Positive electrode active material, positive electrode including same, and all-solid-state battery

Abstract

The present invention relates to a positive electrode active material, a positive electrode including same, and an all-solid-state battery. The positive electrode active material includes a composite of a sulfur-based material, a metal halide salt, and a carbon-based material, wherein the sulfur-based material includes at least one of S8 or Li2Sn (1≤n≤ 8, n is an integer), and the metal halide salt includes a first metal halide salt containing an alkali metal and a second metal halide salt containing a boron group metal.

Description

Cathode active material, cathode and all-solid-state battery containing the same

[0001] The present invention relates to a cathode active material, a cathode including the same, and an all-solid-state battery.

[0002] Recent industrial demands have led to the active development of batteries with high energy density and safety. For example, secondary batteries are used in a variety of applications, including information technology, communication devices, and automobiles. Because automobiles are life-threatening, safety is also crucial.

[0003] Secondary batteries using liquid electrolytes may increase the risk of fire and / or explosion in the event of a short circuit. Solid-state batteries using solid electrolytes instead of liquid electrolytes have been proposed. Solid electrolytes are less likely to catch fire than liquid electrolytes.

[0004] Solid-state batteries can reduce the risk of fire or explosion and provide improved safety by using solid electrolytes instead of liquid electrolytes.

[0005] When lithium sulfide is used as the positive electrode active material in solid-state batteries, lithium sulfide is an insulator with virtually no electrical or ionic conductivity. Therefore, a material with high electrical and ionic conductivity is required when manufacturing the positive electrode. Furthermore, since no solvent is used in the manufacture of the positive electrode, electrolyte layer, and negative electrode containing lithium sulfide, the solid electrolyte layer, positive electrode, and negative electrode are virtually solvent-free. Consequently, electronic and lithium ion conductivity are low, making it difficult to secure sufficient capacity during charge and discharge.

[0006] One aspect is to provide a cathode active material having improved ionic and electronic conductivity, including a heterogeneous metal halide salt.

[0007] Another aspect is to provide a positive electrode comprising the positive electrode active material.

[0008] Another aspect is to provide an all-solid-state battery comprising the above positive electrode.

[0009] According to one embodiment, the cathode active material may include a composite of a sulfur-based material, a metal halide salt, and a carbon-based material. The sulfur-based material may be S8 and Li2S. n (1 ≤ n ≤ 8, n is an integer) may include at least one of the following, and the metal halide salt may include a first metal halide salt including an alkali metal and a second metal halide salt including a boron group metal.

[0010] According to another embodiment, a positive electrode may include a positive electrode current collector; and a positive electrode active material layer disposed on one or both surfaces of the positive electrode current collector. The positive electrode active material layer may include the above-described positive electrode active material and a solid electrolyte.

[0011] According to another embodiment, an all-solid-state battery may include the above-described positive electrode; a negative electrode including a negative electrode current collector and a negative electrode coating layer disposed on the negative electrode current collector; and a solid electrolyte layer disposed between the positive electrode and the negative electrode.

[0012] According to one aspect, an all-solid-state battery having improved life characteristics can be provided by having a positive electrode active material with improved electronic conductivity and ionic conductivity.

[0013] Figure 1 is a cross-sectional view of an all-solid-state battery according to an exemplary embodiment.

[0014] Figure 2 is a schematic diagram for explaining the ion conduction path of lithium ions in the positive electrode active material layer.

[0015] Figure 3 is an enlarged schematic diagram illustrating an ion conduction path of lithium ions in a positive electrode active material layer according to an exemplary embodiment.

[0016] Figure 4 is an enlarged view illustrating a positive electrode active material according to an exemplary embodiment.

[0017] Figures 5 to 9 are cross-sectional views of an all-solid-state battery according to an exemplary embodiment.

[0018] Figure 10 is a perspective view of an all-solid-state battery according to an exemplary embodiment.

[0019] Fig. 11 is an SEM photograph of a positive electrode active material according to an exemplary embodiment.

[0020] Figure 12 is a graph showing the capacity retention rate of a secondary battery manufactured according to one implementation example.

[0021] To fully understand the structure and effects of the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms and subject to various modifications. However, the description of these embodiments is provided solely to ensure a complete disclosure of the present invention and to fully inform those skilled in the art of the invention of the scope of the invention.

[0022] In this specification, when a component is referred to as being on another component, it means that it can be formed directly on the other component, or a third component may be interposed between them. Furthermore, in the drawings, the thicknesses of the components are exaggerated for the sake of clarity. Parts designated by the same reference numerals throughout the specification represent the same components.

[0023] Embodiments described herein will be described with reference to cross-sectional and / or plan views, which are ideal illustrations of the present invention. In the drawings, the thicknesses of films and regions are exaggerated for the purpose of effectively explaining the technical contents. Accordingly, the regions illustrated in the drawings have a schematic nature, and the shapes of the regions illustrated in the drawings are intended to illustrate specific shapes of regions of the device and are not intended to limit the scope of the invention. Although terms such as first, second, and third are used to describe various components in various embodiments of the present specification, these components should not be limited by such terms. These terms are used only to distinguish one component from another. The embodiments described and illustrated herein also include complementary embodiments thereof.

[0024] The terminology used herein is for the purpose of describing embodiments and is not intended to limit the present invention. In this specification, the singular also includes the plural unless specifically stated otherwise. As used herein, the words "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components.

[0025] In this specification, “metal” includes both metals and metalloids such as silicon and germanium, in their elemental or ionic state.

[0026] As used herein, “alloy” means a mixture of two or more metals.

[0027] In this specification, “electrode active material” means an electrode material capable of undergoing lithiation and delithiation.

[0028] In this specification, “positive electrode active material” means a positive electrode material capable of undergoing lithiation and delithiation.

[0029] In this specification, “negative electrode active material” means a negative electrode material capable of undergoing lithiation and delithiation.

[0030] In this specification, “lithiation” and “lithiate” mean a process of adding lithium to an electrode active material.

[0031] In this specification, “delithiation” and “delithiate” refer to a process of removing lithium from an electrode active material.

[0032] In this specification, “charging” and “charging” mean the process of providing electrochemical energy to a battery.

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

[0034] In this specification, “positive electrode” and “cathode” mean an electrode where electrochemical reduction and lithiation occur during the discharge process.

[0035] In this specification, “cathode” and “anode” mean electrodes where electrochemical oxidation and delithiation occur during the discharge process.

[0036] While specific implementations have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are not currently anticipated or unforeseen may occur to the applicant or those skilled in the art. Accordingly, the appended claims, as filed and as amended, are intended to encompass all such alternatives, modifications, variations, improvements, and substantial equivalents.

[0037] Figure 1 is a cross-sectional view of an all-solid-state battery according to an exemplary embodiment.

[0038] Referring to FIG. 1, an all-solid-state battery according to an exemplary embodiment may include a positive electrode layer (100), a negative electrode layer (200), and a solid electrolyte layer (300) disposed between the positive electrode layer (100) and the negative electrode layer (200).

[0039] Referring to FIG. 1, a positive electrode layer (100) according to an exemplary embodiment may include a positive electrode current collector (110) and a positive electrode active material layer (120) disposed on one or both sides of the positive electrode current collector (110).

[0040] The positive electrode current collector (110) can provide a reference surface on which the positive electrode active material layer (120) is arranged. The positive electrode current collector (110) can include a plate or foil including, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel (SUS), titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof.

[0041] According to another embodiment, the positive electrode current collector (110) may be omitted. Although not illustrated, a carbon layer having a thickness of 0.1 μm to 4 μm may be additionally disposed between the positive electrode current collector (110) and the positive electrode active material layer (120) to increase the bonding strength between the positive electrode current collector (110) and the positive electrode active material layer (120). The carbon layer may include amorphous carbon, crystalline carbon, or the like.

[0042] Referring to FIGS. 2 and 3, a positive electrode active material layer (120) according to one embodiment may include a positive electrode active material (10, 11), a solid electrolyte (20, 21), and a conductive material (30). In another embodiment, the conductive material (30) may be omitted.

[0043] Fig. 2 is a schematic diagram for explaining the ion conduction path (R1) and the blocked ion conduction path (R2) of lithium ions in the positive electrode, and Fig. 3 is an enlarged schematic diagram for explaining the ion conduction path (R1) of lithium ions in the positive electrode active material layer (120) according to one embodiment. In Figs. 2 and 3, an area corresponding to area A of Fig. 1 is enlarged and illustrated.

[0044] The cathode active material (10, 11) may include elemental sulfur (S). Sulfur has a high theoretical capacity (1,672 mAh / g), is abundant on Earth, and is relatively inexpensive, so it is attracting attention as a next-generation cathode material. In one embodiment, elemental sulfur (S) is S8 and Li2S. n (1 ≤ n ≤ 8, n is an integer) may exist in the form of a sulfur-based material including at least one of the following. Such sulfur-based materials have relatively low ionic conductivity. Therefore, the positive electrode active material layer (120) may include a solid electrolyte (20) to form an ionic conduction path (R1).

[0045] Referring to FIG. 2, the solid electrolyte (20) can form an ion conduction path (R1) to move lithium ions. However, if the solid electrolyte (20) is not sufficient within the positive electrode active material layer (120), a blocked ion conduction path (R2) may be formed. In addition, a solid electrolyte (21) isolated by the positive electrode active material (11) may occur. The blocked ion conduction path (R2) and the isolated solid electrolyte (21) may reduce the ion conductivity of the positive electrode active material layer (120) and unnecessarily waste the positive electrode active material (11) and the solid electrolyte (20, 21), thereby lowering the energy density of the battery.

[0046] The positive electrode active material (10) according to one embodiment may have relatively excellent ionic conductivity. The ionic conductivity of the positive electrode active material (10) according to one embodiment is 3 x 10 at 25°C. -6 It can be more than S / cm. For example, the ionic conductivity of the positive electrode active material (10) is 3.5 x 10 -6 It can be more than S / cm, 4 x 10 -6 It can be more than S / cm, 5 x 10 -6 It can be more than S / cm, 6 x 10 -6 S / cm or more, and 6.75 x 10 -6It may be S / cm or more. The ionic conductivity of the positive electrode active material (10) according to one embodiment is 1 x 10 -4 It can be less than S / cm. Ionic conductivity can be measured using the DC polarization method. Alternatively, ionic conductivity can be measured using the complex impedance method.

[0047] Referring to FIG. 3, a positive electrode active material (10) according to an embodiment may have ionic conductivity. A positive electrode active material layer (120) including a positive electrode active material (10) according to an embodiment may form an ionic conduction path (R1) passing through a solid electrolyte (20) - positive electrode active material (10) - solid electrolyte (20). A positive electrode active material layer (120) including a positive electrode active material (10) according to an embodiment may form an ionic conduction path (R1) passing through an isolated solid electrolyte (21). A positive electrode active material layer (120) including a positive electrode active material (10) according to an embodiment may reduce a blocked ionic conduction path (R2), thereby improving ionic conductivity and increasing energy density.

[0048] According to one embodiment, the positive electrode active material (10) may include 40 to 90 parts by weight based on 100 parts by weight of the positive electrode active material layer (120). For example, according to one embodiment, the positive electrode active material (10) may include 50 to 85 parts by weight, or 60 to 80 parts by weight, or 65 to 75 parts by weight based on 100 parts by weight of the positive electrode active material layer (120). When the above range is satisfied, the secondary battery according to one embodiment may have excellent capacity characteristics.

[0049] The solid electrolyte (20) according to one embodiment may include 10 to 60 parts by weight based on 100 parts by weight of the positive electrode active material layer (120). For example, the solid electrolyte (20) according to one embodiment may include 15 to 50 parts by weight, 20 to 40 parts by weight, or 25 to 35 parts by weight based on 100 parts by weight of the positive electrode active material layer (120). When the above range is satisfied, the secondary battery according to one embodiment may have excellent capacity characteristics.

[0050] Fig. 4 is an enlarged view illustrating a positive electrode active material (10) according to an exemplary embodiment. Fig. 4 illustrates an enlarged view of an area corresponding to area B of Fig. 3. Hereinafter, the positive electrode active material (10) according to the exemplary embodiment will be described in detail with reference to Fig. 4.

[0051] Referring to FIG. 4, the cathode active material (10) according to the embodiment may include a composite of a sulfur-based material (1), a metal halide salt (2, 3), and a carbon-based material (4).

[0052] The positive electrode active material (10) may have a particle form. The particle size of the positive electrode active material (10), i.e., the size of the composite particles, may be, for example, 50 μm or less, 30 μm or less, or 10 μm or less. The size of the composite particles may be, for example, 0.1 μm to 50 μm or 1 μm to 10 μm. Since the composite particles have a size within this range, the volume change during charge and discharge is suppressed, thereby suppressing the deterioration of the positive electrode active material (10) including the composite during charge and discharge. If the size of the composite particles increases excessively, the volume change of the composite during charge and discharge may increase, thereby accelerating the deterioration of the positive electrode active material (10) including the composite. As a result, the cycle characteristics of a secondary battery including such a positive electrode active material (10) may deteriorate.

[0053] Therefore, the cycle characteristics, for example, the life characteristics, of the secondary battery including the positive electrode active material (10) can be improved. The size of the composite particles can be, for example, the particle diameter of the composite. The particle diameter of the composite can be measured using, for example, laser diffraction, a scanning electron microscope, etc. The particle diameter of the composite is, for example, the arithmetic mean value of the particle diameters of multiple particles measured using software from a scanning electron microscope image.

[0054] The cathode active material (10) may include a sulfur-based material (1). The sulfur-based material (1) may include S8 and Li2S. n (1 ≤ n ≤ 8, n is an integer) may include at least one of the following. The sulfur-based material (1) undergoes a continuous oxidation / reduction reaction of sulfur and / or lithium sulfide. For example, the reaction process of lithium polysulfide and lithium sulfide by the continuous reduction reaction of sulfur in the sulfur-based material (1) may be expressed as S8→Li2S8→Li2S6→Li2S4→Li2S2→Li2S, etc. In this process, lithium ions move between the positive electrode / negative electrode, and at the same time, electrons move through an external circuit to generate current.

[0055] The content of the sulfur-based material (1) according to one embodiment may be 20 to 80 wt% with respect to the total weight of the composite. For example, the content of the sulfur-based material (1) according to one embodiment may be 30 to 70 wt% or 35 to 60 wt% with respect to the total weight of the composite.

[0056] The cathode active material (10) may include a metal halide salt (2, 3). The metal halide salt (2, 3) may include a first metal halide salt (2) containing an alkali metal and a second metal halide salt (3) containing a boron group metal. The metal halide salt (2, 3) according to one embodiment may form a composite with the above-described sulfur series material (1).

[0057] According to one embodiment, the content of the metal halide salt (2, 3) may be 10 to 60 wt% based on the total weight of the composite. For example, according to one embodiment, the content of the metal halide salt (2, 3) may be 20 to 50 wt% or 25 to 45 wt% based on the total weight of the composite.

[0058] The first metal halide salt (2) may be, for example, a binary compound composed of an alkali metal and one element selected from Group 17 of the periodic table of elements. The first metal halide salt (2) may be, for example, a lithium salt. The first metal halide salt (2) may include, for example, LiF, LiCl, LiBr, LiI, or a combination thereof. This first metal halide salt (2) may form a composite with a sulfur-based material (1), thereby improving the ionic conductivity of a positive electrode active material (10) including the sulfur-based material (1). This first metal halide salt (2) may, for example, more easily form a solid solution with the sulfur-based material (1) within the composite.

[0059] The content of the first metal halide salt (2) according to one embodiment may be 2.5 to 15 wt% with respect to the total weight of the composite. For example, the content of the first metal halide salt (2) according to one embodiment may be 5 to 12.5 wt% or 7 to 10 wt% with respect to the total weight of the composite.

[0060] According to one embodiment, the positive electrode active material (10) may have a weight ratio of the sulfur-based material (1) and the first metal halide salt (2) of 30:1 to 1:1. For example, according to one embodiment, the positive electrode active material (10) may have a weight ratio of the sulfur-based material (1) and the first metal halide salt (2) of 20:1 to 2:1 or 10:1 to 3:1.

[0061] The second metal halide salt (3) may be, for example, a binary compound composed of a boron group metal and one element selected from group 17 of the periodic table. The second metal halide salt (3) may include, for example, AlF3, AlCl3, AlBr3, AlI3, GaF3, GaCl3, GaBr3, GaI3, InF3, InCl3, lnBr3, lnI3, TlF3, TlCl3, TlBr3, TlI3, or a combination thereof. This second metal halide salt (3) forms a composite with the sulfur-based substance (1) and the first metal halide salt (2), thereby maintaining the overall shape of the positive electrode active material (10) including the sulfur-based substance (1) and the first metal halide salt (2) and reducing the interfacial resistance. This second metal halide salt (3) can, for example, more easily form a solid solution with the sulfur-based substance (1) and the first metal halide salt (2) within the composite. This positive electrode active material (10) including the second metal halide salt (3) can suppress the dissolution of lithium polysulfide (Li2Sx) and improve the capacity characteristics of the battery.

[0062] According to one embodiment, the content of the second metal halide salt (3) may be 7.5 to 45 wt% based on the total weight of the composite. For example, according to one embodiment, the content of the second metal halide salt (3) may be 15 to 37.5 wt% or 20 to 31 wt% based on the total weight of the composite.

[0063] According to one embodiment, the positive electrode active material (10) may have a weight ratio of the sulfur-based material (1) and the second metal halide salt (3) of 10:1 to 1:1. For example, according to one embodiment, the positive electrode active material (10) may have a weight ratio of the sulfur-based material (1) and the second metal halide salt (3) of 5:1 to 1:1 or 5:1 to 2:1.

[0064] The cathode active material (10) may include different heterogeneous metal halide salts (2, 3). The different heterogeneous metal halide salts (2, 3) may include the first metal halide salt (2) and the second metal halide salt (3) described above. The cathode active material (10) according to the embodiment may include different heterogeneous metal halide salts (2, 3) to improve ionic conductivity, maintain the overall shape, reduce interfacial resistance, and suppress the dissolution of lithium polysulfide (Li2Sx), thereby improving the capacity characteristics of the battery.

[0065] According to one embodiment, the positive electrode active material (10) may have a weight ratio of the first metal halide salt (2) and the second metal halide salt (3) of 5:1 to 1:20. For example, the weight ratio of the first metal halide salt (2) and the second metal halide salt (3) may be 3:1 to 1:9, or 1:1 to 1:9, or 1:3 to 1:9. The positive electrode active material (10) satisfying the above range may include different types of metal halide salts (2, 3) at an appropriate ratio to maximize the effect of improving the capacity characteristics described above.

[0066] A composite according to one embodiment may include a solid solution of the above-described sulfur series material (1) and a metal halide salt (2, 3).

[0067] According to one embodiment, the ionic conductivity of the composite may increase by including a solid solution of a sulfur-based material (1) and a first metal halide salt (2). For example, since the solid solution of the sulfur-based material (1) and the first metal halide salt (2) includes alkali metal ions arranged within crystallites of the sulfur-based material (1), the ionic conductivity of the solid solution of the sulfur-based material (1) and the first metal halide salt (2) may be improved compared to the ionic conductivity of the sulfur-based material (1). Consequently, the ionic conductivity of the composite may be improved and the internal resistance of the composite may be reduced. By including such a complex in the positive electrode active material (10), the cycle characteristics of a secondary battery including the positive electrode active material (10) may be improved. For example, the high-rate characteristics of a secondary battery including such a positive electrode active material (10) may be improved.

[0068] According to one embodiment, the complex can maintain the overall shape of the complex and reduce the interfacial resistance by including a solid solution of a sulfur-based material (1) and a second metal halide salt (3). For example, since the solid solution of a sulfur-based material (1) and a second metal halide salt (3) maintains the overall shape of the complex, the sulfur-based material (1) can be converted to S8 and Li2S by oxidation / reduction. n Even if the shape is transformed between (1 ≤ n ≤ 8, n is an integer), the shape transformation of the composite and the positive electrode active material (10) can be minimized. By including the composite in the positive electrode active material (10), the shape transformation during the charge / discharge process can be minimized, thereby improving the cycle characteristics.

[0069] A solid solution according to an embodiment of the invention is (1-xy)Li2S n-xAX-yBX3 or (1-xy)S8-xAX-yBX3 may be included. The x and y are 0.01 ≤ x ≤ 0.3, 0.01 ≤ y ≤ 0.3, the n is an integer of 1 ≤ n ≤ 8, the A is an alkali metal, the B is a boron group metal, and the X is a halogen element.

[0070] The cathode active material (10) may include a carbon-based material (4). The carbon-based material (4) may form a composite with the above-described sulfur-based material (1) and the metal halide salt (2, 3). The composite of the carbon-based material (4), the sulfur-based material (1) and the metal halide salt (2, 3) is distinguished from a simple mixture of the carbon-based material (4), the sulfur-based material (1) and the metal halide salt (2, 3). The simple mixture of the carbon-based material (4), the sulfur-based material (1) and the metal halide salt (2, 3) may not maintain a dense interface between the carbon-based material (4), the sulfur-based material (1) and the metal halide salt (2, 3), resulting in a high interfacial resistance and consequently deteriorating the life characteristics of the secondary battery.

[0071] The carbonaceous material (4) may be, for example, any material containing carbon atoms that is used as a conductive material in the relevant technical field. The carbonaceous material (4) may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. The carbonaceous material (4) may include, for example, a sintered product of a carbon precursor. The carbonaceous material (4) may be, for example, a carbon nanostructure. The carbon nanostructure may include, for example, a one-dimensional carbon nanostructure, a two-dimensional carbon nanostructure, a three-dimensional carbon nanostructure, or a combination thereof. The carbon nanostructure may include, for example, carbon nanotubes (CNTs), carbon nanofibers (CNFs), carbon nanobelts, carbon nanorods, graphene, or a combination thereof. The carbonaceous material (4) may be, for example, a porous carbonaceous material or a non-porous carbonaceous material. The porous carbonaceous material may include, for example, periodic and regular two-dimensional or three-dimensional pores. The porous carbon-based material may include, for example, carbon black such as Ketjen Black, acetylene black, Denka Black, thermal black, channel black, graphite, activated carbon, or a combination thereof. The form of the carbon-based material (4) is not limited to, but may include, for example, particle form, sheet form, flake form, etc., and any form that is used as a carbon-based material (4) in the relevant technical field may be used.

[0072] According to one embodiment, the carbonaceous material (4) may include, for example, a fibrous carbonaceous material (4). By including the fibrous carbonaceous material (4), the electronic conductivity of the composite may be further improved. By including the fibrous carbonaceous material (4), electronic conduction may be more easily performed from the surface to the interior of the composite. The internal resistance of a positive electrode active material (10) including such a composite may be reduced, and the cycle characteristics of a secondary battery including the positive electrode active material (10) may be further improved.

[0073] The aspect ratio of the fibrous carbon-based material can be, for example, 2 or more, 3 or more, 4 or more, 5 or more, 10 or more, or 20 or more. The aspect ratio of the fibrous carbon-based material can be, for example, 2 to 30, 3 to 30, 4 to 30, 5 to 30, 10 to 30, or 20 to 30. The aspect ratio of the fibrous carbon-based material can be, for example, 2 to 30, 2 to 20, 2 to 10, 2 to 8, 2 to 5, or 2 to 4. By having the fibrous carbon-based material having an aspect ratio in this range, the overall electronic conductivity of the composite is improved, and local electronic conductivity imbalances within the composite can be further alleviated.

[0074] The diameter of the fibrous carbon-based material may be, for example, 0.01 μm to 10 μm, 0.05 μm to 10 μm, or 0.1 μm to 5 μm. The length of the fibrous carbon-based material may be, for example, 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. Alternatively, the diameter and / or length of the fibrous carbon-based material may be measured by laser diffraction.

[0075] The content of the carbon-based material (4) according to one embodiment may have 1 to 30 wt% with respect to the total weight of the composite. For example, the content of the carbon-based material (4) according to one embodiment may have 1 to 20 wt%, 5 to 20 wt%, or 10 to 20 wt% with respect to the total weight of the composite. If the content of the carbon-based material (4) increases excessively, the energy density of the battery may decrease. If the content of the carbon-based material (4) decreases excessively, the electronic conductivity of the composite may decrease, which may increase the internal resistance of the positive electrode active material (10). A battery including a positive electrode active material (10) that satisfies the content range of the carbon-based material (4) may have improved cycle characteristics.

[0076] The positive electrode active material (10) according to one embodiment may have relatively excellent electronic conductivity by including the carbon-based material (4) described above. The electronic conductivity of the positive electrode active material (10) according to one embodiment at 25°C is 5 x 10 -3 S / cm or more. For example, the electronic conductivity of the positive electrode active material (10) is 6.5 x 10 -3 It can be more than S / cm, 7 x 10 -3 It can be more than S / cm, 8 x 10 -3 S / cm or more. The electronic conductivity of the positive electrode active material (10) according to one embodiment is 1 x 10 -1 It may be less than S / cm.

[0077] The pellet density of the positive electrode active material (10) according to one embodiment may be 1.5 g / cc or more. For example, the pellet density of the positive electrode active material (10) according to one embodiment may be 1.6 g / cc or more, 1.62 g / cc or more, 1.64 g / cc or more, or 1.7 g / cc or more. A secondary battery including the positive electrode active material (10) satisfying the above range may have improved energy density. The pellet density of the positive electrode active material (10) according to one embodiment may be 5 g / cc or less, 4 g / cc or less, or 3 g / cc or less.

[0078] The positive electrode according to the embodiment includes a positive electrode current collector (110); and a positive electrode active material layer (120) disposed on one or both sides of the positive electrode current collector (110), and the positive electrode active material layer (120) may include the positive electrode active material (10) and solid electrolyte (20) described above.

[0079] The solid electrolyte (20) can provide an ion transfer path within the positive electrode active material layer (120). The positive electrode active material layer (120) according to the embodiment can have a further reduced internal resistance by including the positive electrode active material (10) and the solid electrolyte (20) described above.

[0080] Referring to FIGS. 2 and 3, the solid electrolyte (20) may have a particle shape. The solid electrolyte (20) may be dispersed between the positive electrode active materials (10). The solid electrolyte (10) may include a sulfide-based solid electrolyte having excellent lithium ion conductivity characteristics. The sulfide-based solid electrolyte includes, for example, Li2S-P2S5, Li2S-P2S5-LiX (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, capital letter “Z” represents Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p, q are positive numbers, capital letter “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 at least one selected from (0≤x≤2).

[0081] Sulfide-based solid electrolytes include, for example, 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(0≤x≤2) may be an argyrodite-type compound including at least one selected from. In particular, the sulfide-based solid electrolyte may be an argyrodite-type compound including at least one selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I. The density of the argyrodite-type solid electrolyte may be 1.5 g / cc to 2.0 g / cc. Since the argyrodite-type solid electrolyte has a density of 1.5 g / cc or more, the internal resistance of the all-solid-state battery is reduced, and the defect of the solid electrolyte membrane being penetrated and short-circuited due to the formation of lithium dendrites can be prevented. The elastic modulus of the solid electrolyte may be, for example, 15 GPa to 35 GPa.

[0082] According to another embodiment, the solid electrolyte included in the solid electrolyte layer (300) may further include a solid electrolyte such as a sulfide-based solid electrolyte and / or an oxide-based solid electrolyte other than the sulfide-based solid electrolyte including the compound represented by the above-described chemical formula 1 according to one embodiment. For example, Li2S-P2S5, Li2S-P2S5-LiX, 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 PS6-x Br x , 0 ≤ x ≤ 2, and Li 7-x PS 6-x I x , one or more selected from 0 ≤ x ≤ 2 and / or, Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 < x <2, 0 ≤ y <3), BaTiO3, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT)(0≤x<1, 0≤y<1), PB(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, Li3PO4, Li x Ti y (PO4)3(0 <x<2, 0<y<3), Li x Al y Ti z (PO4)3(0 <x<2, 0<y<1, 0<z<3), Li 1+x+y (Al, Ga) x (Ti, Ge) 2-x Si y P 3-y O 12 (0≤x≤1 0≤y≤1), Li x La y TiO3(0 <x<2, 0<y<3), Li2O, LiOH, Li2CO3, LiAlO2, Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2, Li 3+x La3M2O 12 (M = Te, Nb, or Zr, 0≤x≤10), Li7La3Zr2O 12 (LLZO) and Li 3+x La3Zr 2-a M a O 12(M doped LLZO, M=Ga, W, Nb, Ta, or Al, 0 <a<2, 0≤x≤10) 중에서 선택된 가넷계(Garnet-type) 고체전해질 등이나 이들로 한정되지 않으며 당해 기술 분야에서 고체전해질로 사용하는 것이라면 모두 가능하다.

[0083] According to one embodiment, the positive electrode active material (10) may include 40 to 90 parts by weight based on 100 parts by weight of the positive electrode active material layer (120). According to one embodiment, the solid electrolyte (20) may include 10 to 60 parts by weight based on 100 parts by weight of the positive electrode active material layer (120). As described above, the positive electrode active material (10) according to one embodiment includes a complex having electronic conductivity and ion conductivity in itself, so that even if a relatively large amount of the positive electrode active material layer (120) is included, the cycle characteristics of the battery can be maintained at a certain level or higher. According to one embodiment, the positive electrode active material (10) may include 60 to 80 parts by weight based on 100 parts by weight of the positive electrode active material layer (120), and the solid electrolyte (20) may include 20 to 40 parts by weight based on 100 parts by weight of the positive electrode active material layer (120). When the positive electrode active material layer (120) has the positive electrode active material (10) and solid electrolyte (20) contents within the above range, a secondary battery with excellent capacity characteristics can be provided.

[0084] The content of the sulfur-based material (1) in the positive electrode active material layer (120) may be 10 to 60 wt% with respect to the total weight of the positive electrode active material layer (120). For example, the content of the sulfur-based material (1) in the positive electrode active material layer (120) may be 20 to 50 wt% or 25 to 45 wt% with respect to the total weight of the positive electrode active material layer (120).

[0085] The content of the metal halide salt (2, 3) in the positive electrode active material layer (120) may be 10 to 40 wt% with respect to the total weight of the positive electrode active material layer (120). For example, the content of the metal halide salt (2, 3) in the positive electrode active material layer (120) may be 15 to 30 wt% with respect to the total weight of the positive electrode active material layer (120).

[0086] The content of the first metal halide salt (2) in the positive electrode active material layer (120) may be 2.5 to 10 wt% with respect to the total weight of the positive electrode active material layer (120). For example, the content of the first metal halide salt (2) in the positive electrode active material layer (120) may be 3.3 to 6.6 wt% with respect to the total weight of the positive electrode active material layer (120).

[0087] The content of the second metal halide salt (3) in the positive electrode active material layer (120) may be 7.5 to 30 wt% with respect to the total weight of the positive electrode active material layer (120). For example, the content of the second metal halide salt (3) in the positive electrode active material layer (120) may be 10 to 20 wt% with respect to the total weight of the positive electrode active material layer (120).

[0088] According to one embodiment, the content of elemental sulfur (S) contained in the positive electrode active material layer (120) may be 10 to 65 wt% with respect to the total weight of the positive electrode active material layer.

[0089] Referring to FIGS. 2 and 3, the positive electrode active material layer (120) may further include a conductive material (30). The conductive material (30) may have conductivity without causing chemical changes, thereby increasing the electrical conductivity of the positive electrode active material (10) and the solid electrolyte (20). The conductive material may include a carbon-based material. The conductive material may include, for example, one or more selected from graphite, carbon black, acetylene black, carbon nanofibers, and carbon nanotubes.

[0090] The positive electrode active material layer (120) may further include a binder. The binder may bind the positive electrode active material (10), the solid electrolyte (20), and the conductive material (30) within the positive electrode active material layer (120) to each other. The binder may include a material for improving the bonding strength between the positive electrode active material layer (120) and the positive electrode current collector (110). The binder may include, for example, polyvinylidene fluoride, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, and polymethyl methacrylate. The content of the binder included in the positive electrode active material layer (120) may be, for example, 0.5 wt% to 5 wt% or 0.5 wt% to 2 wt% of the total weight of the positive electrode active material layer (120). In one embodiment, the binder may be omitted.

[0091] The positive electrode active material layer (120) may further include additives such as fillers, coating agents, dispersants, and ion-conducting aids in addition to the above-described positive electrode active material (10), solid electrolyte (20), conductive agent (30), and binder. As the fillers, coating agents, dispersants, and ion-conducting aids that the positive electrode active material layer (120) may include, known materials generally used in electrodes of all-solid-state batteries may be used.

[0092] Referring to FIG. 1, an all-solid-state battery (1000) according to one embodiment may include a solid electrolyte layer (300) disposed between a positive electrode layer (100) and a negative electrode layer (200). The solid electrolyte layer (300) may include a sulfide-based solid electrolyte having excellent lithium ion conductivity characteristics. The solid electrolyte in the solid electrolyte layer (300) may be the same as or different from any one of the materials included in the solid electrolyte (20) in the positive electrode active material layer (120) described above.

[0093] Referring to FIG. 1, an all-solid-state battery (1000) according to one embodiment may include a negative electrode layer (200). The negative electrode layer (200) may include a negative electrode current collector (210) and a negative electrode coating layer (220) disposed on the negative electrode current collector (210).

[0094] The negative electrode current collector (210) can provide a reference surface on which the negative electrode coating layer (220) is disposed. The negative electrode current collector (210) can include, for example, a material that does not react with lithium, i.e., does not form an alloy or compound with lithium. The material constituting the negative electrode current collector (210) can include, for example, at least one metal selected from the group consisting of copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni). The thickness of the negative electrode current collector can be 1 to 20 μm, for example, 5 to 15 μm, for example, 7 to 10 μm.

[0095] The negative electrode current collector (210) may be composed of one of the above-described metals, or may include an alloy or coating material of two or more metals. The negative electrode current collector (210) is, for example, in the form of a plate or foil. In another embodiment, the negative electrode current collector (210) may be omitted.

[0096] The negative electrode coating layer (220) may be configured to allow lithium metal to grow between it and the negative electrode current collector (210) when the all-solid-state battery (1000) is charged. The negative electrode coating layer (220) may serve as a protective layer for the lithium metal and at the same time suppress the precipitation and growth of lithium dendrites.

[0097] The cathode coating layer (220) may include a metal-carbon composite. The metal-carbon composite may be a composite of metal particles and a carbon-based material. The metal-carbon composite may have, for example, a particle shape. The average particle diameter of the metal-carbon composite having a particle shape is, for example, 4 μm or less, 3 μm or less, 2 μm or less, 1 μm or less, or 900 nm or less. The average particle diameter of the metal-carbon composite having a particle shape is, for example, 10 nm to 4 μm or less, 10 nm to 3 μm or less, 10 nm to 2 μm or less, 10 nm to 1 μm or less, or 10 nm to 900 nm or less. Since the metal-carbon composite has an average particle diameter in this range, reversible absorption and / or desorption of lithium may be facilitated during charge and discharge. The average particle size of the metal-carbon composite is, for example, the median diameter (D50) measured using a laser particle size distribution meter.

[0098] The metal particles in the metal-carbon composite may include at least one metal or metalloid selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). The carbonaceous material in the metal-carbon composite may include at least one selected from the group consisting of carbon black, acetylene black, furnace black, ketjen black, and graphene. The carbonaceous material in the metal-carbon composite may be amorphous carbon. Amorphous carbon may be carbon that has no crystallinity or very low crystallinity.

[0099] The mixing ratio of the metal particles and the carbon-based material included in the cathode coating layer (220) may be, for example, a weight ratio of 10:1 to 1:2, 5:1 to 1:1, or 4:1 to 2:1. The content of the metal particles included in the cathode coating layer (220) may be 8 to 60 wt%, 10 to 50 wt%, 15 to 40 wt%, or 20 to 30 wt% based on the total weight of the metal-carbon composite. When the metal particles have a content in this range, the cycle characteristics of the all-solid-state battery (1000) may be improved.

[0100] The cathode coating layer (220) may further include other additives in addition to the metal-carbon composite. The cathode coating layer (220) may further include, for example, at least one additive selected from the group consisting of a binder, a filler, a coating agent, a dispersant, and an ion-conducting auxiliary agent.

[0101] The negative electrode coating layer (220) may have a smaller thickness than the positive electrode active material layer (120). The thickness of the negative electrode coating layer (220) may be, for example, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or 5% or less of the thickness of the positive electrode active material layer (120). The thickness of the negative electrode coating layer (220) may be, for example, 1 μm to 20 μm, 2 μm to 10 μm, or 3 μm to 7 μm. If the thickness of the negative electrode coating layer (220) is too thin, lithium dendrites formed between the negative electrode coating layer (220) and the negative electrode current collector (210) may collapse the negative electrode coating layer (220), thereby deteriorating the cycle characteristics of the all-solid-state battery (1000). If the thickness of the cathode coating layer (220) increases excessively, the energy density of the all-solid-state battery (1000) may decrease, and the internal resistance of the all-solid-state battery (1000) due to the cathode coating layer (220) may increase, thereby deteriorating the cycle characteristics of the cell. Meanwhile, although not shown, a carbon layer may be further included to improve adhesion between the cathode coating layer (220) and the solid electrolyte layer (300).

[0102] According to another embodiment, an all-solid-state battery may include a negative electrode active material layer corresponding to the above-described negative electrode coating layer (220). The negative electrode active material in the negative electrode active material layer may include a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide. The material capable of reversibly intercalating / deintercalating lithium ions may be a carbon-based negative electrode active material, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite, such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like. As an alloy of lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used. As a material that can be doped and dedoped with lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (Q is selected from an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (excluding Si), a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and a combination thereof), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination thereof. The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, it may include a secondary particle (core) assembled with silicon primary particles and an amorphous carbon coating layer (shell) positioned on the surface of the secondary particle.Amorphous carbon may also be positioned between the silicon primary particles, so that, for example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed in the amorphous carbon matrix. The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core including crystalline carbon and silicon particles, and an amorphous carbon coating layer positioned on the surface of the core. A Si-based negative electrode active material or a Sn-based negative electrode active material may be used in combination with a carbon-based negative electrode active material. In addition, known negative electrode active materials may, of course, be applied.

[0103] FIG. 5 is for explaining an all-solid-state battery (1000) according to another embodiment. Referring to FIG. 5, the all-solid-state battery (1000) according to one embodiment may further include a lithium metal layer (240) disposed between the negative electrode current collector (210) and the solid electrolyte layer (300) by charging. The all-solid-state battery (1000) according to one embodiment may further include a lithium metal layer (240) disposed between the negative electrode current collector (210) and the negative electrode coating layer (220) by charging. Although not shown in the drawing, the all-solid-state battery (1000) may further include a lithium metal layer (240) disposed between the solid electrolyte layer (300) and the negative electrode coating layer (220) by charging. Although not shown in the drawing, the all-solid-state battery (1000) may further include a lithium metal layer (240) disposed within the negative electrode coating layer (220) by charging.

[0104] The lithium metal layer (240) may include lithium or a lithium alloy. Since the lithium metal layer (240) is a metal layer containing lithium, it may function as a lithium reservoir, for example. The lithium alloy may be, but is not limited to, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, a Li-Si alloy, etc., and any lithium alloy used in the art may be used. The lithium metal layer (240) may be made of one of these alloys or lithium, or may be made of several types of alloys. The lithium metal layer (240) may be, for example, a plated layer. The lithium metal layer (240) may be deposited between the negative electrode coating layer (220) and the negative electrode current collector (210), for example, during the charging process of the all-solid-state battery (1000).

[0105] Thickness (d) of lithium metal layer (240) 240 ) 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 thickness of the lithium metal layer (240) is too thin, it may be difficult for the lithium metal layer (240) to perform the role of a lithium reservoir. If the thickness of the lithium metal layer (240) is too thick, the mass and volume of the all-solid-state battery (1000) may increase, and the cycle characteristics of the all-solid-state battery (1000) may rather deteriorate.

[0106] In another embodiment, the lithium metal layer (240) in the negative electrode layer (200) may be provided between the negative electrode current collector (210) and the negative electrode coating layer (220), for example, before assembling the all-solid-state battery (1000). When the lithium metal layer (240) is disposed between the negative electrode current collector (210) and the negative electrode coating layer (220) before assembling the all-solid-state battery (1000), the lithium metal layer (240) acts as a lithium reservoir because it is a metal layer containing lithium. For example, a lithium foil may be disposed between the negative electrode current collector (210) and the negative electrode coating layer (220) before assembling the all-solid-state battery (1000).

[0107] When the lithium metal layer (240) is precipitated by charging after assembling the all-solid-state battery (1000), the energy density of the all-solid-state battery (1000) can increase because the lithium metal layer (240) is not included during the assembly of the all-solid-state battery (1000). When charging the all-solid-state battery (1000), the charging can exceed the charging capacity of the negative electrode coating layer (220). That is, the negative electrode coating layer (220) is overcharged. At the initial stage of charging, lithium can be absorbed into the negative electrode coating layer (220). When charging exceeds the capacity of the negative electrode coating layer (220), lithium can be precipitated, for example, between the negative electrode coating layer (220) and the negative electrode current collector (210). The precipitated lithium can form a lithium metal layer (230).

[0108] The lithium metal layer (240) may be mainly composed of lithium (i.e., metallic lithium). During discharge, lithium in the lithium metal layer (240) may be ionized and move to the positive electrode layer (100). In other words, lithium may be used as an anode active material in the all-solid-state battery (1000). In addition, since the anode coating layer (220) covers the lithium metal layer (240), the anode coating layer (220) may protect the lithium metal layer (240) and simultaneously suppress the precipitation and growth of lithium dendrites. Therefore, the anode coating layer (220) may suppress short-circuiting and capacity degradation of the all-solid-state battery (1000) and improve the cycle characteristics of the all-solid-state battery (1000).

[0109] When a lithium metal layer (240) is formed by charging after assembling an all-solid-state battery (1000), the negative electrode layer (200), i.e., the negative electrode current collector (210) and the negative electrode coating layer (220) and the region therebetween may be a Li-free region that does not contain lithium (Li) in the initial state of the all-solid-state battery (1000) or in the state after complete discharge.

[0110] Fig. 6 is for explaining an all-solid-state battery (1000) according to another embodiment. Referring to Fig. 6, an all-solid-state battery (1000) according to another embodiment may further include an intermediate layer (130) disposed between a positive electrode current collector (110) and a positive electrode active material layer (120).

[0111] The intermediate layer (130) may be directly disposed on, for example, one side or both sides of the positive electrode current collector (110). No other layer may be disposed between the positive electrode current collector (110) and the intermediate layer (130). By directly disposing the intermediate layer (130) on one side or both sides of the positive electrode current collector (110), the bonding force between the positive electrode current collector (110) and the positive electrode active material layer (120) may be further improved. By disposing the intermediate layer (130) between the positive electrode current collector (110) and the positive electrode active material layer (120), side reactions between the inorganic filler and / or solid electrolyte and the positive electrode current collector (110) may be more effectively suppressed. Therefore, deterioration of the all-solid-state battery (1000) during the charge / discharge process may be suppressed, and the cycle characteristics of the all-solid-state battery (1000) may be further improved.

[0112] Thickness (d) of the middle layer (130) 130 ) is, for example, 0.01 to 20%, 0.1 to 20%, 0.5 to 20%, 1 to 20%, 1 to 15%, 1 to 10%, 2 to 8%, or 3 to 7% of the thickness of the positive electrode current collector (110). The thickness of the intermediate layer (130) is, for example, 10 nm to 5 ㎛, 50 nm to 5 ㎛, 200 nm to 4 ㎛, 500 nm to 3 ㎛, 500 nm to 2 ㎛, 500 nm to 1.5 ㎛, or 700 nm to 1.3 ㎛. When the intermediate layer (130) has a thickness in this range, the bonding force between the positive electrode current collector (110) and the positive electrode active material layer (120) is further improved, and an increase in interface resistance is suppressed. The thickness (d) of the intermediate layer (130) 130 ) can be measured, for example, from scanning electron microscope (SEM) images of the intermediate layer cross-section.

[0113] The intermediate layer (130) includes, for example, a carbon-based conductive material. The carbon-based conductive material included in the intermediate layer (130) may be selected from among the carbon-based conductive materials used in the positive electrode active material layer (120). The intermediate layer (130) may include the same carbon-based conductive material as the carbon-based conductive material used in the positive electrode active material layer (120). Since the intermediate layer (130) includes a carbon-based conductive material, the intermediate layer (130) may be, for example, a conductive layer.

[0114] The intermediate layer (130) may additionally include, for example, a binder. By additionally including a binder in the intermediate layer (130), the bonding strength between the positive electrode current collector (110) and the positive electrode active material layer (120) may be further improved. The binder included in the intermediate layer (130) may be, for example, a conductive binder or a non-conductive binder. The conductive binder may be, for example, an ion-conductive binder and / or an electron-conductive binder. A binder having both ion-conductive and electron-conductive properties may belong to both an ion-conductive binder and an electron-conductive binder.

[0115] The binder included in the intermediate layer (130) may be selected from among the binders used in the positive electrode active material layer (120). The intermediate layer (130) may include the same binder as the binder used in the positive electrode active material layer (120). The binder included in the intermediate layer (130) is, for example, a fluorine-based binder. The fluorine-based binder included in the intermediate layer (130) is, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or a combination thereof. The intermediate layer (130) may be, for example, a bonding layer including a binder. The intermediate layer (130) may be, for example, a conductive layer including a binder and a carbon-based conductive material.

[0116] The intermediate layer (130) may be disposed on the positive electrode current collector (110) in a dry or wet manner, for example. The intermediate layer (130) may be disposed on the positive electrode current collector (110) in a dry manner, for example, by deposition such as CVD or PVD. The intermediate layer (130) may be disposed on the positive electrode current collector (110) in a wet manner, for example, by spin coating, dip coating, or the like. The intermediate layer (130) may be disposed on the positive electrode current collector (110) in a wet manner, for example, by deposition of a carbon-based conductive material on a substrate. The dry-coated intermediate layer (130) may be made of a carbon-based conductive material and may not include a binder. The intermediate layer (130) may be disposed on the positive electrode current collector (110) in a dry manner, for example, by coating a composition including a carbon-based conductive material, a binder, and a solvent on the surface of the electrode current collector and drying it. The intermediate layer (130) may have a single-layer structure or a multi-layer structure including a plurality of layers. The multilayer structure may be a two-layer structure, a three-layer structure, a four-layer structure, etc. In one embodiment, the positive electrode layer (100) may have a positive electrode active material layer (120) directly disposed on the positive electrode current collector (110). In one embodiment, another layer, for example, an intermediate layer, may not be disposed between the positive electrode current collector (110) and the positive electrode active material layer (120).

[0117] Referring to FIG. 6, an all-solid-state battery (1000) according to another embodiment may further include a thin film (230) including an element capable of forming an alloy with lithium on an anode current collector (210). The thin film (230) may be disposed between the anode current collector (210) and the anode coating layer (220). The thin film (230) may include, for example, an element capable of forming an alloy with lithium. The element capable of forming an alloy with lithium includes, but is not limited to, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., and any element capable of forming an alloy with lithium in the art may be used. The thin film (230) may be composed of one of these metals or an alloy of several types of metals.

[0118] Referring to FIG. 7, by placing the thin film (230) on one surface of the negative electrode current collector (210), the deposition shape of the lithium metal layer (240) deposited between the thin film (230) and the negative electrode coating layer (220) becomes flatter, and the cycle characteristics of the all-solid-state battery (1000) can be further improved.

[0119] Thickness (d) of the thin film (230) 230 ) 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 (230) is less than 1 nm, it may be difficult for the function of the thin film (230) to be exerted. If the thickness of the thin film (230) is excessively thick, the thin film (230) itself may absorb lithium, thereby reducing the amount of lithium precipitation from the negative electrode, thereby lowering the energy density of the all-solid-state battery (1000) and deteriorating the cycle characteristics of the all-solid-state battery (1000). The thin film (230) may be disposed on the negative electrode current collector (210) by, for example, a vacuum deposition method, a sputtering method, a plating method, or the like, but is not necessarily limited to these methods, and any method capable of forming the thin film (230) in the relevant technical field may be used.

[0120] Fig. 8 is for explaining an all-solid-state battery (1000) according to another embodiment. Referring to Fig. 8, an all-solid-state battery (1000) according to another embodiment has a width (W) of a positive electrode layer (100) 100 ) is the width (W) of the cathode layer (200) 200 ) may be smaller than the width (W) of the cathode layer (200) of the all-solid-state battery (1000) according to one embodiment. 200 ) and the width of the solid electrolyte layer (300) may have substantially the same area. The all-solid-state battery (1000) according to another embodiment may further include a gasket (400). The gasket (400) may be arranged to surround the positive electrode layer (100). The gasket (400) may fill the lateral step of the all-solid-state battery (1000) caused by the width difference between the positive electrode layer (100) and the negative electrode layer (200). The gasket (400) may surround four sides of the positive electrode layer (100). For example, the thickness of the gasket (400) may be substantially the same as the thickness of the positive electrode layer (100).

[0121] Fig. 9 is for explaining an all-solid-state battery (1000) according to another embodiment. Referring to Fig. 9, a solid electrolyte layer (300) of an all-solid-state battery (1000) according to one embodiment may include a first solid electrolyte layer (310) and a second solid electrolyte layer (320). The first solid electrolyte layer (310) may be adjacent to the positive electrode layer (100), and the second solid electrolyte layer (320) may be adjacent to the negative electrode layer (200). The thickness (d) of the first solid electrolyte layer (310) 310 ) is the thickness (d) of the second solid electrolyte layer (320). 320) may be smaller than the positive electrode layer (100). Referring to FIG. 9, the first solid electrolyte layer (310) according to one embodiment may have substantially the same width as the positive electrode layer (100). The second solid electrolyte layer (320) may have substantially the same width as the negative electrode layer (200). The all-solid-state battery (1000) according to one embodiment may further include a gasket (400). Referring to FIG. 10, the gasket (400) may be arranged to surround the positive electrode layer (100) and the first solid electrolyte layer (310).

[0122] The present invention is further explained in detail through the following examples and comparative examples. However, the examples are intended to illustrate the invention and are not intended to limit the scope of the invention.

[0123] Example 1

[0124] Manufacturing of positive electrode active materials

[0125] Li2S, LiI, and AlI3 were mixed in a weight ratio of 40:15:5. The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI-AlI3 composite. The milling conditions were 25°C, 450 rpm for 10 hours. The milling energy applied to the sample during milling was 20 G. The Li2S-LiI-AlI3 composite thus prepared and carbon nanofibers (CNF) were mixed in a weight ratio of 60:10. The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI-AlI3-CNF composite. The milling conditions were 25°C, 450 rpm for 10 hours. The milling energy applied to the sample during milling was 20 G. The Li2S-LiI-AlI3-CNF composite thus prepared was used as a cathode active material.

[0126] Manufacturing of anodes

[0127] Li6PS5Cl (D50 = 1.0 ㎛, crystalline), an argyrodite-type crystal, was prepared as a solid electrolyte. The positive electrode active material and the solid electrolyte were prepared in a weight ratio of positive electrode active material: solid electrolyte = 70:30, respectively.

[0128] PTFE was prepared as a binder. The positive electrode mixture was prepared by mixing the positive electrode active material, solid electrolyte, and binder. The positive electrode mixture was obtained by dry mixing using a mixer.

[0129] The positive electrode was manufactured by placing the positive electrode active material mixture on one side of a positive electrode current collector made of aluminum foil coated on one side and plate pressing at a pressure of 200 MPa for 10 minutes. The thickness of the positive electrode was approximately 120 μm. The thickness of the positive electrode active material layer was approximately 100 μm, and the thickness of the carbon-coated aluminum foil was approximately 20 μm. The areas of the positive electrode active material layer and the positive electrode current collector were identical.

[0130] Manufacturing of cathode

[0131] A 10 ㎛ thick SUS foil was prepared as a negative electrode collector. Carbon black (CB) particles with a primary particle diameter of approximately 30 nm and silver (Ag) particles with an average particle diameter of approximately 60 nm were prepared as metal-carbon composites.

[0132] A mixed powder of 4 g of carbon black (CB) and silver (Ag) particles in a weight ratio of 3:1 was placed in a container, and 4 g of an NMP solution containing 7 wt% of PVDF binder (Kureha #9300) was added thereto to prepare a mixed solution. A slurry was prepared by stirring the mixed solution while adding NMP little by little to the prepared mixed solution. The prepared slurry was applied to a SUS sheet using a bar coater, dried in air at 80°C for 10 minutes, and then vacuum-dried at 40°C for 10 hours to prepare a laminate. The prepared laminate was cold roll pressed to flatten the surface, thereby preparing a negative electrode having a negative electrode coating layer / negative electrode collector structure. The thickness of the negative electrode coating layer was approximately 15 μm. The areas of the negative electrode coating layer and the negative electrode collector were the same.

[0133] Manufacturing of solid electrolyte layers

[0134] A mixture was prepared by adding 1.5 parts by weight of an acrylic binder to 98.5 parts by weight of a Li6PS5Cl solid electrolyte, which is an argyrodite-type crystal. Octyl acetate was added to the prepared mixture and stirred to prepare a slurry. The prepared slurry was applied using a bar coater onto a 15 μm thick nonwoven fabric placed on a 75 μm thick PET substrate, and dried in air at 80°C for 10 minutes to prepare a laminate. The prepared laminate was vacuum-dried at 80°C for 2 hours to prepare a solid electrolyte layer.

[0135] Manufacturing of all-solid-state batteries

[0136] Referring to Fig. 1, a previously fabricated negative electrode layer, a solid electrolyte layer on the negative electrode layer, and a positive electrode layer on the solid electrolyte layer were sequentially arranged. The prepared laminate was plate pressed at 85°C and a pressure of 500 MPa for 30 min. This pressurization sintered the solid electrolyte layer, thereby improving battery characteristics. The thickness of the sintered solid electrolyte layer was approximately 45 μm. The density of the Li6PS5Cl solid electrolyte, which is an argyrodite-type crystal contained in the sintered solid electrolyte layer, was 1.6 g / cc. The area of ​​the solid electrolyte layer was the same as that of the negative electrode layer.

[0137] The pressurized laminate was placed in a pouch and vacuum-sealed to manufacture an all-solid-state battery. Portions of the positive and negative current collectors were extended outside the sealed battery to serve as positive and negative terminals.

[0138] Example 2

[0139] A cathode active material, a cathode, and an all-solid-state battery were manufactured in the same manner as in Example 1, except that a Li2S-LiI-AlI3 composite was manufactured by mixing Li2S, LiI, and AlI3 in a weight ratio of 40:10:10.

[0140] Example 3

[0141] A cathode active material, a cathode, and an all-solid-state battery were manufactured in the same manner as in Example 1, except that a Li2S-LiI-AlI3 composite was manufactured by mixing Li2S, LiI, and AlI3 in a weight ratio of 40:5:15.

[0142] Example 4

[0143] A cathode active material, a cathode, and an all-solid-state battery were manufactured in the same manner as in Example 1, except that a Li2S-LiI-AlI3 composite was manufactured by mixing Li2S, LiI, and AlI3 in a weight ratio of 40:2:18.

[0144] Comparative Example 1 - Without carbon-based material

[0145] A cathode active material, a cathode, and an all-solid-state battery were manufactured in the same manner as in Example 1, except that a Li2S-LiI-AlI3 composite was manufactured by mixing Li2S, LiI, and AlI3 in a weight ratio of 50:15:5 without including CNF.

[0146] Comparative Example 2 - Without boron group metal halide salt

[0147] A cathode active material, a cathode, and an all-solid-state battery were manufactured in the same manner as in Example 1, except that Li2S and LiI were mixed in a weight ratio of 40:20 without including AlI3 to manufacture a Li2S-LiI complex.

[0148] Comparative Example 3 - Without alkali metal halide salt

[0149] A cathode active material, a cathode, and an all-solid-state battery were manufactured in the same manner as in Example 1, except that Li2S and AlI3 were mixed in a weight ratio of 40:20 without including LiI to manufacture a Li2S-AlI3 composite.

[0150] The compositions of the positive electrode active materials produced in Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 1 below.

[0151] Cathode active material Li2S (wt%) * )LiI (wt%)AlI3(wt%)CNF (wt%)Solid electrolyte(wt%)Example 1Li2S-LiI-AlI3-CNF401551030Example 2Li2S-LiI-AlI3-CNF4010101030Example 3Li2S-LiI-AlI3-CNF405151030Example 4Li2S-LiI-AlI3-CNF402181030Comparative Example 1Li2S-LiI-AlI3501551030Comparative Example 2Li2S-LiI-CNF4020- ** 1030 Comparative Example 3Li2S-AlI3-CNF40-201030

[0152] * The above table represents the sum of the positive electrode active material and solid electrolyte as 100 wt%.** The above ‘-’ indicates that the positive electrode active material was not added during production.

[0153] Evaluation Example 1: Scanning Electron Microscope (SEM) Analysis

[0154] The positive electrode active material (Li2S-LiI-AlI3-CNF composite) manufactured in Example 3 was observed using a scanning electron microscope (SEM). Figure 11 is an SEM photograph of the positive electrode active material manufactured in Example 3. Referring to Figure 11, it was confirmed that LiI and AlI3 did not form a separate phase with Li2S but formed a solid solution to form a single composite. Referring to Figure 11, CNF did not exist separately from the Li2S-LiI-AlI3 solid solution, but was included within the solid solution to form a Li2S-LiI-AlI 3- It was confirmed that a CNF complex was formed.

[0155] Evaluation Example 2: Evaluation of the properties of positive electrode active materials

[0156] The electronic conductivity, ionic conductivity, and pellet density of the positive electrode active materials manufactured in Examples 1 to 4 and Comparative Examples 1 to 3 were measured and are shown in Table 2 below. The electronic conductivity and ionic conductivity were measured using electrochemical impedance spectroscopy.

[0157] Cathode active materialElectronic conductivity (S / cm)Ionic conductivity (S / cm)Pellet density (g / cc)Example 1Li2S-LiI-AlI3-CNF6.87 x 10 -3 3.83 x 10 -6 1.62 Example 2Li2S-LiI-AlI3-CNF7.63 x 10 -3 3.56 x 10 -6 1.74 Example 3Li2S-LiI-AlI3-CNF8.13 x 10 -3 6.78 x 10 -61.75 Example 4Li2S-LiI-AlI3-CNF1.55 x 10 -2 6.75 x 10 -6 1.71 Comparative Example 1Li2S-LiI-AlI31.15 x 10 -6 5.28 x 10 -6 1.53 Comparative example 2Li2S-LiI-CNF4.65 x 10 -3 2.94 x 10 -6 1.64 Comparative example 3Li2S-AlI3-CNF5.23 x 10 -3 6.65 x 10 -6 1.72

[0158] Referring to Table 2, it was confirmed that the positive electrode active materials of Examples 1 to 4, which include a metal halide salt containing an alkali metal and a metal halide salt containing a boron group metal, have superior electrical conductivity compared to the positive electrode active materials of Comparative Examples 1 to 3. Evaluation Example 3: Charge / Discharge Test

[0159] The charge / discharge characteristics of all-solid-state batteries employing the positive electrode active materials manufactured in Examples 1 to 4 and Comparative Examples 1 to 3 were evaluated by the following charge / discharge test.

[0160] Charge-discharge tests were performed on all-solid-state batteries in a constant-temperature chamber at 45°C. Charging was performed in CC mode. The battery voltage was charged to 2.8 V at 0.05C, and discharge was performed in CC mode at 0.05C to 1.0 V.

[0161] The charge and discharge capacities of the first cycle were measured by conducting a charge / discharge test once using the above method. The discharge capacity of the first cycle was used as the standard capacity, and the initial efficiency was calculated using the following mathematical equation (1).

[0162] <Mathematical Formula 1>

[0163] Initial efficiency (%) = [Standard capacity / 1st cycle charge capacity] × 100 (%)

[0164] Charge-discharge tests were conducted twice using the above method. From the third cycle onward, charge-discharge tests were repeated in CC mode at 0.1C, and the discharge capacity was measured at each cycle. The capacity retention rate was calculated using Equation 2 below, and the results are shown in Table 12.

[0165] <Mathematical Formula 2>

[0166] Capacity retention rate (%) = [N+1 cycle discharge capacity / N cycle discharge capacity] × 100 (%)

[0167] The initial efficiency and capacity retention rate calculated through the above charge / discharge test are shown in Table 3 and Fig. 12 below (the capacity retention rate in Table 3 below is the capacity retention rate at N=2).

[0168] Cathode active materialStandard capacity (mAh / g)Initial efficiency (%)Capacity retention (%)Example 1Li2S-LiI-AlI3-CNF85984.181.8Example 2Li2S-LiI-AlI3-CNF87888.087.5Example 3Li2S-LiI-AlI3-CNF93491.794.8Example 4Li2S-LiI-AlI3-CNF91490.491.1Comparative example 1Li2S-LiI-AlI341078.224.5Comparative example 2Li2S-LiI-CNF81276.774.0Comparative example 3Li2S-AlI3-CNF80171.470.2

[0169] Referring to Table 3, it was confirmed that Examples 1 to 4, which applied a positive electrode active material including a first metal halide salt including an alkali metal and a second metal halide salt including a boron group metal, had superior cycle characteristics compared to Comparative Examples 1 to 3.

[0170]

[0171] While embodiments of the present invention have been described with reference to the attached drawings, the present invention can be implemented in other specific forms without altering its technical concept or essential features. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

A composite comprising a sulfur-based substance, a metal halide salt, and a carbon-based substance; The above sulfur series materials are S8 and Li2S n Contains at least one of (1 ≤ n ≤ 8, where n is an integer), The above metal halide salt is a cathode active material comprising a first metal halide salt containing an alkali metal and a second metal halide salt containing a boron group metal. In the first paragraph, The above first metal halide salt is a cathode active material comprising LiF, LiCl, LiBr, LiI or a combination thereof. In the first paragraph, The second metal halide salt is a cathode active material comprising AlF3, AlCl3, AlBr3, AlI3, GaF3, GaCl3, GaBr3, GaI3, InF3, InCl3, lnBr3, lnI3, TlF3, TlCl3, TlBr3, TlI3 or a combination thereof. In the first paragraph, The above carbon-based material includes a fibrous carbon-based material, The above fibrous carbon material includes a carbon nanostructure, A cathode active material comprising the above carbon nanostructures including carbon nanofibers (CNF), carbon nanotubes (CNT), carbon nanobelts, carbon nanorods, or a combination thereof. In the first paragraph, A positive electrode active material having a content of the sulfur series material of 20 to 80 wt% based on the total weight of the complex. In the first paragraph, A positive electrode active material having a content of the metal halide salt of 10 to 60 wt% based on the total weight of the complex. In the first paragraph, A positive electrode active material having a content of the carbon-based material of 1 to 30 wt% based on the total weight of the composite. In the first paragraph, A cathode active material in which the weight ratio of the first metal halide salt and the second metal halide salt is 5:1 to 1:

20. In the first paragraph, A cathode active material in which the weight ratio of the first metal halide salt and the second metal halide salt is 3:1 to 1:

9. In the first paragraph, A cathode active material in which the weight ratio of the sulfur series material and the first metal halide salt is 30:1 to 1:

1. In the first paragraph, A cathode active material in which the weight ratio of the sulfur series material and the second metal halide salt is 10:1 to 1:

1. In the first paragraph, The above complex is a positive electrode active material comprising a solid solution of the sulfur series material and the metal halide salt. In Article 12, The above solid solution is (1-xy)Li2S n -Cathode active material comprising -xAX-yBX3 or (1-xy)S8-xAX-yBX3: The above x and the above y are 0.01 ≤ x ≤ 0.3, 0.01 ≤ y ≤ 0.3, the above n is an integer of 1 ≤ n ≤ 8, the above A is an alkali metal, the above B is a boron group metal, and the above X is a halogen element. A positive electrode current collector; and a positive electrode active material layer disposed on one or both sides of the positive electrode current collector, A positive electrode, wherein the positive electrode active material layer comprises a positive electrode active material according to claim 1 and a solid electrolyte. In Article 14, The content of the positive electrode active material is 40 to 90 parts by weight per 100 parts by weight of the positive electrode active material layer, A positive electrode having a content of the solid electrolyte of 10 to 60 parts by weight based on 100 parts by weight of the positive electrode active material layer. In Article 14, A positive electrode having a content of the sulfur series material of 10 to 60 wt% based on the total weight of the positive electrode active material layer. In Article 14, A positive electrode having a content of the metal halide salt of 10 to 40 wt% based on the total weight of the positive electrode active material layer. In Article 17, The content of the first metal halide salt is 2.5 to 10 wt% based on the total weight of the positive electrode active material layer, The content of the second metal halide salt is 7.5 to 30 wt% based on the total weight of the positive electrode active material layer, An anode in which the weight ratio of the first metal halide salt and the second metal halide salt is 5:1 to 1:

20. In Article 14, A positive electrode having a content of elemental sulfur (S) contained in the positive electrode active material layer of 10 to 65 wt% based on the total weight of the positive electrode active material layer. The anode according to Article 14; A negative electrode comprising a negative current collector and a negative electrode coating layer disposed on the negative current collector; and An all-solid-state battery comprising a solid electrolyte layer disposed between the positive electrode and the negative electrode.

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