JP2012150909A - Lithium metal solid body, lithium metal film made of the same, solid electrolyte membrane-lithium electrode assembly including the metal film, lithium air battery provided with the solid electrolyte membrane-lithium electrode assembly, and method for manufacturing the solid electrolyte membrane-lithium electrode assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium metal solid or the like which has novel orientation.SOLUTION: The lithium metal solid has the highest orientation in a {200} plane.

Description

  The present invention relates to a lithium metal solid having a novel orientation.

  The secondary battery converts the decrease in chemical energy associated with the chemical reaction into electrical energy, and can discharge the battery. The battery can be stored (charged). Among secondary batteries, a metal secondary battery represented by a lithium secondary battery has a high energy density, and is therefore widely applied as a power source for notebook personal computers, cellular phones, and the like.

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.)
The electrons generated by the reaction of the above 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 above formula (I) move from the negative electrode side to the positive electrode side by electroosmosis 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.

  Lithium secondary batteries have a larger amount of output energy per unit volume than conventional nickel hydride batteries and nickel cadmium secondary batteries. Unfortunately, the commercialization of rechargeable lithium secondary batteries has not been successful. The main reason why a rechargeable lithium secondary battery cannot be commercialized is the problem of the charge / discharge cycle of the cell. When the charge / discharge cycle is repeated, lithium dendrite generated from the lithium electrode gradually grows, penetrates the electrolyte, and finally reaches the anode. Since this lithium dendrite causes an internal short circuit in the battery, the conventional lithium secondary battery becomes unusable after several cycles.

  On the other hand, for the purpose of improving the charge / discharge cycle behavior of lithium, a structure in which the electrolyte side of the lithium electrode is covered with a protective layer has been proposed. Patent Document 1 discloses a cathode structure including an active metal anode having a first surface and a second surface, an electronically conductive component, an ionic conductive component, and an electrochemically active component, wherein at least 1 A cathode structure in which one cathode structure component includes an aqueous component, and an ion conductive protective film formed on the first surface of the anode, the active metal of the anode being formed from one or more materials And is substantially impermeable to the first surface in contact with the anode, chemically compatible with the cathode structure, and the cathode. A battery cell is disclosed that includes an ion conductive protective film configured to provide a second surface in contact with the structure.

JP-T-2007-513464

Paragraphs [0056] and [FIG. 4A] of Patent Document 1 describe that lithium nitride and lithium are deposited on the surface of an ion conductive glass ceramic material. However, as a result of studies by the present inventors, when lithium is vapor-deposited on the solid electrolyte, a gap is formed between the lithium foil and the solid electrolyte, and a lithium secondary battery using the obtained solid electrolyte membrane / lithium electrode assembly is obtained. It became clear that the secondary battery cannot exhibit sufficient power generation performance.
The present invention has been accomplished in view of the above-mentioned circumstances, and has a novel orientation and a lithium metal solid that provides an electrode body with a small interfacial gap when bonded to a solid electrolyte, the lithium metal solid A lithium metal film comprising a solid electrolyte membrane / lithium electrode assembly including the metal film, a lithium-air battery including the solid electrolyte membrane / lithium electrode assembly, and a method for producing the solid electrolyte membrane / lithium electrode assembly The purpose is to do.

  The lithium metal solid of the present invention is characterized by having the highest orientation in the {200} plane.

  The lithium metal film of the present invention is characterized by comprising the above lithium metal solid.

  The solid electrolyte membrane / lithium electrode assembly of the present invention is a solid electrolyte membrane / lithium electrode assembly comprising a solid electrolyte membrane and a lithium electrode layer formed on at least one surface of the solid electrolyte membrane, The lithium electrode layer includes the lithium metal film.

  The lithium-air battery of the present invention is a lithium-air battery comprising at least an air electrode, a lithium metal negative electrode, and a solid electrolyte membrane interposed between the air electrode and the lithium metal negative electrode and bonded to at least the lithium metal negative electrode. The bonded lithium metal negative electrode and the solid electrolyte membrane are the solid electrolyte membrane / lithium electrode assembly.

  The method for producing a solid electrolyte membrane / lithium electrode assembly of the present invention is a production of a solid electrolyte membrane / lithium electrode assembly comprising a solid electrolyte membrane and a lithium electrode layer formed on at least one surface of the solid electrolyte membrane. A step of preparing a lithium target and the solid electrolyte membrane, a step of preparing a vacuum chamber including a resistance heating evaporation source for heating and evaporating lithium by a resistance heating method, and the lithium heating to the resistance heating evaporation source A step of arranging a target, and arranging the solid electrolyte membrane in the vacuum chamber so that a distance between the solid electrolyte membrane and the lithium target is 0.5 cm or more and less than 8 cm, and the vacuum After evacuating the tank, lithium was evaporated from the resistance heating evaporation source onto at least one surface of the solid electrolyte membrane by a resistance heating method. , Characterized by having a step, of forming the lithium electrode layer.

  According to the present invention, since it has the highest orientation in the {200} plane, a solid electrolyte membrane / lithium electrode assembly with few interfacial gaps when bonded to the solid electrolyte membrane can be obtained. Moreover, according to the manufacturing method of the present invention, a novel lithium metal layer having the highest orientation on the {200} plane can be formed on the solid electrolyte membrane by using resistance heating.

It is a figure which shows an example of the laminated constitution of the lithium air battery which concerns on this invention, Comprising: It is the figure which showed typically the cross section cut | disconnected in the lamination direction. It is the graph which arranged and showed the XRD pattern of Example 1, the comparative example 1, and the comparative example 2. FIG. It is a bar graph which compared the thickness of the lithium which melt | dissolved at the time of discharge or deposited about the Example 1 and the comparative example 2 at the time of charge. 5 is a graph showing the relationship between the thickness of lithium deposited during charging and the voltage for Example 1. FIG. 6 is a graph showing the relationship between the thickness of lithium deposited during charging and the voltage for Comparative Example 2.

1. Lithium metal solid and lithium metal film The lithium metal solid of the present invention is characterized by having the highest orientation in the {200} plane. The lithium metal film of the present invention is made of the lithium metal solid.

  In the present specification, equivalent face groups are shown in braces for crystal face notation. For example, the (200) plane, (020) plane, (002) plane, (* 00) plane, (0 * 0) plane, (00 *) plane (the number indicated by the asterisk (*) is “2”. ”And so on) are all expressed as {200} planes.

  In recent years, in order to suppress the generation of dendrites, techniques for providing a solid electrolyte between a positive electrode and a negative electrode have been actively studied. However, it is extremely difficult to form a dense solid electrolyte / lithium metal interface using a conventional lithium foil. Moreover, even if a solid electrolyte membrane / lithium electrode assembly produced using a conventional lithium foil is incorporated in a lithium-air battery, an overvoltage of 3 V or more is generated in the lithium dissolution precipitation reaction. Since this overvoltage is larger than the voltage of a lithium air battery using lithium metal as a negative electrode, such a solid electrolyte membrane / lithium electrode assembly cannot be used for a lithium air battery.

Such a large overvoltage occurs when a lithium compound film made of lithium carbonate (Li ₂ CO ₃ ) or lithium oxide (Li ₂ O ₂ ) is formed between the lithium metal and the solid electrolyte. Such a film inhibits the formation of a dense solid electrolyte / lithium metal interface. Further, even when the lithium metal foil is simply joined to the solid electrolyte, a gap is generated at the solid electrolyte / lithium metal interface, and as a result, a large overvoltage is generated.
The present inventors have found that a dense solid electrolyte / lithium metal interface can be formed by depositing lithium metal on a solid electrolyte by resistance heating, and completed the present invention.

As shown in the examples described later, the lithium metal solid produced by vapor deposition using resistance heating has the highest orientation on the {200} plane. The joined body of a lithium metal solid having the highest orientation on the {200} plane and a solid electrolyte dissolves and deposits thick lithium of 50 μm or more with a smaller overvoltage than a conventional lithium secondary battery using lithium metal as a negative electrode. can do.
In the lithium metal solid having the highest orientation on the {200} plane, lithium ions are conducted through the {200} plane, so that even when lithium is dissolved and precipitated, gaps at the solid electrolyte / lithium metal interface or lithium dendrite Is not expected to occur.

The shape of the lithium metal solid is not particularly limited. For example, when it is used for a lithium secondary battery, it is preferably a film.
The thickness of the lithium metal film is not particularly limited, but when used for the negative electrode of a lithium secondary battery, the thickness is preferably 0.1 to 5000 μm.

  As will be described later, the lithium metal film of the present invention can be used as a solid electrolyte membrane / lithium electrode assembly in combination with a lithium conductive solid electrolyte membrane. However, in addition to such a combination, for example, it can be used in a lithium-air battery in combination with a lithium ion conductive electrolyte. By using the lithium metal film of the present invention in combination with a lithium ion conductive electrolyte in a lithium air battery, generation of lithium dendrite during charging can be mainly suppressed.

As the lithium ion conductive electrolyte, for example, a non-aqueous electrolyte can be used.
The nonaqueous electrolytic solution used in the present invention usually contains a lithium salt and a nonaqueous solvent. Examples of the lithium salt include inorganic lithium salts such as LiBF ₄ , LiPF ₆ , LiClO _4, and LiAsF ₆ ; and LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ (LiTFSI), LiN (SO ₂ C ₂ F ₅ ). ₂ and organic lithium salts such as LiC (SO ₂ CF ₃ ) ₃ . Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethyl carbonate, butylene carbonate, γ-butyrolactone, sulfolane, Acetonitrile, 1,2-dimethoxyethane, 1,3-dimethoxypropane, diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, and mixtures thereof can be exemplified. From the viewpoint that dissolved oxygen can be efficiently used in the reaction, the non-aqueous solvent is preferably a solvent having high oxygen solubility. The concentration of the lithium salt in the nonaqueous electrolytic solution is, for example, in the range of 0.5 to 3 mol / L.
In the present invention, examples of the non-aqueous electrolyte or non-aqueous solvent include N-methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) imide (PP13TFSI), N-methyl-N-propylpyrrolidinium. Bis (trifluoromethanesulfonyl) imide (P13TFSI), N-butyl-N-methylpyrrolidinium Bis (trifluoromethanesulfonyl) imide (P14TFSI), N, N-diethyl-N-methyl-N- (2-methoxyethyl) Low volatile liquids such as ionic liquids such as ammonium bis (trifluoromethanesulfonyl) imide (DEMETFSI), N, N, N-trimethyl-N-propylammonium bis (trifluoromethanesulfonyl) imide (TMPATFSI) Using Good.

2. Solid electrolyte membrane / lithium electrode assembly The solid electrolyte membrane / lithium electrode assembly of the present invention comprises a solid electrolyte membrane and a lithium electrode layer formed on at least one surface of the solid electrolyte membrane. An electrode assembly, wherein the lithium electrode layer includes the lithium metal film.

  The solid electrolyte membrane used in the present invention serves as a support for the lithium electrode layer, and when the solid electrolyte membrane / lithium electrode assembly according to the present invention is incorporated in a lithium-air battery, the air electrode layer and It is held between the negative electrode layers and has a role of exchanging lithium ions between the air electrode layer and the negative electrode layer.

  As the lithium ion conductive solid electrolyte, a lithium ion conductive inorganic solid electrolyte, a lithium ion conductive organic solid electrolyte, or the like can be used.

Specifically, as the lithium ion conductive inorganic solid electrolyte, a lithium ion conductive solid oxide electrolyte, a lithium ion conductive solid sulfide electrolyte, or the like can be used.
Specifically, as the lithium ion conductive solid oxide electrolyte, LiPON (lithium phosphate oxynitride), Li _1.3 Al _0.3 Ti _0.7 (PO ₄ ) ₃ , Li ₂ Ti (PO ₄₎ ) ₃ -AlPO ₄ , La _0.51 Li _0.34 TiO _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 Examples include _0.5 Ge _1.5 (PO ₄ ) ₃ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₇ BaLa ₂ Ta ₂ O _{12, and the} like.
Specifically, as the lithium ion conductive solid sulfide electrolyte, 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, Li 7} P 3 may be exemplified _{S 11} or the like.
Examples of the lithium ion conductive inorganic solid electrolyte other than the above include Li ₃ N.

  Specifically, as the lithium ion conductive organic solid electrolyte, a polymer electrolyte, a gel electrolyte, or the like can be used.

  The polymer electrolyte used in the present invention preferably contains a lithium salt and a polymer. As the lithium salt, the same lithium salt used in the non-aqueous electrolyte solution described above can be used. The polymer is not particularly limited as long as it forms a complex with a lithium salt, and examples thereof include polyethylene oxide.

The gel electrolyte used in the present invention preferably contains a lithium salt, a polymer and a nonaqueous solvent.
As the lithium salt and the non-aqueous solvent, those similar to the lithium salt and the non-aqueous solvent used in the above-described non-aqueous electrolyte can be used, respectively. Moreover, an ionic liquid can also be used as a non-aqueous solvent.
The polymer is not particularly limited as long as it can be gelled, and examples thereof include polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyvinylidene fluoride (PVDF), polyurethane, polyacrylate, and cellulose. Can be mentioned.

  The solid electrolyte membrane used in the present invention may contain two or more lithium conductive solid electrolytes. Specifically, the solid electrolyte membrane used in the present invention may be a single membrane containing two or more types of the lithium conductive solid electrolyte, or two or more types of the lithium conductive solid electrolyte. It may be a laminate of different films.

The solid electrolyte membrane / lithium electrode assembly according to the present invention may further include a current collector on the lithium electrode side.
The material of the current collector used in the present invention is not particularly limited as long as it has conductivity, and examples thereof include copper, stainless steel, nickel, and carbon. Examples of the shape of the current collector include a foil shape, a plate shape, and a mesh (grid) shape. When the solid electrolyte membrane / lithium electrode assembly according to the present invention is incorporated into a lithium-air battery, a battery case described later may also have the function of a current collector.

3. Lithium-air battery The lithium-air battery of the present invention comprises at least an air electrode, a lithium metal negative electrode, and a lithium air provided between the air electrode and the lithium metal negative electrode and at least a solid electrolyte membrane joined to the lithium metal negative electrode. In the battery, the bonded lithium metal negative electrode and the solid electrolyte membrane are the solid electrolyte membrane / lithium electrode assembly.

FIG. 1 is a diagram illustrating an example of a layer configuration of a lithium-air battery according to the present invention, and is a diagram schematically illustrating a cross section cut in a stacking direction. The lithium air battery according to the present invention is not necessarily limited to this example.
The lithium air battery 100 is sandwiched between an air electrode 6 including an air electrode layer 2 and an air 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 air electrode 6 and the negative electrode 7. The solid electrolyte membrane 1 is provided.
Among the lithium-air batteries according to the present invention, the joined lithium metal negative electrode and the solid electrolyte membrane are as described above. Hereinafter, the air electrode which comprises the lithium air battery which concerns on this invention, a suitable separator, a battery case, etc. are demonstrated in detail.

(Air electrode)
The air electrode used in the present invention preferably includes an air electrode layer, and usually includes an air electrode current collector and an air electrode lead connected to the air electrode current collector. It is.

(Air electrode layer)
The air electrode layer used in the present invention preferably contains at least a catalyst and a conductive material. The air electrode layer used in the present invention may further contain a binder as necessary.

Examples of the catalyst used for the air electrode layer include an oxygen active catalyst. Examples of oxygen active catalysts include, for example, platinum groups such as palladium and platinum; perovskite oxides containing transition metals such as cobalt, manganese or iron; inorganic compounds containing noble metal oxides such as ruthenium, iridium or palladium; porphyrins Metal coordination organic compounds having a skeleton or a phthalocyanine skeleton; manganese oxide and the like.
From the viewpoint that the electrode reaction is performed more smoothly, it is preferable that the catalyst is supported on a conductive material described later.

The conductive material used for the air electrode layer is not particularly limited as long as it has conductivity. For example, a carbon material, a perovskite-type conductive material, a porous conductive polymer, a metal porous body, etc. Can be mentioned. In particular, the carbon material may have a porous structure or may not have a porous structure, but in the present invention, the carbon material preferably has a porous structure. This is because the specific surface area is large, so that many reaction fields can be provided, and it also serves as a gas diffusion layer. Specific examples of the carbon material having a porous structure include mesoporous carbon. On the other hand, specific examples of the carbon material having no porous structure include graphite, acetylene black, carbon nanotube, and carbon fiber.
As a content rate of the electroconductive material in an air electrode layer, it is preferable to exist in the range of 65-99 mass%, for example in the range of 75-95 mass% especially. If the content ratio of the conductive material is too small, the reaction field may decrease, and the battery capacity may be reduced. If the content ratio of the conductive material is too large, the content of the catalyst is relatively reduced and sufficient. This is because it may not be possible to exert a proper catalytic function.

  The air electrode layer only needs to contain at least a catalyst and a conductive material, but preferably further contains a binder. Examples of the binder include rubber resins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and styrene / butadiene rubber (SBR rubber). Although it does not specifically limit as a content rate of the binder in an air electrode layer, For example, it is preferable that it is in the range of 30 mass% or less, especially 1-10 mass%.

The air electrode layer can be formed by applying an air electrode mixture in which at least an air electrode catalyst, and optionally a conductive material and a binder are mixed, to a support such as an air electrode current collector described later. preferable.
In the preparation of the air electrode mixture, a solvent may be used. As a solvent used for the preparation of the air electrode mixture, a solvent having a boiling point of 200 ° C. or lower is preferable. For example, acetone, N, N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), or the like is used. be able to.

  The thickness of the air electrode layer varies depending on the use of the air battery, but is preferably in the range of 2 to 500 μm, and more preferably in the range of 5 to 300 μm.

(Air current collector)
The air electrode current collector used in the present invention collects current in the air electrode layer. The material for the air electrode current collector is not particularly limited as long as it has conductivity, and examples thereof include stainless steel, nickel, aluminum, iron, titanium, and carbon. Examples of the shape of the air electrode current collector include a foil shape, a plate shape, and a mesh (grid) shape. Especially, in this invention, it is preferable that the shape of an air electrode electrical power collector is a mesh form. This is because the current collection efficiency is excellent. In this case, usually, a mesh-shaped air electrode current collector is disposed inside the air electrode layer. Furthermore, the lithium-air battery of the present invention may include another air electrode current collector (for example, a foil-shaped current collector) that collects the charges collected by the mesh-shaped air electrode current collector. . In the present invention, a battery case to be described later may also have the function of an air electrode current collector.
The thickness of the air electrode current collector is, for example, preferably in the range of 10 to 1000 μm, and more preferably in the range of 20 to 400 μm.

  The lithium air battery according to the present invention may further include another electrolyte between the solid electrolyte membrane and the air electrode. As other electrolytes, specifically, the lithium ion conductive electrolyte described in the section of “1. Lithium metal solid and lithium metal film” or the “2. Solid electrolyte film / lithium electrode assembly” described above. The lithium ion conductive solid electrolyte described in the section can be used.

(Separator)
The lithium air battery according to the present invention preferably includes a separator between the air electrode and the negative electrode. Examples of the separator include porous films such as polyethylene and polypropylene; and nonwoven fabrics such as a resin nonwoven fabric and a glass fiber nonwoven fabric.
These materials used for the separator can also be used as an electrolyte support material by impregnating the above-described electrolyte.

(Battery case)
The air battery according to the present invention usually includes a battery case that houses an air electrode, a negative electrode, an electrolyte, and the like. Specific examples of the shape of the battery case include a coin type, a flat plate type, a cylindrical type, and a laminate type. The battery case may be an open-air battery case or a sealed battery case. An open-air battery case is a battery case having a structure in which at least the air electrode layer can sufficiently come into contact with the atmosphere. On the other hand, when the battery case is a sealed battery case, it is preferable to provide a gas (air) introduction pipe and an exhaust pipe in the sealed battery case. In this case, the gas to be introduced / exhausted preferably has a high oxygen concentration, and more preferably pure oxygen. In addition, it is preferable to increase the oxygen concentration during discharging and decrease the oxygen concentration during charging.

4). Method for Producing Solid Electrolyte Membrane / Lithium Electrode Assembly The method for producing a solid electrolyte membrane / lithium electrode assembly of the present invention comprises a solid electrolyte membrane and a lithium electrode layer formed on at least one surface of the solid electrolyte membrane. A method for producing a solid electrolyte membrane / lithium electrode assembly comprising a step of preparing a lithium target and the solid electrolyte membrane, and a vacuum chamber provided with a resistance heating evaporation source for heating and evaporating lithium by a resistance heating method The lithium target is disposed in the resistance heating evaporation source, and the solid is placed in the vacuum chamber so that the distance between the solid electrolyte membrane and the lithium target is 0.5 cm or more and less than 8 cm. A step of arranging an electrolyte membrane, and after exhausting the inside of the vacuum chamber, the solid electrolyte is removed from the resistance heating evaporation source by a resistance heating method. And depositing lithium on at least one surface of the film to form the lithium electrode layer.

  As the solid electrolyte membrane used in the present invention, the solid electrolyte membrane described in the above section “2. Solid electrolyte membrane / lithium electrode assembly” can be used. Moreover, the lithium target used for this invention will not be specifically limited if it is a lithium metal normally used for vapor deposition.

  As a vacuum chamber provided with a resistance heating evaporation source, a vacuum chamber conventionally used for vapor deposition can be used. The resistance heating evaporation source plays a role of supporting a lithium target, evaporating the lithium target during vapor deposition, and heating a solid electrolyte film serving as a substrate to promote crystal growth of the deposited lithium metal.

The shape of the resistance heating evaporation source is not particularly limited, and a linear evaporation source such as a filament type, a helical coil type, or a basket type; a foil evaporation source such as a boat type can be used.
The material of the resistance heating evaporation source is not particularly limited as long as it is a material that vaporizes lithium and does not deteriorate when heated by resistance heating. Alloys such as cobalt alloy and nickel alloy, alumina and ITO (indium titanium) Oxide) and the like can be used.

In the present invention, since lithium is deposited by resistance heating, the distance between the lithium target and the solid electrolyte membrane serving as the substrate is set to 0.5 cm or more and less than 8 cm.
Usually, masking is used for lithium deposition in order to obtain a lithium thin film having a desired size and shape. If the distance between the lithium target and the substrate is shorter than 8 cm, the masking becomes dirty and maintenance becomes difficult, and it is considered difficult to reuse the masking. Therefore, it has been conventionally considered that there is no advantage in lithium deposition by such resistance heating.
However, as a result of the study by the present inventors, as shown in an example described later, by making the distance between the lithium target and the substrate shorter than 8 cm, the initial expectation is far exceeded and it has completely new orientation. It has been found that a solid electrolyte membrane / lithium electrode assembly including a lithium electrode layer can be obtained.

If the distance between the lithium target and the solid electrolyte membrane is less than 0.5 cm, lithium film formation itself becomes practically difficult. If the distance is 8 cm or more, the effect of using resistance heating may not be fully enjoyed. is there.
The distance between the lithium target and the solid electrolyte membrane is preferably 1 to 6 cm, and more preferably 2 to 4 cm.

In order to deposit lithium, the vacuum chamber must be evacuated. The inside of the vacuum chamber is not particularly limited as long as it is under a reduced pressure condition capable of performing lithium deposition, but it is preferably under a high vacuum, and specifically, preferably under a high vacuum of 10 ⁻³ Pa or less. Note that the deposition of lithium is preferably performed after replacing the inside of the vacuum chamber with an inert atmosphere. The inert gas used for replacement in the vacuum chamber is preferably argon.

The dimension of lithium film formation varies depending on the use of the obtained solid electrolyte membrane / lithium electrode assembly. Area of the lithium film is preferably 0.01~100cm ^2, 0.05~10cm ² is more preferable. Moreover, 0.0001-10000 micrometers is preferable and, as for the thickness of lithium, 0.1-500 micrometers is more preferable.

  In the present invention, vapor deposition is performed with the distance between the target lithium and the solid electrolyte film being shorter than before, so that the temperature of the solid electrolyte film is increased and the growth of lithium crystals after vapor deposition is promoted. Since the lithium crystal produced using resistance heating in this manner has the highest orientation on the {200} plane, the lithium crystal newly precipitated by the electrode reaction is also considered to precipitate along the orientation of the {200} plane. It is done. Therefore, lithium dentlite is not generated, and it is considered that lithium crystals can be deposited uniformly.

  In the present invention, since vapor deposition is preferably performed under a high vacuum, the reaction between lithium and impurities such as oxygen does not occur. Therefore, unlike the conventional lithium deposition, a lithium oxide film is not formed at the interface between the lithium electrode layer and the solid electrolyte film. Further, since the lithium fine particles are densely deposited on the solid electrolyte membrane by vapor deposition, no gap is generated at the interface between the lithium electrode layer and the solid electrolyte membrane. Further, since resistance overheating is used, impurities in the lithium target are not dissolved. Therefore, impurities are not deposited, and the purity of lithium in the solid electrolyte membrane / lithium electrode assembly obtained by the present invention is extremely high. In addition, the resistance heating increases the temperature of the solid electrolyte membrane during vapor deposition and promotes crystal growth. As a result, the solid electrolyte membrane / lithium electrode including the above-described lithium electrode layer having the highest orientation on the {200} plane A joined body is obtained.

  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 solid electrolyte membrane / lithium electrode assembly [Example 1]
First, a Li ₂ Ti (PO ₄ ) ₃ —AlPO ₄ (manufactured by OHARA INC .; hereinafter may be referred to as OHARA glass) film was prepared as a solid electrolyte film. The details of OHARA glass are shown below.
Dimensions: 13 x 13 x 0.150 mm
Conductivity: 1 × 10 ⁻⁴ S / cm

Next, a LiPON (lithium phosphate oxynitride) film was formed on the OHARA glass film by a known method using Li ₃ PO ₄ as a target. Details of the film forming conditions and the LiPON film are shown below.
<Film formation conditions>
_Pressure: N 2, 4Pa
Temperature: Room temperature (15-25 ° C)
<LiPON film>
Dimensions: 13 x 13 x 0.0025mm
Conductivity: 1.92 × 10 ⁻⁶ S / cm

Subsequently, a lithium target was prepared. A lithium target was placed in a resistance heating evaporation source in a vacuum chamber under an argon atmosphere. The OHARA glass-LiPON laminated body was arrange | positioned in a vacuum chamber so that the distance between the said laminated body and a lithium target might be 3 cm. At this time, the OHARA glass-LiPON laminate was disposed so that the surface on which the LiPON film was formed faced the lithium target.
After evacuating the vacuum chamber until the inside of the vacuum chamber becomes a high vacuum of 10 ⁻³ Pa or less, lithium is deposited on the LiPON film of the OHARA glass-LiPON laminate by resistance heating of a resistance heating evaporation source. Thus, the solid electrolyte membrane / lithium electrode assembly of Example 1 including a lithium electrode layer having a diameter of 5φ (0.196 cm ² ) and a thickness of 50 to 100 μm was obtained.

[Comparative Example 1]
The process is the same as in Example 1 until the LiPON film is formed on the OHARA glass film.
Subsequently, a lithium target was prepared. A lithium target was placed in a vacuum chamber under an argon atmosphere. The OHARA glass-LiPON laminated body was arrange | positioned in a vacuum chamber so that the distance between the said laminated body and a lithium target might be 8 cm. At this time, the OHARA glass-LiPON laminate was disposed so that the surface on which the LiPON film was formed faced the lithium target.
After the inside of the vacuum chamber was evacuated until the inside of the vacuum chamber became a high vacuum of 10 ⁻³ Pa or less, lithium was vapor-deposited on the LiPON film of the OHARA glass-LiPON laminate in the same manner as in the past, and a diameter of 5φ ( 0.196 cm ² ) and a lithium electrode layer having a thickness of 50 to 100 μm, a solid electrolyte membrane / lithium electrode assembly of Comparative Example 1 was obtained.

2. Structural Analysis of Lithium Electrode Layer Chemical Structure of Lithium Electrode Layer in Solid Electrolyte Membrane / Lithium Electrode Assembly of Example 1 and Comparative Example 1, and Lithium Foil (Honjo Metal Co., Ltd., Thickness 250 μm: Comparative Example 2) Were examined by X-ray crystal structure analysis. For the measurement, an X-ray diffractometer (RINT-Ultima III, manufactured by Rigaku Corporation) was used. Using Cu K _alpha rays for the measurement, the tube voltage was set to 40 kV, tube current was 40 mA.
FIG. 2 is a diagram showing the XRD patterns of Example 1, Comparative Example 1, and Comparative Example 2 side by side.
As can be seen from FIG. 2, in the XRD pattern of Comparative Example 2, a diffraction peak on the (110) plane, a diffraction peak on the (200) plane, and a diffraction peak on the (211) plane are observed. Among these diffraction peaks, since the intensity of the diffraction peak on the (211) plane is the strongest, it can be seen that lithium foils conventionally used in lithium secondary batteries exhibit the highest orientation on the (211) plane. .

Further, as can be seen from FIG. 2, no conspicuous diffraction peak is observed in the XRD pattern of Comparative Example 1. Therefore, it can be seen that the lithium film obtained by the conventional vapor deposition method is a film made of crystals with low order without having specific orientation.
On the other hand, as can be seen from FIG. 2, only the diffraction peak of (200) plane is observed in the XRD pattern of Example 1. From this result, it can be seen that the lithium film obtained by evaporation by resistance heating is different from the lithium films of Comparative Example 1 and Comparative Example 2 described above, and particularly shows the highest orientation on the (200) plane.
Table 1 below is a table summarizing the ratio of the intensity of each diffraction peak when the intensity of the (200) plane diffraction peak is 1 in the XRD pattern of Example 1. It can be seen that the (200) plane orientation of the lithium electrode of the present invention is about 4 to 5 times higher in peak intensity than the (110) plane orientation and the (211) plane orientation.

3. Comparison of change in thickness of lithium electrode layer About the solid electrolyte membrane / lithium electrode assembly of Example 1 and the lithium foil of Comparative Example 2, a cell having the following configuration was assembled, a charge / discharge experiment was performed, and lithium used for charging and discharging The thickness of was measured. The lithium foil of Comparative Example 2 was bonded to the following solid electrolyte membrane to obtain a solid electrolyte membrane / lithium electrode assembly.
Cell configuration: Lithium sample (working electrode) / solid electrolyte membrane / electrolyte / lithium foil (counter electrode)
Lithium sample of working electrode: lithium electrode layer in Example 1 or lithium foil of Comparative Example 2 Solid electrolyte membrane: OHARA glass-LiPON laminate Electrolyte solution: Electrolyte solution in which 1M LiTFSI is dissolved in propylene carbonate (PC) Lithium foil: manufactured by Honjo Metal Co., Ltd. Measurement method: Constant current measurement, 1.0 mA / cm ² , cut voltage 5 V, measurement temperature 50 ° C.

FIG. 3 is a bar graph comparing the thicknesses of lithium dissolved in discharging or deposited during charging for Example 1 and Comparative Example 2.
As can be seen from FIG. 3, the lithium foil in Comparative Example 2 has only a thickness change of less than 1 μm in both the dissolution reaction and the precipitation reaction. As a result, in the solid electrolyte membrane / lithium electrode assembly of Comparative Example 2 obtained by simply joining the conventional lithium foil to the solid electrolyte membrane, the lithium conductivity at the interface between the solid electrolyte membrane and the lithium foil is extremely low. It shows that.
On the other hand, as can be seen from FIG. 3, the lithium electrode layer in Example 1 was able to dissolve 58 μm thick lithium during the dissolution reaction and deposit 58 μm thick lithium during the precipitation reaction. . As a result, the lithium electrode layer having the highest orientation on the (200) plane is firmly bonded to the solid electrolyte membrane. As a result, in the solid electrolyte membrane / lithium electrode assembly of Example 1, the solid electrolyte membrane The lithium conductivity at the interface between the electrode and the lithium electrode layer is extremely high.

FIG. 4 is a graph showing the relationship between the thickness of lithium deposited during charging and the voltage for Example 1. FIG. 5 is a graph showing the relationship between the thickness of lithium deposited during charging and the voltage in Comparative Example 2.
As can be seen from FIG. 5, the lithium air battery including the lithium foil of Comparative Example 2 shows that the voltage drops to −3 V only by depositing a few nm of lithium. On the other hand, as can be seen from FIG. 4, the lithium-air battery including the solid electrolyte membrane / lithium electrode assembly of Example 1 maintains a constant voltage until lithium is deposited to a thickness of 58 μm.

DESCRIPTION OF SYMBOLS 1 Solid electrolyte membrane 2 Air electrode layer 3 Negative electrode active material layer 4 Air electrode current collector 5 Negative electrode current collector 6 Air electrode 7 Negative electrode 100 Lithium air battery

Claims (5)

  A lithium metal solid characterized by having the highest orientation in the {200} plane.   A lithium metal film comprising the lithium metal solid according to claim 1. A solid electrolyte membrane / lithium electrode assembly comprising a solid electrolyte membrane and a lithium electrode layer formed on at least one surface of the solid electrolyte membrane,
3. The solid electrolyte membrane / lithium electrode assembly, wherein the lithium electrode layer includes the lithium metal film according to claim 2. A lithium-air battery comprising at least an air electrode, a lithium metal negative electrode, and a solid electrolyte membrane interposed between the air electrode and the lithium metal negative electrode and joined to at least the lithium metal negative electrode;
The lithium-air battery, wherein the bonded lithium metal negative electrode and the solid electrolyte membrane are the solid electrolyte membrane / lithium electrode assembly according to claim 3. A method for producing a solid electrolyte membrane / lithium electrode assembly comprising a solid electrolyte membrane and a lithium electrode layer formed on at least one surface of the solid electrolyte membrane,
Preparing a lithium target and the solid electrolyte membrane;
Preparing a vacuum chamber equipped with a resistance heating evaporation source for heating and evaporating lithium by a resistance heating method;
The lithium target is disposed in the resistance heating evaporation source, and the solid electrolyte membrane is placed in the vacuum chamber so that the distance between the solid electrolyte membrane and the lithium target is 0.5 cm or more and less than 8 cm. Arranging, and
And evacuating the inside of the vacuum chamber and then depositing lithium on at least one surface of the solid electrolyte membrane from the resistance heating evaporation source by a resistance heating method to form the lithium electrode layer. A method for producing a solid electrolyte membrane / lithium electrode assembly.

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