JP2008293678A - Half cell and air secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a half cell in which a one-electron oxidation-reduction reaction between O<SB>2</SB>and O<SB>2</SB><SP>-</SP>occurs reversibly and which is hardly affected by reaction inhibition due to water, while being satisfactory in charge/discharge cycle characteristics, even under open-air conditions and does not require expensive catalyst, such as a noble metal, a metal oxide, and a metal composite oxide for an air electrode in a half cell made of ionic liquid and an air electrode. <P>SOLUTION: The half cell is constituted of an ionic liquid and an air electrode. The air electrode comprises nickel particles and a binder. An air secondary battery is constituted of the air electrode of the half cell as a positive electrode, the ionic liquid as an electrolytic solution, and a negative electrode that uses any one from among lithium, aluminum, iron, zinc, sodium, magnesium, and cadmium as negative-electrode active material. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a half cell composed of an ionic liquid, an air electrode having gas diffusibility and capable of both oxygen generation and oxygen reduction, and an air basically composed of an air electrode, an ionic liquid, and a negative electrode. The present invention relates to a secondary battery.

  An air battery uses an air electrode that combines a conductive material such as carbon powder, a water-repellent binder such as polytetrafluoroethylene (PTFE), and an oxygen reduction catalyst, and one of zinc, aluminum, iron, and hydrogen. Equipped with a negative electrode as an active material and an aqueous electrolyte such as an alkaline aqueous solution, the air electrode as the positive electrode reduces oxygen in the air, and the negative electrode causes an oxidation reaction of the negative electrode active material to extract power to the outside It is generally known as a primary battery capable of

Further, air batteries that use aqueous solutions are not only primary batteries, but Patent Documents 1 and 2 disclose air secondary batteries that use an air electrode capable of both oxygen reduction and oxygen generation at the positive electrode. Patent Document 3 discloses an air secondary battery provided with a diamond electrode together with an air electrode and a negative electrode as a third electrode for charging the negative electrode.

JP 2002-158013 A JP-A-2005-190833 JP 2006-93022 A

As shown below, the reaction of the air electrode in the air secondary battery using these aqueous solutions is as follows: 2 mol of H ₂ O and 4 mol of electrons react with 1 mol of O ₂ during discharge. This is a so-called four-electron reaction in which a molar hydroxide ion is generated and the reaction proceeds in the opposite direction at the time of charging. It is a redox pair reaction in which O ₂ is an oxidant and hydroxide ion is a reductant. is there.

Discharge _{reaction: O 2 + 2H 2 O +} 4e → 4OH -
Charging _{^{reaction: 4OH - → O 2 + 2H}} 2 O + 4e

For such a four-electron reaction between O ₂ and hydroxide ions, a material carrying a metal catalyst or metal oxide catalyst on carbon powder or carbon fiber is widely known in the air electrode, In order to improve the cycle characteristics of the air electrode with respect to charging and discharging, Patent Document 4 discloses an air secondary battery using carbon nanotubes or fullerene as the air electrode material.

JP 2003-178816 A

On the other hand, an air battery using a non-aqueous electrolyte instead of an aqueous electrolyte has been studied. For example, Patent Document 5 and Patent Document 6 disclose air secondary batteries that use an organic solvent such as propylene carbonate (PC), ethylene carbonate (EC), or a mixed solution thereof as an electrolytic solution. Among them, an air electrode using carbon powder and polytetrafluoroethylene (PTFE) is used as in the case of an air battery using an aqueous electrolyte.
JP 2003-7357 A JP 2003-17143 A

Further, Patent Document 7 discloses an air-lithium secondary battery using an organic solid electrolyte in which a lithium salt is dissolved in polyethylene oxide (PEO) or polyvinylidene fluoride (PVDF), among which activated carbon or active A secondary battery using an air electrode composed of carbon fiber, a cobalt catalyst, and a binder is described.
Japanese Patent Laid-Open No. 2005-166585

  In the air battery using the organic solvent electrolyte or the organic solid electrolyte as described above, the electrochemical window of the electrolyte or electrolyte is wider than that of the aqueous electrolyte. Such negative electrode materials can be used, and even if the same air electrode material is used, the electromotive force of the air battery is increased, and the energy density and the output density are improved. On the other hand, organic solvent electrolytes and organic solid electrolytes are volatile and flammable, so in the event of depletion or deterioration of the electrolyte during long-term storage in an unused state, or even when the battery is damaged There is a problem that there is a risk of causing explosive destruction by combustible components.

  On the other hand, an ionic liquid has attracted attention as an electrolyte solution for a new air battery that replaces an organic solvent or an organic solid electrolyte. The ionic liquid is also called a room temperature molten salt, a room temperature molten salt, or a room temperature ionic liquid, and is generally a molten salt (molten salt) that is liquid at room temperature (25 ° C.). The component is basically composed of a cation and an anion, and is different from that based on a molecular organic compound containing no so-called ions such as the above organic solvent or organic solid electrolyte. There may be one kind of cation and anion each constituting one ionic liquid, or a single cation and multiple anions, multiple cations and single anions, or multiple cations and multiple anions as one ion It may be contained as a liquid component. In either case, the balance between the charge and concentration of anions and cations is maintained so that the ionic liquid as a whole is electrically neutral. Such an ionic liquid is nonflammable, unlike an organic solvent or an organic solid electrolyte. Moreover, since the vapor pressure is low and there is almost no volatility, the problem of the organic solvent as described above can be solved. Further, many ionic liquids have a wide electrochemical window, and by using the ionic liquid, there is a possibility that an electrochemically base metal such as lithium can be used as the negative electrode active material.

Already, an air battery using such an ionic liquid is disclosed as “non-aqueous electrolyte air battery” in Patent Document 8, Patent Document 9, and Patent Document 10, and an ionic liquid (room temperature molten salt), an air electrode, and The results of a discharge test are described for an air battery comprising a negative electrode that occludes and releases lithium ions.
JP 2004-119278 A JP-A-2005-26023 JP-A-2005-190880

Further, Patent Document 11 discloses an air battery including an air electrode, a metal negative electrode, and a room temperature molten salt having a melting point of 60 ° C. or less as a hydrophobic nonaqueous electrolyte, and the terminal voltage of the battery after long-term storage is disclosed. The measurement results of are described.
JP 2005-116317 A

As described above, air batteries using ionic liquids have advantages that are not available when using aqueous electrolytes, organic solvent electrolytes, or organic solid electrolytes. However, conventional air batteries using ionic liquids only consider discharge. The air primary battery is not used as a secondary battery. In order to enable use as a secondary battery, in a half-cell composed of an air electrode and an ionic liquid, it is necessary to reversibly generate oxygen, which is a reduction reaction of oxygen and its reverse reaction, As disclosed in Non-Patent Document 1, this reaction is not a four-electron reaction like an aqueous electrolyte but a one-electron reaction as shown below.

Discharge _{reaction: O 2 + e → O 2} -
Charging ^{_{reaction: O 2 - → O 2 +}} e

Journal of The Electrochemical Society, 151 (1), pp. A59-A63 (2004).

According to Non-Patent Document 1, from the result of cyclic voltammogram obtained by saturating oxygen in an ionic liquid and immersing a disk-shaped graphite electrode in the ionic liquid in an inert gas atmosphere measurement system. The one-electron reaction proceeds relatively reversibly in both directions, but it is disclosed that the addition of a small amount of water to the ionic liquid inhibits the oxidation of O ₂ ⁻ shown above as a charging reaction. Yes.
Similarly, Non-Patent Document 2 discloses a result of examining the oxidation-reduction reaction of O ₂ in an oxygen-saturated ionic liquid from the measurement of a cyclic voltammogram in an inert gas atmosphere. As a result of comparison of the catalytic properties of various kinds of electrode materials, it is described that glassy carbon is the best, followed by gold, and finally platinum, carbon materials have better catalytic properties than noble metal materials. This is completely opposite to the catalytic property for the four-electron reaction when using an aqueous electrolyte, and the characteristics of the electrocatalyst material for the one-electron redox reaction of O ₂ at the interface between the ionic liquid and the electrode are Unlike the case of using, it is not clear what kind of electrocatalyst material is excellent in characteristics.
Journal of The Electrochemical Society, 151 (4), pp. D31-D37 (2004).

As described above, in developing an air secondary battery using an ionic liquid, in a half cell composed of an air electrode and an ionic liquid, oxygen reduction and reverse generation of oxygen occur reversibly. There is a need. However, water, which is not a problem in aqueous systems, is a cause that hinders the progress of the reaction, and the relationship between the electrode material and the catalytic property that has become apparent in the four-electron reaction of oxygen is the one-electron reaction that occurs when an ionic liquid is used. A similar trend has not been observed. Therefore, O ₂ reducing the O ₂ ^- of oxidation and reversibly, and the half-cell comprised of a combination of the air electrode and the ionic liquid influenced using less susceptible electrode material of water, an ionic liquid Necessary for the realization of the air secondary battery to be used, but the reversible one-electron reaction does not proceed due to the influence of water in the half cell composed of the air electrode and the ionic liquid using the carbon-based material studied so far. There was a problem. Further, in Non-Patent Document 1 and Non-Patent Document 2, the results are obtained under the condition that oxygen is bubbled into the ionic liquid and saturated in the measurement system in an inert gas atmosphere. in the case of half-cell that combines an air electrode and an ionic liquid with a noble metal such as a carbon-based material and catalyst as the conductive material, O ₂ and O ₂ ^- cycle of the oxidation-reduction reaction between the poor There is a problem that it cannot be used as a chargeable / dischargeable half-cell. Furthermore, from the above problems, the air battery using an ionic liquid has been disclosed so far as the discharge characteristics as a primary battery, while the charge / discharge characteristics of the air electrode in the open atmosphere condition deteriorates with the cycle, There was a problem that the cycle performance as an air secondary battery could not be maintained.

For the above object, the present invention provides a half-cell consisting of the ionic liquid and the air electrode, O ₂ and O ₂ ^- 1 electron oxidation-reduction reaction occurs reversibly, the influence of the reaction inhibition by water between the A half-cell that is not easily affected, has good charge / discharge cycle characteristics even under open air conditions, and does not require an expensive catalyst such as a noble metal, metal oxide, metal composite oxide, or metal sulfide at the air electrode. For the purpose of provision. Further, the present invention, O ₂ and O ₂ in the air electrode ^- reaction with occurs reversibly, and small influence of the water at the air electrode, is excellent in cycle characteristics of charge and discharge by this, the air electrode It is an object of the present invention to provide an air secondary battery that uses an ionic liquid that can be charged and discharged and has excellent cycle performance, without using an expensive catalyst.

  The present inventor has developed a new half-cell consisting of an air electrode and an ionic liquid in response to the above-mentioned problems. Based on the knowledge obtained from the results of various studies on the evaluation of the characteristics of the obtained half-cell and the production and evaluation of the air secondary battery using this half-cell, the present invention has been made. .

That is, the present invention is a half-cell composed of an ionic liquid and an air electrode, and the air electrode is composed of nickel particles and a binder. The present inventor has shown that a half-cell consisting of an air electrode and an ionic liquid comprising nickel particles and a binder as constituent materials exhibits excellent catalytic properties for oxygen generation and oxygen reduction by a one-electron reaction under atmospheric release conditions. The present inventors have found that a half-cell capable of being charged / discharged has good charge / discharge characteristics without being affected by the moisture contained in the air over time and having good cycleability. Although details of the catalytic mechanism are not clear, in the air electrode of the present invention, one-electron reduction of O ₂ occurs promptly and is generated by electronic and chemical interaction at the interface between nickel and ionic liquid. This is because O ₂ ⁻ is stably present, and this one-electron oxidation of O ₂ ⁻ occurs promptly in the same manner. Carbon-based materials such as carbon fiber, activated carbon, activated carbon fiber, carbon nanotube, and fullerene have good affinity with water and have pores and surface morphology that can adsorb and retain water. In the case of nickel particles, since there is no such feature, the water present and accumulated inside the air electrode using nickel particles is extremely small compared to the air electrode using carbon-based materials, and the water repellency due to the binder is low. In addition to the effect, the influence of water on the redox reaction between O ₂ and O ₂ ⁻ is effectively suppressed. Also, O ₂ and O ₂ ^- with respect to the oxidation-reduction reaction between the nickel is very stable, since it hardly proceeds redox reaction of the nickel particles, also electrochemical stability of the nickel itself, the This is the reason why the half-cell of the invention has excellent cycle characteristics.

In the air electrode according to the present invention, nickel particles are electrically connected, and the nickel particles have a function of maintaining the conductivity of the entire air electrode, as well as the surface of the nickel particles formed inside the air electrode, the ionic liquid, and the atmosphere. in the three-phase interface of, it performs the reduction of O _2, resulting O ₂ ^- has both a catalytic function that results in oxidation of. These functions are new functions that have not been found in air batteries using conventional aqueous solutions, organic solvents, or ionic liquids. In addition, in a conventional air battery using an aqueous solution, an organic solvent, or an ionic liquid, a nickel net as a current collector may be integrally molded when a mixture of a carbon-based material and a binder is molded. The function of the nickel particles in the half-cell of the present invention is completely different from the nickel used as such a current collector as described above. In addition, in a conventional air battery using an aqueous solution or an organic solvent, it is also known that nickel powder is used as a constituent material of the air electrode. In this case, nickel powder alone is used as a catalyst for oxygen four-electron redox reaction. Does not function, and a redox catalyst such as noble metals and oxides is always required together with nickel powder. Therefore, the one-electron redox reaction of oxygen occurring at the interface between the air electrode and the ionic liquid as in the present invention proceeds promptly and with good cycle characteristics at the nickel particle / ionic liquid interface. It is difficult to easily predict from the knowledge about the four-electron reaction of oxygen at the air electrode using a reduction catalyst as a constituent material, and has been newly found in the present invention.

  Here, commercially available granular nickel, powdered nickel, etc. can be used for the nickel particles in the present invention. The purity is preferably higher, but 99% or more is more preferable because the catalytic property for one-electron reaction of oxygen is deteriorated by impurities. The particle diameter of the nickel particles used at the time of producing the air electrode is preferably 0.1 μm to 100 μm when produced by mixing and pressure forming the nickel particles and the binder particles. When the particle size of the nickel particles is smaller than 0.1 μm, when the air electrode is produced, the inside of the air electrode is almost filled with the binder and the nickel particles, and as a result, oxygen in the atmosphere can be taken in. This is not preferable because it is difficult and also prevents the ionic liquid from penetrating into the air electrode, and as a result, the one-electron redox reaction of oxygen hardly occurs. In addition, when the particle size of the nickel particles is larger than 100 μm, when the air electrode is produced, the gap inside the air electrode becomes too large, so that the ionic liquid easily leaks to the outside and passes through the air electrode. Therefore, air easily penetrates into the ionic liquid, and at the same time, moisture contained in the air dissolves in the ionic liquid and inhibits the one-electron redox reaction of oxygen. In addition, a nickel foam having gaps manufactured from particulate nickel, powdered nickel, or nickel having a similar shape can also be used as a constituent material of the air electrode of the present invention. The shape and size of nickel as a raw material in this case are not particularly limited to the above range.

  Next, the binder according to the present invention has water repellency and allows air to permeate and diffuse into the gap while binding nickel particles to each other. Materials such as fluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-butadiene rubber (EPBR), styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC) are used, but satisfy the above conditions If it is, it will not be limited to these in particular.

The blending ratio between the nickel particles and the binder is preferably 99.5-60: 0.5-40 in terms of mass ratio. When the amount of the binder is less than 0.5% by mass, water repellency cannot be sufficiently imparted inside the air electrode, air permeability and diffusibility are lowered, and polarization during oxygen reduction is increased. Since the ionic liquid penetrates to the atmosphere side through the air electrode and leaks to the outside and cannot function as the air electrode, it is not preferable, and if it exceeds 40% by mass, the water repellency in the air electrode becomes strong. Therefore, it becomes difficult for the ionic liquid to penetrate into the air electrode, and in the oxygen generation reaction, the area where O ₂ ⁻ in the ionic liquid comes into contact with the nickel particles in the air electrode decreases, and the polarization at the time of oxygen generation increases. Therefore, it is not preferable.

  In the present invention, various molten salts that are generally liquid at room temperature (25 ° C.), which are also called room temperature molten salts, room temperature molten salts, and room temperature ionic liquids, can be used. In particular, a hydrophobic ionic liquid that separates into two layers without being uniform when mixed with the same volume of water at room temperature is used. This hydrophobic ionic liquid is composed of a combination of various types of cations and anions. Specific examples of cations include N, N, N, N-tetramethylammonium ions, N in the case of ammonium cations, N , N, N-trimethylethylammonium ion, N, N, N-trimethylpropylammonium ion, N, N, N-trimethylbutylammonium ion, N, N, N-trimethylpentylammonium ion, N, N, N-trimethyl Hexylammonium ion, N, N, N-trimethylheptylammonium ion, N, N, N-trimethyloctylammonium ion, N, N, N-trimethyldecylammonium ion, N, N, N-trimethyldodecylammonium ion, N- Ethyl-N, N-dimethyl Propylammonium ion, N-ethyl-N, N-dimethylbutylammonium ion, N-ethyl-N, N-dimethylhexylammonium ion, 2-methoxy-N, N, N-trimethylethylammonium ion, 2-ethoxy- N, N, N-trimethylethylammonium ion, 2-propoxy-N, N, N-trimethylethylammonium ion, N- (2-methoxyethyl) -N, N-dimethylpropylammonium ion, N- (2-methoxy) Ethyl) -N, N-dimethylbutylammonium ion and the like.

  Similarly, in the case of an imidazolium cation as a specific example of the cation, 1,3-dimethylimidazolium ion, 1-ethyl-3-methylimidazolium ion, 1-methyl-3-propylimidazolium ion, 1-butyl -3-methylimidazolium ion, 1-methyl-3-pentylimidazolium ion, 1-hexyl-3-methylimidazolium ion, 1-heptyl-3-methylimidazolium ion, 1-methyl-3-octylimidazolium ion Ion, 1-decyl-3-methylimidazolium ion, 1-dodecyl-3-methylimidazolium ion, 1-ethyl-3-propylimidazolium ion, 1-butyl-3-ethylimidazolium ion, 3-ethyl- 1,2-dimethyl-imidazolium ion, 1,2-di Til-3-propylimidazolium ion, 1-butyl-2,3-dimethylimidazolium ion, 1,2-dimethyl-3-hexylimidazolium ion, 1,2-dimethyl-3-octylimidazolium ion, 1- Examples include ethyl-3,4-dimethylimidazolium ion.

  Similarly, in the case of a pyrrolidinium cation as a specific example of the cation, N, N-dimethylpyrrolidinium ion, N-ethyl-N-methylpyrrolidinium ion, N-methyl-N-propylpyrrolidinium ion, N- Butyl-N-methylpyrrolidinium ion, N-methyl-N-pentylpyrrolidinium ion, N-hexyl-N-methylpyrrolidinium ion, N-methyl-N-octylpyrrolidinium ion, N-decyl-N-methylpyrrole Dinium ion, N-dodecyl-N-methylpyrrolidinium ion, N- (2-methoxyethyl) -N-methylpyrrolidinium ion, N- (2-ethoxyethyl) -N-methylpyrrolidinium ion, N- (2 -Propoxyethyl) -N-methylpyrrolidinium ion, N- (2-isopropyl) Pokishiechiru) -N- such methylpyrrolidinium ion.

  Similarly, in the case of piperidinium cation as a specific example of the cation, N, N-dimethylpiperidinium ion, N-ethyl-N-methylpiperidinium ion, N-methyl-N-propylpiperidinium ion, N- Butyl-N-methylpiperidinium ion, N-methyl-N-pentylpiperidinium ion, N-hexyl-N-methylpiperidinium ion, N-methyl-N-octylpiperidinium ion, N-decyl-N-methylpipe Lidinium ion, N-dodecyl-N-methylpiperidinium ion, N- (2-methoxyethyl) -N-methylpiperidinium ion, N- (2-methoxyethyl) -N-ethylpiperidinium ion, N- (2 -Ethoxyethyl) -N-methylpiperidinium ion, N-methyl-N- ( -Methoxyphenyl) piperidinium ion, N-methyl-N- (4-methoxyphenyl) piperidinium ion, N-ethyl-N- (2-methoxyphenyl) piperidinium ion, N-ethyl-N- (4-methoxy Phenyl) piperidinium ion.

  Similarly, in the case of a morpholinium cation as a specific example of the cation, N, N-dimethylmorpholinium ion, N-ethyl-N-methylmorpholinium ion, N-methyl-N-propylmorpholinium ion N-butyl-N-methylmorpholinium ion, N-methyl-N-pentylmorpholinium ion, N-hexyl-N-methylmorpholinium ion, N-methyl-N-octylmorpholinium ion, N -Decyl-N-methylmorpholinium ion, N-dodecyl-N-methylmorpholinium ion, N- (2-methoxyethyl) -N-methylmorpholinium ion, N- (2-methoxyethyl) -N -Ethylmorpholinium ion, N- (2-ethoxyethyl) -N-methylmorpholinium ion, N-methyl-N- ( -Methoxyphenyl) morpholinium ion, N-methyl-N- (4-methoxyphenyl) morpholinium ion, N-ethyl-N- (2-methoxyphenyl) morpholinium ion, N-ethyl-N- ( 4-methoxyphenyl) morpholinium ion and the like.

The anions that constitute the ionic liquid together with the above cations include PF ₆ ⁻ , BF ₄ ⁻ , CF ₃ SO ₃ ⁻ , C ₄ F ₉ SO ₃ ⁻ , [(CF ₃ SO ₂ ) ₂ N] ⁻ , [(C ₂ F ₅ SO ₂ ) ₂ N] ⁻ , [(CN) ₂ N] ^{− and the} like. Among the ionic liquids composed of a combination of the above cation and anion, the ammonium cation and [(CF ₃ SO ₂ ) ₂ are particularly excellent in hydrophobicity, wide electrochemical window, and excellent conductivity. N] ^- or _{[(C 2 F 5 SO 2} ) 2 N] - ionic liquids composed desirable.
In addition, the present invention is a half cell, wherein the ionic liquid is N, N, N-trimethyl-N-propylammonium bis (trifluoromethanesulfonyl) imide. N, N, N-trimethyl-N-propylammonium bis (trifluoromethanesulfonyl) imide is superior in hydrophobicity, has a wide electrochemical window, and has excellent conductivity among ionic liquids. Dissolution of moisture in the atmosphere is suppressed and deterioration of charge / discharge cycleability due to the influence of moisture can be prevented, and a wide electrochemical window makes it possible to use electrochemically base metals for the negative electrode and is high Since the ohmic loss generated in the ionic liquid can be reduced by the conductivity, the electromotive force and the operating discharge voltage of the air secondary battery can be increased, and the operating charging voltage can be decreased.

In addition, the present invention includes a negative electrode using the air electrode of the above half cell as a positive electrode, an ionic liquid as an electrolyte, and any one of lithium, aluminum, iron, zinc, sodium, magnesium, and cadmium as a negative electrode active material. It is the air secondary battery comprised.
For the negative electrode using lithium as an active material, metal oxides, metal sulfides, metal nitrides, lithium metals, lithium alloys, lithium oxides, carbon materials that occlude and release lithium ions, and the like can be used. For example, tin oxide, silicon oxide, lithium titanium oxide, niobium oxide, tungsten oxide etc. as metal oxide, tin sulfide, titanium sulfide etc. as metal sulfide, lithium cobalt as metal nitride Examples of lithium alloys such as nitride, lithium iron nitride, and lithium manganese nitride include lithium aluminum alloy, lithium tin alloy, lithium lead alloy, and lithium silicon alloy. Carbon materials that occlude and release lithium ions include graphite, coke, carbon fiber, spherical carbon and other graphite materials or carbonaceous materials, thermosetting resins, isotropic pitch, mesophase pitch, mesophase pitch carbon fiber Examples thereof include graphite materials or carbonaceous materials obtained by subjecting mesophase spherules to heat treatment at 500 to 3000 ° C.
As the negative electrode using any element of aluminum, iron, and zinc as an active material, a negative electrode used in a conventional aluminum-air battery, iron-air battery, or zinc-air battery can be used.

For negative electrodes that use sodium, magnesium, or cadmium as the active material, various shapes of metals such as plates, nets, rods, squares, spirals, etc., alloys, metal oxides, metal sulfides, metals Nitride etc. are mentioned.
Moreover, the shape and structure of the container of the secondary battery of this invention can utilize the thing similar to what is used with the air primary battery and air secondary battery which use aqueous solution system or an organic solvent. An example of the air secondary battery according to the present invention is shown in FIG. In FIG. 1, 1 is an air electrode, 2 is a negative electrode, 3 is an electrolyte, 4 is a case, 5 is a positive electrode terminal, and 6 is a negative electrode terminal.

As described above, the present invention has the following effects.
(1) According to the half cell of the present invention, a one-electron redox reaction between O ₂ and O ₂ ⁻ is reversibly generated at the interface between the ionic liquid and the air electrode under an open air condition, and Since the influence of water reaction inhibition on the reaction is suppressed and the charge / discharge cycle performance as a half-cell is improved, in an air secondary battery using an air electrode, an ionic liquid, and a negative electrode using this, It has an effect of providing an air secondary battery having battery characteristics with good discharge cycle characteristics and small changes in battery characteristics with respect to changes in the atmospheric environment under use conditions and the surrounding environment during storage.

(2) According to the air secondary battery of the present invention, an air electrode having excellent charge / discharge cycle characteristics, which is excellent in reversibility of oxygen one-electron redox reaction and hardly affected by water, is used as a positive electrode. In addition, the charge / discharge cycle performance of the air secondary battery using the ionic liquid is greatly improved. In addition, this makes it possible to maintain high electromotive force, energy density, and output density in an air secondary battery that utilizes the high electromotive force, nonflammability, and non-volatility unique to ionic liquids, without causing deterioration in characteristics due to volatilization of the electrolyte. It has the effect that it can be maintained in. In addition, since the air secondary battery of the present invention does not require an expensive noble metal, metal oxide or metal composite oxide catalyst for the air electrode, the use of an expensive catalyst such as other air secondary batteries This has the effect of suppressing an increase in manufacturing cost.

EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example and a comparative example, this invention is not limited to a following example.

Nickel particles (manufactured by Niraco Corporation, product number NI-314013, purity 99.9% or more, particle size 3-7 μm) and polytetrafluoroethylene (PTFE) particle suspension (manufactured by Daikin Industries, Ltd., product name Polyflon PTFE D-) 1E) was stirred and mixed to form a clay. At this time, nickel particles were 90% by mass and PTFE particles were 10% by mass. After drying this at room temperature, it was press-formed into a disk shape (diameter 13 mm) at 100 kgf / cm ² on a nickel net (Niraco, product number NI-318100, 100 mesh, thickness 0.1 mm) to be a current collector. After that, heat treatment was performed at 370 ° C. for 12.5 minutes in a nitrogen atmosphere to produce an air electrode.

(Comparative Example 1)
Porous carbon powder (Ketjen Black EC600JD ^™ ) and polytetrafluoroethylene (PTFE) particle suspension (Daikin Kogyo Co., Ltd., product name Polyflon PTFE D-1E) were stirred and mixed to form a clay. At this time, the porous carbon powder was 40% by mass and the PTFE particles were 60% by mass. After drying this at room temperature, using the same press machine and press die as Example 1 on a nickel net (Niraco, product number NI-318100, 100 mesh, thickness 0.1 mm) to be a current collector, After press-molding into a disk shape (diameter 13 mm) at 100 kgf / cm ² , heat treatment was performed at 370 ° C. for 12.5 minutes in a nitrogen atmosphere to produce an air electrode.

For each air electrode obtained in Example 1 and Comparative Example 1, the counter electrode is a platinum plate (14 cm ² ), the reference electrode is a silver electrode, the ionic liquid is N, N, N-trimethyl-N-propylammonium bis (trifluoro) Cyclic voltammograms were measured using (romethanesulfonyl) imide. Measurement is performed at room temperature using a fully automatic electrochemical analyzer, and the counter electrode is immersed in an ionic liquid in a glass beaker, and the air electrode is set in a PTFE holder, and then the holder is immersed in the ionic liquid. In this state, one side of the air electrode was in contact with the ionic liquid, and the opposite side was opened to the atmosphere.

The cyclic voltammogram obtained in Example 1 is shown in FIG. 2, and the cyclic voltammogram obtained in Comparative Example 1 is shown in FIG. Figure is a reduction current to flow from the vicinity of -1.1V by a first potential from 2 in onset potential more scanning the minus side, which O ₂ is O ₂ by one-electron reaction ^- current due to be reduced to It is. Next, when the potential scanning direction is reversed at −1.5 V and the potential scanning is performed on the positive side, an oxidation current having a peak at about −1.1 V is observed, and the generated O ₂ ⁻ is changed to O ₂ . It was shown to be oxidized. That is, in Example 1, the redox reaction between O ₂ and O ₂ ⁻ progressed reversibly under the open air condition. In general, when both the oxidant and the reductant involved in the reaction are dissolved in the electrolyte and the redox reaction between them proceeds reversibly, either the reduction reaction or the oxidation reaction A reduction wave and an oxidation wave having a peak are also observed. However, when the oxidant (O ₂ ) is a gas as in the half-cell of the present invention, and the oxidant is in a state that can be continuously supplied from one side of the air electrode, the supply of the oxidant is diffused. Since the limit is not reached, the reduction current does not have a peak shape. On the other hand, the reductant O ₂ ⁻ is generated by the reduction of O ₂ , and the amount of O ₂ ⁻ in the ionic liquid generated during the potential scan is finite. Therefore, O ₂ ^- in the oxidizing O ₂ ^- is the current because the diffusion limiting has a shape having a peak. Furthermore, as a result of continuously measuring cyclic voltammograms in the same potential range shown in FIG. 2, the shape shown in FIG. 2 did not change at all, and it was shown that the cycle characteristics were very good.

Next, in the cyclic voltammogram of FIG. 3 obtained in Comparative Example 1, when the potential is first scanned to the minus side from the starting potential, a reduction current flows as in Example 1, and in Comparative Example 1, O ₂ is It is reduced to the indicated ^- O ₂ by one-electron reaction. However, even when the potential scanning direction was reversed at −1.5 V and the potential scanning was performed to the plus side, an oxidation current with a peak as in Example 1 was not observed. In Example 1, the maximum value of the reduction current almost coincided with the peak value of the oxidation current, but in Comparative Example 1, the maximum value of the oxidation current was less than half of the maximum value of the reduction current. That is, in Comparative Example 1, a reduction reaction from O ₂ to O ₂ ⁻ occurred, but the reverse reaction, O ₂ ⁻ to O ₂ oxidation, did not proceed reversibly. Furthermore, as a result of continuously measuring cyclic voltammograms in the same potential range shown in FIG. 3, the shape shown in FIG. 3 changes with an increase in the number of repetitions of potential scanning, and in particular, a decrease in oxidation current is observed. Example 1 showed poor cycle performance.

  Next, using an automatic charging / discharging device, each electrode and ionic liquid are arranged in the same state as when the above cyclic voltammogram was measured, and a constant current pulse that periodically reverses polarity is used in Example 1. And the charging / discharging test of each air electrode of Comparative Example 1 was performed. First, as shown in FIG. 4, in Example 1, a stable potential was observed in both discharging at 1 mA and charging at 0.1 mA, and a charge / discharge cycle was possible. Furthermore, as shown in FIG. 5, even when the charging current was changed with the discharging current being a constant value, charging and discharging could be repeated repeatedly, and no potential change was observed with respect to the charging / discharging cycle. Further, no change in the electrode shape was observed in the air electrode of Example 1 taken out from the holder after the charge / discharge cycle.

On the other hand, in the case of the air electrode of Comparative Example 1, discharge at 1 mA (reduction of O ₂ ) was possible, but immediately after charging at 0.1 mA, the potential suddenly increased and the automatic charge / discharge device It was impossible to measure beyond the measurable potential range. This was the same whether the discharge time was 30 seconds or 5 minutes, for example. Furthermore, although the measurement was performed in the same manner by changing the values of the discharge current and the charge current, both of them exceeded the measurable potential range immediately after the start of charging, and therefore the charge / discharge cycle could not be performed in Comparative Example 1. Further, in the air electrode of Comparative Example 1 taken out from the holder after this, the disk-shaped central portion swells, and deformation of the electrode shape is recognized.

  The present invention can be used for mobile devices, personal computers, memory backup batteries, small electronic devices, hearing aids, hybrid vehicles, electric vehicles, distributed household power sources, distributed business power sources, power storage batteries, and the like.

The schematic structure of the air secondary battery of this invention is shown. The cyclic voltammogram of Example 1 is shown. The cyclic voltammogram of the comparative example 1 is shown. The charging / discharging curve of Example 1 is shown. The charging / discharging curve of Example 1 is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Air electrode 2 Negative electrode 3 Ionic liquid 4 Case 5 Positive electrode terminal 6 Negative electrode terminal

Claims (3)

  A half cell comprising an ionic liquid and an air electrode, wherein the air electrode comprises nickel particles and a binder.   The half cell according to claim 1, wherein the ionic liquid is N, N, N-trimethyl-N-propylammonium bis (trifluoromethanesulfonyl) imide. The air electrode of the half-cell according to claim 1 or 2 is a positive electrode, the ionic liquid is an electrolytic solution, and any one of lithium, aluminum, iron, zinc, sodium, magnesium, and cadmium is a negative electrode active material. An air secondary battery composed of a negative electrode.

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