Sulfide-based solid electrolyte, method for manufacturing same, and all-solid-state battery comprising same

Abstract

Disclosed in the present invention are: a sulfide-based solid electrolyte capable of achieving high ion conductivity and improving the rate performance of a battery by using three kinds of halogen elements and adjusting the doping concentrations thereof; a method for manufacturing same; and an all-solid-state battery comprising same.

Description

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

[0001] This invention claims the benefit of Korean Patent Application No. 10-2023-0129763 filed with the Korean Intellectual Property Office on September 26, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a sulfide-based solid electrolyte having high ionic conductivity by controlling the doping concentration of a halogen element, a method for producing the same, and an all-solid-state battery including the same.

[0003] All-solid-state batteries replace the liquid electrolyte that fills the space between the anode and cathode of conventional lithium secondary batteries with a solid electrolyte. These all-solid-state batteries are safe because they do not use flammable solvents, eliminating the risk of explosion. Furthermore, because they allow the use of lithium metal or lithium alloys as a cathode material, they offer higher energy density than conventional batteries, attracting attention as next-generation batteries.

[0004] The core materials that make up solid electrolytes include polymers, sulfides, and oxides, but among them, sulfide-based solid electrolytes with high ductility and high ionic conductivity are considered suitable for manufacturing high-capacity, large-scale batteries.

[0005] Sulfide-based solid electrolytes with an argyrodite-type crystal structure, represented by Li6PS5Cl, have a lithium ion conductivity of approximately 2 mS / cm, which is somewhat superior to existing materials, but are not satisfactory for application to next-generation battery technology that requires a high lithium ion conductivity of 5 mS / cm or more.

[0006] In order to further increase the ionic conductivity of a sulfide-based solid electrolyte with an argyrodite crystal structure, a method of doping the sulfide-based solid electrolyte with both Cl and Br as halogen elements, and doping Cl and Br in an excess of 1 or more, is known. However, when such a sulfide-based solid electrolyte is used as the negative electrode of an all-solid-state battery, the excessively doped halogen element may cause a side reaction with the lithium metal, which may lower the battery performance. Therefore, a method of suppressing the side reaction by using a lithium / indium alloy, etc. instead of lithium metal as the negative electrode is also being attempted. However, in this case, the battery voltage may drop to the level of 0.6 V, which may cause another problem of increased energy density loss, and therefore, it is difficult to say that this method is a desirable alternative.

[0007] Meanwhile, some literature mentions that ionic conductivity can be improved by additionally doping I (iodine), a halogen element, along with Cl and Br. However, these solid electrolytes still have limitations in applying them to next-generation technologies because they exhibit low ionic conductivity of less than 4 mS / cm.

[0008] The present invention aims to provide a sulfide-based solid electrolyte capable of maintaining high ionic conductivity and improving the rate characteristics of a battery, and a method for producing the same.

[0009] The present invention provides a sulfide-based solid electrolyte represented by the following chemical formula 1:

[0010] [Chemical Formula 1]

[0011] Li 7-(x+y)-z PS 6-(x+y)-z Cl x Br y F z

[0012] (In the above chemical formula 1, 1.3 ≤ x+y ≤1.7, and 0 < z < 0.2)

[0013] The present invention provides a method for producing a sulfide-based solid electrolyte, comprising the steps of: producing a mixture by mixing a lithium-containing compound, a P and S-containing compound, a Cl-containing compound, a Br-containing compound, and an F-containing compound; a heat treatment step; and a pulverizing step.

[0014] The present invention provides an all-solid-state battery comprising a positive electrode; a negative electrode; and a solid electrolyte layer interposed between the positive electrode and the negative electrode, wherein the solid electrolyte layer comprises a sulfide-based solid electrolyte represented by chemical formula 1.

[0015] The sulfide-based solid electrolyte according to the present invention uses three halogen elements, and by appropriately controlling the doping concentration thereof, it has high ionic conductivity due to the use of halogen elements, while at the same time preventing problems such as performance degradation that occur when lithium metal is used as a negative electrode of an all-solid-state battery.

[0016] Figure 1 is an XRD spectrum of the sulfide-based solid electrolytes of Examples 1 and 2.

[0017] Figures 2 to 7 are graphs comparing the C-rate performance of all-solid-state batteries including the sulfide-based solid electrolytes of Examples 1 to 2 and Comparative Examples 1 to 4.

[0018] Hereinafter, a sulfide-based solid electrolyte, its manufacturing method, and its use according to a specific embodiment of the invention will be described in more detail.

[0019] Unless otherwise defined herein, all technical and scientific terms used herein are used merely to describe exemplary embodiments and are not intended to be limiting of the present invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, it should be understood that the terms "comprises," "includes," or "has" indicate the presence of a feature, number, step, component, or combination thereof, but do not preclude the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0020] The present invention is susceptible to various modifications and takes various forms. Specific embodiments are illustrated and described in detail below. However, this is not intended to limit the present invention to specific disclosed forms, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

[0021] Sulfide-based solid electrolyte

[0022] The sulfide-based solid electrolyte of the present invention contains lithium, phosphorus, sulfur and a halogen element, and contains three types of elements, Cl, Br and F, as the halogen element.

[0023] Specifically, the sulfide-based solid electrolyte is represented by the following chemical formula 1:

[0024] [Chemical Formula 1]

[0025] Li 7-(x+y)-z PS 6-(x+y)-z Cl x Br y F z

[0026] (In the above chemical formula 1, 1.3 ≤ x+y ≤1.7, and 0 < z < 0.2)

[0027] The sulfide-based solid electrolyte having the above chemical formula has an argyrodite-type crystal structure.

[0028] A solid electrolyte with a basic composition such as Li6PS5Cl having an argyrodite crystal structure has a low ionic conductivity of about 2 mS / cm, and when a halogen element is excessively doped, the ionic conductivity can be improved. However, when a halogen element is excessively doped, a side reaction with the lithium metal, which is the negative electrode, may occur, and the battery performance may be reduced due to the generation of dendrites. Therefore, the inventors of the present invention have discovered that the sulfide-based solid electrolyte can contain three halogen elements, namely Cl, Br, and F, while limiting the composition ratio of each halogen element as in Chemical Formula 1, thereby increasing the ionic conductivity while suppressing side reactions and dendrite generation at the negative electrode, thereby improving the battery performance, and have completed the present invention.

[0029] The argyrodite crystal structure is PS4 3- The structure is a structure in which the main unit structure of the skeleton is used, and the sites around it are occupied by S and halogen surrounded by Li. In the unit cell of the argyrodite-type crystal structure, there are a total of eight 4a sites and 4d sites, and these sites are occupied randomly by S, which is an anion, and halogen ions. Since halogen has a weaker attraction force toward Li than S, the density of Li around the sites occupied by the halogen elements is reduced. This difference in Li density increases the mobility of Li ions, which consequently improves ionic conductivity. When an excess of halogen elements is used, the occupancy rate of the halogen elements for the sites can be increased, and thus the mobility and ionic conductivity of Li can be improved. In the present invention, all three types of halogen elements, Cl, Br, and F, are used, and due to the differences in the sizes and reactivities of Cl, Br, and F, the degree of disorder caused by the halogen elements can be increased, and thus the mobility of Li can also be further increased.

[0030] In the above chemical formula 1, x > 0 and y > 0. That is, as described above, the sulfide-based solid electrolyte of the present invention includes three types of halogen elements, i.e., Cl, Br, and F.

[0031] The ionic conductivity of the sulfide-based solid electrolyte according to the present invention is affected by the doping concentrations of Cl and Br among the halogen elements. In chemical formula 1, x represents the composition ratio (doping concentration) of the Cl element, y represents the composition ratio (doping concentration) of the Br element, x+y represents the sum of the composition ratios of Cl and Br (sum of doping concentrations), and x / y represents the composition ratio of Cl to Br (doping concentration ratio). At this time, the range is 1.3 ≤ x+y ≤ 1.7, 1.4 ≤ x+y ≤ 1.6, and it is preferable that the relationship x / y > 1 is satisfied. At this time, 0.1 ≤ x ≤ 1.6, 0.6 ≤ x ≤ 1.2, 0.1 ≤ y ≤ 1.2, 0.4 ≤ y ≤ 1.0, most preferably x=1, and y can be 0.4 to 0.6.

[0032] When having these ranges, the sulfide-based solid electrolyte of the present invention can achieve a high ionic conductivity of 7.0 mS / cm or more, and can be applied to an all-solid-state battery to improve its performance. The co-doped F can contribute to maintaining the high ionic conductivity due to the Cl and Br, and can also play a role in suppressing side reactions between the negative electrode of the all-solid-state battery and the solid electrolyte.

[0033] Typically, when lithium metal is used as the anode in an all-solid-state battery, the low reduction stability of the solid electrolyte causes a side reaction in which the sulfide-based solid electrolyte is reduced by the lithium anode during charge-discharge cycles. This increases interfacial resistance and reduces battery performance. Furthermore, dendrites, in which lithium grows unevenly toward the anode during charge-discharge cycles, can occur, causing battery degradation.

[0034] The sulfide-based solid electrolyte according to the present invention suppresses the above-mentioned side reaction by additionally doping F as a halogen element, thereby reducing the increase in interface resistance, and prevents deterioration of battery performance while maintaining high ionic conductivity by suppressing dendrites.

[0035] The composition ratio (doping concentration) of F, a halogen element, can be expressed as z, and has a range of 0 < z < 0.2, preferably 0.01 ≤ z ≤ 0.15, 0.01 ≤ z ≤ 0.1. If z, the composition ratio (doping concentration) of F, is outside the above range, the ionic conductivity may decrease below the standard, and the battery performance may also decrease as F reacts with Li ions to form an excessive amount of LiF within the battery.

[0036] According to one embodiment, the sulfide-based solid electrolyte of chemical formula 1 is Li 5.45 PS 4.45 ClBr 0.5 F 0.05 or Li 5.4 PS 4.4 ClBr 0.5 F 0.1 It could be.

[0037] The sulfide-based solid electrolyte of Chemical Formula 1 according to the present invention has a lithium ion conductivity sufficient for the operation of a lithium battery at room temperature, i.e., 25°C, and specifically, has an ion conductivity of 7.0 mS / cm or more, 7.5 mS / cm or more, and 18.0 mS / cm or less. The ion conductivity is derived from the resistance value of a Nyquist plot obtained by placing 0.15 g of the sulfide-based solid electrolyte into a 13ф(mm) SUS mold, pressurizing it at 370 MPa for 1 minute, and then measuring the AC impedance in the range of 0.1 Hz to 7 MHz while maintaining 100 MPa. At this time, the measurement of all physical property values ​​is performed in a dry room at room temperature and a relative humidity of 0.7%.

[0038] The sulfide-based solid electrolyte of the present invention can exhibit peaks at positions of 2θ = 14.5° to 16.5°, 2θ = 24° to 26°; 2θ = 28.5° to 30.5°; 2θ = 30.5° to 32.5°; and 2θ = 44° to 46° when measuring a powder X-ray diffraction (XRD) pattern according to a Cu-Kα line at X-ray wavelengths (λ) of 1.5406 Å and 1.5444 Å.

[0039] Method for manufacturing sulfide-based solid electrolyte

[0040] In one embodiment of the present invention, a method for producing a sulfide-based solid electrolyte may be provided by mixing compounds including a lithium-containing compound, a P and S-containing compound, a Cl-containing compound, a Br-containing compound, and an F-containing compound to produce a mixture, and then performing a heat treatment.

[0041] Each step is explained in detail below.

[0042] Mixing stage (S1)

[0043] First, lithium-containing compounds, P and S-containing compounds, Cl-containing compounds, Br-containing compounds, and F-containing compounds are prepared, and these are mixed to prepare a mixture.

[0044] Compounds containing lithium (Li), which is one of the raw materials, include lithium compounds such as lithium sulfide (Li2S), lithium oxide (Li2O), lithium carbonate (Li2CO3), or lithium metal monohydrate.

[0045] Compounds containing the above sulfur (S) include lithium sulfide and phosphorus sulfide.

[0046] Compounds containing phosphorus (P) include, for example, phosphorus sulfides such as phosphorus trisulfide (P2S3) and phosphorus pentasulfide (P2S5), phosphorus compounds such as sodium phosphate (Na3PO4), and phosphorus single particles.

[0047] Compounds containing Cl, Br and F can be used, which are denoted as MQ.

[0048] Here, M can be Li, P, S, or a combination of these elements with oxygen or sulfur, and Q can be Cl, Br, or F.

[0049] For example, Cl-containing compounds include LiCl, PCl3, PCl5, POCl3, P2Cl4, SCl2, S2Cl2, etc. Preferably, it is LiCl, PCl5, PCl3, etc., and more preferably, it is LiCl.

[0050] Br-containing compounds include LiBr, PBr3, POBr3, S2Br2, etc. Preferably, it is at least one selected from the group consisting of LiBr, PBr5, and PBr3, and more preferably, it is at least one selected from the group consisting of LiBr and PBr3.

[0051] F-containing compounds include LiF, PF3, PF5, SF2, SF4, SF6, and S2F. 10 It can be used as a backbone. Preferably, it is LiF.

[0052] The content ratio of the lithium-containing compound, phosphorus-containing compound, sulfur-containing compound, and halogen-containing compound can be variously adjusted depending on the composition ratio of the final sulfide-based solid electrolyte to be manufactured, and is not particularly limited in the present invention.

[0053] The mixing step of the present invention can be performed by a grinding and mixing process. Specifically, the grinding and mixing can be performed while applying mechanical energy, such as by a planetary mill, a mechano-fusion mill, a dynamo, an induction mill, or an auto-grinder. If necessary, a non-polar organic solvent, such as xylene, heptane, or octane, can be added. The material of the balls used for the grinding and mixing is not particularly limited, and examples thereof include alumina balls, zirconia balls, stainless steel balls, silicon nitride balls, and tungsten carbide balls.

[0054] According to one embodiment, when a planetary ball mill is used as a mixing device, the rotation speed may be 100 rpm to 800 rpm for 1 to 50 hours, but is not limited thereto. Preferably, 10 mm zirconia balls are placed in the planetary ball mill, and then crushed at a speed of 400 rpm to 700 rpm, followed by further crushing using a mortar or auto grinder.

[0055] Heat treatment stage (S2)

[0056] In the above heat treatment step, the obtained crushed mixture is heat treated to have an argyrodite-type crystal structure.

[0057] The heat treatment process can be performed at 300°C to 600°C. When the heat treatment process is performed within the above temperature range, the ionic conductivity can be improved while maintaining an argyrodite-type crystal structure due to a homogeneous reaction. In addition, the heat treatment process can be performed in an inert atmosphere, and the inert atmosphere can be an Ar atmosphere, an N2 atmosphere, or a combination thereof.

[0058] Crushing stage (S3)

[0059] The grinding step can be performed using either dry grinding or wet grinding.

[0060] The device used for pulverization is not particularly limited as long as the purpose of the present invention is achieved. For example, media-type pulverization such as a bead mill or a planetary ball mill, jet pulverization, or cavitation pulverization may be used. Among these, a planetary ball mill is preferred. The pulverization conditions can be set so as to pulverize the solid electrolyte into a desired particle size.

[0061] Dry grinding is performed by introducing the sulfide-based solid electrolyte particles to be ground in a dry state into a device such as a ball mill as described above. Wet grinding is performed by dispersing the sulfide-based solid electrolyte particles in an organic solvent and grinding them in a slurry state.

[0062] Organic solvents usable for wet grinding include at least one of aliphatic organic solvents such as heptane, decane, hexane, and cyclohexane; and aromatic organic solvents such as toluene, xylene, 1,2,4-trimethylbenzene, anisole, dimethoxybenzene, chlorobenzene, ethyl benzoate, and benzyl acetate. At this time, the solid content concentration in the slurry for wet grinding is preferably in the range of 2 to 90 wt%, and more preferably in the range of 10 to 80 wt%.

[0063] In the grinding process, either dry grinding or wet grinding can be used, and these can be used in combination or performed two or more times.

[0064] After crushing, further classification processes can be performed if necessary.

[0065] When wet grinding is performed, the organic solvent is removed through a drying process prior to the classification process, and if necessary, a solid-liquid separation process such as filtration, centrifugation, pressure filtration, or reduced pressure filtration may be further performed prior to the drying process to separate the solid electrolyte particles and the organic solvent.

[0066] All-solid-state batteries

[0067] In one embodiment of the present invention, an all-solid-state battery including a sulfide-based solid electrolyte is provided.

[0068] Specifically, the all-solid-state battery includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a solid electrolyte layer including a sulfide-based solid electrolyte according to the present invention disposed between the positive electrode and the negative electrode.

[0069] The sulfide-based solid electrolyte of the present invention exhibits high ionic conductivity by controlling the doping concentration of three types of halogen elements. Furthermore, when lithium metal is applied as the negative electrode, side reactions between the negative electrode and the solid electrolyte are suppressed, thereby preventing degradation of battery performance.

[0070] The all-solid-state battery of the present invention can be manufactured according to conventional methods known in the art. For example, it can be manufactured by laminating and pressurizing a solid electrolyte layer so that it exists between the positive and negative electrodes. At this time, the solid electrolyte layer can be adjusted to various thicknesses by controlling the performance of the all-solid-state battery and various process variables. Preferably, the thickness can be 1 mm to 10 mm, and more preferably, it can have a thickness of 3 mm to 4 mm.

[0071] In the present invention, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

[0072] The above-mentioned positive electrode active material layer includes a positive electrode active material, a binder, and a conductive agent. The positive electrode can be manufactured by coating a positive electrode slurry including a positive electrode active material, a binder, a conductive agent, and a solvent on a positive electrode current collector.

[0073] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the bonding strength of the positive electrode active material may be strengthened by forming fine irregularities on the surface, and may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0074] The above positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically may include a lithium metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum.

[0075] More specifically, the lithium metal oxide is a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese oxide (e.g., LiNi 1-Y Mn Y O2 (here, 0 <Y<1), LiMn 2-z Ni z O4 (where 0<Z<2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y 1O2(here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2 (here, 0 <Y2<1), LiMn 2-z1 Co z1 O4 (wherein, 0<Z1<2) etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r1 )O2(wherein, 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1) or Li(Ni p1 Co q1 Mn r2 )O4 (wherein, 0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2) etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 MS2)O2 (wherein, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r3 and s2 are atomic fractions of independent elements, respectively, 0<p2<1, 0<q2<1, 0<r3<1, 0<s2<1, p2+q2+r3+s2=1), etc.), and one or more compounds of these may be included.

[0076] The above lithium metal oxide is LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn02Co02)O2, Li(Ni 0.5 Mn 0.3 Co02)O2, Li(Ni07Mn0 15 Co 0.15 )O2 and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.) are more preferable in that they can increase the capacity characteristics and stability of the battery.

[0077] The above lithium composite metal oxide is Li(Ni 0.6 Mn 0.2 Co02)O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc. is more preferable in that the improvement effect is excellent according to the control of the type and content ratio of the constituent elements forming the lithium composite metal oxide.

[0078] The above positive electrode active material may be included in an amount of 60 wt% to 99 wt%, preferably 70 wt% to 99 wt%, and more preferably 80 wt% to 98 wt%, based on the total weight of the solid content excluding the solvent in the positive electrode slurry.

[0079] The above binder is a component that helps bond between the conductive material, the active material, and the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0080] Typically, the binder may be included in an amount of 1 wt% to 20 wt%, preferably 1 wt% to 15 wt%, and more preferably 1 wt% to 10 wt%, based on the total weight of the solid content excluding the solvent in the positive electrode slurry.

[0081] The above-mentioned conductive agent is a component for further improving the conductivity of the positive electrode active material.

[0082] The conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, carbon-based materials such as graphite; carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as fluorinated carbon, aluminum, and nickel powders; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used.

[0083] Typically, the conductive agent may be included in an amount of 1 wt% to 20 wt%, preferably 1 wt% to 15 wt%, and more preferably 1 wt% to 10 wt%, based on the total weight of solids excluding the solvent in the positive electrode slurry.

[0084] The solvent may include an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a desirable viscosity when including the positive electrode active material and optionally a binder and a conductive material. For example, the solvent may be included so that the concentration of the solid content including the positive electrode active material and optionally a binder and a conductive material is 50 wt% to 95 wt%, preferably 70 wt% to 95 wt%, and more preferably 70 wt% to 90 wt%.

[0085] The negative electrode can be manufactured, for example, by coating a negative electrode slurry containing a negative electrode active material, a binder, a conductive material, and a solvent on a negative electrode current collector, or a graphite electrode made of carbon (C) or the metal itself can be used as the negative electrode.

[0086] For example, when manufacturing a negative electrode by coating a negative electrode slurry on the negative electrode current collector, the negative electrode current collector generally has a thickness of 3 to 500 μm. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, like the positive electrode current collector, the bonding strength of the negative electrode active material can be strengthened by forming fine unevenness on the surface, and can be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc.

[0087] The negative electrode active material may include one or more negative electrode active materials selected from the group consisting of natural graphite, artificial graphite, carbonaceous materials; lithium-containing titanium composite oxide (LTO); Si, SiOx, Sn, Li, Zn, Mg, Cd, Ce, Ni or Fe metals (Me); alloys composed of the metals (Me); oxides (MeOx) of the metals (Me); and complexes of the metals (Me) and carbon. Specifically, the negative electrode active material may be a silicon-based negative electrode active material including silicon (Si), silicon oxide (SiOx) or a silicon alloy. In this case, a thin and stable SEI layer containing a siloxane bond is formed, thereby further improving the high-temperature stability and lifespan characteristics of the battery.

[0088] The above negative electrode active material may be included in an amount of 60 wt% to 99 wt%, preferably 70 wt% to 99 wt%, and more preferably 80 wt% to 98 wt%, based on the total weight of solids excluding the solvent in the negative electrode slurry.

[0089] The above binder is a component that helps bond between the conductive material, the active material, and the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0090] Typically, the binder may be included in an amount of 1 wt% to 20 wt%, preferably 1 wt% to 15 wt%, and more preferably 1 wt% to 10 wt%, based on the total weight of solids excluding the solvent in the slurry for the negative electrode.

[0091] The above conductive agent is a component for further improving the conductivity of the negative electrode active material. The conductive agent is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber or metal fiber; metal powders such as fluorocarbon, 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.

[0092] The above-mentioned conductive agent may be included in an amount of 1 wt% to 20 wt%, preferably 1 wt% to 15 wt%, and more preferably 1 wt% to 10 wt%, based on the total weight of solids excluding the solvent in the negative electrode slurry.

[0093] The solvent may include water or an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a desirable viscosity when including the negative electrode active material and optionally a binder and a conductive material. For example, the solvent may be included so that the concentration of the solid content including the negative electrode active material and optionally a binder and a conductive material is 50 wt% to 95 wt%, preferably 70 wt% to 90 wt%.

[0094] When using the metal itself as the above-mentioned cathode, it can be manufactured by physically bonding, rolling, or depositing the metal onto the metal thin film itself or the cathode current collector. The deposition method can use an electrical deposition method or a chemical vapor deposition method.

[0095] For example, the metal to be bonded / rolled / deposited on the metal thin film itself or the negative electrode current collector may include one metal selected from the group consisting of lithium (Li), nickel (Ni), tin (Sn), copper (Cu), and indium (In), or an alloy of two metals.

[0096] The manufacture of an all-solid-state battery having the above-described configuration is not particularly limited in the present invention, and a known method can be used.

[0097] When manufacturing the all-solid-state battery of the present invention, electrodes including a positive electrode and a negative electrode are placed and then pressure-molded to assemble the battery.

[0098] The assembled battery is then installed within an outer packaging material and sealed by heat pressing, etc. As the outer packaging material, a laminate pack made of aluminum, stainless steel, etc., or a cylindrical or square metal container is highly suitable.

[0099] As described above, the all-solid-state battery according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0100] [Example]

[0101] Hereinafter, the present invention will be described in more detail by way of examples. However, the scope of the present invention is not limited to these examples.

[0102] [Example 1]

[0103] As raw material powders, Li2S, P2S5, LiCl, LiBr, and LiF were prepared in amounts of 1.585 g, 1.935 g, 0.701 g, 0.756 g, and 0.023 g according to the composition, and placed in a ZrO2 container together with 10 mm ZrO2 balls (6 times the total amount of precursors), and mixed 16 times for 20 minutes at 600 rpm using a planetary ball mill, and then the resultant was obtained from the container using a tool and coarsely ground for 10 minutes using an autogrinder.

[0104] Then, it was placed in a furnace under an Ar atmosphere and heat-treated at 500°C for 12 hours, and then coarsely ground for 10 minutes with an autogrinder. Next, 1.3 mm ZrO2 balls and anisole (200 volume% of the solid electrolyte amount) were placed in a planetary ball mill, and ground three times at 300 rpm for 10 minutes each. Then, it was classified through a 25 μm sieve, centrifuged at 10,000 rpm for 10 minutes, and the supernatant was discarded and vacuum-dried at 80°C to obtain an argyrodite-type sulfide-based solid electrolyte.

[0105] [Example 2 and Comparative Examples 1 to 4]

[0106] Sulfide-based solid electrolytes of Example 2 and Comparative Examples 1 to 4 were manufactured using the same method as Example 1 except that the content of the raw material powder was changed as shown in Table 1 below.

[0107] Li2S(g)P2S5(g)LiCl(g)LiBr(g)LiF(g)LiI(g)Example 11.5851.9350.7010.7560.0230Example 21.5901.9400.6660.7580.0450Comparative Example 11.5811.9290.7360.7540.0000Comparative Example 21.5991.9520.5960.7630.0910Comparative Example 31.5181.9000.7250.74200.113Comparative Example 41.3421.8190.6940.71100.434

[0108] [Example 1]

[0109] The sulfide-based solid electrolytes manufactured in Examples 1 and 2 were pulverized and charged into a sample holder for X-ray powder diffraction, and a Bruker D8 Endeavor XRD was used. The X-rays were measured by scanning at a step of 0.02° with Cu Kα (λ = 1.5406 Å and 1.5444 Å), an applied voltage of 40 KV, and an applied current of 15 mA.

[0110] As a result of XRD measurement, peaks originating from the argyrodite-type crystal structure were observed. Specifically, as shown in Fig. 1, the sulfide-based solid electrolytes of Examples 1 and 2 all exhibited peaks at positions of 2θ = 14.5° to 16.5°, 2θ = 24° to 26°; 2θ = 28.5° to 30.5°; 2θ = 30.5° to 32.5°; and 2θ = 44° to 46°.

[0111] [Example 2]

[0112] The composition ratio (doping concentration) and ionic conductivity of the sulfide-based solid electrolytes manufactured in the examples and comparative examples were measured and are shown in Table 2 below.

[0113] (1) ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscope) analysis

[0114] The sulfide-based solid electrolyte was crushed and placed in a glass vial, dissolved using concentrated nitric acid, and the sample was completely decomposed with hydrogen peroxide. The sample was diluted to three different volumes and elementally analyzed using an ICP-AES (GDC Integra XMP) according to standard methods.

[0115] (2) Ionic conductivity measurement

[0116] After injecting 0.15 g of sulfide-based solid electrolyte into a 13ф SUS mold, pressurizing at 370 MPa for 1 minute, maintaining 100 MPa, measuring AC impedance in the range of 0.1 Hz to 7 MHz, the resistance value is derived from the Nyquist plot. All measurements were conducted in a dry room at room temperature and relative humidity of 0.7%.

[0117] Chemical formula x+yx / yzσ (mS / cm) Example 1Li 5.45 PS 4.45 ClBr 0.5 F 0.05 1.520.057.9 Example 2Li 5.4 PS 4.4 ClBr 0.5 F 0.1 1.520.17.6 Comparative Example 1Li 5.5 PS 4.5 ClBr 0.5 1.5208.4 Comparative Example 2Li 5.3 PS 4.3 ClBr 0.5 F 0.2 1.520.24.8 Comparative Example 3Li 5.45 PS 4.45 ClBr 0.5 I 0.05 1.5206.5 Comparative Example 4Li 5.3 PS 4.3 ClBr 0.5 I 0.2 1.5203.8

[0118] As shown in Table 2 above, the sulfide-based all-solid-state electrolytes of Examples 1 and 2 showed ionic conductivities of 7.9 mS / cm and 7.6 mS / cm, respectively, which were both higher than 7.0 mS / cm, as the composition ratio (doping concentration) of Cl and Br and the composition ratio (doping concentration) of F satisfied the range of Chemical Formula 1. In contrast, in the case of Comparative Example 2, since F was included in excess, the ionic conductivity was found to be significantly lower than that of the Examples. In addition, even when I was included in excess, as in Comparative Example 4, the ionic conductivity was found to be significantly lower than that of the Examples.

[0119] Comparative Example 1, which does not include F as a halogen source, had higher ionic conductivity than the sulfide-based solid electrolytes of Examples 1 and 2, but as described below, when applied to an actual battery, the battery performance was found to be inferior to that of the Examples.

[0120] In addition, in the case of Comparative Example 3, which does not include F as a halogen source and partially includes I as a halogen element, it was found to have higher ionic conductivity than the sulfide-based solid electrolytes of Comparative Examples 2 and 4, but lower ionic conductivity than the sulfide-based solid electrolytes of Examples 1 and 2.

[0121] Comparative Example 4 can be seen to have practically used I as a halogen element compared to Comparative Example 3, and in this case, it was confirmed that the ionic conductivity was less than 4 mS / cm.

[0122] [Example 3]

[0123] After manufacturing an all-solid-state battery using the sulfide-based solid electrolyte manufactured in the examples and comparative examples, a performance test was performed.

[0124] (1) Battery manufacturing

[0125] LiNi 0.8 Co 0.1 Mn 0.1 A cathode active material (LG Chem), Li6PS5Cl solid electrolyte (LG Chem), and CNF conductive material (Sigma Aldrich) were mixed in a weight ratio of 70:25:5, and then laminated on a SUS current collector and pressurized at 480 MPa to manufacture a cathode.

[0126] The sulfide-based solid electrolyte of the examples and comparative examples was laminated on the positive electrode and pressurized to 370 MPa, and a Li foil (100 um thick) was added as the negative electrode and pressurized to 30 MPa to assemble the battery.

[0127] (2) Rate performance measurement

[0128] The manufactured battery was charged and discharged once each at 0.05C, 0.05C, 0.1C, 0.2C, 0.33C, 0.5C, 1.0C, and 0.1C. The rate performance was calculated as the ratio of the discharge capacity at each C-rate to the initial discharge capacity (100%). The results are shown in FIGS. 2 to 7 and Table 3 below.

[0129] Chemical formula rate performance 0.1C 1.0C Example 1Li 5.45 PS 4.45 ClBr 0.5 F 0.05 90.6%69.4%Example 2Li 5.4 PS 4.4 ClBr 0.5 F 0.1 88.9%68.6%Comparative Example 1Li 5.5 PS 4.5 ClBr 0.5 87.5%29.2%Comparative Example 2Li 5.3 PS 4.3 ClBr 0.5 F 0.2 78.6%17.0%Comparative Example 3Li 5.45 PS 4.45 ClBr 0.5 I 0.05 88.0%18.8%Comparative Example 4Li 5.3 PS 4.3 ClBr 0.5 I 0.2 85.5%12.19%

[0130] As shown in Table 3 above, the batteries including the solid electrolytes of Examples 1 and 2 had superior rate performance compared to the battery including the solid electrolyte of Comparative Example 1.

[0131] As shown in Table 3 above, although the solid electrolyte of Comparative Example 1 has higher ionic conductivity than the examples, it can be confirmed that the battery performance (rate performance) is lower when applied to an actual battery. This can be understood as a result of the occurrence of a side reaction between the halogen element (Cl, Br) and the lithium negative electrode in the case of the sulfide-based solid electrolyte of Comparative Example 1, which resulted in a decrease in the rate performance of the battery. As a result, when the rate performance of the battery was measured at a high-rate discharge (1.0C) using the sulfide-based solid electrolyte of Comparative Example 1, it was confirmed that the rate performance was significantly lowered compared to the examples.

[0132] Comparative Example 2, which was overdoped with F, not only had low ionic conductivity but also showed a greater decrease in rate performance.

[0133] As observed, each battery according to the examples and comparative examples showed a greater difference in performance at high-rate discharge (1.0C) than at 0.1C. In particular, in the case of comparative examples 3 and 4, the rate performance at 0.1C showed a similar level to that of the examples, but it was confirmed that the rate performance was significantly reduced at high-rate discharge (1.0C).

[0134] This shows that when the halogen element I (iodine) is additionally doped together with Cl and Br, side reactions between the halogen element (Cl, Br) and the lithium negative electrode occur more frequently during high-rate discharge (1.0C) than when I is not additionally doped, which may lower the performance of the battery.

[0135] That is, when additional doping of I with Cl and Br is performed, ionic conductivity may be reduced and the performance of the battery may be degraded under high-rate discharge (1.0C) conditions.

[0136] These results show that a battery including the sulfide-based solid electrolyte of the present invention has very stable charge / discharge cycles, and that the capacity does not decrease relatively significantly even when the current density is increased by a factor of 10.

Claims

1. A sulfide-based solid electrolyte represented by the following chemical formula 1: [Chemical Formula 1] Li 7-(x+y)-z PS 6-(x+y)-z Cl x Br y F z (In the above chemical formula 1, 1.3 ≤ x+y ≤1.7, and 0 < z < 0.2) 2. In paragraph 1, Sulfide-based solid electrolyte with x / y > 1.

3. In paragraph 1, A sulfide-based solid electrolyte where x > 0 and y > 0.

4. In paragraph 1, A sulfide-based solid electrolyte, wherein 0.1 ≤ x ≤ 1.6 and 0.1 ≤ y ≤ 1.

2.

5. In paragraph 1, The above sulfide-based solid electrolyte is Li 5.45 PS 4.45 ClBr 0.5 F 0.05 and Li 5.4 PS 4.4 ClBr 0.5 F 0.1 A sulfide-based solid electrolyte, one or more selected from:

6. In paragraph 1, The above sulfide-based solid electrolyte is a sulfide-based solid electrolyte having an argyrodite-type crystal structure.

7. In paragraph 1, The above sulfide-based solid electrolyte is a sulfide-based solid electrolyte having an ionic conductivity of 7.0 mS / cm or more at 25°C.

8. A step of preparing a mixture by mixing a lithium-containing compound, a P and S-containing compound, a Cl-containing compound, a Br-containing compound, and a F-containing compound; heat treatment step; and A method for producing a sulfide-based solid electrolyte of claim 1, comprising a crushing step.

9. In paragraph 8, A method for producing a sulfide-based solid electrolyte, wherein the above heat treatment is performed at 300°C to 600°C.

10. In paragraph 8, A method for producing a sulfide-based solid electrolyte, wherein the above-mentioned grinding step is performed by dry grinding or wet grinding.

11. An all-solid-state battery comprising a positive electrode; a negative electrode; and a solid electrolyte layer interposed between the positive electrode and the negative electrode, An all-solid-state battery, wherein the solid electrolyte layer comprises a sulfide-based solid electrolyte according to any one of claims 1 to 7.

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