JP5675694B2 - Method for manufacturing electrolyte layer / electrode laminate and method for manufacturing sulfide-based solid battery - Google Patents

Description

  The present invention relates to a method for producing an electrolyte layer / electrode laminate capable of selecting a wide range of materials in forming an electrolyte layer, and a method for producing a sulfide-based solid battery.

  The secondary battery can convert the decrease in chemical energy associated with the chemical reaction into electrical energy and perform discharge. In addition, the secondary battery converts electrical energy into chemical energy by flowing current in the opposite direction to that during discharge. The battery can be stored (charged). Among secondary batteries, lithium secondary batteries are widely used as power sources for notebook personal computers, mobile phones, and the like because of their high energy density.

In the lithium secondary battery, when graphite (expressed as C) is used as the negative electrode active material, the reaction of the following formula (I) proceeds in the negative electrode during discharge.
Li _x C → C + xLi ⁺ + xe ⁻ (I)
(In the above formula (I), 0 <x <1.)
Electrons generated by the reaction of formula (I) reach the positive electrode after working with an external load via an external circuit. Then, lithium ions (Li ⁺ ) generated by the reaction of the formula (I) move by electroosmosis from the negative electrode side to the positive electrode side in the electrolyte sandwiched between the negative electrode and the positive electrode.

When lithium cobaltate (Li _1-x CoO ₂ ) is used as the positive electrode active material, the reaction of the following formula (II) proceeds at the positive electrode during discharge.
Li _1-x CoO ₂ + xLi ⁺ + xe ⁻ → LiCoO ₂ (II)
(In the above formula (II), 0 <x <1.)
At the time of charging, reverse reactions of the above formulas (I) and (II) proceed in the negative electrode and the positive electrode, respectively, and in the negative electrode, graphite (Li _x C) containing lithium by graphite intercalation is Since lithium cobaltate (Li _1-x CoO ₂ ) is regenerated, re-discharge is possible.

Among lithium secondary batteries, a lithium secondary battery in which the electrolyte is a solid electrolyte and the battery is completely solid does not use a flammable organic solvent in the battery. It is considered to be excellent in productivity. A sulfide-based solid electrolyte is known as a solid electrolyte material used for such a solid electrolyte.
However, since the all-solid lithium secondary battery is substantially made of a solid material, it has poor flexibility and workability, and there is a problem that it is particularly difficult to make the electrolyte layer thin and large in area. For this reason, there is room for improvement in handling at the time of battery manufacture.

  Techniques for solving such problems specific to all-solid-state lithium secondary batteries have been developed so far. In Patent Document 1, a solid electrolyte layer is formed by mixing a sulfide-based solid electrolyte material and a binder polymer in a solvent comprising a compound that does not contain a polar group that reacts with sulfide in the molecular structure. Disclosed is a solid electrolyte layer manufacturing method comprising a solid electrolyte layer forming slurry preparation step for obtaining a slurry, and a solid electrolyte layer forming step for forming a solid electrolyte layer using the solid electrolyte layer formation slurry. Has been.

JP 2010-212058 A

In the production method disclosed in Patent Document 1, a solvent composed of a compound that does not contain a polar group that reacts with sulfide in the molecular structure is used in the preparation of a slurry. In paragraph [0034] of the specification of the document, halogen-based solvents such as a fluorine-based solvent and a chlorine-based solvent are listed as specific examples of the solvent. However, these solvents have a problem that they have a higher environmental load than other organic solvents.
The present invention has been accomplished in view of the above circumstances, and provides a method for manufacturing an electrolyte layer / electrode laminate and a method for manufacturing a sulfide-based solid battery in which a wide range of materials can be selected in forming an electrolyte layer. With the goal.

The method for producing an electrolyte layer / electrode laminate of the present invention is an electrolyte layer containing a sulfide-based solid electrolyte, and a method for producing an electrolyte layer / electrode laminate comprising an electrode, comprising the steps of preparing the electrode, , A step of mixing a sulfide-based solid electrolyte, a binder, and a fatty acid ester represented by the following formula (1) to prepare a sulfide-based solid electrolyte slurry, and at least one surface of the electrode And a step of coating the sulfide-based solid electrolyte slurry to form an electrolyte layer.
R ¹ —CO ₂ —R ² formula (1)
(In the above formula (1), R ¹ is a linear or branched aliphatic group having 3 to 10 carbon atoms , and R ² is a linear or branched aliphatic group having 3 to 10 carbon atoms. is there.)

  In the method for producing an electrolyte layer / electrode laminate according to the present invention, the binder may be a fluoropolymer.

  In the method for producing an electrolyte layer / electrode laminate of the present invention, when the total mass of the sulfide solid electrolyte and the binder is 100% by mass, the content ratio of the binder is 0.00. It is preferable that it is 1-10 mass%.

In the method for producing an electrolyte layer / electrode laminate according to the present invention, the ionic conductivity of the electrolyte layer is preferably 1.0 × 10 ⁻⁴ S / cm or more.

The sulfide-based solid battery manufacturing method of the present invention includes at least a positive electrode, a negative electrode, and a sulfide-based solid electrolyte that includes a sulfide-based solid electrolyte and includes an electrolyte layer interposed between the positive electrode and the negative electrode. A method for producing a solid battery, comprising the steps of preparing the positive electrode and the negative electrode, mixing at least a sulfide solid electrolyte, a binder, and a fatty acid ester represented by the following formula (1): A step of preparing a solid electrolyte slurry, a step of forming an electrolyte layer by applying the sulfide-based solid electrolyte slurry to at least one surface of either the positive electrode or the negative electrode; and A step of laminating either the positive electrode or the negative electrode on the surface of the electrode on which the electrolyte layer is formed.
R ¹ —CO ₂ —R ² formula (1)
(In the above formula (1), R ¹ is a linear or branched aliphatic group having 3 to 10 carbon atoms , and R ² is a linear or branched aliphatic group having 3 to 10 carbon atoms. is there.)

  In the method for producing a sulfide-based solid battery of the present invention, the binder may be a fluoropolymer.

  In the method for producing a sulfide-based solid battery of the present invention, when the total mass of the sulfide-based solid electrolyte and the binder is 100% by mass, the content ratio of the binder is 0.1. It is preferable that it is -10 mass%.

In the method for producing a sulfide-based solid battery according to the present invention, the ionic conductivity of the electrolyte layer is preferably 1.0 × 10 ⁻⁴ S / cm or more.

  According to the present invention, in preparing a sulfide-based solid electrolyte slurry used for forming an electrolyte layer, a fatty acid ester is employed, so that a binder that could not be conventionally used for forming an electrolyte layer can be used. A wide variety of materials can be selected in the formation of the electrolyte layer.

It is a figure which shows an example of the laminated structure of the sulfide type solid battery manufactured by this invention, Comprising: It is the figure which showed typically the cross section cut | disconnected in the lamination direction. Example 2 is a graph plotting ionic conductivity and binding force for the electrolyte layer of Example 4. It is the cross-sectional schematic diagram which showed the outline of the measurement aspect of binding force.

  The method for producing an electrolyte layer / electrode laminate and the method for producing a sulfide-based solid battery according to the present invention include a step of preparing at least one of a positive electrode and a negative electrode, and a step of preparing a sulfide-based solid electrolyte slurry. And it is common in the point which has the process of forming an electrolyte layer in an electrode. Therefore, first, a manufacturing method of the electrolyte layer / electrode laminate will be described, and then, a manufacturing method of the sulfide-based solid battery will be described focusing on differences from the manufacturing method.

1. Method for Producing Electrolyte Layer / Electrode Laminate The method for producing an electrolyte layer / electrode laminate of the present invention is an electrolyte layer containing a sulfide-based solid electrolyte, and a method for producing an electrolyte layer / electrode laminate comprising an electrode. A step of preparing the electrode, a step of mixing at least a sulfide-based solid electrolyte, a binder, and a fatty acid ester to prepare a sulfide-based solid electrolyte slurry, and at least one surface of the electrode And a step of coating the sulfide-based solid electrolyte slurry to form an electrolyte layer.

  The sulfide-based solid electrolyte reacts with water or a compound having a functional group containing an oxygen atom (for example, an alcohol such as methanol, an ester such as ethyl acetate, an amide such as N-methylpyrrolidone), etc., and has an ionic conductivity. It is known that it falls abruptly by 3 digits or more. Therefore, conventionally, only a solvent having a functional group not containing an oxygen atom has been used in the preparation of a sulfide-based solid electrolyte slurry used for forming an electrolyte layer. Furthermore, from the viewpoint of handleability, only a very limited type of binder that dissolves in the solvent has been used as the binder.

  Due to the above circumstances, combinations of binders and solvents have been extremely limited. Therefore, the binder and the solvent used for forming the electrolyte layer and the binder and the solvent used for forming the electrode are often the same. In such a case, when the electrolyte layer is formed on the electrode that has already been applied and dried, the binder used for the electrode is dissolved again by the solvent used to form the electrolyte layer, and the current collector is collected. The problem that an electrode peeled from foil etc. occurred. Thus, there are many disadvantages from the viewpoint of manufacturing efficiency that the range of material selection in the formation of the electrolyte layer is limited, particularly that the combination of the binder and the solvent is limited.

  The present inventors have found that a specific fatty acid ester and a binder that has been dissolved in the fatty acid ester and has not been conventionally used in the manufacture of sulfide-based solid batteries are both sulfide-based solid electrolytes and I found it very difficult to react. The present inventors have found that by combining the fatty acid ester and the binder as appropriate, a wider selection of materials can be selected in the formation of the electrolyte layer than in the past, and the present invention has been completed.

The present invention includes (1) a step of preparing either a positive electrode or a negative electrode, (2) a step of preparing a sulfide-based solid electrolyte slurry, and (3) a step of forming an electrolyte layer on the electrode. . The present invention is not necessarily limited to only the above three steps.
Hereinafter, the steps (1) to (3) will be described in order.

1-1. Step of Preparing Electrode In the present invention, either the positive electrode or the negative electrode is prepared.
The positive electrode used in the present invention preferably includes a positive electrode current collector and a positive electrode lead connected to the positive electrode current collector, and more preferably includes a positive electrode active material layer containing a positive electrode active material. The negative electrode used in the present invention preferably includes a negative electrode current collector and a negative electrode lead connected to the negative electrode current collector, and more preferably includes a negative electrode active material layer containing a negative electrode active material.

Specific examples of the positive electrode active material used in the present invention include LiCoO ₂ , LiNi ₂ Co ₁₅ Al ₃ O ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNiPO ₄ , LiMnPO ₄ , LiNiO. ₂ , LiMn ₂ O ₄ , LiCoMnO ₄ , Li ₂ NiMn ₃ O ₈ , Li ₃ Fe ₂ (PO ₄ ) ₃ and Li ₃ V ₂ (PO ₄ ) ₃ . Among these, in the present invention, LiCoO ₂ , LiNi ₂ Co ₁₅ Al ₃ O ₂ , and LiNi _1/3 Mn _1/3 Co _1/3 O ₂ are preferably used as the positive electrode active material.

  The thickness of the positive electrode active material layer used in the present invention varies depending on the intended use of the sulfide-based solid battery, but is preferably in the range of 5 to 250 μm, preferably in the range of 20 to 200 μm. Is particularly preferred, and most preferred is in the range of 30 to 150 μm.

  The average particle diameter of the positive electrode active material is, for example, preferably in the range of 1 to 50 μm, more preferably in the range of 1 to 20 μm, and particularly preferably in the range of 3 to 5 μm. If the average particle size of the positive electrode active material is too small, the handleability may be deteriorated. If the average particle size of the positive electrode active material is too large, it may be difficult to obtain a flat positive electrode active material layer. Because. The average particle diameter of the positive electrode active material can be determined by measuring and averaging the particle diameter of the active material carrier observed with, for example, a scanning electron microscope (SEM).

The positive electrode active material layer may contain a conductive material, a binder, and the like as necessary.
The conductive material contained in the positive electrode active material layer used in the present invention is not particularly limited as long as the conductivity of the positive electrode active material layer can be improved. For example, carbon such as acetylene black and ketjen black Black etc. can be mentioned. Moreover, although content of the electrically conductive material in a positive electrode active material layer changes with kinds of electrically conductive material, it is in the range of 1-10 mass% normally.

Examples of the binder contained in the positive electrode active material layer used in the present invention include rubber-based binders. In addition, the content of the binder in the positive electrode active material layer may be an amount that can fix the positive electrode active material or the like, and is preferably smaller. The content of the binder is usually in the range of 1 to 10% by mass.
Moreover, you may use the binder used for formation of the electrolyte layer mentioned later for formation of the positive electrode active material layer used for this invention.

The positive electrode current collector used in the present invention is not particularly limited as long as it has a function of collecting the positive electrode active material layer.
Examples of the material for the positive electrode current collector include aluminum, SUS, nickel, iron, and titanium. Of these, aluminum and SUS are preferable. Moreover, as a shape of a positive electrode electrical power collector, foil shape, plate shape, mesh shape etc. can be mentioned, for example, Foil shape is preferable.

As the positive electrode electrolyte contained in the positive electrode used in the present invention, a solid electrolyte can be used. As the solid electrolyte, specifically, an oxide-based solid electrolyte can be used in addition to the sulfide-based solid electrolyte described in detail later.
Specifically, as the oxide-based solid electrolyte, LiPON (lithium phosphate oxynitride), Li _1.3 Al _0.3 Ti _0.7 (PO ₄ ) ₃ , La _0.51 Li _0.34 TiO _Examples include _0.74 , Li ₃ PO ₄ , Li ₂ SiO ₂ , Li ₂ SiO ₄ , Li _0.5 La _0.5 TiO ₃ , Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) _{3 and the} like. can do.
After the positive electrode active material layer is formed, the positive electrode active material layer may be pressed in order to improve the electrode density.

  The negative electrode active material used for the negative electrode active material layer is not particularly limited as long as it can absorb and release metal ions. In the case of using lithium ions as metal ions, for example, lithium alloys, metal oxides, carbon materials such as graphite, and the like can be given. The negative electrode active material may be in the form of a powder or a thin film.

The negative electrode active material layer may contain a conductive material, a binder, and the like as necessary.
What was mentioned above can be used for the electrically conductive material and binder which can be used in a negative electrode active material layer. Moreover, it is preferable to select suitably the usage-amount of a electrically conductive material and a binder according to the use etc. of a sulfide type solid battery. Further, the film thickness of the negative electrode active material layer is not particularly limited, but is preferably in the range of, for example, 5 to 150 μm, and more preferably in the range of 10 to 80 μm.
As the negative electrode electrolyte contained in the negative electrode used in the present invention, a solid electrolyte can be used. Specifically, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or the like can be used as the solid electrolyte.

As the material and shape of the negative electrode current collector, the same materials and shapes as those of the positive electrode current collector described above can be employed.
As a manufacturing method of the negative electrode used in the present invention, a method similar to the manufacturing method of the positive electrode as described above can be adopted.

1-2. Step of preparing a sulfide-based solid electrolyte slurry This step is a step of preparing a sulfide-based solid electrolyte slurry by mixing at least a sulfide-based solid electrolyte, a binder, and a fatty acid ester.

The sulfide solid electrolyte used in the present invention is not particularly limited as long as it is an electrolyte containing a sulfur atom in its molecular structure or composition.
Specific examples of the sulfide-based solid electrolyte used in the present invention include Li ₂ S—P ₂ S ₅ , Li ₂ S—P ₂ S ₃ , Li ₂ S—P ₂ S ₃ —P ₂ S ₅ , _{Li 2 S-SiS 2, LiI} -Li 2 S-P 2 S 5, LiI-Li 2 S-SiS 2 -P 2 S 5, Li 2 S-SiS 2 -Li 4 SiO 4, Li 2 S-SiS 2 _{-Li 3 PO 4, Li 3 PS} 4 -Li 4 GeS 4, Li 3.4 P 0.6 Si 0.4 S 4, Li 3.25 P 0.25 Ge 0.76 S 4, Li 4-x Ge _1-x P _x S _{4 and the} like can be exemplified.

  The binder used in the present invention is dispersed in the fatty acid ester when preparing the sulfide-based solid electrolyte slurry, and has a function of keeping the sulfide-based solid electrolyte etc. in the electrolyte layer. There is no particular limitation. It is preferable that the binder used in the present invention does not react with the sulfide solid electrolyte and dissolves in the fatty acid ester. Therefore, the binder used in the present invention preferably has a polar group. Examples of polar groups include halogen-containing groups such as fluorine atoms and fluorine-containing aliphatic hydrocarbon groups.

As a binder used for this invention, fluoropolymers, such as a vinylidene fluoride resin and polytetrafluoroethylene (PTFE), etc. can be mentioned, for example. Especially, the fluorine-type copolymer whose content rate of a vinylidene fluoride monomer unit is 40-70 mol% is preferable from viewpoints, such as the solubility to a specific fatty acid ester. When the said content rate of a vinylidene fluoride monomer unit is less than 40 mol%, and when the said content rate exceeds 70 mol%, there exists a possibility that the solubility of the fluorine-type copolymer with respect to fatty acid ester may fall.
The content ratio of the vinylidene fluoride monomer unit in the fluorinated copolymer in the present invention is the fluorination when the total amount of the monomer units constituting the fluorinated copolymer is 100 mol%. This is the ratio of the amount of the vinylidene monomer unit substance. The content ratio of the vinylidene fluoride monomer unit in the fluorine-based copolymer can be calculated by, for example, a known method from the integration ratio of each signal in the ¹⁹ FNMR spectrum.
The content ratio of the vinylidene fluoride monomer unit in the fluorine-based copolymer is more preferably 45 to 65 mol%, and further preferably 50 to 60 mol%.

  The fluorine-based copolymer contains another fluorine-based monomer unit together with the vinylidene fluoride monomer unit. As used herein, the fluorine-based monomer unit includes a main chain skeleton composed of carbon-carbon bonds (the main chain includes a polymer side chain such as a graft chain) and a main chain skeleton. A monomer unit having a chemical structure that contains a fluorine atom bonded directly or indirectly to a carbon atom, and the carbon atom and fluorine atom occupy most of the spatial extent of the monomer unit. is there. Examples of the fluorine-based monomer unit other than the vinylidene fluoride monomer unit include, for example, a tetrafluoroethylene monomer unit, a hexafluoropropylene monomer unit, a vinyl fluoride monomer unit, and a trifluoroethylene unit. Examples thereof include a monomer unit, a chlorotrifluoroethylene monomer unit, a perfluoromethyl vinyl ether monomer unit, and a perfluoroethyl vinyl ether monomer unit. Among these fluorine-based monomer units, it is particularly preferable to include at least one of a tetrafluoroethylene monomer unit and a hexafluoropropylene monomer unit.

  Examples of the fluorine-based copolymer that can be used in the present invention include vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer. Examples thereof include a polymer and a vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer. Among these fluorinated copolymers, it is preferable to use a vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer.

  The fluorine-based copolymer may be a block copolymer in which vinylidene fluoride monomer units and other fluorine-based monomer units are copolymerized with blocks in which a certain number of repeating units are linked to each other. Alternatively, an alternating copolymer in which different repeating units are alternately polymerized may be used. Further, it may be a random copolymer having no order in the arrangement of repeating units.

  The fluorinated copolymer is preferably not water-soluble. Moreover, when using the sulfide type solid electrolyte mentioned later especially, it is preferable that the water | moisture content contained in a fluorine-type copolymer is 100 ppm or less. The sulfide solid electrolyte reacts with water to generate hydrogen sulfide, which may reduce the ionic conductivity of the sulfide solid electrolyte.

It is preferable that the content rate of a binder is 0.1-10 mass% when the total mass of a sulfide type solid electrolyte and a binder is 100 mass%. If the content ratio of the binder is less than 0.1% by mass, the content ratio of the binder is too small, so that the sulfide-based solid electrolyte leaks out of the electrolyte layer, and the formation of the electrolyte layer is hindered. There is a fear. On the other hand, if the content ratio of the binder exceeds 10% by mass, the content ratio of the binder is too large, so that the ionic conductivity of the electrolyte layer may be too low.
When the total mass of the sulfide-based solid electrolyte and the binder is 100% by mass, the content ratio of the binder is more preferably 1 to 7% by mass, and 2 to 5% by mass. More preferably.

The fatty acid ester used in the present invention is not particularly limited as long as it can disperse the sulfide-based solid electrolyte and the binder. The fatty acid ester used in the present invention is preferably one that can dissolve both the sulfide-based solid electrolyte and the binder.
The fatty acid ester used in the present invention is preferably a compound represented by the following formula (1).
R ¹ —CO ₂ —R ² formula (1)
(In the above formula (1), R ¹ is a linear or branched aliphatic group having 3 to 10 carbon atoms, and R ² is a linear or branched aliphatic group having 3 to 10 carbon atoms. is there.)
When R ¹ is an aliphatic group having 2 or less carbon atoms, as shown in Examples described later, the ionic conductivity when mixed with a sulfide solid electrolyte may be significantly reduced. Further, when R ¹ is an aliphatic group having 11 or more carbon atoms, the fatty acid ester may not be able to disperse the sulfide-based solid electrolyte and the binder.
The fatty acid ester used in the present invention is preferably butyl butyrate, butyl pentanoate, butyl hexanoate, pentyl butyrate, pentyl pentanoate, pentyl hexanoate, hexyl butyrate, hexyl pentanoate, or hexyl hexanoate. These fatty acid esters may be used alone or in combination of two or more. Of these fatty acid esters, butyl butyrate is more preferably used.

The content ratio of the fatty acid ester is preferably 35 to 90% by mass when the total mass of the sulfide-based solid electrolyte, the binder, and the fatty acid ester is 100% by mass. If the content ratio of the fatty acid ester is less than 35% by mass, the content ratio of the fatty acid ester is too small, so that the sulfide-based solid electrolyte and the binder are not dispersed in the slurry, which hinders the formation of the electrolyte layer. May occur. On the other hand, when the said content rate of fatty acid ester exceeds 90 mass%, since there are too many content rates of fatty acid ester, there exists a possibility that control of a fabric weight (coating) may become difficult.
When the total mass of the sulfide-based solid electrolyte, the binder, and the fatty acid ester is 100% by mass, the content ratio of the fatty acid ester is more preferably 40 to 70% by mass, and 50 to 65% by mass. More preferably.
In addition, it is preferable that the solid content ratio in sulfide type solid electrolyte slurry is 10-65 mass%.

  The sulfide-based solid electrolyte slurry may contain a material other than the above materials. However, the content ratio of the material is preferably 1% by mass or less when the mass of the entire sulfide-based solid electrolyte slurry is 100% by mass.

  The method of mixing the sulfide-based solid electrolyte, the binder, and the fatty acid ester is not particularly limited as long as these materials are uniformly mixed. Examples of a method for mixing these materials include mixing using a mortar and mechanical milling such as a ball mill, but are not necessarily limited to these methods.

1-3. Step of Forming Electrolyte Layer on One Electrode This step is a step of forming the electrolyte layer by applying the sulfide-based solid electrolyte slurry to at least one surface of the electrode.
The electrolyte layer may be formed only on one side of the electrode, or may be formed on both sides of the electrode.

The electrolyte layer formed by this step is a layer that performs metal ion exchange between the positive electrode active material and the negative electrode active material described above. Therefore, the electrode includes an electrode active material layer (the electrode active material layer here refers to a positive electrode active material layer when the electrode is a positive electrode and a negative electrode active material layer when the electrode is a negative electrode). In some cases, it is preferable to form an electrolyte layer on the electrode active material layer.
The method for forming the electrolyte layer is not particularly limited. As a method for forming the electrolyte layer, for example, an electrolyte layer may be formed on the electrode surface by applying a sulfide-based solid electrolyte slurry to the electrode surface and drying it. Other methods for forming the electrolyte layer include, for example, applying a sulfide-based solid electrolyte slurry to the surface of the transfer substrate and drying it to produce a transfer sheet, and then applying the transfer sheet to the electrode by thermocompression bonding or the like. After the bonding, the electrolyte layer may be formed on the electrode surface by a method of peeling the base film of the transfer sheet.

A method for applying the sulfide-based solid electrolyte slurry, a method for drying, and the like can be appropriately selected. Examples of the coating method include a spray method, a screen printing method, a doctor blade method, a gravure printing method, and a die coating method. Examples of the drying method include reduced pressure drying, heat drying, and reduced pressure heat drying. There is no restriction | limiting in the specific conditions in reduced pressure drying and heat drying, What is necessary is just to set suitably.
The coating amount of the sulfide-based solid electrolyte slurry varies depending on the composition of the sulfide-based solid electrolyte slurry, but may be about 3 to 8 mg / cm ² . The thickness of the electrolyte layer is not particularly limited, but may be about 15 to 40 μm.

The ionic conductivity of the electrolyte layer formed by this step is preferably 1.0 × 10 ⁻⁴ S / cm or more. If the ionic conductivity is less than 1.0 × 10 ⁻⁴ S / cm, the discharge performance of the sulfide-based solid battery produced according to the present invention may be too low.
The ionic conductivity of the electrolyte layer formed by this step is more preferably 4.0 × 10 ^{−4 to} 1.0 × 10 ⁻² S / cm.

2. Method for Producing Sulfide Solid Battery The method for producing a sulfide solid battery of the present invention includes at least a positive electrode, a negative electrode, and a sulfide solid electrolyte, and is interposed between the positive electrode and the negative electrode. A method for manufacturing a sulfide-based solid battery including an electrolyte layer, the step of preparing the positive electrode and the negative electrode, mixing at least a sulfide-based solid electrolyte, a binder, and a fatty acid ester, A step of preparing an electrolyte slurry, a step of forming an electrolyte layer by applying the sulfide-based solid electrolyte slurry on at least one surface of either the positive electrode or the negative electrode, and the electrode A step of laminating either the positive electrode or the negative electrode on the surface on which the electrolyte layer is formed.

  In the present invention, both the positive electrode and the negative electrode described above are prepared. In addition to the three steps described in the section “1. Method for Manufacturing Electrolyte Layer / Electrode Laminate”, the present invention further includes a step of laminating the other electrode on the surface on which the electrolyte layer of one electrode is formed. Have The present invention is not necessarily limited to the above four steps, and may include, for example, a step of storing in a battery case as described later, in addition to the above four steps.

2-1. The process of laminating the other electrode on the surface of the electrolyte layer of one electrode This process is a process of laminating the electrode that was not used for forming the electrolyte layer on the surface of the electrode layer formed above. . When the electrolyte layer is formed on the positive electrode in the electrolyte layer forming step, in this step, the negative electrode is laminated on the surface of the positive electrode on which the electrolyte layer is formed. When the electrolyte layer is formed on the negative electrode in the electrolyte layer forming step, in this step, the positive electrode is laminated on the surface of the negative electrode on which the electrolyte layer is formed.
In this step, the electrode laminated on the electrolyte layer is an electrode active material layer (the electrode active material layer here refers to the positive electrode active material layer and the electrode laminated on the electrolyte layer when the electrode laminated on the electrolyte layer is a positive electrode) In the case of a negative electrode, it refers to a negative electrode active material layer.) When provided, the electrode is preferably laminated so that the electrode active material layer is in contact with the electrolyte layer.
In addition, after lamination | stacking, in order to improve the ion conductivity of the interface of each electrode and an electrolyte layer, you may crimp | bond a laminated body suitably by a thermocompression bonding method etc.

2-2. Other Steps As other steps, for example, a step of storing a sulfide-based solid battery in a battery case and the like can be mentioned.
The shape of the battery case used in the present invention is not particularly limited as long as it can accommodate the positive electrode, the negative electrode, the electrolyte layer, and the like described above. Specifically, a cylindrical shape, a square shape, a coin shape, and the like. And a laminate type.

FIG. 1 is a view showing an example of a laminated structure of a sulfide-based solid battery manufactured according to the present invention, and is a view schematically showing a cross section cut in the stacking direction. The sulfide-based solid battery produced according to the present invention is not necessarily limited to this example.
The sulfide-based solid battery 100 includes a positive electrode 6 including a positive electrode active material layer 2 and a positive electrode current collector 4, a negative electrode 7 including a negative electrode active material layer 3 and a negative electrode current collector 5, and the positive electrode 6 and the negative electrode 7. An electrolyte layer 1 to be sandwiched is provided.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples.

1. Preparation of green compact containing fatty acid ester [Example 1]
100 mg of LiI—Li ₂ S—P ₂ S ₅ which is a kind of sulfide-based solid electrolyte and 5 mL of butyl butyrate (manufactured by Tokyo Chemical Industry Co., Ltd.) which is a kind of fatty acid ester were mixed, and the mixture was dried. The dried mixture was pelletized at a pressure of 4.3 t / cm ² to produce a green compact of Example 1.

[Comparative Example 1]
In Example 1, except that 5 mL of butyl butyrate was changed to 5 mL of butyl acetate (manufactured by Nacalai Tesque), the raw materials were mixed, dried and pelletized in the same manner as in Example 1, and the green compact of Comparative Example 1 was used. The body was made.

2. Measurement of Ionic Conductivity For the green compacts of Example 1 and Comparative Example 1, AC impedance measurement was performed at a frequency of 1 MHz to 0.1 Hz using an impedance analyzer (Solartron: SI-1260), and the measurement results were obtained. Based on this, the ionic conductivity was calculated.
Table 1 below summarizes the ionic conductivity of the green compacts of Example 1 and Comparative Example 1.

As can be seen from Table 1 above, the ionic conductivity of the green compact of Comparative Example 1 using butyl acetate is 9.4 × 10 ⁻⁶ S / cm, whereas that of Example 1 using butyl butyrate. The ionic conductivity of the green compact is 9.3 × 10 ⁻⁴ S / cm. That is, the order of the ionic conductivity of Example 1 is two digits higher than the order of the ionic conductivity of Comparative Example 1. These results suggest that butyl butyrate is less reactive with sulfide-based solid electrolytes than butyl acetate, and therefore does not impair the ionic conductivity of sulfide-based solid electrolytes.

3. Preparation of electrolyte layer / electrode laminate [Example 2]
LiI-Li ₂ S—P ₂ S ₅ , which is a kind of sulfide-based solid electrolyte, and a fluorine-based copolymer (vinylidene fluoride monomer unit: tetrafluoroethylene monomer unit: hexafluoropropylene as a binder) Monomer unit = 55 mol%: 25 mol%: 20 mol%) in a ratio of sulfide-based solid electrolyte: binder = 98.9 mass%: 1.1 mass%, A certain butyl butyrate was added to the mixture, and the solid content ratio of the mixture was adjusted to 43% by mass to prepare a sulfide-based solid electrolyte slurry. The obtained sulfide-based solid electrolyte slurry was subjected to ultrasonic treatment for 30 seconds, and further stirred with a shaker for 30 minutes.
The sulfide-based solid electrolyte slurry after stirring was applied onto an aluminum foil (electrode) with a doctor blade to obtain an electrolyte layer / electrode laminate of Example 2.

[Example 3]
Ultrasonic treatment, stirring, and the like, except that the mixing ratio of the sulfide-based solid electrolyte and the binder was sulfide-based solid electrolyte: binder = 98 mass%: 2 mass%. Then, an electrolyte layer / electrode laminate of Example 3 was obtained.

[Example 4]
Except for the mixing ratio of the sulfide-based solid electrolyte and the binder, sulfide-based solid electrolyte: binder = 95% by mass: 5% by mass, ultrasonic treatment, stirring, Then, an electrolyte layer / electrode laminate of Example 4 was obtained.

[Comparative Example 2]
Butylene rubber is used in place of the fluorocopolymer as the binder, and the mixing ratio of the sulfide solid electrolyte and the binder is sulfide solid electrolyte: binder = 98 mass%: 2 mass%. In the same manner as in Example 2, ultrasonic treatment, stirring, and coating were performed except that heptane was added instead of butyl butyrate and the solid content ratio of the mixture was adjusted to 43% by mass. An electrolyte layer / electrode laminate was obtained.

4). Measurement of Ion Conductivity and Binding Force For the electrolyte layers of Example 2 to Example 4 and Comparative Example 2, ion conductivity and binding force were measured. The ion conductivity is measured in the same manner as described above.
The measurement of the binding force was performed at room temperature in an atmosphere of argon in a glove box using a tensile load measuring machine (Model 2257 manufactured by Aiko Engineering Co., Ltd.).
FIG. 3 is a schematic cross-sectional view showing an outline of a measurement mode of binding force. In FIG. 3, double wavy lines mean that the drawing is omitted. First, the sample 13 was fixed to the pedestal 15 with the double-sided tape 14 with the surface 13 a coated with the sulfide-based solid electrolyte slurry facing up. Another double-sided tape 12 was affixed to the attachment tip 11a of the tensile load measuring device 11, and the adhesive surface of the double-sided tape was directed to the sample 13 side. The tensile load measuring device 11 is lowered vertically with respect to the sample 13 at a constant speed (about 20 mm / min), and the double-sided tape 12 and the surface 13a coated with the sulfide-based solid electrolyte slurry are brought into contact with each other. The load measuring machine 11 was raised. The tensile load when the coating film of the sulfide-based solid electrolyte slurry was peeled was defined as the binding force of the sample.

FIG. 2 is a graph plotting ionic conductivity and binding force for the electrolyte layers of Example 2 to Example 4. FIG. 2 is a graph in which the horizontal axis represents the binder content, the left vertical axis represents the ionic conductivity (S / cm), and the right vertical axis represents the binding force (N / cm ² ). is there. Moreover, the black circle plot shows the data of ion conductivity, and the white circle plot shows the data of binding force. In addition, the thick broken line in a graph shows the reference value (1.1 * 10 < ^-3 > S / cm) of ion conductivity. Moreover, the thin broken line in a graph shows the reference value (2.0 N / cm < ² >) of binding force.
As can be seen from FIG. 2, the ionic conductivity of Example 2 (binding agent content: 1.1 mass%) is 1.2 × 10 ⁻³ S / cm, and the binding force is 1.75 N / cm ² . . Therefore, the ionic conductivity of Example 2 exceeds the reference value, and the binding force is about the same as the standard value.
Further, as can be seen from FIG. 2, the ionic conductivity of Example 3 (binding agent content: 2.0 mass%) is 9.7 × 10 ⁻⁴ S / cm, and the binding force is 5.4 N / cm ^2. It is. Therefore, the ionic conductivity of Example 3 is about 90% of the reference value, and the binding force exceeds 2.5 times the standard value. Further, as can be seen from FIG. 2, the ionic conductivity of Example 4 (binding agent content ratio: 5.0 mass%) is 8.7 × 10 ⁻⁴ S / cm, and the binding force is 22.4 N / cm ^2. It is. The binding force of Example 4 exceeds 11 times the reference value. Moreover, the ionic conductivity of Example 4 is about 80% of the reference value. In addition, when Example 2-Example 4 are compared, it turns out that the ionic conductivity is not falling rapidly by addition of a binder. Therefore, in Example 2 to Example 4, a specific chemical reaction occurs between the sulfide-based solid electrolyte and the binder, and as a result, the ionic conductivity of the sulfide-based solid electrolyte is impaired. It is estimated that it is not.

On the other hand, the ionic conductivity of Comparative Example 2 (butylene rubber, binder content: 2.0 mass%) is 4.6 × 10 ⁻⁴ S / cm, and the binding force is 18.1 N / cm ² . Therefore, it can be seen that when butylene rubber is used as the binder, only about 40% of the ionic conductivity is exhibited as compared with Example 2.

  As described above, the binder containing the sulfide-based solid electrolyte, the binder, and the fatty acid ester, and the total mass of the sulfide-based solid electrolyte, the binder, and the fatty acid ester being 100% by mass. It can be seen that the electrolyte layer of Example 2 to Example 4 in which the content ratio is 0.1 to 10% by mass can achieve both excellent ion conductivity and high binding force.

DESCRIPTION OF SYMBOLS 1 Electrolyte layer 2 Positive electrode active material layer 3 Negative electrode active material layer 4 Positive electrode collector 5 Negative electrode collector 6 Positive electrode 7 Negative electrode 11 Tensile load measuring device 11a Attachment tip 12 Double-sided tape 13 Sample 13a Sulfide-based solid electrolyte slurry in a sample Coated surface 14 Double-sided tape 15 Base 100 Sulfide-based solid battery

Claims (8)

An electrolyte layer containing a sulfide-based solid electrolyte, and a method for producing an electrolyte layer / electrode laminate including an electrode,
Preparing the electrode;
At least a step of mixing a sulfide-based solid electrolyte, a binder, and a fatty acid ester represented by the following formula (1) to prepare a sulfide-based solid electrolyte slurry; and
A method for producing an electrolyte layer / electrode laminate, comprising a step of coating the sulfide-based solid electrolyte slurry on at least one surface of the electrode to form an electrolyte layer.
R ¹ —CO ₂ —R ² formula (1)
(In the above formula (1), R ¹ is a linear or branched aliphatic group having 3 to 10 carbon atoms , and R ² is a linear or branched aliphatic group having 3 to 10 carbon atoms. is there.) The method for producing an electrolyte layer / electrode laminate according to claim 1, wherein the binder is a fluoropolymer. The content rate of the said binder is 0.1-10 mass% when the total mass of the said sulfide type solid electrolyte and the said binder is 100 mass%, The claim 1 or 2 characterized by the above-mentioned. Manufacturing method of electrolyte layer / electrode laminate. The ionic conductivity of the electrolyte layer, 1.0 × is 10 -4 ^{S / cm} or more, a manufacturing method of the electrolyte layer-electrode stack according to any one of claims 1 to 3. A method for producing a sulfide-based solid battery comprising at least a positive electrode, a negative electrode, and a sulfide-based solid electrolyte, and comprising an electrolyte layer interposed between the positive electrode and the negative electrode,
Preparing the positive electrode and the negative electrode;
A step of mixing at least a sulfide-based solid electrolyte, a binder, and a fatty acid ester represented by the following formula (1) to prepare a sulfide-based solid electrolyte slurry;
A step of coating the sulfide-based solid electrolyte slurry on at least one surface of either the positive electrode or the negative electrode to form an electrolyte layer; and
And a step of laminating either the positive electrode or the negative electrode on the surface of the electrode on which the electrolyte layer is formed.
R ¹ —CO ₂ —R ² formula (1)
(In the above formula (1), R ¹ is a linear or branched aliphatic group having 3 to 10 carbon atoms , and R ² is a linear or branched aliphatic group having 3 to 10 carbon atoms. is there.) The method for producing a sulfide-based solid battery according to claim 5, wherein the binder is a fluoropolymer. The sulfide-based solid electrolyte, and when the total weight of the binder and 100 mass%, the content of the binder is 0.1 to 10 mass%, according to claim 5 or 6 Method for producing a sulfide-based solid battery. 8. The method for producing a sulfide-based solid battery according to claim 5 , wherein an ionic conductivity of the electrolyte layer is 1.0 × 10 ⁻⁴ S / cm or more.

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