KR20110056803A - Air electrode for metal-air secondary battery, method for preparing the same and metal-air secondary battery - Google Patents

Abstract

PURPOSE: An air electrode for a metal-air secondary battery is provided to realize oxygen reduction and oxygen evolution as a catalyst and to enable reversible charging/discharging. CONSTITUTION: A method for preparing an air electrode for a metal-air secondary battery comprises the steps of: wet injecting La(NO3)36H2O into a platinum-loaded gas diffusion electrode; drying the gas diffusion electrode to which lanthanum(La) is injected in a vacuum atmosphere; and drying the gas diffusion electrode at 200-250 °C for 3 hours in an atmospheric condition.

Description

Air electrode for a metal air secondary battery, a method of manufacturing the same and a metal air secondary battery comprising the air electrode {Air electrode for metal-air secondary battery, method for preparing the same and metal-air secondary battery}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air electrode for a metal air secondary battery, a method for manufacturing the same, and a metal air secondary battery including the air electrode, and catalyzes both an oxygen reduction and an oxygen evolution reaction. By introducing an air electrode to provide a stable metal air secondary battery capable of reversible charging and discharging.

Due to the rapid development of electronic products and high expectations of high performance electric power sources of consumers, many products with high energy consumption are appearing. However, current fuel cell or battery technologies have not yet met this demand. In recent years, lithium ion batteries are considered to be the most widely used secondary batteries and have the highest power generation potential. However, despite the extensive research, there are still many problems to be solved, and various limitations such as relatively low theoretical energy unit density and natural reserves of lithium have been derived. Therefore, there is a need for a next-generation secondary battery capable of reducing manufacturing costs while exhibiting high performance to replace a lithium ion secondary battery.

Among them, the most feasible battery is a metal air battery. The metal-air secondary battery eliminates the problems related to the generation and storage of hydrogen, which is a challenge for fuel cells, because the metal is used as a fuel, and the anode is a battery that attracts and discharges using oxygen in the air as a fuel. It is expected to be the next generation secondary battery that can replace lithium secondary battery in the future.

Metal air batteries have many advantages such as high energy, competitive cost, abundant resources, and environmentally friendly characteristics in specific areas. As a result, it is highly promising as a future power source and energy storage medium. For example, Goldstein et al. Reported that zinc ion batteries have four times higher unit density and are five times cheaper than lithium ion batteries.

There are two types of metal air batteries, primary batteries and rechargeable batteries. Metal air primary batteries are widely used in low power electronic products such as hearing aids. Rechargeable metal air batteries, however, are still commercially available and there are some technical problems. A key challenge lies in the development of high performance air electrodes. Problems of zinc electrodes include low cycle stability, high decomposition rate, passivation, and self-discharge, which have been gradually improved through recent studies on electrochemical cells using zinc electrodes.

However, disadvantages of air electrodes have not yet been overcome due to the complexity of the electrochemical reactions on the electrodes. Oxygen reduction and evolution reactions (ORR / OER) are the most basic processes for charging and discharging rechargeable metal air batteries. Since air electrodes are used in irreversible systems with high activation voltages in aqueous solutions, the choice of electrolytes for such reactions is limited to precious metals or their alloys, transition metal oxides and the like.

Although several air electrode catalysts have recently been introduced, there are no extensive studies on metal air batteries, and few studies have shown the reversibility within a limited charge / discharge cycle.

The current state of the technology of metal-air batteries is limited to primary batteries in Korea, and there are no studies conducted on it except for the initial stage. In foreign countries, several companies use their own systems to manage the shortcomings and lifetime of other fuel cells. In order to improve the environmental problems, the production and storage of hydrogen, and the price to overcome the research, but most of the electrical charging (electrical charging), rather than mechanical charging (mechanical charging) research is in progress. In addition, the study of the electrical charging method is mainly at the basic stage due to technical barriers, and in the case of patents, the invention is mainly related to the structure of the battery, the peripheral device of the battery and the primary battery.

Therefore, the first problem to be solved by the present invention is to provide an air electrode having a complex function as a catalyst for both the reduction and generation reaction of oxygen.

The second problem to be solved by the present invention is to provide a metal air secondary battery capable of reversible charging and discharging by employing the air electrode.

A third object of the present invention is to provide a method for manufacturing the secondary electrode air electrode.

In order to achieve the first object, in the gas diffusion electrode loaded with platinum (Pt), lanthanum nitrate acting as a catalyst for both a reduction and generation reaction of oxygen is introduced. Provide an electrode.

According to one embodiment of the present invention, the amount of platinum loaded on the gas diffusion electrode is preferably 0.1 to 1.0 mg / cm ² , more preferably 0.5 mg / cm ² .

In addition, according to an embodiment of the present invention, the thickness of the gas diffusion electrode is preferably 400 to 500 μm, more preferably 410 μm.

In addition, according to another embodiment of the present invention, the amount of lanthanum injected into the gas diffusion electrode is preferably 3 to 30% by weight.

In order to solve the second technical problem, the present invention provides a metal electrode made of a metal selected from the group consisting of Zn, Al, Mg, Fe, and Li, and air in which lanthanum nitrate is added as a catalyst to a gas diffusion electrode loaded with platinum. Provided is a metal air secondary battery including an electrode. In this case, the metal electrode is preferably a zinc (Zn) electrode.

In order to solve the third technical problem, the present invention comprises the steps of wet injecting La (NO ₃ ) 36H ₂ O to the platinum (Pt) loaded gas diffusion electrode; Drying the lanthanum (La) -injected gas diffusion electrode under vacuum; It provides a method for producing a secondary electrode air electrode comprising a; and drying the dried electrode under atmospheric conditions for 3 hours at 200-250 ℃.

The air electrode according to the present invention has a complex function capable of oxygen reduction and oxygen evolution by adding lanthanum nitrate as a catalyst to a platinum-loaded gas diffusion electrode. By using the electrode, the metal-air primary battery currently used can be used as a secondary battery. Therefore, it is possible to accelerate the commercialization of next-generation secondary batteries that can replace lithium secondary batteries in the future with secondary batteries having improved energy density, rich reserves of components, and low price than lithium secondary batteries.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The air electrode for a metal air secondary battery according to the present invention is characterized in that lanthanum nitrate, which acts as a catalyst for both a reduction and generation reaction of oxygen, is introduced into a gas diffusion electrode loaded with platinum (Pt).

According to one embodiment of the present invention, the amount of platinum loaded on the gas diffusion electrode is preferably 0.1 to 1.0 mg / cm ² , more preferably 0.5 mg / cm ² .

In addition, the thickness of the gas diffusion electrode is preferably 400 to 500 µm, more preferably 410 µm. In addition, the amount of lanthanum injected into the gas diffusion electrode is preferably 3 to 30% by weight.

In addition, the metal-air secondary battery according to the present invention includes a metal electrode made of a metal selected from the group consisting of Zn, Al, Mg, Fe, Li, and an air electrode in which lanthanum nitrate is added as a catalyst to the gas diffusion electrode loaded with platinum. In this case, the metal electrode is preferably a zinc (Zn) electrode.

On the other hand, the method of manufacturing an air electrode for a secondary battery according to the present invention comprises the steps of wet injection of La (NO ₃ ) 36H ₂ O to the platinum (Pt) loaded gas diffusion electrode; Drying the lanthanum (La) -injected gas diffusion electrode under vacuum; And drying the dried electrode under atmospheric conditions at 200-250 ° C. for 3 hours.

Hereinafter, the present invention will be described in more detail with reference to preferred examples. However, these examples are intended to illustrate the present invention in more detail, it will be apparent to those skilled in the art that the scope of the present invention is not limited thereby.

Example 1 Preparation of Zinc Electrode (Anode)

82 wt% commercially available ZnO powder (manufactured by Umicore, 99.8%), a solution in which 10 wt% Ketjen Black (KB) is dispersed, 3 wt% Bi ₂ O ₃ (made by Daejung), 1 wt% Ca (OH) ₂ (Manufactured by Junsei Co., Ltd.) and 4% by weight of polytetrafluoroethylene (PTFE) was pasted on a porous Ni foam support to prepare a zinc electrode. The addition of KB improves the mechanical and electrochemical properties, and Ca (OH) ₂ forms a passivation film of calcium zincate at the electrode / electrolyte interface, greatly reducing the solubility of zinc, thereby suppressing morphological changes and Extends life Although calcium zincate has many advantages, there is a problem of limiting battery performance due to low conductivity. To solve this problem, Bi ₂ O ₃ was added as a conductive additive, and the prepared zinc electrode was dried at 70 ° C. and pressed to a thickness of 0.3 mm.

Example 2 Preparation of Air Electrode (cathode)

Commercially available Pt / C gas diffusion electrode (GDE, E-Tek HT-140E-W, Pt loading = 0.5 mg / cm) using La (NO ₃ ) ₃ · 6H ₂ O (manufactured by Aldrich, 99.99%) as a precursor ² , thickness = 410㎛) La-Pt / C air electrode was prepared by varying the La loading using a conventional wet injection method. The La injected GDE was dried under vacuum and then heated at atmospheric conditions at 200-250 ° C. for 3 hours. La composition of the air electrode thus prepared was 3.43, 14.0 and 28.6% by weight.

Test Example: Charge / Discharge Characteristics Test

The structure of the sample was confirmed by X-ray diffraction (XRD) using Rigaku DMAX-III and Bruker D8 Focus diffractometers equipped with Cu targets. In addition, the morphology and distribution of components in the sample were examined by FE-SEM-EDS (Hitachi S-4300 and Jeol JSM-7500F) analysis. And, in order to measure the electrochemical performance, the main components such as Zn and zinc electrodes, electrolytes, separators were assembled, zinc electrode and air electrode was prepared according to the above embodiment.

On the other hand, the electrolyte using the aqueous solution containing 3.8 M KOH, 2.5 M NaOH, and 1.2 M LiOH, has the maximum ion conductivity, to minimize the shape change of the zinc electrode. In addition, the charge and discharge test was performed using a WBCS 3000 instrument (manufactured by Won-A Tech Co., Ltd., Korea).

To test the chargeability of the cell, the charge / discharge cycle of the cell with ZnO and a commercially available common gas diffusion electrode (GDE) was monitored (rate and extent of the oxygen evolution reaction).

1 is a graph showing charge and discharge voltage results using a zinc electrode and Pt loaded GDE (charge: 1.25 mA / cm ² and discharge: 0.25 mA / cm ² ). As shown in Figure 1, the initial charging and discharging process shows a relatively normal state, but after the charge and discharge shows a meaningless result. In other words, the charge and discharge characteristics were very unstable, and as the number of cycles increased, the cycling performance decreased steeply, and after some cycles, the cell could not function as a secondary battery.

In air-zinc cells, the reaction at the cathode during charging and discharging is influenced by the catalyst. When platinum (Pt) was introduced into the oxygen reduction catalyst as in the present invention, the oxygen reduction reaction proceeded considerably during the discharge process. However, even when using a gas diffusion electrode in which platinum was introduced, no oxygen generation reaction occurred during the charging process. That is, platinum (Pt) is a catalyst for the oxygen reduction reaction, and shows a normal discharge in the first cycle, but since there is no catalytic activity for the oxygen generating reaction during charging, charging does not occur normally, except for the first cycle. Show you Therefore, in the present invention, the oxygen generating catalyst was added to the air electrode.

In the reversible charging and discharging process, it is necessary to provide oxygen generation and / or bifunctional catalyst to the air electrode. In the present invention, in order to enhance reversibility, lanthanum was injected into the electrode and observed. In other words, a catalyst containing lanthanum was used as an oxygen generation and / or bifunctional (for oxygen reduction and generation reaction) catalyst. For example, like transition metal oxide catalysts, La ₂ O ₃ is used as an oxidation catalyst that allows both oxygen evolution and reduction due to its non-stoichiometry. In addition, the catalytic activity of lanthanum-containing catalysts is closely related to defect sites or nonstoichiometric properties, and oxygen transport on the catalyst can increase its activity. The relationship between catalyst activity and defect structure is not fully explained, but the relationship is generally accepted.

Specifically, in the embodiment of the present invention after preparing the air electrode by injecting a gas diffusion layer (GDL: La (NO ₃ ) _{3 ·} 6H ₂ O showing catalytic activity in both the oxygen reduction and generation reaction, The experiment was conducted by assembling with a zinc electrode.

Figure 2 is a SEM and EDS results of the air electrode loaded with a lanthanum-based catalyst by the injection method. As can be seen in the EDS it can be seen that the lanthanum catalysts are evenly distributed throughout the electrode.

Figure 2 shows the morphology and La distribution of the air electrode made of La composition 14.0 wt.%. The morphology of the air electrode shown in FIG. 2 (a) did not change as compared to the morphology of simple Pt / C GDE. Figure 2 (b) shows the La distribution of the air electrode obtained from the EDS, and shows the La uniformly distributed over the entire air electrode. The detailed morphology of the lanthanum-containing air electrode is shown in FIG. 2 (c). XRD data (not shown) of an air electrode containing lanthanum shows a mixed state of partially oxidized or decomposed lanthanum lanthanum nitrate, such as lanthanum oxynitrate, lanthanum carbonate and lanthanum hydroxide.

The decomposition of lanthanum nitrate is dependent on the ambient conditions such as residual water vapor pressure, oxidation conditions, inert conditions, and reducing conditions. It is also well known that fully or partially oxidized lanthanum usually reacts with H ₂ O and CO _{2 in the} atmosphere, which forms carbonates and / or hydroxides. This is also likely due to the reaction of the final product with gas molecules in the atmosphere. However, the formation of carbonates and hydroxides cannot be ruled out as a major product during the manufacturing of air electrodes.

In addition, FIG. 3 is a result of charging and discharging a battery using a zinc electrode and an air electrode loaded with a lanthanum-based catalyst. Unlike platinum, which acts only as an oxygen reduction catalyst, the lanthanum-based catalyst reacts with oxygen reduction and oxygen generation as compared with FIG. 1. Since it has activity on both sides, it shows the charge and discharge characteristics of a normal secondary battery.

At constant charging conditions, the cycling characteristics of the cells with ZnO and 14.0 wt.% La loaded Pt / C gas diffusion electrodes were investigated for reversibility and cycling stability evaluations, and cycling stability and discharge capacity were shown in FIGS. 3 and 4, respectively. It is clearly shown that reversibility and stability have been enhanced.

On the other hand, in the 43 wt.% La loaded air electrode, the charge and discharge characteristics were similar to those of the Pt / C electrode. As the amount of La loading increased, the performance of the battery gradually improved. After a few tenth cycles, the formation of white powder on the outer surface of the air electrode was observed, which turned out to be oxide by Fourier transform IR spectroscopy. It is assumed that this was produced by the reaction between hydroxide ions in the electrolyte and CO ₂ in the atmosphere. The formation of carbon oxides causes chemical species and catalyst reactions by changing the diffusion rate and path of oxygen to the air electrode, and the discharge capacity decreases as the number of cycles increases because the rate of oxygen reduction reaction decreases. Become one.

After the charge and discharge test, the morphology of the zinc electrode was examined by SEM, and a small amount of dendrite and morphology change were observed. Addition of an additive containing bismuth oxide and calcium hydroxide to the zinc electrode can effectively inhibit the formation and morphology of Zn dentrite.

The present invention demonstrated the reversibility of rechargeable zinc-air cells using lanthanum loaded air electrodes. The lanthanum-loaded air electrode was prepared by a wet injection method using La (NO ₃ ) ₃ 6H ₂ O precursor and commercially available Pt / C GDE. This has been shown to enhance the reversibility and stability of rechargeable zinc air batteries. Reversibility is unstable even when loading a small amount of lanthanum, but the performance of the cell gradually increased as the lanthanum loading increased. This is meaningful in that it shows the possibility that the rechargeable zinc air battery can be one of the next generation secondary batteries.

1 is a graph of charge and discharge voltage using a gas diffusion electrode (GDE) loaded with a zinc electrode and platinum.

FIG. 2 is a photograph showing (a) SEM results and (b) EDS results for lanthanum of an air electrode loaded with a lanthanum nitrate catalyst, and FIG. 2 (c) shows a more detailed morphology.

3 is a charge and discharge voltage graph of an air-zinc secondary battery using a lanthanum nitrate catalyst.

4 is a graph showing the discharge capacity of an air-zinc secondary battery using a lanthanum nitrate catalyst.

Claims (11)

An air electrode for a secondary battery, characterized in that lanthanum nitrate, which acts as a catalyst, is introduced into a gas diffusion electrode loaded with platinum (Pt). The method of claim 1, The amount of platinum loaded on the gas diffusion electrode is 0.1 ~ 1.0 mg / cm ² Air electrode for a metal air secondary battery, characterized in that. The method of claim 1, The thickness of the gas diffusion electrode is a metal air secondary battery air electrode, characterized in that 400 ~ 500㎛. The method of claim 1, The amount of lanthanum injected into the gas diffusion electrode is an air electrode for a metal air secondary battery, characterized in that 3 to 30% by weight. A metal-air secondary battery comprising a metal electrode made of a metal selected from the group consisting of Zn, Al, Mg, Fe, and Li, and an air electrode in which lanthanum nitrate is added to a gas diffusion electrode loaded with platinum. The method of claim 5, The metal electrode is a metal air secondary battery, characterized in that the zinc (Zn) electrode. Wet injecting La (NO ₃ ) 36H ₂ O into the platinum (Pt) loaded gas diffusion electrode; Drying the lanthanum (La) -injected gas diffusion electrode under vacuum; And Drying the dried electrode under atmospheric conditions for 3 hours at 200-250 ℃; manufacturing method of a secondary electrode air electrode comprising a. The method of claim 7, wherein The metal electrode is a zinc (Zn) electrode manufacturing method of a secondary battery air electrode, characterized in that. The method of claim 7, wherein The amount of platinum loaded on the gas diffusion electrode is a method of manufacturing a secondary electrode air electrode, characterized in that 0.1 ~ 1.0 mg / cm ² . The method of claim 7, wherein The thickness of the gas diffusion electrode is a manufacturing method of the secondary electrode air electrode, characterized in that 400 ~ 500㎛. The method of claim 7, wherein The amount of lanthanum (La) injected into the gas diffusion electrode is a method of manufacturing a secondary electrode air electrode, characterized in that 3 to 30% by weight.

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