Solid electrolyte and method for producing the same

Abstract

This solid electrolyte includes a crystal phase that has an argyrodite crystal structure, and contains elemental lithium (Li), elemental phosphorus (P), elemental sulfur (S), and elemental halogen (X). The crystallite size of the crystal phase having the argyrodite crystal structure is no more than 40 nm. In an XRD pattern, Ia / Ib is no more than 0.2 when the intensity of a peak A observed in the range 2θ = 27.0° ± 0.5° is Ia and the intensity of a peak B observed in the range 2θ = 25.5° ± 1.0° is Ib.

Description

[Technical Field]

[0001] The present invention relates to a solid electrolyte and a method for producing the same, and also to an electrode mixture, a solid electrolyte layer, and a battery containing the solid electrolyte. [Background technology]

[0002] In recent years, solid electrolytes have been attracting attention as an alternative to the liquid electrolytes used in many liquid batteries. Solid-state batteries using solid electrolytes are safer than liquid-state batteries that use flammable organic solvents, and are expected to be put to practical use as batteries that also have high energy density. As solid electrolytes, for example, sulfide solid electrolytes containing lithium (Li), phosphorus (P), sulfur (S), and halogen elements have been proposed (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US2020 / 091552A1 [Patent Document 2] WO2020 / 095937A1 Summary of the Invention

[0004] In recent years, research into solid electrolytes has been actively conducted, and there is a demand for the development of solid electrolytes that can provide better battery characteristics. Therefore, an object of the present invention is to provide a solid electrolyte having excellent battery characteristics and a method for producing the same.

[0005] The present invention includes lithium (Li), phosphorus (P), sulfur (S) and halogen (X) elements, It contains a crystalline phase having an argyrodite-type crystal structure, the crystallite size of the crystalline phase having an argyrodite-type crystal structure is 40 nm or less; The present invention provides a solid electrolyte in which, when the intensity of peak A observed in the range of 2θ=27.0°±0.5° in an X-ray diffraction pattern measured by an X-ray diffractometer (XRD) using CuKα1 radiation is defined as Ia, and the intensity of peak B observed in the range of 2θ=25.5°±1.0° is defined as Ib, the ratio Ia / Ib of Ia to Ib is 0.2 or less.

[0006] The present invention also provides a method for producing a fired product, comprising: a firing step of firing a raw material composition containing lithium (Li), phosphorus (P), sulfur (S), and a halogen (X) at 200°C or higher to obtain a fired product; and a grinding step of grinding the fired product by applying a grinding energy E represented by the following formula (1) of 200 J·sec / g or more to the fired product. E(J·sec / g)=1 / 2ntmv 2 / s (1) In the formula, n represents the number of grinding media, t represents the grinding time (sec), m represents the mass of one grinding media (kg), v represents the speed of the grinding media (m / sec), and s represents the mass of the object to be ground (g). [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 shows the X-ray diffraction patterns of the solid electrolytes obtained in Examples 1 to 3. [Figure 2] FIG. 2 is a diagram showing the X-ray diffraction patterns of the solid electrolytes obtained in Comparative Examples 1 and 2. As shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention will be described below based on preferred embodiments thereof. First, the solid electrolyte of the present invention will be described. The solid electrolyte of the present invention contains Li, P, S and X elements.

[0009] Examples of the X element include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). The X element may be one of these elements or a combination of two or more of them. From the viewpoint of facilitating the formation of an argyrodite-type crystal structure (described later) by a solid-state reaction and enhancing lithium ion conductivity, the solid electrolyte preferably contains at least Cl or Br as the X element, and more preferably contains Cl and Br.

[0010] When the solid electrolyte contains Br and Cl as the X element, the ratio of Br to the sum of the number of moles of Br and the number of moles of Cl, i.e., the value of Br / (Br+Cl), is, for example, preferably 0.2 or more, more preferably 0.3 or more, and even more preferably 0.4 or more. On the other hand, the value of Br / (Br+Cl) is, for example, preferably 0.8 or less, more preferably 0.7 or less, and even more preferably 0.6 or less.

[0011] In the solid electrolyte of the present invention, it is preferable to set the molar ratio of X element to P element (X / P) to a relatively high value. For example, the X / P is preferably 1.1 or more, more preferably 1.5 or more, and even more preferably 1.8 or more. On the other hand, the X / P is preferably 4.0 or less, more preferably 3.5 or less, and even more preferably 2.4 or less. When the X / P is within the specified range, the solid electrolyte of the present invention exhibits superior lithium ion conductivity. Furthermore, when the solid electrolyte of the present invention is used in a solid battery, the solid battery exhibits superior battery characteristics. The X / P can be measured, for example, by ICP atomic emission spectroscopy.

[0012] In the solid electrolyte of the present invention, the molar ratio of S element to P element (S / P) is, for example, preferably 4.9 or less, more preferably 4.5 or less, and even more preferably 4.2 or less. On the other hand, the S / P is preferably 3.2 or more, more preferably 3.5 or more, and even more preferably 3.8 or more. When the S / P is within the specified range, the solid electrolyte of the present invention exhibits better lithium ion conductivity. Furthermore, when the solid electrolyte of the present invention is used in a solid battery, the solid battery exhibits better battery characteristics. The S / P can be measured, for example, by ICP atomic emission spectroscopy.

[0013] The solid electrolyte may contain elements other than Li, P, S, and X. For example, part of the Li element may be replaced with another alkali metal element, part of the P element may be replaced with another pnictogen element, or part of the S element may be replaced with another chalcogen element.

[0014] The solid electrolyte may contain materials containing other elements other than the elements Li, P, S, and X, as long as the effects of the present invention are not impaired. The content of other materials can be, for example, at most less than 5 mol %, preferably less than 3 mol %, and particularly preferably less than 1 mol %.

[0015] The solid electrolyte of the present invention is preferably a crystalline compound. A crystalline compound is a substance in which a diffraction peak due to a crystalline phase is observed when measured using an X-ray diffractometer (XRD). In particular, the solid electrolyte preferably contains a crystalline phase having an argyrodite-type crystal structure, which can enhance the lithium ion conductivity of the solid electrolyte.

[0016] The argyrodite-type crystal structure is a crystal structure possessed by a group of compounds derived from a mineral represented by the chemical formula: AgGeS. Whether or not a solid electrolyte has a crystalline phase with the argyrodite-type crystal structure can be confirmed by measurement such as XRD. For example, in a diffraction pattern measured by XRD using CuKα1 radiation, the crystalline phase with the argyrodite-type crystal structure exhibits characteristic diffraction peaks at 2θ = 15.3° ± 1.0°, 17.7° ± 1.0°, 25.5° ± 1.0°, 30.0° ± 1.0°, 30.9° ± 1.0°, and 44.3° ± 1.0°. Depending on the elemental species constituting the solid electrolyte, in addition to the diffraction peaks described above, characteristic diffraction peaks may also be observed at 2θ=47.2°±1.0°, 51.7°±1.0°, 58.3°±1.0°, 60.7°±1.0°, 61.5°±1.0°, 70.4°±1.0°, and 72.6°±1.0°. The diffraction peaks attributable to the argyrodite-type crystal structure can be identified using data from PDF No. 00-034-0688, for example.

[0017] The solid electrolyte may or may not have a crystalline phase other than the argyrodite-type crystalline structure. In the present invention, for example, it is preferable that the crystalline phase having the argyrodite-type crystalline structure is contained as the main phase. Here, the "main phase" refers to the phase that accounts for the largest proportion of all crystalline phases constituting the solid electrolyte. Therefore, the content of the crystalline phase having the argyrodite-type crystalline structure is preferably, for example, 60 mass% or more, more preferably 70 mass% or more, 80 mass% or more, 90 mass% or more, or 95 mass% or more, of all crystalline phases constituting the solid electrolyte. The proportion of the crystalline phase can be confirmed, for example, by XRD. When the crystalline phase having the argyrodite-type crystalline structure is the main phase, lithium ion conductivity can be effectively increased, and the performance of a battery containing the solid electrolyte, particularly the output characteristics, can be further improved.

[0018] The solid electrolyte of the present invention preferably does not have, for example, a LiS crystalline phase. Furthermore, if a LiS crystalline phase is present, its presence ratio is preferably as low as possible. When the solid electrolyte has a LiS crystalline phase, a diffraction peak is observed at 2θ=27.0°±0.5° in an X-ray diffraction pattern measured by XRD using CuKα1 radiation. Therefore, in the present invention, when the intensity of diffraction peak A observed at 2θ=27.0°±0.5° is defined as Ia and the intensity of diffraction peak B observed in the range of 2θ=25.5°±1.0° is defined as Ib, the ratio Ia / Ib of Ia to Ib is preferably 0.20 or less, more preferably 0.17 or less, even more preferably 0.15 or less, and even more preferably 0. Note that diffraction peak B is a diffraction peak derived from an argyrodite-type crystal structure. When Ia / Ib is equal to or less than the above value, the movement of lithium ions at the interface between the active material and the solid electrolyte is improved, and as a result, the input / output characteristics of the battery can be improved. The method for measuring Ia and Ib will be described in detail in the Examples below. In this specification, the intensity of a diffraction peak refers to the height of the peak.

[0019] The solid electrolyte preferably does not contain any crystalline phase other than the LiS crystalline phase described above. For example, depending on the manufacturing conditions of the solid electrolyte, a diffraction peak C may be observed in the X-ray diffraction pattern in the range of 2θ = 21.3° ± 0.3°. This diffraction peak C is derived from a crystalline phase other than the argyrodite-type crystalline structure. The inventors believe that this diffraction peak C is derived from the crystalline phase disclosed in Patent Document 2 described in the Background Art section. The crystalline phase derived from diffraction peak C is thermodynamically more stable than the argyrodite-type crystalline structure, and therefore may be formed in the solid electrolyte depending on the manufacturing conditions of the solid electrolyte. In the present invention, when the maximum count number of diffraction peak C observed in the range of 2θ = 21.3° ± 0.3° is defined as IC and the background intensity observed in the range of 2θ = 23.5° ± 0.5° is defined as I0, the ratio of IC to I0, IC / I0, is preferably 1.55 or less, more preferably 1.40 or less, and even more preferably 1.25 or less. This is because the lithium ion conductivity can be improved more effectively. From the same viewpoint as above, when the intensity of the diffraction peak C observed in the range of 2θ=21.3°±0.3° is defined as Ic, the count number of Ic is preferably 300 counts or less, more preferably 200 counts or less, and even more preferably 100 counts or less, because this can more effectively improve the lithium ion conductivity. The method for measuring the maximum count number IC and the count number Ic of the diffraction peak C will be described in detail in the examples below.

[0020] As described above, the solid electrolyte has a crystalline phase having an argyrodite-type crystal structure. It is preferable that the crystalline phase has low crystallinity in order to improve the performance of a battery containing the solid electrolyte, particularly in terms of improving its output characteristics. The inventors believe that a lower crystallinity of the solid electrolyte makes the solid electrolyte more susceptible to plastic deformation during the fabrication of an all-solid-state battery, thereby improving contact with the active material. The crystallinity of the crystalline phase having an argyrodite-type crystal structure can be evaluated using the crystallite size of the crystalline phase as a measure. The crystallite size of the crystalline phase having an argyrodite-type crystal structure in the solid electrolyte is preferably, for example, 40 nm or less, more preferably 35 nm or less, and even more preferably 30 nm or less. The crystallite size may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more. The method for measuring the crystallite size will be described in detail in the Examples below.

[0021] The particle size of the solid electrolyte is measured by the volume cumulative particle size D at 50% cumulative volume using the laser diffraction scattering particle size distribution measurement method. 50 However, for example, the thickness is preferably 5 μm or less, more preferably 3 μm or less, even more preferably 1.5 μm or less, even more preferably 1.3 μm or less, and even more preferably 1.1 μm or less, because the contact points and contact area between the solid electrolyte and the active material particles become large, thereby effectively improving the input / output characteristics of the battery. The particle size of the solid electrolyte D 50 is, for example, preferably 0.1 μm or more, more preferably 0.3 μm or more, and particularly preferably 0.5 μm or more. This is because an excessive increase in the surface area of ​​the solid electrolyte can be suppressed, thereby suppressing an increase in resistance. Also, this is because mixing with the active material becomes easier. Particle size D 50 The method for measuring this will be described in detail in the Examples below.

[0022] The solid electrolyte of the present invention preferably has lithium ion conductivity in a solid state. For example, it preferably has a lithium ion conductivity of 0.1 mS / cm or more, particularly 0.2 mS / cm or more, and particularly 0.4 mS / cm or more at room temperature, i.e., 25°C. The lithium ion conductivity can be measured using the method described in the Examples below.

[0023] A preferred method for producing the solid electrolyte of the present invention will now be described. This method comprises a firing step of firing a raw material composition for the solid electrolyte, and a pulverization step of strongly pulverizing the fired product obtained in the firing step.

[0024] Known methods for producing a solid electrolyte include, for example, a method in which a raw material composition is not fired but the target product is produced by mechanical milling instead, as described in the above-mentioned Patent Document 1, and a method in which a raw material composition is fired but the target product is produced without mechanical milling, as described in the above-mentioned Patent Document 2. In the method described in Patent Document 1, when a solid electrolyte is prepared by mechanical milling, lithium sulfide, a component contained in the raw material composition, is thought to remain in the solid electrolyte even when the milling time is extended, etc. Lithium sulfide is a substance that reduces the movement of lithium ions between the active material and the solid electrolyte when a solid-state battery is made, and is one of the factors that deteriorates the input / output characteristics of the battery. On the other hand, when the method described in Patent Document 2 is adopted, the amount of remaining lithium sulfide is improved, but depending on the firing conditions, a different crystalline phase that is thermodynamically more stable than the argyrodite-type crystalline structure is generated instead of the argyrodite-type crystalline structure. This different phase is the crystalline phase corresponding to the diffraction peak C mentioned above, and is one of the factors that reduces lithium ion conductivity. Unlike the manufacturing methods described in Patent Documents 1 and 2, the present manufacturing method combines calcination of the raw material composition with strong pulverization by mechanical milling of the calcined product. This reduces the likelihood of lithium sulfide remaining and facilitates the formation of an argyrodite-type crystal structure as the main phase. The reasons for this are thought to be as follows. For example, the crystalline phase corresponding to the aforementioned diffraction peak C is a crystalline phase that undergoes a phase transition to the argyrodite-type crystal structure at high temperatures. However, conventional calcination methods tend to produce a stable crystalline phase corresponding to diffraction peak C. In contrast, the present manufacturing method maintains the argyrodite-type crystal structure, which is a metastable phase, even at room temperature by performing mechanical milling after calcination. In other words, it is thought that the formation of the crystalline phase corresponding to diffraction peak C can be suppressed.

[0025] As described above, this manufacturing method first involves a firing step in which a raw material composition for the solid electrolyte is fired. The raw material composition can be obtained by mixing predetermined raw materials. The raw materials are substances containing elements that constitute the solid electrolyte, specifically, compounds containing Li, S, P, and X.

[0026] Examples of compounds containing Li element include lithium compounds such as lithium sulfide (Li2S), lithium oxide (Li2O), and lithium carbonate (Li2CO3), as well as elemental lithium metal. Examples of compounds containing S element include phosphorus sulfides such as diphosphorus trisulfide (P2S3) and diphosphorus pentasulfide (P2S5). Furthermore, elemental sulfur (S) can also be used as a compound containing sulfur (S) element. Examples of compounds containing phosphorus element include phosphorus sulfides such as diphosphorus trisulfide (P2S3) and diphosphorus pentasulfide (P2S5), phosphorus compounds such as sodium phosphate (Na3PO4), and elemental phosphorus.

[0027] Examples of compounds containing an X element include compounds of one or more elements selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I), and one or more elements selected from the group consisting of sodium (Na), lithium (Li), boron (B), aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), germanium (Ge), arsenic (As), selenium (Se), tin (Sn), antimony (Sb), tellurium (Te), lead (Pb), and bismuth (Bi), or compounds in which oxygen or sulfur is further bonded to the above compounds. More specifically, lithium halides such as LiF, LiCl, LiBr, and LiI; phosphorus halides such as PF3, PF5, PCl3, PCl5, POCl3, PBr3, POBr3, PI3, P2Cl4, and P2I4; SF2, SF4, SF6, and S2F 10 Examples of suitable halides include sulfur halides such as SCl2, S2Cl2, and S2Br2, sodium halides such as NaI, NaF, NaCl, and NaBr, and boron halides such as BCl3, BBr3, and BI3. These compounds can be used alone or in combination of two or more. Among these, it is preferable to use lithium halides (LiX (X represents a halogen)).

[0028] As an apparatus for preparing the raw material composition by mixing the above-mentioned respective raw materials, for example, an attritor, a paint shaker, a planetary ball mill, a ball mill, a bead mill, a homogenizer, etc. The amounts of the respective raw materials added when mixing are appropriately adjusted so as to satisfy the composition of the intended solid electrolyte.

[0029] The resulting raw material composition is calcined to cause a solid-state reaction, thereby obtaining a calcined product containing a crystalline phase having an argyrodite-type crystal structure. The calcination atmosphere can be, for example, an inert gas atmosphere such as an argon atmosphere or a nitrogen atmosphere, or a hydrogen sulfide atmosphere.

[0030] From the viewpoint of ensuring that a solid-phase reaction of the raw material composition occurs, the firing temperature is, for example, 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, in consideration of industrial producibility and economic efficiency, the firing temperature is, for example, preferably 700° C. or lower, more preferably 600° C. or lower, and even more preferably 550° C. or lower.

[0031] The firing time is not critical, and may be any time that allows a fired product of the desired composition to be obtained. Specifically, the firing time is preferably long enough for the solid-phase reaction of the raw material composition to occur sufficiently. The firing time may be, for example, 30 minutes or more, 2 hours or more, or 3 hours or more. On the other hand, the firing time may be, for example, 10 hours or less, or 5 hours or less.

[0032] Once the desired fired product is obtained in this way, it is subjected to a grinding process in which it is strongly ground. For strong grinding, for example, an attritor, paint shaker, planetary ball mill, ball mill, bead mill, homogenizer, etc. can be used. When performing strong grinding using these devices, it is advantageous to strongly stir the fired product to impart high energy. The energy imparted to the fired product is defined as the grinding energy E, expressed by the following formula (1): E(J·sec / g)=1 / 2ntmv 2 / s (1) In the formula, n represents the number of grinding media, t represents the grinding time (sec), m represents the mass of one grinding media (kg), v represents the speed of the grinding media (m / sec), and s represents the mass of the object to be ground (g). The velocity v of the grinding media can be calculated from equation (2), for example, in the case of a planetary ball mill. v(m / sec)=dπRα / 60 (2) In the formula, d is the diameter (m) of the pot container, R is the rotation speed (rpm), and α is the rotation-revolution ratio. In addition, in a grinding machine having a stirring mechanism such as a bead mill, the speed of the grinding media corresponds to the peripheral speed v (m / sec) of the stirring mechanism (disk, etc.).

[0033] In the pulverization step, it is preferable to apply a pulverization energy E, as defined by the above formula, of 200 J·sec / g or more to the fired product. Pulverization using such high energy is referred to herein as strong pulverization. Applying such high energy to the fired product has the advantage of obtaining a solid electrolyte containing a crystalline phase with an argyrodite-type crystal structure in which no heterophase or a very low heterophase ratio is present. To further enhance this advantage, the pulverization energy E applied to the fired product is preferably 200 J·sec / g or more and 200,000 J·sec / g or less, more preferably 500 J·sec / g or more and 100,000 J·sec / g or less, even more preferably 2,000 J·sec / g or more and 100,000 J·sec / g or less, particularly preferably 7,000 J·sec / g or more and 50,000 J·sec / g or less, and most preferably 7,000 J·sec / g or more and 20,000 J·sec / g or less.

[0034] The following conditions are examples of the grinding conditions for imparting the above-mentioned range of grinding energy E to the fired product. Equipment: Planetary ball mill Rotation speed: 100 rpm to 1000 rpm Grinding media material: zirconia or alumina Grinding media diameter: 2mm to 30mm Grinding time: 0.5 hours to 100 hours

[0035] The kinetic energy W (J) of one grinding media is W=1 / 2mv 2 (3) The definitions of m and v are as described above. This value means that the collision energy of one grinding medium is large. From the viewpoint of promoting the mechanochemical reaction, it is preferable that the grinding step includes a step in which the kinetic energy W defined by the above formula (3) is 0.0001 J or more. The kinetic energy W is more preferably 0.001 J or more and 1.0 J or less, even more preferably 0.005 J or more and 0.1 J or less, and even more preferably 0.01 J or more and 0.05 J or less.

[0036] After the fired product has been subjected to strong pulverization in this manner, it may be subjected to a known pulverization treatment in which lower energy than that applied in strong pulverization is applied, for the purpose of adjusting particle size, etc. The pulverization treatment is carried out to obtain the particle diameter D of the solid electrolyte of the present invention. 50 is preferably 5 μm or less, more preferably 3 μm or less, even more preferably 1.5 μm or less, even more preferably 1.3 μm or less, and still more preferably 1.1 μm or less, because the contact area between the solid electrolyte and the active material increases, improving the output characteristics of the battery. In the present production method, it is also preferable that the total grinding energy of the above-mentioned strong grinding and the known grinding process (a grinding process with lower energy than the strong grinding) be within the above-mentioned range, because applying such a grinding energy makes it easier to obtain a solid electrolyte containing a crystalline phase having an argyrodite-type crystal structure in which no heterophase exists or in which the heterophase exists at an extremely low ratio.

[0037] The solid electrolyte of the present invention obtained by the above method is slightly blackish, unlike the solid electrolyte described in Patent Document 1, for example. The solid electrolyte described in Patent Document 1 is whitish, unlike the solid electrolyte of the present invention. The present inventors believe that this difference is due to the difference in the manufacturing method. Specifically, the solid electrolyte of the present invention is obtained through the firing step as described above, and it is believed that the firing step causes the solid electrolyte to become slightly blackish. In contrast, the solid electrolyte described in Patent Document 1 is whitish because it is obtained without the firing step. The color of the solid electrolyte of the present invention is L * a * b * Lightness L in the color system * Expressed in terms of value, it is preferably 90 or less, more preferably 50 or more and 90 or less, even more preferably 60 or more and 85 or less, and even more preferably 75 or more and 82 or less. Lightness L * The method for measuring the value will be described in detail in the Examples below.

[0038] The solid electrolyte obtained by the above method can be used as a material for 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 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. 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. The lithium solid-state battery may be a primary battery or a secondary battery. The shape of the battery is not particularly limited, and for example, a laminated type, a cylindrical type, a prismatic type, or the like can be adopted. The term "solid-state battery" includes not only solid-state batteries that do not contain any liquid or gel-like substance as an electrolyte, but also batteries that contain, for example, 50% by mass or less, 30% by mass or less, or 10% by mass or less of a liquid or gel-like substance as an electrolyte.

[0039] When the solid electrolyte layer contains the solid electrolyte of the present invention, the solid electrolyte layer can be produced by, for example, a method of dropping a slurry containing the solid electrolyte, a binder, and a solvent onto a substrate and scraping it off with a doctor blade or the like, a method of contacting the substrate with the slurry and then cutting it with an air knife, a method of forming a coating film by screen printing or the like and then removing the solvent by heating and drying, etc. Alternatively, the solid electrolyte can also be produced by compacting a powdered solid electrolyte by pressing or the like and then processing it appropriately. The thickness of the solid electrolyte layer is typically preferably 5 μm or more and 300 μm or less, more preferably 10 μm or more and 100 μm or less, in order to balance short circuit prevention and volumetric capacity density.

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

[0041] The cathode material constituting the cathode layer can be any cathode material used as a cathode active material in lithium-ion batteries. For example, lithium-containing cathode active materials, specifically spinel-type lithium transition metal oxides and lithium metal oxides with layered structures, can be used. The use of a high-voltage cathode material as the cathode material can improve energy density. In addition to the cathode active material, the cathode material may contain a conductive material or other materials.

[0042] As the negative electrode material constituting the negative electrode layer, a negative electrode material used as a negative electrode active material in a lithium ion battery can be appropriately used. Since the solid electrolyte of the present invention is electrochemically stable, it can be used at a potential comparable to that of lithium metal or a lower potential (about 0.1 V vs. Li +Carbonaceous materials such as graphite, artificial graphite, natural graphite, and non-graphitizable carbon (hard carbon), which are materials that are charged and discharged using a lithium-ion battery (Li / Li), can be used as the anode material. This can significantly improve the energy density of solid-state batteries. Silicon or tin, which are promising high-capacity materials, can also be used as the active material. In batteries using conventional electrolytes, the electrolyte reacts with the active material during charging and discharging, causing corrosion on the active material surface, resulting in significant deterioration of battery characteristics. In contrast, using the solid electrolyte of the present invention instead of an electrolyte and silicon or tin as the anode active material prevents the above-mentioned corrosion reaction, thereby improving the durability of the battery. The anode material may also contain a conductive material or other materials in addition to the anode active material. [Example]

[0043] 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.

[0044] Example 1 (1) Preparation of raw material composition Lithium sulfide (Li2S) powder, diphosphorus pentasulfide (P2S5) powder, lithium chloride (LiCl) powder, and lithium bromide (LiBr) powder were weighed out to a total of 5 g each to achieve a composition of Li5PS4ClBr. 10 mL of heptane was added to these powders to prepare a slurry. This slurry was placed in an 80 mL zirconia container and placed in a planetary ball mill (Fritsch P-5). 90 g of 5 mm diameter ZrO2 balls were used as the milling media. The ball mill was operated at 100 rpm and milled for 10 hours. The resulting slurry was vacuum dried at room temperature to remove the solvent, yielding a raw material composition.

[0045] (2) Firing The raw material composition was fired to obtain a fired product. The firing was carried out using a tubular electric furnace. During firing, 100% pure nitrogen gas was circulated inside the electric furnace. The firing temperature was set to 600°C and firing was carried out for 4 hours.

[0046] (3) Strong crushing The fired material was strongly pulverized using a planetary ball mill (Fritsch P-5). The fired material was weighed so that the total amount was 5 g. 10 mL of heptane was added to this powder to prepare a slurry. This slurry was placed in a zirconia container with a volume of 80 mL. 90 g of ZrO2 balls with a diameter of 10 mm were used as the grinding media. The operating conditions of the ball mill were 370 rpm, and the grinding time was 2 hours. The strong grinding was performed to obtain a powder particle size D 50 The slurry was vacuum dried at room temperature to remove the solvent.

[0047] (4) Fine grinding The powder obtained by the strong grinding was finely ground using a planetary ball mill. The powder was weighed out so that the total amount was 2 g. 10 mL of toluene and a dispersant were added to this powder to prepare a slurry. This slurry was placed in an 80 mL zirconia container. 90 g of 0.8 mm diameter ZrO2 balls were used as the grinding media. The ball mill was operated at 100 rpm and ground for 3 hours. The resulting slurry was vacuum dried at 150 °C to remove the solvent. In this way, the desired solid electrolyte powder was obtained. The X / P molar ratio measured by ICP atomic emission spectroscopy was 2, and the S / P molar ratio was 4.

[0048] The grinding energy E [J·sec / g] in this example was calculated as follows. First, the grinding energy for strong grinding and fine grinding was calculated. (Strong crushing) The density of the ZrO2 grinding media used in this example was 6.0 g / cm 2 The number of grinding media n and the mass (kg) of one grinding media were calculated based on an input mass of 90g, assuming that the grinding media were spherical. As a result, the number of balls n was 28.6. The mass of one grinding media was 0.00314kg. The speed of the grinding media (m / sec) when the planetary ball mill was operated at 370 rpm was calculated using the above-mentioned formula (2). The rotation-revolution ratio α of the planetary ball mill used for grinding was 2.19, and the inner diameter of the mill pot used for grinding was 0.065 m, so the ball speed was calculated to be 2.76 (m / sec). Based on this value, the grinding energy E was calculated using the above-mentioned formula (1) to be 493 J·sec / g. (finely pulverized) The grinding energy during fine grinding was calculated in the same manner as for strong grinding, and was found to be 135 J·sec / g. Therefore, by adding up the grinding energy from the strong grinding process and the fine grinding process, we obtained the grinding energy E of 628 J·sec / g, as shown in Table 1 below.

[0049] Examples 2 and 3 The pulverization time in the strong pulverization step of Example 1 was set to 10 hours and 50 hours, respectively. Except for this, the same procedure as in Example 1 was carried out to obtain powders of solid electrolytes.

[0050] Comparative Example 1 This comparative example corresponds to the example in Patent Document 2. (1) Preparation of raw material composition The same procedure as in Example 1 was carried out. (2) Firing The raw material composition was fired to obtain a fired product. The firing was carried out using a tubular electric furnace. During firing, 100% pure nitrogen gas was circulated inside the electric furnace. The firing temperature was set to 600°C and firing was carried out for 4 hours. (3) Weak grinding The fired material was weakly pulverized using a planetary ball mill. The fired material was weighed out so that the total amount was 5 g. 10 mL of toluene and a dispersant were added to this powder to prepare a slurry. This slurry was placed in an 80 mL zirconia container. 90 g of 5 mm diameter ZrO2 balls were used as the grinding media. The ball mill was operated at 100 rpm, and the weak grinding was carried out for 3 hours. The resulting slurry was vacuum dried at room temperature to remove the solvent. (4) Fine grinding The same procedure as in Example 1 was carried out.

[0051] Comparative Example 2 This comparative example corresponds to the example in Patent Document 1. (1) Preparation of raw material composition The same procedure as in Example 1 was carried out. (2) Mechanical milling The raw material composition was subjected to mechanical milling using a planetary ball mill. Each raw material composition was weighed out so that the total amount was 5 g. 10 g of heptane was added to these powders to prepare a slurry. This slurry was placed in an 80 mL zirconia container. 90 g of 10 mm diameter ZrO2 balls were used as the milling media. The ball mill was operated at 370 rpm, and the milling time was 50 hours. The resulting slurry was vacuum dried at room temperature to remove the solvent. (3) Fine grinding The same procedure as in Example 1 was carried out.

[0052] [Rating 1] The solid electrolytes obtained in the examples and comparative examples were subjected to XRD measurement, and the Ia / Ib values ​​were calculated. The results are shown in Table 1. The XRD patterns are shown in Figures 1 and 2. The graphs for Examples 1, 2, and 3 and Comparative Examples 1 and 2 are offset by +3000, +6000, +9000, +12000, and +18000 counts from the measured values, respectively. The calculation method for Ia / Ib is as follows. The average count number of the peak intensity at 2θ = 23.5° ± 0.5° was defined as the background I0. The maximum count number of the peak intensity in the range of 2θ = 25.5° ± 1.0° was defined as IB. The value obtained by subtracting the background I0 from IB was defined as the peak intensity Ib due to the argyrodite-type crystal structure. The maximum count number of the peak intensity in the range of 27.0°±0.5° was defined as IA. The value obtained by subtracting the background I0 from IA was defined as the peak intensity Ia due to the Li2S crystal structure. In this XRD measurement, the measurement was carried out so that the background I0 value was 400 to 800 counts. In addition, the measurement was carried out so that the maximum peak intensity in this XRD measurement was 1500 counts or more. The maximum count number IC of the diffraction peak C was defined as the maximum count number in the range of 2θ=21.3°±0.3°. The count number Ic of the diffraction peak C was determined by subtracting the background I0 from the maximum count number IC. Furthermore, the obtained X-ray diffraction patterns were loaded into Smart Lab Studio II, and the crystallite size of the crystalline phase having an argyrodite-type crystal structure was calculated using the WPPF method for the sulfide solid electrolytes obtained in the examples and comparative examples. The instrument-derived parameters were corrected using a standard sample. The results are shown in Table 1. NIST SRM 640f Si was used as the standard sample for angle correction. NIST SRM 660c LaB6 was used as the standard sample for width correction. A Rigaku Corporation airtight holder for ASC (A00012149) was used for the air-tight cell. The airtight cover was a transparent airtight film, and the atmosphere was Ar. XRD measurements were performed using an X-ray diffractometer "Smart Lab SE" manufactured by Rigaku Corporation. The measurement conditions were: no exposure to air, scanning axis: 2θ / θ, scanning range: 10° to 120°, step width: 0.02°, scanning speed: 1° / min. The X-ray source was CuKα1 radiation. The tube voltage was 40 kV and the tube current was 80 mA. Measurements under these conditions resulted in a background I0 count within the range of 400 to 800, with a maximum peak intensity of over 1500 counts.

[0053] [Rating 2] The particle diameter D50 of the solid electrolytes obtained in the examples and comparative examples was measured by the following method, and the results are shown in Table 1 below. Using an automatic sample feeder for a laser diffraction particle size distribution analyzer ("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 ultrasound for 60 seconds. Then, the particle size distribution was measured using a laser diffraction particle size distribution analyzer "MT3000II" manufactured by Nikkiso Co., Ltd., and the particle sizes at which the cumulative volume was 10 vol%, 50 vol%, and 95 vol% were determined from the obtained volume-based particle size distribution chart. 10 , D 50 and D 95 In addition, D 10 , D 50 and D 95 When measuring, 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. The measurement was performed twice, and the arithmetic mean value of the obtained measurement values ​​was calculated as D 10 , D 50 and D 95 It was decided.

[0054] [Rating 3] The solid electrolytes obtained in the examples and comparative examples were evaluated for brightness L by the following method. * The results are shown in Table 1 below. The solid electrolyte powder was filled into a glass holder used for XRD measurement, and measurements were performed using a spectrophotometer (Konica Minolta, CM-2600d). The CIE standard illuminant D65 was used as the light source.

[0055] [Rating 4] Solid-state batteries were fabricated using the solid electrolytes obtained in the examples and comparative examples, and the rate characteristics of the solid-state batteries were measured by the following method. The results are shown in Table 1 below. (material) The layered compound LiNi is used as the positive electrode active material. 0.6 Co 0.2 Mn 0.2O2 (NCM) powder with a coating layer made of Li-Nb-O was used. Graphite was used as the negative electrode active material. The solid electrolyte used in the positive electrode layer was the solid electrolyte obtained in the Examples or Comparative Examples. A common argyrodite-type sulfide solid electrolyte was used for the separator layer and the negative electrode layer. (Preparation of Positive Electrode Mixture and Negative Electrode Mixture) The positive electrode mixture was prepared by mixing the positive electrode active material, the solid electrolyte, and the conductive additive (acetylene black) powder in a mortar at a mass ratio of 60:37:3. The negative electrode mixture was prepared by mixing graphite and a solid electrolyte in a mass ratio of 64:36 in a mortar. (Fabrication of solid-state battery cells) A ceramic cylinder (opening diameter 10.5 mm, height 18 mm) was opened at both ends. The lower opening was blocked with a stainless steel electrode, and 0.05 g of solid electrolyte was poured into the cylinder. An electrode was attached to the upper opening, and the electric field of approximately 0.8 tf / cm was obtained. 2 The electrolyte layer was fabricated by uniaxial press molding. The upper electrode was temporarily removed, a positive electrode mixture was poured onto the electrolyte layer, and the positive electrode mixture was smoothed and then reattached to the upper electrode. Next, the lower electrode was temporarily removed, and a negative electrode mixture was poured onto the electrolyte layer. The lower electrode was reattached, and the negative electrode mixture was applied to the lower electrode at a pressure of about 4.6 tf / cm. 2 The battery was then uniaxially press molded. The upper and lower electrodes were then clamped together and restrained with a torque pressure of 4 N m to produce an all-solid-state battery equivalent to 1 mAh. The all-solid-state battery fabrication process was carried out in a glove box filled with dry air with an average dew point of -70°C. The all-solid-state battery thus obtained was placed in an environmental test chamber maintained at 25°C, and connected to a charge / discharge measuring device to evaluate the battery characteristics. The battery was charged and discharged at 1 mA at 1 C. It was charged at 0.2 C up to 4.5 V using CC-CV method to obtain the initial charge capacity. It was discharged at 0.2 C up to 2.5 V using CC method to obtain the initial discharge capacity. Next, the battery was charged at 0.2C up to 4.5V using CC-CV charging, and then discharged at 5C down to 2.5V using CC discharging to obtain the discharge capacity at 5C. The rate characteristic (5C / 0.2C [%]) was obtained by calculating the ratio of the discharge capacity at 5C to the discharge capacity at 0.2C, which was taken as 100%.

[0056] [Table 1]

[0057] As is clear from the results shown in Table 1, the solid state batteries obtained using the solid electrolytes obtained in the examples have higher rate characteristics than the comparative examples. As is clear from the XRD patterns shown in FIGS. 1 and 2, no diffraction peaks of lithium sulfide were observed in the solid electrolytes obtained in the examples. [Industrial Applicability]

[0058] As described above in detail, the solid electrolyte of the present invention can provide excellent battery characteristics. Moreover, the production method of the present invention can easily produce such a solid electrolyte.

Claims

1. containing lithium (Li), phosphorus (P), sulfur (S) and halogen (X), It contains a crystalline phase having an argyrodite-type crystal structure, the crystallite size of the crystalline phase having an argyrodite-type crystal structure is 40 nm or less; In an X-ray diffraction pattern measured by an X-ray diffractometer (XRD) using CuKα1 radiation, when the intensity of Peak A observed in the range of 2θ=27.0°±0.5° is defined as Ia and the intensity of Peak B observed in the range of 2θ=25.5°±1.0° is defined as Ib, the ratio of Ia to Ib (Ia / Ib) is 0.2 or less, A solid electrolyte having a lightness L* value of 90 or less in the L*a*b* color system.

2. 2. The solid electrolyte according to claim 1, wherein, in the X-ray diffraction pattern, when the maximum count number of peak C observed in the range of 2θ = 21.3° ± 0.3° is defined as IC and the intensity of background observed in the range of 2θ = 23.5° ± 0.5° is defined as I0, the ratio of IC to I0, IC / I0, is 1.55 or less.

3. Volume cumulative particle size D at 50% cumulative volume by laser diffraction scattering particle size distribution measurement method ５０ The solid electrolyte according to claim 1 or 2, wherein the average particle size is 5 μm or less.

4. a molar ratio of the halogen (X) element to the phosphorus (P) element is 1.1 or more; 4. The solid electrolyte according to claim 1, wherein a molar ratio of said sulfur (S) element to said phosphorus (P) element is 4.9 or less.

5. 5. The solid electrolyte according to claim 1, wherein the halogen (X) element is chlorine (Cl) element and bromine (Br) element.

6. a firing step of firing a raw material composition containing lithium (Li), phosphorus (P), sulfur (S), and a halogen (X) at 200°C or higher to obtain a fired product; and a grinding step of grinding the fired product by applying a grinding energy E represented by the following formula (1) of 200 J·sec / g or more to the fired product. E(J・sec / g)=1 / 2ntmv ２ / s (1) In the formula, n represents the number of grinding media, t represents the grinding time (sec), m represents the mass of one grinding media (kg), v represents the speed of the grinding media (m / sec), and s represents the mass of the object to be ground (g).

7. Volume cumulative particle size D at 50% cumulative volume by laser diffraction scattering particle size distribution measurement method ５０ The method according to claim 6, wherein the powder is pulverized until the particle size becomes 5 μm or less.

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

9. A solid electrolyte layer comprising the solid electrolyte according to claim 1 .

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, the battery containing the solid electrolyte according to claim 1 .

Images