JP5233267B2 - Electric storage device and positive electrode material thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power storage device capable of storing a high-capacity energy. <P>SOLUTION: The power storage device comprises a lithium negative electrode, a positive electrode containing a fullerene derivative represented by the formula (1), and an electrolyte interposed between the positive electrode and the lithium negative electrode. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an electricity storage device and a positive electrode material thereof.

Lithium has a standard reduction potential of −3.05 V and is the most basic metal in the electrochemical series. For this reason, the operating voltage of an electricity storage device using lithium as a negative electrode is high and becomes high energy. On the other hand, since the atomic weight of lithium is the smallest among metals, its theoretical capacity is very large at 3862 mAh / g. Therefore, when lithium is used for the negative electrode, an energy storage device with high energy density can be obtained. As an electricity storage device using lithium as a negative electrode, a carbon material is often used for a positive electrode. For example, a 3V-class lithium primary battery using graphite fluoride has been realized and widely used since the 1970s. Graphite, which is a typical carbon material, has a theoretical capacity of 372 mAh / g because one Li ion is inserted into six C atoms. On the other hand, since the presence of the fullerene C ₆₀ is the first time confirmed in 1985, it has also been proposed power storage device using the fullerene to the positive electrode. For example, Patent Document 1 describes that by adding fullerene to the positive electrode of an alkaline battery, good discharge characteristics can be obtained even in heavy load discharge after high-temperature storage.
JP 2004-139807 A

However, when the present inventor fabricated a lithium battery in which a non-aqueous electrolyte was injected between a lithium negative electrode and a positive electrode to which fullerene C ₆₀ was added and measured the discharge capacity per positive electrode member weight, it was 600 mAh / g ( It was not so much that it could be said to be a high-capacity energy storage device.

  The present invention has been made to solve such problems, and an object of the present invention is to provide an electricity storage device capable of storing high-capacity energy. Another object is to provide a positive electrode material suitable for obtaining such an electricity storage device.

  In order to achieve the above-described object, the present inventors made an electricity storage device using a lithium negative electrode and a positive electrode containing a positive electrode material obtained by adding a pyrrolidinium salt to fullerene. As a result, it has been found that an extremely large amount of energy can be stored, and the present invention has been completed.

That is, the electricity storage device of the present invention includes a lithium negative electrode, a positive electrode containing a fullerene derivative represented by the following formula (1), and an electrolyte interposed between the positive electrode and the lithium negative electrode. .
(In the formula (1), n is an integer of 1 to 8, and Fu is fullerene C ₆₀ , C ₇₀ , C ₇₄ , C ₇₆ , C ₇₈ , C ₈₀ , C ₈₂ , C ₈₄ , C ₉₀ or C ₉₆ , R ¹ and R ² are each independently a hydrogen atom or an optionally substituted alkyl group, and X ⁻ is a chlorine ion, bromine ion or iodine ion)

  The positive electrode material of the present invention is a material used for the positive electrode of an electricity storage device in which an electrolyte is interposed between the positive electrode and the lithium negative electrode, and is composed of a fullerene derivative represented by the above formula (1). is there.

  According to the electricity storage device of the present invention, it is possible to store much higher capacity energy than an electricity storage device that uses a positive electrode containing mere fullerene.

  In the electricity storage device of the present invention, the lithium negative electrode may be, for example, metallic lithium or a lithium alloy. The lithium alloy may be, for example, an alloy of lithium with aluminum, tin, magnesium, indium, calcium, or the like.

In the electricity storage device of the present invention, the positive electrode contains a fullerene derivative represented by the above formula (1) as a positive electrode material. Such fullerene derivatives can be synthesized by, for example, an existing method described in Journal of American Chemical Society, vol. 115, page 9798. Here, n in Formula (1) represents the number of pyrrolidinium groups bonded to Fu, and is an integer of 1 to 8. This n may be one value or two or more values. Fu may be one of fullerenes C ₆₀ , C ₇₀ , C ₇₄ , C ₇₆ , C ₇₈ , C ₈₀ , C ₈₂ , C ₈₄ , C ₉₀ and C ₉₆ , or a mixture of two or more. However, fullerene C ₆₀ is preferable because the production cost is the lowest. R ¹ and R ² are each independently a hydrogen atom or an alkyl group which may have a branch, but an alkyl group having 1 to 4 carbon atoms is an alkyl group having 5 or more carbon atoms. It is preferable because the yield during synthesis of the fullerene derivative is extremely low, and a straight chain having no branch is preferable because the yield during synthesis is higher than that having a branch. Examples of such an alkyl group include a methyl group, an ethyl group, an n-propyl group, and an n-butyl group. X ⁻ is any one of a chlorine ion, a bromine ion and an iodine ion, and among these, a bromine ion or an iodine ion is preferable because a yield upon introduction of a halogen ion is high.

  In the electricity storage device of the present invention, the positive electrode may contain a conductive material. The conductive material is not particularly limited as long as it is a conductive material. For example, carbon blacks such as ketjen black, acetylene black, channel black, furnace black, lamp black and thermal black may be used, and natural graphite such as flake graphite, graphite such as artificial graphite and expanded graphite may be used. Further, conductive fibers such as carbon fibers and metal fibers, metal powders such as copper, silver, nickel, and aluminum, or organic conductive materials such as polyphenylene derivatives may be used. These may be used alone or in combination.

  In the electricity storage device of the present invention, the positive electrode may contain a binder. Although it does not specifically limit as a binder, A thermoplastic resin, a thermosetting resin, etc. are mentioned. For example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin) , Polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrif Examples include olefin copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, and ethylene-acrylic acid copolymer. . These materials may be used alone or in combination.

In the electricity storage device of the present invention, the positive electrode may be formed by, for example, mixing a fullerene derivative represented by the above formula (1), a conductive material, and a binder and then press-molding the current collector. The current collector is not particularly limited, for example, InSnO _2, SnO _2, ZnO, transparent conductive material such as an In ₂ O _2, fluorine-doped tin oxide (SnO _2: F), antimony-doped tin oxide ( Those materials doped with impurities such as SnO ₂ : Sb), tin-doped indium oxide (In ₂ O ₃ : Sn), ZnO, Al-doped zinc oxide (ZnO: Al), and Ga-doped zinc oxide (ZnO: Ga) A single layer or a laminated layer such as glass or a polymer can be used. The film thickness is not particularly limited, but is preferably about 3 nm to 10 μm. The glass or polymer surface may be flat, or the surface may be uneven. Further, a metal plate such as stainless steel, aluminum, or copper can be used as the current collector plate.

In the electricity storage device of the present invention, the electrolyte is not particularly limited, but an electrolytic solution containing a supporting salt, a gel electrolyte, a solid electrolyte, or the like can be used. Examples of the supporting salt include LiPF ₆ , LiClO ₄ , LiBF ₄ , Li (CF ₃ SO ₂ ) ₂ N, (C ₂ H ₅ ) ₄ NBF ₄ , (C ₄ H ₉ ) ₄ NBF ₄ , (C ₂ H ₅ ) Known supporting salts such as ₄ NPF ₆ and (C ₄ H ₉ ) ₄ NPF ₆ can be used. As the supporting salt, ionic liquids such as 1-methyl-3-propylimidazolium bis (trifluorosulfonyl) imide and 1-ethyl-3-butylimidazolium tetrafluoroborate can also be used. The concentration of the supporting salt is preferably 0.1 to 2.0M, and more preferably 0.8 to 1.2M. As an electrolytic solution, for example, ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (γ-BL), diethyl carbonate (DEC), dimethyl carbonate (DMC) and the like are used for conventional secondary batteries and capacitors. An organic solvent is mentioned. These may be used alone or in combination. The gel electrolyte is not particularly limited. For example, a polymer such as polyvinylidene fluoride, polyethylene glycol, or polyacrylonitrile, or a saccharide such as an amino acid derivative or sorbitol derivative is added with an electrolyte containing a supporting salt. And a gel electrolyte. Examples of the solid electrolyte include inorganic solid electrolytes and organic solid electrolytes. Well-known inorganic solid electrolytes include, for example, Li nitrides, halides, oxyacid salts, and the like. Among _{them, Li 4 SiO 4, Li 4} SiO 4 -LiI-LiOH, xLi 3 PO 4 - (1-x) Li 4 SiO 4, Li 2 SiS 3, Li 3 PO 4 -Li 2 S-SiS 2, sulfide Examples thereof include phosphorus compounds. These may be used alone or in combination. Examples of the organic solid electrolyte include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyvinylidene fluoride, polyphosphazene, polyethylene sulfide, polyhexafluoropropylene, and derivatives thereof. These may be used alone or in combination.

  The electricity storage device of the present invention may include a separator between the lithium negative electrode and the positive electrode. The separator is not particularly limited as long as it is a composition that can withstand the usage range of the electricity storage device. For example, a polymer nonwoven fabric such as a polypropylene nonwoven fabric or a polyphenylene sulfide nonwoven fabric, or a microporous film of an olefin resin such as polyethylene or polypropylene is used. Can be mentioned. These may be used alone or in combination.

  The shape of the electricity storage device 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. An example of the electricity storage device of the present invention is schematically shown in FIG. The electricity storage device 10 includes an electrolytic solution 18 between a lithium negative electrode 14 and a positive electrode 16. Among these, the positive electrode 16 is produced by mixing the fullerene derivative 16a of the above formula (1) with the conductive material 16b and the binder 16c and then press-molding the current collector 16d.

0.1 g of fullerene C ₆₀ (manufactured by Tokyo Chemical Industry Co., Ltd.) is dissolved in 100 mL of toluene at 50 ° C., 23 mg of formaldehyde (manufactured by Aldrich) and 26 mg of N-methylglycine (manufactured by Aldrich) are added thereto, and immediately heated to 120 ° C. Toluene was refluxed. After cooling for 2 hours, the mixture was cooled to obtain a dark brown transparent liquid. Over the solution chromatographed on silica gel to give the C _{60-N-methylpyrrolidine.} After 17 mg of this C ₆₀ -N-methylpyrrolidine was dissolved in 25 mL of toluene in a sample bottle at room temperature, 15 mL of methyl iodide (manufactured by Tokyo Chemical Industry Co., Ltd.) was added, and the sample bottle was covered with aluminum foil. Stirring was continued for 96 hours at room temperature. The product precipitated in this solution was filtered to obtain a fullerene derivative. The obtained fullerene derivative was subjected to mass spectrometry. The chart at that time is shown in the upper part of FIG. According to this chart, the obtained fullerene derivative is compound 1 in which one N, N-dimethylpyrrolidinium iodide is attached to fullerene C ₆₀ (in the following formula (2), n = 1, R ¹ = R ² = CH ₃ , X = I). The mass spectrometry here was MALDI-MS analysis, and was performed using Autoflex manufactured by Bruker Daltonics.

  The positive electrode was produced as follows. 80 mg of Ketjen black (Mitsubishi Chemical ECP-600), 20 mg of fullerene derivative and 5 mg of Teflon powder (Daikin Industries) were kneaded dry using a mortar to obtain a sheet-like positive electrode member. 6 mg of the positive electrode member was pressure-bonded to a nickel mesh as a current collector to obtain a positive electrode. For the negative electrode, metallic lithium (made by Honjo Metal) having a diameter of 10 mm and a thickness of 0.5 mm was used. And F type electrochemical cell 20 made by Hokuto Denko was assembled using these. An F-type electrochemical cell 20 is shown in FIG. First, in a glove box under an argon atmosphere, a negative electrode 24 and a positive electrode 26 are set in a SUS casing 22 so as to face each other, and a 1M lithium hexafluorophosphate ethylene carbonate / diethyl carbonate solution (manufactured by Toyama Pharmaceutical) Was injected into the space 28 between the negative electrode 24 and the positive electrode 26 as an electrolytic solution 30. Thereafter, the foamed nickel plate 32 was placed on the positive electrode 26 and sealed in a state where the gas reservoir 34 was filled with nitrogen gas. The F type electrochemical cell 20 thus obtained was set in a charge / discharge device (model name HJ1001SM8A) manufactured by Hokuto Denko, and a current of 0.25 mA was passed between the negative electrode 24 and the positive electrode 26 to open the open end. The battery was discharged until the voltage was 2.4V. FIG. 4 is a graph showing a change in open-circuit voltage with respect to time. The discharge capacity per weight of the positive electrode member was determined from this graph and found to be 3280 mAh / g. Although not shown, the casing 22 can be separated into an upper part that contacts the positive electrode 26 and a lower part that contacts the negative electrode 24, and an insulating resin is interposed between the upper part and the lower part. Thereby, the positive electrode 26 and the negative electrode 24 are electrically insulated.

  A fullerene derivative was obtained in the same manner as in Example 1, except that 46 mg of paraformaldehyde (manufactured by Aldrich) and 38 mg of N-methylglycine (manufactured by Aldrich) were used. When the fullerene derivative was subjected to mass spectrometry, a chart shown in the middle of FIG. 2 was obtained. From this chart, it was confirmed that the obtained fullerene derivative was a mixture containing Compound 1 as a main component and Compound 2 to Compound 5. Compounds 2 to 5 have the same structure as Compound 1 except that n in the above formula (2) is 2 to 5. With respect to the fullerene derivative thus obtained, an F-type electrochemical cell was assembled in the same manner as in Example 1, and the discharge capacity per weight of the positive electrode member was measured. The result was 3560 mAh / g.

  A fullerene derivative was obtained in the same manner as in Example 1 except that 86 mg of paraformaldehyde (manufactured by Aldrich) and 112 mg of N-methylglycine (manufactured by Aldrich) were used in Example 1. When the mass spectrometry of this fullerene derivative was performed, the chart shown in the lower stage of FIG. 2 was obtained. From this chart, it was confirmed that the obtained fullerene derivative was a mixture containing compounds 1 to 8. Compounds 6 to 8 have the same structure as Compound 1 except that n in the above formula (2) is 6 to 8. With respect to the fullerene derivative thus obtained, an F-type electrochemical cell was assembled in the same manner as in Example 1, and the discharge capacity per weight of the positive electrode member was measured. The result was 6200 mAh / g. The graph showing the change of the open end voltage with respect to the time at that time is shown in FIG.

In Example 1, fullerene derivatives (in the above formula (2), n = 1, R ¹ = H, R ² = CH ₃ , except that glycine was used instead of N-methylglycine) X = I) was obtained. With respect to the fullerene derivative thus obtained, an F-type electrochemical cell was assembled in the same manner as in Example 1, and the discharge capacity per weight of the positive electrode member was measured. The result was 4438 mAh / g. A graph showing a change in the open-circuit voltage with respect to the time is shown in FIG.

In Example 1, fullerene derivatives (n = 1 to 8, R ¹ = R in the above formula (2) were used in the same manner as in Example 1 except that ethyl bromide (manufactured by Aldrich) was used instead of methyl iodide. ² = CH ₃ , X = Br). With respect to the fullerene derivative thus obtained, an F-type electrochemical cell was assembled in the same manner as in Example 1, and the discharge capacity per weight of the positive electrode member was measured. The result was 3627 mAh / g. A graph showing a change in the open-circuit voltage with respect to the time is shown in FIG.

  In Example 1, except that the gas reservoir 34 was filled with dry oxygen instead of nitrogen gas, the open-circuit voltage was discharged at 0.1 mA to 2.0 V, and then charged to 4.2 V at 0.1 mA. An F-type electrochemical cell was assembled in the same manner as in Example 1, and the charge / discharge capacity per weight of the positive electrode member was measured. As a result, the discharge capacity was 4397 mAh / g, and the charge capacity was 3758 mAh / g. The graph showing the change of the open end voltage with respect to the time at that time is shown in FIG.

Comparative Example 1

  In Example 1, except that the fullerene derivative was not used, an F-type electrochemical cell was assembled in the same manner as in Example 1, and a current of 0.05 mA was passed between the positive electrode and the negative electrode to discharge per weight of the positive electrode member. When the capacity was measured, it was 560 mAh / g. The graph showing the change of the open end voltage with respect to the time at that time is shown in FIG.

Comparative Example 2

In Example 1, except that fullerene C ₆₀ (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of the fullerene derivative, an F-type electrochemical cell was assembled and the discharge capacity per weight of the positive electrode member was measured in the same manner as in Example 1. However, the discharge capacity up to 1.3 V was 600 mAh / g. The graph showing the change of the open end voltage with respect to time at that time is shown in FIG.

Comparative Example 3

  In Example 1, an F-type electrochemical cell was assembled in the same manner as in Example 1 except that mesoporous carbon beads (trade name MCMB2528 manufactured by Osaka Gas Co., Ltd.) were used instead of the fullerene derivative, and the discharge capacity per weight of the positive electrode member. Was 332 mAh / g. A graph showing a change in the open-circuit voltage with respect to time at that time is shown in FIG.

  The electricity storage device of the present invention can be used mainly in the electrochemical industry. For example, it can be used for power sources of hybrid vehicles and electric vehicles, power sources for consumer electronics such as mobile phones and personal computers, and load leveling (load leveling). It can be used for electrochemical devices.

It is a schematic diagram of the electrical storage device of this invention. It is a chart showing the result of mass spectrometry about Examples 1-3. 2 is a cross-sectional view of an F-type electrochemical cell 20. FIG. It is a graph showing the change of the open end voltage with respect to time about Example 1 and Comparative Example 1. It is a graph showing the change of the open end voltage with respect to time about Example 3 and Comparative Example 2. FIG. It is a graph showing the change of the open end voltage with respect to time about Example 4. FIG. 10 is a graph showing a change in open-circuit voltage with respect to time for Example 5. It is a graph showing the change of the open end voltage with respect to time about Example 6. FIG. 10 is a graph showing a change in open-circuit voltage with respect to time for Comparative Example 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electric storage device, 14 Lithium negative electrode, 16 Positive electrode, 16a Fullerene derivative, 16b Conductive material, 16c Binder, 16d Current collector, 18 Electrolyte, 20 F type electrochemical cell, 22 Casing, 24 Negative electrode, 26 Positive electrode, 28 Space, 30 Electrolyte, 32 Foamed nickel plate, 34 Gas reservoir.

Claims (5)

A lithium negative electrode that is metallic lithium or a lithium alloy ;
A positive electrode containing a fullerene derivative represented by the following formula (1);
An electrolyte interposed between the positive electrode and the lithium negative electrode;
An electricity storage device.
(In the formula (1), n is an integer of 1 to 8, and Fu is fullerene C ₆₀ , C ₇₀ , C ₇₄ , C ₇₆ , C ₇₈ , C ₈₀ , C ₈₂ , C ₈₄ , C ₉₀ or C ₉₆ , R ¹ and R ² are each independently a hydrogen atom or an optionally substituted alkyl group, and X ⁻ is a chlorine ion, bromine ion or iodine ion) In the fullerene derivative represented by the formula (1), Fu is fullerene C ₆₀ .
The electricity storage device according to claim 1. In the fullerene derivative represented by the formula (1), R ¹ and R ² are each independently a hydrogen atom, a methyl group, an ethyl group, an n-propyl group, or an n-butyl group.
The electricity storage device according to claim 1 or 2. The positive electrode includes a conductive material and a binder in addition to the fullerene derivative represented by the formula (1).
The electrical storage device in any one of Claims 1-3. A material used for a positive electrode of an electricity storage device in which an electrolyte is interposed between a positive electrode and a lithium negative electrode that is metallic lithium or a lithium alloy ,
A positive electrode material comprising a fullerene derivative represented by the formula (1).
(In the formula (1), n is an integer of 1 to 8, and Fu is fullerene C ₆₀ , C ₇₀ , C ₇₄ , C ₇₆ , C ₇₈ , C ₈₀ , C ₈₂ , C ₈₄ , C ₉₀ or C ₉₆ , R ¹ and R ² are each independently a hydrogen atom or an optionally substituted alkyl group, and X ⁻ is a chlorine ion, bromine ion or iodine ion)