Composite active material for lithium-sulfur battery, manufacturing method thereofor, and lithium-sulfur battery comprising same

Abstract

A composite active material for a lithium-sulfur battery, according to the present invention, comprises a lithium salt, a positive electrode active material, an LPS inducer, and a conductive material, and may be a viscous fluid. The positive electrode active material may comprise lithium sulfide and lithium polysulfides. The LPS inducer may comprise at least one of polyethylene glycol dimethyl ether, polyethylene glycol diglycidyl ether, or a combination thereof.

Description

Composite active material for lithium-sulfur batteries, method for manufacturing the same, and lithium-sulfur battery including the same

[0001] The invention relates to a composite active material for a lithium-sulfur battery, a method for manufacturing the same, and a lithium-sulfur battery containing the same.

[0002]

[0003] Lithium-sulfur batteries are batteries that use a sulfur-containing material as the cathode active material. Compared to metals such as nickel, cobalt, manganese, aluminum, and iron, sulfur has the advantages of a low molecular weight, non-toxicity, and low cost. Therefore, as high-capacity and high-energy-density batteries, lithium-sulfur batteries can serve as a next-generation battery to replace lithium-ion batteries. However, there are several issues that need to be resolved for commercialization.

[0004] Lithium sulfide (Li₂S), primarily used as the cathode active material in lithium-sulfur batteries, has low solubility, making it difficult to be sufficiently contained within the cathode. Furthermore, the conversion process into lithium polysulfide requires high activation energy, which leads to a problem of reduced reactivity.

[0005] Furthermore, lithium-sulfur batteries have a problem where their lifespan is shortened due to significant volume changes during the charging and discharging process. Volume expansion occurring inside the battery causes active materials to separate, which weakens electrical contact and can lead to performance degradation.

[0006] Furthermore, lithium-sulfur batteries also have the problem of low ion conductivity. This is because the inherent low ion conductivity of sulfur-based materials restricts ion movement between active materials during charging and discharging. To fully utilize the target capacity, it is necessary to add electrode materials that facilitate ion conduction, which causes a decrease in the battery's energy density.

[0007]

[0008] One problem that the present invention aims to solve is to provide a composite active material for a lithium-sulfur battery in the form of a gel with high viscosity and a high content of sulfide-based cathode active material.

[0009] Another problem that the present invention aims to solve is to provide a lithium-sulfur battery comprising the above-mentioned composite active material.

[0010]

[0011] The composite active material for a lithium-sulfur battery according to the present invention comprises a lithium salt, a positive electrode active material, an LPS inducer, and a conductive material, and may be a viscous fluid. The positive electrode active material may include lithium sulfide and lithium polysulfide. The LPS inducer may include at least one of polyethylene glycol dimethyl ether, polyethylene glycol diglycidyl ether, or a combination thereof.

[0012]

[0013] The composite active material for a lithium-sulfur battery according to the present invention can realize a high-capacity battery by having a high content of a sulfide-based cathode active material. In addition, the composite active material according to the present invention is in the form of a viscous gel, which can provide high ion conductivity and may have the effect of buffering volume change.

[0014] Lithium-sulfur batteries containing this can exhibit excellent performance.

[0015]

[0016] FIG. 1 is a plan view of a lithium-sulfur battery according to embodiments of the present invention.

[0017] Figure 2 is a cross-sectional view along the line A-A' of Figure 1.

[0018] Figure 3 is an enlarged cross-sectional view of the M region of Figure 2.

[0019] FIG. 4 is a flowchart illustrating a method for manufacturing a composite active material according to embodiments of the present invention.

[0020] FIG. 5 is a flowchart schematically illustrating a method for manufacturing a composite active material according to embodiments of the present invention.

[0021] Figure 6 is a schematic diagram of a method for manufacturing a positive electrode active material according to a comparative example.

[0022] FIGS. 7 to 9 are cross-sectional views of a lithium-sulfur battery according to embodiments of the present invention.

[0023] Figure 10 is experimental data according to one evaluation example of the present invention.

[0024]

[0025] In order to fully understand the structure and effects of the present invention, preferred embodiments of the present invention are described with reference to the attached drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms and various modifications can be made. The description of these embodiments is provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention.

[0026] In this specification, when a component is described as being on another component, it means that it may be formed directly on the other component or that a third component may be interposed between them. Additionally, in the drawings, the thicknesses of the components are exaggerated for the effective description of the technical content. Throughout the specification, parts indicated by the same reference numeral represent the same components.

[0027] The embodiments described herein will be described with reference to cross-sectional and / or plan views, which are exemplary illustrations of the invention. In the drawings, the thicknesses of films and regions are exaggerated for effective description of the technical content. Accordingly, the regions illustrated in the drawings are schematic in nature, and the shapes of the regions illustrated in the drawings are intended to illustrate specific forms of regions of the device and are not intended to limit the scope of the invention. Although terms such as first, second, third, etc., have been used to describe various components in the various embodiments of this specification, these components should not be limited by such terms. These terms are used merely to distinguish one component from another. The embodiments described and illustrated herein also include their complementary embodiments.

[0028] The terms used herein are for describing the embodiments and are not intended to limit the invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. As used herein, 'comprises' and / or 'comprising' do not exclude the presence or addition of one or more other components to the mentioned components.

[0029] Unless otherwise defined in this specification, the particle size may be the average particle size. Additionally, the particle size refers to the average particle size (D50), which means the diameter of the particle whose cumulative volume in the particle size distribution is 50% by volume. The average particle size (D50) may be measured by methods widely 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) image or a scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) value may be obtained by measuring using a measuring device utilizing dynamic light scattering, performing data analysis to count the number of particles for each particle size range, and then calculating from this. Alternatively, it may be measured using a laser diffraction method. When measuring by laser diffraction, more specifically, after dispersing the particles to be measured 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 ultrasound of about 28 kHz at an output of 60 W, and then the average particle size (D50) at 50% of the particle size distribution in the measuring device can be calculated.

[0030] In this specification, “metal” includes both metals and metalloids such as silicon and germanium in an elemental or ionic state. In this specification, “alloy” means a mixture of two or more metals.

[0031] In this specification, “electrode active material” refers to an electrode material capable of undergoing lithiation and delithiation. In this specification, “anode active material” refers to an anode material capable of undergoing lithiation and delithiation. In this specification, “anode active material” refers to an anode material capable of undergoing lithiation and delithiation.

[0032] In this specification, “lithiation” and “to lithiate” refer to the process of adding lithium to an electrode active material. In this specification, “delithiation” and “to delithiate” refer to the process of removing lithium from an electrode active material.

[0033] In this specification, “charge” and “to charge” refer to the process of providing electrochemical energy to a battery. In this specification, “discharge” and “to discharge” refer to the process of removing electrochemical energy from a battery.

[0034] In this specification, “anode” and “cathode” refer to electrodes where electrochemical reduction and lithiation occur during the discharge process. In this specification, “negative electrode” and “anode” refer to electrodes where electrochemical oxidation and delithiation occur during the discharge process.

[0035] A lithium-sulfur battery can be charged and discharged through the following process. A lithium-sulfur battery may be a battery that uses a material containing sulfur as the positive active material. The positive active material is cyclic sulfur (S8), lithium polysulfide (Li2S n It may include , n≥4), and / or lithium sulfide (Li2S).

[0036] During the discharge process, lithium ions and electrons can move from the negative electrode to the positive electrode. At this time, cyclic sulfur molecules within the positive electrode can be gradually converted into various forms of lithium polysulfides through reduction reactions. As discharge progresses, lithium polysulfides can be converted into lithium sulfide, a more stable form. In other words, energy can be released as the conversion proceeds in the order of cyclic sulfur → lithium polysulfide → lithium sulfide.

[0037] Conversely, during the charging process, lithium sulfide is gradually oxidized and converted into lithium polysulfide, eventually returning to cyclic sulfur. During this process, lithium ions move from the anode to the cathode, and energy can be stored as electrons are recovered.

[0038] During the stepwise conversion process between cyclic sulfur, lithium polysulfide, and lithium sulfide that occurs during charging and discharging, multiple electron transfer reactions may be involved at each stage. These multi-stage reactions contribute to the high capacity characteristics of lithium-sulfur batteries and enable the realization of high energy density. Therefore, measures to ensure the efficient transfer of lithium ions and electrons, such as lowering the activation energy of each stage, may be important.

[0039]

[0040] lithium sulfur battery (10)

[0041] FIG. 1 is a plan view of a lithium-sulfur battery (10) according to embodiments of the present invention. FIG. 2 is a cross-sectional view along line A-A' of FIG. 1.

[0042] Referring to FIGS. 1 and 2, a lithium-sulfur battery (10) according to the present invention may include a positive electrode (100), a negative electrode (200) facing the positive electrode (100), and a solid electrolyte layer (300) disposed between the positive electrode (100) and the negative electrode (200). However, not limited thereto, the lithium-sulfur battery (10) may further include an additional functional layer, such as an adhesion-enhancing layer, disposed between the positive electrode (100) and the solid electrolyte layer (300) or between the negative electrode (200) and the solid electrolyte layer (300).

[0043]

[0044] positive electrode (100)

[0045] A positive electrode (100) according to embodiments of the present invention will be described with reference to FIGS. 1 and FIGS. 2. The positive electrode (100) according to embodiments 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).

[0046]

[0047] positive current collector (110)

[0048] A positive current collector (110) according to embodiments of the present invention will be described with reference to FIGS. 1 and FIGS. 2. A positive current collector (110) according to one embodiment of the present invention may provide a reference surface on which a positive active material layer (120) is disposed. The positive current collector (110) 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), lithium (Li), or an alloy thereof. The positive current collector (110) may include a plate or a foil. In another embodiment of the present invention, the positive current collector (110) may be omitted. The thickness of the positive current collector (110) may be, for example, 1 μm to 100 μm, 1 μm to 50 μm, 5 μm to 25 μm, or 10 μm to 20 μm.

[0049] The positive 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.

[0050] The base film may be, for example, an insulator. Since the base film contains an insulating thermoplastic polymer, the base film may soften or liquefy upon the occurrence of a short circuit, thereby interrupting battery operation and suppressing a sudden increase in current.

[0051] 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 alloys thereof. The metal layer may act as an electrochemical fuse and cut off in the event of an overcurrent to perform a short-circuit prevention function. The limit current and maximum current can be controlled by adjusting the thickness of the metal layer. The metal layer may be plated or deposited on a base film. As the thickness of the metal layer decreases, the limit current and / or maximum current of the positive current collector (110) decreases, thereby improving the stability of the lithium battery in the event of a short circuit.

[0052] 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 melt, allowing the metal layer to be electrically connected to the lead tab.

[0053] To make the weld between the metal layer and the lead tab more robust, a metal chip may be added between the metal layer and the lead tab. The metal chip may be a thin sheet of the same material as the metal of the metal layer. The metal chip may be, for example, metal foil, metal mesh, etc. The metal chip may be, for example, aluminum foil, copper foil, SUS foil, etc. The lead tab may be welded to a metal chip / metal layer laminate or a metal chip / metal layer / base film laminate by placing the metal chip on the metal layer and then welding it to the lead tab. During welding, as the base film, metal layer, and / or metal chip melt, the metal layer or the metal layer / metal chip laminate may be electrically connected to the lead tab. A metal chip and / or lead tab may be added to a portion of the metal layer.

[0054] 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. By having the base film within this thickness range, the weight of the electrode assembly can be reduced more effectively. The melting point of the base film may be, for example, 100 to 300 °C, 100 to 250 °C or lower, or 100 to 200 °C. By having the base film within this melting point range, the base film can melt during the welding process of the lead tab and be easily bonded to the lead tab. Surface treatments, such as corona treatment, may be performed on the base film to improve the adhesion between the base film and the metal layer.

[0055] The thickness of the metal layer may be, for example, 0.01 to 3 μm, 0.1 to 3 μm, 0.1 to 2 μm, or 0.1 to μm. By having the metal layer within this range of thickness, the stability of the electrode assembly can be ensured while maintaining conductivity. The thickness of the metal piece may be, for example, 2 to 10 μm, 2 to 7 μm, or 4 to 6 μm. By having the metal piece within this range of thickness, the connection between the metal layer and the lead tab can be performed more easily. Since the positive current collector (110) has a laminated structure of the base film and the metal layer described above, the weight of the positive electrode (100) can be reduced and, consequently, the energy density of the lithium-sulfur battery (10) can be improved.

[0056]

[0057] positive active material layer (120)

[0058] A positive active material layer (120) according to embodiments of the present invention will be described with reference to FIGS. 1 and FIGS. 2. The content of the positive active material in the positive active material layer (120) according to embodiments of the present invention 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 active material layer (120). If the content of the positive active material is excessively reduced, the energy density of the lithium-sulfur battery (10) may decrease. If the content of the positive active material is excessively increased, the degradation of the lithium-sulfur battery (10) may be accelerated due to changes in the volume of the positive during charging and discharging.

[0059] The positive active material within the positive active material layer (120) can reversibly absorb and desorb lithium ions. The positive active material may include a plurality of particles. When manufacturing the positive active material layer (120), the positive active material may be added alone or added in a form included in a composite active material. The composite active material may include the positive active material and electrode materials that produce synergy therewith. The positive active material may include a sulfide-based positive active material and, if necessary, may further include an oxide-based positive active material.

[0060] Sulfide-based cathode active materials include, for example, cyclic sulfur (S8), nickel sulfide, copper sulfide, lithium sulfide (Li2S), Li2S-containing composites, and lithium polysulfide (Li2S n It may include , n≥4), or a combination thereof. For example, the sulfide-based cathode active material may include lithium sulfide and lithium polysulfide. A more specific description of the cathode active material according to the present invention will be provided later.

[0061] The oxide-based cathode active material may include, for example, lithium transition metal oxides, metal oxides, or combinations thereof. Lithium transition metal oxides 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 combinations thereof. Lithium oxides may include, for example, iron oxide, vanadium oxide, or combinations thereof.

[0062] For oxide-based cathode active materials, one or more types of composite oxides of lithium and a metal selected from, for example, cobalt, manganese, nickel, and combinations thereof may be used. For lithium-containing oxide-based cathode active materials, for example, Li a A 1-b B' b D2(wherein 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 O 4-c D c (In the above equation, 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 G d O2(wherein 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(wherein 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 equation, 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li a CoG b O2(in the above equation, 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li a MnG b O2(in the above equation, 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4(wherein 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) It may include a compound represented by any one of the chemical formulas of Fe2(PO4)3(0 ≤ f ≤ 2); LiFePO4.

[0063] 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; and J may be V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0064] 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 and metal atomic layers are alternately and regularly arranged in a specific direction, thereby forming a two-dimensional plane for each atomic layer. The "cubic rock salt type structure" represents a sodium chloride (NaCl) type structure, which is a type of crystal structure; specifically, it exhibits a structure in which face-centered cubic lattices (fcc) formed by cations and anions, respectively, are offset from each other by half the ridge of the unit lattice. Lithium transition metal oxides having such a layered rock salt type structure are, for example, LiNi x Co y Al zO2(NCA) or LiNi x Co y Mn z O2(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, 리튬황 전지(10)의 에너지 밀도가 커지고 열안정성이 향상될 수 있다.

[0065] The oxide-based cathode active material may be covered by a coating layer (not shown). The oxide-based cathode active material may also be used as a mixture of the compound described above and the compound to which the coating layer is added. Meanwhile, the coating layer added to the surface of the cathode active material may include, for example, oxides, hydroxides, oxyhydroxides, oxycarbonates, or hydroxycarbonates of the following coating elements. The compounds forming this coating layer are 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 for forming the coating layer may be selected within a range that does not adversely affect the physical properties of the cathode active material. The method for forming the coating layer may include, for example, spray coating or immersion methods.

[0066] When the oxide-based positive electrode active material contains nickel (Ni) as a ternary lithium transition metal oxide such as NCA or NCM, for example, the capacity density of the lithium-sulfur battery (10) is increased, and the metal leaching of the positive electrode active material in the charged state can be reduced. As a result, the cycle characteristics of the lithium-sulfur battery (10) in the charged state are improved. Meanwhile, "cycle characteristics" is a characteristic that indicates the degree of degradation of the lithium-sulfur battery (10) due to charging and discharging of the lithium-sulfur battery (10). A lithium-sulfur battery (10) with high cycle characteristics has a small degree of degradation due to charging and discharging, while a lithium-sulfur battery (10) with low cycle characteristics may have a large degree of degradation due to charging and discharging.

[0067] The oxide-based cathode active material may have a particle shape such as a sphere or an ellipsoid. 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, single-crystal particles or polycrystalline particles.

[0068]

[0069] complex active material

[0070] FIG. 3 is an enlarged cross-sectional view of region M of FIG. 2. Hereinafter, a composite active material for a lithium-sulfur battery according to an embodiment of the present invention will be described with reference to FIG. 3.

[0071] A positive active material layer according to one embodiment of the present invention may include a composite active material. The composite active material may include a lithium salt (122), a positive active material (121, 124), an LPS inducer (123), and a conductive material (125). The positive active material (121, 124) may include lithium sulfide (121) and lithium polysulfide (124). The LPS inducer (123) may include at least one of polyethylene glycol dimethyl ether (PEGDME), polyethylene glycol diglycidyl ether (PEGDE), or a combination thereof. A positive active material layer according to one embodiment of the present invention may be a viscous fluid.

[0072] Even when applied to a battery including a solid electrolyte layer, the composite active material may not include a solid electrolyte. The positive electrode active material layer of a lithium-sulfur battery generally includes a solid electrolyte to overcome the low ionic conductivity of the positive electrode active material. However, the composite active material according to the present invention possesses sufficient ionic conductivity and can exhibit excellent performance even without a solid electrolyte.

[0073] The composite active material according to the present invention can be applied to both liquid electrolyte batteries and solid electrolyte batteries. Generally, in batteries containing a liquid electrolyte, a shuttle effect may occur in which lithium polysulfide (124) dissolves in the electrolyte and moves to the negative electrode, resulting in loss. However, the composite active material of the present invention includes an LPS inducer (123), so that even if lithium polysulfide (124) is lost, lithium polysulfide (124) can be induced and replenished within the positive electrode.

[0074] More preferably, the composite active material of the present invention can be applied to a battery containing a solid electrolyte. In a solid electrolyte battery, since there is no liquid electrolyte and thus no shuttle effect occurs, the desired composition, such as lithium polysulfide (124) and lithium sulfide (121), can be stably maintained within the composite active material. This allows the performance of the positive electrode active material to be stably maintained during charge and discharge cycles, thereby further improving the lifespan and performance of the battery.

[0075]

[0076] lithium salt (122)

[0077] The lithium salt (122) contained within the composite active material may be a substance that is dissolved in the composite active material and acts as a source of lithium ions. Any substance that performs the above role may be applied as the lithium salt (122) without limitation. The lithium salt (122) may be, for example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 It may include SO2)(x and y are integers from 1 to 20), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, lithium difluoro(oxalate)borate (LiDFOB), lithium difluorobis(oxalate)phosphate (LiDFBOP), lithium bis(oxalate)borate (LiBOB), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), etc.

[0078]

[0079] positive active material (121, 124)

[0080] The positive electrode active material (121, 124) within the composite active material may include lithium sulfide (121) and lithium polysulfide (124). The lithium sulfide (121) and lithium polysulfide (124) may be the sulfide-based positive electrode active material described above.

[0081] Lithium sulfide (121) may be dispersed within the LPS inducer (123). However, since lithium sulfide (121) has low solubility in the LPS inducer (123), it may not be completely dissolved and may be dispersed in the form of fine crystals. Lithium sulfide (121) has a solid crystal structure formed by ionic bonding, and may have high lattice energy and relatively non-polar characteristics. Due to these characteristics, it may be difficult to completely dissolve in the LPS inducer (123).

[0082] On the other hand, lithium polysulfide (124) can be completely dissolved in the LPS inducer (123). Lithium polysulfide (124) has a structure in which chain-shaped sulfur atoms are bonded to lithium ions, and it can have low lattice energy and relatively polar characteristics. In particular, its solubility can be increased through electrostatic interaction with oxygen in the LPS inducer (123).

[0083] Since lithium sulfide (121) and lithium polysulfide (124) are mutually converted during charging and discharging, their respective contents within the composite active material may not be fixed but may change during charging and discharging. Lithium sulfide (121) has low solubility and can act as a resistor, and as its content increases, the resistance of the battery may increase. On the other hand, lithium polysulfide (124) can be dissolved in the LPS inducer (123) to increase ion conductivity, so as its content increases, the internal resistance of the battery decreases, and the lifespan of the battery may be improved.

[0084] Lithium polysulfide (124) Li2S nIt may have the chemical formula, and n may be an integer between 4 and 8. Within the above range, the composite active material may provide optimal viscosity and ion conductivity. If the chain of lithium polysulfide (124) becomes excessively long, the reactivity of lithium polysulfide (124) decreases and the viscosity of the composite active material may increase excessively. This may hinder the movement of lithium ions within the composite active material, thereby degrading the charge / discharge performance of the battery.

[0085] The content of the lithium sulfide (121) may be 1 wt% to 90 wt%, or 5 wt% to 75 wt%, or 10 wt% to 60 wt% based on the total weight of the composite active material.

[0086] The content of the lithium polysulfide (124) may be 20 wt% to 40 wt% based on the total weight of the composite active material.

[0087] The ratio of the weight of the lithium polysulfide to the weight of the lithium sulfide (121) may be 1:3 to 2:1.

[0088] When lithium sulfide (121) and lithium polysulfide (124) are within the above range of content and weight ratio, the composite active material can provide a high capacity through a high sulfur content and can improve the charge and discharge efficiency of the battery by having optimal viscosity and ion conductivity.

[0089] If the content of lithium sulfide (121) is excessive, the resistance of the battery may increase, and if the content of lithium polysulfide (124) is excessive, the viscosity of the composite active material may become excessively high. Since lithium sulfide (121) has low solubility and acts as a resistor, there may be a limit to increasing its content. However, if some of the lithium sulfide (121) is converted into lithium polysulfide (124), more sulfur can be included in the composite active material, which can help to further increase the battery capacity.

[0090] The sulfur content in the above composite active material may be 20 wt% to 60 wt%, or 25 wt% to 50 wt%, or 29 wt% to 42 wt% based on the total weight of the above composite active material.

[0091]

[0092] LPS inducer (123)

[0093] The LPS inducer (123) may include at least one of polyethylene glycol dimethyl ether (PEGDME), polyethylene glycol diglycidyl ether (PEGDE), or a combination thereof.

[0094] The LPS inducer (123) can coordinate with lithium ions (Li) within the composite active material to dissociate anions, and the dissociated anions may include sulfur anions (S). The dissociated sulfur anions may react with lithium sulfide (121) to form lithium polysulfide (124).

[0095] The LPS inducer (123) can induce the conversion of lithium sulfide (121) into lithium polysulfide (124). By converting the lithium sulfide (121), which acts as a resistor, into lithium polysulfide (124), the resistance within the composite active material can be lowered. Additionally, the battery capacity can be increased by allowing a larger amount of positive active material to be contained compared to when only lithium sulfide (121) is dispersed.

[0096] The LPS inducer (123) can maintain a certain amount of lithium polysulfide (124) within the composite active material. By doing so, the activation energy required for the conversion of lithium sulfide (121) into lithium polysulfide (124) is lowered, thereby increasing the efficiency of the conversion reaction during charging and discharging and improving battery performance.

[0097] In one embodiment, when charging and discharging are performed 100 times each, the minimum content of lithium polysulfide (124) in the composite active material may be 40 wt% or more.

[0098] Number average molecular weight (M) of LPS inducer (123) n The viscosity may be 100 g / mol to 3000 g / mol, or 200 g / mol to 2000 g / mol, or 250 g / mol to 1000 g / mol. The LPS inducer (123) can impart viscous fluid properties to the composite active material, and this viscosity can serve to buffer changes in electrode volume during charging and discharging. In addition, the viscosity can penetrate between the positive electrode active materials to increase the ion conductivity of the battery.

[0099] When the number average molecular weight is within the above range, the buffering function and the ion conductivity improvement function can exhibit optimal effects. If the number average molecular weight is excessively large, the viscosity of the composite active material becomes too high, which may hinder lithium ion movement. If the number average molecular weight is excessively small, the composite active material may not possess sufficient viscosity.

[0100] Sulfur has low ionic conductivity due to its physical properties, so if the amount of positive active material is increased to increase battery capacity, there may be a problem where only the positive active material located at the interface participates in the reaction. The LPS inducer (123) according to the present invention penetrates between the positive active materials within the composite active material to form a network, thereby allowing all the internal positive active materials to participate in the battery reaction. Through this, efficiency close to the theoretical capacity can be achieved in actual batteries.

[0101] The viscosity of the composite active material may be 50 cP to 500 cP.

[0102] The viscosity of the composite active material can be measured by the following method. A sample of 10 ml to 20 ml can be prepared from the composite active material. The temperature of the sample can be adjusted to approximately 25°C. The viscosity can be measured by applying rotation of 50 rpm to 500 rpm to the sample. Five samples can be prepared at any location, and the viscosity of the composite active material can be obtained by averaging the measurements of the five samples.

[0103] The above viscosity measuring device may be applied without limitation as long as it is a device capable of satisfying the above conditions. The above viscosity measuring device may use, for example, a rotational viscometer, a capillary viscometer, a vibrational viscometer, a falling sphere viscometer, etc. As for the above rotational viscometer, for example, a Brookfield viscometer (model name: LVDV-II+PCP) may be used.

[0104] The content of the LPS inducer (123) may be 5 wt% to 40 wt%, or 10 wt% to 30 wt%, or 15 wt% to 24 wt% based on the total weight of the composite active material.

[0105] When the content of the LPS inducer (123) satisfies the above range, the composite active material can satisfy the desired viscosity range. In this viscosity range, the composite active material has optimal ion conductivity and viscosity, which can increase the charge and discharge efficiency of the battery and maintain a stable electrode structure. If the viscosity exceeds the above range, it may be difficult for the LPS inducer (123) to penetrate between the positive electrode active materials within the composite active material and form a network. If the viscosity is below the above range, the LPS inducer (123) may not form sufficient coordination bonds with lithium ions, and thus the lithium polysulfide (124) induction reaction may not occur smoothly.

[0106] Polyethylene glycol dimethyl ether (PEGDME) and polyethylene glycol diglycidyl ether (PEGDE) may belong to the polyethylene glycol (PEG) series of compounds. Among the PEG series of compounds, PEGDME and PEGDE have excellent interaction with lithium sulfide (121), so they can effectively induce lithium polysulfide (124) and provide appropriate viscosity.

[0107] For example, polyethylene oxide (PEO) and polyethylene glycol diacrylate (PEGDA) can be used as PEG-based compounds. PEO and PEGDA have large molecular weights and long chain structures, which results in relatively high viscosity, which can cause the viscosity of the composite active material to increase excessively. Additionally, due to their low fluidity, PEO and PEGDA have limited interaction with lithium sulfide (121), which can lead to reduced performance in inducing lithium polysulfide (124).

[0108]

[0109] Challenger (125)

[0110] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fiber, carbon nanofiber, carbon nanotube, and graphene; metal-based materials in the form of metal powder or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0111] The conductive material (125) may be a carbon nanostructure and may include a one-dimensional carbon nanostructure, a two-dimensional carbon nanostructure, a three-dimensional carbon nanostructure, or a combination thereof. For example, the carbon nanostructure may include carbon nanotubes (CNT), carbon nanofibers (CNF), carbon nanobelts, carbon nanorods, graphene, or a combination thereof.

[0112] The conductive material (125) may be a porous carbon-based material or a non-porous carbon-based material and may include periodic and regular two-dimensional or three-dimensional pores. For example, the conductive material (125) may include carbon black such as Ketjen black, acetylene black, Denka black, thermal black, channel black, graphite, activated carbon, or a combination thereof.

[0113] The conductive material (125) may include a fibrous carbon-based material. The carbon-based material facilitates electron conduction from the surface to the interior of the composite active material, thereby further improving electron conductivity. As a result, the internal resistance of the composite active material may be reduced, and the lifespan characteristics of the battery containing it may be further improved.

[0114] The aspect ratio of the fibrous carbon-based material may be 2 or more, 3 or more, 4 or more, 5 or more, 10 or more, or 20 or more, and may be 2 to 30, 2 to 20, 2 to 10, 2 to 8, 2 to 5, 2 to 4, 3 to 30, 4 to 30, 5 to 30, 10 to 30, or 20 to 30. By satisfying the above ranges for the aspect ratio of the fibrous carbon-based material, the effect of improving the electronic conductivity of the composite active material containing it can be maximized, while also mitigating the imbalance of local electronic conductivity within the composite active material.

[0115] The diameter of the fibrous carbon-based material may be 0.01 μm to 10 μm, 0.05 μm to 10 μm, or 0.1 μm to 5 μm, and the length may be 1 μm to 50 μm or 1 μm to 20 μm. The diameter and length of the fibrous carbon-based material may be measured from scanning electron microscope (SEM) or transmission electron microscope (TEM) images, or may be measured by laser diffraction.

[0116] The content of the conductive material (125) may be 1 wt% to 30 wt%, or 3 wt% to 20 wt%, or 5 wt% to 15 wt% based on the total weight of the composite active material. Within the above range, the conductive material (125) can improve the ion conductivity of the battery by forming a network through which ions and electrons can move within the composite active material. If the content of the conductive material (125) is excessive, the energy density of the battery may be lowered.

[0117]

[0118] bookbinder

[0119] The composite active material according to the embodiments of the present invention may further include a binder. Any binder that serves to effectively adhere particles to each other within the composite active material may be applied without limitation. Representative examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0120]

[0121] additives

[0122] To finely control the viscosity of the composite active material, an additive may be additionally included. The additive may be a substance that has viscosity at room temperature. For example, in one embodiment of the present invention, the additive may include a dinitrile-based compound. Dinitrile-based compounds have a high decomposition voltage and excellent electrochemical stability, and viscosity can be controlled by adjusting the carbon chain length. Therefore, the composite active material containing the dinitrile-based compound can maintain an appropriate level of viscosity.

[0123] The dinitrile-based compound may be a dinitrile-based compound having 4 to 12 carbon atoms. Within the above range of carbon atoms, the composite active material can maintain an appropriate viscosity.

[0124] Dainitrile-based compounds may include, for example, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, or combinations thereof.

[0125]

[0126] solid electrolyte layer (300)

[0127] Referring again to FIGS. 1 and FIGS. 2, the lithium-sulfur battery (10) according to the present invention may include a solid electrolyte layer (300). The solid electrolyte layer (300) may be provided between the positive electrode (100) and the negative electrode (200). The solid electrolyte layer (300) may include a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof.

[0128] Sulfide-based solid electrolytes contain, for example, Li, S, and P, and may optionally further contain halogen elements. Sulfide-based solid electrolytes contain, for example, 1×10⁻⁶ at room temperature. -5It can have an ionic conductivity of S / cm or higher. Sulfide-based solid electrolytes are, 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 PS 6-x I x It may include one or more selected from , 0≤x≤2.

[0129] The above sulfide-based solid electrolyte may include an argyrodite-type solid electrolyte. The above argyrodite-type solid electrolyte is 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 It may be an azirodite-type compound comprising one or more selected from (0≤x≤2). For example, it may comprise one or more selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0130] The density of the above azirodite-type solid electrolyte may be 1.5 g / cc to 2.0 g / cc. By satisfying the above range for the density of the azirodite-type solid electrolyte, the internal resistance of the battery containing it can be reduced, and defects such as penetration or short-circuiting of the solid electrolyte film due to lithium dendrite formation can be prevented. In addition, the elastic modulus of the above azirodite-type solid electrolyte may be 15 GPa to 35 GPa or 15 GPa to 30 GPa.

[0131] In addition, the above sulfide-based solid electrolyte is 1 × 10⁻⁶ at room temperature -6 It can have an ionic conductivity of S / cm or greater. For example, the ionic conductivity of the above sulfide-based solid electrolyte is 1 × 10⁻⁶ at room temperature. -5 S / cm or greater, 1.5 × 10 -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 may be greater than S / cm.

[0132] Oxide-based solid electrolytes contain, for example, Li, O, and transition metal elements, and may optionally contain other elements. Oxide-based solid electrolytes contain, for example, 1×10⁻⁶ at room temperature. -5 It may be a solid electrolyte having an ionic conductivity of S / cm or greater. The oxide-based solid electrolyte may be, for example, a mixture of a 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.

[0133] Polymer solid electrolytes may be, for example, electrolytes containing a mixture of a lithium salt and a polymer, or electrolytes containing a polymer having ion-conducting functional groups.

[0134] The polymers included in the polymeric solid electrolyte are, for example, polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyethylene oxide (PEO), poly(styrene-b-ethylene oxide) block copolymer (PS-PEO), poly(styrene-butadiene), poly(styrene-isoprene-styrene), poly(styrene-b-divinylbenzene) block copolymer, poly(styrene-ethylene oxide-styrene) block copolymer, polystyrene sulfonate (PSS), polyvinyl fluoride (PVF), poly(methylmethacrylate) (PMMA), polyethylene glycol (PEG), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), polyethylenedioxythiophene (PEDOT), polypyrrole (PPY), polyacrylonitrile (PAN), polyaniline, Polyacetylene, Nafion, Aquivion, Flemion, Gore, Aciplex, Morgane ADP, sulfonated poly(ether ether ketone) (SPEEK), sulfonated poly(arylene ether ketone ketone sulfone) (SPAEKKS), sulfonated poly(aryl ether ketone) (SPAEK), poly[bis(benzimidazobenzisoquinolinones)] (SPBIBI), polystyrene sulfonate (PSS), lithium 9,10-Diphenylanthracene-2-sulfonate (lithium 9,10-diphenylanthracene-2-sulfonate, DPASLi +It may be ) or a combination thereof. However, it is not limited to these, and any that are used as polymer solid electrolytes in the relevant technical field may be applied. Lithium salts may be applied without limitation as long as they can be used as lithium salts in the relevant technical field. Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 It may be SO2)(x and y are each 1 to 20), LiCl, LiI, or a mixture thereof. The polymer included in the polymeric solid electrolyte may be, for example, a compound containing 10 or more, 20 or more, 50 or more, or 100 or more repeating units. The weight-average molecular weight (M) of the polymer included in the polymeric solid electrolyte w ) can be, for example, 1,000 Dalton or more, 10,000 Dalton or more, 100,000 Dalton or more, or 1,000,000 Dalton or more.

[0135] As described above, since the composite active material according to the present invention has excellent ion conductivity, it can have sufficient conductivity even without including a solid electrolyte. However, a solid electrolyte may be added to the composite active material as needed. In this case, the content of the solid electrolyte may be 10 wt% to 60 wt% with respect to the total weight of the composite active material layer. For example, the content of the sulfide-based solid electrolyte in the composite active material layer may be 10 wt% to 50 wt%, or 15 wt% to 30 wt%, with respect to the total weight of the composite active material layer.

[0136] 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 anode (100), and the second solid electrolyte layer (320) may be adjacent to the cathode (200).

[0137] 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. Additionally, the solid electrolyte may include sulfur (S), phosphorus (P), and lithium (Li) as at least constituent elements among the sulfide-based solid electrolyte materials described above, for example. 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 the solid electrolyte, the molar ratio of Li2S and P2S5 may be, for example, in the range of Li2S : P2S5 = 50 : 50 to 90 : 10.

[0138] In one embodiment, the first solid electrolyte is 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 It may include an argyrodite-type compound comprising one or more selected from (0≤x≤2). The first solid electrolyte may include an argyrodite-type compound comprising one or more selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0139] In another embodiment, the first solid electrolyte is Li 7-a Ma PS 6-c X c It may include an argyrodite-type compound comprising. Here, 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. a and c may each be a real number between 0 and 2.

[0140] The density of the azyrodite-type solid electrolyte may be 1.5 g / cc to 2.0 g / cc. Since the azyrodite-type solid electrolyte has a density of 1.5 g / cc or higher, the internal resistance of the all-solid-state battery is reduced, and defects such as penetration and short circuit of the solid electrolyte film due to lithium dendrite formation can be prevented. The elastic modulus of the first solid electrolyte is, for example, 15 GPa to 35 GPa.

[0141] 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 or similar as 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 composition similar to that of the first solid electrolyte.

[0142] The second solid electrolyte can come into direct contact with the negative electrode coating layer (220). By doing so, 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 side reactions. By doing so, the cell performance of the all-solid-state battery (10) according to the present invention can be improved.

[0143] Each of the first and second solid electrolyte layers (310, 320) may further include a binder. The binder in the solid electrolyte layer (300) is, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., but is not limited to these. The binder in the solid electrolyte layer (300) may be the same as or different from the binder in the positive active material layer (120) or the binder in the negative coating layer (220).

[0144] 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).

[0145] 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).

[0146] Referring again to FIGS. 1 and FIGS. 2, the anode (100) and the first solid electrolyte layer (310) can form an anode composite layer (CSH). The cathode (200) and the second solid electrolyte layer (320) can form a cathode composite layer (ASH). An anode composite layer (CSH) can be laminated on the cathode composite layer (ASH).

[0147] The area of ​​the cathode composite layer (ASH) and the area of ​​the anode composite layer (CSH) may differ from each other. Specifically, the area of ​​the cathode composite layer (ASH) may be larger than the area of ​​the anode composite layer (CSH). The anode composite layer (CSH) may completely overlap within the cathode composite layer (ASH).

[0148] In one embodiment of the present invention, the first solid electrolyte layer (310) may have substantially the same area as the anode (100). The second solid electrolyte layer (320) may have substantially the same area as the cathode (200).

[0149] 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 a 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 a second direction (D2). The negative electrode composite layer (ASH) may have a fourth width (WI4) in a second direction (D2). The third width (WI3) may be smaller than the fourth width (WI4).

[0150] 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 and 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).

[0151] In one embodiment, as shown in FIG. 2, the positive active material layer (120) in a discharged state may have a first thickness (TK1). The all-solid-state battery (10) may have a first height (HE1) in a third direction (D3). The first height (HE1) may be the sum of the thickness of the positive composite layer (CSH) and the thickness of the negative composite layer (ASH).

[0152]

[0153] Various examples of lithium-sulfur batteries

[0154] Various embodiments of a lithium-sulfur battery according to the present invention will be described below. In the embodiments described below, detailed descriptions of technical features that overlap with those previously described with reference to FIGS. 1 to 3 will be omitted, and differences will be described in detail.

[0155] FIG. 7 is a cross-sectional view along line A-A' of FIG. 1, illustrating a lithium-sulfur battery according to another embodiment of the present invention. Referring to FIG. 7, in one embodiment, a lithium-sulfur battery (10) in a charged state may further include a lithium metal layer (230) provided between a negative electrode current collector (210) and a negative electrode coating layer (220). The negative electrode (200) according to the present embodiment may include a negative electrode current collector (210), a negative electrode coating layer (220), and a lithium metal layer (230) between them.

[0156] 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, for example, a lithium reservoir. The lithium alloy may be, for example, 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, but is not limited to these; any alloy used as a lithium alloy in the relevant technical field may be possible. The lithium metal layer (230) may be composed of one of these alloys or lithium, or may be composed of various 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) during the charging process of the lithium-sulfur battery (10), for example.

[0157] 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 excessively 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 excessively thick, the mass and volume of the lithium-sulfur battery (10) increase, and the cycle characteristics of the lithium-sulfur battery (10) may actually deteriorate.

[0158] In another embodiment of the present invention, a lithium metal layer (230) within the negative electrode (200) may be provided, for example, between the negative electrode current collector (210) and the negative electrode coating layer (220) before assembly of the lithium-sulfur battery (10). When the lithium metal layer (230) is placed between the negative electrode current collector (210) and the negative electrode coating layer (220) before assembly of the lithium-sulfur 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 placed between the negative electrode current collector (210) and the negative electrode coating layer (220) before assembly of the lithium-sulfur battery (10).

[0159] When a lithium metal layer (230) is deposited by charging after the assembly of the lithium-sulfur battery (10), the energy density of the lithium-sulfur battery (10) can be increased because the lithium metal layer (230) is not included during the assembly of the lithium-sulfur battery (10). When charging the lithium-sulfur battery (10), it can be charged beyond the charging capacity of the negative electrode coating layer (220). That is, the negative electrode coating layer (220) is overcharged. At the beginning of charging, lithium can be absorbed in the negative electrode coating layer (220). When charging beyond the capacity of the negative electrode coating layer (220), lithium can be deposited, for example, between the negative electrode coating layer (220) and the negative electrode current collector (210). A lithium metal layer (230) can be formed by the deposited lithium.

[0160] The lithium metal layer (230) can be composed mainly of lithium (i.e., metallic lithium). During discharge, the lithium in the lithium metal layer (230) can be ionized and move to the positive electrode (100). In other words, lithium can be used as a negative electrode active material in the lithium-sulfur battery (10). In addition, since the negative electrode coating layer (220) covers the lithium metal layer (230), the negative electrode coating layer (220) can protect the lithium metal layer (230) and simultaneously suppress the precipitation growth of lithium dendrites. Therefore, the negative electrode coating layer (220) can suppress short circuits and capacity degradation of the lithium-sulfur battery (10) and improve the cycle characteristics of the lithium-sulfur battery (10).

[0161] When a lithium metal layer (230) is formed by charging after assembly of the lithium-sulfur battery (10), the negative electrode (200), that is, the negative electrode current collector (210) and the negative electrode coating layer (220) and the region between them may be a Li-free region that does not contain lithium (Li) in the initial state or after complete discharge of the lithium-sulfur battery (10).

[0162] The positive active material layer (120) from which lithium ions are released by charging the lithium-sulfur battery (10) may have a second thickness (TK2). The second thickness (TK2) of the positive active material layer (120) may be smaller than the first thickness (TK1) of FIG. 2.

[0163] In one embodiment of the present invention, the difference between the first thickness (TK1) and the second thickness (TK2) may be substantially the same 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 active material layer (120) may be reduced by the same amount as the thickness of the lithium metal layer (230) formed by charging the lithium-sulfur battery (10).

[0164] Although not illustrated, the lithium-sulfur battery (10) may operate (i.e., charge and / or discharge) while being pressurized by a pressurizing jig. In one embodiment, the lithium-sulfur battery (10) may be pressurized to 0.5 MPa to 2 MPa. For example, the lithium-sulfur battery (10) may have an internal pressure of about 1 MPa when discharged, and the lithium-sulfur battery (10) may have an internal pressure of about 1.5 MPa when charged. The ratio of the internal pressure of the lithium-sulfur battery (10) in the charged state of FIG. 7 to the internal pressure of the lithium-sulfur battery (10) in the discharged state of FIG. 3 may be 0.5 to 2.5, 1.0 to 2.0, or 1.2 to 1.8.

[0165] The height (or thickness or volume) of the lithium-sulfur battery (10) may change according to charging and discharging under the aforementioned pressurized state. In the lithium-sulfur battery (10) according to the present embodiment, the thickness of the positive active material layer (120) may decrease in correspondence with the lithium metal layer (230) formed by charging. Accordingly, the second height (HE2) of the charged lithium-sulfur battery (10) shown in FIG. 7 may be similar to the first height (HE1) of the discharged lithium-sulfur battery (10) shown in FIG. 2. For example, the second height (HE2) may be 1 to 1.5 times, or 1 to 1.2 times, the first height (HE1).

[0166] Since the lithium-sulfur battery (10) according to one embodiment of the present invention contains a composite active material which is a viscous fluid, the pressure applied by the pressurizing jig may be small. The lithium-sulfur battery (10) according to one embodiment of the present invention can operate with excellent performance even at low pressure. The low pressure may be, for example, 1 MPa or less.

[0167] A lithium-sulfur battery (10) according to one embodiment of the present invention includes a composite active material which is a viscous fluid, so the change in its height (or thickness or volume) may be small depending on charging and discharging under pressurized conditions. For example, the volume expansion rate of the positive active material layer (120) may be 20% or less, 10% or less, 5% or less, or 2% or less. The volume expansion rate of the composite active material layer may be the rate of change in volume after charging and discharging under pressurized conditions at least once each with respect to the initial volume.

[0168] FIG. 8 is a cross-sectional view along line A-A' of FIG. 1, intended to illustrate a lithium-sulfur battery according to another embodiment of the present invention. Referring to FIG. 8, the lithium-sulfur battery (10) according to the present embodiment may further include a gasket (GSK). The gasket (GSK) may be provided to surround the positive electrode composite layer (CSH). The gasket (GSK) may fill the step difference on the side of the lithium-sulfur battery (10) caused by the difference in area between the negative electrode composite layer (ASH) and the positive electrode composite layer (CSH). The gasket (GSK) may surround the four sides of the positive electrode composite layer (CSH). For example, the thickness of the gasket (GSK) may be substantially the same as the thickness of the positive electrode 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 lithium-sulfur battery (10) and / or during the charging and discharging of the lithium-sulfur battery (10). This can improve the cycle characteristics of the lithium-sulfur battery (10). If the lithium-sulfur battery (10) does not include the gasket (GSK), uneven pressure is applied to the negative electrode composite layer (ASH) in contact with the positive electrode composite layer (CSH), causing cracking in the solid electrolyte layer (300), and the likelihood of a short circuit occurring due to the growth of lithium metal through this may increase.

[0171] The thickness of the gasket (GSK) may be greater than the thickness of the positive composite layer (CSH) or substantially equal to the thickness of the positive composite layer (CSH). Since the thickness of the gasket (GSK) is equal to the thickness of the positive composite layer (CSH), a uniform pressure is applied between the positive composite layer (CSH) and the negative composite layer (ASH), and the positive composite layer (CSH) and the negative composite layer (ASH) are sufficiently in contact, thereby reducing the interfacial resistance between the first solid electrolyte layer (310) and the second solid electrolyte layer (320). Additionally, the internal resistance of the solid electrolyte layer (300) may be reduced as the solid electrolyte layer (300) is sufficiently sintered during the pressurized manufacturing process of the lithium-sulfur battery (10).

[0172] The gasket (GSK) may have a single-layer structure, for example. Alternatively, although not shown in the drawings, the gasket (GSK) may have a multi-layer structure. In a gasket (GSK) having a multi-layer structure, each layer may have a different composition. A gasket (GSK) having a multi-layer structure may have, for example, a two-layer structure, a three-layer structure, a four-layer structure, or a five-layer structure. A gasket (GSK) having a multi-layer structure 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 member. By providing flame retardancy, the flame-retardant inert member can prevent thermal runaway and the possibility of ignition of the lithium-sulfur battery (10). Consequently, the gasket (GSK) can further enhance the safety of the lithium-sulfur battery (10). By absorbing residual moisture within the lithium-sulfur battery (10), the flame-retardant inert member prevents the deterioration of the lithium-sulfur battery (10), thereby improving the lifespan characteristics of the lithium-sulfur battery (10).

[0174] FIG. 9 is a cross-sectional view along line A-A' of FIG. 1, illustrating a lithium-sulfur battery according to another embodiment of the present invention. Referring to FIG. 9, the positive electrode (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 placed directly, for example, on one or both sides of the positive electrode current collector (110). The coating layer (CTL) may be coated on one or both sides of the positive electrode current collector (110). No other layer may be placed between the positive electrode current collector (110) and the coating layer (CTL).

[0175] By placing the coating layer (CTL) directly on one or both sides of the positive current collector (110), the bonding strength between the positive current collector (110) and the positive active material layer (120) can be further improved. By placing the coating layer (CTL) between the positive current collector (110) and the positive active material layer (120), side reactions between the solid electrolyte or positive active material (121, 124) and the positive current collector (110) can be more effectively suppressed. For example, the coating layer (CTL) can prevent corrosion of the sulfide-based positive active material (e.g., Li2S) by the positive current collector (110). Consequently, the coating layer (CTL) can suppress the degradation of the lithium-sulfur battery (10) during the charging and discharging process and improve the cycle characteristics of the lithium-sulfur battery (10).

[0176] 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 current collector (110). The thickness of the coating layer (CTL) may be, for example, 10 nm to 5 µm, 50 nm to 5 µm, 200 nm to 4 µm, 500 nm to 3 µm, 500 nm to 2 µm, 500 nm to 1.5 µm, or 700 nm to 1.3 µm. By having the coating layer (CTL) have a thickness within this range, the bonding strength between the positive current collector (110) and the positive active material layer (120) is further improved, and the 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).

[0177] 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 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 active material layer (120). By including the carbon-based conductive material, the coating layer (CTL) may be, for example, a conductive layer.

[0178] The coating layer (CTL) may additionally include, for example, a binder. By additionally including a binder in the coating layer (CTL), the bonding strength between the positive current collector (110) and the positive active material layer (120) can be further improved. The binder included in the coating layer (CTL) is, for example, a conductive binder or a non-conductive binder. The conductive binder is, for example, an ion-conducting binder and / or an electron-conducting binder. A binder having both ion conductivity and electron conductivity may belong to both an ion-conducting binder and an electron-conducting binder.

[0179] The binder included in the coating layer (CTL) may be selected from among the binders used in the positive active material layer (120). The coating layer (CTL) may include the same binder as the binder used in the positive active material layer (120). The binder included in the coating layer (CTL) is, for example, a fluorine-based binder. The fluorine-based 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 containing a binder. The coating layer (CTL) may be, for example, a conductive layer containing a binder and a carbon-based conductive material.

[0180] The coating layer (CTL) can be disposed on the positive current collector (110) in a dry or wet manner, for example. The coating layer (CTL) can be disposed on the positive current collector (110) in a dry manner by deposition, for example, CVD, PVD, etc. The coating layer (CTL) can be disposed on the positive current collector (110) in a wet manner by, for example, spin coating, dip coating, etc. The coating layer (CTL) can be disposed on the positive current collector (110) by, for example, depositing a carbon-based conductive material onto a substrate by deposition. The dry-coated coating layer (CTL) may be made of a carbon-based conductive material and may not contain a binder. The coating layer (CTL) can be disposed on the positive current collector (110) by, for example, coating a composition comprising a carbon-based conductive material, a binder, and a solvent onto the surface of the electrode current collector and drying it. The coating layer (CTL) may have a single-layer structure or a multi-layer structure including multiple layers. The multi-story structure can be a 2-story structure, a 3-story structure, a 4-story structure, etc.

[0181] The cathode (200) may further include a thin film (TFL) provided between the cathode current collector (210) and the cathode coating layer (220). The thin film (TFL) may be provided on one side of the cathode current collector (210) to form an alloy with lithium.

[0182] 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, for example, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., but are not necessarily limited to these, and any element capable of forming an alloy with lithium in the relevant technical field is possible. The thin film (TFL) may be composed of one of these metals or may be composed of an alloy of various types of metals.

[0183] By placing the thin film (TFL) on one side of the negative electrode current collector (210), the deposition pattern of the lithium metal layer (230, see FIG. 7) deposited between, for example, the thin film (TFL) and the negative electrode coating layer (220) is further flattened, and the cycle characteristics of the lithium sulfur battery (10) can be further improved.

[0184] 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 to perform the function of the thin film (TFL). If the thickness of the thin film (TFL) is excessively thick, the thin film (TFL) itself absorbs lithium, and the amount of lithium precipitated at the negative electrode (200) decreases, which lowers the energy density of the lithium-sulfur battery (10) and may lower the cycle characteristics of the lithium-sulfur battery (10). The thin film (TFL) may be formed on the negative electrode current collector (21) by, for example, vacuum deposition, sputtering, plating, etc., but is not necessarily limited to these methods, and any method capable of forming a thin film in the relevant technical field may be possible.

[0185]

[0186] Method for manufacturing a composite active material for a lithium-sulfur battery

[0187] Hereinafter, with reference to FIGS. 4 to 6, a method for manufacturing a composite active material for a lithium-sulfur battery according to embodiments of the present invention will be described.

[0188] Referring to FIGS. 4 and 5, a method for manufacturing a composite active material for a lithium-sulfur battery according to embodiments of the present invention may include: preparing a first gel by dispersing a first lithium sulfide (121a) and a lithium salt (122) in an LPS inducer (123) (S100); inducing a lithium polysulfide (124) from the first lithium sulfide (121a) to form a second gel from the first gel (S200); and mixing the second gel, the second lithium sulfide (121b), and a conductive material (125) (S300). The LPS inducer (123) may include at least one of polyethylene glycol dimethyl ether, polyethylene glycol diglycidyl ether, or a combination thereof.

[0189] In another embodiment of the present invention, preparing a first gel (S100) and forming a second gel from the first gel (S200) may be omitted. That is, without inducing lithium polysulfide in advance, a composite active material may be manufactured by mixing lithium sulfide (121), a lithium salt (122), an LPS inducer (123), and a conductive material (125) and then performing a single lithium polysulfide induction treatment.

[0190] Referring again to FIGS. 4 and 5, a first gel can be prepared by dispersing a first lithium sulfide (121a) and a lithium salt (122) in an LPS inducer (123) (S100). The content of the first lithium sulfide (121a) may be 10 wt% to 40 wt% based on the total weight of the first gel. To increase the sulfur content, it may be desirable to increase the content of the first lithium sulfide (121a) to 40 wt%, which is a saturated state. The first lithium sulfide (121a) may not dissolve in the LPS inducer (123) and may precipitate in a crystalline form. The dispersion solution may be stirred or ultrasonically treated at 50°C to 90°C for 9 to 24 hours. After the above treatment, a first gel can be prepared in which the first lithium sulfide (121a) and the lithium salt (122) are evenly dispersed within the LPS inducer (123). The first gel may be a transparent or white gel.

[0191] A second gel can be formed from a first gel (S200). The second gel can be prepared by leaving the first gel for one to two weeks. Since the first gel contains an LPS inducer (123), separate heating may not be required. However, to shorten the preparation period, the second gel can be prepared by heating at 50°C to 90°C for one to three days. In the second gel, all of the first lithium sulfide (121a) can be converted into lithium polysulfide (124), and the second gel may take on a brown color due to the lithium polysulfide (124).

[0192] The second gel, the second lithium sulfide (121b), and the conductive material (125) can be mixed (S300). After leaving it for a predetermined time, a portion of the second lithium sulfide (121b) may be converted into lithium polysulfide (124). As a result, the second gel may take on a darker brown color. Finally, a composite active material can be manufactured.

[0193] The method for manufacturing a composite active material according to the present invention converts lithium sulfide (121) into lithium polysulfide (124), thereby enabling more lithium sulfide (121) to be effectively dispersed within the composite active material. As shown in FIG. 4, if a lithium polysulfide (124) pre-induction process is performed to convert the first lithium sulfide (121a) into lithium polysulfide (124) in advance, more lithium sulfide (121) can be effectively dispersed within the composite active material.

[0194] This can contribute to increasing the sulfur content within the composite active material and further increasing the theoretical capacity. Additionally, the LPS inducer (123) continuously induces lithium polysulfide (124) during charging and discharging, thereby maintaining the lithium polysulfide (124) content within the composite active material above a certain level, which allows for the smooth conversion of lithium sulfide (121) into lithium polysulfide (124). Through this, the charging and discharging efficiency of the battery can be further increased, and the battery's lifespan and performance can be significantly improved by forming a uniform conduction path and a stable electrode structure.

[0195] FIG. 6 is a comparative example illustrating a method for manufacturing a general positive electrode active material for a lithium-sulfur battery, in which a dispersion medium (126) is applied instead of the LPS inducer (124) of the present invention. The dispersion medium (126) may be a general dispersion medium used in manufacturing a lithium-sulfur battery positive electrode active material. The dispersion medium (126) may be, for example, distilled water, deionized water, methanol, ethanol, propanol, isopropanol and butanol, dimethylformamide, isopropyl alcohol, or acetonitrile.

[0196] Referring to FIG. 6, a positive electrode active material can be prepared by mixing lithium sulfide (121), a lithium salt (122), a conductive material (125), and a dispersion medium (126). At this time, the lithium sulfide (121) may precipitate without dissolving. Since lithium polysulfide is not induced, the mixture of FIG. 6 may be transparent or white. Although lithium sulfide (121) can be dispersed through heating and rotation, there is a limit to increasing its content because lithium sulfide (121) acts as a strong resistor within the positive electrode active material. Accordingly, there may be limitations in increasing the capacity of the battery.

[0197]

[0198] Examples and comparative examples of the present invention are described below. However, the following examples are merely one example of the present invention, and the present invention is not limited to the following examples.

[0199] Example 1

[0200] (1) Preparation of complex active material

[0201] A first gel was prepared by dispersing the first lithium sulfide and LiTFSI in polyethylene glycol dimethyl ether (PEGDME). The weight ratio of PEGDME:first lithium sulfide:LiTFSI was 3:4:3.

[0202] The first gel was stirred at 100 rpm for about 1 day while maintaining a temperature of about 60°C to induce lithium polysulfide. Finally, the second gel was prepared.

[0203] The second gel, the second lithium sulfide, and carbon nanofiber (CNF) were mixed. The weight ratio of the second gel:second lithium sulfide:CNF was 80:10:10. The second gel was stirred at 200 rpm for about 2 days while maintaining a temperature of about 40°C to induce lithium polysulfide. Finally, a composite active material was prepared.

[0204] (2) Manufacturing of the anode

[0205] A positive electrode active material slurry was prepared by mixing the composite active material prepared in step (1) above and polytetrafluoroethylene (PTFE) in a weight ratio of 99:1.

[0206] The above anode slurry was applied onto an Al foil with a thickness of 15 μm, dried at 100°C, and then pressed to manufacture an anode.

[0207] (3) Preparation of the cathode

[0208] A stainless steel (SUS) foil with a thickness of 10 μm was prepared as a cathode current collector. As a metal-carbon composite, carbon black (CB) with a primary particle size of about 30 nm and silver (Ag) particles with an average particle diameter of about 60 nm were prepared.

[0209] 4 g of a mixed powder, prepared by mixing the carbon black (CB) and silver (Ag) particles in a weight ratio of 3:1, was placed in a container, and 4 g of a methylpyrrolidone (NMP) solution containing 7 wt% of a polyvinylidene fluoride (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 at 80°C in air for 10 minutes, and then vacuum dried at 40°C for 10 hours to produce a laminate. The surface of the manufactured laminate was flattened by cold roll pressing to produce a cathode having a cathode coating layer / cathode current collector structure. At this time, the thickness of the cathode coating layer was approximately 15 μm, and the area of ​​the cathode coating layer and the cathode current collector were the same.

[0210] (4) Preparation of a solid electrolyte layer

[0211] 98.5 wt% of Li6PS5Cl solid electrolyte, which is an argyrodite-type crystal, and 1.5 wt% of an acrylic binder were mixed. Octyl acetate was added to the mixture while stirring 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, dried at 80°C in air for 10 minutes, and then vacuum dried at 40°C for 2 hours to prepare a solid electrolyte layer.

[0212] (5) Manufacture of lithium-sulfur batteries

[0213] A laminate was prepared by placing a solid electrolyte layer prepared in step (4) on the negative electrode coating layer prepared in step (3), and placing a positive electrode such that the positive active material layer prepared in step (2) contacts the solid electrolyte layer. The laminate was subjected to plate pressing at 85°C and a pressure of 500 MPa for 30 minutes. By this pressing treatment, the solid electrolyte layer is sintered, which can improve battery characteristics. The thickness of the sintered solid electrolyte layer was approximately 45 μm. In addition, 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 the area of ​​the negative electrode coating layer.

[0214] Subsequently, a lithium-sulfur battery was manufactured by placing the pressurized laminate into a pouch and vacuum sealing it. Parts of the positive and negative current collectors were extended outside the sealed battery to serve as the positive and negative terminals.

[0215]

[0216] Examples 2 to 4

[0217] A composite active material and a lithium-sulfur battery were prepared in the same manner as in Example 1, except that the contents of PEGDME, first lithium sulfide, LiTFSI, and second lithium sulfide were changed. The detailed composition is described in Table 1 below.

[0218]

[0219] Comparative Examples 1 to 3

[0220] Step (1) of Example 1 was replaced with the following method. Except for this, a lithium-sulfur battery was manufactured in the same way as in Example 1.

[0221] Lithium sulfide, carbon nanofibers (CNF), and a solid electrolyte (SE) were dry-mixed. As the solid electrolyte, Li6PS5Cl, an argyrodite-type crystal, was used. The detailed composition is described in Table 2 below.

[0222]

[0223] Comparative Example 4

[0224] In step (1) of Example 1, polyethylene oxide (PEO, Mw=100,000) was used instead of polyethylene glycol dimethyl ether (PEGDME). Except for this, the composite active material and lithium-sulfur battery were prepared in the same manner as in Example 1.

[0225]

[0226] Evaluation Example 1: Analysis of whether LPS derivatives induce lithium polysulfide

[0227] The first to third samples (SPL1 to SPL3) were prepared under the following conditions. The samples were stirred at 200 rpm for about 2 days while maintaining a temperature of about 60°C to induce lithium polysulfide. The results are attached in Fig. 10.

[0228] [Sample 1] PEGDA(Mn700):Lithium Sulfide:LiTFSI = 3:4:3

[0229] [Sample 2] PEGDME(Mn500):Lithium Sulfide:LiTFSI = 3:4:3

[0230] [Sample 3] PEGDME(Mn250):Lithium Sulfide:LiTFSI = 3:4:3

[0231]

[0232] Evaluation Example 2: Evaluation of Cathode Active Material

[0233] The specific capacity and electrode capacity of the composite active materials of the examples and comparative examples were evaluated using the following method. The results are described in Table 3 below.

[0234] The battery was discharged for 20 hours in the range of 1.0 to 2.8 V to measure the charge (current x time, mAh). The specific capacity was calculated by dividing the charge by the weight of Li2S contained in the positive electrode active material. The electrode capacity was calculated by dividing the charge by the weight of the positive electrode active material.

[0235]

[0236] Evaluation Example 3: Charge / Discharge Evaluation

[0237] For the lithium-sulfur batteries of the examples and comparative examples, the initial coulombic efficiency (ICE) and lifespan were evaluated in the following manner.

[0238] The charging (CC) conditions were '45℃, 0.1C, 2.8V'. The discharging (CC) conditions were '45℃, 0.1C, and 1.0V Cut-off'. 1st and 2nd Since the reliability of cycles as life evaluation data is low due to numerous variables such as SEI formation, the discharge capacity of the 3rd cycle was set as the standard capacity. Charge and discharge were repeated until the discharge capacity reached 80% of the standard capacity (SOH 80). The number of cycles required to reach SOH 80 was defined as the lifespan.

[0239] The initial Coulomb efficiency was calculated according to Equation 1 below. The results are described in Table 3.

[0240] [Equation 1]

[0241] Initial Coulomb efficiency (%) = (Discharge capacity of 1st cycle / Charge capacity of 1st cycle) * 100

[0242]

[0243] LPS derivative (wt%) 1st Lithium sulfide (wt%) LiTFSI (wt%) 2nd Lithium sulfide (wt%) CNF (wt%) Example 1 243 224 1010 Example 2 212 8212 010 Example 3 1824 183 010 Example 4 1520 154 010

[0244] Lithium Sulfide (wt%) CNF (wt%) SE (wt%) Comparative Example 1 30 10 60 Comparative Example 2 40 10 50 Comparative Example 3 50 10 40 Comparative Example 4 PEO:1st Lithium Sulfide:LiTFSI:2nd Lithium Sulfide:CNF = 24:32:24:10:10

[0245] Tables 1 and 2 above show the weight of each composition relative to the total weight of the positive electrode active material layer in wt%.

[0246] Specific capacity (mAh / g) Li2S ) Electrode Capacity (mAh / g) ICE (%) Lifetime (cycles, @SOH80) Example 19 00 37 88 570 Example 28 50 40 88 258 Example 37 50 40 57 842 Example 46 00 360 75 20 Comparative Example 18 00 240 78 15 Comparative Example 26 00 240 715 Comparative Example 33 00 150 581 Comparative Example 44 00 160 531

[0247] Referring to FIG. 10, it can be confirmed that PEGDME induces lithium polysulfide through the fact that the second and third samples turned brown. Referring to Tables 1 to 3, it can be confirmed that the specific capacity and electrode capacity of the examples are higher than those of the comparative examples. This demonstrates that the composite active material according to the present invention can realize a high-capacity battery by containing a larger amount of sulfur. In addition, it can be confirmed that the ICE and lifetime of the examples are higher than those of the comparative examples. It can be confirmed that the composite active material according to the present invention is in the form of a viscous gel, provides high ion conductivity, and buffers volume changes to improve battery performance.

Claims

It includes a lithium salt, a positive electrode active material, an LPS inducer, and a conductive material, The above positive active material includes lithium sulfide and lithium polysulfide, and The above LPS derivative comprises at least one of polyethylene glycol dimethyl ether, polyethylene glycol diglycidyl ether, or a combination thereof. Composite active material for lithium-sulfur batteries. In paragraph 1, The content of the lithium sulfide is 10 wt% to 60 wt% based on the total weight of the composite active material, Composite active material for lithium-sulfur batteries. In paragraph 1, The content of the lithium polysulfide is 20 wt% to 40 wt% based on the total weight of the composite active material, Composite active material for lithium-sulfur batteries. In paragraph 1, The weight ratio of the lithium polysulfide to the weight of the lithium sulfide is 1:3 to 2:1, Composite active material for lithium-sulfur batteries. In paragraph 1, When charging and discharging were performed 100 times each, The minimum content of the lithium polysulfide in the above composite active material is 40 wt% or more, Composite active material for lithium-sulfur batteries. In paragraph 1, The content of the above LPS inducer is 15 wt% to 24 wt% based on the total weight of the above composite active material, Composite active material for lithium-sulfur batteries. In paragraph 1, The above conductive material comprises at least one of carbon nanofibers, carbon nanotubes, graphene, or a combination thereof. Composite active material for lithium-sulfur batteries. In paragraph 1, The above composite active material further comprises a binder, Composite active material for lithium-sulfur batteries. In paragraph 1, The above composite active material further comprises a dinitrile-based compound, Composite active material for lithium-sulfur batteries. In paragraph 1, The above lithium polysulfide is Li2S n Having the chemical formula, n is an integer between 4 and 8, Composite active material for lithium-sulfur batteries. In paragraph 1, The viscosity of the above composite active material is 50 cP to 500 cP, Composite active material for lithium-sulfur batteries. In paragraph 1, The number average molecular weight (M) of the above LPS inducer n ) is 100 g / mol to 3000 g / mol, Composite active material for lithium-sulfur batteries. In paragraph 1, The sulfur content in the above composite active material is 29 wt% to 42 wt% based on the total weight of the above composite active material, Composite active material for lithium-sulfur batteries. A positive electrode comprising a positive current collector and a positive active material layer on the positive current collector; A cathode comprising a cathode current collector and a cathode coating layer on the cathode current collector; A solid electrolyte layer interposed between the anode and the cathode; comprising, The above positive active material layer comprises a lithium salt, a positive active material, an LPS inducer, and a conductive material, and The above positive active material includes lithium sulfide and lithium polysulfide, and The above LPS derivative comprises at least one of polyethylene glycol dimethyl ether, polyethylene glycol diglycidyl ether, or a combination thereof. Lithium-sulfur battery. In Paragraph 14, The weight ratio of the lithium polysulfide to the weight of the lithium sulfide is 1:3 to 2:1, Lithium-sulfur battery. In Paragraph 14, The content of the above LPS inducer is 15 wt% to 24 wt% based on the total weight of the above positive electrode active material layer, Lithium-sulfur battery. Preparing a first gel by dispersing a first lithium sulfide and a lithium salt in an LPS inducer; Deriving lithium polysulfide from the first lithium sulfide to form a second gel from the first gel; Mixing the above-mentioned second gel, second lithium sulfide, and conductive material; wherein The above LPS derivative comprises at least one of polyethylene glycol dimethyl ether, polyethylene glycol diglycidyl ether, or a combination thereof. Method for manufacturing a composite active material for a lithium-sulfur battery. In Paragraph 17, In preparing the first gel, The content of the first lithium sulfide is 10 wt% to 40 wt% based on the total weight of the first gel, Method for manufacturing a positive electrode active material for a lithium-sulfur battery.

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