Sulfide-based solid electrolyte

Abstract

The present invention relates to a sulfide-based solid electrolyte including elemental lithium (Li), elemental phosphorus (P), elemental sulfur (S), and an elemental halogen (Ha), and having an argyrodite-based crystal structure, wherein at least a portion of the crystal structure is doped with a first compound including a Group 13 element (M) and a second compound including elemental oxygen (O).

Description

Sulfide-based solid electrolyte

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0068009, filed May 24, 2024, and Korean Patent Application No. 10-2025-0067849, filed May 23, 2025, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a sulfide-based solid electrolyte.

[0003] Recent reports of explosion risks in batteries using liquid electrolytes have led to active development of all-solid-state secondary batteries. All-solid-state secondary batteries are composed entirely of solid materials, specifically those using solid electrolytes. These all-solid-state secondary batteries are safe, eliminating the risk of explosion due to electrolyte leakage, and offer the advantage of being easy to manufacture in thinner sizes.

[0004] However, solid electrolytes have lower ionic conductivity than liquid electrolytes, and have problems such as resistance occurring at the interface between solid electrolyte particles or resistance occurring at the interface with other solid particles, such as positive electrode active materials in the battery, which reduces ionic conductivity.

[0005] Among solid electrolytes, research on sulfide-based solid electrolytes with relatively high ionic conductivity is actively being conducted. Sulfide-based solid electrolytes are generally LGPS (Li 10 GeP2S 12 ) system, LPS(Li7P3S 11 ) system, LPSH(Li 7-x PS 6-x Ha x) system (Ha is a halogen element or a polyatomic anion (molecular anion) or a combination of two or more thereof, 0.5 < x < 2), etc., and at this time, the solid electrolyte composed of LGPS, LPS, or LPSH compounds has a characteristic of having a weak bonding force of the phosphorus-sulfur bond in the unit crystal structure of the compound because the difference in electronegativity between the phosphorus element and the sulfur element is only 0.39. For this reason, when charge and discharge are repeated, the phosphorus-sulfur bond is destroyed and the electrolyte is decomposed, which reduces the lifespan of the battery, and there is a problem that it is difficult to handle due to low moisture stability. For example, a sulfide-based solid electrolyte has a high reactivity to moisture, so that a side reaction occurs on the surface due to moisture in the air during the manufacturing process, transportation process, or insertion into the battery, generating a harmful gas, hydrogen sulfide (H2S), which lowers the performance of the solid electrolyte and may cause a threatening situation to workers during the battery process.

[0006] In order to solve the problem of such sulfide-based solid electrolytes, a method of reducing the generation of hydrogen sulfide gas is being studied by partially replacing the Li site of the sulfide-based solid electrolyte using metal sulfide or by changing the PS bond of the sulfide-based solid electrolyte to a PO bond using elements such as lithium oxide (Li2O) or diphosphorus pentoxide (P2O5) containing oxygen.

[0007] However, in the case of metal sulfide, the price is very high because it does not exist naturally and must be artificially synthesized, and in the case of elements such as lithium oxide (Li2O) and diphosphorus pentoxide (P2O5), they are classified as substances harmful to the human body in themselves and are difficult to handle. In particular, there is a limitation that the ionic conductivity of the solid electrolyte drops sharply, reducing the performance of the all-solid-state battery.

[0008] The problem to be solved by the present invention is to provide a structurally stable sulfide-based solid electrolyte and a method for manufacturing the same.

[0009] According to one aspect of the present invention, a sulfide-based solid electrolyte is provided, which comprises lithium element (Li), phosphorus element (P), sulfur element (S), and halogen element (Ha), has an argyrodite-based crystal structure, and at least a portion of the crystal structure is doped with a first compound comprising a Group 13 element (M) and a second compound comprising an oxygen element (O).

[0010] According to one embodiment of the present invention, a sulfide-based solid electrolyte is provided, wherein the group 13 element (M) includes at least one selected from boron (B), aluminum (Al), gallium (Ga), indium (In), and titanium (Ti).

[0011] According to one embodiment of the present invention, the first compound provides a sulfide-based solid electrolyte including aluminum oxide (Al2O3), aluminum sulfide (Al2S3), aluminum chloride (AlCl3), boron sulfide (B2S3), boron oxide (B2O3), or boron dioxide (B2O5).

[0012] According to one embodiment of the present invention, the second compound provides a sulfide-based solid electrolyte including lithium oxide (Li2O) or diphosphorus pentoxide (P2O5).

[0013] According to one embodiment of the present invention, a sulfide-based solid electrolyte satisfying the following equation 1 is provided.

[0014] <Formula 1>

[0015] 0.5 ≤ [M] / {[Li]+3[M]}

[0016] In the above equation 1,

[0017] [M] represents the number of moles of group 13 elements, and [Li] represents the number of moles of lithium elements.

[0018] According to one embodiment of the present invention, a sulfide-based solid electrolyte satisfying the following equation 2 is provided.

[0019] <Formula 2>

[0020] 2 ≤ [O] / [S] X 100 ≤ 3

[0021] In the above equation 2,

[0022] [O] represents the number of moles of oxygen element, and [S] represents the number of moles of sulfur element.

[0023] According to one embodiment of the present invention, a sulfide-based solid electrolyte represented by the following chemical formula 1 is provided.

[0024] [Chemical Formula 1]

[0025] Li (7-x-3a) M (a) PS (6-x-b) O (b) Ha (x)

[0026] In the above chemical formula 1,

[0027] Ha is F, Cl, Br, I or a combination thereof, M is B, Al, Ga, In, Ti or a combination thereof, 1≤x≤2, 0.025≤a≤0.3, and 0.07≤b≤0.15.

[0028] According to another aspect of the present invention, a method for producing a sulfide-based solid electrolyte is provided, comprising the steps of: (S1) preparing a precursor solution by introducing a precursor including an alkali metal sulfide, a phosphorus sulfide, a halogen compound, a first compound, and a second compound into a solvent; (S2) milling the precursor solution to produce an intermediate product; (S3) drying the intermediate product; and (S4) heat-treating the dried intermediate product, wherein the first compound and the second compound are doped simultaneously.

[0029] According to another aspect of the present invention, an electrochemical cell is provided, comprising: a positive electrode; a negative electrode; and a solid electrolyte layer positioned between the positive electrode and the negative electrode, wherein at least one of the positive electrode, the negative electrode, and the solid electrolyte layer comprises a sulfide-based solid electrolyte according to any one of claims 1 to 8.

[0030] A sulfide-based solid electrolyte according to one embodiment of the present invention can improve atmospheric stability by reducing reactivity with moisture, and can improve the life characteristics of a battery by preventing decomposition of the electrolyte and a decrease in ionic conductivity due to a reaction with oxygen generated from the positive electrode during repeated charge and discharge in battery configuration.

[0031] The present invention is capable of various modifications and embodiments. Specific embodiments are illustrated in the drawings and described in detail in the detailed description. The effects and features of the present invention, as well as the methods for achieving them, will become clearer with reference to the embodiments described in detail below, along with the drawings. However, the present invention is not limited to the embodiments disclosed below and can be implemented in various forms.

[0032] In the examples below, the terms first, second, etc. are not used in a limiting sense, but are used for the purpose of distinguishing one component from another.

[0033] In the examples below, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0034] In the examples below, terms such as “include” or “have” mean that a feature or component described in the specification is present, and do not preclude the possibility that one or more other features or components may be added.

[0035] In the following examples, when a part such as a film, region, component, etc. is said to be on or above another part, it includes not only a case where it is directly on top of the other part, but also a case where another film, region, component, etc. is interposed in between.

[0036]

[0037] Sulfide-based solid electrolyte

[0038] A sulfide-based solid electrolyte according to one embodiment of the present invention includes lithium element (Li), phosphorus element (P), sulfur element (S), and halogen element (Ha), and has an argyrodite-based crystal structure, and at least a portion of the crystal structure may be substituted with a first compound including a Group 13 element (M) and a second compound including an oxygen element (O).

[0039] The crystal structure of the baby rhodite system is orthorhombic, for example, A 7-x BC 6-x D x The compound may include a crystal structure having a general formula of , wherein the A site includes an alkali metal (e.g., lithium (Li)) having a single positive charge, the B site includes phosphorus (P) or arsenic (As) having a pentavalent positive charge, the C site includes oxygen (O), sulfur (S), or selenium (Se) having a divalent negative charge, and the D site includes a halogen (Ha) having a single negative charge. The alkali metal may include lithium (Li), sodium (Na), or potassium (K), and the halogen may include fluorine (F), chlorine (Cl), bromine (Br), or iodine (I).

[0040] The above-mentioned agarodite compound has excellent crystallinity and lattice constant, and thus can exhibit excellent ionic conductivity for lithium ions. Therefore, it can be used as an electrolyte for an all-solid-state battery to improve the electrical performance (discharge capacity, discharge efficiency, lifespan, etc.) of the battery.

[0041] For example, the chemical formula LPSH(Li 7-x PS 6-x Ha x ) (Ha is a halogen element or a polyatomic anion (molecular anion) and a combination of two or more of them. 0.5 < x < 2) agirodite compounds have a main structure of PS4 3-The unit structure consists of phosphorus and sulfur. Phosphorus and sulfur have a small difference in electronegativity (0.39), and thus, they are bound by a weak bond. Therefore, during charge and discharge of an all-solid-state battery, the electrolyte may decompose, deteriorating the battery's lifespan characteristics and electrical performance.

[0042] The agerrodite compound may further include a Group 13 element (M), and a portion of the compound having an agerrodite crystal may be substituted with the Group 13 element (M). For example, in a compound having an agerrodite crystal that includes a lithium (Li) element at the A site, a phosphorus (P) element at the B site, a sulfur (S) element at the C site, and a halogen (Ha) element at the D site, a portion of the lithium (Li) element occupying the A site of the agerrodite crystal structure may be substituted with a Group 13 element (M).

[0043] When some of the lithium (Li) elements occupying the A site of the agilodite compound are replaced with a group 13 element (e.g., boron (B)), the agilodite crystal structure is strengthened by forming a [Bo]S3triangle structure that has a very strong bonding force with sulfur (S), thereby making the agilodite crystal structure structurally stable and increasing its density.

[0044] The group 13 element (M) may include at least one selected from boron (B), aluminum (Al), gallium (Ga), indium (In), and titanium (Ti), and the group 13 element (M) may be partially substituted with the lithium (Li) element occupying the A site of the agilodite compound. At this time, the group 13 element (M) may be positioned at the A site of the agilodite compound by replacing three lithium elements (Li) occupying the A site of the agilodite compound as shown in the following chemical formula 1, and may have high structural stability by forming a [M]S3triangle structure. This can be predicted through the results of DFT (Density functional theory) calculations using a supercomputer.

[0045] [Chemical Formula 1]

[0046] Li (7-x-3a) M (a) PS (6-x-b) O (b) Ha (x)

[0047] In the above chemical formula 1,

[0048] Ha is F, Cl, Br, I or a combination thereof, M is B, Al, Ga, In, Ti or a combination thereof, 1≤x≤2, 0.025≤a≤0.3, and 0.07≤b≤0.15.

[0049] A first compound can be introduced to substitute the agarodite compound with a Group 13 element (M), and the first compound containing the Group 13 element (M) can include aluminum oxide (Al2O3), aluminum sulfide (Al2S3), aluminum chloride (AlCl3), boron sulfide (B2S3), boron oxide (B2O3), or boron dioxide (B2O5).

[0050] A sulfide-based solid electrolyte according to one embodiment of the present invention can satisfy the following equation 1.

[0051] <Formula 1>

[0052] 0.5 ≤ [M] / {[Li]+3[M]}

[0053] In the above equation 1,

[0054] [M] represents the number of moles of Group 13 elements, and [Li] represents the number of moles of lithium elements. The value {[Li]+3[M]} in the denominator can be the number of moles of the entire parent lithium element. The parent composition refers to the number of moles of lithium in a sulfide-based solid electrolyte when Group 13 elements (M) and oxygen elements (O) are not doped.

[0055] Specifically, the above [M] / {[Li]+3[M]} may mean a ratio of the number of moles of a Group 13 element to the number of moles of a lithium element, and the lower limit of the above [M] / {[Li]+3[M]} X 100 may be 0.5, 0.6, 0.7, 0.8, 0.85, 0.9, 0.95, or 1, and the upper limit of the above [M] / {[Li]+3[M]} X 100 may be 5, 4, 3, 2, 1.5, 1.45, 1.4, 1.35, 1.3, or 1.25.

[0056] If the value of [M] / {[Li]+3[M]} X 100 is less than the above range, it means that the substitution of the Group 13 element (M) is too small, so the change in structural stability due to doping is not large, making it difficult to expect an improvement in atmospheric stability. If the value of [M] / {[Li]+3[M]} X 100 exceeds the above range, it means that the substitution of the Group 13 element (M) is too large, so the ionic conductivity may drop sharply as the absolute amount of lithium decreases.

[0057] According to embodiments of the present invention, a sulfide-based solid electrolyte can improve the movement of lithium ions, minimize the decrease in ionic conductivity, secure electrochemical stability, and improve atmospheric stability by replacing a portion of the crystal structure with an appropriate amount of a Group 13 element (M) included in the first compound.

[0058] In general, in the agerrodite crystal structure, sulfur generally has two bonds, Li-S and PS, and when it meets moisture in the atmosphere, the Li-S or PS bond changes to Li-O or PO bond, which forms an HS bond, which may generate hydrogen sulfide (H2S) gas that is harmful to the human body. However, in the sulfide-based solid electrolyte according to an embodiment of the present invention, a part of the crystal structure is substituted with a Group 13 element (M) within the above range, so that the weak Li-S bond among the Li-S bond or PS bond is partially replaced with a relatively strong MS bond, and thus the HS bond is not easily formed due to the strong MS bond, so that the generation of hydrogen sulfide (H2S) gas is suppressed, and atmospheric stability can be improved.

[0059] Meanwhile, although the side reaction in which Li-S bonds are replaced by Li-O bonds can be prevented by the introduction of the first compound, there is a limit to preventing the side reaction in which PS bonds are replaced by PO bonds.

[0060] Accordingly, by simultaneously substituting the oxygen element (O) with a group 13 element to partially create a PS bond into a PO bond in advance, the side reaction of changing the PS bond into a PO bond can be effectively suppressed.

[0061] A second compound may be introduced to replace the agarodite compound with oxygen element (O), and the second compound containing oxygen element (O) may include lithium oxide (Li2O) or diphosphorus pentoxide (P2O5).

[0062] A sulfide-based solid electrolyte according to one embodiment of the present invention can satisfy the following equation 2.

[0063] <Formula 2>

[0064] 2 ≤ [O] / [S] X 100 ≤ 3

[0065] In the above equation 2,

[0066] [O] represents the number of moles of oxygen element, and [S] represents the number of moles of sulfur element.

[0067] Specifically, the above [O] / [S] may mean a ratio of the number of moles of oxygen element to the number of moles of sulfur element, and the lower limit of the above [O] / [S] X 100 may be 2, 2.1, 2.2, 2.3, 2.4, or 2.5, and the upper limit of the above [O] / [S] X 100 may be 3, 2.9, 2.8, 2.7, or 2.6.

[0068] If the value of [O] / [S] X 100 is less than the above range, it means that the substitution of oxygen elements (O) is too little, so it is difficult to prevent a side reaction in which PS bonds are replaced by PO bonds, and if the value of [O] / [S] X 100 exceeds the above range, it means that the substitution of oxygen elements (O) is too much, so as PO bonds with strong bonding force increase, the movement of lithium ions may be hindered, and ion conductivity may rapidly decrease.

[0069] The sulfide-based solid electrolyte according to one embodiment of the present invention can secure electrochemical stability by improving the movement of lithium ions when oxygen element (O) replaces sulfur element (S) within the above range, thereby not significantly reducing ion conductivity, and can improve atmospheric stability by partially forming PS bonds into PO bonds in advance.

[0070] According to one embodiment of the present invention, a sulfide-based solid electrolyte is doped with at least a portion of a crystal structure of a Group 13 element (M) and an oxygen element (O). At this time, the Group 13 element (M) and the oxygen element (O) are doped independently of each other. In other words, the doping amounts of the Group 13 element (M) and the oxygen element (O) do not have a fixed correlation, but can be randomly and independently controlled. Since the Group 13 element (M) and the oxygen element (O) are doped independently of each other, a large number of vacancies due to lithium ion deficiency can be generated. Accordingly, various lithium ion paths (channels) are formed, so that the lithium ion conductivity is greatly improved, and the cell capacity characteristics can be improved. At this time, the doping amounts of the Group 13 element (M) and the oxygen element (O) can be appropriately and independently controlled to maximize the above effect.

[0071] A sulfide-based solid electrolyte according to one embodiment of the present invention can be represented by the following chemical formula 1.

[0072] [Chemical Formula 1]

[0073] Li (7-x-3a) M (a) PS (6-x-b) O (b) Ha (x)

[0074] In the above chemical formula 1,

[0075] Ha is F, Cl, Br, I or a combination thereof, M is B, Al, Ga, In, Ti or a combination thereof, 1≤x≤2, 0.025≤a≤0.3, and 0.07≤b≤0.15.

[0076]

[0077] In the above chemical formula 1, the group 13 element (M) and the oxygen element (O) are doping elements. In this specification, "doping" may mean not only replacing some elements of a compound with a new element, but also the doped element becoming a component of the crystalline phase of the compound.

[0078] And, in the above chemical formula 1, a represents the doping amount of the Group 13 element (M), which is a doping element, expressed in moles. At this time, the lower limit of the doping amount of the Group 13 element (M) may be 0.025, 0.03, 0.035, 0.04, 0.05, 0.055, or 0.06, and the upper limit of the doping amount of the Group 13 element (M) may be 0.3, 0.25, 0.2, 0.1, 0.09, 0.085, 0.08, 0.075, 0.07, or 0.065.

[0079] If a is less than the above range, it means that the doping amount of the Group 13 element (M) is too small, and the change in structural stability due to doping is not significant, so it is difficult to expect an improvement in atmospheric stability. On the other hand, if a exceeds the above range, it means that the doping amount of the Group 13 element (M) is too large, and the absolute amount of lithium that conducts ions is insufficient, so that the ionic conductivity drops sharply, which may lead to a decrease in performance when configuring a battery. Therefore, excellent ionic conductivity can be realized when a satisfies the above range.

[0080] In addition, in the above chemical formula 1, b represents the doping amount of oxygen element (O), which is a doping element, expressed in moles. At this time, the lower limit of the doping amount of oxygen element (O) may be 0.07, 0.075, 0.08, 0.085, 0.09, 0.095, or 0.1, and the upper limit of the doping amount of oxygen element (O) may be 0.15, 0.145, 0.14, 0.135, 0.13, 0.125, 0.12, 0.115, or 0.11.

[0081] If b is below the above range, it means that the doping amount of oxygen element (O) is too low, and the change in structural stability due to doping is not significant, so it is difficult to expect an improvement in atmospheric stability. On the other hand, if b exceeds the above range, it means that the doping amount of oxygen element (O) is too high, and as the number of PO bonds with strong bonding increases, the movement of lithium ions may be hindered, which may cause a sharp decrease in ionic conductivity. Therefore, excellent ionic conductivity can be realized when b satisfies the above range.

[0082] In the above chemical formula 1, Ha represents a halogen element, and may be at least one of fluorine (F), chlorine (Cl), bromine (Br), or iodine (I).

[0083] More specifically, the halogen element (Ha) may be chlorine (Cl). The use of chlorine, particularly among the halogen elements, may have the effect of stabilizing the structure of the agarodite-based solid electrolyte, and may be advantageous in that it is easier to synthesize and less expensive than other elements.

[0084] The above solid electrolyte may be in the form of particles or powder, and may be amorphous, glassy, ​​or crystalline. In addition, the above solid electrolyte may be used for the positive electrode or for the solid electrolyte layer.

[0085]

[0086] Method for manufacturing sulfide-based solid electrolyte

[0087] A method for manufacturing a sulfide-based solid electrolyte according to another embodiment of the present invention may include a step (S1) of preparing a precursor solution by introducing a precursor including an alkali metal sulfide, a phosphorus sulfide, a halogen compound, a first compound, and a second compound into a solvent; a step (S2) of milling the precursor solution to manufacture an intermediate product; a step (S3) of drying the intermediate product; and a step (S4) of heat-treating the dried intermediate product.

[0088] In the step (S1) of preparing a precursor solution, the precursor may include an alkali metal sulfide, a phosphorus sulfide, or a halide. The alkali metal sulfide is not particularly limited as long as it is used in the art for producing a sulfide-based solid electrolyte. For example, the alkali metal sulfide may be lithium sulfide (Li2S), sodium sulfide (Na2S), or potassium sulfide (K2S), and preferably lithium sulfide (Li2S).

[0089] The phosphosulfide is not particularly limited as long as it is used in the manufacture of sulfide-based solid electrolytes in the art. For example, the phosphosulfide may be diphosphorus pentasulfide (P2S5).

[0090] The halogen compound is not particularly limited as long as it is used in the art for manufacturing a sulfide-based solid electrolyte. For example, it may include one or more substances selected from the group consisting of lithium bromide (LiBr), lithium chloride (LiCl), lithium iodide (LiI), and lithium fluoride (LiF). Alternatively, the halogen compound may include two substances, for example, lithium bromide (LiBr) and lithium iodide (LiI) may be used together.

[0091] If the alkali metal sulfide is lithium sulfide (Li2S), the phosphorus sulfide is diphosphorus pentasulfide (P2S5), and the halogen compound is lithium bromide (LiBr) and lithium iodide (LiI), there is no particular limitation as long as the amounts are those used in the manufacture of sulfide-based solid electrolytes in the art. For example, the molar ratio of lithium sulfide (Li2S): diphosphorus pentasulfide (P2S5): lithium bromide (LiBr): lithium iodide (LiI) may be 6:2:1:1. The lithium sulfide (Li2S)-phosphorus pentasulfide (P2S5)-based lithium secondary battery solid electrolyte has higher ionic conductivity than the oxide-based solid electrolyte, and therefore, the content of lithium sulfide (Li2S) needs to be about 60 mol% or more in the starting material. However, when the content of lithium sulfide (Li2S) is excessive, the amount of lithium sulfide (Li2S) remaining in the final glass-ceramic increases, which increases moisture reactivity and reactivity with the active material interface, and lowers electrochemical stability. Therefore, the above-described mixing ratio may be the optimal ratio for improving ionic conductivity while reducing the content of lithium sulfide (Li2S) remaining in the final glass-ceramic.

[0092] The precursor comprising alkali metal sulfide, phosphorus sulfide, or halide may be replaced with a precursor further comprising the first compound and the second compound in reduced amounts.

[0093] The first compound may include aluminum oxide (Al2O3), aluminum sulfide (Al2S3), aluminum chloride (AlCl3), boron sulfide (B2S3), boron oxide (B2O3), or boron pentoxide (B2O5), and by doping a Group 13 element (M) in the agilorhodite crystal structure by introducing the first compound, a side reaction in which Li-S bonds are replaced with Li-O bonds can be prevented.

[0094] If the Group 13 element (M) is added in an amount less than the above range based on the entire precursor, the BS3 triangle structure may be implemented too little, resulting in minimal effect, and it may be difficult to suppress the generation of hydrogen sulfide gas. If the Group 13 element (M) is added in an amount exceeding the above range based on the entire precursor, the parent structure may collapse, resulting in the generation of impurities, which may result in a decrease in ionic conductivity.

[0095] The second compound may include lithium oxide (Li2O) or diphosphorus pentoxide (P2O5), and by doping oxygen elements (O) in the agilorodite crystal structure through the introduction of the second compound, a side reaction in which PS bonds are replaced with PO bonds can be prevented.

[0096] At this time, in order to replace the lithium (Li) element, a sulfide precursor including a Group 13 element (M), a divalent element, and a tetravalent element, which are cheaper than lithium sulfide (Li2S), can be used instead of the expensive lithium sulfide (Li2S). By using a sulfide precursor using a Group 13 element (M), a divalent element, and a tetravalent element, the amount of expensive lithium sulfide (Li2S) used can be reduced by a small amount, thereby improving the price competitiveness of the material.

[0097] However, when the lithium element (Li) occupying the A site of the agilodite compound is partially replaced using a divalent element precursor, the overall structure of the sulfide-based solid electrolyte having the agilodite structure may change, and when the lithium element (Li) occupying the A site of the agilodite compound is partially replaced using a tetravalent element precursor, tetravalent elements that can be used as precursors, such as silicon (Si) and germanium (Ge), are more expensive than group 13 elements (M), making it difficult to secure economic feasibility.

[0098] That is, the price competitiveness of the sulfide-based solid electrolyte according to one embodiment of the present invention can be improved by replacing part of the crystal structure with a Group 13 element (M) and a divalent element.

[0099] At this time, the first compound and the second compound can be doped simultaneously. This has a lower synthesis energy compared to doping a Group 13 element (M) and an oxygen element (O) with one type of substance, and the optimal ratio can be controlled through additional doping of cations or anions.

[0100] The solvent can be a nonpolar solvent that dissolves the precursors to prepare a precursor solution. The solvent is not particularly limited as long as it is used in the art for manufacturing sulfide-based solid electrolytes. For example, the solvent may be one or more selected from the group consisting of heptane, hexane, cyclohexane, and toluene.

[0101] In the step (S2) of milling a precursor solution to produce an intermediate product, the milling method of the precursor solution may be performed using a ball, such as a planetary milling method, a ball milling method, a bead mill method, a turbo mill method, or a disk mill method. The milling may form an intermediate product by mixing and grinding the precursor. At this time, the intermediate product may be a sulfide-based amorphous solid electrolyte. The ball milling may be performed at 250 rpm to 350 rpm for 65 to 78 hours.

[0102] The step (S2) of milling the precursor solution to produce an intermediate product can be performed for 5 to 40 hours. Specifically, the lower limit of the milling time can be 5 hours, 10 hours, 15 hours, or 20 hours, and the upper limit of the milling time can be 40 hours, 35 hours, 30 hours, or 25 hours. If the milling time is less than 5 hours, mixing is not performed properly, making it impossible to produce an amorphous solid electrolyte with a consistent composition. If the milling time exceeds 40 hours, there is a concern that the temperature at which crystallinity locally increases may exceed 170°C. Therefore, if the milling time satisfies the above range, an amorphous solid electrolyte with a consistent composition and uniformity can be produced.

[0103] The balls used in milling assist in dispersion by transmitting impact energy to the precursor during mixing and crushing of the precursor, and the mass and size of the balls may affect the mixing and crushing. For example, the balls may include at least one selected from the group consisting of glass, alumina, zirconia, and combinations thereof, and zirconia balls are preferably used.

[0104] In the step (S2) of manufacturing an intermediate product by milling a precursor solution, the milling can be performed by adjusting the mass ratio of the precursor and the balls to 1:10 to 1:20. If the mass ratio of the precursor and the balls exceeds the above range, it is difficult to mix the precursors, making it difficult to manufacture a sulfide-based amorphous solid electrolyte that satisfies uniformity. If the mass ratio of the precursor and the balls is less than the above range, it may be difficult to grind the precursor. Therefore, if the mass ratio of the precursor and the balls satisfies the above range, mixing and grinding of the precursor can be sufficiently achieved.

[0105] The diameter (size) of the balls used in milling may be 0.5 mm to 5 mm. The diameter (size) of the balls refers to the average particle size based on the volume average, and specifically, the lower limit of the ball diameter may be 0.5 mm, 0.8 mm, 1 mm, 1.5 mm, 2 mm, or 2.5 mm, and the upper limit of the ball diameter may be 5 mm, 4.5 mm, 4 mm, 3.5 mm, or 3 mm. If the diameter (size) of the balls exceeds the above range, the average particle size of the sulfide-based solid electrolyte may be formed to be too large, and if the diameter (size) of the balls is less than the above range, sufficient energy is not transferred to the precursor, making it difficult to synthesize. Therefore, if the diameter (size) of the balls satisfies the above range, a sulfide-based solid electrolyte having an appropriate particle size can be synthesized and milled.

[0106] The step (S3) of drying the intermediate product may correspond to a solvent removal process of evaporating the solvent after the step (S2) of milling the precursor solution to produce the intermediate product. The drying step may be performed at a temperature of 60°C to 100°C for a predetermined period of time. For example, drying may be performed using a spray dryer in an inert atmosphere, vacuum drying, a solvent separator, or centrifugation.

[0107] The step (S4) of heat-treating the dried intermediate product may be performed at a temperature of 400°C to 550°C for 3 to 12 hours under an inert gas atmosphere. The inert gas may be, for example, argon (Ar) gas, but is not limited thereto.

[0108]

[0109] All-solid-state battery

[0110] A sulfide-based solid electrolyte according to one embodiment of the present invention can be used in an all-solid-state battery, and the all-solid-state battery or electrochemical cell can include a cathode, an anode, and a solid electrolyte layer disposed between the cathode and the anode.

[0111] The negative electrode may include a negative electrode current collector and a negative electrode active material layer formed on one surface of the negative electrode current collector.

[0112] The negative electrode active material that may be included in the negative electrode active material layer may include at least one selected from the group consisting of lithium (Li), amorphous carbon, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn).

[0113] A binder that may be included in the negative electrode active material layer can improve the bonding between the negative electrode active material and the conductive material and the bonding to the negative electrode current collector. Examples of the negative electrode binder include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluoroelastomer, and various copolymers thereof.

[0114] A conductive material that can be included in the negative electrode active material layer can be used to further improve the conductivity of the negative electrode active material. The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fiber or metal fiber; metal powders such as fluorocarbon, aluminum, copper, nickel, and silver powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives, carbon nanotubes, and the like.

[0115] The negative electrode current collector may be made of a material that is conductive and does not react with lithium without causing a chemical change in the battery, and may include various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc. having fine irregularities formed on the surface. For example, the negative electrode current collector may include at least one selected from the group consisting of copper (Cu), stainless steel (SS), titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni).

[0116] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on one surface of the positive electrode current collector.

[0117] The cathode active material that can be included in the cathode active material layer may include at least one selected from lithium transition metal oxides such as lithium cobalt oxide (LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium manganese oxide, lithium iron phosphate, nickel sulfide, copper sulfide, lithium sulfide, iron oxide, or vanadium oxide, but is not necessarily limited thereto, and any cathode active material used in the relevant technical field may be used.

[0118] A binder that can be included in the positive electrode active material layer can improve the bonding between the positive electrode active material and the conductive material, as well as the bonding to the positive electrode current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluoroelastomer, and various copolymers thereof.

[0119] A conductive material that can be included in the positive electrode active material layer can be used to further improve the conductivity of the positive electrode active material. The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fiber or metal fiber; metal powders such as fluorocarbon, aluminum, copper, nickel, and silver powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives, and carbon nanotubes.

[0120] The positive electrode current collector may be made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. In addition, the positive electrode current collector may form fine irregularities on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0121] The solid electrolyte layer can be disposed between the negative electrode active material layer and the positive electrode active material layer.

[0122] The solid electrolyte may contain sulfur (S) and have the ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table. The solid electrolyte may be represented by the chemical formula 1.

[0123] Hereinafter, examples are presented to help understand the present invention, but the examples are only illustrative of the present disclosure, and the scope of the present application is not construed as being limited to the examples described below, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present disclosure, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

[0124]

[0125] Example 1-1: Preparation of solid electrolyte

[0126] A precursor solution was prepared by mixing precursors (60 g in total) of lithium sulfide (Li2S), diphosphorus pentasulfide (P2S5), lithium chloride (LiCl), lithium bromide (LiBr), aluminum sulfide (Al2S3), and lithium oxide (Li2O) in heptane, a nonpolar organic solvent. The amounts of aluminum sulfide (Al2S3) and lithium oxide (Li2O) added were adjusted so that the doping ratios of group 13 elements (M) and oxygen elements (O) in the sulfide-based solid electrolyte satisfied the following Table 1.

[0127] Then, an intermediate product was synthesized by ball milling using a 3mm ball. After synthesis, the intermediate product was vacuum dried at 80℃ for 12 hours to remove the organic solvent, and the balls were removed using a 200um sieve. Afterwards, a sulfide-based solid electrolyte was manufactured by heat treatment at 500℃ for 6 hours while maintaining an inert gas atmosphere.

[0128]

[0129] Examples 1-2 to 1-7 and Comparative Example 1-1: Preparation of solid electrolyte

[0130] Examples 1-2 to 1-7 and Comparative Example 1-1 produced sulfide-based solid electrolytes in the same manner as Example 1-1, except that aluminum sulfide (Al2S3) and lithium oxide (Li2O) were added to the precursor of the above-described manufacturing example so that the doping ratio of the Group 13 element (M) and the oxygen element (O) in the sulfide-based solid electrolyte satisfied Table 1 below.

[0131]

[0132] [M] / {[Li]+3[M]} X 100[O] / [S] X 100Chemical Formula Example 1-11.12.0Li 5.224 Al 0.0586 PS 4.312 O 0.088 Cl 1.44 Br 0.16 Example 1-21.42.5Li 5.18 Al 0.073 PS 4.29 O 0.11 Cl 1.44 Br 0.16 Example 1-31.73.0Li 5.118 Al 0.094 PS 4.259 O 0.141 Cl 1.44 Br 0.16 Example 1-40.82.0Li 5.268 Al 0.044 PS 4.312 O 0.088 Cl 1.44 Br 0.16 Example 1-51.42.0Li 5.180 Al 0.073 PS 4.312 O 0.088 Cl 1.44 Br 0.16 Example 1-61.12.5Li 5.224 Al 0.0586 PS 4.29 O 0.11 Cl 1.44 Br 0.16 Example 1-71.13.0Li 5.224 Al 0.0586 PS 4.268 O 0.132 Cl 1.44 Br 0.16 Comparative Example 1-1--Li 5.4PS 4.4 Cl 1.44 Br 0.16

[0133]

[0134] Example 2-1: Manufacturing of a pressurized cell

[0135] The sulfide-based solid electrolyte manufactured in the above Example 1-1 was mixed with heptane, a non-polar organic solvent, 1 mm zirconia balls, and a dispersant (dibutyl ether) to produce a sulfide-based solid electrolyte with a particle size of approximately 1 μm through a high-energy milling machine (Fritsch, P7 line). The ratio of the non-polar organic solvent to the dispersant was 125:1.

[0136] A NCM811 cathode active material having a particle size of 5 μm to 7 μm coated with 0.5 wt% LiNbO3, a sulfide-based solid electrolyte having a particle size of approximately 1 μm, and a carbon black-based conductive material were mixed in a weight ratio of 70:30:2 to manufacture the material.

[0137] A pressurized cell was constructed using Li metal foil as a counter electrode and the solid electrolyte of Comparative Example 1-1, which was not substituted, as a separator layer.

[0138]

[0139] Examples 2-2 to 2-7 and Comparative Example 2-1: Manufacture of pressurized cell

[0140] A pressurized cell was manufactured in the same manner as in Example 2-1, except that the sulfide-based solid electrolyte manufactured in Examples 1-2 to 1-7 and Comparative Example 1-1 was used.

[0141]

[0142] Evaluation Example 1: Measurement of ionic conductivity and compressive density

[0143] The sulfide-based solid electrolytes manufactured according to Examples 1-1 to 1-7 and Comparative Example 1-1 were pressurized at 6.6 tons in a mold-shaped pressure cell with a diameter of 13 mm, and then maintained at a temperature of 30°C in an oven for more than 3 hours. The lithium ion conductivity was measured, and the thickness and weight were measured to determine the compressed density. The ion conductivity and compressed density are shown in Table 2 below.

[0144]

[0145] Ionic Conductivity (mS / cm) Compressed Density (g / cc) Example 1-14.6 1.48 Example 1-24.3 1.60 Example 1-34.0 1.60 Example 1-45.1 41.59 Example 1-55.0 1.63 Example 1-63.4 1.56 Example 1-74.6 1.61 Comparative Example 1-16.4 1.57

[0146]

[0147] Referring to Table 2, it can be confirmed that the sulfide-based solid electrolytes according to Examples 1-1 to 1-7 doped with a Group 13 element (M) and an oxygen element (O) do not have a large difference in ionic conductivity compared to the undoped Comparative Example 1-1. That is, it can be confirmed that when doped with a Group 13 element (M) and an oxygen element (O), the structural stability is maintained, thereby suppressing the generation of hydrogen sulfide gas and minimizing the decrease in ionic conductivity.

[0148]

[0149] Evaluation Example 2: Initial Charge-Discharge Characteristics Evaluation

[0150] Charge and discharge tests were conducted on the pressurized cells of Examples 2-1 to 2-7 and Comparative Example 2-1.

[0151] The results of charge and discharge were compared with those measured once in a 30-degree atmosphere at a current density corresponding to 0.05C.

[0152] At this time, the coulombic efficiency (CCE) in the 1st cycle was derived using the following calculation formula. The results are shown in Table 3 below.

[0153] - Coulomb efficiency (%) = {Discharge capacity in the 1st cycle (mAh / g) / Charge capacity in the 1st cycle (mAh / g)}Х100

[0154]

[0155] Capacity (mAh / g) Coulombic efficiency Charge capacity Discharge capacity Example 2-1 237.40 180.05 75.84 Example 2-2 230.21 180.8 178.54 Example 2-3 251.68 198.69 78.94 Example 2-4 231.46 179.58 77.58 Example 2-5 234.86 186.16 79.26 Example 2-6 230.15 180.34 78.3 Example 2-7 234.96 186.58 79.41 Comparative example 2-1223.05 185.20 79.47

[0156]

[0157] Referring to Table 3 above, it can be confirmed that the cells according to Examples 2-1 to 2-7 have improved electrical conductivity by replacing the sulfide-based solid electrolyte with a Group 13 element and an oxygen element, and thus have a higher initial charge capacity than the undoped Comparative Example 2-1.

[0158] Therefore, when doping with a Group 13 element, structural stability is improved, and even when sulfur combined with lithium is exposed to moisture in the atmosphere, it is prevented from being replaced by oxygen, preventing the generation of hydrogen sulfide gas. In addition, when doping with an oxygen element, since a strong bond, PO, is created, the PS bond is somewhat prevented from being replaced by PO, thereby enhancing atmospheric stability. Accordingly, the decrease in discharge capacity due to charging can be prevented, and the life characteristics can be improved.

Claims

1. A sulfide-based solid electrolyte comprising lithium element (Li), phosphorus element (P), sulfur element (S), and halogen element (Ha), having an argyrodite-based crystal structure, and wherein at least a portion of the crystal structure is doped with a first compound comprising a group 13 element (M) and a second compound comprising an oxygen element (O).

2. In paragraph 1, A sulfide-based solid electrolyte comprising at least one element of Group 13 (M) selected from boron (B), aluminum (Al), gallium (Ga), indium (In), and titanium (Ti).

3. In paragraph 1, The above first compound is a sulfide-based solid electrolyte comprising aluminum oxide (Al2O3), aluminum sulfide (Al2S3), aluminum chloride (AlCl3), boron sulfide (B2S3), boron oxide (B2O3), or boron pentoxide (B2O5).

4. In paragraph 1, The second compound is a sulfide-based solid electrolyte containing lithium oxide (Li2O) or diphosphorus pentoxide (P2O5).

5. In paragraph 1, A sulfide-based solid electrolyte satisfying the following equation 1: <Formula 1> 0.5 ≤ [M] / {[Li]+3[M]} In the above equation 1, [M] represents the number of moles of group 13 elements, and [Li] represents the number of moles of lithium elements.

6. In paragraph 1, A sulfide-based solid electrolyte satisfying the following equation 2: <Formula 2> 2 ≤[O] / [S] X 100 ≤ 3 In the above equation 2, [O] represents the number of moles of oxygen element, and [S] represents the number of moles of sulfur element.

7. In paragraph 1, A sulfide-based solid electrolyte represented by the following chemical formula 1: [Chemical Formula 1] Li (7-x-3a) M (a) P.S. (6-x-b) About (b) Yes (x) In the above chemical formula 1, Ha is F, Cl, Br, I or a combination thereof, M is B, Al, Ga, In, Ti or a combination thereof, 1≤x≤2, 0.025≤a≤0.3, and 0.07≤b≤0.

15.

8. A step (S1) of preparing a precursor solution by introducing a precursor including alkali metal sulfide, phosphorus sulfide, halogen compound, first compound and second compound into a solvent; A step (S2) of milling the precursor solution to produce an intermediate product; A step (S3) of drying the above intermediate product; and A step (S4) of heat-treating the above-described dried intermediate product; A method for producing a sulfide-based solid electrolyte, wherein the first compound and the second compound are doped simultaneously.

9. Including an anode; a cathode; and a solid electrolyte layer positioned between the anode and the cathode, An electrochemical cell, wherein at least one of the positive electrode, negative electrode and solid electrolyte layer comprises a sulfide-based solid electrolyte according to any one of claims 1 to 8.