JP2021018859A - Lithium ion conductor and electricity storage device - Google Patents

Abstract

To sufficiently improve lithium ion conductivity of a lithium ion conductor.SOLUTION: The lithium ion conductor contains lithium ion conductive powder having a garnet type structure containing at least Li, La, Zr, and O. The lithium ion conductor further contains an ionic liquid having lithium ion conductivity. When an atomic concentration of each element is specified by X-ray photoelectron spectroscopy (XPS), a ratio R1(=C2/C1) of a total atomic concentration C2 of each element of specified elements to a total concentration C1 of each atomic concentration of Li element, La element, and Zr element is 0.25 to 0.90, the specified elements referring to those among elements contained in the ionic liquid (however, excluding O element and C element), which are not contained in the lithium ion conductive powder.SELECTED DRAWING: Figure 1

Description

The techniques disclosed herein relate to lithium ion conductors and energy storage devices.

In recent years, with the spread of electronic devices such as personal computers and mobile phones, the spread of electric vehicles, and the expansion of the use of natural energy such as solar power and wind power, the demand for high-performance batteries is increasing. In particular, the use of an all-solid-state lithium-ion secondary battery (hereinafter referred to as an "all-solid-state battery") in which all battery elements are solid is expected. The all-solid-state battery is safer than the conventional lithium ion secondary battery that uses an organic electrolytic solution in which a lithium salt is dissolved in an organic solvent, because there is no risk of leakage or ignition of the organic electrolytic solution. Since the exterior can be simplified, the energy density per unit mass or unit volume can be improved.

Lithium having a garnet-type structure containing at least Li (lithium), La (lantern), Zr (zirconium), and O (oxygen) as lithium ion conductors constituting the solid electrolyte layer and electrodes of an all-solid-state battery. Lithium ion conductors containing ionic conductive powder are known. Examples of the lithium ion conductive powder contained in such a lithium ion conductor include Li ₇ La ₃ Zr ₂ O ₁₂ (hereinafter referred to as “LLZ”) and Mg (magnesium) and A with respect to LLZ. (A is at least one element selected from the group consisting of Ca (calcium), Sr (strontium) and Ba (barium)) and at least one element is substituted (for example, with respect to LLZ). Those in which the elements of Mg and Sr are substituted (hereinafter referred to as "LLZ-MgSr")) are known (see, for example, Patent Document 1). Hereinafter, these lithium ion conductive powders are referred to as "LLZ-based lithium ion conductive powders".

Japanese Unexamined Patent Publication No. 2016-40767

The LLZ-based lithium ion conductive powder has high resistance between particles in the state of a molded product (compact powder) obtained by pressure molding the powder because the contact between the particles is point contact, and the lithium ion conductivity is high. Is relatively low. Lithium-ion conductivity can be increased by firing the LLZ-based lithium-ion conductive powder at a high temperature, but it is difficult to increase the size of the battery due to warpage and deformation caused by high-temperature firing, and the temperature is high. A high resistance layer may be formed due to the reaction with the electrode active material or the like during firing, and the lithium ion conductivity may decrease.

It should be noted that such a problem is not limited to the lithium ion conductor used for the solid electrolyte layer and the electrode of the all-solid-state battery, but is a problem common to all lithium ion conductors including the lithium ion conductive powder.

This specification discloses a technique capable of solving the above-mentioned problems.

The technique disclosed in the present specification can be realized, for example, in the following forms.

(1) The lithium ion conductor disclosed in the present specification is a lithium ion conductor containing a lithium ion conductive powder having a garnet-type structure containing at least Li, La, Zr, and O, and further lithium ions. When the atomic concentration of each element is specified by X-ray photoelectron spectroscopy (XPS), which contains a conductive ionic liquid, among the elements contained in the ionic liquid (excluding O element and C element). The ratio of the total atomic concentration of each of the specific elements C2 to the total atomic concentration of each of the specific element, which is an element not contained in the lithium ion conductive powder, the Li element, the La element, and the Zr element R1 ( = C2 / C1) is 0.25 or more and 0.90 or less. In this lithium ion conductor, regardless of the particle size of the lithium ion conductive powder contained in the lithium ion conductor, the ionic liquid is present in a portion near the surface of the lithium ion conductor at a ratio that is neither excessively low nor high. Therefore, the lithium ion conductivity of the lithium ion conductor can be sufficiently improved.

(2) In the lithium ion conductor, the particle size (D90) of the lithium ion conductive powder may be 10 μm or less. According to this lithium ion conductor, when the lithium ion conductor is configured as a green compact, the packing property of the green compact can be improved, and as a result, the porosity is lowered to improve the lithium ion conductivity. It can be further improved, and when the lithium ion conductor is configured as a sheet-shaped molded body, the thickness of the sheet can be reduced, and the lithium ion conductivity can be further improved.

(3) Further, the power storage device disclosed in the present specification includes a solid electrolyte layer, a positive electrode, and a negative electrode, and at least one of the solid electrolyte layer, the positive electrode, and the negative electrode is described above. Includes lithium ion conductor. According to this power storage device, at least one lithium ion conductivity between the solid electrolyte layer, the positive electrode and the negative electrode can be sufficiently improved, and thus the electrical performance of the power storage device can be sufficiently improved.

The technique disclosed in the present specification can be realized in various forms, for example, a lithium ion conductor, a solid electrolyte layer or electrode containing the lithium ion conductor, the solid electrolyte layer or the said. It can be realized in the form of a power storage device provided with electrodes, a method for manufacturing the same, and the like.

Explanatory drawing schematically showing the cross-sectional structure of the all-solid-state lithium ion secondary battery 102 in this embodiment. Explanatory drawing schematically showing the structure of the lithium ion conductor 202 Explanatory drawing showing the result of performance evaluation Explanatory drawing showing the result of performance evaluation

A. Embodiment:
A-1. Configuration of all-solid-state battery 102:
(overall structure)
FIG. 1 is an explanatory view schematically showing a cross-sectional configuration of an all-solid-state lithium ion secondary battery (hereinafter, referred to as “all-solid-state battery”) 102 in the present embodiment. FIG. 1 shows XYZ axes that are orthogonal to each other to specify the direction. In the present specification, for convenience, the Z-axis positive direction is referred to as an upward direction, and the Z-axis negative direction is referred to as a downward direction.

The all-solid-state battery 102 includes a battery body 110, a positive electrode side current collecting member 154 arranged on one side (upper side) of the battery body 110, and a negative electrode side current collecting member 154 arranged on the other side (lower side) of the battery body 110. It includes a member 156. The positive electrode side current collecting member 154 and the negative electrode side current collecting member 156 are substantially flat plate-shaped members having conductivity, and are, for example, stainless steel, Ni (nickel), Ti (titanium), Fe (iron), Cu (copper). , Al (aluminum), a conductive metal material selected from these alloys, a carbon material, and the like. In the following description, the positive electrode side current collecting member 154 and the negative electrode side current collecting member 156 are also collectively referred to as a current collecting member.

(Configuration of battery body 110)
The battery body 110 is a lithium ion secondary battery body in which all battery elements are solid. In the present specification, the fact that the battery elements are all made of solid means that the skeletons of all the battery elements are made of solid, for example, a form in which the skeleton is impregnated with a liquid or the like. It does not exclude it. The battery body 110 includes a positive electrode 114, a negative electrode 116, and a solid electrolyte layer 112 arranged between the positive electrode 114 and the negative electrode 116. In the following description, the positive electrode 114 and the negative electrode 116 are also collectively referred to as electrodes. The battery body 110 corresponds to a power storage device within the scope of the claims.

(Structure of solid electrolyte layer 112)
The solid electrolyte layer 112 is a member having a substantially flat plate shape, and contains a lithium ion conductor 202 having lithium ion conductivity.

(Structure of positive electrode 114)
The positive electrode 114 is a member having a substantially flat plate shape, and contains a positive electrode active material 214. Examples of the positive electrode active material 214 include S (sulfur), TiS ₂ , LiCoO ₂ (hereinafter referred to as “LCO”), LiMn ₂ O ₄ , LiFePO ₄ , and Li (Co _1/3 Ni _1/3 Mn _{1 /). 3} ) O ₂ (hereinafter referred to as “NCM”), LiNi _0.8 Co _0.15 Al _0.05 O _{2 and the} like are used. Further, the positive electrode 114 contains a lithium ion conductor 204 as a lithium ion conduction auxiliary agent. The positive electrode 114 may further contain an electron conductive auxiliary agent (for example, conductive carbon, Ni (nickel), Pt (platinum), Ag (silver)).

(Structure of negative electrode 116)
The negative electrode 116 is a member having a substantially flat plate shape, and contains a negative electrode active material 216. Examples of the negative electrode active material 216 include Li metal, Li—Al alloy, Li ₄ Ti ₅ O ₁₂ (hereinafter referred to as “LTO”), carbon (graphite, natural graphite, artificial graphite, and low crystalline carbon on the surface). (Coated core-shell type graphite), Si (silicon), SiO and the like are used. Further, the negative electrode 116 contains a lithium ion conductor 206 as a lithium ion conduction aid. The negative electrode 116 may further contain an electron conductive auxiliary agent (for example, conductive carbon, Ni, Pt, Ag).

A-2. Lithium-ion conductor composition:
Next, the configuration of the lithium ion conductor 202 contained in the solid electrolyte layer 112 will be described. Since the configurations of the lithium ion conductor 204 contained in the positive electrode 114 and the lithium ion conductor 206 contained in the negative electrode 116 are the same as the configurations of the lithium ion conductor 202 contained in the solid electrolyte layer 112, the description thereof will be omitted. To do.

In the present embodiment, the lithium ion conductor 202 contained in the solid electrolyte layer 112 contains a lithium ion conductive powder. More specifically, the lithium ion conductor 202 is a lithium ion conductive powder having a garnet-type structure containing at least the above-mentioned LLZ-based lithium ion conductive powder (Li, La, Zr, and O), for example, LLZ. And LLZ-MgSr). It can be confirmed by analyzing with an X-ray diffractometer (XRD) that the lithium ion conductive powder has a garnet-type structure containing at least Li, La, Zr and O. Specifically, an X-ray diffraction pattern is obtained by analyzing the lithium ion conductive powder with an X-ray diffractometer. The obtained X-ray diffraction pattern was compared with the ICDD (International Center for Diffraction Data) card (01-080-4497) (Li ₇ La ₃ Zr ₂ O ₁₂ ) corresponding to LLZ, and the diffraction of the diffraction peak in both was compared. If the angles and the diffraction intensity ratios are substantially the same, it can be determined that the lithium ion conductive powder has a garnet-type structure containing at least Li, La, Zr, and O. For example, each lithium ion conductive powder (LLZ-based lithium ion conductive powder) described in "A-5. Preferred aspects of LLZ-based lithium ion conductive powder" described later is X-ray diffraction obtained from the powder. Since the diffraction angles and diffraction intensity ratios of the diffraction peaks in both the pattern and the ICDD card corresponding to LLZ are substantially the same, it is determined that the pattern has a garnet-type structure containing at least Li, La, Zr, and O. To.

Further, in the present embodiment, the lithium ion conductor 202 further contains an ionic liquid having lithium ion conductivity. The ionic liquid having lithium ion conductivity is, for example, an ionic liquid in which a lithium salt is dissolved. The ionic liquid is a substance that is liquid at room temperature and consists of only cations and anions.

Examples of the lithium salt include lithium tetrafluoride (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), and lithium trifluoromethanesulfonate (CF ₃ SO ₃ Li). ), Lithium bis (trifluoromethanesulfonyl) imide (LiN (SO ₂ CF ₃ ) ₂ ) (hereinafter referred to as "Li-TFSI"), Lithium bis (fluorosulfonyl) imide (LiN (SO ₂ F) ₂ ) (hereinafter , "Li-FSI"), lithium bis (pentafluoroethanesulfonyl) imide (LiN (SO ₂ C ₂ F ₅ ) ₂ ) and the like are used.

Further, as the ionic liquid, as a cation,
Ammonium-based products such as butyltrimethylammonium and trimethylpropylammonium,
Imidazoles such as 1-ethyl-3 methylimidazolium and 1-butyl-3-methylimidazolium,
Piperidinium-based products such as 1-butyl-1-methylpiperidinium and 1-methyl-1-propylpiperidinium,
Pyridinium-based products such as 1-butyl-4-methylpyridinium and 1-ethylpyridinium,
Pyrrolidiniums such as 1-butyl-1-methylpyrrolidinium and 1-methyl-1-propylpyrrolidinium,
Sulfonium-based products such as trimethylsulfonium and triethylsulfonium,
Phosphonium type,
Morphorinium-based,
Etc. are used.

Further, as the ionic liquid, as an anion,
Halides such as Cl ⁻ and Br ⁻ ,
BF ₄ ^- such as boron hydride system,
_(NC) 2 N ^-,
(CF ₃ SO ₂ ) ₂ N ⁻ , (FSO ₂ ) ₂ N ^{− and} other amines,
CH ₃ SO ₄ ^-,
CF ₃ SO ₃ ^- etc. Sulfate, sulphonate system,
Phosphoric acid type such as PF ₆ ⁻
Etc. are used.

More specifically, the ionic liquids include butyltrimethylammonium bis (trifluoromethanesulfonyl) imide, trimethylpropylammonium bis (trifluoromethanesulfonyl) imide, and 1-ethyl-3-methylimidazolium bis (fluorosulfonyl) imide (hereinafter , "EMI-FSI"), 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-methyl-1-propylpyrrolidinium bis (trifluoromethanesulfonyl) imide, 1-ethyl-3-methylimidazolium Bis (trifluoromethanesulfonyl) imide, 1-methyl-1-propylpyrrolidinium bis (fluorosulfonyl) imide (hereinafter referred to as "P13-FSI"), 1-methyl-1-propylpiperidinium bis (fluorosulfonyl) ) Imide (hereinafter referred to as "PP13-FSI") and the like are used.

The lithium ion conductor 202 of the present embodiment is not a sintered body formed by high-temperature firing. Therefore, the lithium ion conductor 202 of the present embodiment contains a hydrocarbon. More specifically, the ionic liquid constituting the lithium ion conductor 202 of the present embodiment contains a hydrocarbon. The fact that the lithium ion conductor 202 (ion liquid) contains hydrocarbons means that NMR (nuclear magnetic resonance), Raman spectroscopy, LC-MS (liquid chromatography-mass spectrometry), and GC-MS (gas chromatography) It can be specified by one or a combination of methods such as graf mass spectrometry) and FT-IR (Fourier transform infrared spectroscopy).

As described above, the lithium ion conductor 202 of the present embodiment contains an ionic liquid having lithium ion conductivity in addition to the LLZ-based lithium ion conductive powder, and is a pressure-molded molded body (compact powder). ), It exhibits high lithium ion conductivity. The reason why the lithium ion conductor 202 of the present embodiment has such high lithium ion conductivity is not necessarily clear, but it is presumed as follows.

Since the LLZ-based lithium ion conductive powder is harder than other oxide-based lithium ion conductors and non-oxide-based lithium ion conductors (for example, sulfide-based lithium ion conductors), the powder is added. In the state of the pressure-molded molded body (compact powder), the contact between the particles becomes point contact, the resistance between the particles increases, and the lithium ion conductivity is relatively low. Further, although the lithium ion conductivity can be increased by firing the LLZ-based lithium ion conductive powder at a high temperature, it is difficult to increase the size of the battery because warpage and deformation occur due to the high temperature firing. , There is a risk that a high resistance layer will be formed due to the reaction with the electrode active material and the like accompanying high temperature firing, and the lithium ion conductivity will decrease. However, the lithium ion conductor 202 of the present embodiment contains an ionic liquid having lithium ion conductivity in addition to the LLZ-based lithium ion conductive powder. Therefore, in the state of the compact formed under pressure, an ionic liquid that functions as a lithium ion conduction path intervenes in the grain boundaries of the LLZ-based lithium ion conductive powder throughout the molded body, and lithium ion conduction in the grain boundaries. It is considered that the property was improved, and as a result, the lithium ion conductivity of the lithium ion conductor 202 was improved.

Further, the lithium ion conductor 202 of the present embodiment may further contain a binder in addition to the LLZ-based lithium ion conductive powder and the ionic liquid, and may be formed in a sheet shape. Examples of the binder include polyvinylidene fluoride (PVDF), a copolymer of polyvinylidene fluoride (PVDF) and hexafluoropropylene (HFP) (hereinafter referred to as “PVDF-HFP”), polytetrafluoroethylene (PTFE), and the like. Polyethylene, polyamide, silicone (polysiloxane), styrene-butadiene rubber (SBR), acrylic resin (PMMA), polyethylene oxide (PEO) and the like are used. With such a configuration, it is possible to improve the moldability and handling of the lithium ion conductor 202 while improving the lithium ion conductivity of the lithium ion conductor 202.

Here, the inventor of the present application has studied diligently and uses the ionic liquid element ratio R1 described below in order to specify a preferable configuration of the lithium ion conductor 202 containing the lithium ion conductive powder and the ionic liquid. Was newly found. The ionic liquid element ratio R1 is the lithium ion conduction among the elements contained in the ionic liquid (excluding the O element and the C element) when the atomic concentration of each element is specified by X-ray photoelectron spectroscopy (XPS). Each atom of the above-mentioned specific element with respect to the total atomic concentration of each of the specific element which is an element not contained in the sex powder, the Li element, the La element, and the Zr element (hereinafter, referred to as "total element atomic concentration C1"). It is a ratio of the total concentration (hereinafter, referred to as "total ion liquid element atomic concentration C2"). That is, the ratio of ionic liquid elements R1 = total ionic liquid element atomic concentration C2 / total element atomic concentration C1. For example, when the lithium ion conductor 202 contains LiTFSI (EMI-FSI) as an ionic liquid and LLZ-Mg, Sr as a lithium ion conductive powder, the specific elements are the elements N, S, F. The total elemental atomic concentration C1 is the total atomic concentration of each of the elements Li, La, Zr, N, S, and F, and the total ionic liquid element atomic concentration C2 is the total atomic concentration of the specific elements N, S, and F, respectively. Is the total atomic concentration of.

Since XPS is an analysis method for examining the characteristics of an object near the surface, the ionic liquid element ratio R1 indicates how much ionic liquid is present in the portion near the surface of the lithium ion conductor 202. It can be said that it is an index value. For example, it is conceivable to measure the thickness of the ionic liquid existing on the surface of the lithium ion conductor by SEM observation or the like, but since the thickness of the ionic liquid is very thin (on the order of nm) and is very weak to electron beams. SEM observation cannot be performed. In this respect, XPS is considered to be able to appropriately grasp the state of the ionic liquid existing on the surface of the lithium ion conductor.

In the lithium ion conductor 202 containing the lithium ion conductive powder and the ionic liquid, if the amount of the ionic liquid is too small, the amount of the ionic liquid functioning as the lithium ion conduction path decreases at the grain boundary of the lithium ion conductive powder, and lithium. Ion conductivity does not improve sufficiently. On the other hand, if the amount of ionic liquid is too large, the total conductivity including non-lithium ions (anions, etc.) will be high, but the conduction will be mainly ionic liquid with low transport number, resulting in lithium ion conductivity. Will decrease. Therefore, in order to improve the lithium ion conductivity of the lithium ion conductor 202, the content of the ionic liquid in the lithium ion conductor 202 is important.

Conventionally, in order to specify the content of the ionic liquid in the lithium ion conductor 202, the content of the ionic liquid is relative to the total of the content of the lithium ion conductive powder (vol%) and the content of the ionic liquid (vol%). The content ratio (hereinafter referred to as "ionic liquid volume ratio R2") has been used. However, as described below, the ionic liquid volume ratio R2 cannot appropriately specify a preferable configuration (a configuration having high lithium ion conductivity) of the lithium ion conductor 202.

FIG. 2 is an explanatory diagram schematically showing the configuration of the lithium ion conductor 202. In columns A and B of FIG. 2, the configuration of the lithium ion conductor 202 having the same ionic liquid volume ratio R2 is shown. In the lithium ion conductor 202 shown in column A of FIG. 2, the entire surface of the lithium ion conductive powder SE is covered with the ionic liquid IL. Therefore, in the lithium ion conductor 202 shown in column A of FIG. 2, an ionic liquid IL that functions as a lithium ion conduction path intervenes over the entire grain boundary of the lithium ion conductive powder SE, and the lithium ion conductivity is sufficiently improved. Has been done. On the other hand, in the lithium ion conductor 202 shown in column B of FIG. 2, only a part of the surface of the lithium ion conductive powder SE is covered with the ionic liquid IL. This is because the lithium ion conductor 202 shown in column B of FIG. 2 has a smaller diameter of the lithium ion conductive powder SE than the lithium ion conductor 202 shown in column A of FIG. 2 (D2 <D1), and lithium ions. This is because the specific surface area of the conductive powder SE is large. Therefore, in the lithium ion conductor 202 shown in column B of FIG. 2, the ionic liquid IL does not intervene in a part of the grain boundaries of the lithium ion conductive powder SE, and the lithium ion conductivity is not sufficiently improved. As described above, even if the ionic liquid volume ratio R2 is the same value, the distribution state of the ionic liquid IL on the surface of the lithium ion conductive powder SE may be different. Therefore, in the ionic liquid volume ratio R2, the lithium ion conductor 202 It is not possible to properly specify a preferred configuration (a configuration having high lithium ion conductivity).

On the other hand, the above-mentioned ionic liquid element ratio R1 is an index value indicating how much ionic liquid IL is present in the portion near the surface of the lithium ion conductor 202, and therefore is a preferable configuration of the lithium ion conductor 202. It is considered that (a configuration having high lithium ion conductivity) can be appropriately specified.

Specifically, the lithium ion conductor 202 of the present embodiment is configured so that the ionic liquid element ratio R1 is 0.25 or more and 0.90 or less. That is, in the present embodiment, the ionic liquid is present in the portion near the surface of the lithium ion conductor 202 at a ratio that is neither excessively low nor high. In this way, the lithium ion conductivity of the lithium ion conductor 202 can be sufficiently improved. In order to further improve the lithium ion conductivity of the lithium ion conductor 202, the ionic liquid element ratio R1 is more preferably 0.36 or more, further preferably 0.52 or more, and 0. It is more preferably 57 or more. Further, in order to further improve the lithium ion conductivity of the lithium ion conductor 202, the ionic liquid element ratio R1 is more preferably 0.90 or less, and further preferably 0.80 or less.

Further, in the lithium ion conductor 202 of the present embodiment, the particle size (D90) of the lithium ion conductive powder is preferably 10 μm or less. By doing so, when the lithium ion conductor 202 is configured as the green compact, the packing property of the green compact can be improved, and as a result, the porosity is lowered and the lithium ion conductivity is further improved. Can be made to. Further, in this way, when the lithium ion conductor 202 is configured as a sheet-shaped molded body, the thickness of the sheet can be reduced, and the lithium ion conductivity can be further improved.

Regarding XPS, when the lithium ion conductor 202 is a powder, XPS is performed on the surface of the lithium ion conductor 202, and when the lithium ion conductor 202 is a green compact, the XPS is performed. XPS shall be performed on the cross section of the lithium ion conductor 202, and when the lithium ion conductor 202 is a sheet-shaped molded body, XPS shall be performed on the surface or cross section of the lithium ion conductor 202. To do.

A-3. Manufacturing method of all-solid-state battery 102:
Next, an example of the manufacturing method of the all-solid-state battery 102 of the present embodiment will be described. First, the solid electrolyte layer 112 is prepared. Specifically, a lithium ion conductive powder is prepared, the lithium ion conductive powder and an ionic liquid are mixed to prepare a lithium ion conductor 202, and the lithium ion conductor 202 is pressurized at a predetermined pressure. The solid electrolyte layer 112, which is a molded body of the lithium ion conductor 202, is produced by molding or by adding a binder to form a sheet.

Further, the positive electrode 114 and the negative electrode 116 are separately manufactured. Specifically, the powder of the positive electrode active material 214, the lithium ion conductor 204 containing the ionic liquid, and the powder of the electron conduction aid, if necessary, are mixed at a predetermined ratio and pressure-molded at a predetermined pressure. The positive electrode 114 is produced by adding a binder and molding it into a sheet. Further, the powder of the negative electrode active material 216, the lithium ion conductor 206 containing the ionic liquid, and the powder of the electron conduction aid, if necessary, are mixed and pressure-molded at a predetermined pressure, or a binder is added to the sheet. The negative electrode 116 is manufactured by molding it into a shape.

Next, the positive electrode side current collecting member 154, the positive electrode 114, the solid electrolyte layer 112, the negative electrode 116, and the negative electrode side current collecting member 156 are laminated in this order and pressurized to integrate them. Through the above steps, the all-solid-state battery 102 having the above-described configuration is manufactured.

A-4. Performance evaluation:
Performance evaluation was performed on lithium ion conductors containing lithium ion conductive powder and ionic liquid. 3 and 4 are explanatory views showing the results of performance evaluation.

As shown in FIGS. 3 and 4, nine lithium ion conductor samples (S1 to S5, S11 to S14) were used for the performance evaluation. Each sample is common in that it contains LLZ-Mg and Sr powders, which are lithium ion conductive powders, and LiTFSI (EMI-FSI), which is an ionic liquid, but its composition (each component). (Vol%)) and the particle size (D90) of LLZ-Mg and Sr are different from each other. Specifically, in the samples S1 to S5, the particle size (D90) of LLZ-Mg and Sr is 5.1 μm, and in the samples S11 to S14, the particle size (D90) of LLZ-Mg and Sr is 3.2 μm. Met. The composition of each sample is as shown in FIGS. 3 and 4.

The method for producing each sample is as follows. First, a powder of LLZ-Mg · Sr, which is a lithium ion conductive powder, was prepared. Specifically, the composition: Li _2.95 Mg _0.15 La _2.75 Sr _0.25 Zr _2.0 O ₁₂ (LLZ-Mg · Sr), Li ₂ CO ₃ , MgO, La ( OH) ₃ , SrCO ₃ , and ZrO ₂ were weighed. At that time, in consideration of the volatilization of Li during firing, Li ₂ CO ₃ was further added so as to be excessive by about 15 mol% in terms of elements. This raw material was put into a nylon pot together with zirconia balls, and pulverized and mixed in an organic solvent for 15 hours with a ball mill. After pulverization and mixing, the slurry was dried and reduced and calcined on an MgO plate at 1200 ° C. for 10 hours to prepare a powder of LLZ-Mg · Sr. The particle size (D90) of the LLZ-Mg and Sr powders was adjusted to 5.1 μm or 3.2 μm by wet pulverizing the obtained powder with a planetary ball mill in an air-free environment.

In addition, LiTFSI (EMI-FSI), which is an ionic liquid, was produced. Specifically, the lithium salt Li-TFSI was dissolved in the ionic liquid EMI-FSI so that the lithium salt concentration was equivalent to 0.8 mol / L to obtain LiTFSI (EMI-FSI).

Next, the powder of LLZ-Mg · Sr, which is a lithium ion conductive powder, and LiTFSI (EMI-FSI), which is an ionic liquid, are mixed on a dairy pot at the ratios (vol%) shown in FIGS. 3 and 4. A lithium ion conductor (a composite of a lithium ion conductive powder and an ionic liquid) was obtained.

XPS measurements were performed on each sample in a non-atmospheric exposure state to identify the atomic concentration of each element. From the specific result of the atomic concentration of each element, the specific element which is not contained in the lithium ion conductive powder among the total element atomic concentration C1 (elements contained in the ionic liquid (excluding O element and C element)). And the ionic liquid element ratio R1 which is the ratio of the total atomic concentration C2 of the ionic liquid element (the total atomic concentration of each of the above-mentioned specific elements) to the total atomic concentration of each of the Li element, the La element and the Zr element). Calculated. In this performance evaluation, each sample contains LiTFSI (EMI-FSI) as an ionic liquid and LLZ-Mg, Sr powder as a lithium ion conductive powder. Therefore, the total elemental atomic concentration C1 is the element Li, It is the total atomic concentration of each of La, Zr, N, S, and F, and the total atomic concentration of ionic liquid elements C2 is the total atomic concentration of each of the elements N, S, and F. The concentration of each atom was specified by XPS measurement under the following conditions.
-Measuring device: PHI Quantera SXM manufactured by ULVAC FI Co., Ltd.
-Excited X-ray source: Monochromatic AlKα ray (25 W, 15 kV, 100 μm diameter)
・ Photoelectron extraction angle: 45 °
・ Analysis software: MultiPack

In addition, the lithium ion conductivity of each sample was measured while each sample was pressurized at 500 MPa.

For each sample, if ionic liquid exudation occurs during molding or if the lithium ion conductivity is less than 1.0 × ^10-6 S / cm, it is judged as rejected (×). When the ionic liquid did not exude during molding and the lithium ion conductivity was 1.0 × ^10-6 S / cm or more, it was judged to be acceptable (◯).

In the samples S1 and S11, the lithium ion conductivity was less than 1.0 × ^10-6 S / cm, so that it was determined to be rejected (×). In these samples, the ionic liquid element ratio R1 was less than 0.25, and a sufficient amount of ionic liquid was not present in the portion near the surface of the lithium ion conductor, resulting in low lithium ion conductivity. it is conceivable that.

On the other hand, in sample S5, since the ionic liquid exuded during molding, it was determined to be unacceptable (x). In this sample, the ionic liquid element ratio R1 exceeds 0.90, and an excessive amount of ionic liquid is present in the vicinity of the surface of the lithium ion conductor, so that the ionic liquid exudes. it is conceivable that.

On the other hand, in the samples S2 to S4 and S12 to S14, the ionic liquid did not exude during molding and the lithium ion conductivity was 1.0 × ^10-6 S / cm or more, so that the sample passed ( 〇) was judged. In these samples, the ionic liquid element ratio R1 is 0.25 or more and 0.90 or less, and an appropriate amount of ionic liquid, not excessively large or small, is present in the vicinity of the surface of the lithium ion conductor. Therefore, it is considered that the ionic liquid does not exude and the lithium ion conductivity is increased.

With reference to the performance evaluation results described above, in the lithium ion conductor containing the lithium ion conductive powder and the ionic liquid, when the ionic liquid element ratio R1 is 0.25 or more and 0.90 or less, the ionic liquid stains. It can be said that the lithium ionic conductivity can be improved without generating a discharge.

From the results of this performance evaluation, in the lithium ion conductor containing the lithium ion conductive powder and the ionic liquid, the ionic liquid volume ratio R2 (content of the lithium ion conductive powder (vol%)) and the content of the ionic liquid ( It can be said that it was confirmed that the value of the ionic liquid element ratio R1 was different when the particle size of the lithium ion conductive powder was different even if the ratio of the content of the ionic liquid to the total of vol%) was equal to each other. For example, the sample S2 and the sample S12 have the same ionic liquid volume ratio R2, but the sample S12 has a smaller particle size of the lithium ion conductive powder, so that the specific surface area of the lithium ion conductive powder is larger. As a result, the value of the ionic liquid element ratio R1 is small. The same can be said between the sample S4 and the sample S13, and between the sample S5 and the sample S14. However, between the sample S1 and the sample S11, the value of the ionic liquid element ratio R1 is larger in the sample S11 even though the particle size of the lithium ion conductive powder is smaller in the sample S11. This is because in both the sample S1 and the sample S11, since the amount of the ionic liquid added is extremely small, a part of the surface of the lithium ion conductive powder is not covered with the ionic liquid, and the ionic liquid element ratio R1 is determined depending on the measurement position. This is probably because the values varied.

A-5. Preferred embodiments of the LLZ-based lithium ion conductive powder:
As described above, the lithium ion conductor in the present embodiment contains an LLZ-based lithium ion conductive powder (a lithium ion conductive powder having a garnet-type structure containing at least Li, La, Zr, and O). .. Examples of the LLZ-based lithium ion conductive powder include Mg, Al, Si, Ca (calcium), Ti, V (vanadium), Ga (gallium), Sr, Y (ittium), Nb (niobium), Sn (tin), and so on. Adopt one containing at least one element selected from the group consisting of Sb (antimony), Ba (barium), Hf (hafnium), Ta (tantalum), W (tungsten), Bi (bismus) and lanthanoid elements. Is preferable. With such a configuration, the LLZ-based lithium ion conductive powder exhibits good lithium ion conductivity.

Examples of the LLZ-based lithium ion conductor having a garnet-type structure include the following.
Li ₆ La ₃ Zr _1.5 W _0.5 O ₁₂
Li _6.15 La ₃ Zr _1.75 Ta _0.25 Al _0.2 O ₁₂
Li _6.15 La ₃ Zr _1.75 Ta _0.25 Ga _0.2 O ₁₂
Li _6.25 La ₃ Zr ₂ Ga _0.25 O ₁₂
Li _6.4 La ₃ Zr _1.4 Ta _0.6 O ₁₂
Li _6.5 La ₃ Zr _1.75 Te _0.25 O ₁₂
Li _6.75 La ₃ Zr _1.75 Nb _0.25 O ₁₂
Li _6.9 La ₃ Zr _1.675 Ta _0.289 Bi _0.036 O ₁₂
Li _6.46 Ga _0.23 La ₃ Zr _1.85 Y _0.15 O ₁₂
Li _6.8 La _2.95 Ca _0.05 Zr _1.75 Nb _0.25 O ₁₂
Li _7.05 La _3.00 Zr _1.95 Gd _0.05 O ₁₂

Further, the LLZ-based lithium ion conductive powder having a garnet-type structure contains at least one of Mg and element A (A is at least one element selected from the group consisting of Ca, Sr and Ba). It is preferable to use an element having a molar ratio of each element satisfying the following formulas (1) to (3). Since Mg and element A have a relatively large reserve and are inexpensive, if Mg and / or element A is used as a substitution element for the LLZ-based lithium ion conductive powder, the LLZ-based lithium ion conductive powder is stable. Supply can be expected and the cost can be reduced.
(1) 1.33 ≤ Li / (La + A) ≤ 3
(2) 0 ≤ Mg / (La + A) ≤ 0.5
(3) 0 ≦ A / (La + A) ≦ 0.67

Further, as the LLZ-based lithium ion conductive powder, one containing both Mg and element A, in which each contained element satisfies the following formulas (1') to (3') in terms of molar ratio, is adopted. Is more preferable.
(1') 2.0 ≤ Li / (La + A) ≤ 2.5
(2') 0.01 ≤ Mg / (La + A) ≤ 0.14
(3') 0.04 ≤ A / (La + A) ≤ 0.17

In other words, the LLZ-based lithium ion conductive powder preferably satisfies any of the following (a) to (c), and more preferably (c) among these, (d). It can be said that it is more preferable to satisfy.
(A) It contains Mg, and the content of each element satisfies 1.33 ≦ Li / La ≦ 3 and 0 ≦ Mg / La ≦ 0.5 in terms of molar ratio.
(B) It contains element A, and the content of each element satisfies 1.33 ≦ Li / (La + A) ≦ 3 and 0 ≦ A / (La + A) ≦ 0.67 in terms of molar ratio.
(C) Contains Mg and element A, and the content of each element is 1.33 ≤ Li / (La + A) ≤ 3, 0 ≤ Mg / (La + A) ≤ 0.5, and 0 ≤ A / ( La + A) ≤0.67 is satisfied.
(D) Contains Mg and element A, and the content of each element is 2.0 ≤ Li / (La + A) ≤ 2.5, 0.01 ≤ Mg / (La + A) ≤ 0.14, and 0 in molar ratio. .04 ≦ A / (La + A) ≦ 0.17 is satisfied.

The LLZ-based lithium ion conductive powder is good lithium when the above (a) is satisfied, that is, when Li, La, Zr and Mg are contained so as to satisfy the above formulas (1) and (2) in molar ratio. Shows ionic conductivity. The mechanism is not clear, but for example, when the LLZ-based lithium ion conductive powder contains Mg, the ionic radius of Li and the ionic radius of Mg are close to each other, so that the Li site where Li is arranged in the LLZ crystal phase Mg is easily arranged, and Li is replaced with Mg, so that the difference in charge between Li and Mg causes vacancies in the Li site in the crystal structure, which makes it easier for Li ions to move, and as a result, lithium ion conduction. It is thought that the rate will improve. In the LLZ-based lithium ion conductive powder, when the molar ratio of Li to the sum of La and element A is less than 1.33 or more than 3, not only the lithium ion conductive powder having a garnet-type crystal structure but also another metal Oxides are likely to be formed. As the content of another metal oxide increases, the content of the lithium ion conductive powder having a garnet-type crystal structure becomes relatively small, and the lithium ion conductivity of another metal oxide is low, so that lithium ion conduction The rate drops. As the content of Mg in the LLZ-based lithium ion conductive powder increases, Mg is arranged at the Li site, pores are formed at the Li site, and the lithium ion conductivity is improved, but the Mg with respect to the sum of La and the element A When the molar ratio exceeds 0.5, another metal oxide containing Mg is likely to be formed. As the content of the other metal oxide containing Mg increases, the content of the lithium ion conductive powder having a garnet-type crystal structure becomes relatively small. Since the lithium ion conductivity of another metal oxide containing Mg is low, if the molar ratio of Mg to the sum of La and the element A exceeds 0.5, the lithium ion conductivity decreases.

The LLZ-based lithium ion conductive powder is good when the above (b) is satisfied, that is, when Li, La, Zr and the element A are contained so as to satisfy the above formulas (1) and (3) in molar ratio. Shows lithium ion conductivity. The mechanism is not clear, but for example, when the LLZ-based lithium ion conductive powder contains the element A, the ionic radius of La and the ionic radius of the element A are close to each other, so that La is arranged in the LLZ crystal phase. Element A is easily placed at the site, and La is replaced with element A, which causes lattice strain, and the difference in charge between La and element A increases free Li ions, improving lithium ionic conductivity. It is thought that. In the LLZ-based lithium ion conductive powder, when the molar ratio of Li to the sum of La and element A is less than 1.33 or more than 3, not only the lithium ion conductive powder having a garnet-type crystal structure but also another metal Oxides are likely to be formed. As the content of another metal oxide increases, the content of the lithium ion conductive powder having a garnet-type crystal structure becomes relatively small, and the lithium ion conductivity of another metal oxide is low, so that lithium ion conduction The rate drops. As the content of element A in the LLZ-based lithium ion conductive powder increases, element A is arranged at the La site, the lattice strain increases, and free Li ions increase due to the difference in charge between La and element A. Lithium ion conductivity is improved, but when the molar ratio of element A to the sum of La and element A exceeds 0.67, another metal oxide containing element A is likely to be formed. The larger the content of another metal oxide containing the element A, the smaller the content of the lithium ion conductive powder having a garnet-type crystal structure, and the larger the content of the other metal oxide containing the element A. Since the lithium ion conductivity is low, the lithium ion conductivity is lowered.

The element A is at least one element selected from the group consisting of Ca, Sr and Ba. Ca, Sr and Ba are Group 2 elements in the periodic table and tend to be divalent cations, all of which have a common property of having close ionic radii. Since Ca, Sr and Ba all have an ionic radius close to that of La, they are easily replaced with La arranged at the La site in the LLZ-based lithium ion conductive powder. It is preferable that the LLZ-based lithium ion conductive powder contains Sr among these elements A because it can be easily formed by sintering and a high lithium ion conductivity can be obtained.

When the LLZ-based lithium ion conductive powder satisfies the above (c), that is, when it contains Li, La, Zr, Mg and element A in a molar ratio so as to satisfy the above formulas (1) to (3). It can be easily formed by sintering, and the lithium ion conductivity is further improved. Further, when the LLZ-based lithium ion conductive powder satisfies the above (d), that is, Li, La, Zr, Mg and the element A satisfy the above formulas (1') to (3') in molar ratio. When included in, the lithium ion conductivity is further improved. The mechanism is not clear, but for example, Li at the Li site in the LLZ-based lithium ion conductive powder is replaced with Mg, and La at the La site is replaced with the element A, so that holes are formed in the Li site. It is considered that the generated and free Li ions increase, and the lithium ion conductivity becomes even better. Further, the LLZ-based lithium ion conductive powder so that Li, La, Zr, Mg and Sr satisfy the above formulas (1) to (3), particularly satisfy the above formulas (1') to (3'). It is preferable to include in the above from the viewpoint that high lithium ion conductivity can be obtained and a lithium ion conductor having a high relative density can be obtained.

In any of the above cases (a) to (d), the LLZ-based lithium ion conductive powder preferably contains Zr in a molar ratio so as to satisfy the following formula (4). By containing Zr in this range, a lithium ion conductive powder having a garnet-type crystal structure can be easily obtained.
(4) 0.33 ≤ Zr / (La + A) ≤ 1

B. Modification example:
The technique disclosed in the present specification is not limited to the above-described embodiment, and can be transformed into various forms without departing from the gist thereof. For example, the following modifications are also possible.

The configuration of the all-solid-state battery 102 in the above embodiment is merely an example and can be changed in various ways. For example, in the above embodiment, the lithium ion conductor is contained in all of the solid electrolyte layer 112, the positive electrode 114, and the negative electrode 116, and the lithium ion conductor is the solid electrolyte layer 112, the positive electrode 114, and the negative electrode 116. It may be included in at least one of.

Further, the technique disclosed in the present specification is not limited to the solid electrolyte layer and electrodes constituting the all-solid-state battery 102, and constitutes other power storage devices (for example, lithium air battery, lithium flow battery, solid capacitor, etc.). It is also applicable to solid electrolyte layers and electrodes.

102: All-solid-state lithium-ion secondary battery 110: Battery body 112: Solid electrolyte layer 114: Positive electrode 116: Negative electrode 154: Positive electrode side current collector 156: Negative electrode side current collector 202: Lithium ion conductor 204: Lithium ion conductor 206: Lithium ion conductor 214: Positive electrode active material 216: Negative electrode active material

Claims (3)

In a lithium ion conductor containing a lithium ion conductive powder having a garnet-type structure containing at least Li, La, Zr, and O, further
Contains ionic liquids with lithium-ion conductivity,
When the atomic concentration of each element is specified by X-ray photoelectron spectroscopy (XPS), it is not contained in the lithium ion conductive powder among the elements contained in the ionic liquid (excluding the O element and the C element). The ratio R1 (= C2 / C1) of the total atomic concentration of each of the specific elements to the total C1 of the atomic concentrations of the specific element, the Li element, the La element, and the Zr element is 0. 25 or more, 0.90 or less,
A lithium ion conductor characterized by that. In the lithium ion conductor according to claim 1,
The particle size (D90) of the lithium ion conductive powder is 10 μm or less.
A lithium ion conductor characterized by that. In a power storage device including a solid electrolyte layer, a positive electrode, and a negative electrode,
At least one of the solid electrolyte layer, the positive electrode, and the negative electrode includes the lithium ion conductor according to claim 1 or 2.
A power storage device characterized by this.

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