JP6090290B2 - COMPOSITE, BATTERY, COMPOSITE MANUFACTURING METHOD AND ION CONDUCTIVE SOLID MANUFACTURING METHOD - Google Patents

Description

  The present invention relates to a composite, a battery, a method for manufacturing the composite, and a method for manufacturing an ion conductive solid.

Conventionally, ion-conductive solids that can conduct ions are known. For example, in Patent Document 1, a composition represented by the general formula Li _{2 + x} C _{1−x + y By} O _{3 + 2y} (where 0.03 ≦ x ≦ 0.7, 0 ≦ y ≦ 0.2) What consists of is proposed (refer patent document 1). These are made of a solid solution of Li ₂ CO ₃ and Li ₃ BO ₃ , the crystal structure of which is similar to Li ₂ CO _3, and is chemically stable. In addition, the lithium ion conductivity is remarkably improved by forming a solid solution with Li ₃ BO ₃ . Further, Non-Patent Document 1 examines conductivity such as Li _{2 + x} C _1-x B _x O ₃ and Li _2.25 C _0.75 B _0.25 O ₃ . In Non-Patent Document 1, for example, the conductivity of Li _2.25 C _0.75 B _0.2 O ₃ is 4.7 × 10 ⁻⁷ (Ω · cm ⁻¹ ) at room temperature, and 1 × 10 ⁻² (Ω · cm at 300 ° C. ^-1 ).

JP-A-5-54712

Electrochimica Acta, 1977, Vol. 22, pp. 783-796

  However, although the ion conductive solids of Patent Document 1 and Non-Patent Document 1 can increase the ion conductivity, when a complex with an active material or a solid electrolyte is produced using the ion conductive solid, the ion conductive solid is used. There was a case where the sex decreased. And when the composite_body | complex with which ion conductivity fell was used for the battery, the capacity | capacitance might fall.

  The present invention has been made in order to solve such a problem, and a main object of the present invention is to further suppress a decrease in ion conductivity in a composite containing an ion conductive solid and an active material or a solid electrolyte. To do.

In order to achieve the above-mentioned object, the present inventors conducted intensive research. Then, when a mixture of the positive electrode active material and Li _2.2 B _0.2 C _0.8 O ₃ was melted and then held at a predetermined temperature to produce a composite, the composite using the composite did not hold the battery. It has been found that the discharge capacity can be increased as compared with the battery using. That is, it was found that this composite can suppress a decrease in ion conductivity that contributes to a decrease in battery capacity, and the present invention has been completed.

That is, the complex of the present invention is
An ion conductive solid represented by the general formula Li _{2 + x} B _x C _1-x O ₃ (0 <x <1);
At least one of an active material and a solid electrolyte dispersed in an ion conductive solid;
With
In the Raman scattering spectrum, a vibration peak of CO ₃ ²⁻ is confirmed.

  The battery of the present invention includes the above-described composite.

The method for producing the composite of the present invention comprises:
Melting to produce a molten mixture containing at least one of an active material and a solid electrolyte and a raw material melt of an LBCO compound represented by the general formula Li _{2 + x} B _x C _1-x O ₃ (0 <x <1) A mixing step;
After the melting step, a holding step of holding at a holding temperature of 300 ° C. or higher and lower than the melting point of the LBCO compound;
Is included.

The method for producing an ion conductive solid according to the present invention comprises:
A raw material of the LBCO compound represented by the general formula Li _{2 + x} B _x C _1-x O ₃ (0 <x <1) is heated at a melting heating temperature equal to or higher than the melting point of the LBCO compound to produce a melt. Melting process;
After the melting step, a holding step of holding at a holding temperature of 300 ° C. or higher and lower than the melting point of the LBCO compound;
Is included.

In the composite of the present invention, the method for producing a composite, and the method for producing an ion conductive solid, a decrease in ion conductivity can be further suppressed. The reason why such an effect can be obtained is assumed as follows. For example, when a composite containing an active material or a solid electrolyte and Li _{2 + x} B _x C _1-x O ₃ is produced, when Li _{2 + x} B _x C _1-x O ₃ is melted, When used in a battery, it is expected that ions are exchanged smoothly between the two. However, when Li _{2 + x} B _x C _1-x O ₃ is melted, it is decomposed into insulating Li ₂ O and Li ₃ BO ₃ having low ion conductivity, and so on, and thus expected ion conductivity. May not be obtained. Therefore, if it is held at a predetermined holding temperature after melting, CO ₂ is absorbed from the atmosphere or the like, and insulating Li ₂ O is Li ₂ CO ₃ with low ion conductivity, and Li ₃ BO ₃ with low ion conductivity is ion It becomes highly conductive Li _{2 + x} B _x C _1-x O ₃ . Thus, it is presumed that the decrease in ion conductivity can be suppressed as compared with the case where the holding is not performed.

Explanatory drawing explaining the derivation | leading-out method of the value of the symmetry parameter S. FIG. The schematic diagram which shows an example of the crystal structure of ion conductive solid. An explanatory view showing an example of structure of solid battery. An explanatory view showing an example of structure of solid battery. Graph showing the relationship between the value and the conductivity of x in _{Li 2 + x B x C 1} -x O 3. The cross-sectional SEM photograph of the laminated body (composite and solid electrolyte) of the battery of Experimental Example 5. The graph which shows the discharge characteristic of Experimental Examples 1-6. The Raman scattering spectrum of Experimental Examples 1-4 and 6. Raman scattering spectra of Reference Examples 1 to 4 and 8. Graph showing the relation between _{Li 2 + x B x C 1} -x O 3 x and Raman shift R _max. The Raman scattering spectrum used for the composition examination of Experimental example 2. The TG * DTA analysis result of the sample of Reference Example 2 (x = 0.2). The TG * DTA analysis result of the sample of Reference Example 2 (x = 0.2). Explanatory drawing which shows the manufacturing process of Experimental example 5 notionally.

(Complex)
The composite of the present invention includes an ion conductive solid represented by the general formula Li _{2 + x} B _x C _1-x O ₃ (0 <x <1), an active material dispersed in the ion conductive solid, and a solid electrolyte And a vibration peak of CO ₃ ²⁻ is confirmed in the Raman scattering spectrum. In these ones, ion-conductive solid is considered to be a solid solution of Li ₂ CO ₃ and Li ₂ BO ₃ containing Li ₂ CO ₃ certain amount or more.

In the composite of the present invention, at the CO ₃ ²⁻ vibration peak in the Raman scattering spectrum, the area on the lower wave number side than the Raman shift R _max where the intensity is maximum is S _L , and the area on the higher wave number side than R _max is S _{When H} is set, the value of the symmetry parameter S (hereinafter referred to as S value) represented by S = | S _L −S _H | / (S _L + S _H ) is preferably 0.5 or less. Among these, 0.3 or less is more preferable, and 0.15 or less is more preferable. In such a range, ion conductivity can be further increased. Although the minimum of S value is not specifically limited, For example, it is good also as 0.005 or more, 0.01 or more, 0.015 or more. Here, how to obtain the S value will be described with reference to the drawings. FIG. 1 is an explanatory diagram for explaining a method of deriving the value of the symmetry parameter S. As shown in FIG. 1, with respect to the vibration peak of CO ₃ ²⁻ , when the horizontal axis is Raman shift and the vertical axis is intensity, the curve on the lower wave number side than R _{max of} the peak, and the straight line indicating the background Let S _L be the area of a region surrounded by a vertical line extending from the peak top toward the horizontal axis. Similarly, the R _max higher-wavenumber side curve of the peak, the straight line indicating the background, a perpendicular line toward the horizontal axis from the peak top, the area of the region surrounded by the S _H To do. The straight line indicating the background was obtained by connecting a peak between 1060 cm ⁻¹ and 1110 cm ⁻¹ with a straight line. Incidentally, S _L and S _H thus obtained can be greater than S _L is S _H, even small, may be equal, but it is preferably S _L is greater than S _H.

The composite of the present invention preferably has a Raman shift R _max at which the intensity is maximum at a vibration peak of CO ₃ ²⁻ in the Raman scattering spectrum in the range of 1085 cm ^{−1 to} 1089 cm ⁻¹ . more preferably in the range of 5 cm ^-1 or more 1087.5Cm ^-1 or less, and still more preferably in the range of 1086cm ^-1 or 1087cm ^-1 or less. In such a range, ion conductivity can be further increased. Alternatively, R _max is preferably in the range of 1088.5-13x to 1087.5-13x (where x is x in the general formula Li _{2 + x} B _x C _1-x O ₃ of an ion conductive solid). .

In the composite of the present invention, the ion conductive solid is represented by the general formula Li _{2 + x} B _x C _1-x O ₃ (0 <x <1). In the general formula _{Li 2 + x B x C 1} -x O 3 (0 <x <1), it is preferred that x is 0.02 or more, more preferably 0.08 or more, 0.14 or more More preferably. Further, x is preferably 0.8 or less, more preferably 0.6 or less, and further preferably 0.4 or less. In such a range, ion conductivity can be further increased. The ion conductive solid may be of a non-stoichiometric composition other than that of the stoichiometric composition, for example, a part of the element is deficient or excessive. For example, a part of Li or B may be replaced with Al or Si, or may be replaced with C, Si, Ga, Ge, In, Sn, or the like. Even such a thing can suppress the fall of ionic conductivity more.

  This ion conductive solid may be solidified after being melted at a temperature equal to or higher than its melting point. Thus, by melting and solidifying, it is possible to more closely adhere to the active material, the solid electrolyte, etc., and to further increase the ionic conductivity at the interface. The temperature above the melting point (melting heating temperature) is not particularly limited, but is preferably higher than 700 ° C. Among these, it is preferable that it is 750 degreeC or more, It is more preferable that it is 760 degreeC or more, It is further more preferable that it is 770 degreeC or more, It is much more preferable that it is 780 degreeC or more. The upper limit of the melting and heating temperature is not particularly limited, but a temperature of 1000 ° C. or less at which Li and C are less likely to volatilize is preferable. Among these, it is preferable that it is 900 degrees C or less, It is more preferable that it is 890 degrees C or less, It is further more preferable that it is 870 degrees C or less. If it is such a temperature range, ion conductivity can be improved more. Further, the melting heating temperature is preferably a temperature that is 25 ° C. or more higher than the melting point, and more preferably a temperature that is 50 ° C. or more higher. If it is such a temperature range, ion conductivity can be improved more. Since the melting point varies depending on the composition of the ion conductive solid, etc., the preferred range of the melt heating temperature may vary depending on the composition, etc., so the melt heating temperature may be determined empirically depending on the composition, etc. .

This ion conductive solid may have a crystal structure as shown in FIG. That is, there is a LiO ₄ tetrahedron between the CO ₃ tricoordinate planes, a part of the C ⁴⁺ site is replaced with B ³⁺ , and Li ⁺ is in any site for compensation of the accompanying charge. It may have an existing crystal structure. This structure is a structure in which CO ₃ ²⁻ is laminated, but the distance between the CO ₃ ²⁻ (c-axis length) is preferably 6.295 mm or more. Among these, it is more preferable that it is 6.30cm or more, it is more preferable that it is 6.32cm, and it is more preferable that it is 6.33cm or more. Although an upper limit is not specifically limited, For example, it is good also as 6.35 or less, and good also as 6.34 or less.

This ion conductive solid preferably has a diffraction peak confirmed in the range of 2θ = 31.0 to 31.2 ° in powder X-ray diffraction using CuKα rays. Moreover, it is preferable that a diffraction peak is confirmed in the range of 2θ = 30.0 to 30.2 °. This is because it is considered that a diffraction peak is not confirmed in such a range in the case of a sintered body. Further, it is preferable that a diffraction peak indicating the presence of Li ₂ CO ₃ or Li ₃ BO ₃ is not confirmed or is extremely small even if confirmed. These are single phase Li _{2 + x} B _x C _1-x O ₃ and contain no or very little impurities such as Li ₂ CO ₃ and Li ₃ BO ₃ , thus increasing ionic conductivity. Because it can. In Li _{2 + x} B _x C _1-x O ₃ , x = 0.4 is the solid solution limit, and therefore it is considered that Li ₃ BO _{3 as an} impurity is generated when x> 0.4.

This ionic conductive solid preferably has an ionic conductivity at 25 ° C. of 6.1 × 10 ⁻⁷ S / cm or more. Among these, it is preferably 1.2 × 10 ⁻⁶ S / cm or more, more preferably 2 × 10 ⁻⁶ S / cm or more, and 2.5 × 10 ⁻⁶ S / cm or more. Is more preferable.

  In the ion conductive solid, at least one of an active material and a solid electrolyte is dispersed. The active material may be a positive electrode active material or a negative electrode active material.

As the positive electrode active material, a sulfide containing a transition metal element, an oxide containing lithium and a transition metal element, or the like can be used. Specifically, transition metal sulfides such as TiS ₂ , TiS ₃ , MoS ₃ , FeS ₂ , Li _(1-x) MnO ₂ (0 <x <1, etc., the same shall apply hereinafter), Li _(1-x) Mn Lithium manganese composite oxide such as ₂ O ₄ , lithium cobalt composite oxide such as Li _(1-x) CoO ₂ , lithium nickel composite oxide such as Li _(1-x) NiO ₂ , lithium such as LiV ₂ O ₃ Vanadium composite oxides, transition metal oxides such as V ₂ O _{5, and the} like can be used. Of these, lithium transition metal composite oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , and LiV ₂ O ₃ are more preferable.

  Examples of the negative electrode active material include inorganic compounds such as lithium, lithium alloys and tin compounds, carbonaceous materials capable of inserting and extracting lithium ions, and conductive polymers. Of these, lithium and lithium alloys are preferable because they can reduce the interfacial resistance with the solid electrolyte. As the lithium alloy, a lithium alloy containing at least one or more additive elements among Mg, Al, Si, In, Ag, and Sn is more preferable, and one containing Al or one containing In is more preferable. In particular, those containing In are preferable because even when the number of added atoms is smaller, the interface resistance between the solid electrolyte and the negative electrode can be further reduced. The negative electrode preferably contains an additive element in the range of 10% by mass to 30% by mass of the lithium alloy, and more preferably contains the additive element in a range of 15% by mass to 25% by mass. It is more preferable that the additive element contains mass%. When the additive element contained is 10% by mass or more, the interface resistance can be further reduced, and when it is 30% by mass or less, the uniformity of the lithium alloy can be further improved. In addition, since the detail about the lithium alloy used for a negative electrode is described in Unexamined-Japanese-Patent No. 2011-70939, description is abbreviate | omitted here.

As the solid electrolyte, a lithium ion conductive oxide is preferable. Among these, a garnet-type lithium ion conductive oxide is preferable. The garnet-type lithium ion conductive oxide has, for example, a basic composition Li _x A ₃ B ₂ O ₁₂ (where A and B are one or more elements, and x is a number that compensates for the overall charge balance). Can be represented. Among them, the garnet-type lithium ion conductive oxide has a basic composition Li _{5 + x} La ₃ Zr _x A _2−x O ₁₂ (where A is Sc, Ti, V, Y, Nb, Hf, Ta, It is more preferable that one or more elements selected from the group consisting of Al, Si, Ga and Ge, x is represented by 1.4 ≦ x <2). Here, since x is 1.4 ≦ x <2, the conductivity is higher and the activity is higher than that of the garnet-type oxide Li ₇ La ₃ Zr ₂ O ₁₂ (that is, x = 2) not containing the element A. The chemical energy is also reduced. For example, when the element A is Nb, the conductivity is 2.5 × 10 ⁻⁴ Scm ⁻¹ or more and the activation energy is 0.34 eV or less. Therefore, when this oxide is used for an all-solid-state lithium ion secondary battery, lithium ions are easily conducted, so that the output of the battery is improved. Further, since the activation energy is small, that is, the rate of change in conductivity with respect to temperature is small, the output of the battery is stabilized. Further, it is preferable that x satisfies 1.6 ≦ x ≦ 1.95 because conductivity is higher and activation energy is lower. Furthermore, it is more preferable that x satisfies 1.65 ≦ x ≦ 1.9 because the conductivity is almost maximum and the activation energy is almost minimum. The details of the garnet-type lithium ion conductive oxide represented by the basic composition Li _{5 + x} La ₃ Zr _x A _2−x O ₁₂ are described in, for example, Japanese Patent Application Laid-Open No. 2010-202499. The description is omitted here. As the solid electrolyte, various inorganic solid electrolytes, organic solid electrolytes, and the like can be used in addition to those described above. Well-known inorganic solid electrolytes include, for example, Li nitrides, halides, oxyacid salts, and the like. Among _{them, Li 4 SiO 4, Li 4} SiO 4 -LiI-LiOH, xLi 3 PO 4 - (1-x) Li 4 SiO 4, Li 2 SiS 3, Li 3 PO 4 -Li 2 S-SiS 2, sulfide Examples thereof include phosphorus compounds. Examples of the organic solid electrolyte include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyvinylidene fluoride, polyphosphazene, polyethylene sulfide, polyhexafluoropropylene, and derivatives thereof. These may be used alone or in combination.

(battery)
Next, the battery of the present invention will be described. The battery of the present invention includes the above-described composite. That is, in the battery of the present invention, at least one of the positive electrode active material, the negative electrode active material, and the solid electrolyte is dispersed in the ion conductive solid. At this time, the ion conductive solid is preferably one that has been melted and solidified so as to include at least one particle of a positive electrode active material, a negative electrode active material, and a solid electrolyte. Since the positive electrode active material particles, the negative electrode active material particles, the solid electrolyte particles, etc. are dispersed in the liquid phase ion conductive solid and then solidified, the ion conductive solid enters the gaps between the particles, and the This is because it is easy to secure a conduction path. The battery of the present invention is preferably a solid battery. Below, the case where the battery of this invention is a solid battery is mainly demonstrated. The battery of the present invention may include a liquid or the like in part. Although the type of the battery is not particularly limited, the following mainly describes a lithium ion battery using lithium ions as charge carriers.

  The battery of the present invention includes a positive electrode, a negative electrode, and a solid electrolyte interposed between the positive electrode and the negative electrode.

In the battery of the present invention, the positive electrode has a positive electrode active material. Examples of the material for the positive electrode active material include those described above, and LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiV ₂ O _{3 and the} like are more preferable. The negative electrode has a negative electrode active material. Examples of the material for the negative electrode active material include those described above, and lithium and lithium alloys are more preferable. The positive electrode and the negative electrode may have a current collector. Current collectors include aluminum, copper, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymer, conductive glass, etc., as well as aluminum and copper for the purpose of improving adhesion, conductivity and oxidation resistance. What processed the surface of copper etc. with carbon, nickel, titanium, silver, etc. can be used. For these, the surface can be oxidized. Examples of the shape of the current collector include foil, film, sheet, net, punched or expanded, lath, porous, foam, and formed fiber group.

In the solid battery of the present invention, examples of the solid electrolyte include those described above, and the garnet-type lithium ion conductive oxide represented by the basic composition Li _x A ₃ B ₂ O ₁₂ described above is more preferable.

  In the battery of the present invention, it is preferable to use the composite described above for at least the positive electrode. That is, in the battery of the present invention, it is preferable that at least the positive electrode active material is dispersed in the above-described ion conductive solid. Hereinafter, a positive electrode active material dispersed in an ion conductive solid is also referred to as a positive electrode composite. The positive electrode composite is preferably in close contact with the positive electrode surface of the solid electrolyte. Here, “close contact” means not two-dimensional contact but two-dimensional or three-dimensional contact (bonding). Whether or not it is “in close contact” can be confirmed, for example, by whether or not it is in point contact when a cross section is observed at a magnification of 5000 times using a scanning electron microscope. In order for the positive electrode composite to be in close contact with the surface of the solid electrolyte on the positive electrode side, for example, a molded body containing a positive electrode active material and an ion conductive solid material is formed on the surface of the solid electrolyte, and then subjected to a predetermined treatment. It may be solidified after being melted at a temperature (for example, the melting heating temperature described above). In forming the positive electrode composite, a molded body (for example, a layer) containing a mixture of the positive electrode active material and the ion conductive solid material may be formed, or after forming the molded body containing the positive electrode active material, A molded body containing a conductive solid material may be formed, or a molded body containing a positive electrode active material may be formed after forming a molded body containing an ion conductive solid material. Moreover, you may form alternately the molded object containing a positive electrode active material, and the molded object containing an ion conductive solid. When forming such a composite molded body and each molded body forming the composite molded body, for example, a paste formed by adding a binder or the like may be used. As the binder, cellulose binders such as ethyl cellulose, methyl cellulose, and carboxymethyl cellulose, and various binders such as butyral resins and acrylic resins can be used. Moreover, you may use organic solvents, such as a terpionel, acetone, and toluene, as a solvent or a dispersion medium. The predetermined processing temperature may be appropriately selected from the above-described melting and heating temperatures. Among these, it is preferable that it is 900 degrees C or less from a viewpoint of suppressing reaction with a positive electrode active material and a solid electrolyte. The same applies to a negative electrode composite in which a negative electrode active material is dispersed in an ion conductive solid.

  Although the structure of the battery of the present invention is not particularly limited, for example, the structure shown in FIGS. 3 and 4 may be used. The battery 20 of FIG. 3 has a solid electrolyte layer 10, a positive electrode 12 formed on one side of the solid electrolyte layer 10, and a negative electrode 14 formed on the other side of the solid electrolyte layer 10. Among these, the positive electrode 12 is composed of a positive electrode composite 12a in contact with the solid electrolyte layer 10 (an ion conductive solid in which the positive electrode active material is dispersed) and a current collector 12b in contact with the positive electrode composite 12a. It consists of a negative electrode active material layer 14a in contact with the electrolyte layer 10 and a current collector 14b in contact with the negative electrode active material layer 14a. On the other hand, the solid battery 20 of FIG. 4 is formed through the solid electrolyte layer 10, the positive electrode 12 formed on one side of the solid electrolyte layer 10, and the polymer electrolyte layer 16 on the other side of the solid electrolyte layer 10. A negative electrode 14. Among these, the positive electrode 12 includes a positive electrode composite 12a and a current collector 12b, and the negative electrode 14 includes a negative electrode active material layer 14a and a current collector 14b.

  The shape of the battery of the present invention is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type. Moreover, you may apply to the large sized thing etc. which are used for an electric vehicle etc.

(Production method of composite)
Next, the manufacturing method of the composite_body | complex of this invention is demonstrated. The manufacturing method of the composite of the present invention may include (A) a melt mixing step, (B) a holding step, and (C) a reheating step. Below, each process is demonstrated.

(A) In the melt mixing step melt mixing step, at least one of the active material and the solid electrolyte and the general formula _{Li 2 + x B x C 1} -x O 3 (0 <x <1) of LBCO compound represented by the raw material A molten mixture containing the melt is made. Examples of the active material include the positive electrode active material and the negative electrode active material described above. Moreover, the solid electrolyte mentioned above is mentioned as a solid electrolyte. The raw material of the LBCO compound is not particularly limited as long as it contains a Li component, a B component, and a C component so as to have a desired composition. For example, Li ₂ O may be included as the Li component, Li ₃ BO ₃ may be included as the Li component and the B component, B ₂ O ₃ may be included as the B component, and Li as the Li component and the C component. ₂ CO ₃ may be included, and others may be included. Among preferably contains Li ₃ BO ₃ and Li ₂ CO _3. This is because if Li ₃ BO ₃ and Li ₂ CO ₃ are mixed at a molar ratio of x: 1-x, the composition becomes Li _{2 + x} B _x C _1-x O _{3 and} the composition can be easily controlled. The raw material may include Li _{2 + x} B _x C _1-x O ₃ (0 <x <1) as the Li component, the B component, and the C component.

  This melt mixing process may include, for example, (A-1) a mixing process and (A-2) a melting process.

(A-1) Mixing step In the mixing step, at least one of the active material and the solid electrolyte and the raw material of the LBCO compound are mixed to obtain a mixture. For example, the active material and solid electrolyte used in the mixing step preferably have a particle size of 0.01 μm to 20 μm, and more preferably 0.05 μm to 10 μm. In such a thing, it can mix with the raw material of a LBCO compound more uniformly. In addition, the raw material of the LBCO compound preferably has a particle size of 0.01 μm or more and 20 μm or less, and more preferably 0.05 μm or more and 5 μm or less. In such a thing, it can mix with an active material and a solid electrolyte more uniformly. In addition, in this specification, a particle size shall show the median diameter D50 calculated | required by laser diffraction or SEM observation. The mixture may be in the form of a paste or earth containing a binder in addition to the active material, the solid electrolyte, and the raw material of the LBCO compound. As the binder, cellulose binders such as ethyl cellulose, methyl cellulose, and carboxymethyl cellulose, and various binders such as butyral resins and acrylic resins can be used. Moreover, you may use organic solvents, such as a terpionel, acetone, and toluene, as a solvent or a dispersion medium. Such a mixture may be heated as it is in the melting step, or may be heated in the melting step after forming a molded body formed into a desired shape. Examples of a method for forming a molded body include a method of applying a paste-like mixture on a substrate, and a method of forming a soil-like mixture.

(A-2) Melting step In the melting step, the mixture obtained in the mixing step is heated at a melting heating temperature equal to or higher than the melting point of the LBCO compound. The melt heating temperature is not particularly limited, but may be set similarly to the melt heat temperature described above. The heating time may be a value empirically obtained from the relationship with the heating temperature, and may be, for example, 10 minutes or longer, 30 minutes or longer, or 1 hour or longer. Also, it may be 24 hours or less, 12 hours or less, or 6 hours or less. The treatment atmosphere at the time of melting is not particularly limited, but is preferably an air atmosphere or an oxidizing atmosphere. This is because in such an atmosphere, desorption of oxygen from Li _{2 + x} B _x C _1-x O ₃ is suppressed, and the composition can be easily controlled. Moreover, it is preferable that the treatment atmosphere at the time of melting is sufficiently low in moisture and CO ₂ . Further, it may be solidified after being melted in a pressurized state by a press or the like.

(B) Holding step The holding step is a step performed after the melting step. Although it will not specifically limit if it is after a melting process, It is preferable to carry out in the temperature-fall process after melting. In this holding step, the molten mixture obtained in the melt mixing step is held at a holding temperature of 300 ° C. or higher and lower than the melting point of the LBCO compound. The holding temperature is preferably 350 ° C. or higher, and more preferably 400 ° C. or higher. Moreover, 600 degrees C or less is preferable, 500 degrees C or less is more preferable, and 450 degrees C or less is further more preferable. In the holding step, the temperature may be held at a constant temperature, or the temperature may be changed within a predetermined holding temperature range. The holding time may be a value empirically obtained from the relationship with the holding temperature, and may be, for example, 5 minutes or more, 10 minutes or more, or 30 minutes or more. Also, it may be 12 hours or less, 6 hours or less, or 1 hour or less. The treatment atmosphere in the holding step preferably includes carbon, more preferably includes carbon dioxide, and may be, for example, an air atmosphere.

(C) Reheating process A reheating process is a process performed after a holding process. If it is after a holding process, it will not specifically limit, However, When a holding process is complete | finished, it is preferable to reheat as it is, without lowering | hanging temperature. In this reheating step, reheating is performed to a reheating temperature higher than the above-described holding temperature and lower than the melting point of the LBCO compound. The reheating temperature is preferably 450 ° C. or higher, and more preferably 500 ° C. or higher. Moreover, 700 degrees C or less is preferable and 650 degrees C or less is more preferable. The treatment atmosphere in the reheating step preferably contains carbon, more preferably contains carbon dioxide, and may be, for example, an air atmosphere.

(Method for producing ion conductive solid)
Next, the manufacturing method of the ion conductive solid of this invention is demonstrated. The method for producing an ion conductive solid according to the present invention may include (A ′) a melting step, (B) a holding step, and (C) a reheating step. In this method for producing an ion conductive solid, (B) the holding step and (C) the reheating step are the same as the method for producing the composite described above, and therefore (A ′) the melting step will be described below. Description of other steps is omitted.

(A ′) Melting Step In the melting step, a raw material of the LBCO compound represented by the general formula Li _{2 + x} B _x C _1-x O ₃ (0 <x <1) is melted at a melting heating temperature equal to or higher than the melting point of the LBCO compound. To produce a melt. The melt may be made of an LBCO compound or may contain subcomponents other than the LBCO compound. As the subcomponent, a material having a higher melting point than the LBCO compound and a low reactivity with the raw material of the LBCO compound or the LBCO compound is preferable. As the raw material for the LBCO compound, the same materials as those described in the above-mentioned “(A) melt mixing step” can be used. The raw material of the LBCO compound preferably has a particle size of 0.05 μm or more and 10 μm or less, and more preferably 0.05 μm or more and 5 μm or less. In such a case, a dense ion conductive solid can be produced relatively easily. In the melting step, the raw material of the LBCO compound and the mixture containing the LBCO compound and the auxiliary component may be melted as they are, or, as in the above-described “(A) melt mixing step”, a molding formed into a desired shape. You may heat after making it into a body. In addition, since heating conditions etc. are the same as said "(A-2) melting process", detailed description is abbreviate | omitted.

In the composite of the present invention described above, the method of manufacturing a composite, and the method of manufacturing an ion conductive solid, a decrease in ion conductivity can be further suppressed. The reason why such an effect can be obtained is assumed as follows. For example, when a composite containing an active material or a solid electrolyte and Li _{2 + x} B _x C _1-x O ₃ is produced, when Li _{2 + x} B _x C _1-x O ₃ is melted, When used in a battery, it is expected that ions are exchanged smoothly between the two. However, when Li _{2 + x} B _x C _1-x O ₃ is melted, it is decomposed into insulating Li ₂ O and Li ₃ BO ₃ having low ion conductivity, and Li _{2 + x} B _x C _{1. The} ion conductivity expected for _-x O ₃ may not be obtained. Therefore, if it is held at a predetermined holding temperature after melting, CO ₂ is absorbed from the atmosphere or the like, and insulating Li ₂ O is compared with Li ₂ CO ₃ with low ionic conductivity, and Li ₃ BO ₃ with low ionic conductivity is compared. Li _{2 + x} B _x C _1-x O ₃ with high ionic conductivity. Thus, it is presumed that the decrease in ion conductivity can be suppressed as compared with the case where the holding is not performed. In addition, when reheating is performed up to a predetermined heating temperature after holding at the holding temperature, a single phase of Li _{2 + x} B _x C _1-x O ₃ having high ion conductivity is obtained. Thus, it is presumed that the decrease in ion conductivity can be suppressed as compared with the case where reheating is not performed.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  For example, in the manufacturing method of the composite body and the manufacturing method of the ion conductive solid of the embodiment described above, (C) the reheating step is included, but this step may be omitted. Even if it does in this way, the fall of ion conductivity can be suppressed more. (B) When the holding temperature in the holding step is, for example, less than 500 ° C. or less than 450 ° C., the reheating step can increase the ion conductivity and increase the battery capacity. More preferably, the process is performed.

  For example, in the manufacturing method of the composite according to the above-described embodiment, (A) the melt mixing step includes (A-1) the mixing step and (A-2) the melting step. The process may not be included. For example, the raw material of the LBCO compound may be melted in advance in accordance with the (A-2) melting step to obtain a melt, and this melt may be mixed with an active material or a solid active material.

In the following, an example of examining the composition of _{Li 2 + x B x C 1} -x O 3, is described as a reference example.

1. Sample synthesis [Reference Example 1]
The sample was synthesized by a solid phase reaction method. Specifically, first, Li ₂ CO ₃ and Li ₃ BO ₃ as raw materials were weighed and mixed so that Li ₂ CO ₃ : Li ₃ BO ₃ was in a molar ratio of 9: 1. Subsequently, press molding was performed and heat treatment was performed. The treatment temperature was 650 ° C., and the atmosphere was sufficiently water and CO ₂ . Thus, a sample of Reference Example 1 (x = 0.1) was obtained.

[Reference Examples 2 to 8]
A sample of Reference Example 2 (x = 0.2) was obtained through the same steps as Reference Example 1 except that Li ₂ CO ₃ : Li ₃ BO ₃ was weighed so as to have a molar ratio of 4: 1. A sample of Reference Example 3 (x = 0.3) was obtained through the same steps as Reference Example 1, except that Li ₂ CO ₃ : Li ₃ BO ₃ was weighed so as to have a molar ratio of 7: 3. A sample of Reference Example 4 (x = 0.4) was obtained through the same steps as Reference Example 1 except that Li ₂ CO ₃ : Li ₃ BO ₃ was weighed so that the molar ratio was 3: 2. In addition, the sample of Reference Example 5 (x = 0.6) was obtained through the same steps as Reference Example 1 except that Li ₂ CO ₃ : Li ₃ BO ₃ was weighed so as to have a molar ratio of 2: 3. It was. In addition, the sample of Reference Example 6 (x = 0.8) was obtained through the same steps as Reference Example 1 except that Li ₂ CO ₃ : Li ₃ BO ₃ was weighed so that the molar ratio was 1: 4. It was. A sample (x = 1) of Reference Example 7 was obtained through the same steps as Reference Example 1, except that Li ₂ CO ₃ : Li ₃ BO ₃ was weighed so that the molar ratio was 0: 1. A sample (x = 0) of Reference Example 8 was obtained through the same steps as Reference Example 1, except that Li ₂ CO ₃ : Li ₃ BO ₃ was weighed so that the molar ratio was 1: 0.

2. Measurement of ionic conductivity (conductivity) Gold was vapor-deposited on both sides of the obtained sample to form electrodes, and the conductivity was measured using the AC impedance method. Specifically, the real part of the frequency at which blocking occurs in the Nyquist plot was used as the resistance value, and the conductivity was calculated from this resistance value.

3. Results and Discussion FIG. 5 is a graph showing the relationship between the value of x and the conductivity in Li _{2 + x} B _x C _1-x O ₃ prepared based on Reference Examples 1 to 8. From FIG. 5, when x is 0.02 or more and 0.8 or less, the conductivity is 8.0 × 10 ⁻¹⁰ S / cm or more, and when x is 0.08 or more and 0.6 or less, the conductivity is It was found that the conductivity was as high as 7.0 × 10 ⁻⁸ S / cm or higher, and that the conductivity was further increased to 3.0 × 10 ⁻⁷ S / cm or higher when it was 0.14 or more and 0.4 or less. In Reference Examples 1 to 8, although the processing temperature is 650 ° C., it is assumed that the same tendency is exhibited even when the processing temperature is different. That is, if x is 0.02 or more and 0.8 or less, the conductivity is high, if x is 0.08 or more and 0.6 or less, it is higher than the conductivity, and if x is 0.14 or more and 0.4 or less, the conductivity is high. The rate was estimated to be even higher. When x = 0.2, the melting point Tm was 700 ° C. <Tm <750 ° C.

  Next, an example in which the composite of the present invention is specifically produced will be described as an experimental example. Experimental examples 2 to 6 correspond to examples of the present invention, and experimental example 1 corresponds to a comparative example. The present invention is not limited to the following examples.

1. Production of battery [Experiment 1]
(1) Preparation of solid electrolyte Li ₂ CO ₃ , La (OH) ₃ , ZrO ₂ , and Nb ₂ O ₅ are used as starting materials, and Li _6.75 La ₃ Zr _1.75 Nb _0.25 O ₁₂ (hereinafter also referred to as LLZONb) This starting material was weighed so as to have a stoichiometric ratio of the basic composition, and mixed and pulverized in ethanol in a planetary ball mill (300 rpm / zirconia ball) for 4 hours. Next, after the mixed powder of the starting material (inorganic material) was separated from zirconia balls and ethanol, calcination was performed in an Al ₂ O ₃ crucible at 950 ° C. for 10 hours in an air atmosphere. Thereafter, Li ₂ CO ₃ is added to the calcined powder so that the Li amount is 5 at% with respect to the Li amount in the inorganic material for the purpose of making up for the loss of Li in the main firing. For the purpose of pulverizing and mixing the obtained powder, it was pulverized and mixed in a planetary ball mill (300 rpm / zirconia ball) for 6 hours in ethanol. The obtained powder was again calcined under atmospheric pressure at 950 ° C. for 5 hours. Subsequently, the obtained powder was molded to a diameter of 13 mm and a thickness of 2 mm and subjected to isostatic pressing (CIP) between cold water, and then the sintering temperature was set to 1150 ° C. for 36 hours under atmospheric conditions. To obtain a pellet-shaped solid electrolyte. CIP was performed under the conditions of 27 ° C. and 200 MPa using water as a solvent.

(2) Preparation of positive electrode active material powder Using Li ₂ CO ₃ and CoO as starting materials, the starting materials are weighed so that the molar ratio of Li ₂ CO ₃ and CoO is 1: 2 (total amount is about 50 g). The mixture was pulverized in ethanol (100 ml) with a planetary ball mill (300 rpm / zirconia pod (500 cc) / zirconia beads (3 mmφ, 500 g)) for 1 hour. Then, after removing the solvent in a dryer at a set temperature of 80 ° C., the zirconia beads and the raw material mixed powder were separated by a sieve. LiCoO ₂ powder was synthesized by heat-treating the powder in an alumina crucible at 850 ° C. for 20 hours under atmospheric conditions.

(3) Preparation of LBCO Compound Raw Material Powder The sample of Reference Example 2 was wet-ground for 1 hour with a planetary ball mill (600 rpm) to obtain an LBCO compound raw material powder (hereinafter also referred to as LBCO powder).

(4) Preparation of positive electrode paste Positive electrode active material powder (particle size 5 μm) and LBCO powder (particle size 0.2 μm) were kneaded by dry kneading in a mortar at a volume ratio of 1: 1 to obtain a mixed powder. . 1.5 g of this mixed powder and 1 g of binder (manufactured by Nisshin Kasei Co., Ltd., EC vehicle (mixture of ethyl cellulose and terpionol)) were mixed to prepare a positive electrode paste.

(5) Production of Battery The surface of the produced pellet-shaped solid electrolyte was polished with sandpaper (# 6000). A positive electrode paste was applied to the polished surface by screen printing. At this time, the size of the screen was 10 mmφ. And the solvent removal was performed over 5 minutes in the dryer set to 150 degreeC. The coated body thus obtained was heated in the atmosphere at 780 ° C. for 1 hour (melt mixing step), and then rapidly cooled to prepare a positive electrode composite on the solid electrolyte. Note that at 780 ° C., the LBCO powder melted into a liquid phase. Au as a current collector was sputter coated on the surface of the obtained positive electrode composite. Then, metal Li as a negative electrode was vapor-deposited on the surface opposite to the surface on which the solid electrolyte positive electrode composite was formed to form a negative electrode. The obtained laminate was put in a sealed container, and the insulated lead wire was taken out of the container to produce a battery of Experimental Example 1.

[Experiment 2]
The battery of Experimental Example 2 was the same as Experimental Example 1 except that in “(5) Production of Battery”, a holding step of holding at 400 ° C. for 30 minutes was performed instead of quenching after the melt mixing step. Was made.

[Experimental Examples 3 to 6]
A battery of Experimental Example 3 was fabricated in the same manner as Experimental Example 2 except that a reheating process of heating to 500 ° C. was performed after the holding process. A battery of Experimental Example 4 was produced in the same manner as Experimental Example 3, except that the heating temperature in the reheating process was changed from 500 ° C to 600 ° C. A battery of Experimental Example 5 was produced in the same manner as Experimental Example 3, except that the heating temperature in the reheating process was changed from 500 ° C. to 650 ° C. A battery of Experimental Example 6 was produced in the same manner as Experimental Example 3, except that the heating temperature in the reheating process was changed from 500 ° C. to 680 ° C.

2. Scanning Electron Microscope (SEM) Observation A cross-sectional photograph (fracture surface when the laminate is broken) of the laminate used in the battery of Experimental Example 5 is shown in FIG. From FIG. 6, it was found that LBCO filled the gaps in the active material to form ion conduction paths.

2. Charge / Discharge Test Using the prepared battery, the battery was charged to 4.05 V at 5 μA, and then discharged to 2.5 V at 1 mA, 500 μA, 200 μA, 100 μA, 50 μA, 20 μA, 10 μA, 5 μA, and the discharge capacity was measured. Table 1 and FIG. 7 show the discharge characteristics.

3. CO ₃ ^2- ion analysis in electrode For the positive electrodes of Experimental Examples 1 to 6, Raman spectroscopy measurement was performed with excitation light having a wavelength of 532 nm using a laser Raman spectrometer (manufactured by Nanophoton, Raman-touch), and CO ₃ ² The peak in the vicinity of 1090 cm ⁻¹ indicating the laminated structure of ⁻ was analyzed, and the above-described S value and R _max were obtained. For reference, Raman spectroscopic measurements were similarly performed on the samples of Reference Examples 1 to 4 and 8. FIG. 8 shows the Raman scattering spectra of Experimental Examples 1 to 6, and FIG. 9 shows the Raman scattering spectra of Reference Examples 1 to 4 and 8. FIG. 10 shows the relationship between the value of x and R _{max of} Li _{2 + x} B _x C _1-x O ₃ read from FIG.

From FIG. 8, in Experimental Example 1 in which the holding step was not performed, the peak (carbonic acid peak) indicating the laminated structure of CO ₃ ²⁻ was not confirmed, and there was almost no Li _{2 + x} B _x C _1−x O _3. I understood it. Moreover, it turned out that a carbonate peak recovers in Experimental Examples 2-6 which performed the holding process. Among them, in Experimental Example 2 in which the reheating process was not performed, the carbonic acid peak had a tail on the low wavenumber side, as in general Li _{2 + x} B _x C _1-x O ₃ (FIG. 9). It was not symmetrical. In general Li _{2 + x} B _x C _1-x O ₃ , a linear relationship was observed between the B doping amount (value of x) and the Raman shift (R _max ) (FIG. 10). In Example 2, it was guessed that the thing in the state from which B dope amount differs was mixed. Further examination of this point revealed that the carbonic acid peak of Experimental Example 2 has a shape similar to the cumulative fit peak of Li ₂ CO ₃ (x = 0) and Li _2.4 B _0.4 C _0.6 O ₃ as shown in FIG. Had. From this, it is inferred that in Experimental Example 2, Li ₂ CO ₃ (x = 0) and Li _2.4 B _0.4 C _0.6 O ₃ (x = 0.4) are mixed (phase-separated). It was. On the other hand, in Experimental Examples 3 to 6 in which the reheating step was performed, the carbonic acid peak changed to a substantially symmetrical one. From this, in Experimental Examples 3 to 6, it was inferred that the phases were not separated but became a single phase, or the phases were separated to a relatively close composition even if the phases were separated. Table 2 summarizes the compositions (Raman compositions) determined from the results of Raman spectroscopic measurements of Experimental Examples 1 to 6 and the value of R _max . Table 2 also shows the discharge capacity when 1 mA discharge was performed in the charge / discharge test. From these results, it was found that the discharge capacity was improved by recovering the carbonic acid peak (increasing CO ₂ ) by the holding step. Further, it was found that by reheating at 500 ° C. or more and 600 ° C. or less in the reheating step, CO ₂ is increased and a single phase is formed, and the discharge capacity is improved. Further, in the reheating step, it was found that when reheating was performed at a temperature exceeding 600 ° C., particularly at a temperature exceeding 650 ° C., CO ₂ decreased as the temperature was increased, and accordingly, the discharge capacity tended to decrease. .

Incidentally, the increase and decrease and CO ₂ as described above, for the decrease in discharge capacity due to it was suggested that a similar thing Thermogravimetric (TG) · differential thermal (DTA) analysis. FIG. 12 shows the TG / DTA analysis results of the sample of Reference Example 2 (x = 0.2). As shown in FIG. 12, in the sample of Reference Example 2, TG was greatly reduced near the melting point. From this, the Li ₂ CO ₃ component constituting Li _{2 + x} B _x C _1-x O ₃ is decomposed into Li ₂ O as an insulator and CO _{2 as a} gas near the melting point, and CO ₂ is evaporated. It was speculated that the TG decreased and the discharge capacity decreased. FIG. 13 shows the TG / DTA analysis results of the sample of Reference Example 2 (x = 0.2) (FIG. 13A). In the analysis, temperature control as shown in FIG. 13B was performed. From FIG. 13, it is understood that the weight (CO ₂ ) is recovered by holding at a predetermined temperature after melting, and particularly a large recovery is confirmed at around 450 ° C., and then the recovery is almost finished at around 300 ° C. It was. From this, it was inferred that CO ₂ was recovered by the holding step of holding at 300 ° C. or higher, and the decrease in discharge capacity was suppressed.

4). Summary As described above, in Experimental Examples 2 to 6, by producing by a production method including a holding step and a reheating step, the ionic conductivity of the composite is further increased than in the case where such a step is not included. It was found that the capacity can be further increased. The reason why such an effect was obtained was considered using Experimental Example 5 as an example. FIG. 14 is an explanatory diagram conceptually showing the manufacturing process of Experimental Example 5. In this manufacturing process, for the purpose of improving the adhesion between the active material or solid electrolyte and Li _{2 + x} B _x C _1-x O ₃ , first, Li _2.2 B _0.2 C is heated at 780 ° C. for 1 hour. A melt mixing process for melting _0.8 O ₃ was performed. By the way, when Li _2.2 B _0.2 C _0.8 O ₃ was melted, the ion conductivity was lowered, and the expected ion conductivity could not be obtained (the capacity was low). This is because when Li _2.2 B _0.2 C _0.8 O ₃ is melted, it is decomposed into insulating Li ₂ O and Li ₃ BO ₃ having low ion conductivity, and active materials and solid electrolytes resulting from these decomposition products This was presumed to be due to a decrease in the interface between Li _{2 + x} B _x C _1-x O ₃ and a narrowing of the ion conduction path in the composite. Therefore, a holding step of holding at 400 ° C. for 30 minutes was performed after the melt mixing step. In this holding step, CO ₂ is absorbed from the atmosphere, etc., insulating Li ₂ O is Li ₂ CO ₃ having low ion conductivity, and Li ₃ BO ₃ having low ion conductivity is Li ion having relatively high ion conductivity. _2.4 B _0.4 C _0.6 O ₃ . This improves the ionic conductivity, but Li ₂ CO ₃ having a low ionic conductivity still exists. Therefore, a reheating step of heating to 650 ° C. was further performed. In this reheating step, Li _2.4 B _0.4 C _0.6 O ₃ having a relatively high ion conductivity reacts with Li ₂ CO ₃ having a low ion conductivity, whereby Li _2.2 B _0.2 C _0.8 O having a high ion conductivity is reacted. It became ₃ . Thus, it was speculated that the ionic conductivity was further improved, and the decrease in ionic conductivity could be suppressed as compared with the case of producing by a production method not including a holding step and a reheating step.

  The present invention can be used in the field of the battery industry.

  10 solid electrolyte layer, 11 electrode, 12 positive electrode, 12a positive electrode composite, 12b current collector, 14 negative electrode, 14a negative electrode active material layer, 14b current collector, 16 polymer electrolyte layer, 20 battery.

Claims (11)

An ion conductive solid represented by the general formula Li _{2 + x} B _x C _1-x O ₃ (0 <x <1);
At least one of an active material and a solid electrolyte dispersed in an ion conductive solid;
With
In the Raman scattering spectrum, a vibration peak of CO ₃ ^2- is confirmed.
Complex. 2. The composite according to claim 1, wherein the vibration peak of CO ₃ ²⁻ has a Raman shift R _{max at} which the intensity is maximum in a range of 1085 cm ^{−1 to} 1089 cm ⁻¹ . The CO ₃ ^2- vibrational peak in intensity Raman shift is maximum R _max the than the area of lower wave numbers S _L, the area of from R _max higher wave number side when the S _H, S = | S _L -S _H | / the value of (S _L + S _H) symmetry parameter represented by S is 0.5 or less, the composite body according to claim 1 or 2.   The composite according to claim 3, wherein the value of the symmetry parameter S is in the range of 0.01 to 0.3.   The battery provided with the composite_body | complex of any one of Claims 1-4. Melting to produce a molten mixture containing at least one of an active material and a solid electrolyte and a raw material melt of an LBCO compound represented by the general formula Li _{2 + x} B _x C _1-x O ₃ (0 <x <1) A mixing step;
After the melting step, a holding step of holding at a holding temperature of 300 ° C. or higher and lower than the melting point of the LBCO compound;
The manufacturing method of the composite_body | complex containing.   The manufacturing method of the composite_body | complex of Claim 6 including the reheating process reheated to the reheating temperature higher than the said holding temperature and less than melting | fusing point of the said LBCO compound after the said holding process.   The said reheating temperature is a manufacturing method of the composite_body | complex of Claim 7 which exists in the range of 500 to 650 degreeC.   The said holding temperature is a manufacturing method of the composite_body | complex of any one of Claims 6-8 which exists in the range of 350 to 450 degreeC. The melt mixing step includes
A mixing step of mixing at least one of an active material and a solid electrolyte and a raw material of the LBCO compound;
A melting step of heating the mixture obtained in the mixing step at a melting heating temperature equal to or higher than the melting point of the LBCO compound;
The manufacturing method of the composite_body | complex of any one of Claims 6-9 containing this. A raw material of the LBCO compound represented by the general formula Li _{2 + x} B _x C _1-x O ₃ (0 <x <1) is heated at a melting heating temperature equal to or higher than the melting point of the LBCO compound to produce a melt. Melting process;
After the melting step, a holding step of holding at a holding temperature of 300 ° C. or higher and lower than the melting point of the LBCO compound;
A method for producing an ion conductive solid, comprising: