Sulfide solid electrolyte, method for producing same, and battery

Abstract

The purpose of the present invention is to suppress deterioration of a sulfide solid electrolyte containing a lithium (Li) element, a phosphorus (P) element, a sulfur (S) element, and a halogen (X) element, and a battery using the same. The sulfide solid electrolyte contains a lithium (Li) element, a phosphorus (P) element, a sulfur (S) element, and a halogen (X) element. The sulfide solid electrolyte has a peak in a range of 2θ = 20.66° ± 1.00° in an X-ray diffraction pattern measured by an X-ray diffraction device using CuKα 1 rays. In surface analysis by X-ray photoelectron spectroscopy, the peak top position of the spectrum of the P2p orbit is preferably 132.5 eV or more.

Description

Sulfide solid electrolyte, its manufacturing method, and battery

[0001] The present invention relates to a sulfide solid electrolyte, a method for producing the same, and a battery using the sulfide solid electrolyte.

[0002] In recent years, CO ２ Secondary batteries have been attracting attention as an effort to prevent global warming by reducing CO2 emissions. Among these, all-solid-state batteries using sulfide solid electrolytes synthesized using starting materials such as lithium sulfide have attracted attention. All-solid-state batteries using sulfide solid electrolytes do not use flammable organic solvents, which allows for simplified safety devices and offers advantages such as low manufacturing costs and productivity. Furthermore, this type of solid electrolyte is advantageous from the perspective of improving safety and durability, since ionic species other than lithium ions do not migrate within the electrolyte, preventing side reactions due to the migration of anions.

[0003] The present applicant has previously reported that a surface of a compound containing lithium, phosphorus, sulfur, and a halogen and having a cubic argyrodite-type crystal structure is coated with a compound containing lithium, phosphorus, and sulfur and having a non-argyrodite-type crystal structure, and the compound having a non-argyrodite-type crystal structure has the composition formula: Li ３ P.S. ４－Ｒ O Ｒ (0≦R<4) as the main phase of the sulfide solid electrolyte for lithium secondary batteries (Patent Document 1). ３ P.S. ４－Ｒ O Ｒ By coating the crystalline structure with the crystalline structure, moisture resistance can be imparted to the cubic argyrodite crystal structure, which has low water resistance, and there is an advantage in that generation of hydrogen sulfide can be suppressed.

[0004] US2019 / 0312304A1

[0005] In a lithium-ion battery using a sulfide solid electrolyte containing lithium, phosphorus, sulfur, and a halogen, when stored under conditions of high-voltage charging, particularly under conditions of high-temperature charging, the sulfide solid electrolyte may react with the active material and its coating components to produce a layer of reaction products and / or decomposition products. The formation of the layer of reaction products and / or decomposition products may impede the exchange of lithium ions between the solid electrolyte and the active material, or may result in partial degradation of the solid electrolyte, reducing the amount of solid electrolyte available for lithium ion exchange, resulting in battery degradation and an increase in internal resistance.

[0006] The present inventors have found that deterioration of battery performance can be suppressed by incorporating into a sulfide solid electrolyte a compound having a peak at a specific position in an X-ray diffraction pattern measured by an X-ray diffractometer using CuKα1 radiation.

[0007] The present invention has been made based on the above findings, and provides a sulfide solid electrolyte containing lithium (Li), phosphorus (P), sulfur (S), and a halogen (X), the sulfide solid electrolyte having a peak in the range of 2θ=20.66°±1.00° in an X-ray diffraction pattern measured with an X-ray diffractometer using CuKα1 radiation.

[0008] The present invention also provides a compound having an argyrodite-type crystal structure containing lithium (Li), phosphorus (P), sulfur (S), and a halogen (X), and a compound containing 0.1 to 7 mol% of P relative to the phosphorus (P) element contained in the compound. ２ O ５ and heating the pulverized product obtained in the wet-pulverized step at 150 to 350°C in an inert atmosphere.

[0009] Fig. 1 shows X-ray diffraction patterns of the sulfide solid electrolytes produced in Examples 1 to 4 and Comparative Example 1. Fig. 2 shows the P2p orbital spectrum in the XPS surface analysis of the sulfide solid electrolyte produced in Example 3. Fig. 3 shows the P2p orbital spectrum in the XPS surface analysis of the sulfide solid electrolyte produced in Comparative Example 1.

[0010] The present invention will be described below based on preferred embodiments. First, the sulfide solid electrolyte of the present invention will be described. The sulfide solid electrolyte of the present invention preferably contains lithium (Li), phosphorus (P), sulfur (S), and a halogen (X). In an X-ray diffraction pattern measured using an X-ray diffractometer with CuKα radiation, the sulfide solid electrolyte preferably has a peak (hereinafter also referred to as a "specific peak") in the range of 2θ = 20.66° ± 1.00°. The sulfide solid electrolyte of the present invention contains Li, phosphorus (P), sulfur (S), and a halogen (X). As long as the sulfide solid electrolyte has the specific peak and exhibits lithium ion conductivity, the type and composition of the sulfide solid electrolyte are not particularly limited and can be appropriately selected depending on the application, desired physical properties, and the like. Examples of the halogen (X) element include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). The halogen (X) element may be one of these elements or a combination of two or more of these elements.

[0011] The sulfide solid electrolyte containing lithium (Li), phosphorus (P), sulfur (S), and halogen (X) elements is preferably composed mainly of a compound containing lithium (Li), phosphorus (P), sulfur (S), and halogen (X). ２ S-P ２ S ５ -LiX (where "X" represents one or more halogen elements; the same applies hereinafter); Li ｘ Si ｙ P ｚ S ａ X ｗ (Preferably, 2.4<(x-y) / (y+z)<3.3, the S content is 55 to 73 mass%, the Si content is 2 to 11 mass%, and the halogen content is 0.02 mass% or more); Li ａ P.S.ｂ X ｃ (compounds having a crystalline phase of an argyrodite-type crystal structure) and the like. Among them, compounds having a crystalline phase of an argyrodite-type crystal structure are preferred because of their high ionic conductivity. Compounds containing lithium (Li), phosphorus (P), sulfur (S), and halogen (X) elements will be described later.

[0012] The present inventors have conducted extensive research into a configuration capable of preventing deterioration of a sulfide solid electrolyte containing lithium (Li), phosphorus (P), sulfur (S), and a halogen (X). As a result, they have found that a sulfide solid electrolyte having the specific peak can more effectively prevent deterioration of the sulfide solid electrolyte and a battery containing the same under high voltage charging conditions, compared to a sulfide solid electrolyte not having the specific peak. In addition, the sulfide solid electrolyte of the present invention has a structure in which Li is present on the surface of the sulfide solid electrolyte, as determined by X-ray photoelectron spectroscopy analysis described below. ４ P ２ O ７ The existence of a compound consisting of Li ４ P ２ O ７ is a stable compound. When the sulfide solid electrolyte of the present invention contains this stable compound, a battery containing this solid electrolyte can be prevented from reacting with the active material or a coating layer of the active material even when the battery is stored in a state charged at a high voltage, particularly when the battery is stored in a state charged at a high voltage at a high temperature. This makes it possible to suppress deterioration of the sulfide solid electrolyte and the battery containing it.

[0013] The sulfide solid electrolyte of the present invention has a peak intensity I of a peak (hereinafter also referred to as “peak A”) observed in the range of 2θ = 15.18 ° ± 1.00 ° in an X-ray diffraction pattern measured by an X-ray diffractometer using CuKα1 radiation. Ａ , the peak intensity I of a specific peak observed in the range of 2θ = 20.66 ° ± 1.00 ° Ｓ The ratio (I Ｓ / I Ａ) is preferably 0.25 or more. The peak A is one of the characteristic peaks in the preferred sulfide solid electrolyte of the present invention containing element (Li), element (P), element (S), and element (X). The peak intensity I Ａ Whereas, the intensity I of the specific peak Ｓ The ratio (I Ｓ / I Ａ ) is equal to or greater than the lower limit, deterioration of the sulfide solid electrolyte of the present invention and the battery containing the same can be effectively prevented. From this viewpoint, the ratio of the specific peak intensities (I Ｓ / I Ａ ) is more preferably 0.30 or more, and particularly preferably 0.38 or more. ｓ / I Ａ To calculate the background intensity, I Ｓ and I Ａ In the present invention, the value of 2θ=18.00° was used for the background intensity.

[0014] In Example 5 of the Patent Document 1, in order to suppress the generation of hydrogen sulfide due to a reaction with moisture, diphosphorus pentoxide is used to deposit Li on the surface of a compound having an argyrodite-type crystal structure. ３ P.S. １．５ O ２．５ In contrast, in the present invention, Li ３ P.S. ４－Ｒ O Ｒ Li, rather than sulfur-containing compounds such as ４ P ２ O ７ This product contains a compound consisting of lithium, phosphorus, and oxygen, and is completely different from the product of the invention described in Patent Document 1.

[0015] Specific peaks and peak intensity ratios (I Ｓ / I Ａ In order to obtain the sulfide solid electrolyte of the present invention having the above-mentioned structure, a suitable method for producing a sulfide solid electrolyte, which will be described later, may be adopted.

[0016] As described above, the present invention ４ P ２ O ７The existence of Li ４ P ２ O ７ is preferably present on the surface of the sulfide solid electrolyte. This makes it possible to further improve the effect of preventing deterioration of the sulfide solid electrolyte and the battery containing the sulfide solid electrolyte. ４ P ２ O ７ The presence of the sulfide solid electrolyte of the present invention can be confirmed by the P2p orbital spectrum in X-ray photoelectron spectroscopy (hereinafter also referred to as "XPS"). XPS is a measurement method that can analyze the constituent elements and their electronic states of the sample surface by measuring the photoelectron energy generated from the sample surface by irradiating the sample with X-rays. Therefore, the chemical state of the surface of the sulfide solid electrolyte of the present invention can be observed by XPS. Specifically, the sulfide solid electrolyte of the present invention preferably has a peak top position of 132.5 eV or higher in the P2p orbital spectrum in surface analysis by XPS. In the P2p orbital spectrum in XPS, pyrophosphate groups (P ２ O ７ On the other hand, the peak position of the P2p orbital spectrum derived from a compound containing (Li), phosphorus (P), sulfur (S) and halogen (X), which is the main component of the sulfide solid electrolyte, for example, a compound having an argyrodite crystal structure, is less than 132.5 eV. Therefore, specifying the peak top position of the P2p orbital spectrum to be 132.5 eV or more is effective in preventing the formation of Li on the surface. ４ P ２ O ７ This further demonstrates the existence of

[0017] From the above viewpoint, in the sulfide solid electrolyte of the present invention, in surface analysis by XPS, the peak top position of the P2p orbital spectrum is preferably 132.5 eV or more, and particularly preferably 133.0 eV or more.

[0018] The sulfide solid electrolyte of the present invention is preferably an aggregate of particles. In this case, from the viewpoint of suppressing an increase in resistance due to an increase in surface area and from the viewpoint of facilitating mixing with an active material, the sulfide solid electrolyte is preferably an aggregate of particles having a volume cumulative particle size D at 50% cumulative volume as measured by a laser diffraction / scattering particle size distribution measurement method. ５０ From the viewpoint of suppressing adhesion, aggregation, and particle size growth due to heating, the volume cumulative particle size D ５０ is preferably 250 μm or less, more preferably 100 μm or less, even more preferably 50 μm or less, still more preferably 20 μm or less, still more preferably 10 μm or less, and particularly preferably 3 μm or less.

[0019] The sulfide solid electrolyte of the present invention has ionic conductivity in a solid state. The ionic conductivity of the solid electrolyte of the present invention is, for example, 1.3 × 10 at room temperature, i.e., 25°C. －４ S / cm or more, and －４ S / cm or more is more preferable, and 7.5×10 －４ S / cm or more, especially 1.3 × 10 －３ The ionic conductivity can be measured by the method described in the examples below.

[0020] As described above, the sulfide solid electrolyte of the present invention preferably exhibits a diffraction peak A in the range of 2θ = 15.18° ± 1.00° in an X-ray diffraction pattern measured with an X-ray diffractometer using CuKα1 radiation. Furthermore, from the viewpoint of improving ionic conductivity, depending on the element species constituting the sulfide solid electrolyte, it is preferable that the X-ray diffraction pattern measured with an X-ray diffractometer using CuKα1 radiation have a diffraction peak B at a position of 2θ = 17.60° ± 1.00° in addition to the diffraction peak A.

[0021] From the viewpoint of further improving ion conductivity, the sulfide solid electrolyte of the present invention preferably has peaks at the following positions in an X-ray diffraction pattern measured by an X-ray diffractometer using CuKα1 radiation: 25.11 ° ± 1.00 ° (hereinafter also referred to as "Peak C"), 29.60 ° ± 1.00 ° (hereinafter also referred to as "Peak D"), 30.96 ° ± 1.00 ° (hereinafter also referred to as "Peak E"), 44.51 ° ± 1.00 ° (hereinafter also referred to as "Peak F"), 47.41 ° ± 1.00 ° (hereinafter also referred to as "Peak G"), and 51.94 ° ± 1.00 ° (hereinafter also referred to as "Peak H").

[0022] Peaks A, B, C, D, E, F, G, and H are preferably peaks derived from a compound containing element (Li), element (P), element (S), and element (X), and particularly preferably derived from a compound having argyrodite-type crystals containing element (Li), element (P), element (S), and element (X). In a diffraction pattern measured by XRD using CuKα1 radiation, the diffraction peaks derived from the argyrodite-type crystal structure are identified using, for example, data from PDF No. 00-034-0688.

[0023] When the sulfide solid electrolyte of the present invention includes a crystal structure having a crystal phase of an argyrodite-type crystal structure, the sulfide solid electrolyte has a composition formula (I): Li ａ P.S. ｂ X ｃ (X is at least one of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I)) is preferred from the viewpoint of improving ionic conductivity.

[0024] In composition formula (I), a, which indicates the molar ratio of Li element, is preferably, for example, 3.0 or more, more preferably 4.0 or more, and particularly preferably 5.0 or more. On the other hand, a is preferably, for example, 6.5 or less, more preferably 5.9 or less, and particularly preferably 5.6 or less. When a is in this range, the cubic argyrodite-type crystal structure at around room temperature (25°C) becomes more stable, allowing lithium ion vacancies to be sufficiently introduced into the structure, and as a result, lithium ion conductivity can be effectively increased.

[0025] In composition formula (I), b is preferably, for example, 3.5 or more, more preferably 4.0 or more, and particularly preferably 4.2 or more. On the other hand, b is preferably, for example, 5.5 or less, more preferably 4.9 or less, and particularly preferably 4.7 or less. When b is within the above range, the argyrodite-type crystal structure becomes more stable at around room temperature (25°C), and lithium ion conductivity is effectively increased.

[0026] In composition formula (I), c is preferably, for example, 0.1 or more, more preferably 1.1 or more, and particularly preferably 1.4 or more, while c is preferably, for example, 2.5 or less, more preferably 2.0 or less, and particularly preferably 1.8 or less.

[0027] The sulfide solid electrolyte has the composition formula (II): Li ７－ｄ P.S. ６－ｄ X ｄ The composition represented by composition formula (II) is a stoichiometric composition of a crystalline phase having an argyrodite-type crystal structure. In composition formula (II), X has the same meaning as in composition formula (I).

[0028] In composition formula (II), d is preferably, for example, 0.4 or more, more preferably 0.8 or more, and particularly preferably 1.2 or more, while d is preferably, for example, 2.2 or less, more preferably 2.0 or less, and particularly preferably 1.8 or less.

[0029] The sulfide solid electrolyte has the composition formula (III): Li ７－ｄ－２ｅ P.S. ６－ｄ－ｅ X ｄ It may be expressed as:

[0030] The argyrodite-type crystalline phase having the composition represented by the composition formula (III) can be obtained by, for example, combining an argyrodite-type crystalline phase having the composition represented by the composition formula (II) with P ２ S ５ It is produced by reaction with diphosphorus pentasulfide.

[0031] In the composition formula (III), e is the Li from the stoichiometric composition represented by the composition formula (II). ２ e is a value indicating the deviation of the S component. For example, e is preferably −0.9 or more, more preferably −0.6 or more, and particularly preferably −0.3 or more. On the other hand, e is preferably (−d+2) or less, more preferably (−d+1.6) or less, and particularly preferably (−d+1.0) or less.

[0032] In the sulfide solid electrolyte, the atomic ratio X / P of the X element to the P element is, for example, preferably greater than 1.0, more preferably 1.1 or more, even more preferably 1.2 or more, and even more preferably 1.4 or more. On the other hand, the atomic ratio X / P is, for example, preferably 2.5 or less, more preferably 2.3 or less, and even more preferably 2.2 or less. When the atomic ratio X / P is within the above range, the ionic conductivity is further improved. The atomic ratio X / P can be measured, for example, by inductively coupled plasma atomic emission spectroscopy (ICP atomic emission spectroscopy) or a scanning electron microscope equipped with EDS (SEM-EDS analysis).

[0033] In particular, when the X element includes at least Cl and Br, the atomic ratio (Cl + Br) / P of the total of Cl and Br to P is preferably greater than 1.0, more preferably 1.1 or greater, even more preferably 1.2 or greater, and even more preferably 1.4 or greater. On the other hand, the atomic ratio (Cl + Br) / P is preferably 2.5 or less, more preferably 2.3 or less, and even more preferably 2.0 or less. The atomic ratio (Cl + Br) / P within the above range is preferable because it further improves lithium ion conductivity. The atomic ratio (Cl + Br) / P can be measured by elemental analysis, for example, using ICP atomic emission spectroscopy or SEM-EDS analysis.

[0034] The sulfide solid electrolyte is, among the above-mentioned composition formulas (I) to (III), particularly, composition formula (IV) Li ７－ｆ＋ｇ P.S. ６－ｆ Cl ｆ＋ｇ Or composition formula (V) Li ７－ｄ P.S. ６－ｄ Cl ｄ１ Br ｄ２ It is particularly preferable that the compound be represented by composition formula (V).

[0035] In composition formula (IV), f is preferably 0.05 or more and 0.4 or less, and more preferably 0.05 or more and 0.2 or less, and g is preferably −3.0f+1.8 or more and −3.0f+5.7 or less, more preferably −3.0f+3.9 or more and −3.0f+5.7 or less, and even more preferably −3.0f+4.2 or more and −3.0f+5.1 or less.

[0036] In the composition formula (V), the total molar ratio d (= d1 + d2) of Cl and Br is preferably, for example, greater than 1.0, more preferably 1.2 or more, and particularly preferably 1.4 or more. On the other hand, the total molar ratio d is, for example, preferably less than 2.5, more preferably less than 2.0, particularly preferably 1.8 or less, and further preferably 1.7 or less. When the total molar ratio d is within the above range, the formation of heterophases can be sufficiently controlled, and the decrease in ionic conductivity can be effectively suppressed.

[0037] In the composition formulas (I)-(III) and (V), the ratio of the molar ratio of Br to the molar ratio of Cl (d2 / d1) is, for example, preferably 0.1 or more, more preferably 0.3 or more, and particularly preferably 0.5 or more. On the other hand, the molar ratio is, for example, preferably 10 or less, more preferably 5 or less, and particularly preferably 3 or less. When the molar ratio is within the above-mentioned range, lithium ion conductivity can be further improved.

[0038] In the composition formulas (I)-(III) and (V), d1, which indicates the molar ratio of Cl, is preferably, for example, 0.3 or more, more preferably 0.4 or more, and particularly preferably 0.6 or more. On the other hand, d1 is preferably, for example, 1.5 or less, more preferably 1.2 or less, and particularly preferably 1.0 or less. When d1 is equal to or greater than the lower limit, lithium ion conductivity can be further increased. On the other hand, when d1 is equal to or less than the upper limit, the solid electrolyte can be more easily obtained.

[0039] In the composition formulas (I)-(III) and (V), d2, which indicates the molar ratio of Br, is preferably, for example, 0.3 or more, more preferably 0.4 or more, and particularly preferably 0.6 or more. On the other hand, d2 is, for example, preferably 1.5 or less, more preferably 1.2 or less, and particularly preferably 1.0 or less. When d2 is equal to or greater than the lower limit, a sulfide solid electrolyte is easily obtained. On the other hand, when d2 is equal to or less than the upper limit, lithium ion conductivity can be further increased.

[0040] In any case where the solid electrolyte is represented by any of the composition formulas (I), (II), (III) and (V), it is preferable that the X element contains Br, since this further improves the lithium ion conductivity.

[0041] The sulfide solid electrolyte of the present invention can be used as an electrode mixture containing the sulfide solid electrolyte and an active material. Alternatively, the sulfide solid electrolyte of the present invention can be used as a solid electrolyte layer containing the sulfide solid electrolyte. By using the sulfide solid electrolyte of the present invention, for example, a solid battery can be produced that has a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer, and that contains the sulfide solid electrolyte of the present invention.

[0042] Next, a specific example of a suitable method for producing the sulfide solid electrolyte of the present invention will be described below. The sulfide solid electrolyte of the present invention is a sulfide solid electrolyte obtained by mixing a compound having an argyrodite-type crystal structure containing lithium (Li), phosphorus (P), sulfur (S), and a halogen (X) with 0.1 to 7 mol % of diphosphorus pentoxide (P) relative to the phosphorus element contained in the compound. ２ O ５ The sulfide solid electrolyte of the present invention having a specific peak can be obtained by this production method. In contrast, in Example 5 of Patent Document 1, a compound having an argyrodite-type crystal structure and P ２ O ５ and baked at 200°C. ２ O ５ The amount of P used is as large as 14 mol % relative to the compound having an argyrodite-type crystal structure. In addition, the firing at 200°C is not carried out in an inert atmosphere, but in a glass vial, so heating is carried out under vacuum conditions. Therefore, the manufacturing method described in the document does not involve atmospheric conditions and P ２ O ５ The amount used differs from that of this manufacturing method.

[0043] The compound having an argyrodite-type crystal structure containing lithium (Li), phosphorus (P), sulfur (S), and a halogen (X) (hereinafter also referred to as "compound A") is not particularly limited in type and composition, and may be the same as the type and composition of the compound containing lithium (Li), phosphorus (P), sulfur (S), and a halogen (X) used in the sulfide solid electrolyte of the present invention, as described above.

[0044] The powder of compound A used in this production method before the mixing step has a volume cumulative particle size D at 50% by volume of cumulative volume measured by a laser diffraction scattering particle size distribution measurement method. ５０ is preferably 0.1 μm or more and 100 μm or less, more preferably 0.4 μm or more and 10 μm or less, and even more preferably 0.6 μm or more and 5 μm or less.

[0045] Diphosphorus pentoxide (P) for Compound A ２ O ５ The amount of 0.1 to 7 mol % of the added element P) is the ratio to the phosphorus element contained in the compound A. From the viewpoint of successfully producing a sulfide solid electrolyte having the specific peak, the ratio of P to the compound A is ２ O ５ The amount of addition is preferably 0.1 to 7 mol %, more preferably 2 to 5.5 mol %, and even more preferably 3 to 5 mol %.

[0046] Compounds A and P ２ O ５ By mixing these materials by wet pulverization, it is possible to prevent a decrease in the properties of the sulfide solid electrolyte, such as ionic conductivity. When wet pulverization is performed, it is preferable to use an organic solvent as a dispersion medium, as this can suppress the generation of hydrogen sulfide gas resulting from the reaction between the sulfide solid electrolyte and water. Examples of organic solvents include aromatic organic solvents such as toluene, xylene, benzene, and solvent naphtha, and aliphatic organic solvents such as heptane, decane, normal hexane, cyclohexane, and mineral spirits. These organic solvents can be used alone or in combination of two or more. The solid content of the slurry produced during wet pulverization can be, for example, 10 to 30 mass%.

[0047] A media mill can be used for wet grinding. Examples of media mills include planetary ball mills, ball mills, bead mills, paint shakers, and homogenizers. Among these, the use of a planetary ball mill is preferred in the present invention because it increases the grinding energy per rotation speed. Balls or beads made of various ceramics, such as alumina and zirconia, are used as grinding media for the media mill. The diameter of the grinding media can be, for example, 0.5 mm to 10 mm, more preferably 0.8 mm to 5 mm. From the viewpoint of not reducing the ionic conductivity of the resulting sulfide solid electrolyte and suppressing the incorporation of impurities, the grinding time is preferably 0.5 hours to 10 hours, more preferably 1 hour to 3 hours.

[0048] Examples of the inert atmosphere in the heating step include an argon atmosphere and a nitrogen atmosphere. As described above, the temperature in the heating step is preferably 150°C or higher and 350°C or lower, more preferably higher than 200°C and 350°C or lower, and particularly preferably higher than 200°C and 300°C or lower. In this production method, a small amount of P, such as 0.1 to 7 mol%, is used. ２ O ５ By mixing the compound A with compound A and firing the mixture at a relatively high temperature, a stable coating film having the specific peak can be successfully formed, and a sulfide solid electrolyte having excellent resistance to deterioration can be obtained. It is believed that firing at a relatively high temperature makes it easier for oxygen to volatilize, making it more likely to produce a pyrophosphate-type compound having a lower oxygen / phosphorus element ratio than phosphoric acid.

[0049] The inert atmosphere preferably contains substantially no water from the viewpoint of preventing decomposition and surface deterioration of the sulfide solid electrolyte due to moisture. Specifically, the dew point of the inert atmosphere is preferably −30° C. or lower, more preferably −35° C. or lower, and even more preferably −40° C. or lower.

[0050] Compounds A and P ２ O ５The heating time of the mixed powder is preferably 30 minutes or more, more preferably 1 hour or more, and even more preferably 3 hours or more from the viewpoint of allowing the oxidation reaction to proceed sufficiently. The heating time of the mixed powder is preferably 18 hours or less, more preferably 12 hours or less, and even more preferably 6 hours or less from the viewpoint of suppressing a decrease in the ionic conductivity of the sulfide solid electrolyte due to excessive progression of the oxidation reaction.

[0051] In order to easily incorporate the compound having the specific peak and more easily suppress deterioration of the sulfide solid electrolyte, the compounds A and P used in the present production method before the heating step are ２ O ５ The mixed powder is measured by a laser diffraction scattering particle size distribution measurement method to determine the volume cumulative particle size D at 50% by volume of the cumulative volume. ５０ is preferably 0.1 μm or more and 125 μm or less, more preferably 0.1 μm or more and 50 μm or less, and even more preferably 0.1 μm or more and 20 μm or less.

[0052] When the sulfide solid electrolyte obtained by such a method is used in a solid-state battery, an increase in the internal resistance of the solid-state battery can be suppressed even when the solid-state battery is stored at high temperatures or in a high-voltage state.

[0053] The above-described embodiments of the present invention encompass the following technical concepts. [1] A sulfide solid electrolyte containing lithium (Li), phosphorus (P), sulfur (S), and a halogen (X), wherein the sulfide solid electrolyte has a peak in the range of 2θ = 20.66° ± 1.00° in an X-ray diffraction pattern measured by an X-ray diffractometer using CuKα1 radiation. [2] The sulfide solid electrolyte according to [1], wherein the peak top position of the spectrum of the P2p orbital is 132.5 eV or higher in a surface analysis by X-ray photoelectron spectroscopy. [3] The sulfide solid electrolyte according to [1] or [2], wherein the X-ray diffraction pattern measured by an X-ray diffractometer using CuKα1 radiation has peaks at positions of 2θ = 15.18° ± 1.00°. [4] The sulfide solid electrolyte according to any one of [1] to [3], wherein the sulfide solid electrolyte has a peak at 2θ = 17.60° ± 1.00° in an X-ray diffraction pattern measured by an X-ray diffractometer using CuKα1 radiation. [5] The sulfide solid electrolyte according to any one of [1] to [4], wherein the sulfide solid electrolyte has peaks at 2θ = 25.11° ± 1.00°, 29.60° ± 1.00°, 30.96° ± 1.00°, 44.51° ± 1.00°, 47.41° ± 1.00°, and 51.94° ± 1.00° in an X-ray diffraction pattern measured by an X-ray diffractometer using CuKα1 radiation. [6] In an X-ray diffraction pattern of the sulfide solid electrolyte measured by an X-ray diffractometer using CuKα1 radiation, the peak intensity I of a peak observed in the range of 2θ = 15.18° ± 1.00° Ａ The peak intensity I of the peak observed in the range of 2θ = 20.66 ° ± 1.00 ° Ｓ Peak intensity ratio (I Ｓ / I Ａ [7] The sulfide solid electrolyte according to any one of [3] to [5], wherein the sulfide solid electrolyte has a surface area of ​​1.3 × 10 at 25°C. －４The sulfide solid electrolyte according to any one of [1] to [6], having an ionic conductivity of 100 S / cm or more. [8] An electrode mixture comprising the sulfide solid electrolyte according to any one of [1] to [7] and an active material. [9] A solid electrolyte layer containing the sulfide solid electrolyte according to any one of [1] to [7].

[10] A battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer between the positive electrode layer and the negative electrode layer, wherein the solid electrolyte layer contains the sulfide solid electrolyte according to any one of [1] to [7].

[11] A battery comprising a compound having an argyrodite-type crystal structure containing lithium (Li), phosphorus (P), sulfur (S), and a halogen (X), and 0.1 to 7 mol% of P relative to the compound. ２ O ５ and heating the pulverized product obtained in the wet-pulverization step at 150 to 350°C in an inert atmosphere.

[0054] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[0055] [Example 1] Composition formula Li ５．４ P.S. ４．４ Br ０．８ Cl ０．８ 2.0 g of powder of Compound A containing a crystalline phase having an argyrodite-type crystal structure (D ５０ The powder was prepared by adding 3 mol % of phosphorus pentoxide (P ２ O ５ ) was added, and toluene was further added as an organic solvent (dispersion medium) to obtain a slurry with a solid content of 20% by mass. This slurry was wet-milled in a planetary ball mill. Zirconia balls with a diameter of 0.8 mm were used as the milling media. The ball mill was operated at a rotation speed of 100 rpm, and wet mixing was carried out for 1 hour. All of the above operations were carried out in a glove box purged with sufficiently dried Ar gas (dew point -60°C or lower). The D of the mixture obtained in this way was ５０The resulting mixture was dried to remove the organic solvent, and then heated in a firing furnace at 300°C for 4 hours in a nitrogen atmosphere. Through the above operations, a sulfide solid electrolyte whose surface was coated with a phosphate compound was obtained.

[0056] [Examples 2 to 4] Diphosphorus pentoxide (P ２ O ５ A sulfide solid electrolyte having a surface coated with a phosphate compound was obtained in the same manner as in Example 1, except that the amounts of the phosphate compound and the sulfide solid electrolyte were changed as shown in Table 1.

[0057] Comparative Example 1 The same powder of Compound A as in Example 1 was used as the sulfide solid electrolyte of Comparative Example 1 without any modification.

[0058] [Evaluation] The sulfide solid electrolytes produced in each Example and Comparative Example were evaluated by the following criteria: ５０ The following measurements were made and the following evaluations were carried out.

[0059] [XRD Measurement] The sulfide solid electrolytes obtained in the Examples and Comparative Examples were filled into an airtight holder that was not exposed to the atmosphere in a glove box purged with sufficiently dried Ar gas (dew point -60°C or lower), and XRD measurement was performed. The measurement conditions were as follows. The XRD charts for each Example and Comparative Example are shown in Figure 1.・Device name: Tabletop X-ray diffraction device Aeris (manufactured by Malvern Panalytical) ・Radiation source: CuKα1 ・Tube voltage: 40 kV ・Tube current: 15 mA ・Measurement method: Focusing method (reflection method) ・Optical system: Multilayer mirror divergent beam method (CBO-α) ・Detector: One-dimensional semiconductor detector ・Incident Soller slit: Soller slit 0.02 rad ・Length limiting slit: 10 mm ・Receiving Soller slit: 0.02 rad ・Incident slit: 1 / 2° ・Receiving slit: 2 mm (open) ・Measurement range: 2θ = 10 to 105° ・Step width: 0.01° ・Scan speed: 1.67° / min

[0060] [P2p Peak Position] The particle surfaces of the sulfide solid electrolytes obtained in the examples and comparative examples were analyzed using a PHI Quantes XPS device manufactured by ULVAC-PHI, Inc. The conditions used for the measurement were as follows: Excitation X-ray: Monochromated Al beam (1486.7 eV) Output: 50 W Acceleration voltage: 15 kV X-ray irradiation diameter: 200 μmφ Measurement area: 1000 μm × 300 μm Take of angle: 45° Pass energy: 26.0 eV Energy step: 0.1 eV

[0061] XPS data was analyzed using data analysis software (ULVAC-PHI, Inc., "MultiPak Ver. 9.9"). The background mode used was Iterated Shirley. P2p was selected as the orbital used for calculation. Energy correction was performed using the C1s hydrocarbon peak (corrected position: 284.8 eV).

[0062] [D ５０ The sulfide solid electrolytes obtained in the examples and comparative examples were measured for particle size D by the following method. ５０ The results are shown in Table 1 below. Using an automatic sample feeder for a laser diffraction particle size distribution measuring device ("Microtorac SDC" manufactured by Nikkiso Co., Ltd.), the flow rate of the measurement sample containing the solid electrolyte was set to 50%, and the measurement sample containing the solid electrolyte was irradiated with 30 W ultrasonic waves for 60 seconds. Thereafter, the particle size distribution was measured using a laser diffraction particle size distribution measuring device "MT3000II" manufactured by Nikkiso Co., Ltd., and the particle size at which the cumulative volume was 50% by volume was determined from the obtained volume-based particle size distribution chart. ５０ In addition, D ５０ During the measurement, the organic solvent was passed through a 60 μm filter. The solvent refractive index was set to 1.50, the particle permeability condition was set to "transmission", the particle refractive index was set to 1.59, the shape was set to "non-spherical", the measurement range was set to 0.133 μm to 704.0 μm, and the measurement time was set to 10 seconds.

[0063] [Ionic Conductivity] The sulfide solid electrolyte powder obtained in each Example and Comparative Example was measured in a glove box purged with sufficiently dried Ar gas (dew point -60°C or lower) at a pressure of about 6 t / cm ２The pellets were uniaxially pressed under a load of 1000 kJ / cm2 to prepare samples for measuring lithium ion conductivity. The lithium ion conductivity was measured using a Solartron 1255B electrochemical measurement system (1280C) and an impedance / gain-phase analyzer (SI 1260) manufactured by Solartron Analytical. The measurement conditions were an AC impedance method at a temperature of 25°C, a frequency of 100 Hz to 1 MHz, and an amplitude of 100 mV.

[0064] [DC Internal Resistance (DCIR) before and after Float Charging] (Materials) Positive electrode active material powder was a ternary layered compound LiNi ０．６ Co ０．２ Mn ０．２ O ２ The positive electrode mixture powder was prepared by mixing the positive electrode active material powder, the solid electrolyte powder, and a conductive additive (acetylene black) in a mass ratio of 60:37:3 in a mortar, and then uniaxially pressing the mixture at 340 MPa to obtain positive electrode mixture pellets. The negative electrode mixture powder was prepared by mixing graphite powder and a standard solid electrolyte powder that had not been subjected to heat treatment (i.e., the sulfide solid electrolyte powder of Comparative Example 1) in a mass ratio of 64:36 in a mortar.

[0065] (Battery Fabrication) The lower opening of a polypropylene cylinder (opening diameter 10.5 mm, height 18 mm) with top and bottom openings was blocked with a positive electrode (made of SUS), and a positive electrode mixture pellet was placed on the positive electrode. A standard solid electrolyte powder that had not been heat-treated was placed on top of it and uniaxially pressed at 180 MPa to form a positive electrode layer and a solid electrolyte layer. A negative electrode mixture powder was then placed on top of it, and the negative electrode (made of SUS) was then blocked and uniaxially pressed at 550 MPa. This resulted in a die battery consisting of a three-layer structure: a positive electrode layer approximately 100 μm thick, a solid electrolyte layer approximately 300 μm thick, and a negative electrode layer approximately 20 μm thick. The positive electrode surface capacity was 1.15 mAh / cm ２ It was decided.

[0066] (Battery Evaluation) Using the battery prepared as described above, an initial charge / discharge test, a storage test under high temperature and high voltage, and a direct current internal resistance (DCIR) measurement were carried out as follows. The battery was placed in an environmental tester set to an environmental temperature of 25°C for charging and discharging, and left to stand so that the battery temperature reached the environmental temperature. The battery was charged and discharged at 0.1 mA at 1 C as follows: First, the battery was charged at a constant current of 0.1 C up to 4.5 V. Then, the battery was charged at a constant voltage of 4.5 V until the current flowed to 0.25 C or less. Next, the battery was left to stand in an open circuit state for 2 hours, and the open circuit voltage [V] of the battery was measured (V ０ Next, the battery was discharged at a discharge rate of 1 C, and the voltage [V] was measured 10 seconds after the start of discharge (V １０ｓｅｃ ). The current [A] at 1C rate was also measured (I). These results were calculated using the formula R = (V ０ -V １０ｓｅｃ ) / I to obtain the DC resistance of the battery before float charging.

[0067] <Float charging> Next, the battery was subjected to constant current charging at a charge rate of 1 C up to 4.5 V in an environment of 60° C. Thereafter, the battery was continuously charged at a constant voltage of 4.5 V for 60 hours (float charging).

[0068] <Resistance Increase Rate and Resistance Value> After float charging, the DC resistance of the battery was measured in the same manner as described above.

[0069] The DC resistance during float charging relative to the DC resistance before float charging was defined as the resistance increase rate, and the DC resistance after float charging was defined as the resistance value.

[0070] These results are shown in Table 1. The results of X-ray diffraction measurement of the sulfide solid electrolytes obtained in Examples 1 to 4 and Comparative Example 1 are shown in Figure 1. The P2p peak top spectra by XPS of the sulfide solid electrolytes obtained in Example 3 and Comparative Example 1 are shown in Figures 2 and 3, respectively. In Table 1, "-" means that the measurement was not performed.

[0071]

[0072] As is clear from Table 1, the sulfide solid electrolytes of each Example had low DCIR after float charging at an ambient temperature of 60°C and a voltage of 4.5 V, and it was found that an increase in internal resistance of the solid battery was suppressed when stored in a charged state at high temperature and high voltage. Furthermore, in each Example, the ionic conductivity of the sulfide solid electrolyte was slightly reduced by the addition and mixing of diphosphorus pentoxide and by heating, but the amount of reduction was not of a practical concern.

[0073] As described above in detail, according to the present invention, it is possible to suppress deterioration of a sulfide solid electrolyte containing lithium, phosphorus, sulfur, and a halogen, and a battery using the same.

Claims

1. A sulfide solid electrolyte containing lithium (Li), phosphorus (P), sulfur (S), and a halogen (X), the sulfide solid electrolyte having a peak in the range of 2θ=20.66°±1.00° in an X-ray diffraction pattern measured with an X-ray diffractometer using CuKα1 radiation.

2. The sulfide solid electrolyte according to claim 1, wherein, in a surface analysis by X-ray photoelectron spectroscopy, the peak top position of the spectrum of the P2p orbital is 132.5 eV or higher.

3. The sulfide solid electrolyte according to claim 1 or 2, wherein the sulfide solid electrolyte has a peak at 2θ=15.18°±1.00° in an X-ray diffraction pattern measured by an X-ray diffractometer using CuKα1 radiation.

4. The sulfide solid electrolyte according to claim 3, wherein the sulfide solid electrolyte has a peak at 2θ=17.60°±1.00° in an X-ray diffraction pattern measured by an X-ray diffractometer using CuKα1 radiation.

5. The sulfide solid electrolyte according to claim 3 or 4, wherein the sulfide solid electrolyte further has peaks at the following positions: 25.11°±1.00°, 29.60°±1.00°, 30.96°±1.00°, 44.51°±1.00°, 47.41°±1.00°, and 51.94°±1.00° in an X-ray diffraction pattern measured by an X-ray diffractometer using CuKα1 radiation.

6. In the X-ray diffraction pattern of the sulfide solid electrolyte measured by an X-ray diffractometer using CuKα1 radiation, the peak intensity I of the peak observed in the range of 2θ = 15.18° ± 1.00° Ａ The peak intensity I of the peak observed in the range of 2θ = 20.66 ° ± 1.00 ° Ｓ Peak intensity ratio (I Ｓ / I Ａ 5. The sulfide solid electrolyte according to claim 3, wherein the saturation coefficient (S) is 0.25 or more.

7. The sulfide solid electrolyte has a capacitance of 1.3 × 10 at 25 °C. －４ The sulfide solid electrolyte according to claim 1 or 2, having an ionic conductivity of 100 S / cm or more.

8. An electrode mixture comprising the sulfide solid electrolyte according to claim 1 or 2 and an active material.

9. A solid electrolyte layer containing the sulfide solid electrolyte according to claim 1 or 2.

10. A battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer between the positive electrode layer and the negative electrode layer, wherein the solid electrolyte layer contains the solid electrolyte according to claim 1 or 2.

11. A compound having an argyrodite-type crystal structure containing lithium (Li), phosphorus (P), sulfur (S), and halogen (X) elements, and 0.1 to 7 mol% of P relative to the phosphorus (P) element contained in the compound. ２ O ５ and heating the pulverized product obtained in the wet-pulverization step at 150 to 350°C in an inert atmosphere.

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