JP2010102929A - Lithium content garnet type oxide, lithium secondary cell, and method for manufacturing solid electrolyte - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a lithium containing garnet type oxide and a lithium secondary battery having higher battery performance, and a method for manufacturing a solid electrolyte. <P>SOLUTION: In the method for manufacturing the solid electrolyte, inorganic materials (for example, Li<SB>2</SB>CO<SB>3</SB>) in which a gas is formed by calcining them at a prescribed temperature are mixed and crushed in a solvent, the mixed inorganic materials are temporarily calcined at a temporary calcination temperature higher than a prescribed temperature and lower than a molding-calcination temperature to calcine them after molding, a prescribed additive amount of the inorganic materials are added to the calcined material and mixed and crushed in the solvent, the material to which the inorganic materials are added is temporarily calcined further at the temporary calcination temperature, and the material temporarily recalcined without inputting it into the solvent is molded to a molding body and calcined at the molding-calcination temperature. Thus, in the molding and calcination, volume change or the like is smaller and composition drift is suppressed further. For that reason, the solid electrolyte obtained by this method shows high relative density and conductivity. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a lithium-containing garnet-type oxide, a lithium secondary battery, and a method for producing a solid electrolyte.

Conventionally, as a solid electrolyte, a raw material lithium carbonate or the like is mixed so as to have a target composition, and calcined at about 700 ° C. to evaporate gas components, followed by firing at about 1300 ° C. for dissolution. It is a plate-like glass, and then cast at about 600 ° C., and a crystal layer of Li _{1 + x} (M, Al, Ga) _x (Ge _1-y Ti _y ) _2-x (PO ₄ ) is deposited. It has been proposed (see, for example, Patent Document 1). This solid electrolyte is thermally and chemically stable and has high conductivity at room temperature.
JP 2000-34134 A

However, although the solid electrolyte described in Patent Document 1 has high conductivity, a component such as lithium (also referred to as a volatile component) that tends to volatilize easily disappears during firing. When the volatile component disappears, there is a problem in that the obtained solid electrolyte is deficient and the structure becomes unstable or the conductivity is lowered. On the other hand, it is conceivable that the volatile component is added in excess of the target composition when mixing the raw materials, but the excess volatile component reacts with moisture, carbon dioxide, etc., and gas is used during the main firing. As a result, there is a problem in that the density decreases and the conductivity decreases. In addition, as a solid electrolyte used in a lithium secondary battery, as a material of other compositions, lithium having a crystal structure similar to Fe ₃ Al ₂ (SiO ₄ ) ₃ because it has excellent chemical stability and a wide potential window. Containing garnet-type oxides are attracting attention. This lithium-containing garnet-type oxide has still low conductivity, and development of a material exhibiting higher conductivity has been desired.

  The present invention has been made in view of such problems, and has as its main object to provide a method for producing a lithium-containing garnet-type oxide, a lithium secondary battery, and a solid electrolyte having higher battery performance. To do.

  As a result of diligent research to achieve the above-mentioned object, the present inventors mixed an inorganic material that generates gas during calcination, calcined at a predetermined calcining temperature, and an addition amount according to the firing of this inorganic material If the inorganic material is added and further mixed and re-calcined at the calcining temperature, then formed into a molded body and calcined at a main calcining temperature higher than the calcining temperature, a lithium-containing garnet type oxide is suitable. The present invention has been completed by finding that it has a higher battery performance.

That is, the lithium-containing garnet oxide of the present invention is
A lithium-containing garnet-type oxide used in a lithium secondary battery,
The relative density with respect to the theoretical density is 70 (%) or more,
The conductivity is 1.0 × 10 ⁻⁵ (Scm ⁻¹ ) or more.

The lithium secondary battery of the present invention is
A positive electrode having a positive electrode active material;
A negative electrode having a negative electrode active material;
A solid electrolyte composed of the above-described lithium-containing garnet-type oxide that is interposed between the positive electrode and the negative electrode and conducts lithium ions;
It is equipped with.

Moreover, the method for producing the solid electrolyte of the present invention comprises:
A method for producing a solid electrolyte that conducts lithium ions,
A first mixing step of mixing a plurality of types of inorganic materials including those whose state changes by firing at a predetermined temperature;
A first firing step of firing the mixed inorganic material at a predetermined first temperature that is equal to or higher than the predetermined temperature and lower than a molding firing temperature that is fired after molding, to obtain a first material;
A second mixing step of adding and mixing a predetermined addition amount of the inorganic material determined according to the firing of the inorganic material to the first material;
A second baking step of baking the first material added with the inorganic material at a predetermined second temperature that is equal to or higher than the predetermined temperature and lower than the molding baking temperature to obtain a second material;
A molding and firing step of molding the second material into a molded body and firing at the molding and firing temperature;
Is included.

In this method for producing a lithium-containing garnet-type oxide, a lithium secondary battery and a solid electrolyte, higher battery performance can be obtained. The reason why such an effect is obtained is estimated as follows, for example. In the first baking step, the state of the inorganic material is changed in advance, and then the components volatilized in the first baking step are added and supplemented in the second mixing step. Most inorganic materials in the first mixing step change in state, and in the second baking step, the added inorganic material only changes in state, so that volume change and the like can be further reduced. Further, in the second mixing step, it is possible to add an inorganic material including complementation of volatile components in the second baking step and the molding baking step, so that the compositional deviation can be suppressed with higher accuracy. . Thereby, in baking in a shaping | molding baking process, a volume change etc. are smaller and composition shift can be suppressed more. For this reason, it is estimated that the solid electrolyte obtained by the production method of the present invention has higher battery performance. In addition, lithium-containing garnet-type oxides are likely to be affected by volume changes and the like, and the significance of applying the present invention is high. As a result, the relative density can be increased to 70% or more, and the conductivity is increased. It is estimated that it can be further increased to 1.0 × 10 ⁻⁵ or more.

  The lithium secondary battery of the present invention is interposed between a positive electrode having a positive electrode active material capable of occluding and releasing lithium ions, a negative electrode having a negative electrode active material capable of occluding and releasing lithium ions, and the positive electrode and the negative electrode. And a solid electrolyte that conducts lithium ions.

The positive electrode of the lithium secondary battery of the present invention is, for example, a mixture of a positive electrode active material, a conductive material, and a binder, and an appropriate solvent is added to form a paste-like positive electrode material, which is applied to the surface of the current collector. It may be dried and compressed to increase the electrode density as necessary. 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 preferable. The conductive material is not particularly limited as long as it is an electron conductive material that does not adversely affect the battery performance of the positive electrode. For example, graphite such as natural graphite (scale-like graphite, scale-like graphite) or artificial graphite, acetylene black, carbon black, What mixed 1 type (s) or 2 or more types, such as ketjen black, carbon whisker, needle coke, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) can be used. Among these, as the conductive material, carbon black and acetylene black are preferable from the viewpoints of electron conductivity and coatability. The binder serves to bind the active material particles and the conductive material particles, for example, a polytetrafluoroethylene (PTFE), a polyvinylidene fluoride (PVDF), a fluorine-containing resin such as fluorine rubber, or polypropylene, Thermoplastic resins such as polyethylene, ethylene-propylene-dienemer (EPDM), sulfonated EPDM, natural butyl rubber (NBR) and the like can be used alone or as a mixture of two or more. In addition, an aqueous dispersion of cellulose or styrene butadiene rubber (SBR), which is an aqueous binder, can also be used. Examples of the solvent for dispersing the positive electrode active material, the conductive material, and the binder include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, and N, N-dimethylaminopropyl. Organic solvents such as amine, ethylene oxide, and tetrahydrofuran can be used. Moreover, a dispersing agent, a thickener, etc. may be added to water, and an active material may be slurried with latex, such as SBR. As the thickener, for example, polysaccharides such as carboxymethyl cellulose and methyl cellulose can be used alone or as a mixture of two or more. Examples of the application method include roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, and the like, and any of these can be used to obtain an arbitrary thickness and shape. Current collectors include aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymer, conductive glass, and aluminum, copper, etc. for the purpose of improving adhesion, conductivity, and oxidation resistance. A surface treated with carbon, nickel, titanium, silver or the like 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. The thickness of the current collector is, for example, 1 to 500 μm.

  The negative electrode of the lithium secondary battery of the present invention is prepared by, for example, mixing a negative electrode active material, a conductive material, and a binder, and adding a suitable solvent to form a paste-like negative electrode material on the surface of the current collector. It may be dried and compressed to increase the electrode density as necessary. Examples of negative electrode active materials include inorganic compounds such as lithium, lithium alloys and tin compounds, carbonaceous materials capable of occluding and releasing lithium ions, and conductive polymers. Among these, carbonaceous materials are used from the viewpoint of safety. It is preferable to see. The carbonaceous material is not particularly limited, and examples thereof include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. Of these, graphites such as artificial graphite and natural graphite have an operating potential close to that of metallic lithium, can be charged and discharged at a high operating voltage, and suppresses self-discharge when a lithium salt is used as an electrolyte salt. In addition, the irreversible capacity during charging can be reduced, which is preferable. In addition, as the conductive material, binder, solvent, and the like used for the negative electrode, those exemplified for the positive electrode can be used. The negative electrode current collector includes copper, nickel, stainless steel, titanium, aluminum, calcined carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., as well as improved adhesion, conductivity and reduction resistance. For the purpose, for example, a copper surface treated with carbon, nickel, titanium, silver or the like can be used. For these, the surface can be oxidized. The shape of the current collector can be the same as that of the positive electrode.

The solid electrolyte of the lithium secondary battery of the present invention is mainly composed of a lithium-containing garnet oxide. Here, the solid electrolyte has a basic composition of Li _x A _y B _{3 -y} M ₂ O ₁₂ , a relative density with respect to the theoretical density of 70 (%) or more, and a conductivity of 1.0 × 10 ⁻⁵ ( consisting scm ^-1) or more in lithium-containing garnet-type oxides. However, A is any one or more of group 2 elements (for example, Mg, Ca, Sr, Ba, Ra), B is any one or more of lanthanoid elements and Y, Sc, y is a positive number of 0 or more, When x = 7 + y, M is any one or more of Ti, Zr, and Hf, and when x = 5 + y, M is any one or more of V, Nb, and Ta. Of these, A is preferably Ca, Sr, Ba or the like, B is preferably La or Nd, and M is preferably Zr, Nb, Ta or the like. The solid electrolyte is more preferably basic composition is _{Li x A y La 3-y} Zr 2 O 12 and _{Li x A y La 3-y} Nb 2 O 12. As the lithium-containing garnet-type oxide, in addition to this, (Na _1-x Li _x ) _y M ₂ Fe ₃ O ₁₂ (where M is an element that can take an oxidation number +6 state (S, Se, Te, 1 or more of Po), 0.3 ≦ x ≦ 1.0, 2.5 ≦ y ≦ 3.0), and Ca ₃ LiMV ₃ O ₁₂ (where M is Co, Ni, Fe, Mn) 1 or more of them), Ca ₃ Li _x Nb _{(1.5 + x)} Ga _(3.5-2x) O ₁₂ (where x is 0.24 ≦ x ≦ 0.60), and the like. The “basic composition” is intended to include those that differ by 20%, 10%, etc. with respect to the content of each element of this composition. For example, “what the basic composition is Li ₇ La ₃ Zr ₂ O ₁₂ ” is generally the same as the composition, for example, the composition is Li _7.2 La ₃ Zr ₂ O _12.2 or the composition is Li _6.8 La. It is intended to include those that are ₃ Zr ₂ O _11.8 .

In the case where the basic composition of the lithium-containing garnet-type oxide is Li _x A _y La _{3 -y} Zr ₂ O ₁₂ , x is preferably 7 or more and 9 or less, and more preferably 8 or less. Moreover, y is preferably 0 or more and 2 or less, and more preferably 1 or less. Of these, the basic composition of x = 7 and y = 0 is preferably Li ₇ La ₃ Zr ₂ O ₁₂ . At this time, the relative density with respect to the theoretical density is 70 (%) or more, more preferably 90 (%) or more, and still more preferably 92 (%) or more. Further, the conductivity is 1.0 × 10 ⁻⁵ or more, and more preferably 1.0 × 10 ⁻⁴ or more. If the conductivity is 1.0 × 10 ⁻⁴ or more, the battery performance can be further improved.

In the case where the basic composition of the lithium-containing garnet-type oxide is Li _x A _y La _{3 -y} Nb ₂ O ₁₂ , x is preferably 5 or more and 7 or less, and more preferably 6 or less. Moreover, y is preferably 0 or more and 2 or less, and more preferably 1 or less. Of these, the basic composition of x = 5 and y = 0 is preferably Li ₅ La ₃ Nb ₂ O ₁₂ . At this time, the relative density with respect to the theoretical density is 70 (%) or more, more preferably 90 (%) or more, and still more preferably 92 (%) or more. The conductivity is 1.0 × 10 ⁻⁵ or more.

  The shape of the lithium secondary 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. An example of this lithium ion secondary battery is shown in FIG. FIG. 1 is a cross-sectional view schematically showing the configuration of the coin-type battery 20. The coin-type battery 20 includes a cup-shaped battery case 21, a positive electrode 22 having a positive electrode active material and provided at a lower portion of the battery case 21, and a negative electrode active material having a solid electrolyte 24 with respect to the positive electrode 22. A negative electrode 23 provided at a position facing each other, a gasket 25 formed of an insulating material, and a sealing plate 26 disposed in the opening of the battery case 21 and sealing the battery case 21 via the gasket 25. I have. Here, the solid electrolyte 24 is comprised by the lithium containing garnet-type oxide mentioned above.

  Next, a method for manufacturing the solid electrolyte of the lithium secondary battery 20 will be described. The solid electrolyte manufacturing method includes 1) a first mixing step of mixing an inorganic material as a raw material such as a lithium compound whose state changes by firing, and 2) an inorganic material after the state is changed by calcination at a predetermined calcination temperature. 3) a second mixing step in which a predetermined addition amount of inorganic material is added and mixed, and 4) a second baking in which the inorganic material after the second mixing step is calcined at a predetermined calcining temperature. Step 5) A step of molding and firing the inorganic material after the second firing into a molded body and firing at a molding firing temperature. Here, the manufacturing method of a lithium containing garnet-type oxide is demonstrated concretely as a solid electrolyte. Hereinafter, it demonstrates in order of each process.

1) First mixing step In this step, a plurality of types of inorganic materials including those whose state changes by firing at a predetermined temperature are mixed. Specifically, the basic composition of _{Li x A y B 3-y} M 2 O 12 ( where, A is any one or more of the alkaline earth metal, B is any one or more of the lanthanide elements, y is 0 When x = 7 + y, M is one or more of Ti, Zr, and Hf, and when x = 5 + y, M is one or more of V, Nb, and Ta. ) To be mixed and ground. As inorganic materials including those whose state changes, carbonates, sulfates, nitrates, oxalates, chlorides, hydroxides, oxides, etc., of the components contained in the lithium-containing garnet oxide may be used. Of these, carbonates that thermally decompose to generate carbon dioxide and hydroxides that thermally decompose to generate water vapor are preferable because they are relatively easy to process. For example, when mixing the inorganic material basic composition is Li ₇ La ₃ Zr ₂ O _{12 is, Li 2 CO 3, La (} OH) 3, it is preferable to use a ZrO _2. Moreover, when mixing the inorganic material whose basic composition is Li ₅ La ₃ Nb ₂ O ₁₂ , it is preferable to use Li ₂ CO ₃ , La (OH) ₃ , and Nb ₂ O ₅ . Note that “the state changes” may be a gas generation or a predetermined phase change. Here, it is preferable to mix the inorganic material as the raw material so as to obtain a target composition ratio of the basic composition. The mixing method of the inorganic material may be mixed and pulverized dry without adding it to the solvent, or may be mixed and pulverized wet and then mixed with the solvent. From the aspect of improving the properties, it is preferable. As this mixing method, for example, a planetary mill, an attritor, a ball mill, or the like can be used. As the solvent, those in which Li is difficult to dissolve are preferable, and for example, an organic solvent such as ethanol is more preferable. The mixing time depends on the amount of mixing, but can be 2h to 8h, for example.

2) First firing step In this step, the inorganic material after the first mixing step is fired at a predetermined calcining temperature (first temperature) that is equal to or higher than a predetermined temperature at which the state changes and lower than a molding baking temperature for baking after molding. It is a process. As the predetermined temperature, for example, when Li ₂ CO ₃ is included in the inorganic material, a temperature equal to or higher than the temperature at which the carbonate is decomposed is set as the calcining temperature. If it carries out like this, the fall of the density by the gas generation | occurrence | production by thermal decomposition can be suppressed in a subsequent shaping | molding baking process. In calcination of an inorganic material whose basic composition is Li ₇ La ₃ Zr ₂ O ₁₂ , it is preferably 900 ° C. or higher and 1100 ° C. or lower. In calcining an inorganic material whose basic composition is Li ₅ La ₃ Nb ₂ O ₁₂ , it is preferably 900 ° C. or higher and 1150 ° C. or lower. The calcination time can be determined empirically within a range in which the amount of volatilization of a component (also referred to as a volatile component) that easily volatilizes, for example, lithium, can be suppressed.

3) Second mixing step In this step, a predetermined addition amount of an inorganic material determined according to the firing of the inorganic material is added to and mixed with the inorganic material after the first firing (also referred to as the first material). The main purpose of this step is to correct a composition shift caused by volatilization in each firing step. Examples of the inorganic material to be added include inorganic materials containing volatile components (for example, Li ₂ CO ₃ ). The addition amount of the inorganic material can be determined empirically according to each condition of the firing step such as the first firing step, the second firing step, and the molding firing step. For example, it is good also as what adds the amount determined according to changing from a basic composition. As the kind of the inorganic material to be added, the method for mixing the inorganic material, the mixing time, etc., those described in the first mixing step can be used. The second mixing step may be the same inorganic material type, inorganic material mixing method, mixing time, etc. as in the first mixing step, or may be performed under different methods and conditions from the first step. In the second mixing step, when the basic composition is an inorganic material having Li ₇ La ₃ Zr ₂ O ₁₂ , the amount of Li corresponds to a range of 4 atomic% or more and 20 atomic% or less with respect to the amount of Li in the inorganic material. It is preferable to add Li, and it is more preferable to add Li corresponding to a range of 6 atomic% or more and 14 atomic% or less. If it carries out like this, it can have a higher battery characteristic. Further, when the basic composition is an inorganic material having Li ₅ La ₃ Nb ₂ O ₁₂ , Li corresponding to the amount of Li in the range of 7 atomic% to 13 atomic% with respect to the amount of Li in the inorganic material is added. More preferably. If it carries out like this, it can have a higher battery characteristic.

4) Second firing step In this step, an inorganic material (first material) to which an inorganic material is added at a predetermined calcining temperature (second temperature) that is equal to or higher than a predetermined temperature at which the state of the inorganic material changes and lower than the molding baking temperature Calcinate. The main purpose of this step is to change the state of the added inorganic material. In this 2nd baking process, it is good also as what is performed on the conditions similar to the 1st baking process mentioned above. In addition, it is preferable to perform in this 2nd baking process at the temperature more than the predetermined temperature in which the state change of an inorganic material occurs, and below the calcining temperature of the 1st baking process mentioned above. By doing so, the re-calcined material is suppressed from solidifying, and therefore, it is not necessary to pulverize the re-calcined material in the molding and firing step described later. Further, in the second baking step, the amount of the inorganic material that needs to be changed as compared with the first baking step is scarce, and therefore the calcination time may be shortened. By performing this step, it is possible to suppress a decrease in density associated with a change in the state of the inorganic material added in order to suppress composition deviation in the subsequent molding and firing step.

5) Molding and firing step In this step, the inorganic material (also referred to as second material) obtained through the second firing step is formed into a molded body, and the molded body is fired at a molding and firing temperature higher than the calcining temperature. . In this molding and firing step, it is preferable not to pulverize the second material in a solvent before molding into a molded body. In some cases, the second material may contain an excessive amount of components that volatilize in the molding and firing step, and this prevents the excessive volatile components from touching the solvent and changing the state. It is possible to more reliably suppress a decrease in density associated with a change in the state of the inorganic material. For example, when Li ₂ CO ₃ is included in the inorganic material, it can be suppressed that Li ₂ O generated by the second baking step is changed to LiOH or Li ₂ CO ₃ due to being excessively contained. . In the first and second mixing steps described above, when mixing in a solvent is performed, it is more preferable not to perform mixing in the solvent before the molding and firing step. In addition, after the second firing step, the calcination is performed twice, and the second material is hardly solidified and fixed, so that it can be formed into a molded body relatively easily by simple crushing. For example, the molded body is formed into an arbitrary shape using the obtained second material by cold isotropic forming (CIP), hot isotropic forming (HIP), mold forming, hot pressing, or the like. Can do.

According to the manufacturing method of the solid electrolyte of the present embodiment described in detail above, after calcining the inorganic material in the first firing step, the amount of inorganic material empirically obtained is added and re-calcined, and then Since molding and baking are performed, a change in volume accompanying a change in state of the inorganic material can be further reduced, and a shift in composition can be suppressed more accurately. Therefore, it can have higher battery performance. In particular, lithium-containing garnet-type oxides are likely to be affected by volume changes and the like, and the significance of applying the present invention is high. As a result, the relative density can be increased to 90% or more, and the conductivity is increased. It is estimated that it can be further increased to 1.0 × 10 ⁻⁵ or more.

  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 above-described embodiment, the method for producing a solid electrolyte has been described as a method for producing a lithium-containing garnet-type oxide. However, the present invention is not particularly limited thereto, and is not particularly limited as long as the solid electrolyte is molded and fired. The method for producing a solid electrolyte of the present invention can be applied. In addition, it is more preferable to apply to the manufacturing method of the solid electrolyte used for a lithium secondary battery.

  Below, the example which produced the solid electrolyte of the lithium containing garnet-type oxide concretely is demonstrated as an Example.

[Example 1]
Li ₂ CO ₃ , La (OH) ₃ , and ZrO ₂ are used as starting materials. The starting materials are weighed so as to have a stoichiometric ratio of the basic composition of Li ₇ La ₃ Zr ₂ O ₁₂ , and planets are obtained in ethanol. Mixing and grinding were performed for 4 hours with a ball mill (300 rpm / zirconia balls) (first mixing step). Next, after the mixed powder of the starting material (inorganic material) was separated from the balls and ethanol, calcination was performed in an air atmosphere at 950 ° C. for 10 hours in an Al ₂ O ₃ crucible (first firing) Process). Thereafter, Li ₂ CO ₃ is added to the calcined powder so that the amount of Li is 5 atomic% with respect to the amount of Li in the inorganic material for the purpose of compensating 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) in ethanol for 6 hours (second mixing step). The obtained powder was again calcined again at 950 ° C. for 5 hours under atmospheric pressure (second firing step). Subsequently, the obtained powder was molded and subjected to isostatic pressing (CIP) between cold water, and then the firing temperature was set to 1150 ° C. and the main firing was performed under atmospheric conditions for 36 hours. The electrolyte was Example 1. CIP was performed under the conditions of 27 ° C. and 200 MPa using water as a solvent.

[Examples 2 to 6]
In the second mixing step, Li ₂ CO ₃ is adjusted so that the Li amount is 7.5 atomic%, 10.0 atomic%, 12.5 atomic%, 15.0 atomic%, 20.0 atomic% with respect to the Li amount in the inorganic material. Except for the addition, the same steps as in Example 1 were performed, and the obtained solid electrolytes were referred to as Examples 2 to 6, respectively.

[Example 7]
Li ₂ CO ₃ , La (OH) ₃ , and Nb ₂ O ₅ are used as starting materials, and the starting materials are weighed so as to have a stoichiometric ratio of the basic composition of Li ₅ La ₃ Nb ₂ O _12. Then, mixing and pulverization were performed with a planetary ball mill (300 rpm / zirconia ball) for 4 hours (first mixing step). Next, after the mixed powder of the starting material (inorganic material) was separated from the balls and ethanol, calcination was performed in an air atmosphere at 950 ° C. for 10 hours in an Al ₂ O ₃ crucible (first firing) Process). Thereafter, Li ₂ CO ₃ is added to the calcined powder so that the amount of Li is 10.0 atomic% with respect to the amount of Li in the inorganic material, in order to compensate for the loss of Li in the main firing, For the purpose of grinding and mixing the calcined powder, it was ground and mixed in a planetary ball mill (300 rpm / zirconia balls) in ethanol for 6 hours (second mixing step). The obtained powder was again calcined again at 950 ° C. for 5 hours under atmospheric pressure (second firing step). Subsequently, the obtained powder is molded and subjected to isostatic pressing (CIP) between cold water, and then the firing temperature is set to 1200 ° C. and the main firing is performed under atmospheric conditions for 36 hours. The electrolyte was Example 5. CIP was performed under the conditions of 27 ° C. and 200 MPa using water as a solvent.

[Comparative Examples 1-3]
A solid electrolyte obtained through the same steps as in Example 1 except that the second mixing step and the second firing step were omitted was used as Comparative Example 1. Moreover, the solid electrolyte obtained through the process similar to Example 5 was set as the comparative example 2 except having omitted the 2nd mixing process and the 2nd baking process. Moreover, the excess of Li ₂ CO ₃ in 0.35mol in the first mixing step, comparing the second mixing step and the solid electrolyte, except for omitting the second firing step obtained through the same process as in Example 5 Example It was set to 3.

(Relative density measurement)
The relative density of each sample was calculated by dividing the dry weight measured with an electronic balance by the volume obtained from the actual size measured using a caliper, and calculating the theoretical density, calculating the theoretical density, and calculating the measured density to the theoretical density. The value calculated by dividing by 100 and multiplying by 100 was taken as the relative density (%).

(XRD measurement)
The phase of each sample was identified by using a sample powder XRD measuring device (RINT-TTR manufactured by Rigaku Corporation) and setting the range of CuKa, 2θ to 10 to 80 ° and 0.02 ° step / 1 sec.

(Conductivity measurement)
The conductivity of each sample was measured using an AC impedance analyzer (Agilent's impedance analyzer 4294A) in a constant temperature bath set at 25 ° C., with a frequency of 30 MHz to 40 Hz and an amplitude voltage of 100 mV. Thus, the resistance value was obtained and the conductivity was calculated. An Au electrode was used as a blocking electrode when measuring with an AC impedance analyzer. The Au electrode was formed by baking a commercially available Au paste on each sample at 850 ° C. for 30 minutes.

(Experimental result)
2 is an XRD measurement result of Li ₇ La ₃ Zr ₂ O ₁₂ of Comparative Example 1 and Examples 3 and 6, and FIG. 3 is a graph of Li ₅ La ₃ Nb ₂ O ₁₂ of Comparative Example 2 and Example 7. FIG. 4 is a plot showing the relationship between the amount of Li ₂ CO ₃ added and the relative density, and FIG. 5 is a plot showing the relationship between the amount of Li ₂ CO ₃ added and the conductivity. is there. These data are collectively shown in Table 1. In FIGS. 2 and 3, when Li ₂ CO ₃ is not added, Li deficiency occurs due to evaporation of Li during the main firing, and La ₂ Zr ₂ O ₇ , La ₂ Nb ₂ O _8, etc. are generated as subphases. I found out that Here, it was found that a single phase of Li ₇ La ₃ Zr ₂ O ₁₂ or Li ₅ La ₃ Nb ₂ O ₁₂ can be obtained by adding an appropriate amount of Li ₂ CO ₃ after calcination. However, when Li ₂ CO ₃ was excessively added, it became clear that many peaks that could not be identified began to occur, and it was found that the conductivity decreased (see FIG. 5). From this, it was found that there is an optimum addition amount for obtaining a single phase of Li ₇ La ₃ Zr ₂ O ₁₂ or Li ₅ La ₃ Nb ₂ O ₁₂ . It was found that the relative density was low when the amount of Li ₂ CO ₃ added was small. This is thought to be because a subphase is generated due to lack of Li. The presence of a peak which can not be identified in the results of XRD When li ₂ CO ₃ excess is added has been confirmed, the relative density does not decrease but is presumed secondary phase is the conductivity decreases is generated. Further, regarding the conductivity, it was found that when the addition amount is insufficient (less than 4 atomic%, etc.), the relative density is low, and the subphase is also present, so the conductivity is low. On the other hand, when the amount added increased (exceeding 15 atomic%), the relative density was high, but the sub-phase was present, so that the conductivity tended to decrease. When Li ₇ La ₃ Zr ₂ O ₁₂ is used as the basic composition, if the Li content is added in the range of 4 atomic% or more and 20 atomic% or less with respect to the Li content in the inorganic material, the relative density becomes 70% or more. It exhibits a conductivity of 0 × 10 ⁻⁵ Scm ⁻¹ or more, and when added in the range of 6 atomic% or more and 14 atomic% or less, the relative density becomes 80% or more and exhibits a conductivity of 1.0 × 10 ⁻⁴ Scm ⁻¹ or more. Became clear. Further, when Li ₅ La ₃ Nb ₂ O ₁₂ is used as the basic composition, when the Li amount is added in the range of 5 atomic% or more and 20 atomic% or less with respect to the Li amount in the inorganic material, the relative density becomes 70% or more, It exhibits a conductivity of 1.0 × 10 ⁻⁶ Scm ⁻¹ or more, and when added in the range of 7 atomic% or more and 13 atomic% or less, the relative density becomes 80% or more, and the conductivity is 1.0 × 10 ⁻⁵ Scm ⁻¹ or more. It became clear to show the degree.

Here, for Li ₇ La ₃ Zr ₂ O ₁₂ , Angew. Chem. Int. Ed. 2007, 46 7778-7781, its conductivity is reported. However, when the inventors experimented, the conductivity did not exceed 1.0 × 10 ⁻⁵ Scm ⁻¹ in the production method described in the paper. Therefore, it was revealed that the method for producing a solid electrolyte and the solid electrolyte of the present invention have unprecedented high battery performance. In addition, Li ₅ La ₃ Nb ₂ O _{12 is} described in J. Am. Ceram. Soc. 2005, 88 411-418, the conductivity is reported to be 8.0 × 10 ⁻⁶ Scm ^−1, and the solid electrolyte of the present invention is higher than the reported value. The method for producing the solid electrolyte of the present invention and the solid The electrolyte was found to have higher battery performance.

  The present invention is applicable to the battery industry.

2 is a cross-sectional view illustrating a schematic configuration of a coin-type battery 20. FIG. XRD measurement results of Li ₇ La ₃ Zr ₂ O ₁₂ of Comparative Example 1 and Examples 3 and 6 XRD measurement results of Li ₅ La ₃ Nb ₂ O ₁₂ of Comparative Example 2 and Example 7 Plot diagram showing relationship between addition amount of Li ₂ CO ₃ and relative density Plot diagram showing relationship between conductivity and conductivity of Li ₂ CO ₃

Explanation of symbols

  20 coin type battery, 21 battery case, 22 positive electrode, 23 negative electrode, 24 solid electrolyte, 25 gasket, 26 sealing plate.

Claims (11)

A lithium-containing garnet-type oxide used in a lithium secondary battery,
The relative density with respect to the theoretical density is 70 (%) or more,
The conductivity is 1.0 × 10 ⁻⁵ (Scm ⁻¹ ) or more,
Lithium-containing garnet oxide. Basic composition _{Li x A y B 3-y} M 2 O 12 ( where, A is any one or more of the second group elements, B is a lanthanoid element and Y, any one or more of Sc, y is 0 or more (When x = 7 + y, M is at least one of Ti, Zr, and Hf, and when x = 5 + y, M is at least one of V, Nb, and Ta.) The lithium-containing garnet-type oxide according to claim 1, wherein The basic composition is Li ₇ La ₃ Zr ₂ O ₁₂ ;
The lithium-containing garnet-type oxide according to claim 2, wherein the conductivity is 1.0 × 10 ⁻⁴ (Scm ⁻¹ ) or more. The basic composition is _{Li 5 La 3 Nb 2 O 12} , Li-containing garnet-type oxide according to claim 2. A positive electrode having a positive electrode active material;
A negative electrode having a negative electrode active material;
A solid electrolyte comprising the lithium-containing garnet-type oxide according to any one of claims 1 to 3, which is interposed between the positive electrode and the negative electrode and conducts lithium ions.
Rechargeable lithium battery. A method for producing a solid electrolyte that conducts lithium ions,
A first mixing step of mixing a plurality of types of inorganic materials including those whose state changes by firing at a predetermined temperature;
A first firing step of firing the mixed inorganic material at a predetermined first temperature that is equal to or higher than the predetermined temperature and lower than a molding firing temperature that is fired after molding, to obtain a first material;
A second mixing step of adding and mixing a predetermined addition amount of the inorganic material determined according to the firing of the inorganic material to the first material;
A second baking step of baking the first material added with the inorganic material at a predetermined second temperature that is equal to or higher than the predetermined temperature and lower than the molding baking temperature to obtain a second material;
A molding and firing step of molding the second material into a molded body and firing at the molding and firing temperature;
A method for producing a solid electrolyte comprising: In the first mixing step, the inorganic material is mixed and ground in a solvent,
In the second mixing step, the first material is mixed and ground in a solvent,
The method for producing a solid electrolyte according to claim 6, wherein in the molding and firing step, the second material is not pulverized in a solvent before molding into a molded body. In the first mixing step, the basic composition is Li _x A _y B _{3 -y} M ₂ O ₁₂ (where A is one or more of group 2 elements, B is any of lanthanoid elements and Y, Sc) 1 or more, y is a positive number of 0 or more, and when x = 7 + y, M is one or more of Ti, Zr, and Hf, and when x = 5 + y, M is any of V, Nb, and Ta The method for producing a solid electrolyte according to claim 6 or 7, wherein an inorganic material is mixed. In the first mixing step, an inorganic material whose basic composition is Li ₇ La ₃ Zr ₂ O ₁₂ is mixed,
9. The solid electrolyte according to claim 8, wherein in the second mixing step, Li corresponding to a Li amount in a range of 4 atomic% to 20 atomic% with respect to an Li amount in the inorganic material is added as the predetermined addition amount. Manufacturing method.   10. The solid electrolyte according to claim 9, wherein in the second mixing step, Li corresponding to a Li amount in a range of 6 atomic% to 14 atomic% with respect to an Li amount in the inorganic material is added as the predetermined addition amount. Manufacturing method. In the first mixing step, an inorganic material whose basic composition is Li ₅ La ₃ Nb ₂ O ₁₂ is mixed,
9. The solid electrolyte according to claim 8, wherein in the second mixing step, Li corresponding to a Li amount in a range of 7 atomic% or more and 13 atomic% or less is added as the predetermined addition amount with respect to the Li amount in the inorganic material. Manufacturing method.

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