JP2005149792A - Carbonaceous negative electrode material for lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbonaceous negative electrode material for a lithium secondary battery, which has good liquid absorbing property even in a case of high density. <P>SOLUTION: The carbonaceous negative electrode material whose disappearing period at wettability test is 320 second or less is obtained by applying a weak, namely, slight dry type ozone treatment to a carbonaceous material of an ordinary-use lithium secondary battery. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a carbonaceous negative electrode material for a lithium secondary battery. Since the negative electrode made using the carbonaceous negative electrode material according to the present invention is excellent in the liquid absorption characteristics of the electrolytic solution, it can improve the productivity of the lithium secondary battery and is excellent in the output characteristics. Give a secondary battery.

In recent years, high-performance secondary batteries have been demanded as power sources for various devices. Lithium secondary batteries are attracting attention as satisfying this requirement, and they are practically used in a wide range of applications, from the power sources of so-called consumer devices such as mobile phones and laptop computers to in-vehicle power sources for driving automobiles. Is becoming possible.
As a negative electrode material for a lithium secondary battery, graphite such as natural graphite, artificial graphite, graphitized mesophase pitch, and graphitized carbon fiber is used because of its high capacity and excellent flatness of discharge potential. Quality carbon materials are mainly used. Amorphous carbon materials are also used because they are relatively inert to propylene carbonate or the like commonly used as a solvent for electrolytic solutions. Various methods for improving the characteristics of these carbon materials have also been proposed. For example, it has been proposed that the surface of a graphitic carbon material is coated with an amorphous carbon material to obtain a carbon material having both characteristics. The carbon material is subjected to a surface treatment with a fluorinating agent, ozone or nitric acid, and the sum of the amounts of carbon monoxide and carbon dioxide desorbed when the temperature is raised from 25 ° C. to 800 ° C. is 5 to 100 μmol / g. It has also been proposed to use a carbon material as a negative electrode material that can maintain a high capacity even during charge and discharge at a high current density (see Patent Document 1).

In addition to the improvement of the negative electrode material, it has been studied to increase the capacity of the lithium secondary battery by increasing the density of the negative electrode active material layer. However, when the density of the negative electrode active material layer is increased, so-called liquid absorption characteristics in which the electrolytic solution penetrates into the negative electrode active material layer is deteriorated. The decrease in the liquid absorption characteristics leads to an increase in the time required for injecting the electrolyte into the battery in the battery production process, thereby reducing the productivity. Also, the output characteristics of the battery are likely to deteriorate.
JP 2000-306582 A

  The present invention seeks to provide a carbonaceous negative electrode material that provides a negative electrode active material layer that exhibits good liquid absorption characteristics even when densified.

The present inventors have found that a carbonaceous material having a droplet disappearance time of 320 seconds or less in the following wettability test gives a negative electrode active material layer with good liquid absorption characteristics even when the density is increased. Completed the invention. A carbonaceous material satisfying this condition can be obtained by subjecting a carbonaceous material conventionally used as a negative electrode material to a weak dry ozone treatment in a gas phase.
<Wettability test>
(1) Preparation of slurry;
Dissolve 1 g of powdered sodium carboxymethylcellulose (etherification degree: 0.6 to 0.8, viscosity of 100 to 1000 mPa.s at 30 ° C. in ¹ wt% aqueous solution at a shear rate of 40 S ⁻¹ ) in 100 mL of distilled water. . 100 g of the obtained aqueous solution and 100 g of the carbonaceous negative electrode material are mixed and stirred for 10 hours to be sufficiently dispersed. Next, 2 g of an aqueous emulsion (solid content concentration 50% by weight) of styrene butadiene rubber (Tg = −10 to 0 ° C.) is added and stirred to obtain a uniform slurry. All operations are performed at 25 ° C.
(2) Preparation of test piece;
On the copper foil having a thickness of 20 μm, the slurry prepared above is applied by a doctor blade method so that the solid content becomes (13 ± 0.2) mg / cm ² to form a coating film. This is 60-8
Heat to 0 ° C. to dry thoroughly to remove moisture. From this, a 12.5 mmφ disc is punched with a punch, and a test piece is formed by pressing with a press machine so that the film density is (1.5 to 1.6) g / cm ³ .
(3) Measurement of droplet disappearance time;
A solution prepared by dissolving 180 g of lithium hexafluorophosphate (LiPF ₆ ) in a mixed solution consisting of 300 mL of ethylene carbonate and 700 mL of dimethyl carbonate at the center of the test piece prepared above at 25 ° C. in an argon atmosphere was 5 mm. From the height, 1 μL is dropped with a microsyringe. The time from the end of dropping until the solution is absorbed inside the test piece and apparently disappears from the surface is measured, and this measured value is taken as the droplet disappearance time.

By using the carbonaceous negative electrode material according to the present invention, an active material layer having excellent electrolyte permeability and low negative electrode resistance can be formed even if the active material layer has a high density of 1.5 g / cm ³ or more. Can do. Therefore, the productivity of the battery can be improved by using the negative electrode having this active material layer. Further, since the obtained lithium secondary battery has high output, high long-term reliability, and stable quality, it can be suitably used as various power sources from consumer use to in-vehicle use as described above.

  The carbonaceous negative electrode material according to the present invention is characterized in that a droplet disappearance time in a wettability test described later is 320 seconds or less. More preferably, the droplet disappearance time is 280 seconds or less, particularly 200 seconds or less. This can be produced by subjecting various carbonaceous materials conventionally proposed as negative electrode materials for lithium secondary batteries to weak dry ozone treatment. According to the knowledge of the present inventors, this weak dry ozone treatment improves the wettability of the carbonaceous material to the electrolyte, but other physical properties such as average particle size, particle size distribution, specific surface area, apparent density, crystal The degree of conversion and other characteristics as crystals are virtually unchanged. Accordingly, the properties of the carbonaceous material subjected to this treatment as the negative electrode material substantially retain the properties of the carbonaceous material subjected to this treatment as it is, except for wettability and related properties.

Typical carbonaceous materials to be subjected to dry ozone treatment are graphite materials such as natural graphite, artificial graphite, mesophase pitch graphite, mesocarbon microbead graphite, and graphitized carbon fiber. These can be used as they are, or can be used after purification by heating or other various methods. The interplanar spacing (d ₀₀₂ ) of the graphitic carbon material is 0.348 nm
Or less, more preferably 0.338 nm or less, and particularly preferably 0.337 nm or less. The crystallite thickness (Lc) in the C-axis direction is preferably 20 nm or more,
More preferably, it is more than nm, especially more than 90 nm.

As is well known, C ₆ , which is an intercalation compound formed by storing lithium ions between graphite layers.
The theoretical capacity value per gram of graphite based on Li is 372 mAh, but the graphitic carbon material used in the present invention is a half-cell using a lithium metal counter electrode with a charge / discharge rate of 0.2 mA / cm ^2. The capacity when measured is preferably 320 mAhr / g or more. More preferably, the capacity is 340 mAhr / g or more, particularly 350 mAhr / g or more.

The graphitic carbon material has a peak intensity of 1580 cm ^{−1 to} 1620 cm ⁻¹ as I _A and a half width of Δν in a Raman spectrum using an argon ion laser beam having a wavelength of 514.3 nm, and 1350 cm ^{−1 to} 1370 cm. ^When the peak intensity at ⁻¹ is I _B , the peak intensity ratio R (= I _B / I _A ) is preferably 0.7 or less. More preferably, the peak intensity ratio R is 0.6 or less, particularly 0.4 or less. However, the peak intensity ratio R is preferably not less than 0.2. The half-value width Δν is preferably 40 cm ⁻¹ or less, and more preferably 36 cm ⁻¹ or less. In general, the half-value width Δν is preferably as small as possible, but is usually 20 cm ⁻¹ or more.

Further, instead of using these graphitic carbon materials as they are, it is also preferable to use a composite carbonaceous material in which the surface of these graphitic carbon materials is coated with an amorphous carbon material. Such composite carbonaceous materials are known, and the proportion of the amorphous carbon material in the whole is 0.1 to 50% by weight, preferably 2 to 10% by weight. In addition, the interplanar spacing (d ₀₀₂ ) and the crystallite thickness (L _c ) of the graphitic carbon material serving as the central core of the composite carbonaceous material are preferably the same as those of the graphitic carbon material described above. The average particle diameter (D ₅₀ ) measured by the laser diffraction particle size distribution meter is preferably 30 μm or less, particularly preferably 25 μm or less. Most preferably, D ₅₀ is 20 μm or less, more preferably 18 μm or less, but usually it is not necessary to make it smaller than 10 μm. Is preferably a BET specific surface area is less than ^{20m 2 / g, 15m 2 /} g or less, particularly 12m ² /
It is most preferable if it is g or less. The lower limit is preferably 1 m ² / g or more, particularly 4 m ² / g or more.

The composite carbonaceous material can be produced, for example, by the following method.
(1) A graphite carbon material and an amorphous carbon material are mixed and heated.
(2) A graphite carbon material and a carbonaceous precursor are mixed and heated.
(3) A graphite carbon material, an amorphous carbon material, and a carbonaceous precursor are mixed and heated.
The obtained composite carbonaceous material is pulverized and classified to a particle size required for the negative electrode material. Carbon materials used for composites include carbon materials used as negative electrode materials, such as coal-based or petroleum-based heavy oils such as pitch, thermosetting resins such as phenol / formaldehyde resins, and thermoplastic resins such as polyvinyl chloride. Any of those known to be used as precursors can be used. Moreover, the particle size of the amorphous carbon material is usually 1/10 or less of the particle size of the graphitic carbon material which is the central core. Preferred as the amorphous carbon material is one having an interplanar spacing (d ₀₀₂ ) of 0.338 nm or more and a crystallite thickness (Lc) of less than 10 nm. d ₀₀₂ is in 0.340~0.355nm, Lc is more preferably equal to 7nm or less. Lc is preferably as small as possible, and more preferably 5 nm or less, particularly 3 nm or less.

The mixing of the graphitic carbon material with the amorphous carbon material or the carbonaceous precursor can be performed using any known mixing device. The obtained mixture may be heated as it is, but it is also preferable to perform a treatment such as pulverization or classification before heating. The heating condition of the mixture varies depending on the material used for the composite, but is usually 700 ° C. or higher, preferably 900 ° C. or higher. The upper limit is a temperature at which a structure exceeding the crystal structure of the graphite material of the central core is not generated, and is usually 2800 ° C. or less, preferably 1500 ° C. or less. Therefore, the obtained composite carbonaceous material has the peak intensity ratio R, the half-value width Δν, and the interplanar spacing (d ₂₀₀ ) in the Raman spectrum using the argon ion laser beam described above, that of the graphite material used for the composite. The crystallite thickness (Lc) is smaller than that of the graphitic carbon material. The peak intensity ratio R of the composite carbonaceous material is usually 0.01 to 1.0, but is preferably 0.05 to 0.8, particularly preferably 0.2 to 0.7. The most preferable value of the intensity ratio R is 0.3 to 0.5.

The carbonaceous material to be subjected to the dry ozone treatment is not limited to the above-mentioned graphitic carbon material and composite carbonaceous material, and for example, as an anode material such as an amorphous carbon material obtained by various manufacturing methods. Any carbonaceous material known to be usable can be used.
In addition to the conventional carbonaceous materials as described above, carbon whiskers manufactured by vapor phase pyrolysis of carbon monoxide and hydrocarbons in the presence of a metal catalyst such as iron, nickel, cobalt, vanadium, molybdenum, etc. It can also be used. Regardless of the origin of the carbonaceous material, the carbonaceous material subjected to the dry ozone treatment in the present invention preferably has an intensity ratio R in the Raman spectrum using the aforementioned argon ion laser light of 1.1 or less. More preferably, the intensity ratio R is 0.6 or less, more preferably 0.4 or less. Further, the lower limit is 0.01 or more, usually 0.1 or more, but particularly preferably 0.2 or more. The half-width Δν is usually 60cm ^-1 or less but preferably 45cm ^-1 or less. It is more preferable that the value of Δν is 30 cm ⁻¹ or less, particularly 27 cm ⁻¹ or less. The smaller the value of Δν, the better, but it is usually 14 cm ⁻¹ or more.

  The average particle size of the carbonaceous material is preferably 3 μm or more, most preferably 6 μm or more, and most preferably 8 μm or more, as measured by a laser diffraction particle size distribution meter. If the average particle size is too small, it is difficult to form a high-density active material layer. On the other hand, if the average particle size is too large, it may protrude from the surface of the active material layer, penetrate the separator, and cause a short circuit. Therefore, the upper limit is preferably 30 μm or less, particularly 26 μm or less. Moreover, it is preferable that the particle diameter is substantially 50 μm or more, particularly 100 μm or more. In general, it is preferable to use those having an average particle diameter of 20 to 26 μm for consumer use such as a mobile phone and an average particle diameter of about 8 to 13 μm for in-vehicle use.

In general, the specific surface area of the carbonaceous material is preferably 0.5 to ²⁰ m ² / g. The upper limit is 10
It is more preferable if it is m ² / g or less, particularly 5 m ² / g or less. The lower limit depends on the characteristics required of the battery, and may be 0.5 m ² / g or more for applications that emphasize storage characteristics such as standby, but consumer electronics such as home appliances that require both current discharge and storage characteristics. 1.0m ² / g or more in use,
It is preferably 2.0 m ² / g or more for in-vehicle applications that require a large current discharge.

  The average circularity of the carbonaceous material is preferably 0.85 or more, particularly preferably 0.89 or more. If a carbonaceous material having a small average circularity is used, it is generally difficult to produce a negative electrode having excellent rapid charge / discharge characteristics. On the other hand, if the average circularity is too large, the adhesive strength with the binder is reduced during the production of the negative electrode, so that the strength of the negative electrode is weakened and the long-term charge / discharge cycle characteristics of the battery are deteriorated. Therefore, the upper limit of the average circularity is preferably 0.99 or less, particularly 0.97 or less. The circularity is an index defined as a ratio in which the circumference of a perfect circle (equivalent circle) having the same projected area as the particle is a numerator and the circumference of the particle is a denominator. Therefore, when the projected image of the particle is a perfect circle, the circularity is 1, and the circularity is smaller as the particle is longer or more uneven. The average circularity in this specification is a value calculated as an arithmetic average by imaging the shape of 9000 to 11000 particles with a flow type particle image analyzer and obtaining the circularity. In measuring the circularity, the carbon material to be measured and a surfactant (polyoxyethylene (20) sorbitan monolaurate) are added to ion exchange water as a dispersion medium and stirred, and ultrasonic dispersion is performed for 30 minutes. A sample is used.

  A carbonaceous material having a large average circularity can be obtained by subjecting the carbonaceous material to surface pulverization as is well known. For example, using a crusher equipped with a high-speed rotating rotor with a large number of blades installed inside the casing, mechanical treatment such as impact compression, friction, shearing, etc. is applied to the carbonaceous material to perform surface treatment while crushing. Just do it. The peripheral speed of the rotor is preferably 30 to 100 m / sec, particularly 50 to 100 m / sec. The classification after pulverization is generally performed using an airflow classifier such as a forced vortex centrifugal classifier such as a micron separator or turboplex, or an inertia classifier such as an elbow jet. A machine can also be used.

The carbonaceous negative electrode material having a droplet disappearance time of 320 seconds or less in the wettability test according to the present invention can be obtained by subjecting the above-mentioned carbonaceous material to a weak dry ozone treatment. The dry ozone treatment is preferably performed so that the droplet disappearance time is 280 seconds or less, particularly 200 seconds or less. Although it is considered that the productivity of the battery is improved as the droplet disappearance time is shorter, it is not necessary to make the time shorter as it falls below 50 seconds. In general, it is considered sufficient that the droplet disappearance time can be shortened to about 100 seconds.

In dry ozone treatment, a carbonaceous material is charged into a treatment vessel, and an ozone-containing gas is introduced into the treatment vessel at room temperature and held for a predetermined time. As the ozone-containing gas, one obtained from an ozone generator may be used as it is, or it may be diluted with an inert gas such as nitrogen or helium. The ozone concentration in the ozone-containing gas is preferably 0.01 to 5% by volume, particularly preferably 1 to 3% by volume. When a mixed gas of ozone-oxygen-inert gas is used, the oxygen concentration is preferably 1 to 30% by volume. The ozone treatment can be performed at any pressure from reduced pressure to increased pressure, but is usually performed at 1 × 10 ⁻⁵ Pa to normal pressure. The time required for the treatment is generally from 0.1 second to 180 minutes, but varies depending on the ozone concentration and pressure. When the ozone treatment is performed at normal pressure or under pressure, the treatment is usually performed for 1 minute to 180 minutes, but in many cases, the treatment for 1 minute to 30 minutes is sufficient. When the treatment is performed under reduced pressure, the treatment is usually carried out for 1 second to 120 minutes. In many cases, the treatment time is 60 minutes or less, and 30 minutes or less, particularly 10 minutes or less is often sufficient. . When carbonaceous material is stored in a processing vessel and the container is decompressed and ozone-containing gas is supplied, ozone spreads all the way to the pores inside the carbonaceous material. Since a quality material can be obtained, it is preferable. The treatment temperature may be room temperature, and is usually 80 ° C. or less even in the case of treatment at elevated temperature, and in many cases 50 ° C. or less. In addition, 0.01 to 10 g of ozone is sufficient per 1 kg of the carbon material.

  The reason why the liquid absorption property of the carbon material is improved by such mild ozone treatment is unknown. However, in the strong ozone treatment as described in the above-mentioned Patent Document 1, as shown in the comparative example described later, since the excellent liquid absorption characteristics are not expressed, the mild ozone treatment as described above is performed. When this is done, it is considered that a small amount of functional groups are introduced only on the surface of the carbonaceous material without substantially changing the carbonaceous material. In addition, by this ozone treatment, the crystallinity, particle size, surface area, etc. of the carbonaceous material do not change apparently as described above. Therefore, the characteristics of the carbonaceous material that has been subjected to the ozone treatment are the same as those before being subjected to the ozone treatment except those related to the liquid absorption characteristics.

To what extent the liquid absorption characteristics of the carbon material have been improved by the above-described ozone treatment can be confirmed as follows.
1 g of powdered sodium carboxymethylcellulose (viscosity 100-1000 mPa · s under the conditions of etherification degree 0.6-0.8, 1 wt% aqueous solution 30 ° C., shear rate 40S ⁻¹ ) in 100 mL of distilled water at room temperature Dissolve. 100 g of this aqueous solution was added with 100 g of ozone-treated carbon material, and stirred at room temperature for 10 hours to sufficiently disperse, and then an aqueous emulsion (solid content concentration) of styrene-butadiene rubber (Tg = −10 to 0 ° C.). 50 g) 2 g is added and stirred to make a uniform slurry.

This slurry is applied onto a copper foil having a thickness of 20 μm by a doctor blade method so that the solid content becomes (13 ± 0.2) mg / cm ² . This is heated to 60-80 and dried sufficiently to remove moisture. From this, a disk having a diameter of 12.5 mm is punched with a punch, and pressed with a press machine to obtain a test piece having a film density of (1.5 to 1.6) g / cm ³ .

In an argon atmosphere at 25 ° C., 1 μL of the test solution was dropped from the position of 5 mm height into the center of the test piece using a microsyringe, and the test solution was absorbed into the test piece from the end of dropping, and apparently The time until disappearance from the upper surface is measured. Incidentally, use of which is dissolved a mixture solution in lithium hexafluorophosphate (LiPF ₆₎ 180 g of ethylene carbonate 300mL and dimethyl carbonate 700mL as a test piece.

The production of the negative electrode using the carbonaceous negative electrode material according to the present invention can be performed by a conventional method. Usually, the negative electrode material and an organic substance having a binding and thickening effect are dispersed in an appropriate solvent to form a slurry, which is applied onto a current collector such as a metal foil. After drying this, the active material layer is pressed so as to have a predetermined thickness (density) to obtain a negative electrode.
Any negative electrode current collector can be used as long as it is an electronic conductor that does not cause a chemical change in the battery. Examples of current collector materials include metals such as stainless steel, nickel, copper, and titanium, alloys thereof, carbon, and conductive resins, as well as the surface of copper and stainless steel covered with carbon, nickel, or titanium. In particular, copper or a copper alloy is preferable. In addition, the surface of these materials can be oxidized and used. The current collector surface preferably has irregularities. Examples of the shape of the current collector include films, sheets, nets, punched materials, lath bodies, porous bodies, foamed bodies, and molded bodies of fiber groups, in addition to foils. Although thickness is arbitrary, the thing of 1-500 micrometers is preferable.

Any organic material that is commonly used can be used as the organic material having a binding and thickening effect, and usually a thermoplastic resin or a thermosetting resin is used.
Examples of the binder include celluloses such as carboxymethyl cellulose, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetra Fluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer , Ethylene-tetrafluoroethylene copolymer (ETFE resin), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, pro Lene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoro-methyl vinyl ether-tetrafluoroethylene Examples thereof include copolymers, copolymers of ethylene and acrylic acid, methacrylic acid or esters thereof, and salts of these copolymers. Of these, styrene-butadiene rubber, polyvinylidene fluoride, a copolymer of ethylene and acrylic acid, methacrylic acid, or an ester thereof, or a salt of these copolymers is preferable. These can be used alone or in a mixture.

  If necessary, the negative electrode active material layer may contain a negative electrode conductive agent. As the negative electrode conductive agent, any material can be used as long as it is an electron conductive material and does not impair the uniformity of the active material layer. Examples of the negative electrode conductive agent include graphites such as natural graphite, artificial graphite, and expanded graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, carbon fiber, and metal. Examples thereof include conductive fibers such as fibers, metal powders such as copper and nickel, and organic conductive materials such as polyphenylene derivatives. Among these, artificial graphite, acetylene black, or carbon fiber is preferable. These negative electrode conductive agents can be used alone or as a mixture thereof. The average particle diameter of the conductive agent is preferably 3 μm or less, particularly preferably 1 μm or less. Even if the average particle diameter is as small as several nm, there is no problem in the performance of the electrode plate.

  The negative electrode active material layer can further contain additives such as a filler, a dispersant, and an ionic conductor. Any filler can be used as long as it is a fibrous material that does not cause a chemical change in the constructed battery, and examples thereof include olefin polymers such as polypropylene and polyethylene, and fibers such as glass and carbon. . The inclusion of a conductive agent and an additive is preferable because it causes fine disturbance of the particle arrangement in the electrode and improves the electrolyte solution wettability.

Examples of the organic solvent used for the preparation of the slurry include cyclic amides such as N-methylpyrrolidone; linear amides such as N, N-dimethylformamide and N, N-dimethylacetamide; aromatics such as anisole, toluene and xylene Group hydrocarbons and their derivatives; alcohols such as ethanol, butanol, cyclohexanol and the like, among others, cyclic amides such as N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, etc. Linear amides are preferred. In preparing the slurry, a mixed solvent of water and a water-soluble organic solvent such as cyclic amides or alcohols may be used. The water-soluble organic solvent in the mixed solvent is preferably within 30% by weight.

The concentration of the negative electrode active material in the slurry is usually 30% by weight or more and 70% by weight or less, but preferably 40 to 55% by weight. If the concentration of the active material is low, the active material tends to settle during storage of the slurry. Conversely, if the concentration of the active material is high, the active material tends to aggregate.
The concentration of the binder in the slurry is usually 0.1% by weight or more and 30% by weight or less, but preferably 0.5 to 10% by weight. When the concentration of the binder is low, the mechanical strength of the negative electrode is reduced. Conversely, when the concentration of the binder is high, the internal resistance of the battery increases.

Further, the concentration of the negative electrode conductive agent in the slurry is preferably 0 to 5% by weight, and the concentration of additives such as fillers is preferably 0 to 30% by weight.
The negative electrode current collector coated with the slurry is preferably dried at a temperature lower than the boiling point of the solvent used in the slurry. If the drying temperature is too high, the active material layer may become non-uniform and the wettability of the electrolytic solution may be deteriorated. The drying is preferably performed at a temperature of 50 ° C. or higher, particularly 60 ° C. or higher, and 20 ° C. or lower than the boiling point of the solvent used, and particularly 30 ° C. or lower.

The thickness of the active material layer is usually 10 μm or more and 200 μm or less. When the active material layer is thin, short-circuiting easily occurs, so that the thickness is preferably 15 μm or more. On the other hand, if the thickness is too thick, the durability of the battery may be deteriorated.
The density of the active material layer is usually 0.8 g / cm ³ or more and 2.0 g / cm ³ or less. If the density is low, the durability of the battery deteriorates, so 1.2 g / cm ³ or more, particularly 1.4 g / cm ³ or more is preferable. The negative electrode using the carbonaceous negative electrode material according to the present invention is characterized by good wettability even if the active material layer has a high density, but if the density is too high, the battery capacity may decrease. The density of the active material layer is preferably 1.8 g / cm ³ or less, particularly preferably 1.7 g / cm ³ or less.

In order to obtain the above-described thickness and density of the negative electrode active material layer, for example, using a press machine that applies a surface pressure load such as a tablet molding machine, a press machine that applies a linear pressure load such as a roll press machine, etc. What is necessary is just to pressurize.
A lithium secondary battery can be produced by combining the above-described negative electrode with a positive electrode capable of inserting and extracting ordinary lithium and an electrolyte solution in which a lithium salt as an electrolyte is dissolved in a non-aqueous solvent. A positive electrode capable of inserting and extracting lithium is obtained by forming an active material layer containing a positive electrode active material and an organic substance having a binding and thickening effect on a positive electrode current collector. The positive electrode active material is usually a slurry in which an organic substance having a binding and thickening effect with the positive electrode active material is dispersed in water and / or an organic solvent, and this is applied thinly on a current collector such as a metal foil. After drying, it is formed by compacting to a predetermined thickness and density.

As the positive electrode active material, for example, a lithium-containing transition metal oxide such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ is used. Also, a part of Co, Ni or Mn contained in this metal oxide is replaced with other transition metals, Na, Mg, Sc, Y, Fe, Cu, Zn, Al, Cr, Pb, Sb, B, etc. Can also be used. Further, other positive electrode active materials such as transition metal chalcogenides, vanadium oxides and lithium compounds thereof, niobium oxides and lithium compounds thereof, conjugated polymers using organic conductive materials, and chevrel phase compounds can also be used. These positive electrode active materials may be used alone or as a mixture of a plurality of different positive electrode active materials. The average particle diameter of the positive electrode active material particles is preferably 1 to 30 μm.

  Any positive electrode current collector can be used as long as it is an electronic conductor that does not cause a chemical change at the charge / discharge potential of the positive electrode active material. Examples of the current collector material include metals such as stainless steel, aluminum, and titanium, alloys thereof, carbon, conductive resin, and the like, and a surface of aluminum or stainless steel coated with carbon or titanium. In particular, aluminum or an aluminum alloy is preferable. In addition, the surface of these materials can be oxidized and used. The current collector surface preferably has irregularities. Examples of the shape of the current collector include a foil, a film, a sheet, a net, a punched material, a lath body, a porous body, a foamed body, a fiber group, and a molded body of a nonwoven fabric body. Although thickness is arbitrary, the thing of 1-500 micrometers is preferable.

The organic material having a binding and thickening effect used for the positive electrode active material layer can be the same as that used for forming the negative electrode active material layer described above, and is usually a thermoplastic resin or a thermosetting resin. Is used.
The positive electrode active material layer may further contain additives such as the same conductive agent, filler, dispersant, and ion conductor as those used for forming the negative electrode active material layer described above.
In addition, it is preferable to use carbon or graphite so that it may become 1 to 50 weight% with respect to a positive electrode active material, especially 2 to 15 weight% as a electrically conductive agent.
The positive electrode active material slurry may be prepared in the same manner as the negative electrode active material slurry.

  Examples of the nonaqueous solvent for the electrolyte include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinylene carbonate (VC); dimethyl carbonate (DMC), diethyl carbonate (DEC). ), Chain carbonates such as ethyl methyl carbonate (EMC) and dipropyl carbonate (DPC); aliphatic carboxylic acid esters such as methyl formate, methyl acetate, methyl propionate and ethyl propionate; lactones such as γ-butyrolactone Chain ethers such as ethyl ether, 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), ethoxymethoxyethane (EME), ethyl monoglyme; tetrahydrofuran, 2-methyltetrahydro Cyclic ethers such as lofuran, 1,3-dioxolane, dioxolane derivatives and tetrahydrofuran derivatives; aromatic ethers such as anisole; orthoesters such as trimethoxymethane; chain amides such as formamide, acetamide and dimethylformamide; N -Cyclic amides such as methylpyrrolidone, 1,3-dimethyl-2-imidazolidinone and 3-methyl-2-oxazolidinone; Nitrile compounds such as acetonitrile and propylnitrile; Nitro compounds such as nitromethane; Dimethyl sulfoxide, sulfolane and methyl Examples include sulfur-containing compounds such as sulfolane and 1,3-propane sultone; and aprotic organic solvents such as phosphate esters such as phosphate triesters. Among these, a mixed solvent of cyclic carbonate and chain carbonate or a mixed solvent of cyclic carbonate, chain carbonate and aliphatic carboxylic acid ester is preferable.

Examples of the lithium salt dissolved in the non-aqueous solvent include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCl, LiCF ₃ , SO ₃ , LiC.
F ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate, LiCl, LiBr, LiI, chloroborane lithium, tetraphenylborane Lithium acid, imides and the like can be mentioned, and among these, LiPF ₆ is preferable. A lithium salt may be used independently or may use 2 or more types together. When used in combination of two or more it is preferably used in combination as LiPF ₆ and others.

A solid electrolyte combined with a lithium salt can also be used for the lithium secondary battery. Examples of solid electrolytes include inorganic solid electrolytes and organic solid electrolytes. Examples of the inorganic solid electrolyte include inorganic solid electrolytes such as lithium nitride, halide, or oxyacid salt. Among these, Li ₄ SiO ₄ , Li ₄ SiO ₄ —LiI-LiOH, xLi _{3
PO 4 - (1-x)} Li 4 SiO 4, Li 2 SiS 3, Li 3 PO 4 -Li 2 S-SiS 2, phosphorus compounds are preferred sulfide. Examples of the organic solid electrolyte include polyethylene oxide, polypropylene oxide, polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol, polyvinylidene fluoride, polyhexafluoropropylene, etc. and their derivatives, mixtures, composites and other polymer materials such as lithium. Examples include a compound of salt.

The concentration of the lithium salt in the electrolytic solution is preferably 0.2 to 2 mol / L, particularly 0.5 to 1.5 mol / L.
One preferable electrolyte is one in which LiPF ₆ is dissolved in a non-aqueous solvent containing ethylene carbonate and ethyl methyl carbonate.
Other additives may be added to the electrolytic solution for the purpose of improving discharge and charge / discharge characteristics. Examples of the additive include triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, pyridine, hexaphosphoric triamide, nitrobenzene derivatives, crown ethers, quaternary ammonium salts, ethylene glycol dialkyl ether, and the like. It is done.

  A separator that holds the nonaqueous electrolyte may be provided between the positive electrode and the negative electrode. The separator usually uses an insulating microporous thin film with high ion permeability and a predetermined mechanical strength. When the temperature is above a certain level, the pores close and resistance increases, and the current between the electrodes is increased. It is preferable to have a function of preventing the above. As the separator, a sheet, a nonwoven fabric or a woven fabric made of an olefin polymer or glass fiber or the like such as polypropylene or polyethylene having organic solvent resistance and hydrophobicity alone or a combination thereof is preferable. The pore diameter of the separator may be in a range in which the positive and negative electrode materials, the binder, and the conductive agent separated from the electrode do not permeate, and is usually 0.01 to 1 μm. Moreover, the thickness of a separator is 10-300 micrometers normally. Furthermore, the porosity of the separator may be determined according to the permeability of electrons and ions, the material, and the film thickness, and is usually 30 to 80%. Also, a battery in which a polymer material containing an organic electrolyte solution absorbed and held is included in the positive electrode mixture and the negative electrode mixture, and a porous separator made of a polymer that absorbs and holds the organic electrolyte solution is integrated with the positive electrode and the negative electrode. It is also possible to configure. The polymer material is not particularly limited as long as it can absorb and retain the organic electrolyte solution, but a copolymer of vinylidene fluoride and hexafluoropropylene is particularly preferable. The thickness of this separator is usually 10 μm or more and 60 μm or less. When the separator is thin, the positive and negative electrodes are likely to be short-circuited. Conversely, if the separator is too thick, the internal resistance of the battery tends to increase, so 50 μm or less, particularly 40 μm or less is preferable.

The shape of the lithium secondary battery is arbitrary, and examples include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type.
One of the processes that control the takt time in the lithium secondary battery manufacturing process is the electrolyte injection process (“Material Technology, Evaluation and Application Development in High Performance Secondary Batteries” (1998) (Published by the Technical Information Association) (See Section 7). This process is an essential process for many non-aqueous electrolyte secondary batteries except for some polymer batteries. Therefore, the use of the negative electrode active material having good wettability according to the present invention is industrially advantageous because the impregnation rate of the electrolytic solution can be increased and the time required for the pouring step can be shortened.

One of preferred application targets of the negative electrode material according to the present invention is a battery of a type in which industrial production is restricted because the injection process takes too much time. As such a battery, for example, a rectangular battery used for many applications such as a small electronic device such as a mobile phone can be cited. Since a rectangular battery is usually thin with a thickness of about 5 mm, the injection port takes a very small diameter of 1 mm or less, and thus it takes time to inject the liquid. It can be shortened. In addition, in a large battery, if the electrolyte is rapidly injected, uneven distribution of the electrolyte in the negative electrode is likely to occur. Therefore, the injection rate is limited from this point, but the negative electrode material according to the present invention is used. Such restrictions can be avoided, and battery quality can be stabilized and improved.

EXAMPLES The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited by the following examples unless it exceeds the gist. The physical properties of the carbonaceous material were measured by the following method.
(1) Measurement of volume-based average particle diameter About 1 mL of 2% by volume aqueous solution of polyoxyethylene (20) sorbitan monolaurate, 10 mL of ion exchange water and 0.2 g of carbonaceous material are mixed, and ion exchange water is used as a dispersion medium. The volume standard average particle diameter (D50) was measured using a laser diffraction particle size distribution meter (manufactured by Horiba, model number LA-920).
(2) Specific surface area measurement After heating a carbonaceous material to 350 degreeC and flowing nitrogen gas for 15 minutes, the specific surface area was measured by the BET 1 point method in the relative pressure 0.3 by nitrogen gas adsorption | suction.
(3) Measurement of average circularity In 100 mL of ion-exchanged water, 0.2 g of carbonaceous material and 0.1 g of polyoxyethylene (20) sorbitan monolaurate were mixed and stirred and subjected to ultrasonic irradiation for 30 minutes. The average circularity was measured using a flow particle image analyzer “FPIA-1000” manufactured by Toa Medical Electronics Co., Ltd. as a sample.

(Example 1)
Natural graphite powder (volume-based average particle diameter 11 μm, specific surface area 10.8 m ² / g, average circularity 0
. 91) and a petroleum heavy oil obtained during naphtha pyrolysis, and heated to 1100 ° C. in an inert gas, the obtained sintered product is pulverized and classified to obtain a graphite particle surface. Amorphous coated graphite coated with amorphous carbon was obtained. When the residual carbon ratio of this product was measured, it was covered with 10 parts by weight of amorphous carbon with respect to 100 parts by weight of graphite. 5 kg of the obtained amorphous coated graphite is put into a gas flow type container, and at room temperature, a mixed gas of 2 vol% ozone, 25 vol% oxygen and 73 vol% nitrogen is atmospheric pressure and the container is rocked 7 The carbonaceous negative electrode material was obtained by making it distribute | circulate for minutes. About this thing, the laser diffraction type particle size distribution, the specific surface area, and the average circularity were measured, and the wettability test was done. The results are listed in Table 1. Moreover, using this negative electrode material, a negative electrode for a lithium secondary battery and further a lithium secondary battery were prepared by the following method, and the performance of this battery was evaluated.

[Production of positive electrode]
A slurry obtained by mixing 90% by weight of lithium nickelate (LiNiO ₂ ), 5% by weight of acetylene black, and 5% by weight of polyvinylidene fluoride (PVdF) in N-methylpyrrolidone was formed into an aluminum foil having a thickness of 20 μm. This was coated on one side and dried, and further rolled with a press so that the total thickness of the active material layer and the aluminum foil was 60 μm. This was punched into a disk shape with a punch having a diameter of 12.5 mm to obtain a positive electrode for a coin battery. These operations were performed at 25 ° C.

[Production of negative electrode]
What added carboxymethylcellulose and styrene-butadiene rubber (SBR) to 94 weight part of negative electrode active materials so that it might become 3 weight part each in solid content was added to distilled water, and it was set as the slurry. This slurry was uniformly applied to one side of a 18 μm thick copper foil, dried, and then rolled with a press so that the total thickness of the active material layer and the copper foil was 50 μm. This was punched out into a disk shape with a punch having a diameter of 13.0 mm to obtain a negative electrode for a coin battery. These operations were performed at 25 ° C.

[Preparation of electrolyte]
Under a dry argon atmosphere, a well-dried lithium hexafluorophosphate (LiPF ₆₎ was added to a mixed solvent of purified ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) in a volume ratio of 3: 3: 4. ) Was dissolved to a concentration of 1 mol / L to obtain an electrolytic solution.

[Battery assembly]
The electrolyte was sufficiently infiltrated into the positive electrode and the negative electrode, and then the porous polyethylene sheet separator was opposed to each other and stored in a battery can. Thereafter, caulking was performed to produce a coin-type battery.
[Battery evaluation]
1) Initial charge / discharge Charge / discharge (capacity confirmation) was performed at 25 ° C., and the charge state of the lithium secondary battery was adjusted to 50% based on the result.

2) Low temperature output evaluation At -20 ° C, the battery of 1) was discharged at 1 / 4C, 1 / 2C, 1.0C, 1.5C, 2.5C, 3.0C (1C is the rated capacity in 1 hour) Discharge at a constant current for 10 seconds at each current value, and the voltage drop after 10 seconds in the discharge under each condition was measured. When the discharge lower limit voltage is set to 3.0 V from the measured value, the current value I that can flow for 10 seconds is calculated, and the value calculated by the formula 3.0 × I (W) is used as the initial output of the battery. did.

The output of the produced lithium secondary battery was 110% when the output of the lithium secondary battery described in Comparative Example 1 described later was 100%. This means that the battery output has been improved by reducing the interfacial resistance of the negative electrode by mild ozone treatment.
(Example 2)
1 kg of the amorphous coated graphite obtained by the method of Example 1 was put in a cylindrical container having a diameter of 300 mm and a height of 300 mm, and the pressure was reduced to 1 × 10 ⁻⁴ MPa. Into this container, air containing 2% by volume of ozone was introduced at room temperature, the pressure was restored to atmospheric pressure over 30 seconds, and then taken out from the container after 5 minutes to obtain a negative electrode material subjected to vacuum ozone treatment. It was. About this thing, the laser diffraction type particle size distribution, the specific surface area, and the average circularity were measured, and the wettability test was done. The results are listed in Table 1.

(Comparative Example 1)
The amorphous coated graphite obtained by the method of Example 1 was measured for laser diffraction particle size distribution, specific surface area and average circularity, and subjected to a wettability test. The results are listed in Table 1. Moreover, a negative electrode for a lithium secondary battery and further a lithium secondary battery were prepared using this amorphous coated graphite, and the performance of this battery was evaluated.

(Comparative Example 2)
40 g of amorphous coated graphite powder obtained by the method of Example 1 and 100 mL of 0.1N acetic acid were put into a reactor for wet ozone treatment, and an ozone concentration of 10 wt. An ozone-treated carbon material was obtained by performing ozone treatment at room temperature for 2.5 hours while flowing oxygen gas at a flow rate of 3 L / min. About this thing, the laser diffraction type particle size distribution, the specific surface area, and the average circularity were measured, and the wettability test was done. The results are listed in Table 1.

(Example 3)
Commercially available natural graphite powder (volume-based average particle size 24 μm, specific surface area 6.2 m ² / g, average circularity 0.90) and petroleum heavy oil obtained during naphtha pyrolysis are mixed in an inert gas. 1100
Carbonization treatment at 0 ° C. was performed. The obtained sintered product was pulverized and classified to obtain amorphous coated graphite whose graphite particle surfaces were coated with amorphous carbon. When the residual carbon ratio of this product was measured, it was covered with 5 parts by weight of amorphous carbon with respect to 100 parts by weight of graphite. The obtained amorphous coated graphite was subjected to ozone treatment under atmospheric pressure by the method of Example 1 to obtain a negative electrode material. About this thing, the laser diffraction type particle size distribution, the specific surface area, and the average circularity were measured, and the wettability test was done. The results are listed in Table 1.

Example 4
The amorphous coated graphite obtained by the method of Example 3 was subjected to vacuum ozone treatment by the method of Example 2 to obtain a negative electrode material. This was subjected to laser diffraction particle size distribution measurement, specific surface area measurement, average circularity measurement, and wettability test. The results are listed in Table 1.
(Comparative Example 3)
The amorphous coated graphite obtained by the method of Example 3 was measured for laser diffraction particle size distribution, specific surface area and average circularity, and subjected to a wettability test. The results are listed in Table 1.

(Comparative Example 4)
About the ozone-treated carbon material obtained by subjecting the amorphous coated graphite obtained by the method of Example 3 to the wet ozone treatment by the method of Comparative Example 2, the laser diffraction particle size distribution, specific surface area and average circularity are Measured and tested for wettability. The results are listed in Table 1.
(Example 5)
The same method as in Example 1 except that the amount of heavy petroleum oil used was reduced to commercially available natural graphite powder (volume-based average particle size 17 μm, specific surface area 6.9 m ² / g, average circularity 0.95). Amorphous coating treatment was carried out to obtain amorphous coated graphite coated with 1 part by weight of amorphous carbon with respect to 100 parts by weight of graphite. The obtained amorphous coated graphite was subjected to ozone treatment under atmospheric pressure by the method of Example 1 to obtain a negative electrode material. About this thing, the laser diffraction type particle size distribution, the specific surface area, and the average circularity were measured, and the wettability test was done. The results are listed in Table 1.

(Example 6)
The amorphous coated graphite obtained by the method of Example 5 was subjected to vacuum ozone treatment by the method of Example 2 to obtain a negative electrode material. About this thing, the laser diffraction type particle size distribution, the specific surface area, and the average circularity were measured, and the wettability test was done. The results are listed in Table 1.
(Comparative Example 5)
The amorphous coated graphite obtained by the method of Example 5 was measured for laser diffraction particle size distribution, specific surface area and average circularity, and subjected to a wettability test. The results are listed in Table 1.

(Comparative Example 6)
For the ozone-treated carbon material obtained by subjecting the amorphous coated graphite obtained by the method of Example 5 to the wet ozone treatment by the method of Comparative Example 2, the laser diffraction particle size distribution, specific surface area and average circularity are Measured and tested for wettability. The results are listed in Table 1.
(Example 7)
Artificial graphite powder (volume-based average particle diameter of 17 μm, in which a number of graphite fine particles dispersed in a binder pitch are heated to graphitize the binder pitch, and the graphite particles are arranged in multiple directions through the graphitized material of the binder pitch. A specific surface area of 4.7 m ² / g and an average circularity of 0.87) were prepared. The artificial graphite powder was subjected to ozone treatment under atmospheric pressure by the method of Example 1 to obtain a negative electrode material. About this thing, the laser diffraction type particle size distribution, the specific surface area, and the average circularity were measured, and the wettability test was done. The results are listed in Table 1.

(Example 8)
The artificial graphite powder obtained by the method of Example 7 was subjected to vacuum ozone treatment by the method of Example 2 to obtain a negative electrode material. About this thing, the laser diffraction type particle size distribution, the specific surface area, and the average circularity were measured, and the wettability test was done. The results are listed in Table 1.
(Comparative Example 7)
The artificial graphite powder obtained by the method of Example 7 was measured for laser diffraction particle size distribution, specific surface area and average circularity, and subjected to a wettability test. The results are listed in Table 1.

(Comparative Example 8)
Measurement of laser diffraction particle size distribution, specific surface area and average circularity of the ozone-treated artificial graphite powder obtained by subjecting the artificial graphite powder obtained by the method of Example 7 to wet ozone treatment by the method of Comparative Example 2. The wettability test was conducted. The results are listed in Table 1.
Example 9
The amorphous carbon powder obtained by subjecting Needle Coke (Mitsubishi Chemical Corporation) to powder processing was subjected to ozone treatment under atmospheric pressure by the method of Example 1 to obtain a negative electrode material. About this thing, the laser diffraction type particle size distribution, the specific surface area, and the average circularity were measured, and the wettability test was done. The results are listed in Table 1.

(Example 10)
The amorphous carbon powder obtained by the method of Example 9 was subjected to vacuum ozone treatment by the method of Example 2 to obtain a negative electrode material. About this thing, the laser diffraction type particle size distribution, the specific surface area, and the average circularity were measured, and the wettability test was done. The results are listed in Table 1.
(Comparative Example 9)
The amorphous carbon powder obtained by the method of Example 9 was measured for laser diffraction particle size distribution, specific surface area and average circularity, and subjected to a wettability test. The results are listed in Table 1.

(Comparative Example 10)
For the ozone-treated carbon material obtained by subjecting the amorphous carbon powder obtained by the method of Example 9 to wet ozone treatment by the method of Comparative Example 2, the laser diffraction particle size distribution, the specific surface area and the average circularity were determined. Measured and tested for wettability. The results are listed in Table 1.
(Example 11)
Powder processing is performed on graphitized material obtained by firing needle coke (Mitsubishi Chemical Co., Ltd.) at 2800 ° C. or higher using a graphitization furnace, and then subjected to ozone treatment under atmospheric pressure by the method of Example 1. Thus, a negative electrode material was obtained. About this thing, the laser diffraction type particle size distribution, the specific surface area, and the average circularity were measured, and the wettability test was done. The results are listed in Table 1.

(Example 12)
A negative electrode material was obtained by subjecting the graphitized material subjected to the powder processing obtained by the method of Example 11 to vacuum ozone treatment by the method of Example 2. About this thing, the laser diffraction type particle size distribution, the specific surface area, and the average circularity were measured, and the wettability test was done. The results are listed in Table 1.
(Comparative Example 11)
The graphitized material obtained by the method of Example 11 was measured for laser diffraction particle size distribution, specific surface area and average circularity, and subjected to a wettability test. The results are listed in Table 1.

(Comparative Example 12)
About the graphitized material obtained by the method of Example 11, the ozone-treated graphitized material obtained by performing the wet ozone treatment by the method of Comparative Example 2, the laser diffraction particle size distribution, the specific surface area and the average circularity are measured, A wettability test was performed. The results are listed in Table 1.
(Example 13)
The natural graphite powder used in Example 5 was subjected to ozone treatment under atmospheric pressure by the method of Example 1 to obtain a negative electrode material. About this thing, the laser diffraction type particle size distribution, the specific surface area, and the average circularity were measured, and the wettability test was done. The results are listed in Table 1.

(Example 14)
The natural graphite powder used in Example 5 was vacuum ozone treated by the method of Example 2 to obtain a negative electrode material. About this thing, the laser diffraction type particle size distribution, the specific surface area, and the average circularity were measured, and the wettability test was done. The results are listed in Table 1.
(Comparative Example 13)
The natural graphite powder used in Example 5 was measured for laser diffraction particle size distribution, specific surface area and average circularity, and subjected to a wettability test. The results are listed in Table 1.

(Comparative Example 14)
For the ozone-treated graphite powder obtained by subjecting the natural graphite powder used in Example 5 to wet ozone treatment by the method of Comparative Example 2, the laser diffraction particle size distribution, the specific surface area and the average circularity were measured and wetted. A sex test was performed. The results are listed in Table 1.
(Example 15)
The natural graphite powder used in Example 3 was subjected to ozone treatment under atmospheric pressure by the method of Example 1 to obtain a negative electrode material. About this thing, the laser diffraction type particle size distribution, the specific surface area, and the average circularity were measured, and the wettability test was done. The results are listed in Table 1.

(Example 16)
The natural graphite powder used in Example 3 was subjected to vacuum ozone treatment by the method of Example 2 to obtain a negative electrode material. About this thing, the laser diffraction type particle size distribution, the specific surface area, and the average circularity were measured, and the wettability test was done. The results are listed in Table 1.
(Comparative Example 15)
The natural graphite powder used in Example 3 was measured for laser diffraction particle size distribution, specific surface area and average circularity, and subjected to a wettability test. The results are listed in Table 1.

(Comparative Example 16)
For the ozone-treated graphite powder obtained by subjecting the natural graphite powder used in Example 3 to wet ozone treatment by the method of Comparative Example 2, the laser diffraction particle size distribution, specific surface area and average circularity were measured, and the wetness was measured. A sex test was performed. The results are listed in Table 1.

From Table 1, the carbonaceous negative electrode material for a lithium secondary battery according to the present invention obtained by subjecting a carbonaceous material to a weak dry ozone treatment is the same carbonaceous material as the wet ozone treatment described in Patent Document 1. It can be seen that the disappearance time of the wettability test is shorter than that of the negative electrode material obtained by applying, and exhibits excellent liquid absorption characteristics.

Claims (7)

A carbonaceous negative electrode material for a lithium secondary battery, wherein a droplet disappearance time in the following wettability test is 320 seconds or less.
<Wettability test>
(1) Preparation of slurry;
Dissolve 1 g of powdered sodium carboxymethylcellulose (etherification degree: 0.6 to 0.8, viscosity of 100 to 1000 mPa.s at 30 ° C. in ¹ wt% aqueous solution at a shear rate of 40 S ⁻¹ ) in 100 mL of distilled water. . 100 g of the obtained aqueous solution and 100 g of the carbonaceous negative electrode material are mixed and stirred for 10 hours to be sufficiently dispersed. Next, 2 g of an aqueous emulsion (solid content concentration 50% by weight) of styrene butadiene rubber (Tg = −10 to 0 ° C.) is added and stirred to obtain a uniform slurry. All operations are performed at 25 ° C.
(2) Preparation of test piece;
On the copper foil having a thickness of 20 μm, the slurry prepared above is applied by a doctor blade method so that the solid content becomes (13 ± 0.2) mg / cm ² to form a coating film. This is 60-8
Heat to 0 ° C. to dry thoroughly to remove moisture. From this, a 12.5 mmφ disc is punched with a punch, and a test piece is formed by pressing with a press machine so that the film density is (1.5 to 1.6) g / cm ³ .
(3) Measurement of droplet disappearance time;
A solution prepared by dissolving 180 g of lithium hexafluorophosphate (LiPF ₆ ) in a mixed solution consisting of 300 mL of ethylene carbonate and 700 mL of dimethyl carbonate at the center of the test piece prepared above at 25 ° C. in an argon atmosphere was 5 mm. From the height, 1 μL is dropped with a microsyringe. The time from the end of dropping until the solution is absorbed inside the test piece and apparently disappears from the surface is measured, and this measured value is taken as the droplet disappearance time.   The carbonaceous negative electrode material according to claim 1, wherein the droplet disappearance time is 200 seconds or less.   The carbonaceous negative electrode material according to claim 1 or 2, wherein the average circularity is 0.85 or more. In a Raman spectrum using an argon ion laser beam having a wavelength of 514.3 nm, the peak intensity in the range of 1580 cm ^{−1 to} 1620 cm ⁻¹ is I _A , and the half width is Δν, 135
0cm peak intensity ratio of the peak intensity in the range of ^{-1 ~1370cm -1} when the _{I B R (= I B /} I A) is 1.1 or less, and the half-value width Δν is at 60cm ^-1 or less The carbonaceous negative electrode material according to any one of claims 1 to 3, wherein: A powdery carbonaceous material having an average particle diameter of 30 μm or less and a specific surface area of 20 m ² / g or less is subjected to dry ozone treatment in which 0.01 to 10 g of ozone per 1 kg of the material is contacted in a gas phase. The carbonaceous negative electrode material according to any one of claims 1 to 4, wherein   6. A negative electrode for a lithium secondary battery, comprising a negative electrode active material layer containing the carbonaceous negative electrode material according to claim 1 and a binder on a current collector.   A lithium secondary battery comprising: the negative electrode according to claim 6; a positive electrode capable of inserting and extracting lithium ions; and a non-aqueous electrolyte.