Solid electrolyte and method for producing same

Abstract

The solid electrolyte contains a lithium element, a phosphorus element, a sulfur element, a halogen element and a nitrogen element. The molar ratio of the difference between the lithium element and the sulfur element to the phosphorus element is 1.5-2.2. The molar ratio of the sum of the lithium element and the halogen element to the phosphorus element is preferably from 7.1 to 10.0 (inclusive). In an X-ray diffraction pattern measured by an X-ray diffraction device, it is also appropriate that peaks exist at positions of 2 [theta] = 25.5 DEG + / -1.0 DEG, 29.8 DEG + / -0.5 DEG, and 31.2 DEG + / -1.0 DEG.

Description

Technical Field

[0001] This invention relates to a solid electrolyte and its manufacturing method. Background Technology

[0002] In recent years, secondary batteries have garnered attention as a measure to prevent global warming by reducing CO2 emissions. Among these, all-solid-state batteries using sulfide solid electrolytes synthesized from lithium sulfide and other starting materials have attracted particular interest. All-solid-state batteries using sulfide solid electrolytes do not use flammable organic solvents, thus offering advantages such as simplified safety devices and superior manufacturing costs and productivity. Furthermore, with this type of solid electrolyte, ions other than lithium ions do not move within the electrolyte, preventing side reactions caused by anion migration, which is also advantageous from the perspective of improved safety and durability.

[0003] As a solid electrolyte, a sulfide solid electrolyte comprising lithium (Li), phosphorus (P), sulfur (S) and halogen elements has been proposed (see Patent Documents 1 and 2).

[0004] Prior technology documents

[0005] Patent documents

[0006] Patent Document 1: US2020 / 091552A1

[0007] Patent Document 2: US2020 / 127325A1 Summary of the Invention

[0008] Sulfide solid electrolytes are substances containing sulfur; therefore, depending on the environment, sulfur may react with moisture to produce hydrogen sulfide. Therefore, the objective of this invention is to provide a solid electrolyte that suppresses the production of hydrogen sulfide.

[0009] To address the aforementioned issues, the inventors conducted in-depth research and discovered that by reducing the sulfur (S) content in sulfide solid electrolytes while simultaneously introducing nitrogen (N) content, the generation of hydrogen sulfide can be suppressed while maintaining the properties of the solid electrolyte.

[0010] This invention is based on the foregoing insights and provides a solid electrolyte that solves the aforementioned problems. The solid electrolyte comprises lithium (Li), phosphorus (P), sulfur (S), halogen (X), and nitrogen (N).

[0011] The molar ratio of the difference between the aforementioned lithium (Li) and sulfur (S) elements relative to the aforementioned phosphorus (P) elements is 1.5 or more and 2.2 or less.

[0012] The molar ratio of the sum of the aforementioned lithium (Li) and halogen (X) elements to the aforementioned phosphorus (P) element is 7.1 or more and 10.0 or less.

[0013] In addition, the present invention also provides a method for manufacturing a solid electrolyte, wherein the solid electrolyte comprises lithium (Li), phosphorus (P), sulfur (S), halogen (X), and nitrogen (N).

[0014] The aforementioned manufacturing method includes a step of calcining the aforementioned raw material composition of the solid electrolyte.

[0015] The aforementioned raw material composition comprises one or more compounds and includes ammonium halide, wherein the compounds contain at least one of lithium (Li), phosphorus (P), sulfur (S) and halogen (X). Attached Figure Description

[0016] Figure 1 These are X-ray diffraction patterns of the solid electrolytes obtained in Examples 1, 2, 3, 4, and Comparative Examples 1 and 3.

[0017] Figure 2 These are X-ray diffraction patterns of the solid electrolytes obtained in Example 5 and Comparative Example 2.

[0018] Figure 3 These are enlarged views of the main part of the X-ray diffraction pattern of the solid electrolyte obtained in Example 1, and enlarged views of the main part of the X-ray diffraction pattern of the solid electrolyte obtained in Comparative Example 1.

[0019] Figure 4 This is a graph showing the initial charge-discharge characteristics of a solid-state battery having the solid electrolyte obtained in Examples 1 and 2. Detailed Implementation

[0020] The present invention will now be described based on its preferred embodiments. The solid electrolyte of the present invention comprises lithium (Li), phosphorus (P), sulfur (S), halogen (X), and nitrogen (N). That is, the solid electrolyte of the present invention is a sulfide solid electrolyte.

[0021] Examples of element X include at least one of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). In particular, from the viewpoint of improving lithium-ion conductivity, solid electrolytes may contain at least Cl or Br, or both Cl and Br, as element X.

[0022] The solid electrolyte of this invention contains nitrogen (N) to suppress the production of hydrogen sulfide. The reason for this is not yet clear, but it can be speculated as follows: Because the solid electrolyte contains N, some of the PS bonds in the solid electrolyte are replaced by PN bonds, resulting in a reduction in the sulfur content and suppression of hydrogen sulfide production. Furthermore, it can be assumed that when the solid electrolyte comes into contact with water, the reaction of PN bonds with water occurs preferentially compared to the reaction of PS bonds with water, thus suppressing hydrogen sulfide production.

[0023] The nitrogen element can be substituted with a portion of the constituent elements in a compound containing Li, P, S, and X. Alternatively, the nitrogen element can exist independently of each of the constituent elements in the compound containing Li, P, S, and X. In this invention, from the viewpoint of the above-described mechanism of action, it is preferable that the nitrogen element is substituted with a portion of the constituent elements in the compound containing Li, P, S, and X.

[0024] When nitrogen (N) exists independently of a solid electrolyte containing lithium (Li), phosphorus (P), sulfur (S), and x, nitrogen can exist in the form of compounds containing nitrogen (hereinafter also referred to as "compounds containing nitrogen").

[0025] As a compound containing nitrogen, there are no particular limitations; for example, ammonium halides can be cited.

[0026] Examples of ammonium halides include ammonium chloride, ammonium bromide, and ammonium iodide.

[0027] In solid electrolytes, there may be only one type of nitrogen-containing compound or there may be two or more types.

[0028] From the viewpoint that batteries using the solid electrolyte of the present invention can perform more effectively, the N-containing compound is preferably ammonium chloride.

[0029] As a solid electrolyte containing Li, S, P, and X elements, there are no particular limitations as long as the material possesses the functions of a solid electrolyte. For example, known sulfide solid electrolytes can be cited. Specific examples include: Li₂S-P₂S₅, Li₂S-P₂S₅-LiX, Li₂S-P₂S₅-P₂O₅, Li₂S-Li₃PO₄-P₂S₅, Li₃PS₄, Li₄P₂S₆, and Li₂S₅. 10 GeP2S 12 Li 3.25 Ge 0.25 P 0.75 S4, Li7P3S 11 Li 3.25 P 0.95 S4, Li a PSb X c (a represents a number greater than or equal to 3.0 and less than 6.0. b represents a number greater than or equal to 3.5 and less than 4.8. c represents a number greater than or equal to 0.1 and less than 3.0) represents compounds, etc.

[0030] In the solid electrolyte of the present invention, when the molar ratio of the difference between Li and S elements relative to P element is expressed as (Li-S) / P, it is preferable to set the value of (Li-S) / P to 1.5 or more, more preferably 1.6 or more, and even more preferably 1.7 or more. Furthermore, the value of (Li-S) / P is preferably, for example, 2.2 or less, more preferably 2.0 or less, and even more preferably 1.8 or less. By keeping the value of (Li-S) / P within the above range, the generation of hydrogen sulfide can be suppressed more effectively.

[0031] It should be noted that "the molar ratio of the difference between Li and S elements relative to P element" refers to the ratio of the molar ratio of the solid electrolyte to the molar ratio of the solid electrolyte, for example, composed of Li... 7-x PS 6-x X x When expressed, {(7-x)-(6-x)} / 1=1.

[0032] From the viewpoint of more effectively suppressing hydrogen sulfide from the solid electrolyte, in the solid electrolyte of the present invention, when the molar ratio of the sum of Li and X elements to P element is expressed as (Li+X) / P, it is preferable to set the value of (Li+X) / P to, for example, 7.1 or more, more preferably 7.2 or more, and even more preferably 7.25 or more. From the same viewpoint, it is preferable to set the value of (Li+X) / P to, for example, 10.0 or less, more preferably 8.5 or less, and even more preferably 7.6 or less.

[0033] It should be noted that "the molar ratio of the sum of Li and X elements relative to P element" refers to the ratio of the molar ratio of the sum of Li and X elements relative to P element when the solid electrolyte is composed of, for example, Li... 7-x PS 6-x X x When expressed, {(7-x)+x} / 1=7.

[0034] From the viewpoint of more effectively suppressing hydrogen sulfide generation from solid electrolytes, in the solid electrolyte of the present invention, when the molar ratio of S element to P element is set as S / P, it is preferable to set the S / P value to, for example, 2.0 or more, more preferably 2.5 or more, further preferably 2.9 or more, and even more preferably 3.1 or more. By appropriately increasing the amount of S element relative to P element, it is possible to suppress chemical structures that are highly reactive with water and readily generate hydrogen sulfide gas, namely S cross-linked with P (e.g., P2S7). 4- The generation of (etc.) and promotes the production of less PS4 and hydrogen sulfide gas. 3-The generation of the unit. On the other hand, the S / P value is preferably set to, for example, 4.5 or less, more preferably 4.0 or less, and even more preferably 3.5 or less. By appropriately reducing the amount of S element relative to P element, it is possible to suppress S, which does not bind to P and has high reactivity. 2- The generation of PS4 and the promotion of less hydrogen sulfide gas production. 3- Unit generation.

[0035] From the viewpoint of more effectively suppressing hydrogen sulfide from the solid electrolyte, in the solid electrolyte of the present invention, when the molar ratio of element X to element P is set as X / P, the value of X / P is preferably set to, for example, 1.5 or more, more preferably 1.9 or more, and even more preferably 2.2 or more. On the other hand, from the viewpoint of sufficiently improving the lithium-ion conductivity of the solid electrolyte, the value of X / P is preferably set to, for example, 4.5 or less, more preferably 3.5 or less, even more preferably 2.8 or less, and even more preferably 2.5 or less.

[0036] As described above, the solid electrolyte of the present invention contains nitrogen (N) element. By including nitrogen (N) element in the solid electrolyte, the generation of hydrogen sulfide from the solid electrolyte is suppressed. Regarding the amount of nitrogen (N) element contained in the solid electrolyte, for the purpose of effectively utilizing this advantage, when expressing the molar ratio of N element to P element as N / P, it is preferable to set the value of N / P to 0.01 or more, more preferably 0.05 or more, further preferably 0.06 or more, and even more preferably 0.1 or more.

[0037] From the viewpoint of fully improving the lithium-ion conductivity of the solid electrolyte, the N / P ratio is preferably 0.5 or less, more preferably 0.4 or less, even more preferably 0.25 or less, and even more preferably 0.2 or less.

[0038] In summary, in the solid electrolyte of the present invention, it is preferable to set the N / P value to 0.01 or more and 0.5 or less, more preferably to 0.05 or more and 0.4 or less, even more preferably to 0.06 or more and 0.25 or less, and even more preferably to 0.1 or more and 0.2 or less.

[0039] The amounts of each element constituting the solid electrolyte, represented by Li (excluding N and S), can be determined, for example, by ICP emission spectroscopy. The amount of N can be determined using an oxygen, nitrogen, and hydrogen analyzer. The amount of S can be determined by the barium sulfate gravimetric method. The aforementioned molar ratios (Li-S) / P and (Li+X) / P can be calculated based on the measured amounts of each element.

[0040] The solid electrolyte of the present invention may also contain elements other than Li, P, S, X, and N. For example, a portion of the Li element may be replaced with other alkali metal elements, or a portion of the P element may be replaced with other nitrogen group elements, or a portion of the S element may be replaced with oxygen (O) or other chalcogen elements. In addition to the elements mentioned above, the solid electrolyte of the present invention may contain impurities within a range that does not impair the effects of the present invention. The impurity content may, for example, be less than 5 mol%, preferably less than 3 mol%, and particularly less than 1 mol%.

[0041] The solid electrolyte of the present invention can be either a crystalline material or an amorphous material such as glass ceramics or glass. When the solid electrolyte of the present invention is a crystalline material, from the viewpoint of effectively improving ionic conductivity, it is preferable to include, for example, a crystal phase having a sulforaphite-germanium-type crystal structure. The aforementioned sulforaphite-germanium-type crystal structure refers to a crystal structure possessed by compounds derived from the group of minerals represented by the chemical formula Ag8GeS6.

[0042] Existing solid electrolytes containing crystal phases with a sulfide-germanium sulfide-type crystal structure tend to generate hydrogen sulfide in their sulfide solid electrolytes. However, the solid electrolyte of the present invention, due to its low sulfur content and high x content, suppresses hydrogen sulfide generation compared to existing solid electrolytes. Therefore, the solid electrolyte of the present invention can significantly enhance the effect of suppressing hydrogen sulfide generation even when containing crystal phases with a sulfide-germanium sulfide-type crystal structure.

[0043] From the viewpoint of further suppressing hydrogen sulfide generated from the solid electrolyte, in the diffraction pattern measured by XRD using CuKα1 rays, the solid electrolyte of the present invention preferably exhibits characteristic diffraction peaks caused by the crystal phase at positions of 2θ = 25.5° ± 1.0°, 29.8° ± 0.5°, and 31.2° ± 1.0°.

[0044] From the viewpoint of further suppressing hydrogen sulfide generated from solid electrolytes, it is preferable to observe characteristic diffraction peaks at positions of 2θ = 44.7°±1.0°, 47.8°±1.0°, and 52.5°±1.0°, in addition to the aforementioned diffraction peaks.

[0045] Furthermore, in the X-ray diffraction pattern measured using CuKα1 rays, when the solid electrolyte of the present invention has at least two peaks at the position of 2θ = 25.5° ± 1.0°, hydrogen sulfide generated from the solid electrolyte can be further suppressed, and is therefore particularly preferred.

[0046] In this case, when the ratio of the intensity of the second most intense peak to the intensity of the most intense peak (hereinafter also referred to as the "peak intensity ratio") among the multiple peaks located at 2θ = 25.5° ± 1.0° is 0.2 or more, hydrogen sulfide generated from the solid electrolyte can be further suppressed, and is therefore particularly preferred.

[0047] Furthermore, when there are three peaks with an intensity ratio of 0.2 or more at the position of 2θ = 25.5° ± 1.0°, and these peaks are designated as peak A, peak B, and peak C in order of increasing angle, the ratio of the intensity of peak B to the intensity of peak A, i.e., peak B / peak A, is preferably 2.0 or less, more preferably 1.6 or less, further preferably 1.0 or less, and even more preferably 0.5 or less.

[0048] For the solid electrolyte of the present invention, its particle size is defined as the volumetric cumulative particle size D at a cumulative volume of 50% obtained by laser diffraction random particle size distribution determination method. 50 The particle size is expressed as, for example, preferably 10 μm or less, more preferably 5 μm or less, further preferably 3 μm or less, even more preferably 1.5 μm or less, and still even more preferably 1.0 μm or less. By having such a particle size, the contact points and contact area between the solid electrolyte and the active material particles are increased, which can effectively improve the input and output characteristics of the battery.

[0049] In addition, the particle size D of the solid electrolyte 50 For example, a particle size of 0.1 μm or more is preferred, 0.3 μm or more is more preferred, and 0.5 μm or more is particularly preferred. By having such a particle size, excessive increase in the surface area of ​​the solid electrolyte is suppressed, thereby preventing an increase in electrical resistance. Furthermore, mixing with the active material becomes easier.

[0050] The solid electrolyte of the present invention exhibits lithium-ion conductivity in a solid state. The lithium-ion conductivity of the solid electrolyte of the present invention is preferably 0.1 mS / cm or more, more preferably 0.5 mS / cm or more, and even more preferably 1.0 mS / cm or more at room temperature (25°C).

[0051] Lithium-ion conductivity is determined, for example, by the following method. In a glove box purged with thoroughly dried argon gas (dew point below -60°C), a solid electrolyte is subjected to an application rate of approximately 6 t / cm. 2 Samples for lithium-ion conductivity measurement were fabricated by uniaxial compression molding under load, consisting of particles with a diameter of 10 mm and a thickness of approximately 1 mm to 8 mm. The lithium-ion conductivity was measured using a TOYO Corporation Solartron 1255B impedance measuring machine. Measurement conditions were set as follows: temperature 25°C, frequency 100 Hz to 1 MHz, and amplitude 100 mV using AC impedance method.

[0052] Next, a suitable method for manufacturing the solid electrolyte of the present invention, namely a solid electrolyte containing Li, P, S, X, and N elements, will be described. Suitablely, the solid electrolyte can be synthesized by a solid-phase reaction involving heating and sintering a raw material composition. The aforementioned raw material composition refers to a mixture of raw materials containing the aforementioned elements constituting the solid electrolyte. The raw material composition contains one or more compounds and includes ammonium halide, said compound containing at least one of Li, P, S, and X elements.

[0053] The aforementioned compounds may be, for example, compounds containing Li, compounds containing S, compounds containing P, compounds containing X, and compounds containing N.

[0054] Furthermore, the aforementioned compounds may contain at least two or more elements selected from Li, P, S, X, and N. For example, the aforementioned compounds may include: compounds containing Li and X, compounds containing P and S, compounds containing Li and S, compounds containing P and X, compounds containing S and X, and compounds containing N and X.

[0055] Lithium halides can be used as compounds containing both Li and X elements.

[0056] As compounds containing both phosphorus (P) and sulfur (S) elements, phosphorus sulfides such as phosphorus trisulfide (P2S3) and phosphorus pentasulfide (P2S5) can be used.

[0057] As a compound containing both Li and S elements, lithium sulfide (Li2S) can be used, for example.

[0058] As compounds containing both P and X elements, phosphine halides such as PX3 and P2X5 can be used.

[0059] As compounds containing both sulfur (S) and x (X) elements, for example, SX2, SX4, SX6, and S2X can be used. 10 Isohalated sulfur.

[0060] Ammonium halides can be used as compounds containing nitrogen (N) and x (X). From the viewpoint of readily obtaining the target solid electrolyte, ammonium halides such as ammonium chloride, ammonium bromide, or ammonium iodide are preferred. Ammonium chloride is particularly preferred.

[0061] In particular, from the viewpoint that solid electrolytes containing nitrogen can be synthesized smoothly, the aforementioned raw material composition preferably includes lithium sulfide, phosphorus sulfide, lithium halide and ammonium halide as the aforementioned compounds.

[0062] In preparing the aforementioned raw material composition, when expressing it using an elemental formula excluding N, from the viewpoint of suppressing hydrogen sulfide generated from the solid electrolyte, Li is preferred. a PS b X c The amounts shown are used to mix the compounds. From this point of view, in the aforementioned composition, a is preferably 3.0 or more and 6.0 or less, more preferably 4.0 or more and 5.5 or less, and even more preferably 4.5 or more and 5.2 or less.

[0063] In the aforementioned composition, b is preferably 2.0 or more and 4.8 or less, more preferably 2.5 or more and 4.0 or less, and even more preferably 3.0 or more and 3.4 or less.

[0064] In the aforementioned composition, c is preferably 1.5 or more and 4.5 or less, more preferably 1.9 or more and 3.5 or less, and even more preferably 2.2 or more and 2.5 or less.

[0065] In preparing the aforementioned raw material composition, when expressing it using an elemental formula other than N, from the viewpoint of suppressing hydrogen sulfide generated from the solid electrolyte, Li is also preferred. 7-x PS 6-x X x The amounts shown are used to mix the compounds. From this point of view, x is preferably greater than 1.0 and less than 3.0, more preferably greater than 1.4 and less than 2.6, and even more preferably greater than 1.8 and less than 2.2.

[0066] The above compounds are mixed to prepare a raw material composition. Mixing can be performed using, for example, a grinder, paint mixer, planetary ball mill, ball mill, bead mill, homogenizer, etc. The amount of each raw material added during mixing can be appropriately adjusted to meet the composition of the target solid electrolyte.

[0067] The obtained raw material composition is fed into a calcination process to undergo a solid-phase reaction, yielding a crystalline calcined product. The calcination atmosphere can be an inert gas atmosphere, such as argon or nitrogen, or a hydrogen sulfide atmosphere. From the viewpoint of reducing the proportion of sulfur in the solid electrolyte, an inert gas atmosphere is preferred.

[0068] From the viewpoint of ensuring a solid-state reaction of the raw material composition, the calcination temperature is preferably 200°C or higher, more preferably 300°C or higher, even more preferably 350°C or higher, and even more preferably 400°C or higher. On the other hand, considering industrial manufacturability and economic benefits, the calcination temperature is preferably, for example, 700°C or lower, more preferably 600°C or lower, and even more preferably 550°C or lower.

[0069] The calcination time is not a critical time; it is simply the time required to obtain a calcined product with the desired composition. Specifically, a calcination time that allows the raw material composition to undergo sufficient solid-phase reaction is preferred. The calcination time can be, for example, 30 minutes or more, 2 hours or more, or 3 hours or more. On the other hand, the calcination time can be, for example, 10 hours or less, or 5 hours or less.

[0070] It should be noted that during the roasting process, the sulfur in the sulfides contained in the raw material composition will react with the hydrogen in the ammonium halide to produce hydrogen sulfide. Therefore, the composition of each element contained in the roasted product may sometimes differ from the theoretical composition of the raw material composition.

[0071] After roasting, the roasted material can be crushed or pulverized as needed, or it can be graded as required. For example, it is preferable to use pulverizers such as planetary ball mills, vibratory mills, rotary mills, or mixers for crushing or pulverizing.

[0072] The resulting solid electrolyte can be used alone or mixed with other solid electrolytes.

[0073] The solid electrolyte of the present invention can be used as a material constituting a solid electrolyte layer, a positive electrode layer, or a negative electrode layer. Specifically, the solid electrolyte of the present invention can be used in batteries having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive and negative electrode layers. That is, the solid electrolyte can be used in so-called solid-state batteries. More specifically, it can be used in lithium solid-state batteries. Lithium solid-state batteries can be either primary or secondary batteries. The shape of the battery is not particularly limited; for example, it can be laminated, cylindrical, or prismatic. "Solid-state battery" includes not only solid-state batteries that do not contain any liquid or gel-like substances as electrolytes, but also those containing, for example, less than 50% by mass, less than 30% by mass, or less than 10% by mass as electrolytes.

[0074] When the solid electrolyte layer contains the solid electrolyte of the present invention, the solid electrolyte layer can be manufactured by, for example, the following methods: dripping a slurry composed of a solid electrolyte, a binder, and a solvent onto a substrate and smoothing it with a scraper or the like; cutting the substrate with an air knife after it comes into contact with the slurry; forming a coating film by screen printing or the like, and then removing the solvent by heating and drying; etc. Alternatively, the powdered solid electrolyte can be manufactured by pressing or the like into a pressed powder and then performing appropriate processing.

[0075] From the perspective of balancing short circuit prevention and volumetric capacity density, the thickness of the solid electrolyte layer is typically preferred to be 5 μm or more and 300 μm or less, and more preferably 10 μm or more and 100 μm or less.

[0076] The solid electrolyte of this invention can be used with active substances to form an electrode mixture. The proportion of solid electrolyte in the electrode mixture is typically 10% by mass or more and 50% by mass or less. The electrode mixture may also contain other materials such as conductive materials, as needed.

[0077] Electrodes such as positive and negative electrodes can be made by mixing electrode binders, binders and solvents, coating them onto current collectors such as aluminum foil and drying them.

[0078] As the cathode material constituting the cathode layer, cathode materials used as cathode active materials in lithium-ion batteries can be appropriately used. Examples include lithium-containing cathode active materials, specifically spinel-type lithium transition metal oxides and lithium metal oxides with layered structures. By using high-voltage cathode materials, energy density can be increased. In addition to cathode active materials, cathode materials can also contain conductive materials or other materials.

[0079] As the negative electrode material constituting the negative electrode layer, a negative electrode material used as the negative electrode active material in lithium-ion batteries can be appropriately used. The solid electrolyte of this invention is electrochemically stable, therefore lithium metal can be used, or materials with a low potential comparable to lithium metal (approximately 0.1V vs. Li) can be used. + Carbon-based materials such as graphite, artificial graphite, natural graphite, and hard carbon (difficult-to-graphite carbon) used in solid-state batteries (SSDs) for charging and discharging can be used as anode materials. This can significantly improve the energy density of SSDs. Additionally, silicon or tin, which are expected to be high-capacity materials, can also be used as active materials. Regarding anode materials, in addition to the active anode material, conductive materials or other materials may also be included.

[0080] In addition to the above embodiments, the present invention also discloses the following solid electrolyte, electrode mixture, electrode, battery, and method for manufacturing solid electrolyte.

[0081] <1>

[0082] A solid electrolyte comprising lithium (Li), phosphorus (P), sulfur (S), halogen (X), and nitrogen (N).

[0083] The molar ratio of the difference between the aforementioned lithium (Li) and sulfur (S) elements relative to the aforementioned phosphorus (P) elements is 1.5 or more and 2.2 or less.

[0084] The molar ratio of the sum of the aforementioned lithium (Li) and halogen (X) elements to the aforementioned phosphorus (P) element is 7.1 or more and 10.0 or less.

[0085] <2>

[0086] According to the solid electrolyte described in <1>, peaks are present at positions of 2θ = 25.5° ± 1.0°, 29.8° ± 0.5° and 31.2° ± 1.0° in the X-ray diffraction pattern measured using an X-ray diffraction apparatus.

[0087] <3>

[0088] According to the solid electrolyte described in <1> or <2>, there are peaks at positions of 2θ = 44.7°±1.0°, 47.8°±1.0° and 52.5°±1.0° in the X-ray diffraction pattern measured using an X-ray diffraction apparatus.

[0089] <4>

[0090] The solid electrolyte according to any one of <1> to <3>, wherein, in the X-ray diffraction pattern, it has at least two peaks at a position of 25.5°±1.0°.

[0091] <5>

[0092] The solid electrolyte according to any one of <1> to <4>, wherein the molar ratio of the aforementioned nitrogen (N) element to the aforementioned phosphorus (P) element is 0.01 or more and 0.5 or less.

[0093] <6>

[0094] An electrode mixture comprising any one of <1> to <5>, an active substance, a solid electrolyte, and a conductive material.

[0095] <7>

[0096] An electrode comprising the electrode mixture and binder described in <6>.

[0097] <8>

[0098] A battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer.

[0099] The battery contains any one of <1> to <5> solid electrolytes.

[0100] <9>

[0101] A method for manufacturing a solid electrolyte, wherein the solid electrolyte comprises lithium (Li), phosphorus (P), sulfur (S), halogen (X), and nitrogen (N).

[0102] The aforementioned manufacturing method includes a step of calcining the raw material composition of the aforementioned solid electrolyte.

[0103] The aforementioned raw material composition comprises one or more compounds and includes ammonium halide, wherein the compounds contain at least one of lithium (Li), phosphorus (P), sulfur (S) and halogen (X).

[0104] <10>

[0105] According to the manufacturing method described in <9>, the aforementioned raw material composition comprises lithium sulfide, phosphorus sulfide and lithium halide as the aforementioned compounds.

[0106] <11>

[0107] According to the manufacturing method described in <9> or <10>, the aforementioned raw material composition contains ammonium chloride as the aforementioned ammonium halide.

[0108] Example

[0109] The present invention will now be described in more detail through embodiments. However, the scope of the present invention is not limited to these embodiments. Unless otherwise specified, "%" refers to "mass %".

[0110] [Comparative Example 1]

[0111] (1) Preparation of raw material composition

[0112] Lithium sulfide (Li₂S) powder, phosphorus pentasulfide (P₂S₅) powder, lithium chloride (LiCl) powder, and lithium ozonide (LiBr) powder were weighed out according to the raw material mass ratios shown in Table 1. Heptane was added to these powders to prepare a slurry. The slurry was placed in a zirconia container and then placed in a planetary ball mill. Zirconia balls with a diameter of 5 mm were used as the grinding medium. The ball mill was operated at 100 rpm for 10 hours for wet mixing. The mixed slurry was then vacuum dried at room temperature to remove the heptane. The resulting raw material composition was obtained.

[0113] (2) Calcination

[0114] The raw material composition was calcined to obtain a calcined product. Calcination was performed using a tubular electric furnace. During calcination, 100% pure nitrogen gas was circulated within the furnace. For calcination, the temperature was increased to 300°C at a rate of 200°C / h and maintained at 300°C for 4 hours, then increased to 500°C at a rate of 200°C / h and maintained at 500°C for 4 hours, for a total of 10.5 hours.

[0115] (3) Crushing

[0116] The calcined material was ground in a mortar and passed through a 250 μm sieve to obtain a powder. This powder was then coarsely ground using a planetary ball mill. Zirconia balls with a diameter of 5 mm were used as the grinding medium. Heptane was used as the solvent. The ball mill was operated at 100 rpm for 3 hours for coarse grinding. The resulting slurry was then vacuum-dried at room temperature to remove the solvent. This yielded the powder of the target solid electrolyte.

[0117] [Examples 1, 2 and 3]

[0118] Lithium sulfide (Li₂S) powder, phosphorus pentasulfide (P₂S₅) powder, lithium chloride (LiCl) powder, lithium bromide (LiBr) powder, and ammonium chloride (NH₄Cl) powder were weighed in the manner shown in Table 1 below to obtain a raw material composition. Otherwise, a solid electrolyte powder was obtained in the same manner as in Comparative Example 1.

[0119] [Example 4]

[0120] Lithium sulfide (Li₂S) powder, phosphorus pentasulfide (P₂S₅) powder, lithium chloride (LiCl) powder, lithium bromide (LiBr) powder, lithium iodide (LiI) powder, and ammonium chloride (NH₄Cl) powder were weighed in the manner shown in Table 1 below to obtain the raw material composition. Otherwise, a solid electrolyte powder was obtained in the same manner as in Comparative Example 1.

[0121] [Comparative Example 2]

[0122] Lithium sulfide (Li₂S) powder, phosphorus pentasulfide (P₂S₅) powder, lithium chloride (LiCl) powder, and lithium bromide (LiBr) powder were weighed in the manner shown in Table 1 below to obtain a raw material composition. Otherwise, a solid electrolyte powder was obtained in the same manner as in Comparative Example 1.

[0123] [Example 5]

[0124] Lithium sulfide (Li₂S) powder, phosphorus pentasulfide (P₂S₅) powder, lithium chloride (LiCl) powder, lithium bromide (LiBr) powder, and ammonium chloride (NH₄Cl) powder were weighed in the manner shown in Table 1 below to obtain a raw material composition. Otherwise, a solid electrolyte powder was obtained in the same manner as in Comparative Example 1.

[0125] [Comparative Example 3]

[0126] This comparative example is an attempt to reduce hydrogen sulfide production by decreasing the S / P molar ratio in a solid electrolyte containing Li, P, S, and X elements but not N.

[0127] Lithium sulfide (Li₂S) powder, phosphorus pentasulfide (P₂S₅) powder, lithium chloride (LiCl) powder, and lithium bromide (LiBr) powder were weighed in the manner shown in Table 1 below to obtain a raw material composition. Otherwise, a solid electrolyte powder was obtained in the same manner as in Comparative Example 1.

[0128] 〔evaluate〕

[0129] For the solid electrolytes obtained in the examples and comparative examples, each element was quantified by the method described below, and the molar ratios shown in Table 1 were calculated.

[0130] For Li, P, Br, Cl and I, the substances obtained by melting solid electrolyte powder using the alkali fusion method were quantified using an ICP emission spectrometer (HITACHI-HIGHTECH Co., Ltd. "SPS3520DDUV").

[0131] For S, S is oxidized to sulfate ions, and then quantified using the barium sulfate gravimetric method.

[0132] For N, an oxygen, nitrogen, and hydrogen analyzer (EMGA930 manufactured by Horiba Manufacturing Co., Ltd.) was used. The powder of the solid electrolyte was melted in a graphite crucible. For the generated gas, CO2 and H2O were removed using a CO2 removal agent and a H2O removal agent. Then, N2 was extracted using a thermal conductivity detector to quantify the N content.

[0133] In addition, the amount of hydrogen sulfide produced and the particle size D were determined by the following method. 50 .

[0134] Furthermore, the characteristics of solid-state batteries containing solid electrolytes are evaluated using the following method.

[0135] The results are shown in Table 1.

[0136] Furthermore, XRD measurements were performed on the solid electrolytes obtained in Examples 1 to 5 and Comparative Examples 1 to 3 to obtain diffraction patterns. The XRD measurements were performed using a "Smart Lab SE" X-ray diffraction apparatus manufactured by Rigaku Corporation. The measurement conditions were set as follows: no exposure to atmosphere, scanning axis: 2θ / θ, scanning range: 10° to 120°, step size: 0.02°, and scanning speed: 1° / min. The X-ray source was set to CuKα1 rays. The tube voltage was set to 40 kV and the tube current to 80 mA. The measurement results are shown below. Figure 1 and Figure 2 .

[0137] Table 1 shows the number of peaks with a peak intensity ratio of 0.2 or higher among the multiple peaks located at 2θ = 25.5° ± 1.0° of the solid electrolytes of the Examples and Comparative Examples, where the ratio of the peak intensity of the second strongest peak to the peak intensity of the strongest peak is 0.2 or higher.

[0138] With three peaks located at 2θ = 25.5° ± 1.0°, the values ​​of peak B / peak A are shown in Table 1.

[0139] The above peak intensities are calculated using the average of the intensities from 2θ = 75.5° to 76.0° as the background value.

[0140] Figure 3 In the diagram, the peaks measured under the aforementioned conditions in Example 1 and Comparative Example 1 are represented by the symbol "▼".

[0141] In the XRD pattern of the solid electrolyte in Example 5, diffraction peaks were observed at positions of 2θ = 25.5° ± 1.0°, 29.8° ± 0.5°, 31.2° ± 1.0°, 44.7° ± 1.0°, 47.8° ± 1.0°, and 52.5° ± 1.0°, but no more than two diffraction peaks were observed at the position of 2θ = 25.5° ± 1.0°.

[0142] [Amount of hydrogen sulfide produced]

[0143] The amount of hydrogen sulfide generated from the solid electrolyte was measured using a detection tube.

[0144] In a glove box purged with thoroughly dried Ar gas (dew point below -60°C), 2 mg of solid electrolyte is weighed in a metal container each time, placed in a laminated bag, and sealed.

[0145] In an atmosphere with a dew point of -30°C prepared by mixing dry air with atmospheric air, a 1000 ml glass detachable flask was placed in a constant temperature and humidity bath maintained at room temperature (25°C) until the internal environment of the detachable flask was identical to that of the constant temperature and humidity bath. Next, the sealed bag containing the solid electrolyte was opened in the constant temperature and humidity bath, and the solid electrolyte was quickly prepared into the detachable flask, which was then sealed. The hydrogen sulfide produced up to 30 minutes after sealing was measured using a gas detector (manufactured by GASTEC SERVICE, INC., No. 4LL).

[0146] Particle size D 50 ]

[0147] Using an automatic sample feeder (Nikkiso Co., Ltd.'s "Microtorac SDC") for laser diffraction particle size distribution measurement, the flow rate of the sample containing the solid electrolyte was set to 50%, and the sample containing the solid electrolyte was irradiated with 30W ultrasound for 60 seconds. Then, the particle size distribution was measured using a Nikkiso Co., Ltd. laser diffraction particle size distribution measuring machine "MT3000II". Based on the obtained volume-based particle size distribution graph, the particle size at which the cumulative volume reaches 50% was determined, and this value was taken as D. 50 .

[0148] [Battery Characteristics]

[0149] As the positive electrode active material, a ternary layered compound, LiNi, whose surface is coated with lithium niobate, is used. 0.6 Co 0.2 Mn 0.2 O2 (NCM) powder. Graphite (Gr) powder was used as the negative electrode active material. The solid electrolyte powder was a material obtained by micronizing the solid electrolytes obtained in Examples 1 and 2 using a planetary ball mill apparatus (D50 = 0.7 μm).

[0150] The positive electrode mixture is prepared by mixing positive electrode active material powder, solid electrolyte powder, and conductive additive in a mortar at a mass ratio of 60:37:3. The positive electrode mixture is then uniaxially pressed at 20 MPa to produce positive electrode mixture particles.

[0151] The negative electrode powder is made by mixing graphite powder and solid electrolyte powder in a mortar at a mass ratio of 64:36.

[0152] The lower opening of a polypropylene cylinder (10.5 mm in diameter and 18 mm in height) with openings at both ends is sealed using a positive electrode (made of SUS). Positive electrode additive particles are then loaded onto the positive electrode. Solid electrolyte powder is then loaded onto it and uniaxially pressed at 180 MPa to form a positive electrode additive and a solid electrolyte layer. Negative electrode additive powder is then loaded onto it. This process creates an all-solid-state battery cell consisting of a positive electrode additive, a solid electrolyte layer of approximately 300 μm, and a negative electrode additive layer of approximately 20 μm.

[0153] Using the all-solid-state battery cells fabricated as described above, the battery characteristics (initial charge-discharge characteristics) were evaluated according to the following method.

[0154] A solid-state battery cell was installed in an environmental testing chamber maintained at 25°C and connected to a charge-discharge device to evaluate the battery characteristics. The battery was charged and discharged using 1mA as 1C. Charging was performed at 0.1C using the CC-CV method until 4.5V was obtained, yielding the initial charge capacity. Discharging was performed at 0.1C using the CC method until 2.5V was obtained, yielding the initial discharge capacity. The initial charge-discharge curves of Examples 1 and 2 are shown below. Figure 4 .

[0155] [Table 1]

[0156]

[0157] As shown in Table 1, the solid electrolytes obtained in each embodiment are solid electrolytes with reduced hydrogen sulfide production.

[0158] according to Figure 4 The results show that the initial charge capacity of Example 1 was 217.4 mAh / g and the initial discharge capacity was 182.2 mAh / g. The initial charge capacity of Example 2 was 211.4 mAh / g and the initial discharge capacity was 176.8 mAh / g.

[0159] These results show that the solid electrolytes obtained in each embodiment fully utilize their function as solid electrolytes.

[0160] Industrial availability

[0161] As detailed above, according to the present invention, a solid electrolyte that suppresses the generation of hydrogen sulfide and a method for manufacturing the same are provided.

Claims

1. A solid electrolyte comprising lithium (Li), phosphorus (P), sulfur (S), halogen (X), and nitrogen (N). The molar ratio of the difference between lithium (Li) and sulfur (S) elements relative to phosphorus (P) is 1.5 or more and 2.2 or less. The molar ratio of the sum of lithium (Li) and halogen (X) to phosphorus (P) is 7.1 or more and 10.0 or less.

2. The solid electrolyte according to claim 1, wherein, In the X-ray diffraction pattern measured using an X-ray diffraction device, peaks are observed at positions of 2θ = 25.5° ± 1.0°, 29.8° ± 0.5°, and 31.2° ± 1.0°.

3. The solid electrolyte according to claim 2, wherein, In the X-ray diffraction pattern measured using an X-ray diffraction device, peaks are observed at positions of 2θ = 44.7°±1.0°, 47.8°±1.0°, and 52.5°±1.0°.

4. The solid electrolyte according to claim 2, wherein, In the X-ray diffraction pattern, there are at least two peaks at a position of 25.5°±1.0°.

5. An electrode mixture comprising the active substance, solid electrolyte, and conductive material as described in any one of claims 1 to 4.

6. An electrode comprising the electrode compound and binder as described in claim 5.

7. A battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer. The battery contains a solid electrolyte as described in any one of claims 1 to 4.

8. A method for manufacturing a solid electrolyte, said solid electrolyte comprising lithium (Li), phosphorus (P), sulfur (S), halogen (X), and nitrogen (N). The manufacturing method includes a step of calcining the raw material composition of the solid electrolyte. The raw material composition comprises one or more compounds and includes ammonium halide, wherein the compounds contain at least one of lithium (Li), phosphorus (P), sulfur (S) and halogen (X).

9. The manufacturing method according to claim 8, wherein, The raw material composition comprises lithium sulfide, phosphorus sulfide and lithium halide as the compound.

10. The manufacturing method according to claim 8 or claim 9, wherein, The raw material composition contains ammonium chloride as the ammonium halide.

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