JP7501110B2 - Non-aqueous electrolyte storage element - Google Patents

Description

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

Non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, as well as automobiles, due to their high energy density. The non-aqueous electrolyte secondary batteries generally have a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes, and 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 storage elements.

In recent years, there has been a demand for higher-capacity negative electrodes in order to increase the capacity of non-aqueous electrolyte secondary batteries. Lithium metal has a significantly larger discharge capacity per active material mass than graphite, which is currently widely used as the negative electrode active material in lithium-ion secondary batteries. For this reason, non-aqueous electrolyte secondary batteries using lithium metal as the negative electrode active material have been proposed (see JP 2011-124154 A).

JP 2011-124154 A

However, in non-aqueous electrolyte storage elements that use lithium metal as the negative electrode active material, lithium metal may precipitate in a dendritic form on the surface of the negative electrode during charging (hereinafter, lithium metal in a dendritic form is referred to as a "dendrite"). When this dendrite grows, it may penetrate the separator and come into contact with the positive electrode, causing a short circuit.

The present invention was made based on the above circumstances, and aims to provide a non-aqueous electrolyte storage element that is highly effective in suppressing the occurrence of short circuits.

One aspect of the present invention, which has been made to solve the above problems, is a nonaqueous electrolyte storage element comprising a negative electrode having a negative electrode active material layer, a positive electrode having a positive electrode active material layer, a nonaqueous electrolyte containing a nonaqueous solvent, a separator interposed between the negative electrode active material layer and the positive electrode active material layer, and a first inorganic particle layer interposed between the separator and the negative electrode active material layer, in which the negative electrode active material layer contains lithium metal and the nonaqueous solvent contains a fluorinated carbonate.

The present invention provides a non-aqueous electrolyte storage element that is highly effective in preventing the occurrence of short circuits.

FIG. 1 is an external perspective view showing a nonaqueous electrolyte electricity storage element according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing an electricity storage device formed by assembling a plurality of nonaqueous electrolyte electricity storage elements according to one embodiment of the present invention.

First, we will provide an overview of the nonaqueous electrolyte storage element disclosed in this specification.

A nonaqueous electrolyte storage element according to one aspect of the present invention comprises a negative electrode having a negative electrode active material layer, a positive electrode having a positive electrode active material layer, a nonaqueous electrolyte containing a nonaqueous solvent, a separator interposed between the negative electrode active material layer and the positive electrode active material layer, and a first inorganic particle layer interposed between the separator and the negative electrode active material layer, wherein the negative electrode active material layer contains lithium metal and the nonaqueous solvent contains a fluorinated carbonate.

The nonaqueous electrolyte storage element has a high effect of suppressing the occurrence of short circuits. The reason for this is unclear, but the following reason is presumed. The nonaqueous electrolyte of the nonaqueous electrolyte storage element contains a fluorinated carbonate as a nonaqueous solvent, and thus a coating having a high content of lithium fluoride, which is a reductive decomposition product of the fluorinated carbonate, is formed on the surface of the negative electrode active material layer. This coating having a high content of lithium fluoride is uniform and stable, and the current distribution is maintained uniformly, so that the formation of dendrites is suppressed. In addition, the negative electrode active material layer contains lithium metal, and the first inorganic particle layer is interposed between the negative electrode active material layer and the separator, so that the resistance to the blockage of the separator pores due to compression caused by the volume change of lithium metal is increased. Therefore, the current distribution at the interface between the lithium metal and the separator is maintained uniformly, so that the formation of dendrites is suppressed. In this way, the nonaqueous electrolyte storage element has an excellent effect of suppressing the formation of dendrites, and thus has a high effect of suppressing the occurrence of short circuits.

It is preferable that the fluorinated carbonate contains a fluorinated cyclic carbonate. By containing a fluorinated cyclic carbonate, the effect of suppressing the formation of dendrites in the nonaqueous electrolyte storage element can be further enhanced.

It is preferable that the content of the fluorinated cyclic carbonate in the nonaqueous solvent is 10% by volume or more and 50% by volume or less. By having the content of the fluorinated cyclic carbonate in the nonaqueous solvent in the above range, the effect of suppressing the formation of dendrites in the nonaqueous electrolyte storage element can be further enhanced.

It is preferable to further have a second inorganic particle layer interposed between the separator and the positive electrode active material layer. By further having a second inorganic particle layer interposed between the separator and the positive electrode active material layer, clogging of the separator due to decomposition products of the nonaqueous electrolyte on the surface of the positive electrode active material layer during long-term charge-discharge cycles is suppressed by the porous second inorganic particle layer. As a result, it is believed that the current distribution at the interface between the positive electrode and the separator is maintained uniform. Therefore, by further having a second inorganic particle layer interposed between the separator and the positive electrode active material layer, the effect of suppressing the occurrence of short circuits can be further improved.

The nonaqueous electrolyte storage element according to one embodiment of the present invention will be described in detail below. Note that the names of the components (elementary components) used in each embodiment may differ from the names of the components (elementary components) used in the background art.

<Non-aqueous electrolyte electricity storage element>
The nonaqueous electrolyte storage element according to one embodiment of the present invention includes a negative electrode, a positive electrode, and a nonaqueous electrolyte. Hereinafter, a nonaqueous electrolyte secondary battery will be described as an example of a nonaqueous electrolyte storage element. The positive electrode and the negative electrode are usually stacked or wound alternately with a separator interposed therebetween to form an electrode body. The electrode body is housed in a case, and the case is filled with a nonaqueous electrolyte. The nonaqueous electrolyte is interposed between the positive electrode and the negative electrode. In addition, as the case, a known metal case, a resin case, or the like that is usually used as a case for a nonaqueous electrolyte secondary battery can be used.

[Negative electrode]
The negative electrode includes a negative electrode substrate and a negative electrode active material layer laminated directly or indirectly on at least one surface of the negative electrode substrate. The negative electrode may include an intermediate layer disposed between the negative electrode substrate and the negative electrode active material layer.

(Negative electrode substrate)
The negative electrode substrate has electrical conductivity. Metals such as copper, nickel, stainless steel, and nickel-plated steel, or alloys thereof, are used as the material of the negative electrode substrate. Among these, copper or a copper alloy is preferred. Examples of the negative electrode substrate include foils and vapor-deposited films, and foils are preferred from the viewpoint of cost. Therefore, copper foil or a copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil. Incidentally, "electrically conductive" means that the volume resistivity measured in accordance with JIS-H0505 (1975) is 1×10 ⁷ Ω·cm or less, and "non-electrically conductive" means that the volume resistivity is more than 1×10 ⁷ Ω·cm.

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 volume of the nonaqueous electrolyte secondary battery. The "average thickness of the substrate" refers to the value obtained by dividing the punched mass when a substrate of a given area is punched out by the true density and punched area of the substrate.

(Negative Electrode Active Material Layer)
The negative electrode active material layer contains lithium metal as a negative electrode active material. When the negative electrode active material contains lithium metal, the discharge capacity per active material mass can be improved. The lithium metal includes lithium simple substance as well as lithium alloys. Examples of the lithium alloy include lithium aluminum alloys, lithium magnesium alloys, and lithium indium alloys. The negative electrode active material layer containing lithium metal can be manufactured by cutting foil-like lithium metal into a predetermined shape or forming it into a predetermined shape by rolling, vapor deposition, or the like.

Furthermore, the negative electrode active material layer may contain elements such as Na, K, Ca, Fe, Mg, Si, and N.

The lower limit of the lithium metal content in the negative electrode active material is preferably 80% by mass, more preferably 90% by mass, and even more preferably 95% by mass. On the other hand, the upper limit of this content may be 100% by mass.

[Positive electrode]
The positive electrode has a positive electrode substrate and a positive electrode active material layer. The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer is laminated directly or via an intermediate layer along at least one surface of the positive electrode substrate.

The positive electrode substrate is conductive. Metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof, are used as the material of the substrate. Among these, aluminum and aluminum alloys are preferred in terms of the balance between potential resistance, high conductivity, and cost. The form of the positive electrode substrate may be foil, vapor deposition film, etc., and foil is preferred in terms of cost. In other words, aluminum foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, etc., as specified in JIS-H4000 (2014).

The positive electrode active material layer is formed from a so-called positive electrode mixture that contains a positive electrode active material. In addition, the positive electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler as necessary.

The positive electrode active material can be appropriately selected from known positive electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the positive electrode active material for a lithium ion secondary battery. Examples of the positive electrode active material 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, sulfur, and the like. Examples of lithium transition metal composite oxides having an α-NaFeO2 _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) 2} ]O ₂ (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1), etc. Examples of lithium transition metal composite oxides having a spinel crystal structure include Li _x Mn ₂ O ₄ and Li _x Ni _γ Mn _(2-γ) O ₄ , etc. 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, etc. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, and molybdenum dioxide, etc. Atoms or polyanions in these materials may be partially substituted with atoms or anion species consisting of other elements. The surface of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more of them may be mixed. In the positive electrode active material layer, one of these compounds may be used alone, or two or more of them may be mixed. The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but the lower limit is preferably 50% by mass, more preferably 80% by mass, and even more preferably 90% by mass. On the other hand, the upper limit of this content is preferably 99% by mass, and more preferably 98% by mass.

The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include carbonaceous materials, metals, conductive ceramics, and the like. Examples of carbonaceous materials include graphitized carbon, non-graphitized carbon, graphene-based carbon, and the like. Examples of non-graphitized carbon include carbon nanofiber, pitch-based carbon fiber, carbon black, and the like. Examples of carbon black include furnace black, acetylene black, ketjen black, and the like. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), fullerene, and the like. Examples of the conductive agent include powder and fiber. As the conductive agent, one of these materials may be used alone, or two or more types may be mixed and used. These materials may also be used in combination. For example, a material in which carbon black and CNT are combined may be used. Among these, carbon black is preferred from the viewpoints of electronic conductivity and coatability, and acetylene black is preferred among them.

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, and more preferably 3% by mass or more and 9% by mass or less. By setting the content of the conductive agent in the above range, the energy density of the nonaqueous electrolyte secondary battery can be increased.

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

Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. In addition, if the thickener has a functional group that reacts with lithium, it is preferable to deactivate this functional group in advance by methylation or the like.

The filler is not particularly limited. Examples of the filler 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 ion crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and man-made products thereof.

The intermediate layer is a coating layer on the surface of the positive electrode substrate, and contains conductive particles such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. As with the negative electrode, the configuration of the intermediate layer is not particularly limited, and can be formed, for example, from a composition containing a resin binder and conductive particles.

[Non-aqueous electrolyte]
The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous solvent includes a fluorinated carbonate. The non-aqueous electrolyte is not limited to a liquid. That is, the non-aqueous electrolyte is not limited to a liquid, but includes a solid or gel electrolyte.

(Non-aqueous solvent)
The non-aqueous solvent contains a fluorinated carbonate. By containing the fluorinated carbonate, a coating having a high content of lithium fluoride, which is a reductive decomposition product of the fluorinated carbonate, is formed on the surface of the negative electrode active material layer. This coating having a high content of lithium fluoride is uniform and stable, and the current distribution is maintained uniform, so that the formation of dendrites is suppressed. The fluorinated carbonate refers to a compound in which some or all of the hydrogen atoms of a carbonate are substituted with fluorine atoms. One or more types of fluorinated carbonate can be used. Examples of the fluorinated carbonate include fluorinated cyclic carbonates and fluorinated chain carbonates.

Examples of the fluorinated cyclic carbonate include fluorinated ethylene carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate, fluorinated propylene carbonates such as fluoromethylethylene carbonate, and fluorinated butylene carbonates such as trifluoroethylethylene carbonate. Among these, fluorinated ethylene carbonate is preferred, and fluoroethylene carbonate is more preferred. The fluoroethylene carbonate has high oxidation resistance and is highly effective in suppressing side reactions (such as oxidative decomposition of nonaqueous solvents) that may occur during charging and discharging of nonaqueous electrolyte storage elements. In addition, fluoroethylene carbonate is reductively decomposed at a relatively noble potential to quickly form a stable coating on lithium metal, thereby suppressing continuous reductive decomposition of nonaqueous electrolytes on lithium metal.

Examples of fluorinated chain carbonates include trifluoroethyl methyl carbonate (TFEMC) and bis(trifluoroethyl) carbonate (FDEC).

It is preferable that the fluorinated carbonate contains a fluorinated cyclic carbonate. When the fluorinated carbonate contains a fluorinated cyclic carbonate, the effect of suppressing the formation of dendrites in the nonaqueous electrolyte storage element can be further enhanced. It is more preferable to use a fluorinated cyclic carbonate and a fluorinated chain carbonate in combination. By using a fluorinated chain carbonate, the viscosity of the nonaqueous electrolyte can be kept low. When a fluorinated cyclic carbonate and a fluorinated chain carbonate are used in combination, the volume ratio of the fluorinated cyclic carbonate to the fluorinated chain carbonate (fluorinated cyclic carbonate:fluorinated chain carbonate) is, for example, preferably in the range of 5:95 to 80:20, more preferably in the range of 20:80 to 70:30, even more preferably in the range of 30:70 to 60:40, and even more preferably in the range of 40:60 to 50:50.

The non-aqueous solvent may contain an organic solvent other than a fluorinated carbonate. Examples of the other organic solvent include a chain carbonate other than a fluorinated chain carbonate, a cyclic carbonate other than a fluorinated cyclic carbonate, an ester, an ether, an amide, a lactone, a nitrile, a sulfone, and a sulfite.

Examples of chain carbonates other than the above fluorinated chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diphenyl carbonate, etc. Examples of cyclic carbonates other than the above fluorinated cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, styrene carbonate, catechol carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc.

Examples of the above esters include methyl 3,3,3-trifluoropropionate, 2,2,2-trifluoroethyl acetate, tris(2,2-difluoroethyl) phosphate, and tris(2,2,2-trifluoroethyl) phosphate.

Examples of the above ethers include 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, methyl heptafluoropropyl ether, and methyl nonafluorobutyl ether.

As the organic solvent other than the fluorinated carbonate, a chain carbonate other than the fluorinated chain carbonate is preferable from the viewpoint of keeping the viscosity of the non-aqueous electrolyte low.

The lower limit of the content of the fluorinated carbonate in the nonaqueous solvent is preferably 10% by volume, and more preferably 30% by volume. The upper limit of the content of the fluorinated carbonate is preferably 100% by volume, and more preferably 50% by volume. When the content of the fluorinated carbonate in the nonaqueous solvent is within the above range, the effect of suppressing the formation of dendrites in the nonaqueous electrolyte storage element can be further enhanced.

The lower limit of the content of the fluorinated cyclic carbonate in the nonaqueous solvent is preferably 10% by volume, more preferably 20% by volume. The upper limit of the content of the fluorinated cyclic carbonate is preferably 50% by volume, more preferably 40% by volume. When the content of the fluorinated cyclic carbonate in the nonaqueous solvent is within the above range, the effect of suppressing the formation of dendrites in the nonaqueous electrolyte storage element can be further enhanced. In addition, continuous reduction and decomposition of the nonaqueous electrolyte on the lithium metal is suppressed, and the amount of gas generated as a decomposition product is reduced.

The lower limit of the content of the fluorinated solvent in the nonaqueous solvent is preferably 50% by volume, more preferably 70% by volume, even more preferably 90% by volume, and even more preferably 99% by volume. It is particularly preferable that the content of the fluorinated solvent in the total nonaqueous solvent is 100% by volume. By constituting the nonaqueous solvent substantially only from a fluorinated solvent, it is possible to further increase the oxidation resistance of the nonaqueous electrolyte. Note that the fluorinated solvent refers to a nonaqueous solvent that includes a fluorinated carbonate (a fluorinated chain carbonate and a fluorinated cyclic carbonate) and has a fluorine atom in the molecule, such as a fluorinated ester or a fluorinated ether.

(Electrolyte Salt)
The electrolyte salt may be any known electrolyte salt that is commonly used as an electrolyte salt for a general non-aqueous electrolyte, such as lithium salt, sodium salt, potassium salt, magnesium salt, onium salt, etc., with lithium salt being preferred.

Examples of the lithium salt include inorganic lithium salts such as _LiPF6 , _{LiPO2F2 , LiBF4} , _LiClO4 , _and LiN( _SO2F ) ₂ , and lithium salts having _a fluorohydrocarbon group such as _LiSO3CF3 , LiN( _SO2CF3 ) ₂ , LiN _{( SO2C2F5} ) ₂ , LiN _{( SO2CF3} )( _{SO2C4F9 )} , LiC( _{SO2CF3 )3, and LiC(SO2C2F5)3 . Among these} , inorganic lithium salts are preferred, _{and LiPF6 is more preferred} .

The lower limit of the content of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol dm ^-3 , more preferably 0.3 mol dm ^-3 , and even more preferably 0.5 mol dm ^-3 , while the upper limit is not particularly limited, but is preferably 3 mol dm ^-3 , and more preferably 2 mol dm ^-3 .

(Other additives, etc.)
The non-aqueous electrolyte may contain other additives as long as they do not impair the effects of the present invention. Examples of the other additives include various additives contained in general non-aqueous electrolytes. Examples of the other additives include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the 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; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, and itaconic anhydride. , cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, etc. These additives may be used alone or in combination of two or more.

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

The non-aqueous electrolyte can usually be obtained by adding and dissolving each component, such as the electrolyte salt, in the non-aqueous solvent.

[Separator]
The separator is interposed between the negative electrode active material layer and the positive electrode active material layer. The form of the separator may be, for example, a woven fabric, a nonwoven fabric, a porous resin film, or the like, and a porous resin film is preferred. The material of the separator is usually a resin. As the resin material 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 oxidation decomposition resistance. A material obtained by combining these resins may be used as the separator.

The average thickness of the separator is preferably, for example, 3 μm or more and 50 μm or less, and more preferably 6 μm or more and 25 μm or less. When the average thickness of the separator is equal to or more than the above lower limit, the occurrence of short circuits can be further suppressed. On the other hand, when the average thickness of the separator is equal to or less than the above upper limit, the energy density of the nonaqueous electrolyte storage element can be increased. The average thickness of the separator is the average value of thicknesses measured at any 10 points.

[Inorganic particle layer]
The first inorganic particle layer is interposed between the separator and the negative electrode active material layer. The first inorganic particle layer is a porous layer containing inorganic particles. The first inorganic particle layer may contain other components such as a binder. The first inorganic particle layer may be formed integrally on the surface of the separator, or may be formed on the surface of the negative electrode active material layer. The first inorganic particle layer is interposed between the negative electrode active material layer and the separator, thereby increasing the resistance to blocking of the separator pores due to pressure caused by volume change of lithium metal. Therefore, the current distribution at the interface between the lithium metal and the separator is maintained uniform, and the formation of dendrites is suppressed. In this way, the nonaqueous electrolyte storage element has an excellent effect of suppressing the formation of dendrites, and as a result, has a high effect of suppressing the occurrence of short circuits.

It is preferable to further have a second inorganic particle layer interposed between the separator and the positive electrode active material layer. The second inorganic particle layer has the same configuration as the first inorganic particle layer. In addition, the second inorganic particle layer may be formed integrally on the surface of the separator, or may be formed on the surface of the positive electrode active material layer. By further having a second inorganic particle layer interposed between the separator and the positive electrode active material layer, clogging of the separator due to decomposition products of the non-aqueous electrolyte on the surface of the positive electrode active material layer during long-term charge/discharge cycles is suppressed by the porous second inorganic particle layer. As a result, it is believed that the current distribution at the interface between the positive electrode and the separator is maintained uniform. Therefore, by further having a second inorganic particle layer interposed between the separator and the positive electrode active material layer, the effect of suppressing the occurrence of short circuits can be further improved.

Specific types of materials constituting the inorganic particles include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, barium titanate, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate; hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide; 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 and barium fluoride; covalent crystals such as silicon and diamond; mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. As inorganic particles, those with lower density are preferred from the viewpoint of weight reduction. As inorganic particles, these substances may be used alone or in combination, or two or more of them may be used.

The content of inorganic particles in the inorganic particle layer is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 99% by mass or less, and even more preferably 70% by mass or more and 98% by mass or less.

When the inorganic particle layer contains a binder, the content of the binder in the inorganic particle layer is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less.

The upper limit of the average particle size of the inorganic particles is preferably 10 μm, more preferably 8 μm, and even more preferably 5 μm. The lower limit of the average particle size is not particularly limited, and may be, for example, 5 nm or 50 nm, or may be 500 nm. In addition, the inorganic particles having a small particle size have a larger number of pores per area of the inorganic layer than those having a large particle size, which increases the current distribution, thereby making it possible to more effectively achieve the effects of the present invention. Here, the "average particle size" refers to the value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50%, 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 in accordance with JIS-Z-8825 (2013).

The binder for the inorganic particle layer can be the same as the binder for the positive electrode active material layer.

The average thickness of the inorganic particle layer is preferably, for example, 2 μm or more and 10 μm or less, and more preferably 3 μm or more and 6 μm or less. When the average thickness of the inorganic particle layer is equal to or more than the above lower limit, the occurrence of short circuits can be further suppressed. On the other hand, when the average thickness of the inorganic particle layer is equal to or less than the above upper limit, a high energy density can be maintained. The average thickness of the inorganic particle layer is the average value of thicknesses measured at any 10 points.

The average thickness of the separator and inorganic particle layer as a whole is preferably, for example, 5 μm or more and 60 μm or less, and more preferably 9 μm or more and 30 μm or less. When the average thickness of the separator and inorganic particle layer as a whole is equal to or more than the above lower limit, the occurrence of a short circuit can be further suppressed. On the other hand, when the average thickness of the separator and inorganic particle layer as a whole is equal to or less than the above upper limit, the energy density of the nonaqueous electrolyte storage element can be increased. The average thickness of the separator and inorganic particle layer as a whole is the average value of thicknesses measured at any 10 points.

[Specific Configuration of Nonaqueous Electrolyte Storage Element]
The shape of the nonaqueous electrolyte storage element of this embodiment is not particularly limited, and examples thereof include a cylindrical battery, a pouch film battery, a square battery, a flat battery, a coin battery, and a button battery.

Figure 1 shows a square nonaqueous electrolyte secondary battery as an example of a nonaqueous electrolyte storage element 1. Note that this figure is a see-through view of the inside of the case. An electrode body 2 having a positive electrode and a negative electrode wound with a separator sandwiched between them is housed in a square case 3. The positive electrode is electrically connected to a positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to a negative electrode terminal 5 via a negative electrode lead 51.

[Method of manufacturing nonaqueous electrolyte storage element]
The method for manufacturing the nonaqueous electrolyte storage element according to the present embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, a step of preparing an electrode body, a step of preparing a nonaqueous electrolyte, and a step of housing the electrode body and the nonaqueous electrolyte in a case. The step of preparing the electrode body includes a step of preparing a positive electrode and a negative electrode, and a step of forming the electrode body by stacking or winding the positive electrode and the negative electrode with a separator interposed therebetween.

The process of housing the nonaqueous electrolyte in the case can be appropriately selected from known methods. For example, when using a liquid nonaqueous electrolyte (also called "electrolyte"), the electrolyte can be injected through an injection port formed in the case, and then the injection port can be sealed. Details of each element constituting the nonaqueous electrolyte storage element obtained by this manufacturing method are as described above.

[Other embodiments]
The nonaqueous electrolyte storage element according to the present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the scope of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and part of the configuration of one embodiment may be replaced with the configuration of another embodiment or a well-known technique. Furthermore, part of the configuration of one embodiment may be deleted. Also, a well-known technique may be added to the configuration of one embodiment.

In the above embodiment, the nonaqueous electrolyte storage element is mainly a nonaqueous electrolyte secondary battery, but other nonaqueous electrolyte storage elements may be used. Examples of other nonaqueous electrolyte storage elements include capacitors (electric double layer capacitors, lithium ion capacitors), etc. Examples of nonaqueous electrolyte secondary batteries include lithium ion nonaqueous electrolyte secondary batteries.

The present invention can also be realized as an electricity storage device having a plurality of the above-mentioned nonaqueous electrolyte electricity storage elements. In addition, an electricity storage unit can be formed by using one or more nonaqueous electrolyte electricity storage elements (cells) of the present invention, and this electricity storage unit can be used to form an electricity storage device. The above-mentioned electricity storage device can be used as a power source for automobiles such as electric vehicles (EVs), hybrid vehicles (HEVs), and plug-in hybrid vehicles (PHEVs). Furthermore, the above-mentioned electricity storage device can be used in various power supply devices such as engine starting power supply devices, auxiliary power supply devices, and uninterruptible power supplies (UPS).

Figure 2 shows an example of an energy storage device 30 in which an energy storage unit 20, which is an assembly of two or more electrically connected nonaqueous electrolyte energy storage elements 1, is further assembled. The energy storage device 30 may include a bus bar (not shown) that electrically connects two or more nonaqueous electrolyte energy storage elements 1, and a bus bar (not shown) that electrically connects two or more energy storage units 20. The energy storage unit 20 or the energy storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more nonaqueous electrolyte energy storage elements.

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

[Example 1]
(Preparation of Positive Electrode)
The positive electrode active material used was a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure and expressed as Li _1+α Me _1-α O ₂ (Me is a transition metal), where the molar ratio Li/Me of Li to Me was 1.33, and Me was composed of Ni and Mn in a molar ratio of Ni:Mn=1:2.

A positive electrode paste was prepared containing the positive electrode active material, acetylene black (AB) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in a mass ratio of 94:4.5:1.5, with N-methylpyrrolidone (NMP) as the dispersion medium. The positive electrode paste was applied to one side of an aluminum foil with an average thickness of 20 μm as the positive electrode substrate, dried, pressed, and then cut to prepare a positive electrode with a positive electrode active material layer arranged in a rectangular shape with a width of 30 mm and a length of 40 mm.

(Preparation of negative electrode)
A lithium metal foil (lithium metal 100% by mass) having an average thickness of 60 μm was laminated as a negative electrode active material layer on one side of a copper foil having an average thickness of 10 μm, which was the negative electrode substrate. After pressing, the laminate was cut into a rectangular shape having a width of 32 mm and a length of 42 mm, thereby preparing a negative electrode.

(Preparation of non-aqueous electrolyte)
_LiPF6 was dissolved at a concentration of 1 mol/ ^dm3 in a mixed solvent in which fluoroethylene carbonate (FEC) and 2,2,2-trifluoroethyl methyl carbonate (TFEMC) were mixed in a volume ratio of 30:70 to prepare a non-aqueous electrolyte.

(Separator and inorganic particle layer)
The separator used was made of polyolefin resin only and had an average thickness of 15 μm. The first inorganic particle layer and the second inorganic particle layer were each integrally formed on the surface of the separator, and the first inorganic particle layer was disposed between the separator and the negative electrode active material layer, and the second inorganic particle layer was disposed between the separator and the positive electrode active material layer. The first inorganic particle layer and the second inorganic particle layer each had an average thickness of 6 μm, and contained inorganic particles and a binder in a mass ratio of 95:5. Aluminosilicate was used as the inorganic particles.

(Preparation of non-aqueous electrolyte storage element)
The positive electrode and the negative electrode were laminated with the separator and the inorganic particle layer interposed therebetween to produce an electrode assembly, which was then housed in a case, the nonaqueous electrolyte was poured into the case, and the case was sealed to obtain a nonaqueous electrolyte storage element (secondary battery) of Example 1.

[Examples 2 to 6 and Comparative Examples 1 to 4]
Nonaqueous electrolyte storage elements of Examples 2 to 6 and Comparative Examples 1 to 4 were obtained in the same manner as in Example 1, except that the configuration of the inorganic particle layer and the composition of the nonaqueous solvent of the nonaqueous electrolyte were as shown in Table 1.

(Initial charge/discharge)
The obtained nonaqueous electrolyte storage elements were initially charged and discharged under the following conditions. At 25° C., constant current and constant voltage charging was performed with a charging current of 0.1 C and a charge end voltage of 4.6 V. The charge end condition was that the charging current was until the charging current reached 0.02 C. Then, a rest period of 10 minutes was provided. Then, constant current discharging was performed with a discharge current of 0.1 C and a discharge end voltage of 2.0 V, and then a rest period of 10 minutes was provided. This charge and discharge was performed for two cycles.

(Charge-discharge cycle test)
Next, the following charge-discharge cycle test was carried out. At 25°C, constant current and constant voltage charging was carried out with a charging current of 0.2C and a charge cut-off voltage of 4.6V. The charge was terminated until the charging current reached 0.05C. A rest period of 10 minutes was then provided. Thereafter, constant current discharging was carried out with a discharge current of 0.1C and a discharge cut-off voltage of 2.0V, followed by a rest period of 10 minutes. This charge-discharge cycle was repeated, and the number of cycles until a short circuit occurred was recorded. The results are shown in Table 1. In addition, "-" means that the corresponding component is not included.

As shown in Table 1, in the nonaqueous electrolyte storage elements of Examples 1 to 6, which had a first inorganic particle layer interposed between the separator and the negative electrode active material layer and in which the nonaqueous solvent contained a fluorinated carbonate, the number of cycles until a short circuit occurred exceeded 50, resulting in sufficient suppression of the occurrence of a short circuit. Moreover, Examples 1 and 3 to 6, which further had a second inorganic particle layer interposed between the separator and the positive electrode active material layer, showed a higher effect of suppressing the occurrence of a short circuit than Example 2, which had only the first inorganic particle layer interposed between the separator and the negative electrode active material layer.
On the other hand, Comparative Examples 1, 3, and 4, which do not have a first inorganic particle layer interposed between the separator and the negative electrode active material layer, and Comparative Example 2, which has the first inorganic particle layer but the non-aqueous solvent does not contain a fluorinated carbonate, showed low effects in suppressing the occurrence of short circuits.

The above results show that the nonaqueous electrolyte storage element has a high effect of suppressing the occurrence of short circuits.

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

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

Claims (6)

a negative electrode having a negative electrode active material layer;
a positive electrode having a positive electrode active material layer;
A non-aqueous electrolyte containing a non-aqueous solvent;
a separator interposed between the negative electrode active material layer and the positive electrode active material layer;
a first inorganic particle layer interposed between the separator and the negative electrode active material layer,
the negative electrode active material layer contains lithium metal,
the non-aqueous solvent comprises a fluorinated carbonate,
The first inorganic particle layer has an average thickness of 3 μm or more . a negative electrode having a negative electrode active material layer;
a positive electrode having a positive electrode active material layer;
A non-aqueous electrolyte containing a non-aqueous solvent;
a separator interposed between the negative electrode active material layer and the positive electrode active material layer;
a first inorganic particle layer interposed between the separator and the negative electrode active material layer;
Equipped with
the negative electrode active material layer contains lithium metal,
the non-aqueous solvent comprises a fluorinated carbonate,
The first inorganic particle layer contains inorganic particles, and the inorganic particles have an average particle size of 5 nm or more and 5 μm or less. a negative electrode having a negative electrode active material layer;
a positive electrode having a positive electrode active material layer;
A non-aqueous electrolyte containing a non-aqueous solvent;
a separator interposed between the negative electrode active material layer and the positive electrode active material layer;
a first inorganic particle layer interposed between the separator and the negative electrode active material layer;
Equipped with
the negative electrode active material layer contains lithium metal,
the non-aqueous solvent comprises a fluorinated carbonate,
The nonaqueous electrolyte storage element, wherein the fluorinated carbonate includes a fluorinated cyclic carbonate, and the content of the fluorinated cyclic carbonate in the nonaqueous solvent is 30% by volume or more and 50% by volume or less. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the fluorinated carbonate comprises a fluorinated cyclic carbonate. 5. The nonaqueous electrolyte storage element according to claim 4 , wherein the content of the fluorinated cyclic carbonate in the nonaqueous solvent is from 10% by volume to 50% by volume. 6. The nonaqueous electrolyte storage element according to claim 1, further comprising a second inorganic particle layer interposed between the separator and the positive electrode active material layer.

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