JP2015069960A - Lithium air secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium air secondary battery which is low in the charge voltage, small in the difference between charge and discharge voltages, and even after the repetition of charge and discharge cycles, small in the reduction in discharge capacity, and which allows a lithium air secondary battery to work as a high-capacity secondary battery.SOLUTION: A lithium air secondary battery according to the present invention comprises: an air electrode; a negative electrode; and an organic electrolytic solution in contact with the air electrode and the negative electrode. The air electrode includes a conductive material, a catalyst and a binding agent. The negative electrode includes metallic lithium or a lithium-containing substance. The organic electrolytic solution includes a lithium salt, and an organic solvent. The catalyst of the air electrode includes a ruthenium oxide. The organic solvent of the organic electrolytic solution includes tetraethylene glycol dimethyl ether.

Description

  The present invention relates to a lithium air secondary battery. In particular, the present invention relates to a lithium-air secondary battery that is smaller and lighter than a conventional secondary battery such as a lead-acid battery or a lithium ion battery, and that can realize a much larger discharge capacity.

  A lithium-air secondary battery that uses oxygen in the air as a positive electrode active material is always supplied with oxygen from the outside of the battery, and a large amount of metallic lithium, which is a negative electrode active material, can be filled in the battery. For this reason, it has been reported that the value of the discharge capacity per unit volume of the battery can be greatly increased.

  As reported in Non-Patent Document 1 and Non-Patent Document 2 so far, by adding various catalysts to the gas diffusion type air electrode as the positive electrode, battery performance such as discharge capacity and cycle characteristics can be improved. Has been tried.

Transition metal oxides have been studied as electrode catalysts for gas diffusion air electrodes. For example, in the above document, transition metal oxides such as λ-MnO ₂ are used in Non-Patent Document 1, and in Non-Patent Document 2, mainly iron oxide (Fe ₂ O ₃ ), cobalt oxide (Co ₃ O ₄ ), and the like are used. Transition metal oxides have been investigated. These documents show the results of the battery characteristic test of the lithium air secondary battery as follows.

  In the secondary battery disclosed in Non-Patent Document 1, a charge / discharge cycle was possible, but after 4 cycles, the discharge capacity was reduced to about 1/4, and the performance as a secondary battery was low. . Further, the secondary battery disclosed in Non-Patent Document 1 has a problem that the charging voltage is about 4.0 V, which is very large compared to the average discharge voltage of 2.7 V, and the energy efficiency is low. .

On the other hand, in Non-Patent Document 2, nine types of catalysts are examined, and a very large discharge capacity of 1000 to 3000 mAh / g is obtained per weight of carbon contained in the air electrode. However, when charge and discharge are repeated, the discharge capacity is remarkably reduced. For example, in the case of Co ₃ O ₄ , the capacity retention rate becomes about 65% in 10 cycles. As described above, the lithium-air secondary battery of Non-Patent Document 2 also shows a significant decrease in capacity, and sufficient characteristics as a secondary battery are not obtained. In most cases, the average discharge voltage is about 2.5 V, while the charging voltage is 4.0 to 4.5 V, and the lowest is about 3.9 V. For this reason, the lithium-air secondary battery of Non-Patent Document 2 has low charge / discharge energy efficiency.

In many reports including Non-Patent Documents 1 and 2, lithium salt such as LiClO ₄ , LiPF ₆ , LiTFSI (lithium bistrifluoromethanesulfonylimide), propylene carbonate, or the like is used as the organic electrolyte of the lithium air secondary battery. A solution dissolved in a carbonate ester solvent at a concentration of about 1.0 mol / l is used.

J. Read, Journal of The Electrochemical Society, Vol.149, pp.A1190-A1195 (2002). Aurelie Debart et al., Journal of Power Sources, Vol.174, pp.1177 (2007).

  The present invention operates a lithium-air secondary battery as a high-capacity secondary battery, and has a low charge voltage, a small voltage difference between charge and discharge, and a small decrease in discharge capacity even after repeated charge and discharge cycles. The purpose is to provide.

The lithium air secondary battery according to the present invention includes an air electrode, a negative electrode, and an organic electrolyte in contact with the air electrode and the negative electrode,
The air electrode includes a conductive material, a catalyst, and a binder,
The negative electrode includes metallic lithium or a lithium-containing material,
The organic electrolyte contains a lithium salt and an organic solvent,
The air electrode catalyst includes ruthenium oxide, and the organic solvent of the organic electrolyte includes tetraethylene glycol dimethyl ether.

In one embodiment of the present invention, the ruthenium oxide is selected from RuO ₂ , RuO ₄ , Ru ₂ O ₃ , Sr ₂ RuO _4, or SrRuO ₃ .

  In one embodiment of the present invention, the solvent of the organic electrolyte is tetraethylene glycol dimethyl ether. In another embodiment of the present invention, the organic solvent of the organic electrolyte solution is a mixed solvent containing a first component and a second component, the first component is tetraethylene glycol dimethyl ether, and the second component is a carbonate ester. It contains at least one kind of system solvent. In the present embodiment, in the mixed solvent, the content of the carbonate ester solvent is preferably 5 to 35% by volume based on the total volume of the mixed solvent. Furthermore, in this embodiment, in the mixed solvent, the content of the carbonate ester solvent is more preferably 10 to 30% by volume based on the total volume of the mixed solvent. Furthermore, in one embodiment of the present invention, the carbonate solvent is dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate (MBC), Diethyl carbonate (DEC), ethyl propyl carbonate (EPC), ethyl isopropyl carbonate (EIPC), ethyl butyl carbonate (EBC), dipropyl carbonate (DPC), diisopropyl carbonate (DIPC), dibutyl carbonate (DBC), ethylene carbonate (EC), It is selected from propylene carbonate (PC) or 1,2-butylene carbonate (1,2-BC).

  With the above-described lithium-air secondary battery of the present invention, battery performance can be improved.

  By adopting the configuration of the lithium-air secondary battery of the present invention, it is possible to provide a secondary battery with a low charging voltage and a small voltage difference between charging and discharging. Further, with the above configuration, even when the charge / discharge cycle is repeated, the reduction in discharge capacity is small, and a high energy density lithium-air secondary battery can be provided. And the lithium air secondary battery which has such an outstanding characteristic can extend the drive time of various drive systems including electric equipments, such as mobile devices, such as an electric vehicle and a smart phone, significantly.

1 is a schematic view of a lithium air secondary battery according to the present invention. It is a schematic sectional drawing for showing the structure of the lithium air secondary battery used for measurement in an example. 2 is a graph showing an initial charge / discharge curve of the lithium-air secondary battery of Example 1. FIG.

  Hereinafter, an embodiment of a lithium-air secondary battery according to the present application will be described in detail with reference to the drawings.

[Configuration of lithium-air secondary battery]
As shown in FIG. 1, the lithium-air secondary battery 100 according to the present invention includes at least an air electrode 102, a negative electrode 104, and an organic electrolyte 106, and the air electrode 102 functions as a positive electrode.

  More specifically, the air electrode 102 may include a catalyst, a conductive material, and a binder as components. The negative electrode 104 can be composed of a material such as a lithium-containing alloy capable of releasing and absorbing metallic lithium or lithium ions. Moreover, an organic electrolyte solution can be disposed between the air electrode and the negative electrode.

  Each of the above components will be described below. In the present specification, the electrolytic solution refers to a case where the electrolyte is in a liquid form.

(I) Air electrode (positive electrode)
In the present invention, the air electrode may include a catalyst, a conductive material, a binder, and the like.

(I-1) Catalyst In the lithium air secondary battery of the present invention, ruthenium oxide is included as a catalyst for the air electrode. In particular, the air electrode preferably contains ruthenium oxide (RuO ₂ ), which is highly active for both oxygen reduction (discharge) and oxygen generation (charge) reactions, as an electrode catalyst. By including ruthenium oxide, the lithium air secondary battery of the present invention can enhance the performance as a secondary battery.

  In the air electrode of the lithium secondary battery of the present invention, the electrode reaction proceeds in the three-phase portion of electrolyte / electrode catalyst / gas (oxygen). That is, the organic electrolyte solution 106 penetrates into the air electrode 102, and oxygen gas in the atmosphere is supplied at the same time, so that a three-phase site where electrolyte solution-electrode catalyst-gas (oxygen) coexists is formed. If the electrode catalyst is highly active, oxygen reduction (discharge) and oxygen generation (charge) proceed smoothly and battery performance is greatly improved.

The reaction at the air electrode can be expressed as follows.
2Li ⁺ + (1/2) O ₂ + 2e ⁻ → Li ₂ O (1)
2Li ⁺ + O ₂ + 2e ⁻ → Li ₂ O ₂ (2)

Lithium ions (Li ⁺ ) in the above formula are dissolved in the organic electrolytic solution from the negative electrode by electrochemical oxidation, and move through the organic electrolytic solution to the air electrode surface. Oxygen (O ₂ ) is taken into the air electrode from the atmosphere (air). The material that dissolves from the negative electrode ^(Li +), the material to be deposited at the cathode _(LiO 2), and showed air _{(O 2)} together with the components of FIG.

Ruthenium in ruthenium oxide (RuO ₂ ), which is preferable as an electrode catalyst for the air electrode (positive electrode), can exist as ions having a valence of +4, +3, and the like. Further, depending on conditions for the synthesis of ruthenium oxide, there may be a vacancy (also referred to as an oxygen vacancy in this specification) capable of taking oxygen into the ruthenium oxide.

  Since such ruthenium oxide has a strong interaction with oxygen which is a positive electrode active material, many oxygen species can be adsorbed on the surface of ruthenium oxide, or oxygen species can be occluded in oxygen vacancies.

  Thus, the oxygen species adsorbed on the surface of ruthenium oxide or occluded in the oxygen vacancies is used as an oxygen source (active intermediate reactant) of the above formulas (1) and (2) for the oxygen reduction reaction. The above reaction can easily proceed. Moreover, said ruthenium oxide has activity also with respect to the charging reaction which is a reverse reaction of Formula (1) and Formula (2). Therefore, charging of the battery, that is, the oxygen generation reaction on the air electrode proceeds efficiently. Thus, ruthenium oxide functions effectively as an electrode catalyst.

In the lithium-air secondary battery of the present invention, in order to increase the efficiency of the battery, it is desirable that there are more reaction sites (the above-described three-phase portion of electrolyte / electrode catalyst / air (oxygen)) that cause an electrode reaction. . From this point of view, in the present invention, it is important that the above-mentioned three-phase sites are present in a large amount on the surface of the electrode catalyst, and it is desirable that the catalyst used has a high specific surface area. In the present invention, for example, ruthenium oxide preferably has a specific surface area of 30 m ² / g or more.

  The ruthenium oxide preferably used in the present invention can be obtained by various methods. For example, ruthenium oxide can be obtained by various synthetic methods using known processes such as a solid phase method and a liquid phase method.

For example, a method of preparing a ruthenium oxide precursor by a liquid phase method using a metal chloride of ruthenium (RuCl ₃ ) or a metal nitrate [Ru (NO ₃ ) ₃ ] and then heat-treating this precursor can be mentioned. In the present invention, it is desirable to prepare ruthenium oxide by a method including this liquid phase method. Specific procedures of the liquid phase method include a method in which an aqueous solution is evaporated to dryness, a precipitation method in which an alkaline aqueous solution is dropped into the aqueous solution, and a method in which a ruthenium metal alkoxide is hydrolyzed.

  Next, the ruthenium oxide precursor obtained by the liquid phase method is heat-treated. In many cases, the ruthenium oxide precursor obtained by the liquid phase method is in an amorphous state because crystallization has not progressed. Crystalline ruthenium oxide can be obtained by heat-treating this amorphous precursor at a temperature of 100 ° C. or higher. The ruthenium oxide thus obtained exhibits high performance even when used as an electrode catalyst for the air electrode of the lithium-air secondary battery of the present invention.

Here, as described above, in the present invention, the specific surface area of ruthenium oxide is preferably 30 m ² / g or more, but this is a value after heat treatment when ruthenium oxide is prepared by a liquid phase method. is there.

In addition, the specific surface area of ruthenium oxide produced by heat treatment is significantly reduced, and only about 10 m ² / g may be obtained. In particular, the specific surface area decreases when fired at a high temperature. In order to prevent such a decrease in specific surface area, the amorphous precursor is preferably heat-treated at a temperature of 100 ° C. or higher as described above, and more preferably heat-treated at a relatively low temperature of about 100 to 200 ° C. Moreover, the time of this heat processing is 0.5 to 24 hours, Preferably it is 1 to 5 hours. Ruthenium oxide having a high specific surface area can be obtained by heat treatment in such a temperature range and treatment time. That is, the ruthenium oxide powder obtained by heat-treating an amorphous ruthenium oxide precursor at a relatively low temperature is hardly sintered, and thus has a low crystallinity, but is in a nano-sized microcrystalline state, and is 100 m. It can have a very large specific surface area of about ² / g. Therefore, when used as an electrode catalyst of the present invention, it is suitable as a catalyst and can realize excellent battery performance.

In the present invention, in addition to the ruthenium oxide (RuO ₂ ), other ruthenium oxides such as ruthenium tetroxide (RuO ₄ ) and Ru ₂ O ₃ can be used as the air electrode catalyst. Alternatively, a metal oxide containing ruthenium such as Sr ₂ RuO ₄ or SrRuO ₃ can be used. In this specification, metal oxides containing ruthenium such as ruthenium oxide, ruthenium tetroxide (RuO ₄ ), Ru ₂ O _{3 and the} like are collectively referred to as “ruthenium oxide”. Furthermore, with respect to ruthenium itself, its isotopes can also be used. In the lithium secondary battery of the present invention, ruthenium oxide (RuO ₂ ) that can be synthesized at a low temperature is suitable as a catalyst for the air electrode.

(I-2) Conductive material In this invention, a conductive material can be included in an air electrode. An example of the conductive material is carbon. Specific examples include carbon blacks such as ketjen black and acetylene black, activated carbons, graphites, and carbon fibers. In order to secure sufficient reaction sites in the air electrode, carbon having a large specific surface area is suitable. Specifically, a material having a BET specific surface area of 300 m ² / g or more is desirable. These carbons can be obtained, for example, as commercial products or by known synthesis.

  In the lithium air secondary battery of the present invention, as described above, it is desirable that the specific surface area of the catalyst and carbon used for the air electrode have a predetermined value. In the present invention, the specific surface area can be measured using a commercially available apparatus. For example, the specific surface area can be measured by a procedure using liquid nitrogen as a cooling medium using a commercially available measuring device.

(I-3) Binder (binder)
The air electrode can contain a binder (binder). The binder is not particularly limited, and examples thereof include polytetrafluoroethylene (PTFE), polyethylene, polypropylene, polyvinylidene fluoride (PVDF), and styrene butadiene rubber. These binders can be used as a powder or as a dispersion.

(I-4) Preparation of air electrode An air electrode can be prepared as follows. An air electrode can be formed by mixing a catalyst such as ruthenium oxide powder, carbon powder and a binder powder such as polytetrafluoroethylene (PTFE), and pressing the mixture onto a support such as a titanium mesh. it can. Moreover, an air electrode can be formed by disperse | distributing the above-mentioned mixture in solvents, such as an organic solvent, and making it into a slurry form, apply | coating on a metal mesh or a carbon cloth, or a carbon sheet, and drying.

  In the lithium air secondary battery of the present invention, the catalyst content in the air electrode is preferably 1 to 50% by weight, more preferably 5 to 30% by weight.

  Moreover, in order to increase the strength of the electrode and prevent leakage of the electrolytic solution, it is possible to produce a more stable air electrode by applying not only a cold press but also a hot press.

  In the air electrode, one surface of the electrode constituting the air electrode is exposed to the atmosphere, and the other surface is in contact with the electrolytic solution.

(II) Negative Electrode The lithium air secondary battery of the present invention contains a negative electrode active material in the negative electrode. The negative electrode active material is not particularly limited as long as it is a material that can be used as a negative electrode material for a lithium secondary battery. For example, metallic lithium can be mentioned. Alternatively, examples of the lithium-containing substance include lithium and silicon or tin alloy, or lithium nitride such as Li _2.6 Co _0.4 N, which is a substance that can release and occlude lithium ions. be able to.

  In addition, when using said silicon or tin alloy as a negative electrode, the silicon | silicone or tin etc. which do not contain lithium can also be used when synthesize | combining a negative electrode. However, in this case, prior to the production of the air battery, a chemical method or an electrochemical method (for example, a method in which an electrochemical cell is assembled and lithium and silicon or tin are alloyed) is used to form silicon or silicon. It is necessary to treat so that tin is in a state containing lithium. Specifically, it is preferable that the working electrode contains silicon or tin, the counter electrode is lithium, and a treatment such as alloying is performed by flowing a reducing current in the organic electrolyte.

  The negative electrode of the lithium air secondary battery of the present invention can be formed by a known method. For example, when lithium metal is used as the negative electrode, the negative electrode may be produced by stacking a plurality of metal lithium foils into a predetermined shape.

  Here, the reaction of the negative electrode (metallic lithium) during discharge can be expressed as follows.

(Discharge reaction)
Li → Li ⁺ + e ⁻ (3)

  In addition, in the negative electrode at the time of charge, the lithium precipitation reaction which is the reverse reaction of Formula (3) occurs.

(III) Electrolyte (organic electrolyte)
The lithium air secondary battery of the present invention includes an electrolyte. This electrolyte should just be what can move a lithium ion between an air electrode (positive electrode) and a negative electrode. In the present invention, an organic electrolytic solution in which a metal salt containing lithium ions is dissolved in an appropriate solvent can be used. Specific examples of the solute metal salt include lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), and LiTFSI [(CF ₃ SO ₂ ) ₂ NLi]. Examples of the solvent include tetraethylene glycol dimethyl ether (TEGDME) or a mixed solvent containing at least this.

  In the present invention, the solvent of the electrolyte (organic electrolyte solution) includes at least TEGDME. In one embodiment of the present invention, the solvent of the organic electrolyte is a single solvent for TEGDME. In another embodiment, the solvent of the organic electrolyte includes TEGDME as the first component and at least one carbonate ester solvent as the second component. Examples of the carbonate solvent include dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate (MBC), diethyl carbonate (DEC), and ethyl propyl carbonate. (EPC), ethyl isopropyl carbonate (EIPC), ethyl butyl carbonate (EBC), dipropyl carbonate (DPC), diisopropyl carbonate (DIPC), dibutyl carbonate (DBC), ethylene carbonate (EC), propylene carbonate (PC), carbonic acid 1, 2-butylene (1,2-BC) or the like can be used. In the present invention, carbonate ester solvents such as EC, PC, DMC are particularly desirable.

  In the present invention, the mixing ratio of TEGDME and the carbonate ester solvent preferably includes 5 to 35% by volume, more preferably 10 to 30% by volume of the carbonate ester solvent based on the total volume of the mixed solvent. In this invention, the performance of a battery can be improved further by containing a carbonate ester solvent at a rate of 10 to 30% by volume, compared with the case of TEGDME alone.

(IV) Other Elements The lithium air secondary battery of the present invention is required for structural members such as separators, battery cases, metal meshes (for example, titanium mesh), and other lithium air secondary batteries in addition to the above components. Can contain elements. Conventionally known ones can be used.

  Embodiments of a lithium-air secondary battery according to the present invention will be described below in detail with reference to the accompanying drawings. In addition, this invention is not limited to what was shown to the following Example, In the range which does not change the summary, it can change suitably and can implement.

Example 1
(Preparation of ruthenium oxide)
Ruthenium oxide (RuO ₂ ) powder used as an electrode catalyst in the air electrode of the lithium secondary battery of the present invention was synthesized as follows.

Commercially available ruthenium chloride (RuCl ₃ ) (manufactured by Kanto Chemical Co., Inc.) is dissolved in distilled water, and while stirring, an aqueous sodium hydroxide solution (1 mol / l) is gradually added dropwise until pH 7.0 is reached. A precipitate of ruthenium hydroxide (amorphous state) was obtained. The precipitate was collected by suction filtration, and washed with distilled water five times so that no chlorine remained. The obtained powder was heat-treated in air at 100 ° C. for 12 hours. The formation phase of the powder after the heat treatment was identified using X-ray diffraction (XRD) measurement.

Powder after the heat treatment, it was confirmed that ruthenium oxide than XRD measurement is _(RuO 2, PDF files Nanba40-1290) single phase. In addition, the specific surface area of the obtained ruthenium oxide was 125 m < ² > / g.

Next, using the obtained ruthenium oxide (RuO ₂ ) powder, an air electrode and a lithium-air secondary battery cell using the air electrode were produced as follows.

(Preparation of air electrode)
Ruthenium oxide (RuO ₂ ) powder, ketjen black powder and polytetrafluoroethylene (PTFE) powder in a weight ratio of 5:57:38 are sufficiently pulverized and mixed using a milling machine, roll molded, and sheet Electrode (thickness: 0.5 mm) was produced. The sheet electrode was cut into a circle having a diameter of 23 mm and pressed onto a titanium mesh to obtain a gas diffusion type air electrode.

(Preparation of lithium secondary battery cell)
A cylindrical lithium-air secondary battery cell having the cross-sectional structure shown in FIG. 2 was produced. FIG. 2 is a cross-sectional view of a lithium air secondary battery cell. The lithium air battery cell was produced in the following procedure in dry air having a dew point of −60 ° C. or less.

The air electrode (positive electrode) 1 prepared by the above method was placed in the concave portion of the air electrode support 2 covered with PTFE, and fixed with the PTFE ring 3 for fixing the air electrode. The portion where the air electrode 1 and the air electrode support 2 are in contact with each other is not covered with PTFE in order to make electrical contact. Moreover, the effective area of the electrode which the air electrode 1 and air contact was 2 cm < ² >.

Next, a separator 5 for a lithium secondary battery was disposed on the bottom surface of the recess on the surface opposite to the surface where the air electrode 1 and the atmosphere contacted. Subsequently, four metal lithium foils (effective area: 2 cm ² ) having a thickness of 150 μm as the negative electrode 8 were stacked on the concentric circle and bonded to the negative electrode fixing washer 7 as shown in FIG. Subsequently, the negative electrode fixing PTFE ring 6 was disposed in a concave portion opposite to the concave portion in which the air electrode 1 is disposed, and a negative electrode fixing washer 7 having metallic lithium bonded thereto was further disposed in the center. Subsequently, the O-ring 9 was disposed at the bottom of the positive electrode support 2 as shown in FIG.

  Next, the inside of the cell (between the positive electrode 1 and the negative electrode 8) was filled with the organic electrolyte solution 10, covered with the negative electrode support 11, and the entire cell was fixed with the cell fixing screws 12. As the organic electrolyte 10, a 1 mol / l LiTFSI / TEGDME solution was used.

  Subsequently, the positive electrode terminal 4 was installed on the positive electrode support 2, and the negative electrode terminal 13 was installed on the negative electrode support 11.

(Battery performance)
The battery performance of the lithium air secondary battery cell prepared by the above procedure was measured. In addition, the positive electrode terminal 4 and the negative electrode terminal 13 shown in FIG. 2 were used for the battery performance measurement test.

In the battery cycle test, a charge / discharge measurement system (manufactured by Bio Logic) was used, and a current density of 0.1 mA / cm ² per effective area of the air electrode 1 was applied. The discharge voltage was measured until the voltage dropped to 0.0V. The battery charge test was performed at the same current density as during discharge and for the same time as discharge time. The charge / discharge test of the battery was performed in a normal living environment. The charge / discharge capacity was expressed as a value (mAh / g) per weight of the air electrode (carbon + ruthenium oxide + PTFE).

  The initial discharge and charge curves are shown in FIG. As shown in the figure, the average charge / discharge voltage is defined as a discharge voltage and a charge voltage at an intermediate value of the total discharge capacity. Table 1 summarizes the performance of this example.

As shown in FIG. 3, it can be seen that when ruthenium oxide (RuO ₂ ) is used for the air electrode catalyst, the average discharge voltage is 2.62 V and the initial discharge capacity is 870 mAh / g. Moreover, the difference (ΔV) between the average discharge voltage and the average charge voltage was 1.04V. The value of ΔV was found to be lower than those reported in Non-Patent Documents 1 and 2.

  Table 1 shows the cycle dependency of the discharge capacity. As shown in Table 1, in this example (Example 1), even when the charge / discharge cycle was repeated 100 times, the discharge capacity retention rate was about 80%, indicating a high value.

(Examples 2-3)
In this example, an example in which the following mixed solvent is used as the organic solvent of the electrolytic solution is shown.

(Example 2): TEGDME: PC (volume ratio) = 70: 30 (volume ratio)
(Example 3): TEGDME: EC: DMC (volume ratio) = 70: 15: 15 (volume ratio)

  A cell was prepared under the same conditions as in Example 1 except for the electrolytic solution, and the battery performance was evaluated.

  The measurement results of this example are also shown in Table 1. As shown in Table 1, it can be seen that the discharge voltage is increased, the charging voltage is decreased, and the cycle characteristics are improved. Thus, it was confirmed that the battery performance of the lithium air secondary battery of the present invention can be further improved by using a mixed solvent of a TEGDME solvent and a carbonate ester solvent.

(Examples 4 to 7)
In this example, in order to verify the effectiveness of the mixing ratio of the carbonate-based solvent according to the present invention, the mixed solvent of TEGDME-EC was evaluated. In this example, the following mixed solvents were used.
(Example 4): TEGDME: EC (volume ratio) = 95: 5 (volume ratio)
(Example 5): TEGDME: EC (volume ratio) = 90: 10 (volume ratio)
(Example 6): TEGDME: EC (volume ratio) = 70: 30 (volume ratio)
(Example 7): TEGDME: EC (volume ratio) = 65: 35 (volume ratio)

  A cell was prepared under the same conditions as in Example 1 except for the electrolytic solution, and the battery performance was evaluated. The measurement results of this example are also shown in Table 1.

(result)
As shown in Example 1, by using RuO ₂ for the air electrode (positive electrode) and using TEGDME as the electrolyte solvent, the battery characteristics (charge / discharge voltage) are superior to those of conventional lithium air secondary batteries. It was revealed that charge / discharge capacity, cycle characteristics, etc.) can be realized.

  In addition, when the results of Examples 2 to 7 are summarized, as shown in Table 1, a battery similar to that of Example 1 in a volume ratio of the carbonate ester solvent to TEGDME in the mixed solvent is in the range of 5 to 35% It can be seen that the characteristics can be realized. Furthermore, in Example 5 or 6 and Example 2 or 3 in which the volume ratio of the carbonate ester solvent to TEGDME in the mixed solvent is in the range of 10 to 30%, the energy at the time of charging and discharging exceeds Example 1. It can be seen that the efficiency and cycle characteristics are particularly excellent.

(Comparative example)
As a comparative example for the present invention, an example in which manganese oxide (MnO ₂ ) is used as a catalyst for an air electrode, and a 1 mol / l LiTFSI / EC-DMC (1: 1 by volume) that is known as an organic electrolyte are used. The example used is shown below.

(Comparative Example 1)
A lithium air secondary battery cell was produced in the same manner as in Example 1 using a known manganese oxide (MnO ₂ ) as a catalyst for the air electrode. Further, manganese oxide (MnO ₂₎ was a commercially available reagent (manufactured by Kanto Chemical Co., Inc.). The production conditions of the battery other than the catalyst and the conditions of the cycle test are the same as in Example 1.

(Comparative Example 2)
A lithium air secondary battery cell was produced in the same manner as in Example 1 using 1 mol / l LiTFSI / EC-DMC (1: 1 by volume) as the organic electrolyte. Moreover, the organic electrolyte used the commercial reagent (made by Toyama Chemical). Battery fabrication conditions and cycle test conditions other than the organic electrolyte are the same as in Example 1.

  The battery performance of the lithium air secondary battery of the comparative example is shown in Table 1. As shown in Table 1, in any of the comparative examples, the initial discharge capacity was a large value exceeding 1,000 mAh / g. However, when the charge / discharge cycle was repeated, the discharge capacity decreased significantly, and after 100 cycles. Only a small value of about 100 mAh / g was obtained.

  Compared to these comparative examples, it is clear that the lithium-air battery according to the present invention has excellent performance.

  From the above results, it was shown that the combination of the catalyst and the organic solvent of the lithium-air secondary battery of the present invention greatly contributed to the realization of excellent battery performance. Here, the reason why the characteristics are particularly improved by combining two kinds of solvents is not clear, but it is considered that dissociation of Li salt into ions is promoted by a carbonate ester solvent having a high dielectric constant. Moreover, when the ratio of carbonate ester increases too much, the effect of the battery characteristic improvement by TEGDME will decrease, and it will be thought that a characteristic falls.

  In the present invention, in particular, ruthenium oxide is used as an air electrode catalyst, and tetraethylene glycol dimethyl ether (TEGDME) alone or a mixed solvent containing at least one of TEGDME and a carbonate ester solvent as an organic electrolyte (for example, a carbonate ester solvent). The battery performance can be improved by using together 5 to 35% by volume based on the total volume of the mixed solvent. In such a configuration, as the organic electrolyte, a mixed solvent containing at least one of tetraethylene glycol dimethyl ether (TEGDME) and a carbonate ester solvent, in particular, the content of the carbonate ester solvent is the total volume of the mixture solvent. By using 10 to 30% by volume of the standard, further improvement in battery performance can be achieved.

  By using the configuration of the lithium-air battery according to the present invention, it is possible to produce a high energy density / lithium-air secondary battery that operates at a low charge voltage and has excellent charge / discharge cycle performance. It can be effectively used as a drive source.

1 Air electrode (positive electrode)
2 Positive electrode support (PTFE coating)
3 Positive electrode fixing ring (PTFE ring)
4 Air electrode terminal 5 Separator 6 Negative electrode fixing ring (PTFE ring)
7 Washer for fixing negative electrode 8 Negative electrode 9 O-ring 10 Organic electrolyte 11 Negative electrode support 12 Cell fixing screw (PTFE coating)
13 Negative terminal 100 Lithium air secondary battery 102 Air electrode 104 Negative electrode 106 Organic electrolyte

Claims (7)

A lithium-air secondary battery comprising an air electrode, a negative electrode, and an organic electrolyte in contact with the air electrode and the negative electrode,
The air electrode includes a conductive material, a catalyst, and a binder,
The negative electrode includes metallic lithium or a lithium-containing material,
The organic electrolyte contains a lithium salt and an organic solvent,
The lithium air secondary battery, wherein the air electrode catalyst includes ruthenium oxide, and the organic solvent of the organic electrolyte includes tetraethylene glycol dimethyl ether. _2. The lithium air secondary battery according to claim 1, wherein the ruthenium oxide is selected from RuO ₂ , RuO ₄ , Ru ₂ O ₃ , Sr ₂ RuO _4, or SrRuO ₃ .   The lithium air secondary battery according to claim 1, wherein the solvent of the organic electrolyte is tetraethylene glycol dimethyl ether.   The organic solvent of the organic electrolyte is a mixed solvent containing a first and a second component, the first component is tetraethylene glycol dimethyl ether, and the second component contains at least one carbonate ester solvent. The lithium-air secondary battery according to claim 1 or 2, characterized in that:   5. The lithium air secondary battery according to claim 4, wherein the content of the carbonate ester solvent in the mixed solvent is 5 to 35% by volume based on the total volume of the mixed solvent.   5. The lithium air secondary battery according to claim 4, wherein the content of the carbonate ester solvent in the mixed solvent is 10 to 30% by volume based on the total volume of the mixed solvent.   The carbonate solvent is dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate (MBC), diethyl carbonate (DEC), ethyl propyl carbonate ( EPC), ethyl isopropyl carbonate (EIPC), ethyl butyl carbonate (EBC), dipropyl carbonate (DPC), diisopropyl carbonate (DIPC), dibutyl carbonate (DBC), ethylene carbonate (EC), propylene carbonate (PC), or carbonic acid 1, The lithium-air secondary battery according to any one of claims 4 to 6, wherein the lithium-air secondary battery is selected from 2-butylene (1,2-BC).

Images