KR101914173B1 - Sodium electrode and sodium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a sodium electrode including a porous carbon body having an inserted sodium metal and an ion conductive protective layer, and a sodium secondary battery including the sodium electrode.
The sodium electrode according to the present invention prevents dendrite growth through uniform distribution of electrons in the electrode. In addition, the sodium electrode according to the present invention can improve the problem of battery short-circuit due to the growth of sodium dendrite because the ion conductive protective layer is not peeled off even during charging / discharging of the battery.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a sodium electrode and a sodium secondary battery including the same,

The present invention relates to a sodium electrode including a porous carbon body having an inserted sodium metal and an ion conductive protective layer, and a sodium secondary battery including the sodium electrode.

With the rapid development of the electronics, communications and computer industries, applications of energy storage technology to camcorders, mobile phones, notebooks, PCs, and even electric vehicles are expanding. Accordingly, development of high performance secondary batteries which are light and long-lasting and highly reliable is underway.

A lithium secondary battery having a high energy density is attracting attention as a battery satisfying such a demand. However, lithium is a scarce substance. As the demand increases, the price will rise. Therefore, it is necessary to develop alternative materials in terms of cost.

Sodium is the sixth most abundant element on the planet, and it is attracting attention as a substitute for lithium because it is inexpensive and has a much wider variety of compounds than lithium. Since the sodium secondary battery follows the manufacturing process of the lithium secondary battery, there is no need to provide a new manufacturing facility, the manufacturing cost can be reduced, and the load characteristics can be improved as compared with the lithium secondary battery.

However, since sodium is chemically active, it has a problem in safety such as reacting violently with water, and when sodium metal is used as an electrode, sodium dendrite grows due to cell driving, causing a short circuit of the cell .

In order to protect the sodium metal from moisture and prevent the growth of sodium dendrites, a method of forming a protective layer having ionic conductivity on the surface of the electrode as in the case of the lithium electrode is considered. However, when such a protective layer is applied to a conventional sodium metal electrode manufactured by attaching a sodium foil on a flat collector, the protective layer is peeled off from the electrode surface due to reduction and increase of sodium metal during charge and discharge.

Therefore, it is necessary to develop a new sodium electrode which can inhibit the growth of sodium dendrites and which does not peel off the protective film even after repeated charge and discharge.

Korean Patent No. 1460282, a lithium electrode and a lithium metal battery manufactured using the same

In order to solve the above problems, the present inventors prepared a sodium electrode containing a porous carbon body as a current collector and an ion conductive protective layer thereon, the protective layer separation phenomenon does not occur in the sodium electrode thus produced, And thus the present invention has been completed.

Accordingly, an object of the present invention is to provide a sodium electrode and a sodium secondary battery including the sodium electrode, in which growth of sodium dendrites is suppressed and peeling of the protective layer does not occur.

In order to achieve the above object,

A porous carbon body into which a sodium metal is inserted; And

And an ion conductive protective layer formed on the surface of the porous carbon body.

The content of the sodium metal may be 1 to 50 wt% based on the total weight of the porous carbon body and the sodium metal.

The porous carbon body may be at least one selected from activated carbon, graphite, graphene, carbon nanotube (CNT), carbon fiber, and carbon black.

The porosity of the porous carbon body may be 50 to 99%.

The average pore size of the porous carbon material may be 5 to 500 μm.

The thickness of the porous carbon body may be 10 to 300 mu m.

The sodium ion conductivity of the ion conductive protective layer may be 10 ^-7 S / cm or more.

The ion conductive protective layer may be at least one selected from the group consisting of NaPON, beta alumina, a hydride compound, a NASICON compound, and a perovskite compound.

The ion conductive protective layer may be made of polyethylene oxide (PEO); Polyacrylonitrile (PAN); Polymethylmethacrylate (PMMA); Polyvinylidene fluoride (PVDF); Polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP); And -SO ₃ Na, may be at least one selected from polymers containing a -COONa or -ONa.

The thickness of the ion conductive protective layer may be 0.01 to 50 탆.

The present invention also provides a sodium secondary battery comprising the electrode as a cathode.

The sodium electrode according to the present invention prevents dendrite growth through uniform distribution of electrons in the electrode. In addition, the sodium electrode according to the present invention can improve the problem of battery short-circuit due to the growth of sodium dendrite because the ion conductive protective layer is not peeled off even during charging / discharging of the battery.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention.

Sodium electrode

A sodium electrode according to the present invention comprises: a porous carbon body into which a sodium metal is inserted; And an ion conductive protective layer formed on the surface of the porous carbon body.

Conventional sodium electrodes were prepared by attaching a sodium foil on a flat collector. In this case, when the cell is driven, electrons moving to the sodium foil through the planar current collector move in a unidirectional flow, resulting in nonuniformity of the electron density on the surface of the sodium foil, which causes formation of sodium dendrites There was a problem. Such sodium dendrites cause damage to the separator, and short-circuiting of the battery may occur, which is a problem.

In order to solve this problem, a method of introducing a protective layer on the surface of sodium metal is used. This protective layer prevents contact between the sodium metal and the electrolytic solution and prevents sodium dendrites from forming and / or growing on the electrode surface. However, the protective layer formed on the planar sodium foil is peeled off due to the decrease and increase of the sodium metal during charging and discharging of the battery, so that the dendritic growth preventing effect can not be sufficiently secured.

Thus, in the present invention, the above effect is ensured by using the porous carbon body as the collector and sodium metal as the electrode layer by inserting the sodium metal into the porous carbon body. That is, the sodium electrode according to the present invention has a wide contact area between the sodium metal and the porous carbon so that the electron distribution on the surface of the sodium metal becomes uniform, thereby preventing the growth of the sodium dendrite.

In addition, since the ion conductive protective layer of the present invention is in direct contact with the porous current collector, the state of being bonded to the electrode layer can be maintained regardless of decrease or increase of the sodium metal upon charge / discharge of the battery, Does not occur. Accordingly, the sodium electrode according to the present invention is capable of inhibiting effective sodium dendrite growth, thereby exhibiting improved cell performance and safety.

In the sodium electrode according to the present invention, the porous carbon body means a carbon-based material having a plurality of pores and serves as a carrier and a collector of sodium metal. Since the porous carbon body is about 70% lighter than the weight of the conventional metal collector, the energy density per unit weight of the electrode can be increased.

The porous carbon body may be at least one selected from the group consisting of activated carbon, graphite, graphene, carbon nanotube (CNT), carbon fiber, and carbon black, but is not limited thereto. The shape of the porous carbon body may be mesh, paper or foam.

The porosity of the porous carbon body is preferably 50 to 99%, more preferably 60 to 80%. The porosity at this time means the ratio of the pores to the total volume of the porous carbon body, which can be calculated as (actual weight of the porous carbon body) / (measured volume of the porous carbon body * theoretical density). The porosity can be measured, for example, by using a commonly used porous material porosimeter (CFP-1500AEL (PMI, USA)). Specifically, a test solution having a constant surface tension is used to measure the porosity Can be measured by completely wetting the sieve sample and then measuring the flow rate of air through the sample through the bottom while varying the air pressure at the top of the sample.

When the porosity of the porous carbon material satisfies the above range, the effect of inhibiting the growth of sodium dendrites is excellent. If the porosity of the porous carbon body is less than 50%, there is a problem that the space for inserting sodium metal is insufficient. If the porosity exceeds 99%, there is a problem that it is difficult to serve as an electrode.

The average pore diameter of the porous carbon material is preferably 5 to 500 μm, more preferably 10 to 300 μm. When the pore average particle diameter of the porous carbon material satisfies the above range, the dendrite inhibiting effect and the durability of the porous carbon material are secured, and the contact area with the inserted sodium metal can be maximized.

In the present invention, the thickness of the porous carbon body is preferably 10 to 200 占 퐉. If the thickness of the porous carbon body exceeds the above range, it is not suitable for use as an electrode. If the thickness is less than the above range, the energy density of the electrode becomes insufficient.

In the present invention, the content of the sodium metal inserted into the porous carbon body is preferably 1 to 50% by weight, more preferably 5 to 30% by weight, based on the total weight of the porous carbon body and the sodium metal.

If the content of the sodium metal exceeds the above range, the dendritic growth inhibiting effect obtained by employing the porous carbon body is not sufficiently exhibited. If the content is less than the above range, the active material amount becomes insufficient and it is difficult to perform the role as the sodium electrode. .

The method of filling the sodium metal into the pores of the porous carbon body is not particularly limited and may vary. For example, sodium metal is filled in the pores by an electroplating method, a melting method, a thin film manufacturing technique, or a method in which sodium particles are uniformly filled in pores of a collector by a paste coating method.

The 'thin film manufacturing technique' refers to a technique of physically depositing in a moisture-free atmosphere. Examples of such thin film manufacturing techniques include a thermal evaporation method, an electron beam evaporation method, an ion beam evaporation method, a sputtering method, an arc evaporation method and a laser ablation evaporation method .

The paste application method includes a method of applying sodium or sodium alloy particles and a solvent in paste form, or a method in which a binder such as sodium particles and PVdF is mixed with a solvent and paste is applied.

In addition, a sodium metal foil is placed on the porous current collector, followed by compression, to produce a high-density sodium anode. The term 'squeeze' refers to the densification by applying pressure, and the means used for squeezing is a roll press or a plate press. The pressure applied at this time is usually 1 to 10 kg / cm ² , but is not limited thereto.

In the sodium electrode according to the present invention, the ion conductive protective layer prevents the sodium metal from directly contacting with the electrolytic solution and suppresses dendrite growth, and is not limited as long as it has sodium ion conductivity. In addition, such an ion conductive protective layer may take the role of a separation membrane. Preferably, the ion conductivity of the ion conductive protective layer is at least 10 ^-7 S / cm.

In the sodium electrode according to the present invention, the ion conductive protective layer may include at least one selected from an inorganic compound and an organic compound.

The inorganic compound may be at least one selected from the group consisting of NaPON (sodium phosphorus oxynitride), beta alumina, hydride compound, NASICON compound, and perovskite compound .

Specifically, the beta alumina is expressed by a composition formula of Na ₂ OxAl ₂ O ₃ (x = 5 to 11), and β-alumina, β "-alumina, or a mixture thereof can be used.

The hydride compound is selected from the group consisting of NaBH ₄ , Na ₃ N, Na ₂ NH, Na ₂ BNH ₆ , Na _1.8 N _0.4 Cl _0.6 , NaBH ₄ , Na ₃ P-NaCl, Na ₄ SiO ₄ , Na ₃ PS ₄ Or Na ₃ SiS ₄ .

The NASICON-based compound may be a complex oxide of Na-Zr-Si-O system, a complex oxide of Na-Zr-Si-PO system, a composite oxide of Y-doped Na-Zr- A complex oxide of Na-Zr-Si-PO system or a mixture thereof, and more specifically, Na ₃ Zr ₂ Si ₂ PO ₁₂ , Na _{1 + x} Si _x Zr ₂ P _{3 -x} O ₁₂ (1.6 (real number <x <2.4), Y or Fe is doped Na ₃ Zr ₂ Si ₂ PO ₁₂ , Y or Fe-doped Na _{1 + x} Si _x Zr ₂ P _{3 -x} O ₁₂ , Or mixtures thereof.

And the perovskite (Perovskite) based compound is Na _x La _{1 -} may be in the _{x TiO 3 (0 <x <} 1) or _{Na 7 La 3 Zr 2 O 12} , specifically, Na _{0. 35} La _{0 . 55} TiO ₃ , Na _{0 . 5} La _{0 . 5} TiO ₃ or Na ₇ La ₃ Zr ₂ O ₁₂ .

The organic compound may be selected from the group consisting of polyethylene oxide (PEO); Polyacrylonitrile (PAN); Polymethylmethacrylate (PMMA); Polyvinylidene fluoride (PVDF); Polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP); And -SO ₃ Na, may be at least one selected from polymers containing a -COONa or -ONa.

The protective layer proposed in the present invention may further comprise an ion supplying compound such as a metal oxide, a hydrate or a salt to further improve ion conductivity. The ion-supplying compound may be selected from the group consisting of Li ₂ O, Na ₂ O, MgO, CaO, ZnO, LiOH, KOH, NaOH, CaCl ₂ , AlCl ₃ , MgCl ₂ , Na ₃ PO ₄ , Na ₂ HPO ₄ , NaBO ₂ , Na ₂ B _{4 O 7, H 3 BO 3} , NaClO 4, NaAsF 6, NaBF 4, NaPF 4, NaPF 6, NaSbF 6, NaCF 3 SO 3, NaN (SO 2 CF 3) 2, NaTFSI, Na [(C 2 F 5 ) ₃ PF ₃ ] (NaFAP), Na [B (C ₂ O ₄ ) ₂ ] (NaBOB), Na [N (SO ₂ F) ₂ ] (NaFSI), and NaN [SO ₂ C ₂ F ₅ ] ₂ But it is not limited to these.

The thickness of the protective layer is not particularly limited and may be within a range that does not increase the internal resistance of the battery while ensuring dendrite growth inhibiting effect, and may be, for example, 0.01 to 50 μm, preferably 0.1 to 10 μm. If the thickness is less than the above range, the protective layer can not be performed. On the contrary, when the thickness exceeds the above range, the interfacial resistance is increased to deteriorate the battery characteristics.

The method of forming the ion conductive protective layer on the surface of the porous carbon body is not particularly limited, and the methods commonly used in the art can be used without limitation. For example, a solution casting method, a dip coating method, a spray coating method, a spin coating method, a sputtering method using PVD (physical vapor deposition), a CVD (chemical vapor deposition a general method of forming a layer such as an ALD (atomic layer deposition) method of deposition can be used.

Sodium secondary battery

The sodium secondary battery according to the present invention includes a cathode, a cathode, and an electrolyte, and may further include a separator. The cathode uses the sodium electrode according to the present invention. According to the present invention, the dendrite growth of the sodium electrode is effectively suppressed, thereby improving battery performance and safety.

The constitution of the anode, the separator and the electrolyte of the sodium secondary battery is not particularly limited in the present invention, and is well known in the art.

The positive electrode includes a positive electrode active material formed on the positive electrode current collector.

The positive electrode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. For example, carbon, nickel , Titanium, silver, or the like may be used. At this time, the cathode current collector may use various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric having fine irregularities formed on the surface so as to increase the adhesive force with the cathode active material.

As the cathode active material constituting the electrode layer, all of the cathode active materials available in the related art can be used, and a transition metal compound which reversibly occludes and releases sodium ions is preferably used. Specific examples of such a cathode active material include NaCrO ₂ , NaNi _0.5 Mn _0.5 O ₂ , NaMn _{1 . 5} Ni _{0 . 5 O 4, NaFeO 2, NaFe} x (Ni 0. 5 Mn 0 .5) Na 2/3 Fe 1/3 Mn 2/3 O 2, NaMnO 2, Na x NiO 2, Na x CoO 2, Na 0. ₄₄ MnO ₂ , Na ₄ Co ₃ (PO ₄ ) ₂ P ₂ O ₇ , Na ₄ Ni ₃ (PO ₄ ) ₂ P ₂ O ₇ , and the like.

At this time, the electrode layer may further include a binder resin, a conductive material, a filler, and other additives in addition to the cathode active material.

The binder resin is used for bonding between the electrode active material and the conductive material and bonding to the current collector. Non-limiting examples of such binder resins include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polymethacrylic acid (PMA), polymethylmethacrylate (PMMA) (PAM), polymethacrylamide, polyacrylonitrile (PAN), polymethacrylonitrile, polyimide (PI), alginic acid, alginate, chitosan, carboxymethylcellulose Propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), polyvinylpyrrolidone, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ), Fluorine rubber, various copolymers thereof, and the like.

The conductive material is used to further improve the conductivity of the electrode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Polyphenylene derivatives and the like can be used.

The filler is optionally used as a component for suppressing the expansion of the electrode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The separator may be made of a porous substrate. The porous substrate may be any porous substrate commonly used in an electrochemical device. For example, the porous substrate may be a polyolefin porous film or a nonwoven fabric. no.

The separator may be formed of a material selected from the group consisting of polyethylene, polypropylene, polybutylene, polypentene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, A porous substrate made of any one selected from the group consisting of polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalate, or a mixture of two or more thereof.

As the electrolyte of the sodium secondary battery, a non-aqueous electrolyte, an organic solid electrolyte, and an inorganic solid electrolyte containing a sodium salt and a non-aqueous organic solvent are used.

The Na salt may be, for example, NaClO ₄ , NaAsF ₆ , NaBF ₄ , NaPF ₄ , NaPF ₆ , NaSbF ₆ , NaCF ₃ SO ₃ , NaN (SO ₂ CF ₃ ) ₂ , NaTFSI, Na [(C ₂ F ₅ ) _{3 PF 3] (NaFAP),} Na [B (C 2 0 4) 2] (NaBOB), Na [N (S0 2 F) 2] (NaFSI), and _{NaN [S0 2 C 2 F 5} ] 2 (Na Bet i) may be used.

Non-aqueous organic solvents include, for example, N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate (EC), butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate Tetrahydrofuran, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran franc, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, Diethyl ether, formamide, dimethyl formamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, Propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, ethyl propionate and the like can be used as the organic solvent.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer including a secondary dissociation group, or the like may be used, and may further include an ion supplying compound as described above in order to improve ion conductivity.

Examples of the inorganic solid electrolyte include Na ₃ N, NaI, Na ₅ NI ₂ , Na ₃ N-NaI-NaOH, NaSiO ₄ , NaSiO ₄ -NaI-NaOH, Na ₂ SiS ₃ , Na ₄ SiO ₄ , _{Na 4 SiO 4 -NaI-NaOH,} Na 3 PO 4 -Na 2 has a nitride, a halide, a sulfate such as Na, such as S-SiS ₂ can be used.

Further, the electrolyte may further contain other additives for the purpose of improving the charge-discharge characteristics, flame retardancy, and the like. Examples of the additive include pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, (N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, trichloroaluminum, fluoroethylene carbonate (FEC), propenesultone (PRS), vinylene carbonate VC), and the like.

The sodium secondary battery according to the present invention can be laminated, stacked, and folded in addition to winding, which is a general process. The battery case may have a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention. Such variations and modifications are intended to be within the scope of the appended claims.

[Example]

Example 1

(1) Preparation of positive electrode

A cathode active material slurry containing 95 wt.%, 2.5 wt.% And 2.5 wt.% Of NaCoO ₂ as a cathode active material, Super P as a conductive material and polyvinylidene fluoride (PVDF) as a binder was prepared, The slurry was coated on an aluminum current collector having a thickness of 12 mu m to a thickness of 70 mu m and dried to prepare a positive electrode.

(2) Manufacture of cathodes

Sodium foil was placed on a 50 mu m thick collector of carbon foam having an average pore size of 20 mu m and porosity of 70% and then inserted into pores of the copper foam through roll pressing to obtain an electrode composite . At this time, the sodium metal was adjusted to be 10% by weight based on the total weight of the electrode composite. Thereafter, a negative electrode was prepared by forming a 5 탆 thick polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP) sodium ion conductive protective film on the electrode composite by a doctor blade coating method.

(3) Preparation of sodium secondary battery

An electrode assembly having a polypropylene porous film interposed between the anode and the cathode was inserted into a battery case of a pouch type and then a non-aqueous electrolyte was injected into the battery case. After that, the battery was completely sealed to prepare a sodium secondary battery . At this time, an electrolytic solution containing 1M NaPF ₆ as a sodium salt was used as a non-aqueous electrolyte in a solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 3: 7 (volume ratio).

Example 2

A sodium secondary battery was prepared in the same manner as in Example 1, except that a negative electrode to which an electrode composite containing a carbon foam having a porosity of 50% was used was used as the negative electrode.

Example 3

A sodium secondary battery was prepared in the same manner as in Example 1, except that a negative electrode to which an electrode composite containing a carbon foam having a porosity of 95% was used was used as the negative electrode.

Example 4

A sodium secondary battery was prepared in the same manner as in Example 1, except that a negative electrode to which an electrode composite containing 5% by weight of sodium metal as a weight of the electrode composite was applied was used as the negative electrode.

Example 5

A sodium secondary battery was prepared in the same manner as in Example 1, except that a negative electrode to which an electrode composite containing a sodium metal in an amount of 50% by weight based on the weight of the electrode composite was used was used as the negative electrode.

Comparative Example 1

A sodium secondary battery was prepared in the same manner as in Example 1, except that an electrode composite in which a sodium ion conductive protective film was not formed was used as the cathode.

Comparative Example 2

As a negative electrode, a copper foil having a general thickness of 8 mu m instead of a carbon foam was coated with a 50 mu m thick sodium foil and a 5 mu m thick polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP) And a protective film were successively laminated on one another, a sodium secondary battery was produced in the same manner as in Example 1.

Comparative Example 3

A sodium secondary battery was prepared in the same manner as in Example 1, except that a sodium foil having a thickness of 50 탆 was laminated on a general copper current collector, which is not a carbon foam, as a cathode.

Experimental Example 1: Short Circuit Measurement of Sodium Secondary Battery

The sodium secondary batteries prepared in the above-mentioned Examples and Comparative Examples were subjected to repetition of charging at a current density of 0.1 C and discharging at a current density of 0.1 C, and the time point at which the battery was short-circuited was measured and shown in Table 1 below.

Kinds Cycle of battery Example 1 280 Example 2 110 Example 3 105 Example 4 150 Example 5 92 Comparative Example 1 80 Comparative Example 2 43 Comparative Example 3 21

Referring to Table 1, it can be seen that the sodium battery of the Example exhibits significantly improved battery life characteristics as compared with the sodium battery of the Comparative Example. That is, formation and growth of sodium dendrites were greatly suppressed when the porous carbon body was used as a current collector and all the constitutions of the present invention including a protective layer were satisfied. In particular, Example 1 in which the carbon foam having the porosity of 70% was used and the content of sodium metal was 10% by weight of the total weight of the electrode composite showed the best cell performance.

However, in the case where any one of the above components was not satisfied, that is, in the case where there was no protective layer (Comparative Example 1), or when a conventional copper foil was used in place of the porous carbon body as the collector (Comparative Examples 2 and 3) It can be confirmed that the short circuit occurs early.

On the other hand, it was confirmed from the above experiment that the effect of the porosity of the porous carbon body on dendrite growth inhibition was confirmed. Examples 2 and 3, in which the porosities of the carbon foam were 50% and 95%, respectively, showed remarkably excellent performance as compared with the comparative examples, but the dendrite inhibitory effect was somewhat reduced as compared with Example 1.

The effect of sodium metal content on dendritic growth inhibitory effect was also confirmed. Example 5, in which the sodium content was 50 wt% based on the total weight of the porous carbon body and the sodium metal, showed that the sodium dendrite growth inhibitory effect was somewhat reduced as compared with Example 1. However, when the content of sodium metal is too small, the battery performance may be lowered due to reduction of the active material, and therefore it is preferable that the content is in the range of 1 to 50% by weight.

As described above, the sodium electrode of the present invention uses a porous carbon body as a current collector and includes an ion conductive protective layer on its surface, so that the sodium dendritic blocking effect is superior to that of a sodium electrode using a conventional planar current collector, Thereby exhibiting significantly improved lifetime characteristics of 100% or more. In addition, the sodium electrode of the present invention can further suppress dendrite formation and growth by controlling the porosity of the porous carbon body and the content of the sodium metal to be filled.

Claims (11)

A porous carbon body into which a sodium metal is inserted; And
And an ion conductive protective layer formed on the surface of the porous carbon body,
Wherein the content of the sodium metal is 1 to 50 wt% based on the total weight of the porous carbon body and the sodium metal. delete The method according to claim 1,
Wherein the porous carbon body is at least one selected from the group consisting of activated carbon, graphite, graphene, carbon nanotube (CNT), carbon fiber, and carbon black. The method according to claim 1,
And the porosity of the porous carbon body is 50 to 99%. The method according to claim 1,
The average pore size of the porous carbon body is 5 to 500 占 퐉. The method according to claim 1,
Wherein the thickness of the porous carbon body is 10 to 300 占 퐉. The method according to claim 1,
Wherein the sodium ion conductivity of the ion conductive protective layer is 10 &lt; ^-7 &gt; S / cm or more. The method according to claim 1,
Wherein the ion conductive protective layer is at least one selected from the group consisting of NaPON, beta alumina, a hydride-based compound, a NASICON-based compound, and a perovskite-based compound. The method according to claim 1,
The ion conductive protective layer may be made of polyethylene oxide (PEO); Polyacrylonitrile (PAN); Polymethylmethacrylate (PMMA); Polyvinylidene fluoride (PVDF); Polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP); And -SO ₃ Na, 1 jong or more, a sodium electrode selected from polymers containing a -COONa or -ONa. The method according to claim 1,
Wherein the thickness of the ion conductive protective layer is 0.01 to 50 占 퐉. A sodium secondary battery comprising the sodium electrode according to any one of claims 1 to 10.