JPH06236754A - Negative electrode material, its manufacture, and lithium secondary battery - Google Patents

Abstract

PURPOSE:To remarkably improve the discharge capacity per unit volume by containing a carbon material of a specified atomic ratio or more in the reaction quantity of lithium to carbon when a negative electrode material for lithium secondary battery is reacted with n-butyl lithium. CONSTITUTION:A negative electrode 3 is formed by the use of a carbon material in which the reaction quantity of lithium Li to carbon C when a carbonizable maternal is baked at a temperature less than 1000 deg.C in nonoxidizing atmosphere, carbonized, and reacted with n-butyl lithium is an atomic ratio Li/C=0.001 or more. A separator 2 consisting of a porous polypropylene nonwoven fabric is impregnated with an nonaqueous solvent electrolyte, and nipped between the negative electrode 3 and a positive electrode 1 formed of a positive electrode active material such as V2O5. This is housed in a case 4 through a current collector 6 such as nickel mesh, and sealed by a sealing plate 5 through an insulating packing 7 to form a lithium secondary battery.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode material for a lithium secondary battery having an extremely large discharge capacity, a method for producing the same, and a lithium secondary battery using the negative electrode material.

[0002]

2. Description of the Related Art Lithium secondary batteries have attracted attention as a type of high energy density secondary batteries. In the lithium secondary battery, lithium is used as the negative electrode active material, metal chalcogenide or metal oxide is used as the positive electrode active material, and an electrolytic solution prepared by dissolving various salts in an aprotic organic solvent is used as the electrolytic solution. ing. Further, the lithium secondary battery has high electromotive force and energy density, and is expected to be used as a distributed or portable battery in a wide range of fields such as electronic devices, electric devices, electric vehicles, and power storage.

However, in the conventional lithium secondary battery, since a metallic lithium simple substance such as a foil is often used as the negative electrode active material, various problems occur. That is, when a metallic lithium simple substance is used, dendritic lithium dendrites are deposited on the electrode surface due to repeated charging and discharging. Moreover, the dendritic lithium dendrite grows through the diaphragm, and there is a high risk of short circuit with the positive electrode. Therefore, the charge / discharge cycle life is short.

Therefore, a method has been proposed in which a fusible alloy containing aluminum, lead, cadmium and indium is used to deposit lithium as an alloy during charging and to elute lithium from the alloy during discharging (US Pat. No. 4).
No. 002492). Although this method can prevent the deposition of dendritic lithium, it deteriorates the workability as an electrode. Further, the energy density per unit weight or unit volume is lowered, and the life is shortened as the metal is deteriorated.

[0005] In recent years, in order to solve such problems, researches for supporting lithium on various carbon materials such as graphite have been actively conducted. However, when lithium metal is used as the negative electrode material, the theoretical capacity is about 3800 Ah / kg.
(Lithium metal base), the theoretical capacity of a lithium secondary battery in which graphite is loaded with lithium is
When calculated from the composition C ₆ Li, it is about 372 Ah / kg (carbon base). Therefore, even if a negative electrode material in which lithium is supported on a carbon material is used, the capacity of 372 Ah / kg (carbon base) is not necessarily a sufficiently high capacity. Therefore, even the graphite intercalation compounds that have been conventionally proposed have a problem that the lithium storage capacity is low and the capacity of the lithium secondary battery is low.

[0006]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a negative electrode material which does not generate dendrites, has high safety, and has a large discharge capacity per unit volume, and a lithium secondary battery. Especially.

Another object of the present invention is to provide a method for efficiently producing a negative electrode material having the above-mentioned excellent properties.

[0008]

The present inventors have made earnest studies to achieve the above-mentioned object, and as a result, when carbonizing a carbonizable material by firing at a relatively low temperature, many structural defects are generated in the generated carbon material. Among these carbon materials, it was found that a carbon material showing reactivity with n-butyllithium surprisingly significantly increases the capacity of the secondary battery, and has completed the present invention.

That is, the negative electrode material for a lithium secondary battery of the present invention contains carbon C when reacted with n-butyllithium.
The reaction amount of lithium Li with respect to the atomic ratio Li / C =
It contains a carbon material of 0.001 or more.

Further, the lithium secondary battery of the present invention comprises the above negative electrode material.

Further, according to the method of the present invention, when a carbonizable material is fired in a non-oxidizing atmosphere at a temperature of 1000 ° C. or less to carbonize and react with n-butyllithium, lithium Li to carbon C is added. The reaction amount of the atomic ratio Li / C
A negative electrode material is manufactured using a carbon material having a value of 0.001 or more.

In this specification, "carbonization" means
It refers to all the treatments to obtain a carbon material by firing at a temperature that is higher than the temperature at which carbonization is possible and is 1000 ° C. or lower. The “resin” also includes a resin composition containing a resin in an oligomer region having a low degree of polymerization.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings as needed.

The carbon material contained in the negative electrode material of the present invention is
(A) When reacted with n-butyllithium, the reaction amount of lithium Li with respect to carbon C has an atomic ratio of Li / C = 0.
001 or more, preferably 0.003 to 3.0, more preferably 0.005 to 3.0 (for example, 0.005 to 3.0).
1.0) and is useful as a negative electrode material for lithium secondary batteries. It is possible to increase the discharge capacity, probably because such a carbon material having a high reaction activity with lithium has a larger proportion of an amorphous portion than a crystalline portion.

It has been reported that carbon materials having a laminated structure such as graphite do not generally cause an intercalation reaction with n-butyllithium (J. Electroche
m. Soc., Vol. 124, 1387-1388). However, the present inventors have found that among carbon materials, there is a carbon material that reacts with n-butyllithium to incorporate lithium into the carbon, and such carbon material is used as a negative electrode material of a lithium secondary battery. Then, it was found that the discharge capacity remarkably increased. It should be noted that the discharge capacity of the lithium secondary battery does not always increase as the reactivity of the carbon material with n-butyllithium increases, and that the carbon material having the atomic ratio Li / C has a high discharge capacity. can get.

The reaction amount of n-butyllithium with respect to the carbon material is, for example, by adding a predetermined amount of the carbon material to an organic solvent solution of n-butyllithium having a predetermined concentration, and at an appropriate time (for example, about 1 to 6 hours). Stir to react and react with unreacted n
It can be calculated by decomposing butyl lithium by adding water and titrating the produced lithium hydroxide with an acid such as hydrochloric acid.

The preferred carbonaceous material is (B) Raman spectrum which has a peak at 1360 cm ^-1 and a peak at 15
Intensity ratio with peak at 80 cm ⁻¹ R = I ₁₃₆₀ / I
₁₅₈₀ = 0.4 or more, preferably 0.4 to 2.0, more preferably about 0.6 to 1.2. The Raman spectrum of the graphite crystal was 1580 cm ^-1.
The absorption line appears at 1, and when the plane symmetry is reduced due to a structural defect or the like, the absorption line appears at 1360 cm ⁻¹ due to the amorphous portion. Therefore, when the intensity ratio R is less than 0.4, the discharge capacity of the lithium secondary battery becomes small.

The (C) BET specific surface area of the carbon material of the present invention is 70 m ² / g or less, preferably 50 m ² / g or less, more preferably 40 m ² / g or less. BET
The specific surface area is, for example, 0.1 to 40 m ² / g, preferably 0.5 to 35 m ² / g in many cases. When the specific surface area exceeds 70 m ² / g, the discharge capacity of the lithium secondary battery tends to decrease.

Further, the carbonaceous material contained in the negative electrode material of the present invention often exhibits the following characteristics in addition to the above characteristics.

(D) X depends on the type of carbon material,
The average lattice constant d (002) by wide-angle diffraction is 3.4.
It is angstrom or more (for example, about 3.4 to 3.6 angstrom). If the average lattice constant d (002) is less than 3.4 Å, the discharge capacity of the lithium secondary battery may decrease.

(E) The true specific gravity according to the specific gravity bottle method (JIS R7212) is 1.8 g / cc or less (for example, 1.3 to
It is about 1.8 g / cc). True specific gravity is 1.8g / cc
If it exceeds, the discharge capacity of the lithium secondary battery may decrease.

(F) The carbon / hydrogen atomic ratio C / H varies from 2 to 40 (for example, from 2 to 2) although it depends on the type of carbon material.
5, preferably about 3 to 15). When the atomic ratio C / H is less than 2, the conductivity as an electrode is likely to be lowered.
If it exceeds 0, the discharge capacity of the lithium secondary battery may decrease.

The atomic ratio C / H of the carbon material using a resin as the carbonizable material is usually 10 or less, preferably about 4.0 to 9.5 in many cases. Further, the atomic ratio C / H of the carbon material using fine particles as the carbonizable material
Is usually about 2 to 10, preferably about 3 to 9.

(G) ESR (Electron Spin Resonance
) Sometimes there is a single absorption spectrum in the spectrum. The linewidth of this single absorption spectrum is usually
It is 1 to 5 gauss (for example, 1 to 3.5 gauss, preferably about 2 to 3 gauss).

(H) When the carbon material is carbonaceous particles exhibiting a single absorption spectrum, the average particle diameter of the carbon material is 0.
The particle size is about 5 to 1.5 μm, and the particle size at a cumulative frequency distribution of 90% by volume is about 0.8 to 3.5 μm.

The carbonaceous material can be composed of carbides of various carbonizable materials as long as it has the above-mentioned characteristics, but preferably (a) a fired product of an aromatic resin obtained by crosslinking an aromatic component with a crosslinking agent, (b) ) Selected from a calcined product of mesocarbon microbeads, (c) a carbonaceous particle exhibiting a single absorption spectrum with a line width of 1 to 5 gauss in the ESR spectrum, and (d) a calcined product of coal-based or petroleum-based pitch. It is composed of at least one kind of carbide. (B) In the case of a carbide obtained by firing mesocarbon microbeads, considering the ease of electrode preparation and the electrode characteristics, the particle size distribution is 0.1 to 1 with a cumulative frequency distribution of 10% by volume (D10).
0 μm (preferably 0.5 to 5 μm), cumulative frequency distribution 5
2% to 80 μm (preferably 2 to 50) at 0% by volume (D50)
μm), cumulative frequency distribution 90% by volume (D90) 15 to 90
It is preferably about μm (preferably 20 to 85 μm). In such a particle size distribution, not only a single peak but also two or more peaks may be present. The carbide having such a particle size distribution is classified and / or
Alternatively, it can be obtained by a crushing operation.

The average particle size of the carbonaceous particles (c) is, for example, 0.5 to 1.5 μm, and the particle size in a cumulative frequency distribution of 90% by volume is, for example, about 0.8 to 3.5 μm.

In the method of the present invention, a carbonizable material is fired in a non-oxidizing atmosphere at a relatively low temperature to produce a negative electrode material which is carbonized.

As the carbonizable material, various materials that can be used as raw materials for carbon materials, for example, carbonizable polymers (phenolic resin, furan resin, polyacrylonitrile, rayon, cellulose, etc.), carbonaceous powders (eg, The mesocarbon microbeads (b), carbonaceous particles (c), etc.) and (d) petroleum or coal pitch are included.

Preferred materials include carbonizable polymers,
In particular, (a) an aromatic resin in which an aromatic component is crosslinked with a crosslinking agent, carbonaceous powder, particularly (b) mesocarbon microbeads, and (c) a line width of 0.
Included are carbonaceous particles exhibiting a single absorption spectrum of 5 to 3.0 Gauss, and (d) coal-based or petroleum-based pitch. The average particle size of the carbonaceous particles (c) is, for example,
The particle size at 0.5 to 1.5 μm and 90% by volume of the cumulative frequency distribution is about 0.8 to 3.5 μm.

The aromatic resin (a) can be obtained by reacting an aromatic component with a crosslinking agent in the presence of an acid catalyst. The aromatic resin is a so-called carbonizable C
It constitutes a carbon precursor made of OPNA resin. Therefore, as the aromatic component, a component forming a carbon precursor composed of a COPNA resin is used.

Examples of the aromatic component include naphthalene, azulene, indacene, fluorene, fluoranthene, acenaphthene, acenaphthylene, anthracene,
Phenanthrene, triphenylene, pyrene, chrysene,
Condensed polycyclic hydrocarbons having two or more carbon 6-membered rings such as naphthacene, picene, benzophenanthrene, perylene, benzopyrene, pentaphene, pentacene, hexacene, coronene, heptacene; indole, isoindole, isoquinoline, quinoline, phthalazine, carbazole. , Acridine, phenazine, phenanthrazine, and the like, condensed heterocyclic compounds in which three or more heterocycles containing a nitrogen atom, a sulfur atom, an oxygen atom, etc. as heteroatoms and an aromatic carbon are condensed; anthracene oil, decrystallized anthracene Oils, naphthalene oil, methylnaphthalene oil, creosote oil, ethylene bottom oil, carbole oil, heavy oil of petroleum type such as solvent naphtha; tar, pitch, hydrogenated pitch and the like. These aromatic components are
One kind or two or more kinds can be used.

The aromatic component may have a substituent which does not adversely affect the crosslinking reaction, for example, a halogen atom, an alkyl group, a hydroxyl group, an alkoxy group, a carboxyl group or an alkoxycarbonyl group. Further, it may be used in combination with a ring assembly compound such as biphenyl or binaphthalene.

Preferred aromatic components include compounds having two or more aromatic rings, especially three or more aromatic rings and their hydrides (eg, hydrogenated pitch).

As the crosslinking agent, various compounds that can crosslink the aromatic component can be used. The cross-linking agent includes a compound having an aromatic ring similar to the aromatic component, preferably about 1 to 3 aromatic rings, and more preferably an aromatic compound having 1 to 2 aromatic rings.

Examples of the cross-linking agent include aromatic dimethylene halides such as xylylene dichloride; aromatic dimethanols such as xylylene glycol; terephthaloyl dichloride, isophthaloyl dichloride, phthaloyl dichloride, terephthaloyl dibromide, Isophthaloyl dibromide, phthaloyl dibromide, 1,
Aromatic dicarboxylic acid halides such as 5-naphthalenedicarboxylic acid chloride, 2,6-naphthalenedicarboxylic acid chloride, 1,5-anthracene dicarboxylic acid chloride and 2,6-anthracene dicarboxylic acid chloride;
An aromatic dicarboxylic acid corresponding to the aromatic dicarboxylic acid halide; a lower alkyl ester of an aromatic dicarboxylic acid corresponding to the aromatic dicarboxylic acid halide (for example,
Lower alkyl ester having about 1 to 4 carbon atoms such as terephthalic acid dimethyl ester and terephthalic acid diethyl ester); benzaldehyde, p-hydroxybenzaldehyde, p-methoxybenzaldehyde, 2,5-dihydroxybenzaldehyde, benzaldehyde dimethylacetal, terephthalaldehyde, isophthalate Aromatic aldehydes such as aldehydes and salicylaldehydes; pyromellitic dianhydride, etc. are exemplified. These cross-linking agents may be used either individually or in combination of two or more.

Preferred cross-linking agents include aromatic dimethylene halides, aromatic dimethanol, aromatic dicarboxylic acid halides, aromatic aldehydes and the like.

The amount of the cross-linking agent to be used can be selected within a wide range depending on the characteristics of the carbon precursor and the carbon material. For example, it is 0.2 to 10 mol, preferably 0 per mol of the aromatic component. It is about 5 to 3 mol.

The crosslinking of the aromatic component with the crosslinking agent is usually carried out in the presence of an acid catalyst. As the acid catalyst, for example, a conventional acid such as Lewis acid or Brenstedt acid can be used. Examples of Lewis acids include ZnCl ₂ and B.
F ₃ , AlCl ₃ , SnCl ₂ , SnCl ₄ , TiCl
₃ , TiCl ₄ , FeCl _{3 and the} like are included, and Bronsted acids include, for example, organic acids such as p-toluenesulfonic acid, fluoromethanesulfonic acid and xylenesulfonic acid; inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid. Acids, etc. are included. Preferred acid catalysts include, for example, Bronsted acids such as sulfuric acid and Lewis acids such as AlCl ₃ .

The amount of the catalyst used can be appropriately selected depending on the reaction conditions and the reactivity of the aromatic component.
The amount is 0.01 to 10 molar equivalents, preferably 0.5 to 3 molar equivalents, relative to the crosslinking agent.

The crosslinking reaction may be carried out in the presence of a suitable organic solvent inert to the reaction, for example, a hydrocarbon solvent such as n-heptane, n-octane or cyclohexane,
It may be carried out in the absence of a solvent. The cross-linking reaction can be carried out, for example, at a temperature of 80 to 250 ° C, preferably about 100 to 200 ° C. The reaction is usually carried out with stirring in an inert atmosphere of nitrogen, helium, argon or the like, and the point at which stirring is not possible can be the end point of the reaction. The reaction time is usually about 30 minutes to 24 hours.

The degree of polymerization of the produced resin depends on the reaction temperature and the reaction time, and the reaction time is short, for example, 10 minutes to 1 minute.
When the time is set to about time, a resin having a low degree of polymerization can be obtained. The degree of polymerization n of the resin is usually 2 to 100, preferably about 3 to 50.

After completion of the reaction, if necessary, concentration, drying,
The aromatic resin can be obtained by a conventional method such as a solvent fractionation method. An aromatic resin produced by the crosslinking reaction,
That is, the carbon precursor usually exhibits thermosetting property.

The carbonizable polymer as a carbon precursor can be processed into powder, granules, plates, films such as films, and fibers.

The powdery granular carbon precursor can be obtained by pulverizing a carbonizable polymer with a general pulverizer such as a hammer mill or a ball mill and, if necessary, sizing. The granular or granular carbon precursor can be obtained by heating and granulating.

Further, the plate-like carbon precursor can be obtained by pressing the plate-like carbon precursor into a plate-like form.
In that case, you may shape | mold while heating as needed. In addition, a film-like carbon precursor such as a film can be formed by a conventional film forming / molding means such as a casting method using a suitable soluble solvent and a spin coating method, and the carbon precursor is melted by heating to form a film. It can also be obtained by melting. At that time, it can be formed into a flat plate shape or a film shape corresponding to the electrode.

The fibrous carbon precursor can be obtained by melt spinning a carbonizable polymer to make it infusible. In the case of preventing melting, a resin having a small crosslink density can be used as the curable resin such as the aromatic resin. In addition,
The crosslink density of the carbon precursor can be adjusted by the reaction time and the reaction temperature.

As is clear from the above, the use of the carbon precursor has the advantage that it can be formed into a flat plate corresponding to the electrode without using a binder.

The granular, granular or fibrous carbon precursor is a carbonizable binder such as phenol resin, furan resin, polyacrylonitrile, rayon, cellulose, anisotropic or isotropic pitch; Thermosetting resins such as epoxy resin, vinyl ester resin, unsaturated polyester, urea resin, polyimide; polyamide, polyvinyl chloride,
It may be mixed with a thermoplastic resin such as polyvinyl acetate, ethylene-vinyl acetate, an acrylic resin, a saturated polyester, a polyacetal, a polycarbonate, a fluororesin, etc., and molded into a flat plate corresponding to the electrode.

The mesocarbon microbeads (b)
Include coal tar, coal tar pitch, heavy petroleum oil (eg asphalt), ethylene bottom oil, etc.
For example, normal pressure to 20 kg / cm ² · G, temperature 350 to 4
It is obtained by heat-treating at about 50 ° C. and separating and purifying the generated spherulite.

The mesocarbon microbeads are optically anisotropic spherical fine particles and have a structure in which a carbon six-membered ring network is laminated in layers. The average particle size of the mesocarbon microbeads is usually about ^{2 to} 80 μm, and the BET specific surface area is usually 70 m ² / g or less. Furthermore, after removing low molecular weight components from such mesocarbon microbeads, carbonization treatment can finally further increase the discharge capacity of the battery. The low molecular weight component is
For example, the organic solvent such as toluene, xylene, quinoline, tar oil, or anthracene oil can be used to remove the mesocarbon microbeads by treating them with a method such as washing or extraction.

The carbonaceous particles (c) correspond to, for example, the quinoline-insoluble matter in tar produced by carbonization of coal or the like. The carbonization temperature can be selected according to the scale of the carbonization device, and may be, for example, about 800 to 1250 ° C. in a coke oven, or about 300 to 900 ° C. in a laboratory scale electric furnace. The above-mentioned particles can be obtained by collecting the tar fraction that is distilled off, mixing it with quinoline, and collecting the quinoline insoluble matter.

The particle (c) exhibits a single absorption spectrum in the ESR spectrum, and its line width is as described above. Further, the atomic ratio of carbon to hydrogen C / H = 3 to
It is about 6 and is insoluble in quinoline. The BET specific surface area is usually 70 m ² / g or less.

Further, the kind of the coal-based or petroleum-based pitch (d) is not particularly limited, and examples thereof include petroleum distillation residue, naphtha pyrolysis residue, ethylene bottom oil, coal liquefied oil, coal tar and other coal-based or petroleum. Examples include pitches obtained by distilling heavy oils to remove low boiling point components, and those obtained by subjecting such pitches to heat treatment or hydrogenation treatment. More specifically, pitch includes isotropic pitch, mesophase pitch, hydrogenated mesophase pitch, and the like. The softening point of the pitch (d) is, for example,
It is 150 to 350 ° C, preferably about 200 to 330 ° C. In many cases, the quinoline insoluble matter of the pitch (d) is, for example, about 35 to 50% by weight, and the benzene insoluble matter is, for example, about 60 to 90% by weight.

The granular carbon material, such as the mesocarbon microbeads (b), the carbonaceous particles (c) and the coal-based or petroleum-based pitch (d), may be the granular or granular COPNA resin. Similar to the carbonizable polymer, it may be mixed with a carbonizable binder, a thermosetting resin, a thermoplastic resin, etc., and molded into a flat plate corresponding to the electrode.

The main feature of the method of the present invention is that the carbonizable material is heat-treated at a relatively low temperature and carbonized by firing to obtain a carbon material. At that time, the temperature rising rate also has a great influence on the characteristics of the carbon material. When fired at a relatively low temperature, many structural defects are generated inside carbon. And, because of these structural defects, a gap between crystal structures (hereinafter referred to as a void) is generated inside, or in the lithium secondary battery provided with the carbon negative electrode material obtained by the method of the present invention, There is a feature that a discharge capacity exceeding the theoretical value can be obtained.

The heat treatment is performed in a non-oxidizing atmosphere, for example,
It can be performed in an atmosphere of an inert gas such as nitrogen, helium, argon, neon, carbon dioxide, or under vacuum.

In the method of the present invention, the heating rate is set to 0.1.
It is important to set the temperature to -30 ° C / minute, preferably 0.3 to 30 ° C / minute. When the scale of the manufacturing apparatus is large, the temperature rising rate is often about 0.5 to 10 ° C./minute. By heating at such a temperature rising rate, it is possible to obtain a carbon material having at least the characteristic (A).

The firing temperature is 1000 ° C. or lower, preferably 500 to 975 ° C., more preferably 600 to 950.
C., especially about 650 to 925.degree. Firing temperature is 50
If the temperature is lower than 0 ° C, the electrical conductivity of the carbon material itself changes abruptly and the carbon material does not function as an electrode.
If it exceeds, crystallization will proceed and the amount of voids inside carbon will be significantly reduced. The firing time can be appropriately selected according to the firing temperature and the like, and is, for example, 15 minutes to 24 hours, preferably 30 minutes to 12 hours.

When lithium is supported on such a carbon material, it is presumed that the voids absorb and release lithium via the carbon intercalation compound. That is, when occluding lithium, first, a carbon intercalation compound is formed by lithium ions, and then lithium is stored in the void.
On the contrary, when releasing lithium, it is presumed that the lithium ions existing between the carbon layers are released to some extent, and then the lithium in the voids is released via the carbon layers.

As described above, not only the layered structure of carbon but also the voids remaining inside the carbon can be utilized for the occlusion / desorption of lithium and the charge / discharge reaction, and it is possible to dramatically increase the capacity. Become. In the present invention, a negative electrode carbon material of a lithium secondary battery having a discharge capacity exceeding the theoretical discharge amount (about 370 Ah / kg), for example, a value of 400 Ah / kg or more can be obtained. On the other hand, when compared with a lithium secondary battery using a carbon material obtained by firing the carbonizable material at 1100 ° C. as a negative electrode, the lithium secondary battery using the carbon material of the present invention has about twice the discharge capacity. To be Therefore, with the same performance, the volume and weight of the lithium secondary battery negative electrode can be reduced by half.

The negative electrode material containing the carbon material may be obtained by firing a carbon precursor processed into a flat plate shape or a film shape. When powdery, granular, or fibrous carbon precursors are used, these are fired to form a carbon material, and the obtained carbon material and the binder, and a thermosetting resin and a thermoplastic resin are mixed and molded. You may process and may obtain a negative electrode material.

The carbon material obtained by the method of the present invention is suitable as a negative electrode for lithium secondary batteries. Therefore, the secondary battery of the present invention only needs to include the negative electrode material. The secondary battery can be assembled by a conventional method using battery constituent elements such as a negative electrode containing the carbon material, a positive electrode, an electrolytic solution, a separator, a current collector, a gasket, a sealing plate, and a case. FIG. 1 is a partial cross-sectional view showing an example of a lithium secondary battery.

The lithium secondary battery comprises a positive electrode 1 made of a positive electrode active material, a negative electrode 3 containing the carbon material, and the positive electrode 1.
The separator 2 is provided between the negative electrode 3 and the negative electrode 3.
The separator 2 is impregnated with a non-aqueous solvent electrolyte. The positive electrode 1, the separator 2 and the negative electrode 3 are housed in a case 4, and the opening of the case 4 is sealed with a sealing plate 5. Further, a current collector 6 made of nickel mesh, metal wire mesh or the like is arranged between the case 4 and the negative electrode 1. Reference numeral 7 is an insulating packing.

As the positive electrode active material, for example, TiS ₂ ,
Metal chalcogenides having a layered structure such as MoS ₃ , NbSe ₃ , FeS, Vs ₂ , VSe ₂ , CoO ₂ , C
_{r 3 O 5, TiO 2,} CuO, V 3 O 6, Mo 3 O, V
₂ O ₅ , V ₂ O ₅ (.P ₂ O ₅ ), Mn ₂ O (.Li ₂
It is possible to use a metal oxide such as O), a conjugated polymer having conductivity such as polyacetylene, polyaniline, polyparaphenylene, polythiophene, polypyrrole, or the like. Preferred positive electrode active materials include V ₂ O ₅ , Mn
O _{2 and the} like are included. Such a positive electrode active material can also be used after being bound with a binder such as polytetrafluoroethylene.

As the electrolytic solution, for example, propylene carbonate, ethylene carbonate, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, 4-methyldioxolane, sulfolane, 1,2-dimethoxyethane, dimethylsulfoxide, acetonitrile, Examples include aprotic solvents such as N, N-dimethylformamide, diethylene glycol, dimethyl ether and the like. Among these electrolytes, ether solvents such as tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, and 4-methyldioxolane which are stable even under a strongly reducing environment are preferable.

As the electrolytic solution, LiPF ₆ , LiClO ₄ , LiBF ₄ , Li in one or more of the above solvents is used.
_{ClF 4, LiAsF 6, LiSbF 6} , LiAl
O ₄ , LiAlCl ₄ , LiPF ₆ , LiCl, LiI
A solvent in which a salt that produces an anion that is difficult to solvate is dissolved is often used.

Further, as the separator, a material having a liquid retaining property, for example, a polyolefin type porous film such as a porous polypropylene nonwoven fabric can be used.

The secondary battery may have any shape such as a cylindrical shape, a rectangular shape or a button shape.

The secondary battery of the present invention can be used in a wide variety of applications such as power supplies for portable electronic devices, backup power supplies for various memories and solar batteries, electric vehicles, and batteries for storing electric power.

[0071]

INDUSTRIAL APPLICABILITY The negative electrode material of the present invention and the lithium secondary battery provided with the negative electrode material do not generate dendrites, are highly safe, and have a large discharge capacity. In particular, it is possible to obtain a discharge capacity exceeding the theoretical value.

According to the method of the present invention, since the carbonizable material may be fired at a relatively low temperature, no dendrite is generated, the safety is high, and the discharge capacity per unit volume is large. A negative electrode material for a secondary battery can be efficiently obtained.

[0073]

EXAMPLES The present invention will be described in more detail based on the following examples.

The reactivity with n-butyllithium was examined as follows.

0.2 g of carbon material is reacted in 5 ml of 1.6 M n-butyllithium / n-hexane solution for 3 hours. After completion of the reaction, excess n-butyllithium is hydrolyzed by adding 10 ml of diethyl ether and 10 ml of distilled water. The generated lithium hydroxide was titrated with 0.5 N hydrochloric acid using phenolphthalein as an indicator,
Calculate the amount of lithium taken into the carbonaceous material.

Further, in measuring the Raman absorption spectrum,
NR-1100 manufactured by JASCO Corporation was used. further,
The specific surface area is measured by a BET specific surface area measuring device [manufactured by Micromeritics, model: ASAP240
0] was used for the measurement by the nitrogen adsorption method.

For reference, for carbonaceous particles, the average lattice constant d (002) was measured by an X-ray wide-angle diffractometer (manufactured by Rigaku Denki Co., Ltd., model: RAD-B) to obtain carbon / hydrogen. The atomic ratio (C / H) of was determined using an elemental analyzer (Perkin Elmer, model: 2400).

Example 1 (1) Preparation of COPNA Resin and Carbon Material As an aromatic component, a softening point of 76.6 ° C., a carbon / hydrogen atomic ratio C / H = 1.678, an aromatic index fa0.931,
Quinoline insoluble matter 0.05% by weight, benzene insoluble matter 14.
A hydrogenated pitch having a weight average molecular weight of 252 of benzene soluble component in FD mass of 01 wt% was used. As a cross-linking agent,
1.5 equivalents (40 g, 0.29 mol) of paraxylylene glycol to the hydrogenated pitch in terms of molar ratio.
As a reaction catalyst, p-toluenesulfonic acid was added in an amount of 0.1 equivalent (5.5 g, in terms of molar ratio) with respect to the amount of the crosslinking agent.
0.029 mol) was added.

The mixture was stirred at 120 ° C. for 1 hour, the obtained COPNA resin carbon precursor was pulverized and heat-cured at 300 ° C. in a nitrogen gas atmosphere, and then the temperature rising rate was 2 in a nitrogen gas atmosphere. The temperature was raised at 0.5 ° C./min, and the mixture was combusted and carbonized at 700 ° C. for 2 hours. The obtained carbonaceous powder was pulverized to obtain a powder having an average particle size of 10 μm.

(2) Preparation of negative electrode body 99 parts by weight of carbonaceous powder, dispersion type polytetrafluoroethylene (manufactured by Daikin Industries, Ltd., D-
1) 1 part by weight was mixed, uniformly stirred in a liquid phase, and then dried to obtain a paste. 30 mg of the obtained paste-like negative electrode material was pressed onto a nickel mesh as a current collector and vacuum dried at 200 ° C. for 6 hours to prepare a negative electrode body.

(3) Production of Battery Using the obtained negative electrode body, positive electrode body, LiCoO ₂ , propylene carbonate in which LiClO ₄ was dissolved at a concentration of 1 mol / L as an electrolytic solution, and polypropylene nonwoven fabric as a separator. A lithium secondary battery having the structure shown was produced.

(4) Measurement of battery characteristics The discharge characteristics of the obtained lithium secondary battery was 0.1 mA /
It was measured under a constant flow charge / discharge of cm ² , and the discharge capacity was defined as the capacity until the battery voltage dropped to 2.0V.

Examples 2 to 3 C obtained in Example 1 was heated at a heating rate of 2.5 ° C./min.
A battery was prepared in the same manner as in Example 1 except that the OPNA resin was fired at 800 ° C. (Example 2) and 900 ° C. (Example 3) to be carbonized, and the battery characteristics were evaluated.

Comparative Example 1 C obtained in Example 1 was heated at a heating rate of 2.5 ° C./min.
A battery was prepared in the same manner as in Example 1 except that the OPNA resin was fired at 1100 ° C. and carbonized, and the battery characteristics were evaluated.

The results of Examples 1 to 3 and Comparative Example 1 are shown in Table 1.

[0086]

[Table 1] As is clear from Table 1, by using a carbon material, which has a reactivity with n-butyllithium, among the carbon materials fired at a relatively low temperature as the negative electrode of the lithium secondary battery, the discharge capacity remarkably increases. In particular, when a carbon material fired at a low firing temperature is used, a discharge capacity far exceeding the theoretical value can be obtained.

Example 4 (1) Preparation of Mesocarbon Microbeads Dehydrated coal tar was used at 3 kg / cm ² · G and a temperature of 385.
After heat treatment at ℃ for 14 hours, the generated spherulites were separated using a high temperature centrifuge, washed with toluene, and then dried at 150 ℃ for 3 hours under a nitrogen gas atmosphere.

The resulting mesocarbon microbeads were
In an inert gas atmosphere, the temperature is raised at a heating rate of 2.5 ° C / min,
It heat-processed at 700 degreeC for 1 hour, and carbonized.

(2) Preparation of Negative Electrode Body and Battery, and Measurement of Battery Properties In the same manner as in Example 1 except that the carbonaceous powder of the obtained mesocarbon microbeads was used instead of the carbonaceous powder of Example 1. A negative electrode body and a battery were produced and the battery characteristics were measured.

Examples 5 and 6 The mesocarbon microbeads obtained in Example 4 were heated to 800 ° C. (Example 5), 9 at a heating rate of 2.5 ° C./min.
Example 1 except firing and carbonizing at 00 ° C (Example 6)
A battery was prepared in the same manner as above, and the battery characteristics were evaluated.

Comparative Example 2 A battery was prepared in the same manner as in Example 1 except that the mesocarbon microbeads obtained in Example 4 were heated at a temperature rising rate of 2.5 ° C./min to be carbonized by firing at 1100 ° C. Was prepared and the battery characteristics were evaluated.

The results of Examples 4 to 6 and Comparative Example 2 are shown in Table 2.

[0093]

[Table 2] As is clear from Table 2, when a carbon material showing reactivity with n-butyllithium among carbon materials fired at a relatively low temperature, especially at a low firing temperature, is used as the negative electrode of the lithium secondary battery, the discharge capacity is increased. Is significantly increased.

Example 7 (1) Preparation of carbonaceous particles Pittston charcoal was charged into an electric furnace, heated to 700 ° C. at a temperature rising rate of 3 ° C./min, and the tar component to be distilled was simultaneously distilled. It was collected in a tar pool previously cooled with ice together with the cheap water. Note that the supernatant liquid, an ammonium hydroxide, collected in the tar reservoir was sucked with a pump, heated to 90 ° C. with a ribbon heater, and reused for showering tar distilled through a collecting pipe.

After completion of the dry distillation, the tar reservoir was rapidly cooled to solidify the tar, and the tar was removed from the tar reservoir. The obtained tar and quinoline were mixed, and the quinoline insoluble matter was recovered. The obtained carbonaceous particles composed of quinoline-insoluble matter have d (002)
Shows a single absorption spectrum with a line width of 2.00 Gauss in the ESR spectrum of 3.47 Å,
Specific surface area 24.10 m ² / g, atomic ratio C / H = 4.0
1, the average particle size was 0.72 μm, and the 90% by volume particle size in the cumulative frequency distribution was 1.39 μm.

The carbonaceous particles made of the quinoline-insoluble matter thus obtained were heated in an inert gas atmosphere at a temperature rising rate of 25 ° C./min and heat-treated at 700 ° C. for 1 hour to carbonize them.

The obtained carbon material had an atomic ratio of Li / C = 0.
050, R = I ₁₃₆₀ / I ₁₅₈₀ = 0.95, the ESR spectrum shows a single absorption spectrum with a line width of 2.9 gausses, a specific surface area of 26.20 m ² / g, and an average particle size of 0.
The particle size was 70 μm, and the particle size of 90% by volume in the cumulative frequency distribution was 1.37 μm.

(2) Preparation of Negative Electrode Body and Battery, and Measurement of Battery Characteristics In place of the carbonaceous powder of Example 1, the carbonaceous particles of quinoline-insoluble matter obtained in (1) above were used. A negative electrode body and a battery were prepared in the same manner as in Example 1, and the battery characteristics were measured. The discharge capacity was 515 Ah / kg.
Met.

As is clear from these results, when a carbon material which has a reactivity with n-butyllithium among carbon materials fired at a relatively low temperature, especially a low firing temperature, is used as the negative electrode of a lithium secondary battery, The discharge capacity is significantly increased.

Example 8 Example 4 was repeated except that a crushed product obtained by crushing the carbide of the mesocarbon microbeads obtained in Example 4 with a ball mill was used instead of the carbide of the mesocarbon microbeads.
A battery was prepared in the same manner as in.

Example 9 Example 5 was repeated except that a crushed product obtained by crushing the carbide of the mesocarbon microbeads obtained in Example 5 with a ball mill was used instead of the carbide of the mesocarbon microbeads.
A battery was prepared in the same manner as in.

Example 10 Example 6 was repeated except that a crushed product obtained by crushing the carbide of the mesocarbon microbeads obtained in Example 6 with a ball mill was used instead of the carbide of the mesocarbon microbeads.
A battery was prepared in the same manner as in.

Comparative Example 3 Comparative Example 2 except that a crushed product obtained by crushing the carbide of the mesocarbon microbeads obtained in Comparative Example 2 with a ball mill was used instead of the carbide of the mesocarbon microbeads.
A battery was prepared in the same manner as in.

Example 11 Coal pitch having a softening point of 309 ° C. was heat-treated at 700 ° C. for 1 hour in an inert gas atmosphere for carbonization, and the obtained carbonaceous material was crushed by a ball mill. Example 1 except that the obtained powdery granular carbide was used instead of the carbonaceous powder of Example 1.
A negative electrode body and a battery were produced in the same manner as in.

Example 12 A petroleum pitch having a softening point of 270 ° C. was carbonized by heat treatment at 700 ° C. for 1 hour in an inert gas atmosphere, and the obtained carbonaceous material was pulverized with a ball mill. Example 1 except that the obtained powdery granular carbide was used instead of the carbonaceous powder of Example 1.
A negative electrode body and a battery were produced in the same manner as in.

Then, the characteristics of the carbon materials and the battery characteristics of the batteries prepared in Examples 8 to 12 and Comparative Example 3 were measured, and the results shown in Table 3 were obtained.

[0107]

[Table 3]

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing an example of a lithium secondary battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Positive electrode 2 ... Separator 3 ... Negative electrode 4 ... Case 5 ... Sealing plate 6 ... Current collector 7 ... Insulating packing

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical indication location H01M 10/36 Z (72) Inventor Takakazu Kazaka 4-1-2, Hirano-cho, Chuo-ku, Osaka-shi Within Osaka Gas Co., Ltd.

Claims (11)

[Claims] 1. When reacted with n-butyllithium,
The reaction amount of lithium Li with respect to carbon C is the atomic ratio Li /
A negative electrode material for a lithium secondary battery, which contains a carbon material having C = 0.001 or more. 2. In Raman spectrum, 1360c
The negative electrode material according to claim 1, wherein the intensity ratio of the peak at m ^{-1 and} the peak at 1580 cm ^-1 is R = I ₁₃₆₀ / I ₁₅₈₀ = 0.4 or more. 3. The carbon material has a BET specific surface area of 70 m ² / g.
The negative electrode material according to claim 1, which is the following carbonaceous particles. 4. The negative electrode material according to claim 1, wherein the carbon material is at least one kind of carbide selected from the following (a), (b), (c) and (d). (A) A fired product of an aromatic resin in which an aromatic component is crosslinked with a crosslinking agent, (b) a fired product of mesocarbon microbeads, (c) a single absorption spectrum having a line width of 1 to 5 gauss in ESR spectrum Carbonaceous particles, and (d) a fired product of coal-based or petroleum-based pitch 5. A lithium secondary battery comprising the negative electrode material according to claim 1. 6. A carbonizable material is provided in a non-oxidizing atmosphere,
Lithium Li with respect to carbon C when baked at a temperature of 1000 ° C. or lower to carbonize and react with n-butyllithium
The method for producing a negative electrode material using a carbon material having an atomic ratio of Li / C of 0.001 or more. 7. The method for producing a negative electrode material according to claim 6, wherein at least one carbonizable material selected from the following (a), (b), (c) and (d) is fired and carbonized. (A) Aromatic resin in which an aromatic component is cross-linked by a cross-linking agent, (b) Mesocarbon microbeads, (c) Carbonaceous material showing a single absorption spectrum with a line width of 0.5 to 3.0 gauss in ESR spectrum. Particles, and (d) coal-based or petroleum-based pitch 8. The method for producing a negative electrode material according to claim 7, wherein an aromatic resin obtained by reacting an aromatic component and a crosslinking agent in the presence of an acid catalyst is used as the aromatic resin. 9. The aromatic component is a condensed polycyclic aromatic compound,
The method for producing a negative electrode material according to claim 8, which is at least one component selected from the group consisting of a condensed heterocyclic compound, a petroleum-based or coal-based heavy oil, tar, and pitch. 10. The negative electrode material according to claim 8, wherein the crosslinking agent is at least one compound selected from the group consisting of aromatic dimethylene halide, aromatic dimethanol, aromatic dicarbonyl halide and aromatic aldehyde. Production method. 11. The method for producing a negative electrode material according to claim 6, wherein the temperature is raised at a temperature rising rate of 0.1 to 30 ° C./min and the firing is performed at a temperature of 1000 ° C. or less.