JP2010086924A - Magnesium air secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnesium air secondary battery capable of charging and discharging. <P>SOLUTION: In an F type electrochemical cell 20, a positive electrode 23 containing a poly (2,2,6,6-tetramethyl piperidinyloxy-methacrylate) radical as a redox catalyst for oxygen, and a negative electrode 25 composed of metal lithium are set opposing to each other via a separator 27 in a casing 21, and a non-aqueous electrolytic solution 28 is injected between the positive electrode 23 and the negative electrode 25. A foamed nickel plate 22 is mounted on the positive electrode 23, while the foamed nickel plate 22 is held down by a holding member 29 through which oxygen in a gas pool 30 can be circulated to the positive electrode 23 side. In addition, although not shown, the casing 21 can be separated into the upper part that is contacted with the positive electrode 23 and the lower part that is contacted with the negative electrode 25, and an insulating resin is interposed between the upper part and the lower part. The F type electrochemical cell 20 is capable of not only discharging but also charging, and in addition, can be charged and discharged repeatedly for a plurality of times. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a magnesium air secondary battery.

  In recent years, the market for portable information devices such as mobile phones and e-mail terminals is rapidly expanding. In addition, expectations for hybrid vehicles and electric vehicles are increasing from the viewpoint of environmental problems and the energy crisis. In light of this background, there is a need for high-energy storage devices. An example of such an electricity storage device is a metal-air battery. A metal-air battery includes a negative electrode capable of releasing metal ions and a positive electrode capable of using oxygen in the atmosphere. Since oxygen is supplied from the outside, the metal-air battery becomes a high-capacity electricity storage device. As such a metal-air battery, a lithium-air secondary battery using lithium as a negative electrode is well known (for example, see Patent Document 1).

By the way, lithium has a Clark number that reflects the ratio of elements existing on the ground surface of 0.006. If a large amount of lithium is consumed, there is a risk that the cost will increase rapidly. On the other hand, the standard electrode potential of magnesium is as low as -2.375V, it is lightweight, is cheaper and easier to handle than lithium, and is abundant in resources (Clark number 1.93). Because of these advantages, magnesium can be said to be an excellent material for the negative electrode of a battery. For example, the above-mentioned Patent Document 1 shows a specific example relating to a lithium air secondary battery, and the possibility of a magnesium air secondary battery using a material capable of occluding and releasing magnesium ions as a negative electrode active material. Has been suggested.
JP2003-7357

  However, Patent Document 1 merely suggests the possibility of a magnesium-air secondary battery, and does not describe any specific examples regarding the magnesium-air secondary battery. In fact, when a battery having a negative electrode using metallic magnesium as a negative electrode active material and a positive electrode using oxygen as a positive electrode active material was produced, it could only be discharged but could not be charged, so it could only function as a primary battery, not a secondary battery. It was. In order to function as a secondary battery, magnesium oxide must be decomposed into magnesium ions and oxygen at the positive electrode during charging, but it is considered that the magnesium oxide did not function because it did not easily decompose. .

  The present invention has been made to solve such a problem, and a main object of the present invention is to provide a chargeable / dischargeable magnesium-air secondary battery.

  In order to achieve the above-mentioned object, the present inventors made a non-aqueous electrolysis of a negative electrode made of magnesium metal and a positive electrode containing a compound having a nitroxyl radical that is a stable radical skeleton and oxygen as a positive electrode active material. When a battery arranged separately in the liquid was produced, it was found that charging as well as discharging was possible, and the present invention was completed.

  That is, the magnesium-air secondary battery of the present invention includes a negative electrode capable of inserting and extracting magnesium ions, a positive electrode containing a compound having a stable radical skeleton and oxygen as a positive electrode active material, and between the negative electrode and the positive electrode. And a non-aqueous magnesium ion conductor interposed between the two.

According to the magnesium air secondary battery of the present invention, not only discharging but also charging can be performed. Charging is possible in this way because a compound having a stable radical skeleton contained in the positive electrode causes a redox reaction (FIG. 1), which decomposes magnesium oxide into magnesium ions, oxygen and electrons during charging in the positive electrode. It is presumed that this was promoted. The reaction during charging in the positive electrode and the negative electrode is shown in the following formula. The redox reaction is expected to occur at 3.0 to 3.2 V on the Mg basis.
[Positive electrode] 2MgO → 2Mg ²⁺ + O ₂ + 4e ⁻
[Negative] Mg ²⁺ + 2e ^- → Mg

  The magnesium-air secondary battery of the present invention includes a negative electrode capable of inserting and extracting magnesium ions, a positive electrode containing a compound having a stable radical skeleton and oxygen as a positive electrode active material, and interposed between the negative electrode and the positive electrode A non-aqueous magnesium ion conductor.

  In the magnesium-air secondary battery of the present invention, the negative electrode is capable of occluding and releasing magnesium ions. As such a negative electrode, in addition to metallic magnesium, magnesium alloys such as magnesium aluminum, magnesium silicon, and magnesium gallium can be used, and graphite, coke, spherical carbon, and the like can also be used.

In the magnesium-air secondary battery of the present invention, the positive electrode uses oxygen as the positive electrode active material. The oxygen is preferably oxygen in the air. The positive electrode contains a compound having a stable radical skeleton. A compound having a stable radical skeleton functions as an oxygen redox catalyst. Here, a stable radical skeleton refers to a long radical that exists as a radical. For example, the spin density measured by electron spin resonance analysis is 10 ¹⁹ spins / g or more, preferably 10 ²¹ spins / g or more. It is good. Examples of such a stable radical skeleton include a skeleton having a nitroxyl radical, a skeleton having an oxy radical, a skeleton having a nitrogen radical, a skeleton having a sulfur radical, a skeleton having a carbon radical, and a skeleton having a boron radical. Selected ones are preferred. Specifically, a skeleton having a nitroxyl radical as shown in formulas (1) to (9), a skeleton having a phenoxy radical (oxy radical) as shown in formula (10), and formulas (11) to (13) And a skeleton having a hydrazyl radical (nitrogen radical), a skeleton having a carbon radical as shown in formulas (14) and (15), and the like. Among these, a skeleton having a nitroxyl radical is particularly preferable. For example, a 2,2,6,6-tetraalkyl-1-oxylpiperidinyl skeleton (see formula (1)), 2,2,5,5-tetra Those selected from the group consisting of an alkyl-1-oxylpyrrolinyl skeleton (see formula (2)) and a 2,2,5,5-tetraalkyl-1-oxylpyrrolidinyl skeleton (see formula (3)) preferable. Further, the amount of the compound having a stable radical skeleton is preferably 0.1 to 60% by weight, more preferably 10 to 55% by weight based on the total weight of the positive electrode. If it is less than 0.1% by weight, reduction of magnesium oxide may not be sufficiently promoted, and if it exceeds 60% by weight, current collection may not be sufficiently performed.

The compound having a stable radical skeleton may be a compound having a structure in which a polymer is linked to a stable radical skeleton, or a compound having a structure in which a polycyclic aromatic ring is linked to a stable radical skeleton. Good. In the former case, the oxygen redox catalyst function can be exerted over a long period because it does not easily flow out from the positive electrode. In the latter case, the oxygen redox catalyst is easily dispersed and present in the positive electrode. The function can be fully demonstrated. Examples of the polymer include polyethylene and polypropylene. Examples of the polycyclic aromatic ring include naphthalene, phenalene, triphenylene, anthracene, perylene, phenanthrene, and pyrene. The polymer or polycyclic aromatic ring may be directly connected to the radical skeleton, or may be selected from the group consisting of ester bond, amide bond, urea bond, urethane bond, carbamide bond, ether bond and sulfide bond. A spacer may be connected to the radical skeleton via the spacer. Formula (16) is an example of a compound having a structure in which a polymer (polypropylene) is linked to a stable radical skeleton via a spacer (ester bond), and Formula (17) is a polycyclic aromatic ring (pyrene) is a spacer ( It is an example of a compound having a structure linked to a stable radical skeleton via an amide bond).

In the magnesium-air secondary battery of the present invention, the positive electrode may be formed by mixing a predetermined amount of a conductive additive and a binder in addition to a compound having a stable radical skeleton, and then press-molding the positive electrode. Specifically, the binder may be 3 to 10 parts by weight with respect to 100 parts by weight of the conductive additive. As a mixing method, wet mixing may be performed together with carbon powder and a binder in a solvent of N-methylpyrrolidone, or dry mixing may be performed using a mortar or a ball mill. Here, a known carbon powder such as ketjen black can be used as the conductive assistant. As the binder, poly (vinylidene fluoride), polytetraethylene fluoride, polyacrylonitrile, or the like can be used. In press molding, press molding may be performed on a substrate that can collect electricity. As such a substrate, a metal plate such as stainless steel (for example, SUS), platinum, nickel, aluminum, or a mesh plate can be used. A transparent conductive material such as InSnO ₂ , SnO ₂ , ZnO, or In ₂ O ₃ can also be used. Further, fluorine-doped tin oxide (SnO ₂ : F), antimony-doped tin oxide (SnO ₂ : Sb), tin-doped indium oxide (In ₂ O ₃ : Sn), ZnO, Al-doped zinc oxide (ZnO: Al), Ga It is also possible to use a single layer or stacked body of a material doped with impurities such as doped zinc oxide (ZnO: Ga) formed on glass or a polymer. The film thickness is not particularly limited, but may be about 3 nm to 10 μm. The glass or polymer surface may be flat or may have irregularities on the surface.

In the magnesium-air secondary battery of the present invention, a non-aqueous electrolyte containing a supporting salt can be used as the non-aqueous magnesium ion conductor. Examples of the supporting salt include magnesium perchlorate (Mg (ClO ₄ ) ₂ ), magnesium bis (trifluoromethylsulfonyl) imide (Mg [N (CF ₃ SO ₂ ) ₂ ]), magnesium trifluoromethanesulfonate (Mg (CF ₃ SO ₃ ) ₂ ), known support salts such as magnesium fluorobutanesulfonate (Mg (C ₄ F ₉ SO ₃ ) ₂ ) and organic magnesium aluminate can be used. Examples of non-aqueous electrolytes include ethylene carbonate, propylene carbonate, gamma butyl lactone, diethyl carbonate, dimethyl carbonate, dimethoxyethane, and other cyclic esters, chain esters, chain ethers or mixtures thereof used in conventional secondary batteries and capacitors. A solvent can be used. The concentration of the supporting salt may be 0.1 to 2.0M, preferably 0.3 to 0.6M. In addition, as the magnesium ion conductor, an ionic liquid, a gel electrolyte, a solid electrolyte, or the like may be used. Examples of ionic liquids include trimethylpropylammonium bis (trifluoromethylsulfonyl) imide, 1-methyl-3-propylimidazolium bis (trifluorosulfonyl) imide, and 1-ethyl-3-butylimidazolium tetrafluoroborate. Can be used. As the gel electrolyte, a known gel electrolyte can be used. For example, a polymer compound such as poly (vinylidene fluoride), polyethylene glycol, and polyacrylonitrile, saccharides such as amino acid derivatives and sorbitol derivatives, and an electrolyte solution containing a supporting salt. And gel electrolytes.

  The magnesium air secondary battery of the present invention may include a separator between the negative electrode and the positive electrode. The separator is not particularly limited as long as it has a composition that can withstand the range of use of the magnesium-air secondary battery. For example, a polymer nonwoven fabric such as a polypropylene nonwoven fabric or a polyphenylene sulfide nonwoven fabric, or a fine olefin resin such as polyethylene or polypropylene. A porous film is mentioned. These may be used alone or in combination.

  The shape of the magnesium-air secondary battery of the present invention is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type. Moreover, you may apply to the large sized thing etc. which are used for an electric vehicle etc.

[Example 1]
As the oxygen redox catalyst, the radical polymer represented by the above formula (16) was used. According to Chem. Phys. Lett. Vol. 359, p351 (2002), this radical polymer is a 2,2,6,6-tetramethylpiperidine methacrylate monomer using 2,2′-azobisisobutyronitrile as an initiator. And then oxidized with 3-chloroperbenzoic acid. This radical polymer had a number average molecular weight of 92,000 and a weight average molecular weight of 22.9 million. This radical polymer has a 2,2,6,6-tetramethylpiperidoxyl radical (TEMPO radical) as a radical skeleton, and the TEMPO radical is known as a stable radical skeleton (for example, Japanese Patent Application Laid-Open No. 2002-2002). -1511084).

  The positive electrode was produced as follows. First, 166 mg of radical polymer of formula (16) (54 wt% per positive electrode material), 116 mg of ketjen black (ECP grade manufactured by Mitsubishi Chemical), Teflon powder (manufactured by Daikin Industries, “Teflon” is a registered trademark, the same applies hereinafter) A sheet was prepared by kneading 8 mg dry using a mortar. 5 mg of the sheet was pressure-bonded to a SUS mesh (Nicola) to obtain a positive electrode. For the negative electrode, 10 mm square and 0.2 mm thick metal magnesium (manufactured by Wako Pure Chemical Industries) was prepared. And F type electrochemical cell 20 made by Hokuto Denko was assembled using these. An F-type electrochemical cell 20 is shown in FIG.

  The F-type electrochemical cell 20 was assembled as follows. First, in a glove box under an argon atmosphere, a negative electrode 25 was placed on a casing 21 made of SUS, and the positive electrode 23 was set to face the negative electrode 25 through a separator 27 (E25MMS made by Tapils). Then, 0.5 M magnesium perchlorate propylene carbonate / diethyl carbonate (volume mixing ratio 1: 1) was used as the non-aqueous electrolyte solution 28, and 5 mL of this non-aqueous electrolyte solution 28 was injected between the positive electrode 23 and the negative electrode 25. . Thereafter, the foamed nickel plate 22 was placed on the positive electrode 23, and the cell was fixed by pressing with a pressing member 29 from above. The gas reservoir 30 provided inside the hollow of the pressing member 29 was filled with pure oxygen, and then the gas reservoir 30 was sealed. A plurality of holes are provided in the surface of the pressing member 29 that contacts the foamed nickel plate 22, and oxygen in the gas reservoir 30 can come into contact with the positive electrode 23 through the holes and the foamed nickel plate 22. Yes. Although not shown, the casing 21 can be separated into an upper part that contacts the positive electrode 23 and a lower part that contacts the negative electrode 25, and an insulating resin is interposed between the upper part and the lower part. Thereby, the positive electrode 23 and the negative electrode 25 are electrically insulated.

  The F-type electrochemical cell 20 thus obtained was connected to a charge / discharge device (model name HJ1001SM8A) manufactured by Hokuto Denko, and a current of 0.01 mA between the positive electrode 23 and the negative electrode 25 (2 mA per positive electrode material). / G) and discharged to 300 mAh / g per positive electrode material. Thereafter, the polarities of both electrodes were switched, a current of 0.005 mA (1 mA / g per positive electrode material) was passed, and constant current charging was performed until it reached 3.3 V, followed by constant voltage charging at 3.3 V. This operation was repeated 5 times. FIG. 3 is a graph showing a first charge / discharge curve, and FIG. 4 is a graph showing a relationship between the number of charge / discharge repetitions (number of cycles) and the charge capacity per positive electrode material. From these results, it was found that the F-type electrochemical cell 20 of Example 1 can be charged as well as discharged, and charging and discharging can be repeated a plurality of times.

[Example 2]
In Example 1, a 0.5 M magnesium bis (trifluoromethylsulfonyl) imide propylene carbonate / diethyl carbonate (volume mixing ratio 1: 1) solution (manufactured by Central Glass) was used as the non-aqueous electrolyte, and the formula (16) The electrochemical cell was prepared and charged / discharged in the same manner as in Example 1 except that the ratio of the radical polymer was 40.9% by weight per positive electrode material and the upper limit of the charging voltage was changed from 3.3V to 3.5V. Went. FIG. 5 is a graph showing a first charge / discharge curve. From FIG. 5, it was found that the electrochemical cell of Example 2 can be charged as well as discharged as in Example 1.

[Comparative Example 1]
In Example 1, instead of the radical polymer of formula (16), electrolytic oxidation dioxide that is a typical oxidation-reduction catalyst for lithium-air batteries (Angevande Chemie International Edition, 47, 4521-4524, 2008) An electrochemical cell was prepared and charged / discharged in the same manner as in Example 1 except that manganese (made by Mitsui Mine) was used at 10 wt% per positive electrode material and discharging was performed up to 900 mAh / g. FIG. 6 is a graph showing a charge / discharge curve at that time. From FIG. 6, it was found that the electrochemical cell of Comparative Example 1 was a primary battery that discharged but could not be charged.

[Comparative Example 2]
In Example 1, instead of the radical polymer of the formula (16), cobalt phthalocyanine (manufactured by Tokyo Chemical Industry), which is a typical redox catalyst of a lithium air battery, was used at 5 wt% per positive electrode material, and the discharge was 300 mAh / g. Except for the above, an electrochemical cell was prepared and charged / discharged in the same manner as in Example 1. FIG. 7 is a graph showing a charge / discharge curve at that time. From FIG. 7, it was found that the electrochemical cell of Comparative Example 2 was a primary battery that discharged but could not be charged.

  In addition, this invention is not limited to the Example mentioned above at all, and as long as it belongs to the technical scope of this invention, it cannot be overemphasized that it can implement with a various aspect.

  For example, in Examples 1 and 2, the gas reservoir 30 is filled with pure oxygen and sealed, but the gas reservoir 30 may be opened to the atmosphere to supply oxygen in the atmosphere to the positive electrode 23.

It is explanatory drawing of the redox reaction of the compound which has a stable radical skeleton. 2 is a cross-sectional view of an F-type electrochemical cell 20. FIG. 2 is a graph showing a first charge / discharge curve of Example 1. FIG. It is a graph which shows the relationship between the charge capacity per positive electrode material, and the number of cycles. 6 is a graph showing a first charge / discharge curve of Example 2. 5 is a graph showing a charge / discharge curve of Comparative Example 1. 10 is a graph showing a charge / discharge curve of Comparative Example 2.

Explanation of symbols

20 F-type electrochemical cell, 21 casing, 22 expanded nickel plate, 23 positive electrode, 25 negative electrode, 27 separator, 28 electrolyte, 29 holding member, 30 gas reservoir.

Claims (4)

A negative electrode capable of occluding and releasing magnesium ions;
A positive electrode comprising a compound having a stable radical skeleton and oxygen as a positive electrode active material;
A non-aqueous magnesium ion conductor interposed between the negative electrode and the positive electrode;
Magnesium air secondary battery equipped with. The negative electrode is magnesium metal,
The magnesium air secondary battery according to claim 1. The stable radical skeleton is a nitroxyl radical;
The magnesium air secondary battery according to claim 1 or 2. The compound having a stable radical skeleton is a compound in which a nitroxyl radical is bonded to a polymer or a polycyclic aromatic ring directly or via a spacer.
The magnesium air secondary battery in any one of Claims 1-3.