Sulfide-based solid electrolyte and method for preparing same

Abstract

The present invention relates to a sulfide-based solid electrolyte comprising a lithium element, a phosphorus element, a sulfur element, a halogen element, and a boron-based element while comprising an argyrodite-based compound having an argyrodite crystal structure. The sulfide-based solid electrolyte of the present invention can exhibit improvements in electrochemical stability and stability in the air by substitution of some in the crystal structure with boron-based elements.

Description

Sulfide-based solid electrolyte and its manufacturing method

[0001] The present invention relates to a sulfide-based solid electrolyte and a method for producing the same.

[0002] Lithium secondary batteries have been used in small devices such as mobile phones and laptops, but recently, as they are being put to practical use in medium and large devices such as energy storage systems (ESS) and electric vehicles (EVs), lithium secondary batteries are required to have high energy density and high stability.

[0003] Meanwhile, lithium secondary batteries use organic liquid electrolytes with added lithium salts, so they carry the potential risk of electrolyte leakage as well as fire and explosion.

[0004] Accordingly, interest in all-solid-state batteries that use solid electrolytes rather than liquid electrolytes to improve the safety of lithium secondary batteries has been increasing recently.

[0005] Solid electrolytes are divided into oxide and sulfide types. Sulfide solid electrolytes have higher lithium ion conductivity than oxide solid electrolytes and are stable over a wide voltage range, so sulfide solid electrolytes are mainly used.

[0006] 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) and a combination of two or more of them. 0.5 < x < 2), etc., and at this time, the solid electrolyte composed of LGPS, LPS, or LPSX 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, so the life of the battery is reduced, and the operation of the battery is unstable, such as sulfur meeting with moisture in the air to generate hydrogen sulfide, which is harmful to the human body.

[0007] The present invention provides a stable sulfide-based solid electrolyte whose structure is not deformed or decomposed even after repeated charging and discharging by manufacturing a structurally stable electrolyte.

[0008] One embodiment of the present invention for achieving the above-described purpose relates to a sulfide-based solid electrolyte comprising an agilodite-based compound containing lithium element, phosphorus element, sulfur element, halogen element and boron element and having an agilodite crystal structure.

[0009] The sulfide-based solid electrolyte of the present invention can have improved electrochemical stability and atmospheric stability by substituting a portion of the crystal structure with a boron-based element.

[0010] FIG. 1 is a schematic flowchart illustrating a method for manufacturing a sulfide-based solid electrolyte according to one embodiment of the present invention.

[0011] Figure 2 is a schematic flowchart illustrating a method for manufacturing a sulfide-based solid electrolyte according to another embodiment of the present invention.

[0012] Figure 3 is a graph showing XRD measurement results according to one embodiment.

[0013] Fig. 4 is a graph showing XRD measurement results according to other embodiments.

[0014] One embodiment of the present invention for achieving the above-described purpose relates to a sulfide-based solid electrolyte comprising an agilodite-based compound containing lithium element, phosphorus element, sulfur element, halogen element and boron element and having an agilodite crystal structure.

[0015] The substitution amount of the above boron element may be 0.5 mol% to 5 mol%.

[0016] The above boron-based element may include at least one element selected from boron, aluminum, gallium, and indium.

[0017] The above boron element can suppress the generation of hydrogen sulfide gas by combining with the above sulfur element.

[0018] Another embodiment of the present invention for achieving the above-described object comprises the steps of preparing at least two kinds of precursors including lithium element, phosphorus element, sulfur element, halogen element and boron element, mixing the precursors to produce a precursor mixture and heat treating the precursor mixture, wherein the precursor including the boron element is B2S. 3, Al2S 3, Ga2S3 and The present invention relates to a method for manufacturing a sulfide-based solid electrolyte comprising at least one compound selected from In2S3.

[0019] A step of drying the precursor mixture may be further included before the heat treatment step.

[0020] The precursor containing the above boron element may be added in an amount of 0.5 mol% to 5 mol% relative to the total lithium element.

[0021] In the step of mixing the precursors to create a precursor mixture, the precursors may be mixed through a mechanical milling method or a wet milling method.

[0022] Before describing in detail the preferred embodiments of the present invention below, it should be noted that the terms and words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical spirit of the present invention.

[0023] Throughout this specification, the terms first, second, etc. are used not in a limiting sense but for the purpose of distinguishing one component from another.

[0024] Throughout this specification, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0025] Throughout this specification, 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.

[0026] Throughout this specification, when it is said that a part such as a film, region, component, etc. is on or above another part, it includes not only the case where it is directly on top of the other part, but also the case where another film, region, component, etc. is interposed between them.

[0027] The identifiers used in each step are for convenience of explanation and do not indicate the order of the steps. The steps may be performed in a different order than stated, unless the context clearly dictates otherwise. In other words, the steps may be performed in the same order as stated, substantially simultaneously, or in the opposite order.

[0028] Hereinafter, embodiments of the present invention will be described. However, the scope of the present invention is not limited to the following preferred embodiments, and those skilled in the art can implement various modified forms of the contents described herein within the scope of the present invention.

[0029] The present invention relates to a sulfide-based solid electrolyte and a method for producing the same.

[0030] One embodiment of the present invention relates to a sulfide-based solid electrolyte, and according to this embodiment, the sulfide-based solid electrolyte can have improved electrochemical stability and atmospheric stability by substituting a part of the crystal structure with a boron-based element.

[0031] A sulfide-based electrolyte for an all-solid-state battery according to one embodiment of the present invention can be used in an all-solid-state battery, and the all-solid-state battery can include a cathode, an anode, and a solid electrolyte layer disposed between the cathode and the anode.

[0032] 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.

[0033] 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).

[0034] 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.

[0035] 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.

[0036] 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).

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] The solid electrolyte layer can be disposed between the negative electrode active material layer and the positive electrode active material layer.

[0043] 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. That is, it may include a sulfide-based solid electrolyte.

[0044] A sulfide-based solid electrolyte according to one embodiment of the present invention may include lithium element, phosphorus element, sulfur element, halogen element, and boron element, and may include an agilodite-based compound having an agilodite crystal structure.

[0045] The above-mentioned agrirodite crystal structure may include a crystal structure of a compound having a general formula of, for example, A6BC5D, in which an alkali metal having a single positive charge is included in the A site, phosphorus (P) or arsenic (As) having a pentavalent positive charge is included in the B site, oxygen, sulfur, or selenium (Se) having a double negative charge is included in the C site, and a halogen having a single negative charge is included in the D site. The alkali metal may include lithium, sodium, or potassium, and the halogen may include fluorine, chlorine, bromine, or iodine.

[0046] 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 lithium battery to improve the electrical performance (discharge capacity, discharge efficiency, lifespan, etc.) of the battery.

[0047] 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) The agirodite compounds have the main structure PS4 3- The unit structure consists of phosphorus and sulfur elements. 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 lithium battery, the electrolyte may decompose, deteriorating the battery's lifespan and electrical performance.

[0048] As an optional embodiment, the agilodite compound may further include a boron element, and a portion of the compound having the agilodite crystal may be substituted with the boron element. For example, the agilodite compound may be a compound having an agilodite crystal that includes a lithium (Li) element at an A site, a phosphorus (P) element at a B site, a sulfur (S) element at a C site, and a halogen (Ha) element at a D site, and a portion of the lithium (Li) element occupying the A site of the agilodite crystal structure may be substituted with the boron element [Bo].

[0049] Meanwhile, when a portion of the lithium (Li) element occupying the A site of the agilodite compound is replaced with a boron element [Bo], the agilodite crystal structure is strengthened by forming a [Bo]S3triangle structure that has a very strong bonding force with sulfur (S), thereby making it structurally stable and increasing its density.

[0050] As a specific example, it may include at least one element selected from boron (B), aluminum (Al), gallium (Ga), and indium (In), and the boron-based element [Bo] may be partially substituted with the lithium (Li) element occupying the A site of the agilodite-based compound. At this time, the boron-based element [Bo] may be positioned at the A site of the agilodite-based compound by replacing three lithium (Li) elements occupying the A site of the agilodite-based compound as in the following chemical formula 1, and may have high structural stability by forming a [Bo]S3triangle structure.

[0051] (Chemical formula 1)

[0052] Li (7-x-3y) [Bo tribe] y PS (6-x) Ha x (0.5 <x<2, 0.5mol%<y<5mol%)

[0053] Meanwhile, it can be predicted through the results of DFT (Density functional theory) calculations using a supercomputer that the boron element [Bo] forms a [Bo]S3triangle structure by replacing three lithium (Li) elements occupying the A site of the above-mentioned agarodite compound, thereby exhibiting high structural stability.

[0054] In an optional embodiment, the agarodite compound can be prepared by synthesizing precursors including Li2S, P2S5, LiCl, and LiBr, and the sulfide-based solid electrolyte according to embodiments of the present invention can be synthesized by including a boron element [Bo] in a precursor including Li2S, P2S5, LiCl, and LiBr.

[0055] At this time, the precursors including Li2S, P2S5, LiCl and LiBr can be replaced with precursors including boron elements [Bo] by reducing some of the amount. For example, the precursor including boron elements [Bo] can be replaced in an amount of 0.5 mol% to 5 mol% relative to the entire precursor.

[0056] In an optional embodiment, the boron element [Bo] may include one or more elements selected from boron (B), aluminum (Al), gallium (Ga), and indium (In), and as a specific example, may include the element boron (B) or aluminum (Al).

[0057] For example, the sulfide-based solid electrolyte according to embodiments of the present invention may further include a compound of a boron-based element [Bo] and sulfur (S) in addition to a precursor including Li2S, P2S5, LiCl, and LiBr. As a specific example, the compound of a boron-based element [Bo] and sulfur (S) may include B2S3 or Al2S3.

[0058] At this time, B2S3 or Al2S3 may be added in an amount of 0.2 mol% to 5 mol% based on the total precursor including Li2S, P2S5, LiCl and LiBr, preferably in an amount of 0.5 mol% to 5 mol%, and more preferably in an amount of 0.5 mol% to 1.5 mol%.

[0059] Meanwhile, if B2S3 is added in an amount less than 0.2 mol% based on the entire precursor including Li2S, P2S5, LiCl, and LiBr, 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, which will be described later. In addition, if B2S3 exceeds 5 mol% based on the entire precursor including Li2S, P2S5, LiCl, and LiBr, the parent structure may collapse, resulting in the generation of impurities, which may decrease ionic conductivity.

[0060] Meanwhile, if Al2S3 is added in an amount less than 0.2 mol% based on the entire precursor including Li2S, P2S5, LiCl, and LiBr, the AlS3 triangle structure may be implemented too little, resulting in minimal effect, and it may be difficult to suppress the generation of hydrogen sulfide, which will be described later. In addition, if Al2S3 exceeds 5 mol% based on the entire precursor including Li2S, P2S5, LiCl, and LiBr, the parent structure may collapse, resulting in the generation of impurities, which may decrease ionic conductivity.

[0061] Meanwhile, in the present invention, precursors including Li2S, P2S5, LiCl and LiBr and compounds of boron elements [Bo] and sulfur (S) are described as examples for synthesizing an agilodite compound, but various precursors may be used in the manufacturing process to partially replace the lithium (Li) element occupying the A site of the agilodite compound.

[0062] At this time, in order to replace lithium (Li) element, instead of expensive Li2S precursor, sulfide precursor containing boron elements, divalent elements, and tetravalent elements, which are cheaper than Li2S, can be used. By using sulfide precursors using boron elements, divalent elements, and tetravalent elements, the amount of expensive Li2S used can be reduced by a small amount, thereby improving the price competitiveness of the material.

[0063] However, when the lithium (Li) element 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 (Li) element 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 boron-based elements, making it difficult to secure economic feasibility.

[0064] That is, the price competitiveness of the sulfide-based solid electrolyte according to one embodiment of the present invention can be improved by replacing a portion of the crystal structure with a boron-based element.

[0065] Meanwhile, in the agilodite 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, since a part of the crystal structure is substituted with a boron-based element, among the Li-S bond or PS bond that changes to Li-O or PO bond when it meets moisture in the atmosphere, the weak Li-S bond is partially replaced with a relatively strong Bo-S bond, so that the HS bond is not easily formed due to the strong Bo-S bond, and thus the generation of hydrogen sulfide (H2S) gas is suppressed, and atmospheric stability can be improved.

[0066] As a result, according to embodiments of the present invention, the electrochemical stability and atmospheric stability of the sulfide-based solid electrolyte can be improved by substituting a part of the crystal structure with a boron-based element.

[0067] Another embodiment of the present invention relates to a method for manufacturing a sulfide-based solid electrolyte, and is described with reference to FIG. 1, which summarizes the manufacturing method sequence. According to this embodiment, a sulfide-based solid electrolyte manufactured by the method for manufacturing a sulfide-based solid electrolyte can have improved electrochemical stability and atmospheric stability by substituting a portion of the crystal structure with a boron-based element.

[0068] A method for manufacturing a sulfide-based solid electrolyte according to another embodiment of the present invention may include a step (S100) of preparing two or more precursors including lithium, phosphorus, sulfur, a halogen element, and a boron-based element, a step (S200) of mixing the precursors to create a precursor mixture, and a step (S300) of heat-treating the precursor mixture.

[0069] In the step of preparing a precursor (S100), the precursor may include a lithium compound such as lithium sulfide (Li2S), lithium halide (LiA; A is halogen), or a combination thereof, and may also include a sulfur compound such as phosphorus pentasulfide (P2S5), or a boron compound such as boron sulfide (B2S3) and aluminum sulfide (Al2S3), or a combination thereof.

[0070] In the step (S200) of mixing the precursors to produce a precursor mixture, the precursors may be mixed by a mechanical synthesis method such as mechanical milling or a wet synthesis method using an organic solvent. For example, the mechanical milling may include ball milling, and the ball milling may be performed by any known ball milling device used for high-energy ball milling, such as a vibratory mill, a Z-mill, a planetary ball-mill, an attrition mill, a SPEX mill, a low-temperature pulverizer, a friction mill, a shaker mill, a stirred ball mill, a mixer ball mill, a vertical and horizontal attritor, and is not particularly limited thereto, and any method that can be used in the technical field as a method of bringing the precursors into contact using a machine may be used.

[0071] Additionally, as an example, the wet synthesis method may be a method in which the precursor is mixed with a reactive or non-reactive solvent by ball milling or planetary milling. As a specific example, the precursor may be mixed with a non-reactive solvent, heptane, by ball milling using balls of 2 mm to 5 mm.

[0072] In the step (S300) of heat-treating the precursor mixture, the heat treatment may be performed at a temperature of 400 to 550°C for 5 to 24 hours under an Ar atmosphere.

[0073] Referring to FIG. 2, a method for manufacturing a sulfide-based solid electrolyte may include a step (S101) of preparing two or more precursors including lithium, phosphorus, sulfur, halogen elements, and boron elements, a step (S201) of mixing the precursors to create a precursor mixture, and a step (S301) of heat-treating the precursor mixture, and may further include a step (S401) of drying the precursor mixture before the heat-treating step.

[0074] In the step (S101) of preparing two or more precursors including lithium, phosphorus, sulfur, halogen elements, and boron elements, the precursor may include lithium compounds such as lithium sulfide (Li2S), lithium halide (LiA; A is halogen), or a combination thereof, and may also include sulfur compounds such as phosphorus pentasulfide (P2S5), or boron compounds such as boron sulfide (B2S3), aluminum sulfide (Al2S3), or a combination thereof.

[0075] In the step (S201) of mixing the precursors to produce a precursor mixture, the precursors may be mixed by a mechanical synthesis method such as mechanical milling or a wet synthesis method using an organic solvent. For example, the mechanical milling may include ball milling, and the ball milling may be performed by any known ball milling device used for high-energy ball milling, such as a vibratory mill, a Z-mill, a planetary ball-mill, an attrition mill, a SPEX mill, a low-temperature pulverizer, a friction mill, a shaker mill, a stirred ball mill, a mixer ball mill, a vertical and horizontal attritor, and is not particularly limited thereto, and any method available in the technical field as a method of bringing the precursors into contact with each other using a machine may be used.

[0076] Additionally, as an example, the wet synthesis method may be a method in which a precursor is mixed with a reactive or non-reactive solvent by ball milling or planetary milling. As a specific example, the precursor may be mixed with a non-reactive solvent, heptane, by ball milling using balls of 0.1 mm to 5 mm.

[0077] In the step (S301) of heat-treating the precursor mixture, the heat treatment may be performed at a temperature of 400°C to 550°C for 5 to 24 hours under an Ar atmosphere.

[0078] In the step of drying the precursor mixture (S401), the mixed precursor may be vacuum-dried at 60°C to 120°C to remove the organic solvent. In addition, in the step of generating the precursor mixture (S201), balls of 0.1 mm to 5 mm introduced may be separated from the dried precursor mixture using a 200 μm sieve.

[0079]

[0080] [Example 1]

[0081] Li2S, P2S5, LiCl, and LiBr were prepared as precursors, and B2S3 corresponding to 0.8 mol% based on the total prepared precursor was added to adjust the mass of the total precursor to 60 g.

[0082] After performing ball milling using a 3 mm ball with heptane, a non-reactive solvent, the ball-milled solution was vacuum-dried at 80 degrees to remove the organic solvent, and then the balls used in ball milling were removed using a 200 μm sieve to obtain precursor powder.

[0083] Afterwards, the precursor powder was heat-treated at 500 degrees for 6 hours to manufacture Example 1.

[0084]

[0085] [Example 2]

[0086] It was manufactured in the same manner as Example 1, except that 1.1 mol% of B2S3 was added to the precursor.

[0087]

[0088] [Example 3]

[0089] It was manufactured in the same manner as Example 1, except that 1.4 mol% of B2S3 was added to the precursor.

[0090]

[0091] [Example 4]

[0092] It was manufactured in the same manner as Example 1, except that 1.6 mol% of B2S3 was added to the precursor.

[0093]

[0094] [Example 5]

[0095] Li2S, P2S5, LiCl, and LiBr were prepared as precursors, and Al2S3 corresponding to 0.8 mol% based on the total prepared precursor was added to adjust the total mass of the precursor to 60 g.

[0096] After performing ball milling using a 3 mm ball with heptane, a non-reactive solvent, the ball-milled solution was vacuum-dried at 80 degrees to remove the organic solvent, and then the balls used in ball milling were removed using a 200 μm sieve to obtain precursor powder.

[0097] Afterwards, the precursor powder was heat-treated at 500 degrees for 6 hours to manufacture Example 1.

[0098]

[0099] [Example 6]

[0100] It was manufactured in the same manner as Example 5, except that 1.1 mol% of Al2S3 was added to the precursor.

[0101]

[0102] [Example 7]

[0103] It was manufactured in the same manner as Example 1, except that 1.4 mol% of Al2S3 was added to the precursor.

[0104]

[0105] [Example 8]

[0106] It was manufactured in the same manner as Example 1, except that 1.6 mol% of Al2S3 was added to the precursor.

[0107]

[0108] [Comparative example]

[0109] Li2S, P2S5, LiCl, and LiBr were prepared as precursors, and the mass of the precursors was adjusted to 60 g.

[0110] After performing ball milling using a 3 mm ball with heptane, a non-reactive solvent, the ball-milled solution was vacuum-dried at 80 degrees to remove the organic solvent, and then the balls used in ball milling were removed using a 200 μm sieve to obtain precursor powder.

[0111] Afterwards, a comparative example was manufactured by heat-treating the precursor powder at 500 degrees for 6 hours.

[0112]

[0113] [Manufacturing example]

[0114] NCM811 cathode active material having a particle size of 8 to 10 μm coated with 1 wt% LiNbO3, electrolyte synthesized by the methods of Examples 1 to 8 and Comparative Examples, and carbon black-based conductive material were mixed in a mortar and pestle at a weight ratio of 70:30:3.

[0115] Li-In is used as the counter electrode and unsubstituted Li is used as the separator layer. 5.5 PS 4.5 Cl 0.75 Br 0.75 A pressurized cell was manufactured using an electrolyte.

[0116]

[0117] [Experimental Example 1]

[0118] Ionic conductivity was measured using a pressure cell. At this time, the thickness and weight of the pressure pellet created during the pressure cell measurement were measured together to determine the compressed density.

[0119]

[0120] [Experimental Example 2]

[0121] Charge and discharge tests were conducted using a pressurized cell, and the charge and discharge were measured at a current density corresponding to 0.05 C at 30°C.

[0122]

[0123] Fig. 3 is a graph showing the results of XRD measurement according to one embodiment.

[0124] Referring to Fig. 3, a graph measuring XRD for Examples 1 to 4 in which B2S3 was added to the precursor can be confirmed along with a comparative example.

[0125] Looking at the graph in Fig. 3, it can be confirmed that Examples 1 to 4, in which B2S3 was added to the precursor, a peak is formed at the same point as the comparative example in which nothing was added. In other words, it can be seen that Examples 1 to 4, in which B2S3 was added to the precursor, all formed an agarodite structure.

[0126]

[0127] SampleIonic conductivityCompressed densityComparative Example 7.54 mS / cm1.7838Example 17.27 mS / cm1.798Example 27.34 mS / cm1.8011Example 36.65 mS / cm1.8171Example 44.88 mS / cm1.8425

[0128] Table 1 shows the ionic conductivity and compaction density of Examples 1 to 4 and Comparative Examples measured by the method of Experimental Example 1. It can be confirmed that the ionic conductivity of Example 2, to which 1.1 mol% of B2S3 precursor was added, is 7.34 mS / cm, which is similar to the ionic conductivity of 7.54 mS / cm of the Comparative Example, to which nothing was added. In addition, it can be seen that the compaction density increases from 1.798 to 1.8425 from Example 1 to Example 4. That is, it can be seen that the more B2S3 precursor is added, the more the compaction density of the sulfide-based solid electrolyte increases. From this, it can be confirmed that as the amount of lithium element occupying the A site of the agilodite-based compound is replaced by boron (B), the more [Bo]S3triangle structures with very strong bonding forces with sulfur are formed, thereby strengthening the agilodite crystal structure, making it structurally stable and increasing the density.

[0129]

[0130] SampleCapacityCoulombic efficiency (%)Charge (mAh / g)Discharge (mAh / g)Comparative Example 2 14.35 169.4 279.04Example 1 227.85 172.0 975.53Example 2 232.65 182.3 178.36Example 3 235.28 179.97 76.49Example 4 222.65 172.4 977.47

[0131] Table 2 shows the charge / discharge results of Examples 1 to 4 and Comparative Examples measured by the method of Experimental Example 2. Referring to Table 2, it can be seen that Examples 1 to 3 show a tendency for the structurally stabilized portion to increase and the degree of capacity expression to increase as the doping amount of boron (B) increases. As confirmed in Table 1 above, Examples 1 to 4 show a tendency for the ionic conductivity to decrease as the doping amount of boron (B) increases. However, as can be seen in Table 2, it can be confirmed that similar Coulombic efficiency and high discharge capacity are expressed as compared to the Comparative Example despite the decrease in ionic conductivity.

[0132] That is, in the case of boron (B) having a small element size and a large binding force, when a pressurized cell is manufactured using Examples 1 to 4, the ionic conductivity decreases linearly, but in the case of Example 2 where B2S3 corresponding to about 1.1 mol% is added, it can be confirmed that the ionic conductivity does not decrease significantly and a high discharge capacity and high Coulombic efficiency are exhibited.

[0133] Fig. 4 is a graph showing XRD measurement results according to another embodiment.

[0134] Referring to Fig. 4, a graph of XRD measurements of Examples 5 to 8 in which Al2S3 was added to the precursor can be confirmed along with a comparative example.

[0135] Looking at the graph of Fig. 4, it can be confirmed that Examples 5 to 8, in which Al2S3 was added to the precursor, a peak is formed at the same point as the comparative example in which nothing was added. In other words, it can be seen that Examples 5 to 8, in which Al2S3 was added to the precursor, all formed an agarodite structure.

[0136]

[0137] SampleIonic conductivityCompressed densityComparative Example 7.54 mS / cm1.7838Example 57.14 mS / cm1.8049Example 66.43 mS / cm1.7975Example 76.71 mS / cm1.8Example 86.99 mS / cm1.8142

[0138] Table 3 shows the ionic conductivity and compaction density of Examples 5 to 8 and the Comparative Example measured by the method of Experimental Example 1. It can be confirmed that the ionic conductivity of Example 5, with 0.8 mol% of Al2S3 precursor added, is 7.14 mS / cm, which is similar to the ionic conductivity of 7.54 mS / cm of the Comparative Example, with nothing added. In addition, when comparing Examples 5 and 8, it can be seen that the compaction density increases from 1.8049 to 1.8142. This shows that the compaction density of the sulfide-based solid electrolyte can increase depending on the amount of Al2S3 precursor added. From this, it can be confirmed that as the amount of lithium (Li) element occupying the A site of the agilodite-based compound is replaced by aluminum (Al), more [Bo]S3triangle structures with very strong bonding force with sulfur are formed, thereby strengthening the agilodite crystal structure, making it structurally stable and increasing the density.

[0139]

[0140] SampleCapacityCoulombic efficiency (%)Charge (mAh / g)Discharge (mAh / g)Comparative Example 2 14.35 169.4 279.04Example 5 230.04 177.5 4 77.18Example 6 224.74 173.15 77.04Example 7 219.22 169.0 177.10Example 8 234.29 183.5 9 78.36

[0141] Table 4 shows the charge / discharge results of Examples 5 to 8 and Comparative Examples measured by the method of Experimental Example 2. Referring to Table 4, it can be seen that Examples 5 to 8 show a tendency for the portion of the structure to be stabilized to increase and the degree of capacity expression to increase as the doping amount of aluminum (Al) increases. As confirmed in Table 3 above, Examples 5 to 8 show a tendency for the ionic conductivity to decrease as the doping amount of aluminum (Al) increases. However, as can be seen in Table 4, it can be confirmed that they show a tendency to exhibit similar Coulombic efficiency and high discharge capacity to the Comparative Examples despite the decrease in ionic conductivity.

[0142] That is, in the case of aluminum (Al) having a relatively large element size and relatively small bonding force compared to boron (B), when manufacturing a pressurized cell using Examples 5 to 8, it can be confirmed that Examples 5 to 7, in which 0.8 mol% to 1.4 mol% of Al2S3 was added, showed a decrease in ionic conductivity to some extent, but Example 8, in which 1.6 mol% of Al2S3 was added, showed a characteristic of high ionic conductivity, high discharge capacity, and high coulombic efficiency.

[0143] As a result, according to embodiments of the present invention, the sulfide-based solid electrolyte can have improved electrochemical stability and atmospheric stability, and electrochemical characteristics, by substituting a portion of the crystal structure with a boron-based element.

[0144] While the present invention has been described with reference to the embodiments illustrated in the drawings, these are merely exemplary, and those skilled in the art will appreciate that various modifications and variations of the embodiments are possible. Therefore, the true scope of technical protection of the present invention should be determined by the technical spirit of the appended claims.

Claims

1. Containing an agarrodite compound containing lithium elements, phosphorus elements, sulfur elements, halogen elements and boron elements, and having an agarrodite crystal structure; The above-mentioned agarrodite compound is a sulfide-based solid electrolyte in which a portion of the lithium element is substituted with the boron element in the agarrodite crystal structure.

2. In paragraph 1, A sulfide-based solid electrolyte having a substitution amount of the boron-based element of 0.5 mol% to 5 mol%.

3. In paragraph 1, The above boron-based element is a sulfide-based solid electrolyte containing at least one element selected from boron, aluminum, gallium, and indium.

4. In paragraph 1, The above boron element is a sulfide-based solid electrolyte that combines with the sulfur element to suppress the generation of hydrogen sulfide gas.

5. A step of preparing at least two kinds of precursors including lithium element, phosphorus element, sulfur element, halogen element and boron element; a step of mixing the above precursors to produce a precursor mixture; and comprising a step of heat treating the precursor mixture; The precursor containing the above boron element is B2S 3, Al2S 3, Ga2S3 and A method for producing a sulfide-based solid electrolyte comprising at least one compound selected from In2S3.

6. In paragraph 5, A method for producing a sulfide-based solid electrolyte further comprising a step of drying the precursor mixture before the heat treatment step.

7. In paragraph 5, A method for producing a sulfide-based solid electrolyte, wherein the precursor containing the above boron-based element is added in an amount of 0.5 mol% to 5 mol% relative to the total lithium elements.

8. In paragraph 5, A method for producing a sulfide-based solid electrolyte, wherein the precursors are mixed through a mechanical milling method or a wet milling method in a step of generating a precursor mixture by mixing the precursors.

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