JP2017103002A - Lithium air secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to suppress the reduction in discharge capacity in a lithium air secondary battery even in the case of repeatedly charging and discharging the battery.SOLUTION: A lithium air secondary battery comprises: an air electrode 101; a negative electrode 102 including Li; an electrolyte 103 disposed between the air electrode 101 and negative electrode 102; and a catalyst supported by the air electrode 101. The catalyst includes: a metal selected from Cr, Mn, Fe, Co, Ni, Pd, Sn, In, Ir and Au; Pt; and Ru.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium air secondary battery using oxygen as a positive electrode active material.

  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 weight of the battery can be greatly increased.

  So far, as reported in Non-Patent Document 1 and Non-Patent Document 2, battery performance such as discharge capacity and cycle characteristics is improved by adding various catalysts to the gas diffusion air electrode as the positive electrode. Attempts have been made.

In Non-Patent Document 1, transition metal oxides such as λ-MnO ₂ are used. In Non-Patent Document 2, transition metal oxides such as iron oxide (Fe ₂ O ₃ ) and cobalt oxide (Co ₃ O ₄ ) are used. Are being considered as the above-mentioned catalysts. 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 is possible, but after 4 cycles, the discharge capacity decreases to about ¼, and the performance as a secondary battery is low. Further, in the secondary battery disclosed in Non-Patent Document 1, the charging voltage is about 4.0V, which is very large compared to the average discharge voltage of 2.7V, and the charge / discharge energy efficiency is low. There is.

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 charging and discharging 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% after 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 energy efficiency of charge / discharge.

J. Read, "Characterization of the Lithium / Oxygen Organic Electrolyte Battery", Journal of The Electrochemical Society, vol.149, no.9, pp.A1190-A1195, 2002. A. Debart et al., "An O2 cathode for rechargeable lithium batteries: The effect of a catalyst", Journal of Power Sources, vol.174, pp.1177-1182, 2007.

  As described above, the conventional lithium-air secondary battery has a problem that the discharge capacity decreases when charging and discharging are repeated.

  The present invention has been made to solve the above-described problems, and it is an object of the present invention to suppress a decrease in discharge capacity even when charging and discharging are repeated in a lithium air secondary battery.

  A lithium-air secondary battery according to the present invention includes an air electrode, a catalyst carried on the air electrode, a negative electrode including lithium, and an organic electrolyte disposed between the air electrode and the negative electrode. The catalyst is made of a metal selected from Cr, Mn, Fe, Co, Ni, Pd, Sn, In, Ir, and Au, and Pt and Ru.

In the lithium air secondary battery, the catalyst is Pt _x Ru _y M _z [M = Cr, Mn, Fe, Co, Ni, Pd, Sn, In, Ir, Au, x ≦ y, 0.2 ≦ z / (X + y + z) ≦ 0.5] may be satisfied.

  As described above, according to the present invention, in the lithium air secondary battery, it is possible to obtain an excellent effect that a decrease in discharge capacity can be suppressed even when charging and discharging are repeated.

FIG. 1 is a configuration diagram showing a configuration of a lithium-air secondary battery according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a more detailed configuration example of the lithium air secondary battery. FIG. 3 is a characteristic diagram showing an initial discharge and charge curve of Sample 7 in Example 1.

  Hereinafter, an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a configuration diagram showing a configuration of a lithium-air secondary battery according to an embodiment of the present invention.

  This lithium air secondary battery is a positive electrode gas diffusion type air electrode 101, and a negative electrode 102 including lithium (Li), like a general well-known lithium air secondary battery, An electrolyte 103 disposed between the air electrode 101 and the negative electrode 102 is provided. One surface of the air electrode 101 is exposed to the atmosphere, and the other surface is in contact with the electrolyte 103. Further, the surface of the negative electrode 102 on the side of the electrolyte 103 is in contact with the electrolyte 103. The electrolyte 103 may be either an electrolytic solution or a solid electrolyte. The electrolytic solution refers to a case where the electrolyte is in a liquid form. Moreover, a solid electrolyte means the case where electrolyte is a gel form or a solid form.

In addition to the basic configuration described above, the embodiment of the present invention includes a catalyst supported on the air electrode 101, and the catalyst is selected from Cr, Mn, Fe, Co, Ni, Pd, Sn, In, Ir, and Au. A major feature is that it is composed of Pt and Ru. The catalyst is Pt _x Ru _y M _z [M = Cr, Mn, Fe, Co, Ni, Pd, Sn, In, Ir, Au, x ≦ y, 0.2 ≦ z / (x + y + z) ≦ 0.5] If it is. As described above, the Pt _x Ru _y M _z (M = Cr, Mn, Fe, Co, Ni, Pd, Sn, In, Ir, Au) is supported on the air electrode 101 as a catalyst. Even if it repeats, the fall of discharge capacity can be suppressed and the energy efficiency of charging / discharging can be made high.

A catalyst composed of platinum (Pt) and ruthenium (Ru) has been reported to be highly active for oxygen reduction (discharge) and oxygen generation (charge reaction). As a result of the inventors' extensive research and examination, Pt _x Ru _y M _{z in} which any one of Cr, Mn, Fe, Co, Ni, Pd, Sn, In, Ir, and Au is added to Pt and Ru as M It has been found that a higher activity is exhibited by using as a catalyst.

The Pt _x Ru _{y Mz} which is the air electrode catalyst of the present invention has a relation that the Ru content (composition) y is not less than the Pt content (composition) x (x ≦ y) in terms of atomic ratio, and further the above M content When the amount (composition) z is set, the composition ratio may satisfy the relationship of [20 ≦ [100z / (x + y + z)] ≦ 50 ”. As M, Sn is the most preferable, and as a factor of high activation due to the addition of tin (Sn), finer particles are advanced by addition of Sn, the specific surface area of the air electrode catalyst is improved, and the number of reaction sites is increased. It is.

  As is well known, the air electrode 101 is made of a conductive material, supports the catalyst, and adds a binder or the like as necessary.

  In the air electrode 101, an electrode reaction proceeds at a three-phase interface site of electrolyte / electrode catalyst / air (oxygen). An electrolyte 103 such as an organic electrolyte penetrates into the air electrode 101, and oxygen gas in the atmosphere is simultaneously supplied to form a three-phase interface site in which electrolyte-electrode catalyst-air (oxygen) coexists. 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 101 can be expressed as follows.

2Li ⁺ + O ₂ + 2e ⁻ → Li ₂ O ₂ (1)

Lithium ions (Li ⁺ ) in the above formula are dissolved in the electrolyte 103 such as an organic electrolytic solution from the negative electrode 102 by electrochemical oxidation, and move in the electrolyte 103 to the surface of the air electrode 101. Oxygen (O ₂ ) is taken into the air electrode 101 from the atmosphere (air). A substance (Li ⁺ ) dissolved from the negative electrode 102, a substance (Li ₂ O ₂ ) precipitated at the air electrode 101, and air (O ₂ ) are shown together with the components shown in FIG.

The preferred platinum ruthenium and tin as an electrode catalyst of the air electrode 101 serving as a positive electrode _{(Pt x Ru y Sn z)} , when is contained (carried) to the air electrode 101, a strong interaction with the oxygen, due to the high addition a specific surface area Many oxygen species can be adsorbed on the surface of the catalyst. Thus, the oxygen species adsorbed on the surface of the catalyst are used for the oxygen reduction reaction as the oxygen source (active intermediate reactant) of the above formula (1), and the reaction proceeds easily. Further, Pt _x Ru _y M _z has activity also for the charging reaction which is the reverse reaction of the formula (1). Therefore, charging of the battery, that is, the oxygen generation reaction on the air electrode proceeds efficiently. Thus, Pt _x Ru _y M _z functions effectively as a catalyst for the air electrode 101.

In the lithium air secondary battery, in order to increase the efficiency of the battery, it is desirable that there are more reaction sites (the above-described electrolyte / electrode catalyst / air (oxygen) three-phase portion) that cause an electrode reaction. From such a viewpoint, it is important that the above-mentioned three-phase sites are present in a large amount on the electrode catalyst surface, and it is desirable that the catalyst used has a high specific surface area. For example, the catalyst Pt _x Ru _y M _z has a BET specific surface area of 30 m ² / g or more, preferably 50 m ² / g or more.

Pt _x Ru _y M _z can be obtained by various methods. For example, Pt _x Ru _y M _z can be obtained by various synthesis methods using known processes such as a solid phase method and a liquid phase method. Hereinafter, as an example Pt _x Ru _y Sn _z describes this production.

Preparation of Pt _x Ru _y Sn _z precursor by liquid phase method using soluble compounds of Pt such as H ₂ PtCl ₆ , soluble compounds of Ru such as RuCl ₃ and soluble compounds of Sn such as SnCl ₂ and, it is possible to synthesize Pt _x Ru _y Sn _z by heat-treating it.

As described above, a metal chloride or nitrate, in a variety of manufacturing methods including a liquid phase method and the like acetates may be prepared Pt _x Ru _y Sn _z. The liquid phase method includes a method in which an aqueous solution of the above-described metal chloride, nitrate, acetate or the like is evaporated to dryness and hydrogen reduced. As a more specific procedure, an aqueous solution of a soluble compound of Pt, a soluble compound of Ru, and a soluble compound of Sn is mixed, and the resulting solution is evaporated to dryness, and then dried under a reducing atmosphere such as H ₂ gas. There is a method of heat treatment with. The heat treatment procedure includes temperature reduction at a temperature of 100 ° C. or higher, preferably 150 to 600 ° C.

Further, by heat treatment at Pt _x Ru _y Sn a low temperature of 100 ° C. or less with _z precursor the reducing agent, it is possible to synthesize Pt _x Ru _y Sn _z oxygen in the precursor is removed. As the reducing agent, it is preferable to use a metal particle such as a nonionic surfactant [poly (oxyethylene) 5-nonylphenyl ether or the like] containing no metal or zinc.

The Pt _x Ru _y Sn _z thus obtained exhibits high performance when used as an electrode catalyst for the air electrode of the lithium air secondary battery of the present invention. The obtained Pt _x Ru _y Sn _z (Pt _x Ru _y M _z ) is considered to be in various forms including solid solutions and alloy states such as intermetallic compounds.

Next, basic materials other than the catalyst constituting the air electrode 101 will be described. First, the conductive material constituting the air electrode 101 will be described. 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 101, 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, as described above, it is desirable that the specific surface area of the catalyst and carbon used for the air electrode 101 have a predetermined value. This specific surface area can be measured using a commercially available apparatus. For example, the specific surface area can be measured by a BET method using liquid nitrogen as a cooling medium using a commercially available measuring apparatus.

  Next, the binder (binder) constituting the air electrode 101 will be described. As described above, the air electrode 101 may be manufactured using a binder. Although this binder is not specifically limited, Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, etc. can be mentioned as an example. These binders can be used as powders or dispersions.

Next, the manufacture of the air electrode 101 will be briefly described. The air electrode 101 may be manufactured as follows. Mix Pt _x Ru _{y Mz} catalyst powder, carbon powder, and optionally binder powder such as polytetrafluoroethylene (PTFE), and press the mixture onto a support such as titanium mesh. Thus, the air electrode 101 may be formed.

  Alternatively, the air electrode 101 may be formed by dispersing the mixture in a solvent such as an organic solvent to form a slurry, and applying the slurry onto a metal mesh or carbon cloth or carbon sheet and drying.

  In addition, in order to increase the strength of the electrode and prevent leakage of the electrolyte 103 in liquid form, the air electrode 101 with higher stability can be produced not only by cold pressing but also by applying hot pressing. Can do.

One surface of the air electrode 101 is exposed to the atmosphere, and the other surface is in contact with the electrolyte 103. As described above, by producing the air electrode 101 to which platinum ruthenium-based metal (Pt _x Ru _y M _z ) is added (supported), it is possible to obtain the air electrode 101 that is highly active with respect to charging and discharging reactions. Can do. Furthermore, by producing the air electrode 101 of the lithium-air secondary battery having the above-described configuration, battery performance such as a charge / discharge cycle can be improved.

Next, the negative electrode 102 will be described. The negative electrode 102 is composed of a negative electrode active material. 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-air secondary battery. For example, metallic lithium can be mentioned. Alternatively, an example of an alloy of Li and silicon (Si) or tin (Sn), or a lithium nitride such as Li _2.6 Co _0.4 N, which is a substance capable of inserting and extracting lithium ions can be given. .

  In the case where an alloy of Si or Sn is used as the negative electrode 102, Si or Sn that does not contain Li can be used when the negative electrode 102 is formed. However, in this case, prior to the production of the lithium-air secondary battery, by a chemical method or an electrochemical method (for example, a method in which an electrochemical cell is assembled and Li and Si or Sn are alloyed). , Si or Sn must be processed so as to be in a state containing Li.

  Specifically, it is preferable to perform electrochemical treatment such as alloying by using Si or Sn as the working electrode, Li as the counter electrode, and flowing a reducing current in the organic electrolyte.

  The negative electrode 102 can be formed by a known method. For example, in the case where lithium metal is used as the negative electrode 102, the negative electrode 102 may be manufactured by stacking a plurality of metal lithium foils into a predetermined shape.

  In addition, the reaction at the time of the discharge in the negative electrode 102 comprised from metallic lithium can be expressed as follows.

Li → Li ⁺ + e ⁻ (2)

  On the other hand, in the negative electrode 102 at the time of charging, a lithium precipitation reaction which is the reverse reaction of the formula (2) occurs.

Next, the electrolyte 103 will be described. The electrolyte 103 may be any substance that can move lithium ions between the air electrode 101 (positive electrode) and the negative electrode 102. For example, the electrolyte 103 may be a nonaqueous solvent (organic solvent) in which a metal salt containing lithium ions is dissolved. Specifically, examples of the metal salt containing lithium ions include metals containing lithium ions such as lithium bistrifluoromethanesulfonylamide (LiTFSA), lithium perchlorate (LiClO ₄ ), and lithium hexafluorophosphate (LiPF ₆ ). Mention may be made of salts.

  Nonaqueous solvents 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, Carbonate ester solvents such as 2-butylene (1,2-BC), ether solvents such as 1,2-dimethoxyethane (DME) and tetraethylene glycol dimethyl ether (TEGDME), and lactone systems such as γ-butyrotactone (GBL) Solvent, or dimethylsulfoxy (DMSO) can be mentioned sulfoxide solvents solvent or a mixture of two or more from these, such as. Examples of the solvent in which two or more kinds are mixed include a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 1: 1), a mixed solvent such as EC and diethyl carbonate (DEC). it can.

Other materials constituting the electrolyte 103 include a solid electrolyte that passes lithium ions (eg, a sulfide-based solid electrolyte containing Li ₂ S and P ₂ S ₅ ), and a polymer electrolyte that passes lithium ions (eg, polyethylene oxide). System, specifically, for example, a material obtained by compositing the organic electrolyte and polyethylene oxide). However, the material constituting the electrolyte 103 is not limited to these, and can be suitably used as long as it is a known solid electrolyte that passes lithium ions or a polymer electrolyte that passes lithium ions used in lithium-air secondary batteries. .

  In addition to the above configuration, the lithium-air secondary battery can include structural members such as a separator, a battery case, and a metal mesh (for example, titanium mesh), and elements required for the lithium-air secondary battery. Conventionally known ones can be used.

  Next, a manufacturing method will be described. The lithium air secondary battery of the present invention includes an air electrode, a negative electrode, and an electrolyte obtained by an air electrode manufacturing method, which will be described later, together with other necessary elements based on the structure of a desired lithium air secondary battery. It can be produced by appropriately arranging in an appropriate container. A conventionally known method can be applied to the manufacturing procedure of these lithium air secondary batteries.

  This will be described in more detail below. In the lithium air secondary battery of the present invention, the air electrode, the negative electrode, and the electrolyte are appropriately arranged in an appropriate container such as a case together with other necessary elements based on the structure of the desired lithium air secondary battery. Can be produced. A conventionally known method can be applied to the manufacturing procedure of these lithium air secondary batteries.

  Hereinafter, it demonstrates in detail using an Example. Below, the lithium air secondary battery was actually produced and the change of the discharge capacity was measured about each produced sample. First, the configuration of the actually used battery will be described with reference to FIG. FIG. 2 is a cross-sectional view showing a more detailed configuration example of the lithium air secondary battery.

  The lithium-air secondary battery includes an air electrode 201, a negative electrode 202, an electrolyte 203, a separator 204, an air electrode support 205, an air electrode fixing ring 206, a negative electrode fixing ring 207, a negative electrode fixing washer 208, and a negative electrode support 209. , Fixing screw 210, O-ring 211, air electrode terminal 221, and negative electrode terminal 222.

  The air electrode 201, the negative electrode 202, the electrolyte 203, and the separator 204 are accommodated in a cylindrical air electrode support 205. The air electrode support 205 has a partition 251 at the center in the cylinder, and is partitioned into a first region 205 a where the air electrode 201 is disposed and a second region 205 b where the negative electrode 202 and the separator 204 are disposed. ing. The partition 251 has an opening at the center, and the first region 205a and the second region 205b communicate with each other through the opening.

The liquid electrolyte 203 is disposed in the opening of the partition 251 and is sandwiched between the air electrode 201 and a separator 204 serving as a salt bridge. The separator 204 is impregnated with the electrolyte 203. Note that the electrolyte 203 is also disposed around the separator 204. The electrolyte 203 is a 1 mol / L lithium bistrifluoromethanesulfonylamide / propylene carbonate [(CF ₃ SO ₂ ) ₂ NLi / PC] solution.

The air electrode 201 is sandwiched between an air electrode fixing ring 206 made of polytetrafluoroethylene (PTFE) and a partition 251, and is fixed to a first region 205 a in the cylinder of the air electrode support 205. Yes. In the opening of the air electrode fixing ring 206, the effective area of the electrode in contact with the air electrode 101 and air is 2 cm ² . On the other hand, the separator 204 is sandwiched between a negative electrode fixing ring 207 made of PTFE and a partition 251, and is fixed to a second region 205 b in the cylinder of the air electrode support 205. In this way, the liquid electrolyte 203 is sealed between the air electrode 201 and the separator 204 at the opening of the partition 251.

The negative electrode 202 has a negative electrode fixing washer 208 laminated inside a negative electrode fixing ring 207, and a negative electrode support 209 made of a metal covered thereon. The negative electrode 202 is configured by concentrating four metal lithium foils having a thickness of 150 μm on concentric circles, and is pressure-bonded to the negative electrode fixing washer 208. The negative electrode 202 has an effective area of 2 cm ² . The negative electrode support 209 is fixed to the air electrode support 205 by a fixing screw 210. Further, an O-ring 211 is disposed between the air electrode support 205 and the negative electrode support 209.

  The negative electrode 202 is pressed in the direction of the separator 204 through the negative electrode fixing washer 208 by the negative electrode support 209 pressed against the air electrode support 205 by the fixing screw 210, and is pressed against the separator 204. The lithium air secondary batteries having these configurations were produced in dry air having a dew point of −60 ° C. or lower.

  Although the air electrode support 205 is made of metal, although not shown, it is covered with PTFE and insulated and separated from the electrolyte 203, the separator 204, and the like. Note that the portion where the air electrode 201 and the air electrode support 205 are in contact with each other is not covered with PTFE in order to make electrical contact. Further, although not shown, the fixing screw 210 made of metal is covered with PTFE so that the air electrode support 205 and the negative electrode support 209 are electrically separated.

[Example 1]
First, Example 1 will be described. In the first embodiment, the case where Pt _x Ru _y M _z (x = y = z) is used as the catalyst of the air electrode will be described. Sample 1 is M = Cr, Sample 2 is M = Mn, Sample 3 is M = Fe, Sample 4 is M = Co, Sample 5 is M = Ni, Sample 6 is M = Pd, Sample 7 Are M = Sn, Sample 8 is M = In, Sample 9 is M = Ir), and Sample 10 is M = Au.

Commercially available hexachloride platinic acid (H ₂ PtCl ₆ ) (manufactured by Sigma-Aldrich), commercially available ruthenium chloride hydrate (RuCl ₃ · nH ₂ O) (manufactured by Furuya Metal Co., Ltd.) Were dissolved in distilled water and adjusted so that Pt, Ru, and M were 1: 1: 1 by atomic weight ratio. The total concentration of the metal salt was 0.3 mol / L.

The metal chlorides of Samples 1 to 10 are chromium chloride (CrCl ₃ , Sigma-Aldrich), manganese chloride (MnCl ₂ , Sigma-Aldrich), iron chloride (FeCl ₂ , Sigma-Aldrich), and chloride. Cobalt (CoCl ₂ , Sigma Aldrich), nickel chloride (NiCl ₂ , Sigma Aldrich), palladium chloride (PdCl ₂ , Sigma Aldrich), tin chloride (SnCl ₂ , Sigma Aldrich), indium chloride ( InCl ₃ , Sigma-Aldrich), iridium chloride (IrCl ₃ , Sigma-Aldrich), tetrachloride gold (III) acid (HAuCl ₄ , Sigma-Aldrich).

  A nonionic surfactant poly (oxyethylene) 5 nonylphenyl ether (manufactured by Kao Corporation) was added to the above-described solution so as to be 50 wt%. The mixture was stirred at 40 ° C. overnight to obtain a gel containing Pt—Ru—M. Further, zinc (Zn) particles that can be dispersed throughout the gel were mixed and stirred in the gel. Due to the mixed diffusion of Zn particles, the gel had a deeper black color, suggesting that it was reduced to metal. The resulting black gel was washed three times in the order of washing with acetone, washing with ion exchange water, and washing with hydrochloric acid (2 mol / l) to remove the surfactant and zinc.

The powder obtained by washing was heat-treated at 100 ° C. for 12 hours in air. The Pt _x Ru _{y Mz} powder was dissolved in an HCl-HNO ₃ aqueous solution to prepare an analysis sample, and the prepared analysis sample was analyzed by high frequency inductively coupled plasma (ICP) emission analysis. The obtained powder was analyzed by X-ray diffraction (XRD) measurement. Further, the BET specific surface area was measured and evaluated.

  The powder after the heat treatment is Pt: Ru: M = 1: 1.10: 0.95 to 1.05 (atomic ratio) by ICP emission analysis, and can be synthesized with a composition ratio almost as designed. Was confirmed. Further, when XRD measurement was performed on the obtained sample, no peak indicating a crystal phase or a peak attributed to by-products such as oxides of contained metals was observed, so the sample had an amorphous structure. I found out that

Note that Pt _x Ru _y M _z has an amorphous structure, which indicates that crystallization has not progressed and particle growth is also suppressed. Such a phenomenon leads to an increase in the surface area of Pt _x Ru _{y Mz} and is considered to be advantageous as a catalyst.

Actually, when the specific surface area of the powder was measured by the BET method for PtRuM of each sample 1 to 10 in the practical example 2, the sample 1 was 42 m ² / g, the sample 2 was 35 m ² / g, and the sample 3 was 43 m ² / g, Sample 4 is 31 m ² / g, Sample 5 is 28 m ² / g, Sample 6 is 55 m ² / g, Sample 7 is 92 m ² / g, Sample 8 is 60 m ² / g, Sample 9 was 52 m ² / g and Sample 10 was 71 m ² / g.

Next, an air electrode was produced using the above-described Pt _x Ru _{y Mz} powder of each sample. PtRuM powder, ketjen black powder and polytetrafluoroethylene (PTFE) powder are sufficiently pulverized and mixed using a roughing machine at a weight ratio of 10:70:20, roll-formed, and a sheet having a thickness of 0.5 mm A shaped electrode was prepared. 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.

  Next, the air electrode produced about each sample was made into the air electrode 201 of the lithium air secondary battery demonstrated using FIG. 2, and the lithium air secondary battery was assembled about each sample. First, the produced air electrode 201 was arranged in a state in contact with the partition 251 in the first region 205 a of the air electrode support 205 and fixed with the air electrode fixing ring 206.

Next, the separator 204 was disposed in contact with the partition 251 in the second region 205 b of the air electrode support 205. Next, four lithium metal foils (effective area: 2 cm ² ) having a thickness of 150 μm were stacked on the negative electrode fixing ring 207 as the negative electrode 202 and pressed on the concentric circles. Next, the negative electrode fixing ring 207 was disposed in the second region 205b of the air electrode support 205, and the negative electrode fixing ring 207 to which the negative electrode 202 was pressure-bonded was fitted into the center portion.

  Next, an organic electrolytic solution constituting the electrolyte 203 is filled between the air electrode 201 and the negative electrode 202, and in this state, an O-ring 211 is disposed on the bottom surface of the air electrode support 205 to cover the negative electrode support 209. The fixing screw 210 was fixed to the air electrode support 205. As the organic electrolyte, a 1 mol / liter lithium bistrifluoromethanesulfonylamide / tetraethylene glycol dimethyl ether (LiTFSA / TEGDME) solution was used. Thereafter, the air electrode terminal 221 was installed on the air electrode support 205 and the negative electrode terminal 222 was installed on the negative electrode support 209.

Next, the result of Example 1 which measured the battery performance of the lithium air secondary battery actually produced is demonstrated. The air electrode terminal 221 and the negative electrode terminal 222 were used for a battery performance measurement test. In the battery cycle test, a charge / discharge measurement system (VMP3, manufactured by Bio Logic) was used, and a current density of 0.1 mA / cm ² was applied per effective area of the air electrode. The discharge voltage was measured until the voltage dropped to 0.0V. Further, the battery charge test was performed until the battery voltage increased to 4.2 V at the same current density as during discharge. The battery discharge test 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 + catalyst (Pt _x Ru _{y Mz} powder) + PTFE).

  First, FIG. 3 shows the initial discharge and charge curves of Sample 7 using PtRuSn as a catalyst. As shown in FIG. 3, when PtRuSn is used for the air electrode catalyst, the average discharge voltage is 2.48V, the average charge voltage is 4.11V, and the discharge capacity is 990 mAh / g. The average charge / discharge voltage is defined as a discharge voltage and a charge voltage at an intermediate value of the total discharge capacity in FIG.

  Next, the cycle dependency of the discharge capacity in Samples 1 to 10 is shown in Table 1 below. In any sample, although the discharge capacity is decreased by repeating the cycle, about 90% of the initial capacity is maintained even after 100 cycles, and the cycle characteristics are clearly more stable than the comparative examples described later. You can see that it is obtained. Among these, especially in the sample 7 using M = Sn, even when the charge / discharge cycle is repeated 100 times, the discharge capacity is maintained at a particularly high value of 905 mAh / g.

  The order of these catalytic activities largely depends on the BET specific surface area of the catalyst, and it is considered that the Sn system that provides the highest surface area showed high activity. From the above samples, it was found that PtRuM, and among these, PtRuSn powder has very excellent activity as a catalyst for the air electrode of a lithium air secondary battery.

  Next, the conditions of the effective metal composition ratio (Pt: Ru: M) in the present invention will be described by exemplifying the Pt—Ru—Sn system showing the highest activity among the samples in Example 1 described above. .

[Example 2]
Next, Example 2 will be described. In Example 2, Pt: Ru: Sn = 1: 1: 2 (sample 11), Pt: Ru: Sn = 1: 2: 1 (sample 12), Pt: Ru: Sn = 1: 3: 1 (sample) The case where 13) is used as the air electrode catalyst will be described.

Commercially available hexachloride platinic acid (H ₂ PtCl ₆ ) (manufactured by Sigma-Aldrich), commercially available ruthenium chloride hydrate (RuCl ₃ · nH ₂ O) (manufactured by Furuya Metal), and tin chloride (SnCl ₂ , Sigma Aldrich) was dissolved in distilled water, and each was adjusted so that the atomic weight ratio of Pt, Ru, and Sn would be the above values. Thereafter, the lithium air secondary batteries of Sample 11, Sample 12, and Sample 13 were produced in the same manner as in Example 1.

Similar to Example 1, the powder of the prepared Pt _x Ru _y Sn _z was dissolved in HCl-HNO ₃ aqueous solution was prepared analytical sample, an analysis sample prepared was analyzed by ICP emission spectrometry. Further, the obtained powder was analyzed by XRD measurement. Further, the BET specific surface area was measured and evaluated.

Powder of the prepared Pt _x Ru _y Sn _z, as in the case of the first embodiment has substantially the composition ratio of the design by ICP emission spectrometry, it was found to have an amorphous structure by XRD measurement. When the specific surface area of the powder was measured by the BET method, the sample 11 was 35 m ² / g, the sample 12 was 92 m ² / g, the sample 13 was 132 m ² / g, and the composition ratio of Ru was high. It was found that when the composition ratio of Sn is low, the metal powder has a high specific surface area.

Next, Pt _x Ru _y Sn _z powder initial discharge capacity and average discharge voltage of lithium-air secondary battery using as an electrode catalyst of the air electrode of the sample 11 to 13, the discharge capacity at the 50th cycle and 100th cycle, It shows in Table 2 with the result of the sample 7. As shown in Table 2, the larger the Ru content, the larger the discharge capacity and the higher cycle stability, and the sample 13 showed the most excellent performance. This tendency coincides with the tendency of the BET specific surface area of the catalyst powder, and it can be seen that the increase in the specific surface area greatly contributes to the improvement of the air electrode activity.

  Next, a sample having a composition ratio outside the scope of the present invention with respect to Example 2 described above will be described. In the following, Pt: Ru: Sn = 0.9: 1: 1 (sample 14), 1: 1: 2.1 (sample 15), 1: 3: 0.9 (sample 16) are produced at respective composition ratios. A case will be described in which the prepared catalyst is applied to the air electrode.

Commercially available hexachloride platinic acid (H ₂ PtCl ₆ ) (manufactured by Sigma-Aldrich), commercially available ruthenium chloride hydrate (RuCl ₃ · nH ₂ O) (manufactured by Furuya Metal), and tin chloride (SnCl ₂ , Sigma Aldrich) was dissolved in distilled water, and each was adjusted so that the atomic weight ratio of Pt, Ru, and Sn would be the above values. Thereafter, the lithium-air secondary batteries of Sample 14, Sample 15, and Sample 16 were produced in the same manner as in Example 1.

Powder of the prepared Pt _x Ru _y Sn _z, as in the case of the first embodiment has substantially the composition ratio of the design by ICP emission spectrometry, it was found to have an amorphous structure by XRD measurement. Moreover, when the specific surface area of the powder was measured by the BET method, the sample 14 was 8 m ² / g, the sample 15 was 6 m ² / g, and the sample 16 was 10 m ² / g. Compared with the samples 11 to 13 The specific surface area was found to be quite small.

  Further, in the region deviating from the composition range x ≦ y, Pt aggregation occurs, while in the region deviating from the composition range where the tin content [100z / (x + y + z)] is 20% or more and 50% or less, Ru aggregation or Sn aggregation Aggregation was confirmed by observation with an electron microscope (SEM).

  As is clear from the above, it is considered that the samples 14 to 16 have a reduced surface area due to a decrease in uniformity.

Pt _x Ru _y Sn _z powder initial discharge capacity and average discharge voltage of lithium-air secondary battery using as a catalyst of the air electrode of the sample 14 to 16, the discharge capacity at the 50th cycle and 100th cycle, sample 7,11 It shows in Table 2 with the result of -13. As shown in Table 2, the battery performance of Samples 14 to 16 is clearly lower than that of Samples 7 and 11 to 13 with a low discharge voltage and a small initial discharge capacity, and a significant decrease in capacity when the cycle is repeated. I understood.

The results outside the composition range in the present invention indicate that the composition requirement of Pt _x Ru _{y Mz} in the present invention is very beneficial for improving battery performance.

[Example 3]
Next, Example 3 will be described. Example 3 shows a case where M in Pt _x Ru _y M _z is a metal other than Sn. More specifically, the sample 17-19 by Pt _x Ru _y Cr _z where a range of conditions of the present invention, for samples 20-22) by Pt _x Ru _y Cr _z was outside the range of the conditions of the present invention, the above-mentioned As in the first and second embodiments, Table 3 shows the results of producing an air electrode, producing a lithium-air secondary battery, and measuring the cycle dependency of the discharge capacity.

Also, sample 23-25 by Pt _x Ru _y Mn _z was in the range of conditions of the present invention, for samples 26-28 according to Pt _x Ru _y Mn _z was outside the range of the conditions of the present invention, the embodiment described above form 1 Table 2 shows the results of manufacturing the air electrode and the lithium-air secondary battery and measuring the cycle dependency of the discharge capacity in the same manner as in FIGS.

Further, the above-described first embodiment is described for the sample 29-31 made of Pt _x Ru _y Fe _z within the range of the conditions of the present invention and the sample 32-34 made of Pt _x Ru _y Fe _z outside the range of the conditions of the present invention. Table 5 shows the results of producing an air electrode, producing a lithium-air secondary battery, and measuring the cycle dependency of the discharge capacity in the same manner as in FIGS.

Further, the above-described first embodiment is described with respect to the sample 35-37 by Pt _x Ru _y Co _{z set as} the range of the conditions of the present invention and the sample 38-40 by Pt _x Ru _y Co _{z set} outside the range of the conditions of the present invention. Table 6 shows the results of measuring the cycle dependency of the discharge capacity by preparing an air electrode and a lithium-air secondary battery in the same manner as in FIGS.

Further, the above-described first embodiment is described with respect to the sample 41-43 made of Pt _x Ru _y Ni _z within the range of the conditions of the present invention and the sample 44-46 made of Pt _x Ru _y Ni _z outside the range of the conditions of the present invention. Table 7 shows the results of manufacturing the air electrode and the lithium-air secondary battery and measuring the cycle dependency of the discharge capacity in the same manner as in FIGS.

Further, the above-described first embodiment is applied to the samples 47 to 49 based on Pt _x Ru _y Pd _{z set as} the range of the conditions of the present invention and the samples 50 to 52 based on Pt _x Ru _y Pd _{z set} outside the range of the conditions of the present invention. Table 8 shows the results of manufacturing the air electrode and the lithium-air secondary battery and measuring the cycle dependency of the discharge capacity in the same manner as in FIGS.

Further, the above-described first embodiment is described with respect to the sample 53-55 based on Pt _x Ru _y In _z within the range of the conditions of the present invention and the sample 56-58 based on Pt _x Ru _y In _z outside the range of the conditions of the present invention. Table 9 shows the results of manufacturing the air electrode and the lithium-air secondary battery and measuring the cycle dependency of the discharge capacity in the same manner as in FIGS.

Further, the above-described first embodiment is described for the sample 59-61 based on Pt _x Ru _y Ir _z within the range of the conditions of the present invention and the sample 62-64 based on Pt _x Ru _y Ir _z outside the range of the conditions of the present invention. Table 10 shows the results of manufacturing the air electrode and the lithium-air secondary battery and measuring the cycle dependency of the discharge capacity in the same manner as in FIGS.

Also, sample 65-67 by Pt _x Ru _y Au _z was in the range of conditions of the present invention, for samples 68-70 according to Pt _x Ru _y Au _z was outside the range of the conditions of the present invention, the embodiment described above form 1 Table 11 shows the results of manufacturing the air electrode, the lithium-air secondary battery, and measuring the cycle dependency of the discharge capacity in the same manner as in FIGS.

  From the results shown in Tables 3 to 11, when x ≦ y and M content [100z / (x + y + z)] satisfy the conditions of the present invention of 20% or more and 50% or less, the discharge capacity is large and stable. On the other hand, in the case where the cycle characteristics are shown, the cases where the cycle stability is low were observed even when the initial discharge capacity was large in the case outside the range of the present invention. The effectiveness of the present invention was demonstrated from the results of experiments with each of these samples.

[Comparative example]
Next, a comparative example will be described. Using a known iron oxide (Fe ₂ O ₃ ) as an electrode catalyst for the air electrode, a lithium air secondary battery cell was produced in the same manner as the above-described sample. For Fe ₂ O ₃ , a commercially available reagent (manufactured by Wako Pure Chemical Industries, Ltd.) was used. The production conditions and evaluation methods of the air electrode and the air battery are the same as in the case of each sample described above.

  Table 12 shows the cycle performance regarding the discharge capacity of the lithium-air secondary battery in the comparative example, together with the result of the sample 13 that showed the highest performance.

  As shown in Table 12, in the comparative example, the initial discharge capacity was 1450 mAh / g, which was larger than that of the sample 13. However, when the charge / discharge cycle is repeated, unlike the sample 13, an extreme decrease in the discharge capacity is observed, and the capacity retention rate after 50 cycles is very low at about 50% in the initial stage and about 7% after 100 cycles. Value.

From the above results, the lithium-air secondary battery using the air electrode using Pt _x Ru _{y Mz} as an electrode catalyst has better charge / discharge cycle characteristics than the case where a conventional electrode catalyst is used, and Pt _x It was confirmed that Ru _{y Mz} is effective as an air electrode catalyst for a lithium-air secondary battery.

As described above, according to the present invention, since Pt _x Ru _{y Mz} is used as a catalyst for the air electrode, it is possible to suppress a decrease in discharge capacity even after repeated charge and discharge. According to the lithium-air secondary battery of, it can be effectively used as a drive source for various electronic devices.

  The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious.

  101 ... Air electrode, 102 ... Negative electrode, 103 ... Electrolyte.

Claims (2)

The air electrode,
A catalyst carried on the air electrode;
A negative electrode comprising lithium;
An organic electrolyte disposed between the air electrode and the negative electrode,
The lithium air secondary battery, wherein the catalyst is composed of a metal selected from Cr, Mn, Fe, Co, Ni, Pd, Sn, In, Ir, and Au, and Pt and Ru. The lithium air secondary battery according to claim 1,
The catalyst is Pt _x Ru _y M _z [M = Cr, Mn, Fe, Co, Ni, Pd, Sn, In, Ir, Au, x ≦ y, 0.2 ≦ z / (x + y + z) ≦ 0.5. ] Lithium air secondary battery characterized by the above-mentioned.

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