KR20220017081A - Air electrode active material and electrochemical device including the same - Google Patents

Abstract

The present invention relates to a cathode active material and an electrochemical device including the same. The electrochemical device comprises: an anode and an electrolyte layer positioned on the anode. On the electrolyte layer, a cathode having a composition of Ca_3Co_4O_(9-δ) (0 < δ < 1) and having an active material doped with an alkali metal at the Ca site is positioned. The cathode active material has a misfit structure and can improve the electrochemical catalytic properties and electrical conductivity as well as the durability of the electrochemical device by controlling the doping material and the doping amount.

Description

Air electrode active material and electrochemical device including the same

The present invention relates to an active material, and more particularly, to a cathode active material.

A fuel cell is a device that directly converts the chemical energy of fuel and air into a cell and heat through an electrochemical reaction. Unlike the existing power generation technology, which takes the combustion of fuel, steam generation, turbine driving, and generator driving processes, the fuel cell has no combustion process or driving device, so it not only has high efficiency but also does not cause environmental problems. Such a fuel cell emits almost no air pollutants such as SOx and NOx, generates less carbon dioxide, is pollution-free power generation, and has advantages such as low noise and no vibration.

Fuel cells are phosphoric acid fuel cell (PAFC), alkaline fuel cell (AFC), anion exchange membrane fuel cell (AEMFC), polymer electrolyte fuel cell (Polymer electrolyte) There are various types, such as a membrane fuel cell (PEMFC), a direct methanol fuel cell (DMFC), and a solid oxide fuel cell (SOFC). Among them, for example, a solid oxide fuel cell (SOFC) is an electrochemical device that produces electricity and hydrogen through an electrochemical reaction of hydrogen and oxygen based on a ceramic-based material. are receiving However, it is necessary to study how to lower the temperature due to the high manufacturing cost and low durability due to the high operating temperature.

In order to solve this problem, a solid oxide fuel cell (SOFC) operating at a medium and low temperature and a protonic ceramic fuel cell (PCFC) using a proton conductive ceramic have been recently developed. Meanwhile, anion exchange membrane fuel cell (AEMFC) includes an electrolyte membrane that selectively transports hydroxide ions (OH ⁻ ), and is used at a low temperature from room temperature to about 80° C.

Therefore, both solid oxide fuel cells (SOFC) based on oxygen ion conductors, proton conductive ceramic fuel cells (PCFCs) based on hydrogen ion conductors, and anion exchange membrane fuel cells (AEMFCs) have low and medium temperature In terms of performance, the development of cathodes that exhibit high performance is the most important.

On the other hand, the electrolytic cell reaction, which is the reverse reaction of the fuel cell reaction, is a reaction that produces hydrogen through electrochemical decomposition of water. This hydrogen production is more environmentally friendly than the conventional hydrogen production method and shows high production efficiency.

That is, based on these advantages, research is being actively conducted on the fuel cell as a reversible electrochemical device that not only produces electricity through a fuel cell reaction, but also produces hydrogen through an electrolytic cell reaction. For the development of a reversible fuel cell, an electrode material having high catalytic activity is essential not only for the reaction step of the electrodes for the previously reported reaction of the fuel cell, but also for the reaction step of the electrodes for the electrolytic cell. In particular, the electrolytic cell reaction also has a mechanism different from the cathode reaction of the fuel cell, although the cathode is the main reaction rate determining step like the fuel cell reaction. Therefore, it is required to develop a dual-functional cathode material with better performance based on an understanding of the reaction mechanism in both the fuel cell and the electrolytic cell reaction.

An object of the present invention is to provide a cathode active material that can be used in both fuel cells and electrolytic cells, and can improve electrochemical catalytic properties and facilitate ion and electron migration. Accordingly, it is an object to provide an electrochemical device having improved electrochemical performance and durability by such a cathode active material.

In order to achieve the above object, an aspect of the present invention provides an electrochemical device. The electrochemical device includes an anode and an electrolyte layer positioned on the anode. Doedoe having a composition of Ca ₃ Co ₄ O _9-δ (0<δ<1) on the electrolyte layer, An cathode having an active material doped with an alkali metal is positioned at the Ca site.

The active material has a composition of M _x Ca _3-x Co ₄ O _9-δ (0 < δ < 1), wherein x is 0.1 to 0.3, and M may be Li, Na, or K. Specifically, M is Na, The x may be 0.13 to 0.18. As an example, the active material may be Na _0.15 Ca _2.85 Co ₄ O _9-δ .

The active material is, [CdI ₂ ] CoO ₂ layer having a crystal structure, and M _a Ca _2-a CoO _3-δ layer having a rock-salt structure (M is an alkali metal, 0.06≤a≤0.3, 0 ≤ δ ≤ 1) may have an alternately stacked crystal structure.

The active material may be particles having a diameter of several tens to several hundreds of nm. Specifically, the active material may be particles having an average diameter of 100 to 200 nm. The electrochemical device may be a proton conductive ceramic battery. In this case, the cathode may include a mixture of the active material and the proton conductive oxide. The proton conductive oxide is yttrium-doped barium zirconate (BZY), yttrium-doped barium cerate (BCY), yttrium-doped barium-zirconate-cerate (BZCY) or Yttrium- and ytterbium-doped barium-cerate-zirconate (BCZYYb) yl can

In order to achieve the above object, an aspect of the present invention provides another example of an electrochemical device. The electrochemical device includes an anode and an electrolyte layer positioned on the anode. On the electrolyte layer, a CoO ₂ layer having a crystal structure of [CdI ₂ ] and a M _a Ca _2-a CoO _3-δ layer having a rock-salt structure (M is an alkali metal, 0.06≤a≤ 0.3, 0 ≤ δ ≤ 1) is located in the cathode having an active material having a stacked crystal structure alternately. In the Ma Ca _{2-a CoO 3-δ} layer, a may be 0.09 to 0.12. The active material may be particles having a diameter of several tens to several hundreds of nm.

Another aspect of the present invention provides an active material to achieve the above object. The active material has a composition of Ca ₃ Co ₄ O _9-δ (0<δ<1), The Ca site is doped with an alkali metal. The active material has a composition of M _x Ca _3-x Co ₄ O _9-δ (0 < δ < 1), wherein x is 0.1 to 0.3, and M may be Li, Na, or K.

Another aspect of the present invention provides another example of an active material in order to achieve the above object. The active material is a CoO ₂ layer having a crystal structure of [CdI ₂ ] and a M _a Ca _2-a CoO _3-δ layer having a rock-salt structure (M is an alkali metal, 0.06≤a≤0.3, 0 ≤ δ ≤ 1) has an alternately stacked crystal structure.

The active material may be particles having a diameter of several tens to several hundreds of nm. Specifically, the active material may be particles having an average diameter of 100 to 200 nm.

According to the present invention, it is possible to provide a cathode active material having dual functionality for a fuel cell and an electrolytic cell. The cathode active material has a misfit structure, and by controlling the doping material and the doping amount, electrochemical catalytic properties and electrical conductivity as well as durability of the electrochemical device can be improved.

The technical effects of the present invention are not limited to those mentioned above, and other technical effects not mentioned will be clearly understood by those skilled in the art from the following description.

1A is a cross-sectional view schematically showing the structure of an electrochemical device according to an embodiment of the present invention.
FIG. 1b shows the crystal structure of the active material in the cathode of FIG. 1a in detail.
2 schematically shows a half-cell (a) according to the following half-cell manufacturing examples and a full battery (b) according to the following full-cell manufacturing examples.
3A is an X-ray diffraction (XRD) graph of active materials according to Preparation Examples B1, B3, and B5 of the active material, and FIG. 3B is an X-ray diffraction graph of the active materials according to Preparation Examples B6 to B10 of the active material, and FIG. 3c is an X-ray diffraction graph of the active materials according to Preparation Examples B11, B13, and B15 of the active material.
4 is an SEM image of the active material according to Preparation Example A8 of the active material.
5 is a graph (b) showing an SEM image (a) and a particle size distribution (PSD) of the active material according to Preparation Example B8 of the active material.
6 is a graph (b) showing an SEM image (a) and a particle size distribution (PSD) of the active material according to Preparation Example B13 of the active material.
7 is an SEM image of the active material according to Preparation Example B10 of the active material.
8 is a graph showing electrical conductivity in dry air atmosphere (a) and humidified air atmosphere (b) of batteries according to Half-cell Preparation Examples B1, B3, and B5, and Comparative Examples of half-cells.
9 is a graph showing the electrical conductivity in dry air atmosphere (a) and humidified air atmosphere (b) of batteries according to Half-cell Preparation Examples B6 to B10 and Comparative Examples of half-cells.
10 is a graph showing electrical conductivity in dry air atmosphere (a) and humidified air atmosphere (b) of batteries according to Half-cell Preparation Examples B11, B13, and B15.
11 is a graph showing electrical conductivity in dry air atmosphere (a) and humidified air atmosphere (b) of batteries according to Half-cell Preparation Examples B1, B6, and B11, and Comparative Examples of half-cells.
12 is a graph showing polarization and power density graphs (a, c, e) and impedance graphs (b, d, f) obtained while operating the batteries according to Full Cell Manufacturing Examples B6, B8, and B10 in a fuel cell mode; show
13 is a graph showing durability when the battery according to Preparation Example B8 of the full cell is operated in a fuel cell mode.
14 is an initial IV graph (a) obtained while operating the battery according to Preparation Example B8 of a full battery in electrolytic cell mode and an IV graph (b) obtained after a 50-hour durability test under constant current (200 mA/cm ² ) conditions. show
15 is a graph obtained while performing a 50-hour durability test under constant current (200 mA/cm ² ) conditions in an electrolytic cell mode for a battery according to Preparation Example B8 of a full battery.
16 is a graph showing polarization resistance (Rp) values obtained when the batteries according to Preparation Examples B6 to B10 of the full cell are operated at 650 degrees in a fuel cell mode (dry air) and an electrolytic cell mode (humidified air).
17 is a scanning electron microscope (SEM) image showing the results of post-mortem analysis after durability evaluation (FIG. 13) of the battery according to Preparation Example B8 of the full battery, (a) and (b) are cross-sections of the entire battery, (c) is a cross-section of the anode, (d) is a cross-section of the cathode, and (e) is a cross-section of the electrolyte.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

While the invention is susceptible to various modifications and variations, specific embodiments thereof are illustrated and illustrated in the drawings and will be described in detail hereinafter. However, it is not intended to limit the invention to the particular form disclosed, but rather the invention includes all modifications, equivalents and substitutions consistent with the spirit of the invention as defined by the claims.

It will be understood that when an element, such as a layer, region, or substrate, is referred to as being “on” another component, it may be directly on the other element or intervening elements in between. .

1A is a cross-sectional view schematically showing the structure of an electrochemical device according to an embodiment of the present invention, and FIG. 1B is a detailed view showing the crystal structure of the active material in the cathode of FIG. 1A.

Referring to FIG. 1A , in the electrochemical device according to an embodiment of the present invention, an anode 10, an electrolyte layer 20, and a cathode 30 are sequentially formed, and the cathode 30 is misfit. It has a structure, and may include an active material having a doping material.

The electrochemical device may be a fuel cell as a cell or an electrolytic cell operated by a reverse reaction thereof. Specifically, the electrochemical device is a phosphoric acid battery (PAC), an alkaline battery (AC), an anion exchange membrane cell (AEMC), a polymer electrolyte battery (PEMC), a direct methanol battery (DMC), molten It may be a carbonate cell (MCC), a solid oxide cell (SOC), and a protonic ceramic cell (PCC). However, the present invention is not limited thereto, and any electrochemical device including the cathode 30 may be used.

Specifically, the electrochemical device may be an anion exchange membrane cell (AEMC), an oxygen ion conductive solid oxide battery (SOC), or a protonic ceramic cell (PCC).

The anode 10 may include an ion conductor and a catalyst metal. The type of fuel oxidized in the anode 10 may vary depending on the type of the battery, and the catalyst metal may be in the form of an oxide.

When the electrochemical device is a proton conductive ceramic cell (PCC), the anode 10 may include a proton conductive oxide and a catalyst metal. The proton conductive oxide is, for example, BZY (yttrium-doped barium zirconate), BCY (yttrium-doped barium cerate), BZCY (yittrium-doped barium-zirconate-cerate) or BCZYYb (Yttrium- and ytterbium-doped barium-) cerate-zirconate), for example, BCZYYb (BaCe _0.7 Zr _0.1 Y _0.1 Yb _0.1 O _3-δ ). The catalyst metal may be any one or more selected from the group consisting of nickel (Ni), ruthenium (Ru), copper (Cu), palladium (Pd), rhodium (Rh), and platinum (Pt).

When the electrochemical device is an oxygen ion conductive solid oxide cell (SOC), the anode 10 may include an oxygen ion conductor and a catalyst metal. The oxygen ion conductor is an oxygen ion conductive metal oxide having a fluorite structure, and includes rare-earth-doped ceria (RDC), for example, neodymium-doped ceria (NDC), GDC ( gadolinium-doped ceria), and samarium-doped ceria (SDC); YSZ (yttria stabilized zirconia, ZrO ₂ /Y ₂ O ₃ ); and ScSZ (scandia stabilized zirconia, ZrO ₂ /Sc ₂ O ₃ ) may include one or more selected from the group consisting of. Exemplary materials of the catalyst metal may be the same as described above.

When the electrochemical device is an anion exchange membrane cell (AEMC), the anode 10 may include a hydroxide ion conductive oxide and a catalyst metal. The hydroxide ion conductive oxide may be the same as the oxygen ion conductor. In addition, the catalyst metal may be the same as described above.

As an example, the electrochemical device according to an embodiment of the present invention may be a proton conductive ceramic cell, wherein the anode 10 is BaCe _0.7 Zr _0.1 Y _0.1 Yb _0.1 O _3-δ (BCZYYb) and NiO may be a mixture of For example, the anode 10 may be a thin film having a thickness of about 1 μm to 50 μm, specifically, 10 μm to 30 μm.

The electrolyte layer 20 may vary depending on the type of the fuel cell. The electrolyte layer 20 may have a thickness of about 1 μm to 50 μm, specifically, about 5 μm to 10 μm, and may be in the form of a dense membrane having few pores.

When the electrochemical device is a proton conductive ceramic battery, the electrolyte layer 20 may include a proton conductive solid oxide to exhibit high proton conductivity. As an example, the proton conductive solid oxide is, for example, yttrium-doped barium zirconate (BZY), yttrium-doped barium cerate (BCY), yittrium-doped barium-zirconate-cerate (BZCY), or Yttrium- and ytterbium (BCZYYb). -doped barium-cerate-zirconate), for example, may be BCZYYb (BaCe _0.7 Zr _0.1 Y _0.1 Yb _0.1 O _3-δ ), but is not limited thereto.

When the electrochemical device is an oxygen ion conductive solid oxide battery, the electrolyte layer 20 may be an oxygen ion conductor layer. For example, the electrolyte layer 20 may be Yttria Stabilized Zirconia (YSZ), Scandia Stabilzied Zirconia (ScSZ), or Gadolinium doped Ceria (GDC), but is not limited thereto.

When the fuel cell is an anion exchange membrane cell, the electrolyte layer 20 may have high hydroxide ion conductivity, mechanical strength, and resistance to dehydration. For example, the electrolyte layer 20 may use an alkaline polymer film, for example, a polystyrene-based or polyamide-based polymer film, but is not limited thereto.

As an example, the electrochemical device according to an embodiment of the present invention may be a proton conductive ceramic battery, and the electrolyte layer 20 may be BCZYYb (BaCe _0.7 Zr _0.1 Y _0.1 Yb _0.1 O _3-δ ). .

The cathode 30 may include an active material having a M _x Ca _3-x Co ₄ O _9-δ (0< δ <1) composition having a misfit crystal structure. M is an alkali metal, and may be Li, Na, or K as an example. That is, the active material may be Ca ₃ Co ₄ O _9-δ (CCO) (0< δ <1) doped with an alkali metal. The x may be 0.05 to 0.5, specifically, 0.1 to 0.3, more specifically, 0.12 to 0.21, more specifically, 0.13 to 0.18, for example, 0.15. In other words, the Ca site is an alkali metal (M) in 3 to 15 mol%, specifically 3.3 to 10 mol%, more specifically 4 to 7 mol%, more specifically 4.5 to 6 mol%, for example 5 mol% may be substituted. However, the active material is not limited thereto, and Ca ₃ Co ₄ O _9-δ (CCO) may be doped with an alkali metal as well as a transition metal. In this case, the transition metal may be doped at the Co site. The transition metal may be copper (Cu), iron (Fe), manganese (Mn), or nickel (Ni).

The active material of the M _x Ca _3-x Co ₄ O _9-δ (0≤ δ ≤1) composition has a diameter of several tens to hundreds of nm, for example, a diameter of 50 to 300 nm, specifically having an average diameter of 100 to 200 nm. may be particles. As such, the relatively small particle diameter can improve the electrochemical performance of the active material. Also, these particles may be plate-shaped particles. Here, the plate-shaped particles have substantially flat upper and lower surfaces, and may refer to particles having a ratio of the height between the upper and lower surfaces to the width of the upper surface or the lower surface, that is, particles having an aspect ratio of 0.1 to 0.5.

Referring to FIG. 1b together, the active material having the M _x Ca _3-x Co ₄ O _9-δ composition has a CoO ₂ layer having a crystal structure of [CdI ₂ ], a rock-salt structure, and oxygen deficiency. It may have a structure in which Ma Ca _{2-a CoO 3-δ} layers (0.06 ≤ a ≤ 0.3, 0 ≤ δ ≤ 1) serving as a layer are alternately stacked. Even in the M _a Ca _2-a CoO _3-δ layer, Ca sites are 3 to 15 mol%, specifically 3.3 to 10 mol%, more specifically 4 to 7 mol%, more specifically 4.5 to 6, as an alkali metal (M). It may be substituted with mol%, for example 5 mol%. Accordingly, a may be 0.06 to 0.3, specifically 0.066 to 0.2, more specifically 0.08 to 0.14, more specifically 0.09 to 0.12, for example, 0.1. Doping an alkali metal to the Ca site, that is, doping an alkali metal having a monovalent oxidation number to the Ca site having a divalent oxidation number, causes oxygen vacancies and holes to be induced by the acceptor effect, thereby greatly improving electrical conductivity. have.

The layered structure exhibits high oxygen ion conductivity and high surface exchange coefficient (1.6 x 10 ^-7 cm s ^-1 , 700° C.), and cobalt having multiple valences of 2 ⁺ , 3 ⁺ , 4 ⁺ It can serve as a catalyst in oxygen reduction and oxidation reactions. Thereby, it can serve as a mixed ionic and electronic conductor in the cathode.

In addition, layers having different crystal structures such as a CoO ₂ layer having a crystal structure of [CdI ₂ ] and a Ma Ca _2-a CoO _3-δ layer having _a rock-salt structure are alternately stacked. The misfit structure, which is a structure, has an advantage in that it has a relatively low coefficient of thermal expansion due to the electrochemical balance of the two layers, despite containing cobalt, and thus has excellent bonding strength with the electrolyte layer 20 . This may improve the durability of the electrochemical device.

Referring back to FIG. 1A , the cathode 30 may include a mixture of the M _x Ca _3-x Co ₄ O _9-δ active material and the ion conductive oxide. The ion conductive oxide may be a proton conductive oxide. The proton conductive oxide is, for example, yttrium-doped barium zirconate (BZY), yttrium-doped barium cerate (BCY), yittrium-doped barium-zirconate-cerate (BZCY) or Yttrium- and ytterbium-doped barium-cerate (BCZYYb). -zirconate), for example, BCZYYb (BaCe _0.7 Zr _0.1 Y _0.1 Yb _0.1 O _3-δ ). The cathode 30 may have a thickness of 1 μm to 50 μm, specifically, 10 μm to 30 μm.

The cathode 30 may have dual functions for a fuel cell and an electrolytic cell. The cathode active material has a misfit structure, and by controlling the doping material and the doping amount, it is possible to improve electrochemical catalytic properties, facilitate electron transfer, and improve durability in the aforementioned fuel cell and electrolytic cell.

In a method of manufacturing an electrochemical device according to an embodiment of the present invention, for example, a proton conductive ceramic fuel cell, the anode 10 may be prepared. As an example, the anode 10 may have an anode functional layer formed on an anode support. The anode support may be formed using a method such as tape casting or pressing. The anode functional layer may be deposited on the anode support using a method such as drop coating or deep coating. As an example, the anode support may be formed by pressing a mixture of BCZYYb (BaCe _0.7 Zr _0.1 Y _0.1 Yb _0.1 O _3-δ ) and NiO. The anode functional layer may be formed as a thin film having a thickness of 10 μm to 30 μm by drop-coating a mixture of BCZYYb (BaCe _0.7 Zr _0.1 Y _0.1 Yb _0.1 O _3-δ ) and NiO on the anode support.

The electrolyte layer 20 is formed by sintering the BCZYYb (BaCe _0.7 Zr _0.1 Y _0.1 Yb _0.1 O _3-δ ) for 5 to 10 hours at 1500° C. to 1600° C. for 5 to 10 hours to make the structure more densified, and then the anode ( 10), specifically, it may be formed in the form of a thin film having a thickness of 10 μm to 20 μm on the anode functional layer.

The cathode 30 is formed by preparing an active material having a composition of M _x Ca _3-x Co ₄ O _9-δ and screen-printing a mixture of the active material and the ion conductive oxide on the electrolyte layer 20 to form 10 μm to 30 μm. It may be formed as a thin film having a thickness of μm.

The active material is a Ca precursor, a Co precursor, and an alkali metal (M) precursor in a molar ratio suitable for the composition, mixed with glycine in a solvent, and then subjected to primary heat treatment to obtain black ash, and then the black ash is secondary It may be formed by heat-treating and calcining. For example, the Ca precursor, the Co precursor, and the alkali metal (M) precursor may be nitrates of respective metals. The first heat treatment may be performed at 200 °C to 300 °C. The secondary heat treatment may be performed at 800°C to 950°C, for example, for 10 to 30 hours. The solvent may be water. The obtained active material may be pulverized through a ball mill to reduce particle size. The pulverized particles may have a diameter of several tens to hundreds of nm, for example, a diameter of 50 to 300 nm, specifically, an average diameter of 100 to 200 nm.

The ion conductive oxide in the cathode 30 may be a proton conductive oxide, for example, BCZYYb (BaCe _0.7 Zr _0.1 Y _0.1 Yb _0.1 O _3-δ ), and the M _x Ca _3-x Co ₄ O _9-δ composition. The cathode layer 40 may be formed by mixing the active material and the proton conductive oxide in an organic solvent at a ratio of, for example, 6:4, screen printing on the electrolyte layer, and sintering at 900° C. for 2 hours. .

Hereinafter, in order to explain the present invention in more detail, preferred experimental examples according to the present invention will be described in more detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms.

<Active Material Preparation Examples A1 to A15: Preparation of Cathode Active Material (MCCO)>

Ca(NO ₃ ) ₂ , Co(NO ₃ ) ₂ , and MNO ₃ (M is Li, Na, or K) were prepared, and then put them together with glycine in pure water according to the component ratios shown in Table 1 below After heating to 280 °C to obtain black ash, the black ash was calcined at 900 °C for 24 hours. As a result, the active materials shown in Table 1 below were prepared.

molar ratio obtained active material Content of M at Ca sites MNO ₃ Ca(NO ₃ ) ₂ Co(NO ₃ ) ₂ Preparation A1 M=Li, 0.1 2.9 4 Li _0.1 Ca _2.9 Co ₄ O _9-δ 3.3 mol% Preparation A2 M=Li, 0.12 2.88 4 Li _0.12 Ca _2.88 Co ₄ O _9-δ 4 mol% Preparation A3 M=Li, 0.15 2.85 4 Li _0.15 Ca _2.85 Co ₄ O _9-δ 5 mol% Preparation A4 M=Li, 0.21 2.79 4 Li _0.21 Ca _2.79 Co ₄ O _9-δ 7 mol% Preparation A5 M=Li, 0.3 2.7 4 Li _0.3 Ca _2.7 Co ₄ O _9-δ 10 mol% Preparation A6 M=Na, 0.1 2.9 4 Na _0.1 Ca _2.9 Co ₄ O _9-δ 3.3 mol% Preparation A7 M=Na, 0.12 2.88 4 Na _0.12 Ca _2.88 Co ₄ O _9-δ 4 mol% Preparation A8 M=Na, 0.15 2.85 4 Na _0.15 Ca _2.85 Co ₄ O _9-δ 5 mol% Preparation A9 M=Na, 0.21 2.79 4 Na _0.21 Ca _2.79 Co ₄ O _9-δ 7 mol% Production Example A10 M=Na, 0.3 2.7 4 Na _0.3 Ca _2.7 Co ₄ O _9-δ 10 mol% Production Example A11 M=K, 0.1 2.9 4 K _0.1 Ca _2.9 Co ₄ O _9-δ 3.3 mol% Production Example A12 M=K, 0.12 2.88 4 K _0.12 Ca _2.88 Co ₄ O _9-δ 4 mol% Preparation A13 M=K, 0.15 2.85 4 K _0.15 Ca _2.85 Co ₄ O _9-δ 5 mol% Preparation A14 M=K, 0.21 2.79 4 K _0.21 Ca _2.79 Co ₄ O _9-δ 7 mol% Production Example A15 M=K, 0.3 2.7 4 K _0.3 Ca _2.7 Co ₄ O _9-δ 10 mol%

<Active Material Preparation Examples B1 to B15: Preparation of Cathode Active Material (MCCO)>

Each of the cathode active materials according to Preparation Examples A1 to A15 was ball milled at 180 rpm for 48 hours to obtain cathode active materials according to Preparation Examples B1 to B15 of the active material having a reduced particle size.

<Comparative example of active material: Preparation of cathode active material (CCO)>

MNO ₃ (M is Li, Na, or K) is not used and Ca(NO ₃ ) ₂ and Co(NO ₃ ) ₂ having a molar ratio of 3:4 are used, except that the same method as in Preparation Example A1 of the active material is used. A cathode active material having a Ca ₃ Co ₄ O _9-δ composition was obtained.

2 schematically shows a half-cell (a) according to the following half-cell manufacturing examples and a full battery (b) according to the following full-cell manufacturing examples.

Referring to FIG. 2 , the half-cell (a) may include cathodes 30a and 30b disposed on both sides of the electrolyte layer 20 ′ as described in the following half-cell manufacturing examples.

The full cell (b) includes an electrolyte layer 20″ sequentially disposed on an anode 10″ including an anode support 10a and an anode functional layer 10b, as described in Examples of Full Cell Manufacturing below; An air electrode 30″ may be provided.

<Half-cell manufacturing examples B1 to B15>

After mechanically pressing 2 g of BaCe _0.7 Zr _0.1 Y _0.1 Yb _0.1 O _3-δ (BCZYYb), it was sintered at 1550° C. for 10 hours to obtain a button-shaped electrolyte layer having a dense structure. The active material (MCCO) of any one of Preparation Examples B1 to B15 and BCZYYb (BaCe _0.7 Zr _0.1 Y _0.1 Yb _0.1 O _3-δ ) are mixed in a mass ratio of 6:4, and ESL (Electroscience), which is a mixture of a solvent and a binder After ink production using 441 products from Laboratories, this ink was applied on both sides of the electrolyte layer to a thickness of 30 μm using a screen printing method, followed by sintering at 800° C. for 2 hours. A half-cell with an electrolyte layer/cathode structure was obtained.

<Comparative example of half battery>

A half-cell was obtained in the same manner as in Preparation Example B1 of the half-cell, except that the active material (CCO) according to the active material Comparative Example was used instead of the active material (MCCO) of any one of Preparation Examples B1 to B15.

<Complete battery manufacturing examples B1 to B15>

65 parts by weight of NiO, 35 parts by weight of BCZYYb (BaCe _0.7 Zr _0.1 Y _0.1 Yb _0.1 O _3-δ ), 2 parts by weight of pore former polymethyl methacrylate (PMMA), 8 parts by weight of plasticizer BBP (Butyl Benzyl Phthalate) and 1 weight Parts of PEG (Polyethylene Glycol), 9 parts by weight of binder PVB (Polyvinyl Butyral), 1 part by weight of fish oil, and 21 parts by weight of toluene as a solvent and 21 parts by weight of ethanol (99.9%) were mixed to form an anode slurry After that, the slurry was tape-casted to form a button-shaped support having a diameter of 25 mm and a thickness of 50 μm. The support was pre-sintered at 900°C. The anode slurry was coated twice on the upper surface of the pre-sintered support using a screen printing method, and then sintered at 400° C. to form an anode functional layer (thickness: 10 μm). Then, on the anode functional layer, BCZYYb (BaCe _0.7 Zr _0.1 Y _0.1 Yb _0.1 O _3-δ ), PVB (Polyvinyl Butyral) as a binder, and ethanol (99.9%) as a solvent were applied to an electrolyte slurry using a screen printing method. and then sintered at 1450° C. for 4 hours to obtain an electrolyte layer (thickness: 13.7 μm)/anode functional layer/support structure. Thereafter, the active material (MCCO) of any one of Preparation Examples B1 to B15 and BCZYYb (BaCe _0.7 Zr _0.1 Y _0.1 Yb _0.1 O _3-δ ) were mixed in a 6:4 mass ratio, and ESL, which is a mixture of a solvent and a binder (Electroscience Laboratories) 441 product was used to prepare the ink, and then this ink was applied on the electrolyte layer in a circular shape having a diameter of 6 mm. Thereafter, sintering was performed at 900° C. for 2 hours to obtain a complete cell having a cathode (thickness: 40 μm)/electrolyte layer/anode functional layer/support structure.

<Comparative example of half battery>

A half-cell was obtained in the same manner as in Preparation Example B1 of the half-cell, except that the active material (CCO) according to the active material Comparative Example was used instead of the active material (MCCO) of any one of Preparation Examples B1 to B15.

Table 2 below shows the active material compositions used in the preparation examples of the active material, the preparation examples of the half-cell, and the preparations of the full battery.

obtained active material at Ca's place
content of M Active material preparation example Half battery manufacturing example Full battery manufacturing example Li _0.1 Ca _2.9 Co ₄ O _9-δ 3.3 mol% A1 B1 B1 B1 Li _0.12 Ca _2.88 Co ₄ O _9-δ 4 mol% A2 B2 B2 B2 Li _0.15 Ca _2.85 Co ₄ O _9-δ 5 mol% A3 B3 B3 B3 Li _0.21 Ca _2.79 Co ₄ O _9-δ 7 mol% A4 B4 B4 B4 Li _0.3 Ca _2.7 Co ₄ O _9-δ 10 mol% A5 B5 B5 B5 Na _0.1 Ca _2.9 Co ₄ O _9-δ 3.3 mol% A6 B6 B6 B6 Na _0.12 Ca _2.88 Co ₄ O _9-δ 4 mol% A7 B7 B7 B7 Na _0.15 Ca _2.85 Co ₄ O _9-δ 5 mol% A8 B8 B8 B8 Na _0.21 Ca _2.79 Co ₄ O _9-δ 7 mol% A9 B9 B9 B9 Na _0.3 Ca _2.7 Co ₄ O _9-δ 10 mol% A10 B10 B10 B10 K _0.1 Ca _2.9 Co ₄ O _9-δ 3.3 mol% A11 B11 B11 B11 K _0.12 Ca _2.88 Co ₄ O _9-δ 4 mol% A12 B12 B12 B12 K _0.15 Ca _2.85 Co ₄ O _9-δ 5 mol% A13 B13 B13 B13 K _0.21 Ca _2.79 Co ₄ O _9-δ 7 mol% A14 B14 B14 B14 K _0.3 Ca _2.7 Co ₄ O _9-δ 10 mol% A15 B15 B15 B15

3A is an X-ray diffraction (XRD) graph of active materials according to Preparation Examples B1, B3, and B5 of the active materials. 3B is an X-ray diffraction graph of active materials according to Preparation Examples B6 to B10 of the active materials. 3C is an X-ray diffraction graph of active materials according to Preparation Examples B11, B13, and B15 of the active materials.

Referring to FIG. 3A , when Li is doped with 3.3 mol%, the same single phase as Ca ₃ Co ₄ O _9-δ is maintained, but when Li is doped with 5 mol% or more, Ca ₃ Co ₄ O _9-δ is not It can be seen that the same phase as Ca ₃ Co ₂ O ₆ is formed.

Referring to FIGS. 3b and 3c , it can be seen that when 3.3 to 10 mol% of Na and K were doped, a single phase identical to Ca ₃ Co ₄ O _9-δ was formed without secondary phases and impurities.

4 is an SEM image of the active material according to Preparation Example A8 of the active material, and FIG. 5 is a graph showing the SEM image (a) and the particle size distribution (PSD) of the active material according to Preparation Example B8 of the active material ( b), and FIG. 6 is a graph (b) showing an SEM image (a) and a particle size distribution (PSD) of the active material according to Preparation Example B13 of the active material. 7 is an SEM image of the active material according to Preparation Example B10 of the active material.

Referring to FIG. 4, the active material according to Preparation Example A8 of the active material using the self-propagating high temperature synthesis using glycine, that is, Na _0.15 Ca _2.85 Co ₄ O _9-δ has a diameter of approximately 1 um. It can be seen that the plate-shaped particles are formed.

5, the active material according to Preparation Example A8, that is, Na _0.15 Ca _2.85 Co ₄ O _9-δ obtained by ball milling the active material according to Preparation Example B8 has a diameter of about 50 to 300 nm, specifically, an average of about 139 nm It can be seen that the plate-shaped particles having a diameter are formed.

6, it can be seen that the active material according to Preparation B13, that is, K _0.15 Ca _2.85 Co ₄ O _9-δ is formed of plate-shaped particles having a diameter of about 50 to 300 nm, specifically, an average diameter of about 119 nm. have.

Referring to FIG. 7 , the active material according to Preparation Example B10, that is, Na _0.3 Ca _2.7 Co ₄ O _9-δ is a plate-shaped type having a relatively large average diameter of about 200 nm compared to Na _0.15 Ca _2.85 Co ₄ O ₉ -δ of FIG. 5 . It can be seen that the particles are formed.

[Measurement of electrical conductivity]

After connecting one of the half-cells obtained through the half-cell manufacturing examples or the comparative example to a quartz reactor capable of forming an air atmosphere, it is placed in a high-temperature electric furnace and subjected to electrochemical analysis in a temperature range of 450 to 800°C ( Biologic, VSP) was performed. At this time, the air flow rate was 200 sccm, but dry air or humidified air (3% H ₂ O-97% Air) containing 3% moisture was used.

8 is a graph showing electrical conductivity in dry air atmosphere (a) and humidified air atmosphere (b) of batteries according to Half-cell Preparation Examples B1, B3, and B5, and Comparative Examples of half-cells. 9 is a graph showing electrical conductivity in dry air atmosphere (a) and humidified air atmosphere (b) of batteries according to Half-cell Preparation Examples B6 to B10, and Comparative Examples of half-cells. 10 is a graph showing electrical conductivity in dry air atmosphere (a) and humidified air atmosphere (b) of batteries according to Half-cell Preparation Examples B11, B13, and B15. 11 is a graph showing electrical conductivity in dry air atmosphere (a) and humidified air atmosphere (b) of batteries according to Half-cell Preparation Examples B1, B6, and B11, and Comparative Examples of half-cells.

8, 9, 10, and 11, compared to the battery according to the comparative example of the half-cell containing Ca ₃ Co ₄ O _9-δ as an active material in the cathode, the alkali metal, specifically, Li, Na, or The half-cell containing M _x Ca _(3-x) Co ₄ O _9-δ (0.1≤x≤0.3) doped with K of 3.3 to 10 mol% as an active material was higher in all temperature ranges in the case of dry air atmosphere. It showed electrical conductivity, and in the case of humidified air atmosphere, it showed higher electrical conductivity at least in the low temperature range (600 °C or less, 1000/T(K ^-1 ) is 1.1 or more). It can be estimated that the conductivity is improved because oxygen vacancies and holes are induced by the acceptor effect by doping the alkali metal having a monovalent oxidation number to the site of Ca having a divalent oxidation number.

In addition, the half-cell containing M _x Ca _(3-x) Co ₄ O _9-δ (0.1≤x≤0.3) doped with 3.3 to 10 mol% of Li, Na, or K as an active material is humidified compared to dry air environment. It showed higher electrical conductivity in the environment. The humidification environment considers the generation or consumption of water at the cathode of the proton ceramic battery, and M _x Ca _(3-x) Co ₄ O _9-δ (0.1≤x≤0.3) is a mixture in which electrons and ions can move. As it has the properties of an ion-electron conductor (MIEC, Mixed Ionic/Electronic Conductor), it is estimated that it has a high hydrogen ion mobility in a humidified environment, and the reaction degree is remarkably accelerated.

On the other hand, when Li or K was doped, the lower the temperature, that is, the 1000/T(K ⁻¹ ) increased, the higher the electrical conductivity compared to Ca ₃ Co ₄ O _9-δ at low doping concentration (FIG. 8). , Fig. 10).

On the other hand, when Na is doped, it can be seen that the electrical conductivity is relatively increased compared to the undoped Ca ₃ Co ₄ O _9-δ in all temperature ranges of dry and humidified environments. High electrical conductivity in all temperature ranges means that the performance and efficiency of the proton ceramic battery can be improved. In addition, when 5 mol% of Na was doped, the improvement of electrical conductivity was the greatest. In addition, compared to dry air, in humidified air atmosphere, the tendency was the same as that in the case of K-doping, and electrical conductivity was measured to be low at high temperature and high at low temperature ( FIGS. 9 and 11 ).

Referring back to FIG. 11 , the case in which Na is doped has slightly higher electrical conductivity at high temperatures compared to the case in which K is doped, and shows a slight difference from the case in which K is doped at low temperatures. In addition, the ionic radius of Na is 227 pm, which is similar to that of Ca, 230 pm, but considering that the ionic radius of K is 280 pm, which is very large compared to the ionic radius of Ca, doping Na in the place of Ca is the structure It was estimated that the stability could be improved.

[Current-voltage characteristics, power density, and impedance measurement]

The complete cell was placed in a ceramic reactor, and a ceramic bond was used as a sealing agent to prevent leakage of gas injected between the anode and the cathode. In addition, the reactor was placed in a high-temperature electric furnace and the temperature was lowered in the range of 450 to 750 ° C. The current-voltage characteristics, power density, and impedance were measured using Potentiostat/Galvanostat equipment (Biologic, SP-240).

Meanwhile, the full cell can be operated in both the fuel cell mode and the electrolytic cell mode. In the fuel cell mode, hydrogen and dry air containing 3 vol% of water vapor were supplied to the anode and cathode, respectively, and in the electrolytic cell mode, the anode and the cathode were supplied. were supplied with air containing 30 sccm of dried hydrogen and 20 vol% of water vapor, respectively.

12 is a graph showing polarization and power density graphs (a, c, e) and impedance graphs (b, d, f) obtained while operating the batteries according to the full cell manufacturing examples B6, B8, and B10 in the fuel cell mode; show

Referring to FIG. 12 , when an active material doped with Na 5 mol% is used (c) over the entire temperature range of 450 to 750 degrees, when an active material doped with Na 3.3 mol% is used (a) or an active material doped with Na 10 mol% It can be seen that the output density was excellent compared to the case (e) used, and the decrease in the output density was small as the temperature decreased. Specifically, in the case of using an active material doped with Na 5 mol% (c) at 750, 700, 650, 600, 550, 500, and 450 degrees, the power densities are 2310, 1860, 1310, 840, 510, 250, and 110 mW/cm ² were shown, and Rp (polarization resistance) was 0.03, 0.05, 0.11, 0.28, 0.75, 2.64, and 9.16Ω·cm ² , respectively.

As described above, it can be seen that excellent properties can be obtained when the active material doped with Na 5 mol% is used as the cathode active material of a proton ceramic battery used at medium and low temperatures.

13 is a graph showing durability when the battery according to Preparation Example B8 of the full cell is operated in a fuel cell mode. At this time, the battery was operated in the fuel cell mode for 800 hours at 650 ℃ constant current (300mA/cm ² ) condition.

Referring to FIG. 13 , it can be seen that the battery according to Preparation Example B8 of the full battery, such as the voltage maintained for 800 hours, has very excellent durability.

14 is an initial IV graph (a) obtained while operating the battery according to Preparation Example B8 of a full battery in electrolytic cell mode and an IV graph (b) obtained after a 50-hour durability test under constant current (200 mA/cm ² ) conditions. show 15 is a graph obtained while performing a 50-hour durability test under constant current (200 mA/cm ² ) conditions in an electrolytic cell mode for a battery according to Preparation Example B8 of a full battery.

Referring to FIG. 14 , in the initial state, -1.11 (500° C.), -3.14 (600° C.), -8.12 (700° C.), -10.53 A/cm ² (750° C.) are the current densities based on the voltage of 1.6V. could be obtained (a).

Referring to FIG. 15 , after the performance measurement, the battery was subjected to a durability test under constant current (200 mA/cm ² ) condition for about 50 hours, and it was confirmed that the battery had good durability by keeping the voltage constant.

Referring back to FIG. 14 , after the durability measurement, it was confirmed that the current density slightly increased compared to the initial performance after the durability test (b).

16 is a graph showing polarization resistance (Rp) values obtained when the batteries according to Preparation Examples B6 to B10 of the full cell are operated at 650 degrees in a fuel cell mode (dry air) and an electrolytic cell mode (humidified air).

Referring to FIG. 16 , it can be seen that the battery according to Preparation Example B8 of the full battery using the cathode active material doped with 5 mol% Na exhibits lower polarization resistance compared to the full battery using the cathode active material having different doping concentrations.

17 is a scanning electron microscope (SEM) image showing the results of post-mortem analysis after durability evaluation (FIG. 13) of the battery according to Preparation Example B8 of the full battery, (a) and (b) are cross-sections of the entire battery, (c) is a cross-section of the anode, (d) is a cross-section of the cathode, and (e) is a cross-section of the electrolyte.

Referring to FIG. 17 , it was confirmed that the electrolyte layer and the cathode were well adhered even after the durability evaluation, and it was confirmed that the microstructure of the cathode was not significantly deteriorated.

On the other hand, the embodiments of the present invention disclosed in the present specification and drawings are merely presented as specific examples to aid understanding, and are not intended to limit the scope of the present invention. It will be apparent to those of ordinary skill in the art to which the present invention pertains that other modifications based on the technical spirit of the present invention can be implemented in addition to the embodiments disclosed herein.

10: anode
20: electrolyte layer
30: air electrode

Claims (18)

anode;
an electrolyte layer positioned on the anode; and
It is located on the electrolyte layer and has a composition of Ca ₃ Co ₄ O _9-δ (0<δ<1), An electrochemical device comprising a cathode having an active material doped with an alkali metal at the Ca site. According to claim 1,
The active material has a composition of M _x Ca _3-x Co ₄ O _9-δ (0 < δ < 1),
Wherein x is 0.1 to 0.3,
Wherein M is Li, Na, or K, the electrochemical device. 3. The method of claim 2,
wherein M is Na, Wherein x is 0.13 to 0.18, the electrochemical device. According to claim 1,
The active material is Na _0.15 Ca _2.85 Co ₄ O _9-δ , the electrochemical device. According to claim 1,
The active material is, [CdI ₂ ] CoO ₂ layer having a crystal structure, and M _a Ca _2-a CoO _3-δ layer having a rock-salt structure (M is an alkali metal, 0.06≤a≤0.3, The electrochemical device, wherein 0≤ δ ≤1) has an alternatingly stacked crystal structure. According to claim 1,
The active material is particles having a diameter of several tens to several hundreds of nm, an electrochemical device. 7. The method of claim 6,
The active material is particles having an average diameter of 100 to 200 nm, an electrochemical device. According to claim 1,
The electrochemical device is a proton conductive ceramic cell, an electrochemical device. 9. The method of claim 8,
The cathode is an electrochemical device comprising a mixture of the active material and the proton conductive oxide. 10. The method of claim 9,
The proton conductive oxide is BZY (yttrium-doped barium zirconate), BCY (yttrium-doped barium cerate), BZCY (yittrium-doped barium-zirconate-cerate) or BCZYYb (Yttrium- and ytterbium-doped barium-cerate-zirconate) , electrochemical devices. anode;
an electrolyte layer positioned on the anode; and
Located on the electrolyte layer, a CoO ₂ layer having a crystal structure of [CdI ₂ ], and a M _a Ca _2-a CoO _3-δ layer having a rock-salt structure (M is an alkali metal, 0.06≤a) ≤0.3, 0≤ δ ≤1) comprising an electrode comprising an active material having an alternatingly laminated crystal structure. 12. The method of claim 11,
In the Ma Ca _{2-a CoO 3-δ} layer, a is 0.09 to 0.12, an electrochemical device. 12. The method of claim 11,
The active material is particles having a diameter of several tens to several hundreds of nm, an electrochemical device. Ca ₃ Co ₄ O _9-δ (0<δ<1) having a composition,
An alkali metal doped at the Ca site, the active material. 15. The method of claim 14,
The active material has a composition of M _x Ca _3-x Co ₄ O _9-δ (0 < δ < 1),
Wherein x is 0.1 to 0.3,
Wherein M is Li, Na, or K, the active material. A CoO ₂ layer having a crystal structure of [CdI ₂ ],
An active material having a rock-salt structure and a crystal structure in which M _a Ca _2-a CoO _3-δ layers (M is an alkali metal, 0.06 ≤ a ≤ 0.3, 0 ≤ δ ≤ 1) are alternately stacked. 17. The method of claim 14 or 16,
The active material is particles having a diameter of several tens to several hundreds of nm, the active material. 18. The method of claim 17,
The active material is particles having an average diameter of 100 to 200 nm, the active material.

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