Solid electrolyte and all-solid-state battery including the same

Abstract

The present invention relates to a sulfide-based solid electrolyte including a compound containing lithium (Li), phosphorus (P), sulfur (S), and a halogen element (D), and having an argyrodite-based crystal structure, at least a portion of the crystal structure being doped with oxygen (O) and a transition metal element (M) consisting of Nb, Ta, V, or a combination thereof.

Description

Technical Field

[0001] This invention relates to a solid electrolyte and an all-solid-state battery including the same. Background Technology

[0002] With increasing attention being paid to the safety issues and energy density of high-capacity batteries, all-solid-state batteries are attracting much attention as the next generation of batteries.

[0003] The all-solid-state battery replaces the explosive liquid electrolyte with a solid electrolyte, thus eliminating the use of flammable solvents within the battery and preventing fires or explosions caused by reactions such as decomposition similar to those in traditional electrolytes. Therefore, it is a battery that can ensure battery safety.

[0004] As the solid electrolyte used in the all-solid-state battery, inorganic solid electrolytes are usually used. Among them, sulfide solid electrolytes with Argyrodite crystal structure are being studied in various ways due to their high ionic conductivity.

[0005] On the other hand, in the case of all-solid-state batteries, the energy density of the battery relative to its mass and volume can be improved because lithium metal or lithium alloy can be used as the negative electrode material.

[0006] However, when using lithium metal or lithium alloy as the negative electrode material, repeated charging and discharging can cause lithium dendrites to form on the surface of the negative electrode, which can lead to a short circuit in the battery. Summary of the Invention

[0007] (a) Technical problems to be solved Therefore, the object of the present invention is to provide a solid electrolyte that is a sulfide-based solid electrolyte having an Argyrodite-based crystal structure, capable of suppressing the formation of lithium dendrites, and an all-solid-state battery including the present invention.

[0008] (II) Technical Solution One embodiment of the present invention provides a sulfide-based solid electrolyte comprising a compound containing lithium (Li), phosphorus (P), sulfur (S) and halogen element (D) and having an Argyrodite-based crystal structure, wherein at least a portion of the crystal structure is doped with oxygen (O) and a transition metal element (M) consisting of Nb, Ta, V or a combination thereof.

[0009] The molar ratio of transition metal element (M) to phosphorus (P) in the compound ([M] / [P]) can be from 0.01 to 1.1.

[0010] The molar ratio of oxygen (O) to phosphorus (P) in the compound ([O] / [P]) can be from 0.03 to 2.5.

[0011] The molar ratio of lithium (Li) to phosphorus (P) in the compound ([Li] / [P]) can be from 5.5 to 6.5.

[0012] The molar ratio of sulfur (S) to phosphorus (P) in the compound ([S] / [P]) can be from 4.5 to 5.5.

[0013] The molar ratio of halogen (D) to phosphorus (P) in the compound ([D] / [P]) can be from 0.5 to 1.5.

[0014] The compound exhibits a first peak in the range of 15.4°≤2θ≤15.8° during X-ray diffraction (XRD) pattern analysis.

[0015] The compound exhibits a second peak in the range of 25.4°≤2θ≤25.7° during X-ray diffraction (XRD) pattern analysis.

[0016] The compound exhibits a third peak in the range of 34.7°≤2θ≤34.9° during X-ray diffraction (XRD) pattern analysis.

[0017] The ratio of the intensity of the second peak to the intensity of the first peak of the compound can be from 2.4 to 2.9.

[0018] The ratio of the intensity of the third peak to the intensity of the first peak of the compound can be from 0.03 to 0.8.

[0019] The compound can be represented by the following chemical formula 1.

[0020] [Chemical Formula 1] Li 7a-ax P a M 2-2a S 6a-ax O 5-5a D ax In the chemical formula 1, 1≤x≤2, 0.65≤a≤0.995, M is a transition metal element composed of Nb, Ta, V or a combination thereof, and D is a halogen element composed of F, Cl, Br, I or a combination thereof.

[0021] In the chemical formula 1, the value can be 0.8 ≤ a ≤ 0.96.

[0022] Another embodiment of the present invention provides an all-solid-state battery, which includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer, wherein at least one of the positive electrode layer, the negative electrode layer, and the solid electrolyte layer includes the aforementioned solid electrolyte.

[0023] (III) Beneficial Effects According to one embodiment of the present invention, the solid electrolyte has an Argyrodite-based crystal structure, at least a portion of which is doped with oxygen (O) and a transition metal element (M) consisting of Nb, Ta, V, or a combination thereof. Therefore, when applied to all-solid-state batteries using lithium metal or lithium alloy anodes, the formation of lithium dendrites can be suppressed, thereby preventing battery short circuits caused by excessive lithium dendrite formation. Attached Figure Description

[0024] Figure 1 These are X-ray diffraction pattern analysis results of the solid electrolytes manufactured according to Examples 1 to 4. Detailed Implementation

[0025] The terms "first," "second," and "third," etc., are used to describe various parts, components, regions, layers, and / or segments, but are not limited thereto. These terms are only used to distinguish one part, component, region, layer, or segment from other parts, components, regions, layers, or segments. Therefore, without departing from the scope of the invention, the first part, component, region, layer, or segment described below may be referred to as the second part, component, region, layer, or segment.

[0026] The technical terms used herein are for reference only to specific embodiments and are not intended to limit the invention. The singular forms used herein include the plural forms unless the context clearly indicates otherwise. The word "comprising" as used in this specification embodies a particular feature, region, integer, step, operation, element, and / or component, and does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0027] When referring to one part as being "above" or "on top of" another part, it can be directly above or on the other part, or it can be accompanied by other parts. Conversely, when referring to one part as being "directly above" another part, no other parts are involved.

[0028] Unless otherwise defined, all terms, including technical and scientific terms used herein, shall have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms as defined in commonly used dictionaries are further interpreted as having meanings consistent with relevant technical literature and current disclosure, and should not be construed as having ideal or highly formal meanings unless otherwise defined.

[0029] In addition, unless otherwise specified, % means weight, 1 ppm is 0.0001 weight.

[0030] In this specification, the term "combination thereof" as described in the Markush form means a mixture or combination of one or more of the groups of constituent elements described in the Markush form, meaning including any one or more of the groups of constituent elements.

[0031] The embodiments of the present invention will now be described in detail to enable those skilled in the art to readily implement the invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

[0032] 1. Solid electrolytes The solid electrolyte according to one embodiment of the present invention contains lithium (Li), phosphorus (P), sulfur (S) and halogen elements (D), and includes compounds having an Argyrodite-based crystal structure. Therefore, excellent ionic conductivity can be achieved.

[0033] At this point, at least a portion of the sulfide-germanium ore-based crystal structure of the compound is doped with oxygen (O) and a transition metal element (M) consisting of Nb, Ta, V, or a combination thereof. In this specification, "doping" refers not only to replacing a portion of the elements in the compound with a new element, but also extends to the point where the doped element becomes a constituent element of the compound's crystal phase.

[0034] Therefore, when applied to all-solid-state batteries using lithium metal or lithium alloy anodes, it can suppress the formation of lithium dendrites during charging and discharging. This prevents battery short circuits caused by excessive lithium dendrite formation. Furthermore, it can improve the battery's capacity characteristics.

[0035] More specifically, the molar ratio of transition metal element (M) to phosphorus (P) in the compound ([M] / [P]) can be from 0.01 to 1.1, and more specifically from 0.08 to 0.4. If the molar ratio of transition metal element (M) to phosphorus (P) ([M] / [P]) is too small, the dendrite formation suppression effect or the battery capacity improvement effect caused by the aforementioned transition metal element doping may be negligible. If the molar ratio of transition metal element (M) to phosphorus (P) ([M] / [P]) is too large, M acts as an impurity phase, resulting in a worsening of the lithium dendrite formation suppression effect and battery capacity improvement effect, and the large deformation of the silver-germanium sulfide crystal structure leads to a deterioration of ionic conductivity.

[0036] The molar ratio of oxygen (O) to phosphorus (P) in the compound ([O] / [P]) can be from 0.03 to 2.5, more specifically from 0.2 to 0.8. If the molar ratio of oxygen (O) to phosphorus (P) ([O] / [P]) is too small, the dendrite formation suppression effect or the battery capacity improvement effect caused by the aforementioned oxygen doping may be small. If the molar ratio of oxygen (O) to phosphorus (P) ([O] / [P]) is too large, the lithium dendrite formation suppression effect and the battery capacity improvement effect will actually worsen, and the large deformation of the silver sulfide germanite crystal structure will lead to a deterioration in ionic conductivity.

[0037] The molar ratio of lithium (Li) to phosphorus (P) in the compound ([Li] / [P]) can be from 5.5 to 6.5, more specifically from 5.8 to 6.2. When the molar ratio of lithium (Li) to phosphorus (P) ([Li] / [P]) meets the range described above, the sulfogermanium ore crystal structure is fully maintained, thereby preferably achieving the ionic conductivity of the solid electrolyte or the electrochemical characteristics of the battery.

[0038] The molar ratio of sulfur (S) to phosphorus (P) in the compound ([S] / [P]) can be from 4.5 to 5.5, more specifically from 4.8 to 5.2. When the molar ratio of sulfur (S) to phosphorus (P) ([S] / [P]) meets the above range, the crystal structure of the silver-germanium sulfide system is fully maintained, thereby preferably achieving the ionic conductivity of the solid electrolyte or the electrochemical characteristics of the battery.

[0039] The molar ratio of halogen (D) to phosphorus (P) in the compound ([D] / [P]) can be from 0.5 to 1.5, more specifically from 0.8 to 1.2. When the molar ratio of halogen (D) to phosphorus (P) ([D] / [P]) meets the above range, the sulfogermanium ore crystal structure is fully maintained, thereby preferably achieving the ionic conductivity of the solid electrolyte or the electrochemical characteristics of the battery.

[0040] Furthermore, there are no particular restrictions on the halogen element (D) as long as it is a halogen element, such as F, Cl, Br, I or a combination thereof.

[0041] However, from the perspective of stabilizing the structure of solid electrolytes, ease of synthesis, and reduction of process costs, the halogen element (D) can be Cl.

[0042] Furthermore, from the perspective of preferably achieving ionic conductivity, the halogen element (D) may also include any one or more elements selected from Br and I other than Cl, and more specifically, the halogen element (D) may include Cl and Br.

[0043] On the other hand, the compound exhibits a first peak in the range of 15.4° ≤ 2θ ≤ 15.8° during X-ray diffraction (XRD) pattern analysis. This first peak within this range can be a peak found in Argyrodite-based crystal structures.

[0044] The compound exhibits a second peak in the range of 25.4° ≤ 2θ ≤ 25.7° during X-ray diffraction (XRD) pattern analysis. This second peak within this range may be a characteristic peak resulting from the addition of oxygen (O) and transition metal elements (M) consisting of Nb, Ta, V, or combinations thereof to the solid electrolyte compound according to the invention.

[0045] The compound exhibits a third peak in the range of 34.7° ≤ 2θ ≤ 34.9° during X-ray diffraction (XRD) pattern analysis. This third peak within this range can also be a characteristic peak resulting from the addition of oxygen (O) and transition metal elements (M) consisting of Nb, Ta, V, or combinations thereof to the solid electrolyte compound according to the invention.

[0046] At this point, the ratio of the second peak intensity to the first peak intensity of the compound can be 2.4 to 2.9, more specifically 2.55 to 2.73. When the ratio of the second peak intensity to the first peak intensity satisfies the aforementioned range, oxygen (O) and transition metal elements (M) composed of Nb, Ta, V, or combinations thereof are doped in appropriate amounts, thereby optimally achieving the aforementioned dendrite formation suppression effect, battery capacity characteristic improvement effect, and good ionic conductivity effect.

[0047] The ratio of the intensity of the third peak to the intensity of the first peak in the compound can be from 0.03 to 0.8, more specifically from 0.3 to 0.65. When the ratio of the intensity of the third peak to the intensity of the first peak meets the range, oxygen (O) and transition metal elements (M) consisting of Nb, Ta, V, or combinations thereof are doped in appropriate amounts, thereby optimally achieving the aforementioned dendrite formation suppression effect, battery capacity characteristic improvement effect, and good ionic conductivity effect.

[0048] The compound can be more specifically represented by the following chemical formula 1.

[0049] [Chemical Formula 1] Li 7a-ax P a M 2-2a S 6a-ax O 5-5a D ax In the chemical formula 1, 1≤x≤2, 0.65≤a≤0.995, M is a transition metal element composed of Nb, Ta, V or a combination thereof, and D is a halogen element composed of F, Cl, Br, I or a combination thereof.

[0050] In the aforementioned chemical formula 1, x is 1 ≤ x ≤ 2. If x is too small, the ionic conductivity of the solid electrolyte may deteriorate. If x is too large, the ionic conductivity of the solid electrolyte is improved, but electrochemical properties such as water stability and battery capacity characteristics may deteriorate.

[0051] In the aforementioned chemical formula 1, 'a' is 0.65 ≤ a ≤ 0.995, more specifically, it can be 0.8 ≤ a ≤ 0.96. 'a' is inversely proportional to the amount of transition metal element or oxygen doping. Therefore, if 'a' is too small, the dendrite formation suppression effect and the battery capacity improvement effect may actually worsen with excessive doping of transition metal element or oxygen, and the ionic conductivity of the solid electrolyte may deteriorate. If 'a' is too large, the dendrite formation suppression effect or the battery capacity improvement effect caused by transition metal element or oxygen doping may be negligible.

[0052] 2. Solid electrolyte manufacturing method Another embodiment of the present invention provides a method for manufacturing a sulfide-based solid electrolyte, comprising the steps of mixing lithium raw material, phosphorus raw material, halogen element raw material and dopant raw material to form a mixture; and the step of heat-treating the mixture to form a sulfide-based solid electrolyte having an Argyrodite-based crystal structure, wherein the dopant raw material includes a transition metal (M) raw material. Here, the transition metal (M) is a transition metal element composed of Nb, Ta, V or a combination thereof.

[0053] The following describes, step by step, a method for manufacturing a sulfide-based solid electrolyte according to another embodiment of the present invention.

[0054] First, lithium raw materials, phosphorus raw materials, halogen element raw materials, and dopant raw materials are mixed to form a mixture. The dopant raw materials include transition metal (M) raw materials. Here, the transition metal (M) is a transition metal element composed of Nb, Ta, V, or a combination thereof.

[0055] The lithium raw material can be, for example, Li2S, Li2S2 or a combination thereof, but is not necessarily limited to this.

[0056] The phosphorus raw material can be, for example, P2S5, P2O5 or a combination thereof, but is not necessarily limited to this.

[0057] The halogen element raw material can be, for example, LiF, LiCl, LiBr, LiI, or a combination thereof, but is not necessarily limited to these. More specifically, the halogen element raw material can be LiCl.

[0058] The transition metal (M) raw material is not particularly limited as long as it is a compound containing a transition metal (M), but more specifically it can be a transition metal (M) oxide. Therefore, transition metal (M) and oxygen (O) can be simultaneously doped into the silver sulfide germanium compound.

[0059] The transition metal (M) oxide can be, for example, Nb2O5, Ta2O5, V2O5, or a combination thereof.

[0060] The amounts of lithium raw materials, phosphorus raw materials, halogen element raw materials, and doping raw materials added can be appropriately adjusted and added according to the stoichiometric ratio of the composition of the target sulfide-based solid electrolyte.

[0061] The mixing can be carried out through mechanical mixing or chemical mixing.

[0062] The mechanical mixing can be carried out, for example, by means of a planetary mill, a paint shaker, a ball mill, a bead mill, a homogenizer, a hammer mill, a turbine mill, a disc mill, a planetary mill, a mechanical fusion machine, etc.

[0063] The chemical mixing can be carried out, for example, by melt quenching.

[0064] The mixing process can take 4 to 12 hours, specifically 6 to 10 hours, and more specifically 7 to 9 hours. If the mixing time is too short, insufficient mixing may occur. If the mixing time is too long, the mixing will be complete after a certain period, and even if further mixing is carried out, the mixing state will remain the same, which may cause problems with process efficiency.

[0065] The mixing can be carried out at a rotational speed of 100 to 500 rpm, specifically 150 to 450 rpm, and more specifically 200 to 400 rpm. If the rotational speed is too slow, the ball may not be able to penetrate into the powder, resulting in insufficient mixing between the powder particles, or the energy may be too low, leading to insufficient particle refinement. Conversely, if the rotational speed is too fast, the powder may be biased to one side, resulting in uneven mixing.

[0066] Next, as needed, optionally, after the step of forming the mixture, a step of compressing the mixture to form particles may also be included.

[0067] At this point, the compression can be performed at a pressure of 100 to 500 MPa, specifically 150 to 450 MPa, and more specifically 200 to 400 MPa. If the pressure is too low, the interfacial resistance may become high due to insufficient bonding between the powder particles. Conversely, if the pressure is too high, the bonding between the powder particles is already complete, and even with the application of higher pressure, the bonding state will not change, which may cause problems with process efficiency. Therefore, from a productivity perspective, forming particles at an appropriate pressure is preferred.

[0068] Next, the mixture is heat-treated to form a sulfide-based solid electrolyte with an Argyrodite-based crystal structure.

[0069] At this point, the heat treatment can be carried out at a temperature of 400 to 700°C, more specifically at 500 to 600°C. If the heat treatment temperature is too low, the synthesis of the solid electrolyte with a sulforaphite-germanium ore crystal structure may be insufficient, or an amorphous crystal structure may be synthesized, which may lead to a decrease in the ionic conductivity of the solid electrolyte. If the heat treatment temperature is too high, the elements constituting the solid electrolyte may vaporize, resulting in the loss of the solid electrolyte, or impurity phases may be generated, which may also lead to a decrease in the ionic conductivity of the solid electrolyte.

[0070] Furthermore, the heat treatment can be carried out for 2 to 8 hours, more specifically 3 to 5 hours. If the heat treatment time is too short, the synthesis of the solid electrolyte with a sulforaphite-germanium ore crystal structure may be insufficient, or an amorphous crystal structure may be synthesized, which may lead to a decrease in the ionic conductivity of the solid electrolyte. If the heat treatment time is too long, the elements constituting the solid electrolyte may vaporize, resulting in the loss of the solid electrolyte, or impurity phases may be generated, which may also lead to a decrease in the ionic conductivity of the solid electrolyte.

[0071] Furthermore, the heat treatment can be performed in an inert gas atmosphere. Performing the heat treatment in an inert gas atmosphere has the advantage of preventing contact with moisture in the atmosphere. The inert gas atmosphere can be, for example, Ar, N2, H2, or He, and more specifically, Ar.

[0072] 3. All-solid-state battery Another embodiment of the present invention provides an all-solid-state battery, which includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer, wherein at least one of the positive electrode layer, the negative electrode layer, and the solid electrolyte layer includes the aforementioned solid electrolyte.

[0073] (Positive electrode layer) More specifically, the positive electrode layer may include a positive electrode current collector and a layer of positive electrode active material disposed on the positive electrode current collector.

[0074] The positive electrode active material layer may further include, for example, a positive electrode active material and a solid electrolyte selectively chosen as needed. The solid electrolyte included in the positive electrode active material layer may be the same as or different from the solid electrolyte included in an embodiment of the present invention, and may also be the same as or different from the solid electrolyte included in the solid electrolyte layer.

[0075] The positive electrode active material is a substance capable of reversibly inserting and desorbing lithium ions. Examples of positive electrode active materials include 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 manganate, lithium iron phosphate, nickel sulfide, copper sulfide, lithium sulfide, iron oxide, or vanadium oxide, but are not necessarily limited to these; any material used as a positive electrode active material in this technical field is acceptable. The positive electrode active material can be used alone or as a mixture of two or more.

[0076] The lithium transition metal oxide is, for example, made of Li a A 1-b B b D2 (in the formula, 0.90≤a≤1, and 0≤b≤0.5); Li a E 1-b B b O 2-c D c (In the formula, 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05); LiE 2-b B b O 4-c D c (In the formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b B c D α (In the formula, 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); Li a Ni 1-b-c Co b B c O 2-α F α (In the formula, 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni 1-b-c Co b B c O 2-α F2 (in the formula, 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni 1-b-c Mn b B c D α (In the formula, 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); Li a Ni 1-b-c Mn b B c O 2-α F α (In the formula, 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni 1-b- c Mn b B c O 2-α F2 (in the formula, 0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Lia Ni b E c G d O2 (in the formula, 0.90≤a≤1, 0≤b≤0.9, 0≤c≤0.5, 0.001≤d≤0.1); Li a Ni b Co c Mn d GeO2 (in the formula, 0.90≤a≤1, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0.001≤e≤0.1); Li a NiG b O2 (in the formula, 0.90≤a≤1, 0.001≤b≤0.1); Li a CoG b O2 (in the formula, 0.90≤a≤1, 0.001≤b≤0.1); Li a MnG b O2 (in the formula, 0.90≤a≤1, 0.001≤b≤0.1); Li a Mn2G b O4 (in the formula, 0.90≤a≤1, 0.001≤b≤0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiIO2; LiNiVO4; Li (3-f) J2(PO4)3 (0≤f≤2); Li (3-f)Compounds represented by any of the chemical formulas Fe2(PO4)3 (0≤f≤2) and LiFePO4. In these compounds, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof. Compounds with an attached coating on their surface can also be used, as well as mixtures of the above compounds and compounds with an attached coating. The coating on the surface of these compounds may include, for example, oxides, hydroxides, hydroxy oxides, hydroxide carbonates, or hydroxycarbonates of the coating element. The compounds constituting these coatings are amorphous or crystalline. Coating elements included in the coatings are Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating formation method is selected within a range that does not adversely affect the physical properties of the positive electrode active material. Coating methods include, for example, spraying and dipping. Specific coating methods are well understood by those skilled in the art, therefore detailed descriptions will be omitted.

[0077] The positive electrode active material layer may include, for example, an adhesive. Adhesives may be, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, etc., but are not limited to these; any adhesive used in this technical field may be used.

[0078] The positive electrode active material layer may include, for example, a conductive material. Conductive materials include, for example, graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powder, etc., but are not limited to these; any material used as a conductive material in this technical field is acceptable.

[0079] In addition to the aforementioned positive electrode active material, solid electrolyte, binder, and conductive material, the positive electrode active material layer may further include additives such as filler, coating agent, dispersant, and ion conductivity aid.

[0080] The positive electrode active material layer may include fillers, coating agents, dispersants, ion conductivity aids, etc., and commonly known materials used in the electrodes of all-solid-state secondary batteries can usually be used.

[0081] The positive electrode current collector can be, for example, a plate or foil composed of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or alloys thereof. The thickness of the positive electrode current collector can be, for example, 1µm to 100µm, 1µm to 50µm, 5µm to 25µm, or 10µm to 20µm.

[0082] (Negative electrode layer) More specifically, the negative electrode layer may include a negative electrode current collector and a layer of negative electrode active material disposed on the negative electrode current collector.

[0083] The negative electrode active material layer may include, for example, a negative electrode active material and a binder, and may selectively further include a solid electrolyte as needed.

[0084] The negative electrode active material may include, for example, carbon-based negative electrode active materials, metal / quasi-metal negative electrode active materials, or combinations thereof.

[0085] The carbon-based negative electrode active material can be amorphous carbon, crystalline carbon, or a mixture or composite thereof. Examples of amorphous carbon include carbon black (CB), acetylene black (AB), furnace black (FB), ketjen black (KB), and graphene, but it is not necessarily limited to these; any material classified as amorphous carbon in this technical field is acceptable. Amorphous carbon is carbon that is non-crystalline or has very low crystallinity, distinguishing it from crystalline carbon or graphitic carbon. Crystalline carbon can be, for example, natural graphite, artificial graphite, or a combination thereof.

[0086] Metal / quasi-metal anode active materials include one or more of the group consisting of lithium (Li), gold (Au), platinum (Pt), indium (In), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn), but are not necessarily limited to these, as long as they are metal or quasi-metal anode active materials used in this art to form alloys or compounds with lithium.

[0087] The binder included in the negative electrode active material layer is, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, PVDF / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, etc., but is not necessarily limited to these; any binder used in this technical field is acceptable. The binder can be a single agent or a combination of multiple different binders.

[0088] The negative electrode active material layer, including a binder, is stabilized on the negative electrode current collector. Furthermore, during charging and discharging, cracking of the negative electrode active material layer is suppressed despite volume changes and / or relative positional shifts.

[0089] The negative electrode active material layer may further include additives used in conventional all-solid-state batteries, such as fillers, coating agents, dispersants, and ion-conducting aids.

[0090] The all-solid-state battery may further include a second negative electrode active material layer disposed between the negative electrode current collector and the negative electrode active material layer during charging. The second negative electrode active material layer may be deposited between the negative electrode current collector and the negative electrode current collector during charging, or it may be further disposed on the negative electrode active material layer during electrode assembly. Such a second negative electrode active material layer may be a metal layer comprising lithium or a lithium alloy. The lithium alloy may be, for example, Li-Al alloy, Li-Sn alloy, Li-In alloy, Li-Ag alloy, Li-Au alloy, Li-Zn alloy, Li-Ge alloy, Li-Si alloy, etc., but is not limited to these; any lithium alloy used in this technical field is acceptable. The second negative electrode active material layer may be composed of one of these alloys and / or lithium, or it may be composed of multiple alloys and / or lithium.

[0091] The negative electrode current collector can be made of a material that does not react with lithium, i.e., it neither forms an alloy nor a compound. Examples of negative electrode current collectors include copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni), but are not necessarily limited to these; any material used as an electrode current collector in this technical field is acceptable. The negative electrode current collector can be composed of one of the aforementioned metals, or an alloy or coating material of two or more metals. The negative electrode current collector can be in plate or foil form, for example.

[0092] When the negative electrode active material layer includes a solid electrolyte, the solid electrolyte contained in the negative electrode active material layer may be the same as or different from the solid electrolyte according to an embodiment of the present invention, and may be the same as or different from the solid electrolyte included in the solid electrolyte layer.

[0093] (Solid electrolyte layer) The solid electrolyte layer can be manufactured by mixing and drying the aforementioned solid electrolyte and binder, or by calendering the aforementioned solid electrolyte powder in a constant shape under a pressure of 1 ton to 10 tons.

[0094] At this time, the solid electrolyte can be in the form of powder or molded article. The solid electrolyte in the form of molded article can be, for example, in the form of particles, sheets, films, etc., but is not necessarily limited to these, and can have a variety of forms depending on the application.

[0095] The solid electrolyte layer may, as needed, include, in addition to the aforementioned solid electrolytes, traditional sulfide-based solid electrolytes and / or oxide-based solid electrolytes.

[0096] The binder is, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polyvinyl alcohol, etc., but is not limited to these; any binder used in this technical field may be used. The binder for the solid electrolyte layer may be the same as or different from the binders for the positive and negative electrode layers.

[0097] Another embodiment of the present invention provides an electric vehicle including the all-solid-state battery.

[0098] The embodiments of the present invention will be described in more detail below. However, the following embodiments are merely preferred embodiments of the present invention, and the present invention is not limited to the following embodiments.

[0099] Example 1: Li 5.94 P 0.99 Nb 0.02 S 4.95 O 0.05 Cl 0.99 Manufacturing of solid electrolytes (1) Solid electrolyte manufacturing (Mixed) Reactants Li₂S, P₂S₅, LiCl, and Nb₂O₅ are added in stoichiometric ratios to produce the final product Li. 7a- ax P a M 2-2a S 6a-ax O 5-5a D axIn the solid electrolyte, x=1 and a=0.99, a mixture was formed by mixing at 300 rpm for about 8 hours using a planetary ball mill.

[0100] (Particle manufacturing) Next, a pressure of 300 MPa is applied to the mixture to form particles.

[0101] (Heat Treatment) Next, the particles were heat-treated in an argon (Ar) atmosphere at 550°C for approximately 4 hours to produce Li. 5.94 P 0.99 Nb 0.02 S 4.95 O 0.05 Cl 0.99 Solid electrolyte.

[0102] (2) All-solid-state battery manufacturing The solid electrolyte produced was used as the electrolyte, and Li1Ni was employed. 0.8 Co 0.1 Mn 0.1 An all-solid-state battery was manufactured using O2 as the positive electrode active material and In-Li alloy as the negative electrode active material.

[0103] 138 Comparative Example 1: Preparation of Li6PS5Cl solid electrolyte A mixture was formed by mixing Li2S, P2S5 and LiCl, which are the reactants, at 300 rpm for about 8 hours using a planetary ball mill.

[0104] Next, a pressure of 300 MPa was applied to the mixture to form particles.

[0105] Next, the particles were heat-treated at 550°C for about 4 hours in an argon (Ar) atmosphere to produce Li6PS5Cl solid electrolyte.

[0106] Other embodiments and reference examples In the mixing step, besides adding reactants Li₂S, P₂S₅, LiCl, and Nb₂O₅ in stoichiometric proportions to produce the final product Li 7a-ax P a M 2-2a S 6a-ax O 5-5a D ax Except for the values ​​of x and a in the solid electrolyte recorded in Table 1 below, the same procedure as in Example 1 was followed to manufacture a solid electrolyte and an all-solid-state battery.

[0107] Table 1 below shows the x and a values ​​of the examples, comparative examples, and reference examples, as well as the composition of the solid electrolytes thus manufactured.

[0108] Table 1 (In Table 1, [Li], [P], [Nb], [S], [O], and [Cl] represent the molar ratios relative to 1 mol of the manufactured solid electrolyte.) Table 2 Table 3 below summarizes the X-ray diffraction analysis results, ionic conductivity, and evaluation results of the short-circuit C-rate, initial discharge capacity, and lifetime characteristics of the solid electrolytes based on Experimental Examples 1 and 2 described below.

[0109] Table 3 Experimental Example 1: XRD Analysis and Ionic Conductivity Evaluation of Solid Electrolytes (1) XRD analysis of solid electrolytes X-ray diffraction (XRD) analysis was performed on the solid electrolyte to evaluate the presence of peaks in the ranges of 15.4°≤2θ≤15.8° (first peak), 25.4°≤2θ≤25.7° (second peak), and 34.7°≤2θ≤34.9° (third peak). The intensity ratios of the second and third peaks relative to the first peak were also evaluated. The XRD analysis charts from Examples 1 to 4 are then displayed. Figure 1 middle.

[0110] (2) Evaluation of ionic conductivity (30℃, 0.1C) After pulverizing the manufactured solid electrolyte, it was granulated under a pressure of 300 MPa. Subsequently, using SUS as the working electrode, a battery cell was fabricated under a pressure of 70 MPa. The impedance was then measured by applying a voltage of 10 mV at 30°C.

[0111] Referring to Table 3, it can be confirmed that in the examples and reference examples doped with Nb and O, a second peak and a third peak appeared alongside the first peak. Furthermore, it can be confirmed that as the doping amount of Nb and O increases, the ratio of the intensity of the second peak to the intensity of the first peak decreases, while the ratio of the intensity of the third peak to the intensity of the first peak increases.

[0112] Conversely, it can be confirmed that in the case of Comparative Example 1, which is composed of basic silver-germanium sulfide without Nb and O doping, only the first peak is observed, and the second and third peaks are not observed.

[0113] Examining the ionic conductivity confirms that it decreases compared to Comparative Example 1, which uses a basic silver-germanium sulfide composition, as the doping amount of Nb and O in the solid electrolyte increases. As explained in conjunction with the experimental examples described later, it can be confirmed that, compared to blindly increasing the doping amount of Nb and O, achieving good ionic conductivity in the solid electrolyte with appropriate doping amounts results in improved short-circuit prevention, increased discharge capacity, and improved lifetime.

[0114] Experimental Example 2: Evaluation of Electrochemical Characteristics of All-Solid-State Batteries (1) Initial discharge capacity evaluation The battery was charged at 0.1C to 4.25V (vs. Li+ / Li) at room temperature (25°C) and the charging current was stopped at 0.02C at the corresponding voltage. The initial discharge capacity was evaluated after discharging to 2.50V (vs. Li+ / Li) at 0.1C under the same conditions.

[0115] (2) Lifespan characteristics evaluation After a formation cycle at 0.1C, the percentage of discharge capacity at the 50th cycle at a current density of 0.5C relative to the discharge capacity at the 1st cycle was determined.

[0116] (3) Evaluation of short-circuit C-rate All-solid-state batteries were fabricated and their short-circuit C-rate was evaluated.

[0117] Evaluation of the short-circuit C-rate confirmed that, in the examples and reference examples doped with Nb and O, the short-circuit prevention effect was improved compared to Comparative Example 1, which consisted of a basic silver-germanium sulfide composition. In particular, it was confirmed that when Nb and O were doped in appropriate amounts, i.e., when the molar ratio of niobium (Nb) to phosphorus (P) ([Nb] / [P]), the molar ratio of oxygen (O) to phosphorus (P) ([O] / [P]), or the a value was adjusted to an appropriate range, the short-circuit prevention effect was preferably achieved.

[0118] Evaluation of the initial discharge capacity revealed that, after an initial increase in initial discharge capacity compared to Comparative Example 1 with the basic silver-germanium sulfide composition, it tended to deteriorate again with increasing Nb and O doping amounts. Therefore, it can be confirmed that the capacity characteristics are preferably achieved when Nb and O are doped in appropriate amounts, i.e., when the molar ratio of niobium (Nb) to phosphorus (P) ([Nb] / [P]), the molar ratio of oxygen (O) to phosphorus (P) ([O] / [P]), or the a value is adjusted to an appropriate range.

[0119] Evaluation of lifetime characteristics revealed that while lifetime characteristics initially improved compared to Comparative Example 1 with the basic silver-germanium sulfide composition upon increasing Nb and O doping levels, they subsequently tended to deteriorate again. Therefore, it can be confirmed that lifetime characteristics are preferably achieved when Nb and O are doped in appropriate amounts, specifically when the molar ratio of niobium (Nb) to phosphorus (P) ([Nb] / [P]), the molar ratio of oxygen (O) to phosphorus (P) ([O] / [P]), or the a value is adjusted to an appropriate range.

[0120] The preferred embodiments of the present invention have been described above, but the present invention is not limited thereto. Various modifications can be made within the scope of the claims, the specification and the drawings, which are of course also within the scope of the present invention.

[0121] Therefore, it can be said that the substantive scope of the invention is defined by the appended patent claims and their equivalents.

Claims

1. A sulfide-based solid electrolyte, characterized in that, include: Compounds containing lithium (Li), phosphorus (P), sulfur (S), and halogen elements (D), and exhibiting a sulfide-germanium ore crystal structure. At least a portion of the crystal structure is doped with oxygen (O) and transition metal elements (M) consisting of Nb, Ta, V, or combinations thereof.

2. The sulfide-based solid electrolyte according to claim 1, characterized in that, The molar ratio of transition metal element (M) to phosphorus (P) in the compound ([M] / [P]) is from 0.01 to 1.

1.

3. The sulfide-based solid electrolyte according to claim 1, characterized in that, The molar ratio of oxygen (O) to phosphorus (P) in the compound ([O] / [P]) is from 0.03 to 2.

5.

4. The sulfide-based solid electrolyte according to claim 1, characterized in that, The molar ratio of lithium (Li) to phosphorus (P) in the compound ([Li] / [P]) is 5.5 to 6.

5.

5. The sulfide-based solid electrolyte according to claim 1, characterized in that, The molar ratio of sulfur (S) to phosphorus (P) in the compound is 4.5 to 5.

5.

6. The sulfide-based solid electrolyte according to claim 1, characterized in that, The molar ratio of halogen (D) to phosphorus (P) in the compound is 0.5 to 1.

5.

7. The sulfide-based solid electrolyte according to claim 1, characterized in that, The compound exhibits a first peak in the range of 15.4°≤2θ≤15.8° during X-ray diffraction pattern analysis.

8. The sulfide-based solid electrolyte according to claim 7, characterized in that, The compound exhibited a second peak in the range of 25.4°≤2θ≤25.7° during X-ray diffraction pattern analysis.

9. The sulfide-based solid electrolyte according to claim 7, characterized in that, The compound exhibited a third peak in the range of 34.7°≤2θ≤34.9° during X-ray diffraction pattern analysis.

10. The sulfide-based solid electrolyte according to claim 8, characterized in that, The ratio of the intensity of the second peak to the intensity of the first peak of the compound is 2.4 to 2.

9.

11. The sulfide-based solid electrolyte according to claim 9, characterized in that, The ratio of the intensity of the third peak to the intensity of the first peak of the compound is from 0.03 to 0.

8.

12. The sulfide-based solid electrolyte according to claim 1, characterized in that, The compound is a sulfide-based solid electrolyte represented by the following chemical formula 1. [Chemical Formula 1] Li 7a-ax P a M 2-2a S 6a-ax Oh 5-5a D ax In the chemical formula 1, 1≤x≤2, 0.65≤a≤0.995, M is a transition metal element composed of Nb, Ta, V or a combination thereof, and D is a halogen element composed of F, Cl, Br, I or a combination thereof.

13. The sulfide-based solid electrolyte according to claim 12, characterized in that, 0.8≤a≤0.96。 14. An all-solid-state battery, characterized in that, include: A positive electrode layer; a negative electrode layer and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer. At least one of the positive electrode layer, the negative electrode layer, and the solid electrolyte layer includes the solid electrolyte according to claim 1.

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