Sulfide solid electrolyte, positive electrode mixture, and solid-state battery

Abstract

This sulfide solid electrolyte contains elemental lithium (Li), elemental silicon (Si), elemental phosphorus (P), elemental sulfur (S), and elemental oxygen (O). The contained amount of elemental halogens in the sulfide solid electrolyte is at most 5.4 mass%. It is preferable that a peak is observed in the wavenumber range of not less than 400 to less than 423 cm-1 in a Raman spectrum measurement.<sp / > It is also preferable that a crystal phase having an argyrodite crystal structure is included. It is further preferable that the molar ratio O / S of the elemental oxygen (O) to the elemental sulfur (S) is more than 0 to not more than 0.13.

Description

Sulfide solid electrolyte, positive electrode mixture, and solid battery

[0001] This invention relates to a sulfide solid electrolyte. Furthermore, this invention relates to a positive electrode mixture and a solid-state battery containing the sulfide solid electrolyte.

[0002] In recent years, secondary batteries have attracted attention as an initiative to prevent global warming by reducing carbon dioxide emissions. Among these, solid-state batteries using sulfide solid electrolytes are attracting particular attention. Solid-state batteries using sulfide solid electrolytes do not use flammable organic solvents, which allows for the simplification of safety devices and offers advantages in terms of manufacturing cost and productivity. Furthermore, this type of solid electrolyte is advantageous from the standpoint of improving safety and durability, as ions other than lithium ions do not move within the electrolyte, thus preventing side reactions caused by anion movement.

[0003] Solid electrolytes used in solid-state batteries are required to have the highest possible conductivity and electrochemical stability. From this perspective, the applicant previously proposed Li ７ PS ６ It has a structural framework and its composition formula is Li, in which part of the P is replaced with Si. ７＋ｘ P １－ｙ Si ｙ S ６ We proposed a sulfide solid electrolyte represented by the formula (wherein x is between -0.6 and 0.6, and y is between 0.1 and 0.6) (see Patent Document 1).

[0004] Japanese Patent Publication No. 2013-137889

[0005] Incidentally, one of the challenges of solid-state batteries is that when the positive electrode active material containing oxygen comes into contact with the sulfide solid electrolyte, a reaction occurs, generating high-resistance decomposition products at the interface between the two, thereby increasing the interfacial resistance of the battery. This reaction is thought to be an exchange reaction between the oxygen element contained in the positive electrode active material and the sulfur element contained in the sulfide solid electrolyte. This exchange reaction may also occur in the sulfide solid electrolyte described in Patent Document 1 mentioned above, and is more pronounced in sulfide solid electrolytes with poor oxidation resistance.

[0006] Therefore, the object of the present invention is to provide a sulfide solid electrolyte having excellent oxidation resistance.

[0007] The present invention provides a sulfide solid electrolyte containing lithium (Li), silicon (Si), phosphorus (P), sulfur (S), and oxygen (O), with a halogen content of 5.4% by mass or less.

[0008] The present invention also provides a positive electrode mixture comprising the sulfide solid electrolyte and a positive electrode active material.

[0009] Furthermore, the present invention provides a solid-state battery comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, wherein the positive electrode layer contains the sulfide solid electrolyte and a positive electrode active material.

[0010] Figure 1 shows the X-ray diffraction patterns of the sulfide solid electrolytes obtained in each example and Comparative Example 2. Figure 2(a) shows the impedance measurement results after storing the solid batteries containing the sulfide solid electrolytes obtained in Example 4 and Comparative Examples 1 and 2 at high temperatures in a charged state, and Figure 2(b) shows the discharge curve after storing the solid batteries under the same conditions.

[0011] The present invention will be described below based on its preferred embodiments. [Solid Electrolyte] The present invention relates to a sulfide solid electrolyte. The sulfide solid electrolyte of the present invention contains lithium (Li), silicon (Si), phosphorus (P), sulfur (S), and oxygen (O) as constituent elements. The sulfide solid electrolyte of the present invention may further contain halogen elements as constituent elements, or may not contain them. Examples of halogen elements include at least one selected from the group consisting of chlorine (Cl), bromine (Br), iodine (I), and fluorine (F).

[0012] The sulfide solid electrolyte of the present invention is based on a sulfide solid electrolyte containing Li element, P element and S element, wherein part of the P element in the sulfide solid electrolyte is substituted with Si element, and part of the S element is substituted with O element. The present inventors have found that a sulfide solid electrolyte that contains Li element, P element and S element, and has a limited content of halogen elements has high oxidation resistance. Furthermore, the present inventors have found that, in a sulfide solid electrolyte containing Li element, P element and S element with a limited halogen element content, by substituting part of P element with Si element and substituting part of S element with O element, the oxidation resistance of the sulfide solid electrolyte can be further improved, and thus completed the present invention.

[0013] As described above, in the present invention, the amount of halogen elements contained in the sulfide solid electrolyte is limited. The reason therefor is as follows. Since halogen ions have monovalent charge, the electrical restraint on Li ions (Li ＋ ) is stronger for S ions (S ２－ ) and O ions (O ２－ ), which have divalent charge, than for halogen ions. Therefore, by reducing the amount of halogen elements contained in the sulfide solid electrolyte and increasing the amount of S element or O element, the bonding between atoms in the crystal structure of the sulfide solid electrolyte can be strengthened. As a result, the oxidation resistance of the sulfide solid electrolyte is improved. From this viewpoint, the smaller the amount of halogen elements contained in the sulfide solid electrolyte of the present invention is, the more preferable it is. Specifically, from the viewpoint of improving oxidation resistance, it is advantageous that the amount of halogen elements contained in the sulfide solid electrolyte is, for example, 5.4 mass% or less. From this viewpoint, the halogen element content is preferably, for example, 2.5 mass% or less, more preferably 0.3 mass% or less, and still more preferably 0.03 mass% or less. The amount of halogen elements contained in the sulfide solid electrolyte may be substantially zero. That is, the sulfide solid electrolyte may be substantially free of halogen elements. The amount of halogen elements contained in the sulfide solid electrolyte can be measured by, for example, ion chromatography, ICP emission spectroscopy, titration using silver ions, or the like.

[0014] When the sulfide solid electrolyte of the present invention is substantially free of halogen elements, the sulfide solid electrolyte has compositional formula (I): Li ａ Si ｂ P ｃ S ｄ O ｅ It is preferable from the viewpoint of improving oxidation resistance that it be expressed as follows: In formula (I), a represents a number between 10 and 28, b represents a number greater than 0 and less than 3.5, c represents a number greater than 0 and less than 2.8, d represents a number between 12 and 21, and e represents a number greater than 0 and less than or equal to 9.

[0015] From the viewpoint of further improving the oxidation resistance of the sulfide solid electrolyte of the present invention, it is preferable that in formula (I), a is 13 or more, particularly 16 or more, and especially 19 or more. It is also preferable that a is 27 or less, particularly 24 or less, and especially 21 or less. From the same viewpoint as above, it is preferable that in formula (I), b is 0.25 or more, particularly 0.5 or more, and especially 0.9 or more. It is also preferable that b is 3.0 or less, particularly 2.0 or less, and especially 1.1 or less. From the same viewpoint as above, it is preferable that in formula (I), c is 0.5 or more, particularly 1.0 or more, and especially 1.8 or more. It is also preferable that c is 2.6 or less, particularly 2.4 or less, and especially 2.2 or less. From the same viewpoint as above, it is preferable that in formula (I), d is 13 or more, particularly 15 or more, and especially 16 or more. It is also preferable that d is 20 or less, particularly 18 or less, and especially 17 or less. From the same viewpoint as described above, it is preferable that e in formula (I) is 0.025 or more, particularly 0.05 or more, and especially 0.075 or more. Furthermore, it is preferable that e is 5 or less, particularly 2 or less, and especially 0.5 or less. In order to determine the values ​​of a, b, c, d, and e in the composition formula represented by formula (I), the sulfide solid electrolyte can be subjected to elemental analysis. Of the elements constituting the sulfide solid electrolyte, Li, Si, S, and P can be subjected to elemental analysis by ICP emission spectrometry. For O, elemental analysis can be performed by inert gas fusion-infrared absorption spectrometry.

[0016] The sulfide solid electrolyte of the present invention is preferably crystalline. In particular, if the solid electrolyte contains a crystalline phase having an argyrodite-type crystal structure, it is advantageous from the viewpoint of further increasing the oxidation resistance and lithium ion conductivity of the sulfide solid electrolyte.

[0017] Argyrodite crystal structure is defined by the chemical formula: Ag ８ GeS ６ This is the crystalline structure of a group of compounds derived from the mineral represented by [the given symbol]. Whether or not a sulfide solid electrolyte has a crystalline phase with an argyrodite-type crystalline structure can be confirmed by X-ray diffraction measurements. For example, in the diffraction pattern measured by XRD using CuKα1 rays, the crystalline phase with an argyrodite-type crystalline structure shows characteristic diffraction peaks at 2θ = 15.4°±1.0°, 17.8°±1.0°, 25.3°±1.0°, 29.8°±1.0°, 31.1°±1.0°, and 44.6°±1.0°. For identifying diffraction peaks derived from the argyrodite-type crystalline structure, for example, the data in PDF number 00-034-0688 can be used.

[0018] The sulfide solid electrolyte of the present invention may or may not have crystalline phases other than the argyrodite type crystal structure. In particular, the sulfide solid electrolyte of the present invention preferably contains a crystalline phase having an argyrodite type crystal structure as the main phase. In this specification, "main phase" refers to the phase that has the largest proportion of the total amount of all crystalline phases constituting the solid electrolyte. Therefore, the content of the crystalline phase having an argyrodite type crystal structure is preferably, for example, 60% by mass or more, and more preferably 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more, relative to all crystalline phases constituting the solid electrolyte. The proportion of crystalline phases can be measured, for example, by XRD. By having a crystalline phase having an argyrodite type crystal structure as the main phase, lithium ion conductivity can be effectively increased, and consequently, the performance of the battery containing the solid electrolyte can be improved, particularly the output characteristics can be further improved.

[0019] When the sulfide solid electrolyte of the present invention has a crystalline phase having an algyrodite-type crystal structure as the main phase, the secondary phase may be, for example, lithium phosphate (Li ３ PO４ ) and silicon dioxide (SiO ２ Examples include the following. When lithium phosphate and silicon dioxide are included as subphases in the sulfide solid electrolyte of the present invention, the proportion of these subphases in the sulfide solid electrolyte depends on the amount to which S element is substituted by O element. Generally speaking, as the amount of substitution by O element increases, the proportion of subphases in the sulfide solid electrolyte tends to increase.

[0020] When lithium phosphate is included as a secondary phase in the sulfide solid electrolyte of the present invention, a diffraction peak P is observed at the position 2θ = 22.32° ± 0.04 in X-ray diffraction measurements using CuKα1 rays. ａ The intensity of I ａ Assuming this, the diffraction peak P is observed at the position 2θ = 29.78° ± 0.01. ｍ The intensity of I ｍ And the background intensity is set to I ０ When that happens, (I ａ -I ０ ) / (I ｍ -I ０ A value of ) of 0.15 or less is preferable from the viewpoint of improving the oxidation resistance of the sulfide solid electrolyte. Diffraction peak P ａ This is the main peak originating from lithium phosphate. Diffraction peak P ｍ This is the main peak derived from the argyrodite crystal structure. From the viewpoint of further improving the oxidation resistance of the sulfide solid electrolyte of the present invention, (I ａ -I ０ ) / (I ｍ -I ０ The value of (I) is preferably 0.11 or less, more preferably 0.05 or less, and even more preferably 0.03 or less. From the same viewpoint as above, ａ -I ０ ) / (I ｍ -I ０ The value of ) is preferably 0.01 or higher, more preferably 0.015 or higher, and even more preferably 0.02 or higher. The method for X-ray diffraction measurement targeting sulfide solid electrolytes will be explained in the examples described later.

[0021] When the sulfide solid electrolyte of the present invention includes a crystalline phase having an argyrodite-type crystal structure, the S element present in the argyrodite-type crystal structure is PS. ４ ３－ The S element and PS that make up the unit ４ ３－ There are S elements that do not constitute a unit. ４ ３－ The unit is known as the main unit structure of the argyrodite type crystal structure. In this invention, any of the S elements may be substituted with O elements. For example, PS ４ ３－ It is preferable, from the viewpoint of further improving the oxidation resistance of the solid electrolyte, that some of the sulfur (S) elements constituting the unit are replaced with oxygen (O) elements. ４ ３－ A specific example of a unit in which some of the S elements are replaced by O elements is, for example, PS ３ O ３－ PS ２ O ２ ３－ and PSO ３ ３－ (Hereafter, these three structures will be referred to as "Derived PS" ４ ３－ Also called a "unit." ) is an example. In this case, the solid electrolyte of the present invention includes derived PS ４ ３－ The presence of the unit is preferable from the viewpoint of further improving the oxidation resistance of the solid electrolyte. The solid electrolyte of the present invention is derived from PS ４ ３－ The present invention may have at least one of the units, any two of the units, or three units. The sulfide solid electrolyte of the present invention is PS ４ ３－ While there are also S elements that do not constitute a unit (hereinafter also referred to as "free S elements"), it is preferable from the viewpoint of further improving the oxidation resistance of the solid electrolyte if the free S elements are substituted with O elements.

[0022] O atoms have a smaller ionic radius than S atoms. Therefore, the binding force on Li atoms is stronger with O atoms than with S atoms. As a result, PS ４ ３－ By substituting some of the sulfur (S) elements constituting the unit and / or some of the free sulfur (S) elements with oxygen (O) elements, the argyrodite-type crystal structure is stabilized, and the oxidation resistance of the sulfide solid electrolyte is improved. From this viewpoint, it is preferable that the sulfide solid electrolyte of the present invention contains more than a certain amount of oxygen. On the other hand, if the amount of oxygen contained in the solid electrolyte of the present invention is excessively large, it becomes difficult to maintain the argyrodite-type crystal structure, and the ionic conductivity of the solid electrolyte tends to decrease. From this viewpoint, there is an upper limit to the amount of oxygen contained in the solid electrolyte of the present invention.

[0023] The lattice constant of the sulfide solid electrolyte of the present invention is preferably 9.98 Å or less, and more preferably 9.96 Å or less. When the lattice constant is small, the distance between atoms constituting the crystal becomes small, and the restraining force between atoms becomes large. As a result, the oxidation resistance of the sulfide solid electrolyte is improved.

[0024] When the sulfide solid electrolyte of the present invention includes a crystalline phase having an argyrodite-type crystal structure, PS ４ ３－ In this unit, some of the P elements are substituted with Si elements. In a sulfide solid electrolyte containing Li, P, S, and halogen elements, limiting the amount of halogen elements makes it impossible to maintain the argyrodite crystal structure (space group: F-43m). As a result, the ionic conductivity of the sulfide solid electrolyte decreases. On the other hand, even if the amount of halogen elements is limited, the argyrodite crystal structure (space group: F-43m) can be maintained by substituting some of the P elements with Si elements. This makes it possible to maintain high ionic conductivity while improving oxidation resistance in the sulfide solid electrolyte.

[0025] The inventors' research has shown that reducing the amount of halogen elements in a sulfide solid electrolyte, substituting some of the sulfur elements with oxygen elements, and substituting some of the phosphorus elements with silicon elements significantly improves oxidation resistance, even with trace amounts of oxygen and silicon substitution. Furthermore, the inventors' research has shown that by using only trace amounts of oxygen substitution, it is possible to improve oxidation resistance while maintaining the ionic conductivity of the solid electrolyte at a level comparable to that of sulfide solid electrolytes that are not substituted with oxygen.

[0026] Furthermore, the inventors' investigations revealed that in the sulfide solid electrolyte of the present invention, substituting the sulfur element with the oxygen element shifts the peak originating from the P-S bond in the Raman spectrum to a lower wavenumber than in the case where the sulfur element is not substituted. Surprisingly, it was also found that the sulfide solid electrolyte with the shifted peak to the lower wavenumber side exhibits improved oxidation resistance. This indicates that the distance between P and S atoms increases. Therefore, substituting the S element in the sulfide solid electrolyte with the O element, which has a smaller ionic radius, increases the distance between P and S atoms. As a result, it is presumed that the distance between the S atom and the Li atom adjacent to the S atom (S-Li distance) decreases. This increases the binding force of the S atom on the Li atom, improving the oxidation resistance of the sulfide solid electrolyte.

[0027] When the sulfide solid electrolyte of the present invention is subjected to Raman spectroscopy, it yields a reading of 400 cm⁻¹. －１ 423cm －１ A peak is observed in the wavenumber range below 402 cm⁻¹. From the viewpoint of further improving the oxidation resistance of the sulfide solid electrolyte of the present invention, the peak of the Raman spectrum is 402 cm⁻¹. －１ It is preferable to observe the above, 404 cm －１ It is even more preferable to observe the above, at 408 cm. －１It is even more preferable to observe the above. This is because if the distance between P and S becomes too large due to a low wavenumber shift of the peak, it is expected that the ionic conductivity will decrease due to the collapse of the crystal structure of the sulfide solid electrolyte, such as the argyrodite type crystal structure. In contrast, by setting the peak range to the above range, it is expected that the ionic conductivity of the sulfide solid electrolyte can be maintained. From the same viewpoint as above, the Raman spectrum peak is 420 cm⁻¹. －１ Preferably, it is observed as follows: 416 cm －１ It is even more preferable to observe the following: 412 cm －１ The following observations are even more preferable. The method for measuring the Raman spectrum will be explained in the examples described later.

[0028] As described above, when a portion of the sulfur element in a sulfide solid electrolyte is replaced with oxygen, even a trace amount of oxygen substitution significantly contributes to improving oxidation resistance. Specifically, in the sulfide solid electrolyte of the present invention, the molar ratio of oxygen to sulfur element (O / S) may be 0.1 or less, 0.05 or less, or 0.01 or less. Furthermore, the molar ratio of oxygen to sulfur element (O / S) may be greater than 0, 0.001 or more, 0.002 or more, or 0.005 or more. The method for measuring the molar ratio (O / S) will be explained in the examples described later.

[0029] The sulfide solid electrolyte of the present invention has a volume cumulative particle size D at 50% of the cumulative volume, as measured by laser diffraction scattering particle size distribution analysis. ５０ The particle size is preferably less than 50.0 μm, more preferably 35.0 μm or less, and even more preferably 20.0 μm or less. Having such a particle size increases the contact points and contact area between the sulfide solid electrolyte and the active material particles, which effectively improves the input / output characteristics of the battery. Particle size D ５０There is no particular limit to the lower limit of the particle size; for example, it may be 0.1 μm or larger, or 0.2 μm or larger, or 0.3 μm or larger. Having such a particle size suppresses an excessive increase in the surface area of ​​the sulfide solid electrolyte, thereby suppressing an increase in resistance. Furthermore, mixing with the active material becomes easier. Particle size D ５０ The particle size distribution can be determined by the laser diffraction scattering particle size distribution method. For example, using an automatic sample feeder for laser diffraction particle size distribution analyzers ("Microtorac SDC" manufactured by Nikkiso Co., Ltd.), a sulfide solid electrolyte is added to toluene, and after irradiating with 40W ultrasound for 360 seconds at a flow rate of 40%, the particle size distribution is measured using the "MT3000II" laser diffraction particle size distribution analyzer manufactured by Nikkiso Co., Ltd. The particle size D can be determined from the obtained volume-based particle size distribution chart. ５０ Measure.

[0030] The solid electrolyte of the present invention has lithium ion conductivity in a solid state. Preferably, the solid electrolyte has a lithium ion conductivity of 1.5 mS / cm or more at room temperature, i.e., 25°C; more preferably, a lithium ion conductivity of 2.0 mS / cm or more; and even more preferably, a lithium ion conductivity of 2.5 mS / cm or more. The lithium ion conductivity can be measured by the following method: The sulfide solid electrolyte is subjected to a test of approximately 6 t / cm in a glove box purged with sufficiently dry Ar gas (dew point -60°C or below). ２ A sample for measuring lithium ion conductivity is prepared by applying a load and uniaxial compression molding, consisting of pellets with a diameter of 10 mm and a thickness of approximately 0.5 mm to 8 mm. The lithium ion conductivity of the sample is measured by electrochemical impedance spectroscopy by connecting it to a potentiometer / galvanostat (VSP-300, BioLogic). The measurement is performed by AC impedance spectroscopy under conditions of a temperature of 25°C and a frequency of 0.1 Hz to 1 MHz.

[0031] [Method for Manufacturing Sulfide Solid Electrolytes] Next, a preferred method for manufacturing the sulfide solid electrolyte of the present invention will be described. The sulfide solid electrolyte can preferably be manufactured by a solid-phase reaction in which a raw material composition is heated and sintered. The raw material composition is a mixture of raw material powders containing each of the above-mentioned elements that constitute the solid electrolyte. The raw material composition contains one or more compounds containing at least one of Li, P, S, O, and Si. The raw material powders may be, for example, compounds containing Li, compounds containing S, compounds containing P, compounds containing O and Si, compounds containing Li and O, and compounds containing S and Si. In addition, Si element and S element alone can be used as the raw material powder.

[0032] In the raw material powder, one compound may contain at least two or more elements from among Li, P, S, O, and Si. For example, as the raw material powder, compounds containing Li and S, compounds containing P and S, compounds containing P and O, compounds containing Li and O, compounds containing Si and O, and compounds containing S and Si can be used. As a compound containing Li and S, for example, lithium sulfide can be used. As a compound containing P and S, for example, diphosphorus trisulfide (P ２ S ３ ) and phosphorus pentasulfide (P ２ S ５ Phosphorus sulfides such as ) can be used. Examples of compounds containing elements P and O include phosphorus pentoxide (P ２ O ５ ) and the like can be used. Examples of compounds containing Si and O elements include silicon dioxide (SiO ２ ) and the like can be used. Examples of compounds containing Li and O elements include lithium oxide (Li ２ O) and others can be used. Examples of compounds containing S and Si elements include silicon monosulfide (SiS) and silicon disulfide (SiS ２ Silicon sulfide such as ) can be used.

[0033] Each raw material powder may be subjected to a pulverization step to adjust the particle diameter to a predetermined size before being mixed. For pulverization, a media agitation mill apparatus such as a ball mill or a bead mill can be used, for example. Next, the raw material powders are mixed to prepare a raw material composition. It is preferable to use a media agitation mill apparatus for mixing.

[0034] After preparing the raw material composition, it is subjected to a firing step to cause a solid-phase reaction, thereby obtaining a fired product. As the firing atmosphere, an inert gas atmosphere such as an argon atmosphere or a nitrogen atmosphere, or a hydrogen sulfide atmosphere can be used, for example. In derived PS in the solid electrolyte ４ ３－ From the viewpoint of successfully generating the unit, it is preferable to employ an inert gas atmosphere, for example, an argon atmosphere.

[0035] From the viewpoint of reliably causing the solid-phase reaction of the raw material composition, the firing temperature is preferably, for example, 200°C or higher, more preferably 300°C or higher, still more preferably 350°C or higher, and even more preferably 400°C or higher. On the other hand, considering industrial producibility and economic efficiency, the firing temperature is preferably, for example, 900°C or lower, more preferably 800°C or lower, and still more preferably 750°C or lower. Firing may be single-stage firing in which the temperature is continuously increased from room temperature to the target firing temperature and the firing temperature is maintained for a certain period of time, or may be multi-stage firing in which a period for keeping the temperature constant is provided between two or more temperature rising periods.

[0036] The firing time is not critical, and any time that allows obtaining a fired product of the target composition is acceptable. Specifically, it is preferable that the firing time is of a degree sufficient to allow sufficient solid-phase reaction of the raw material composition to occur. The firing time may be, for example, 30 minutes or longer, 2 hours or longer, or 3 hours or longer. On the other hand, the firing time may be, for example, 10 hours or shorter, or 5 hours or shorter. When multi-stage firing is performed, it is preferable that the firing time in each stage is independently within the above range.

[0037] After calcination, the calcined material may be crushed or pulverized as needed, and further classified as necessary. This will yield the desired solid electrolyte powder.

[0038] [Electrode mixture and solid battery] The solid electrolyte obtained in this manner can be used alone or in mixture with other solid electrolytes. For example, the solid electrolyte of the present invention can be used as a material constituting a lithium battery, such as a solid electrolyte layer, a positive electrode layer, or a negative electrode layer.

[0039] Specifically, the solid electrolyte of the present invention can be used in a battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive and negative electrode layers. In other words, the solid electrolyte can be used in so-called solid batteries. More specifically, it can be used in lithium solid batteries. The lithium solid battery may be a primary battery or a secondary battery. There are no particular restrictions on the shape of the battery; for example, laminated, cylindrical, and prismatic shapes can be used. The term "solid battery" includes not only solid batteries that do not contain any liquid or gel-like substances as an electrolyte, but also embodiments that contain, for example, 50% by mass or less, 30% by mass or less, or 10% by mass or less of a liquid or gel-like substance as an electrolyte.

[0040] The sulfide solid electrolyte of the present invention can be used together with an active material to constitute an electrode mixture. The proportion of the solid electrolyte in the electrode mixture is typically 10% by mass or more and 50% by mass or less. The electrode mixture may contain other materials such as conductive materials as needed. An electrode layer, such as a positive electrode layer or a negative electrode layer, can be produced by mixing the electrode mixture, a binder, and a solvent to make a paste, applying it to a current collector such as aluminum foil, and drying it.

[0041] As the positive electrode material constituting the positive electrode layer, any positive electrode material used as the positive electrode active material in lithium-ion batteries can be used as appropriate. For example, positive electrode active materials containing lithium, specifically spinel-type lithium transition metal oxides and lithium transition metal oxides having a layered structure can be used. By using a high-voltage positive electrode material, the energy density can be improved. In addition to the positive electrode active material, the positive electrode material may also contain a conductive material or other materials.

[0042] As the negative electrode material constituting the negative electrode layer, any negative electrode material used as the negative electrode active material in lithium-ion batteries can be used as appropriate. Since the solid electrolyte of the present invention is electrochemically stable, it can withstand lithium metal or a low potential comparable to lithium metal (approximately 0.1 V vs Li ＋ Carbon-based materials such as graphite, artificial graphite, natural graphite, and non-graphitizable carbon (hard carbon), which are charged and discharged using lithium (Li), can be used as negative electrode materials. This can significantly improve the energy density of solid-state batteries. Silicon or tin, which are promising as high-capacity materials, can also be used as active materials. In addition to the negative electrode active material, conductive materials may be included, or other materials may be included.

[0043] In particular, the positive electrode mixture containing the sulfide solid electrolyte and positive electrode active material of the present invention exhibits high oxidation resistance of the sulfide solid electrolyte. Therefore, even when the sulfide solid electrolyte comes into contact with the positive electrode active material in the positive electrode mixture, an exchange reaction between sulfur in the sulfide solid electrolyte and oxygen in the positive electrode mixture is less likely to occur. As a result, the solid-state battery containing the positive electrode mixture has the advantages of suppressing an increase in resistance and improving charge-discharge cycle characteristics.

[0044] The sulfide solid electrolyte of the present invention can also be contained in a solid electrolyte layer. In this case, the solid electrolyte layer can be produced, for example, by a method of dropping a slurry composed of a sulfide solid electrolyte, a binder and a solvent onto a substrate and scraping it with a doctor blade or the like, a method of cutting with an air knife after bringing the substrate and the slurry into contact, a method of forming a coating film by a screen printing method or the like, and then removing the solvent through heating and drying, or the like. Alternatively, a powdery solid electrolyte may be formed into a green compact by pressing or the like, and then appropriately processed to produce the solid electrolyte layer. The thickness of the solid electrolyte layer is typically preferably 5 µm or more and 300 µm or less in view of the balance between short-circuit prevention and volumetric capacity density, and more preferably 10 µm or more and 100 µm or less among them.

[0045] With respect to the above-described embodiments, the present invention further discloses the following sulfide solid electrolytes, positive electrode mixtures and solid batteries. [1] A sulfide solid electrolyte comprising lithium (Li) element, silicon (Si) element, phosphorus (P) element, sulfur (S) element and oxygen (O) element, wherein the content of a halogen element is 5.4% by mass or less. [2] In Raman spectrum measurement, 400 cm －１ or more and 423 cm －１ The sulfide solid electrolyte according to [1], wherein a peak is observed in a wavenumber range of less than . [3] The sulfide solid electrolyte according to [1] or [2], comprising a crystal phase having an argyrodite-type crystal structure. [4] The sulfide solid electrolyte according to any one of [1] to [3], wherein a molar ratio O / S of oxygen (O) element to sulfur (S) element is more than 0 and 0.13 or less. [5] In X-ray diffraction measurement using CuKα1 radiation, the intensity of a diffraction peak observed at a position of 2θ = 22.32° ± 0.04 is defined as I ａ , the intensity of a diffraction peak observed at a position of 2θ = 29.78° ± 0.01 is defined as I ｍ , and the background intensity is defined as I ０ , then (I ａ -I ０ ) / (I ｍ -I ０ ) The sulfide solid electrolyte according to any one of [1] to [4], wherein the value of is 0.15 or less. [6] Composition formula (I): Li ａ Si ｂ Pｃ S ｄ O ｅ A sulfide solid electrolyte as described in any one of [1] to [5], represented by formula (I). In formula (I), a represents a number between 10 and 28, b represents a number greater than 0 and less than 3.5, c represents a number greater than 0 and less than 2.8, d represents a number between 12 and 21, and e represents a number greater than 0 and less than or equal to 9. [7] A positive electrode mixture comprising a sulfide solid electrolyte as described in any one of [1] to [6] and a positive electrode active material. [8] A solid-state battery comprising a positive electrode layer, a negative electrode layer and a solid electrolyte layer, wherein the positive electrode layer comprises a sulfide solid electrolyte as described in any one of [1] to [6] and a positive electrode active material. [9] Use of a sulfide solid electrolyte as a component constituting a positive electrode mixture as described in any one of [1] to [6].

[0046] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. Unless otherwise specified, "%" means "mass%".

[0047] [Example 1] (1) Production of sulfide solid electrolyte Lithium sulfide (Li ２ S) Powder, phosphorus pentasulfide (P ２ S ５ ) powder, sulfur (S) powder, silicon (Si) powder, and silicon dioxide (SiO ２ The following powders were used as raw materials. Each raw material powder was weighed to a total of 5 g and mixed to achieve the composition shown in Table 1 below. Heptane was then added to prepare a slurry. This slurry was placed in a zirconia container and set in a planetary ball mill apparatus. Zirconia balls with a diameter of 5 mm were used as the grinding media. The ball mill apparatus was operated at 100 rpm, and wet mixing was carried out for 10 hours. The heptane was removed from the slurry after mixing by vacuum drying at room temperature. The raw material composition was thus obtained.

[0048] The raw material composition was calcined to obtain a calcined product. The calcination was carried out using a tubular electric furnace. During the calcination, 100% pure argon gas was circulated in the electric furnace at a flow rate of 0.5 L / min. The calcination was carried out at 700°C for 4 hours. In this way, a calcined product was obtained.

[0049] The resulting calcined material was crushed in a mortar to obtain a powder. This powder was then pulverized using a planetary ball mill. Zirconia balls with a diameter of 5 mm were used as the pulverizing media. The container was also made of zirconia. Heptane was used as the solvent. The ball mill was operated at 100 rpm for 3 hours. The solvent was removed from the resulting slurry by vacuum drying at room temperature. In this way, a sulfide solid electrolyte powder was obtained. The lattice constant obtained from the analysis of Example 1 was 9.951 Å.

[0050] [Examples 2 to 10] Each raw material powder used in Example 1 was weighed and mixed to obtain the composition shown in Table 1 below. A sulfide solid electrolyte powder was obtained in the same manner as in Example 1. The lattice constants obtained by analysis of Examples 2 to 10 were: Example 2: 9.951 Å, Example 3: 9.952 Å, Example 4: 9.952 Å, Example 5: 9.951 Å, Example 6: 9.951 Å, Example 7: 9.952 Å, Example 8: 9.956 Å, Example 9: 9.958 Å, and Example 10: 9.960 Å.

[0051] [Comparative Example 1] Lithium sulfide (Li ２ S) Powder, phosphorus pentasulfide (P ２ S ５ ) powder, lithium chloride (LiCl) powder, and lithium bromide (LiBr) powder were used as raw material powders. Each raw material powder was weighed and mixed to the composition shown in Table 1 below. A raw material composition was obtained by wet mixing and vacuum drying in the same manner as in Example 1. The raw material composition was calcined using a tubular electric furnace. A calcined product was obtained by flowing 100% pure argon gas through the electric furnace at a flow rate of 0.5 L / min and performing the process at 500°C for 4 hours. A sulfide solid electrolyte powder was obtained in the same manner as in Example 1, except for the above.

[0052] [Comparative Example 2] Lithium sulfide (Li ２ S) Powder, phosphorus pentasulfide (P ２ S ５Sulfur (S) powder and silicon (Si) powder were used as raw material powders. Each raw material powder was weighed and mixed to achieve the composition shown in Table 1 below. A sulfide solid electrolyte powder was obtained in the same manner as in Example 1.

[0053] [Evaluation] [Raman Spectroscopy Measurement] Raman spectra were measured for the sulfide solid electrolytes obtained in the examples and comparative examples using XploRA PLUS (manufactured by Horiba, Ltd.) without exposure to air. The measurement conditions were as follows: Laser wavelength: 532 nm Grating: 1800 Wavenumber range: 100 cm －１ ~2000cm －１ • Exposure time: 30 seconds • Number of integrations: 5 • Objective lens magnification: 100x • Slit width: 50 μm • Confocal hole: 100 μm From this Raman spectroscopy measurement, wavenumber 400 cm －１ 423cm －１ The wavenumber positions of peaks observed in the range less than were determined.

[0054] [X-ray Diffraction Measurement] X-ray diffraction measurements were performed on the sulfide solid electrolytes obtained in each example and Comparative Example 2 using a Malvern Panalogical tabletop X-ray diffractometer "Aeris" under non-exposure to air. The measured X-ray diffraction patterns are shown in Figure 1. The measurement conditions were as follows: ・Source: CuKα ・Tube voltage: 40kV ・Tube current: 15mA ・Measurement method: Focusing method (reflection method) ・Detector: One-dimensional semiconductor detector ・Ingress solar slit: Solar slit 0.02rad ・Longitudinal limiting slit: 20mm ・Receiving solar slit: 0.02rad ・Ingress slit: 1 / 2° ・Receiving slit: Open ・Measurement range: 2θ = 10 to 60° ・Step width: 0.01° ・Scan speed: 1.67° / min Furthermore, the background intensity obtained from the Kapton film of the non-exposure holder was subtracted before analyzing the measurement results.

[0055] [Analysis Method] The X-ray diffraction patterns obtained by X-ray diffraction measurements were loaded into HighScore Plus, and the lattice constants were calculated by performing Rietveld analysis. Peak profiling was refined using a segmented pseudo-Voight function for the peak shape and Finger, Cox, and Jephcoat for the asymmetric function type. ICDD 04-024-1044 was used as the analysis card.

[0056] [Reaction start temperature with manganese dioxide] Lithium spinel-type manganate (LiMn), known as a positive electrode active material for lithium batteries. ２ O ４ As a model compound for ), manganese dioxide (MnO ２ The reactivity of manganese dioxide with the sulfide solid electrolytes obtained in the examples and comparative examples was evaluated using the following method. Manganese dioxide simulates the positive electrode in a charged state obtained by desorption of lithium ions from spinel-type lithium manganate. Manganese dioxide (manufactured by Kojunkagaku Co., Ltd.) and the sulfide solid electrolyte were mixed in a mass ratio of 70:30 and sieved using a 53 μm sieve. 2 mg of the mixture below the sieve was packed into an aluminum pan and subjected to differential thermal analysis (DTA). The temperature range for differential thermal analysis was from 25°C to 500°C. Differential thermal analysis was performed using STA 2500 Regulus (manufactured by NETZSH). The heating rate was 10°C / min. The measurement atmosphere was nitrogen flow. The peak top temperature of the exothermic peak observed by differential thermal analysis was measured and this temperature was taken as the reaction start temperature with manganese dioxide. The higher the reaction initiation temperature, the less readily the sulfide solid electrolyte reacts with manganese dioxide, meaning the sulfide solid electrolyte has higher oxidation resistance.

[0057] [Battery Test] Solid-state batteries were prepared using the sulfide solid electrolytes obtained in Example 4 and Comparative Examples 1 and 2, following the procedure below. The battery characteristics of these solid-state batteries were measured after charging and storage at 90°C for one week using the following method. The results are shown in Figures 2(a) and (b) below. A positive electrode mixture powder was prepared by mixing the positive electrode active material (NCM), the sulfide solid electrolyte obtained in the Examples and Comparative Examples, and conductive carbon (VGCF), which is a conductive material, in a mass ratio of 70:27:3 using a mortar and pestle. A negative electrode active material (graphite powder) and solid electrolyte (Li ５．４ PS ４．４ Cl ０．８ Br ０．８ A negative electrode mixture powder was prepared by mixing ) and in a mortar in a mass ratio of 1:1. The lower opening of a polypropylene cylinder (opening diameter 10.5 mm, height 18 mm) with both top and bottom open was closed with a positive electrode (made of SUS), and a solid electrolyte (Li) was placed on top of it. ５．４ PS ４．４ Cl ０．８ Br ０．８ A solid electrolyte layer was formed by placing a material on top of the material, sealing it with a negative electrode (made of SUS), and then uniaxially pressing it at 180 MPa. Next, the negative electrode was temporarily removed, negative electrode mixture powder was placed on top of the solid electrolyte layer, and the negative electrode was sealed again. After that, the cylinder was inverted, the positive electrode was temporarily removed, positive electrode mixture powder was placed on top of the solid electrolyte layer, and the positive electrode was sealed again, and then uniaxially pressing it at 550 MPa was performed to produce a solid battery consisting of a three-layer structure of positive electrode mixture, solid electrolyte layer, and negative electrode mixture.

[0058] Charge and discharge tests were performed on the solid-state batteries obtained in this manner. Specifically, the solid-state batteries were placed in an environmental test chamber set to an ambient temperature of 25°C for charging and discharging. The solid-state batteries were charged at 0.1C with a constant current to 4.3V, and once 4.3V was reached, they were charged at a constant potential to 0.01C. Next, they were discharged at 0.1C with a constant current to 2.5V. This charge and discharge operation was repeated three times. After that, they were again charged at 0.1C with a constant current and constant potential to 4.3V. The charged solid-state batteries were placed in a constant temperature bath at 90°C and stored for one week. After one week, the solid-state batteries were removed and returned to room temperature (25°C), and then connected to a potentiometer / galvanostat (VSP-300, BioLogic), and the impedance was measured by electrochemical impedance spectroscopy. The results are shown in Figure 2(a). In this figure, the horizontal axis represents the real component Z of the impedance. ｒｅ This shows the imaginary component of impedance -Z on the vertical axis. ｉｍ The following is shown. After the solid battery was stored for one week and then returned to room temperature (25°C), it was placed in an environmental test chamber at 25°C and discharged at a constant current of 0.1C to 2.5V. Subsequently, it was charged at a constant current and constant potential of 0.1C to 4.3V, and then discharged at a constant current of 0.1C to 2.5V to measure the discharge capacity. The discharge curve is shown in Figure 2(b).

[0059]

[0060] As is clear from the results shown in Figure 1, the sulfide solid electrolytes obtained in each example have an argyrodite-type crystal structure. Furthermore, as is clear from the results shown in Table 1, the sulfide solid electrolytes obtained in each example have a high reaction initiation temperature with manganese dioxide and excellent oxidation resistance. This is supported by the fact that the solid battery obtained using the sulfide solid electrolyte of Example 4 has a low impedance and high discharge capacity, as shown in Figures 2(a) and (b).

[0061] The sulfide solid electrolyte of the present invention exhibits excellent oxidation resistance. This suppresses reactions at the interface with the positive electrode active material, and as a result, it can suppress the increase in the interfacial resistance of the battery.

Claims

1. A sulfide solid electrolyte containing lithium (Li), silicon (Si), phosphorus (P), sulfur (S), and oxygen (O), with a halogen content of 5.4% by mass or less.

2. Raman spectroscopy at 400 cm⁻¹ －１ 423cm －１ The sulfide solid electrolyte according to claim 1, wherein a peak is observed in the wavenumber range of less than 1.

3. The sulfide solid electrolyte according to claim 1, comprising a crystalline phase having an argyrodite-type crystal structure.

4. The sulfide solid electrolyte according to claim 1, wherein the molar ratio of oxygen (O) to sulfur (S) (O / S) is greater than 0 and less than or equal to 0.

13.

5. In X-ray diffraction measurement using CuKα1 ray, the intensity of the diffraction peak observed at a position of 2θ=22.32°±0.04 is I ａ , the intensity of the diffraction peak observed at a position of 2θ=29.78°±0.01 is I ｍ , and when the background intensity is I ０ , (I ａ -I ０ ) / (I ｍ -I ０ ) has a value of 0.15 or less, the sulfide solid electrolyte according to claim 1.

6. Composition formula (I): Li ａ Si ｂ P ｃ S ｄ O ｅ A sulfide solid electrolyte according to claim 1, represented by formula (I). In formula (I), a represents a number between 10 and 28, b represents a number greater than 0 and less than 3.5, c represents a number greater than 0 and less than 2.8, d represents a number between 12 and 21, and e represents a number greater than 0 and less than or equal to 9.

7. A positive electrode mixture comprising a sulfide solid electrolyte according to any one of claims 1 to 6 and a positive electrode active material.

8. A solid-state battery comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, wherein the positive electrode layer comprises a sulfide solid electrolyte according to any one of claims 1 to 6 and a positive electrode active material.

9. Use of the sulfide solid electrolyte according to any one of claims 1 to 6 as a component constituting a positive electrode mixture.

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