JP6178757B2 - Lithium air secondary battery and method for producing positive electrode used in the lithium secondary battery - Google Patents

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. Furthermore, this invention relates to the preparation method of the positive electrode which can be used as a positive electrode (air electrode) of this lithium secondary battery.

  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, various battery catalysts are added to a gas diffusion type air electrode, which is a positive electrode mainly composed of carbon, to improve battery performance such as discharge capacity and cycle characteristics. Has been tried.

In Non-Patent Document 1, for the positive electrode mainly composed of carbon, carbon alone and nine types of catalysts were examined, and a very large discharge capacity of 1000 to 3000 mAh / g was obtained per weight of carbon contained in the air electrode. ing. However, when charging / discharging is repeated, the discharge capacity is significantly reduced. For example, in the case of carbon alone, the capacity retention rate is about 10% in two cycles, and a significant decrease in capacity is observed. Even when the catalyst is supported, 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 1 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 1 has low energy efficiency of charge and discharge.

  Non-Patent Document 2 discloses a positive electrode (air electrode) mainly made of a metal porous body without using carbon. Non-Patent Document 2 examines gold (Au) as a metal porous body, and reports a lithium-air secondary battery having a very excellent cycle performance with a capacity retention rate of 95% or more in 100 cycles. Yes. Moreover, the average discharge voltage of this lithium air secondary battery is about 2.6V, and a charging voltage is about 3.5V. For this reason, high energy efficiency is obtained also about charging / discharging. However, since no catalyst is supported on the air electrode (positive electrode), sufficient activity cannot be obtained, and the discharge capacity is only about 300 mAh / g.

Aurelie Debart, et al., Journal of Power Sources, Vol. 174, pp. 1177 (2007). Zhangquan Peng, et al., Science, Vol. 337, pp. 563 (2012).

  The present invention operates a lithium-air secondary battery as a high-capacity secondary battery and uses a highly active air electrode for charging and discharging reactions, so that the voltage difference between charging and discharging is small and the charging / discharging cycle is repeated. Another object of the present invention is to provide a lithium-air secondary battery with a small reduction in discharge capacity.

The lithium air secondary battery of the present invention for solving the above problems is
An air electrode including a co-continuous porous material containing a catalyst in a metal co-continuous porous material;
A negative electrode comprising metallic lithium or a lithium-containing material;
An organic electrolyte solution in contact with the air electrode and the negative electrode,
The metal co-continuous porous body has a three-dimensional network structure containing metal (X) and nanoporous, and the catalyst is ruthenium oxide (RuO ₂ ).

  The metal (X) of the metal co-continuous porous material is aluminum (Al), silicon (Si), titanium (Ti), iron (Fe), nickel (Ni), copper (Cu), palladium (Pd), silver ( Ag), tin (Sn), tantalum (Ta), platinum (Pt), and gold (Au).

  The present invention includes a method for producing a positive electrode for the lithium-air secondary battery.

The method for producing a positive electrode for a lithium-air secondary battery according to the present invention comprises contacting a metal co-continuous porous body with a reducing gas and an oxidizing solution containing perruthenate ion (RuO ₄ ⁻ ), It is characterized in that ruthenium oxide (RuO ₂ ) is supported on the co-continuous porous body.

The lithium air secondary battery of the present invention can greatly improve battery characteristics such as capacity and cycle performance. Further, the sodium secondary battery of the present invention, the metal co-continuous porous body, by which contains ruthenium oxide (RuO ₂₎ as electrode catalyst, to exhibit excellent cycle characteristics than traditional, energy efficiency, etc. Can do. Specifically, the voltage difference of charge / discharge is small, and even when the charge / discharge cycle is repeated, a decrease in discharge capacity can be suppressed.

In addition, according to the method for producing an air electrode of a lithium air secondary battery of the present invention, an air electrode for constituting the high performance lithium air secondary battery as described above can be produced easily and reliably. Further, according to the production method of the present invention, it is possible to carry ruthenium oxide (RuO ₂ ) as a catalyst uniformly and in a large area in the pores of the metal co-continuous porous body. Thereby, a lithium air secondary battery can maintain high performance.

It is a figure which shows the basic composition of the lithium air secondary battery 100 which concerns on this invention. It is sectional drawing which shows the structure of the lithium air secondary battery cell 200 used by the present Example. It is a figure which shows the charging / discharging curve of the lithium air secondary battery cell 200 which concerns on Example 1 and 2. FIG. It is a figure which shows the cycle dependence of the discharge capacity of the lithium air secondary battery which concerns on Example 1 and 2 and the comparative example 1. FIG.

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

[Configuration of lithium-air secondary battery]
A basic structure of a lithium air secondary battery according to the present invention is shown in FIG. As shown in FIG. 1, the lithium-air secondary battery 100 of the present invention includes at least an air electrode (positive electrode) 1, a negative electrode 2, and an electrolyte 3.

  More specifically, the air electrode 1 can include a metal and an electrode catalyst as components. The negative electrode 2 can have a constituent element such as metallic lithium or a lithium-containing alloy capable of releasing and absorbing lithium ions. Moreover, the electrolyte 3 can be arrange | positioned between these air electrodes and a 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)
(I-1) Material of Air Electrode (Positive Electrode) In the present invention, the air electrode can contain a metal. The air electrode of the present invention is preferably a metal co-continuous porous body in which the metal has a co-continuous porous structure.

  In the lithium air secondary battery of the present invention, the metal of the air electrode is aluminum (Al), silicon (Si), titanium (Ti), iron (Fe), nickel (Ni), copper (Cu), palladium (Pd). , Silver (Ag), tin (Sn), tantalum (Ta), platinum (Pt), and gold (Au). The air electrode may be an alloy containing the metal.

In the present invention, the air electrode contains ruthenium oxide (RuO ₂ ), which is a highly active electrode catalyst for both oxygen reduction (discharge) and oxygen generation (charge) reactions, on a metal co-continuous porous body.
. Thus, by including ruthenium oxide (RuO ₂ ) in the air electrode, the performance of the lithium air secondary battery of the present invention is enhanced.

  In the air electrode of the lithium-air secondary battery of the present invention, an electrode reaction proceeds at a three-phase interface site of electrolyte / electrode / gas (oxygen). That is, for example, when an organic electrolytic solution (including a solid electrolyte impregnated with an organic electrolytic solution) is used as the electrolyte, the organic electrolytic solution penetrates into the air electrode, and oxygen gas in the atmosphere is supplied at the same time. A three-phase interface site where liquid-electrode-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 electrolyte from the negative electrode by electrochemical oxidation, and move through the electrolyte to the surface of the air electrode. Oxygen (O ₂ ) is taken into the air electrode from the atmosphere (air). In FIG. 1, a material (Li ⁺ ) that dissolves from the negative electrode, a material (Li ₂ O) that precipitates at the air electrode, and air (O ₂ ) are shown together with constituent elements.

Ruthenium in ruthenium oxide (RuO ₂ ) serving as an electrode catalyst for the air electrode (positive electrode) exists as ions having a valence of +4, +3, and oxygen vacancies also exist depending on the synthesis conditions.

Such ruthenium oxide (RuO ₂ ) has a strong interaction with oxygen, which is a positive electrode active material, and can absorb many oxygen species on the oxide surface or store them in oxygen vacancies.

Such a state becomes an intermediate reactant of the above formulas (1) and (2), and the oxygen reduction reaction easily proceeds. In addition, the ruthenium oxide (RuO ₂ ) is also active in the charging reaction that is the reverse reaction of the formulas (1) and (2), and the battery charging, that is, the oxygen generation reaction on the air electrode is also efficient. Proceed well. Thus, ruthenium oxide (RuO ₂ ) functions as an electrode catalyst.

The metal co-continuous porous body of the air electrode (positive electrode) has fine open pores depending on the production conditions. In the present invention, since ruthenium oxide (RuO ₂ ) is supported on the surface of the metal co-continuous porous body having such fine openings, the interaction with oxygen as the positive electrode active material can be enhanced, In addition, many oxygen species can be adsorbed on the electrode surface. As a result, the above-described three-phase interface site is efficiently formed, oxygen reduction (discharge) and oxygen generation (charge) proceed smoothly, and battery performance is greatly improved.

In the present invention, ruthenium oxide (RuO ₂ ) is preferably deposited on the surface of the continuous porous body with a thickness of 1 to 50 nm, preferably 2 to 30 nm.

  In the present specification, the “metal co-continuous porous body” refers to a co-continuous porous body in which the metal has a co-continuous porous structure. Specifically, a metal co-continuous porous body made of the above-described metal or an alloy containing the above-described metal is preferable. In the present invention, the metal co-continuous porous body has a three-dimensional network structure having through holes (holes) in which the metal is continuous and nanoporous.

(I-2) Preparation of Air Electrode The metal co-continuous porous material used as the air electrode in the present invention can be prepared by using a known method such as a sintering method or a dealloying method. For example, the sintering method may use a procedure for sintering the above-described fine metal powder at 800 ° C. or lower. Further, the dealloying method includes, for example, a procedure in which an alloy containing a metal that is electrochemically lower than the metal described above is immersed in an acidic solution, and the base metal in the alloy is eluted. More specifically, for example, a desired metal co-continuous porous sheet is obtained by immersing a commercially available metal or metal alloy and manganese alloy sheet in an aqueous solution such as ammonium sulfate for 1 to 8 hours, and drying after washing. Can be obtained. If necessary, the air electrode can be manufactured by cutting the obtained sheet into a predetermined shape (for example, a circle).

In the lithium-air secondary battery of the present invention, in order to increase the efficiency of the battery, it is desirable that more reaction sites (the above-described electrolyte / electrode / air (oxygen) three-phase interface sites) that cause an electrode reaction exist. From such a point of view, in the present invention, it is important that the above-mentioned three-phase interface site is present in a large amount on the electrode surface, and the metal co-continuous porous material used preferably has a high specific surface area. In the present invention, the metal co-continuous porous material preferably has, for example, an average pore diameter of 1 μm or less and a specific surface area of 20 m ² / g or more. For this reason, in the present invention, the metal co-continuous porous body is desirably used by a dealing method in which the electrochemically base metal of the alloy is eluted with an acidic solution or the like.

  Here, the average pore diameter is obtained by enlarging the metal co-continuous porous body with a scanning electron microscope (SEM) or the like, measuring the number of pores per 10 μm square (10 μm × 10 μm), and the diameter of the pores. This is the value obtained.

    Average pore diameter = total pore diameter / number of pores

Here, the specific surface area is defined as the specific surface area determined by the BET method using N ₂ adsorption.

Next, a method for supporting ruthenium oxide (RuO ₂ ) on the metal co-continuous porous body will be described.

  The first embodiment is a method using a liquid phase. In this method, a metal co-continuous porous sheet prepared by the above procedure is impregnated with an aqueous solution of ruthenium chloride, ruthenium nitrate, etc., and the aqueous solution is evaporated to dryness. And a known method such as a precipitation method in which the aqueous solution is impregnated and an aqueous alkali solution is dropped, and a sol-gel method in which the metal co-continuous porous material is impregnated in a ruthenium alkoxide solution and hydrolyzed.

The second embodiment is a method of depositing ruthenium oxide (RuO ₂ ) on a metal co-continuous porous body by a process using a gas-liquid interface.

In the present invention, in the air electrode (positive electrode), it is important that a large amount of three-phase interface sites are generated on the surface of the electrode catalyst, and the catalyst to be used preferably has a high specific surface area. Therefore, it is more preferable to deposit ruthenium oxide (RuO ₂ ) on the metal co-continuous porous body in the second embodiment, which is a process using a gas-liquid interface.

In the method using the gas-liquid interface, the metal co-continuous porous sheet obtained by the dealloying method or the like is brought into contact with a reducing gas and an oxidizing solution containing perruthenate ion (RuO ₄ ⁻ ), The metal co-continuous porous sheet carries ruthenium oxide (RuO ₂ ). If necessary, the air electrode can be manufactured by cutting the obtained sheet into a predetermined shape (for example, a circle).

The metal co-continuous porous material supporting RuO ₂ produced by this method can further enhance the catalytic activity. By using the metal co-continuous porous material carrying RuO ₂ manufactured in the second embodiment, the lithium-air secondary battery of the present invention can realize further excellent battery performance.

The reducing gas used in the method utilizing the gas-liquid interface includes formic acid (HCOOH), diisobutylaluminum hydride ([(CH ₃ ) ₂ CHCH ₂ ] ₂ AlH), hydrazine (N ₂ H ₄ ), carbon monoxide. (CO), hydrogen sulfide (H ₂ S), sulfur dioxide (SO ₂ ), hydrogen (H ₂ ), formaldehyde (HCHO) and the like are included. The oxidizing solution containing the perruthenate ion (RuO ₄ ⁻ ) includes potassium perruthenate (KRuO ₄ ), tetrapropylammonium perruthenate (CH ₃ CH ₂ CH ₂ ) ₄ NRuO ₄ , tetraoxide. Ruthenium (RuO ₄ ) and the like are included.

As described above, by incorporating ruthenium oxide (RuO ₂ ) into the metal co-continuous porous body, the activity of the electrode is improved, and when used as the air electrode of the lithium-air secondary battery of the present invention, high cycle performance Indicates.

  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 The lithium air secondary battery of the present invention contains 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 a suitable nonaqueous solvent can be used. Specifically, solute metal salts include lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), lithium bistrifluoromethanesulfonylimide (LiTFSI) [(CF ₃ SO ₂ ) ₂ NLi And the like. Examples of the solvent include 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), carbonic acid 1,2 Carbonate ester solvents such as butylene (1,2-BC), ether solvents such as 1,2-dimethoxyethane (DME) and tetraethylene glycol dimethyl ether (TEGDME), and lactone solvents such as γ-butyrotactone (GBL) Or dimethyl sulfoxide DMSO) can be mentioned sulfoxide type solvents such as. Furthermore, the solvent which mixed 2 or more types from these can also be used.

As another electrolyte of the lithium air secondary battery of the present invention, a solid electrolyte having lithium ion conductivity [for example, a glassy substance such as 75Li ₂ S · 25P ₂ S ₅ , a LISICON (Li ₁₄ ZnGe ₄ O ₁₆ or the like) ⁺ Super Ionic Conductor)], polymer electrolytes having lithium ion conductivity [for example, a composite material of the above-mentioned organic electrolyte and polyethylene oxide (PEO)], and the like, but are not limited thereto. In the present invention, any known solid electrolyte that passes lithium ions or polymer electrolyte that passes lithium ions used in lithium-air secondary batteries can be used.

(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.

Next, a method for producing the positive electrode for the lithium air secondary battery of the present invention will be described. In this production method, a metal co-continuous porous body is brought into contact with a reducing gas and an oxidizing solution containing perruthenate ions (RuO ₄ ⁻ ), and ruthenium oxide (RuO ₂ ) is added to the metal co-continuous porous body. Including the step of supporting.

Specifically, a method of depositing ruthenium oxide (RuO ₂ ) on a metal co-continuous porous material by a process using a gas-liquid interface (described as the second embodiment of the preparation of the above (I-2) air electrode) Is).

A more specific procedure is as follows. First, a perruthenate ion (RuO ₄ ⁻ ) -containing aqueous solution in which a perruthenate salt (for example, potassium salt (KRuO ₄ )) and a base (for example, potassium hydroxide) are dissolved in distilled water is prepared, and a metal co-continuous porous body Prepare a beaker with a smile. Further, a solution of a reducing agent (for example, hydrazine (N ₂ H ₄ )) is prepared. These are installed in a sealed space such as a glass desiccator, and left in this sealed container for a predetermined time, preferably 1 to 10 hours, at a temperature of 15 ° C to 90 ° C, preferably 20 ° C to 50 ° C. Then, the inside of the sealed container is filled with the reducing agent gas by self-volatilizing the reducing agent. The ruthenium oxide (RuO ₄ ⁻ ) -containing aqueous solution, the metal co-continuous porous body, and the reducing agent gas are reduced with the reducing agent gas so that the ruthenium oxide (RuO ₄ ⁻ ) is reduced by the reducing agent gas. RuO ₂ ) is deposited on the surface of the metal co-continuous porous body.

By the procedure as described above, an air electrode material (for example, a sheet-like metal co-continuous porous material) in which ruthenium oxide (RuO ₂ ) is supported on the surface of the metal co-continuous porous material can be prepared. If necessary, the metal co-continuous porous body (for example, a sheet-like material) in which the obtained ruthenium oxide (RuO ₂ ) is supported on the surface of the metal co-continuous porous body is cut into a predetermined shape (for example, a circular shape), thereby Can be manufactured.

  Hereinafter, embodiments of the lithium-air secondary battery according to the present invention will be described 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
Using metal (X) as the metal (X) of the metal co-continuous porous body, a metal co-continuous porous body having a nanoporous three-dimensional network structure used as an electrode of the air electrode was synthesized as follows.

A commercially available gold manganese (Au ₃₀ Mn ₇₀ ) sheet having a thickness of 50 μm was immersed in a 1.0 mol / l aqueous solution of ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) for 6 hours to obtain a gold (Au) co-continuous porous body. It was. The obtained gold (Au) co-continuous porous material was repeatedly washed with distilled water five times so that ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) did not remain. The obtained sheet was dried at 60 ° C. overnight, and evaluated by performing X-ray diffraction (XRD) measurement, SEM observation, and BET specific surface area measurement.

The metal produced by the dealloying method has a film thickness of 40 μm and was confirmed to be a gold (Au, JCPDS card No. 04-0784) single phase by XRD measurement. Moreover, it was confirmed by SEM observation that the average pore diameter was 50 nm. Moreover, it was 57 m < ² > / g when the specific surface area of the gold | metal | money (Au) co-continuous porous body was measured by BET method.

Next, commercially available ruthenium chloride (RuCl ₃ ) is dissolved in distilled water and impregnated in the gold (Au) co-continuous porous material produced as described above, and gradually aqueous ammonia (28%) is adjusted to pH 7.0. Was added dropwise to precipitate ruthenium hydroxide. The precipitate was repeatedly washed with distilled water five times so that no chlorine remained. The resulting gold (Au) co-continuous porous material containing ruthenium hydroxide was heat-treated at 110 ° C. for 6 hours to produce a gold (Au) co-continuous porous material containing ruthenium oxide (RuO ₂ ). When the prepared gold (Au) co-continuous porous material containing ruthenium oxide (RuO ₂ ) was observed with a TEM, most of the ruthenium oxide (RuO ₂ ) was precipitated in the form of particles with an average of 50 nm on the outer surface of the hole. Was observed.

Using such a gold (Au) co-continuous porous material containing ruthenium oxide (RuO ₂ ), an air electrode 1 and a lithium-air secondary battery cell using the air electrode 1 were produced as follows.

This gold (Au) co-continuous porous material containing ruthenium oxide (RuO ₂ ) was cut out into a circle having a diameter of 23 mm to obtain a gas diffusion type air electrode 1.

  Next, a cylindrical lithium-air secondary battery cell 200 having a 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 secondary battery cell was produced according to the following procedure in dry air having a dew point of −60 ° C. or less.

The air electrode 1 prepared by the above method was placed in the concave portion of the PTFE-coated air electrode support 10 and fixed with the PTFE ring 8 for fixing the air electrode. Note that the portion where the air electrode 1 and the air electrode support 10 are in contact with each other was not covered with PTFE in order to make electrical contact. The effective area of the electrode in contact between the air electrode 1 and air is 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 of the air electrode 1 that contacts the atmosphere. Subsequently, four metal lithium foils (effective area: 2 cm ² ) having a thickness of 150 μm as the negative electrode 2 were stacked on the concentric circle and pressure-bonded to the negative electrode fixing washer 7 as shown in FIG. The negative electrode fixing PTFE ring 6 was disposed in a concave portion opposite to the concave portion in which the air electrode 1 was installed, and a negative electrode fixing washer 7 having metal lithium bonded thereto was further disposed in the center. Subsequently, the O-ring 9 was disposed at the bottom of the air electrode support 10 as shown in FIG. Next, in the cell (between the positive electrode 1 and the negative electrode 2), a 1 mol / l lithium bistrifluoromethanesulfonylimide / propylene carbonate [(CF ₃ SO ₂ ) ₂ NLi / PC] solution that is an organic electrolyte 3 is added. The whole cell was fixed with a cell fixing screw 12 after filling with the negative electrode support 11.

  Subsequently, the positive electrode terminal 4 was installed on the air electrode support 10, and the negative electrode terminal 13 was installed on the negative electrode support 11.

  The battery performance of the lithium air secondary battery cell 200 prepared by the above procedure was measured. Note that the positive electrode terminal 4 and the negative electrode terminal 13 shown in FIG. 2 were used for a 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. Measurements were taken until the voltage dropped to 0.0V. The battery charge test was performed until the battery voltage increased to 4.0 V at the same current density as during discharge. 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 made of a gold (Au) co-continuous porous material containing ruthenium oxide (RuO ₂ ).

The initial discharge and charge curves are shown in FIG. As shown in FIG. 3, when a gold (Au) co-continuous porous material containing ruthenium oxide (RuO ₂ ) is used for the air electrode, the average discharge voltage is 2.7 V and the discharge capacity is 450 mAh / g. I understand.

  In addition, the initial charge capacity is 460 mAh / g, which is substantially the same as the discharge capacity, and it can be seen that the lithium-air secondary battery of this example is excellent in reversibility.

  The cycle dependency of the discharge capacity is shown in FIG. 4 and Table 1. In this example (Example 1), even when the charge / discharge cycle was repeated 100 times, the discharge capacity (mAh / g) was hardly reduced. .

  In addition, it was found from FIG. 3 that the voltage at the time of charging had a flat portion at about 3.3 V, which was lower than the conventional report.

The charge / discharge cycle was repeated to measure the transition of the charge / discharge voltage. The results are shown in Table 2 below. In this example (Example 1), it was found that a slight increase in overvoltage was observed during charging and discharging, but an almost stable voltage was exhibited. Thus, it was found that the gold (Au) co-continuous porous material containing ruthenium oxide (RuO ₂ ) has very excellent activity as an air electrode of a lithium air secondary battery.

(Example 2)
The present example is an example of a gas diffusion type air electrode using a gold (Au) co-continuous porous material supporting ruthenium oxide (RuO ₂ ). This metal co-continuous porous material is used in the second embodiment. The following procedure was followed.

A gold (Au) co-continuous porous material was prepared in the same manner as the first process shown in Example 1. Next, an aqueous solution containing perruthenate ion (RuO ₄ ⁻ ) prepared by dissolving 0.02 mol / l potassium perruthenate (KRuO ₄ ) and 0.05 mol / l potassium hydroxide in distilled water in a beaker is prepared. The gold (Au) co-continuous porous body was floated on this. This beaker was placed in a glass desiccator, and a hydrazine (N ₂ H ₄ ) solution was placed in the glass desiccator. Thereafter, hydrazine (N ₂ H ₄ ) was volatilized at room temperature for 6 hours in the glass desiccator, and the glass desiccator was filled with hydrazine (N ₂ H ₄ ) gas. At the three-phase interface of the aqueous solution containing perruthenate ion (RuO ₄ ⁻ ), the gold (Au) co-continuous porous material and the hydrazine (N ₂ H ₄ ) gas, the perruthenate ion (RuO ₄ ⁻ ) is converted into the hydrazine. Reduction with (N ₂ H ₄ ) gas. Thereby, ruthenium oxide (RuO ₂ ) was deposited on the surface of the gold (Au) co-continuous porous body. Further, when TEM observation was performed, it was confirmed that ruthenium oxide (RuO ₂ ) was uniformly deposited on the surface of the gold (Au) co-continuous porous body evenly into the nanoporous pores with an average of 3 nm.

  The conditions of the battery cycle test are the same as in Example 1.

  The initial discharge and charge curves of the lithium-air secondary battery according to this example (Example 2) and the cycle performance related to the discharge capacity are shown in FIG. 3, FIG. 4, and Table 1 together with the results of Example 1.

3 and 4, the average discharge when a gold (Au) co-continuous porous material containing ruthenium oxide (RuO ₂ ) produced by the manufacturing method shown in this example (Example 2) was used for the air electrode. The voltage is 2.8 V, and the initial discharge capacity is 630 mAh / g. The gold (Au) co-continuous porous material containing ruthenium oxide (RuO ₂ ) prepared by the liquid phase method as in Example 1 It showed better battery characteristics. Moreover, even if it repeated the cycle, it turned out that the lithium air secondary battery of a present Example shows the stable behavior.

  Table 2 shows the results of measuring the transition of the charge / discharge voltage by repeating the charge / discharge cycle. As shown in Table 2, with respect to the charge / discharge voltage, a decrease in overvoltage was observed as compared with Example 1, and an improvement in energy efficiency of charge / discharge could be achieved. Further, even when the cycle was repeated, no significant increase in overvoltage was observed, and it was confirmed that the lithium-air secondary battery of this example also operated stably.

The improvement in characteristics as described above is because the electrode catalyst ruthenium oxide (RuO ₂ ) is uniformly supported on the metal co-continuous porous body, and the metal co-continuous porous body has a large specific surface area. This is considered to be due to an increase in the deposition site of lithium oxide at the time of discharge, an improvement in oxygen adsorption capability, and the metal co-continuous porous material functioned efficiently as a catalyst.

From the above results, ruthenium oxide (RuO ₂ ) is brought into contact with an oxidizing solution containing a reducing gas and perruthenate ion (RuO ₄ ⁻ ) in contact with the metal co-continuous porous material as in this example. The production method of the air electrode to be carried is a method superior in improving the characteristics of the lithium-air secondary battery such as capacity and voltage as compared with the production method by the known liquid phase method. It was confirmed that the method was effective as a method for manufacturing an electrode.

In Example 1 and Example 2, a gold (Au) co-continuous porous material supporting ruthenium oxide (RuO ₂ ) was used, but in Examples 3 to 13 shown below, the metal (X ) As aluminum (Al), silicon (Si), titanium (Ti), iron (Fe), nickel (Ni), copper (Cu), palladium (Pd), silver (Ag), tin (Sn), tantalum ( The performance of the lithium-air secondary battery was further examined using Ta) and platinum (Pt).

The metal co-continuous porous material containing ruthenium oxide (RuO ₂ ) was obtained by applying the gold manganese (Au ₃₀ Mn ₇₀ ) sheet of the first process shown in Example 1 to a manganese alloy (X ₃₀ Mn ₇₀ X: Al, Si, Ti, Fe, Ni, Cu, Pd, Ag, Sn, Ta, Pt). The method of supporting ruthenium oxide (RuO ₂ ) on the metal co-continuous porous body is performed in the same manner as in the procedure of Example 2, and the gold (Au) co-continuous porous body is made of the above metals (Al, Si, Ti, Fe, Ni , Cu, Pd, Ag, Sn, Ta, or Pt), a metal co-continuous porous material containing the target ruthenium oxide (RuO ₂ ) was produced. The production of the electrode and the battery, and the evaluation of the lithium air secondary battery were performed in the same manner as in Example 1.

(Example 3)
As the gas diffusion type air electrode 1, an aluminum (Al) co-continuous porous material supporting ruthenium oxide (RuO ₂ ) was used.

Example 4
As the gas diffusion type air electrode 1, a silicon (Si) co-continuous porous material supporting ruthenium oxide (RuO ₂ ) was used.

(Example 5)
As the gas diffusion type air electrode 1, a titanium (Ti) co-continuous porous material carrying ruthenium oxide (RuO ₂ ) was used.

(Example 6)
As the gas diffusion type air electrode 1, an iron (Fe) co-continuous porous material supporting ruthenium oxide (RuO ₂ ) was used.

(Example 7)
As the gas diffusion type air electrode 1, a nickel (Ni) co-continuous porous material containing ruthenium oxide (RuO ₂ ) was used.

(Example 8)
As the gas diffusion type air electrode 1, a copper (Cu) co-continuous porous body supporting ruthenium oxide (RuO ₂ ) was used.

Example 9
As the gas diffusion type air electrode 1, a palladium (Pd) co-continuous porous material carrying ruthenium oxide (RuO ₂ ) was used.

(Example 10)
As the gas diffusion type air electrode 1, a silver (Ag) co-continuous porous material supporting ruthenium oxide (RuO ₂ ) was used.

(Example 11)
As the gas diffusion type air electrode 1, a tin (Sn) co-continuous porous material supporting ruthenium oxide (RuO ₂ ) was used.

(Example 12)
As the gas diffusion type air electrode 1, a tantalum (Ta) co-continuous porous material supporting ruthenium oxide (RuO ₂ ) was used.

(Example 13)
As the gas diffusion type air electrode 1, a platinum (Pt) co-continuous porous material carrying ruthenium oxide (RuO ₂ ) was used.

  Table 1 shows the BET specific surface area of the metal co-continuous porous materials produced in Examples 3 to 13 and the discharge capacity when charging and discharging are repeated.

  As shown in Table 1, the discharge capacity of the lithium-air secondary battery of each example (Examples 3 to 13) is 400 mAh / g or more at the first time, and gold (Au) as in Non-Patent Document 2 is continuous. The value was larger than that of the porous body alone (no catalyst supported). It was also found that the lithium-air secondary battery showed stable behavior even when the cycle was repeated.

  Moreover, as shown in Table 2, the charge / discharge voltage also had a small overvoltage, and the energy efficiency of charge / discharge could be improved. In addition, no significant increase in overvoltage was observed even when the cycle was repeated, and it was confirmed that the lithium-air secondary battery of each example operated stably.

The above characteristic improvement is due to the smooth reaction of both oxygen reduction (discharge) and oxygen generation (charge) by using ruthenium oxide (RuO ₂ ) having very large activity as an electrode catalyst. It is believed that there is.

Moreover, as shown in Table 1, there is a tendency that a large discharge capacity can be realized by using a metal co-continuous porous body having a large BET specific surface area. As shown in Table 1, a lithium-air secondary battery using a metal co-continuous porous material containing ruthenium oxide (RuO ₂ ) as an air electrode is a gold (Au) co-continuous porous material as described in Non-Patent Document 2. In order to have a discharge capacity of 300 mAh / g or more, which is the discharge capacity of a single body (no catalyst supported), the BET specific surface area is preferably 20 m ² / g or more. This is because the air electrode having a high specific surface area can generate a larger amount of reaction sites between lithium ions (Li ⁺ ) and oxygen (O ₂ ).

(Comparative Example 1)
As a comparative example, an example in which carbon (Ketjen Black EC600JD) and ruthenium oxide (RuO ₂ ), which are known materials, are used for the electrode for the air electrode 1 is shown. A lithium-air secondary battery cell using this air electrode was produced as follows.

Ruthenium oxide (RuO ₂ ) powder, ketjen black powder and polytetrafluoroethylene (PTFE) powder in a weight ratio of 50:30:20 are sufficiently pulverized and mixed using a milling machine, roll-formed, and sheet Electrode (thickness: 0.5 mm) was produced. The sheet-like 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 1. As for ruthenium oxide (RuO ₂ ), a commercially available reagent (manufactured by High Purity Chemical Laboratory) was used. The conditions of the battery cycle test are the same as in Example 1.

  The cycle performance related to the discharge capacity of the lithium-air secondary battery according to this comparative example is shown in FIG. 4 together with the results of Examples 1 and 2, and is shown in Table 1 together with the results of Examples 1-13.

  As shown in FIG. 4, in the first comparative example, the initial discharge capacity was about 800 mAh / g, which was larger than those in the first and second examples. However, when the charge / discharge cycle was repeated, an extreme decrease in the discharge capacity was observed unlike Example 1 and Example 2, and the capacity retention rate after 20 cycles was about 20% of the initial value.

  Moreover, the cycle dependency of the charge / discharge voltage is shown in Table 2 together with the results of Examples 1-13.

  As can be seen from Table 2, the charging voltage according to Comparative Example 1 is clearly higher than those of Examples 1 to 13, and the overvoltage clearly increases when the cycle is repeated, and the cycle is repeated at the 20th time. Became difficult.

From the above results, the air electrode including a metal co-continuous porous material containing ruthenium oxide (RuO ₂ ) as in the present invention has better cycle characteristics with respect to capacity and voltage than known materials. It was confirmed to be effective as an air electrode for a secondary battery.

By using a metal co-continuous porous material having a nanoporous three-dimensional network structure containing ruthenium oxide (RuO ₂ ), a lithium-air secondary battery excellent in charge / discharge cycle performance can be produced, and various electronic devices It can be effectively used as a drive source.

1 Air electrode (positive electrode)
2 Negative electrode 3 Organic electrolyte 4 Air electrode terminal 5 Separator 6 Negative electrode fixing ring (PTFE ring)
7 Washer for fixing negative electrode 8 Ring for fixing positive electrode (PTFE ring)
9 O-ring 10 Cathode support (PTFE coating)
11 Negative electrode support 12 Cell fixing screw (PTFE coating)
13 Negative terminal 100 Lithium air secondary battery 200 Lithium air secondary battery cell

Claims (3)

An air electrode including a co-continuous porous material containing a catalyst in a metal co-continuous porous material;
A negative electrode comprising metallic lithium or a lithium-containing material;
An organic electrolyte solution in contact with the air electrode and the negative electrode,
The metal co-continuous porous material contains a metal (X) and has a three-dimensional network structure that is nanoporous, and the catalyst is ruthenium oxide (RuO ₂ ), battery.   The metal (X) of the metal co-continuous porous material is aluminum (Al), silicon (Si), titanium (Ti), iron (Fe), nickel (Ni), copper (Cu), palladium (Pd), silver ( The lithium air secondary battery according to claim 1, wherein the lithium air secondary battery is selected from the group consisting of Ag), tin (Sn), tantalum (Ta), platinum (Pt), and gold (Au). A method for producing a positive electrode for a lithium-air secondary battery, wherein a metal co-continuous porous body is brought into contact with a reducing gas and an oxidizing solution containing perruthenate ion (RuO ₄ ⁻ ), A method comprising a step of supporting ruthenium oxide (RuO ₂ ) on a continuous porous body.