KR101827155B1 - Air electrode for lithium air battery and manufacturing method thereof - Google Patents

Abstract

The present invention relate to an air cell for lithium air cells, and a production method thereof. More specifically, the present invention relates to an air cell for lithium air cells, which is capable of remarkably increasing conductivity and catalytic activities by enlarging effective reaction area while minimizing a loss of weight in electrodes. To this end, a nitride-based nanorod catalyst is directly grown on one or both sides of a three-dimensional network-like carbon nanofiber structure to produce a nitride-based nanorod-carbon nanofiber composite. The present invention further relates to a production method thereof.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an air electrode for a lithium air battery,

The present invention relates to an air electrode for a lithium air cell and a method of manufacturing the same. More particularly, the present invention relates to an air electrode for a lithium air cell, and more particularly, to a method of manufacturing a nitride based nano- The present invention relates to an air electrode for a lithium air cell and a method for manufacturing the same, which can increase the effective reaction area by greatly improving the catalytic activity and conductivity and minimize the weight loss in the electrode.

Lithium air cells are electrochemical energy conversion devices consisting of a lithium cathode, a lithium ion conductive electrolyte, and an air electrode capable of reversible electrochemical reaction between oxygen and lithium ions.

In general, lithium air cells have a high theoretical energy density of 11,000 Wh / kg, which can provide higher energy densities than currently commercially available lithium ion batteries. In addition, it is inexpensive, environmentally friendly, and excellent in stability compared to conventional lithium ion batteries, and active research and development are progressing as an electric vehicle power source.

However, there are still many points to be improved in order to commercialize such a lithium air battery. Specifically, the current collector used in the lithium air battery should be light, and the reaction area should be kept wide so that high wettability with the electrolyte and oxygen permeability should be maintained. Porous metal mesh or metal foam is mainly used as the most commonly used lithium air battery current collector. Such a porous metal has deterioration characteristics due to oxidation, and there is a problem that the volume capacity per unit volume is lowered because the distance between wires (> 100 mu m) is very wide.

In addition, the ratio of the heavy metal to the amount of the active material is high, so that the energy density per weight is lowered, and the specific surface area is lowered due to the thick diameter (> 10 μm) of the wires constituting the mesh.

On the other hand, in a lithium air battery, an air electrode is a space where lithium, oxygen, and electrons meet to form lithium oxide (Li ₂ O ₂ ) and decompose. A composite in which a catalyst (active material), a conductive material and a binder are mixed on the surface of a current collector made of a porous metal mesh is applied to electrodes in the form of a slurry to prepare an air electrode.

Such a cathode has a problem in that a catalyst not exposed to the surface of the lithium air cell does not participate in the reaction. Further, there is a problem that the amount of catalyst loading is relatively reduced because the conductive material and the binder take up a considerable amount of the electrode plate weight. In addition, there are problems such as inhibiting the movement path of electrons due to disordered mixing of the catalyst and the conductive material, and forming excessive side reaction products (Li ₂ CO ₃ ) due to exposure to carbon.

Lithium air cells are required to use catalyst materials excellent in oxygen evolution reaction and oxygen reduction reaction activity in order to solve the above problems and have high lifetime characteristics.

In recent years, oxide catalysts have been widely used as cathode catalysts, but their life characteristics are poor due to low conductivity of the catalyst [Nano Lett. 2013, 13, 4190-4197].

In addition, research has been conducted on a technique in which a catalyst is loaded on a collector such as a Ni foam or a Ni mesh together with a conductive agent and a binder. However, this not only increases the weight of an actual battery but also causes a side reaction problem of an inactive component (Electrochimica Acta 132 (2014) 297306].

 [Nano Lett. 2013, 13, 4190-4197]  [Electrochimica Acta 132 (2014) 297306]

In order to solve the above-mentioned problems, the present invention provides a nitride-based nano-scale structure capable of replacing a metal current collector having a low specific surface area and a heavy weight while utilizing a metal nitride catalyst capable of replacing a metal oxide catalyst having low conductivity. Rod-carbon nanofiber composites, it has been found that by increasing the effective reaction area, the catalytic activity and conductivity can be greatly improved and the weight loss in the electrode can be minimized.

Accordingly, an object of the present invention is to provide an air electrode for a lithium air battery in which the catalyst characteristics are greatly improved while minimizing weight loss in the electrode.

Another object of the present invention is to provide a method of manufacturing an air electrode for a lithium air battery.

The present invention relates to a nitride-based nanorod-carbon nanofiber composite wherein a nitride nanorod is grown on one side or both sides of a three-dimensional network-shaped carbon nanofiber (CNF) structure, wherein the carbon nanofiber structure comprises a carboxyl group (-COOH ), A hydroxyl group (-OH), a sulfone group (-SO ₃ H), an amino group (-NH ₂ ) and an ammonium group (-NH ₄ ) Thereby providing a battery air electrode.

The present invention also provides a method for producing a polymer fiber, comprising: (a) preparing a polymer fiber; (b) heat treating the polymer fibers to produce a carbon nanofiber structure having a three-dimensional network shape; (c) modifying the surface of the carbon nanofiber structure by reacting the carbon nanofiber structure with an acid; (d) growing a metal oxide nanorod on one surface or both surfaces of the carbon nanofiber structure by hydrothermal synthesis after mixing a metal precursor with the surface-modified carbon nanofiber structure; and (e) Or both surfaces of the carbon nanofiber structure is subjected to a heat treatment in a nitrogen atmosphere to convert the metal oxide nanorods into nitride-based nanorods to produce a nitride-based nanorod-carbon nanofiber composite air electrode. A method of manufacturing an air electrode is provided.

The air electrode for a lithium air battery according to the present invention can be produced by growing a nitride-based nanoload catalyst directly on a three-dimensional network-shaped carbon nanofiber structure without using a binder, a conductive material, and a metal mesh or a metal foam- By manufacturing the nano-rod-carbon nanofiber composite material, the energy density per weight can be maintained, the current collecting characteristic can be maintained, and the weight loss in the electrode can be minimized.

Also, since the nitride-based nano-rods grown on the carbon nanofiber structure have a wide reaction area, the catalyst characteristics are excellent and the conductivity is excellent, which can greatly improve the charge / discharge capacity and lifetime characteristics.

In addition, it can serve as a carbon nanofiber-based collector, and has a three-dimensional network shape, which has an advantage of increasing the effective reaction area with a wide specific surface area.

In addition, it can be replaced with a conventional heavy nickel mesh to ensure light weight, excellent air permeability, electrolyte wettability (> 90%, oxygen permeability), excellent reaction stability and high price competitiveness.

1 is a schematic diagram illustrating a charge / discharge reaction of carbon nanofibers on which a nitride-based nanoload catalyst according to the present invention is grown.
FIG. 2 is a schematic view illustrating a process of manufacturing a carbon nanofiber in which a nitride nanorod according to the present invention is grown.
3 is a cross-sectional view of an air electrode for a lithium air battery according to the present invention.
4 is a photograph showing CNF, Co (OH) F / CNF, and Co ₄ N / CNF produced in the embodiment of the present invention.
5 is a SEM photograph of CNF, Co (OH) F / CNF, and Co ₄ N / CNF prepared in an embodiment of the present invention.
6 is a front and back SEM photograph of Co (OH) F / CNF prepared in an embodiment of the present invention.
7 is an EDS mapping image showing the distribution of Co and C elements in the cross section of Co (OH) F / CNF prepared in the embodiment of the present invention.
8 is a graph showing initial charging / discharging results of a lithium air cell manufactured in an embodiment (Co (OH) F / CNF) of the present invention and a comparative example (CNF).
FIG. 9 is a graph showing the results of life characteristics according to the number of cycles of a lithium air battery manufactured in Comparative Example (CNF) of the present invention.
FIG. 10 is a graph showing life characteristics of lithium air cells manufactured according to the embodiment of the present invention (Co (OH) F / CNF) according to the number of cycles.
FIG. 11 is a graph showing cell capacity changes according to the number of cycles of lithium air cells manufactured in Examples (Co (OH) F / CNF) and Comparative Examples (CNF) of the present invention.

Hereinafter, the present invention will be described in more detail with reference to one embodiment.

The present invention relates to an air electrode for a lithium air battery and a method of manufacturing the same.

Specifically, the present invention includes a nitride-based nanorod-carbon nanofiber composite wherein a nitride-based nanorod is grown on one side or both sides of a three-dimensional network-shaped carbon nanofiber structure, wherein the carbon nanofiber structure has a carboxyl group (-COOH) Modified with at least one member selected from the group consisting of a hydroxyl group (-OH), a sulfone group (-SO ₃ H), an amino group (-NH ₂ ) and an ammonium group (-NH ₄ ) Thereby providing an air electrode.

According to a preferred embodiment of the present invention, the carbon nanofiber structure may include a plurality of carbon nanofibers having a three-dimensional network shape. Specifically, the carbon nanofiber structure of the three-dimensional network shape may be a mesh, a non-woven fabric, or a paper. The carbon nanofiber structure has a very high conductivity, and a plurality of carbon nanofibers having an average diameter of 100 nm to 2 μm are formed in a network shape, and thus have excellent specific surface area and excellent air permeability, so that they can act as an ultra-light current collector .

The carbon nanofiber structure may have a porosity of 50 to 90% and an average thickness of 10 to 500 μm. If the porosity is less than 50%, oxygen is not sufficiently supplied to the electrolyte, which hinders a smooth reaction. If the porosity is more than 90%, the electrolyte may easily evaporate and the lifetime characteristics may deteriorate.

According to a preferred embodiment of the present invention, the nitride-based catalyst is a material which has not been studied much in the field of air electrode catalyst for lithium air cells, and has electric conduction characteristic comparable to metal, have. The nitride-based nano-rods used as the nitride-based catalyst in the present invention may be one or more selected from the group consisting of Co ₄ N, Co ₃ N, Co ₂ N and CoN.

According to a preferred embodiment of the present invention, the nitride-based nanorod-carbon nanofiber composite may be a nitride nanorod grown on one side or both sides of the carbon nanofiber structure. In some cases, the nitride-based nano-rods may be grown on the entire surface.

The growth amount of the nitride-based nano-rods may include 20 to 80 wt% based on the total content of the nitride-based nano-rods-carbon nanofiber composite. If the content is less than 20% by weight, the front surface of the carbon nanofiber structure can not be coated, thereby failing to achieve sufficient catalytic activity. If the content exceeds 80% by weight, the weight of the catalyst The capacity per weight can be excessively reduced.

According to a preferred embodiment of the present invention, the air electrode for a lithium air battery may further include a current collector layer if necessary. At this time, the material of the current collector layer may be at least one material selected from the group consisting of nickel, aluminum, gold, and carbon (carbon paper).

1 is a schematic diagram illustrating a charge / discharge reaction of carbon nanofibers on which a nitride-based nanoload catalyst according to the present invention is grown. Referring to FIG. 1, lithium ions in the electrolyte are reduced by electrons supplied from a carbon nanofiber structure during an oxygen reduction reaction (ORR) to form a solid lithium oxide (Li ₂ O ₂ ) on the surface of the nano rod . On the contrary, the oxygen evolution reaction (OER) reversibly decomposes lithium oxide to decompose into electrons and lithium ions, and the electrons migrate back to the carbon nanofiber structure and decompose lithium ions toward the electrolyte.

The method for producing an air electrode for a lithium air battery according to the present invention comprises the steps of: (a) preparing a polymer fiber; (b) heat treating the polymer fibers to produce a carbon nanofiber structure having a three-dimensional network shape; (c) modifying the surface of the carbon nanofiber structure by reacting the carbon nanofiber structure with an acid; (d) growing a metal oxide nanorod on one surface or both surfaces of the carbon nanofiber structure by hydrothermal synthesis after mixing a metal precursor with the surface-modified carbon nanofiber structure; and (e) Or both surfaces of the carbon nanofiber structure are heat treated in a nitrogen atmosphere to convert the metal oxide nanorods into nitride-based nanorods to produce a nitride-based nanorod-carbon nanofiber composite air electrode.

That is, the air electrode for a lithium air battery according to the present invention is manufactured by preparing a carbon nanofiber structure having a porous three-dimensional network shape through electrospinning and high-temperature carbonization, and forming a high-conductivity nitride- Based nano-rod-carbon nanofiber composite air electrode.

According to a preferred embodiment of the present invention, in the step (a), the polymer fiber is selected from the group consisting of polyurethane, cellulose acetate, cellulose, acetate butyrate, polymethylmethacrylate polymethyl methacrylate (PMMA), polymethyl acrylate (PMA), polyvinyl acetate (PVAc), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA) (PE), polypropylene oxide (PPO), polycarbonate (PC), polyvinylchloride (PVC), polycaprolactone, polyvinyl fluoride, poly Polyacrylate, polyimide, polyacrylonitrile (PAN), polyvinyl alcohol (PVA), polycarbonate (PC), polyaniline (PANI) At least one selected from the group consisting of polyvinylidene fluoride (PVDF), polyethylene terephthalate (PET), polypropylene (PP), and polyethylene (PE) have.

According to a preferred embodiment of the present invention, in the step (b), the carbon nanofiber structure may have a porosity of 50 to 90% and an average thickness of 10 to 500 μm.

According to a preferred embodiment of the present invention, the heat treatment in the step (b) comprises: (b-1) performing a first heat treatment in an air atmosphere at a temperature of 230 to 400 ° C for 30 minutes to 2 hours; And (b-2) conducting a second heat treatment at a temperature of 600 to 1000 DEG C for 1 to 6 hours under an argon atmosphere.

At this time, in the first heat treatment step, the carbon molecular structure can be stabilized by cyclizing the nitrile group to a ladder structure. The first heat treatment is preferably conducted in an air atmosphere or an oxygen atmosphere.

Next, the second heat treatment step is a carbonization step of removing an amine group and forming a ribbon structure in which carbon atoms are arranged in a hexagonal pattern. In the carbonization step, heat treatment is performed in a non-oxidizing gas atmosphere such as argon, nitrogen, .

Since the surface of the carbon nanofiber structure produced in the step (c) is hydrophobic, it impedes the growth of the nanorod during the hydrothermal synthesis. Therefore, in order to facilitate the growth of the nanorod, it is preferable that the carbon nanofiber structure is surface- modified to be hydrophilic. Specifically, the (c) nano-carbon fiber structures in the step is a carboxyl group (-COOH), hydroxyl (-OH), sulfonic group (-SO ₃ H), amino groups (-NH _2), and an ammonium group (-NH ₄₎ Or at least one hydrophilic surface modification selected from the group consisting of

According to a preferred embodiment of the present invention, the acid in step (c) is at least one selected from the group consisting of nitric acid (HNO ₃ ), hydrochloric acid (HCl) and sulfuric acid (H ₂ SO ₄ ) For 1 to 6 hours. If the heat treatment temperature is lower than 25 ° C, there is a problem that the surface modification takes a longer time. If the heat treatment temperature is higher than 60 ° C, excessive surface modification may occur and the carbon nanofibers may deteriorate the electrical conductivity.

According to a preferred embodiment of the present invention, the metal precursor in step (d) is selected from the group consisting of cobalt nitrate (CO (NO ₃ ) ₂ 6H ₂ O), cobalt acetate (CH ₃ COO) ₂ CO, cobalt acetate hydrate CH ₃ COO) may be selected from ₂ 4H ₂ O), cobalt chloride (CoCl _2), and cobalt acetylacetonate (at least one member selected from the group consisting of _{Co (C 5 H 7 O 2} ) 3). In such a metal precursor, cobalt is a transition metal having a very high OER activity upon charging and excellent in price competitiveness.

According to a preferred embodiment of the present invention, the hydrothermal synthesis in step (d) may be performed at 100 to 140 ° C for 6 to 12 hours. When the hydrothermal synthesis temperature is less than 100 ° C, the metal oxide nanorod may grow irregularly in a plate form or a particle form. If the hydrothermal synthesis temperature is higher than 140 ° C, the metal oxide nanorod may grow into a very large cubic form. And preferably at a temperature of 110 to 120 DEG C for 6 to 8 hours. More preferably, the metal oxide nanorods may be uniformly grown on the surface of the carbon nanofiber structure by hydrothermal synthesis at a temperature of 120 ° C for 6 hours.

According to a preferred embodiment of the present invention, in the step (e), the metal oxide nanorod may be at least one selected from the group consisting of Co (OH) F, CoO and Co ₃ O ₄ . The metal oxide nanorod may have an average diameter of 20 nm to 100 μm.

According to a preferred embodiment of the present invention, in the step (e), the nitride-based nano-rod may be at least one selected from the group consisting of Co ₄ N, Co ₃ N, Co ₂ N and CoN. The nitride-based nano-rods may have an average diameter of 10 nm to 100 μm.

According to a preferred embodiment of the present invention, the heat treatment in step (e) may be performed at 400 to 550 ° C for 1 to 8 hours. If the annealing temperature is lower than 400 ° C., there is a problem that a single nitride-based nano-rod phase is not sufficiently formed. If the annealing temperature is higher than 550 ° C., the nano-rod structure may not be maintained and collapse may occur.

According to a preferred embodiment of the present invention, the growth amount of the nitride-based nano-rods in the step (e) may be 20 to 80 wt% based on the total content of the nitride-based nano-rod-carbon nanofiber composite.

FIG. 2 is a schematic view illustrating a process of manufacturing a carbon nanofiber in which a nitride nanorod according to the present invention is grown. In FIG. 2, the nitride nanorods are grown on one carbon nanofiber. Specifically, a polyacrylonitrile (PAN) fiber is heat-treated with a polymer fiber to produce a strand of a carbon nanofiber structure, and the surface of the carbon nanofiber structure is reacted with an acid to form a hydrophilic surface having a carboxyl group (-COOH) . And then a cobalt-based metal precursor is mixed to grow a metal oxide nanorod on both surfaces of the carbon nanofiber structure, followed by heat treatment in a nitrogen atmosphere to produce a nitride-based nanorod-carbon nanofiber composite.

3 is a cross-sectional view of an air electrode for a lithium air battery according to the present invention. Referring to FIG. 3, an air electrode for a lithium air battery in which a nitride nanorod-carbon nanofiber composite is laminated on a current collector layer is shown as an example. However, the current collector layer in the air electrode is not necessarily included because the nitride-based nano-rod has excellent metallic conductivity and excellent electric conductivity.

Therefore, the air electrode for a lithium air battery of the present invention can be produced by growing a nitride-based nanoload catalyst directly on a carbon nanofiber structure without using a conventional binder, a conductive material, and a metal mesh or a metal foam- By manufacturing a nano-rod-carbon nanofiber composite material, the energy density per weight can be very high compared to the conventional collector, and excellent current collecting characteristics can be maintained.

Particularly, the nitride-based nano-rods grown on the carbon nanofiber structure have a wide reaction area and are excellent in catalytic properties and conductivity. Furthermore, by providing a highly conductive nitride-based nano-rod-carbon nanofiber composite air electrode without the use of a binder and a conductive material, there is a great advantage that weight loss in the electrode can be minimized.

In addition, it can serve as a carbon nanofiber-based collector, and has a three-dimensional network shape, which has an advantage of increasing the effective reaction area with a wide specific surface area. As a result, the catalyst characteristics are excellent and the conductivity is excellent, so that the charge-discharge capacity and the life characteristic can be greatly improved.

In addition, it can secure lightness by replacing the existing heavy nickel mesh, and it can have excellent air permeability and electrolyte wettability (> 90%, oxygen permeability) because it is porous.

In addition, it has an advantage of excellent reaction stability and high price competitiveness.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by the following Examples.

Example: Lithium air cell manufacturing

(1) Synthesis of carbon nanofibers (CNF)

Carbon nanofiber (CNF) was fabricated by electrospinning and post-heat treatment. First, 1 g of polyacrylonitrile (PAN, Mw = 150,000 g / mol) was dissolved in 6 g of N, N-dimethylformamide (DMF, 99.8%) and stirred at 80 ° C for 3 hours to prepare a viscous polymer solution Respectively. The solution was injected into the syringe for electrophoresis and the gap between the syringe and the drum type collector was reduced to about 15 cm. Then, a voltage of 12 kV was applied and the scanning speed was maintained at 12 μL / min. Thereafter, the charged polymer solution was ejected from the tip of the injection needle by an electrical repulsive force, and the polymer was stretched by viscosity with the grounded collecting part and collected. The PAN nanofibers thus obtained were stabilized by heating at about 250 ° C for 1 hour in an air atmosphere, followed by carbonization at 900 ° C for 2 hours in an argon atmosphere to obtain pure amorphous CNF.

 (2) Synthesis of CO (OH) F / CNF

The synthesized CNF paper had a hydrophobic surface and was stirred for 2 hours in a 70% aqueous solution of nitric acid in order to modify it to be hydrophilic. The surface-modified CNF was washed several times with distilled water (DI water) and then dried in an oven at 50 ° C. Next, 0.291 g of cobalt nitrate hydrate (Co (NO ₃ ) ₂ 6H ₂ O) and 0.093 g of ammonium fluoride (NH ₄ F) were added to prepare a cobalt (Co) catalyst solution for hydrothermal reaction ) And 0.3 g of element (Urea, Co (NH ₂ ) ₂ ) were added to 20 ml of distilled water and stirred for 30 minutes or more to obtain a solution for hydrothermal synthesis. Then, the surface-modified CNF was added to the solution, stirred for 1 hour or more, placed in a 50 ml Teflon-lined autoclave container, and maintained at 120 ° C for 6 hours. At this time, one side of CNF was masked with polyimide tape for electrical contact. After the reaction was completed and the vessel was cooled, the resulting Co (OH) F / CNF paper was washed several times with distilled water and ethanol, and sufficiently dried in an oven at 50 ° C.

(3) Synthesis of Co ₄ N / CNF

The dried Co (OH) F / CNF paper was flowed at a flow rate of 100 sccm of ammonia (NH ₃ ) gas in a tube furnace at 450 ° C. for 2 hours, and the cobalt nitride (Co ₄ N) coated Co ₄ N / CNF Were synthesized.

(4) Manufacture of lithium air cell

Finally, to analyze the electrochemical characteristics, the Co ₄ N / CNF paper was punched with a punch of 11.8 mm diameter and used as an air electrode. The surface coated with Co ₄ N was oriented in the direction of the lithium negative electrode, And a gas diffusion layer. Then, a Swagelok type cell was assembled. The electrolyte used was tetra (ethylene) glycol dimethyl ether (TEGDME) in which 1 M lithium bis (trifluoromethane) sulfonimide (LiTFSI) salt was dissolved and the air electrode maintained 1 atm of oxygen.

Comparative Example: Production of carbon nanofiber (CNF)

A lithium air cell was manufactured in the same manner as in the above example, except that the carbon nanofibers prepared in (1) of the above Example were used as the air electrode.

Experimental Example 1: SEM measurement of CNF, Co (OH) F / CNF and Co ₄ N / CNF prepared in the above Examples and Comparative Examples

The cross sections of CNF, Co (OH) F / CNF and Co ₄ N / CNF prepared in the above Examples and Comparative Examples were measured by scanning electron microscopy (SEM). The results are shown in Figs. 4-7.

4 is a photograph showing CNF, Co (OH) F / CNF and Co ₄ N / CNF produced in the above embodiment. Referring to FIG. 4, since pure CNF is composed only of carbon, it is black, and when hydrothermal synthesis proceeds, Co (OH) F is coated on the surface of CNF to show purple color. When it is nitrided again, Co (OH) F is converted to Co ₄ N and black again.

5 is a SEM photograph of CNF, Co (OH) F / CNF and Co ₄ N / CNF prepared in the above embodiment. Referring to FIG. 5, it has been confirmed that CNF has a structure in which fibers on a smooth surface are disorderly entangled. After hydrothermal synthesis, the nanorods of Co (OH) F were grown vertically on the surface of CNF. Finally, after the nitridation heat treatment, Co (OH) F crystallized as Co ₄ N, and the thickness was partially contracted, but the one-dimensional nanorod shape was well maintained.

6 is a front and back SEM photograph of Co (OH) F / CNF prepared in the above embodiment. Referring to FIG. 6, it can be seen that Co ₄ N nanorods are uniformly grown on the front surface of Co (OH) F / CNF, and Co ₄ N nanorods are hardly grown on the back surface. It was found that Co ₄ N was formed on the front surface and CNF surface was exposed on the back surface because the masking was performed only on the back surface during the hydrothermal synthesis. As a result, it was confirmed that Co ₄ N nanorods catalyzed on the front surface and high current collecting characteristics of pure CNF on the back surface.

7 is an EDS mapping picture showing the distribution of Co and C elements in the cross section of Co (OH) F / CNF prepared in the above embodiment. Referring to FIG. 7, it can be guessed that Co ₄ N is selectively formed on the front surface during the subsequent heat treatment, since Co is mainly distributed on the front surface since hydrothermal synthesis is performed after masking on the back surface. Only CNF was present.

Experimental Example 2: Evaluation of characteristics of the lithium air cells prepared in the above Examples and Comparative Examples

The electrochemical characteristics of the lithium air cells prepared in the above Examples and Comparative Examples were evaluated at initial charging / discharging characteristics at a rate of 100 mA / g and charge / discharge life characteristics were evaluated at a rate of 200 mA / g. The results are shown in Figures 8-11.

FIG. 8 is a graph showing initial charging / discharging results of lithium air cells manufactured in the above-described examples (Co (OH) F / CNF) and Comparative Example (CNF). Referring to FIG. 8, it is confirmed that the Co ₄ N / CNF electrode exhibits a higher charge / discharge capacity, efficiency, and lower overvoltage than the CNF electrode. The results show that the Co ₄ N / CNF electrode not only enhanced the reaction specific surface area but also catalyzed the Co ₄ N nanorod on the surface to facilitate the formation and decomposition of lithium oxide.

FIG. 9 is a graph showing life characteristics of lithium air cells manufactured in the comparative example (CNF) according to the number of cycles. Referring to FIG. 9, it can be seen that the number of cycles of the lithium air battery follows a constant charge / discharge curve at an early stage, and the overvoltage suddenly increases from 30 cycles or more.

FIG. 10 is a graph showing the results of life characteristics according to the number of cycles of a lithium air battery manufactured in the embodiment (Co (OH) F / CNF). Referring to FIG. 10, it can be seen that the cycle number of the lithium air battery follows a very stable charge / discharge curve up to the initial 50 times, and the discharge overvoltage increases slightly from the number of cycles of 55 or more, I could.

9 and 10, the gap between the charge and discharge curves is 1.93 V for the CNF electrode, while the Co ₄ N / CNF electrode is 1.66 V for the Co ₄ N nano-rod. there was.

FIG. 11 is a graph showing changes in cell capacity according to the number of cycles of lithium air cells manufactured in the above-described embodiment (Co (OH) F / CNF) and Comparative Example (CNF). Referring to FIG. 11, it can be seen that the CN ₄ electrode maintains a limited capacity value of 55 mA or more while the Co ₄ N / CNF electrode maintains a limited capacity value of 1000 mAh / g for 30 times while rapidly decreasing .

As a result, when porous noble metal (Co ₄ N / CNF) is used as an air electrode by growing cobalt nitride (Co ₄ N) on a carbon nanofiber (CNF) structure as in the above embodiment, And it was confirmed that it exhibited excellent electrochemical characteristics and long-life lithium air battery characteristics.

Claims (17)

Based nano-rod-carbon nanofiber composite in which a nitride-based nano-rod is grown on one side or both sides of a three-dimensional network-shaped carbon nanofiber structure,
The carbon nanofiber structure is a carboxyl group (-COOH), hydroxyl (-OH), sulfonic group (-SO ₃ H), amino groups (-NH _2), and an ammonium group at least one member selected from the group consisting of (-NH ₄₎ The air electrode for a lithium air battery according to claim 1,
The method according to claim 1,
Wherein the carbon nanofiber structure is in the form of a mesh, a nonwoven fabric or a paper.
The method according to claim 1,
Wherein the carbon nanofiber structure has a porosity of 50 to 90% and an average thickness of 10 to 500 μm.
The method according to claim 1,
Wherein the nitride-based nano-rods are at least one selected from the group consisting of Co ₄ N, Co ₃ N, Co ₂ N and CoN, and the average diameter of the nitride-based nanorods is 10 nm to 100 μm. Battery air electrode.
The method according to claim 1,
Wherein the growth amount of the nitride-based nano-rods is 20 to 80 wt% based on the total content of the nitride-based nano-rods-carbon nanofiber composite.
(a) preparing a polymer fiber;
(b) heat treating the polymer fibers to produce a carbon nanofiber structure having a three-dimensional network shape;
(c) modifying the surface of the carbon nanofiber structure by reacting the carbon nanofiber structure with an acid;
(d) growing a metal oxide nanorod on one side or both sides of the carbon nanofiber structure by hydrothermal synthesis after mixing the metal precursor with the surface-modified carbon nanofiber structure; and
(e) heat treating the carbon nanofiber structure in which the metal oxide nanorods are grown on one surface or both surfaces in a nitrogen atmosphere to convert the metal oxide nanorods into nitride-based nanorods to form a nitride nanorod-carbon nanofiber composite air electrode Producing;
Wherein the air electrode is made of a metal.
The method according to claim 6,
In the step (a), the polymer fiber may be selected from the group consisting of polyurethane, cellulose acetate, cellulose, acetate butyrate, polymethyl methacrylate (PMMA), polymethyl acrylate Polymers such as polymethyl acrylate (PMA), polyvinyl acetate (PVAc), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polypyryl alcohol (PPFA) ), Polyethylene oxide (PEO), polypropylene oxide (PPO), polycarbonate (PC), polyvinylchloride (PVC), polycaprolactone, polyvinyl fluoride, polyimide, polyacrylonite Polyacrylonitrile (PAN), polyvinyl alcohol (PVA), polycarbonate (PC), polyaniline (PANI), polyvinylidene fluoride The present invention relates to a method for manufacturing an air electrode for a lithium air battery, which comprises at least one member selected from the group consisting of polyvinylidene fluoride (PVDF), polyethylene terephthalate (PET), polypropylene (PP), and polyethylene .
The method according to claim 6,
Wherein the carbon nanofiber structure has a porosity of 50 to 90% and an average thickness of 10 to 500 m in the step (b).
The method according to claim 6,
The heat treatment in the step (b)
(b-1) a first heat treatment in an air atmosphere at a temperature of 230 to 400 ° C for 30 minutes to 2 hours; And
(b-2) conducting a second heat treatment at a temperature of 600 to 1000 DEG C for 1 to 6 hours in an argon atmosphere;
The method of claim 1, further comprising:
The method according to claim 6,
(C) the carbon nanofibers in the step structure is the group consisting of carboxyl group (-COOH), hydroxyl (-OH), sulfonic group (-SO ₃ H), amino groups (-NH _2), and an ammonium group (-NH ₄₎ Wherein the surface modification is performed on at least one member selected from the group consisting of Ni, Ti, and Ni.
The method according to claim 6,
In the step (c), the acid is at least one selected from the group consisting of nitric acid (HNO ₃ ), hydrochloric acid (HCl) and sulfuric acid (H ₂ SO ₄ ) and is heat treated at a temperature of 25 to 60 ° C. for 1 to 6 hours Wherein the air electrode is made of a metal.
In the sixth aspect,
In step (d), the metal precursor may be at least one selected from the group consisting of cobalt nitrate (CO (NO ₃ ) ₂ 6H ₂ O), cobalt acetate (CH ₃ COO) ₂ CO, cobalt acetate hydrate (Co (CH ₃ COO) ₂ 4H ₂ O) , Cobalt chloride (CoCl ₂ ), and cobalt acetylacetonate (Co (C ₅ H ₇ O ₂ ) ₃ ). The method of manufacturing an air electrode for a lithium air battery according to claim 1,
The method according to claim 6,
Wherein the hydrothermal synthesis in step (d) is performed at 100 to 140 ° C for 6 to 12 hours.
The method according to claim 6,
In the step (e), the metal oxide nanorod is at least one selected from the group consisting of Co (OH) F, CoO and Co ₃ O ₄ , and the average diameter of the metal oxide nanorod is 20 nm to 100 μm Wherein the air electrode is made of a metal.
The method according to claim 6,
In the step (e), the nitride-based nano-rods are at least one selected from the group consisting of Co ₄ N, Co ₃ N, Co ₂ N and CoN, and the average diameter of the nitride- Wherein the air electrode is made of a metal.
The method according to claim 6,
Wherein the heat treatment in step (e) is performed at 400 to 550 ° C for 1 to 8 hours.
The method according to claim 6,
Wherein the growth amount of the nitride-based nano-rods in the step (e) is 20 to 80 wt% based on the total content of the nitride-based nano-rods-carbon nanofiber composite.

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