Non-aqueous electrolyte storage element and power storage device

Abstract

One aspect of the present invention relates to a non-aqueous electrolyte power storage element comprising a non-aqueous electrolyte, a positive electrode, and a negative electrode that contains a lithium metal and a lithium alloy containing gold, wherein: the negative electrode has a negative electrode substrate that has a metal foil and a coating layer that covers the negative electrode substrate; the metal foil has copper, nickel, or stainless steel as the main component thereof; and the coating layer has gold as the main component thereof.

Description

Technical Field

[0001] The present invention relates to a non-aqueous electrolyte storage element and a power storage device.

Background Art

[0002] Non-aqueous electrolyte secondary batteries typified by lithium-ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, and automobiles because of their high energy density. Generally, the non-aqueous electrolyte secondary battery has a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes, and is configured to charge and discharge by transferring ions between both electrodes. In addition, as non-aqueous electrolyte storage elements other than non-aqueous electrolyte secondary batteries, capacitors such as lithium-ion capacitors and electric double layer capacitors are also widely spread.

[0003] In recent years, in order to increase the capacity of non-aqueous electrolyte secondary batteries, an increase in the capacity of the negative electrode has been demanded. 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 of lithium-ion secondary batteries. That is, the theoretical capacity per mass of graphite is 372 mAh / g, while the theoretical capacity per mass of lithium metal is 3860 mAh / g, which is significantly larger. For this reason, a non-aqueous electrolyte secondary battery using lithium metal as the negative electrode active material has been proposed (see Japanese Patent Application Laid-Open No. 2011-124154).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in a non-aqueous electrolyte storage element in which the negative electrode contains lithium metal, lithium metal may deposit dendritically on the surface of the negative electrode during charging (hereinafter, lithium metal in dendritic form is referred to as "dendrite"). Since this dendrite is likely to be electrically isolated when the lithium metal on the surface of the negative electrode dissolves during subsequent discharging, the Coulombic efficiency of the non-aqueous electrolyte storage element may decrease.

[0006] The present invention has been made based on the above circumstances, and an object thereof is to provide a non-aqueous electrolyte storage element and a power storage device capable of improving the Coulombic efficiency when the negative electrode contains lithium metal.

Means for Solving the Problems

[0007] One aspect of the present invention includes a negative electrode containing a lithium alloy containing gold and lithium metal, a positive electrode, and a non-aqueous electrolyte. The negative electrode has a negative electrode substrate having a metal foil and a coating layer covering the negative electrode substrate. The metal foil is mainly composed of copper, nickel, or stainless steel, and the coating layer is mainly composed of gold. It is a non-aqueous electrolyte storage element.

[0008] Another aspect of the present invention is a power storage device including two or more non-aqueous electrolyte storage elements and one or more non-aqueous electrolyte storage elements according to one aspect of the present invention.

Effects of the Invention

[0009] According to the non-aqueous electrolyte storage element and the power storage device according to one aspect of the present invention, the Coulombic efficiency can be improved when the negative electrode contains lithium metal.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0011] First, an overview of the non-aqueous electrolyte storage element disclosed by this specification will be described.

[0012] The non-aqueous electrolyte storage element according to one aspect of the present invention includes a negative electrode containing a lithium alloy containing gold and lithium metal, a positive electrode, and a non-aqueous electrolyte. The negative electrode has a negative electrode substrate having a metal foil and a coating layer covering the negative electrode substrate. The metal foil contains copper, nickel, or stainless steel as a main component, and the coating layer contains gold as a main component.

[0013] Even though the negative electrode of the non-aqueous electrolyte storage element contains lithium metal, the Coulombic efficiency can be improved. The reason for this is not clear, but the following reasons are speculated. Generally, when lithium metal is contained in the negative electrode of a non-aqueous electrolyte storage element, since an electrolytic solution is mainly used as the non-aqueous electrolyte, the degree of freedom regarding the deposition sites of lithium metal is high, and the current tends to concentrate on sites where lithium metal is likely to deposit in response to the non-uniformity of the deposition sites. As a result, the growth of dendrites is promoted on the surface of the negative electrode during charging. These dendrites are liable to become electrically isolated when the lithium metal on the surface of the negative electrode dissolves during subsequent discharging. Since the electrically isolated lithium metal cannot contribute to charge and discharge, the Coulombic efficiency of the non-aqueous electrolyte storage element decreases. In contrast, in this non-aqueous electrolyte storage element, the deposition of dendrites can be suppressed by containing a lithium alloy containing gold in the negative electrode. In addition, by coating the negative electrode substrate with a coating layer mainly composed of gold, a lithium alloy containing gold is appropriately formed in the coating layer, and as a result, the deposition of dendrites can be further suppressed. Therefore, since the electrical isolation of dendrites is suppressed, it is considered that this non-aqueous electrolyte storage element can improve the Coulombic efficiency. Here, the "main component" means the component with the highest content, and refers to a component contained in an amount of 50% by mass or more based on the total mass.

[0014] In this non-aqueous electrolyte storage element, it is preferable that the ratio of the total molar amount of gold contained in the coating layer to the total molar amount of lithium contained in the negative electrode and the positive electrode is 0.4 or less. When the ratio of the total molar amount of gold to the total molar amount of lithium is 0.4 or less, the excessive formation of a lithium alloy containing gold in the coating layer due to the alloying reaction between gold and lithium is suppressed, so that the Coulombic efficiency can be further improved.

[0015] It is preferable that the negative electrode substrate has a lithium metal layer laminated directly or indirectly on the surface of the metal foil. By having a lithium metal layer laminated directly or indirectly on the surface of the metal foil, the amount of electricity corresponding to lithium that has become unable to contribute to charge and discharge due to electrical isolation of dendrites can be compensated for by the lithium metal layer. Therefore, the Coulomb efficiency can be further improved. Also, even when a positive electrode active material that does not initially contain lithium is used for the positive electrode, it can exhibit the function as a good non-aqueous electrolyte storage element.

[0016] It is preferable that the average thickness of the lithium metal layer is 1 μm or more and 300 μm or less. By the average thickness of the lithium metal layer being 1 μm or more, good charge and discharge cycle performance can be exhibited. Also, by the average thickness of the lithium metal layer being 300 μm or less, the mass of the non-aqueous electrolyte storage element becomes small, and the energy density can be improved.

[0017] Another aspect of the present invention is a power storage device including two or more non-aqueous electrolyte storage elements and one or more non-aqueous electrolyte storage elements according to one aspect of the present invention.

[0018] Hereinafter, a non-aqueous electrolyte storage element and a power storage element according to an embodiment of the present invention will be described in detail. Note that the names of the respective constituent members (each constituent element) used in each embodiment may be different from the names of the respective constituent members (each constituent element) used in the background art.

[0019] <Non-aqueous electrolyte storage element> The non-aqueous electrolyte storage element includes a negative electrode containing a lithium alloy containing gold and lithium metal, a positive electrode, and a non-aqueous electrolyte. Hereinafter, as an example of the non-aqueous electrolyte storage element, a non-aqueous electrolyte secondary battery will be described. The positive electrode and the negative electrode usually form an electrode body that is alternately stacked or wound via a separator. This electrode body is housed in a battery container, and the battery container is filled with a non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. In addition, as the battery container, a known metal container, resin container, etc. that are usually used as the container of the non-aqueous electrolyte secondary battery can be used.

[0020] The negative electrode of the non-aqueous electrolyte storage element may initially be in a form that does not contain lithium metal, or may initially be in a form that contains lithium metal. Also, the negative electrode may initially be in a form that does not contain a lithium alloy containing gold, or may initially be in a form that contains a lithium alloy containing gold. The non-aqueous electrolyte storage element in which the negative electrode initially does not contain lithium metal will be described in the first embodiment, and the form in which the negative electrode initially contains lithium metal will be described in the second embodiment.

[0021] <First Embodiment> The negative electrode of the non-aqueous electrolyte storage element according to the first embodiment of the present invention has a negative electrode substrate having a metal foil and a coating layer covering the negative electrode substrate, and initially does not contain lithium metal. Also, the positive electrode of the non-aqueous electrolyte storage element of this embodiment contains a positive electrode active material that initially contains lithium.

[0022] [Negative Electrode] The negative electrode of the non-aqueous electrolyte storage element according to the first embodiment contains a lithium alloy containing gold and lithium metal. Further, the negative electrode has a negative electrode substrate having a metal foil and a coating layer mainly composed of gold. The negative electrode of this embodiment does not initially contain lithium metal, but as a result of lithium ions being supplied from the positive electrode active material containing lithium initially during the initial charge, the negative electrode comes to contain lithium metal. In addition, when the negative electrode does not initially contain a lithium alloy containing gold, a lithium alloy containing gold is appropriately formed in the coating layer by the alloying reaction between this lithium metal and gold which is the main component of the coating layer, and as a result, the negative electrode comes to contain a lithium alloy containing gold. Thereby, the precipitation of dendrites can be suppressed. Therefore, since the electrical isolation of dendrites is suppressed, the non-aqueous electrolyte storage element can improve the Coulomb efficiency.

[0023] In the non-aqueous electrolyte storage element, the upper limit of the ratio of the total molar amount of gold contained in the coating layer to the total molar amount of lithium contained in the negative electrode and the positive electrode is preferably 0.4, more preferably 0.1, and even more preferably 0.05. When the ratio of the total molar amount of gold to the total molar amount of lithium is below the above upper limit, the excessive formation of a lithium alloy containing gold in the coating layer due to the alloying reaction between gold and lithium is suppressed, so that the Coulomb efficiency can be further improved. On the other hand, the lower limit of the ratio of the total molar amount of gold to the total molar amount of lithium is preferably 0.00001, and more preferably 0.0001. When the ratio of the total molar amount of gold to the total molar amount of lithium is above the above lower limit, a lithium alloy containing gold with an appropriate composition is formed in the coating layer by the alloying reaction between gold and lithium, so that the precipitation of dendrites is suppressed and the Coulomb efficiency can be further improved. Here, the "total molar amount of lithium contained in the negative electrode and the positive electrode" is the total molar amount of lithium present in the negative electrode active material and the positive electrode active material in the non-aqueous electrolyte storage element, and does not include lithium contained in the non-aqueous electrolyte. Further, the "total molar amount of gold" is the total number of moles of gold derived from the coating layer.

[0024] (Negative electrode substrate) The negative electrode substrate has conductivity and has a metal foil. The above metal foil has copper, nickel, or stainless steel as the main component. Further, these alloys may be used for the above metal foil. Among these, copper or a copper alloy is preferable. As the negative electrode substrate, a copper foil or a copper alloy foil is preferable. Examples of the copper foil include a rolled copper foil, an electrolytic copper foil, etc. Note that having "conductivity" means that the volume resistivity measured in accordance with JIS-H0505(1975) is 1×10 7 Ω·cm or less, and "non-conductive" means that the above volume resistivity is more than 1×10 7 Ω·cm.

[0025] The average thickness of the metal foil is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, still more preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the metal foil within the above range, while increasing the strength of the metal foil, the energy density per volume of the non-aqueous electrolyte storage element can be increased. Here, the "average thickness of the metal foil" means a value obtained by dividing the punching mass when punching out a metal foil of a predetermined area by the true density and the punching area of the metal foil. The same applies to the positive electrode substrate and the lithium metal layer described later.

[0026] (Coat layer) The coat layer has gold as the main component. The coat layer may contain silver, copper, platinum, aluminum, etc. as other components other than gold. As the lower limit of the gold content in the coat layer, 50% by mass is preferable, and 90% by mass is more preferable.

[0027] As the lower limit of the average thickness of the coat layer, 1 nm is preferable, 5 nm is more preferable, and 15 nm is still more preferable. On the other hand, as the upper limit of the average thickness of the coat layer, 1000 nm is preferable, 800 nm is more preferable, 500 nm is still more preferable, 200 nm is even more preferable, and 150 nm is particularly preferable. By setting the average thickness of the coat layer within the above range, a lithium-gold alloy with an appropriate composition is formed in the coat layer by the alloying reaction between gold and lithium, so the precipitation of dendrites can be suppressed and the Coulomb efficiency can be further improved.

[0028] [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.

[0029] The positive electrode substrate has conductivity. As the material of the substrate, metals such as aluminum, titanium, tantalum, and stainless steel or their alloys are used. Among these, aluminum and aluminum alloys are preferred in terms of the balance of potential resistance, high conductivity, and cost. Also, as the form of the positive electrode substrate, a foil, a vapor deposition film, etc. are mentioned, and a foil is preferred in terms of cost. That is, an aluminum foil is preferred as the positive electrode substrate. Note that examples of aluminum or aluminum alloy include A1085, A3003, etc. defined in JIS-H4000(2014).

[0030] The average thickness of the positive electrode substrate is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, still more preferably 8 μm or more and 30 μm or less, and particularly preferably 10 μm or more and 25 μm or less. By setting the average thickness of the positive electrode substrate within the above range, it is possible to increase the strength of the positive electrode substrate while increasing the energy density per volume of the non-aqueous electrolyte storage element.

[0031] The positive electrode active material layer is formed from a so-called positive electrode mixture containing a positive electrode active material. Also, the positive electrode mixture forming the positive electrode active material layer may contain optional components such as a conductive agent, a binder, a thickener, and a filler as necessary.

[0032] In the first embodiment, a material in which the positive electrode active material contains lithium and can occlude and release lithium ions is used. The positive electrode active material can be appropriately selected from known positive electrode active materials. For example, lithium transition metal composite oxides having an α-NaFeO2-type crystal structure, lithium transition metal composite oxides having a spinel-type crystal structure, polyanion compounds, and the like can be mentioned. Examples of the lithium transition metal composite oxide having an α-NaFeO2-type crystal structure include Li[Li x Ni 1-x O2(0≦x<0.5), Li[Li x Ni γ Co (1-x-γ) O2(0≦x<0.5, 0<γ<1), Li[Li x Co (1-x) O2(0≦x<0.5), Li[Li x Ni γ Mn (1-x-γ) O2(0≦x<0.5, 0<γ<1), Li[Li x Ni γ Mn β Co (1-x-γ-β) O2(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) O2(0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1), etc. Examples of the lithium transition metal composite oxide having a spinel-type crystal structure include Li x Mn2O4, Li x Ni γ Mn (2-γ) O4, etc. Examples of the polyanion compound include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. These materials may have their surfaces coated with other materials. Atoms or polyanions in these materials may be partially substituted with atoms or anion species composed of other elements. In the positive electrode active material layer, one of these materials may be used alone, or two or more of them may be mixed and used. In the positive electrode active material layer, one of these compounds may be used alone, or two or more of them may be mixed and used.

[0033] The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but as the lower limit, 50% by mass is preferable, 80% by mass is more preferable, and 90% by mass is even more preferable. On the other hand, as the upper limit of this content, 99% by mass is preferable, and 98% by mass is more preferable.

[0034] The conductive agent is not particularly limited as long as it is a material having conductivity. Examples of such conductive agents include carbonaceous materials; metals; conductive ceramics, etc. Examples of carbonaceous materials include graphite and carbon black. Examples of the types of carbon black include furnace black, acetylene black, ketjen black, etc. Among these, from the viewpoints of conductivity and coatability, carbonaceous materials are preferable. Among them, acetylene black and ketjen black are preferable. Examples of the shape of the conductive agent include powdery, sheet-like, fibrous, etc.

[0035] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 20% by mass or less, and more preferably 2% by mass or more and 15% by mass or less.

[0036] Examples of the binder include fluororesins (such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; polysaccharide polymers, etc.

[0037] When using a binder, the content of the binder in the positive electrode active material layer is preferably 0.5% by mass or more and 15% by mass or less, and more preferably 1% by mass or more and 10% by mass or less.

[0038] Examples of the above thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. Also, when 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.

[0039] When using a thickener, the proportion of the thickener in the entire positive electrode active material layer can be approximately 8% by mass or less, and usually it is preferably approximately 5.0% by mass or less.

[0040] The filler is not particularly limited. Examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, aluminum oxide, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate, 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 substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, mica, or artificial products thereof, etc.

[0041] When using a filler, the proportion of the filler in the entire positive electrode active material layer can be approximately 8.0% by mass or less, and usually it is preferably approximately 5.0% by mass or less.

[0042] The above intermediate layer is a coating layer on the surface of the positive electrode substrate, and by containing conductive particles such as carbon particles, the contact resistance between the positive electrode substrate and the positive electrode active material layer is reduced. The configuration of the intermediate layer is not particularly limited, and for example, it can be formed by a composition containing a resin binder and conductive particles.

[0043] The positive electrode active material layer may contain typical non-metal elements such as B, N, P, F, Cl, Br, I, typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0044] [Separator] As the separator, for example, woven fabric, non-woven fabric, porous resin film, etc. are used. Among these, from the viewpoint of strength, a porous resin film is preferable, and from the viewpoint of the liquid retention property of the non-aqueous electrolyte, non-woven fabric is preferable. As the main component of the separator, from the viewpoint of strength, polyolefins such as polyethylene and polypropylene are preferable, and from the viewpoint of oxidation decomposition resistance, polyimides, aramids, etc. are preferable. Also, these resins may be combined.

[0045] Note that an inorganic layer may be laminated between the separator and the positive electrode or the negative electrode. This inorganic layer is a porous layer also called a heat-resistant layer, etc. Also, a separator having an inorganic layer formed on one or both surfaces of a porous resin film can be used. The inorganic layer is usually composed of inorganic particles and a binder, and other components may be contained.

[0046] [Non-aqueous electrolyte] As the non-aqueous electrolyte, known non-aqueous electrolytes usually used in general non-aqueous electrolyte energy storage elements excluding inorganic solid electrolytes can be used. The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Also, as the non-aqueous electrolyte, room temperature molten salts, ionic liquids, polymer solid electrolytes, gel electrolytes, etc. can be used. Thus, the non-aqueous electrolyte energy storage element solves the problems in the case of using a non-aqueous electrolyte in which the transport rate of lithium ions in the non-aqueous electrolyte is not 1 (for example, about 0.4), the degree of freedom regarding the deposition sites of lithium metal is high, and dendrites are likely to occur. Therefore, a non-aqueous electrolyte energy storage element using an inorganic solid electrolyte in which the transport rate of lithium ions is 1 does not belong to the technical scope of the present invention.

[0047] As the non-aqueous solvent, known non-aqueous solvents commonly used as non-aqueous solvents for general non-aqueous electrolytes of power storage elements can be used. Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, esters, ethers, amides, sulfones, lactones, nitriles, etc. Among these, it is preferable to use at least a cyclic carbonate or a chain carbonate, and it is more preferable to use a cyclic carbonate and a chain carbonate in combination. When a cyclic carbonate and a chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate: chain carbonate) is not particularly limited, but it is preferably, for example, from 5:95 to 50:50.

[0048] Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), fluoropropylene carbonate, fluorobutylene carbonate, styrene carbonate, catechol carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc. Among these, EC or FEC is preferable.

[0049] Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate (TFEMC), bis(trifluoroethyl) carbonate, etc. Among these, DMC, EMC or TFEMC is preferable.

[0050] As the electrolyte salt, known electrolyte salts commonly used as electrolyte salts for general non-aqueous electrolytes of power storage elements can be used. Examples of the electrolyte salt include lithium salts, sodium salts, potassium salts, magnesium salts, onium salts, etc., and lithium salts are preferable.

[0051] Examples of the lithium salt include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, LiN(SO2F)2, and lithium salts having a hydrocarbon group in which hydrogen is substituted with fluorine, 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.

[0052] The lower limit of the concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / dm 3 more preferably 0.3 mol / dm 3 even more preferably 0.5 mol / dm 3 particularly preferably 0.7 mol / dm 3 Although not particularly limited, the upper limit is preferably 2.5 mol / dm 3 more preferably 2.0 mol / dm 3 even more preferably 1.5 mol / dm 3 even more preferably.

[0053] The non-aqueous electrolyte may contain an additive. Examples of the additive include aromatic compounds such as biphenyl, alkyl biphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran; partial halides of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, 3,5-difluoroanisole; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, 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, tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphate, tetrakis(trimethylsilyl) titanate, etc. These additives may be used alone or in combination of two or more.

[0054] The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 7% by mass or less, still more preferably 0.2% by mass or more and 5% by mass or less, and particularly preferably 0.3% by mass or more and 3% by mass or less, based on the total non-aqueous electrolyte.

[0055] [Specific Configuration of Non-aqueous Electrolyte Energy Storage Element] The shape of the energy storage element of this embodiment is not particularly limited, and examples include cylindrical batteries, pouch film batteries, square batteries, flat batteries, coin batteries, button batteries, etc.

[0056] FIG. 1 shows a rectangular non-aqueous electrolyte secondary battery 1 as an example of a non-aqueous electrolyte storage element. Note that this figure is a perspective view of the inside of the battery container. An electrode body 2 having a positive electrode and a negative electrode wound with a separator interposed therebetween is housed in a rectangular battery container 3. The positive electrode is electrically connected to a positive electrode terminal 4 via a positive electrode current collector 41. The negative electrode is electrically connected to a negative electrode terminal 5 via a negative electrode current collector 51.

[0057] According to the non-aqueous electrolyte storage element according to the first embodiment of the present invention, the precipitation of dendrites can be suppressed. Therefore, since the electrical isolation of dendrites is suppressed, the non-aqueous electrolyte storage element can improve the Coulomb efficiency when the negative electrode contains lithium metal.

[0058] <Second Embodiment> The negative electrode of the non-aqueous electrolyte storage element according to the second embodiment of the present invention has a negative electrode substrate having a metal foil and a coating layer covering the negative electrode substrate, and initially contains lithium metal. The non-aqueous electrolyte storage element according to the second embodiment has a lithium metal layer in which the negative electrode substrate is directly or indirectly laminated on the surface of the metal foil. That is, in the non-aqueous electrolyte storage element according to the second embodiment, the negative electrode substrate has a metal foil and a lithium metal layer. Thus, the non-aqueous electrolyte storage element according to the second embodiment is different from the first embodiment in that the negative electrode initially contains lithium metal. Therefore, the coating layer is coated on the surface of the lithium metal layer. By having the lithium metal layer in which the negative electrode substrate is directly or indirectly laminated on the surface of the metal foil, the amount of lithium included in the negative electrode substrate increases, and as a result, the Coulomb efficiency can be further improved. Further, even when the positive electrode does not initially contain lithium, good storage element performance can be exhibited.

[0059] The lithium metal includes, in addition to lithium alone, a lithium alloy. Examples of the lithium alloy include a lithium-copper alloy and a lithium-aluminum alloy. The lithium metal layer can be composed of a lithium metal foil, a vapor-deposited lithium metal layer, or the like.

[0060] As the lower limit of the average thickness of the lithium metal layer, 1 μm is preferable, 5 μm is more preferable, and 10 μm is even more preferable. On the other hand, as the upper limit of the average thickness of the lithium metal layer, 300 μm is preferable, 200 μm is more preferable, and 100 μm is even more preferable. By setting the average thickness of the lithium metal layer within the above range, it is possible to achieve both good charge-discharge cycle performance and high energy density of the non-aqueous electrolyte storage element.

[0061] In the negative electrode substrate of the present embodiment, an alloy layer containing a metal (such as copper), which is a component of the metal foil, and lithium may be formed between the metal foil (such as a copper foil) and the lithium metal layer.

[0062] The positive electrode of the non-aqueous electrolyte storage element according to the second embodiment can be appropriately selected from known positive electrode active materials, and a positive electrode active material not containing lithium may be used. Examples of the positive electrode active material in the present embodiment include chalcogen compounds, sulfur, etc., in addition to the positive electrode active materials containing lithium listed in the first embodiment above. Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc.

[0063] Regarding other configurations of the non-aqueous electrolyte storage element according to the second embodiment, they are the same as those of the non-aqueous electrolyte storage element according to the first embodiment.

[0064] According to the non-aqueous electrolyte storage element of the second embodiment, since the negative electrode substrate has a lithium metal layer laminated directly or indirectly on the surface of the metal foil, the amount of lithium included in the negative electrode substrate increases. As a result, when the negative electrode contains lithium metal, the Coulomb efficiency of the non-aqueous electrolyte storage element can be further improved.

[0065] <The manufacturing method of the non-aqueous electrolyte storage element> The manufacturing method of the non-aqueous 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 non-aqueous electrolyte, and a step of housing the electrode body and the non-aqueous electrolyte in a battery container. 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 laminating or winding the positive electrode and the negative electrode with a separator interposed therebetween.

[0066] In the manufacturing method of the non-aqueous electrolyte storage element according to the first embodiment, in the step of preparing the negative electrode, a coating layer is formed by sputtering, vapor deposition, plating, coating, etc. a material for the coating layer on the surface of the metal foil which is the negative electrode substrate.

[0067] In the manufacturing method of the non-aqueous electrolyte storage element according to the second embodiment, in the step of preparing the negative electrode, a lithium metal layer is laminated on the surface of the metal foil to form a negative electrode substrate. The lamination of the metal foil and the lithium metal layer can be performed by pressing or the like. Next, a coating layer is formed by sputtering, vapor deposition, plating, coating, etc. a material for the coating layer on the surface of the lithium metal layer.

[0068] The method of housing the non-aqueous electrolyte in the battery container can be appropriately selected from known methods. For example, when using a liquid non-aqueous electrolyte (also referred to as "electrolyte solution"), after injecting the electrolyte solution from the injection port formed in the battery container, the injection port may be sealed. Details of the other elements constituting the non-aqueous electrolyte storage element obtained by the manufacturing method are as described above.

[0069] As described above, in the non-aqueous electrolyte storage element according to the first embodiment, during the initial charging, lithium ions are supplied from the positive electrode active material, so that the negative electrode contains a lithium alloy containing gold and lithium metal.

[0070] [Other Embodiments] Note that the non-aqueous electrolyte storage element according to the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the gist of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Further, a part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment.

[0071] In the above embodiment, the case where the non-aqueous electrolyte storage element is used as a rechargeable non-aqueous electrolyte secondary battery (for example, a lithium secondary battery) has been described. However, the type, shape, dimensions, capacity, etc. of the non-aqueous electrolyte storage element are arbitrary. The non-aqueous electrolyte storage element of the present invention can also be applied to various non-aqueous electrolyte secondary batteries, electric double layer capacitors, or capacitors such as lithium ion capacitors.

[0072] The present invention can also be realized as a power storage device including a plurality of the above non-aqueous electrolyte power storage elements. Further, a battery pack can be configured by using one or more non-aqueous electrolyte power storage elements (cells) of the present invention, and a power storage device can be configured by using this battery pack. A power storage device according to an embodiment of the present invention includes two or more non-aqueous electrolyte power storage elements and one or more non-aqueous electrolyte power storage elements according to the above embodiment of the present invention (hereinafter referred to as "3rd embodiment"). For at least one non-aqueous electrolyte power storage element included in the power storage device according to the 3rd embodiment, the technology according to an embodiment of the present invention may be applied. It may include one non-aqueous electrolyte power storage element according to the above embodiment of the present invention and one or more non-aqueous electrolyte power storage elements not according to the above embodiment of the present invention, or may include two or more non-aqueous electrolyte power storage elements according to the above embodiment of the present invention. Fig. 2 shows an embodiment of the power storage device according to the 3rd embodiment. In Fig. 2, a power storage device 30 according to the 3rd embodiment includes a plurality of electrically connected power storage units 20. Each power storage unit 20 includes a plurality of electrically connected non-aqueous electrolyte power storage elements 1. The above power 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). Further, the above power storage device can be used for various power source devices such as engine starting power source devices, auxiliary machine power source devices, and uninterruptible power supply devices (UPSs).

[0073] The power storage device 30 may include a bus bar (not shown) that electrically connects two or more non-aqueous electrolyte power storage elements 1 and a bus bar (not shown) that electrically connects two or more power storage units 20. The power storage unit 20 or the power storage device 30 may include a state monitoring device (not shown) that monitors the state of one or more non-aqueous electrolyte power storage elements.

Examples

[0074] Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to the following examples.

[0075] [From Example 1 to Example 7 and from Comparative Example 1 to Comparative Example 6] (Fabrication of the negative electrode) As the metal foil constituting at least a part of the negative electrode substrate, a copper foil with an average thickness of 10 μm was prepared. For Examples 1 to 4 and Comparative Examples 2 to 5, the coating layer shown in Table 1 was formed on one side of the above copper foil. For Examples 5 to 7 and Comparative Example 6, after laminating lithium metal with the average thickness described in Table 2 on the above copper foil to form a lithium metal layer constituting the negative electrode substrate, in Examples 5 to 7, the coating layer shown in Table 2 was formed on the surface of the above lithium metal layer. All of the negative electrodes thus obtained were rectangular in shape with a width of 30 mm and a length of 40 mm.

[0076] (Formation of the coating layer) When the material of the coating layer was gold (Au) or tin (Sn), a coating layer was formed on the surface of the negative electrode substrate by the following procedure using the sputtering method. As the sputtering device, JEOL's MAGNETRON SPUTTERING DEVICE (JUC-5000) was used, and pure Au or Sn with a purity of 99.99% was used as the target. The height from the surface of the negative electrode substrate to the target was set to 25 mm, the coating current was set to 10 mA, and gold or tin was sputtered on the surface of the negative electrode substrate. Also, the average thickness of the coating layer was adjusted by adjusting the coating time. All of the above operations were performed in a dry room. When the material of the coating layer was silver (Ag) or zinc oxide (ZnO), a coating layer was formed on the surface of the negative electrode substrate by the following procedure using the coating method. As the above silver material, Dotaite D550 manufactured by Fujikura Kasei Co., Ltd. was prepared. As the above zinc oxide material, zinc oxide particles with a particle size of 20 nm were prepared. Using N-methylpyrrolidone as the dispersion medium, a coating layer paste containing the above silver or zinc oxide material: polyvinylidene fluoride = 95:5 by mass ratio was prepared and coated on the surface of the negative electrode substrate using an applicator. Then, the dispersion medium was volatilized by drying at 100 °C for 30 minutes. All of the above operations were performed in a dry room.

[0077] (Fabrication of the positive electrode) As the positive electrode active material, having an α-NaFeO2 type crystal structure, Li 1+α Me 1-αA lithium transition metal composite oxide represented by O2 (where Me is a transition metal) was used. Here, the molar ratio of Li to Me, Li / Me, was 1.33, and Me consisted of Ni and Mn and contained them in a molar ratio of Ni:Mn = 0.33:0.67.

[0078] Using N-methylpyrrolidone (NMP) as a dispersion medium, a positive electrode paste containing the above positive electrode active material, acetylene black (AB) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in a mass ratio of 92.5:4.5:3.0 was prepared. The positive electrode paste was coated on one side of an aluminum foil with an average thickness of 15 μm, which was the positive electrode substrate, dried, pressed, cut, and 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 was prepared.

[0079] (Preparation of non-aqueous electrolyte) As a non-aqueous solvent, fluoroethylene carbonate (FEC) and 2,2,2-trifluoroethyl methyl carbonate (TFEMC) were used. Then, LiPF6 was dissolved in a mixed solvent mixed at a volume ratio of FEC:TFEMC = 30:70 at a concentration of 1 mol / dm 3 to obtain a non-aqueous electrolyte.

[0080] (Preparation of non-aqueous electrolyte storage element) An electrode body was prepared by laminating the above positive electrode and the above negative electrode via a separator. This electrode body was housed in a container, the above non-aqueous electrolyte was injected therein, and then sealed by heat welding to obtain a non-aqueous electrolyte storage element (secondary battery) of Example 1, which was a pouch cell.

[0081] (Initial charge and discharge) For each of the obtained non-aqueous electrolyte storage elements, initial charge and discharge cycles were performed under the following conditions at 25°C. As the first charge, constant current and constant voltage charging was carried out with a charge amount of 0.1C and a charge cut-off voltage of 4.6V. The end condition of charging was until the charging current reached 0.05C. Thereafter, a rest period of 10 minutes was provided. Then, as the first discharge, constant current discharge was carried out with a discharge current of 0.1C and a discharge cut-off voltage of 2.0V, and then a rest period of 10 minutes was provided. The charge and discharge of the second cycle was performed under the same conditions as the above first charge and discharge, and the discharge capacity (mAh / g) per mass of the positive electrode active material was calculated based on the discharge capacity of the second cycle and defined as the "positive electrode discharge capacity of the second cycle". Note that the current value of 1C was 270 mA / g per mass of the positive electrode active material.

[0082] (Coulombic efficiency of the second cycle) The percentage of the discharge capacity of the second cycle with respect to the charge amount of the second cycle in the above initial charge and discharge was determined as the "Coulombic efficiency (%) of the second cycle".

[0083] (Positive electrode discharge capacity after charge and discharge cycle test) For the non-aqueous electrolyte storage elements according to Examples 5 to 7 and Comparative Example 6 after the above initial charge and discharge, the following charge and discharge cycle test was further performed. 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 end condition of charging was until the charging current reached 0.05C. Thereafter, a rest period of 10 minutes was provided. Then, constant current discharge was carried out with a discharge current of 0.1C and a discharge cut-off voltage of 2.0V, and then a rest period of 10 minutes was provided. This charge and discharge was repeated 120 cycles, and the discharge capacity (mAh / g) per mass of the positive electrode active material was calculated based on the discharge capacity of the 120th cycle and defined as the "positive electrode discharge capacity after 120 cycles".

[0084] (Evaluation of dendrite precipitation after the first charge) Regarding the surface of the negative electrode after the first charge, the presence or absence of dendrite deposition was visually determined. Further, regarding the surface of the negative electrode after the first charge, observation was carried out using JSM-7001F manufactured by JEOL Ltd. as a field emission scanning electron microscope (FE-SEM). The acceleration voltage was set to 1 kV. Fig. 4 shows an image obtained by scanning electron microscope (SEM) observation of Example 1 after the first charge, and Fig. 5 shows an image obtained by SEM observation of Comparative Example 1 after the first charge.

[0085] (Amount of lithium contained in the positive electrode) The amount of lithium (mmol) contained in the positive electrode was determined by calculation of the molar amount of all lithium contained in the positive electrode active material in the positive electrode active material layer of 12 cm above. 2

[0086] (Amount of lithium alloyed with gold) The amount of lithium (mmol) alloyed with gold was determined by calculating the molar amount of alloyed lithium assuming that all gold contained in the coating layer of the negative electrode of 12 cm above forms Li 2 Au4. 15

[0087] (Identification of the negative electrode phase after the first charge) Regarding each of the negative electrodes after the first charge according to the above Examples and Comparative Examples, X-ray diffraction measurement was carried out using an X-ray diffractometer (manufactured by Rigaku Corporation, model name: MiniFlex II). Here, the X-ray source was CuKα, the acceleration voltage and current were 30 kV and 15 mA respectively, the sampling width was 0.01 deg, the scanning time was 15 minutes (scan speed was 5.0), the divergence slit width was 0.625 deg, the receiving slit width was open, and the scattering slit was 8.0 mm. In addition, the sample was encapsulated in an argon atmosphere, and a sample stage sealed with an O-ring was used. Fig. 3 shows X-ray diffraction (XRD) diagrams of the negative electrodes of Example 1, Comparative Example 1 and Comparative Example 2 in the range of 2θ = 10° to 80°.

[0088] ​​The results such as the amount of lithium contained in the positive electrode, the amount of lithium alloyed with gold, the ratio of the total molar amount of gold contained in the coating layer to the total molar amount of lithium contained in the negative electrode and the positive electrode, the Coulomb efficiency of the second cycle, the positive electrode discharge capacity of the second cycle in the initial charge and discharge, the positive electrode discharge capacity of the 120th cycle after the charge and discharge cycle test, and the dendrite precipitation evaluation after the first charge are shown in Table 1 and Table 2. For Examples 1 to 4 and Comparative Examples 1 to 7, they are shown in Table 1, and for Examples 5 to 7 and Comparative Example 6, they are shown in Table 2. Here, the "Au / Li molar ratio in the energy storage element system" in Table 1 and Table 2 is the ratio of the total molar amount of gold contained in the coating layer to the total molar amount of lithium contained in the negative electrode and the positive electrode. In Examples 1 to 4 and Comparative Example 2 above, the total molar amount of lithium contained in the negative electrode and the positive electrode is the "amount of lithium contained in the positive electrode" above. In Examples 5 to 7 above, it is the sum of the "amount of lithium contained in the positive electrode" and the molar amount corresponding to the lithium metal layer constituting the negative electrode substrate. The amount of lithium contained in the non-aqueous electrolyte is not included here.

[0089] [Table 1]

[0090] [Table 2]

[0091] As shown in Table 1, in Examples 1 to 4 having a negative electrode containing a lithium alloy containing gold and lithium metal and having a negative electrode substrate having a metal foil and a coating layer mainly composed of gold covering the negative electrode substrate, the Coulomb efficiency of the second cycle was good. Also, as shown in the X-ray diffraction pattern of the negative electrode after the first charge in FIG. 3, in the negative electrode of Example 1 having a coating layer mainly composed of gold, an XRD pattern of a lithium alloy containing lithium metal and gold was observed after the first charge. On the other hand, in the negative electrode of Comparative Example 1 not having a coating layer mainly composed of gold, no XRD pattern of a lithium alloy containing gold was observed, indicating that a lithium alloy containing gold was not formed. Further, in the negative electrode of Comparative Example 2 in which the coating layer mainly composed of gold was excessively coated and the Coulomb efficiency in the second cycle was 0%, an XRD pattern of a copper alloy containing gold and a lithium alloy containing gold was observed after the first charge. From this, it is considered that in Comparative Example 2, by excessively coating the coating layer mainly composed of gold, the lithium metal that reversibly dissolves and deposits disappeared, resulting in the inability to charge and discharge. Furthermore, from the dendrite precipitation evaluation in Table 1 and the SEM images of the surfaces of the negative electrodes of Example 1 and Comparative Example 1 after the first charge shown in FIGS. 4 and 5, it can be seen that the precipitation of dendrites is suppressed by coating the negative electrode substrate with a coating layer mainly composed of gold. From these results, it is considered that in this non-aqueous electrolyte storage element, the Coulomb efficiency is improved by suppressing the precipitation of dendrites in the negative electrode.

[0092] From the results of Comparative Example 3, Comparative Example 4, and Comparative Example 5 in Table 1, when having a coating layer mainly composed of tin, silver, or zinc oxide, the Coulomb efficiency in the second cycle was lower than that of the example having a coating layer mainly composed of gold. This is presumably as follows. Tin, silver, or zinc oxide alloy-react with lithium metal in the same way as gold, and a lithium alloy containing tin, silver, or zinc is formed in the coating layer. Although tin, silver, or zinc oxide all have an affinity with lithium metal in the state before alloying, when they become a lithium alloy, unlike the lithium alloy containing gold in the example, they no longer have an affinity with lithium metal, resulting in a decrease in Coulomb efficiency.

[0093] Comparing Examples 5 to 7 and Comparative Example 6 in which the negative electrode substrate shown in Table 2 has a metal foil and a lithium metal layer, Examples 5 to 7 having a coating layer mainly composed of gold were excellent not only in the Coulomb efficiency at the second cycle but also in the positive electrode discharge capacity after 120 cycles. Further, in Examples 5 to 7, the Coulomb efficiency at the 120th cycle was also 100%.

[0094] As a result of the above, it was shown that the non-aqueous electrolyte storage element can improve the Coulomb efficiency when the negative electrode contains lithium metal.

Industrial Applicability

[0095] The present invention can be applied to electronic devices such as personal computers and communication terminals, non-aqueous electrolyte storage elements used as power sources for automobiles, and storage devices.

Explanation of Signs

[0096] 1 Non-aqueous electrolyte storage element 2 Electrode body 3 Battery container 4 Positive electrode terminal 41 Positive electrode current collector 5 Negative electrode terminal 51 Negative electrode current collector 20 Storage unit 30 Storage device

Claims

1. A non-aqueous electrolyte storage element comprising: a negative electrode containing a lithium alloy containing gold and lithium metal; a positive electrode; and a non-aqueous electrolyte. The negative electrode has a negative electrode substrate having a metal foil and a coating layer covering the negative electrode substrate. The metal foil contains copper, nickel, or stainless steel as a main component. The coating layer contains gold as a main component.

2. The non-aqueous electrolyte storage element according to Claim 1, wherein the ratio of the total molar amount of gold contained in the coating layer to the total molar amount of lithium contained in the negative electrode and the positive electrode is 0.4 or less.

3. The non-aqueous electrolyte storage element according to Claim 1 or Claim 2, wherein the negative electrode substrate has a lithium metal layer laminated directly or indirectly on the surface of the metal foil.

4. The non-aqueous electrolyte storage element according to Claim 3, wherein the average thickness of the lithium metal layer is 1 μm or more and 300 μm or less.

5. A power storage device comprising two or more non-aqueous electrolyte storage elements and one or more non-aqueous electrolyte storage elements according to any one of Claims 1 to 4. ​

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