WO2019131725A1 - 固体電解質 - Google Patents
固体電解質 Download PDFInfo
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- WO2019131725A1 WO2019131725A1 PCT/JP2018/047756 JP2018047756W WO2019131725A1 WO 2019131725 A1 WO2019131725 A1 WO 2019131725A1 JP 2018047756 W JP2018047756 W JP 2018047756W WO 2019131725 A1 WO2019131725 A1 WO 2019131725A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
- H01B1/06—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of other non-metallic substances
- H01B1/10—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of other non-metallic substances sulfides
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B25/00—Phosphorus; Compounds thereof
- C01B25/14—Sulfur, selenium, or tellurium compounds of phosphorus
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- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
- H01B1/06—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of other non-metallic substances
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- H—ELECTRICITY
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- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
- H01B1/06—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of other non-metallic substances
- H01B1/12—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of other non-metallic substances organic substances
- H01B1/122—Ionic conductors
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0561—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of inorganic materials only
- H01M10/0562—Solid materials
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/381—Alkaline or alkaline earth metals elements
- H01M4/382—Lithium
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/386—Silicon or alloys based on silicon
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0065—Solid electrolytes
- H01M2300/0068—Solid electrolytes inorganic
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0065—Solid electrolytes
- H01M2300/0068—Solid electrolytes inorganic
- H01M2300/008—Halides
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Definitions
- the present invention relates to a solid electrolyte that can be suitably used, for example, as a solid electrolyte of a lithium secondary battery.
- the lithium secondary battery is a secondary battery having a structure in which lithium is dissolved out as ions from the positive electrode during charging, moves to the negative electrode, and is occluded, and lithium ions return from the negative electrode to the positive electrode during discharging.
- Lithium secondary batteries have features such as high energy density and long life, so home appliances such as video cameras, portable electronic devices such as laptop computers and mobile phones, and electric tools such as power tools It is widely used as a power source for tools and the like, and has recently been applied to a large battery mounted on an electric vehicle (EV) or a hybrid electric vehicle (HEV).
- EV electric vehicle
- HEV hybrid electric vehicle
- This type of lithium secondary battery is composed of a positive electrode, a negative electrode, and an ion conductive layer sandwiched between the two electrodes, and conventionally, as the ion conductive layer, a separator made of a porous film such as polyethylene or polypropylene is not used. Those filled with aqueous electrolytes have generally been used. However, in such an ion conductive layer, since an organic electrolytic solution using a flammable organic solvent as a solvent was used, it was necessary to improve the structure and material in order to prevent volatilization and leakage. It is necessary to improve the structure and material in order to prevent the short circuit by installing a safety device to suppress the temperature rise at the short circuit.
- the composition formula Li x Si y P z S a Ha w (wherein Ha is any one or two of Br, Cl, I and F) Including the above, it is represented by 2.4 ⁇ (xy) / (y + z) ⁇ 3.3), the content of S is 55 to 73% by mass, and the content of Si is 2 to 11% by mass
- a crystalline solid electrolyte characterized in that the content of the Ha element is 0.02 mass% or more.
- Patent Document 2 contains a compound having a cubic crystal structure belonging to the space group F-43 m and represented by a composition formula: Li 7-x PS 6-x Ha x (Ha is Cl or Br). And sulfur in the above composition formula, wherein x is 0.2 to 1.8, and the lightness L * value of the L * a * b * color system is 60.0 or more.
- An organic solid electrolyte is disclosed.
- Patent Document 3 contains a sulfide-based solid electrolyte for a lithium ion battery, which contains a crystal phase of cubic Argyrodite type crystal structure and is represented by a composition formula: Li 7-x + y PS 6-x Cl x + y A compound, wherein x and y in the above composition formula are characterized by satisfying 0.05 ⁇ y ⁇ 0.9 and ⁇ 3.0x + 1.8 ⁇ y ⁇ ⁇ 3.0x + 5.7.
- a sulfide-based solid electrolyte compound for ion batteries is disclosed.
- Patent Document 4 contains a compound having a cubic crystal structure of Argyrodite type and represented by a composition formula: Li 7-x-2 y PS 6-xy Cl x , and in the composition formula, 0.
- a sulfide-based solid electrolyte for a lithium ion battery characterized by satisfying 8 ⁇ x ⁇ 1.7 and 0 ⁇ y ⁇ ⁇ 0.25x + 0.5 is disclosed.
- a sulfide-based solid electrolyte containing lithium, phosphorus and sulfur has high ion conductivity, but has a problem that hydrogen sulfide is generated when it is exposed to moisture in the air, and the ion conductivity is lowered.
- the present invention relates to a sulfide-based solid electrolyte containing halogen in addition to lithium, phosphorus and sulfur, and a new solid electrolyte capable of suppressing the generation of hydrogen sulfide and ensuring ion conductivity. It is intended to be provided.
- the present invention contains Li 7-a PS 6-a Ha a (Ha represents a halogen, a is 0.2 ⁇ a ⁇ 1.8) consisting of an Argyrodite type crystal structure, and Li 3 PS 4
- XRD X-ray diffraction method
- the solid electrolyte proposed by the present invention can suppress the generation of hydrogen sulfide while securing the ion conductivity. Therefore, even if it touches dry air such as a dry room (typically, the water concentration is 100 ppm or less and the dew point is -45 ° C. or less), the generation of hydrogen sulfide and the deterioration of the quality can be suppressed. Easy to use. Moreover, when manufacturing a battery using the solid electrolyte proposed by the present invention, the manufacturing operation can be performed with more simple equipment and protective equipment, so safety can be high and mass productivity can be improved. .
- FIG. 6 is an XRD spectrum of the compound powder (sample) obtained in Examples 1 to 3 and Comparative Example 1.
- FIG. It is the figure which showed the composition range (range of x and y) of the compound powder (sample) obtained by the Example and the comparative example. It is the figure which showed the result of having produced all the solid battery cells using the compound powder (sample) obtained in Example 1 and 3, and performed battery evaluation (initial charge / discharge capacity characteristic).
- It is a XRD spectrum of the compound powder (sample) obtained in Examples 3 and 8.
- a solid electrolyte (referred to as “the present solid electrolyte”) according to an embodiment of the present invention has a composition formula (1) consisting of an Argyrodite crystal structure: Li 7-a PS 6-a Ha a (Ha represents a halogen) A is a solid electrolyte containing 0.2 ⁇ a ⁇ 1.8) and the composition formula (2): Li 3 PS 4 .
- the above “Argyrodite type crystal structure” is a crystal structure possessed by a group of compounds derived from a mineral represented by a chemical formula: Ag 8 GeS 6 .
- the compound represented by the above “Li 3 PS 4", ⁇ -Li 3 PS 4, ⁇ -Li 3 PS 4, ⁇ -Li 3 PS 4 is known.
- the solid electrolyte, the as Li 3 PS 4, ⁇ -Li 3 PS 4 may also contain only one of ⁇ -Li 3 PS 4 and ⁇ -Li 3 PS 4, of which May be contained, or all three of them may be contained.
- the type of Li 3 PS 4 contained in the present solid electrolyte can be confirmed by, for example, an X-ray diffraction pattern obtained by measurement by XRD. Specifically, the presence of ⁇ -Li 3 PS 4 can be confirmed by the appearance of a peak derived from the ⁇ phase in the X-ray diffraction pattern, and the appearance of a peak derived from the ⁇ phase causes ⁇ -Li 3 PS 4 The presence of ⁇ -Li 3 PS 4 can be confirmed by the appearance of a peak derived from the ⁇ phase.
- any one of ⁇ phase ( ⁇ -Li 3 PS 4 ), ⁇ phase ( ⁇ -Li 3 PS 4 ) and ⁇ phase ( ⁇ -Li 3 PS 4 ) is Li 3 PS.
- Li 3 PS 4 is evaluated as the single phase of the phase, that is, at least 65 mol% of the phase.
- Li 3 PS 4 is evaluated as a mixed phase of two or three of ⁇ phase, ⁇ phase and ⁇ phase.
- “a” indicating the molar ratio of halogen elements is preferably more than 0.2 and not more than 1.8. If “a” is larger than 0.2, the cubic Argyrodite crystal structure is stable near room temperature, high ion conductivity can be secured, and if it is 1.8 or less, formation of Li 3 PS 4 It is preferable because the amount can be easily controlled and the conductivity of lithium ions can be increased. From this point of view, “a” is preferably greater than 0.2 and less than or equal to 1.8, and more preferably 0.4 or more or 1.7 or less, and more preferably 0.5 or more or 1.65 or less. Particularly preferred. When halogen (Ha) is a combination of Cl and Br, “a” in the above composition formula (1) is the total value of the molar ratio of each element of Cl and Br.
- the ratio of the peak intensity appearing at the position of the diffraction angle 2 ⁇ of 26.0 to 28.8 ° derived from Li 3 PS 4 is 0.04 to 0.3. If the ratio is 0.04 or more, the presence of Li 3 PS 4 can reduce the amount of hydrogen sulfide generation, which is preferable. If the ratio is 0.3 or less, practical conductivity can be ensured. preferable. Therefore, from such a viewpoint, the ratio is preferably 0.04 to 0.3, and more preferably 0.06 or more or 0.2 or less, and still more preferably 0.065 or more or 0.1 or less. .
- peak intensity means the value of the said count (cps) of the peak with the largest count (cps) of X-ray photons in the range of the said diffraction angle 2 (theta).
- the diffraction angle 2 ⁇ 26.0 to 28.8 °
- the count number of peaks having the largest X-ray photon count number (cps) and the peak derived from the ⁇ phase ( ⁇ -Li 3 PS 4 ) or the ⁇ phase ( ⁇ -Li 3 PS 4 ) (Cps) is the peak intensity of Li 3 PS 4 .
- Li 3 PS 4 is a mixed phase of ⁇ phase ( ⁇ -Li 3 PS 4 ) or ⁇ phase ( ⁇ -Li 3 PS 4 )
- the diffraction angle 2 ⁇ is in the range of 26.0 to 28.8 °.
- the largest counts of X-ray photon counts (cps), and the counts of peaks derived from ⁇ phase ( ⁇ -Li 3 PS 4 ) or ⁇ phase ( ⁇ -Li 3 PS 4 ) cps) is the peak intensity of Li 3 PS 4 .
- the peak of the surface, the peak of the (400) surface, and the peak of the (210) surface and the (020) surface derived from ⁇ -Li 3 PS 4 can be mentioned.
- the present solid electrolyte contains ⁇ -Li 3 PS 4
- the (121) plane, (311) Peaks of the plane and the (400) plane appear.
- the present solid electrolyte contains ⁇ -Li 3 PS 4
- the (210) plane and the (020) are located at the diffraction angle 2 ⁇ of 26.0 to 28.8 °. Face peaks appear.
- the present solid electrolyte is a sulfide-based solid electrolyte containing lithium, phosphorus, sulfur and halogen, and it can be considered that the same effect can be obtained as long as it has the above characteristics.
- the composition formula (3) Li 7-xy PS 6-x Ha x- (Ha represents a halogen, Cl or Br, or both of them)
- x and y are numerical values that satisfy predetermined numerical ranges and relationships.
- the present solid electrolyte is not limited to the compound represented by the above composition formula (3).
- composition formula (3) is a composition formula based on the molar ratio of each element which is obtained by completely dissolving the present solid electrolyte and measuring the amount of each element, and is represented by, for example, Li 3 PS 4
- a mixed phase of a compound represented by Li 7-a PS 6-a Ha a it can be determined as a total value corresponding to the molar ratio of each compound.
- halogen (Ha) is chlorine (Cl) alone
- “x” in the above composition formula (3) is preferably 0.65 ⁇ x ⁇ 1.8
- “y” in the above composition formula (3) “Preferably satisfies ( ⁇ x / 3 + 2/3) ⁇ y ⁇ ( ⁇ x / 3 + 1.87) and y ⁇ x ⁇ 0.2.
- halogen (Ha) is chlorine (Cl) alone
- hydrogen sulfide is generated if the “y” satisfies ( ⁇ x / 3 + 2/3) ⁇ y under the condition of y ⁇ x ⁇ 0.2 The conductivity can be maintained while reducing the amount.
- halogen (Ha) is Br alone, and in the case of a combination of Cl and Br, “y” in the above composition formula (3) satisfies 0 ⁇ y ⁇ ( ⁇ x / 3 + 1.87), and y It is preferable to satisfy ⁇ x ⁇ 0.2.
- halogen (Ha) is Br alone, and in the case of Cl and Br, under the condition of y ⁇ x-0.2, if the “y” satisfies 0 ⁇ y, the amount of hydrogen sulfide generation is reduced While maintaining conductivity.
- the present solid electrolyte is a compound represented by the composition formula (1): Li 7-a PS 6-a Ha a in a molar ratio of 30% or more, preferably 40% or more with respect to the whole compounds in the present solid electrolyte Alternatively, it is preferable that the content be 95% or less, and more preferably 50% or more or 90% or less.
- the present solid electrolyte is a compound represented by the composition formula (2): Li 3 PS 4 in a molar ratio of 3% or more, and in particular, 5% or more or 60% or less with respect to the whole compound in the solid electrolyte. Among them, the content is preferably 10% or more or 50% or less.
- the compound represented by Li 3 PS 4 it is particularly preferable to contain ⁇ -Li 3 PS 4 in an amount of 50 mol% or more, in particular 60 mol% or more, and more preferably 70 mol% or more.
- the molar ratio (%) of the compound can be determined by Rietveld analysis of XRD data.
- the content is less than 5 mol%, preferably less than 3 mol%, particularly preferably less than 1 mol% of the solid electrolyte, Desirable from the viewpoint of low impact on performance.
- the present solid electrolyte is preferably in the form of particles, and D50 (referred to as "average particle diameter (D50)" or “D50") due to volume particle size distribution obtained by measurement by laser diffraction scattering particle size distribution measurement method is 0 Preferably, it is 1 ⁇ m to 10 ⁇ m. If D50 of the present solid electrolyte is 0.1 ⁇ m or more, it is preferable because the resistance increase due to the increase of the surface area of the solid electrolyte particles and the mixing with the active material do not become difficult.
- the average particle size (D50) of the present solid electrolyte is preferably 0.1 ⁇ m to 10 ⁇ m, more preferably 0.3 ⁇ m or more or 7 ⁇ m or less, and particularly preferably 0.5 ⁇ m or more or 5 ⁇ m or less preferable.
- the average particle size (D50) in the case of adding the present solid electrolyte into the electrode is preferably 1 to 100% of the average particle size (D50) of the positive electrode active material or the average particle size (D50) of the negative electrode active material. If the average particle size (D50) of the present solid electrolyte is 1% or more of the average particle size (D50) of the positive electrode active material or the average particle size (D50) of the negative electrode active material, the active material may be filled without gaps It is preferable because it can be done. On the other hand, if it is 100% or less, the active material ratio can be increased while increasing the filling rate of the electrode, so this is preferable from the viewpoint of increasing the energy density of the battery.
- the average particle size (D50) of the present solid electrolyte is preferably 1 to 100% of the average particle size (D50) of the positive electrode active material or the average particle size (D50) of the negative electrode active material. % Or more and 50% or less, more preferably 5% or more or 30% or less.
- lithium sulfide (Li 2 S) powder, phosphorus sulfide (P 2 S 5 ) powder and halogen compound powder are respectively weighed, ball mill, bead mill, It is preferable to grind and mix with a homogenizer or the like. However, it is not limited to this manufacturing method.
- the above-mentioned composition is prepared by adjusting and mixing the raw material powders such that y> 0.
- the phase of the Argyrodite type crystal structure represented by the formula (1): Li 7-a PS 6-a Ha a and the phase of the above composition formula (2): Li 3 PS 4 can be in a mixed phase state.
- the diffraction angle derived from Li 3 PS 4 with respect to the peak intensity appearing at the position of the diffraction angle 2 ⁇ 24.9 to 26.3 ° derived from the Argyrodite type crystal structure
- halogen compound examples include lithium chloride (LiCl) and lithium bromide (LiBr).
- the present solid electrolyte crystallizes from about 200 to 300 ° C., which is a relatively low temperature range, and therefore, is spared in the low temperature range under an inert atmosphere or under a flow of hydrogen sulfide gas (H 2 S). It is preferable to bake at 350 ° C. or higher after heating. By doing so, the present solid electrolyte, which is a sulfide of a target chemical composition with stable crystallization and almost no sulfur deficiency, can be produced more reliably.
- H 2 S hydrogen sulfide gas
- the sulfur partial pressure in the vicinity of the fired sample can be increased by the sulfur gas generated by decomposition of hydrogen sulfide at the time of firing.
- Electron conductivity can be lowered. Therefore, when firing is performed in an atmosphere containing hydrogen sulfide gas, the firing temperature is preferably 350 to 650 ° C., and more preferably 450 ° C. or more or 600 ° C. or less, and more preferably 500 ° C. or more or 550 ° C. or less Is particularly preferred.
- H 2 S hydrogen sulfide gas
- the firing temperature is preferably 350 to 500 ° C., and particularly preferably 350 ° C. or more or 450 ° C. or less, and particularly preferably 400 ° C. or more or 450 ° C. or less.
- the raw material powder having a small particle size and high reactivity is preferable.
- the firing may be performed in an inert atmosphere.
- the above-mentioned raw materials are extremely unstable in the atmosphere, react with water and decompose, and generate hydrogen sulfide gas or oxidize them. Is preferably set in a furnace for firing.
- the present solid electrolyte is a solid that passes ions such as Li ions, and has high chemical stability. Therefore, the solid electrolyte should be slurried using a polar solvent such as N-methyl-2-pyrrolidone (NMP), acetone, DMF, etc. Can.
- NMP N-methyl-2-pyrrolidone
- the conductivity after being immersed in these solvents can be maintained high. Specifically, the conductivity after immersion in NMP can be set to 1 ⁇ 10 ⁇ 5 S / cm or more.
- the present solid electrolyte can be used as a solid electrolyte layer of an all solid lithium secondary battery, or a solid electrolyte to be mixed with a positive electrode-negative electrode mixture.
- Examples of the shape of the battery include laminate type, cylindrical type and square type.
- an all solid lithium secondary battery can be configured by forming a layer containing the present solid electrolyte between the positive electrode and the negative electrode.
- this solid electrolyte is excellent in moisture resistance, and there is little characteristic deterioration even if it handles in dry air, the assembly operation of all the solid-type lithium secondary batteries can be performed also in a dry room etc., for example.
- a slurry comprising the present solid electrolyte, a binder and a solvent is dropped on a substrate, and scraped off with a doctor blade or the like;
- the coating film can be formed by screen printing or the like, and then dried by heating to remove the solvent.
- the powder of the present solid electrolyte is formed into a green compact by a press or the like, it can be processed appropriately and manufactured.
- the porosity of the layer containing the present solid electrolyte is preferably 50% or less, more preferably 30% or less, and still more preferably 20% or less. Therefore, it is preferable to press and manufacture the powder
- the thickness of the layer containing the present solid electrolyte is typically 5 to 300 ⁇ m, preferably 10 to 100 ⁇ m, from the viewpoint of short circuit prevention and capacity balance.
- the positive electrode material currently used as a positive electrode active material of a lithium secondary battery can be used suitably.
- a positive electrode active material containing lithium specifically, a spinel lithium transition metal compound, a lithium metal oxide having a layered structure, and the like can be mentioned.
- the energy density can be improved by using the high voltage system positive electrode material.
- the positive electrode material may contain, in addition to the positive electrode active material, a conductive material or another material.
- a negative electrode material used as a negative electrode active material of a lithium secondary battery can be appropriately used.
- the present solid electrolyte since the present solid electrolyte is electrochemically stable, it can be charged / discharged with lithium metal or lithium metal at a potential lower than that of lithium metal (about 0.1 V vs Li + / Li), artificial graphite, natural graphite And carbon-based materials such as non-graphitizable carbon (hard carbon) can be used. Therefore, the energy density of the all solid lithium secondary battery can be greatly improved.
- silicon and tin which are promising as high-capacity materials, can also be used as active materials.
- the electrolytic solution and the active material react with each other during charging and discharging to cause corrosion on the surface of the active material, and therefore, the battery characteristics significantly deteriorate.
- the present solid electrolyte is used as the electrolyte of a lithium secondary battery and silicon or tin is used as the negative electrode, such a corrosion reaction does not occur, so that the durability of the battery can be improved.
- the negative electrode material may also contain, in addition to the negative electrode active material, a conductive material or another material.
- solid electrolyte refers to any substance to which ions such as Li + can move in a solid state.
- X to Y X and Y are arbitrary numbers
- preferably greater than X or “preferably Y” with the meaning of “X or more and Y or less” unless otherwise specified.
- smaller also includes the meaning of "smaller”.
- X or more” or “X ⁇ ” X is an arbitrary number
- Example 1 Lithium sulfide (Li 2 S) powder and diphosphorus pentasulfide (P 2 S 5 ) so that the composition of the compound having a cubic crystal structure of Argyrodite type is Li 5.0 PS 4.4 Cl 1.2
- the powder and lithium chloride (LiCl) powder were respectively weighed so as to be 5 g in total, and pulverized and mixed for 15 hours in a ball mill.
- the mixed powder obtained is filled in a carbon container and heated at 300 ° C. for 4 hours while flowing hydrogen sulfide gas at 1.0 l / min in a tubular electric furnace, and further heated at 500 ° C. for 4 hours did.
- the temperature rise / fall rate was 200 ° C./h.
- Li 2 S lithium sulfide
- P 2 S 5 diphosphorus pentasulfide
- LiCl lithium chloride
- Examples 4 to 6 and Comparative Example 2 Example except that the lithium sulfide (Li 2 S) powder, the diphosphorus pentasulfide (P 2 S 5 ) powder, and the lithium chloride (LiCl) powder were weighed and mixed such that the compositions shown in Table 2 were obtained. Similar to 1, a compound powder (sample) was obtained.
- Li 2 S lithium sulfide
- P 2 S 5 diphosphorus pentasulfide
- LiCl lithium chloride
- Example 7 Example 9, and Comparative Example 3
- the lithium sulfide (Li 2 S) powder, the diphosphorus pentasulfide (P 2 S 5 ) powder, the lithium chloride (LiCl) powder, and the lithium bromide (LiBr) powder have the compositions shown in Table 3.
- a compound powder (sample) was obtained in the same manner as in Example 1 except for weighing and mixing.
- Example 8 The lithium sulfide (Li 2 S) powder, the diphosphorus pentasulfide (P 2 S 5 ) powder, the lithium chloride (LiCl) powder, and the lithium bromide (LiBr) powder have the compositions shown in Table 3.
- a compound powder (sample) was obtained in the same manner as in Example 1 except that the mixture was weighed and mixed, and the baking temperature was set to 400 ° C. for 4 hours.
- Comparative Examples 5 to 7 Compound powder (the same as in Example 1, except that the lithium sulfide (Li 2 S) powder and diphosphorus pentasulfide (P 2 S 5 ) powder were weighed and mixed so as to obtain the composition shown in Table 4 I got a sample).
- Li 2 S lithium sulfide
- P 2 S 5 diphosphorus pentasulfide
- ⁇ X-ray Rietveld analysis> The Rietveld analysis shown below is carried out using the XRD data of the compound powder (sample) obtained in each example, and the molar ratio of the compound having an Argyrodite crystal structure to the whole compound obtained in each example When it asked for, it was able to confirm that all were 30 mol% or more.
- Rietveld analysis similarly shown below was performed using the XRD data of the compound powder (sample) obtained in Example 1, and as a result of quantifying the composition of the compound having an Argyrodite crystal structure, the composition formula is It became Li 5.55 PS 4.51 Cl 1.53 .
- the sealed bag containing the sample was opened in the constant temperature and humidity chamber, and the sample was quickly placed in the separable flask.
- the sample was placed in a separable flask, and the hydrogen sulfide concentration was measured with a hydrogen sulfide sensor (GX-2009, manufactured by Riken Keiki Co., Ltd.) for hydrogen sulfide generated immediately after sealing until 60 minutes elapsed. Then, the volume of hydrogen sulfide was calculated from the concentration of hydrogen sulfide after 60 minutes to determine the amount of hydrogen sulfide generated.
- the ionic conductivity was measured by an AC impedance method at room temperature (25 ° C.) using Solartron 1255B, which is an apparatus manufactured by Toyo Corporation, under the measurement frequency of 0.1 Hz to 1 MHz. S / cm) was measured. The results are shown in Tables 1 to 4.
- the sample obtained in the example was used as a solid electrolyte powder.
- the positive electrode mixture powder is prepared by mixing the positive electrode active material powder, the solid electrolyte powder, and the conductive auxiliary (acetylene black) powder in a mortar at a mass ratio of 60: 37: 3, and uniaxial press molding at 20 MPa. Thus, a positive electrode mixture pellet was obtained.
- the negative electrode mixture powder was prepared by mortar mixing a graphite powder and a solid electrolyte powder at a mass ratio of 64:36.
- the battery characteristic measurement was evaluated by placing the all solid battery cell in an environmental tester maintained at 25 ° C. and connecting it to a charge / discharge measurement device. The battery was charged and discharged with 1 mA as 1C. The battery was charged by the CC-CV system at 0.1 C to 4.5 V to obtain an initial charge capacity. The discharge was performed by CC method up to 2.5 V at 0.1 C to obtain an initial discharge capacity.
- FIG. 3 shows the results of the initial charge and discharge capacity characteristics. The discharge capacity at the time of discharging to 2.5 V at 0.1 C was 160 mAh / g or more. Since the solid electrolyte secures practicable ion conductivity, it can be considered that high discharge capacity can be expressed.
- Li 3 PS 4 contained in the compound powder obtained in Examples 1, 2, 5, 7 and 9 is the ⁇ phase occupied in Li 3 PS 4 And the proportion of the ⁇ phase was less than 65% in molar proportion, and was a mixed phase of ⁇ -Li 3 PS 4 and ⁇ -Li 3 PS 4 .
- Li 3 PS 4 contained in the compound powder obtained in Example 3, 4 and 6, the proportion of gamma phase occupying the Li 3 PS 4 is not less than 65% by mol ratio, gamma-Li 3 PS It was a single phase of 4 (gamma phase).
- Li 3 PS 4 contained in the compound powder obtained in Example 8 has a ratio of ⁇ phase to Li 3 PS 4 of 65% or more in molar ratio, and a single phase of ⁇ -Li 3 PS 4 ( (beta single phase).
- the composition Li 7-x PS 6-x Ha x (Ha represents a halogen, where x is 0.2 ⁇ x ⁇ ) of the Argyrodite crystal structure. by shifting the composition from 1.8.), with Li 7-a PS 6-a Ha a (Ha is .a showing the halogen is 0.2 ⁇ a ⁇ 1.8.), Li 3 It was found that PS 4 can be included, and at this time, by adjusting the content of Li 3 PS 4 in a predetermined range, it is possible to suppress the generation of hydrogen sulfide while securing the ion conductivity.
- Li 7-a PS 6-a Ha a (Ha represents a halogen; a is 0.2 ⁇ a ⁇ 1.8) composed of an Argyrodite type crystal structure and Li 3 PS 4 is contained.
- XRD X-ray diffraction method
- Li 7-a PS 6-a Ha a (Ha represents a halogen; a is 0.2 ⁇ a ⁇ 1.8) consisting of an Argyrodite type crystal structure and Li.
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Abstract
Description
本発明の実施形態の一例に係る固体電解質(「本固体電解質」と称する)は、Argyrodite型結晶構造からなる組成式(1):Li7-aPS6-aHaa(Haはハロゲンを示す。aは0.2<a≦1.8である。)及び組成式(2):Li3PS4を含有する固体電解質である。
また、上記「Li3PS4」で表される化合物として、α‐Li3PS4、β‐Li3PS4、γ‐Li3PS4が知られている。本発明において「Li3PS4」と記載した場合、特に断わらない限り、これら全てを包含する意味である。したがって、本固体電解質は、前記Li3PS4として、α-Li3PS4、β-Li3PS4及びγ-Li3PS4のうちの1種のみを含有していてもよいし、そのうちの2種を含有していてもよいし、そのうちの3種全てを含有していてもよい。
なお、本固体電解質に含まれるLi3PS4の種類は、例えばXRDにより測定して得られたX線回折パターンにより確認することができる。具体的には、X線回折パターンにおいて、α相に由来するピークの出現によりα-Li3PS4の存在を確認することができ、β相に由来するピークの出現によりβ-Li3PS4の存在を確認することができ、γ相に由来するピークの出現によりγ-Li3PS4の存在を確認することができる。
他方、α相(α-Li3PS4)、β相(β-Li3PS4)及びγ相(γ-Li3PS4)のうちのいずれも、Li3PS4に占める存在割合が、mol比率で65%未満である場合には、Li3PS4はα相、β相及びγ相のうちの2種または3種の混相と評価する。
「a」が0.2より大きければ、室温近傍で立方晶系Argyrodite型結晶構造が安定であり、高いイオン伝導率を確保することができ、1.8以下であればLi3PS4の生成量を制御しやすくリチウムイオンの伝導性を高めることができるため好ましい。
かかる観点から、「a」は0.2より大きく且つ1.8以下であるのが好ましく、中でも0.4以上或いは1.7以下、その中でも0.5以上或いは1.65以下であるのが特に好ましい。
なお、ハロゲン(Ha)がCl及びBrの組み合わせの場合、上記組成式(1)における「a」は、ClとBrの各元素のモル比の合計値である。
よって、かかる観点から、当該比率は0.04~0.3であるのが好ましく、中でも0.06以上或いは0.2以下、その中でも0.065以上或いは0.1以下であるのがさらに好ましい。
例えばLi3PS4が、β相(β-Li3PS4)又はγ相(γ-Li3PS4)からなる単相の場合には、回折角2θ=26.0~28.8°の範囲中で、最も大きなX線光子のカウント数(cps)を有し、且つ、β相(β-Li3PS4)又はγ相(γ-Li3PS4)に由来するピークの当該カウント数(cps)がLi3PS4のピーク強度となる。
他方、Li3PS4が、β相(β-Li3PS4)又はγ相(γ-Li3PS4)の混相の場合には、回折角2θ=26.0~28.8°の範囲中で、最も大きなX線光子のカウント数(cps)を有し、且つ、β相(β-Li3PS4)又はγ相(γ-Li3PS4)に由来するピークの当該カウント数(cps)がLi3PS4のピーク強度となる。
また、CuKα線を用いたXRD測定において、回折角2θ=26.0~28.8°の位置に出現するピークとしては、例えばβ‐Li3PS4に由来する(121)面、(311)面、(400)面のピーク、及びγ‐Li3PS4に由来する(210)面、(020)面のピークを挙げることができる。したがって、本固体電解質がβ‐Li3PS4を含有するとき、本固体電解質のXRD測定において、回折角2θ=26.0~28.8°の位置には、(121)面、(311)面及び(400)面のピークが出現する。また、本固体電解質がγ‐Li3PS4を含有するとき、本固体電解質のXRD測定において、回折角2θ=26.0~28.8°の位置には、(210)面及び(020)面のピークが出現する。
中でも、本固体電解質の好ましい組成例を挙げるとすれば、組成式(3):Li7-x-yPS6-xHax-y(Haはハロゲンを示し、Cl又はBr、又はこれら両方の組み合わせである。x及びyは所定の数値範囲及び関係を満す数値である。)で示される化合物を挙げることができる。但し、本固体電解質は、上記組成式(3)で示される化合物に限定されるものではない。
なお、上記「組成式(3)」は、本固体電解質を全溶解して各元素量を測定して求めた各元素モル比に基づいた組成式であり、例えば、Li3PS4で表される化合物と、Li7-aPS6-aHaaで表される化合物との混相の場合は、各々の化合物のモル比に応じた合算値として求めることができる。
当該「x」が0.2より大きければ、高いイオン伝導率を確保することができ、1.8以下であれば、生成するLi3PS4の生成量を制御しやすくなるから好ましい。
かかる観点から、当該「x」は0.2<x≦1.8であるのが好ましく、中でも0.5以上、その中でも0.6以上或いは1.7以下、その中でも特に0.8以上或いは1.6以下であるのがさらに好ましい。
ハロゲン(Ha)が塩素(Cl)単独である場合に、y<x-0.2という条件の下において、当該「y」が(-x/3+2/3)<yを満たせば、硫化水素発生量を低減しつつ、導電率を維持できる。他方、さらにy<(-x/3+1.87)を満たせば、本固体電解質を用いて全固体電池を作製した場合に高い放電容量を発現できるため、好ましい。
かかる観点から、ハロゲン(Ha)が塩素(Cl)単独である場合、当該「y」は、y<x-0.2の条件の下、(-x/3+2/3)<y<(-x/3+1.87)を満たすのが好ましく、中でも(-x/3+5/6)<y、或いは、y<(-x/3+1.8)を満たすのがより好ましく、その中でもy<(-x/3+1.7)を満たすのがより好ましく、その中でも特に(-x/3+1)<y、或いは、y<(-x/3+1.6)を満たすのがさらに好ましい。
ハロゲン(Ha)がBr単独の場合、並びにCl及びBrの組み合わせの場合、y<x-0.2という条件の下において、当該「y」が0<yを満たせば、硫化水素発生量を低減しつつ、導電率を維持できる。他方、y<(-x/3+1.87)を満たせば、本固体電解質を用いて全固体電池を作製した場合に高い放電容量を発現できるため、好ましい。
かかる観点から、ハロゲン(Ha)がBr単独であるか或はCl及びBrの組み合わせである場合、当該「y」は、0.2<x-y<1.8の条件の下、0<y<(-x/3+1.87)を満たすのが好ましく、中でも(-x/3+2/3)<y、その中でも(-x/3+5/6)<y、或いは、y<(-x/3+1.8)を満たすのがより好ましく、さらにその中でもy<(-x/3+1.7)を満たすのがより好ましく、その中でも特に(-x/3+1)<y、或いは、y<(-x/3+1.6)を満たすのがさらに好ましい。
なお、ハロゲン(Ha)がCl及びBrの組み合わせの場合、上記組成式(3)における「x-y」は、ClとBrの各元素のモル比の合計値である。
また、本固体電解質は、組成式(2):Li3PS4で表される化合物を、本固体電解質中の化合物全体に対してmol比率で3%以上、中でも5%以上或いは60%以下、その中でも10%以上或いは50%以下の割合で含有するのが好ましい。
さらに、Li3PS4で表される化合物の内訳として、β‐Li3PS4を50mol%以上、中でも60mol%以上、中でも70mol%以上含有するのが特に好ましい。
この際、上記化合物のmol比率(%)は、XRDデータをリートベルト解析して求めることができる。
本固体電解質は、粒子であるのが好ましく、レーザー回折散乱式粒度分布測定法によりにより測定して得られる体積粒度分布によるD50(「平均粒径(D50)」又は「D50」と称する)が0.1μm~10μmであるのが好ましい。
本固体電解質のD50が0.1μm以上であれば、固体電解質粒子の表面積が増えることによる抵抗増大や、活物質との混合が困難となることがないから好ましい。他方、該D50が10μm以下であれば、活物質や、組み合わせて用いる固体電解質の隙間に本固体電解質が入りやすくなり、接触点及び接触面積が大きくなるから好ましい。
かかる観点から、本固体電解質の平均粒径(D50)は0.1μm~10μmであるのが好ましく、中でも0.3μm以上或いは7μm以下、その中でも特に0.5μm以上或いは5μm以下であるのがさらに好ましい。
本固体電解質の平均粒径(D50)が、正極活物質の平均粒径(D50)又は負極活物質の平均粒径(D50)の1%以上であれば、活物質間を隙間なく埋めることができるため好ましい。他方、100%以下であれば、電極の充填率を高めつつ、活物質比率を高くできるので、電池の高エネルギー密度化の観点から好ましい。
かかる観点から、本固体電解質の平均粒径(D50)は、正極活物質の平均粒径(D50)又は負極活物質の平均粒径(D50)の1~100%であるのが好ましく、中でも3%以上或いは50%以下、その中でも5%以上或いは30%以下であるのがさらに好ましい。
次に、本固体電解質の製造方法の一例について説明する。但し、ここで説明する製造方法はあくまでも一例であり、この方法に限定するものではない。
これに対し、本固体電解質は、比較的低温域である200~300℃程度から結晶化が進むため、不活性雰囲気下もしくは硫化水素ガス(H2S)流通下において、上記低温度域で予備加熱を行った後に350℃以上で焼成するのが好ましい。このようにすることによって、結晶化が安定して硫黄欠損がほとんど無い目的の化学組成の硫化物である本固体電解質をより確実に作製することができる。
このように硫化水素ガス(H2S)流通下で焼成する際、350~650℃で焼成することにより、硫化物中の硫黄を欠損させることなく焼成することができる。
また、上記の原料は、大気中で極めて不安定で、水分と反応して分解し、硫化水素ガスを発生したり、酸化したりするため、不活性ガス雰囲気に置換したグローブボックス等を通じて、原料を炉内にセットして焼成を行うのが好ましい。
本固体電解質は、Liイオンなどのイオンを通じる固体であり、化学的安定性が高いため、例えばN-メチル-2-ピロリドン(NMP)、アセトン、DMFなどの極性溶媒を用いてスラリー化することができる。しかも、これらの溶媒に浸漬した後の導電率を高く維持することができる。具体的には、NMPに浸漬した後の導電率を1×10-5S/cm以上とすることができる。
電池の形状としては、例えばラミネート型、円筒型および角型等を挙げることができる。
この際、本固体電解質は、耐湿性に優れており、乾燥空気中で取り扱っても特性劣化が少ないため、例えばドライルームなどでも全固体型リチウム二次電池の組立作業を行うことができる。
ここで、空隙率は、例えば液相法(アルキメデス法)で求めた、本固体電解質を含む層の真密度と見かけの密度から、下記に示す関係式により算出することができる。
空隙率=(真密度-見かけの密度)÷真密度×100
正極材は、正極活物質のほかに、導電化材或いはさらに他の材料を含んでいてもよい。
負極材についても、負極活物質のほかに、導電化材或いはさらに他の材料を含んでいてもよい。
本発明において「固体電解質」とは、固体状態のままイオン、例えばLi+が移動し得る物質全般を意味する。
また、本発明において「X~Y」(X、Yは任意の数字)と記載した場合、特に断らない限り「X以上Y以下」の意と共に、「好ましくはXより大きい」又は「好ましくはYより小さい」の意も包含する。
また、「X以上」又は「X≦」(Xは任意の数字)と記載した場合、「Xより大きいことが好ましい」旨の意図を包含し、「Y以下」又は「Y≧」(Yは任意の数字)と記載した場合、「Yより小さいことが好ましい」旨の意図を包含する。
立方晶系Argyrodite型結晶構造を有する化合物の組成がLi5.0PS4.4Cl1.2となるように、硫化リチウム(Li2S)粉末と、五硫化二リン(P2S5)粉末と、塩化リチウム(LiCl)粉末とを、全量で5gとなるようにそれぞれ秤量し、ボールミルで15時間粉砕混合を行った。得られた混合粉末をカーボン製の容器に充填し、これを管状電気炉にて硫化水素ガスを1.0l/min流通させながら、300℃で4時間加熱した後、さらに500℃で4時間加熱した。昇降温速度は200℃/hとした。その後試料を乳鉢で解砕し、目開き53μmの篩いで整粒して粉末状のサンプルを得た。この際、前記秤量、混合、電気炉へのセット、電気炉からの取り出し、解砕及び整粒作業は全て、十分に乾燥されたArガス(露点-60℃以下)で置換されたグローブボックス内で実施し、組成式:Li5.0PS4.4Cl1.2、すなわち、Li7-x-yPS6-aHax―yにおいて「x=1.6、y=0.4」)で示される化合物粉末(サンプル)を得た。
前記硫化リチウム(Li2S)粉末と、五硫化二リン(P2S5)粉末と、塩化リチウム(LiCl)粉末を、表1に示す組成となるように秤量して混合した以外、実施例1と同様に、化合物粉末(サンプル)を得た。
前記硫化リチウム(Li2S)粉末と、五硫化二リン(P2S5)粉末と、塩化リチウム(LiCl)粉末を、表2に示す組成となるように秤量して混合した以外、実施例1と同様に、化合物粉末(サンプル)を得た。
前記硫化リチウム(Li2S)粉末と、五硫化二リン(P2S5)粉末と、塩化リチウム(LiCl)粉末と、臭化リチウム(LiBr)粉末を、表3に示す組成となるように秤量して混合した以外、実施例1と同様に、化合物粉末(サンプル)を得た。
前記硫化リチウム(Li2S)粉末と、五硫化二リン(P2S5)粉末と、塩化リチウム(LiCl)粉末と、臭化リチウム(LiBr)粉末を、表3に示す組成となるように秤量して混合し、焼成温度を400℃で4時間加熱とした以外、実施例1と同様に、化合物粉末(サンプル)を得た。
前記硫化リチウム(Li2S)粉末と、五硫化二リン(P2S5)粉末を、表4に示す組成となるように秤量して混合した以外、実施例1と同様に、化合物粉末(サンプル)を得た。
実施例・比較例で得られた化合物粉末(サンプル)を全溶解してICP発光分析法により元素組成を測定した。表1~4に示した組成式の通りとなっていることを確認した。
実施例1~9及び比較例1~7で得た化合物粉末(サンプル)の組成範囲(x及びyの範囲)を図2に示した。
実施例・比較例で得られた化合物粉末(サンプル)をX線回折法(XRD、Cu線源)で分析し、X線回折パターンを得て、各位置におけるピーク強度(cps)を測定した。
実施例1~3および比較例1で得た化合物粉末(サンプル)のXRDスペクトルを図1に示し、実施例3および8で得た化合物粉末(サンプル)のXRDスペクトルを図4に示した。
また、リガク社製のXRD装置「Smart Lab」を用いて、走査軸:2θ/θ、走査範囲:10~140deg、ステップ幅0.01deg、走査速度1deg/minの条件の下で行った。Argyrodite型結晶構造に由来する回折角2θ=24.9~26.3°の位置に出現するピーク強度に対する、Li3PS4に由来する回折角2θ=26.0~28.8°の位置に出現するピーク強度の比率(Int(Li3PS4)/Int(Li7-aPS6-aHaa))を表1~4に示した。
なお、上記比率が0.04未満の場合は、Li7-aPS6-aHaaに対してLi3PS4の相が実質的に存在しないとみなし、表中の「Argyrodite相以外の含有相」の欄には「無」と表した。
各実施例で得られた化合物粉末(サンプル)のXRDデータを用いて、下記に示すリートベルト解析を実施し、各実施例で得られた化合物全体に対する、Argyrodite型結晶構造からなる化合物のmol比率を求めたところ、いずれも30mol%以上であることを確認することができた。
また、実施例1で得られた化合物粉末(サンプル)のXRDデータを用いて、同じく下記に示すリートベルト解析を実施し、Argyrodite型結晶構造からなる化合物の組成を定量した結果、その組成式はLi5.55PS4.51Cl1.53となった。この値は、仕込み原料化合物の配合比から算出した組成式:Li5.5PS4.5Cl1.5(すなわち、Li7-aPS6-aHaaにおいて「a=1.5」)と良く整合していた。そこで、表1~4には、実施例・比較例で得られた化合物粉末(サンプル)の、仕込み原料化合物の配合比から算出して、Argyrodite型結晶構造からなる化合物の組成:Li7-aPS6-aHaaにおける「a」の値を示した。
実施例・比較例で得た化合物粉末(サンプル)を、十分に乾燥されたArガス(露点-60℃以下)で置換されたグローブボックス内で50mgずつ秤量し、ラミネートフィルムで密閉された袋に入れた。その後、乾燥空気ガスと大気を混合することで調整した露点-30℃雰囲気で室温(25℃)に保たれた恒温恒湿槽の中に、容量1500cm3のガラス製のセパラブルフラスコを入れ、セパラブルフラスコの内部が恒温恒湿槽内の環境と同一になるまで保持してから、サンプルが入った密閉袋を恒温恒湿槽の中で開封し、素早くセパラブルフラスコにサンプルを配置した。サンプルをセパラブルフラスコに配置し、密閉した直後から60分経過までに発生した硫化水素について、硫化水素センサー(理研計器製GX-2009)にて硫化水素濃度を測定した。そして、60分経過後の硫化水素濃度から硫化水素の容積を算出して硫化水素発生量を求めた。
表1~3には、Argyrodite型結晶構造の組成式:Li7-x-yPS6-xHax-yにおいて、「y=0」とした組成の硫化水素発生量を基準として、組成をずらした場合(すなわちy≠0)の硫化水素発生量の比率を示した(表中で「Argyrodite 基準組成に対する、硫化水素発生量の比率」と記載。)。y>0の場合、硫化水素発生量が低減していることが確認できる。
実施例・比較例で得た化合物粉末(サンプル)を、十分に乾燥されたArガス(露点-60℃以下)で置換されたグローブボックス内で一軸加圧成形し、さらにCIP(冷間等方圧加圧装置)にて200MPaで直径10mm、厚み約4~5mmのペレットを作製した。更にペレット上下両面に電極としてのカーボンペーストを塗布した後、180℃で30分間の熱処理を行い、イオン伝導率測定用サンプルを作製した。
イオン伝導率測定は、室温(25℃)にて、東陽テクニカ社製の装置である、ソーラトロン1255Bを用いて、測定周波数0.1Hz~1MHzの条件下、交流インピーダンス法にて、イオン伝導率(S/cm)を測定した。結果を表1~4に示した。
実施例1及び3で得られた化合物粉末(サンプル)を固体電解質として用いて正極合材、負極合材を調製し、全固体電池を作製して、電池特性評価(初回充放電容量)を行った。
正極活物質として、層状化合物であるLiNi0.5Co0.2Mn0.3O2(NCM)粉末(D50=6.7μm)を用い、負極活物質としてグラファイト(D50=20μm)を用い、固体電解質粉末として実施例で得たサンプルを用いた。
正極合材粉末は、正極活物質粉末、固体電解質粉末及び導電助剤(アセチレンブラック)粉末を、質量比で60:37:3の割合で乳鉢混合することで調製し、20MPaで1軸プレス成型して正極合材ペレットを得た。
負極合材粉末は、グラファイト粉末と固体電解質粉末を、質量比で64:36の割合で乳鉢混合することで調製した。
上下を開口したポリプロピレン製の円筒(開口径10.5mm、高さ18mm)の下側開口部を正極電極(SUS製)で閉塞し、正極電極上に正極合材ペレットを載せた。その上から実施例で得た粉末固体電解質を載せて、180MPaにて1軸プレスし正極合材と固体電解質層を形成した。その上から負極合材粉末を載せた後、負極電極(SUS製)で閉塞して550MPaにて1軸成形し、およそ100μm厚の正極合材、およそ300μm厚の固体電解質層、およそ20μm厚の負極合材の3層構造からなる全固体電池セルを作製した。この際、上記全固体電池セルの作製においては、平均露点-45℃の乾燥空気で置換されたグローブボックス内で行った。
電池特性測定は、25℃に保たれた環境試験機内に全固体電池セルを入れて充放電測定装置に接続して評価した。1mAを1Cとして電池の充放電を行った。0.1Cで4.5VまでCC-CV方式で充電し、初回充電容量を得た。放電は0.1Cで2.5VまでCC方式で行い初回放電容量を得た。
図3に初回充放電容量特性の結果を示す。0.1Cで2.5Vまで放電した際の放電容量は160 mAh/g以上であった。固体電解質が実用可能なイオン伝導性を確保しているため、高い放電容量を発現できたと考えることができる。
実施例1~9で得られた化合物(サンプル)のXRDデータをリートベルト解析した結果、Argyrodite型結晶構造からなるLi7-aPS6-aHaa(Haはハロゲンを示す。aは0.2<a≦1.8である。)及びLi3PS4を含み、Argyrodite型結晶構造からなる化合物を30mol%以上含んでいることを確認することができた。
一方、実施例3、4、6で得られた化合物粉末に含まれるLi3PS4は、Li3PS4に占めるγ相の割合が、mol比率で65%以上であり、γ-Li3PS4の単相(γ相)であった。
さらに、実施例8で得られた化合物粉末に含まれるLi3PS4は、Li3PS4に占めるβ相の割合がmol比率で65%以上であり、β-Li3PS4の単相(β単相)であった。
以上の観点から、Argyrodite型結晶構造からなるLi7-aPS6-aHaa(Haはハロゲンを示す。aは0.2<a≦1.8である。)及びLi3PS4を含有し、X線回折法(XRD)により測定して得られたX線回折パターンにおいて、前記Argyrodite型結晶構造に由来する回折角2θ=24.9~26.3°の位置に出現するピーク強度に対する、Li3PS4に由来する回折角2θ=26.0~28.8°の位置に出現するピーク強度の比率が0.04~0.3である固体電解質であれば、イオン伝導性を確保しつつ硫化水素の発生を抑えることができることが分かった。
Claims (5)
- Argyrodite型結晶構造からなるLi7-aPS6-aHaa(Haはハロゲンを示す。aは0.2<a≦1.8である。)及びLi3PS4を含有し、
X線回折法(XRD)により測定して得られたX線回折パターンにおいて、前記Argyrodite型結晶構造に由来する回折角2θ=24.9~26.3°の位置に出現するピーク強度に対する、Li3PS4に由来する回折角2θ=26.0~28.8°の位置に出現するピーク強度の比率が0.04~0.3であることを特徴とする固体電解質。 - 組成式:Li7-x-yPS6-xHax-y(Haはハロゲンを示し、Cl又はBr、又はこれら両方の組み合わせである。HaがCl単独の場合、xは0.65<x≦1.8であり、yは-x/3+2/3<y<-x/3+1.87を満たし、且つy<x-0.2を満たす。HaがBr単独の場合並びにCl及びBrの組み合わせの場合、xは0.2<x≦1.8であり、yは0<y<-x/3+1.87を満たし、且つy<x-0.2を満たす。)で示される化合物からなることを特徴とする請求項1に記載の固体電解質。
- 請求項1又は2に記載の固体電解質を備えたリチウム二次電池。
- 請求項1又は2に記載の固体電解質と、炭素又はケイ素含む負極活物質とを有するリチウム二次電池。
- 請求項1又は2に記載の固体電解質と、リチウムを含む正極活物質とを有するリチウム二次電池。
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JP2023051068A (ja) * | 2021-09-30 | 2023-04-11 | Agc株式会社 | 硫化物系固体電解質粉末の製造方法 |
JP7095795B1 (ja) | 2021-09-30 | 2022-07-05 | Agc株式会社 | 硫化物系固体電解質粉末の製造方法 |
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EP3734616A4 (en) | 2021-08-04 |
CN111512397A (zh) | 2020-08-07 |
US11631887B2 (en) | 2023-04-18 |
US20210075058A1 (en) | 2021-03-11 |
KR20200087207A (ko) | 2020-07-20 |
EP3734616A1 (en) | 2020-11-04 |
JPWO2019131725A1 (ja) | 2020-10-22 |
JP6997216B2 (ja) | 2022-01-17 |
KR102428153B1 (ko) | 2022-08-01 |
CN111512397B (zh) | 2021-07-30 |
EP3734616B1 (en) | 2022-10-12 |
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