KR20220130529A - Sodium metal anode, manufacturing method thereof and secondary battery including the same - Google Patents

Abstract

The present invention relates to a sodium metal including a protective film, a manufacturing method thereof, and a secondary battery including the same. A polymer protective film is formed on the surface of the sodium metal in advance using a 1,4-dioxane solvent to implement a stable sodium metal negative electrode in the secondary battery.

Description

Sodium metal including a protective film, a manufacturing method thereof, and a secondary battery including the same

The present invention relates to sodium metal, a method for manufacturing the same, and a secondary battery including the same, and more particularly, to a sodium metal having a polymer solid-electrolyte interface protective film formed on its surface, a method thereof, and a secondary battery including the same.

Recently, renewable energy has been in the spotlight as an energy source to replace fossil fuels. Although renewable energy has the advantage of being eco-friendly, it can be done only in a situation where power production is limited, so an energy storage device that can store the generated electrical energy and supply it stably and efficiently when necessary is essential.

Currently, power storage sources include lithium ion batteries, redox flow batteries, high-temperature sodium-sulfur batteries, lead-acid batteries, and the like, and among them, lithium ion batteries in particular are spotlighted as medium and large-sized energy storage devices.

Lithium-ion batteries are energy storage devices that can be charged and discharged. Since the first commercialization in 1991, the market has been expanding into various fields such as electric vehicles and energy storage systems, following portable small devices.

However, lithium has a very low elemental proportion in the earth's crust and is limitedly distributed in a specific region, so the price of raw materials is gradually increasing. It is not efficient from an economic point of view.

On the other hand, research on sodium metal as one of the alternative materials for overcoming the problems of lithium is being conducted. Unlike lithium, sodium has a uniform resource distribution and can be extracted from seawater, so it has excellent economic efficiency. However, there are still problems to be solved in using sodium metal as a negative electrode of a secondary battery.

1 is a view showing the problems of the conventional sodium metal cathode.

Specifically, sodium has strong reducibility and reacts with the electrolyte during charging and discharging to form a solid-electrolyte interphase of various chemical species on the sodium metal surface. The solid-electrolyte interface formed in this process has different chemical species and physical properties, so the structure of the part with weak physical properties may collapse due to the volume change of the cathode during charging and discharging, which causes sodium dentrite growth. .

Accordingly, in order to commercialize a sodium metal secondary battery, a method for stabilizing a sodium metal anode is required.

An object of the present invention is to provide a sodium metal including a protective film, a method for manufacturing the same, and a secondary battery including the same.

Another object of the present invention is to provide a sodium metal including a protective film on its surface, a method for manufacturing the same, and a secondary battery including the same to realize a stable negative electrode.

In addition, an object of the present invention is to provide a method for economically manufacturing sodium metal including a protective film on the surface to be advantageous for commercialization.

However, these problems are exemplary, and the scope of the present invention is not limited thereto.

According to the present invention, sodium metal constitutes the negative electrode of the secondary battery, and it is characterized in that it includes a protective film formed of a compound represented by the following Structural Formula 1 on one surface.

[Structural Formula 1]

In an embodiment of the present invention, the protective film is characterized in that it is uniformly formed on the one surface.

According to the present invention, the secondary battery includes a positive electrode and a negative electrode; a separator disposed between the anode and the cathode; and an electrolyte, wherein the negative electrode includes: sodium metal; and a protective film formed of a compound represented by the following Structural Formula 1 on one surface of the sodium metal.

[Structural Formula 1]

In an embodiment of the present invention, the protective film is characterized in that it is uniformly formed on the one surface.

In an embodiment of the present invention, the positive electrode comprises at least one of a sodium transition metal oxide-based, sodium transition metal sulfide-based, sodium transition metal fluoride-based, carbon-sulfur support, and carbon paper carrying a catalyst. do it with

In an embodiment of the present invention, the electrolyte is a sodium salt; and an organic solvent consisting of at least one of a carbonate series and an ether series.

According to the present invention, the method for producing sodium metal comprises the steps of (a) preparing sodium metal; (b) immersing the sodium metal in a 1,4-dioxane solvent for a predetermined time; and (c) drying the sodium metal from the 1,4-dioxane solvent, wherein the sodium metal prepared through the steps (a) to (c) constitutes the negative electrode of the secondary battery, It is characterized in that it includes a protective film formed of a compound represented by the following structural formula (1).

[Structural Formula 1]

In an embodiment of the present invention, the protective film is characterized in that it is uniformly formed on the one surface.

In an embodiment of the present invention, the step (a) is characterized in that it is prepared by evenly spreading the sodium metal.

In an embodiment of the present invention, the step (b) is characterized in that the ring-opening polymerization reaction of the 1,4-dioxane solvent is carried out by the sodium metal.

Effects of sodium metal including a protective film, a method for manufacturing the same, and a secondary battery including the same according to the present invention are as follows.

The present invention can realize a stable negative electrode of a secondary battery by the polymer solid-electrolyte interface formed on the sodium metal surface.

In addition, 1,4-dioxane used for forming the protective film in the present invention is relatively inexpensive, so sodium metal capable of implementing a stable negative electrode can be manufactured at an economical cost, and there is an advantage that no additional equipment is required during manufacturing.

In addition, in the case of using 1,4-dioxane, the mechanism of forming a protective film on the sodium metal surface is simple, so the manufacturing time is shortened, and it is easy to synthesize a large area.

However, these effects are exemplary, and the effects of the present invention are not limited to the aforementioned effects.

1 is a view showing the problems of the conventional sodium metal cathode.
2 is a view showing a sodium metal having a protective film formed on the surface according to the present invention.
3 is a diagram schematically illustrating a process of forming a protective film on a surface of sodium metal.
4(a) and (b) are surface SEM images of BNa and DTNa of FIG. 3, and FIGS. 4(c) and (d) are cross-sectional SEM images of BNa and DTNa.
5 is a graph showing surface binding analysis data of oil, BNa and DTNa through ATR FT-IR.
6 (a) to (c) is a graph showing the surface binding analysis data of DTNa through XPS.
7 (a) to (d) are graphs showing the voltage profile according to the change in current density of a symmetric battery composed of BNa and DTNa.
8 (a) and (b) are graphs showing the rate characteristic voltage curves of BNa and DTNa.
9(a) and (b) are surface SEM images of a symmetric battery composed of BNa and DTNa in a state of being charged and discharged for 50 cycles at various current densities.
10 (a) and (b) are graphs showing EIS analysis data of a symmetric battery composed of BNa and DTNa.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments described below are only examples for describing the present invention in detail, and it will be apparent to those of ordinary skill in the art that the scope of the present invention is not limited by the embodiments.

In addition, all terms related to technology used herein have the same meaning as commonly understood by those of ordinary skill in the art unless otherwise defined herein, and if the meanings conflict, definitions The description of the present specification including

Meanwhile, in the present specification, in order to clearly explain the invention shown in the drawings, descriptions related thereto are omitted, and similar reference numerals are used for similar components. And, when a component "includes" other components, this means that other components may be further included, rather than excluding other components, unless otherwise stated. Also, in the specification, when a “part” is described with respect to a certain component, it should be understood to mean one unit or block that performs a specific function.

In addition, in the steps described in this specification, identification numbers (eg, first, second, etc.) are used for convenience of description and should not be limited to describing the order of each step, and each step is Unless a specific order is clearly indicated, the implementation may be performed differently from the specified order. That is, the steps may be performed in the same order as specified, may be performed substantially simultaneously, or may be performed in the reverse order.

The present invention relates to a sodium metal constituting an anode in a sodium metal secondary battery, a method for manufacturing the same, and a secondary battery including the same.

In order to use sodium metal as a negative electrode of a secondary battery, the stability problem described above must be solved. A representative method for ensuring the stability of sodium metal is to form a solid-electrolyte interface (or a protective film) on the sodium metal surface.

When the solid-electrolyte interface is formed on the sodium metal surface, dentrite growth is suppressed and stability can be secured. The solid-electrolyte interface may be formed naturally by the reaction between the sodium metal and the electrolyte, but when using an artificial method, a solid-electrolyte interface with a uniform thickness and chemical species can be formed on the sodium metal surface.

Conventionally, a solid-electrolyte interface with a nano-level thickness was formed on the sodium metal surface through processes such as atomic layer deposition (ALD) and molecular layer deposition (MLD). However, since this method requires additional equipment, there is a limit to commercialization.

Accordingly, the present invention forms a solid-electrolyte interface (hereinafter, referred to as a protective film) on the surface of a sodium metal by a simple process, and intends to utilize the sodium metal prepared by the above process as an anode of a secondary battery.

2 is a view showing a sodium metal having a protective film formed on the surface according to the present invention. Referring to FIG. 2 , the sodium metal 100 according to the present invention may include a protective layer 110 formed of a compound represented by the following Structural Formula 1 on one surface.

[Structural Formula 1]

According to the present invention, the protective layer 110 may be uniformly formed on one surface of the sodium metal 100 . In detail, the protective layer 110 may be formed on one surface of the sodium metal 100 to have a uniform thickness.

The above-described sodium metal 100 may be a negative electrode of the secondary battery.

The secondary battery according to the present invention may include a positive electrode and a negative electrode, a separator and an electrolyte disposed between the positive electrode and the negative electrode, and the sodium metal 100 including the protective film 110 may be the negative electrode.

In this case, since dentrite growth is suppressed on the surface of the sodium metal serving as the negative electrode, stability can be secured, the lifespan is improved, and there is an advantageous effect in terms of securing space when configuring the battery. A detailed description of the above effects will be described later.

The cathode may be a cathode material for a sodium ion battery, a cathode material for a sodium sulfur battery, or a cathode material for a sodium-air battery.

For example, the anode may be a sodium transition metal oxide-based, sodium transition metal sulfide-based, sodium transition metal fluoride-based, carbon-sulfur support, or carbon paper on which a catalyst is supported.

The separator may include polyolefin-based materials such as polyethylene and polypropylene, and in addition, may include one or more polymer materials such as polyester-based, polyacrylonitrile-based, and fluorine-based materials.

The electrolyte may include a sodium salt and an organic solvent. In detail, the electrolyte may be a sodium salt dissolved in an organic solvent consisting of at least one of carbonate-based and ether-based.

For example, the organic solvent is ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethylene glycol dimethyl ether, It may include one or more of tetraethylene glycol dimethyl ether.

In addition, the sodium salt may include at least one of sodium perchlorate (NaClO ₄ ), sodium tetrafluoroborate (NaBF ₄ ), sodium hexafluorophosphate (NaPF ₆ ), and sodium triflate (NaOTf).

However, the positive electrode, the separator, and the electrolyte are not limited to the materials listed above, and materials commonly used in the art may be used without limitation.

3 is a diagram schematically illustrating a process of forming a protective film on a surface of sodium metal. Referring to FIG. 3 , the sodium metal 100 according to the present invention includes (a) preparing sodium metal (Bare Na metal, BNa) 10; (b) immersing the sodium metal 10 in a 1,4-dioxane solvent for a predetermined time; and (c) drying the sodium metal from the 1,4-dioxane solvent. The sodium metal (Dioxane Treated Na metal, DTNa) 100 manufactured through the steps (a) to (c) may include a protective layer 110 formed of a compound represented by Structural Formula 1 on one surface. The passivation layer 110 may be uniformly formed on one surface of the sodium metal.

Hereinafter, a method of manufacturing the sodium metal 100 according to the present invention will be described through an experimental example. However, the manufacturing method is not limited by the following experimental examples.

(Experimental example)

reagent preparation

In order to prepare the sodium metal 100 according to the present invention, sodium cubes (99.9%), 1,4-dioxane (anhydrous, 99.8%) in a state of Sigma-Aldrich's mineral oil , Diethylene glycol dimethyl ether (anhydrous, 99.5%) and TCI chemicals' Sodium Trifluoromethanesulfonate (NaOTf, 98%) were prepared, and then in a glove box under argon atmosphere. was stored in

DTNa production

(a) preparing sodium metal (BNa)

After completely removing the oxidized side of the sodium cube, cut out enough sodium to use the clean part. The cut sodium is evenly spread to a certain thickness, and then cut into several sodium metal pieces 10' having the same size using a punch.

(b) immersing sodium metal (BNa) in a 1,4-dioxane solvent for a predetermined time

Using a syringe, about 20 ml of 1,4-dioxane solvent was placed in a beaker, and the cut sodium metal piece (10') was immersed in the beaker for 10 minutes.

In this step, a ring-opening polymerization reaction of a 1,4-dioxane solvent may proceed by the sodium metal piece 10', and a protective film may be formed on the sodium metal surface through this. Chemical Scheme 1 below shows the reaction proceeding in the beaker.

[Chemical Scheme 1]

Although 1,4-dioxane is a relatively stable organic solvent, it can be decomposed by sodium with strong reducibility. Specifically, when the sodium metal surface and 1,4-dioxane come into contact, electrons move from the sodium metal surface to the oxygen of 1,4-dioxane to break the ring, and then a sodium alkoxide radical is formed. The formed radical receives a proton and becomes a neutral molecule, and the formed molecule reacts with sodium again to form two types of nucleophiles. The nucleophile attacks the carbon of 1,4-dioxane to induce a ring opening reaction, and when this reaction continues, the surface of the sodium metal 100 has a protective film 110 made of a polymer similar to polyethylene oxide. ) is formed.

(c) drying the sodium metal (DTNa) from the 1,4-dioxane solvent

After removing the sodium metal 100 from the beaker and transferring it to a vial, it is dried in a glove box for at least 6 hours. The drying process is preferably carried out for a long time so that 1,4-dioxane on the surface of the sodium metal 100 can be removed as much as possible.

As described above, the protective film 110 can be formed on the surface of the sodium metal 100 according to the present invention through a very simple process without requiring a separate facility or the like. In addition, since 1,4-dioxane is used, the protective film 110 can be formed at a relatively low cost, and the reaction time is short, so that it is easy to synthesize a large area.

4 to 6 are images and data for comparing pure sodium metal (BNa) and sodium metal treated with 1,4-dioxane according to the present invention (DTNa).

Comparison of surface SEM images of BNa and DTNa

The surface SEM image was observed to confirm whether a 1,4-dioxane-based protective film was actually formed on the sodium metal surface subjected to the manufacturing method of the present invention. In the case of pure sodium metal (BNa), a relatively smooth surface was observed (Fig. 4(a)), whereas in the case of 1,4-dioxane-treated sodium metal (DTNa), a rough surface was observed (Fig. 4(b)). )). This means that the protective film 110 is formed on the surface of the sodium metal that has undergone the manufacturing method.

Comparison of cross-sectional SEM images and EDX mapping results of BNa and DTNa

Pure sodium metal (BNa) and 1,4-dioxane-treated sodium metal (DTNa) were cut and subjected to EDX mapping analysis from cross-sectional SEM images. Tables 1 and 2 below show EDX mapping analysis data of BNa and DTNa, respectively.

Element Weight (%) Atomic (%) C K 2.47 4.05 O K 33.82 41.52 Na K 63.70 54.43

Element Weight (%) Atomic (%) C K 5.39 8.59 O K 34.68 41.50 Na K 49.91 49.91

In the case of pure sodium metal (BNa), only a small amount of carbon could be visually confirmed as a whole in the cross section (FIG. 4(c)), and in fact, as shown in [Table 1], the carbon content was found to be very low with an atomic weight of 4.05%. The content of carbon and oxygen is predicted to be generated by rapidly reacting with carbon dioxide and oxygen due to the strong reactivity of sodium at the moment of short exposure to the outside in the process of acquiring the SEM image.

On the other hand, in the 1,4-dioxane-treated sodium metal (DTNa), carbon was detected as a whole in the cross section, and in particular, it was confirmed that a large amount of carbon was concentrated at the upper end of the cross section (FIG. 4(d)). The proportion of carbon atoms was also found to be 8.59%, which is twice that of general sodium metal (BNa).

These results mean that a 1,4-dioxane-based protective film is actually formed on the surface of the sodium metal 100 that has undergone the manufacturing method of the present invention.

Comparison of ATR FT-IR Analysis of Mineral Oil, BNa, DTNa

ATR FT-IR analysis was performed to confirm whether the protective film 110 was formed on the surface of the 1,4-dioxane-treated sodium metal 100 according to the manufacturing method of the present invention.

FT-IR analysis was carried out in a state soaked in mineral oil that was not reactive with sodium and could block air at the same time in order to suppress the rapid reaction of sodium in the air even a little.

6, mineral oil has peaks at 2900cm ^-1 , 1883 to 2391 cm ^-1 , 1455 cm ^-1 , 1366 cm ^-1 , these peaks are pure sodium metal (BNa) and 1,4-dioxane-treated sodium All metals (DTNa) can be identified.

All peaks detected in pure sodium metal (BNa) can be confirmed in 1,4-dioxane-treated sodium metal (DTNa), and 1600cm ^-1 , 1112cm ^-1 , 872cm ^-1 peaks are 1,4-dioxane-treated. It is found only in sodium metal (DTNa). The peaks represent sodium anhydride bonds (1600 cm ^-1 , 872 cm ^-1 ) and ether bonds (1112 cm ^-1 ).

This result means that the actual sodium meets with 1,4-dioxane to form the protective layer 110 having the above bonding.

XPS analysis result of DTNa

XPS was measured using equipment connected to the glove box after it was completely sealed in a glove box in an argon atmosphere.

Referring to FIG. 6( a ), the C 1s peaks appeared at 284.8 eV, 285.9 eV, and 289.1 eV.

The 284.8 eV peak showing the highest intensity indicates a C-C bond, which is consistent with the binding energy of the negative carbon. The 285.9 eV peak means a C-O-C bond, which exactly matches the strength of the C-O-C bond in a polyethylene oxide (PEO) polymer. The 289.1 eV peak shows a C=O bond, which is a bond that does not exist in the polymer predicted to be formed on the surface of the sodium metal 100 through the manufacturing method according to the present invention. As a result of this peak, it is estimated that sodium alkoxide radicals generated in the middle of the reaction with sodium and 1,4-dioxane cause a side reaction when carbon dioxide or carbonate series, which is often used as an electrolyte solvent, is vaporized in the glove box.

Referring to FIG. 6(b), the O 1s peaks appeared at 531.08 eV, 531.93 eV, and 535.63 eV.

The 531.08 eV and 531.93 eV peaks indicate Na-O bonding and C-O bonding, respectively, and these two types of peaks correspond to the peaks originating from the polymeric bazaar material generated through the expected reaction. The peak that appears widely at 535.63 eV is a peak that appears as the Auger electrons of sodium are emitted, and it can be considered as a reasonable result because the analysis sample basically contains sodium.

Finally, referring to Fig. 6(c), the Na 1s peak is detected only at 1071.3 eV, which is presumed to be a Na-O bond.

Combining the analysis results discussed above, when sodium metal is treated with 1,4-dioxane, a ring-opening polymerization reaction with 1,4-dioxane proceeds on the surface of sodium metal, and on the surface of sodium metal, through this reaction It can be seen that a protective film made of the generated polymer material is formed.

Hereinafter, when the sodium metal (DTNa) 100 including the protective film 110 is applied to a battery, an experiment for confirming whether a stable sodium metal anode can be realized and the results thereof will be described.

For the experiment, a symmetrical battery having a capacity of 1 mAhcm ⁻¹ was manufactured using pure sodium metal (BNa) (Comparative Example) and 1,4-dioxane-treated sodium metal (DTNa) (Example).

Comparison of voltage profiles of BNa symmetric cells and DTNa symmetric cells

The manufactured BNa symmetric battery and DTNa symmetric battery were operated at various current densities to check the lifespan. Table 3 below shows the lifespan data of the BNa symmetric battery and the DTNa symmetric battery according to the current density.

division BNa DTNa 1mAcm ^-2 470h > 2500h 2mAcm ^-2 120h > 1750h 3mAcm ^-2 150h > 1150h 5mAcm ^-2 37h > 800h

Referring to Figure 7(a), at a current density of 1mAcm ^-2 , the BNa symmetric battery had an overvoltage of 200mV or more within 500 hours and a battery short circuit occurred, but the DTNa symmetrical battery had a constant overvoltage of less than 15mV for 2500 hours. lifespan was maintained with

Referring to FIG. 7(b), at a current density of 2mAcm ^-2 , the BNa symmetric battery stopped driving when it reached about 130 hours, but the DTNa symmetric battery maintained an overvoltage of about 30mV until 1750 hours. After that, it can be seen that the overvoltage rises high.

According to FIGS. 7(c) and 7(d), the DTNa symmetrical battery operated stably for 1150 hours and 800 hours with overvoltages of 40mV and 50mV, respectively, under the current density 3mAcm ^-2 condition and 5mAcm ^-2 condition. However, the BNa symmetric battery exhibited a short lifespan of less than 200 hours, which is presumed to be due to the high overvoltage and dentrite formation due to the side reaction between the electrolyte and sodium.

As shown in the experimental results above, the fact that the DTNa symmetrical battery operated stably for more than 2500 hours can be seen as having stability enough to have no problem even when directly applied to the battery.

Comparison of Overvoltage Changes for BNa Simetric Cells and DTNa Simetric Cells

The overvoltage change was confirmed by driving the fabricated BNa symmetric battery and DTNa symmetric battery at various current densities.

Referring to FIG. 8( a ), in the case of a BNa symmetric battery, when the current density of 1, 2, 3, 5, 8, 15mAcm ^-2 is sequentially returned for 10 cycles, the overvoltage is up to the current density of 1mAcm ^-2 It can be seen that the overvoltage gradually increases when it returns stably without change and reaches 2mAcm ^-2 after 10 cycles. At current densities of 2mAcm ^-2 and 3mAcm ^-2 , the graph rogudd was maintained relatively stable up to 10 cycles, but from the current density of 5mAcm ^-2 , high overvoltage and very unstable voltage curves were shown.

On the other hand, at high current densities of 8mAcm ^-2 and 15mAcm ^-2 , it was found that a relatively low overvoltage was shown. This can be seen as due to high Joule heat, which is generated due to the high current density, which causes a lot of electrical energy to be applied to the battery itself, and the internal resistance of the battery.

Sodium, which has a relatively low melting point of about 98°C, is heated by the heat generated by itself and becomes a fluid state.

Referring to FIG. 8(b), in the case of DTNa symmetrical battery, it continues to be stably driven at current densities of 1, 2, 3, 5, 8, and 15mAcm ^-2 , and is driven again after 10 cycles at all current densities. Even when returning to a current density of 5mAcm ^-2 , it was found that the cell was still driven with a low and stable overvoltage.

This result can be considered because the protective film 110 artificially formed on the surface of the sodium metal 100 according to the manufacturing method of the present invention is maintained even when the battery is driven, thereby suppressing the growth of dentrite on the surface of the sodium metal.

Comparison of surface SEM images after 50 cycles of charging and discharging of BNa symmetric cells and DTNa symmetric cells

In order to check whether dentrites are grown on the surface of the BNa and DTNa symmetric battery when the actual battery is driven, the BNa and DTNa symmetric battery were charged and discharged for 50 cycles under current density conditions of 1, 3, 5 mAcm ^-2 . Then, the surface SEM image was observed.

Referring to FIG. 9( a ), it can be confirmed that dentrites are grown on the surface of the BNa electrode from the surface SEM image. In addition, the porous, non-dense surface can be seen even in the low magnification image. In addition, it can be seen that the porous structure on the surface of the BNa electrode gradually worsens when the battery is driven at a high current density.

That is, when a BNa battery is used as an anode, dentrites easily grow on the surface of the anode, and a large amount of electrochemically inactive sodium is produced to have low coulombic efficiency and lifespan characteristics.

On the other hand, referring to FIG. 9(b), it can be seen that the sodium metal is distributed more uniformly and densely on the surface of the DTNa electrode than on the surface of the BNa electrode under the same current density condition.

In particular, it can be seen that the DTNa electrode surface is densely accumulated with few voids under the current density condition of 1 mAcm ^-2 , which is evidence of a structure in which dentrite cannot easily grow, and additional damage caused by damage to the protective film 110 Electrolyte consumption and electrochemically inactive sodium is not formed.

In addition, in the case of the DTNa electrode, even at a current density of 3, 5 mAcm ^-2 , the surface had a relatively dense structure, and almost no dentrite was observed.

Comparison of EIS analysis results of BNa symmetric cells and DTNa symmetric cells

As a result of EIS (Electrochemical Impedance Spectroscopy) analysis of BNa and DTNa symmetric cells, the following results were obtained.

First, in the case of the BNa symmetric battery, the electrolyte resistance was measured to be greater than that of the DTNa symmetric battery. Electrolyte resistance is a value determined by a decrease in salt concentration due to a side reaction during battery driving, transport characteristics of the electrolyte itself, and the like, and the starting point of a semicircle in the graph of FIG. 10 corresponds to this.

10(a) and (b), the electrolyte resistance of the BNa symmetric electrode is 13Ω, and the electrolyte resistance of the DTNa symmetric electrode is confirmed to be less than 10Ω. Since the same concentration and type of electrolyte were used in this analysis, the difference in these results appears to be due to whether or not the protective layer 110 is included.

That is, in the case of the DTNa symmetric electrode, the protective film 110 has an effect of suppressing the side reaction of the electrolyte, which means that a decrease in the concentration of the salt is small accordingly.

Second, the BNa and DTNa symmetric cells show differences in the first cycle. In detail, in the case of the DTNa symmetric battery, it can be seen that a very large semicircle is drawn as a result of measuring the EIS after driving the first cycle. Here, the semicircle means the resistance required to transfer ions in the protective layer 110 , and in the case of the DTNa symmetric battery, it is confirmed that the resistance is about 40Ω. In contrast, in the case of the BNa symmetric battery, the resistance was measured to be very low, about 5Ω.

From these results, the protective film 110 of a certain thickness is formed on the surface of the sodium metal 100 according to the present invention, and the sodium ions are not sufficiently penetrated into the protective film 110 at the beginning of battery operation, so the ion conductivity is not high. It takes a great deal of resistance for ions to pass through the protective film 110 made of a polymer material to reach the sodium metal, but when charging and discharging are continued at a certain level, sodium ions penetrate the protective film 110 and the conductivity of sodium ions is improved. can

Finally, the BNa symmetric battery showed that the resistance due to the interface between the sodium metal and the electrolyte gradually increased as 1, 10, 50, 70, and 90 cycles passed. From this, it can be confirmed that dentrite is continuously generated on the surface of the sodium metal by driving the battery, and the thickness thereof increases, and sodium without electrochemical activity is generated.

On the other hand, in the DTNa symmetric battery, the resistance due to the sodium metal and electrolyte interface did not increase significantly until 1, 10, 50, 70, and even 1800 cycles were driven. It can be confirmed that the protective film 110 previously formed on the sodium metal surface according to the sodium metal manufacturing method of the present invention is a polymer layer that physically inhibits the formation of dentrites and is not easily collapsed by the dentrites.

The effects of the sodium metal according to the present invention discussed above are summarized as follows.

The sodium metal 100 according to the present invention uses a small amount of 1,4-dioxane, which is an inexpensive organic solvent, to form the protective film 110 on the sodium metal surface in advance, and has the advantage that the process is very economical and simple, In particular, large-area synthesis may be facilitated due to a simple process. The present invention can greatly reduce the economic burden when used in a large-capacity energy storage device thanks to such process advantages.

In addition, when the sodium metal 100 according to the present invention is used as a negative electrode of a battery, it has a long lifespan even at a high current density. can be driven by

In addition, according to the present invention, since the protective film 110 is formed on the surface of the sodium metal 100 to a very thin thickness of about 100 nm, the amount of unnecessary materials occupying mass and volume in addition to the active material in the complete paper is greatly reduced, so that high energy density can be obtained.

In the above, preferred embodiments of the present invention have been described, but the present invention is not limited to the above-described embodiments and experimental examples, and various changes and modifications may be made within the scope without departing from the technical spirit of the present invention.

Claims (10)

A sodium metal constituting the negative electrode of a secondary battery, and including a protective film formed of a compound represented by the following Structural Formula 1 on one surface.
[Structural Formula 1]

According to claim 1,
The protective film is uniformly formed on the one surface, sodium metal. positive and negative electrodes;
a separator disposed between the anode and the cathode; and
containing an electrolyte;
The negative electrode, sodium metal; and
A secondary battery comprising a protective film formed of a compound represented by the following Structural Formula 1 on one surface of the sodium metal.
[Structural Formula 1]

4. The method of claim 3,
The protective film is uniformly formed on the one surface, the secondary battery. 4. The method of claim 3,
The positive electrode, a secondary battery comprising at least one of a sodium transition metal oxide-based, sodium transition metal sulfide-based, sodium transition metal fluoride-based, carbon-sulfur support and a catalyst-supported carbon catalyst. 4. The method of claim 3,
The electrolyte, sodium salt; and
A secondary battery comprising an organic solvent consisting of at least one of a carbonate series and an ether series. (a) preparing sodium metal;
(b) immersing the sodium metal in a 1,4-dioxane solvent for a predetermined time; and
(c) drying the sodium metal from the 1,4-dioxane solvent,
The sodium metal prepared through the steps (a) to (c) constitutes the negative electrode of the secondary battery, and includes a protective film formed of a compound represented by the following Structural Formula 1 on one surface.
[Structural Formula 1]

8. The method of claim 7,
The protective film is uniformly formed on the one surface, a method of manufacturing sodium metal. 8. The method of claim 7,
In the step (a), the method for producing sodium metal, characterized in that preparing the sodium metal evenly. 8. The method of claim 7,
The (b) step, the method for producing a sodium metal, characterized in that the ring opening polymerization of the 1,4-dioxane solvent by the sodium metal proceeds.

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