Closed-type lithium-oxygen battery

Abstract

The present disclosure provides a means by which the charge / discharge efficiency of a closed-type lithium-oxygen battery can be improved. Provided is a battery for a closed-type lithium-oxygen battery, said battery having: electrodes in which an electrode active material layer containing lithium oxide, a catalyst, and a gel-forming polymer is disposed on the surface of a current collector; and an electrolyte layer in which an electrolyte solution is impregnated in a separator disposed adjacent to the electrodes, wherein the porosity x [%] of the electrode active material layer, the ratio y [%] of the volume of the gel-forming polymer to the volume of the electrode active material layer, and the liquid absorption ratio z [%] of the gel-forming polymer with respect to the electrolyte solution satisfy 0 < yz / x ≤ 8.7.

Description

Closed-type lithium-oxygen battery

[0001] The present invention relates to a closed-type lithium-oxygen battery.

[0002] In recent years, the widespread use of various electric vehicles is expected to help solve environmental and energy problems. Secondary batteries have been actively developed as on-board power sources for driving motors and other applications, which are key to the widespread use of these electric vehicles. Non-aqueous electrolyte secondary batteries, such as lithium-ion secondary batteries, have been attracting attention as they are expected to have high energy density and high output.

[0003] Lithium-oxygen batteries (lithium-oxygen secondary batteries) are known as one type of non-aqueous electrolyte secondary battery. These lithium-oxygen batteries have the highest theoretical energy density of all secondary batteries, including next-generation batteries, and are expected to offer battery performance with a high energy density that far exceeds that of current lithium-ion secondary batteries. However, sufficient capacity characteristics have yet to be achieved, and further improvements are currently required.

[0004] Lithium-oxygen batteries use gaseous molecular oxygen (O ２ ) is used, and O ２ When charging, ２ and a lithium-air battery that generates ２ The latter is a battery that does not consume or generate oxygen (lithium-oxygen battery in the narrow sense). ２ Since there is no exchange of electricity, the battery can be constructed as a sealed cell and can be called a "closed-type lithium-oxygen battery."

[0005] JP 2015-159098 A discloses the above-mentioned closed-type lithium-oxygen battery. This document describes a closed-type lithium-oxygen battery that prevents atmospheric moisture and carbon dioxide from entering the cell while retaining lithium oxide (LiO) as an electrode active material. ２ O) and a catalyst containing a transition metal atom (Co ３ O ４They are attempting to achieve high capacity electrode active materials by pulverizing raw material compositions containing these materials through mechanochemical treatment.

[0006] According to the studies of the present inventors, it has been found that when a closed-type lithium-oxygen battery is fabricated using the technology disclosed in JP 2015-159098 A, it may not be possible to achieve sufficient charge-discharge efficiency (the ratio of discharge capacity to charge capacity).

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a means for improving the charge / discharge efficiency of a closed-type lithium-oxygen battery.

[0008] One aspect of the present invention relates to a closed-type lithium-oxygen battery having an electrode in which an electrode active material layer containing lithium oxide, a catalyst, and a gel-forming polymer is disposed on the surface of a current collector, and an electrolyte layer in which an electrolytic solution is impregnated in a separator disposed adjacent to the electrode. The battery is characterized in that, when the porosity of the electrode active material layer is x [%], the volume ratio of the gel-forming polymer to the volume of the electrode active material layer is y [%], and the liquid absorption rate of the gel-forming polymer with respect to the electrolytic solution is z [%], the battery satisfies the relationship of the following formula (1): 0<yz / x≦8.7 ... formula (1)

[0009] 1 is a cross-sectional view schematically illustrating a stacked (flat) closed-type lithium oxygen battery according to one embodiment of the present invention.

[0010] One aspect of the present invention is a battery for a closed-type lithium-oxygen battery, which comprises an electrode having an electrode active material layer including a lithium oxide, a catalyst, and a gel-forming polymer disposed on the surface of a current collector, and an electrolyte layer formed by impregnating a separator disposed adjacent to the electrode with an electrolytic solution, and which satisfies the relationship of the following formula (1), where the porosity of the electrode active material layer is x [%], the volume ratio of the gel-forming polymer to the volume of the electrode active material layer is y [%], and the liquid absorption rate of the gel-forming polymer with respect to the electrolytic solution is z [%]: 0<yz / x≦8.7 ... formula (1) While searching for a means for improving the charge / discharge efficiency of a closed-type lithium-oxygen battery, the present inventors discovered that the electrode active material layer contains lithium oxide (Li２ They have found that containing a gel-forming polymer in addition to the catalyst and the catalyst, and controlling the above parameters (x, y, z) to have a predetermined relationship, is useful for improving charge-discharge efficiency.

[0011] The above-mentioned embodiments of the present invention will be described below with reference to the drawings. However, the technical scope of the present invention should be defined based on the claims and is not limited to the following embodiments. Note that the dimensional ratios in the drawings are exaggerated for the convenience of explanation and may differ from the actual ratios. In this specification, the range "X to Y" means "X or more and Y or less." Furthermore, unless otherwise specified, operations and measurements of physical properties, etc. are performed at room temperature (20 to 25°C) and a relative humidity of 40 to 50% RH.

[0012] FIG. 1 is a cross-sectional view showing a schematic representation of a stacked (flat) closed-type lithium-oxygen battery (hereinafter also simply referred to as a "stacked-type lithium-oxygen battery") according to one embodiment of the present invention. In this specification, the term "closed-type lithium-oxygen battery" refers to a battery in which charge and discharge reactions proceed in a sealed cell (i.e., the battery is free from the exchange of molecular oxygen (O ２ This "closed-type lithium-oxygen battery" refers to a lithium-oxygen battery (without the exchange of charge and discharge). This "closed-type lithium-oxygen battery" is disclosed in the above-mentioned JP 2015-159098 A, as well as in a document such as (Wang, J. et al., Reversible Conversion between Lithium Superoxide and Lithium Peroxide: A Closed "Lithium-Oxygen" Battery. Inorganics 2023, 11, 69.). In addition, in this embodiment, a case where the electrode according to this embodiment is a positive electrode will be described as an example, but the electrode can also be used as a negative electrode in a closed-type lithium-oxygen battery.

[0013] As shown in FIG. 1 , the stacked lithium-oxygen battery 10a of this embodiment has a structure in which a substantially rectangular power-generating element 21, where charge and discharge reactions actually proceed, is sealed inside a laminate film 29. Here, the power-generating element 21 has a configuration in which a positive electrode, in which a positive electrode active material layer 13 is disposed on both sides of a positive electrode current collector 11′, an electrolyte layer 17 made of a separator containing an electrolytic solution, and a negative electrode, in which a negative electrode active material layer 15 is disposed on both sides of a negative electrode current collector 12, are laminated. Specifically, the positive electrode, the electrolyte layer, and the negative electrode are laminated in this order, with one positive electrode active material layer 13 and the adjacent negative electrode active material layer 15 facing each other with the electrolyte layer 17 interposed therebetween. As a result, the positive electrode, the electrolyte layer, and the negative electrode constitute one unit cell layer 19. Therefore, the stacked lithium-oxygen battery 10a shown in FIG. 1 can also be said to have a configuration in which a plurality of unit cell layers 19 are stacked and electrically connected in parallel.

[0014] A positive electrode current collector 25 and a negative electrode current collector 27 that are electrically connected to the electrodes (positive and negative electrodes) are attached to the positive electrode current collector 11′ and the negative electrode current collector 12, respectively, and are configured to be sandwiched between the ends of the laminate film 29 and led out of the laminate film 29. The positive electrode current collector 25 and the negative electrode current collector 27 may be attached to the positive electrode current collector 11′ and the negative electrode current collector 12 of the electrodes by ultrasonic welding, resistance welding, or the like, via a positive electrode terminal lead and a negative electrode terminal lead (not shown), respectively, as needed.

[0015] The main components of the stacked lithium-oxygen battery according to this embodiment will be described below.

[0016] [Current Collector] The current collector has a function of mediating the movement of electrons from the positive electrode active material layer and the negative electrode active material layer described later. There are no particular limitations on the material constituting the current collector. For example, metals and conductive resins can be used as the material constituting the current collector.

[0017] [Electrode active material layer] The electrode active material layer is disposed on the surface of the current collector and contains lithium oxide as an electrode active material, a catalyst, and a gel-forming polymer. In particular, from the viewpoint of more significant contribution to the improvement of charge / discharge efficiency, the electrode active material layer is preferably a positive electrode active material layer. In this case, the electrode active material (lithium oxide) functions as a positive electrode active material.

[0018] (Lithium oxide) Lithium oxide is a compound in which lithium is covalently bonded to oxygen, and there are several compounds depending on the atomic ratio. Specifically, lithium oxide is Li ２ O, LiO, Li ２ O ２ and LiO ２ It is preferable that the lithium oxide contains one or more selected from the group consisting of Li ２ O, Li ２ O ２ or LiO ２ In particular, from the viewpoint of having a higher theoretical capacity and being chemically stable (hard to decompose and low in reactivity with moisture in the air and carbon dioxide) compared to other lithium oxides, it is more preferable to include Li ２ It is particularly preferred that O is contained.

[0019] When the electrode is a positive electrode, a conventionally known material can be used as the negative electrode active material constituting the negative electrode. Examples of such negative electrode active materials include carbon materials such as graphite, soft carbon, and hard carbon, lithium-transition metal composite oxides (e.g., Li ４ Ti ５ O １２ ), metal materials (tin, silicon), silicon-containing alloy-based negative electrode materials (e.g., Si ６０ Sn １０ Ti ３０ and lithium alloy-based negative electrode materials (e.g., lithium-tin alloy, lithium-silicon alloy, lithium-aluminum alloy, lithium-aluminum-manganese alloy, etc.). From the viewpoint of capacity and output characteristics, silicon-containing alloy-based negative electrode materials, carbon materials, lithium-transition metal composite oxides, and lithium alloy-based negative electrode materials are preferably used as the negative electrode active material.

[0020] (Catalyst) A catalyst is a substance that has the function of promoting the bonding / dissociation reaction between the lithium oxide and oxygen by reducing the activation energy of these reactions. Any conventionally known compound can be used as a catalyst as long as it can exhibit this function. As an example, the catalyst is preferably a compound containing a transition metal (a transition metal-containing compound). This transition metal-containing compound is preferably in the form of, for example, an oxide (including composite oxides), sulfide, halide, nitride, carbide, or the like containing the transition metal. Among these, from the viewpoint of excellent catalytic activity, the catalyst preferably contains a transition metal-containing oxide. When the catalyst contains a transition metal-containing compound, there are no particular limitations on the type of transition metal contained in the compound, and the atom may be any metal classified as a transition metal, and one or more types may be used. Among these, from the viewpoint of catalytic activity, the transition metal is preferably at least one transition metal belonging to Groups 6 to 11 of the periodic table, more preferably one or more selected from the group consisting of cobalt, manganese, iron, nickel, molybdenum, iridium, and rhodium, particularly preferably one or more selected from the group consisting of cobalt, manganese, and iron, and most preferably cobalt. Examples of transition metal-containing compounds include transition metal-containing oxides such as cobalt oxide, manganese oxide, iron oxide, nickel oxide, molybdenum oxide, iridium oxide, and rhodium oxide. Among these, cobalt oxide, manganese oxide, and iron oxide are preferred, and cobalt oxide (e.g., Co ３ O ４ ) is particularly preferred.

[0021] The content of the catalyst in the electrode active material layer is not particularly limited, and although it depends on the types of lithium oxide and catalyst, it is preferably 50 to 500 mass%, more preferably 100 to 450 mass%, even more preferably 200 to 400 mass%, and particularly preferably 250 to 350 mass%, relative to 100 mass% of the total amount of the lithium oxide when the battery is fully discharged.

[0022] (Gel-forming polymer) The gel-forming polymer is an ion-conductive polymer, and can form a structure together with the electrode active material to play a role in ion conduction. From the viewpoint of charge / discharge efficiency and output characteristics, the gel-forming polymer preferably contains at least one selected from the group consisting of polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene (PVdF-HEP), polymethyl methacrylate (PMMA), polyethylene glycol dimethacrylate, polyethylene glycol diacrylate, polypropylene glycol dimethacrylate, polypropylene glycol diacrylate, polymethyl methacrylate, and copolymers thereof. Furthermore, from the viewpoint of further improving charge / discharge efficiency and output characteristics, the gel-forming polymer is preferably selected from polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HEP), and polymethyl methacrylate (PMMA). Furthermore, in a more preferred embodiment, the gel-forming polymer includes one containing a structural unit derived from vinylidene fluoride in the main chain (e.g., polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HEP), etc.). In a particularly preferred embodiment, the gel-forming polymer includes polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HEP). PVdF-HFP has high swelling properties in electrolytes, which can improve the ionic conductivity of lithium ions and the like in the electrode active material layer. Furthermore, because PVdF-HFP is highly flexible, it can penetrate into the gaps between other components (electrode active materials, catalysts, conductive additives, etc.) contained in the electrode active material layer, improving their dispersibility. As a result, it is believed that electron conduction paths are well formed, enabling excellent charge / discharge efficiency.

[0023] PVdF-HFP is not particularly limited as long as it is a copolymer of vinylidene fluoride and hexafluoropropylene. The lower limit of the proportion of hexafluoropropylene-derived structural units contained in PVdF-HFP is preferably 4 mol% or more, more preferably 6 mol% or more, and even more preferably 6.5 mol% or more, relative to the total structural units of PVdF-HFP. The lower limit of the proportion of hexafluoropropylene-derived structural units contained in PVdF-HFP is preferably 20 mol% or less, more preferably 10 mol% or less, and even more preferably 8 mol% or less. By having the proportion of hexafluoropropylene-derived structural units in the above range, swelling in the electrolyte and flexibility can be further improved. As a result, the ionic conductivity and electronic conductivity of the electrode active material layer are improved, and excellent charge / discharge efficiency can be exhibited.

[0024] The content of the gel-forming polymer in the electrode active material layer is not particularly limited, and although it depends on the types of lithium oxide and gel-forming polymer, it is preferably 10 to 100% by mass, more preferably 12 to 70% by mass, and even more preferably 15 to 60% by mass relative to 100% by mass of the total amount of the lithium oxide when the battery is fully discharged.

[0025] (Binders other than gel-forming polymers) The electrode active material layer may further contain binders other than the gel-forming polymers described above. Examples of such binders include polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide. However, the lower the content of these binders, the better. Specifically, the content of the gel-forming polymer in 100% by mass of the total amount of binders is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass.

[0026] (Conductive Aid) The electrode active material layer may further contain a conductive aid. The conductive aid has the function of forming an electron conduction path (conductive passage) in the electrode active material layer. When such an electron conduction path is formed in the positive electrode active material layer, the internal resistance of the battery may be reduced and the rate characteristics may be improved.

[0027] Examples of the conductive aid include particulate carbon materials such as acetylene black, carbon black, channel black, thermal black, and Ketjen Black (registered trademark), and fibrous carbon materials such as carbon nanotubes (single-walled carbon nanotubes and multi-walled carbon nanotubes), carbon nanofibers, vapor-grown carbon fibers, electrospun carbon fibers, polyacrylonitrile-based carbon fibers, and pitch-based carbon fibers. One type of conductive aid may be used alone, or two or more types may be used in combination.

[0028] The content of the conductive additive contained in the electrode active material layer is preferably 15% by mass or less, more preferably 12% by mass or less, and even more preferably 10% by mass or less, relative to 100% by mass of the total solids content of the electrode active material layer. At such an upper limit, aggregation of the conductive additives is suppressed, thereby favorably forming an electron conduction path, thereby further improving charge / discharge efficiency. The lower limit of the conductive additive content is not particularly limited, but is preferably greater than 0% by mass, more preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more. At such a lower limit, sufficient conductive additive is present to form an electron conduction path, thereby further improving charge / discharge efficiency.

[0029] While there are no particular limitations on the form in which each component (lithium oxide, catalyst, gel-forming polymer, and optional conductive additive) in the electrode active material layer exists, it is preferable that these components are present so that the lithium oxide and catalyst involved in the battery reaction are in contact with each other. In particular, it is more preferable that the lithium oxide and catalyst are in the form of composite particles combined with a gel-forming polymer. Here, the lithium oxide and catalyst are "in the form of composite particles" means that when a charge / discharge reaction is carried out in a closed-type lithium-oxygen battery, the particles do not collapse and maintain their particle shape even if the lithium oxide expands and contracts during charge / discharge. This configuration allows the charge / discharge reaction to proceed more smoothly when the lithium oxide is used as an electrode material, which can effectively contribute to further improving the capacity characteristics of the battery.

[0030] [Relationship between Porosity of Electrode Active Material Layer, Volume Proportion of Gel-Forming Polymer, and Liquid Absorption Rate of Gel-Forming Polymer] As described above, the battery according to this embodiment is characterized in that it satisfies the formula (1): 0<yz / x≦8.7, where x [%] is the porosity of the electrode active material layer, y [%] is the volume proportion of the gel-forming polymer in the volume of the electrode active material layer, and z [%] is the liquid absorption rate of the gel-forming polymer with respect to the electrolyte solution contained in the electrolyte layer. The present inventors have found that there are appropriate ranges for the porosity of the electrode active material layer (x), the volume proportion of the gel-forming polymer in the volume of the electrode active material layer (y), and the liquid absorption rate of the gel-forming polymer with respect to the electrolyte solution contained in the electrolyte layer (z) from the perspective of battery charge / discharge efficiency, and have quantified this finding using the above formula.

[0031] If the yz / x value exceeds 8.7 (i.e., if the volume fraction of the gel-forming polymer is too high or the liquid absorption rate is too high), sufficient charge / discharge efficiency cannot be achieved. This is thought to be due to the fact that when the lithium oxide, which is the electrode active material, shrinks, the gel-forming polymer penetrates between the electrode active material and the catalyst, reducing the contact point (reaction field) between them and making it difficult for the subsequent battery reaction to proceed. In contrast, if the yz / x value is 8.7 or less, the gel-forming polymer can appropriately follow the shrinkage of the lithium oxide, and sufficient contact between the electrode active material and the catalyst is maintained throughout the charge / discharge reaction. Furthermore, the flexibility of the gel-forming polymer suppresses the movement of the electrode active material and catalyst within the active material layer, effectively preventing the detachment of these materials. These mechanisms are thought to enable the initial contact state between the electrode active material and the catalyst to be maintained even after repeated charge / discharge, thereby maintaining the initial capacity (i.e., improving charge / discharge efficiency). However, the above mechanism is merely based on speculation, and the correctness of this mechanism does not affect the technical scope of the present invention.

[0032] From the viewpoint of further improving the charge-discharge efficiency, the value of yz / x preferably satisfies the formula (2): 1.4≦yz / x≦8.7, more preferably satisfies the formula (3): 3.2≦yz / x≦5.7, and even more preferably satisfies the formula (4): 3.8≦yz / x≦4.8. When the value of yz / x is within these ranges, the gel-forming polymer exhibits better compliance with the contraction of the lithium oxide, thereby further improving the charge-discharge efficiency. The values ​​of x, y, and z are calculated by the method described in the Examples below. In addition, in this specification, "improved charge-discharge efficiency" means that when the battery according to the present embodiment is constructed, the initial charge-discharge efficiency is improved compared to when a battery (comparative battery) having the same configuration except that it does not satisfy the specifications of the battery according to the present embodiment is constructed. There is no particular limitation on the degree of improvement in the initial charge-discharge efficiency, but the initial charge-discharge efficiency of the battery according to this embodiment is preferably 105 or more, more preferably 119 or more, even more preferably 125 or more, and particularly preferably 127 or more, when the initial charge-discharge efficiency of the comparative battery is taken as 100. The initial charge-discharge efficiency is measured using the method described in the Examples section below.

[0033] The above x can be controlled by adjusting the particle size of the electrode active material, the amount of gel-forming polymer charged, the thickness of the electrode active material layer, the pressing conditions during electrode production, etc. From the viewpoint of further improving charge / discharge efficiency, the porosity (x) of the electrode active material layer preferably satisfies 25≦x≦70, more preferably 25≦x≦50, even more preferably 28≦x≦37, and particularly preferably 30≦x≦37.

[0034] The above y can be controlled by adjusting the content of the gel-forming polymer in the electrode active material layer, etc. From the viewpoint of further improving charge / discharge efficiency, the ratio (y) of the volume of the gel-forming polymer to the volume of the electrode active material layer preferably satisfies 7.0≦y≦15.0, more preferably 9.0≦y≦13.0, and even more preferably 10.5≦y≦12.5.

[0035] Furthermore, the above z can be controlled by changing the type of gel-forming polymer or the composition of the electrolyte solution. From the viewpoint of further improving charge / discharge efficiency, the liquid absorption rate (z) of the gel-forming polymer preferably satisfies 10≦z≦100, and more preferably 12≦x≦50.

[0036] The thickness of the electrode active material layer is not particularly limited, and conventionally known knowledge about batteries can be appropriately referenced. For example, the thickness of the electrode active material layer is usually about 1 to 1000 μm, preferably 20 to 800 μm, more preferably 30 to 500 μm, and even more preferably 40 to 200 μm. The thicker the electrode active material layer, the more electrode active material can be retained to achieve sufficient capacity (energy density). On the other hand, the thinner the electrode active material layer, the more the discharge rate characteristics can be improved.

[0037] [Electrolyte Layer] The electrolyte layer contains an electrolytic solution (liquid electrolyte) and preferably has a configuration in which a separator is impregnated with the electrolytic solution.

[0038] (Electrolyte) The electrolyte functions as a carrier of lithium ions. The electrolyte has a form in which a lithium salt is dissolved in a non-aqueous solvent. Preferably, the electrolyte is obtained by further adding a fluorine-containing carbonate to the non-aqueous solvent in which the lithium salt is dissolved.

[0039] The non-aqueous solvent is preferably one that can easily dissolve lithium salts, and examples thereof include chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and methyl ethyl carbonate (MEC); fluorine-containing chain carbonates in which some of the hydrogen atoms of these chain carbonates have been substituted with fluorine atoms; ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (MC). fluorine-containing cyclic carbonates in which some of the hydrogen atoms of these cyclic carbonates have been substituted with fluorine atoms; methyl propionate (MP), methyl acetate (MA), methyl formate (MF), 4-methyldioxolane (4MeDOL), dioxolane (DOL), 2-methyltetrahydrofuran (2MeTHF), tetrahydrofuran (THF), dimethoxyethane (DME), dimethyl sulfoxide (DMSO), and γ-butyrolactone (GBL).

[0040] In particular, from the viewpoint of further improving the rapid charging characteristics and output characteristics, the non-aqueous solvent preferably contains a chain carbonate, and more preferably contains at least one selected from the group consisting of diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

[0041] The lithium salt is Li(FSO ２ ) ２ N(lithium bis(fluorosulfonyl)imide; LiFSI), Li(C ２ F ５ SO ２ ) ２ N, LiPF ６ , LiBF ４ , LiClO ４ , LiAsF ６ , LiCF ３ SO ３ etc.

[0042] The concentration of the lithium salt in the non-aqueous solvent is preferably 0.1 to 3.0 mol / L, and more preferably 0.8 to 2.2 mol / L.

[0043] In addition, it is preferable that the electrolyte solution further contains a fluorine-containing carbonate such as a fluorine-containing cyclic carbonate or a fluorine-containing chain carbonate. By doing so, the battery can have excellent durability even when operated at high voltage. In addition, these fluorine-containing carbonates can form a protective film on the surface of the positive electrode active material, thereby improving the voltage resistance of the positive electrode active material.

[0044] In this case, as the fluorine-containing carbonate, fluorine-containing cyclic carbonates such as fluoroethylene carbonate (FEC), difluoroethylene carbonate, and 4-fluoropropylene carbonate; and fluorine-containing chain carbonates such as ethyl trifluoromethyl carbonate, 2,2,2-trifluoroethyl methyl carbonate, and bis(2,2,2-trifluoroethyl) carbonate can be preferably used. The content of the fluorine-containing carbonate is not particularly limited. In a preferred embodiment, the electrolytic solution contains 0.5 to 10 mass% of the fluorine-containing carbonate, particularly fluoroethylene carbonate, based on the total amount of the finally obtained electrolytic solution. This can more significantly achieve the above-mentioned effect. Note that when the electrolytic solution contains two or more types of fluorine-containing carbonates, it is preferable that the total amount thereof is within the above-mentioned range.

[0045] The electrolyte may further contain additives other than the above-mentioned components. Specific examples of such compounds include vinylene carbonate, methyl vinylene carbonate, dimethyl vinylene carbonate, phenyl vinylene carbonate, diphenyl vinylene carbonate, ethyl vinylene carbonate, diethyl vinylene carbonate, vinyl ethylene carbonate, 1,2-divinyl ethylene carbonate, 1-methyl-1-vinyl ethylene carbonate, 1-methyl-2-vinyl ethylene carbonate, 1-ethyl-1-vinyl ethylene carbonate, and 1-ethyl-2-vinyl ethylene carbonate. ester, vinyl vinylene carbonate, allyl ethylene carbonate, vinyloxymethyl ethylene carbonate, allyloxymethyl ethylene carbonate, acryloxymethyl ethylene carbonate, methacryloxymethyl ethylene carbonate, ethynyl ethylene carbonate, propargyl ethylene carbonate, ethynyloxymethyl ethylene carbonate, propargyloxyethylene carbonate, methylene ethylene carbonate, 1,1-dimethyl-2-methylene ethylene carbonate, etc. These additives may be used alone or in combination of two or more. In addition, when an additive is used in the electrolytic solution, the amount used can be appropriately adjusted.

[0046] (Separator) The separator constituting the electrolyte layer has the function of retaining the electrolyte to ensure lithium ion conductivity between the positive electrode and the negative electrode, and also functions as a partition wall between the positive electrode and the negative electrode.

[0047] The separator may be in the form of, for example, a porous sheet separator made of polymer or fiber that absorbs and retains the electrolyte solution, or a nonwoven fabric separator.

[0048] As a separator made of a porous sheet of polymer or fiber, for example, a microporous material (microporous membrane) can be used. Specific forms of the porous sheet made of polymer or fiber include microporous (microporous membrane) separators made of polyolefins such as polyethylene (PE) and polypropylene (PP), laminates of multiple layers of these (for example, a laminate with a three-layer structure of PP / PE / PP), hydrocarbon resins such as polyimide, aramid, and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and glass fibers.

[0049] As the nonwoven fabric separator, conventionally known materials such as cotton, rayon, acetate, nylon, polyester; polyolefins such as PP and PE; polyimide, aramid, etc. may be used alone or in combination.

[0050] The thickness of the separator may be the same as that of the electrolyte layer, and is preferably 5 to 200 μm, and particularly preferably 10 to 100 μm.

[0051] Furthermore, a separator having a heat-resistant insulating layer laminated on a porous substrate (a separator with a heat-resistant insulating layer) can be used. The heat-resistant insulating layer is a ceramic layer containing inorganic particles and a binder. A separator with a heat-resistant insulating layer is used that has high heat resistance, with a melting point or thermal softening point of 150°C or higher, preferably 200°C or higher. The presence of a heat-resistant insulating layer can mitigate the internal stress of the separator that increases with temperature rise, thereby suppressing thermal shrinkage. As a result, short circuits between battery electrodes can be prevented, resulting in a battery configuration that is less susceptible to performance degradation due to temperature rise. Furthermore, the presence of a heat-resistant insulating layer improves the mechanical strength of the separator with a heat-resistant insulating layer, making it less likely to rupture. Furthermore, the heat-shrinkage suppression effect and high mechanical strength make the separator less likely to curl during the battery manufacturing process.

[0052] [Positive electrode current collector plate and negative electrode current collector plate] The material constituting the current collector plate (25, 27) is not particularly limited, and known highly conductive materials conventionally used as current collector plates for lithium ion secondary batteries can be used. Metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferred as constituent materials of the current collector plate. From the viewpoints of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. The positive electrode current collector plate 25 and the negative electrode current collector plate 27 may be made of the same material or different materials.

[0053] As described above, the closed-type lithium-oxygen battery according to the present invention has excellent charge / discharge efficiency, and is therefore suitable for use as a power source for driving EVs and HEVs.

[0054] The above describes a closed-type lithium-oxygen battery according to one embodiment of the present invention. However, the present invention is not limited to the configurations described in the above-described embodiments, and can be modified as appropriate based on the claims.

[0055] The following embodiments are also included within the scope of the present invention: a battery according to claim 1 having the features of claim 2; a battery according to claim 1 or 2 having the features of claim 3; a battery according to any one of claims 1 to 3 having the features of claim 4; a battery according to any one of claims 1 to 4 having the features of claim 5; a battery according to any one of claims 1 to 5 having the features of claim 6; a battery according to claim 6 having the features of claim 7; a battery according to any one of claims 1 to 7 having the features of claim 8; a battery according to any one of claims 1 to 8 having the features of claim 9; a battery according to any one of claims 1 to 9 having the features of claim 10; and a battery according to any one of claims 1 to 10 having the features of claim 11.

[0056] The present invention will be described in more detail below with reference to examples, although the technical scope of the present invention is not limited to the following examples.

[0057] <<Fabrication of Closed-Type Lithium-Oxygen Battery>> [Measurement Methods] In the following examples and comparative examples, the values ​​of x, y, and z were measured using the following measurement methods.

[0058] (Measurement of Porosity (x) of Porosity Layer) The porosity (x) of the positive electrode active material layer was measured as follows: (1) The mass per unit area of ​​the positive electrode active material layer was measured. Then, the mass of each material per unit area of ​​the positive electrode active material layer was determined from the compounding ratio of the materials. (2) The thickness [A] of the positive electrode active material layer was measured using a micrometer. (3) The thickness [B] of the positive electrode active material layer when the porosity was 0% was calculated using the mass of each material determined in (1) and the density of each material. (4) The pore volume of the positive electrode active material layer was calculated from the difference (A - B) between the measured thickness of the positive electrode active material layer and the calculated thickness of the positive electrode active material layer, and the pore volume per m of the positive electrode active material layer was calculated. ３ The pore volume per unit area was determined, and the percentage of the obtained value was taken as the porosity x [%].

[0059] (Measurement of Volume Proportion (y) of Gel-Forming Polymer to the Volume of Positive Electrode Active Material Layer) With regard to the volume proportion (y) of the gel-forming polymer to the volume of the positive electrode active material layer, the volume proportion y [%] of the gel-forming polymer to the volume of the positive electrode active material layer obtained was calculated based on the following formulas: Volume of gel-forming polymer = (mass of gel-forming polymer) / (density of gel-forming polymer) Volume proportion (y) of gel-forming polymer = (volume of gel-forming polymer) / [total volume of positive electrode active material layer × (1 - x / 100)].

[0060] (Measurement of Absorption Ratio (z) of Gel-Forming Polymer for Electrolyte) The absorption ratio (z) of the gel-forming polymer for the electrolyte was calculated by measuring the weight of the gel-forming polymer before and after immersion in the electrolyte and using the following formula: Absorption ratio (%) = [(Weight of gel-forming polymer after immersion in electrolyte - Weight of gel-forming polymer before immersion in electrolyte) / Weight of gel-forming polymer before immersion in electrolyte] × 100. The electrolyte used here was the same as the electrolyte used in producing the battery.

[0061] [Example 1] (Preparation of Positive Electrode Material) Lithium oxide (Li ２ O, manufactured by Kojundo Chemical Laboratory Co., Ltd.) and cobalt oxide (Co ３ O ４ , manufactured by Kojundo Chemical Laboratory Co., Ltd.) and another 70 mL pot for a planetary ball mill were placed in each pot and crushed in a planetary ball mill (crushing conditions: treatment for 1 hour at 400 rpm using 40 g of 3 mmφ zirconia balls and 15 g of 15 mmφ zirconia balls).

[0062] Next, 5 g of the crushed lithium oxide and 15 g of cobalt oxide were placed in a 70 mL planetary ball mill pot and mixed in a planetary ball mill (mixing conditions: treatment for 1 hour at 400 rpm using 40 g of 3 mmφ zirconia balls and 15 15 mmφ zirconia balls).

[0063] On the other hand, a gel-forming polymer, PVdF-HFP (Kyner Flex 2501, manufactured by Arkema, proportion of the number of constitutional units derived from hexafluoropropylene: 6.9 mol%; liquid absorption (z) = 13[%]), and an appropriate amount of a solvent, N-methyl-2-pyrrolidone (NMP, manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), were kneaded (kneading conditions: 2000 rpm for 5 minutes) using a planetary stirring mixer kneader "Awatori Rentaro" (ARE-310, manufactured by Thinky Corporation), to dissolve the PVdF-HFP in NMP. The mixture of lithium oxide and cobalt oxide mixed in the ball mill described above and the conductive additive acetylene black (AB) (Li-400, manufactured by Denka Co., Ltd., average primary particle size: 48 nm, aspect ratio: 1) were added to the NMP solution of PVdF-HFP obtained in this way, and further kneading was performed using the above-mentioned mixing and kneading device (kneading conditions: 2000 rpm for 5 minutes). The resulting mixture was transferred to a metal tray and placed on a hot plate heated to 120°C to volatilize the NMP. The remaining powder was then collected and mixed by hand in an agate mortar for 5 minutes to prepare the positive electrode material of Example 1. In the positive electrode material of this example, the mixing ratio (mass ratio) of lithium oxide:cobalt oxide:acetylene black:PVdF-HFP was 20:60:10:10.

[0064] (Preparation of Positive Electrode) NMP was added to the positive electrode material prepared above to adjust the solid content to 25% by mass, and the viscosity was adjusted to prepare a positive electrode slurry. The positive electrode slurry was uniformly applied to aluminum foil placed on a smooth plate using a doctor blade so that the final thickness of the positive electrode active material layer was 200 μm. The resultant laminate was then dried for 30 minutes on a hot plate heated to 80°C, and then pressed using a roll press. The resultant laminate was then transferred to a vacuum dryer and dried under vacuum at 130°C for 8 hours to prepare a positive electrode of this example in which a positive electrode active material layer was formed on the surface of the aluminum foil. The porosity (x) of the positive electrode active material layer was 28%. The volume ratio (y) of the gel-forming polymer (PVdF-HFP) to the volume of the positive electrode active material layer was 12.2. As a result, the value of yz / x was calculated to be 12.2 × 13 / 28 = 5.7.

[0065] (Fabrication of Closed-Type Lithium-Oxygen Battery (Coin Cell)) The positive electrode and lithium counter electrode fabricated above were placed opposite each other, and a separator (polyolefin, thickness: 20 μm) was placed between them. Next, the laminate of the positive electrode, separator, and lithium counter electrode was placed in a coin cell (CR2032, material: stainless steel (SUS316)), and the following electrolyte solution was injected using a syringe and sealed to fabricate the closed-type lithium-oxygen battery (coin cell) of this example. The electrolyte solution was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a ratio of EC:DEC = 3:7 (volume ratio), dissolved in an organic solvent containing lithium hexafluorophosphate (LiPF ６ ) dissolved at a concentration of 1 mol / L was used.

[0066] [Examples 2 to 4] Closed-type lithium-oxygen batteries (coin cells) of these examples were produced using the same method as in Example 1 described above, except that the conditions for the press treatment were changed so that the porosity (x [%]) of the positive electrode active material layer and the volume ratio (y [%]) of the gel-forming polymer to the volume of the positive electrode active material layer were the values ​​shown in Table 1 below.

[0067] Example 5 A closed-type lithium-oxygen battery (coin cell) of this example was produced using the same method as in Example 1 described above, except that the amounts of the positive electrode active material (lithium oxide) and the catalyst (cobalt oxide) used were changed to the values ​​shown in Table 1 below, and the conditions of the pressing process were changed so that the porosity (x [%]) of the positive electrode active material layer and the volume ratio (y [%]) of the gel-forming polymer to the volume of the positive electrode active material layer were the values ​​shown in Table 1 below.

[0068] Example 6 A closed-type lithium-oxygen battery (coin cell) of this example was produced using the same method as in Example 1 described above, except that PVdF-HFP (Kyner Flex 2501) was replaced with PVdF-HFP (Kyner Flex 2851, manufactured by Arkema; ​​proportion of the number of constitutional units derived from hexafluoropropylene: 2.4 mol %; liquid absorption rate (z)=45[%]) as the gel-forming polymer, and the conditions of the pressing treatment were changed so that the porosity (x[%]) of the positive electrode active material layer and the volume ratio (y[%]) of the gel-forming polymer to the volume of the positive electrode active material layer were the values ​​shown in Table 1 below.

[0069] Example 7 A closed-type lithium-oxygen battery (coin cell) of this example was produced using the same method as in Example 5 described above, except that PVDF (Kureha KF Polymer W#9700, manufactured by Kureha; liquid absorption rate (z)=95[%]) was used as the gel-forming polymer instead of PVdF-HFP (Kyner Flex 2501), and the conditions for the press treatment were changed so that the porosity (x[%]) of the positive electrode active material layer and the volume ratio (y[%]) of the gel-forming polymer to the volume of the positive electrode active material layer were the values ​​shown in Table 1 below.

[0070] Comparative Example 1 A closed-type lithium-oxygen battery (coin cell) of this comparative example was produced using the same method as in Example 1 described above, except that the amounts of the positive electrode active material (lithium oxide), catalyst (cobalt oxide), and gel-forming polymer (PVdF-HFP) used were changed to the values ​​shown in Table 1 below, and the conditions of the pressing process were changed so that the porosity (x [%]) of the positive electrode active material layer and the volume ratio (y [%]) of the gel-forming polymer to the volume of the positive electrode active material layer were the values ​​shown in Table 1 below.

[0071] Comparative Example 2 A closed-type lithium-oxygen battery (coin cell) of this comparative example was produced using the same method as in Example 5 described above, except that PVDF (Kureha KF Polymer W#7200, manufactured by Kureha; liquid absorption rate (z) = 120 [%]) was used as the gel-forming polymer instead of PVdF-HFP (Kyner Flex 2501), and the conditions of the press treatment were changed so that the porosity (x [%]) of the positive electrode active material layer and the volume ratio (y [%]) of the gel-forming polymer to the volume of the positive electrode active material layer were the values ​​shown in Table 1 below.

[0072] <<Evaluation of Coin Cells (Measurement of Initial Charge-Discharge Efficiency)>> The closed-type lithium-oxygen batteries (coin cells) of the Examples and Comparative Examples prepared above were subjected to the following charge-discharge test (initial charge-discharge) in a thermostatic chamber set at 300 K (27°C), and the charge capacity and discharge capacity were measured. The ratio of the discharge capacity to the charge capacity was calculated to provide the initial charge-discharge efficiency. The results are shown in Table 1 below. The initial charge-discharge efficiency values ​​shown in Table 1 are relative values, with the measured value for Comparative Example 2 set to 100.

[0073] (Charge / Discharge Test Conditions) Charge / Discharge Tester: TOSCAT-3000, Model TYS-30TU10 (manufactured by Toyo Systems Co., Ltd.) Charge / Discharge Conditions: [Charge process] 0.02 C (current density 18 mA / g), 1.8 V → 4.6 V (CCCV; 0.01 C cutoff) [Discharge process] 0.02 C (current density 18 mA / g), 4.6 V → 1.8 V (CC) Rest time between charge and discharge processes: 30 minutes.

[0074]

[0075] From the results shown in Table 1, according to the present invention, it is possible to obtain a positive electrode active material layer containing lithium oxide (Li ２ It can be seen that the charge-discharge efficiency of a closed-type lithium-oxygen battery can be improved by incorporating a gel-forming polymer in addition to the catalyst (x, y, z) and controlling the above parameters (x, y, z) to have a predetermined relationship.

[0076] 10a: laminated lithium-oxygen battery; 11': positive electrode current collector; 12: negative electrode current collector; 13: positive electrode active material layer; 15: negative electrode active material layer; 17: electrolyte layer; 19: single cell layer; 21: power generating element; 25: positive electrode current collector (positive electrode tab); 27: negative electrode current collector (negative electrode tab); 29: laminate film.

Claims

The battery comprises an electrode in which an electrode active material layer containing lithium oxide, a catalyst, and a gel-forming polymer is disposed on the surface of a current collector, and an electrolyte layer in which a separator disposed adjacent to the electrode is impregnated with an electrolytic solution, A closed-type lithium-oxygen battery, wherein the relationship of the following formula (1) is satisfied when the porosity of the electrode active material layer is x [%], the volume ratio of the gel-forming polymer to the volume of the electrode active material layer is y [%], and the liquid absorption rate of the gel-forming polymer with respect to the electrolyte is z [%]: 0<yz / x≦8.7 Formula (1) 　 The closed-type lithium-oxygen battery according to claim 1, further satisfying the following formula (2): 1.4≦yz / x≦8.7...Formula (2) 　 The closed-type lithium-oxygen battery according to claim 2, further satisfying the following formula (3): 3.2≦yz / x≦5.7...Formula (3) 3. The closed-type lithium-oxygen battery according to claim 1, wherein y satisfies 7.0≦y≦15.

0.

3. The closed-type lithium-oxygen battery according to claim 1, wherein x satisfies 25≦x≦50.

3. The closed-type lithium-oxygen battery according to claim 1, wherein the gel-forming polymer contains a structural unit derived from vinylidene fluoride in the main chain.

7. The closed-type lithium-oxygen battery of claim 6, wherein the gel-forming polymer comprises vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP). 　 The lithium oxide is Li ２ O, LiO, Li ２ O ２ and LiO ２ 3. The closed-type lithium-oxygen battery according to claim 1, comprising one or more selected from the group consisting of:

3. The closed-type lithium-oxygen battery according to claim 1, wherein the catalyst comprises a transition metal-containing oxide.

10. The closed-type lithium-oxygen battery according to claim 9, wherein the transition metal contained in the transition metal-containing oxide comprises one or more selected from the group consisting of cobalt, manganese, iron, nickel, molybdenum, iridium, and rhodium.

3. The closed-type lithium-oxygen battery according to claim 1, wherein the electrode active material layer is a positive electrode active material layer.

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