Dual-ion battery

Abstract

To provide a dual ion battery excellent in charge / discharge capacity.SOLUTION: A dual ion battery comprises: a positive electrode including a positive electrode active material capable of inserting and removing anions; a negative electrode including a negative electrode active material capable of inserting and removing cations; and a non-aqueous electrolyte solution. The positive electrode active material comprises a carbon material having a structure in which graphene having oxygen and nanopores introduced therein is regularly stacked. The non-aqueous electrolyte solution comprises lithium bis (fluorosulfonyl) imide.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to a dual-ion battery. [Background technology]

[0002] In recent years, high-performance rechargeable batteries have been needed for various mobility applications, smart grids, and other uses. In particular, rechargeable batteries used in personal mobility devices such as small electric vehicles and for applications like power frequency leveling require further improvements in input / output characteristics.

[0003] Dual-ion batteries (DIBs) are attracting attention as secondary batteries with excellent input / output characteristics. Dual-ion batteries are secondary batteries in which charging and discharging proceed through the insertion and removal of anions from the electrolyte into the positive electrode and the insertion and removal of cations from the electrolyte into the negative electrode. Among DIBs, batteries that use carbon materials for both the positive and negative electrodes are called dual-carbon batteries (DCBs).

[0004] For example, Non-Patent Document 1 discloses a non-aqueous energy storage element characterized by having a positive electrode containing a carbon material having a structure in which oxygen and nanopore-introduced graphene are regularly stacked as a positive electrode active material, a negative electrode containing a negative electrode active material, and a non-aqueous electrolyte containing a non-aqueous solvent and LiPF6. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] J. Inamoto, K. Sekito, N. Kobayashi, Y. Matsuo, J. Electrochem. Soc. 168 (2021) 010528. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, the non-aqueous energy storage element disclosed in Non-Patent Document 1 has insufficient charge and discharge capacity, and further improvements in charge and discharge capacity are required.

[0007] This disclosure is made in view of the above-mentioned prior circumstances and aims to provide a dual-ion battery with superior charge and discharge capacity. [Means for solving the problem]

[0008] The specific means for achieving the aforementioned objectives are as follows: <1> A positive electrode containing a positive electrode active material capable of inserting and removing anions, A negative electrode containing a negative electrode active material capable of inserting and removing cations, A non-aqueous electrolyte is provided, The positive electrode active material comprises a carbon material having a structure in which oxygen and nanopore-introduced graphene are regularly stacked, and the non-aqueous electrolyte comprises lithium bis(fluorosulfonyl)imide, in a dual-ion battery. <2> The carbon material is a carbon material represented by the following general formula (1). <1> Dual-ion battery as described. C8O x H y ...(1) (In equation (1), x is between 0.10 and 1.50, and y is between 0 and 1.00.) <3> The molar ratio of oxygen atoms to carbon atoms in the carbon material is between 0.010 and 0.200. <1> or <2> Dual-ion battery as described. <4> The negative electrode active material includes a carbon material. <1> ~ <3> A dual-ion battery as described in one of the following: <5> The concentration of lithium bis(fluorosulfonyl)imide in the aforementioned non-aqueous electrolyte is 1 mol / L to 5 mol / L. <1> ~ <4> A dual-ion battery as described in one of the following: <6> The non-aqueous electrolyte contains ethylene glycol ether. <1> ~ <5> A dual-ion battery as described in one of the following: [Effects of the Invention]

[0009] According to the present disclosure, a dual-ion battery excellent in charge-discharge capacity can be provided.

Brief Description of the Drawings

[0010] [Figure 1] It is a graph showing the results of charge-discharge tests in Example 1 and 2 and Comparative Example 1 and 2. [Figure 2] It is a graph showing the results of charge-discharge tests in Example 3. [Figure 3] It is a graph showing the results of charge-discharge tests in Comparative Example 3.

Modes for Carrying Out the Invention

[0011] Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, its components (including element steps, etc.) are not essential unless specifically stated. The same applies to numerical values and their ranges, which do not limit the present invention. Also, various changes and modifications can be made by those skilled in the art within the scope of the technical idea in the present disclosure. In the present disclosure, the term "step" includes not only a step independent of other steps but also the step even if it cannot be clearly distinguished from other steps as long as the purpose of the step is achieved. In the numerical range indicated by "~" in the present disclosure, the numerical values described before and after "~" are included as the minimum value and the maximum value, respectively. In the numerical ranges described step by step in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other step-by-step descriptions. Also, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. In the present disclosure, each component may contain a plurality of corresponding substances. When there are a plurality of substances corresponding to each component, the content rate of each component means the total content rate of the plurality of substances unless otherwise specified. In the present disclosure, the particles corresponding to each component may include a plurality of types. When there are a plurality of types of particles corresponding to each component, the particle diameter of each component means a value for a mixture of the plurality of types of particles, unless otherwise specified. In the present disclosure, the terms "layer" or "film" include not only the case where the layer or film is formed over the entire region where it exists, but also the case where it is formed only in a part of the region when observing the region where the layer or film exists. In the present disclosure, the "solid content" of the positive electrode active material or the negative electrode active material means the remaining components obtained by removing volatile components such as organic solvents from the slurry of the positive electrode active material or the slurry of the negative electrode active material. In the present disclosure, the "positive electrode active material capable of inserting and extracting anions" means a positive electrode active material in which anions can be reversibly inserted and extracted into the crystallites of the positive electrode active material. In the present disclosure, the "negative electrode active material capable of inserting and extracting cations" means a negative electrode active material in which cations can be reversibly inserted and extracted into the crystallites of the negative electrode active material.

[0012] <Dual-ion battery> The dual-ion battery of the present disclosure includes a positive electrode containing a positive electrode active material capable of inserting and extracting anions, a negative electrode containing a negative electrode active material capable of inserting and extracting cations, and a non-aqueous electrolyte. The positive electrode active material includes a carbon material having a structure in which graphene into which oxygen and nanopores are introduced is regularly stacked. The non-aqueous electrolyte contains lithium bis(fluorosulfonyl)imide.

[0013] Generally, graphite-based carbon materials are used as the positive electrode active material of dual-ion batteries. On the other hand, the inventors have found that a carbon material having a structure in which graphene into which oxygen and nanopores are introduced is regularly stacked (hereinafter also referred to as "specific carbon material") obtained by heat-treating graphite oxide is used as the positive electrode active material (Non-Patent Document 1). Furthermore, by fabricating a positive electrode using the specific carbon material, it has been found that hexafluorophosphate ions (PF6 - ions) can be inserted at a lower potential than that of the graphite-based carbon material, and the insertion amount is also large.

[0014] In the case of a specific carbon material described in Non-Patent Document 1, it is possible to adjust the amount of nanopores, the amount of oxygen, etc. by changing the method for synthesizing graphite oxide, the heat treatment temperature, etc. However, depending on the composition, physical properties, etc. of the specific carbon material, PF6 - It was found that the storage amount of ions may extremely decrease.

[0015] On the other hand, in the dual-ion battery of the present disclosure, by using a non-aqueous electrolyte containing lithium bis(fluorosulfonyl)imide, it is possible to increase the storage amount of ions as compared with the case of using a non-aqueous electrolyte that does not contain lithium bis(fluorosulfonyl)imide and contains lithium hexafluorophosphate, and the charge-discharge capacity is excellent.

[0016] The reason why the dual-ion battery of the present disclosure has an excellent charge-discharge capacity is presumed as follows. Since a specific carbon material has a structure in which graphene is regularly stacked, ions are stabilized by being accommodated between the graphene layers during charging, and the ions sandwiched between the graphene layers are released during discharging. However, due to the introduction of nanopores on the surface of the regularly stacked graphene, regions where the graphene layers are not regularly arranged are generated, and ions do not fit between the graphene layers during charging, making the ions liable to become unstable. In particular, when ions with high spherical symmetry such as PF6 - ions are inserted into the positive electrode active material, PF6 - ions may not fit between the graphene layers and become unstable during charging, and as a result, the charge-discharge capacity tends to be low. On the other hand, in the dual-ion battery of the present disclosure, by using a non-aqueous electrolyte containing lithium bis(fluorosulfonyl)imide, bis(fluorosulfonyl)imide ions (FSI - ions) are inserted into a specific carbon material that is the positive electrode active material during charging. At this time, nanopores are introduced on the surface of the regularly stacked graphene, regions where the graphene layers are not regularly arranged are generated, and even when FSI - ions do not fit between the graphene layers, FSI -Ions can be stabilized by interacting with the edges of the nanopores, such as by bonding. As a result, it is presumed that the dual-ion battery of this disclosure will have superior charge and discharge capacity. The above inferences are not intended to restrict the interpretation of the dual-ion battery described herein, but are provided as an example.

[0017] Furthermore, the dual-ion battery of this disclosure tends to have improved cycle stability when a non-aqueous electrolyte containing lithium bis(fluorosulfonyl)imide is used.

[0018] Preferred configurations of the positive electrode, negative electrode, and non-aqueous electrolyte used in the dual-ion battery of this disclosure are described below.

[0019] (positive electrode) The dual-ion battery of this disclosure comprises a positive electrode containing a positive electrode active material capable of inserting and deinserting anions. The positive electrode active material contained in the positive electrode includes a carbon material (a specific carbon material) having a structure in which oxygen and nanopore-introduced graphene are regularly stacked. For example, the positive electrode may have a configuration comprising a positive electrode current collector and a positive electrode mixture layer disposed on its surface and containing the positive electrode active material.

[0020] The positive electrode active material is not particularly limited as long as it contains a specific carbon material. The positive electrode active material may consist solely of a specific carbon material, or it may be a combination of a specific carbon material and other positive electrode active materials. A specific carbon material may be used alone, or two or more may be used in combination.

[0021] The specific carbon material is preferably a carbon material represented by the following general formula (1). C8O x H y ...(1) In equation (1), x is between 0.10 and 1.50, and y is between 0 and 1.00.

[0022] x may be between 0.20 and 0.80, or between 0.25 and 0.60. y may be 0 or 0.30 to 0.80, or 0 or 0.50 to 0.70.

[0023] For example, when y is 0.30 or higher in general formula (1), the charge-discharge capacity tends to be superior. In particular, combining a non-aqueous electrolyte containing lithium bis(fluorosulfonyl)imide with a carbon material represented by general formula (1) where y is 0.30 or higher tends to improve charge-discharge characteristics.

[0024] The molar ratio of oxygen atoms to carbon atoms in a particular carbon material (oxygen atoms / carbon material) may be 0.010 to 0.200, 0.020 to 0.150, or 0.030 to 0.080, from the viewpoint of electrical conductivity and reduction stability.

[0025] The chemical formula representing a specific carbon material, and the molar ratio of oxygen atoms to carbon atoms contained in that specific carbon material, can be determined by conventionally known elemental analysis methods. For example, they can be determined by methods such as combustion, secondary ion mass spectrometry (SIMS), and energy-dispersive X-ray spectroscopy (EDX).

[0026] For certain carbon materials, the average interplanar spacing d is determined by X-ray diffraction. 002 From the viewpoint of lowering the storage potential of the anion, the wavelength may be 0.330 nm to 0.440 nm, or 0.334 nm to 0.380 nm. Average spacing d 002 The theoretical value for this value is 0.3354 nm for graphite crystals, and beyond this value, the energy density tends to increase.

[0027] d is the average interplanar spacing of a specific carbon material. 002 This can be calculated using Bragg's formula from the diffraction profile obtained by irradiating a specific carbon material with X-rays (CuKα rays) and measuring the diffraction lines with a goniometer, specifically from the diffraction peak corresponding to the carbon 002 plane that appears around the diffraction angle 2θ = 24° to 27°.

[0028] The full width at half maximum (FWMH) of the diffraction peak corresponding to the carbon 002 plane when X-rays (CuKα rays) are irradiated onto a specific carbon material may be 0.30 to 2.50, or 0.50 to 1.60.

[0029] The average particle size of a particular carbon material may be 1 μm to 50 μm or 5 μm to 20 μm, from the viewpoint of reducing irreversible capacity and improving rapid charge and discharge performance. The average particle diameter (d50) is the volume-average particle diameter obtained by measuring the volume-based particle size distribution using a particle size distribution analyzer that utilizes laser light scattering (e.g., SALD-3000, Shimadzu Corporation), and then calculating d50 (median diameter).

[0030] The specific surface area of ​​certain carbon materials is considered to be 1 m² from the viewpoint of reducing irreversible capacity and improving rapid charge / discharge performance. 2 / g~100m 2 It may also be / g, or 5m 2 / g~50m 2 / g is also acceptable. The specific surface area can be measured from the nitrogen adsorption capacity in accordance with JIS Z 8830:2013. When measuring the specific surface area, it is preferable to first perform a pretreatment to remove moisture by heating, as moisture adsorbed on the sample surface and within its structure is thought to affect the gas adsorption capacity. In the pretreatment, a measurement cell containing 0.05 g of the sample is subjected to a vacuum pump to reduce the pressure to 10 Pa or less, then heated to 110°C and maintained at that temperature for 3 hours or more. After this, it is allowed to cool naturally to room temperature (25°C) while maintaining the reduced pressure. After this pretreatment, the evaluation temperature is set to 77 K, and the evaluation pressure range is set to less than 1 in relative pressure (equilibrium pressure relative to saturated vapor pressure) for measurement. Nitrogen adsorption is measured using the multi-point method, and the specific surface area is calculated using the BET method.

[0031] The method for manufacturing a specific carbon material is not particularly limited, and for example, a specific carbon material can be manufactured based on the aforementioned Non-Patent Document 1 (J. Inamoto, K. Sekito, N. Kobayashi, Y. Matsuo, J. Electrochem. Soc. 168 (2021) 010528).

[0032] For example, carbon materials such as graphite and graphene are prepared, and the carbon materials are mixed with strong acids such as concentrated sulfuric acid and fuming nitric acid. An oxidizing agent such as potassium chlorate, potassium permanganate, or sodium periodate is added to the mixture. The carbon materials are oxidized by the action of the oxidizing agent to obtain a carbon oxide material. The carbon oxide material is then subjected to high-temperature treatment, for example, heat treatment at 300°C to 1100°C under vacuum to obtain a specific carbon material.

[0033] The molar ratio of oxygen atoms to carbon atoms, and the introduction of hydrogen atoms, in a specific carbon material can be adjusted by appropriately changing the manufacturing conditions of that carbon material. For example, hydrogen atoms can be introduced into a specific carbon material by performing high-temperature heat treatment of an oxide carbon material in a hydrogen gas atmosphere.

[0034] The content of the specific carbon material may be 50% to 100% by mass, or 80% to 100% by mass, relative to the total amount of positive electrode active material.

[0035] The positive electrode active material may be a combination of a specific carbon material and other positive electrode active materials. Other positive electrode active materials are not particularly limited and include graphite, carbon nanotubes, graphene other than the specific carbon material, nanocarbon, graphite oxide, hard carbon, soft carbon, and other carbon materials. Other positive electrode active materials may be used individually or in combination of two or more.

[0036] The positive electrode may have a configuration comprising a positive electrode current collector and a positive electrode mixture layer disposed on its surface and containing a positive electrode active material.

[0037] When the positive electrode mixture layer contains positive electrode active material, the content of the positive electrode active material is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more, based on the total amount of the positive electrode mixture layer, from the viewpoint of increasing the battery capacity.

[0038] Next, the positive electrode mixture layer and the positive electrode current collector will be described in detail. The positive electrode mixture layer contains a positive electrode active material, a binder, etc., and is placed on the positive electrode current collector. There are no restrictions on the method of forming the positive electrode mixture layer, and for example, it can be formed as follows: The positive electrode mixture layer can be formed by dry mixing the positive electrode active material, a binder, and other materials such as conductive agents and thickeners used as needed to form a sheet, and then pressing this sheet onto the positive electrode current collector (dry method). Alternatively, the positive electrode mixture layer can be formed by dissolving or dispersing the positive electrode active material, a binder, and other materials such as conductive agents and thickeners used as needed in a dispersion solvent to form a slurry of the positive electrode mixture, applying this slurry to the positive electrode current collector, and drying it (wet method).

[0039] Examples of conductive materials for the positive electrode include metallic materials such as copper and nickel; graphite such as natural graphite and artificial graphite; carbon black such as acetylene black; and carbon materials such as amorphous carbon such as needle coke. The conductive material for the positive electrode may be used individually or in combination of two or more types.

[0040] The content of the conductive agent relative to the mass of the positive electrode mixture layer may be 0.01% to 10% by mass, 0.1% to 5% by mass, or 1% to 3% by mass. A conductive agent content of 0.01% by mass or more tends to easily obtain sufficient conductivity. A conductive agent content of 10% by mass or less tends to suppress the decrease in battery capacity.

[0041] The binder for the positive electrode is not particularly limited, and when forming the positive electrode mixture layer by a wet method, a material with good solubility or dispersibility in the dispersion solvent is selected. Specifically, examples include resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polyimide, and cellulose; rubbery polymers such as SBR (styrene-butadiene rubber) and NBR (acrylonitrile-butadiene rubber); fluorine-based polymers such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene, polytetrafluoroethylene-vinylidene fluoride copolymer, and fluorinated polyvinylidene fluoride; copolymers in which acrylic acid and linear ether groups are added to a polyacrylonitrile backbone; and polymer compositions having ionic conductivity for alkali metal ions (especially lithium ions). The binder for the positive electrode may be used alone or in combination of two or more types.

[0042] The binder content relative to the mass of the positive electrode mixture layer is preferably 0.1% to 10% by mass, more preferably 0.5% to 5% by mass, and even more preferably 1% to 3% by mass. When the binder content is 0.1% by mass or more, the positive electrode active material can be sufficiently bound, sufficient mechanical strength of the positive electrode composite layer can be obtained, and battery performance such as cycle characteristics tends to improve. When the binder content is 10% by mass or less, sufficient battery capacity and conductivity tend to be obtained.

[0043] The positive electrode mixture layer formed on the positive electrode current collector using a wet or dry method is preferably compacted by hand pressing or roller pressing in order to improve the packing density of the positive electrode active material.

[0044] There are no particular restrictions on the material of the positive electrode current collector, but metal materials are preferred, and stainless steel coated with aluminum, molybdenum, or titanium nitride is more preferred. There are no particular restrictions on the shape of the positive electrode current collector, and materials processed into various shapes can be used. Examples of metal materials include metal foil, metal plate, metal thin film, and expanded metal, and among these, the use of a metal thin film is preferred. The thin film may be formed in a mesh shape as appropriate.

[0045] (Negative electrode) The dual-ion battery of this disclosure comprises a negative electrode containing a negative electrode active material capable of inserting and removing cations. For example, the negative electrode may have a negative electrode current collector and a negative electrode mixture layer disposed on its surface and containing the negative electrode active material.

[0046] The negative electrode active material is not particularly limited, but preferably contains a carbon material. Examples of carbon materials included in the negative electrode active material include graphite, carbon nanotubes, graphene, nanocarbon, hard carbon, and soft carbon. The graphene may be a carbon material having a structure in which graphene with oxygen and nanopores is regularly stacked (the specific carbon material mentioned above), or it may be graphene other than the specific carbon material mentioned above. The negative electrode active material more preferably contains a specific carbon material. The negative electrode active material may consist solely of carbon material, or it may be a combination of carbon material and a negative electrode active material other than carbon material. The negative electrode active material may be used alone or in combination of two or more types.

[0047] The carbon materials that can be used as negative electrode active materials are the same as the carbon materials described in the positive electrode active material section. For negative electrode active materials, the preferred configuration of a carbon material having a structure in which oxygen and nanopore-introduced graphene are regularly stacked is the same as the preferred configuration of the specific carbon materials described in the positive electrode section above.

[0048] When the negative electrode mixture layer contains negative electrode active material, the content of the negative electrode active material is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more, relative to the total amount of the negative electrode mixture layer, from the viewpoint of increasing the capacity of the battery.

[0049] Next, the negative electrode mixture layer and the negative electrode current collector will be described in detail. The negative electrode mixture layer contains a negative electrode active material, a binder, etc., and is placed on the negative electrode current collector. There are no restrictions on the method of forming the negative electrode mixture layer, and for example, it can be formed as follows: The negative electrode active material, a binder, and other materials such as conductive agents and thickeners used as needed are dissolved or dispersed in a dispersion solvent to form a slurry of the negative electrode mixture, which is then applied to the negative electrode current collector and dried (wet method) to form the negative electrode mixture layer.

[0050] As conductive agents for the negative electrode, carbon black such as acetylene black, amorphous carbon such as needle coke, etc., can be used. One type of conductive agent may be used alone, or two or more types may be used in combination. In this way, adding a conductive agent to the negative electrode mixture tends to yield effects such as reducing the resistance of the electrode.

[0051] The content of the conductive agent relative to the mass of the negative electrode mixture layer is preferably 1% to 10% by mass, more preferably 2% to 7% by mass, and even more preferably 3% to 5% by mass, from the viewpoint of improving conductivity and reducing initial irreversible capacity. A conductive agent content of 1% by mass or more tends to easily obtain sufficient conductivity. A conductive agent content of 10% by mass or less tends to suppress the decrease in battery capacity.

[0052] The binder for the negative electrode is not particularly limited as long as it is a material that is stable with non-aqueous electrolytes or dispersion solvents used in electrode formation. Specifically, examples include resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, cellulose, and nitrocellulose; rubbery polymers such as SBR (styrene-butadiene rubber) and NBR (acrylonitrile-butadiene rubber); fluorine-based polymers such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene, and fluorinated polyvinylidene fluoride; and polymer compositions having ionic conductivity for alkali metal ions (especially lithium ions). The binder for the negative electrode may be used alone or in combination of two or more types.

[0053] The binder content relative to the mass of the negative electrode mixture layer is preferably 0.1% to 20% by mass, more preferably 0.5% to 15% by mass, and even more preferably 0.6% to 10% by mass. When the binder content is 0.1% by mass or more, the negative electrode active material can be sufficiently bound, and sufficient mechanical strength of the negative electrode mixture layer tends to be obtained. When the binder content is 20% by mass or less, sufficient battery capacity and conductivity tend to be obtained.

[0054] Furthermore, when a fluorine-based polymer, such as polyvinylidene fluoride, is used as the main component of the binder, the binder content relative to the mass of the negative electrode mixture layer is preferably 1% to 15% by mass, more preferably 2% to 10% by mass, and even more preferably 3% to 8% by mass.

[0055] Thickening agents are used to adjust the viscosity of the slurry. There are no particular limitations on the thickening agents; specifically, examples include carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, starch oxide, starch phosphorylated, casein, and salts thereof. Thickening agents may be used individually or in combination of two or more.

[0056] From the viewpoint of input / output characteristics and battery capacity, the content of the thickener relative to the mass of the negative electrode mixture layer is preferably 0.1% to 5% by mass, more preferably 0.5% to 3% by mass, and even more preferably 0.6% to 2% by mass.

[0057] The dispersion solvent used to form the slurry is not limited to any particular type, as long as it is capable of dissolving or dispersing the negative electrode active material, binder, and, if necessary, conductive agents, thickeners, etc., and can be either an aqueous or organic solvent. Examples of aqueous solvents include water, alcohol, and mixed solvents of water and alcohol. Examples of organic solvents include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethyl sulfoxide, benzene, xylene, and hexane. When using an aqueous solvent, it is particularly preferable to use a thickener.

[0058] There are no particular restrictions on the material of the negative electrode current collector; specific examples include metal materials such as copper, nickel, stainless steel, and nickel-plated steel. Among these, copper is preferred from the standpoint of ease of processing and cost.

[0059] There are no particular restrictions on the shape of the negative electrode current collector, and materials processed into various shapes can be used. Specific examples include metal foil, metal plate, metal thin film, and expanded metal. Among these, metal foil is preferred, and copper foil is more preferred. Copper foil includes rolled copper foil formed by a rolling method and electrolytic copper foil formed by an electrolytic method, both of which are suitable as negative electrode current collectors.

[0060] (Non-aqueous electrolyte) The dual-ion battery of this disclosure comprises a non-aqueous electrolyte, the non-aqueous electrolyte containing LiFSI (lithium bis(fluorosulfonyl)imide). The non-aqueous electrolyte contains LiFSI as a lithium salt. In the non-aqueous electrolyte, one lithium salt may be used alone, or two or more lithium salts may be used in combination.

[0061] When using two or more lithium salts in combination, the non-aqueous electrolyte may contain LiFSI and other lithium salts other than LiFSI.

[0062] Other lithium salts include LiPF6, LiBF4, LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, and LiN(SO2CF2CF3)2. These other lithium salts may be used individually or in combination of two or more.

[0063] The non-aqueous electrolyte is not limited to a composition containing LiFSI, and may also contain LiTFSI (lithium bis(trifluoromethanesulfonyl)imide). If the non-aqueous electrolyte contains LiTFSI, it may also contain lithium salts other than LiTFSI.

[0064] The LiFSI content may be 50% to 100% by mass, 70% to 100% by mass, or 90% to 100% by mass, relative to the total amount of lithium salt.

[0065] The concentration of lithium bis(fluorosulfonyl)imide in the non-aqueous electrolyte (which may be read as "concentration of lithium salt in the non-aqueous electrolyte") is preferably 1 mol / L to 5 mol / L, more preferably 2 mol / L to 4 mol / L, and even more preferably 2.5 mol / L to 3.5 mol / L.

[0066] The non-aqueous electrolyte may contain a non-aqueous solvent. The non-aqueous solvent is not particularly limited, but from the viewpoint of lithium salt solubility, a linear carbonate is preferred.

[0067] Examples of linear carbonates include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propionate. Among these, ethyl methyl carbonate is preferred from the viewpoint of oxidation resistance and reduction resistance. The chain-like carbonate may be used alone or in combination of two or more types.

[0068] The non-aqueous electrolyte may contain a cyclic carbonate. Examples of cyclic carbonates include vinylene carbonate (VC), propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and fluoroethylene carbonate (FEC). Cyclic carbonates may be used individually or in combination of two or more types.

[0069] The content of cyclic carbonate may be 0% to 90% by mass or 0% to 20% by mass relative to the total amount of non-aqueous electrolyte.

[0070] The non-aqueous electrolyte may contain ethylene glycol ether. This tends to suppress the decomposition of the non-aqueous electrolyte when it is adsorbed onto the positive electrode surface. Examples of ethylene glycol ether include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether. Among these, ethylene glycol monobutyl ether is preferred. Ethylene glycol ether may be used alone or in combination of two or more types.

[0071] The ethylene glycol ether content may be 0.5% to 15% by mass, or 1% to 5% by mass, relative to the total amount of the non-aqueous electrolyte.

[0072] (Separator) The dual-ion battery of this disclosure may include a separator between the positive and negative electrodes to insulate them from each other. The separator is not particularly limited as long as it insulates the positive and negative electrodes while being ion permeable and resistant to oxidation on the positive electrode side and reduction on the negative electrode side. Materials such as resins and inorganic materials can be used for the separator that satisfy these characteristics. Examples of resins used include olefin polymers, fluorine polymers, cellulose polymers, polyimides, and nylon. Among these, it is preferable to use porous sheets or nonwoven fabrics made from polyolefins such as polyethylene and polypropylene. Inorganic materials that can be used include oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and glass. For example, the above inorganic materials in fibrous or granular form can be used as separators when attached to a substrate in the form of a nonwoven fabric, woven fabric, or thin film such as a microporous film. As for the thin film substrate, one with a pore size of 0.01 μm to 1 μm and an average thickness of 5 μm to 50 μm is preferably used. Alternatively, the above inorganic materials in fibrous or granular form can be used as separators when formed into a composite porous layer using a binder such as a resin. Furthermore, this composite porous layer may be formed on the surface of another separator to form a multilayer separator. In addition, this composite porous layer may be formed on the surface of the positive or negative electrode to form a separator.

[0073] (Manufacturing method for dual-ion batteries) The method for manufacturing a dual-ion battery according to this disclosure comprises a step of housing a positive electrode containing a positive electrode active material capable of inserting and deinserting anions, a negative electrode containing a negative electrode active material capable of inserting and deinserting cations, and a non-aqueous electrolyte in a battery container (housing step). In this case, the positive electrode active material contains a carbon material having a structure in which oxygen and nanopores are introduced into graphene in an orderly stacked manner, and the non-aqueous electrolyte contains lithium bis(fluorosulfonyl)imide.

[0074] In the housing process, each component of the dual-ion battery is housed in the battery container. The separator may be housed in the battery container so that it is positioned between the positive and negative electrodes to insulate them from each other.

[0075] For example, the aforementioned non-aqueous electrolyte can be supplied into the battery container with the positive electrode and negative electrode, and optionally a separator between the positive and negative electrodes, placed inside the battery container. [Examples]

[0076] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0077] (Preparation of carbon material 1) 10 g of graphite powder (Z-5F, manufactured by Ito Graphite Industry Co., Ltd., average particle size 5 μm) was placed in a 500 mL beaker, and 200 mL of fuming nitric acid was added, and the mixture was heated to 60°C. Then, while stirring the mixture, 80 g of potassium chlorate was slowly added and held for 3 hours. After that, the resulting reaction solution was transferred to 2 L of water, filtered by suction, and washed with pure water until the pH was 5 or higher to obtain graphite oxide powder. The obtained graphite oxide powder was dried overnight at 60°C. This graphite oxide powder was placed in an alumina container and heated under vacuum at a rate of 1 °C / min to 170°C, then at a rate of 0.1 °C / min to 250°C, and then at a rate of 1 °C / min to 700°C and held for 5 hours to obtain carbon material 1.

[0078] (Preparation of carbon material 2) 5 g of graphite powder (Z-5F, manufactured by Ito Graphite Industry Co., Ltd., average particle size 5 μm) and 200 mL of concentrated sulfuric acid were mixed and stirred at 25°C for 30 minutes. Then, the mixture was irradiated with ultrasound for 60 minutes, and 60 g of sodium periodate (NaIO4) was added to it over 2 hours at 0°C. After stirring at room temperature for 4 days, the entire reaction solution was added to 750 mL of distilled water, and then 25 mL of 30% hydrogen peroxide solution was added little by little, and the mixture was stirred for 1 hour. The reaction product was centrifuged and washed with water to obtain graphite oxide powder. The obtained graphite oxide powder was dried overnight at 60°C. This graphite oxide powder was placed in an alumina container and heated under vacuum at a rate of 1 °C / min to 170°C, then at a rate of 0.1 °C / min to 250°C, and then at a rate of 1 °C / min to 700°C, where it was held for 5 hours to obtain carbon material 2.

[0079] The composition and properties of the obtained carbon material 1 and carbon material 2 are shown in Table 1 below. In Table 1, the O / C ratio means "the molar ratio of oxygen atoms to carbon atoms contained in carbon material 1 or carbon material 2," and d(002) means "the average interplanar spacing d determined by X-ray diffraction." 002FWMH means "the full width at half maximum of the diffraction peak corresponding to the carbon 002 plane when X-rays (CuKα rays) are irradiated onto carbon material 1 or carbon material 2".

[0080] [Table 1]

[0081] [Example 1] (Fabrication of battery cell 1) A mixture was obtained by mixing 90 parts by mass of the obtained carbon material 1 with 5 parts by mass of acetylene black and 5 parts by mass of polytetrafluoroethylene. The mixture containing carbon material 1 was pressed onto an aluminum mesh (Niraco Co., Ltd., 100 mesh) to produce the positive electrode 1 (working electrode). The obtained working electrode was placed in a trielectrode cell using metallic lithium as the reference electrode and counter electrode, and 5 mL of 3 mol / L lithium bis(fluorosulfonyl)imide (LiFSI)-ethylmethyl carbonate electrolyte was injected into the trielectrode cell to fabricate battery cell 1.

[0082] (Charge / discharge measurement) Charge and discharge measurements were performed using the fabricated battery cell 1. The charge and discharge measurements were performed at 2.0V~4.8V vs Li + The charging and discharging capacities were measured using a constant current method of 10 mA / g within the range of / Li, and the charge-discharge efficiency was also determined. The results are shown in Figure 1 and Table 2.

[0083] [Example 2] Battery cell 2 was fabricated in the same manner as in Example 1, except that carbon material 1 was changed to carbon material 2, and charge / discharge measurements were performed using battery cell 2. The results are shown in Figure 1 and Table 2.

[0084] [Comparative Example 1] Battery cell 3 was prepared in the same manner as in Example 1, except that the electrolyte was changed to 3 mol / L lithium hexafluorophosphate (LiPF6)-ethylmethyl carbonate, and charge / discharge measurements were performed using battery cell 3. The results are shown in Figure 1 and Table 2.

[0085] [Comparative Example 2] Battery cell 4 was prepared in the same manner as in Example 2, except that the electrolyte was changed to 3 mol / L lithium hexafluorophosphate (LiPF6)-ethylmethyl carbonate, and charge / discharge measurements were performed using battery cell 4. The results are shown in Figure 1 and Table 2.

[0086] [Table 2]

[0087] As shown in Table 2, Examples 1 and 2, which used LiFSI as the lithium salt, exhibited superior charging and discharging capacities compared to Comparative Examples 1 and 2, which used LiPF6 as the lithium salt. In Examples 1 and 2 and Comparative Examples 1 and 2, charge-discharge measurements were performed to evaluate the performance of the positive electrode when combined with the electrolyte used in a dual-ion battery. It is presumed that similar results to those in Examples 1 and 2 and Comparative Examples 1 and 2 would be obtained when a dual-ion battery is constructed using the positive electrode, negative electrode, and electrolyte. Furthermore, the reason why the charge-discharge efficiency exceeded 100% in Comparative Example 2 is presumed to be that oxygen was removed or solvated, and lithium ions were inserted, contributing to the discharge.

[0088] Below, dual-ion batteries were fabricated using a positive electrode, negative electrode, and electrolyte containing carbon material 1, and the charge-discharge characteristics of the fabricated dual-ion batteries were investigated.

[0089] [Example 3] (Fabrication of battery cell 5) Positive electrode 1 was fabricated in the same manner as in Example 1. A mixture was obtained by mixing 90 parts by mass of carbon material 1, 5 parts by mass of acetylene black, and 5 parts by mass of polyvinylidene fluoride. The mixture was slurryed with N-methyl-2-pyrrolidone, and the slurry was applied to copper foil and then dried to produce negative electrode 1. A positive electrode 1 and a negative electrode 1 were placed in a two-electrode cell, and 5 mL of 3 mol / L lithium bis(fluorosulfonyl)imide (LiFSI)-ethylmethyl carbonate electrolyte was injected to fabricate battery cell 5.

[0090] (Charge / discharge measurement) Charge and discharge measurements were performed using the fabricated battery cell 5. The measurements were taken using a constant current method of 6 mA / g in the range of 1.0V to 4.2V. After activating the battery cell 5 by performing one charge and discharge cycle, the charge and discharge capacities were measured, and the charge and discharge efficiency was determined. The results are shown in Figure 2 and Table 3.

[0091] [Comparative Example 3] Battery cell 6 was prepared in the same manner as in Example 3, except that the electrolyte was changed to 3 mol / L lithium hexafluorophosphate (LiPF6)-ethylmethyl carbonate, and charge / discharge measurements were performed using battery cell 6. The results are shown in Figure 3 and Table 3.

[0092] [Table 3]

[0093] As shown in Table 3, Example 3, which used LiFSI as the lithium salt, exhibited superior charging and discharging capacities compared to Comparative Example 3, which used LiPF6 as the lithium salt, confirming a trend similar to that observed in Examples 1 and 2 and Comparative Examples 1 and 2. [Industrial applicability]

[0094] The applications of the dual-ion battery disclosed herein are not particularly limited and can be used in various known applications. Specific examples include laptop computers, e-book players, mobile phones, game consoles, and watches. The dual-ion battery disclosed herein can also be applied to applications such as power storage, electric vehicles, hybrid vehicles, and other transportation equipment.

Claims

1. A positive electrode containing a positive electrode active material capable of inserting and removing anions, A negative electrode containing a negative electrode active material capable of inserting and removing cations, A non-aqueous electrolyte is provided, The positive electrode active material comprises a carbon material having a structure in which oxygen and nanopore-introduced graphene are regularly stacked, and the non-aqueous electrolyte comprises lithium bis(fluorosulfonyl)imide. The aforementioned negative electrode active material is a dual-ion battery containing a carbon material.

2. The dual-ion battery according to claim 1, wherein the carbon material is a carbon material represented by the following general formula (1). C ８ O ｘ H ｙ ・・・・(1) (In equation (1), x is between 0.10 and 1.50, and y is between 0 and 1.00.)

3. The dual-ion battery according to claim 1 or claim 2, wherein the molar ratio of oxygen atoms to carbon atoms contained in the carbon material is 0.020 to 0.

150.

4. The dual-ion battery according to any one of claims 1 to 3, wherein the concentration of lithium bis(fluorosulfonyl)imide in the non-aqueous electrolyte is 1 mol / L to 5 mol / L.

5. The dual-ion battery according to any one of claims 1 to 4, wherein the non-aqueous electrolyte comprises ethylene glycol ether.

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