Negative electrode mixture for sodium-ion battery, sodium-ion battery, and method for producing same

Abstract

The present disclosure provides a negative electrode mixture for a sodium-ion battery capable of improving charge capacity, discharge capacity, and charge / discharge efficiency, a sodium-ion battery containing such a negative electrode mixture, and a method for manufacturing the same. This negative electrode mixture for a sodium ion battery has a negative electrode active material and zirconium oxide, the negative electrode active material contains hard carbon, and the ratio of the mass of zirconium oxide to the total mass of the hard carbon and zirconium oxide is 1-20 mass%. A sodium ion battery (1) according to the present disclosure has a negative electrode active material layer (20), and the negative electrode active material layer contains the negative electrode mixture according to the present disclosure. A method for manufacturing a sodium ion battery according to the present disclosure includes forming a negative electrode active material layer, and the negative electrode active material layer contains the negative electrode mixture according to the present disclosure.

Description

Technical Field

[0001] The present disclosure relates to a negative electrode mixture for a sodium ion battery, a sodium ion battery and a method for producing the same. Background Art

[0002] Lithium-ion batteries are used as power sources for mobile devices and vehicles due to their high capacity and light weight. On the other hand, sodium-ion batteries using sodium have attracted attention in recent years as a material to replace lithium from the perspective of resource quantity.

[0003] For example, Patent Document 1 discloses a sodium ion secondary battery including a positive electrode, a negative electrode having a negative electrode active material, and a nonaqueous electrolyte solution containing a nonaqueous solvent, wherein the negative electrode active material is hard carbon.

[0004] Patent Document 2 discloses an electrode for a sodium secondary battery, which has an electrode mixture layer, wherein the electrode mixture layer contains an electrode active material and a binder, and the binder contains a polycarboxylic acid and / or an alkali metal salt of a polycarboxylic acid.

[0005] Prior art literature

[0006] Patent Document 1: International Publication No. 2010 / 109889

[0007] Patent Document 2: Japanese Patent Application Publication No. 2013-229319 Summary of the invention

[0008] In sodium ion batteries, there is still room for improvement in terms of charge capacity and discharge capacity, as well as charge and discharge efficiency.

[0009] The present disclosure aims to provide a negative electrode mixture for a sodium ion battery capable of improving charging capacity, discharging capacity, and charging and discharging efficiency, a sodium ion battery containing the negative electrode mixture, and a method for producing the same.

[0010] The author of the present invention has found that the above-mentioned problems can be solved by the following means.

[0011] <Method 1>

[0012] A negative electrode mixture for a sodium ion battery,

[0013] With negative electrode active material and zirconium oxide,

[0014] The negative electrode active material comprises hard carbon, and

[0015] The ratio of the mass of the zirconium oxide to the total mass of the hard carbon and the zirconium oxide is 1 mass % or more and 20 mass % or less.

[0016] <Method 2>

[0017] A sodium ion battery,

[0018] having a negative electrode active material layer, and

[0019] The negative electrode active material layer contains the negative electrode mixture described in Embodiment 1.

[0020] <Method 3>

[0021] A method for manufacturing a sodium ion battery,

[0022] comprising the step of forming a negative electrode active material layer, and

[0023] The negative electrode active material layer contains the negative electrode mixture described in Embodiment 1.

[0024] <Method 4>

[0025] The method for manufacturing a sodium ion battery according to Embodiment 3 comprises forming the negative electrode active material layer by a method comprising the following steps:

[0026] Providing a negative electrode mixture slurry containing the negative electrode mixture according to embodiment 1 and a dispersion medium; and

[0027] The negative electrode mixture slurry is applied to a substrate, and then the dispersion medium is dried and removed.

[0028] According to the present disclosure, a negative electrode mixture for a sodium ion battery capable of improving charging capacity, discharging capacity, and charging and discharging efficiency, a sodium ion battery containing the negative electrode mixture, and a method for producing the same can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic cross-sectional view showing an example of the sodium ion battery of the present disclosure.

[0030] Figure 2 It is a graph showing the charge and discharge curve (current value: 0.1 C) of the cell of Example 3.

[0031] Figure 3 It is a graph showing the charge and discharge curve (current value: 0.3 C) of the cell of Example 3.

[0032] Figure 4 It is a graph showing the charge and discharge curve (current value: 0.1 C) of the cell of Example 1.

[0033] Figure 5 It is a graph showing the charge and discharge curve (current value: 0.1 C) of the cell of Example 2.

[0034] Figure 6 It is a graph showing the charge and discharge curve (current value: 0.3 C) of the cell of Comparative Example 1.

[0035] Figure 7 It is a graph showing the charge and discharge curve (current value: 0.3 C) of the cell of Comparative Example 2.

[0036] Figure 8 It is a graph showing the charge and discharge curve (current value: 0.3 C) of the cell of Comparative Example 3.

[0037] Fig. 9 It is a graph showing the charge and discharge curve (current value: 0.3 C) of the cell of Comparative Example 4.

[0038] Description of Reference Numerals

[0039] 1. Sodium-ion battery

[0040] 10 Negative electrode collector

[0041] 20Negative electrode active material layer

[0042] 30 Diaphragm

[0043] 40 Positive electrode active material layer

[0044] 50 Positive electrode collector DETAILED DESCRIPTION

[0045] Hereinafter, the embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the disclosed gist.

[0046] 《Anode mixture for sodium ion batteries》

[0047] The negative electrode mixture for sodium ion battery disclosed herein comprises a negative electrode active material and zirconium oxide. The negative electrode active material contains hard carbon, and the mass ratio of zirconium oxide to the total mass of hard carbon and zirconium oxide is 1 mass % or more and 20 mass % or less.

[0048] Although not intending to be limited by theory, in a sodium ion battery including a negative electrode mixture having such a structure, zirconium oxide promotes insertion and extraction of sodium into hard carbon, thereby improving charging and discharging capacity and charging and discharging efficiency, that is, charging and discharging characteristics.

[0049] Furthermore, in the present disclosure, "negative electrode mixture" refers to a composition that can constitute a negative electrode active material layer as it is or by further containing other components. In addition, in the present disclosure, "negative electrode mixture slurry" refers to a slurry that contains a dispersion medium in addition to the "mixture" and can form a negative electrode active material layer by coating and drying.

[0050] The negative electrode mixture for a sodium ion battery disclosed in the present invention comprises a negative electrode active material and zirconium oxide, and may optionally comprise a conductive auxiliary agent and a binder.

[0051] <Negative Electrode Active Material>

[0052] The negative electrode active material contains hard carbon. The negative electrode mixture disclosed in the present invention may contain, for example, 50% by mass or more, 70% by mass or more, 99% by mass or less, or 95% by mass or less of the negative electrode active material. The content of hard carbon relative to the total amount of the negative electrode active material may be 50% by mass or more, 70% by mass or more, 90% by mass or more, 95% by mass or more, or 99% by mass or more, or may be 100% by mass. That is, the negative electrode active material may be hard carbon. The average particle size of the hard carbon is not particularly limited, and may be, for example, in the range of 50 nm to 100 μm.

[0053] Hard carbon may be a commercial product or may be hard carbon produced by conventional methods. Hard carbon may be produced, for example, by carbonizing a raw material containing carbon element. The carbonization temperature may be, for example, about 1000 to 2000°C. In addition, carbonization may be performed under an inert atmosphere. The raw material for hard carbon is not particularly limited as long as it is a raw material that can produce hard carbon. For example, organic compounds such as alcohols such as ethanol, phenols, and aldehydes such as formaldehyde may be used as raw materials. In addition, resins such as phenolic resins, polyacrylonitrile, and polyimide may also be used as raw materials. These raw materials may be used alone or in combination.

[0054] <Zirconium Oxide>

[0055] The ratio of the mass of zirconium oxide to the total mass of hard carbon and zirconium oxide is 1 mass % to 20 mass %. The range of this ratio may vary depending on the current value assumed when charging and discharging the sodium ion battery including the negative electrode mixture of the present disclosure.

[0056] For example, when the current value is 0.1C, the ratio may be 6% by mass or more, 7% by mass or more, 8% by mass or more, 9% by mass or more, or 10% by mass or more, and may be 18% by mass or less, 15% by mass or less, 13% by mass or less, 12% by mass or less, 11% by mass or less, or 10% by mass or less. In addition, for example, when the current value is 0.3C, the ratio may be 2% by mass or more, 3% by mass or more, 4% by mass or more, 5% by mass or more, 6% by mass or more, 7% by mass or more, 8% by mass or more, 9% by mass or more, or 10% by mass or less, and may be 18% by mass or less, 15% by mass or less, 13% by mass or less, 12% by mass or less, 11% by mass or less, or 10% by mass or less. That is, when the sodium ion battery containing the negative electrode mixture of the present disclosure is used for charging and discharging at a larger current value, the charge and discharge characteristics of the battery can be improved even when a smaller amount of zirconium oxide is contained.

[0057] <Conductive additive>

[0058] The conductive aid may be, for example, a carbon material, a metal material, or the like. Specific examples of carbon materials include carbon black such as acetylene black, ketjen black, furnace black, thermal black, etc.; carbon fibers such as VGCF; graphite; hard carbon; coke, etc. As metal materials, Fe, Cu, Ni, Al, etc. may be mentioned. The content of the conductive aid in the negative electrode mixture is not particularly limited. For example, the negative electrode mixture may contain a conductive aid in an amount of 1% by mass or more and 50% by mass or less.

[0059] <Adhesive>

[0060] As a binder, a chemically stable and electrically stable binder can be used. As a specific example of a binder, for example, a fluorine-based binder such as a polyvinylidene fluoride (PVdF)-based binder, a polytetrafluoroethylene (PTFE)-based binder, a rubber-based binder such as a styrene butadiene rubber (SBR)-based binder, an olefin-based binder such as a polypropylene (PP)-based binder, a polyethylene (PE)-based binder, a cellulose-based binder such as a carboxymethyl cellulose (CMC)-based binder, or a polyacrylic acid (PAA)-based binder can be cited. The content of the binder in the negative electrode mixture is not particularly limited and can be appropriately determined according to the target adhesiveness.

[0061] Sodium-ion battery

[0062] like Figure 1 As shown, the sodium ion battery 1 of the present disclosure has a negative electrode active material layer 20, and the negative electrode active material layer 20 contains the negative electrode mixture of the present disclosure. The sodium ion battery of the present disclosure may have a negative electrode collector 10, a negative electrode active material layer 20, a separator 30, a positive electrode collector 40, and a positive electrode active material layer 50 in sequence, and they may be impregnated with an electrolyte.

[0063] <Negative Electrode Collector>

[0064] Examples of the material of the negative electrode current collector include SUS, aluminum, copper, nickel, and carbon.

[0065] The negative electrode current collector may be in a foil, mesh, or porous form, for example.

[0066] <Negative Electrode Active Material Layer>

[0067] The negative electrode active material layer contains the negative electrode mixture of the present disclosure. For the negative electrode mixture of the present disclosure, the above description on the negative electrode mixture of the present disclosure can be referred to.

[0068] The negative electrode active material layer may have a certain thickness. The thickness of the negative electrode active material layer is not particularly limited, and may be, for example, 0.1 μm or more and 1 mm or less.

[0069] <Diaphragm>

[0070] As the material of the separator, there is no particular limitation as long as it has the function of electrically separating the negative electrode material layer and the positive electrode active material layer, for example, porous sheets composed of resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, polyamide, etc., non-woven fabrics, porous insulating materials such as glass fiber non-woven fabrics, etc., or combinations thereof can be cited. The thickness of the separator is not particularly limited, for example, it can be 5 μm or more and 1 mm or less. The separator acts as an electrolyte layer by being impregnated with an electrolyte.

[0071] <Electrolyte>

[0072] The electrolyte may contain a sodium salt and a non-aqueous solvent. Examples of the sodium salt include inorganic sodium salts such as NaPF6, NaBF4, NaClO4, and NaAsF6, and organic sodium salts such as NaCF3SO3, NaN(CF3SO2)2, NaN(C2F5SO2)2, NaN(FSO2)2, and NaC(CF3SO2)3.

[0073] As non-aqueous solvent, as long as sodium salt is dissolved, there is no particular limitation. For example, as high dielectric constant solvent, cyclic esters (cyclic carbonates), γ-butyrolactone, cyclopentane, N-methyl-2-pyrrolidone (NMP), 1,3-dimethyl-2-imidazolidinone (DMI) etc. such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) etc. can be cited. On the other hand, as low viscosity solvent, chain esters (chain carbonates), methyl acetate, ethyl acetate etc. such as acetates, ethers such as 2-methyltetrahydrofuran etc. such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) etc. can be cited. As non-aqueous solvent, a mixed solvent in which a high dielectric constant solvent and a low viscosity solvent are mixed can also be used.

[0074] <Positive Electrode Active Material Layer>

[0075] The positive electrode active material layer contains a positive electrode active material, and may optionally contain a conductive auxiliary agent and a binder.

[0076] Examples of positive electrode active materials include oxides containing Na such as layered active materials, spinel-type active materials, and olivine-type active materials. Specifically, examples include NaFeO2, NaNiO2, NaCoO2, NaMnO2, NaVO2, Na(Ni X Mn 1-X )O2(0 <X<1),Na(Fe X Mn 1-X)O2(0 < X < 1), NaVPO4F, Na2FePO4F, Na3V2(PO4)3, etc. The shape of the positive electrode active material is not particularly limited. The positive electrode active material can be in the form of particles. In this case, its average particle diameter can be, for example, 1 nm or more or 10 nm or more, and can be 100 μm or less or 30 μm or less. The higher the content of the positive electrode active material in the positive electrode active material layer, the higher the capacity of the positive electrode. The positive electrode active material layer can contain, for example, 50% by mass or more or 70% by mass or more, and can contain 99% by mass or less or 95% by mass or less.

[0077] Regarding the conductive additive and the binder, reference can be made to the above description of the negative electrode binder for the sodium ion battery of the present disclosure.

[0078] The positive electrode active material layer can have a certain thickness. The thickness of the positive electrode active material layer is not particularly limited and can be, for example, 0.1 μm or more and 1 mm or less.

[0079] <Positive electrode current collector>

[0080] As materials for the positive electrode current collector, for example, SUS, aluminum, nickel, iron, titanium, carbon, etc. can be cited.

[0081] The positive electrode current collector can be, for example, in the form of a foil, a mesh, or a porous shape, etc.

[0082] <Other components>

[0083] The sodium ion battery of the present disclosure can include a battery case for housing the layers of the battery and terminals connected to the current collector, etc. In addition, in order to reduce the contact resistance, the sodium ion battery of the present disclosure can include a constraint member for constraining each layer along the stacking direction. For this, the same members as those in the prior art can be used.

[0084] As the shape of the sodium ion battery of the present disclosure, for example, a button type, a laminated type, a cylindrical type, and a square type, etc. can be cited.

[0085] "Method for manufacturing a sodium ion battery"

[0086] The method for manufacturing a sodium ion battery of the present disclosure includes the formation of a negative electrode active material layer, and the negative electrode active material layer contains the negative electrode binder of the present disclosure.

[0087] The method of the present disclosure can include forming a negative electrode active material layer by a method including the following steps: providing a negative electrode binder slurry containing the negative electrode binder of the present disclosure and a dispersion medium; and coating the negative electrode binder slurry on a substrate and then drying and removing the dispersion medium.

[0088] Regarding the negative electrode binder of the present disclosure, reference can be made to the above description of the negative electrode binder of the present disclosure.

[0089] The dispersion medium is not particularly limited, and examples thereof include alcohols, glycols, cellosolves, amines, ketones, carboxylic acid amides, phosphoric acid amides, sulfoxides, carboxylic acid esters, phosphoric acid esters, ethers, and nitriles, etc. Specifically, ethanol, 2-propanol, methyl ethyl ketone, and N-methyl-2-pyrrolidone can be mentioned.

[0090] The substrate is not particularly limited, and may be, for example, a negative electrode current collector.

[0091] The drying temperature, drying time and the like can be appropriately designed according to the boiling point and the amount of the dispersion medium used.

[0092] [Example]

[0093] 《Example 1》

[0094] <Manufacturing of Evaluation Unit>

[0095] (Preparation of negative electrode mixture)

[0096] A mixture of hard carbon (HC) and zirconium oxide (ZrO2) as negative electrode active materials in a ratio of 0.49:0.01 (mass ratio) and polyvinylidene fluoride (PVdF) as a binder were weighed in a ratio of 95:5 (mass ratio), dispersed in N-methyl-2-pyrrolidone (NMP), and stirred at 2000 rpm for 10 minutes. Thus, a slurry-like negative electrode mixture (negative electrode mixture slurry) was obtained.

[0097] (Formation of Negative Electrode Active Material Layer)

[0098] The obtained negative electrode mixture slurry was applied to an aluminum (Al) current collector foil using a 75 μm bar coater. The obtained coating was dried, punched into φ16 mm pieces, and then formed by a press. Thus, a negative electrode active material layer was formed on the Al current collector foil.

[0099] (Unit Production)

[0100] A stack of Al collector foil and negative electrode active material layer was used as the working electrode, metallic sodium (Na) was used as the counter electrode, and a material consisting of three layers of 25μm polypropylene / polyethylene / polypropylene (PP / PE / PP) was used as the separator. Then, 1M NaPF6 with EC:DMC=1:1 (volume ratio) was used as the electrolyte to produce a 2032-type button unit.

[0101] "evaluate"

[0102] <Evaluation of Charge Capacity and Discharge Capacity>

[0103] A charge and discharge test was carried out at a voltage range of 0.01 to 1.5 V and a current value of 0.1 C in an environment of 25° C. to evaluate the Na insertion capacity (charge capacity) and Na extraction capacity (discharge capacity) of the button cell.

[0104] 《Examples 2 to 4 and Comparative Examples 1 to 4》

[0105] The cell was prepared and evaluated in the same manner as in Example 1 except that the type of metal oxide (MO), the ratio of the mass of the metal oxide to the total mass of the negative electrode active material and the metal oxide (MO / MO+HC), and the current value during charge and discharge in the above evaluation were changed as shown in Table 1.

[0106] "result"

[0107] Table 1 shows the charge capacity and discharge capacity, and the charge and discharge efficiency (discharge capacity / charge capacity percentage) of each example.

[0108]

[0109] As shown in Table 1, when the current value is 0.1C, the batteries of Examples 3 and 4, in which the mass ratio of zirconium oxide to the total mass of hard carbon and zirconium oxide is 10 mass % and 20 mass %, have larger discharge capacity than the battery of Comparative Example 1 to which zirconium oxide is not added. In addition, the battery of Example 3 has higher charge and discharge efficiency than the battery of Comparative Example 1.

[0110] On the other hand, when the current value is 0.3C, the batteries of Examples 1 to 4 in which the ratio of the mass of zirconium oxide to the total mass of hard carbon and zirconium oxide is 2 mass % to 20 mass % have a larger charge and discharge capacity and higher charge and discharge efficiency than the battery of Comparative Example 1 in which zirconium oxide is not added.

[0111] In addition, when the ratio of the mass of metal oxide to the total mass of hard carbon and metal oxide is 10 mass%, regardless of the current value, the battery of Example 3 using zirconium oxide as the metal oxide has higher charge and discharge efficiency than the batteries of Comparative Examples 2 to 4 using titanium oxide.

Claims

1. A negative electrode mixture for a sodium ion battery, With negative electrode active material and zirconium oxide, The negative electrode active material comprises hard carbon, and The ratio of the mass of the zirconium oxide to the total mass of the hard carbon and the zirconium oxide is 1 mass % or more and 20 mass % or less.

2. A sodium ion battery, having a negative electrode active material layer, and The negative electrode active material layer contains the negative electrode mixture according to claim 1 .

3. A method for manufacturing a sodium ion battery, comprising the step of forming a negative electrode active material layer, and The negative electrode active material layer contains the negative electrode mixture according to claim 1 .

4. The method for manufacturing a sodium ion battery according to claim 3, comprising forming the negative electrode active material layer by a method comprising the following steps: A negative electrode mixture slurry comprising the negative electrode mixture according to claim 1 and a dispersion medium is provided; and The negative electrode mixture slurry is applied to a substrate, and then the dispersion medium is dried and removed.

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