WO2022163125A1

WO2022163125A1 - Nonaqueous electrolyte power storage element, power storage device, and method for producing nonaqueous electrolyte power storage element

Info

Publication number: WO2022163125A1
Application number: PCT/JP2021/044382
Authority: WO
Inventors: 弘将村松
Original assignee: 株式会社Ｇｓユアサ
Priority date: 2021-01-26
Filing date: 2021-12-03
Publication date: 2022-08-04
Also published as: JPWO2022163125A1

Abstract

One aspect of the present invention is a nonaqueous electrolyte power storage element which is provided with: a negative electrode that comprises a negative electrode active material layer and a coat layer that covers the negative electrode active material layer; a positive electrode; and a nonaqueous electrolyte. With respect to this nonaqueous electrolyte power storage element, the negative electrode active material layer contains lithium metal, while the coat layer contains elemental tin and elemental lithium.

Description

NON-AQUEOUS ELECTROLYTE STORAGE ELEMENT, ELECTRICAL STORAGE DEVICE, AND METHOD FOR MANUFACTURING NON-AQUEOUS ELECTROLYTE STORAGE ELEMENT

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

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

In recent years, in order to increase the capacity of non-aqueous electrolyte secondary batteries, there has been a demand for higher capacity negative electrodes. Lithium metal has a remarkably large discharge capacity per active material mass compared to graphite, which is currently widely used as a negative electrode active material for lithium ion secondary batteries. That is, while the theoretical capacity per mass of graphite is 372 mAh/g, the theoretical capacity per mass of lithium metal is 3860 mAh/g, which is significantly large. For this reason, a non-aqueous electrolyte secondary battery using lithium metal as a negative electrode active material has been proposed (see Japanese Patent Application Laid-Open No. 2011-124154).

JP 2011-124154 A

However, in a non-aqueous electrolyte storage device in which the negative electrode contains lithium metal, lithium metal may be deposited in the form of dendrites on the surface of the negative electrode during charging (hereinafter, lithium metal in the form of dendrites is referred to as "dendrite"). called.). These dendrites tend to become electrically isolated due to dissolution of lithium metal on the surface of the negative electrode during subsequent discharge. When the charge/discharge cycle is repeated, the deposition and electrical isolation of the dendrite are likely to occur repeatedly, which may reduce the coulombic efficiency of the non-aqueous electrolyte storage element after the charge/discharge cycle.

The present invention has been made based on the above circumstances, and provides a non-aqueous electrolyte storage element and a storage device that can improve the coulombic efficiency after charge-discharge cycles when the negative electrode contains lithium metal. With the goal.

One aspect of the present invention includes a negative electrode having a negative electrode active material layer and a coating layer covering the negative electrode active material layer, a positive electrode, and a non-aqueous electrolyte, the negative electrode active material layer containing lithium metal, and the coating It is a non-aqueous electrolyte storage element whose layer contains tin element and lithium element.

Another aspect of the present invention comprises laminating a coating material on the surface of a negative electrode active material layer containing lithium metal, wherein the coating material contains tin metal or a compound containing tin element as a main component. A device manufacturing method.

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

According to the non-aqueous electrolyte power storage element and the power storage device according to one aspect of the present invention, when the negative electrode contains lithium metal, the coulomb efficiency after charge-discharge cycles can be improved.

FIG. 1 is a see-through perspective view showing one embodiment of a non-aqueous electrolyte storage element. FIG. 2 is a schematic diagram showing an embodiment of a power storage device configured by assembling a plurality of non-aqueous electrolyte power storage elements. FIG. 3 is an image obtained by scanning electron microscope observation of the surface of the negative electrode after the initial charge in the example. FIG. 4 is a scanning electron microscope image of the surface of the negative electrode of the comparative example after the initial charge.

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

A non-aqueous electrolyte storage element according to one aspect of the present invention includes a negative electrode having a negative electrode active material layer and a coating layer covering the negative electrode active material layer, a positive electrode, and a non-aqueous electrolyte, wherein the negative electrode active material layer is Lithium metal is included, and the coating layer includes tin element and lithium element.

The non-aqueous electrolyte storage element can improve the coulomb efficiency after charge-discharge cycles even though the negative electrode contains lithium metal. Although the reason for this is not clear, the following reasons are presumed. When lithium metal is contained in the negative electrode of the non-aqueous electrolyte storage element, dendrites may precipitate on the surface of the negative electrode during charging. In particular, when a non-aqueous electrolyte is used as the non-aqueous electrolyte, there is a high degree of freedom regarding the deposition sites of lithium metal, and the current tends to concentrate on the sites where lithium metal is likely to deposit in response to the non-uniformity of the deposition sites. . This promotes the growth of dendrites on the surface of the negative electrode during charging. These dendrites tend to become electrically isolated due to dissolution of lithium metal on the surface of the negative electrode during subsequent discharge. Repeated charge/discharge cycles tend to cause this dendrite deposition and electrical isolation to occur repeatedly. Since the electrically isolated lithium metal cannot contribute to charge/discharge, the coulombic efficiency of the non-aqueous electrolyte storage element after charge/discharge cycles decreases. In contrast, in the non-aqueous electrolyte storage element, the negative electrode active material layer containing lithium metal is covered with the coating layer containing tin element and lithium element, so that dendrite deposition can be suppressed. Therefore, repeated occurrence of dendrite deposition and electrical isolation is suppressed even if charge-discharge cycles are repeated, so the non-aqueous electrolyte storage element is considered to be able to improve coulombic efficiency after charge-discharge cycles.

In the non-aqueous electrolyte storage element, the coat layer preferably has an average thickness of 10 nm or more. By setting the average thickness of the coating layer to the above lower limit or more, the affinity between tin and lithium is improved, so that the deposition of dendrites can be suppressed and the coulomb efficiency after charge-discharge cycles can be further improved. The above-mentioned "average thickness of the coat layer" refers to a value obtained by the following method. First, a negative electrode before charge/discharge is prepared. Alternatively, when the negative electrode is prepared from a charged/discharged non-aqueous electrolyte storage element, the non-aqueous electrolyte storage element is discharged at a current of 0.1 C to the discharge cut-off voltage in normal use to be in a completely discharged state. The fully discharged non-aqueous electrolyte storage element is disassembled, and the negative electrode is taken out. The negative electrode was cut into a predetermined area, the mass and average thickness of the negative electrode were measured, and then immersed in a large excess amount of water to react lithium metal in the negative electrode active material layer with water to form lithium hydroxide in water. Dissolve. After the negative electrode active material layer is completely dissolved, the negative electrode substrate is taken out and its mass and average thickness are measured. The insoluble matter is taken out by filtration or the like, and its mass is measured. The mass of the negative electrode active material layer is obtained by subtracting the mass of the negative electrode base material and the insoluble matter from the mass of the negative electrode. The mass of the negative electrode active material layer was divided by the area of the negative electrode active material layer and the true density of the negative electrode active material layer (for example, 0.534 g/cm ³ when the negative electrode active material layer consists essentially of elemental lithium). Let the value be the "average thickness of the negative electrode active material layer". A value obtained by subtracting the average thickness of the negative electrode base material and the average thickness of the negative electrode active material layer from the average thickness of the negative electrode is defined as the “average thickness of the coat layer”. When the negative electrode active material layer and the coating layer are laminated on both sides of the negative electrode substrate, the “average thickness of the coating layer” is calculated from the average thickness of the negative electrode and the average thickness of the negative electrode substrate and the negative electrode active material layer. The value obtained by subtracting the average thickness of is further divided by 2.

The average thickness of the negative electrode active material layer is preferably 1 μm or more and 300 μm or less. When the negative electrode active material layer has an average thickness of 1 μm or more, good charge-discharge cycle performance can be exhibited. Further, since the negative electrode active material layer has an average thickness of 300 μm or less, the mass of the non-aqueous electrolyte storage element can be reduced, and the energy density can be improved. The above-mentioned "average thickness of the negative electrode active material layer" refers to the "negative electrode active material layer thickness" obtained by the above-described method when the negative electrode active material layer and the coating layer are laminated on one side of the negative electrode substrate. In the case where the negative electrode active material layer and the coating layer are laminated on both sides of the negative electrode base material, the "average thickness of the negative electrode active material layer" obtained by the above method is further increased by 2. It means the value divided by

A method for manufacturing a non-aqueous electrolyte storage element according to another aspect of the present invention comprises laminating a coating material on the surface of a negative electrode active material layer containing lithium metal, wherein the coating material contains tin metal or a tin element. A compound is the main component. The method for manufacturing the non-aqueous electrolyte storage element includes laminating a coating material on the surface of the negative electrode active material layer containing lithium metal, and the coating material is mainly composed of tin metal or a compound containing tin element, A non-aqueous electrolyte storage element can be produced in which a negative electrode active material layer containing lithium metal is coated with a coating layer containing tin element and lithium element. Therefore, in the non-aqueous electrolyte storage element manufactured by the method for manufacturing a non-aqueous electrolyte storage element, the deposition of dendrites is suppressed, so that the coulomb efficiency after charge-discharge cycles can be improved. Here, the "main component" in the coating material means the component with the highest content, and refers to a component that is contained in an amount of 99% by mass or more relative to the total mass of the coating material, and may be 100% by mass.

Another aspect of the present invention is a power storage device including two or more non-aqueous electrolyte power storage elements and one or more non-aqueous electrolyte power storage elements according to one aspect of the present invention. The power storage device can improve coulombic efficiency after charge-discharge cycles even though the negative electrode contains lithium metal.

Hereinafter, a non-aqueous electrolyte storage element, a power storage device, a method for manufacturing a non-aqueous electrolyte storage element, and other embodiments according to one embodiment of the present invention will be described in detail. Note that the name of each component (each component) used in each embodiment may be different from the name of each component (each component) used in the background art.

<Non-aqueous electrolyte storage element>
The nonaqueous electrolyte storage element includes a negative electrode having a negative electrode active material layer and a coating layer covering the negative electrode active material layer, a positive electrode, and a nonaqueous electrolyte. A non-aqueous electrolyte secondary battery will be described below as an example of the non-aqueous electrolyte storage element. The positive electrode and the negative electrode generally form an electrode body alternately stacked by lamination or winding with a separator interposed therebetween. This electrode assembly 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. As the battery container, known metal containers, resin containers, and the like, which are usually used as containers for non-aqueous electrolyte secondary batteries, can be used.

[Negative electrode]
The negative electrode of the non-aqueous electrolyte storage element has a negative electrode active material layer and a coating layer covering the negative electrode active material layer. Further, the negative electrode active material layer contains lithium metal, and the coat layer contains tin element and lithium element. Thereby, precipitation of dendrites can be suppressed. Therefore, repeated occurrence of dendrite deposition and electrical isolation is suppressed even if charge/discharge cycles are repeated, so that the non-aqueous electrolyte storage element can improve the coulomb efficiency after charge/discharge cycles.

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

The average thickness of the negative electrode substrate is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, even more preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode substrate within the above range, the energy density per volume of the non-aqueous electrolyte secondary battery can be increased while increasing the strength of the negative electrode substrate.

(Negative electrode active material layer)
The negative electrode active material layer contains a negative electrode active material. 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 mass of the active material can be improved. The above-mentioned lithium metal includes a lithium alloy as well as elemental lithium. Lithium alloys include, for example, lithium aluminum alloys, lithium silver alloys, lithium zinc alloys, lithium calcium alloys, lithium magnesium alloys, lithium indium alloys, and the like. The lithium alloy may contain multiple metal elements other than lithium. The negative electrode active material layer containing lithium metal can be composed of a lithium metal foil, a deposited lithium metal layer, or the like.

When a metal foil (e.g., copper foil) is used as the negative electrode base material, an alloy containing a metal (e.g., copper) that is a component of the metal foil and lithium is placed between the metal foil and the negative electrode active material layer that is a negative electrode active material layer. Layers may be formed.

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 layer 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.

The lower limit of the average thickness of the negative electrode active material layer is preferably 1 μm, more preferably 5 μm, and even more preferably 10 μm. On the other hand, the upper limit of the average thickness of the negative electrode active material layer is preferably 300 μm, more preferably 200 μm, and even more preferably 100 μm. By setting the average thickness of the negative electrode active material layer within the above range, both good charge/discharge cycle performance and high energy density of the non-aqueous electrolyte power storage element can be achieved.

(Coating layer)
The coat layer covers the negative electrode active material layer. The coating layer is formed using a coating material containing tin metal or a compound containing tin element. Due to the reaction between the coating material containing the tin metal or the compound containing the tin element and the lithium metal contained in the negative electrode active material layer, a reaction product containing the tin element and the lithium element is formed in the coat layer. contains tin and lithium elements. Tin metal is preferable as the tin metal or the compound containing tin element. The tin metal includes elemental tin and tin alloys, and elemental tin is preferred. In the case of tin metal, the effect of suppressing dendrite precipitation is higher than in the case of a compound containing tin element such as an oxide. The tin alloy may contain multiple metal elements other than tin.

The lower limit of the tin element content in the coat layer is preferably 95% by mass, more preferably 99% by mass.

The lower limit of the average thickness of the coat layer is preferably 10 nm, more preferably 15 nm, and even more preferably 30 nm. By setting the average thickness of the coating layer to the above lower limit or more, a reaction product containing tin element and lithium element is appropriately formed, so dendrite precipitation is suppressed and the coulomb efficiency after charge-discharge cycles is improved. can improve.

[Positive electrode]
The positive electrode has a positive electrode base material and a positive electrode active material layer disposed directly on the positive electrode base material or via an intermediate layer.

The positive electrode base material has conductivity. As the material for the positive electrode substrate, metals such as aluminum, titanium, tantalum and stainless steel, or alloys thereof are used. Among these, aluminum or an aluminum alloy is preferable from the viewpoint of potential resistance, high conductivity, and cost. Examples of the positive electrode substrate include foil, deposited film, mesh, porous material, and the like, and foil is preferable from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferable as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, A1N30, etc. defined in JIS-H-4000 (2014) or JIS-H4160 (2006).

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

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

The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer contains arbitrary components such as a conductive agent, a binder (binding agent), a thickener, a filler, etc., as required.

The positive electrode active material can be appropriately selected from known positive electrode active materials. As a positive electrode active material for lithium ion secondary batteries, a material capable of intercalating and deintercalating lithium ions is usually used. Examples of positive electrode active materials include lithium-transition metal composite oxides having an α-NaFeO ₂ type crystal structure, lithium-transition metal composite oxides having a spinel-type crystal structure, polyanion compounds, chalcogen compounds, and sulfur. Examples of lithium transition metal composite oxides having an α-NaFeO ₂ type crystal structure include Li[Li _x Ni _(1-x) ]O ₂ (0≦x<0.5), Li[Li _x Ni _γ Co _{( 1-x-γ)} ]O ₂ (0≦x<0.5, 0<γ<1), Li[Li _x Co _(1-x) ]O ₂ (0≦x<0.5), Li[ Li _x Ni _γ Mn _(1-x-γ) ]O ₂ (0≦x<0.5, 0<γ<1), Li[Li _x Ni _γ Mn _β Co _(1-x-γ-β) ] O ₂ (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1), Li[Li _x Ni _γ Co _β Al _(1-x-γ-β) ]O ₂ ( 0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1) and the like. Examples of lithium transition metal composite oxides having a spinel crystal structure include Li _x Mn ₂ O ₄ and Li _x Ni _γ Mn _(2-γ) O ₄ . Examples of _polyanion compounds include _LiFePO4 , _LiMnPO4 _, _LiNiPO4 , _{LiCoPO4, Li3V2(PO4)3} _, _Li2MnSiO4 _, _Li2CoPO4F _and _the like. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. The atoms or polyanions in these materials may be partially substituted with atoms or anionic species of other elements. These materials may be coated with other materials on their surfaces. In the positive electrode active material layer, one kind of these materials may be used alone, or two or more kinds may be mixed and used.

The positive electrode active material is usually particles (powder). The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By making the average particle size of the positive electrode active material equal to or more than the above lower limit, manufacturing or handling of the positive electrode active material becomes easy. By setting the average particle size of the positive electrode active material to the above upper limit or less, the electron conductivity of the positive electrode active material layer is improved. Note that when a composite of a positive electrode active material and another material is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material. "Average particle size" is based on JIS-Z-8825 (2013), based on the particle size distribution measured by a laser diffraction / scattering method for a diluted solution in which particles are diluted with a solvent, JIS-Z-8819 -2 (2001) means a value at which the volume-based integrated distribution calculated according to 50%.

Pulverizers, classifiers, etc. are used to obtain powder with a predetermined particle size. Pulverization methods include, for example, a method using a mortar, ball mill, sand mill, vibrating ball mill, planetary ball mill, jet mill, counter jet mill, whirling jet mill, or sieve. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane is allowed to coexist can also be used. As a classification method, a sieve, an air classifier, or the like is used as necessary, both dry and wet.

The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass or more and 99% by mass or less, more preferably 70% by mass or more and 98% by mass or less, and even more preferably 80% by mass or more and 97% by mass or less. By setting the content of the positive electrode active material within the above range, it is possible to achieve both high energy density and manufacturability of the positive electrode active material layer.

The conductive agent is not particularly limited as long as it is a conductive material. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Carbonaceous materials include graphite, non-graphitic carbon, graphene-based carbon, and the like. Examples of non-graphitic carbon include carbon nanofiber, pitch-based carbon fiber, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Graphene-based carbon includes graphene, carbon nanotube (CNT), fullerene, and the like. The shape of the conductive agent may be powdery, fibrous, or the like. As the conductive agent, one type of these materials may be used alone, or two or more types may be mixed and used. Also, these materials may be combined for use. For example, a composite material of carbon black and CNT may be used. Among these, carbon black is preferable from the viewpoint of electron conductivity and coatability, and acetylene black is particularly preferable.

The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, more preferably 1.5% by mass or more and 9% by mass or less. By setting the content of the conductive agent within the above range, the energy density of the non-aqueous electrolyte secondary battery can be increased.

Binders include, for example, fluorine resins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, polyacryl, and polyimide; ethylene-propylene-diene rubber (EPDM), sulfone Elastomers such as modified EPDM, styrene-butadiene rubber (SBR) and fluororubber; polysaccharide polymers and the like.

The content of the binder in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, more preferably 2% by mass or more and 9% by mass or less. By setting the content of the binder within the above range, the active material can be stably retained.

Examples of thickeners include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. When the thickener has a functional group that reacts with lithium or the like, the functional group may be previously deactivated by methylation or the like.

The filler is not particularly limited. Fillers include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide and aluminosilicate, magnesium hydroxide, calcium hydroxide, hydroxide Hydroxides such as aluminum, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, talc, montmorillonite, boehmite, zeolite, Mineral resource-derived substances such as apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof may be used.

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

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

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

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

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

[Non-aqueous electrolyte]
The non-aqueous electrolyte can be appropriately selected from known non-aqueous electrolytes. A non-aqueous electrolytic solution in which an electrolyte salt is dissolved in a non-aqueous solvent may be used as the non-aqueous electrolyte. As the non-aqueous electrolyte, a room-temperature molten salt, an ionic liquid, a polymer solid electrolyte, a gel electrolyte, or the like can also be used. Furthermore, an inorganic solid electrolyte can also be used. Also, these non-aqueous electrolytes may be used in combination. In the non-aqueous electrolyte storage element, when a non-aqueous electrolyte, a room temperature molten salt, an ionic liquid, a polymer solid electrolyte, a gel electrolyte, or the like is used as the non-aqueous electrolyte, the transference number of lithium ions in the non-aqueous electrolyte is 1. However, the degree of freedom of deposition sites for lithium metal is high (for example, about 0.4), so current tends to concentrate on sites where lithium metal is likely to deposit in response to the non-uniformity of the deposition sites. Furthermore, the deposition and dissolution of lithium metal destabilizes the film (SEI) on the surface of the negative electrode, and current concentrates on the sites where lithium metal is likely to deposit, promoting the growth of dendrites on the negative electrode surface during charging. On the other hand, in inorganic solid electrolytes, the transference number of lithium ions is 1, and since they are solids, there is no degree of freedom in terms of precipitation sites. Decrease in coulombic efficiency after charge/discharge cycles is less likely to occur. Therefore, when a non-aqueous electrolyte, a room temperature molten salt, an ionic liquid, a solid polymer electrolyte, a gel electrolyte, or the like is used as the non-aqueous electrolyte, dendrites are likely to precipitate, so the non-aqueous electrolyte storage element is more effective. can demonstrate.

The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Non-aqueous solvents include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphoric acid esters, sulfonic acid esters, ethers, amides, nitriles and the like. As the non-aqueous solvent, those in which some of the hydrogen atoms contained in these compounds are substituted with halogens may be used.

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

Examples of chain carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diphenyl carbonate, trifluoroethylmethyl carbonate, bis(trifluoroethyl) carbonate, and the like. Among these, EMC and DMC are preferred.

As the non-aqueous solvent, it is preferable to use a cyclic carbonate or a chain carbonate, and it is more preferable to use a combination of a cyclic carbonate and a chain carbonate. By using a cyclic carbonate, it is possible to promote the dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. By using a chain carbonate, the viscosity of the non-aqueous electrolyte can be kept low. When a cyclic carbonate and a chain carbonate are used together, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is preferably in the range of, for example, 5:95 to 70:30.

The electrolyte salt can be appropriately selected from known electrolyte salts. Lithium salt is usually used as the electrolyte salt.

Lithium salts include inorganic lithium salts such as LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ and LiN(SO ₂ F) ₂ , lithium bis(oxalate) borate (LiBOB), lithium difluorooxalate borate (LiFOB). , lithium oxalate salts such as lithium bis(oxalate) difluorophosphate ( _LiFOP ), _LiSO3CF3 , LiN ₍ _SO2CF3 ) ₂ , LiN ₍ _SO2C2F5 ) ₂ _, LiN ₍ _SO2CF3 ) (SO ₂ C ₄ F ₉ ), LiC(SO ₂ CF ₃ ) ₃ , LiC(SO ₂ C ₂ F ₅ ) ₃ and other lithium salts having a halogenated hydrocarbon group. Among these, inorganic lithium salts are preferred, and _LiPF6 is more preferred.

The content of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol/dm3 or more and 2.5 mol/dm3 or less ^, and 0.3 mol/dm3 or more and 2.0 mol/dm3 or less at ²⁰ °C and ¹ atm. It is more preferably ³ or less, more preferably 0.5 mol/dm ³ or more and 1.7 mol/dm ³ or less, and particularly preferably 0.7 mol/dm ³ or more and 1.5 mol/dm ³ or less. By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and electrolyte salt. Examples of additives include halogenated carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), lithium bis(oxalate ) oxalates such as difluorophosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene , t-amylbenzene, diphenyl ether, dibenzofuran and other aromatic compounds; 2-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene and other partial halides of the above aromatic compounds; 2,4-difluoroanisole, 2 Halogenated anisole compounds such as ,5-difluoroanisole, 2,6-difluoroanisole, 3,5-difluoroanisole; vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, anhydride Citraconic acid, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethylsulfone, diethyl Sulfone, dimethylsulfoxide, diethylsulfoxide, tetramethylenesulfoxide, diphenylsulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo- 1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propenesultone, 1,3-propanesultone, 1,4-butanesultone, 1,4-butenesultone, perfluorooctane, boric acid Tristrimethylsilyl, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate, lithium difluorophosphate and the like. These additives may be used singly or in combination of two or more.

The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass or more and 20% by mass or less, and 0.1% by mass or more and 15% by mass or less with respect to the total mass of the non-aqueous electrolyte. More preferably, it is 0.2% by mass or more and 12% by mass or less, and particularly preferably 0.3% by mass or more and 10% by mass or less. By setting the content of the additive within the above range, it is possible to improve capacity retention performance or cycle performance after high-temperature storage, or to further improve safety.

The inorganic solid electrolyte can be selected from any material that has lithium ion conductivity and is solid at room temperature (for example, 15°C to 25°C). Examples of inorganic solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, and oxynitride solid electrolytes.

Examples of sulfide solid electrolytes include Li ₂ SP ₂ S ₅ , LiI—Li ₂ SP ₂ S ₅ , Li ₁₀ Ge—P ₂ S ₁₂ and the like.

[Specific configuration of non-aqueous electrolyte storage element]
The shape of the non-aqueous electrolyte storage element of the present embodiment is not particularly limited, and examples thereof include cylindrical batteries, rectangular batteries, flat batteries, coin batteries, button batteries, and the like.

Fig. 1 shows a non-aqueous electrolyte storage element 1 as an example of a square battery. In addition, the same figure is taken as the figure which saw through the inside of a container. An electrode body 2 having a positive electrode and a negative electrode wound with a separator sandwiched therebetween is housed in a rectangular container 3 . The positive electrode is electrically connected to the positive electrode terminal 4 via a positive electrode lead 41 . The negative electrode is electrically connected to the negative terminal 5 via a negative lead 51 .

<Configuration of power storage device>
The power storage device of this embodiment includes two or more non-aqueous electrolyte power storage devices and one or more non-aqueous electrolyte power storage devices of this embodiment. The non-aqueous electrolyte storage element of the present embodiment is a power source for automobiles such as electric vehicles (EV), hybrid vehicles (HEV), and plug-in hybrid vehicles (PHEV), power sources for electronic devices such as personal computers and communication terminals, or electric power. It can be installed in a power source for storage or the like as a power storage unit (battery module) configured by collecting a plurality of non-aqueous electrolyte power storage elements 1 . In this case, the technology of the present invention may be applied to at least one non-aqueous electrolyte storage element included in the storage unit.
FIG. 2 shows an example of a power storage device 30 in which a power storage unit 20 in which two or more electrically connected non-aqueous electrolyte power storage elements 1 are assembled is further assembled. The power storage device 30 may include a bus bar (not shown) that electrically connects two or more power storage elements 1, a bus bar (not shown) that electrically connects two or more power storage units 20, and the like. The power storage unit 20 or the power storage device 30 may include a state monitoring device (not shown) that monitors the state of one or more non-aqueous electrolyte power storage elements.

<Method for producing non-aqueous electrolyte storage element>
The method for manufacturing the non-aqueous electrolyte storage element includes, in the step of preparing the negative electrode, laminating a coating material on the surface of the negative electrode active material layer containing lithium metal, wherein the coating material is tin metal or a compound containing a tin element. is the main component. The method for manufacturing a non-aqueous electrolyte storage element can manufacture a non-aqueous electrolyte storage element in which the negative electrode active material layer containing lithium metal is coated with a coating layer containing tin element and lithium element by including the above steps. Therefore, in the non-aqueous electrolyte storage element manufactured by the method for manufacturing a non-aqueous electrolyte storage element, the deposition of dendrites is suppressed, so that the coulomb efficiency after charge-discharge cycles can be improved. As a method for laminating the coating material, sputtering or vapor deposition is preferable.

Further, the step of preparing the negative electrode in the method for manufacturing the non-aqueous electrolyte storage element includes the step of stacking a negative electrode active material layer containing lithium metal on the surface of the negative electrode substrate before the step of stacking the coating material. is preferred. Lamination of the negative electrode substrate and the negative electrode active material layer can be performed by pressing or the like.

The method for manufacturing the non-aqueous electrolyte storage element includes, as other steps, for example, a step of preparing an electrode body, a step of preparing a non-aqueous electrolyte, and a step of accommodating the electrode body and the non-aqueous electrolyte in a container. The step of preparing the electrode body may include a step of preparing the positive electrode and the 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.

The method for housing the non-aqueous electrolyte in the container can be appropriately selected from known methods. For example, when a liquid non-aqueous electrolyte is used, the non-aqueous electrolyte may be injected through an injection port formed in the container, and then the injection port may be sealed. The details of other elements constituting the non-aqueous electrolyte storage element obtained by the manufacturing method are as described above.

[Other embodiments]
It should be noted that the electric storage device of 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 another embodiment can be added to the configuration of one embodiment, and part of the configuration of one embodiment can be replaced with the configuration of another embodiment or a known technique. Furthermore, some of the configurations of certain embodiments can be deleted. Also, well-known techniques can be added to the configuration of a certain embodiment.

In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable/dischargeable nonaqueous electrolyte secondary battery (for example, a lithium secondary battery). etc. are optional. The present invention can also be applied to capacitors such as various secondary batteries, electric double layer capacitors, and lithium ion capacitors.

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

[Examples 1 to 5 and Comparative Examples 1 to 4]
(Preparation of negative electrode)
A copper foil having an average thickness of 10 μm was prepared as a negative electrode substrate. In Examples 1 to 5 and Comparative Examples 1 to 4, lithium metal having an average thickness shown in Table 1 was laminated as a negative electrode active material layer on one side of the copper foil. Each of the negative electrodes thus obtained had a rectangular shape with a width of 31 mm and a length of 42 mm.

(Formation of coat layer)
Next, for Examples 1 to 5 and Comparative Examples 2 and 3, a coat layer shown in Table 1 was formed on the surface of the negative electrode active material layer. For Comparative Example 4, a coat layer shown in Table 1 was formed on one side of the negative electrode substrate. In Examples 1 to 5 and Comparative Example 4 in which the coating material was tin metal (Sn), a coating layer was formed on the surface of the negative electrode active material layer or the negative electrode substrate by the following procedure using a sputtering method. A MAGNETRON SPUTTERING DEVICE (JUC-5000) manufactured by JEOL was used as a sputtering apparatus, and tin metal with a purity of 99.99% was used as a target. The height from the surface of the negative electrode active material layer or the negative electrode substrate to the target was 25 mm, and the current was 10 mA, and tin metal was sputtered onto the surface of the negative electrode active material layer or the negative electrode substrate. Moreover, the average thickness of the coat layer was adjusted by adjusting the coating time. All the above operations were performed in a dry room.
For Comparative Examples 2 and 3 in which the coating materials were zinc oxide (ZnO) and silver (Ag), respectively, a coating layer was formed on the surface of the negative electrode active material layer by the following procedure. Zinc oxide particles with a particle size of 20 nm were prepared as the zinc oxide material. Dotite D550 manufactured by Fujikura Kasei Co., Ltd. was prepared as a material for the silver metal. Using N-methylpyrrolidone as a dispersion medium, a coating layer paste containing the zinc oxide or silver metal material: polyvinylidene fluoride = 95:5 mass ratio was prepared, and an applicator roll was used to coat the surface of the negative electrode active material layer. coated on. After that, the dispersion medium was volatilized by drying at 100° C. for 30 minutes. All the above operations were performed in a dry room.

(Preparation of positive electrode)
As a positive electrode active material, a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure and represented by Li ₁₊ αMe ₁ -αO ₂ (Me is a transition metal) was used. Here, the molar ratio Li/Me between Li and Me is 1.33, and Me consists of Ni and Mn, and is contained in a molar ratio of Ni:Mn=0.33:0.67, The particle surface was coated with 0.3% by mass of Al ₂ O ₃ .

Using N-methylpyrrolidone (NMP) as a dispersion medium, the positive electrode active material, acetylene black (AB) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder are mixed at a ratio of 92.5:4.5:3.0. A positive electrode material mixture paste containing the components by mass ratio was prepared. On one side of an aluminum foil having an average thickness of 15 μm, which is a positive electrode base material, the above positive electrode mixture paste is applied, dried, pressed, and cut to form a rectangular positive electrode active material layer having a width of 30 mm and a length of 40 mm. An arranged positive electrode was produced. A positive electrode mixture comprising a positive electrode active material, a conductive aid and a binder was applied to the prepared positive electrode in a mass of 3.0 g/100 cm ² .

(Preparation of non-aqueous electrolyte)
Fluoroethylene carbonate (FEC) and 2,2,2-trifluoroethylmethyl carbonate (TFEMC) were used as non-aqueous solvents. Then, after dissolving LiPF ₆ at a concentration of 1 mol/dm ³ in a mixed solvent in which FEC: TFEMC is mixed at a volume ratio of 30:70, 1,3-propene sultone (PRS) as an additive is added at 2 % by mass to form a non-aqueous electrolyte.

(Preparation of non-aqueous electrolyte storage element)
An electrode assembly was produced by laminating the above positive electrode and the above negative electrode with a polyethylene microporous film as a separator interposed therebetween. This electrode body was housed in a container, 0.5 mL of the non-aqueous electrolyte was injected into the interior, and then the opening was sealed by heat welding. An electrolyte storage device was obtained.

(initial charge/discharge)
Two cycles of initial charging and discharging were performed on each obtained non-aqueous electrolyte storage element at 25° C. under the following conditions. As the initial charging, constant current and constant voltage charging was performed with a charging current of 0.1 C and a charging end voltage of 4.6 V. The charging termination condition was until the charging current reached 0.05C. A rest period of 10 minutes was then provided. After that, as the first discharge, constant current discharge was performed with a discharge current of 0.1 C and a discharge final voltage of 2.0 V, followed by a rest period of 10 minutes. A second cycle of charging and discharging was performed under the same conditions as the first charging and discharging. The current value at 1C was set to 270 mA/g per mass of the positive electrode active material.

(Positive electrode discharge capacity at 2nd cycle)
Based on the discharge capacity at the second cycle, the discharge capacity (mAh/g) per mass of the positive electrode active material was calculated and shown in Table 1 as "second cycle positive electrode discharge capacity".

(Coulomb efficiency after charge-discharge cycle test)
After the initial charge/discharge, the non-aqueous electrolyte storage elements of Examples 1 to 5 and Comparative Examples 1 to 4 were further subjected to a charge/discharge cycle test under the following conditions. At 25° C., constant-current and constant-voltage charging was performed with a charging current of 0.2 C and a charging final voltage of 4.6 V. The charging termination condition was until the charging current reached 0.05C. A rest period of 10 minutes was then provided. Thereafter, constant current discharge was performed with a discharge current of 0.1 C and a discharge final voltage of 2.0 V, followed by a rest period of 10 minutes. This charging and discharging was repeated 100 cycles. Based on the charged amount of electricity at the 100th cycle, the charged amount of electricity per mass of the positive electrode active material (mAh/g) is calculated and defined as the "positive electrode charged amount of electricity at the 100th cycle", based on the discharge capacity at the 100th cycle. The discharge capacity (mAh/g) per mass of the positive electrode active material was calculated and defined as "the positive electrode discharge capacity at the 100th cycle".
Table 1 shows the percentage of the positive electrode discharge capacity at the 100th cycle to the positive electrode charge quantity of electricity at the 100th cycle as "100th cycle coulomb efficiency (%)".

(Discharge capacity retention rate after charge-discharge cycle test)
The percentage of the positive electrode discharge capacity at the 100th cycle to the positive electrode discharge capacity at the 2nd cycle in the initial charge/discharge is shown in Table 1 as "100th cycle discharge capacity retention rate (%)".

(Scanning electron microscope observation of negative electrode surface after initial charge)
The surface of the negative electrode after the initial charge was observed using a field emission scanning electron microscope (FE-SEM), JSM-7001F manufactured by JEOL. The acceleration voltage was set to 1 kV. FIG. 3 shows a scanning electron microscope (SEM) image of Example 1 after initial charging, and FIG. 4 shows an SEM image of Comparative Example 1 after initial charging. In addition, the above-mentioned "after initial charge" means a state in which the battery is charged only once (a state in which no discharge is performed).

As shown in Table 1, Examples 1 to 5 having a negative electrode active material layer containing lithium metal and a coating layer containing tin element and covering the negative electrode active material layer are positive electrodes in the second cycle. Both the discharge capacity, the coulomb efficiency at the 100th cycle, and the discharge capacity retention rate were good, and better results were obtained when the thickness of the coating layer was increased.

On the other hand, in Comparative Example 1, which has a negative electrode active material layer containing lithium metal but does not have the coating layer, the positive electrode discharge capacity at the 2nd cycle is good, but the coulomb efficiency at the 100th cycle is low. was This is considered to be due to the fact that dendrites were deposited by repeating the charge/discharge cycle, causing an internal short circuit. From the SEM images of the surfaces of the negative electrodes of Example 1 and Comparative Example 1 after the initial charging shown in FIGS. Recognize. In addition, in Comparative Examples 2 and 3, in which the coating material did not contain the tin element, the coulombic efficiency and the discharge capacity retention rate at the 100th cycle were inferior. Furthermore, in Comparative Example 4, which has a coating layer containing a tin element but does not have a negative electrode active material layer containing lithium metal, almost no decrease in the coulombic efficiency at the 100th cycle was observed. , the discharge capacity retention rate at the 100th cycle was greatly reduced because the negative electrode did not have a sufficient amount of usable lithium metal.
The coating layers in Examples 1 to 5 and Comparative Examples 2 to 4 contained an element derived from the coating material and a lithium element. This is presumed to be due to the formation of a reaction product between the coating material and the lithium metal contained in the negative electrode active material layer.

The above results showed that the non-aqueous electrolyte storage element can improve the coulombic efficiency after charge-discharge cycles when the negative electrode contains lithium metal.

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

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

Claims

a negative electrode having a negative electrode active material layer and a coat layer covering the negative electrode active material layer;
a positive electrode;
comprising a non-aqueous electrolyte and
The negative electrode active material layer contains lithium metal,
A non-aqueous electrolyte power storage device, wherein the coating layer contains tin element and lithium element.
The non-aqueous electrolyte storage element according to claim 1, wherein the coating layer has an average thickness of 10 nm or more.
3. The non-aqueous electrolyte storage element according to claim 1, wherein the negative electrode active material layer has an average thickness of 1 μm or more and 300 μm or less.
Laminating a coating material on the surface of the negative electrode active material layer containing lithium metal,
A method for producing a non-aqueous electrolyte storage element, wherein the coating material contains tin metal or a compound containing tin element as a main component.
A power storage device comprising two or more non-aqueous electrolyte power storage elements and one or more non-aqueous electrolyte power storage elements according to any one of claims 1 to 3.