JPH0737590A - Alkali metal storage carbon material - Google Patents

Abstract

PURPOSE:To provide a secondary battery of high capacity excellent in cycle stability and further capable of resisting against charge/discharge of high current density. CONSTITUTION:An alkali metal storage carbon system material has a contracted ring aromatic structure to store an alkali metal in a carbon system material formed of a disordered lamination structure, and the alkali metal storage carbon system material, in which C/A atomic ratio (where represented carbon by C and alkali metal element by A) is 1 to 8 to provide at least two values of a peak of chemical shift delta of an NMR spectrum of an alkali atomic nucleus with the one peak (B) + or -2ppm and the other peak (A) provided in a plus side from this peak (B), is used in an electrode. In this alkali metal storage carbon system material, an amount of storing an alkali ion can be markedly increased, and also a structural change in the case of storage/removal can be eliminated. Alkali ion storage emitting reaction can be also increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkali metal storage carbonaceous material, and more specifically to an electrode material for a secondary battery,
In particular, the present invention relates to an alkali metal-occluding carbon-based material suitable as an electrode material for a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art In recent years, miniaturization of electronic devices has progressed, and along with this demand for higher energy density of batteries, various non-aqueous electrolyte batteries have been proposed. For example, as a negative electrode for a non-aqueous electrolyte battery, metallic lithium has been conventionally known mainly for primary batteries, and a lithium alloy represented by an aluminum / lithium alloy, a carbon negative electrode, and the like are also known.
However, it is known that metallic lithium, when used as a negative electrode of a secondary battery, is inferior in cycle stability due to generation of dendrite and the like. Further, a lithium alloy negative electrode typified by an aluminum / lithium alloy has improved cycle stability as compared with metallic lithium, but cannot be said to sufficiently bring out the performance of a lithium battery.

In order to solve such a problem, it has been proposed to use a carbon negative electrode that absorbs and desorbs lithium and utilizes the fact that a carbon intercalation compound of lithium can be easily electrochemically formed. There are various types of such carbon negative electrodes. For example, a carbon substance obtained by calcining crystalline cellulose at 1,800 ° C. under a flow of nitrogen gas (Japanese Patent Laid-Open No. 3-176963), coal pitch or Petroleum pitch that has been graphitized at 2,500 ° C. or higher in an inert atmosphere (JP-A-2-82466),
A highly graphitized material that has been treated at a high temperature of more than 2,000 ° C. is used, and a material having cycle stability is obtained although the capacity is lower than that of metallic lithium or a lithium alloy. However, even with such a negative electrode, sufficient cycle stability is not obtained in charge and discharge at high current density.

[0004]

Such a carbon negative electrode has a sufficiently mild reaction with water even in a charged state, that is, in a state where lithium is intercalated in carbon, as compared with metallic lithium or a lithium alloy. The formation of dendrites due to charge / discharge was hardly seen, which is excellent. However, depending on the type of carbon, it can hardly be charged and discharged, and the theoretical capacity (L
In many cases, the capacity is extremely low compared to the iC ₆ state (assuming the maximum capacity). In addition, even if the initial capacity is relatively large, it deteriorates due to repeated charging and discharging, the capacity drops sharply, and even in a carbon negative electrode with a relatively large capacity,
When the charge and discharge are repeated at a high current density, deterioration is severe and the performance as a secondary battery cannot be satisfied. For example, a conventional carbon negative electrode has not been able to provide a negative electrode with satisfactory performance.

This is presumed to be because such a carbon negative electrode utilizes an intercalation reaction. That is, the storage amount of alkali ions is limited by the composition ratio of the intercalation compound, and the capacity cannot be increased. Further, since the intercalation reaction is accompanied by a change in the interlayer distance, the structure of the layered compound is destroyed by repeated occlusion and release, resulting in a short cycle life. Furthermore, since the alkali ions can enter only from the direction parallel to the crystal layer, the occluding / releasing reaction rate is low, and charging / discharging with a large current is difficult.

Therefore, the storage amount of alkali ions is large,
There has been a demand for an alkali metal-occluding carbon-based material in which the structure is not destroyed even after repeated occlusion and desorption, and which has a high reaction rate of occlusion and release of alkali ions. The present invention has been made against the background of the conventional technical problems as described above, and has a large storage capacity of alkali metal, no structural change in the compound that adsorbs and desorbs alkali metal, and a large storage and release reaction rate. And an alkaline metal-occluding carbon-based material, which has a high capacity, excellent cycle stability, and can be used for high-output (high current density) charge / discharge, and a secondary battery electrode material and a secondary battery. Aim to get.

[0007]

DISCLOSURE OF THE INVENTION The present invention is an alkali metal-occlusion carbon-based material obtained by absorbing an alkali metal in a carbon-based material having a condensed aromatic structure and having a disordered laminated structure, which comprises C / A atomic ratio (where C is carbon and A is an alkali metal element) is 1 to 8 and N of the alkali nucleus is
The peak of chemical shift δ of MR spectrum is at least 2
There is provided a value, one peak (B) is 0 ± 2 ppm, and the other peak (A) is on the plus side of the peak (B).

The carbon-based material of the present invention has a condensed ring aromatic structure, and its structure is a disordered laminated structure. Here, the disordered laminated structure refers to a structure in which the condensed aromatic ring planes are completely disordered or have no more than four, preferably more than three, orientations. What has a developed laminated structure, not a disordered laminated structure, intercalates only alkali ions between layers, and does not occlude covalently bonding alkali metals or alkali ions between carbon-carbon atoms, It cannot be said to be the carbon-based material used in the present invention. Such a material can be obtained by firing an organic polymer, which is essentially a graphitizable material, into which a factor that inhibits lamination is introduced.

The organic compound which is essentially a graphitizing material may be any organic compound as long as it has an aromatic structure. For example, poly (p-phenylene) (PPP),
Poly (p-phenylene vinylene) (PPV), poly (p
-Phenylene xylene) (PPX), polystyrene, novolac resin and the like. Examples of the factor that inhibits the laminated structure include a bent structure (o-, m-position structure), a branched structure, and a crosslinked structure. In addition, these organic compounds may include organic compounds having 5 members or 7 members. The carbon-based material used in the present invention may be obtained by firing these organic compounds at a temperature not so high and a temperature at which electrical conductivity is low, which is usually 300 to 1,000 ° C.

The carbon-based material used in the present invention has a hydrogen / carbon atomic ratio (H / C) of 0.05 to 0.6, preferably 0.15 to 0.6. If it is less than 0.05, the graphite structure will develop, and the crystal structure will be destroyed by the expansion and contraction of the crystal during the lithium doping / de-doping reaction during charge / discharge, and the cycle stability will decrease, while if it exceeds 0.6, The discharge capacity is significantly reduced.

The alkali metal storage carbonaceous material of the present invention is
The carbon-based material thus obtained, alkali metal,
Lithium is preferably occluded, and the C / A atomic ratio is 1 to 8, preferably 1.5 to 3. Here, as the C / A atomic ratio becomes less than 1, lithium is not occluded, while when it exceeds 8, the peak (A) is not expressed, that is, lithium ions that directly affect discharge are not occluded, and charge / discharge is performed. The effect becomes difficult to be exhibited.

Further, in the alkali metal-occluding carbon material of the present invention, the peak of chemical shift δ of the NMR spectrum must have at least two values, and one peak (B) is 0 ±.
2 ppm, and the other peak (A) exists on the plus side of the peak (B), preferably 4 to 100 ppm, more preferably 10 ± 7 ppm. Here, when the alkali element is lithium, the observed nucleus is ⁷ Li,
The standard of chemical shift is when the peak of a 1 mol / l aqueous solution of LiCl is 0. The peak (B) of the chemical shift δ being in the above range means that the unpaired electron density on the alkali ion is almost 0, that is, the alkali ion is a covalent Li ₂ molecule. This means that the alkali ions are occluded by adsorption at the same time as the intercalation, and the carbon and the alkali ions are separated from each other.

On the other hand, it has been reported that the intercalated lithium chemical shift takes a positive value (for example,
Tanaka et al., Proc. Of Autumn 1992 Electrochemical Fall Conference p12
9), in the alkali metal storage carbonaceous material of the present invention, it appears as a peak (A). The cause of this positive chemical shift is the paramagnetic shift due to the radicals of the carbon-based material. At the same time that lithium is occluded, the carbon-based material receives electrons and maintains electrical neutrality. The carbon that receives the electron becomes a radical anion. Therefore, the carbon-based material that occludes lithium has an unpaired electron, and a chemical shift occurs due to the interaction between the magnetic moment of the electron and the magnetic moment of the nucleus. According to theory, the sign of the chemical shift due to the interaction with the electron spin matches the sign of the hyperfine coupling constant of the electron and the nucleus. The sign of the hyperfine coupling constant of ⁷ Li is positive, and the chemical shift due to radicals is positive.
The magnitude of the chemical shift is proportional to the unpaired electron density on the measured nucleus. Since the intercalated lithium ion is confined between the graphite layers, when the graphite layer becomes a radical anion, some unpaired electron density also exists on the lithium ion, which causes a positive chemical shift.

The alkali metal storage carbonaceous material of the present invention is
Although it adsorbs and desorbs alkali ions, it exhibits excellent performance especially with lithium ions. Although the alkali metal-occluding carbon-based material of the present invention has a condensed aromatic ring, the laminated structure is not developed, and covalently bonded molecules and ions of an alkali metal such as lithium are occluded in the condensed ring. , The intercalation is performed between the layers, and an extremely large amount of alkali metal can be occluded in the carbon-based material. Such adsorption / desorption reaction is
Since the composition ratio of the alkali metal storage carbonaceous material is not limited, the adsorption / desorption amount of alkali ions can be made very large.

Further, since alkali ions do not enter and leave only between the layers, the structural change of the material due to adsorption and desorption is small, and the laminated structure is not developed. It is not limited to one parallel direction, it can enter from any direction, and the adsorption / desorption reaction rate is high. Therefore, by using such an alkali metal-occluding carbon-based material of the present invention as an electrode material, the battery can have a very high capacity, the cycle stability can be improved, and a large current charge / discharge can be achieved. INDUSTRIAL APPLICABILITY The alkali metal storage carbon material of the present invention is extremely excellent as a material for an electrode for a secondary battery.

Next, the method for producing the alkali metal storage carbonaceous material of the present invention will be specifically described. First, as the carbon-based material used in the present invention, an organic compound having a condensed aromatic structure is generally used in an inert gas such as argon, helium, or nitrogen, or in a reducing gas such as hydrogen.
It is obtained by heat treatment at a temperature of 00 to 1,000 ° C., preferably 600 to 800 ° C. for 0 to 6 hours, preferably 0 to 1 hour.

As a specific heat treatment method, in the thermal analysis, any heating rate may be used up to the weight reduction start temperature of the organic compound as a raw material, and the temperature decrease rate from the weight reduction start temperature to the heat treatment temperature is 5 ° C./hour. There may be mentioned a method of raising the temperature at a rate of 200 ° C./hour, preferably 20 ° C./hour to 100 ° C./hour. Here, the heat treatment temperature refers to a temperature at which a weight reduction of 70 to 95% by weight is shown with respect to the weight reduced until the weight does not decrease in thermal analysis.

The heat-treated product thus obtained is usually powder or solid, and this carbonaceous material can be mechanically crushed to obtain an excellent secondary battery electrode material. When a negative electrode is manufactured using this electrode material, the particle size of the electrode material is not necessarily limited, but a high performance negative electrode can be manufactured by using a material having an average particle size of 5 μm or less. In this case, a binder such as polyethylene powder may be added to and mixed with these powders and rolled to form a negative electrode. The binder content is 5 to 50 parts by weight, preferably 5 to 30 parts by weight, based on 100 parts by weight of the electrode material.

Here, as the binder, both organic and inorganic binders can be used. As the organic binder, in addition to the poly (ethylene), many binders such as fluoro resins such as polytetrafluoroethylene and polyvinylidene fluoride, polyvinyl alcohol, polyvinyl chloride and the like can be used. In this case, except for polyethylene, heat treatment near the carbonization temperature of the binder is required. Further, as the inorganic binder, a silicon-based binder such as silicon glass can be used,
In this case as well, heat treatment at a temperature exceeding the melting point is necessary in order to exert the performance as a binder.

In this case, the negative electrode body can be directly obtained by mixing the organic compound as the starting material and these binders, molding the mixture, and heat-treating as described above.
In this case, it is necessary to pay attention to the shape change of the negative electrode body,
The performance as a negative electrode for a lithium battery is equivalent to that obtained by compacting the electrode material of the present invention and polyethylene.
The negative electrode body thus obtained can be used as a negative electrode for a lithium battery by supporting lithium or an alkali metal mainly containing lithium thereon.

As a method of supporting, a lithium foil is brought into contact to thermally diffuse, or lithium is electrochemically doped in a lithium salt solution, or it is immersed in molten lithium to diffuse lithium into carbon. Any better method may be used. The alkali metal storage carbonaceous material of the present invention can be widely used as a negative electrode of a lithium battery, various positive electrodes such as manganese dioxide,
It can be used in combination with an oxide such as vanadium pentoxide or a positive electrode using an organic polymer such as polypyrrole.

The non-aqueous electrolyte used in the battery using the electrode material comprising the alkali metal-occluding carbon material of the present invention is chemically stable with respect to the positive electrode material and the negative electrode material, and is lithium ion. Any non-aqueous substance can be used as long as it is capable of moving to undergo an electrochemical reaction with the positive electrode active material, and in particular, it is a compound composed of a combination of a cation and an anion, and the cation is L
i ⁺ , and examples of anions include PF ₆ ⁻ , As
Halide anions of Va group elements such as F ₆ ⁻ and SbF ₆ ⁻ , halogen anions such as I ⁻ , I ₃ ⁻ , Br ⁻ and Cl ⁻ , perchlorate anions such as ClO ₄ ⁻ ,
_{^{HF 2 -, CF 3 SO 3}} -, SCN - can be exemplified compounds having an anion such as, but not necessarily limited to these anions. Specific examples of the electrolyte having such cations and anions include LiP
F ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , Li
ClO ₄ , LiI, LiBr, LiCl, LiAlCl
₄ , LiHF ₂ , LiSCN, LiCF ₃ SO _{3 and the} like can be mentioned. Among these, especially LiPF ₆ , Li
AsF ₆ , LiSbF ₆ , LiBF ₄ , LiClO ₄ ,
LiCF ₃ SO ₃ is preferred.

The non-aqueous electrolyte is usually used in a state of being dissolved in a solvent. In this case, the solvent is not particularly limited, but a solvent having a relatively large polarity is preferably used. Specifically, propylene carbonate, ethylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, dioxane, dimethoxyethane, glymes such as diethylene glycol dimethyl ether, lactones such as γ-butyrolactone, phosphoric acid esters such as triethyl phosphate, boric acid. Boric acid esters such as triethyl, sulfolane, sulfur compounds such as dimethyl sulfoxide, nitriles such as acetonitrile, amides such as dimethylformamide and dimethylacetamide, dimethyl sulfate, nitromethane,
Mention may be made of one kind or a mixture of two or more kinds such as nitrobenzene and dichloroethane. Of these, propylene carbonate, ethylene carbonate, butylene carbonate, tetrahydrofuran, 2-
One or a mixture of two or more selected from methyltetrahydrofuran, dioxane, dimethoxyethane, dioxolane and γ-butyrolactone is preferable.

Further, as the non-aqueous electrolyte, the above non-aqueous electrolyte is impregnated with a polymer such as polyethylene oxide, polypropylene oxide, an isocyanate cross-linked product of polyethylene oxide, or a phosphazene polymer having an ethylene oxide oligomer as a side chain. It is also possible to use an organic solid electrolyte, an inorganic ion derivative such as Li ₃ N or LiBCl ₄ , or an inorganic solid electrolyte such as lithium glass such as Li ₄ SiO ₄ or Li ₃ BO ₃ .

The lithium secondary battery using the electrode material made of the alkali metal storage carbonaceous material of the present invention will be described in more detail with reference to the drawings. That is, the lithium secondary battery using the electrode material made of the alkali metal occluding carbon-based material of the present invention for the negative electrode has the opening 10 as shown in FIG.
Button-shaped positive electrode case 1 in which a is sealed with a negative electrode cover plate 20
0 is divided by a separator 30 having fine holes, and a positive electrode 50 having a positive electrode current collector 40 arranged on the positive electrode case 10 side is housed in the partitioned positive electrode side space, while a negative electrode current collector is arranged in the negative electrode side space. The negative electrode 70 in which the body 60 is arranged on the negative electrode cover plate 20 side is stored.

As the separator 30, a non-woven fabric, a woven fabric or a knitted fabric, which is porous and capable of passing or containing an electrolytic solution, such as polytetrafluoroethylene, polypropylene or polyethylene, is used. can do. Further, as the positive electrode material used for the positive electrode 50, burned particles such as lithium-containing vanadium pentoxide and lithium-containing manganese dioxide can be used. Reference numeral 80 denotes a polyethylene insulating packing that is provided around the inner peripheral surface of the positive electrode case 10 to insulate and support the negative electrode cover plate 20.

[0027]

The alkali metal storage carbon material of the present invention has a condensed ring aromatic structure, but a carbon material in which a laminated structure is not developed is used. Therefore, alkali metal such as lithium and alkali ions are While being occluded in the condensed ring,
It is intercalated between the layers and adsorbs and desorbs on the condensed aromatic ring surface. Since the adsorption / desorption reaction is not limited by the composition ratio of the intercalation compound, the adsorption / desorption amount of alkali ions can be made very large. Therefore, by using this as an electrode material, the battery can have a very high capacity.

Further, since ions do not enter and leave only between the layers, the structural change of the material due to adsorption and desorption is small, and when used as an electrode material, the battery has excellent cycle stability. Further, since the laminated structure has not been developed, the ions are not limited to one direction parallel to the laminating direction, and ions can enter from any direction, the reaction speed is high, and large current charging / discharging becomes possible. Therefore, by using the alkali metal storage carbon-based material of the present invention as an electrode material of a secondary battery, particularly a non-aqueous electrolyte secondary battery, for example, a lithium battery, it has a high capacity and excellent cycle stability in charge and discharge, Moreover, it is possible to obtain a battery that can withstand high current density charge and discharge.

[0029]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Example 1 Poly (p-phenylene) was synthesized by the Kovacic method. That is, cupric chloride (CuCl
₂ ), aluminum chloride (anhydrous) (AlCl ₃ ), and benzene (C ₆ H ₆ ) were mixed at a molar ratio of 1: 1: 4, and stirred under an inert gas atmosphere. The obtained powder was washed several times with hydrochloric acid (6N-HCl), washed with water, further washed with acetone, and then washed with water, and then vacuum dried at 100 ° C. The poly (p-phenylene) thus synthesized contains stacking inhibiting factors such as bending, branched structure and quinoid structure.

The poly (p-phenylene) thus synthesized was fired at 700 ° C. in a hydrogen stream to obtain a carbon-based material (hereinafter also referred to as “700 ° C. fired body”). In particular,
The temperature is raised from room temperature to 500 ° C at a heating rate of 250 ° C / hour, from 500 ° C to 700 ° C at 40 ° C / hour, and when 700 ° C is reached, heating is stopped and cooled to room temperature. A carbonaceous material was obtained. The inter-plane distance of the (002) plane obtained by X-ray diffraction measurement of the obtained carbon-based material is 3.
It was 65Å. The diffraction peak of the (002) plane is very wide, and the size of the crystallite in the C-axis direction is estimated to be 10Å or less. That is, the number of laminated sheets was 3 or less. In addition, poly (p-phenylene) was added in the same manner as above.
The carbon-based material was obtained by firing at 0 ° C. (hereinafter, also referred to as “820 ° C. fired body”), and the X-ray diffraction result of this was 700
It was similar to the ℃ fired body.

Polyethylene powder was added to each of these carbonaceous materials as a binder in a weight ratio of 30%, and pressure-molded to obtain electrodes. This electrode was used as a working electrode, lithium foil was used as a counter electrode and a reference electrode, and PC (propylene carbonate) and DME (dimethyl ether) were used as an electrolytic solution.
A half-battery cell was constructed by using a solvent (volume ratio = 1: 1) in which lithium perchlorate was dissolved at a concentration of 1 mol / l. Using this cell, charging / discharging was repeated at a current density of 1.6 mA / cm ² , a charge end potential of 0 mV, a discharge end potential of 3 V, and a rest time of 20 minutes. This electrode electrochemically absorbed and desorbed lithium ions and functioned as a negative electrode for a lithium secondary battery.

(Capacity) FIGS. 1A to 1B show charge / discharge potential curves. FIG. 1A shows an example using a 700 ° C. fired body, and FIG. 1B shows an example using an 820 ° C. fired body.
From FIGS. 1 (A) and 1 (B), if it is assumed that the portion that does not reach 100% efficiency during charging / discharging up to 20 cycles remains in carbon, 700 ° C. fired body = 785 mAh / g, 820
℃ fired body = 622mAh / g, 900 ℃ fired body = 475
mAh / g remains in the carbon, 300m further from there
Ah / g can be charged, 700 ° C fired body = 1,
085mAh / g, 820 ° C fired body = 922mAh /
This means that a 900 ° C. calcined product = 775 mAh / g can be charged.

(NMR) A sample was prepared by charging 1,000 Ah / kg of the electrode prepared from the 700 ° C. fired body, and the solid-state resolution NMR spectrum of occluded lithium was measured. The measurement sample was washed and dried with DME in a dry argon atmosphere glove box to remove the electrolytic solution, then mixed with KBr and filled in an NMR sample tube. The observation nucleus is
⁷ Li. As a standard for chemical shift, the peak of a 1 mol / l aqueous solution of LiCl was set to 0 ppm. The NMR spectrum is shown in FIG. As is clear from FIG. 2, 0 ± 2p
pm, the peak (B) is approximately 0 ppm in the present embodiment, and is on the plus side of the peak (B), approximately 10 in the present embodiment.
It can be seen that the peak (A) is present in ppm.

The peak (B) is the Lorentzian (Lo).
Renzian) linear, suggesting a liquid movement. Since the chemical shift is almost 0 ppm, it can be assigned to a covalent Li ₂ molecule. 300 Ah / kg
Up to, almost (B) site is occupied. On the other hand, the peak (A) is Gaussian.
It has a linear shape and is solid. Since it has a positive chemical shift, it can be assigned to ionic Li ⁺ . The cause of this chemical shift is the interaction between the electron spin and the nuclear spin of the radical formed by the electron injected into carbon during charging. It is Li ⁺ at the (A) site that can be discharged. The peak (C) belongs to the ionic crystal of Li,
It is presumed that this is due to lithium carbonate (by-product) detected by ESA measurement.

(Structure Diagram) From the results shown in FIG. 2, it was found that there are two sites [(A) site and (B) site] that can be taken by lithium when lithium is occluded in the carbonaceous material. . From the NMR spectrum analysis and X-ray diffraction results of FIG. 2, a modeled structural diagram of the crystal of the alkali metal-occluding carbon-based material obtained from the 700 ° C. fired body is shown in FIG.
FIG. 3A is a plan structural view, and FIG. 3B is a sectional structural view thereof. As is clear from FIG. 3A, in the conventional lithium intercalation compound, LiC ₆
If the lithium ion (Ion Li) enters into the benzene ring of carbon, the surrounding one row cannot be used and a rhombic structure is formed. Therefore, the occluded lithium ions are dominated by the carbon skeleton, and only one of them is not allowed to move to the next, becoming solid, forming a lattice, and becoming a linear Gaussian of peak (A).

On the other hand, the (B) site is a covalent lithium molecule (covalentLi), which is Lorentzian in contrast, exhibits liquid-like behavior, and does not have a fixed position. As for the charging mechanism, the ionized ion [Ion Li, (A) site] is discharged and the seat becomes vacant. On the other hand, the covalent lithium molecule [covalent Li, site (B)] cannot be immediately discharged, but it is considered that it becomes a lithium reservoir and moves to the vacant portion to be discharged. Therefore, Li
Discharge capacities in excess of C ₆ are possible, for example LiC _1.93
Alkali metal storage carbon materials such as

As described above, when the crystal structure of the alkali metal-containing carbonaceous material of the present invention is considered in plan view, the covalently bound lithium and lithium ions are occluded in the condensed rings and between the condensed rings. As is clear from (B), covalently bonded lithium and lithium ions are intercalated also between the layers, and it can be seen that the storage amount of lithium (alkali metal) can be significantly increased.

[0038]

INDUSTRIAL APPLICABILITY The alkali metal storage carbonaceous material of the present invention can greatly increase the storage amount of alkali ions and eliminate the structural change during adsorption and desorption. It is also possible to increase the alkali ion storage / release reaction. Therefore, this material is very useful as an electrode material, and by using this material, it is possible to obtain a secondary battery having high capacity, excellent cycle stability, and capable of withstanding charge / discharge with high current density.

[Brief description of drawings]

1 is a charging / discharging potential curve in Example 1, and FIG.
1A shows an example using a 700 ° C. fired body, and FIG. 1B shows an example using an 820 ° C. fired body.

FIG. 2 is an NMR spectrum in Example 1.

FIG. 3 is a structural diagram in which a crystal of an alkali metal storage carbonaceous material of the present invention is modeled, FIG. 3 (A) is a plan structural diagram,
FIG. 3B is a sectional structural view.

FIG. 4 is a front view including a partial cross-sectional view of a lithium secondary battery using the alkali metal storage carbonaceous material of the present invention as a negative electrode.

[Explanation of symbols]

 30 Separator 50 Positive electrode 70 Negative electrode

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[Procedure amendment]

[Submission date] September 28, 1993

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[0007]

DISCLOSURE OF THE INVENTION The present invention is an alkali metal-occlusion carbon-based material obtained by absorbing an alkali metal in a carbon-based material having a condensed aromatic ring structure and having a disordered laminated structure. C atomic ratio (where A is an alkali metal element,
C is 0.125 to 1), the peak (B) of the chemical shift in the NMR spectrum of the alkali nucleus is 0 ± 2 ppm, and the peak (A) is on the plus side of the peak (B). The present invention provides an alkali metal-occluding carbon-based material characterized by the above.

[Procedure 3]

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The organic compound which is essentially a graphitizing material may be any as long as it has an aromatic structure, and examples thereof include polyphenylene, polyphenylene vinylene, polyphenylene xylene, polystyrene and novolac resins. . Examples of the factor that inhibits the laminated structure include a bent structure (o-, m-position structure), a branched structure, and a crosslinked structure. Further, these organic compounds may include organic compounds having a 5-membered ring or a 7-membered ring. The carbon-based material used in the present invention may be obtained by firing these organic compounds at a temperature not so high and a temperature at which electrical conductivity is low, which is usually 300 to 1,000 ° C.

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The alkali metal storage carbonaceous material of the present invention is
The carbon-based material thus obtained, alkali metal,
Preferably, lithium is occluded, and the A / C atomic ratio is 0.125 to 1, preferably 0.33 to 0.6.
7 If the A / C atomic ratio is less than 0.125, the peak (A) is not expressed, that is, the lithium ions that directly act on the discharge are not occluded, and the charging / discharging effect becomes difficult to be exhibited. Is hard to be occluded. The alkali metal storage carbonaceous material having an A / C atomic ratio within the above range is a stoichiometric limit of the lithium graphite intercalation compound as a charge capacity when the material is used as a negative electrode of a lithium secondary battery. It is possible to exceed 372 Ah / kg.

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In addition, the alkali metal storage carbonaceous material of the present invention has at least one chemical shift δ peak in the NMR spectrum and a peak (B) shift of 0 ± 2 ppm, preferably another peak (A). And there is a shift on the positive side. Here, when the alkali element is lithium, the observed nucleus is ⁷ Li, and the standard of chemical shift is LiC.
1 when the peak of 1 mol / l aqueous solution is 0. The peak (B) of the chemical shift δ being in the above range means that the unpaired electron density on the alkali ion is almost 0, that is, the alkali ion is a covalent Li ₂ molecule. Means

[Procedure correction 6]

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Next, the method for producing the alkali metal storage carbonaceous material of the present invention will be specifically described. First, the carbon-based material used in the present invention is an organic compound having a condensed aromatic structure, that is, an aromatic compound having a main chain in which a factor that inhibits the development of a laminated structure (bending, branching, crosslinking, etc.) is introduced. The polymer possessed is usually used in an inert gas such as argon, helium, or nitrogen, or in a reducing gas such as hydrogen.
It is obtained by heat treatment at a temperature of 00 to 1,000 ° C., preferably 600 to 800 ° C. for 0 to 6 hours, preferably 0 to 1 hour.

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[0029]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Example 1 Polyphenylene was synthesized by the Kovacic method. That is, cupric chloride (CuCl ₂ ), aluminum chloride (anhydrous) (AlCl ₃ ), benzene (C
₆ H ₆ ) was mixed at a molar ratio of 1: 1: 4 and stirred under an inert gas atmosphere. The powder obtained was treated with hydrochloric acid (6
After washing several times with (N-HCl), washing with water, washing with acetone and washing with water were repeated, and vacuum drying was performed at 100 ° C. Polyphenylene synthesized in this way is bent,
It contains stacking inhibition factors such as branched structures and quinoid structures.

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The polyphenylene thus synthesized was fired at 700 ° C. in a hydrogen stream to obtain a carbon-based material (hereinafter also referred to as “700 ° C. fired body”). Specifically, the temperature is raised from room temperature to 500 ° C. at a heating rate of 250 ° C./hour,
From 0 ° C to 700 ° C, the temperature is raised at 40 ° C / hour to 700 ° C.
When the temperature reached ℃, the heating was stopped and the temperature was cooled to room temperature to obtain a carbon-based material. The inter-plane distance of the (002) plane determined by X-ray diffraction measurement of the obtained carbon-based material was 3.65Å. The diffraction peak of the (002) plane is very wide and is C
The size of the crystallite in the axial direction is estimated to be 10 Å or less.
That is, the number of laminated sheets was 3 or less.

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(Capacity) FIG. 1 shows a charge / discharge potential curve. FIG. 1 is an example using a 700 ° C. fired body.

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On the other hand, the (B) site is a covalent lithium molecule (covalentLi), which is Lorentzian in contrast, exhibits liquid-like behavior, and does not have a fixed position. The mechanism of the discharge is that the ionized ion [Ion Li, (A) site] is discharged and the seat becomes vacant. On the other hand, the covalent lithium molecule [covalent Li, site (B)] cannot be immediately discharged, but it is considered that it becomes a lithium reservoir and moves to the vacant portion to be discharged. Therefore, Li
Discharge capacities in excess of C ₆ are possible, for example LiC _1.93
Alkali metal storage carbon materials such as

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FIG. 1 is a charge / discharge potential curve in Example 1.

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[Figure 1]

Front Page Continuation (72) Inventor Atsushi Demachi 1-4-1 Chuo 1-4 Wako, Saitama Prefecture Honda R & D Co., Ltd.

Claims (4)

[Claims] 1. An alkali metal storage carbon-based material having a condensed aromatic structure and a disordered laminated structure in which an alkali metal is stored, wherein the C / A atomic ratio (where C Is carbon and A is an alkali metal element) is 1 to 8
And the peak of chemical shift δ in the NMR spectrum of the alkali nucleus has at least two values, one peak (B) is 0 ± 2 ppm, and the other peak (A) is on the plus side of the peak (B). An alkali metal storage carbon-based material characterized by: 2. The alkali metal is lithium.
The described alkali metal-occluding carbon-based material. 3. An electrode material for a secondary battery, comprising the alkali metal storage carbonaceous material according to claim 1 or 2. 4. A secondary battery using the electrode material for a secondary battery according to claim 3 as a negative electrode.