KR102289711B1 - electrolyte for sodium secondary battery and sodium secondary battery using the same - Google Patents

Abstract

The present invention relates to a cathode electrolyte for a sodium secondary battery comprising a sodium salt and an ionic liquid, and a secondary battery employing the electrolyte of the present invention can be driven at a low temperature with high efficiency and has excellent lifespan characteristics.

Description

Sodium secondary battery positive electrolyte and sodium secondary battery containing the same {electrolyte for sodium secondary battery and sodium secondary battery using the same}

The present invention relates to a sodium secondary battery cathode electrolyte and a sodium secondary battery containing the same, and more particularly, to a sodium secondary battery cathode electrolyte comprising a sodium salt and an ionic liquid, and a sodium secondary battery containing the same.

As the use of renewable energy is rapidly increasing, the need for an energy storage device using a battery is rapidly increasing. Among these batteries, a lead battery, a nickel/hydrogen battery, a vanadium battery, and a lithium battery may be used.

However, lead batteries and nickel/hydrogen batteries have very small energy densities, so there is a problem that requires a lot of space to store the same amount of energy. There is a problem in that the performance deteriorates due to the small amount of material moving between the anode and the anode through the membrane separating the cathode and the anode, so it cannot be commercialized on a large scale.

On the other hand, in the case of a lithium battery having very excellent energy density and output characteristics, it is technically very advantageous, but due to the resource scarcity of the lithium material, it has a problem that it is not economical to be used as a secondary battery for large-scale power storage.

Therefore, in order to solve this problem, there have been many attempts to use the resource-rich sodium on the earth as a material for secondary batteries. Among them, as in US Patent Publication No. 20030054255, a sodium-sulfur battery in which beta-alumina having selective conductivity for sodium ions is used, sodium is supported on the negative electrode, and sulfur is supported on the positive electrode is currently used as a large-scale power storage device. .

However, conventional sodium-based secondary batteries such as sodium-sulfur batteries or sodium-nickel chloride batteries, in consideration of conductivity and the melting point of the battery components, must operate at least 250°C or higher, such as sodium-nickel chloride batteries, The sodium-sulfur battery has a disadvantage of having an operating temperature of at least 300° C. or higher. Due to these problems, there are many disadvantages in terms of economic feasibility in terms of manufacturing or operation in order to maintain temperature, maintain airtightness, and reinforce safety aspects.

Currently, room temperature-type sodium-based batteries are being developed to solve the above problems, but their output is very low, so their competitiveness is very low compared to nickel-hydrogen batteries or lithium batteries. is being requested

US Patent Publication No. 20030054255

The present invention provides a cathode electrolyte for a sodium secondary battery having a high ionic conductivity and a low melting point.

In addition, the present invention provides a sodium secondary battery containing the sodium secondary battery positive electrolyte of the present invention, which has high stability and high output efficiency of the battery and can operate at a low temperature.

The present invention provides a sodium secondary battery cathode electrolyte comprising a sodium salt and an ionic liquid represented by the following formula (1).

[Formula 1]

[In Formula 1,

R ¹ is hydrogen, (C1-C10)alkyl or (C1-C10)haloalkyl;

R ² is hydrogen or (C1-C10)alkyl;

는 단일 또는 이중결합을 나타내며;remind

represents a single or double bond;

X ^- is (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , BF ₄ ^- , PF ₆ ^- , AlCl ₄ ^- , halogen ^- , CH ₃ CO ₂ ^- , CF ₃ CO ₂ ^- , CH ₃ SO ₄ ^- , CF ₃ SO ₃ ^- , (CF ₃ SO ₂ )N ^- , NO ₃ ^- , SbF ₆ ^- , MePhSO ₃ ^- , (CF ₃ SO ₂ ) ₃ C ^- or (R" ₂ PO ₂ ^- , wherein R" is C1-C5 alkyl or C1-C5 alkoxy.);

A is CR ¹¹ R ¹² or NR ¹³ , R ¹¹ and R ¹² are independently of each other hydrogen, (C1-C10)alkyl or (C1-C10)haloalkyl, and R ¹³ is hydrogen or (C1-C10)alkyl .]

In Formula 1 of the present invention, X ⁻ may be the same anion as the anion of the sodium salt, and preferably, R ¹ and R ² in Formula 1 may be each independently hydrogen or (C1-C10)alkyl.

The ionic liquid of Formula 1 according to an embodiment of the present invention may be preferably represented by Formula 2 or Formula 3 below.

[Formula 2]

[Formula 3]

[In Formula 2 or 3,

R ¹ , R ² and R ¹³ are each independently hydrogen or (C1-C10)alkyl;

X ^- is (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , BF ₄ ^- , PF ₆ ^- , AlCl ₄ ^- , halogen ^- , CH ₃ CO ₂ ^- , CF ₃ CO ₂ ^- , CH ₃ SO ₄ ^- , CF ₃ SO ₃ ^- , (CF ₃ SO ₂ )N ^- , NO ₃ ^- or SbF ₆ ^- is.]

The sodium salt according to an embodiment of the present invention is NaBF ₄ , NaI, NaCl, NaF, NaBr, Na(CF ₃ SO ₂ ) ₂ N, (FSO ₂ ) ₂ NNa, NaPF ₆ , NaAlCl ₄ , CH ₃ CO ₂ Na, CF ₃ CO ₂ Na, CH ₃ SO ₄ Na, CF ₃ SO ₃ Na, (CF ₃ SO ₂ )N Na, NaNO ₃ , NaSbF ₆ or a mixture thereof.

The sodium secondary battery cathode electrolyte according to an embodiment of the present invention may have a melting point of 200° C. or less, and a viscosity of 0.1 to 10000 cps.

The sodium secondary battery cathode electrolyte according to an embodiment of the present invention may further include a dissociation inducing agent, and a preferred dissociation inducing agent may be a crown ether, a Lewis acid, or a mixture thereof.

In addition, the present invention provides a sodium secondary battery comprising the sodium secondary battery positive electrolyte of the present invention, the sodium secondary battery of the present invention in detail a negative electrode containing sodium; anode containing a transition metal; and a sodium ion conductive solid electrolyte provided between the negative electrode and the positive electrode, wherein the positive electrode is impregnated with the sodium secondary battery positive electrolyte of the present invention.

The sodium secondary battery positive electrolyte of the present invention lowers the melting point without lowering the charge conductivity compared to the existing sodium secondary battery electrolyte, including sodium salt and ionic liquid. drive is possible

In addition, the sodium secondary battery positive electrolyte of the present invention includes a sodium salt and an ionic liquid, so that the sodium secondary battery employing the same has improved stability and cycle characteristics, thereby remarkably improving the stability and lifespan characteristics of the battery.

1 is a conceptual diagram schematically showing the structure of a sodium secondary battery according to an embodiment of the present invention.

The present invention is to provide a sodium secondary battery cathode electrolyte that can be driven at a low temperature by controlling the melting point while improving ionic conductivity without decreasing ionic conductivity. ionic liquids indicated.

[Formula 1]

[In Formula 1,

R ¹ is hydrogen, (C1-C10)alkyl or (C1-C10)haloalkyl;

R ² is hydrogen or (C1-C10)alkyl;

는 단일 또는 이중결합을 나타내며;remind

represents a single or double bond;

X ^- is (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , BF ₄ ^- , PF ₆ ^- , AlCl ₄ ^- , halogen ^- , CH ₃ CO ₂ ^- , CF ₃ CO ₂ ^- , CH ₃ SO ₄ ^- , CF ₃ SO ₃ ^- , (CF ₃ SO ₂ )N ^- , NO ₃ ^- , SbF ₆ ^- , MePhSO ₃ ^- , (CF ₃ SO ₂ ) ₃ C ^- or (R" ₂ PO ₂ ^- , wherein R" is C1-C5 alkyl or C1-C5 alkoxy.);

A is CR ¹¹ R ¹² or NR ¹³ , R ¹¹ and R ¹² are independently of each other hydrogen, (C1-C10)alkyl or (C1-C10)haloalkyl, and R ¹³ is hydrogen or (C1-C10)alkyl .]

The sodium secondary battery cathode electrolyte of the present invention includes a sodium salt and the ionic liquid represented by Formula 1, thereby lowering the melting point of the electrolyte and controlling the viscosity without lowering the ionic conductivity or improving the ionic conductivity at the same time. The adopted sodium secondary battery has the advantage of having high output efficiency and being able to operate at a low temperature.

In terms of high ionic conductivity and low melting point, preferably in Formula 1, X ⁻ may be the same anion as the anion of the sodium salt.

That is, by making the anion of the sodium salt equal to the anion of the ionic liquid represented by Chemical Formula 1 of the present invention, X ⁻ prevents an anion exchange reaction from occurring, thereby improving ionic conductivity.

Preferably, in Formula 1 according to an embodiment of the present invention, R ¹ and R ² may be hydrogen or (C1-C10)alkyl.

Preferably, Chemical Formula 1 according to an embodiment of the present invention may be represented by Chemical Formula 2 or Chemical Formula 3 below.

[Formula 2]

[Formula 3]

[In Formula 2 or 3,

R ¹ , R ² and R ¹³ are each independently hydrogen or (C1-C10)alkyl;

X ^- is (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , BF ₄ ^- , PF ₆ ^- , AlCl ₄ ^- , halogen ^- , CH ₃ CO ₂ ^- , CF ₃ CO ₂ ^- , CH ₃ SO ₄ ^- , CF ₃ SO ₃ ^- , (CF ₃ SO ₂ )N ^- , NO ₃ ^- or SbF ₆ ^- is.]

The ionic liquid of Formula 1 according to an embodiment of the present invention may be specifically selected from the following compounds, but is not limited thereto.

The substituents including "alkyl" and other "alkyl" moieties described in the present invention include both straight-chain or pulverized forms.

Haloalkyl as used in the present invention means that one or more halogens different or identical to alkyl are substituted.

The sodium salt according to an embodiment of the present invention is NaBF ₄ , NaI, NaCl, NaF, NaBr, Na(CF ₃ SO ₂ ) ₂ N, (FSO ₂ ) ₂ NNa, NaPF ₆ , NaAlCl ₄ , CH ₃ CO ₂ Na, CF ₃ CO ₂ Na, CH ₃ SO ₄ Na, CF ₃ SO ₃ Na, (CF ₃ SO ₂ )N Na, NaNO ₃ , It _{may be NaSbF 6} and a mixture thereof, preferably NaBF ₄ , NaPF _{6 ,} or a mixture thereof.

Preferably, in terms of high ionic conductivity, low melting point and thermal stability, the combination _{of NaBF 4 , NaPF 6} or a sodium salt of a mixture thereof and a combination of Chemical Formula 2 is preferable.

The electrolyte according to an embodiment of the present invention may have a melting point of 200° C. or less, and preferably, a melting point of 100° C. or less.

The electrolyte according to an embodiment of the present invention may have a viscosity of 0.1 to 10000 cps, preferably a viscosity of 0.1 to 50 cps, and preferably a melting point of 100° C. or less and a viscosity of 0.1 to 50 cps. can

The electrolyte according to an embodiment of the present invention may further include a dissociation inducing agent, and the dissociation inducing agent according to an embodiment of the present invention may be a crown ether, a Lewis acid, or a mixture thereof.

Specifically, as a dissociation inducing agent according to an embodiment of the present invention, the crown ether is a crown-shaped complex made of polyether, and the oxyethylene group _{is connected in the form of -(OCH 2} CH ₂ )n- to form a large ring-shaped polyethylene ether skeleton. means a compound having

Specifically, it may be one or a mixture of two or more selected from the structural formulas shown below.

,

,

,

,

,

,

,

,

In such a crown ether, the oxygen element (O) of the crown ether ^{coordinates the sodium ion (Na +} ) of the molten salt electrolyte to directly dissociate the molten salt electrolyte, thereby improving the ionization degree of the molten salt electrolyte.

In addition, the Lewis acid included as the dissociation inducing agent is an electron pair acceptor according to the Lewis definition, specifically, aluminum chloride (AlCl ₃ ), aluminum iodide (AlI ₃ ), zinc chloride (ZnCl ₂ ), iodide, which are compounds containing a lone pair. It may be one or more of zinc (ZnI ₂ ), boron chloride (BCl ₃ ), boron fluoride (BF ₃ ), and tris(pentafluorophenyl)borane (TPFPB; Tris(pentafluorophenyl)borane). The dissociation inducing agent composed of such a Lewis acid attracts anions of the molten salt electrolyte to dissociate the molten salt electrolyte, ^{thereby increasing the amount of free-Na +} ions in the molten salt electrolyte, thereby improving the ionization degree of the molten salt electrolyte. there is.

The sodium secondary battery cathode electrolyte according to an embodiment of the present invention may contain a mixture of the crown ether and the Lewis acid as a dissociation inducing agent. That is, as described above, the crown ether coordinates the cation to dissociate the alkali metal halide of the positive electrode, and the Lewis acid can dissociate the alkali metal halide of the positive electrode by attracting the anion. Therefore, when the mixture of the crown ether and the Lewis acid is contained as a dissociation inducer, the ionization degree of the molten salt electrolyte can be significantly improved by simultaneously inducing dissociation of the cation and anion of the alkali metal halide.

In this case, the dissociation inducing agent included in the molten salt electrolyte employed in the sodium secondary battery according to the present invention may contain a dissociation inducing agent having a molar concentration of 10 μM to 1000 mM. Here, when the content of the dissociation inducing agent in the molten salt electrolyte is less than 10 μM, the effect of improving the conductivity of ions in the molten salt electrolyte by the dissociation inducing agent may be insignificant, and the conductivity of ions participating in the electrochemical reaction of the battery, such as sodium ions, is This may decrease the efficiency of the battery, and the capacity of the battery itself may be too low. In addition, when the content of the dissociation inducer in the molten salt electrolyte exceeds 1000 mM molar concentration, the ion concentration in the molten salt electrolyte is excessively increased, which may cause a risk of overheating during discharging of the battery, and the number of ions combined with the dissociation inducing agent is relatively If it becomes too large, the overall ionic conductivity may decrease due to the lack of free-ions in the electrolyte. Therefore, when the content of the dissociation inducer in the molten salt electrolyte is in a molar concentration of 10 mM to 1000 mM, it is possible to obtain an optimal result in which overheating of the battery does not occur while the conductivity of ions in the molten salt electrolyte is improved.

And when a mixture of a crown ether and a Lewis acid as a dissociation inducer is contained in the molten salt electrolyte employed in the sodium secondary battery according to the present invention, the mixture may be mixed in a molar ratio of crown ether: Lewis acid of 1: 0.1 to 10. there is. The molar ratio of the crown ether to the Lewis acid affects the degree of dissociation of the molten salt electrolyte. If the molar ratio of the Lewis acid to 1 mol of the crown ether is less than 0.1 mol, the Na ⁺ ) increase is relatively insignificant, and if the molar ratio of Lewis acid to 1 mol of crown ether exceeds 10 mol, the increase in free-anion due to dissociation of the molten salt electrolyte is relatively insignificant and the effect is reduced. can do.

Also, the present invention

a negative electrode containing sodium;

anode containing a transition metal; and

It includes a sodium ion conductive solid electrolyte provided between the negative electrode and the positive electrode,

It provides a sodium secondary battery in which the positive electrode is impregnated in the sodium secondary battery positive electrolyte according to the present invention.

The sodium secondary battery of the present invention adopts the sodium secondary battery cathode electrolyte of the present invention containing sodium salt and an ionic liquid, so that the ionic conductivity is high, the melting point and the viscosity are controlled, and the output efficiency is high compared to the conventional sodium secondary battery It is stable and can be operated at lower temperatures.

The sodium secondary battery according to an embodiment of the present invention may have a structure of a conventional sodium-sulfur battery or sodium-nickel hydroxide battery having molten sodium as an anode.

The negative electrode according to an embodiment of the sodium secondary battery of the present invention may be any material commonly used as the negative electrode, but may include metal sodium or a sodium alloy. Specifically, the negative electrode of the sodium secondary battery may be a sodium halide or a halide of a sodium alloy material.

The positive electrode according to an embodiment of the sodium secondary battery of the present invention may include a foam, a foil, a mesh, a felt, or a porous film. As a practical example, the positive electrode may comprise a foam, foil, mesh, felt or porous foil of nickel or a nickel-containing alloy.

Specifically, in the sodium secondary battery according to an embodiment of the present invention, the positive electrode may contain a transition metal and an alkali metal halide. In this case, the transition metal may include copper, silver, gold, nickel, palladium, platinum, cobalt, rhodium, iridium, iron, manganese, chromium, vanadium, molybdenum, etc., preferably nickel (Ni), copper (Cu) ) and iron (Fe) may be selected from one metal. And, as the alkali metal halide, it is possible to employ sodium halide (NaX; X=halide), in this case, as the halide (X), fluorine (F), chlorine (Cl), bromine (Br), iodine (I), All of astatine (At) is possible, but among them, it may be preferable to employ chlorine (Cl), bromine (Br) and iodine (I).

In one embodiment according to the sodium secondary battery of the present invention, the positive electrode (based on the discharge state) is pure nickel; alloys containing nickel; a laminate in which pure nickel or a nickel alloy and a conductive material are laminated; Alternatively, metal particles containing nickel may be supported on a porous conductor.

In one embodiment according to the sodium secondary battery of the present invention, when the positive electrode is an alloy containing nickel, the alloy containing nickel may be at least one alloy selected from a nickel-copper alloy and a nickel-iron alloy, and substantially one For example, it may be an alloy containing 0.01% to 99.9% by weight of nickel.

In one embodiment according to the sodium secondary battery of the present invention, when the positive electrode is a laminate, pure nickel or nickel alloy is laminated in contact with the surface of the porous conductor in the form of foam, foil, mesh, felt, porous foil or rod, It may be embedded within the porous conductor.

In one embodiment according to the sodium secondary battery of the present invention, the positive electrode may be one in which a metal particle containing nickel is supported or coated on a porous conductor.

The porous conductor has excellent conductivity and can be used as long as it is chemically stable during charging and discharging of the battery. As a practical example, the porous conductor may be a conductive carbon including graphite, graphene, or carbon nanotubes, and may be formed of a foam, a film, a mesh, a felt, or a porous (perforated) foil. may be in the form

In an embodiment according to the sodium secondary battery of the present invention, the solid electrolyte having sodium ion conductivity may include a solid electrolyte commonly used in the battery field for selective conduction of sodium ions, and physically separate the positive and negative electrodes Any material having selective conductivity with respect to sodium ions may be sufficient, and any solid electrolyte commonly used in the battery field for selective conduction of sodium ions is sufficient. As a non-limiting example, the solid electrolyte of the present invention may be a sodium super ionic conductor (NaSICON), β-alumina or β″-alumina. In addition, as a non-limiting example, sodium superion conductor (NASICON) is a Na-Zr-Si-O-based composite oxide, Na-Zr-Si-PO-based composite oxide, Y-doped Na-Zr-Si-PO may include a composite oxide based on Fe-doped Na-Zr-Si-PO, or a mixture thereof, specifically, Na3Zr2Si2PO12, Na ₁ +xSixZr ₂ P ₃ -xO ₁₂ (1.6<x<2.4 real number), Y or Fe doped Na ₃ Zr ₂ Si ₂ PO ₁₂ , Y or Fe doped Na ₁ +xSixZr ₂ P ₃ -xO ₁₂ (real numbers 1.6<x<2.4) or mixtures thereof there is.

In the sodium secondary battery according to an embodiment of the present invention, based on the shape of the solid electrolyte that separates the negative electrode and the positive electrode to partition the negative electrode space and the positive electrode space, the sodium secondary battery is a flat plate containing a flat solid electrolyte It may have a battery-type battery structure or a tubular battery structure including a tube-shaped solid electrolyte with one end sealed.

Hereinafter, a sodium secondary battery according to the present invention will be described in detail with reference to the accompanying drawings. The drawings introduced below are provided as examples in order to sufficiently convey the spirit of the present invention to those skilled in the art. Accordingly, the present invention is not limited to the drawings presented below and may be embodied in other forms, and the drawings presented below may be exaggerated to clarify the spirit of the present invention. Also, like reference numerals refer to like elements throughout.

At this time, if there is no other definition in the technical terms and scientific terms used, it has the meaning commonly understood by those of ordinary skill in the technical field to which this invention belongs, and the gist of the present invention in the following description and accompanying drawings Descriptions of known functions and configurations that may be unnecessarily obscure will be omitted.

Example 1 Preparation of 2-methylpyrrolinium tetrafluoromethylboron

After 10 g of 2-methyl-1-pyrroline was added to a round bottom flask, the temperature was lowered to 0° C., and 16 ml of a 48% aqueous fluoroboric acid solution was slowly added thereto, followed by stirring for 2 hours. Water was removed through distillation under reduced pressure and Dean-Stark distillation using benzene, and 20 g of 2-methyl-1-pyrroline tetrafluoroborate from which the solvent was removed through distillation under reduced pressure was prepared. The melting point of the product is 17.1 °C.

Example 2 Preparation of 1-methylpyrazole tetrafluoroborate

After 10 g of 1-methylpyrazole was added to a round-bottom flask, the temperature was lowered to 0° C., and 16 ml of a 48% aqueous fluoroboric acid solution was slowly added thereto, followed by stirring for 2 hours. Water was removed through distillation under reduced pressure and Dean-Stark distillation using benzene, and 20 g of 1-methylpyrazole tetrafluoroborate from which the solvent was removed through distillation under reduced pressure was prepared. The melting point of the product is -5.9 °C.

Example 3 Measurement of ionic conductivity of the ionic liquids of Examples 1 and 2 of the present invention

The ionic conductivity of the positive electrolyte obtained by adding 30 wt% _{of sodium tetrafluoroborate (NaBF 4} ) to the ionic liquid of Preparation 1 was measured in a glove box using M300 (4-electrode sensor) manufactured by METTLER TOLEDO. At this time, the moisture and oxygen concentrations were 0.1 ppm or less, respectively, and the ionic conductivity was 8.93 mS/cm at 95.63 °C.

1: Sodium secondary battery
10: cathode
30: positive electrode
35: positive electrolyte
50: solid electrolyte

Claims (10)

It contains a sodium salt and an ionic liquid represented by the following formula (2),
^{X −} in Formula 2 is the same anion as the anion of the sodium salt, a cathode electrolyte for a sodium secondary battery.
[Formula 2]

[In Formula 2,
R ¹ and R ² are each independently hydrogen or (C1-C10)alkyl;
X ^- is (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , BF ₄ ^- , PF ₆ ^- , AlCl ₄ ^- , halogen ^- , CH ₃ CO ₂ ^- , CF ₃ CO ₂ ^- , CH ₃ SO ₄ ^- , CF ₃ SO ₃ ^- , (CF ₃ SO ₂ )N ^- , NO ₃ ^- or SbF ₆ ^- is.] delete delete delete The method of claim 1,
The sodium salt is NaBF ₄ , NaI, NaCl, NaF, NaBr, Na(CF ₃ SO ₂ ) ₂ N, (FSO ₂ ) ₂ NNa, NaPF ₆ , NaAlCl ₄ , CH ₃ CO ₂ Na, CF ₃ CO ₂ Na, CH ₃ SO ₄ Na, CF ₃ SO ₃ Na, (CF ₃ SO ₂ )N Na, NaNO ₃ , NaSbF ₆ and a mixture thereof, a sodium secondary battery positive electrolyte. The method of claim 1,
The cathode electrolyte is a sodium secondary battery cathode electrolyte having a melting point of 200° C. or less. According to claim 1,
The positive electrolyte is a sodium secondary battery positive electrolyte having a viscosity of 0.1 to 10000 cps. According to claim 1,
The cathode electrolyte is a sodium secondary battery cathode electrolyte further comprising a dissociation inducing agent. 9. The method of claim 8,
The dissociation inducing agent is a sodium secondary battery cathode electrolyte which is a crown ether, a Lewis acid, or a mixture thereof. a negative electrode containing sodium;
anode containing a transition metal; and
It includes a sodium ion conductive solid electrolyte provided between the negative electrode and the positive electrode,
A sodium secondary battery in which the positive electrode is impregnated with the electrolyte of any one of claims 1 and 5 to 9.

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