JP6953700B2 - Laminated green sheet, continuous laminated green sheet, all-solid-state secondary battery, and their manufacturing method - Google Patents

Description

The present invention is a technique relating to a laminated green sheet and an all-solid-state secondary battery using the laminated green sheet.

In recent years, power consumption has been increasing with the sophistication of small electronic devices such as 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, the demand for higher energy density for secondary batteries is accelerating.
Furthermore, the lithium-ion secondary battery currently used for the above-mentioned applications uses an organic electrolytic solution, and there is a possibility that the electrolytic solution may leak or ignite depending on the usage conditions. Therefore, improvement in safety is required. Has been done.

On the other hand, the all-solid-state secondary battery is excellent in safety because it does not use an organic electrolytic solution and is composed of only a solid material, so that there is no possibility of liquid leakage or ignition. Therefore, it is promising as a post-lithium ion secondary battery.
However, the only all-solid-state secondary battery currently in practical use is a thin-film all-solid-state secondary battery, which has a low energy density. Further, since the positive electrode layer, the solid electrolyte layer, and the negative electrode layer are manufactured by a vapor deposition method and a sputtering method, they need to be manufactured in 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 as follows: A positive electrode layer green sheet, a solid electrolyte layer green sheet, and a negative electrode layer green sheet are made of a thick film by a coating method and a printing method similar to those of a conventional lithium ion secondary battery, and each layer green sheet is attached. This is a method of forming a laminated green sheet together, firing the laminated green sheet all at once, and then sandwiching the laminated green sheet with a current collector.

Japanese Unexamined Patent Publication No. 2000-340255 International Publication No. 2011/111555

When a laminated fired body composed of 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 as in Patent Documents 1 and 2, the positive electrode current collector, the positive electrode layer, and the negative electrode current collector are sandwiched between the positive electrode current collector and the negative electrode current collector. There is a problem that the interface resistance between the electrode and the negative electrode layer is high and the battery performance is poor. Further, there is a problem that the production efficiency is poor because the firing is performed twice.
Further, when the green sheet is fired, gas is generated due to the decomposition of the binder. However, in Patent Documents 1 and 2, there is a problem that it takes a long time to fire because the pores in the green sheet are small and the gas escape is poor. ..

Here, when the gas release is poor, the interface between the electrode layer and the solid electrolyte layer is peeled off at the time of the gas release, so that the interface resistance becomes large and the battery performance is poor.
An object of the present invention is a green sheet or laminate that improves gas release during binder decomposition, contributes to improving the performance of an all-solid-state secondary battery, simplifies the manufacturing process, and suppresses interfacial resistance of each layer. It is an object of the present invention to provide a green sheet, a continuous laminated green sheet and a method for producing them, and a method for producing an all-solid-state secondary battery.

As a result of diligent 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 at the time of firing and forms voids is added. That is, it has been found that the material added at the time of firing forms voids by thermal decomposition, and the gas escape is improved at the time of decomposition of the binder, so that a good interface with low electrical resistance can be formed in each layer in a short time.

The green sheet according to one aspect of the present invention is a green sheet for an all-solid secondary battery containing an active material or a solid electrolyte and a binder, and is thermally decomposed by heat during firing to form voids. The void-forming material is added, and 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 the solid electrolyte, and the void-forming material is added in the form of particles. The particle size of the granules is in the range of 5 μm or more and 30 μm or less.

According to one aspect of the present invention, the gas release property in the green sheet at the time of firing is improved.
Therefore, it is possible to manufacture an all-solid-state secondary battery by simplifying the manufacturing process of the all-solid-state secondary battery while suppressing the interfacial resistance of each layer between the laminated green sheets.

It is a schematic diagram of the laminated 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 which concerns on embodiment based on this 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 the current collector on both sides 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 firing process which concerns on embodiment based on this invention.

Next, an embodiment of the present invention will be described with reference to the drawings.
The embodiments of the present invention are not limited to the embodiments described below, and changes in design and the like can be made based on the knowledge of those skilled in the art, and such changes have been made. The embodiments are also included in the scope of the embodiments of the present invention.
FIG. 1 shows an example of the laminated green sheet, which is a laminated green sheet in which the solid electrolyte layer green sheet 12 and the positive electrode layer green sheet 11 are laminated in this order on one surface of the negative electrode layer green sheet 13. Then, for example, when a 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 becomes. It becomes the second electrode layer green sheet.

The negative electrode layer green sheet 13 contains negative electrode active material particles 5, a conductive auxiliary agent, and a binder.
The solid electrolyte layer green sheet 12 contains the solid electrolyte particles 2 and the binder.
The positive electrode layer green sheet 11 contains positive electrode active material particles 1, a conductive auxiliary agent 3, and a binder.
In the example of FIG. 1, a particulate void-forming material, which is a material that thermally decomposes by heat during firing to form voids, is added to each green sheet. The void forming material 4 may be added only to a part 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.
The amount of the void forming material 4 added is preferably 1 to 20 parts by mass with respect to 100 parts by mass of the active material contained in the green sheet to which the void forming material is 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 preferably 1 to 20 parts by mass with respect to the mass part.

The void forming material is added in the form of granules, and the particle size of the granules is preferably in the range of 5 μm or more and 30 μm or less.
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 oxide (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.} Further, a metallic lithium foil may be used.

The solid electrolyte particles 2 are not particularly limited as long as they are materials having low electron conductivity and high lithium ion conductivity. As the solid electrolyte particles 2, for example, an amorphous body (glass body), a crystal body, or glass ceramics of an oxide-based solid electrolyte or a sulfide-based solid electrolyte can be used. In particular, an oxide-based solid electrolyte capable of high-temperature firing is preferable, and NASICON-type oxides, perovskite-type oxides, LISION-type oxides, garnet-type oxides, oxide glasses, and 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 may be any material having conductivity, and is not particularly limited. As the conductive auxiliary agent 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 additive 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 agent is more than a part by mass, the mass of the active material particles may be insufficient and the lithium occlusion capacity may decrease.

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 auxiliary agent 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 is a material having a thermal decomposition temperature lower than the thermal decomposition temperature of the binder. As the void forming material 4, for example, microcapsules, microbeads, sublimable substances and the like can be used.
As constituent materials of microcapsules and microbeads, polyurethanes, polyureas, polyamides, polyesters, polycarbonates, polyacrylates, polystyrenes, polymethylmethacrylates, vinylidene chloride, urea-formaldehyde resin, melamine resin and the like. Examples thereof include copolymers thereof, and the present invention is not particularly limited as long as the thermal decomposition temperature is lower than that of the binder.

Sublimative substances include naphthalene, 1,7,7-trimethylbicycloheptane-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 cartoate, 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. For example, 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, it is 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the active material particles. If the content of the void forming material 4 is more than 30 parts by mass, the mass of the active material particles may be insufficient and the lithium occlusion capacity may decrease. If the content of the void-forming material 4 is less than 0.5 parts by mass, the void-forming material 4 may be too small to sufficiently form voids through which gas can escape.

The particle size of the void forming material 4 is preferably 1 μm or more and 40 μm or less. More preferably, it is 5 μm or more and 30 μm or less. If the particle size 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 decrease. If the particle size of the void forming material 4 is less than 1 μm, the voids formed are too small, the gas release property is poor, and the effect of the void forming material 4 is almost lost.
FIG. 2 shows the state of the laminated green sheet of FIG. 1 after sintering. The void forming material 4 is thermally decomposed by sintering to form voids in the target green sheet after sintering.

(Laminated green sheet)
As shown in FIG. 3, the laminated 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 the current collector 14 constituting the first current collector. It is formed in the order of 11. The arrangement of the positive electrode layer green sheet 11 and the negative electrode layer green sheet 13 may be reversed. That is, the laminated 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 the second current collector may be provided on the positive electrode layer green sheet 11 located on the upper surface side of the stack.
The current collector 14 may be any material as long as it has conductivity, and is not particularly limited. As the current collector 14, for example, metal materials such as stainless steel, nickel, aluminum, iron, titanium, copper, palladium, gold and platinum can be used. It is preferable that the material of the current collector 14 is 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.

In the positive electrode layer green sheet 11 and the negative electrode layer green sheet 13, a binder containing active material particles, solid electrolyte particles 2, and a conductive additive 3 is mixed with a solvent to obtain a positive electrode slurry and a negative electrode slurry, and these positive electrode slurry and negative electrode are obtained. 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 the solid electrolyte particles 2 and the binder together with a solvent to form a solid electrolyte slurry, which is coated or printed on the positive electrode layer green sheet or the negative electrode layer green sheet, and then dried. Will be 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 may be used in combination in the same green sheet. Is 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 preferably 3 parts by mass or more and 40 parts by mass or less. If it is less than 3 parts by mass, sufficient binding cannot be achieved, and if it is larger than 40 parts by mass, the capacitance per electrode volume is greatly reduced. More preferably, it is 3 parts by mass or more and 25 parts by mass or less.

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, dioctylphthalate and dioctyl adipate. Organic solvents such as benzyl alcohol, N, N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), and water can be used. These solvents may be used alone or in combination of two or more. The boiling point of the solvent is preferably 200 ° C. or lower because the slurry can be easily dried.

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 during firing of the positive electrode layer green sheet 11, the solid electrolyte layer green sheet 12, and the negative electrode layer green sheet 13, and are fired. It may further contain a firing aid that lowers the 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 the softening point temperature is 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 of the firing aid and the firing temperature of each green sheet, cracks due to internal strain and internal stress of each layer are prevented and the formation of a matrix structure is promoted when the laminated fired body is formed by firing. can do.

As described above, the positive electrode slurry, the solid electrolyte slurry and the negative electrode slurry include the above-mentioned active material particles, solid electrolyte particles 2, conductive auxiliary agent 3, void forming material 4 which is thermally decomposed to form voids, binder, and a solvent. , It can be produced by mixing a firing aid or the like as needed. Further, the method of mixing the slurry is not particularly limited, and materials such as a thickener, a plasticizer, a defoaming agent, a leveling agent, and an adhesion imparting agent may be added as needed.

Specific examples of the coating and printing methods for the positive electrode slurry, the solid electrolyte slurry and the negative electrode slurry include the doctor blade method, the calendar method, the spin coating method, the dip coating method, the inkjet method, the offset method, the die coating method, the spray method, and the screen. A printing method or the like can be used.
The method for drying the positive electrode slurry, the solid electrolyte slurry and the negative electrode slurry is not particularly limited. For example, heat drying, vacuum drying, heat vacuum drying and the like can be used. The dry atmosphere is not particularly limited. For example, it can be performed in an atmospheric 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 the desired battery capacity.
Solid Electrolyte Layer The thickness of the solid electrolyte layer formed by the green sheet 12 is preferably in the range of 1 μm or more and 500 μm or less. If it is thinner than 1 μm, the positive electrode layer and the negative electrode layer are short-circuited, which may not only reduce the performance of the all-solid-state secondary battery but also reduce the safety. If it is thicker than 500 μm, the movement of conducting ions such as lithium ions in the solid electrolyte layer is hindered, and the output of the all-solid secondary battery may decrease.

In the laminated fired body according to the present embodiment, in the firing step, voids are formed from the laminated green sheet according to the present embodiment with the void forming material 4, the binder is degreased, and then the particles are sintered with each other. It is formed.
The heating temperature in the firing step is a temperature equal to or higher than the thermal decomposition temperature of the binder contained in the laminated 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, and more preferably 300 ° C. or higher and 900 ° C. or lower. If the temperature is lower than 300 ° C., the binder will not burn completely and will become a residue, which may become a resistor in the layer. If the temperature is higher than 1100 ° C., the active material particles and the solid electrolyte particles may be melted and denatured, which may deteriorate the battery performance.

The atmosphere in the firing process is not particularly limited. For example, it can be carried out in an atmospheric atmosphere or a nitrogen atmosphere, but when there is 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 is carried out in an inert atmosphere. It is desirable to do it. The firing time is not particularly limited as long as the binder to be used is sufficiently decomposed.
As shown in FIG. 5, the continuous laminated green sheet 15 according to the present embodiment is a continuous laminate of a plurality of laminated green sheets shown in FIG. At this time, the first current collector of the upper laminated green sheet is laminated on the second electrode layer green sheet of the lower laminated green sheet, and the current collectors are sequentially laminated. In this way, the current collector of one laminated green sheet and the positive electrode layer green sheet or the negative electrode layer green sheet of the other laminated green sheet are laminated so as to be adjacent to each other and are sequentially laminated. The method of laminating the laminated green sheet is not particularly limited. For example, a flat plate press, a roll press, a hot press, a cold hydrostatic press, a hot hydrostatic press and the like can be used.

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

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 laminated green sheet or the continuous laminated green sheet 15. The bodies 14 can be bonded together to form a laminated body shown in FIGS. 4 and 6, and then collectively fired to form the body 14. As the firing conditions, the same conditions as the firing conditions in the formation of the laminated fired body can be used.

As described above, in the present embodiment, the void forming material 4 in which voids are formed by thermal decomposition is added to the green sheet-making slurry, and the slurry is used by a coating method on the first current collector. A laminated green sheet was prepared by laminating a first electrode layer green sheet and 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 in this order.

Then, the second current collector was laminated on the second electrode layer green sheet of the laminated green sheet and fired all at once to prepare an all-solid-state secondary battery.
During firing, voids were formed, gas release was improved, and the interfacial resistance of each layer could be reduced.
Further, the laminated green sheets are continuously laminated, and a current collector is provided between the plurality of laminated green sheets and further outside the outer surface of the laminated green sheets in the stacking direction. 14 were laminated to prepare a continuous laminated green sheet 15, and the continuous laminated green sheet 15 was collectively fired to prepare an in-series all-solid-state secondary battery.

In addition, by firing all at once, 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. Bonds are formed.
As a result, the proportion 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.

The step of producing the laminated green sheet according to the present embodiment is different from the conventional transfer method, and it is possible to continuously produce the laminated green sheet, and by further firing all at once, the interfacial resistance between the layers It has become possible to perform the firing process once while suppressing the above.
Further, the continuous laminated green sheet can be produced by continuously laminating the laminated green sheet, and the series all-solid-state secondary battery can be produced by firing the continuous laminated green sheet all at once. Is now 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 in firing, voids in which the gas diffuses 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 improves the gas release property in the green sheet during firing during the production of the all-solid-state secondary battery, suppresses the interfacial resistance of each layer, and suppresses the interfacial resistance of each layer. It is possible to manufacture an all-solid-state secondary battery that simplifies the manufacturing process of.

The following is a laminated green sheet according to the present embodiment, which is characterized in that a material that is thermally decomposed at the time of firing to form voids is added to the green sheet, and an all-solid secondary using the laminated green sheet. Specific examples and comparative examples of the batteries and their manufacturing methods will be described. The present embodiment is not limited to the following examples.

(Example 1)
<Preparation of positive electrode slurry>
_{50 parts by mass of lithium cobaltate (LiCoO 2} ) powder as 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 solid electrolyte particles, conductive aid 6 parts by mass of acetylene black, 16 parts by mass of polyvinyl butyral (PVB) as a binder, 4.8 parts by mass 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 microcapsules having a material as a shell and a solvent (tarpineol) 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 a binder, 4.8 parts by mass of DBP as a plasticizer, and a solvent (tarpineol) 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 (tarpineol) Was mixed to form a slurry, and this slurry was defoamed to prepare a negative electrode slurry.

<Laminated green sheet manufacturing process>
A 15 μm nickel foil was used as the current collector, which was used as the negative electrode current collector, and the negative electrode slurry was applied onto the current collector and dried to prepare a negative electrode layer green sheet. The solid electrolyte layer green sheet is prepared by applying and drying the solid electrolyte slurry, and the positive electrode slurry is applied and dried on the solid electrolyte layer green sheet to prepare a positive electrode layer green sheet. A sheet was prepared.

<Cutting process>
The same nickel foil as above was placed on the positive electrode layer green sheet of the produced laminated green sheet as another current collector, and this was used as the positive electrode current collector, and this current collector was used at 80 ° C. and 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 laminated green sheet.

<Baking process>
The laminated green sheet was heated at a heating rate of 80 ° C./min in a nitrogen stream. The temperature was raised from room temperature to 700 ° C., and the temperature was maintained for 30 minutes for firing. Then, it was cooled to room temperature by allowing it to cool in the furnace to prepare an all-solid-state secondary battery made of the laminated fired body of Example 1.
(Example 2)
The same operation as in Example 1 was carried out except that the microcapsules of Example 1 were not added to the positive electrode and 10 parts by mass was added to the solid electrolyte layer with respect to 100 parts by mass of LAGP.

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

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

(Example 7)
<Laminated green sheet manufacturing process>
In Example 7, the laminated green sheet was prepared by the same operation as in Example 6.
<Continuous laminated green sheet manufacturing process>
The prepared laminated green sheet was cut into a predetermined size. Five of these laminated green sheets were produced. These five laminated green sheets were continuously laminated to prepare a continuous laminated green sheet. Finally, the same nickel foil as the laminated green sheet is placed as another current collector on the negative electrode layer green sheet which is the outer surface in the stacking direction that is not in contact with the current collector, and the whole is 80 ° C., 1000 kgf / cm ² (98 MPa). ) Was applied to prepare a continuous laminated green sheet before the firing step of Example 7.

<Continuous laminated fired body manufacturing process>
The temperature rise rate of the continuous laminated green sheet was 80 ° C./min in a nitrogen stream. The temperature was raised from room temperature to 700 ° C., and the temperature was maintained for 30 minutes, and then cooled to room temperature by allowing to cool in a furnace to prepare an in-series all-solid-state secondary battery composed of the continuous 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 by the same operation as in Example 1.

(Comparative Example 2)
An all-solid-state secondary battery of Comparative Example 2 was produced by the same operation 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)
An all-solid-state secondary battery of Comparative Example 3 was produced by the same operation 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-state secondary battery of Comparative Example 4 was produced by the same operation 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 by the same operation 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. Other than that, the all-solid-state secondary battery of Comparative Example 6 was produced by the same operation as in Example 7.
<Electrochemical evaluation>
The electrochemical evaluation was carried out by the following method.

(Battery evaluation method of Examples 1, 2, 3, 4, 5, 6 Comparative Examples 1, 2, 3, 4, 5)
Ten all-solid-state secondary batteries were evaluated. It is charged to 2.7 V by the constant current method of 0.2 C, and then discharged to 1.5 V at 0.2 C, and this discharge capacity is defined as the reference capacity X. The reference capacity X is an average value of 10 pieces. After that, 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. The discharge capacity retention rate represented by the ratio (Y / X (%)) of the discharge capacity of 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 criteria. The higher the evaluation, the better the output characteristics of the 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. It is charged to 13.5V by the constant current method of 0.2C, and then discharged to 7.5V at 0.2C, and this discharge capacity is defined as the reference capacity X. The reference capacity X is an average value of 10 pieces. After that, 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. The discharge capacity retention rate represented by the ratio (Y / X (%)) of the discharge capacity of 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 criteria. The higher the evaluation, the better the output characteristics of the 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 above evaluation are shown in Table 1 below.

From Table 1, it can be seen that the examples in which the microcapsules having a particle size of 30 μm or less and the addition amount of 20 parts by mass or less with respect to 100 parts by mass of the active material or the solid electrolyte were added were highly evaluated as compared with the comparative examples. It was found that the interfacial resistance between the particles was reduced due to the composite of the particles.
Further, when Example 1 and Comparative Examples 2 and 3 are compared, Example 1 has a higher evaluation. If the amount of microcapsules added is too large, the electrodes will be damaged when the microcapsules are disassembled, resulting in poor battery performance. If the amount of microcapsules added is too small, the effect of adding microcapsules will be lost. That is, it can be said that the amount of microcapsules added has a suitable range, and it has been confirmed that the effects of this embodiment can be obtained.

Further, when Example 1 and Comparative Examples 4 and 5 are compared, Example 1 has a higher evaluation. If the particle size of the microcapsules is too large, the electrodes will be damaged when the microcapsules are disassembled, resulting in poor battery performance. If the amount of the microcapsules added is too small, the effect of adding the microcapsules will be 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 same result as described above is obtained, and the effect of the present embodiment can be obtained even in the series all-solid-state secondary battery in which a single-layer all-solid-state secondary battery is laminated. 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. Further, the all-solid-state secondary battery of the present invention is an all-solid-state secondary battery in which the interfacial resistance of each layer is suppressed, has both cost reduction and battery performance, and is an invention that can be widely used industrially.

1 ... Positive electrode active material particles 2 ... Solid electrolyte particles 3 ... Conductive aid (carbon material)
4 ... Void forming material 5 ... Negative electrode active material particles 11 ... Positive electrode layer green sheet 12 ... Solid electrolyte layer green sheet 13 ... Negative electrode layer green sheet 14 ... Current collector 15 ... Continuous laminate green sheet

Claims (9)

A first current collector, a first electrode layer green sheet provided on the first current collector and containing a first active material, and a solid electrolyte layer provided on the first electrode layer green sheet and containing a solid electrolyte. In the laminated green sheet including the green sheet and the second electrode layer green sheet provided on the solid electrolyte layer green sheet and containing the second active material.
At least one of the plurality of green sheets is a green sheet for an all-solid secondary battery containing an active material or a solid electrolyte and a binder.
A void forming material, which is a material that thermally decomposes 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 the solid electrolyte.
The void-forming material is added in the form of granules, and the particle size of the granules is in the range of 5 μm or more and 30 μm or less.
The void forming material is polyurethanes, polyureas, polyamides, polyesters, polycarbonates, polyacrylates, polystyrenes, polymethylmethacrylates, vinylidene chloride, urea-formaldehyde resin, melamine resin and copolymers thereof. Or, naphthalene, 1,7,7-trimethylbicycloheptane-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, gallic acid It is composed of at least one of methyl, 1,7-dihydronaphthalene, 4,4'-dihydroxybenzophenone, and 2,2', 4,4'-tetrahydroxybenzophenone.
A binder is contained in the green sheet to which the void forming material is added, and the binder is contained therein.
A laminated green sheet characterized in that the thermal decomposition temperature of the void forming material is lower than the thermal decomposition temperature of the binder. A first current collector, a first electrode layer green sheet provided on the first current collector and containing a first active material, and a solid electrolyte layer provided on the first electrode layer green sheet and containing a solid electrolyte. In the laminated green sheet including the green sheet and the second electrode layer green sheet provided on the solid electrolyte layer green sheet and containing the second active material.
At least one of the plurality of green sheets is a green sheet to which a void forming material, which is a material for forming voids by thermal decomposition by heat during firing, and a binder are 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 the solid electrolyte.
The void-forming material is added in the form of granules, and the particle size of the granules is in the range of 5 μm or more and 30 μm or less.
A laminated green sheet characterized in that the thermal decomposition temperature of the void forming material is lower than the thermal decomposition temperature of the binder. It is configured by laminating a plurality of laminated green sheets according to claim 1 or 2.
The lamination is a continuous laminate characterized in that the first current collector of another laminate green sheet is laminated on the second electrode layer green sheet of one laminate green sheet. Green sheet. It is characterized by having a laminated fired body obtained by firing a laminated body composed of the laminated green sheet according to claim 1 or 2 and a second current collector provided on the second electrode layer green sheet. All-solid-state secondary battery. The continuous laminated green sheet according to claim 3 and
Among the second electrode layer green sheets constituting the laminated body green sheet, the second current collector provided on the second electrode layer green sheet on which the first current collector is not laminated, and
A method for manufacturing an all-solid-state secondary battery, which comprises firing a laminate comprising. A first electrode slurry layer forming step of applying or printing a first electrode slurry containing a first active material on the first current collector to form a first electrode slurry layer.
A solid electrolyte slurry layer forming step of applying or printing a solid electrolyte slurry containing a solid electrolyte on the slurry layer for the first electrode to form a solid electrolyte slurry layer.
A second electrode slurry layer forming step of applying or printing a second electrode slurry containing a second active material on the solid electrolyte slurry layer to form a second electrode slurry layer.
Including
A void-forming material, which is a material that thermally decomposes by heat during firing to form voids, is added to at least one of the plurality of slurries.
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 the solid electrolyte.
A method for producing a laminated green sheet, wherein the void-forming material is added in the form of granules, and the particle size of the granules is in the range of 5 μm or more and 30 μm or less. The laminated green sheet produced by the method for producing a laminated green sheet according to claim 6 is placed on the slurry layer for the second electrode of one laminated green sheet, and the other laminated green sheet is described. A method for producing a continuous laminated green sheet, which comprises a green sheet laminating step of laminating two or more so that the first current collector is laminated. A second current collector in which a second current collector is bonded onto a second electrode layer green sheet exposed on the surface of the laminated green sheet manufactured by the method for manufacturing a laminated green sheet according to claim 6. The bonding process and
A firing step of firing the laminated body including the laminated body green sheet and the second current collector attached thereto, and a firing step.
A method for manufacturing an all-solid-state secondary battery, which comprises. The second collection in which the second current collector is bonded onto the second electrode layer green sheet exposed on the surface of the laminated green sheet manufactured by the method for manufacturing the continuous laminated green sheet according to claim 7. Electrode bonding process and
A firing step of firing a continuous laminate including the laminate green sheet and the second current collector attached thereto, and a firing step.
A method for manufacturing an all-solid-state secondary battery, which comprises.

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