Anode mixture for sodium ion batteries, sodium ion battery and manufacturing method thereof

Abstract

To provide an anode mixture for sodium ion batteries capable of enhancing a charge capacity, a discharge capacity and charge / discharge efficiency, a sodium ion battery containing such an anode mixture and a manufacturing method thereof.SOLUTION: An anode mixture for sodium ion batteries contains an anode active material and zirconium oxide, the anode active material contains hard carbon and a ratio of a mass of zirconium oxide with respect to a total mass of the hard carbon and the zirconium oxide is 1 mass% or more to 20 mass% or less. A sodium ion battery 1 comprises an anode active material layer 20, and the anode active material layer contains the anode mixture. A method of manufacturing the sodium ion battery includes forming the anode active material layer, and the anode active material layer contains the anode mixture.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a negative electrode composite material for a sodium ion battery, a sodium ion battery, and a method for manufacturing the same.

Background Art

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

[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 non-aqueous electrolyte containing a non-aqueous solvent, wherein the negative electrode active material is hard carbon.

[0004] Patent Document 2 discloses an electrode for a sodium secondary battery having an electrode binder layer containing an electrode active material and a binder containing a polycarboxylic acid and / or an alkali metal salt of a polycarboxylic acid.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In sodium ion batteries, there is room for improvement in charge capacity, discharge capacity, and charge-discharge efficiency.

[0007] The present disclosure aims to provide a negative electrode composite material 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 composite material, and a method for manufacturing the same.

Means for Solving the Problems

[0008] The present inventors have found that the above problems can be solved by the following means. <Aspect 1> A negative electrode composite material for a sodium-ion battery, having a negative electrode active material and zirconium oxide, wherein the negative electrode active material contains 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% by mass or more and 20% by mass or less. <Aspect 2> A sodium-ion battery having a negative electrode active material layer, and wherein the negative electrode active material layer contains the negative electrode composite material according to Aspect 1. <Aspect 3> A method for manufacturing a sodium-ion battery, including forming a negative electrode active material layer, and wherein the negative electrode active material layer contains the negative electrode composite material according to Aspect 1. <Aspect 4> The method according to Aspect 3, including forming the negative electrode active material layer by a method including the following steps: providing a negative electrode composite material slurry containing the negative electrode composite material according to Aspect 1 and a dispersion medium, and coating the negative electrode composite material slurry on a substrate and drying and removing the dispersion medium.

Advantages of the Invention

[0009] According to the present disclosure, it is possible to provide a negative electrode composite material 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 composite material, and a method for manufacturing the same.​​​

Brief Description of the Drawings

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Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present disclosure will be described in detail. It should be noted that the present disclosure is not limited to the following embodiments and can be variously modified and implemented within the scope of the gist of the disclosure.

[0012] 《Negative Electrode Composite Material for Sodium-Ion Battery》 The negative electrode composite material for a sodium-ion battery of the present disclosure 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 hard carbon and zirconium oxide is 1% by mass or more and 20% by mass or less.

[0013] Although not limited to theory, in a sodium-ion battery including a negative electrode composite material having such a configuration, zirconium oxide promotes the insertion and desorption of sodium into and from hard carbon, thereby improving the charge capacity, discharge capacity, and charge-discharge efficiency, that is, the charge-discharge characteristics.

[0014] Regarding the present disclosure, the "negative electrode composite material" means a composition that can form a negative electrode active material layer as it is or by further containing other components. Further, regarding the present disclosure, the "negative electrode composite material slurry" means a slurry that contains a dispersion medium in addition to the "composite material" and can form a negative electrode active material layer by coating and drying it.

[0015] The negative electrode composite material for a sodium-ion battery of the present disclosure has a negative electrode active material and zirconium oxide, and may optionally have a conductive assistant and a binder.

[0016] 〈Negative electrode active material〉 The negative electrode active material contains hard carbon. The negative electrode composite material of the present disclosure may contain the negative electrode active material, for example, in an amount of 50% by mass or more, 70% by mass or more, 99% by mass or less, or 95% by mass or less. 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, and 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, but can be, for example, in the range of 50 nm to 100 μm.

[0017] Hard carbon may be a commercially available product or may be one produced by a conventional method. Hard carbon can be produced, for example, by carbonizing a raw material containing a carbon element. The carbonization temperature may be, for example, about 1000 to 2000 °C. Also, the carbonization can be carried out in an inert atmosphere. The raw material for hard carbon is not particularly limited as long as it can produce hard carbon. For example, organic compounds such as alcohols such as ethanol, phenols, and aldehydes such as formaldehyde can be used as raw materials. In addition, phenolic resins, resins such as polyacrylonitrile and polyimide can be used as raw materials. These raw materials may be used alone or in combination of multiple types.

[0018] 〈Zirconium Oxide〉 The ratio of the mass of zirconium oxide to the total mass of hard carbon and zirconium oxide is 1% by mass or more and 20% by mass or less. This ratio range may vary depending on the current value assumed when charging and discharging a sodium-ion battery including the negative electrode composite material of the present disclosure.

[0019] For example, when the above current value is 0.1C, this 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. Also, for example, when the above current value is 0.3C, this 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 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. That is, when the sodium-ion battery including the negative electrode composite material of the present disclosure is used for charging and discharging at a higher large current value, even when a smaller amount of zirconium oxide is contained, the charge and discharge characteristics of the battery can be improved.

[0020] 〈Conductive Aid〉 The conductive aid may be, for example, a carbon material, a metal material, or the like. Specific examples of the carbon material include carbon black such as acetylene black, ketjen black, furnace black, and thermal black; carbon fibers such as VGCF; graphite; hard carbon; coke; and the like. Examples of the metal material include Fe, Cu, Ni, Al, and the like. The content of the conductive aid in the negative electrode composite material is not particularly limited. For example, the negative electrode composite material may contain 1% by mass or more and 50% by mass or less of the conductive aid.

[0021] 〈Binder〉 As the binder, a chemically and electrically stable one may be used. Specific examples of the binder include, for example, fluorine-based binders such as polyvinylidene fluoride (PVdF)-based binders and polytetrafluoroethylene (PTFE)-based binders, rubber-based binders such as styrene-butadiene rubber (SBR)-based binders, olefin-based binders such as polypropylene (PP)-based binders and polyethylene (PE)-based binders, cellulose-based binders such as carboxymethyl cellulose (CMC)-based binders, or polyacrylic acid (PAA)-based binders. The content of the binder in the negative electrode composite material is not particularly limited and may be appropriately determined according to the desired binding property.

[0022] 《Sodium Ion Battery》 As shown in FIG. 1, 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 composite material of the present disclosure. The sodium ion battery of the present disclosure may have a negative electrode current collector 10, a negative electrode active material layer 20, a separator 30, a positive electrode current collector 40, and a positive electrode active material layer 50 in this order, and these may be impregnated with an electrolytic solution.

[0023] 〈Negative Electrode Current Collector〉 Examples of the material of the negative electrode current collector include SUS, aluminum, copper, nickel, carbon, and the like.

[0024] The negative electrode current collector may be, for example, in the form of a foil, a mesh, or a porous material, etc.

[0025] 〈Negative electrode active material layer〉 The negative electrode active material layer contains the negative electrode composite material of the present disclosure. Regarding the negative electrode composite material of the present disclosure, reference can be made to the above description regarding the negative electrode composite material of the present disclosure.

[0026] The negative electrode active material layer may have a certain thickness. The thickness of the negative electrode active material layer is not particularly limited, but may be, for example, 0.1 μm or more and 1 mm or less.

[0027] 〈Separator〉 The material of the separator is not particularly limited as long as it has the function of electrically separating the negative electrode material layer and the positive electrode active material layer. Examples include porous sheets made of resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, polyamide, etc., non-woven fabrics such as non-woven fabrics and glass fiber non-woven fabrics, porous insulating materials such as these, or combinations thereof. The thickness of the separator is not particularly limited and may be, for example, 5 μm or more and 1 mm or less. The separator also functions as an electrolyte layer by being impregnated with the electrolytic solution.

[0028] 〈Electrolytic solution〉 The electrolytic solution may contain a sodium salt and a non-aqueous solvent. Examples of the sodium salt include inorganic sodium salts such as NaPF 6 , NaBF 4 , NaClO 4 and NaAsF 6 etc.; and NaCF 3 SO 3 , NaN(CF 3 SO 2 ) 2 , NaN(C 2 F 5 SO 2 ) 2 , NaN(FSO 2 ) 2 , NaC(CF 3 SO 2 ) 3Examples thereof include organic sodium salts and the like.

[0029] The non-aqueous solvent is not particularly limited as long as it can dissolve the sodium salt. For example, as the high dielectric constant solvent, cyclic esters (cyclic carbonates) such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), γ-butyrolactone, sulfolane, N-methyl-2-pyrrolidone (NMP), 1,3-dimethyl-2-imidazolidinone (DMI), etc. can be mentioned. On the other hand, as the low viscosity solvent, chain esters (chain carbonates) such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), acetates such as methyl acetate and ethyl acetate, ethers such as 2-methyltetrahydrofuran, etc. can be mentioned. As the non-aqueous solvent, a mixed solvent of a high dielectric constant solvent and a low viscosity solvent may also be used.

[0030] 〈Positive electrode active material layer〉 The positive electrode active material layer contains a positive electrode active material and may optionally contain a conductive aid and a binder.

[0031] Examples of the positive electrode active material include Na-containing oxides such as layered active materials, spinel-type active materials, and olivine-type active materials. Specifically, NaFeO 2 , NaNiO 2 , NaCoO 2 , NaMnO 2 , NaVO 2 , Na(Ni X Mn 1-X )O 2 (0 < X < 1), Na(Fe X Mn 1-X )O 2 (0 < X < 1), NaVPO 4 F, Na 2 FePO 4 F, Na 3 V 2 (PO 4 ) 3Examples include the like. The shape of the positive electrode active material is not particularly limited. The positive electrode active material may be particulate. In this case, its average particle diameter may be, for example, 1 nm or more or 10 nm or more, and may 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 may contain, for example, 50% by mass or more or 70% by mass or more, and 99% by mass or less or 95% by mass or less of the positive electrode active material.

[0032] Regarding the conductive assistant and the binder, reference can be made to the above description of the negative electrode composite material for a sodium ion battery of the present disclosure.

[0033] The positive electrode active material layer may have a certain thickness. The thickness of the positive electrode active material layer is not particularly limited, but may be, for example, 0.1 μm or more and 1 mm or less.

[0034] 〈Positive electrode current collector〉 Examples of the material of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, carbon, etc.

[0035] The positive electrode current collector may be, for example, in the form of a foil, a mesh, or a porous material.

[0036] 〈Other configurations〉 The sodium ion battery of the present disclosure may include a battery case for housing each layer of the battery, and terminals connected to a current collector or the like. Further, the sodium ion battery of the present disclosure may include a restraining member for restraining each layer along the stacking direction in order to reduce the contact resistance. For these, those similar to the conventional ones may be used.

[0037] Examples of the shape of the sodium ion battery of the present disclosure include a coin type, a laminate type, a cylindrical type, and a prismatic type.

[0038] 《Method for manufacturing a sodium ion battery》 The method of the present disclosure for manufacturing a sodium ion battery includes forming a negative electrode active material layer, and the negative electrode active material layer contains the negative electrode composite material of the present disclosure.

[0039] The method of the present disclosure may include forming a negative electrode active material layer by a method including the following steps: providing a negative electrode composite material slurry containing the negative electrode composite material of the present disclosure and a dispersion medium, and applying the negative electrode composite material slurry to a substrate and drying and removing the dispersion medium.

[0040] Regarding the negative electrode composite material of the present disclosure, reference may be made to the above description regarding the negative electrode composite material of the present disclosure.

[0041] The dispersion medium is not particularly limited, and examples include alcohols, glycols, cellosolves, amines, ketones, carboxylic acid amides, phosphoric acid amides, sulfoxides, carboxylic acid esters, phosphoric acid esters, ethers, nitriles, etc. Specifically, ethanol, 2-propanol, methyl ethyl ketone, and N-2-methylpyrrolidone are exemplified.

[0042] The substrate is not particularly limited, and may be, for example, a negative electrode current collector.

[0043] The drying temperature, drying time, etc. can be appropriately designed according to the boiling point and usage amount of the dispersion medium, etc.

Examples

[0044] 《Example 1》 〈Manufacture of Evaluation Cell〉 (Preparation of Negative Electrode Composite Material) Hard carbon (HC) as a negative electrode active material and zirconium oxide (ZrO 2 ) were mixed in a mass ratio of 0.4 9 :0.0 1 A mixture was weighed so as to have a mass ratio of 95:5 (mass ratio) with polyvinylidene fluoride (PVdF) as a binder, dispersed in N-methyl-2-pyrrolidone (NMP), and stirred at 2000 rpm for 10 minutes. Thereby, a slurry-like negative electrode composite material (negative electrode composite material slurry) was obtained.

[0045] (Formation of the negative electrode active material layer) The obtained negative electrode composite slurry was coated on an aluminum (Al) current collector foil using a 75-μm bar coater. The obtained coated film was dried, punched into a φ16 mm disc, and then formed by a press machine. Thereby, a negative electrode active material layer was formed on the Al current collector foil.

[0046] (Cell fabrication) A laminate of an Al current collector foil and a negative electrode active material layer was used as the working electrode, metallic sodium (Na) was used as the counter electrode, a material composed of three layers of 25-μm polypropylene / polyethylene / polypropylene (PP / PE / PP) was used as the separator, and 1 M NaPF 6 EC:DMC = 1:1 (volume ratio) was used to fabricate a 2032-type coin cell.

[0047] 《Evaluation》 〈Evaluation of charge capacity and discharge capacity〉 Under an environment of 25 °C, a charge-discharge test was carried out at a voltage range of 0.01 - 1.5 V and a current value of 0.1 C, and the Na insertion capacity (charge capacity) and Na desorption capacity (discharge capacity) of the coin cell were evaluated.

[0048] 《Example 2~ 4 and Comparative Example 1~ 4 》 Cells were fabricated and evaluated in the same manner as in Example 1, except that the type of metal oxide (MO) and 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.

[0049] 《Results》 The charge capacity, discharge capacity, and charge-discharge efficiency (percentage of discharge capacity / charge capacity) of each example are shown in Table 1.

[0050]

Table 1

[0051] As shown in Table 1, in the case where the current value is 0.1C, the ratio of the mass of zirconium oxide to the total mass of hard carbon and zirconium oxide is 10% by mass and 20% by mass in the examples 3 and 4 in the battery of acid the battery of Comparative Example 1 without addition of zirconium oxide also also had a larger discharge capacity Also, in the battery of Example 3, the charge-discharge efficiency was higher than that of the battery of Comparative Example 1.

[0052] On the other hand, in the case where the current value is 0.3C, the ratio of the mass of zirconium oxide to the total mass of hard carbon and zirconium oxide is 2% by mass to 20% by mass in the examples 1~4 in the battery of 1 the battery had a larger charge-discharge capacity and a higher charge-discharge efficiency than the battery of Comparative Example

[0053] Also, when the ratio of the mass of the metal oxide to the total mass of hard carbon and the metal oxide is 10% by mass, in the examples where zirconium oxide is used as the metal oxide regardless of the magnitude of the current value 3 in the battery of 2~4 the battery had a higher charge-discharge efficiency than the battery of Comparative Example using titanium oxide

Description of Signs

[0054] 1 Sodium ion battery 10 Negative electrode current collector 20 Negative electrode active material layer 30 Separator 40 Positive electrode active material layer 50 Positive electrode current collector

Claims

1. A negative electrode composite material having a negative electrode active material and zirconium oxide, wherein the negative electrode active material contains 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% by mass or more and 20% by mass or less. A negative electrode composite material for a sodium ion battery.

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

3. A method for manufacturing a sodium ion battery, including forming a negative electrode active material layer, and the negative electrode active material layer contains the negative electrode composite material according to Claim 1. A method for manufacturing a sodium ion battery.

4. The method according to Claim 3, including forming the negative electrode active material layer by a method including the following steps: providing a negative electrode composite material slurry containing the negative electrode composite material according to Claim 1 and a dispersion medium, and coating the negative electrode composite material slurry on a substrate and drying and removing the dispersion medium.

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