JP7068845B2 - Manufacturing method of all-solid-state battery - Google Patents

Description

The present invention relates to a method for manufacturing an all-solid-state battery.

Lithium secondary batteries are known to have a high energy density among various secondary batteries. However, since the commonly used lithium secondary battery uses a flammable organic electrolyte as the electrolyte, the lithium secondary battery has more safety measures against liquid leakage, short circuit, overcharge, etc. than other batteries. It is strictly required. Therefore, in recent years, research and development on an all-solid-state battery using an oxide-based or sulfide-based solid electrolyte as an electrolyte has been actively carried out. The solid electrolyte is a material composed mainly of an ionic conductor capable of ionic conduction in a solid, and various problems caused by a flammable organic electrolyte solution like a conventional lithium secondary battery occur in principle. do not.

An all-solid-state battery is an integral 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). It also 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 (hereinafter, also referred to as a green sheet method). The procedure for producing a laminated electrode body by the green sheet method is as follows: First, a slurry-like positive electrode layer material containing an amorphous solid electrolyte that becomes an ionic conductor when sintered and crystallized from a positive electrode active material having sinterability. A slurry-like negative electrode layer material containing a sintered negative electrode active material and an amorphous solid electrolyte, and a slurry-like electrolyte layer material containing a solid electrolyte are each formed into a sheet to prepare a green sheet. Next, a laminated body is produced by sandwiching the green sheet made of the electrolyte layer material between the green sheet made of the positive electrode layer material and the green sheet made of the negative electrode layer material. Then, by firing the laminated body, a laminated electrode body made of a sintered body can be obtained.

As a method for producing a green sheet for each layer, there is a well-known doctor blade method. In the doctor blade method, a slurry obtained by mixing a binder and a solvent (anhydrous alcohol, etc.) with ceramic powder such as an inorganic oxide before firing is formed into a thin plate by a coating process or a printing process to prepare a green sheet. do. Then, as the ceramic powder to be contained in the slurry, each powder of the positive electrode active material, the solid electrolyte, and the negative electrode active material is used.

The most characteristic material in an all-solid-state battery is a solid electrolyte, and as described in Non-Patent Document 1 below, a _NASICON type oxide represented by the general formula Li _a X _b Y _c P _d Oe. Etc. are used as solid electrolytes. As the positive electrode active material and the negative electrode active material (hereinafter, also collectively referred to as electrode active materials), materials used in conventional lithium secondary batteries can be used. In addition, since the all-solid-state battery does not use a flammable electrolytic solution, research is being conducted on an electrode active material that can obtain a higher potential difference.

The following Patent Document 1 describes a basic method for manufacturing an all-solid-state battery. Further, Non-Patent Document 1 describes an outline of an all-solid-state battery. The following Patent Document 2 describes a method for manufacturing a laminated composite electronic component in which two different types of laminated electronic components (such as a laminated inductor and a laminated capacitor) are integrated by using the green sheet method. Then, in the invention described in Patent Document 2, in order to suppress the warp due to the difference in the heat shrinkage rate when the green sheets of different laminated electronic components are laminated and sintered, each laminated electronic component is used. The type of binder included in the green sheet is changed.

Japanese Unexamined Patent Publication No. 2009-206094 Japanese Unexamined Patent Publication No. 2000-331881

Osaka Metropolitan University Inorganic Chemistry Research Group, "Forefront of All Solid-State Batteries", [online], [Searched on December 15, 2017], Internet <URL: http://www.chem.osakafu-u.ac. jp / ohka / ohka2 / research / battery_li.pdf ＞

An all-solid-state battery manufactured by firing a laminated body made of a green sheet is cracked into a laminated electrode body after firing by surely sintering each layer at the time of firing and adjusting the shrinkage rate between layers. It is necessary to prevent warping and the like. In the conventional method for manufacturing an all-solid-state battery, the green sheet of each layer before firing contains a filler to ensure that each layer is sintered and the shrinkage rate between layers is controlled. However, the filler is a substance that does not contribute to the electrochemical reaction related to ionic conduction and charge / discharge, and when the electrode layer material containing the filler is sintered, the desired battery performance such as deterioration of ionic conductivity and decrease in capacity can be obtained. It may not be possible. Further, if the filler reacts with the active material or is not uniformly dispersed, there is a concern that the battery performance may be further deteriorated.

As in the invention described in Patent Document 2, different binders may be added to the green sheet serving as the positive electrode layer and the negative electrode layer (hereinafter collectively referred to as the electrode layer) and the green sheet serving as the electrolyte layer. Conceivable. However, in the all-solid-state battery, the green sheet for the electrode layer contains an amorphous solid electrolyte, and the electrolyte layer contains a mixture of the amorphous solid electrolyte and the crystallized solid electrolyte. Then, the amorphous solid electrolyte melts at the time of firing, shrinks, and then crystallizes. Therefore, in an all-solid-state battery, it is difficult to match the shrinkage rate of each layer by changing the type of binder contained in the green sheet of each layer.

Therefore, an object of the present invention is to provide a method for manufacturing an all-solid-state battery having excellent sinterability by matching the heat shrinkage between the electrode layer and the electrolyte layer.

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 layered solid electrolyte is sandwiched between a layered positive electrode and a negative electrode in an integral sintered body. There,
A positive electrode for producing a positive electrode layer sheet by molding a slurry-like positive electrode layer material containing an electrode active material for a positive electrode, a solid electrolyte composed of an amorphous material, a first binder, and a second binder into a sheet shape. Layer sheet preparation step and
A slurry-like negative electrode layer material containing the electrode active material for the negative electrode, the solid electrolyte composed of amorphous material, the first binder, and the second binder is formed into a sheet to form a negative electrode layer sheet. Negative electrode layer sheet preparation step to be manufactured and
An electrolyte layer sheet preparation step for forming an electrolyte layer sheet by molding a slurry-like electrolyte layer material containing the solid electrolyte made of amorphous material, the crystallized solid electrolyte, and the first binder into a sheet shape. When,
The first degreasing step of heat-treating the laminate formed by laminating the positive electrode layer sheet, the electrolyte layer sheet, and the negative electrode layer sheet in this order to decompose the first binder.
A second degreasing step in which the laminate that has undergone the first degreasing step is heat-treated to thermally decompose the second binder,
The firing step for producing the laminated electrode body and
Including
The temperature at which the second binder thermally decomposes is higher than the temperature at which the first binder thermally decomposes.
In the second degreasing step , the solid electrolyte composed of amorphous material is transferred to glass.
This is a method for manufacturing an all-solid-state battery.

INDUSTRIAL APPLICABILITY According to the present invention, there is provided a method for manufacturing an all-solid-state battery having excellent sinterability by matching the heat shrinkage between the electrode layer and the electrolyte layer. Other effects will be clarified in the following description.

It is a figure which shows the manufacturing method of the all-solid-state battery which concerns on Example of this invention. It is a figure which shows the thermal weight (TG) characteristic of the binder used in the manufacturing method of the all-solid-state battery which concerns on the said Example, and the differential thermal (DTA) characteristic of a solid electrolyte (LAGP). It is a figure which shows the electron micrograph of the all-solid-state battery manufactured by the method of the said Example, and the all-solid-state battery manufactured by a conventional method. It is a figure for demonstrating the concept that the heat shrinkage ratio is adjusted between layers of a laminated electrode body by the manufacturing method of the all-solid-state battery of the said Example.

=== Example ===
In the method for manufacturing an all-solid-state battery according to an embodiment of the present invention, a laminate obtained by laminating each of the green sheets of the positive electrode layer, the negative electrode layer, and the electrolyte layer produced by the green sheet method is fired. A laminated electrode body made of a body is manufactured. Then, the heat shrinkage of each layer is matched by appropriately incorporating a material that decomposes or shrinks by the heat treatment executed until the laminated electrode body is obtained in the green sheet of each layer.

=== Sample ===
In each layer constituting the laminated electrode body, the substance decomposed by heat treatment is a plasticizer or a binder, and the heat-shrinkable substance is an amorphous solid electrolyte. In the method for manufacturing an all-solid-state battery according to an embodiment of the present invention, the same type of plasticizer and the same type of binder (hereinafter referred to as "binders") are used as materials for thermally decomposing or thermally shrinking the positive electrode layer, the negative electrode layer, and the electrolyte layer. , Also referred to as binder 1), and an amorphous solid electrolyte. Further, the positive electrode layer and the negative electrode layer (hereinafter, also collectively referred to as an electrode layer) contain a binder (hereinafter, also referred to as a binder 2) whose thermal decomposition temperature is higher than that of the binder 1. Then, by adjusting the shrinkage rate when the binder 2 is thermally decomposed in the electrode layer and the shrinkage rate when the amorphous solid electrolyte is melted in the electrolyte layer at the time of firing, the electrode layer and the electrolyte are adjusted. It is matched with the shrinkage rate of the layer.

In the following, the all-solid-state battery produced by the method according to the embodiment of the present invention is used as a sample (hereinafter referred to as the sample according to the example), and the resistance values at 1 kHz are compared with respect to the sample by AC impedance measurement. The consistency of the heat shrinkage between layers was evaluated. Further, as a sample according to the comparative example, an all-solid-state battery was produced in which the electrode layer did not contain the binder 2 and only the binder 1 was used as the binder, as in the conventional method for producing an all-solid-state battery.

<Solid electrolyte>
In the method for manufacturing an all-solid-state battery according to an embodiment of the present invention, a well-known LAGP is used as the solid electrolyte. As is well known, LAGP is a compound represented by the chemical formula Li _{1 + x} Al _x Ge _2-x (PO ₄ ) ₃ with 0 <x <1. In this embodiment, the green sheet of the electrode layer (hereinafter, also referred to as the electrode layer sheet) contains amorphous LAGP, and the green sheet of the electrolyte layer (hereinafter, also referred to as the electrolyte layer sheet) is used. Amorphous LAGP and crystallized LAGP are included.

LAGP can be produced, for example, by using the solid phase method. As a procedure for producing LAGP using the solid phase method, powders of Li ₂ CO ₃ , Al ₂ O ₃ , GeO ₂ , and NH ₄ H ₂ PO ₄ are used as raw materials, and these raw materials are mixed in a magnetic mortar or a ball mill. do. Next, the mixture was placed in an aluminal pot or the like and calcined at a temperature of 300 ° C. to 400 ° C. for 3 hours to 5 hours, and the calcined powder obtained was heat-treated at a temperature of 1200 ° C. to 1400 ° C. for 1h to 2h. And dissolve the calcined powder. Then, the dissolved sample is rapidly cooled and vitrified to obtain an amorphous LAGP powder. Amorphous LAGP can be produced in this way. Further, the amorphous LAGP powder was crushed using a ball mill or the like, and then the crushed amorphous LAGP powder was calcined by firing under the condition of, for example, 600 ° C. for 5 hours. LAGP powder can be obtained. Then, in this example, a sample is prepared using these amorphous or crystallized LAGPs.

<Sample preparation procedure>
FIG. 1 shows a sample preparation procedure. First, an electrode layer sheet constituting a sample and an electrolyte layer sheet are prepared (s1a, s2a, s1b, s2b, s1c, s2c). As for the electrode layer sheet, a slurry-like electrode material containing an electrode active material, an amorphous LAGP, a conductive auxiliary agent, a binder, and a plasticizer is formed into a sheet by the above-mentioned doctor blade method. Further, in the sample according to the example, as described above, the first and second binders having different thermal decomposition temperatures are used as the binder. In this example, an acrylic binder was used as the binder 1. As the binder 2, polyvinyl butyral having a molecular weight of 50,000 or more was used. Only binder 1 was used for the sample according to the comparative example.

The paste-like electrode layer material used as the material for the electrode layer sheet is a ceramic powder obtained by mixing amorphous LAGP powder and an electrode active material so as to have a mass ratio of, for example, 50:50. There is. Then, the binder 1 and the binder 2 are added to the ceramic powder, for example, 10 wt% to 15 wt%, respectively. For the sample according to the comparative example, the binder 1 is added, for example, 20 wt% to 30 wt%. Next, a mixture obtained by adding 30 wt% to 50 wt% of anhydrous alcohol such as ethanol as a solvent to the ceramic powder is mixed with a ball mill or the like for, for example, 20 hours. Thereby, a slurry-like electrode layer material is obtained. As the electrode active material, as long as it is a positive electrode, lithium vanadium phosphate (Li ₃ V ₂ (PO ₄ ) ₃ ) or the like can be used. If it is a negative electrode, titanium oxide (TiO ₂ ) or the like can be used. Further, a conductive auxiliary agent made of a carbon material or the like is added to the electrode layer as needed.

On the other hand, in the paste-like electrolyte layer material used as the material of the electrolyte layer sheet, amorphous LAGP powder and crystallized LAGP powder are mixed, for example, in a mass ratio of 50:50. The thing is made into ceramic powder. Then, a mixture obtained by adding, for example, 20 wt% to 30 wt% of binder 1 to the ceramic powder and 30 wt% to 50 wt% of anhydrous alcohol such as ethanol as a solvent to the ceramic powder is obtained. It is produced by mixing for 20 hours with a ball mill or the like.

The paste-like electrode layer material and electrolyte layer material produced as described above are defoamed in vacuum and then coated on a PET film by the doctor blade method, respectively, to form a positive electrode layer and a negative electrode layer, respectively. A sheet-shaped electrode layer material corresponding to the above and a sheet-shaped electrolyte layer material corresponding to the electrolyte layer are obtained. Further, in order to adjust the sheet of each layer to the desired thickness, a plurality of sheets of one sheet-like material obtained by one coating are laminated, and the laminated material is press-pressed. The electrode layer sheets of the positive electrode layer and the negative electrode layer, which are green sheets, and the electrolyte layer sheet are completed by cutting into the plane size of.

Next, the electrolyte layer sheet sandwiched between the electrode layer sheets of the positive electrode layer and the negative electrode layer is press-bonded to prepare a laminated body (s3). Then, a two-step degreasing step is performed on the laminated body. This two-step degreasing step includes a first degreasing step (s4) in which the binder 1 is thermally decomposed, and a second degreasing step (s5) in which the binder 2 is thermally decomposed and the amorphous LAGP is melted. I'm out. Then, as the binder 2, a binder that thermally decomposes at a temperature equivalent to the temperature at which the amorphous LAGP melts and shrinks is used.

FIG. 2 shows the thermogravimetric (TG) characteristics of the binder 1 and the binder 2 and the differential thermal (DTA) characteristics of LAGP. As shown in FIG. 2, the binder 1 decomposes at about 310 ° C. and the binder 2 decomposes at about 530 ° C. The glass transition point of LAGP is about 530 ° C, which is the same as the temperature at which the binder 2 is thermally decomposed. The sample according to the comparative example was also subjected to a two-step heat treatment in the same manner as the two-step degreasing step. The laminated body that has undergone the two-step degreasing step (heat treatment) (s5) is fired in a reducing atmosphere at a temperature higher than that of the second degreasing step to obtain a laminated electrode body (sample) that is a sintered body (s6). ). Here, firing was performed under the conditions of 600 ° C. for 5 hours. Then, a thin film made of a metal such as gold was formed on the surfaces of the uppermost layer and the lowermost layer of the laminated electrode body 10 by sputtering or vapor deposition to form a current collector 20, and the all-solid-state battery 1 was completed.

=== Characteristic evaluation ===
By the above-mentioned procedure, 7 samples each of the sample according to the example and the sample according to the comparative example were prepared. Then, the AC impedance was measured for all the individuals, and the frequency of 1 kHz was compared.

Table 1 below shows the measurement results of the impedance of each sample.

表１において、サンプル１～７が実施例に係るサンプルであり、サンプル８～１４が比較例に係るサンプルである。そして、比較例に係るサンプル８～１４のインピーダンスを見ると、サンプル８でインピーダンスが最小値７４．２Ωとなり、サンプル１０で最大値１２０．２Ωとなった。そして、最大値と最小値との差は４６．０Ωであり、ばらつきが大きかった。また、平均値は、８６．４Ωであった。

In Table 1, Samples 1 to 7 are samples according to Examples, and Samples 8 to 14 are samples according to Comparative Examples. Looking at the impedances of the samples 8 to 14 according to the comparative example, the impedance was the minimum value of 74.2 Ω in the sample 8 and the maximum value of 120.2 Ω in the sample 10. The difference between the maximum value and the minimum value was 46.0 Ω, and the variation was large. The average value was 86.4 Ω.

On the other hand, among the samples 1 to 7 according to the examples, the minimum value of the impedance was 73.4 Ω in the sample 2, and the maximum value was 77.2 Ω in the sample 4. The difference between the maximum value and the minimum value was 3.8Ω, and a uniform impedance characteristic was obtained. The average value was 75.3Ω, and it was confirmed that the resistance was low with respect to the sample according to the comparative example.

As described above, the reason why the impedance of the sample according to the comparative example varies with respect to the sample according to the example and the average value is also high is that in the sample according to the comparative example, between the electrode layer and the electrolyte layer. It can be considered that there was an inconsistency in the heat shrinkage rate in the above, and cracks and sintering defects occurred between the layers. Therefore, the state between the layers was observed with an electron microscope for each of the sample according to the example and the sample according to the comparative example. FIG. 3 shows electron micrographs of samples according to Examples and Comparative Examples. FIG. 3A shows a sample according to an example, which is an electron micrograph of sample 3 in Table 1. FIG. 3B shows a sample according to a comparative example, and is an electron micrograph of sample 10 in Table 1. As shown in FIG. 3A, in the sample (Sample 3) according to the example, it can be seen that there are no cracks or sintering defects between the layers and the layers are smoothly continuous. On the other hand, in the sample (sample 10) according to the comparative example shown in FIG. 3B, it can be confirmed that cracks are generated between the layers.

As described above, in the method for manufacturing an all-solid-state battery according to the embodiment of the present invention, the heat shrinkage rate between layers is adjusted by the binder and LAGP. FIG. 4 conceptualizes and shows a method for adjusting the heat shrinkage rate between layers. FIG. 4 shows the breakdown of the materials in each layer of the laminated body in each state of the green sheet, after the first degreasing step, and after firing. The amorphous LAGP is referred to as "electrolyte 1", and the crystallized LAGP is referred to as "electrolyte 2". The ratio of shrinkage due to melting of the electrolyte 1 differs between the electrolyte layer and the electrode layer, and in the conventional method for manufacturing an all-solid-state battery using one type of binder, the ratio is higher than that of the electrode layer. The electrolyte layer was larger. That is, the electrolyte layer shrank more. Therefore, in the method for manufacturing an all-solid-state battery of this embodiment, the shrinkage of the electrolyte 1 that is insufficient in the electrode layer is supplemented by the shrinkage of the second binder. As a result, it becomes possible to match the heat shrinkage ratio between the layers in the laminated electrode body, suppress the occurrence of cracks at the interface between the electrode layer and the electrolyte layer, and improve the sinterability. As a result, the impedance of the battery can be reduced. By reducing the impedance, it is possible to improve the charge / discharge characteristics of the all-solid-state battery.

=== Other Examples ===
The first binder and the second binder are not limited to the above-mentioned examples. The thermal decomposition temperature of the second binder may be higher than the thermal decomposition temperature of the first binder and may be about the same as the glass transition point of the solid electrolyte.

The blending ratio of the first and second binders is not limited to the above-mentioned examples. The blending ratio may be adjusted according to the shrinkage ratio of each binder or solid electrolyte. The heat shrinkage rate of the binder solid electrolyte is determined according to the type thereof, and the blending ratio may be adjusted according to the type of the binder or the solid electrolyte so that the heat shrinkage rate is the same.

As a matter of course, the solid electrolyte, the positive electrode active material, and the negative electrode active material used in the all-solid-state battery according to the present invention are not limited to those used in the above examples. The solid electrolyte may be any material having lithium ion conductivity, and examples thereof include various NASICON type oxides and sulfide-based inorganic solid electrolytes. As the electrode active material, the same material as that used for a conventional lithium secondary battery using a non-aqueous electrolytic solution can be used. For example, a positive electrode active material has a layered oxide such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ), lithium iron phosphate (LiFePO ₄ ) having an olivine structure, and a spinel structure. Examples thereof include lithium manganate (LiMn ₂ O ₄ , Li ₂ MnO ₃ , LiMO ₂ ) and the like. The negative electrode active material is not particularly limited as long as it is a substance classified for lithium ion batteries. Examples thereof include metal oxides such as carbon materials (natural graphite, artificial graphite, graphite carbon fiber, etc.) and lithium titanate (Li ₄ Ti ₅ O ₁₂ ). Further, on the surfaces of the positive electrode active material and the negative electrode active material, zirconia (ZrO ₂ ), alumina (Al ₂ O ₃ ), lithium titanate (Li ₄ Ti ₅ O ₁₂ ), lithium niobate (LiNbO ₃ ), carbon (C). Etc. may be coated. Of course, the solvent used when manufacturing the all-solid-state battery is not limited to the above-mentioned one.

s2a Positive electrode layer sheet manufacturing process, s2b Electrolyte layer sheet manufacturing process, s2c Negative electrode layer sheet manufacturing process, s4 1st degreasing step, s5 2nd degreasing step, s6 firing step

Claims (1)

It is a method for manufacturing an all-solid-state battery provided with a laminated electrode body in which a layered solid electrolyte is sandwiched between a layered positive electrode and a negative electrode in an integrally sintered body.
A positive electrode for producing a positive electrode layer sheet by molding a slurry-like positive electrode layer material containing an electrode active material for a positive electrode, a solid electrolyte composed of an amorphous material, a first binder, and a second binder into a sheet shape. Layer sheet preparation step and
A slurry-like negative electrode layer material containing the electrode active material for the negative electrode, the solid electrolyte composed of amorphous material, the first binder, and the second binder is formed into a sheet to form a negative electrode layer sheet. Negative electrode layer sheet preparation step to be manufactured and
An electrolyte layer sheet preparation step for forming an electrolyte layer sheet by molding a slurry-like electrolyte layer material containing the solid electrolyte made of amorphous material, the crystallized solid electrolyte, and the first binder into a sheet shape. When,
The first degreasing step of heat-treating the laminate formed by laminating the positive electrode layer sheet, the electrolyte layer sheet, and the negative electrode layer sheet in this order to decompose the first binder.
A second degreasing step in which the laminate that has undergone the first degreasing step is heat-treated to thermally decompose the second binder,
The firing step for producing the laminated electrode body and
Including
The temperature at which the second binder thermally decomposes is higher than the temperature at which the first binder thermally decomposes.
In the second degreasing step , the solid electrolyte composed of amorphous material is transferred to glass.
A method for manufacturing an all-solid-state battery.

Images