Electroconductive-material-containing dispersion, method for producing same, and method for producing electrode slurry

Abstract

[Problem] To provide: an electroconductive-material-containing dispersion useful in a variety of batteries such as lithium-ion batteries, but particularly semi-solid-state batteries such as clay batteries; an electrode slurry; and an electrode and a battery that use the dispersion and the slurry. [Solution] Provided is an electroconductive-material-containing dispersion containing at least (i) an electroconductive material, (ii) a dispersant, (iii) an electrolyte, and (iv) a dispersion medium.

Description

Conductive material-containing dispersion, its manufacturing method, and electrode slurry manufacturing method

[0001] The present invention relates to a conductive material-containing dispersion and electrode slurry that are useful in various batteries including lithium ion batteries, particularly semi-solid batteries including clay-type batteries, and to electrodes and batteries using these.

[0002] Lithium-ion batteries have been developed as batteries with advantages such as high energy density, high power density, long life, and low cost. A lithium-ion secondary battery consists of a positive electrode formed by coating an aluminum current collector with an electrode slurry obtained by kneading a positive electrode active material, conductive additive, binder, and solvent, and a negative electrode formed by coating a copper current collector with an electrode slurry obtained by kneading a negative electrode active material, binder, conductive additive, and dispersion thickener. These are arranged between a porous membrane separator and the battery is filled with an electrolyte. In contrast to conventional batteries that use liquid electrolytes, in recent years, rapid development has been progressing toward all-solid-state batteries, which use solid electrolytes to prevent leakage and fire, and semi-solid batteries, which use both solid and liquid electrolytes, for the purpose of improving safety.

[0003] Among these, semi-solid batteries include gel polymer types in which a gel-like polymer is impregnated with an electrolyte (Patent Publication No. 2001-176551), inorganic oxide particle types in which inorganic oxide particles carrying an electrolyte are dispersed in an ionic liquid (Patent Publication No. 2021-177470), clay types that use clay-like materials with electrolyte kneaded into the electrode material for the positive and negative electrodes (Patent Publication Nos. 2014-513857, 2016-511521), and liquid-added types in which a small amount of ionic liquid is added to fill the gap between the active material and solid electrolyte (Patent Publication No. 2017-168435). However, with clay types in particular, it is thought that the uniformity of the active material, conductive material, and electrolyte that make up the electrodes can affect performance, and it is therefore necessary to ensure high uniformity in such systems.

[0004] Patent Publication No. 2001-176551, Patent Publication No. 2021-177470, Patent Publication No. 2014-513857, Patent Publication No. 2016-511521, Patent Publication No. 2017-168435

[0005] An electrode material that ensures high uniformity between the active material, conductive material, and electrolyte that constitute the electrode is desired.

[0006] As a result of extensive research, the present inventors have found that excellent battery performance can be achieved by using a specific conductive material-containing dispersion liquid.

[0007] According to the present invention, a conductive material-containing dispersion liquid capable of exhibiting excellent battery performance can be provided.

[0008] FIG. 1 is a graph showing the relationship between measurement time and volume resistance value in Example 1 and Comparative Example 1. FIG. 2 is a photograph showing electrode plates produced using electrode slurries using the dispersions of Example 1 and Comparative Example 1.

[0009] The present invention will be described in detail below. The present invention relates to: (1) a conductive material-containing dispersion containing at least (i) a conductive material, (ii) a dispersant, (iii) an electrolyte, and (iv) a dispersion medium; (2) a method for producing a conductive material-containing dispersion, which comprises previously mixing a conductive material and a dispersant with a dispersion medium to disperse the conductive material, and then adding an electrolyte; (3) a conductive material-containing dispersion containing at least (i) a conductive material, (ii) a dispersant, and (iii) an electrolytic solution;

[0010] (4) A method for producing an electrode, comprising a step of applying an electrode slurry obtained by mixing at least the conductive material-containing dispersion liquid described in (1) or (3) above with an active material to a current collector; (5) A method for producing an electrode slurry, comprising mixing a conductive material and a dispersant with a dispersion medium to disperse the conductive material, then adding an electrolyte and further mixing the conductive material with the active material; (6) A method for producing an electrode, comprising a step of applying the electrode slurry obtained by the method described in (5) above to a current collector; and (7) A method for producing a semi-solid battery, comprising a step of applying the electrode slurry described in (5) above to a negative electrode current collector and bringing the negative electrode current collector into contact with a semi-solid positive electrode via a separator.

[0011] [Conductive Material-Containing Dispersion] The conductive material-containing dispersion of the present invention contains at least (i) a conductive material, (ii) a dispersant, (ii) an electrolyte, and (iii) a dispersion medium. These components are described below.

[0012] [Conductive Material] The conductive material of the present invention is not particularly limited as long as it is a substance that has conductivity and can increase the conductivity of the electrode, and various substances that have conventionally been known as so-called conductive assistants (which may also be called conductive materials, conductive agents, etc.) can be used. Among these, various conductive carbon materials such as carbon black, carbon nanofibers, carbon nanotubes, graphene, graphite, hard carbon, and fullerenes including buckyballs can be mentioned, but are not limited to these, and these can be used alone or in combination.

[0013] Carbon black includes furnace black, thermal black, channel black, acetylene black, and Ketjenblack. Carbon black generally forms a structure in which primary particles are strung together like grape clusters, and the degree of structure development is indicated by the oil absorption. Depending on the manufacturing conditions, carbon black has a wide variety of properties, such as primary particle size, oil absorption, and specific surface area. Furthermore, there are various types of carbon black, including hollow carbon black and those that have undergone various surface treatments such as oxidation or graphitization. In the present invention, highly conductive carbon black is preferred. Examples of conductive carbon black include Denka Black (registered trademark, manufactured by Denka Co., Ltd.), Ketjenblack EC, EC600JD, EC300J, Lionite CB, and Carbon ECP (all trade names, manufactured by Lion Specialty Chemicals Co., Ltd.), the VULCAN® XC family (manufactured by Cabot Corporation), ENSACO, and super P (all registered trademarks, manufactured by Imerys SA).

[0014] Carbon nanofibers (also referred to as CNFs) refer to nano-level fibrous carbon materials, while carbon nanotubes (also referred to as CNTs) refer to nano-level cylindrical (tubular) carbon materials, but these terms are used without strict distinction. Representative carbon nanofibers include the VGCF and VGCF-S (registered trademarks of Resonac, Inc., highly crystalline carbon fibers synthesized using the CVD method) series. Carbon nanotubes are called single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs) depending on the number of cylindrical layers, and come in various length distributions and winding patterns (chirality). Some MWCNTs have properties similar to CNFs.

[0015] In the present invention, an appropriate conductive aid can be selected from these existing conductive aids, but it is particularly preferable to use acetylene black such as Denka Black alone or in combination with CNF such as VGCF.

[0016] [Dispersant] One of the features of the present invention is that a dispersant is contained. Here, the dispersant is a substance that has the function of making the conductive material more easily dispersible in the dispersion medium, and substances conventionally known as so-called dispersants can be used. For example, resins, cationic surfactants, and nonionic surfactants that have a thickening effect and / or a surfactant effect can be mentioned.

[0017] Among these, in the present invention, those with high affinity for the electrolyte solution or the nonaqueous solvent and electrolyte constituting the electrolyte solution, which will be described later, are preferred. Nonionic polymers are also suitable so as not to inhibit the movement of lithium ions within lithium-ion secondary batteries. Nonionic polymers have hydrophilic portions that do not ionize, and typical examples include water-soluble polymers such as cellulose-based polymers, butyral-based polymers, acetal-based polymers, and polyvinylpyrrolidone (PVP). Furthermore, if the weight-average molecular weight of a nonionic polymer resin exceeds 1,000,000, the viscosity of the conductive material-containing dispersion becomes too high, resulting in poor handling. On the other hand, if the weight-average molecular weight is below 1,000, dispersibility is poor, making the production of the conductive material-containing dispersion difficult. A weight-average molecular weight of 5,000 to 300,000 is even more preferred. For water-soluble polymers such as polyvinylpyrrolidone, the degree of polymerization is generally indicated by the K value (characteristic viscosity value), which is grouped into groups ranging from 10 to 120. In the present invention, a K value of 15 to 90 is preferred, with a K value of 30 being particularly preferred. Acetal-based polymers include BL-10 (product name, manufactured by Sekisui Chemical Co., Ltd.), with BL-10 being particularly preferred. These polymers are highly effective in uniformly dispersing conductive materials and also have excellent affinity with electrolytes. Among these, polyvinylpyrrolidone is particularly preferred, as it offers an excellent balance between affinity and dispersibility with electrolytes and is effective in dispersing conductive materials even in small amounts. The amount of dispersant to be added is preferably 40 to 150 parts by weight per 100 parts by weight of conductive material. A range of 60 to 110 parts by weight is particularly preferred, with 70 to 100 parts by weight being most preferred. Using a small amount of dispersant can make it difficult to finely and uniformly disperse the conductive material, potentially resulting in reduced electrical properties. On the other hand, if the amount of dispersant is too large, the viscosity of the dispersion increases, making it difficult to handle, and the dispersant has high electrical resistance, so it acts as a component that increases resistance, preventing a sufficient decrease in resistance and resulting in a risk of deteriorating electrical properties.

[0018] [Dispersion Medium] The dispersion medium is usually mainly composed of a non-aqueous solvent. Many organic solvents have been proposed, including cyclic carbonates (cyclic carbonates) such as ethylene carbonate, propylene carbonate, butylene carbonate, and chlorinated or fluorinated derivatives thereof, and acyclic dialkyl carbonates (chain carbonates) such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dibutyl carbonate, butyl methyl carbonate, butyl ethyl carbonate, and butyl propyl carbonate. Other solvents include y-butyrolactone, dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-dibutoxyethane, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propiononitrile, ethyl acetate, methyl propionate, ethyl propionate, dimethyl carbonate, tetraglyme, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, propyl acetate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone, acetonitrile, dimethylformamide, etc. These non-aqueous solvents can be used alone or in combination of two or more. Among these, cyclic carbonates, such as ethylene carbonate (EC) and propylene carbonate (PC), are particularly excellent in performance, but using a mixture of the above nonaqueous solvents further improves battery performance, such as cycle characteristics, discharge capacity, and capacity retention. Combinations of cyclic carbonates and acyclic dialkyl carbonates are particularly preferred, with the combination of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC / DMC) and the combination of ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC) (EC / DEC / PC) being the most excellent.The blending ratio of these is preferably 30 to 200 parts by volume of the acyclic dialkyl carbonate esters to 100 parts by volume of the cyclic carbonate esters, more preferably 50 to 150 parts by volume, and most preferably 80 to 130 parts by volume.

[0019] [Electrolyte] The electrolyte that can be used in the present invention can be appropriately selected from those generally used for battery applications. Preferably, a lithium salt is used, specifically, LiPF ６ , LiBF ４ , LiClO ４ , LiAsF ６ , LiFSI, LiTFSI, LiTFS, LiDFOB, LiBOB, LiPO ２ F ２ , LiBETI, LiDFOP and LiTFOP are representative, and Li(C ２ F ５ SO ２ ) ２ N, LiCF ３ SO ３These may be used alone or in combination. The amount of electrolyte to be added is preferably 0.1 to 10.0 mol / L, more preferably 0.5 to 5.0 mol / L, even more preferably 0.8 to 3.0 mol / L, and most preferably 0.9 to 2.0 mol / L, as a concentration in the conductive material-containing dispersion. The electrolyte may be dissolved in the aforementioned dispersion medium to prepare an electrolytic solution, which may then be used as the dispersion medium, and the conductive material and dispersant may be added to the dispersion medium. Alternatively, the conductive material may be finely dispersed by mixing the conductive material with the dispersant and the dispersion medium, and then the electrolyte may be added. By finely dispersing the conductive material in this way before adding the electrolyte, the conductive material is well dispersed and the dangers associated with handling the electrolyte are minimized. The presence of an electrolyte in an open dispersion process is undesirable because lithium hexafluoride and other components in the electrolyte react with moisture in the air, generating fluorine and other dangerous substances. Furthermore, it has traditionally been considered best to avoid dispersants as much as possible because they act as a resistive component. However, after extensive research, the inventors discovered that adding a certain amount of dispersant to prevent the conductive materials from agglomerating and achieve a uniform state actually reduces resistance and also suppresses battery degradation. In other words, if a sufficiently uniform state is achieved by dispersing the conductive materials with beads or other media while adding a dispersant, the surface will have a uniform, smooth, and glossy appearance. In this state, the conductive materials are almost completely agglomerated, suppressing roughness and uneven reflection. Therefore, it is believed that the network between the conductive materials is uniform, increasing resistance and achieving good electrical properties.

[0020] [Blending ratio] The content ratio of each of these components is as follows. The concentration of the conductive material in the liquid can be selected appropriately as needed, but is usually 0.1 to 30% by weight, preferably 0.5 to 20% by weight, and particularly preferably 2 to 20% by weight. The ratio of the conductive material to the electrolyte is 100 to 14,000 parts, preferably 800 to 3,000 parts, by volume, of electrolyte to 100 parts of conductive material.

[0021] [Dispersion Step] In the present invention, these components are mixed to form a dispersion. The dispersion method is not particularly limited, and may be media dispersion using beads or the like, media-less dispersion using a colloid mill or high-pressure disperser (such as "BERYU MINI" manufactured by Biryu Co., Ltd. or "STARBURST" manufactured by Sugino Machine Co., Ltd.), or a simple disperser or a planetary centrifugal mixer (such as "Awatori Rentaro" manufactured by Thinky Corporation). The process is complete when no clumps of conductive additive are visible and the mixture is uniform; typically, gloss, viscosity, and fluidity can be visually observed.

[0022] When the electrolyte is dispersed in a medium such as a bead dispersion, the beads can be removed by filtering through a mesh. Note that, as the electrolyte solution, a liquid in which an electrolyte is dissolved in a dispersion medium such as a nonaqueous solvent may be blended with a conductive additive and dispersed, but dispersion may also be performed by mixing at least (i) a conductive additive, (ii) an electrolyte, and (iii) a dispersion medium.

[0023] [Physical properties of conductive material-containing dispersion] The obtained dispersion exhibits a uniform and glossy appearance. This is because there are no agglomerates of the conductive material, the conductive paths are long and uniform, and it is expected that it will mix well with the electrolyte and exhibit excellent electrical properties. The viscosity of the dispersant is not limited. As mentioned above, the dispersion obtained by the present invention has fluidity and mixes well with the electrolyte. The dispersed particle size of the conductive material in the dispersion exhibits sufficient performance when D50 is 3000 nm or less as measured by Microtrack UPA.

[0024] [Electrode Slurry] An active material can be further added to the conductive material-containing dispersion liquid described above to prepare an electrode slurry. The active material has the function of releasing ions during charging and absorbing ions during discharging. As the positive electrode active material, a lithium compound is usually preferably used. For example, as described in Patent No. 7285060, LiMn ２ O ４ , LiCoO ２ , LiNiO ２ , Li(Ni-Mn-Co)O ２Examples of lithium-transition metal composite oxides, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds include those in which part of the transition metal is replaced by another element. Lithium iron phosphate (LFP), Mg-doped LiCoO ２ , Li(Ni,Co,Al)O ２ (known as "NCA"), Li(Ni,Mn,Co)O ２ (known as "NMC"), LiMn ２ O ４ From the viewpoint of capacity and output characteristics, lithium-transition metal composite oxides, more preferably composite oxides containing lithium and nickel, and even more preferably Li(Ni—Mn—Co)O ２ and those in which a part of these transition metals has been replaced by other elements (Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu, Ag, Zn, etc.) are used. More generally, various solid compounds known to those skilled in the art for use as active materials in NiMH (nickel-metal hydride) or nickel-cadmium (NiCd) batteries, more specifically those used in carbon monofluoride batteries called CFx, or metal fluoride compounds having MF2 or MF3 (M is, for example, Fe, Bi, Ni, Co, Ti, or V), alkali metal transition metal oxides, or phosphates are mentioned, but preferred are the olivine structure compound LiMPO4 or doped compounds thereof, and olivine structure compounds (Li 1-x Z x) MPO4, and thermally stable transition metal-doped lithium transition metal phosphates. These positive electrode active materials may be used alone or in combination. Negative electrode active materials include lithium metal, carbon, lithium-intercalated carbon, lithium nitride, lithium alloys, and lithium alloy-forming compounds such as silicon, bismuth, boron, gallium, indium, zinc, tin, tin oxide, antimony, aluminum, titanium oxide, molybdenum, germanium, manganese, niobium, vanadium, tantalum, gold, platinum, iron, copper, chromium, nickel, cobalt, zirconium, yttrium, molybdenum oxide, germanium oxide, silicon oxide, silicon carbide, any other material or alloy thereof, and any other combination thereof.

[0025] [Electrode and Battery] The electrode slurry described above can be applied to a current collector by a known method to obtain an electrode. This electrode is then assembled by a known method to produce a battery. Specifically, as described in, for example, Patent No. 6,967,346, the electrode can be used as the negative or positive electrode in a semi-solid battery structure including a positive electrode current collector, a negative electrode current collector, and a separator disposed between the positive and negative electrode current collectors and acting as an ion-permeable membrane, with a semi-solid positive electrode between the positive electrode current collector and the separator, and a negative electrode between the separator and the negative electrode current collector. For example, a semi-solid battery can be assembled by applying the electrode slurry of the present invention to a positive or negative electrode current collector, placing a separator thereon, and then providing a semi-solid positive electrode. Alternatively, an electrode can be produced by blending a binder component, if necessary, during or after the preparation of the electrode slurry of the present invention, applying the slurry to a current collector, and calendering the resulting mixture under high pressure to increase density and control thickness. The laminate may then be cut to a desired size and / or shape, wound or laminated together with a separator layer, placed in a metal or polymer case, and infiltrated with a liquid electrolyte to form a semi-solid battery.

[0026] The present invention will be described in more detail below with reference to examples. Example 1 (Preparation of Conductive Material-Containing Dispersion) 94.3 parts by mass (37.72 g) of a dispersion medium (EC / DMC = volume ratio 1:1), 2.7 parts by mass (1.08 g) of PVP K-30, and 3.0 parts by mass (1.20 g) of Ketjen Black EC600JD (manufactured by Lion Specialty Chemicals Co., Ltd.) were dispersed together with 72 g of zirconia beads (2 mm) in an "Awatori Rentaro" (a rotation / revolution type mixer manufactured by Thinky Corporation) at 2000 rpm for 5 minutes, and then the mixture was filtered to remove the zirconia beads, thereby obtaining a conductive material-containing dispersion 1.

[0027] (Evaluation of Conductive Material-Containing Dispersion) 1. Liquid Properties (1) Shear Viscosity Using a "Rheometer CP-35-1" (manufactured by Eiko Seiki Co., Ltd.), the shear viscosity of the Conductive Material-Containing Dispersion 1 was measured. The results are shown in Table 1.

[0028]

[0029] (2) Dispersed particle size Conductive material-containing dispersion 1 was diluted 1000 times with EC / DMC (1:1), and the particle sizes (D10, D50, D90) of the conductive material in the dispersion were measured using a particle size distribution analyzer (UPA, manufactured by Microtrac) using the dynamic light scattering method. The results are shown in Table 2.

[0030]

[0031] 2. Measurement of surface resistance Conductive material-containing dispersion 1 and PVDF were mixed so that the carbon content was 8.3 wt% (1.0 g of dispersion, 3.81 g of PVDF (KF-#7208 manufactured by Kureha Corporation, solids content 8 wt%)) and stirred at 2000 rpm for 2 minutes in a "Thinner Mixer." The resulting solution was applied to a glass substrate. Two substrates, 8 mil and 10 mil, were prepared using an applicator. The glass substrates coated with this solution were dried at 100°C for 30 minutes and then measured at an applied voltage of 10 V using a resistance measuring device (Loresta manufactured by Mitsubishi Chemical Analytech Co., Ltd.). The results are shown in Table 3.

[0032]

[0033] (Evaluation of Electrode Slurry) 1. Measurement of Volume Resistivity of Semi-Solid Battery Electrode Slurry (1) 100 parts by weight of conductive material-containing dispersion 1 was mixed with 68.4 parts by weight of active material (solid content of the mixture: 44 wt%) and mixed at 2000 rpm for 2 minutes in a "Thinner Mixer" to obtain electrode slurry for semi-solid batteries. 4 g of this electrode slurry for semi-solid batteries was poured into a two-electrode cell. (2) Resistance (Ω) was measured using a digital multimeter (CD732, Sanwa Electric Instruments Co., Ltd.). The results are shown in Table 4 and Figure 1.

[0034]

[0035] 2. Measurement of Electrode Plate Resistance (1) Preparation of Electrode Slurry (1) 16.50 g of positive electrode active material (LNCM, Nichia Chemical) and 2.08 g of binder (PVdF, Solvay Japan "Solef 5130", solids content 8 wt%) were mixed in a "Thinner Mixer" at 2000 rpm for 2 minutes. (2) 0.5 g of NMP was added and mixed in a "Thinner Mixer" at 2000 rpm for 1 minute. This process was repeated five times (a total of 2.5 g of NMP). (3) The entire amount of the conductive material-containing dispersion 1 was added to the mixture and further mixed in a "Thinner Mixer" at 2000 rpm for 2 minutes to obtain electrode slurry 1 (positive electrode active material: binder: conductive material = 95.00:3.00:2.00 (weight ratio)).

[0036] (2) Preparation of Electrode Plates: The electrode slurry was applied to aluminum foil with a doctor blade to a film thickness of 20 mil (508 μm), dried in a 100°C oven for 30 minutes, pressed at 130 kgf using an "HSRP-60150LC" (a tabletop roll press with a load monitor manufactured by Hosen Co., Ltd.), and then punched into coin shapes approximately 14 mm in diameter using an "HSNG-EP-14-C4" (an electrode punching hand punch manufactured by Nogami Giken Co., Ltd.). (3) Measurement of Composite Layer Resistance and Interface Resistance: The electrode plate resistance (composite layer resistance and interface resistance) of the above electrode plates was measured using an "RM2610" (an electrode resistance measurement system manufactured by Hioki E.E. Corporation). The results are shown in Table 5.

[0037]

[0038] Comparative Example 1 (Production of Conductive Material-Containing Dispersion Liquid) 94.3 parts by mass (37.72 g) of a dispersion medium (EC / DMC=1:1) and 3.0 parts by mass (1.20 g) of (600JD) were dispersed together with 72 g of zirconia beads (2 mm) in an "Awatori Rentaro" (a rotation / revolution type mixer manufactured by Thinky Corporation) at 2000 rpm for 5 minutes to obtain a conductive material-containing dispersion liquid 2.

[0039] (Production and Evaluation of Electrode Slurry) An electrode slurry for a semi-solid battery was produced and evaluated in the same manner as in "1. Measurement of volume resistivity of electrode slurry for a semi-solid battery" in (Evaluation of electrode slurry) of Examples, except that conductive material-containing dispersion 2 was used instead of conductive material-containing dispersion 1, and electrode slurry 2 was produced and evaluated in the same manner as in "2. Measurement of electrode plate resistance." The results are shown in Tables 4 and 5, respectively.

[0040] Example 2 (Production of Conductive Material-Containing Dispersion) 94.3 parts by mass (37.72 g) of NMP as a dispersion medium, 2.7 parts by mass (1.08 g) of PVP K-30, and 3.0 parts by mass (1.20 g) of (600JD) were dispersed together with 72 g of zirconia beads (2 mm) in a "Thinner Mixer" (a rotation / revolution type mixer manufactured by Thinky Corporation) at 2000 rpm for 5 minutes to obtain a conductive material-containing dispersion 3.

[0041] (Production and Evaluation of Electrode Slurry) An electrode slurry was produced in the same manner as in "2. Measurement of Electrode Plate Resistance" in (Evaluation of Electrode Slurry) of the Examples, except that the conductive material-containing dispersion 3 was used instead of the conductive material-containing dispersion 1. The evaluation results are shown in Table 5. Example 3 (Production of Conductive Material-Containing Dispersion) 94.3 parts by mass (37.72 g) of an electrolyte solution "LBG-00022" (product code, manufactured by Kishida Chemical Co., Ltd.) in which 1 mol / L of LiPF6 was dissolved in a dispersion medium (EC / DMC = volume ratio 1:1), 2.7 parts by mass (1.08 g) of PVP K-30, and 3.0 parts by mass (1.20 g) of Ketjen Black EC600JD (manufactured by Lion Specialty Chemicals Co., Ltd.) were dispersed together with 72 g of zirconia beads (2 mm) in an "Awatori Rentaro" (a rotation / revolution type mixer manufactured by Thinky Corporation) at 2000 rpm for 5 minutes, and the mixture was then filtered to remove the zirconia beads, thereby obtaining a conductive material-containing dispersion 4.

[0042] Comparative Example 2 (Production of Conductive Material-Containing Dispersion Liquid) 94.3 parts by mass (37.72 g) of NMP as a dispersion medium and 3.0 parts by mass (1.20 g) of (600JD) were dispersed together with 72 g of zirconia beads (2 mm) in an "Awatori Rentaro" (a rotation / revolution type mixer manufactured by Thinky Corporation) at 2000 rpm for 5 minutes to obtain a conductive material-containing dispersion liquid 5. Comparative Example 3 (Production of Conductive Material-Containing Dispersion) 94.3 parts by mass (37.72 g) of electrolyte "LBG-00022" (product code, manufactured by Kishida Chemical Co., Ltd.) in which 1 mol / L of LiPF6 was dissolved in a dispersion medium (EC / DMC = volume ratio 1:1) and 3.0 parts by mass (1.20 g) of (600JD) were dispersed together with 72 g of zirconia beads (2 mm) in an "Awatori Rentaro" (a rotation / revolution type mixer manufactured by Thinky Corporation) at 2000 rpm for 5 minutes to obtain Conductive Material-Containing Dispersion 6. (Measurement of Surface Roughness) The arithmetic mean roughness of each of Conductive Material-Containing Dispersion 4 and Conductive Material-Containing Dispersion 6 was measured by the following method. A commercially available polyvinylidene fluoride binder (KF-#7208, 8 wt% solids, manufactured by Kureha Corporation) was diluted to 8.0% with N-methyl-2-pyrrolidone as a solvent. A conductive material-containing dispersion was weighed and mixed into the diluted solution to a concentration of 8.3 wt% of the conductive material. The mixture was stirred at 2000 rpm for 2 minutes in a planetary centrifugal mixer (Thinky Corporation, Awatori Rentaro) to prepare a paste. This paste was applied to a glass plate using a 10 mil applicator to a dry film thickness of 7.5 to 8.5 μm. The coating was then dried in a hot air dryer at 100°C for 30 minutes to remove the solvent, yielding a coating film. The resulting coating film was designated the "dispersibility evaluation coating film." The arithmetic mean roughness (Ra) of this coating film for dispersibility evaluation was measured and calculated using a contact-type surface roughness meter (Tokyo Seimitsu Co., Ltd., Surfcomtouch 50 with printer). The results are shown in Table 6.

[0043] Example 4 (Preparation of Conductive Material-Containing Dispersion) 81.0 parts by mass (32.40 g) of NMP as a dispersion medium, 9.0 parts by mass (3.60 g) of PVP K-30, and 10.00 parts by mass (4.00 g) of "C-NERGY SUPER C45" (conductive carbon black manufactured by Imerys) were dispersed together with 72 g of zirconia beads (2 mm) in a "Thinky Mixer" (a centrifugal mixer manufactured by Thinky Corporation) at 2000 rpm for 5 minutes to obtain Conductive Material-Containing Dispersion 7. (Evaluation of Conductive Material-Containing Dispersion) Particle size and surface resistance were measured in the same manner as in "(2) Dispersed Particle Size" and "2. Measurement of Surface Resistivity" in "1. Liquid Properties" of Example 1. The results are shown in Tables 2 and 3.

[0044] Comparative Example 4 (Preparation of Conductive Material-Containing Dispersion) 90.0 parts by mass (36.00 g) of NMP as a dispersion medium and 10.00 parts by mass (4.00 g) of "C-NERGY SUPER C45" (conductive carbon black manufactured by Imerys) were dispersed together with 72 g of zirconia beads (2 mm) in an "Awatori Rentaro" (a centrifugal mixer manufactured by Thinky Corporation) at 2000 rpm for 5 minutes to obtain Conductive Material-Containing Dispersion 8. (Evaluation of Conductive Material-Containing Dispersion) Particle size and surface resistance were measured in the same manner as in "(2) Dispersed Particle Size" and "2. Measurement of Surface Resistance" in "1. Liquid Properties" of Example 1. The results are shown in Tables 2 and 3.

[0045] Examples 5 to 13 Conductive material-containing dispersions 9 to 17 were obtained in the same manner as in Example 1 (production of conductive material-containing dispersion), except that the conductive materials shown in Table 3 were used instead of 3.0 parts by mass (1.20 g) of Ketjen Black EC600JD in Example 1 (production of conductive material-containing dispersion). For these conductive material-containing dispersions, the surface resistance was measured in the same manner as in "2. Measurement of surface resistance" of Example 1. For Examples 8 to 11, the dispersed particle size and shear viscosity were also measured in the same manner as in "1. Liquid properties" of Example 1. The results are shown in Table 1.

[0046] Example 14 (Production of conductive material-containing dispersion) 94.3 parts by mass (37.72 g) of a dispersion medium (EC / DMC=1:1), 2.4 parts by mass (0.96 g) of "S-LEC BL-10" (a butyral resin manufactured by Sekisui Chemical Co., Ltd.), and 3.0 parts by mass (1.20 g) of 600JD were dispersed together with 144 g of zirconia beads (2 mm) in a paint shaker for 2 hours to obtain a conductive material-containing dispersion 18.

[0047] Examples 15 to 28 Conductive material dispersions 19 to 32 were obtained in the same manner as in Example 14, except that the type and concentration of the conductive material, the dispersion medium, the dispersant and its blending ratio relative to the conductive material, and the presence or absence of AMP blending were changed as shown in Table 7. In the table, "concentration (%)" indicates the concentration (wt%) of the conductive material in the entire dispersion, EC indicates ethylene carbonate, DEC indicates diethyl carbonate, DMC indicates dimethyl carbonate, and PC indicates propylene carbonate, and the ratios thereof indicate volume ratios, and "vs CB100 (parts)" indicates the amount of dispersant added in parts by weight relative to 100 parts by weight of the conductive material. In the table, "AB" represents acetylene black (manufactured by Denka Co., Ltd.), "600JD" represents Ketjenblack manufactured by Lion Specialty Chemicals Co., Ltd., "C45" represents conductive carbon black "C-NERGY SUPER C45" manufactured by Imerys, "VGCF" represents carbon nanofiber manufactured by Resonac Co., Ltd., "K-nanos 300T" represents bundle-structured carbon nanotubes manufactured by Kumho, "S-LEC BL-10" represents butyral resin manufactured by Sekisui Chemical Co., Ltd., "BYK LP-N24712" represents a dispersant manufactured by BYK Chemie, and "PVP K-30" represents polyvinylpyrrolidone with a K value of 30. These dispersions were visually observed immediately after dispersion and one week later, and the viscosity was measured immediately after dispersion. Viscosity measurements were performed using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) at the rotation speeds indicated in the table.

[0048]

[0049] (Evaluation of Battery Performance) (1) Battery Assembly Using the electrode plate obtained in Example 1, "(Evaluation of Electrode Slurry) 2. Measurement of Plate Resistance (1) Preparation of Electrode Plate," a CR2032 coin battery was assembled by stacking a lid (SUS316L, circular, manufactured by Honjo Metals Co., Ltd.), the electrode plate, a separator (17 mm diameter circular ("Selion P2010," material: polypropylene, manufactured by CS TECH Co., Ltd.)), an electrolyte (1.0 M LiPF6 EC:DEC (1:1 v / v%), manufactured by Kishida Chemical Co., Ltd.), and a case (SUS316L, circular, manufactured by Honjo Metals Co., Ltd.)) in this order under argon substitution, and crimping them together. A coin battery was similarly assembled using the electrode plate obtained in "(Evaluation of Electrode Slurry) 2. Measurement of Plate Resistance (1) Preparation of Electrode Plate" using the conductive material-containing dispersion 2 of Comparative Example 1. (2) Measurement of discharge capacity and calculation of capacity retention rate The two coin batteries described above were simultaneously placed in a charge-discharge tester (580-type high-performance charge-discharge system, Scribner Associates) and charged at 25°C with a constant current of 1.0 C and low voltage until the voltage reached 4.3 V, and then discharged at a constant current of 1.0 C until the voltage reached 3.0 V. This cycle was repeated for a total of 50 cycles. The discharge capacities after 30 and 50 cycles were measured and compared with the initial discharge capacity at 1.0 C to calculate the capacity retention rate. The results are shown in Table 7.

[0050] (Examples 29 and 30) A conductive material-containing dispersion was prepared using the same materials, composition, and method as in Example 1. This was designated as conductive material-containing dispersion 33. A conductive material-containing dispersion was prepared using the same materials, composition, and method as in Example 2. This was designated as conductive material-containing dispersion 34. Using these, electrode plates were prepared in the same manner as in "(Evaluation of electrode slurry) 2. Measurement of electrode plate resistance (1) Preparation of electrode plate" in Example 1, and coin batteries were prepared using the obtained electrode plates in the same manner as in (Evaluation of battery performance) above. These two coin batteries were simultaneously placed in a charge / discharge tester, and measurements and calculations were similarly performed. The results are shown in Table 8.

[0051]

[0052] (Preparation and Observation of Electrode Plates) Electrode plates were prepared using the conductive material-containing dispersions prepared in Example 1 and Comparative Example 1 by the following method. (1) 16.50 g of positive electrode active material (LNCM, manufactured by Nichia Corporation) and 2.08 g of binder (PVdF, Solef 5130, manufactured by Solvay Japan, solids content 8 wt%) were mixed in a THINNER BLENDER at 2000 rpm for 2 minutes. (2) 0.5 g of NMP was added and mixed in a THINNER BLENDER at 2000 rpm for 1 minute. This process was repeated five times (a total of 2.5 g of NMP). (3) The entire amount of the conductive material-containing dispersion described above was added to each of the plates, and the mixture was further mixed in a THINNER BLENDER at 2000 rpm for 2 minutes to obtain electrode slurries (positive electrode active material: binder: conductive material = 95.00:3.00:2.00 (weight ratio)). (4) The electrode slurry was applied to aluminum foil with a doctor blade to a film thickness of 20 mil (508 μm), and then dried in an oven at 100°C for 30 minutes to obtain an electrode plate. (5) The electrode plate was visually observed and photographed. The results are shown in Figure 2. The upper photograph was obtained using the conductive material-containing dispersion liquid prepared in Comparative Example 1, and the lower photograph was obtained using the conductive material-containing dispersion liquid prepared in Example 1.

[0053] Table 4 and Figure 1 show the volume resistivity measurement results for slurries containing a conductive material and an active material but not a binder resin. Such slurries can be used as electrode slurries for semi-solid batteries, including clay-type batteries, by coating them on a positive electrode current collector or a negative electrode current collector. It can be seen that all electrode slurries of the present invention are suitable for semi-solid battery applications. As can be seen from Table 1, Example 3, which uses an electrolyte solution dissolved in a solvent as a dispersion medium, has a higher viscosity than Example 1, which does not contain an electrolyte. However, it has sufficient fluidity and is easy to handle. It can be mixed with other components to obtain a highly uniform electrode slurry. As shown in Table 6, when the electrode slurry of Example 3 was formed into a coating, a smooth and even coating film was obtained. As shown in Table 4, when the electrode slurry of Example 3 was used, the resistance value was lower than Example 1, which does not contain an electrolyte, and was even lower than Comparative Example 3, which does contain an electrolyte, demonstrating extremely excellent properties. Thus, it can be seen that the electrode slurry of the present invention is particularly suitable for semi-solid battery applications. Table 7 also shows the results of evaluating battery performance when an electrode slurry containing a binder in addition to a conductive material and an active material was used. These measurement results demonstrate that all batteries obtained with electrode slurries using the conductive material dispersion of the present invention exhibited excellent performance, with a capacity retention rate of 75% or more, even 80% or more, at 1.0C for 50 cycles. Furthermore, when the dispersions were applied to glass plates in the above-described (surface roughness measurement) study, the dispersion of Example 3 had sufficient fluidity to easily apply the resulting film, which was visually smooth. In contrast, the dispersion of Comparative Example 3 had clumps and tended to remain attached to the doctor blade, making it difficult to apply uniformly. Furthermore, as shown in Table 6, the surface roughness of the resulting coating film was significantly improved by using the dispersion of the present invention, resulting in a coating film with a smooth surface, particularly a surface roughness of Ra = 0.4 μm or less. This condition is believed to be related to improved electrical properties. Furthermore, as can be seen from Figure 2, the electrode plate formed with the electrode slurry using the conductive material-containing dispersion of Example 1 had a uniform surface, whereas the electrode plate formed with the electrode slurry using the conductive material-containing dispersion of Comparative Example 1 had striated and poorly formed coatings.Furthermore, the following can be seen from the above-mentioned measurement results of the electrical properties, battery performance, and physical properties of the dispersion: According to the present invention, the dispersion containing the conductive additive, dispersant, and electrolyte has excellent electrical properties, and also exhibits a uniform and glossy appearance, and when other materials such as electrolytes are blended, it is expected that they will be easily mixed uniformly and exhibit excellent electrical properties, and is useful for various batteries such as lithium-ion batteries, and in particular for semi-solid batteries such as clay-type batteries.

Claims

1. A conductive material-containing dispersion liquid containing at least (i) a conductive material, (ii) a dispersant, (iii) an electrolyte, and (iv) a dispersion medium.

2. A method for producing a dispersion liquid containing a conductive material, which comprises mixing a conductive material and a dispersant with a dispersion medium in advance to disperse the conductive material, and then adding an electrolyte.

3. A conductive material-containing dispersion containing at least (i) a conductive material, (ii) a dispersant, and (iii) an electrolyte.

4. A method for producing an electrode, comprising the step of applying an electrode slurry, which is obtained by mixing at least the conductive material-containing dispersion liquid according to claim 1 or 3 with an active material, onto a current collector.

5. A method for producing an electrode slurry, comprising mixing a conductive material and a dispersant with a dispersion medium to disperse the conductive material, then blending an electrolyte therein, and further mixing the mixture with an active material.

6. A method for manufacturing an electrode, comprising the step of applying the electrode slurry obtained by the method of claim 5 to a current collector.

7. A method for producing a semi-solid battery, comprising the step of applying the electrode slurry according to claim 5 to a negative electrode current collector and bringing it into contact with a semi-solid positive electrode via a separator.

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