JPH10284080A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide high efficiency in a first cycle and keep high capacity in quick charge/discharge by convering the surface of a graphitized carbonaceous material with a carbonizable organic material, baking, and crushing to form an amorphous carbon-converging graphitized carbonaceous material, and treating the carbonaceous material with an acidic or alkaline solution, and using the treated carbonaceous material in a negative electrode. SOLUTION: A graphitized carbonaceous material is covered with a carbonizable organic material, they are baked to carbonize the carbonizable organic material, then the baked material is crushed to particles having a mean particle size of 5-50 μm (preferably 20-25 μm). The particle obtained are dispersed in an acidic solution or an alkaline solution, stirred, shaken at a temperature of 20-150 deg.C during 0.5 hr.-1 week or treated by superimposing ultrasonic waves, washed with pure water to wash out the acidic solution or the alkaline solution attached to the particles, and dried at temperature of 350 deg.C or lower. Property capable of absorbing/releasing lithium ions is developed, lithium undoing potential of 0.5 V or lower to Li/Li<+> is provided, and capacity exceeding the theoretical capacity of graphite is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion secondary battery having a high capacity and excellent in rapid charge / discharge characteristics, charge / discharge potential flatness and cycle characteristics.

[0002]

2. Description of the Related Art In recent years, high-capacity secondary batteries have been desired to have higher capacities as electronic devices have become smaller. Therefore, lithium-ion secondary batteries having higher energy density than nickel-cadmium and nickel-metal hydride batteries have been attracting attention. As the negative electrode material, it was first attempted to use lithium metal, but while repeating charge and discharge, dendritic lithium was deposited and penetrated the separator,
It was found that the battery could reach the positive electrode and cause a short circuit and cause a fire accident. Therefore, at present, attention has been paid to use of a carbon material capable of preventing the deposition of lithium metal by allowing a non-aqueous solvent to enter and exit during a charge / discharge process between layers, as a negative electrode material.

As this carbon material, Japanese Patent Application Laid-Open No. 57-20
8079 proposes the use of a graphite material. In particular, it has been known that when graphite having good crystallinity is used as a carbon anode material for a lithium secondary battery, a capacity close to 372 mAh / g, which is the theoretical capacity for absorbing lithium of graphite, is obtained, which is preferable as a material. . However, the graphite material is active with respect to the electrolyte, so at the time of the first charge and discharge,
It generally showed an irreversible capacity of several tens mAh / g or more due to film formation and side reactions.

On the other hand, the capacity of the low-temperature calcined amorphous carbon larger than the theoretical capacity of graphite can be increased to about 500 mAh / g depending on the setting of the cut-off potential. Since the potential is significantly higher than that of graphite, and has a large hysteresis in the potential characteristics during charging and discharging, it is difficult to obtain a potential difference from the positive electrode, and as a result, a large capacity, high power battery cannot be obtained. There was a problem. There is also a problem that a large capacity loss is caused at the time of initial charge / discharge. Further, it has been found that a rapid decrease in capacity causes a remarkable decrease in capacity.

Japanese Patent Application Laid-Open No. H5-299074 discloses that a carbon material is subjected to a chemical pretreatment with an inorganic acid or heated sodium hydroxide and then subjected to a vacuum heating treatment at a temperature of 800 ° C. or more to charge and discharge. It is disclosed that the cycle efficiency can be improved. Also, JP-A-6-2069
No. 0 discloses a method of producing an amorphous carbonaceous material while oxidizing the surface by chemical solution oxidation, electrolytic oxidation, or gas phase oxidation, and measuring an increase in negative electrode capacity. In addition, Japanese Unexamined Patent Publication No.
No. 44959 discloses a method in which an acid is added to a carbonaceous material and heated to obtain a capacity (370 mAh / g) close to the theoretical capacity of graphite. However, since graphite uses the intercalation of lithium ions into graphite crystals as the principle of charge and discharge, 372 mAh / g calculated from the maximum lithium-introduced compound LiC6 at normal temperature and normal pressure.
There is a problem that the above capacity cannot be obtained. Therefore, 372 mAh, which is the theoretical capacity of graphite, is obtained by any method.
/ G is not obtained. In addition, the low wettability of the graphite material with the electrolytic solution is due to the fact that the lithium undoping capacity at the initial stage of charge / discharge can be reduced by 350%, at which the graphite material should be able to express.
There was a problem that the capacity was lower than mAh / g or more.

[0006] Japanese Patent Application Laid-Open No. 7-022037 and the like disclose:
A carbonaceous material in which the surface of a graphitic carbonaceous material is coated with a carbonizable organic material and fired is disclosed. This material has the advantage that the potential at the time of charging and discharging is close to the oxidation-reduction potential of lithium metal, similar to that of graphite, and can obtain a higher capacity than the graphitic carbonaceous material.
A capacity exceeding 72 mAh / g has not been obtained.

In addition, LiNiO ₂ is expected to be newly used as a positive electrode material for a lithium secondary battery in terms of capacity, price and reserves of raw materials, instead of LiCoO ₂ which has been widely used as a positive electrode active material in the future. However, this substance has a lower potential with respect to Li / Li ⁺ than LiCoO _2, making it difficult to obtain a potential difference with the negative electrode. So LiNi
In order to take advantage of O ₂ , it is considered necessary to use a negative electrode material that can exhibit high capacity at a potential closer to 0 V than Li / Li ⁺ . Further, depending on the use of the lithium secondary battery, for example, it may be sufficiently considered that rapid recharging is required as an application for loading on an electric vehicle or the like, and for this, an electrode material having excellent rate resistance characteristics is used. The need has arisen.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a graphite material having a capacity exceeding the theoretical capacity of graphite when used as a negative electrode material for a lithium secondary battery.
In addition, as compared with the case where amorphous carbon is used, the change in potential during lithium doping and
It is close to the potential of i / Li +, has no potential hysteresis due to charging and discharging, can easily take the difference from the positive electrode potential, can exhibit high efficiency from the first charging and discharging cycle, has a large charging and discharging capacity, a small irreversible capacity, and a large charging and discharging capacity. An object of the present invention is to provide a high-performance lithium ion secondary battery having excellent rate resistance characteristics and cycle characteristics with respect to discharge current density.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems. As a result, the surface of a graphitic carbonaceous material was coated with a carbonizable organic material, fired, pulverized, and then acidified or pulverized. By treating with an alkaline solution, it is possible to develop a capacity that exceeds the theoretical capacity of graphite, and compared to the case of using amorphous carbon, the change in potential during lithium doping and undoping is similar to that of graphite. It is close to the Li / Li + potential and has no potential hysteresis due to charging and discharging.
The inventors have found that a negative electrode material that can easily obtain a difference from the positive electrode potential and can exhibit high efficiency from the first charge / discharge cycle can be produced, and the present invention has been completed. That is, the present invention is characterized in that the surface of the graphitic carbonaceous material is coated with a carbonizable organic material, fired, pulverized, and then the carbonaceous material treated with an acidic or alkaline solution is used as a negative electrode. It relates to a secondary battery.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below. `` Amorphous carbon-coated graphite-based carbonaceous material '' In the present invention, the term "amorphous carbon-coated graphite-based carbonaceous material" means that a graphitic carbonaceous material is coated with an organic material capable of being carbonized, and the coated body is fired. Carbonized and crushed, occludes lithium ions,
Has releasable properties. Specifically, the value of d002, which is the interlayer distance between carbon crystals determined by X-ray diffraction, is:
It has a value of not less than 3.35 ° and not more than 3.39 °, and in the Raman spectrum analysis, the above R value is not less than the R value of the graphitic carbonaceous material before coating, more preferably from 0.15 to 1.15.
The target is carbonaceous material particles having a particle size of 0 or less, more preferably 0.2 or more and 0.5 or less. The “amorphous carbon-coated graphite-based carbonaceous material” is not particularly limited as long as it is within the above numerical range, but in order to easily obtain the above material, for example, the following materials can be used. .

Graphitic carbonaceous material for producing "amorphous carbon-coated graphite-based carbonaceous material" As the shape of the graphitic carbonaceous material used in the present invention, various shapes such as spherical, plate-like and fibrous shapes are used. Although possible, it is preferable that the average particle size is smaller than the crushed particle size of the “amorphous carbon-coated graphite-based carbonaceous material”. Particularly preferably, the average particle diameter or the average major axis of the graphite material is in the range of 20 to 99% of the average particle diameter of the “amorphous carbon-coated graphite-based carbonaceous material”. Preferred specific examples of the graphitic carbonaceous material include acetylene black, graphitized conductive carbon black such as Ketjen black, artificial graphite, and the like.
Examples include graphite powder such as natural graphite and purified products thereof, and carbon fibers such as vapor-grown carbon fibers. Any of such graphitic carbonaceous materials may be used, but graphite powder having the following relationship between specific particle size and specific surface area, Raman R value, and half width is more preferable.

1) When the value of the specific surface area measured by the BET method is y (m 2 / g) and the value of the particle size (μm) of the powder is x, 4 ≦ x ≦ 40, 0.1 ≦ y ≦ 25 and y ≦ a
^xb , graphite powder in the region represented by (where a = 52, b = -0.6) 2) Further, in Raman spectrum analysis using argon ion laser light having a wavelength of 5145 °, 1570 to 1
The intensity of the peak existing in the range of 620 cm ^-1 was IA, 1
When the intensity of the peak existing in the range of 350 to 1370 cm ^-1 is defined as IB, an R value (= IB / IA) which is a ratio thereof
But not less than 0.001 and not more than 0.2. 3) In addition, is the half width of peaks present in 1570~1620cm ^-1 △ v magnitude of value, the graphite powder is 14~22cm ^-1.

"Graphite powder" As for the type of graphite powder, if the properties of the graphite are known, natural graphite having high crystallinity, artificial graphite having high crystallinity, or natural graphite or artificial graphite may be used. A heat-treated product, a re-heat-treated product of expanded graphite, or a high-purity purified product of these graphites is preferable. The types of graphite material powder include (1) natural graphite and artificial graphite having high crystallinity, and (2)
Re-heat-treated natural graphite, artificial graphite, or expanded graphite at 2000 ° C. or higher, and further graphitize an organic material capable of graphitizing graphite having performance equivalent to those of the specific examples (1) and (2). (3) coal tar pitch, coal-based heavy oil, atmospheric residual oil, petroleum-based heavy oil, aromatic hydrocarbon, nitrogen-containing cyclic compound, sulfur-containing cyclic compound, polyphenylene, polyvinyl chloride Baking of at least one organic substance selected from the group consisting of polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymer, polyphenylene sulfide, polyphenylene oxide, furfuryl alcohol resin, phenol-formaldehyde resin, and imide resin at 2500 ° C to 3200 ° C (4) The graphitizable organic substance of (3) above is converted to lithium, beryllium, U, magnesium, aluminum, silicon, potassium, calcium, titanium, vanadium, chromium, manganese, copper, zinc, nickel, platinum,
Palladium, cobalt, ruthenium, tin, lead, iron, germanium, zirconium, molybdenum, silver, barium,
In the presence of at least one kind of powder selected from tantalum, tungsten, rhenium, or a catalyst such as a thin film, the temperature is 400 ° C or more and 2500 ° C or less, more preferably 1000 ° C or more.
Graphitized by firing at 2000 ° C or lower can be selected. In addition, (5) the particle size of the graphite powder is measured and Raman spectroscopy is performed, and the numerical value is determined to be within a certain range that can be expected to have a high negative electrode capacity and a high withstand rate characteristic against high-speed charge and discharge. Even if it is not a graphite material to be taken, by re-baking those materials again at a temperature of 2000 to 3200 ° C., the particle size of the fired material and the value obtained from Raman spectroscopy will be within a certain range If possible, such a material can also be selected. (6) Further, the specific surface area of the graphite powder measured by the BET method and the Raman spectroscopic analysis are performed. Even if it is not a graphite material with a numerical value in the range, it can be obtained from the particle size, specific surface area and Raman spectroscopy of the fired material by re-baking it at a temperature of 2000 ° C to 3200 ° C again. Such a material can be selected as long as the value can be kept within a certain range.

"Method of Measuring Graphite Material" First, the particle size of graphite powder is measured. The particle size can be measured by a laser diffraction method, an electric resistance method, a direct particle size evaluation method by processing a photographic image of a CCD high-sensitivity camera, and the like. Has an average particle size of 4μ
Those having a size of m to 40 μm are selected. For the measurement of the specific surface area, a BET method by gas molecule adsorption, an organic molecule adsorption method, and an organic solvent adsorption method can be used, and the specific surface area of the graphite powder having the above particle size range when the BET method is 0.1 is used. ~ 25m ² /
Select more items in g. Furthermore, from this (specific surface area)
≤52 (particle size) Those satisfying the range of ^-0.6 have preferable properties as a negative electrode material of a lithium ion secondary battery. Among them, those having an average particle diameter of 4 μm to 30 μm and a specific surface area of 0.1 to ²⁰ m ² / g (specific surface area) ≦ 42
(Particle size) Those satisfying the range of ^-0.6 are more preferable.

The graphite material satisfying the above relationship between the average particle size and the specific surface area was subjected to Raman spectrum analysis using an argon ion laser beam having a wavelength of 5145 ° to obtain 1570-16
The intensity of the peak existing in the range of 20 cm ^-1 was IA, 1350 to
When the intensity of the peak existing in the range of 1370 cm ⁻¹ is defined as IB, the R value (= IB / IA), which is the ratio, is more than 0.001 and 0.2 or less, and the peak existing in the range of 1570 to 1620 cm ^−1. The magnitude of the Δν value, which is the half width of
It is preferable to use those having a ^{value of} m ^-1 or less as a negative graphite material for a lithium secondary battery. Those having an R value of 0.001 or more and 0.15 or less are more preferable, and those having an R value of 0.001 or more and 0.15 or less are preferred.
07 or less are more preferred. In the graphite material of the present invention, other physical property values are not necessarily required. However, if other physical property values defining the properties of other graphite materials are to be described together, the plane spacing of the (002) plane by X-ray diffraction can be used. d002 is preferably equal to or less than 3.38 °, and more preferably equal to or less than 3.36 °. Further, the crystallite size (Lc) in the c-axis direction is preferably 1000 ° or less.

Organic substance for producing "amorphous carbon-coated graphite-based carbonaceous substance" The organic substance which can be used in the present invention includes coal tar pitch from soft pitch to hard pitch, as organic substance which progresses carbonization in a liquid phase. Coal-based heavy oil such as dry-distilled liquefied oil, direct-current heavy oil such as atmospheric residual oil, vacuum residual oil, etc., and petroleum oil such as cracked heavy oil such as ethylene tar by-produced during thermal cracking of crude oil and naphtha Heavy oil. Further, aromatic hydrocarbons such as acenaphthylene, decacyclene, and anthracene; nitrogen-containing cyclic compounds such as phenazine and acridine; sulfur-containing cyclic compounds such as thiophene; pressurization of 30 MPa or more are required; alicyclic rings such as adamantane; Polyphenylene such as phenyl, polyvinyl chloride,
Examples include polymers such as polyvinyl alcohol.

As organic substances which undergo carbonization in the solid phase,
Examples include natural polymers such as cellulose and saccharides, thermoplastic resins such as polyphenylene sulfide, and polyphenylene oxide; and thermosetting resins such as furfuryl alcohol resin, phenol-formaldehyde resin, and imide resin. The above organic substance and the graphitic carbonaceous substance are mixed, and 4
00 to 2800 ° C, more preferably 700 to 1500 ° C
By firing and grinding, "amorphous carbon-coated graphite-based carbonaceous material" is obtained. The “amorphous carbon-coated graphite-based carbonaceous material” is preferably used as particles having an average particle size of 4 to 100 μm, more preferably 5 to 50 μm, by pulverization.

[0018] In the "amorphous carbon-coated graphite-based carbonaceous material" finally adjusted through steps such as firing and pulverization, the proportion of the graphitic carbonaceous material is 99 to 50% by weight, and the composition of the fired organic material is 1 to 5%.
0% by weight, and the graphitic carbonaceous material is 99% by weight.
７５75% by weight, and the composition of the baked organic material is 1-25% by weight
More preferably, the graphitic carbonaceous material is 90 to 99% by weight, and the composition of the burned material of the organic material is 1 to 99% by weight.
10% by weight. As the properties of the particles, the plane spacing d002 of the (002) plane by X-ray diffraction is 3.36 ° or more,
In a Raman spectrum analysis using an argon ion laser beam with a wavelength of 5145 ° having a peak of 3.39 ° or less, R = IB / IA (in the Raman spectrum,
Having a peak PA in the range of 1580 to 1620 cm ^-1 ,
Having a peak PB in the range of 1350-1370 cm ^-1 ,
PA intensity is IA, PB intensity is IB) is 0.15 or more and 1.0 or less, and the specific surface area measured by BET method is 13 m ² / g or less and 0.1 m ² / g or more. preferably 10 m ² / g or less, and most preferably, 4m ²
/ G or less are preferred.

When the composition of the baked product of the organic substance is above the above range,
The effect of the treatment with an acid or alkali, which is preferably performed as a subsequent step in order to reduce the potential and improve the rapid charge / discharge characteristics little and further improve the performance, may not be so remarkable in some cases. The above range is not the raw material charging ratio but the content at the final adjustment stage. Therefore, at the time of preparation, it is necessary to determine the compounding amount of the raw materials in consideration of the composition ratio at the final stage. A lithium ion secondary battery using the thus prepared “amorphous carbon-coated graphite-based carbonaceous material” as a negative electrode exhibits higher battery capacity, superior rate characteristics, and cycle characteristics as compared with a non-coated graphite negative electrode.

"Acid solution""Acidsolution" for treating the "amorphous carbon-coated graphite-based carbonaceous material" used in the present invention.
Any may be used as long as it does not exceed the gist of the patented invention, but hydrofluoric acid, hydrochloric acid, bromic acid, halogen-containing acids including iodic acid, sulfuric acid, nitric acid, or acetic acid, trichloroacetic acid, trifluoroacetic acid, Organic acids such as oxalic acid, mixed acids of these acids or solutions of these acids are preferred.
Further, a solution obtained by heating these solutions at a temperature equal to or lower than the boiling point of water is also preferable. Most preferred is hydrochloric acid. The preferred concentration range of these acids is at least 5N.

"Alkaline solution" The "alkaline solution" for treating the "amorphous carbon-coated graphite-based carbonaceous material" used in the present invention may be any one as long as it does not exceed the gist of the patented invention. Examples thereof include a solution of an alkali metal hydroxide such as sodium hydroxide and potassium hydroxide, ammonia, tetraalkylammonium, and urea, and a solution of an organic amine such as pyridine, quinoline, quinoxaline, and piperidine. Further, a solution obtained by heating these solutions at a temperature equal to or lower than the boiling point of water is more preferable. Most preferred is an aqueous solution of an alkali metal hydroxide. A preferable concentration range of these alkaline solutions is, for example, 5N or more in the case of an alkali metal hydroxide.

Next, a method for producing the negative electrode of the present invention will be described. The method for producing the negative electrode of the present invention is not particularly limited, as long as the `` amorphous carbon-coated graphite-based carbonaceous material '' obtained by the above method and the `` acid solution '' or `` alkaline solution '' as the treatment solution are used. A method can be adopted. For example, an organic material and a graphite material are mixed in a mixer having a heating means at a charge ratio such that the final composition is within the above range, deaeration / devolatilization treatment is performed, and 400 to 2000 ° C., 0.1 to 12 hours, Preferably, baking is performed at 700 to 1500 ° C. for 0.5 to 5 hours. This fired product is preferably 1 to 100 μm
m, more preferably in the range of 5 to 50 μm in average particle size to obtain “amorphous carbon-coated graphite-based carbonaceous material”. This is dispersed in an “acidic solution” or “alkaline solution”, preferably for 20 hours or more and 0.5 hours or less and 20 weeks or less.
After agitation, shaking, or superposition of ultrasonic waves at a temperature of 150 ° C., the “acid solution” or “alkaline solution” adhered to the powder is washed away with ultrapure water or distilled water. Thereafter, the powder is preferably dried at a temperature of 80 ° C. or more and 350 ° C. or less, more preferably 80 ° C. or more and 150 ° C. or less. do not have to.

That is, the negative electrode material for a lithium ion secondary battery of the present invention has an amorphous carbon phase already on the surface in a state before modification, and can be used as an “acid solution” or “alkaline solution”. After treatment and modification, simply wash with water and 80-1
Only drying at a temperature of up to 50 ° C. does not require heat treatment at a high temperature. The lithium ion secondary battery using the acid or alkali treated “amorphous carbon-coated graphite-based carbonaceous material” thus prepared as a negative electrode is much higher than when using the “amorphous carbon-coated graphite-based carbonaceous material” without treatment. Shows battery capacity, and further excellent rate and cycle characteristics.

Next, a method for producing the negative electrode of the present invention will be described. The method for producing an electrode of the present invention is not limited, and any conventionally known method can be adopted as long as the above-mentioned sorted graphite powder is used as a negative electrode. For example, the graphite powder as a negative electrode material, a binder, a solvent, etc. are added to the positive electrode material to form a slurry, and the slurry is applied and dried on a metal current collector substrate such as a copper foil. Electrodes. Further, the electrode material can be directly formed into an electrode shape by a method such as roll molding or compression molding.

Examples of the binder that can be used for the above purpose include:
Solvent-stable, polyethylene, polypropylene,
Polyethylene terephthalate, aromatic polyamide, resin-based polymers such as cellulose, styrene-butadiene rubber,
Rubber-like polymers such as isoprene rubber, butadiene rubber, and ethylene / propylene rubber, styrene / butadiene / styrene block copolymer, hydrogenated products thereof, styrene / ethylene / butadiene / styrene copolymer, and styrene / isoprene / styrene block copolymer Polymers, thermoplastic elastomeric polymers such as hydrogenated products thereof, syndiotactic 1,2-polybutadiene, ethylene / vinyl acetate copolymer, propylene / α-olefin (2 to 12 carbon atoms)
Soft resinous polymers such as copolymers, fluorine-based polymers such as polyvinylidene fluoride, polytetrafluoroethylene, polytetrafluoroethylene / ethylene copolymers, and alkali metal ions, particularly lithium ions Molecular compositions.

Examples of the polymer having ion conductivity include polyether polymer compounds such as polyethylene oxide and polypropylene oxide, crosslinked polymers of polyether compounds, polyepichlorohydrin, polyphosphazene, polysiloxane, polyvinylpyrrolidone, and the like. Polyvinylidene carbonate, a polymer compound such as polyacrylonitrile, a lithium salt, or a system in which an alkali metal salt mainly composed of lithium is combined, or propylene carbonate, ethylene carbonate, having a high dielectric constant such as γ-butyrolactone A system containing an organic compound can be used. The ionic conductivity of such an ion-conductive polymer composition at room temperature is preferably 10 ^-5 S / cm or more, more preferably 10 ^-3 S / cm or more.

The graphite powder used in the present invention and the above-mentioned binder can be mixed in various forms.
That is, a form in which both particles are mixed, a form in which a fibrous binder is entangled with the carbonaceous material particles, or a form in which a binder layer is attached to the surface of the carbonaceous material particles are exemplified. The mixing ratio of the carbonaceous material and the binder is preferably 0.1 to 30% by weight, more preferably 0.5 to 10% by weight, based on the carbonaceous material. If the binder is added in an amount larger than this, the internal resistance of the electrode increases, which is not preferable. If the amount is smaller than this, the binding property between the current collector and the carbonaceous powder is poor.

The secondary battery is constructed by combining the negative electrode plate thus prepared, the electrolyte solution described below, and the positive electrode plate with other battery components such as a separator, a gasket, a current collector, a sealing plate, and a cell case. . The batteries that can be created are not particularly limited, such as cylindrical, square, coin type,
Basically, a current collector and a negative electrode material are placed on a cell floor plate, an electrolytic solution and a separator are further placed thereon, and a positive electrode is placed on the cell floor plate so as to face the negative electrode.

Non-aqueous solvents that can be used for the electrolyte include:
Propylene carbonate, ethylene carbonate, chloroethylene carbonate, trifluoropropylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, γ-butyrolactone, tetrahydrofuran, tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, 1,3 -Organic solvents such as dioxolane can be used alone or in combination of two or more.
In addition, a gas such as CO _2, N ₂ O, CO, and SO ₂ , and polysulfide S _x ^2- , vinylene carbonate, and catechol carbonate, which form a good film capable of efficiently charging and discharging lithium ions on the negative electrode surface, are added. The agent may be added to the above-mentioned single or mixed solvent at an arbitrary ratio.

In these solvents, L of about 0.5 to 2.0 M is added.
iCLO_Four, LiPF₆, LiBF _Four, LiAsF₆,
Inorganic lithium salts such as LiCl and LiBr, LiCF_Three
SO _Three, LiN (SO_TwoCF_Three)_Two, LiN (SO_TwoC
_TwoF_Five)_Two, LiC (SO_TwoCF_Three)_Three, LiN (SO
_ThreeCF_Three)_TwoUsing organic lithium salt such as above as electrolyte
Dissolve in a solvent to form an electrolyte.

In addition, alkali metal such as lithium ion
Using a solid polymer electrolyte, which is a conductor of thione
Can also. Although the material of the positive electrode body is not particularly limited,
Absorbs alkali metal cations such as
It is preferably composed of a metal chalcogen compound that can be stored and released.
Good. Such metal chalcogen compounds include vana
Indium oxide, vanadium sulfide, molybdenum acid
, Molybdenum sulfide, manganese oxide, chromium
Oxides, titanium oxides, titanium sulfides and these
Composite oxides and composite sulfides. Preferably
Is Cr_ThreeO₈, V_TwoO_Five, V_FiveO₁₃, VO_Two, Cr_Two
O_Five, MnO_Two, TiO_Two, MoV_TwoO₈, TiS_TwoV
_TwoS_FiveMoS_Two, MoS_ThreeVS_Two, Cr_0.25V
_0.75S_Two, Cr_0.5V_0.5S_TwoAnd so on. Also, LiM
Y_Two(M is a transition metal such as Co and Ni. Y is a metal such as O and S.
Lucogen compound), LiM_TwoY_Four(M is Mn, Y is
O), WO_ThreeOxides such as CuS, Fe_0.25V
_0.75S_Two, Na_0.1CrS_TwoSuch as sulfide, NiPS_Three,
FePS_ThreeSuch as phosphorus, sulfur compounds, VSe_Two, NbSe
_ThreeAnd the like can also be used. these
Like the negative electrode material, mix with the binder and apply it on the current collector.
A positive electrode plate is used. The separator that holds the electrolyte is generally
It is a material with excellent liquid retention properties.
Using non-woven resin or porous film
The electrolyte is impregnated.

[0032]

Next, the present invention will be described in more detail by way of examples, which should not be construed as limiting the present invention. Among the evaluation contents of "Electrode material evaluation method", the particle size was measured by a laser diffraction type particle size evaluation apparatus, and the automatically calculated average particle size was used as an evaluation standard. The specific surface area was measured using the BET one-point method. The Raman spectrum was measured by JASCO Corporation NR-1800, and irradiated with an argon ion laser beam having a wavelength of 5145 ° at an intensity of 30 mW. Here 1570
Peak intensity in the range of ~ 1620 cm ^-1 and 13
The intensities of the peaks in the range of 50 to 1370 cm ^-1 were measured, and the R values obtained therefrom and the Δν value, which was the half width of the peaks in the range of 1570 to 1620 cm ^-1 , were determined.

(Example 1) Raman using an argon ion laser beam having a particle size of 22 to 23 µm, a (002) plane spacing of 3.36 by X-ray diffraction, and a wavelength of 5145 ° in a stainless steel tank having an inner volume of 20 liters. In the spectrum analysis, R = IB / IA (in the Raman spectrum, a peak PA was found in the range of 1580 to 1620 cm -1, a peak PB was found in the range of 1350 to 1370 cm -1, and the PA intensity was IA and PB. Strength is defined as IB) is 0.11; specific surface area measured by BET method is 4.
3.0 kg of artificial graphite powder of 7 m ² / g was mixed with 1.0 kg of ethylene heavy end tar (EHE; manufactured by Mitsubishi Chemical Corporation) obtained during naphtha decomposition. The resulting slurry-like mixture was devolatilized by heat treatment at 700 ° C. for 1 hour in a batch heating furnace under an inert atmosphere. Next, the temperature was raised to 1300 ° C. and maintained for 2 hours. This is crushed and the particle size is reduced to 20 to 2 by a vibrating sieve.
It was adjusted to 5 μm. This was put into 12.5 L of 5N hydrochloric acid, and stirred for 3 days. The post-treated acid solution was removed by filtration, and the remaining precipitate was washed with pure water. This process was repeated until the pH of the washing water in which the precipitate was in a dispersed state returned to neutral. The obtained precipitate was heated and dried at 120 ° C. to obtain a sample powder.

A solution of polyvinylidene fluoride (PVdF) in dimethylacetamide of 10% by weight in terms of solid content was added to 5 g of this electrode material sample to obtain a slurry. This slurry was applied on a copper foil and pre-dried at 80 ° C. After further pressure bonding, it was punched into a disk having a diameter of 20 mm, and dried under reduced pressure at 110 ° C. to form an electrode. The obtained electrode was sandwiched with a separator made of polypropylene impregnated with an electrolytic solution, and a coin-shaped cell facing the lithium metal electrode was prepared, and a charge / discharge test was performed.
As the electrolytic solution, a solution in which lithium perchlorate was dissolved at a ratio of 1.0 mol / L in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1 was used.

In the standard charge / discharge test, the current density was 0.16 mA.
/ Cm ² until the potential difference between the electrodes becomes 0 V,
A current density of 0.33 mA / cm ² and a potential difference between the electrodes of 1.5 V
Dedoping was performed until. The capacity value was evaluated by performing a charge / discharge test on each of three coin-type cells, and averaging the doping capacity, the undoping capacity, the initial charge / discharge efficiency, and the like in the first cycle and the fourth cycle. Table 1 shows the doping capacity, undoping capacity, and initial charge / discharge efficiency of the first cycle and the fourth cycle.

Comparative Example 1 The same operation as in Example 1 was performed except that the artificial graphite powder used in Example 1 was used as an electrode material without acid treatment or the like. Table 1 shows the doping capacity, undoping capacity, and initial charge / discharge efficiency of the first cycle and the fourth cycle.

Comparative Example 2 The artificial graphite powder used in Example 1 was put into 12.5 L of 5N hydrochloric acid, stirred for 3 days, the treated acid solution was removed by filtration, and the remaining precipitate was removed. Washed with pure water. This process was repeated until the pH of the washing water in which the precipitate was in a dispersed state returned to neutral. The obtained precipitate was heated and dried at 120 ° C. to obtain a sample powder. Except for this, the same operations as in Example 1 were performed for the method of preparing the electrode plate, the separator, the electrolytic solution, and the charge / discharge test method.
Table 1 shows the doping capacity, undoping capacity, and initial charge / discharge efficiency of the first cycle and the fourth cycle.

Comparative Example 3 Ethylene heavy end tar (EHE; manufactured by Mitsubishi Chemical Corporation) used in Example 1
0 kg was devolatilized by keeping it at 700 ° C. in an inert atmosphere in a batch heating furnace and heat-treating for 1 hour. next,
The temperature was raised to 1300 ° C. and held for 2 hours. This was pulverized, and the particle size was adjusted to 20 to 25 μm by a vibrating sieve. This was put into 12.5 L of 5N hydrochloric acid, and stirred for 3 days. The post-treated acid solution was removed by filtration, and the remaining precipitate was washed with pure water. This process was repeated until the pH of the washing water in which the precipitate was in a dispersed state returned to neutral. The obtained precipitate was heated and dried at 120 ° C. to obtain a sample powder. Except for this, the same operations as in Example 1 were performed for the method of preparing the electrode plate, the separator, the electrolytic solution, and the charge / discharge test method. Table 1 shows the doping capacity, the undoping capacity, and the initial charge / discharge efficiency of the first cycle and the fourth cycle.

(Comparative Example 4) Ethylene heavy end tar (EHE; manufactured by Mitsubishi Chemical Corporation) used in Example 1
0kg in a batch heating furnace under an inert atmosphere at 1300 ° C
Devolatilized by heat treatment for 1 hour. This was pulverized, and the particle size was adjusted to 20 to 25 μm by a vibrating sieve. Other electrode making methods, separators, electrolytes,
The charge / discharge test method was the same as in Example 1. Table 1 shows the doping capacity, the undoping capacity, and the initial charge / discharge efficiency of the first cycle and the fourth cycle.

Comparative Example 5 Ethylene Heavy End Tar (EHE; manufactured by Mitsubishi Chemical Corporation) used in Example 1
0 kg is kept in an inert atmosphere at 700 ° C. in a batch heating furnace, and heat-treated for 1 hour, except for devolatilization.
The same operation as in Comparative Example 4 was performed. Table 1 shows the doping capacity, the undoping capacity, and the initial charge / discharge efficiency of the first cycle and the fourth cycle.

[0041]

[Table 1]

(Examples 2 to 5) Negative electrodes were prepared in the same manner as in Example 1 except that the treatment solutions shown in Table 2 were used instead of the 5N hydrochloric acid in Example 1. A coin battery similar to that of Example 1 was produced using the produced negative electrode, and a reference charge / discharge test and a rate resistance test for high-speed charge / discharge were performed. The withstand rate test for high-speed charge and discharge
Doping was performed at a current density of 0.16 mA / cm ² until the potential difference between the electrodes became 0 V, and a current density of 2.8 mA / c was applied.
Dedoping was performed at m ² and a current density of 5.6 mA / cm ² until the potential difference between the electrodes became 1.5 V. The capacity value was obtained by conducting a charge / discharge test on each of three coin-type cells, and determining the ratio of the doping capacity and the undoping capacity in the first cycle to the initial efficiency, the doping capacity in the fourth cycle, the undoping capacity, and 2 Table 2 shows the results of averaging the undoped capacities at 8.8 mA / cm ² and 5.6 mA / cm ² together with the results of the negative electrode obtained in Example 1.

Comparative Example 6 Table 2 shows the results of the same charge / discharge test as in Examples 2 to 5 except that the acid-treated artificial graphite powder prepared in Comparative Example 2 was used as a negative electrode. . Comparative Example 7 Table 2 shows the results of the same charge / discharge test as in Examples 2 to 5 except that the acid-treated carbon powder prepared in Comparative Example 3 was used as the negative electrode. Comparative Example 8 Table 2 shows the results of the same charge / discharge test as in Examples 2 to 5 except that the carbon powder prepared in Comparative Example 4 was used as the negative electrode.

[0044]

[Table 2]

[0045]

From the above results, the negative electrode for a lithium ion secondary battery of the present invention exhibits a capacity not less than the theoretical capacity of the graphite in a particularly preferred embodiment from the vicinity of the theoretical capacity of graphite, and the potential of the graphite is higher than the theoretical capacity. , Li / Li + to give a lithium undoping potential of 0.5 V or less,
It is excellent in dedoping characteristics from the first time and can maintain a high capacity even at the time of high-speed charge and discharge, and has an excellent effect.

Claims (9)

[Claims] An amorphous carbon-coated graphite-based carbonaceous material obtained by coating the surface of a graphitic carbonaceous material with an organic material capable of being carbonized, calcining, and pulverizing the material to obtain a carbonaceous material treated with an acidic or alkaline solution. A lithium ion secondary battery used as a negative electrode. 2. The method according to claim 1, wherein the acidic solution is at least one acidic solution selected from hydrofluoric acid, hydrochloric acid, bromic acid, iodic acid, sulfuric acid, nitric acid, acetic acid, trichloroacetic acid, trifluoroacetic acid and oxalic acid. Item 7. The lithium ion secondary battery according to Item 1. 3. An alkaline solution comprising: an alkali metal hydroxide, ammonia, tetraalkylammonium, urea,
The lithium ion secondary battery according to claim 1, wherein the solution is a solution containing at least one compound selected from pyridine, quinoline, quinoxaline, and piperidine. 4. The graphitic carbonaceous material has a specific surface area measured by a BET method of y (m 2 / g) and a powder particle size (μm).
Is x, 4 ≦ x ≦ 40, 0.1 ≦ y ≦ 25, and y ≦ ax ^b ,
4. A graphite powder in a region represented by (where a = 52, b = -0.6).
The lithium ion secondary battery according to any one of the above. 5. The graphitic carbonaceous material further has a wavelength of 5145.
In Raman spectrum analysis using an argon ion laser beam of Å, the intensity of a peak existing in the range of 1570~1620cm ^-1 IA, 1350~1370cm ^-1
When the intensity of the peak existing in the range is defined as IB, the R value (= IB / IA), which is the ratio, is 0.001 or more and 0.
2, and the magnitude of the Δv value, which is the half width of the peak existing at 1570 to 1620 cm ⁻¹ , is 14 to 2
5. The lithium ion secondary battery according to claim 4, wherein the lithium ion secondary battery is 2 cm ^-1 . 6. The organic matter capable of being carbonized includes coal tar pitch, coal-based heavy oil, petroleum-based heavy oil, aromatic hydrocarbon,
At least one selected from nitrogen-containing cyclic compounds, sulfur-containing cyclic compounds, polyphenylene, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, natural polymers, polyphenylene sulfide, polyphenylene oxide, furfuryl alcohol resin, phenol-formaldehyde resin, and imide resin The lithium ion secondary battery according to claim 1, wherein the lithium ion secondary battery is an organic material. 7. The lithium ion secondary battery according to claim 1, wherein a firing temperature is 450 to 2000 ° C. 8. The lithium ion secondary battery according to claim 1, wherein the treatment temperature with an acidic or alkaline solution is 20 to 150 ° C. 9. After treatment with an acidic or alkaline solution,
The lithium ion secondary battery according to any one of claims 1 to 8, wherein washing and drying are performed at 60 to 350 ° C.