JP2020119782A - Solid electrolyte, and lithium ion power storage element - Google Patents

Abstract

To provide a solid electrolyte superior in ion conductivity under a low- or high- temperature condition, and a lithium ion power storage element arranged by use of such a solid electrolyte.SOLUTION: An embodiment of the present invention is a solid electrolyte having a crystal structure which can assigned to a space group F-43m, and containing lithium, phosphorus, sulfur and an element A, provided that the element A is magnesium or indium.SELECTED DRAWING: Figure 1

Description

The present invention relates to a solid electrolyte and a lithium-ion power storage element.

Non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles and the like because of their high energy density. The non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically isolated by a separator, and a non-aqueous electrolyte interposed between the electrodes, and a charge such as lithium ion between the electrodes. Is configured to be charged and discharged. In addition, capacitors such as lithium ion capacitors and electric double layer capacitors have been widely spread as non-aqueous electrolyte storage elements other than non-aqueous electrolyte secondary batteries.

In recent years, as a non-aqueous electrolyte, a storage element using a solid electrolyte such as a sulfide-based solid electrolyte in place of the non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a liquid such as an organic solvent has been proposed. As one of sulfide-based solid electrolytes, Argyrodite type solid electrolytes containing lithium, phosphorus, sulfur and halogen are known (see Patent Documents 1 and 2 and Non-Patent Documents 1 and 2). This solid electrolyte is said to have a crystal structure belonging to the space group F-43m.

JP, 2018-67552, A JP, 2017-117753, A

Prasada Rao Rayavarapu et al., "Variation in structure and Li+-ion migration in argyrodite-type Li6PS5X (X=Cl,Br,I) solid electolytesl8eS10e12eS18,Solid telyte", 18Solid. Sylvain Boulineau other, "Mechanochemical synthesis of Li-argyrodite Li6PS5X (X = Cl, Br, I) as sulfur-based solid electrolytes for all solid state batteries application", Solid State Ionics 221 (2012) 1-5

Ionic conductivity is one of the important performances in a solid electrolyte used for a power storage device. On the other hand, the electricity storage device is required to have various performances depending on the use environment and application, for example, in consideration of use in a low temperature or high temperature environment, good charge/discharge performance may be exhibited even at low temperature or high temperature. desired. Therefore, even in the Argyrodite type solid electrolyte, further improvement of the ionic conductivity at low temperature (for example, −30° C.) or high temperature (for example, 50° C.) is desired.

The present invention has been made based on the above circumstances, and an object thereof is to provide a solid electrolyte having excellent ionic conductivity at low temperature or high temperature, and a lithium ion storage element using such a solid electrolyte. Is to provide.

One embodiment of the present invention made to solve the above problem has a crystal structure that can be assigned to the space group F-43m, contains lithium, phosphorus, sulfur, and element A, and the element A is magnesium or It is a solid electrolyte that is indium.

Another embodiment of the present invention is a lithium ion storage element containing the solid electrolyte.

According to the present invention, it is possible to provide a solid electrolyte having excellent ionic conductivity at low temperature or high temperature, and a lithium ion storage element using such a solid electrolyte.

FIG. 1 is a schematic cross-sectional view of an all-solid-state battery that is an embodiment of the lithium-ion storage device of the present invention. FIG. 2 is an X-ray diffraction pattern of Examples 1-2 and Comparative Example 1. FIG. 3 is an X-ray diffraction pattern of Examples 3 to 9 and Comparative Example 1.

The solid electrolyte according to one embodiment of the present invention has a crystal structure that can be assigned to the space group F-43m, contains lithium, phosphorus, sulfur, and element A, and the element A is magnesium or indium. It is an electrolyte.

The solid electrolyte has excellent ionic conductivity at low temperature or high temperature. The reason why such an effect occurs is not clear, but the following reason is presumed. The solid electrolyte has a crystal structure that can be assigned to the space group F-43m, and further contains the element A in addition to the conventional solid electrolyte containing lithium, phosphorus and sulfur. The element A is magnesium or indium, which has an ionic radius similar to that of lithium and is capable of taking a 4-coordination like lithium ion. The ionic radius of lithium ion (Li ⁺ ) is 0.590 Å, the ionic radius of magnesium ion (Mg ²⁺ ) is 0.570 Å, and the ionic radius of trivalent indium ion (In ³⁺ ) is 0.620 Å. Therefore, when the element A is further contained in the conventional solid electrolyte having a crystal structure that can be assigned to the space group F-43m and containing lithium, phosphorus, and sulfur, a part of lithium is replaced by magnesium or magnesium. The element A, which is indium, can be substituted, and a solid electrolyte having a new composition can be obtained while maintaining its crystal structure. Further, while lithium ions are monovalent cations, magnesium ions are divalent cations and trivalent indium ions are trivalent cations. Therefore, when the element A is magnesium, one magnesium is substituted for two lithiums, and when the element A is indium, one indium is substituted for three lithiums. It will be possible. By substituting a part of lithium with the element A while maintaining the crystal structure in this manner, the occupancy of the site occupied by lithium (48h site) is reduced, and thus the conductivity of lithium ion is improved. It is supposed to be.

It should be noted that "-4" in the space group "F-43m" represents the target element of the four-fold anti-axis, and should be originally described by adding a bar "-" over "4". It is confirmed by powder X-ray diffraction measurement that the solid electrolyte has a crystal structure that can be assigned to the space group F-43m. The powder X-ray diffraction measurement is performed by the following procedure. An airtight sample holder for X-ray diffraction measurement is filled with a solid electrolyte powder to be used for measurement under an argon atmosphere having a dew point of -50°C or lower. The powder X-ray diffraction measurement is performed using an X-ray diffractometer (“MiniFlex II” manufactured by Rigaku). The radiation source is CuKα rays, the tube voltage is 30 kV, the tube current is 15 mA, and the diffracted X-rays are detected by a high-speed one-dimensional detector (model number: D/teX Ultra 2) through a Kβ filter having a thickness of 30 μm. The sampling width is 0.01°, the scan speed is 5°/min, the divergence slit width is 0.625°, the light receiving slit width is 13 mm (OPEN), and the scattering slit width is 8 mm. In addition, the obtained X-ray diffraction pattern is automatically analyzed using PDXL (analysis software, manufactured by Rigaku). Here, "Refine background" and "Automatic" are selected in the work window of the PDXL software, and refining is performed so that the intensity error between the actually measured pattern and the calculated pattern is 4000 or less. Background processing is performed by this refinement, and the value of the peak intensity of each diffraction line and the value of the crystal lattice constant a are obtained based on the result of subtracting the baseline.

In the solid electrolyte, the substitution degree DS (%) of the element A represented by the following formula (1) is preferably 0.1% or more and 1.5% or less.
DS={[A]/([Li]+m[A])}×100 (1)
(In the formula (1), [Li] is the content ratio of the lithium atom based on the atomic number. [A] is the content ratio of the element A based on the atomic number. m is the valence of the element A. It is a number.)
With such a substitution degree, the ionic conductivity is further improved by substituting a part of lithium with the element A. Further, when such a substitution degree is satisfied, good ionic conductivity is exhibited especially at high temperatures.

The solid electrolyte is preferably represented by the following formula (2).
_{Li 7-mx-y A x} PS 6-y Ha y ··· (2)
(In the formula (2), A is the element A. Ha is chlorine, bromine or iodine. x is a number of 0.01 or more and 0.08 or less. y is 0.2 or more. The number is 1.8 or less, and m is the valence of the element A.)
When the solid electrolyte has such a composition, the ionic conductivity is further improved, and good ionic conductivity is exhibited particularly at high temperatures.

It is preferable that the element A is indium, and the substitution degree DS (%) of indium represented by the following formula (1b) is 0.1% or more and 2.5% or less.
DS={[In]/([Li]+3[In])}×100 (1b)
(In the formula (1b), [Li] is the content ratio of lithium based on the number of atoms. [In] is the content ratio of the indium based on the number of atoms.)
In such a case, particularly good ionic conductivity is exhibited at a low temperature.

A lithium ion storage element according to an embodiment of the present invention is a lithium ion storage element containing the solid electrolyte. Since the solid-state electrolyte having excellent ionic conductivity at low temperature or high temperature is used for the lithium ion storage element, sufficient charge/discharge performance at low temperature or high temperature is exhibited.

Hereinafter, the solid electrolyte and the lithium-ion power storage device according to the embodiment of the present invention will be described in detail.

<Solid electrolyte>
The solid electrolyte according to one embodiment of the present invention has a crystal structure that can be assigned to the space group F-43m. The solid electrolyte may have a crystal structure belonging to the space group F-43m. The solid electrolyte is a cubic crystal and has an Argyrodite type crystal structure.

The crystal lattice constant a in the solid electrolyte is not particularly limited, but is preferably within the range of 9.852±0.015Å, within the range of 9.852±0.010Å or within the range of 9.852±0.002Å It may be more preferable that it is within. Further, it may be preferable that the crystal lattice constant a is less than 9.852Å. When the crystal lattice constant of the solid electrolyte is within the above range, the Argyrodite type crystal structure containing no element A is maintained as it is, and the ionic conductivity tends to be further enhanced at low temperature or high temperature. Further, when the crystal lattice constant of the solid electrolyte is equal to or more than the above lower limit, the diffusion path of ions is suppressed from being shortened, and the ionic conductivity at low temperature or high temperature is further increased. Note that 9.852Å is the crystal lattice constant a of the Argyrodite-type solid electrolyte represented by Li ₆ PS ₅ Cl, which was measured by the above-described powder X-ray diffraction measurement method.

The solid electrolyte contains lithium, phosphorus, sulfur, and element A. The element A is magnesium or indium. Usually, the solid electrolyte is a solid electrolyte containing lithium, phosphorus, and sulfur and having a part of lithium in the solid electrolyte having an Argyrodite type crystal structure (for example, Li ₆ PS ₅ Cl) substituted with the element A. You can

Regarding the degree of substitution of the element A for lithium, the value obtained by the following equation (1) is defined as the substitution degree DS (%) of the element A in the solid electrolyte.
DS={[A]/([Li]+m[A])}×100 (1)
In the formula (1), [Li] is the content ratio based on the number of atoms (the number of moles) of lithium. [A] is the content ratio of the element A based on the number of atoms. m is the valence of the element A. That is, when the element A is magnesium, m may be 2, and when the element A is indium, m may be 3.

When the element A is magnesium, the substitution degree DS is represented by the following formula (1a). When the element A is indium, the substitution degree DS is represented by the following formula (1b).
DS={[Mg]/([Li]+2[Mg])}×100 (1a)
DS={[In]/([Li]+3[In])}×100 (1b)
In formulas (1a) and (1b), [Li] is the content ratio of lithium based on the number of atoms. [Mg] is the content ratio of magnesium based on the number of atoms. [In] is the content ratio of indium based on the number of atoms.

The lower limit of the substitution degree DS is preferably 0.1%, more preferably 0.2%. Especially when the element A is magnesium, the lower limit of the substitution degree DS may be more preferably 0.3% or 0.4%. By setting the substitution degree DS to be equal to or higher than the above lower limit, the effect of reducing the site occupancy rate due to the substitution of the element A is sufficiently produced, and thus the ionic conductivity at low temperature or high temperature can be sufficiently increased.

The upper limit of the substitution degree DS is, for example, 3%, preferably 2.5%, more preferably 2.2%, and even more preferably 1.5%, 1.0% or 0.5%. .. By setting the substitution degree DS to be equal to or less than the above upper limit, the state of a good crystal structure may be maintained, and the ionic conductivity at low temperature or high temperature may be further increased.

It is preferable that the solid electrolyte contains halogen as an element other than lithium, phosphorus, sulfur, and element A. Examples of the halogen include chlorine, bromine and iodine, and chlorine is preferable.

The content ratio of each constituent element in the solid electrolyte is not particularly limited as long as it has a predetermined crystal structure. The lower limit of the content ratio of lithium to phosphorus in the solid electrolyte is preferably 5.4 in terms of molar ratio (atomic number basis), and 5.5, 5.6, 5.7, 5.8 or 5.9 is more preferable. Sometimes preferred. The upper limit of the lithium content is preferably 5.98, and more preferably 5.97, 5.96, 5.95 or 5.94.

As a lower limit of the content ratio of sulfur to phosphorus, the molar ratio is preferably 4, more preferably 4.5, still more preferably 4.9, still more preferably 5. The upper limit of the content ratio of sulfur is preferably 6, more preferably 5.5, further preferably 5.1, still more preferably 5.

The lower limit of the content ratio of the element A with respect to phosphorus is preferably 0.01 and more preferably 0.02 in terms of molar ratio. By setting the content ratio of the element A to be equal to or higher than the above lower limit, the ionic conductivity at low temperature or high temperature tends to be further increased. This tendency remarkably occurs especially when the element A is magnesium. On the other hand, the upper limit of the content ratio of the element A is preferably 0.2, more preferably 0.15, further preferably 0.13, and even more preferably 0.08, 0.05 or 0.03. .. By setting the content ratio of the element A to be equal to or less than the above upper limit, the ionic conductivity at low temperature or high temperature tends to be further increased.

The lower limit of the content ratio of halogen to phosphorus is preferably 0.2 and more preferably 0.5 in terms of molar ratio. The upper limit of the halogen content is preferably 1.8, more preferably 1.5. The halogen content is more preferably 1.

The solid electrolyte may further contain an element other than lithium, phosphorus, sulfur, element A and halogen. However, the content ratio of the other element to phosphorus in the solid electrolyte is preferably less than 0.01 and more preferably less than 0.001 in terms of molar ratio, and may not be substantially contained.

The solid electrolyte is preferably represented by the following formula (2).
_{Li 7-mx-y A x} PS 6-y Ha y ··· (2)
In the formula (2), A is the element A. Ha is chlorine, bromine or iodine. x is a number of 0.01 or more and 0.2 or less. y is a number of 0.2 or more and 1.8 or less. m is the valence of the element A.

The lower limit of x is 0.01, and 0.02 is preferable. By setting x to the above lower limit or more, the ionic conductivity at low temperature or high temperature tends to be further increased. Especially when the element A is magnesium, 0.02 is more preferable. In the case where the element A is magnesium, if the content is at least the above lower limit, this tendency remarkably occurs. On the other hand, the upper limit of x is 0.2, preferably 0.15, more preferably 0.13, and even more preferably 0.08, 0.05 or 0.03. By setting x to the above upper limit or lower, the ionic conductivity at low temperature or high temperature tends to be further increased.

The lower limit of y is 0.2, and 0.5 is preferable. The upper limit of y is 1.8 and preferably 1.5. The above y is more preferably 1.

The m may be 2 when the element A is magnesium and 3 when the element A is indium.

As a lower limit of the ionic conductivity of the solid electrolyte at −30° C., 7.92×10 ⁻⁵ S/cm is preferable, 8.5×10 ⁻⁵ S/cm is more preferable, and 1.0×10 ^−4. S/cm is more preferable. When the ionic conductivity of the solid electrolyte at −30° C. is equal to or higher than the above lower limit, the charge/discharge performance of the lithium ion storage element at low temperature can be further improved. The upper limit of the ionic conductivity is, for example, 2.0×10 ⁻⁴ S/cm.

As a lower limit of the ionic conductivity of the solid electrolyte at 50° C., 6.2×10 ⁻³ S/cm is preferable, 6.3×10 ⁻³ S/cm is more preferable, and 6.5×10 ⁻³ S. /Cm is more preferable. When the ionic conductivity of the solid electrolyte at 50° C. is equal to or higher than the above lower limit, the charge/discharge performance of the lithium ion storage element at high temperature can be further improved. The upper limit of the ionic conductivity is, for example, 8.0×10 ⁻³ S/cm.

The ionic conductivity of the solid electrolyte is determined by measuring AC impedance by the following method. In an argon atmosphere with a dew point of -50°C or less, 120 mg of the sample powder is put into a powder molding machine having an inner diameter of 10 mm, and then uniaxial pressure molding is performed with a hydraulic press at 50 MPa or less. After the pressure is released, SUS316L powder is charged as a collector on the upper surface and the lower surface of the sample, and then uniaxial pressure molding is performed at 360 MPa for 5 minutes to obtain an ion conductivity measuring pellet. The pellet for ion conductivity measurement is inserted into an HS cell manufactured by Hosen Co., Ltd., and AC impedance measurement is performed. The measurement conditions are an applied voltage amplitude of 20 mV and a frequency range of 1 MHz to 100 mHz.

The shape of the solid electrolyte is not particularly limited and is usually granular, lumpy or the like. The solid electrolyte can be preferably used as an electrolyte of a lithium-ion power storage device such as a lithium-ion secondary battery. Among them, it can be particularly preferably used as an electrolyte of an all-solid-state battery. The solid electrolyte can be used for any of the positive electrode layer, the isolation layer, the negative electrode layer, and the like in the lithium ion power storage device.

<Method for producing solid electrolyte>
The method for producing the solid electrolyte is not particularly limited, and examples thereof include a method in which a precursor containing lithium, phosphorus, sulfur, and element A is prepared, and the precursor is fired. In addition, it is preferable that all of the production of the solid electrolyte is performed in an inert atmosphere such as an argon atmosphere.

As a method for producing the precursor, a mechanical milling method, a melt quenching method, a liquid phase method or the like can be adopted. For example, in the case of the mechanical milling method, as a raw material, a compound containing Li, P, S, halogen, and Mg or In is used at a predetermined ratio corresponding to the composition of the intended solid electrolyte, and mechanical milling treatment is performed on these materials. A precursor can be obtained. As the raw material, Li ₂ S, P ₂ S ₅ , LiCl, MgCl ₂ , InCl ₃ , LiBr, MgBr ₂ , InBr ₃ , MgS, InS or the like can be used.

The firing condition of the precursor is not particularly limited as long as it is heated enough to confirm that a crystal structure that can be assigned to the space group F-43m is formed by powder X-ray diffraction measurement. For example, the firing temperature may be 450° C. or higher and 550° C. or lower. The firing time may be, for example, 1 hour or more and 24 hours or less.

<Lithium-ion storage element>
As an embodiment of the lithium-ion storage element of the present invention, an all-solid-state battery will be described below as a specific example. The all-solid-state battery 10 in FIG. 1 is a secondary battery in which a positive electrode layer 1 and a negative electrode layer 2 are arranged with an isolation layer 3 interposed therebetween. The positive electrode layer 1 has a positive electrode base material 4 and a positive electrode active material layer 5, and the positive electrode base material 4 is the outermost layer of the positive electrode layer 1. The negative electrode layer 2 has a negative electrode base material 7 and a negative electrode active material layer 6, and the negative electrode base material 7 is the outermost layer of the negative electrode layer 2. In the all-solid-state battery 10 shown in FIG. 1, the negative electrode active material layer 6, the isolation layer 3, the positive electrode active material layer 5, and the positive electrode base material 4 are laminated in this order on the negative electrode base material 7.

The all-solid-state battery 10 contains a solid electrolyte according to an embodiment of the present invention in at least one of the positive electrode layer 1, the negative electrode layer 2, and the isolation layer 3. More specifically, at least one of the positive electrode active material layer 5, the negative electrode active material layer 6, and the isolation layer 3 contains the solid electrolyte according to one embodiment of the present invention. Since the all-solid-state battery 10 contains the solid electrolyte, good charge/discharge performance is exhibited at low temperature or high temperature.

The all-solid-state battery 10 may also use a solid electrolyte other than the solid electrolyte according to the embodiment of the present invention. Examples of other solid electrolytes include sulfide-based solid electrolytes other than the solid electrolyte, oxide-based solid electrolytes, dry polymer electrolytes, gel polymer electrolytes, pseudo-solid electrolytes, and the like, and sulfide-based solid electrolytes are preferable. In addition, a plurality of different types of solid electrolytes may be contained in one layer of the all-solid-state battery 10, or different solid electrolytes may be contained in each layer.

The sulfide-based solid electrolyte, for example, _{Li 2 S-P 2 S 5} , Li 2 S-P 2 S 5 -LiI, Li 2 S-P 2 S 5 -LiCl, Li 2 S-P 2 S 5 -LiBr _{, Li 2 S-P 2 S} 5 -Li 2 O, Li 2 S-P 2 S 5 -Li 2 O-LiI, Li 2 S-P 2 S 5 -Li 3 N, Li 2 S-SiS 2, Li _{2 S-SiS 2 -LiI, Li} 2 S-SiS 2 -LiBr, Li 2 S-SiS 2 -LiCl, Li 2 S-SiS 2 -B 2 S 3 -LiI, Li 2 S-SiS 2 -P 2 S _{5 -LiI, Li 2 S-B} 2 S 3, Li 2 S-P 2 S 5 -Z m S 2n ( except, m, n is a positive number, Z is is either Ge, Zn, and Ga _{.), Li 2 S-GeS} 2, Li 2 S-SiS 2 -Li 3 PO 4, Li 2 S-SiS 2 -Li x MO y ( provided that, x, y are positive numbers, M is, P, Si , Ge, B, Al, Ga, In)), and Li ₁₀ GeP ₂ S _{12 and the} like.

[Positive layer]
The positive electrode layer 1 includes a positive electrode base material 4 and a positive electrode active material layer 5 laminated on the surface of the positive electrode base material 4. The positive electrode layer 1 may have an intermediate layer between the positive electrode base material 4 and the positive electrode active material layer 5. The intermediate layer can be, for example, a layer containing conductive particles and a resin binder.

(Positive electrode substrate)
The positive electrode base material 4 has conductivity. Having “conductivity” means that the volume resistivity measured according to JIS-H-0505 (1975) is 10 ⁷ Ω·cm or less, and “non-conductivity” means It means that the volume resistivity is more than 10 ⁷ Ω·cm. As a material of the positive electrode base material 4, a metal such as aluminum, titanium, tantalum, indium, stainless steel, or an alloy thereof is used. Among these, aluminum or aluminum alloy is preferable from the viewpoints of potential resistance, high conductivity, and cost. Examples of the positive electrode base material include a foil and a vapor deposition film, and the foil is preferable from the viewpoint of cost. Therefore, the positive electrode base material is preferably an aluminum foil or an aluminum alloy foil. Examples of aluminum or aluminum alloy include A1085P, A3003P and the like specified in JIS-H-4000 (2014).

The lower limit of the average thickness of the positive electrode substrate is preferably 5 μm, more preferably 10 μm. The upper limit of the average thickness of the positive electrode substrate is preferably 50 μm, more preferably 40 μm. By setting the average thickness of the positive electrode base material to the above lower limit or more, the strength of the positive electrode base material can be increased. By setting the average thickness of the positive electrode substrate to be the above upper limit or less, the energy density per volume of the all-solid-state battery can be increased. For these reasons, the average thickness of the positive electrode base material is preferably 5 μm or more and 50 μm or less, and more preferably 10 μm or more and 40 μm or less. "Average thickness" refers to an average value of thicknesses measured at arbitrary 10 points. The same definition is applied when the "average thickness" is used for other members.

The intermediate layer is a layer disposed between the positive electrode base material and the positive electrode active material layer. The intermediate layer contains particles having conductivity such as carbon particles, thereby reducing the contact resistance between the positive electrode base material and the positive electrode active material layer. The structure of the intermediate layer is not particularly limited, and includes, for example, a resin binder and conductive particles.

(Cathode active material layer)
The positive electrode active material layer 5 contains a positive electrode active material. The positive electrode active material layer 5 can be formed from a so-called positive electrode mixture containing a positive electrode active material. The positive electrode active material layer 5 may contain a mixture or complex containing a positive electrode active material and a solid electrolyte. The positive electrode active material layer 5 may include optional components such as a conductive agent, a binder (binder), a thickener, and a filler, if necessary. One kind or two or more kinds of each of these optional components may not be substantially contained in the positive electrode active material layer 5.

The positive electrode active material contained in the positive electrode active material layer 5 can be appropriately selected from known positive electrode active materials usually used in lithium ion secondary batteries and all-solid-state batteries. A material capable of inserting and extracting lithium ions is usually used as the positive electrode active material. Examples thereof include a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, a lithium transition metal oxide having a spinel type crystal structure, a polyanion compound, a chalcogen compound, and sulfur. Examples of the lithium-transition metal composite oxide having an α-NaFeO ₂ type crystal structure include, for example, Li[Li _x Ni _1-x ]O ₂ (0≦x<0.5), Li[Li _x Ni _γ Co _{(1- x-γ)] O 2 (} 0 ≦ x <0.5,0 <γ <1), Li [Li x Ni γ Mn β Co (1-x-γ-β] O 2 (0 ≦ x <0. 5, 0<γ, 0<β, 0.5<γ+β<1), etc. As the lithium transition metal oxide having a spinel type crystal structure, Li _x Mn ₂ O ₄ , Li _x Ni _γ Mn _{(2 -Γ)} O ₄ etc. Examples of the polyanion compound include LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F and the like. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc. Atoms or polyanions in these materials may be partially substituted with atoms or anion species composed of other elements. The surface of the positive electrode active material may be covered with an oxide such as lithium niobate, lithium titanate, lithium phosphate, etc. In the positive electrode active material layer, one of these positive electrode active materials may be used alone. Well, two or more kinds may be mixed and used.

The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By setting the average particle diameter of the positive electrode active material to the above lower limit or more, the production or handling of the positive electrode active material becomes easy. By setting the average particle size of the positive electrode active material to be equal to or less than the above upper limit, the electron conductivity of the positive electrode active material layer is improved. Here, the “average particle size” is based on JIS-Z-8825 (2013), and is based on the particle size distribution measured by a laser diffraction/scattering method with respect to a diluted solution prepared by diluting particles with a solvent. It means a value at which the volume-based cumulative distribution calculated according to Z-8819-2 (2001) is 50%.

A crusher, a classifier, or the like is used to obtain the particles in a predetermined shape. Examples of the pulverization method include a method using a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling airflow type jet mill, a sieve, or the like. Wet grinding in which water or an organic solvent such as hexane is allowed to coexist may be used during grinding. As a classification method, a sieve, an air classifier, or the like is used as needed, both dry and wet.

The lower limit of the content of the positive electrode active material in the positive electrode active material layer 5 is preferably 10% by mass, more preferably 30% by mass, and further preferably 50% by mass. The upper limit of the content of the positive electrode active material is preferably 90% by mass, more preferably 80% by mass. By setting the content of the positive electrode active material within the above range, the electric capacity of the all-solid-state battery 10 can be further increased.

When the positive electrode active material layer 5 contains a solid electrolyte, the lower limit of the content of the solid electrolyte is preferably 10% by mass, more preferably 20% by mass. The upper limit of the content of the solid electrolyte in the positive electrode active material layer 5 is preferably 90% by mass, more preferably 70% by mass, and further preferably 50% by mass. By setting the content of the solid electrolyte within the above range, the electric capacity of the all-solid-state battery can be increased. When the solid electrolyte according to one embodiment of the present invention is used for the positive electrode active material layer 5, the content of the solid electrolyte according to one embodiment of the present invention in the total solid electrolyte in the positive electrode active material layer 5 is 50 mass. % Or more is preferable, 70% by mass or more is more preferable, 90% by mass or more is further preferable, and substantially 100% by mass is even more preferable.

The mixture of the positive electrode active material and the solid electrolyte is a mixture prepared by mixing the positive electrode active material, the solid electrolyte and the like by mechanical milling or the like. For example, the mixture of the positive electrode active material and the solid electrolyte can be obtained by mixing the particulate positive electrode active material and the particulate solid electrolyte. As the composite of the positive electrode active material and the solid electrolyte, a composite having a chemical or physical bond between the positive electrode active material and the solid electrolyte, mechanically composite the positive electrode active material and the solid electrolyte, etc. Examples of the complex include: The composite is one in which the positive electrode active material and the solid electrolyte are present in one particle, for example, those in which the positive electrode active material and the solid electrolyte and the like form an aggregated state, the surface of the positive electrode active material Examples thereof include those having a film containing a solid electrolyte or the like formed on at least a part thereof.

(Arbitrary ingredient)
The conductive agent is not particularly limited as long as it is a material having conductivity. Examples of such a conductive agent include graphite; carbon black such as furnace black and acetylene black; metal; conductive ceramics. Examples of the shape of the conductive agent include powder and fibrous shapes. Among these, acetylene black is preferable from the viewpoint of electronic conductivity and the like.

As a minimum of content of a conductive agent in cathode active material layer 5, 1 mass% is preferred and 3 mass% is more preferred. As a maximum of content of a conductive agent, 10 mass% is preferred and 9 mass% is more preferred. By setting the content of the conductive agent within the above range, the electric capacity of the all-solid-state battery can be increased. For these reasons, the content of the conductive agent is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less.

Examples of the binder include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyimide; ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, Elastomers such as styrene-butadiene rubber (SBR) and fluororubber; polysaccharide polymers and the like.

The lower limit of the content of the binder in the positive electrode active material layer 5 is preferably 1% by mass, more preferably 3% by mass. The upper limit of the binder content is preferably 10% by mass, more preferably 9% by mass. By setting the content of the binder within the above range, the active material can be stably retained. For these reasons, the content of the binder is preferably 1% by mass or more and 10% by mass or more, and more preferably 3% by mass or more and 9% by mass or less.

Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, the functional group may be deactivated by methylation or the like in advance.

The filler is not particularly limited. Examples of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, glass, and alumina silicate.

The positive electrode active material layer 5 includes typical non-metal elements such as B, N, P, F, Cl, Br and I, typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga and Ge, Containing transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb and W as components other than the positive electrode active material, conductive agent, binder, thickener and filler. You may.

The lower limit of the average thickness of the positive electrode active material layer 5 is preferably 30 μm, more preferably 60 μm. The upper limit of the average thickness of the positive electrode active material layer 5 is preferably 1000 μm, more preferably 500 μm. By setting the average thickness of the positive electrode active material layer 5 to the above lower limit or more, an all-solid battery having a high energy density can be obtained. By setting the average thickness of the positive electrode active material layer 5 to be equal to or less than the above upper limit, the size of the all-solid battery can be reduced.

[Negative electrode layer]
The negative electrode layer 2 has a negative electrode base material 7 and a negative electrode active material layer 6 arranged on the negative electrode base material 7 directly or via an intermediate layer. The structure of the intermediate layer is not particularly limited, and can be selected from the structures exemplified for the positive electrode layer, for example.

(Negative electrode substrate)
The negative electrode base material 7 has conductivity. As a material of the negative electrode base material 7, a metal such as copper, nickel, stainless steel, nickel plated steel, or aluminum, or an alloy thereof is used. Among these, copper or copper alloy is preferable. Examples of the negative electrode base material include a foil and a vapor deposition film, and the foil is preferable from the viewpoint of cost. Therefore, the negative electrode base material is preferably a copper foil or a copper alloy foil. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

The lower limit of the average thickness of the negative electrode substrate 7 is preferably 3 μm, more preferably 5 μm. The upper limit of the average thickness of the negative electrode substrate 7 is preferably 30 μm, more preferably 20 μm. By setting the average thickness of the negative electrode base material to the above lower limit or more, the strength of the negative electrode base material 7 can be increased. By setting the average thickness of the negative electrode base material to the above upper limit or less, the energy density per volume of the all solid state battery can be increased. For these reasons, the average thickness of the negative electrode base material 7 is preferably 3 μm or more and 30 μm or less, and more preferably 5 μm or more and 20 μm or less.

(Negative electrode active material layer)
The negative electrode active material layer 6 contains a negative electrode active material. The negative electrode active material layer 6 can be formed from a so-called negative electrode mixture containing a negative electrode active material. The negative electrode active material layer 6 may contain a mixture or composite containing a negative electrode active material and a solid electrolyte. The negative electrode active material layer 6 contains optional components such as a conductive agent, a binder, a thickener, and a filler, if necessary. The types and suitable contents of the optional components in these negative electrode active material layers are the same as the respective optional components in the positive electrode active material layer described above. One or two or more of each of these optional components may not be substantially contained in the negative electrode active material layer.

The negative electrode active material layer 6 includes typical non-metal elements such as B, N, P, F, Cl, Br and I, typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga and Ge, Transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W, etc. other than the negative electrode active material, conductive agent, binder, thickener and filler. It may be contained as a component.

The negative electrode active material can be appropriately selected from known negative electrode active materials usually used in lithium ion secondary batteries and all-solid-state batteries. A material capable of inserting and extracting lithium ions is usually used as the negative electrode active material. Examples of the negative electrode active material include metal Li; metals such as Si and Sn or metalloids; metal oxides such as Si oxides, Ti oxides and Sn oxides or metalloid oxides; Li ₄ Ti ₅ O ₁₂ ; Titanium-containing oxides such as LiTiO _{2 and} TiNb ₂ O ₇ ; polyphosphoric acid compounds; silicon carbide; carbon materials such as graphite (graphite) and non-graphitizable carbon (graphitizable carbon or non-graphitizable carbon). To be Among these materials, graphite and non-graphitic carbon are preferable. In the negative electrode active material layer, one kind of these materials may be used alone, or two or more kinds thereof may be mixed and used.

“Graphite” refers to a carbon material having an average lattice spacing (d ₀₀₂ ) of (002) planes determined by an X-ray diffraction method of 0.33 nm or more and less than 0.34 nm before or after charge/discharge. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferable from the viewpoint that a material having stable physical properties can be obtained.

“Non-graphitic carbon” refers to a carbon material having an average lattice spacing (d ₀₀₂ ) of (002) plane of 0.34 nm or more and 0.42 nm or less, which is determined by an X-ray diffraction method before or after charge/discharge. Say. The crystallite size Lc of non-graphitic carbon is usually 0.80 to 2.0 nm. Examples of the non-graphitizable carbon include non-graphitizable carbon and easily graphitizable carbon. Examples of the non-graphitic carbon include resin-derived materials, petroleum pitch-derived materials, alcohol-derived materials, and the like.

Here, the “discharge state” refers to a state in which an open circuit voltage is 0.7 V or more in a single-pole battery using a negative electrode containing a carbon material as a negative electrode active material as a working electrode and metal Li as a counter electrode. Since the potential of the counter electrode of metal Li in the open circuit state is almost equal to the oxidation-reduction potential of Li, the open-circuit voltage in the above unipolar battery is almost equal to the potential of the negative electrode containing the carbon material with respect to the oxidation-reduction potential of Li. .. That is, an open circuit voltage of 0.7 V or more in the above-mentioned single-pole battery means that the carbon material, which is the negative electrode active material, has sufficiently released lithium ions that can be stored and released during charging and discharging. ..

The "non-graphitizable carbon" refers to a carbon material having d ₀₀₂ of 0.36 nm or more and 0.42 nm or less. The non-graphitizable carbon usually has a property that a graphite structure having a three-dimensional stacking regularity is unlikely to be formed among non-graphitic carbons.

The “graphitizable carbon” refers to a carbon material having the above-mentioned d ₀₀₂ of 0.34 nm or more and less than 0.36 nm. The easily graphitizable carbon usually has a property of easily forming a graphite structure having a three-dimensional stacking regularity among non-graphitic carbons.

The average particle size of the negative electrode active material can be, for example, 1 μm or more and 100 μm or less. By setting the average particle size of the negative electrode active material to the above lower limit or more, the production or handling of the negative electrode active material becomes easy. By setting the average particle size of the negative electrode active material to be equal to or less than the above upper limit, the electron conductivity of the active material layer is improved. A crusher, a classifier, or the like is used to obtain the particles in a predetermined shape. The pulverization method and the powder classification method can be selected from the methods exemplified for the positive electrode layer, for example.

When the negative electrode active material layer 6 contains a solid electrolyte, the lower limit of the content of the solid electrolyte is preferably 10% by mass, more preferably 20% by mass. The upper limit of the content of the solid electrolyte in the negative electrode active material layer 6 is preferably 90% by mass, more preferably 70% by mass, and further preferably 50% by mass. By setting the content of the solid electrolyte within the above range, the electric capacity of the all-solid-state battery can be increased. When the solid electrolyte according to one embodiment of the present invention is used for the negative electrode active material layer 6, the content of the solid electrolyte according to one embodiment of the present invention in the total solid electrolyte in the negative electrode active material layer 6 is 50 mass. % Or more is preferable, 70% by mass or more is more preferable, 90% by mass or more is further preferable, and substantially 100% by mass is even more preferable.

The mixture or composite of the negative electrode active material and the solid electrolyte may be the above-described mixture or composite of the positive electrode active material and the solid electrolyte in which the positive electrode active material is replaced with the negative electrode active material.

The lower limit of the average thickness of the negative electrode active material layer 6 is preferably 30 μm, more preferably 60 μm. The upper limit of the average thickness of the negative electrode active material layer 6 is preferably 1000 μm, more preferably 500 μm. By setting the average thickness of the negative electrode active material layer 6 to the above lower limit or more, an all-solid battery having a high energy density can be obtained. By setting the average thickness of the negative electrode active material layer 6 to be equal to or less than the above upper limit, the size of the all-solid-state battery can be reduced.

[Isolation layer]
The isolation layer 3 contains a solid electrolyte. As the solid electrolyte contained in the isolation layer 3, various solid electrolytes other than the solid electrolyte according to the embodiment of the present invention described above can be used, and among these, a sulfide-based solid electrolyte is preferably used. The content of the solid electrolyte in the isolation layer 3 is preferably 70% by mass or more, more preferably 90% by mass or more, further preferably 99% by mass or more, and even more preferably substantially 100% by mass. is there. When the solid electrolyte according to the embodiment of the present invention is used for the isolation layer 3, the content of the solid electrolyte according to the embodiment of the present invention in the total solid electrolyte in the isolation layer 3 is 50% by mass or more. Is preferred, 70% by mass or more is more preferred, 90% by mass or more is still more preferred, and substantially 100% by mass is even more preferred.

The isolation layer 3 may contain optional components such as oxides such as Li ₃ PO ₄ , halogen compounds, binders, thickeners and fillers. Optional components such as a binder, a thickener, and a filler can be selected from the materials exemplified for the positive electrode layer.

The lower limit of the average thickness of the isolation layer 3 is preferably 1 μm, more preferably 3 μm. The upper limit of the average thickness of the isolation layer 3 is preferably 50 μm, more preferably 20 μm. By setting the average thickness of the isolation layer 3 to the above lower limit or more, it becomes possible to reliably insulate the positive electrode and the negative electrode. By setting the average thickness of the isolation layer 3 to the upper limit or less, it becomes possible to increase the energy density of the all-solid-state battery.

<Method for manufacturing lithium-ion storage element>
A method for manufacturing a lithium-ion storage element according to an embodiment of the present invention is generally known except that a solid electrolyte according to an embodiment of the present invention is used for producing at least one of a positive electrode layer, an isolation layer, and a negative electrode layer. It can be performed by the method of. Specifically, the manufacturing method is, for example, (1) preparing a positive electrode mixture, (2) preparing a material for an isolation layer, (3) preparing a negative electrode mixture, and (4) a positive electrode. Laminating a layer, an isolation layer and a negative electrode layer. Hereinafter, each step will be described in detail.

(1) Positive Electrode Mixture Preparation Step In this step, a positive electrode mixture for forming a positive electrode layer (positive electrode active material layer) is usually prepared. The method for producing the positive electrode mixture is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include mechanical milling treatment of the material of the positive electrode mixture, compression molding of the positive electrode active material, and sputtering using a target material of the positive electrode active material. If the positive electrode mixture contains a mixture or complex containing a positive electrode active material and a solid electrolyte, this step, for example, by mixing the positive electrode active material and the solid electrolyte using a mechanical milling method or the like, the positive electrode active material and Making a mixture or complex with a solid electrolyte can be included.

(2) Isolation Layer Material Preparation Step In this step, a material for forming the isolation layer is usually prepared. When the lithium-ion power storage device is an all-solid-state battery, the material for the isolation layer is usually a solid electrolyte. The solid electrolyte as the material for the isolation layer can be produced by a conventionally known method. For example, it can be obtained by processing a predetermined material by a mechanical milling method. The isolation layer material may be produced by heating a predetermined material to a temperature equal to or higher than the melting temperature by a melt quenching method, melting and mixing both at a predetermined ratio, and then rapidly cooling. Other methods for synthesizing the material for the isolation layer include, for example, a solid-phase method of sealing under reduced pressure and firing, a liquid-phase method such as dissolution and precipitation, a vapor-phase method (PLD), and firing in an argon atmosphere after mechanical milling. Can be mentioned.

(3) Negative electrode mixture preparation step In this step, a negative electrode mixture for forming a negative electrode layer (negative electrode active material layer) is usually prepared. The specific manufacturing method of the negative electrode mixture is the same as that of the positive electrode mixture. If the negative electrode mixture contains a mixture or complex containing a negative electrode active material and a solid electrolyte, this step, for example, by mixing the negative electrode active material and the solid electrolyte by using a mechanical milling method or the like, the negative electrode active material and Making a mixture or complex with a solid electrolyte can be included.

(Lamination process)
In this step, for example, a positive electrode layer having a positive electrode base material and a positive electrode active material layer, an isolation layer, and a negative electrode layer having a negative electrode base material and a negative electrode active material layer are laminated. In this step, the positive electrode layer, the isolation layer, and the negative electrode layer may be sequentially formed in this order, or vice versa, and the order of forming each layer is not particularly limited. The positive electrode layer is formed, for example, by pressure molding a positive electrode base material and a positive electrode mixture, the isolation layer is formed by pressure molding a material for an isolation layer, and the negative electrode layer is a negative electrode base material. And the negative electrode mixture are pressure-molded. The positive electrode layer, the positive electrode mixture, the separator layer material, the negative electrode mixture, and the negative electrode substrate may be pressure-molded at one time to laminate the positive electrode layer, the separator layer, and the negative electrode layer. The positive electrode layer and the negative electrode layer may be preliminarily molded, and pressure-molded and laminated with the isolation layer.

[Other Embodiments]
The present invention is not limited to the above embodiment, and can be carried out in various modified and improved modes other than the above modes. For example, the lithium-ion storage element according to the present invention may be provided with a layer other than the positive electrode layer, the isolation layer, and the negative electrode layer. In addition, the lithium-ion storage element according to the present invention may include a liquid in one or more of the layers. The lithium-ion power storage element according to the present invention may be a capacitor or the like in addition to an all-solid-state battery that is a secondary battery.

<Example>
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

[Example 1]
Li ₂ S (0.4373 g), P ₂ S ₅ (0.4141 g), LiCl (0.1548 g) and MgCl ₂ (0.0035 g) as raw material compounds were mixed in an agate mortar. This mixture was processed by the dry ball mill method as follows. The mixture was put into a closed 80 mL zirconia pot containing 160 g of zirconia balls having a diameter of 4 mm. These steps were performed in an argon atmosphere with a dew point of −50° C. or lower. A planetary ball mill (Model number P-7 manufactured by FRITSCH, model number P-7) was subjected to mechanical milling treatment for 1 hour×25 times at a revolution speed of 370 rpm to obtain a precursor. The mechanical milling process was performed every 1 hour with a pause of 2 minutes. The obtained precursor was molded into pellets in a glove box that maintained an argon atmosphere with a dew point of -50°C or lower. This precursor was fired by heating at 500° C. for 4 hours, and the precursor of Example 1 represented by the composition formula Li _6-mx A _x PS ₅ Cl (A=Mg, m=2, x=0.010) was used. A solid electrolyte was obtained.

[Examples 2 to 9 and Comparative Example 1]
The same operations as in Example 1 were carried out except that the kinds and amounts of the raw material compounds were set as shown in Table 1, and Examples 2 to 9 and Comparative Examples represented by the composition formulas shown in Tables 2 to 3 were used. Each solid electrolyte of 1 was obtained. Tables 2 to 3 also show the substitution degree of the element A represented by the above formula (1) in the obtained solid electrolyte. Note that Tables 2 and 3 include overlapping Examples and Comparative Examples.

[Evaluation]
(1) Powder X-ray diffraction measurement The powder X-ray diffraction measurement was performed by the above method. As the airtight sample holder for X-ray diffraction measurement, a product name "general-purpose atmosphere separator" manufactured by Rigaku Co. was used.

FIG. 2 shows X-ray diffraction (XRD) patterns of the solid electrolytes of Examples 1 and 2 and Comparative Example 1. FIG. 3 shows X-ray diffraction (XRD) patterns of the solid electrolytes of Examples 3 to 9 and Comparative Example 1. Further, Tables 1 and 2 show the crystal lattice constant a of each solid electrolyte obtained from these results.

As shown in FIGS. 2 and 3, the solid electrolytes of Examples and Comparative Examples each had a diffraction pattern that could be assigned to the space group F-43m. That is, in the solid electrolytes of Examples 1 to 9 in which a part of lithium was replaced with magnesium or indium with respect to the solid electrolyte (Li ₆ PS ₅ Cl) of Comparative Example 1, its crystal structure was maintained. Can be confirmed.

(2) Ionic Conductivity The ionic conductivity of the solid electrolytes of Examples 1 to 6 and Comparative Example 1 at 50° C. was measured for AC impedance by the above method using “VMP-300” manufactured by Bio-Lobic, I asked. Table 2 shows the ionic conductivity of the solid electrolytes of Examples 1 to 6 and Comparative Example 1 at 50°C.

Further, the ionic conductivity at −30° C. of the solid electrolytes of Examples 3 to 9 and Comparative Example 1 was similarly determined. Table 3 shows the ionic conductivity of the solid electrolytes of Examples 3 to 9 and Comparative Example 1 at -30°C.

As shown in Table 2, it is understood that the solid electrolytes of Examples 1 to 6 have improved ionic conductivity at a high temperature of 50°C. Further, as shown in Table 3, it is understood that the solid electrolytes of Examples 3 to 9 have improved ionic conductivity at a low temperature of −30° C.

The solid electrolyte according to the present invention is preferably used as a solid electrolyte of a storage element such as an all-solid battery.

DESCRIPTION OF SYMBOLS 1 Positive electrode layer 2 Negative electrode layer 3 Isolation layer 4 Positive electrode base material 5 Positive electrode active material layer 6 Negative electrode active material layer 7 Negative electrode base material 10 All solid state battery

Claims (5)

It has a crystal structure that can be assigned to the space group F-43m,
Contains lithium, phosphorus, sulfur, and element A,
A solid electrolyte in which the element A is magnesium or indium. The solid electrolyte according to claim 1, wherein the substitution degree DS (%) of the element A represented by the following formula (1) is 0.1% or more and 1.5% or less.
DS={[A]/([Li]+m[A])}×100 (1)
(In the formula (1), [Li] is the content ratio of the lithium atom based on the atomic number. [A] is the content ratio of the element A based on the atomic number. m is the valence of the element A. It is a number.) The solid electrolyte according to claim 1 or 2, which is represented by the following formula (2).
_{Li 7-mx-y A x} PS 6-y Ha y ··· (2)
(In the formula (2), A is the element A. Ha is chlorine, bromine or iodine. x is a number of 0.01 or more and 0.08 or less. y is 0.2 or more. The number is 1.8 or less, and m is the valence of the element A.) The element A is indium,
The solid electrolyte according to claim 1, wherein the substitution degree DS (%) of the indium represented by the following formula (1b) is 0.1% or more and 2.5% or less.
DS={[In]/([Li]+3[In])}×100 (1b)
(In the formula (1b), [Li] is the content ratio of lithium based on the number of atoms. [In] is the content ratio of the indium based on the number of atoms.) A lithium ion storage element containing the solid electrolyte according to claim 1.

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