JP6166584B2 - Lithium ion conductive solid electrolyte and composite and battery using the same - Google Patents

Description

  The present invention relates to a lithium ion conductive solid electrolyte, a solid electrolyte-electrode composite using the same, and a battery.

A solid electrolyte with a basic composition of Li ₇ La ₃ Zr ₂ O ₁₂ having a garnet crystal structure (hereinafter sometimes referred to as an LLZ-based solid electrolyte) has a high lithium ion conductivity and a feature that is not reduced by a lithium metal negative electrode potential. Have. Therefore, this material is expected to suppress the short circuit between the positive and negative electrodes due to lithium dendrite precipitation, and is desired to be applied to next-generation batteries such as all-solid-state batteries and lithium-air batteries. Under such technical background, various substitutional elements have been studied in order to further improve the lithium ion conduction performance, and attempts have been made to improve the conduction performance by improving the composition.

For example, Patent Document 1 (Japanese Patent Publication No. 2007-528108) discloses a garnet-type solid ion conductor having a composition of L _{5 + x} A _y G _z M ₂ O ₁₂ . Patent Document 2 (Japanese Patent Laid-Open No. 2011-051800) discloses that the addition of Al in addition to Li, La, and Zr, which are basic elements of LLZ, can improve the denseness and lithium ion conductivity. . Patent Document 3 (Japanese Patent Application Laid-Open No. 2011-073962) discloses that lithium ion conductivity can be further improved by adding Nb and / or Ta in addition to Li, La and Zr, which are basic elements of LLZ. ing. Patent Document 4 (Japanese Patent Laid-Open No. 2011-073963) includes Li, La, Zr, and Al, and the density can be further improved by setting the molar ratio of Li to La to 2.0 to 2.5. Is disclosed. In order to provide a higher performance battery, further improvement in lithium ion conduction performance in the LLZ solid electrolyte material is desired.

As another application, Patent Document 5 (Japanese Patent Laid-Open No. 2011-147875) includes a composition formula Li _{5 + X} La ₃ Zr _X M _{2 -X} O ₁₂ (X is a number satisfying 1.5 ≦ X ≦ 1.925). And M is Nb, Ta, Sc, Ti, V, Y, Hf, Si, Al, Ga, Ge, or Sn).

Special table 2007-528108 gazette JP 2011-051800 A JP 2011-073962 A JP 2011-073963 A JP 2011-147875 A

  The inventors of the present invention have recently included carbon (C) in the crystal lattice of at least a part of the crystal structure of the LLZ-based solid electrolyte, and secured a region where lithium carbonate is substantially absent on the surface of the solid electrolyte. As a result, it was found that the lithium ion conductivity of the LLZ-based solid electrolyte can be significantly improved. Further, the region where lithium carbonate is not substantially present constitutes at least a part of the interface between the solid electrolyte and the electrode, thereby improving the ionic conductivity of the LLZ-based solid electrolyte. The knowledge that it can be maximized in the body and battery was also obtained.

  Accordingly, an object of the present invention is to provide an LLZ-based solid electrolyte with significantly improved lithium ion conductivity, and a solid electrolyte-electrode composite and battery using the same.

  According to one embodiment of the present invention, the crystal structure has a garnet-type or garnet-like crystal structure composed of at least Li, La, Zr, and O, and at least part of the crystal structure includes C in the crystal lattice. A lithium ion conductive solid electrolyte is provided, which has a region where lithium carbonate is substantially absent on the surface of the solid electrolyte.

According to another aspect of the present invention, the solid electrolyte of the present invention,
An electrode formed by bonding to the solid electrolyte;
A solid electrolyte-electrode composite is provided, wherein the region substantially free of lithium carbonate constitutes at least part of the interface between the solid electrolyte and the electrode.

  According to still another aspect of the present invention, a battery including the solid electrolyte-electrode composite of the present invention and a counter electrode is provided.

It is a schematic cross section of an example of the solid electrolyte-electrode composite of the present invention. It is a schematic cross section of another example of the solid electrolyte-electrode composite of the present invention. It is a schematic diagram which shows the structure of the film-forming apparatus used by Example A1 and A2. It is a schematic perspective view which shows the carbon electrode for ion conductivity evaluation produced in Example A1. It is a figure which shows the (422) plane peak in the XRD profile measured about solid electrolyte AD film in Example A1. It is a figure which shows the relationship between the ionic conductivity measured about solid electrolyte AD membrane in Example A1, and measurement temperature. It is a photograph which shows the carbon electrode for ion conductivity evaluation produced in Example B1. It is a figure which shows the relationship between the ionic conductivity measured about the solid electrolyte sintered compact in Example B1, and measurement temperature.

Lithium ion conductive solid electrolyte The lithium ion conductive solid electrolyte of the present invention has a garnet-type or garnet-like crystal structure (hereinafter referred to as LLZ-type crystal structure) composed of at least Li, La, Zr, and O. And at least part of this crystal structure comprises carbon (C) in the crystal lattice. In addition, the solid electrolyte has a region on the surface substantially free of lithium carbonate (Li ₂ CO ₃ ). Thus, by containing C in at least a part of the crystal lattice of the LLZ-based crystal structure and securing a region where lithium carbonate is not substantially present on the surface of the solid electrolyte, lithium of the LLZ-based solid electrolyte is obtained. The ionic conductivity can be significantly improved. The introduction of C into such a crystal lattice includes, for example, incorporating C ₂ derived from CO ₂ into the crystal lattice of the solid electrolyte by exposing it to a CO ₂ -containing atmosphere such as an air atmosphere and performing an aging treatment. Can be performed. In the first place, the effect of containing C in the crystal lattice is that the LLZ solid electrolyte membrane produced by a deposition method such as the aerosol deposition (AD) method or the LLZ solid electrolyte sintered body produced by sintering is put into the atmosphere. This is based on the knowledge of an unexpected phenomenon that the lithium ion conduction performance has been improved by leaving it alone.

Although the details of the mechanism by which lithium ion conductivity is improved by including C in the crystal lattice are not clear, the following two mechanisms are conceivable. As a first mechanism, it is considered that CO ₃ ²⁻ or CO ₂ is substituted and dissolved in the O site of the LLZ crystal lattice to expand the lattice, thereby improving the lithium ion mobility in the crystal grains. . As a second mechanism, it is considered that the volume of the crystal lattice expands due to absorption of CO ₃ ²⁻ or CO ₂ , thereby improving the adhesion between the particles and improving the lithium ion mobility at the crystal grain boundary. It is done.

However, even if C is included in the crystal lattice, it is not always possible to improve the lithium ion conductivity. This is because when LLZ-based solid electrolyte coexists with CO ₂ and H ₂ O in the atmosphere, lithium carbonate is deposited on the surface, and this lithium carbonate provides a high-resistance layer and inhibits lithium ion conduction. This is because In view of the formation of this high resistance layer, it has been conventionally believed that the LLZ solid electrolyte should not be left in the atmosphere for a long time. Therefore, as far as the present inventors know, the above-mentioned advantage by including C in the crystal lattice has not been recognized so far. However, by ensuring a region where lithium carbonate is not substantially present on the surface of the solid electrolyte, the lithium ion conduction of the LLZ-based solid electrolyte improved by the inclusion of C in the crystal lattice is inhibited by the high resistance layer. It can be avoided. That is, the effect of improving the lithium ion conductivity due to the inclusion of C in the crystal lattice can be maximized.

Such a region substantially free of lithium carbonate may be secured by an arbitrary method, and is controlled by preventing the precipitation of lithium carbonate by controlling the atmosphere, or by scraping the surface on which lithium carbonate is deposited. Just do it. For example, the formation of such a region is a process in which precipitation of lithium carbonate is not desired, such as a process of preparing a solid electrolyte (for example, an AD film forming process or a sintered body manufacturing process) or a process of bonding the solid electrolyte to an electrode. Is preferably performed in an atmosphere in which CO ₂ and H ₂ O are not substantially coexistent. Alternatively, the solid electrolyte may be exposed to an atmosphere in which CO ₂ and H ₂ O coexist, and in that case, a region where lithium carbonate is substantially not present by scraping the surface exposed to the atmosphere as necessary. Should be secured. However, even if the predetermined process is performed in an atmosphere in which CO ₂ and H ₂ O are not substantially coexisting, it passes through an atmosphere in which CO ₂ and H ₂ O coexist when moving from one process to another. Or may be temporarily left in such an atmosphere, and even if lithium carbonate does not substantially precipitate or does not precipitate, there is no problem as long as the level is not harmful from the viewpoint of conductivity ( If it is a practically harmful level, it is sufficient to secure a region where lithium carbonate is not substantially present by scraping the surface exposed to the atmosphere). The method for scraping the surface of the solid electrolyte is not particularly limited as long as the surface layer can be removed by, for example, mechanical polishing or cutting, dissolution cleaning with a solution of water, acid, alkali, or the like, ion milling, sputtering, or the like. Among these, mechanical polishing and cutting are preferable because the process is simple and side reactions are unlikely to occur. Further, the treatment by sputtering is preferable in that damage such as a decrease in crystallinity of the base material and a composition shift can be suppressed. Moreover, you may perform these processes, heating.

  The solid electrolyte of the present invention has a region where lithium carbonate is not substantially present on the surface thereof. “Substantially no lithium carbonate” means that the presence of a very small amount of lithium carbonate having no harm from the viewpoint of lithium ion conductivity does not depart from the spirit of the present invention. However, it goes without saying that it is desirable that no lithium carbonate exist in the region. The region where lithium carbonate is substantially absent is most preferably the entire surface of the solid electrolyte, but from the viewpoint of securing the entrance and exit of the lithium ion conduction path, the solid electrolyte in a form where lithium carbonate is present on the surface Even so, it is sufficient to have at least two regions that are substantially free of lithium carbonate. Typically, one location is located on the surface of the solid electrolyte and the other location is located on the back surface of the solid electrolyte. However, in the case of constituting a solid electrolyte-electrode composite, it is sufficient that a region where lithium carbonate is not substantially present is located at the junction interface with the electrode, and lithium carbonate is present in other portions. Also, when joining with other members, it may be appropriately cut off as necessary.

  In the solid electrolyte of the present invention, at least a part of the garnet-type or garnet-like crystal structure contains C in the crystal lattice, and preferably contains C in the crystal lattice over most or almost the entire crystal structure. . The content of C in the crystal lattice is determined by using a reference solid electrolyte having the same composition except that C is not included in the crystal lattice, and the shift amount of the (422) plane peak position and / or the a-axis in X-ray diffraction. This can be confirmed by measuring the amount of increase in the lattice constant. That is, the peak of the (422) plane in X-ray diffraction is preferable on the low angle side compared to a reference solid electrolyte having the same composition as that of the solid electrolyte, except that the solid electrolyte does not contain C in the crystal lattice. Has a crystal structure shifted by 0 <2θ <1 °, more preferably 0.1 <2θ <1 °. Further, the solid electrolyte of the present invention has an a-axis lattice constant of preferably 0.01 Å or more as compared with a reference solid electrolyte having the same composition as the solid electrolyte except that C is not included in the crystal lattice. More preferably, it has a crystal structure increased by 0.05% or more.

The solid electrolyte of the present invention has a garnet type or a garnet type-like crystal structure composed of at least Li, La, Zr and O. The garnet-based ceramic material has an advantage that no reaction occurs even if it is in direct contact with the negative electrode lithium. In particular, the garnet-type ceramic material has a garnet-type or garnet-type similar crystal structure including Li, La, Zr and O. It is preferable because it has excellent sinterability, is easily densified, and has high ionic conductivity. A garnet-type or garnet-like crystal structure of this type of composition is called an LLZ crystal structure, and is referred to as an X-ray diffraction file No. of CSD (Cambridge Structural Database). It has an XRD pattern similar to 422259 (Li ₇ La ₃ Zr ₂ O ₁₂ ). In addition, No. Compared to 422259, the constituent elements are different and the Li concentration in the ceramics may be different, so the diffraction angle and the diffraction intensity ratio may be different. The molar ratio Li / La of Li to La is preferably 2.0 or more and 2.5 or less, and the molar ratio Zr / La to La is preferably 0.5 or more and 0.67 or less. This garnet-type or garnet-like crystal structure may further comprise Nb and / or Ta. That is, by replacing a part of Zr of LLZ with one or both of Nb and Ta, the conductivity can be improved as compared with that before the substitution. The substitution amount (molar ratio) of Zr with Nb and / or Ta is preferably set such that the molar ratio of (Nb + Ta) / La is 0.03 or more and 0.20 or less. The solid electrolyte preferably further contains Al and / or Mg, and these elements may exist in the crystal lattice or may exist in other than the crystal lattice. The addition amount of Al is preferably 0.01 to 1% by mass of the solid electrolyte, and the molar ratio Al / La to La is preferably 0.008 to 0.12. The amount of Mg added is preferably 0.01 to 1% by mass or more, more preferably 0.05 to 0.30% by mass of the solid electrolyte. It is preferable that the molar ratio Mg / La of Mg to La is 0.0016 to 0.07. Such LLZ-based ceramics can be manufactured according to a known technique as described in Patent Documents 2 to 4, or by appropriately modifying it.

  The form of the solid electrolyte of the present invention is preferably in the form of a membrane, plate, or other bulk form in constructing the solid electrolyte-electrode composite, but other forms such as particles, powders, etc. It may be a form and is not particularly limited.

Solid Electrolyte-Electrode Composite and Battery According to one aspect of the present invention, a solid electrolyte-electrode composite provided with the solid electrolyte of the present invention is provided. Moreover, according to another one aspect | mode of this invention, the battery provided with the solid electrolyte-electrode composite_body | complex of this invention and a counter electrode is provided. This battery may have a configuration of an all-solid battery, or may be a liquid battery in which the solid electrolyte is a separator and an electrolyte is further provided between the separator and the counter electrode. A typical example of the former is an all-solid-state lithium ion secondary battery, and a typical example of the latter is a lithium-air battery.

  FIG. 1A shows a schematic cross-sectional view of an example of the solid electrolyte-electrode assembly 10. A solid electrolyte-electrode complex 10 shown in FIG. 1A includes a solid electrolyte 12 of the present invention and an electrode 14 joined to the solid electrolyte 12. The electrode 14 may be either a positive electrode or a negative electrode. Further, as shown in FIG. 1B, a counter electrode 15 may be provided on the opposite side of the electrode 14 of the solid electrolyte 12, and one electrode may be a positive electrode and the other electrode may be a negative electrode. The solid electrolyte 12 is the above-described LLZ-based solid electrolyte of the present invention, and a region where lithium carbonate is not substantially present constitutes at least a part of the interface 13 between the solid electrolyte 12 and the electrode 14. According to this configuration, since a region where lithium carbonate is not substantially present is located at the bonding interface 13 between the solid electrolyte 12 and the electrode 14, the solid electrolyte 12 can be connected to the solid electrolyte 12 without interposing a high resistance layer made of lithium carbonate. A lithium ion conduction path is ensured with the electrode 14. As a result, the lithium ion conductivity improving effect due to the inclusion of C in the crystal lattice can be maximized in the composite or battery including the solid electrolyte. Therefore, it can be said that it is more preferable that the region substantially free of lithium carbonate constitutes the entire interface between the solid electrolyte and the electrode. On the other hand, lithium carbonate may be present on the surface of the solid electrolyte 12 other than the interface 13 with the electrode 14 (for example, the side surface 12a and the back surface 12b of the solid electrolyte 12), and in that case, it is joined to another member. At this time, if necessary, the surface portion where the conductivity is secured may be appropriately cut off.

  As described above, in order to constitute the solid electrolyte-electrode composite, the solid electrolyte 12 and the electrode 14 each have a film shape, a plate shape, or another bulk shape, and the electrode 14 is connected to the solid electrolyte 12. It is preferable to be integrated.

  The electrode 14 may be either a positive electrode or a negative electrode. For example, when it is configured as a lithium ion secondary battery, the electrode 14 is preferably a positive electrode, whereby the solid electrolyte 12 can function as an electrolyte solution substitute to configure an all-solid battery. In the case of constituting a lithium-air battery, the electrode 14 is preferably a negative electrode, so that the solid electrolyte 12 can function as a separator that separates the negative electrode from the electrolytic solution. Below, the aspect of a preferable electrode is demonstrated about each of an all-solid-state lithium ion secondary battery and a lithium air battery.

(1) All-solid lithium ion secondary battery When the solid electrolyte-electrode composite 10 is configured for an all-solid lithium ion secondary battery, the electrode 14 is configured as a positive electrode. Although the form is not specifically limited, It is preferable to comprise as a plate-shaped positive electrode. The plate-like positive electrode is preferably made of a ceramic sintered body containing a positive electrode active material. The positive electrode active material is not particularly limited as long as it can function as an active material in the positive electrode of the all-solid-state energy storage device, but is preferably a lithium-transition metal composite oxide. The positive electrode active material, particularly the lithium-transition metal composite oxide preferably has a layered rock salt structure or a spinel structure, and more preferably has a layered rock salt structure. The layered rock salt structure has a property that the oxidation-reduction potential decreases due to occlusion of lithium ions and the oxidation-reduction potential increases due to elimination of lithium ions, and a composition containing a large amount of Ni is particularly preferable. Here, the layered rock salt structure is a crystal structure in which transition metal layers other than lithium and lithium layers are alternately stacked with an oxygen atom layer interposed therebetween, that is, an ion layer and lithium ions of transition metals other than lithium. Crystal structure in which layers are alternately stacked with oxide ions in between (typically α-NaFeO ₂ type structure: structure in which transition metal and lithium are regularly arranged in the [111] axis direction of cubic rock salt type structure ). Typical examples of the lithium-transition metal composite oxide having a layered rock salt structure include lithium cobaltate, lithium nickelate, lithium manganate, nickel / lithium manganate, nickel / lithium cobaltate, cobalt / nickel / lithium manganate. Cobalt, lithium manganate, etc., and these materials include Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, One or more elements such as Ag, Sn, Sb, Te, Ba, and Bi may be further included.

That is, the lithium-transition metal composite oxide is Li _x M1O ₂ or Li _x (M1, M2) O ₂ (where 0.5 <x <1.10, M1 is a group consisting of Ni, Mn, and Co) At least one transition metal element selected from the group consisting of Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Ag, Sn , Sb, Te, Ba, and Bi, and a composition represented by Li _x M1O ₂ and more preferably a composition in which M1 is Co. Or a composition represented by Li _x (M1, M2) O ₂ , wherein M1 is Ni and Co, and M2 is Al. The proportion of Ni in the total amount of M1 and M2 is preferably 0.6 or more in atomic ratio. Any of such compositions can take a layered rock salt structure. A ceramic having a Li _x (Ni, Co, Al) O ₂ -based composition in which M1 is Ni and Co and M2 is Al may be referred to as NCA ceramics. Particularly preferred NCA ceramics have the general formula: Li _p (Ni _x , Co _y , Al _z ) O ₂ (where 0.9 ≦ p ≦ 1.3, 0.6 <x ≦ 0.9, 0.1 <Y ≦ 0.3, 0 ≦ z ≦ 0.2, x + y + z = 1), and has a layered rock salt structure.

  Typically, the positive electrode active material is a polycrystal composed of a plurality of crystal particles, and the plurality of crystal particles are preferably oriented. This orientation is preferably oriented so that the (003) plane of the layered rock salt structure intersects the plate surface (principal surface) of the plate-like positive electrode, more preferably a plane other than (003) ( For example, the (104) plane) is preferably oriented parallel to the plate surface of the plate-like positive electrode. This facilitates insertion / removal of ions such as lithium ions, and improves the rate characteristics when a power storage element is configured. The degree of orientation in such a plate-like positive electrode is the ratio of the diffraction intensity (peak intensity) by the (003) plane to the diffraction intensity by the (003) plane in the X-ray diffraction from the plate surface of the plate-like positive electrode [003] / [ 104], and a preferable [003] / [104] ratio is 2 or less, more preferably 1 or less, and further preferably 0.5 or less. Note that such a low [003] / [104] ratio means that the ratio of the appearance of the (003) plane parallel to the plate surface in the plate surface or inside of the plate-like positive electrode is reduced.

  The plate-like positive electrode is made of a ceramic sintered body containing a positive electrode active material. This ceramic sintered body may contain optional components such as a conductive additive and a binder in addition to the positive electrode active material, but it is also possible to have a configuration substantially free of such optional components. . For example, in the case of using a positive electrode active material in which crystal particles are oriented, ion mobility can be improved without using a conductive aid or the like, so that the active material filling rate can be maximized. . Accordingly, the plate-like positive electrode preferably consists essentially of only the positive electrode active material, and more preferably consists only of the positive electrode active material.

The plate-like positive electrode and the positive electrode active material constituting the plate-like positive electrode preferably have pores. The presence of pores in the plate-like positive electrode can relieve stress that may be caused by expansion or contraction associated with insertion / extraction of lithium ions due to charge / discharge. Moreover, (8.0 × ¹⁰ -6 in LCO ceramics example described later, in the LLZ ceramic 4.0 × ^{10 -6)} difference in thermal expansion coefficient caused during bonding suppressing generation of cracks and cracks due to. As a result, it is possible to effectively prevent peeling at the interface that may occur when the dense plates are joined together. The positive electrode active material preferably has a porosity of 3 to 30%, more preferably 5 to 25%, and still more preferably 10 to 20%. The voidage is a volume ratio of pores (including open pores and closed pores) in the plate-like positive electrode, and is sometimes referred to as porosity, and the bulk density and true density of the plate-like positive electrode It can be calculated from

The positive electrode active material having such pores may be manufactured from positive electrode active material precursor particles prepared in advance. The positive electrode active material precursor particles are preferably precursor particles that can become a positive electrode active material containing a lithium-transition metal composite oxide having a layered rock salt structure by introducing lithium. Particularly preferred positive electrode active material precursor particles are formed in a substantially spherical shape, and a large number of voids are substantially uniformly provided therein, the average particle diameter D50 (volume basis) is 0.5 to 5 μm, and the specific surface area is 3 ~25m a ² / g, relative tap density is a value obtained by dividing the tap density by the theoretical density of 0.25 to 0.4. When such conditions are satisfied, when the positive electrode active material is generated through the subsequent molding step and firing step (lithium introduction step), the firing environment is stabilized and the lithium introduction (diffusion) state is made uniform, Thereby, the internal fine structure is made as uniform as possible. In addition, the shape stability and crystallographic synthesis degree of the positive electrode active material that is the final object are improved.

  Preferably, the positive electrode active material includes (a) a granulated body containing a large number of plate-like particles of transition metal hydroxide constituting the main raw material of the lithium composite oxide and having a large number of voids provided therein substantially uniformly. A granulating step, and (b) a heat treatment step of forming the positive electrode active material precursor particles by heat-treating the granulated body, and (c) forming a large number of positive electrode active material precursor particles into a predetermined shape. Thus, the molded body is produced by a method having a molding step, and (d) a firing step of firing the compact to produce a lithium composite oxide. The granulation step (a) is preferably a step of forming a granulated body by spray drying a slurry prepared by mixing raw material powder containing a transition metal hydroxide while being pulverized wet. In particular, four-fluid nozzle type spray drying can be used preferably. The raw material powder may contain nickel and cobalt hydroxides as transition metal hydroxides. The raw material powder may contain a metal compound other than a transition metal such as an aluminum oxide hydrate or an aluminum hydroxide. The lithium compound can be added at the time of molding or before firing after molding. That is, for example, the lithium compound can be added to the molding slurry described above together with the positive electrode active material precursor particles during molding. Alternatively, a compact that does not contain a lithium compound is temporarily calcined (molded calcined), and then a mixture of the calcined compact and the lithium compound is calcined (main calcining) in two stages (lithium Step) may be performed.

  The dimension of the plate-shaped positive electrode is not particularly limited, but the thickness is preferably 0.1 to 300 μm, more preferably 10 to 200 μm, and still more preferably 50 to 100 μm, from the viewpoint of the active material capacity per unit area. The size of the surface is preferably 0.2 mm × 0.2 mm to 100 mm × 100 mm, more preferably 5 mm × 5 mm to 30 mm × 30 mm, from the viewpoint of suppressing warpage in the plate surface and ease of electrode production.

  According to a preferred aspect of the present invention, a plurality of plate-like positive electrodes are prepared, and the plurality of plate-like positive electrodes are arranged in a tile shape on the plate-like solid electrolyte. Accordingly, there is an advantage that the active material can be filled in the electrode with higher density.

  The plate-like positive electrode may be provided with a negative electrode through a solid electrolyte. For example, as described above, the solid electrolyte-electrode composite 10 ′ shown in FIG. 1B may be used. The negative electrode material is not particularly limited as long as it can function as an active material in the negative electrode, and metals, alloys, metal oxides, metal sulfides, metal nitrides, carbon materials, and the like can be used. Examples of the metal material include metal lithium, metal that can form an alloy with lithium (In, Sn, Si, Al, Ge, Sb, P), and derivatives thereof. Examples of the alloy material include lithium alloys (LiM, where M is at least one of In, Sn, Si, Al, Ge, Sb, and P) and derivatives thereof. Examples of the carbon material include graphite, soft carbon, hard carbon, carbon nanotube, graphene, and derivatives thereof. A composite of carbon and lithium can also be used. The current collector may be a film or foil formed of gold, silver, copper, aluminum, titanium, nickel, stainless steel, carbon or the like, and is formed by, for example, a sputtering method. Further, other configurations such as a laminating method and an exterior may be appropriately selected from known configurations and are not particularly limited.

(2) Lithium-air battery When the solid electrolyte-electrode composite 10 is configured for a lithium-air battery, the electrode 14 is configured as a negative electrode. The negative electrode includes lithium, and is not particularly limited as long as lithium is oxidized into lithium ions at the negative electrode at the time of discharge, and may include metal lithium, a lithium alloy, a lithium compound, and the like. Lithium is excellent as a negative electrode material in that it has a higher theoretical capacity than other metal elements, while dendrite may grow during charging. However, the solid electrolyte separator can prevent the dendrite from penetrating and avoid a short circuit between the positive and negative electrodes. Preferred examples of the material constituting the negative electrode include metallic lithium, lithium alloy, lithium compound and the like, and examples of the lithium alloy include lithium aluminum, lithium silicon, lithium indium, lithium tin and the like. Examples include lithium nitride and lithium carbon, but metallic lithium is more preferable from the viewpoint of large capacity and cycle stability. The negative electrode may be provided with a negative electrode current collector. Preferable examples of the negative electrode current collector include metal plates such as stainless steel, copper, nickel, platinum, and noble metals, metal mesh, carbon paper, and oxide conductors. In addition, what is necessary is just to employ | adopt well-known structures suitably as other structures, such as an air electrode (positive electrode) and electrolyte solution, and is not specifically limited.

Production Method A preferred method for producing a solid electrolyte-electrode composite using the lithium ion conductive solid electrolyte of the present invention will be described below. This manufacturing method includes a solid electrolyte preparation step, an electrode bonding step, and an aging step. The solid electrolyte preparation step is a step of preparing a lithium ion conductive solid electrolyte having a garnet-type or garnet-like crystal structure (hereinafter referred to as LLZ-based crystal structure) composed of at least Li, La, Zr, and O. In the atmosphere, CO ₂ and H ₂ O are not substantially coexisting. The electrode joining step is a step of obtaining a solid electrolyte-electrode composite by joining a solid electrolyte to an electrode, and is performed in an atmosphere in which CO ₂ and H ₂ O are not substantially coexisting. In the aging step, before or after the electrode bonding step, the solid electrolyte or the solid electrolyte-electrode complex is exposed to a CO ₂ -containing atmosphere and subjected to an aging treatment, whereby C derived from CO ₂ is crystal lattice of the solid electrolyte. It is the process of making it contain in. Thus, in the production method of the present invention, the solid electrolyte preparation step and the electrode joining step are performed in an atmosphere in which CO ₂ and H ₂ O are substantially not coexisting, while the aging step is coexisting with H ₂ O. It is carried out in a CO ₂ -containing atmosphere which may be present. Thereby, an LLZ-based solid electrolyte-electrode composite with significantly improved lithium ion conductivity can be produced.

(1) Preparation Step of Solid Electrolyte The method of the present invention is a garnet-type or garnet-type similar crystal composed of at least Li, La, Zr and O in an atmosphere in which CO ₂ and H ₂ O are not substantially coexisting. Providing a lithium ion conductive solid electrolyte having a structure. Such a lithium ion conductive solid electrolyte can be prepared according to a known technique, but in an atmosphere in which CO ₂ and H ₂ O are not substantially coexisting to avoid precipitation of lithium carbonate that results in a high resistance layer. It is desired to make it through. Atmosphere CO ₂ and H _{2 O} does not substantially co-exist, preferably a atmosphere of inert gas such as Ar, one of CO ₂ and H _{2 O} may be present. By preparing the LLZ-based solid electrolyte in such an atmosphere, it is possible to prevent the precipitation of lithium carbonate that results in a high resistance layer. In the case where the LLZ solid electrolyte may contain CO ₂ and H ₂ O due to contact of the raw material powder with the atmosphere, etc., CO ₂ and H ₂ O are substantially coexistent. It is preferable that the heat treatment is performed under an atmosphere (preferably an inert gas atmosphere such as Ar), thereby removing CO ₂ and H ₂ O that may be contained in the solid electrolyte. Such heat treatment is preferably performed at a temperature of 650 ° C. or higher, more preferably 680 ° C. or higher, more preferably 800 ° C. or higher, preferably 10 minutes or longer, more preferably 1 hour or longer.

  The form of the solid electrolyte before joining to the electrode may be any form of particulate, powder, film, plate, or other bulk form. For example, when the subsequent electrode bonding step is performed by an aerosol deposition (AD) method, it is preferably in the form of an LLZ-based raw material powder for the AD method. On the other hand, when the subsequent electrode bonding step is performed by bonding such as hot pressing, it is preferably in the form of an LLZ-based sintered body, more preferably in the form of a plate.

The solid electrolyte thus prepared is subjected to the subsequent (2) electrode bonding step or (3) aging step. It is preferable that the transition to these subsequent steps, particularly the electrode bonding step in which an atmosphere in which CO ₂ and H ₂ O are not substantially coexisting is used, is performed without coexistence of CO ₂ and H ₂ O. However, there may be a point in time when the process passes through an atmosphere in which CO ₂ and H ₂ O coexist or is temporarily left in such an atmosphere, and lithium carbonate is not substantially precipitated or Even if it deposits, it is acceptable if it is at a level that is not harmful from the viewpoint of conductivity (if it is at a level that is harmful, if a region that is substantially free of lithium carbonate is secured by scraping the surface exposed to the atmosphere) Good).

(2) Electrode Joining Step The method of the present invention includes a step of obtaining a solid electrolyte-electrode composite by joining a solid electrolyte to an electrode in an atmosphere in which CO ₂ and H ₂ O are not substantially coexisting. The method of joining the solid electrolyte to the electrode is not particularly limited as long as a desired solid electrolyte-electrode composite is finally obtained, and various particle jet coating methods, solid phase methods, solution methods, and gas phase methods may be used. it can. Examples of the particle jet coating method include an aerosol deposition (AD) method, a gas deposition (GD) method, a powder jet deposition (PJD) method, a cold spray (CS) method, and a thermal spraying method. Examples of the solution method include hydrothermal synthesis method, sol-gel method, precipitation method, microemulsion method, solvent evaporation method and the like. In addition, microcrystals synthesized using these methods may be deposited on the positive electrode or may be directly deposited on the positive electrode. Examples of the gas phase method include laser deposition (PLD) method, sputtering method, evaporation condensation (PVD) method, gas phase reaction method (CVD) method, vacuum deposition method, molecular beam epitaxy (MBE) method and the like. In addition, a sintered body (preferably a plate-like sintered body) and a solid electrolyte (preferably a plate-like solid electrolyte) are prepared in advance and bonded by a known method such as a hot press method or a direct bonding (direct bonding) method. May be. In any case, it is desirable that the solid electrolyte and the electrode be joined in an atmosphere in which CO ₂ and H ₂ O are not substantially coexisting so as to avoid the precipitation of lithium carbonate resulting in a high resistance layer. Atmosphere CO ₂ and H _{2 O} does not substantially co-exist, preferably a atmosphere of inert gas such as Ar, one of CO ₂ and H _{2 O} may be present. By bonding the solid electrolyte to the electrode in such an atmosphere, it is possible to prevent the precipitation of lithium carbonate that results in a high resistance layer. As a result, the solid electrolyte and the electrode can be joined at the interface without the presence of lithium carbonate, and thereby the lithium ion conductivity improved by the inclusion of C in the crystal lattice is inhibited by the high resistance layer. It can be suppressed or prevented.

  The electrode may be either a positive electrode or a negative electrode. For example, in the case of constituting as a lithium ion secondary battery, the electrode is preferably a positive electrode, whereby the solid electrolyte 12 can be made to function as an electrolyte substitute to constitute an all-solid battery. In the case of a lithium-air battery, the electrode is preferably a negative electrode, so that the solid electrolyte can function as a separator that separates the negative electrode from the electrolyte.

When the plate-like positive electrode and the plate-like solid electrolyte are both ceramic sintered bodies, the plate-like positive electrode and the plate-like solid electrolyte are laminated, and this laminate is heated and pressurized at the same time and integrated by solid phase reaction. It is preferable to do so. The bonding between the sintered ceramics does not require the sintering of powders as required for the lamination of green sheets, thus suppressing the generation of a high-resistance reaction layer that can occur between highly active dissimilar powders. be able to. In addition, the firing temperature can be lowered by simultaneous heating and pressurization as compared with the case of joining by heating alone. Thereby, the production | generation of the highly resistant reaction layer which can be formed in the temperature range with a high sintering temperature can be suppressed. Moreover, the adhesiveness of the joint interface of the composite obtained by simultaneous heating and pressurization is surprisingly high. Thus, according to the method of the present invention, it is possible to bond at a relatively low temperature to suppress the formation of a high-resistance reaction layer at the interface, and to improve the adhesion between the plate-like positive electrode and the plate-like solid electrolyte at the interface. It can be increased to maximize the bonding area. It is preferable that the heating and pressurization are performed at the same time, as long as it includes a stage of pressurization while heating, and the timing of heating and pressurization may be shifted. Examples of methods for performing heating and pressurization simultaneously include hot press method (HP), hot isostatic press method (HIP), and discharge plasma sintering method (SPS). Is preferable because the hot pressing method (HP) is preferable. Heating is preferably performed at a temperature of 600 to 800 ° C, more preferably 650 to 750 ° C, and even more preferably 675 to 725 ° C. Pressurization is preferably carried out at a pressure of 5~3000kgf / cm ^2, more preferably 500~2500kgf / cm ^2, more preferably 1000~2000kgf / cm ^2. Moreover, it is preferable that the time to reach the target pressure is 0.1 to 10 hours, more preferably 1 to 7 hours, and further preferably 3 to 5 hours. Furthermore, it is preferable that the timing of the pressurization start is after the end of the temperature raising process in the firing profile. Heating and pressing are preferably performed for 0.05 to 10 hours, more preferably 1 to 8 hours, and further preferably 2 to 5 hours. Within such a range, the generation of a high-resistance reaction layer at the interface can be more reliably suppressed, and the adhesion between the plate-like positive electrode and the plate-like solid electrolyte at the interface can be further enhanced. Such joining by heating and pressurization is performed in an atmosphere in which CO ₂ and H ₂ O are not substantially coexisting.

(3) aging step method of the present invention, a solid electrolyte or a solid electrolyte - comprising the step of aging treatment exposing electrode assembly into a CO ₂ containing atmosphere. This aging treatment may be performed after the electrode bonding step or may be performed before the electrode bonding step. By aging treatment, C derived from CO ₂ can be contained in the crystal lattice of the solid electrolyte, and thereby lithium ion conductivity can be improved. The aging treatment is preferably performed at a temperature of 600 ° C. or less, more preferably 0 to 500 ° C., further preferably 0 to 400 ° C., preferably 5 hours or more, more preferably 10 hours or more, and still more preferably. It is performed for 50 hours or more.

  Conditions for the aging treatment are appropriately determined so that at least a part of the LLZ-based crystal structure includes C in the crystal lattice, and preferably includes C in the crystal lattice over most or almost the entire crystal structure. do it. The content of C in the crystal lattice is determined by measuring the amount of shift of the (422) plane peak position and / or the increase of the a-axis lattice constant in X-ray diffraction using the solid electrolyte before aging treatment as a reference. Can be confirmed. That is, the solid electrolyte after the aging treatment has a peak of the (422) plane in X-ray diffraction on the low angle side, preferably 0 <2θ <1 °, more preferably 0. 0, compared with the solid electrolyte before the aging treatment. It has a crystal structure shifted by 1 <2θ <1 °. Further, the solid electrolyte after the aging treatment has a crystal structure in which the lattice constant of the a-axis is preferably increased by 0.01 or more, more preferably by 0.05 or more compared with the solid electrolyte before the aging treatment.

CO ₂ containing atmosphere is not particularly limited as long as the atmosphere containing CO _2, can be preferably utilized atmospheric air is most conveniently available from CO ₂ containing atmosphere. When it is desired to avoid deposition of lithium carbonate on the surface of the solid electrolyte (for example, when an aging treatment is performed before the electrode bonding step), the CO ₂ -containing atmosphere is preferably a dry atmosphere, more preferably An atmosphere having a relative humidity of 1% or less, more preferably substantially free of H ₂ O.

The CO ₂ -containing atmosphere may contain H ₂ O. This is because, in the case of a solid electrolyte with electrodes already joined, significantly improved lithium ion conductivity is ensured between the solid electrolyte and the electrodes without the presence of lithium carbonate at the joint interface. is there. However, even if the aging treatment is performed before the electrode bonding step, the CO ₂ -containing atmosphere may contain H ₂ O, and in that case, the surface of the solid electrolyte exposed to the CO ₂ -containing atmosphere It is preferable to further perform a step of scraping at least a portion to be joined to the electrode. This is because when the CO ₂ -containing atmosphere contains H ₂ O, lithium carbonate that provides a high resistance layer is deposited on the surface of the solid electrolyte. The method for scraping the surface of the solid electrolyte is not particularly limited as long as the surface layer can be removed by, for example, mechanical polishing or cutting, dissolution cleaning with a solution of water, acid, alkali, or the like, ion milling, sputtering, or the like. Among these, mechanical polishing and cutting are preferable because the process is simple and side reactions are unlikely to occur. Further, the treatment by sputtering is preferable in that damage such as a decrease in crystallinity of the base material and a composition shift can be suppressed. Moreover, you may perform these processes, heating.

The present invention is more specifically described by the following examples. Note that the Ar atmosphere used in the following examples is an inert atmosphere substantially free of CO ₂ and H ₂ O.

Example A1 : Preparation and Evaluation of Solid Electrolyte AD Film (1) Synthesis and Heat Treatment of AD Film Raw Material Powder Lithium hydroxide (Kanto Chemical Co., Inc.), lanthanum hydroxide (Shin-Etsu Chemical) as raw material components for preparing the raw material for firing Industrial Co., Ltd.), zirconium oxide (Tosoh Corporation), and tantalum oxide were prepared. These powders are weighed and blended so as to be LiOH: La (OH) ₃ : ZrO ₂ : Ta ₂ O ₅ = 7: 3: 1.625: 0.1875, and mixed by a laika machine to be a raw material for firing. Got.

  As the first firing step, the firing raw material was placed in an alumina crucible, heated at 600 ° C./hour in the air atmosphere, and held at 900 ° C. for 6 hours.

As a second firing step, γ-Al ₂ O ₃ is added to the powder obtained in the first firing step so as to have a concentration of 0.6% by mass, and this powder and cobblestone are mixed to form a vibration mill. And pulverized for 3 hours to obtain a powder having a starting material composition of Li _7.0 La _3.0 Zr _1.625 Ta _0.375 O ₁₂ Al _0.1 . The amount of γ-Al ₂ O ₃ added is such that the compositional formula Li _7.0 La _3.0 Zr _1.625 Ta _0.375 assumes that the primary calcined powder has a composition as charged. This corresponds to an amount of 0.1 Al in molar ratio to O ₁₂ . The obtained raw material powder was put in a magnesia sheath and heat-treated at 800 ° C. for 1 hour in an Ar atmosphere to remove CO ₂ and H ₂ O that can be contained in the raw material powder. In the raw material powder thus obtained, although Li and O may deviate from 7 and 12, which are the number of moles of the charged composition, due to defects during firing, etc., the charged composition of Li _7.0 La _3.0 Zr _It has a composition generally based on _1.625 Ta _0.375 O ₁₂ Al _0.1 and does not contain lithium carbonate.

(2) Production of Solid Electrolyte AD Film After the heat-treated raw material powder was crushed using a nylon mesh with an opening diameter of 75 μm in a glove box in an Ar atmosphere, aerosol deposition was performed using N ₂ gas as a carrier gas ( Film formation was performed by the AD) method. This AD film formation was performed using a film formation apparatus 20 as shown in FIG. A film forming apparatus 20 shown in FIG. 2 is configured as an apparatus used for the AD method in which a raw material powder is injected onto a substrate in an atmosphere at a pressure lower than atmospheric pressure. The film forming apparatus 20 includes an aerosol generating unit 22 that generates an aerosol of a raw material powder containing a raw material component, and a film forming unit 30 that sprays the raw material powder onto a substrate 21 to form a film containing the raw material component. . The aerosol generation unit 22 contains a raw material powder, receives an supply of a carrier gas from a gas cylinder (not shown), generates an aerosol, a raw material supply pipe 24 that supplies the generated aerosol to the film forming unit 30, and An aerosol generation chamber 23 and a vibrator 25 that applies vibration to the aerosol in the aerosol generation chamber 23 at a frequency of 10 to 100 Hz are provided. The film forming unit 30 includes a film forming chamber 32 that injects aerosol onto the substrate 21, a substrate holder 34 that is disposed inside the film forming chamber 32 and fixes the substrate 21, and the substrate holder 34 in the X axis-Y axis direction. And an XY stage 33 that moves. The film forming unit 30 includes a spray nozzle 36 that has a slit 37 formed at the tip thereof and sprays aerosol onto the substrate 21, and a vacuum pump 38 that decompresses the film forming chamber 32. The film forming apparatus 20 may be configured to heat the raw material powder by providing a heating device, a heat-resistant member, or the like in the film forming chamber 32. For example, a heat-resistant member such as quartz glass or ceramics may be used so that heat treatment can be performed at a temperature at which the raw material powder is single-crystallized.

  The production conditions of the solid electrolyte membrane by the film forming apparatus 20 were as follows. As the substrate, a 20 mm square MgO plate having a thickness of 1 mm was used. Further, nitrogen gas having a flow rate of 2 L / min is used as a carrier gas, and the pressure in the film forming chamber is adjusted to 0.1 to 0.2 kPa and the pressure in the aerosol chamber is adjusted to 50 to 70 kPa to form a film. Went. At that time, the opening size of the nozzle was set to 10 mm × 1.8 mm, and scanning was performed simultaneously with the film formation for 60 reciprocations at a scanning distance of 10 mm and a scanning speed of 5 mm / sec in the short side direction of the nozzle. Thus, a solid electrolyte AD film was obtained.

(3) Production of Evaluation Electrode As shown in FIG. 3, a carbon paste 44 (made by JEOL Ltd., Dotite Paste) was formed on the surface of the solid electrolyte AD film 42 formed on the MgO substrate 40 in an Ar atmosphere glove box. XC-12) was applied to form a carbon electrode for ion conductivity evaluation.

(4) Exposure to the atmosphere The solid electrolyte AD film thus formed with the electrodes was exposed to the atmosphere. This exposure was performed at room temperature for 16 hours, 58 hours, and 171 hours in order to confirm the effect of exposure time to the atmosphere, and after each time, characteristic evaluation and analysis were performed.

(5) XRD Measurement Using an XRD apparatus (manufactured by Rigaku Corporation, Geiger Flex RAD-IB), XRD measurement was performed on the AD film before and after exposure to the atmosphere. For comparison, the AD film before being exposed to the atmosphere was also measured in the same manner as described above. As a result, the (422) plane peak shown in FIG. 4 was observed. As shown in FIG. 4, it was confirmed that the peak before exposure to the atmosphere shifted 0.1 <2θ <1 to the low angle side after exposure to the atmosphere. From this result, it is understood that C is introduced into the lattice by being left in the atmosphere and the lattice constant is expanded. Indeed, where on the basis of the difference between (422) plane peak position after air exposure before exposure to the atmosphere (422) plane peak position and the 5 8 hours was calculated the increase of the lattice constant of a-axis, 0. It was 08cm.

(6) Evaluation of ion conductivity Li ion conductivity of solid electrolyte AD membrane exposed to the atmosphere was measured at temperatures of 100 ° C, 150 ° C and 200 ° C by an AC impedance method using a 4-terminal method in an Ar atmosphere glove box. evaluated. Specifically, Au sputtering was performed on the AD film, further vacuum-dried at 110 ° C. or more for 5 hours or more, and introduced into a glove box in an Ar atmosphere as it was, and incorporated in a CR2032 coin cell. The coin cell was taken out into the atmosphere, and AC impedance measurement was performed at a frequency of 1 MHz to 0.1 Hz and a voltage of 10 mV using an electrochemical measurement system (potentiometer / galvano stud, frequency response analyzer) manufactured by Solartron. For comparison, the AD film before being exposed to the atmosphere was also measured in the same manner as described above. As a result, the ionic conductivity shown in FIG. 5 was measured. For reference, FIG. 5 also shows the ionic conductivity of a sample of the sintered body having the same composition as the AD film that is not exposed to the atmosphere. As shown in FIG. 5, it was confirmed that the intragranular conductivity was improved at each measurement temperature as compared with that before exposure to the atmosphere.

Example A2 : Preparation and Evaluation of Solid Electrolyte AD Membrane / Positive Electrode Composite (1) Preparation of Positive Electrode Active Material Plate (1A) Slurry Preparation Co ₃ O ₄ Powder (Particle Size 1-5 μm, D50 = 1.2, Justo Chemical) Manufactured by Kogyo Co., Ltd.), 100 parts by weight of a dispersion medium (toluene: isopropanol = 1: 1), 10 parts by weight of a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), and a plasticizer (DOP: 4 parts by weight of di (2-ethylhexyl) phthalate, manufactured by Kurokin Kasei Co., Ltd., and 2 parts by weight of a dispersant (Leodol SP-O30, manufactured by Kao Corporation) were mixed. The mixture was defoamed by stirring under reduced pressure and adjusted to a viscosity of 500 to 700 cP. The viscosity was measured with an LVT viscometer manufactured by Brookfield.

(1D) Molding Using the obtained molding slurry, a sheet having a thickness of 50 μm was formed by a doctor blade method. By punching the dried sheet, an 11 mm square green sheet molded body was obtained.

(1E) Firing (Lithium introduction)
The green body molded body of 10 mm square obtained as described above was heat-treated at 1000 ° C. in an air atmosphere, whereby the molded body was degreased and temporarily fired. A composition obtained by spraying a predetermined amount of an ethanol dispersion of lithium hydroxide with an airbrush onto both surfaces of the obtained calcined molded body is heat-treated at 750 ° C. for 24 hours (atmosphere), thereby having a composition of LiCoO _2. A positive electrode active material plate having a thickness of 10 mm and a thickness of 50 μm was obtained.

The above-mentioned lithium hydroxide ethanol dispersion was prepared as follows. First, LiOH.H ₂ O powder (manufactured by Wako Pure Chemical Industries, Ltd.) was pulverized using a jet mill so as to have a visual particle diameter of 1 to 5 μm by observation with an electron microscope. What added this powder in the ratio of 1 weight part with respect to 100 weight part of ethanol (made by Katayama Chemical Co., Ltd.) was disperse | distributed until it became impossible to confirm powder visually by an ultrasonic wave.

(2) Synthesis of AD film raw material powder and heat treatment In the same manner as in Example A1, AD film raw material powder from which CO ₂ and H ₂ O were removed was obtained.

(3) Production of Solid Electrolyte AD Film A solid electrolyte AD film was produced in the same manner as in Example A1, except that the positive electrode active material plate obtained above was used instead of the MgO plate as the film formation substrate. It was.

(4) Preparation of electrode for evaluation Carbon paste (JEOL Co., Ltd. Dotite Paste XC-12) in an Ar atmosphere glove box on the upper surface of the solid electrolyte AD film formed on the active material plate and the back surface of the active material plate The carbon electrode for ion conductivity evaluation was formed by coating.

(5) Exposure to the atmosphere The solid electrolyte AD film thus formed with the electrodes was exposed to the atmosphere. This exposure was conducted at room temperature for 171 hours.

(6) Evaluation of ion conductivity Li ion conductivity was evaluated by an alternating current impedance method using a pseudo 4-terminal (2-terminal) method in an Ar atmosphere glove box for an AD film exposed to the atmosphere. The details of the evaluation method were the same as in Example A1, except that the pseudo 4-terminal (2-terminal) method was used instead of the 4-terminal method. As a result, as in Example A1, it was found that the intragranular conductivity was improved as compared with that before the treatment.

Example B1 : Production and Evaluation of Solid Electrolyte Sintered Body (1) Production of Solid Electrolyte Sintered Body As raw material components for preparing a raw material for firing, lithium hydroxide (Kanto Chemical Co., Ltd.), lanthanum hydroxide (Shin-Etsu Chemical) Industrial Co., Ltd.), zirconium oxide (Tosoh Corporation), and tantalum oxide were prepared. These powders are weighed and blended so as to be LiOH: La (OH) ₃ : ZrO ₂ : Ta ₂ O ₅ = 7: 3: 1.625: 0.1875, and mixed by a laika machine to be a raw material for firing. Got.

  As the first firing step, the firing raw material was placed in an alumina crucible, heated at 600 ° C./hour in the air atmosphere, and held at 900 ° C. for 6 hours.

As a second firing step, γ-Al ₂ O ₃ is added to the powder obtained in the first firing step so as to have a concentration of 0.6% by mass, and this powder and cobblestone are mixed to form a vibration mill. And pulverized for 3 hours to obtain a pulverized powder having a composition of Li _7.0 La _3.0 Zr _1.625 Ta _0.375 O ₁₂ Al _0.1 . The amount of γ-Al ₂ O ₃ added is such that the compositional formula Li _7.0 La _3.0 Zr _1.625 Ta _0.375 assumes that the primary calcined powder has a composition as charged. This corresponds to an amount of 0.1 Al in molar ratio to O ₁₂ . After pulverizing this pulverized powder, the obtained powder was press-molded at about 100 MPa using a mold into pellets. The obtained pellets were placed on a magnesia setter, put together with the setter in a magnesia sheath, heated at 200 ° C./hour in an Ar atmosphere, and held at 1000 ° C. for 36 hours to obtain a 55 mm × 55 mm A sintered body having a size of 10 mm was obtained, and a rod-shaped solid electrolyte sintered body having a size of 3 mm × 4 mm and a length of 40 mm was obtained therefrom by machining. As the Ar atmosphere, the inside of the furnace having a capacity of about 3 L was evacuated in advance, and then Ar gas having a purity of 99.99% or more was flowed into the electric furnace at 2 L / min. In the sintered body thus obtained, although Li and O may deviate from 7 and 12, which are the moles of the feed composition, due to defects at the time of firing, the charge composition of Li _7.0 La _3.0 It has a generally based composition _{Zr 1.625 Ta 0.375 O 12 Al 0.1} , contains no lithium carbonate.

(2) Production of electrode for evaluation As shown in FIG. 6, a carbon paste (Dotite Paste XC-12, manufactured by JEOL Ltd.) was applied in an Ar atmosphere glove box, and a carbon electrode for ion conductivity evaluation was applied. It was fabricated and formed as a voltage measurement terminal.

(3) Exposure to the atmosphere
The solid electrolyte sintered body with the electrodes thus formed was exposed to the atmosphere. This exposure was carried out at 200 ° C. for 24 hours.

(4) Evaluation of ion conductivity For solid-state electrolyte sintered body exposed to the atmosphere, metal lithium foil is adhered to both ends in the longitudinal direction of the produced rod-shaped solid electrolyte sintered body in an Ar atmosphere glove box for current conduction Li ion conductivity was evaluated by an AC impedance method using a four-terminal method as a terminal. The measurement was carried out using an electrochemical measurement system (potenti / galvano stud, frequency response analyzer) manufactured by Solartron, and AC impedance was measured at a frequency of 1 MHz to 0.1 Hz and a voltage of 10 mV. For comparison, the sintered plate before being exposed to the atmosphere was also measured in the same manner as described above. As a result, the ionic conductivity shown in FIG. 7 was measured. As shown in the figure, the measurement temperature was measured in the range of room temperature to 200 ° C., and it was confirmed that the intragranular conductivity was improved as compared with that before exposure to the atmosphere.

Example B2 : Production and Evaluation of Solid Electrolyte Sintered Body / Positive Electrode Composite (1) Production of Solid Electrolyte Sintered Body A solid electrolyte sintered body was obtained in the same manner as in Example B1.

(2) Production of positive electrode active material plate A positive electrode active material plate having a composition of LiCoO ₂ and a thickness of 1 mm and a thickness of 1 mm was obtained in the same manner as in Example A2 except that the size of the positive electrode active material plate was changed.

(3) Positive electrode formation The obtained solid electrolyte sintered body and the obtained positive electrode active material plate were joined using a hot press. Specifically, nine 1 mm square positive electrode active material plates having a thickness of 50 μm were arranged in three rows and three columns on a solid electrolyte plate having a thickness of 1 mm processed to 10 mm square. A solid electrolyte sintered body / positive electrode composite is obtained by sandwiching the upper and lower surfaces of this arrayed body with Pt foils for preventing adhesion to a firing jig and firing at 700 ° C. for 5 hours by hot pressing at a pressure of 2000 kgf / cm ^2. Got.

(4) Production of electrode for evaluation A carbon paste (Denite Paste XC-12, manufactured by JEOL Ltd.) was applied to each surface of the joined positive electrode active material and solid electrolyte in an Ar atmosphere glove box, and the ionic conductivity. A carbon electrode for evaluation was formed.

(5) Exposure to the atmosphere
The solid electrolyte sintered body with the electrodes thus formed was exposed to the atmosphere. This exposure was carried out at room temperature for 50 hours.

(6) XRD evaluation Using an XRD apparatus (manufactured by Rigaku Corporation, Geiger Flex RAD-IB), XRD measurement was performed on the solid electrolyte sintered body before and after exposure to the atmosphere. The lattice constant increased in the XRD measurement result by leaving in the atmosphere.

(7) Evaluation of ion conductivity The film exposed to the atmosphere was evaluated for Li ion conductivity by an AC impedance method using a pseudo 4-terminal (2-terminal) method in an Ar atmosphere glove box. The details of the evaluation method were the same as in Example B1, except that the pseudo 4-terminal (2-terminal) method was used instead of the 4-terminal method. As a result, as in Example B1, it was found that the intragranular conductivity was improved more than before the treatment.

Example B3 : Example of performing aging treatment in the coexistence of CO ₂ and H ₂ O In Example B1, exposure of the solid electrolyte sintered body to the atmosphere (ie, aging treatment) was performed from production of an electrode for evaluation (ie, bonding step) even before the CO ₂ and H _{2 O} were carried out in the coexistence, and No. 1200 of the surface to be contacted with the solid electrolyte of the electrode exposed to the atmosphere (CO ₂ containing atmosphere) in an Ar atmosphere glove box A solid electrolyte sintered body / positive electrode composite was produced in the same manner as in Example B1, except that it was scraped off using SiC abrasive paper. At that time, when the thickness before and after polishing was measured using a micrometer, it was confirmed that the thickness of the solid electrolyte layer was reduced by about 20 μm.

DESCRIPTION OF SYMBOLS 10 Solid electrolyte-electrode complex 12 Solid electrolyte 13 Joint interface 14 Electrode 15 Counter electrode

Claims (23)

A lithium ion conductive solid electrolyte having a garnet-type or garnet-like crystal structure composed of at least Li, La, Zr, and O, wherein at least part of the crystal structure includes C in the crystal lattice. there are, further comprising a solid electrolyte and Mg, the surface of the solid electrolyte, have a region in which lithium carbonate is substantially absent,
Lithium having a crystal structure with an a-axis lattice constant increased by 0.08% or more compared to a solid electrolyte having a composition similar to that of the solid electrolyte except that the solid electrolyte does not contain C in the crystal lattice Ion conductive solid electrolyte.   The solid electrolyte according to claim 1, which has a form of a film, a plate, or other bulk.   The solid electrolyte according to claim 1, wherein the solid electrolyte has at least two regions substantially free of lithium carbonate.   The solid electrolyte as described in any one of Claims 1-3 whose area | region where the said lithium carbonate does not substantially exist is the whole surface of the said solid electrolyte.   Compared with a solid electrolyte having the same composition as the solid electrolyte except that the solid electrolyte does not contain C in the crystal lattice, the peak of the (422) plane in X-ray diffraction is 0 <2θ on the low angle side. The solid electrolyte according to any one of claims 1 to 4, which has a crystal structure shifted by <1 °. The solid electrolyte according to any one of claims 1 to 5 , wherein a molar ratio Li / La of La to La is 2.0 to 2.5. The solid electrolyte according to any one of claims 1 to 6 , wherein a molar ratio Zr / La of Zr to La is 0.5 to 0.67. The solid electrolyte according to any one of claims 1 to 7 , wherein the garnet-type or garnet-like crystal structure further contains Nb and / or Ta. The solid electrolyte according to claim 8 , wherein a molar ratio (Nb + Ta) / La of a total amount of Nb and Ta to La is 0.03 to 0.20. The solid electrolyte further comprises a Al, solid electrolyte according to any one of claims 1-9. The Al, based on the total weight of the solid electrolyte, in an amount of 0.01 to 1 wt%, the solid electrolyte according to claim 1 0. The solid electrolyte according to any one of claims 1 to 11, comprising Mg in an amount of 0.01 to 1 mass% with respect to a total weight of the solid electrolyte. A solid electrolyte according to any one of claims 1 to 1 2,
An electrode formed by bonding to the solid electrolyte;
A solid electrolyte-electrode complex, wherein the region substantially free of lithium carbonate constitutes at least part of the interface between the solid electrolyte and the electrode. It said region where lithium carbonate is not substantially present, constitutes the entire interface between the electrode and the solid electrolyte, the solid electrolyte according to claim 1 3 - electrode assembly. The solid electrolyte and the electrodes, respectively, film-like, plate-shaped or have other bulk form, said electrodes are integral with said solid electrolyte, according to claim 1 3 or 1 4 solid Electrolyte-electrode composite. The solid electrolyte according to any one of claims 1 3 to 1 5 - with the electrode composite, and a counter electrode, a battery. The battery according to claim 16 , which is an all-solid battery. The battery according to claim 16 , wherein the solid electrolyte is a separator, and further includes an electrolytic solution between the separator and the counter electrode. CO ₂ And H ₂ Preparing a lithium ion conductive solid electrolyte having a garnet-type or garnet-like crystal structure composed of at least Li, La, Zr and O in an atmosphere in which O is not substantially coexistent; and ,
The solid electrolyte is CO ₂ CO2 by aging treatment exposed to the atmosphere ₂ An aging step of containing C derived from the above in the crystal lattice of the solid electrolyte,
CO of the aging process ₂ The manufacturing method of the solid electrolyte as described in any one of Claims 1-12 whose containing atmosphere is a dry atmosphere. CO ₂ And H ₂ Preparing a lithium ion conductive solid electrolyte having a garnet-type or garnet-like crystal structure composed of at least Li, La, Zr and O in an atmosphere in which O is not substantially coexistent; and ,
The solid electrolyte is CO ₂ CO2 by aging treatment exposed to the atmosphere ₂ An aging step of containing C derived from the above in the crystal lattice of the solid electrolyte,
CO of the aging process ₂ Containing atmosphere is H ₂ O, and after the aging treatment, the CO ₂ The manufacturing method of the solid electrolyte as described in any one of Claims 1-12 with which the process of scraping off the one part or the whole surface of the solid electrolyte exposed in the containing atmosphere is further performed. CO ₂ And H ₂ A solid electrolyte preparation step of preparing a lithium ion conductive solid electrolyte having a garnet-type or garnet-type similar crystal structure composed of at least Li, La, Zr and O in an atmosphere in which O does not substantially coexist;
The solid electrolyte is CO ₂ CO2 by aging treatment exposed to the atmosphere ₂ An aging step in which C derived from is contained in the crystal lattice of the solid electrolyte;
CO ₂ And H ₂ An electrode joining step of joining the solid electrolyte with an electrode to obtain a solid electrolyte-electrode composite in an atmosphere in which O does not substantially coexist,
The aging process is performed before the electrode bonding process, and the aging treatment CO ₂ The method for producing a solid electrolyte-electrode composite according to any one of claims 13 to 15, wherein the containing atmosphere is a dry atmosphere. CO ₂ And H ₂ A solid electrolyte preparation step of preparing a lithium ion conductive solid electrolyte having a garnet-type or garnet-type similar crystal structure composed of at least Li, La, Zr and O in an atmosphere in which O does not substantially coexist;
The solid electrolyte is CO ₂ CO2 by aging treatment exposed to the atmosphere ₂ An aging step in which C derived from is contained in the crystal lattice of the solid electrolyte;
CO ₂ And H ₂ An electrode joining step of joining the solid electrolyte with an electrode to obtain a solid electrolyte-electrode composite in an atmosphere in which O does not substantially coexist,
The aging process is performed before the electrode bonding process, and the aging treatment CO ₂ Containing atmosphere is H ₂ O, and after the aging treatment, the CO ₂ The method for producing a solid electrolyte-electrode composite according to any one of claims 13 to 15, further comprising a step of scraping at least a portion to be bonded to the electrode on the surface of the solid electrolyte exposed to the atmosphere. . CO ₂ And H ₂ Preparing a lithium ion conductive solid electrolyte having a garnet-type or garnet-like crystal structure composed of at least Li, La, Zr and O in an atmosphere in which O is not substantially coexistent; and ,
CO ₂ And H ₂ An electrode joining step of joining the solid electrolyte with an electrode to obtain a solid electrolyte-electrode composite in an atmosphere in which O does not substantially coexist;
The solid electrolyte-electrode composite is converted to CO. ₂ CO2 by aging treatment exposed to the atmosphere ₂ An aging step of containing C derived from the above in the crystal lattice of the solid electrolyte,
The method for producing a solid electrolyte-electrode composite according to any one of claims 13 to 15, wherein the aging step is performed after the electrode joining step.