KR102226920B1 - Electrode for lithium-air battery and method for producing the same - Google Patents

Abstract

The electrode for a lithium-air battery according to the present invention is a carbon nanotube; _{And RuO 2} deposited on the surface of the carbon nanotube.

Description

Electrode for lithium-air battery and manufacturing method thereof {ELECTRODE FOR LITHIUM-AIR BATTERY AND METHOD FOR PRODUCING THE SAME}

The present invention relates to an electrode for a lithium-air battery and a lithium-air battery including the same.

Rechargeable lithium-air (Li-O ₂ ) batteries have a much higher theoretical energy density than lithium-ion batteries, and are attracting attention as a promising technology in electric energy storage systems that will support long-distance electric vehicles.

In general, an electrode of a lithium-air battery contains carbon and a polymeric binder. However, carbon and polymer binders of lithium-air batteries cause unwanted parasitic decomposition reactions during charging and discharging, and as a result, there is a problem in that the performance of the battery is deteriorated.

Accordingly, there have been several efforts to enhance the activity against _{electrochemical Li 2} O ₂ decomposition while stabilizing carbon against parasitic reactions. _{For example, Al 2} O _{3 was} coated on the surface of carbon or carbon black powder (Super P Li) using an atomic layer deposition (ALD) process to passivate the surface defect. Subsequently, in order to improve the charging performance, a Pd nano catalyst was deposited on the carbon powder surface-modified with _{Al 2} O _{3 through an ALD process.}

This carbon surface engineering strategy has been proven to be effective in improving the circulation potential of lithium-air (Li-O _{2) batteries.} However, the procedure is complicated and time consuming in that the two ALD processes are used to separately deposit oxides and noble metals.

Furthermore, even if carbon is stabilized, the negative electrode (or positive electrode) for a _{lithium-air (Li-O 2} ) battery contains a polymeric binder that is easily decomposed in the presence _{of Li 2} O _2. For example, PVdF (polyvinylidene fluoride) is decomposed to form LiF and Li ₂ CO ₃ , and thus the electrode may be passivated.

Accordingly, there is a need for a new technology for an electrode for a lithium-air battery that will improve the above-described problems.

An object of the present invention is to improve the performance and stability of a lithium-air battery by inhibiting the parasitic decomposition reaction during the charging and discharging process and promoting the decomposition of the discharge product.

The electrode for a lithium-air battery according to an embodiment of the present invention includes a carbon nanotube; And RuO2 deposited on the surface of the carbon nanotube.

In one embodiment, the RuO2 is characterized in that it is deposited on the surface defect site of the carbon nanotube.

In one embodiment, the RuO2 is characterized in that the particle size is 1.0 ~ 4.0nm.

In one embodiment, the RuO2 is characterized in that it suppresses the decomposition of carbon at the surface defect site of the carbon nanotubes, and promotes the decomposition of _{Li 2} O _{2 formed on the surface of the carbon nanotubes.}

In one embodiment, the surface-modified carbon electrode is characterized in that it does not contain a binder.

In one embodiment, the lithium-air battery electrode is characterized in that the positive electrode in the lithium-air battery.

In an embodiment, the RuO2 is deposited by an atomic layer deposition (ALD) process.

Lithium-air battery electrode manufacturing method according to an embodiment of the present invention comprises the steps of forming a sheet of carbon nanotubes; And depositing RuO2 on the surface of the carbon nanotube.

In one embodiment, the step of depositing the RuO2 is characterized in that the RuO2 is deposited on a surface including a surface defect site on the surface of the carbon nanotube.

In an embodiment, the RuO2 is deposited by an atomic layer deposition (ALD) process.

In one embodiment, the forming of the sheet from the carbon nanotubes is characterized in that the free-standing sheet is formed from the carbon nanotubes without a binder.

According to the present invention, RuO ₂ is deposited on the surface of the carbon nanotube and the surface is modified, thereby suppressing parasitic decomposition reactions in the charging and discharging process, and promoting decomposition of the discharge product, thereby having excellent electrochemical performance, and has excellent electrochemical performance, and the charge and discharge cycle life is reduced. It is possible to provide an electrode for an enhanced lithium-air battery and a method of manufacturing the same.

1 shows a method of manufacturing an electrode for a lithium-air (Li-O _{2) battery according to an embodiment of the present invention.}
2 shows the results of analyzing the crystal structure and phase of the carbon nanotubes before the ALD process and the carbon nanotubes on which RuO _{2 is deposited by the ALD process through X-ray diffraction analysis (XRD).}
3 is a TEM (transmission electron microscope) image of detailed morphology and microstructure of _{RuO 2} nanoparticles deposited on carbon nanotubes through an ALD process.
4 is a TEM image of a carbon nanotube on which _{RuO 2 is deposited at low magnification.}
5 is an image of a carbon nanotube and a carbon nanotube on which RuO ₂ is deposited with a scanning electron microscope (SEM).
6 is an SEM photograph of a cross section of a carbon nanotube (N _{cycle ) on which RuO 2} is deposited together with energy dispersive spectroscopy (EDS) data.
7 shows charge/discharge profiles of a carbon electrode including a carbon nanotube and a surface-modified carbon electrode including a carbon nanotube on which _{RuO 2 is deposited.}
FIG. 8 is an image of an ex-situ SEM of a surface-modified carbon electrode including carbon nanotubes on _{which discharged and charged RuO 2} is deposited to confirm a reaction product during operation of a lithium-air battery.
9 shows the Li 1s XPS spectrum for the discharged and charged surface modified carbon electrode (N _{cycle =20).}
10 shows the O 1s XPS spectrum for the discharged and charged surface modified carbon electrode (N _{cycle =20).}
11 shows the test results of testing the cycle stability of the surface-modified carbon electrode with ^{a limited capacity of 0.5 mAh/cm 2.}

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings in order to clarify the technical idea of the present invention. In describing the present invention, if it is determined that a detailed description of a related known function or component may unnecessarily obscure the subject matter of the present invention, a detailed description thereof will be omitted. For convenience of explanation, if necessary, a device and a method will be described together.

The present invention provides a surface-modified carbon electrode including a carbon nanotube surface-modified by depositing on the surface of _{RuO 2} acting as an inhibitor-accelerator as a _{rechargeable lithium-air (Li-O 2} ) battery electrode. . That is, the surface-modified carbon electrode includes a carbon nanotube surface-modified by depositing _{RuO 2 on the surface.} The surface-modified carbon electrode may not contain a binder. The surface-modified carbon electrode may be formed by arranging carbon nanotubes in a plate shape. The surface-modified carbon electrode may be formed in the form of a fabric in which carbon nanotubes are woven with weft and warp. The surface-modified carbon electrode may be formed in a plate shape having a network structure in which carbon nanotubes form a three-dimensional network.

The surface-modified carbon electrode exhibits excellent electrochemical performance with a small voltage gap (0.9V) between charging and discharging. In addition, the surface-modified carbon electrode has excellent charge/discharge cycle characteristics of 80 cycles or more without reducing the capacity.

1 shows a method of manufacturing an electrode for a lithium-air (Li-O _{2) battery according to an embodiment of the present invention.}

Referring to FIG. 1, a method of manufacturing an electrode for a lithium-air battery may include forming a carbon-based material and depositing a metal oxide on the carbon-based material using an atomic layer deposition (ALD) process.

In one embodiment, the carbon-based material used in an electrode for a lithium-air battery may be a carbon nanotube. The carbon nanotubes may have improved stability compared to an electrode containing a binder. In one embodiment, the carbon nanotube sheet may be manufactured using a vacuum filtration method. The carbon nanotube sheet may be manufactured as a free-standing sheet through a filtration process without using a binder.

A method of manufacturing the carbon nanotube sheet according to an embodiment is as follows. First, a 150 ml beaker containing 100 ml of deionized water (DI Water) and 0.1 g of carbon nanotubes is prepared. While stirring the deionized water and carbon nanotubes using a stirrer, 1 g of TritonX was added, and homogeneously dispersed for 1 hour using an ultrasonic device. Heat generated during ultrasonic dispersion can be cooled using an ice bath. In addition to the cooling operation, the ultrasonic dispersion operation is repeated 2-3 times. Thereafter, a first vacuum filtration was performed by adding 200 ml of methanol to 15 ml of a carbon nanotube solution, and a second vacuum filtration was performed by adding 250 ml of distilled water. When performing vacuum filtration, a porous membrane filter (Membrance Filter, PVDF Membrane, 0.22 micropore size) may be used as a filter paper. Finally, the carbon nanotube sheet may have a thickness of about 26 to 34 μ (micron) and a diameter of 42 mm. The carbon nanotube sheet may be dried at 70° C. for 12 hours and applied to an atomic layer deposition process.

In one embodiment, the metal oxide used in the lithium-air battery electrode may be _RuO-2. The RuO ₂ may be deposited on the surface of the carbon nanotube. The RuO ₂ may be deposited on a surface defect site present on the surface of the carbon nanotube. The RuO ₂ may be deposited on the surface of the carbon nanotubes to perform a dual role as an inhibitor-accelerator of the carbon nanotubes. More specifically, the RuO ₂ may serve as an inhibitor that is deposited on the surface of the carbon nanotube at the defect site to inhibit carbon decomposition that mainly proceeds at the defective site of the carbon nanotube.

Meanwhile, a carbon-based material such as the carbon nanotube is a negative electrode (or positive electrode) material most widely used in a lithium-air battery, and carbon causes a parasitic decomposition reaction with _{Li 2} O _{2 to generate carbonate species.} Accordingly, the cathode (or anode) including carbon may be problematic due to a large voltage gap and poor cycling performance. In addition, according to recent studies, it is reported that the surface structure and chemical properties of carbon have a significant effect on the stability of lithium-known batteries. In particular, in the case of the carbon-based material having a structural defect of carbon, a parasitic reaction may occur more actively in defects (dangling bonds, kinks, functional groups, etc.) existing on the carbon surface. In addition, the carbon-based material may increase the number of defect sites vulnerable to carbon decomposition during repeated charge/discharge cycles.

According to an embodiment of the present invention, the RuO ₂ is deposited on the surface defect site of the carbon nanotube to passivate the structural defect of the carbon nanotube. Therefore, the RuO ₂ acts as an inhibitor that inhibits decomposition of carbon at the defective site of the carbon nanotube, thereby reducing parasitic reactions and reducing the number of defective sites.

In addition, the RuO ₂ may serve as an accelerator for accelerating the decomposition of _{Li 2} O- ₂ in the carbon nanotubes. In general, the electrode of a lithium-air battery _{does not sufficiently decompose the discharge product (Li 2} O ₂ ) during the charging and discharging process and accumulates on the surface, and this prevents lithium ions and oxygen from contacting the electrode surface, and thus the capacity cannot be expressed. It is known to have a limitation of. The RuO ₂ is deposited on the surface of the carbon nanotubes _{and acts as an accelerator for electrochemically promoting the decomposition of Li 2} O ₂ , thereby improving the above-described problems.

The RuO- ₂ may be deposited on the surface of the carbon nanotube by an atomic layer deposition (ALD) process. The RuO- ₂ is deposited on the surface of the carbon nanotube by the ALD process, thereby reducing the load of Ru while maintaining high catalytic performance.

The ALD process comprises (1,5-hexadiene)(I-isopropyl-4-methylbenzene)((1,5-hexadiene)(I-isopropyl-4-methylbenzene))Ru complex and O ₂ at 250°C. It can be done while feeding alternately. The ALD process may be performed to form _{Ru and/or RuO 2} according to deposition conditions such as temperature, pressure, gas flow rate and pulse time. Deposition conditions for the ALD process may RuO ₂ may be determined in consideration of exhibiting a high activity against a Li ₂ O ₂ decomposition, to allow the RuO ₂ selectively deposited on the carbon nanotube surface.

2 shows the results of analyzing the crystal structure and phase of the carbon nanotubes before the ALD process and the carbon nanotubes on which RuO _{2 is deposited by the ALD process through X-ray diffraction analysis (XRD).}

Referring to FIG. 2, _{it can be seen that the RuO 2} was deposited on the surface of the carbon nanotube by the ALD process. In Figure 2 (a), the X-ray diffraction (XRD) pattern of the carbon nanotube electrode on which _{RuO 2 is deposited is the phase of the square crystal rutile RuO-2} (space 17 group P4 ₂ /mnm, JCPDS No. 43-1027). In (b) of FIG. 2 _{, the X-ray photoelectron spectroscopy (XPS) data for the carbon nanotube electrode on which RuO 2} is deposited is a typical characteristic of _{RuO 2} in addition to the C 1s peak at which the binding energy (BE) of the carbon nanotubes is ~ 284.6 eV. _{It can be seen that the Ru 3d 5/2} peak is exhibited at ~280.7 eV of phosphorus.

The loading (or particle size) of the RuO ₂ can be controlled by changing the number of cycles of the ALD process. On the other hand, the RuO ₂ can generate and grow nuclei at a low temperature at a high speed (short culture cycle) by a Ru precursor treated to have evaporation and pyrolysis properties.

3 is a TEM (transmission electron microscope) image of detailed morphology and microstructure of _{RuO 2} nanoparticles deposited on the surface of a carbon nanotube through an ALD process. 4 is a TEM image of a carbon nanotube on which _{RuO 2 is deposited at low magnification.}

Referring to FIG. 3, it can be seen that _{the particle size of the RuO 2} increases from 1.3 nm to 2.5 nm and 3.4 nm, respectively, as the number of cycles of the ALD process is increased from 10 to 20 and 40. That is, _{it can be seen that the particle size of the RuO 2} can be controlled by adjusting the number of cycles in the ALD process. The particle size of the RuO ₂ may be 1.0nm ~ 4.0nm.

On the other hand, referring to FIG. 4, it can be confirmed that the density of the number of particles is similar while the _{number of cycles of the ALD process increases and the particles of RuO 2 become larger. According to this, it can be seen that the region where RuO 2} , a precursor of the ALD process, is deposited on the surface of the carbon nanotube is determined by the surface properties of the carbon nanotube. That is, _{it can be seen that the RuO 2} mainly aggregates at the defect site of the carbon nanotube.

5 is an image of a carbon nanotube and a carbon nanotube on which RuO ₂ is deposited with a scanning electron microscope (SEM). 6 is an SEM photograph of a cross section of a carbon nanotube (N _{cycle ) on which RuO 2} is deposited together with energy dispersive spectroscopy (EDS) data.

The carbon nanotubes are formed in a porous structure, and may have a porous structure even after _{the RuO-2 is deposited.} Referring to FIG. 5, it can be seen that the carbon nanotubes can be formed in a porous structure regardless of the number of cycles in the ALD process. That is, the microstructure of the carbon nanotubes may be preserved even during the ALD process. Referring to FIG. 6, it can be seen that the carbon nanotube on which RuO-2 is deposited has a thickness of 30 μm, and Ru and O elements are uniformly distributed over the thickness direction.

7 shows a charge/discharge profile of a carbon electrode including a carbon nanotube and a surface-modified carbon electrode including a carbon nanotube on which _{RuO 2 is deposited.} Referring to FIG. 7, when the carbon electrode including the carbon nanotubes before the ALD process and the surface-modified carbon electrode including the carbon nanotubes subjected to the ALD process at the number of cycles of 10, 20, and 40 are completely discharged, they are all similar per unit area. It can be seen that it shows a capacity (~1.5mAh/cm ² ₎ and a stable potential (~2.7V vs. Li/Li ^{+ ).} On the other hand, the charge-voltage gap between the discharge can determine the (reduced from ~ 1.58V to about 0.90V ~) The carbon nanotube also greatly reduced in the electrode RuO _2- is deposited by an ALD process.

8 is an image of an ex-situ SEM of a surface-modified carbon electrode including a carbon nanotube on _{which discharged and charged RuO 2} is deposited to confirm a reaction product during operation of a lithium-air battery. Specifically, 2.0V vs. After discharging with Li/Li ⁺ , afterwards 4.35V vs. Charged with Li/Li ^+. Referring to FIG. 8, it can be seen that the completely discharged electrode is _{covered with toroid-shaped Li 2} O ₂ particles having a size of 200 to 300 nm. After recharging, it can be confirmed that the Li ₂ O ₂ particles, which are discharge products, are completely decomposed and are not found in the electrode.

9 shows the Li 1s XPS spectrum for the discharged and charged surface modified carbon electrode (N _{cycle =20).} 10 shows the O 1s XPS spectrum for the discharged and charged surface modified carbon electrode (N _{cycle =20). Referring to FIG. 9, it can be confirmed that Li 2} O ₂ (BE 54.7 eV) was the main discharge product through the Li 1s XPS spectrum of the discharged surface-modified carbon electrode. Small traces of Li ₂ CO ₃ (BE 55.3 eV) species can emerge from electrolyte decomposition. In addition, through the Li 1s XPS spectrum of the charged surface-modified carbon electrode, _{it can be confirmed that Li 2} O- ₂ was completely decomposed and disappeared during charging. _{In addition, referring to FIG. 10, it can be seen that Li 2} O- ₂ is reversibly formed and decomposed during operation of the battery in the spectrum of the surface-modified carbon electrode.

11 shows the test results of testing the cycle stability of the surface-modified carbon electrode with ^{a limited capacity of 0.5 mAh/cm 2.} Referring to (a) of FIG. 11, the electrode including the carbon nanotubes before the ALD process is 4.5V vs. It can be seen that charging is required above Li/Li ^+. The need for such a high voltage is due to the large amount of carbonate by-products formed as a result of carbon decomposition and electrolyte decomposition. Furthermore, the high voltage can further accelerate the decomposition of the electrolyte and electrode. On the other hand, the surface-modified carbon electrode on which _{RuO 2 is deposited is ~ 4.0V vs.} Li/Li ⁺ at 4.0V vs. It can be seen that it has a voltage of Li/Li ^+.

In addition, referring to (b) of FIG. 11, the surface-modified carbon electrode on which _{RuO 2 is deposited (N cycle} = 20 and 40) exhibits excellent cycle performance without any signs of capacity reduction for 80 cycles, but the exposed surface-modified carbon It can be seen that the electrode failed after 32 cycles.

From the results of FIGS. 7 to 11 described above, it was confirmed that the RuO ₂ nanoparticles deposited on the surface of the carbon nanotube by the ALD process act as an efficient accelerator capable of promoting the electrochemical decomposition of carbon and Li ₂ O _2. I can. The surface-modified carbon electrode formed of highly porous carbon nanotubes surface-modified with nanoparticles of RuO _{2 described above is suitable for applications requiring high capacity, such as electric vehicles.} For example, lithium-air (Li-O ₂ ) In addition to the negative electrode (or positive electrode) for a battery, it may be applied to a super capacitor.

An embodiment of the present invention is as follows. The following examples are illustrative of the technical features of the present invention, and the present invention is not limited to the examples.

<Example>

1. Preparation of binder-free carbon nanotubes

Using Triton X-100 (1.0 g) as a surfactant, 0.1 g of carbon nanotubes (diameter 15-30 nm and length 15-30 μm) were dispersed in 100 ml of deionized water, followed by sonication for 1 hour. The well-dispersed carbon nanotube suspension was vacuum filtered through a polytetrafluoroethylene (PTFE) membrane and washed with water and methanol to remove any residual surfactant. The resulting carbon nanotube sheet was peeled off from the PTFE membrane and dried at 60° C. for 12 hours in a vacuum state. Typical diameters, thicknesses and weights of the obtained carbon nanotube sheets were ~3.5 cm, ~30 μm, and ~1.4 mg/cm ^2, respectively.

2. ALD process of _{RuO 2}

The ALD process of RuO ₂ was carried out in traveling wave mode via an on-demand alternating flow reactor. The raw material of Ru was (1,5-hexadiene) (1-isopropyl-4-methylbenzene) Ru _{having the chemical formula C 16} H ₂₄ Ru (Mw = 317.43 gmol ^{-1 ).} The Ru canister and delivery line were heated at 100° C. and 110° C., respectively. The Ru reactant was fed through a glass bubbler at a flow rate of 20 cm 3 /min, which ensured a sufficient vapor pressure for the Ru reactant. Oxygen (20 cm ³ /min) was supplied as an oxidizing agent in the reaction chamber. Ar gas was used as a carrier (40cm ³ /min). The ALD process was _{carried out under an operating pressure of 400 Pa in a circulation mode of C 16} H ₂₄ Ru feed (16s)-Ar purge (120s)-O2 feed (10s)-Ar purge (90s).

So far, the present invention has been looked at in detail centering on the preferred embodiments shown in the drawings. These embodiments are not intended to limit the present invention, but are merely illustrative, and should be considered from an illustrative point of view rather than a restrictive point of view. Those of ordinary skill in the technical field to which the present invention pertains will understand that various modifications and other equivalent embodiments are possible without departing from the essential technical idea of the present invention claimed in the claims.

Claims (11)

delete delete delete delete delete delete delete Forming a sheet of carbon nanotubes; And
Including the step of depositing _{RuO 2} on the surface of the carbon nanotube,
The step of depositing the RuO2,
_{Depositing the RuO 2} on the surface of the carbon nanotube including the surface defect site by an atomic layer deposition (ALD) process,
The RuO ₂ inhibits carbon decomposition at the surface defect site of the carbon nanotube,
The ALD process comprises (1,5-hexadiene)(I-isopropyl-4-methylbenzene)((1,5-hexadiene)(I-isopropyl-4-methylbenzene))Ru complex and O ₂ at 250°C. Lithium-air battery electrode manufacturing method, characterized in that carried out while alternately supplying delete delete delete

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