Binder composition for all-solid-state secondary battery, slurry composition for all-solid-state secondary battery, solid electrolyte-containing layer, and all-solid-state secondary battery

Abstract

The purpose of the present invention is to provide a binder composition for an all-solid-state secondary battery, which is capable of imparting excellent dispersibility and storage stability to a slurry composition for an all-solid-state secondary battery using a sulfide-based inorganic solid electrolyte as a solid electrolyte. And a solid electrolyte-containing layer formed using the slurry composition for all-solid secondary batteries can exhibit excellent ion conductivity. The present invention is a binder composition for an all-solid-state secondary battery using a sulfide-based inorganic solid electrolyte, the binder composition for an all-solid-state secondary battery comprising a polymer containing an alkyl (meth) acrylate monomer unit and an acetate solvent in which a hydrocarbon group having 6-9 carbon atoms is bonded to a non-carbonyl oxygen atom, the alkyl (meth) acrylate monomer units include a first alkyl (meth) acrylate monomer unit in which an alkyl group having 3-8 carbon atoms is bonded to a non-carbonyl oxygen atom, and a second alkyl (meth) acrylate monomer unit in which an alkyl group having 1-2 carbon atoms is bonded to a non-carbonyl oxygen atom. The mass ratio of the first alkyl (meth) acrylate monomer unit to the second alkyl (meth) acrylate monomer unit is from 2.1 to 2.5 (inclusive).

Description

Technical Field

[0001] The present invention relates to a binder composition for all-solid-state secondary batteries, a slurry composition for all-solid-state secondary batteries, an all-solid-state secondary battery including a solid electrolyte layer, and an all-solid-state secondary battery. Background Art

[0002] In recent years, secondary batteries such as lithium ion secondary batteries have been in increasing demand not only for portable terminals such as mobile information terminals and portable electronic devices, but also for various applications such as household small power storage devices, two-wheeled motor vehicles, electric vehicles, and hybrid electric vehicles. Moreover, with the expansion of applications, secondary batteries are required to further improve safety.

[0003] Therefore, as a secondary battery with high safety, an all-solid-state secondary battery using a solid electrolyte instead of an organic solvent electrolyte with high flammability and high fire risk when leaking has attracted attention. Here, as the solid electrolyte, inorganic solid electrolytes such as sulfide-based inorganic solid electrolytes and oxide-based inorganic solid electrolytes can be used; polymer solid electrolytes such as polyethylene oxide and polypropylene oxide can be used, and these solid electrolytes are contained in an all-solid-state secondary battery, for example, as a solid electrolyte layer (electrode composite layer, solid electrolyte layer) formed by bonding components such as a solid electrolyte with a binder material.

[0004] When forming the above-mentioned solid electrolyte layer-containing layer, a slurry composition for a solid electrolyte layer-containing layer is used, and the slurry composition for a solid electrolyte layer-containing layer is prepared using a binder composition containing a polymer as a binder material and a solvent.

[0005] For example, an electrode composite layer can be formed by removing a solvent from a slurry composition for an electrode composite layer containing a binder composition, a solid electrolyte, and an electrode active material. In addition, for example, a solid electrolyte layer can be formed by removing a solvent from a slurry composition for a solid electrolyte layer containing a binder composition and a solid electrolyte.

[0006] Moreover, in order to improve the performance of all-solid-state secondary batteries, improvements have been made to binder compositions and methods for forming solid electrolyte layer-containing layers using binder compositions (for example, refer to Patent Documents 1 and 2).

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2010-205449;

[0010] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2019-91632. Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] However, in the case of using a sulfide-based inorganic solid electrolyte as the solid electrolyte, there is still room for improvement in the above-described conventional binder composition in terms of improving the dispersibility and storage stability of the slurry composition and improving the ionic conductivity of the solid electrolyte-containing layer formed using the slurry composition.

[0013] Therefore, an object of the present invention is to provide a binder composition for an all-solid-state secondary battery that can impart excellent dispersibility and storage stability to a slurry composition for an all-solid-state secondary battery using a sulfide-based inorganic solid electrolyte as the solid electrolyte, and can cause a solid electrolyte-containing layer formed using the slurry composition for the all-solid-state secondary battery to exhibit excellent ionic conductivity.

[0014] In addition, an object of the present invention is to provide a slurry composition for an all-solid-state secondary battery that has excellent dispersibility and storage stability and can form a solid electrolyte-containing layer having excellent ionic conductivity.

[0015] Furthermore, an object of the present invention is to provide a solid electrolyte-containing layer having excellent ionic conductivity and an all-solid-state secondary battery having the solid electrolyte-containing layer.

[0016] Solutions to the Problems

[0017] The present inventors conducted intensive studies for the purpose of solving the above problems. Then, the present inventors newly found that if a binder composition for an all-solid-state secondary battery contains a polymer containing (meth)acrylic acid alkyl ester monomer units in a specified ratio and a specified acetate solvent, the above problems can be solved, and thus the present invention was completed.

[0018] That is, an object of the present invention is to advantageously solve the above problems. [1] The present invention is a binder composition for an all-solid-state secondary battery using a sulfide-based inorganic solid electrolyte. The binder composition for the all-solid-state secondary battery contains a polymer containing (meth)acrylic acid alkyl ester monomer units and an acetate solvent in which a hydrocarbon group having 6 or more and 9 or less carbon atoms is bonded to a non-carbonyl oxygen atom. The (meth)acrylic acid alkyl ester monomer units include a first (meth)acrylic acid alkyl ester monomer unit in which an alkyl group having 3 or more and 8 or less carbon atoms is bonded to a non-carbonyl oxygen atom and a second (meth)acrylic acid alkyl ester monomer unit in which an alkyl group having 1 or more and 2 or less carbon atoms is bonded to a non-carbonyl oxygen atom. The mass ratio of the first (meth)acrylic acid alkyl ester monomer unit to the second (meth)acrylic acid alkyl ester monomer unit is 2.1 or more and 2.5 or less.

[0019] If it is a binder composition for an all-solid-state secondary battery as described above, it is possible to impart excellent dispersibility and storage stability to a slurry composition for an all-solid-state secondary battery using a sulfide-based inorganic solid electrolyte as a solid electrolyte, and it is possible to make a solid electrolyte layer-containing layer formed using this slurry composition for an all-solid-state secondary battery exhibit excellent ionic conductivity.

[0020] In the present specification, “(meth)acrylic acid” means “acrylic acid and / or methacrylic acid”.

[0021] In the present specification, “containing a monomer unit” means “containing a structural unit derived from a monomer in a polymer obtained using the monomer”.

[0022] [2] In the binder composition for an all-solid-state secondary battery of the above [1], it is preferable that the polymer further contains a cyanated vinyl monomer unit.

[0023] If the polymer further contains a cyanated vinyl monomer unit, it is possible to impart more excellent dispersibility and storage stability to a slurry composition for an all-solid-state secondary battery using a sulfide-based inorganic solid electrolyte as a solid electrolyte, and it is possible to make a solid electrolyte layer-containing layer formed using this slurry composition for an all-solid-state secondary battery exhibit more excellent ionic conductivity.

[0024] [3] In the binder composition for an all-solid-state secondary battery of the above [2], it is preferable that when the total repeating units constituting the polymer are 100% by mass, the content ratio of the cyanated vinyl monomer unit is 3% by mass or more and less than 7% by mass.

[0025] If the content ratio of the cyanated vinyl monomer unit is at least the above lower limit, it is possible to improve the dispersibility and storage stability of the slurry composition for an all-solid-state secondary battery and the ionic conductivity of the solid electrolyte layer-containing layer. In addition, even if the content ratio of the cyanated vinyl monomer unit is less than the above upper limit, it is possible to improve the dispersibility and storage stability of the slurry composition for an all-solid-state secondary battery and the ionic conductivity of the solid electrolyte layer-containing layer.

[0026] In the present specification, the content ratio (mass%) of the monomer unit in the polymer can be measured using 1 nuclear magnetic resonance (NMR) methods such as 1H-NMR.

[0027] [4] In the binder composition for an all-solid-state secondary battery according to any one of the above [1] to [3], it is preferable that the weight average molecular weight of the polymer is 800,000 or more and 1,500,000 or less.

[0028] If the weight average molecular weight of the polymer is at least the above lower limit, it is possible to improve the storage stability of the slurry composition for an all-solid-state secondary battery.

[0029] On the other hand, if the weight-average molecular weight of the polymer is below the above upper limit, the dispersibility of the slurry composition for all-solid-state secondary batteries can be improved.

[0030] In the present specification, the "weight-average molecular weight" can be measured by the method described in the examples of the present specification.

[0031] [5] In the binder composition for all-solid-state secondary batteries according to any one of the above [1] to [4], it is preferable that the polymer further contains an aromatic monomer unit, and when the total repeating units constituting the polymer are 100% by mass, the content ratio of the aromatic monomer unit is 10% by mass or more and 30% by mass or less.

[0032] If the polymer further contains an aromatic monomer unit, the strength of the polymer can be ensured, and excellent shape stability can be imparted to the layer containing the solid electrolyte.

[0033] Moreover, if the content ratio of the aromatic monomer unit is above the above lower limit, the strength of the polymer can be improved, and the shape stability of the layer containing the solid electrolyte can be improved.

[0034] On the other hand, if the content ratio of the aromatic monomer unit is below the above upper limit, the flexibility of the polymer can be improved, and the adhesiveness of the layer containing the solid electrolyte can be improved.

[0035] [6] In the binder composition for all-solid-state secondary batteries according to any one of the above [1] to [5], it is preferable that when the total repeating units constituting the polymer are 100% by mass, the total content ratio of the first (meth)acrylic acid alkyl ester monomer unit and the second (meth)acrylic acid alkyl ester monomer unit is 50% by mass or more and 85% by mass or less.

[0036] If the total content ratio of the first (meth)acrylic acid alkyl ester monomer unit and the second (meth)acrylic acid alkyl ester monomer unit is above the above lower limit, the storage stability of the slurry composition for all-solid-state secondary batteries can be improved.

[0037] On the other hand, if the total content ratio of the first (meth)acrylic acid alkyl ester monomer unit and the second (meth)acrylic acid alkyl ester monomer unit is below the above upper limit, a decrease in the ionic conductivity of the layer containing the solid electrolyte can be suppressed.

[0038] In addition, an object of the present invention is to advantageously solve the above problems. [7] The present invention is a slurry composition for all-solid-state secondary batteries, which contains the binder composition for all-solid-state secondary batteries according to any one of the above [1] to [6] and a sulfide-based inorganic solid electrolyte.

[0039] In the case of the slurry composition for an all-solid-state secondary battery as described above, the dispersibility and storage stability are excellent, and a solid electrolyte-containing layer having excellent ionic conductivity can be formed.

[0040] In addition, an object of the present invention is to advantageously solve the above problems, and [8] the present invention provides a solid electrolyte-containing layer formed by using the slurry composition for an all-solid-state secondary battery described in [7] above.

[0041] The ionic conductivity of the solid electrolyte-containing layer as described above is excellent.

[0042] In addition, an object of the present invention is to advantageously solve the above problems, and [9] the present invention provides an all-solid-state secondary battery having the solid electrolyte-containing layer described in [8] above.

[0043] In the case of the all-solid-state secondary battery as described above, battery performances such as output characteristics are excellent.

[0044] Advantages of the Invention

[0045] According to the present invention, it is possible to provide a binder composition for an all-solid-state secondary battery, which can impart excellent dispersibility and storage stability to a slurry composition for an all-solid-state secondary battery using a sulfide-based inorganic solid electrolyte as a solid electrolyte, and can cause a solid electrolyte-containing layer formed by using the slurry composition for an all-solid-state secondary battery to exhibit excellent ionic conductivity.

[0046] In addition, according to the present invention, it is possible to provide a slurry composition for an all-solid-state secondary battery, which has excellent dispersibility and storage stability, and can form a solid electrolyte-containing layer having excellent ionic conductivity.

[0047] Furthermore, according to the present invention, it is possible to provide a solid electrolyte-containing layer having excellent ionic conductivity and an all-solid-state secondary battery having the solid electrolyte-containing layer. Detailed Description of Embodiments

[0048] Hereinafter, embodiments of the present invention will be described in detail.

[0049] The binder composition for all-solid-state secondary batteries of the present invention (hereinafter sometimes simply referred to as "binder composition") is used to prepare a slurry composition for all-solid-state secondary batteries (hereinafter sometimes simply referred to as "slurry composition") using a sulfide-based inorganic solid electrolyte as a solid electrolyte. Here, the slurry composition for all-solid-state secondary batteries of the present invention is used when forming an electrode composite layer (positive electrode composite layer, negative electrode composite layer), a solid electrolyte layer, etc. containing a solid electrolyte layer such as in all-solid-state secondary batteries such as all-solid-state lithium-ion secondary batteries. In addition, the solid electrolyte layer-containing layer of the present invention is formed using the slurry composition for all-solid-state secondary batteries of the present invention. Furthermore, the all-solid-state secondary battery of the present invention has the solid electrolyte layer-containing layer of the present invention.

[0050] (Binder composition for all-solid-state secondary batteries)

[0051] The binder composition for all-solid-state secondary batteries of the present invention contains a polymer containing (meth)acrylic acid alkyl ester monomer units (hereinafter sometimes simply referred to as "polymer") and an acetate solvent in which a hydrocarbon group having 6 or more and 9 or less carbon atoms is bonded to a non-carbonyl oxygen atom (hereinafter sometimes simply referred to as "acetate solvent"), and can optionally further contain other components. Moreover, in the binder composition of the present invention, the above-mentioned (meth)acrylic acid alkyl ester monomer units include a first (meth)acrylic acid alkyl ester monomer unit in which an alkyl group having 3 or more and 8 or less carbon atoms is bonded to a non-carbonyl oxygen atom and a second (meth)acrylic acid alkyl ester monomer unit in which an alkyl group having 1 or more and 2 or less carbon atoms is bonded to a non-carbonyl oxygen atom, and the mass ratio of the first (meth)acrylic acid alkyl ester monomer unit to the second (meth)acrylic acid alkyl ester monomer unit is 2.1 or more and 2.5 or less. In addition, the binder composition of the present invention generally does not contain solid electrolytes such as sulfide-based inorganic solid electrolytes and electrode active materials.

[0052] If it is a binder composition as described above, excellent dispersibility and storage stability can be imparted to the slurry composition using a sulfide-based inorganic solid electrolyte as a solid electrolyte. The reason for this is presumably that the polymer (especially each alkyl group of the first (meth)acrylic acid alkyl ester monomer unit and the second (meth)acrylic acid alkyl ester monomer unit), the acetate solvent, and the surface of the sulfide-based inorganic solid electrolyte interact with each other.

[0053] In addition, in the case of the binder composition as described above, an ion-conductive solid electrolyte layer formed using a slurry composition containing the binder composition can exhibit excellent ion conductivity. It is presumably because, by incorporating a first (meth)acrylic acid alkyl ester monomer unit and a second (meth)acrylic acid alkyl ester monomer unit in a mass ratio (first (meth)acrylic acid alkyl ester monomer unit / second (meth)acrylic acid alkyl ester monomer unit) of 2.1 or more and 2.5 or less, the polymer is appropriately dissolved in the acetate solvent. In the formed ion-conductive solid electrolyte layer, the balance between the portion of the surface of the sulfide-based inorganic solid electrolyte covered by the polymer and the portion of the surface of the sulfide-based inorganic solid electrolyte exposed becomes good. As a result, while maintaining the binding performance of the polymer, the conductivity of the surface of the sulfide-based inorganic solid electrolyte is also well maintained.

[0054] <Polymer>

[0055] The polymer is a component that can bind components such as a sulfide-based inorganic solid electrolyte to each other in an ion-conductive solid electrolyte layer formed from a slurry composition containing the binder composition, and the polymer contains a specified (meth)acrylic acid alkyl ester monomer unit described later. In addition to the (meth)acrylic acid alkyl ester monomer unit, the polymer may optionally contain a cyanovinyl monomer unit, an aromatic monomer unit, or other repeating units.

[0056] [(Meth)acrylic acid alkyl ester monomer unit]

[0057] (The (meth)acrylic acid alkyl ester monomer unit includes a first (meth)acrylic acid alkyl ester monomer unit in which an alkyl group having 3 or more and 8 or less carbon atoms is bonded to a non-carbonyl oxygen atom and a second (meth)acrylic acid alkyl ester monomer unit in which an alkyl group having 1 or more and 2 or less carbon atoms is bonded to a non-carbonyl oxygen atom, and may optionally include a (meth)acrylic acid alkyl ester monomer unit other than the first (meth)acrylic acid alkyl ester monomer unit and the second (meth)acrylic acid alkyl ester monomer unit (hereinafter sometimes referred to as "other (meth)acrylic acid alkyl ester monomer unit"). Here, as the other (meth)acrylic acid alkyl ester monomer unit, for example, a (meth)acrylic acid alkyl ester monomer unit in which an alkyl group having 9 or more carbon atoms is bonded to a non-carbonyl oxygen atom can be cited.

[0058] The alkyl group having 3 or more and 8 or less carbon atoms bonded to the non-carbonyl oxygen atom of the first (meth)acrylic acid alkyl ester monomer unit may be a linear alkyl group such as a n-butyl group or a 2-ethylhexyl group, or a cyclic alkyl group such as a cyclohexyl group. From the viewpoint of improving the dispersibility and storage stability of the slurry composition and the ion conductivity of the ion-conductive solid electrolyte layer, a linear alkyl group is preferred.

[0059] In addition, in the present specification, "chain alkyl" means an alkyl group without a cyclic structure, and "cyclic alkyl" means an alkyl group having a cyclic structure in at least a part thereof.

[0060] Examples of the first (meth)acrylic acid alkyl ester monomer capable of forming the first (meth)acrylic acid alkyl ester monomer unit include, for example: acrylic acid n-propyl ester, acrylic acid isopropyl ester, acrylic acid n-butyl ester, acrylic acid tert-butyl ester, acrylic acid pentyl ester, acrylic acid hexyl ester, acrylic acid heptyl ester, acrylic acid octyl ester, acrylic acid 2-ethylhexyl ester, acrylic acid cyclohexyl ester, etc., which are acrylic acid alkyl ester monomers in which an alkyl group having 3 or more and 8 or less carbon atoms is bonded to a non-carbonyl oxygen atom; methyl methacrylate n-propyl ester, methyl methacrylate isopropyl ester, methyl methacrylate n-butyl ester, methyl methacrylate tert-butyl ester, methyl methacrylate pentyl ester, methyl methacrylate hexyl ester, methyl methacrylate heptyl ester, methyl methacrylate octyl ester, methyl methacrylate 2-ethylhexyl ester, methyl methacrylate cyclohexyl ester, etc., which are methyl methacrylate alkyl ester monomers in which an alkyl group having 3 or more and 8 or less carbon atoms is bonded to a non-carbonyl oxygen atom, and the like. These may be used alone or in combination of two or more.

[0061] Among these, n-butyl acrylate, 2-ethylhexyl acrylate, n-butyl methacrylate, and 2-ethylhexyl methacrylate are preferred, and n-butyl acrylate and 2-ethylhexyl acrylate are more preferred. That is, the first (meth)acrylic acid alkyl ester monomer unit is preferably at least one monomer unit selected from a n-butyl acrylate unit, a 2-ethylhexyl acrylate unit, a n-butyl methacrylate unit, and a 2-ethylhexyl methacrylate unit, and more preferably at least any one monomer unit of a n-butyl acrylate unit and a 2-ethylhexyl acrylate unit.

[0062] Examples of the second (meth)acrylic acid alkyl ester monomer capable of forming the second (meth)acrylic acid alkyl ester monomer unit include methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate. These may be used alone or in combination of two or more.

[0063] Among these, methyl acrylate and ethyl acrylate are preferred, and ethyl acrylate is more preferred. That is, the second (meth)acrylic acid alkyl ester monomer unit is preferably at least any one monomer unit of a methyl acrylate unit and an ethyl acrylate unit, and more preferably an ethyl acrylate unit.

[0064] Here, in the binder composition of the present invention, the mass ratio of the first (meth)acrylic acid alkyl ester monomer unit to the second (meth)acrylic acid alkyl ester monomer unit (first (meth)acrylic acid alkyl ester monomer unit / second (meth)acrylic acid alkyl ester monomer unit) is 2.1 or more and 2.5 or less.

[0065] Moreover, the mass ratio of the first (meth)acrylic acid alkyl ester monomer unit to the second (meth)acrylic acid alkyl ester monomer unit is preferably 2.2 or more and preferably 2.4 or less.

[0066] If the mass ratio of the first (meth)acrylic acid alkyl ester monomer unit to the second (meth)acrylic acid alkyl ester monomer unit is 2.2 or more, the solubility of the polymer in the acetate solvent can be effectively reduced, and in the formed solid electrolyte-containing layer, the proportion of the surface of the sulfide-based inorganic solid electrolyte covered by the polymer can be effectively reduced (that is, the proportion of the surface of the sulfide-based inorganic solid electrolyte exposed can be effectively increased). As a result, the ionic conductivity of the solid electrolyte-containing layer can be improved.

[0067] On the other hand, if the mass ratio of the first (meth)acrylic acid alkyl ester monomer unit to the second (meth)acrylic acid alkyl ester monomer unit is 2.4 or less, the solubility of the polymer in the acetate solvent can be effectively increased, and as a result, the storage stability of the slurry composition can be improved.

[0068] When the total of all repeating units (the sum of monomer units and structural units; the same applies hereinafter) constituting the polymer is 100% by mass, the total content ratio of the first (meth)acrylic acid alkyl ester monomer unit and the second (meth)acrylic acid alkyl ester monomer unit is preferably 50% by mass or more, more preferably 55% by mass or more, further preferably 60% by mass or more, preferably 85% by mass or less, more preferably 82.5% by mass or less, and further preferably 80% by mass or less.

[0069] If the total content ratio of the first (meth)acrylic acid alkyl ester monomer unit and the second (meth)acrylic acid alkyl ester monomer unit is at least the above lower limit, the solubility of the polymer in the acetate solvent can be effectively increased, and as a result, the storage stability of the slurry composition can be improved.

[0070] On the other hand, if the total content ratio of the first (meth)acrylic acid alkyl ester monomer unit and the second (meth)acrylic acid alkyl ester monomer unit is at most the above upper limit, the solubility of the polymer in the acetate solvent can be effectively reduced, and in the formed solid electrolyte-containing layer, the proportion of the surface of the sulfide-based inorganic solid electrolyte covered by the polymer can be effectively reduced (that is, the proportion of the surface of the sulfide-based inorganic solid electrolyte exposed can be effectively increased). As a result, the ionic conductivity of the solid electrolyte-containing layer can be improved.

[0071] When the total repeating units constituting the polymer are 100% by mass, the content ratio of the first (meth)acrylic acid alkyl ester monomer unit is preferably 40% by mass or more, more preferably 42.5% by mass or more, still more preferably 45% by mass or more, preferably 58% by mass or less, more preferably 56.5% by mass or less, and still more preferably 55% by mass or less.

[0072] If the content ratio of the first (meth)acrylic acid alkyl ester monomer unit is at least the above lower limit, the solubility of the polymer in the acetate solvent can be effectively reduced, and in the formed solid electrolyte-containing layer, the proportion of the surface of the sulfide-based inorganic solid electrolyte covered by the polymer can be effectively reduced (i.e., the proportion of the surface of the sulfide-based inorganic solid electrolyte exposed can be effectively increased). As a result, the ionic conductivity of the solid electrolyte-containing layer can be improved.

[0073] On the other hand, if the content ratio of the first (meth)acrylic acid alkyl ester monomer unit is at most the above upper limit, the content ratio of the second (meth)acrylic acid alkyl ester monomer unit relatively increases, and the solubility of the polymer in the acetate solvent can be effectively increased. As a result, the storage stability of the slurry composition can be improved.

[0074] When the total repeating units constituting the polymer are 100% by mass, the content ratio of the second (meth)acrylic acid alkyl ester monomer unit is preferably 10% by mass or more, more preferably 12.5% by mass or more, still more preferably 15% by mass or more, preferably 27% by mass or less, more preferably 26% by mass or less, and still more preferably 25% by mass or less.

[0075] If the content ratio of the second (meth)acrylic acid alkyl ester monomer unit is at least the above lower limit, the solubility of the polymer in the acetate solvent can be effectively increased. As a result, the storage stability of the slurry composition can be improved.

[0076] On the other hand, if the content ratio of the second (meth)acrylic acid alkyl ester monomer unit is at most the above upper limit, the content ratio of the first (meth)acrylic acid alkyl ester monomer unit relatively increases, and the solubility of the polymer in the acetate solvent can be effectively reduced. In the formed solid electrolyte-containing layer, the proportion of the surface of the sulfide-based inorganic solid electrolyte covered by the polymer can be effectively reduced (i.e., the proportion of the surface of the sulfide-based inorganic solid electrolyte exposed can be effectively increased). As a result, the ionic conductivity of the solid electrolyte-containing layer can be improved.

[0077] Examples of other (meth)acrylic acid alkyl ester monomers capable of forming other (meth)acrylic acid alkyl ester monomer units include, for example: acrylic acid nonyl ester, acrylic acid decyl ester, acrylic acid lauryl ester, acrylic acid n-tetradecyl ester, acrylic acid stearyl ester, etc., which are acrylic acid alkyl ester monomers in which an alkyl group having 9 or more carbon atoms is bonded to a non-carbonyl oxygen atom; methacrylic acid nonyl ester, methacrylic acid decyl ester, methacrylic acid lauryl ester, methacrylic acid tridecyl ester, methacrylic acid n-tetradecyl ester, methacrylic acid stearyl ester, etc., which are methacrylic acid alkyl ester monomers in which an alkyl group having 9 or more carbon atoms is bonded to a non-carbonyl oxygen atom, and the like.

[0078] These can be used alone or in combination of two or more.

[0079] When the total repeating units constituting the polymer are 100% by mass, the content ratio of other (meth)acrylic acid alkyl ester monomer units is preferably 5% by mass or less, more preferably 3% by mass or less, still more preferably 1% by mass or less, and particularly preferably 0% by mass or less, that is, it is particularly preferred that the polymer does not contain other (meth)acrylic acid alkyl ester monomer units.

[0080] [Vinyl cyanide monomer unit]

[0081] The polymer preferably further contains a vinyl cyanide monomer unit.

[0082] If the polymer further contains a vinyl cyanide monomer unit, it is possible to impart more excellent dispersibility and storage stability to the slurry composition using a sulfide-based inorganic solid electrolyte as the solid electrolyte, and to make the solid electrolyte layer formed using this slurry composition exhibit more excellent ion conductivity. The reason for these is presumably that the surface of the sulfide-based inorganic solid electrolyte interacts with the cyano group of the vinyl cyanide monomer unit of the polymer.

[0083] Examples of vinyl cyanide monomers capable of forming vinyl cyanide monomer units include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, etc. These can be used alone or in combination of two or more.

[0084] Moreover, among these, acrylonitrile and methacrylonitrile are preferred, and acrylonitrile is more preferred. That is, the vinyl cyanide monomer unit preferably contains at least one of an acrylonitrile unit and a methacrylonitrile unit, and more preferably an acrylonitrile unit.

[0085] When the total repeating units constituting the polymer are 100% by mass, the content ratio of the vinyl cyanide monomer unit is preferably 3% by mass or more, more preferably 3.5% by mass or more, still more preferably 4% by mass or more, preferably less than 7% by mass, more preferably 6.5% by mass or less, and still more preferably 6% by mass or less.

[0086] If the content ratio of the cyanated vinyl monomer unit is at least the above lower limit, the solid electrolyte can be well dispersed, and as a result, the dispersibility and storage stability of the slurry composition, and the ionic conductivity of the layer containing the solid electrolyte can be improved. In addition, even if the content ratio of the cyanated vinyl monomer unit is less than the above upper limit, the solubility of the polymer in the acetate solvent will not be excessively reduced, and the dispersing effect of the solid electrolyte possessed by the polymer will be ensured, and as a result, the dispersibility and storage stability of the slurry composition, and the ionic conductivity of the layer containing the solid electrolyte can be improved.

[0087] [Aromatic monomer unit]

[0088] The polymer preferably further contains an aromatic monomer unit.

[0089] If the polymer further contains an aromatic monomer unit, the strength of the polymer can be ensured, and excellent shape stability can be imparted to the layer containing the solid electrolyte.

[0090] As the aromatic monomer capable of forming the aromatic monomer unit, there is no particular limitation as long as it has an aromatic ring. Examples of the aromatic monomer include aromatic vinyl monomers and (meth)acrylate monomers having an aromatic hydrocarbon ring.

[0091] In addition, in the present specification, the aromatic vinyl monomers do not include monomers belonging to the (meth)acrylate monomers having an aromatic hydrocarbon ring (in other words, the aromatic vinyl monomer units do not include (meth)acrylate monomer units having an aromatic hydrocarbon ring).

[0092] Examples of the aromatic vinyl monomer include styrene, styrenesulfonic acid and its salts, α-methylstyrene, p-tert-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, vinylnaphthalene and the like.

[0093] There is no particular limitation on the aromatic hydrocarbon ring contained in the (meth)acrylate monomer unit having an aromatic hydrocarbon ring, and examples thereof include a benzene ring, a naphthalene ring, an anthracene ring and the like. Among these, a benzene ring is preferred. In addition, the monomer unit may have one aromatic hydrocarbon ring or two or more aromatic hydrocarbon rings.

[0094] Examples of the (meth)acrylate monomer having an aromatic hydrocarbon ring include phenoxyethyl (meth)acrylate, phenyl (meth)acrylate, ethoxylated o-phenylphenol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate and the like.

[0095] In addition, in the present specification, “(meth)acrylate” means acrylate and / or methacrylate.

[0096] The above aromatic monomers may be used alone or in combination of two or more. Among these, from the viewpoint of improving the interaction between the polymer and the sulfide-based inorganic solid electrolyte and further enhancing the dispersibility and storage stability of the slurry composition, styrene and phenoxyethyl acrylate are preferred, and styrene is more preferred. That is, the aromatic monomer unit is preferably at least one of a styrene unit and a phenoxyethyl acrylate unit, and more preferably a styrene unit.

[0097] When the total repeating units constituting the polymer are 100% by mass, the content ratio of the aromatic monomer unit is preferably 10% by mass or more, more preferably 12.5% by mass or more, still more preferably 15% by mass or more, preferably 30% by mass or less, more preferably 27.5% by mass or less, and still more preferably 25% by mass or less.

[0098] If the content ratio of the aromatic monomer unit is at least the above lower limit, the strength of the polymer can be increased and the shape stability of the solid electrolyte layer-containing layer can be improved.

[0099] On the other hand, if the content ratio of the aromatic monomer unit is at most the above upper limit, the flexibility of the polymer can be increased and the adhesiveness of the solid electrolyte layer-containing layer can be improved.

[0100] [Other repeating units]

[0101] In the present specification, other repeating units refer to monomer units other than the above (meth)acrylic acid alkyl ester monomer units, vinyl cyanide monomer units, and aromatic monomer units.

[0102] Examples of other repeating units include aliphatic conjugated diene monomer units, alkylene structural units, (meth)acrylate monomer units (excluding the above (meth)acrylic acid alkyl ester monomer units and (meth)acrylate monomer units having an aromatic hydrocarbon ring), and the like.

[0103] Examples of aliphatic conjugated diene monomers capable of forming aliphatic conjugated diene monomer units include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and the like.

[0104] The alkylene structural unit is a repeating unit composed only of an alkylene structure represented by the general formula: -C n H 2n -[wherein, n is an integer of 2 or more]. The alkylene structural unit may be linear or branched, but the alkylene structural unit is preferably linear, that is, a linear alkylene structural unit. Moreover, as a method for introducing an alkylene structural unit into the polymer, there is no particular limitation, and examples thereof include the following methods (1) or (2):

[0105] (1) A method of polymerizing a monomer composition containing an aliphatic conjugated diene monomer and hydrogenating the resulting polymer, thereby converting the aliphatic conjugated diene monomer unit into an alkylene structural unit;

[0106] (2) A method of polymerizing a monomer composition containing a 1-alkene monomer to prepare a polymer.

[0107] In addition, as the aliphatic conjugated diene monomer used in the method (1) above, the aliphatic conjugated diene monomers listed above as the aliphatic conjugated diene monomers capable of forming aliphatic conjugated diene monomer units can be cited. Moreover, the selective hydrogenation of the aliphatic conjugated diene monomer unit can be carried out using known methods such as the oil layer hydrogenation method and the water layer hydrogenation method.

[0108] In addition, as the 1-alkene monomer in the method (2) above, for example, ethylene, propylene, 1-butene, 1-hexene, etc. can be cited.

[0109] These aliphatic conjugated diene monomers and 1-alkene monomers can be used alone or in combination of two or more.

[0110] As the (meth)acrylate monomer capable of forming a (meth)acrylate monomer unit (excluding the above-mentioned (meth)acrylic acid alkyl ester monomer and the (meth)acrylate monomer having an aromatic hydrocarbon ring), the following can be cited: alkoxy acrylates such as 2-methoxyethyl acrylate and 2-ethoxyethyl acrylate; 2-(perfluoroalkyl)ethyl acrylates such as 2-(perfluorobutyl)ethyl acrylate and 2-(perfluoropentyl)ethyl acrylate; alkoxy methacrylates such as 2-methoxyethyl methacrylate and 2-ethoxyethyl methacrylate; 2-(perfluoroalkyl)ethyl methacrylates such as 2-(perfluorobutyl)ethyl methacrylate and 2-(perfluoropentyl)ethyl methacrylate, etc.

[0111] When the total repeating units constituting the polymer are 100% by mass, the content ratio of other repeating units is preferably 5% by mass or less, more preferably 3% by mass or less, further preferably 1% by mass or less, and particularly preferably 0% by mass or less, that is, it is particularly preferred that the polymer does not contain other repeating units.

[0112] [Weight-average molecular weight of the polymer]

[0113] The weight-average molecular weight of the polymer is preferably 800,000 or more, more preferably 850,000 or more, further preferably 900,000 or more, preferably 1,500,000 or less, more preferably 1,400,000 or less, and further preferably 1,300,000 or less.

[0114] If the weight-average molecular weight of the polymer is above the above lower limit, the storage stability of the slurry composition can be improved.

[0115] On the other hand, if the weight-average molecular weight of the polymer is below the above upper limit, the dispersibility of the slurry composition can be improved.

[0116] [Method for preparing polymer]

[0117] The method for preparing the polymer is not particularly limited, and it can be prepared by polymerizing a monomer composition containing the above monomers. In addition, after polymerizing the monomer composition, the obtained polymer can be optionally hydrogenated (hydrogenated).

[0118] The polymerization method is not particularly limited, and any one of solution polymerization method, suspension polymerization method, bulk polymerization method, emulsion polymerization method, etc. can be used. In each polymerization method, known emulsifiers (such as sodium lauryl sulfate, etc.) and polymerization initiators (such as ammonium persulfate, etc.) can be used as needed. In addition, as the polymerization reaction, any one of ionic polymerization, radical polymerization, living radical polymerization, etc. can be used.

[0119] The method for hydrogenation is not particularly limited, and a usual method using a catalyst can be used (for example, refer to International Publication No. 2012 / 165120, International Publication No. 2013 / 080989, and Japanese Patent Laid-Open No. 2013-8485).

[0120] [Content ratio of polymer]

[0121] The content ratio of the polymer in the binder composition is preferably 2% by mass or more, more preferably 5% by mass or more, preferably 20% by mass or less, and more preferably 15% by mass or less based on all components (including the solvent) in the binder composition.

[0122] <Acetate solvent>

[0123] Examples of the hydrocarbon group having 6 to 9 carbon atoms bonded to the non-carbonyl oxygen atom as the acetate solvent include aliphatic hydrocarbon groups such as alkyl groups, alkenyl groups, and alkynyl groups; aromatic hydrocarbon groups such as aryl groups, etc. Among these, aliphatic hydrocarbon groups are preferred, and alkyl groups are more preferred.

[0124] Hereinafter, an acetate solvent in which the hydrocarbon group having 6 to 9 carbon atoms bonded to the non-carbonyl oxygen atom is an alkyl group will be described, but the acetate solvent used in the binder composition of the present invention is not limited thereto.

[0125] Examples of the acetate solvent in which the carbon atom bonded to the non-carbonyl oxygen atom is a hydrocarbon group having 6 to 9 carbon atoms and is an alkyl group include acetate solvents in which a linear alkyl group is bonded, such as n-hexyl acetate (number of carbon atoms: 6), n-heptyl acetate (number of carbon atoms: 7), n-octyl acetate (number of carbon atoms: 8), and n-nonyl acetate (number of carbon atoms: 9); acetate solvents in which a branched alkyl group is bonded, such as 2-ethylbutyl acetate (number of carbon atoms: 6), 3-methylpentyl acetate (number of carbon atoms: 6), and 2-ethylhexyl acetate (number of carbon atoms: 8); and acetate solvents in which a cycloalkyl group is bonded, such as cyclohexyl acetate (number of carbon atoms: 6) and methylcyclohexyl acetate (number of carbon atoms: 7). In addition, the number of carbon atoms in parentheses refers to the number of carbon atoms of the alkyl group bonded to the non-carbonyl oxygen atom.

[0126] These can be used alone or in combination of two or more. Among these, from the aspects of improving the dispersibility and storage stability of the slurry composition and the ionic conductivity of the solid electrolyte layer-containing layer, acetate solvents in which a linear alkyl group is bonded and acetate solvents in which a branched alkyl group is bonded are preferred. In addition, from the aspect of further improving the dispersibility and storage stability of the slurry composition, acetate solvents in which a linear alkyl group is bonded are more preferred, and n-heptyl acetate and n-octyl acetate are further preferred.

[0127] In addition, in this specification, "linear alkyl group" refers to a linear alkyl group without a branched chain in the above-mentioned "chain-like alkyl group". "Branched alkyl group" refers to an alkyl group having a branched chain in the above-mentioned "chain-like alkyl group". "Cycloalkyl group" refers to an alkyl group having a cyclic structure in at least a part as described above.

[0128] <Other Components>

[0129] As other components that the binder composition can optionally contain, there is no particular limitation as long as the object of the present invention is not impaired, and examples include binder materials other than the above-mentioned polymers, solvents other than the above-mentioned acetate solvents, dispersants, leveling agents, antifoaming agents, reinforcing materials, and the like.

[0130] In addition, from the viewpoints of improving the dispersibility and storage stability of the slurry composition and the ionic conductivity of the solid electrolyte layer-containing layer, the binder composition of the present invention preferably does not contain a binder material other than the above-mentioned polymer and a solvent other than the above-mentioned acetate solvent.

[0131] <Preparation Method of Binder Composition>

[0132] As the preparation method of the binder composition of the present invention, there is no particular limitation, and examples include a method of mixing the above-mentioned polymer and any other components in an acetate solvent.

[0133] (Slurry Composition for All-Solid-State Secondary Battery)

[0134] The slurry composition for an all-solid-state secondary battery of the present invention contains at least the binder composition of the present invention described above and a sulfide-based inorganic solid electrolyte. More specifically, the slurry composition of the present invention contains the above polymer, the above acetate solvent, and a sulfide-based inorganic solid electrolyte, and may optionally further contain at least one selected from an electrode active material (a positive electrode active material or a negative electrode active material), a conductive material, and other components. Here, the acetate solvent contained in the slurry composition may all be the solvent from the binder composition, or may be a newly added solvent to the slurry composition that is different from the acetate solvent from the binder composition. In addition, other components that can be contained in the slurry composition may all be components from the binder composition, or may be newly added components to the slurry composition that are different from other components from the binder composition.

[0135] Moreover, since the slurry composition of the present invention contains the binder composition of the present invention, a solid electrolyte-containing layer excellent in dispersibility, storage stability, and ion conductivity can be formed.

[0136] In addition, in the present specification, the slurry composition for an all-solid-state secondary battery containing at least the above polymer, the above acetate solvent, a sulfide-based inorganic solid electrolyte, and a positive electrode active material is sometimes referred to as a slurry composition for a positive electrode of an all-solid-state secondary battery.

[0137] Furthermore, in the present specification, the slurry composition for an all-solid-state secondary battery containing at least the above polymer, the above acetate solvent, a sulfide-based inorganic solid electrolyte, and a negative electrode active material is sometimes referred to as a slurry composition for a negative electrode of an all-solid-state secondary battery.

[0138] Furthermore, in the present specification, the slurry composition for an all-solid-state secondary battery containing at least the above polymer, the above acetate solvent, and a sulfide-based inorganic solid electrolyte but not containing an electrode active material is sometimes referred to as a slurry composition for an electrolyte layer of an all-solid-state secondary battery.

[0139] <Polymer>

[0140] As the polymer contained in the slurry composition of the present invention, the same polymers as those described in the "Polymer" item of the above "Binder Composition for an All-Solid-State Secondary Battery" can be cited.

[0141] Here, the amount of the polymer contained in the slurry composition of the present invention is not particularly limited, and is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, still more preferably 1 part by mass or more, preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and still more preferably 4 parts by mass or less with respect to 100 parts by mass of the sulfide-based inorganic solid electrolyte.

[0142] If the content of the polymer in the slurry composition is 0.1 part by mass or more with respect to 100 parts by mass of the sulfide-based inorganic solid electrolyte, the function as a binder can be fully exerted and the sulfide-based inorganic solid electrolyte can be well dispersed. Therefore, the dispersibility and storage stability of the slurry composition can be further improved, and the ionic conductivity of the solid electrolyte-containing layer can be further improved.

[0143] On the other hand, if the content of the polymer in the slurry composition is 10 parts by mass or less with respect to 100 parts by mass of the solid electrolyte, the ionic conductivity of the solid electrolyte-containing layer can be sufficiently ensured.

[0144] <Acetate solvent>

[0145] As the acetate solvent contained in the slurry composition of the present invention, the same acetate solvents as those described in the "acetate solvent" item of the above-mentioned "binder composition for all-solid-state secondary battery" can be cited.

[0146] <Sulfide-based inorganic solid electrolyte>

[0147] The sulfide-based inorganic solid electrolyte is not particularly limited as long as it is composed of inorganic solid particles having ionic conductivity and containing a sulfur atom.

[0148] In addition, within the scope not impairing the object of the present invention, the slurry composition of the present invention may also contain solid electrolytes other than the sulfide-based inorganic solid electrolyte (for example, oxide-based inorganic solid electrolytes, etc.). From the aspect of improving dispersibility, storage stability, and ionic conductivity of the solid electrolyte-containing layer, it is preferable to contain only the sulfide-based inorganic solid electrolyte as the solid electrolyte.

[0149] As the sulfide-based inorganic solid electrolyte, as long as it is the above-mentioned particles, there is no particular limitation, and a crystalline inorganic ion conductor, an amorphous inorganic ion conductor, or a mixture thereof can be used.

[0150] Moreover, in the case where the all-solid-state secondary battery is an all-solid-state lithium-ion secondary battery, for example, as the sulfide-based inorganic solid electrolyte, a crystalline inorganic lithium ion conductor, an amorphous inorganic lithium ion conductor, or a mixture thereof can generally be used.

[0151] In addition, hereinafter, as an example, the case where the slurry composition for an all-solid-state secondary battery is a slurry composition for an all-solid-state lithium-ion secondary battery will be described, but the present invention is not limited to the following example.

[0152] As the crystalline inorganic lithium ion conductor, for example, Thio-LISICON (Li 3.25 Ge0.25 P 0.75 S 4 )、 argyrodite type (e.g., Li 5.6 PS 4.4 Cl 1.8 ) etc.

[0153] As an amorphous inorganic lithium ion conductor, examples include glass Li-Si-S-O, Li-P-S, and an amorphous inorganic lithium ion conductor formed from a raw material composition using a sulfide containing Li 2 S and elements of Groups 13 to 15 of the periodic table, etc.

[0154] Here, as the elements of Groups 13 to 15, examples include Al, Si, Ge, P, As, Sb, etc. In addition, as sulfides of the elements of Groups 13 to 15, specifically, examples include Al 2 S 3 , SiS 2 , GeS 2 , P 2 S 3 , P 2 S 5 , As 2 S 3 , Sb 2 S 3 etc. Further, as a method for synthesizing an amorphous inorganic lithium ion conductor using a raw material composition, examples of amorphization methods include mechanical grinding method, melt quenching method, etc. Moreover, as an amorphous inorganic lithium ion conductor formed from a raw material composition using a sulfide containing Li 2 S and elements of Groups 13 to 15 of the periodic table, Li 2 S-P 2 S 5 , Li 2 S-SiS 2 , Li 2 S-GeS 2 or Li 2 S-Al 2 S 3 is preferred, and Li 2 S-P 2 S 5 is more preferred.

[0155] The above amorphous inorganic lithium ion conductors can be used alone or in combination of two or more.

[0156] Among the above, as a sulfide-based inorganic solid electrolyte for an all-solid-state lithium-ion secondary battery, from the viewpoint of forming a solid electrolyte layer with excellent ionic conductivity, an amorphous sulfide containing Li and P is preferred. The amorphous sulfide containing Li and P has high lithium-ion conductivity. Therefore, by using it as the sulfide-based inorganic solid electrolyte, the internal resistance of the battery can be reduced, and the output characteristics can be improved.

[0157] From the viewpoints of reducing the internal resistance of the battery and improving the output characteristics, the amorphous sulfide containing Li and P is more preferably a sulfide glass composed of Li 2 S and P 2 S 5 In particular, it is preferably a sulfide glass manufactured from a mixed raw material of Li 2 S∶P 2 S 5 with a molar ratio of 65∶35 to 85∶15 of Li 2 S to P 2 S 5 In addition, the amorphous sulfide containing Li and P is preferably a sulfide glass-ceramic obtained by reacting a mixed raw material of Li 2 S∶P 2 S 5 with a molar ratio of 65∶35 to 85∶15 of Li 2 S to P 2 S 5 by a mechanochemical method. Further, from the viewpoint of maintaining the lithium-ion conductivity at a high level, the mixed raw material preferably has a molar ratio of Li 2 S∶P 2 S 5 of 68∶32 to 80∶20.

[0158] In addition, within the extent that does not reduce the ionic conductivity, in addition to containing the above Li 2 S, P 2 S 5 the sulfide-based inorganic solid electrolyte may further contain at least one sulfide selected from Al 2 S 3 B 2 S 3 and SiS 2 as a starting material. If this sulfide is added, the glass component in the sulfide-based inorganic solid electrolyte can be stabilized.

[0159] Similarly, in addition to containing Li 2 S and P 2 S 5 the sulfide-based inorganic solid electrolyte may further contain at least one selected from Li 3 PO 4 Li4 SiO 4 、 Li 4 GeO 4 、 Li 3 BO 3 and Li 3 AlO 3 at least one lithium ortho - oxo acid. If the lithium ortho - oxo acid is included, it can stabilize the glass component in the sulfide - based inorganic solid electrolyte.

[0160] Here, in the slurry composition of the present invention, the sulfide - based inorganic solid electrolyte may exist in the form of a plurality of particles (sulfide - based inorganic solid electrolyte particles), or may exist in the form of an aggregate formed by coagulation of at least a part of the plurality of sulfide - based inorganic solid electrolyte particles. This aggregate is an aggregate containing at least the sulfide - based inorganic solid electrolyte and can optionally contain the above - mentioned polymer as a binder.

[0161] Here, the average primary particle diameter of the sulfide - based inorganic solid electrolyte (that is, the average particle diameter when the sulfide - based inorganic solid electrolyte particles exist separately) is preferably 0.1 μm or more, more preferably 0.2 μm or more, further preferably 0.5 μm or more, particularly preferably 1 μm or more, preferably 10 μm or less, more preferably 7 μm or less, further preferably 5 μm or less, and particularly preferably 3 μm or less.

[0162] If the average primary particle diameter of the sulfide - based inorganic solid electrolyte is 0.1 μm or more, the dispersibility and storage stability of the slurry composition can be further improved, and the ionic conductivity of the solid - electrolyte - containing layer can be further improved.

[0163] On the other hand, if the average primary particle diameter of the sulfide - based inorganic solid electrolyte is 10 μm or less, the ionic conductivity of the solid - electrolyte - containing layer can be further improved.

[0164] In this specification, the average primary particle diameter of the sulfide - based inorganic solid electrolyte can be obtained by the following method: Observe 100 sulfide - based inorganic solid electrolyte particles respectively with an electron microscope, measure the particle diameter according to JIS Z8827 - 1:2008, and calculate the arithmetic mean of these values.

[0165] <Electrode active material>

[0166] The electrode active material is a substance that transfers electrons in the electrode of the all - solid - state secondary battery. Moreover, in the case where the all - solid - state secondary battery is an all - solid - state lithium - ion secondary battery, for example, a substance that can store and release lithium is usually used as the electrode active material.

[0167] In addition, hereinafter, as an example, the case where the slurry composition is a slurry composition for an all-solid-state lithium-ion secondary battery will be described, but the present invention is not limited to the following single example.

[0168] The positive electrode active material for an all-solid-state lithium-ion secondary battery is not particularly limited, and examples thereof include a positive electrode active material composed of an inorganic compound and a positive electrode active material composed of an organic compound. In addition, the positive electrode active material may also be a mixture of an inorganic compound and an organic compound.

[0169] Examples of the positive electrode active material composed of an inorganic compound include, for example, transition metal oxides, composite oxides of lithium and transition metals (lithium-containing composite metal oxides), transition metal sulfides, etc. As the above-mentioned transition metals, Fe, Co, Ni, Mn, etc. can be used. Specific examples of the inorganic compound used in the positive electrode active material include: LiCoO 2 (lithium cobaltate), LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , LiFePO 4 , LiFeVO 4 , etc. lithium-containing composite metal oxides; TiS 2 , TiS 3 , amorphous MoS 2 , etc. transition metal sulfides; Cu 2 V 2 O 3 , amorphous V 2 O-P 2 O 5 , MoO 3 , V 2 O 5 , V 6 O 13 , etc. transition metal oxides, etc. These compounds may also be compounds in which part of the elements have been replaced.

[0170] The positive electrode active material composed of the above inorganic compound can be used alone or in combination of two or more.

[0171] Examples of the positive electrode active material composed of an organic compound include, for example, polyaniline, polypyrrole, polyacene, disulfide compounds, polysulfide compounds, N-fluoropyridinium salts, etc.

[0172] The above positive electrode active material composed of an organic compound can be used alone or in combination of two or more.

[0173] Examples of the negative electrode active material for the all-solid-state lithium ion secondary battery include allotropes of carbon such as graphite and coke. In addition, the negative electrode active material composed of allotropes of carbon can also be used in the form of a mixture or coating with metals, metal salts, oxides, etc. Further, as the negative electrode active material, the following can also be used: oxides or sulfates of silicon, tin, zinc, manganese, iron, nickel, etc.; metallic lithium; lithium alloys such as Li-Al, Li-Bi-Cd, and Li-Sn-Cd; lithium transition metal nitrides; silicone, etc.

[0174] The above negative electrode active materials can be used alone or in combination of two or more.

[0175] <Conductive material>

[0176] The conductive material is a material for ensuring electrical contact between electrode active materials in the electrode composite material layer formed using the slurry composition. Moreover, as the conductive material, the following can be used: carbon black (e.g., acetylene black, Ketjen black (registered trademark), furnace black, etc.), single-walled or multi-walled carbon nanotubes (the multi-walled carbon nanotubes include stacked cup type), carbon nanohorns, vapor-grown carbon fibers, ground carbon fibers obtained by sintering and then pulverizing polymer fibers, single-layer or multi-layer graphene, carbon non-woven fabric sheets obtained by sintering non-woven fabrics composed of polymer fibers, etc., which are conductive carbon materials; fibers or foils of various metals, etc.

[0177] These can be used alone or in combination of two or more.

[0178] In addition, the content of the conductive material in the slurry composition is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, preferably 5 parts by mass or less, and more preferably 3 parts by mass or less with respect to 100 parts by mass of the electrode active material. If the amount of the conductive material is within the above range, electrical contact between electrode active materials can be sufficiently ensured, and the all-solid-state secondary battery can exhibit excellent battery characteristics (output characteristics, etc.).

[0179] <Other components>

[0180] Examples of other components that can be included in the slurry composition of the present invention include the same components as those described in the item of "other components" of the "binder composition for all-solid-state secondary battery" above.

[0181] <Solid component concentration of the slurry composition>

[0182] The solid component concentration of the slurry composition is not particularly limited and can be, for example, 30 mass% or more and less than 70 mass%.

[0183] <Manufacturing method of the slurry composition>

[0184] The slurry composition of the present invention is not particularly limited and can be obtained by mixing the above components using any mixing method, for example.

[0185] In one embodiment, the slurry composition of the present invention can be appropriately obtained using, for example, the following manufacturing method, which includes the following steps: a step of preparing a premix (premixing step) by performing a mixing treatment on a composition containing a sulfide-based inorganic solid electrolyte and a binder composition (i.e., a sulfide-based inorganic solid electrolyte, a polymer, and an acetate solvent) and having a solid component concentration of 70% by mass or more; a step of further adding an acetate solvent to the premix having a solid component concentration of 70% by mass or more to obtain a diluent having a solid component concentration greater than 40% by mass and less than 70% by mass (first dilution step); a step of performing a kneading treatment on the diluent having a solid component concentration greater than 40% by mass and less than 70% by mass to prepare a kneaded product (kneading step); and a step of further adding an acetate solvent to the kneaded product for dilution (second dilution step).

[0186] In addition, the manufacturing method of the above slurry composition may also include steps other than the premixing step, the first dilution step, the kneading step, and the second dilution step.

[0187] Furthermore, in the manufacturing method of the above slurry composition, in addition to using a sulfide-based inorganic solid electrolyte, a polymer, and a solvent, an electrode active material, a conductive material, and other components can also be arbitrarily used. The electrode active material, the conductive material, and other components are not particularly limited. For example, they can be included in the premix by performing a mixing treatment together with the sulfide-based inorganic solid electrolyte, the polymer, and the solvent in the premixing step.

[0188] Hereinafter, the premixing step, the first dilution step, the kneading step, and the second dilution step will be described, but the slurry composition of the present invention is not limited to the slurry composition obtained by using a manufacturing method including these steps.

[0189] [Premixing Step]

[0190] In the premixing step, a composition (starting composition) containing at least a sulfide-based inorganic solid electrolyte and a binder composition, that is, at least a sulfide-based inorganic solid electrolyte, a polymer, and an acetate solvent, is mixed in a state where the solid component concentration is 70% by mass or more to prepare a premix having a solid component concentration of 70% by mass or more. By performing a mixing treatment on a composition having a solid component concentration of 70% by mass or more, the sulfide-based inorganic solid electrolyte can be well dispersed in the obtained slurry composition. In addition, the upper limit of the solid component concentration of the starting composition and the premix is not particularly limited and can be, for example, 90% by mass or less, respectively.

[0191] The mixing device used in the mixing process of the premixing process is not particularly limited, and known devices such as a rotary and revolution mixer can be used.

[0192] In addition, when obtaining the premix in the premixing process, the acetate solvent can be added to the mixing device all at once, continuously, or intermittently, and intermittent addition is more preferred. Moreover, in the premixing process, it is preferable to perform multiple mixing processes with different solid component concentrations of the mixing target by adding the acetate solvent. By gradually changing the solid component concentration of the composition to be mixed from a high solid component concentration state to a low solid component concentration state and performing the mixing process at each solid component concentration, the sulfide-based inorganic solid electrolyte can be well dispersed, and the dispersibility and storage stability of the slurry composition, as well as the ion conductivity of the solid electrolyte layer-containing, can be further improved.

[0193] The number of the above mixing processes is not particularly limited, preferably two or more times, more preferably three or more times. If the number of mixing processes is two or more times, the sulfide-based inorganic solid electrolyte can be further well dispersed, and the dispersibility and storage stability of the slurry composition, as well as the ion conductivity of the solid electrolyte layer-containing, can be further improved. On the other hand, the upper limit of the number of mixing processes is not particularly limited, and from the viewpoint of the production efficiency of the slurry composition, it is preferably eight or less times, more preferably seven or less times.

[0194] In addition, the conditions of the mixing process are not particularly limited. For example, the time of each mixing process can be in the range of 10 seconds or more and 10 minutes or less.

[0195] [First dilution process]

[0196] In the first dilution process, an acetate solvent is added to the premix obtained in the premixing process to obtain a diluent (first diluent) with a solid component concentration greater than 40% by mass and less than 70% by mass. The acetate solvent added in the first dilution process can be the same solvent as the acetate solvent used in the mixture preparation process or a different solvent, and the same solvent is preferred.

[0197] [Kneading process]

[0198] In the kneading step, the first diluent obtained in the first dilution step, having a solid component concentration greater than 40% by mass and less than 70% by mass, is kneaded to obtain a kneaded product. By kneading the first diluent with a solid component concentration within the above range, sufficient shear can be applied to the first diluent to be kneaded. Therefore, the sulfide-based inorganic solid electrolyte can be well dispersed, further improving the dispersibility and storage stability of the slurry composition, as well as the ionic conductivity of the solid electrolyte layer-containing material.

[0199] The kneading device used in the kneading treatment in the kneading step is not particularly limited as long as it can apply shear to the first diluent having a solid component concentration within the above range, and known devices can be used. Moreover, as the kneading device, for example, the mixing device used in the premixing step can be directly used.

[0200] In addition, in the kneading step, it is preferable to perform multiple kneading treatments with different solid component concentrations of the kneading object by adding an acetate solvent. By changing the solid component concentration of the first diluent to be kneaded step by step from a high state to a low state and performing kneading treatment at each solid component concentration in this way, the sulfide-based inorganic solid electrolyte can be well dispersed, further improving the dispersibility and storage stability of the slurry composition, as well as the ionic conductivity of the solid electrolyte layer-containing material.

[0201] The number of times of the above kneading treatment is not particularly limited, preferably two or more times, more preferably three or more times. If the number of times of the kneading treatment is two or more times, the sulfide-based inorganic solid electrolyte can be further well dispersed, further improving the dispersibility and storage stability of the slurry composition, as well as the ionic conductivity of the solid electrolyte layer-containing material. On the other hand, the upper limit of the number of times of the kneading treatment is not particularly limited, and from the viewpoint of the production efficiency of the slurry composition, it is preferably five or less times, more preferably four or less times.

[0202] In addition, the conditions of the kneading treatment are not particularly limited. For example, the time of each kneading treatment can be in the range of 10 seconds or more and 10 minutes or less.

[0203] [Second Dilution Step]

[0204] In the second dilution step, an acetate solvent is added to the kneaded product obtained in the kneading step. The acetate solvent added in the second dilution step can be the same acetate solvent as that used in the premixing step and the first dilution step, or a different acetate solvent, and preferably the same acetate solvent.

[0205] In addition, the kneaded mixture (second diluent) to which an acetate solvent is added in the second dilution step can be directly made into a slurry composition, or can be made into a slurry composition through other steps such as further mixing treatment.

[0206] (including solid electrolyte layer)

[0207] The solid electrolyte layer-containing layer of the present invention is a layer containing a sulfide-based inorganic solid electrolyte. As the solid electrolyte layer-containing layer, for example, an electrode composite layer (positive electrode composite layer, negative electrode composite layer) that conducts electrons through an electrochemical reaction; a solid electrolyte layer provided between the mutually opposed positive electrode composite layer and negative electrode composite layer, etc. can be cited.

[0208] Moreover, the solid electrolyte layer-containing layer of the present invention is formed using the slurry composition of the present invention, and can be formed by, for example, coating the slurry composition on the surface of a suitable substrate to form a coating film and then drying the formed coating film. That is, the solid electrolyte layer-containing layer of the present invention is composed of the dried product of the above slurry composition, usually contains a sulfide-based inorganic solid electrolyte and a polymer, and can optionally further contain at least one selected from electrode active materials, conductive materials, and other components. In addition, each component contained in the solid electrolyte layer-containing layer is the component contained in the above slurry composition, and the content ratio of these components is usually equal to the content ratio in the above slurry composition.

[0209] Moreover, since the solid electrolyte layer-containing layer of the present invention is formed from the slurry composition of the present invention, it can exhibit excellent ion conductivity.

[0210] <Substrate>

[0211] Here, the substrate for coating the slurry composition is not limited. For example, a coating film of the slurry composition can be formed on the surface of a release substrate, and the coating film can be dried to form a solid electrolyte layer-containing layer, and the release substrate can be peeled off from the solid electrolyte layer-containing layer. In this way, the solid electrolyte layer-containing layer peeled off from the release substrate can also be used as a self-supporting film for forming battery components (such as electrodes, solid electrolyte layers, etc.) of an all-solid-state secondary battery.

[0212] However, from the viewpoint of improving the manufacturing efficiency of battery components by omitting the step of peeling off the solid electrolyte layer-containing layer, a current collector or an electrode is preferably used as the substrate. Specifically, when preparing an electrode composite layer, it is preferable to coat the slurry composition on a current collector as the substrate. In addition, when preparing a solid electrolyte layer, it is preferable to coat the slurry composition on an electrode (positive electrode or negative electrode).

[0213] [Current collector]

[0214] As the current collector, a material having conductivity and electrochemical durability can be used. Specifically, as the current collector, a current collector made of, for example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, etc. can be used. Among them, as the current collector used in the negative electrode, copper foil is particularly preferred. In addition, as the current collector used in the positive electrode, aluminum foil is particularly preferred. In addition, the above materials can be used alone or in combination of two or more in any ratio.

[0215] [Electrode]

[0216] As the electrode (positive electrode and negative electrode), there is no particular limitation, and an electrode in which an electrode composite material layer containing an electrode active material, a solid electrolyte, and an electrode binder is formed on the above current collector can be cited.

[0217] As the electrode active material, solid electrolyte, and electrode binder contained in the electrode composite material layer in the electrode, there is no particular limitation, and known ones can be used. Here, as the solid electrolyte contained in the electrode composite material layer in the electrode, as long as it is particles composed of a solid having ion conductivity, there is no particular limitation, and for example, the above-mentioned sulfide-based inorganic solid electrolyte, oxide-based inorganic solid electrolyte, etc. can be used.

[0218] In addition, the electrode composite material layer in the electrode may also belong to the solid electrolyte-containing layer of the present invention.

[0219] <Method for forming solid electrolyte-containing layer>

[0220] As a method for forming a solid electrolyte-containing layer on the above current collector, electrode, etc. substrates, the following methods can be cited.

[0221] 1) A method of applying the slurry composition of the present invention to the surface of the substrate (in the case of an electrode, the surface on the side of the electrode composite material layer, the same below), and then drying;

[0222] 2) A method of impregnating the substrate in the slurry composition of the present invention and then drying it; and

[0223] 3) A method of applying the slurry composition of the present invention to a release substrate, drying to produce a solid electrolyte-containing layer, and transferring the obtained solid electrolyte-containing layer to the surface of an electrode, etc.

[0224] Among these, the method of 1) above is particularly preferred because it is easy to control the layer thickness of the solid electrolyte-containing layer. The method of 1) above specifically includes: a step of applying the slurry composition to the substrate (coating step); and a step of drying the slurry composition applied to the substrate to form a solid electrolyte-containing layer (solid electrolyte-containing layer forming step).

[0225] [Coating Process]

[0226] In the coating process, as a method for coating the slurry composition on the substrate, there is no particular limitation, and examples thereof include a doctor blade method, a reverse roll coating method, a direct roll coating method, a gravure printing method, an extrusion method, a brush coating method, and the like.

[0227] [Solid-State Electrolyte Layer Formation Process]

[0228] In addition, in the solid-state electrolyte layer formation process, as a method for drying the slurry composition on the substrate, there is no particular limitation, and known methods can be used. As the drying method, examples include a drying method using warm air, hot air, or low-humidity air; a vacuum drying method; a drying method using irradiation with infrared rays, electron rays, or the like.

[0229] In addition, when the solid-state electrolyte layer is an electrode composite material layer, it is preferably subjected to a pressing treatment using a roll press or the like after drying. By performing the pressing treatment, the obtained electrode composite material layer can be further densified.

[0230] (Electrode)

[0231] The electrode formed by forming an electrode composite material layer on a current collector using the slurry composition for all-solid-state secondary batteries of the present invention has an electrode composite material layer containing a sulfide-based inorganic solid electrolyte, a polymer as a binder, and an electrode active material, and optionally further contains at least one selected from a conductive material and other components, and can exhibit excellent ionic conductivity.

[0232] (Solid-State Electrolyte Layer)

[0233] The solid-state electrolyte layer formed using the slurry composition for all-solid-state secondary batteries of the present invention contains a sulfide-based inorganic solid electrolyte and a polymer as a binder, and optionally further contains other components, and can exhibit excellent ionic conductivity. In addition, the solid-state electrolyte layer usually does not contain an electrode active material.

[0234] (All-Solid-State Secondary Battery)

[0235] The all-solid-state secondary battery of the present invention is characterized in that it generally has a positive electrode, a solid electrolyte layer, and a negative electrode, and at least one of the positive electrode composite material layer of the positive electrode, the negative electrode composite material layer of the negative electrode, and the solid electrolyte layer is the solid electrolyte layer-containing layer of the present invention. That is, the all-solid-state secondary battery of the present invention has at least one of the following components: a positive electrode having a positive electrode composite material layer formed using the all-solid-state secondary battery positive electrode paste composition as the paste composition for the all-solid-state secondary battery of the present invention; a negative electrode having a negative electrode composite material layer formed using the all-solid-state secondary battery negative electrode paste composition as the paste composition for the all-solid-state secondary battery of the present invention; and a solid electrolyte layer formed using the all-solid-state secondary battery electrolyte layer paste composition as the paste composition for the all-solid-state secondary battery of the present invention.

[0236] Moreover, since the all-solid-state secondary battery of the present invention has the solid electrolyte layer-containing layer of the present invention, battery performances such as output characteristics are excellent.

[0237] Here, the all-solid-state secondary battery electrode having an electrode composite material layer that does not belong to the solid electrolyte layer-containing layer of the present invention and can be used in the all-solid-state secondary battery of the present invention is not particularly limited, and any all-solid-state secondary battery electrode can be used.

[0238] In addition, the solid electrolyte layer that does not belong to the solid electrolyte layer-containing layer of the present invention and can be used in the all-solid-state secondary battery of the present invention is not particularly limited, and any solid electrolyte layer such as the solid electrolyte layer described in Japanese Unexamined Patent Application Publication No. 2012-243476, Japanese Unexamined Patent Application Publication No. 2013-143299, and Japanese Unexamined Patent Application Publication No. 2016-143614 can be used.

[0239] Moreover, the all-solid-state secondary battery of the present invention can be obtained by laminating the positive electrode and the negative electrode such that the positive electrode composite material layer of the positive electrode and the negative electrode composite material layer of the negative electrode face each other with the solid electrolyte layer interposed therebetween, optionally applying pressure to obtain a laminate, and then, depending on the battery shape, placing it in a battery container in its original state or after winding, folding, etc., and sealing it. Additionally, if necessary, overcurrent protection elements such as a porous metal mesh, a fuse, a PTC element, and a guide plate can be placed in the battery container to prevent an increase in the internal pressure of the battery and overcharge / discharge. The shape of the battery can be any one of coin type, button type, sheet type, cylindrical type, square type, flat type, etc.

[0240] Examples

[0241] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In addition, in the following description, "%" and "parts" indicating amounts are based on mass unless otherwise specified.

[0242] In addition, in a polymer produced by polymerizing a plurality of monomers, unless otherwise specified, the proportion of the monomer unit formed by polymerizing a certain monomer in the polymer generally coincides with the ratio (feed ratio) of the monomer in all the monomers used in the polymerization of the polymer.

[0243] Furthermore, in the examples and comparative examples, the weight-average molecular weight of the polymer, the dispersibility and storage stability of the slurry composition, and the ionic conductivity of the solid electrolyte layer-containing layer were measured and evaluated by the following methods.

[0244] <Weight-average molecular weight of polymer>

[0245] The weight-average molecular weight of the polymer was measured as follows: First, the binder composition prepared in each of the examples and comparative examples was dried and cured, and the dried polymer was dissolved in a 10 mM LiBr-DMF solution (dimethylformamide solution containing lithium bromide) to prepare a solution containing the polymer, and the prepared solution was analyzed by gel permeation chromatography (GPC) under the following measurement conditions.

[0246] · Separation column: Shodex KD-806M (manufactured by Showa Denko K.K.)

[0247] · Detector: Differential refractive index detector RID-10A (manufactured by Shimadzu Corporation)

[0248] · Flow rate of eluent: 0.3 mL / minute

[0249] · Column temperature: 40 °C

[0250] · Standard polymer: TSK standard polystyrene (manufactured by Tosoh Corporation)

[0251] <Dispersibility of slurry composition>

[0252] The viscosity of the slurry composition was measured by a Brookfield B-type viscometer at 60 rpm (25 °C) and evaluated according to the following criteria. The smaller the viscosity value, the more excellent the dispersibility of the slurry composition.

[0253] A: Less than 3000 mPa·s

[0254] B: 3000 mPa·s or more and less than 4000 mPa·s

[0255] C: 4000 mPa·s or more and less than 5000 mPa·s

[0256] D: 5000 mPa·s or more or non-dispersed (no fluidity)

[0257] <Storage stability of slurry composition>

[0258] The freshly prepared slurry composition of 1 g was dried on a hot plate at 130 °C for 1 hour to vaporize the solvent, and the initial solid content concentration (%) was measured.

[0259] In addition, the freshly prepared slurry composition was stored in a sealed state at 25 °C. After 1 week of storage, 1 g of the supernatant of the slurry composition was sampled, and the solid content concentration (%) after storage was measured in the same manner as the initial solid content concentration.

[0260] Then, the solid content concentration retention rate = solid content concentration after storage / initial solid content concentration × 100 (%) was calculated. The larger the solid content concentration retention rate, the smaller the precipitation degree of the solid content, and the more excellent the storage stability of the slurry composition.

[0261] A: The solid content concentration retention rate is 90% or more

[0262] B: The solid content concentration retention rate is 80% or more and less than 90%

[0263] C: The solid content concentration retention rate is 50% or more and less than 80%

[0264] D: The solid content concentration retention rate is less than 50%

[0265] <Ionic conductivity of the solid electrolyte layer>

[0266] The slurry composition was dried on a hot plate at 120 °C in a glove box (with a moisture content of 1 ppm or less), and the obtained powder was formed into a cylindrical shape with a diameter of 10 mm and a thickness of 1 mm as a measurement sample. The Li-ion conductivity (25 °C) of this measurement sample was measured by the alternating current impedance method and evaluated according to the following criteria. The larger the Li-ion conductivity, the better the conduction on the surface of the sulfide-based inorganic solid electrolyte is maintained, and the more excellent the ionic conductivity of the solid electrolyte layer prepared using this slurry composition can be exerted. In addition, a frequency response analyzer (manufactured by Solartron Analytical, product name "Solartron (registered trademark) 1260") was used in the measurement, and the measurement conditions were an applied voltage of 10 mV and a measurement frequency range of 0.01 MHz to 1 MHz.

[0267] A: The Li-ion conductivity is 1 mS / cm or more

[0268] B: The Li-ion conductivity is 0.5 mS / cm or more and less than 1 mS / cm

[0269] C: The Li-ion conductivity is 0.1 mS / cm or more and less than 0.5 mS / cm

[0270] D: The Li ion conductivity is less than 0.1 mS / cm

[0271] (Example 1)

[0272] <Preparation of the binder composition>

[0273] 90 parts of ion-exchanged water and 0.5 part of sodium lauryl sulfate as an emulsifier were added to a 1-L flask (reaction vessel) with a rubber stopper equipped with a stirrer. The gas phase was replaced with nitrogen, and the temperature was raised to 60°C. Then, 0.3 part of ammonium persulfate (APS) as a polymerization initiator was dissolved in 20.0 parts of ion-exchanged water and added.

[0274] On the other hand, 30 parts of ion-exchanged water, 0.5 part of sodium lauryl sulfate as an emulsifier, 15 parts of styrene as an aromatic monomer, 55 parts of n-butyl acrylate as a first (meth)acrylic acid alkyl ester monomer, 24.5 parts of ethyl acrylate as a second (meth)acrylic acid alkyl ester monomer, and 5.5 parts of acrylonitrile as a vinyl cyanide monomer were mixed in another container (emulsion container) to obtain a monomer composition. This monomer composition was continuously added to the above 1-L flask with a rubber stopper over 3 hours for polymerization. During the addition, the reaction was carried out at 60°C. After the addition was completed, the mixture was further stirred at 80°C for 2 hours to obtain an aqueous dispersion of the polymer.

[0275] Next, n-octyl acetate as an acetate solvent was appropriately added to the obtained aqueous dispersion of the polymer to obtain a mixture. Thereafter, vacuum distillation was carried out at 80°C to remove water and excess n-octyl acetate from the mixture, thereby obtaining a binder composition (solid content concentration: 10%). The weight-average molecular weight of the polymer was measured using the obtained binder composition. The results are shown in Table 1.

[0276] <Preparation of the slurry composition>

[0277] The slurry composition was prepared by multi-stage mixing and kneading as follows.

[0278] [Premixing step]

[0279] 100 parts of a sulfide glass composed of Li 2 S and P 2 S 5 constituting a sulfide-based inorganic solid electrolyte (Li 2 S / P 2 S 5= 70 mol% / 30 mol%, average primary particle size: 1.0 μm) and 2 parts (equivalent amount of solid content) of the above binder composition (mixing treatment 1). n-Octyl acetate was added to the mixed solution obtained in mixing treatment 1 to prepare a composition with a solid content concentration of 80%. This composition was mixed at 2000 rpm for 2 minutes using a rotary mixer (product name "Awatori Rentaro (registered trademark) ARE310", the same hereinafter) (mixing treatment 2). n-Octyl acetate was added to the mixed solution obtained in mixing treatment 2 to prepare a composition with a solid content concentration of 70%. This composition was mixed at 2000 rpm for 2 minutes using a rotary mixer (mixing treatment 3).

[0280] [First dilution step]

[0281] Next, n-Octyl acetate was added to the mixed solution (pre-mixture) with a solid content concentration of 70% obtained in mixing treatment 3 to prepare a composition (first diluent) with a solid content concentration of 65%.

[0282] [Kneading step]

[0283] Then, the first diluent with a solid content concentration of 65% obtained in the first dilution step was kneaded at 2000 rpm for 2 minutes using a rotary mixer (kneading treatment 1). n-Octyl acetate was added to the mixed solution obtained in kneading treatment 1 to prepare a composition with a solid content concentration of 60%. This composition was mixed at 2000 rpm for 2 minutes using a rotary mixer (kneading treatment 2). n-Octyl acetate was added to the mixed solution (solid content concentration 60%) obtained in kneading treatment 2 to prepare a composition with a solid content concentration of 55%. This composition was kneaded at 2000 rpm for 2 minutes using a rotary mixer (kneading treatment 3).

[0284] [Second dilution step]

[0285] Furthermore, n-Octyl acetate was added to the mixed solution (kneaded product) obtained in kneading treatment 3 to prepare a composition (second diluent) with a solid content concentration of 50%.

[0286] This composition was mixed at 2000 rpm for 2 minutes using a rotary mixer to prepare a slurry composition (solid content concentration 50%).

[0287] Then, the obtained slurry composition was used to evaluate dispersibility, storage stability, and ionic conductivity. The results are shown in Table 1.

[0288] (Example 2)

[0289] In the preparation of the binder composition and the preparation of the slurry composition, all of the n-octyl acetate was changed to n-heptyl acetate, and other than this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0290] (Example 3)

[0291] In the preparation of the binder composition, 55 parts of n-butyl acrylate as the first (meth)acrylic acid alkyl ester monomer was changed to 55 parts of 2-ethylhexyl acrylate, and other than this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0292] (Example 4)

[0293] In the preparation of the binder composition and the preparation of the slurry composition, all of the n-octyl acetate was changed to n-nonyl acetate, and other than this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0294] (Example 5)

[0295] In the preparation of the binder composition and the preparation of the slurry composition, all of the n-octyl acetate was changed to n-hexyl acetate, and other than this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0296] (Example 6)

[0297] In the preparation of the binder composition, the amount of styrene as the aromatic monomer was changed from 15 parts to 20 parts, the amount of n-butyl acrylate as the first (meth)acrylic acid alkyl ester monomer was changed from 55 parts to 53 parts, and the amount of ethyl acrylate as the second (meth)acrylic acid alkyl ester monomer was changed from 24.5 parts to 21.5 parts. Other than this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0298] (Example 7)

[0299] In the preparation of the binder composition, the amount of styrene as the aromatic monomer was changed from 15 parts to 22.5 parts, the amount of n-butyl acrylate as the first (meth)acrylic acid alkyl ester monomer was changed from 55 parts to 49 parts, and the amount of ethyl acrylate as the second (meth)acrylic acid alkyl ester monomer was changed from 24.5 parts to 23 parts. Other than this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0300] (Example 8)

[0301] In the preparation of the binder composition, the amount of styrene as the aromatic monomer was changed from 15 parts to 14 parts, and the amount of acrylonitrile as the vinyl cyanide monomer was changed from 5.5 parts to 6.5 parts. Except for this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0302] (Example 9)

[0303] In the preparation of the binder composition, the amount of styrene as the aromatic monomer was changed from 15 parts to 17 parts, and the amount of acrylonitrile as the vinyl cyanide monomer was changed from 5.5 parts to 3.5 parts. Except for this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0304] (Example 10)

[0305] In the preparation of the binder composition, the amount of ammonium persulfate (APS) as the polymerization initiator was changed from 0.3 parts to 0.35 parts. Except for this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0306] (Example 11)

[0307] In the preparation of the binder composition, the amount of ammonium persulfate (APS) as the polymerization initiator was changed from 0.3 parts to 0.2 parts. Except for this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0308] (Example 12)

[0309] In the preparation of the binder composition and the slurry composition, all of the n-octyl acetate was changed to 2-ethylhexyl acetate. Except for this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0310] (Comparative Example 1)

[0311] In the preparation of the binder composition and the slurry composition, all of the n-octyl acetate was changed to n-decyl acetate. Except for this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0312] (Comparative Example 2)

[0313] In the preparation of the binder composition and the slurry composition, all of the n-octyl acetate was changed to n-amyl acetate. Except for this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0314] (Comparative Example 3)

[0315] In the preparation of the binder composition, the amount of styrene as an aromatic monomer was changed from 15 parts to 26.5 parts, the amount of n-butyl acrylate as a first (meth)acrylic acid alkyl ester monomer was changed from 55 parts to 50 parts, and the amount of ethyl acrylate as a second (meth)acrylic acid alkyl ester monomer was changed from 24.5 parts to 18 parts. Other than this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0316] (Comparative Example 4)

[0317] In the preparation of the binder composition, the amount of styrene as an aromatic monomer was changed from 15 parts to 19.5 parts, the amount of n-butyl acrylate as a first (meth)acrylic acid alkyl ester monomer was changed from 55 parts to 50 parts, and the amount of ethyl acrylate as a second (meth)acrylic acid alkyl ester monomer was changed from 24.5 parts to 25 parts. Other than this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0318] (Comparative Example 5)

[0319] In the preparation of the binder composition and the slurry composition, all of the n-octyl acetate was changed to n-butyl butyrate (not an acetate solvent). Other than this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0320] In addition, in Table 1 shown below,

[0321] "BA" represents a n-butyl acrylate unit,

[0322] "2EHA" represents a 2-ethylhexyl acrylate unit,

[0323] "EA" represents an ethyl acrylate unit,

[0324] "AN" represents an acrylonitrile unit,

[0325] "ST" represents a styrene unit,

[0326] "Number of carbon atoms" represents the number of carbon atoms of an alkyl or hydrocarbon group bonded to a non-carbonyl oxygen atom,

[0327] "Mass ratio of the first to the second" represents the mass ratio of the first (meth)acrylic acid alkyl ester monomer unit to the second (meth)acrylic acid alkyl ester monomer unit,

[0328] "Total content ratio of the first and the second" represents the total content ratio of the first (meth)acrylic acid alkyl ester monomer unit and the second (meth)acrylic acid alkyl ester monomer unit.

[0329] [Table 1]

[0330]

[0331] As can be seen from Table 1, the binder composition of the example can impart excellent dispersibility and storage stability to the slurry composition using a sulfide-based inorganic solid electrolyte as the solid electrolyte, and can enable the solid electrolyte layer-containing layer formed using the slurry composition to exhibit excellent ionic conductivity.

[0332] Industrial availability

[0333] According to the present invention, it is possible to provide a binder composition for an all-solid-state secondary battery, which can impart excellent dispersibility and storage stability to a slurry composition for an all-solid-state secondary battery using a sulfide-based inorganic solid electrolyte as the solid electrolyte, and can enable the solid electrolyte layer-containing layer formed using the slurry composition for an all-solid-state secondary battery to exhibit excellent ionic conductivity.

[0334] Furthermore, according to the present invention, it is possible to provide a slurry composition for an all-solid-state secondary battery, which has excellent dispersibility and storage stability, and can form a solid electrolyte layer-containing layer having excellent ionic conductivity.

[0335] Furthermore, according to the present invention, it is possible to provide a solid electrolyte layer-containing layer having excellent ionic conductivity and an all-solid-state secondary battery having the solid electrolyte layer-containing layer.

Claims

1. A binder composition for an all-solid-state secondary battery, which is a binder composition for an all-solid-state secondary battery using a sulfide-based inorganic solid electrolyte, The binder composition for an all-solid-state secondary battery contains a polymer containing (meth)acrylic acid alkyl ester monomer units and an acetate solvent in which a hydrocarbon group having 6 or more and 9 or less carbon atoms is bonded to a non-carbonyl oxygen atom, The (meth)acrylic acid alkyl ester monomer units include a first (meth)acrylic acid alkyl ester monomer unit in which an alkyl group having 3 or more and 8 or less carbon atoms is bonded to a non-carbonyl oxygen atom and a second (meth)acrylic acid alkyl ester monomer unit in which an alkyl group having 1 or more and 2 or less carbon atoms is bonded to a non-carbonyl oxygen atom, The mass ratio of the first (meth)acrylic acid alkyl ester monomer unit to the second (meth)acrylic acid alkyl ester monomer unit is 2.1 or more and 2.5 or less.

2. The binder composition for an all-solid-state secondary battery according to claim 1, wherein, The polymer further contains a cyanated vinyl monomer unit.

3. The binder composition for an all-solid-state secondary battery according to claim 2, wherein, When the total repeating units constituting the polymer are 100% by mass, the content ratio of the cyanated vinyl monomer unit is 3% by mass or more and less than 7% by mass.

4. The binder composition for an all-solid-state secondary battery according to any one of claims 1 to 3, wherein, The weight-average molecular weight of the polymer is 800,000 or more and 1,500,000 or less.

5. The binder composition for an all-solid-state secondary battery according to any one of claims 1 to 4, wherein, The polymer further contains an aromatic monomer unit, When the total repeating units constituting the polymer are 100% by mass, the content ratio of the aromatic monomer unit is 10% by mass or more and 30% by mass or less.

6. The binder composition for an all-solid-state secondary battery according to any one of claims 1 to 5, wherein, When the total repeating units constituting the polymer are 100% by mass, the total content ratio of the first (meth)acrylic acid alkyl ester monomer unit and the second (meth)acrylic acid alkyl ester monomer unit is 50% by mass or more and 85% by mass or less.

7. A slurry composition for an all-solid-state secondary battery, which contains the binder composition for an all-solid-state secondary battery according to any one of claims 1 to 6 and a sulfide-based inorganic solid electrolyte.

8. A solid electrolyte-containing layer, which is formed using the slurry composition for an all-solid-state secondary battery according to claim 7.

9. An all-solid-state secondary battery, which has the solid electrolyte-containing layer according to claim 8.

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