Solid electrolyte, method for producing the same, and all-solid-state battery including the same

Abstract

The present invention relates to a sulfide-based solid electrolyte having excellent water stability and ionic conductivity, a method for producing the same, and an all-solid-state battery including the same. The present invention provides a solid electrolyte including a core portion containing sulfide-based solid electrolyte particles and a surface portion formed on the core portion and containing fluorine-doped sulfide-based solid electrolyte particles, wherein the surface portion includes a concentration gradient region in which the concentration of F atoms decreases from the surface of the surface portion toward the core portion, a method for producing the same, and an all-solid-state battery including the same.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0142618, filed October 31, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a sulfide-based solid electrolyte having excellent water stability and ionic conductivity, a method for producing the same, and an all-solid-state battery including the same. [Background technology]

[0003] All-solid-state batteries replace the liquid electrolyte currently used between the positive and negative electrodes of lithium secondary batteries with a solid electrolyte. These batteries are safe and explosion-free, and have a higher energy density than conventional batteries, drawing attention as next-generation batteries. The solid electrolyte used in all-solid-state batteries is a solid-state material that allows lithium ions to be conducted within the battery, and has high ionic conductivity comparable to that of the liquid electrolytes currently used in lithium secondary batteries. Key materials for solid electrolytes include polymers, sulfides, and oxides. Among these, sulfide-based solid electrolytes, which are highly flexible and have high ionic conductivity, are considered suitable for the production of large-capacity batteries.

[0004] However, sulfide-based solid electrolytes have a problem in that they are highly reactive to moisture and react with moisture in the atmosphere to generate the toxic gas hydrogen sulfide, which not only adversely affects the safety of workers but also reduces the ionic conductivity of the sulfide-based solid electrolyte itself.

[0005] To solve these problems of sulfide-based solid electrolytes, methods of doping the electrolyte with Al and N or forming a polymer coating layer have been studied, but the improvement in water stability is minimal, and the coating layer actually increases resistance.

[0006] Therefore, there is a need to develop sulfide-based solid electrolytes that have excellent water stability, low resistance, and excellent ionic conductivity. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] KR2017-0050562 A Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been devised to solve the above-mentioned problems, and an object of the present invention is to provide a solid electrolyte that, when contained in a battery, does not adversely affect the resistance of the battery and has excellent water stability.

[0009] Another object of the present invention is to provide a method for producing the above solid electrolyte.

[0010] A further object of the present invention is to provide an all-solid-state battery containing the above solid electrolyte. [Means for solving the problem]

[0011] In order to solve the above problems, the present invention provides a solid electrolyte, a method for producing the same, and an all-solid-state battery including the same.

[0012] (1) The present invention provides a solid electrolyte comprising: a core portion containing sulfide-based solid electrolyte particles; and a surface portion formed on the core portion and containing fluorine-doped sulfide-based solid electrolyte particles, wherein the surface portion includes a concentration gradient region in which the concentration of F atoms decreases from the surface of the surface portion toward the core portion.

[0013] (2) In the present invention, in the above (1), the fluorine-doped sulfide-based solid electrolyte particles provide a solid electrolyte represented by the following chemical formula 1: [Chemical formula 1] Li(12-x-b) BS (6-x-a-b) X a F b Y x In the above Chemical Formula 1, B is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb or Ta; X is Se or Te; Y is Cl, Br, I, CN, OCN, SCN or N3; x is 0≦x≦2, a is 0≦a≦2, and b is 0.1 <b≦1.0である。

[0014] (3) In the present invention, in the above (1) or (2), the fluorine-doped sulfide-based solid electrolyte particles provide a solid electrolyte represented by the following chemical formula 1-1. [Chemical formula 1-1] Li6PS5Cl (1-b) F b In the above chemical formula 1-1, b is 0.1 <b≦1.0である。

[0015] (4) The present invention provides a solid electrolyte according to any one of (1) to (3) above, wherein the sulfide-based solid electrolyte particles are an argyrodite-type solid electrolyte.

[0016] (5) In any one of the above (1) to (4), the present invention provides a solid electrolyte in which the sulfide-based solid electrolyte particles are represented by the following chemical formula 2: [Chemical formula 2] Li (12-x) BS (6-x-a) X a Y x In the above Chemical Formula 2, B is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb or Ta; X is Se or Te; Y is Cl, Br, I, CN, OCN, SCN or N3; x is in the range of 0≦x≦2, and a is in the range of 0≦a≦2.

[0017] (6) The present invention provides a solid electrolyte according to any one of (1) to (5) above, wherein the concentration gradient region includes a region extending from the surface of the solid electrolyte toward the core portion at a distance of 30 nm or more and less than 1,200 nm.

[0018] (7) The present invention provides the solid electrolyte according to any one of the above (1) to (6), wherein the average particle size is 2 μm to 10 μm.

[0019] (8) The present invention provides a method for producing a solid electrolyte, comprising a step of heat-treating sulfide-based solid electrolyte particles in the presence of ammonium fluoride in an inert gas atmosphere, wherein the ammonium fluoride is used in an amount of 1 part by weight to 10 parts by weight per 100 parts by weight of the sulfide-based solid electrolyte particles.

[0020] (9) The present invention provides the method for producing a solid electrolyte according to the above (8), wherein the sulfide-based solid electrolyte particles are an argyrodite-type solid electrolyte.

[0021] (10) The present invention provides the method for producing a solid electrolyte according to (8) or (9), wherein the heat treatment is carried out by sequentially carrying out a first heat treatment step and a second heat treatment step, the first heat treatment step being carried out at a temperature of 200°C to 300°C for 1 to 5 hours, and the second heat treatment step being carried out at a temperature of 400°C to 600°C for 5 to 10 hours.

[0022] (11) The present invention provides an all-solid-state battery including a positive electrode, a negative electrode, and the solid electrolyte according to any one of (1) to (7) above. [Effects of the Invention]

[0023] The solid electrolyte according to the present invention includes a surface portion including hydrophobic fluorine-doped sulfide-based solid electrolyte particles on the surface of a sulfide-based solid electrolyte particle, and includes a concentration gradient region in which the concentration of F atoms decreases from the surface toward the center of the solid electrolyte particle. This not only provides excellent water stability but also low resistance, resulting in excellent ion conductivity. [Brief explanation of the drawings]

[0024] The following drawings attached to this specification illustrate specific embodiments of the present invention and, together with the above-described content of the invention, serve to further understand the technical concept of the present invention, and the present invention should not be interpreted as being limited solely to the matters depicted in such drawings.

[0025] [Figure 1] 1 is a SEM image of the solid electrolyte prepared in Example 1. [Figure 2] 1 shows SEM-EDS result images of the solid electrolyte prepared in Example 1, showing (a) an S element map, (b) a P element map, (c) a Cl element map, and (d) an F element map. [Figure 3] 1 is a graph showing the results of TOF-SIMS of the solid electrolyte prepared in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention will now be described in more detail to facilitate understanding of the present invention.

[0027] The terms and words used in this specification should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0028] Definition of Terms The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0029] As used herein, the term "concentration gradient" generally refers to a gradual change in solute concentration, and in the solid electrolyte of the present invention, the concentration gradient refers to a gradual change in the concentration of atomic components that constitute the solid electrolyte.

[0030] In this specification, the term "particle" refers to a microscopic object such as an elementary particle, atom, molecule, or colloid that constitutes a substance.

[0031] In this specification, the terms "comprises," "includes," "has," and the like are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but are not intended to preclude the possible presence or addition of one or more different features, numbers, steps, components, or combinations thereof.

[0032] Measurement method In this specification, the term "average particle size (D 50 ) is measured using a particle size analyzer (PSA) and is the particle size corresponding to 50% cumulative volume, calculated from the smallest particle size in the particle size distribution measured by laser diffraction.

[0033] solid electrolyte The present invention provides a solid electrolyte having excellent water stability and excellent ionic conductivity by including a concentration gradient region on the surface of sulfide-based solid electrolyte particles and a surface portion including fluorine-doped sulfide-based solid electrolyte particles.

[0034] A solid electrolyte according to one embodiment of the present invention includes a core portion including sulfide-based solid electrolyte particles, and a surface portion formed on the core portion and including fluorine-doped sulfide-based solid electrolyte particles, wherein the surface portion includes a concentration gradient region in which the concentration of F atoms decreases from the surface of the surface portion toward the core portion.

[0035] Sulfide-based solid electrolytes react with moisture in the atmosphere to generate hydrogen sulfide gas, which not only reduces ionic conductivity but also adversely affects stability due to the toxicity of hydrogen sulfide gas.

[0036] Therefore, research has been conducted into methods such as doping sulfide-based solid electrolytes with Al and N or forming a polymer coating layer on their surfaces, but the improvement in water stability has been minimal. Furthermore, sulfide-based solid electrolyte particles have a hydrophobic surface, making it difficult to form a polymer coating layer, including a styrene-butadiene copolymer or an acrylonitrile-butadiene copolymer, on their surfaces. Therefore, methods have been considered to form a hydrophilic oxide buffer layer to aid in the formation of the polymer coating layer, but these methods have problems such as increased resistance and poor flexibility, making them susceptible to breakage during the formation of the polymer coating layer.

[0037] As another example, a method of forming an oxide coating layer by oxidizing the surface of the sulfide-based solid electrolyte has been studied. However, while this method improves water stability, it has a problem of poor ionic conductivity due to increased resistance caused by the oxide coating layer.

[0038] However, in the solid electrolyte of the present invention, sulfide-based solid electrolyte particles are heat-treated with ammonium fluoride adjusted to a specific content in a nitrogen atmosphere to form fluorine-doped sulfide-based solid electrolyte particles in which fluorine (F) substitutes for sulfur (S) in the sulfide-based solid electrolyte only in specific regions on the surface of the sulfide-based solid electrolyte particles, thereby forming a surface region with a concentration gradient region. This effectively prevents reaction with moisture when exposed to the atmosphere, resulting in excellent moisture stability and ionic conductivity.

[0039] Specifically, the sulfide-based solid electrolyte particles may be a sulfide-based solid electrolyte containing Li, P, and S, or may be an argyrodite-type solid electrolyte in terms of high ionic conductivity and low reactivity with the lithium negative electrode.

[0040] More specifically, the sulfide-based solid electrolyte particles may be represented by the following chemical formula 2.

[0041] [Chemical formula 2] Li (12-x) BS (6-x-a) X a Y x

[0042] In the above Chemical Formula 2, B is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb or Ta; X is Se or Te; Y is Cl, Br, I, CN, OCN, SCN or N3; x is in the range of 0≦x≦2, and a is in the range of 0≦a≦2.

[0043] As another example, the sulfide-based solid electrolyte particles may be represented by Chemical Formula 2, where B is P, As, or Ga, X is Se, and Y is Cl, Br, or I.

[0044] As another example, the sulfide-based solid electrolyte particles may be represented by the following Formula 2-1, 2-2, or 2-3.

[0045] [Chemical formula 2-1] Li6PS5Z

[0046] In the above chemical formula 2-1, Z can be Cl, Br, or I.

[0047] [Chemical formula 2-2] Li6BS 5-a X a Y

[0048] In the above chemical formula 2-2, B is P, As or Sb, X is Se or Te, Y is Se, Br, I, CN, OCN, SCN or N3, and 0≦a≦2.

[0049] [Chemical formula 2-3] Li7BS 6-a X a

[0050] In the above chemical formula 2-3, B is P, As or Sb, X is Se or Te, and 0≦a≦2.

[0051] The surface portion includes fluorine-doped sulfide-based solid electrolyte particles, and includes a concentration gradient region in which the concentration of F atoms decreases from the surface of the surface portion toward the core portion.

[0052] Specifically, the surface portion is formed by heat-treating sulfide-based solid electrolyte particles together with ammonium fluoride in a nitrogen atmosphere to fluorinate the sulfide-based solid electrolyte up to a predetermined region on the surface of the particle, whereby sulfur (S) is substituted with fluorine (F) on the core portion including the sulfide-based solid electrolyte particles, and the amount of substituted fluorine decreases from the surface toward the inside of the core portion, making it possible to include fluorine-doped sulfide-based solid electrolyte particles and have a concentration gradient region of F atoms.

[0053] The fluorine-doped sulfide-based solid electrolyte particles at the surface are obtained by doping the sulfide-based solid electrolyte particles with fluorine, and may be obtained by substituting a portion of sulfur in the sulfide-based solid electrolyte particles with fluorine. Specifically, the sulfide-based solid electrolyte particles may be represented by the following Chemical Formula 1:

[0054] [Chemical formula 1] Li (12-x-b) BS (6-x-a-b) X a F b Y x

[0055] In the above Chemical Formula 1, B is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb or Ta; X is Se or Te; Y is Cl, Br, I, CN, OCN, SCN or N3; x is 0≦x≦2, a is 0≦a≦2, and b is 0.1 <b≦1.0である。

[0056] More specifically, the fluorine-doped sulfide-based solid electrolyte particles may be represented by the following Formula 1-1.

[0057] [Chemical formula 1-1] Li6PS5Cl (1-b) F b

[0058] In the above chemical formula 1-1, b is 0.1 <b≦1.0である。

[0059] Furthermore, the concentration gradient region of the surface portion may include a region extending from the surface of the surface portion toward the core portion at a distance of 30 nm or more but less than 1,200 nm, specifically, a region extending from 30 nm to 1,000 nm, 100 nm to 1,000 nm, or 200 nm to 800 nm. When the concentration gradient region is within this range, reaction with moisture can be effectively blocked when exposed to the atmosphere, thereby achieving excellent moisture stability and ionic conductivity. To achieve a balanced effect between effective blocking of reaction with moisture and excellent ionic conductivity, it is more preferable that the concentration gradient region does not deviate from this range.

[0060] In addition, the solid electrolyte according to one embodiment of the present invention may have an average particle size of 2 μm to 10 μm, or 2 μm to 5 μm. If the average particle size is less than 2 μm, an excessive amount of electrolyte interface may be formed, resulting in increased resistance. If the average particle size is more than 10 μm, an excessive amount of pores may be formed, resulting in increased resistance.

[0061] Method for producing solid electrolyte The present invention provides a method for producing the solid electrolyte.

[0062] A method for producing a solid electrolyte according to one embodiment of the present invention includes a step of heat-treating sulfide-based solid electrolyte particles in a nitrogen atmosphere in the presence of ammonium fluoride, and is characterized in that the ammonium fluoride is used in an amount of 1 part by weight to 10 parts by weight per 100 parts by weight of the sulfide-based solid electrolyte.

[0063] The heat treatment step is a step of forming a surface portion on the surface of the sulfide-based solid electrolyte particles, and can be performed by preparing sulfide-based solid electrolyte particles and heat treating them in a nitrogen atmosphere in the presence of ammonium fluoride.

[0064] Here, the ammonium fluoride can be used in an amount of 1 to 10 parts by weight, specifically 1 to 5 parts by weight or 1 to 3 parts by weight, relative to 100 parts by weight of the sulfide-based solid electrolyte particles. In this case, a surface portion having the above-mentioned concentration gradient region can be formed.

[0065] The heat treatment can be carried out by sequentially carrying out a first heat treatment step and a second heat treatment step, with the first heat treatment step being carried out at a temperature of 200°C to 300°C for 1 to 5 hours, and the second heat treatment step being carried out at a temperature of 400°C to 600°C for 5 to 10 hours.

[0066] Meanwhile, in one embodiment of the present invention, the sulfide-based solid electrolyte may be prepared by a method commonly known in the art or may be purchased. When prepared, for example, the sulfide-based solid electrolyte may be prepared by dissolving lithium sulfide, other sulfide-based raw materials, and a halogen compound in a solvent to obtain a precursor solution, followed by drying and heat treatment, or by milling and mixing the lithium sulfide, other sulfide-based raw materials, and a halogen compound in a powder state, followed by heat treatment.

[0067] Here, the lithium sulfide may be lithium sulfide (LiS), and the sulfide-based raw material may be P2S3, P2S5, P4S3, P4S5, P4S 10The sulfide-based raw material may be phosphorus sulfide such as As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, Ta, Se, and / or Te.

[0068] The halogen compound can also be lithium bromide, lithium chloride, lithium iodide, and combinations thereof.

[0069] all solid state battery The present invention provides an all-solid-state battery containing the solid electrolyte.

[0070] Specifically, the all-solid-state battery includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a solid electrolyte layer containing the solid electrolyte according to the present invention disposed between the positive electrode and the negative electrode.

[0071] The all-solid-state battery according to the present invention has little decrease in ionic conductivity due to moisture, and can have excellent initial efficiency, life characteristics, and output characteristics.

[0072] The all-solid-state battery of the present invention can be manufactured by a conventional method known in the art, for example, by stacking a positive electrode and a negative electrode so that a solid electrolyte layer is present between them and applying pressure.

[0073] positive electrode The positive electrode may be prepared by coating a positive electrode current collector with a positive electrode slurry containing a positive electrode active material, a binder, a conductive material, and a solvent.

[0074] The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used. Also, fine irregularities can be formed on the surface to strengthen the binding force of the positive electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabric bodies, etc.

[0075] The positive electrode active material can include a compound capable of reversible intercalation and deintercalation of lithium, specifically, a lithium metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium. More specifically, the lithium metal oxide includes lithium-manganese-based oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (e.g., LiCoO2, etc.), lithium-nickel-based oxides (e.g., LiNiO2, etc.), lithium-nickel-manganese-based oxides (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2)O4 (where 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 M S2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are the atomic fractions of independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), etc.), and any one or two or more of these compounds can be included.

[0076] Among them, in terms of being able to enhance the capacity characteristics and stability of the battery, the 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 Mn 0.2 Co 0.2 )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.), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.), and considering the significance of the improvement effect by controlling the types and content ratios of the constituent elements forming the lithium composite metal oxide, the lithium composite metal oxide is Li(Ni 0.6 Mn[[ID=BO]] 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15Co 0.15 )O2, and Li(Ni 0.8 Mn 0.1 Co 0.1 ) O2, etc., and any one or a mixture of two or more of these can be used.

[0077] The positive electrode active material may be contained in an amount of 60% by weight to 99% by weight, preferably 70% by weight to 99% by weight, and more preferably 80% by weight to 98% by weight, based on the total weight of solids other than the solvent in the positive electrode slurry.

[0078] The binder is a component that helps bind the conductive material, active material, and current collector together. 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.

[0079] Typically, the binder can be contained 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 other than the solvent in the positive electrode slurry.

[0080] The conductive material is a component for further improving the conductivity of the positive electrode active material.

[0081] The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity, and examples thereof include 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 fiber and metal fiber; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0082] Typically, the conductive material can be contained 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 other than the solvent in the positive electrode slurry.

[0083] The solvent may include an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a desired viscosity when the positive electrode active material and, optionally, a binder and a conductive material are included. For example, the solvent may be included so that the concentration of the solids 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 %.

[0084] negative electrode The negative electrode can be prepared by, for example, coating a negative electrode current collector with a negative electrode slurry containing a negative electrode active material, a binder, a conductive material, and a solvent, or a graphite electrode made of carbon (C) or a metal itself can be used as the negative electrode.

[0085] For example, when the negative electrode is manufactured by coating the negative electrode slurry onto the negative electrode current collector, the negative electrode current collector typically has a thickness of 3 to 500 μm. Such a negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. Examples of such a negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys. Furthermore, similar to the positive electrode current collector, the surface can be formed with fine irregularities to strengthen the binding strength of the negative electrode active material, and the negative electrode current collector can be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0086] The negative electrode active material may be natural graphite, artificial graphite, carbonaceous material, lithium-containing titanium composite oxide (LTO), Si, SiO x , Sn, Li, Zn, Mg, Cd, Ce, Ni or Fe (Me); alloys composed of the above metals (Me); oxides of the above metals (Me) (MeO x and composites of the metals (Me) with carbon. Specific examples of the negative electrode active material include silicon (Si), silicon oxide (SiO x Silicon-based negative electrode active materials, such as silicon dioxide, silicon nitride, silicon alloys, etc., can be used. In this case, a thin and stable SEI layer containing siloxane bonds is formed, which can further improve the high-temperature stability and life characteristics of the battery.

[0087] The negative electrode active material may be contained in an amount of 60% by weight to 99% by weight, preferably 70% by weight to 99% by weight, and more preferably 80% by weight to 98% by weight, based on the total weight of solids other than the solvent in the negative electrode slurry.

[0088] The binder is a component that helps bind the conductive material, active material, and current collector together. 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.

[0089] Typically, the binder can be contained 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 other than the solvent in the negative electrode slurry.

[0090] The conductive material is a component for further improving the conductivity of the negative electrode active material. Such a conductive material is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity, and examples thereof include graphite such as natural graphite and 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 and metal fiber; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0091] The conductive material may be contained 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 other than the solvent in the negative electrode slurry.

[0092] The solvent may include a non-polar solvent such as toluene or xylene, and may be used in an amount that provides a suitable viscosity when the negative electrode active material, and optionally a binder and a conductive material, are included. For example, the solvent may be included so that the concentration of the solids, 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 %.

[0093] When a metal is used as the anode, the anode can be fabricated by physically bonding, rolling, or depositing a metal thin film or a metal on the anode current collector. The deposition method can be electrochemical deposition or chemical vapor deposition.

[0094] For example, the metal thin film itself or the metal bonded / rolled / deposited on the negative electrode current collector may include one metal or an alloy of two metals selected from the group consisting of lithium (Li), nickel (Ni), tin (Sn), copper (Cu), and indium (In).

[0095] solid electrolyte layer The solid electrolyte layer may further contain a binder in addition to the solid electrolyte according to the present invention.

[0096] The binder is a component that helps bind the conductive material, active material, and current collector together. 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.

[0097] Generally, the binder can be contained in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, and more preferably 1 to 10% by weight, based on the total weight of the solid electrolyte layer.

[0098] The present invention provides a battery module including the all-solid-state battery as a unit cell, and a battery pack including the same. The battery module and battery pack include the secondary battery having high capacity, excellent rate-limiting characteristics, and excellent cycle characteristics, and can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0099] In the following, preferred embodiments will be presented to facilitate understanding of the present invention. However, the above embodiments are merely illustrative of the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the scope and technical ideas of the present description. It goes without saying that such changes and modifications fall within the scope of the appended claims.

[0100] Example 1 Li2S, P2S5, and LiCl were mixed in a ball mill in a molar ratio of 5:1:2 and heat-treated at 550°C for 10 hours to prepare a sulfide-based solid electrolyte (Li6PS5Cl) with an average particle size of 3 μm.

[0101] In a nitrogen gas atmosphere and in the presence of 10 mg of NHF, 1 g of the Li6PS5Cl was heat-treated at 250°C for 3 hours and then at 550°C for 10 hours to produce a solid electrolyte comprising a sulfide-based solid electrolyte core and a surface region having a fluorine concentration gradient.

[0102] Example 2 A solid electrolyte including a sulfide-based solid electrolyte core and a surface portion having a fluorine concentration gradient was produced in the same manner as in Example 1, except that 1 g of Li6PS5Cl was heat-treated in the presence of 20 mg of NH4F.

[0103] Example 3 A solid electrolyte including a sulfide-based solid electrolyte core and a surface portion having a fluorine concentration gradient was produced in the same manner as in Example 1, except that 1 g of Li6PS5Cl was heat-treated in the presence of 30 mg of NH4F.

[0104] Comparative Example 1 Li2S, P2S5, and LiCl were mixed in a ball mill in a molar ratio of 5:1:2 and heat-treated at 550°C for 10 hours to prepare a sulfide-based solid electrolyte, Li6PS5Cl.

[0105] Comparative Example 2 Li2S, P2S5, and LiCl were mixed in a ball mill in a molar ratio of 5:1:2 and heat-treated at 550°C for 10 hours to prepare a sulfide-based solid electrolyte (Li6PS5Cl) with an average particle size of 3 μm.

[0106] Nitrogen gas and oxygen gas were flowed at a volume ratio of 9:1, and 1 g of the Li6PS5Cl was heat-treated at 250°C for 3 hours to prepare a solid electrolyte having an oxide coating layer formed thereon.

[0107] Comparative Example 3 A solid electrolyte in which fluorine was present throughout the particles was produced in the same manner as in Example 1, except that 1 g of Li6PS5Cl was heat-treated in the presence of 1 g of NH4F.

[0108] Experimental Example 1 The surface components of the solid electrolyte prepared in Example 1 were analyzed by SEM and SEM-EDS mapping analysis and TOF-SIMS analysis, and the results are shown in FIGS.

[0109] In addition, the concentration gradient of elemental fluorine in the surface region of the solid electrolyte prepared in Example 1 was analyzed, and the results are shown in Figure 3. Meanwhile, the analysis results of the concentration gradient of elemental fluorine in the surface region were shown as relative intensities with Comparative Example 1 as a control group.

[0110] The composition and concentration distribution were analyzed by TOF-SIMS and SEM.

[0111] The TOF-SIMS (Time of Flight-Secondary Ion Mass Spectroscopy) analysis was carried out using a TOF-SIMS 5 (ION-TOF GmbH, Munster, Germany) under the following conditions.

[0112] Primary Ion Beam:Bi1 Primary Beam Voltage: 30 KeV Primary Beam Current: 1.0 pA Analysis Region: 150μm×150μm(surface×depth) Polarity:Negative mode Sputter Beam:Cs + Sputter Beam Voltage / Current:2 KeV / 134 nA Sputter Area: 500 μm x 500 μm

[0113] The SEM and SEM-EDS analyses were carried out using a JEOL-7800F instrument with an accelerating voltage set at 15 kV, and sampling was carried out in a glove box filled with argon gas.

[0114] With reference to FIGS. 1 and 2, it can be seen that F is present on the surface of the solid electrolyte of Example 1, and with reference to FIG. 3, it can be seen that the solid electrolyte of Example 1 has a concentration gradient region in which F decreases from the surface toward the core.

[0115] Experimental Example 2 The water stability and ionic conductivity of the solid electrolytes of the examples and comparative examples were compared and analyzed, and the results are shown in Table 1 below.

[0116] (1) Moisture stability The moisture stability was confirmed by measuring the amount of hydrogen sulfide generated when the solid electrolyte was exposed to the atmosphere. 100 mg of each solid electrolyte was placed in a sealed container equipped with a thermo-hygrometer and a hydrogen sulfide gas concentration measuring device, and after 30 minutes of exposure to the atmosphere at room temperature (23±5°C) and 40% RH, the amount of hydrogen sulfide generated (cm 3 / g, the amount of hydrogen sulfide generated per 1 g of electrolyte) was measured.

[0117] (2) Ionic conductivity To confirm the lithium ion conductivity of each solid electrolyte, AC impedance analysis was carried out at room temperature.

[0118] 0.15 g of each solid electrolyte was placed in a lithium ion conductivity test fixture and subjected to a pressure of several hundred MPa to produce pellets. The lithium ion conductivity test fixture containing the pellet-shaped solid electrolyte was placed in a thermo-hygrostat and left at room temperature for 40 minutes. An AC potential of 100 mV was then applied, and a frequency sweep from 1000 Hz to 1 MHz was performed to measure the impedance.

[0119] [Table 1]

[0120] As shown in Table 1, the solid electrolytes of Examples 1 to 3 were confirmed to have a lower ionic conductivity reduction rate of less than 5% and a significant reduction in the amount of hydrogen sulfide generated of 50% to 83% compared to Comparative Example 1. On the other hand, the solid electrolyte of Comparative Example 2 having an oxide coating layer showed a significantly lower reduction in the amount of hydrogen sulfide generated compared to Examples 1 to 3, and a significant reduction rate of ionic conductivity of more than two times.

[0121] In addition, in the case of the solid electrolyte of Comparative Example 3 in which fluorine is present up to the core portion, the amount of hydrogen sulfide generated is reduced compared to the Examples, but the rate of decrease in ionic conductivity is about 4 to 9 times greater than that of the Examples, failing to demonstrate excellent balance between moisture stability and ionic conductivity.

[0122] From the above results, it was confirmed that the solid electrolyte according to the present invention includes a surface portion including hydrophobic fluorine-doped sulfide-based solid electrolyte particles on the surface of a sulfide-based solid electrolyte particle, and includes a concentration gradient region in which the concentration of F atoms decreases from the surface toward the center of the solid electrolyte particle. This provides excellent ion conductivity comparable to that of a sulfide-based solid electrolyte without any surface treatment, and also significantly suppresses the generation of hydrogen sulfide when exposed to moisture, thereby providing excellent moisture stability.

Claims

1. a core portion including sulfide-based solid electrolyte particles; a surface portion formed on the core portion and including fluorine-doped sulfide-based solid electrolyte particles; The surface portion includes a concentration gradient region in which the concentration of F atoms decreases from the surface of the surface portion toward the core portion.

2. The solid electrolyte of claim 1 , wherein the fluorine-doped sulfide-based solid electrolyte particles are represented by the following chemical formula 1: [Chemical formula 1] Li （１２－ｘ－ｂ） BS （６－ｘ－ａ－ｂ） X ａ F ｂ Y ｘ In the above Chemical Formula 1, B is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb or Ta; X is Se or Te; Y is Cl, Br, I, CN, OCN, SCN or N ３ and x is 0≦x≦2, a is 0≦a≦2, and b is 0.1<b≦1.

0.

3. The solid electrolyte according to claim 1, wherein the fluorine-doped sulfide-based solid electrolyte particles are represented by the following chemical formula 1-1: [Chemical formula 1-1] Li ６ PS ５ Cl （１－ｂ） F ｂ In the above chemical formula 1-1, b is in the range of 0.1<b≦1.

0.

4. The solid electrolyte according to claim 1 , wherein the sulfide-based solid electrolyte particles are argyrodite-type solid electrolyte particles.

5. The solid electrolyte according to claim 1 , wherein the sulfide-based solid electrolyte particles are represented by the following chemical formula 2: [Chemical formula 2] Li （１２－ｘ） BS （６－ｘ－ａ） X ａ Y ｘ In the above Chemical Formula 2, B is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb or Ta; X is Se or Te; Y is Cl, Br, I, CN, OCN, SCN or N ３ and x is in the range of 0≦x≦2, and a is in the range of 0≦a≦2.

6. 2. The solid electrolyte according to claim 1, wherein the concentration gradient region includes a region extending from a surface of the solid electrolyte toward a center thereof at a distance of 30 nm or more and less than 1,200 nm.

7. 2. The solid electrolyte according to claim 1, wherein the average particle size is 2 μm to 10 μm.

8. heat-treating sulfide-based solid electrolyte particles in the presence of ammonium fluoride under an inert gas atmosphere; The method for producing a solid electrolyte, wherein the ammonium fluoride is used in an amount of 1 to 10 parts by weight per 100 parts by weight of the sulfide-based solid electrolyte particles.

9. 9. The method for producing a solid electrolyte according to claim 8, wherein the sulfide-based solid electrolyte particles are argyrodite-type solid electrolyte particles.

10. The heat treatment is carried out by sequentially carrying out a first heat treatment step and a second heat treatment step, The first heat treatment step is carried out at a temperature of 200°C to 300°C for 1 to 5 hours; 9. The method for producing a solid electrolyte according to claim 8, wherein the second heat treatment step is carried out at a temperature of 400° C. to 600° C. for 5 to 10 hours.

11. A positive electrode and a negative electrode; An all-solid-state battery comprising the solid electrolyte according to claim 1.

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