JP2002289195A - Secondary battery and positive electrode active material for it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new positive electrode active material for a secondary battery as well as a secondary battery using it. SOLUTION: An organic material containing a carbon comprising conjugate electron cloud where electron attractive radical is coupled is used as a positive electrode active material for a secondary battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a positive electrode active material which can be used for a secondary battery such as a lithium secondary battery, and a secondary battery using the same.

[0002]

2. Description of the Related Art In recent years, with the spread and development of portable devices,
The demand for higher energy density of the battery, which is the power source, has been further increased. Since a lithium secondary battery can be expected to have a high energy density, various systems have been studied.

As for the negative electrode, lithium metal, lithium alloy, carbon material and metal oxide material have been studied.
At present, carbon materials are practically used because of their excellent reversibility and abundant resources, though they are the smallest in capacity.

As for the positive electrode, oxides, halides,
Although chalcogenides and the like are promising, at present Mn
Transition metal oxides such as O ₂ , V ₂ O ₅ and LiCoO ₂ have been put to practical use. These transition metal oxides contain heavy metals and have problems such as being expensive.

Other positive electrode active materials for secondary batteries include:
A simple element of sulfur, a sulfur compound, and a conductive polymer are exemplified.
However, since the elemental sulfur and the sulfur compound contain sulfur, they have a problem such as a bad smell and a problem with environmental compatibility. In addition, since the conductive polymer carries an electric charge during charge and discharge, not lithium ions, but anions, the battery capacity is governed by the concentration of anions in the electrolytic solution, which is a fatal problem in increasing the battery capacity. There is.

As a positive electrode active material of a lithium primary battery,
Fluorinated graphite is used. Fluorinated graphite is formed by CF bonding, and the electrode reaction is such that CF becomes Li
Is a reaction to produce LiF and C.
Since the reaction product is LiF which hardly dissolves in the electrolytic solution, the charging reaction hardly occurs, and it is difficult to use it as an electrode for a secondary battery.

[0007]

As described above, as a positive electrode active material for a lithium secondary battery, a positive electrode active material which does not contain heavy metals and is environmentally compatible has been demanded.

An object of the present invention is to provide a novel positive electrode active material for a secondary battery which can solve the above problems, and a secondary battery using the same.

[0009]

The positive electrode active material for a secondary battery according to the present invention is characterized by comprising an organic material containing carbon having a conjugated electron cloud, to which an electron-withdrawing group is bonded.

When the electron-withdrawing group is bonded to carbon having a conjugated electron cloud, the electron density in the conjugated electron cloud is reduced, and the conjugated electron cloud is in a state similar to a state in which electrons have been extracted. It will be in the state that was done. When the conjugated electron cloud is in an oxidized state, the doping potential of Li (lithium) ions shifts to a more noble side as compared with that having a conjugated electron cloud in a normal neutral state. Therefore, charge and discharge at a high potential can be performed, and it can be used as a positive electrode active material.

During discharge, doping of the conjugate electron cloud with Li ions and injection of electrons into the conjugate electron cloud occur, and during discharge, elimination of Li ions from the conjugate electron cloud and conjugate electron cloud. Electrons are extracted from the substrate. Since these reactions are reversible reactions, charging and discharging at a high potential is possible.

The active material of the present invention includes an organic material having an aromatic ring at least partially substituted with an electron-withdrawing group. An example of such an organic substance is an aromatic condensed polycyclic hydrocarbon in which at least a part is substituted with an electron-withdrawing group. This is a compound such as anthracene, pyrene and naphthacene in which a polycyclic hydrocarbon in which an aromatic ring is condensed has at least a part of hydrogen substituted by an electron-withdrawing group.

Another example is a polymer of an aromatic compound such as benzene, at least partially substituted with an electron-withdrawing group. Examples of the benzene polymer at least partially substituted with an electron-withdrawing group include a polymer represented by the following general formula.

[0014]

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(Where X, Y, Z and T are hydrogen, fluorine or C _n F _{2n + 1} (n is an integer of 0 or more)
At least one of them is fluorine or C _n F _{2n + 1}
It is. m is an integer of 0 or more. Specifically, for example, a polymer of fluorobenzene, a polymer of trifluoromethylbenzene and the like can be mentioned.

Examples of fluorobenzene polymers include monofluorobenzene, paradifluorobenzene, orthodifluorobenzene, metadifluorobenzene, 1,2,2
3-trifluorobenzene, 1,2,4-trifluorobenzene, 1,3,5-trifluorobenzene, 1,
2,3,4-tetrafluorobenzene, 1,2,3,5
-Tetrafluorobenzene and polymers of 1,2,4,5-tetrafluorobenzene.

The polymers of trifluoromethylbenzene include α, α, α-trifluorotoluene, paraditrifluoromethylbenzene, orthoditrifluoromethylbenzene, 1,2,3-tristrifluoromethylbenzene, 1,2,4-tristrifluoromethylbenzene, 1,3,5-tristrifluoromethylbenzene, 1,2,3,4-tetratrifluoromethylbenzene, 1,2,3,5-tetratrifluoromethylbenzene And polymers such as 1,2,4,5-tetratrifluoromethylbenzene.

As described above, the electron-withdrawing group includes a fluorine or fluorinated alkyl group. The fluorinated alkyl _{group, C n F2 2n + 1 (} n is a natural number) include groups represented by, and specific examples thereof include trifluoromethyl group as described above.

The positive electrode active material for a secondary battery according to another aspect of the present invention comprises a material obtained by calcining a fluorocarbon resin in an inert atmosphere at a temperature within a range from the decomposition initiation temperature of the resin to 1000 ° C. Features. As fluororesin,
Polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polyfluoroethylene propylene,
And a copolymer of vinylidene fluoride and hexafluoropropylene.

The positive electrode active material for a secondary battery according to another aspect of the present invention comprises a material obtained by calcining fluorinated graphite at a temperature in a range of decomposition initiation temperature to 1000 ° C. in an inert atmosphere. Features. The heat treatment temperature of the fluorinated graphite is preferably about 400 to 550 ° C.

A secondary battery according to the present invention is characterized by comprising a positive electrode containing the positive electrode active material of the present invention, a negative electrode, and a non-aqueous electrolyte. In the secondary battery of the present invention, it is preferable that the negative electrode contains an active material that absorbs and releases an alkali metal or an alkaline earth metal.

In the present invention, the alkali metal is preferably lithium, and the secondary battery is preferably a lithium secondary battery. In the present invention, the negative electrode active material is a carbon material,
It is preferably at least one selected from silicon, tin, and aluminum.

In the secondary battery of the present invention, it is preferable that the positive electrode active material or the negative electrode active material contains an alkali metal or an alkaline earth metal in advance. Solvent of the electrolyte used when the secondary battery of the present invention is a lithium secondary battery is not particularly limited, ethylene carbonate, propylene carbonate, butylene carbonate, cyclic carbonate such as vinylene carbonate, and dimethyl carbonate, A mixed solvent with a chain carbonate such as methyl ethyl carbonate and diethyl carbonate is exemplified. Further, a mixed solvent of the cyclic carbonate and an ether solvent such as 1,2-dimethoxyethane and 1,2-diethoxyethane is also exemplified. The solutes of the electrolyte include LiPF ₆ , LiBF ₄ , L
iCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅
SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC
(CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) _{3 and the} like and mixtures thereof are exemplified. Further, as an electrolyte, a gel polymer electrolyte obtained by impregnating an electrolyte with a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or L
Examples thereof include inorganic solid electrolytes such as iI and Li ₃ N. The electrolyte of a lithium secondary battery can be used without restriction as long as the Li compound as a solvent that develops ionic conductivity and the solvent that dissolves and retains it do not decompose at the voltage during battery charging, discharging, or storage. it can.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.
The present invention can be implemented with appropriate changes.

[Preparation of Positive Electrode] Polyvinylidene fluoride was converted to N
After dissolving in -methyl-2-pyrrolidone, applying this on an aluminum foil and drying, it was baked at 400 ° C for 30 hours in a vacuum atmosphere. After baking, the product was vacuum-dried at 110 ° C., and cut into a size of 2 cm × 2 cm to produce a positive electrode.

[Preparation of Test Cell] A test cell was prepared using the positive electrode prepared as described above as a working electrode and metallic lithium as a counter electrode and a reference electrode. As the electrolytic solution, a solution obtained by dissolving 1 mol / liter of LiPF _{6 in} a mixed solvent of propylene carbonate and dimethyl carbonate at a volume ratio of 1: 1 was used. In the test cell, reduction of the working electrode is defined as charging, and oxidation is defined as discharging.

[Charge / Discharge Test] Regarding the above test cell, 2
A charge / discharge test was performed at 5 ° C. Discharge is constant current 0.5μA /
cm ² until the potential with respect to the reference electrode reached 1.5 V, and charging was performed at a constant current of −0.5 μA / cm ² until the potential with reference to the reference electrode reached 3.94 V.

FIG. 1 is a diagram showing charge / discharge curves of discharging in the first and second cycles and charging in the second cycle. As is clear from FIG. 1, the prepared electrode can be charged and discharged, has a high voltage of 1.5 V or more, and has excellent reversibility.

[0029]

According to the present invention, it is possible to provide a reversible positive electrode active material for a secondary battery, which does not contain expensive heavy metals or substances having poor environmental compatibility, such as sulfur.

[Brief description of the drawings]

FIG. 1 is a diagram showing a charge / discharge curve of a secondary battery using a positive electrode manufactured in an example according to the present invention.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shin Fujitani 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. F-term (reference) 4G046 AA09 AB02 5H029 AJ00 AK04 AK15 AK16 AL06 AL11 AL12 AL13 AM03 AM04 AM05 AM16 CJ02 CJ08 CJ15 CJ28 DJ16 DJ17 EJ12 HJ02 HJ13 HJ14 5H050 AA17 BA15 BA17 CA10 CA19 CA22 CA23 CA27 CB07 CB11 CB12 FA17 FA19 GA02 GA10 GA16 GA27 HA02 HA13 HA14

Claims (17)

[Claims] 1. A positive electrode active material for a secondary battery, comprising an organic material containing carbon having a conjugated electron cloud and having an electron-withdrawing group bonded thereto. 2. The cathode active material for a secondary battery according to claim 1, wherein the cathode active material comprises an organic material having an aromatic ring at least partially substituted with an electron-withdrawing group. 3. The positive electrode active material for a secondary battery according to claim 1, wherein the positive electrode active material comprises a fused aromatic polycyclic hydrocarbon at least partially substituted with an electron-withdrawing group. 4. The positive electrode active material for a secondary battery according to claim 1, wherein the electron-withdrawing group is a fluorine or a fluorinated alkyl group. 5. The method according to claim 4, wherein the fluorinated alkyl group is a group represented by C _n F _{2n + 1} (n is a natural number).
4. The positive electrode active material for a secondary battery according to 4. 6. A positive electrode active material for a secondary battery, comprising a material obtained by calcining a fluororesin in an inert atmosphere at a temperature within a range from the decomposition initiation temperature of the resin to 1000 ° C. 7. The method according to claim 7, wherein the fluororesin is polyvinyl fluoride,
Polyvinylidene fluoride, polytetrafluoroethylene,
The cathode active material for a secondary battery according to claim 6, wherein the cathode active material is at least one fluororesin selected from polyfluoroethylene propylene and a copolymer of vinylidene fluoride and hexafluoropropylene. 8. A positive electrode active material for a secondary battery, comprising a material obtained by sintering fluorinated graphite at a temperature in a range from a decomposition initiation temperature to 1000 ° C. in an inert atmosphere. 9. The positive electrode active material for a secondary battery according to claim 8, wherein the firing temperature is 400 to 550 ° C. 10. The positive electrode active material for a secondary battery according to claim 1, wherein the organic substance is a polymer of fluorobenzene. 11. The method according to claim 11, wherein the organic substance is monofluorobenzene, paradifluorobenzene, orthodifluorobenzene, metadifluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene,
At least one selected from 3,5-trifluorobenzene, 1,2,3,4-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene, and 1,2,4,5-tetrafluorobenzene The positive electrode active material for a secondary battery according to claim 1, 2 or 4, which is a polymer of fluorobenzene. 12. The method according to claim 12, wherein the organic substance is α, α, α-trifluorotoluene, paraditrifluoromethylbenzene,
Orthoditrifluoromethylbenzene, 1,2,3-tristrifluoromethylbenzene, 1,2,4-tristrifluoromethylbenzene, 1,3,5-tristrifluoromethylbenzene, 1,2,3,4- At least one selected from tetratrifluoromethylbenzene, 1,2,3,5-tetratrifluoromethylbenzene, and 1,2,4,5-tetratrifluoromethylbenzene
6. The positive electrode active material for a secondary battery according to claim 1, wherein the positive electrode active material is a polymer of trifluoromethylbenzene. 13. A secondary battery, comprising: a positive electrode containing the active material according to claim 1; a negative electrode; and a non-aqueous electrolyte. 14. The secondary battery according to claim 13, wherein the negative electrode contains an active material that stores and releases an alkali metal or an alkaline earth metal. 15. The active material is a carbon material, silicon,
The secondary battery according to claim 14, wherein the secondary battery is at least one selected from tin and aluminum. 16. The secondary battery according to claim 13, wherein an alkali metal or an alkaline earth metal is previously contained in the positive electrode active material or the negative electrode active material. battery. 17. The method according to claim 17, wherein the alkali metal is lithium,
The secondary battery according to any one of claims 13 to 16, wherein the secondary battery is a lithium secondary battery.