JP2010108882A - Method of manufacturing ion-conducting solid electrolyte - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an ion-conducting solid electrolyte using a green sheet having mechanical characteristics such that the sheet can sufficiently endure a variety of mechanical stresses during a manufacturing process. <P>SOLUTION: Using a ceramic green sheet that can endure mechanical stresses in a detachment process for a carrier film, a lamination process for the green sheet or the like by adjusting a percentage of water of the ceramic green sheet after a drying process and/or an environment under which the ceramic green sheet is disposed, an ion-conducting solid electrolyte is manufactured. In this way, it is possible to effectively prevent occurrence of defects within the green sheet in transportation, carrier film detachment or a lamination process. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a solid electrolyte of a lithium battery. More specifically, the present invention relates to a method for producing the solid electrolyte green sheet and a method for handling the produced green sheet.

In recent years, with higher performance and smaller size of portable electronic devices such as mobile phones, it is desired to increase the energy density and size of batteries used in these portable electronic devices. In general, since a high voltage is obtained and a high energy density is obtained in a lithium battery, it is expected as a power source for these portable electronic devices. Usually, in such a lithium battery, lithium transition metal composite oxides such as lithium cobaltate (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), and lithium nickelate (LiNiO ₂ ) are used as the positive electrode active material. Yes. Moreover, carbon materials, such as graphite and fibrous carbon, are used as a negative electrode active material. An organic electrolyte is used for such a lithium battery, but a polymer electrolyte obtained by mixing a polymer electrolyte and an organic electrolyte is also being studied. Since these lithium batteries or polymer electrolyte batteries use a liquid as the electrolyte, they have low reliability such as liquid leakage or fire. In addition, freezing of the electrolytic solution at a low temperature or vaporization of the electrolytic solution at a high temperature may significantly impair the performance of the battery, so that the use temperature of such a battery is limited. Therefore, development of a lithium battery using a solid electrolyte having lithium ion conductivity instead of an organic electrolyte is desired as a highly reliable lithium battery.

Since a lithium battery using such a solid electrolyte does not use a flammable organic solvent, there is no risk of liquid leakage or ignition and excellent safety. For example, in Patent Document 1, Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ solid electrolyte powder is used for a solid electrolyte green sheet serving as a solid electrolyte layer. Further, a polyvinyl butyral resin as a binder and a solvent are used. A certain n-butyl acetate and a plasticizer dibutyl phthalate are used (for example, Patent Document 1, paragraph [0189]). As for a method for producing a solid electrolyte green sheet, a solid electrolyte slurry is applied on a carrier film mainly composed of polyester using a doctor blade, and dried to obtain a solid electrolyte green sheet. It is written.

  The applied coating has substantially the same components as the slurry immediately after application and has similar mechanical properties (for example, viscosity as a fluid), but is completely different by being dried by volatilization of a solvent or the like. A green sheet having mechanical properties (for example, mechanical strength as a solid) is obtained. Since such a large change in characteristics is caused by a physical phenomenon such as drying from the coating film to the green sheet, sufficient control of this physical phenomenon has been the biggest problem. For example, when a slurry is applied in a sheet form on a carrier film and dried in a drying furnace or the like, cracks, warpage, undulations occur in the green sheet, or the solvent rapidly evaporates, causing bump marks on the green sheet. There has been a problem that it is generated or cracks occur, and a device has been devised for drying in two drying steps (for example, Patent Document 2). Further, it has been proposed to create a ceramic green sheet free from sheet defects by eliminating a difference in drying between the sheet surface and the inside by applying a ceramic slurry on a carrier film and drying in a specific temperature range (for example, Patent Document 3). And in order to prevent the generation | occurrence | production of the crack at the time of drying by use of an aqueous binder, the technique which made this binder contain water-soluble polyvinyl acetal resin is disclosed (for example, patent document 4).

However, these techniques can effectively prevent defects such as cracks in the drying process, but are not necessarily effective in preventing the occurrence of sheet defects in other processes. Further, in a method for producing a multilayer ceramic sheet in which a green sheet is formed and laminated and debindered and fired, the green sheet laminate is subjected to constant humidity at a relative humidity of 45% to 55% before debinding. A technique for holding the inside and adjusting the amount of moisture absorption of the laminate is disclosed (for example, Patent Document 5). Thereby, it aims at obtaining the ceramic sheet | seat with little warpage in a binder removal and a baking process.
JP 2007-5279 A JP 2007-91526 A JP-A-7-172903 JP 2003-192449 A JP-A-2005-212194

  However, with these technologies, it may be possible to prevent defects in the green sheet when the coating film is dried, or it may be possible to prevent defects in the ceramic sheet in the binder removal and firing process of the laminate. It is not always effective in the process. That is, after the drying step and before the lamination step, various mechanical stresses are applied to the ceramic green sheet, but it is important to have mechanical characteristics that can sufficiently withstand it. For example, the occurrence of cracks in the ceramic green sheet due to tension or shear force during the conveyance of the ceramic green sheet becomes a defect that cannot be cured in a later process, and such a phenomenon needs to be effectively prevented.

  In the present invention, in view of the above-mentioned problems, earnest research has been conducted, and it is the carrier film peeling process that generates a lot of mechanical stress in the process after the drying process and before the firing process. Focusing on the laminating process, the following was found. That is, in the ceramic green sheet after the drying process, the water content has a great influence on the mechanical resistance against the stress, and in the carrier film peeling process and the green sheet laminating process, it is dried. This is different from the mechanical characteristics for preventing defects in the process and the binder removal process and the firing process of the laminate. Specifically, it has been found that by setting the moisture content in the green sheet within a predetermined range, for example, it is possible to effectively prevent the occurrence of defects in the green sheet in the transport and carrier film peeling and laminating processes. It was.

More specifically, the following can be provided.
(1) In a method for producing an ion conductive solid electrolyte by firing a green sheet containing an inorganic compound powder exhibiting lithium ion conductivity and an organic binder at least after heat treatment, the slurry is obtained by mixing the inorganic compound powder and the organic binder. A slurry manufacturing process to be prepared, a coating process in which the slurry is applied to a carrier film to prepare a coating film, a drying process to dry the coating film, and the coating film is peeled from the carrier film to produce a green sheet. A peeling step and a laminating step of laminating the green sheets to produce a laminate, wherein the moisture content of the coating film immediately after the peeling step is 0.1 to 5%. A method for producing an ion conductive solid electrolyte can be provided.

  Here, the moisture content affects the plasticity and flexibility of the green sheet, and if the moisture content is less than 0.1%, the flexibility is remarkably reduced, and even a slight deformation causes cracks, cracks, etc. Produce. For example, if peeling is performed such that a load is applied to several points of the green sheet so as to peel off the seal, tearing is likely to occur. In addition, when the entire green sheet is pressed against another film or the like to peel off the carrier film, cracks are likely to occur. Therefore, the water content is more preferably 0.2 or more, and still more preferably 0.3 or more. On the other hand, if the water content exceeds 5%, the plasticity and flexibility are high, but if it is peeled off from the carrier film, it is easily plastically deformed and stretched, and if pulled further, it may be broken. In addition, when the carrier film is peeled off by pressing the entire surface of the green sheet against another film or the like, the green sheet may not be stretched, and the thickness of the green sheet may be inhomogeneous. Therefore, the moisture content is more preferably 4.5% or less, and further preferably 4% or less.

  Such moisture content is the ratio of the mass of moisture contained in the measurement object to the mass of the measurement object, for example, the weight of moisture contained in the green sheet as a percentage of the weight of the dry green sheet. It is a representation. The amount of moisture contained can be measured by a Karl Fischer coulometric titration moisture measuring device (see JIS K 2275). For example, it can be determined from water vapor released when heated to 200 ° C. using MKC-610 manufactured by Kyoto Electronics.

  Here, the green sheet is a mixture of organic binders, plasticizers, solvents, etc., mixed into the powder mainly of ceramics such as glass and inorganic oxide before firing, and formed into a thin plate shape. It can mean an unfired body. This molding can be performed by a doctor blade, calendar method, spin coating, dip coating or other coating method, ink jet, bubble jet (registered trademark), offset printing method, die coater method, spray method, etc., mixed slurry From this, a thin plate-like green sheet can be made. In general, the mixed slurry is formed on a film such as PET that has been subjected to a release treatment, and is peeled off after drying. The green sheet before firing is flexible, and can be cut into an arbitrary shape or laminated.

  Here, the organic binder may be one that can bind inorganic particles, and a general-purpose binder marketed as a molding aid for press molding, rubber press, extrusion molding, or injection molding can be used. Specifically, acrylic resin, ethyl cellulose, polyvinyl butyral, methacrylic resin, urethane resin, butyl methacrylate, vinyl copolymer and the like can be used.

(2) The water content of the green sheet immediately before the laminating step is 0.1 to 5%, and the method for producing an ion conductive solid electrolyte according to the above (1) can be provided.

  Here, the moisture content affects the plasticity and flexibility of the green sheet, and if the moisture content is less than 0.1%, the flexibility is remarkably reduced, and even a slight deformation causes cracks, cracks, etc. Produce. For example, if peeling is performed such that a load is applied to several points of the green sheet so as to peel off the seal, tearing is likely to occur. In addition, when the entire green sheet is pressed against another film or the like to peel off the carrier film, cracks are likely to occur. Therefore, the water content is more preferably 0.2 or more, and still more preferably 0.3 or more. On the other hand, if the water content exceeds 5%, the plasticity and flexibility are high, but if it is peeled off from the carrier film, it is easily plastically deformed and stretched, and if pulled further, it may be broken. In addition, when the carrier film is peeled off by pressing the entire surface of the green sheet against another film or the like, the green sheet may not be stretched, and the thickness of the green sheet may be inhomogeneous. Therefore, the moisture content is more preferably 4.5% or less, and further preferably 4% or less.

(3) Between the drying step and the peeling step, the temperature is kept at 5 to 60 ° C. and the relative humidity is kept at 1 to 50%, as described in (1) or (2) above A method for producing an ion conductive solid electrolyte can be provided.

  In general, the moisture content decreases as the retained temperature increases. Moreover, it falls when the relative humidity of the environment to hold | maintain falls. Moisture in the green sheet enters and exits according to thermodynamic energy with the surrounding environment. This moving speed is closely related to the thermodynamic energy and is greatly influenced by these environmental conditions. Therefore, it is considered that storing the green sheet in such a temperature and humidity range is effective for maintaining a predetermined moisture content for a predetermined time.

(4) Any of (1) to (3) above, wherein the temperature is kept at 5 to 60 ° C. and the relative humidity is kept at 1 to 50% between the peeling step and the laminating step. The method of manufacturing the ion conductive solid electrolyte as described in 1 above can be provided.

  In general, the moisture content decreases as the retained temperature increases. Moreover, it falls when the relative humidity of the environment to hold | maintain falls. Moisture in the green sheet enters and exits according to thermodynamic energy with the surrounding environment. This moving speed is closely related to the thermodynamic energy and is greatly influenced by these environmental conditions. Therefore, it is considered that storing the green sheet in such a temperature and humidity range is effective for maintaining a predetermined moisture content for a predetermined time.

(5) The ion conductive solid electrolyte according to (3) or (4) above, wherein in the peeling step and the laminating step, the coating film and the green sheet are held at a temperature exceeding a dew point. A method of manufacturing can be provided.

  Generally, at the dew point, condensation begins when air containing water vapor is cooled. Therefore, if it is kept at a temperature lower than that, there is a risk of condensation on the surface of a member such as a green sheet, and if water as a liquid adheres to the surface of the green sheet, the characteristics of the green sheet may be deteriorated. Therefore, it is preferable to keep the green sheet above the dew point temperature.

(6) The method for producing an ion conductive solid electrolyte according to any one of (1) to (5) above, wherein the green sheet has a thickness of 1 to 100 μm.

  Here, it is desirable to form the green sheet with a uniform thickness. This is because it is easy to produce a green sheet laminate. Moreover, when the produced green sheet laminated body is baked, it becomes easy to perform heating uniformly, and it is considered that warpage of each layer of the laminated body and peeling between the layers hardly occur. A dense electrolyte layer with a porosity of 20 vol% or less can be obtained. More specifically, the difference obtained by subtracting the minimum value from the maximum value of the thickness in one green sheet is preferably 20% or less of the average value of the thickness of the entire sheet. Moreover, it is preferable that the maximum value is + 10% or less of the average value. The minimum value is preferably −10% or more of the average value.

  Here, the maximum value and the minimum value are used, but an abnormal value may occur due to a measurement error or the like. Therefore, it is preferable to devise a method for eliminating abnormal values. For example, when obtaining a predetermined number of thickness data in order to obtain such maximum and minimum values, two more thickness data are taken, the maximum and minimum values are deleted, and the remaining data The arithmetic average value, the maximum value, and the minimum value may be obtained by just using the above. Alternatively, the maximum value and the minimum value may be obtained after analyzing all data after the measurement is completed and adding a process of removing abnormal values. Here, for example, when taking an average of all measured data, an average value exceeding + 50% or less than −50% can be set as an abnormal value.

  The thickness of each green sheet to be laminated is preferably 100 μm or less, more preferably 90 μm or less, and most preferably 80 μm or less so that the dispersion medium can be easily volatilized. On the other hand, if the thickness is too thin, productivity and mechanical strength are reduced, and therefore the thickness of each green sheet is preferably 0.5 μm or more, more preferably 1 μm or more, and most preferably 3 μm or more. As for the thickness of the green sheet, for example, the thickness of a plurality of points selected at random on the upper surface or lower surface of the sheet can be measured with a film thickness meter. The selected points are pre-assigned evenly (for example, grid points by equally divided vertical and horizontal grids, etc. However, there is a possibility that the vertical or horizontal length of the sheet will be 5% from the edge of the sheet. It may be excluded.)

(7) Any of the above (1) to (6), further comprising a laminating step of laminating at least two of the green sheets that have undergone the drying step and pressurizing them at a predetermined pressure to produce a laminate. It is possible to provide a method for producing the ion conductive solid electrolyte according to the above.

  In the present specification, the green sheet may include a solid electrolyte green sheet to be a solid electrolyte, and the green sheet laminate may include a solid electrolyte green sheet laminate. Moreover, it becomes that it becomes what can function as a solid electrolyte layer by baking the green sheet laminated body mentioned later to become a solid electrolyte layer by heat processing. For example, it has predetermined ion conductivity.

  In the stacking step, a plurality of green sheets may be stacked in order without particularly applying pressure. The stacked temporary laminates may be heated simultaneously with pressurization in the press-contacting step. The green sheet may be coated on a carrier film, for example, and is usually left at room temperature to volatilize a dispersion medium (for example, water). Further, since the dispersion medium is mainly volatilized from the upper surface, which is the surface, the upper part has relatively little dispersion medium. The electrolyte component is, for example, lithium ion conductive glass ceramics, the binder is a plastic organic material, and the dispersion medium is, for example, water. Therefore, in the former case, the vicinity of the lower surface (lower part) is relatively hard, and the vicinity of the upper surface (upper part) is relatively flexible. However, in the latter case, conversely, the vicinity of the lower surface (lower part) is relatively flexible and the vicinity of the upper surface (upper part) is relatively hard. Therefore, it is preferable to sufficiently grasp these characteristics in the laminating step. For example, it is considered that the adhesion is relatively improved when a soft surface is brought into contact with a hard surface and compressed. Therefore, when the green sheet is dried on the carrier film, it is preferable to stack the lower surface of the other green sheet that is in contact with the carrier film on the upper surface of the green sheet.

(8) The method for producing an ion conductive solid electrolyte according to any one of (1) to (7) above, wherein in the laminating step, the thickness of the laminate is 10 to 1000 μm. .

  The thickness of the laminate in which each green sheet is laminated is preferably 1000 μm or less, more preferably 750 μm or less, and most preferably 500 μm or less so that the binder can be stably removed in a short time in the degreasing step. On the other hand, if the thickness is too thin, handling after firing becomes poor, so 10 μm or more is preferable, 15 μm or more is more preferable, and 20 μm or more is most preferable.

(9) The method for producing an ion-conducting solid electrolyte according to any one of (1) to (8) above, wherein in the laminating step, the pressing time when laminating is 5 seconds or more. Can be provided.

  The pressurization time is preferably 5 seconds or more, more preferably 10 seconds or more, and most preferably 15 seconds or more in order to provide sufficient adhesion. If the pressurization time is too short, the green sheet laminate tends to be peeled off and the adhesion may be insufficient.

  In the press-contacting step of pressing the green sheet laminate and pressing the green sheets together, it is desirable to use means capable of simultaneously pressing the entire surface of the green sheet laminate with a uniform pressure in order to apply a uniform pressure. . For example, a uniaxial press, an isotropic pressure press, or the like can be used. In the uniaxial press, the maximum compression stress is likely to be generated on the upper surface because it is pressed by the piston, and when the tip end surface area of the piston is small, it is difficult to uniformly press the entire upper surface of the green sheet laminate. Therefore, it is preferable to use an isotropic pressure press. In the isotropic press, since the pressure medium is a fluid such as water, the heating can be performed by heating the pressure medium to a predetermined temperature. Moreover, although a green sheet laminated body is a comparatively flat sheet | seat, when it increases in thickness until it can be said that it is a block shape, a hydrostatic pressure is equally applied also to a side surface. The pressing force on the side surface is not preferable because it does not press between the layers of the sheet and does not contribute to adhesion, but rather may promote delamination. Therefore, it is preferable that the thickness is sufficiently smaller than the length and width. For example, the thickness is 25% or less, more preferably 20% or less, and most preferably 15% or less of the shortest side in the vertical and horizontal lengths. Further, since the green sheet laminate is a relatively soft and flexible sheet, the green sheet laminate is sandwiched from both sides of the green sheet laminate by a rigid plate-like member having a size larger than the sheet surface of the green sheet laminate. It is preferable.

  The maximum holding pressure in the pressing step is preferably 1 MPa or more, more preferably 5 MPa or more, and further preferably 10 MPa or more, which is a pressure sufficient to press the green sheet layer. The upper limit of the pressure is not particularly limited, but if it is too high, the industrial cost is excessive and the productivity is lowered, so 500 MPa or less is preferable.

  Moreover, although the whole green sheet laminated body can be heated at the time of press-contact, when using an isotropic pressure press, the temperature of a pressure medium can be made into heating temperature substantially.

  This temperature is preferably a temperature at which the respective layers of the green sheet laminate can be sufficiently bonded. For example, it is preferably 15 to 99 ° C, more preferably 20 to 90 ° C, and most preferably 25 to 85 ° C. If this temperature is low, the binder component may not be sufficiently softened. On the other hand, if the temperature for pressure bonding is too high, the binder, solvent, etc. contained in the green sheet may vaporize, which may cause internal pore rupture due to volume.

(10) In the laminating step, the specific gravity of the green sheet to be laminated is 1.1 to 2.4. The ion conductive solid electrolyte according to any one of (1) to (9), A method of manufacturing can be provided.

  The specific gravity of the green sheet is preferably 1.1 to 2.4, more preferably 1.2 to 2.3, and most preferably 1.3 to 2.2. If the specific gravity is too large, it may become too dense and it may be difficult to remove the binder in the firing step. On the other hand, if the specific gravity is too small, a dense solid electrolyte may not be obtained after firing. The specific gravity of the green sheet can be measured with an X-ray film pressure gauge and a balance.

(11) The method for producing an ion conductive solid electrolyte according to any one of (1) to (10), wherein in the slurry production step, the inorganic compound particles include glass or glass ceramics. Can be provided.

  Here, the glass ceramics can include a material obtained by precipitating a crystal phase in a glass phase by heat-treating the glass. A material composed of an amorphous solid and a crystal may be included. The crystal precipitation can be detected by, for example, an X-ray diffraction method or the like when a crystal layer is formed by sufficient growth after generation of crystal nuclei. Furthermore, the glass ceramics can include those in which all of the glass phase is phase-transformed into a crystalline phase when there are almost no vacancies, that is, those having a crystal content of 100% by mass (crystallinity of 100%). In general, ceramics that are difficult to melt tend to have vacancies and crystal grain boundaries between crystal grains remaining after sintering. However, in the glass ceramic here, since crystals are precipitated from the mother glass, it is possible to prevent vacancies and grain boundaries from remaining. Since ionic conduction is remarkably suppressed by vacancies and grain boundaries between crystal grains, in the case of ceramics, the ionic conductivity is considered to be considerably lower than the conductivity of the crystal grains themselves. Since glass ceramics can suppress a decrease in ionic conductivity between crystals by controlling the crystallization process, the ionic conductivity of the same degree as that of crystal particles can be maintained as a whole. The inorganic particles may be glass as long as a lithium ion conductive crystal phase is precipitated in the glass phase by heat treatment. This glass becomes glass ceramics when the green sheet is sintered.

(12) In the slurry production step, the inorganic compound particles include glass that exhibits lithium ion conductivity by heat treatment, and the ion conductivity according to any one of (1) to (11) above A method for producing a solid electrolyte can be provided.

The glass constituting the inorganic compound particles may mean a glass that precipitates lithium ion conductive crystals by heat treatment. When these glasses in the green sheet are sintered, the individual powders are united, and lithium ion conductive crystals are deposited to express lithium ion conductivity. Thus, a solid electrolyte having high density and high lithium ion conductivity is obtained. Obtainable. As such a glass _{Li 1 + x + z M x} (Ge 1-y Ti y) 2-x Si z P 3-z O 12 ( where, 0 ≦ x ≦ 0.8,0 ≦ y ≦ 1.0,0 ≦ a glass having a Li ₂ O—Al ₂ O ₃ —TiO ₂ —SiO ₂ —P ₂ O ₅ -based composition for precipitating crystals of z ≦ 0.6, one or more selected from M = Al and Ga, There are sulfide-based glasses that precipitate crystals such as Li ₇ PS ₆ , Li ₄ P ₂ S ₆ , and Li ₃ PS ₄ .

(13) The glass is expressed in mol% based on oxide,
Li ₂ O 10-25%, and Al ₂ O ₃ and / or Ga ₂ O ₃ 0-15%, and TiO ₂ and / or GeO ₂ 25-50%, and SiO ₂ 0-15%, and P ₂ O ₅ 26-40%
It is possible to provide a method for producing an ion conductive solid electrolyte as described in (12) above, wherein

The glass having the above composition is subjected to heat treatment to produce Li _{1 + x + z} M _x (Ge _1−y Ti _y ) _2−x Si _z P _3−z O ₁₂ (where 0 ≦ x ≦ 0.8, 0 ≦ y ≦ 1. 0, 0 ≦ z ≦ 0.6, M = one or more selected from Al and Ga), and crystals are deposited to have high lithium ion conductivity.

  When the glass having the above composition is included in the slurry, the aqueous solvent is preferable in terms of high dispersion, and in this case, the water content immediately after the peeling step and immediately before the laminating step should be within the above range. Enables stable peeling and lamination.

(14) In the slurry manufacturing process, the inorganic compound particles are lithium ion conductive glass ceramics, and the ion conductive solid electrolyte according to any one of (1) to (13) is manufactured. Can provide a method.

Examples of the lithium ion conductive glass ceramics include glass ceramics having sulfide crystals such as Li ₇ PS ₆ , Li ₄ P ₂ S ₆ , Li ₃ PS _4, and Li _{1 + x + z} M _x (Ge _1-y Ti _{y 2-x} Si _z P _3-z O ₁₂ (where 0 ≦ x ≦ 0.8, 0 ≦ y ≦ 1.0, 0 ≦ z ≦ 0.6, M = Al, Ga, one or more selected from Glass ceramics having a crystal of In particular _{Li 1 + x + z M x} (Ge 1-y Ti y) 2-x Si z P 3-z O 12 ( where, 0 ≦ x ≦ 0.8,0 ≦ y ≦ 1.0,0 ≦ z ≦ 0.6 , M = Al or one selected from Al and Ga) is preferable because of its high chemical stability.

  In addition, it is advantageous in terms of ion conduction that the crystal does not include a crystal grain boundary that impedes ion conduction, but glass ceramics in particular have almost no vacancies or crystal grain boundaries that impede ion conduction. In view of high ion conductivity and excellent chemical stability, it is preferable compared to ceramics and the like. In addition to glass ceramics, examples of a material that has almost no vacancies or crystal grain boundaries that hinder ion conduction include single crystals of the above crystals, which are difficult to manufacture and expensive. Lithium ion conductive glass ceramics are also advantageous from the viewpoint of ease of production and cost.

Here, lithium ion conductivity means that the lithium ion conductivity shows a value of 1 × 10 ⁻⁸ S · cm ⁻¹ or more at 25 ° C. Further, vacancies and grain boundaries that hinder ion conduction mean that the conductivity of the entire inorganic substance including lithium ion conductive crystals is 1/10 of the conductivity of the lithium ion conductive crystals themselves in the inorganic substance. It refers to ionic conductivity inhibitors such as vacancies and grain boundaries that decrease below.

(15) The method for producing an ion conductive solid electrolyte according to any one of (1) to (13), wherein in the slurry production step, the inorganic compound particles are lithium ion conductive ceramics. Can provide.

(16) The inorganic compound particles include Li _{1 + x + z} M _x (Ge _1-y Ti _y ) _2−x Si _z P _3−z O ₁₂ (however, 0 ≦ x ≦ 0.8, 0 ≦ y ≦ 1.0). , 0 ≦ z ≦ 0.6, one or more selected from M = Al and Ga). The ion-conductive solid electrolyte according to (14) or (15) is manufactured. Can provide a method.

Examples of lithium ion conductive ceramics include crystals having a perovskite structure having lithium ion conductivity such as LiN, LISICON, La _0.55 Li _0.35 TiO _3, and LiTi ₂ P ₃ O ₁₂ having a NASICON type structure. Ceramics having the following crystals are raised. From the viewpoint of lithium ion conductivity, chemical stability, cost, etc., Li _{1 + x + z} M _x (Ge _1-y Ti _y ) _2−x Si _z P _3−z O ₁₂ (however, 0 ≦ x ≦ 0.8, Ceramics having a crystal of 0 ≦ y ≦ 1.0, 0 ≦ z ≦ 0.6, and one or more selected from M = Al and Ga are preferable.

(17) The ion conductive solid according to any one of (3), (6), (8), and (10) above, further comprising a step of heat-treating the laminate at 500 ° C. to 1200 ° C. A method for producing an electrolyte can be provided.

  The heat treatment step can include a degreasing step and a sintering step. A degreasing process is a process of processing a green sheet laminated body at high temperature, gasifying components, such as organic binders other than the inorganic substance to comprise, and discharging | emitting from a green sheet laminated body. The sintering step is a step of sintering and bonding inorganic particles constituting the green sheet laminate by treating the green sheet laminate at a higher temperature than the degreasing step. In any of the degreasing step and the sintering step, it is preferable to perform exhaust in order to keep the atmosphere in the furnace constant. Although a known firing furnace such as a gas furnace or a microwave furnace can be used for the firing step, it is preferable to use an electric furnace for reasons such as environment, temperature distribution in the furnace, and cost.

(18) A battery comprising the solid electrolyte produced by the method for producing an ion conductive solid electrolyte according to any one of (1) to (17) can be provided.

  As described above, in the manufacturing process of the green sheet, since it pays special attention to the carrier film peeling process and the green sheet laminating process with high mechanical stress, it is possible to sufficiently grasp the preferable mechanical resistance against the stress, and the drying process. By setting the water content of the subsequent ceramic green sheet within a predetermined range, it is possible to obtain mechanical characteristics different from those for preventing defects in the drying process, the debinding process of the laminate, and the firing process.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the following description is made for explaining the embodiments of the present invention, and the present invention is limited to these embodiments. It is not a thing. The same or the same type of elements are denoted by the same or related symbols, and redundant description is omitted.

  FIG. 1 relates to an embodiment of the present invention, and in a method for producing an ion conductive solid electrolyte containing an inorganic compound powder and an organic binder, a step of applying a slurry to a carrier film to produce a coating film; It is a schematic diagram of the line 10 which performs the process of drying and producing a green sheet. A coating film 19 is applied onto the carrier film 16 that is fed from the carrier film roll 14 by the doctor blade 12 and is conveyed by the conveying roller 18. A schematic diagram of this doctor blade is shown in FIG. The slurry stored in the slurry dam 13 of the doctor blade exits from the opening 15 and is applied onto the carrier film 16. Next, the coating film 19 is transported to a drying furnace 20 and dried therein. Drying in the drying oven 20 is performed in two stages in order to prevent cracks, warpage, undulations in the green sheet, or sudden evaporation of the solvent, causing bump marks or cracks in the green sheet. It is preferable that primary drying is performed at 40 ° C to 60 ° C and secondary drying is performed at 80 ° C to 120 ° C. Moreover, in order to make it easy to adjust the water content immediately after the peeling step and immediately before the laminating step to a desired value, the drying step is preferably performed within the above temperature range. Thereafter, the dried green sheet is wound around the drum 22 together with the carrier film 16. As shown in FIG. 3, the green sheet with the carrier film 16 of the drum 22 is partially developed outside the line, and the sample portion 24 is sampled and cut out. The sample part 24 cut out in this way is peeled off from the carrier film 16, the water content is measured by the Karl Fischer method, and the water content is determined.

  Although not clearly shown in the figure, after leaving the drying furnace 21, the green sheets 18 are belts 24, 36 in an environment in which the temperature is maintained at 5 to 60 ° C. and the relative humidity is maintained at 1 to 50%. Carried over. Under the same environment, the green sheet with a carrier film is wound around the drum 22. And the wound green sheet with a carrier film is preserve | saved under the same environment.

[Example]
(Preparation of green sheet for solid electrolyte)
H ₃ PO ₄ , Al (PO ₃ ) ₃ , Li ₂ CO ₃ , SiO ₂ , and TiO ₂ are used as raw materials, and these are mol% in terms of oxide, 33.8% of P ₂ O ₅ and Al ₂ O. ₃ was 7.6%, Li ₂ O was 14.5%, TiO ₂ was 41.3%, and SiO ₂ was 2.8%. The glass melt was heated and melted for 3 hours at 1450 ° C. in an electric furnace while stirring. Thereafter, the glass melt was dropped into running water to obtain flaky glass.

  The obtained glass flakes were pulverized and classified by a ball mill to obtain glass fine particles having an average particle diameter of 1.1 μm. Further, the mixture was finely pulverized using a wet bead mill using ethanol, and the slurry was further dried by spray drying to obtain glass microparticles having an average particle size of 0.5 μm.

  As a binder dispersed in the glass fine particles and water, a dispersant was added to an acrylic resin and stirred for 48 hours with a ball mill to prepare a slurry. The glass fine particles contained in the slurry at this time were 61.5 mass%, and the acrylic resin was 11.0 mass%.

  The obtained slurry was molded as a 40 μm-thick coating film on a PET film that had been subjected to a release treatment with the doctor blade of FIG. 1, and was primarily dried at 40 ° C. Moreover, primary drying was performed in the range of 40-60 degreeC in a drying furnace, and secondary drying was performed in the range of 80-120 degreeC in the drying furnace, and the green sheet was obtained. Here, sampling was performed from the green sheet immediately after leaving the drying furnace, and the water content in the green sheet was measured at 200 ° C. by the Karl Fischer method. The water content was 2.3%.

The green sheet exiting the drying furnace is directly conveyed to a constant temperature and humidity chamber set at a temperature of 22 ° C. and a relative humidity of 30%, and is held in the constant temperature and humidity chamber. After cutting, peeling from the PET film was performed. At this time, the green sheet was not found to be broken or stretched. After the peeling step, the water content in the green sheet was again measured by sampling at 200 ° C. by the Karl Fischer method. The water content was 1.9 to 2.0%. Here, the green sheets of the same lot were cut into the same size and 8 sheets were stacked and sandwiched between PET films that had been subjected to a release treatment, and pressed by a hydrostatic pressure press at 198 MPa for lamination. The laminated green sheet (hereinafter referred to as green sheet laminate) had no defects such as cracking and stretching, and the specific gravity was 1.98. Next, the green sheet laminate is placed on a quartz glass plate, heated at 50 ° C./h in an electric furnace, held at 600 ° C. for 3 h to remove the binder, and cooled to room temperature at 50 ° C./h to degrease the body. Got. After that, sandwiched between the quartz glass plates, heated to 30 ° C./h up to 500 ° C. in an electric furnace, held for 3 hours, then heated at 650 ° C./h, heat treated at 1015 ° C. for 30 minutes, sintered, The temperature was lowered to room temperature at 50 ° C./h to obtain a solid electrolyte. When the ionic conductivity of the obtained solid electrolyte was determined by an alternating current impedance method, it was 3.1 × 10 ⁻⁴ S · cm ⁻¹ at 25 ° C. and the porosity was 1.7%.

Here, the porosity is a ratio of pores contained in a unit volume, and is represented by the following formula.
Porosity (%) = (true density−bulk density) / true density × 100
Here, the true density is the density of the substance itself, and the density of each substance constituting the solid electrolyte is obtained and calculated based on the content ratio of the constituting substance. On the other hand, the bulk density is a density obtained by dividing the weight of an object by an apparent volume, and is a density including pores. The bulk density is determined according to the Archimedes method for a solid electrolyte obtained by firing.

  From the same slurry as the above examples, a coating film is formed with the same thickness, and the average moisture content of the green sheet obtained by drying under various drying conditions is summarized for each drying condition and holding condition of each step, in combination, The evaluation results of these green sheets are summarized in Table 1. These green sheets were obtained by the same apparatus as that used for obtaining the above experimental example. Therefore, if the evaluation result is good, as described above, if cutting and lamination are performed and heat treatment is performed, a solid electrolyte having a preferable ionic conductivity as described above can be obtained. In this table, the moisture content is calculated with two significant digits. For example, when the moisture content is 0.08%, there is a significant difference with respect to the criterion that the moisture content is 0.1% or more. Judged here.

  In general, the resistance of a material to be treated (e.g., a green sheet) to be treated or operated should be grasped by the characteristics of the material to be treated before these treatments or effects are performed. In this experiment, the moisture content of the green sheet could not be measured immediately before peeling. However, using the result of the moisture content immediately after peeling was sufficient to grasp the mechanical properties of the green sheet at the time of peeling. Moreover, it is also possible to estimate the moisture content immediately before peeling using the data immediately after peeling from the environmental conditions of the line.

  As can be seen from this table, the water content ranges from 0.1 to 5%, and the range of temperature and relative humidity from the drying step to the peeling step, and from the peeling step to the lamination step ranges from 5 to 60. What was hold | maintained at (degreeC) and 1 to 50% was favorable in any evaluation. However, in Comparative Example 1, the film was stretched by peeling and stretched by lamination. Moreover, in the comparative example 2, it had already cracked at the time of peeling. And in the comparative example 3, it extended | stretched by peeling and it cracked in the lamination process. Furthermore, in Comparative Example 4, it was already cracked at the time of peeling.

  As can be seen from the above examples, it is possible to prevent the generation of defects (stretching, cracking, etc.) due to the mechanical action after the drying process by adjusting the environmental conditions for the treatment and storage of the coating film or green sheet. it is obvious. In particular, the ability to resist an external mechanical force in the peeling process of the carrier film that seems to have high mechanical stress can be ensured by setting the moisture content of the green sheet within a predetermined range.

It is a schematic diagram of the line which performs the process of apply | coating a slurry with a doctor blade and drying the coating film. It is a perspective view which shows the detail of a doctor blade. It is a figure which shows typically a mode that it samples from the green sheet with a carrier film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Coating line 12 Doctor blade 13 Slurry dam 16 Carrier film 18 Conveyance roller 19 Coating film 20 Drying furnace

Claims (18)

In a method for producing an ion conductive solid electrolyte by firing a green sheet containing an inorganic compound powder exhibiting lithium ion conductivity and an organic binder at least after heat treatment,
A slurry manufacturing process for preparing a slurry by mixing the inorganic compound powder and the organic binder;
A coating film step of applying the slurry to a carrier film to prepare a coating film;
A drying step for drying the coating film;
A peeling step of peeling the coating film from the carrier film to produce a green sheet;
Laminating step of laminating the green sheets to produce a laminate,
A method for producing an ion conductive solid electrolyte, wherein the water content of the coating film immediately after the peeling step is 0.1 to 5%.   The method for producing an ion conductive solid electrolyte according to claim 1, wherein a moisture content of the green sheet immediately before the lamination step is 0.1 to 5%.   Between the said drying process and the said peeling process, temperature is kept at 5-60 degreeC, and relative humidity is hold | maintained at 1 to 50%, The ion conductive solid electrolyte of Claim 1 or 2 characterized by the above-mentioned. How to manufacture.   Between the said peeling process and the said lamination | stacking process, temperature is kept at 5-60 degreeC, and relative humidity is hold | maintained at 1-50%, The ion conductivity in any one of Claim 1 to 3 characterized by the above-mentioned. A method for producing a solid electrolyte.   5. The method for producing an ion conductive solid electrolyte according to claim 3, wherein in the peeling step and the laminating step, the coating film and the green sheet are held at a temperature exceeding a dew point.   The method for producing an ion conductive solid electrolyte according to claim 1, wherein the green sheet has a thickness of 1 to 100 μm.   7. The ion conduction according to claim 1, further comprising a laminating step of laminating at least two green sheets that have undergone the drying step and pressurizing them at a predetermined pressure to produce a laminate. For producing a conductive solid electrolyte. In the lamination step,
The method for producing an ion conductive solid electrolyte according to claim 1, wherein a thickness of the laminate is 10 to 1000 μm. In the lamination step,
The method for producing an ion-conductive solid electrolyte according to any one of claims 1 to 8, wherein the pressurizing time for lamination is 5 seconds or more. In the lamination step,
10. The method for producing an ion conductive solid electrolyte according to claim 1, wherein the green sheet to be laminated has a specific gravity of 1.1 to 2.4. In the slurry manufacturing process,
The method for producing an ion conductive solid electrolyte according to claim 1, wherein the inorganic compound particles include glass or glass ceramics. In the slurry manufacturing process,
The method for producing an ion conductive solid electrolyte according to claim 1, wherein the inorganic compound particles include glass that exhibits lithium ion conductivity by heat treatment. The glass is expressed in mol% based on oxide,
Li ₂ O 10-25%, and Al ₂ O ₃ and / or Ga ₂ O ₃ 0-15%, and TiO ₂ and / or GeO ₂ 25-50%, and SiO ₂ 0-15%, and P ₂ O ₅ 26-40%
The method for producing an ion conductive solid electrolyte according to claim 12, comprising: In the slurry manufacturing process,
The method for producing an ion conductive solid electrolyte according to claim 1, wherein the inorganic compound particles are lithium ion conductive glass ceramics. In the slurry manufacturing process,
The method for producing an ion conductive solid electrolyte according to claim 1, wherein the inorganic compound particles are lithium ion conductive ceramics. The inorganic compound particles are Li _{1 + x + z} M _x (Ge _1−y Ti _y ) _2−x Si _z P _3−z O ₁₂ (where 0 ≦ x ≦ 0.8, 0 ≦ y ≦ 1.0, 0 ≦ 16. The method for producing an ion-conductive solid electrolyte according to claim 14 or 15, comprising a crystal of z ≦ 0.6 and one or more selected from M = Al and Ga.   Furthermore, the process of heat-processing the said laminated body at 500 degreeC-1200 degreeC is included, The method of manufacturing the ion conductive solid electrolyte in any one of Claim 3, 6, 8, 10 characterized by the above-mentioned.   A battery comprising a solid electrolyte produced by the method for producing an ion conductive solid electrolyte according to claim 1.

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