JP2012199003A - Slurry, production method of solid electrolyte layer and production method of electrode active material layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide slurry which enhances dispersibility of a sulfide solid electrolyte material, and can deposit a film with high uniformity.SOLUTION: The slurry contains a sulfide solid electrolyte material, and alcohol having 6 or more carbon atoms in the principal chain, and a side-chain of alkyl radical in a carbon atom of the principal chain up to the third position counting from the carbon atom bonded with an OH radical in the principal chain.

Description

  The present invention relates to a slurry capable of improving the dispersibility of a sulfide solid electrolyte material and forming a highly uniform film.

  With the rapid spread of information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones in recent years, development of batteries that are used as power sources has been regarded as important. Also in the automobile industry and the like, development of high-power and high-capacity batteries for electric vehicles or hybrid vehicles is being promoted. Currently, lithium batteries are attracting attention among various batteries from the viewpoint of high energy density.

  Since lithium batteries currently on the market use an electrolyte containing a flammable organic solvent, it is possible to install safety devices that suppress the temperature rise during short circuits and to improve the structure and materials to prevent short circuits. Necessary. On the other hand, an all-solid lithium battery in which the electrolyte is changed to a solid electrolyte layer to make the battery all solid does not use a flammable organic solvent in the battery. It is considered to be excellent in productivity.

  A sulfide solid electrolyte material is known as a solid electrolyte material used for such a solid electrolyte layer. As a solvent for applying the sulfide solid electrolyte material by a wet process, for example, Non-Patent Document 1 discloses the use of a nonpolar solvent such as toluene or heptane.

Taro Inada et al., “Silicone as a binder in composite electrolytes”, Journal of Power Sources 119-121 (2003) 948-950

  However, a nonpolar solvent such as toluene or heptane has a problem that even if the sulfide solid electrolyte material is dispersed, the sedimentation rate of the sulfide solid electrolyte material is high and uniform coating cannot be performed. Moreover, when only such a nonpolar solvent is used as a dispersion medium, there exists a problem that coating adjuvants, such as a dispersing agent, cannot be used. The present invention has been made in view of the above problems, and a main object of the present invention is to provide a slurry capable of improving the dispersibility of the sulfide solid electrolyte material and forming a highly uniform film.

  In order to solve the above-described problems, in the present invention, the sulfide solid electrolyte material and the main chain have 6 or more carbon atoms, and the third to the third counted from the carbon atoms in the main chain to which the OH group is bonded. And an alcohol having a side chain of an alkyl group on the carbon atom in the main chain at the position.

  According to the present invention, by using the alcohol as a dispersion medium for the slurry, the dispersibility of the sulfide solid electrolyte material is improved, and a slurry capable of forming a highly uniform film can be obtained.

  In the above invention, the alcohol is preferably 2-ethylhexanol or 2,6-dimethyl-4-heptanol.

In the above-mentioned invention, the sulfide-based solid electrolyte material is preferably made of using a raw material composition containing Li 2 _S and P ₂ S _5. This is because a sulfide solid electrolyte material having high Li ion conductivity can be obtained.

In the above invention, the ratio of Li ₂ S and _P 2 _{S 5} in the raw material composition at a molar _{ratio, Li 2 S: P 2 S} 5 = 70: 30~80: is preferably in the range of 20 . This is because a stable sulfide solid electrolyte material can be obtained and reaction with the alcohol can be suppressed.

  In the said invention, it is preferable that the said sulfide solid electrolyte material contains LiI. This is because a sulfide solid electrolyte material having high Li ion conductivity can be obtained.

  Moreover, in the present invention, the main electrolyte in the sulfide solid electrolyte material and the main chain having 6 or more carbon atoms in the main chain and up to the third position counted from the carbon atom in the main chain to which the OH group is bonded. Kneading an alcohol having an alkyl side chain on a carbon atom in the chain to prepare a slurry for forming a solid electrolyte layer; and applying the slurry for forming a solid electrolyte layer on a substrate to form a solid electrolyte layer A method for producing a solid electrolyte layer comprising: a coating process for forming a coating film for coating; and a drying process for drying the coating film for forming a solid electrolyte layer to form a solid electrolyte layer. To do.

  According to the present invention, by using the alcohol as a dispersion medium of the slurry for forming the solid electrolyte layer, the dispersibility of the sulfide solid electrolyte material is improved in the kneading step, and the solid electrolyte layer is formed with high uniformity in the coating step. The coating film can be formed. For this reason, a uniform solid electrolyte layer can be obtained.

  In the present invention, the electrode active material, the sulfide solid electrolyte material, and the main chain have 6 or more carbon atoms, and up to the third counting from the carbon atoms in the main chain to which the OH group is bonded. A kneading step of kneading an alcohol having an alkyl side chain to a carbon atom in the main chain at a position to prepare a slurry for forming an electrode active material layer; and applying the slurry for forming an electrode active material layer on a substrate A coating step for forming an electrode active material layer forming coating film; and a drying step for drying the electrode active material layer forming coating film to form an electrode active material layer. An electrode active material layer manufacturing method is provided.

  According to the present invention, by using the alcohol as a dispersion medium for the slurry for forming the electrode active material layer, the dispersibility of the sulfide solid electrolyte material is improved in the kneading process, and the electrode active material having high uniformity in the coating process. A film for forming a layer can be formed. For this reason, a uniform electrode active material layer can be obtained.

  In this invention, the dispersibility of sulfide solid electrolyte material improves, and there exists an effect that the slurry which can be formed into a film with high uniformity can be provided.

It is a flowchart which shows an example of the manufacturing method of the solid electrolyte layer of this invention. It is a flowchart which shows an example of the manufacturing method of the electrode active material layer of this invention. 4 is a graph showing the results of charge / discharge measurement of evaluation batteries obtained in Example 2 and Comparative Example 2. 6 is a graph showing the results of AC impedance measurement of evaluation batteries obtained in Example 2 and Comparative Example 2. It is a graph which shows the result of the sedimentation rate measurement of the slurry obtained in Example 3 and Comparative Example 3.

  Hereinafter, the slurry of the present invention, the method for producing a solid electrolyte layer, and the method for producing an electrode active material layer will be described in detail.

A. Slurry First, the slurry of this invention is demonstrated. The slurry of the present invention has a sulfide solid electrolyte material and a main chain having 6 or more carbon atoms in the main chain at the third position counting from the carbon atoms in the main chain to which OH groups are bonded. And an alcohol having an alkyl side chain on the carbon atom.

According to the present invention, by using the alcohol as a dispersion medium for the slurry, the dispersibility of the sulfide solid electrolyte material is improved, and a slurry capable of forming a highly uniform film can be obtained.
Hereinafter, the slurry of this invention is demonstrated for every structure.

1. Alcohol First, the alcohol in the present invention will be described. The alcohol in the present invention has 6 or more carbon atoms in the main chain, and an alkyl group is bonded to the carbon atom in the main chain at the third position counting from the carbon atom in the main chain to which the OH group is bonded. It has a side chain.

  One feature of the alcohol in the present invention is that the main chain has 6 or more carbon atoms. When the number of carbon atoms in the main chain is 6 or more, an alcohol with low water solubility can be obtained, and a reaction with the sulfide solid electrolyte material can be suppressed. In the present invention, the main chain means “the longest carbon chain containing a carbon atom to which an OH group is bonded”. The number of carbon atoms in the main chain may be 6 or more, but it is preferably in the range of 6 to 10 among them. This is because by setting the number of carbon atoms in the main chain to 10 or less, a liquid alcohol can be obtained at room temperature. The water content of the alcohol is preferably lower from the viewpoint of reactivity with the sulfide solid electrolyte material, and specifically, it is preferably 100 ppm or less.

  In addition, the alcohol in the present invention is characterized by having a side chain of an alkyl group on the carbon atom in the main chain at the third position counting from the carbon atom in the main chain to which the OH group is bonded. Here, the carbon atom in the main chain to which the OH group is bonded is defined as the carbon atom in the main chain at the first position. Since the side chain of the alkyl group is close to the OH group, steric hindrance is caused, so that the dissolution of the sulfide solid electrolyte material can be prevented. In the present invention, the side chain refers to “a carbon chain other than the main chain bonded to the main chain”. Examples of the alkyl group include a methyl group and an ethyl group. Moreover, the said alcohol should just have at least 1 side chain of the said alkyl group, and may have multiple.

The alcohol in the present invention has a dispersion effect (surface active effect). Here, the dispersion effect refers to an effect in which the sedimentation rate of particles existing in the liquid is slower than the sedimentation rate obtained from the Stokes equation shown in the following equation (1). In the present invention, the dispersibility of the sulfide solid electrolyte material is improved by slowing the sedimentation rate of the sulfide solid electrolyte material in the alcohol. In the formula, U: settling velocity, d: particle diameter, ρ _p : particle specific gravity, ρ _f : liquid specific gravity, η: viscosity, g: gravitational acceleration. Moreover, although the said alcohol is used as a dispersion medium of a slurry, it functions also as a dispersing agent.

  In addition, the alcohol in the present invention does not significantly reduce the Li ion conductivity of the sulfide solid electrolyte material before and after the dispersion of the sulfide solid electrolyte material into the alcohol, and usually after being dispersed in the alcohol. The Li ion conductivity of the sulfide solid electrolyte material is not lowered to 1/10 or less of the Li ion conductivity of the sulfide solid electrolyte material before being dispersed in alcohol. Here, the Li ion conductivity of the sulfide solid electrolyte material after being dispersed in alcohol is the Li ion conductivity of a sample obtained by forming a powder obtained by applying a slurry and drying it into a pellet. It shall be obtained by measurement.

  Specific examples of such alcohol include 2-ethylhexanol and 2,6-dimethyl-4-heptanol. The alcohol in the present invention may be a single alcohol or a mixture of a plurality of alcohols.

  The slurry of the present invention may contain a conventional nonpolar solvent such as heptane, xylene, toluene and the like in addition to the alcohol. The ratio of the alcohol to the total solvent contained in the slurry of the present invention is, for example, preferably 0.1% by weight or more, more preferably 10% by weight or more, and 30% by weight or more. Further preferred. Note that the solvent contained in the slurry of the present invention may be only the alcohol. Moreover, when the slurry of this invention contains a binder and the solubility of the binder with respect to the said alcohol is low, it is preferable to use together the nonpolar solvent mentioned above. In this case, the ratio of the alcohol to the total solvent contained in the slurry of the present invention is preferably, for example, in the range of 0.1 wt% to 50 wt%, and in the range of 30 wt% to 40 wt%. More preferably.

2. Sulfide solid electrolyte material Next, the sulfide solid electrolyte material in the present invention will be described. The sulfide solid electrolyte material in the present invention is not particularly limited as long as it contains sulfur (S) and has ion conductivity. Here, when the slurry of the present invention is used in a lithium battery, as the sulfide solid electrolyte material, for example, a raw material composition containing Li ₂ S and a sulfide of an element belonging to Group 13 to Group 15 is used. What is used can be mentioned.

Examples of the Group 13 to Group 15 elements include B, Al, Si, Ge, P, As, and Sb. Moreover, as a sulfide of an element of Group 13 to Group 15, specifically, B ₂ S ₃ , Al ₂ S ₃ , SiS ₂ , GeS ₂ , P ₂ S ₃ , P ₂ S ₅ , As ₂ S ₃ , Sb ₂ S _{3 and the} like can be mentioned. In particular, in the present invention, a sulfide solid electrolyte material using a raw material composition containing Li ₂ S and a sulfide of an element belonging to Group 13 to Group 15 is Li ₂ S—P ₂ S _5. The material is preferably a Li ₂ S—SiS ₂ material, a Li ₂ S—GeS ₂ material or a Li ₂ S—Al ₂ S ₃ material, and more preferably a Li ₂ S—P ₂ S ₅ material. This is because the Li ion conductivity is excellent. _{Incidentally,} Li and the 2 _S-P 2 _{S 5} material, a sulfide solid electrolyte material obtained by using a raw material composition containing Li ₂ S and _P 2 _{S 5,} Li ₂ S and _P 2 _{S 5} the main What is necessary is just to contain as a raw material, and also other materials may be included.

Li ₂ S contained in the raw material composition preferably has few impurities. This is because side reactions can be suppressed. Examples of the method for synthesizing Li ₂ S include the method described in JP-A-7-330312. Furthermore, Li ₂ S is preferably purified using the method described in WO2005 / 040039. In addition to Li ₂ S and Group 13 to Group 15 element sulfides, the raw material composition includes Li ₃ PO ₄ , Li ₄ SiO ₄ , Li ₄ GeO ₄ , Li ₃ BO _3, and Li ₃ BO _3. It may contain at least one kind of lithium orthooxo acid selected from the group consisting of ₃ AlO ₃ . By adding such a lithium orthooxo acid, a more stable sulfide solid electrolyte material can be obtained.

  The sulfide solid electrolyte material in the present invention preferably contains substantially no cross-linking sulfur. This is because the reaction with the alcohol can be suppressed, and the decrease in ionic conductivity can be suppressed. Since bridging sulfur has high reactivity, it reacts with the alcohol to cause deterioration of the sulfide solid electrolyte material. Here, “bridged sulfur” refers to a sulfur element having an —S— bond that is generated during the synthesis of the sulfide solid electrolyte material. “Substantially free of bridging sulfur” means that the proportion of bridging sulfur contained in the sulfide solid electrolyte material is so small as not to be affected by the reaction with the alcohol. In this case, the ratio of cross-linking sulfur is, for example, preferably 10 mol% or less, and more preferably 5 mol% or less.

Further, “substantially free of bridging sulfur” can be confirmed by measuring a Raman spectrum. For example, when the sulfide solid electrolyte material is Li ₂ S—P ₂ S ₅ material, the peak of S ₃ P—S—PS ₃ unit (P ₂ S ₇ unit) having bridging sulfur is usually 402 cm ^−1. Appear in Therefore, in the present invention, it is preferable that this peak is not detected. Further, the peak of PS ₄ ^3- unit usually appears at 417 cm ⁻¹ . In the present invention, the intensity _{I 402} at 402 cm ^-1 is preferably smaller than the intensity _{I 417} at 417 cm ^-1. More specifically, with respect to the intensity I ₄₁₇ , the intensity I ₄₀₂ is, for example, preferably 70% or less, more preferably 50% or less, and even more preferably 35% or less. As for the sulfide solid electrolyte material other than Li 2 _{S-P 2} S ₅ material, to identify the unit containing the crosslinking sulfur, by measuring the peak of the unit, it is substantially free of bridging sulfur It can be judged that there is no. Note that “substantially free of cross-linking sulfur” can be confirmed using the raw material composition ratio when synthesizing the sulfide solid electrolyte material and the NMR measurement result in addition to the Raman spectroscopic spectrum measurement result. Can do.

Also, the sulfide solid electrolyte material, if it is made by using the raw material composition containing Li 2 _S, the sulfide solid electrolyte material is preferably substantially free of Li 2 _S. “Substantially free of Li ₂ S” means that Li ₂ S derived from the starting material is not substantially contained. Li ₂ S is preferably not included because it has a high reactivity like bridging sulfur. “Substantially free of Li ₂ S” can be confirmed by X-ray diffraction. Specifically, when it does not have a Li ₂ S peak (2θ = 27.0 °, 31.2 °, 44.8 °, 53.1 °), it is determined that it does not substantially contain Li ₂ S. can do. If the ratio of Li ₂ S in the raw material composition is too large, the sulfide solid electrolyte material tends to contain Li ₂ S. Conversely, if the ratio of Li ₂ S in the raw material composition is too small, the sulfide The solid electrolyte material tends to contain the above-mentioned crosslinked sulfur.

Also, the sulfide solid electrolyte material, if substantially free of bridging sulfur and Li 2 _S, usually, the sulfide solid electrolyte material has a composition of ortho-composition or the vicinity thereof. Here, ortho generally refers to one having the highest degree of hydration among oxo acids obtained by hydrating the same oxide. In the present invention, the crystal composition in which Li ₂ S is added most in the sulfide is called the ortho composition. For example, in the Li ₂ S—P ₂ S ₅ system, Li ₃ PS ₄ corresponds to the ortho composition, in the Li ₂ S—SiS ₂ system, Li ₄ SiS ₄ corresponds to the ortho composition, and in the Li ₂ S—GeS ₂ system. Li ₄ GeS ₄ corresponds to the ortho composition, and in the Li ₂ S—Al ₂ S ₃ system, Li ₃ AlS ₃ corresponds to the ortho composition.

In the case of a Li ₂ S—P ₂ S ₅ -based sulfide solid electrolyte material, the ratio of Li ₂ S and P ₂ S ₅ to obtain the ortho composition is Li ₂ S: P ₂ S ₅ = 75 on a molar basis. : 25. The same applies to the case of a Li ₂ S—Al ₂ S ₃ -based sulfide solid electrolyte material. On the other hand, in the case of a Li ₂ S—SiS ₂ -based sulfide solid electrolyte material, the ratio of Li ₂ S and SiS ₂ to obtain the ortho composition is Li ₂ S: SiS ₂ = 66.7: 33.3 on a molar basis. It is. The same applies to the case of a Li ₂ S—GeS ₂ -based sulfide solid electrolyte material.

The raw material composition is, when containing Li ₂ S and _P 2 _{S 5,} the proportion of Li ₂ S and _P 2 _{S 5} is on a molar _{basis, Li 2 S: P 2 S} 5 = 72: 28~78: 22 is preferable, Li ₂ S: P ₂ S ₅ = 73: 27 to 77:23 is more preferable, and Li ₂ S: P ₂ S ₅ = 74: 26 to 76 is preferable. : More preferably within the range of 24. By setting the ratio of both to a ratio including the ratio of obtaining an ortho composition (Li ₂ S: P ₂ S ₅ = 75: 25) and its vicinity, a sulfide solid electrolyte material having low reactivity with the alcohol is obtained. Because it can. The same applies when the raw material composition contains Li ₂ S and Al ₂ S ₃ . On the other hand, the raw material composition is, when containing Li ₂ S and SiS _2, the ratio of Li ₂ S and SiS ₂ are on a molar _{basis, Li 2 S: SiS 2 =} 63: 37~70: 30 in the range of It is preferable that Li ₂ S: SiS ₂ = 64: 36 to 69:31, and Li ₂ S: SiS ₂ = 65: 35 to 68:32 is preferable. Is more preferable. By setting the ratio of both to a range including the ratio of obtaining an ortho composition (Li ₂ S: SiS ₂ = 66.7: 33.3) and the vicinity thereof, a sulfide solid electrolyte material having low reactivity with the alcohol It is because it can obtain. The same applies when the raw material composition contains Li ₂ S and GeS ₂ .

Moreover, it is preferable that the sulfide solid electrolyte material in this invention contains LiI. This is because a sulfide solid electrolyte material having high Li ion conductivity can be obtained. Also, the sulfide solid electrolyte material in the present invention preferably contains a Li 2 _O. It is because it can be set as the sulfide solid electrolyte material with little hydrogen sulfide generation amount.

The sulfide solid electrolyte material in the present invention may be sulfide glass, or sulfide glass ceramic obtained by heat-treating the sulfide glass. The sulfide glass can be obtained, for example, by subjecting the raw material composition to an amorphization method. Examples of the amorphization method include a mechanical milling method and a melt quenching method, and among them, the mechanical milling method is preferable. This is because processing at room temperature is possible, and the manufacturing process can be simplified. Mechanical milling is not particularly limited as long as the raw material composition is mixed while imparting mechanical energy, and examples thereof include a ball mill, a turbo mill, a mechano-fusion, and a disk mill. A ball mill is preferable, and a planetary ball mill is particularly preferable. This is because a desired sulfide solid electrolyte material can be obtained efficiently. Moreover, it is preferable to set the conditions of mechanical milling so that a desired sulfide solid electrolyte material can be obtained. On the other hand, sulfide glass ceramics can be obtained, for example, by heat-treating sulfide glass at a temperature higher than the crystallization temperature. That is, a sulfide glass ceramic can be obtained by subjecting the raw material composition to an amorphization method and further heat treatment. Depending on the heat treatment conditions, bridging sulfur and Li ₂ S may be generated or a stable phase may be generated. Therefore, in the present invention, the heat treatment temperature and the heat treatment time are adjusted so that they are not formed. It is preferable to do.

Examples of the shape of the sulfide solid electrolyte material include a particle shape, and among them, a spherical shape or an elliptical shape is preferable. Moreover, when the sulfide solid electrolyte material has a particle shape, the average particle diameter is preferably in the range of 0.1 μm to 50 μm, for example. The sulfide solid electrolyte material preferably has high Li ion conductivity, and the Li ion conductivity at room temperature is preferably 1 × 10 ⁻⁵ S / cm or more, for example, 1 × 10 ⁻⁴ S. / Cm or more is more preferable.

  The content of the sulfide solid electrolyte material in the slurry of the present invention is, for example, preferably in the range of 10 wt% to 70 wt%, and more preferably in the range of 40 wt% to 50 wt%. .

3. Slurry The slurry of the present invention contains at least the alcohol and sulfide solid electrolyte material described above, but may contain other materials as necessary. Examples of such a material include a binder. By containing a binder, flexibility can be imparted to the layer formed using the slurry of the present invention. Furthermore, the slurry of the present invention may contain an electrode active material and a conductive material. By containing an electrode active material and a conductive material, an electrode active material layer can be formed using the slurry of the present invention. The slurry of the present invention may contain a dispersion medium and a dispersant other than the alcohol.

  The slurry of the present invention can be used, for example, when producing a solid electrolyte layer of an all-solid battery. By using the slurry, a uniform solid electrolyte layer can be formed. Moreover, when the slurry of this invention contains an electrode active material, it can be used when manufacturing the electrode active material layer of a battery. By using the slurry, a uniform electrode active material layer can be formed. As a manufacturing method of the slurry of this invention, the method similar to the manufacturing method of a general slurry can be used.

B. Next, a method for producing a solid electrolyte layer of the present invention will be described. The method for producing a solid electrolyte layer according to the present invention includes a sulfide solid electrolyte material, and a main chain having 6 or more carbon atoms, and up to the third counting from the carbon atoms in the main chain to which the OH group is bonded. Kneading an alcohol having an alkyl side chain on a carbon atom in the main chain at a position, and preparing a slurry for forming a solid electrolyte layer; and applying the slurry for forming a solid electrolyte layer on a substrate; It has the coating process which forms the coating film for solid electrolyte layer formation, and the drying process which dries the said coating film for solid electrolyte layer formation and forms a solid electrolyte layer, It is characterized by the above-mentioned.

  According to the present invention, by using the alcohol as a dispersion medium of the slurry for forming the solid electrolyte layer, the dispersibility of the sulfide solid electrolyte material is improved in the kneading step, and the solid electrolyte layer is formed with high uniformity in the coating step. The coating film can be formed. For this reason, a uniform solid electrolyte layer can be obtained.

FIG. 1 is a flowchart showing an example of a method for producing a solid electrolyte layer of the present invention. In FIG. 1, first, the main chain of the sulfide solid electrolyte material and the main chain having the number of carbon atoms of the main chain of 6 or more and the third position counted from the carbon atom in the main chain to which the OH group is bonded. An alcohol having an alkyl side chain on a carbon atom is prepared. Next, these are kneaded to prepare a slurry for forming a solid electrolyte layer (kneading step). Then, the slurry for solid electrolyte layer formation is applied on a board | substrate, and the coating film for solid electrolyte layer formation is formed into a film (coating process). Furthermore, the solid electrolyte layer forming coating film is dried to form a solid electrolyte layer (drying step).
Hereinafter, the manufacturing method of the solid electrolyte layer of this invention is demonstrated for every process.

1. Kneading process First, the kneading process in the present invention will be described. The kneading step in the present invention includes the sulfide solid electrolyte material and the main chain having the number of carbon atoms of the main chain of 6 or more and the third position counting from the carbon atom in the main chain to which the OH group is bonded. In this step, an alcohol having an alkyl group side chain is kneaded with carbon atoms in the chain to prepare a slurry for forming a solid electrolyte layer. The sulfide solid electrolyte material and the alcohol are the same as those described in the above “A. Slurry”, and thus description thereof is omitted here.

  The slurry for forming a solid electrolyte layer prepared in this step contains at least the sulfide solid electrolyte material and the alcohol, but further contains other materials such as a binder as necessary. Also good. Examples of the binder include fluorine-containing binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

  The content of the sulfide solid electrolyte material in the slurry for forming the solid electrolyte layer is, for example, preferably in the range of 10 wt% to 70 wt%, and in the range of 40 wt% to 50 wt%. Is more preferable. Further, the other matters of the solid electrolyte layer forming slurry are the same as the contents described in the above “A. Slurry”.

  The kneading method in this step is not particularly limited as long as a highly dispersible slurry can be obtained. For example, a dissolver, homomixer, kneader, roll mill, sand mill, attritor, ball mill, vibrator mill, high-speed impeller mill A general method such as an ultrasonic homogenizer or a shaker can be employed.

2. Next, the coating process in the present invention will be described. The coating process in this invention is a process of coating the said slurry for solid electrolyte layer formation on a board | substrate, and forming the coating film for solid electrolyte layer formation.

  As a board | substrate used for this process, what can peel, such as a fluorine resin sheet, an electrode active material layer, etc. can be mentioned, for example. In this step, the method for coating the slurry for forming the solid electrolyte layer is not particularly limited. For example, a doctor blade method, a die coating method, a gravure coating method, a spray coating method, an electrostatic coating method, A general method such as a bar coating method can be employed. Moreover, the film thickness of the coating film for forming a solid electrolyte layer formed by this step is appropriately selected according to the thickness of the target solid electrolyte layer.

3. Next, the drying process in the present invention will be described. The drying step in the present invention is a step of drying the solid electrolyte layer forming coating film to form a solid electrolyte layer.

  In this step, the method for drying the coating film for forming the solid electrolyte layer is not particularly limited as long as the coating film for forming the solid electrolyte layer is not deteriorated, for example, hot air / hot air drying, General methods such as infrared drying, vacuum drying, and dielectric heating drying can be employed. In addition, examples of the dry atmosphere in this step include an inert gas atmosphere such as an Ar gas atmosphere and a nitrogen gas atmosphere, an air atmosphere, and a vacuum. In addition, the thickness of the solid electrolyte layer formed by this step is, for example, preferably in the range of 0.1 μm to 1000 μm, and more preferably in the range of 0.1 μm to 300 μm.

4). Other Steps The method for producing a solid electrolyte layer of the present invention may have an optional step in addition to the steps described above. As such a process, a compression process etc. can be mentioned, for example. By having the compression step, a high-density solid electrolyte layer can be obtained, and the capacity can be increased by improving ion conductivity and reducing the thickness of the solid electrolyte layer.

C. Next, a method for manufacturing the electrode active material layer of the present invention will be described. The method for producing an electrode active material layer of the present invention includes an electrode active material, a sulfide solid electrolyte material, and a main chain having 6 or more carbon atoms, counting from the carbon atoms in the main chain to which OH groups are bonded. A kneading step of kneading an alcohol having an alkyl side chain with carbon atoms in the main chain at the third position to prepare a slurry for forming an electrode active material layer; and A coating process for coating on a substrate to form a coating film for forming an electrode active material layer, and a drying process for drying the electrode active material layer forming coating film to form an electrode active material layer. It is characterized by having.

  According to the present invention, by using the alcohol as a dispersion medium for the slurry for forming the electrode active material layer, the dispersibility of the sulfide solid electrolyte material is improved in the kneading process, and the electrode active material having high uniformity in the coating process. A film for forming a layer can be formed. For this reason, a uniform electrode active material layer can be obtained.

FIG. 2 is a flowchart showing an example of a method for producing an electrode active material layer of the present invention. In FIG. 2, first, the electrode active material, the sulfide solid electrolyte material, the main chain has 6 or more carbon atoms, and up to the third counted from the carbon atoms in the main chain to which the OH group is bonded. An alcohol having a side chain of an alkyl group on a carbon atom in the main chain at the position is prepared. Next, these are kneaded to prepare an electrode active material layer forming slurry (kneading step). Subsequently, the electrode active material layer forming slurry is applied onto the substrate to form an electrode active material layer forming coating film (coating step). Furthermore, the electrode active material layer forming coating film is dried to form an electrode active material layer (drying step).
Hereinafter, the manufacturing method of the electrode active material layer of this invention is demonstrated for every process.

1. Kneading process First, the kneading process in the present invention will be described. In the kneading step in the present invention, the electrode active material, the sulfide solid electrolyte material, and the main chain have 6 or more carbon atoms, and up to the third counting from the carbon atoms in the main chain to which the OH group is bonded. This is a step of kneading an alcohol having an alkyl side chain with a carbon atom in the main chain at a position to prepare a slurry for forming an electrode active material layer. The sulfide solid electrolyte material and the alcohol are the same as those described in the above “A. Slurry”, and thus description thereof is omitted here.

  The electrode active material in the present invention differs depending on the type of conductive ions of the battery in which the electrode active material layer produced according to the present invention is used. For example, when the electrode active material layer is used in a lithium secondary battery, the electrode active material occludes / releases lithium ions. The electrode active material used in the present invention may be a positive electrode active material or a negative electrode active material.

Examples of the positive electrode active material used in the present invention include rock salt layered active materials such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , and LiMn ₂ O. ₄ , spinel type active materials such as Li (Ni _0.5 Mn _1.5 ) O ₄ , and olivine type active materials such as LiFePO ₄ and LiMnPO ₄ . Si-containing oxides such as Li ₂ FeSiO ₄ and Li ₂ MnSiO ₄ may be used as the positive electrode active material.

  On the other hand, examples of the negative electrode active material used in the present invention include a metal active material and a carbon active material. Examples of the metal active material include In, Al, Si, and Sn. On the other hand, examples of the carbon active material include mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon.

  Examples of the shape of the electrode active material include a particle shape. Among them, a true spherical shape or an elliptical spherical shape is preferable. Moreover, when an electrode active material is a particle shape, it is preferable that the average particle diameter exists in the range of 0.1 micrometer-50 micrometers, for example.

  The electrode active material layer-forming slurry prepared in this step contains at least the electrode active material, the sulfide solid electrolyte material, and the alcohol. If necessary, a conductive material, a binder, etc. Other materials may be further contained. By adding a conductive material, the conductivity of the electrode active material layer produced according to the present invention can be improved. Examples of the conductive material include acetylene black, ketjen black, and carbon fiber. The binder is the same as that described in “B. Method for producing a solid electrolyte layer”, and therefore the description thereof is omitted here.

  The ratio of the electrode active material and the solid electrolyte material contained in the electrode active material layer forming slurry is, by weight ratio, within the range of electrode active material: solid electrolyte material = 1: 9 to 9: 1. The electrode active material: solid electrolyte material = 2 is more preferably in the range of 2: 8 to 6: 4. The solid content in the electrode active material layer forming slurry is preferably in the range of 10% by weight to 80% by weight, and more preferably in the range of 40% by weight to 70% by weight. Here, solid content means the ratio of the total weight of the said electrode active material and the said solid electrolyte material with respect to the weight of the said slurry for electrode active material layer formation. Further, the other matters of the electrode active material layer forming slurry are the same as the contents described in “A. Slurry”.

  The kneading method in this step is the same as that described in “B. Production method of solid electrolyte layer” above, and thus the description thereof is omitted here.

2. Next, the coating process in the present invention will be described. The coating process in this invention is a process of coating the said slurry for electrode active material layer formation on a board | substrate, and forming the coating film for electrode active material layer formation.

  As a board | substrate used for this process, what can peel, such as a fluororesin sheet | seat, a collector, etc. can be mentioned, for example. Moreover, when the electrode active material layer manufactured by this invention is used for an all-solid-state battery, a solid electrolyte layer can also be used as a board | substrate. In this step, the method for applying the electrode active material layer forming slurry is the same as that described in the above-mentioned “B. Method for producing solid electrolyte layer”, so description thereof is omitted here. Moreover, the film thickness of the electrode active material layer forming coating film formed in this step is appropriately selected according to the thickness of the target electrode active material layer.

3. Next, the drying process in the present invention will be described. The drying step in the present invention is a step of drying the electrode active material layer forming coating film to form an electrode active material layer.

  In this step, the method for drying the electrode active material layer-forming coating film and the drying atmosphere are the same as those described in “B. Method for producing a solid electrolyte layer”, and therefore the description here is as follows. Omitted. Moreover, it is preferable that the thickness of the electrode active material layer formed by this process exists in the range of 0.1 micrometer-1000 micrometers, for example.

4). Other Steps The method for producing an electrode active material layer of the present invention may have an optional step in addition to the steps described above. Since such steps are the same as the contents described in “B. Method for producing solid electrolyte layer”, description thereof is omitted here.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  The present invention will be described more specifically with reference to the following examples. Unless otherwise specified, each operation was performed in an Ar gas filled glove box or in an Ar gas atmosphere.

[Example 1-1]

(Synthesis of sulfide solid electrolyte materials)
As starting materials, lithium sulfide (Li ₂ S) and phosphorus pentasulfide (P ₂ S ₅ ) were used. First, these powders were weighed so as to have a molar ratio of Li ₂ S: P ₂ S ₅ = 75: 25, and mixed in an agate mortar. Next, 2 g of this mixture was charged into a 45 ml zirconia pot, 4 g of dehydrated heptane (moisture content of 30 ppm or less) was charged, zirconia balls (φ5.5 mm, 53 g) were further charged, and the pot was completely sealed. This pot was attached to a planetary ball mill (P7 made by Fritsch), and mechanical milling was performed 20 times with a base plate rotation speed of 500 rpm and a one-hour treatment and a 15-minute pause. Furthermore, after adding 6 mol% of Li ₂ O, mechanical milling was performed under the same conditions as described above. Thereafter, the obtained sample was dried on a hot plate set at 100 ° C. so as to remove heptane, and a sulfide solid electrolyte material (sulfide glass, Li ₂ S—Li ₂ O—P ₂ S ₅ ) was used. Obtained.

(Preparation of slurry)
The above-mentioned sulfide solid electrolyte material and 2-ethylhexanol were weighed and kneaded so that the weight ratio of sulfide solid electrolyte material: 2-ethylhexanol = 40: 60 was obtained, thereby obtaining a slurry.

[Example 1-2]
A slurry was obtained in the same manner as in Example 1 except that 2,6-dimethyl-4-heptanol was used instead of 2-ethylhexanol.

[Example 1-3]
A slurry was obtained in the same manner as in Example 1 except that the sulfide solid electrolyte material was synthesized as follows.

(Synthesis of sulfide solid electrolyte materials)
As starting materials, lithium sulfide (Li ₂ S), phosphorus pentasulfide (P ₂ S ₅ ) and lithium iodide (LiI) were used. First, Li ₂ S and P ₂ S ₅ were weighed so as to have a molar ratio of Li ₂ S: P ₂ S ₅ = 75: 25, and then LiI was weighed so that LiI was 30 mol%. Mixed in agate mortar. Next, 1 g of this mixture was put into a 45 ml zirconia pot, 4 g of dehydrated heptane (moisture content of 30 ppm or less) was added, and further zirconia balls (φ5.5 mm, 53 g) were added, and the pot was completely sealed. This pot was attached to a planetary ball mill (P7, manufactured by Fritsch), and mechanical milling was performed 40 times at a base plate rotation speed of 500 rpm for 1 hour and 15 minutes of rest. Thereafter, the obtained sample was dried on a hot plate set at 100 ° C. so as to remove heptane to obtain a sulfide solid electrolyte material (sulfide glass, LiI—Li ₂ S—P ₂ S ₅ ). .

[Comparative Examples 1-1 to 1-7]
The same steps as in Example 1 were used except that ethanol, ethylene glycol, 1-butanol, 1-hexanol, 1-heptanol, 2-methylcyclohexanol and cycloheptanol were used instead of 2-ethylhexanol. Although it went, the sulfide solid electrolyte material melt | dissolved in each solvent (alcohol), and the slurry was not obtained.

[Evaluation 1]
(Li ion conductivity measurement)
A sample obtained by scraping the powder obtained by coating and drying the slurry obtained in Examples 1-1 to 1-3 on stainless steel or aluminum foil, and forming it into a cylindrical shape of φ 11.28 mm × 0.5 mm On the other hand, Li ion conductivity (normal temperature) was measured by the AC impedance method. Solartron 1260 was used for measurement, and the measurement conditions were an applied voltage of 5 mV and a measurement frequency range of 0.01 MHz to 1 MHz. The results are shown in Table 1. As shown in Table 1, all the samples prepared from the slurries obtained in Examples 1-1 to 1-3 have a high Li ion conductivity of 1 × 10 ⁻⁴ S / cm or more. confirmed.

[Example 2]
(Preparation of positive electrode active material layer)
First, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ as a positive electrode active material, LiI-Li ₂ S—P ₂ S ₅ synthesized earlier as a sulfide solid electrolyte material, and hydrogenated butylene rubber as a binder. After preparing these materials and weighing them so that the positive electrode active material: sulfide solid electrolyte material: binder = 66.2: 33.3: 0.5 (weight ratio), the solid content becomes 70 wt%. Thus, a mixed solvent of heptane: 2-ethylhexanol = 60: 40 (weight ratio) was added to obtain a slurry for forming a positive electrode active material layer. Next, this slurry was applied onto a SUS foil as a positive electrode current collector at a basis weight of 18.8 mg / cm ² and dried at 100 ° C. for 30 minutes. Finally, the obtained film was cut into a cell size (1 cm ² ) to obtain a positive electrode active material layer.

(Preparation of negative electrode active material layer)
First, graphite as a negative electrode active material and LiI—Li ₂ S—P ₂ S ₅ previously synthesized as a sulfide solid electrolyte material are prepared, and these materials are prepared as a negative electrode active material: sulfide solid electrolyte material = 50: 50 ( Weight ratio), and heptane was added so that the solid content was 62 wt% to obtain a slurry for forming a negative electrode active material layer. Next, this slurry was applied on a Cu foil as a negative electrode current collector at a basis weight of 20 mg / cm ² and dried at 100 ° C. for 30 minutes. Finally, the obtained film was cut into a cell size (1 cm ² ) to obtain a negative electrode active material layer.

(Production of evaluation battery)
First, it was prepared _{LiI-Li 2 S-P 2} S 5 the previously synthesized as a material for forming a solid electrolyte layer. Next, the solid electrolyte layer forming material was pressed at a pressure of 1 ton / cm ² to obtain a solid electrolyte layer. Subsequently, the positive electrode active material layer was placed on one surface of the solid electrolyte layer and pressed at a pressure of 1 ton / cm ² . Furthermore, the negative electrode active material layer was disposed on the other surface of the solid electrolyte layer and pressed at a pressure of 4.3 ton / cm ² to obtain an evaluation battery.

[Comparative Example 2]
In the preparation of the positive electrode active material layer, an evaluation battery was prepared in the same manner as in Example 2, except that only heptane was used instead of the mixed solvent of heptane: 2-ethylhexanol = 60: 40 (weight ratio). Obtained.

[Evaluation 2]
(Charge / discharge measurement)
Using the evaluation batteries obtained in Example 2 and Comparative Example 2, charge / discharge measurement was performed. The charge / discharge conditions were a voltage range of 2.5 V to 4.55 V, a charge / discharge current of 0.1 C, and an environmental temperature of 25 ° C. The result is shown in FIG. As shown in FIG. 3, it was confirmed that the specific capacity at the end of discharge (low SOC) was improved in the evaluation battery obtained in Example 2 as compared with the evaluation battery obtained in Comparative Example 2. It was. This is considered because the evaluation battery of Example 2 has a positive electrode active material layer having higher uniformity than the evaluation battery of Comparative Example 2.

(AC impedance measurement)
Using the evaluation batteries obtained in Example 2 and Comparative Example 2, AC impedance measurement was performed. First, the evaluation battery was charged so that the SOC was 20%. The charging conditions were an upper limit voltage of 3.6 V, a charging current of 0.1 C, and an environmental temperature of 25 ° C. After charging, AC impedance measurement was performed. The conditions for AC impedance measurement were a voltage amplitude of 10 mV, a measurement frequency of 1 MHz to 0.1 Hz, and 25 ° C. The result is shown in FIG. As shown in FIG. 4, the evaluation battery of Example 2 was confirmed to have a lower interface resistance between the positive electrode active material layer and the solid electrolyte layer than the evaluation battery of Comparative Example 2. This is considered because the evaluation battery of Example 2 has a positive electrode active material layer having higher uniformity than the evaluation battery of Comparative Example 2.

[Example 3]
50 mg of a sulfide solid electrolyte material (sulfide glass, LiI—Li ₂ S—P ₂ S ₅ ) having a particle size of 20 μm to 40 μm was dispersed in 3 ml of 2-ethylhexanol to obtain a slurry. The specific gravity and viscosity of 2-ethylhexanol were 0.843 and 9.6 mPa · s, respectively.

[Comparative Example 3]
A sample was obtained in the same manner as in Example 3 except that heptane was used instead of 2-ethylhexanol. The specific gravity and viscosity of heptane were 0.686 and 0.41 mPa · s, respectively.

[Evaluation 3]
(Settling velocity measurement)
Using the slurries obtained in Example 3 and Comparative Example 3, the sedimentation rate of the sulfide solid electrolyte material was measured. Specifically, the sedimentation rate was measured by measuring the time-dependent change in the absorption rate of the slurry using a spectrophotometer. The result is shown in FIG. As shown in FIG. 5, in Example 3, the sedimentation speed was 1.9 mm / hr, whereas in Comparative Example 3, the sedimentation speed was 720 mm / hr. It was confirmed that it was 1/300 or less of the sedimentation rate of Example 3. From this, it was shown that 2-ethylhexanol can sufficiently slow down the sedimentation rate of the sulfide solid electrolyte material as compared with heptane.

Claims (7)

A sulfide solid electrolyte material;
An alcohol having a main chain having 6 or more carbon atoms and having a side chain of an alkyl group on the carbon atom in the main chain at the third position counting from the carbon atom in the main chain to which the OH group is bonded; The slurry characterized by containing.   The slurry according to claim 1, wherein the alcohol is 2-ethylhexanol or 2,6-dimethyl-4-heptanol. The slurry according to claim 1 or 2, wherein the sulfide solid electrolyte material is a raw material composition containing Li ₂ S and P ₂ S ₅ . The ratio of Li ₂ S and P ₂ S ₅ in the raw material composition is in a range of Li ₂ S: P ₂ S ₅ = 70: 30 to 80:20 in terms of molar ratio. The slurry described in 1.   The slurry according to any one of claims 1 to 4, wherein the sulfide solid electrolyte material contains LiI. A sulfide solid electrolyte material, and the main chain has 6 or more carbon atoms, and the carbon atoms in the main chain at positions up to the third position counted from the carbon atoms in the main chain to which an OH group is bonded are alkylated. A kneading step of kneading alcohol having a side chain of a group to prepare a slurry for forming a solid electrolyte layer;
A coating step of coating the solid electrolyte layer forming slurry on a substrate and forming a solid electrolyte layer forming coating film;
The method for producing a solid electrolyte layer, comprising: drying the solid electrolyte layer forming coating film to form a solid electrolyte layer. In the main chain of the electrode active material, the sulfide solid electrolyte material, and the main chain having 6 or more carbon atoms in the main chain and counting from the carbon atom in the main chain to which the OH group is bonded. A kneading step of kneading an alcohol having an alkyl group side chain on a carbon atom to prepare a slurry for forming an electrode active material layer;
A coating step of coating the electrode active material layer forming slurry on a substrate and forming an electrode active material layer forming coating film;
And drying the electrode active material layer-forming coating film to form an electrode active material layer. A method for producing an electrode active material layer, comprising:

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