positive electrode mixture containing a phosphorus element, preparing a negative electrode containing lithium metal, and preparing a non-aqueous electrolyte containing compound a.

Preparing a positive electrode having a positive electrode mixture containing phosphorus may also be considered as manufacturing a positive electrode having a positive electrode mixture containing phosphorus. The positive electrode can be manufactured, for example, by applying a positive electrode mixture paste directly to a positive electrode substrate or via an intermediate layer, and then drying it. The positive electrode mixture paste contains phosphorus. The positive electrode mixture layer further contains a positive electrode active material and optional components such as a conductive agent, binder, thickener, and filler, which constitute the positive electrode mixture.

The phosphorus element in the positive electrode mixture paste is preferably in the form of phosphorus oxoacid, and among phosphorus oxoacids, phosphonic acid is more preferred. The phosphorus element in the positive electrode mixture paste being in the above form facilitates the formation of a good film containing phosphorus atoms on the positive electrode surface. Furthermore, the formation of such a phosphorus-containing film on the positive electrode surface promotes the formation of a uniform and good film derived from compound a on the negative electrode.

The phosphorus oxoacid content is preferably 0.1% to 1.0% by mass, more preferably 0.2% to 0.8% by mass, and even more preferably 0.25% to 0.6% by mass, relative to the total mass of the positive electrode paste. By setting the phosphorus oxoacid content within the above range, a good coating is easily formed on both the positive and negative electrodes.

Preparing a negative electrode containing lithium metal may also mean fabricating a negative electrode containing lithium metal. The fabrication of the negative electrode may involve, for example, bonding a foil-like negative electrode active material layer containing lithium metal directly to a negative electrode substrate or via an intermediate layer.

Preparing a non-aqueous electrolyte containing compound a may also be interpreted as preparing a non-aqueous electrolyte containing compound a. The preparation of a non-aqueous electrolyte can be carried out, for example, by mixing a non-aqueous solvent, an electrolyte salt (which may contain compound a), and an additive (which may contain compound a). At least one of the electrolyte salt and the additive contains compound a.

The method for manufacturing the non-aqueous electrolyte energy storage element may include, in addition to preparing a positive electrode having the phosphorus element-containing positive electrode mixture described above, preparing a negative electrode containing lithium metal, and preparing a non-aqueous electrolyte containing compound a, forming an electrode body in which the positive electrode and negative electrode are alternately superimposed by stacking or winding them with a separator in between, housing the positive electrode and negative electrode (electrode body) in a container, and injecting the non-aqueous electrolyte into the container. After injection, the non-aqueous electrolyte energy storage element can be obtained by sealing the injection port.

<Other Embodiments>
Furthermore, the non-aqueous electrolyte energy storage element of the present invention is not limited to the above embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and a part of the configuration of one embodiment may be replaced with the configuration of another embodiment or known technology. In addition, a part of the configuration of one embodiment may be deleted. Also, known technology may be added to the configuration of one embodiment.

In the above embodiment, the case in which the non-aqueous electrolyte energy storage element is used as a rechargeable non-aqueous electrolyte secondary battery (e.g., a lithium secondary battery) was described, but the type, shape, dimensions, capacity, etc., of the non-aqueous electrolyte energy storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double-layer capacitors, or capacitors such as lithium-ion capacitors.

In the above embodiment, an electrode body in which a positive electrode and a negative electrode are stacked with a separator in between has been described, but the electrode body does not need to have a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other, with a non-conductive layer formed on the positive electrode mixture layer or the negative electrode active material layer.

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

[Example 1]
(Fabrication of the positive electrode)
As the positive electrode active material, a lithium transition metal composite oxide was used in which the molar ratio of lithium (Li) to the transition metal (Me) (Li/Me) was 1.33, and the transition metal (Me) was nickel (Ni) and manganese (Mn), with a Ni:Mn molar ratio of 1:2. The positive electrode active material was mixed in a mass ratio on a solid basis to the ratio of the above positive electrode active material: polyvinylidene fluoride (PVDF): acetylene black (AB): phosphonic acid = 92.5-z:3.0:4.5:z (z=0.5), and an appropriate amount of N-methylpyrrolidone (NMP) was added as a dispersant to adjust the viscosity and prepare a positive electrode mixture paste. The positive electrode paste was coated onto one side of an aluminum foil with an average thickness of 15 μm, which served as the positive electrode substrate, dried, and pressed to produce a positive electrode with the positive electrode mixture layer in place. The coating amount of the cathode mixture layer on the fabricated cathode was 26.5 mg/ ^cm² , and the porosity was 40%. The fabricated cathode was rectangular in shape with a width of 30 mm and a length of 40 mm.

(Fabrication of the negative electrode)
A lithium metal plate measuring 31 mm in width, 42 mm in length, and 600 μm in thickness was used as the negative electrode. A stainless steel negative electrode substrate measuring 31 mm in width and 5 mm in length was attached to only one end of the lithium metal plate in the longitudinal direction.

(Preparation of non-aqueous electrolytes)
A saturated solution was prepared by mixing FEC and TFEMC in a volume ratio of 30:70 in a non-aqueous solvent, dissolving _LiPF6 as an electrolyte salt at a concentration of ^1.0 mol/dm³, and then adding lithium difluorophosphate (LiDFP), compound a, as an additive at a concentration of approximately 0.5% by mass relative to the total mass of the non-aqueous electrolyte. The above saturated solution was obtained as the non-aqueous electrolyte.

(Fabrication of non-aqueous electrolyte energy storage elements)
A microporous membrane made of polyolefin was used as a separator. An electrode body was fabricated by stacking the positive electrode and the negative electrode with this separator in between. This electrode body was placed in a container made of a metal-resin composite film, the non-aqueous electrolyte was injected into the container, and then the container was sealed by heat welding to obtain a non-aqueous electrolyte energy storage element in the form of a pouch cell.

[Example 2 and Comparative Examples 1 to 4]
Non-aqueous electrolyte energy storage elements of Example 2 and Comparative Examples 1 to 4 were fabricated in the same manner as in Example 1, except that the amount of phosphonic acid mixed in the positive electrode paste z and the type of additive compound a of the non-aqueous electrolyte were changed as shown in Table 1.

[Reference Examples 1 to 4]
Non-aqueous electrolyte energy storage elements of Reference Examples 1 to 4 were fabricated in the same manner as in Example 1, except that the type of negative electrode active material, the amount of phosphonic acid mixed in the positive electrode paste, and the type of additive in the non-aqueous electrolyte were changed as shown in Table 1. In the fabrication of the negative electrodes of Reference Examples 1 to 4, a negative electrode paste was prepared by mixing graphite:SBR:CMC in a mass ratio of 96.7:2.1:1.2 on a solid basis, with water as a dispersant. This negative electrode paste was coated onto one side of a copper foil, which was the negative electrode substrate, and the negative electrode was fabricated by drying and pressing. The coating amount of the negative electrode active material layer of the fabricated negative electrode was 22 mg/ ^cm² , and the porosity was 35%. The fabricated negative electrode was rectangular in shape with a width of 32 mm and a length of 42 mm.

The following tests were performed on each of the non-aqueous electrolyte energy storage elements in the Examples, Comparative Examples, and Reference Examples.

(Initial charge/discharge)
Of the obtained non-aqueous electrolyte energy storage elements, the non-aqueous electrolyte energy storage elements of Examples 1 and 2 and Comparative Examples 1 to 4 were charged with a constant current of 0.1C at a charging current of 4.7V under a temperature environment of 25°C, followed by constant voltage charging. The charging termination condition was when the charging current became 0.05C. After a 10-minute rest period, constant current discharge was performed at a discharge current of 0.1C with a discharge termination voltage of 2.0V. For the non-aqueous electrolyte energy storage elements of Reference Examples 1 to 4, initial charging and discharging were performed under the same conditions as above, except that the charging termination voltage was set to 4.6V. Here, 1C is defined as the current per unit area of the positive electrode, which is 6.0mA/ ^cm² .

(Charge-discharge cycle life test)
A charge-discharge cycle life test was performed on each non-aqueous electrolyte energy storage element after the initial charge-discharge described above. For each non-aqueous electrolyte energy storage element in Examples 1 and 2, and Comparative Examples 1 to 4, constant current charging was performed at a charging current of 0.2C with a charge termination voltage of 4.7V under a temperature environment of 25°C, followed by constant voltage charging. The charging termination condition was when the charging current became 0.05C. After a 10-minute pause, constant current discharge was performed at a discharge current of 0.1C with a discharge termination voltage of 2.0V. A 10-minute pause was then performed. This was repeated a predetermined number of times. For each non-aqueous electrolyte energy storage element in Reference Examples 1 to 4, the charge-discharge cycle life test was performed under the same conditions as above, except that the charge termination voltage was set to 4.6V.

(Measurement of internal resistance)
The internal resistance was measured after two initial charge-discharge cycles. Subsequently, the internal resistance was measured again after 50 charge-discharge cycle life tests. The percentage increase in internal resistance was calculated using the following formula 1, where _R1 is the internal resistance after the initial charge-discharge cycles and _R2 is the internal resistance after 50 cycles.
(R ₂ /R ₁ )×100-100...1
The above internal resistance was obtained by measuring the AC resistance at 1 kHz at room temperature while the device was discharged. A 3560 AC milliohm high tester (manufactured by HIOKI) was used for the measurement.

(Measurement of the number of cycles until an internal short circuit occurs)
The charge-discharge cycle life test described above was performed on the non-aqueous electrolyte energy storage elements of Example 1, Example 2, and Comparative Examples 1 to 4 until an internal short circuit occurred, and the number of cycles until an internal short circuit occurred was measured. The presence or absence of a short circuit was confirmed by the decrease in Coulomb efficiency due to the increase in the amount of charge during the charge-discharge cycle. Specifically, a short circuit was determined to have occurred when the amount of charge increased compared to the amount of charge in the previous cycle, and the Coulomb efficiency fell below 99%. The above "Coulomb efficiency" is the percentage of the discharge capacity to the amount of charge in that cycle.

As shown in Table 1 above, Example 1, in which phosphonic acid was mixed into the positive electrode paste and LiDFP was added to the non-aqueous electrolyte, showed a reduced rate of increase in internal resistance and an increased number of cycles until a short circuit occurred compared to Comparative Examples 1 to 3. Similarly, Example 2, in which phosphonic acid was mixed into the positive electrode paste and LiDFOB (manufactured by Sigma-Aldrich) was added to the non-aqueous electrolyte, showed a reduced rate of increase in internal resistance and an increased number of cycles until a short circuit occurred compared to Comparative Examples 2 to 4. In other words, when lithium metal is used for the negative electrode, it can be seen that by including phosphorus in the positive electrode paste and compound a containing oxygen, fluorine, and at least one of phosphorus and boron in the non-aqueous electrolyte, the rate of increase in internal resistance is reduced and the number of cycles until a short circuit occurs is increased, which is an excellent effect.

On the other hand, in Reference Example 1 of Table 1, phosphonic acid was mixed into the positive electrode paste and LiDFP was added to the non-aqueous electrolyte, but the rate of increase in internal resistance was not reduced compared to Reference Examples 2 to 4. From this, it can be seen that the above effect is specific to the case where lithium metal is used for the negative electrode, and the above effect cannot be obtained when graphite is used for the negative electrode. The reason for this is that when graphite is used for the negative electrode, LiDFP does not react selectively on the negative electrode surface as it does when lithium metal is used for the negative electrode, and both a film derived from phosphonic acid and a film derived from LiDFP are formed on the positive electrode, which is presumed to lead to a decrease in the electronic conductivity of the positive electrode and an increase in the charge transfer resistance. As a result, it is thought that the internal resistance increases significantly. Although not shown in Table 1, Reference Examples 1 to 4 had a much lower energy density than Examples 1 and 2 and Comparative Examples 1 to 4.

As described above, the non-aqueous electrolyte energy storage element was shown to have a high energy density, be able to suppress the increase in internal resistance associated with charge-discharge cycles, and be able to delay the occurrence of internal short circuits.

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

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

Claims (5)

A positive electrode having a positive electrode mixture containing phosphorus oxoacid or phosphorus oxoacid ester ,
A negative electrode containing lithium metal,
A non-aqueous electrolyte containing compound a is provided,
The above compound a is a lithium phosphate containing lithium, oxygen, and fluorine.
A non-aqueous electrolyte energy storage element comprising at least one of the following: a lithium oxalate containing the elements of lithium, boron, and fluorine, and a lithium oxalate containing the elements of lithium, phosphorus, and fluorine . The non-aqueous electrolyte energy storage element according to claim 1, wherein the compound a is lithium difluorophosphate (LiDFP) or lithium difluorooxalate borate (LiDFOB). The non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein the peak position of P2p in the spectrum of the positive electrode mixture obtained by X-ray electron spectroscopy is 135 eV or less. A power storage device comprising two or more non-aqueous electrolyte energy storage elements, and further comprising one or more non-aqueous electrolyte energy storage elements as described in any one of claims 1 to 3. A positive electrode having a positive electrode mixture containing phosphorus oxoacid or phosphorus oxoacid ester,
A negative electrode containing lithium metal,
A non-aqueous electrolyte containing compound a and
Equipped with,
The above compound a is a lithium phosphate containing lithium, oxygen, and fluorine.
Lithium oxalate containing the elements of lithium, boron, and fluorine, and lithium Non-hydrogen containing at least one lithium oxalate containing phosphorus and fluorine A method for manufacturing a desaturates energy storage element.