JP6660766B2 - Manufacturing method of all solid state battery - Google Patents

Description

  The present invention relates to an all-solid-state battery manufacturing method and an all-solid-state battery manufactured by the manufacturing method.

  Lithium secondary batteries are known for their high energy density among various secondary batteries. However, lithium secondary batteries, which are widely used, use flammable organic electrolytes as electrolytes, so safety measures against liquid leakage, short-circuiting, overcharging, etc. are stricter in lithium secondary batteries than in other batteries. It has been demanded. Therefore, in recent years, all-solid-state batteries using an oxide or sulfide-based solid electrolyte as an electrolyte have been actively researched and developed. A solid electrolyte is a material composed mainly of an ion conductor that can conduct ions in a solid. Various problems caused by a flammable organic electrolyte like a conventional lithium secondary battery occur in principle. do not do.

  An all-solid-state battery is an integrated sintered body (hereinafter referred to as a laminated electrode body) in which a layered solid electrolyte (electrolyte layer) is sandwiched between a layered positive electrode (positive electrode layer) and a layered negative electrode (negative electrode layer). ) Has a structure in which a current collector is formed. As a method for manufacturing a laminated electrode body, there is a method using a well-known green sheet. Schematically, a slurry-like positive electrode layer material containing an amorphous solid electrolyte that becomes an ion conductor when sintered and crystallized with a positive electrode active material having sinterability, and a negative electrode active material having sinterability The slurry-like negative electrode layer material containing the solid electrolyte and the slurry-like solid electrolyte layer material containing the solid electrolyte are each formed into a sheet (green sheet), and the green sheet of the solid electrolyte layer material is formed into a positive electrode layer material and a negative electrode layer. It is produced by firing a laminate sandwiched between green sheets of material to form a sintered body. As a method for producing the green sheet of each layer, there is a well-known doctor blade method. In the doctor blade method, a binder (polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinylidene fluoride (PVDF), acrylic, ethyl methylcellulose, etc.) and a solvent (anhydrous alcohol, etc.) are added to ceramic powder such as inorganic oxide before firing. Is formed into a thin plate by a coating step or a printing step to produce a green sheet. Each powder of the positive electrode active material, the solid electrolyte, and the negative electrode active material is used as the ceramic powder contained in the slurry.

Total solids most characteristic material in the battery is a solid electrolyte, the following as described in Non-Patent Document 1, the general formula _{Li a X b Y c P d} O NASICON type oxide represented by _e Are used as solid electrolytes. As the positive electrode active material and the negative electrode active material (hereinafter, also collectively referred to as an electrode active material), materials used in conventional lithium secondary batteries can be used. Further, since an all-solid-state battery does not use a flammable electrolyte, an electrode active material capable of obtaining a higher potential difference has been studied.

  Patent Literature 1 below describes a basic method for manufacturing an all-solid-state battery, and Non-Patent Literature 1 describes an outline of an all-solid-state battery. Patent Document 2 describes a technique of coating particles of an electrode active material with a solid electrolyte in order to increase the ion conductivity of a positive electrode layer and a negative electrode layer (hereinafter, also collectively referred to as an electrode layer). Describes a method for manufacturing an all-solid-state battery by forming a thin-film electrode layer and an electrolyte layer on a substrate using a sputtering method, a PVD (physical vapor deposition) method, or a sol-gel method without using a green sheet. Have been.

JP 2009-206094 A JP 2010-80168 A JP 2011-108533 A

Osaka Prefectural University Inorganic Chemistry Research Group, "Overview of All-Solid-State Batteries", [online], [Search January 28, 2016], Internet <URL: http://www.chem.osakafu-u.ac.jp /ohka/ohka2/research/battery_li.pdf>

  As a method of manufacturing an all-solid-state battery, there are generally a method using a green sheet (hereinafter, also referred to as a green sheet method) and a method of depositing a thin film on a substrate as described in Patent Document 3. However, in the latter method, since an electrode active material or a solid electrolyte is deposited on a substrate by crystal growth or the like, the manufacturing process is complicated, the manufacturing apparatus becomes large, and the manufacturing cost increases. Therefore, at present, it can be said that it is more realistic to manufacture an all-solid-state battery using the green sheet method.

When manufacturing an all-solid-state battery, it is important to obtain ion conduction characteristics (for example, 1 × 10 ⁻⁶ S / cm) that can operate as a battery. It can be said that coating the solid surface of the particle of the electrode active material with the solid electrolyte as one of the inventions is one of effective means for improving the ionic conduction characteristics. However, in the invention described in Patent Document 2, an aqueous solution of Li-containing sulfate (Li ₂ SO ₄ ), which is a raw material of a solid electrolyte, is sprayed on the particle surface of the electrode active material using a tumbling fluidized bed. Therefore, a step of preparing an aqueous solution of Li ₂ SO ₄ and a complicated step of spraying the aqueous solution of Li ₂ SO ₄ using a tumbling fluidized bed are required, and the production cost increases. When preparing an aqueous solution of Li ₂ SO _4, it is recommended to work in an isolated environment such as a dry room or a dry area in consideration of safety. Costly.

  Therefore, the present invention provides an all-solid-state battery manufacturing method capable of forming an electrode layer having excellent ionic conductivity by a simpler process without the need for advanced safety management while using a green sheet method. It is intended to provide an all solid state battery.

The present invention for achieving the above object is a method for manufacturing an all-solid-state battery including a laminated electrode body in which a solid electrolyte layer is sandwiched between a positive electrode layer and a negative electrode layer in an integrated sintered body. hand,
Between a green sheet made of a slurry-like positive electrode material and a green sheet made of a slurry-like negative electrode material, a stacked body formed by sandwiching a green sheet made of a solid electrolyte material is fired to produce a stacked electrode body,
A mixing step of mixing the positive electrode material and the negative electrode material with an electrode active material powder and an amorphous solid electrolyte powder; and A heat treatment step of heating at a temperature at which the crystallinity is reached, a step of crushing the powder after the heat treatment, and a step of adding a binder and a solvent to the crushed powder to form the slurry. ,
In the heat treatment step, the solid electrolyte has a crystallinity of 40% or more and 50% or less,
This is a method for manufacturing an all-solid-state battery.

Good the solid body electrolyte in suitable are LAGP, in the heat treatment step, the total solids median diameter is heated the powder following the solid electrolyte 2.0μm or 0.5μm at a temperature of 500 ° C. or higher 525 ° C. or less A method for manufacturing a battery, or the solid electrolyte is LAGP, and in the heat treatment step, a method for manufacturing an all-solid battery in which a powder of the solid electrolyte having a median diameter of 0.2 μm is heated at a temperature of 500 ° C. preferable.
The method for manufacturing an all-solid battery according to any one of the above, wherein the solid electrolyte is LAGP, and in the mixing step, a median diameter of the solid electrolyte is equal to or less than a median diameter of the electrode active material. be a method for manufacturing a solid-state battery is also possible.

  According to the method for manufacturing an all-solid-state battery of the present invention, while using a green sheet method that can basically manufacture an all-solid-state battery at low cost, ionic conductivity can be improved by a simpler process that does not require advanced safety management. It is possible to form an excellent electrode layer. Therefore, a high-performance all-solid-state battery can be provided at lower cost. Other effects will be clarified in the following description.

It is a figure which shows the electron micrograph of the state after the heat treatment of the electrode layer which comprises an all solid state battery. It is a figure which shows the electron micrograph of the state of the said electrode layer sintered at the temperature of 650 degreeC after the said heat processing. It is a figure which shows the electron micrograph of the state of the said electrode layer sintered at the temperature of 590 degreeC after the said heat processing. It is a figure which shows the electron micrograph of the state of the said electrode layer sintered at the temperature of 660 degreeC after the said heat processing. It is a figure which shows the electron micrograph of the state of the said electrode layer sintered at the temperature of 650 degreeC without passing through the said heat processing.

=== Process to arrive at the present invention ===
In order to put the all-solid-state battery into practical use, it is preferable to adopt the manufacturing method using the green sheet method as described above in consideration of the basic manufacturing cost. However, in the green sheet method, when preparing a green sheet (hereinafter also referred to as an electrode layer sheet) to be an electrode layer, different materials of an electrode active material and a solid electrolyte are mixed together, and a powder made of the mixture is sintered. Therefore, it is necessary to uniformly disperse different kinds of materials to enhance sinterability.

  It is also necessary to improve the ionic conductivity of the electrode layer. For this purpose, it is effective to form a solid electrolyte film on the particle surface of the electrode active material as in the invention described in Patent Document 2 described above. It is. However, as described above, the conventional manufacturing method described in Patent Document 2 requires an all-solid-state battery because the manufacturing process is complicated and manufacturing facilities and facilities for ensuring safety are costly. Was difficult to provide at a lower cost.

  Therefore, the present inventor considered a basic mechanism for coating the surface of the electrode active material with the solid electrolyte in a simpler process. When the solid electrolyte is melted, the solid electrolyte is placed around the electrode active material during the melting process, and the solid electrolyte is crystallized by firing in that state, so that the surface of the electrode active material is coated with the solid electrolyte. I thought it might be.

Using the basic mechanism described above as a starting point, we examined the conditions for effectively coating the surface of the electrode active material with the solid electrolyte, and found that the solid electrolyte had already crystallized before firing, It has been found that practical ionic conductivity cannot be obtained after firing if the crystalline state is maintained. Furthermore, as a result of repeated studies based on this finding, a solid electrolyte that is already coated on the surface of the electrode active material in the ceramic powder to be included in the green sheet and contributes to the improvement of ion conductivity, If a solid electrolyte in an amorphous state contributing to the improvement of sinterability by being melted by subsequent sintering can be mixed, the solid electrolyte in an amorphous state is sintered and crystallized. At this time, it was thought that the solid conductivity of the solid electrolyte coated on the surface of the electrode active material could be improved to improve the ionic conductivity of the entire electrode layer. Then, a heat treatment is performed at a temperature lower than the firing temperature to adjust the solid electrolyte to an appropriate crystallinity, and a ceramic powder obtained by crushing a mixture of the electrode active material and the solid electrolyte having the adjusted crystallinity is obtained. I came up with the technical idea of sintering the body. The present invention has been made as a result of intensive studies based on such considerations and technical ideas.
=== Crystallinity of solid electrolyte ===
First, based on the above considerations and technical ideas, conditions for heat treatment for adjusting the crystallinity of the solid electrolyte were determined. Here, it is well known as a solid electrolyte for an all-solid battery. Using a compound (0 <x <1, hereinafter, LAGP) represented by the chemical formula Li _{1 + x} Al _x Ge _2-x (PO ₄ ) ₃ , the relationship between the median diameter of LAGP, heat treatment conditions, and crystallinity is examined. Was. As a procedure for producing LAGP, first, powders of Li ₂ CO ₃ , Al ₂ O ₃ , GeO ₂ , and NH ₄ H ₂ PO ₄ , which are raw materials for LAGP, are weighed so as to have a predetermined composition ratio, and are then weighed into a magnetic mortar or ball mill. Then, the mixture is put into an alumina crucible or the like, and calcined at a temperature of 300 ° C. to 400 ° C. for 3 hours to 5 hours. The calcined powder obtained by the calcining is heat-treated at a temperature of 1200 ° C. to 1400 ° C. for 1 hour to 2 hours to dissolve the calcined powder. Then, the melted sample is rapidly cooled and vitrified to obtain amorphous LAGP powder. Next, the amorphous LAGP powder is coarsely crushed so as to have a particle diameter of 200 μm or less, and the coarsely crushed solid electrolyte powder is crushed using a crushing device such as a ball mill. The LAGP powder is adjusted to have a target particle diameter (median diameter).

  Using amorphous LAGP powders having different median diameters as samples, heat treatment was performed on each sample at various temperatures. The crystallinity was measured by measuring differential heat during the heat treatment. Specifically, each sample was heated at a rate of 100 ° C./h until the temperature of the heat treatment was reached in the furnace of the differential heat measurement apparatus, and when the temperature reached the heat treatment temperature, the temperature was maintained for 10 hours (h). Then, the crystallinity was measured based on the differential thermal characteristics of LAGP during the heating period and the holding period at the heat treatment temperature. Here, the crystallinity of 53 types of samples having different combinations of the median diameter and the temperature of the heat treatment were examined.

  Table 1 below shows the crystallinity of each sample.

As shown in Table 1, it is understood that LAGP does not crystallize when the heat treatment temperature is 450 ° C. or 475 ° C. At 500 ° C. or higher, the higher the temperature is, the higher the crystallinity is if the median diameter is the same. At the same temperature, the smaller the median diameter, the higher the crystallinity. At a temperature of 500 ° C. to 525 ° C., there is a median diameter having a degree of crystallinity of 40% to 50% which is an intermediate state between a crystal and an amorphous state. The amorphous state became inferior.
=== Production of electrode layer material ===
Based on the above technical idea, in order to increase the ionic conductivity of the electrode layer, the solid electrolyte and the electrode active material are melted in the process of heat treatment to coat the surface of the electrode active material particles with the solid electrolyte, and the solid electrolyte is fired. It is required to reliably crystallize the electrolyte. Therefore, a sample was prepared by heat-treating a mixture of an electrode active material and an amorphous solid electrolyte, and sintering an electrode layer material using the mixture after the heat treatment. Here, anatase-type titanium oxide (TiO ₂ ) is used as an electrode active material, and an electrode layer material containing the electrode active material and LAGP having a crystallinity of about 40 to 50% as a solid electrolyte is changed in firing temperature. And sintered. Then, the ionic conductivity of the sintered body was examined.

As a specific sample preparation procedure, first, an amorphous LAGP is prepared as described above. Note that the median diameter of the amorphous solid electrolyte to be produced should be equal to or smaller than the median diameter of the electrode active material in consideration of sintering these mixtures reliably while coating the solid surface on the particle surface of the electrode active material. And Since the median diameter of TiO ₂ used here was 0.2 μm, the conditions for the crystallinity of LAGP to be in the range of 40 to 50% by heat treatment and the median diameter to be 0.2 μm or less were satisfied. This is the sample 16 shown in Table 1. LAGP of Sample 16 has a median diameter of 0.2 μm, and has a crystallinity of 48% by heat treatment at 500 ° C. for 10 hours. Therefore, first, an amorphous LAGP having a median diameter of 0.2 μm was produced. Next, powdery TiO ₂ having a median diameter of 0.2 μm and amorphous LAGP are weighed so as to have a mass ratio of 50:50, and the weighed TiO ₂ and amorphous LAGP are VGCF serving as a conductive additive. The mixture to which (gas-phase carbon nanofibers) was added was mixed in a mortar, and the mixture was press-formed at a pressure of 200 kgf / cm ^{2 into} pellets having a diameter of 20 mm, and the pellets were kept at a temperature of 500 ° C. for 10 hours. Then, a heat treatment was performed. FIG. 1 is an electron micrograph of a cross section of the pellet 1 after the heat treatment. Since the surface of the granular electrode active material is smooth, it can be confirmed that LAGP is coated on the surface of the electrode active material. . Furthermore, since a smooth structure is interposed between the granular electrode active materials, it can be confirmed that molten LAGP is interposed between the electrode active materials.

  When the pellets are heat-treated as described above, the pellets are crushed in a mortar, and the crushed material is formed into pellets of φ20 mm again. Then, the pellets were fired at various temperatures equal to or higher than the heat treatment temperature in a reducing atmosphere containing no oxygen to prevent the combustion of the carbon-based conductive additive to obtain a sintered body. Au was formed into a film with a thickness of 0.1 μm as an electrode, and this was used as a sample. The impedance was measured for each of the various samples prepared in this manner, and the ionic conductivity was determined.

  Table 2 below shows the ionic conductivity of each sample.

As shown in Table 2, in Samples 56 to 61 which were heat-treated and fired at 600 ° C. to 650 ° C., 1 × 10 ⁻⁶ (1 × 10 ⁻⁶⁾ which can generally operate without any problem in an all solid state battery (S / cm) or more. FIG. 2 shows a photograph of a cross section of the sample 61 taken with a microscope. No granular structure is observed in the cross section, and the LAGP structure 10 having a smooth outline can be confirmed. In addition, no granular structure can be confirmed in the LAGP structure 10, and it can be confirmed that LAGP is reliably interposed between the particulate electrode active materials and sinterability is ensured. On the other hand, in Samples 52 to 55 fired at 590 ° C. or lower, a decrease in ionic conductivity, which is considered to be due to insufficient sinterability and insufficient crystallization of LAGP, was confirmed. FIG. 3 is a micrograph showing a cross section of the sample 52, and a fine granular structure showing insufficient sinterability is confirmed. In Samples 62 to 64 fired at a temperature of 660 ° C. or higher, it can be considered that the firing temperature was too high and amorphous LAGP was foamed in the course of crystallization. FIG. 4 shows a micrograph of a cross section of Sample 62. As shown in FIG. 4, although an amorphous small structure 11 having a smooth contour which seems to be crystallized LAGP can be confirmed, the structure 11 has black fine-grained regions 12 which are considered to be voids generated by foaming. Are scattered.

Sample 65 shown in Table 2 was a sample fired at the same temperature of 650 ° C. as sample 61 having the highest ion conductivity, but fired without heat treatment, and had an ion conductivity of 1 × 10 ^{−. 6} (S / cm). It is considered that LAGP was not well coated on the surface of TiO ₂ because it did not undergo heat treatment. The LAGP also sinterability can not be firmly bonded to TiO ₂ together cover the surface of the TiO ₂ seems to have decreased. FIG. 4 shows an electron micrograph of the sample 64. As is clear from the comparison with FIG. 2, almost no tissue having a smooth contour can be confirmed.
=== Method of Manufacturing All-Solid-State Battery According to Example ===
The above-described sample is used to determine the heat treatment conditions for the solid electrolyte contained in the electrode layers constituting the stacked electrode assembly of the all-solid battery, and to determine the sintering conditions for the all-solid battery. In the process of preparing the sample, the mixture of the electrode layer materials and the crushed material after the heat treatment were formed into pellets by press molding, but this press molding step is not always necessary when manufacturing an all-solid-state battery. The method for manufacturing an all-solid-state battery according to an embodiment of the present invention includes a method in which a green sheet made of a solid electrolyte material is sandwiched between a green sheet made of a slurry-like positive electrode material and a green sheet made of a slurry-like negative electrode material. Based on the green sheet method of producing a laminated electrode body by firing the laminated body, the heat treatment is performed in the process of producing the green sheet, and the laminated body composed of the produced green sheet is formed based on the sintering conditions. It is characterized by being sintered.

Hereinafter, an example of a method for manufacturing the all-solid-state battery according to the present embodiment will be described. Here, a procedure for producing a green sheet corresponding to the electrode layer is mainly described. That is, as described above, a procedure for manufacturing green sheets corresponding to each of the positive electrode layer and the negative electrode layer using amorphous LAGP adjusted to have a particle diameter (median diameter) capable of obtaining a desired degree of crystallinity. explain. First, a mixture of the amorphous LAGP and the electrode active material is heat-treated to crystallize the LAGP to a desired degree of crystallinity. If the electrode active material is a positive electrode active material, for example, layered oxides such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ), lithium iron phosphate having an olivine structure (LiFePO ₄ ), spinel Lithium manganate having a structure (LiMn ₂ O ₄ , Li ₂ MnO ₃ , LiMO ₂ ) and the like. As the negative electrode active material, in addition to TiO ₂ used for the sample, for example, a metal material such as a carbon material (natural graphite, artificial graphite, graphite carbon fiber, etc.) and lithium titanate (Li ₄ Ti ₅ O ₁₂ ) may be used. No.

  When the mixture of the amorphous LAGP and the electrode active material is heat-treated, the mixture after the heat treatment is crushed, and the crushed material is used as a final ceramic powder, and a binder is added to the ceramic powder at a predetermined mass ratio. (For example, 20 wt% to 30 wt%), and an anhydrous alcohol such as ethanol as a solvent is added to the ceramic powder at a predetermined mass ratio (for example, 30 wt% to 50 wt%). Also, an appropriate amount of filler is added as needed. Then, a raw material for an electrode layer (hereinafter, referred to as an electrode layer material) containing the above-mentioned ceramic powder and various additives is mixed for a long time (for example, 20 hours) using a ball mill or the like to produce a paste-like electrode layer material. Further, after degassing the paste-like solid electrolyte layer material in a vacuum, the electrode layer material is applied on a PET film by a doctor blade method to obtain a sheet-like electrode layer material. In addition, in order to obtain a green sheet having a desired thickness, a predetermined number of sheet-like electrode layer materials obtained by one coating are laminated, and a laminate obtained by press-pressing the laminated material is subjected to a predetermined process. The green sheet of the electrode layer is completed by cutting into a plane size. For the green sheet of the solid electrolyte layer, a crushed amorphous LAGP may be used as the ceramic powder. Then, a thin-film electrode is formed on the laminated electrode body obtained by firing the laminate in which the green sheets of the solid electrolyte layer are sandwiched between the green sheets of the positive electrode layer and the negative electrode layer produced by the above procedure under the above firing conditions. When formed, an all-solid-state battery is completed.

As described above, the method for manufacturing an all-solid-state battery according to the present embodiment is based on the green sheet method, which is essentially advantageous in reducing the manufacturing cost. When coating the surface of the electrode active material with the solid electrolyte to improve the ionic conductivity of the electrode layer, it is not necessary to use a tumbling fluidized bed as in the related art, and the median diameter of the electrode active material and the solid electrolyte is reduced. It is only necessary to control the temperature of the heat treatment prior to sintering, and it becomes possible to manufacture an all-solid-state battery having excellent ion conduction characteristics at a lower cost.
=== Other Examples ===
In the method for manufacturing an all-solid-state battery according to the embodiment of the present invention, the amorphous solid electrolyte and the electrode active material used as the raw material of the electrode layer are not limited to those used in the above sample. Further, the solid electrolyte in the ceramic powder contained in the green sheet is adjusted to a crystallinity of 40% to 50%, which is an intermediate state between crystallization and amorphous state, by heat treatment. In order to obtain a practical ion conductivity, other parameters such as the types of the electrode active material and the amorphous solid electrolyte, the median diameter, and the temperature during heat treatment and firing are also included in order to obtain a practical ion conductivity. It is easily expected to consider. Preferably, the degree of crystallinity of 40% to 50%, which was empirically found in the process of conceiving the present invention, that is, in the intermediate state between the amorphous state and the crystalline state, in order to enhance sinterability by crystallization by firing. Although the crystallinity at which 50% or more of the amorphous state exists is adopted, the crystallinity is not necessarily limited to this crystallinity depending on other parameters. In any case, the embodiment of the present invention is to improve the ionic conductivity of the electrode layer constituting the all-solid-state battery, and to dissolve the powdered electrode active material and the amorphous solid electrolyte by heat treatment. The ceramic powder obtained by the crushing may be included in the grease sheet of the electrode layer, and the solid electrolyte in the ceramic powder may be adjusted to a predetermined crystallinity by heat treatment.

  1 pellet, 10 solid electrolyte in electrode layer, 11 void

Claims (4)

An integrated sintered body, a method for manufacturing an all-solid battery including a stacked electrode body in which a solid electrolyte layer is sandwiched between a positive electrode layer and a negative electrode layer,
Between a green sheet made of a slurry-like positive electrode material and a green sheet made of a slurry-like negative electrode material, a stacked body formed by sandwiching a green sheet made of a solid electrolyte material is fired to produce a stacked electrode body,
A mixing step of mixing the positive electrode material and the negative electrode material with an electrode active material powder and an amorphous solid electrolyte powder; and A heat treatment step of heating at a temperature at which the crystallinity is reached, a step of crushing the powder after the heat treatment, and a step of adding a binder and a solvent to the crushed powder to form the slurry. ,
In the heat treatment step, the solid electrolyte has a crystallinity of 40% or more and 50% or less,
A method for manufacturing an all-solid-state battery, comprising: The solid electrolyte according to claim 1 , wherein the solid electrolyte is LAGP, and in the heat treatment step, a powder of the solid electrolyte having a median diameter of 0.5 μm to 2.0 μm is heated at a temperature of 500 ° C. to 525 ° C. A method for manufacturing an all-solid-state battery. 2. The method according to claim 1 , wherein the solid electrolyte is LAGP, and in the heat treatment step, the solid electrolyte powder having a median diameter of 0.2 μm is heated at a temperature of 500 ° C. .   The method according to any one of claims 1 to 3, wherein in the mixing step, a median diameter of the solid electrolyte is equal to or less than a median diameter of the electrode active material.