Method for dehydrating carbonaceous material dispersions and method for producing carbonaceous material dispersions

Abstract

To provide a production method of a carbonaceous material dispersion for removing moisture easily and quickly from a carbonaceous material dispersion without deterioration of stability of the dispersion.SOLUTION: There is provided a production method of a carbonaceous material dispersion in which carbonaceous material particles are dispersed in an organic dispersion medium, the method comprising: a step for adding the carbonaceous material particles into the organic dispersion medium and dispersing the particles for forming a carbonaceous material dispersion, then blowing a dry inert gas into the dispersion whose temperature is held to 20-120°C for bringing the dispersion into contact with the dry inert gas for evaporating moisture in the dispersion.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a method for dehydrating a carbonaceous material dispersion and a method for producing a carbonaceous material dispersion. More specifically, this invention relates to a method for dehydrating a carbonaceous material dispersion and a method for producing a carbonaceous material dispersion, which involves removing water from a carbonaceous material dispersion for all-solid-state batteries, in which carbonaceous material particles are dispersed in an organic dispersion medium. [Background technology]

[0002] Conventionally, lithium-ion secondary batteries have used an electrolyte as a medium for ion transfer. However, batteries using such electrolytes can lead to problems such as electrolyte leakage, ignition, and explosion. Therefore, development is underway on all-solid-state lithium-ion secondary batteries, which use a solid electrolyte instead of a liquid electrolyte and are composed entirely of solid components. All-solid-state lithium-ion secondary batteries have very low charge transfer resistance between the solid electrolyte and lithium ions, thus reducing the internal resistance of the battery. Furthermore, because the electrolyte is solid, there is less risk of ignition, leakage, and degradation of battery performance due to corrosion.

[0003] All-solid-state lithium-ion secondary batteries are equipped with a positive electrode layer, a negative electrode layer, and a solid electrolyte layer placed between them, and the electrolyte is made of solid material.

[0004] When constructing an electrode layer using only electrode active material by powder molding as a solid electrolyte layer, the electrolyte is solid, making it difficult for it to penetrate into the electrode layer. This reduces the interface between the electrode active material and the electrolyte, resulting in decreased battery performance. Furthermore, because the electrode layer is made of solid material, it lacks flexibility and processability, making it difficult to handle.

[0005] To address these problems, it has been proposed to form an electrode layer using a slurry prepared by dispersing an electrode active material, a solid electrolyte material, and a binder in a solvent.

[0006] Conventional lithium-ion secondary batteries use electrode slurries prepared by dispersing active materials and conductive additives in a polymer solution in which polyvinylidene fluoride (PVDF) is dissolved as a binder in N-methyl-2-pyrrolidone (NMP) solvent, or by dispersing active materials and conductive additives in an aqueous solution in which styrene-butadiene rubber (SBR) is emulsified as a binder in water, with the addition of thickeners such as carboxymethylcellulose (CMC). However, in the case of all-solid-state lithium-ion secondary batteries, if the solid electrolyte is exposed to a highly polar solvent, the ionic conductivity decreases, and sufficient battery performance cannot be obtained. Therefore, it is undesirable to use NMP or water as a solvent for electrode slurries, and low-polarity or non-polar solvents are used.

[0007] Furthermore, as mentioned above, moisture can reduce the ionic conductivity of solid electrolytes and can also cause hydrolysis of other materials that make up the solid electrolyte. Therefore, carbonaceous material dispersions used in the manufacture of all-solid-state batteries must contain as little moisture as possible.

[0008] One method for obtaining low-moisture carbonaceous material dispersions is to keep the moisture content of each individual material used in preparing the dispersion as low as possible.

[0009] For example, methods for removing water from non-aqueous solvents include, for example, using an ion exchange resin as described in Patent Document 1, using a zeolite as described in Patent Documents 2 and 3, and treating with at least one selected from the group consisting of fluorophosgene, phosgene, and phosgene dimer, as well as a metal oxide, as shown in Patent Document 4. Furthermore, there are methods for dehydrating general polymers, such as heating and distillation dehydration or azeotropic dehydration as shown in Patent Document 5, which involve reducing viscosity with an auxiliary solvent and using a dehydration adsorbent, as well as dehydration by distillation. These methods can be considered for the dehydration treatment of carbonaceous material dispersions.

[0010] However, dehydration methods using dehydration adsorbents such as molecular sieves and alumina microparticles have electrochemical adverse effects for several reasons, including the presence of residual auxiliary solvents used to reduce viscosity, the inclusion of impurities originating from molecular sieves and alumina microparticles, the adhesion and retention of molecular sieves and alumina microparticles on the electrolyte, negative electrode surface, and separator, the possibility of adsorption of components other than water and removal of components that are actually needed, and insufficient reduction in moisture content.

[0011] Furthermore, in dehydration methods using such adsorbents, for example, if the water content of a dispersion is 1000 ppm, dehydrating this dispersion to, for example, 50 ppm or less using only the adsorbent would require a large amount of adsorbent relative to the dispersion, and the time required for dehydration would also be considerably long, making it inefficient.

[0012] Furthermore, Patent Document 6 proposes that in the manufacturing process of conductive paste for lithium-ion battery cathodes, dehydrating agents such as solid dehydrating agents like zeolite and silica gel, phosphate esters, phosphine oxides, orthoesters, and acid anhydrides are added, and that moisture contamination is prevented by, for example, carrying out the manufacturing process in a low dew point environment.

[0013] However, as mentioned above, there are problems with using dehydrating agents, and if the manufacturing process is carried out in a low dew point environment, it is necessary to introduce glove boxes or dry rooms. Furthermore, a pretreatment process is required to remove moisture already present in all materials, including the dispersion medium, and there are also problems with the workability when manufacturing in glove boxes or dry rooms.

[0014] Furthermore, as a method for removing water from an aqueous solvent, as shown in Patent Documents 7 and 8, a method is known in which water is evaporated and removed from the solvent by blowing a dry, inert gas into the liquid. However, the methods disclosed in these documents were all applied to solvents or solutions, and it was unclear whether they could be applied to carbonaceous material dispersions in which particles tend to aggregate. [Prior art documents]

Patent Document

[0015]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Summary of the Invention

Problems to be Solved by the Invention

[0016] Therefore, an object of the present invention is to provide a method for removing moisture from a carbonaceous material dispersion and a method for producing a carbonaceous material dispersion that solve the above problems. Another object of the present invention is to provide a method for dehydrating a carbonaceous material dispersion and a method for producing a carbonaceous material dispersion that can simply and quickly provide a low-moisture carbonaceous material dispersion capable of suppressing deterioration of a solid electrolyte when used as a conductive assistant for an all-solid-state lithium-ion secondary battery without impairing the stability of the dispersion.

Means for Solving the Problems

[0017] The present invention, which solves the above problems, is a method for removing water from a carbonaceous material dispersion in which carbonaceous material particles are dispersed in an organic dispersion medium, characterized by comprising the step of blowing 6 to 30 L of dry inert gas per 100 g of dispersion into a dispersion maintained at 20 to 120°C, and bringing the dispersion into contact with the dry inert gas to evaporate the water in the dispersion.

[0018] In one embodiment of the method for removing water from a carbonaceous material dispersion according to the present invention, the carbonaceous material dispersion is characterized in that the carbonaceous material dispersion is stirred while the inert gas is blown in, and the inert gas is blown in from the bottom side of the container containing the carbonaceous material dispersion.

[0019] In one embodiment of the method for removing moisture from a carbonaceous material dispersion according to the present invention, the method for dehydrating a carbonaceous material dispersion is also described, characterized in that when blowing in the inert gas, the inert gas is blown in while generating bubbles with a number average particle size of about 5 mm to 0.5 mm in the carbonaceous material dispersion.

[0020] In one embodiment of the method for removing moisture from a carbonaceous material dispersion according to the present invention, a method for dehydrating a carbonaceous material dispersion is provided, characterized in that the pressure inside the system is reduced to -5 kPa to -95 kPa compared to atmospheric pressure when blowing in the inert gas.

[0021] In one embodiment of the method for removing moisture from a carbonaceous material dispersion according to the present invention, a method for dehydrating a carbonaceous material dispersion is provided, characterized by blowing in an inert gas and then degassing the gas in the dispersion by reducing the pressure.

[0022] In one embodiment of the method for removing water from a carbonaceous material dispersion according to the present invention, a method for dehydrating a carbonaceous material dispersion is also provided, wherein the organic dispersion medium is at least one selected from the group consisting of ester solvents, ketone solvents, hydrocarbon solvents, and mixtures thereof.

[0023] In one embodiment of the method for removing water from a carbonaceous material dispersion according to the present invention, a method for dehydrating a carbonaceous material dispersion is further described, wherein the organic dispersion medium is at least one selected from the group consisting of butyl butyrate, xylene, mesitylene, and heptane.

[0024] In one embodiment of the method for removing water from a carbonaceous material dispersion according to the present invention, a method for dehydrating a carbonaceous material dispersion in which the carbonaceous material is carbon black is provided.

[0025] In one embodiment of the method for removing water from a carbonaceous material dispersion according to the present invention, a method for dehydrating a carbonaceous material dispersion in which the inert gas is nitrogen is also provided.

[0026] In one embodiment of the method for removing water from a carbonaceous material dispersion according to the present invention, a method for dehydrating a carbonaceous material dispersion is provided in which the inert gas has a dew point of -50°C or lower.

[0027] One embodiment of the method for removing water from a carbonaceous material dispersion according to the present invention is described, wherein the carbonaceous material dispersion comprises a carbonaceous material, an organic dispersion medium, and a dispersant.

[0028] One embodiment of the method for removing water from a carbonaceous material dispersion according to the present invention is a method for dehydrating a carbonaceous material dispersion, in which the carbonaceous material dispersion is an electrode slurry for an all-solid-state lithium-ion secondary battery, which is obtained by compounding a carbonaceous material, a dispersant, a binder resin, and a positive electrode active material or a negative electrode active material in a dispersion medium which is compounded with a carbonaceous material, an organic dispersion medium, a dispersant, a binder resin, and a positive electrode active material or a negative electrode active material.

[0029] In one embodiment of the method for removing water from a carbonaceous material dispersion according to the present invention, the change in the non-volatile content of the dispersion before and after the step of contacting the dispersion with a dry inert gas to evaporate the water in the dispersion is 0.5% by mass or less, and the water content of the dispersion after the step is 5 × 10⁻⁶ by mass fraction. -5The following method for dehydrating a carbonaceous material dispersion is presented.

[0030] The present invention, which solves the above problems, is also a method for producing a carbonaceous material dispersion in which carbonaceous material particles are dispersed in an organic dispersion medium, characterized in that the method comprises the steps of adding carbonaceous material particles to an organic dispersion medium and dispersing them to form a carbonaceous material dispersion, and then blowing 6 to 30 L of dry inert gas per 100 g of dispersion into the dispersion, which is maintained at 20 to 120°C, and bringing the dispersion into contact with the dry inert gas to evaporate the water in the dispersion.

[0031] One embodiment of the method for producing a carbonaceous material dispersion according to the present invention is shown, wherein the carbonaceous material dispersion comprises a carbonaceous material, an organic dispersion medium, and a dispersant.

[0032] In one embodiment of the method for producing a carbonaceous material dispersion according to the present invention, the carbonaceous material dispersion is an electrode slurry for an all-solid-state lithium-ion secondary battery, comprising a carbonaceous material, an organic dispersion medium, a dispersant, a binder resin, and a positive electrode active material or a negative electrode active material. [Effects of the Invention]

[0033] According to the present invention, low-polarity or non-polar solvents used as solvents for electrode slurries for solid electrolyte electrode preparation, such as ester substances represented by butyl butyrate, ketone substances represented by methyl isobutyl ketone, water-insoluble aromatic substances such as xylene and toluene, and hydrocarbon substances such as heptane and cyclohexane, almost always have an azeotrope with water, so water can be evaporated along with them. Furthermore, even solvents without an azeotrope are often used if they have a boiling point higher than water for environmental reasons, so sufficient dehydration can be achieved by aeration with a dry gas. This eliminates the need for pretreatment steps or additives or consumables that are difficult to separate and remove, and makes it possible to provide a low-moisture carbonaceous material dispersion quickly and easily without compromising the stability of the dispersion. Moreover, making the carbonaceous material dispersion low in moisture can contribute to improving the stability and properties of the dispersion. Furthermore, when the low-moisture carbonaceous material dispersion obtained in this way is used as a conductive additive for all-solid-state lithium-ion secondary batteries, it can suppress the degradation of the solid electrolyte, and the carbonaceous material can be dispersed at a high concentration and uniformly, allowing for low-viscosity and high-concentration dispersion of the solid components when mixed with the electrode active material. As a result, it becomes possible to manufacture secondary batteries with excellent and stable performance in terms of charge-discharge characteristics, cycle characteristics, and electrode conductivity. [Brief explanation of the drawing]

[0034] [Figure 1] This is a schematic diagram illustrating a dehydration apparatus that may be used in one embodiment of the dehydration method for carbonaceous material dispersions according to the present invention. [Modes for carrying out the invention]

[0035] The present invention will be described in detail below based on embodiments.

[0036] <Method for removing water from carbonaceous material dispersions> Figure 1 is a schematic diagram showing a dewatering apparatus that may be used in one embodiment of the water removal method of the present invention. The present invention, in its first aspect, is a method for removing moisture from a carbonaceous material dispersion 10, which is obtained by dispersing carbonaceous material particles in an organic dispersion medium (hereinafter also simply referred to as "the moisture removal method of the present invention"), characterized by comprising the step of blowing 6 to 30 L of dry inert gas 20 per 100 g of dispersion into a dispersion 10 maintained at 20 to 120°C, and bringing the dispersion into contact with the dry inert gas to evaporate the moisture in the dispersion.

[0037] By setting the temperature of the dispersion during processing to 20-120°C, moisture can be efficiently removed by an inert gas that comes into contact with the dispersion without adversely affecting the composition, physical properties, and characteristics of the dispersion, as well as the properties of the components within the dispersion. Although it depends to some extent on the type of organic dispersion medium used for the dispersion, the dispersion temperature is more preferably around 30-90°C, and even more preferably around 40-60°C. Heating the side carrying the dry, inert gas through the vents could also be considered, but this is not efficient.

[0038] Furthermore, the permeability of the dry inert gas is calculated based on a moisture content of 1 × 10⁻⁶ by mass fraction. -3 ~1 × 10 -2 By using 6 to 30 L of air per 100 g of dispersion, sufficient moisture can be removed without significantly affecting the dispersion's composition. If the airflow is too low, it becomes difficult to effectively remove moisture, while if it is too high, a large amount of organic dispersion medium will be removed from the dispersion, potentially causing excessive fluctuations in the dispersion's composition (non-volatile content). The permeability of the dry inert gas mentioned above is the volume at normal temperature and pressure. In this specification, "normal temperature and pressure" refers to conditions in the range of 10-30°C and 96kPa-105kPa, and more specifically, conditions of 23°C and 101.325kPa (1 atmosphere).

[0039] In one embodiment of the moisture removal method of the present invention, as described above, the dispersion 10 is brought into contact with a dry inert gas 20 and the moisture in the dispersion is evaporated together with a small amount of organic dispersion medium, wherein the change in the non-volatile content of the dispersion before and after this processing step is 0.5% by mass or less, more preferably 0.1% by mass or less, and the moisture content of the dispersion after the process is 5 × 10⁻⁶ by mass fraction. -5 The following is more preferable: 2 × 10 -5 Further, preferably 1 × 10 -5 It is preferable that it be less than [a certain value].

[0040] In the water removal method of the present invention, it is preferable that the water content of the dispersion after treatment be as low as possible. However, if the organic dispersion medium in the dispersion is removed more than necessary by the inert gas, and the composition of the dispersion and the variation in the non-volatile content of the dispersion change more than necessary, there is a risk of changes in the dispersion state, an increase in viscosity, and aggregation of the dispersed phase. However, in the water removal method of the present invention, the water content of the dispersion after treatment is 5 × 10⁻⁶ by mass fraction. -5 Even after thorough dehydration to the extent shown below, it is desirable because the change in the non-volatile content of the dispersion before and after the processing step typically remains below 0.5% by mass. A method of adding an excess of organic dispersion medium beforehand and evaporating the excess organic dispersion medium along with the water to remove the water has also been considered, but this is not recommended from an environmental perspective because it increases the use of excessive organic materials and the amount of exhaust gas emitted.

[0041] The change in the non-volatile content of the dispersion before and after the processing step can be calculated from the weight of the residue after drying at 140°C. Furthermore, the moisture content of the dispersion can be determined using, for example, a Karl Fischer moisture meter, a near-infrared absorbance type trace moisture meter, or a refractive index type meter. Alternatively, it can be determined with greater accuracy by gas chromatography using an ionic liquid column.

[0042] In one embodiment illustrated in Figure 1, a carbonaceous material dispersion 10 is contained in a processing container (flask) 40 that is sealed except for the introduction and exit paths of the inert gas 20. Dry nitrogen gas, which is the dry inert gas 20, is blown into the carbonaceous material dispersion 10 at a predetermined flow rate, while measuring the flow rate with a gas flow meter 22, from a blowing nozzle 24 whose opening is located on the bottom side of the processing container 40 containing the carbonaceous material dispersion.

[0043] The outer circumference of the processing container 40 is surrounded by a heating jacket (mantle heater) 42 for heating the carbonaceous material dispersion contained inside the processing container. By measuring the temperature of the carbonaceous material dispersion 10 with a liquid thermometer 44 and activating the heating jacket 42 as needed, the temperature of the carbonaceous material dispersion 10 is maintained at a predetermined temperature during the moisture removal process.

[0044] Furthermore, a magnetic stirrer 30 is installed at the bottom of the processing container 40, and a stirrer tip 32 is placed inside the processing container 40. By activating these as needed, the contact efficiency between the inert gas 20 introduced into the carbonaceous material dispersion 10 during the moisture removal process and the dispersion is increased, and the dispersion state of the carbonaceous material in the carbonaceous material dispersion 10 is maintained.

[0045] An inert gas 20 is passed through a carbonaceous material dispersion 10 to transfer water from the dispersion 10 into the inert gas 20. The water is then transported to the gas phase above the dispersion 10 within the processing container 40. However, the inert gas 20 may also contain a small amount of organic dispersion medium, so it is passed through a capture trap 50 that goes through the aqueous phase to remove the associated components before being discharged from the system.

[0046] Furthermore, the dehydration apparatus that can be used in the moisture removal method of the present invention is not limited in any way to the laboratory-scale apparatus shown in Figure 1, as long as it is capable of blowing a dry inert gas 20 at a predetermined flow rate into a carbonaceous material dispersion 10 maintained at a predetermined temperature according to the method of the present invention. For example, it is possible to use a continuous apparatus instead of a batch apparatus, and of course, it is also possible to use a plant-scale apparatus that corresponds to the scale of industrial production.

[0047] Furthermore, regarding the individual configurations, in the apparatus shown in Figure 1, the inert gas 20 is blown into the dispersion from an injection nozzle 24 whose opening is located at the bottom of the processing container 40 containing the carbonaceous material dispersion 10, and the dispersion is stirred by a magnetic stirrer 30 to improve the efficiency of gas-liquid contact. However, the stirring device for the dispersion is not limited in any way, and any known stirring device can be used, such as a stirring device with various stirring bars or a stirring device with a flow channel structure that does not have stirring bars.

[0048] Furthermore, by using a diffuser that passes the inert gas 20 through various porous materials or porous tanks instead of the blowing nozzle 24 that introduces the inert gas 20, or by blowing the inert gas into the dispersion in the form of fine bubbles, for example by applying a pressure wave caused by ultrasonic vibration to the liquid immediately after introducing the inert gas, the moisture removal process can be sufficiently performed without using the stirring device described above. Of course, in this embodiment of blowing in the form of fine bubbles, it is possible to use the stirring device described above in conjunction with it.

[0049] Here, when introducing an inert gas in the form of fine bubbles, the term "fine bubbles" is not particularly limited, but it is desirable to have bubbles with a number-average particle size of approximately 5 mm to 0.5 mm. Bubbles with a number-average particle size of approximately 5 mm to 0.5 mm, more preferably 3 to 1 mm, can exist in the carbonaceous material dispersion with sufficient residence time to remove moisture and with good contact efficiency.

[0050] While smaller bubble diameters generally improve contact efficiency with the dispersion, extremely small bubble diameters require extra energy to create them. Furthermore, bubbles may remain or persist for extended periods within the dispersion, particularly at the interface between carbonaceous material particles and the organic dispersion medium, potentially hindering dehydration or even causing the dispersion to become trapped in gas, thus degrading its properties.

[0051] Here, the average bubble size can be determined from images captured by a high-speed camera. In this specification, the average particle size of bubbles was calculated from 1000 images taken at 1-second intervals using a high-speed camera GX-1 (NAC Corporation) at an exposure time of 50 μs, 20 mm from the outlet of the bubble generator, using a transparent imitation material with the same viscosity and surface tension as the carbonaceous material dispersion 10 being processed. Specifically, one bubble in the center of each photograph that was in focus was selected, and its diameter was measured. At this time, the focus was fixed, and the length of the in-focus area was calculated from the scale. After performing the above operation for 1000 photographs, the bubble diameters were averaged to calculate the average particle size.

[0052] Furthermore, in order to release the inert gas 20 introduced into the carbonaceous material dispersion 10 into the gas phase along with moisture without causing it to remain in the dispersion for longer than necessary, the pressure inside the system can be reduced to -5kPa to -95kPa compared to atmospheric pressure, although this is not particularly limited.

[0053] Furthermore, it is possible to degas the gas in the dispersion medium by reducing the pressure after blowing in an inert gas. In this case, it is appropriate to reduce the pressure to, for example, -5kPa to -95kPa compared to atmospheric pressure.

[0054] Furthermore, in one embodiment illustrated in Figure 1, the inert gas 20 discharged from the processing container 40 is passed through the capture trap 50 and then discharged out of the system. However, it is also possible to recycle the inert gas after passing it through the capture trap 50 by subjecting it to an appropriate drying treatment, such as passing it through a molecular sieve or a dehydration membrane.

[0055] Furthermore, in one embodiment illustrated in Figure 1, an example using nitrogen as the inert gas 20 is shown. However, the inert gas is not particularly limited as long as it is a gas that can remove water from the carbonaceous material dispersion without substantially causing a chemical change to the carbonaceous material dispersion upon contact. In addition to nitrogen, for example, argon, helium, neon, etc., can also be used. However, from the viewpoint of economy and environmental friendliness, it is desirable to use nitrogen as the inert gas.

[0056] Furthermore, the "degree of dryness" of the dry inert gas 20 used in the present invention is not particularly limited as long as it has a moisture content that is at least less than the moisture content of the carbonaceous material dispersion to be treated and can effectively remove moisture. However, for example, it is desirable that the dew point be -50°C or lower, and more preferably -60°C or lower.

[0057] Next, the carbonaceous material dispersion to be treated in the moisture removal method of the present invention will be described.

[0058] (Carbonaceous material dispersion) The carbonaceous material dispersion to be processed is not particularly limited, as long as it is a dispersion in which carbonaceous material particles are dispersed in an organic dispersion medium.

[0059] (carbonaceous material) The carbonaceous material contained in the carbonaceous material dispersion is not particularly limited as long as it can take the form of a powder or granules so as to be able to form a dispersion in an organic dispersion medium. Typical examples include graphite, carbon black (CB), carbon nanotubes (CNT), carbon nanofibers (CNF), carbon fibers (CF), fullerenes, and natural graphite, and these can be used individually or in combination of two or more. Among the carbonaceous materials, CB is particularly preferred. Furthermore, examples of CB include furnace black, channel black, acetylene black, and thermal black, and any of these can be used. Of these, acetylene black, for example, has an inherently low metal content due to its manufacturing process, making it preferable for incorporation into carbonaceous material dispersions used for secondary battery applications.

[0060] In addition, carbon black (CB) can also be oxidized or graphitized, which are commonly used. The oxidation treatment of CB involves treating the carbon black at high temperatures in air or secondarily treating it with nitric acid, nitrogen dioxide, ozone, etc., to directly introduce (covalently bond) oxygen-containing polar functional groups such as phenol groups, quinone groups, carboxyl groups, and carbonyl groups onto the carbon black surface, thereby improving the dispersibility of the CB.

[0061] In this specification, the "granular" form of carbonaceous material is not particularly limited as long as it can form a uniform dispersion when dispersed in a dispersion medium. For example, it may include primary particles with an average particle diameter of about 10 to 60 nm, secondary particles with an average particle diameter of about 1 to 1000 μm formed by aggregation of such primary particles, or processed particles with an average particle diameter of about 0.5 to 5 mm obtained by further compression or granulation. Furthermore, its shape is not particularly limited and is not limited to generally spherical, but may include elliptical, flaky, needle-like or short-fiber-like, or irregular shapes. The average particle diameter of the carbonaceous material is more preferably about 0.5 mm to 5 mm. After preparing the carbonaceous material dispersion by dispersion in a dispersion medium, it is desirable that the average particle diameter of the carbonaceous material in the dispersion medium be about 10 μm or less.

[0062] In this specification, "average particle diameter" refers to the volume-based average particle diameter d50 (so-called median diameter) measured using a laser diffraction scattering particle size distribution analyzer.

[0063] Regarding carbon black, as explained on the website of the Carbon Black Association (https: / / carbonblack.biz / index.html), for example, the smallest non-degradable unit of carbon black is the aggregate (primary aggregate), and a part of it (domain) is commonly referred to as a particle. This particle can be considered to correspond to the particle defined as the smallest unit in nanomaterials, but it is only a part of the aggregate. The aggregate forms agglomerate (secondary aggregate) through physical forces such as van der Waals forces. Furthermore, carbon black products are almost always transported and sold in the form of processed particles called beads, which are compressed or granulated to prevent scattering and improve handling.

[0064] For example, this may include primary aggregates with an average particle size of about 10 to 100 nm, secondary aggregates formed by the aggregation of such primary aggregates with an average particle size of about 0.1 to 100 μm, or particles that have been further processed to have an average particle size of about 500 to 5000 μm through compression or granulation treatment, taking into consideration handling properties.

[0065] Furthermore, from the viewpoint of carbon black conductivity, aggregates of conductive carbon nanoparticles, in which primary particles are linked together to form a chain-like or cluster-like structure, are preferred. The linkage of primary particles in the aggregate is also called a structure, and the degree of such development can be determined by particle size distribution measurement (dynamic light scattering method or laser diffraction / light scattering method) or electron microscope observation (either scanning or transmission type can be used). Such structures can efficiently form conductive paths between electrode active material particles. Therefore, excellent conductivity can be imparted to the electrode active material layer with a smaller amount of material used.

[0066] (Organic dispersion medium) On the other hand, the organic dispersion medium used to disperse the carbonaceous material described above is not particularly limited and can be appropriately selected depending on the intended use of the resulting carbonaceous material dispersion.

[0067] While not particularly limited, examples of organic dispersion media include esters such as dibutyl ether, ethyl acetate, ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, hexyl propionate, heptyl propionate, octyl propionate, ethyl butyrate, propyl butyrate, butyl butyrate, pentyl butyrate, hexyl butyrate, heptyl butyrate, octyl butyrate, ethyl valerate, propyl valerate, butyl valerate, amyl valerate, hexyl valerate, heptyl valerate, octyl valerate, ethyl caproate, propyl caproate, butyl caproate, pentyl caproate, hexyl caproate, heptyl caproate, octyl caproate, ethyl heptanoate, propyl heptanoate, butyl heptanoate, pentyl heptanoate, hexyl heptanoate, heptyl heptanoate, and octyl heptanoate. Examples of solvents include: ketone solvents such as diethyl ketone, dimethyl ketone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), and cyclohexanone (anone); aprotic polar solvents such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methyl-2-pyrrolidone (NMP); alkane solvents such as pentane, cyclopentane, hexane, cyclohexane, heptane, cycloheptane, octane, cyclooctane, nonane, and decane; linear carbonates such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; cyclic carbonates such as ethylene carbonate and propylene carbonate; and toluene, xylene, benzene, mesitylene, paraffin, and carbon tetrachloride. These can be used individually or in combination.

[0068] Of these, butyl butyrate, xylene, mesitylene, and heptane are particularly preferred.

[0069] (Other ingredients) Furthermore, the carbonaceous material dispersion to be treated may contain, in addition to the carbonaceous material and organic dispersion medium described above, dispersants, pH adjusters, or other additives. Other additives may include dispersion aids, stabilizers, and may also include, for example, binder resins, positive electrode active materials, or negative electrode active materials.

[0070] In other words, the dehydration method for carbonaceous material dispersions according to the present invention can be used not only for carbonaceous material slurries containing, for example, a carbonaceous material, an organic dispersion medium, and a dispersant, but also for carbonaceous material dispersions containing more components, such as electrode slurries for all-solid-state lithium-ion secondary batteries, which are composed of a carbonaceous material, an organic dispersion medium, a dispersant, a binder resin, and a positive electrode active material or a negative electrode active material.

[0071] (Dispersant) While not particularly limited, examples of dispersants include polyvinyl butyral (PVB), polyvinyl acetal, polyvinyl acetate, polyester resins, epoxy resins, polyether resins, alkyd resins, and urethane resins.

[0072] One preferred example of a dispersant is one in which polyvinyl butyral is the main component, particularly in an amount of 80% by mass or more, and furthermore, in which the entire amount of the dispersant, i.e., 100% by mass, is polyvinyl butyral. When a carbonaceous material dispersion is used for all-solid-state lithium-ion secondary battery applications, by using polyvinyl butyral as a dispersant in this way and combining it with the above-mentioned organic dispersion medium as a dispersion agent, good dispersibility of the carbonaceous material in the carbonaceous material dispersion can be obtained, and low viscosity can be achieved.

[0073] The polyvinyl butyral is not particularly limited, but it is preferably one with a relatively low hydroxyl group content. Specifically, for example, it is preferable that the hydroxyl group content in the polymer is 5% by mass or more and 25% by mass or less, more preferably 10% by mass or more and 20% by mass or less, and even more preferably 12.5% ​​by mass or more and 17.5% by mass or less. Also, although not particularly limited, the acetate group content of the polyvinyl butyral is preferably about 1 to 7% by mass, and the viscosity of the ethanol solution of 10% by mass of polyvinyl butyral, measured at 20°C in accordance with DIN53015, is preferably 10 to 100 mPa·s, particularly 20 to 60 mPa·s.

[0074] (pH adjuster) Examples of pH adjusting agents include tertiary amines, secondary amines, primary amines, cyclic amines, and alkanolamines or amino alcohols which are compounds having an amino group and a hydroxyl group in an alkane skeleton, or amine compounds such as diglycolamine, tris(hydroxymethyl)aminomethane (THAM), morpholine, and other amines. While not particularly limited, among these, 2-methylaminoethanol, 2-amino-1-butanol, 4-ethylamino-1-butanol, triethylamine, 2-amino-2-ethyl-1,3-propanediol (AEPD), 2-amino-2-methyl-1-propanol (AMP), and THAM are preferred.

[0075] (Binder resin) In embodiments where the carbonaceous material dispersion to be treated is an electrode slurry for an all-solid-state lithium-ion secondary battery, the binder resin blended into the dispersion medium is not particularly limited, but polymers that are insoluble in water can be used. Specifically, for example, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polyamide, polyamideimide, butadiene rubber, isobutylene rubber, styrene-butadiene rubber, ethylene propylene rubber, and nitrile-butadiene rubber can be used. Of these, styrene-butadiene rubber is particularly preferred.

[0076] (Electrode active material) In an embodiment where the carbonaceous material dispersion as the object to be treated is an electrode slurry for an all-solid-state lithium-ion secondary battery, the positive electrode active material that can be blended is not particularly limited, but metal compounds such as metal oxides and metal sulfides capable of doping or intercalating lithium ions, and conductive polymers can be used.

[0077] For example, oxides of transition metals such as Fe, Co, Ni, Mn, composite oxides with lithium, inorganic compounds such as transition metal sulfides, etc. can be mentioned. Specifically, transition metal oxide powders such as MnO, V2O5, V6O 13 , TiO2, etc., composite oxide powders of lithium and transition metals such as layered lithium nickelate, lithium cobaltate, lithium manganate, spinel-structured lithium manganate, lithium iron phosphate-based materials which are olivine-structured phosphate compounds, transition metal sulfide powders such as TiS2, FeS, etc. can be mentioned. Also, conductive polymers such as polyaniline, polyacetylene, polypyrrole, polythiophene can be used. Further, the above inorganic compounds and organic compounds may be mixed and used.

[0078] On the other hand, in an embodiment where the carbonaceous material dispersion as the object to be treated is an electrode slurry for an all-solid-state lithium-ion secondary battery, the negative electrode active material that can be blended is not particularly limited as long as it can dope or intercalate lithium ions. For example, metal Li, alloy systems such as its alloys tin alloy, silicon alloy, lead alloy, etc., Li X Fe2O3, Li X Fe3O4, Li XExamples of carbonaceous materials include metal oxides such as WO2, lithium titanate, lithium vanadate, and lithium siliconate; conductive polymers such as polyacetylene and poly-p-phenylene; amorphous carbonaceous materials such as soft carbon and hard carbon; artificial graphite such as highly graphitized carbonaceous materials; carbonaceous powders such as natural graphite; carbon black; mesophase carbon black; resin-fired carbonaceous materials; vapor-grown carbon fibers; and carbon fibers. These negative electrode active materials can be used individually or in combination.

[0079] These electrode active materials preferably have an average particle diameter in the range of 0.05 to 100 μm, and more preferably in the range of 0.1 to 50 μm. In this specification, the average particle diameter of the electrode active material refers to the average value of particle diameters measured with an electron microscope.

[0080] (Formulation ratio in the dispersion) In the carbonaceous material dispersion to be treated, although not particularly limited, the carbonaceous material is adjusted to, for example, 10 to 25% by mass, more preferably 12 to 18% by mass, relative to the total mass of the dispersion in an organic dispersion medium. If a dispersant is added, although not particularly limited, the amount added is adjusted to, for example, 5% by mass or more and less than 20% by mass, more preferably 6% by mass or more and less than 12% by mass, relative to the mass of the carbonaceous material (i.e., relative to 100% by mass of the carbonaceous material). If the amounts of carbonaceous material and dispersant are both within this range, it is possible to create a dispersion containing a high concentration of carbonaceous material while maintaining good dispersibility and low viscosity of the carbonaceous material. If the concentration of carbonaceous material is lower than above, the energy required for solvent removal in product manufacturing increases, and the transportation costs of the dispersion and solvent also increase. On the other hand, if the concentration of carbonaceous material is higher than above, it becomes difficult to obtain sufficient fluidity, resulting in poor handling.

[0081] Furthermore, as mentioned above, when incorporating a pH adjuster, although not particularly limited, the amount of pH adjuster added is generally 0.01 to 5%, more preferably 0.05 to 3%, relative to the total amount of the dispersion. By incorporating a pH adjuster within this range, it is possible to obtain better dispersibility of the carbonaceous material.

[0082] (Characteristics of carbonaceous material dispersions as treated materials) Furthermore, the carbonaceous material dispersion obtained by performing a dispersion treatment, for example, as illustrated below, on the composition and proportions described above is not particularly limited, but has a viscosity of approximately 10 to 1000 mPa·s, preferably 10 to 500 mPa·s, and more preferably 10 to 300 mPa·s, at 25°C. In embodiments where the carbonaceous material dispersion is an electrode slurry for an all-solid-state lithium-ion secondary battery further containing a binder resin and an electrode active material, by using the predetermined components described above, if the solid content concentration of the slurry is 65 to 75% by mass, the viscosity at 25°C may be approximately 500 to 5000 mPa·s, more preferably 1000 to 4000 mPa·s.

[0083] In this specification, the viscosity of a carbonaceous material dispersion is the value measured immediately after thoroughly stirring the dispersion with a spatula (for example, for 1 minute) using a B-type viscometer at a measurement temperature of 25°C and a B-type viscometer rotor rotation speed of 60 rpm.

[0084] Furthermore, the water content in the carbonaceous material dispersion to be treated (i.e., before treatment by the water removal method of the present invention) is not particularly limited, but for example, 1 × 10⁻⁶ by mass fraction. -3 ~2×10 -2 To a certain extent, more preferably 1 × 10 -3 ~1 × 10 -2 It is considered to be of a certain degree.

[0085] (Preparation of carbonaceous material dispersion as the material to be treated) The method for preparing the carbonaceous material dispersion to be treated is not particularly limited, but it is prepared by adding the carbonaceous material and, if necessary, a dispersant, pH adjuster, or other components to an organic dispersion medium in the predetermined proportions described above, and then stirring and mixing to disperse them. The order of addition of the components is not particularly limited, and any configuration falls within the scope of the present invention.

[0086] The dispersion device is not particularly limited, and any dispersion machine commonly used for pigment dispersion can be used. For example, mixers such as dispersers, homomixers, and planetary mixers; homogenizers (such as M-Technic's "Clearmix," PRIMIX's "Filmix," and Silverson's "Abramix"); paint conditioners (Red Devil); colloid mills (such as PUC's "PUC Colloid Mill" and IKA's "Colloid Mill MK"); cone mills (such as IKA's "Corn Mill MKO"); ball mills; and sand mills (Shinmaru). Examples include, but are not limited to, media-type dispersers such as Enterprises' "Dinomill," Atlighter, Pearlmill (Eirich's "DCPmill," etc.), Coballmill, wet jet mills (Genus' "Genus PY," Sugino Machine's "Starburst," Nanomizer's "Nanomizer," etc.), media-less dispersers such as M-Technique's "CREA SS-5" and Nara Machinery's "MICROS," and other roll mills.

[0087] Preferably, the carbonaceous material is ultimately prepared by dispersing it in a media mill, particularly a media mill using beads with an average particle size of 0.05 to 2 mm. More preferably, the material is prepared by first performing a dispersion treatment using a shear-type dispersion device, as detailed below, prior to the dispersion treatment with such a media mill, and then subsequently performing the dispersion treatment with a media mill.

[0088] Furthermore, prior to dispersion processing using such a media mill, it is possible to perform preliminary dispersion processing using other stirring devices, such as shear-type stirrers like dispersers and homomixers.

[0089] Prior to preparing the carbonaceous material dispersion, each component used can be dehydrated using any known method, such as dehydration with adsorbents like ion exchange resins, zeolites, molecular sieves, alumina nanoparticles, phosgene compounds, and metal oxides, distillation dehydration, azeotropic dehydration, or dehydration by heating.

[0090] (Method for producing low-moisture carbonaceous material dispersions) A method for producing a carbonaceous material dispersion according to a second aspect of the present invention is a method for producing a carbonaceous material dispersion in which carbonaceous material particles are dispersed in an organic dispersion medium, and is characterized by having the following steps: for example, after going through the carbonaceous material dispersion preparation step as described above, carbonaceous material particles are added to an organic dispersion medium and dispersed to form a carbonaceous material dispersion, and then, similar to the water removal method according to the first aspect of the present invention as detailed above, 6 to 30 L of dry inert gas per 100 g of dispersion is blown into the dispersion, which is maintained at 20 to 120°C, and the dispersion is brought into contact with the dry inert gas to evaporate the water in the dispersion.

[0091] In the method for producing a carbonaceous material dispersion according to the second aspect of the present invention, the various conditions, particularly preferred conditions, for the water removal method according to the first aspect of the present invention, as described in detail above, are applicable in the same manner, and therefore, to avoid duplication, they are omitted here.

[0092] Furthermore, in the method for producing a carbonaceous material dispersion according to the second aspect of the present invention, the steps other than the step of evaporating the water described above are not particularly limited. For example, the preparation step of the carbonaceous material dispersion prior to the step of evaporating the water is not limited to the preparation step described above and can take various forms. Also, in the method for producing a carbonaceous material dispersion according to the second aspect of the present invention, with regard to water removal or dehydration, the step of evaporating the water described above is essential, but it is optional to provide other treatments or steps. For example, it is possible to provide a step of separately performing a dehydration treatment or drying treatment on the organic dispersion medium and carbonaceous material, which are the materials of the carbonaceous material dispersion that are treated in the step of evaporating the water described above. [Examples]

[0093] The present invention will be described more specifically below based on examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention.

[0094] (Preparation of carbonaceous material dispersion A for testing) First, the carbonaceous material dispersion A for the test, which was to be used as the material to be treated in the following Examples 1-3 and Comparative Examples 1-4, was prepared as follows. Specifically, 15 parts by mass of acetylene black, 84 parts by mass of butyl butyrate as a dispersion medium, and 1 part by mass of polyvinyl butyral as a dispersant were blended and dispersed in a bead mill to prepare 300 g of acetylene black dispersion, which was used as the carbonaceous material dispersion for the test. The water content of this carbonaceous material dispersion for the test was 2.056 × 10⁻⁶ by mass fraction. -3 The non-volatile content was 16.00% by mass. Moisture content (mass fraction) was measured using a Karl Fischer moisture meter, and non-volatile content was measured by the weight of the residue after drying at 140°C. Then, this test carbonaceous material dispersion A was subjected to the following conditions: moisture mass fraction 3.0 × 10 -5 Dehydration was performed with the aim of lowering the value to below a certain level.

[0095] (Example 1) Using the apparatus schematically shown in Figure 1, 100 g of the prepared carbonaceous material dispersion A(10) was placed in a 300 ml flask (40) and stirred with a stirrer (30, 32). The dispersion was heated to 60°C using a heating jacket (42), and dewatering treatment was performed by blowing dry nitrogen (20) from the bottom of the dispersion at a flow rate of 0.1 L / min for 150 minutes (total 15 L). As a result, the water content of the carbonaceous material dispersion after dehydration was 2.9 × 10⁻⁶ by mass fraction. -5 The non-volatile content was 16.05% by mass.

[0096] (Example 2) Similar to Example 1, using the apparatus schematically shown in Figure 1, 100 g of the prepared test carbonaceous material dispersion A(10) was placed in a 300 ml flask (40), the pressure inside the system was reduced to -50 kPa compared to atmospheric pressure, and the mixture was stirred with a stirrer (30, 32). The dispersion was heated to 40°C in a heating jacket (42), and dry nitrogen (20) was blown into the bottom of the dispersion at a flow rate of 0.1 L / min for 120 minutes (total 12 L) to dehydrate it. As a result, the water content of the carbonaceous material dispersion after dehydration was 2.2 × 10⁻⁶ by mass fraction. -5 The non-volatile content was 16.2% by mass.

[0097] (Example 3) 100 g of the carbonaceous material dispersion A(10) prepared above was placed in a 300 ml flask (40), and the dispersion was heated to 40°C using a heating jacket (42). In this example, without using a stirrer (30, 32), a diffuser (not shown) made of sintered glass was placed at the tip of an inert gas blowing nozzle 24 at the bottom of the flask (40), and dry nitrogen (20) was blown into the bottom of the dispersion (10) at a flow rate of 0.1 L / min for 120 minutes (total 12 L) to dehydrate it. The average particle size of the dry nitrogen bubbles released into the dispersion from the diffuser at this time was 2 mm. As a result, the water content of the carbonaceous material dispersion after dehydration was 2.8 × 10⁻⁶ by mass fraction. -5 The non-volatile content was 16.02% by mass.

[0098] (Comparative Example 1) Dehydration treatment was carried out in the same manner as in Example 1, except that the dispersion was kept at 10°C. As a result, the water content of the carbonaceous material dispersion after treatment was 6.0 × 10⁻⁶ by mass fraction. -4 The non-volatile content was 16.00% by mass.

[0099] (Comparative Example 2) In Example 1, the dispersion was kept at 130°C, but the dehydration treatment was carried out in the same manner as in Example 1. As a result, the dispersed phase aggregated during the treatment, and the dispersion solidified.

[0100] (Comparative Example 3) In Example 1, the dewatering treatment was carried out in the same manner as in Example 1, except that the amount of dry nitrogen (20) blown in was 0.1 L / min for 50 minutes (total 5 L). As a result, the water content of the treated carbonaceous material dispersion was 1.1 × 10⁻⁶ by mass fraction. -4 The non-volatile content was 16.00% by mass.

[0101] (Comparative Example 4) In Example 1, the dewatering treatment was carried out in the same manner as in Example 1, except that the amount of dry nitrogen (20) blown in was 0.1 L / min for 360 minutes (total 36 L). As a result, the water content of the treated carbonaceous material dispersion was 7.0 × 10⁻⁶ by mass fraction. -6 The non-volatile content was 16.85% by mass.

[0102] (Preparation of carbonaceous material dispersion B for testing) In carrying out the following Example 5, a test carbonaceous material dispersion B, which is intended to be used as the material to be processed and is intended to be an electrode slurry for an all-solid-state lithium-ion secondary battery, was prepared as follows. Specifically, 10.0 g of the test carbonaceous material dispersion A prepared as described above was mixed with LiNi as the positive electrode active material. 1 / 3 Co 1 / 3 Mn 1 / 330.0 g of O2 powder (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., particle size 1 to several μm), a binder solution prepared by dissolving styrene-butadiene rubber in 10% by mass butyl butyrate, and butyl butyrate were mixed to achieve a total solids content of 65% by mass. The mixture was then treated for 5 minutes using a rotary-rotating agitator and defoamer at a rotational speed of 1200 rpm in both directions. The water content of the resulting carbonaceous material dispersion B was 1.5 × 10⁻⁶ by mass fraction. -3 The non-volatile content was 65.00% by mass. The method for measuring the water content and non-volatile content was the same as described above. This carbonaceous material dispersion B for the test was then subjected to a water content of 3.0 × 10⁻⁶. -5 Dehydration was performed with the aim of lowering the value to below a certain level.

[0103] (Example 5) Similar to Example 1, using the apparatus schematically shown in Figure 1, 100 g of the test carbonaceous material dispersion B(10) prepared above was placed in a 300 ml flask (40) and stirred with a stirrer (30, 32). The slurry was heated to 60°C in a heating jacket (42), and dewatered by blowing dry nitrogen (20) from the bottom of the slurry at a flow rate of 0.1 L / min for 150 minutes (total 15 L). As a result, the water content of the slurry after dewatering was 2.8 × 10⁻⁶ by mass fraction. -5 The non-volatile content was 65.08% by mass. [Explanation of symbols]

[0104] 10 Carbonaceous material dispersion 20 Dry Nitrogen 24 Injection nozzles 30, 32 Stirrers 40 flasks 42 Heated Jacket

Claims

1. A method for producing a carbonaceous material dispersion obtained by dispersing carbonaceous material particles in an organic dispersion medium, A method for producing a carbonaceous material dispersion, characterized by the steps of: adding carbonaceous material particles to an organic dispersion medium and dispersing them to obtain a carbonaceous material dispersion having a water content of 1 × 10⁻³ to 2 × 10⁻² by mass fraction; and then blowing a dry inert gas into the dispersion, which is maintained at 20 to 120°C, to bring the dispersion into contact with the dry inert gas and evaporate the water in the dispersion.

2. A method for producing a carbonaceous material dispersion according to claim 2, wherein the dry inert gas is blown into the dispersion at a ratio of 6 to 30 L per 100 g of the dispersion.

3. A method for producing a carbonaceous material dispersion according to claim 1 or 2, wherein the carbonaceous material dispersion comprises a carbonaceous material, an organic dispersion medium, and a dispersant.

4. A method for producing a carbonaceous material dispersion according to any one of claims 1 to 3, wherein the carbonaceous material dispersion is an electrode slurry for an all-solid-state lithium-ion secondary battery comprising a carbonaceous material, an organic dispersion medium, a dispersant, a binder resin, and a positive electrode active material or a negative electrode active material.

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