Positive electrode for air cell and lithium-air cell comprising the same

Abstract

The present invention relates to a cathode for an air cell and a lithium-air cell comprising the same. The cathode for an air cell comprises: a porous conductive material; and an alkali-resistant compound on a surface of the porous conductive material, the alkali-resistant compound having a positive Gibbs free energy at 2 V to 4.5 V vs. Li / Li + at a pH of about 7 to about 14.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority and benefits, and all benefits arising therefrom, to U.S. Provisional Application Serial No. 62 / 963,811 filed with the U.S. Patent and Trademark Office on January 21, 2020, and Korean Patent Application No. 10-2020-021771 filed with the Korean Intellectual Property Office on February 21, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to cathodes containing alkali-resistant compounds and lithium-air batteries containing the same. Background Technology

[0004] In lithium-air batteries, lithium itself is used as the negative electrode, and it is not necessary to store air, which is the active material for the positive electrode, in the battery. Therefore, lithium-air batteries can be implemented as high-capacity batteries.

[0005] In addition, lithium-air batteries have a relatively high theoretical specific energy, which is equal to or greater than 3,500 Wh / kg. This specific energy is about 10 times greater than that of conventional lithium-ion batteries.

[0006] In lithium-air batteries, a voltage of approximately 4.5V is generated when moisture-containing air is used as the positive electrode active material, while a voltage of approximately 3V is generated when oxygen is used. Therefore, it is advantageous to use moisture-containing air as the positive electrode active material.

[0007] However, when moisture-containing air is used as the positive electrode active material, strongly alkaline LiOH is generated as a discharge product from the discharge reaction, and the material currently used as the positive electrode material can decompose undesirably due to the strong alkalinity of the material.

[0008] Therefore, there is a need for cathode materials that are electrochemically stable even under strongly alkaline conditions, as well as cathodes that include them. Summary of the Invention

[0009] Provides an alkali-resistant (alkali-tolerant) positive electrode.

[0010] A lithium-air battery including the positive electrode is provided.

[0011] A method for preparing the positive electrode is provided.

[0012] Other aspects will be set forth in part in the following description and will also be apparent from the description.

[0013] According to one aspect, a positive electrode for an air battery is provided, the positive electrode comprising:

[0014] Porous conductive materials; and

[0015] An alkali-resistant compound on the surface of the porous conductive material, the alkali-resistant compound being resistant to pH at a ratio of Li / Li at a pH of about 7 to about 14. + It has a positive Gibbs free energy from 2V to 4.5V.

[0016] According to one aspect, a lithium-air battery is provided, comprising:

[0017] The positive electrode;

[0018] Including lithium anodes; and

[0019] The electrolyte is disposed between the positive electrode and the negative electrode.

[0020] According to one aspect, a method for preparing a positive electrode is provided, which includes the following steps:

[0021] A composition comprising a lithium-containing metal oxide and a binder is provided;

[0022] The composition is molded to prepare a sheet; and

[0023] The positive electrode is prepared by heat-treating the sheet at a temperature of about 900°C to about 1300°C in an oxidizing atmosphere.

[0024] For use as the positive electrode in an air battery, the positive electrode comprises:

[0025] Porous conductive materials; and

[0026] An alkali-resistant compound on the surface of the porous conductive material, wherein the alkali-resistant compound includes at least one of the following: CeO2, Dy2O3, Er2O3, Gd2O3, HfO2, Ho2O3, Lu2O3, Nd2O3, PuO2, Sc2O3, Sm2O3, Ta2O5, Tb2O3, ThO2, TiO2, Tm2O3, Y2O3, or ZrO2. Attached Figure Description

[0027] The above and other aspects, features, and advantages of some embodiments of this disclosure will become more apparent from the following description taken in conjunction with the accompanying drawings, wherein:

[0028] Figure 1 To illustrate the following bar chart: when applied relative to Li / Li + The amount of metal dissolved (dissolved amount, (mg / L)) when the positive electrode prepared in Examples 1-3 and Comparative Example 1 is used as the working electrode in a 1 molar concentration (M) LiOH aqueous solution and a Pt electrode is used as the counter electrode at a voltage of 2.8V for 18 hours.

[0029] Figure 2 The potential (volts (V)) is relative to Li / Li + A graph of capacity (mAh) shows the results of charge-discharge cycle tests for the first and second cycles in the lithium-air battery manufactured in Example 4.

[0030] Figure 3 The potential (V, relative to Li / Li) + A graph of capacity (mAh) shows the results of charge-discharge cycle tests for the first and second cycles in the lithium-air battery manufactured in Example 5.

[0031] Figure 4 The potential (V, relative to Li / Li) + A graph of capacity (mAh) shows the results of charge-discharge cycle tests for the first and second cycles in the lithium-air battery manufactured in Example 6.

[0032] Figure 5 A graph showing the intensity (arbitrary units, au) of the cathode material of the lithium-air battery manufactured in Example 4 as measured after 10 charge-discharge cycles using X-ray diffraction analysis with CuKα radiation against the diffraction angle (°2θ).

[0033] Figure 6 A graph showing the intensity (arbitrary units, au) of the cathode material of the lithium-air battery manufactured in Example 5 as measured after 10 charge-discharge cycles using X-ray diffraction analysis with CuKα radiation against the diffraction angle (°2θ).

[0034] Figure 7 A graph showing the intensity (arbitrary units, au) of the cathode material of the lithium-air battery manufactured in Comparative Example 2 as determined by X-ray diffraction analysis using CuKα radiation, as measured after 10 charge-discharge cycles; and

[0035] Figure 8 A schematic diagram illustrating an embodiment of the structure of a lithium-air battery. Detailed Implementation

[0036] Embodiments will now be described in detail, examples of which are shown in the accompanying drawings, wherein the same reference numerals always denote the same elements. In this respect, embodiments may take different forms and should not be construed as limited to the description set forth herein. Therefore, embodiments are described below only by reference to the accompanying drawings to illustrate aspects. As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one” modify the entire list of elements and not individual elements of the list when appearing before or after the list of elements.

[0037] In the following description, since the inventive concept allows for various modifications and numerous embodiments, specific embodiments will be shown in the figures and described in detail in the specific description. However, this is not intended to limit the inventive concept to specific implementation modes, but rather to encompass all modifications, equivalents, and substitutions that do not depart from the spirit and scope of the invention.

[0038] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the inventive concept. Singular expressions cover plural expressions unless they have a distinct meaning in the context. As used herein, it will be understood that terms such as “comprising,” “having,” and “including” are intended to indicate the presence of the features, quantities, steps, actions, components, parts, ingredients, materials, or combinations thereof disclosed in the specification, but do not preclude the possibility that one or more additional features, quantities, steps, actions, components, parts, ingredients, materials, or combinations thereof may be present or added. The symbol “ / ” used herein may be interpreted as “and” or “or” depending on the context.

[0039] In the figures, for clarity, the diameters, lengths, and thicknesses of layers and regions are enlarged or reduced. Throughout the specification, the same reference numerals denote the same elements. Throughout the specification, it will be understood that when a component, such as a layer, film, region, or plate, is referred to as being "on" another component, the component may be directly on the other component, or an intermediate component may be present thereon. Throughout the specification, the terms "first," "second," etc., are used to describe various elements, and these elements should not be limited by these terms. These terms are used only to distinguish one element from another.

[0040] As used herein, “about” or “approximately” includes the stated value and means within an acceptable range of deviations from the specific value, as determined by a person skilled in the art taking into account the measurement in question and the errors associated with the measurement of the specific quantity (i.e., limitations of the measurement system). For example, “about” may mean within one or more standard deviations relative to the stated value, or within ±30%, 20%, 10%, or 5%.

[0041] The following will describe in further detail the positive electrode according to exemplary embodiments, the lithium-air battery including the positive electrode, and the method for preparing the positive electrode thereto.

[0042] The positive electrode according to the embodiment uses air containing moisture and oxygen as the positive electrode active material, and includes an alkali-resistant compound.

[0043] In existing lithium-air batteries, when oxygen is used as the positive electrode active material, Li₂O₂ is generated on the surface of the positive electrode as a discharge product during discharge. However, in lithium-air batteries including a positive electrode according to an embodiment, air comprising moisture and oxygen is used as the positive electrode active material, and therefore LiOH is generated on the surface of the positive electrode as a discharge product during discharge. While not wishing to be bound by theory, it is understood that LiOH is generated through a reaction represented by reaction formula 1:

[0044] Reaction 1

[0045] 4Li + +4e - +O₂ + 2H₂O → 4LiOH

[0046] During the discharge of a lithium-air battery, the lithium anode provides lithium ions and electrons, and the lithium ions are transferred to the positive electrode surface through the solid electrolyte, while the electrons are transferred from the lithium anode to the positive electrode surface through an external circuit. Here, air containing oxygen and moisture, present on the positive electrode surface, reacts with the lithium ions and electrons to produce LiOH as a reaction product. Since LiOH is a strongly alkaline alkali metal hydroxide, a positive electrode material that is stable upon contact with LiOH and does not deteriorate in the presence of a strong alkali is desirable. Porous carbon or ruthenium (Ru)-based metals have been used in lithium-air batteries as positive electrode materials with electronic and ionic conductivity. However, such materials deteriorate under strongly alkaline conditions. Therefore, the use of moisture-containing air as a positive electrode active material has been limited.

[0047] The inventors have identified that the compounds having specific compositions, as described below, are electrochemically stable under alkaline conditions, such as strongly alkaline conditions, and are relatively stable relative to Li / Li + Surprisingly, the compounds are structurally and chemically stable within a voltage range of 2V to 4.5V (corresponding to the charge / discharge voltage range of lithium-air batteries). The identified compounds can be used to prepare positive electrodes for lithium-air batteries.

[0048] The alkali-resistant compound included in the positive electrode is structurally and chemically stable at pH values ​​of about 7 or greater, such as about 8 or greater, about 9 or greater, about 10 or greater, about 11 or greater, or about 12 or greater. For example, the alkali-resistant compound may be electrochemically stable at pH values ​​of about 9 or greater. The alkali-resistant compound may be electrochemically stable at pH values ​​of about 7 to about 14, about 8 to about 13, or about 9 to about 12.

[0049] According to an embodiment, the alkali-resistant compound is electrochemically stable at a pH of about 12 to about 14. A pH of about 12 to about 14 (which is the pH of an aqueous solution in which LiOH is dissolved) can be the pH value produced by the discharge products of a lithium-air battery using air containing moisture as the positive electrode active material.

[0050] According to an embodiment, the alkali-resistant compound is in relation to Li / Li + It is thermodynamically stable from 2V to 4.5V, for example, relative to Li / Li + It can have 0 or positive Gibbs free energy at 2V to 4.5V, for example, relative to Li / Li + The alkali-resistant compound exhibits a Gibbs free energy of approximately 5 eV to 0 eV, approximately 3 eV to approximately 0.1 eV, or equal to or greater than 0 eV at voltages ranging from 2 V to 4.5 V. The alkali-resistant compound has a Gibbs free energy difference (ΔG) of 0 eV under voltage conditions ranging from 2 V to 4.5 V. Therefore, the alkali-resistant compound is electrochemically stable during the charging and discharging of lithium-air batteries and thus does not undergo a phase transition.

[0051] The Gibbs free energy of the alkali-resistant compound within a specific pH range is calculated using quantum computing with the Pourbaix algorithm.

[0052] According to an embodiment, the alkali-resistant compound is in relation to Li / Li + The alkali-resistant compound is electrochemically stable for lithium metal or lithium-containing alloys at voltages of 2V to 4.5V and pH values ​​of approximately 9 to approximately 14. For example, the alkali-resistant compound is electrochemically stable relative to Li / Li + The alkali-resistant compound is electrochemically stable for lithium metal at voltages of 2V to 4.5V and pH values ​​of 12 to 14. Therefore, since the alkali-resistant compound is structurally and chemically stable in alkaline or strongly alkaline pH environments and at specific charge / discharge voltages, lithium-air batteries incorporating the alkali-resistant compound can exhibit improved durability and thus possess desirable long-life characteristics. Furthermore, lithium-air batteries can provide higher output characteristics when using water as the positive electrode active material compared to when water is not used.

[0053] According to an embodiment, the alkali-resistant compound is in relation to Li / Li + Suitable oxidation resistance (oxidative resistance) and reduction resistance (reduction resistance) can be achieved for lithium metal at voltages of 2V to 4.5V and pH values ​​of approximately 12 to approximately 14. As used herein, the term "oxidation resistance" refers to tolerance to oxidation by not participating in an oxidation reaction. Similarly, the term "reduction resistance" refers to tolerance to reduction by not participating in a reduction reaction. Therefore, the alkali-resistant compound can be substantially non-reactive, for example, inert, at the aforementioned pH environment and charge / discharge voltage. In one aspect, at the aforementioned pH environment within the charge / discharge voltage range, the alkali-resistant compound is not involved in the oxidation and reduction of lithium and oxygen.

[0054] According to embodiments, the alkali-resistant compound may include at least one binary or ternary compound. For example, the binary and ternary compounds may include oxides, fluorides, oxyfluorides, or fluorine oxides of metals or alloys of two or more metals.

[0055] According to embodiments, the alkali-resistant compound may include at least two of the following: K, Be, Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf, Nb, Ta, Mo, W, Fe, Zn, Cd, B, Al, Ga, In, C, Si, Ge, Sn, P, As, Sb, Bi, O, S, Te, F, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, U, or Pu. For example, the alkali-resistant compound may include a binary or ternary compound containing two or three of the aforementioned elements. At least one element included in the binary and ternary compounds may be at least one of O or F.

[0056] According to an embodiment, the alkali-resistant compound can be represented by chemical formula 1:

[0057] Chemical Formula 1

[0058] M1 α X1 β

[0059] In chemical formula 1,

[0060] M1 is at least one of the following: K, Be, Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf, Nb, Ta, Mo, W, Fe, Zn, Cd, B, Al, Ga, In, C, Si, Ge, Sn, P, As, Sb, Bi, S, Te, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, U, or Pu;

[0061] X1 is at least one of O or F; and

[0062] \(0 \lt \alpha \leq 32\), and \(0 \lt \beta \leq 68\).

[0063] According to an embodiment, the alkali-resistant compound can be represented by at least one of Chemical Formula 2 or Chemical Formula 3:

[0064] Chemical Formula 2

[0065] M2 a1 X2 b1

[0066] Chemical Formula 3

[0067] M3 a2 M4 a3 X3 b2

[0068] Wherein in Chemical Formula 2,

[0069] M2 is at least one of the following: Be, Sc, Y, Ti, Zr, Hf, Ta, In, Sn, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, U, or Pu;

[0070] X2 is at least one of O or F; and

[0071] \(0 \lt a1 \leq 2\), and \(0 \lt b1 \leq 5\), and

[0072] Wherein in Chemical Formula 3,

[0073] M3 and M4 are each independently at least one of the following: K, Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf, Nb, Ta, Mo, W, Fe, Zn, Cd, B, Al, Ga, In, C, Si, Ge, Sn, P, As, Sb, Bi, S, Te, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, or U;

[0074] X3 is at least one of O or F; and

[0075] 0 < a2 ≤ 29, 0 < a3 ≤ 29, and 0 < b2 ≤ 68.

[0076] According to an embodiment, the alkali-resistant compound may be represented by Chemical Formula 4:

[0077] Chemical Formula 4

[0078] M3’ a2’ M4’ a3’ X3’ b2’

[0079] Wherein in Chemical Formula 4,

[0080] M3’ is at least one of the following: K, Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, Ta, Zn, Cd, Al, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, or U,

[0081] M4’ is at least one of the following: Sc, Y, Ti, Zr, Hf, Nb, Ta, Mo, W, Fe, Zn, Cd, B, Al, Ga, In, C, Si, Ge, Sn, P, As, Sb, Bi, S, Te, Ho, Tm, Th, or U,

[0082] X3’ is at least one of O or F, and

[0083] 0 < a2’ ≤ 29, 0 ≤ a3’ ≤ 25, and 0 < b2’ ≤ 68.

[0084] According to an embodiment, when a3’ is 0 in Chemical Formula 4, X3’ may include O and F.

[0085] According to an embodiment, the alkali-resistant compound may include at least one of the following: Y2O3, HfO2, Ta2O5, CeO2, ZrO2, Nd2O3, PuO2, Tb2O3, Dy2O3, Gd2O3, Sm2O3, Ho2O3, TiO2, Er2O3, Sc2O3, Tm2O3, Lu2O3, ThO2, UO3, Eu2O3, In2O3, BeO, SnO2, YbF2, Al2ZnO4, BaTa2O6, BaUO4, CaTa2O6, CaUO4, Cd(GaO2)2, Cd2Sb2O7, CdIn2O4, CdSnO3, CeTh9O 20 、Dy 11 Y5O 24 、Dy 29 Y3O 48Dy2CO5, Dy2GeO5, Dy2Hf2O7, Dy2SiO5, Dy2Sn2O7, Dy2Ti2O7, Dy2WO6, Dy2Zr8O 19 、Dy3Al5O 12 、Dy3Ga5O 12 、Dy3GaO6、Dy3Y5O 12 、DyAsO4、DyNbO4、DyOF、DyPO4、DyTaO4、DyY3O6、DyY7O 12 Er 10 W2O 21 Er2GeO5, Er2SiO5, Er2Sn2O7, Er2TiO5, Er3Al5O 12 Er3Ga5O 12 Er4Zr3O 12 、ErAsO4、ErBO3、ErNbO4、ErPO4、ErTaO4、Eu2Hf2O7、Eu2SiO5、Eu2Sn2O7、Eu3Ga5O 12 Eu3GaO6, Eu3NbO7, Eu6WO 12 、EuOF、Gd2GeO5、Gd2Hf2O7、Gd2MoO6、Gd2SiO5、Gd2Sn2O7、Gd2TiO5、Gd3Al5O 12 Gd3Ga5O 12 Gd3GaO6, Gd3SbO7, Gd3Y 13 O 24 Gd3Y5O 12 Gd5Y3O 12 Gd6WO 12 、GdAsO4、GdInO3、GdNbO4、GdOF、GdPO4、GdTaO4、Ho2SiO5、Ho2Sn2O7、Ho2Ti2O7、Ho2WO6、Ho2Zr8O 19 、Ho3Al5O 12 、Ho3Ga5O 12 、Ho3GaO6、Ho3ScO6、HoAsO4、HoBO3、HoNbO4、HoOF、HoPO4、HoTaO4、KTa5O 13 La2CO5, La2GeO5, La2Hf2O7, La2MoO6, La2Si2O7, La2Sn2O7, La2SO6, La2TeO6, La2Th8O 19 La2Ti2O7, La2UO6, La2WO6, La2Zr2O7, La3Ga5O 12、La4Ga2O9、LaAlO3、LaAsO4、LaBO3、LaNbO4、LaOF、LaPO4、LaSbO4、LaScO3、LaTaO4、Lu2SiO5、Lu2Sn2O7、Lu2TiO5、Lu4Hf3O 12 Lu4Zr3O 12 Lu6UO 12 Lu6WO 12 、LuGaO3、LuNbO4、LuSbO4、LuTaO4、Mg(GaO2)2、MgTa2O6、MgTi2O5、Nd2GeO5、N d2Hf2O7、Nd2MoO6、Nd2SiO5、Nd2Sn2O7、Nd2TeO6、Nd2Ti2O7、Nd2WO6、Nd2Zr8O 19 Nd3Ga5O 12 Nd3GaO6, Nd3U2O 10 、Nd4Ga2O9、NdAlO3、NdAsO4、NdBO3、NdFeO3、NdNbO4、NdOF、N dPO4、NdSbO4、NdScO3、NdTaO4、PrTaO4、Sc2Ti2O7、ScTaO4、Sm 27 Y5O 48 Sm2Ge2O7, Sm2Hf2O7, Sm2MoO6, Sm2SiO5, Sm2Sn2O7, Sm2TeO6, Sm2Th8O 19 Sm2TiO5, Sm2WO6, Sm2Zr8O 19 Sm3Ga5O 12 、Sm3GaO6、SmAlO3、SmAsO4、SmBO3、SmNbO4、SmOF、SmPO4、SmSbO4、SmScO3、SmTaO4、SmY 15 O 24 Sr3U 11 O 36 SrTa2O6, Ta 12 MoO 33 Ta2Cd2O7, Ta2Zn3O8, Ta2ZnO6, TaAlO4, TaBiO4, TaInO4, Tb2Ge2O7, Tb2SiO5, Tb2Sn2O7, Tb2Ti2O7, Tb2WO6, Tb2Zr8O 19 Tb3Al5O 12 Tb3Ga5O 12, Tb3GaO6, TbAsO4, TbNbO4, TbOF, TbPO4, TbTaO4, ThTa2O7, ThTi2O6, Ti3Zn2O8, TiCdO3, Tm2Si2O7, Tm2Sn2O7, Tm2Ti2O7, Tm2Zr8O 19 Tm3Al5O 12 Tm3Ga5O 12 Tm6WO 12 , TmNbO4, TmOF, TmPO4, TmTaO4, UCdO4, Y 11 Tm5O 24 Y 13 Ho 19 O 48 Y 13 Ho3O 24 Y 13 Tm3O 24 Y 15 TmO 24 , Y2GeO5, Y2Hf2O7, Y2HfO5, Y2SiO5, Y2Sn2O7, Y2Th8O 19 Y2TiO5, Y2Zr8O 19 Y3Al5O 12 Y3Ga5O 12 Y3GaO6, Y3SbO7, Y5Tm 11 O 24 Y6WO 12 Y7HoO 12 Y7TmO 12 YAsO4, Yb4Ta 25 O 68 , YbCO3, YBO3, YbTiO3, YNbO4, YOF, YPO4, YTaO4, Zn(GaO2)2, or Zr8Sc2O 19 .

[0086] These alkali-resistant compounds exhibit relative Li / Li ratios at pH values ​​of approximately 12 to approximately 14. + The lithium anode is electrochemically stable at voltages from 2V to 4.5V, which allows lithium-air batteries, which use air including moisture as the positive electrode active material, to operate for extended periods.

[0087] According to an embodiment, the alkali-resistant compound may be included in the positive electrode in an amount from about 1 part by weight to less than 100 parts by weight, based on 100 parts by weight of the positive electrode. For example, the amount of the alkali-resistant compound included in the positive electrode may be from about 10 parts by weight to less than 100 parts by weight, from about 50 parts by weight to less than 100 parts by weight, from about 60 parts by weight to less than 100 parts by weight, from about 70 parts by weight to less than 100 parts by weight, from about 80 parts by weight to less than 100 parts by weight, or from about 90 parts by weight to less than 100 parts by weight. When the amount of the alkali-resistant compound included in the positive electrode is within these ranges, a positive electrode with sufficiently high durability for discharge products can be obtained.

[0088] The positive electrode may include a conductive material, a catalyst for the oxidation / reduction of oxygen, or a binder.

[0089] The air may include moisture from about 1 volume percentage (volume %) to less than 100 volume %, based on the total volume of the air. For example, the volume percentage of moisture in the air may be about 5 volume % to about 99 volume %, about 10 volume % to about 98 volume %, about 20 volume % to about 97 volume %, about 30 volume % to about 96 volume %, about 40 volume % to about 95 volume %, about 50 volume % to about 94 volume %, about 55 volume % to about 93 volume %, about 60 volume % to about 92 volume %, about 65 volume % to 91 volume %, or about 70 volume % to 90 volume %. When the air includes about 5% or more, for example about 10% or more, of moisture by volume, the moisture is used as a positive electrode active material, thereby generating a sufficiently high power output.

[0090] A lithium-air battery according to an embodiment includes: the positive electrode; a negative electrode including lithium; and an electrolyte disposed between the positive electrode and the negative electrode.

[0091] By using the positive electrode comprising the alkali-resistant compound, the degradation of the lithium-air battery is suppressed, and high output power can be achieved.

[0092] The lithium-air battery includes a positive electrode. The positive electrode is an air electrode, and the air contained in the air electrode is air containing moisture and oxygen. The positive electrode may be arranged, for example, on a positive electrode current collector.

[0093] The positive electrode is inert to discharge products with a pH of 9 or higher. For example, the positive electrode is inert to discharge products at pH 12 to 14. Therefore, in lithium-air batteries using air containing moisture as the positive electrode active material, the positive electrode is structurally stable and its degradation is suppressed, and thus the lithium-air battery can have long lifespan characteristics.

[0094] The discharge products may include LiOH, generated through the reaction between lithium ions and gaseous water (H₂O(g)). The discharge products can be represented by the above chemical formula. Alkali metal hydroxides, such as LiOH, are strongly alkaline and have a pH of 12 to 14 in an aqueous state.

[0095] In an embodiment, the positive electrode includes a porous layer comprising, for example, the alkali-resistant compound. The amount of the alkali-resistant compound included in the positive electrode can be, for example, 1 part by weight to less than 100 parts by weight, 10 parts by weight to less than 100 parts by weight, 50 parts by weight to less than 100 parts by weight, 60 parts by weight to less than 100 parts by weight, 70 parts by weight to less than 100 parts by weight, 80 parts by weight to less than 100 parts by weight, or 90 parts by weight to less than 100 parts by weight, based on 100 parts by weight of the positive electrode. The positive electrode may substantially comprise, for example, the porous layer. The porous layer may substantially comprise, for example, the alkali-resistant compound. For example, the porous layer may consist substantially of the alkali-resistant compound. The positive electrode has a simplified construction and can be readily manufactured by substantially comprising the porous layer, which includes the alkali-resistant compound. The positive electrode is permeable to, for example, gases such as moisture, oxygen, or air. Therefore, the positive electrode differs from a positive electrode that is substantially impermeable to gases such as moisture or oxygen. Moisture, oxygen, or air can easily diffuse into the positive electrode through its porous and / or gas-permeable structure, and thus the electrochemical reaction between lithium ions, electrons, oxygen, and moisture can easily occur on the surface of the positive electrode.

[0096] Alternatively, the positive electrode may comprise a porous layer, which may comprise a conductive material as described later, and may further comprise a coating on its surface, the coating comprising an alkali-resistant compound. Alternatively, the coating may be made of an alkali-resistant compound. Thus, the positive electrode can be distinguished from available electrodes that are substantially impermeable to gases such as moisture or oxygen. Furthermore, moisture, oxygen, or air can readily diffuse into the positive electrode through the porous and / or gas-permeable structure, and lithium ions and / or electrons can readily migrate through the porous layer, thus facilitating electrochemical reactions between lithium ions, electrons, oxygen, and moisture on the surface of the positive electrode. Moreover, the coating comprising the alkali-resistant compound prevents degradation of the positive electrode caused by discharge products, thus resulting in a long lifespan for the positive electrode.

[0097] The conductive material may be a porous and / or conductive material, and any suitable material with suitable porosity and suitable conductivity may be used. For example, the conductive material may be a porous carbon-based material. Examples of carbon-based materials include, but are not limited to, carbon black, graphite, graphene, activated carbon, and carbon fiber materials. Any suitable carbon-based material may be used. The conductive material may be, for example, a metallic material. The metallic material may be, for example, metal fibers, metal mesh, or metal powder. The metal powder may be, for example, copper, silver, nickel, or aluminum. The conductive material may be, for example, an organic conductive material. The conductive material may be, for example, a polyphenylene derivative or a polythiophene derivative. The conductive material may be used alone or in combination. The positive electrode may include a composite conductor as a conductive material, and may further include the above-described conductive materials in addition to the composite conductor.

[0098] The positive electrode may further include a catalyst for promoting the oxidation / reduction of oxygen. Examples of such catalysts include, but are not limited to, noble metal-based catalysts such as platinum (Pt), gold (Au), silver (Ag), palladium (Pd), ruthenium (Ru), rhodium (Rh), and osmium (Os); oxide-based catalysts such as manganese oxide, iron oxide, cobalt oxide, and nickel oxide; or organometallic catalysts such as cobalt phthalocyanine. Any suitable catalyst for the oxidation / reduction of oxygen may be used.

[0099] The catalyst can be disposed on a support. The support can be, for example, an oxide support, a zeolite support, a clay mineral support, or a carbon support. The oxide support can be, for example, a metal or half-metal oxide support including at least one of the following: Al, Si, Zr, Ti, Ce, Pr, Sm, Eu, Tb, Tm, Yb, Sb, Bi, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, or W. The oxide support can include, for example, alumina, silica, zirconium oxide, and titanium dioxide. The carbon support can include, but is not limited to, carbon black materials such as Ketjen black, acetylene black, channel black, or lampblack; graphite materials such as natural graphite, artificial graphite, or expanded graphite; activated carbon materials; or carbon fiber materials. Any suitable support can be used.

[0100] The positive electrode may further include, for example, an adhesive. The adhesive may include, for example, a thermoplastic resin or a thermosetting resin. Examples of the adhesive may include, but are not limited to, at least one of the following: polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, or ethylene-acrylic acid copolymer. The adhesive may be used alone or in combination. Any suitable adhesive may be used.

[0101] The positive electrode is prepared by mixing, for example, a conductive material, a catalyst for oxygen oxidation / reduction, and a binder, then adding a suitable solvent to prepare a positive electrode slurry, coating the positive electrode slurry onto the surface of a substrate, and then drying or molding the positive electrode slurry on the substrate to increase the electrode density. The substrate may be, for example, a positive electrode current collector, a separator, or a solid electrolyte layer. The positive electrode current collector may be, for example, a gas diffusion layer. The conductive material may include a composite conductor, and depending on the type of positive electrode desired, the catalyst and binder for oxygen oxidation / reduction may not be present in the positive electrode.

[0102] The lithium-air battery includes a negative electrode. The negative electrode includes lithium.

[0103] The negative electrode may be, for example, a lithium metal film or a lithium-based alloy film. For example, the lithium-based alloy may be an alloy of lithium with aluminum, tin, magnesium, indium, potassium, titanium, or vanadium.

[0104] The lithium-air battery includes an electrolyte layer disposed between the positive electrode and the negative electrode.

[0105] The electrolyte layer includes at least one of a solid electrolyte, a gel electrolyte, or a liquid electrolyte. There are no particular limitations on the solid electrolyte, gel electrolyte, and liquid electrolyte, and any suitable electrolyte can be used.

[0106] The solid electrolyte may include, but is not limited to, at least one of the following: ion-conducting inorganic materials, solid electrolytes comprising polymeric ionic liquids (PILs) and lithium salts, solid electrolytes comprising ion-conducting polymers and lithium salts, and solid electrolytes comprising electron-conducting polymers, or any suitable solid electrolyte.

[0107] The ion-conducting inorganic material may include, but is not limited to, at least one of the following: glass or amorphous metal ion conductors, ceramic active metal ion conductors, and glass-ceramic active metal ion conductors, or any suitable ion-conducting inorganic material. The ion-conducting inorganic material may be in the form of, for example, ion-conducting inorganic particles or sheets formed from the ion-conducting inorganic material.

[0108] Examples of the ion-conducting inorganic material may include at least one of the following: BaTiO3, Pb(Zr a Ti 1-a )O3 (PZT) where 0 ≤ a ≤ 1, Pb 1-x La x Zr 1-y Ti y O3 (PLZT) (where 0 ≤ x < 1 and 0 ≤ y < 1), Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3 (PMN-PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, SiC, lithium phosphate (e.g., Li3PO4), lithium titanium phosphate (e.g., Li x Ti y (PO4)3 where 0 < x < 2 and 0 < y < 3), lithium aluminum titanium phosphate (e.g., Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, and 0 < z < 3), Li 1+x+y (Al a Ga 1-a ) x (Ti b Ge 1-b ) 2-x Si y P 3-y O 12 (where 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ a ≤ 1, and 0 ≤ b ≤ 1), lithium lanthanum titanate (e.g., Li x La y TiO3 where 0 < x < 2 and 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, and 0 < w < 5), lithium nitride (e.g., Li x N y , where 0 < x < 4 and 0 < y < 2), SiS2-based glass (e.g., Lix Si y S z , where 0 < x < 3, 0 < y < 2, and 0 < z < 4), glass based on P2S5 (e.g., Li x P y S z , where 0 < x < 3, 0 < y < 3, and 0 < z < 7), Li2O, LiF, LiOH, Li2CO3, LiAlO2, ceramics based on Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2, or garnet-based ceramics (e.g., Li 3+x La3M2O 12 , where 0 ≤ x ≤ 8 and M is at least one of tellurium (Te), niobium (Nb), or zirconium (Zr)).

[0109] Examples of the polymer ionic liquid (PIL) may include repeating units comprising: i) at least one of the following: ammonium-based cations, pyrrolidinium -based cations, pyridinium -based cations, pyrimidinium -based cations, imidazolium -based cations, piperidinium -based cations, pyrazolium -based cations, azolium -based cations, pyridazinium -based cations, -based cations, sulfonium-based cations, or triazolium -based cations; and ii) at least one of the following: BF4-, PF6 - , AsF6 - , SbF6 - , AlCl4 - , HSO4 - , ClO4 - , CH3SO3 - , CF3CO2 - , (CF3SO2)2N - , Cl - , Br - , I - , SO4 2- , CF3SO3 - , (C2F5SO2)2N - , (C2F5SO2)(CF3SO2)N - , NO3 - , Al2Cl7 - , CH3COO - , (CF3SO2)3C- (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - SF5CF2SO3 - SF5CHFCF2SO3 - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - , or (O(CF3)2C2(CF3)2O)2PO - Examples of the polymeric ionic liquid may include: poly(bis(trifluoromethanesulfonyl)imide diallyl dimethylammonium) (polyTFSI (diallyl dimethylammonium)), poly(bis(trifluoromethanesulfonyl)imide 1-allyl-3-methylimidazolium) ), or poly(bis(trifluoromethanesulfonyl)imide N-methyl-N-propylpiperidine) )).

[0110] The ion-conducting polymer may include at least one ion-conducting repeating unit derived from an ether-based monomer, an acryloyl-based monomer, a methacryloyl-based monomer, or a siloxane-based monomer.

[0111] Examples of the ion-conducting polymers may include, but are not limited to, polyethylene oxide (PEO), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyvinyl sulfone, polysulfone, polypropylene oxide (PPO), polymethyl methacrylate, polyethyl methacrylate, polydimethylsiloxane, polyacrylic acid, polymethyl methacrylate, polyethyl methacrylate, 2-ethylhexyl polyacrylate, polybutyl methacrylate, 2-ethylhexyl polymethacrylate, polydecyl acrylate, polyvinyl acetate, phosphate polymers, polyester sulfides, and polyvinylidene fluoride (PVdF), Li-substituted Nafion, or any suitable ion-conducting polymer.

[0112] Examples of the electron-conducting polymer may include, but are not limited to, polyphenylene derivatives and polythiophene derivatives, or any suitable electron-conducting polymer.

[0113] The gel electrolyte can be obtained by adding a low molecular weight solvent to a solid electrolyte, for example, disposed between the positive and negative electrodes. The gel electrolyte can also be obtained by adding a solvent, such as a low molecular weight organic compound or oligomer, to a polymer.

[0114] The liquid electrolyte comprises a solvent and a lithium salt.

[0115] The solvent includes, but is not limited to, at least one of organic solvents, ionic liquids and oligomers, or any suitable solvent that is liquid at room temperature (25°C).

[0116] The organic solvent may include at least one of the following: ether-based solvents, carbonate-based solvents, ester-based solvents, or ketone-based solvents. Examples of the organic solvent may include at least one of the following: propylene carbonate, ethylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, butyl carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate, benzyl nitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, dimethylacetamide, dimethyl sulfoxide, di... Alkane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, succinate, diethylene glycol dimethyl ether (DEGDME), tetraethylene glycol dimethyl ether (TEGDME), polyethylene glycol dimethyl ether (PEGDME, Mn = ~500), dimethyl ether, diethyl ether, dibutyl ether, or dimethoxyethane, but not limited thereto, and any suitable organic solvent may be used, provided that it is in the liquid phase at room temperature.

[0117] Examples of the ionic liquid (IL) may include: i) at least one of the following: ammonium-based cations, pyrrolidine-based... cations, based on pyridine Cations, pyrimidine-based cationic, imidazole-based Cations based on piperidine cationic, pyrazole-based cations, based azole cationic, based on pyridazine cations, based Cations, sulfonium-based cations, or triazole-based cations ii) a cation; and at least one of the following: BF4 - PF6 - AsF6 - SbF6 - AlCl4 - HSO4 - ClO4 - CH3SO3 - CF3CO2 - (CF3SO2)2N - Cl - ,Br - I- SO4 2- CF3SO3 - (C2F5SO2)2N - (C2F5SO2)(CF3SO2)N - NO3 - Al2Cl7 - CH3COO - (CF3SO2)3C - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - SF5CF2SO3 - SF5CHFCF2SO3 - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - , or (O(CF3)2C2(CF3)2O)2PO - .

[0118] The lithium salt may include, but is not limited to, at least one of the following: lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2, LiTFSI), LiPF6, LiBF4, LiAsF6, LiClO4, LiNO3, lithium bis(oxalate)borate (LiBOB), LiN(SO2C2F5)2, LiC(SO2CF3)3, LiN(SO3CF3)2, LiC4F9SO3, LiAlCl4, lithium trifluoromethanesulfonate (LiCF3SO3, LiTfO), or any suitable lithium salt. The concentration of the lithium salt may be, for example, from about 0.01 M to about 5.0 M.

[0119] The lithium-air battery may further include, for example, a separator disposed between the positive and negative electrodes. The separator is not limited, provided it has a composition suitable for the operating conditions of the lithium-air battery. The separator may include, for example, a nonwoven polymer fabric comprising polypropylene or polyphenylene sulfide, a porous membrane comprising an olefin-based resin such as polyethylene or polypropylene, glass fiber, or a combination of two or more of these materials.

[0120] The electrolyte layer may have, for example, a solid polymer electrolyte impregnated in the separator or a liquid electrolyte impregnated in the separator. A solid polymer electrolyte impregnated in the separator can be prepared by disposing of a solid polymer electrolyte membrane on the opposite surface of the separator and simultaneously rolling the resulting structure. A liquid electrolyte impregnated in the separator can be prepared by injecting a liquid electrolyte comprising a lithium salt into the separator.

[0121] The lithium-air battery can be manufactured by: mounting the negative electrode on the inside of the casing, sequentially arranging the electrolyte layer on the negative electrode, arranging the positive electrode on the electrolyte layer, and arranging a porous positive electrode current collector on the positive electrode; then, arranging a pressing member on the porous positive electrode current collector to press the resulting cell structure, thereby allowing air including moisture and oxygen to transfer to the air electrode. The casing can be divided into an upper portion and a lower portion that respectively contact the negative electrode and the air electrode, and an insulating resin can be disposed between the upper portion and the lower portion of the casing to electrically insulate the positive electrode and the negative electrode from each other.

[0122] The lithium-air battery can be used as a primary lithium battery or a secondary lithium battery. The lithium-air battery can have any suitable shape, such as a coin, button, sheet, stack, cylinder, plane, or angle, but is not limited thereto. The lithium-air battery can be used in medium or large batteries for electric vehicles.

[0123] A schematic structure of a lithium-air battery 500 according to an embodiment is shown in Figure 8The lithium-air battery 500 includes: a positive electrode 200 adjacent to a first current collector 210, using air including moisture and oxygen as an active material; a negative electrode 300 adjacent to a second current collector 310 and including lithium; and a first electrolyte 400 disposed between the positive electrode 200 and the negative electrode 300. The first electrolyte layer 400 is a separator having a liquid electrolyte impregnated therein. A second electrolyte layer 450 is disposed between the positive electrode 200 and the first electrolyte layer 400. The second electrolyte layer 450 is a lithium-ion conductive solid electrolyte layer. The first current collector 210 may be porous and may function as a gas diffusion layer that allows air including moisture and oxygen to diffuse. Alternatively, the gas diffusion layer may be additionally disposed between the first current collector 210 and the positive electrode 200. A pressing member 220 for transferring air including moisture and oxygen to the positive electrode 200 may be arranged on the first current collector 210. A shell 320 made of insulating resin may be disposed between the positive electrode 200 and the negative electrode 300 to electrically insulate the positive electrode 200 and the negative electrode 300 from each other. Air may be supplied to the lithium-air battery 500 through air inlet 230a and discharged through air outlet 230b. The lithium-air battery 500 may be disposed in a stainless steel container. The air present in the cavity between the first current collector and the positive electrode comprises moisture and oxygen, and the volume percentage of moisture in the air may be 1 vol% to less than 100 vol%, for example 5 vol% to less than 100 vol%, 10 vol% to less than 100 vol%, 30 vol% to less than 100 vol%, 40 vol% to less than 100 vol%, 50 vol% to less than 100 vol%, 60 vol% to less than 100 vol%, 70 vol% to less than 100 vol%, 80 vol% to less than 100 vol%, or 90 vol% to less than 100 vol%, based on the total volume of the air.

[0124] The term "air" used in lithium-air batteries is not limited to atmospheric air, but can refer to a combination of gases including oxygen. This broad definition of "air" can also be applied to other applications, such as air batteries or air electrodes.

[0125] The method for preparing a positive electrode according to an embodiment includes the following steps: preparing a composition comprising an alkali-resistant compound and an adhesive; molding the composition to prepare a sheet; and heat-treating the sheet at a temperature of about 900°C to about 1300°C in an oxidizing atmosphere.

[0126] The composition may include, for example, the alkali-resistant compound, adhesive, dispersant, or plasticizer. There are no particular limitations on the type and amount of the adhesive, dispersant, and plasticizer used, and any suitable adhesive, dispersant, and plasticizer for forming green sheets including ceramics may be used. The composition may include, for example, about 5 parts by weight to about 20 parts by weight of adhesive, about 1 part by weight to about 10 parts by weight of dispersant, and about 1 part by weight to about 10 parts by weight of plasticizer, based on 100 parts by weight of the alkali-resistant compound. The composition may further include a solvent. The amount of the solvent may be, for example, about 1 part by weight to about 500 parts by weight, based on the total solids content of 100 parts by weight of the alkali-resistant compound, adhesive, dispersant, or plasticizer.

[0127] The steps for preparing the sheet may include, for example, coating the composition onto a substrate to prepare a coating and drying the composition on the substrate to prepare a dried coating; and stacking and laminating a plurality of dried layers to prepare the sheet.

[0128] The composition can be applied to a substrate, such as a release film, to a thickness of about 1 to about 1000 μm using a doctor blade, and then dried to prepare a dried coating.

[0129] Multiple dried coatings are prepared on the release film and stacked face to face, then laminated to prepare a green sheet. The lamination can be performed by hot rolling at a predetermined pressure.

[0130] The prepared green sheet can be heat-treated in an oxidizing atmosphere at 500°C to 700°C for 1 to 4 hours, and then further heat-treated in an oxidizing atmosphere at a temperature of about 900°C to about 1300°C for about 3 to about 10 hours.

[0131] As a result of heat treatment at a temperature of about 500°C to about 700°C in an oxidizing atmosphere for about 1 hour to about 4 hours, the organic material in the green sheet can be stably decomposed and removed. Furthermore, as a result of heat treatment at a temperature of about 900°C to about 1300°C in an oxidizing atmosphere for about 3 to about 10 hours, the alkali-resistant compound powder is sintered, thus preparing a stable and robust porous layer. During the heat treatment, the heating rate can be, for example, 5°C / min until the heat treatment temperature is reached, and cooling can be achieved by natural cooling.

[0132] The inventive concept will be described in further detail with reference to the following embodiments and comparative examples. However, the embodiments provided are for illustrative purposes only, and the scope of the inventive concept is not limited thereto.

[0133] Preparation of positive electrode

[0134] Example

[0135] Example 1: Positive electrode including Y2O3

[0136] Y₂O₃ (Sigma Aldrich) was milled in a ball mill to obtain a powder with an average diameter of 100 nanometers (nm). The Y₂O₃ powder and polyacrylic acid (molecular weight: 1,800 Daltons) as a dispersant were added to ethanol and stirred to prepare a suspension. The amount of Y₂O₃ was 0.1 wt% and the amount of dispersant was 0.05 wt%.

[0137] Carbon paper (SGL, 29BA) was used as both the negative and positive electrodes in the suspension. The carbon paper used had a thickness of approximately 190 μm, a porosity of approximately 89%, and a porosity of less than 10 mΩ·cm. -2 Area resistance (through the plane resistance).

[0138] The fibrous carbon contained in the carbon paper has an average diameter of approximately 7 μm. A voltage of 100 V / cm is applied between the positive and negative electrodes for 10 minutes to deposit Y2O3 onto the carbon paper by electrophoretic deposition.

[0139] The loading level of the deposited metal oxide coating was 2 mg / cm³. 2 The carbon paper with metal oxide deposited on it was removed from the suspension and dried at 25°C for 2 hours to prepare the positive electrode. The positive electrode has a porosity of approximately 89%.

[0140] Examples 2 and 3

[0141] The positive electrode was prepared in the same manner as in Example 1, except that HfO2 (Sigma Aldrich) and Ta2O5 (Sigma Aldrich) were used instead of Y2O3, respectively.

[0142] Comparative Example 1: Li 0.34 La 0.55 RuO3

[0143] According to Li 0.34 La 0.55 The composition of RuO3 involves adding powdered Li2CO3, La2O3, and RuO2 to ethanol and mixing them. The amount of ethanol is approximately 4 parts by weight, based on the total weight of 100 parts by weight of Li2CO3, La2O3, and RuO2.

[0144] The mixture was placed in a ball mill for grinding and mixing for 4 hours. The mixed product was dried and heated to 800°C at a heating rate of about 5°C / min, and then subjected to a heat treatment at 800°C in air for 4 hours.

[0145] The powder obtained from the first heat treatment is ground to prepare a powder with a primary particle size of about 0.3 μm. The prepared powder is pressed to prepare cylindrical sheets, each with a diameter of about 1.3 cm, a height of about 0.5 cm, and a weight of about 0.3 g. The prepared sheets are subjected to a second heat treatment at 1200 °C in air for about 24 hours to obtain the desired product. When the temperature is increased to 1200 °C for the second heat treatment, the heating rate is about 5 °C / min.

[0146] Using the prepared Li 0.34 La 0.55 The positive electrode was prepared in the same manner as in Example 1, using RuO3 instead of Y2O3.

[0147] Evaluation Example 1: Evaluation of Stability to Strong Bases

[0148] In a 1M LiOH aqueous solution, using the positive electrode prepared in Examples 1-3 and Comparative Example 1 as the working electrode and a Pt electrode as the counter electrode, a voltage of 2.8V was applied for 18 hours, and the metals dissolved in the aqueous solution, excluding Li ions, were analyzed. The results are shown in Table 1 and... Figure 1 Furthermore, the Gibbs free energies of Y₂O₃, HfO₂, and Ta₂O₅ in 1M LiOH aqueous solution, respectively, calculated using quantum computing with the Pourbaix algorithm, were 0 eV, and the Li used in Comparative Example 1 was also 0 eV. 0.34 La 0.55 The Gibbs free energy of RuO3 is -0.26 eV.

[0149] Table 1

[0150] Target metal to be analyzed Solubility (mg / L) Comparative Example 1 Ru 0.81 Example 1 Y 0 Example 2 Hf 0 Example 3 Ta 0

[0151] As can be seen from Table 1, the electrodes used in Examples 1-3, comprising oxides based on Y, Hf, and Ta respectively, are insoluble in strong alkaline aqueous solutions, while the Ru-based oxide in Comparative Example 1 dissolves in strong alkaline aqueous solutions (e.g., lithium aqueous solutions). Therefore, it is confirmed that the materials used in Examples 1-3 are stable in the presence of strong alkalis.

[0152] Manufacturing of lithium-air batteries

[0153] Example 4

[0154] The separator (Celgard 3501) is placed on the negative electrode of the lithium metal foil.

[0155] 0.2 mL of an electrolyte solution containing 1 M LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) dissolved in propylene carbonate (PC) was injected into the separator to prepare the negative electrode intermediate layer.

[0156] A lithium aluminum titanium phosphate (LATP) solid electrolyte layer (250 μm thick, Ohara Corp., Japan) is arranged on the separator to prepare a lower structure comprising a negative electrode / negative electrode intermediate layer / solid electrolyte layer.

[0157] The lower structure is covered with a bag containing aluminum coated on a polyolefin film. A window of predetermined size is installed at the top of the bag to allow the LATP solid electrolyte to be exposed to the outside of the bag.

[0158] The positive electrode prepared in Example 1 is arranged on an exposed LATP solid electrolyte. Next, a gas diffusion layer (GDL) (SGL, 25BC) is arranged on the positive electrode, and a nickel mesh is arranged on the GDL. The space between the positive electrode and the GDL is filled with air containing moisture and oxygen. A pressing member is then arranged on the nickel mesh to press the resulting cell, thereby allowing air to transfer to the positive electrode, thus manufacturing a lithium-air battery.

[0159] Examples 5 and 6 and Comparative Example 2

[0160] The lithium-air battery was manufactured in the same manner as in Example 4, except that the positive electrode prepared in Examples 2-3 and Comparative Example 1 was used instead.

[0161] Evaluation Example 2: Evaluation of Lithium-Air Batteries

[0162] Charging and discharging are performed in an oxygen atmosphere at 40°C, 1 atm, and 100% relative humidity.

[0163] The lithium-air batteries manufactured in Examples 4-6 were subjected to 10 repeated charge-discharge cycles at 0.05 mA / cm². 2 It is charged and discharged with a constant current for 10 hours.

[0164] The results of the first and second charge-discharge cycle tests are shown below. Figure 2 (Example 4) Figure 3 (Example 5), and Figure 4 In (Example 6). For example... Figure 2-4 As shown, the lithium-air batteries prepared in Examples 4-6 using cathodes each comprising alkali-resistant compounds exhibited charge-discharge curves without short circuits, confirming that cathodes comprising alkali-resistant compounds can be used in lithium-air batteries using air containing moisture and oxygen as the cathode active material.

[0165] Evaluation Example 3: XRD Evaluation of Alkali-Resistant Compounds After Charge-Discharge Cycles in Lithium-Air Batteries

[0166] The XRD spectra of the alkali-resistant cathode materials (Y₂O₃ and HfO₂) used in Examples 1 and 2 were measured, and the XRD spectra of the alkali-resistant cathode materials (Y₂O₃ and HfO₂) used in Examples 4 and 5 were measured after 10 charge-discharge cycles of Example 2. The measurement results are shown in the figures below. Figure 5 (Y2O3) and Figure 6 (HfO2) in.

[0167] In addition, the XRD spectrum of the cathode material (Ru-based oxide) used in Comparative Example 1 was measured, and the XRD spectrum of the cathode material (Ru-based oxide) included in the cathode of Comparative Example 2 was measured after 10 charge-discharge cycles of Evaluation Example 2. The measurement results are shown in... Figure 7 middle.

[0168] Reference Figure 5-7 Even after 10 charge-discharge cycles, no crystallographic changes of the alkali-resistant compound were observed in the lithium-air battery using a cathode comprising the alkali-resistant compound, confirming the structural stability of the lithium-air battery. Conversely, the cathode material used in Comparative Example 1 was degraded by discharge products (e.g., LiOH) during repeated charge-discharge cycles, exhibiting a decrease in the perovskite peak and an increase in the RuO2 peak, indicating that the discharge products led to the disintegration of the crystal structure of the cathode material.

[0169] According to one aspect, by including an alkali-resistant compound in the positive electrode, the electrochemical stability of the positive electrode and the lithium-air battery containing it can be improved.

[0170] It should be understood that the embodiments described herein are to be considered in the descriptive sense only and are not intended for limiting purposes. The descriptions of features, aspects, or advantages within each embodiment should be considered applicable to other similar features, aspects, or advantages in other embodiments. Although one or more embodiments have been described with reference to the accompanying drawings, those skilled in the art will understand that various changes in form and detail may be made therein without departing from the spirit and scope defined by the appended claims.

Claims

1. The positive electrode for an air battery, the positive electrode comprising: A porous conductive material; And An alkali-resistant compound on the surface of the porous conductive material, the alkali-resistant compound being resistant to pH 7 to 14 relative to Li / Li + It has 0 or positive Gibbs free energy at 2V to 4.5V. where the positive electrode includes the alkali-resistant compound in an amount of 60 parts by weight to less than 100 parts by weight, based on 100 parts by weight of the positive electrode, and where the alkali-resistant compound is represented by Chemical Formula 1: Chemical Formula 1 M1 α X1 β where in Chemical Formula 1, M1 is at least one of the following: K, Be, Mg, Ca, Sr, Ba, Sc, Y, Hf, Nb, Ta, Mo, W, Cd, B, Al, Ga, In, C, Si, Ge, Sn, P, As, Sb, Bi, Te, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, U, or Pu, X1 is at least one of O or F, and 0 < α ≤ 32 and 0 < β ≤ 68.

2. The positive electrode according to claim 1, wherein the alkali-resistant compound is electrochemically stable at a pH of 9 to 14.

3. The positive electrode of claim 1, wherein the alkali-resistant compound is relative to Li / Li + It has a Gibbs free energy difference (ΔG) of 0 eV under voltage conditions from 2V to 4.5V.

4. The positive electrode of claim 1, wherein the alkali-resistant compound is effective at pH 12 to 14 relative to Li / Li + Lithium metal is electrochemically stable at voltages from 2V to 4.5V.

5. The positive electrode of claim 1, wherein the alkali-resistant compound is effective at pH 12 to 14 relative to Li / Li + It exhibits oxidation and reduction resistance to lithium metal at voltages ranging from 2V to 4.5V.

6. The positive electrode according to claim 1, wherein the alkali-resistant compound includes at least one of the following: Y, Hf, and Ta.

7. The positive electrode according to claim 6, wherein the alkali-resistant compound includes at least one of a binary compound or a ternary compound.

8. The positive electrode according to claim 1, wherein the alkali-resistant compound is represented by at least one of Chemical Formula 2 or Chemical Formula 3: Chemical Formula 2 M2 a1 X2 b1 where in Chemical Formula 2, M2 is at least one of the following: Be, Sc, Y, Hf, Ta, In, Sn, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, U, or Pu, X2 is at least one of O or F, and 0 < a1 ≤ 2, and 0 < b1 ≤ 5, Chemical Formula 3 M3 a2 M4 a3 X3 b2 where in Chemical Formula 3, M3 and M4 are each independently at least one of the following: K, Mg, Ca, Sr, Ba, Sc, Y, Hf, Nb, Ta, Mo, W, Cd, B, Al, Ga, In, C, Si, Ge, Sn, P, As, Sb, Bi, Te, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, or U, X3 is at least one of O or F, and 0 < a2 ≤ 29, 0 < a3 ≤ 29, and 0 < b2 ≤ 68.

9. The positive electrode according to claim 1, wherein the alkali-resistant compound is represented by Chemical Formula 4: Chemical Formula 4 M3’ a2’ M4’ a3’ X3’ b2’ where in Chemical Formula 4, M3' is at least one of the following: K, Mg, Ca, Sr, Ba, Sc, Y, Ta, Cd, Al, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, or U, M4' is at least one of the following: Sc, Y, Hf, Nb, Ta, Mo, W, Cd, B, Al, Ga, In, C, Si, Ge, Sn, P, As, Sb, Bi, Te, Ho, Tm, Th, or U, X3' is at least one of O or F, 0 < a2' ≤ 29, 0 ≤ a3' ≤ 25, and 0 < b2' ≤ 68.

10. The positive electrode of claim 9, wherein when a3' is 0, X3' comprises O and F.

11. The positive electrode according to claim 1, wherein the alkali-resistant compound comprises at least one of the following: Y₂O₃, HfO₂, Ta₂O₅, Nd₂O₃, PuO₂, Tb₂O₃, Dy₂O₃, Gd₂O₃, Sm₂O₃, Ho₂O₃, Er₂O₃, Sc₂O₃, Tm₂O₃, Lu₂O₃, ThO₂, UO₃, Eu₂O₃, In₂O₃, BeO, SnO₂, YbF₂, BaTa₂O₆, BaUO₄, CaTa₂O₆, CaUO₄, Cd(GaO₂)₂, Cd₂Sb₂O₇, CdIn₂O₄, CdSnO₃, Dy₂O₇, Dy₂O₃, HfO₂, Ta₂O₅, Nd₂O₃, PuO₂, Tb₂O₃, Dy₂O₇, Gd₂O₃, Sm₂O₃, Ho₂O₃, Er₂O₃, Sc₂O₃, Tm₂O₇, Lu₂O₃, ThO₂, Tb₂O₆, Tb₂O₆, Dy₂O₇, Gd₂O₃, Sm₂O₆, HfO₂O₆, Tb₂O₆, Dy₂O� 11 Y5O 24 Dy 29 Y3O 48 , Dy2CO5, Dy2GeO5, Dy2Hf2O7, Dy2SiO5, Dy2Sn2O7, Dy2WO6, Dy3Al5O 12 Dy3Ga5O 12 Dy3GaO6, Dy3Y5O 12 , DyAsO4, DyNbO4, DyOF, DyPO4, DyTaO4, DyY3O6, DyY7O 12 Er 10 W2O 21 , Er2GeO5, Er2SiO5, Er2Sn2O7, Er3Al5O 12 Er3Ga5O 12 , ErAsO4, ErBO3, ErNbO4, ErPO4, ErTaO4, Eu2Hf2O7, Eu2SiO5, Eu2Sn2O7, Eu3Ga5O 12 Eu3GaO6, Eu3NbO7, Eu6WO 12 , EuOF, Gd2GeO5, Gd2Hf2O7, Gd2MoO6, Gd2SiO5, Gd2Sn2O7, Gd3Al5O 12 Gd3Ga5O 12 Gd3GaO6, Gd3SbO7, Gd3Y 13 O 24 Gd3Y5O 12 Gd5Y3O 12 Gd6WO 12 , GdAsO4, GdInO3, GdNbO4, GdOF, GdPO4, GdTaO4, Ho2SiO5, Ho2Sn2O7, Ho2WO6, Ho3Al5O 12 Ho3Ga5O 12 、Ho3GaO6、Ho3ScO6、HoAsO4、HoBO3、HoNbO4、HoOF、HoPO4、HoTaO4、KTa5O 13 Lu2SiO5, Lu2Sn2O7, Lu4Hf3O 12 Lu6UO 12 Lu6WO 12 、LuGaO3、LuNbO4、LuSbO4、LuTaO4、Mg(GaO2)2、MgTa2O6、Nd2GeO5、 Nd2Hf2O7、Nd2MoO6、Nd2SiO5、Nd2Sn2O7、Nd2TeO6、Nd2WO6、Nd3Ga5O 12 Nd3GaO6, Nd3U2O 10 、Nd4Ga2O9、NdAlO3、NdAsO4、NdBO3、NdNbO4、NdOF、NdPO4、NdSbO4、NdScO3、NdTaO4、PrTaO4、ScTaO4、Sm 27 Y5O 48 Sm2Ge2O7, Sm2Hf2O7, Sm2MoO6, Sm2SiO5, Sm2Sn2O7, Sm2TeO6, Sm2Th8O 19 Sm2WO6, Sm3Ga5O 12 、Sm3GaO6、SmAlO3、SmAsO4、SmBO3、SmNbO4、SmOF、SmPO4、SmSbO4、SmScO3、SmTaO4、SmY 15 O 24 Sr3U 11 O 36 SrTa2O6, Ta 12 MoO 33 Ta2Cd2O7, TaAlO4, TaBiO4, TaInO4, Tb2Ge2O7, Tb2SiO5, Tb2Sn2O7, Tb2WO6, Tb3Al5O 12 Tb3Ga5O 12 Tb3GaO6, TbAsO4, TbNbO4, TbOF, TbPO4, TbTaO4, ThTa2O7, Tm2Si2O7, Tm2Sn2O7, Tm3Al5O 12 Tm3Ga5O 12 Tm6WO 12 、TmNbO4、TmOF、TmPO4、TmTaO4、UCdO4、Y 11 Tm5O 24 Y 13 Ho 19 O 48 、 Y 13 Ho3O 24 、 Y 13 Tm3O 24 、 Y 15 TmO 24 、 Y2GeO5, Y2Hf2O7, Y2HfO5, Y2SiO5, Y2Sn2O7, Y2Th8O 19 、 Y3Al5O 12 、 Y3Ga5O 12 、 Y3GaO6, Y3SbO7, Y5Tm 11 O 24 、 Y6WO 12 、 Y7HoO 12 、 Y7TmO 12 、 YAsO4, Yb4Ta 25 O 68 、 YbCO3, YBO3, YNbO4, YOF, YPO4, or YTaO4.

12. The positive electrode of claim 1, wherein the air comprises 1 volume percentage to less than 100 volume percentage of water, based on the total volume of the air.

13. The positive electrode of claim 1, wherein the alkali-resistant compound comprises at least one of the following: Dy2O3, Er2O3, Gd2O3, HfO2, Ho2O3, Lu2O3, Nd2O3, PuO2, Sc2O3, Sm2O3, Ta2O5, Tb2O3, ThO2, Tm2O3, or Y2O3.

14. Lithium-air batteries, including: The positive electrode as described in any one of claims 1-13; Including lithium metal anodes; and The electrolyte is disposed between the positive electrode and the negative electrode.

15. The lithium-air battery of claim 14, wherein the positive electrode is inert in the presence of discharge products having a pH of 9 to 14.

16. The lithium-air battery of claim 15, wherein the discharge products include LiOH.

17. The lithium-air battery of claim 14, wherein the electrolyte comprises a solid electrolyte.

18. The lithium-air battery of claim 14, wherein the positive electrode comprises a porous layer, and The porous layer includes the alkali-resistant compound.

Images