WO2017047523A1 - グラフェン分散液およびその製造方法、グラフェン-活物質複合体粒子の製造方法ならびに電極用ペーストの製造方法 - Google Patents
グラフェン分散液およびその製造方法、グラフェン-活物質複合体粒子の製造方法ならびに電極用ペーストの製造方法 Download PDFInfo
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Definitions
- the present invention relates to a graphene dispersion, a method for producing the same, a method for producing graphene-active material composite particles using the same, and a method for producing an electrode paste.
- Graphene is a two-dimensional crystal composed of carbon atoms, and has been attracting much attention since it was discovered in 2004. Graphene has excellent electrical, thermal, optical, and mechanical properties and is expected to be widely applied in areas such as battery materials, energy storage materials, electronic devices, and composite materials.
- Examples of the method for producing graphene include a mechanical peeling method, a CVD (Chemical Vapor Deposition) method, a CEG (Crystal Epoxy Growth) method, and the like.
- the oxidation-reduction method that is, the method of producing graphene by the reduction reaction after obtaining graphite oxide or graphene oxide by oxidation treatment of natural graphite is promising as an industrial production method because mass production is possible. It is.
- flaky graphite having a high specific surface area is produced by heating and reducing graphene oxide and simultaneously exfoliating and peeling.
- Patent Document 2 graphene powder with high dispersibility is produced by chemically reducing graphene and freeze-drying it.
- a graphene powder is produced by drying a dispersion medium from a graphene dispersion obtained by applying ultrasonic waves to a mixed liquid containing graphite particles.
- An object of the present invention is to provide graphene in a form that is highly dispersible and that can maintain high conductivity and ion conductivity when used as a raw material for producing an electrode material.
- the present invention for solving the above problems is a graphene dispersion obtained by dispersing graphene in an organic solvent, and the median diameter of graphene measured by a laser diffraction / scattering particle size distribution measurement method is D ( ⁇ m),
- D the median diameter of graphene measured by a laser diffraction / scattering particle size distribution measurement method
- S the average value of the surface direction of graphene obtained by the arithmetic mean of the longest and shortest diameters of graphene observed with a laser microscope.
- the method for producing the graphene dispersion of the present invention includes: A reduction step of reducing graphene oxide dispersed in a dispersion medium containing water; A refining step for refining graphene oxide or graphene contained in the intermediate dispersion before or after the reduction step or during the reduction step; An organic solvent mixing step of mixing the intermediate dispersion liquid that has undergone the reduction step and the miniaturization step and the organic solvent; A strong stirring step of stirring an intermediate dispersion containing an organic solvent at a shear rate of 5000 to 50,000 per second; A method of combining organic solvent addition and suction filtration, or a water removal step of removing at least part of the water from the intermediate dispersion by distillation; It is a manufacturing method of the graphene dispersion which has this.
- the present invention it is possible to provide a graphene dispersion in which sufficiently thin graphene to function as a conductive additive is sufficiently dispersed in an organic solvent, and excessive aggregation is suppressed.
- a graphene dispersion By using such a graphene dispersion, the dispersibility of graphene in the resin or electrode paste is improved. Further, since graphene can be easily adsorbed on the surface of the active material, high electron conductivity and ion conductivity can be maintained for a long time when an electrode is formed.
- the graphene dispersion of the present invention is a graphene dispersion in which graphene is dispersed in an organic solvent, and the median diameter of graphene measured by a laser diffraction / scattering particle size distribution measurement method is D ( ⁇ m), measured by a laser microscope.
- D the median diameter of graphene measured by a laser diffraction / scattering particle size distribution measurement method
- S the average value of the graphene surface direction obtained by the arithmetic mean of the longest diameter and the shortest diameter of the graphene.
- the following expressions (1) and (2) are simultaneously satisfied. is there. 0.5 ⁇ m ⁇ S ⁇ 15 ⁇ m (1) 1.0 ⁇ D / S ⁇ 3.0 (2)
- the median diameter D of the graphene dispersion is a particle diameter corresponding to the median value of the particle size distribution measured using the graphene dispersion directly on a laser diffraction / scattering particle size distribution measuring apparatus.
- the average value S of the size in the plane direction of the graphene obtained by the arithmetic average of the longest diameter and the shortest diameter of the graphene observed with a laser microscope is a value obtained as follows.
- the graphene dispersion is diluted to 0.002% by mass with N-methylpyrrolidone (NMP), and dropped on a glass substrate and dried. Then, the graphene on the glass substrate is observed with a laser microscope, and for each piece of graphene, the longest diameter and the shortest diameter are measured, and then the size of the graphene in the plane direction is calculated from the arithmetic mean value. In this way, the size in the plane direction is randomly calculated for 50 graphene pieces, and the average value is S.
- NMP N-methylpyrrolidone
- S When S is less than 0.5 ⁇ m, the number of contact points between graphene pieces increases when applied to an electrode, and the electrical resistance value increases. In addition, when S is larger than 15 ⁇ m, the degree of exfoliation of graphene and the dispersibility in a solvent are low, and there is a concern about the deterioration of the coating property and the quality of the coating film surface when used as an electrode paste. A conductive path may not be formed.
- S is preferably 1.0 ⁇ m or more and 10.0 ⁇ m or less, and more preferably 1.5 ⁇ m or more and 4.0 ⁇ m or less.
- D / S is less than 1.0, that is, when the size S in the surface direction of graphene is larger than the median diameter D, the graphene pieces are not in a surface shape but are folded in a solvent. Is shown. In this case, the graphene pieces are isolated from each other, and a good conductive path may not be formed when the electrode is formed.
- D / S exceeds 3.0, it indicates that the graphene pieces are excessively aggregated, and sufficient peeling and dispersibility cannot be obtained.
- D / S is preferably 1.4 or more and 2.5 or less.
- the graphene dispersion liquid of this invention satisfy
- the average value T of the thicknesses of the graphene pieces a value obtained as follows is used.
- the graphene dispersion is diluted to 0.002% by mass with NMP, and dropped on a glass substrate and dried.
- substrate is observed with the laser microscope which can measure a solid shape, and thickness is measured about each graphene small piece.
- the area average is obtained.
- thickness is calculated about 50 graphene pieces at random, and the average value is defined as T.
- S / T When S / T is less than 100, it means that the thickness of the graphene pieces in the layer direction is larger than the size of the graphene pieces in the surface direction. In this case, when it is set as an electrode, there exists a tendency for electroconductivity to deteriorate. Moreover, when S / T is larger than 1500, it means that the thickness of the graphene piece in the layer direction is smaller than the size of the graphene piece in the surface direction. In this case, the viscosity of the dispersion itself or the electrode paste increases, which may reduce workability during handling. In the graphene dispersion of the present invention, it is more preferable that 200 ⁇ S / T ⁇ 800.
- the solid content ratio (G) of the graphene dispersion of the present invention is preferably 0.3% by mass or more and 40% by mass or less.
- the solid content exceeds 40% by mass, graphene stacks easily occur in the dispersion.
- the solid content is less than 0.3% by mass, the solid content of the electrode paste decreases due to the solvent in the dispersion and the viscosity decreases when used in the production of an electrode paste. Tend to get worse.
- the solid content is more preferably 20% by mass or less, further preferably 10% by mass or less, still more preferably 7% by mass or less, and particularly preferably 5% by mass or less. When the solid content is 5% by mass or less, fluidity is easily obtained and the handleability is excellent.
- the solid content is more preferably 0.7% by mass or more, and further preferably 1% by mass or more.
- the solid fraction G of the graphene dispersion can be calculated by measuring the weight after drying the solvent from the graphene dispersion and dividing the measured value by the weight of the graphene dispersion itself. Specifically, about 1 g of graphene dispersion is attached on a glass substrate of known weight, and the weight of graphene remaining when the solvent is volatilized by heating on a hot plate adjusted to 120 ° C. for 1.5 hours. Is measured and calculated.
- the graphene dispersion of the present invention preferably contains a surface treatment agent having an acidic group (hereinafter sometimes simply referred to as “surface treatment agent”).
- the surface treatment agent having an acidic group exhibits an effect of improving the dispersibility of graphene by at least a part of the surface treatment agent being attached to the surface of graphene.
- the acidic group is a hydroxy group, a phenolic hydroxy group, a nitro group, a carboxyl group or a carbonyl group.
- the surface treatment agent is not particularly limited as long as it is a compound having an acidic group, and may be a high molecular compound or a low molecular compound.
- polymer compound having an acidic group examples include polyvinyl pyrrolidone, polyvinyl alcohol, and polymethyl vinyl ether.
- a compound having an aromatic ring is preferable from the viewpoint of affinity with the graphene surface. From the viewpoint of increasing the conductivity of graphene, a low molecular compound is preferable to a high molecular compound.
- a compound having a catechol group is preferable as a surface treatment agent because of its high adhesion to graphene and dispersibility in a solvent.
- Examples of the compound having a catechol group include catechol, dopamine hydrochloride, 4- (1-hydroxy-2-aminoethyl) catechol, 3,4-dihydroxybenzoic acid, 3,4-dihydroxyphenylacetic acid, caffeic acid, 4- Examples include methyl catechol and 4-tert-butylpyrocatechol.
- the acidic group of the surface treatment agent is preferably a phenolic hydroxy group.
- the compound having a phenolic hydroxy group include phenol, nitrophenol, cresol, catechol, and compounds having a structure in which a part thereof is substituted.
- a surfactant having an acidic group is also suitably used as a surface treatment agent.
- the surfactant any of cationic surfactants, anionic surfactants, nonionic surfactants and the like can be used. However, since anions and cations themselves may participate in electrochemical reactions, When used as a material, a nonionic surfactant that is not ionized is suitable.
- the surface treatment agent may have a basic group in addition to the acidic group, and the dispersibility is improved particularly by having an amino group. Therefore, a compound having both a catechol group and an amino group is particularly preferable as the surface treatment agent.
- a compound having both a catechol group and an amino group is particularly preferable as the surface treatment agent.
- An example of such a compound is dopamine hydrochloride.
- the graphene contained in the graphene dispersion of the present invention preferably has a ratio of oxygen to carbon (O / C ratio) of 0.08 or more and 0.30 or less as measured by X-ray photoelectron spectroscopy.
- the oxygen atom on the surface of graphene is an oxygen atom contained in an acidic group bonded to the graphene itself or an acidic group included in the surface treatment agent attached to the graphene surface. Such oxygen atoms have the effect of improving the dispersed state of graphene, and if the number of oxygen atoms on the graphene surface is too small, the dispersibility is deteriorated.
- the O / C ratio of graphene is more preferably 0.10 or more. On the other hand, if there are too many oxygen atoms on the surface of graphene, the conductivity is lowered.
- the O / C ratio of graphene is more preferably 0.20 or less, and further preferably 0.15 or less.
- a graphene dispersion is preliminarily dried with a vacuum dryer or freeze dryer, and then the dried sample is introduced into a measurement chamber with a high vacuum chamber and softened on the surface of the sample placed in an ultrahigh vacuum.
- X-rays are irradiated and photoelectrons emitted from the surface are detected by an analyzer.
- the photoelectrons are measured by wide scan and narrow scan, and the binding energy value of bound electrons in the substance is obtained, whereby elemental information on the substance surface can be obtained. Specifically, it can be measured by the method described in Measurement Example 5 described later.
- a signal derived from carbon is detected in a form in which respective peaks around 284 eV, 286.5 eV, 287.5 eV, and 288.5 eV are superimposed.
- an N1s peak derived from nitrogen is detected in the vicinity of 402 eV
- an O1s peak derived from oxygen is detected in the vicinity of 533 eV.
- the O / C ratio can be obtained from the peak areas of the C1s peak and the O1s peak.
- the O / C ratio of graphene can be controlled by changing the degree of oxidation of graphene oxide as a raw material or changing the amount of the surface treatment agent. For example, the higher the degree of oxidation of graphene oxide, the greater the amount of oxygen remaining after reduction, and the lower the degree of oxidation, the smaller the amount of oxygen atoms after reduction. Moreover, the amount of oxygen atoms can be increased by increasing the adhesion amount of the surface treatment agent having an acidic group.
- the graphene dispersion of the present invention is a dilute solution in which the organic solvent is a solvent containing 50% by mass or more of NMP, and the graphene weight fraction is adjusted to 0.000013 using NMP, with the whole diluted solution being 1 after dilution.
- the weight extinction coefficient (hereinafter simply referred to as “weight extinction coefficient”) calculated using the following formula (4) at a wavelength of 270 nm is preferably 25000 cm ⁇ 1 or more and 200000 cm ⁇ 1 or less.
- Weight extinction coefficient (cm ⁇ 1 ) absorbance / ⁇ (0.000013 ⁇ cell optical path length (cm) ⁇ (4)
- the absorbance per unit weight of graphene varies depending on the degree of graphene peeling, and the single-layer graphene is the highest, and is decreased by increasing the number of layers or forming agglomerates, so there is a preferable range.
- the weight extinction coefficient is 25000 cm ⁇ 1 or more and 200000 cm ⁇ 1 or less, it has an appropriate surface area and dispersibility, and it is easy to form and maintain a good conductive path in a resin or electrode paste.
- the weight extinction coefficient is more preferably 40000 cm ⁇ 1 or more and 150,000 cm ⁇ 1 or less, and further preferably 45000 cm ⁇ 1 or more and 100000 cm ⁇ 1 or less.
- the value of the absorbance ratio (hereinafter simply referred to as “absorbance ratio”) calculated using the following formula (5) at wavelengths of 270 nm and 600 nm of the diluted solution prepared as described above is 1.70 or more. It is preferably 4.00 or less, more preferably 1.80 or more and 3.00 or less, and further preferably 1.90 or more and 2.50 or less.
- Absorbance ratio absorbance (270 nm) / absorbance (600 nm) (5)
- Absorbance includes a light absorbing component and a scattering component, and the scattering component increases or decreases depending on the surface state of graphene.
- the ratio of the scattering component to the absorbance is small, but at the wavelength of 600 nm, the absorption component is small, so the ratio of the scattering component to the absorbance is large. If the graphene contained contains a large amount of aggregation, the absorbance ratio is less than 1.70, and it tends to be difficult to form and maintain a good conductive path in the resin or electrode paste. Further, when graphene is excessively atomized, the absorbance ratio becomes larger than 4.00 and tends to aggregate in the resin or electrode paste.
- the absorbance of the diluted solution prepared from the graphene dispersion can be measured with an ultraviolet-visible spectrophotometer.
- the absorbance of graphene in the above formulas (4) and (5) can be obtained by subtracting the absorbance of the solvent of the diluent from the absorbance of the diluent adjusted from the graphene dispersion.
- the graphene dispersion of the present invention has a moisture content at 130 ° C. measured by the Karl Fischer method, W1 (mass%), and also measured by the Karl Fischer method, and the moisture content at 250 ° C. is W2 (mass%).
- the solid content ratio of graphene is G (mass%)
- the value of (W2-W1) / G is preferably 0.005 or more and 0.05 or less.
- W1 means an approximate total water content of free water contained in the organic solvent in the graphene dispersion and an approximate amount of adsorbed water adsorbed on the graphene but easily desorbed.
- W2 is a water content obtained by adding the water content of the free water and adsorbed water to the water content of the combined water that is firmly bonded to the graphene surface and does not desorb even at 130 ° C. That is, W2-W1 represents an approximate value of the water content of the bound water that is firmly bonded to the graphene.
- Bonded water is strongly bonded through a hydroxyl group, carboxyl group, epoxy group, carbonyl group, etc. contained in graphene.
- the presence of this bound water facilitates the interaction between graphene and the organic solvent, resulting in dispersion stabilization. Therefore, it is preferable to control the ratio of the weight of bound water to the weight of graphene within an appropriate range.
- the effect of improving the ionic conductivity of graphene can be obtained due to the presence of bound water.
- Graphene has a thin plate-like structure and also has a ⁇ - ⁇ interaction between graphene planes. It is difficult for ions to move in graphene stacked without gaps.
- graphene with appropriate bound water tends to have a gap even when stacked with graphene, and there is a tendency that ion conduction paths increase and ion conductivity is improved.
- (W2-W1) / G By controlling the value of (W2-W1) / G in the range of 0.005 or more and 0.05 or less, it can be dispersed well in an organic solvent, and a good conductive path can be formed in a lithium ion battery electrode. And high ion conductivity can be achieved.
- the value of (W2-W1) / G is preferably 0.008 or more, and more preferably 0.01 or more. Further, the value of (W2 ⁇ W1) / G is preferably 0.03 or less, and more preferably 0.02 or less.
- W1 and W2 are measured by the Karl Fischer method. Specifically, it shall be measured by the moisture vaporization / coulometric titration method shown in 8.3 of JIS K 0113: 2005. There is no restriction
- An example of such a moisture content measuring device is a Karl Fischer moisture meter AQ-2200 manufactured by Hiranuma Sangyo Co., Ltd.
- the specific surface area (hereinafter simply referred to as “specific surface area”) of the graphene contained in the graphene dispersion of the present invention measured by the BET measurement method is 80 m 2 / g or more and 250 m 2 / g or less. Is preferred.
- the specific surface area of graphene reflects the thickness of graphene and the degree of peeling of graphene, and the larger the graphene, the thinner the graphene and the higher the degree of peeling.
- the specific surface area of graphene is more preferably 100 m 2 / g or more, and more preferably 130 m 2 / g or more. Similarly, it is preferably 200 meters 2 / g or less, more preferably 180 m 2 / g or less.
- the BET measurement method is performed by the method described in JIS Z8830: 2013 on the dried sample after the graphene dispersion is preliminarily dried by a vacuum dryer, a freeze dryer, or the like. It is assumed that the adsorption method is analyzed by the gas method and the single point method.
- the value obtained by dividing the value of (W2-W1) / G of the graphene dispersion of the present invention by the specific surface area measured by the graphene BET measurement method is 0.000025 g / m 2 or more and 0.00025 g / m 2 or less. Preferably, it is 0.000035 g / m 2 or more and 0.00015 g / m 2 or less, and more preferably 0.000050 g / m 2 or more and 0.00010 g / m 2 or less.
- Organic solvent Although there is no restriction
- an organic solvent having a high polarity an organic solvent having a dipole moment of 3.0 Debye or more is preferable. Examples of such an organic solvent include NMP, ⁇ -butyrolactone, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, acetonitrile, and mixtures thereof.
- a solvent with high boiling point is preferable because it is difficult to handle stably.
- the boiling point of the organic solvent is preferably 150 ° C. or higher, and more preferably 180 ° C. or higher.
- NMP is particularly preferably used as a solvent having a high polarity and a high boiling point.
- the organic solvent preferably contains 50% by mass or more of NMP.
- a graphene dispersion obtained by dispersing the graphene of the present invention in an organic solvent is as follows: A reduction step of reducing graphene oxide dispersed in a dispersion medium containing water; A refining step for refining graphene oxide or graphene contained in the intermediate dispersion before or after the reduction step or during the reduction step; An organic solvent mixing step of mixing the intermediate dispersion liquid that has undergone the reduction step and the miniaturization step and the organic solvent; A strong stirring step of stirring an intermediate dispersion containing an organic solvent at a shear rate of 5000 to 50,000 per second; A method of combining organic solvent addition and suction filtration, or a water removal step of removing at least part of the water from the intermediate dispersion by distillation; It can produce with the manufacturing method which has this.
- the graphite used as the raw material for graphene oxide may be either artificial graphite or natural graphite, but natural graphite is preferably used.
- the number of meshes of graphite used as a raw material is preferably 20000 or less, and more preferably 5000 or less.
- the ratio of each reactant is 150 to 300 ml of concentrated sulfuric acid, 2 to 8 g of sodium nitrate, 10 to 40 g of potassium permanganate, and 40 to 80 g of hydrogen peroxide with respect to 10 g of graphite.
- sodium nitrate and potassium permanganate use an ice bath to control the temperature.
- hydrogen peroxide and deionized water are added, the mass of deionized water is 10 to 20 times the mass of hydrogen peroxide.
- Concentrated sulfuric acid preferably has a mass content of 70% or more, more preferably 97% or more.
- Graphene oxide has high dispersibility, but it is insulating itself and cannot be used as a conductive additive. If the degree of oxidation of graphene oxide is too high, the conductivity of the graphene powder obtained by reduction may deteriorate, so the ratio of carbon atoms to oxygen atoms measured by X-ray photoelectron spectroscopy of graphene oxide is It is preferable that it is 0.5 or more. When graphene oxide is measured by X-ray photoelectron spectroscopy, it is performed in a state where the solvent is sufficiently dried.
- the degree of oxidation of graphene oxide can be adjusted by changing the amount of oxidizing agent used for the oxidation reaction of graphite. Specifically, the higher the amount of sodium nitrate and potassium permanganate used in the oxidation reaction, the higher the degree of oxidation, and the lower the amount, the lower the degree of oxidation.
- the weight ratio of sodium nitrate to graphite is not particularly limited, but is preferably 0.200 or more and 0.800 or less, more preferably 0.250 or more and 0.500 or less, and 0.275 or more. More preferably, it is 0.425 or less.
- the ratio of potassium permanganate to graphite is not particularly limited, but is preferably 1.00 or more, more preferably 1.40 or more, and even more preferably 1.65 or more. Further, it is preferably 4.00 or less, more preferably 3.00 or less, and even more preferably 2.55 or less.
- the dispersion medium containing water may be water alone or a solvent other than water.
- the solvent other than water is preferably a polar solvent, and examples thereof include ethanol, methanol, 1-propanol, 2-propanol, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and ⁇ -butyrolactone.
- a polar solvent examples thereof include ethanol, methanol, 1-propanol, 2-propanol, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and ⁇ -butyrolactone.
- the micronization process is performed after the completion of the surface treatment process and then the process is directly transferred to the reduction process or diluted with the same solvent used in the surface treatment process. Thus, it is preferable to perform the reduction step.
- the reducing agent for reducing graphene oxide is not particularly limited, and various organic reducing agents and inorganic reducing agents can be used. Among these, an inorganic reducing agent is more preferable because of easy washing after reduction.
- Examples of the organic reducing agent include aldehyde-based reducing agents, hydrazine derivative reducing agents, and alcohol-based reducing agents. Among them, alcohol-based reducing agents are particularly suitable because they can be reduced relatively gently. Examples of the alcohol-based reducing agent include methanol, ethanol, propanol, isopropyl alcohol, butanol, benzyl alcohol, phenol, ethanolamine, ethylene glycol, propylene glycol, diethylene glycol, and the like.
- inorganic reducing agents examples include sodium dithionite, potassium dithionite, phosphorous acid, sodium borohydride, hydrazine, etc.
- sodium dithionite and potassium dithionite have relatively acidic groups. Since it can be reduced, graphene with high dispersibility in a solvent can be produced and used suitably.
- a gel-like dispersion liquid in which graphene is dispersed in water is obtained by preferably performing a washing step of diluting with water and filtering.
- intermediates in the process of production in which graphene or graphene oxide is dispersed in some dispersion medium other than the graphene dispersion according to the present invention, which has been finally completed include gel-like intermediates. For convenience, they are all referred to as “intermediate dispersions”.
- both the graphene oxide and the surface treatment agent are completely dissolved, but some of them may be dispersed in a solid state without being dissolved.
- a refinement process is performed to refine the graphene oxide or the reduced graphene contained in the intermediate dispersion.
- the miniaturization step is preferably performed before the reduction step or during the reduction step.
- the size S in the plane direction of graphene oxide or graphene can be set to an appropriate size.
- a method of miniaturization in the case of a method of crushing and dispersing graphene oxide or graphene by mixing pulverized media such as beads and balls with a dispersion and colliding the pulverized media, In order to induce aggregation of graphene oxide or graphene, a medialess dispersion method in which a strong shearing force is applied to the dispersion without using a pulverizing medium is preferably used.
- a method in which an intermediate dispersion liquid under pressure is collided with a single ceramic ball, or a method using a liquid-liquid shear type wet jet mill in which intermediate dispersion liquid under pressure is collided with each other to perform dispersion can be mentioned.
- a method of applying ultrasonic waves to the intermediate dispersion liquid is also a medialess dispersion method and is a preferable method.
- graphene oxide or graphene tends to become finer as the processing pressure and output in the medialess dispersion method are higher, and tends to become finer as the treatment time is longer.
- a preferred size S in the plane direction of graphene is as described above.
- the size of graphene after reduction can be adjusted according to the type, processing conditions, and processing time of the micronization process in the micronization process.
- the solid content concentration of graphene oxide or graphene is preferably 0.01% to 2%, more preferably 0.05% to 1%. preferable.
- the ultrasonic output is preferably 100 W or more and 3000 W or less, and more preferably 200 W or more and 2000 W or less.
- the treatment time is preferably from 10 minutes to 10 hours, more preferably from 20 minutes to 5 hours, and particularly preferably from 30 minutes to 3 hours.
- Organic solvent mixing step In order to replace the water in the intermediate dispersion liquid that has undergone the reduction process and the refinement process with an organic solvent, an organic solvent mixing process is performed in which the intermediate dispersion liquid and the organic solvent are mixed.
- the organic solvent mixing step the intermediate dispersion obtained through the reduction step and the miniaturization step, or the intermediate dispersion obtained by further performing the washing step and / or the surface treatment step as necessary, and the organic solvent Mix directly. That is, from the end of the reduction step to the mixing with the organic solvent in the organic solvent mixing step, the intermediate dispersion is always in the state of dispersion, and the dispersion medium is removed from the intermediate dispersion to recover graphene as a powder state. Do not perform operations such as freeze-drying.
- the mixing ratio of the intermediate dispersion liquid and the organic solvent in the organic solvent mixing step is not particularly limited, but if the amount of the organic solvent to be mixed is too small, it is difficult to handle because the viscosity becomes high, and if the amount of the organic solvent to be mixed is too large, the unit Since the amount of graphene per processing amount decreases, processing efficiency deteriorates.
- the organic solvent is preferably 10 to 3000 parts by weight, more preferably 20 parts per 100 parts by weight of the intermediate dispersion after the reduction step. It is advisable to mix up to 2000 parts by mass, more preferably 50-1500 parts by mass.
- the shear rate in the strong stirring process is 5000 to 50000 per second.
- the shear rate is a value obtained by dividing the peripheral speed at the maximum diameter of the rotary blade of the mixer by the distance to the wall surface of the tip of the mixer rotary blade (the cutting edge that determines the maximum diameter).
- the peripheral speed of the rotary blade of the mixer is defined by peripheral length ⁇ rotational speed. If the shear rate is too low, graphene peeling is difficult to occur and the degree of graphene peeling is low. On the other hand, when the shear rate is too large, the degree of exfoliation of graphene becomes too high and the dispersibility decreases.
- the shear rate is preferably 10,000 or more per second, and more preferably 15,000 or more per second. Similarly, it is preferably 45,000 or less per second, and more preferably 40000 or less per second.
- the treatment time of the strong stirring step is preferably 15 seconds to 300 seconds, more preferably 20 seconds to 120 seconds, and further preferably 30 seconds to 80 seconds.
- the distance between the rotating blade and the wall surface is a short shape of 10 mm or less, and a medialess mixer is preferable.
- a medialess mixer for example, Fillmix (registered trademark) 30-30 type (manufactured by Primics), Claremix (registered trademark) CLM-0.8S (manufactured by M Technique Co., Ltd.), Super Share Mixer SDRT0.35- 0.75 (manufactured by Satake Chemical Machinery Co., Ltd.).
- the water removal step in the present invention is a step of removing at least a part of the water contained in the intermediate dispersion by a technique combining organic solvent addition and suction filtration or distillation.
- the solvent removal means that applies a strong force to the graphene contained in the dispersion, such as pressure filtration or centrifugation, the graphene tends to be laminated and aggregated.
- the water removal step is preferably performed at any stage after the end of the strong stirring step, but may be performed before the strong stirring step as long as it is after the organic solvent mixing step.
- the vacuum suction filtration can be performed by a method of filtering using a Buchner funnel, Kiriyama funnel or the like while sucking with a diaphragm pump or the like. By repeating the step of mixing with an organic solvent and the operation of suction filtration a plurality of times, it is possible to remove free water and adsorbed water in the intermediate dispersion.
- the organic solvent those described above can be used.
- heating step it is preferable to perform a step (heating step) of heating the intermediate dispersion to 70 ° C. or higher at any stage after the reduction step.
- the heating step can be performed, for example, by putting the intermediate dispersion into a heating and stirring apparatus and stirring while heating without drying.
- the heating temperature is more preferably 80 ° C. or higher.
- the heating temperature is preferably 150 ° C. or lower, more preferably 120 ° C. or lower. Further, it is particularly preferable to perform the heating step simultaneously with the strong stirring step from the viewpoint of efficiently removing moisture.
- the heating step can be performed simultaneously by performing distillation while heating to 70 ° C. or higher, and free water, adsorbed water, and bound water can be removed simultaneously in a single treatment. Therefore, this is a preferred embodiment.
- a method of vacuum distillation while heating to 70 ° C. or higher is particularly preferable.
- a device such as a rotary evaporator or a heating stirrer with a vacuum line.
- Vacuum distillation is preferable at the point which can remove a water
- graphene dispersion of the present invention is not limited, as an example, the graphene dispersion is usefully used when combining electrode active material particles such as lithium ion battery electrode active material particles and graphene.
- composite means that the state in which graphene is in contact with the surface of the electrode active material particles is maintained.
- the composite mode include one obtained by granulating graphene and electrode active material particles integrally, and one obtained by attaching graphene to the surface of electrode active material particles.
- the active material When applied to the production of graphene-electrode active material composite particles, the active material may be either a positive electrode active material or a negative electrode active material. That is, the graphene dispersion of the present invention can be used for manufacturing a positive electrode and a negative electrode.
- the positive electrode active material is not particularly limited, but lithium cobaltate (LiCoO 2 ), lithium nickelate (LiNiO 2 ), spinel type lithium manganate (LiMn 2 O 4 ), Alternatively, cobalt ternary system was replaced partially with nickel-manganese (LiMn x Ni y Co 1- x-y O 2), a composite oxide of lithium and a transition metal such as spinel-type lithium manganese oxide (LiMn 2 O 4) Products, olivine-based (phosphate-based) active materials such as lithium iron phosphate (LiFePO 4 ), metal oxides such as V 2 O 5 , metal compounds such as TiS 2 , MoS 2 , and NbSe 2 .
- lithium cobaltate LiCoO 2
- LiNiO 2 lithium nickelate
- LiMn 2 O 4 spinel type lithium manganate
- cobalt ternary system was replaced partially with nickel-manganese (LiMn x Ni y Co 1-
- the negative electrode active material is not particularly limited, natural graphite, artificial graphite, carbon-based materials such as hard carbon, SiO or SiC, silicon compounds having a basic constituent element SiOC, etc., lithium titanate (Li 4 Ti 5 O 12 ), Metal oxides such as manganese oxide (MnO) and cobalt oxide (CoO) that can undergo a conversion reaction with lithium ions.
- the graphene-electrode active material composite particles can be produced by mixing the graphene dispersion of the present invention and the active material particles and then drying them by a technique such as spray drying or freeze drying.
- a technique such as spray drying or freeze drying.
- the method of mixing the graphene dispersion and the active material particles include a method using a triple roll, a wet bead mill, a wet planetary ball mill, a homogenizer, a planetary mixer, a biaxial kneader, and the like.
- the graphene dispersion of the present invention can also be used for the production of electrode pastes used in the production of lithium ion battery electrodes and the like. That is, the electrode paste can be prepared by mixing the electrode active material and the binder with the graphene dispersion of the present invention as a conductive auxiliary agent after adding an appropriate amount of a solvent as necessary. .
- the same active material as described above can be used as the electrode active material when applied to the production of an electrode paste for a lithium ion battery.
- Fluoropolymers such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), rubbers, such as styrene butadiene rubber (SBR) and natural rubber, polysaccharides, such as carboxymethylcellulose , Polyimide precursor and / or polyimide resin, polyamideimide resin, polyamide resin, polyacrylic acid, sodium polyacrylate, acrylic resin, polyacrylonitrile and the like. These may be used as a mixture of two or more.
- PVDF polyvinylidene fluoride
- PTFE polytetrafluoroethylene
- SBR styrene butadiene rubber
- polysaccharides such as carboxymethylcellulose
- Polyimide precursor and / or polyimide resin polyamideimide resin
- polyamide resin polyamide resin
- polyacrylic acid sodium polyacrylate
- acrylic resin polyacrylonitrile and the like.
- the conductive auxiliary agent may be only graphene contained in the graphene dispersion of the present invention, or an additional conductive auxiliary agent may be added.
- additional conductive support agent For example, graphites, such as furnace black, ketjen black (trademark), acetylene black, etc., natural graphite (flaky graphite etc.), artificial graphite, Examples thereof include conductive fibers such as carbon fiber and metal fiber, and metal powders such as copper, nickel, aluminum and silver. Additional solvents used include NMP, ⁇ -butyrolactone, water, dimethylacetamide and the like.
- the measurement was carried out by repeating the washing step of filtering the reduced graphene water dispersion prepared in the following examples with a suction filter, diluting to 0.5% by mass with ion-exchanged water and suction filtering, Further, the graphene powder obtained by freeze-drying was used.
- the graphene dispersion prepared in each Example / Comparative Example was 1.5 parts by mass as a graphene solid, and 100 parts by mass of LiNi 0.5 Co 0.2 Mn 0.3 O 2 as an electrode active material.
- a mixture of 1.5 parts by mass of acetylene black as an agent, 5 parts by mass of polyvinylidene fluoride as a binder, and 100 parts by mass of NMP as a solvent was mixed with a planetary mixer to obtain an electrode paste.
- This electrode paste was applied to an aluminum foil (thickness: 18 ⁇ m) using a doctor blade (300 ⁇ m), dried at 80 ° C. for 15 minutes, and then vacuum dried to obtain an electrode plate.
- the produced electrode plate was cut into a diameter of 15.9 mm to be used as a positive electrode, and a negative electrode composed of 98 parts by mass of graphite, 1 part by mass of sodium carboxymethylcellulose, and 1 part by mass of an SBR aqueous dispersion was cut out to have a diameter of 16.1 mm.
- the charge / discharge measurement was performed three times each in the order of the rate 0.1C, 1C, and 5C at the upper limit voltage of 4.2 V and the lower limit voltage of 3.0 V, and then the charge / discharge measurement was further performed 491 times at 1C for a total of 500 times. .
- the discharge capacities at the third rate 1C, the third rate 5C, and the subsequent 491 times rate 1C were measured.
- a weight extinction coefficient defined by the following formula (4) was calculated from the obtained absorbance at 270 nm.
- Weight extinction coefficient (cm ⁇ 1 ) absorbance / ⁇ (0.000013 ⁇ cell optical path length (cm) ⁇ (4) Further, the absorbance ratio defined by the following formula was calculated.
- Absorbance ratio absorbance (270 nm) / absorbance (600 nm) (5)
- Example 1 The graphene oxide gel prepared in Synthesis Example 1 was diluted with ion exchange water to a concentration of 30 mg / ml and treated with an ultrasonic cleaner for 30 minutes to obtain a uniform graphene oxide dispersion.
- the graphene oxide dispersion was diluted to 5 mg / ml with ion-exchanged water, 0.3 g of sodium dithionite was added to 20 ml of the diluted dispersion, and the mixture was kept at 40 ° C. for a reduction reaction for 1 hour. (Reduction process). Then, it filtered with the vacuum suction filter, and also the process of diluting to 0.5 mass% with ion-exchange water and carrying out suction filtration was washed 5 times (washing process).
- the dipole moment is diluted to 0.5 mass% with NMP of 4.1 Debye (organic solvent mixing step), and 60 ⁇ m at a peripheral speed of 40 m / s with Filmix (registered trademark) Model 30-30 (Primics) Second treatment (strong stirring step).
- NMP organic solvent mixing step
- Filmix registered trademark
- Model 30-30 Principals Second treatment
- the distance between the rotary blade and the wall surface was 2 mm (0.02 m).
- the shear rate can be calculated from (peripheral speed) / (distance from the wall surface) and is 20000 per second.
- the obtained intermediate dispersion was subjected to suction filtration under reduced pressure, diluted with NMP to a concentration of 0.5% by mass, and treated with homodisper type 2.5 (Primics Co., Ltd.) for 30 minutes at 3000 rpm.
- the vacuum suction filtration step was repeated twice (moisture removal step) to obtain a graphene dispersion in which graphene was dispersed in NMP.
- Example 1-2 The ultrasonic application time was changed to 10 minutes in the micronization step, and the peripheral speed of the fill mix was changed to 20 m / s (shear rate: 10,000 per second) in the strong stirring step, as in Example 1. Thus, a graphene dispersion was prepared.
- Example 1-3 A graphene dispersion was prepared in the same manner as in Example 1 except that the graphene dispersion was distilled at 90 ° C. for 2 hours before the final suction filtration of Example 1.
- Example 2 A graphene dispersion was prepared in the same manner as in Example 1 except that the ultrasonic wave application time was changed to 20 minutes in the miniaturization step.
- Example 3 A graphene dispersion was prepared in the same manner as in Example 1 except that the peripheral speed of the fill mix was changed to 120 m treatment at 50 m / s (shear rate: 25000 per second) in the strong stirring step.
- Example 4 The graphene dispersion obtained in the same manner as in Example 1 was placed under vacuum for 10 minutes, a part of the solvent was removed, and the solid content rate was adjusted to 9.8% by mass.
- Example 5 A graphene dispersion was prepared in the same manner as in Example 1 except that the amount of the surface treatment agent mixed was changed to 0.6 g.
- Example 6 A graphene dispersion was prepared in the same manner as in Example 1 except that the surface treatment agent was not mixed.
- Example 2 In place of the fill mix treatment in Example 1, homodisper type 2.5 (Primics Co., Ltd.) having a shearing force weaker than that of the fill mix was used for 30 minutes at 3000 rpm. At this time, the diameter of the rotary blade of the homodisper is 30 mm, and the peripheral speed can be calculated as 4.7 m / s. The inner diameter of the container used during stirring was 50 mm, and the distance between the wall surface and the rotary blade was 10 mm. The shear rate can be calculated as 470 per second. Other than that was carried out similarly to Example 1, and produced the graphene dispersion liquid.
- Example 3 A graphene dispersion was prepared in the same manner as in Example 1 except that the peripheral speed of the fill mix used in the strong stirring process of Example 1 was changed to 5 m / s (shear rate: 2500 per second).
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Abstract
Description
0.5μm≦S≦15μm ・・・(1)
1.0≦D/S≦3.0 ・・・(2)
水を含む分散媒に分散した酸化グラフェンを還元する還元工程;
還元工程の前後または還元工程の最中の中間体分散液に含まれる酸化グラフェンまたはグラフェンを微細化する微細化工程;
還元工程および微細化工程を経た中間体分散液と有機溶媒とを混合する有機溶媒混合工程;
有機溶媒を含む中間体分散液をせん断速度毎秒5000~毎秒50000で撹拌処理する強撹拌工程;
有機溶媒添加と吸引濾過を組み合わせる手法、または蒸留により中間体分散液から水分の少なくとも一部を除去する水分除去工程;
を有するグラフェン分散液の製造方法である。
本発明のグラフェン分散液は、グラフェンが有機溶媒に分散してなるグラフェン分散液であって、レーザー回折/散乱式粒度分布測定法により測定されるグラフェンのメジアン径をD(μm)、レーザー顕微鏡により観察したグラフェンの最長径と最短径の相加平均により求めたグラフェンの面方向の大きさの平均値をS(μm)とした場合に、下記式(1)および(2)を同時に満たすものである。
0.5μm≦S≦15μm ・・・(1)
1.0≦D/S≦3.0 ・・・(2)
100≦S/T≦1500 ・・・(3)
グラフェン分散液を、NMPを用いて0.002質量%に希釈し、ガラス基板上に滴下、乾燥する。そして、基板上のグラフェンを立体形状の測定が可能であるレーザー顕微鏡で観察し、個々のグラフェン小片について、厚さを測定する。一つの小片中で厚みにバラつきがある場合には、面積平均を求める。このようにランダムに50個のグラフェン小片について厚さを算出し、その平均値をTとする。
重量吸光係数(cm-1)=吸光度/{(0.000013×セルの光路長(cm)} ・・・(4)
吸光度比=吸光度(270nm)/吸光度(600nm) ・・・(5)
本発明のグラフェン分散液に使用する有機溶媒に制限はないが、極性の高い有機溶媒が好ましい。極性が高い有機溶媒として、双極子モーメントが3.0Debye以上の有機溶媒が好ましい。このような有機溶媒としてNMP、γ―ブチロラクトン、ジメチルアセトアミド、ジメチルホルムアミド、ジメチルスルホキシド、アセトニトリル、およびこれらの混合物が例示できる。
本発明のグラフェンが有機溶媒に分散してなるグラフェン分散液は、一例として、
水を含む分散媒に分散した酸化グラフェンを還元する還元工程;
還元工程の前後または還元工程の最中の中間体分散液に含まれる酸化グラフェンまたはグラフェンを微細化する微細化工程;
還元工程および微細化工程を経た中間体分散液と有機溶媒とを混合する有機溶媒混合工程;
有機溶媒を含む中間体分散液をせん断速度毎秒5000~毎秒50000で撹拌処理する強撹拌工程;
有機溶媒添加と吸引濾過を組み合わせる手法、または蒸留により中間体分散液から水分の少なくとも一部を除去する水分除去工程;
を有する製造方法で作製することができる。
酸化グラフェンの作製法に特に限定は無く、ハマーズ法等の公知の方法を使用できる。また市販の酸化グラフェンを購入してもよい。酸化グラフェンの作製方法として、ハマーズ法を用いる場合を以下に例示する。
還元工程においては、水を含む分散媒中に分散した酸化グラフェンをグラフェンに還元する。
還元工程を終えた後、好ましくは水で希釈し濾過する洗浄工程を行うことで、グラフェンが水に分散したゲル状の分散液が得られる。なお、本明細書においては、最終的に完成した本発明に係るグラフェン分散液以外の、グラフェンまたは酸化グラフェンが何らかの分散媒に分散した状態にある製造途中の中間体を、ゲル状のものも含め、便宜的に全て「中間体分散液」と呼ぶものとする。
還元工程の前後、または最中に、必要に応じて、酸性基を有する表面処理剤を中間体分散液と混合する表面処理工程を加えても良い。表面処理剤としては、前述のものを用いることができる。
還元工程の前後、または最中に、還元工程の前後または還元工程の最中の中間体分散液に含まれる酸化グラフェンまたは還元後のグラフェンを微細化する微細化工程を行う。本発明のグラフェン分散液を得るためには、酸化グラフェンを微細化した状態で還元工程を行うことが好ましいことから、微細化工程は還元工程の前または還元工程の最中に行うことが好ましい。
還元工程および微細化工程を経た中間体分散液中の水を有機溶媒に置換するために、中間体分散液と有機溶媒とを混合する有機溶媒混合工程を行う。有機溶媒混合工程においては、還元工程および微細化工程を経て得られた中間体分散液、または必要に応じてさらに洗浄工程および/または表面処理工程を行った中間体分散液と、有機溶媒とを直接混合する。すなわち、還元工程終了後から有機溶媒混合工程における有機溶媒との混合まで、中間体分散液は常に分散液の状態にあり、中間体分散液から分散媒を除去してグラフェンを粉末状態として回収する凍結乾燥等の操作は行わない。
有機溶媒混合工程の後、中間体分散液をせん断速度毎秒5000~毎秒50000で撹拌処理する工程(強撹拌工程)を実施する。強撹拌工程でグラフェンを剥離することで、グラフェン同士のスタックを解消することができる。なお、本明細書においては、中間体分散液にこのようなせん断力を与えられる回転刃ミキサーを「高せん断ミキサー」と呼ぶ。
本発明における水分除去工程は、有機溶媒添加と吸引濾過を組み合わせる手法、または蒸留により中間体分散液に含まれる水分の少なくとも一部を除去する工程である。加圧濾過や遠心分離のような分散液に含有するグラフェンに対し強い力がかかる溶媒除去手段では、グラフェンが積層凝集する傾向がある。水分除去工程は、強撹拌工程終了後のいずれかの段階で行うことが好ましいが、有機溶媒混合工程の後であれば強撹拌工程の前に行ってもよい。
さらに、還元工程後のいずれかの段階で、中間体分散液を70℃以上に加熱する工程(加熱工程)を行うことが好ましい。加熱工程を行うことで、中間体分散液中の結合水を減少させることができる。加熱工程は、例えば、中間体分散液を加熱攪拌装置に投入し、乾燥させずに加熱しながら攪拌することで行うことができる。加熱温度は80℃以上がさらに好ましい。一方、グラフェンは高温条件では、ヒドロキシル基など一部の官能基が脱離することがあるため、加熱温度は150℃以下が好ましく、120℃以下が更に好ましい。また、加熱工程を強攪拌工程と同時に行うことが、効率よく水分を除去する観点から特に好ましい。
本発明のグラフェン分散液の用途は限定されるものではないが、一例として、リチウムイオン電池電極活物質粒子等の電極活物質粒子とグラフェンとを複合化する際に有益に用いられる。ここにおいて複合化とは、電極活物質粒子の表面にグラフェンが接した状態を維持せしめることを意味する。複合化の態様としては、グラフェンと電極活物質粒子を一体として造粒したものや、電極活物質粒子の表面にグラフェンを付着せしめたものが挙げられる。
本発明のグラフェン分散液は、リチウムイオン電池用電極等の製造に用いられる電極用ペーストの製造に用いることもできる。すなわち、電極活物質、バインダーに対して、導電助剤としての本発明のグラフェン分散液を、必要に応じて適量の溶媒を加えた上で混合することにより、電極用ペーストを調製することができる。
グラフェン分散液を、NMPを用いて0.5質量%に希釈して、HORIBA社製粒度分布測定装置LASER SCATTERING PARTICLE SIZE DISTRIBUTION ANALYZER LA-920を使用したレーザー回折/散乱式粒度分布測定法で測定した粒度分布の中央値に対応する粒子径をメジアン径(D、μm)とした。装置内の溶媒は、グラフェン分散液の溶媒と同一のものを使用し、測定前処理としての超音波の印加は実施せずに測定した。グラフェンの屈折率は1.43とした。
グラフェン分散液を、NMPを用いて0.002質量%に希釈し、ガラス基板上に滴下・乾燥し、基板上に付着させた。基板上のグラフェンをキーエンス社製レーザー顕微鏡VK-X250で観察して、個々のグラフェン小片の最長径(μm)と最短径(μm)を測定し、相加平均を算出した。これをランダムに50個のグラフェン粒子について行い、その平均をグラフェンの面方向の大きさ(S、μm)とした。
グラフェン分散液を、NMPを用いて0.002質量%に希釈し、ガラス基板上に滴下・乾燥し、基板上に付着させた。基板上のグラフェンをキーエンス社製レーザー顕微鏡VK-X250で観察して、個々のグラフェン小片の厚みを測定した。一つの小片中で厚みにバラつきがあった場合は面積平均を求めた。これをランダムに50個のグラフェン小片について測定し、その平均値をT(μm)とした。
グラフェン分散液を重量既知のガラス基板上に付着させて重量を測定し、120℃に温度調整したホットプレート上で1.5時間加熱して溶媒を揮発させた。加熱前のグラフェン分散液の付着量と、加熱前後の重量差から算出した溶媒揮発量から、グラフェン分散液の固形分率G(質量%)を測定した。これを3回繰り返し、平均して求めた。
X線光電子測定はPHI社製Quantera SXMを使用して測定した。励起X線は、monochromatic Al Kα1,2 線(1486.6eV)であり、X線径は200μm、光電子脱出角度は45°である。炭素原子に基づくC1sメインピークを284.3eVとし、酸素原子に基づくO1sピークを533eV付近のピークに帰属し、各ピークの面積比からO/C比を求めた。測定は、下記実施例で作製した還元後のグラフェン水分散液を吸引濾過器で濾過後、イオン交換水で0.5質量%まで希釈して吸引濾過する洗浄工程を5回繰り返して実施し、さらに凍結乾燥して得たグラフェン粉末に対して行った。
各実施例・比較例で調製したグラフェン分散液をグラフェン固形分として1.5質量部、電極活物質としてLiNi0.5Co0.2Mn0.3O2を100質量部、追加の導電助剤としてアセチレンブラックを1.5質量部、バインダーとしてポリフッ化ビニリデン5質量部、溶媒としてNMPを100質量部配合したものをプラネタリーミキサーで混合して電極用ペーストを得た。この電極用ペーストをアルミニウム箔(厚さ18μm)にドクターブレード(300μm)を用いて塗布し、80℃15分間乾燥後、真空乾燥して電極板を得た。
各サンプルの吸光度は、U-3010形分光光度計(日立ハイテクサイエンス社製)を使用して測定した。セルは光路長10mmの石英製を用いた。測定は、下記実施例で調製したグラフェン分散液またはグラフェン粉末に、グラフェン重量分率が0.000013となるようNMPを加え、出力130W、発振周波数40kHzの超音波洗浄機(ASU-6M、アズワン社製)を用いて出力設定Highで10分間処理した希釈液に対して、事前に希釈液が含有する比率の混合溶媒でのベースライン測定をした上で行った。得られた270nmの吸光度から、下記式(4)で定義した重量吸光係数を算出した。
重量吸光係数(cm-1)= 吸光度/{(0.000013× セルの光路長(cm)} ・・・(4)
また、下記式で定義した吸光度比を算出した。
吸光度比=吸光度(270nm)/吸光度(600nm) ・・・(5)
グラフェンの比表面積測定はHM Model-1210(Macsorb社製)を使用して測定した。測定はJIS Z8830:2013に準拠し吸着ガス量の測定方法はキャリアガス法で、吸着データの解析は一点法で測定した。脱気条件は、100℃×180分とした。測定は、下記実施例で調製した還元後のグラフェン水分散液を吸引濾過器で濾過後、水で0.5質量%まで希釈して吸引濾過する洗浄工程を5回繰り返して洗浄、さらに凍結乾燥して得たグラフェン粉末に対して行った。
グラフェン分散液の水分率測定は、カールフィッシャー水分計AQ-2200と水分気化装置EV-2010(平沼産業株式会社製)を用いて、JIS K 0113:2005の8.3項に示される水分気化-電量滴定法により測定した。水分気化装置にグラフェン分散液を投入して、130℃または250℃に加熱することで測定し、水分率W1(質量%)、W2(質量%)の値を得た。
酸化グラフェンの作製方法:1500メッシュの天然黒鉛粉末(上海一帆石墨有限会社製)を原料として、氷浴中の10gの天然黒鉛粉末に、220mlの98%濃硫酸、5gの硝酸ナトリウム、30gの過マンガン酸カリウムを入れ、1時間機械攪拌し、混合液の温度を20℃以下で保持した。この混合液を氷浴から取り出し、35℃水浴中で4時間攪拌反応し、その後イオン交換水500mlを入れて得られた懸濁液を90℃で更に15分反応を行った。最後に600mlのイオン交換水と50mlの過酸化水素を入れ、5分間の反応を行い、酸化グラフェン分散液を得た。熱いうちにこれを濾過し、希塩酸溶液で金属イオンを洗浄し、イオン交換水で酸を洗浄し、pHが7になるまで洗浄を繰り返して酸化グラフェンゲルを調製した。調製した酸化グラフェンゲルの、X線光電子分光法により測定される酸素原子の炭素原子に対する元素比は0.53であった。
合成例1で調製した酸化グラフェンゲルを、イオン交換水で濃度30mg/mlに希釈し、超音波洗浄機で30分処理し、均一な酸化グラフェン分散液を得た。
微細化工程で超音波印加時間を10分に変更し、強攪拌工程でフィルミックスの周速を20m/s(せん断速度:毎秒10000)で20秒処理に変更した以外は実施例1と同様にして、グラフェン分散液を作製した。
実施例1の最後の吸引濾過の前に、グラフェン分散液を90℃で2時間蒸留処理した以外は実施例1と同様にして、グラフェン分散液を作製した。
微細化工程で超音波印加時間を20分に変更した以外は実施例1と同様にして、グラフェン分散液を作製した。
強攪拌工程でフィルミックスの周速を50m/s(せん断速度:毎秒25000)で120秒処理に変更した以外は実施例1と同様にして、グラフェン分散液を作製した。
実施例1と同様にして得たグラフェン分散液を真空下に10分間置き、溶剤を一部除去して、固形分率を9.8質量%に調整した。
表面処理剤の混合量を0.6gに変更した以外は実施例1と同様にして、グラフェン分散液を作製した。
表面処理剤を混合しなかったこと以外は実施例1と同様にして、グラフェン分散液を作製した。
微細化工程を行わなかったこと以外は実施例1と同様にして、グラフェン分散液を作製した。
実施例1における、フィルミックス処理の代わりに、フィルミックスよりもせん断力の弱いホモディスパー2.5型(プライミクス社)を使用して回転数3000rpmで30分処理した。このとき、ホモディスパーの回転刃の径は30mmであり、周速は4.7m/sと計算できる。攪拌時に使用した容器の内径は、50mmであり、壁面と回転刃の距離は10mmであった。せん断速度は毎秒470と計算できる。それ以外は実施例1と同様にして、グラフェン分散液を作製した。
実施例1の強攪拌工程で使用したフィルミックスの周速を5m/s(せん断速度:毎秒2500)に変更した以外は実施例1と同様にして、グラフェン分散液を作製した。
Claims (15)
- グラフェンが有機溶媒に分散してなるグラフェン分散液であって、レーザー回折/散乱式粒度分布測定法により測定されるグラフェンのメジアン径をD(μm)、レーザー顕微鏡により観察したグラフェンの最長径と最短径の相加平均により求めたグラフェンの面方向の大きさの平均値をS(μm)とした場合に、下記式(1)および(2)を同時に満たすグラフェン分散液。
0.5μm≦S≦15μm ・・・(1)
1.0≦D/S≦3.0 ・・・(2) - レーザー顕微鏡により観察したグラフェンの厚さの平均値をT(μm)とした場合に、下記式(3)を満たす、請求項1に記載のグラフェン分散液。
100≦S/T≦1500 ・・・(3) - 固形分率(G)が0.3質量%以上40質量%以下である、請求項1または2に記載のグラフェン分散液。
- 前記グラフェンの、X線光電子分光法により測定される炭素に対する酸素の元素の比(O/C比)が、0.08以上0.30以下である、請求項1~3のいずれかに記載のグラフェン分散液。
- さらに、酸性基を有する表面処理剤を含む、請求項1~4のいずれかに記載のグラフェン分散液。
- 前記有機溶媒が、双極子モーメントが3.0Debye以上の有機溶媒である、請求項1~5のいずれかに記載のグラフェン分散液。
- 前記有機溶媒がN-メチルピロリドンを50質量%以上含む溶媒であり、N-メチルピロリドンでグラフェン重量分率0.000013に調整した希釈液の、波長270nmにおける下記式(4)を用いて算出される重量吸光係数が25000cm-1以上200000cm-1以下である、請求項6に記載のグラフェン分散液。
重量吸光係数(cm-1)=吸光度/{(0.000013×セルの光路長(cm)} ・・・(4) - カールフィッシャー法で測定した、130℃における水分率をW1(質量%)、250℃における水分率をW2(質量%)とし、グラフェンの固形分率をG(質量%)としたとき、(W2-W1)/Gの値が0.005以上0.05以下である、請求項1~7のいずれかに記載のグラフェン分散液。
- 請求項1~8のいずれかに記載のグラフェン分散液と、電極活物質粒子とを混合した後に乾燥することを含む、グラフェン-電極活物質複合体粒子の製造方法。
- 電極活物質、バインダーおよび請求項1~8のいずれかに記載のグラフェン分散液を混合することを含む、電極用ペーストの製造方法。
- 水を含む分散媒に分散した酸化グラフェンを還元する還元工程;
還元工程の前後または還元工程の最中の中間体分散液に含まれる酸化グラフェンまたはグラフェンを微細化する微細化工程;
還元工程および微細化工程を経た中間体分散液と有機溶媒とを混合する有機溶媒混合工程;
有機溶媒を含む中間体分散液をせん断速度毎秒5000~毎秒50000で撹拌処理する強撹拌工程;
有機溶媒添加と吸引濾過を組み合わせる手法、または蒸留により中間体分散液から水分の少なくとも一部を除去する水分除去工程;
を有するグラフェン分散液の製造方法。 - 前記還元工程からの全ての工程を、グラフェンが分散媒に分散した状態で一度も粉末状態を経由せずに行う、請求項11に記載のグラフェン分散液の製造方法。
- 前記微細化工程をメディアレス分散法により行う、請求項11または12に記載のグラフェン分散液の製造方法。
- 前記微細化工程のメディアレス分散法として超音波処理を行う、請求項13に記載のグラフェン分散液の製造方法。
- さらに、前記還元工程後のいずれかの段階で、
中間体分散液を70℃以上に加熱する加熱工程;
を有する、請求項11~14のいずれかに記載のグラフェン分散液の製造方法。
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CN108028352A (zh) | 2018-05-11 |
JP6152925B1 (ja) | 2017-06-28 |
JPWO2017047523A1 (ja) | 2017-09-14 |
EP3358650A4 (en) | 2019-07-17 |
EP3358650B1 (en) | 2020-08-26 |
TWI694055B (zh) | 2020-05-21 |
US10654721B2 (en) | 2020-05-19 |
EP3358650A1 (en) | 2018-08-08 |
US20180269465A1 (en) | 2018-09-20 |
TW201711960A (zh) | 2017-04-01 |
CN108028352B (zh) | 2019-08-23 |
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