Sulfide-based solid electrolyte, method for preparing sulfide-based solid electrolyte, and all-solid-state battery including sulfide-based solid electrolyte

Abstract

To provide: a sulfide-based solid electrolyte having improved ionic conductivity; a method for preparing the sulfide-based solid electrolyte; and an all-solid-state battery including the sulfide-based solid electrolyte.SOLUTION: The present invention provides a sulfide-based solid electrolyte containing a Group 3 element and having an argyrodite-type crystal structure, the sulfide-based solid electrolyte being represented by the chemical formula Li7-x-3yMyPS6-xHax, where M is at least one element selected from Group 3 elements, Ha is at least one element selected from halogen elements, 1.0<x<2.5, and 0<y≤0.2.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a sulfide-based solid electrolyte, a method for manufacturing a sulfide-based solid electrolyte, and an all-solid-state battery including the sulfide-based solid electrolyte.

Background Art

[0002] For high safety, long life, and high energy density, the development of all-solid-state batteries in which the electrolyte of a lithium-ion battery is replaced with a solid electrolyte has been underway. Among several solid electrolytes, sulfide-based solid electrolytes such as Li 10 GeP2S 12 have high ionic conductivity close to that of an electrolyte solution and have advantages such as being soft and easily obtaining good adhesion to an active material, and the practical application of all-solid-state batteries using sulfide-based solid electrolytes is expected.

[0003] Lithium metal has attracted attention as a negative electrode material for all-solid-state batteries because it can increase the mass energy density (Wh / kg) due to its low mass per unit volume and large theoretical capacity. However, sulfide-based solid electrolytes such as Li 10 GeP2S 12 have a problem that they have low stability against lithium metal and are difficult to use together with a lithium metal negative electrode.

[0004] To solve this problem, Patent Documents 1 to 3 report sulfide-based solid electrolytes having an argyrodite-type crystal structure represented by Li 7-x-2y PS 6-x-y Cl x Patent Document 4 reports a sulfide-based solid electrolyte with improved stability against lithium metal by precisely controlling the composition of a sulfide-based solid electrolyte having a Li 10 GeP2S 12 crystal structure.

[0005] However, in the prior art, there is a problem that the ionic conductivity of the sulfide-based solid electrolyte is low.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present disclosure aims to provide a sulfide - based solid electrolyte with improved ionic conductivity, a method for manufacturing a sulfide - based solid electrolyte, and an all - solid - state battery including the sulfide - based solid electrolyte.

Means for Solving the Problems

[0008] To achieve the above object, the present disclosure provides a sulfide - based solid electrolyte containing a Group 3 element and having an argyrodite - type crystal structure, wherein the sulfide - based solid electrolyte has the chemical formula Li 7-x-3y M y PS 6-x Ha x and is represented by in the chemical formula, M is one or more elements selected from Group 3 elements, Ha is one or more elements selected from halogen elements, and 1.0 < x < 2.5, 0 < y ≤ 0.2 are satisfied.

[0009] In one embodiment, M may be Y and 0 < y < 0.2.

[0010] In one embodiment, M may be La.

[0011] In one embodiment, y may satisfy 0 < y < 0.05.

[0012] In one embodiment, the Ha may contain Br.

[0013] In one embodiment, x may satisfy 1.3 ≤ x ≤ 2.0.

[0014] In one embodiment, the lattice volume of the sulfide-based solid electrolyte may be 940 Å 3 or more and 980 Å 3 or less.

[0015] The present disclosure is a method for producing a sulfide-based solid electrolyte described in the above embodiment, mixing a lithium source, a group 3 element source, a phosphorus source, a sulfur source, and a halogen source to obtain a mixture, firing the mixture at a temperature of 250°C to 600°C, and provides a method including the above steps.

[0016] The present disclosure is an all-solid-state battery including a positive electrode, a negative electrode, and a solid electrolyte layer, wherein the solid electrolyte layer contains the sulfide-based solid electrolyte described in the above embodiment, and provides an all-solid-state battery.

Advantages of the Invention

[0017] The present disclosure can provide a sulfide-based solid electrolyte with improved ionic conductivity, a method for producing a sulfide-based solid electrolyte, and an all-solid-state battery including a sulfide-based solid electrolyte.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0019] Hereinafter, the present disclosure will be described in more detail.

[0020] The terms and words used in this specification and the claims should not be construed in a limited sense in accordance with ordinary or dictionary meanings, and should be construed in a meaning and concept that conforms to the technical idea of the present disclosure in accordance with the principle that the inventor can appropriately define the concept of the terms in order to explain his invention in the best way.

[0021] [Solid Electrolyte for All-Solid-State Battery] The solid electrolyte for an all-solid-state battery of the present disclosure may include one or more of a sulfide-based solid electrolyte, an oxide-based solid electrolyte, and a polymer-based solid electrolyte. Preferably, the solid electrolyte for an all-solid-state battery of the present disclosure is a sulfide-based solid electrolyte. The solid electrolyte for an all-solid-state battery may be mixed with a positive electrode binder and used as a positive electrode material, may be mixed with a negative electrode binder and used as a negative electrode material, or may be used as a separator. The solid electrolyte for an all-solid-state battery can further contain additives such as a lithium salt, a conductive material, and a binder resin according to the application.

[0022] [Sulfide-Based Solid Electrolyte]< The sulfide-based solid electrolyte is not particularly limited as long as it contains sulfur (S), and known sulfide-based solid electrolytes can be used.

[0023] The sulfide-based solid electrolyte may have a crystal structure. The sulfide-based solid electrolyte having a crystal structure can promote the conduction of lithium ions and can have a high lithium ion conductivity.

[0024] The sulfide-based solid electrolyte may have a crystal structure of the argyrodite type, NASICON type, perovskite type, garnet type, or LGPS type. Preferably, the sulfide-based solid electrolyte has an argyrodite-type crystal structure. Since the sulfide-based solid electrolyte having an argyrodite-type crystal structure has high stability against lithium metal, it enables the use of lithium metal having a high mass energy density as a negative electrode material.

[0025] The sulfide-based solid electrolyte may be in the form of amorphous, glass, or glass-ceramic.

[0026] The sulfide-based solid electrolyte has ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table and can include Li-P-S-based glass and Li-P-S-based glass-ceramic. Non-limiting examples of such sulfide-based solid electrolytes include Li2S-P2S5, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, Li2S-GeS2-ZnS, etc., and one or more of these can be included. However, it is not particularly limited to these.

[0027] Sulfide-based solid electrolytes can include a crystalline phase and an amorphous phase. The sulfide-based solid electrolyte can include a crystalline phase having an argyrodite-type crystal structure (also referred to herein as the argyrodite phase) and other phases (also referred to herein as impurity phases or unknown phases). The argyrodite-type crystal structure is preferably cubic. The other phases may be crystalline phases or amorphous phases. The other phases can include, regardless of whether they are crystalline phases or amorphous phases, Li2S phase, P2S5 phase, LiCl phase, LiBr phase, Li3PS4 phase, Sc2S3 phase, Y2S3 phase, La2S3 phase, and Ac2S3 phase, etc. Preferably, the sulfide-based solid electrolyte does not contain or substantially does not contain impurity phases other than the argyrodite phase. That is, preferably, the sulfide-based solid electrolyte may consist only of the argyrodite phase. When the sulfide-based solid electrolyte does not contain or substantially does not contain impurity phases, lithium ion conduction is less likely to be inhibited, so the sulfide-based solid electrolyte can have a high lithium ion conductivity.

[0028] The proportion of the crystalline phase contained in the sulfide-based solid electrolyte can be evaluated quantitatively or semi-quantitatively from the XRD pattern. As one method, the proportion of the crystalline phase can be evaluated by comparing the peak intensities (height or area) of the XRD pattern.

[0029] The sulfide-based solid electrolyte according to one embodiment of the present disclosure has the chemical formula Li 7-x-3y M y PS 6-x Ha x and is represented by. In the above chemical formula, M is one or more elements selected from Group 3 elements, Ha is one or more elements selected from halogen elements, and 1.0 < x < 2.5, 0 < y ≦ 0.2 are satisfied. Such a sulfide-based solid electrolyte can have a high lithium ion conductivity.

[0030] The sulfide-based solid electrolyte according to one embodiment of the present disclosure is Li 7-x PS 6-x Ha xA part of lithium therein is substituted by a Group 3 element M which can become a trivalent cation. The Group 3 element M substituting lithium may be one or more selected from the group consisting of scandium (Sc), yttrium (Y), lanthanum (La), and actinium (Ac). The ionic radius (6 - coordination) of lithium (Li) is 76 pm, and the ionic radii (6 - coordination) of scandium (Sc), yttrium (Y), lanthanum (La), and actinium (Ac) are 88 pm, 104 pm, 117 pm, and 126 pm, respectively. Based on the valence of the element, three lithiums can be substituted by one Group 3 element M. By substituting the lithium sites with the Group 3 element M, lithium - site vacancies are generated, and the lithium - ion conductivity can be improved. Also, by substituting the lithium sites with the Group 3 element M, the lattice constant and lattice volume of the sulfide - based solid electrolyte change, and it can have a crystal structure suitable for lithium - ion conduction.

[0031] In addition, when a Group 3 element M which can become a trivalent cation enters into the crystal lattice of Li 7-x PS 6-x Ha x a sulfide - based solid electrolyte according to an embodiment of the present disclosure can be formed. The Group 3 element M entering into the crystal lattice may be one or more selected from the group consisting of scandium (Sc), yttrium (Y), lanthanum (La), and actinium (Ac). Scandium (Sc), yttrium (Y), lanthanum (La), and actinium (Ac) can be used alone or in combination. Li 7-x PS 6-x Ha x By the entry of the Group 3 element M into the crystal lattice of Li

[0032] Preferably, the Group 3 element M is yttrium (Y) and / or lanthanum (La), and particularly preferably, it is yttrium (Y). When the Group 3 element M is yttrium (Y) and / or lanthanum (La), the sulfide-based solid electrolyte can have a high crystallinity, and therefore, the sulfide-based solid electrolyte can have a high ionic conductivity.

[0033] The chemical formula Li 7-x-3y M y PS 6-x Ha x The addition amount y of the Group 3 element M in is 0 < y ≤ 0.2. It is preferable that y satisfies 0 < y < 0.05.

[0034] When the Group 3 element M is yttrium (Y), preferably, y satisfies 0 < y < 0.2, more preferably, 0 < y ≤ 0.1, still more preferably, 0 < y ≤ 0.05, even more preferably, 0 < y ≤ 0.025, and most preferably, 0.01 ≤ y ≤ 0.02.

[0035] When the Group 3 element M is lanthanum (La), preferably, y satisfies 0 < y < 0.2, more preferably, 0 < y ≤ 0.1, even more preferably, 0 < y ≤ 0.05, and most preferably, 0.01 ≤ y ≤ 0.03.

[0036] When y satisfies the above range, the sulfide-based solid electrolyte can have a high ionic conductivity. When y = 0, no change in the crystal structure due to the substitution of the Group 13 element M can be obtained, and the ionic conductivity may be low. When y exceeds 0.2, the argyrodite-type crystal structure of the sulfide-based solid electrolyte may not be maintained, and the impurity phase that inhibits lithium ion conduction in the sulfide-based solid electrolyte may increase, resulting in a decrease in ionic conductivity.

[0037] The chemical formula Li 7-x-3y M y PS 6-x Ha xThe halogen (Ha) therein is one or more elements selected from halogen elements. The halogen (Ha) preferably contains bromine (Br). More preferably, the halogen (Ha) contains chlorine (Cl) and bromine (Br). When sulfur (S) is a divalent anion, it has a stronger ability to attract lithium ions compared to monovalent halogens and can significantly inhibit the movement of lithium ions. By including bromine (Br) as the halogen, the occupancy of sulfur (S) at specific sites in the argyrodite-type crystal structure decreases, the halogen occupancy at those sites increases, and the lithium ion mobility around the bromine (Br) sites can become active. As a result, the lithium ion conductivity can be improved. Also, bromine (Br) can combine with Li in the sulfide-based solid electrolyte to form lithium bromide (LiBr), which is a water-absorbing substance. Lithium bromide (LiBr) can adsorb moisture that can reduce the lithium ion conductivity and improve the lithium ion conductivity of the sulfide-based solid electrolyte.

[0038] The chemical formula Li 7-x-3y M y PS 6-x Ha x The ratio x of the halogen (Ha) therein satisfies 1.0 < x < 2.5, preferably satisfies 1.1 ≦ x ≦ 2.3, more preferably satisfies 1.3 ≦ x ≦ 2.0, and even more preferably satisfies 1.3 ≦ x ≦ 1.8. When x satisfies the above range, the argyrodite-type crystal structure is stabilized, and the sulfide-based solid electrolyte can have high ionic conductivity.

[0039] The stoichiometric composition of the sulfide-based solid electrolyte of the present invention is very important. Therefore, sulfide-based solid electrolytes not represented by the chemical formula Li 7-x-3y M y PS 6-x Ha x are not included in the sulfide-based solid electrolyte of the present disclosure. Sulfide-based solid electrolytes not represented by the chemical formula Li 7-x-3y M y PS 6-x Ha x may contain a large amount of impurities and may have poor crystallinity. For example, the reference composition Li 5.3Y 0.1 PS 4.5 Cl 0.8 Br 0.8 is a sulfide-based solid electrolyte containing yttrium (Y), and the chemical formula Li 7-x-3y M y PS 6-x Ha x When trying to apply it to, it can be inferred that x = 1.6 from the contents of chlorine (Cl) and bromine (Br) as halogen (Ha). However, in this case, when applying it to the chemical formula for the content of sulfur (S), S 4.4 results, but in the reference composition, S 4.5 is, and the two are different. Also, it can be inferred that y = 0.1 from the content of yttrium (Y). However, in this case, when applying it to the chemical formula for the content of lithium (Li), Li 5.1 results, but in the reference composition, Li 5.3 is, and the two are different.

[0040] The ionic conductivity of the sulfide-based solid electrolyte can be affected by the crystallinity of the sulfide-based solid electrolyte. The crystallinity can be evaluated from the XRD pattern. In the XRD pattern, when no other phases (crystalline phases or amorphous phases such as Li2S phase, P2S5 phase, LiCl phase, LiBr phase, Li3PS4 phase, Sc2S3 phase, Y2S3 phase, La2S3 phase, and Ac2S3 phase) other than the argyrodite crystal phase are observed or hardly observed, the sulfide-based solid electrolyte can have high ionic conductivity.

[0041] The lattice volume of the sulfide-based solid electrolyte can change due to the substitution of lithium sites by group 3 element M. Although not bound by theory, when group 3 element M exhibits the characteristics of a trivalent cation, the interaction with other anions present in the sulfide-based solid electrolyte is strengthened, and it is considered that the lattice volume changes, that is, increases or decreases. Such a change in the lattice volume leads to a crystal structure suitable for lithium ion conduction, and the sulfide-based solid electrolyte can have high ionic conductivity.

[0042] The lattice volume of the sulfide-based solid electrolyte is 940 Å 3 or more and 980 Å3 is as follows, preferably 950 Å 3 or more, 970 Å 3 is as follows, more preferably 954 Å 3 or more, 966 Å 3 is as follows, more preferably 955 Å 3 or more, 964 Å 3 is as follows. The lattice constant and lattice volume can be evaluated from the XRD pattern. The lattice volume of the sulfide-based solid electrolyte can vary depending on the firing temperature even with the same composition. When the lattice volume satisfies the above range, lithium ion conduction in the sulfide-based solid electrolyte is promoted, and the sulfide-based solid electrolyte can have a high ionic conductivity.

[0043] The ionic conductivity of the sulfide-based solid electrolyte (also referred to as "lithium ion conductivity" in this specification) means the ionic conductivity at room temperature (25 °C, 298 K) and normal pressure (1 atm) unless otherwise specified. When the sulfide-based solid electrolyte is used in an all-solid-state battery, it is preferably 4 mS / cm or more in practical use. The ionic conductivity of the sulfide-based solid electrolyte according to one embodiment of the present disclosure is 1.5 mS / cm or more, preferably 4 mS / cm or more, more preferably 8 mS / cm or more, even more preferably 10.8 mS / cm or more, and most preferably 11.5 mS / cm or more.

[0044] The sulfide-based solid electrolyte according to one embodiment of the present disclosure can be obtained by a manufacturing method including a step of mixing a lithium source, a group 3 element source, a phosphorus source, a sulfur source, and a halogen source to obtain a mixture, and a step of firing the mixture at a temperature of 250 °C to 600 °C. The firing of the mixture may be performed in an inert atmosphere such as argon gas and nitrogen gas.

[0045] The lithium source, group 3 element source, phosphorus source, sulfur source, and halogen source may be compounds such as sulfides, oxides, nitrides. Lithium sulfide (Li2S) can be used as the lithium source, diphosphorus pentasulfide (P2S5) can be used as the phosphorus source, and lithium halides (LiHa) such as lithium chloride (LiCl) and lithium bromide (LiBr) can be used as the halogen source. For example, a sulfide can be used as the group 3 element source. Alternatively, sulfur can be supplied from other element sources. That is, one or more of the lithium source, group 3 element source, phosphorus source, and halogen source may also serve as the sulfur source.

[0046] In the case of a sulfide-based solid electrolyte having an argyrodite-type crystal structure, the firing temperature is preferably 350°C to 550°C, more preferably 380°C to 500°C, and even more preferably 410°C to 450°C. When the firing temperature satisfies the above range, the formation of the argyrodite-type crystal structure is promoted, and the sulfide-based solid electrolyte can have a high crystallinity. Thereby, a sulfide-based solid electrolyte having a high ionic conductivity can be obtained.

[0047] [All-solid-state battery] The sulfide-based solid electrolyte of the present disclosure can be used as an electrolyte for an all-solid-state battery in an all-solid-state battery including a positive electrode, a negative electrode, and a solid electrolyte layer. The sulfide-based solid electrolyte of the present disclosure can be used together with an active material in the electrode active material layers of the positive electrode and the negative electrode. The solid electrolyte for an all-solid-state battery can be used as the material of the solid electrolyte layer. The average particle size of the electrolyte for an all-solid-state battery can be controlled according to the application. By controlling the average particle size of the electrolyte for an all-solid-state battery, the ionic conductivity can be improved.

[0048] [Solid electrolyte layer] In the present disclosure, the solid electrolyte layer may have a thickness of about 50 μm or less, preferably about 15 μm to 50 μm. The thickness may have an appropriate value considering the ionic conductivity, physical strength, energy density of the applicable battery, etc. within the above-mentioned range. For example, in terms of ionic conductivity and energy density, the thickness may be 10 μm or more, 20 μm or more, or 30 μm or more. On the other hand, in terms of physical strength, the thickness may be 50 μm or less, 45 μm or less, or 40 μm or less. Further, the solid electrolyte layer may have a tensile strength of about 100 kgf / cm 2 to about 2,000 kgf / cm 2 and may have a porosity of 15 vol% or less, or about 10 vol% or less. Thus, the solid electrolyte layer according to the present disclosure can have high mechanical strength despite being a thin film.

[0049] <Positive electrode and negative electrode> In the present disclosure, the positive electrode and the negative electrode each include a current collector and an electrode active material layer formed on at least one surface of the current collector, and the electrode active material layer includes a plurality of electrode active material particles and a solid electrolyte. Further, the electrode can further include one or more of a conductive material and a binder resin as necessary. Further, the electrode can further include various additives for the purpose of complementing and improving the physicochemical properties of the electrode.

[0050] In the present disclosure, as the negative electrode active material, any material that can be used as the negative electrode active material of a lithium-ion secondary battery can be used. For example, the negative electrode active material is carbon such as graphitizable carbon and graphite carbon; Li x Fe2O3 (0 ≦ x ≦ 1), Li x WO2 (0 ≦ x ≦ 1), Sn x Me 1-x Me’ y O z(Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8), etc. metal composite oxides; lithium metal; lithium alloy; silicon metal; silicon-based alloy; indium metal; indium alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4 and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; titanium oxides; lithium titanium oxides, etc. One or more selected therefrom can be used. In a specific embodiment, the negative electrode active material can include a carbon-based material and / or Si.

[0051] In the case of the positive electrode, the electrode active material can be used without limitation as long as it can be used as the positive electrode active material of a lithium ion secondary battery. For example, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x O4 (x is 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x A x O2 (A = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 to 0.3) nickel-site type lithium nickel oxide represented by; chemical formula LiMn 2-x A x O2 (A = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or lithium manganese composite oxide represented by Li2Mn3AO8 (A = Fe, Co, Ni, Cu or Zn); LiNi x Mn 2-x O4 spinel structure lithium manganese composite oxide represented by; Li(Ni a Co b Mn c)An NCM-based composite oxide represented by O2 (where a, b, and c are atomic fractions of independent elements, 0 < a < 1, 0 < b < 1, 0 < c < 1, and a + b + c = 1); LiMn2O4 in which part of the Li in the chemical formula is substituted with alkaline earth metal ions; a disulfide compound; Fe2(MoO4)3, etc. can be included, but it is not limited thereto.

[0052] In the present disclosure, as the current collector, a current collector having electrical conductivity such as a metal plate, which is known in the secondary battery field, can be appropriately used according to the polarity of the electrode.

[0053] In the present disclosure, the conductive material is usually added in an amount of 1% to 30% by mass based on the total mass of the mixture containing the electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, nickel powder; conductive whiskers such as zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; and one or more mixtures selected from conductive materials such as polyphenylene derivatives can be included.

[0054] In the present disclosure, the binder resin is not particularly limited as long as it is a component that aids in the binding of the active material and the conductive material, etc., and the binding to the current collector. For example, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers, etc. can be mentioned. The binder resin can usually be included in the range of 1 to 30% by mass, or 1 to 10% by mass, based on 100% by mass of the electrode active material layer.

[0055] In the present disclosure, the electrode active material layer can contain one or more additives such as an oxidation stabilizer, a reduction stabilizer, a flame retardant, a heat stabilizer, an anti-fogging agent, etc., as necessary.

[0056] The present disclosure provides a secondary battery having the above-described structure. Further, the present disclosure provides a battery module including the secondary battery as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. At this time, specific examples of the device include power tools driven by receiving power from an electric motor; electric vehicles including electric vehicles (Electric Vehicle: EV), hybrid electric vehicles (Hybrid Electric Vehicle: HEV), plug-in hybrid electric vehicles (Plug-in Hybrid Electric Vehicle: PHEV), etc.; electric two-wheel vehicles including electric bicycles (E-bike) and electric scooters (E-scooter); electric golf carts; power systems, etc., but are not limited thereto.

[0057] Hereinafter, the present disclosure will be described in more detail with reference to examples. However, the following examples are for illustrating the present disclosure, and the scope of the present disclosure is not limited thereto.

[0058] Example 1 As raw materials, lithium sulfide (Li2S, Mitsuwa Chemical), phosphorus pentasulfide (P2S5, Aldrich), yttrium sulfide (Y2S3, High Purity Chemical), lithium chloride (LiCl, Aldrich), and lithium bromide (LiBr, Aldrich) were used, and the composition was Li 5.4-3y M y PS 4.4 Cl 1.0 Br 0.6Weighed and mixed in an Ar gas flow glove box so that the addition amount y of Group 3 element M was 0.0125 to obtain a mixed powder. This mixed powder was placed in a ZrO2 pot together with ZrO2 balls to obtain a sealed pot. This sealed pot was installed in a planetary ball mill apparatus and ball milled at 380 rpm for 20 hours. Then, the pot was opened in the glove box and the powder was recovered. This powder was placed in a carbon crucible, sealed, and fired at 430 °C for 8 hours while flowing Ar gas. The fired powder was pulverized in a mortar for 10 minutes to obtain a solid electrolyte.

[0059] Example 2 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the addition amount y of Group 3 element M was 0.025.

[0060] Example 3 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the addition amount y of Group 3 element M was 0.075.

[0061] Comparative Example 1 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the addition amount y of Group 3 element M was 0.2.

[0062] Example 4 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that lanthanum sulfide (La2S3, high-purity chemical) was used instead of yttrium sulfide (Y2S3, high-purity chemical) as the raw material of Group 3 element M.

[0063] Example 5 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 4, except that the addition amount y of Group 3 element M was 0.025.

[0064] Example 6 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 4, except that the addition amount y of Group 3 element M was 0.075.

[0065] Example 7 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 4, except that the addition amount y of Group 3 element M was 0.2.

[0066] Comparative Example 2 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that Group 3 element M was not added, that is, the addition amount y of Group 3 element M was 0.

[0067] Comparative Example 3 As raw materials, lithium sulfide (Li2S, Mitsuwa Chemical), phosphorus pentasulfide (P2S5, Aldrich), yttrium sulfide (Y2S3, High Purity Chemical), lithium chloride (LiCl, Aldrich), and lithium bromide (LiBr, Aldrich) were used. Weighed and mixed in a mortar in an Ar gas flow glove box so that the composition was Li 5.3 Y 0.1 PS 4.5 Cl 0.8 Br 0.8 to obtain a mixed powder. This mixed powder was placed in a ZrO2 pot together with ZrO2 balls to obtain a sealed pot. This sealed pot was installed in a planetary ball mill apparatus and ball milled at 380 rpm for 20 hours. Then, the pot was opened in the glove box and the powder was recovered. This powder was placed in a carbon crucible, sealed, and then fired at 430 °C for 8 hours while flowing Ar gas. The fired powder was pulverized in a mortar for 10 minutes to obtain a solid electrolyte.

[0068] Comparative Example 4 As raw materials, lithium sulfide (Li2S, Mitsuwa Chemical), phosphorus pentasulfide (P2S5, Aldrich), lanthanum(III) sulfide (La2S3, High Purity Chemical), and lithium chloride (LiCl, Aldrich) were used. The composition was Li 6.15 La 0.075 P 0.925Weighed and mixed in an Ar gas flow glove box to obtain S5Cl, and a mixed powder was obtained. This mixed powder was placed in a ZrO2 pot together with ZrO2 balls to obtain a sealed pot. This sealed pot was installed in a planetary ball mill device and ball milled at 380 rpm for 20 hours. Then, the pot was opened in the glove box and the powder was recovered. This powder was placed in a carbon crucible, sealed, and then fired at 430 °C for 8 hours while flowing Ar gas. The fired powder was ground in a mortar for 10 minutes to obtain a solid electrolyte.

[0069]

Table 1

[0070]

Table 2

[0071] [Evaluation] The following evaluations were performed using the obtained solid electrolyte.

[0072] (XRD measurement) A predetermined amount of the solid electrolyte was placed in a sealed holder in an Ar gas flow glove box, and XRD measurement was performed. The lattice constant, lattice volume, and full width at half maximum were calculated from the obtained XRD (X-ray diffraction) pattern. The full width at half maximum was calculated from the (311) plane crystal peak of the alluaudite-type crystal structure observed around 2θ = 30° in Figures 1 and 2.

[0073] The measuring device and conditions are as follows. · X-ray diffractometer: Rigaku Smartlab · Radiation source: Cu-Kα ray (λ = 1.5418 Å) · Voltage: 45 kV · Current: 200 mA · Scan range (2θ): 10 - 60 ° · Step size: 0.01 °

[0074] (Ionic conductivity measurement) A predetermined amount of solid electrolyte was placed inside a Macor tube. The Macor tube and a pellet forming jig (upper press pin and lower press pin) were combined and press-molded at 5 MPa using a uniaxial press. Thereafter, a predetermined amount of gold powder was placed on both sides of the pellet, and then press-molded at 7.5 MPa using a uniaxial press to obtain a Macor tube cell. The obtained Macor tube cell was installed in an electrochemical measurement jig cell, and pressurized up to 5.0 N·m using a torque wrench to obtain an ion conductivity measurement cell. The obtained ion conductivity measurement cell was connected to an impedance measurement device, and the resistance value of the solid electrolyte pellet was measured at room temperature (298 K) and normal pressure (1 atm) to derive the ion conductivity [mS / cm] of the solid electrolyte.

[0075] (Initial charge-discharge capacity measurement) An NCM-based cathode active material with an Ni content of 80 mol% and a solid electrolyte were weighed at a mass ratio of 70:30. To this, carbon black was added as a conductive assistant at 1.5 mass% and mixed to obtain a cathode mixture. After weighing 80 mg of the solid electrolyte obtained above, it was placed in a forming jig and pressure-molded at 6 MPa for 1 minute to obtain a solid electrolyte pellet. After placing 10 mg of the cathode mixture obtained above on one surface of the obtained solid electrolyte pellet, the SUS press pin of the forming jig was pressed against it to flatten and form a cathode layer. An Al plate was placed on the obtained cathode layer and pressure-molded at 30 MPa for 1 minute. Thereafter, an Li-Cu foil was placed on the surface of the solid electrolyte pellet opposite to the cathode layer, and pressure-molded at 2 MPa for 30 seconds. This was combined with an SUS press pin to fabricate a Macor tube cell. The obtained Macor tube cell was installed in a battery cell, and a torque of 2 N·m was applied to obtain an all-solid-state battery cell.

[0076] Using the obtained all-solid-state battery, a charge-discharge test was performed with a voltage range of 4.25 V - 3.0 V, a charging condition of CC (0.05C) - CV (0.01C cut-off), and a discharging condition of CC (0.05C). The initial charge capacity and the initial discharge capacity were determined from the obtained charge-discharge curve.

[0077] [Evaluation results] (Crystal phase) The evaluation results of the crystal phases (crystal structures) identified from the XRD patterns by XRD measurement are shown in Tables 1 and 2. Also, the measured XRD patterns are shown in Figures 1 and 2.

[0078] As shown in Table 1, in Example 1 and Comparative Example 2, almost no impurity phase (also called unknown phase) was observed, and there were almost only the peaks of the argyrodite phase. Also, in Examples 2 to 7, there were the peaks of the argyrodite phase and a small amount of impurity phases other than the argyrodite phase. On the other hand, in Comparative Example 1, almost no peak of the argyrodite phase was observed, and a large amount of impurity phases other than the argyrodite phase were present. The impurity phases were phases derived from raw materials such as Li2S and Y2S3, for example.

[0079] As shown in Table 2, in Comparative Example 3, a large amount of impurity phases other than the argyrodite phase were present. Also, in Comparative Example 4, almost no argyrodite phase was observed, and a large amount of impurity phases were present.

[0080] Figures 1 and 2 show the XRD patterns of Examples 1 to 7 and Comparative Examples 1 and 2. Regarding Example 1 where the addition amount of Y as the Group 3 element was y = 0.0125 and Comparative Example 2 where the addition amount of the Group 3 element was y = 0, almost only the peaks of the argyrodite phase were observed. Also, regarding Examples 2 and 3 where the addition amounts of Y as the Group 3 element were y = 0.025 and 0.075 respectively, and Examples 4 to 7 where the addition amounts of La as the Group 3 element were y = 0.0125, 0.025, 0.075, and 0.2 respectively, almost only the peaks of the argyrodite phase were observed, but the peaks of impurity phases derived from raw materials such as Li2S, Y2S3, and La2S3 were also observed. On the other hand, regarding Comparative Example 1 where the addition amount of Y as the Group 3 element was y = 0.2, almost no peak of the argyrodite phase was observed, and a large amount of peaks of impurity phases were observed.

[0081] In Examples 1 to 7 and Comparative Example 2, a sulfide-based solid electrolyte having an argyrodite-type crystal structure without or with almost no impurity phase was obtained. A sulfide-based solid electrolyte with high crystallinity can promote the hopping conduction of lithium ions and contribute to an increase in ionic conductivity.

[0082] (Lattice volume) The lattice constants derived from the XRD patterns were in the range of 9.8518 Å to 9.8773 Å in the examples, and the lattice volume was 956.2 Å 3 to 963.6 Å 3 in the range. On the other hand, in Comparative Example 1 where the addition amount of Y as the Group 3 element was y = 0.2, since there were many impurities, it was impossible to measure the lattice constant. Also, in Comparative Example 2 where the lithium sites of the sulfide-based solid electrolyte were not substituted with the Group 3 element M, the lattice constant was 9.9471 Å and the lattice volume was 984.2 Å 3 It was shown that by substituting the lithium sites of the argyrodite-type crystal structure with the Group 3 element M, the lattice volume of the crystal decreased by about 2.1 to 2.8%. Although not bound by theory, it is considered that the crystal volume of the sulfide-based solid electrolyte can change because one of the three lithium sites is substituted with the Group 3 element M and the other becomes a lithium vacancy. The lithium vacancy serves as a path for the hopping conduction of lithium ions and is considered to contribute to an increase in ionic conductivity. Also, the Group 3 element M substituted in the lithium site can have a trivalent valence, and the force attracting anions around the Group 3 element M site can change compared to the monovalent lithium ion. As a result, it is considered that the crystal volume of the sulfide-based solid electrolyte changes and becomes a structure suitable for the hopping conduction of lithium ions.

[0083] The full width at half maximum of the (311) plane crystal peak of the argyrodite crystal structure was in the range of 0.07° to 0.09° in the examples. On the other hand, the measurement of the full width at half maximum was impossible in Comparative Example 1, and the full width at half maximum was 0.08° in Comparative Example 2. In particular, Examples 1 and 2 with the addition amount y = 0.0125 and 0.025 of Y as the Group 3 element M, and Example 5 with the addition amount y = 0.025 of La as the Group 3 element M showed a small full width at half maximum of 0.07° and a high ionic conductivity of 10.8 mS / cm or more. A small full width at half maximum corresponds to a large crystallite size and is considered to contribute to the increase in ionic conductivity.

[0084] (Ionic conductivity) The measurement results of ionic conductivity are shown in Tables 1 and 2. Also, for the composition Li of the sulfide-based solid electrolyte 5.4-3y M y PS 4.4 Cl 1.0 Br 0.6 Figure 3 shows a graph with the addition amount y of the Group 3 element M on the horizontal axis and the ionic conductivity measured at 25°C and normal pressure on the vertical axis. Each point in Figure 3 corresponds to Examples 1 to 3 doped with Y as the Group 3 element M and Comparative Example 1, Examples 4 to 7 doped with La as the Group 3 element M, and Comparative Example 2 not doped with the Group 3 element M (corresponding to "undoped" in the figure).

[0085] As can be seen from Figure 3 and Table 1, in Examples 1 to 7, the ionic conductivity was in the range of 2.84 mS / cm to 11.7 mS / cm. In Example 1 with the addition amount y = 0.0125 of Y as the Group 3 element M, the ionic conductivity showed the highest value of 11.7 mS / cm. On the other hand, in Comparative Example 1 with the addition amount y = 0.2 of Y as the Group 3 element M, the ionic conductivity was 0.000061 mS / cm. Thus, the ionic conductivity of each example could be increased compared to that of Comparative Example 1. In Comparative Example 1, since the addition amount y of Y as the Group 3 element M was too large, the crystallinity of the argyrodite-type crystal structure decreased, resulting in a decrease in ionic conductivity.

[0086] In Comparative Example 2 where no Group 3 element M was added, the ionic conductivity was 10.7 mS / cm. In Examples 1 and 2 where the addition amount y of Y as the Group 3 element M was y ≤ 0.025 and in Examples 4 and 5 where the addition amount y of La as the Group 3 element M was y ≤ 0.025, an ionic conductivity of 10.8 mS / cm or higher, which is higher than that of Comparative Example 2, was exhibited. The increase in ionic conductivity is considered to be due to an increase in the crystallinity of the argyrodite-type crystal structure due to a decrease in impurities present in the sulfide-based solid electrolyte. However, from the XRD results in FIGS. 1 and 2 and Table 1, Examples 2, 4, and 5, which have a higher ionic conductivity than Comparative Example 2, contain more impurity phases than Comparative Example 2. That is, Examples 2, 4, and 5, which have a higher ionic conductivity than Comparative Example 2, have a lower crystallinity than Comparative Example 2. Therefore, it can be seen that not only the crystallinity of the argyrodite-type crystal structure but also the presence of the Group 3 element M can affect the ionic conductivity.

[0087] As can be seen from Table 2, in Comparative Example 3 with a different stoichiometric composition, the ionic conductivity was 1.5 mS / cm. In Comparative Example 4 with a different stoichiometric composition, the ionic conductivity was 0.09 mS / cm. This is considered to be due to a decrease in the crystallinity of the argyrodite-type crystal structure and the presence of a large amount of impurities, resulting in a decrease in ionic conductivity.

[0088] (Battery characteristics) When the sulfide-based solid electrolyte of Example 1 was used in an all-solid-state battery, the sulfide-based solid electrolyte had high stability against lithium metal as a negative electrode material, and the all-solid-state battery exhibited excellent charge-discharge characteristics and capacity characteristics. The relative ratio of the initial discharge capacity of the all-solid-state battery capacity when the solid electrolyte of Example 1 was used in the all-solid-state battery to the all-solid-state battery capacity when the sulfide-based solid electrolyte of Comparative Example 2 without adding a Group 3 element was used in the all-solid-state battery was 105%. Also, when the sulfide-based solid electrolyte of Example 5 was used in the all-solid-state battery, the sulfide-based solid electrolyte had high stability against lithium metal as a negative electrode material, and the all-solid-state battery exhibited excellent charge-discharge characteristics and capacity characteristics. The relative ratio of the initial discharge capacity of the all-solid-state battery capacity when the solid electrolyte of Example 5 was used in the all-solid-state battery to the all-solid-state battery capacity when the sulfide-based solid electrolyte of Comparative Example 2 without adding a Group 3 element was used in the all-solid-state battery was 106%. That is, by using the sulfide-based solid electrolytes of Examples 1 and 5 having high ionic conductivity in the all-solid-state battery, the initial discharge capacity of the all-solid-state battery could be improved.

[0089] As described above, the present disclosure has been described by way of limited examples and drawings. However, the present disclosure is not limited thereto, and it goes without saying that various modifications and variations can be made within the equivalent scope of the technical idea of the present disclosure and the appended claims by those having ordinary knowledge in the technical field to which the present disclosure pertains.

Claims

1. A sulfide-based solid electrolyte containing a Group 3 element and having an argyrodite-type crystal structure, wherein the sulfide solid electrolyte is represented by the chemical formula Li ７－ｘ－３ｙ M ｙ PS ６－ｘ Ha ｘ and wherein in the chemical formula, M is one or more elements selected from Group 3 elements, Ha is one or more elements selected from halogen elements, and 1.0 < x < 2.5, 0 < y ≤ 0.2 are satisfied, a sulfide-based solid electrolyte.

2. The sulfide-based solid electrolyte according to Claim 1, wherein M is Y and 0 < y < 0.

2.

3. The sulfide-based solid electrolyte according to Claim 1, wherein M is La.

4. The sulfide-based solid electrolyte according to Claim 2 or 3, wherein 0 < y < 0.05 is satisfied for y.

5. The sulfide-based solid electrolyte according to Claim 4, wherein Ha contains Br.

6. The sulfide-based solid electrolyte according to Claim 1, wherein 1.3 ≤ x ≤ 2.0 is satisfied for x.

7. The lattice volume of the sulfide-based solid electrolyte is 940 Å ３ or more and 980 Å ３ or less. The sulfide-based solid electrolyte according to claim 1.

8. A method for manufacturing the sulfide-based solid electrolyte according to Claim 1, comprising the steps of mixing a lithium source, a Group 3 element source, a phosphorus source, a sulfur source, and a halogen source to obtain a mixture, and firing the mixture at a temperature of 250°C to 600°C. A method comprising the above steps.

9. An all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer, wherein the solid electrolyte layer contains the sulfide-based solid electrolyte according to Claim 1.

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