Method for producing solid electrolyte and solid electrolyte

Abstract

The present invention relates to a method for producing a solid electrolyte, comprising the steps of: mixing a sulfide-based solid electrolyte raw material and a solvent to produce a precursor mixture (S1); and heat-treating the precursor mixture (S2), wherein the solvent has a relative polarity with respect to water of 0.15 or less, and the content of the solvent is more than 2 wt % and 5 wt % or less with respect to the total content of the precursor mixture.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0117224, filed September 16, 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 method for producing a solid electrolyte that prevents adhesion of a sulfide-based solid electrolyte precursor and prevents non-uniform mixing, and to a solid electrolyte. [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 have a problem in that they are highly reactive to moisture and react with moisture in the atmosphere to generate hydrogen sulfide, a toxic gas, which not only poses a risk to worker safety but also reduces the ionic conductivity of the sulfide-based solid electrolyte itself.

[0005] In addition, when dry mixing is performed to synthesize a sulfide solid electrolyte, the precursors may stick to the container, causing uneven mixing and resulting in a reduced electrolyte yield. Furthermore, when wet mixing is performed using a large amount of solvent, the precursors may not stick, but the final product may have a relatively high electronic conductivity and may not function as a normal solid electrolyte. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] KR2018-0057423A Summary of the Invention [Problem to be solved by the invention]

[0007] The problem to be solved by the present invention is to provide a method for producing a solid electrolyte in which a trace amount of a low-polarity or non-polar solvent is added to a sulfide-based solid electrolyte precursor, thereby preventing the precursor from sticking and preventing non-uniform mixing, and improving the yield of the sulfide-based solid electrolyte.

[0008] Another problem to be solved by the present invention is to provide a solid electrolyte having increased ionic conductivity and decreased electronic conductivity by uniformly mixing solid electrolyte precursors to reduce the content of unreacted or unreacted impurities. [Means for solving the problem]

[0009] The present invention provides a method for producing a solid electrolyte and a solid electrolyte.

[0010] (1) The present invention provides a method for producing a solid electrolyte, comprising the steps of: mixing a sulfide-based solid electrolyte raw material and a solvent to produce a precursor mixture (S1); and heat-treating the precursor mixture (S2), wherein the solvent has a relative polarity with respect to water of 0.15 or less, and the content of the solvent is more than 2 wt % and 5 wt % or less with respect to the total content of the precursor mixture.

[0011] (2) The present invention provides the method for producing a solid electrolyte according to (1) above, wherein the solvent has a dielectric constant of 4.0 or less.

[0012] (3) The present invention provides the method for producing a solid electrolyte according to (1) or (2), wherein the solvent is at least one selected from the group consisting of xylene, benzene, toluene, pentane, hexane, and cyclohexane.

[0013] (4) The present invention provides a method for producing a solid electrolyte according to any one of (1) to (3), wherein the content of the nonpolar solvent is 2.5% by weight or more and 4% by weight or less with respect to the total content of the precursor mixture.

[0014] (5) The present invention provides a method for producing a solid electrolyte according to any one of the above (1) to (4), wherein the solid electrolyte is a sulfide-based solid electrolyte having an argyrodite-type crystal structure.

[0015] (6) The present invention provides a method for producing a solid electrolyte according to any one of (1) to (5), wherein the sulfide-based solid electrolyte raw material contains a sulfur precursor, a phosphorus precursor, and a LiX precursor, and X is a halogen element.

[0016] (7) The present invention provides a method for producing a solid electrolyte according to any one of (1) to (6), wherein the sulfide-based solid electrolyte raw material contains LiS, PS, and LiX, and X is F, Cl, Br, or I.

[0017] (8) The present invention provides a method for producing a solid electrolyte according to any one of (1) to (7), wherein the step (S1) is carried out by ball milling a sulfide-based solid electrolyte raw material and the solvent using a planetary mill including two types of zirconia (Zr) balls having different average particle sizes.

[0018] (9) The present invention provides the method for producing a solid electrolyte according to any one of the above (1) to (8), wherein the precursor mixture produced in the step (S1) is in a powder form.

[0019] (10) The present invention provides the method for producing a solid electrolyte according to any one of the above (1) to (9), wherein in the step (S2), the heat treatment temperature is 350°C to 650°C.

[0020] (11) The present invention provides a method for producing a solid electrolyte according to any one of (1) to (10), wherein the heat-treated precursor mixture in step (S2) has a sticking ratio of 1% or less as calculated by the following mathematical formula 1: [Mathematical formula 1] Adhesion rate (%) = (amount (g) of precursor mixture powder that adheres to the inner surface of the container after the milling process and does not fall when pulled apart with a force of 20 kgf or less and then turned upside down) / total amount (g) of precursor mixture put into the container) × 100

[0021] (12) The present invention provides a method for producing a solid electrolyte according to any one of the above (1) to (11), wherein the solid electrolyte is represented by the following chemical formula 1: [Chemical formula 1] Li a M b P c S d A e In the above Chemical Formula 1, M is one or more elements selected from the group consisting of Si, Ge, Sn, Al, Zr, Zn, As, Ga, Sb, Nb, V, Ti, Hf, Mg, In, Cu, Tl, Pb, W, and Ni; A is one or more elements selected from the group consisting of F, Cl, Br and I; 5.5≦a≦7.0, 0≦b≦0.7, 0.3≦c≦1, 4≦d≦5.6 and 0.4≦e≦2.

[0022] (13) The present invention provides a solid electrolyte having a composition represented by the following chemical formula 1, in which the total content of impurities is 1% by weight or less: [Chemical formula 1] Li a M b P c S d A e In the above Chemical Formula 1, M is one or more elements selected from the group consisting of Si, Ge, Sn, Al, Zr, Zn, As, Ga, Sb, Nb, V, Ti, Hf, Mg, In, Cu, Tl, Pb, W, and Ni; A is one or more elements selected from the group consisting of F, Cl, Br and I; 5.5≦a≦7.0, 0≦b≦0.7, 0.3≦c≦1, 4≦d≦5.6 and 0.4≦e≦2.

[0023] (14) The present invention provides a solid electrolyte having an ionic conductivity of 5.0 mS / cm or more.

[0024] (15) The present invention is directed to a solid electrolyte having an electronic conductivity of 1.0×10 -9 mS / cm or more 5.0×10 -6 Provided is a solid electrolyte having a conductivity of mS / cm or less. [Effects of the Invention]

[0025] According to the method for producing a solid electrolyte of the present invention, by using a low-polarity or non-polar solvent that does not cause side reactions in the sulfide solid electrolyte precursor, it is possible to prevent the generation of hydrogen sulfide gas, which is harmful to the human body, during the production process of the solid electrolyte.

[0026] Furthermore, in the method for producing a solid electrolyte of the present invention, a small amount of a low-polarity or non-polar solvent is used during the production process of the precursor mixture, thereby preventing the precursor from sticking together, thereby preventing a decrease in yield and mitigating the need for pulverization and mixing of non-uniform precursors.

[0027] Furthermore, in the method for producing a solid electrolyte of the present invention, the crystallinity of the precursor particles may be reduced during the heat treatment process due to uniform grinding and mixing of the precursor powder, and the spacing between the particles may be narrowed, which may increase the reactivity of the solid electrolyte phase formation. This may result in a lower phase synthesis temperature during the heat treatment, thereby reducing impurities and providing a solid electrolyte with increased ionic conductivity.

[0028] Furthermore, the solid electrolyte of the present invention has a significantly reduced content of unreacted or unreacted impurities, which increases ionic conductivity and decreases electronic conductivity, thereby improving performance characteristics when applied to an all-solid-state battery. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a schematic diagram showing the steps of a method for producing a solid electrolyte of the present invention. FIG. [Figure 2] 1 is a photograph showing the state of the solid electrolyte present in a container after production of the solid electrolyte and the state of the solid electrolyte when transferred to a storage container after production of the solid electrolyte for Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention will be described in more detail below to facilitate understanding of the present invention. The terms and words used in the specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as 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 to best describe their inventions.

[0031] 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.

[0032] 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.

[0033] The term "all solid state battery" as used herein 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 a liquid electrolyte together.

[0034] Method for producing solid electrolyte The method for producing a solid electrolyte according to the present invention includes the steps of (S1) mixing a sulfide-based solid electrolyte precursor material and a solvent to produce a precursor mixture, and (S2) heat-treating the precursor mixture. The solvent may have a relative polarity with respect to water of 0.15 or less, and the content of the solvent may be more than 2 wt % and not more than 5 wt % of the total content of the precursor mixture.

[0035] 1 is a schematic diagram illustrating a method for manufacturing a solid electrolyte according to the present invention. Referring to FIG. 1, step (S1) can be performed by mixing a powdery precursor of a sulfide-based solid electrolyte with a small amount of a solvent having a relative polarity to water of 0.15 or less, and ball milling the mixture using a planetary mill to prepare a precursor mixture.

[0036] According to one embodiment of the present invention, the solvent may be one or more selected from the group consisting of xylene, benzene, toluene, pentane, hexane, and cyclohexane. The solvent has a relative polarity of 0.15 or less with respect to water, where the relative polarity is the relative polarity of the solvent relative to the polarity of water, which is defined as 1. That is, a solvent having a relative polarity of 0.15 or less with respect to water is a low-polarity or non-polar solvent with low relative polarity with respect to water. The relative polarity with respect to water may be 0.15 or less, 0.13 or less, 0.11 or less, 0.10 or less, or 0.08 or less. During the preparation of the sulfide-based solid electrolyte, raw materials for the sulfide-based solid electrolyte are highly reactive with water, and therefore may generate hydrogen sulfide, a harmful gas, when mixed with a polar solvent. However, the method for preparing a solid electrolyte of the present invention includes mixing the raw materials with a solvent having a low relative polarity with respect to water, thereby preventing side reactions with the sulfide-based solid electrolyte precursor and suppressing the generation of hydrogen sulfide gas. More specifically, the method for producing a solid electrolyte of the present invention can include xylene or hexane as the solvent.

[0037] Furthermore, according to one embodiment of the present invention, the solvent may have a dielectric constant of 4.0 or less. The dielectric constant of the solvent may be 4.0 or less, 3.5 or less, 3.0 or less, 2.5 or less, 2.3 or less, 2.1 or less, 2.0 or less, or 1.9 or less. When the dielectric constant of the solvent satisfies the above range, the solvent is close to polar or non-polar, and does not cause a side reaction with the precursor during the preparation of the solid electrolyte, thereby suppressing the generation of hydrogen sulfide gas.

[0038] According to one embodiment of the present invention, the solvent content may be greater than 2 wt. % and less than 5 wt. % of the total content of the sulfide-based solid electrolyte precursor mixture. Specifically, the solvent content may be greater than 2 wt. %, at least 2.1 wt. %, at least 2.5 wt. %, at least 3 wt. %, at most 5 wt. %, at most 4.5 wt. %, at most 4 wt. %, or at most 3.5 wt. % of the total content of the sulfide-based solid electrolyte. If the solvent content is outside the lower limit of the above range, the problem of precursor adhesion occurring during the solid electrolyte preparation process may not be resolved. Furthermore, since the solid electrolyte preferably has low electronic conductivity and high ionic conductivity, if the solvent content is outside the upper limit of the above range, the amount of residual carbon generated from the solvent increases. This increases the electronic conductivity of the solid electrolyte after drying and heat treatment processes, potentially affecting the function of the solid electrolyte, which is required to conduct only lithium ions and prevent electron movement. Specifically, when the electronic conductivity of the solid electrolyte increases, side reactions with the positive electrode material may increase in the electrode layer, and the current efficiency in the solid electrolyte layer may decrease, causing problems such as self-discharge or short circuits.

[0039] According to one embodiment of the present invention, the sulfide-based solid electrolyte precursor material of the solid electrolyte manufacturing method of the present invention may include a sulfur precursor, a phosphorus precursor, and a LiX precursor, where X may be a halogen element. Specifically, the sulfide-based solid electrolyte precursor material may include LiS, P2S5, and LiX, where X may be F, Cl, Br, or I.

[0040] According to an embodiment of the present invention, the sulfide-based solid electrolyte may include lithium, phosphorus, sulfur, and a halogen, and may have an argyrodite-type crystal structure. The sulfide ions included in the sulfide-based solid electrolyte have a large ionic radius, which widens the gaps between anions that serve as ion conduction paths. The high polarizability of the sulfide ions weakens the binding force on lithium ions, allowing the lithium ions to move more easily, thereby improving lithium ion conductivity.

[0041] Furthermore, 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 negative electrode. 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 contained in the sulfide-based solid electrolyte is preferably 80% by mass or more, more preferably 85% by mass or more, 90% by mass or more, or 95% by mass or more, of the total crystalline phases constituting the sulfide-based solid electrolyte.

[0042] In addition, the sulfide-based solid electrolyte may be represented by the following Chemical Formula 1.

[0043] [Chemical formula 1] Li a M b P c S d A e

[0044] In the above Chemical Formula 1, M is one or more elements selected from the group consisting of Si, Ge, Sn, Al, Zr, Zn, As, Ga, Sb, Nb, V, Ti, Hf, Mg, In, Cu, Tl, Pb, W, and Ni; A is one or more elements selected from the group consisting of F, Cl, Br and I; 5.5≦a≦7.0, 0≦b≦0.7, 0.3≦c≦1, 4≦d≦5.6 and 0.4≦e≦2.

[0045] Generally, when high-energy milling is performed to mix and grind powders, the powder may become atomized and stick to the wall. In particular, in the case of sulfide-based solid electrolytes having an argyrodite-type crystal structure, the powder may become non-uniformly and strongly stuck to the wall before being uniformly mixed and atomized by the LiX precursor. The key to the solid-phase reaction performed through a heat treatment process during the solid electrolyte preparation process is to atomize and uniformly mix the precursors. When the precursors are atomized and uniformly mixed, a solid electrolyte with minimal impurities and a uniform composition can be prepared. However, if the precursor powder is mixed non-uniformly due to its sticking, the purity and performance of the solid electrolyte may be adversely affected.

[0046] Therefore, in the method for producing a solid electrolyte of the present invention, by adding and mixing a trace amount of a solvent having a relative polarity to water of 0.15 or less in the process of producing a sulfide-based solid electrolyte having an argyrodite-type crystal structure, the sticking phenomenon can be efficiently suppressed and the ionic conductivity of the produced solid electrolyte can be improved.

[0047] According to one embodiment of the present invention, step (S1) may be performed by ball milling a sulfide-based solid electrolyte precursor and a solvent having a relative polarity to water of 0.15 or less using a planetary mill containing two types of zirconia (Zr) balls with different average particle sizes. Specifically, step (S1) may be performed by adding a sulfur precursor, a phosphorus precursor, and a LiX precursor as the sulfide-based solid electrolyte precursor to a zirconia container, adding two or more types of ZrO2 balls with different average particle sizes, and stirring and ball milling the mixture. The precursor mixture prepared in step (S1) may be in powder form.

[0048] When preparing a solid electrolyte by wet mixing, such as by forming a slurry or solution, a problem occurs in that the solvent remains partially in a carbonized state in the precursor mixture or solid electrolyte even after drying or heat treatment, resulting in increased electronic conductivity. Therefore, the method for preparing a solid electrolyte according to the present invention includes dry mixing a sulfide-based solid electrolyte precursor in powder form, and adding a trace amount of a solvent having a relative polarity of 0.15 or less with respect to water to prevent solidification, thereby inducing uniform mixing and maximizing the ionic conductivity of the prepared solid electrolyte.

[0049] Meanwhile, during the ball milling process using the planetary mill, the faster the stirring speed, the faster the production rate of the solid electrolyte precursor mixture 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.

[0050] According to one embodiment of the present invention, the heat treatment temperature in step (S2) after step (S1) may be 350°C to 650°C. More specifically, the heat treatment temperature may be 300°C or higher, 350°C or higher, 450°C or higher, 500°C or higher, 650°C or lower, 600°C or lower, or 550°C or lower. When the heat treatment temperature is within this range, an argyrodite phase may be formed from the precursor mixture. In particular, when high-energy milling at 600 rpm or higher is performed in step (S1), the powdery precursor mixture that has been amorphized through the heat treatment process may be crystallized into an argyrodite solid electrolyte.

[0051] In addition, before carrying out the heat treatment process, a step of drying the amorphized powdery precursor mixture can be further carried out. This is to remove any solvent remaining in the homogeneously mixed precursor mixture, and can be carried out under vacuum drying, thermal drying, or vacuum conditions at room temperature to 200°C for 1 minute to 10 hours. Specifically, vacuum drying can be carried out in a vacuum oven at a temperature of 80°C for 1 hour.

[0052] FIG. 2 is a photograph showing the state of the solid electrolyte in the container immediately after the preparation of the solid electrolyte for Example 1 and Comparative Example 1, and the state of the solid electrolyte when the prepared solid electrolyte was transferred to a storage container. Specifically, FIG. 2(a) shows the state of the solid electrolyte in the reactor container immediately after the preparation of the solid electrolyte of Example 1, and it can be seen that it is mixed as a uniform powder, and the zirconia balls used are embedded in the powder. FIG. 2(b) shows the state of the solid electrolyte in the reactor container immediately after the preparation of the solid electrolyte of Comparative Example 1, and it can be seen that the powder adheres to the container walls and the zirconia balls located in the center of the container. Furthermore, FIG. 2(c) shows the state of the solid electrolyte in Example 1 after the container is turned upside down and transferred to a storage container and the zirconia balls are separated, and it can be seen that the solid electrolyte powder does not adhere to the container and is transferred smoothly to the storage container. FIG. 2(d) shows the state of the storage container after the solid electrolyte of Comparative Example 1 was transferred to a storage container by turning the container upside down immediately after production and the zirconia balls were separated. This shows that the solid electrolyte powder adhered to the container wall and the zirconia balls, and the solid electrolyte powder was not transferred to the storage container.

[0053] In one embodiment of the present invention, the precursor mixture heat-treated in step (S2) may have a fixation ratio calculated by the following Equation 1 of 1% or less.

[0054] [Mathematical formula 1] Adhesion rate (%) = (amount (g) of precursor mixture powder that adheres to the inner surface of the container after the milling process and does not fall when turned upside down after being pulled apart with a force of 20 kgf or less / total amount (g) of precursor mixture put into the container) × 100

[0055] The applied force in Equation 1 refers to the maximum instantaneous force applied to the container when using a tool such as a laboratory spoon, chisel, or rubber hammer, or a power tool. A force exceeding 20 kgf may cause damage to the container. Furthermore, in Equation 1, the milling process may be a ball milling process using a planetary mill, and may be performed within the above-mentioned stirring time and stirring speed ranges. Furthermore, the container may be one selected from the group consisting of a zirconia container, an agate container, an alumina container, a silicon nitride container, and a tungsten carbide container.

[0056] According to the method for manufacturing a solid electrolyte of the present invention, when the solvent is added in a predetermined amount and mixed using a planetary mill, the solid electrolyte precursor mixture has a solidification ratio of 1% or less according to Equation 1, which can reduce the difficulty of production, increase the yield, and improve the ionic conductivity of the manufactured solid electrolyte. Specifically, the solidification ratio can be 1% or less, 0.8% or less, 0.6% or less, 0.5% or less, 0.3% or less, 0.2% or less, or 0.1% or less.

[0057] solid electrolyte The present invention provides a solid electrolyte having a composition represented by the following Chemical Formula 1, and a total impurity content of 1 wt % or less. The solid electrolyte according to the present invention can be manufactured by various methods for manufacturing a solid electrolyte, and the method for manufacturing a solid electrolyte described above in this specification can be one example of various methods for manufacturing a solid electrolyte.

[0058] [Chemical formula 1] Li a M b Pc S d A e

[0059] In the above Chemical Formula 1, M is one or more elements selected from the group consisting of Si, Ge, Sn, Al, Zr, Zn, As, Ga, Sb, Nb, V, Ti, Hf, Mg, In, Cu, Tl, Pb, W, and Ni; A is one or more elements selected from the group consisting of F, Cl, Br and I; 5.5≦a≦7.0, 0≦b≦0.7, 0.3≦c≦1, 4≦d≦5.6 and 0.4≦e≦2.

[0060] According to the present invention, the solid electrolyte may be a sulfide-based solid electrolyte, and more specifically, may be a sulfide-based solid electrolyte having an argyrodite-type crystal structure.

[0061] The impurities may include unreacted materials or by-products generated by side reactions during the production of the solid electrolyte, and specifically, the impurities may be LiS or LiA. Among the impurities, A may be one or more elements selected from the group consisting of F, Cl, Br, and I. The content of the impurities may be obtained by analyzing XRD data of the solid electrolyte powder using a Rietveld refinement program.

[0062] The total content of the impurities may be 1 wt % or less. The impurity content is based on 100 wt % of the solid electrolyte. For example, the impurity content may be 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 impurity content satisfies the above range, it can be confirmed that the precursor is finely divided and prepared by uniform mixing, and a solid electrolyte having a desired uniform composition can be obtained. In addition, the solid electrolyte prepared by uniform mixing can have high ionic conductivity and low electronic conductivity, and when applied to an all-solid-state battery, the solid electrolyte can exhibit excellent performance characteristics.

[0063] According to one embodiment of the present invention, the solid electrolyte may have an ionic conductivity of 5.0 mS / cm or more. For example, the ionic conductivity may be 5.0 mS / cm or more, 5.1 mS / cm or more, 5.3 mS / cm or more, 5.5 mS / cm or more, 5.7 mS / cm or more, 5.9 mS / cm or more, 6.0 mS / cm or more, 6.1 mS / cm or more, or 6.2 mS / cm or more. Specifically, the ionic conductivity of the solid electrolyte may be 5.9 mS / cm or more.

[0064] The solid electrolyte has an electronic conductivity of 1.0×10 -9 mS / cm or more 5.0×10 -6 mS / cm or less. For example, 1.0×10 -9 mS / cm or more, 2.0×10 -9 mS / cm or more, 5.0×10 -9 mS / cm or more, 7.0×10 -9 mS / cm or more, 9.0×10 -9 mS / cm or more, 1.0×10 -8 mS / cm or more, 2.0×10 -8 mS / cm or more, 5.0×10 -8 mS / cm or more, 7.0×10 -8 mS / cm or more, 9.0×10 -8 mS / cm or more, 1.0×10-7 mS / cm or more, 1.1×10 -7 mS / cm or more, 1.3×10 -7 mS / cm or more, 1.5×10 -7 mS / cm or more, 1.6×10 -7 mS / cm or more, 5.0×10 -6 mS / cm or less, 3.0×10 -6 mS / cm or less, 1.0×10 -6 mS / cm or less, 7.0×10 -7 mS / cm or less, 5.0×10 -7 mS / cm or less, 3.0×10 -7 mS / cm or less, 2.9×10 -7 mS / cm or less, 2.8×10 -7 mS / cm or less, 2.7×10 -7 mS / cm or less, 2.6×10 -7 mS / cm or less, and specifically, the electronic conductivity of the solid electrolyte is 1.3×10 -7 mS / cm or more 2.7×10 -7 The solid electrolyte of the present invention can simultaneously satisfy the above-mentioned ranges of ionic conductivity and electronic conductivity, and when the above-mentioned ranges of ionic conductivity and electronic conductivity are satisfied, it is possible to prevent the movement of electrons and allow the smooth movement of lithium ions, thereby providing an all-solid-state battery excellent in initial efficiency, life characteristics, and output characteristics.

[0065] All solid state battery The present invention provides an all-solid-state battery containing the solid electrolyte.

[0066] According to one embodiment of the present invention, the all-solid-state battery includes a positive electrode, a negative electrode (or anode-less), and a solid electrolyte layer containing a solid electrolyte disposed between the positive electrode and the negative electrode. The all-solid-state battery according to the present invention exhibits little decrease in ionic conductivity and low electronic conductivity of the solid electrolyte, thereby enabling the all-solid-state battery to have excellent initial efficiency, life characteristics, and output characteristics. The all-solid-state battery of the present invention can be manufactured by a conventional method well known in the art. For example, the all-solid-state battery can be manufactured by stacking the positive electrode and the negative electrode so that the solid electrolyte layer is present between them and applying pressure.

[0067] (1) 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.

[0068] The positive electrode current collector may be any material that does not cause chemical changes in the battery and has conductivity, and may be, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. Furthermore, the surface may be provided with fine irregularities to enhance the bonding strength of the positive electrode active material, and may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0069] The positive electrode active material may include a lithium metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum as a compound capable of reversible intercalation and deintercalation of lithium. More specifically, the lithium metal oxide may include 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 YO2 (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) oxides (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 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.

[0070] 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 Co0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 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.

[0071] The positive electrode active material may be included in an amount of 60 wt % or more, 70 wt % or more, 80 wt % or more, or 99 wt % or less, 98 wt % or less, based on the total weight of solids other than the solvent in the positive electrode slurry.

[0072] 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.

[0073] 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.

[0074] The conductive material is a component for further improving the conductivity of the positive electrode active material.

[0075] 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.

[0076] Typically, the conductive material may be contained in an amount of 1 wt % or more, 20 wt % or less, 15 wt % or less, or 10 wt % or less based on the total weight of solids other than the solvent in the positive electrode slurry.

[0077] The solvent may include an organic solvent such as N-methyl-2-pyrrolidone (NMP) and may be used in an amount that provides a desired viscosity when the positive electrode active material and, optionally, the binder and 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, the binder and conductive material, is 50 wt % or more, 60 wt % or more, 70 wt % or more, 95 wt % or less, 90 wt % or less, or 85 wt % or less.

[0078] (2) Negative electrode The negative electrode may 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 may be prepared by using a graphite electrode made of carbon (C) or lithium metal itself having a thickness of 50 μm or less as the negative electrode. Alternatively, the negative electrode may be eliminated by making the negative electrode anode-less.

[0079] 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.

[0080] 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.

[0081] The negative electrode active material may be included in an amount of 60 wt % or more, 70 wt % or more, 80 wt % or more, 99 wt % or less, or 98 wt % or less based on the total weight of solids other than the solvent in the negative electrode slurry.

[0082] 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.

[0083] Typically, the binder may be included in an amount of 1 wt % or more, 20 wt % or less, 15 wt % or less, or 10 wt % or less based on the total weight of solids other than the solvent in the negative electrode slurry.

[0084] 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.

[0085] The conductive material may be contained in an amount of 1 wt % or more, 20 wt % or less, 15 wt % or less, or 10 wt % or less based on the total weight of solids other than the solvent in the negative electrode slurry.

[0086] The solvent may include water or an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount that provides a desired viscosity when the negative electrode active material and, optionally, the binder and 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, the binder and conductive material, is 50 wt % or more, 60 wt % or more, 70 wt % or more, 95 wt % or less, 90 wt % or less, or 85 wt % or less.

[0087] 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.

[0088] 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).

[0089] (3) Solid electrolyte layer The solid electrolyte layer may further contain a binder in addition to the solid electrolyte according to the present invention.

[0090] The binder is a component that helps bind the solid electrolyte particles together, and 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.

[0091] The binder may be contained in an amount of 0.1 wt % or more, 5 wt % or less, 3 wt % or less, or 2 wt % or less based on the total weight of the solid electrolyte layer.

[0092] 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.

[0093] While the present invention may be embodied in various different forms, it is to be understood that the invention is not limited to the specific embodiments set forth herein, and that the invention may be embodied in various different forms without departing from the spirit or scope of the present invention.

[0094] Examples and Comparative Examples Example 1 Li2S powder, P2S5 powder, and LiCl powder were used as raw material powders. These powders were weighed to a total weight of 5 g to achieve the composition Li6PS5Cl. 15 g of 5 mm and 10 mm diameter ZrO2 balls (zirconia balls) were placed in a 45 ml ZrO2 (zirconia) container, totaling 30 g, at a 1:1 ratio. 5 g of the raw material powders and 0.125 g of xylene (2.5 wt% of the total precursor powder content) were then added. Ball milling was performed using a high-energy ball milling machine (Fritsch Pulverisette 7 premium) at 400 rpm for 3 hours using a planetary mill. The resulting powder material with the Li6PS5Cl composition was dried in a vacuum oven at 80 °C for 2 hours. It was then heat-treated at 550 °C for 12 hours to obtain the solid electrolyte powder material.

[0095] Example 2 The same procedure as in Example 1 was carried out, except that 0.2 g of xylene (4 wt % based on the total content of the precursor powder) was added.

[0096] Example 3 The same procedure as in Example 1 was carried out, except that 0.125 g of hexane (2.5 wt % based on the total content of the precursor powder) was added.

[0097] Comparative Example 1 The same procedure as in Example 1 was carried out except that xylene was not added.

[0098] Comparative Example 2 The same procedure as in Example 1 was carried out, except that 0.075 g of xylene (1.5 wt % based on the total content of the precursor powder) was added.

[0099] Comparative Example 3 The same procedure as in Example 1 was carried out, except that 0.075 g of hexane (1.5 wt % based on the total content of the precursor powder) was added.

[0100] Comparative Example 4 The same procedure as in Example 1 was carried out, except that 0.3 g of xylene (6 wt % based on the total content of the precursor powder) was added.

[0101] Comparative Example 5 The same procedure as in Example 1 was carried out, except that 0.125 g of tetrahydrofuran (2.5 wt % based on the total content of the precursor powder) was added.

[0102] Experimental Example 1 Measurement of adhesion ratio: In the examples and comparative examples, the total amount of solid electrolyte powder material charged into the zirconia container was measured, and then ball milling was performed using a planetary mill. Thereafter, a pressure of 20 kgf was applied to the zirconia container using a tool such as a laboratory spoon without damaging it, and the amount of detachable solid electrolyte powder was measured, and the ratio of the amount of powder that adhered to the inner surface of the container to the total amount of the solid electrolyte powder material was calculated.

[0103] Experimental Example 2 Measurement of ionic conductivity: 150 mg of the solid electrolyte Li6PS5Cl prepared in the examples and comparative examples was placed in a metal mold having a diameter of 13 mm, and a pressure of 370 MPa was applied to form a solid electrolyte layer. The ionic conductivity was then measured at room temperature (25°C) with an amplitude of 10 mV and a frequency range of 0.1 Hz to 7 MHz using a potentiostat (Biologics, SP-200).

[0104] Experimental Example 3 Measurement of impurity ratio: The impurity ratio of the solid electrolyte powder was calculated using XRD measurement and Rietveld refinement analysis. The XRD instrument used was a Bruker D8 Endeavor, Cu Kα radiation, 1.5406 Å wavelength. The measurement conditions were non-air-exposed, scan rate 2° / min, 2 theta angle 10–90°. The impurities were identified and quantified using the TOPAS Rietveld refinement program.

[0105] Experimental Example 4 Measurement of electronic conductivity: 150 mg of the solid electrolyte Li6PS5Cl prepared in the examples and comparative examples was placed in a mold having a diameter of 13 mm, and a pressure of 370 MPa was applied to form a solid electrolyte layer. Then, using a potentiostat (SP-200, manufactured by Biologics) at room temperature (25°C), DC 1 V was applied for 6 hours, and the current value after saturation was measured so that there was no change in the current, and the electronic conductivity was measured.

[0106] The adhesion ratio, ionic conductivity, impurity ratio, and electronic conductivity measured in Experimental Examples 1 to 4 are shown in Table 1 below.

[0107] [Table 1]

[0108] Referring to Table 1, Examples 1 to 3, which contain a trace amount of solvent with a relative polarity to water of 0.15 or less, exhibit very low solidification rates and impurity ratios. This indicates that the ionic conductivity is high and the electronic conductivity is low, resulting in excellent solid electrolyte performance. Referring to FIG. 2, it can be seen that in Example 1, the precursors were uniformly mixed to prepare a precursor mixture, with only 0.2% of the powder adhering to the container. In contrast, in Comparative Example 1, in which no solvent was used, the solidification rate and impurity ratio were very high, resulting in low ionic conductivity and poor performance of the prepared solid electrolyte. Referring to FIG. 2, it can be seen that in Comparative Example 1, 99.9% of the powder from the prepared precursor mixture adhering to the container and not being transferred to a storage container. Furthermore, Comparative Examples 2 to 4, in which solvent contents outside the range of the present invention were used, exhibited poor solidification rates and / or impurity ratios, and also exhibited low ionic conductivity. In particular, Comparative Example 4 had low ionic conductivity and high electronic conductivity, which confirmed that it was not suitable for use as a solid electrolyte. Furthermore, although tetrahydrofuran has strong polarity, Comparative Example 5, which used tetrahydrofuran as a solvent rather than a solvent with a relative polarity to water of 0.15 or less, had a high impurity ratio, low ionic conductivity, and high electronic conductivity, which confirmed that it was not suitable for use as a solid electrolyte.

Claims

1. A step (S1) of mixing a sulfide-based solid electrolyte raw material and a solvent to prepare a precursor mixture; and (S2) heat-treating the precursor mixture; the solvent has a relative polarity to water of 0.15 or less; A method for producing a solid electrolyte, wherein the content of the solvent is more than 2 wt % and not more than 5 wt % based on the total content of the precursor mixture.

2. The method for producing a solid electrolyte according to claim 1 , wherein the solvent has a dielectric constant of 4.0 or less.

3. 2. The method for producing a solid electrolyte according to claim 1, wherein the solvent is at least one selected from the group consisting of xylene, benzene, toluene, pentane, hexane, and cyclohexane.

4. The method for producing a solid electrolyte according to claim 1 , wherein the content of the solvent is 2.5% by weight or more and 4% by weight or less with respect to the total content of the precursor mixture.

5. 2. The method for producing a solid electrolyte according to claim 1, wherein the solid electrolyte is a sulfide-based solid electrolyte having an argyrodite-type crystal structure.

6. 2. The method for producing a solid electrolyte according to claim 1, wherein the sulfide-based solid electrolyte raw material comprises a sulfur precursor, a phosphorus precursor, and a LiX precursor, and X is a halogen element.

7. The sulfide-based solid electrolyte raw material is Li ２ S, P ２ S ５ and LiX, wherein X is F, Cl, Br, or I.

8. 2. The method of claim 1, wherein step (S1) is performed by ball milling the sulfide-based solid electrolyte raw material and the solvent using a planetary mill including two types of zirconia (Zr) balls having different particle sizes.

9. The method for producing a solid electrolyte according to claim 1 , wherein the precursor mixture produced in step (S1) is in a powder form.

10. 2. The method for producing a solid electrolyte according to claim 1, wherein in step (S2), the heat treatment temperature is 350°C to 650°C.

11. 2. The method for preparing a solid electrolyte according to claim 1, wherein the heat-treated precursor mixture in step (S2) has a solidification ratio calculated by the following Equation 1 of 1% or less: [Mathematical formula 1] Adhesion rate (%) = (amount (g) of precursor mixture powder that adheres to the inner surface of the container after the milling process and does not fall when pulled apart with a force of 20 kgf or less and then turned upside down / total amount (g) of precursor mixture charged into the container) × 100

12. The method for producing a solid electrolyte according to claim 1 , wherein the solid electrolyte is represented by the following chemical formula 1: [Chemical formula 1] Li ａ M ｂ P ｃ S ｄ A ｅ In the above Chemical Formula 1, M is one or more elements selected from the group consisting of Si, Ge, Sn, Al, Zr, Zn, As, Ga, Sb, Nb, V, Ti, Hf, Mg, In, Cu, Tl, Pb, W, and Ni; A is one or more elements selected from the group consisting of F, Cl, Br, and I; 5.5≦a≦7.0, 0≦b≦0.7, 0.3≦c≦1, 4≦d≦5.6 and 0.4≦e≦2.

13. It has a composition represented by the following chemical formula 1: A solid electrolyte having a total impurity content of 1% by weight or less. [Chemical formula 1] Li ａ M ｂ P ｃ S ｄ A ｅ In the above Chemical Formula 1, M is one or more elements selected from the group consisting of Si, Ge, Sn, Al, Zr, Zn, As, Ga, Sb, Nb, V, Ti, Hf, Mg, In, Cu, Tl, Pb, W, and Ni; A is one or more elements selected from the group consisting of F, Cl, Br, and I; 5.5≦a≦7.0, 0≦b≦0.7, 0.3≦c≦1, 4≦d≦5.6 and 0.4≦e≦2.

14. 14. The solid electrolyte according to claim 13, wherein the solid electrolyte has an ionic conductivity of 5.0 mS / cm or more.

15. The solid electrolyte has an electronic conductivity of 1.0×10 －９ mS / cm or more 5.0×10 －６ The solid electrolyte according to claim 13, having a conductivity of mS / cm or less.

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