Positive electrode for lithium-sulfur battery and manufacturing method thereof

Abstract

The present invention relates to a positive electrode for a lithium-sulfur battery. More specifically disclosed is a positive electrode for a lithium-sulfur battery, the positive electrode comprising: a positive electrode current collector; a first positive electrode active material layer positioned on the positive electrode current collector; and a second positive electrode active material layer positioned on the first positive electrode active material layer, the first positive electrode active material layer and the second positive electrode active material layer each independently comprising a positive electrode active material, a sulfide-based solid electrolyte and a binder, wherein: the positive electrode active material comprises a carbon-based material and a composite of a sulfur compound, a lithium salt and a metal halide; the sulfur compound comprises at least one among S8 and Li2Sn (1≤n≤8, n being an integer); the metal halide comprises at least one selected from the group consisting of aluminium (Al), silver (Ag), gold (Au), platinum (Pt), palladium (Pd), bismuth (Bi), tin (Sn), and zinc (Zn); and the content of the positive electrode active material in the first positive electrode active material layer is greater than the content of the positive electrode active material in the second positive electrode active material layer.

Description

Cathode for lithium-sulfur battery and method for manufacturing same

[0001] It relates to a lithium-sulfur all-solid-state battery containing a sulfide-based positive electrode active material.

[0002]

[0003] Lithium-sulfur batteries use sulfur-based materials as the positive electrode active material and lithium metal as the negative electrode active material. Sulfur, the primary ingredient, is abundant and has a low weight per atom. Compared to lithium-ion batteries, which have a relatively low energy density per weight, lithium-sulfur batteries theoretically have a higher energy density, and technological development is underway.

[0004] During discharge, lithium-sulfur batteries oxidize as lithium releases electrons and ionizes into lithium cations. The sulfur-based material, the cathode active material, accepts electrons and is reduced. Meanwhile, the sulfur-based material is converted into sulfur anions through a reduction reaction.

[0005] Lithium cations generated by lithium oxidation reaction are transferred to the positive electrode through the electrolyte, and sulfur compounds combine with sulfur anions generated by reduction reaction to form salts. Before discharge, sulfur has a cyclic S8 structure and is converted into lithium polysulfide (Li2S) by reduction reaction. x , the battery is driven by a shuttle mechanism that is converted into (1≤x≤8).

[0006]

[0007] The problem to be solved by the present invention is to provide a lithium-sulfur all-solid-state battery with improved ionic conductivity, capacity, and lifespan characteristics by introducing a multilayer positive electrode.

[0008]

[0009] A positive electrode for a lithium-sulfur battery according to the concept of the present invention may include a positive electrode current collector; a first positive electrode active material layer positioned on the positive electrode current collector; and a second positive electrode active material layer positioned on the first positive electrode active material layer. Each of the first positive electrode active material layer and the second positive electrode active material layer includes a positive electrode active material, a sulfide-based solid electrolyte, and a binder, and the positive electrode active material includes a composite and a carbon-based material, and the composite includes a sulfur compound, a lithium salt, and a metal halide, and the sulfur compound includes S8 and Li2S. n (1 ≤ n ≤ 8, n is an integer), wherein the metal of the metal halide includes at least one selected from the group consisting of aluminum (Al), silver (Ag), gold (Au), platinum (Pt), palladium (Pd), bismuth (Bi), tin (Sn), and zinc (Zn), and the content of the positive electrode active material in the first positive electrode active material layer may be greater than the content of the positive electrode active material in the second positive electrode active material layer.

[0010] A positive electrode for a lithium-sulfur battery according to another concept of the present invention may include a positive electrode current collector; and a positive electrode active material layer having a multilayer structure sequentially arranged on the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, a sulfide-based solid electrolyte, and a binder, and the positive electrode active material includes a solid solution of a sulfur compound, a lithium halide, and an aluminum halide, and the sulfur compound is S8 and Li2S. n (1 ≤ n ≤ 8, n is an integer), and the content of the positive electrode active material in the positive electrode active material layer may decrease as it moves away from the positive electrode current collector.

[0011]

[0012] According to the present invention, a lithium-sulfur battery can be provided with reduced resistance of the positive electrode and improved rate and cycle life characteristics. In addition, a lithium-sulfur battery with improved ionic conductivity and energy density can be provided.

[0013]

[0014] FIG. 1 is a plan view of a lithium sulfur battery according to embodiments of the present invention.

[0015] Figure 2 is a cross-sectional view taken along line AA` of Figure 1.

[0016] FIG. 3 is a cross-sectional view illustrating a positive electrode active material layer according to embodiments of the present invention, which is an enlarged view of area M of FIG. 2.

[0017] Figure 4 is a cross-sectional view of a lithium sulfur battery according to one embodiment of the present invention.

[0018] Figure 5 is a cross-sectional view of a lithium sulfur battery according to one embodiment of the present invention.

[0019] Figure 6 is a cross-sectional view of a lithium sulfur battery according to one embodiment of the present invention.

[0020] Figure 7 is a cross-sectional view of a lithium sulfur battery according to one embodiment of the present invention.

[0021] Figure 8 is a cross-sectional view of an anode according to one embodiment of the present invention.

[0022] Figure 9 is a cross-sectional view of an anode according to one embodiment of the present invention.

[0023] Figure 10 is an enlarged cross-sectional view of area X of Figure 9.

[0024] Figures 11 to 16 illustrate a method for manufacturing a lithium sulfur positive electrode according to one embodiment of the present invention.

[0025]

[0026] To fully understand the structure and effects of the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms and subject to various modifications. However, the description of these embodiments is provided solely to ensure a complete disclosure of the present invention and to fully inform those skilled in the art of the invention of the scope of the invention.

[0027] In this specification, when a component is referred to as being on another component, it means that it can be formed directly on the other component, or a third component may be interposed between them. Furthermore, in the drawings, the thicknesses of the components are exaggerated for the sake of clarity. Parts designated by the same reference numerals throughout the specification represent the same components.

[0028] Embodiments described herein will be described with reference to cross-sectional and / or plan views, which are ideal illustrations of the present invention. In the drawings, the thicknesses of films and regions are exaggerated for the purpose of effectively explaining the technical contents. Accordingly, the regions illustrated in the drawings have a schematic nature, and the shapes of the regions illustrated in the drawings are intended to illustrate specific shapes of regions of the device and are not intended to limit the scope of the invention. Although terms such as first, second, and third are used to describe various components in various embodiments of the present specification, these components should not be limited by such terms. These terms are used only to distinguish one component from another. The embodiments described and illustrated herein also include complementary embodiments thereof.

[0029] The terminology used herein is for the purpose of describing embodiments and is not intended to limit the present invention. In this specification, the singular also includes the plural unless specifically stated otherwise. As used herein, the words "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components.

[0030] Unless otherwise defined herein, the particle size may be the average particle size. In addition, the particle size refers to the average particle size (D50), which means the diameter of particles with a cumulative volume of 50% by volume in a particle size distribution. The average particle size (D50) can be measured by a method well known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with a transmission electron microscope (TEM) photograph or a scanning electron microscope (SEM) photograph. Alternatively, the average particle size (D50) value can be obtained by measuring with a measuring device that utilizes dynamic light-scattering, performing data analysis to count the number of particles for each particle size range, and calculating from the counted number. Alternatively, the average particle size (D50) value can be obtained by measuring with a laser diffraction method. When measuring by laser diffraction, more specifically, after the particles to be measured are dispersed in a dispersion medium, they are introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000) and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W, and the average particle size (D50) based on 50% of the particle size distribution in the measuring device can be calculated.

[0031] In this specification, “metal” includes both metals and metalloids such as silicon and germanium, in their elemental or ionic state.

[0032] As used herein, “alloy” means a mixture of two or more metals.

[0033] In this specification, “electrode active material” means an electrode material capable of undergoing lithiation and delithiation.

[0034] In this specification, “positive electrode active material” means a positive electrode material capable of undergoing lithiation and delithiation.

[0035] In this specification, “negative electrode active material” means a negative electrode material capable of undergoing lithiation and delithiation.

[0036] In this specification, “lithiation” and “lithiate” mean a process of adding lithium to an electrode active material.

[0037] In this specification, “delithiation” and “delithiate” refer to a process of removing lithium from an electrode active material.

[0038] In this specification, “charging” and “charging” mean the process of providing electrochemical energy to a battery.

[0039] In this specification, “discharge” and “discharge” mean the process of removing electrochemical energy from a battery.

[0040] In this specification, “positive electrode” and “cathode” mean an electrode where electrochemical reduction and lithiation occur during the discharge process.

[0041] In this specification, “cathode” and “anode” mean electrodes where electrochemical oxidation and delithiation occur during the discharge process.

[0042]

[0043] Fig. 1 is a plan view of an all-solid-state battery according to embodiments of the present invention. Fig. 2 is a cross-sectional view taken along line A-A' of Fig. 1. Fig. 3 is an enlarged cross-sectional view of area M of Fig. 2, which is intended to explain a positive electrode active material layer according to one embodiment of the present invention.

[0044] Referring to FIGS. 1 and 2, the all-solid-state battery (10) according to the present invention may include a positive electrode layer (100), a negative electrode layer (200) facing the positive electrode layer (100), and a solid electrolyte layer (300) disposed between the positive electrode layer (100) and the negative electrode layer (200). However, the present invention is not limited thereto, and the all-solid-state battery (10) may further include an additional functional layer, such as an adhesion enhancing layer, disposed between the positive electrode layer (100) and the solid electrolyte layer (300) or between the negative electrode layer (200) and the solid electrolyte layer (300).

[0045] A positive electrode layer (100) according to one embodiment of the present invention may include a positive electrode current collector (110) and a positive electrode active material layer (120) disposed on the positive electrode current collector (110). The positive electrode active material layer (120) may include a positive electrode active material, a solid electrolyte, a conductive material, and a binder.

[0046] The positive electrode current collector (110) can provide a reference surface on which the positive electrode active material layer (120) is arranged. The positive electrode current collector (110) can include, for example, 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 an alloy thereof. The positive electrode current collector (110) can include a plate or a foil. In another embodiment of the present invention, the positive electrode current collector (110) can be omitted. The thickness of the positive electrode current collector (110) can be, for example, 1 ㎛ to 100 ㎛, 1 ㎛ to 50 ㎛, 5 ㎛ to 25 ㎛, or 10 ㎛ to 20 ㎛.

[0047] The cathode current collector (110) may include, for example, a base film and a metal layer disposed on one or both sides of the base film. The base film may include, for example, a polymer. The polymer may be, for example, a thermoplastic polymer. The polymer may include, for example, polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or a combination thereof.

[0048] The base film may be, for example, an insulator. If the base film includes an insulating thermoplastic polymer, the base film may soften or liquefy when a short circuit occurs, thereby blocking battery operation and suppressing a rapid increase in current.

[0049] The metal layer may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), or an alloy thereof. The metal layer may act as an electrochemical fuse to prevent short circuits by being cut off in the event of overcurrent. The limit current and maximum current can be controlled by controlling the thickness of the metal layer. The metal layer may be plated or deposited on the base film. When the thickness of the metal layer is reduced, the limit current and / or maximum current of the positive electrode current collector (110) decrease, thereby improving the stability of the lithium battery in the event of a short circuit.

[0050] A lead tab may be added to the metal layer for external connection. The lead tab may be welded to the metal layer or the metal layer / base film laminate by ultrasonic welding, laser welding, spot welding, etc. During welding, the base film and / or metal layer may melt, electrically connecting the metal layer to the lead tab.

[0051] In order to make the welding between the metal layer and the lead tab more solid, a metal chip may be added between the metal layer and the lead tab. The metal chip may be a thin piece of the same material as the metal of the metal layer. The metal chip may be, for example, a metal foil, a metal mesh, etc. The metal chip may be, for example, aluminum foil, copper foil, SUS foil, etc. By placing the metal chip on the metal layer and then welding it with the lead tab, the lead tab may be welded to the metal chip / metal layer laminate or the metal chip / metal layer / base film laminate. During welding, the base film, the metal layer, and / or the metal chip may melt, so that the metal layer or the metal layer / metal chip laminate may be electrically connected to the lead tab. The metal chip and / or the lead tab may be added to a portion of the metal layer.

[0052] The thickness of the base film may be, for example, 1 to 50 μm, 1.5 to 50 μm, 1.5 to 40 μm, or 1 to 30 μm. When the base film has a thickness in this range, the weight of the electrode assembly can be more effectively reduced. The melting point of the base film may be, for example, 100 to 300 °C, 100 to 250 °C or less, or 100 to 200 °C. When the base film has a melting point in this range, the base film can be melted during the process of welding the lead tab and easily bonded to the lead tab. In order to improve the adhesion between the base film and the metal layer, a surface treatment such as corona treatment may be performed on the base film.

[0053] The thickness of the metal layer may be, for example, 0.01 to 3 ㎛, 0.1 to 3 ㎛, 0.1 to 2 ㎛, or 0.1 to ㎛. By having a thickness in this range of the metal layer, conductivity can be maintained while ensuring the stability of the electrode assembly. The thickness of the metal piece may be, for example, 2 to 10 ㎛, 2 to 7 ㎛, or 4 to 6 ㎛. By having a thickness in this range of the metal piece, the connection between the metal layer and the lead tab can be performed more easily. By having the laminated structure of the base film and the metal layer as described above, the positive electrode current collector (110) can reduce the weight of the positive electrode layer (100), and consequently, the energy density of the all-solid-state battery (10) can be improved.

[0054] In one embodiment of the present invention, the content of the positive electrode active material in the positive electrode active material layer (120) may be 10 wt% to 99 wt%, 30 wt% to 80 wt%, 40 wt% to 70 wt%, or 40 wt% to 50 wt% of the total weight of the positive electrode active material layer (120). If the content of the positive electrode active material is excessively reduced, the energy density of the all-solid-state battery (10) may be reduced. If the content of the positive electrode active material is excessively increased, the deterioration of the all-solid-state battery (10) may be accelerated due to a change in the volume of the positive electrode during charge and discharge.

[0055] The positive electrode active material within the positive electrode active material layer (120) can reversibly absorb and desorb lithium ions. The positive electrode active material may include a plurality of particles. The positive electrode active material according to the present invention may include an oxide-based positive electrode active material, a sulfide-based positive electrode active material, or a combination thereof.

[0056] The oxide-based cathode active material may include, for example, a lithium transition metal oxide, a metal oxide, or a combination thereof. The lithium transition metal oxide may include, for example, lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt mangense oxide, lithium manganate, lithium iron phosphate, or a combination thereof. The lithium oxide may include, for example, iron oxide, vanadium oxide, or a combination thereof.

[0057] The sulfide-based cathode active material may include, for example, nickel sulfide, copper sulfide, Li2S, a Li2S-containing complex, or a combination thereof. A more specific description of the sulfide-based cathode active material according to an embodiment of the present invention will be provided below.

[0058] The oxide-based cathode active material may be, for example, one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof. The lithium-containing oxide-based cathode active material may be, for example, Li. a A 1-b B' b D2 (in the above formula, 0.90 ≤ a ≤ 1, and 0 ≤ b ≤ 0.5); Li a E 1-b B' b O 2-c D c (In the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE 2-b B' b O4-c D c (In the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b B' c D α (In the above equation, 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 above equation, 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 above equation, 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 above equation, 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 above equation, 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 above equation, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni b E c Gd O2 (in the above 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 G e O2 (in the above 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 above formula, 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li a CoG b O2 (in the above formula, 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li a MnG b O2 (in the above formula, 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4 (in the above formula, 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); LiV2O5; LiI'O2; LiNiVO4; Li (3-f) J2(PO4)3(0 ≤ f ≤ 2); Li (3-f) Fe2(PO4)3(0 ≤ f ≤ 2); may include a compound represented by any one of the chemical formulas of LiFePO4.

[0059] In the chemical formula representing the compound described above, A is Ni, Co, Mn, or a combination thereof; B' is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, 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 may be V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0060] The oxide-based cathode active material may include, for example, a lithium salt of a transition metal oxide having a layered rock salt type structure among the lithium transition metal oxides described above. The "layered rock salt type structure" is, for example, a cubic rock salt type structure. <111> It is a structure in which oxygen atomic layers and metal atomic layers are alternately and regularly arranged in a direction, and thereby each atomic layer forms a two-dimensional plane. The "cubic rock salt structure" refers to the sodium chloride type (NaCl type) structure, which is a type of crystal structure, and specifically refers to a structure in which the face-centered cubic lattice (fcc) formed by each cation and anion is arranged with a displacement of half of the ridge of the unit lattice. Lithium transition metal oxides having this layered rock salt structure include, for example, LiNi x Co y Al z O2(NCA) or LiNi x Co y Mn zO2(NCM) (0 <x<1,0<y<1, 0<z<1, x+y+z=1) 등의 삼원계 리튬전이금속산화물일 수 있다. 양극 활물질이 층상암염형 구조를 갖는 삼원계 리튬전이금속산화물을 포함하는 경우, 전고체 전지(10)의 에너지 밀도가 커지고 열안정성이 향상될 수 있다.

[0061] The oxide-based positive electrode active material may be covered by a coating layer (not shown). The oxide-based positive electrode active material may also be a mixture of the above-described compound and a compound to which a coating layer is added. Meanwhile, the coating layer added to the surface of the positive electrode active material may include, for example, an oxide, a hydroxide, an oxyhydroxide, an oxycarbonate, or a hydroxycarbonate of the coating elements below. The compound forming the coating layer may be amorphous or crystalline. The coating elements included in the coating layer may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating layer may include, for example, Li2O-ZrO2 (LZO). The method of forming the coating layer may be selected within a range that does not adversely affect the physical properties of the positive electrode active material. The method of forming the coating layer may include, for example, spray coating, dipping, etc.

[0062] When the oxide-based cathode active material is a ternary lithium transition metal oxide such as NCA or NCM and contains nickel (Ni), it is possible to increase the capacity density of the all-solid-state battery (10) and reduce metal dissolution of the cathode active material in a charged state. As a result, the cycle characteristics of the all-solid-state battery (10) in a charged state are improved. Meanwhile, the "cycle characteristics" are characteristics indicating the degree to which the all-solid-state battery (10) is deteriorated due to charge / discharge of the all-solid-state battery (10). An all-solid-state battery (10) with high cycle characteristics may have a small degree of deterioration of the all-solid-state battery (10) due to charge / discharge, and an all-solid-state battery (10) with low cycle characteristics may have a large degree of deterioration of the all-solid-state battery (10) due to charge / discharge.

[0063] The oxide-based cathode active material may have a particle shape such as a sphere or an ellipsoid, for example. The particle size and content of the oxide-based cathode active material are not particularly limited. The size of the oxide-based cathode active material may be, for example, 0.1 to 30 μm, 0.5 to 20 μm, or 1 to 15 μm. The oxide-based cathode active material may be, for example, a single-crystal particle or a polycrystalline particle.

[0064] The cathode active material layer (120) according to embodiments of the present invention may include a sulfide-based cathode active material. Specifically, referring to FIG. 3, the sulfide-based cathode active material may include a Li2S-containing cathode active material (CAC). The Li2S-containing cathode active material (CAC) may include, for example, a complex of Li2S and carbon, a complex of Li2S, carbon, and a solid electrolyte, a complex of Li2S and a solid electrolyte, a complex of Li2S and a lithium salt, a complex of Li2S, a lithium salt, and carbon, a complex of Li2S, a lithium salt, a metal halide, and carbon, a complex of Li2S and a metal carbide, a complex of Li2S, carbon, and a metal carbide, a complex of Li2S and a metal nitride, a complex of Li2S, carbon, and a metal nitride, or a combination thereof.

[0065] The cathode active material (CAC) may include a sulfide-based composite (CAM) and a conductive material (CMA). In one embodiment, the sulfide-based composite (CAM) may have a particle shape such as a spherical shape or an elliptical shape. The particle size of the sulfide-based composite (CAM) is not particularly limited and may be within a range applicable to general cathode active materials. The size of the sulfide-based composite (CAM) may be, for example, 0.1 to 50 μm, 0.5 to 30 μm, 0.5 to 20 μm, or 1 to 10 μm. The conductive material (CMA) may cover the surface of the sulfide-based composite (CAM).

[0066] The conductive material (CMA) may include carbon. The conductive material (CMA) may include, without limitation, any material containing carbon atoms used as a conductive material in the art. For example, the conductive material (CMA) may include crystalline carbon, amorphous carbon, or a combination thereof. The conductive material (CMA) may include, for example, a sintered product of a carbon precursor. The conductive material (CMA) may include, for example, carbon nanostructures.

[0067] The conductive material (CMA) may include, for example, porous carbon or non-porous carbon. The porous carbon may include, for example, periodic and regular two-dimensional or three-dimensional pores. The porous carbon may be, for example, carbon black such as Ketjen Black, acetylene black, Denka Black, thermal black, channel black, etc.; graphite, activated carbon, or a combination thereof. The form of the carbon in the conductive material (CMA) may be, but is not limited to, particle form, sheet form, fiber form, etc., and any form used as carbon in the art may be used.

[0068] In one embodiment of the present invention, the conductive material (CMA) may include a fibrous carbon-based material. Since the conductive material (CMA) includes a fibrous carbon-based material, the electronic conductivity of the cathode active material (CAC) may be further enhanced. Since the conductive material (CMA) includes a fibrous carbon-based material, electronic conduction may be facilitated from the surface to the interior of the cathode active material (CAC). The internal resistance of the sulfide-based composite (CAM) may be reduced by the conductive material (CMA), and the cycle characteristics of the secondary battery may be further improved.

[0069] The aspect ratio of the fibrous carbon-based material can be, for example, 2 or more, 3 or more, 4 or more, 5 or more, 10 or more, or 20 or more. The aspect ratio of the fibrous carbon-based material can be, for example, 2 to 30, 3 to 30, 4 to 30, 5 to 30, 10 to 30, or 20 to 30. The aspect ratio of the fibrous carbon-based material can be, for example, 2 to 30, 2 to 20, 2 to 10, 2 to 8, 2 to 5, or 2 to 4. When the fibrous carbon-based material has an aspect ratio in this range, the overall electronic conductivity of the cathode active material (CAC) is improved, and local electronic conductivity imbalance within the cathode active material (CAC) can be further alleviated.

[0070] The fibrous carbon-based material may include, for example, carbon nanostructures. The carbon nanostructures may include, for example, carbon nanofibers (CNFs), carbon nanotubes (CNTs), carbon nanobelts, carbon nanorods, or combinations thereof. The carbon nanostructures may form a primary carbon nanostructure composed of a single carbon nanostructure and a secondary carbon nanostructure composed of multiple carbon nanostructures aggregated together.

[0071] The diameter of the primary carbon nanostructure can be, for example, 1 nm to 200 nm, 1 nm to 150 nm, 1 nm to 100 nm, 1 nm to 50 nm, 1 nm to 30 nm, or 1 nm to 20 nm. The length of the primary carbon nanostructure can be, for example, 10 nm to 2 μm, 10 nm to 1.5 μm, 10 nm to 1 μm, 10 nm to 500 nm, 10 nm to 400 nm, 10 nm to 300 nm, 10 nm to 200 nm, or 10 nm to 100 nm. The diameter and length of the primary carbon nanostructure can be measured from scanning electron microscope (SEM) or transmission electron microscope (TEM) images. Alternatively, the diameter and / or length of the primary carbon nanostructure can be measured by laser diffraction.

[0072] The secondary carbon nanostructure may be, for example, a structure formed by assembling primary carbon nanostructures in whole or in part to form a bundle or bunch shape. The secondary carbon nanostructure may include, for example, a bundle-type carbon nanostructure, a rope-type carbon nanostructure, or a combination thereof. The diameter of the secondary carbon nanostructure may be, for example, 2 nm to 200 nm, 3 nm to 150 nm, 5 nm to 100 nm, 5 nm to 50 nm, 5 nm to 30 nm, or 5 nm to 20 nm. The length of the secondary carbon nanotube structure can be, for example, 20 nm to 2 ㎛, 30 nm to 1.5 ㎛, 50 nm to 1 ㎛, 50 nm to 500 nm, 50 nm to 400 nm, 50 nm to 300 nm, 50 nm to 200 nm, or 50 nm to 100 nm or more. The diameter and length of the secondary carbon nanostructure can be measured from a scanning electron microscope (SEM) image or an optical microscope. Alternatively, the diameter and / or length of the secondary carbon nanostructure can be measured by laser diffraction. The secondary carbon nanostructure can be converted into the primary carbon nanostructure by, for example, dispersing it in a solvent or the like and then used in the manufacture of a cathode active material (CAC).

[0073] The method for manufacturing the cathode active material (CAC) according to the present embodiments may be, but is not limited to, a dry method, a wet method, or a combination thereof. In the art, methods for manufacturing the cathode active material (CAC) include, but are not necessarily limited to, milling, heat treatment, or deposition, and any method used in the art may be used.

[0074] In one embodiment of the present invention, the sulfide-based composite (CAM) in the cathode active material (CAC) may include a composite of Li2S and a solid electrolyte. The solid electrolyte may be, for example, an amorphous solid electrolyte, and any material used as an ion-conducting material in the art may be used. The solid electrolyte may be, for example, an inorganic solid electrolyte. The solid electrolyte may be, for example, a crystalline solid electrolyte, an amorphous solid electrolyte, or a combination thereof. The solid electrolyte may be, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a combination thereof. The sulfide-based solid electrolyte includes, for example, Li, S, and P, and may optionally further include a halogen element. The sulfide-based solid electrolyte may be selected from among sulfide-based solid electrolytes used in the solid electrolyte layer. The sulfide-based solid electrolyte may have, for example, a molecular weight of 1×10 at room temperature. -5 It can have an ionic conductivity of S / cm or more. Sulfide-based solid electrolytes include, for example, Li3PO4-Li2SO4, Li2S-P2S5, Li2S-P2S5-LiX, where X is a halogen element, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n , m, n are positive numbers, Z is one of Ge, Zn or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga In, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS6-x I x , may include one or more selected from 0≤x≤2.

[0075] The oxide-based solid electrolyte contains, for example, Li, O, and transition metal elements, and may optionally contain other elements. The oxide-based solid electrolyte has, for example, a 1×10 -5 It may be a solid electrolyte having an ionic conductivity of S / cm or more. The oxide-based solid electrolyte may be selected from oxide-based solid electrolytes used in the solid electrolyte layer. The solid electrolyte may be, for example, a mixture of a sulfide-based solid electrolyte and a lithium salt. For example, it may be a mixture of Li3PO4-Li2SO4 and a binary lithium salt, or a mixture of Li3PO4-Li2SO4 and a ternary lithium salt.

[0076] In one embodiment of the present invention, the sulfide-based composite (CAM) within the cathode active material (CAC) may include a composite of Li2S and a lithium salt. In other words, the composite (CAM) may include Li2S and a lithium salt compound. The lithium salt compound may not include, for example, sulfur (S) atoms.

[0077] The lithium salt compound may be, for example, a binary compound composed of lithium and one element selected from groups 13 to 17 of the periodic table. The binary compound may include, for example, one or more selected from LiF, LiCl, LiBr, LiI, LiH, Li2S, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, LiI3, and LiB3. The lithium salt compound may be, for example, a ternary compound composed of lithium and two elements selected from groups 13 to 17 of the periodic table. The ternary compound may include, for example, one or more selected from Li3OCl, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiNO3, Li2CO3, LiBH4, Li2SO4, Li3BO3, Li3PO4, Li4NCl, Li5NCl2, and Li3BN2. For example, the lithium salt compound may be one or more lithium halide compounds selected from LiF, LiCl, LiBr, and LiI.

[0078] In one embodiment of the present invention, the sulfide-based composite (CAM) may include a composite of Li2S and a metal carbide. The metal carbide may be, for example, a two-dimensional metal carbide. The two-dimensional metal carbide may be, for example, MXene. The two-dimensional metal carbide may be, for example, M n+1 C n T x (M is a transition metal, T is a terminal group, T is O, OH and / or F, n=1, 2, or 3, and x is the number of terminal groups) can be expressed as 2D metal carbides, for example, Ti2CT x , (Ti 0.5 , Nb 0.5 )2CT x , Nb2CT x , V2CT x , Ti3C2T x , (V 0.5 , Cr 0.5)3C2T x , Ti3CNT x , Ta4C3T x , Nb4C3T x or a combination thereof. The surface of the two-dimensional metal carbide may be terminated with O, OH and / or F.

[0079] In one embodiment of the present invention, the sulfide-based composite (CAM) may include a composite of Li2S and a metal nitride. The metal nitride may be, for example, a two-dimensional metal nitride. The two-dimensional metal nitride may be, for example, M n+1 N n T x (M is a transition metal, T is a terminal group, T is O, OH and / or F, n=1, 2, or 3, and x is the number of terminal groups) can be expressed as The surface of the two-dimensional metal nitride can be terminated with O, OH and / or F.

[0080] A composite (CAM) containing a cathode active material (CAC) and Li2S according to one embodiment of the present invention will be described in more detail. The cathode active material (CAC) may include a composite of Li2S, a lithium salt, and carbon. More specifically, the cathode active material (CAC) may include a composite of Li2S, a lithium halide, and carbon.

[0081] The composite (CAM) according to the present embodiments may have ductility. The composite (CAM) may function as a buffer material within the positive electrode active material layer (120). The composite (CAM) may prevent the occurrence of defects due to volume changes in the positive electrode active material layer (120).

[0082] In one embodiment, the composite (CAM) comprises Li2S-Li a X b(1≤a≤5, 1≤b≤5) may include a compound represented by X. The X may be I, Br, Cl, F, H, O, Se, Te, N, P, As, Sb, Al, B, OCl, PF6, BF4, SbF6, AsF6, ClO4, AlO2, AlCl4, NO3, CO3, BH4, SO4, BO3, PO4, NCl, NCl2, BN2 or a combination thereof. a may be, for example, 1, 2, 3, 4 or 5. b may be, for example, 1, 2, 3, 4 or 5.

[0083] In one embodiment, the composite (CAM) may include a solid solution of Li2S and a lithium salt. The ionic conductivity of the composite (CAM) may be improved by the composite (CAM) including the solid solution of Li2S and a lithium salt. For example, since the solid solution of Li2S and a lithium salt includes lithium ions arranged within Li2S crystallites, the ionic conductivity of the solid solution of Li2S and a lithium salt may be improved compared to the ionic conductivity of Li2S. Consequently, the composite (CAM) according to the present invention may have high ionic conductivity and low internal resistance. The cycle characteristics of an all-solid-state secondary battery including the composite (CAM) of the present invention may be improved.

[0084] The size of the Li2S crystallites of the complex (CAM) obtained from the XRD spectrum may be, for example, 20 nm or less, 15 nm or less, or 10 nm or less. The size of the Li2S crystallites of the complex (CAM) obtained from the XRD spectrum may be, for example, 1 to 20 nm, 1 to 15 nm, or 3 to 10 nm. As the size of the Li2S crystallites decreases, the contact area between Li2S and the lithium salt may increase. As the contact area between Li2S and the lithium salt increases, the ionic conductivity of the complex of Li2S and the lithium salt may be improved.

[0085] The complex (CAM) according to one embodiment may further comprise a metal halide. In other words, the complex (CAM) may comprise a complex of Li2S, a lithium salt, and a metal halide. The metal halide may contain a metal other than lithium.

[0086] The complex (CAM) is Li2S-Li a X1 b -MX2 c A compound represented by may include a compound represented by. a may be an integer from 1 to 5, b may be an integer from 1 to 5, and c may be an integer from 1 to 5. M may be selected from the group consisting of aluminum (Al), silver (Ag), gold (Au), platinum (Pt), palladium (Pd), bismuth (Bi), tin (Sn), and zinc (Zn). Each of X1 and X2 may be selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

[0087] The composite (CAM) may include a solid solution of Li2S, a lithium salt, and a metal halide. For example, the composite (CAM) may include a compound (or solid solution) represented by Li2S-LiI-AlI3. As described above, the composite (CAM) and a conductive material (CMA, e.g., carbon nanostructure) may constitute a cathode active material (CAC) according to the present invention.

[0088] The Mohs hardness of the composite (CAM) may be lower than that of the lithium salt. The composite (CAM) may have improved ductility compared to the lithium salt. The improved ductility of the composite (CAM) effectively prevents internal defects due to volume changes in the positive electrode active material layer (120).

[0089] The Mohs hardness of Li2S is, for example, 0.6. The Mohs hardness of the composite (CAM) may be, for example, less than 2, less than 1.5, less than 1, or less than 0.7. If the Mohs hardness of the composite (CAM) increases excessively, it may be difficult to provide ductility.

[0090] The Mohs hardness of the lithium salt may be 0.7 or more, 0.8 or more, 0.9 or more, 1.0 or more, 1.5 or more, or 2.0 or more. For example, the Mohs hardness of LiI is 2.0. Since the lithium salt has a Mohs hardness within this range, the pulverization of Li2S can be performed more easily during the milling process, and a solid solution of Li2S and the lithium salt can be formed more easily.

[0091] Since Li2S has relatively low ionic conductivity, a complex of Li2S and a lithium salt can be formed to improve ionic conductivity. The complex (CAM), which is a complex of Li2S and a lithium salt, can have improved ionic conductivity compared to Li2S alone. The content of Li2S in the complex (CAM) can be 50 wt% to 95 wt%, 50 wt% to 90 wt%, 50 wt% to 80 wt%, or 50 wt% to 70 wt% of the total weight of the complex (CAM). When the complex (CAM) has a Li2S content in this range, the complex (CAM) can have both improved ionic conductivity and excellent ductility.

[0092] The content of the lithium salt in the composite (CAM) can be 5 wt% to 50 wt%, 10 wt% to 50 wt%, 20 wt% to 50 wt%, or 30 wt% to 50 wt% of the total weight of the composite (CAM). By having the lithium salt content in this range, the composite (CAM) can have both improved ionic conductivity and excellent ductility.

[0093] The content of the metal halide in the composite (CAM) may be 5 wt% to 30 wt%, or 5 wt% to 20 wt%, of the total weight of the composite (CAM). By having the metal halide content in this range, the composite (CAM) can simultaneously have improved ionic conductivity and excellent ductility.

[0094] In one embodiment, the content of Li2S in the composite (CAM) may be greater than the content of the lithium salt. The content of Li2S in the composite (CAM) may be greater than the content of the metal halide. For example, the molar ratio of Li2S to the lithium salt in the composite (CAM) may be 51:49 to 95:5, 55:45 to 90:10, 60:40 to 90:10, or 70:30 to 90:10. By having such a molar ratio, the composite (CAM) may have both enhanced ionic conductivity and excellent ductility.

[0095] The ionic conductivity of the complex (CAM) according to embodiments of the present invention is, for example, 1×10 at 25°C. -5 S / cm or more, 2×10 -5 S / cm or more, 4×10 -5 S / cm or more, 6×10 -5 S / cm or more, 8×10 -5 S / cm or more or 1×10 -4 It can be S / cm or more. For example, the ionic conductivity can be measured using an electrochemical impedance spectroscopy, a direct current polarization method, etc. Since the composite (CAM) has an ionic conductivity in this range, the internal resistance of the positive electrode active material layer (120) including the composite (CAM) can be further reduced.

[0096] The average particle diameter (D50) of the composite (CAM) may be, for example, 2 μm or less, 1.5 μm or less, or 1 μm or less. The average particle diameter of the composite (CAM) may be, for example, 0.1 μm to 2 μm, 0.1 μm to 1.5 μm, or 0.1 μm to 1 μm.

[0097] The size of the Li2S particles in the composite (CAM) can be, for example, 2 μm or less, 1.5 μm or less, or 1 μm or less. The size of the Li2S particles can be, for example, 0.1 μm to 2 μm, 0.1 μm to 1.5 μm, or 0.1 μm to 1 μm.

[0098] Referring back to FIGS. 2 and 3, the positive electrode active material layer (120) may further include a solid electrolyte (SEP) in addition to the Li2S-containing positive electrode active material (CAC). The solid electrolyte (SEP) in the positive electrode active material layer (120) may be the same as or different from the solid electrolyte in the solid electrolyte layer (300) described below.

[0099] The solid electrolyte (SEP) in the positive electrode active material layer (120) may have a smaller average particle diameter (D50) than the solid electrolyte in the solid electrolyte layer (300). For example, the average particle diameter of the solid electrolyte (SEP) in the positive electrode active material layer (120) may be 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, or 20% or less of the average particle diameter of the solid electrolyte in the solid electrolyte layer (300).

[0100] In one embodiment, the content of the cathode active material (CAC) in the cathode active material layer (120) may be 40 wt% to 90 wt%, 50 wt% to 90 wt%, or 60 wt% to 90 wt% of the total weight of the cathode active material layer (120). Among the components in the cathode active material layer (120), the cathode active material (CAC) may have the largest content. The content of the solid electrolyte (SEP) in the cathode active material layer (120) may be 10 wt% to 70 wt%, 10 wt% to 60 wt%, or 10 wt% to 40 wt% of the total weight of the cathode active material layer (120).

[0101] The solid electrolyte (SEP) may be, for example, a sulfide-based solid electrolyte. The sulfide-based solid electrolyte may be, for example, Li2S-P2S5, Li2S-P2S5-LiX, where X is a halogen element, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z. m S n , m, n are positive numbers, Z is one of Ge, Zn or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga In, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x, may be at least one selected from 0≤x≤2. The sulfide-based solid electrolyte is manufactured by treating starting materials such as Li2S and P2S5 by a melting rapid cooling method or a mechanical milling method. In addition, heat treatment may be performed after the treatment. The solid electrolyte may be amorphous, crystalline, or a mixture thereof. In addition, the solid electrolyte may be, for example, one containing sulfur (S), phosphorus (P), and lithium (Li) as at least constituent elements among the above-described sulfide-based solid electrolyte materials. For example, the solid electrolyte may be a material containing Li2S-P2S5. When using a sulfide-based solid electrolyte material containing Li2S-P2S5 to form a solid electrolyte, the mixing molar ratio of Li2S and P2S5 is, for example, in the range of Li2S:P2S5=20:80 to 90:10, 25:75 to 90:10, 30:70 to 70:30, 40:60 to 60:40.

[0102] The sulfide-based solid electrolyte may include, for example, an argyrodite type solid electrolyte represented by the following chemical formula 1:

[0103] <Chemical Formula 1>

[0104] Li + 12-n-x A n+ X 2- 6-x Y - x

[0105] In the above formula, A is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb or Ta, X is S, Se or Te, Y is Cl, Br, I, F, CN, OCN, SCN or N3, and 1≤n≤5, 0≤x≤2. The sulfide-based solid electrolyte is, for example, Li 7-x PS 6-x Cl x , 0≤x≤2, Li7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x , may be an argyrodite-type compound including at least one selected from 0≤x≤2. The sulfide-based solid electrolyte may be an argyrodite-type compound including at least one selected from, for example, Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0106] Alternatively, the sulfide-based solid electrolyte is Li 7-a M a PS 6-c X c It may be an argyrodite-type compound containing (0≤a≤2, (0≤c≤2)), where X may be F, Br, Cl, or a combination thereof. M is candium (Sc), yttrium (Y), titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), mercury (Hg), aluminum (Al), gallium (Ga), indium (In), thallium (Tl), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), or a combination thereof. Can be.

[0107] The density of the argyrodite-type solid electrolyte may be 1.5 to 2.0 g / cc. Since the argyrodite-type solid electrolyte has a density of 1.5 g / cc or more, the internal resistance of the all-solid-state secondary battery is reduced, and penetration of the solid electrolyte layer by Li can be effectively suppressed.

[0108] The positive electrode active material layer (120) may further include a filler (FIL). In one embodiment, the content of the filler (FIL) in the positive electrode active material layer (120) may be 0.1 to 20 wt%, 0.1 to 10 wt%, or 0.1 to 5 wt% of the total weight of the positive electrode active material layer (120).

[0109] According to embodiments of the present invention, the filler (FIL) may be an inorganic filler, an organic filler, or a combination thereof. In one embodiment, the filler (FIL) may include an amorphous inorganic filler. The inorganic filler may be, for example, an amorphous lithium metal oxyhalide. In one embodiment, after preparing a crystalline lithium metal oxyhalide, the crystalline lithium metal oxyhalide may be melted to prepare a molten salt, which may then be cooled to prepare an amorphous lithium metal oxyhalide. In another embodiment, the composition of the lithium metal oxyhalide may be controlled to directly prepare the amorphous lithium metal oxyhalide. The amorphous inorganic filler may have, for example, ductility. Since the amorphous inorganic filler has ductility, it can more effectively accommodate volume changes during charge and discharge of the all-solid-state battery (10). In contrast, the crystalline lithium metal oxyhalide may be relatively brittle compared to the amorphous lithium metal halide. Whether or not the inorganic filler is amorphous can be confirmed using an XRD spectrum.

[0110] The inorganic filler may be, for example, glassy. The inorganic filler may include, for example, a glassy lithium metal oxyhalide having a glass transition temperature (Tg). The glassy lithium metal oxyhalide may have ductility. Since the inorganic filler has ductility, the volume change of the all-solid-state secondary battery (10) can be effectively accommodated during charge and discharge or can be easily deformed according to the volume change of the all-solid-state secondary battery (10).

[0111] The glass transition temperature of the inorganic filler may be, for example, 20°C or lower, 10°C or lower, 0°C or lower, or -10°C or lower. Because the inorganic filler has such a low glass transition temperature, it can easily transition from a brittle, crystalline metal salt state to a ductile, glassy state. For example, the inorganic filler can be easily transitioned from a crystalline, molten salt state to a glassy state by melting and then cooling it. Alternatively, the glassy state can be obtained during the manufacturing process of the inorganic filler. The glass transition temperature can be measured, for example, using a differential scanning calorimeter (DSC). The glass transition temperature can be measured, for example, using a dynamic mechanical analyzer (DMA).

[0112] The melting point of the inorganic filler may be, for example, 100°C or higher, 105°C or higher, 110°C or higher, 115°C or higher, 120°C or higher, 125°C or higher, 130°C or higher, 135°C or higher, 140°C or higher, or 145°C or higher. The melting point of the inorganic filler may be, for example, 200°C or lower, 190°C or lower, 180°C or lower, 170°C or lower, 160°C or lower, or 150°C or lower. Since the inorganic filler has a melting point within this range, the inorganic filler can be melted to form a molten salt state and then cooled to easily produce an amorphous inorganic filler. The melting point of the inorganic filler can be measured, for example, using differential scanning calorimetry (DSC).

[0113] The inorganic filler may be an ionic conductive inorganic filler. The inorganic filler may have, for example, an ionic conductivity of 0.01 mS / cm or more, 0.05 mS / cm or more, 0.1 mS / cm or more, 0.3 mS / cm or more, 0.5 mS / cm or more, 0.7 mS / cm or more, or 1.0 mS / cm or more at 25°C1 atm. The ionic conductivity may be measured by AC impedance analysis. The voltage amplitude used in the AC impedance analysis may be 5 to 10 mV, and the frequency may be 1 MHz to 1 Hz. Since the inorganic filler has ionic conductivity, it can effectively suppress an increase in the interfacial resistance between the positive electrode active material (CAC) particles, between the solid electrolyte (SEP) particles, and / or between the positive electrode active material (CAC) and the solid electrolyte (SEP) within the positive electrode active material layer (120) (see FIG. 3).

[0114] The elastic modulus (elastic modulus or Young's modulus) of the inorganic filler at 30°C may be 10 GPa or less, 5 GPa or less, 3 GPa or less, or 2 GP a or less. Since the inorganic filler has an elastic modulus in this low range, the positive electrode active material layer (120) can effectively accommodate the volume change of the all-solid-state battery (10). Accordingly, the cycle characteristics of the all-solid-state battery (10) according to the present invention can be improved. The elastic modulus of the inorganic filler can be measured, for example, using a dynamic mechanical analyzer (DMA).

[0115] The elastic modulus of the inorganic filler may be, for example, lower than the elastic modulus of the solid electrolyte (SEP). The elastic modulus of the solid electrolyte (SEP) at 30° C. may be, for example, 22 GPa to 30 GPa. The elastic modulus of the inorganic filler may be, for example, 90% or less, 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less of the elastic modulus of the solid electrolyte (SEP).

[0116] An inorganic filler, i.e., a filler (FIL) can be uniformly provided within the positive electrode active material layer (120) (see FIG. 3). In the all-solid-state battery (10) of the present invention, since the inorganic filler has a lower elastic modulus than the solid electrolyte (SEP), the inorganic filler can easily fill the pores between the solid electrolytes (SEP) and / or the pores between the solid electrolyte (SEP) and the positive electrode active material (CAC), thereby reducing the internal resistance of the positive electrode active material layer (120) and easily accommodating a volume change of the positive electrode active material layer (120) during charge and discharge. As a result, the cycle characteristics of the all-solid-state battery (10) can be further improved. The elastic modulus of the solid electrolyte (SEP) can be measured, for example, using a dynamic mechanical analyzer (DMA).

[0117] The inorganic filler may have, for example, viscoelasticity. The inorganic filler may have, for example, viscoelastic creep. The viscoelastic creep rate of the inorganic filler may be, for example, 1×10-4 % / s or more, 2×10-4 % / s or more, or 4×10-4 % / s or more. % / s is the ratio of the deformed size to the initial size per unit time (second). Since the inorganic filler has viscoelasticity, the volume change during charge and discharge of the all-solid-state battery (10) can be easily accommodated, and the shape can be continuously deformed without defects. The creep rate is the change rate over time of the inorganic filler under stress at a constant temperature, i.e., the strain rate. The creep rate can be measured using, for example, a universal testing machine.

[0118] Weapon filler is Li a Al b M c O d Cl e (0 <a≤3; 0<b≤3; 0≤c<2; 0<d≤2; 1<e≤4; d<e, M은 원소주기율표 3족 내지 15족에서 선택되는 금속) 표시되는 리튬금속옥시할라이드(lithium metal oxyhalide)를 포함할 수 있다. 리튬금속옥시할라이드의 금속 M은 예를 들어 Fe, Ga, In, As, Sb, Mo, Bi, B 또는 이들의 조합을 포함할 수 있다.

[0119] Lithium metal oxyhalides are, for example, Li a Al b O d Cl e (0 <a≤3; 0<b≤3; 0<d≤2; 1<e≤4; d<e), Li a Al b Fe c O d Cl e(0 <a≤3; 0<b≤3; 0≤c<2; 0<d≤2; 1<e≤4; d<e), Li a Al b Ga c O d Cl e (0 <a≤3; 0<b≤3; 0≤c<2; 0<d≤2; 1<e≤4; d<e), Li a Al b In c O d Cl e (0 <a≤3; 0<b≤3; 0≤c<2; 0<d≤2; 1<e≤4; d<e), Li a Al b As c O d Cl e (0 <a≤3; 0<b≤3; 0≤c<2; 0<d≤2; 1<e≤4; d<e), Li a Al b Sb c O d Cl e (0 <a≤3; 0<b≤3; 0≤c<2; 0<d≤2; 1<e≤4; d<e), Li a Al b Mo c O d Cl e (0 <a≤3; 0<b≤3; 0≤c<2; 0<d≤2; 1<e≤4; d<e), ), Li a Al b Bi c O d Cl e (0 <a≤3; 0<b≤3; 0≤c<2; 0<d≤2; 1<e≤4; d<e), Li a Al b B c O d Cl e (0 <a≤3; 0<b≤3; 0≤c<2; 0<d≤2; 1<e≤4; d<e) 또는 이들의 조합을 포함할 수 있다.

[0120] Lithium metal oxyhalides are, for example, LiAl x O z Cl w(0 <x≤2; 0<z≤1; 2<w<4; z<w), LiAlxFeyOzClw (0<x≤2; 0≤y<1; 0<z≤1; 2<w<4; z<w), LiAl x Yes y Oh z Cl w (0 <x≤2; 0≤y<1; 0<z≤1; 2<w<4; z<w), LiAl x In y Oh z Cl w (0 <x≤2; 0≤y<1; 0<z≤1; 2<w<4; z<w), LiAl x I y Oh z Cl w (0 <x≤2; 0≤y<1; 0<z≤1; 2<w<4; z<w), LiAl x Sat y Oh z Cl w (0 <x≤2; 0≤y<1; 0<z≤1; 2<w<4; z<w), LiAl x Mo y Oh z Cl w (0 <x≤2; 0≤y<1; 0<z≤1; 2<w<4; z<w), LiAl x Bi y Oh z Cl w (0 <x≤2; 0≤y<1; 0<z≤1; 2<w<4; z<w), LiAl x B y Oh z Cl w (0 <x≤2; 0≤y<1; 0<z≤1; 2<w<4; z<w) 또는 이들의 조합을 포함할 수 있다.

[0121] The content of the inorganic filler in the positive electrode active material layer (120) may be smaller than the content of the solid electrolyte (SEP). The weight ratio of the solid electrolyte (SEP) and the inorganic filler in the positive electrode active material layer (120) may be 99:1 to 50:50, 99:1 to 60:40, 99:1 to 70:30, 99:1 to 80:20, or 99:1 to 90:10. Since the solid electrolyte (SEP) and the inorganic filler have a weight ratio in this range, the volume change during charge and discharge of the positive electrode active material layer (120) can be more easily accommodated. As a result, the cycle characteristics of the all-solid-state battery (10) can be further improved.

[0122] In another embodiment, the filler (FIL) may include an organic filler. The organic filler may include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polypropylene (PP), cycloolefin polymers, and combinations thereof.

[0123] The positive electrode active material layer (120) may further include a conductive material. The conductive material may be, for example, a carbon-based material, a metal-based material, or a combination thereof. In one embodiment of the present invention, as shown in FIG. 3, the conductive material (CMA) within the positive electrode active material layer (120) may form a positive electrode active material (CAC) together with a composite material (CAM).

[0124] The conductive material content in the positive electrode active material layer (120) may be, for example, 1 wt% to 30 wt%, 1 wt% to 20 wt%, or 1 wt% to 10 wt% of the total weight of the positive electrode active material layer (120).

[0125] The metal-based material may be, but is not limited to, metal powder, metal fiber, or a combination thereof, and any metal-based material used as a conductive material in the relevant technical field may be used.

[0126] The carbon-based material may include, for example, amorphous carbon. By including amorphous carbon in the carbon-based material, side reactions between the carbon-based material and the solid electrolyte (SEP) can be suppressed. Therefore, the cycle characteristics of the all-solid-state battery (10) including the carbon-based material can be further improved. The specific description of the carbon-based material may be the same as or similar to that described above regarding the conductive agent (CMA).

[0127] The positive electrode active material layer (120) may further include a binder (BID). The binder may be, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyethylene, etc., but is not limited thereto, and any binder used in the relevant technical field may be used. The content of the binder (BID) in the positive electrode active material layer (120) may be, for example, 0.1 wt% to 10 wt%, 0.5 to 5 wt%, or 0.5 to 2 wt% of the total weight of the positive electrode active material layer (120). The binder (BID) may be omitted.

[0128] The positive electrode active material layer (120) may further include additives such as a coating agent, a dispersant, an ion-conducting aid, etc., in addition to the above-described positive electrode active material (e.g., CAM), solid electrolyte (SEP), binder (BID), conductive agent (CMA), and filler (FIL). The coating agent, dispersant, ion-conducting aid, etc. that may be included in the positive electrode active material layer (120) may be a known material generally used in the electrode of an all-solid-state battery.

[0129] The negative electrode layer (200) may include a negative electrode current collector (210) and a negative electrode coating layer (220) on the negative electrode current collector (210). The negative electrode current collector (210) may provide a reference surface on which the negative electrode coating layer (220) is disposed. The negative electrode current collector (210) may include, for example, a material that does not react with lithium, i.e., does not form an alloy or a compound with lithium. For example, the negative electrode current collector (210) may include at least one metal selected from the group consisting of copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni). The thickness of the negative electrode current collector (210) may be 1 μm to 20 μm, more specifically 5 μm to 15 μm, and more specifically 7 μm to 10 μm.

[0130] The negative electrode current collector (210) may be composed of one of the above-described metals, or may include an alloy or coating material of two or more metals. The negative electrode current collector (210) may have, for example, a plate shape or a foil shape. Meanwhile, in one embodiment, the negative electrode current collector (210) may be omitted.

[0131] Although not shown, an anode current collector (210) according to one embodiment may include a base film and a metal layer disposed on one or both sides of the base film. The base film may include, for example, a polymer. The polymer may be, for example, a thermoplastic polymer. The polymer may include, for example, polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or a combination thereof. The polymer may be an insulating polymer. Since the base film includes an insulating thermoplastic polymer, when a short circuit occurs, the base film may soften or liquefy, thereby blocking battery operation and suppressing a rapid increase in current. The metal layer may include, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), or an alloy thereof. The anode current collector (210) may additionally include a metal piece and / or a lead tab. For more specific details regarding the base film, metal layer, metal chip, and lead tab of the negative electrode current collector (210), refer to the positive electrode current collector (110) described above. Since the negative electrode current collector (210) has this structure, the weight of the negative electrode layer (200) can be reduced, and as a result, the energy density of the all-solid-state battery (10) can be improved.

[0132] The negative electrode coating layer (220) can be configured to allow lithium metal to grow between it and the negative electrode current collector (210) when the all-solid-state battery (10) is charged. The negative electrode coating layer (220) can serve as a protective layer for the lithium metal and simultaneously suppress the precipitation and growth of lithium dendrites.

[0133] The cathode coating layer (220) may include a metal and carbon. For example, the cathode coating layer (220) may include at least one metal selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). The cathode coating layer (220) may include at least one carbon selected from the group consisting of carbon black, acetylene black, furnace black, ketjen black, and graphene. In one embodiment, the cathode coating layer (220) may include a mixture of carbon black and silver (Ag).

[0134] The cathode coating layer (220) may further include additives other than metal and carbon. The cathode coating layer (220) may further include, for example, at least one additive selected from the group consisting of a binder, a filler, a coating agent, a dispersant, and an ion conductive additive.

[0135] The negative electrode coating layer (220) may have a smaller thickness than the positive electrode active material layer (120). The thickness of the negative electrode coating layer (220) may be, for example, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or 5% or less of the thickness of the positive electrode active material layer (120). The thickness of the negative electrode coating layer (220) may be, for example, 1 um to 20 um, 2 um to 10 um, or 3 um to 7 um. If the thickness of the negative electrode coating layer (220) is too thin, lithium dendrites formed between the negative electrode coating layer (220) and the negative electrode current collector (210) may cause the negative electrode coating layer (220) to collapse, thereby deteriorating the cycle characteristics of the all-solid-state battery (10). If the thickness of the cathode coating layer (220) increases excessively, the energy density of the all-solid-state battery (10) may decrease and the internal resistance of the all-solid-state battery (10) due to the cathode coating layer (220) may increase, thereby deteriorating the cycle characteristics of the cell.

[0136] Meanwhile, although not shown, a carbon layer may be further included to improve adhesion between the cathode coating layer (220) and the solid electrolyte layer (300).

[0137] A solid electrolyte layer (300) may be provided between the positive electrode layer (100) and the negative electrode layer (200). The solid electrolyte layer (300) may include a sulfide-based solid electrolyte having excellent lithium ion conductivity characteristics. The solid electrolyte in the solid electrolyte layer (300) may be the same as or different from any one of the materials included in the solid electrolyte (SEP, see FIG. 3) in the positive electrode active material layer (120) described above.

[0138] The solid electrolyte layer (300) may include a first solid electrolyte layer (310) and a second solid electrolyte layer (320). The first solid electrolyte layer (310) may be adjacent to the positive electrode layer (100), and the second solid electrolyte layer (320) may be adjacent to the negative electrode layer (200).

[0139] Referring to FIG. 2, the first solid electrolyte layer (310) may include a first solid electrolyte. The first solid electrolyte may have a particle shape such as a sphere or an ellipsoid. The first solid electrolyte may include a sulfide-based solid electrolyte. The first solid electrolyte may be amorphous, crystalline, or a mixture thereof. In addition, the solid electrolyte may include, for example, at least sulfur (S), phosphorus (P), and lithium (Li) as constituent elements among the above-described sulfide-based solid electrolyte materials. For example, the solid electrolyte may be a material including Li2S-P2S5. When using a sulfide-based solid electrolyte material including Li2S-P2S5 to form the solid electrolyte, the mixing molar ratio of Li2S and P2S5 may be, for example, in the range of Li2S:P2S5=50:50 to 90:10.

[0140] In one embodiment, the first solid electrolyte is Li 7-x PS6-x Cl x (0≤x≤2), Li 7-x PS 6-x Br x (0≤x≤2), and Li 7-x PS 6-x I x The first solid electrolyte may include an argyrodite-type compound including at least one selected from (0≤x≤2). The first solid electrolyte may include an argyrodite-type compound including at least one selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0141] In another embodiment, the first solid electrolyte is Li 7-a M a PS 6-c X c Argyrodite-type compounds may include, wherein X may be Cl, Br, or a combination thereof. M may be Na, K, Fe, Mg, Ca, Ag, Cu, Zr, Zn, or a combination thereof. Each of a and c may be a real number between 0 and 2.

[0142] The density of the argyrodite-type solid electrolyte may be 1.5 g / cc to 2.0 g / cc. When the argyrodite-type solid electrolyte has a density of 1.5 g / cc or more, the internal resistance of the all-solid-state battery is reduced, and the defect of the solid electrolyte membrane being penetrated and short-circuited due to the formation of lithium dendrites can be prevented. The elastic modulus of the first solid electrolyte is, for example, 15 GPa to 35 GPa.

[0143] The second solid electrolyte layer (320) may include a second solid electrolyte. The second solid electrolyte may have a particle shape such as a sphere or an ellipsoid. The second solid electrolyte may include a sulfide-based solid electrolyte. The description of the second solid electrolyte may be the same as or similar to that described above for the first solid electrolyte. In one embodiment, the second solid electrolyte may have substantially the same composition as the first solid electrolyte. In another embodiment, the second solid electrolyte may have a similar composition as the first solid electrolyte.

[0144] The second solid electrolyte can be in direct contact with the negative electrode coating layer (220). As a result, the second solid electrolyte can suppress lithium dendrites formed between the negative electrode coating layer (220) and the negative electrode current collector (210). The second solid electrolyte can effectively suppress negative electrode side reactions. As a result, the cell performance of the all-solid-state battery (10) according to the present invention can be improved.

[0145] Each of the first and second solid electrolyte layers (310, 320) may further include a binder. The binder in the solid electrolyte layer (300) may be, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, or the like, but is not limited thereto. The binder in the solid electrolyte layer (300) may be the same as or different from the binder in the positive electrode active material layer (120) or the binder in the negative electrode coating layer (220).

[0146] The content of the binder in the solid electrolyte layer (300) may be 0.1 to 10 wt%, 0.1 to 5 wt%, 0.1 to 3 wt%, 0.1 to 1 wt%, 0 to 0.5 wt%, or 0 to 0.1 wt% with respect to the total weight of the solid electrolyte layer (300).

[0147] In another embodiment of the present invention, the solid electrolyte layer (300) may be provided as a single-layer structure rather than a double-layer structure of the first solid electrolyte layer (310) and the second solid electrolyte layer (320).

[0148] Referring back to FIGS. 1 and 2, the positive electrode layer (100) and the first solid electrolyte layer (310) may form a positive electrode composite layer (CSH). The negative electrode layer (200) and the second solid electrolyte layer (320) may form a negative electrode composite layer (ASH). The positive electrode composite layer (CSH) may be laminated on the negative electrode composite layer (ASH).

[0149] The area of ​​the cathode composite layer (ASH) and the area of ​​the cathode composite layer (CSH) may be different. Specifically, the area of ​​the cathode composite layer (ASH) may be larger than that of the cathode composite layer (CSH). The cathode composite layer (CSH) may be completely overlapped within the cathode composite layer (ASH).

[0150] In one embodiment of the present invention, the first solid electrolyte layer (310) may have substantially the same area as the positive electrode layer (100). The second solid electrolyte layer (320) may have substantially the same area as the negative electrode layer (200).

[0151] Specifically, the positive electrode composite layer (CSH) may have a first width (WI1) in a first direction (D1). The negative electrode composite layer (ASH) may have a second width (WI2) in the first direction (D1). The first width (WI1) may be smaller than the second width (WI2). The positive electrode composite layer (CSH) may have a third width (WI3) in the second direction (D2). The negative electrode composite layer (ASH) may have a fourth width (WI4) in the second direction (D2). The third width (WI3) may be smaller than the fourth width (WI4).

[0152] The all-solid-state battery (10) according to the present embodiment can be manufactured by forming a negative electrode composite layer (ASH) on a first carrier film, forming a positive electrode composite layer (CSH) on a second carrier film, and then laminating the negative electrode composite layer (ASH) and the positive electrode composite layer (CSH).

[0153] In one embodiment, as shown in FIG. 2, the discharged positive electrode active material layer (120) may have a first thickness (TK1). The all-solid-state battery (10) may have a first height (HE1) in the third direction (D3). The first height (HE1) may be the sum of the thickness of the positive electrode composite layer (CSH) and the thickness of the negative electrode composite layer (ASH).

[0154]

[0155] In the embodiments described below, detailed descriptions of technical features that overlap with those described above with reference to FIGS. 1 to 3 will be omitted, and differences will be described in detail.

[0156] FIG. 4 is a cross-sectional view taken along line A-A' of FIG. 1 to explain an all-solid-state battery according to another embodiment of the present invention. Referring to FIG. 4, in one embodiment, the all-solid-state battery (10) in a charged state may further include a lithium metal layer (230) provided between the negative electrode current collector (210) and the negative electrode coating layer (220). The negative electrode layer (200) according to the present embodiment may include the negative electrode current collector (210), the negative electrode coating layer (220), and the lithium metal layer (230) therebetween.

[0157] The lithium metal layer (230) may include lithium or a lithium alloy. Since the lithium metal layer (230) is a metal layer containing lithium, it may function as a lithium reservoir, for example. The lithium alloy may be, but is not limited to, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, a Li-Si alloy, etc., and any lithium alloy used in the art may be used. The lithium metal layer (230) may be formed of one of these alloys or lithium, or may be formed of several types of alloys. The lithium metal layer (230) may be, for example, a plated layer. The lithium metal layer (230) may be deposited between the negative electrode coating layer (220) and the negative electrode current collector (210), for example, during the charging process of the all-solid-state battery (10).

[0158] The lithium metal layer (230) may have a third thickness (TK3). The third thickness (TK3) is not particularly limited, but may be, for example, 1 μm to 500 μm, 1 μm to 200 μm, 1 μm to 150 μm, 1 μm to 100 μm, or 1 μm to 50 μm. If the third thickness (TK3) of the lithium metal layer (230) is too thin, it may be difficult for the lithium metal layer (230) to perform the role of a lithium reservoir. If the third thickness (TK3) of the lithium metal layer (230) is too thick, the mass and volume of the all-solid-state battery (10) may increase, and the cycle characteristics of the all-solid-state battery (10) may rather deteriorate.

[0159] In another embodiment of the present invention, the lithium metal layer (230) in the negative electrode layer (200) may be provided between the negative electrode current collector (210) and the negative electrode coating layer (220), for example, before assembling the all-solid-state battery (10). When the lithium metal layer (230) is disposed between the negative electrode current collector (210) and the negative electrode coating layer (220) before assembling the all-solid-state battery (10), the lithium metal layer (230) acts as a lithium reservoir because it is a metal layer containing lithium. For example, a lithium foil may be disposed between the negative electrode current collector (210) and the negative electrode coating layer (220) before assembling the all-solid-state battery (10).

[0160] When the lithium metal layer (230) is precipitated by charging after assembling the all-solid-state battery (10), the energy density of the all-solid-state battery (10) can increase because the lithium metal layer (230) is not included when assembling the all-solid-state battery (10). When charging the all-solid-state battery (10), the charging can exceed the charging capacity of the negative electrode coating layer (220). That is, the negative electrode coating layer (220) is overcharged. At the initial stage of charging, lithium can be absorbed into the negative electrode coating layer (220). When charging exceeds the capacity of the negative electrode coating layer (220), lithium can be precipitated, for example, between the negative electrode coating layer (220) and the negative electrode current collector (210). The precipitated lithium can form a lithium metal layer (230).

[0161] The lithium metal layer (230) may be mainly composed of lithium (i.e., metallic lithium). When discharging, lithium in the lithium metal layer (230) may be ionized and move to the positive electrode layer (100). In other words, lithium may be used as an anode active material in the all-solid-state battery (10). In addition, since the anode coating layer (220) covers the lithium metal layer (230), the anode coating layer (220) may protect the lithium metal layer (230) and simultaneously suppress the precipitation and growth of lithium dendrites. Therefore, the anode coating layer (220) may suppress short-circuiting and capacity reduction of the all-solid-state battery (10) and improve the cycle characteristics of the all-solid-state battery (10).

[0162] When a lithium metal layer (230) is formed by charging after assembling the all-solid-state battery (10), the negative electrode layer (200), i.e., the negative electrode current collector (210) and the negative electrode coating layer (220) and the region therebetween may be a Li-free region that does not contain lithium (Li) in the initial state of the all-solid-state battery (10) or in the state after complete discharge.

[0163] The positive electrode active material layer (120) from which lithium ions are released by charging the all-solid-state battery (10) may have a second thickness (TK2). The second thickness (TK2) of the positive electrode active material layer (120) may be smaller than the first thickness (TK1) of FIG. 2.

[0164] In one embodiment of the present invention, the difference between the first thickness (TK1) and the second thickness (TK2) may be substantially the same as or similar to the third thickness (TK3) of the lithium metal layer (230). For example, the third thickness (TK3) may be 1.0 to 1.5 times, or 1.0 to 1.2 times, the difference between the first thickness (TK1) and the second thickness (TK2). According to the present invention, the thickness of the positive electrode active material layer (120) may be correspondingly reduced by the thickness of the lithium metal layer (230) formed by charging the all-solid-state battery (10).

[0165] Although not shown, the all-solid-state battery (10) can operate (i.e., charge and / or discharge) while pressurized by a pressurizing jig. In one embodiment, the all-solid-state battery (10) can be pressurized to 0.8 MPa to 2 MPa. For example, the all-solid-state battery (10) can have an internal pressure of about 1 MPa when discharging, and the all-solid-state battery (10) can have an internal pressure of about 1.5 MPa when charging. The ratio of the internal pressure of the all-solid-state battery (10) in a charged state of FIG. 4 to the internal pressure of the all-solid-state battery (10) in a discharged state of FIG. 3 can be 1.0 to 2.0, or 1.2 to 1.8.

[0166] The all-solid-state battery (10) can change its height (or thickness or volume) depending on charging and discharging under the pressurized state described above. In the all-solid-state battery (10) according to the present embodiment, the thickness of the positive electrode active material layer (120) can decrease corresponding to the lithium metal layer (230) formed by charging. Therefore, the second height (HE2) of the charged all-solid-state battery (10) shown in FIG. 4 can be similar to the first height (HE1) of the discharged all-solid-state battery (10) shown in FIG. 2. For example, the second height (HE2) can be 1 to 1.5 times, or 1 to 1.2 times, the first height (HE1).

[0167]

[0168] FIG. 5 is a cross-sectional view taken along line A-A' of FIG. 1 to explain an all-solid-state battery according to another embodiment of the present invention. Referring to FIG. 5, the all-solid-state battery (10) according to the present embodiment may further include a gasket (GSK). The gasket (GSK) may be provided to surround the cathode composite layer (CSH). The gasket (GSK) may fill a step in the side surface of the all-solid-state battery (10) caused by the difference in area between the anode composite layer (ASH) and the cathode composite layer (CSH). The gasket (GSK) may surround four side surfaces of the cathode composite layer (CSH). For example, the thickness of the gasket (GSK) may be substantially the same as the thickness of the cathode composite layer (CSH).

[0169] The upper surface of the second solid electrolyte layer (320) may include a first region in contact with the first solid electrolyte layer (310) and a second region in contact with the gasket (GSK). The second region may be a peripheral region of the upper surface of the second solid electrolyte layer (320). The second region may surround the first region.

[0170] The gasket (GSK) can prevent cracking of the solid electrolyte layer (300) during the manufacture of the all-solid-state battery (10) and / or during charging and discharging of the all-solid-state battery (10). This can improve the cycle characteristics of the all-solid-state battery (10). If the all-solid-state battery (10) does not include the gasket (GSK), cracks may occur in the solid electrolyte layer (300) due to uneven pressure applied to the negative electrode composite layer (ASH) in contact with the positive electrode composite layer (CSH), and the possibility of a short circuit occurring due to the growth of lithium metal through the cracks may increase.

[0171] The thickness of the gasket (GSK) may be greater than the thickness of the cathode composite layer (CSH) or substantially the same as the thickness of the cathode composite layer (CSH). Since the thickness of the gasket (GSK) is the same as the thickness of the cathode composite layer (CSH), a uniform pressure is applied between the cathode composite layer (CSH) and the anode composite layer (ASH), and the cathode composite layer (CSH) and the anode composite layer (ASH) are sufficiently adhered to each other, so that the interfacial resistance between the first solid electrolyte layer (310) and the second solid electrolyte layer (320) can be reduced. In addition, since the solid electrolyte layer (300) is sufficiently sintered during the pressurized manufacturing process of the all-solid-state battery (10), the internal resistance of the solid electrolyte layer (300) can be reduced.

[0172] The gasket (GSK) may have, for example, a single-layer structure. Alternatively, although not illustrated in the drawing, the gasket (GSK) may have a multi-layer structure. In a multi-layer gasket (GSK), each layer may have a different composition. A multi-layer gasket (GSK) may have, for example, a two-layer structure, a three-layer structure, a four-layer structure, or a five-layer structure. A multi-layer gasket (GSK) may include, for example, one or more adhesive layers and one or more support layers.

[0173] The gasket (GSK) may include, for example, a flame-retardant inert material. The flame-retardant inert material provides flame retardancy, thereby preventing thermal runaway and ignition of the all-solid-state battery (10). Consequently, the gasket (GSK) may further enhance the safety of the all-solid-state battery (10). The flame-retardant inert material may absorb residual moisture within the all-solid-state battery (10), thereby preventing deterioration of the all-solid-state battery (10), thereby improving the lifespan characteristics of the all-solid-state battery (10).

[0174]

[0175] FIG. 6 is a cross-sectional view taken along line A-A' of FIG. 1 to explain an all-solid-state battery according to another embodiment of the present invention. Referring to FIG. 6, the positive electrode layer (100) may further include a coating layer (CTL) provided between the positive electrode current collector (110) and the positive electrode active material layer (120). The coating layer (CTL) may be directly disposed on, for example, one side or both sides of the positive electrode current collector (110). The coating layer (CTL) may be coated on one side or both sides of the positive electrode current collector (110). No other layer may be disposed between the positive electrode current collector (110) and the coating layer (CTL).

[0176] By directly disposing the coating layer (CTL) on one or both sides of the positive electrode current collector (110), the bonding force between the positive electrode current collector (110) and the positive electrode active material layer (120) can be further improved. By disposing the coating layer (CTL) between the positive electrode current collector (110) and the positive electrode active material layer (120), side reactions between the filler (FIL), the solid electrolyte (SEP), or the positive electrode active material (CAC) and the positive electrode current collector (110) can be more effectively suppressed. For example, the coating layer (CTL) can prevent corrosion of the sulfide-based positive electrode active material (e.g., Li2S) by the positive electrode current collector (110). As a result, the coating layer (CTL) can suppress deterioration of the all-solid-state battery (10) during the charge / discharge process and improve the cycle characteristics of the all-solid-state battery (10).

[0177] The thickness of the coating layer (CTL) is, for example, 0.01 to 20%, 0.1 to 20%, 0.5 to 20%, 1 to 20%, 1 to 15%, 1 to 10%, 2 to 8%, or 3 to 7% of the thickness of the positive electrode current collector (110). The thickness of the coating layer (CTL) may be, for example, 10 nm to 5 ㎛, 50 nm to 5 ㎛, 200 nm to 4 ㎛, 500 nm to 3 ㎛, 500 nm to 2 ㎛, 500 nm to 1.5 ㎛, or 700 nm to 1.3 ㎛. When the coating layer (CTL) has a thickness in this range, the bonding force between the positive electrode current collector (110) and the positive electrode active material layer (120) is further improved, and an increase in interfacial resistance can be suppressed. The thickness of the coating layer (CTL) can be measured, for example, from a scanning electron microscope (SEM) image of a cross-section of the coating layer (CTL).

[0178] The coating layer (CTL) may include, for example, a carbon-based conductive material. The carbon-based conductive material included in the coating layer (CTL) may be selected from among the carbon-based conductive materials used in the positive electrode active material layer (120). The coating layer (CTL) may include the same carbon-based conductive material as the carbon-based conductive material used in the positive electrode active material layer (120). Since the coating layer (CTL) includes a carbon-based conductive material, the coating layer (CTL) may be, for example, a conductive layer.

[0179] The coating layer (CTL) may additionally include, for example, a binder. By the coating layer (CTL) additionally including a binder, the bonding strength between the positive electrode current collector (110) and the positive electrode active material layer (120) may be further improved. The binder included in the coating layer (CTL) may be, for example, a conductive binder or a non-conductive binder. The conductive binder may be, for example, an ion-conductive binder and / or an electron-conductive binder. A binder having both ion-conductivity and electron-conductivity may belong to both an ion-conductive binder and an electron-conductive binder.

[0180] The binder included in the coating layer (CTL) may be selected from among the binders used in the positive electrode active material layer (120). The coating layer (CTL) may include the same binder as the binder used in the positive electrode active material layer (120). The binder included in the coating layer (CTL) is, for example, a fluorinated binder. The fluorinated binder included in the coating layer (CTL) is, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or a combination thereof. The coating layer (CTL) may be, for example, a binding layer including a binder. The coating layer (CTL) may be, for example, a conductive layer including a binder and a carbon-based conductive material.

[0181] The coating layer (CTL) can be disposed on the positive electrode current collector (110) in a dry or wet manner, for example. The coating layer (CTL) can be disposed on the positive electrode current collector (110) in a dry manner, for example, by deposition such as CVD or PVD. The coating layer (CTL) can be disposed on the positive electrode current collector (110) in a wet manner, for example, by spin coating, dip coating, or the like. The coating layer (CTL) can be disposed on the positive electrode current collector (110) in a dry manner, for example, by deposition of a carbon-based conductive material on a substrate by deposition. A dry-coated coating layer (CTL) is made of a carbon-based conductive material and may not include a binder. The coating layer (CTL) can be disposed on the positive electrode current collector (110) in a dry manner, for example, by coating a composition including a carbon-based conductive material, a binder, and a solvent on the surface of the electrode current collector and drying it. The coating layer (CTL) can have a single-layer structure or a multi-layer structure including a plurality of layers. Multi-layer structures can be two-layer, three-layer, four-layer, etc.

[0182] The negative electrode layer (200) may further include a thin film (TFL) provided between the negative electrode current collector (210) and the negative electrode coating layer (220). The thin film (TFL) is provided on one surface of the negative electrode current collector (210) and may form an alloy with lithium.

[0183] The thin film (TFL) may include, for example, an element capable of forming an alloy with lithium. Elements capable of forming an alloy with lithium include, but are not limited to, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., and any element capable of forming an alloy with lithium within the scope of the art may be used. The thin film (TFL) may be composed of one of these metals, or may be composed of an alloy of multiple metals.

[0184] By placing the thin film (TFL) on one surface of the negative electrode current collector (210), for example, the deposition shape of the lithium metal layer (230, see FIG. 4) deposited between the thin film (TFL) and the negative electrode coating layer (220) becomes flatter, and the cycle characteristics of the all-solid-state battery (10) can be further improved.

[0185] The thickness of the thin film (TFL) may be, for example, 1 nm to 800 nm, 10 nm to 700 nm, 50 nm to 600 nm, or 100 nm to 500 nm. If the thickness of the thin film (TFL) is less than 1 nm, it may be difficult for the thin film (TFL) to exhibit its function. If the thickness of the thin film (TFL) is excessively thick, the thin film (TFL) itself may absorb lithium, which may reduce the amount of lithium precipitation in the negative electrode layer (200), thereby lowering the energy density of the all-solid-state battery (10) and deteriorating the cycle characteristics of the all-solid-state battery (10). The thin film (TFL) may be formed on the negative electrode current collector (21) by, for example, a vacuum deposition method, a sputtering method, a plating method, or the like, but is not necessarily limited to these methods, and any method capable of forming a thin film in the relevant technical field may be used.

[0186]

[0187] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Fig. 7 is a cross-sectional view of a lithium-sulfur battery according to an embodiment of the present invention. As described above, the lithium-sulfur battery according to embodiments of the present invention may include a positive electrode layer (100), a negative electrode layer (200), and a solid electrolyte layer (300) between the positive electrode layer (100) and the negative electrode layer (200). That is, the lithium-sulfur battery in the present specification may be substantially the same as a lithium-sulfur all-solid-state battery or an all-solid-state battery.

[0188] The positive electrode according to embodiments of the present invention may include a positive electrode active material layer (120) on a positive electrode current collector (110). The positive electrode active material layer (120) may include a positive electrode active material (CAC), a solid electrolyte (SEP), and a binder (BID). The positive electrode active material layer may also include other additives such as organic or inorganic fillers. The positive electrode active material layer (120) may include a sulfide-based positive electrode active material.

[0189] The positive electrode active material layer (120) may be manufactured using a dry process. That is, the positive electrode active material layer (120) may be a dry positive electrode active material layer. For example, the positive electrode active material layer (120) may be a dry positive electrode film. By introducing a dry positive electrode active material layer, a positive electrode active material layer in which the constituent materials are more uniformly distributed can be provided.

[0190] The positive electrode active material layer (120) may be a dry positive electrode film. For example, the positive electrode active material layer (120) may be a self-standing film. The positive electrode active material layer (120) can maintain a film form without a support. Therefore, the positive electrode active material layer (120) may be prepared as a separate self-standing film and then placed on the positive electrode current collector (110). Since the positive electrode active material layer (120) is manufactured by a dry process, it does not contain an intentionally added process solvent. For example, it does not contain a residual processing solvent. Although a trace amount of unintended solvent may remain in the dry positive electrode film, such solvent is not an intentionally added process solvent. Therefore, in the case of a positive electrode active material layer manufactured by a dry process, some or all of the process solvent is removed by drying after mixing the components and the solvent, and it can be distinguished from a wet positive electrode manufactured by a dry process. The thickness of the dry positive electrode film may be, for example, 30 μm to 100 μm, 40 μm to 150 μm, 50 μm to 500 μm, 50 μm to 400 μm, 50 μm to 300 μm, or 50 μm to 250 μm. If the thickness of the dry positive electrode film is too thin, the number of current collectors increases, which may lower the energy density per unit volume of the secondary battery. If the thickness of the dry positive electrode film is too large, the internal resistance of the positive electrode increases, which may lower the cycle characteristics of the secondary battery.

[0191] As shown in Fig. 3, the sulfide-based cathode active material (CAC) may include a composite (CAM) and a conductive material (CMA). The composite (CAM) may be a mixture or complex of a sulfur compound and an ion-conductive material.

[0192] Sulfur compounds are S8 and Li2S n(1 ≤ n ≤ 8, n is an integer) may include at least one of the following. The sulfur compound may improve the capacity of the positive electrode active material. The sulfur compound may be a lithium source for a lithium-sulfur battery. Through the continuous oxidation / reduction reaction of the sulfur compound, lithium ions may move between the positive electrode / negative electrode, and at the same time, electrons may move through an external circuit to generate current.

[0193] The ion-conducting material may include at least one of a lithium halide and a metal halide.

[0194] The lithium halide may include a compound of lithium and a halogen group element. In one embodiment, the lithium halide may include LiF, LiCl, LiBr, LiI, or a combination thereof. The lithium halide may improve the ionic conductivity of the positive electrode active material. In one embodiment, the composite (CAM) may include a solid solution of a sulfur compound and a lithium halide. The composite (CAM) may form a solid solution, thereby improving energy density, ionic conductivity, etc. For example, by including lithium ions arranged within the crystallites of the sulfur compound, the ionic conductivity of the solid solution of the sulfur compound and the lithium halide may be improved compared to the ionic conductivity of the sulfur compound.

[0195] The metal halide may include a compound of a metal and a halogen group element. The metal of the metal halide may include at least one selected from the group consisting of aluminum, aluminum (Al), silver (Ag), gold (Au), platinum (Pt), palladium (Pd), bismuth (Bi), tin (Sn), and zinc (Zn). For example, the metal halide may include AlI3, AgI, SnI4, etc. The metal halide may include a compound of a boron group element and a halogen group element. For example, the metal halide may include a compound of GaI3, InI3, TiI3, etc. The metal halide may improve the ionic conductivity of the positive electrode active material. The metal halide may maintain the overall shape of the composite (CAM) and reduce the interfacial resistance.

[0196] In one embodiment, the composite (CAM) may include a solid solution of a sulfur compound, a lithium halide, and a metal halide. For example, the composite (CAM) may include a compound (or solid solution) represented by Li2S-LiI-AlI3. The composite (CAM) may form a solid solution, thereby improving energy density, ionic conductivity, and the like.

[0197] The content of the sulfur compound in the composite (CAM) may be 50 wt% to 95 wt%, 50 wt% to 90 wt%, 50 wt% to 80 wt%, or 50 wt% to 70 wt% of the total weight of the composite (CAM). When the composite (CAM) has a sulfur compound content in this range, the composite can have both improved ionic conductivity and excellent ductility.

[0198] The content of lithium halide in the composite (CAM) can be 5 wt% to 50 wt%, 10 wt% to 50 wt%, 20 wt% to 50 wt%, or 30 wt% to 50 wt% of the total weight of the composite (CAM). By having the lithium halide content in this range in the composite (CAM), the composite (CAM) can have both improved ionic conductivity and excellent ductility.

[0199] The content of the metal halide in the composite (CAM) may be 5 wt% to 30 wt%, or 5 wt% to 20 wt%, of the total weight of the composite (CAM). By having the metal halide content in this range, the composite (CAM) can simultaneously have improved ionic conductivity and excellent ductility.

[0200] The weight ratio of the lithium halide to the metal halide within the complex (CAM) can be from 1:27 to 3:1, from 1:3 to 3:1, or about 1:1. The weight fraction of the metal halide to the weight of the lithium halide within the complex can be from 0.03 to 3.0, or from 0.3 to 3.0. The molar ratio of the lithium halide to the metal halide within the complex (CAM) can be from 1:9 to 9:1, from 1:3 to 3:1, or about 1:1. The molar fraction of the metal halide to the lithium halide within the complex can be from 0.1 to 9.0, or from 0.3 to 3.0.

[0201] The molar ratio of the sulfur compound and the ion-conducting material in the composite (CAM) can be 51:49 to 95:5, 55:45 to 90:10, 60:40 to 90:10, or 70:30 to 90:10. By having this molar ratio in the composite (CAM), the composite (CAM) can have both improved ion conductivity and excellent ductility.

[0202] In one embodiment, the content of the sulfur compound in the complex (CAM) may be greater than the content of the lithium halide. The content of the sulfur compound in the complex (CAM) may be greater than the content of the metal halide. For example, the mole fraction of the sulfur compound in the complex (CAM) may be from 0.9 to 0.99. The mole fraction of the lithium halide in the complex (CAM) may be from 0.01 to 0.10. The mole fraction of the metal halide in the complex (CAM) may be from 0.01 to 0.10.

[0203] The cathode active material (CAC) may include a composite material (CAM) and a conductive material (CMA). The cathode active material (CAC) may be a mixture of the cathode composite material (CAM) and the conductive material (CMA). The conductive material (CMA) may cover the surface of the composite material (CAM). By including the conductive material (CMA), the electronic conductivity of the cathode active material (CAC) may be improved.

[0204] The conductive material (CMA) may include carbon. The conductive material (CMA) may include, without limitation, any material containing carbon atoms used as a conductive material in the art. For example, the conductive material (CMA) may include crystalline carbon, amorphous carbon, or a combination thereof. The conductive material (CMA) may include, for example, a sintered product of a carbon precursor. The conductive material (CMA) may include, for example, carbon nanostructures.

[0205] The carbon nanostructure may include, for example, carbon nanofibers (CNF), carbon nanotubes (CNT), carbon nanobelts, carbon nanorods, or combinations thereof. The carbon nanostructure may form a primary carbon nanostructure composed of a single carbon nanostructure, and a secondary carbon nanostructure composed of multiple carbon nanostructures aggregated together.

[0206] The content of the sulfur compound in the cathode active material (CAC) may be 40 wt% to 90 wt%, 30 wt% to 80 wt%, 40 wt% to 60 wt%, 50 wt% to 70 wt%, or 50 wt% to 60 wt% based on the total weight of the cathode active material (CAC).

[0207] The content of the ion-conducting material in the cathode active material (CAC) may be 10 wt% to 50 wt%, 20 wt% to 40 wt%, 10 wt% to 30 wt%, or 20 wt% to 30 wt%. The molar ratio of the lithium halide and the metal halide in the ion-conducting material may be about 1:2 to 2:1, 1:1.5 to 1.5:1, or about 1:1.

[0208] The content of the conductive material in the positive electrode active material may be 1 wt% to 20 wt%, 1 wt% to 10 wt%, 5 wt% to 10 wt%, 5 wt% to 20 wt%, 10 wt% to 20 wt%, or 10 wt% to 15 wt% based on the total weight of the positive electrode active material (CAC).

[0209] The positive electrode active material layer (120) may further include a solid electrolyte (SEP) in addition to the positive electrode active material (CAC). The solid electrolyte in the positive electrode active material layer (120) may be the same as or different from the solid electrolyte in the aforementioned solid electrolyte layer. The solid electrolyte in the positive electrode active material layer may have a smaller average particle diameter than the solid electrolyte in the solid electrolyte layer.

[0210] The positive electrode active material layer (120) may include a binder (BID). The binder (BID) may be a dry binder. The dry binder may be, for example, a binder that is not impregnated, dissolved, or dispersed in a process solvent during the manufacturing process. The dry binder may be, for example, a binder that includes a process solvent or does not come into contact with a process solvent during the manufacturing process. The dry binder may be a fibrillated binder or a fibrous binder. The fibrillated binder or the fibrous binder may have an aspect ratio of, for example, 10 or more, 20 or more, 50 or more, or 100 or more. The dry binder may serve as a porous matrix that supports and binds the positive electrode active material and other components. The dry binder intermittently arranges on the surface of the positive electrode active material without aggregation, thereby binding multiple positive electrode active materials together, thereby effectively suppressing an increase in internal resistance of the positive electrode active material layer. For example, a scanning electron microscope image of a cross-section of the positive electrode active material layer confirms that the dry binder has a fibrous form. By introducing the dry binder, non-uniform aggregation of the composite and binder within the positive electrode active material layer can be prevented. Consequently, a positive electrode active material layer having a uniform composition can be provided.

[0211] Dry binders include, but are not necessarily limited to, polytetrafluoroethylene (PTFE), polyvinylidene fluoride-hexapropylene (PVDF-HFP) copolymers, polyvinylidene fluoride (PVDF), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomers, or copolymers thereof. The dry binder may particularly include a fluorinated binder. Fluorinated binders include, for example, polytetrafluoroethylene, polyvinylidene fluoride-hexapropylene (PVDF-HFP) copolymer, or polyvinylidene fluoride (PVDF).

[0212] The discharge capacity, ionic conductivity, and electronic conductivity of the cathode active material (CAC) can be improved by including a composite of a sulfur compound such as Li2S and an ion-conducting material and a carbon-based material. Since the composite (CAM) includes a sulfur compound such as Li2S, the sulfur compound can act as a lithium source, thereby eliminating the need for a lithium source in the negative electrode. Consequently, the energy density of the lithium-sulfur all-solid-state battery can be improved.

[0213] As the composite (CAM) includes an ion-conducting material, the ion conductivity of the cathode active material (CAC) can be improved and the internal resistance of the cathode active material layer can be reduced. Consequently, the cycle characteristics of a lithium-sulfur all-solid-state battery including the cathode active material layer can be improved.

[0214] By intermittently bonding the dry binder to a portion of the surface of a plurality of dry positive electrode active material particles, an increase in the internal resistance of the positive electrode active material layer due to the binder can be effectively suppressed. In contrast, by widely coating the surface of a plurality of positive electrode active material particles during the drying process after being dissolved in a solvent, the wet binder can increase the internal resistance of the positive electrode active material layer.

[0215] In one embodiment, the content of the cathode active material (CAC) in the cathode active material layer (120) may be 40 wt% to 90 wt%, 50 wt% to 90 wt%, or 60 wt% to 90 wt% of the total weight of the cathode active material layer (120). Among the components in the cathode active material layer (120), the cathode active material (CAC) may have the largest content.

[0216] In one embodiment, the content of the solid electrolyte (SEP) in the positive electrode active material layer (120) may be 10 wt% to 70 wt%, 10 wt% to 60 wt%, 10 wt% to 40 wt%, or 10 wt% to 30 wt% of the total weight of the positive electrode active material layer (120).

[0217] In one embodiment, the content of the binder (BID) in the positive electrode active material layer (120) may be, for example, 0.1 wt% to 5 wt%, 0.5 to 5 wt%, 1 wt% to 5 wt%, or 1 to 3 wt% of the total weight of the positive electrode active material layer (120). The binder (BID) may also be omitted.

[0218] By having a composition within the above range, the binding strength of the positive electrode active material layer is enhanced, and the positive electrode active material layer can maintain increased energy density. By providing a positive electrode active material layer with a uniform composition, internal resistance can be reduced. This can solve the problem of reduced cycle life or rate characteristics due to internal resistance. Even if the thickness of the positive electrode active material layer increases, cell characteristics can be stably maintained. Consequently, a lithium-sulfur battery with improved performance, such as energy density and cycle life, can be provided.

[0219]

[0220] FIG. 8 is a cross-sectional view of a positive electrode for a lithium-sulfur battery according to one embodiment of the present invention. Referring to FIG. 8, the positive electrode may include a positive electrode current collector (110) and a positive electrode active material layer (120) on the positive electrode current collector (110). The positive electrode active material layer (120) may have a double layer form. More specifically, the positive electrode active material layer (120) may include a first positive electrode active material layer (120_1) on the positive electrode current collector (110) and a second positive electrode active material layer (120_2) on the first positive electrode active material layer (120_1). The second positive electrode active material layer (120_2) may be in contact with the solid electrolyte layer (300).

[0221] Fig. 9 is an enlarged cross-sectional view of the X region of Fig. 8. Referring to Fig. 9, each of the first positive electrode active material layer (120_1) and the second positive electrode active material layer (120_2) may include a positive electrode active material (CAC), a solid electrolyte (SEP), and a binder (BID). The content of the positive electrode active material (CAC) in the first positive electrode active material layer (120_1) and the content of the positive electrode active material (CAC) in the second positive electrode active material layer (120_2) may be different from each other. The content of the solid electrolyte (SEP) in the first positive electrode active material layer (120_1) and the content of the solid electrolyte (SEP) in the second positive electrode active material layer (120_2) may be different from each other.

[0222] In one embodiment, the content of the cathode active material (CAC) in the first cathode active material layer (120_1) may be greater than the content of the cathode active material (CAC) in the second cathode active material layer (120_2). For example, the content of the cathode active material (CAC) in the first cathode active material layer (120_1) may be 70 wt% to 90 wt%, 70 wt% to 85 wt%, or 75 wt% to 90 wt% with respect to the total weight of the first cathode active material layer (120_1). For example, the content of the cathode active material (CAC) in the second cathode active material layer (120_2) may be 60 wt% to 80 wt%, 60 wt% to 75 wt%, or 65 wt% to 75 wt% with respect to the total weight of the second cathode active material layer (120_2).

[0223] Since the content of the positive electrode active material (CAC) in the first positive electrode active material (120_1) layer disposed adjacent to the positive electrode current collector (110) is greater than the content of the positive electrode active material (CAC) in the second positive electrode active material layer (120_2) disposed adjacent to the solid electrolyte layer (300), the interfacial resistance between the positive electrode current collector (110) and the positive electrode active material layer (120) can be reduced more effectively. Since the positive electrode active material layer (120) includes a complex of a sulfur compound and an ion conductive material and a carbon-based material, when the content of the positive electrode active material (CAC) in the first positive electrode active material layer (120_1) increases, the electronic conductivity of the first positive electrode active material layer (120_1) can increase. Therefore, electronic conduction between the positive electrode current collector (110) and the positive electrode active material layer (120) becomes easier, and the reversibility of the electrode reaction can be further improved.

[0224] In one embodiment, the content of the solid electrolyte (SEP) in the first positive electrode active material layer (120_1) may be less than the content of the solid electrolyte (SEP) in the second positive electrode active material layer (120_2). For example, the content of the solid electrolyte (SEP) in the first positive electrode active material layer (120_1) may be 10 wt% to 30 wt%, 15 wt% to 30 wt%, or 10 wt% to 25 wt% with respect to the total weight of the first positive electrode active material layer (120_1). For example, the content of the solid electrolyte (SEP) in the second positive electrode active material layer (120_2) may be 20 wt% to 40 wt%, 25 wt% to 40 wt%, or 25 wt% to 35 wt% with respect to the total weight of the second positive electrode active material layer (120_2).

[0225] Since the solid electrolyte (SEP) content in the first positive electrode active material layer (120_1) disposed adjacent to the positive electrode current collector (110) is smaller than the solid electrolyte (SEP) content in the second positive electrode active material layer (120_2) disposed adjacent to the solid electrolyte layer (300), the interfacial resistance between the solid electrolyte layer (300) and the positive electrode active material layer (120) can be effectively reduced. As the solid electrolyte (SEP) content in the second positive electrode active material layer (120_1) adjacent to the solid electrolyte layer (300) increases, the ionic conductivity of the second positive electrode active material layer (120_2) can increase. Therefore, ion movement between the solid electrolyte layer (300) and the positive electrode active material layer (120) becomes easier, and the reversibility of the electrode reaction can be further improved.

[0226] The binder (BID) content in the first positive electrode active material layer (120_1) may be substantially the same as the binder (BID) content in the second positive electrode active material layer (120_2). Alternatively, the binder (BID) content in the first positive electrode active material layer (120_1) may be greater than the binder (BID) content in the second positive electrode active material layer (120_2). The ratio of the binder (BID) content in the first positive electrode active material layer (120_1) to the binder (BID) content in the second positive electrode active material layer (120_2) may be, for example, 3:1 to 1.1:1, 2:1 to 1.1:1, or 1.5:1 to 1.1:1. As the binder (BID) content within the first positive electrode active material layer (120_1) increases, the binding force of the positive electrode active material (CAC) particles within the first positive electrode active material layer (120_1) can be improved. Consequently, the cycle characteristics of the dry positive electrode active material layer can be improved.

[0227] The thickness of the positive electrode active material layer (120) may be the sum of the thickness of the first positive electrode active material layer (120_1) and the thickness of the second positive electrode active material layer (120_2). The thickness of the first positive electrode active material layer (120_1) may be 50 μm to 100 μm, or 50 μm to 200 μm. The thickness of the second positive electrode active material layer (120_2) may be 50 μm to 100 μm, or 50 μm to 200 μm.

[0228] The thickness of the first positive electrode active material layer (120_1) may be substantially the same as the thickness of the second positive electrode active material layer (120_2). Alternatively, the thickness of the first positive electrode active material layer (120_1) may be different from the thickness of the second positive electrode active material layer (120_2). For example, the thickness ratio of the first positive electrode active material layer (120_1) to the thickness of the second positive electrode active material layer (120_2) may be 1:9 to 9:1, 3:1 to 1:3, 2:1 to 1:2, or 1.1:1 to 1:1.1.

[0229] For example, increasing the thickness of the first positive electrode active material layer, which has a high positive electrode active material content, can improve the energy density. Increasing the thickness of the second positive electrode active material layer, which has a high solid electrolyte content, can improve the cycle characteristics of the battery.

[0230] The energy density and cycle characteristics of a lithium-sulfur all-solid-state battery can be easily controlled by controlling the thickness of the first positive electrode active material layer (120_1) and the thickness of the second positive electrode active material layer (120_2) in the positive electrode active material layer (120).

[0231]

[0232] FIG. 10 is a cross-sectional view of a positive electrode for a lithium-sulfur battery according to an embodiment of the present invention. Referring to FIG. 8, the positive electrode may include a positive electrode current collector (110) and a positive electrode active material layer (120) on the positive electrode current collector (110). The positive electrode active material layer (120) may have a multilayer structure in which a plurality of layers are laminated. More specifically, the positive electrode active material layer (120) may include a first positive electrode active material layer (120_1) on the positive electrode current collector (120) and an m-th positive electrode active material layer (120_m) sequentially laminated on the first positive electrode active material layer (120_1). That is, the positive electrode active material layer (120) may be a multilayer having an m-layer structure. For example, the positive electrode active material layer (120) may have a four-layer structure in which a first positive electrode active material layer (120_1), a second positive electrode active material layer (120_2), a third positive electrode active material layer (120_3), and a fourth positive electrode active material layer (120_4) are sequentially arranged on the positive electrode current collector (110).

[0233] The positive electrode active material layer (120) may be stacked in the order of the first positive electrode active material layer (120_1) to the mth positive electrode active material layer (120_m) in the third direction (D3) with respect to the positive electrode current collector (110). That is, the mth positive electrode active material layer (120_m) may be further away from the positive electrode current collector (110) as m increases.

[0234] Each of the first to mth positive electrode active material layers may include a positive electrode active material, a solid electrolyte, and a binder. The positive electrode active material content in the first to mth positive electrode active material layers may be different from each other. The solid electrolyte content in the first to mth positive electrode active material layers may be different from each other.

[0235] The positive electrode active material layer (120) may have a positive electrode active material content gradient within the positive electrode active material layer. The positive electrode active material layer (120) may have a solid electrolyte content gradient within the positive electrode active material layer. In one embodiment, the positive electrode active material content within the positive electrode active material layer may decrease as it moves away from the positive electrode current collector (110). That is, the positive electrode active material content may decrease as it moves away from the positive electrode current collector (110) in the third direction (D3). In one embodiment, the solid electrolyte content within the positive electrode active material layer may increase as it moves away from the positive electrode current collector (110). That is, the solid electrolyte content may increase as it moves away from the positive electrode current collector (110) in the third direction (D3).

[0236] For example, in a plurality of sequentially stacked positive electrode active material layers, the positive electrode active material (CAC) content in the m-1th positive electrode active material layer (120_m-1) may be greater than the positive electrode active material (CAC) content in the m-th positive electrode active material layer (120_2). Conversely, in a plurality of sequentially stacked positive electrode active material layers, the solid electrolyte (SEP) content in the m-1th positive electrode active material layer (120_m-1) may be less than the solid electrolyte (SEP) content in the m-th positive electrode active material layer (120_m). As described above, as the positive electrode active material content increases closer to the positive electrode current collector in the positive electrode active material layer, the electronic conductivity of the positive electrode active material layer may be improved. In addition, as the solid electrolyte content increases closer to the solid electrolyte layer in the positive electrode active material layer, the ionic conductivity may be improved.

[0237] By introducing multilayer cathode active material layers with different compositions, physical properties such as ionic and electronic conductivity can be improved, while the content of cathode active material within the cathode active material layers can be increased, thereby enhancing energy density. Consequently, a lithium-sulfur battery can be provided with comprehensively improved performance, including rate characteristics, cycle life, and capacity.

[0238]

[0239] Hereinafter, a method for manufacturing a positive electrode for a lithium sulfur battery according to embodiments of the present invention will be described in detail with reference to FIGS. 11 to 16.

[0240] A method for manufacturing a positive electrode for a lithium sulfur battery may include forming a first mixture; forming a second mixture; forming a third mixture; forming a fourth mixture; and laminating positive electrode sheets.

[0241] Figure 11 is a schematic diagram showing the formation of a first mixture (MI1). Referring to Figure 11, a sulfur compound (SCM), an ion-conducting material (ICM), and balls (BA) may be provided within a first container (CON1). The sulfur compound (SCM) may be lithium polysulfide. Specifically, the sulfur compound (SCM) may be Li2S. n(1 ≤ n ≤ 8, where n is an integer). The ion conducting material (ICM) may include at least one of a lithium halide and a metal halide. The lithium halide may include a compound of lithium and a halogen group element. In one embodiment, the lithium halide may include LiF, LiCl, LiBr, LiI, or a combination thereof. The metal halide may include a compound of a metal and a halogen group element. The metal of the metal halide may include at least one selected from the group consisting of aluminum, aluminum (Al), silver (Ag), gold (Au), platinum (Pt), palladium (Pd), bismuth (Bi), tin (Sn), and zinc (Zn). For example, the metal halide may include AlI3, AgI, SnI4, etc. The metal halide may include a compound of a boron group element and a halogen group element. For example, it may include compounds such as GaI3, InI3, and TiI3.

[0242] The formation of the first mixture (MI1) can be performed through a ball milling process. At this time, the balls (BA) can help the sulfur compound (SCM) and the ion conductive material (ICM) to be uniformly mixed. Specifically, mechanical grinding and uniform mixing can be performed by the balls (BA) within the first container (CON1). The sulfur compound (SCM) and the ion conductive material (ICM) can be mixed to form the first mixture (MI1). The first mixture (MI1) can be a positive electrode composite. For example, the first mixture can be a composite of Li2S-LiI-AlI3.

[0243] FIG. 12 is a schematic diagram illustrating the formation of a second mixture (MI2). Referring to FIG. 12, a conductive material (CMA) may be added to the first mixture in the first container (CON1). The conductive material (CMA) may include carbon. The conductive material (CMA) may include, without limitation, any material containing carbon atoms used as a conductive material in the art. For example, the conductive material (CMA) may include crystalline carbon, amorphous carbon, or a combination thereof. The conductive material (CMA) may include, for example, a sintered product of a carbon precursor. The conductive material (CMA) may include, for example, a carbon nanostructure. The carbon nanostructure may include, for example, carbon nanofibers (CNF), carbon nanotubes (CNT), carbon nanobelts, carbon nanorods, or a combination thereof. The carbon nanostructure may form a primary carbon nanostructure composed of a single carbon nanostructure and a secondary carbon nanostructure in which a plurality of carbon nanostructures are aggregated.

[0244] The formation of the second mixture (MI2) can be performed through a ball milling process. At this time, the balls (BA) can help the first mixture (MI1) and the conductive material (CMA) to be uniformly mixed. Specifically, mechanical grinding and uniform mixing can be performed by the balls (BA) within the first container (CON1). The first mixture (MI1) and the conductive material (CMA) can be mixed to form the second mixture (MI2). The second mixture (MI2) can be a positive electrode active material. For example, the second mixture (MI2) can be a composite of Li2S-LiI-AlI3-CNF.

[0245] The sulfur compound (SCM) may be 40 to 90 parts by weight based on 100 parts by weight of the second mixture (MI2). The ion conductive material (ICM) may be 10 to 60 parts by weight based on 100 parts by weight of the second mixture (MI2). The conductive material may be 10 to 20 parts by weight based on 100 parts by weight of the second mixture. By satisfying the above ranges, a positive electrode active material satisfying both high energy density and conductivity can be manufactured.

[0246] FIG. 13 is a schematic diagram showing the formation of a third mixture, and FIG. 14 is a schematic diagram showing the formation of a fourth mixture. Referring to FIG. 13, a second mixture and a solid electrolyte (SE) may be provided within a second container (CON2). Forming the third mixture (MI3) may be performed through a mixing process. The second mixture (MI2) and the solid electrolyte (SE) may be uniformly mixed within the second container (CON2).

[0247] Solid electrolyte (SE) is Li 7-a M a PS 6-c X cAn argyrodite-type sulfide-based solid electrolyte represented by (0≤a≤2, 0≤c≤2), wherein X is F, Br, Cl or a combination thereof, and M is candium (Sc), yttrium (Y), titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), mercury (Hg), aluminum (Al), gallium (Ga), Indium (In), thallium (Tl), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), or a combination thereof may be present. For example, the solid electrolyte (SE) may be an argyrodite-type compound including at least one selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0248] Referring to FIG. 14, a binder (BID) may be added to a third mixture (MI3) in a second container (CON2). Forming a fourth mixture (MI4) may be performed through a mixing process. The third mixture (MI3) and the binder (BID) may be uniformly mixed in the second container (CON2). The binder (BID) may be a dry binder. The dry binder may particularly include a fluorinated binder. The fluorinated binder may be, for example, polytetrafluoroethylene (PTFE), a polyvinylidene fluoride-hexapropylene (PVdF-HFP) copolymer, or polyvinylidene fluoride.

[0249] The fourth mixture (MI4) may be a positive electrode composition. In some cases, the fourth mixture (MI4) may be further mixed using a kneader. The fourth mixture (MI4) may be passed between calender rolls to form a sheet-shaped positive electrode active material layer (SSH). In this case, the positive electrode active material layer may be a self-standing film.

[0250] The content of the positive electrode active material (CAC) in the fourth mixture (MI4) may be 40 wt% to 90 wt%, 50 wt% to 90 wt%, or 60 wt% to 90 wt% of the total weight of the fourth mixture (MI4). Among the components in the fourth mixture (MI4), the positive electrode active material (CAC) may have the largest content.

[0251] The content of the solid electrolyte (SEP) in the fourth mixture (MI4) may be 10 wt% to 70 wt%, 10 wt% to 60 wt%, 10 wt% to 40 wt%, or 10 wt% to 30 wt% of the total weight of the fourth mixture (MI4).

[0252] The content of the binder (BID) in the fourth mixture (MI4) may be, for example, 0.1 wt% to 5 wt%, 0.5 to 5 wt%, 1 wt% to 5 wt%, or 1 to 3 wt% of the total weight of the fourth mixture (MI4). The binder (BID) may also be omitted.

[0253] Referring to FIG. 16, a plurality of positive electrode sheets may be laminated to form a positive electrode active material layer (120). For example, a first positive electrode sheet (SSH1) may be placed on a positive electrode current collector, and a second positive electrode sheet (SSH2) may be placed on the first positive electrode sheet (SSH1). Thereafter, a positive electrode active material layer (120) may be formed through a pressurizing or heat treatment process. Although not illustrated, the positive electrode active material layer (120) may be manufactured in a multilayer structure in which a plurality of positive electrode sheets are laminated.

[0254] There is a need to increase the capacity or energy density of lithium-sulfur batteries. To achieve this, the cathode active material layer must contain a large amount of cathode active material. Furthermore, manufacturing a thick-film electrode plate with a thicker cathode active material layer can be a method. However, excessive amounts of cathode active material or excessive thickness can increase the resistance of the cathode. This can actually reduce battery performance. For example, the thicker the cathode active material layer, the more uneven its composition can become. Furthermore, plate performance can deteriorate due to factors such as binder aggregation and conductive material clumping.

[0255] By introducing a dry process, a positive electrode can be manufactured in which components such as a positive electrode active material and a binder are uniformly distributed. The dry process may not include an aqueous solvent or a non-aqueous organic solvent in the mixture. By introducing a dry process, a positive electrode active material layer with a uniform composition can be manufactured. Even if the thickness of the positive electrode active material layer is increased, the components within the positive electrode active material layer can be uniformly distributed. Consequently, the capacity of the battery can be increased, while the stability and lifespan characteristics of the battery can be improved.

[0256]

[0257] Below, the present creative idea is described in more detail through examples and comparative examples. However, the examples are intended to illustrate the present creative idea and are not intended to limit the scope of the present creative idea.

[0258]

[0259] [Cathode manufacturing]

[0260] Manufacturing of positive electrode active materials

[0261] Manufacturing Example 1: Composite positive electrode active material

[0262] (Stage 1)

[0263] (Stage 1)

[0264] The sulfur compound Li2S and the ion-conducting material (LiI-AlI3) were mixed. The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI-AlI3 composite. The milling conditions were 25°C, 600 rpm, and 10 h. The milling energy applied to the sample during milling was approximately 28 G.

[0265] (Stage 2)

[0266] A Li2S-LiI-AlI3 composite was mixed with carbon nanofibers (CNF). The mixture was mechanically milled using a ball mill to produce a Li2S-LiI-AlI3-CNF cathode active material. The milling conditions were 25°C, 600 rpm, and 10 h. The milling energy applied to the sample during milling was approximately 28 G.

[0267] Based on the total manufactured positive electrode active material, Li2S 57.1 wt%, (LiI-AlI3) 28.6 wt% of LiI and 14.3 wt% of CNF were mixed. In the case of ion conductive materials, LiI and AlI3 were mixed and used in a 1:1 molar ratio.

[0268] Manufacturing of positive electrode active material layer

[0269] Manufacturing Example 2: Manufacturing of a mixed positive electrode active material layer (positive electrode active material / solid electrolyte / binder)

[0270] As a cathode active material, the one manufactured in Manufacturing Example 1 was prepared. As a solid electrolyte, an argyrodite-based solid electrolyte (Li6PS5Cl, D50 = 3.0 μm) was prepared. PTFE was prepared as a binder.

[0271] The positive electrode active material and solid electrolyte were placed in a mixer and mixed for 2 minutes. A binder was added to the mixed powder and mixed for 20 seconds. The mixed powder was further mixed using a kneader and then passed between calender rolls to produce a film-shaped positive electrode active material layer. The binder was fiberized during the additional mixing and calendering process using the kneader.

[0272] A positive electrode was manufactured by placing a layer of a manufactured positive electrode active material on a positive electrode current collector made of carbon-coated aluminum foil. The manufactured positive electrode active material layers were laminated in a single-layer or multi-layer structure to manufacture a positive electrode.

[0273] [Cathode manufacturing]

[0274] A SUS foil with a thickness of approximately 10 μm was prepared as a negative electrode current collector. Carbon black (CB) particles with a primary particle diameter of approximately 30 nm and silver (Ag) particles with an average particle diameter of approximately 60 nm were prepared as negative electrode coating materials.

[0275] A mixed powder of 4 g of carbon black (CB) and silver particles in a weight ratio of 3:1 was placed in a container, and 4 g of an NMP solution containing 7 wt% of a PVdF binder (Kureha #9300) was added to prepare a mixed solution. A slurry was prepared by stirring the mixed solution while adding NMP little by little to the prepared mixed solution. The prepared slurry was applied to a SUS sheet using a bar coater, dried in air at 80°C for 10 minutes, and then vacuum-dried at 40°C for 10 hours to prepare a laminate. The prepared laminate was cold roll pressed to flatten the surface, and an anode having a negative electrode coating layer / negative electrode collector structure was prepared. The thickness of the negative electrode coating layer was approximately 15 μm. The areas of the negative electrode coating layer and the negative electrode collector were the same.

[0276] [Inert Absence]

[0277] A flame-retardant inert member was manufactured by forming a slurry containing pulp fiber (cellulose fiber), glass fiber, aluminum hydroxide (Al(OH)3), an acrylic binder, and a solvent into a gasket shape and then removing the solvent.

[0278] The weight ratio of cellulose fiber, glass fiber, aluminum hydroxide (Al(OH)3), and acrylic binder was 20:8:70:2. The thickness of the inert member was 120 ㎛. Before placing the manufactured flame-retardant inert member on the solid electrolyte layer, moisture, etc. of the flame-retardant inert member was removed by vacuum heat treatment at 80°C for 5 hours.

[0279] [Manufacturing of solid electrolyte layer]

[0280] A mixture was prepared by adding an acrylic binder to a Li6PS5Cl solid electrolyte, which is an argyrodite-type crystal. The solid electrolyte and the acrylic binder were mixed in an amount of 98.5 parts by weight and 1.5 parts by weight, respectively. Octyl acetate was added to the prepared mixture and stirred to prepare a slurry. The prepared slurry was applied using a bar coater onto a 15 μm-thick nonwoven fabric placed on a 75 μm-thick PET substrate, and dried in air at 80°C for 10 minutes to prepare a laminate. The prepared laminate was vacuum-dried at 80°C for 2 hours, and then the solid electrolyte layer was separated from the PET substrate to prepare a solid electrolyte layer.

[0281] [Manufacturing of lithium-sulfur batteries]

[0282] A solid electrolyte layer was placed so that the cathode coating layer and the solid electrolyte layer were in contact, and an anode was placed on the solid electrolyte layer. A laminate was prepared by placing a gasket surrounding the anode and in contact with the solid electrolyte layer. The thickness of the gasket was approximately 120 μm. The above-mentioned flame-retardant inert material was used as the gasket. The gasket was placed so as to be in contact with the side surface of the anode and the solid electrolyte layer. The anode was placed at the center of the solid electrolyte layer, and the gasket surrounded the anode and extended the solid electrolyte layer to the end portion. The area of ​​the anode was approximately 90% of the area of ​​the solid electrolyte layer, and the gasket was placed over the entire remaining 10% of the area of ​​the solid electrolyte layer where the anode was not placed.

[0283] The prepared laminate was plate-pressed at 85°C and a pressure of 500 MPa for 30 minutes. This pressurization process sintered the solid electrolyte layer, thereby improving battery characteristics. The thickness of the sintered solid electrolyte layer was approximately 45 μm. The density of the Li6PS5Cl solid electrolyte, which is an argyrodite-type crystal contained in the sintered solid electrolyte layer, was 1.6 g / cc. The area of ​​the solid electrolyte layer was the same as that of the negative electrode.

[0284]

[0285] Example 1: Multilayer dry cathode active material layer of first layer (50 μm) / second layer (50 μm)

[0286] A lithium-sulfur all-solid-state battery was manufactured by stacking the first positive electrode active material layer with a thickness of 50 μm and the second positive electrode active material layer with a thickness of 50 μm. At this time, the compositions of the first positive electrode active material layer and the second positive electrode active material layer were manufactured differently. The first positive electrode active material layer was prepared by mixing the positive electrode active material, solid electrolyte, and dry binder at a weight ratio of 80:19:1. The second positive electrode active material layer was prepared by mixing the positive electrode active material, solid electrolyte, and dry binder at a weight ratio of 70:29:1. The positive electrode active material of Manufacturing Example 1 was used as the positive electrode active material.

[0287]

[0288] Example 2: Multilayer dry cathode active material layer of first layer (60 μm) / second layer (40 μm)

[0289] A lithium-sulfur all-solid-state battery was manufactured by stacking the first positive electrode active material layer with a thickness of 60 μm and the second positive electrode active material layer with a thickness of 40 μm. At this time, the compositions of the first positive electrode active material layer and the second positive electrode active material layer were manufactured differently. The first positive electrode active material layer was prepared by mixing the positive electrode active material, solid electrolyte, and dry binder at a weight ratio of 80:19:1. The second positive electrode active material layer was prepared by mixing the positive electrode active material, solid electrolyte, and dry binder at a weight ratio of 70:29:1. The positive electrode active material of Manufacturing Example 1 was used as the positive electrode active material.

[0290]

[0291] Example 3: Multilayer dry cathode active material layer of first layer (40 μm) / second layer (60 μm)

[0292] A lithium-sulfur all-solid-state battery was manufactured by stacking the first positive electrode active material layer with a thickness of 40 μm and the second positive electrode active material layer with a thickness of 60 μm. At this time, the compositions of the first positive electrode active material layer and the second positive electrode active material layer were manufactured differently. The first positive electrode active material layer was prepared by mixing the positive electrode active material, solid electrolyte, and dry binder at a weight ratio of 80:19:1. The second positive electrode active material layer was prepared by mixing the positive electrode active material, solid electrolyte, and dry binder at a weight ratio of 70:29:1. The positive electrode active material of Manufacturing Example 1 was used as the positive electrode active material.

[0293]

[0294] Comparative Example 1-1: Dry positive electrode active material layer with a single-layer structure

[0295] A cathode active material layer was prepared by mixing a cathode active material, a solid electrolyte, and a dry binder at a weight ratio of 60:39:1. A lithium-sulfur battery including a single-layer cathode active material layer having a thickness of 100 μm was prepared.

[0296]

[0297] Comparative Example 1-2: Dry positive electrode active material layer with single-layer structure

[0298] A cathode active material layer was prepared by mixing a cathode active material, a solid electrolyte, and a dry binder at a weight ratio of 70:29:1. A lithium-sulfur battery including a single-layer cathode active material layer having a thickness of 100 μm was prepared.

[0299]

[0300] Comparative Example 1-3: Dry positive electrode active material layer with a single-layer structure

[0301] A cathode active material layer was prepared by mixing a cathode active material, a solid electrolyte, and a dry binder at a weight ratio of 80:19:1. A lithium-sulfur battery including a single-layer cathode active material layer having a thickness of 100 μm was prepared.

[0302]

[0303] Comparative Example 1-4: Wet positive electrode active material layer with a single-layer structure

[0304] A cathode active material layer was prepared by mixing a cathode active material, a solid electrolyte, and a binder at a weight ratio of 70:29:1. A lithium-sulfur battery including a 100 μm-thick single-layer cathode active material layer was prepared. Unlike Comparative Examples 1-1 to 1-3, Comparative Example 1-4 was prepared using a wet process.

[0305]

[0306] Comparative Example 2-1: Double-layer structured positive electrode active material layer

[0307] A lithium-sulfur all-solid-state battery was manufactured by stacking the first positive electrode active material layer with a thickness of 50 μm and the second positive electrode active material layer with a thickness of 50 μm. At this time, the compositions of the first positive electrode active material layer and the second positive electrode active material layer were manufactured differently. The first positive electrode active material layer was a mixture of a positive electrode active material, a solid electrolyte, and a dry binder at a weight ratio of 80:19:1. The second positive electrode active material layer was a mixture of a positive electrode active material, a solid electrolyte, and a dry binder at a weight ratio of 70:29:1. However, instead of the positive electrode active material of Manufacturing Example 1, a Li2S-LiI-CNF positive electrode active material was used as the positive electrode active material. Li2S, LiI, and CNF were mixed at a weight ratio of 3:2:1.

[0308]

[0309] Comparative Example 2-2: Double-layer structured positive electrode active material layer

[0310] A lithium-sulfur all-solid-state battery was manufactured by stacking the first positive electrode active material layer with a thickness of 60 μm and the second positive electrode active material layer with a thickness of 40 μm. At this time, the compositions of the first positive electrode active material layer and the second positive electrode active material layer were manufactured differently. The first positive electrode active material layer was a mixture of a positive electrode active material, a solid electrolyte, and a dry binder at a weight ratio of 80:19:1. The second positive electrode active material layer was a mixture of a positive electrode active material, a solid electrolyte, and a dry binder at a weight ratio of 70:29:1. However, instead of the positive electrode active material of Manufacturing Example 1, a Li2S-LiI-CNF positive electrode active material was used as the positive electrode active material. Li2S, LiI, and CNF were mixed at a weight ratio of 3:2:1.

[0311]

[0312] Comparative Example 2-3: Double-layer structured positive electrode active material layer

[0313] A lithium-sulfur all-solid-state battery was manufactured by stacking the first positive electrode active material layer with a thickness of 40 μm and the second positive electrode active material layer with a thickness of 60 μm. At this time, the compositions of the first positive electrode active material layer and the second positive electrode active material layer were manufactured differently. The first positive electrode active material layer was a mixture of a positive electrode active material, a solid electrolyte, and a dry binder at a weight ratio of 80:19:1. The second positive electrode active material layer was a mixture of a positive electrode active material, a solid electrolyte, and a dry binder at a weight ratio of 70:29:1. However, instead of the positive electrode active material of Manufacturing Example 1, a Li2S-LiI-CNF positive electrode active material was used as the positive electrode active material. Li2S, LiI, and CNF were mixed at a weight ratio of 3:2:1.

[0314]

[0315] The above examples and comparative examples are shown in Table 1 below.

[0316] Structure Manufacturing method Positive electrode active material (wt%) Solid electrolyte (wt%) Binder (wt%) Electrode thickness (μm) Example 1 First layer Dry 80 wt% 19 wt% 1.0 wt% 50 μm Second layer Dry 70 wt% 29 wt% 1.0 wt% 50 μm Example 2 First layer Dry 80 wt% 19 wt% 1.0 wt% 60 μm Second layer Dry 70 wt% 29 wt% 1.0 wt% 40 μm Example 3 First layer Dry 80 wt% 19 wt% 1.0 wt% 40 μm Second layer Dry 70 wt% 29 wt% 1.0 wt% 60 μm Comparative Example 1-1 Single layer Dry 60 wt% 39 wt% 1.0 wt% 100 μm Comparative Example 1-2 Single layer dry 70 wt% 29 wt% 1.0 wt% 100 μm Comparative example 1-3 Single layer dry 80 wt% 19 wt% 1.0 wt% 100 μm Comparative example 1-4 Single layer wet 70 wt% 29 wt% 1.0 wt% 100 μm Comparative example 2-1 First layer dry 80 wt% 19 wt% 1.0 wt% 50 μm Second layer dry 60 wt% 39 wt% 1.0 wt% 50 μm Comparative example 2-2 First layer dry 80 wt% 19 wt% 1.0 wt% 60 μm Second layer dry 60 wt% 39 wt% 1.0 wt% 40 μm Comparative example 2-3 First layer dry 80 wt% 19 wt% 1.0 wt% 40 μm Second layer dry 60 wt%39 wt%1.0 wt%60 μm

[0317]

[0318] Evaluation Example 1: XRD Analysis and SEM Analysis

[0319] XRD spectra were measured using Cu K α radiation for the raw materials bare Li2S, pulverized Li2S, and the manufactured Li2S-LiI-AlI3-CNF positive electrode active material used in Manufacturing Example 1. The measurement results are shown in Table 1 below. The Li2S crystallite size and lattice constant were derived from the first peak for the (111) crystal plane appearing at a diffraction angle of 2θ = 27° ± 2.0° in the XRD spectrum.

[0320] The particle size (i.e., D50) of the composites was measured using a laser-assisted particle size analyzer for bare Li2S, crushed Li2S, and Li2S-LiI-AlI3-CNF cathode active materials.

[0321] The measurement results are shown in Table 2 below.

[0322] Li2S crystallite size (nm) particle size (μm) Bare Li2S 6 4.67 10 Crushed Li2S 12.3 5 5.9 Li2S-LiI-AlI3-CNF cathode active material 13.2 3 6.7

[0323] As shown in Table 2, the particle size and crystallite size of the Li2S-LiI-AlI3-CNF cathode active material of Preparation Example 1 were significantly reduced compared to bare Li2S. This is believed to be because LiI-AlI3 was dissolved within the Li2S crystal. Therefore, it can be seen that Li2S and LiI-AlI3 form a solid solution in the Li2S-LiI-AlI3-CNF cathode active material.

[0324]

[0325] Evaluation Example 2: Charge / Discharge Test

[0326] The charge-discharge characteristics of lithium-sulfur batteries manufactured according to the examples and comparative examples of the present invention were evaluated. The charge-discharge tests were performed by placing the lithium-sulfur batteries in a 45°C constant-temperature chamber.

[0327] The first cycle involved charging for 20 hours at a constant current of 0.05 C until the battery voltage reached 2.8 V. Subsequently, discharging was performed for 20 hours at a constant current of 0.05 C until the battery voltage reached 1.0 V.

[0328] The second cycle was performed by charging for 10 hours at a constant current of 0.1 C until the battery voltage reached 2.8 V. Subsequently, discharging was performed for 10 hours at a constant current of 0.1 C until the battery voltage reached 1.0 V.

[0329] For the second cycle discharge capacity, the specific capacity based on Li2S and the specific capacity based on the entire electrode were measured, respectively.

[0330] After the second cycle, charging and discharging were performed for up to 20 cycles under the same conditions as the second cycle. The capacity retention rate is as shown in Equation 1 below.

[0331] <Mathematical Formula 1>

[0332] Capacity retention rate [%] = [20th cycle discharge capacity / 1st cycle discharge capacity] x 100

[0333] The measurement results are shown in Table 3 below.

[0334] 2nd cycle (0.1 C) discharge capacity [mAh / g, Li2S] 2nd cycle (0.1 C) discharge capacity [mAh / g, electrode] Rate characteristics (%) (0.1 C / 0.05 C discharge capacity) Capacity retention rate [%] (0.1 C, capacity retention rate after 20 cycles) Example 1 (1st layer 50 μm / 2nd layer 50 μm) 95940997.494.4 Example 2 (1st layer 60 μm / 2nd layer 40 μm) 95341397.994.2 Example 3 (1st layer 40 μm / 2nd layer 60 μm) 96440697.393.9 Comparative example 1-1 (single layer 100 μm) 96031896.186.5 Comparative example 1-2 (single layer 100 μm)94036494.582.2Comparative Example 1-3 (single layer 100 μm)93039192.980.7Comparative Example 1-4 (single layer 100 μm)86633595.674Comparative Example 2-1 (1st layer 50 μm / 2nd layer 50 μm)93432696.189.1Comparative Example 2-2 (1st layer 60 μm / 2nd layer 40 μm)93133495.988.4Comparative Example 2-3 (1st layer 40 μm / 2nd layer 60 μm)93633895.788.1

[0335] Referring to the results in Table 4, it can be seen that the charge / discharge characteristics of the lithium-sulfur battery according to the embodiments of the present invention are further improved.

[0336] More specifically, when comparing Examples 1 to 3 with Comparative Examples 1-1 to 1-4, it can be seen that the overall performance is improved. This means that, compared to a single-layer positive electrode, a multi-layer structure can exhibit more stable performance even when the thickness of the positive electrode active material layer is increased. In addition, it can be seen that the performance is significantly improved compared to the wet positive electrode of Comparative Example 1-4.

[0337] When comparing Examples 1 to 3 and Comparative Examples 2-1 to 2-3, it can be seen that the positive electrode structure is the same, but the positive electrode composite contains more metal halides. This indicates that the overall performance of the battery, including rate characteristics and charge / discharge efficiency, is improved by the positive electrode composite containing more metal halides.

[0338] Referring to the results for specific capacity (mAh / g, Li2S) based on Li2S, it can be seen that the specific capacity of Examples 1 to 3 is higher than that of Comparative Examples 2-1 to 2-3. This means that the discharge capacity per mass of Li2S, which acts as a lithium source in the positive electrode active material, is high. Consequently, it can be seen that the energy density is improved per the same mass.

Claims

1. Bipolar collector; A first positive electrode active material layer positioned on the positive electrode current collector; and Including a second positive electrode active material layer positioned on the first positive electrode active material layer, Each of the first positive electrode active material layer and the second positive electrode active material layer includes a positive electrode active material, a sulfide-based solid electrolyte, and a binder, The above positive electrode active material comprises a composite and a carbon-based material, and the composite comprises a sulfur compound, a lithium salt, and a metal halide. The above sulfur compounds are S8 and Li2S n (1 ≤ n ≤ 8, n is an integer), wherein the metal of the metal halide comprises at least one selected from the group consisting of aluminum (Al), silver (Ag), gold (Au), platinum (Pt), palladium (Pd), bismuth (Bi), tin (Sn), and zinc (Zn), The content of the positive electrode active material in the first positive electrode active material layer is greater than the content of the positive electrode active material in the second positive electrode active material layer. Cathode for lithium sulfur batteries.

2. In paragraph 1, The lithium salt comprises LiF, LiCl, LiBr, LiI or a combination thereof. Cathode for lithium sulfur batteries.

3. In paragraph 1, The above carbon-based material comprises at least one carbon nanostructure selected from the group consisting of carbon nanofibers, carbon nanotubes, carbon nanobelts, and carbon nanorods. Cathode for lithium sulfur batteries.

4. In paragraph 1, The above sulfide-based solid electrolyte is Li 7-c PS 6-c X c It is an argyrodite-type compound represented by (0≤c≤2), wherein X is F, Br, Cl or a combination thereof, Cathode for lithium sulfur batteries.

5. In paragraph 1, The complex comprises a solid solution of the sulfur compound, the lithium salt, and the metal halide. Cathode for lithium sulfur batteries.

6. In paragraph 1, The lithium salt is LiI, and the metal halide is AlI3. Cathode for lithium sulfur batteries.

7. In paragraph 1, The above binder comprises polytetrafluoroethylene (PTFE). Cathode for lithium sulfur batteries.

8. In paragraph 1, The thickness of the first positive electrode active material layer is 50 μm to 100 μm, The thickness of the second positive electrode active material layer is 50 μm to 100 μm, Cathode for lithium sulfur batteries.

9. In paragraph 1, The content of the positive electrode active material in the first positive electrode active material layer is 70 to 90 wt%, The content of the positive electrode active material in the second positive electrode active material layer is 60 to 80 wt%, Cathode for lithium sulfur batteries.

10. In paragraph 1, The content of the sulfide-based solid electrolyte in the first positive electrode active material layer is 10 to 30 wt%, The content of the sulfide-based solid electrolyte in the second positive electrode active material layer is 20 to 40 wt%, Cathode for lithium sulfur batteries.

11. In paragraph 1, The content of the sulfur compound is 40 to 90 wt% based on the total weight of the positive electrode active material. Cathode for lithium sulfur batteries.

12. In paragraph 1, The weight ratio of the lithium salt and the metal halide in the positive electrode active material is 1:27 to 3:1, Cathode for lithium sulfur batteries.

13. In paragraph 1, The molar ratio of the lithium salt and the metal halide in the positive electrode active material is 1:9 to 9:1, Cathode for lithium sulfur batteries.

14. In paragraph 1, The content of the sulfide-based solid electrolyte in the first positive electrode active material layer is less than the content of the sulfide-based solid electrolyte in the second positive electrode active material layer. Cathode for lithium sulfur batteries.

15. Anode current collector; and Including a multi-layered positive electrode active material layer sequentially arranged on the positive electrode current collector, The above positive electrode active material layer includes a positive electrode active material, a sulfide-based solid electrolyte, and a binder, The above positive electrode active material comprises a solid solution of a sulfur compound, a lithium salt, and an aluminum halide, The above sulfur compounds are S8 and Li2S n Contains at least one of (1 ≤ n ≤ 8, where n is an integer), The content of the positive electrode active material in the positive electrode active material layer decreases as it moves away from the positive electrode current collector. Cathode for lithium sulfur batteries.

16. In Article 15 The thickness of the positive electrode active material layer is 100 μm to 200 μm, Cathode for lithium sulfur batteries.

17. In paragraph 15, The content of the sulfur compound is 40 to 90 wt% based on the total weight of the positive electrode active material. Cathode for lithium sulfur batteries.

18. An anode according to any one of paragraphs 1 to 17; cathode; and Comprising a solid electrolyte layer disposed between the positive and negative electrodes, Lithium-sulfur solid-state battery.

19. In paragraph 18, The above negative electrode includes a negative electrode current collector and a negative electrode coating layer on the negative electrode current collector, The above cathode coating layer includes first particles and second particles, The first particle is amorphous carbon, crystalline carbon, porous carbon, or a combination thereof, The second particle comprises gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, zinc or a combination thereof. Lithium-sulfur solid-state battery.

20. In paragraph 19, Further comprising a lithium metal layer between the negative electrode current collector and the negative electrode coating layer, The lithium metal layer comprises lithium or a lithium alloy. Lithium-sulfur solid-state battery.

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