Lithium-containing composition, and positive electrode material for a sealed lithium-oxygen battery, positive electrode for a sealed lithium-oxygen battery, and sealed lithium-oxygen battery using the same

Abstract

This disclosure provides a solution for improving the capacity characteristics of a hermetically sealed lithium-oxygen battery. A lithium-containing composition comprising lithium oxide, a catalyst, and a conductive polymer is disclosed. This composition is useful as a positive electrode material for hermetically sealed lithium-oxygen batteries.

Description

Technical Field

[0001] This invention relates to lithium-containing compositions, positive electrode materials for sealed lithium-oxygen batteries using the same, positive electrodes for sealed lithium-oxygen batteries, and sealed lithium-oxygen batteries. Background Technology

[0002] In recent years, the widespread adoption of electric vehicles has been highly anticipated in order to address environmental and energy issues. As a key factor in the widespread adoption of these electric vehicles, on-board power supplies, such as the power source for the electric motor drive, are being actively developed into secondary batteries. Among these secondary batteries, high-energy-density, high-power lithium-ion batteries and other non-aqueous electrolyte secondary batteries are expected to attract significant attention.

[0003] Lithium-oxygen batteries (Li-Oxygen secondary batteries) are a type of non-aqueous electrolyte secondary battery. Among all secondary batteries, including next-generation batteries, Li-Oxygen batteries have the highest theoretical energy density, and are expected to possess battery performance with energy densities far exceeding those of existing lithium-ion secondary batteries. However, their full capacity characteristics have not yet been achieved, and further improvements are needed.

[0004] Lithium-oxygen batteries can be broadly categorized into two types: those that use gaseous molecular oxygen (O2) as an oxygen source, consuming O2 during discharge and generating O2 during charging (lithium-air batteries); and those that do not involve such O2 consumption or generation (lithium-oxygen batteries in the narrow sense). Since the latter does not involve O2 exchange with the atmosphere, it can be constructed as a sealed battery cell, and can be called a "sealed lithium-oxygen battery."

[0005] Currently, Japanese Patent Application Publication No. 2015-159098 discloses the aforementioned sealed lithium-oxygen battery. In this document, as a sealed type, atmospheric moisture, carbon dioxide, etc., are prevented from entering the battery cell. Furthermore, a raw material composition containing lithium oxide (Li₂O) as the electrode active material and oxides containing transition metal atoms (such as Co₃O₄) as a catalyst is micronized using mechanochemical processing, thereby attempting to achieve high capacity of the electrode active material. Summary of the Invention

[0006] The problem the invention aims to solve

[0007] According to the research of the inventors, even when using the technology disclosed in Japanese Patent Application Publication No. 2015-159098 to manufacture a sealed lithium-oxygen battery, it is sometimes still impossible to achieve sufficient capacity characteristics.

[0008] Therefore, the purpose of this invention is to provide a solution that can improve the capacity characteristics of a sealed lithium-oxygen battery.

[0009] Solution for solving the problem

[0010] One aspect of the present invention is a lithium-containing composition comprising lithium oxide, a catalyst, and a conductive polymer. Attached Figure Description

[0011] Figure 1 This is a schematic cross-sectional view of a stacked (flat) hermetically sealed lithium-oxygen battery as one embodiment of the present invention. Detailed Implementation

[0012] One aspect of the invention comprises a lithium-containing composition comprising lithium oxide, a catalyst, and a conductive polymer. This lithium-containing composition is useful as a positive electrode material for a hermetically sealed lithium-oxygen battery.

[0013] In exploring cathode materials that can improve the capacity characteristics of sealed lithium-oxygen batteries, the inventors discovered that using a lithium-containing composition that further contains a conductive polymer, in addition to lithium oxide (Li₂O) and a catalyst, as the cathode material is useful for improving capacity characteristics. Hereinafter, an example will be given using the lithium-containing composition of this method as the cathode material of a sealed lithium-oxygen battery; however, this lithium-containing composition can also be used for other applications.

[0014] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the scope of the present invention should be determined based on the claims and is not limited to the following description. It should be noted that the scale of the accompanying drawings is exaggerated for ease of explanation and may sometimes differ from the actual scale. In this specification, "X~Y" indicating a range means "X and above and Y and below". Furthermore, unless otherwise specified, measurements of operation and physical properties are performed at room temperature (20~25°C) and relative humidity 40~50%RH.

[0015] Figure 1 This is a schematic cross-sectional view illustrating a stacked (flat) type sealed lithium-oxygen battery (hereinafter also simply referred to as a "stacked lithium-oxygen battery") according to one embodiment of the present invention. It should be noted that, in this specification, a "sealed lithium-oxygen battery" refers to a lithium-oxygen battery in which the battery cells undergo charging and discharging reactions in a sealed state (therefore, no exchange of molecular oxygen (O2) with the atmosphere occurs during the charging and discharging reactions). Regarding this "sealed lithium-oxygen battery," in addition to the aforementioned Japanese Patent Application Publication No. 2015-159098, it has also been disclosed in documents such as (Wang, J. et al., Reversible Conversion between Lithium Superoxide and Lithium Peroxide: A Closed “Lithium-Oxygen” Battery. Inorganics 2023, 11, 69.).

[0016] like Figure 1 As shown, the stacked lithium-oxygen battery 10a of this embodiment has a structure in which a generally rectangular power generation element 21, which actually performs the charge-discharge reaction, is sealed inside a laminated film 29. Here, the power generation element 21 has the following configuration: a positive electrode on which a positive active material layer 13 is disposed on both sides of the positive current collector 11', an electrolyte layer 17 composed of a separator containing electrolyte, and a negative electrode on which a negative active material layer 15 is disposed on both sides of the negative current collector 12. Specifically, the positive electrode, electrolyte layer, and negative electrode are stacked sequentially with one positive active material layer 13 and an adjacent negative active material layer 15 facing each other across the electrolyte layer 17. Thus, the positive electrode, electrolyte layer, and negative electrode constitute a single cell layer 19. Therefore, Figure 1 The stacked lithium-oxygen battery 10a shown can be described as having a configuration in which multiple single-cell layers 19 are electrically connected in parallel. It should be noted that, although the positive active material layer 13 is only disposed on one side of the two outermost positive current collectors located on the power generation element 21, active material layers can also be disposed on both sides. That is, not only can a current collector dedicated to the outermost layer with an active material layer disposed on only one side be used, but a current collector with active material layers on both sides can also be directly used as the outermost current collector. Furthermore, the arrangement of the positive and negative electrodes can be adjusted... Figure 1 Instead, the outermost negative electrode current collector is located on the two outermost layers of the power generation element 21, and a negative electrode active material layer is disposed on one or both sides of the outermost negative electrode current collector.

[0017] A positive current collector plate 25 and a negative current collector plate 27, respectively connected to each electrode (positive and negative), are mounted on the positive current collector 11' and the negative current collector 12, and are led out to the outside of the laminated film 29 by being clamped at the end of the laminated film 29. The positive current collector plate 25 and the negative current collector plate 27 can be mounted to the positive current collector 11' and the negative current collector 12 of each electrode via positive terminal leads and negative terminal leads (not shown), respectively, by ultrasonic welding, resistance welding, etc., as needed.

[0018] The main components of the stacked lithium-oxygen battery of this embodiment will be described below.

[0019] [Current Collector]

[0020] The current collector has the function of dispersing the movement of electrons from the positive electrode active material layer and the negative electrode active material layer, which will be described later. There are no particular limitations on the materials used to construct the current collector. For example, metals or conductive resins can be used as materials to construct the current collector.

[0021] Specifically, metals such as aluminum, nickel, iron, stainless steel, titanium, and copper can be used. In addition, cladding materials of nickel and aluminum, or copper and aluminum, can also be used. Furthermore, foils formed by coating a metal surface with aluminum can also be used. From the viewpoints of electronic conductivity, battery operating potential, and the adhesion of the negative electrode active material sputtered to the current collector, aluminum, stainless steel, copper, and nickel are preferred. Furthermore, as conductive resins, resins in which conductive fillers are added to non-conductive polymer materials can be cited.

[0022] It should be noted that the current collector can be a single-layer structure made of a single material, or it can be a stacked structure formed by appropriately combining layers made of these materials. From the viewpoint of lightweighting the current collector, it is preferable to include at least a conductive resin layer made of a conductive resin. Furthermore, from the viewpoint of blocking the movement of lithium ions between single cell layers, a metal layer may also be provided in part of the current collector. Moreover, if the positive electrode active material layer and the negative electrode active material layer described later are themselves conductive and can perform current collection functions, then a current collector that is a component different from these electrode active material layers may not be used. In this configuration, the positive electrode active material layer described later directly constitutes the positive electrode, and the negative electrode active material layer described later directly constitutes the negative electrode.

[0023] [Positive electrode active material layer]

[0024] In this embodiment, the positive electrode active material layer comprises a lithium-containing composition of one aspect of the present invention as the positive electrode material.

[0025] <Lithium-containing composition (cathode material)>

[0026] As described above, one aspect of the lithium-containing composition of the present invention comprises lithium oxide, a catalyst, and a conductive polymer. The composition of this lithium-containing composition will be described below.

[0027] (Lithium oxide)

[0028] Lithium oxides are compounds formed by the covalent bonding of lithium and oxygen, and various compounds exist depending on their atomic ratios. Specifically, lithium oxides preferably contain one or more of the following: Li₂O, LiO, Li₂O₂, and LiO₂. Li₂O, Li₂O₂, or LiO₂ are more preferred. In particular, Li₂O is preferred from the viewpoint of higher theoretical capacity and chemical stability (less prone to decomposition and lower reactivity with moisture and carbon dioxide in the air) compared to other lithium oxides. These lithium oxides release lithium ions during charging (reacting towards a decreasing atomic ratio of lithium to oxygen), or absorb lithium ions during discharging (reacting towards an increasing atomic ratio of lithium to oxygen), or possess both functions. In summary, lithium oxides can be considered to function as the positive electrode active material in lithium-oxygen batteries.

[0029] (catalyst)

[0030] A catalyst is a substance that promotes the reaction of lithium oxides and oxygen by lowering the activation energy of the aforementioned bonding / dissociation reaction. Any known compound can be used as a catalyst as long as it can perform this function. For example, a catalyst is preferably a compound containing a transition metal (a transition metal-containing compound). This transition metal-containing compound is preferably, for example, an oxide (including a complex oxide), sulfide, halide, nitride, carbide, etc., containing a transition metal. From the viewpoint of excellent catalytic activity, the catalyst preferably contains a transition metal oxide. When the catalyst contains a transition metal-containing compound, there is no particular limitation on the type of transition metal contained in the compound; it can be atoms of any metal classified as a transition metal, and one or more types can be used. From the viewpoint of catalytic activity, the transition metal is preferably at least one type from groups 6 to 11 of the periodic table, more preferably one or more types selected from the group consisting of cobalt, manganese, iron, nickel, molybdenum, iridium, and rhodium, particularly preferably one or more types selected from the group consisting of cobalt, manganese, and iron, and most preferably cobalt. Examples of transition metal compounds include cobalt oxides, manganese oxides, iron oxides, nickel oxides, molybdenum oxides, iridium oxides, and ruthenium oxides. Among these, cobalt oxides, manganese oxides, and iron oxides are preferred, and cobalt oxides (e.g., Co3O4) are particularly preferred.

[0031] The content of catalyst in the lithium-containing composition is not particularly limited, and depends on the type of lithium oxide and catalyst. When the battery is fully discharged, it is preferably 50 to 500% by mass relative to 100% of the total amount of the lithium oxide, more preferably 100 to 450% by mass, further preferably 200 to 400% by mass, and particularly preferably 250 to 350% by mass.

[0032] (Conductive polymer)

[0033] Conductive polymers are high molecular weight compounds that exhibit electronic conductivity. As long as this definition is met, there are no particular restrictions on their specific composition. Preferably, conductive polymers are high molecular weight compounds with an alternating arrangement of double and single bonds in their molecular structure and a well-developed π-conjugated backbone, exhibiting a π-electron conjugation system. These conductive polymers can also generate charge carriers and exhibit electronic conductivity by doping them with acceptor or donor molecules, known as dopants. Examples of dopants include Li. + Na + K + Cs + Alkali metal ions, alkylammonium ions such as tetraethylammonium, halogens, Lewis acids, protons, transition metal halides, etc. The conductive polymer used in this invention is not particularly limited; for example, the electronic conductivity of the polymer film, measured by the four-probe method, is 10. -3 S / cm or higher, preferably 0.01S / cm or higher, more preferably 0.1S / cm or higher.

[0034] As a conductive polymer, for example, a polymer having one or more structural units selected from the group consisting of substituted or unsubstituted aniline, pyrrole, thiophene, furan, benzene, phenyleneethylene, thiopheneethylene, fluorene, naphthalene, and 3,4-ethylenedioxythiophene can be used. Substituents are not particularly limited, and examples include halogen atoms, alkyl, alkenyl, alkynyl, alkoxy, acyl, alkoxycarbonyl, nitro, amino, sulfonyl, alkylsulfonyl, carboxyl, alkylcarboxyl, hydroxyl, etc.

[0035] There are no particular limitations on the conductive polymers used. From the viewpoint of excellent conductivity, polyaniline (PANI), polypyrrole (PPy), polythiophene, polyfuran, poly(p-phenylene), poly(p-phenyleneethylene), polythiophene ethylene, polyfluorene, polynaphthalene, poly(3,4-ethylenedioxythiophene), and their derivatives are preferred. As derivatives, substances having substituents on the monomers constituting these polymers can be cited. There are no particular limitations on the substituents, and examples include halogen atoms, alkyl, alkenyl, alkoxy, acyl, alkoxycarbonyl, nitro, amino, sulfonyl, alkylsulfonyl, carboxyl, alkylcarboxyl, and hydroxyl groups.

[0036] The conductive polymer preferably comprises one or more selected from the group consisting of polyaniline, polypyrrole, polythiophene, and poly(3,4-ethylenedioxythiophene) (PEDOT), and more preferably comprises one or more selected from the group consisting of polyaniline, polypyrrole, polythiophene, and poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid (PEDOT:PSS). These conductive polymers readily exhibit high electronic conductivity. Furthermore, they are preferred because they are resistant to the high-potential region (oxidizing environment) used in high-capacity cathodes and to reactive oxygen species generated by the cathode active material.

[0037] Polyaniline (PANI), polypyrrole (PPy), polythiophene, and PEDOT:PSS are polymers that each have a repeating structure represented by the following chemical formula and exhibit electrical conductivity.

[0038]

[0039] It should be noted that there is no particular limitation on the average molecular weight of the conductive polymer in the lithium-containing composition of this method, and existing knowledge can be appropriately referred to. As an example, the weight-average molecular weight (converted to polystyrene) using gel permeation chromatography is 1,000 to 1,000,000, preferably 5,000 to 50,000, and more preferably 10,000 to 30,000.

[0040] Furthermore, the content of the conductive polymer in the lithium-containing composition of this method is not particularly limited, and depends on the type of lithium oxide, catalyst, and conductive polymer. Here, for example, from the viewpoint of greatly improving the capacity characteristics of the battery when used as a positive electrode material for a sealed lithium-oxygen battery, when the battery is fully discharged, the content relative to the total amount of the lithium oxide and catalyst is preferably 0.5 to 5.0% by mass, more preferably 1.0 to 5.0% by mass, and even more preferably 1.0 to 2.0% by mass.

[0041] There are no particular restrictions on the form in which the constituent components (lithium oxide, catalyst, and conductive polymer) of the lithium-containing composition exist, but it is preferable that these constituent components exist in a manner where the lithium oxide and catalyst participating 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 formed by the composite of conductive polymer. Here, "composite particle form" of the lithium-containing compound refers to a state in which, when the lithium-containing composition is used as the positive electrode material in a closed-cell lithium-oxygen battery and a charge-discharge reaction is carried out, the particles do not disintegrate but retain their particle shape even when the lithium oxide expands and contracts during charge-discharge. By adopting such a configuration, when lithium oxide is used as the positive electrode material, the charge-discharge reaction proceeds more smoothly, which can effectively contribute to further improvement of the battery's capacity characteristics.

[0042] As described above, the lithium-containing composition of this method has been found to be useful as a positive electrode material for closed-cell lithium-oxygen batteries. By using the above composition as a positive electrode material for closed-cell lithium-oxygen batteries, capacity characteristics can be improved. While the mechanism exhibiting this effect is not fully understood, it is speculated to be as follows: By including a conductive polymer in the lithium-containing composition, more contact points between the lithium oxide (the positive electrode active material) and the catalyst can be maintained compared to the case without a conductive polymer. As a result, during the charge-discharge reaction of the closed-cell lithium-oxygen battery, the exchange of electrons between the lithium oxide and the catalyst is sufficient, which is believed to effectively contribute to the improvement of the battery's capacity characteristics. Furthermore, the conductive polymer also has the function of binding the lithium oxide and the catalyst; therefore, maintaining the shape of the lithium-containing composition as the positive electrode material and minimizing its disintegration is also considered to be related to the improvement of capacity characteristics. However, these mechanisms are all based on speculation, and their correctness will not affect the scope of the present invention.

[0043] It should be noted that the lithium-containing composition having the above-described structure can be obtained, for example, by dry mixing lithium oxide and a catalyst using a mechanical mixing method such as a mechanochemical method, followed by mixing with a conductive polymer solution and allowing the solvent to evaporate, as described in the examples section below. The lithium-containing composition thus obtained is typically in the form of composite particles.

[0044] The content of the positive electrode material of one aspect of the present invention contained in the positive electrode active material layer (the total amount when two or more types are included) is not particularly limited, and is preferably 60 to 99% by mass, more preferably 80 to 95% by mass, relative to 100% by mass of the total solid content of the positive electrode active material layer.

[0045] <Added Ingredients>

[0046] In addition to the aforementioned positive electrode material, the positive electrode active material layer preferably also includes conductive additives and / or binders as additives.

[0047] (Conductive additive)

[0048] Conductive additives can form electron conduction pathways in the positive electrode active material layer. When such electron conduction pathways are formed in the positive electrode active material layer, the internal resistance of the battery decreases, which can improve the rate performance.

[0049] Examples of conductive additives include granular carbon materials such as acetylene black, carbon black, channel black, thermally cracked carbon black, and Ketjen black (registered trademark), as well as fibrous carbon materials such as carbon nanotubes (single-layer and multi-layer carbon nanotubes), carbon nanofibers, vapor-grown carbon fibers, electric field-spun carbon fibers, polyacrylonitrile-based carbon fibers, and pitch-based carbon fibers. Conductive additives can be used alone or in combination with two or more.

[0050] The content of conductive additives that may be included in the positive electrode active material layer (the total amount when two or more types are included) is not particularly limited, but is preferably 0.5 to 10% by mass relative to 100% by mass of the total solid content of the positive electrode active material layer, and more preferably 1 to 5% by mass.

[0051] (Adhesive)

[0052] There are no particular limitations on the binder that can be used as a binder for any component in the positive electrode active material layer; for example, the following materials can be cited:

[0053] Polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are replaced by other halogen atoms), polyethylene, polypropylene, polymethylpentene, polybutene, polyether nitrile, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), ethylene-propylene-diene copolymer, styrene-butadiene-styrene block copolymer and its hydrides, styrene-isoprene-styrene block copolymer and its hydrides, and other thermoplastic polymers, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (P... Fluoropolymers include CTFE, ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinylidene fluoride (PVF), vinylidene fluoride-hexafluoropropylene fluororubber (VDF-HFP), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluororubber (VDF-HFP-TFE), vinylidene fluoride-pentafluoropropylene fluororubber (VDF-PFP), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene fluororubber (VDF-PFP-TFE), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluororubber (VDF-PFMVE-TFE), and vinylidene fluoride-chlorotrifluoroethylene fluororubber (VDF-CTFE), as well as epoxy resins. Among these, polyvinylidene fluoride (PVDF), polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are preferred.

[0054] The content of binder that the positive electrode active material layer may contain (the total amount when it contains two or more types) is not particularly limited, but it is preferably 0.5 to 10% by mass, more preferably 1 to 5% by mass, relative to the total solid content of the positive electrode active material layer.

[0055] There are no particular limitations on the thickness of the positive electrode active material layer, and existing knowledge about batteries can be appropriately referenced. For example, the thickness of the positive electrode active material layer is typically around 1~1000 μm, preferably 20~800 μm, more preferably 30~500 μm, and even more preferably 40~200 μm. The greater the thickness of the positive electrode active material layer, the better it can retain the positive electrode active material to achieve sufficient capacity (energy density). On the other hand, the smaller the thickness of the positive electrode active material layer, the better it can improve the discharge rate characteristics.

[0056] [Negative electrode active material layer]

[0057] (Negative electrode active material)

[0058] The negative electrode active material layer contains the negative electrode active material. There are no particular limitations on the types of negative electrode active materials; examples include carbon materials, metal oxides, and metal active materials. Examples of carbon materials include natural graphite, artificial graphite, mesophase carbon microspheres (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. Examples of metal oxides include Nb₂O₅ and Li₄Ti₅O₅. 12 Furthermore, silicon-based and tin-based anode active materials can also be used. Silicon and tin, belonging to Group 14 elements, are known to be anode active materials that can significantly improve the capacity of secondary batteries. These elements can absorb and release a large amount of charge carriers (lithium ions, etc.) per unit volume (mass), thus becoming high-capacity anode active materials. Here, elemental Si is preferred as a silicon-based anode active material. Similarly, SiO2, which disproportionates into both a Si phase and a silicon oxide phase, is also preferred. x Silicon oxides such as (0.3≤x≤1.6). In this case, the range of x is more preferably 0.5≤x≤1.5, and even more preferably 0.7≤x≤1.2. Furthermore, silicon-containing alloys (silicon alloy-based anode active materials) can also be used. On the other hand, as anode active materials containing tin (tin-based anode active materials), examples include elemental Sn, tin alloys (Cu-Sn alloys, Co-Sn alloys), amorphous tin oxides, and tin-silicon oxides. Among these, SnB can be exemplified as an amorphous tin oxide. 0.4 P 0.6 O 3.1Furthermore, SnSiO3 can be exemplified as a tin-silicon oxide. Additionally, lithium-containing metals can also be used as the negative electrode active material. There are no particular limitations on such a negative electrode active material as long as it contains lithium; lithium alloys can be used in addition to lithium metal. There are no particular limitations on the lithium alloy; for example, alloys of Li with at least one of In, Al, Si, Sn, Mg, Au, Ag, and Zn can be used. Depending on the situation, two or more negative electrode active materials can be used together. It should be noted that negative electrode active materials other than those mentioned above can also be used. The negative electrode active material preferably contains lithium metal, a lithium alloy, a silicon-based negative electrode active material, or a tin-based negative electrode active material, and is particularly preferably containing lithium metal or a lithium alloy. Therefore, when the negative electrode active material contains lithium metal or a lithium alloy, the lithium-oxygen battery of this embodiment can be a so-called lithium deposition type battery, in which lithium metal or a lithium alloy is deposited on the negative electrode current collector during charging. In this case, the layer composed of lithium metal or a lithium-containing alloy deposited on the negative electrode current collector during charging becomes the negative electrode active material layer of the lithium-oxygen battery of this embodiment. Therefore, the thickness of the negative electrode active material layer increases as the charging process proceeds and decreases as the discharging process proceeds. The negative electrode active material layer may not exist during complete discharge, but depending on the circumstances, a certain degree of negative electrode active material layer composed of lithium metal or a lithium-containing alloy may be provided during complete discharge.

[0059] The shape of the negative electrode active material can be, for example, particulate (spherical, fibrous) or thin film. When the negative electrode active material is particulate, its average particle size is preferably in the range of 1 nm to 100 μm, more preferably in the range of 10 nm to 50 μm, even more preferably in the range of 100 nm to 20 μm, and particularly preferably in the range of 1 to 20 μm.

[0060] The content of the negative electrode active material in the negative electrode active material layer, relative to 100% by mass of the total solid content, is, for example, 60% by mass or more and less than 100% by mass, preferably 80% by mass or more and 99.5% by mass or less, more preferably greater than 95% by mass and less than 99.0% by mass, and even more preferably 97% by mass or more and 98.5% by mass or less. If the content of the negative electrode active material is within the above range, both battery capacity and output characteristics can be balanced.

[0061] In addition, similar to the above description of the positive electrode active material layer, the negative electrode active material layer may also contain other additives such as conductive additives and binders, as needed.

[0062] The thickness of the negative electrode active material layer (in lithium deposition type secondary batteries, the thickness when fully charged) varies depending on the structure of the target stacked battery, but is preferably in the range of 0.1 to 1000 μm, for example.

[0063] [Electrolyte layer]

[0064] The electrolyte layer contains an electrolyte (liquid electrolyte). Preferably, the electrolyte layer has a configuration in which the electrolyte is impregnated in a separator.

[0065] (electrolyte)

[0066] The electrolyte functions as a carrier of lithium ions. The electrolyte is in the form of a lithium salt dissolved in a non-aqueous solvent. Preferably, the electrolyte is prepared by further adding a fluorocarbonate to a solution obtained by dissolving the lithium salt in a non-aqueous solvent.

[0067] As a non-aqueous solvent, non-aqueous solvents that readily dissolve lithium salts are preferred, such as 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); fluorinated chain carbonates formed by replacing some hydrogen atoms with fluorine atoms in these chain carbonates; cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC); fluorinated cyclic carbonates formed by replacing some hydrogen atoms with fluorine atoms in these cyclic carbonates; 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).

[0068] From the viewpoint of further improving fast charging characteristics and output characteristics, the non-aqueous solvent preferably includes chain carbonate, and more preferably includes at least one selected from the group consisting of diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC).

[0069] Examples of lithium salts include Li(FSO2)2N (lithium bisfluorosulfonylimide; LiFSI), Li(C2F5SO2)2N, LiPF6, LiBF4, LiClO4, LiAsF6, and LiCF3SO3.

[0070] The concentration of lithium salt in the above-mentioned non-aqueous solvent is preferably 0.1~3.0 mol / L, more preferably 0.8~2.2 mol / L.

[0071] Furthermore, the electrolyte preferably also contains fluorinated carbonates such as fluorinated cyclic carbonates and fluorinated chain carbonates. This ensures excellent durability even when the battery is operated at high voltages. Moreover, these fluorinated carbonates can form a protective film on the surface of the positive electrode active material, improving its voltage resistance. Preferably, fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), difluoroethylene carbonate, and 4-fluoropropylene carbonate, and fluorinated chain carbonates such as ethyl trifluoromethyl carbonate, 2,2,2-trifluoroethylmethyl carbonate, and bis(2,2,2-trifluoroethyl) carbonate are used as fluorinated carbonates. The content of the fluorinated carbonate is not particularly limited. In a preferred embodiment, the electrolyte contains 0.5 to 10% by mass of fluorinated carbonate, particularly fluoroethylene carbonate, relative to the total amount of the final electrolyte. This allows for a more significant attainment of the aforementioned effects. It should be noted that when the electrolyte contains two or more fluorocarbonates, the total amount is preferably within the range mentioned above.

[0072] The electrolyte may also contain additives other than those mentioned above. 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, 1-ethyl-2-vinyl ethylene carbonate, vinyl vinylene carbonate, allyl ethylene carbonate, ethyleneoxymethyl ethylene carbonate, allyloxymethyl ethylene carbonate, acryloyloxymethyl ethylene carbonate, methacryloyloxymethyl ethylene carbonate, ethynyl ethylene carbonate, propynyl ethylene carbonate, propynyloxymethyl ethylene carbonate, propynyloxymethyl ethylene carbonate, methylene ethylene carbonate, and 1,1-dimethyl-2-methylene ethylene carbonate. These additives can be used alone or in combination of two or more. Furthermore, the dosage can be adjusted appropriately when using additives in electrolytes.

[0073] (Separator)

[0074] The separators that make up the electrolyte layer have the functions of retaining the electrolyte and ensuring lithium-ion conductivity between the positive and negative electrodes, as well as serving as a partition between the positive and negative electrodes.

[0075] Examples of separators include porous sheets made of polymers or fibers that absorb and retain the electrolyte, and nonwoven fabric separators.

[0076] As a separator for a porous sheet made of polymers or fibers, a microporous material (microporous membrane) can be used, for example. Specific forms of porous sheets made of such polymers or fibers include microporous materials (microporous membranes) composed of polyolefins such as polyethylene (PE) and polypropylene (PP); laminates formed by stacking multiple of these (e.g., a laminate with a 3-layer structure of PP / PE / PP); polyimide; aromatic polyamide; hydrocarbon resins such as polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP); and glass fibers.

[0077] As a nonwoven fabric separator, it can be made alone or in combination with existing known materials such as cotton, rayon, cellulose acetate, nylon, polyester; polyolefins such as PP and PE; and polyimide and aromatic polyamide.

[0078] The thickness of the separator can be the same as that of the electrolyte layer, preferably 5~200μm, and particularly preferably 10~100μm.

[0079] Furthermore, as a separator, a separator with a heat-resistant insulating layer laminated on a porous matrix (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. The separator with the heat-resistant insulating layer uses a material with a melting point or thermal softening point of 150°C or higher, preferably 200°C or higher, and high heat resistance. By having a heat-resistant insulating layer, the internal stress of the separator that increases with temperature rise is mitigated, thus achieving a heat shrinkage suppression effect. As a result, short circuits between the electrodes of the battery can be prevented, thus creating a battery structure that is less prone to performance degradation due to temperature rise. In addition, by having a heat-resistant insulating layer, the mechanical strength of the separator with the heat-resistant insulating layer is improved, making it less prone to separator film rupture. Furthermore, due to the heat shrinkage suppression effect and high mechanical strength, the separator is less likely to curl during the battery manufacturing process.

[0080] [Positive current collector and negative current collector]

[0081] The materials constituting the current collectors (25, 27) are not particularly limited, and well-known highly conductive materials conventionally used in current collectors for lithium-ion secondary batteries can be used. For example, aluminum, copper, titanium, nickel, stainless steel (SUS), and their alloys are preferred as constituent materials of the current collectors. From the viewpoints of lightweight, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. It should be noted that the same material or different materials can be used in the positive electrode current collector 25 and the negative electrode current collector 27.

[0082] The closed-cell lithium-oxygen battery using the positive electrode material of this method retains excellent rate performance even after charge-discharge cycles. Therefore, the closed-cell lithium-oxygen battery using the positive electrode material of this method is suitable for use as a power source for EVs and HEVs.

[0083] The above describes one embodiment of the lithium-containing composition of the present invention (positive electrode material for a sealed lithium-oxygen battery). However, the present invention is not limited to the configuration described in the above embodiment and can be appropriately modified based on the claims.

[0084] It should be noted that the following embodiments are also included within the scope of the present invention: the lithium-containing composition of claim 1, having the features of claim 2; the lithium-containing composition of claim 1 or 2, having the features of claim 3; the lithium-containing composition of any one of claims 1 to 3, having the features of claim 4; the lithium-containing composition of any one of claims 1 to 4, having the features of claim 5; the lithium-containing composition of any one of claims 1 to 5, having the features of claim 6; the lithium-containing composition of any one of claims 1 to 6, having the features of claim 7; the lithium-containing composition of any one of claims 1 to 7, having the features of claim 8; the lithium-containing composition of any one of claims 1 to 8, having the features of claim 9; the positive electrode for a sealed lithium-oxygen battery of claim 11, comprising the lithium-containing composition of any one of claims 1 to 10; the positive electrode for a sealed lithium-oxygen battery of claim 12, having the features of claim 11; the sealed lithium-oxygen battery of claim 13, comprising the positive electrode of claim 11 or 12.

[0085] Furthermore, according to another aspect of the present invention, the use of a lithium-containing composition as a positive electrode material for a sealed lithium-oxygen battery is also provided, the lithium-containing composition comprising lithium oxide, a catalyst, and a conductive polymer (preferably the lithium oxide and the catalyst being in the form of composite particles formed by compounding the conductive polymer).

[0086] Furthermore, according to another aspect of the present invention, a method for improving the capacity characteristics of a sealed lithium-oxygen battery is also provided, comprising using a lithium-containing composition comprising lithium oxide, a catalyst, and a conductive polymer (preferably the lithium oxide and the catalyst being in the form of composite particles formed by compounding the conductive polymer) as the positive electrode material of the sealed lithium-oxygen battery. It should be noted that, in this specification, "improvement of capacity characteristics" means that, in the case of a sealed lithium-oxygen battery using the lithium-containing composition of this method as the positive electrode material, compared to the case of a battery constructed using a comparative positive electrode material having the same composition except that it does not contain a conductive polymer, at least one of the initial charge capacity and discharge capacity (e.g., charge capacity and discharge capacity per mass of lithium oxide) is improved.

[0087] Example

[0088] The present invention will now be described in more detail through embodiments. However, the scope of the present invention is not limited to the following embodiments.

[0089] Fabrication of Sealed Lithium-Oxygen Batteries

[0090] [Example 1]

[0091] (Preparation of cathode materials)

[0092] Lithium oxide (Li2O, manufactured by High Purity Chemical Research Institute Co., Ltd.) as the positive electrode active material (lithium oxide) and cobalt oxide (Co3O4, manufactured by High Purity Chemical Research Institute Co., Ltd.) as the catalyst were placed into 70mL jars for planetary ball mills and respectively subjected to planetary ball milling (milling conditions: using 40g of 3mmφ zirconia balls and 15 15mmφ zirconia balls, processing at 400rpm for 1 hour).

[0093] Next, 5g of pulverized lithium oxide and 15g of cobalt oxide were placed in the jar of a 70mL planetary ball mill and mixed by planetary ball milling (mixing conditions: using 40g of 3mmφ zirconia balls and 15 15mmφ zirconia balls, processing at 400rpm for 30 minutes).

[0094] On the other hand, using a planetary mixing apparatus, a degassing mixer (ARE-310, manufactured by Thinky Co., Ltd.), 0.0125 g of polyaniline (PANI, manufactured by Sigma-Aldric Co., LLC) as the conductive polymer and 11 g of N-methyl-2-pyrrolidone (NMP, manufactured by Fujifilm and Hikari Pure Chemicals Co., Ltd.) as the solvent were mixed (mixing conditions: 2000 rpm for 5 minutes) to dissolve the polyaniline in NMP. 2.5 g of a mixture of lithium oxide and cobalt oxide, mixed by ball milling as described above, was added to the resulting NMP solution of polyaniline, and further mixed using the aforementioned mixing apparatus (mixing 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 allow the NMP to evaporate. Then, the remaining powder was recovered and manually mixed for 5 minutes using an agate mortar to prepare the positive electrode material (composite particle morphology) of Example 1. It should be noted that in the cathode material of this embodiment, the content of conductive polymer (PANI) is 0.5% by mass relative to the total amount of lithium oxide (Li2O) and catalyst (Co3O4).

[0095] (The production of the positive electrode)

[0096] Prepare a solid composition consisting of 80% by mass of the above-prepared positive electrode material, 10% by mass of acetylene black (AB, Li-400, manufactured by Denka, average primary particle size: 48 nm, aspect ratio: 1) as a conductive additive, and 10% by mass of PVDF (KUREHA KF PolymerW#9700, manufactured by KUREHA) as a binder. First, mix the positive electrode material (total amount) and the conductive additive (total amount of acetylene black). Add N-methyl-2-pyrrolidone (NMP) to a solid composition concentration of 85%, and mix at 2000 rpm for 5 minutes using the above-mentioned mixing apparatus. Add N-methyl-2-pyrrolidone (NMP) to a solid composition concentration of 35% by mass, and mix at 2000 rpm for 2 minutes using the above-mentioned mixing apparatus. Add the binder (total amount of PVDF), and mix at 2000 rpm for 4 minutes using the above-mentioned mixing apparatus. The viscosity was adjusted by adding N-methyl-2-pyrrolidone (NMP) to the slurry at a solid content concentration of 25% by mass, thus preparing a positive electrode slurry. The slurry was then uniformly coated onto an aluminum foil placed on a smooth table using a doctor blade, achieving a positive electrode active material layer thickness of 20 μm. Afterward, it was dried on a hot plate heated to 80°C for 30 minutes, transferred to a vacuum dryer, and dried under vacuum at 130°C for 8 hours, thereby preparing the positive electrode of this embodiment.

[0097] (The fabrication of a sealed lithium-oxygen battery (coin cell))

[0098] The prepared positive electrode and the counter electrode lithium were positioned opposite each other, with a separator (polyolefin, thickness: 20 μm) placed between them. Next, the stack of the positive electrode, separator, and counter electrode lithium was placed into a coin cell (CR2032, material: stainless steel (SUS316)), and the electrolyte described below was injected using a syringe and sealed to produce the sealed lithium-oxygen battery (coin cell) of this embodiment. It should be noted that the electrolyte described above was prepared by dissolving lithium hexafluorophosphate (LiPF6) as a lithium salt in an organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a ratio of EC:DEC = 3:7 (volume ratio) at a concentration of 1 mol / L.

[0099] [Example 2]

[0100] The amount of polyaniline (PANI) used in preparing the cathode material was changed to 0.025 g. Otherwise, the sealed lithium-oxygen battery (coin battery) of this embodiment was prepared by the same method as in Example 1 above. In the cathode material of this embodiment, the content of conductive polymer (PANI) is 1.0% by mass relative to the total amount of lithium oxide (Li2O) and catalyst (Co3O4).

[0101] [Example 3]

[0102] The amount of polyaniline (PANI) used in preparing the cathode material was changed to 0.05 g. Otherwise, the sealed lithium-oxygen battery (coin battery) of this embodiment was prepared by the same method as in Example 1 above. In the cathode material of this embodiment, the content of conductive polymer (PANI) is 2.0% by mass relative to the total amount of lithium oxide (Li2O) and catalyst (Co3O4).

[0103] [Example 4]

[0104] The amount of polyaniline (PANI) used in preparing the cathode material was changed to 0.125 g. Otherwise, the sealed lithium-oxygen battery (coin battery) of this embodiment was prepared by the same method as in Example 1 above. In the cathode material of this embodiment, the content of conductive polymer (PANI) is 5.0% by mass relative to the total amount of lithium oxide (Li2O) and catalyst (Co3O4).

[0105] [Comparative Example 1]

[0106] Polyaniline (PANI) was not added during the preparation of the positive electrode material. Otherwise, the closed lithium-oxygen battery (coin battery) of this comparative example was prepared by the same method as in Example 1 above.

[0107] Evaluation of Sealed Lithium-Oxygen Batteries

[0108] The sealed lithium-oxygen battery (coin cell) fabricated above was subjected to the following charge-discharge test (initial charge-discharge) to measure the charging and discharging capacities. It should be noted that the experiment was conducted in a constant temperature bath at 300K (27℃).

[0109] (Charge / discharge test conditions)

[0110] Charge and discharge test machine:

[0111] TOSCAT-3000, Model TYS-30TU10 (manufactured by Toyo Systems Co., Ltd.)

[0112] Charge and discharge conditions:

[0113] [Charging process] 0.02C (current density 18mA / g), 1.8V→4.6V (CCCV)

[0114] [Discharge process] 0.02C (current density 18mA / g), 4.6V→1.8V (CC)

[0115] The pause time between the charging and discharging processes is 30 minutes.

[0116] The results of the charge-discharge capacity measured by the above-described charge-discharge test are shown in Table 1 below. It should be noted that the charge-discharge capacity values ​​shown in Table 1 are relative values ​​with the measured value of Comparative Example 1 set to 1. Furthermore, after the charge-discharge test, the coin battery was disassembled and the state of the positive electrode material of Examples 1 to 4 was checked. The results confirmed that the particles of the positive electrode material composed of the lithium-containing composition did not disintegrate and maintained their particle shape.

[0117] [Table 1]

[0118]

[0119] As shown in Table 1, according to the present invention, by using a composition containing a conductive polymer in addition to lithium oxide (Li2O) and a catalyst as the positive electrode material of a closed-cell lithium-oxygen battery, the capacity characteristics of the closed-cell lithium-oxygen battery can be improved.

[0120] Explanation of reference numerals in the attached figures

[0121] 10A tandem lithium-oxygen battery

[0122] 11' Positive Current Collector

[0123] 12 Negative current collector

[0124] 13. Positive electrode active material layer

[0125] 15. Negative electrode active material layer

[0126] 17 Electrolyte layer

[0127] 19 Single-cell layer

[0128] 21. Power generation components

[0129] 25 Positive current collector plate (positive electrode tab),

[0130] 27. Negative current collector (negative electrode tab)

[0131] 29-layer laminated film.

Claims

1. A lithium-containing composition comprising: Lithium oxide, catalyst, and Conductive polymers.

2. The lithium-containing composition according to claim 1, wherein, The lithium oxide and the catalyst are in the form of composite particles formed by combining the conductive polymer.

3. The lithium-containing composition according to claim 1, which is used as a positive electrode material for a sealed lithium-oxygen battery.

4. The lithium-containing composition according to claim 1 or 3, wherein, The content of the conductive polymer in the composition is 0.5 to 5.0% by mass relative to the total amount of the lithium oxide and the catalyst.

5. The lithium-containing composition according to claim 1 or 3, wherein, The content of the conductive polymer in the composition is 1.0 to 5.0% by mass relative to the total amount of the lithium oxide and the catalyst.

6. The lithium-containing composition according to claim 1 or 3, wherein, The content of the conductive polymer in the composition is 1.0 to 2.0% by mass relative to the total amount of the lithium oxide and the catalyst.

7. The lithium-containing composition according to claim 1 or 3, wherein, The lithium oxide comprises one or more of the following selected from the group consisting of Li2O, LiO, Li2O2 and LiO2.

8. The lithium-containing composition according to claim 1 or 3, wherein, The conductive polymer comprises one or more selected from the group consisting of polyaniline (PANI), polypyrrole (PPy), polythiophene, polyfuran, poly(p-phenylene), poly(p-phenyleneethylene), polythiophene ethylene, polyfluorene, polynaphthalene, poly(3,4-ethylenedioxythiophene) and their derivatives.

9. The lithium-containing composition according to claim 1 or 3, wherein, The catalyst contains transition metal oxides.

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

11. A positive electrode for a sealed lithium-oxygen battery, wherein, The positive electrode active material layer comprises the lithium-containing composition as described in claim 1 or 3 as the positive electrode material.

12. The positive electrode for a sealed lithium-oxygen battery according to claim 11, wherein, The positive electrode active material layer also includes conductive additives and / or binders as additives.

13. A sealed lithium-oxygen battery comprising the positive electrode as described in claim 11.

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