WO2022260001A1

WO2022260001A1 - Polymer solid electrolyte, power storage element, and power storage device

Info

Publication number: WO2022260001A1
Application number: PCT/JP2022/022777
Authority: WO
Inventors: 栄人渡邉; 雄也伊丹
Original assignee: 株式会社Ｇｓユアサ
Priority date: 2021-06-10
Filing date: 2022-06-06
Publication date: 2022-12-15
Also published as: JPWO2022260001A1

Abstract

A polymer solid electrolyte according to one aspect of the present invention contains: a polymer material containing, as a constituent unit, a carbonate structure represented by the following general formula (1); and, a salt having lithium bis(trifluoromethanesulfonyl)imide or lithium bis(fluorosulfonyl)imide as a main component. The concentration of the salt is 1.0 mol/kg or greater. (In the formula, R¹ and R² independently represent H, F, or an alkyl group.)

Description

Polymer solid electrolyte, power storage element and power storage device

The present invention relates to solid polymer electrolytes, power storage elements, and power storage devices.

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 storage elements other than non-aqueous electrolyte secondary batteries.

In recent years, solid non-aqueous electrolytes have been proposed because there is no concern about liquid leakage. For example, a secondary battery using a solid electrolyte having polyether crosslinked with a crosslinkable functional group as such a non-aqueous electrolyte has been proposed (see Patent Document 1).

JP-A-2004-234879

However, it is difficult to say that the solid electrolyte described in Patent Document 1 has both lithium ion conductivity and oxidation resistance.

An object of the present invention is to provide a polymer solid electrolyte that has both lithium ion conductivity and oxidation resistance, and an electric storage element and an electric storage device comprising the same.

An embodiment according to one aspect of the present invention, which has been made to solve the above problems, is a polymer material containing a carbonate structure represented by the following general formula (1) as a structural unit, and lithium bis (trifluoromethanesulfonyl) imide Alternatively, it is a polymer solid electrolyte containing a salt containing lithium bis(fluorosulfonyl)imide as a main component, wherein the concentration of the salt is 1.0 mol/kg or more.

(Wherein R ¹ and R ² are independently H, F, or an alkyl group.)

Another aspect of the present invention is a power storage device comprising the polymer solid electrolyte according to one aspect of the present invention.

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

The solid polymer electrolyte according to one aspect of the present invention can achieve both ionic conductivity and oxidation resistance.

A power storage device according to another aspect of the present invention can achieve both ionic conductivity and oxidation resistance of the polymer solid electrolyte included in the power storage device.

FIG. 1 is a schematic cross-sectional view of a power storage device (all-solid-state battery) according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing a power storage device configured by assembling a plurality of power storage elements according to one embodiment of the present invention. FIG. 3 is a diagram showing the results of LSV (Linear Sweep Voltage) measurement according to Example 1. FIG. FIG. 4 is a diagram showing the results of LSV measurement according to Comparative Example 4. FIG.

First, an outline of the solid polymer electrolyte, the power storage element, and the power storage device disclosed by the present specification will be described.

A polymer solid electrolyte according to one aspect of the present invention comprises a polymer material containing a carbonate structure represented by the general formula (1) as a constituent unit, and lithium bis(trifluoromethanesulfonyl)imide or lithium bis(fluorosulfonyl) ) and a salt containing imide as a main component, wherein the concentration of the salt is 1.0 mol/kg or more.

The polymer solid electrolyte according to one embodiment of the present invention is a carbonate structure represented by the general formula (1) having high oxidation resistance, and a high concentration of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or By containing lithium bis(fluorosulfonyl)imide (LiFSI), both ionic conductivity and oxidation resistance can be achieved. Although the reason why the polymer solid electrolyte has good ion conductivity and oxidation resistance is not clear, the following reasons are presumed. Since LiTFSI and LiFSI have high solubility in the carbonate structure represented by the general formula (1), the above salt is contained in the polymer solid electrolyte at a high concentration of 1.0 mol / kg or more. It is possible to Therefore, in a polymer solid electrolyte containing a polymer material containing the carbonate structure as a structural unit, the TFSI ion or FSI ion is preferentially coordinated to the lithium ion rather than the carbonate structure. Conductive paths are formed and ionic conductivity is increased. Due to the high ionic conductivity and the high oxidation resistance of the carbonate structure represented by the general formula (1), the polymer solid electrolyte according to one embodiment of the present invention can achieve both ionic conductivity and oxidation resistance. is assumed to be possible. On the other hand, even though it is the same imide salt, lithium bis(pentafluoroethanesulfonyl)imide (LiBETI) has a larger ionic radius than TFSI ions and FSI ions. Since the distance between the charge centers of is large, it is difficult for BETI ions and the like to preferentially coordinate with lithium ions. Similarly, lithium difluoro(oxalato)borate (LiDFOB) has a large ionic radius of DFOB ions, which makes it difficult for DFOB ions to preferentially coordinate with lithium ions. presumed to be impossible. Furthermore, when the salt is lithium bis(fluorosulfonyl)imide (LiFSI), the Young's modulus of the self-supporting membrane made of the polymer solid electrolyte is also good.

"Solid electrolyte" refers to an electrolyte that is substantially composed only of solid components. A solid component refers to a component that is solid at 20°C. The expression that the electrolyte is substantially composed only of solid components means that the content of solid components in the electrolyte is 99% by mass or more.

A power storage device according to another aspect of the present invention includes the polymer solid electrolyte according to one aspect of the present invention. Since the electric storage device includes the solid polymer electrolyte, it can achieve both ionic conductivity and oxidation resistance. Therefore, for example, even when a positive electrode active material having a high oxidation-reduction potential is used, good ion conductivity is exhibited.

The power storage device according to another aspect of the present invention has a positive electrode potential of 4.7 V vs. 4.7 V when fully charged by a charging method during normal use. It is preferably Li/Li ⁺ or more. Since the electric storage element includes the polymer solid electrolyte with good oxidation resistance, even in a usage pattern in which the positive electrode potential is high when fully charged by the charging method during normal use, good ion conduction is achieved. It is possible to obtain a power storage element having a high energy density.

Note that "during normal use" is when the storage element is used under the charging and discharging conditions recommended or specified for the storage element, and a charger for the storage element is prepared. If there is, it means the case of using the storage device by applying the charger. Further, "the positive electrode potential in a fully charged state" is the positive electrode potential in a state in which the battery is not energized after being fully charged.

A power storage device according to another aspect of the present invention includes two or more power storage elements, and one or more power storage elements according to another aspect of the present invention.

Since the power storage device includes the solid polymer electrolyte, it can achieve both ionic conductivity and oxidation resistance.

A polymer solid electrolyte, a structure of an electric storage element, a structure of an electric storage device, a method for manufacturing an electric 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.

<Polymer solid electrolyte>
The polymer solid electrolyte is mainly composed of a polymer material containing a carbonate structure represented by the above general formula (1) as a structural unit, and lithium bis(trifluoromethanesulfonyl)imide or lithium bis(fluorosulfonyl)imide. and a salt having a concentration of 1.0 mol/kg or more.

(Polymer material)
A polymeric material according to one embodiment of the present invention contains a carbonate structure represented by the general formula (1) as a structural unit. R ¹ and R ² in general formula (1) are independently H, F, or alkyl groups. At least one of R ¹ and R ² is preferably H. When R ¹ and R ² are alkyl groups, the number of carbon atoms is not particularly limited, but is preferably 20 or less, more preferably 10 or less, and even more preferably 8 or less. The polymer material may contain the carbonate structure represented by the general formula (1) as a structural unit, and may be a homopolymer having only the carbonate structure represented by the general formula (1) as a structural unit. It may be composed of a copolymer containing a carbonate structure represented by the general formula (1) and a structure other than the carbonate structure represented by the general formula (1) as structural units. , may consist of the copolymer. The content of the carbonate structure represented by the general formula (1) in the polymer material is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 20% by mass or more, and 40% by mass or more. Even more preferably, 60% by mass or more is even more preferable, and 80% by mass or more is even more preferable. The lower limit of the number average molecular weight of the polymer material is preferably 5,000, more preferably 10,000. The upper limit of the number average molecular weight is preferably 500,000, more preferably 100,000. By setting the number average molecular weight of the polymer material to be equal to or more than the lower limit or equal to or less than the upper limit, it is possible to improve not only oxidation resistance but also handleability, moldability, and the like.

(salt)
A salt according to one embodiment of the present invention is based on lithium bis(trifluoromethanesulfonyl)imide or lithium bis(fluorosulfonyl)imide. Here, the “main component” means the component with the highest content in the salt contained in the polymer solid electrolyte, preferably 50% by mass or more, more preferably 90% by mass or more, and further 100% by mass. preferable. The concentration of the salt is 1.0 mol/kg or more relative to the polymer solid electrolyte. When the concentration of the salt is equal to or higher than the lower limit, it is possible to increase not only the ionic conductivity but also the lithium ion transference number. In addition, as said salt, 1 type of these salts may be used individually, and 2 types may be mixed and used. The above salts may further contain salts other than lithium bis(trifluoromethanesulfonyl)imide or lithium bis(fluorosulfonyl)imide.

(other ingredients)
The polymer solid electrolyte is mainly composed of a polymer material containing a carbonate structure represented by the above general formula (1) as a structural unit, and lithium bis(trifluoromethanesulfonyl)imide or lithium bis(fluorosulfonyl)imide. It may further contain other components other than the salt.

Other components include non-aqueous solvents and other additives.

As other additives, conventionally known various additives that are added to the electrolyte of a general electric storage element can be used. The content of other additives in the polymer solid electrolyte can be, for example, 0.01% by mass or more and 10% by mass or less, and can be 7% by mass or less, 3% by mass or less, or 1% by mass or less. preferable.

The content of solid components in the solid polymer electrolyte is 99% by mass or more, preferably 99.9% by mass or more, and more preferably 100% by mass. When the solid polymer electrolyte is applied to a power storage device having a negative electrode containing metallic lithium, for example, it can suppress deposition of dendritic metallic lithium (dendrite) on the surface of the negative electrode.

The polymer solid electrolyte can be suitably used as an electrolyte for a storage element such as a lithium ion secondary battery, especially a lithium battery. Moreover, the polymer solid electrolyte can be particularly suitably used as an electrolyte for an all-solid battery. The polymer solid electrolyte can be used for any of the positive electrode layer, isolation layer, negative electrode layer, and the like in the electric storage element.

<Method for Producing Solid Polymer Electrolyte>
Although the method for producing the polymer solid electrolyte according to one embodiment of the present invention is not particularly limited, the following method is preferred. That is, a method for producing a polymer solid electrolyte according to one embodiment of the present invention includes a polymer material containing a carbonate structure represented by the general formula (1) as a structural unit, and lithium bis(trifluoromethanesulfonyl)imide or with a salt based on lithium bis(fluorosulfonyl)imide.

This mixing method is not particularly limited. This mixing may be performed under heating by melting the polymer material containing the carbonate structure represented by the general formula (1) as a structural unit, and the carbonate structure represented by the general formula (1) is Even if the polymer material contained as a structural unit and the salt containing lithium bis(trifluoromethanesulfonyl)imide or lithium bis(fluorosulfonyl)imide as a main component are dissolved or dispersed in a liquid solvent, good. When mixed in a state of being dissolved or dispersed in a liquid solvent, the polymer solid electrolyte can be obtained by removing the solvent after mixing. During this mixing, the above other components can be further mixed as necessary. Moreover, after mixing, the polymer solid electrolyte obtained may be formed into a predetermined shape.

In the present invention, for example, vinylene carbonate, which is a precursor of polyvinylene carbonate (PVCA), and a salt containing lithium bis(trifluoromethanesulfonyl)imide or lithium bis(fluorosulfonyl)imide as a main component are mixed and dissolved in advance. After that, a precursor solution is prepared by mixing a polymerization initiator such as a radical polymerization initiator, and after the precursor solution is injected into the storage element, the storage element is heated to convert vinylene carbonate in the storage element. A polymer solid electrolyte can also be obtained by polymerizing to produce polyvinylene carbonate.

<Storage element>
The electric storage element is an electric storage element including the polymer solid electrolyte. As a storage device according to one embodiment of the present invention, an all-solid-state battery will be described below as a specific example. The storage element 10 in FIG. 1 is an all-solid battery, and is a secondary battery in which a positive electrode layer 1 (positive electrode) and a negative electrode layer 2 (negative electrode) are arranged with an isolation layer 3 interposed therebetween. The positive electrode layer 1 has a positive electrode substrate 4 and a positive electrode active material layer 5 , and the positive electrode substrate 4 is the outermost layer of the positive electrode layer 1 . The negative electrode layer 2 has a negative electrode substrate 7 and a negative electrode active material layer 6 , and the negative electrode substrate 7 is the outermost layer of the negative electrode layer 2 . In the electric storage element 10 shown in FIG. 1, the negative electrode active material layer 6, the isolation layer 3, the positive electrode active material layer 5, and the positive electrode substrate 4 are laminated on the negative electrode substrate 7 in this order.

At least one of the positive electrode layer 1, the negative electrode layer 2, and the isolation layer 3 of the storage element 10 contains the polymer solid electrolyte according to one embodiment of the present invention. More specifically, at least one of the positive electrode active material layer 5, the negative electrode active material layer 6, and the isolation layer 3 contains the polymer solid electrolyte according to one embodiment of the present invention. Since the solid polymer electrolyte according to one embodiment of the present invention has good oxidation resistance, at least one of the positive electrode active material layer 5 and the isolation layer 3 contains the solid polymer electrolyte according to one embodiment of the present invention. It is preferably contained.

In the electric storage element 10, other solid electrolytes than the polymer solid electrolyte according to one embodiment of the present invention may be used together. Other solid electrolytes include sulfide-based solid electrolytes, oxide-based solid electrolytes, polymer solid electrolytes other than the polymer solid electrolyte according to one embodiment of the present invention, and the like. Moreover, a plurality of different types of solid electrolytes may be contained in one layer in the electric storage element 10, and different solid electrolytes may be contained in each layer.

[Positive electrode layer]
The positive electrode layer 1 includes a positive electrode substrate 4 and a positive electrode active material layer 5 laminated on the surface of the positive electrode substrate 4 . The positive electrode layer 1 may have an intermediate layer between the positive electrode substrate 4 and the positive electrode active material layer 5 .

(Positive electrode base material)
The positive electrode base material 4 has conductivity. Having “conductivity” means having a volume resistivity of 10 ⁷ Ω·cm or less as measured in accordance with JIS-H-0505 (1975), and “non-conductivity” It means that the volume resistivity is more than 10 ⁷ Ω·cm. As the material of the positive electrode substrate 4, metals such as aluminum, titanium, tantalum, indium, 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 4 include foil, deposited film, mesh, porous material, and the like, and foil is preferable from the viewpoint of cost. Therefore, the positive electrode substrate 4 is preferably aluminum foil or aluminum alloy foil. Examples of aluminum or aluminum alloy include A1085P, A3003P, A1N30, etc. defined in JIS-H-4000 (2014) or JIS-H-4160 (2006).

The average thickness of the positive electrode substrate 4 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 4 within the above range, the energy density per volume of the storage element 10 can be increased while increasing the strength of the positive electrode substrate 4 . The "average thickness" of the positive electrode base material 4 and the negative electrode base material 7, which will be described later, refers to a value obtained by dividing the mass of the base material in a predetermined area by the true density and area of the base material.

The intermediate layer is a layer arranged between the positive electrode substrate 4 and the positive electrode active material layer 5 . The intermediate layer reduces the contact resistance between the positive electrode substrate 4 and the positive electrode active material layer 5 by containing a conductive agent such as carbon particles. The composition of the intermediate layer is not particularly limited, and includes, for example, a binder and a conductive agent.

(Positive electrode active material layer)
The positive electrode active material layer 5 contains a positive electrode active material. The positive electrode active material layer 5 can be formed from a so-called positive electrode mixture containing a positive electrode active material. The positive electrode active material layer 5 may contain optional components such as a polymer solid electrolyte, a conductive agent, a binder, a thickener, a filler, and the like, if necessary. One or more of these optional components may not be substantially contained in the positive electrode active material layer 5 .

The positive electrode active material contained in the positive electrode active material layer 5 can be appropriately selected from known positive electrode active materials commonly used in lithium ion secondary batteries and all-solid-state batteries. A material capable of intercalating and deintercalating lithium ions is usually used as the positive electrode active material. Examples thereof include lithium transition metal composite oxides having an α-NaFeO ₂ type crystal structure, lithium transition metal composite oxides having a spinel 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 Ni _γ Mn _β Co _(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. The surface of the positive electrode active material may be coated with a compound such as lithium niobate, lithium titanate, or lithium phosphate. In the positive electrode active material layer, one kind of these positive electrode active materials may be used alone, or two or more kinds may be mixed and used.

Examples of positive electrode active materials include lithium transition metal composite oxides having an α-NaFeO ₂ -type crystal structure or spinel-type crystal structure, and polyanion compounds containing nickel, cobalt, or manganese elements (LiMnPO ₄ , LiNiPO ₄ , LiCoPO 4 , LiCoPO ₄ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F, etc.) are preferable, and a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure is more preferable. Among the lithium-transition metal composite oxides having the α-NaFeO ₂ type crystal structure, those containing one or more of nickel, cobalt and manganese as transition metal elements are more preferable. These positive electrode active materials have a particularly high oxidation-reduction potential, and by using such positive electrode active materials, the energy density and the like of the electric storage element can be increased. In addition, since the polymer solid electrolyte having good oxidation resistance according to one embodiment of the present invention is used for the storage element 10, even when these positive electrode active materials having a high oxidation-reduction potential are used, good It is possible to maintain good charge and discharge performance.

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 diameter of the positive electrode active material to the above upper limit or less, the conductivity of the positive electrode active material layer 5 is improved. Here, the "average particle size" is based on the particle size distribution measured by a laser diffraction/scattering method for a diluted solution in which the particles are diluted with a solvent in accordance with JIS-Z-8825 (2013). Z-8819-2 (2001) means the value at which the volume-based integrated distribution calculated according to 50%.

Pulverizers, classifiers, etc. are used to obtain particles in a predetermined shape. Pulverization methods include, for example, methods using a mortar, ball mill, sand mill, vibrating ball mill, planetary ball mill, jet mill, counter jet mill, whirling jet mill, 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 5 is preferably 10% by mass or more and 95% by mass or less, more preferably 30% by mass or more, and further preferably 50% by mass or more. By setting the content of the positive electrode active material within the above range, the electric capacity of the storage element 10 can be increased.

When the positive electrode active material layer 5 contains a solid electrolyte, the content of the solid electrolyte is preferably 10% by mass or more and 90% by mass or less, more preferably 20% by mass or more and 70% by mass or less, and further 50% by mass or less. preferable. By setting the content of the solid electrolyte within the above range, the electrical capacity of the storage element 10 can be increased. When the solid polymer electrolyte according to one embodiment of the present invention is used for the positive electrode active material layer 5, the content of the solid polymer electrolyte according to one embodiment of the present invention with respect to the total solid electrolyte in the positive electrode active material layer 5 is , preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, and even more preferably substantially 100% by mass. In the positive electrode active material layer 5, the positive electrode active material and the solid electrolyte may form a composite.

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 conductivity and coatability, and acetylene black is particularly preferable.

The content of the conductive agent in the positive electrode active material layer 5 is preferably 1% by mass or more and 10% by mass or less, more preferably 3% by mass or more and 9% by mass or less. By setting the content of the conductive agent within the above range, the electric capacity of the electric storage element 10 can be increased.

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

The binder content in the positive electrode active material layer 5 is preferably 1% by mass or more and 10% by mass or less, more preferably 3% by mass or more and 9% by mass or less. By setting the content of the binder within the above range, the active material can be stably retained.

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

The filler is not particularly limited. Fillers 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, magnesium hydroxide, calcium hydroxide, and water. Hydroxides such as aluminum oxide, 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, and zeolite , apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, mica, and other mineral resource-derived substances or artificial products thereof.

The positive electrode active material layer 5 is composed of typical nonmetallic elements such as B, N, P, F, Cl, Br, I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba Typical metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W are used as positive electrode active materials, solid electrolytes, conductive agents, binders, and thickeners. You may contain as a component other than a sticky agent and a filler.

The average thickness of the positive electrode active material layer 5 is preferably 30 µm or more and 1000 µm or less, more preferably 60 µm or more and 500 µm or less. By setting the average thickness of the positive electrode active material layer 5 to the above lower limit or more, it is possible to obtain the electric storage device 10 having a high energy density. By making the average thickness of the positive electrode active material layer 5 equal to or less than the upper limit, it is possible to reduce the size of the electric storage device 10 . Let the average thickness of the positive electrode active material layer 5 be the average value of the thickness measured at arbitrary five places. The same applies to the average thicknesses of the negative electrode active material layer 6 and the separation layer 3, which will be described later.

[Negative electrode layer]
The negative electrode layer 2 has a negative electrode base material 7 and a negative electrode active material layer 6 disposed on the negative electrode base material 7 directly or via an intermediate layer. The structure of the intermediate layer is not particularly limited, and can be selected from the structures exemplified for the positive electrode layer 1, for example.

(Negative electrode base material)
The negative electrode base material 7 has conductivity. As materials for the negative electrode substrate 7, metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, alloys thereof, carbonaceous materials, and the like are used. Among these, copper or a copper alloy is preferred. Examples of negative electrode substrates include foils and vapor deposition films, and foils are preferred 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 7 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 making the average thickness of the negative electrode base material 7 equal to or more than the above lower limit, the strength of the negative electrode base material 7 can be increased. By making the average thickness of the negative electrode base material 7 equal to or less than the above upper limit, the energy density per volume of the storage element 10 can be increased.

(Negative electrode active material layer)
The negative electrode active material layer 6 contains a negative electrode active material. The negative electrode active material layer 6 can be formed, for example, from a so-called negative electrode mixture containing a negative electrode active material. The negative electrode active material layer 6 contains optional components such as a solid electrolyte, a conductive agent, a binder, a thickener, a filler, and the like, if necessary. The types and suitable contents of these optional components in the negative electrode active material layer 6 are the same as those of the above-described optional components in the positive electrode active material layer 5 . One or more of these optional components may not be substantially contained in the negative electrode active material layer 6 .

The negative electrode active material layer 6 is composed of typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba. Typical metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W, etc. are used as negative electrode active materials, solid electrolytes, and conductive agents. , a binder, a thickener, and a component other than a filler.

The negative electrode active material can be appropriately selected from known negative electrode active materials commonly used in lithium ion secondary batteries and all-solid batteries. A material capable of intercalating and deintercalating lithium ions is usually used as the negative electrode active material. Examples of the negative electrode active material include metal Li; metals or metalloids such as Si and Sn; metal oxides and metalloid oxides such as Si oxide, Ti oxide and Sn oxide; Li ₄ Ti ₅ O ₁₂ ; Titanium-containing oxides such as LiTiO _{2 and} TiNb ₂ O ₇ ; polyphosphate compounds; silicon carbide; carbon materials such as graphite and non-graphitizable carbon (easily graphitizable carbon or non-graphitizable carbon) be done. In the negative electrode active material layer 6, one kind of these materials may be used alone, or two or more kinds may be mixed and used.

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

“Non-graphitic carbon” refers to a carbon material having an average lattice spacing (d ₀₀₂ ) of the (002) plane of 0.34 nm or more and 0.42 nm or less as determined by X-ray diffraction before charging/discharging or in a discharged state. . Non-graphitizable carbon includes non-graphitizable carbon and graphitizable carbon. Examples of non-graphitic carbon include resin-derived materials, petroleum pitch-derived materials, and alcohol-derived materials.

Here, the "discharged state" means a state in which the carbon material, which is the negative electrode active material, is discharged such that lithium ions that can be inserted and released are sufficiently released during charging and discharging. For example, in a cell using a negative electrode containing a carbon material as a negative electrode active material as a working electrode and metal Li as a counter electrode, the open circuit voltage is 0.7 V or higher.

The term “non-graphitizable carbon” refers to a carbon material having a d ₀₀₂ of 0.36 nm or more and 0.42 nm or less.

“Graphitizable carbon” refers to a carbon material having a d ₀₀₂ of 0.34 nm or more and less than 0.36 nm.

Metallic lithium is preferable as the negative electrode active material. Metallic lithium may exist as pure metallic lithium consisting essentially of lithium, or may exist as a lithium alloy containing other metal elements. Lithium alloys include lithium silver alloys, lithium zinc alloys, lithium calcium alloys, lithium aluminum 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 6 is preferably a layer consisting essentially of metallic lithium. In this case, the content of metallic lithium in the negative electrode active material layer 6 is preferably 90% by mass or more, more preferably 99% by mass or more, and even more preferably 100% by mass. The negative electrode active material layer 6 is preferably a pure metal lithium foil or a lithium alloy foil.

Particles (powder) can be used as the negative electrode active material. The average particle size of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. When the negative electrode active material is, for example, a carbon material, its average particle size is preferably 1 μm or more and 100 μm or less. When the negative electrode active material is a metal, a metalloid, a metal oxide, a metalloid oxide, a titanium-containing oxide, a polyphosphate compound, or the like, the average particle size is preferably 1 nm or more and 10 μm or less. By making the average particle size of the negative electrode active material equal to or greater than the above lower limit, the production or handling of the negative electrode active material is facilitated. By setting the average particle size of the negative electrode active material to the above upper limit or less, the conductivity of the active material layer is improved. A pulverizer, a classifier, or the like is used to obtain powder having a predetermined particle size. The pulverization method and classification method can be selected from the methods exemplified for the positive electrode layer 1, for example.

When the negative electrode active material is particles (powder), the content of the negative electrode active material in the negative electrode active material layer 6 is preferably 10% by mass or more and 95% by mass or less, more preferably 30% by mass or more, and further 50% by mass or more. more preferred. By increasing the content of the negative electrode active material, the electric capacity of the storage element 10 can be increased.

When the negative electrode active material layer 6 contains a solid electrolyte, the content of the solid electrolyte is preferably 10% by mass or more and 90% by mass or less, more preferably 20% by mass or more and 70% by mass or less, and further preferably 50% by mass or less. preferable. By setting the content of the solid electrolyte within the above range, the electric capacity of the electric storage element 10 can be increased. When the solid polymer electrolyte according to one embodiment of the present invention is used for the negative electrode active material layer 6, the content of the solid polymer electrolyte according to one embodiment of the present invention with respect to the total solid electrolyte in the negative electrode active material layer 6 is , preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, and even more preferably substantially 100% by mass.

The average thickness of the negative electrode active material layer 6 is not particularly limited. By making the average thickness of the negative electrode active material layer 6 equal to or greater than the above lower limit, the charge/discharge performance and the like of the storage element 10 can be enhanced. In particular, when the negative electrode active material is metallic lithium, charging/discharging is sufficiently possible even if the average thickness of the negative electrode active material layer 6 is as thin as less than 1 μm. By making the average thickness of the negative electrode active material layer 6 equal to or less than the above upper limit, it is possible to reduce the size of the storage element 10 .

[Isolation layer]
The isolation layer 3 preferably contains a solid electrolyte. As the solid electrolyte contained in the isolation layer 3, various solid electrolytes can be used in addition to the polymer solid electrolyte according to the embodiment of the present invention described above. The content of the solid electrolyte in the isolation layer 3 is preferably 70% by mass or more, more preferably 90% by mass or more, still more preferably 99% by mass or more, and even more preferably substantially 100% by mass. Further, when the solid polymer electrolyte according to one embodiment of the present invention is used for the isolation layer 3, the content of the solid polymer electrolyte according to one embodiment of the present invention in the total solid electrolyte in the isolation layer 3 is It is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, and even more preferably substantially 100% by mass.

The isolation layer 3 may contain optional components such as fillers in addition to the solid electrolyte. Optional components such as fillers can be selected from the materials exemplified for the positive electrode active material layer 5 . In addition, a woven fabric, a non-woven fabric, a porous resin film, or the like may be arranged in the isolating layer 3 in order to increase the mechanical strength.

The average thickness of the isolation layer 3 is preferably 1 μm or more and 200 μm or less, more preferably 3 μm or more and 100 μm or less. By setting the average thickness of the isolation layer 3 to the above lower limit or more, it is possible to reliably insulate the positive electrode layer 1 and the negative electrode layer 2 from each other. By making the average thickness of isolation layer 3 equal to or less than the above upper limit, it is possible to increase the energy density of storage element 10 .

The positive electrode potential of the storage element 10 fully charged by the charging method during normal use is, for example, 3.5 V vs. Li/Li ⁺ or more, preferably 4.0 V vs. Li/Li ⁺ or more is more preferable, and 4.5 V vs. More preferably Li/Li ⁺ or more, 4.6 V vs. More preferably Li/Li ⁺ or more, 4.7 V vs. More preferably Li/Li ⁺ or more, 4.8 V vs. Li/Li ⁺ or more is even more preferable. The energy density and voltage of the storage element 10 can be increased by setting the positive electrode potential in a fully charged state by the charging method during normal use to the lower limit or higher. In addition, since the solid polymer electrolyte having good oxidation resistance according to one embodiment of the present invention is used for the storage element 10, the positive electrode potential in a fully charged state by the charging method during normal use is Even when it is high, good charge/discharge performance can be maintained.

The upper limit of the positive electrode potential in a fully charged state by the charging method during normal use of the storage element 10 is, for example, 6.0 V vs. Li/Li ⁺ , 5.5V vs. Li/Li ⁺ is preferred, 5.2V vs. Li/Li ⁺ is more preferred.

<Power storage device>
The power storage device 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 power sources for power storage. For example, it can be mounted as a power storage unit (battery module) configured by assembling a plurality of power storage elements. In this case, the technology according to one embodiment of the present invention may be applied to at least one power storage element included in the power storage unit.
A power storage device according to one embodiment of the present invention includes two or more power storage elements and one or more power storage elements according to one embodiment of the present invention (hereinafter referred to as "second embodiment"). It is sufficient that the technology according to one embodiment of the present invention is applied to at least one power storage element included in the power storage device according to the second embodiment. One or more energy storage elements not related to one embodiment of the present invention may be provided, or two or more energy storage elements according to one embodiment of the present invention may be included.

FIG. 2 shows an example of a power storage device 30 according to the second embodiment, in which power storage units 20 each including two or more electrically connected power storage elements 10 are assembled. The power storage device 30 may include a bus bar (not shown) that electrically connects two or more power storage elements 10, a bus bar (not shown) that electrically connects two or more power storage units 20, and the like. The power storage unit 20 or power storage device 30 may include a state monitoring device (not shown) that monitors the state of one or more power storage elements.

<Method for manufacturing power storage element>
The method for producing an electric storage element according to one embodiment of the present invention is generally known except that the polymer solid electrolyte according to one embodiment of the present invention is used to produce at least one of the positive electrode layer, the isolation layer, and the negative electrode layer. It can be done by the method of The production method includes, for example, (1) preparing a positive electrode layer-forming material such as a positive electrode mixture and a positive electrode base material, (2) preparing a separation layer material, and (3) a negative electrode mixture, a negative electrode base material, and the like. and (4) laminating the positive electrode layer, the isolation layer and the negative electrode layer. As for the specific forms and preferred forms of the prepared positive electrode layer forming material, separation layer material, and negative electrode layer forming material, the above-described forms of the positive electrode layer, the separating layer, and the negative electrode layer provided in the electric storage element can be applied. For example, when metallic lithium is used as the negative electrode active material, metallic lithium foil or the like can be used as an example of the negative electrode layer forming material.

<Other embodiments>
The present invention is not limited to the above-described embodiments, and can be implemented in various modified and improved modes in addition to the above-described modes. For example, the power storage device according to the present invention may include layers other than the positive electrode layer, the isolation layer, and the negative electrode layer. Each structure of the positive electrode layer, the isolation layer, and the negative electrode layer is not limited to the above-described structures. For example, the negative electrode layer (negative electrode) may be composed only of the negative electrode base material without the negative electrode active material layer. In addition, the electric storage device according to the present invention may contain a liquid in one or more of the layers. The positive electrode, negative electrode, etc. of the storage device according to the present invention may not have a layered structure. The storage element according to the present invention may be a storage element that is a secondary battery, or may be a capacitor or the like.

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

[Example 1]
After mixing vinylene carbonate and LiTFSI, a precursor was prepared by adding azobisisobutyronitrile (AIBN) as a polymerization initiator.
Using a working electrode and a counter electrode made of SUS foil (diameter 26 mm) with a thickness of 12 μm and a separation layer made of a cellulose nonwoven fabric with a thickness of 35 μm, the separation layer was sandwiched between the working electrode and the counter electrode, and the precursor was injected and then sealed. By doing so, a cell for ionic conductivity evaluation was manufactured. After that, the ion conductivity evaluation cell is left in a constant temperature bath at 60° C. for 24 hours to polymerize the precursor in the ion conductivity evaluation cell, and polyvinylene carbonate (PVCA) is used as the polymer material. An ionic conductivity evaluation cell comprising the polymer solid electrolyte of Example 1 was obtained. The concentration of salt (LiTFSI) in the polymer solid electrolyte of Example 1 was 1.4 mol/kg.

[Examples 2 to 8, Comparative Examples 1, 2, 3 and 5]
Examples 2 to 8 and Comparative Examples 1, 2, 3 and 5 were prepared in the same manner as in Example 1 except that the salt, polymer material, and salt concentration were as shown in Tables 1 and 2. An ionic conductivity evaluation cell having a molecular solid electrolyte was obtained.

[Comparative Example 4]
Polypropylene carbonate (PPC, number average molecular weight: 50000) and LiTFSI were dissolved in dimethylformamide and mixed, and then the dimethylformamide was removed by drying to prepare a polymer solid electrolyte of Comparative Example 4. A cell for evaluating ionic conductivity comprising the solid polymer electrolyte of Comparative Example 4 was sandwiched between a working electrode and a counter electrode made of SUS foil (diameter: 26 mm) with a thickness of 12 μm and sealed with this polymer solid electrolyte as an isolation layer. got The salt concentration was as shown in Table 1.

[Ionic conductivity]
The ionic conductivity of each polymer solid electrolyte was determined by an electrochemical impedance method using an ionic conductivity evaluation cell provided with each polymer solid electrolyte of Examples and Comparative Examples. Under the environment of 25° C., the measurement frequency was set to 7 MHz to 100 mHz, and the ionic conductivity was obtained by a conventional method from the obtained complex impedance.

[Oxidation resistance]
Except for using a 12 μm thick SUS foil (diameter 26 mm) for the working electrode and a 60 μm thick Li foil (diameter 20 mm) for the counter electrode, in the same manner as the cell for evaluating ionic conductivity, Examples 1 to 3 and Comparative Oxidation resistance evaluation cells comprising the polymer solid electrolytes of Examples 1 to 5 were prepared. LSV (Linear Sweep Voltage) measurement was performed using each oxidation resistance evaluation cell. The voltage sweep rate was 1 mV/sec, and measurements were taken from the open circuit voltage to 6.0V. The measurement results obtained for Example 1 and Comparative Example 4 are shown in FIGS. 3 and 4, respectively.
Table 1 shows a summary of the measurement results.

[Young's modulus]
The Young's modulus of the self-supporting membrane composed of each polymer solid electrolyte of Examples 4 to 8 was obtained by the following procedure. As samples for Young's modulus evaluation, two self-supporting membranes of each solid polymer electrolyte having length, width and thickness of 0.5 cm, 0.5 cm and 300 to 500 μm were prepared. Using a microcompression tester (MCT-211 manufactured by Shimadzu Corporation), the amount of displacement of the obtained self-supporting membrane was measured. The measurement conditions were the maximum test force of 100 mN, the minimum test force of 0.49 mN, the load speed of 9.68 mN/sec, and the load retention time and unload retention time of 0 seconds in the test mode of the load-unload test. The amount of displacement was measured three times for each sample, and the average value was taken as the amount of displacement for each sample.
Young's modulus was obtained by applying the obtained displacement amount to the following formula (2).
ε=ΔL/t (2)
(where ε is Young's modulus, ΔL is the amount of displacement [μm], and t is the thickness [μm] of the self-supporting film in the formula (2).)
The average value of the displacement amount and the Young's modulus of two self-supporting membranes made of each of the solid polymer electrolytes obtained in Examples 4 to 8 was obtained. Table 2 shows the results obtained.

As shown in Table 1, it was confirmed that the polymer solid electrolytes of Examples 1 to 3 had good oxidation resistance and good ionic conductivity. As shown in FIGS. 3 and 4, the voltage at which the current abruptly increases, that is, the voltage at which the oxidative decomposition of the solid polymer electrolyte occurs is high in Example 1 and low in Comparative Example 4. It can be seen that the molecular solid electrolyte has good oxidation resistance and Comparative Example 4 has poor oxidation resistance.

As shown in Table 2, it was confirmed that the Young's modulus of the self-supporting membranes composed of the solid polymer electrolytes of Examples 4 to 7 was also good.

The polymer solid electrolyte according to the present invention is suitably used as an electrolyte for power storage elements such as all-solid batteries.

1 positive electrode layer (positive electrode)
2 negative electrode layer (negative electrode)
3 Separation layer 4 Positive electrode substrate 5 Positive electrode active material layer 6 Negative electrode active material layer 7 Negative electrode substrate 10 Power storage element (all-solid battery)
20 power storage unit 30 power storage device

Claims

a polymer material containing a carbonate structure represented by the following general formula (1) as a structural unit;
a salt containing lithium bis(trifluoromethanesulfonyl)imide or lithium bis(fluorosulfonyl)imide as a main component,
A polymer solid electrolyte in which the salt concentration is 1.0 mol/kg or more.

(Wherein R 1 and R 2 are independently H, F, or an alkyl group.)
The polymer solid electrolyte according to claim 1, wherein the salt contains lithium bis(fluorosulfonyl)imide as a main component.
An electricity storage device comprising the polymer solid electrolyte according to claim 1 .
The positive electrode potential in a fully charged state by the charging method for normal use is 4.7 V vs. The electric storage device according to claim 3, wherein Li/Li + or more.
An electric storage device comprising two or more electric storage elements and one or more electric storage elements according to claim 3 or 4.