WO2014157318A1 - 炭素材、その炭素材を用いた非水系二次電池 - Google Patents
炭素材、その炭素材を用いた非水系二次電池 Download PDFInfo
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- WO2014157318A1 WO2014157318A1 PCT/JP2014/058498 JP2014058498W WO2014157318A1 WO 2014157318 A1 WO2014157318 A1 WO 2014157318A1 JP 2014058498 W JP2014058498 W JP 2014058498W WO 2014157318 A1 WO2014157318 A1 WO 2014157318A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
- H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Definitions
- the present invention relates to a carbon material, preferably a carbon material used for a non-aqueous secondary battery negative electrode, and a non-aqueous secondary battery including a negative electrode formed using the carbon material.
- lithium ion secondary batteries having higher energy density and excellent large current charge / discharge characteristics have attracted attention as compared to nickel / cadmium batteries and nickel / hydrogen batteries.
- the increase in capacity of lithium ion secondary batteries has been widely studied, but the demand for higher performance of lithium ion secondary batteries in recent years has also increased, and it is required to achieve further increase in capacity. ing.
- graphite material and amorphous carbon are often used in terms of cost and durability.
- a design has been made in which as many charge / discharge active materials as possible are packed into a limited battery volume by increasing the electrode density.
- the anode material carbon materials mainly composed of natural graphite, artificial graphite, carbon fiber, amorphous carbon, etc. are used. Among these, natural graphite is superior in terms of performance and cost. Development is actively underway.
- Natural graphite is naturally produced as an ore, and is now produced all over the world, including China, Brazil, Madagascar, Vietnamese, India, Sri Lanka, Mexico, and the Korean Peninsula.
- these produced natural graphites are not uniform and contain a large amount of impurities, so that it is difficult to use them unless various impurities are removed by a treatment such as purification.
- the technology to remove these impurities has been known for a long time.
- natural graphite was applied to lithium ion secondary batteries, it had to be treated with higher purity than natural graphite used in other fields. .
- spheroidizing natural graphite is produced by performing spheroidizing treatment (mechanical energy treatment) using natural graphite
- spheroidizing treatment mechanical energy treatment
- Technologies have been developed in which spheroidized natural graphite is used as nuclear graphite and the surface thereof is coated with amorphous carbon.
- Patent Document 2 discloses that the amount of acidic functional groups present on the surface of natural graphite is reduced to spherical graphite at a high temperature of 1200 ° C. Techniques have been developed to reduce the amount of acidic functional groups present on the graphite surface by heating the particles. Patent Document 3 discloses that the surface functional group amount O / C value, the surface functional group amount Cl / C value of natural graphite, the surface, for the purpose of suppressing gas generation at a high temperature when a non-aqueous secondary battery is formed. In order to control the functional group amount S / C, a method is disclosed in which natural graphite is acid-treated with concentrated sulfuric acid or the like and then heat-treated at 100 ° C. to 600 ° C.
- the spheroidized natural graphite alone disclosed in Patent Document 1 has a high capacity and good rapid charge / discharge performance, but is not sufficient in terms of battery performance including cycle characteristics and initial irreversible capacity. Improvement was needed. The inventors of the present invention thought that it would be difficult to expect further improvement in battery performance only by the technique of coating the surface of natural graphite as described in Patent Document 1 with amorphous carbon. In addition, using natural graphite with a different method of production and purification as described above, the quality of the graphite itself may not be stable, and in some cases, the high-temperature storage characteristics and cycle characteristics of non-aqueous secondary batteries may deteriorate. I understand.
- these performance deterioration factors are high activity such as sulfur components mixed as impurities in graphite, especially sulfur-containing organic compounds such as sulfuric acid, thiol and thiophene. They succeeded in identifying the sulfur component present in the state.
- the oxygen-containing functional group of natural graphite which is a factor for controlling the pH of the dispersion, begins to partially desorb from a heat treatment of about 300 ° C. depending on the type, and at 1000 ° C. or higher.
- heat treatment is performed, almost all the oxygen-containing functional groups are eliminated and the oxygen-containing functional groups are reduced, so that the pH of the dispersion is increased.
- natural graphite is heat-treated at a high temperature of 1000 ° C. or higher, the oxygen-containing functional group is completely removed, and the pH of the dispersion becomes strongly basic.
- Patent Document 3 the surface of natural graphite is modified by a method of acid treatment with concentrated sulfuric acid or the like followed by heat treatment at 100 ° C. to 600 ° C.
- acidic functional groups are treated with sulfuric acid or the like. Since it is a heat treatment for positive introduction, a large amount of sulfuric acid component remains after this treatment. Even if it sees an Example concretely, the heat processing temperature is 300 degreeC, Even if it heat-processes at this temperature, the natural graphite processed in this way will have a large amount of sulfuric acid components. It has been found that the effects of the present invention cannot be achieved only by applying these techniques.
- the present invention has been made in view of such background art, and its problem is to provide a non-aqueous secondary battery having high electrode strength, excellent processability, and excellent high-temperature storage characteristics and cycle characteristics.
- a carbon material that can be produced a composite carbon material obtained by using the carbon material and excellent in initial efficiency, and a mixed carbon material, and, as a result, to provide a high-capacity non-aqueous secondary battery. It is in.
- the present inventors have found that there is a sulfur oxide that desorbs at a specific temperature rise, that is, a sulfur component that exists in a highly active state within a specific range. If a carbon material having a pH within a specific range is used for the negative electrode of the non-aqueous secondary battery, excessive reaction with the electrolyte during charging / discharging or during high-temperature storage is suppressed. The present inventors have found that the irreversible capacity reduction, gas generation suppression, high-temperature storage characteristics and cycle characteristics of lithium ion secondary batteries can be improved.
- the carbon material has a strong interaction with the binder used for electrode preparation, and can provide a non-aqueous secondary battery such as a lithium ion secondary battery with excellent cycle characteristics, and is also very useful for high-strength electrode preparation. It has been found effective and has led to the present invention.
- the gist of the present invention is as follows.
- the carbon material (A) contains graphite and satisfies (a) and (b).
- (A) The amount of desorbed sulfur oxide gas up to 500 ° C. measured by a temperature rising pyrolysis mass spectrometer (TPD-MS) of the carbon material is 0.39 ⁇ mol / g or less.
- TPD-MS temperature rising pyrolysis mass spectrometer
- the pH of the dispersion when 5 parts by mass of the carbon material is suspended and dispersed in 30 parts by mass of distilled water is 9 or less.
- the carbon material of the present invention can provide a non-aqueous secondary battery excellent in high-temperature storage characteristics and cycle characteristics by using it as an active material for non-aqueous secondary batteries.
- Carbon material (A) contains graphite and satisfies (a) and (b).
- the carbon material (A) of the present invention is not particularly limited as long as it satisfies (a) and (b) and further contains graphite.
- a preferred carbon material (A) is a carbon material (A) containing graphite that satisfies (a) and (b).
- the term “graphite contained” as used herein means that the graphite content is not particularly limited with respect to the total amount of the carbon material (A), but is usually 0.1% by mass or more, preferably 30% by mass. % Or more, more preferably 50% by mass or more, still more preferably 70% by mass or more, and particularly preferably 100% by mass.
- a high graphite content tends to suppress a decrease in discharge capacity and input / output characteristics.
- Examples of the contained state include a mixture of a carbon material and a metal / metal compound material as described later, a composite with a carbonaceous material, a coating with a carbonaceous material, and an organic polymer. Or a state of being covered with an inorganic salt.
- These contained states include, for example, X-ray wide angle diffraction (XRD), Raman spectroscopy, field emission scanning electron microscope-energy dispersive X-ray (SEM-EDX) analysis, X-ray photoelectron spectroscopy ( This can be confirmed by observing the particle surface and particle cross section of the active material for a non-aqueous secondary battery negative electrode using a technique such as XPS analysis.
- XRD X-ray wide angle diffraction
- Raman spectroscopy Raman spectroscopy
- SEM-EDX field emission scanning electron microscope-energy dispersive X-ray
- X-ray photoelectron spectroscopy This can be confirmed by observing the particle surface and particle cross
- graphite is a carbon material having a d-value (interlayer distance, also referred to as d002 value) of a lattice plane (002 plane) determined by X-ray diffraction by the Gakushin method is 0.335 nm or more and less than 0.340 nm. That means.
- the d002 value is preferably 0.339 nm or less, more preferably 0.337 nm or less.
- a d002 value of less than 0.340 nm indicates that the crystallinity of graphite is high, and the initial irreversible capacity tends to decrease.
- 0.335 nm is a theoretical value of graphite.
- natural graphite or artificial graphite can be mentioned, but if it is appropriately selected so as to be a carbon material (A) satisfying (a) and (b), it is not particularly limited, and any one of them is used alone. Two or more kinds may be used in any combination and composition. It is preferable to use natural graphite because it has a theoretically high charge / discharge capacity of 372 mAh / g, is excellent in charge / discharge characteristics at a high current density, and is easily commercially available.
- Natural graphite Natural graphite is readily available commercially, theoretically has a high charge / discharge capacity of 372 mAh / g, and even at a higher current density than when other negative electrode active materials are used. Significant improvement in charge / discharge characteristics. Among them, natural graphite is preferably one having few impurities, and can be used after being subjected to various known purification treatments if necessary.
- Natural graphite is classified into scale black (Flake Graphite), scale graphite (Crystal Line (Vein) Graphite), and soil graphite (Amorphous Graphite) depending on its properties (Refer to "HANDBOOKOF CARBON, GRAPHITE, DIAMOND AND FULLERENES” (published by NoyesPubLications)).
- the degree of graphitization is highest at 100% for scaly graphite, followed by 99.9% for scaly graphite.
- These natural graphites having a high degree of graphitization are suitable in the present invention.
- Natural graphite is produced in Madagascar, China, Brazil, Ukraine, Canada, etc., and scaly graphite is produced mainly in Sri Lanka.
- the main producers of soil graphite are the Korean Peninsula, China and Mexico.
- natural graphites for example, flaky, massive or plate-like natural graphite, highly purified flaky graphite and spheroidized natural graphite are preferably mentioned.
- natural graphite obtained by subjecting scaly graphite to spheroidization treatment as will be described later is more preferable from the viewpoint of particle filling properties and charge / discharge load characteristics.
- artificial graphite for example, coal tar pitch, coal heavy oil, atmospheric residue, petroleum heavy oil, aromatic hydrocarbon, nitrogen-containing cyclic compound, sulfur-containing cyclic compound, polyphenylene, polyvinyl chloride, polyvinyl
- organic substances such as alcohol, polyacrylonitrile, polyvinyl butyral, natural polymer, polyphenylene sulfide, polyphenylene oxide, furfuryl alcohol resin, phenol-formaldehyde resin, and imide resin.
- the firing temperature can be in the range of 2500 ° C. or more and 3200 ° C. or less, and a silicon-containing compound, a boron-containing compound, or the like can be used as a graphitization catalyst during firing.
- a carbon material means the carbon material which can be contained in the carbon material (A) of this invention other than graphite.
- the carbon material is not particularly limited as long as it is a substance capable of occluding and releasing lithium ions, sodium ions, etc., and examples thereof include amorphous carbon, carbonaceous particles having a low graphitization degree, and silicon-carbon composites. . These can be used alone or in combination of two or more.
- the state in the carbon material (A) of these carbon materials and natural graphite is not particularly limited as described above.
- Examples of the amorphous carbon include particles obtained by baking a bulk mesophase and particles obtained by infusibilizing and baking a carbon precursor.
- Examples of the carbonaceous particles having a low degree of graphitization include those obtained by firing an organic material at a temperature usually less than 2500 ° C.
- Organic substances include coal-based heavy oil such as coal tar pitch and dry distillation liquefied oil; straight-run heavy oil such as atmospheric residual oil and vacuum residual oil; ethylene tar produced as a by-product during thermal decomposition of crude oil, naphtha, etc.
- Heavy oils such as cracked heavy oils; aromatic hydrocarbons such as acenaphthylene, decacyclene and anthracene; nitrogen-containing cyclic compounds such as phenazine and acridine; sulfur-containing cyclic compounds such as thiophene; and aliphatic cyclics such as adamantane
- Polyphenylene such as biphenyl and terphenyl, polyvinyl esters such as polyvinyl chloride, polyvinyl acetate, and polyvinyl butyral, and thermoplastic polymers such as polyvinyl alcohol.
- the firing temperature can be 600 ° C. or higher, preferably 900 ° C. or higher, more preferably 950 ° C. or higher, and usually less than 2500 ° C. Preferably, it is 2000 degrees C or less, More preferably, it is the range of 1400 degrees C or less.
- acids such as phosphoric acid, boric acid and hydrochloric acid, alkalis such as sodium hydroxide and the like can be mixed with the organic matter.
- the carbon material (A) of the present invention is characterized by satisfying the following (a) and (b).
- ⁇ mol / g is usually larger than 0 ⁇ mol / g, preferably 0.01 ⁇ mol / g or more, more preferably 0.02 ⁇ mol / g or more, further preferably 0.03 ⁇ mol / g or more, particularly Preferably it is 0.04 ⁇ mol / g or more, most preferably 0.05 ⁇ mol / g or more, and 0.39 ⁇ mol / g or less, preferably 0.35 ⁇ mol / g or less, more preferably 0.30 ⁇ mol / g or less, More preferably, it is 0.25 ⁇ mol / g or less, and particularly preferably 0.2 ⁇ mol / g or less.
- the amount of desulfurized sulfur oxide gas up to 500 ° C. means that sulfur components existing in a highly active state such as sulfur-containing organic compounds such as sulfuric acid, thiol and thiophene, and graphite surface sulfur-containing functional groups such as sulfo groups and sulfonyl groups. means. If the amount of desorbed sulfur oxide gas is too large, the side reaction with the electrolyte proceeds excessively, which tends to cause a decrease in initial efficiency, a high temperature storage characteristic, and a cycle characteristic.
- sulfur organic compounds certain sulfur-containing organic compounds and graphite surface sulfur-containing functional groups play an important role in the formation of SEI in terms of battery characteristics, and therefore there are traces of highly active sulfur components. This is preferable from the viewpoint of good charge-discharge irreversible capacity, high-temperature storage characteristics, and cycle characteristics.
- the pH of the dispersion is 9 or less, preferably 8.5 or less, more preferably 8 or less, and even more preferably 7 0.5 or less, particularly preferably 7 or less, and the lower limit is not particularly limited, but is usually 4.5 or more, preferably 4.8 or more, more preferably 5.0 or more, still more preferably 5.4 or more, particularly Preferably, it is 5.6 or more.
- the dispersion liquid is usually between weakly acidic and neutral when 5 parts by mass of the carbon material is suspended and dispersed in 30 parts by mass of distilled water.
- the pH of the dispersion when the carbon material 5 parts by mass is suspended and dispersed in 30 parts by mass of distilled water is the amount of inorganic acid such as sulfuric acid, hydrochloric acid or nitric acid contained as impurities, the carboxy group present on the graphite surface, It is thought to correlate with the amount of acidic functional groups such as phenol groups.
- the fact that the carbon material (A) containing graphite satisfies the above-mentioned conditions (a) and (b) means that impurities in graphite are a cause of deterioration in high-temperature storage characteristics and cycle characteristics of the non-aqueous secondary battery.
- An X-ray photoelectron spectrometer (for example, ESCA manufactured by ULVAC-PHI) is used as an X-ray photoelectron spectroscopy measurement, and a sample is measured so that the surface is flat (here, a carbon material).
- the spectrum of C1s (280 to 300 eV) and O1s (525 to 545 eV) is measured by multiplex measurement using an aluminum K ⁇ ray as an X-ray source.
- the obtained C1s peak top is corrected to be 284.3 eV, the peak areas of the C1s and O1s spectra are obtained, and the device sensitivity coefficient is multiplied to calculate the surface atomic concentrations of C and O, respectively.
- the obtained O / C atomic concentration ratio O / C (O atom concentration / C atom concentration) is defined as the surface functional group amount O / C value of the carbon material.
- the O / C value obtained from XPS is usually 0.8% or more, preferably 1% or more, more preferably 1.2% or more, still more preferably 1.4% or more, and usually 8% or less, preferably 4 % Or less, more preferably 3.5% or less, and still more preferably 3% or less.
- volume-based average particle size (average particle size d50) The volume-based average particle diameter (also referred to as “average particle diameter d50”) of the carbon material (A) is usually 5 ⁇ m or more, preferably 10 ⁇ m or more, more preferably 15 ⁇ m or more, still more preferably 19 ⁇ m or more, and particularly preferably 20 ⁇ m or more. is there.
- the average particle diameter d50 is 50 ⁇ m or less, more preferably 40 ⁇ m or less, still more preferably 35 ⁇ m or less, and particularly preferably 31 ⁇ m or less.
- the average particle diameter d50 When the average particle diameter d50 is equal to or greater than the lower limit value, an increase in irreversible capacity and loss of initial battery capacity of the nonaqueous secondary battery obtained using the carbon material (A) tends to be suppressed, whereas the average When the particle size d50 is less than or equal to the above upper limit value, inconveniences in the process such as streaking in slurry application, a decrease in high current density charge / discharge characteristics, and a decrease in low temperature input / output characteristics tend to be suppressed.
- the average particle size d50 is obtained by adding 10 mL of a 0.2 mass% aqueous solution of polyoxyethylene sorbitan monolaurate (for example, Tween 20 (registered trademark)) as a surfactant to a carbon material. 0.01 g is suspended, and this is introduced as a measurement sample into a commercially available laser diffraction / scattering particle size distribution measurement device (for example, LA-920 manufactured by HORIBA), and the measurement sample is irradiated with 28 kHz ultrasonic waves at an output of 60 W for 1 minute. After that, the volume is defined as a volume-based median diameter measured by the measuring device.
- a commercially available laser diffraction / scattering particle size distribution measurement device for example, LA-920 manufactured by HORIBA
- Circularity The circularity of the carbon material (A) is 0.88 or more, preferably 0.90 or more, more preferably 0.91 or more. Further, the circularity is usually 1 or less, preferably 0.98 or less, more preferably 0.97 or less. When the circularity is not less than the lower limit, the high current density charge / discharge characteristics of the nonaqueous secondary battery tend to be improved.
- the circularity is defined by the following formula, and when the circularity is 1, a theoretical sphere is obtained.
- Circularity (perimeter of equivalent circle having the same area as the particle projection shape) / (actual circumference of particle projection shape)
- a flow type particle image analyzer for example, FPIA manufactured by Sysmex Industrial Co., Ltd.
- FPIA flow type particle image analyzer
- about 0.2 g of a sample (carbon material) is added to polyoxyethylene (20) sorbitan as a surfactant.
- the detection range is designated as 0.6 to 400 ⁇ m, and the particle size is The value measured for particles in the range of 1.5-40 ⁇ m is used.
- the method for improving the circularity is not particularly limited.
- a spheroidized sphere is preferable because the shape of the interparticle void when the negative electrode is formed is preferable.
- spheroidizing treatment include a method of mechanically approaching a sphere by applying a shearing force and a compressive force, and a mechanical / physical treatment in which a plurality of carbon material fine particles are granulated by the adhesive force of the binder or the particles themselves. Methods and the like.
- the average particle diameter of the carbon material has been reduced. It has become possible to balance the diameter.
- the tap density of the carbon material (A) is usually 0.7 g / cm 3 or more, preferably 0.8 g / cm 3 or more, more preferably 0.82 g / cm 3 or more, and further preferably 0.85 g / cm 3. Above, most preferably 0.90 g / cm 3 or more, and usually 1.3 g / cm 3 or less, preferably 1.2 g / cm 3 or less, more preferably 1.1 g / cm 3 or less. is there.
- the tap density is equal to or higher than the lower limit value, it is excellent in processability and high-speed charge / discharge characteristics such as streaking suppression during electrode plate production, and when the tap density is equal to or lower than the upper limit value, the intra-particle carbon density decreases. There exists a tendency for rolling property to become favorable and to form a high-density negative electrode sheet easily.
- the tap density is measured by dropping a carbon material through a sieve having a mesh size of 300 ⁇ m into a cylindrical tap cell having a diameter of 1.6 cm and a volume capacity of 20 cm 3 using a powder density measuring device, and filling the cell with a stroke. This is defined as the density obtained from the volume of the sample and the mass of the sample after performing 1000 taps with a length of 10 mm.
- the d value (interlayer distance, d002) of the lattice plane (002 plane) of the carbon material (A) obtained by X-ray diffraction by the Gakushin method is usually 0.335 nm or more and less than 0.340 nm.
- the d002 value is preferably 0.339 nm or less, more preferably 0.337 nm or less.
- the d002 value is less than or equal to the above upper limit value, it indicates that the crystallinity of graphite is high and the initial irreversible capacity tends to decrease.
- 0.335 nm is a theoretical value of graphite.
- the crystallite size (Lc) of the carbon material (A) determined by X-ray diffraction by the Gakushin method is usually in the range of 1.5 nm or more, preferably 3.0 nm or more. Within this range, the particles have high crystallinity, and the reversible capacity tends to increase when a non-aqueous secondary battery is formed.
- the lower limit of Lc is the theoretical value of graphite.
- Ash content The ash content contained in the carbon material (A) is usually 1% by mass or less, preferably 0.5% by mass or less, and preferably 0.1% by mass or less, based on the total mass of the carbon material (A). It is more preferable. Moreover, it is preferable that the minimum of ash content is 1 ppm or more.
- the ash content is within the above range, when the non-aqueous secondary battery is used, deterioration of battery performance due to the reaction between the carbon material (A) and the electrolytic solution during charge / discharge tends to be suppressed. On the other hand, if it falls below the above range, the production of the carbon material requires a lot of time, energy, and equipment for preventing contamination, which may increase the cost.
- the specific surface area (SA) of the carbon material (A) measured by the BET method is usually 3 m 2 / g or more, preferably 4 m 2 / g or more, more preferably 4.5 m 2 / g or more, particularly preferably. 5.1 m 2 / g or more. Moreover, it is 11 m ⁇ 2 > / g or less normally, Preferably it is 9 m ⁇ 2 > / g or less, More preferably, it is 8 m ⁇ 2 > / g or less.
- the value of the specific surface area is less than or equal to the above upper limit value, when a negative electrode is formed using a carbon material, reactivity with the electrolyte is suppressed, gas generation is suppressed, and a preferred non-aqueous secondary A battery tends to be easily obtained.
- the BET specific surface area is determined by using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken), preliminarily drying the carbon material sample at 350 ° C. for 15 minutes under nitrogen flow, and then relative pressure of nitrogen to atmospheric pressure. This is defined as a value measured by a nitrogen adsorption BET one-point method using a gas flow method, using a nitrogen-helium mixed gas accurately adjusted so that the value of ⁇ is 0.3.
- the pore volume in the range of 10 nm to 1000 nm is a value measured using a mercury intrusion method (mercury porosimetry), and is usually 0.05 mL / g or more, preferably 0.07 mL / g or more, more preferably 0.1 mL / g or more, and usually 0.3 mL / g or less, preferably 0.28 mL / g or less, more preferably 0.25 mL / g or less. is there.
- the pore volume in the range of 10 nm to 1000 nm is equal to or greater than the lower limit of the above range, there are sufficient voids into which the non-aqueous electrolyte solution can enter, so that insertion and desorption of lithium ions and the like can occur when rapid charge / discharge is performed. Proceeding well, along with this, precipitation of lithium metal or the like is suppressed, and the cycle characteristics tend to be good.
- the amount is not more than the upper limit of the above range, it is suppressed that the binder is excessively absorbed in the gap during electrode plate production, and accordingly, a decrease in electrode plate strength and a decrease in initial efficiency tend to be suppressed.
- the total pore volume of the carbon material of the present invention is usually 0.1 mL / g or more, preferably 0.2 mL / g or more, more preferably 0.25 mL / g or more, and further preferably 0.5 mL / g. g or more.
- the total pore volume is usually 10 mL / g or less, preferably 5 mL / g or less, more preferably 2 mL / g or less, and still more preferably 1 mL / g or less.
- the average pore diameter of the carbon material is usually 0.03 ⁇ m or more, preferably 0.05 ⁇ m or more, more preferably 0.1 ⁇ m or more, and further preferably 0.5 ⁇ m or more.
- the average pore diameter is usually 80 ⁇ m or less, preferably 50 ⁇ m or less, more preferably 20 ⁇ m or less.
- the mercury porosimetry apparatus a mercury porosimeter (Autopore 9520: manufactured by Micromeritex Corporation) can be used. A sample (carbon material) is weighed to a value of about 0.2 g, enclosed in a powder cell, and pretreated by degassing at room temperature and under vacuum (50 ⁇ mHg or less) for 10 minutes.
- the pressure is reduced to 4 psia (about 28 kPa)
- mercury is introduced into the cell
- the pressure is increased stepwise from 4 psia (about 28 kPa) to 40000 psia (about 280 MPa), and then the pressure is reduced to 25 psia (about 170 kPa).
- the number of steps at the time of pressure increase is 80 points or more, and the mercury intrusion amount is measured after an equilibration time of 10 seconds in each step.
- the pore distribution is calculated from the mercury intrusion curve thus obtained using the Washburn equation. Note that the surface tension ( ⁇ ) of mercury is calculated as 485 dyne / cm and the contact angle ( ⁇ ) is 140 °.
- the average pore diameter is defined as the pore diameter when the cumulative pore volume is 50%.
- the true density of the carbon material (A) is usually 1.9 g / cm 3 or more, preferably 2 g / cm 3 or more, more preferably 2.1 g / cm 3 or more, and further preferably 2.2 g / cm 3. 3 or more, and the upper limit is 2.26 g / cm 3 .
- the upper limit is the theoretical value of graphite. Below this range, the crystallinity of the carbon is too low, and the initial irreversible capacity of a non-aqueous secondary battery may increase.
- the aspect ratio of the carbon material (A) in the powder state is theoretically 1 or more, preferably 1.1 or more, more preferably 1.2 or more.
- the aspect ratio is usually 10 or less, preferably 8 or less, more preferably 5 or less.
- streaking of the slurry containing the carbon material (negative electrode forming material) at the time of forming the electrode plate is suppressed, or a uniform coated surface can be easily obtained.
- Current density charge / discharge characteristics tend to improve.
- the aspect ratio is expressed as A / B, where the longest diameter A of the carbon material particles when observed three-dimensionally and the shortest diameter B among the diameters perpendicular to the diameter A.
- the carbon material particles are observed with a scanning electron microscope capable of magnifying observation.
- Arbitrary 50 carbon material particles fixed to the end face of a metal having a thickness of 50 microns or less are selected, and the stage on which the sample is fixed is rotated and tilted to measure A and B, and A / B Find the average value of.
- the maximum particle diameter dmax of the carbon material is usually 200 ⁇ m or less, preferably 150 ⁇ m or less, more preferably 120 ⁇ m or less, still more preferably 100 ⁇ m or less, and particularly preferably 80 ⁇ m or less. If dmax is less than or equal to the upper limit value, the occurrence of process inconvenience such as streaking tends to be suppressed.
- the maximum particle size is defined as the largest particle size value measured for the particles in the particle size distribution obtained when measuring the average particle size d50.
- the value of the Raman R value of the carbon material (A) is usually 0.1 or more, preferably 0.15 or more, more preferably 0.2 or more. Further, the Raman R value is usually 0.6 or less, preferably 0.5 or less, more preferably 0.4 or less.
- the Raman R value is measured and the intensity I A of the peak P A in the vicinity of 1580 cm -1 in the Raman spectrum obtained by Raman spectroscopy, the intensity I B of a peak P B in the vicinity of 1360 cm -1, the intensity Defined as the ratio (I B / I A ).
- the range of "1580 cm -1 vicinity" is 1580 ⁇ 1620 cm -1, a range of 1350 ⁇ 1370 cm -1
- the "1360cm around -1" respectively.
- the Raman R value is equal to or more than the lower limit, the crystallinity of the surface of the carbon material particles does not become too high, and when the density is increased, the crystals are difficult to be oriented in the direction parallel to the negative electrode plate, and the load characteristics tend to be improved. There is.
- the Raman R value is less than or equal to the above upper limit value, the disorder of the crystal on the particle surface is suppressed, the reactivity of the negative electrode with the electrolytic solution is suppressed, the charge / discharge efficiency of the nonaqueous secondary battery is reduced, and the gas There is a tendency to suppress the increase in occurrence.
- the Raman spectrum can be measured with a Raman spectrometer. Specifically, the sample particles are naturally dropped into the measurement cell to fill the sample, and the measurement cell is rotated in a plane perpendicular to the laser beam while irradiating the measurement cell with an argon ion laser beam. Measure.
- the measurement conditions are as follows. Argon ion laser light wavelength: 514.5 nm Laser power on sample: 25 mW Resolution: 4cm -1 Measurement range: 1100 cm ⁇ 1 to 1730 cm ⁇ 1 Peak intensity measurement, peak half-width measurement: background processing, smoothing processing (convolution 5 points by simple averaging)
- the DBP (dibutyl phthalate) oil absorption of the carbon material (A) is usually 65 ml / 100 g or less, preferably 62 ml / 100 g or less, more preferably 60 ml / 100 g or less, still more preferably 57 ml / 100 g or less.
- the DBP oil absorption is usually 30 ml / 100 g or more, preferably 40 ml / 100 g or more.
- the DBP oil absorption amount is defined as a measured value when 40 g of a measurement material (carbon material) is added, a dropping speed is 4 ml / min, a rotation speed is 125 rpm, and a set torque is 500 N ⁇ m, in accordance with JIS K6217.
- a measurement material carbon material
- a dropping speed is 4 ml / min
- a rotation speed is 125 rpm
- a set torque is 500 N ⁇ m
- the particle size (d10) corresponding to 10% cumulative from the small particle side of the particle size measured on a volume basis of the carbon material (A) is usually 30 ⁇ m or less, preferably 20 ⁇ m or less, more preferably 17 ⁇ m or less, and usually It is 1 ⁇ m or more, preferably 5 ⁇ m or more, more preferably 10 ⁇ m or more, further preferably 11 ⁇ m or more, and particularly preferably 13 ⁇ m or more.
- d10 When d10 is equal to or higher than the lower limit, the tendency of aggregation of particles is suppressed, and the occurrence of process inconveniences such as an increase in slurry viscosity, the decrease in electrode strength and the decrease in initial charge / discharge efficiency in nonaqueous secondary batteries tend to be suppressed. There is. When d10 is less than or equal to the above upper limit value, the high current density charge / discharge characteristics and the low temperature input / output characteristics tend to be suppressed. d10 is defined as a value obtained by integrating 10% from a particle size having a small particle frequency% in the particle size distribution obtained when measuring the average particle size d50.
- the particle size (d90) corresponding to 90% of the particle size measured on a volume basis of the carbon material (A) is usually 100 ⁇ m or less, preferably 70 ⁇ m or less, more preferably 60 ⁇ m or less, and even more preferably 50 ⁇ m. Hereinafter, it is particularly preferably 45 ⁇ m or less, most preferably 42 ⁇ m or less, usually 20 ⁇ m or more, preferably 26 ⁇ m or more, more preferably 30 ⁇ m or more, and further preferably 34 ⁇ m or more.
- d90 is defined as a value in which the frequency% of particles is 90% integrated from a small particle size in the particle size distribution obtained when measuring the average particle size d50. It is preferable that the conditions (a) and (b) described above are satisfied, and any one or more of the above physical properties are simultaneously satisfied.
- the carbon material of the present invention that satisfies such various conditions includes a natural graphite as a constituent element.
- the amount of desorbed sulfur oxide gas up to 500 ° C. measured with a temperature rising pyrolysis mass spectrometer (TPD-MS) of the carbon material is 0.39 ⁇ mol / g or less, and 5 parts by mass of the carbon material is distilled water.
- TPD-MS temperature rising pyrolysis mass spectrometer
- the process of selecting the graphite which is a raw material for manufacturing a carbon material (A) is although it does not specifically limit, Preferably it is a natural graphite. Natural graphite is produced in Madagascar, China, Brazil, Ukraine, Canada, etc., and scaly graphite is produced mainly in Sri Lanka. The main producers of soil graphite are the Korean Peninsula, China and Mexico. Among natural graphites, for example, scaly, massive, or plate-like natural graphite is preferable, and among these, scaly graphite is more preferable.
- the amount of sulfur element obtained by fluorescent X-ray analysis (XRF) of natural graphite as a raw material is usually 5 ppm or more, preferably 10 ppm or more, more preferably 15 ppm or more, still more preferably 20 ppm or more, and usually 500 ppm or less. It is preferably 300 ppm or less, more preferably 200 ppm or less, still more preferably 170 ppm or less, still more preferably 150 ppm or less, still more preferably 130 ppm or less, particularly preferably 120 ppm or less, and most preferably 100 ppm or less.
- XRF fluorescent X-ray analysis
- the amount of sulfur element is less than or equal to the above upper limit, a carbon material in which sulfur components existing in a highly active state, such as sulfur-containing organic compounds such as sulfuric acid, thiol and thiophene and graphite surface sulfur-containing functional groups, are sufficiently reduced is produced. This makes it easy to suppress the side reaction with the electrolytic solution from proceeding excessively, and thus tends to suppress a decrease in initial efficiency, a decrease in high-temperature storage characteristics, and a decrease in cycle characteristics.
- sulfur-containing organic compounds such as sulfuric acid, thiol and thiophene and graphite surface sulfur-containing functional groups
- the amount of sulfur element (ppm) obtained by fluorescent X-ray analysis (XRF) was mixed with 5 g of graphite particles to be measured, 1 g of stearic acid, and 600 ⁇ l of ethanol, and dried at 80 ° C. After that, it was made into a molded body, and this was used as a measurement sample to perform X-ray fluorescence analysis measurement using a fluorescent X-ray analyzer (ZSX Primus II) manufactured by RIGAKU, and the amount of sulfur element (ppm) calculated using the attached SQX software It is defined as
- the aspect ratio of graphite as a raw material is usually 3 or more, preferably 5 or more, more preferably 10 or more, and still more preferably 15 or more. Moreover, it is 1000 or less normally, Preferably it is 500 or less, More preferably, it is 100 or less, More preferably, it is 50 or less.
- the aspect ratio is measured by the method described above. If the aspect ratio is less than or equal to the above upper limit value, it tends to be suppressed that large particles having a particle size of about 100 ⁇ m are formed, and particles having an aspect ratio that is too small have a small contact area when pressed from one direction.
- the surface spacing (d002) of the 002 plane by X-ray wide angle diffraction of the raw material graphite is usually 3.37 mm or less and Lc is 900 mm or more, and the surface spacing (d002) of the 002 plane (d002) is 3.36 mm or less and Lc is It is preferable that it is 950 mm or more.
- the face spacing (d002) and the crystallite size (Lc) are values indicating the crystallinity of the negative electrode material bulk. The smaller the (002) face spacing (d002) value, the larger the crystallite size. Larger (Lc) indicates a negative electrode material with higher crystallinity, and the capacity increases because the amount of lithium entering the graphite layer approaches the theoretical value.
- the above-mentioned ranges are combined for the interplanar spacing (d002) and the crystallite size (Lc).
- X-ray diffraction is measured by the following method. Carbon powder is mixed with X-ray standard high-purity silicon powder of about 15% by mass of the total amount, and the material is CuK ⁇ rays monochromatized with a graphite monochromator, and the wide angle X is measured by the reflective diffractometer method. A line diffraction curve is measured. Thereafter, the interplanar spacing (d002) and the crystallite size (Lc) are obtained using the Gakushin method.
- the filling structure of graphite which is the raw material, depends on the size, shape, degree of interaction force between particles, etc., but in this specification, the tap density is one of the indicators for quantitatively discussing the filling structure. It is also possible to apply.
- the lead density of the lead-like particles whose true density is almost equal to the average particle diameter shows a higher tap density as the shape is spherical. That is, in order to increase the tap density, it is important to make the shape of the particles round and close to a spherical shape. When the particle shape is close to a spherical shape, the powder filling property is greatly improved.
- the tap density of the flaky graphite is usually 0.1 g / cm 3 or more, preferably 0.2 g / cm 3 or more, and more preferably 0.3 g / cm 3 or more.
- the tap density is measured by the method described later in the examples.
- the argon ion laser Raman spectrum of graphite which is a raw material, is used as an indicator for expressing the surface properties of particles.
- Raman R value is the peak intensity ratio in the vicinity of 1360 cm -1 to the peak intensity near 1580 cm -1 in the argon ion laser Raman spectrum of the flake graphite is usually 0.05 to 0.9, 0.05 or 0. It is preferably 7 or less, more preferably 0.05 or more and 0.5 or less.
- the R value is an index representing the crystallinity in the vicinity of the surface of the carbon particle (from the particle surface to about 100 °), and the smaller the R value, the higher the crystallinity or the disordered crystal state.
- the Raman spectrum is measured by the method shown below.
- the sample particle is naturally dropped into the Raman spectrometer measurement cell, and the sample cell is filled with the sample. While irradiating the measurement cell with an argon ion laser beam, the measurement cell is placed in a plane perpendicular to the laser beam. Measure while rotating. Note that the wavelength of the argon ion laser light is 514.5 nm.
- the X-ray wide angle diffraction method of graphite as a raw material is used as an index representing the crystallinity of the entire particle.
- the ratio 3R / 2H of the intensity 3R (101) of the 101 plane based on the rhombohedral crystal structure by the X-ray wide angle diffraction method and the intensity 2H (101) of the 101 plane based on the hexagonal crystal structure is usually 0. 1 or more, preferably 0.15 or more, and more preferably 0.2 or more.
- the rhombohedral crystal structure is a crystal form in which a stack of graphite network structures is repeated every three layers.
- the hexagonal crystal structure is a crystal form in which a stack of graphite network structures is repeated every two layers.
- acceptability of Li ions and the like is higher than graphite particles with a low ratio of rhombohedral crystal structure 3R.
- BET specific surface area of graphite as a raw material is usually less than 1 m 2 / g or more 30 m 2 / g, preferably not more than 2m 2 / g or more 15m 2 / g, 5m 2 / g or more 10 m 2 / g The following is more preferable.
- the specific surface area by the BET method is measured by the method described above. If the specific surface area of the flaky graphite is too small, the acceptability of Li ions and the like is deteriorated, and if it is too large, the battery capacity tends to be prevented from decreasing due to an increase in irreversible capacity.
- the average particle size (d50) of the raw material graphite is usually 2 ⁇ m to 200 ⁇ m, preferably 3 ⁇ m to 100 ⁇ m, and more preferably 5 ⁇ m to 50 ⁇ m.
- the average particle diameter is measured by the method described above. There exists a tendency which can suppress the increase in the irreversible capacity
- (2nd process) The process of performing the spheroidization process with respect to the graphite which is a raw material
- an apparatus used for the spheronization treatment for example, an apparatus that repeatedly gives mechanical effects such as compression, friction, shearing force, etc. including the interaction of graphite carbonaceous particles, mainly to impact force, to the particles can be used.
- a rotor with a large number of blades installed inside the casing, and when the rotor rotates at high speed, mechanical action such as impact compression, friction, shearing force, etc. is applied to the carbon material introduced inside.
- An apparatus that provides a surface treatment is preferable.
- a hybridization system manufactured by Nara Machinery Co., Ltd.
- a kryptron manufactured by Earth Technica
- a CF mill manufactured by Ube Industries
- a mechano-fusion system Hosokawa Micron
- theta composer manufactured by Deoksugaku Kosakusha
- a hybridization system manufactured by Nara Machinery Co., Ltd. is preferable.
- the peripheral speed of the rotating rotor is usually 30 to 100 m / sec, preferably 40 to 100 m / sec, more preferably 50 to 100 m / sec.
- the treatment for giving a mechanical action to the carbon material can be performed by simply passing graphite, but it is preferable to circulate or stay the graphite in the apparatus for 30 seconds or longer, and to process it for 1 minute or longer in the apparatus. More preferably, the treatment is performed by circulation or retention.
- (Third Step) A step of subjecting the graphite to an acid contact treatment containing nitric acid or hydrochloric acid.
- an acid treatment containing nitric acid or hydrochloric acid is carried out, the graphite without introducing a sulfate which can be a highly active sulfur source into the system. It is preferable because impurities such as metal, metal compound and inorganic compound can be removed.
- the acid treatment may be performed using nitric acid or an acid containing hydrochloric acid, and other acids such as inorganic acids such as bromic acid, hydrofluoric acid, boric acid or iodic acid, or citric acid, formic acid, acetic acid, An acid appropriately mixed with an organic acid such as oxalic acid, trichloroacetic acid or trifluoroacetic acid can also be used. Concentrated hydrofluoric acid, concentrated nitric acid and concentrated hydrochloric acid are preferable, and concentrated nitric acid and concentrated hydrochloric acid are more preferable. In this production method, graphite may be treated with sulfuric acid, but it is used in such an amount and concentration that does not impair the effects and physical properties of the present invention.
- the mixing ratio of the mixed acids when the types of acids are combined is usually 10% by mass or more, preferably 20% by mass or more, and more preferably 25% by mass or more.
- the upper limit is a value obtained by mixing all equal amounts (represented by 100% by mass / acid type). If this amount is equal to or greater than the lower limit, the effect of using a plurality of acids is improved, and the impurities tend to be efficiently removed.
- the mixing ratio of graphite and acid is usually 100: 10 or more, preferably 100: 20 or more, more preferably 100: 30 or more, still more preferably 100: 40 or more, and also 100: 1000 or less, preferably Is 100: 500 or less, more preferably 100: 300 or less.
- the amount of acid in the mixing ratio is less than or equal to the above upper limit value because the amount of graphite that can be washed at one time is increased, so that a decrease in productivity and an increase in cost can be suppressed.
- the acid treatment is performed by immersing graphite in the acidic solution as described above.
- the immersion time is usually 0.5 to 48 hours, preferably 1 to 40 hours, more preferably 2 to 30 and even more preferably 3 to 24 hours.
- productivity reduction and cost increase tend to be suppressed
- the immersion time is equal to or more than the lower limit value
- the impurities tend to be sufficiently removed.
- the immersion temperature is usually 25 ° C. or higher, preferably 40 ° C. or higher, more preferably 50 ° C. or higher, and still more preferably 60 ° C. or higher.
- the theoretical upper limit in the case of using an aqueous acid is 100 ° C., which is the boiling point of water. There exists a tendency which can fully remove the said impurity as this temperature is more than the said lower limit.
- cleans the said processed graphite with water It is preferable to implement the 4th process for the purpose of removing the acid content which remained by acid washing, and raising pH from weakly acidic to a neutral range.
- the pH of the treated graphite is usually 3 or more, preferably 3.5 or more, more preferably 4 or more, and still more preferably 4.5 or more, washing with water can be omitted. If it is not in the above range, it is preferable to wash with water as necessary. It is preferable to use ion-exchanged water or distilled water as the water to be washed from the viewpoint of improving the washing efficiency and preventing impurities from being mixed.
- the specific resistance which is an index of the amount of ions in water, is usually 0.1 M ⁇ ⁇ cm or more, preferably 1 M ⁇ ⁇ cm or more, more preferably 10 M ⁇ ⁇ cm or more.
- the theoretical upper limit at 25 ° C. is 18.24 M ⁇ ⁇ cm. When this numerical value is small, it indicates that the amount of ions in water increases, and there is a tendency for contamination by impurities and a reduction in cleaning efficiency.
- the time for washing with water, that is, stirring the treated graphite and water is usually 0.5 to 48 hours, preferably 1 to 40 hours, more preferably 2 to 30 hours, still more preferably 3 to 24 hours. It's time. When the time is less than or equal to the upper limit, production efficiency tends to improve, and when the time is greater than or equal to the lower limit, residual impurities / acid content tends to decrease.
- the mixing ratio of the treated graphite and water is usually 100: 10 or more, preferably 100: 30 or more, more preferably 100: 50 or more, still more preferably 100: 100 or more, and 100: 1000 or less. Preferably it is 100: 700 or less, More preferably, it is 100: 500 or less, More preferably, it is 100: 400 or less. When the mixing ratio is less than or equal to the upper limit, production efficiency tends to be improved, and when it is greater than or equal to the lower limit, residual impurities / acid content tends to decrease.
- the stirring temperature is usually 25 ° C. or higher, preferably 40 ° C. or higher, more preferably 50 ° C. or higher, and still more preferably 60 ° C. or higher.
- the upper limit is 100 ° C., which is the boiling point of water.
- the stirring temperature is equal to or higher than the lower limit, residual impurities and acid content tend to decrease.
- the water washing treatment is performed in a batch system, it is preferable from the viewpoint of removing impurities and acids to carry out washing by repeating the stirring-filtration treatment step in pure water a plurality of times.
- the above treatment may be repeated so that the above-mentioned treated graphite has a pH in the above range. Usually, it is 1 time or more, preferably 2 times or more, more preferably 3 times or more.
- the wastewater ion concentration of the obtained graphite is usually 200 ppm or less, preferably 100 ppm or less, more preferably 50 ppm or less, more preferably 30 ppm or less, and usually 1 ppm or more, preferably 2 ppm or more, more preferably 3 ppm or more, and further preferably 4 ppm or more. If the ion concentration is less than or equal to the above upper limit value, the remaining acid content tends to be suppressed and the pH is likely to be lowered. There is a tendency to lead to.
- the amount of sulfur element determined by XRF in the obtained graphite by performing the treatment as described above is 130 ppm or less, preferably 120 ppm or less, more preferably 100 ppm or less, still more preferably 80 ppm or less, It is preferably 60 ppm or less, particularly preferably 30 ppm or less, and usually 1 ppm or more, preferably 5 ppm or more, more preferably 10 ppm or more, and further preferably 15 ppm or more.
- the process which heat-processes the said graphite at 200 degreeC or more and 800 degrees C or less is sulfur which exists in a state with high activity, such as sulfur-containing organic compounds, such as sulfuric acid, thiol, and thiophene, and a graphite surface sulfur-containing functional group. It is preferable to carry out for the purpose of controlling the abundance of the components to an appropriate amount.
- the heat treatment temperature is 200 ° C. or higher, preferably 250 ° C. or higher, more preferably 300 ° C. or higher, still more preferably 350 ° C. or higher, and 800 ° C. or lower, preferably 700 ° C.
- the heat treatment temperature is not more than the above upper limit, acidic functional groups such as carboxyl groups and phenol groups existing on the graphite surface are suppressed from desorption, and the slurry viscosity, electrode plate strength, and further deterioration in cycle characteristics are suppressed. Tend.
- the heat treatment temperature is equal to or higher than the lower limit, sulfur components remaining in a highly active state such as sulfur-containing organic compounds such as sulfuric acid, thiol and thiophene, and sulfur-containing functional groups on the graphite surface are suppressed, and initial efficiency and high-temperature storage are suppressed. Deterioration of characteristics and cycle characteristics tends to be suppressed.
- the heat treatment time is usually 0.5 to 48 hours, preferably 1 to 40 hours, more preferably 2 to 30 hours, still more preferably 3 to 24 hours.
- productivity is improved, and when the heat treatment time is greater than or equal to the lower limit, the heat treatment effect tends to be sufficiently exerted.
- the heat treatment atmosphere may be an active atmosphere such as an air atmosphere, or an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere.
- heat treatment is performed at 200 ° C. to 300 ° C., there is no particular limitation, but heat treatment is performed at 300 ° C. or higher.
- the carbon material (A) of the present invention can be manufactured by controlling various conditions regarding the processes as described above.
- the carbon material (A) may be subjected to the following treatment to form a carbon material (hereinafter, referred to as carbon material (B)).
- carbon material (B) a carbon material (hereinafter, referred to as carbon material (B)).
- -Treatment for compounding carbonaceous material with carbon material (A)-Treatment for mixing carbon material (A) and carbon material different from carbon material (A) The control conditions for each treatment are described below.
- a carbonaceous material is added to the carbon material (A) for the purpose of suppressing side reactions with the electrolytic solution and improving rapid charge / discharge characteristics.
- the composite material can be processed (hereinafter, the carbon material (B) obtained by compositing the carbonaceous material with the carbon material (A) may be referred to as “carbonaceous material composite carbon material”).
- the treatment for combining the carbonaceous material with the carbon material (A) is carried out by mixing in order to uniformly coat the organic material on the carbon material (A) having undergone the above-described steps, and preferably in a non-oxidizing atmosphere, preferably nitrogen.
- the organic compound is carbonized or graphitized by heating under a flow of argon, carbon dioxide or the like.
- organic compounds include various soft or hard coal tar pitches, carbon heavy oils such as coal liquefied oil, petroleum heavy oils such as crude oil normal pressure or vacuum distillation residue oil, ethylene by naphtha cracking Various things, such as cracked heavy oil which is a by-product of manufacture, can be used.
- the organic compound include heat-treated pitches such as ethylene tar pitch, FCC decant oil, and Ashland pitch obtained by heat-treating cracked heavy oil.
- vinyl polymers such as polyvinyl chloride, polyvinyl acetate, polyvinyl butyral, and polyvinyl alcohol, substituted phenol resins such as 3-methylphenol formaldehyde resin and 3,5-dimethylphenol formaldehyde resin, and aromatics such as acenaphthylene, decacyclene, and anthracene
- substituted phenol resins such as 3-methylphenol formaldehyde resin and 3,5-dimethylphenol formaldehyde resin
- aromatics such as acenaphthylene, decacyclene, and anthracene
- hydrocarbons nitrogen ring compounds such as phenazine and acridine
- sulfur ring compounds such as thiophene.
- Organic compounds that promote carbonization in the solid phase include natural polymers such as cellulose, chain vinyl resins such as polyvinylidene chloride and polyacrylonitrile, aromatic polymers such as polyphenylene, furfuryl alcohol resins, phenol- Examples thereof include thermosetting resins such as formaldehyde resin and imide resin, and thermosetting resin raw materials such as furfuryl alcohol. Among these, petroleum heavy oil is preferable.
- the heating temperature (firing temperature) varies depending on the organic compound used for the preparation of the mixture, but is usually 800 ° C. or higher, preferably 900 ° C. or higher, more preferably 950 ° C. or higher to sufficiently carbonize or graphitize.
- the upper limit of the heating temperature is a temperature at which the carbide of the organic compound does not reach a crystal structure equivalent to that of the scaly graphite in the mixture, and is usually 3500 ° C. at the highest.
- the upper limit of the heating temperature is 3000 ° C., preferably 2000 ° C., more preferably 1500 ° C.
- the carbonaceous material composite carbon material of the present invention can be obtained by performing crushing and / or grinding treatment.
- the shape is arbitrary, but the average particle size is usually 2 to 50 ⁇ m, preferably 5 to 35 ⁇ m, and particularly 8 to 30 ⁇ m.
- Crushing and / or pulverization is performed so as to be in the above particle size range.
- the content of the carbonaceous material in the carbonaceous material composite carbon material is usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 0.1% by mass relative to the carbon material (A) as a raw material.
- the content is usually 20% by mass or less, preferably 15% by mass or less, more preferably 10% by mass or less, and particularly preferably 7% by mass. % Or less, most preferably 5% by mass or less.
- the carbonaceous material content in the carbonaceous material composite carbon material is less than or equal to the above upper limit value, the carbon material is damaged when rolled at a sufficient pressure to achieve a high capacity in a non-aqueous secondary battery. Therefore, the occurrence of material destruction is suppressed, and the increase in charge / discharge irreversible capacity during initial cycle and the decrease in initial efficiency tend to be suppressed.
- the content is equal to or more than the lower limit value, the effect of coating tends to be sufficiently obtained.
- the content of the carbonaceous material in the carbonaceous material composite carbon material can be calculated from the sample mass before and after the material firing as in the following formula. At this time, it is calculated assuming that there is no mass change before and after the firing of the carbon material (A).
- Carbonaceous material content [(w2-w1) / w1] ⁇ 100 (W1 is the mass (kg) of the carbon material (A), and w2 is the mass (kg) of the carbonaceous composite carbon material)
- the carbon material (A) can be mixed with a carbon material different from the carbon material (A) (hereinafter, the carbon material (A) is mixed with a carbon material different from the carbon material (A)).
- the carbon material (B) obtained in this way may be referred to as “mixed carbon material”).
- the carbon material different from the carbon material (A) is not particularly limited as long as it is other than the carbon material satisfying the above (a) and (b).
- natural graphite, artificial graphite, and carbon material are coated with a carbonaceous material.
- a material selected from the coated graphite, amorphous carbon, carbon material containing metal particles and metal compounds can be used. Any one of these materials may be used alone, or two or more of these materials may be used in any combination and composition.
- high purification means that ash contained in low-purity natural graphite is usually treated in an acid such as hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, or a combination of a plurality of acid treatment steps. It means an operation of dissolving and removing metal and metal, etc., and usually, after the acid treatment step, a water washing treatment or the like is performed to remove the acid content used in the high purification treatment step. Moreover, you may evaporate and remove ash, a metal, etc. by processing at high temperature 2000 degreeC or more instead of an acid treatment process. Moreover, you may remove ash, a metal, etc. by processing in halogen gas atmosphere, such as chlorine gas, at the time of high temperature heat processing. Furthermore, these methods may be used in any combination.
- an acid such as hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, or a combination of a plurality of acid treatment steps. It means an operation of dissolving and removing metal and metal, etc.
- the volume-based average particle diameter of natural graphite is usually 5 ⁇ m or more, preferably 8 ⁇ m or more, more preferably 10 ⁇ m or more, particularly preferably 12 ⁇ m or more, and usually 60 ⁇ m or less, preferably 40 ⁇ m or less, particularly preferably 30 ⁇ m or less. Range. If the average particle diameter is within this range, it is preferable because high-speed charge / discharge characteristics and processability are improved.
- the BET specific surface area of natural graphite is usually 3.5 m 2 / g or more, preferably 4.5 m 2 / g or more, and usually 8 m 2 / g or less, preferably 6 m 2 / g or less. is there.
- the tap density of natural graphite is usually 0.6 g / cm 3 or more, preferably 0.7 g / cm 3 or more, more preferably 0.8 g / cm 3 or more, and further 0.85 g / cm 3 or more. preferable. Moreover, it is 1.3 g / cm ⁇ 3 > or less normally, 1.2 g / cm ⁇ 3 > or less is preferable and 1.1 g / cm ⁇ 3 > or less is more preferable. If it is this range, since a high-speed charge / discharge characteristic and process property become favorable, it is preferable.
- Examples of the artificial graphite include particles obtained by graphitizing a carbon material. For example, a single graphite precursor particle is fired while being powdered, a graphitized particle, and a plurality of graphite precursor particles are molded and fired. Granulated particles that have been graphitized and crushed can be used.
- the volume-based average particle diameter of artificial graphite is usually 5 ⁇ m or more, preferably 10 ⁇ m or more, and usually 60 ⁇ m or less, preferably 40 ⁇ m, more preferably 30 ⁇ m or less. If it is this range, since suppression of an electrode plate swelling and process property become favorable, it is preferable.
- the artificial graphite has a BET specific surface area of usually 0.5 m 2 / g or more, preferably 1.0 m 2 / g or more, and usually 8 m 2 / g or less, preferably 6 m 2 / g or less, more preferably 4 m. 2 / g or less. If it is this range, since suppression of an electrode plate swelling and process property become favorable, it is preferable.
- the tap density of the artificial graphite is usually 0.6 g / cm 3 or more, preferably 0.7 g / cm 3 or more, more preferably 0.8 g / cm 3 or more, and further 0.85 g / cm 3 or more. preferable. Moreover, it is 1.5 g / cm ⁇ 3 > or less normally, 1.4 g / cm ⁇ 3 > or less is preferable and 1.3 g / cm ⁇ 3 > or less is more preferable. If it is this range, since suppression of an electrode plate swelling and process property become favorable, it is preferable.
- Examples of the coated graphite obtained by coating a carbon material with a carbonaceous material include, for example, particles obtained by coating, firing and / or graphitizing an organic compound which is a precursor of the above-described carbonaceous material on natural graphite or artificial graphite, natural graphite or artificial graphite.
- particles obtained by coating a carbonaceous material by CVD can be used.
- the volume-based average particle diameter of the coated graphite is usually 5 ⁇ m or more, preferably 8 ⁇ m or more, more preferably 10 ⁇ m or more, particularly preferably 12 ⁇ m or more, and usually 60 ⁇ m or less, preferably 40 ⁇ m or less, particularly preferably 30 ⁇ m.
- the range is as follows. If the average particle diameter is within this range, it is preferable because high-speed charge / discharge characteristics and processability are improved.
- the BET specific surface area of the coated graphite is usually 1 m 2 / g or more, preferably 2 m 2 / g or more, more preferably 2.5 m 2 / g or more, and usually 8 m 2 / g or less, preferably 6 m. It is 2 / g or less, More preferably, it is the range of 4 m ⁇ 2 > / g or less. If the specific surface area is within this range, it is preferable because high-speed charge / discharge characteristics and processability are improved.
- the tap density of the coated graphite is usually 0.6 g / cm 3 or more, preferably 0.7 g / cm 3 or more, more preferably 0.8 g / cm 3 or more, and further 0.85 g / cm 3 or more. preferable. Moreover, it is 1.3 g / cm ⁇ 3 > or less normally, 1.2 g / cm ⁇ 3 > or less is preferable and 1.1 g / cm ⁇ 3 > or less is more preferable. If the tap density is within this range, it is preferable because high-speed charge / discharge characteristics and processability are improved.
- amorphous carbon for example, particles obtained by firing a bulk mesophase or particles obtained by infusibilizing an easily graphitizable organic compound and firing can be used.
- the volume-based average particle diameter of the amorphous carbon is usually 5 ⁇ m or more, preferably 12 ⁇ m or more, and usually 60 ⁇ m or less, preferably 40 ⁇ m or less. If it is this range, since a high-speed charge / discharge characteristic and process property become favorable, it is preferable.
- the amorphous carbon has a BET specific surface area of usually 1 m 2 / g or more, preferably 2 m 2 / g or more, more preferably 2.5 m 2 / g or more, and usually 8 m 2 / g or less, preferably Is 6 m 2 / g or less, more preferably 4 m 2 / g or less. If the specific surface area is within this range, it is preferable because high-speed charge / discharge characteristics and processability are improved.
- the tap density of amorphous carbon is usually 0.6 g / cm 3 or more, preferably 0.7 g / cm 3 or more, more preferably 0.8 g / cm 3 or more, and 0.85 g / cm 3 or more. Is more preferable. Moreover, it is 1.3 g / cm ⁇ 3 > or less normally, 1.2 g / cm ⁇ 3 > or less is preferable and 1.1 g / cm ⁇ 3 > or less is more preferable. If the tap density is within this range, it is preferable because high-speed charge / discharge characteristics and processability are improved.
- Examples of carbon materials containing metal particles and metal compounds include Fe, Co, Sb, Bi, Pb, Ni, Ag, Si, Sn, Al, Zr, Cr, P, S, V, Mn, Nb, and Mo. , Cu, Zn, Ge, In, Ti, and the like, or a material obtained by combining a metal selected from the group consisting of, for example, graphite with graphite.
- a metal selected from the group consisting of, for example, graphite with graphite.
- the metal or the compound that can be used an alloy composed of two or more kinds of metals may be used, and the metal particles may be alloy particles formed of two or more kinds of metal elements.
- SiOx is obtained using Si dioxide (SiO 2 ) and metal Si (Si) as raw materials, and the value of x is usually 0 ⁇ x ⁇ 2, preferably 0.2 or more, 1.8 Hereinafter, more preferably 0.4 or more and 1.6 or less, and further preferably 0.6 or more and 1.4 or less. If it is this range, it will become high capacity
- the volume-based average particle diameter of the metal particles is usually 0.005 ⁇ m or more, preferably 0.01 ⁇ m or more, more preferably 0.02 ⁇ m or more, and further preferably 0.03 ⁇ m or more. It is 10 ⁇ m or less, preferably 9 ⁇ m or less, more preferably 8 ⁇ m or less.
- the BET specific surface area of the metal particles is usually 0.5 m 2 / g or more and 120 m 2 / g or less, and preferably 1 m 2 / g or more and 100 m 2 / g or less. It is preferable that the specific surface area is within the above range because the battery has high charge / discharge efficiency and high discharge capacity, lithium can be taken in and out at high speed charge / discharge, and the rate characteristics are excellent.
- the apparatus used for mixing the carbon material (A) and the carbon material (A) is not particularly limited.
- a rotary mixer a cylindrical mixer or a twin cylinder type is used. Mixers, double cone mixers, regular cubic mixers, vertical mixers, etc. can be used.
- spiral mixers ribbon mixers, Muller mixers, Helical A Flight type mixer, a Pugmill type mixer, a fluidized type mixer, or the like can be used.
- a negative electrode for a non-aqueous secondary battery of the present invention (hereinafter also referred to as an “electrode sheet” as appropriate) includes a current collector and an active material layer formed on the current collector, and the active material layer is at least the present material layer. It contains the carbon material of the invention. More preferably, it contains a binder.
- the binder one having an olefinically unsaturated bond in the molecule is used.
- the type is not particularly limited, and specific examples include styrene-butadiene rubber, styrene / isoprene / styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene / propylene / diene copolymer.
- styrene-butadiene rubber is preferred because of its availability.
- the strength of the negative electrode plate can be increased.
- the strength of the negative electrode is high, deterioration of the negative electrode due to charge / discharge is suppressed, and the cycle life can be extended.
- the negative electrode according to the present invention has high adhesive strength between the active material layer and the current collector, even when the binder content in the active material layer is reduced, the negative electrode is wound to produce a battery. It is speculated that the problem that the active material layer peels from the current collector does not occur.
- the binder having an olefinically unsaturated bond in the molecule one having a large molecular weight or one having a large proportion of unsaturated bonds is desirable.
- the weight average molecular weight is usually 10,000 or more, preferably 50,000 or more, and usually 1,000,000 or less, preferably 300,000 or less. Is desirable.
- the number of moles of olefinically unsaturated bonds per gram of all binders is usually 2.5 ⁇ 10 ⁇ 7 mol or more, preferably 8 ⁇ 10 ⁇
- the amount is 7 mol or more, and usually 1 ⁇ 10 ⁇ 6 mol or less, preferably 5 ⁇ 10 ⁇ 6 mol or less.
- the binder only needs to satisfy at least one of these regulations regarding molecular weight and regulations regarding the proportion of unsaturated bonds, but it is more preferable to satisfy both regulations simultaneously.
- the mechanical strength is excellent
- the molecular weight is equal to or lower than the upper limit
- the flexibility is excellent.
- the strength improvement effect is sufficiently obtained when the ratio of the olefinically unsaturated bond in the binder is equal to or higher than the lower limit value, and the flexibility is excellent when the ratio is equal to or lower than the upper limit value.
- the binder having an olefinically unsaturated bond has an unsaturation degree of usually 15% or more, preferably 20% or more, more preferably 40% or more, and usually 90% or less, preferably 80%. % Or less.
- the degree of unsaturation represents the ratio (%) of the double bond to the repeating unit of the polymer.
- a binder that does not have an olefinically unsaturated bond can also be used in combination with the above-described binder that has an olefinically unsaturated bond as long as the effects of the present invention are not lost.
- the mixing ratio of the binder having no olefinically unsaturated bond to the binder having an olefinically unsaturated bond is usually 150% by mass or less, preferably 120% by mass or less.
- the coatability can be improved. However, if the combined amount is too large, the strength of the active material layer may be reduced.
- the binder having no olefinic unsaturated bond include thickening polysaccharides such as methylcellulose, carboxymethylcellulose, starch, carrageenan, pullulan, guar gum, xanthan gum (xanthan gum), polyethers such as polyethylene oxide and polypropylene oxide, Vinyl alcohols such as polyvinyl alcohol and polyvinyl butyral, polyacids such as polyacrylic acid and polymethacrylic acid, metal salts of these polymers, fluorine-containing polymers such as polyvinylidene fluoride, alkane polymers such as polyethylene and polypropylene, and these A copolymer etc. are mentioned.
- the ratio of the binder used for the active material layer can be reduced as compared with the conventional material.
- the carbon material of the present invention and a binder in some cases, it may be a mixture of a binder having an unsaturated bond and a binder having no unsaturated bond as described above).
- the mass ratio of each is usually 90/10 or more, preferably 95/5 or more, and usually 99.9 / 0.1 or less, preferably 99.5 / 0.5 in terms of each dry mass ratio.
- the range is as follows. If the binder ratio is less than or equal to the above upper limit value, capacity reduction and resistance increase are suppressed, and if the binder ratio is greater than or equal to the lower limit value, the electrode plate strength tends to be improved.
- the negative electrode of the present invention is formed by dispersing the above-described carbon material of the present invention and a binder in a dispersion medium to form a slurry, which is applied to a current collector.
- a dispersion medium an organic solvent such as alcohol or water can be used.
- a conductive agent may be added to the slurry.
- the conductive agent include carbon black such as acetylene black, ketjen black, and furnace black, and fine powder made of Cu, Ni having an average particle diameter of 1 ⁇ m or less, or an alloy thereof.
- the addition amount of the conductive agent is usually about 10% by mass or less with respect to the carbon material of the present invention.
- a conventionally well-known thing can be used as a collector which apply
- Specific examples include metal thin films such as rolled copper foil, electrolytic copper foil, and stainless steel foil.
- the thickness of the current collector is usually 4 ⁇ m or more, preferably 6 ⁇ m or more, usually 30 ⁇ m or less, preferably 20 ⁇ m or less.
- This slurry was applied to a width of 5 cm using a doctor blade so that the negative electrode material was 14.5 ⁇ 0.3 mg / cm 2 on a 18 ⁇ m-thick copper foil as a current collector, and air-dried at room temperature. I do. Further, after drying at 110 ° C. for 30 minutes, roll pressing is performed using a roller having a diameter of 20 cm to adjust the density of the active material layer to 1.70 ⁇ 0.03 g / cm 3 to obtain an electrode sheet.
- the slurry After applying the slurry on the current collector, the slurry is usually dried at a temperature of 60 ° C. or higher, preferably 80 ° C. or higher, and usually 200 ° C. or lower, preferably 195 ° C. or lower, in dry air or an inert atmosphere. A material layer is formed.
- the thickness of the active material layer obtained by applying and drying the slurry is usually 5 ⁇ m or more, preferably 20 ⁇ m or more, more preferably 30 ⁇ m or more, and usually 200 ⁇ m or less, preferably 100 ⁇ m or less, more preferably 75 ⁇ m or less.
- the thickness of the active material layer is equal to or greater than the lower limit value, it has practicality as a negative electrode in consideration of the particle size of the active material, and if the thickness is equal to or less than the upper limit value, sufficient Li for a high-density current value is obtained. It is easy to obtain occlusion / release functions.
- the density of the carbon material in the active material layer varies depending on the application, but in an application in which capacity is important, it is usually 1.55 g / cm 3 or more, preferably 1.6 g / cm 3 or more, more preferably 1.65 g / cm 3 or more, more preferably 1.7 g / cm 3 or more.
- the density is equal to or higher than the lower limit, the battery capacity per unit volume can be sufficiently obtained.
- a rate characteristic will fall when a density is too high, it is 1.9 g / cm ⁇ 3 > or less normally.
- the method and selection of other materials are not particularly limited.
- the selection of members necessary for the battery configuration such as the positive electrode and the electrolytic solution constituting the lithium ion secondary battery.
- the details of the negative electrode for lithium ion secondary battery and the lithium ion secondary battery using the carbon material of the present invention will be exemplified, but usable materials, production methods and the like are not limited to the following specific examples. Absent.
- the nonaqueous secondary battery of the present invention is not particularly limited as long as it includes a negative electrode including a negative electrode active material composed of the carbon material described above.
- a lithium ion secondary battery when the non-aqueous secondary battery is a lithium ion secondary battery, materials and techniques used for known lithium ion secondary batteries can be appropriately employed.
- a lithium ion secondary battery usually includes a positive electrode, an electrolyte, and a negative electrode, and may include a separator.
- the structure of the non-aqueous secondary battery of the present invention is not particularly limited, and when distinguished by the form and structure, any conventionally known one such as a stacked (flat) battery or a wound (cylindrical) battery can be used.
- the positive electrode usually includes a current collector and a positive electrode active material layer formed on the surface thereof, and the positive electrode active material layer includes a positive electrode active material, a conductive material, and a binder.
- the negative electrode includes a current collector and a negative electrode active material layer formed on the surface thereof, and the negative electrode active material layer includes a negative electrode active material and a binder.
- a negative electrode mixture containing the carbon material of the present invention as a negative electrode active material supported on a negative electrode current collector, an electrode capable of inserting and extracting lithium ions in the state of lithium metal or lithium alloy, etc. can be used.
- Specific types of materials such as positive electrodes (current collectors, positive electrode active materials, conductive materials, binders, etc.), negative separators, electrolytes and the like in the non-aqueous secondary battery of the present invention, and methods for producing the same are, for example, international Since the contents described in the publication No. 2012/157590 can be adopted as appropriate, the description in this specification will be omitted.
- a negative electrode material 20.00 ⁇ 0.02 g of a negative electrode material, 20.00 ⁇ 0.02 g of a 1% by mass aqueous solution of carboxymethylcellulose sodium salt (0.200 g in terms of solid content), and styrene having a weight average molecular weight of 270,000 -Aqueous dispersion of butadiene rubber 0.50 ⁇ 0.05 g (0.2 g in terms of solid content) was stirred for 5 minutes with a hybrid mixer manufactured by Keyence, and defoamed for 30 seconds to obtain a slurry.
- This slurry was applied to a width of 5 cm using a doctor blade so that the negative electrode material was 12.0 ⁇ 0.3 mg / cm 2 on a 18 ⁇ m-thick copper foil as a current collector, and air-dried at room temperature. Went. Further, after drying at 110 ° C. for 30 minutes, roll pressing was performed using a roller having a diameter of 20 cm to adjust the density of the active material layer to be 1.60 ⁇ 0.03 g / cm 3 to obtain a negative electrode sheet.
- Electrolysis in which LiPF 6 was dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate (volume ratio 3: 3: 4) so as to be 1 mol / L, and further 2% by volume of vinylene carbonate was added as an additive. 250 ⁇ l of the liquid was injected to prepare a laminate type battery.
- the discharge capacity (mAh / g) at the time of battery charge / discharge was measured by the following measurement method. Charge to 5 mV with respect to the lithium counter electrode at a current density of 0.05 C, and further charge to a current density of 0.005 C at a constant voltage of 5 mV. After doping lithium into the negative electrode, the current density of 0.1 C Then, the lithium counter electrode was discharged to 1.5V.
- the discharge capacity (mAh / g) at this time is defined as the discharge capacity (mAh / g) of the present carbon material, and the difference between the charge capacity (mAh / g) and the discharge capacity (mAh / g) is the irreversible capacity (mAh / g). did. Further, the first cycle discharge capacity (mAh / g) obtained here was divided by the charge capacity (mAh / g), and a value multiplied by 100 was defined as the initial efficiency (%).
- the voltage change ( ⁇ V / s) was measured by the following measurement method. After charging to 5 mV with respect to the lithium counter electrode at a current density of 0.05 C at 25 ° C., charging until a current density of 0.005 C at a constant voltage of 5 mV, and doping the lithium into the negative electrode, 0. Three cycles of charge / discharge were performed to discharge to 1.5 V with respect to the lithium counter electrode at a current density of 1C.
- the battery was paused, the cell voltage was measured for 1800 seconds after 1800 seconds after the start of the pause, and after 3600 seconds, and the amount of voltage change per unit time ( ⁇ V / s ) was calculated.
- TPD-MS analysis method sulfur oxide gas amount
- TPD-MS temperature rising pyrolysis mass spectrometer
- a carbon material (0.01 g) is suspended in 10 mL of a 0.2 mass% aqueous solution of polyoxyethylene sorbitan monolaurate (for example, Tween 20 (registered trademark)), which is a surfactant, and this is a measurement sample. And introduced into a commercially available laser diffraction / scattering particle size distribution measuring device (for example, LA-920 manufactured by HORIBA), and the measurement sample was irradiated with 28 kHz ultrasonic waves at an output of 60 W for 1 minute, and then the volume-based median diameter was measured in the measuring device. As measured.
- a commercially available laser diffraction / scattering particle size distribution measuring device for example, LA-920 manufactured by HORIBA
- the carbon material of the present invention was dropped into a cylindrical tap cell having a diameter of 1.6 cm and a volume capacity of 20 cm 3 using a powder density measuring instrument through a sieve having an opening of 300 ⁇ m and filled into the cell, and then the stroke length was 10 mm.
- the stroke length was 10 mm.
- PH pH meter
- LAQUA 9615-10D pH measurement electrode
- HORIBA a pH measurement electrode
- 5 g of graphite powder and 30 g of ultrapure water were placed in a polypropylene container, and the mixture was stirred to adjust the graphite and water.
- ultrasonic dispersion treatment was performed for 30 minutes.
- the slurry solution was allowed to stand at 25 ° C. for 30 minutes, and then the pH measurement electrode was placed in the supernatant to measure the pH at 25 ° C.
- an X-ray photoelectron spectrometer for example, ESCA manufactured by ULVAC-PHI
- a measurement target here, a graphite material
- K ⁇ rays of aluminum was used as an X-ray source
- the spectra of C1s (280 to 300 eV) and O1s (525 to 545 eV) were measured by multiplex measurement.
- the obtained C1s peak top was 284.3 eV, and the charge was corrected.
- the peak areas of the C1s and O1s spectra were calculated, and the surface sensitivity of C and O were calculated by multiplying the device sensitivity coefficient.
- the obtained O / C atomic concentration ratio O / C (O atom concentration / C atom concentration) was defined as the surface functional group amount O / C value of the carbon material.
- waste liquid ion concentration The electrical conductivity of the waste liquid was measured using a TDS (Total Dissolved Solids) meter, and the value converted into the NaCl concentration (ppm) was defined as the waste liquid ion concentration in this specification.
- Example 1 Using a spheronizing device having a crushing rotor on naturally produced scaly graphite having a sulfur element content of 140 ppm determined by XRF, mechanical actions such as shear compression, friction, shearing force, etc. were repeatedly applied to scaly graphite particles. Thereafter, classification treatment was performed to obtain spherical natural graphite having a d50 of 20 ⁇ m. The spherical natural graphite was stirred in a mixed acid of concentrated hydrofluoric acid (30% by mass), concentrated hydrochloric acid (31% by mass), and concentrated nitric acid (40% by mass) at 80 ° C. for 15 hours.
- Example 2 The sample obtained in Example 1 was further heat-treated at 380 ° C. for 1 hour to obtain a sample. About this, the same measurement as Example 1 was performed. The results are shown in Tables 1 and 2.
- Example 3 Using a spheronizing device having a pulverizing rotor on naturally produced scale-like graphite having a sulfur element content of 530 ppm determined by XRF, mechanical actions such as shear compression, friction, and shear force were repeatedly given to the scale graphite particles. Thereafter, classification treatment was performed to obtain spherical natural graphite having a d50 of 20 ⁇ m. The spherical natural graphite was stirred in a mixed acid of concentrated hydrofluoric acid (30% by mass), concentrated hydrochloric acid (31% by mass), and concentrated nitric acid (40% by mass) at 80 ° C. for 15 hours.
- Example 4 The sample obtained in Example 1 was further heat-treated at 500 ° C. for 1 hour under a nitrogen atmosphere to obtain a sample. About this, the same measurement as Example 1 was performed. The results are shown in Tables 1 and 2.
- Comparative Example 1 Using a spheronizing device having a pulverizing rotor on naturally produced scale-like graphite having a sulfur element content of 530 ppm determined by XRF, mechanical actions such as shear compression, friction, and shear force were repeatedly given to the scale graphite particles. Thereafter, classification treatment was performed to obtain spherical natural graphite having a d50 of 20 ⁇ m. The spherical natural graphite was stirred in a mixed acid of concentrated hydrofluoric acid (30% by mass), concentrated hydrochloric acid (31% by mass), and concentrated nitric acid (40% by mass) at 80 ° C. for 15 hours.
- Comparative Example 2 Using a spheronizing device having a pulverizing rotor on naturally produced scale-like graphite having a sulfur element content of 530 ppm determined by XRF, mechanical actions such as shear compression, friction, and shear force were repeatedly given to the scale graphite particles. Thereafter, classification treatment was performed to obtain spherical natural graphite having a d50 of 20 ⁇ m. The spherical natural graphite was stirred in a mixed acid of concentrated hydrofluoric acid (30% by mass), concentrated hydrochloric acid (31% by mass), and concentrated nitric acid (40% by mass) at 80 ° C. for 15 hours.
- Comparative Example 3 The sample obtained in Comparative Example 1 was further heat treated at 320 ° C. for 1 hour to obtain a sample. About this, the same measurement as Example 1 was performed. The results are shown in Tables 1 and 2.
- Comparative Example 4 The sample obtained in Comparative Example 1 was further heat-treated at 1300 ° C. for 1 hour under a nitrogen atmosphere to obtain a sample. About this, the same measurement as Example 1 was performed. The results are shown in Tables 1 and 2.
- Comparative Example 5 The sample obtained in Comparative Example 1 was further heat-treated at 1800 ° C. for 1 hour under a nitrogen atmosphere to obtain a sample. About this, the same measurement as Example 1 was performed. The results are shown in Tables 1 and 2.
- Example 6 The sample obtained in Example 1 was further heat-treated at 1300 ° C. for 1 hour under a nitrogen atmosphere to obtain a sample. About this, the same measurement as Example 1 was performed. The results are shown in Tables 1 and 2. In Table 2, “-” means not evaluated.
- Comparative Examples 1 to 3 have a large amount of desorbed sulfur oxide gas up to 500 ° C., the side reaction with the electrolyte proceeds excessively, resulting in a large voltage change during storage, deterioration in high-temperature storage characteristics, A decrease in maintenance rate was observed.
- the amount of desorbed sulfur oxide gas up to 500 ° C. was within the specified range, but since the pH was higher than the specified range, a decrease in peel strength and a decrease in cycle retention were observed.
- Example 4 by setting the amount of desorbed sulfur oxide gas up to 500 ° C. and the pH within the specified range, the voltage change during storage and storage characteristics are excellent, and good peel strength and The cycle maintenance rate was shown.
- Example 4 it is considered that an excellent cycle retention ratio can be achieved by having excellent peel strength, and that a high voltage storage characteristic is excellent by having a small voltage change during storage.
- Example 5 Using a spheronizing device having a crushing rotor on naturally produced scaly graphite having a sulfur element content of 140 ppm determined by XRF, mechanical actions such as shear compression, friction, shearing force, etc. were repeatedly applied to scaly graphite particles. Thereafter, classification treatment was performed to obtain spherical natural graphite having a d50 of 15 ⁇ m. The spherical natural graphite was stirred in a mixed acid of concentrated hydrofluoric acid (30% by mass), concentrated hydrochloric acid (31% by mass), and concentrated nitric acid (40% by mass) at 80 ° C. for 15 hours.
- Example 5 using the sample before complexing with amorphous carbon, the particle size, SA, Tap, pH, O / C, sulfur element amount, SO 2 amount, initial efficiency, discharge capacity were measured by the above measurement method. Was measured. The results are shown in Tables 3 and 4.
- Example 6 Using a spheronizing device having a pulverizing rotor on naturally produced scale-like graphite having a sulfur element content of 530 ppm determined by XRF, mechanical actions such as shear compression, friction, and shear force were repeatedly given to the scale graphite particles. Thereafter, classification treatment was performed to obtain spherical natural graphite having a d50 of 11 ⁇ m. The spherical natural graphite was stirred in a mixed acid of concentrated hydrofluoric acid (30% by mass), concentrated hydrochloric acid (31% by mass), and concentrated nitric acid (40% by mass) at 80 ° C. for 15 hours.
- This multilayer carbon material and the spherical natural graphite of Reference Example 1 were mixed so that the mixing ratio was 10% by mass: 90% by mass to obtain a sample. About this, the initial efficiency and discharge capacity were measured by the said measuring method. The results are shown in Table 4.
- Example 7 A mixed carbon material sample was obtained in the same manner as in Example 6 except that the multilayered carbon material and the spherical natural graphite of Reference Example 1 were mixed so that the mixing ratio was 30% by mass: 70% by mass. It was. About this, the initial efficiency and discharge capacity were measured by the said measuring method. The results are shown in Table 4.
- Comparative Example 7 Using a spheronizing device having a pulverizing rotor on naturally produced scale-like graphite having a sulfur element content of 530 ppm determined by XRF, mechanical actions such as shear compression, friction, and shear force were repeatedly given to the scale graphite particles. Thereafter, classification treatment was performed to obtain spherical natural graphite having a d50 of 11 ⁇ m. The spherical natural graphite was stirred in a mixed acid of concentrated hydrofluoric acid (30% by mass), concentrated hydrochloric acid (31% by mass), and concentrated nitric acid (40% by mass) at 80 ° C. for 15 hours.
- the carbonaceous material-coated graphite (Example 5) obtained by coating the carbonaceous material (A) with a carbonaceous material is different from the carbonaceous material (A) (Reference Example 1) and the carbonaceous material (A) not coated with the carbonaceous material. It was found that the initial efficiency was further improved as compared with the carbonaceous material-coated graphite coated with the carbonaceous material (Comparative Example 7).
- the carbonaceous material (A) and the carbonaceous material (A) are different from the carbonaceous material-coated graphite (Examples 6 and 7) in the mixed carbon material (Examples 6 and 7). I found out that
- the carbon material of the present invention as an active material for a negative electrode of a non-aqueous secondary battery, it is possible to provide a lithium ion secondary battery that is excellent in high capacity and high temperature storage characteristics and has a small amount of gas generation. . Moreover, according to the manufacturing method of the said material, since there are few processes, it can manufacture stably and efficiently and cheaply.
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Abstract
Description
その負極材料として、天然黒鉛、人造黒鉛、炭素繊維、非晶質炭素等々を主成分とする炭素材が用いられているが、これらの中でも天然黒鉛は、性能面、コスト面において優れており技術開発が盛んに行われている。
本発明者らは、特許文献1に記載のような天然黒鉛の表面を非晶質炭素で被覆する技術だけでは更なる電池性能の向上を期待することは難しいと考えた。また、上述したような産地や高純度化する方法が異なる天然黒鉛を用いると、黒鉛自体の品質が安定せず、場合によっては非水系二次電池の高温保存特性やサイクル特性が悪化することがわかってきた。
本発明の炭素材の上述する条件を制御するためには、例えば、熱処理に供する黒鉛中の脱離硫黄酸化物ガス量を制御する方法、熱処理の温度を厳密に制御する方法等が挙げられる。このように特定の昇温時に脱離硫黄酸化物ガス量を制御することにより、酸化還元活性や酸性度の高い硫黄成分を低減させた材となり、電解液との副反応が抑制されると考えられる。
また、分散液のpHを特定の範囲に調整することにより、電極作製に用いるバインダとの強い相互作用を持つことが可能となる。
(a)炭素材の昇温熱分解質量分析計(TPD-MS)による500℃までの脱離硫黄酸化物ガス量が0.39μmol/g以下である。
(b)炭素材5質量部を蒸留水30質量部中に懸濁分散した際の分散液のpHが9以下である。
本発明の炭素材(以下、炭素材(A)という場合もある)は、黒鉛を含み、(a)及び(b)を満たすものである。
本発明の炭素材(A)は(a)及び(b)を満たしつつ、更に黒鉛が含有されていれば特に制限はない。好ましい炭素材(A)としては、(a)及び(b)を満たす黒鉛を含んだ炭素材(A)である。
なお、本明細書でいう黒鉛が含有されているとは、炭素材(A)全量に対して、黒鉛の含有率が、特に制限はないが、通常0.1質量%以上、好ましくは30質量%以上、より好ましくは50質量%以上、更に好ましくは70質量%以上、特に好ましくは100質量%であることを意味する。黒鉛の含有率が高いことで、放電容量の低下や入出力特性の低下が抑制される傾向がある。
これらの含有されている状態は、例えば、X線広角回折法(XRD)、ラマン分光法、電界放射型走査型電子顕微鏡-エネルギー分散型X線(SEM-EDX)分析、X線光電子分光法(XPS)分析等の手法を用いて非水系二次電池負極用活物質の粒子表面、及び粒子断面を観察することにより確認することができる。これらの確認方法は、炭素材(A)が製造された時点で行なってもよいし、本発明に係る炭素材(A)を含む負極や非水系二次電池として製造された製品について行ってもよい。
黒鉛としては天然黒鉛もしくは人造黒鉛が挙げられるが、(a)及び(b)を満たす炭素材(A)となるように適宜選択すれば、特に制限されず、何れかを一種を単独で用いても良く、二種以上を任意の組み合わせ及び組成で併用してもよい。理論上372mAh/gの高い充放電容量を有し、高電流密度での充放電特性に優れ、商業的に容易に入手可能である点から天然黒鉛を用いることが好ましい。
天然黒鉛は、商業的に容易に入手可能であり、理論上372mAh/gの高い充放電容量を有し、さらには他の負極用活物質を用いた場合と比較して、高電流密度での充放電特性の改善効果が大きく見込める。なかでも天然黒鉛は不純物の少ないものが好ましく、必要に応じて、公知である種々の精製処理を施して用いることができる。
天然黒鉛の中でも、例えば、鱗片状、塊状又は板状の天然黒鉛、高純度化した鱗片状黒鉛や球形化処理を施した天然黒鉛が好ましく挙げられる。中でも、粒子の充填性や充放電負荷特性の観点から、鱗片状黒鉛に後述するような球形化処理を施した天然黒鉛が更に好ましい。
人造黒鉛としては、例えば、コールタールピッチ、石炭系重質油、常圧残油、石油系重質油、芳香族炭化水素、窒素含有環状化合物、硫黄含有環状化合物、ポリフェニレン、ポリ塩化ビニル、ポリビニルアルコール、ポリアクリロニトリル、ポリビニルブチラール、天然高分子、ポリフェニレンサルファイド、ポリフェニレンオキシド、フルフリルアルコール樹脂、フェノール-ホルムアルデヒド樹脂、イミド樹脂などの有機物を焼成し、黒鉛化したものが挙げられる。
本明細書において、炭素材料とは本発明の炭素材(A)中に黒鉛以外に含むことのできる炭素材料のことをいう。
炭素材料としては、リチウムイオン、ナトリウムイオン等を吸蔵・放出可能な物質であれば特に限定されず、例えば、非晶質炭素、黒鉛化度の小さい炭素質物粒子またはシリコン‐炭素複合体が挙げられる。これらを単独で、又は二種以上を組み合わせて使用することができる。これらの炭素材料と天然黒鉛の炭素材(A)中の状態は上述したように特に制限はされない。
黒鉛化度の小さい炭素質物粒子としては、有機物を通常2500℃未満の温度で焼成したものが挙げられる。有機物としては、コールタールピッチ、乾留液化油などの石炭系重質油;常圧残油、減圧残油などの直留系重質油;原油、ナフサなどの熱分解時に副生するエチレンタール等の分解系重質油などの石油系重質油;アセナフチレン、デカシクレン、アントラセンなどの芳香族炭化水素;フェナジンやアクリジンなどの窒素含有環状化合物;チオフェンなどの硫黄含有環状化合物;アダマンタンなどの脂肪族環状化合物;ビフェニル、テルフェニルなどのポリフェニレン、ポリ塩化ビニル、ポリ酢酸ビニル、ポリビニルブチラールなどのポリビニルエステル類、ポリビニルアルコールなどの熱可塑性高分子などが挙げられる。
焼成の際、有機物に燐酸、ホウ酸、塩酸などの酸類、水酸化ナトリウム等のアルカリ類などを混合することもできる。
本発明の炭素材(A)は、以下の(a)及び(b)を満たすことを特徴とする。
(a)炭素材の昇温熱分解質量分析計(TPD-MS)による500℃までの脱離硫黄酸化物ガス量
本発明の炭素材(A)の昇温熱分解質量分析計(TPD-MS)による500℃までの脱離硫黄酸化物ガス量は、通常0μmol/gより大きく、好ましくは0.01μmol/g以上、より好ましくは0.02μmol/g以上、更に好ましくは0.03μmol/g以上、特に好ましくは0.04μmol/g以上、最も好ましくは0.05μmol/g以上であり、また0.39μmol/g以下であり、好ましくは0.35μmol/g以下、より好ましくは0.30μmol/g以下、更に好ましくは0.25μmol/g以下、特に好ましくは0.2μmol/g以下である。
500℃までの脱離硫黄酸化物ガス量とは、硫酸、チオール及びチオフェンといった含硫黄有機化合物、スルホ基及びスルホニル基などの黒鉛表面含硫黄官能基など、活性の高い状態で存在する硫黄成分を意味する。
脱離硫黄酸化物ガス量が多すぎると電解液との副反応が過剰に進行することにより、初期効率の低下、高温保存特性の低下、サイクル特性の低下を招く傾向がある。一方、硫黄有機化合物の中でも特定の含硫黄有機化合物や黒鉛表面含硫黄官能基は電池特性においてSEI形成において重要な働きをしているため、活性の高い硫黄成分が微量に存在していることが充放電不可逆容量や高温保存特性やサイクル特性が良好となる点から好ましい。
本発明の炭素材5質量部を蒸留水30質量部中に懸濁分散した際の分散液のpHは、9以下であり、好ましくは8.5以下、より好ましくは8以下、更に好ましくは7.5以下、特に好ましくは7以下であり、下限は特に制限はないが、通常4.5以上、好ましくは4.8以上、より好ましくは5.0以上、更に好ましくは5.4以上、特に好ましくは、5.6以上である。言い換えれば、通常、炭素材5質量部を蒸留水30質量部中に懸濁分散した際の分散液が弱酸性から中性の間であることが特に好ましい。
炭素材5質量部を蒸留水30質量部中に懸濁分散した際の分散液のpHは、不純物として含まれる硫酸や塩酸や硝酸などの無機酸の量や、黒鉛表面に存在するカルボキシ基やフェノール基などの酸性官能基の量に相関していると考えられる。
以下に、本発明の炭素材(A)の上述した以外の物性を記載する。
X線光電子分光法測定としてX線光電子分光器(例えば、アルバック・ファイ社製ESCA)を用い、測定対象(ここでは炭素材)を表面が平坦になるように試料台に載せ、アルミニウムのKα線をX線源とし、マルチプレックス測定により、C1s(280~300eV)とO1s(525~545eV)のスペクトルを測定する。得られたC1sのピークトップを284.3eVとして帯電補正し、C1sとO1sのスペクトルのピーク面積を求め、更に装置感度係数を掛けて、CとOの表面原子濃度をそれぞれ算出する。得られたそのOとCの原子濃度比O/C(O原子濃度/C原子濃度)を炭素材の表面官能基量O/C値と定義する。
炭素材(A)の体積基準平均粒径(「平均粒径d50」とも記載する)は通常5μm以上、好ましくは10μm以上、より好ましくは15μm以上、更に好ましくは19μm以上、特に好ましくは20μm以上である。また平均粒径d50は50μm以下、より好ましくは40μm以下、更に好ましくは35μm以下、特に好ましくは31μm以下である。平均粒径d50が前記下限値以上であると、前記炭素材(A)を用いて得られる非水系二次電池の不可逆容量の増加及び初期電池容量の損失が抑制される傾向があり、一方平均粒径d50が前記上限値以下であると、スラリー塗布における筋引きなどの工程上の不都合の発生、高電流密度充放電特性の低下及び低温入出力特性の低下が抑制される傾向がある。
炭素材(A)の円形度は、0.88以上、好ましくは0.90以上、より好ましくは0.91以上である。また、円形度は通常1以下、好ましくは0.98以下、より好ましくは0.97以下である。円形度が前記下限値以上であると、非水系二次電池の高電流密度充放電特性が向上する傾向がある。なお、円形度は以下の式で定義され、円形度が1のときに理論的真球となる。
=(粒子投影形状と同じ面積を持つ相当円の周囲長)/(粒子投影形状の実際の周囲長)
円形度の値としては、例えば、フロー式粒子像分析装置(例えば、シスメックスインダストリアル社製FPIA)を用い、試料(炭素材)約0.2gを、界面活性剤であるポリオキシエチレン(20)ソルビタンモノラウレートの0.2質量%水溶液(約50mL)に分散させ、分散液に28kHzの超音波を出力60Wで1分間照射した後、検出範囲を0.6~400μmに指定し、粒径が1.5~40μmの範囲の粒子について測定した値を用いる。
従来の球形化処理技術では、以上説明したような高い円形度を達成しようとすると、炭素材の平均粒径が小さくなってしまったが、近年の技術の進歩により、高い円形度と大きな平均粒径とを両立できるようになった。
炭素材(A)のタップ密度は通常0.7g/cm3以上、好ましくは0.8g/cm3以上、より好ましくは0.82g/cm3以上、更に好ましくは0.85g/cm3以上、最も好ましくは0.90g/cm3以上であり、また通常1.3g/cm3以下であり、好ましくは1.2g/cm3以下であり、より好ましくは1.1g/cm3以下である。
前記タップ密度は、粉体密度測定器を用い、直径1.6cm、体積容量20cm3の円筒状タップセルに、目開き300μmの篩を通して炭素材を落下させて、セルに満杯に充填した後、ストローク長10mmのタップを1000回行なって、その時の体積と試料の質量から求めた密度として定義する。
炭素材(A)の、学振法によるX線回折で求めた格子面(002面)のd値(層間距離、d002)は、通常0.335nm以上、0.340nm未満である。ここで、d002値は好ましくは0.339nm以下、更に好ましくは0.337nm以下である。d002値が前記上限値以下であるということは黒鉛の結晶性が高いことを示し、初期不可逆容量が低下する傾向がある。一方0.335nmは黒鉛の理論値である。
また、学振法によるX線回折で求めた前記炭素材(A)の結晶子サイズ(Lc)は、通常1.5nm以上、好ましくは3.0nm以上の範囲である。この範囲内であると、結晶性が高い粒子となり、非水系二次電池とした場合に可逆容量が増加する傾向がある。なお、Lcの下限は黒鉛の理論値である。
炭素材(A)に含まれる灰分は、炭素材(A)の全質量に対して、通常1質量%以下、0.5質量%以下であることが好ましく、0.1質量%以下であることがより好ましい。また、灰分の下限は1ppm以上であることが好ましい。
灰分が前記の範囲内であると非水系二次電池とした場合に、充放電時の炭素材(A)と電解液との反応による電池性能の劣化が抑制される傾向がある。一方前記の範囲を下回ると、炭素材の製造に多大な時間とエネルギーと汚染防止のための設備とを必要とし、コストが上昇する場合がある。
炭素材(A)のBET法により測定した比表面積(SA)は、通常3m2/g以上、好ましくは4m2/g以上、更に好ましくは4.5m2/g以上、特に好ましくは5.1m2/g以上である。また、通常11m2/g以下、好ましくは9m2/g以下、より好ましくは8m2/g以下である。
比表面積が前記下限値以上であると、Li等が出入りする部位が充分にあり、高速充放電特性出力特性に優れる傾向があり、一方、比表面積が前記上限値以下であると、活物質の電解液に対する活性が抑制され、初期不可逆容量が小さくなるため、高容量電池の製造が容易になる傾向がある。
BET比表面積は、表面積計(例えば、大倉理研製全自動表面積測定装置)を用い、炭素材試料に対して窒素流通下350℃で15分間予備乾燥を行なった後、大気圧に対する窒素の相対圧の値が0.3となるように正確に調整した窒素ヘリウム混合ガスを用い、ガス流動法による窒素吸着BET1点法によって測定した値として定義する。
炭素材(A)において、10nm~1000nmの範囲の細孔容積は、水銀圧入法(水銀ポロシメトリー)を用いて測定した値であり、通常0.05mL/g以上であり、好ましくは0.07mL/g以上、更に好ましくは0.1mL/g以上であり、また、通常0.3mL/g以下であり、好ましくは0.28mL/g以下、更に好ましくは0.25mL/g以下である。
また、本発明の炭素材の全細孔容積は、通常0.1mL/g以上であり、好ましくは0.2mL/g以上、より好ましくは0.25mL/g以上、更に好ましくは0.5mL/g以上である。また全細孔容積は通常10mL/g以下であり、好ましくは5mL/g以下、より好ましくは2mL/g以下、更に好ましくは1mL/g以下である。
また、炭素材の平均細孔径は、通常0.03μm以上であり、好ましくは0.05μm以上、より好ましくは0.1μm以上、更に好ましくは0.5μm以上である。また前記平均細孔径は通常80μm以下であり、好ましくは50μm以下、より好ましくは20μm以下である。
上記水銀ポロシメトリー用の装置として、水銀ポロシメータ(オートポア9520:マイクロメリテックス社製)を用いることができる。試料(炭素材)を0.2g前後の値となるように秤量し、パウダー用セルに封入し、室温、真空下(50μmHg以下)にて10分間脱気して前処理を実施する。
昇圧時のステップ数は80点以上とし、各ステップでは10秒の平衡時間の後、水銀圧入量を測定する。こうして得られた水銀圧入曲線からWashburnの式を用い、細孔分布を算出する。
なお、水銀の表面張力(γ)は485dyne/cm、接触角(ψ)は140°として算出する。平均細孔径は、累計細孔体積が50%となるときの細孔径として定義する。
炭素材(A)の真密度は、通常1.9g/cm3以上であり、好ましくは2g/cm3以上、より好ましくは2.1g/cm3以上、更に好ましくは2.2g/cm3以上であり、また上限は2.26g/cm3である。上限は黒鉛の理論値である。この範囲を下回ると炭素の結晶性が低すぎて、非水系二次電池とした場合の、その初期不可逆容量が増大する場合がある。
炭素材(A)の粉末状態でのアスペクト比は、理論上1以上であり、好ましくは1.1以上、より好ましくは1.2以上である。またアスペクト比は通常10以下、好ましくは8以下、より好ましくは5以下である。
アスペクト比が前記上限値以下であると、極板化時に炭素材を含むスラリー(負極形成材料)のスジ引きが抑制され、あるいは均一な塗布面が容易に得られ、非水系二次電池の高電流密度充放電特性が向上する傾向がある。
炭素材の最大粒径dmaxは、通常200μm以下、好ましくは150μm以下、より好ましくは120μm以下、更に好ましくは100μm以下、特に好ましくは80μm以下である。dmaxが前記上限値以下であるとスジ引きなどの工程不都合の発生が抑制される傾向がある。
また、最大粒径は、平均粒径d50の測定の際に得られた粒度分布において、粒子について測定された最も大きい粒径の値として定義される。
炭素材(A)のラマンR値は、その値は通常0.1以上であり、好ましくは0.15以上、更に好ましくは0.2以上である。また、ラマンR値は通常0.6以下であり、好ましくは0.5以下、より好ましくは0.4以下である。
なお、前記ラマンR値は、ラマン分光法で求めたラマンスペクトルにおける1580cm-1付近のピークPAの強度IAと、1360cm-1付近のピークPBの強度IBとを測定し、その強度比(IB/IA)として算出されたものと定義する。
なお、本明細書において「1580cm-1付近」とは1580~1620cm-1の範囲を、「1360cm-1付近」とは1350~1370cm-1の範囲をそれぞれ指す。
測定条件は以下の通りである。
アルゴンイオンレーザー光の波長 :514.5nm
試料上のレーザーパワー :25mW
分解能 :4cm-1
測定範囲 :1100cm-1~1730cm-1
ピーク強度測定、ピーク半値幅測定:バックグラウンド処理、スムージング処理(単純平均によるコンボリューション5ポイント)
炭素材(A)のDBP(フタル酸ジブチル)吸油量は、通常65ml/100g以下、好ましくは62ml/100g以下、より好ましくは60ml/100g以下、更に好ましくは57ml/100g以下である。また、DBP吸油量は通常30ml/100g以上、好ましくは40ml/100g以上である。
また、DBP吸油量は、JIS K6217に準拠し、測定材料(炭素材)を40g投入し、滴下速度4ml/min、回転数125rpm、設定トルク500N・mとしたときの測定値として定義される。測定には、例えばブラベンダー社製 アブソープトメーター E型を用いることができる。
炭素材(A)の体積基準で測定した粒径の、小さい粒子側から累積10%に相当する粒径(d10)は通常30μm以下であり、好ましくは20μm以下、より好ましくは17μm以下、また通常1μm以上であり、好ましくは5μm以上、より好ましくは10μm以上、更に好ましくは11μm以上、特に好ましくは13μm以上である。
d10は、平均粒径d50の測定の際に得られた粒度分布において、粒子の頻度%が小さい粒径から積算で10%となった値として定義される。
炭素材(A)の体積基準で測定した粒径の、小さい粒子側から累積90%に相当する粒径(d90)は通常100μm以下、好ましくは70μm以下、より好ましくは60μm以下、更に好ましくは50μm以下、特に好ましくは45μm以下、最も好ましくは42μm以下、通常20μm以上、好ましくは26μm以上、より好ましくは30μm以上、更に好ましくは34μm以上である。
d90は、平均粒径d50の測定の際に得られた粒度分布において、粒子の頻度%が小さい粒径から積算で90%となった値として定義される。
以上説明した条件(a)及び(b)を満たし、さらに上記物性の何れか1つ又は複数を同時に満たしていることが好ましい。このような種々の条件を満たす本発明の炭素材は、天然黒鉛を含むことを構成要素としている。
炭素材(A)は、炭素材の昇温熱分解質量分析計(TPD-MS)による500℃までの脱離硫黄酸化物ガス量が0.39μmol/g以下、及び炭素材5質量部を蒸留水30質量部中に懸濁分散した際の分散液のpHが9以下となるように製造すれば特に制限はないが、達成手段の一つとしては、蛍光X線元素分析(XRF)から求められる硫黄元素量が130ppm以下である黒鉛を200℃以上800℃以下の温度で熱処理することによって得ることができる。
炭素材(A)の原料として黒鉛の蛍光X線元素分析(XRF)から求められる硫黄元素量が多すぎる場合、炭素材の昇温熱分解質量分析計(TPD-MS)による500℃までの脱離硫黄酸化物ガス量を0.39μmol/g以下にすることが難しくなる傾向がある。
また、前記熱処理温度が低すぎる場合、やはり、炭素材の昇温熱分解質量分析計(TPD-MS)による500℃までの脱離硫黄酸化物ガス量を0.39μmol/g以下にすることが難しくなる傾向があり、前記熱処理温度が高すぎる場合、炭素材5質量部を蒸留水30質量部中に懸濁分散した際の分散液のpHを9以下にすることが難しくなる傾向がある。
蛍光X線元素分析(XRF)から求められる硫黄元素量が130ppm以下である黒鉛を得、200℃以上800℃以下の温度で熱処理するには、具体的には、以下のような工程を含み、且つこれらを厳密に制御することによって製造できる。
(第1工程)炭素材(A)を製造するための原料である黒鉛を選択する工程
(第2工程)黒鉛に対して球形化処理を行う工程
(第3工程)前記黒鉛に硝酸、もしくは塩酸を含む酸接触処理を施す工程
(第4工程)前記処理黒鉛を水で洗浄する工程
・熱処理する工程
(第5工程)前記黒鉛を200℃以上800℃以下で熱処理をする工程
以下に、(1)~(5)工程ごとの制御条件を記載する。
炭素材(A)の原料となる黒鉛は特に限定されないが、好ましくは天然黒鉛である。天然黒鉛の産地は、マダガスカル、中国、ブラジル、ウクライナ、カナダ等であり、鱗状黒鉛の産地は、主にスリランカである。土壌黒鉛の主な産地は、朝鮮半島、中国、メキシコ等である。天然黒鉛の中でも、例えば、鱗片状、塊状又は板状の天然黒鉛が好ましく、中でも、鱗片状黒鉛がより好ましい。
原料である黒鉛のアスペクト比は通常3以上であり、好ましくは5以上、より好ましくは10以上、更に好ましくは15以上である。また、通常1000以下であり、好ましくは500以下、より好ましくは100以下、更に好ましくは50以下である。アスペクト比は、既述の方法により測定する。アスペクト比が前記上限値以下であると粒径が100μm程度の大きな粒子ができることが抑制される傾向があり、アスペクト比が小さすぎる粒子は、一方向からの加圧をした際に接触面積が小さいため、強固な造粒体が形成されない傾向があり、また粒子を造粒しても鱗片状黒鉛の小さい比表面積が反映して、比表面積が30m2/gを超える造粒体となる傾向がある。
必要に応じて第一工程で選択した原料に対して球形化処理を行う工程を施してもよい。
球形化処理に用いる装置としては、例えば、衝撃力を主体に、黒鉛炭素質物粒子の相互作用も含めた圧縮、摩擦、せん断力等の機械的作用を繰り返し粒子に与える装置を用いることができる。
炭素材料に機械的作用を与える好ましい装置としては、例えば、ハイブリダイゼーションシステム(奈良機械製作所社製)、クリプトロン(アーステクニカ社製)、CFミル(宇部興産社製)、メカノフュージョンシステム(ホソカワミクロン社製)、シータコンポーザ(徳寿工作所社製)等が挙げられる。これらの中で、奈良機械製作所社製のハイブリダイゼーションシステムが好ましい。
硝酸、もしくは塩酸を含む酸処理を行うと、活性の高い硫黄元となりうる硫酸塩を系内に導入することなく黒鉛中の金属、金属化合物、無機化合物などの不純物を除去できるため好ましい。
なお、上記酸処理は、硝酸、もしくは塩酸を含む酸を用いればよく、その他の酸、例えば、臭素酸、フッ酸、ホウ酸あるいはヨウ素酸などの無機酸、または、クエン酸、ギ酸、酢酸、シュウ酸、トリクロロ酢酸あるいはトリフルオロ酢酸などの有機酸を適宜混合した酸を用いることもできる。好ましくは濃フッ酸、濃硝酸、濃塩酸であり、より好ましくは濃硝酸、濃塩酸である。なお、本製法において硫酸にて黒鉛を処理してもよいが、本発明の効果や物性を損なわない程度の量と濃度にて用いることとする。
上記のように酸の種類を組み合わせた場合の混合酸の混合比率は、最も少ないものが通常10質量%以上であり、好ましくは20質量%以上、より好ましくは、25質量%以上である。上限は、全て等量混合した値である(100質量%/酸の種類で表される)。この量が前記下限値以上であると、酸を複数用いた効果が向上して、上記不純物を効率良く除去できる傾向がある。
浸漬温度は、通常25℃以上、好ましくは40℃以上、より好ましくは50℃以上、更に好ましくは、60℃以上である。水系の酸を用いる場合の理論上限は水の沸点である100℃である。この温度が前記下限値以上であると、上記不純物を十分に除去できる傾向がある。
第4工程は、酸洗浄により残った酸分を除去し、pHを弱酸性から中性域にまで上昇させる目的で実施することが好ましい。
例えば、前記処理黒鉛のpHが、通常3以上であり、好ましくは3.5以上、より好ましくは4以上、更に好ましくは4.5以上であれば、水で洗浄することは省略できるし、もし上記範囲でなければ、必要に応じて水で洗浄することが好ましい。洗浄する水は、イオン交換水や蒸留水を用いることが、洗浄効率の向上、不純物混入防止の観点から好ましい。水中のイオン量の指標となる比抵抗が、通常0.1MΩ・cm以上であり、好ましくは1MΩ・cm以上、より好ましくは、更に好ましくは10MΩ・cm以上、である。25℃での理論上限は18.24MΩ・cmである。この数値が小さいと水中のイオン量が多くなることを示しており、不純物混入、洗浄効率低下の傾向がある。
前記処理黒鉛と水との混合割合は、通常100:10以上であり、好ましくは100:30以上、より好ましくは100:50以上、更に好ましくは100:100以上であり、また100:1000以下、好ましくは100:700以下、より好ましくは100:500以下、更に好ましくは100:400以下である。混合割合が前記上限値以下であると生産効率が向上する傾向があり、前記下限値以上であると残留不純物・酸分が減少する傾向になる。
また、水洗浄処理をバッチ式にて行う場合は、純水中での攪拌-ろ過の処理工程を複数回繰り返して洗浄行うことが不純物・酸分除去の観点から好ましい。上記処理は、上述した処理黒鉛のpHが上記範囲になるように繰り返し行ってもよい。通常、1回以上であり、好ましくは2回以上、より好ましくは3回以上である。
硫黄元素量が前記上限値以下であると、初期効率の低下、高温保存特性の低下及びサイクル特性の低下が抑制される傾向があり、前記下限値以上であると、高温保存時のガス発生量の低減に必要な活性硫黄微量成分が充分に存在し高温保存時のガス発生量が減少する傾向がある。
第5工程は硫酸、チオールやチオフェンといった含硫黄有機化合物や黒鉛表面含硫黄官能基など、活性の高い状態で存在する硫黄成分の存在量を、適切な量に制御する目的で実施することが好ましい。
熱処理温度は、200℃以上であり、好ましくは250℃以上、より好ましくは、300℃以上、更に好ましくは、350℃以上であり、また800℃以下であり、好ましくは700℃以下、より好ましくは650℃以下、更に好ましくは600℃以下である。熱処理温度が前記上限値以下であると、黒鉛表面に存在するカルボキシル基やフェノール基などの酸性官能基が脱離が抑制され、スラリー粘度や極板強度、さらにはサイクル特性の低下が抑制される傾向がある。熱処理温度が前記下限値以上であると、硫酸やチオールやチオフェンといった含硫黄有機化合物や黒鉛表面含硫黄官能基など、活性の高い状態で存在する硫黄成分の残留が抑制され、初期効率、高温保存特性及びサイクル特性の低下が抑制される傾向になる。
熱処理の雰囲気は、大気雰囲気などの活性雰囲気、もしくは、窒素雰囲気やアルゴン雰囲気などの不活性雰囲気があげられ、200℃~300℃で熱処理する場合には特段制限はないが、300℃以上で熱処理を行う場合には、黒鉛表面の酸化を防止する観点で、窒素雰囲気やアルゴン雰囲気などの不活性雰囲気が好ましい。
以上、上述したような工程に関し、様々な条件を制御することで、本発明の炭素材(A)を製造することができる。
本発明では、炭素材(A)に対し、下記の処理を施し炭素材としてもよい(以下、炭素材(B)と呼ぶことがある)。
・炭素材(A)に炭素質物を複合化する処理
・炭素材(A)と炭素材(A)とは異なる炭素材料を混合する処理
以下に、各処理の制御条件を記載する。
本発明では、必要に応じて、電解液との副反応抑制や、急速充放電性の向上を目的とし、炭素材(A)に炭素質物を複合化する処理をすることができる(以下、炭素材(A)に炭素質物を複合化して得られた炭素材(B)を「炭素質物複合炭素材」と呼ぶことがある)。
炭素材(A)に炭素質物を複合化する処理は上述のような工程を経た炭素材(A)に有機化合物を均一に被覆するために、混合を行い、非酸化性雰囲気下、好ましくは窒素、アルゴン、二酸化炭素などの流通下に加熱して、有機化合物を炭素化又は黒鉛化させる処理である。
また、有機化合物としては、分解系重質油を熱処理することで得られるエチレンタールピッチ、FCCデカントオイル、アシュランドピッチなどの熱処理ピッチ等を挙げることができる。さらにポリ塩化ビニル、ポリビニルアセテート、ポリビニルブチラール、ポリビニルアルコール等のビニル系高分子と3-メチルフェノールホルムアルデヒド樹脂、3,5-ジメチルフェノールホルムアルデヒド樹脂等の置換フェノール樹脂、アセナフチレン、デカシクレン、アントラセンなどの芳香族炭化水素、フェナジンやアクリジンなどの窒素環化合物、チオフェンなどのイオウ環化合物などを挙げることができる。また、固相で炭素化を進行させる有機化合物としては、セルロースなどの天然高分子、ポリ塩化ビニリデンやポリアクリロニトリルなどの鎖状ビニル樹脂、ポリフェニレン等の芳香族系ポリマー、フルフリルアルコール樹脂、フェノール-ホルムアルデヒド樹脂、イミド樹脂等熱硬化性樹脂やフルフリルアルコールのような熱硬化性樹脂原料などを挙げることができる。これらの中でも石油系重質油が好ましい。
形状は任意であるが、平均粒径は、通常2~50μmであり、5~35μmが好ましく、特に8~30μmである。上記粒径範囲となるように解砕及び/又は粉砕を行う。また、この後に、分級する工程を行うことが好ましい。
なお、本発明の効果を損なわない限り、等方的加圧処理をはじめ他の工程の追加又は上述に記載のない制御条件を追加してもよい。
炭素質物複合炭素材中の炭素質物の含有量は、原料となる炭素材(A)に対して、通常0.01質量%以上であり、好ましくは0.1質量%以上、更に好ましくは0.3%以上、特に好ましくは0.7質量%以上であり、また前記含有量は、通常20質量%以下であり、好ましくは15質量%以下、更に好ましくは10質量%以下、特に好ましくは7質量%以下、最も好ましくは5質量%以下である。
一方、含有量が前記下限値以上であると、被覆による効果が充分に得られる傾向がある。
(w1を炭素材(A)の質量(kg)、w2を炭素質物複合炭素材の質量(kg)とする)
本発明では、極板の配向性、電解液の浸透性、導電パス等を向上させ、サイクル特性、極板膨れ等の改善を目的とし、炭素材(A)に炭素材(A)とは異なる炭素材料を混合することができる(以下、炭素材(A)に炭素材(A)とは異なる炭素材料を混合して得られた炭素材(B)を「混合炭素材」と呼ぶことがある)。
炭素材(A)とは異なる炭素材料としては、上記の(a)及び(b)を満足する炭素材料以外であれば特に制限されず、例えば天然黒鉛、人造黒鉛、炭素材を炭素質物で被覆した被覆黒鉛、非晶質炭素、金属粒子や金属化合物を含有した炭素材の中から選ばれる材料を用いることができる。これらの材料は、何れかを一種を単独で用いてもよく、二種以上を任意の組み合わせ及び組成で併用してもよい。
天然黒鉛のBET比表面積は、通常3.5m2/g以上であり、好ましくは4.5m2/g以上、また、通常8m2/g以下であり、好ましくは6m2/g以下の範囲である。比表面積がこの範囲であれば、高速充放電特性、工程性が良好となるため好ましい。
また、天然黒鉛のタップ密度は、通常0.6g/cm3以上であり、0.7g/cm3以上が好ましく、0.8g/cm3以上がより好ましく、0.85g/cm3以上が更に好ましい。また、通常1.3g/cm3以下であり、1.2g/cm3以下が好ましく、1.1g/cm3以下がより好ましい。この範囲であれば高速充放電特性及び工程性が良好となるため好ましい。
人造黒鉛の体積基準平均粒径は、通常5μm以上であり、好ましくは10μm以上、また、通常60μm以下、好ましくは40μm、更に好ましくは30μm以下の範囲である。この範囲であれば、極板膨れの抑制や工程性が良好となるため好ましい。
人造黒鉛のBET比表面積は、通常0.5m2/g以上であり、好ましくは1.0m2/g以上、また、通常8m2/g以下、好ましくは6m2/g以下、更に好ましくは4m2/g以下の範囲である。この範囲であれば、極板膨れの抑制及び工程性が良好となるため好ましい。
被覆黒鉛のBET比表面積は、通常1m2/g以上であり、好ましくは2m2/g以上、更に好ましくは2.5m2/g以上、また、通常8m2/g以下であり、好ましくは6m2/g以下、更に好ましくは4m2/g以下の範囲である。比表面積がこの範囲であれば、高速充放電特性及び工程性が良好となるため好ましい。
非晶質炭素の体積基準平均粒径は、通常5μm以上であり、好ましくは12μm以上、また、通常60μm以下であり、好ましくは40μm以下の範囲である。この範囲であれば、高速充放電特性及び工程性が良好となるため好ましい。
非晶質炭素のBET比表面積は、通常1m2/g以上であり、好ましくは2m2/g以上、更に好ましくは2.5m2/g以上、また、通常8m2/g以下であり、好ましくは6m2/g以下、更に好ましくは4m2/g以下の範囲である。比表面積がこの範囲であれば、高速充放電特性及び工程性が良好となるため好ましい。
金属粒子の体積基準平均粒径は、サイクル寿命の観点から、通常0.005μm以上であり、好ましくは0.01μm以上、より好ましくは0.02μm以上、更に好ましくは0.03μm以上であり、通常10μm以下であり、好ましくは9μm以下、より好ましくは8μm以下である。平均粒径がこの範囲であると充放電に伴う体積膨張が低減され、充放電容量を維持しつつ、良好なサイクル特性を得ることができる。
金属粒子のBET比表面積は、通常0.5m2/g以上120m2/g以下であり、1m2/g以上100m2/g以下であることが好ましい。比表面積が前記範囲内であると、電池の充放電効率および放電容量が高く、高速充放電においてリチウム等の出し入れが速く、レート特性に優れるので好ましい。
本発明の非水系二次電池用負極(以下適宜「電極シート」ともいう。)は、集電体と、集電体上に形成された活物質層とを備えると共に、活物質層は少なくとも本発明の炭素材とを含有する。更に好ましくはバインダを含有する。
本発明においては、オレフィン性不飽和結合を有さないバインダも、本発明の効果が失われない範囲において、上述のオレフィン性不飽和結合を有するバインダと併用することができる。オレフィン性不飽和結合を有するバインダに対する、オレフィン性不飽和結合を有さないバインダの混合比率は、通常150質量%以下であり、好ましくは120質量%以下の範囲である。
オレフィン性不飽和結合を有さないバインダの例としては、メチルセルロース、カルボキシメチルセルロース、澱粉、カラギナン、プルラン、グアーガム、ザンサンガム(キサンタンガム)等の増粘多糖類、ポリエチレンオキシド、ポリプロピレンオキシド等のポリエーテル類、ポリビニルアルコール、ポリビニルブチラール等のビニルアルコール類、ポリアクリル酸、ポリメタクリル酸等のポリ酸、及びこれらポリマーの金属塩、ポリフッ化ビニリデン等の含フッ素ポリマー、ポリエチレン、ポリプロピレンなどのアルカン系ポリマー及びこれらの共重合体などが挙げられる。
このスラリーを、集電体である厚さ18μmの銅箔上に、負極材料が14.5±0.3mg/cm2付着するように、ドクターブレードを用いて幅5cmに塗布し、室温で風乾を行う。更に110℃で30分乾燥後、直径20cmのローラを用いてロールプレスして、活物質層の密度が1.70±0.03g/cm3になるよう調整し電極シートが得られる。
スラリーを塗布、乾燥して得られる活物質層の厚さは、通常5μm以上であり、好ましくは20μm以上、更に好ましくは30μm以上、また、通常200μm以下であり、好ましくは100μm以下、更に好ましくは75μm以下である。活物質層の厚さが前記下限値以上であると、活物質の粒径との兼ね合いから負極としての実用性を有し、前記上限値以下であると、高密度の電流値に対する十分なLi等の吸蔵・放出の機能が得られ易い。
本発明の非水系二次電池は、前述の炭素材から構成される負極活物質を含む負極を備えるものであれば、その他については特に限定されない。例えば、非水系二次電池がリチウムイオン二次電池の場合、公知のリチウムイオン二次電池に用いられる材料、技術を適宜採用することができる。リチウムイオン二次電池は、通常、正極、電解質、負極を備えるものであり、セパレータを備えるものであってもよい。また、本発明の非水系二次電池の構造も特に限定されず、形態・構造で区別した場合には、積層型(扁平型)電池、捲回型(円筒型)電池等、従来公知のいずれの形態・構造にも適用しうる。さらに電気的な接続形態(電池構造)で見た場合、(内部並列接続タイプ)電池及び双極型(内部直列接続タイプ)電池のいずれにも適用しうるものである。
正極は、通常、集電体とその表面に形成された正極活物質層を含み、正極活物質層は、正極活物質、導電材及び結着剤を含む。負極は、集電体とその表面に形成された負極活物質層を含み、負極活物質層は負極活物質及び結着剤を含む。また、負極としては、負極活物質として本発明の炭素材を含む負極合剤を負極集電体に担持したもの、リチウム金属又はリチウム合金等の状態でリチウムイオンを吸蔵・脱離可能な電極を用いることができる。
本発明の非水系二次電池における正極(集電体、正極活物質、導電材、結着剤等)、負セパレータ、電解質等の具体的な材料の種類およびその製造方法等については、例えば国際公開第2012/157590号等の公報に記載されている内容を適宜採用することができるため、本明細書における記載を省略するものとする。
(負極シートの作製方法)
本発明の炭素材を負極材料として用い、活物質層密度1.60±0.03g/cm3の活物質層を有する極板を作製した。具体的には、負極材料20.00±0.02gに、1質量%カルボキシメチルセルロースナトリウム塩水溶液を20.00±0.02g(固形分換算で0.200g)、及び重量平均分子量27万のスチレン・ブタジエンゴム水性ディスパージョン0.50±0.05g(固形分換算で0.2g)を、キーエンス製ハイブリッドミキサーで5分間撹拌し、30秒脱泡してスラリーを得た。
上記方法で作製した電極シートを4cm×3cmの正方形に切り出し負極とし、LiCoO2からなる正極を同面積で切り出し、負極と正極の間にはセパレータ(多孔性ポリエチレンフィルム製)を置いて組み合わせ、この電極群を2セット積層させた。エチレンカーボネートとジメチルカーボネートとエチルメチルカーボネートの混合溶媒(容積比=3:3:4)に、LiPF6を1mol/Lになるように溶解させ、更に添加剤としてビニレンカーボネートを2容積%添加した電解液を250μl注液してラミネート型電池を作製した。
上述の方法で作製したラミネート型電池を、12時間放置した後、電流密度0.2CmA/cm3で、両電極間の電位差が4.1Vになるまで充電を行い、その後3Vになるまで0.2CmA/cm3で放電を行った。これを2回繰り返し、更に同電流値で、両電極間の電位差が4.2Vになるまで充電を実施した。ここまでに発生する膨れ量a(mL)は、浸漬容積法(アルキメデスの原理に基づく溶媒置換法)により計測した。その後、85℃の恒温槽内に24時間日間放置して、更に膨れる量b(mL)を求め、「a+b(mL)」を「高温耐久試験時のセル膨れ量」とした。表1の結果は、ラミネート型電池2個について、それぞれ測定し平均値を求めることで得た。
上記方法で作製した電極シートを直径12.5mmの円盤状に打ち抜き、リチウム金属箔を直径14mmの円板状に打ち抜き対極とした。両極の間には、エチレンカーボネートとエチルメチルカーボネートの混合溶媒(容積比=3:7)に、LiPF6を1mol/Lになるように溶解させた電解液を含浸させたセパレータ(多孔性ポリエチレンフィルム製)を置き、2016コイン型電池をそれぞれ作製した。
前述の方法で作製した非水系二次電池(2016コイン型電池)を用いて、下記の測定方法で電池充放電時の放電容量(mAh/g)を測定した。
0.05Cの電流密度でリチウム対極に対して5mVまで充電し、さらに5mVの一定電圧で電流密度が0.005Cになるまで充電し、負極中にリチウムをドープした後、0.1Cの電流密度でリチウム対極に対して1.5Vまで放電を行った。このときの放電容量(mAh/g)を本炭素材の放電容量(mAh/g)とし、充電容量(mAh/g)と放電容量(mAh/g)の差分を不可逆容量(mAh/g)とした。また、ここで得られた1サイクル目の放電容量(mAh/g)を充電容量(mAh/g)で割り返し、100倍した値を初回効率(%)とした。
前述の方法で作製した非水系二次電池(2016コイン型電池)を用いて、下記の測定方法で電圧変化(μV/s)を測定した。
25℃で、0.05Cの電流密度でリチウム対極に対して5mVまで充電し、さらに5mVの一定電圧で電流密度が0.005Cになるまで充電し、負極中にリチウムをドープした後、0.1Cの電流密度でリチウム対極に対して1.5Vまで放電を行う充放電を3サイクル行った。さらに、0.05Cの電流密度でSOC50%まで充電をした後、休止し、休止開始1800秒後から3600秒後の1800秒間におけるセル電圧を測定し、単位時間当たりの電圧変化量(μV/s)を算出した。
昇温熱分解質量分析計(TPD-MS)による500℃までの脱離硫黄酸化物ガス量;
黒鉛粉末サンプル300mgを試料台へのせ、ヘリウムガス60ml/min流通下、10℃/minの昇温速度で、室温から500℃まで昇温し、その時に発生した硫黄酸化物ガス量(m/z=48)を質量分析計で測定した。この測定値を、ピロ亜硫酸ナトリウム(Na2S2O5)のTPD-MSによる室温から400℃までの硫黄酸化物ガス量(m/z=48)をもとに炭素材1g当たりの発生量(μmol)へ換算した。
上述の方法で作製した電極シートを25℃で真空乾燥したものを用いて(活物質層の含水分量:200ppm)、後述の方法で作製したラミネート型電池を作製した。これを、0.2Cで4.2VまでCC-CV充電し、60℃で8週間保存した。保存後のセル電圧を測定し、4.2Vからの低下電圧の低下量を算出した。上述の負極活物質層の含水分量は、カールフィッシャー法により算出した。
なお、保存特性は比較例1を基準とした向上率で評価した結果を表に示した。
上述の方法で作製したラミネート型電池を、0.8Cで4.2Vまで充電、0.5Cで3・0Vまでの放電を繰り返し、1サイクル目の放電容量に対する200サイクル目の放電容量の比×100をサイクル維持率(%)とした。
界面活性剤であるポリオキシエチレンソルビタンモノラウレート(例として、ツィーン20(登録商標)が挙げられる)の0.2質量%水溶液10mLに、炭素材0.01gを懸濁させ、これを測定サンプルとして市販のレーザー回折/散乱式粒度分布測定装置(例えばHORIBA製LA-920)に導入し、測定サンプルに28kHzの超音波を出力60Wで1分間照射した後、前記測定装置において体積基準のメジアン径として測定した。
表面積計(大倉理研製全自動表面積測定装置)を用い、炭素材試料に対して窒素流通下350℃で15分間予備乾燥を行なった後、大気圧に対する窒素の相対圧の値が0.3となるように正確に調整した窒素ヘリウム混合ガスを用い、ガス流動法による窒素吸着BET1点法によって測定した。
粉体密度測定器を用い、直径1.6cm、体積容量20cm3の円筒状タップセルに、目開き300μmの篩を通して本発明の炭素材を落下させて、セルに満杯に充填した後、ストローク長10mmのタップを1000回行なって、その時の体積と試料の質量から求めた密度として定義した。
pHの測定には、pHメーター(HORIBA社製 Phemeter F-51)、pH測定用電極(HORIBA社製LAQUA 9615-10D)を用いた。ポリプロピレン製容器に5gの黒鉛粉末と30gの超純水とを入れ、攪拌して黒鉛と水を馴染ませた後、30分間超音波分散処理を行った。このスラリー溶液を25℃で30分静置後、上澄み液に上記pH測定用電極を入れて25℃におけるpHを測定した。
X線光電子分光法測定としてX線光電子分光器(例えば、アルバック・ファイ社製ESCA)を用い、測定対象(ここでは黒鉛材料)を表面が平坦になるように試料台に載せ、アルミニウムのKα線をX線源とし、マルチプレックス測定により、C1s(280~300eV)とO1s(525~545eV)のスペクトルを測定した。得られたC1sのピークトップを284.3eVとして帯電補正し、C1sとO1sのスペクトルのピーク面積を求め、更に装置感度係数を掛けて、CとOの表面原子濃度をそれぞれ算出した。得られたそのOとCの原子濃度比O/C(O原子濃度/C原子濃度)を炭素材料の表面官能基量O/C値と定義した。
測定対象となる黒鉛粒子5gとステアリン酸1gとエタノール600μlを混合し、80℃で乾燥した後、成型体にし、これを測定サンプルとして、RIGAKU社製蛍光X線分析装置(ZSX PrimusII)を用いて蛍光X線分析測定を行い、付属のSQXソフトウェアを用いて算出した硫黄元素量(ppm)を、本明細における蛍光X線分析(XRF)により求めた硫黄元素量(ppm)と定義した。
TDS(Total Dissolved Solids)メーターを用いて廃液の電気伝導度を測定し、NaClの濃度(ppm)に換算した値を、本明細における、廃液イオン濃度と定義した。
負極シートを幅20mmに切断し、試験用SUS板に両面テープで貼付(活物質層側を両面テープ面で貼付)して、水平方向に固定し、負極シートの端部を万能試験機の挟持部に挟んだ。この状態で万能試験機の負極シート固定部分を垂直方向に下降させ、負極シートを両面テープから90度の角度で引っ張ることにより剥離した。この際に、負極シートと両面テープの間に掛かった荷重の平均値を測定し、負極シートサンプル幅(20mm)で割った値をピール強度値(mN/mm)として用いた。
XRFにより求めた硫黄元素量が140ppmである天然に産出する鱗片状黒鉛に粉砕ローターを有する球形化装置を用いて、せん断圧縮、摩擦、せん断力等の機械的作用を繰り返し鱗片黒鉛粒子に与えた後、分級処理を行い、d50が20μmの球状天然黒鉛を得た。この球状天然黒鉛を濃弗酸(30質量%)、濃塩酸(31質量%)、及び濃硝酸(40質量%)の混酸中で80℃、15時間攪拌し、その後純水で廃水イオン濃度が20ppmになるまで洗浄した(XRFにより求めた硫黄元素量は20ppm)。このサンプルを260℃で6時間熱処理してサンプルを得た。これについて、前記測定法で粒径、SA、Tap、pH、O/C、硫黄元素量、SO2量(硫黄酸化物ガス量)、ピール強度、保存特性、保存ガス量、サイクル維持率を測定した。結果を表1、表2に示す。
実施例1で得られたサンプルを、さらに380℃にて1時間熱処理してサンプルを得た。これについて、実施例1と同様の測定を行った。結果を表1、表2に示す。
XRFにより求めた硫黄元素量が530ppmである天然に産出する鱗片状黒鉛に粉砕ローターを有する球形化装置を用いて、せん断圧縮、摩擦、せん断力等の機械的作用を繰り返し鱗片黒鉛粒子に与えた後、分級処理を行い、d50が20μmの球状天然黒鉛を得た。この球状天然黒鉛を濃弗酸(30質量%)、濃塩酸(31質量%)、及び濃硝酸(40質量%)の混酸中で80℃、15時間攪拌し、その後純水で廃水イオン濃度が20ppmになるまで洗浄する工程を2回繰り返した(XRFにより求めた硫黄元素量は68ppm)。このサンプルを260℃で6時間熱処理してサンプルを得た。これについて、実施例1と同様の測定を行った。結果を表1、表2に示す。
実施例1で得られたサンプルを、さらに窒素雰囲気下で500℃にて1時間熱処理してサンプルを得た。これについて、実施例1と同様の測定を行った。結果を表1、表2に示す。
XRFにより求めた硫黄元素量が530ppmである天然に産出する鱗片状黒鉛に粉砕ローターを有する球形化装置を用いて、せん断圧縮、摩擦、せん断力等の機械的作用を繰り返し鱗片黒鉛粒子に与えた後、分級処理を行い、d50が20μmの球状天然黒鉛を得た。この球状天然黒鉛を濃弗酸(30質量%)、濃塩酸(31質量%)、及び濃硝酸(40質量%)の混酸中で80℃、15時間攪拌し、その後純水で廃水イオン濃度が40ppmになるまで洗浄した(XRFにより求めた硫黄元素量は150ppm)。このサンプルを180℃で6時間熱処理してサンプルを得た。これについて、実施例1と同様の測定を行った。結果を表1、表2に示す。
XRFにより求めた硫黄元素量が530ppmである天然に産出する鱗片状黒鉛に粉砕ローターを有する球形化装置を用いて、せん断圧縮、摩擦、せん断力等の機械的作用を繰り返し鱗片黒鉛粒子に与えた後、分級処理を行い、d50が20μmの球状天然黒鉛を得た。この球状天然黒鉛を濃弗酸(30質量%)、濃塩酸(31質量%)、及び濃硝酸(40質量%)の混酸中で80℃、15時間攪拌し、その後純水で廃水イオン濃度が20ppmになるまで洗浄する工程を2回繰り返した(XRFにより求めた硫黄元素量は68ppm)。このサンプルを180℃で6時間熱処理してサンプルを得た。これについて、実施例1と同様の測定を行った。結果を表1、表2に示す。
比較例1で得られたサンプルを、さらに320℃にて1時間熱処理してサンプルを得た。これについて、実施例1と同様の測定を行った。結果を表1、表2に示す。
比較例1で得られたサンプルを、さらに窒素雰囲気下で1300℃にて1時間熱処理してサンプルを得た。これについて、実施例1と同様の測定を行った。結果を表1、表2に示す。
比較例1で得られたサンプルを、さらに窒素雰囲気下で1800℃にて1時間熱処理してサンプルを得た。これについて、実施例1と同様の測定を行った。結果を表1、表2に示す。
実施例1で得られたサンプルを、さらに窒素雰囲気下で1300℃にて1時間熱処理してサンプルを得た。これについて、実施例1と同様の測定を行った。結果を表1、表2に示す。なお、表2中の「-」は未評価であることを意味する。
XRFにより求めた硫黄元素量が140ppmである天然に産出する鱗片状黒鉛に粉砕ローターを有する球形化装置を用いて、せん断圧縮、摩擦、せん断力等の機械的作用を繰り返し鱗片黒鉛粒子に与えた後、分級処理を行い、d50が15μmの球状天然黒鉛を得た。この球状天然黒鉛を濃弗酸(30質量%)、濃塩酸(31質量%)、及び濃硝酸(40質量%)の混酸中で80℃、15時間攪拌し、その後純水で廃水イオン濃度が20ppmになるまで洗浄した(XRFにより求めた硫黄元素量は20ppm)。このサンプルを窒素雰囲気下で500℃にて1時間熱処理した。得られたサンプルと非晶質炭素前駆体としてナフサ熱分解時に得られる石油系重質油を混合し、不活性ガス中で1300℃熱処理を施した後、焼成物を粉砕・分級処理することにより、黒鉛粒子と非晶質炭素とが複合化した複層構造炭素材を得た。
これについて、前記測定法で粒径、SA、Tap、初期効率、放電容量を測定した。結果を表3、表4に示す。
実施例5において、非晶質炭素で複合化する前のサンプルを用いて、前記測定法で粒径、SA、Tap、pH、O/C、硫黄元素量、SO2量、初期効率、放電容量を測定した。結果を表3、表4に示す。
XRFにより求めた硫黄元素量が530ppmである天然に産出する鱗片状黒鉛に粉砕ローターを有する球形化装置を用いて、せん断圧縮、摩擦、せん断力等の機械的作用を繰り返し鱗片黒鉛粒子に与えた後、分級処理を行い、d50が11μmの球状天然黒鉛を得た。この球状天然黒鉛を濃弗酸(30質量%)、濃塩酸(31質量%)、及び濃硝酸(40質量%)の混酸中で80℃、15時間攪拌し、その後純水で廃水イオン濃度が40ppmになるまで洗浄した(XRFにより求めた硫黄元素量は150ppm)。このサンプルを180℃で6時間熱処理し、d50が11.2μm、SAが8.3m2/g、Tap密度が0.85g/cm3の球状天然黒鉛を得た。これに非晶質炭素前駆体としてナフサ熱分解時に得られる石油系重質油を混合し、不活性ガス中で1300℃熱処理を施した後、焼成物を粉砕・分級処理することにより、黒鉛粒子と非晶質炭素とが複合化した複層構造炭素材を得た。
この複層構造炭素材と参考例1の球状天然黒鉛を、混合比が10質量%:90質量%となるように混合してサンプルを得た。これについて、前記測定法で初期効率、放電容量を測定した。結果を表4に示す。
複層構造炭素材と参考例1の球状天然黒鉛を、混合比が30質量%:70質量%となるように混合した以外は実施例6と同様にして、混合された炭素材のサンプルを得た。これについて、前記測定法で初期効率、放電容量を測定した。結果を表4に示す。
XRFにより求めた硫黄元素量が530ppmである天然に産出する鱗片状黒鉛に粉砕ローターを有する球形化装置を用いて、せん断圧縮、摩擦、せん断力等の機械的作用を繰り返し鱗片黒鉛粒子に与えた後、分級処理を行い、d50が11μmの球状天然黒鉛を得た。この球状天然黒鉛を濃弗酸(30質量%)、濃塩酸(31質量%)、及び濃硝酸(40質量%)の混酸中で80℃、15時間攪拌し、その後純水で廃水イオン濃度が40ppmになるまで洗浄した(XRFにより求めた硫黄元素量は150ppm)。このサンプルを180℃で6時間熱処理し、d50が11.2μm、SAが8.3m2/g、Tap密度が0.85g/cm3の球状天然黒鉛を得た。これに非晶質炭素前駆体としてナフサ熱分解時に得られる石油系重質油を混合し、不活性ガス中で1300℃熱処理を施した後、焼成物を粉砕・分級処理することにより、黒鉛粒子と非晶質炭素とが複合化した複層構造炭素材を得た。これについて、前記測定法で粒径、SA、Tap、初期効率、放電容量を測定した。結果を表3、表4に示す。
Claims (9)
- 黒鉛を含み、(a)及び(b)を満たす炭素材。
(a)炭素材の昇温熱分解質量分析計(TPD-MS)による500℃までの脱離硫黄酸化物ガス量が0.39μmol/g以下である。
(b)炭素材5質量部を蒸留水30質量部中に懸濁分散した際の分散液のpHが9以下である。 - 表面官能基量O/Cが0.8%以上4%以下である請求項1に記載の炭素材。
- 該黒鉛が球形化天然黒鉛である請求項1又は2に記載の炭素材。
- 請求項1から3のいずれか一項に記載の炭素材と炭素質物とを含有する複合化した炭素材。
- 請求項1から3のいずれか一項に記載の炭素材と、請求項1から3のいずれか一項に記載の炭素材とは異なる炭素材料とを含有する混合された炭素材。
- 蛍光X線元素分析(XRF)から求められる硫黄元素量が130ppm以下である黒鉛を、200℃以上800℃以下の温度で熱処理する前処理を含む炭素材の製造方法。
- 該黒鉛の硫黄元素量が120ppm以下である請求項6に記載の炭素材の製造方法。
- リチウムイオンを吸蔵・放出可能な正極及び負極、並びに、電解質を備え、該負極が、集電体と、該集電体上に形成された請求項1から3のいずれか一項に記載の炭素材を含有する活物質層とを備える非水系二次電池。
- リチウムイオンを吸蔵・放出可能な正極及び負極、並びに、電解質を備え、該負極が、集電体と、該集電体上に形成された請求項4に記載の複合化した炭素材又は請求項5に記載の混合された炭素材を含有する活物質層とを備える非水系二次電池。
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