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

Abstract

The present invention aims to improve the atmospheric stability of conventional sulfide-based solid electrolytes, and relates to a solid electrolyte having a composition represented by Chemical Formula 1 described herein, 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. 10-2023-0012072, filed January 30, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a solid electrolyte having an argyrodite-type crystal structure with improved atmospheric stability, 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 a next-generation battery. 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 are highly reactive to moisture, and react not only with moisture in the atmosphere but also with moisture under low humidity conditions, generating the toxic gas hydrogen sulfide (H2S). This not only adversely affects the safety of workers, but also degrades the performance of the sulfide-based solid electrolyte itself.

[0005] Therefore, there is a need to develop sulfide-based solid electrolytes that are highly stable in the atmosphere. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] KR10-2017-0021751 A Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a solid electrolyte having improved atmospheric stability, specifically improved water stability.

[0008] However, the problems that the present invention aims to solve are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0009] 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.

[0010] (1) The present invention provides a solid electrolyte having a composition represented by the following chemical formula 1: [Chemical formula 1] Li 11-(5a+3b+c+2x) P a Ga b S 5-(c+x) X 1+c In the above Chemical Formula 1, X is one or more selected from F, Cl, Br, and I; 5.0<5a+3b+c+2x<6.0, 0 <b≦0.5、0≦c<0.7、0<c+x<1、1≦a+b≦1.5である。

[0011] (2) The present invention provides the solid electrolyte according to (1) above, wherein b satisfies the condition 0.01≦b≦0.3.

[0012] (3) The present invention provides a solid electrolyte according to (1) or (2), wherein 5a+3b+c+2x satisfies 5.0<5a+3b+c+2x≦5.7.

[0013] (4) The present invention provides, in any one of the above (1) to (3), a solid electrolyte having an argyrodite-type crystal structure.

[0014] (5) The present invention provides a solid electrolyte according to any one of the above (1) to (4), wherein the solid electrolyte has an ion conductivity retention rate of 60% or more according to the following formula 1:

number

[0015] (6) The present invention provides the solid electrolyte according to (5) above, wherein the initial ionic conductivity is 2.0 mS / cm or more and 20.0 mS / cm or less.

[0016] (7) The present invention provides a solid electrolyte according to (5) or (6) above, wherein the ionic conductivity after the exposure to water is 1.2 mS / cm or more and 12.0 mS / cm or less.

[0017] (8) The present invention provides the solid electrolyte according to any one of the above (1) to (7), wherein the total content of impurities in the solid electrolyte is 2% by weight or less.

[0018] (9) The present invention provides a method for producing a solid electrolyte, comprising the steps of: (S1) dry-mixing a sulfide-based solid electrolyte precursor material and a doping element to produce a precursor mixture; and (S2) heat-treating the precursor mixture, wherein the sulfide-based solid electrolyte precursor material comprises LiS, P2S5, and LiX, where X is F, Cl, Br, or I, the LiS is contained in an amount of more than 0.97 mol and less than 2.5 mol per mol of LiX, and the doping element is Ga.

[0019] (10) The present invention provides the method for producing a solid electrolyte according to (9), wherein the step (S1) is carried out by ball milling the sulfide-based solid electrolyte raw material and the doping element.

[0020] (11) The present invention provides the method for producing a solid electrolyte according to (9) or (10), wherein the heat treatment in the step (S2) is carried out at a temperature of 300°C or higher and 600°C or lower.

[0021] (12) The present invention provides an all-solid-state battery including the solid electrolyte according to any one of (1) to (8) above. [Effects of the Invention]

[0022] The solid electrolyte according to the present invention is doped with Ga, and by adjusting the composition ratio of lithium ions to an appropriate level or less, it is possible to suppress the generation of impurities and improve ionic conductivity and water stability.

[0023] Furthermore, the solid electrolyte according to the present invention has a low content of unreacted or side-reacted impurities and a uniform composition, and therefore has the effect of being excellent in ionic conductivity and atmospheric stability. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 shows XRD data for evaluating impurity detection in Example 1 and Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention will now be described in more detail to facilitate understanding of the present invention.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] The term "all solid state battery" used in this specification means a battery in which all components of the battery are solid, and is distinguished from liquid electrolyte secondary batteries that use a liquid electrolyte such as an electrolytic solution, and gel polymer secondary batteries that use a polymer electrolyte instead of a separator and also use a liquid electrolyte.

[0030] solid electrolyte The solid electrolyte according to the present invention has a composition represented by the following Chemical Formula 1. In this case, the solid electrolyte may have high ionic conductivity and low reactivity with a lithium anode, and decomposition and degradation of the solid electrolyte particles when exposed to moisture or oxygen may be suppressed.

[0031] [Chemical formula 1] Li 11-(5a+3b+c+2x) P a Ga b S 5-(c+x) X 1+c

[0032] In the above Chemical Formula 1, X is one or more selected from F, Cl, Br, and I; 5<5a+3b+c+2x<6, 0 <b≦0.5、0≦c<0.7、0<c+x<1、1≦a+b≦1.5である。

[0033] On the other hand, in the industry, in the case of Li6PS5Cl, Li6PS5Br, etc. which are used as solid electrolytes having an argyrodite-type crystal structure, S 2- ions have a problem of being easily decomposed by reacting with moisture in the air. However, the solid electrolyte having an argyrodite-type crystal structure according to the present invention can improve the air stability by doping with gallium (Ga) cations having excellent binding force with sulfur (S) ions, adjust the composition ratio of lithium (Li) ions to a predetermined level or less to suppress the generation of impurities, and can have an effect of excellent ionic conductivity and air stability.

[0034] According to one embodiment of the present invention, b can be 0 < b ≤ 0.5, and 5a + 3b + c + 2x can be 5.0 < 5a + 3b + c + 2x < 6.0. Specifically, b can be 0.01 or more, 0.05 or more, 0.07 or more, 0.09 or more, 0.5 or less, 0.48 or less, 0.44 or less, 0.4 or less, 0.36 or less, 0.34 or less, 0.3 or less, 0.26 or less, 0.22 or less, 0.20 or less, 0.16 or less, 0.14 or less, 0.12 or less, 0.10 or less. Also, 5a + 3b + c + 2x can be more than 5.1, more than 5.2, more than 5.3, more than 5.4, more than 5.5, less than 6.0, less than 5.9, less than 5.8, less than 5.7, less than 5.6. When the numerical range is satisfied, the doping amount of Ga cations is appropriate, and when exposed to moisture or oxygen, it is possible to suppress the decomposition or deterioration of the solid electrolyte particles. However, when synthesizing the solid electrolyte doped with Ga cations, impurities such as Li2S or LiBr may be generated, and the ionic conductivity may decrease. In this case, by reducing the composition ratio of the lithium element, it is possible to exist as an argyrodite phase having no or low impurity content, and thereby the ionic conductivity can be improved.

[0035] Furthermore, the a may be 0.5 or more and less than 1.5, and the x may be more than 0 and less than 1. Specifically, the a may be 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, 0.9 or more, 0.95 or more, and less than 1.5, less than 1.4, less than 1.3, less than 1.2, less than 1.1, or less than 1.0, and the x may be more than 0, more than 0.1, more than 0.2, more than 0.3, more than 0.4, more than 0.5, less than 1.0, less than 0.9, less than 0.8, less than 0.7, or less than 0.6. When the above numerical ranges are satisfied, the sulfide solid electrolyte can improve lithium ion conductivity.

[0036] According to one embodiment of the present invention, the sulfide-based solid electrolyte of the present invention may have an argyrodite-type crystal structure, which provides high ionic conductivity and low reactivity with a lithium anode. The sulfide-based solid electrolyte having an argyrodite-type crystal structure means that the sulfide-based solid electrolyte has at least a crystalline phase with an argyrodite-type structure as a primary phase. Here, the primary phase refers to the phase that accounts for the largest proportion of all crystalline phases constituting the sulfide solid electrolyte. Therefore, the content of the crystalline phase with an argyrodite-type structure in the sulfide solid electrolyte may be preferably 80% by mass or more, more preferably 85% by mass or more, 90% by mass or more, or even 95% by mass or more, of the total crystalline phases constituting the sulfide solid electrolyte.

[0037] According to one embodiment of the present invention, the solid electrolyte may have an ionic conductivity retention rate according to the following formula 1 of 60% or more, specifically 65% ​​or more, 70% or more, 75% or more, 80% or more, 85% or more, or 90% or more.

[0038]

number

[0039] In the formula 1, The initial ionic conductivity is a value measured immediately after the preparation of the solid electrolyte at 22°C and a relative humidity of 0.7%. The ionic conductivity after exposure to moisture was measured at 22°C immediately after the solid electrolyte was exposed to the atmosphere at a relative humidity of 1.91% for 5 hours.

[0040] According to one embodiment of the present invention, the solid electrolyte may have an initial ionic conductivity of 2.0 mS / cm or more and 20.0 mS / cm or less. Specifically, it may be 3.0 mS / cm or more, 4.0 mS / cm or more, 5.0 mS / cm or more, 6.0 mS / cm or more, 20.0 mS / cm or less, 19.0 mS / cm or less, or 18.0 mS / cm or less. Although a higher ionic conductivity of the electrolyte is preferable, when the initial ionic conductivity satisfies the above range, excellent improvements in process stability and moisture stability can be achieved.

[0041] According to the present invention, the solid electrolyte may have an ionic conductivity of 1.2 mS / cm or more and 12.0 mS / cm or less after the water exposure. Specifically, it may be 1.4 mS / cm or more, 1.5 mS / cm or more, 1.6 mS / cm or more, 1.7 mS / cm or more, 12.0 mS / cm or less, or 11.0 mS / cm or less. In this case, as with the initial ionic conductivity, the higher the ionic conductivity of the electrolyte after water exposure, the more preferable. However, if the ionic conductivity after water exposure satisfies the above range and the numerical range of the ionic conductivity maintenance rate according to Equation 1, there are advantages in that the rate of ionic conductivity deterioration is reduced and the electrolyte structure is maintained despite water exposure during the battery manufacturing process.

[0042] According to one embodiment of the present invention, the solid electrolyte may have a total impurity content of 2 wt % or less. The impurities may include unreacted materials or by-products generated by side reactions during the preparation of the solid electrolyte. Specifically, the impurities may be LiS or LiA. Here, A among the impurities may be one or more elements selected from the group consisting of F, Cl, Br, and I. The impurity content may be obtained by analyzing XRD data of the solid electrolyte powder using a Rietveld refinement program.

[0043] The total content of the impurities may be 2 wt% or less. The content of the impurities is based on 100 wt% of the solid electrolyte. For example, the content of the impurities may be 2.0 wt% or less, 1.9 wt% or less, 1.8 wt% or less, 1.7 wt% or less, 1.6 wt% or less, 1.5 wt% or less, 1.4 wt% or less, 1.3 wt% or less, 1.2 wt% or less, 1.1 wt% or less, 1.0 wt% or less, 0.9 wt% or less, 0.8 wt% or less, 0.7 wt% or less, 0.6 wt% or less, 0.5 wt% or less, 0.4 wt% or less, 0.3 wt% or less, 0.2 wt% or less, or 0.1 wt% or less. When the content of the impurities satisfies the above range, it can be confirmed that the precursor is finely divided and uniformly mixed, and a solid electrolyte having a desired uniform composition can be obtained. In addition, the solid electrolyte prepared by the uniform mixing may have high ionic conductivity and low electronic conductivity, and may have an excellent level of ionic conductivity retention rate by suppressing decomposition or degradation of the solid electrolyte particles when exposed to moisture or oxygen. As a result, when the solid electrolyte is applied to an all-solid-state battery, it may have excellent performance characteristics.

[0044] Method for producing solid electrolyte The method for producing a solid electrolyte of the present invention includes the steps of: (S1) dry-mixing a sulfide-based solid electrolyte precursor material and a doping element to produce a precursor mixture; and (S2) heat-treating the precursor mixture. The sulfide-based solid electrolyte precursor material may include Li2S, P2S5, and LiX, where X may be F, Cl, Br, or I. The Li2S may be present in an amount of more than 0.97 mol and less than 2.5 mol per mol of LiX, and the doping element may be Ga.

[0045] The solid electrolyte produced by the method for producing a solid electrolyte of the present invention can have the technical features of the solid electrolyte described above, and the same content as that described for the solid electrolyte will be omitted.

[0046] According to an embodiment of the present invention, the LiS may be contained in an amount of more than 0.97 mol and less than 2.5 mol relative to 1 mol of LiX, specifically, more than 0.97 mol, less than 2.5 mol, less than 2.4 mol, or less than 2.3 mol. When a solid electrolyte is prepared within this range, the lithium composition ratio can be controlled, impurity generation can be suppressed, and ionic conductivity can be improved.

[0047] According to an embodiment of the present invention, step (S1) may be performed by ball milling the sulfide-based solid electrolyte raw material and the doping element. Specifically, step (S1) may be performed by ball milling the sulfide-based solid electrolyte raw material and the doping element using a planetary mill including zirconia (Zr) balls.

[0048] According to one embodiment of the present invention, step (S1) may be performed by adding sulfur (LiS) precursor, phosphorus (P2S5) precursor, and LiX precursor as the sulfide-based solid electrolyte precursor materials to a zirconia container, adding ZrO2 balls, and stirring and ball milling the mixture. The precursor mixture prepared in step (S1) may be in powder form.

[0049] When a solid electrolyte is prepared by wet mixing such as forming a slurry or a solution, the solvent may remain partially in the precursor mixture or the solid electrolyte in a carbonized state even after drying or heat treatment, resulting in an increase in electronic conductivity. Therefore, the method for preparing a solid electrolyte according to the present invention dry-mixes the precursor of a sulfide-based solid electrolyte in powder form, thereby inducing uniform mixing and maximizing the ionic conductivity of the prepared solid electrolyte.

[0050] Meanwhile, during the ball milling process using the planetary mill, the faster the stirring speed, the faster the solid electrolyte precursor mixture is produced and the smaller the particle size, and the longer the stirring time, the higher the conversion rate to a uniformly mixed solid electrolyte precursor mixture. The stirring time may be 3 hours or more, 6 hours or more, 8 hours or more, 10 hours or more, 12 hours or more, 14 hours or more, or 24 hours or more, and the stirring speed may be 300 rpm or more, 400 rpm or more, 500 rpm or more, 600 rpm or more, 700 rpm or more, or 800 rpm or more.

[0051] According to one embodiment of the present invention, the heat treatment in step (S2) may be performed at a temperature of 300°C to 600°C. More specifically, the heat treatment temperature may be 300°C or higher, 350°C or higher, 400°C or higher, 450°C or higher, 500°C or higher, 600°C or lower, or 550°C or lower. When the heat treatment temperature is within this range, an argyrodite phase can be formed from the precursor mixture. In particular, when high-energy milling at 600 rpm or higher is performed in step (S1), the powdered precursor mixture amorphized by the heat treatment process can be crystallized into an argyrodite solid electrolyte. Furthermore, when the heat treatment temperature range is satisfied, the problem of unreacted precursor residue and the problem of increased electronic conductivity due to sulfur loss can be alleviated.

[0052] all solid state battery The present invention provides an all-solid-state battery containing the solid electrolyte.

[0053] 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.

[0054] 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.

[0055] Here, the all-solid-state battery of the present invention can be manufactured by a conventional method well-known in the art. For example, it can be manufactured by laminating so that a solid electrolyte layer exists between the positive electrode and the negative electrode and applying pressure.

[0056] (1) Positive electrode The positive electrode can be manufactured by coating a positive electrode slurry containing a positive electrode active material, a binder, a conductive material, a solvent, etc. on a positive electrode current collector.

[0057] 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, meshes, porous bodies, foams, non-woven fabric bodies, etc.

[0058] The positive electrode active material can include a lithium metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium as a compound capable of reversible intercalation and deintercalation of lithium. More specifically, the lithium metal oxide is a lithium-manganese-based oxide (for example, LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (for example, LiCoO2, etc.), a lithium-nickel-based oxide (for example, LiNiO2, etc.), a lithium-nickel-manganese-based oxide (for example, LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < Z < 2), etc.), a lithium-nickel-cobalt-based oxide (for example, LiNi 1-Y1 ​​​​​Y2 O2 (where 0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt oxide (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 the respective 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.

[0059] 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 Co0.15 Al 0.05 )O2, etc.), and in consideration of the remarkable improvement effect by controlling the types and content ratios of constituent elements forming the lithium composite metal oxide, the lithium composite metal oxide may be 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., and any one or a mixture of two or more of these can be used.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] The conductive material is a component for further improving the conductivity of the positive electrode active material.

[0064] The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. 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 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 may be used.

[0065] 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.

[0066] 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 %.

[0067] (2) 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.

[0068] 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 enhance 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.

[0069] 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 carbide ...

[0070] 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.

[0071] 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.

[0072] 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.

[0073] The conductive material is a component for further improving the conductivity of the negative electrode active material. The 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.

[0074] 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.

[0075] 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 desired 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 %.

[0076] When a metal is used as the anode, the anode can be fabricated by physically bonding, rolling, or depositing a metal thin film on the anode current collector or the metal thin film itself. The deposition method can be electrolytic deposition or chemical vapor deposition.

[0077] 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).

[0078] (3) Solid electrolyte layer The solid electrolyte layer may further contain a binder in addition to the solid electrolyte according to the present invention.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] Examples and Comparative Examples Example 1 Four precursors, Li2S, P2S5, LiBr, and Ga2S3, were dry mixed (ball milled) in a molar ratio of 2.25:0.45:1:0.05. During the dry mixing, a planetary ball mill equipped with zirconia balls was used, and the rotation speed was 300 rpm to 700 rpm to ensure uniform mixing. The obtained mixed precursor was then heat-treated at 450°C to 550°C for 12 hours to crystallize it, and then pulverized again by ball milling to obtain Li2S with an argyrodite-type crystal structure. 5.5 P 0.9 Ga 0.1 S 4.65 Br 1.0 A solid electrolyte having the composition represented by the formula: was prepared. All of the above steps were carried out under an inert Ar atmosphere.

[0084] The Li having the argyrodite-type crystal structure 5.5 P 0.9 Ga 0.1 S4.65 Br 1.0 was used as the solid electrolyte in Example 1.

[0085] Example 2 Four precursors, Li2S, P2S5, LiBr, and Ga2S3, were dry mixed (ball milled) in a molar ratio of 2.25:0.475:1:0.025. During the dry mixing, a planetary ball mill equipped with zirconia balls was used, and the rotation speed was 300 rpm to 700 rpm to ensure uniform mixing. The obtained mixed precursor was then heat-treated at 450°C to 550°C for 12 hours to crystallize it, and then pulverized again by ball milling to obtain Li2S with an argyrodite-type crystal structure. 5.5 P 0.95 Ga 0.05 S 4.7 Br 1.0 A solid electrolyte having the composition represented by the formula: was prepared. All of the above steps were carried out under an inert Ar atmosphere.

[0086] The Li having the argyrodite-type crystal structure 5.5 P 0.95 Ga 0.05 S 4.7 Br 1.0 was used as the solid electrolyte in Example 2.

[0087] Comparative Example 1 Three precursors, Li2S, P2S5, and LiBr, were dry mixed (ball milled) in a molar ratio of 2.5:0.5:1. During the dry mixing, a planetary ball mill equipped with zirconia balls was used, rotating at a speed of 300 rpm to 700 rpm for uniform mixing. The resulting mixed precursor was then heat-treated at 450°C to 550°C for 12 hours to crystallize it, and then pulverized again by ball milling to obtain Li6PS5Br with an argyrodite-type crystal structure. 1.0 All of the above steps were carried out under an inert Ar atmosphere.

[0088] Li6PS5Br having the argyrodite-type crystal structure 1.0 was used as the solid electrolyte of Comparative Example 1.

[0089] Comparative Example 2 Four precursors, Li2S, P2S5, LiBr, and Ga2S3, were dry mixed (ball milled) in a molar ratio of 2.6:0.45:1:0.05. During the dry mixing, a planetary ball mill equipped with zirconia balls was used, and the rotation speed was 300 rpm to 700 rpm to ensure uniform mixing. The mixed precursor was then heat-treated at 450°C to 550°C for 12 hours to crystallize it, and then pulverized again by ball milling to obtain Li2S with an argyrodite-type crystal structure. 6.2 P 0.9 Ga 0.1 S5Br 1.0 All of the above steps were carried out under an inert Ar atmosphere.

[0090] The Li having the argyrodite-type crystal structure 6.2 P 0.9 Ga 0.1 S5Br 1.0 was used as the solid electrolyte of Comparative Example 2.

[0091] Comparative Example 3 Four precursors, Li2S, P2S5, LiCl, and LiBr, were dry mixed (ball milled) in a molar ratio of 1.9:0.5:1.2:0.4. During the dry mixing, a planetary ball mill equipped with zirconia balls was used, and the rotation speed was 300 rpm to 700 rpm to ensure uniform mixing. The obtained mixed precursor was then heat-treated at 450°C to 550°C for 12 hours to crystallize it, and then pulverized again by ball milling to obtain Li2S, P2S5, LiCl, and LiBr with an argyrodite-type crystal structure. 5.4 PS 4.4 Cl 1.2 Br 0.4 All of the above steps were carried out under an inert Ar atmosphere.

[0092] The Li having the argyrodite-type crystal structure 5.4 PS 4.4 Cl 1.2 Br 0.4 was used as the solid electrolyte of Comparative Example 3.

[0093] Comparative Example 4 Three precursors, Li2S, P2S5, and LiCl, were dry mixed (ball milled) in a molar ratio of 1.9:0.5:1.6. During the dry mixing, a planetary ball mill containing zirconia balls was used, rotating at a speed of 300 rpm to 700 rpm to ensure uniform mixing. The resulting mixed precursor was then heat-treated at 450°C to 550°C for 12 hours to crystallize it, and then pulverized again by ball milling to obtain Li2S with an argyrodite-type crystal structure. 5.4 PS 4.4 Cl 1.6 All of the above steps were carried out under an inert Ar atmosphere.

[0094] The Li having the argyrodite-type crystal structure 5.4 PS 4.4 Cl 1.6 was used as the solid electrolyte of Comparative Example 4.

[0095] Comparative Example 5 Four precursors, Li2S, P2S5, LiCl, and LiBr, were dry mixed (ball milled) in a molar ratio of 1.9:0.5:1.0:0.6. During the dry mixing, a planetary ball mill containing zirconia balls was used, rotating at a speed of 300 rpm to 700 rpm for uniform mixing. The resulting mixed precursor was then heat-treated at 450°C to 550°C for 12 hours to crystallize it, and then pulverized again by ball milling to obtain Li2S, which has an argyrodite-type crystal structure. 5.4 PS 4.4 Cl 1.0 Br 0.6 All of the above steps were carried out under an inert Ar atmosphere.

[0096] The Li having the argyrodite-type crystal structure 5.4 PS 4.4 Cl 1.0 Br 0.6 was used as the solid electrolyte of Comparative Example 5.

[0097] Comparative Example 6 Three precursors, Li2S, P2S5, and LiBr, were dry mixed (ball milled) in a molar ratio of 2.2:0.5:1.0. During the dry mixing, a planetary ball mill containing zirconia balls was used, rotating at a speed of 300 rpm to 700 rpm for uniform mixing. The mixed precursor was then heat-treated at 450°C to 550°C for 12 hours to crystallize it, and then pulverized again by ball milling to obtain Li2S with an argyrodite-type crystal structure. 5.4 PS 4.7 Br 1.0 All of the above steps were carried out under an inert Ar atmosphere.

[0098] The Li having the argyrodite-type crystal structure 5.4 PS 4.7 Br 1.0 was used as the solid electrolyte of Comparative Example 6.

[0099] Comparative Example 7 Three precursors, Li2S, P2S5, and LiBr, were dry mixed (ball milled) in a molar ratio of 2.15:0.5:1.0. During the dry mixing, a planetary ball mill equipped with zirconia balls was used, and the rotation speed was 300 rpm to 700 rpm to ensure uniform mixing. The mixed precursor was then heat-treated at 450°C to 550°C for 12 hours to crystallize it, and then pulverized again by ball milling to obtain Li2S, P2S5, and LiBr with an argyrodite-type crystal structure. 5.3 PS 4.65 Br 1.0 All of the above steps were carried out under an inert Ar atmosphere.

[0100] The Li having the argyrodite-type crystal structure 5.3 PS 4.65 Br 1.0 was used as the solid electrolyte of Comparative Example 7.

[0101] Experimental Example 1: Evaluation of ionic conductivity retention rate -Measurement of initial ionic conductivity Immediately after production, 150 mg of each solid electrolyte powder prepared in Examples 1 and 2 and Comparative Examples 1 to 7 was placed in a 13 mm diameter SUS mold. The mold, along with the insulating PEEK, was attached to a press, and a potentiostat was connected to the SUS mold. After applying a pressure of 370 MPa to sufficiently densify the electrolyte structure, the pressure was gradually reduced to maintain 100 MPa, and AC impedance measurements were performed at frequencies from 1 Hz to 7 MHz. The ionic conductivity was calculated from the measured resistance using a Nyquist plot, and is shown in Table 1 below. All measurements were performed in a dry room at a temperature of 22°C and a relative humidity of 0.7%.

[0102] -Measurement of ionic conductivity after exposure to moisture Immediately after 5 hours of exposure to an atmosphere with a relative humidity of 1.91% for each of the solid electrolyte powders prepared in Examples 1 and 2 and Comparative Examples 1 to 7, 150 mg of each powder was placed in a 13 mm diameter SUS mold. The mold, along with the insulating PEEK, was attached to a press, and a potentiostat was connected to the SUS mold. After applying a pressure of 370 MPa to sufficiently densify the electrolyte structure, the pressure was gradually reduced to maintain 100 MPa, and AC impedance measurements were performed at frequencies from 1 Hz to 7 MHz. The ionic conductivity after moisture exposure was calculated from the measured resistance values ​​using a Nyquist plot, and is shown in Table 1 below. All measurements were performed in a dry room at a temperature of 22°C and a relative humidity of 0.7%.

[0103] The ionic conductivity retention rate was calculated according to the following formula 1 and is shown in Table 1 below.

[0104]

number

[0105] [Table 1]

[0106] In Examples 1 and 2, the lithium mole number (11-(5a+3b+c+2x)) was adjusted to less than 6 by doping with gallium cations. In the case of the solid electrolytes of Examples 1 and 2, it was confirmed that the ionic conductivity retention rate was 60% or more. Therefore, the solid electrolyte of the present invention has an effect of reducing the rate of deterioration of ionic conductivity after exposure to water and maintaining the electrolyte structure despite exposure to water.

[0107] On the other hand, Comparative Examples 1 to 7 were either not doped with gallium cations or had a lithium molar number of 6 or more, and showed lower ionic conductivity retention rates than the solid electrolytes of Examples 1 and 2. In particular, Comparative Example 2 showed a low ionic conductivity retention rate even when doped with gallium cations, because the lithium molar number was 6 or more. Furthermore, Comparative Examples 3 to 7 showed a significant decrease in ionic conductivity after exposure to moisture, resulting in a low ionic conductivity retention rate, which may cause problems with the electrolyte structure and stability of the manufacturing process upon moisture exposure.

[0108] Experimental example 2: Impurity detection evaluation Impurity detection evaluation was performed for Example 1 and Comparative Example 2. Impurity detection in the solid electrolyte powder was calculated using XRD measurement and Rietveld refinement analysis. For the XRD device, a Bruker D8 Endeavor, Cu Kα radiation, 1.5406 Å wavelength was used, and the measurement conditions were non-atmospheric exposure, a scan rate of 2° / min, and a theta angle of 10-90°. Impurities were identified using the TOPAS Rietveld refinement program, and the presence or absence of impurities was evaluated. The XRD data for Example 1 and Comparative Example 2 are shown in Figure 1 and Table 2.

[0109] [Table 2]

[0110] Referring to Table 2 and FIG. 1, it can be seen that in Example 1, where gallium is doped but the number of moles of lithium is less than 6, no impurities were detected, whereas in Comparative Example 2, where the number of moles of lithium is more than 6, impurities such as LiS or LiBr are generated, which may reduce ionic conductivity, and therefore the ionic conductivity retention rate is not good.

Claims

1. A solid electrolyte having a composition represented by the following chemical formula 1: [Chemical formula 1] Li １１－（５ａ＋３ｂ＋ｃ＋２ｘ） P ａ Ga ｂ S ５－（ｃ＋ｘ） X １＋ｃ In the above Chemical Formula 1, X is one or more selected from F, Cl, Br and I; 5.0<5a+3b+c+2x<6.0, 0<b≦0.5, 0≦c<0.7, 0<c+x<1, 1≦a+b≦1.

5.

2. 2. The solid electrolyte according to claim 1, wherein b satisfies the condition 0.01≦b≦0.

3.

3. 2. The solid electrolyte according to claim 1, wherein 5a+3b+c+2x satisfies the formula 5.0<5a+3b+c+2x≦5.

7.

4. The solid electrolyte according to claim 1 , wherein the solid electrolyte has an argyrodite-type crystal structure.

5. 2. The solid electrolyte according to claim 1, wherein the solid electrolyte has an ionic conductivity retention rate of 60% or more according to the following formula 1: [Equation 1] In the formula 1, The initial ionic conductivity is a value measured at 22°C immediately after the production of the solid electrolyte. The ionic conductivity after exposure to moisture is a value measured at 22° C. immediately after the solid electrolyte is exposed to the atmosphere at a relative humidity of 1.91% for 5 hours.

6. 6. The solid electrolyte according to claim 5, wherein the initial ionic conductivity is 2.0 mS / cm or more and 20.0 mS / cm or less.

7. 6. The solid electrolyte according to claim 5, wherein the ionic conductivity after the exposure to water is 1.2 mS / cm or more and 12.0 mS / cm or less.

8. 10. The solid electrolyte of claim 1, wherein the solid electrolyte has a total impurity content of 2 wt% or less.

9. A step (S1) of dry-mixing a sulfide-based solid electrolyte raw material and a doping element to prepare a precursor mixture; and (S2) heat-treating the precursor mixture; The sulfide-based solid electrolyte raw material is Li ２ S, P ２ S ５ and LiX, X is F, Cl, Br or I; The Li ２ S is contained in an amount of more than 0.97 moles and less than 2.5 moles per mole of LiX; The method for producing a solid electrolyte, wherein the doping element is Ga.

10. The method for manufacturing a solid electrolyte according to claim 9 , wherein the step (S1) is performed by ball milling the sulfide-based solid electrolyte raw material and the doping element.

11. The method for producing a solid electrolyte according to claim 9 , wherein the heat treatment in step (S2) is carried out at a temperature of 300° C. or higher and 600° C. or lower.

12. An all-solid-state battery comprising the solid electrolyte according to any one of claims 1 to 8.

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