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

Abstract

The purpose 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 comprising the sulfide-based solid electrolyte. The invention provides a sulfide solid electrolyte containing a group 13 element, the sulfide solid electrolyte has an argyrodite crystal structure, the chemical formula of the sulfide solid electrolyte is Li7-x-3yMyPS6-xHax, M is at least one selected from the group 13 element, Ha is at least one selected from the halogen element and comprises Br, and x is greater than or equal to 1 and less than or equal to 2. 0 < x < 2.5 and 0 < y < 0.2 are satisfied.

Description

Technical Field

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

[0002] This application claims priority from Japanese Patent Application No. 2023-025317 filed on February 21, 2023, the disclosure of which is incorporated herein by reference. Background Art

[0003] In order to achieve higher safety, longer life and higher energy density, all-solid-state batteries using solid electrolytes instead of liquid electrolytes of lithium-ion batteries have been developed. Among the many solid electrolytes, sulfide solid electrolytes (such as Li 10 GeP2S 12 ) has an ionic conductivity as high as that of liquid electrolytes and is easy to come into close contact with flexible active materials, so all-solid-state batteries using sulfide solid electrolytes are expected to be commercialized.

[0004] Lithium metal has attracted much attention as anode material for all-solid-state batteries due to its light weight per unit volume and high theoretical capacity, which can improve mass energy density (Wh / kg). 10 GeP2S 12 ) has low stability to lithium metal and is therefore difficult to use with lithium metal anodes.

[0005] In order to solve this problem, Patent Documents 1 to 3 disclose a method of stabilizing lithium metal with Li 7-x-3y PS 6-x-y Cl x Patent Document 4 discloses a sulfide solid electrolyte having an argyrodite-type crystal structure represented by 10 GeP2S 12 A sulfide-based solid electrolyte having a composition of a crystalline sulfide-based solid electrolyte and having improved stability to lithium metal.

[0006] However, the low ionic conductivity of sulfide-based solid electrolytes is challenging.

[0007] [Prior art literature]

[0008] [Patent Document]

[0009] Patent Document 1: Japanese Patent No. 5873533

[0010] Patent Document 2: Japanese Patent Application Publication No. 2018-45997

[0011] Patent Document 3: Japanese Patent Application Publication No. 2018-203569

[0012] Patent Document 4: Japanese Patent Application Laid-Open No. 2016-27545 Summary of the invention

[0013] Technical issues

[0014] The present disclosure relates to providing 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.

[0015] Technical Solution

[0016] In order to achieve the above object, the present disclosure provides a sulfide-based solid electrolyte containing a Group 13 element, wherein the sulfide-based solid electrolyte has a argyrodite-type crystal structure, wherein the chemical formula of the sulfide-based solid electrolyte is Li 7-x-3y M y PS 6-x Ha x , wherein, in the chemical formula, M is at least one selected from Group 13 elements, wherein Ha is at least one selected from halogen elements and Ha includes Br, and wherein 0<x<2.5 and 0<y<0.2 ​​are satisfied.

[0017] In one embodiment, y may satisfy 0 <y<0.1。

[0018] In one embodiment, M may be Al or Ga.

[0019] In one embodiment, M may be present at the 96i site of the argyrodite-type crystal structure.

[0020] The present disclosure provides a method for preparing a sulfide-based solid electrolyte as defined in any one of the above embodiments, the method comprising mixing a lithium source, a Group 13 element source, a phosphorus source, a sulfur source, and a halogen source to obtain a mixture; and sintering the mixture at a temperature of 250°C to 600°C.

[0021] The present disclosure provides an all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer, wherein the solid electrolyte layer comprises a sulfide-based solid electrolyte defined in any one of the above embodiments.

[0022] Beneficial Effects

[0023] The present disclosure may provide a sulfide-based solid electrolyte having improved ion conductivity, a method for preparing the sulfide-based solid electrolyte, and an all-solid-state battery including the sulfide-based solid electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 X-ray diffraction (XRD) patterns of Examples 1 to 5, Comparative Examples 1 and 3 are shown.

[0025] Figure 2 XRD patterns of Examples 6 to 11, Comparative Examples 2 and 3 are shown.

[0026] Figure 3 is a graph showing changes in lithium ion conductivity depending on the composition of the sulfide-based solid electrolyte. DETAILED DESCRIPTION

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

[0028] It should be understood that the words or terms used in the specification and the appended claims should not be interpreted as limited to the ordinary meaning and dictionary meaning, but should be interpreted based on the meaning and concepts corresponding to the technical aspects of the present disclosure based on the principle of allowing the inventor to appropriately define the terms to obtain the best interpretation.

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

[0030] The solid electrolyte for all-solid-state batteries disclosed herein may include at least one of a sulfide solid electrolyte, an oxide solid electrolyte, and a polymer solid electrolyte. Preferably, the solid electrolyte for all-solid-state batteries disclosed herein is a sulfide solid electrolyte. The solid electrolyte for all-solid-state batteries may be mixed with a positive electrode mixture material and used as a positive electrode material, or may be mixed with a negative electrode mixture material and used as a negative electrode material, and may also be used as a separator. The solid electrolyte for all-solid-state batteries may also include additives such as lithium salts, conductive materials, and binder resins according to the purpose of use.

[0031] <Sulfide solid electrolyte>

[0032] The sulfide-based solid electrolyte may include any sulfur-containing sulfide-based solid electrolyte commonly used in the art, but is not limited thereto.

[0033] The sulfide-based solid electrolyte may have a crystal structure. The sulfide-based solid electrolyte having a crystal structure may have high lithium ion conductivity by accelerating the conduction of lithium ions.

[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 may have an argyrodite-type crystal structure. The sulfide-based solid electrolyte having an argyrodite-type crystal structure has high stability to lithium metal, and thus lithium metal having a higher mass energy density can be used as a negative electrode material.

[0035] Sulfide-based solid electrolytes can be amorphous, glassy, ​​or glass-ceramic.

[0036] Sulfide solid electrolytes have the ionic conductivity of Group 1 or Group 2 metals in the periodic table, and may include Li-PS glass or Li-PS glass ceramics. Non-limiting examples of sulfide solid electrolytes may include at least one of 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 or Li2S-GeS2-ZnS. However, sulfide solid electrolytes are not particularly limited thereto.

[0037] Sulfide solid electrolytes may include a crystalline phase and an amorphous phase. Sulfide solid electrolytes may include a crystalline phase having a argyrodite-type crystal structure (also referred to as an argyrodite phase in this specification) and other phases (also referred to as an impurity phase or an unknown phase in this specification). The argyrodite-type crystal structure is preferably a cubic system. Other phases may be crystalline phases or amorphous phases. Other phases may include Li2S phase, P2S5 phase, LiCl phase, LiBr phase, Li3PS4 phase, Al2S3 phase, Ga2S3 phase and In2S3 phase, whether crystalline phase or amorphous phase. Preferably, the sulfide solid electrolyte does not contain or substantially does not contain an impurity phase other than the argyrodite phase. That is, preferably, the sulfide solid electrolyte may be composed of an argyrodite phase. When the sulfide solid electrolyte does not contain or substantially does not contain an impurity phase, the sulfide solid electrolyte may have a high lithium ion conductivity because the conduction of lithium ions is not easily hindered.

[0038] The proportion of the amorphous phase contained in the sulfide-based solid electrolyte can be quantitatively or non-quantitatively evaluated based on an X-ray diffraction (XRD) pattern. As one method, the proportion of the crystalline phase can be evaluated by comparing the peak intensity (height or area) of the XRD pattern.

[0039] The sulfide-based solid electrolyte of one embodiment of the present disclosure is composed of a chemical formula Li 7-x-3y M y PS 6-x Ha xIn the above chemical formula, M is at least one selected from Group 13 elements, Ha is at least one selected from halogen elements, and 0<x<2.5, 0<y<0.2 are satisfied. The sulfide-based solid electrolyte can have high lithium ion conductivity.

[0040] Sulfide-based solid electrolytes can be prepared by partially replacing Li with a Group 13 element (M) that can form a trivalent cation. 7-x PS 6-x Ha x The lithium in the 13th group is formed. The 13th group element (M) replacing lithium can be at least one 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 76pm, and the ionic radius (6 coordination) of aluminum (Al), gallium (Ga) and indium (In) are 68pm, 76pm and 94pm respectively. Based on the valence of the element, three lithiums (sites) can be replaced by one 13th group element (M). The lithium site is replaced by the 13th group element (M) to form a lithium site vacancy, thereby improving the lithium ion conductivity. In addition, the replacement of the lithium site by the 13th group element (M) changes the lattice constant and lattice volume of the sulfide solid electrolyte, thereby forming a crystal structure suitable for lithium ion conduction.

[0041] In addition, sulfide-based solid electrolytes can be prepared by doping Li with a Group 13 element (M) that can form a trivalent cation. 7-x PS 6-x Ha x The Group 13 element (M) doped into the lattice may be at least one 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. 7-x PS 6-x Ha x The lattice constant and lattice volume of the sulfide solid electrolyte can be changed in the crystal lattice to obtain a crystal structure suitable for lithium ion conduction.

[0042] Preferably, the 13th group element (M) is aluminum (Al) or gallium (Ga). When the 13th group element (M) is aluminum (Al) or gallium (Ga), the sulfide-based solid electrolyte can have high crystallinity, and thus the sulfide-based solid electrolyte can have high ionic conductivity. It is believed that since the ionic radius of lithium (Li) is 76 pm, and the ionic radii of aluminum (Al) and gallium (Ga) are 68 pm and 76 pm, respectively (close to each other), it is easy to maintain the argyrodite-type crystal structure after the substitution of the 13th group element (M).

[0043] Chemical formulaLi7-x-3y M y PS 6-x Ha x The addition amount y of the 13th group element (M) satisfies 0<y<0.2. When the 13th group element (M) is aluminum (Al), preferably y can satisfy 0<y<0.1, more preferably 0.01≤y≤0.08, more preferably 0.02≤y≤0.07, and most preferably 0.03≤y≤0.06. When the 13th group element (M) is gallium (Ga) or indium (In), preferably y can satisfy 0<y<0.1, more preferably 0<y<0.05, more preferably 0<y<0.025, and most preferably 0.01≤y≤0.015. When y satisfies the above range, the sulfide solid electrolyte can have a high ionic conductivity. When y is 0, since the change in the crystal structure cannot be obtained by substitution of the 13th group element (M), a lower ionic conductivity is obtained. When y is 0.2 or more, the argyrodite-type crystal structure of the sulfide-based solid electrolyte cannot be maintained, and the impurity phase that hinders lithium ion conduction in the sulfide-based solid electrolyte increases, resulting in low ion conductivity.

[0044] A relatively large amount of aluminum (Al) y can maintain the argyrodite-type crystal structure of a sulfide solid electrolyte. On the other hand, a relatively small amount of gallium (Ga) or indium (In) y can maintain the argyrodite-type crystal structure of a sulfide solid electrolyte. Although not limited by theory, it is believed that the reason lies in the difference in properties between aluminum (Al) and gallium (Ga) and indium (In). For example, when gallium (Ga) is used as a component of an alloy, the grain boundaries of the alloy are easily diffused, thereby promoting the formation of alloys with other metals. This feature can be observed in indium (In) having electrons in the d orbital in the same way as gallium (Ga). Therefore, it is believed that a relatively small amount of gallium (Ga) or indium (In) y than aluminum (Al) can maintain the argyrodite-type crystal structure of a sulfide solid electrolyte.

[0045] 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 position of the argyrodite type crystal structure. The argyrodite type crystal structure can be a cubic system, a hexagonal system, a tetragonal system, an orthorhombic system, a monoclinic system or a triclinic system. When the argyrodite type crystal structure is a cubic system (space group F43m), the Group 13 element (M) can be present at the 96i site in the crystal structure, thereby forming a lithium site void without hindering the ion conduction path of lithium ions. In this case, the sulfide solid electrolyte can have a high lithium ion conductivity.

[0046] In the formula 7-x-3y M y PS 6-x Ha xIn, halogen (Ha) is at least one selected from halogen elements. Halogen (Ha) preferably includes bromine (Br). More preferably, halogen (Ha) includes chlorine (Cl) and bromine (Br). When sulfur (S) is a divalent anion, it attracts lithium ions more strongly than monovalent halogens, significantly hindering the movement of lithium ions. Containing bromine (Br) as a halogen can result in a low sulfur (S) occupancy rate at a specific site in the argyrodite-type crystal structure, a high halogen occupancy rate at the corresponding site, and a high lithium ion mobility near the bromine (Br) site. As a result, the lithium ion conductivity can be improved. In addition, bromine (Br) combines with Li in the sulfide solid electrolyte to form a water-absorbing material lithium bromide (LiBr). Lithium bromide (LiBr) absorbs moisture that can reduce the lithium ion conductivity, thereby improving the lithium ion conductivity of the sulfide solid electrolyte.

[0047] In the above chemical formula Li 7-x-3y M y PS 6-x Ha x In the embodiment of the present invention, the ratio x of halogen (Ha) satisfies 0<x<2.5, preferably 1.0≤x≤2.3, more preferably 1.3≤x≤2.0, and more preferably 1.3≤x≤1.8. When x satisfies the above range, the argyrodite type crystal structure can be stabilized, and the sulfide-based solid electrolyte can have high ionic conductivity.

[0048] The ionic conductivity of the sulfide solid electrolyte can be affected by the crystallinity of the sulfide solid electrolyte. The crystallinity can be evaluated based on the XRD spectrum. In the XRD spectrum, when almost no or no phase other than the argyrodite crystalline phase is observed (crystalline phase or amorphous phase, such as Li2S phase, P2S5 phase, LiCl phase, LiBr phase, Li3PS4 phase, Al2S3 phase, Ga2S3 phase and In2S3 phase), the sulfide solid electrolyte can have a high ionic conductivity.

[0049] The lattice volume of the sulfide solid electrolyte can be changed by replacing the lithium site with a Group 13 element (M). Although not bound by theory, it is believed that since the Group 13 element (M) has the properties of a trivalent cation, the lattice volume changes, i.e., increases or decreases, due to strong interactions with other anions present in the sulfide solid electrolyte. The change in lattice volume can result in a crystal structure that conducts lithium ions, and the sulfide solid electrolyte can have high ionic conductivity.

[0050] The lattice volume of sulfide solid electrolyte is Above and The following, preferably Above and The following, more preferably Above and The following, more preferably Above and The lattice constant and lattice volume can be evaluated from the XRD pattern. When the lattice volume satisfies the above range, the conduction of lithium ions in the sulfide-based solid electrolyte can be promoted, thereby achieving high ionic conductivity of the sulfide-based solid electrolyte.

[0051] Unless otherwise specified, the ionic conductivity of the sulfide solid electrolyte (referred to as "lithium ion conductivity" in the specification) refers to the ionic conductivity at room temperature (25°C, 298K) and atmospheric pressure (1atm). When the sulfide solid electrolyte is used in an all-solid-state battery, in practice, the ionic conductivity is preferably 4mS / cm or more. The ionic conductivity of the sulfide solid electrolyte of one embodiment of the present disclosure is 1.5mS / cm or more, preferably 4mS / cm or more, more preferably 8mS / cm or more, more preferably 10.8mS / cm or more, and most preferably 12mS / cm or more.

[0052] The sulfide-based solid electrolyte of one embodiment of the present disclosure can be obtained by a preparation method comprising 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 sintering the mixture at a temperature of 250°C to 600°C under an inert atmosphere (e.g., argon and nitrogen).

[0053] Lithium source, Group 13 element source, phosphorus source, sulfur source and halogen source can be compounds, such as sulfide, oxide or nitride. Lithium sulfide (Li2S) can be used as a lithium source, phosphorus pentasulfide (P2S5) can be used as a phosphorus source, and lithium halides (LiHa) such as lithium chloride (LiCl) and lithium bromide (LiBr) can be used as halogen sources. For example, sulfide can be used as a Group 13 element source. Alternatively, sulfur can be supplied by other element sources. That is, at least one of a lithium source, a Group 13 element source, a phosphorus source or a halogen source can also be used as a sulfur source.

[0054] In the case of a sulfide-based solid electrolyte having an argyrodite-type crystal structure, the sintering temperature is preferably 400° C. to 550° C., more preferably 420° C. to 530° C., and more preferably 450° C. to 500° C. When the sintering temperature satisfies the above range, the formation of the argyrodite-type crystal structure can be promoted, thereby achieving high crystallinity of the sulfide-based solid electrolyte. Therefore, a sulfide-based solid electrolyte with high ionic conductivity can be obtained.

[0055] [All-solid-state battery]

[0056] The all-solid-state battery electrolyte disclosed herein can be used in an all-solid-state battery containing a positive electrode, a negative electrode and a solid electrolyte layer. The all-solid-state battery solid electrolyte can be used together with the active materials in the electrode active material layers 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 all-solid-state battery solid electrolyte can have a controlled average particle size according to the purpose of use. The ion conductivity can be improved by controlling the average particle size of the all-solid-state battery solid electrolyte.

[0057] <Solid Electrolyte Layer>

[0058] In the present disclosure, the thickness of the solid electrolyte layer may be about 50 μm or less, preferably about 15 μm to 50 μm. Within the above range, the solid electrolyte layer may have an appropriate thickness in consideration of the ionic conductivity, mechanical strength or energy density of the battery to which it is 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. At the same time, in terms of mechanical strength, the thickness may be 50 μm or less, 45 μm or less, or 40 μm or less. In addition, in addition to the above thickness range, the tensile strength of the solid electrolyte layer may be about 100 kgf / cm 2 To about 2000kgf / cm 2 In addition, the porosity of the solid electrolyte layer may be about 15% by volume or less or about 10% by volume or less. The solid electrolyte layer of the present disclosure is a thin film but may have high mechanical strength.

[0059] <Positive and negative electrodes>

[0060] In the present disclosure, the positive electrode and the negative electrode include a current collector and an electrode active material layer located 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, if necessary, the electrode may further include at least one of a conductive material or a binder resin. In addition, the electrode may further include various additives to supplement or improve the physical and chemical properties of the electrode.

[0061] In the present disclosure, the negative electrode active material may include any type of negative electrode active material for lithium ion secondary batteries. For example, the negative electrode active material may include at least one selected from the following: carbon, such as non-graphitizable carbon, graphite carbon; metal composite oxide, such as 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 Groups 1, 2, and 3 of the periodic table, halogens; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8); 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. In a specific embodiment, the negative electrode active material may include carbon-based materials and / or Si.)

[0062] In the case of the positive electrode, the electrode active material may include, but is not limited to, any type of positive electrode active material for a lithium ion secondary battery. For example, the positive electrode active material may include: layered compounds, such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted by one or more transition metals; lithium manganese oxides with the chemical formula Li 1+x Mn 2-x O4 (x is from 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides, such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; Ni-site type lithium nickel oxides represented by the chemical formula LiNi 1-x A x O2 (A = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, x = 0.01 to 0.3); lithium manganese composite oxides represented by the chemical formula LiMn 2-x A x O2 (A = Co, Ni, Fe, Cr, Zn, or Ta, x = 0.01 to 0.1) or Li2Mn3AO8 (A = Fe, Co, Ni, Cu, or Zn); spinel-structured lithium manganese composite oxides represented by LiNi x Mn 2-x O4; NCM-based composite oxides represented by Li(Ni a Co b Mn c )O2 (a, b, c are each independently the atomic fraction of the element, 0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1); LiMn2O4 in which Li in the chemical formula is partially substituted by alkaline earth metal ions; disulfide compounds; Fe2(MoO4)3, but not limited thereto.)

[0063] In the present disclosure, according to the polarity of the battery, the current collector may include any suitable conductive current collector known in the field of secondary batteries, such as a metal plate.)

[0064] In the present disclosure, the conductive material is generally added in an amount of 1 wt % to 30 wt % based on the total weight of the mixture containing the electrode active material. The conductive material is not limited to a specific type, and may include any material having conductivity without causing any chemical change in the corresponding battery. For example, the conductive material may include one selected from the following: 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; conductive fibers, such as carbon fibers or metal fibers; fluorocarbons; metal powders, such as aluminum powder, nickel powder; conductive whiskers, such as zinc oxide, potassium titanate; conductive metal oxides, such as titanium oxide; conductive polymers, such as polyphenylene derivatives, or mixtures thereof.

[0065] In the present disclosure, the binder resin is not limited to a specific type and may include those that contribute to the bonding of the active material to the conductive material and to the current collector. For example, the binder resin may include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and its various copolymers. Based on 100% by weight of the electrode active material layer, the content of the binder resin may generally be 1% by weight to 30% by weight or 1% by weight to 10% by weight.

[0066] In the present disclosure, if necessary, the electrode active material layer may include at least one additive of an oxidation stabilizer additive, a reduction stabilizer additive, a flame retardant, a heat stabilizer, or an antifogging agent.

[0067] The present disclosure provides a secondary battery having the above structure. The present disclosure also provides a battery pack including the secondary battery as a unit cell, a battery pack including the battery pack, and a device including the battery pack as a power source. In this case, the device may include any type of device that runs using electricity generated by an electric motor, for example, a power tool; an electric vehicle, including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV); an electric two-wheeled vehicle, including an electric bicycle (E-bike) and an electric scooter (E-sccoter); an electric golf cart; and a power system, but is not limited thereto.

[0068] Hereinafter, the present disclosure will be described in more detail by way of examples. However, the following description describes the present disclosure by way of examples, and the scope of the present disclosure is not limited thereto.

[0069] Example 1

[0070] The raw materials, namely lithium sulfide (Li2S, Mitsuwa Chemical), phosphorus pentasulfide (P2S5, Aldrich), aluminum sulfide (Al2S3, Japan Pure Chemical), lithium chloride (LiCl, Aldrich) and lithium bromide (LiBr, Aldrich), were weighed and mixed in a mortar in an argon glove box to a composition of Li 5.4-3y M y PS 4.4 Cl 1.0 Br 0.6 (the amount y of the 13th group element (M) is = 0.00625), thereby obtaining a mixture powder. The mixture powder is placed in a ZrO2 can together with ZrO2 balls to obtain an airtight can. The airtight can is mounted on a planetary ball mill, ball milled at 380 rpm for 20 hours, the can is opened in a glove box, and the powder is collected. The powder is placed in a carbon crucible, which is then sealed and sintered in an argon flow at 460°C for 8 hours. The sintered powder is ground with a mortar and pestle for 10 minutes to obtain a solid electrolyte.

[0071] Example 2

[0072] As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1 except that the addition amount y of the Group 13 element (M) was set to 0.0125.

[0073] Example 3

[0074] As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1 except that the addition amount y of the Group 13 element (M) was set to 0.05.

[0075] Example 4

[0076] As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1 except that the addition amount y of the Group 13 element (M) was set to 0.075.

[0077] Example 5

[0078] As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1 except that the addition amount y of the Group 13 element (M) was set to 0.1.

[0079] Comparative Example 1

[0080] As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1 except that the addition amount y of the Group 13 element (M) was set to 0.2.

[0081] Example 6

[0082] As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that gallium sulfide (Ga2S3, Japan Pure Chemical) was used instead of aluminum sulfide (Al2S3, Japan Pure Chemical) as the raw material of the Group 13 element (M), and the addition amount y of the Group 13 element (M) was set to 0.0125.

[0083] Example 7

[0084] As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 6 except that the addition amount y of the Group 13 element (M) was set to 0.01875.

[0085] Example 8

[0086] As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 6 except that the addition amount y of the Group 13 element (M) was set to 0.025.

[0087] Example 9

[0088] As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 6 except that the addition amount y of the Group 13 element (M) was set to 0.05.

[0089] Example 10

[0090] As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 6 except that the addition amount y of the Group 13 element (M) was set to 0.075.

[0091] Embodiment 11

[0092] As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 6 except that the addition amount y of the Group 13 element (M) was set to 0.1.

[0093] Comparative Example 2

[0094] As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 6 except that the addition amount y of the Group 13 element (M) was set to 0.2.

[0095] Comparative Example 3

[0096] As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1 except that no Group 13 element was added, that is, the addition amount y of the Group 13 element (M) was 0.

[0097] [Table 1]

[0098]

[0099] Ο: Exist in large quantities

[0100] △: Very small amount

[0101] X: There are a lot of impurities

[0102] :Almost non-existent

[0103] Comparative Example 4

[0104] A solid electrolyte was obtained in the same manner as in Comparative Example 3 except that lithium bromide (LiBr, Aldrich) was not used as a halogen source and only lithium chloride (LiCl, Aldrich) was used. That is, the designed composition of the solid electrolyte of Comparative Example 4 was Li 5.4 PS 4.4 Cl 1.6 .

[0105] [Evaluate]

[0106] The following evaluations were performed using the obtained solid electrolyte.

[0107] (XRD measurement)

[0108] A predetermined amount of solid electrolyte was placed on a stand in a hermetically sealed argon glove box and subjected to XRD measurement. The lattice constant, lattice volume, and half-maximum full width were calculated based on the obtained XRD pattern. Figure 1 and Figure 2 The full width at half maximum was calculated for the (311) crystal peak of the argyrodite type crystal structure observed near 2θ=30°.

[0109] The measuring machine and conditions are as follows.

[0110] X-ray diffraction system: Rigaku Smartlab

[0111] X-ray source: Cu-Kα ray

[0112] Voltage: 45kV

[0113] Current: 200mA

[0114] Scanning range (2θ): 10° to 60°

[0115] Step size: 0.01°

[0116] (Determination of ionic conductivity)

[0117] A predetermined amount of solid electrolyte is placed in In the tube, a single screw press is used in combination with The tube and pellet molding fixture (upper pressing pin and lower pressing pin) are pressed at 5MPa. Subsequently, a predetermined amount of gold powder is placed on both sides of the pellets and pressed at 7.5MPa by a single screw press to obtain The obtained The die was mounted on a fixture slot for electrochemical measurement, and a torque wrench was used to apply a maximum torque of 5.0 N·m to obtain an ionic conductivity measurement unit. The obtained ionic conductivity measurement unit was connected to an impedance meter to measure the resistance of the solid electrolyte pellets at room temperature (298K) and atmospheric pressure (1atm), and was used to determine the ionic conductivity [mS / cm] of the solid electrolyte.

[0118] (Determination of initial charge / discharge capacity)

[0119] An NCM-type positive electrode active material with a Ni content of 80 mol% and a solid electrolyte were weighed in a weight ratio of 70:30. 1.5 wt% of carbon black as a conductive aid was added thereto, and then mixed together to obtain a positive electrode mixture material. 80 mg of the obtained solid electrolyte was weighed, installed in a molding fixture, and pressed at 6 MPa for 1 minute to obtain a solid electrolyte pellet. 10 mg of the obtained positive electrode active material was installed on one surface of the obtained solid electrolyte pellets, and then flattened with a SUS press pin of the molding fixture to form a positive electrode layer. An Al plate was set on the obtained positive electrode layer, and pressed at 30 MPa for 1 minute. Subsequently, a Li-Cu foil was installed on the side of the solid electrolyte pellets opposite to the positive electrode layer, and pressed at 2 MPa for 30 seconds. Combine it with the SUS press pin to form a positive electrode layer. The obtained The tube core is mounted on the battery cell and a torque of 2 N·m is applied to obtain an all-solid-state battery cell.

[0120] The obtained all-solid-state battery was used to conduct charge and discharge tests in a voltage range of 4.25 V to 3.0 V, a charging condition of CC (0.05C)-CV (0.01C cutoff), and a discharge condition of CC (0.05C). The initial charge capacity and initial discharge capacity were calculated based on the obtained charge and discharge curves.

[0121] [Evaluation results]

[0122] (Crystalline Phase)

[0123] Table 1 shows the evaluation results of the crystalline phase (crystal structure) determined by XRD measurement from the XRD pattern. Figure 1 and Figure 2 The measured XRD pattern is shown.

[0124] As shown in Table 1, in Examples 1, 3, 5 to 8 and Comparative Example 3, almost no impurity phase (also referred to as an unknown phase) was observed, and only the argyrodite phase peak was mainly observed. In addition, in Examples 2, 4, and 9 to 11, the argyrodite phase peak and very few impurity phases were observed. On the other hand, in Comparative Examples 1 and 2, a large number of impurity phase peaks were observed. For example, the impurity phase is a phase derived from the raw materials Li2S, Al2S3, and Ga2S3.

[0125] Figure 1 and Figure 2 XRD patterns of Examples 1 to 11 and Comparative Examples 1 to 3 are shown. In Examples 1, 3 and 5 where the addition amount y of Al is 0.00625, 0.05 and 0.1, respectively, in Examples 6 to 8 where the addition amount y of Ga is 0.0125, 0.01875 and 0.025, respectively, and in Comparative Example 3 where the addition amount y of the Group 13 element is 0, only the argyrodite phase peak is mainly observed. In addition, in Examples 2 and 4 where the addition amount y of Al is 0.0125 and 0.075, respectively, and in Examples 9 to 11 where the addition amount y of Ga is 0.05, 0.075 and 0.1, respectively, only the argyrodite phase peak is mainly observed, but impurity phase peaks derived from the raw materials Li2S, Al2S3 and Ga2S3 are also observed. On the other hand, in Comparative Example 1 in which the addition amount y of Al was 0.2 and Comparative Example 2 in which the addition amount y of Ga was 0.2, almost no argyrodite phase peak was observed, but a large number of impurity phase peaks were observed.

[0126] In Examples 1, 3, 5 to 8 and Comparative Example 3, a sulfide-based solid electrolyte having an argyrodite-type crystal structure but containing no or almost no impurity phase was obtained. A sulfide-based solid electrolyte having high crystallinity can promote hopping conduction of lithium ions, thereby contributing to enhancing ionic conductivity.

[0127] (lattice volume)

[0128] In the embodiment, the lattice constant obtained from the XRD spectrum is to The lattice volume is to On the other hand, in Comparative Example 1 in which the amount y of Al added was 0.2 and Comparative Example 2 in which the amount y of Ga added was 0.2, a large amount of impurities existed and the lattice constant could not be measured. In addition, in Comparative Example 3 in which the lithium site of the sulfide-based solid electrolyte was not substituted with the Group 13 element (M), the lattice constant was The lattice volume is By substituting the lithium sites of the argyrodite crystal structure with a Group 13 element (M) and / or incorporating the Group 13 element (M) into the lattice of the argyrodite crystal structure, the lattice volume of the crystal is reduced by about 2.4% to 3.1%.

[0129] Although not bound by theory, it is believed that one of the three lithium sites and two lithium voids replaced by the Group 13 element (M) changes the crystal volume of the sulfide solid electrolyte. Alternatively, it is believed that the Group 13 element (M) penetrates into the lattice of the argyrodite-type crystal structure, changing the crystal volume of the sulfide solid electrolyte. It is believed that the lithium void becomes a path for lithium ion hopping conduction, which helps to improve ionic conductivity. In addition, the Group 13 element that replaces the lithium site or penetrates into the lattice can have a trivalent valence, thereby changing the force that attracts anions near the Group 13 element (M) site compared to monovalent lithium ions. Therefore, it is believed that the change in the crystal volume of the sulfide solid electrolyte leads to a structure suitable for lithium ion hopping conduction.

[0130] In the embodiment, the full width at half maximum of the crystal peak of the (311) plane of the argyrodite crystal structure is 0.05° to 0.1°, while in Comparative Examples 1 and 2, it is 0.15° and 0.12°, respectively. In particular, Example 6 in which the amount of Ga y=0.0125 exhibits a smaller full width at half maximum and a higher ionic conductivity. It is believed that the smaller full width at half maximum corresponding to the larger crystal size will contribute to the enhancement of ionic conductivity.

[0131] (Ionic conductivity)

[0132] Table 1 shows the measurement results of ionic conductivity. Figure 3 The sulfide solid electrolyte is composed of Li 5.4-3y M y PS 4.4 Cl 1.0 Br 0.6 The graph shows that the amount y of the Group 13 element (M) added is plotted on the horizontal axis and the ionic conductivity measured at 25° C. and atmospheric pressure is plotted on the vertical axis. Figure 3 The points in the graph correspond to Examples 1 to 5 and Comparative Example 1 doped with Al as the Group 13 element (M), Examples 6 to 11 and Comparative Example 2 doped with Ga as the Group 13 element (M), and Comparative Example 3 (“undoped” in the figure) not doped with the Group 13 element (M).

[0133] from Figure 3As can be seen from Table 1, in Examples 1 to 5, the ionic conductivity is in the range of 9.0 mS / cm to 13.8 mS / cm. In Example 3, in which the addition amount y of Al as the 13th group element (M) is 0.05, a high ionic conductivity of 13.8 mS / cm is exhibited. On the other hand, in Comparative Example 1, in which the addition amount y of Al is 0.2, the ionic conductivity is 0.5 mS / cm. In addition, in Example 6, in which the addition amount y of Ga as the 13th group element (M) is 0.0125, the highest ionic conductivity of 15.7 mS / cm is exhibited. On the other hand, in Comparative Example 2, in which the addition amount y of Ga is 0.2, the ionic conductivity is 0.00098 mS / cm. As described above, by adding the 13th group element (M) in the optimal amount, the ionic conductivity of Examples 1 to 11 is higher than that of Comparative Examples 1 and 2. It is believed that in Comparative Examples 1 and 2, the amount y of Al and Ga added as the Group 13 element (M) is too much, and the crystallinity of the argyrodite-type crystal structure is reduced, resulting in low ion conductivity. In Comparative Example 3 in which the Group 13 element (M) is not added, the ion conductivity is 10.7 mS / cm. Although not shown in Table 1, in Comparative Example 4 which does not contain bromine (Br) as a halogen element, the ion conductivity is 8.1 mS / cm. It is believed that bromine (Br) forms lithium bromide (LiBr) with Li in the sulfide-based solid electrolyte, and lithium bromide (LiBr) absorbs moisture that can reduce ion conductivity, thereby improving ion conductivity.

[0134] In addition, from Figure 3 As can be seen from Table 1, when the addition amount y of Al as the Group 13 element (M) is 0.05 (Example 3), the ion conductivity increases compared to y=0.0125 (Example 2) and y=0.075 (Example 4). Figure 1 In the XRD patterns, almost no impurity phase was observed in Example 3, while very little impurity phase (unknown phase) was observed in Examples 2 and 4. In addition, in Examples 6 to 8 in which the addition amount y of Ga as the Group 13 element (M) was 0.0125 to 0.025, the ion conductivity was improved compared to Examples 9 to 11 in which the addition amount of Ga was 0.05 to 0.1. Figure 2 From the XRD patterns of Examples 6 to 8, almost no impurity phase was observed, while very little impurity phase (unknown phase) was observed in Examples 9 to 11. Therefore, it is believed that the increase in ionic conductivity is due to the increase in crystallinity of the argyrodite type crystal structure caused by the reduction of impurities present in the sulfide-based solid electrolyte. As described above, in order to improve the ionic conductivity of the sulfide-based solid electrolyte, the high crystallinity of the argyrodite type crystal structure containing only the argyrodite phase without the impurity phase is preferred.

[0135] Compared with Comparative Example 3 in which the Group 13 element (M) was not added, Examples 1 to 3 in which y≤0.075 (the addition amount y of Al as the Group 13 element (M)) and Examples 6 and 7 in which y≤0.01875 (the addition amount y of Ga as the Group 13 element (M)) showed higher ionic conductivity. According to the XRD result, it is believed that the crystallinity of the argyrodite type crystal structure of Comparative Example 3 is higher than that of Examples 2 and 4, but in fact, the ionic conductivity of Examples 2 and 4 with lower crystallinity is higher than that of Comparative Example 3 with higher crystallinity. This confirms that not only the crystallinity of the argyrodite type crystal structure but also the presence of the Group 13 element (M), that is, the change in lattice volume due to the presence of the Group 13 element (M) can affect the ionic conductivity.

[0136] like Figure 3 As shown in Table 1, when the addition amount y of Al as the Group 13 element (M) is 0.1 or less, the ionic conductivity is 9.0 mS / cm or more. When the addition amount y of Al as the Group 13 element (M) is 0.075 or less, the ionic conductivity is 11.3 mS / cm or more, which is higher than the ionic conductivity of 10.7 mS / cm of Comparative Example 3 to which the Group 13 element (M) is not added. In addition, when the addition amount y of Ga as the Group 13 element (M) is 0.1 or less, the ionic conductivity is 3.5 mS / cm or more. When the amount y of Ga added as the Group 13 element (M) is 0.01875 or less, the ionic conductivity is 11.9 mS / cm or more, which is higher than the ionic conductivity of 10.7 mS / cm of Comparative Example 3 to which the Group 13 element (M) is not added. In addition, the ion conductivity of Comparative Example 4 not containing bromine (Br) as a halogen element is 8.1 mS / cm, which is lower than the ion conductivity of Comparative Example 3 containing bromine (Br) as a halogen element, which is 10.7 mS / cm.

[0137] (Battery Characteristics)

[0138] When the sulfide solid electrolyte of Example 3 in which the addition amount y of Al as a Group 13 element (M) is 0.05 is used in the solid electrolyte layer of the all-solid-state battery, the sulfide solid electrolyte has high stability for lithium metal as a negative electrode material, and the all-solid-state battery can be stably charged / discharged. The relative ratio of the capacity of the all-solid-state battery using Example 3 in the solid electrolyte layer to the capacity of the all-solid-state battery using Comparative Example 3 in the solid electrolyte layer in terms of initial discharge capacity is 106%. In addition, when the sulfide solid electrolyte of Example 6 in which the addition amount y of Ga as a Group 13 element (M) is 0.0125 is used in the solid electrolyte layer of the all-solid-state battery, the sulfide solid electrolyte has high stability for lithium metal as a negative electrode material, and the all-solid-state battery can be stably charged / discharged. The relative ratio of the capacity of the all-solid-state battery using Example 6 in the solid electrolyte layer to the capacity of the all-solid-state battery using Comparative Example 3 in the solid electrolyte layer in terms of initial discharge capacity is 107%. As described above, when the solid electrolytes of Examples 3 and 6 having high ion conductivity are used in an all-solid-state battery, the capacity of the all-solid-state battery can be improved.

[0139] Although the present disclosure has been described above with a limited number of embodiments and drawings, the present disclosure is not limited thereto, and it is apparent to those skilled in the art that various modifications and changes may be made within the technical scope of the present disclosure and the appended claims and their equivalents.

Claims

1. A sulfide-based solid electrolyte comprising a Group 13 element, in, The sulfide solid electrolyte has an argyrodite-type crystal structure. The chemical formula of the sulfide solid electrolyte is Li 7-x-3y M y PS 6-x Ha x , Wherein, in the chemical formula, M is at least one selected from Group 13 elements, wherein the Ha is at least one selected from halogen elements, and the Ha includes Br, and Here, 0<x<2.5 and 0<y<0.2 ​​are satisfied.

2. The sulfide-based solid electrolyte according to claim 1, wherein y satisfies 0<y<0.

1.

3. The sulfide-based solid electrolyte according to claim 1 or 2, wherein M is Al or Ga.

4. The sulfide-based solid electrolyte according to claim 1, wherein M exists in the 96i site of the argyrodite crystal structure.

5. A method for preparing the sulfide-based solid electrolyte according to claim 1, the method comprising: mixing a lithium source, a Group 13 element source, a phosphorus source, a sulfur source, and a halogen source to obtain a mixture; as well as The mixture is sintered at a temperature of 250°C to 600°C.

6. An all-solid-state battery, comprising: positive electrode, negative electrode and solid electrolyte layer, in, The solid electrolyte layer includes the sulfide-based solid electrolyte according to claim 1 .

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