KR102363506B1 - Sodium Secondary Battery - Google Patents

Abstract

The present invention relates to a sodium secondary battery that can be operated at a low temperature, including a molten salt electrolyte with controlled melting point and viscosity, specifically, a negative electrode containing sodium, a positive electrode containing a transition metal, and between the negative electrode and the positive electrode It relates to a sodium secondary battery comprising a sodium ion conductive solid electrolyte provided, wherein the positive electrode is impregnated in a molten salt electrolyte containing a sulfonylimide-based compound.

Description

Sodium Secondary Battery

The present invention relates to a sodium secondary battery, and more particularly, to a sodium secondary battery comprising a molten salt electrolyte containing a sulfonylimide-based compound.

As the use of renewable energy rapidly increases, 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 energy of the same capacity. In addition, in the case of vanadium batteries, environmental pollutants due to the use of a solution containing heavy metals and a small amount of material between the negative electrode and the positive electrode move through the membrane separating the negative electrode and the positive electrode, thereby reducing performance. It cannot be commercialized. 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.

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, must operate at least 250℃ or higher in the case of sodium-nickel chloride batteries, in consideration of conductivity and the melting point of the battery components, 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. In order to solve the above problems, a room temperature type sodium-based battery has been developed, but its output is very low, so its competitiveness is very low compared to a nickel-hydrogen battery or a lithium battery.

US Patent Publication No. 20030054255

It is an object of the present invention to provide a sodium secondary battery capable of operating at a low temperature while suppressing unnecessary side reactions by employing a molten salt electrolyte containing a sulfonylimide-based compound, and significantly improving the output efficiency of the battery. At the same time, it is intended to provide a sodium secondary battery having improved battery life and improved battery stability by stably maintaining charge/discharging cycle characteristics for a long period of time to prevent deterioration.

A sodium secondary battery according to the present invention includes a negative electrode containing sodium, a positive electrode containing a transition metal, and a sodium ion conductive solid electrolyte provided between the negative electrode and the positive electrode, wherein the positive electrode contains a sulfonylimide-based compound Impregnated in molten salt electrolyte.

In the sodium secondary battery according to an embodiment of the present invention, the transition metal may include one or a mixture of two or more selected from the group consisting of Mn, Fe, Co, Cu and Ni.

In the sodium secondary battery according to an embodiment of the present invention, the sulfonylimide-based compound is an alkali metal-bisfluorosulfonylimide (MFSI), an alkali metal-bistrifluoromethanesulfonylimide (MTFSI) or a mixture thereof.

In the sodium secondary battery according to an embodiment of the present invention, the sulfonylimide-based compound is sodium bisfluorosulfonylimide (NaFSI), sodium bistrifluoromethanesulfonylimide (NaTFSI), or a mixture thereof. can be

In the sodium secondary battery according to an embodiment of the present invention, the sodium secondary battery may be charged according to at least one selected from Schemes 1 and 2 below.

Scheme 1

(anode)Me + (electrolyte)nMFSI -> nM ⁺ + Me(FSI) _n

Scheme 2

(Anode) Me + (electrolyte) nMTFSI -> nM ⁺ + Me(TFSI) _n

In the sodium secondary battery according to an embodiment of the present invention, the sodium secondary battery may be discharged according to at least one selected from the following Schemes 3 and 4.

Scheme 3

nM ⁺ + Me(FSI) _n -> Me + nMFSI

Scheme 4

nM ⁺ + Me(TFSI) _n -> Me + nMTFSI

In Schemes 1 to 4, Me may be an element selected from transition metals, and M may be an element selected from alkali metals. In addition, n is a natural number of 1 to 4, and in detail, may be a natural number corresponding to the positive valence of the transition metal (Me).

In the sodium secondary battery according to an embodiment of the present invention, the sodium secondary battery may be operated at 100 to 300 ℃.

As the sodium secondary battery according to the present invention employs a molten salt electrolyte containing a sulfonylimide-based compound, it is possible to provide a sodium secondary battery capable of operating at a low temperature.

In addition, the sodium secondary battery according to the present invention has the effect of suppressing unnecessary side reactions or gas generation during the charging and discharging reaction, so that the output efficiency of the battery is remarkably improved.

In addition, according to the present invention, a sodium secondary battery employing a molten salt electrolyte with controlled melting point and viscosity maintains stable charge/discharge cycle characteristics for a long period of time to prevent deterioration, thereby having improved battery life and improved battery stability. It works.

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

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 so that the spirit of the present invention can be sufficiently conveyed 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 art 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.

In general, sodium aluminum chloride (NaAlCl ₄ ) has been employed as a molten salt electrolyte of a secondary battery such as a zebra (ZEBRA) battery. Such sodium aluminum chloride (NaAlCl ₄ ) molten salt has been known to be advantageous in terms of stability and ionic conductivity of a sodium secondary battery.

However, in that the sodium aluminum chloride (NaAlCl ₄ ) molten salt has a melting point at 158 to 200° C. depending on the purity, such a sodium aluminum chloride (NaAlCl ₄ ) The operating temperature of the secondary battery in which the molten salt electrolyte is employed is very high. There was a high limit.

Accordingly, an object of the present invention is to provide a secondary battery capable of operating at a relatively low temperature by improving the above limitation and lowering the melting point of the molten salt electrolyte while having excellent ionic conductivity.

As shown in FIG. 1, the sodium secondary battery according to the present invention includes a sodium-containing negative electrode, a transition metal-containing positive electrode, and a sodium ion conductive solid electrolyte provided between the negative electrode and the positive electrode, wherein the positive electrode is It is impregnated with a molten salt electrolyte containing a sulfonylimide-based compound.

In the sodium secondary battery according to an embodiment of the present invention, the negative electrode may include metal sodium or a sodium alloy. As a non-limiting example, the sodium alloy may be sodium and cesium, sodium and rubidium, or a mixture thereof. The negative electrode active material may be in a liquid phase including a solid phase or a molten phase at the operating temperature of the battery. In this case, in order to realize the battery capacity of 50 Wh/kg or more, the anode active material may be molten sodium (molten Na).

And, in the sodium secondary battery according to an embodiment of the present invention, the positive electrode of the sodium secondary battery may contain a transition metal. At this time, the transition metal may include copper, silver, gold, nickel, palladium, platinum, cobalt, rhodium, iridium, iron, manganese, chromium, vanadium, molybdenum, etc., preferably molybdenum (Mo), cobalt (Co) ), nickel (Ni), copper (Cu), and iron (Fe) may be selected from one metal.

And, in the sodium secondary battery according to an embodiment of the present invention, the positive electrode may be configured to be impregnated in a molten salt electrolyte.

In this case, the electrolyte of the sodium secondary battery according to the present invention may be a molten salt electrolyte, and specifically, the molten salt electrolyte of the sodium secondary battery according to an embodiment of the present invention may contain a sulfonylimide-based compound.

A sulfonylimide-based compound is an alkali which is a molten salt in which bisfluorosulfonylimide (FSI- ⁾ or bistrifluoromethanesulfonylimide (TFSI- ⁾ is an anion and an alkali metal (M) is a cation. metal-bisfluorosulfonylimide (MFSI) or alkali metal-bistrifluoromethanesulfonylimide (MTFSI), mixtures thereof are also possible.

Here, the term “imide” refers to an amide containing an imino group. In a strict sense, it is not appropriate to refer to TFSI without an imino group as "imide". However, since the term is currently widely used, it will be used as a common name in the specification of the present invention.

Bisfluorosulfonylimide (FSI- ⁾ or bistrifluoromethanesulfonylimide (TFSI-) constituting the anion of the sulfonylimide ^- based compound constituting the electrolyte of the sodium secondary battery according to the present invention is reactive This is excellent, and oxidation/reduction reactions with transition metals and alkali metals can occur very effectively. For this reason, alkali metal-bisfluorosulfonylimide (MFSI) or alkali metal-bistrifluoromethanesulfonylimide (MTFSI) electrolytes composed of these as anions and alkali metals as cations have a relatively low melting point. can

In addition, since the sodium secondary battery according to the present invention employs the electrolyte constituted as above as a molten salt electrolyte rather than an additive, a charge/discharge reaction of the battery can be expected by a direct reaction between the positive electrode and the molten salt electrolyte.

At this time, the sodium secondary battery of the present invention may be charged according to at least one selected from Schemes 1 and 2 below.

Scheme 1

(anode)Me + (electrolyte)nMFSI -> nM ⁺ + Me(FSI) _n

Scheme 2

(Anode) Me + (electrolyte) nMTFSI -> nM ⁺ + Me(TFSI) _n

And, the sodium secondary battery of the present invention may be discharged according to at least one selected from Schemes 3 and 4 below.

Scheme 3

nM ⁺ + Me(FSI) _n -> Me + nMFSI

Scheme 4

nM ⁺ + Me(TFSI) _n -> Me + nMTFSI

Here, Me may be an element selected from transition metals, and M may be an element selected from alkali metals. In addition, n is a natural number of 1 to 4, and in detail, may be a natural number corresponding to the positive valence of the transition metal (Me).

At this time, since the present invention is a sodium secondary battery, it may be preferable in terms of ionic conductivity that the transition metal of the present invention be selected from sodium, and the transition metal ions (that is, sodium ions) generated according to the charging reaction of the battery are It may be an ion-conducting (transport) material that passes through the solid electrolyte in the battery and is directly transferred to the negative electrode. In addition, M(FSI) ₂ or M(TFSI) ₂ generated according to the charging reaction of the battery is not generated as a gas and is dissolved in the molten salt electrolyte as it is, so it does not act as a factor impeding the transport of transition metal ions, Accordingly, there may be an excellent advantage in terms of ionic conductivity of the molten salt electrolyte.

In addition, the molten salt electrolyte configured as described above is composed of the electrolyte or electrolyte of the secondary battery in which the molten salt itself is molten without a separate solvent, so unnecessary side reactions can be suppressed and the energy density of the battery. can increase Specifically, the sodium secondary battery employing the molten salt electrolyte of the present invention can prevent the risk of volatilization or flammability according to the composition of a separate solvent.

Therefore, by using a molten salt electrolyte as the electrolyte of the sodium secondary battery, it is possible to provide a high energy density compared to using a conventional electrolyte by dissolving it in a solvent, thereby minimizing the weight of the battery and reducing the size of the battery.

In the sodium secondary battery according to the present invention, the above-described molten salt electrolyte may be composed of a mixture of alkali metal-bisfluorosulfonylimide (MFSI) and alkali metal-bistrifluoromethanesulfonylimide (MTFSI). may be In this case, the mixture may be a eutectic salt having a lower melting point than a single salt (especially, MTFSI). In addition, the melting point of the mixture may vary depending on the mixing ratio of the mixed salts (ie, alkali metal-bisfluorosulfonylimide (MFSI) and alkali metal-bistrifluoromethanesulfonylimide (MTFSI)). .

And, when the molten salt electrolyte composed of the mixture is employed as described above, it is natural that the above-described Reaction Schemes 1 and 2 occur simultaneously during the charging reaction, and the above-described Reaction Schemes 3 and 4 simultaneously occur during the discharge reaction.

Specifically, the molten salt electrolyte composed of the mixture may consist of a molar ratio of alkali metal-bisfluorosulfonylimide (MFSI) to alkali metal-bistrifluoromethanesulfonylimide (MTFSI) of 1 to 0.05 to 0.4. there is. This is because the melting point of alkali metal-bisfluorosulfonylimide (MFSI) is generally lower than that of alkali metal-bistrifluoromethanesulfonylimide (MTFSI), so the melting point of alkali metal-bisfluorosulfonylimide (MFSI) is relatively low. To provide the most efficient content as an electrolyte for batteries by increasing the content of sulfonylimide (MFSI) and limiting the content of alkali metal-bistrifluoromethanesulfonylimide (MTFSI), which has a relatively high melting point, to within 50M% am.

More specifically, if the molar ratio of alkali metal-bistrifluoromethanesulfonylimide (MTFSI) to 1 mole of alkali metal-bisfluorosulfonylimide (MFSI) is 0.05 or less, alkali metal-bisfluoro Ineffective in lowering the melting point of alkali metal-bisfluoromethanesulfonylimide (MTFSI) by sulfonylimide (MFSI), compared to 1 mole of alkali metal-bisfluorosulfonylimide (MFSI) If the molar ratio of alkali metal-bistrifluoromethanesulfonylimide (MTFSI) is 0.5 or more, the melting point increases and alkali metal-bisfluorosulfonylimide (MFSI) may be decomposed.

The alkali metal of the sulfonylimide-based compound constituting the electrolyte of the sodium secondary battery according to the present invention may be selected from lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). However, it may be most preferable to select sodium in terms of battery efficiency of the sodium secondary battery.

That is, the sulfonylimide-based compound that is the above-mentioned molten salt electrolyte composed of the electrolyte of the sodium secondary battery according to the present invention is sodium bisfluorosulfonylimide (NaFSI), sodium bistrifluoromethanesulfonylimide ( NaTFSI) or a mixture thereof is most preferred, but not limited thereto.

The melting point of the sodium bisfluorosulfonylimide (NaFSI), sodium bistrifluoromethanesulfonylimide (NaTFSI) or a mixture thereof according to the present invention is lower than that of the conventional molten salt electrolyte, It is possible to overcome the disadvantage that the batteries are operated at a high temperature.

At this time, the melting point of sodium bisfluorosulfonylimide (NaFSI), sodium bistrifluoromethanesulfonylimide (NaTFSI) or a mixture thereof is about 80 to 200 °C, which is lower than that of the conventional electrolyte. It has the advantage of providing a sodium secondary battery that operates at a lower temperature. More specifically, it may be most preferable that the melting point of sodium bisfluorosulfonylimide (NaFSI), sodium bistrifluoromethanesulfonylimide (NaTFSI) or a mixture thereof is 100 to 175°C, but limited thereto is not doing

Accordingly, by having the molten salt electrolyte having a melting point of 200° C. or less of the molten salt electrolyte in the sodium secondary battery, low-temperature operation is possible, deterioration is prevented, and the lifespan of the battery is improved.

And, in the sodium secondary battery according to an embodiment of the present invention, the solid electrolyte is provided between the positive electrode and the negative electrode, and may be composed of a sodium ion conductive solid electrolyte. In this case, the sodium ion conductive solid electrolyte physically separates the positive electrode and the negative electrode and may be any material having selective conductivity with respect to sodium ions, 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, a sodium superionic conductor ( NASICON) is Na-Zr-Si-O-based composite oxide, Na-Zr-Si-PO-based composite oxide, Y-doped Na-Zr-Si-PO-based composite oxide, Fe-doped Na-Zr-Si -PO-based complex oxide or mixtures thereof may be included, and specifically, Na3Zr2Si2PO12, Na ₁ +xSixZr ₂ P ₃ -xO ₁₂ (real number of 1.6<x<2.4), 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 number of 1.6<x<2.4) or a mixture thereof.

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 comprising a flat solid electrolyte It may have a cell-type battery structure or a tubular cell structure including a tube-shaped solid electrolyte with one end sealed.

On the other hand, in the case of a sodium-nickel chloride battery, the conventional sodium-based secondary battery must be operated at at least 250°C in consideration of conductivity and the melting point of the battery components, and in the case of a sodium-sulfur battery, at least 300°C or more It has the disadvantage of having an operating temperature.

However, since the sodium secondary battery according to the present invention employs a molten salt electrolyte containing a sulfonylimide-based compound, the melting point of the electrolyte is controlled without causing a decrease in the ionic conductivity of the sodium secondary battery to operate the battery at a low temperature It may be possible to make Specifically, the operating temperature of the sodium secondary battery according to the present invention may be 300 ℃ or less. More specifically, the temperature may be 100°C or higher and 300°C or lower, and more preferably 100°C or higher and 200°C or lower.

Specifically, when the melting point of sodium bisfluorosulfonylimide (NaFSI), sodium bistrifluoromethanesulfonylimide (NaTFSI) or a mixture thereof is checked, it is shown in Table 1 below.

Hereinafter, specific embodiments according to the present invention will be described in detail.

Examples 1-4. Characteristic evaluation of molten salt electrolyte

The molten salt electrolyte of the present invention, NaFSI (Sodium(I) bis(fluorosulfonyl)imide 99.7%, solvionic), NaTFSI (97% Sodium trifluoromethanesulfonimide, Sigma-Aldrich), a mixture thereof, and the melting temperature (melting) of the molten salt of Comparative Example 1 point) was measured and shown in [Table 1] below.

The melting point of the molten salts is determined by putting a vial containing 1.5 g of the molten salt electrolyte contained in the molar ratio of Examples 1 to 4 of Table 1 below into a heating mantle filled with sand, and gradually increasing the temperature of the mantle so that the internal material is completely liquid. The temperature was measured by visually observing it.

Referring to Table 1, as in Examples 1 to 4, the molten salt electrolyte according to the present invention employs an electrolyte having a lower melting point than the conventional sodium molten salt electrolyte as in Comparative Example 1, so that when used in a secondary battery, low-temperature operation It is possible, and deterioration is prevented, so that the life of the battery is improved, and there are advantages of having high ionic conductivity and non-volatile and non-explosive characteristics at the same time.

In particular, the melting point of the molten salt electrolyte is lowered when NaFSI: NaTFSI of Examples 3 to 4 is mixed than when NaTFSI of Example 2 is used alone, so that the molten salt electrolyte of the NaFSI: NaTFSI mixture is It was found to have a significantly lower melting point than the melting point of the molten electrolyte of NaAlCl4 used in the prior art.

Therefore, when the molten salt electrolyte with a low melting point according to the present invention is used in a sodium secondary battery, compared to the case of using a conventional molten salt electrolyte, it is configured to operate at a lower temperature, thereby reducing manufacturing cost and securing stability. has a remarkable effect.

As described above, the present invention has been described with specific details and limited examples and drawings, but these are only provided to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments, and the present invention is not limited to the above embodiments. Various modifications and variations are possible from these descriptions by those of ordinary skill in the art.

Therefore, the spirit of the present invention should not be limited to the described embodiments, and not only the claims to be described later, but also all those with equivalent or equivalent modifications to the claims will be said to belong to the scope of the spirit of the present invention. .

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

Claims (8)

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 a molten salt electrolyte containing a sulfonylimide-based compound.
According to claim 1,
The transition metal is a sodium secondary battery comprising one or a mixture of two or more selected from the group consisting of Mn, Fe, Co, Cu and Ni.
According to claim 1,
The sulfonylimide-based compound is an alkali metal-bisfluorosulfonylimide (MFSI), an alkali metal-bistrifluoromethanesulfonylimide (MTFSI), or a mixture thereof.
(The above M is an element selected from alkali metals.)
4. The method of claim 3,
The mixture is an alkali metal-bisfluorosulfonylimide (MFSI) to an alkali metal-bistrifluoromethanesulfonylimide (MTFSI) molar ratio of 1 to 0.05 to 0.4 sodium secondary battery.
(The above M is an element selected from alkali metals.)
5. The method of claim 4,
The sulfonylimide-based compound is sodium bisfluorosulfonylimide (NaFSI), sodium bistrifluoromethanesulfonylimide (NaTFSI), or a mixture thereof.
The method of claim 1,
The sodium secondary battery is a sodium secondary battery charged by at least one selected from the following Reaction Formulas 1 and 2.
Scheme 1
(anode)Me + (electrolyte)nMFSI -> nM ⁺ + Me(FSI) _n
Scheme 2
(Anode) Me + (electrolyte) nMTFSI -> nM ⁺ + Me(TFSI) _n
(In Schemes 1 and 2,
Me is an element selected from transition metals,
Wherein M is an element selected from alkali metals,
n is a natural number of 1 to 4, and is a natural number corresponding to the positive valence of the transition metal (Me).
According to claim 1,
The sodium secondary battery is a sodium secondary battery that is discharged according to at least one selected from the following Reaction Formulas 3 and 4.
Scheme 3
nM ⁺ + Me(FSI) _n -> Me + nMFSI
Scheme 4
nM ⁺ + Me(TFSI) _n -> Me + nMTFSI
(In Schemes 3 and 4,
Me is an element selected from transition metals,
Wherein M is an element selected from alkali metals,
n is a natural number of 1 to 4, and is a natural number corresponding to the positive valence of the transition metal (Me).
8. The method according to any one of claims 1 to 7,
The sodium secondary battery is a sodium secondary battery, characterized in that operated at 100 to 300 ℃.

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