Conductive additive paste for manufacturing solid electrolyte positive electrode, positive electrode paste, and method for manufacturing positive electrode paste

Abstract

Provided are: a conductive additive paste for manufacturing a solid electrolyte positive electrode, the conductive paste being used in manufacturing a positive electrode for an all-solid-state lithium-ion secondary battery by a wet process, and facilitating control of dehydration of the positive electrode paste, uniform distribution of a solid electrolyte and the conductive additive in a positive electrode material, and management of the solid content concentration of the positive electrode paste; a positive electrode paste; and a method for manufacturing a positive electrode paste.　The conductive additive paste for producing solid electrolyte positive electrodes is used to produce a positive electrode paste obtained by adding a solid electrolyte to the conductive additive paste. The conductive additive paste contains an organic solvent, a conductive additive used for positive electrode production, and a dispersing additive. The conductive additive is dispersed and the blended amount of the dispersing additive is set according to the amount of the solid electrolyte planned to be added to the conductive additive paste when producing the positive electrode paste. The dispersing additive is blended so as to be 0.5 to 5.0 parts by mass when the total mass of the amount of the conductive additive and the solid electrolyte planned to be added is 100 parts by mass.

Description

Conductive additive paste for manufacturing a solid electrolyte positive electrode, paste for a positive electrode, and method for manufacturing the paste for a positive electrode

[0001] The present invention relates to a conductive additive paste for producing a solid electrolyte positive electrode, a positive electrode paste, and a method for producing the positive electrode paste. More specifically, the present invention relates to a conductive additive paste for producing a solid electrolyte positive electrode, which is used in producing a positive electrode of an all-solid-state lithium-ion secondary battery by a wet process, and which takes into consideration technologies that facilitate the control of low moisture content in the positive electrode paste, uniform distribution of the solid electrolyte and conductive additive in the positive electrode material, and control of the solid content concentration in the positive electrode paste, as well as a positive electrode paste containing the conductive additive paste for producing a solid electrolyte positive electrode, and a method for producing the positive electrode paste.

[0002] BACKGROUND ART In recent years, high-capacity, high-power lithium-ion secondary batteries have been widely used in many fields, such as electronic devices such as portable personal computers, smartphones, and mobile phones, and in automobiles such as electric vehicles and hybrid vehicles.

[0003] In lithium ion secondary batteries, electrolytes that use flammable organic solvents as diluting solvents as a medium for transferring ions have conventionally been used. However, batteries that use such electrolytes may encounter problems such as leakage of the electrolyte, fire, and explosion.

[0004] To solve these problems, development is underway on all-solid-state lithium-ion secondary batteries, which use a solid electrolyte instead of a liquid electrolyte and in which all other elements are solid. All-solid-state lithium-ion secondary batteries have extremely low charge transfer resistance between the solid electrolyte and lithium ions, making it possible to reduce the internal resistance of the battery. In addition, because the electrolyte is solid, there is little risk of fire, no leakage, and problems such as deterioration of battery performance due to corrosion are unlikely to occur.

[0005] Known examples of solid electrolyte materials used in such solid electrolyte layers include sulfide-based solid electrolyte materials (see, for example, Patent Document 1). Sulfide-based solid electrolytes require extremely strict low moisture content control as the moisture content of the solids during use due to concerns that sulfides may react with water to generate toxic hydrogen sulfide.

[0006] Furthermore, when manufacturing a positive electrode using a wet process in the manufacturing process of an all-solid-state battery, a process is required in which a positive electrode paste containing the positive electrode material is applied to a metal foil. In addition to the positive electrode material, the positive electrode paste must contain at least three solid components: a solid electrolyte to replace the electrolyte, a carbon material as a conductive additive, and a binder resin to adhere the metal foil. Furthermore, it is desirable for the paste to be in a state in which each material is properly dispersed without bias.

[0007] As described above, sulfide-based solid electrolytes have high reactivity, and therefore, low-polarity or non-polar organic solvents have conventionally been used as dispersion media for positive electrode pastes, and the organic solvents are required to have a low water content (see, for example, Patent Documents 1 to 4).

[0008] Therefore, considering the low moisture content of solid electrolytes, moisture management is required for all solid components, including the cathode material, binder resin, conductive additive, and dispersion medium, when manufacturing a cathode paste. Furthermore, it is considered preferable to use finely divided carbon materials and other conductive additives to achieve higher performance. However, such finely divided conductive additives are difficult to uniformly disperse. Furthermore, organic solvents used as dispersion media for solid electrolytes are generally highly hydrophobic, and conductive additives such as highly hydrophobic carbon materials tend to aggregate in hydrophobic solvents, making them difficult to disperse. Therefore, additives (dispersion additives) are essential for dispersing the conductive additives. Furthermore, solid electrolytes are often micronized to ensure a fine and uniform distribution in the cathode. However, micronized solid electrolytes are difficult to disperse, similar to the conductive additives such as carbon materials. Therefore, when manufacturing a cathode paste, dispersing and mixing the conductive additives (e.g., carbon materials) and solid components (e.g., cathode materials) into a dispersion medium simultaneously can result in uneven distribution of the conductive additives (e.g., carbon) and the solid electrolyte.

[0009] Furthermore, the final positive electrode paste is adjusted so that the solid content concentration is, for example, 50% to 80%. However, unlike lithium ion secondary batteries that use an electrolytic solution, lithium ion secondary batteries that use a solid electrolyte also contain the solid electrolyte in their solid content, so it was difficult to determine an arbitrary concentration of the solid content of the positive electrode paste by mixing the solid electrolyte paste, conductive additive paste, and binder solution.

[0010] JP 2012-212652 A JP 2013-62228 A JP 2013-118143 A JP 2020-145034 A

[0011] Therefore, an object of the present invention is to provide a conductive additive paste for producing a solid electrolyte positive electrode that solves the above-mentioned problems. Another object of the present invention is to provide a conductive additive paste for producing a solid electrolyte positive electrode, a positive electrode paste, and a method for producing a positive electrode paste, which are used in producing a positive electrode of an all-solid-state lithium-ion secondary battery by a wet process, and which facilitate the control of low moisture content in the positive electrode paste, uniform distribution of the solid electrolyte and conductive additive in the positive electrode material, and control of the solid content concentration of the positive electrode paste.

[0012] In order to solve the above problems, the present inventors have conducted extensive research and studies. As a result, they have discovered that, as the composition of the conductive additive paste that serves as the base for preparing a positive electrode paste containing a solid electrolyte, by blending a dispersing additive in a predetermined ratio according to the amount of solid electrolyte to be added later to the conductive additive paste, rather than using an appropriate amount of dispersing agent relative to the conductive additive, it is possible to suppress deterioration of the solid electrolyte, disperse the conductive additive uniformly at a high concentration, and exhibit excellent conductivity, which led to the present invention.

[0013] The conductive additive paste for producing a solid electrolyte positive electrode of the present invention, which solves the above-mentioned problems, is a conductive additive paste used for producing a positive electrode paste by adding a solid electrolyte to a conductive additive paste, the conductive additive paste including an organic solvent, a conductive additive used in producing a positive electrode, and a dispersing additive, the conductive additive being dispersed, the amount of the dispersing additive being set according to the planned amount of solid electrolyte to be added to the conductive additive paste when producing the positive electrode paste, and the dispersing additive being mixed in an amount of 0.5 parts by mass or more and 5.0 parts by mass or less when the total mass of the conductive additive and the planned amount of solid electrolyte to be added is 100 parts by mass.

[0014] In the conductive additive paste for producing a solid electrolyte positive electrode, the conductive additive and the dispersing additive may be blended so that the blending amount of the dispersing additive relative to 100 parts by mass of the conductive additive is 2 parts by mass or more and 50 parts by mass or less, and the mass of the conductive additive is 5 parts by mass or more and 25 parts by mass or less when the planned addition amount of the solid electrolyte is 100 parts by mass.

[0015] In the conductive additive paste for producing a solid electrolyte positive electrode described above, the concentration of the conductive additive paste is set according to the solid content concentration of a positive electrode paste produced by adding a solid electrolyte, a binder, and a positive electrode material to the conductive additive paste. When the solid content concentration of the positive electrode paste is X, the organic solvent concentration in the conductive additive paste is 1-X. When the solid content concentration of the binder in the positive electrode paste is Y and the total solid content concentration of the conductive additive, the dispersion additive, and the solid electrolyte in the positive electrode paste is A, the solid content concentration A may be in the range of (0.05X-Y) to (0.25X-Y), and the conductive additive paste concentration may be set to 0.051 A / (1-X) to 0.375 A / (1-X).

[0016] In the conductive additive paste for producing a solid electrolyte positive electrode, the amount of water in the conductive additive paste may be 0.005 parts by mass or less per 100 parts by mass of the conductive additive paste. The viscosity of the conductive additive paste for producing a solid electrolyte positive electrode may be 10 mPa·s or more and 2000 mPa·s or less. In the conductive additive paste for producing a solid electrolyte positive electrode, the relative dielectric constant of the organic solvent may be less than 10.

[0017] The positive electrode paste of the present invention, which solves the above-mentioned problems, has a sulfide-based solid electrolyte dispersed in the above-mentioned conductive additive paste.

[0018] The positive electrode paste may have a binder dissolved therein, and may also have a positive electrode material mixed therein.

[0019] The present invention provides a method for producing a positive electrode paste that solves the above-described problems. The method includes the steps of: blending the conductive additive and the dispersing additive into the organic solvent to produce a conductive additive paste; adding the solid electrolyte to the conductive additive paste to produce an electrolyte paste; and adding the positive electrode material to the electrolyte paste. In the step of producing the conductive additive paste, the conductive additive is blended in such an amount that the dispersing additive is 0.5 parts by mass or more and 5.0 parts by mass or less when the total mass of the parts by mass of the conductive additive and the parts by mass of the solid electrolyte is 100 parts by mass.

[0020] In the method for producing a positive electrode paste, in the step of producing the conductive additive paste, the conductive additive and the dispersing additive may be blended so that the amount of the dispersing additive relative to 100 parts by mass of the conductive additive is 2 parts by mass or more and 50 parts by mass or less, and the amount of the conductive additive added relative to 100 parts by mass of the solid electrolyte in the step of producing the electrolyte paste is 5 parts by mass or more and 25 parts by mass or less.

[0021] According to the present invention, it is possible to easily control the reduction in moisture content when producing a positive electrode paste, to uniformly distribute the solid electrolyte and conductive additive in the positive electrode material, and to control the solid content concentration of the positive electrode paste. Furthermore, the composition control, handling, and material quality control (moisture value control) when producing a positive electrode paste are improved, which simplifies the kneading process. Furthermore, it is possible to provide an all-solid-state lithium ion secondary battery that is finally obtained and has excellent performance such as charge / discharge characteristics, cycle characteristics, and electrode conductivity, as well as stable characteristics.

[0022] 1 is a flow chart showing the procedure in an example for producing a positive electrode paste using the conductive additive paste according to the present invention; 2 is a flow chart showing the procedure in another example for producing a positive electrode paste using the conductive additive paste according to the present invention; 3 is a flow chart showing the procedure for producing a positive electrode paste in a comparative example.

[0023] The present invention will be described in detail below based on embodiments.

[0024] (Conductive additive paste for producing solid electrolyte positive electrode) A first conductive additive paste for producing a solid electrolyte positive electrode according to the present invention is a conductive additive paste in which a conductive additive used in producing a solid electrolyte positive electrode is dispersed in an organic solvent, and is characterized in that the conductive additive paste is blended in advance with 0.2 parts by mass or more and 5.0 parts by mass or less, preferably 0.5 parts by mass or more and 3.0 parts by mass or less, of a dispersing additive, where the total of the parts by mass of the conductive additive and the parts by mass of the solid electrolyte (conductive additive + parts by mass of solid electrolyte) is taken as 100 parts by mass, so as to form a paste in which both the conductive additive and a solid electrolyte, which is added to the conductive additive paste later, are uniformly dispersed as solid contents in the organic solvent.

[0025] A first conductive additive paste according to the present invention is a conductive additive paste used in the manufacture of a positive electrode paste by adding a solid electrolyte to the conductive additive paste, and the conductive additive paste contains an organic solvent, a conductive additive used in the manufacture of a positive electrode, and a dispersing additive, the conductive additive is dispersed, the amount of the dispersing additive is set according to the planned amount of solid electrolyte to be added to the conductive additive paste when the positive electrode paste is manufactured, and the dispersing additive is mixed in an amount of 0.2 parts by mass or more and 5.0 parts by mass or less, preferably 0.5 parts by mass or more and 3.0 parts by mass or less, when the total mass of the conductive additive and the planned amounts of solid electrolyte to be added is 100 parts by mass.

[0026] In a preferred embodiment of the first conductive additive paste according to the present invention, the conductive additive and the dispersing additive are blended so that the blending amount of the dispersing additive per 100 parts by mass of the conductive additive is 2 parts by mass or more and 50 parts by mass or less, and the mass of the conductive additive when the planned amount of solid electrolyte to be added is 100 parts by mass is 5 parts by mass or more and 25 parts by mass or less.

[0027] The positive electrode paste referred to in this specification means a paste obtained by adding at least a solid electrolyte to the conductive additive paste of the present invention. As an example, the positive electrode paste further contains either a binder or a positive electrode material, or both.

[0028] The reason for using such a composition for the conductive additive paste for producing a solid electrolyte positive electrode according to the present invention is as follows.

[0029] When manufacturing solid-state batteries using a wet process to produce positive electrodes, a process is required in which a positive electrode paste containing the positive electrode material is applied to a metal foil. In addition to the positive electrode material, the positive electrode paste must contain at least three solid components: a solid electrolyte to replace the electrolyte, a conductive additive, and a binder resin to adhere the metal foil. A paste in which each material is properly dispersed without bias is desirable. To create such a paste, the selection of a dispersion medium, additives to promote and stabilize dispersion (dispersion additives), and dispersion technology are key.

[0030] Because sulfide-based solid electrolytes are highly reactive, the dispersion medium for the positive electrode paste must be a low-polarity organic solvent, and the water content in the organic solvent must be sufficiently low, specifically, for example, less than 0.005 parts by mass per 100 parts by mass of the organic solvent. Therefore, considering the low water content of the solid electrolyte, when producing a positive electrode paste, it is necessary to control the water content of all of the solid components, including the positive electrode material, binder resin, conductive additive, and dispersion medium. While it is possible to mix all materials simultaneously while maintaining low water content, the conductive additive must be finely divided to achieve higher performance, making uniform dispersion difficult. Furthermore, organic solvents used as dispersion media for solid electrolytes are generally highly hydrophobic. Therefore, conductive additives, such as highly hydrophobic carbon materials, tend to aggregate in the solvent and are difficult to disperse. Therefore, a dispersion additive is essential for dispersion.

[0031] Furthermore, the solid electrolyte that replaces the electrolytic solution is often microparticulated because it is desirable to distribute it finely and uniformly on the positive electrode. However, microparticulated solid electrolytes are difficult to disperse, just like the conductive additives mentioned above. Therefore, if the solid electrolyte and the conductive additive are mixed substantially simultaneously to obtain a paste, there is a concern that the distribution of the conductive additive and the solid electrolyte may be uneven.

[0032] There is no problem with the binder resin, as long as it is soluble in the dispersion medium, as it will be uniformly distributed throughout the positive electrode paste. However, the solid electrolyte and conductive additive must be appropriately distributed in the positive electrode material. Therefore, the solid electrolyte and conductive additive are prepared in advance as a dispersion solution, and this is used as the dispersion medium for the positive electrode, thereby making it possible to produce a positive electrode paste in which the conductive additive and solid electrolyte are uniformly distributed in the positive electrode material.

[0033] According to the findings of the present inventors, although the concentration of the dispersing additive required to disperse the conductive additive and the concentration of the dispersing additive required to disperse the solid electrolyte are different, it has been confirmed that both can be dispersed by using the same dispersing additive and subjecting them to a dispersing device.

[0034] For the reasons described above, the present inventors have found the above-described preferred composition for a conductive additive paste in which a conductive additive is dispersed in a dispersion medium, on the premise that the conductive additive, solid electrolyte, and positive electrode material contained as solid components in the positive electrode paste are dispersed in the dispersion medium in this order.

[0035] That is, the conductive additive paste according to the present invention is based on the premise that a solid electrolyte will be added to the conductive additive paste later, and by blending 0.5 to 5.0 parts by mass of a dispersing additive in advance when the amount of solid electrolyte to be added later is 100 parts by mass, not only is the conductive additive uniformly dispersed in the conductive additive paste, but when the solid electrolyte is added later to this conductive additive paste, it is also possible to easily prepare a conductive additive paste containing a solid electrolyte in which both the conductive additive and the solid electrolyte are uniformly dispersed.

[0036] From another viewpoint, the conductive additive paste for producing a second solid electrolyte positive electrode according to the present invention is a conductive additive paste in which a conductive additive used in producing a solid electrolyte positive electrode is dispersed in an organic solvent, and the conductive additive paste contains a dispersing additive that is preset so that both the conductive additive and a solid electrolyte that is added later to the conductive additive paste can be dispersed. The amount of the dispersing additive relative to the conductive additive is 2 to 50 parts by mass, more preferably 6 to 30 parts by mass, when the parts by mass of the conductive additive are taken as 100, and the amount of the dispersing additive relative to the solid electrolyte is 0.5 to 5 parts by mass, more preferably 0.8 to 2 parts by mass, when the parts by mass of the solid electrolyte are taken as 100. The ratio of the conductive additive to the solid electrolyte is 5 to 25 parts by mass, more preferably 5 to 20 parts by mass, when the parts by mass of the solid electrolyte are taken as 100. The amount of the dispersing additive is adjusted so that the conductive additive is 5 to 25 parts by mass, more preferably 5 to 20 parts by mass, when the parts by mass of the solid electrolyte are taken as 100.

[0037] A second conductive additive paste according to the present invention is a conductive additive paste used in the production of a positive electrode paste, which is obtained by adding a solid electrolyte to the conductive additive paste. The conductive additive paste includes an organic solvent, a conductive additive used in the production of a positive electrode, and a dispersing additive. The conductive additive is dispersed in the conductive additive paste. The amount of the dispersing additive is set according to the planned amount of solid electrolyte to be added to the conductive additive paste when the positive electrode paste is produced. The dispersing additive is mixed in an amount of 0.5 parts by mass to 5.0 parts by mass, and preferably 0.8 parts by mass to 2 parts by mass, when the total mass of the conductive additive and the planned amounts of solid electrolyte to be added is taken as 100 parts by mass. Furthermore, the conductive additive and the dispersing additive are mixed in such an amount that the amount of the dispersing additive mixed in per 100 parts by mass of the conductive additive is 2 parts by mass to 50 parts by mass, and preferably 6 parts by mass to 30 parts by mass. The conductive additive and the dispersing additive are mixed in such an amount that the mass of the conductive additive is 5 parts by mass to 25 parts by mass, and preferably 5 parts by mass to 20 parts by mass, when the planned amount of solid electrolyte to be added is taken as 100 parts by mass.

[0038] As in the case of the first conductive additive paste according to the present invention described above, the second conductive additive paste according to the present invention is also based on the premise that a solid electrolyte will be added to the conductive additive paste later, and not only is the conductive additive uniformly dispersed in the conductive additive paste, but when a solid electrolyte is subsequently added to this conductive additive paste, by adjusting and compounding the amount of dispersion additive to be blended in the conductive additive paste so as to satisfy the above-mentioned conditions, it becomes possible to easily prepare a conductive additive paste containing a solid electrolyte in which both the conductive additive and the solid electrolyte are uniformly dispersed.

[0039] In the case of the second conductive additive paste for producing a solid electrolyte positive electrode according to the present invention, the amount of dispersing additive added to the conductive additive paste can be adjusted more appropriately according to the blending ratio of the solid electrolyte and the conductive additive than in the case of the first conductive additive paste for producing a solid electrolyte positive electrode described above, but it is naturally possible that when the condition for the amount of dispersing additive in the second conductive additive paste for producing a solid electrolyte positive electrode is satisfied, the condition for the amount of dispersing additive in the first conductive additive paste for producing a solid electrolyte positive electrode is also satisfied. Of course, such embodiments that satisfy both conditions are encompassed by the present invention.

[0040] In a preferred embodiment of the conductive additive paste for producing the first and second solid electrolyte positive electrodes according to the present invention, the concentration of the conductive additive paste is determined from the solid content concentration of the positive electrode paste in which the cathode material, binder, solid electrolyte, conductive additive, and dispersion additive are all mixed together to form the final positive electrode paste. When the solid content concentration of the positive electrode paste is X, the solvent concentration in the conductive additive paste is 1-X. When the solid content concentration of the binder in the positive electrode paste is Y, the positive electrode The concentration of solids other than the cathode material and binder is determined in the range of (0.05X-Y) to (0.25X-Y), and when the concentration of solids other than the cathode material and binder is A, the concentration of the conductive additive paste for producing a positive electrode in which the solid electrolyte, conductive additive, and dispersing additive are mixed is A / (1-X), and the concentration of the conductive additive paste in which the dispersing additive and conductive additive are mixed in the case where the solid electrolyte is added later is determined in the range of 0.051A / (1-X) to 0.375A / (1-X).

[0041] In a preferred embodiment of the conductive additive paste for producing a solid electrolyte positive electrode according to the first and second aspects of the present invention, the concentration of the conductive additive paste is determined from the solids concentration of the positive electrode paste in which the cathode material, binder, solid electrolyte, conductive additive, and dispersion additive are all mixed together to form the final positive electrode paste. If the solids concentration of the positive electrode paste is X, the organic solvent concentration in the conductive additive paste is 1-X. If the solids concentration of the binder in the positive electrode paste is Y and the total solids concentration of the conductive additive, dispersion additive, and solid electrolyte in the positive electrode paste is A, the solids concentration A is determined in the range of (0.05X-Y) to (0.25X-Y), and the conductive additive paste concentration is set to 0.051A / (1-X) to 0.375A / (1-X). In this embodiment, the concentration of the conductive additive paste for producing a positive electrode in which the solid electrolyte, conductive additive, and dispersion additive are mixed may be A / (1-X).

[0042] A positive electrode paste obtained by adding a solid electrolyte, a binder, and a positive electrode material to a conductive additive paste is generally adjusted to have a solid content concentration of 50% to 80%. However, unlike lithium-ion secondary batteries that use an electrolytic solution, lithium-ion secondary batteries that use a solid electrolyte also include the solid electrolyte in their solid content, so it is difficult to determine an arbitrary solid content concentration for the positive electrode paste by mixing a solid electrolyte paste, a conductive additive paste, and a binder solution. Therefore, if the concentration of the conductive additive paste according to the present invention, which serves as the base used in preparing the positive electrode paste, is set according to the above-mentioned conditions, it becomes easy to mix the conductive additive paste according to the above-mentioned conditions when adding a solid electrolyte, a binder, and a positive electrode material to the conductive additive paste to prepare the final positive electrode paste.

[0043] In a preferred embodiment of the conductive additive paste for producing the first and second solid electrolyte positive electrodes according to the present invention, the moisture content of the conductive additive paste is dehydrated to 0.005 parts by mass or less per 100 parts by mass of the conductive additive paste. An example of the conductive additive paste is dehydrated by the dehydration method disclosed in JP 2022-186527 A, etc., and low moisture control is not required in the subsequent mixing step other than the solid content. Typically, the moisture content of the conductive additive paste is dehydrated to 0.005 parts by mass or less per 100 parts by mass of the conductive additive paste by aeration treatment with such dry gas, and low moisture control is not required in the subsequent mixing step other than the solid content. The dispersion medium for dispersing the conductive additive and solid electrolyte, and the dispersion additive for dispersing the conductive additive and solid electrolyte in a highly hydrophobic dispersion medium, both require moisture management like other materials. However, the conductive additive paste according to the present invention can be easily dehydrated as a whole after mixing and dispersing the conductive additive and dispersion additive according to the method described in JP 2022-186527 A. The relevant portions of the above-mentioned JP 2022-186527 A are incorporated herein by reference. The moisture value of the conductive additive paste may also be adjusted by other methods.

[0044] Furthermore, in one embodiment of the first and second conductive additive pastes for producing a solid electrolyte positive electrode according to the present invention, it is desirable that the conductive additive paste be sufficiently dispersed in advance and have a viscosity adjusted to a range of 10 mPa s to 2000 mPa s, preferably 10 mPa s to 1000 mPa s.

[0045] In this specification, the viscosity of the conductive additive paste is a value measured immediately after the dispersion is thoroughly stirred with a spatula (for example, for 1 minute) using a Brookfield viscometer at a measurement temperature of 25°C and a Brookfield viscometer rotor rotation speed of 60 rpm.

[0046] When the conductive additive paste according to the present invention has the predetermined composition and blending ratio as described above and exhibits the predetermined viscosity, the conductive additive is dispersed uniformly at a high concentration and exhibits stable fluidity, and when the conductive additive paste is mixed with a solid electrolyte, a binder, and a positive electrode material to prepare a positive electrode paste, each component can be dispersed uniformly at a high concentration with an appropriate viscosity suitable for coating.

[0047] Next, each component constituting the conductive additive paste according to the present invention will be described.

[0048] (Conductive Aid) The conductive aid used is not particularly limited as long as it is conductive and can be in a powdery or granular form. Examples of conductive aids include carbon black (CB), carbon nanotubes (CNT), carbon nanofibers (CNF), graphene, fullerene, natural graphite, artificial graphite, non-graphitizable carbon, cokes, and graphites. A single conductive aid may be used, or two or more may be used in combination. Examples of CB include furnace black, ketjen black, channel black, acetylene black, and thermal black, and any of these can be used. Among CBs, acetylene black is preferred because its manufacturing process inherently results in a low metal content. Furthermore, carbon materials used as conductive aids include carbon nanotubes (CNT), carbon nanofibers (CNF), and microparticulated acetylene black, among others, in order to improve the performance of all-solid-state lithium-ion secondary batteries.

[0049] It is to be noted that carbon black may be any carbon black that has undergone a conventional oxidation treatment, graphitization treatment, etc. Oxidation treatment of carbon black involves treating the carbon black at high temperatures in air or secondary treatment 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 carbon black.

[0050] If necessary, the conductive additive may be subjected to a dry magnetic separation process to remove metal impurities prior to the production of the conductive additive dispersion, and / or may be subjected to a wet magnetic separation process after the conductive additive is dispersed in a dispersion medium to prepare a paste.

[0051] Here, in this specification, the "powder-like" form of the conductive additive as a raw material dispersed in a dispersion medium is not limited as long as it can be dispersed in a dispersion medium as described below. Furthermore, the shape is not particularly limited, and it is not limited to a roughly spherical shape, but may include an elliptical shape, a flaky shape, a needle-like or short fiber-like shape, an amorphous shape, etc.

[0052] As explained on the Carbon Black Association website (https: / / carbonblack.biz / index.html), the smallest unit of carbon black that cannot be decomposed is an aggregate (primary agglomerate), and a part of this (domain) is commonly referred to as a particle. This particle can be considered to fall under the definition of the smallest unit of nanomaterials, but it is merely a part of the aggregate. Aggregates form agglomerates (secondary agglomerates) 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 that have been compressed or granulated to prevent scattering and improve handleability.

[0053] For example, it may include primary aggregates having an average particle size of about 10 to 100 nm, secondary aggregates formed by aggregation of such primary aggregates to form particles having an average particle size of about 0.1 to 100 μm, or particles that have been processed to have an average particle size of about 500 to 5000 μm by compression or granulation in consideration of handleability.

[0054] From the viewpoint of carbon black conductivity, conductive carbon fine particles are preferably aggregates in which primary particles are connected to some extent to form a chain-like or cluster-like structure. The connection of the primary particles in the aggregate is also called structure, and the degree of such development can be determined by particle size distribution measurement (dynamic light scattering or laser diffraction / light scattering) or observation with an electron microscope (either scanning or transmission type can be used). Such a structure 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 use.

[0055] (Dispersion Medium) The dispersion medium constituting the conductive additive paste according to the present invention is not particularly limited, but since the sulfide-based solid electrolyte described below is highly reactive, it is desirable that the dispersion medium be at least an organic solvent with low polarity or a non-polar organic solvent.

[0056] The low polarity or non-polar solvent that can be used as the dispersion medium in the present invention is not particularly limited, but specific examples include non-aqueous linear and / or branched or cyclic alkanes having 4 to 30 carbon atoms, such as pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, and methylcyclohexane; linear and / or branched and / or cyclic haloalkanes having 1 to 30 carbon atoms, such as dichloromethane, chloroform, and tetrachloroethane; chloromethane, dichloroethane, trichloroethane, tetrachloroethane, chlorocyclohexane, etc.; aromatic compounds having 6 to 22 carbon atoms, such as benzene, toluene, xylene, mesitylene, etc.; hydrogenated aromatic compounds having 10 to 22 carbon atoms, such as tetralin, cis-decalin and trans-decalin, etc.; halogenated aromatic compounds having 6 to 22 carbon atoms, such as chlorobenzene, fluorobenzene, dichlorobenzene or difluorobenzene, trichlorobenzene or trifluorobenzene, chloronaphthalene or fluoro linear and / or branched and / or cyclic ethers, for example, diethyl ether, dipropyl ether, tert-butyl methyl ether, tert-amyl methyl ether, tert-amyl ethyl ether, dimethoxyethane, diethoxyethane, methoxybenzene, methylthiobenzene, ethoxybenzene, petroleum ether, and the like; linear and / or branched and / or cyclic ketones, for example, acetone, trichloroacetone, butanone, pentanone, hexanone, heptanone, octanone, nonanone, cyclopentanone, linear and / or branched and / or cyclic nitroalkanes, such as nitromethane, nitroethane, nitrocyclohexane, etc.; nitroaromatic compounds having 6 to 22 carbon atoms, such as nitrobenzene, etc.; linear and / or branched and / or cyclic amines, preferably tert-butylamine, diaminoethane, diethylamine, triethylamine, tributylamine, pyrrolidine, piperidine, morpholine, N-methylaniline, N,N-dimethylaniline, etc.;Hexamethyldisilane, diphenyldimethylsilane, chlorophenyltrimethylsilane, phenyltrimethylsilane, phenethyltris(trimethylsiloxy)silane, phenyltris(trimethylsiloxy)silane, polydimethylsiloxane, tetraphenyltetramethyltrisiloxane, poly(3,3,3-trifluoropropylmethylsiloxane), 3,5,7-triphenylnonamethylpentasiloxane, 3,5-diphenyloctamethyltetrasiloxane, 1,1 silicone oils such as 1,5,5-tetraphenyl-1,3,3,5-tetramethyl-trisiloxane and hexamethylcyclotrisiloxane; fluorine-containing solvents such as hydrofluoroethers, chlorodifluoromethane, 1,1,1,2-tetrafluoroethane, pentafluoroethane, difluoromethane, trifluoromethane, 1,1,1,2,3,3,3-heptafluoropropane, 1,1-difluoroethane, 1,1,1,3,3,3-hexafluoropropane, octafluoropropane, etc.; for example, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, butyl propionate, amyl propionate, hexyl propionate, heptyl propionate, octyl propionate, ethyl butyrate, propyl butyrate, butyl butyrate, amyl butyrate, hexyl butyrate, heptyl butyrate, octyl butyrate, ethyl pentanoate, propyl pentanoate, butyl pentanoate, amyl pentanoate, hexyl pentanoate, heptyl pentanoate, pentane octyl hexanoate, ethyl hexanoate, propyl hexanoate, butyl hexanoate, amyl hexanoate, hexyl hexanoate, heptyl hexanoate, octyl hexanoate, ethyl heptanoate, propyl heptanoate, butyl heptanoate, amyl heptanoate, hexyl heptanoate, heptyl heptanoate, octyl heptanoate, ethyl octanoate, propyl octanoate, butyl octanoate, amyl octanoate, hexyl octanoate, heptyl octanoate, octyl octanoate, and the like, for example, R; １ -COOR ２ (However, in the formula, R １ is a C1 to C8 hydrocarbon group, R ２is a C2-C8 alkyl group.) or a mixture of the above-mentioned less polar or non-polar solvents in any ratio.

[0057] The dispersion medium constituting the conductive additive paste according to the present invention is preferably an organic solvent having a relative dielectric constant of less than 10. The relative dielectric constant is more preferably 7 or less, even more preferably 5 or less, and particularly preferably 3 or less. There is no particular restriction on the lower limit of the relative dielectric constant of the organic solvent, but examples thereof include 1 or more.

[0058] Examples of organic solvents having a relative dielectric constant of less than 10 include, but are not limited to, pentane (1.84), hexane (1.88), heptane (1.92), octane (1.95), cyclohexane (2.02), dichloromethane (8.93), chloroform (4.81), benzene (2.27), toluene (2.38), m-xylene (2.57), mesitylene (2.28), chlorobenzene (5.62), chlorobenzene (5.69), diethyl ether (4.20), diisopropyl ether (3.88), 1,2-dimethoxyethane (7.2), piperidine (5.8), morpholine (7.42), ethyl acetate (6.02), butyl acetate (5.01), and butyl butyrate (4.39).

[0059] Here, as the values ​​of the relative dielectric constant of various solvents, for example, the values ​​described in Chemistry Handbook, Basic Edition, Revised 5th Edition, Chemical Society of Japan, Maruzen Publishing, pp. I-770-777, 2004, or the values ​​described in CRC Handbook of Chemistry and Physics Web Edition, Section 6, (pp. 1142-1164) can be referred to, and the contents of the relevant parts of these documents are incorporated herein by reference.

[0060] Of the above-mentioned dispersion media, heptane, xylene, mesitylene, butyl butyrate, etc. are preferred, with butyl butyrate being particularly preferred.

[0061] (Dispersion additive) The dispersion additive constituting the conductive additive paste according to the present invention is not particularly limited, but it is preferable to add a resin-based dispersant as the dispersion additive, in order to impart high dispersibility to both the conductive additive and the solid electrolyte to be subsequently blended into the conductive additive paste.

[0062] Examples of resin-based dispersants include polyvinyl butyral, polyvinyl acetal, polyvinyl acetate, polyester resins, epoxy resins, polyether resins, alkyd resins, urethane resins, and ethyl celluloses. Of these, polyvinyl butyral, polyvinyl acetal, and ethyl cellulose are particularly preferred, with polyvinyl butyral being more preferred.

[0063] Among these, a preferred example of the dispersant is one in which polyvinyl butyral is the main component, particularly 80 mass % or more, and further, the total amount of the dispersant, i.e., 100 mass %, is polyvinyl butyral. When the carbonaceous material dispersion is used for an all-solid-state lithium ion secondary battery, by using polyvinyl butyral as the dispersant in this way and combining it with the above-mentioned organic dispersion medium as the dispersion medium, good dispersibility of the carbonaceous material in the carbonaceous material dispersion can be obtained, and low viscosity can be achieved.

[0064] Although the polyvinyl butyral is not particularly limited, it is preferable that the hydroxyl group content be relatively low, specifically, for example, that the hydroxyl group content in the polymer be 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, in order to improve solubility in the ester solvent used as the dispersion medium. Furthermore, although not particularly limited, the acetate group content of the polyvinyl butyral is preferably about 1 to 7% by mass, and the viscosity of a 10% by mass ethanol solution of polyvinyl butyral measured at 20°C in accordance with DIN 53015 is preferably about 10 to 100 mPa s, particularly about 20 to 60 mPa s.

[0065] (Conductive additive paste containing solid electrolyte) A positive electrode paste according to one embodiment of the present invention is a conductive additive paste containing a solid electrolyte obtained by mixing and dispersing a required amount of a sulfide-based solid electrolyte into the conductive additive paste according to the present invention described above.

[0066] (Solid Electrolyte) In order to obtain the conductive additive paste containing a solid electrolyte according to the present invention, the sulfide-based solid electrolyte to be added in a necessary amount to the conductive additive paste according to the present invention is not particularly limited as long as it contains sulfur (S) and has ion conductivity. ２ Examples include those made using a raw material composition containing S and sulfides of elements of groups 13 to 15.

[0067] Examples of the elements of Groups 13 to 15 include B, Al, Si, Ge, P, As, and Sb. Specific examples of sulfides of elements of Groups 13 to 15 include B, ２ S ３ , Al ２ S ３ , SiS ２ , GeS ２ , P ２ S ３ , P ２ S ５ , As ２ S ３ , Sb ２ S ３ Among these, Li ２ A sulfide-based solid electrolyte material obtained by using a raw material composition containing S and sulfides of elements of groups 13 to 15 is ２ S-P ２ S ５ Material, Li ２ S-SiS ２ Material, Li ２ S-GeS ２ Material or Li ２ S-Al ２ S ３ It is preferable that the material is a sintered body from the viewpoint of excellent Li ion conductivity. ２ S-P ２ S ５ The material is Li２ S and P ２ S ５ A sulfide-based solid electrolyte material obtained by using a raw material composition containing Li ２ S and P ２ S ５ It is sufficient if it contains the above as a main ingredient, and it may also contain other ingredients.

[0068] In addition, the raw material composition contains Li ２ In addition to S and sulfides of elements of groups 13 to 15, Li ３ P.O. ４ , Li ４ SiO ４ , Li ４ GeO ４ , Li ３ BO ３ and Li ３ AlO ３ The sulfide-based solid electrolyte material may contain at least one lithium orthooxoate selected from the group consisting of: By adding such a lithium orthooxoate, a more stable sulfide-based solid electrolyte material can be obtained.

[0069] In addition, it may be preferable that the sulfide-based solid electrolyte material contains LiX (X is a halogen) in order to obtain a sulfide-based solid electrolyte material with high Li ion conductivity. ２ The inclusion of O may be preferable in some cases, since it allows the sulfide-based solid electrolyte material to generate a small amount of hydrogen sulfide.

[0070] The sulfide-based solid electrolyte material of the present invention may be a sulfide glass, or may be a sulfide glass ceramic obtained by heat-treating the sulfide glass, and may have a crystalline structure. The sulfide glass can be obtained, for example, by amorphizing the raw material composition. Examples of amorphizing methods include mechanical milling and melt-quenching, with mechanical milling being preferred. This is because it enables processing at room temperature and simplifies the manufacturing process. Mechanical milling is not particularly limited as long as it is a method for mixing the raw material composition while applying mechanical energy. Examples of the mechanical milling include ball mills, turbo mills, mechanofusion mills, and disk mills. Among these, ball mills are preferred, and planetary ball mills are particularly preferred because they can efficiently obtain the desired sulfide-based solid electrolyte material. Furthermore, it is preferable to set the mechanical milling conditions so that the desired sulfide-based solid electrolyte material can be obtained. On the other hand, sulfide glass ceramics can be obtained by, for example, heat-treating sulfide glass at a temperature equal to or higher than the crystallization temperature. That is, sulfide glass ceramics can be obtained by subjecting a raw material composition to an amorphization method and then further heat-treating it. Depending on the conditions of the heat treatment, the bridging sulfur and Li ２ Since there is a possibility that S or a stable phase may be formed, in the present invention, it is preferable to adjust the heat treatment temperature and heat treatment time so as to prevent these from being formed.

[0071] In addition, the sulfide-based solid electrolyte material preferably has high Li ion conductivity, and the Li ion conductivity at room temperature is, for example, 1×10 －４ S / cm or more, and preferably 1×10 －３ It is more preferable that the viscosity is 200 S / cm or more.

[0072] In preparing the conductive additive paste containing a solid electrolyte according to the present invention, the required amount of sulfide-based solid electrolyte material to be added to the conductive additive paste according to the present invention described above is not particularly limited, but for example, a preferable example is one that satisfies the relationship that the ratio of the solid electrolyte to be added to the conductive additive contained in the conductive additive paste according to the present invention described above is 2.5 to 25 parts by mass, more preferably 5 to 20 parts by mass, when the parts by mass of the solid electrolyte are taken as 100.

[0073] The shape of the sulfide-based solid electrolyte material can be, for example, a particulate shape, and among these, a spherical shape or an oval spherical shape is preferable. When the sulfide-based solid electrolyte material is particulate, the average particle size thereof is, for example, preferably in the range of 0.01 μm to 10 μm, and more preferably in the range of 0.1 μm to 1 μm.

[0074] (Conductive additive paste containing solid electrolyte and binder) A positive electrode paste according to one embodiment of the present invention is a conductive additive paste containing solid electrolyte and binder obtained by adding a binder to the conductive additive paste containing solid electrolyte according to the present invention described above and dissolving the binder sufficiently.

[0075] (Binder) As the binder component, a polymer that exhibits good solubility in the dispersion medium used but has no solubility in water can be used, and although there are no particular limitations, specific examples that can be used include polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polyamide, polyamideimide, butadiene rubber, isobutylene rubber, styrene-butadiene rubber, ethylene-propylene rubber, and nitrile-butadiene rubber. Of these, styrene-butadiene rubber is particularly preferred.

[0076] Furthermore, the weight-average molecular weight of these resins used as binders is preferably 10,000 to 2,000,000, more preferably 100,000 to 1,000,000, and particularly preferably 200,000 to 1,000,000. A small molecular weight may result in a decrease in the resistance and adhesion of the binder. A large molecular weight may improve the resistance and adhesion of the binder, but may increase the viscosity of the binder itself, decreasing workability, and may act as a flocculant, causing significant aggregation of dispersed particles.

[0077] (Positive Electrode Paste) A positive electrode paste according to one embodiment of the present invention is a positive electrode paste prepared by adding a positive electrode material to the conductive additive paste containing the solid electrolyte according to the present invention described above or the conductive additive paste containing the solid electrolyte and binder, and thoroughly mixing the resulting mixture to be uniform.

[0078] (Cathode Material) The cathode material (cathode active material) is not particularly limited, but titanium sulfide (TiS), molybdenum sulfide (MoS ２ ), iron sulfide (FeS, FeS ２ ), copper sulfide (CuS) and nickel sulfide (Ni ３ S ２ ), sulfide-based compounds such as bismuth oxide (Bi ２ O ３ , Bi ２ Pb ２ O ５ ), copper oxide (CuO), vanadium oxide (V ６ O １３ ), lithium-containing cobalt oxides such as lithium cobalt oxide (LiCoO), lithium nickel oxide (LiNiO ２ lithium-containing nickel oxides such as lithium manganese oxide (LiMnO ２ ), LiMn ２ O ４ , Li ０．３３ MnO ２ Oxide-based materials such as lithium-containing manganese oxides, niobium selenide (NbSe ３ ) etc. can be given as examples.

[0079] In one embodiment of each of the conductive additive paste, the conductive additive paste containing a solid electrolyte, the conductive additive paste containing a solid electrolyte and a binder, and the positive electrode paste according to the first and second aspects of the present invention, optional components may be contained in addition to the essential components described above. Examples of optional components include a pH adjuster and a surfactant.

[0080] (pH Adjuster) Examples of pH adjusters that can be added as needed include tertiary amines, secondary amines, primary amines, cyclic amines, alkanolamines or amino alcohols, which are compounds having an amino group and a hydroxy group in an alkane skeleton, and amine compounds such as diglycolamine, tris(hydroxymethyl)aminomethane (THAM), morpholine, and other amines. Although not particularly limited, among these, for example, 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), THAM, and the like are particularly preferred.

[0081] (Surfactant) The surfactant that can be blended as needed is not particularly limited, and examples thereof include anionic surfactants such as sodium dodecylbenzenesulfonate and sodium lauryl sulfate, cationic surfactants such as tetramethylammonium chloride, and nonionic surfactants such as polyoxyethylene alkyl ether compounds and polyoxyethylene fatty acid ester compounds.

[0082] (Method for manufacturing positive electrode paste) A method for manufacturing a positive electrode paste according to one embodiment of the present invention is a method for manufacturing a positive electrode paste including an organic solvent, a conductive additive, a dispersing additive, a solid electrolyte, and a positive electrode material, and includes the steps of blending the conductive additive and the dispersing additive into an organic solvent to manufacture a conductive additive paste, adding the solid electrolyte to the conductive additive paste to manufacture an electrolyte paste, and adding the positive electrode material to the electrolyte paste, and in the step of manufacturing the conductive additive paste, the conductive additive is blended in such an amount that the dispersing additive is 0.5 parts by mass or more and 5.0 parts by mass or less when the total mass of the parts by mass of the conductive additive and the parts by mass of the solid electrolyte is 100 parts by mass.

[0083] In a preferred method for producing a positive electrode paste according to the present invention, in the step of producing a conductive additive paste, the conductive additive and the dispersing additive are blended so that the amount of the dispersing additive relative to 100 parts by mass of the conductive additive is 2 parts by mass or more and 50 parts by mass or less, and in the step of producing an electrolyte paste, the amount of the conductive additive added relative to 100 parts by mass of the solid electrolyte is 5 parts by mass or more and 25 parts by mass or less.

[0084] The method for producing the positive electrode paste according to the present invention is not particularly limited, but may be such that the conductive additive and the dispersion additive are added to an organic solvent as a dispersion medium in the above-described predetermined ratio, and the mixture is stirred and mixed to disperse the conductive additive and the dispersion additive.

[0085] The method for producing a positive electrode paste according to the present invention can be used by appropriately selecting the configuration described above for the conductive additive paste. For example, the conductive additive paste is produced so as to satisfy the solid content concentration described above for the conductive additive paste. In the method for producing a positive electrode paste according to the present invention, a binder may be added together with the solid electrolyte in the step of producing the electrolyte paste, or the binder may be added to the electrolyte paste before adding the positive electrode material.

[0086] In the method for producing a paste for a positive electrode according to the present invention, a dispersing device may be used in the process of producing various pastes, for example, in the process of producing a conductive additive paste. The dispersing device is not particularly limited, and dispersing machines that are commonly used for pigment dispersion and the like can be used. For example, mixers such as a Disper, a Homomixer, and a Planetary Mixer, homogenizers (such as "Clearmix" manufactured by M Technique, "Filmix" manufactured by PRIMIX, and "Abramix" manufactured by Silverson), paint conditioners (manufactured by Red Devil), colloid mills (such as "PUC Colloid Mill" manufactured by PUC and "Colloid Mill MK" manufactured by IKA), cone mills (such as "Cone Mill MKO" manufactured by IKA), ball mills, sand mills (such as "Shinmaru" and "Shinmaru"). Examples of the dispersing machine include media-type dispersers such as "DYNOMILL" manufactured by NYK Enterprises, Inc.), attritors, pearl mills (such as "DCP MILL" manufactured by Eirich), and Coball mills; wet jet mills (such as "GENUS PY" manufactured by NYK Enterprises, "STARBURST" manufactured by Sugino Machine Ltd., and "NANOMIZER" manufactured by Nanomizer Inc.); media-less dispersers such as "CLEAR SS-5" manufactured by M Technique Co., Ltd. and "MICROS" manufactured by Nara Kikai Co., Ltd.; and other roll mills, but are not limited to these.

[0087] Preferably, the conductive additive is finally dispersed in a media mill, particularly in a media mill using beads with an average particle size of 0.05 to 2 mm, and more preferably, the conductive additive is dispersed using a shear-type dispersing device as described below in detail prior to the dispersion treatment using the media mill, and then the conductive additive is dispersed using the media mill.

[0088] If the particle size of the beads used in the media mill is too small, the conductive additive, such as primary aggregates of carbon black, may be broken into small pieces, and excessive energy may be required for the dispersion process. Furthermore, handling becomes difficult, so the average particle size of the beads is preferably 0.05 mm or more, and 0.5 mm or more is particularly preferred. On the other hand, if the beads are too large, the number of beads per unit volume decreases, reducing dispersion efficiency, resulting in insufficient grinding of the conductive additive, and the conductive additive particles may exist with a large aspect ratio, potentially preventing the liquid properties required for paints and coatings. For this reason, the average particle size of the beads is preferably 2 mm or less, and 1.5 mm or less is particularly preferred.

[0089] The material of the beads used as dispersion media in a media mill is not particularly limited, and examples include alumina, zirconia, steel, chromium steel, and glass. However, among these, it is preferable to use zirconia beads, taking into consideration the risk of contamination of the product and the magnitude of kinetic energy resulting from the specific gravity.

[0090] The shape of the beads is not particularly limited, but spherical shapes are generally used.

[0091] The structure of the media mill is not particularly limited, and various known media mills can be used, including various known attritors, sand mills, and bead mills.

[0092] The filling ratio of the beads in the vessel can be determined depending on the vessel, stirring mechanism, structure, etc., and is not particularly limited. However, if the ratio is too low, there is a risk that the conductive additive will not be sufficiently crushed or cut. On the other hand, if the ratio is too high, a large driving force is required for rotation and there is a risk that wear of the beads will increase contamination of the processed medium. For this reason, it is desirable to set the filling ratio of the beads to, for example, about 70 to 85 volume percent of the effective volume of the vessel.

[0093] In addition, operating conditions such as processing time, shaft rotation speed, vessel internal pressure, and motor load are influenced by the amount of conductive additive and the properties of the resin to be dispersed, particularly viscosity and compatibility with the conductive additive, and can be set appropriately depending on the purpose.

[0094] Prior to the dispersion treatment using such a media mill, a preliminary dispersion treatment can be carried out using other stirring devices, for example, shear type stirrers such as a disper or homomixer.

[0095] By carrying out the dispersion treatment in this manner, a dispersion having a viscosity at 25° C. of about 10 mPa·s to 2000 mPa·s is prepared.

[0096] In addition, when a solid electrolyte is added to the conductive additive paste prepared as described above to prepare a conductive additive paste containing a solid electrolyte, when a binder is added to this conductive additive paste containing a solid electrolyte to prepare a conductive additive paste containing a solid electrolyte and a binder, or when a positive electrode material is added to the conductive additive paste containing a solid electrolyte and a binder to prepare a positive electrode paste, a binder having the desired uniform composition can be obtained by performing dispersion treatment using a dispersion treatment device similar to that described above.

[0097] The present invention will be described in detail below based on examples, but the present invention is not limited to the following examples as long as it does not deviate from the gist of the present invention. In these examples, parts represent parts by mass, and % represents mass %, respectively. SE represents sulfide-based solid electrolyte.

[0098] Example 1 A positive electrode paste was prepared according to the procedure shown in the chart of FIG. 1 . Before preparing the positive electrode paste, a conductive additive paste for manufacturing a solid electrolyte positive electrode according to the present invention was prepared in advance. (a) Butyl butyrate (manufactured by Tokyo Chemical Industry Co., Ltd.) was used as the dispersion medium, (b) acetylene black (Denka Black (registered trademark) granular product (average particle size: 35 μm) manufactured by Denka Co., Ltd.) was used as the conductive additive, and (c) polyvinyl butyral (S-LEC BL manufactured by Sekisui Chemical Co., Ltd.) was used as the dispersion additive. Furthermore, (d) Li was used as the sulfide-based solid electrolyte (SE). ２ S-P ２ S５ -LiBr-LiI glass ceramics (particle diameter (D50): 2 μm) was used. Styrene butadiene rubber was used as the binder. (e) LiNi was used as the active material. １／３ Co １／３ Mn １／３ O ２ Powder (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., particle size 1 to several μm) was used.

[0099] The conductive additive paste for producing a solid electrolyte positive electrode according to the present invention was prepared in accordance with the proportions shown in Table 2, with the final composition of the positive electrode paste as shown in Table 1 anticipated. Because the conductive additive paste was prepared with the final composition anticipated, the conductive additive concentration was 4.6%, and the viscosity was 30 mPa·s, significantly lower than that of the comparative example described below. The conductive additive paste was prepared using a laboratory bead mill (manufactured by Aimex Co., Ltd.) with zirconia beads having a diameter of 1 mm. The bead filling rate in the vessel was 30% by volume of the effective volume of the vessel, and the volume ratio of the dispersion to the beads was approximately 1:1. The dispersion was performed in the vessel at a rotation speed of approximately 2000 rpm for approximately 10 minutes.

[0100] Next, moisture-controlled SE was added to this conductive additive paste. The total composition of the solid content of the SE, conductive additive, and additive was 24.6%, and due to the effect of the dispersant added in advance for the SE, the solid content was lower than that of the SE dispersion of Comparative Example 1 described below, and the viscosity was 800 mPa s, making it easy to handle.

[0101] Furthermore, a binder solution prepared from the remaining components could also be produced as a 10% solution, and the viscosity could be controlled to 1000 mPa s or less, as shown in Table 3. The conductive additive paste and binder solution were then mixed in a kneader. This conductive additive paste and binder solution were easy to mix, and after uniformly mixing in the kneader, the active material was added, allowing a positive electrode paste to be produced.

[0102] In this embodiment, as shown in FIG. 1, there are two types of solutions, the conductive additive paste and the binder solution, which simplifies the adjustment of the amount of solvent and reduces the concentration of the conductive additive, resulting in a paste with a low viscosity that is easier to handle.

[0103] In addition, once either solution composition was decided, there was no need to reconsider the composition, as in the comparative example described below. Furthermore, management was simplified compared to the comparative example, with only two types of solution being used: the conductive additive paste and the binder solution.

[0104]

[0105]

[0106]

[0107] Example 2 A paste for a positive electrode was prepared according to the procedure shown in the chart of Figure 2. The materials used were all the same as those used in Example 1.

[0108] The final composition of the positive electrode paste shown in Table 1 above was assumed in advance, and a conductive additive paste for producing a solid electrolyte positive electrode according to the present invention was prepared in the proportions shown in Table 4. Unlike Example 1 above, in which the solvent for the binder solution was separated, all of the solvent was used in this conductive additive paste. As a result, the conductive additive concentration in the conductive additive paste was 3.9%, and the viscosity was 10 mPa s or less, making it possible to handle it almost as a liquid.

[0109] Next, the SE with controlled moisture content was added to this conductive additive paste and dispersed. As shown in Table 5, the total composition of the solid content of the SE, the solid content of the conductive additive, and the solid content of the additive was 21.27%. Due to the effect of the dispersant added in advance for the SE, the viscosity was 500 mPa s, making it even easier to handle than in Example 1.

[0110] The resulting SE-added conductive additive paste was then mixed with a binder and active material in a kneader to produce a positive electrode paste. Although it took time to dissolve the binder, the number of management items was reduced, which ultimately led to cost reductions.

[0111] In this example, moisture control of the solid content is a prerequisite, but other moisture control only required checking the conductive additive paste. In addition, composition adjustment was simple, and once the concentration and amount of the dispersion solution were known, it was only necessary to control the amount of solids of the SE, binder, and active material.

[0112]

[0113]

[0114] (Comparative Example) For comparison, as shown in Figure 3, a positive electrode paste was prepared using a conductive additive paste, binder solution, and SE paste prepared separately, as previously done. As shown in Table 6, the solids concentration of the SE dispersion was approximately 28% with a dispersant, but the viscosity was approximately 700 mPa·s with the dispersant. Increasing the concentration beyond this level resulted in poor dispersibility, so the SE concentration was limited to 28%. Furthermore, the conductive additive paste could be maintained at a viscosity of 1000 mPa·s or less up to approximately 18%, but at approximately 200 mPa·s, the liquid was easily supplied and drained well, so it was set to 15%, as shown in Table 7. In this comparative example, the procedure shown in Figure 3 required adjusting the solvent content based on the binder concentration. Normally, the viscosity exceeds 1000 mPa·s at approximately 10%, but when a 15% solution was used to prepare the binder solution, the viscosity rose sharply to above 5000 mPa·s, making it difficult to add. As a result, the moisture content and composition of the binder solution became unknown, and it was not possible to obtain accurate figures for the final amount of active material supplied. There were many processes and management items, and the complexity of adjusting the composition was clear. The composition of the conductive additive, binder, and SE dispersion solution had to be determined in advance, and each had to be in a concentration and dispersion state that made them easy to handle. Furthermore, the number of pastes increased with each process, necessitating intermediate analyses of moisture and composition for each paste manufacturing process and binder manufacturing process.

[0115]

[0116]

[0117]

Claims

1. A conductive additive paste used in the manufacture of a positive electrode paste, comprising a conductive additive paste to which a solid electrolyte is added, wherein the conductive additive paste contains an organic solvent, a conductive additive used in the manufacture of a positive electrode, and a dispersing additive, and the conductive additive is dispersed in the conductive additive paste; the amount of the dispersing additive is set according to the amount of solid electrolyte to be added to the conductive additive paste when the positive electrode paste is manufactured; and the dispersing additive is blended in such an amount that it is 0.5 parts by mass or more and 5.0 parts by mass or less when the total mass of the conductive additive and the amount of solid electrolyte to be added is 100 parts by mass.

2. The conductive additive paste for producing a solid electrolyte positive electrode according to claim 1, wherein the conductive additive and the dispersing additive are blended so that the blending amount of the dispersing additive per 100 parts by mass of the conductive additive is 2 parts by mass or more and 50 parts by mass or less, and the mass of the conductive additive is 5 parts by mass or more and 25 parts by mass or less when the planned addition amount of the solid electrolyte is 100 parts by mass.

3. The conductive additive paste for producing a solid electrolyte positive electrode according to claim 1 or 2, wherein the concentration of the conductive additive paste is set according to the solid content concentration of a positive electrode paste produced by adding a solid electrolyte, a binder, and a positive electrode material to the conductive additive paste, and wherein, when the solid content concentration of the positive electrode paste is X, the concentration of the organic solvent in the conductive additive paste is 1-X, when the solid content concentration of the binder in the positive electrode paste is Y, and the total solid content concentration of the conductive additive, the dispersion additive, and the solid electrolyte in the positive electrode paste is A, the solid content concentration A is determined in the range of (0.05X-Y) to (0.25X-Y), and the conductive additive paste concentration is set to 0.051 A / (1-X) to 0.375 A / (1-X).

4. The conductive additive paste for producing a solid electrolyte positive electrode according to claim 1 or 2, wherein the amount of water in the conductive additive paste is 0.005 parts by mass or less per 100 parts by mass of the conductive additive paste.

5. The conductive additive paste for producing a solid electrolyte positive electrode according to claim 1 or 2, having a viscosity of 10 mPa·s or more and 2000 mPa·s or less.

6. The conductive additive paste for producing a solid electrolyte positive electrode according to claim 1 or 2, wherein the organic solvent has a relative dielectric constant of less than 10.

7. A paste for a positive electrode, comprising the conductive additive paste according to claim 1 or 2, and a sulfide-based solid electrolyte dispersed therein.

8. The positive electrode paste according to claim 7, further comprising a binder dissolved therein.

9. The positive electrode paste according to claim 7, further comprising a positive electrode material mixed therein.

10. A method for producing a cathode paste containing an organic solvent, a conductive additive, a dispersing additive, a solid electrolyte, and a cathode material, comprising: a step of blending the conductive additive and the dispersing additive into the organic solvent to produce a conductive additive paste; a step of adding the solid electrolyte to the conductive additive paste to produce an electrolyte paste; and a step of adding the cathode material to the electrolyte paste, wherein in the step of producing the conductive additive paste, the conductive additive paste is blended with the dispersing additive in an amount of 0.5 parts by mass or more and 5.0 parts by mass or less when the total mass of the parts by mass of the conductive additive and the parts by mass of the solid electrolyte is 100 parts by mass.

11. The method for producing a positive electrode paste according to claim 10, wherein in the step of producing the conductive additive paste, the conductive additive and the dispersing additive are blended so that the amount of the dispersing additive relative to 100 parts by mass of the conductive additive is 2 parts by mass or more and 50 parts by mass or less, and the amount of the conductive additive added in the step of producing the electrolyte paste is 5 parts by mass or more and 25 parts by mass or less relative to 100 parts by mass of the solid electrolyte.

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