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

Abstract

The objective of the present invention is 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. 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 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.

Description

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

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

[0002] This application claims priority to Japanese Application No. 2023-221544, filed December 27, 2023, the entire disclosure of which is incorporated herein by reference.

[0003] To achieve high-density, long-life, and high-energy density, the development of all-solid-state batteries is underway, replacing the electrolyte of lithium-ion batteries with solid electrolytes. Among the numerous solid electrolytes, Li 10 GeP2S 12 Sulfide-based solid electrolytes have the advantage of high ionic conductivity close to that of electrolytes and are soft, making it easy to obtain adhesion with active materials. Therefore, the practical application of all-solid-state batteries using sulfide-based solid electrolytes is anticipated.

[0004] Lithium metal is attracting attention as an anode 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, Li 10 GeP2S 12 Sulfide-based solid electrolytes have the problem of low stability toward lithium metal, making them difficult to use with lithium metal negative electrodes.

[0005] To solve this problem, patent documents 1 to 3 disclose a stable Li metal for lithium. 7-x-2y PS 6-x-y Cl x Patent Document 4 discloses a sulfide-based solid electrolyte having an argylodite-type crystal structure represented by Li 10 GeP2S 12By precisely controlling the composition of the sulfide-based solid electrolyte having a crystal structure, a sulfide-based solid electrolyte with improved stability toward lithium metal is disclosed.

[0006] However, in conventional technology, there is a problem that the ionic conductivity of the sulfide-based solid electrolyte is low.

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

[0008] To achieve the above purpose, the present invention,

[0009] A sulfide-based solid electrolyte containing a Group 3 element and having an argyrodite-type crystal structure,

[0010] The above sulfide-based solid electrolyte has the chemical formula Li 7-x-3y M y PS 6-x Ha x is displayed as,

[0011] In the above chemical formula, a sulfide-based solid electrolyte is provided, wherein M is at least one element selected from Group 3 elements, Ha is at least one element selected from halogen elements, and satisfies 1.0<x<2.5, 0<y≤0.2.

[0012] In one embodiment, M may be Y, and 0<y<0.2.

[0013] In one embodiment, M may be La.

[0014] In one embodiment, the above y can satisfy 0<y<0.05.

[0015] In one embodiment, the Ha may comprise Br.

[0016] In one embodiment, the x may satisfy 1.3≤x≤2.0.

[0017] In one embodiment, the lattice volume of the sulfide-based solid electrolyte is 940Å. 3 More than 980Å 3 It could be as follows:

[0018] The present invention is a method for producing a sulfide-based solid electrolyte as described in the above embodiment,

[0019] A step of obtaining a mixture by mixing a lithium source, a group 3 element source, phosphorus, sulfur source, and halogen source,

[0020] A method is provided comprising a step of calcining the above mixture at a temperature of 250°C to 600°C.

[0021] The present invention relates to an all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer,

[0022] The above solid electrolyte layer provides an all-solid-state battery including the sulfide-based solid electrolyte described in the above embodiment.

[0023] The present invention 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.

[0024] FIG. 1 is a drawing showing X-ray diffraction (XRD) patterns of Examples 1 to 3, Comparative Examples 1 and 2.

[0025] Figure 2 is a drawing showing the XRD patterns of Examples 4 to 7 and Comparative Example 2.

[0026] Figure 3 is a graph showing lithium ion conductivity for the composition of a sulfide-based solid electrolyte.

[0027] Hereinafter, the present invention will be described in more detail.

[0028] The terms and words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to best explain his or her invention.

[0029] [Solid electrolyte for all-solid-state batteries]

[0030] The solid electrolyte for an all-solid-state battery of the present invention may include at least one 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 invention is a sulfide-based solid electrolyte. The solid electrolyte for an all-solid-state battery may be mixed into a positive electrode mixture and used as a positive electrode material, mixed into a negative electrode mixture and used as a negative electrode material, or used as a separator. Depending on the intended use, 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.

[0031] Sulfide-based solid electrolyte

[0032] There is no particular limitation on the sulfide-based solid electrolyte as long as it contains sulfur (S), and any known sulfide-based solid electrolyte can be used.

[0033] Sulfide-based solid electrolytes may have a crystalline structure. Sulfide-based solid electrolytes with a crystalline structure can promote lithium ion conduction and thus achieve high lithium ion conductivity.

[0034] The sulfide-based solid electrolyte may have an argyrodite-type, NASICON-type, perovskite-type, garnet-type, or LGPS-type crystal structure. Preferably, the sulfide-based solid electrolyte has an argyrodite-type crystal structure. A sulfide-based solid electrolyte having an argyrodite-type crystal structure exhibits high stability toward lithium metal, thereby enabling the use of lithium metal with a high mass energy density as an anode material.

[0035] The sulfide-based solid electrolyte may be in the form of amorphous, glass, or glass ceramic.

[0036] The sulfide-based solid electrolyte has the ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and may include a Li-PS-based glass or a 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, Li2S-GeS2-ZnS, etc., and may include one or more of these. However, the present invention is not particularly limited to these.

[0037] 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 an impurity phase or an unknown phase). The argyrodite-type crystal structure is preferably a cubic system. The other phase may be a crystalline phase or an amorphous phase. The other phase may include a Li2S phase, a P2S5 phase, a LiCl phase, a LiBr phase, a Li3PS4 phase, a Sc2S3 phase, a Y2S3 phase, a La2S3 phase, and an Ac2S3 phase, regardless of whether it is a crystalline phase or an amorphous phase. Preferably, the sulfide-based solid electrolyte does not include or substantially does not include an impurity phase other than the argyrodite phase. That is, preferably, the sulfide-based solid electrolyte may be composed only of the argyrodite phase. Since lithium ion conduction is not easily inhibited when the sulfide-based solid electrolyte does not contain or substantially does not contain an impurity phase, the sulfide-based solid electrolyte can have high lithium ion conductivity.

[0038] The ratio of crystalline phases contained in a sulfide-based solid electrolyte can be quantitatively or semi-quantitatively evaluated from XRD patterns. One method is to compare the peak intensities (height or area) of the XRD patterns to evaluate the ratio of crystalline phases.

[0039] A sulfide-based solid electrolyte according to one embodiment of the present invention has the chemical formula Li 7-x-3y M y PS 6-x Ha x In the chemical formula, M is at least one element selected from Group 3 elements, Ha is at least one element selected from halogen elements, and satisfies 1.0 < x < 2.5, 0 < y ≤ 0.2. Such a sulfide-based solid electrolyte can have high lithium ion conductivity.

[0040] A sulfide-based solid electrolyte according to one embodiment of the present invention comprises Li 7-x PS 6-x Ha x A portion of the lithium in is substituted with a Group 3 element (M) that can become a trivalent cation. The Group 3 element (M) substituting for lithium may be at least one selected from the group consisting of scandium (Sc), yttrium (Y), lanthanum (La), and actinium (Ac). The ionic radius (hexacoordination) of lithium (Li) is 76 pm, and the ionic radii (hexacoordination) 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 elements, three lithiums can be substituted with one Group 3 element (M). The substitution of lithium sites by Group 3 elements (M) creates lithium site vacancies, which can improve lithium ion conductivity. In addition, the lattice constant and lattice volume of the sulfide-based solid electrolyte can be changed by substitution of the lithium site by a Group 3 element (M), thereby obtaining a crystal structure suitable for lithium ion conduction.

[0041] In addition, the sulfide-based solid electrolyte according to one embodiment of the present invention comprises a third group element (M) that can be a trivalent cation, Li 7-x PS 6-x Ha x It can be formed by invading into the crystal lattice. The third group element (M) invading into the crystal lattice may be at least one selected from the group consisting of scandium (Sc), yttrium (Y), lanthanum (La), and actinium (Ac). Scandium (Sc), yttrium (Y), lanthanum (La), and actinium (Ac) may be used alone or in combination. Li 7-x PS 6-x Ha x The lattice constant and lattice volume of a sulfide-based solid electrolyte can be changed by the intrusion of a Group 3 element (M) into the crystal lattice, thereby obtaining a crystal structure suitable for lithium ion conduction.

[0042] Preferably, the Group 3 element (M) is yttrium (Y) and / or lanthanum (La), and particularly preferably 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 thus the sulfide-based solid electrolyte can have a high ionic conductivity.

[0043] The chemical formula Li above 7-x-3y M y PS 6-x Ha x The amount y of the third group element (M) added in satisfies 0<y≤0.2. It is preferable that y satisfies 0<y<0.05.

[0044] When the third group element (M) is yttrium (Y), y preferably satisfies 0<y<0.2, more preferably satisfies 0<y≤0.1, even more preferably satisfies 0<y≤0.05, still more preferably satisfies 0<y≤0.025, and most preferably satisfies 0.01≤y≤0.02.

[0045] When the third group element (M) is lanthanum (La), y preferably satisfies 0<y<0.2, more preferably satisfies 0<y≤0.1, still more preferably satisfies 0<y≤0.05, and most preferably satisfies 0.01≤y≤0.03.

[0046] When y satisfies the above range, the sulfide-based solid electrolyte can have high ionic conductivity. When y is 0, the ionic conductivity may be low because the change in crystal structure due to the substitution of the Group 3 element (M) is not obtained. When y exceeds 0.2, the argyrodite-type crystal structure of the sulfide-based solid electrolyte cannot be maintained, and further, the impurity phase that inhibits lithium ion conduction in the sulfide-based solid electrolyte may increase, lowering the ionic conductivity.

[0047] The chemical formula Li above 7-x-3y M y PS 6-xHa x In the halogen (Ha) is at least one element selected from halogen elements. It is preferable that the halogen (Ha) 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 force for lithium ions than a monovalent halogen, and can significantly inhibit the movement of lithium ions. By including bromine (Br) as a halogen, the sulfur (S) occupancy rate at a specific site in the argyrodite-type crystal structure is lowered, so that the halogen occupancy rate at the site is increased, and the lithium ion mobility around the bromine (Br) site can be activated. As a result, the lithium ion conductivity can be improved. In addition, bromine (Br) can combine with Li in the sulfide-based solid electrolyte to form lithium bromide (LiBr), which is an absorbent material. Lithium bromide (LiBr) can improve the lithium ion conductivity of sulfide-based solid electrolytes by adsorbing moisture that can reduce lithium ion conductivity.

[0048] The chemical formula Li above 7-x-3y M y PS 6-x Ha x The ratio x of halogen (Ha) in 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.

[0049] The stoichiometric composition of the sulfide-based solid electrolyte of the present invention is very important. Therefore, the chemical formula Li 7-x-3y M y PS 6-x Ha x A sulfide-based solid electrolyte not represented by is not included in the sulfide-based solid electrolyte of the present invention. The chemical formula Li 7-x-3y My PS 6-x Ha x Sulfide-based solid electrolytes that are not indicated may contain a large amount of impurities and may have poor crystallinity.

[0050] For example, reference composition Li 5.3 Y 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 In case of application, x=1.6 can be estimated from the content of chlorine (Cl) and bromine (Br) as halogens (Ha). However, in this case, when applying the above chemical formula to the content of sulfur (S), S 4.4 In the above reference composition, S 4.5 The two are different. Also, from the content of yttrium (Y), it can be inferred that y = 0.1. However, in this case, when applying the above chemical formula to the content of lithium (Li), Li 5.1 This is, in the above reference composition, Li 5.3 The two are different.

[0051] The ionic conductivity of a sulfide-based solid electrolyte can be affected by the degree of crystallinity of the sulfide-based solid electrolyte. The degree of crystallinity can be evaluated from an XRD pattern. In the XRD pattern, if no or little phases other than the argyrodite crystal phase (crystalline or amorphous phases such as Li2S phase, P2S5 phase, LiCl phase, LiBr phase, Li3PS4 phase, Sc2S3 phase, Y2S3 phase, La2S3 phase, and Ac2S3 phase) are observed, the sulfide-based solid electrolyte can have high ionic conductivity.

[0052] The lattice volume of sulfide-based solid electrolytes can change due to the substitution of lithium sites by Group 3 elements (M). Although not bound by theory, it is thought that Group 3 elements (M) exhibit the characteristics of trivalent cations, which strengthens their interaction with other anions present in the sulfide-based solid electrolyte, thereby changing, i.e., increasing or decreasing, the lattice volume. This change in lattice volume leads to a crystal structure suitable for lithium ion conduction, enabling sulfide-based solid electrolytes to have high ionic conductivity.

[0053] The lattice volume of the sulfide-based solid electrolyte is 940Å. 3 More than 980Å 3 Below, preferably 950Å 3 More than 970Å 3 or less, and more preferably 954Å 3 More than 966Å 3 or less, more preferably 955Å 3 More than 964Å 3 Below. Lattice constant and lattice volume can be evaluated from XRD patterns. The lattice volume of a sulfide-based solid electrolyte can vary depending on the sintering temperature even if the composition is the same. 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.

[0054] The ionic conductivity of a sulfide-based solid electrolyte (also referred to herein as “lithium ionic conductivity”) refers to the ionic conductivity at room temperature (25°C, 298 K) and atmospheric pressure (1 atm) unless otherwise specified. When a sulfide-based solid electrolyte is used in an all-solid-state battery, it is practically preferable that the ionic conductivity is 4 mS / cm or more. The ionic conductivity of the sulfide-based solid electrolyte according to one embodiment of the present invention is 1.5 mS / cm or more, preferably 4 mS / cm or more, more preferably 8 mS / cm or more, still more preferably 10.8 mS / cm or more, and most preferably 11.5 mS / cm or more.

[0055] A sulfide-based solid electrolyte according to one embodiment of the present invention can be obtained by a manufacturing method comprising the steps of mixing a lithium source, a Group 3 element source, phosphorus, a sulfur source, and a halogen source to obtain a mixture, and calcining the mixture at a temperature of 250°C to 600°C. The calcination of the mixture may be performed under an inert atmosphere such as argon gas or nitrogen gas.

[0056] The lithium source, Group 3 element source, phosphorus, sulfur source, and halogen source may be compounds such as sulfides, oxides, and 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, sulfide can be used as the Group 3 element source. Alternatively, sulfur can be supplied from another element source. That is, at least one of the lithium source, Group 3 element source, phosphorus, and halogen source can also serve as a sulfur source.

[0057] The sintering temperature is preferably 350°C to 550°C, more preferably 380°C to 500°C, and even more preferably 410°C to 450°C for a sulfide-based solid electrolyte having an argyrodite-type crystal structure. When the sintering temperature satisfies the above range, the formation of an argyrodite-type crystal structure is promoted, and the sulfide-based solid electrolyte can have a high degree of crystallinity. Accordingly, a sulfide-based solid electrolyte having high ionic conductivity can be obtained.

[0058] [All-solid-state battery]

[0059] The sulfide-based solid electrolyte of the present invention can be used as an electrolyte for an all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer. The sulfide-based solid electrolyte of the present invention can be used together with an active material in the electrode active material layer of the positive electrode and the negative electrode. The solid electrolyte for an all-solid-state battery can be used as a material for the solid electrolyte layer. The average particle size of the electrolyte for an all-solid-state battery can be controlled depending on the application. By controlling the average particle size of the electrolyte for an all-solid-state battery, the ionic conductivity can be improved.

[0060] Solid electrolyte layer

[0061] In the present invention, the solid electrolyte layer may have a thickness of about 50 μm or less, and preferably about 15 μm to 50 μm. Within the aforementioned range, the solid electrolyte layer may have an appropriate thickness in consideration of ionic conductivity, physical strength, and the energy density of the battery to be applied. For example, in terms of ionic conductivity or energy density, the thickness may be 10 μm or more, 20 μm or more, or 30 μm or more. Meanwhile, in terms of physical strength, the thickness may be 50 μm or less, 45 μm or less, or 40 μm or less. In addition, the solid electrolyte layer may have a tensile strength of about 100 kgf / cm2 to about 2,000 kgf / cm2 while having a thickness range. In addition, the solid electrolyte layer may have a porosity of 15 vol% or less or about 10 vol% or less. In this way, the solid electrolyte layer according to the present invention can have high mechanical strength despite being a thin film.

[0062] <Anode and cathode>

[0063] In the present invention, the positive electrode and the negative electrode 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. In addition, the electrode may further include one or more of a conductive material and a binder resin, as needed. In addition, the electrode may further include various additives for the purpose of supplementing or improving the physicochemical properties of the electrode.

[0064] In the present invention, any material that can be used as an anode active material of a lithium ion secondary battery can be used as the anode active material. For example, the anode active material may be carbon such as non-graphitizable carbon or 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, elements of group 1, 2, and 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 oxide; lithium titanium oxide, etc. One or more selected from the following may be used. In a specific embodiment, the negative electrode active material may include a carbon-based material and / or Si.

[0065] 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 may be 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 Lithium manganese oxides such as O4 (x is 0∼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 lithium nickel oxide represented by O2 (A=Co, Mn, Al, Cu, Fe, Mg, B or Ga, x=0.01∼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∼0.1) or Li2Mn3AO8 (A=Fe, Co, Ni, Cu or Zn); LiNi x Mn 2-xLithium manganese composite oxide with spinel structure represented by O4; Li(Ni a Co b Mn c )O2 (where a, b, and c are atomic fractions of independent elements, 0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1); NCM-based composite oxides; LiMn2O4, where some of the Li in the chemical formula is replaced with an alkaline earth metal ion; disulfide compounds; Fe2(MoO4)3, etc., but are not limited thereto.

[0066] In the present invention, the current collector may be a metal plate or the like having electrical conductivity and known in the secondary battery field, and may be appropriately used depending on the polarity of the electrode.

[0067] In the present invention, 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. The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity, and may include, for example, one or a mixture of two or more selected from the following conductive materials: graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, etc.; conductive fibers such as carbon fiber or metal fiber; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0068] In the present invention, the binder resin is not particularly limited as long as it is a component that assists in bonding the active material and the conductive material, and in bonding to the current collector, and examples thereof include 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, and the like. The binder resin can typically be included in a range of 1 to 30 mass% or 1 to 10 mass% with respect to 100 mass% of the electrode active material layer.

[0069] In the present invention, the electrode active material layer may include one or more additives such as an oxidation stabilizing additive, a reduction stabilizing additive, a flame retardant, a heat stabilizer, and an antifogging agent, as needed.

[0070] The present invention provides a secondary battery having the structure described above. In addition, the present invention provides a battery module including a secondary battery as a unit battery, 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, a power tool driven by an electric motor; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV); an electric two-wheeled vehicle including an electric bicycle (E-bike) and an electric scooter (E-scooter); an electric golf cart; and a power system.

[0071] Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0072] Example 1

[0073] Using lithium sulfide (Li2S, Mitsuwa Chemical product), diphosphorus pentasulfide (P2S5, Aldrich product), yttrium sulfide (Y2S3, Japan Pure Chemical product), lithium chloride (LiCl, Aldrich product), and lithium bromide (LiBr, Aldrich product) as raw materials, the composition is Li 5.4-3y M y PS 4.4 Cl 1.0 Br 0.6 (The amount of the Group 3 element (M) added was y = 0.0125) to obtain a mixed powder by weighing and mortar mixing in an Ar gas glove box. 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 milling was performed at 380 rpm for 20 hours, after which the pot was opened in the glove box to recover the powder. 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 with a mortar for 10 minutes to obtain a solid electrolyte.

[0074] Example 2

[0075] 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 third group element (M) added was set to 0.025.

[0076] Example 3

[0077] 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 third group element (M) added was set to 0.075.

[0078] Comparative Example 1

[0079] 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 3 element (M) added was set to 0.2.

[0080] Example 4

[0081] As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that lanthanum sulfide (La2S3, Japan Pure Chemical product) was used instead of yttrium sulfide (Y2S3, Japan Pure Chemical product) as the raw material for the Group 3 element (M).

[0082] Example 5

[0083] As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 4, except that the amount y of the third group element (M) added was set to 0.025.

[0084] Example 6

[0085] As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 4, except that the amount y of the third group element (M) added was set to 0.075.

[0086] Example 7

[0087] As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 4, except that the amount y of the group 3 element (M) added was set to 0.2.

[0088] Comparative Example 2

[0089] As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the Group 3 element (M) was not added, i.e., the amount y of the Group 3 element (M) added was set to 0.

[0090] Comparative Example 3

[0091] The composition is Li using lithium sulfide (Li2S, Mitsuwa Chemical product), diphosphorus pentasulfide (P2S5, Aldrich product), yttrium sulfide (Y2S3, Japan Pure Chemical product), lithium chloride (LiCl, Aldrich product), and lithium bromide (LiBr, Aldrich product) as raw materials. 5.3 Y 0.1 PS 4.5 Cl 0.8 Br 0.8 To this end, a mixed powder was obtained by weighing and mortar mixing in an Ar gas glove box. 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 milling was performed at 380 rpm for 20 hours, after which the pot was opened in the glove box to recover the powder. 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 with a mortar for 10 minutes to obtain a solid electrolyte.

[0092] Comparative Example 4

[0093] The composition is Li using lithium sulfide (Li2S, Mitsuwa Chemical product), diphosphorus pentasulfide (P2S5, Aldrich product), lanthanum sulfide (Ш) (La2S3, Kojundo Chemical Laboratory product), and lithium chloride (LiCl, Aldrich product) as raw materials. 6.15 La 0.075 P 0.925Weighing and mortar mixing were performed in an Ar gas glovebox to obtain a mixed powder to obtain S5Cl. 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 milling was performed at 380 rpm for 20 hours. After that, the pot was opened in the glovebox to recover the powder. 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.

[0094]

[0095]

[0096] [evaluation]

[0097] The following evaluations were conducted using the obtained solid electrolyte.

[0098] (XRD measurement)

[0099] A predetermined amount of solid electrolyte was placed in a sealed holder in an Ar gas glove box and XRD measurements were performed. 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) plane crystal peak of the argyrodite-type crystal structure observed around 2θ=30° in Figs. 1 and 2.

[0100] The measuring device and conditions are as follows.

[0101] ·X-ray diffraction device: Rigaku Smartlab

[0102] ·Source: Cu-Kα line (λ=1.5418Å)

[0103] ·Voltage: 45kV

[0104] Current: 200mA

[0105] ·Scan range (2θ): 10-60°

[0106] ·Step size: 0.01°

[0107] (Ionic conductivity measurement)

[0108] A predetermined amount of solid electrolyte was placed in a MACOR® pipe, and the MACOR® pipe and pellet forming jig (upper press pin and lower press pin) were combined and press-formed 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-formed at 7.5 MPa using a uniaxial press to obtain a MACOR® pipe cell. The obtained MACOR® pipe cell was installed in an electrochemical measurement jig cell, and a torque wrench was used to apply pressure to 5.0 N m to obtain an ionic conductivity measurement cell. The obtained ionic 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 atmospheric pressure (1 atm) to derive the ionic conductivity [mS / cm] of the solid electrolyte.

[0109] (Initial charge / discharge capacity measurement)

[0110] An NCM-based cathode active material with a nickel content of 80 mol% and a solid electrolyte were weighed at a mass ratio of 70:30. 1.5 mass% of carbon black was added as a conductive additive and mixed to obtain a cathode mixture. 80 mg of the solid electrolyte obtained above was weighed, placed in a molding jig, and pressurized at 6 MPa for 1 minute to obtain a solid electrolyte pellet. 10 mg of the cathode mixture obtained above was placed on one surface of the obtained solid electrolyte pellet, and then pressed flat with a SUS press pin of the molding jig to form a cathode layer. An Al plate was placed on the obtained cathode layer, and pressurized at 30 MPa for 1 minute. Thereafter, a Li-Cu foil was placed on the surface of the solid electrolyte pellet opposite to the cathode layer, and pressurized at 2 MPa for 30 seconds. This was combined with a SUS press pin to produce a Mako pipe cell. The obtained Mako pipe cell was installed in a battery cell, and a torque of 2 N·m was applied to obtain an all-solid-state battery cell.

[0111] Using the obtained all-solid-state battery, a charge-discharge test was conducted with a voltage range of 4.25 V-3.0 V, a charge condition of CC (0.05 C)-CV (0.01 C cutoff), and a discharge condition of CC (0.05 C). The initial charge capacity and initial discharge capacity were obtained from the obtained charge-discharge curve.

[0112] [Evaluation Results]

[0113] (Decision)

[0114] The evaluation results of the crystal phase (crystal structure) identified from the XRD pattern by XRD measurement are shown in Tables 1 and 2. In addition, the measured XRD pattern is shown in Figures 1 and 2.

[0115] As shown in Table 1, in Example 1 and Comparative Example 2, almost no impurity phase (also called unknown phase) was observed, and mostly only peaks of the argyrodite phase were observed. In addition, in Examples 2 to 7, peaks of the argyrodite phase and trace amounts of impurity phases other than the argyrodite phase were present. On the other hand, in Comparative Example 1, almost no peaks of the argyrodite phase were observed, and a large amount of impurity phases other than the argyrodite phase were present. The impurity phases were, for example, phases derived from raw materials such as Li2S and Y2S3.

[0116] As shown in Table 2, in Comparative Example 3, a large amount of impurity phases other than the argyrodite phase were present. In addition, in Comparative Example 4, the argyrodite phase was hardly observed, and a large amount of impurity phases were present.

[0117] In Fig. 1 and Fig. 2, XRD patterns of Examples 2 to 7 and Comparative Examples 1 and 2 are shown. In Example 1, where the addition amount of Y as a Group 3 element was y=0.0125, and in Comparative Example 2, where the addition amount of the Group 3 element was y=0, almost only peaks of the argyrodite phase were observed. In addition, in Examples 2 and 3, where the addition amounts of Y as a Group 3 element were y=0.025 and 0.075, respectively, and in Examples 4 to 7, where the addition amounts of La as a Group 3 element were y=0.0125, 0.025, 0.075, and 0.2, respectively, almost only peaks of the argyrodite phase were observed, but peaks of impurity phases derived from raw materials such as Li2S, Y2S3, and La2S3 were also observed. Meanwhile, in Comparative Example 1, where the amount of Y added as a Group 3 element was y=0.2, the peak of the argyrodite phase was hardly observed, and a large amount of peaks of the impurity phase were observed.

[0118] In Examples 2 to 7 and Comparative Example 2, a sulfide-based solid electrolyte having an argyrodite-type crystal structure with no or little impurity phase was obtained. A sulfide-based solid electrolyte with a high degree of crystallinity can promote hopping conduction of lithium ions, thereby contributing to an increase in ionic conductivity.

[0119] (Grid volume)

[0120] The lattice constant derived from the XRD pattern is in the range of 9.8518Å to 9.8773Å in the example, and the lattice volume is 956.2Å. 3 ∼963.6Å 3 On the other hand, in Comparative Example 1, where the addition amount of Y as a Group 3 element was y=0.2, the lattice constant could not be measured due to the large number of impurities. In addition, in Comparative Example 2, where the lithium site of the sulfide-based solid electrolyte was not replaced by a Group 3 element (M), the lattice constant was 9.9471Å and the lattice volume was 984.2Å. 3It was shown that by substituting the lithium site of the argyrodite-type crystal structure with a Group 3 element (M), the lattice volume of the crystal was reduced by approximately 2.1 to 2.8%. Although not bound by theory, it is thought that the crystal volume of the sulfide-based solid electrolyte may change as one of the three lithium sites is substituted with a Group 3 element (M) and the other becomes a lithium vacancy. The lithium vacancy is thought to serve as a path for hopping conduction of lithium ions, thereby contributing to the increase in ionic conductivity. In addition, the Group 3 element (M) substituted for the lithium site may have a trivalent charge, and thus, compared to a monovalent lithium ion, the force for attracting anions around the Group 3 element (M) site may change. Accordingly, it is thought that the crystal volume of the sulfide-based solid electrolyte changed, resulting in a structure suitable for hopping conduction of lithium ions.

[0121] The half-width 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 half-width could not be measured in Comparative Example 1, and the half-width was 0.08° in Comparative Example 2. In particular, Examples 1 and 2, in which the addition amount of Y as a Group 3 element (M) was y = 0.0125 and 0.025, and Example 5, in which the addition amount of La as a Group 3 element (M) was y = 0.025, exhibited a small half-width of 0.07° and a high ionic conductivity of 10.8 mS / cm or more. It is thought that the small half-width corresponds to a large crystallite size and contributes to the increase in ionic conductivity.

[0122] (ionic conductivity)

[0123] The results of the measurement of ionic conductivity are shown in Tables 1 and 2. In addition, the composition of the sulfide-based solid electrolyte, Li 5.4-3y M y PS 4.4 Cl 1.0 Br 0.6A graph is shown in Fig. 3, with the amount y of the added group element (M) on the horizontal axis and the ionic conductivity measured at 25°C and atmospheric pressure on the vertical axis. Each point in Fig. 3 corresponds to Examples 1 to 3 and Comparative Example 1 in which Y was doped as the group 3 element (M), Examples 4 to 7 in which La was doped as the group 3 element (M), and Comparative Example 2 in which the group 3 element (M) was not doped (corresponding to 'undoped' in the drawing).

[0124] As can be seen from FIG. 3 and Table 1, in Examples 2 to 7, the ionic conductivity was in the range of 2.84 mS / cm to 11.7 mS / cm. In Example 1, where the addition amount y of Y as a Group 3 element (M) was 0.0125, the ionic conductivity was the highest, 11.7 mS / cm. On the other hand, in Comparative Example 1, where the addition amount y of Y as a Group 3 element (M) was 0.2, the ionic conductivity was 0.000061 mS / cm. Thus, the ionic conductivity of each Example could be increased compared to the ionic conductivity of Comparative Example 1. It is thought that in Comparative Example 1, the addition amount y of Y as a Group 3 element (M) was too large, which lowered the crystallinity of the argyrodite-type crystal structure, resulting in a lower ionic conductivity.

[0125] In Comparative Example 2, where no Group 3 element (M) was added, the ionic conductivity was 10.7 mS / cm. Examples 1 and 2, where the addition amount of Y as a Group 3 element (M) was y≤0.025, and Examples 4 and 5, where the addition amount of La as a Group 3 element (M) was y≤0.025, exhibited an ionic conductivity of 10.8 mS / cm or more, which is higher than that of Comparative Example 2. The increase in ionic conductivity is thought to be due to the increase in the crystallinity of the argyrodite-type crystal structure due to the 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 higher ionic conductivities than that of Comparative Example 2, contain more impurity phases than that of Comparative Example 2. That is, Examples 2, 4, and 5, which have higher ionic conductivities than that of Comparative Example 2, have lower crystallinity than that of Comparative Example 2. From this, it can be seen that not only the degree of crystallization of the argyrodite-type crystal structure, but also the presence of a Group 3 element (M) can affect the ionic conductivity.

[0126] As can be seen from Table 2, in Comparative Example 3, which had a different stoichiometric composition, the ionic conductivity was 1.5 mS / cm. In Comparative Example 4, which had a different stoichiometric composition, the ionic conductivity was 0.09 mS / cm. This is thought to be due to the reduced crystallinity of the argyrodite-type crystal structure and the presence of a large amount of impurities, which lowered the ionic conductivity.

[0127] (Battery characteristics)

[0128] 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 an anode material, and the all-solid-state battery exhibited excellent charge-discharge characteristics and capacity characteristics. The initial discharge capacity relative ratio of the all-solid-state battery capacity when the solid electrolyte of Example 1 was used in the all-solid-state battery to the capacity of the all-solid-state battery when the sulfide-based solid electrolyte of Comparative Example 2, in which no Group 3 element was added, was 105%. In addition, when the sulfide-based solid electrolyte of Example 5 was used in an all-solid-state battery, the sulfide-based solid electrolyte had high stability against lithium metal as an anode material, and the all-solid-state battery exhibited excellent charge-discharge characteristics and capacity characteristics. The initial discharge capacity relative ratio of the all-solid-state battery capacity when the solid electrolyte of Example 5 was used in the all-solid-state battery to the capacity of the all-solid-state battery when the sulfide-based solid electrolyte of Comparative Example 2, in which no Group 3 element was added, was 106%. That is, by using the sulfide-based solid electrolytes of Examples 1 and 5 having high ionic conductivity in an all-solid-state battery, the initial discharge capacity of the all-solid-state battery could be improved.

[0129] Above, although the present invention has been described through limited embodiments and drawings, the present invention is not limited thereto, and it goes without saying that various modifications and variations are possible within the scope equivalent to the technical idea and claims of the present invention by a person having ordinary knowledge in the technical field to which the present invention pertains.

Claims

1. A sulfide-based solid electrolyte containing a Group 3 element and having an argyrodite-type crystal structure, The above sulfide-based solid electrolyte has the chemical formula Li 7-x-3y M y PS 6-x Ha x is displayed as, A sulfide-based solid electrolyte, wherein in the chemical formula above, M is at least one element selected from Group 3 elements, Ha is at least one element selected from halogen elements, and satisfies 1.0<x<2.5, 0<y≤0.

2.

2. In paragraph 1, A sulfide-based solid electrolyte wherein M is Y and 0<y<0.

2.

3. In paragraph 1, A sulfide-based solid electrolyte wherein M is La.

4. In paragraph 2 or 3, A sulfide-based solid electrolyte wherein the above y satisfies 0<y<0.

05.

5. In paragraph 1, A sulfide-based solid electrolyte, wherein the above Ha contains Br.

6. In paragraph 1, A sulfide-based solid electrolyte, wherein the above x satisfies 1.3≤x≤2.

0.

7. In paragraph 1, The lattice volume of the above sulfide-based solid electrolyte is 940Å. 3 More than 980Å 3 Below, sulfide-based solid electrolyte.

8. A method for manufacturing a sulfide-based solid electrolyte according to Article 1, A step of obtaining a mixture by mixing a lithium source, a third group element source, a phosphorus source, a sulfur source and a halogen source, and A method comprising a step of calcining the mixture at a temperature of 250°C to 600°C.

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

Images