Inorganic particle dispersed slurry, electrode sheet, electrolyte sheet, and lithium ion battery

Abstract

To provide: an inorganic particle dispersed slurry in which inorganic particle aggregation is not likely to occur even if the concentration of inorganic particles that contain LATP-based crystals is high; and an electrode sheet, an electrolyte sheet and a lithium ion battery that employ the inorganic particle dispersed slurry.SOLUTION: The inorganic particle dispersed slurry contains a solvent and inorganic particles that are present in the solvent in a dispersed state. The inorganic particles contain a lithium ion-conductive crystal which is represented by the general formula Li1+x+yM1xM22-xSiyP3-yO12 (where M1 represents one or both of an Al atom and a Ga atom, M2 represents one or both of a Ti atom and a Ge atom, and x and y are both numerical values within the range from 0 to 1 inclusive). The inorganic particles have a volume-based median diameter (D50) within the range from 0.050 μm to 10.000 μm inclusive. The concentration of the inorganic particles is 5 mass% or more based on the inorganic particle dispersed slurry. The dipole moment of the solvent is 0.50 or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an inorganic particle dispersion slurry, an electrode sheet, an electrolyte sheet, and a lithium ion battery. [Background technology]

[0002] In recent years, lithium ion batteries have been attracting attention as a power source that can provide high voltage and has high energy density, and are being used in applications such as power sources for electric vehicles and mobile terminals.

[0003] A lithium-ion battery includes an electrode assembly having a positive electrode and a negative electrode, and the positive electrode and the negative electrode preferably contain, in addition to a positive electrode active material or a negative electrode active material, inorganic particles having high lithium ion conductivity as an electrode additive.

[0004] Furthermore, it is preferable that the electrolyte located between the positive electrode and the negative electrode also contains inorganic particles having high lithium ion conductivity in order to increase the ion conductivity and improve the mechanical strength of the electrolyte.

[0005] Here, the general formula Li 1+x+y M 1 x M 2 2-x Si y P 3-y O 12 (where M 1 is one or both of Al and Ga atoms, and M 2Glass-ceramics containing crystals represented by the formula (where x is one or both of Ti and Ge atoms, and x and y are both numbers in the range of 0 to 1) (hereinafter sometimes referred to as "LATP-based crystals") have a high ability to improve battery characteristics when used as an electrode additive and have high lithium ion conductivity, making them suitable for use as inorganic particles in electrode additives and electrolytes for lithium ion batteries. To demonstrate the properties of improving battery characteristics and increasing lithium ion conductivity when such LATP-based crystals are incorporated into electrodes or composite electrolytes as an electrode additive or electrolyte, the LATP-based crystals must be uniformly dispersed in the electrode or composite electrolyte, and a slurry in which the LATP-based crystals are uniformly dispersed must be prepared. However, the LATP-based crystals tend to settle or aggregate in the slurry over time.

[0006] For example, Patent Document 1 describes a slurry containing inorganic particles, which contains inorganic particles, an organic binder polymer, and a solvent, and in which the inorganic particles have a diameter of 0.01 μm to 15 μm, and when the average diameter of the inorganic particles is d [μm], the viscosity η is in the range of 40d 2 The lower limit of the slurry is the value obtained by the method described above, and the upper limit is 10,000 cP.

[0007] Patent Document 2 also describes an ion conductor slurry that contains at least an ion conductor powder material and a solvent, where the ion conductor powder material includes one of a garnet-type solid electrolyte material, a NASICON-type solid electrolyte material, a LISICON-type solid electrolyte material, a perovskite-type solid electrolyte material, and a derivative thereof, and the particle size of the ion conductor powder is between 1 nm and 100 μm, and is used as a coating material for a diaphragm, a clad material for a positive electrode material, a clad material for a negative electrode material, an additive for a positive electrode material, an additive for a negative electrode material, an additive for a polymer solid electrolyte, or a solid-liquid mixed solid electrolyte. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Special Publication No. 2015-534710 [Patent Document 2] Special Publication No. 2022-528080 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the slurry disclosed in Patent Document 1 uses alumina inorganic particles or bohemite inorganic particles as inorganic particles, and does not disclose the dispersibility of the inorganic particles in a solvent when crystals having higher lithium ion conductivity than these are included as inorganic particles, much less the aggregation of the inorganic particles contained in the slurry.

[0010] In addition, the ionic conductor slurry described in Patent Document 2 contains Li as inorganic particles. 1.5 Al 0.5 Ti 1.5 Although an example using (PO4)3 has been disclosed, in this example the concentration of inorganic particles was only around 1 mass% relative to the ionic conductor slurry, and when the concentration of inorganic particles was increased, it was necessary to add a dispersant or the like to obtain a slurry in which the inorganic particles were less likely to aggregate. Here, if the concentration of inorganic particles is low, when the ionic conductor slurry is used to form electrodes or electrolytes for lithium ion batteries, the solvent becomes excessive when mixed with other materials such as positive electrode active material and negative electrode active material, making it difficult to adjust the viscosity of the slurry and also difficult to adjust the composition of the slurry.

[0011] The object of the present invention is to provide an inorganic particle dispersion slurry in which aggregation of inorganic particles is unlikely to occur when the concentration of inorganic particles containing LATP-based crystals is high, and an electrode sheet, an electrolyte sheet, and a lithium ion battery using the same. [Means for solving the problem]

[0012] As a result of intensive research and development into the above-mentioned conventional problems, the present inventors have found that by combining inorganic particles containing LATP crystals and having a median diameter in the range of 0.050 μm to 10,000 μm with a solvent having a dipole moment of 0.50 or more to form a slurry, it is possible to obtain an inorganic particle dispersion slurry in which the inorganic particles are less likely to aggregate, even when the concentration of inorganic particles containing LATP crystals is high. The present invention was completed based on this finding.

[0013] In order to achieve the above object, the gist of the present invention is as follows. (1) An inorganic particle dispersion slurry containing a solvent and inorganic particles dispersed in the solvent, wherein the inorganic particles are represented by the general formula Li 1+x+y M 1 x M 2 2-x Si y P 3-y O 12 (where M 1 is one or both of Al and Ga atoms, and M 2 is one or both of a Ti and a Ge atom, and x and y are both numerical values ​​in the range of 0 to 1), the volume-based median diameter (D50) is in the range of 0.050 μm to 10,000 μm, the concentration of the inorganic particles is 5 mass % or more with respect to the inorganic particle dispersion slurry, and the dipole moment of the solvent is 0.50 or more. (2) The inorganic particle dispersion slurry according to (1) above, wherein the lithium ion conductive crystal contains silicon (Si) atoms. (3) The inorganic particle dispersion slurry according to (1) or (2) above, wherein the solvent has a relative dielectric constant of 6.0 or more. (4) The inorganic particle dispersion slurry according to any one of (1) to (3) above, wherein the solvent has a donor number (DN) of 16.0 or more. (5) The inorganic particle dispersion slurry according to any one of (1) to (4) above, wherein the solvent is a single solvent consisting of one type of liquid compound. (6) The inorganic particle dispersion slurry according to any one of (1) to (5) above, which does not contain any dispersant, binder, or additive. (7) The inorganic particle dispersion slurry according to any one of (1) to (6) above, which does not contain a dispersant. (8) The inorganic particle dispersion slurry according to any one of (1) to (7) above, which is a slurry for forming an electrode, further containing an electrode active material. (9) An electrode sheet comprising a current collector and an electrode film formed by applying the electrode-forming slurry described in (8) above to the surface of the current collector and drying the applied slurry. (10) An electrolyte sheet comprising an electrolyte membrane formed by applying and drying an electrolyte-forming slurry comprising the inorganic particle dispersion slurry according to any one of (1) to (7) above. (11) A lithium ion battery having one or both of the electrode sheet described in (9) above and the electrolyte sheet described in (10) above. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide an inorganic particle dispersion slurry in which aggregation of inorganic particles is unlikely to occur when the concentration of inorganic particles containing LATP-based crystals is high, and an electrode sheet, an electrolyte sheet, and a lithium ion battery using the same. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, preferred embodiments of the inorganic particle dispersion slurry, electrode sheet, electrolyte sheet, and lithium ion battery of the present invention will be described in detail. Note that in the component composition of the inorganic particle dispersion slurry of the present invention, "mass %" may be simply represented as "%".

[0016] The inorganic particle dispersion slurry of the present invention contains a solvent and inorganic particles present in a dispersed state in the solvent, and the inorganic particles are represented by the general formula Li 1+x+y M 1 x M 2 2-x Si y P3-y O 12 (where M 1 is one or both of Al and Ga atoms, and M 2 is one or both of a Ti and a Ge atom, and x and y are both numerical values ​​in the range of 0 to 1), the volume-based median diameter (D50) is in the range of 0.050 μm to 10,000 μm, the concentration of the inorganic particles is 5 mass % or more with respect to the inorganic particle dispersion slurry, and the dipole moment of the solvent is 0.50 or more.

[0017] In the inorganic particle dispersion slurry according to the present invention, inorganic particles containing LATP-based crystals and having a median diameter in the range of 0.050 μm or more and 10,000 μm or less are combined with a solvent having a dipole moment of 0.50 or more to form a slurry, thereby obtaining an inorganic particle dispersion slurry in which the inorganic particles are less likely to aggregate, even when the concentration of inorganic particles containing LATP-based crystals is high.

[0018] [1] Inorganic particle dispersion slurry The inorganic particle dispersion slurry of the present invention contains a solvent and inorganic particles present in a dispersed state in the solvent.

[0019] <Inorganic particles> Among these, inorganic particles are those having the general formula Li 1+x+y M 1 x M 2 2-x Si y P 3-y O 12 (where M 1 is one or both of Al and Ga atoms, and M 2is one or both of a Ti and a Ge atom, and x and y are both numbers in the range of 0 to 1. In this way, when the inorganic particle dispersion slurry contains LATP-based crystals having high lithium ion conductivity as inorganic particles, the lithium ion conductivity of an electrode or electrolyte formed using the inorganic particle dispersion slurry can be increased. Furthermore, since LATP-based crystals have high mechanical strength, when the inorganic particle dispersion slurry is used as an electrode additive for an electrode film or when used to form an electrolyte film, the mechanical strength of the resulting electrode film or electrolyte film can be increased by containing LATP-based crystals as inorganic particles.

[0020] For example, as described below, when an inorganic particle dispersion slurry is used as a positive electrode additive, the inorganic particle dispersion slurry contains LATP-based crystals as inorganic particles, and the LATP-based crystals promote the dissociation of Li salts, thereby exhibiting the effect of accelerating the battery reaction, and also exhibiting the effect of suppressing the deterioration of the positive electrode material by capturing HF (hydrogen fluoride), which is generated as the battery reaction progresses and is a cause of deterioration of the positive electrode material, thereby improving the battery characteristics of lithium-ion batteries.

[0021] Here, the constituent elements of the LATP crystal are represented by the general formula Li 1+x+y M 1 x M 2 2-x Si y P 3-y O 12 In this general formula, M 1 is one or both of Al and Ga atoms, and is preferably an Al atom from the viewpoint of increasing the lithium ion conductivity of an electrode film or an electrolyte film formed using the slurry. 2 is an atom of one or both of Ti and Ge, and is preferably a Ti atom, particularly from the viewpoint of increasing the lithium ion conductivity of an electrode film or an electrolyte film formed using the slurry.

[0022] Furthermore, x in the above general formula can be a value ranging from 0 to 1. In particular, from the viewpoint of increasing the lithium ion conductivity of the inorganic particles and making it easier to obtain a base glass before precipitation of LATP-based crystals, x in the above general formula is preferably greater than 0, more preferably 0.01 or greater, even more preferably 0.05 or greater, even more preferably 0.1 or greater, and even more preferably 0.2 or greater. That is, the lithium ion conductive crystal may contain one or both of aluminum (Al) and gallium (Ga) atoms. On the other hand, from the viewpoint of increasing the relative permittivity of the inorganic particles and, when combined with a solvent with a high dipole moment, increasing the affinity with the solvent due to the polarization effect of the inorganic particles, thereby making it even more difficult for the inorganic particles to aggregate, x in the above general formula is preferably 0.6 or less, more preferably 0.5 or less, even more preferably 0.4 or less, and even more preferably 0.3 or less.

[0023] Furthermore, y in the above general formula can be a value in the range of 0 to 1. The LATP-based crystal may be an LATP crystal, which is a crystal in which y is 0 and does not contain silicon (Si) atoms, or an LATSP crystal, which is a crystal in which y is greater than 0 and contains silicon (Si) atoms. Here, the LATP crystal is a crystal represented by the general formula Li 1+x+y M 1 x M 2 2-x Si y P 3-y O 12 (where M 1 is one or both of Al and Ga atoms, and M 2 is one or both of Ti and Ge atoms, and x is a number in the range of 0 to 1, and y=0). The LATSP crystal is represented by the general formula Li 1+x+y M 1 x M 2 2-x Si y P 3-y O 12 (where M 1is one or both of Al and Ga atoms, and M 2 is one or both of Ti and Ge atoms, x is a number in the range of 0 to 1, and y>0).

[0024] The inorganic particles preferably contain LATP-based crystals as the main crystalline phase. Here, the inorganic particles may contain LATP crystals as the main crystalline phase, or may contain LATSP crystals as the main crystalline phase. In this specification, the "main crystalline phase" refers to the crystalline phase that has the largest amount of crystals calculated from peak intensity, peak half-width, etc., among the crystalline phases identified as being contained in the inorganic particles by powder X-ray diffraction.

[0025] Inorganic particles containing LATP crystals as the main crystalline phase have a crystalline structure with a phosphate skeleton (-OPO-Ti-O-). When the phosphate skeleton comes into contact with water molecules, the phosphate skeleton on the outermost surface of the LATP crystals is hydrated, breaking the bond between O and Ti, generating bonds (-OPOH) and (HO-Ti-O-). Here, the -PO-Ti- bond that constitutes the phosphate skeleton is P 5+ The atom is O 2- The electron attraction between the atoms weakens the bond strength between O and Ti, making the above-mentioned hydration reaction more likely to occur. On the other hand, inorganic particles containing LATSP crystals as the main crystalline phase tend to have a P structure in the phosphate skeleton. 5+ The site is Si 4+ By substituting with , some of the -PO-Ti- bonds can be converted to -Si-O-Ti- bonds. This -Si-O-Ti- bond has stronger covalent bond properties than the -PO-Ti- bond and is less likely to be broken by hydration reactions. Therefore, LATSP crystals are preferable to LATP crystals in that they can maintain dispersibility for a longer period of time when dispersed in a solvent.

[0026] In particular, when the LATP-based crystal is a LATSP crystal, in order to increase the lithium ion conductivity of the inorganic particles, to make it easier to obtain the base glass before the LATP-based crystals are precipitated, and to make the precipitation of the LATP-based crystals from the base glass uniform, y in the above general formula is preferably greater than 0, more preferably 0.01 or more, even more preferably 0.05 or more, and even more preferably 0.1 or more. On the other hand, if the amount of Si substitution in the LATSP crystal is too large, the polarizability of the LATSP crystal weakens, the affinity with the solvent decreases, and the inorganic particles aggregate in the solvent. Therefore, in order to increase the relative permittivity of the inorganic particles and, when combined with a solvent with a high dipole moment, to increase the affinity with the solvent due to the polarization effect of the inorganic particles, thereby making the aggregation of the inorganic particles more difficult, y in the above general formula is preferably 0.6 or less, more preferably 0.5 or less, even more preferably 0.4 or less, even more preferably 0.3 or less, and even more preferably 0.2 or less.

[0027] In addition to LATP-based crystals, the inorganic particles may contain other inorganic compounds to the extent that the dispersibility when dispersed in a solvent is not affected. For example, the inorganic particles may be formed of glass ceramics, and in this case, the inorganic particles may contain a glass phase in addition to LATP-based crystals. In addition, the inorganic particles may contain a crystalline phase other than LATP-based crystals. Here, examples of crystalline phases that can be contained in inorganic particles other than LATP-based crystals include, but are not limited to, crystals generated as by-products during the production of LATP-based crystals, such as one or more selected from the group consisting of LiTiPO4, Li4P2O5, Li3PO4, AlPO4, and Al2O3. On the other hand, from the viewpoint of increasing the content of LATP-based crystals and further enhancing the properties provided by the LATP-based crystals, it is preferable that the inorganic particles contain little crystalline phases other than LATP-based crystals or glass phases, and more preferably, they are substantially free of one or both of crystalline phases other than LATP-based crystals and glass phases.

[0028] The inorganic particles containing lithium ion conductive crystals have lithium ion conductivity, and the lithium ion conductivity is preferably high. Here, the lithium ion conductivity of the inorganic material is, for example, 1×10 ―4 S / cm or more is preferable, and 5×10 ―4 S / cm or more is more preferable, and 1×10 ―3 On the other hand, the upper limit of the lithium ion conductivity of the inorganic particles containing lithium ion conductive crystals is not particularly limited, and is, for example, 5×10 ―2 Although the upper limit of lithium ion conductivity may be 100 S / cm, the higher the lithium ion conductivity of the inorganic particles, the more desirable it is. The lithium ion conductivity of the inorganic particles may also be determined by measuring the lithium ion conductivity of the inorganic material bulk before being pulverized into inorganic particles.

[0029] The inorganic particles contained in the inorganic particle dispersion slurry have a volume-based median diameter (D50) in the range of 0.050 μm to 10,000 μm. By increasing the median diameter (D50) of the inorganic particles to 0.050 μm or more, the crystallinity of the LATP-based crystals contained in the inorganic particles is enhanced, thereby improving the dielectric properties of the inorganic particles and increasing the mechanical strength of the resulting electrode film and electrolyte membrane. Additionally, the weakened cohesion between particles reduces the likelihood of coarse particles forming and settling during the grinding and drying processes used to prepare the inorganic particles, thereby improving dispersibility over a longer period of time. In particular, when the inorganic particle dispersion slurry is used as a positive electrode additive, increasing the median diameter (D50) of the inorganic particles to 0.050 μm or more can promote the dissociation of the Li salt and facilitate the battery reaction. Therefore, the median diameter (D50) of the inorganic particles is preferably 0.050 μm or more, more preferably 0.080 μm or more, even more preferably 0.100 μm or more, even more preferably 0.150 μm or more, and even more preferably 0.200 μm or more. On the other hand, by setting the median diameter (D50) of the inorganic particles to 10,000 μm or less, single particle settling is less likely to occur, resulting in a slurry with good long-term dispersibility. In particular, when the inorganic particle dispersion slurry is used as an electrode additive or electrolyte for an electrode, improving the mixability with the electrode active material and other materials can improve the dispersibility of the inorganic particles and other materials contained in the slurry and reduce the likelihood of aggregation. Therefore, the median diameter (D50) of the inorganic particles is preferably 8,000 μm or less, more preferably 5,000 μm or less, even more preferably 4,000 μm or less, even more preferably 3,000 μm or less, even more preferably 2,000 μm or less, even more preferably 1,000 μm or less, and even more preferably 0.800 μm or less.

[0030] Here, the particle size (median size) of the inorganic particles contained in the inorganic particle dispersion slurry tends to increase over time due to aggregation, etc. In this regard, the inorganic particle dispersion slurry of the present invention has excellent dispersibility of the inorganic particles, and aggregation of the inorganic particles is unlikely to occur even over time, so that the particle size of the inorganic particles remains the same as before dispersion and can withstand transportation and temporary storage.

[0031] The concentration of inorganic particles contained in the inorganic particle dispersion slurry is 5% by mass or more relative to the mass of the inorganic particle dispersion slurry. By setting the concentration of inorganic particles to 5% by mass or more relative to the mass of the inorganic particle dispersion slurry, the concentration of inorganic particles relative to the solvent increases, making it easier to adjust the composition and viscosity of the electrode-forming slurry or electrolyte-forming slurry prepared from the inorganic particle dispersion slurry when forming an electrode membrane or an electrolyte membrane. Therefore, the concentration of inorganic particles is preferably 10% by mass or more relative to the mass of the inorganic particle dispersion slurry, more preferably 20% by mass or more, and even more preferably 30% by mass or more. On the other hand, the upper limit of the inorganic particle concentration is not particularly limited, but from the viewpoint of preventing aggregation of the inorganic particles and preventing the median diameter (D50) of the inorganic particles from becoming unnecessarily large, it is preferably 80% by mass or less, more preferably 75% by mass or less relative to the mass of the inorganic particle dispersion slurry.

[0032] The inorganic particles contained in the inorganic particle dispersion slurry may be surface-modified, but from the viewpoint of obtaining the inorganic particles more easily, it is preferable that the surface is not modified. Here, examples of surface modification of the inorganic particles include compounding with an electron-conductive polymer such as polyaniline, polythiophene, and polyacetylene. In addition, examples of surface modification of the inorganic particles include modification with a surface modifier such as sodium dodecylbenzenesulfonate, polyethylene glycol, stearic acid, silicone oil, and a coupling agent. In the inorganic particle dispersion slurry of this embodiment, aggregation of the inorganic particles can be made less likely to occur even without modifying the surface of the inorganic particles.

[0033] <Solvent> The solvent is a liquid that allows the inorganic particles to exist in a dispersed state. By combining the inorganic particles with an appropriate solvent, it is possible to make the inorganic particles less likely to aggregate in the slurry.

[0034] The solvent for dispersing the inorganic particles has a dipole moment of 0.50 or more. That is, the inorganic particles are preferably dispersed in a solvent with a dipole moment of 0.50 or more. Here, the LATP crystals contained in the inorganic particles are highly dielectric materials, so when dispersed in a solvent with a high dipole moment, the Ti atoms and P atoms on the surface of the LATP crystals are slightly positively charged, which causes the LATP crystals to become polarized. This can result in high affinity between the solvent and the LATP crystals, thereby improving the dispersibility of the inorganic particles containing LATP crystals and making the inorganic particles less likely to aggregate. To strengthen this tendency, the dipole moment of the solvent is preferably 1.20 or more, more preferably 1.50 or more, even more preferably 1.70 or more, even more preferably 1.80 or more, even more preferably 1.90 or more, even more preferably 1.95 or more, and even more preferably 2.00 or more. On the other hand, the upper limit of the dipole moment of the solvent is not particularly limited, but may be set to 5.00 or less or 4.50 or less, for example, from the viewpoint of preventing the difficulty of drying the solvent when producing electrode sheets and electrolyte sheets due to excessively high affinity with inorganic particles, thereby facilitating the smooth production of lithium ion batteries.

[0035] Furthermore, the solvent for dispersing the inorganic particles preferably has a dielectric constant of 6.0 or higher. This allows for a high affinity between the solvent with a high dielectric constant and the LATP-based crystals in which Ti atoms and P atoms are positively charged, further reducing the likelihood of aggregation of the inorganic particles containing the LATP-based crystals. Therefore, the dielectric constant of the solvent is more preferably 20.0 or higher, even more preferably 22.0 or higher, and even more preferably 25.0 or higher. On the other hand, the upper limit of the dielectric constant of the solvent is not particularly limited, but may be, for example, 90.0 or lower or 85.0 or lower, from the viewpoint of preventing excessively high affinity with the inorganic particles, which would make it difficult to dry the solvent when preparing electrode sheets and electrolyte sheets, thereby facilitating the production of lithium-ion batteries.

[0036] Furthermore, the solvent for dispersing the inorganic particles preferably has a donor number (DN) of 16.0 or more. Here, the higher the electron donating property (donor number) of the solvent, the more likely the Ti, P, and Ge atoms on the surface of the LATP-based crystals are to be positively charged, resulting in a high affinity between the solvent and the positively charged LATP-based crystals. As a result, the aggregation of inorganic particles containing LATP-based crystals is further reduced. Therefore, the donor number (DN) of the solvent is more preferably 18.0 or more, even more preferably 20.0 or more, even more preferably 21.0 or more, and even more preferably 22.0 or more. On the other hand, the upper limit of the donor number (DN) of the solvent is not particularly limited, but may be, for example, 40.0 or less or 30.0 or less, from the viewpoint of preventing excessively high affinity with the inorganic particles, which makes it difficult to dry the solvent when preparing electrode sheets and electrolyte sheets, thereby facilitating the production of lithium-ion batteries.

[0037] In addition, the solvent for dispersing the inorganic particles is preferably a non-aqueous solvent. By using a non-aqueous solvent as the solvent, the slurry contains almost no water molecules, and the water molecules are contained in the LATP-based crystalline skeleton, making it difficult to form a hydrated gel that causes aggregation. As a result, even over a long period of time, the particle size of the inorganic particles is unlikely to increase, and aggregation of the inorganic particles is unlikely to occur. Therefore, even when transported or stored for a long period of time, the inorganic particles can continue to maintain a dispersed state without agglomerating in the slurry. On the other hand, the solvent for dispersing the inorganic particles may be water.

[0038] Furthermore, the solvent for dispersing the inorganic particles is preferably a single solvent consisting of one type of liquid compound. That is, the solvent for dispersing the inorganic particles is preferably a liquid compound having a dipole moment of 0.50 or more. The solvent is more preferably a liquid compound having a relative dielectric constant of 6.0 or more, and more preferably a liquid compound having a donor number (DN) of 16.0 or more. Here, the liquid compound can be a compound that is in a liquid state at room temperature (e.g., 25°C). By using such a single solvent consisting of one type of liquid compound as the solvent, the dispersibility of the inorganic particles can be further improved and aggregation of the inorganic particles can be made less likely to occur.

[0039] Specific examples of liquid compounds that can be used as solvents in the inorganic particle dispersion slurry of the present invention include N-methylpyrrolidone (dipole moment: 4.09, dielectric constant: 32.0, donor number (DN): 27.3), acetone (dipole moment: 2.69, dielectric constant: 20.7, donor number (DN): 17.0), water (dipole moment: 1.94, dielectric constant: 80.1, donor number (DN): 17.1), ethanol (dipole moment: 1.68, dielectric constant: 23.8, donor number (DN): 20.0), isopropanol (dipole moment: 1.66, dielectric constant: 19.9, donor number (DN): 21.1), tetrahydrofuran (dipole moment: 1.75, dielectric constant: 7.6, donor number (DN): 20.0), and butyl acetate (dipole moment: 1. Examples of suitable dielectric constants include dimethyl sulfoxide (dipole moment: 4.30, dielectric constant: 48.9, donor number (DN): 29.8), dimethylacetamide (dipole moment: 3.72, dielectric constant: 37.8, donor number (DN): 27.8), acetonitrile (dipole moment: 3.44, dielectric constant: 37.5, donor number (DN): 14.1), methanol (dipole moment: 1.66, dielectric constant: 33.1, donor number (DN): 19.0), diethyl ether (dipole moment: 1.12, dielectric constant: 4.2, donor number (DN): 19.2), and N,N-dimethylformamide (dipole moment: 3.86, dielectric constant: 36.7, donor number (DN): 36.7).

[0040] <Other ingredients> The inorganic particle dispersion slurry of the present invention may contain components other than the above-mentioned solvent and inorganic particles.

[0041] For example, when the inorganic particle dispersion slurry is used as an electrode additive in forming an electrode, the inorganic particle dispersion slurry can further contain an electrode active material, a conductive additive, etc., and such a slurry can be used as an electrode-forming slurry. Examples of the electrode active material include a positive electrode active material and a negative electrode active material. Furthermore, when the inorganic particle dispersion slurry is used to form an electrolyte, the inorganic particle dispersion slurry can be used as is as an electrolyte-forming slurry. Note that the electrode-forming slurry and the inorganic particle dispersion slurry may contain small amounts of at least one of a dispersant, a binder, and an additive.

[0042] The positive electrode active material and the negative electrode active material are not particularly limited, and known materials can be used. Examples of the positive electrode active material include lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium iron phosphate, and lithium cobalt phosphate. Examples of the negative electrode active material include carbon materials such as graphite, fibrous carbon, and soft carbon; metal materials such as Li, Si, and Sn; and oxide materials such as lithium titanate.

[0043] The inorganic particle dispersion slurry may further contain a conductive additive. The conductive additive is not particularly limited, and known materials may be used. Here, examples of the conductive additive include materials having electronic conductivity, such as carbon, graphite, carbon nanotubes, aluminum alloys, zinc alloys, silver, and ruthenium.

[0044] In addition, the inorganic particle-dispersed slurry, particularly when used as an electrode-forming slurry, may further contain a dispersant to enhance the dispersibility of electrode materials such as electrode active materials, conductive additives, etc. The inorganic particle-dispersed slurry may further contain one or more additives selected from the group consisting of thickeners, antifoaming agents, plasticizers, flame retardants, gelling agents, antioxidants, and emulsifiers.

[0045] On the other hand, the inorganic particle dispersion slurry preferably contains a small amount of dispersant, binder, and additive, and more preferably contains no dispersant, binder, or additive. These compounds are compounds that do not directly participate in the battery reaction and serve as resistance components. Therefore, by excluding these compounds from the inorganic particle dispersion slurry, the electrode film or electrolyte membrane obtained from the inorganic particle dispersion slurry can further enhance the effect of improving the battery characteristics of the lithium-ion battery. In particular, in the inorganic particle dispersion slurry used to prepare the electrode film or electrolyte membrane, dispersants, binders, additives, etc. are sometimes added during the preparation of the slurry to uniformly disperse the materials or adjust the properties of the slurry. However, increasing the content of these materials tends to deteriorate the battery characteristics of the lithium-ion battery. Therefore, in order to exhibit the properties of LATP-based crystals in the electrodes and electrolytes formed from the inorganic particle dispersion slurry, it is preferable that the content of dispersant, binder, and additive, which are materials that do not contribute to the battery reaction, is small, and more preferably that none of these is included. The inorganic particle dispersion slurry of this embodiment may be one that does not contain at least one of a dispersant, a binder, and an additive, and in particular may be one that does not contain a dispersant such as a surfactant.

[0046] Examples of dispersants include polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE), polyhexafluoropropylene, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, vinyl acetate resin, polydimethylsiloxane, phenolic resin, cellulose resin, acrylic resin, urethane resin, and polyvinyl acetal resin, which are commonly used in lithium-ion batteries. Examples of dispersants include cationic dispersants, a specific example of which is polyethyleneimine. Examples of dispersants include anionic dispersants, specific examples of which are carboxymethyl cellulose and polyoxyethylene ether phosphate. Examples of dispersants include nonionic dispersants, specific examples of which are polyacrylamide and polyoxyethylene alkylphenyl ether. Examples of nonionic dispersants include those having an ester bond in the molecule and those having a hydroxyl group in the side chain. Further, an amphoteric dispersant (amphoteric surfactant) can also be used as the dispersant. In the inorganic particle dispersion slurry of this embodiment, aggregation of inorganic particles can be made less likely to occur even without containing such a dispersant.

[0047] Examples of binders include polymer compounds such as butadiene rubber, PVB (polyvinyl butyral resin), PVDF (polyvinylidene fluoride), PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene), PTFE (polytetrafluoroethylene), PAN (polyacrylonitrile), PMMA (polymethyl methacrylate), PEO (polyethylene oxide), and PPO (polypropylene oxide).

[0048] The additives include one or more selected from the group consisting of thickeners, antifoaming agents, plasticizers, flame retardants, gelling agents, antioxidants, and emulsifiers.

[0049] [2] About electrode sheets The electrode sheet of the present invention includes a current collector and an electrode film formed by applying and drying the above-described electrode-forming slurry to the surface of the current collector. Here, the electrode film of the electrode sheet can be obtained by applying the above-described electrode-forming slurry to the surface of the current collector and drying it. By using the above-described electrode-forming slurry for the electrode film of such an electrode sheet, even if the solids concentration of the electrode-forming slurry, particularly the concentration of inorganic particles, is high, inorganic particle aggregation is unlikely to occur, making it easier to adjust the composition of the electrode film, and as a result, the range of materials for the electrode film can be expanded. Furthermore, because aggregation of the inorganic particles contained in the electrode-forming slurry is unlikely to occur, the concentration of inorganic particles contained in the resulting electrode film can be uniform, making it easier to obtain an electrode sheet with a desired thickness.

[0050] The electrode sheet of the present invention may also have an electrolyte membrane (solid electrolyte membrane) formed by applying and drying an electrolyte-forming slurry composed of the above-described inorganic particle-dispersed slurry to the surface of the electrode membrane not in contact with the current collector. By using the above-described inorganic particle-dispersed slurry for the electrolyte membrane, even if the solids concentration of the electrolyte-forming slurry, particularly the concentration of inorganic particles, is high, inorganic particles are less likely to aggregate, making it easier to adjust the composition of the electrolyte membrane and, as a result, broadening the range of materials to choose for the electrolyte membrane. Furthermore, because the inorganic particles contained in the electrolyte-forming slurry are less likely to aggregate, it is easier to obtain an electrolyte membrane with a desired thickness.

[0051] The material of the current collector in the electrode sheet of the present invention is not particularly limited, but may be at least one metal selected from the group consisting of Fe, Cu, Al, Ti, and Ni, and alloys thereof.

[0052] Furthermore, as a means for applying the inorganic particle dispersion slurry (electrode-forming slurry or electrolyte-forming slurry) to the surface of the current collector or electrode film, known methods such as application methods using a doctor blade, a calendar method, spin coating, or dip coating, or printing, a die coater method, or a spray method can be used.

[0053] [3] About electrolyte sheets The electrolyte sheet of the present invention is composed of an electrolyte membrane (solid electrolyte membrane) formed by applying and drying an electrolyte-forming slurry made from the above-mentioned electrode-forming slurry. By using the above-mentioned inorganic particle-dispersed slurry for the electrolyte membrane, even if the solids concentration of the electrolyte-forming slurry, particularly the concentration of inorganic particles, is high, the inorganic particles are less likely to aggregate, making it easier to adjust the composition of the electrolyte membrane, and as a result, the range of materials to choose from for the electrolyte membrane can be expanded. Furthermore, because the inorganic particles contained in the electrolyte-forming slurry are less likely to aggregate, it is easier to obtain a solid electrolyte membrane with a desired thickness.

[0054] Here, known methods for producing solid electrolyte membranes can be used to prepare the electrolyte sheet. For example, an electrolyte sheet can be obtained by applying a solid electrolyte composition containing inorganic particles and a solvent that will form the solid electrolyte to a support, drying the composition to form a sheet, and then peeling off the support. The resulting electrolyte sheet can also be used as a separator for a semi-solid battery by impregnating it with an electrolytic solution. Furthermore, the resulting electrolyte sheet can be fired to sinter the inorganic particles together, thereby obtaining an electrolyte sheet with high lithium ion conductivity. Furthermore, a positive electrode sheet, a solid electrolyte sheet, and a negative electrode sheet can be stacked and sintered together to obtain an all-solid-state battery, which serves as a lithium ion battery, as described below.

[0055] The inorganic particle dispersion slurry (electrolyte-forming slurry) can be applied to the support by known methods such as a doctor blade method, a calendar method, a coating method such as spin coating or dip coating, a printing method, a die coater method, or a spray method.

[0056] [4] Lithium-ion batteries The lithium ion battery preferably includes one or both of the electrode sheet and the electrolyte sheet described above. For example, a lithium ion battery can be formed by stacking a positive electrode sheet, which is an electrode sheet containing a positive electrode active material, and a negative electrode sheet, which is an electrode sheet containing a negative electrode active material, on the sides not facing the current collector, with an electrolyte sheet sandwiched between them. Here, the lithium ion battery may be a primary battery or a secondary battery. The electrolyte membrane of the lithium ion battery may be the electrolyte sheet described above, or may contain a lithium ion conductive material other than lithium ion conductive crystals. In particular, the lithium ion battery can be an all-solid-state battery by stacking the positive electrode sheet and the negative electrode sheet described above with an electrolyte sheet made of a solid electrolyte sandwiched between them to form a battery cell of the lithium ion battery.

[0057] Although the embodiments have been described above, the present invention is not limited to the above embodiments, but includes all aspects encompassed by the concept and scope of the claims of the present disclosure, and can be modified in various ways within the scope of the present disclosure. [Example]

[0058] Next, examples of the present invention and comparative examples will be described, but the present invention is not limited to these examples of the present invention.

[0059] (Preparation of inorganic particles containing LATSP crystals) Using H3PO4, Al(PO3)3, Li2CO3, SiO2, and TiO2 as raw materials, weighing them so that when all of them are changed to oxides, the composition on an oxide basis contains 15.0 mol% of Li2O, 7.5 mol% of Al2O3, 38.0 mol% of TiO2, 4.5 mol% of SiO2, and 35.0 mol% of P2O5, uniformly mixing them, then putting them into a platinum pot, heating them to 1500 °C in an electric furnace, and heating and melting them for 3 hours while stirring the glass melt. Then, by dropping the glass melt into running water, a flaky glass body (raw glass) with a diameter of about 5 mm was formed. After drying this glass body in a dryer to remove moisture, it was heat-treated at 950 °C for 12 hours to produce flaky glass ceramics. The crystal structure of the crystal phase of the obtained glass ceramics was confirmed by powder X-ray diffraction method to be the main crystal phase of Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (where 0 < x ≤ 0.4 and 0 < y ≤ 0.6). Also, the lithium ion conductivity of this glass ceramics was about 1×10 -3 S / cm, indicating that it has lithium ion conductivity. After grinding this flaky glass ceramics with a dry bead mill until the volume-based median diameter (D50) becomes 1 μm, and further grinding it with a wet bead mill, inorganic particles containing LATSP crystals as lithium ion conductive crystals were produced.

[0060] (Preparation of Inorganic Particles Containing LATP Crystals) Using H3PO4, Al(PO3)3, Li2CO3, and TiO2 as raw materials, weighing them so that when they are all changed to oxides, the composition based on oxides contains 15.5 mol% of Li2O, 8.0 mol% of Al2O3, 40.0 mol% of TiO2, and 36.5 mol% of P2O5, mixing them uniformly, then putting them into a platinum pot, heating them to 1500 °C in an electric furnace, and heating and melting them for 3 hours while stirring the glass melt. Then, by dropping the glass melt between two cooled rollers to rapidly cool it, flaky glass bodies (raw glass) with a diameter of about 2 mm were formed. By heat-treating this glass body at 950 °C for 8 hours, flaky glass ceramics were produced. The crystal structure of the crystal phase of the obtained glass ceramics was confirmed by powder X-ray diffraction method to be Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (where 0 < x ≦ 0.4 and y = 0) was confirmed to be the main crystal phase. Also, the lithium ion conductivity of this glass ceramics was about 2×10 -4 S / cm, and it had lithium ion conductivity. After pulverizing this flaky glass ceramics with a dry bead mill until the volume-based median diameter (D50) became 1 μm, and further pulverizing it with a wet bead mill, inorganic particles containing LATP crystals as lithium ion conductive crystals were produced.

[0061] (Formation of inorganic particle dispersion slurry) For the invention examples and comparative examples in which the "Dispersant" column in Tables 1 and 2 reads "None," inorganic particle dispersion slurries in which the inorganic particles are dispersed in the solvent were obtained by mixing the prepared inorganic particles containing the main crystalline phase listed in Tables 1 and 2 with the solvent listed in Tables 1 and 2 in the ratios listed in Tables 1 and 2. Furthermore, for the invention examples in which the "Dispersant" column in Table 2 reads "Yes," inorganic particle dispersion slurries in which the inorganic particles are dispersed in the solvent were obtained by mixing the prepared inorganic particles containing the main crystalline phase listed in Table 2 with the solvent listed in Table 2 and anionic dispersant polyoxyethylene ether phosphate (manufactured by Croda, trade name: HYPERMER KD24-ss-(RB)) in the ratios listed in Table 2.

[0062] [Various measurement and evaluation methods] The inorganic particle dispersion slurries obtained in the above-mentioned invention examples and comparative examples were used to evaluate the following characteristics. The evaluation conditions for each characteristic were as follows.

[0063] [1] Measurement of the volume-based median diameter (D50) of inorganic particles contained in a slurry The bottom of the obtained inorganic particle dispersion slurry was collected with a dropper and diluted with a solvent listed in Tables 1 and 2 so that the inorganic particle concentration was 0.05% by mass relative to the inorganic particle dispersion slurry to prepare a sample.The volume-based median diameter D50 (diameter at 50% of the cumulative powder volume) of the inorganic particles contained in the sample was immediately measured using a laser diffraction particle size analyzer (Microtrack-Bell Corporation, product name: MT3300EX II).The median diameter D50 of the inorganic particles was measured three times using the solvent listed in Tables 1 and 2 as a blank, and the average of the measurement results was taken as the measured value M0.

[0064] [2] Evaluation of the aggregation of inorganic particles contained in the slurry The resulting inorganic particle dispersion slurry was allowed to stand for three days, after which the bottom of the inorganic particle dispersion slurry was collected with a dropper and diluted with a solvent listed in Tables 1 and 2 so that the inorganic particle concentration was 0.05% by mass relative to the inorganic particle dispersion slurry to prepare a sample. The volume-based median diameter D50 (diameter at 50% of the cumulative powder volume) of the inorganic particles contained in the sample was immediately measured using a laser diffraction particle size analyzer (manufactured by Microtrac-Bell Corporation, product name: MT3300EX II). The median diameter D50 of the inorganic particles at this time was also measured three times using the solvent listed in Tables 1 and 2 as a blank, and the average of the measurement results was taken as the measured value M3.

[0065] Next, the ratio M3 / M0 (hereinafter sometimes referred to as "ratio A") of the measured value M3 of the median diameter D50 of the inorganic particle dispersion slurry sample three days after preparation to the measured value M0 of the median diameter D50 of the inorganic particle dispersion slurry sample immediately after preparation was calculated.

[0066] Similarly, the median diameter D50 of a sample of inorganic particle dispersion slurry seven days after its preparation was measured, and the average of three measurements was designated as the measured value M7. Here, the ratio M7 / M0 (hereinafter sometimes referred to as "ratio B") of the measured value M7 of the median diameter D50 of a sample of inorganic particle dispersion slurry seven days after its preparation to the measured value M0 of the median diameter D50 of a sample of inorganic particle dispersion slurry immediately after its preparation was determined.

[0067] Note that, due to large measurement errors in M0, M3, and M7, which are the measured values ​​of the median diameter D50, the values ​​of ratio A and ratio B have been rounded to one decimal place and are shown in Tables 1 and 2. Also, Tables 1 and 2 include examples where the values ​​of one or both of ratio A and ratio B are calculated to be less than 1, but this is mainly due to large measurement errors in M0, M3, and M7.

[0068] Furthermore, the obtained inorganic particle dispersion slurries were visually observed for the presence or absence of aggregation after being left to stand for 3 days and 7 days. Cases in which aggregation was observed were evaluated as "present," and cases in which aggregation was not observed were evaluated as "absent." Note that, when the inorganic particles and the solvent were mixed, the inorganic particles settled without dispersing in the solvent, and the inorganic particles were considered to have aggregated immediately upon mixing with the solvent, and the presence or absence of aggregation was evaluated as "present."

[0069] Regarding the above-mentioned ratios A and B and the presence or absence of aggregation when left to stand for 3 days and 7 days, if ratio A is 1.20 or less and the presence or absence of aggregation when left to stand for 3 days is evaluated as "none," and if ratio B is 1.20 or less and the presence or absence of aggregation when left to stand for 7 days is evaluated as "none," the inorganic particles are particularly excellent in terms of being less likely to aggregate over the 7 days of standing, and the overall evaluation was evaluated as "Excellent." Furthermore, if ratio B exceeds 1.20, or if the presence or absence of aggregation when left to stand for 7 days is evaluated as "present," and ratio A is 1.20 or less and the presence or absence of aggregation when left to stand for 3 days is evaluated as "none," the inorganic particles are good in terms of being less likely to aggregate over the first 3 days of the 7-day standing, and the overall evaluation was evaluated as "Good." On the other hand, when the ratio A was more than 1.20 or when the presence or absence of aggregation after standing for 3 days was evaluated as "present," the inorganic particles were deemed to be prone to aggregation, and the overall evaluation was evaluated as "× (poor)." The results are shown in Tables 1 and 2.

[0070] [Table 1]

[0071] [Table 2]

[0072] As shown in Tables 1 and 2, in Examples 1 to 29 of the present invention, inorganic particles containing lithium ion conductive crystals having a predetermined atomic ratio have a predetermined median diameter (D50) and are dispersed in a solvent with a dipole moment of 0.50 or more, which is at least favorable in that the inorganic particles are less likely to aggregate over at least the first three days of the seven-day period they are left standing.As a result, it was confirmed that an inorganic particle dispersion slurry in which the inorganic particles are less likely to aggregate can be obtained when the concentration of inorganic particles containing LATP-based crystals is high.

[0073] In particular, in Examples 1 to 10, 14 to 16, 24, 25, 28 and 29 of the present invention, inorganic particles containing lithium ion conductive crystals having a predetermined atomic ratio had a predetermined median diameter (D50) and were dispersed in a non-aqueous solvent with a dipole moment of 0.50 or more, and as a result, the inorganic particles were particularly excellent in that they were less likely to aggregate over a period of 7 days when left standing.

[0074] On the other hand, in Comparative Example 1, in which the median diameter (D50) of the inorganic particles dispersed in the inorganic particle dispersion slurry was outside the appropriate range, the fluidity of the inorganic particle dispersion slurry decreased and aggregation was visually confirmed after the first three days of the seven-day period of standing, and the overall evaluation was poor and did not meet the acceptable level. Also, in Comparative Examples 2 to 5, in which the dipole moment of the solvent was outside the appropriate range, the inorganic particles did not disperse in the solvent but settled out when the inorganic particles and the solvent were mixed, and the overall evaluation was poor and did not meet the acceptable level.

Claims

1. A solvent; Inorganic particles present in a dispersed state in the solvent; An inorganic particle dispersion slurry comprising: The inorganic particles are General formula Li １＋ｘ＋ｙ M １ ｘ M ２ ２－ｘ S ｙ P ３－ｙ O １２ (Here, M １ is one or both of Al and Ga atoms, M ２ is one or both of Ti and Ge atoms, and x and y are both numbers in the range of 0 to 1), The volume-based median diameter (D50) is in the range of 0.050 μm or more and 10.000 μm or less, The concentration of the inorganic particles is 5% by mass or more relative to the inorganic particle dispersion slurry, and The inorganic particle dispersion slurry, wherein the solvent has a dipole moment of 0.50 or more.

2. The inorganic particle dispersion slurry according to claim 1 , wherein the lithium ion conductive crystals contain silicon (Si) atoms.

3. The inorganic particle dispersion slurry according to claim 1 , wherein the solvent has a relative dielectric constant of 6.0 or more.

4. The inorganic particle dispersion slurry according to claim 1 , wherein the solvent has a donor number (DN) of 16.0 or more.

5. The inorganic particle dispersion slurry according to claim 1 , wherein the solvent is a single solvent consisting of one type of liquid compound.

6. 2. The inorganic particle dispersion slurry according to claim 1, which does not contain any of a dispersant, a binder and an additive.

7. The inorganic particle dispersion slurry according to claim 1 , which does not contain a dispersant.

8. The inorganic particle dispersion slurry according to claim 1 , which is an electrode forming slurry further containing an electrode active material.

9. 9. An electrode sheet comprising: a current collector; and an electrode film formed by applying the electrode-forming slurry according to claim 8 to a surface of the current collector and drying the applied slurry.

10. 2. An electrolyte sheet comprising an electrolyte membrane formed by applying and drying an electrolyte-forming slurry comprising the inorganic particle dispersion slurry according to claim 1.

11. A lithium ion battery comprising one or both of the electrode sheet according to claim 9 and the electrolyte sheet according to claim 10.

Images