Sulfide-based solid electrolyte, method for producing sulfide-based solid electrolyte, and all-solid-state battery containing 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 13 element and having an argyrodite-type crystal structure, the sulfide-based solid electrolyte being represented by chemical formula Li7-x-3yMyPS6-xHax, where M is at least one element selected from the Group 13 elements, Ha is at least one element selected from the halogen elements, the Ha comprises Br, 0<x<2.5 and 0<y<0.2 are fulfilled.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] In order to improve safety, lifespan, and energy density, development of all-solid-state batteries is underway, in which the liquid electrolyte in lithium-ion batteries is replaced with a solid electrolyte. 10 GeP2S 12 Sulfide-based solid electrolytes such as these have high ionic conductivity close to that of electrolyte solutions, and have the advantage of being soft and easily adhering to active materials. Therefore, it is expected that all-solid-state batteries using sulfide-based solid electrolytes will become practical.

[0003] Lithium metal has attracted attention as an anode material for solid-state batteries because it can increase the mass energy density (Wh / kg) due to its low weight per unit volume and large theoretical capacity. 10 GeP2S 12 However, sulfide-based solid electrolytes such as those described above have a problem in that they have low stability with respect to lithium metal, making them difficult to use with lithium metal negative electrodes.

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

[0005] However, the conventional technology has a problem in 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 a 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 13 element and having an argyrodite - type crystal structure, wherein the sulfide - based solid electrolyte has a chemical formula Li 7-x-3y M y PS 6-x Ha x represented by in the chemical formula, M is one or more elements selected from Group 13 elements, Ha is one or more elements selected from halogen elements, and Ha includes Br, and provides a sulfide - based solid electrolyte satisfying 0 < x < 2.5 and 0 < y < 0.2.

[0009] In one embodiment, y may satisfy 0 < y < 0.1.

[0010] In one embodiment, M may be Al or Ga.

[0011] In one embodiment, the M may be present at the 96i site of the argyrodite-type crystal structure.

[0012] The present disclosure provides a method for producing a sulfide-based solid electrolyte according to any one of the above embodiments, mixing a lithium source, a Group 13 element source, a phosphorus source, a sulfur source, and a halogen source to obtain a mixture; Calcining the mixture at a temperature of 250°C to 600°C; The present invention provides a method comprising:

[0013] The present disclosure provides: An all-solid-state battery including a positive electrode, a negative electrode, and a solid electrolyte layer, The present invention provides an all-solid-state battery, wherein the solid electrolyte layer includes the sulfide-based solid electrolyte according to any one of the above embodiments. [Effects of the Invention]

[0014] 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 the sulfide-based solid electrolyte. [Brief explanation of the drawings]

[0015] [Figure 1] 1 shows X-ray diffraction (XRD) patterns of Examples 1 to 5 and Comparative Examples 1 and 3. [Figure 2] 1 shows XRD patterns of Examples 6 to 11 and Comparative Examples 2 and 3. [Figure 3] 1 is a graph showing lithium ion conductivity versus composition of a sulfide-based solid electrolyte. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present disclosure will now be described in more detail.

[0017] The terms and words used in this specification and claims should not be interpreted in a limited manner based on their ordinary or dictionary meanings, but should be interpreted in a meaning and concept that is consistent with the technical idea of ​​the present disclosure, in accordance with the principle that an inventor can appropriately define the concept of a term in order to best describe his or her invention.

[0018] [Solid electrolyte for all-solid-state batteries] 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 mixture to be used as a positive electrode material, mixed with a negative electrode mixture to be used as a negative electrode material, or used as a separator. The solid electrolyte for an all-solid-state battery may further include additives such as a lithium salt, a conductive material, and a binder resin depending on the application.

[0019] <Sulfide solid electrolyte> The sulfide-based solid electrolyte is not particularly limited as long as it contains sulfur (S), and any known sulfide-based solid electrolyte can be used.

[0020] The sulfide-based solid electrolyte may have a crystalline structure, which can promote the conduction of lithium ions and have high lithium ion conductivity.

[0021] The sulfide-based solid electrolyte may have an argyrodite, Nasicon, perovskite, garnet, or LGPS crystal structure. Preferably, the sulfide-based solid electrolyte has an argyrodite crystal structure. Sulfide-based solid electrolytes with an argyrodite crystal structure have high stability against lithium metal, allowing lithium metal, which has a high mass energy density, to be used as a negative electrode material.

[0022] The sulfide-based solid electrolyte may be in the form of an amorphous, glass, or glass-ceramic.

[0023] The sulfide-based solid electrolyte has ionic conductivity of a metal belonging to Group 1 or 2 of the periodic table, and can include Li-PS-based glass and Li-PS-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, and Li2S-GeS2-ZnS, and can include one or more of these. However, the sulfide-based solid electrolyte can be used without limitation.

[0024] The sulfide-based solid electrolyte may include a crystalline phase and an amorphous phase. The sulfide-based solid electrolyte may include a crystalline phase having an argyrodite-type crystal structure (also referred to herein as an argyrodite phase) and other phases (also referred to herein as impurity phases or unknown phases). The argyrodite-type crystal structure is preferably a cubic system. The other phases may be crystalline or amorphous. The other phases, whether crystalline or amorphous, may include Li2S phase, P2S5 phase, LiCl phase, LiBr phase, Li3PS4 phase, Al2S3 phase, Ga2S3 phase, In2S3 phase, and the like. Preferably, the sulfide-based solid electrolyte does not include, or is substantially free of, impurity phases other than the argyrodite phase. That is, the sulfide-based solid electrolyte may preferably consist solely of an argyrodite phase. When the sulfide-based solid electrolyte does not contain or is substantially free of an impurity phase, lithium ion conduction is less likely to be inhibited, and the sulfide-based solid electrolyte can have high lithium ion conductivity.

[0025] The proportion of the crystalline phase contained in the sulfide-based solid electrolyte can be quantitatively or semi-quantitatively evaluated from the XRD pattern. As one method, the proportion of the crystalline phase can be evaluated by comparing the peak intensities (heights or areas) of the XRD pattern.

[0026] A sulfide-based solid electrolyte according to an embodiment of the present disclosure has a 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 13 elements, and Ha is one or more elements selected from halogen elements, satisfying 0 < x < 2.5 and 0 < y < 0.2. Such a sulfide-based solid electrolyte can have high lithium ion conductivity.

[0027] The sulfide-based solid electrolyte can be formed by substituting a part of lithium in Li 7-x PS 6-x Ha x with a Group 13 element M that can become a trivalent cation. The Group 13 element M that substitutes lithium may be one or more selected from the group consisting of aluminum (Al), gallium (Ga), and indium (In). Aluminum (Al), gallium (Ga), and indium (In) can be used alone or in combination. The ionic radius (6-coordination) of lithium (Li) is 76 pm, and the ionic radii (6-coordination) of aluminum (Al), gallium (Ga), and indium (In) are 68 pm, 76 pm, and 9 pm, respectively. Based on the valence of the element, three lithiums can be substituted by one Group 13 element M. Substitution of the lithium site by the Group 13 element M generates lithium site vacancies and can improve lithium ion conductivity. Further, substitution of the lithium site by the Group 13 element M changes the lattice constant and lattice volume of the sulfide-based solid electrolyte, and it can have a crystal structure suitable for lithium ion conduction.

[0028] Also, in the sulfide-based solid electrolyte, a Group 13 element M that can become a trivalent cation is Li 7-x PS 6-x Ha xThe Group 13 element M intercalating into the crystal lattice may be one or more selected from the group consisting of aluminum (Al), gallium (Ga), and indium (In). Aluminum (Al), gallium (Ga), and indium (In) may be used alone or in combination. Li 7-x PS 6-x Ha x The incorporation of the Group 13 element M into the crystal lattice of the sulfide-based solid electrolyte can change the lattice constant and lattice volume of the sulfide-based solid electrolyte, resulting in a crystal structure suitable for lithium ion conduction.

[0029] Preferably, the Group 13 element M is aluminum (Al) or gallium (Ga). When the Group 13 element M is aluminum (Al) or gallium (Ga), the sulfide-based solid electrolyte can have a high degree of crystallinity, and therefore, the sulfide-based solid electrolyte can have a high ionic conductivity. This is thought to be because the ionic radius of lithium (Li), 76 pm, and the ionic radii of aluminum (Al) and gallium (Ga), 68 pm and 76 pm, are close to each other, so that the argyrodite-type crystal structure is likely to be maintained even after substitution with the Group 13 element M.

[0030] The chemical formula Li 7-x-3y M y PS 6-x Ha xThe addition amount y of group 13 element M satisfies 0 < y < 0.2. When the group 13 element M is aluminum (Al), preferably, y satisfies 0 < y < 0.1, more preferably, 0.01 ≤ y ≤ 0.08, even more preferably, 0.02 ≤ y ≤ 0.07, and most preferably, 0.03 ≤ y ≤ 0.06. When the group 13 element M is gallium (Ga) or indium (In), preferably, y satisfies 0 < y < 0.1, more preferably, 0 < y < 0.05, even more preferably, 0 < y < 0.025, and most preferably, 0.01 ≤ y ≤ 0.015. When y satisfies the above range, the sulfide-based solid electrolyte can have high ionic conductivity. When y is 0, no change in crystal structure due to substitution of group 13 element M can be obtained, and the ionic conductivity may be low. When y is 0.2 or more, the al-dilrothite 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.

[0031] Aluminum (Al) can maintain the al-dilrothite type crystal structure of the sulfide-based solid electrolyte at a relatively large addition amount y. On the other hand, gallium (Ga) or indium (In) can maintain the al-dilrothite type crystal structure of the sulfide-based solid electrolyte at a relatively small addition amount y. Without being bound by theory, it is considered to be due to the difference in characteristics between aluminum (Al) and gallium (Ga) and indium (In). For example, when gallium (Ga) is used as a component of an alloy, it is easy to diffuse along the grain boundaries of the alloy, so it has the characteristic of promoting alloying with other metal elements. Such characteristics can also be observed in indium (In) which has electrons in the d orbital similar to gallium (Ga). Due to such characteristics, it is considered that gallium (Ga) or indium (In) can maintain the al-dilrothite type crystal structure of the sulfide-based solid electrolyte at a relatively smaller addition amount y than aluminum (Al).

[0032] Preferably, the Group 13 element M is present at the 96i site of the argyrodite-type crystal structure. More preferably, the Group 13 element M is present only at the 96i site of the argyrodite-type crystal structure. The argyrodite-type crystal structure may be a cubic, hexagonal, tetragonal, orthorhombic, monoclinic, triclinic, or other crystal structure. When the argyrodite-type crystal structure is a cubic crystal (space group F43m), the Group 13 element M can be present at the 96i site in the crystal structure, thereby creating lithium site vacancies without blocking the ion conduction pathway of lithium ions. In such a case, the sulfide-based solid electrolyte can have high lithium ion conductivity.

[0033] The chemical formula Li 7-x-3y M y PS 6-x Ha x The halogen (Ha) in (1) is one or more elements selected from the halogen elements. The halogen (Ha) preferably includes bromine (Br). More preferably, the halogen (Ha) includes chlorine (Cl) and bromine (Br). When sulfur (S) is a divalent anion, it has a stronger attraction to lithium ions than monovalent halogens and can significantly inhibit lithium ion mobility. By including bromine (Br) as a halogen, the sulfur (S) occupancy rate of a specific site in the argyrodite-type crystal structure decreases, while the halogen occupancy rate of the site increases, thereby increasing the lithium ion mobility around the bromine (Br) site. As a result, lithium ion conductivity can be improved. Furthermore, bromine (Br) can bond with Li in the sulfide-based solid electrolyte to form lithium bromide (LiBr), a water-absorbing substance. Lithium bromide (LiBr) can adsorb moisture, which can reduce lithium ion conductivity, and thereby improve the lithium ion conductivity of the sulfide-based solid electrolyte.

[0034] The chemical formula Li 7-x-3y M y PS 6-x Ha xThe proportion x of halogen (Ha) therein satisfies 0 < x < 2.5, preferably satisfies 1.0 ≤ 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.

[0035] 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, Al2S3 phase, Ga2S3 phase, and In2S3 phase) other than the argyrodite crystal phase are observed or hardly observed, the sulfide-based solid electrolyte can have high ionic conductivity.

[0036] The lattice volume of the sulfide-based solid electrolyte can change due to the substitution of lithium sites by group 13 element M. Although not bound by theory, it is considered that the interaction between the group 13 element M showing the characteristics of a trivalent cation and other anions present in the sulfide-based solid electrolyte is strengthened, and 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.

[0037] The lattice volume of the sulfide-based solid electrolyte is 940 Å 3 or more and 980 Å 3 or less, preferably 950 Å 3 or more and 970 Å 3 or less, more preferably 954 Å 3 or more and 966 Å 3 or less, more preferably 957 Å 3 or more and 963 Å 3The lattice constant and lattice volume can be evaluated from the XRD pattern. 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 high ionic conductivity.

[0038] Unless otherwise specified, the ionic conductivity of a sulfide-based solid electrolyte (also referred to herein as "lithium ion conductivity") refers to the ionic conductivity at room temperature (25°C, 298K) and atmospheric pressure (1 atm). When a sulfide-based solid electrolyte is used in an all-solid-state battery, it is desirable for the ionic conductivity to be 4 mS / cm or higher 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 higher, preferably 4 mS / cm or higher, more preferably 8 mS / cm or higher, even more preferably 10.8 mS / cm or higher, and most preferably 12 mS / cm or higher.

[0039] A sulfide-based solid electrolyte according to an embodiment of the present disclosure can be obtained by a production method including the steps of: mixing a lithium source, a Group 13 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 in an inert atmosphere such as argon gas and nitrogen gas.

[0040] The lithium source, Group 13 element source, phosphorus source, sulfur source, and halogen source may be compounds such as sulfides, oxides, and nitrides. Lithium sulfide (LiS) can be used as the lithium source, diphosphorus pentasulfide (PS) 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, sulfide can be used as the Group 13 element source. Alternatively, sulfur can be supplied from other element sources. That is, one or more of the lithium source, Group 13 element source, phosphorus source, and halogen source can also serve as the sulfur source.

[0041] In the case of a sulfide-based solid electrolyte having an argyrodite-type crystal structure, the firing temperature is preferably 400°C to 550°C, more preferably 420°C to 530°C, and even more preferably 450°C to 500°C. When the firing temperature is within the above range, the formation of the argyrodite-type crystal structure is promoted, and the sulfide-based solid electrolyte can have a high degree of crystallinity. This makes it possible to obtain a sulfide-based solid electrolyte having high ionic conductivity.

[0042] [All-solid battery] The all-solid-state battery electrolyte of the present disclosure can be used in an all-solid-state battery including a positive electrode, a negative electrode, and a solid electrolyte layer. The all-solid-state battery solid electrolyte can be used together with an active material in the electrode active material layer of the positive electrode and the negative electrode. The all-solid-state battery solid electrolyte can be used as a material for the solid electrolyte layer. The average particle size of the all-solid-state battery electrolyte can be controlled depending on the application. By controlling the average particle size of the all-solid-state battery electrolyte, the ionic conductivity can be improved.

[0043] <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 be an appropriate thickness within the above-mentioned range, taking into consideration the ionic conductivity, physical strength, energy density of the applied battery, and the like. 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. Furthermore, the solid electrolyte layer may have a thickness range and a resistance of about 100 kgf / cm. 2 ~Approx. 2,000kgf / cm 2 The solid electrolyte layer may have a tensile strength of 15 vol% or less, or about 10 vol% or less. In this way, the solid electrolyte layer according to the present disclosure may have high mechanical strength despite being a thin film.

[0044] <Positive and negative electrodes> 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. 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 needed. Additionally, the electrode can further include various additives for the purpose of complementing or improving the physicochemical properties of the electrode.

[0045] 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 can be carbon such as non-graphitizable carbon and graphitic 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, elements of Group 1, Group 2, Group 3 of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8) and other 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 from these can be used. In a specific embodiment, the negative electrode active material can include a carbon-based material and / or Si.

[0046] 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 electrode active material can be a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; the chemical formula Li 1+x Mn 2-xLithium manganese oxides such as O4 (where x is from 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x A x Ni-site type lithium nickel oxide represented by O2 (A = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 to 0.3); chemical formula LiMn 2-x A x Lithium manganese composite oxide represented by O2 (A = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or Li2Mn3AO8 (A = Fe, Co, Ni, Cu or Zn); LiNi x Mn 2-x Lithium manganese composite oxide with a spinel structure represented by O4; Li(Ni a Co b Mn c )O2 (a, b, c are atomic fractions of independent elements, 0 < a < 1, 0 < b < 1, 0 < c < 1, and a + b + c = 1).) NCM-based composite oxide; LiMn2O4 in which part of the Li in the chemical formula is substituted with alkaline earth metal ions; disulfide compounds; It can include, but is not limited to, Fe2(MoO4)3, etc.

[0047] In the present disclosure, the current collector can be an electrically conductive current collector known in the secondary battery field, such as a metal plate, and can be appropriately used according to the polarity of the electrode.

[0048] In the present disclosure, the conductive material is typically added in an amount of 1 wt % to 30 wt % based on the total weight of the mixture including the electrode active material. Such a conductive material is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity, and can include, for example, one or a mixture of two or more conductive materials selected from graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives.

[0049] In the present disclosure, the binder resin is not particularly limited as long as it is a component that assists in bonding between the active material and the conductive material, etc., and to the current collector, and examples thereof include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers, etc. The binder resin can typically be contained in a range of 1 to 30 wt % or 1 to 10 wt % relative to 100 wt % of the electrode active material layer.

[0050] In the present disclosure, the electrode active material layer may contain one or more additives such as oxidation stabilizing additives, reduction stabilizing additives, flame retardants, heat stabilizers, and anti-fogging agents, as needed.

[0051] The present disclosure provides a secondary battery having the above-described structure. The present disclosure also 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. Specific examples of the device include, but are not limited to, power tools driven by electric motors; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters; electric golf carts; and power systems.

[0052] The present disclosure will be described in more detail below with reference to examples. However, the following examples are provided to illustrate the present disclosure and the scope of the present disclosure is not limited thereto.

[0053] Example 1 The raw materials used were lithium sulfide (Li2S, Mitsuwa Chemical), diphosphorus pentasulfide (P2S5, Aldrich), aluminum sulfide (Al2S3, Kojundo Chemical), lithium chloride (LiCl, Aldrich), and lithium bromide (LiBr, Aldrich). 5.4-3y M y PS 4.4 Cl 1.0 Br 0.6 The powder mixture was weighed and mixed in a mortar in a glove box with an Ar gas flow so that the amount of added Group 13 element M was y = 0.00625, yielding 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 then placed in a planetary ball mill and ball milled at 380 rpm for 20 hours, after which 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 460°C for 8 hours while flowing Ar gas. The fired powder was pulverized in a mortar for 10 minutes to obtain a solid electrolyte.

[0054] Example 2 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the amount y of the Group 13 element M added was set to 0.0125.

[0055] Example 3 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the amount y of the Group 13 element M added was set to 0.05.

[0056] Example 4 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the amount y of the Group 13 element M added was set to 0.075.

[0057] Example 5 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the amount y of the Group 13 element M added was set to 0.1.

[0058] Comparative Example 1 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the amount y of the Group 13 element M added was set to 0.2.

[0059] Example 6 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that gallium sulfide (GaS, Kojundo Chemical) was used instead of aluminum sulfide (AlS, Kojundo Chemical) as the raw material of the Group 13 element M, and the added amount y of the Group 13 element M was set to 0.0125.

[0060] Example 7 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 6, except that the amount y of the Group 13 element M added was set to 0.01875.

[0061] Example 8 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 6, except that the amount y of the Group 13 element M added was set to 0.025.

[0062] Example 9 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 6, except that the amount y of the Group 13 element M added was set to 0.05.

[0063] Example 10 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 6, except that the amount y of the Group 13 element M added was set to 0.075.

[0064] Example 11 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 6, except that the amount y of the Group 13 element M added was set to 0.1.

[0065] Comparative Example 2 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 6, except that the amount y of the Group 13 element M added was set to 0.2.

[0066] Comparative Example 3 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the Group 13 element M was not added, that is, the amount y of the Group 13 element M added was set to 0.

[0067] [Table 1]

[0068] Comparative Example 4 A solid electrolyte was obtained in the same manner as in Comparative Example 3, except that lithium bromide (LiBr, Aldrich) was not used as the halogen source, and only lithium chloride (LiCl, Aldrich) was used. That is, the design composition of the solid electrolyte of Comparative Example 4 was Li 5.4 PS 4.4 Cl 1.6 It was.

[0069] [evaluation] The obtained solid electrolyte was subjected to the following evaluations.

[0070] (XRD measurement) A predetermined amount of solid electrolyte was placed in a sealed holder in an Ar gas glove box and subjected to XRD measurement. The lattice constant, lattice volume, and half-width were calculated from the obtained XRD (X-ray diffraction) pattern. The half-width was calculated from the (311) crystal peak of the argyrodite-type crystal structure observed around 2θ = 30° in Figures 1 and 2.

[0071] The measurement apparatus and conditions are as follows. X-ray diffraction equipment: Rigaku Smartlab ·Radiation source: Cu-Kα radiation (λ=1.5418Å) Voltage: 45kV ·Current: 200mA Scan range (2θ): 10-60° Step size: 0.01°

[0072] (Ionic conductivity measurement) A predetermined amount of solid electrolyte was placed in a McCol tube, and the McCol tube and pellet-molding jig (upper and lower press pins) were combined and pressed using a uniaxial press at 5 MPa. A predetermined amount of gold powder was then placed on both sides of the pellet, and the pellet was pressed using a uniaxial press at 7.5 MPa to obtain a McCol tube cell. The resulting McCol tube cell was placed in an electrochemical measurement jig cell, and a torque wrench was used to apply a pressure of 5.0 N m to obtain an ionic conductivity measurement cell. The resulting ionic conductivity measurement cell was connected to an impedance measurement device, and the resistance of the solid electrolyte pellet was measured at room temperature (298 K) and atmospheric pressure (1 atm) to derive the ionic conductivity [mS / cm] of the solid electrolyte.

[0073] (Initial charge / discharge capacity measurement) An NCM-based positive electrode active material with a Ni content of 80 mol% and a solid electrolyte were weighed in a mass ratio of 70:30. 1.5 wt% carbon black was added as a conductive additive and mixed to obtain a positive electrode mixture. 80 mg of the resulting solid electrolyte was weighed, placed in a molding jig, and pressed at 6 MPa for 1 minute to obtain a solid electrolyte pellet. 10 mg of the resulting positive electrode mixture was placed on one side of the resulting solid electrolyte pellet, and the pellet was flattened with a stainless steel press pin of the molding jig to form a positive electrode layer. An Al plate was placed on top of the resulting positive electrode layer and pressed at 30 MPa for 1 minute. Li-Cu foil was then placed on the side of the solid electrolyte pellet opposite the positive electrode layer and pressed at 2 MPa for 30 seconds. This was combined with a stainless steel press pin to produce a Macol tube cell. The resulting Macol tube cell was placed in a battery cell and a torque of 2 N·m was applied to obtain an all-solid-state battery cell.

[0074] Using the obtained all-solid-state battery, a charge-discharge test was performed under the following conditions: voltage range: 4.25 V - 3.0 V, charge condition: CC (0.05 C) - CV (0.01 C cutoff), discharge condition: CC (0.05 C). The initial charge capacity and initial discharge capacity were calculated from the obtained charge-discharge curve.

[0075] [Evaluation results] (crystalline phase) The evaluation results of the crystalline phase (crystalline structure) identified from the XRD pattern obtained by XRD measurement are shown in Table 1. The measured XRD patterns are shown in Figures 1 and 2.

[0076] As shown in Table 1, in Examples 1, 3, and 5 to 8 and Comparative Example 3, almost no impurity phases (also called unknown phases) were observed, and almost only the peak of the argyrodite phase was observed. In addition, in Examples 2, 4, and 9 to 11, the peak of the argyrodite phase and trace amounts of impurity phases other than the argyrodite phase were observed. On the other hand, in Comparative Examples 1 and 2, many impurity phases other than the peak of the argyrodite phase were observed. The impurity phases were phases derived from raw materials such as Li2S, Al2S3, and Ga2S3.

[0077] 1 and 2 show the XRD patterns of Examples 1 to 11 and Comparative Examples 1 to 3. For Examples 1, 3, and 5, in which the Al content y was 0.00625, 0.05, and 0.1, Examples 6 to 8, in which the Ga content y was 0.0125, 0.01875, and 0.025, and Comparative Example 3, in which the Group 13 element content y was 0, almost exclusively argyrodite phase peaks were observed. For Examples 2 and 4, in which the Al content y was 0.0125 and 0.075, and Examples 9 to 11, in which the Ga content y was 0.05, 0.075, and 0.1, almost exclusively argyrodite phase peaks were observed, but peaks of impurity phases derived from the raw materials, such as LiS, AlS, and GaS, were also observed. On the other hand, in Comparative Example 1 in which the amount of Al added y was 0.2, and Comparative Example 2 in which the amount of Ga added y was 0.2, almost no peaks of the argyrodite phase were observed, but a large amount of peaks of the impurity phase were observed.

[0078] In Examples 1, 3, and 5 to 8 and Comparative Example 3, sulfide-based solid electrolytes having an argyrodite-type crystal structure with little or no impurity phase were obtained. A sulfide-based solid electrolyte with a high degree of crystallinity can promote hopping conduction of lithium ions and contribute to an increase in ionic conductivity.

[0079] (lattice volume) The lattice parameters derived from the XRD patterns range from 9.8414 Å to 9.8674 Å in the examples, and the lattice volume is 953.2 Å. 3 to 960.7Å 3 On the other hand, in Comparative Example 1 where the amount of Al added was y=0.2 and Comparative Example 2 where the amount of Ga added was y=0.2, the amount of impurities was so large that it was impossible to measure the lattice constant. In Comparative Example 3 where the lithium site of the sulfide-based solid electrolyte was not substituted with the Group 13 element M, the lattice constant was 9.9471 Å and the lattice volume was 984.2 Å. 3It was shown that the lattice volume of the crystal is reduced by approximately 2.4 to 3.1% by substituting the lithium site of the argyrodite-type crystal structure with the Group 13 element M and / or by the Group 13 element M penetrating into the lattice of the argyrodite-type crystal structure.

[0080] Without being bound by theory, it is believed that the crystalline volume of a sulfide-based solid electrolyte can change when one of the three lithium sites is substituted with a Group 13 element M and the other two become lithium vacancies. Alternatively, it is believed that the crystalline volume of a sulfide-based solid electrolyte can change when the Group 13 element M penetrates into the lattice of an argyrodite-type crystal structure. The lithium vacancies serve as paths for the hopping conduction of lithium ions and contribute to an increase in ionic conductivity. Furthermore, the Group 13 element M substituted at the lithium site or penetrated into the lattice may have a trivalent atom, which may change the force of attraction of anions around the Group 13 element M site compared to monovalent lithium ions. This is believed to change the crystalline volume of the sulfide-based solid electrolyte, resulting in a structure suitable for hopping conduction of lithium ions.

[0081] The half-width of the (311) crystal peak of the argyrodite crystal structure was in the range of 0.05° to 0.1° in the Examples. On the other hand, it was 0.15° in Comparative Example 1 and 0.12° in Comparative Example 2. In particular, Example 6, in which the Ga addition amount was y=0.0125, exhibited a small half-width and high ionic conductivity. The small half-width corresponds to a large crystallite size and is thought to contribute to the increase in ionic conductivity.

[0082] (ionic conductivity) The results of the ionic conductivity measurements are shown in Table 1. The composition of the sulfide-based solid electrolyte Li 5.4-3y M y PS 4.4 Cl 1.0 Br 0.63 is a graph in which the horizontal axis represents the amount y of the Group 13 element M added and the vertical axis represents the ionic conductivity measured at 25°C and normal pressure. The points in Fig. 3 correspond to Examples 1 to 5 and Comparative Example 1, in which Al was doped as the Group 13 element M, Examples 6 to 11 and Comparative Example 2, in which Ga was doped as the Group 13 element M, and Comparative Example 3, in which no Group 13 element M was doped (corresponding to "Undoped" in the figure).

[0083] As can be seen from FIG. 3 and Table 1, the ionic conductivity ranged from 9.0 mS / cm to 13.8 mS / cm in Examples 1 to 5. Example 3, in which the amount of Al added (y=0.05), was the Group 13 element M, exhibited a high ionic conductivity of 13.8 mS / cm. On the other hand, Comparative Example 1, in which the amount of Al added (y=0.2), exhibited an ionic conductivity of 0.5 mS / cm. Furthermore, Example 6, in which the amount of Ga added (y=0.0125), was the Group 13 element M, exhibited the highest ionic conductivity, 15.7 mS / cm. On the other hand, Comparative Example 2, in which the amount of Ga added (y=0.2), exhibited an ionic conductivity of 0.00098 mS / cm. Thus, by adding an appropriate amount of Group 13 element M, the ionic conductivity of Examples 1 to 11 could be increased compared to that of Comparative Examples 1 and 2. In Comparative Examples 1 and 2, the added amount y of Al and Ga, which are the Group 13 element M, was too large, which is thought to have reduced the crystallinity of the argyrodite-type crystal structure and the ionic conductivity. In Comparative Example 3, which did not contain the Group 13 element M, the ionic conductivity was 10.7 mS / cm. Although not shown in Table 1, in Comparative Example 4, which did not contain bromine (Br) as a halogen element, the ionic conductivity was 8.1 mS / cm. Bromine (Br) forms lithium bromide (LiBr) together with Li in the sulfide-based solid electrolyte, and the formed lithium bromide (LiBr) adsorbs moisture that can reduce ionic conductivity, which is thought to have resulted in improved ionic conductivity.

[0084] Furthermore, as can be seen from FIG. 3 and Table 1, when the amount of Al added, y = 0.05 (Example 3), which is the Group 13 element M, is compared to the adjacent cases where y = 0.0125 (Example 2) and y = 0.075 (Example 4). Referring to the XRD pattern in FIG. 1, almost no impurity phase is observed in Example 3, whereas trace amounts of impurity phases (unknown phases) are observed in Examples 2 and 4. Furthermore, in Examples 6 to 8, where the amount of Ga added, y, is 0.0125 to 0.025, the ionic conductivity is increased compared to Examples 9 to 11, where the amount of Ga added is 0.05 to 0.1. Referring to the XRD pattern in FIG. 2, almost no impurity phase is observed in Examples 6 to 8, whereas trace amounts of impurity phases (unknown phases) are observed in Examples 9 to 11. Therefore, the increase in ionic conductivity is thought to be due to an increase in the crystallinity of the argyrodite-type crystal structure due to a decrease in the impurities present in the sulfide-based solid electrolyte. Thus, in order to increase the ionic conductivity of a sulfide-based solid electrolyte, it is preferable that the electrolyte does not contain any impurity phase other than the argyrodite phase, that is, that the argyrodite-type crystal structure has a high degree of crystallinity.

[0085] Examples 1 to 3, in which the amount of Al added as the Group 13 element M was y≦0.075, and Examples 6 and 7, in which the amount of Ga added as the Group 13 element M was y≦0.01875, exhibited higher ionic conductivities than Comparative Example 3, in which no Group 13 element M was added. From the XRD results above, it is believed that Comparative Example 3 has a higher degree of crystallinity of the argyrodite-type crystal structure than Examples 2 and 4. However, in reality, the ionic conductivities of Examples 2 and 4, which have relatively low degrees of crystallinity, are higher than that of Comparative Example 3, which has a relatively high degree of crystallinity. This indicates that not only the crystallinity of the argyrodite-type crystal structure but also the presence of the Group 13 element M, i.e., the change in lattice volume due to the presence of the Group 13 element M, can affect ionic conductivity.

[0086] As shown in FIG. 3 and Table 1, when the amount y of Al added as the Group 13 element M was 0.1 or less, the ionic conductivity was 9.0 mS / cm or more. When the amount y of Al added as the Group 13 element M was 0.075 or less, the ionic conductivity was 11.3 mS / cm or more, which was higher than the ionic conductivity of 10.7 mS / cm of Comparative Example 3 in which no Group 13 element M was added. Furthermore, when the amount y of Ga added as the Group 13 element M was 0.1 or less, the ionic conductivity was 3.5 mS / cm or more. When the amount y of Ga added as the Group 13 element M was 0.01875 or less, the ionic conductivity was 11.9 mS / cm or more, which was higher than the ionic conductivity of 10.7 mS / cm of Comparative Example 3 in which no Group 13 element M was added. Furthermore, the ionic conductivity of Comparative Example 4, which did not contain bromine (Br) as a halogen element, was 8.1 mS / cm, which was lower than the ionic conductivity of Comparative Example 3, which contained bromine (Br) as a halogen element, 10.7 mS / cm.

[0087] (Battery characteristics) When the sulfide-based solid electrolyte of Example 3, in which the additive amount y of Al, the Group 13 element M, was 0.05, was used in the solid electrolyte layer of an all-solid-state battery, the sulfide-based solid electrolyte was highly stable against lithium metal as the anode material, and the all-solid-state battery was able to be stably charged and discharged. The relative ratio of the initial discharge capacity of the all-solid-state battery capacity when Example 3 was used in the solid electrolyte layer to the all-solid-state battery capacity when Comparative Example 3 was used in the solid electrolyte layer was 106%. Furthermore, when the sulfide-based solid electrolyte of Example 6, in which the additive amount y of Ga, the Group 13 element M, was 0.0125, was used in the solid electrolyte layer of an all-solid-state battery, the sulfide-based solid electrolyte was highly stable against lithium metal as the anode material, and the all-solid-state battery was able to be stably charged and discharged. The relative ratio of the initial discharge capacity of the all-solid-state battery capacity when Example 6 was used in the solid electrolyte layer to the all-solid-state battery capacity when Comparative Example 3 was used in the solid electrolyte layer was 107%. In this way, by using the solid electrolytes of Examples 3 and 6 having high ionic conductivity in an all-solid-state battery, it was possible to improve the capacity of the all-solid-state battery.

[0088] While the present disclosure has been described above using limited examples and drawings, the present disclosure is not limited thereto, and it goes without saying that various modifications and variations can be made by a person having ordinary skill in the art to which the present disclosure pertains within the technical spirit of the present disclosure and the equivalent scope of the appended claims.

Claims

1. A sulfide-based solid electrolyte containing a Group 13 element and having an argyrodite-type crystal structure, The sulfide-based solid electrolyte has the chemical formula Li ７－ｘ－３ｙ M ｙ P.S. ６－ｘ Ha ｘ is expressed as In the above chemical formula: M is one or more elements selected from Group 13 elements, M is Al or Ga, The Ha is one or more elements selected from halogen elements, and the Ha includes Br, 1.3≦x<2.5 is satisfied, When M is Al, 0<y≦0.08 is satisfied; A sulfide-based solid electrolyte, wherein when M is Ga, 0<y<0.025 is satisfied.

2. The sulfide-based solid electrolyte according to claim 1, wherein the M is present at the 96i site of an argyrodite-type crystal structure.

3. A method for producing the sulfide-based solid electrolyte according to claim 1, mixing a lithium source, a Group 13 element source, a phosphorus source, a sulfur source, and a halogen source to obtain a mixture; calcining the mixture at a temperature of 250°C to 600°C; A method comprising:

4. An all-solid-state battery including a positive electrode, a negative electrode, and a solid electrolyte layer, An all-solid-state battery, wherein the solid electrolyte layer comprises the sulfide-based solid electrolyte according to claim 1.

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