Electrode layer and all-solid battery

Abstract

An electrode layer used for an all-solid battery, comprising an electrode active material, a sulfide solid electrolyte, and a residual liquid, the residual liquid having a δ P less than 2.9 MPa 1 / 2 , and a boiling point of 190°C or higher. According to the aspect of the present disclosure, an effect of being able to provide an electrode layer that has a good capacity maintenance rate can be obtained.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an electrode layer and an all-solid battery. BACKGROUND

[0002] An all-solid battery is a battery having a solid electrolyte layer between a positive electrode layer and a negative electrode layer, and has an advantage that a safety device can be easily simplified compared to a liquid battery having an electrolyte solution including a flammable organic solvent. For example, International Publication No. 2019 / 203334 discloses a solid electrolyte composition including an inorganic solid electrolyte, a binder, and a dispersion medium. In addition, International Publication No. 2019 / 203334 discloses that the dispersion medium has a solubility parameter of 21 MPa 1 / 2 below. In addition, Japanese Patent Application Publication No. 2021-132010 discloses that butyl butyrate is used as a dispersion medium when the positive electrode layer and the negative electrode layer are produced. SUMMARY

[0003] From the viewpoint of improving the performance of an all-solid battery, an electrode layer having a good capacity retention rate is required. The present disclosure provides an electrode layer having a good capacity retention rate.

[0004] A first aspect of the present disclosure is an electrode layer used for an all-solid battery. The electrode layer includes an electrode active material, a sulfide solid electrolyte, and a residual liquid having a δ P of less than 2.9 MPa 1 / 2 and a boiling point of 190°C or higher.

[0005] According to the first aspect of the present disclosure, the δ P of the residual liquid and the boiling point are in predetermined ranges, and thus the electrode layer becomes one having a good capacity retention rate.

[0006] In the first aspect of the present disclosure, the amount of the residual liquid in the electrode layer can also be 1500 ppm or more and 5000 ppm or less.

[0007] In the first aspect of the present disclosure, the residual liquid can also contain at least one of a naphthalene-based compound, a lauryl group-containing compound, and a monocyclic aromatic-based compound.

[0008] In the first aspect of the present disclosure, the residual liquid can also contain the naphthalene-based compound.

[0009] In the first aspect of the present disclosure, the naphthalene-based compound can be tetrahydronaphthalene.

[0010] In the first aspect of the present disclosure, the residual liquid can also contain the lauryl group-containing compound.

[0011] In the first aspect of the present disclosure, the residual liquid can also contain the monocyclic aromatic-based compound.

[0012] In the first embodiment of this disclosure, the electrode layer can also be a positive electrode layer.

[0013] In the first embodiment of this disclosure, the electrode layer can also be a negative electrode layer.

[0014] Furthermore, the second aspect of this disclosure is an all-solid-state battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer. In the all-solid-state battery, at least one of the positive electrode layer and the negative electrode layer is the aforementioned electrode layer.

[0015] According to the scheme disclosed herein, by using the above-described electrode layer, a solid-state battery with good capacity retention is achieved.

[0016] According to the scheme disclosed herein, an electrode layer that provides good capacity retention can be obtained. Attached Figure Description

[0017] Hereinafter, the features, advantages, and technical and industrial significance of exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings, wherein like reference numerals denote like elements.

[0018] Figure 1 This is a schematic cross-sectional view illustrating the all-solid-state battery of this disclosure. Detailed Implementation

[0019] The electrode layer and all-solid-state battery of this disclosure are described in detail below.

[0020] A. Electrode layer

[0021] The electrode layer disclosed herein is an electrode layer used in all-solid-state batteries. The electrode layer contains an electrode active material, a sulfide solid electrolyte, and a residual liquid. The residual liquid has a Hansen solubility parameter δ... P Less than 2.9 MPa 1 / 2 And its boiling point is above 190℃.

[0022] According to this disclosure, the δ of the residual liquid P With boiling points within the specified range, it becomes an electrode layer with good capacity retention. Here, the δ value in the Hansen solubility parameter (HSP) is... P This is equivalent to the dipole interaction energy between molecules. δ P Large residual liquids can easily dissolve sulfide solid electrolytes, leading to the leaching of elements that constitute the sulfide solid electrolyte. For example, in International Publication No. 2019 / 203334, the SP value is 21 MPa. 1 / 2 The following specific examples of dispersion media disclose various dispersion media such as butyl butyrate. In the case where the electrode layer contains butyl butyrate as a residual liquid, due to the δ-value of butyl butyrate...P large, and thus reacts with the sulfide solid electrolyte, causing degradation of the sulfide solid electrolyte (decrease in ionic conductivity). As a result, the charge-discharge cycle characteristics decrease. In contrast, in the present disclosure, since the electrode layer contains a residual liquid having a small δ P small, and thus the residual liquid and the sulfide solid electrolyte are less likely to react. As a result, the electrode layer is one that has a good capacity retention rate.

[0023] In addition, in the case where the electrode layer is produced using a dispersion medium having a low boiling point, the dispersion medium is easily volatilized from the electrode layer at the time of drying, and, on the contrary, the electrode layer is easily cracked. The reason for this is considered to be that the binder contained in the electrode layer segregates at the time of drying. In contrast, in the present disclosure, since the residual liquid remaining in the electrode layer has a high boiling point, cracking of the electrode layer is suppressed. In particular, since the residual liquid contained in the electrode layer has a small δ P small and a high boiling point, even in the case where the amount of the residual liquid is greatly increased, the electrode layer is one that has a good capacity retention rate, as described in the examples described later. In addition, the δ P and the boiling point of the dispersion medium are specifically shown in Table 1.

[0024] Table 1

[0025] Residual liquid P (MPa 1 / 2 )]]> ​ Boiling point (°C) Tetralin 2.0 205 Butyl butyrate 2.9 165 Diisobutyl ketone 3.7 168.4 Xylene 1.0 138～144 Toluene 1.4 144

[0026] 1. Residual liquid

[0027] The electrode layer in the present disclosure contains a residual liquid. The residual liquid is a liquid component remaining in the electrode layer. The residual liquid is typically the dispersion medium in the paste described later. In addition, the δ P of the residual liquid is typically less than 2.9 MPa 1 / 2 , and the boiling point is 190°C or higher. The electrode layer can contain only one such residual liquid, or can contain two or more.

[0028] The δ P of the residual liquid is typically less than 2.9 MPa 1 / 2 . The δ P may be 2.5 MPa 1 / 2 or more, can be 2.3 MPa 1 / 2 or more, and can also be 2.1 MPa 1 / 2 or more. If the δ P is large, sulfide electrolyte degradation caused by the residual liquid can not be sufficiently suppressed.

[0029] The boiling point of the residual liquid is usually 190°C or higher, can be 200°C or higher, can be 205°C or higher, and can be 210°C or higher. If the boiling point of the residual liquid is low, the cracking of the electrode layer can not be sufficiently suppressed. On the other hand, the boiling point of the residual liquid is, for example, 300°C or lower, and can be 250°C or lower. If the boiling point of the residual liquid is high, for example, the drying temperature needs to be increased in order to remove the residual liquid, and the manufacturing efficiency easily decreases.

[0030] As the residual liquid, for example, a naphthalene-based compound, a compound containing a lauryl group, and a monocyclic aromatic compound can be given. The naphthalene-based compound is a compound having a naphthalene skeleton, and for example, tetrahydronaphthalene (tetrahydronaphthalene) and naphthalene can be given. The residual liquid can be tetrahydronaphthalene or can not be tetrahydronaphthalene. In addition, the compound containing a lauryl group is a compound having a lauryl group (dodecyl group), and for example, N,N-dimethyl laurylamine (N,N-dimethyl dodecylamine) can be given. The monocyclic aromatic compound is a compound having a monocyclic aromatic hydrocarbon (typically, a benzene ring). The monocyclic aromatic compound can have one monocyclic aromatic hydrocarbon, can have two, or can have three or more. As the monocyclic aromatic compound, for example, divinylbenzene, tetramethylbenzene (for example, 1,2,3,5-tetramethylbenzene, 1,2,3,4-tetramethylbenzene), and diphenylmethane can be given.

[0031] The amount of the residual liquid in the electrode layer is, for example, 500 ppm or more and 7000 ppm or less, can be 1000 ppm or more and 6000 ppm or less, or can be 1500 ppm or more and 5000 ppm or less. If the amount of the residual liquid is small, the electrode layer easily cracks. On the other hand, even if the amount of the residual liquid is large, the influence on the capacity maintenance rate is small, but relatively, the volumetric energy density decreases. In addition, in the present disclosure, even if the amount of the residual liquid is large, the capacity maintenance rate does not easily decrease. Therefore, when the electrode layer is produced, it also has the advantage that the drying process can be simplified. As described later, the amount of the residual liquid can be found by gas chromatography-mass spectrometry (GC-MS).

[0032] 2. Electrode active material

[0033] The electrode layer in the present disclosure contains an electrode active material. The electrode active material can be a positive electrode active material or a negative electrode active material.

[0034] As the positive electrode active material, for example, an oxide active material can be given. As the oxide active material, for example, LiCoO2, LiMnO2, LiNiO2, LiVO2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2and the like rock salt layered active material, LiMn2O4, Li(Ni 0.5 Mn1.5 ) O4, spinel-type active material, LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, olivine-type active material. It is preferable that the surface of the positive electrode active material is coated with an ion-conductive oxide. This is because it can suppress the occurrence of a high-resistance layer due to the reaction of the positive electrode active material with the sulfide solid electrolyte. As the ion-conductive oxide, for example, LiNbO3 can be given. The thickness of the ion-conductive oxide is, for example, 1 nm or more and 30 nm or less.

[0035] As the negative electrode active material, for example, Li-based active materials such as metallic lithium, lithium alloy; carbon-based active materials such as graphite, hard carbon; oxide-based active materials such as lithium titanate; Si-based active materials such as Si single substance, Si alloy, silicon oxide (SiO) can be given. Lithium titanate (LTO) is a compound containing Li, Ti, and O. As the composition of lithium titanate, for example, Li4Ti5O12 can be given. The lithium titanate is preferably a compound represented by Li4Ti5O12. x Ti y O z (3.5≤x≤4.5, 4.5≤y≤5.5, 11≤z≤13). x can be 3.7 or more and 4.3 or less, or 3.9 or more and 4.1 or less. y can be 4.7 or more and 5.3 or less, or 4.9 or more and 5.1 or less. z can be 11.5 or more and 12.5 or less, or 11.7 or more and 12.3 or less. The lithium titanate preferably has a composition represented by Li4Ti5O12. 12

[0036] As the shape of the electrode active material, for example, a granular shape can be given. The average particle diameter (D50) of the electrode active material is, for example, 10 nm or more and 50 nm or less, or 100 nm or more and 20 pm or less. 50 50 The average particle diameter (D50) represents the particle diameter of 50% of the cumulative particle size distribution (median diameter), and is calculated, for example, from the measurement by a laser diffraction type particle size distribution meter, a scanning electron microscope (SEM).

[0037] The proportion of the electrode active material in the electrode layer is, for example, 20 vol% or more and 80 vol% or less, or 30 vol% or more and 70 vol% or less, or 40 vol% or more and 65 vol% or less. If the proportion of the electrode active material is small, the volumetric energy density can be low. On the other hand, if the proportion of the electrode active material is large, the ion conduction path can not be sufficiently formed.

[0038] 3. Sulfide solid electrolyte

[0039] ​​The electrode layer in the present disclosure contains a sulfide solid electrolyte. The sulfide solid electrolyte constitutes an ion conduction path in the electrode layer. The sulfide solid electrolyte generally contains sulfur (S) as a main component of an anion element. The sulfide solid electrolyte contains, for example, Li, A (A is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, In), and S. A preferably contains at least P, and in addition, the sulfide solid electrolyte can contain at least one of Cl, Br, and I as a halogen. In addition, the sulfide solid electrolyte can contain O.

[0040] The sulfide solid electrolyte can be a glass-based sulfide solid electrolyte, a glass-ceramic-based sulfide solid electrolyte, or a crystalline-based sulfide solid electrolyte. In addition, in the case where the sulfide solid electrolyte has a crystal phase, as the crystal phase, for example, a Thio-LISICON-type crystal phase, a LGPS-type crystal phase, a argyrodite-type crystal phase can be cited.

[0041] The composition of the sulfide solid electrolyte is not particularly limited, and for example, xLi2S·(100-x)P2S5 (70≤x≤80), yLiI·zLiBr·(100-y-z)(xLi2S·(1-x)P2S5) (0.7≤x≤0.8, 0≤y≤30, 0≤z≤30) can be cited.

[0042] The sulfide solid electrolyte can have a composition represented by a general formula of Li 4-x Ge 1-x P x S4 (0 < x < 1). In the general formula, at least part of Ge can be substituted with at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In the general formula, at least part of P can be substituted with at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In the general formula, part of Li can be substituted with at least one of Na, K, Mg, Ca, and Zn. In the general formula, part of S can be substituted with a halogen (at least one of F, Cl, Br, and I).

[0043] As other compositions of the sulfide solid electrolyte, for example, Li 7-x-2y PS 6-x-y X y , Li 8-x-2y SiS 6-x- y X y , Li 8-x-2y GeS 6-x-y X y In these compositions, X is at least one of F, Cl, Br, and I, and x and y satisfy 0≤x, 0≤y.

[0044] The sulfide solid electrolyte preferably has high Li ion conductivity. The Li ion conductivity of the sulfide solid electrolyte at 25°C is, for example, 1 x 10 -4 S / cm or more, preferably 1 x 10 -3 S / cm or more. The sulfide solid electrolyte preferably has high insulation. The electronic conductivity of the sulfide solid electrolyte at 25°C is, for example, 10 -6 S / cm or less, can be 10 -8 S / cm or less, can be 10 -10 S / cm or less. In addition, as the shape of the sulfide solid electrolyte, for example, a granular shape can be given. The average particle diameter (D 50 ) of the sulfide solid electrolyte is, for example, 0.1 pm or more and 50 pm or less.

[0045] The proportion of the sulfide solid electrolyte in the electrode layer is, for example, 15 vol% or more and 75 vol% or less, can be 15 vol% or more and 60 vol% or less. If the proportion of the sulfide solid electrolyte is small, ion conduction paths can not be sufficiently formed. On the other hand, if the proportion of the sulfide solid electrolyte is high, the volumetric energy density can be low.

[0046] The proportion of the electrode active material with respect to the total of the electrode active material and the sulfide solid electrolyte is, for example, 40 vol% or more and 80 vol% or less, can be 50 vol% or more and 80 vol% or less, or can be 60 vol% or more and 70 vol% or less. If the proportion of the electrode active material is small, the volumetric energy density can be low. On the other hand, if the proportion of the electrode active material is large, ion conduction paths can not be sufficiently formed.

[0047] The total proportion of the electrode active material and the sulfide solid electrolyte in the electrode layer is, for example, 75 vol% or more and less than 100 vol%, can be 80 vol% or more and less than 100 vol%, or can be 90 vol% or more and less than 100 vol%.

[0048] 4. Electrode layer

[0049] The electrode layer in the present disclosure contains the electrode active material, the sulfide solid electrolyte, and the residual liquid described above. The electrode layer can be a positive electrode layer, or can be a negative electrode layer.

[0050] The electrode layer in the present disclosure can contain a conductive material. As the conductive material, for example, a carbon material, a metal particle, a conductive polymer can be cited. As the carbon material, for example, a particulate carbon material such as acetylene black (AB), ketjen black (KB), a fibrous carbon material such as carbon fiber, carbon nanotube (CNT), carbon nanofiber (CNF) can be cited. The proportion of the conductive material in the electrode layer is, for example, 0.1% by volume or more and 10% by volume or less, and can be 0.3% by volume or more and 10% by volume or less.

[0051] The electrode layer in the present disclosure can contain a binder. As the binder, for example, a fluorine-based binder such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a rubber-based binder such as acrylate butadiene rubber (ABR), styrene butadiene rubber (SBR) can be cited. The proportion of the binder in the electrode layer is, for example, 1% by volume or more and 20% by volume or less, and can be 5% by volume or more and 20% by volume or less. In addition, the thickness of the electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

[0052] The manufacturing method of the electrode layer in the present disclosure is not particularly limited. In the present disclosure, a manufacturing method of an electrode layer is also provided, which is a method of manufacturing an electrode layer used for an all-solid-state battery, the method including: a preparation step of preparing a paste containing an electrode active material, a sulfide solid electrolyte, and a dispersion medium; a coating step of forming a coated layer by coating the paste; and a drying step of drying the coated layer to remove the dispersion medium, the dispersion medium having a Hansen solubility parameter in which δ P less than 2.9 MPa 1 / 2 and a boiling point of 190°C or higher. The paste can further contain at least one of a conductive material and a binder. The method of coating the paste is not particularly limited, and for example, a doctor blade method can be cited. The drying temperature of the coated layer is, for example, 80°C or higher and 120°C or lower. The drying time of the coated layer is, for example, 10 minutes or more and 5 hours or less. In addition, the residual amount (residual liquid amount) of the dispersion medium in the electrode layer is preferably in the above range.

[0053] B. All-solid-state battery

[0054] Figure 1 is a schematic cross-sectional view illustrating an all-solid-state battery of the present disclosure. Figure 1 The illustrated all-solid-state battery 10 has a positive electrode layer 1, a negative electrode layer 2, a solid electrolyte layer 3 disposed between the positive electrode layer 1 and the negative electrode layer 2, a positive electrode current collector 4 that collects the positive electrode layer 1, and a negative electrode current collector 5 that collects the negative electrode layer 2. In the present disclosure, at least one of the positive electrode layer 1 and the negative electrode layer 2 has the electrode layer described in the above "A. Electrode layer".

[0055] According to the present disclosure, by using the above electrode layer, an all-solid-state battery with a good capacity maintenance rate is obtained.

[0056] 1. Positive electrode layer and negative electrode layer

[0057] As for the positive electrode layer and the negative electrode layer in the present disclosure, the same applies as described in the "A. Electrode layer", and thus the description is omitted here. In the present disclosure, it can be (i) that the positive electrode layer corresponds to the above-described electrode layer, and the negative electrode layer does not correspond to the above-described electrode layer, it can be (ii) that the positive electrode layer does not correspond to the above-described electrode layer, and the negative electrode layer corresponds to the above-described electrode layer, and it can be (iii) that both the positive electrode layer and the negative electrode layer correspond to the above-described electrode layer.

[0058] 2. Solid electrolyte layer

[0059] The solid electrolyte layer of the present disclosure is disposed between the positive electrode layer and the negative electrode layer. The solid electrolyte layer contains at least a solid electrolyte, and can further contain a binder. As for the solid electrolyte and the binder, the same applies as described in the "A. Electrode layer", and thus the description is omitted here. The thickness of the solid electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less.

[0060] 3. All-solid-state battery

[0061] In the present disclosure, the "all-solid-state battery" refers to a battery provided with a solid electrolyte layer (a layer containing at least a solid electrolyte). In addition, the all-solid-state battery in the present disclosure includes a power generating element having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer. The power generating element generally has a positive electrode current collector and a negative electrode current collector. The positive electrode current collector is disposed, for example, on the surface of the positive electrode layer on the side opposite to the solid electrolyte layer. As a material of the positive electrode current collector, for example, a metal such as aluminum, SUS, nickel, or the like can be given. As a shape of the positive electrode current collector, for example, a foil shape, a mesh shape can be given. On the other hand, the negative electrode current collector is disposed, for example, on the surface of the negative electrode layer on the side opposite to the solid electrolyte layer. As a material of the negative electrode current collector, for example, a metal such as copper, SUS, nickel, or the like can be given. As a shape of the negative electrode current collector, for example, a foil shape, a mesh shape can be given.

[0062] The all-solid-state battery of the present disclosure can be provided with an exterior body that houses the power generating element. As the exterior body, for example, a laminate type exterior body, a shell type exterior body can be given. In addition, the all-solid-state battery in the present disclosure can also be provided with a constraint jig that applies a constraint pressure in the thickness direction to the power generating element. As the constraint jig, a publicly known jig can be used. The constraint pressure is, for example, 0.1 MPa or more and 50 MPa or less, and can be 1 MPa or more and 20 MPa or less. If the constraint pressure is small, it can not be possible to form a good ion conduction path and a good electron conduction path. On the other hand, if the constraint pressure is large, the constraint jig is upsized, and the volumetric energy density can decrease.

[0063] The kind of the all-solid battery in the present disclosure is not particularly limited, and a lithium ion secondary battery is typical. The use of the all-solid battery is not particularly limited, and for example, a power source for a vehicle such as a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), an electric vehicle (BEV), a gasoline vehicle, a diesel vehicle, and the like can be cited. A power source for driving a hybrid electric vehicle, a plug-in hybrid electric vehicle, or an electric vehicle is particularly preferable. In addition, the all-solid battery in the present disclosure can be used as a power source for a moving body other than a vehicle, such as a railway, a ship, an airplane, and the like, and can be used as a power source for an electric product such as an information processing device and the like.

[0064] Further, the present disclosure is not limited to the described embodiments. The described embodiments are examples, and technical solutions having substantially the same structure as the technical ideas described in the claims in the present disclosure, and capable of obtaining the same effects are all included in the technical scope of the present disclosure.

[0065] Experimental Example 1

[0066] To tetrahydronaphthalene (δ P = 2.0 and a boiling point of 205°C), a sulfide solid electrolyte (10LiI·15LiBr·75(0.75Li2S·0.25P2S5)) was added, mixed using an ultrasonic homogenizer (UH-50 manufactured by SMT), and a dispersion liquid was obtained. Then, the solid components were separated using a centrifugal separator, and thus a solution was obtained.

[0067] Experimental Example 2

[0068] A solution was obtained in the same manner as in Experimental Example 1, except that butyl butyrate (δ P = 2.9 and a boiling point of 165°C) was used instead of tetrahydronaphthalene.

[0069] Evaluation

[0070] The amount of Li in the solutions obtained in Experimental Examples 1 and 2 was found by acid decomposition / ICP emission spectroscopy (acid decomposition / ICP-AES). In addition, the amount of S in the solutions obtained in Experimental Examples 1 and 2 was found by oxygen combustion / ion chromatography. The results are shown in Table 2. Further, the amounts of Li and S shown in Table 2 are relative values when the results of Experimental Example 1 are taken as 1.

[0071] Table 2

[0072] Dispersing medium delta P (MPa 1 / 2 )]]> Li amount S amount Experimental Example 1 Tetralin 2.0 1 1 Experimental Example 2 Butyl butyrate 2.9 180 48

[0073] As shown in Table 2, tetrahydronaphthalene has a smaller δ P than butyl butyrate, and thus it was confirmed that the reactivity with the sulfide solid electrolyte is low.

[0074] Example 1

[0075] Li4Ti5O was used as the negative electrode active material. 12 LTO particles. Weigh the negative electrode active material, conductive material (VGCF), binder (PVdF), and dispersion medium (tetrahydronaphthalene, δ-hydroxyl group). P =2.0 and boiling point 205℃), and mixed for 30 minutes using an ultrasonic homogenizer (SMT UH-50). Then, a sulfide solid electrolyte (LiI-LiBr-Li2S-P2S5 glass ceramic) was added, and mixed again for 30 minutes using an ultrasonic homogenizer (SMT UH-50). This yields the negative electrode paste. Next, the negative electrode paste is coated onto the negative electrode current collector (Ni foil). After coating, it is dried on a heating plate at 100℃ for 30 minutes. This forms the negative electrode layer on the negative electrode current collector.

[0076] Comparative Example 1

[0077] In addition to using xylene (δ P Except for tetrahydronaphthalene (1.0 and boiling point 138°C), a negative electrode layer is formed on the negative electrode current collector in the same manner as in Reference Example 3.

[0078] evaluate

[0079] The occurrence of cracks was confirmed by observing the surface of the negative electrode layers fabricated in Example 1 and Comparative Example 1. The results are shown in Table 3.

[0080] Table 3

[0081] Dispersing medium Boiling point (°C) Crack of negative electrode layer Example 1 Tetralin 205 None Comparative Example 1 Xylene 138 Yes

[0082] As shown in Table 3, no cracks were formed in the negative electrode layer in Example 1, but cracks were formed in the negative electrode layer in Comparative Example 1. This is presumably because xylene has a low boiling point, resulting in a large amount of volatilization during drying. In contrast, tetrahydronaphthalene has a high boiling point, so it is presumed that a large amount of volatilization does not occur during drying.

[0083] Example 2

[0084] Making positive electrode paste

[0085] As the positive electrode active material, LiNi with a surface treated by LiNbO3 was used. 1 / 3 Co 1 / 3 Mn 1 / 3 O2. The positive electrode active material, conductive material (VGCF), sulfide solid electrolyte (LiI-LiBr-Li2S-P2S5 glass-ceramic), binder (PVdF), and dispersion medium (tetrahydronaphthalene, δ-hydroxyl group) are then combined. P =2.0 and boiling point 205℃), and mixed using an ultrasonic homogenizer (SMT UH-50). This yields the positive electrode paste.

[0086] Production of negative electrode paste

[0087] As the negative electrode active material, Li4Ti5O 12 particles (LTO) were used. The negative electrode active material, the conductive material (VGCF), the binder (PVdF), and the dispersion medium (tetrahydronaphthalene, δ P = 2.0 and a boiling point of 205°C) were mixed for 30 minutes using an ultrasonic homogenizer (UH-50 manufactured by SMT). Then, the sulfide solid electrolyte (LiI-LiBr-Li2S-P2S5-based glass-ceramic) was added, and the mixture was again mixed for 30 minutes using an ultrasonic homogenizer (UH-50 manufactured by SMT). In this way, the negative electrode paste was obtained.

[0088] Production of SE layer paste

[0089] To a polypropylene-made container, the dispersion medium (heptane), the binder (a heptane solution containing 5 mass% of a butadiene rubber-based binder), and the sulfide solid electrolyte (LiI-LiBr-Li2S-P2S5-based glass-ceramic, average particle diameter D 50 : 2.5 μm) were added, and the mixture was stirred for 30 seconds using an ultrasonic homogenizer (UH-50 manufactured by SMT). Subsequently, the container was shaken with a shaker for 3 minutes. In this way, the paste for the solid electrolyte layer (SE layer paste) was obtained.

[0090] Production of all-solid-state battery

[0091] First, the positive electrode paste was applied to the positive electrode current collector (aluminum foil) by the doctor blade method using an applicator. After the application, the positive electrode was dried on a hot plate at 50°C for 10 minutes and then on a hot plate at 100°C for 10 minutes. In this way, the positive electrode having the positive electrode current collector and the positive electrode layer was obtained. Subsequently, the negative electrode paste was applied to the negative electrode current collector (Ni foil). After the application, the negative electrode was dried on a hot plate at 50°C for 10 minutes and then on a hot plate at 100°C for 10 minutes. In this way, the negative electrode having the negative electrode current collector and the negative electrode layer was obtained. Here, the weight per unit area of the negative electrode layer was adjusted so that the charge specific capacity of the negative electrode was 1.15 times as large as that of the positive electrode, which was 185 mAh / g.

[0092] Subsequently, the positive electrode was pressed. On the surface of the positive electrode layer after the pressing, the SE layer paste was applied by a die coater, and dried on a hot plate at 100°C for 30 minutes. Then, roll-pressing was performed at a line pressure of 5 tons / cm. In this way, the positive electrode-side laminate having the positive electrode current collector, the positive electrode layer, and the solid electrolyte layer was obtained. Subsequently, the negative electrode was pressed. On the surface of the negative electrode layer after the pressing, the SE layer paste was applied by a die coater, and dried on a hot plate at 100°C for 30 minutes. Then, roll-pressing was performed at a line pressure of 5 tons / cm. In this way, the negative electrode-side laminate having the negative electrode current collector, the negative electrode layer, and the solid electrolyte layer was obtained.

[0093] The positive electrode-side laminate and the negative electrode-side laminate were punched, and the un-pressed solid electrolyte layer was disposed between the two laminates. Then, the laminates were rolled at 130°C under a line pressure of 2 ton / cm to obtain a power generating element having a positive electrode, a solid electrolyte layer, and a negative electrode in this order. The obtained power generating element was sealed and restrained at 5 MPa, and thus a full solid battery was obtained.

[0094] Example 3

[0095] A full solid battery was produced in the same manner as in Example 2, except that the drying conditions when producing the positive electrode layer and the negative electrode layer were changed to drying on a hot plate at 80°C for 10 minutes and then drying on a hot plate at 110°C for 10 minutes, respectively.

[0096] Comparative Example 2

[0097] A positive electrode paste and a negative electrode paste were produced in the same manner as in Example 2, except that butyl butyrate (δ P = 2.9 and a boiling point of 165°C) was used instead of tetrahydronaphthalene as the dispersion medium. A full solid battery was produced in the same manner as in Example 2, except that the respective pastes produced were used and the drying conditions when producing the positive electrode layer and the negative electrode layer were changed to drying on a hot plate at 100°C for 30 minutes, respectively.

[0098] Comparative Example 3

[0099] A full solid battery was produced in the same manner as in Comparative Example 2, except that the drying conditions when producing the positive electrode layer and the negative electrode layer were changed to drying on a hot plate at 100°C for 15 minutes, respectively.

[0100] Comparative Example 4

[0101] A full solid battery was produced in the same manner as in Comparative Example 2, except that the drying conditions when producing the positive electrode layer and the negative electrode layer were changed to drying on a hot plate at 95°C for 30 minutes, respectively.

[0102] Comparative Example 5

[0103] A full solid battery was produced in the same manner as in Comparative Example 2, except that the drying conditions when producing the positive electrode layer and the negative electrode layer were changed to drying on a hot plate at 90°C for 30 minutes, respectively.

[0104] Evaluation

[0105] Measurement of residual liquid amount

[0106] The active material layers (positive electrode layer and negative electrode layer) were taken out from the electrodes (positive electrode and negative electrode) produced in Examples 2 and 3 and Comparative Examples 2 to 5, and stirred with methanol. Then, the solid components were separated using a centrifugal separator, and thereby a solution was obtained. The residual liquid amount (residual dispersion medium amount) of the obtained solution was found by gas chromatography-mass spectrometry (GC-MS). The results are shown in Table 4.

[0107] Capacity maintenance rate measurement

[0108] The capacity maintenance rates of the all-solid batteries produced in Examples 2 and 3 and Comparative Examples 2 to 5 were measured. Specifically, the all-solid batteries were subjected to constant current charging at a current corresponding to 0.3 C, and after the single cell voltage reached 2.7 V, constant voltage charging was performed, and the charging was ended at the time when the charging current reached a value corresponding to 0.01 C. Then, constant current discharging was performed at a current corresponding to 0.3 C, and ended at the time when 1.5 V was reached. This discharging capacity was taken as the discharging capacity of the 1st cycle. Then, 5 cycles of charging and discharging were performed under the same conditions, and the discharging capacity of the 5th cycle was found. The capacity maintenance rate was found by dividing the discharging capacity of the 5th cycle by the discharging capacity of the 1st cycle. The results are shown in Table 4.

[0109] Table 4

[0110]

[0111] As shown in Table 4, it was confirmed that the all-solid batteries produced in Examples 2 and 3 had higher capacity maintenance rates than the all-solid batteries produced in Comparative Examples 2 to 5. In addition, in Comparative Examples 2 to 5, it was confirmed that the capacity maintenance rate decreased as the residual liquid amount increased. On the other hand, in Example 2, although an electrode layer having a larger residual liquid amount was used than in Comparative Example 5, a high capacity maintenance rate of 98% was confirmed.

Claims

1. An electrode layer used for an all-solid battery, characterized by, containing an electrode active material, a sulfide solid electrolyte, and a residual liquid, δ in the Hansen solubility parameter of the residual liquid P less than 2.9 MPa 1 / 2 having a boiling point of 190°C or higher, an amount of the residual liquid in the electrode layer is 1500 ppm or more and 5000 ppm or less.

2. The electrode layer according to claim 1, characterized by, the residual liquid contains at least one of a naphthalene-based compound, a lauryl group-containing compound, and a monocyclic aromatic-based compound.

3. The electrode layer according to claim 2, characterized by, the residual liquid contains the naphthalene-based compound.

4. The electrode layer according to claim 3, characterized by, the naphthalene-based compound is tetrahydronaphthalene.

5. The electrode layer according to claim 2, characterized by, the residual liquid contains the lauryl group-containing compound.

6. The electrode layer according to claim 2, characterized by, the residual liquid contains the monocyclic aromatic-based compound.

7. The electrode layer according to any one of claims 1 to 6, characterized by, the electrode layer is a positive electrode layer.

8. The electrode layer according to any one of claims 1 to 6, characterized by, the electrode layer is a negative electrode layer.

9. An all-solid battery, which is an all-solid battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, characterized by, at least one of the positive electrode layer and the negative electrode layer is the electrode layer according to any one of claims 1 to 8.

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