JP2016072210A - Composition for anti-lithium reduction layer formation, film formation method of anti-lithium reduction layer, and lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a composition for anti-lithium reduction layer formation which enables the formation of an anti-lithium reduction layer superior in Li ion conductivity and anti-Li reduction property; a film formation method of an anti-lithium reduction layer by use of such a composition for anti-lithium reduction layer formation; and a lithium secondary battery including such an anti-lithium reduction layer.SOLUTION: A composition for anti-lithium reduction layer formation according to the present invention comprises: a solvent; and a lithium compound, a lanthanum compound, a zirconium compound, and a compound including a metal M, each exhibits solubility in the solvent. With respect to a stoichiometric composition in a compound expressed by the general formula (I), the content of the lithium compound is 1.05-2.50 times, the contents of the lanthanum compound and the zirconium compound are each 0.70-1.00 times, and the content of the compound including the metal M is identical thereto: LiLa(Zr,M)O(I).SELECTED DRAWING: None

Description

  The present invention relates to a composition for forming a lithium-resistant reduction layer, a method for forming a lithium-resistant reduction layer, and a lithium secondary battery.

  Lithium secondary batteries are used as a power source for many electric devices such as portable information devices. This lithium secondary battery includes a positive electrode, a negative electrode, and an electrolyte layer that is disposed between these layers and mediates conduction of lithium ions.

  In recent years, an all-solid-state lithium battery using a solid electrolyte as a constituent material of an electrolyte layer, that is, an all-solid-state lithium battery having a solid electrolyte layer has been proposed as a lithium secondary battery that achieves both high energy density and safety. Yes.

  As a constituent material of the solid electrolyte layer provided in such an all-solid-state lithium battery, a material containing a compound represented by the following general formula (A) (hereinafter simply referred to as “compound A”) is known ( For example, refer to Patent Document 1 and Non-Patent Document 1.)

_{Li 7-x La 3 (Zr} 2-x, Nb x) O 12 ··· (A)
[In formula, X represents 0-2. ]

  In forming the solid electrolyte layer, in Patent Document 1 and Non-Patent Document 1, Compound A is generated by a solid-phase reaction. Specifically, Li compound, La compound, Zr compound, and Nb compound are mixed on a molar ratio basis in an equivalent amount to Compound A according to the stoichiometric composition with respect to Compound A, and the resulting mixture is obtained. Temporary firing. And in order to make up for the Li deficiency in the post-sintering main sintering, after adding a Li compound of 4 to 20 atomic% in terms of Li with respect to the Li amount of the compound A, for example, 900 ° C. to 1150 ° C. It is produced | generated by performing this sintering in a high temperature area | region like this.

  Further, the compound A obtained as described above has excellent Li ion conductivity and excellent Li reduction resistance. Therefore, for example, when the negative electrode is made of lithium, the all-solid-state lithium secondary battery is configured to have a lithium-resistant reduction layer between the negative electrode and the solid electrolyte layer. In order to suppress or prevent the occurrence of a short circuit due to the occurrence of dendrite growth, it is conceivable that the lithium-resistant reduction layer contains the compound A.

  However, when the lithium reduction layer is formed by the above-described solid-phase reaction, the particles forming the solid electrolyte layer and the lithium-resistant reduction layer come into contact with each other by point contact at these interfaces. Therefore, although the lithium reduction layer itself has excellent Li ion conductivity, it cannot be said that excellent Li ion conductivity is obtained at the interface.

Japanese Patent No. 5083336

S. Ohta, T .; Kobayashi, T .; Asaoka, J. et al. Power Sources, 196, 3342 (2011)

  One of the objects of the present invention is a composition for forming a lithium-resistant reduction layer capable of forming a lithium-resistant reduction layer having excellent Li ion conductivity and Li-reduction resistance, and a composition for forming such a lithium-resistant reduction layer. An object of the present invention is to provide a method for forming a lithium-resistant reduction layer using an object, and a lithium secondary battery including such a lithium-resistant reduction layer.

Such an object is achieved by the present invention described below.
The composition for forming a lithium-resistant reduction layer of the present invention comprises a solvent,
A lithium compound, a lanthanum compound, a zirconium compound, and a compound comprising a metal M,
Each of the lithium compound, the lanthanum compound, the zirconium compound and the compound comprising the metal M exhibits solubility in the solvent,
The lithium compound is 1.05 to 2.50 times the stoichiometric composition in the compound represented by the general formula (I),
The lanthanum compound is 0.70 times or more and 1.00 times or less with respect to the stoichiometric composition in the compound represented by the general formula (I),
The zirconium compound is 0.70 times or more and 1.00 times or less with respect to the stoichiometric composition in the compound represented by the general formula (I),
The compound including the metal M is included in the same amount as the stoichiometric composition in the compound represented by the general formula (I).
_{Li 7-x La 3 (Zr} 2-x, M x) O 12 ··· (I)
[Wherein, metal M represents at least one of Nb, Sc, Ti, V, Y, Hf, Ta, Al, Si, Ga, Ge, Sn, and Sb, and X represents 0-2. ]

  According to the composition for forming a lithium-resistant reduction layer having such a composition ratio, a lithium-resistant reduction layer having excellent Li ion conductivity and Li-resistance can be formed.

In the composition for forming a lithium-resistant reduction layer according to the present invention, the lithium compound is at least one of a lithium metal salt compound and a lithium alkoxide compound,
The lanthanum compound is at least one of a lanthanum metal salt compound and a lanthanum alkoxide compound,
The zirconium compound is at least one of a zirconium metal salt compound and a zirconium alkoxide compound,
The compound including the metal M is preferably at least one of a metal salt compound of the metal M and a metal alkoxide compound.

  Thereby, the compound represented with the said general formula (I) can be obtained with a high production rate from the composition for lithium-resistant reduction layer formation which is a mixture of these compounds.

  In the composition for forming a lithium-resistant reduction layer according to the present invention, the solvent is water, a single organic solvent, a mixed solvent containing water and at least one organic solvent, and a mixture containing at least two organic solvents. It is preferably one of the solvents.

  Thereby, a lithium compound, a lanthanum compound, a zirconium compound, and the compound provided with the said metal M can be reliably dissolved in the composition for lithium-resistant reduction layer formation, respectively.

The method for forming a lithium-resistant reduction layer according to the present invention includes a first step of forming a liquid film using the composition for forming a lithium-resistant reduction layer according to the present invention,
A second step of heating the liquid coating,
A lithium-resistant reduction layer containing the compound represented by the general formula (I) is obtained.

  By such a method of forming a lithium-resistant reduction layer, a lithium-resistant reduction layer having excellent Li ion conductivity and Li reduction resistance can be formed.

  In the method for forming a lithium-resistant reduction layer according to the present invention, the liquid film is preferably formed using a coating method.

  According to the coating method, it is possible to easily form a liquid film having a uniform film thickness and thus a lithium-resistant reduction layer.

  In the method for forming a lithium-resistant reduction layer according to the present invention, the second step includes a first heat treatment for drying the liquid film, and a metal oxide of lithium, lanthanum, zirconium, and the metal M. 2 and a third heat treatment for producing and sintering the compound represented by the general formula (I).

  Thereby, in the lithium-resistant reduction layer, the crystal structure of the compound represented by the general formula (I) can have a cubic garnet-type crystal structure, and the general formula forming an adjacent granule Since the crystals of the compound represented by (I) can be sintered together, the lithium-resistant reduction layer exhibits better ionic conductivity.

  In the method for forming a lithium-resistant reduction layer according to the present invention, the heating temperature in the first heat treatment is preferably 50 ° C. or higher and 250 ° C. or lower.

  Thereby, the compound represented with the said general formula (I) which has a cubic garnet-type crystal structure can be obtained with a higher production rate.

  In the method for forming a lithium-resistant reduction layer according to the present invention, the heating temperature in the second heat treatment is preferably 400 ° C. or higher and 550 ° C. or lower.

  Thereby, the compound represented with the said general formula (I) which has a cubic garnet-type crystal structure can be obtained with a higher production rate.

  In the method for forming a lithium-resistant reduction layer according to the present invention, the heating temperature in the third heat treatment is preferably 600 ° C. or higher and 900 ° C. or lower.

  Thereby, the compound represented with the said general formula (I) which has a cubic garnet-type crystal structure can be obtained with a higher production rate.

The lithium secondary battery of the present invention comprises a solid electrolyte layer,
A lithium-resistant reduction layer disposed in contact with the solid electrolyte layer,
The lithium-resistant reduction layer contains a compound represented by the general formula (I),
The interface between the lithium-resistant reduction layer and the solid electrolyte layer is a continuous layer of the lithium-resistant reduction layer and the solid electrolyte layer.
_{Li 7-x La 3 (Zr} 2-x, M x) O 12 ··· (I)
[Wherein, metal M represents at least one of Nb, Sc, Ti, V, Y, Hf, Ta, Al, Si, Ga, Ge, Sn, and Sb, and X represents 0-2. ]

  Thereby, the lithium ion conductivity can be further improved between the lithium-resistant reduction layer and the solid electrolyte layer.

The lithium secondary battery of the present invention further comprises an active material molded body,
The active material molded body is provided such that a first surface, which is a part of the surface, is in contact with the lithium-resistant reduction layer, and a second surface other than the first surface is in contact with the solid electrolyte layer. ,
In the first aspect, it is preferable that a continuous layer of the lithium-resistant reduction layer and the active material molded body is formed at the interface between the lithium-resistant reduction layer and the active material molded body.

  Thereby, the further improvement of lithium ion conductivity between the layers of a lithium-resistant reduction layer, a solid electrolyte layer, and an active material molded object is achieved.

It is a longitudinal cross-sectional view which shows 1st Embodiment of the lithium secondary battery of this invention. It is a figure for demonstrating the manufacturing method of the lithium secondary battery shown in FIG. It is a figure for demonstrating the manufacturing method of the lithium secondary battery shown in FIG. It is a figure for demonstrating the manufacturing method of the lithium secondary battery shown in FIG. It is a longitudinal cross-sectional view which shows 2nd Embodiment of the lithium secondary battery of this invention. It is an X-ray diffraction spectrum measured in Examples 1 to 3 and Comparative Examples 1 and 2. 4 is an X-ray diffraction spectrum measured in Examples 9, 10 and 14. FIG. It is the X-ray-diffraction spectrum measured in Examples 11-13.

  Hereinafter, a composition for forming a lithium-resistant reduction layer, a method for forming a lithium-resistant reduction layer, and a lithium secondary battery according to the present invention will be described in detail based on embodiments shown in the accompanying drawings.

  In the following, prior to explaining the composition for forming a lithium-resistant reduction layer and the method for forming a lithium-resistant reduction layer of the present invention, first, the lithium secondary battery of the present invention will be described.

<Lithium secondary battery>
<< First Embodiment >>
FIG. 1 is a longitudinal sectional view showing a first embodiment of a lithium secondary battery of the present invention. In the following, for convenience of explanation, the upper side of FIG. 1 is referred to as “upper” and the lower side is referred to as “lower”. In FIG. 1, the dimensions and ratios of the constituent elements are appropriately changed in order to make the drawing easier to see.

  The lithium secondary battery 100 includes an electrode assembly 10, a lithium-resistant reduction layer 30 joined on the electrode composite 10, and an electrode 20 joined on the lithium-resistant reduction layer 30. The lithium secondary battery 100 is a so-called all-solid lithium ion secondary battery.

  As shown in FIG. 1, the electrode assembly 10 includes a current collector 1, an active material molded body 2, and a solid electrolyte layer 3. Hereinafter, a configuration in which the active material molded body 2 and the solid electrolyte layer 3 are combined is referred to as a composite 4. The composite 4 is located between the current collector 1 and the lithium-resistant reduction layer 30 and is bonded to each other on a pair of opposing surfaces.

  The current collector 1 is an electrode for taking out the current generated by the battery reaction, and is provided in contact with the active material molded body 2 exposed from the solid electrolyte layer 3 on one surface 4 a of the composite 4.

  The current collector 1 functions as a positive electrode when an active material molded body 2 described later is composed of a positive electrode active material, and functions as a negative electrode when the active material molded body 2 is composed of a negative electrode active material.

  Moreover, as a forming material (component material) of the current collector 1, for example, copper (Cu), magnesium (Mg), titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc ( One metal selected from the group consisting of Zn), aluminum (Al), germanium (Ge), indium (In), gold (Au), platinum (Pt), silver (Ag) and palladium (Pd) And alloys containing two or more metal elements selected from this group.

  The shape of the current collector 1 is not particularly limited, and examples thereof include a plate shape, a foil shape, and a net shape. In addition, the surface of the current collector 1 may be smooth or uneven.

  The active material molded body 2 is a porous molded body using an inorganic electrode active material as a forming material (constituent material).

  The plurality of pores of the active material molded body 2 composed of the porous body form communication holes that are communicated with each other in a mesh shape inside the active material molded body 2.

  The current collector 1 can be either a positive electrode or a negative electrode by appropriately selecting the type of forming material contained in the active material molded body 2.

  In the case where the current collector 1 is used as a positive electrode, for example, a known lithium double oxide as a positive electrode active material can be used as a material for forming the active material molded body 2.

  In the present specification, the “lithium double oxide” refers to an oxide that always contains lithium and contains two or more kinds of metal ions as a whole and in which the presence of oxo acid ions is not recognized.

Examples of such lithium double oxides include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , Li ₂ Mn ₂ O ₃ , LiFePO ₄ , Li ₂ FeP ₂ O ₇ , LiMnPO ₄ , LiFeBO ₃ , Li ₃ V _{2. (PO 4) 3, Li 2} CuO 2, LiFeF 3, Li 2 FeSiO 4, Li 2 MnSiO 4 , and the like. In this specification, solid solutions in which some atoms in the crystal of these lithium double oxides are substituted with other transition metals, typical metals, alkali metals, alkali rare earths, lanthanoids, chalcogenides, halogens, etc. These solid solutions can be used as the positive electrode active material.

Further, when the current collector 1 is a negative electrode, the active material molded body 2 is made of, for example, a lithium composite oxide such as Li ₄ Ti ₅ O ₁₂ or Li ₂ Ti ₃ O ₇ as a negative electrode active material. Can be used.

  Moreover, the porosity of the active material molded body 2 is preferably 10% or more and 50% or less, and more preferably 30% or more and 50% or less. Since the active material molded body 2 has such a porosity, the surface area in the pores of the active material molded body 2 is increased, and the contact area between the active material molded body 2 and the solid electrolyte layer 3 is easily expanded. It becomes easy to increase the capacity of the lithium battery using the electrode assembly 10.

  The porosity is, for example, (1) the volume (apparent volume) of the active material molded body 2 including pores obtained from the outer dimensions of the active material molded body 2, and (2) the mass of the active material molded body 2 (3) The density can be measured based on the following formula (II) from the density of the active material constituting the active material molded body 2.

  Moreover, although mentioned later in detail, the porosity of the active material molded object 2 is controllable by using the pore making material comprised in a particulate organic substance in the process of forming the active material molded object 2. FIG.

  The resistivity of the active material molded body 2 is preferably 700 Ω / cm or less, and more preferably 100 Ω / cm or less. When the active material molded body 2 has such a resistivity, a sufficient output can be obtained when a lithium battery is formed using the electrode composite 10.

  The resistivity can be measured by attaching a copper foil used as an electrode to the surface of the active material molded body 2 and performing DC polarization measurement.

  The solid electrolyte layer 3 is provided in contact with the surface of the active material molded body 2 including the inside of the pores of the active material molded body 2 using the solid electrolyte as a forming material (constituent material).

The solid electrolyte, other compounds represented by the general formula (I) to be described later, for _{example, SiO 2 -P 2 O 5 -Li} 2 O, SiO 2 -P 2 O 5 -LiCl, Li 2 O-LiCl-B ₂ O ₃ , Li _3.4 V _0.6 Si _0.4 O ₄ , Li ₁₄ ZnGe ₄ O ₁₆ , Li _3.6 V _0.4 Ge _0.6 O ₄ , Li _1.3 Ti _1.7 Al _0.3 (PO ₄ ) ₃ , Li _2.88 PO _3.73 N _0.14 , LiNbO ₃ , Li _0.35 La _0.55 TiO ₃ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₂ S—SiS _{2, Li 2 S-SiS 2} -LiI, Li 2 S-SiS 2 -P 2 S 5, LiPON, Li 3 N, LiI, LiI-CaI 2, LiI-CaO, LiAlCl 4, LiAlF 4, LiI-Al 2 O _{, LiF-Al 2 O 3,} LiBr-Al 2 O 3, Li 2 O-TiO 2, La 2 O 3 -Li 2 O-TiO 2, Li 3 NI 2, Li 3 N-LiI-LiOH, Li 3 N _{-LiCl, Li 6 NBr 3, LiSO} 4, Li 4 SiO 4, Li 3 PO 4 -Li 4 SiO 4, Li 4 GeO 4 -Li 3 VO 4, Li 4 SiO 4 -Li 3 VO 4, Li 4 GeO 4 Examples thereof include oxides such as —Zn ₂ GeO ₂ , Li ₄ SiO ₄ —LiMoO ₄ , and LiSiO ₄ —Li ₄ ZrO ₄ , sulfides, halides, and nitrides. These solid electrolytes may be crystalline or amorphous. Further, in the present specification, solid solutions in which some atoms of these compositions are substituted with other transition metals, typical metals, alkali metals, alkali rare earths, lanthanoids, chalcogenides, halogens, and the like may be used as solid electrolytes. it can.

  In addition, by using the compound represented by the following general formula (I) as the solid electrolyte, the interface between the solid electrolyte layer 3 and the lithium-resistant reduction layer 30 becomes more uniform. It can be made better.

The ionic conductivity of the solid electrolyte layer 3 is preferably 1 × 10 ⁻⁵ S / cm or more, and more preferably 5 × 10 ⁻⁵ S / cm or more. Since the solid electrolyte layer 3 has such ionic conductivity, ions contained in the solid electrolyte layer 3 at a position away from the surface of the active material molded body 2 reach the surface of the active material molded body 2, and the active material It becomes possible to contribute to the battery reaction in the molded body 2. Therefore, the utilization factor of the active material in the active material molded body 2 is improved, and the capacity can be increased. At this time, if the ionic conductivity is less than the lower limit value, depending on the type of the solid electrolyte layer 3, only the active material in the vicinity of the surface layer on the surface facing the counter electrode in the active material molded body 2 contributes to the battery reaction. May decrease.

  The “ionic conductivity of the solid electrolyte layer 3” refers to the “bulk conductivity” that is the conductivity of the inorganic electrolyte itself that constitutes the solid electrolyte layer 3, and the crystal in the case where the inorganic electrolyte is crystalline. It means “total ionic conductivity” which is the sum of “flow field ionic conductivity” which is the conductivity between particles.

  The ionic conductivity of the solid electrolyte layer 3 is, for example, that a solid electrolyte powder press-molded into a tablet shape at 624 MPa is sintered at 700 ° C. for 8 hours in an air atmosphere, and has a diameter of 0.5 cm and a thickness of 100 nm by sputtering. It can be measured by forming platinum electrodes on both sides of the press-molded body and performing the AC impedance method. For example, an impedance analyzer (manufactured by Solartron, model number SI1260) is used as the measuring device.

  Further, as will be described in detail later, both surfaces 4 a and 4 b of the composite 4 are preferably polished surfaces polished during manufacturing, and the active material molded body 2 is exposed from the solid electrolyte layer 3. Therefore, when such a polishing process is performed, scratch marks (polishing marks) which are traces of the polishing process are left on both surfaces 4a and 4b.

  The electrode assembly 10 according to the present embodiment includes a binder that joins the active materials together when the active material molded body 2 is molded, and a conductive auxiliary agent that ensures the conductivity of the active material molded body 2. It is molded without using organic substances and is almost composed of inorganic substances only. Specifically, in the electrode assembly 10 of the present embodiment, the mass reduction rate when the composite 4 (the active material molded body 2 and the solid electrolyte layer 3) is heated at 400 ° C. for 30 minutes is 5% by mass or less. It has become. The mass reduction rate is preferably 3% by mass or less, more preferably 1% by mass or less, and particularly preferably no mass reduction is observed or an error range. That is, the mass reduction rate when the composite 4 is heated at 400 ° C. for 30 minutes is preferably 0% by mass or more. Since the composite 4 has such a mass reduction rate, a substance such as a solvent or adsorbed water that evaporates under a predetermined heating condition, or an organic substance that is burned or oxidized under a predetermined heating condition is vaporized in the composite 4. Therefore, only 5% by mass or less is included with respect to the entire configuration.

  Note that the mass reduction rate of the composite 4 is determined by heating the composite 4 under a predetermined heating condition using a differential thermal-thermogravimetric simultaneous measurement device (TG-DTA). The mass of the body 4 is measured and can be calculated from the ratio between the mass before heating and the mass after heating.

In the electrode assembly 10 of the present embodiment, the active material molded body 2 has communication holes in which a plurality of pores communicate with each other in a network shape, and the solid portion of the active material molded body 2 also has a network structure. Forming. For example, LiCoO ₂ that is a positive electrode active material is known to have anisotropy in the electronic conductivity of crystals. Therefore, when trying to form an active material molded body using LiCoO ₂ as a forming material, a structure in which pores are extended in a specific direction, such as forming pores by machining, Depending on the direction of the electron conductivity, it may be difficult to conduct electrons inside. However, if the pores are connected in a network shape like the active material molded body 2 and the solid portion of the active material molded body 2 has a network structure, the anisotropy of the electron conductivity or ion conductivity of the crystal Regardless, an electrochemically lubricious continuous surface can be formed. Therefore, good electronic conduction can be ensured regardless of the type of active material used.

  In addition, in the electrode assembly 10 of the present embodiment, since the composite 4 has the above-described configuration, the amount of the binder and the conductive assistant contained in the composite 4 is suppressed, and the binder and the conductive assistant are suppressed. Compared with the case where an agent is used, the capacity density per unit volume of the electrode assembly 10 is improved.

  In the electrode assembly 10 of the present embodiment, the solid electrolyte layer 3 is also in contact with the surfaces of the pores of the porous active material molded body 2. Therefore, the contact area between the active material molded body 2 and the solid electrolyte layer 3 is larger than when the active material molded body 2 is not a porous body or when the solid electrolyte layer 3 is not formed in the pores. , Interface impedance can be reduced. Therefore, good charge transfer is possible at the interface between the active material molded body 2 and the solid electrolyte layer 3.

  Furthermore, in the electrode assembly 10 of the present embodiment, the current collector 1 is in contact with the active material molded body 2 exposed on one surface of the composite 4, whereas the solid electrolyte layer 3 is porous. It penetrates into the pores of the active material molded body 2 and is in contact with the surface of the active material molded body 2 other than the surface including the inside of the pores and in contact with the current collector 1. In the electrode assembly 10 having such a structure, the contact area between the active material molded body 2 and the solid electrolyte layer 3 (the first contact area) rather than the contact area between the current collector 1 and the active material molded body 2 (first contact area). It is clear that the second contact area) is larger.

  Here, if the electrode composite has the same configuration of the first contact area and the second contact area, the interface between the current collector 1 and the active material molded body 2 is closer to the active material molded body 2. Since the charge transfer is easier than the interface with the solid electrolyte layer 3, the interface between the active material molded body 2 and the solid electrolyte layer 3 becomes a bottleneck for charge transfer. Therefore, good charge transfer is inhibited as the whole electrode assembly. However, in the electrode assembly 10 of the present embodiment, since the second contact area is larger than the first contact area, it is easy to eliminate the bottleneck described above, and the electrode assembly as a whole has good charge transfer. It becomes possible.

  For these reasons, the electrode assembly 10 having the above-described configuration manufactured by the manufacturing method of the present embodiment described below improves the capacity of a lithium battery using the electrode assembly 10 and has a high output. can do.

  The electrode 20 is provided in contact with the surface of the lithium-resistant reduction layer 30 opposite to the composite 4.

  The electrode 20 functions as a negative electrode when the active material molded body 2 is composed of a positive electrode active material, and functions as a positive electrode when the active material molded body 2 is composed of a negative electrode active material.

  As a forming material (constituent material) of this electrode 20, when the electrode 20 is a negative electrode, lithium (Li) is mentioned, for example, When the electrode 20 is a positive electrode, aluminum (Al) is mentioned, for example.

  Although the thickness of the electrode 20 is not specifically limited, For example, it is preferable that they are 10 micrometers or more and 100 micrometers or less, and it is more preferable that they are 10 micrometers or more and 30 micrometers or less.

  The lithium-resistant reduction layer 30 is provided in contact with the composite 4 on the other surface 4b and in contact with the electrode 20 on one surface 30a. The lithium-resistant reduction layer 30 is located between the composite 4 and the electrode 20 and is bonded to each other on a pair of opposed surfaces 30a and 4b.

  By providing such a lithium-resistant reduction layer 30 between the composite 4 and the electrode 20, in the lithium secondary battery 100, the electrode 20 and the current collector 1 are connected via the active material molded body 2. Can be prevented, that is, a short circuit can be prevented. In other words, the lithium-resistant layer 30 functions as a short-circuit prevention layer that prevents a short circuit in the lithium secondary battery 100.

  In the present invention, this lithium-resistant reduction layer 30 contains a compound represented by the following general formula (I) (hereinafter sometimes simply referred to as “compound I”). The compound I is a ceramic material having excellent lithium ion conductivity and resistance to lithium reduction even at room temperature. Moreover, the thin film containing such compound I has sufficient strength as a thin film. Therefore, by using the thin film containing Compound I as the lithium reduction layer 30, it is possible to suppress or prevent the occurrence of a short circuit due to the dendritic growth caused by the tearing of the thin film or the reduction of lithium ions. Therefore, this lithium-resistant reduction layer 30 exhibits excellent lithium ion conductivity and lithium resistance.

_{Li 7-x La 3 (Zr} 2-x, M x) O 12 ··· (I)
[Wherein, M represents at least one of Nb, Sc, Ti, V, Y, Hf, Ta, Al, Si, Ga, Ge, Sn, and Sb, and X represents 0-2. ]

  In the compound I, examples of the metal M include Nb, Sc, Ti, V, Y, Hf, Ta, Al, Si, Ga, Ge, Sn, and Sb, and one or more of these may be used. They can be used in combination. Among these, at least one of Nb (niobium) and Ta (tantalum) is preferable. Thus, the obtained lithium-resistant reduction layer 30 can exhibit more excellent lithium ion conductivity and lithium-reduction resistance, and has excellent strength even when the lithium-resistant reduction layer 30 is a thin film. can do.

  Further, the substitution rate of X in the compound I, that is, the metal M is preferably as large as possible, and is not particularly limited, but is preferably 1 or more and 2 or less, and is 1.4 or more and 2 or less. Is more preferable. If the X is too small, depending on the type of the metal M or the like, the lithium-resistant reduction layer 30 may not be able to fully exhibit the above-described function.

  In addition, the compound I may have a cubic or tetragonal crystal structure in the lithium-resistant reduction layer 30, but preferably has a cubic garnet crystal structure. Thereby, the further improvement of the ionic conductivity of the lithium-resistant reduction layer 30 is achieved.

The ionic conductivity of the lithium resistant layer 30 is preferably 1 × 10 ⁻⁵ S / cm or more, and more preferably 5 × 10 ⁻⁵ S / cm or more. Since the lithium-resistant reduction layer 30 has such ionic conductivity, ions contained in the lithium-resistant reduction layer 30 can reach the surface of the active material molded body 2, and the battery reaction in the active material molded body 2. It becomes possible to contribute to. Therefore, the utilization factor of the active material in the active material molded body 2 is improved, and the capacity can be increased. At this time, if the ionic conductivity is less than the lower limit, depending on the type of the lithium-resistant reduction layer 30, only the active material in the vicinity of the surface layer on the surface facing the counter electrode in the active material molded body 2 contributes to the battery reaction. Capacity may be reduced.

  The “ionic conductivity of the lithium-resistant reduction layer 30” refers to the “bulk conductivity” that is the conductivity of the compound I itself that constitutes the lithium-resistant reduction layer 30 and the crystal particles made of the compound I. It means the “total ionic conductivity” which is the sum of the “flow field ionic conductivity” which is the conductivity.

  The ionic conductivity of the lithium-resistant reduction layer 30 is, for example, a compound I powder pressed into a tablet shape at 624 MPa, sintered at 700 ° C. for 8 hours in an air atmosphere, and sputtered to have a diameter of 0.5 cm and a thickness of It can be measured by forming 100 nm platinum electrodes on both sides of the press-molded body and carrying out an AC impedance method. For example, an impedance analyzer (manufactured by Solartron, model number SI1260) is used as the measuring device.

  Furthermore, the thickness of the lithium-resistant reduction layer 30 is not particularly limited, but is preferably 1 μm or more and 10 μm or less, and more preferably 2 μm or more and 5 μm or less. By setting to such a thickness, both functions of lithium ion conductivity and lithium reduction resistance can be reliably exhibited.

  In this embodiment, the lithium-resistant reduction layer 30 having the above-described configuration is provided in contact with the other surface 4b of the composite 4 as shown in FIG. Moreover, as for the composite body 4, both the active material molded object 2 and the solid electrolyte layer 3 are exposed in the other surface 4b. Therefore, the lithium-resistant reduction layer 30 is in contact with both the active material molded body 2 and the solid electrolyte layer 3 on the other surface 4b.

  At the interface between the lithium-resistant reduction layer 30 and the composite 4, that is, the interface between the lithium-resistant reduction layer 30 and the active material molded body 2, and the interface between the lithium-resistant reduction layer 30 and the solid electrolyte layer 3, A continuous layer (solid solution) in which the lithium-resistant reduction layer 30 and the active material molded body 2 are in solid solution and a continuous layer (solid solution) in which the lithium-resistant reduction layer 30 and the solid electrolyte layer 3 are in solid solution are formed. Yes. As a result, the resistance value at the interface between the lithium-resistant reduction layer 30 and the composite 4 (solid electrolyte layer 3 and active material molded body 2) is lowered, and as a result, lithium ions are more smoothly transferred at the interface. Will come to be. In other words, the lithium ion conductivity can be further improved between the lithium-resistant reduction layer 30 and the composite 4. In addition, although the above continuous layers can be obtained by forming the lithium-resistant reduction layer 30 on the other surface 4b of the composite 4, using the composition for forming a lithium-resistant reduction layer of the present invention, The method (the method for forming a lithium-resistant reduction layer of the present invention) will be described in detail in the method for producing a lithium secondary battery described later.

  In addition, the lithium-resistant reduction layer 30 comprised with the thin film containing the compound I is the porous body which the granule (secondary particle) formed by granulating the crystal | crystallization (primary particle) of the compound I sintered. It is configured. Therefore, the lithium-resistant reduction layer 30 has a configuration including communication holes (pores) communicating in a network, and the communication material is amorphous (glassy, amorphous) filling material at room temperature. It is preferable that a filling portion filled with is formed. Since the porous body can be reinforced by providing such a filling portion, the shape of the lithium-resistant reduction layer 30 can be stabilized even when lithium ions are transferred in the porous body composed of Compound I. Can be achieved.

As a constituent material of the filling portion, for example, a lithium double oxide containing Si or B can be given. Specifically, Li ₂ SiO ₃ , Li ₆ SiO ₅ , Li ₃ BO ₃ , H ₃ BO ₃ and Li _{2 + X} B _X C _1-X O _{3 and the} like can be mentioned, and one or two of these can be used in combination.

[Method for producing lithium secondary battery]
Next, a method for manufacturing the lithium secondary battery 100 of the first embodiment shown in FIG. 1 will be described.

  2-4 is a figure for demonstrating the manufacturing method of the lithium secondary battery shown in FIG. In the following, for convenience of explanation, the upper side of FIGS. 2 to 4 is referred to as “upper” and the lower side is referred to as “lower”. Moreover, in FIGS. 2-4, in order to make drawing easy to see, the dimension of each component, a ratio, etc. are described changing suitably.

  [1] First, as shown in FIG. 2, a forming material containing a particulate lithium double oxide (hereinafter referred to as “active material particles 2X”) is compressed and formed using a forming die F (FIG. 2). 2 (a)), and then the obtained compression molded product is heat-treated to obtain an active material molded body 2 (see FIG. 2 (b)).

  This heat treatment is preferably performed at a processing temperature of 850 ° C. or higher and lower than the melting point of the lithium double oxide to be used. Thereby, the active material particle 2X can be sintered together and the molded object integrated can be obtained reliably. By performing heat treatment in such a temperature range, the resistivity of the obtained active material molded body 2 can be preferably 700 Ω / cm or less without adding a conductive auxiliary. Thereby, the obtained lithium secondary battery 100 is provided with sufficient output.

  At this time, when the treatment temperature is less than 850 ° C., depending on the type of lithium double oxide used, not only the sintering does not proceed sufficiently, but also the electron conductivity itself in the crystal of the active material is lowered, so that it can be obtained. The lithium secondary battery 100 may not be able to obtain a desired output.

  Further, when the processing temperature exceeds the melting point of the lithium double oxide, the lithium ion is excessively volatilized from within the crystal of the lithium double oxide, resulting in a decrease in the electronic conductivity of the lithium double oxide. There is a possibility that the capacity of the electrode assembly 10 may decrease.

  Therefore, in order to obtain an appropriate output and capacity, the treatment temperature is preferably 850 ° C. or more and lower than the melting point of the lithium double oxide, more preferably 875 ° C. or more and 1000 ° C. or less, and 900 ° C. or more and 920 ° C. More preferably, it is not higher than ° C.

  The heat treatment in this step is preferably performed for 5 minutes to 36 hours, more preferably 4 hours to 14 hours.

By performing the heat treatment as described above, the growth of grain boundaries in the active material particles 2X and the sintering between the active material particles 2X proceed, so that the obtained active material molded body 2 can easily maintain its shape, The amount of binder added to the active material molded body 2 can be reduced. Moreover, since a bond is formed between the active material particles 2X by sintering and an electron transfer path between the active material particles 2X is formed, the amount of the conductive additive added can also be suppressed. Note that LiCoO ₂ can be suitably used as a material for forming the active material particles 2X.

  In addition, the obtained active material molded body 2 is constituted by a plurality of pores of the active material molded body 2 that are connected to each other in a mesh shape inside the active material molded body 2.

  The average particle diameter of the active material particles 2X is preferably from 300 nm to 5 μm, more preferably from 450 nm to 3 μm, and even more preferably from 500 nm to 1 μm. When an active material having such an average particle diameter is used, the porosity of the obtained active material molded body 2 can be set to preferably 10% to 40%, more preferably 15% to 35%. As a result, the surface area in the pores of the active material molded body 2 can be increased, and the contact area between the active material molded body 2 and the solid electrolyte layer 3 can be easily expanded, and the lithium battery using the electrode composite 10 can be increased in capacity. It becomes easy.

  If the average particle diameter of the active material particles 2X is less than the lower limit, depending on the type of the following liquid material, the radius of the pores of the formed active material body tends to be as small as several tens of nm. In this step, it is difficult to infiltrate the liquid material containing the inorganic solid electrolyte precursor into the pores, and as a result, it may be difficult to form the solid electrolyte layer 3 in contact with the surface inside the pores.

  Moreover, when the average particle diameter of the active material particles 2X exceeds the upper limit, the specific surface area, which is the surface area per unit mass of the formed active material molded body, becomes small, and the active material molded body 2 and the solid electrolyte layer 3 The contact area becomes smaller. Therefore, when a lithium battery is formed using the electrode assembly 10 obtained, there is a possibility that sufficient output cannot be obtained. Moreover, since the ion diffusion distance from the inside of the active material particle 2X to the solid electrolyte layer 3 becomes long, the lithium double oxide near the center in the active material particle 2X may hardly contribute to the function of the battery.

  The average particle diameter of the active material particles 2X is, for example, the light scattering particle size distribution after the active material particles 2X are dispersed in n-octanol so as to have a concentration in the range of 0.1% by mass to 10% by mass. It can measure by calculating | requiring a median diameter using a measuring apparatus (the Nikkiso Co., Ltd. make, nano track UPA-EX250).

  Further, an organic polymer compound such as polyvinylidene fluoride (PVdF) or polyvinyl alcohol (PVA) may be added as a binder to the forming material used for forming the active material particles 2X. These binders are burned or oxidized in the heat treatment of this step, and the amount thereof is reduced.

In addition, it is preferable to add a particulate pore-forming material using a polymer or carbon powder as a forming material for pores at the time of compacting. By mixing these pore formers, it becomes easy to control the porosity of the active material molded body. Such a pore former is decomposed and removed by combustion or oxidation during heat treatment, and the amount of the resulting active material molded body is reduced.
The average particle diameter of the pore former is preferably 0.5 μm to 10 μm.

  Furthermore, it is preferable that the pore former contains particles (first particles) whose material is a deliquescent material. Since the water generated around the first particles due to the deliquescent of the first particles functions as a binder that joins the particulate lithium double oxide, the process until the particulate lithium double oxide is compression-molded and heat-treated. During this time, the shape can be maintained. Therefore, an active material molded body can be obtained without adding another binder or while reducing the amount of the binder added, and a high-capacity electrode composite can be easily obtained.

  As such 1st particle | grains, the particle | grains which use polyacrylic acid as a forming material can be mentioned.

  Moreover, it is preferable that the pore former further includes particles (second particles) whose material is a material having no deliquescence. The pore former containing such second particles is easy to handle. Also, if the pore former has deliquescence, the porosity of the active material molded body may deviate from a desired set value depending on the amount of moisture around the pore former, but it does not deliquesce as a pore former. By including the second particles at the same time, it is possible to suppress the gap deviation.

[2] Next, as shown in FIG. 3, a liquid 3X containing a precursor of the solid electrolyte layer 3 is applied to the surface of the active material molded body 2 including the inside of the pores of the active material molded body 2 (FIG. 3). 3 (a)) and then firing to form the solid electrolyte layer 3 using the precursor as an inorganic solid electrolyte (FIG. 3B).
Thereby, the composite body 4 including the active material molded body 2 and the solid electrolyte layer 3 is formed.

  The liquid 3X may include a solvent that can dissolve the precursor in addition to the precursor. When the liquid 3X includes a solvent, the solvent may be appropriately removed after the application of the liquid 3X and before firing. For the removal of the solvent, a method known in the art such as heating, reduced pressure, and air blowing, or a method combining two or more types can be employed.

  Here, since the liquid electrolyte 3X having fluidity is applied to form the solid electrolyte layer 3, the solid electrolyte can be satisfactorily formed also on the inner surfaces of the pores of the fine active material molded body 2. Become. Therefore, it is easy to enlarge the contact area between the active material molded body 2 and the solid electrolyte layer 3, the current density at the interface between the active material molded body 2 and the solid electrolyte layer 3 is reduced, and as a result, a large output can be easily obtained. be able to.

  The liquid 3X can be applied by various methods as long as the liquid 3X penetrates into the pores of the active material molded body 2. For example, it may be performed by dropping the liquid material 3X where the active material molded body 2 is placed, or by immersing the active material molded body 2 where the liquid material 3X is stored. Alternatively, the end of the active material molded body 2 may be brought into contact with the location where the liquid 3X is stored, and impregnation into the pores using capillary action. FIG. 3A shows a method of dropping the liquid 3X using the dispenser D among the above.

Moreover, as a precursor of the solid electrolyte layer 3, the following (A) (B) (C) is mentioned, for example.
(A) A composition containing a metal atom contained in an inorganic solid electrolyte in a proportion according to the composition formula of the inorganic solid electrolyte, and having a salt that becomes an inorganic solid electrolyte by oxidation (B) An inorganic solid electrolyte containing a metal atom contained in the inorganic solid electrolyte (C) Inorganic solid electrolyte fine particles containing metal alkoxide in a proportion according to the composition formula of the above, or fine particle sol containing metal atoms in the inorganic solid electrolyte in a proportion according to the composition formula of the inorganic solid electrolyte, or a solvent Dispersion dispersed in (A) or (B)

  In addition, the salt contained in (A) contains a metal complex. Moreover, (B) is a precursor in the case of forming an inorganic solid electrolyte using a so-called sol-gel method.

The precursor is baked at a temperature lower than the heat treatment for obtaining the above-described active material molded body 2 in an air atmosphere. Specifically, the baking temperature is preferably in a temperature range of 300 ° C. or higher and 700 ° C. or lower. By firing, an inorganic solid electrolyte is produced from the precursor, and the solid electrolyte layer 3 is formed. As the material for forming the solid electrolyte _layer, it can be preferably used Li _{0.35 La} 0.55 TiO _3.

  By baking in such a temperature range, a solid-phase reaction occurs due to mutual diffusion of the elements constituting each at the interface between the active material molded body 2 and the solid electrolyte layer 3, and an electrochemically inactive byproduct. Can be suppressed. Further, the crystallinity of the inorganic solid electrolyte is improved, and the ionic conductivity of the solid electrolyte layer 3 can be improved. In addition, a portion to be sintered is generated at the interface between the active material molded body 2 and the solid electrolyte layer 3, and charge transfer at the interface is facilitated. Thereby, the capacity | capacitance and output of a lithium battery using the electrode composite 10 improve.

  The firing may be performed by a single heat treatment, and the first heat treatment for depositing the precursor on the surface of the porous body and the first heat treatment performed at a temperature condition of not less than the processing temperature of the first heat treatment and not more than 700 ° C. It is good also as performing by dividing into 2 heat processing. By firing by such stepwise heat treatment, the solid electrolyte layer 3 can be easily formed at a desired position.

  [3] Next, both surfaces 4a and 4b of the composite 4 are ground and polished to expose both the active material molded body 2 and the solid electrolyte layer 3 from the both surfaces 4a and 4b (FIG. 4A). reference).

  In this case, scratch marks (grinding / polishing traces) that are traces of grinding / polishing are left on the one surface 4a and the other surface 4b.

  In the step [2], when the composite 4 is formed, both the active material molded body 2 and the solid electrolyte layer 3 may be exposed from both surfaces 4a and 4b. In this case, grinding and polishing on both surfaces 4a and 4b of the composite 4 can be omitted.

  [4] Next, the composition for forming a lithium-resistant reduction layer used for forming the lithium-resistant reduction layer 30 containing the compound I on the other surface 4b of the composite 4 (formation of the lithium-resistant reduction layer of the present invention) Composition) is supplied to form a liquid film, and then the liquid film is heated to obtain the lithium-resistant reduction layer 30 containing the compound represented by the general formula (I) (FIG. 4B). )reference).

Hereinafter, this step [4] will be described in detail.
[4-1] First, a lithium-resistant reduction layer forming composition (precursor composition) is prepared, and then a liquid film is formed on the other surface 4b using this lithium-resistant reduction layer forming composition ( First step).

  The composition for forming a lithium-resistant reduction layer (the composition for forming a lithium-resistant reduction layer of the present invention) is used for forming the lithium-resistant reduction layer 30 containing the compound I. , A liquid reactant containing a lithium compound, a lanthanum compound, a zirconium compound, and a compound comprising the metal M, each having a solubility, and the lithium compound is 1.05 times or more and 2.50 times or less, the lanthanum compound and the zirconium compound are 0.70 times or more and 1.00 times or less, and the compound including the metal M is included at the same magnification.

  The lithium compound, the lanthanum compound, the zirconium compound, and the compound including the metal M are not particularly limited. For example, the lithium compound, the lanthanum compound, the zirconium compound, and the metal M may be at least one of metal salts and metal alkoxides. Is preferred. Thereby, the said compound I can be obtained with a high production rate from the composition for lithium-resistant reduction layer forming which is a mixture of these compounds.

  Examples of such a lithium compound (lithium source) include lithium metal salts such as lithium chloride, lithium nitrate, lithium acetate, lithium hydroxide, and lithium carbonate, lithium methoxide, lithium ethoxide, lithium propoxide, lithium isopropoxide. Examples include propoxide, lithium butoxide, lithium isobutoxide, lithium secondary butoxide, lithium tertiary butoxide, lithium alkoxide such as dipivaloylmethanatolithium, etc., and one or more of these may be used in combination Can do.

  Examples of the lanthanum compound (lanthanum source) include lanthanum metal salts such as lanthanum chloride, lanthanum nitrate, and lanthanum acetate, lanthanum methoxide, lanthanum ethoxide, lanthanum propoxide, lanthanum isopropoxide, lanthanum butoxide, and lanthanum isoform. Examples include butoxide, lanthanum secondary butoxide, lanthanum tertiary butoxide, and lanthanum alkoxide such as dipivaloylmethanatrantan. One or more of these can be used in combination.

  Further, as the zirconium compound (zirconium source), for example, zirconium metal salt such as zirconium chloride, zirconium oxychloride, zirconium oxynitrate, zirconium oxyacetate, zirconium acetate, zirconium methoxide, zirconium ethoxide, zirconium propoxide, zirconium Zirconium alkoxides such as isopropoxide, zirconium butoxide, zirconium isobutoxide, zirconium secondary butoxide, zirconium tertiary butoxide, dipivaloylmethanatozirconium, and the like are used, and one or more of these are used in combination. be able to.

  Further, as the compound comprising the metal M, when the metal M is niobium, for example, niobium chloride, niobium oxychloride, niobium metal salt such as niobium oxalate, niobium ethoxide, niobium propoxide, niobium isopropoxide, Examples include niobium alkoxide such as niobium secondary butoxide, niobium acetylacetone, and the like, and one or more of these can be used in combination.

  Moreover, as a solvent, what can melt | dissolve the compound provided with a lithium compound, a lanthanum compound, a zirconium compound, and the said metal M, respectively is used, and the single solvent or mixed solvent of water and an organic solvent is used. Thereby, a lithium compound, a lanthanum compound, a zirconium compound, and the compound provided with the said metal M can be reliably dissolved in the composition for lithium-resistant reduction layer formation, respectively.

  Although it does not specifically limit as an organic solvent, For example, alcohol, such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, and allyl alcohol, ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, pentanediol, hexanediol, Glycols such as heptane diol and dipropylene glycol, ketones such as acetone, methyl ethyl ketone, methyl propyl ketone and methyl isobutyl ketone, esters such as methyl formate, ethyl formate, methyl acetate and methyl acetoacetate, diethylene glycol monomethyl ether, diethylene glycol mono Ethyl ether, diethylene glycol dimethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoe Ethers, ethers such as dipropylene glycol monomethyl ether, and the like.

  In addition, the formation of the liquid film on the other surface 4b is performed by supplying the lithium-resistant reduction layer forming composition onto the other surface 4b. The method is preferably used. According to the coating method, it is possible to easily form the liquid film having a uniform film thickness, and thus the lithium-resistant reduction layer 30, on the other surface 4b.

  The coating method is not particularly limited. For example, spin coating method, casting method, micro gravure coating method, gravure coating method, bar coating method, roll coating method, wire bar coating method, dip coating method, spray coating method, screen Examples thereof include a printing method, a flexographic printing method, an offset printing method, a micro contact printing method, and a droplet discharge method.

  Further, the composition for forming a lithium-resistant reduction layer includes a lithium compound, a lanthanum compound, a zirconium compound, and a compound including the metal M in the composition ratio as described above. Gelation of the reduction layer forming composition is suppressed or prevented over a long period of time, and the lithium resistant reduction layer forming composition can stably maintain the sol state for a long period of time. Therefore, the liquid film formed by supplying the composition for forming a lithium-resistant reduction layer on the other surface 4b can be obtained as having a more uniform thickness. Therefore, the lithium resistant reduction layer obtained in the next step [4-2] can be provided with a more uniform thickness.

  [4-2] Next, the liquid coating is heated to form a lithium-resistant reduction layer 30 containing Compound I on the other surface 4b (second step).

  Here, in the present invention, the composition ratio of the lithium compound, the lanthanum compound, the zirconium compound, and the compound comprising the metal M included in the lithium-resistant reduction layer forming composition constituting the liquid film is within a specific range. It has become. That is, with respect to the stoichiometric composition in Compound I, the lithium compound is 1.05 to 2.50 times, the lanthanum compound and the zirconium compound are 0.70 to 1.00 times, and the metal M is The provided compound has an equal composition ratio. By using such a composition ratio, a ceramic material produced by a liquid phase reaction generated by heating a liquid coating (composition for forming a lithium-resistant reduction layer) can be obtained as a compound I with a high production rate. Can do. Therefore, the lithium-resistant reduction layer 30 containing this compound I exhibits excellent Li ion conductivity and Li reduction resistance.

  Thus, by using the composition for forming a lithium-resistant reduction layer according to the present invention, compound I is produced in one step of heating a liquid film (composition for forming a lithium-resistant reduction layer). The lithium-resistant reduction layer 30 containing can be formed.

  In addition, by heating (heat treatment) the composition for forming a lithium-resistant reduction layer that is a liquid film (liquid material), the compound I can be obtained by the above-described lithium compound, lanthanum compound, zirconium compound, and the metal M It is clear from the study of the present inventor that it depends on the composition ratio of these compounds regardless of the type of the compound comprising

For example, when lithium carbonate is used as the lithium compound, the lithium carbonate also functions as a sintering aid, and a sintering effect that promotes crystallization (grain growth) of the compound I is obtained. When it exceeds 50 times (for example, 3.0 times), decomposition of Compound I occurs and La ₂ Zr ₂ O ₃ and La ₂ O _{3 that} are impurities are generated. On the other hand, when the amount of the lithium compound is less than 1.05 times, La ₂ Zr ₂ O ₃ which is a contaminant is generated, and the sintering effect by lithium carbonate cannot be sufficiently obtained.

  Further, the lithium compound may be 1.05 times or more and 2.50 times or less, but preferably 1.25 times or more and 2.50 times or less. As a result, crystals of compound I (primary particles) having a finer particle diameter are generated, and therefore, the porous body obtained by sintering the particles (secondary particles) formed by granulating the primary particles. Therefore, the ion conductivity of the lithium-resistant reduction layer 30 can be improved.

Further, when the lanthanum compound and the zirconium compound are each less than 0.70 times the amount, impurities La ₂ Zr ₂ O ₃ are produced and the production rate of the compound I tends to be extremely lowered. In addition, when the lanthanum compound and the zirconium compound are each more than 1.00 times, La ₂ Zr ₂ O ₃ that is a contaminant tends to be generated.

  The heating of the liquid film (liquid material) is preferably performed under a temperature condition where the maximum temperature is 900 ° C. or less, and more preferably under a temperature condition where the maximum temperature is 800 ° C. or less. Thereby, the crystal structure of Compound I produced by heating can have a cubic garnet-type crystal structure. As a result, the resulting lithium resistant layer 30 exhibits better ionic conductivity. In addition, by heating in a low temperature region where the maximum temperature is 800 ° C. or less, alteration / deterioration of the constituent materials of the active material molded body 2 and the solid electrolyte layer 3 included in the composite 4 can be accurately suppressed or prevented. .

The heating of the liquid film (liquid material) is preferably performed in multiple stages including a first heat treatment, a second heat treatment, and a third heat treatment for sintering the compound I. In such a multi-stage heat treatment, the liquid film is dried in the first heat treatment, and a metal oxide of lithium, lanthanum, zirconium and the metal M is generated in the second heat treatment. For example, Li ₂ CO ₃ is produced by reacting with CO ₂ in the air via Li ₂ O. Then, in the third heat treatment, the compound I is generated, the generated compound I crystals are grown, and then the granulated compound I crystals are sintered. That is, in the first heat treatment, the liquid film is dried, and in the second heat treatment, an oxide of each metal component constituting the compound I is generated. Then, in the third heat treatment, Compound I is generated and crystals are grown by distillation to sinter the granular Compound I crystals.

  Through such steps, the lithium-resistant reduction layer 30 containing the compound I is formed, whereby the crystal structure of the compound I in the lithium-resistant reduction layer 30 has a cubic garnet-type crystal structure. In addition, since the adjacent crystals of Compound I forming a granular form can be sintered, the lithium-resistant reduction layer 30 exhibits better ionic conductivity.

  In this case, the heating temperature in the first heat treatment is preferably 50 ° C. or higher and 250 ° C. or lower, and more preferably 150 ° C. or higher and 200 ° C. or lower.

  The heating temperature in the second heat treatment is preferably 400 ° C. or higher and 550 ° C. or lower, and more preferably 500 ° C. or higher and 550 ° C. or lower.

  Furthermore, the heating temperature in the third heat treatment is preferably 600 ° C. or higher and 900 ° C. or lower, and more preferably 650 ° C. or higher and 800 ° C. or lower.

  By setting the heating temperature in the first to third heat treatments within the above range, the compound I having a cubic garnet crystal structure can be obtained at a higher production rate.

  In addition, the heating time of the liquid coating is preferably 10 minutes or more and 2 hours or less, and more preferably 10 minutes or more and 1.5 hours or less in all steps.

  Further, in this step [4], as described above, the lithium-resistant reduction layer 30 supplies the composition 4 for forming a lithium-resistant reduction layer forming a liquid phase to the other surface 4b of the composite 4 forming a solid phase. It is formed. Therefore, on the other surface 4b, a liquid film is formed by wetting and spreading the composition for forming a lithium-resistant reduction layer on the active material molded body 2 and the solid electrolyte layer 3 exposed from the other surface 4b, and this liquid film is heated. As a result, the lithium-resistant reduction layer 30 is formed. Therefore, the interface between the lithium-resistant reduction layer 30 and the active material molded body 2 and the interface between the lithium-resistant reduction layer 30 and the solid electrolyte layer 3 formed on the other surface 4b are respectively the lithium-resistant reduction layer 30 and the solid electrolyte layer 3. It is a continuous layer (solid solution) in which the active material molded body 2 is in solid solution, and a continuous layer (solid solution) in which the lithium-resistant reduction layer 30 and the solid electrolyte layer 3 are in solid solution. Thereby, the resistance value at the interface between the lithium-resistant reduction layer 30 and the composite 4 is lowered, and as a result, the delivery of lithium ions at the interface is performed more smoothly.

  In addition, as described above, the lithium-resistant reduction layer 30 obtained in this step [4] is composed of a porous body having communication holes (pores), and the communication holes are filled with an amorphous material at room temperature. When forming the filling portion filled with the material, after the step [4], the filling material which is amorphous at room temperature is supplied onto the lithium-resistant reduction layer 30, and then the filling material is heated. You can do it. Thereby, the said filling part can be formed reliably. Moreover, the temperature which heats the said filling material can be made to be the same as that of the heating conditions in this process [4].

  [5] Next, as shown in FIG. 4C, the current collector 1 is bonded to the one surface 4 a of the composite 4, and the electrode 20 is bonded to the one surface 30 a of the lithium-resistant reduction layer 30.

  The current collector 1 may be joined by joining a current collector formed as a separate body to the one surface 4 a of the composite 4, and the material for forming the current collector 1 described above on the one surface 4 a of the composite 4. The current collector 1 may be formed on one surface 4 a of the composite 4 by forming a film.

  The electrode 20 may be joined by joining a separate electrode to the one surface 30a of the lithium-resistant reduction layer 30. The material for forming the electrode 20 described above is applied to the one surface 30a of the lithium-resistant reduction layer 30. It is good also as forming the electrode and forming the electrode 20 on the one surface 30a of the lithium-resistant reduction layer 30.

Note that various physical vapor deposition methods (PVD) and chemical vapor deposition methods (CVD) can be used as the film formation methods of the current collector 1 and the electrode 20, respectively.
Through the steps as described above, the lithium secondary battery 100 is manufactured.

<< Second Embodiment >>
Next, a second embodiment of the lithium secondary battery of the present invention will be described.
FIG. 5 is a longitudinal sectional view showing a second embodiment of the lithium secondary battery of the present invention.

  Hereinafter, the lithium secondary battery 100A of the second embodiment will be described focusing on the differences from the lithium secondary battery 100 of the first embodiment, and description of similar matters will be omitted.

  In the lithium secondary battery 100 </ b> A shown in FIG. 5, a composite 4 </ b> A having a configuration different from that of the composite 4 is joined between the current collector 1 and the lithium-resistant reduction layer 30 between the current collector 1 and the lithium-resistant reduction layer 30. The lithium secondary battery 100 is the same as the lithium secondary battery 100 shown in FIG.

  That is, in the lithium secondary battery 100A of the second embodiment, the composite body 4A includes an active material molded body 2A and a solid electrolyte layer 3A that are both layered in this order from the current collector 1 side to the electrode 20 side. The one surface 4a of the composite 4 is configured by the active material molded body 2A alone, and the other surface 4b of the composite 4 is configured by the solid electrolyte layer 3A alone.

  In such a lithium secondary battery 100A, the solid electrolyte layer 3A and the lithium-resistant reduction layer 30 are laminated together, and the interface between the lithium-resistant reduction layer 30 and the solid electrolyte layer 3A is the same as that of the first embodiment. Similarly to the form, a continuous layer (solid solution) in which the lithium-resistant reduction layer 30 and the solid electrolyte layer 3A are in solid solution is formed. Thereby, the resistance value at the interface between the lithium-resistant reduction layer 30 and the composite 4A (solid electrolyte layer 3A) is lowered, and as a result, the lithium ions are more smoothly transferred at the interface.

  The effect similar to that of the first embodiment can be obtained by the lithium secondary battery 100A of the second embodiment.

  As mentioned above, although the composition for lithium-resistant reduction layer formation of this invention, the film-forming method of a lithium-resistant reduction layer, and the lithium secondary battery were demonstrated based on embodiment of illustration, this invention is not limited to this. .

  For example, the configuration of each part in the lithium secondary battery of the present invention can be replaced with any configuration having the same function. In addition, any other component may be added to the present invention. Further, the present invention may be a combination of any two or more configurations (features) of the above embodiments.

  Furthermore, one or two or more arbitrary steps may be added to the method for forming a lithium-resistant reduction layer according to the present invention.

Next, specific examples of the present invention will be described.
1. Preparation of each metal compound solution <Preparation of 1.0 mol / kg lithium nitrate in butanol>
In a 30-g Pyrex (registered trademark) reagent bottle containing a magnetic stirrer bar, weigh 1.3789 g of lithium nitrate and 18.62111 g of butanol and stir at room temperature for 30 minutes using a magnetic stirrer. Lithium was completely dissolved to obtain a butanol solution of lithium nitrate having a concentration of 1.0 mol / kg.

<Preparation of 1.0 mol / kg lithium acetate in toluene / propionic acid solution>
In a 30 g Pyrex (registered trademark) reagent bottle containing a magnetic stirrer bar, 1.3198 g of lithium acetate, 13.0761 g of toluene, and 5.6041 g of propionic acid are weighed, and a magnetic stirrer with temperature control is used. The mixture was stirred at 80 ° C. for 30 minutes to completely dissolve lithium acetate and slowly cooled to room temperature to obtain a toluene / propionic acid solution of lithium acetate having a concentration of 1.0 mol / kg.

<Preparation of a 1.0 mol / kg lithium acetate propionic acid solution>
In a 30 g Pyrex (registered trademark) reagent bottle containing a magnetic stirrer bar, 1.3198 g of lithium acetate and 18.6802 g of propionic acid were weighed, and at 80 ° C. using a magnetic stirrer with temperature control. The mixture was stirred for 30 minutes to completely dissolve lithium acetate and slowly cooled to room temperature to obtain a propionic acid solution of lithium acetate having a concentration of 1.0 mol / kg.

<Preparation of 2.0 mol / kg Lithium Nitrate in 2-Butoxyethanol>
Lithium nitrate 2.758 g and 2-butoxyethanol 17.242 g were weighed into a 30 g Pyrex (registered trademark) reagent bottle containing a magnetic stirrer bar, and 160 ° C. using a temperature-controlled magnetic stirrer. The mixture was stirred for 30 minutes to completely dissolve the lithium nitrate to obtain a 2-butoxyethanol solution of lithium nitrate having a concentration of 2.0 mol / kg.

<Preparation of ethanol solution of 1.0 mol / kg lithium nitrate>
In a 30-g Pyrex (registered trademark) reagent bottle containing a magnetic stirrer bar, 0.690 g of lithium nitrate and 9.310 g of ethanol are weighed, and 30 ° C. at 160 ° C. using a magnetic stirrer with temperature control. The mixture was stirred for minutes, and lithium nitrate was completely dissolved to obtain an ethanol solution of lithium nitrate having a concentration of 1.0 mol / kg.

<Preparation of 0.4 mol / kg lanthanum 2-ethylhexanoate in toluene / 2-butoxyethanol>
Weigh 2.2741 g of lanthanum 2-ethylhexanoate, 5.4081 g of toluene, and 2.3178 g of 2-butoxyethanol in a 20 g Pyrex (registered trademark) reagent bottle, and perform ultrasonication with an ultrasonic cleaner at room temperature. And dissolved completely to obtain a toluene / 2-butoxyethanol solution of lanthanum 2-ethylhexanoate having a concentration of 0.4 mol / kg.

<Preparation of 0.4 mol / kg lanthanum acetate hemihydrate in propionic acid solution>
Weigh 2.7445 g of lanthanum acetate hemihydrate and 17.2555 g of propionic acid in a 30 g Pyrex (registered trademark) reagent bottle containing a magnetic stirrer bar, and use a magnetic stirrer with temperature control. The mixture was stirred at 80 ° C. for 30 minutes to completely dissolve the lanthanum acetate hemihydrate, slowly cooled to room temperature, and a 0.4 mol / kg lanthanum acetate hemihydrate monopropionate solution. Got.

<Preparation of a 2-butoxyethanol solution of 1.0 mol / kg lanthanum nitrate hexahydrate>
Weighing 4.330 g of lanthanum nitrate hexahydrate and 5.670 g of 2-butoxyethanol in a 30 g Pyrex (registered trademark) reagent bottle containing a magnetic stirrer bar, and using a magnetic stirrer with temperature control The mixture was stirred at 80 ° C. for 30 minutes to completely dissolve the lanthanum nitrate hexahydrate and slowly cooled to room temperature to obtain a 2-butoxyethanol solution of lanthanum nitrate hexahydrate having a concentration of 1.0 mol / kg. It was.

<Preparation of ethanol solution of 1.0 mol / kg lanthanum nitrate hexahydrate>
In a 30-g Pyrex (registered trademark) reagent bottle containing a magnetic stirrer bar, 4.330 g of lanthanum nitrate hexahydrate and 5.670 g of ethanol were weighed, and a temperature-controlled magnetic stirrer was used. The mixture was stirred at 0 ° C. for 30 minutes to completely dissolve lanthanum nitrate hexahydrate and slowly cooled to room temperature to obtain an ethanol solution of lanthanum nitrate hexahydrate having a concentration of 1.0 mol / kg.

<Preparation of Butanol Solution of 1.0 mol / kg Zirconium Butoxide>
In a 20-g Pyrex (registered trademark) reagent bottle containing a magnetic stirrer bar, 3.8368 g of zirconium butoxide and 6.1632 g of butanol were weighed, stirred at 80 ° C. for 30 minutes, gradually cooled to room temperature, 1 A butanol solution of zirconium butoxide having a concentration of 0.0 mol / kg was obtained.

<Preparation of 0.4 mol / kg zirconium acrylate propionic acid solution>
In a 30-g Pyrex (registered trademark) reagent bottle containing a magnetic stirrer bar, 3.0020 g of zirconium acrylate and 16.9980 g of propionic acid were weighed, and at 80 ° C. using a magnetic stirrer with temperature control. The mixture was stirred for 30 minutes to completely dissolve the zirconium acrylate and slowly cooled to room temperature to obtain a propionic acid solution of zirconium acrylate having a concentration of 0.4 mol / kg.

<Preparation of 2-butoxyethanol solution of 1.0 mol / kg zirconium butoxide>
In a 20-g Pyrex (registered trademark) reagent bottle containing a magnetic stirrer bar, 7.67 g of zirconium butoxide and 12.326 g of 2-butoxyethanol were weighed, stirred at 80 ° C. for 30 minutes, and gradually cooled to room temperature. Thus, a 2-butoxyethanol solution of zirconium butoxide having a concentration of 1.0 mol / kg was obtained.

<Preparation of ethanol solution of 1.0 mol / kg zirconium butoxide>
In a 20-g Pyrex (registered trademark) reagent bottle containing a magnetic stirrer bar, 7.67 g of zirconium butoxide and 12.326 g of ethanol were weighed, stirred at 80 ° C. for 30 minutes, gradually cooled to room temperature, 1 An ethanol solution of zirconium butoxide having a concentration of 0.0 mol / kg was obtained.

<Preparation of 1.0 mol / kg niobium pentaethoxide in 2-butoxyethanol solution>
In a 10-g Pyrex (registered trademark) reagent bottle containing a magnetic stirrer bar, 3.1821 g of niobium pentaethoxide and 6.8179 g of 2-butoxyethanol were weighed, and using a magnetic stirrer with temperature control, The mixture was stirred at 80 ° C. for 30 minutes and gradually cooled to room temperature to obtain a 2-butoxyethanol solution of niobium pentaethoxide having a concentration of 1.0 mol / kg.

<Preparation of ethanol solution of 1.0 mol / kg niobium pentaboxide>
Weigh 3.182 g of niobium pentaboxide and 6.818 g of ethanol in a 10 g Pyrex (registered trademark) reagent bottle with a magnetic stirrer bar, and use a magnetic stirrer with temperature control at 80 ° C. The mixture was stirred for 30 minutes and gradually cooled to room temperature to obtain a 1.0 mol / kg niobium pentaboxide ethanol solution.

<Preparation of 1.0 mol / kg 2-butoxyethanol solution of tantalum pentaethoxide>
In a 10-g Pyrex (registered trademark) reagent bottle containing a magnetic stirrer bar, 3.182 g of tantalum pentaethoxide and 6.818 g of 2-butoxyethanol were weighed, and a magnetic stirrer with temperature control was used. The mixture was stirred at 80 ° C. for 30 minutes and gradually cooled to room temperature to obtain a 2-butoxyethanol solution of tantalum pentaethoxide having a concentration of 1.0 mol / kg.

2. Preparation of composition for forming lithium-resistant reduction layer <Example 1> (Preparation of Li _6.9 La ₃ (Zr _1.9 , Nb _0.1 ) O ₁₂ precursor solution)
10.350 g of a propionate solution of lithium acetate at a concentration of 1.0 mol / kg, 6.375 g of a propionate solution of lanthanum acetate hemihydrate at a concentration of 0.4 mol / kg, zirconium butoxide 1 at a concentration of 1.0 mol / kg .615 g, and 0.100 g of a 2-butoxyethanol solution of niobium pentaethoxide at a concentration of 1.0 mol / kg were weighed, mixed by heating on a hot plate at 90 ° C. for 30 minutes, gradually cooled to room temperature, and Li _{6 .9} La ₃ (Zr _1.9 , Nb _0.1 ) O ₁₂ precursor solution was obtained.

<Example 2> (Preparation of Li _5.1 La ₃ (Zr _0.1 , Nb _1.9 ) O ₁₂ precursor solution)
12.750 g of a 1.0 mol / kg lithium nitrate butanol solution, 5.250 g of a 0.4 mol / kg lanthanum 2-ethylhexanoate toluene / 2-butoxyethanol solution, 1.0 mol / kg zirconium butoxide 0.070 g of butanol solution and 1.900 g of 2-butoxyethanol solution of niobium pentaethoxide at a concentration of 1.0 mol / kg are weighed and mixed on a hot plate at 90 ° C. for 30 minutes and gradually cooled to room temperature. Li _5.1 La ₃ (Zr _0.1 , Nb _1.9 ) O ₁₂ precursor solution was obtained.

<Example 3> (Preparation of Li _6.75 La ₃ (Zr _1.75 , Nb _0.25 ) O ₁₂ precursor solution)
10.125 g of a toluene / propionic acid solution of lithium acetate at a concentration of 1.0 mol / kg, 5.250 g of a toluene / 2-butoxyethanol solution of lanthanum 2-ethylhexanoate at a concentration of 0.4 mol / kg, a concentration of 0.4 mol / kg Weighed 3.719 g of propionic acid solution of zirconium acrylate and 0.250 g of 2-butoxyethanol solution of niobium pentaethoxide at a concentration of 1.0 mol / kg, and heated and mixed on a hot plate at 90 ° C. for 30 minutes. The solution was gradually cooled to room temperature to obtain a Li _6.75 La ₃ (Zr _1.75 , Nb _0.25 ) O ₁₂ precursor solution.

<Example 4> (Preparation of Li _6.75 La ₃ (Zr _1.75 , Nb _0.25 ) O ₁₂ precursor solution)
10.125 g of a propionate solution of lithium acetate at a concentration of 1.0 mol / kg, 6.375 g of a toluene / 2-butoxyethanol solution of lanthanum 2-ethylhexanoate at a concentration of 0.4 mol / kg, of zirconium butoxide at a concentration of 1 mol / kg Weigh 1.313 g of butanol solution and 0.250 g of 2-butoxyethanol solution of niobium pentaethoxide at a concentration of 1.0 mol / kg, heat and mix on a hot plate at 90 ° C. for 30 minutes, and gradually cool to room temperature. Li _6.75 La ₃ (Zr _1.75 , Nb _0.25 ) O ₁₂ precursor solution was obtained.

<Example 5> (Preparation of Li _6.75 La ₃ (Zr _1.75 , Nb _0.25 ) O ₁₂ precursor solution)
13.500 g of a propionate solution of lithium acetate at a concentration of 1.0 mol / kg, 6.000 g of a toluene / 2-butoxyethanol solution of lanthanum 2-ethylhexanoate at a concentration of 0.4 mol / kg, zirconium at a concentration of 0.4 mol / kg Weigh out 3.500 g of propionic acid solution of acrylate and 0.250 g of 2-butoxyethanol solution of niobium pentaethoxide at a concentration of 1.0 mol / kg, mix by heating on a hot plate at 90 ° C. for 30 minutes, and bring to room temperature. The solution was gradually cooled to obtain a Li _6.75 La ₃ (Zr _1.75 , Nb _0.25 ) O ₁₂ precursor solution.

<Example 6> (Preparation of Li _6.6 La ₃ (Zr _1.6 , Nb _0.4 ) O ₁₂ precursor solution)
11.13 g of 1.0 mol / kg lithium nitrate butanol solution, 5.625 g of 0.4 mol / kg lanthanum acetate monohydrate propionate solution, 1.0 mol / kg zirconium butoxide butanol 1.280 g of solution and 0.400 g of niobium pentaethoxide 2-butoxyethanol solution having a concentration of 1.0 mol / kg are weighed, heated and mixed on a 90 ° C. hot plate for 30 minutes, and gradually cooled to room temperature. A Li _6.6 La ₃ (Zr _1.6 , Nb _0.4 ) O ₁₂ precursor solution was obtained.

<Example 7> (Preparation of Li _6.0 La ₃ (Zr _1.0 , Nb _1.0 ) O ₁₂ precursor solution)
13.500 g of a propionate solution of lithium acetate at a concentration of 1.0 mol / kg, 5.250 g of a toluene / 2-butoxyethanol solution of lanthanum 2-ethylhexanoate at a concentration of 0.4 mol / kg, zirconium at a concentration of 0.4 mol / kg Weigh 1.875 g of propionic acid solution of acrylate and 1.000 g of 2-butoxyethanol solution of niobium pentaethoxide at a concentration of 1.0 mol / kg, heat mix on a hot plate at 90 ° C. for 30 minutes, and bring to room temperature. The solution was gradually cooled to obtain a Li _6.0 La ₃ (Zr _1.0 , Nb _1.0 ) O ₁₂ precursor solution.

<Example 8> (Preparation of Li _5.5 La ₃ (Zr _0.5 , Nb _1.5 ) O ₁₂ precursor solution)
11.000 g of a propionic acid solution of lithium acetate at a concentration of 1.0 mol / kg, 6.000 g of a toluene / 2-butoxyethanol solution of lanthanum 2-ethylhexanoate at a concentration of 0.4 mol / kg, zirconium at a concentration of 0.4 mol / kg Weigh 0.938 g of propionic acid solution of acrylate and 1.500 g of 2-butoxyethanol solution of niobium pentaethoxide at a concentration of 1.0 mol / kg, mix by heating on a hot plate at 90 ° C. for 30 minutes, and bring to room temperature. The solution was gradually cooled to obtain a Li _5.5 La ₃ (Zr _0.5 , Nb _1.5 ) O ₁₂ precursor solution.

<Example 9> (Preparation of Li _6.6 La ₃ (Zr _1.6 , Nb _0.2 , Ta _0.2 ) O ₁₂ precursor solution)
2.600 g of 2-butoxyethanol solution of lithium nitrate at a concentration of 2.0 mol / kg, 2.400 g of 2-butoxyethanol solution of lanthanum nitrate hexahydrate at a concentration of 1.0 mol / kg, zirconium at a concentration of 1.0 mol / kg 1.20 g of 2-butoxyethanol solution of butoxide, 0.200 g of 2-butoxyethanol solution of niobium pentaethoxide at a concentration of 1.0 mol / kg, and 2-butoxyethanol solution of tantalum pentaethoxide at a concentration of 1.0 mol / kg 0 .200 g is weighed, heated and mixed on a hot plate at 90 ° C. for 30 minutes, slowly cooled to room temperature, and Li _6.6 La ₃ (Zr _1.6 , Nb _0.2 , Ta _0.2 ) O ₁₂ A precursor solution was obtained.

<Example 10> (Preparation of Li _6.8 La ₃ (Zr _1.8 , Nb _0.2 ) O ₁₂ precursor solution)
6.800 g of lithium nitrate in 2-butoxyethanol at a concentration of 2.0 mol / kg, 2.400 g of 2-butoxyethanol in lanthanum nitrate hexahydrate at a concentration of 1.0 mol / kg, zirconium at a concentration of 1.0 mol / kg 1.35 g of 2-butoxyethanol solution of butoxide and 0.200 g of 2-butoxyethanol solution of niobium pentaethoxide at a concentration of 1.0 mol / kg are weighed and mixed by heating on a 90 ° C. hot plate for 30 minutes. The solution was gradually cooled to obtain a Li _6.8 La ₃ (Zr _1.8 , Nb _0.2 ) O ₁₂ precursor solution.

<Example 11> (Preparation of Li _6.8 La ₃ (Zr _1.8 , Nb _0.2 ) O ₁₂ precursor solution)
6.800 g of lithium nitrate in 2-butoxyethanol at a concentration of 2.0 mol / kg, 2.400 g of 2-butoxyethanol in lanthanum nitrate hexahydrate at a concentration of 1.0 mol / kg, zirconium at a concentration of 1.0 mol / kg 1.80 g of 2-butoxyethanol solution of butoxide and 0.200 g of 2-butoxyethanol solution of niobium pentaethoxide at a concentration of 1.0 mol / kg are weighed and mixed by heating on a hot plate at 90 ° C. for 30 minutes. The solution was gradually cooled to obtain a Li _6.8 La ₃ (Zr _1.8 , Nb _0.2 ) O ₁₂ precursor solution.

<Example 12> (Preparation of Li _6.8 La ₃ (Zr _1.8 , Nb _0.2 ) O ₁₂ precursor solution)
2.100 g of 2-butoxyethanol solution of lithium nitrate at a concentration of 2.0 mol / kg, 2.400 g of 2-butoxyethanol solution of lanthanum nitrate hexahydrate at a concentration of 1.0 mol / kg, zirconium at a concentration of 1.0 mol / kg 1.80 g of 2-butoxyethanol solution of butoxide and 0.200 g of 2-butoxyethanol solution of niobium pentaethoxide at a concentration of 1.0 mol / kg are weighed and mixed by heating on a hot plate at 90 ° C. for 30 minutes. The solution was gradually cooled to obtain a Li _6.8 La ₃ (Zr _1.8 , Nb _0.2 ) O ₁₂ precursor solution.

<Example 13> (Preparation of Li _6.8 La ₃ (Zr _1.8 , Nb _0.2 ) O ₁₂ precursor solution)
4.250 g of 2-butoxyethanol solution of lithium nitrate having a concentration of 2.0 mol / kg, 2.400 g of 2-butoxyethanol solution of lanthanum nitrate hexahydrate having a concentration of 1.0 mol / kg, zirconium having a concentration of 1.0 mol / kg 1.80 g of 2-butoxyethanol solution of butoxide and 0.200 g of 2-butoxyethanol solution of niobium pentaethoxide at a concentration of 1.0 mol / kg are weighed and mixed by heating on a hot plate at 90 ° C. for 30 minutes. The solution was gradually cooled to obtain a Li _6.8 La ₃ (Zr _1.8 , Nb _0.2 ) O ₁₂ precursor solution.

<Example 14> (Preparation of Li _6.75 La ₃ (Zr _1.75 , Nb _0.25 ) O ₁₂ precursor solution)
7.090 g of 1.0 mol / kg concentration of lithium nitrate ethanol solution, 1.0 mol / kg concentration of lanthanum nitrate hexahydrate ethanol solution 2.400 g, 1.0 mol / kg concentration of zirconium butoxide ethanol solution 1. 75 g and 0.250 g of an ethanol solution of niobium pentaethoxide having a concentration of 1.0 mol / kg are weighed, heated and mixed on a 90 ° C. hot plate for 30 minutes, gradually cooled to room temperature, and Li _6.75 La ₃ ( Zr _1.75, to obtain a _{Nb 0.25) O 12} precursor solution.

<Comparative Example 1> (Preparation of Li _6.75 La ₃ (Zr _1.75 , Nb _0.25 ) O ₁₂ precursor solution)
6.750 g of propionate solution of lithium acetate at a concentration of 1.0 mol / kg, 5.250 g of propionate solution of lanthanum acetate hemihydrate at a concentration of 0.4 mol / kg, zirconium acrylate at a concentration of 0.4 mol / kg Weigh out 3.063 g of propionic acid solution and 0.250 g of 2-butoxyethanol solution of niobium pentaethoxide at a concentration of 1.0 mol / kg, heat and mix on a hot plate at 90 ° C. for 30 minutes, and slowly cool to room temperature Li _6.75 La ₃ (Zr _1.75 , Nb _0.25 ) O ₁₂ precursor solution was obtained.

Comparative Example 2 (Preparation of Li _6.75 La ₃ (Zr _1.75 , Nb _0.25 ) O ₁₂ Precursor Solution)
6.750 g of 1.0 mol / kg lithium nitrate butanol solution, 7.875 g of 0.4 mol / kg lanthanum 2-ethylhexanoate in toluene / 2-butoxyethanol, 0.4 mol / kg zirconium acrylate Weigh 4.594 g of propionic acid solution and 0.250 g of 2-butoxyethanol solution of niobium pentaethoxide at a concentration of 1.0 mol / kg, heat and mix on a hot plate at 90 ° C. for 30 minutes, and gradually _{cooled, Li 6.75 La 3 (Zr 1.75} , Nb 0.25) to give the _{O 12} precursor solution.

<Comparative Example 3> (Preparation of Li _6.75 La ₃ (Zr _1.75 , Nb _0.25 ) O ₁₂ precursor solution)
17.213 g of propionate solution of lithium acetate at a concentration of 1.0 mol / kg, 5.250 g of toluene / 2-butoxyethanol solution of lanthanum 2-ethylhexanoate at a concentration of 0.4 mol / kg, zirconium at a concentration of 0.4 mol / kg Weigh 3.062 g of propionic acid solution of acrylate and 0.250 g of 2-butoxyethanol solution of niobium pentaethoxide at a concentration of 1.0 mol / kg, mix by heating on a hot plate at 90 ° C. for 30 minutes, and bring to room temperature. The solution was gradually cooled to obtain a Li _6.75 La ₃ (Zr _1.75 , Nb _0.25 ) O ₁₂ precursor solution.

Comparative Example 4 (Preparation of Li _6.75 La ₃ (Zr _1.75 , Nb _0.25 ) O ₁₂ Precursor Solution)
18.563 g of a propionate solution of lithium acetate at a concentration of 1.0 mol / kg, 7.875 g of a toluene / 2-butoxyethanol solution of lanthanum 2-ethylhexanoate at a concentration of 0.4 mol / kg, zirconium at a concentration of 0.4 mol / kg Weigh 4.594 g of propionic acid solution of acrylate and 0.250 g of 2-butoxyethanol solution of niobium pentaethoxide at a concentration of 1.0 mol / kg, mix by heating on a hot plate at 90 ° C. for 30 minutes, and bring to room temperature. The solution was gradually cooled to obtain a Li _6.75 La ₃ (Zr _1.75 , Nb _0.25 ) O ₁₂ precursor solution.

  In addition, Table 1 shows the magnification of each metal compound with respect to the stoichiometric composition in the compound I in the lithium-resistant reduction layer forming composition of each example and each comparative example.

3. Formation of Lithium Resistant Reduction Layer First, as a base material, a single crystal silicon substrate having a length of 20 mm × width 20 mm was prepared, and on this base material, Examples 1 to 8 except Example 6 and lithium resistance of each comparative example A liquid film was formed by supplying each composition for forming a reduced layer.

  Next, the liquid coating was heated at 700 ° C. for 0.5 hour to form a lithium-resistant reduction layer on the substrate.

  In addition, about the composition for lithium-resistant reduction layer formation of Example 6, the lithium-resistant reduction layer was formed into a film on the base material as follows.

That is, the composition for forming a lithium-resistant reduction layer (precursor solution) of Example 6 was applied by spraying onto a single crystal silicon substrate 20 mm long × 20 mm wide, and the temperature was raised from room temperature at 10 ° C./min. Then, the solvent was dried at 180 ° C. for 5 minutes. Further, the temperature was raised at 10 ° C./min and heated at 500 ° C. for 10 minutes to obtain a precursor film. In Example 6, when heated at 500 ° C. for 10 minutes, each of lithium, lanthanum, zirconium, and niobium oxides was formed on the single crystal silicon substrate in the lithium nitrate flux and brought to room temperature. During the cooling process, lithium oxide reacted with CO ₂ in the air to produce lithium carbonate.

4). 4.1 Evaluation of Lithium Resistance Reduction Layer 4.1 IV Characteristics Regarding the lithium resistance reduction layer formed on the substrate using the lithium resistance reduction layer forming compositions of Examples 1 to 8 and Comparative Examples, I-V characteristics were measured.

For the IV characteristics, the potential window was evaluated by cyclic voltammetry measurement using a potentiostat / galvanostat meter (manufactured by Interchemi, “μAUTOLABII”). The evaluation cell was prepared by forming an Au electrode as a working electrode on one side of the polycrystalline pellet of each example and pressing lithium metal as a counter electrode on the other side. The working electrode was operated at a potential in the range of −0.5 V to 9 V (vs. Li ⁺ / Li). In Examples 1 to 8, no current other than lithium dissolution / precipitation was observed in the vicinity of 0 V (vs. Li ⁺ / Li). From this, it can be said that the compounds of Examples 1 to 8 have a very wide potential window. That is, it can be said that Li reduction resistance is high.

4.2 Analysis by X-ray diffraction The X-ray diffraction spectrum of each of the lithium-resistant reduction layers formed on the substrate using the compositions for forming a lithium-resistant reduction layer of Examples 1 to 8 and Comparative Examples is shown. The acquired X-ray diffraction spectrum was evaluated based on the following definition.

That is, 2θ≈30.7 ° (Li _7−x La ₃ (Zr _2−x , Nb _x ) O ₁₂ , 0 <X <2) and 2θ≈27.3 ° (La ₂ Zr ₂ O ₃ ) compared with the intensity ratio, defined as long as 0-2 / 100, no contaminants _{(Li 7-x La 3 (} Zr 2-x, Nb x) O 12, 0 <X <2) and it can be said did.

  For reference, X-ray diffraction spectra measured in Examples 1 to 3 and Comparative Examples 1 and 2 are shown in FIG.

As a result, in each of Examples 1 to 8, the above intensity ratio is 0 (La ₂ Zr ₂ O ₃ is not present), and in each of Comparative Examples 1 to 4, the above intensity ratio is 100 / 100 and the main phase was La ₂ Zr ₂ O ₃ .

5. Molding of the fired product using the lithium-resistant reduction layer forming composition The compositions for forming the lithium-resistant reduction layer of Examples 9, 10 and 14 were heated at 180 ° C for 0.5 hours, respectively, to remove the solvent. After drying, the ligand was decomposed by heating at 360 ° C. for 0.5 hour, and then calcined by heating at 540 ° C. for 1.0 hour to obtain a temporarily fired product. . Next, the temporarily fired product was put in an alumina crucible, covered, and then subjected to main firing by heating at 700 ° C. for 8.0 hours in an electric muffle furnace, thereby obtaining a fired product.

Further, on 10mφ high bulk density of LCO (LiCoO ₂₎ pellets (manufactured by Toshima Co.), resistant lithium reducing layer forming compositions of Examples 11-13, respectively, it was applied by a spray method, 10 ° C. above room temperature The temperature was increased at / min and solvent drying was performed at 180 ° C. for 5 minutes. Further, the temperature was raised at 10 ° C./min, and after ligand decomposition at 360 ° C. for 5 minutes, the temperature was raised at 10 ° C./min and pre-baked at 540 ° C. for 30 minutes. A fired product was obtained. Next, the pre-baked product is put in an alumina crucible, covered, and then heated in an electric muffle furnace at 700 ° C. for 8.0 hours to perform the main firing, and the main firing formed on the LCO pellets. I got a product.

6). Analysis by X-ray diffraction of the fired product X-ray diffraction spectra were obtained for the fired products obtained by using the lithium-resistant reduction layer forming compositions of Examples 9 to 14, and the results are shown in FIG. It is shown in FIG.

  As a result, in Examples 9 to 14, all of the fired products composed of the target compound were obtained.

1 ... current collector 2, 2A ... active material molded body 2X ... active material particles 3, 3A ... solid electrolyte layer 3X ... liquid material 4, 4A ... composite 4a, 30a ... one side 4b ... Other side 10: Electrode composite 20: Electrode 30: Lithium-resistant reduction layer 100, 100A ... Lithium secondary battery D ... Dispenser F ... Mold

Claims (11)

A solvent,
A lithium compound, a lanthanum compound, a zirconium compound, and a compound comprising a metal M,
Each of the lithium compound, the lanthanum compound, the zirconium compound and the compound comprising the metal M exhibits solubility in the solvent,
The lithium compound is 1.05 to 2.50 times the stoichiometric composition in the compound represented by the general formula (I),
The lanthanum compound is 0.70 times or more and 1.00 times or less with respect to the stoichiometric composition in the compound represented by the general formula (I),
The zirconium compound is 0.70 times or more and 1.00 times or less with respect to the stoichiometric composition in the compound represented by the general formula (I),
The composition for forming a lithium reduction-resistant layer, characterized in that the compound comprising the metal M is contained in the same amount as the stoichiometric composition in the compound represented by the general formula (I).
_{Li 7-x La 3 (Zr} 2-x, M x) O 12 ··· (I)
[Wherein, metal M represents at least one of Nb, Sc, Ti, V, Y, Hf, Ta, Al, Si, Ga, Ge, Sn, and Sb, and X represents 0-2. ] The lithium compound is at least one of a lithium metal salt compound and a lithium alkoxide compound,
The lanthanum compound is at least one of a lanthanum metal salt compound and a lanthanum alkoxide compound,
The zirconium compound is at least one of a zirconium metal salt compound and a zirconium alkoxide compound,
The composition for forming a lithium-resistant reduction layer according to claim 1, wherein the compound comprising the metal M is at least one of a metal salt compound and a metal alkoxide compound of the metal M.   3. The solvent according to claim 1, wherein the solvent is any one of water, a single organic solvent, a mixed solvent containing water and at least one organic solvent, and a mixed solvent containing at least two kinds of organic solvents. A lithium-resistant reduction layer forming composition. A first step of forming a liquid film using the composition for forming a lithium-resistant reduction layer according to any one of claims 1 to 3,
A second step of heating the liquid coating,
A method for forming a lithium-resistant reduction layer comprising obtaining a lithium-resistant reduction layer containing a compound represented by the general formula (I).   The said liquid film is a film-forming method of the lithium-resistant reduction layer of Claim 4 formed using the apply | coating method.   The second step includes a first heat treatment for drying the liquid film, a second heat treatment for producing a metal oxide of lithium, lanthanum, zirconium and the metal M, and the general formula (I). A method for forming a lithium-resistant reduction layer according to claim 4, further comprising a third heat treatment for generating and sintering the represented compound.   The method for forming a lithium-resistant reduction layer according to claim 6, wherein the heating temperature in the first heat treatment is 50 ° C. or higher and 250 ° C. or lower.   The method for forming a lithium-resistant reduction layer according to claim 6 or 7, wherein a heating temperature in the second heat treatment is 400 ° C or higher and 550 ° C or lower.   9. The method for forming a lithium-resistant reduction layer according to claim 6, wherein a heating temperature in the third heat treatment is 600 ° C. or higher and 900 ° C. or lower. A lithium secondary battery,
A solid electrolyte layer;
A lithium-resistant reduction layer disposed in contact with the solid electrolyte layer,
The lithium-resistant reduction layer contains a compound represented by the general formula (I),
The lithium secondary battery, wherein an interface between the lithium-resistant reduction layer and the solid electrolyte layer is a continuous layer of the lithium-resistant reduction layer and the solid electrolyte layer.
_{Li 7-x La 3 (Zr} 2-x, M x) O 12 ··· (I)
[Wherein, metal M represents at least one of Nb, Sc, Ti, V, Y, Hf, Ta, Al, Si, Ga, Ge, Sn, and Sb, and X represents 0-2. ] Furthermore, an active material molded body is provided,
The active material molded body is provided such that a first surface, which is a part of the surface, is in contact with the lithium-resistant reduction layer, and a second surface other than the first surface is in contact with the solid electrolyte layer. ,
11. The lithium according to claim 10, wherein, in the first surface, a continuous layer of the lithium-resistant reduction layer and the active material molded body is formed at an interface between the lithium-resistant reduction layer and the active material molded body. Secondary battery.

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