JP2018063809A - Green sheet, laminate green sheet, continuous laminate green sheet, all-solid type secondary battery, and fabrication methods thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a laminate green sheet which can make contribution to the enhancement in the performance of an all-solid type secondary battery, which enables the simplification of its fabrication process, and which allows the interface resistance of each layer to be kept down; an all-solid type secondary battery arranged by use of the laminate green sheet; and fabrication methods thereof.SOLUTION: A laminate green sheet is manufactured by the steps of: adding a material, which is thermally decomposed to form cavities when baked, to a slurry for making one or more kinds of electrode layers; and using the resultant slurry to laminate, on a first current collector, a first electrode layer green sheet, a solid electrolyte layer green sheet and a second electrode layer green sheet in this order. An all-solid type secondary battery is manufactured by putting together a second current collector on the second electrode layer green sheet of the laminate green sheet, followed by collective baking. A series all-solid type secondary battery is manufactured by collectively baking a continuous laminate green sheet manufactured by successively laminating laminate green sheets identical to the above laminate green sheet.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a multilayer green sheet and an all-solid secondary battery using the multilayer green sheet.

In recent years, power consumption has increased with the advancement of functions of small electronic devices typified by personal computers (PCs) and smartphones. In addition, demand for in-vehicle applications such as hybrid vehicles and electric vehicles, and stationary applications such as household storage batteries is increasing. Along with this, demands for higher energy density for secondary batteries are accelerating.
Furthermore, the lithium ion secondary battery currently used for the above applications uses an organic electrolyte, and depending on the usage situation, there is a possibility of leakage of the electrolyte, ignition, etc. It has been.

On the other hand, the all-solid-state secondary battery is composed of only a solid material without using an organic electrolytic solution, and therefore has no possibility of leakage or ignition and is excellent in safety. Therefore, it is promising as a post lithium ion secondary battery.
However, all solid-state secondary batteries currently in practical use are only thin-film all-solid secondary batteries and have a low energy density. Furthermore, since the positive electrode layer, the solid electrolyte layer, and the negative electrode layer are produced by vapor deposition or sputtering, it is necessary to produce them under a reduced pressure atmosphere, which is not suitable for large area and mass production.

  As a method for manufacturing a high capacity all solid state secondary battery, there are manufacturing methods described in Patent Documents 1 and 2. The manufacturing method is to produce a positive electrode layer green sheet, a solid electrolyte layer green sheet and a negative electrode layer green sheet with a thick film by the same coating method and printing method as a conventional lithium ion secondary battery, and paste each layer green sheet. In addition, a laminate green sheet is formed, and the laminate green sheet is fired at once and then sandwiched between current collectors.

JP 2000-340255 A International Publication No. 2011-111555

As in Patent Documents 1 and 2, when a laminated fired body including a positive electrode layer, a solid electrolyte layer, and a negative electrode layer is sandwiched between a positive electrode current collector and a negative electrode current collector, the positive electrode current collector, the positive electrode layer, and the negative electrode current collector There is a problem that the interfacial resistance between the electrode and the negative electrode layer is high and the battery performance is poor. Furthermore, there is a problem that the firing efficiency is poor since there are two firings.
Further, when the green sheet is fired, gas due to the decomposition of the binder is generated. However, Patent Documents 1 and 2 have a problem that firing takes time because the pores in the green sheet are small and gas escape is bad. .

Here, when the gas escape is bad, there is a problem that the interface between the electrode layer and the solid electrolyte layer peels when the gas escapes, resulting in an increase in interface resistance and poor battery performance.
An object of the present invention is to provide a green sheet and a laminate that improve gas escape during binder decomposition, contribute to improving the performance of an all-solid secondary battery, simplify the manufacturing process, and suppress interface resistance of each layer. It is to provide a green sheet, a continuous laminate green sheet, a manufacturing method thereof, and a manufacturing method of an all-solid secondary battery.

  As a result of intensive studies to solve the above problems, the present inventors have come up with the idea of producing a green sheet to which a material that thermally decomposes and forms voids is added during firing. That is, it was found that the material added at the time of firing thermally decomposes to form voids, and the gas escape is improved at the time of binder decomposition, so that each layer can form a good interface with low electrical resistance in a short time.

  The green sheet according to one embodiment of the present invention is a green sheet for an all-solid secondary battery including an active material or a solid electrolyte and a binder, and is thermally decomposed by heat during firing to form voids. A void forming material, which is a material to be added, is added to 1 to 20 parts by mass with respect to 100 parts by mass of the active material or solid electrolyte, and the void forming material is added in the form of granules, The particle size of the granule is in the range of 5 μm to 30 μm.

According to one embodiment of the present invention, the gas release property in the green sheet during firing is good.
For this reason, it becomes possible to produce an all-solid secondary battery in which the production process of the all-solid secondary battery is simplified while suppressing the interface resistance of each layer between the stacked green sheets.

It is a schematic diagram of the laminated | stacked green sheet which concerns on embodiment based on this invention. It is a schematic diagram of the green sheet after decomposition of the additive material according to the embodiment of the present invention. It is a schematic diagram of the laminated body green sheet which concerns on embodiment based on this invention. It is a schematic diagram of the laminated body green sheet with a both-sides collector which concerns on embodiment based on this invention. It is a schematic diagram of the continuous laminated body green sheet which concerns on embodiment based on this invention. It is a schematic diagram of the continuous laminated body green sheet before the baking process which concerns on embodiment based on this invention.

Next, embodiments of the present invention will be described with reference to the drawings.
Note that the embodiments of the present invention are not limited to the embodiments described below, and it is possible to make design changes based on the knowledge of those skilled in the art, and such changes have been made. Embodiments are also included in the scope of the embodiments of the present invention.
FIG. 1 shows an example of a laminated green sheet, which is a laminated green sheet in which a solid electrolyte layer green sheet 12 and a positive electrode layer green sheet 11 are laminated in this order on one surface of a negative electrode layer green sheet 13. For example, when the current collector as the first current collector is provided on the other surface of the negative electrode layer green sheet 13, the negative electrode layer green sheet 13 becomes the first electrode layer green sheet, and the positive electrode layer green sheet 11 It becomes a 2nd electrode layer green sheet.

The negative electrode layer green sheet 13 includes negative electrode active material particles 5, a conductive additive and a binder.
The solid electrolyte layer green sheet 12 includes solid electrolyte particles 2 and a binder.
The positive electrode layer green sheet 11 includes positive electrode active material particles 1, a conductive additive 3, and a binder.
In the example of FIG. 1, a particulate void forming material, which is a material that is thermally decomposed by heat during firing to form voids, is added to each green sheet. The void forming material 4 may be added only to some of the green sheets of the positive electrode layer green sheet 11, the negative electrode layer green sheet 13, and the solid electrolyte layer green sheet 12.

The thermal decomposition temperature of the void forming material 4 is preferably lower than the thermal decomposition temperature of the binder.
Moreover, it is preferable that the addition amount of the space | gap formation material 4 is 1-20 mass parts with respect to 100 mass parts of active materials contained in the green sheet to which the space | gap formation material was added. When the void forming material 4 is added to the solid electrolyte layer green sheet 12, the amount of the void forming material 4 added is the solid electrolyte 100 contained in the solid electrolyte layer green sheet 12 to which the void forming material is added. It is preferable that it is 1-20 mass parts with respect to a mass part.

It is preferable that the void forming material is added in the form of granules, and the particle diameter of the granules is in the range of 5 μm to 30 μm.
The active material particles may be any material that can occlude and release lithium ions, and are not particularly limited. Among the active material particles, those showing a more noble potential can be used as the positive electrode active material particles 1 on the positive electrode side, and those showing a lower potential can be used as the negative electrode active material particles 5 on the negative electrode side.

The positive electrode active material particles 1, for example, lithium nickel cobalt manganese oxide _{(LiNi x Co 1-y-} x Mn y O 2), lithium cobalt oxide (LiCoO _2), lithium nickelate (LiNiO _2), lithium manganate ( LiMn ₂ O ₄ ), lithium iron phosphate (LiFePO ₄ ), lithium cobalt phosphate (LiCoPO ₄ ), lithium manganese phosphate (LiMnPO ₄ ), lithium vanadium phosphate (Li ₃ V ₂ (PO ₄ ) ₃ ), etc. Lithium transition metal compounds can be used.

Examples of the negative electrode active material particles 5 include carbon materials such as hard carbon, soft carbon, and graphite, alloy materials such as Sn-based alloys and Si-based alloys, nitrides such as LiCoN, and lithium titanate (Li ₄ Ti ₅ O). ₁₂ ), lithium transition metal oxides such as lithium vanadium phosphate (Li ₃ V ₂ (PO ₄ ) ₃ ) can be used. Moreover, you may use metal lithium foil.

The solid electrolyte particles 2 are not particularly limited as long as they have a low electron conductivity and a high lithium ion conductivity. As the solid electrolyte particles 2, for example, an oxide solid electrolyte or a sulfide solid electrolyte amorphous body (glass body), crystal body, glass ceramic, or the like can be used. In particular, an oxide-based solid electrolyte that can be fired at high temperature is preferable, and a NASICON type oxide, a perovskite type oxide, a LISICON type oxide, a garnet type oxide, an oxide glass, or the like can be used. For example, Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ , Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ , Li _0.29 La _0.571 TiO ₃ , Li _{4 SiO 4 -Li 3 PO 4,} Li 3 BO 3 -Li 3 PO 4, Li 7 La 3 Zr 2 O 12, Li 3.4 V 0.6 Si 0.4 O 4 and the like can be used.

  The conductive auxiliary agent 3 is not particularly limited as long as it is a conductive material. As the conductive assistant 3, for example, a conductive carbon material, particularly carbon black, activated carbon, carbon carbon fiber, or the like can be used. The content of the conductive auxiliary agent 3 is preferably less than 90 parts by mass with respect to 100 parts by mass of the active material particles. If the content of the conductive auxiliary is not less than part by mass, the mass of the active material particles may be insufficient and the lithium storage capacity may be reduced.

  The binder is not particularly limited as long as it is a material that binds to the active material particles, the solid electrolyte particles, and the conductive additive and decomposes under the firing conditions described later. As the binder, for example, polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl butyral, polyvinyl acetal, polyvinylidene fluoride, polytetrafluoroethylene, ethyl cellulose, acrylic resin, and the like can be used.

The void forming material 4 in the green sheet is not particularly limited as long as it has a lower pyrolysis temperature than that of the binder. As the void forming material 4, for example, microcapsules, microbeads, sublimation substances, or the like can be used.
The constituent materials of microcapsules and microbeads include polyurethanes, polyureas, polyamides, polyesters, polycarbonates, polyacrylates, polystyrenes, polymethyl methacrylates, vinylidene chloride, urea-formaldehyde resins, melamine resins and These copolymers and the like can be mentioned, and there is no particular limitation as long as the thermal decomposition temperature is lower than that of the binder.

  Sublimable substances include naphthalene, 1,7,7-trimethylbicycloheptan-2-one, solid carbon dioxide, iodine, ice, cyclohexane-1,2-dicarboxylic acid, cyclohexane-1,3-dicarboxylic acid, cyclohexane- 1,4-dicarboxylic acid, cyclohexane-1,2,4-dicarboxylic acid, phthalic acid, aminoacetophenone, vanillin, 4-hydroxyphthalic acid, trimetic acid, trimetic anhydride, dimethoxyacetophenone, 5-hydroxyisophthalic acid, gallic acid Methyl gallate, 1,7-dihydronaphthalene, 4,4'-dihydroxybenzophenone, 2,2 ', 4,4'-tetrahydroxybenzophenone, etc., and the sublimation point is lower than the thermal decomposition temperature of the binder. There is no particular limitation.

  The content of the void forming material 4 is preferably 0.5 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the active material particles. More preferably, they are 1 mass part or more and 20 mass parts or less with respect to 100 mass parts of active material particles. When there is more content of the space | gap formation material 4 than 30 mass parts, the mass of an active material particle may run short and lithium storage capacity may fall. When the content of the void forming material 4 is less than 0.5 parts by mass, the void forming material 4 is too small, and the void through which the gas escapes may not be formed sufficiently.

The particle diameter of the void forming material 4 is preferably 1 μm or more and 40 μm or less. More preferably, they are 5 micrometers or more and 30 micrometers or less. If the particle diameter of the void-forming material 4 is larger than 40 μm, the active material particles per battery volume may be insufficient and the lithium storage capacity may be reduced. When the particle diameter of the void forming material 4 is less than 1 μm, the formed voids are too small, the gas releasing property is poor, and the effect of the void forming material 4 is almost lost.
FIG. 2 shows a state after the laminated green sheet of FIG. 1 is sintered. The void forming material 4 is thermally decomposed by the sintering to form voids in the target green sheet after sintering.

(Laminated green sheet)
As shown in FIG. 3, the laminate green sheet according to the present embodiment has a negative electrode layer green sheet 13, a solid electrolyte layer green sheet 12, and a positive electrode layer green sheet on a current collector 14 constituting a first current collector. 11 are formed in this order. The arrangement of the positive electrode layer green sheet 11 and the negative electrode layer green sheet 13 may be reversed. That is, the laminate green sheet according to the present embodiment may be formed on the current collector 14 in the order of the positive electrode layer green sheet 11, the solid electrolyte layer green sheet 12, and the negative electrode layer green sheet 13.

Further, as shown in FIG. 4, a current collector 14 constituting a second current collector may be provided on the positive electrode layer green sheet 11 positioned on the upper surface side of the stack.
The current collector 14 is not particularly limited as long as it is a conductive material. As the current collector 14, for example, a metal material such as stainless steel, nickel, aluminum, iron, titanium, copper, palladium, gold, and platinum can be used. The material of the current collector 14 is preferably selected in consideration of not melting and decomposing under the firing conditions described later, and the battery operating potential and conductivity applied to the current collector 14.

  The positive electrode layer green sheet 11 and the negative electrode layer green sheet 13 are prepared by mixing a binder containing active material particles, solid electrolyte particles 2 and conductive aid 3 together with a solvent to form a positive electrode slurry and a negative electrode slurry. The slurry is formed by coating or printing on a current collector or the like and then drying. The method for preparing the positive electrode slurry and the negative electrode slurry is not particularly limited.

The solid electrolyte layer green sheet 12 is formed by mixing solid electrolyte particles 2 and a binder together with a solvent to form a solid electrolyte slurry, which is applied or printed on the positive electrode layer green sheet or the negative electrode layer green sheet, and then dried. Is done. The method for preparing the solid electrolyte slurry is not particularly limited.
The solid electrolyte particles 2 in the positive electrode layer green sheet 11, the solid electrolyte layer green sheet 12, and the negative electrode layer green sheet 13 may be the same or different, and two or more kinds are used in the same green sheet. Also good.

  The binder in the positive electrode layer green sheet 11, the solid electrolyte layer green sheet 12, and the negative electrode layer green sheet 13 is desirably 3 parts by mass or more and 40 parts by mass or less. When the amount is less than 3 parts by mass, sufficient binding cannot be achieved, and when the amount is greater than 40 parts by mass, the capacity per electrode volume is greatly reduced. More preferably, they are 3 to 25 mass parts.

  The solvent used for the positive electrode slurry, the solid electrolyte slurry, and the negative electrode slurry is not particularly limited as long as the binder can be dissolved. Examples of the solvent include alcohols such as ethanol, isopropanol, and n-butanol, toluene, ethyl acetate, butyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, ethylene glycol ethyl ether, isophorone, butyl lactate, dioctyl phthalate, dioctyl adipate, Organic solvents such as benzyl alcohol, N, N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), and water can be used. In addition, these solvents may be used independently and may use 2 or more types together. Since the slurry can be easily dried, the boiling point of the solvent is preferably 200 ° C. or lower.

  Although not shown, the positive electrode slurry, the solid electrolyte slurry, and the negative electrode slurry promote the formation of a matrix structure in each green sheet when the positive electrode layer green sheet 11, the solid electrolyte layer green sheet 12, and the negative electrode layer green sheet 13 are fired. You may further contain the baking auxiliary agent which reduces temperature. The firing aid is not particularly limited as long as it does not react with the active material particles and the solid electrolyte particles 2 and has a softening point temperature lower than the firing temperature of the solid electrolyte particles 2. As the firing aid, for example, a boron compound can be used. By adjusting the content and firing temperature of the firing aid of each green sheet, when forming a laminated fired body by firing, it prevents cracking due to internal strain and internal stress of each layer and promotes the formation of a matrix structure can do.

  As described above, the positive electrode slurry, the solid electrolyte slurry, and the negative electrode slurry include the active material particles, the solid electrolyte particles 2, the conductive auxiliary agent 3, the void forming material 4 that is thermally decomposed to form voids, the binder, the solvent, If necessary, it can be prepared by mixing a baking aid or the like. Moreover, the mixing method of a slurry is not specifically limited, You may add materials, such as a thickener, a plasticizer, an antifoamer, a leveling agent, and an adhesive provision agent, as needed.

Specifically, the application method and printing method of the positive electrode slurry, the solid electrolyte slurry, and the negative electrode slurry include a doctor blade method, a calendar method, a spin coating method, a dip coating method, an ink jet method, an offset method, a die coating method, a spray method, and a screen. A printing method or the like can be used.
The drying method of the positive electrode slurry, the solid electrolyte slurry, and the negative electrode slurry is not particularly limited. For example, heat drying, reduced pressure drying, heat reduced pressure drying and the like can be used. The drying atmosphere is not particularly limited. For example, it can be performed in an air atmosphere or a nitrogen atmosphere.

The thickness of the positive electrode layer formed by the positive electrode layer green sheet 11 and the thickness of the negative electrode layer formed by the negative electrode layer green sheet 13 can be determined according to a desired battery capacity.
The thickness of the solid electrolyte layer formed by the solid electrolyte layer green sheet 12 is preferably in the range of 1 μm to 500 μm. If it is thinner than 1 μm, the positive electrode layer and the negative electrode layer are short-circuited, and not only the performance of the all-solid-state secondary battery is lowered, but also the safety may be lowered. If it is thicker than 500 μm, the movement of conductive ions such as lithium ions in the solid electrolyte layer is hindered, and the output of the all-solid secondary battery may be lowered.

In the firing process, the laminated fired body according to the present embodiment forms voids with the gap forming material 4 from the laminated green sheet according to the present embodiment, further degreases the binder, and then sinters the particles. It is formed.
The heating temperature in the firing step is equal to or higher than the thermal decomposition temperature of the binder contained in the laminate green sheet and lower than the oxidation temperature of the active material particles or lower than the combustion temperature of the current collector, specifically 300 ° C. or higher. It is preferably 1100 ° C. or lower, more preferably 300 ° C. or higher and 900 ° C. or lower. When the temperature is lower than 300 ° C., the binder does not completely burn but becomes a residue, which may become a resistor in the layer. When the temperature is higher than 1100 ° C., the active material particles and the solid electrolyte particles may be melted and deteriorated to deteriorate the battery performance.

The atmosphere in the firing step is not particularly limited. For example, the reaction can be performed in an air atmosphere or a nitrogen atmosphere, but when there is a concern about the reaction between the active material particles and the current collector 14 or the decrease in the conductivity of the current collector 14, it may be performed in an inert atmosphere. It is desirable to do. The firing time is not particularly limited as long as the binder used is sufficiently decomposed.
As shown in FIG. 5, the continuous laminate green sheet 15 according to the present embodiment is obtained by continuously laminating a plurality of laminate green sheets shown in FIG. 3. At this time, the first current collector of the upper laminate green sheet is laminated on the second electrode layer green sheet of the lower laminate green sheet sequentially. In this way, the current collector of one laminate green sheet and the positive electrode layer green sheet or the negative electrode layer green sheet of the other laminate green sheet are bonded and sequentially laminated. The method for laminating the laminate green sheet is not particularly limited. For example, a flat plate press, roll press, hot press, cold isostatic press, hot isostatic press and the like can be used.

The continuous laminate green sheet 15 shown in FIG. 6 is obtained by further laminating a current collector 14 on the upper surface side where the laminate green sheets are continuously laminated as shown in FIG.
The continuous laminated fired body according to the present embodiment is formed by firing the continuous laminated green sheet 15. The firing conditions can be the same as the firing conditions in the formation of the laminated fired body.

  The all-solid-state secondary battery according to the present embodiment has another current collector on the positive electrode layer green sheet 11 or the negative electrode layer green sheet 13 farthest from the first current collector of the laminate green sheet or the continuous laminate green sheet 15. The body 14 can be bonded to form a laminated body shown in FIGS. 4 and 6 and then fired at once. The firing conditions can be the same as the firing conditions in the formation of the laminated fired body.

  As described above, in this embodiment, the void forming material 4 in which voids are formed by thermal decomposition is added to the green sheet preparation slurry, and the slurry is used to apply the slurry onto the first current collector. A laminate green sheet was produced in which a first electrode layer green sheet, a solid electrolyte layer green sheet as a positive electrode or a negative electrode, and a second electrode layer green sheet as a counter electrode were laminated in this order.

Then, the 2nd electrical power collector was bonded together on the 2nd electrode layer green sheet of the laminated body green sheet, and the all-solid-state secondary battery was produced by baking collectively.
At the time of firing, voids were formed, the gas releasing property was improved, and the interfacial resistance of each layer could be reduced.
The laminated green sheets are continuously laminated, and a current collector is disposed between the laminated green sheets and on the outer side in the stacking direction of the laminated green sheets. 14 were laminated to produce a continuous laminate green sheet 15, and the continuous laminate green sheet 15 was collectively fired to produce a series all solid state secondary battery.

In addition, by batch firing, the chemistry of particles in adjacent layers at the interface between the first current collector and the first electrode layer green sheet and at the interface between the second current collector and the second electrode layer green sheet. A bond is formed.
As a result, the ratio of the active material particles in direct contact with the solid electrolyte particles has been dramatically improved, and the interfacial resistance between the particles can be reduced.

Unlike the conventional transfer method, the laminate green sheet production process according to the present embodiment can be produced continuously, and further the interfacial resistance between the layers by performing simultaneous firing. It became possible to carry out the firing process once while suppressing the above.
Moreover, it becomes possible to produce a continuous laminate green sheet by continuously laminating the laminate green sheet, and producing an all-solid-state secondary battery in series by collectively firing the continuous laminate green sheet. Became possible.

Here, the thermal decomposition temperature of the void forming material 4 is lower than the thermal decomposition temperature of the binder in the green sheet. As a result, when the binder is decomposed during firing, voids for diffusing gas are formed in the green sheet, so that the gas release property is good.
As described above, according to the present embodiment, the all-solid-state secondary battery is improved while improving the gas release property in the green sheet and suppressing the interfacial resistance of each layer during firing in the production of the all-solid-state secondary battery. It is possible to produce an all-solid secondary battery in which the production process is simplified.

  Below, according to the present embodiment, a laminate green sheet characterized in that a material that thermally decomposes and forms voids at the time of firing is added into the green sheet, and an all-solid secondary using the laminate green sheet. Specific examples and comparative examples relating to the batteries and their manufacturing methods will be described. In addition, this embodiment is not restrict | limited by the following Example.

Example 1
<Preparation of positive electrode slurry>
50 parts by mass of lithium cobaltate (LiCoO ₂ ) powder as the active material particles of the positive electrode, 50 parts by mass of LAGP (Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ ) powder as the solid electrolyte particles, and conductive assistant 6 parts by weight of acetylene black, 16 parts by weight of polyvinyl butyral (PVB) as a binder, 4.8 parts by weight of dibutyl phthalate (DBP) as a plasticizer, and acrylonitrile / vinylidene chloride / methyl methacrylate copolymer having a particle size of 10 μm as an additive material 5 parts by mass of a microcapsule having a shell as a product and a solvent (terpineol) were mixed to form a slurry, and this slurry was defoamed to prepare a positive electrode slurry.

<Preparation of solid electrolyte slurry>
100 parts by mass of LAGP powder as solid electrolyte particles, 16 parts by mass of PVB as binder, 4.8 parts by mass of DBP as plasticizer, and solvent (terpineol) were mixed to form a slurry, and this slurry was defoamed to prepare a solid electrolyte slurry. .
<Preparation of negative electrode slurry>
50 parts by mass of lithium titanate (L ₄ Ti ₅ O ₁₂ ) powder as negative electrode active material particles, 50 parts by mass of LAGP powder as solid electrolyte, 16 parts by mass of PVB as binder, 4.8 parts by mass of DBP as plasticizer, and solvent (terpineol) Were mixed to form a slurry, and the slurry was defoamed to prepare a negative electrode slurry.

<Laminated green sheet production process>
A 15 μm nickel foil was used as a current collector, and this was used as a negative electrode current collector. A negative electrode slurry was applied on the current collector and dried to prepare a negative electrode layer green sheet. On the negative electrode layer green sheet, The solid electrolyte slurry is applied and dried to produce a solid electrolyte layer green sheet. On the solid electrolyte layer green sheet, the positive electrode slurry is applied and dried to produce a positive electrode layer green sheet. A sheet was produced.

<Cutting process>
On the positive electrode layer green sheet of the produced laminate green sheet, the same nickel foil as described above was placed as another current collector, which was used as the positive electrode current collector, and this current collector was 80 ° C., 1000 kgf / cm ² (98 MPa). The positive electrode current collector and the negative electrode current collector were cut into individual elements so as to be exposed on different surfaces of the laminate green sheet.

<Baking process>
The laminate green sheet was heated in a nitrogen stream at a heating rate of 80 ° C./min. The temperature was raised from room temperature to 700 ° C. and held at that temperature for 30 minutes for firing. Then, it cooled to room temperature by standing to cool in a furnace, and produced the all-solid-state secondary battery which consists of a laminated fired body of Example 1.
(Example 2)
The same operation as in Example 1 was performed except that 10 parts by mass of the microcapsule of Example 1 was not added to the positive electrode and 10 parts by mass of LAGP was added to 100 parts by mass of the solid electrolyte layer.

(Example 3)
The same operation as in Example 1 was performed except that 10 parts by mass of the microcapsule of Example 1 was not added to the positive electrode and 10 parts by mass of 100 parts by mass of lithium titanate was added to the negative electrode layer.
Example 4
In addition to Example 1, it carried out by the same operation as Example 1 except having added 10 mass parts of microcapsules to 100 mass parts of LAGP in the solid electrolyte layer.

(Example 5)
In addition to Example 1, it carried out by the same operation as Example 1 except having added 10 mass parts of microcapsules with respect to 100 mass parts of lithium titanates to the negative electrode layer.
(Example 6)
In addition to Example 1, 10 parts by mass of microcapsules were added to 100 parts by mass of LAGP in the solid electrolyte layer, and 10 parts by mass of microcapsules were added to 100 parts by mass of lithium titanate in the negative electrode layer. The same operation as in Example 1 was performed.

(Example 7)
<Laminated green sheet production process>
In Example 7, the production of the laminate green sheet was performed in the same manner as in Example 6.
<Continuous laminate green sheet production process>
The produced laminate green sheet was cut into a predetermined size. Five laminate green sheets were produced. The five laminated green sheets were continuously laminated to produce a continuous laminated green sheet. Finally, the same nickel foil as that of the laminate green sheet as another current collector is placed on the negative electrode layer green sheet that is not in contact with the current collector in the lamination direction, and the whole is placed at 80 ° C. and 1000 kgf / cm ² (98 MPa). ) To produce a continuous laminate green sheet before the firing step of Example 7.

<Continuous laminated fired body manufacturing process>
The continuous laminate green sheet was heated at a rate of temperature increase of 80 ° C./min. The temperature was raised from room temperature to 700 ° C. and held at that temperature for 30 minutes, and then cooled to room temperature by allowing it to cool in the furnace to produce a serial all-solid secondary battery comprising the continuously laminated fired body of Example 4.
(Comparative Example 1)
The microcapsules in Example 1 were not used in Comparative Example 1. Other than that, the all-solid-state secondary battery of Comparative Example 1 was produced in the same manner as in Example 1.

(Comparative Example 2)
The all-solid-state secondary battery of Comparative Example 2 was produced in the same manner as in Example 1, except that the amount of microcapsules added in Example 1 was 25 parts by mass with respect to 100 parts by mass of the positive electrode active material.
(Comparative Example 3)
The all-solid-state secondary battery of Comparative Example 3 was produced in the same manner as in Example 1 except that the amount of microcapsules added in Example 1 was 0.5 parts by mass with respect to 100 parts by mass of the positive electrode active material. .

(Comparative Example 4)
An all-solid secondary battery of Comparative Example 4 was produced in the same manner as in Example 1 except that the particle size of the microcapsules in Example 1 was 40 μm.
(Comparative Example 5)
An all-solid-state secondary battery of Comparative Example 5 was produced in the same manner as in Example 1 except that the particle size of the microcapsules in Example 1 was 3 μm.

(Comparative Example 6)
The microcapsules in Example 7 were not used in Comparative Example 6. Otherwise, the all-solid-state secondary battery of Comparative Example 6 was produced in the same manner as in Example 7.
<Electrochemical evaluation>
The electrochemical evaluation was performed by the following method.

(Examples 1, 2, 3, 4, 5, 6 Battery evaluation method of Comparative Examples 1, 2, 3, 4, 5)
Ten all-solid secondary batteries were evaluated. The battery is charged to 2.7 V by a constant current method of 0.2 C, and then discharged to 1.5 V at 0.2 C. This discharge capacity is defined as a reference capacity X. The reference capacity X is an average value of 10 pieces. Thereafter, the battery is charged to 2.7 V at 0.2 C, discharged to 1.5 V at 5 C, and the 3 C discharge capacity Y is obtained. The 3C discharge capacity Y is also an average value of 10 pieces. A discharge capacity maintenance ratio represented by a ratio (Y / X (%)) of the discharge capacity between the 3C discharge capacity Y and the reference capacity X is obtained, and this is used as an evaluation standard for electrochemical evaluation, and is evaluated according to the following standard. The higher the evaluation, the better the output characteristics as a battery, that is, the smaller the internal resistance.
A: 70% or more B: 50% or more and less than 70% C: 40% or more and less than 50% D: 30% or more and less than 40% E: Less than 30%

(Battery evaluation method of Example 7 and Comparative Example 6)
Ten series all solid state secondary batteries were evaluated. The battery is charged to 13.5 V by a constant current method of 0.2 C, and then discharged to 7.5 V at 0.2 C. This discharge capacity is set as a reference capacity X. The reference capacity X is an average value of 10 pieces. Thereafter, the battery is charged to 13.5 V at 0.2 C, discharged to 7.5 V at 5 C, and the 3 C discharge capacity Y is obtained. The 3C discharge capacity Y is also an average value of 10 pieces. A discharge capacity maintenance ratio represented by a ratio (Y / X (%)) of the discharge capacity between the 3C discharge capacity Y and the reference capacity X is obtained, and this is used as an evaluation standard for electrochemical evaluation, and is evaluated according to the following standard. The higher the evaluation, the better the output characteristics as a battery, that is, the smaller the internal resistance.
A: 70% or more B: 50% or more and less than 70% C: 40% or more and less than 50% D: 30% or more and less than 40% E: Less than 30%

(Evaluation results)
The results of the evaluation are shown in Table 1 below.

From Table 1, it can be seen that the example in which the microcapsules having a particle size of 30 μm or less and an addition amount of 20 parts by mass or less with respect to 100 parts by mass of the active material or the solid electrolyte have higher evaluation than the comparative example. It was found that the interfacial resistance between the particles was reduced due to the composite of the particles.
Moreover, when Example 1 and Comparative Examples 2 and 3 are compared, Example 1 has a higher evaluation. If the added amount of microcapsules is too large, the electrode performance is damaged when the microcapsules are decomposed, so that the battery performance deteriorates. If the added amount of microcapsules is too small, the effect of adding the microcapsules is lost. That is, it can be said that there is a suitable range for the addition amount of the microcapsules, and it was confirmed that the effect of this embodiment can be obtained.

Moreover, when Example 1 is compared with Comparative Examples 4 and 5, Example 1 has a higher evaluation. If the particle size of the microcapsule is too large, the battery performance is deteriorated because the electrode is damaged when the microcapsule is decomposed. If the amount of the microcapsule added is too small, the effect of adding the microcapsule is lost. That is, it can be said that there is a range suitable for the particle size of the microcapsules, and it was confirmed that the effect of this embodiment can be obtained.
Further, when Example 7 and Comparative Example 6 are compared, the result is the same as described above, and the effect of this embodiment can be obtained even in a series all-solid secondary battery in which single-layer all-solid secondary batteries are stacked. Was confirmed.

  The present invention greatly contributes to the improvement of the performance of the all solid state secondary battery, and can simplify the manufacturing process of the all solid state secondary battery. Moreover, the all-solid-state secondary battery of the present invention is an all-solid-state secondary battery in which the interface resistance of each layer is suppressed, and it is an invention that can be used greatly industrially, having both cost reduction and battery performance.

DESCRIPTION OF SYMBOLS 1 ... Positive electrode active material particle 2 ... Solid electrolyte particle 3 ... Conductive auxiliary agent (carbon material)
DESCRIPTION OF SYMBOLS 4 ... Void formation material 5 ... Negative electrode active material particle 11 ... Positive electrode layer green sheet 12 ... Solid electrolyte layer green sheet 13 ... Negative electrode layer green sheet 14 ... Current collector 15 ... Continuous laminated body green sheet

Claims (10)

A green sheet for an all-solid secondary battery comprising an active material or a solid electrolyte and a binder,
A void forming material, which is a material that is thermally decomposed by heat during firing to form voids, is added,
The void forming material is added in an amount of 1 to 20 parts by mass with respect to 100 parts by mass of the active material or solid electrolyte.
The green sheet, wherein the void forming material is added in the form of granules, and the grain size of the granules is in the range of 5 μm to 30 μm. A first current collector, a first electrode layer green sheet provided on the first current collector and including a first active material, and a solid electrolyte layer including a solid electrolyte provided on the first electrode layer green sheet In a laminate green sheet comprising: a green sheet; and a second electrode layer green sheet provided on the solid electrolyte layer green sheet and containing a second active material,
At least one green sheet among the plurality of green sheets is a green sheet to which the void forming material according to claim 1 is added. Including a binder in the green sheet to which the void forming material is added,
The laminate green sheet according to claim 2, wherein a thermal decomposition temperature of the void forming material is lower than a thermal decomposition temperature of the binder. It is constituted by laminating a plurality of laminate green sheets according to claim 2 or claim 3,
The laminated body is laminated such that the first current collector of another laminated green sheet is laminated on the second electrode layer green sheet of one laminated green sheet. Green sheet.   A laminate fired body obtained by firing a laminate comprising the laminate green sheet according to claim 2 or 3 and a second current collector provided on the second electrode layer green sheet. All solid state secondary battery. The continuous laminate green sheet according to claim 4,
A second current collector provided on a second electrode layer green sheet on which the first current collector is not laminated among the second electrode layer green sheets constituting the laminate green sheet;
A method for producing an all-solid-state secondary battery, comprising firing a laminate comprising: A first electrode slurry layer forming step of applying or printing the first electrode slurry on the first current collector to form a first electrode slurry layer; and
A solid electrolyte slurry layer forming step of forming or solid electrolyte slurry layer by applying or printing a solid electrolyte slurry containing a solid electrolyte material on the first electrode slurry layer;
On the solid electrolyte slurry layer, a second electrode slurry layer is formed by applying or printing a second electrode slurry to form a second electrode slurry layer;
Including
Production of a laminate green sheet, wherein a void forming material, which is a material that is thermally decomposed by heat during firing to form voids, is added to at least one of the plurality of slurries. Method.   A laminate green sheet produced using the method for producing a laminate green sheet according to claim 7, wherein the other laminate green sheet is placed on the second electrode slurry layer of one laminate green sheet. A method for producing a continuous laminate green sheet, comprising a step of laminating two or more green sheets so that the first current collector is laminated. A second current collector in which a second current collector is bonded onto the second electrode layer green sheet exposed on the surface of the laminate green sheet produced using the method for producing a laminate green sheet according to claim 7. Bonding process;
A firing step of firing the laminate including the laminate green sheet and the second current collector bonded thereto;
The manufacturing method of the all-solid-state secondary battery characterized by including. A second current collector, wherein a second current collector is bonded onto the second electrode layer green sheet exposed on the surface of the multilayer green sheet produced using the method for producing a continuous laminate green sheet according to claim 8. Electric body laminating process,
A firing step of firing a continuous laminate including the laminate green sheet and the second current collector bonded thereto;
The manufacturing method of the all-solid-state secondary battery characterized by including.

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