Positive electrode and lithium secondary battery comprising same

Abstract

Provided are a positive electrode and a lithium secondary battery, the positive electrode comprising a positive electrode current collector and a positive electrode active material layer, which is disposed on one or both surfaces of the positive electrode current collector and contains a positive electrode active material, a gamma sulfur-fibrous carbon-based material composite, and a sulfide-based solid electrolyte, wherein the positive electrode active material comprises Li2S, a Li2S composite, or a combination thereof, and the gamma sulfur-fibrous carbon-based material composite has a structure in which monoclinic gamma phase sulfur (S) is disposed on a fibrous carbon-based material.

Description

Anode and lithium secondary battery containing the same

[0001] It relates to a positive electrode and a lithium secondary battery including the same.

[0002] Recent industrial demands have led to the active development of batteries with high energy density and safety. For example, lithium 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] Lithium secondary batteries using liquid electrolytes may have an increased risk of fire and / or explosion in the event of a short circuit. All-solid-state secondary batteries, which use solid electrolytes instead of liquid electrolytes, are being proposed. Solid electrolytes are less likely to catch fire than liquid electrolytes.

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

[0005] However, all-solid-state secondary batteries do not use solvents in the manufacture of the cathode, electrolyte, and anode, resulting in reduced ionic conductivity and high interfacial resistance. To address this, high pressure is required during cell fabrication. Furthermore, when using a lithium precipitation layer as the anode, additional pressurization is necessary to ensure uniform lithium deposition. Therefore, to improve the pressurization process, it is necessary to design a polymer membrane that facilitates uniform lithium deposition between the electrolyte and anode.

[0006] One aspect is to provide an anode with improved specific capacity through improved electronic and ionic conductivity.

[0007] Another aspect is to provide a lithium secondary battery with improved capacity retention and charge / discharge characteristics by employing the above-described positive electrode.

[0008] A cathode current collector according to one side; and a cathode active material layer disposed on one or both sides of the cathode current collector and containing a cathode active material, a gamma sulfur-fibrous carbon-based material composite, and a sulfide-based solid electrolyte, wherein the cathode active material includes Li2S, a Li2S composite, or a combination thereof, and the gamma sulfur-fibrous carbon-based material composite has a structure in which monoclinic gamma phase sulfur (S) is disposed on a fibrous carbon-based material.

[0009] According to another aspect, a lithium secondary battery is provided, which comprises a positive electrode; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein the negative electrode includes a negative electrode current collector and a first negative electrode active material layer disposed on one surface of the negative electrode current collector, and wherein the positive electrode includes the positive electrode described above.

[0010] According to one aspect, an all-solid-state secondary battery can be provided with improved capacity retention and charge / discharge characteristics by improving the ion and electron networks in the electrode, thereby improving rate characteristics and minimizing the anode overvoltage.

[0011] Figures 1 to 5 are cross-sectional views of an all-solid-state secondary battery according to an exemplary embodiment.

[0012] Figure 6 shows an X-ray diffraction (XRD) spectrum for a gamma sulfur-carbon nanofiber composite.

[0013] [Explanation of symbols]

[0014] 10 Anode 11 Anode current collector

[0015] 12 positive electrode active material layer 20 negative electrode

[0016] 21 Negative current collector 22 First negative electrode active material layer

[0017] 30 electrolyte layer 40 inert member

[0018] Unless otherwise defined, all terms (including technical and scientific terms) used in this disclosure have the same meaning as commonly understood by those of ordinary skill in the art to which this disclosure pertains. Furthermore, terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning within the context of the relevant technology and this disclosure, and should not be interpreted in an idealized or overly formal sense.

[0019] Exemplary embodiments are described in this disclosure with reference to cross-sectional drawings that are schematic representations of idealized embodiments. As such, variations from the shapes depicted are to be expected, for example, as a result of manufacturing techniques and / or tolerances. Therefore, the embodiments described in this disclosure should not be construed as limited to the specific shapes of regions as depicted in this disclosure, but should encompass variations in shapes resulting from, for example, manufacturing. For example, regions depicted or described as flat may typically have rough and / or non-linear features. Moreover, angles depicted as sharp may be rounded. Therefore, the regions depicted in the drawings are schematic in nature, and their shapes are not intended to depict the precise shapes of the regions, nor are they intended to limit the scope of the claims.

[0020] This creative idea may be embodied in many different forms and should not be construed as limited to the embodiments described in this disclosure. These embodiments are provided so that this disclosure will be thorough and complete, and so that it will fully convey the scope of the creative idea to those skilled in the art. Like reference numerals in the drawings indicate like elements.

[0021] When a component is referred to as being "on" another component, it can be understood that it is either directly on top of the other component or that other components may be intervening between them. Conversely, when a component is referred to as being "directly on" another component, no intervening components are present.

[0022] Although terms such as "first," "second," "third," etc. may be used herein to describe various components, elements, regions, layers, and / or zones, these components, elements, regions, layers, and / or zones should not be limited by these terms. These terms are only used to distinguish one component, element, region, layer, or zone from another component, element, region, layer, or zone. Thus, a first component, element, region, layer, or zone described below may be referred to as a second component, element, region, layer, or zone without departing from the teachings of this disclosure.

[0023] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms including "at least one," unless the content clearly dictates otherwise. "At least one" should not be construed as limiting to the singular. As used herein, the term "and / or" includes any and all combinations of one or more of the listed items. The terms "comprises" and / or "comprising" as used in the detailed description specify the presence of stated features, regions, integers, steps, operations, components, and / or ingredients, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, components, ingredients, and / or groups thereof.

[0024] Spatially relative terms such as "below," "under," "lower," "above," "upper," and the like may be used herein to readily describe the relationship of one component or feature to another. It will be understood that spatially relative terms are intended to encompass different orientations of the device when in use or operation in addition to the orientations depicted in the drawings. For example, if the device in the drawings were turned over, a component described as "below" or "below" another component or feature would then be oriented "above" the other component or feature. Thus, the exemplary term "below" can encompass both the above and below orientations. The device may be arranged in other orientations (rotated 90 degrees or otherwise rotated), and the spatially relative terms used herein may be interpreted accordingly.

[0025] "Group" means a group in the periodic table of elements according to the International Union of Pure and Applied Chemistry ("IUPAC") Group 1-18 classification system.

[0026] In the present disclosure, “particle diameter”, “particle size”, or “crystallite size” refers to the average diameter when the particles or crystallites are spherical, and refers to the average major axis length when the particles are non-spherical. The “particle diameter”, “particle size”, or “crystallite size” can be measured using a particle size analyzer (PSA). The “particle diameter” is, for example, the average particle diameter. The “average particle diameter” is, for example, D50, which is the median particle diameter.

[0027] D50 is the particle size corresponding to 50% cumulative volume when calculated from the side of particles with a small particle size in the size distribution of particles measured by laser diffraction, D90 is the particle size corresponding to 90% cumulative volume when calculated from the side of particles with a small particle size in the size distribution of particles measured by laser diffraction, and D10 is the particle size corresponding to 10% cumulative volume when calculated from the side of particles with a small particle size in the size distribution of particles measured by laser diffraction.

[0028] In the present disclosure, “metal” includes both metals and metalloids such as silicon and germanium, in their elemental or ionic states, and “alloy” means a mixture of two or more metals.

[0029] In the present disclosure, “electrode active material” means an electrode material capable of undergoing lithiation and delithiation.

[0030] In the present disclosure, “positive electrode active material” means a positive electrode material capable of undergoing lithiation and delithiation, and “negative electrode active material” means a negative electrode material capable of undergoing lithiation and delithiation.

[0031] In the present disclosure, “lithiation” and “lithiating” mean a process of adding lithium to an electrode active material, and “delithiation” and “delithiating” mean a process of removing lithium from an electrode active material.

[0032] In the present disclosure, “charging” and “charging” mean a process of providing electrochemical energy to a battery, and “discharging” and “discharging” mean a process of removing electrochemical energy from a battery.

[0033] In the present disclosure, “positive electrode” and “cathode” mean an electrode where electrochemical reduction and lithiation occur during a discharge process, and “negative electrode” and “anode” mean an electrode where electrochemical oxidation and delithiation occur during a discharge process.

[0034] In this disclosure, “length,” “thickness,” and “width” represent average length, average thickness, and average width, respectively. Furthermore, the length, thickness, and width can be evaluated using a scanning electron microscope.

[0035] In the present disclosure, the aspect ratio represents the ratio (L1 / L2) of the major axis length L1 (e.g., length) and the minor axis length L2 (e.g., diameter). Here, the aspect ratio, major axis length, minor axis length, length, and diameter represent the average aspect ratio, average major axis length, average minor axis length, average length, and average diameter. The aspect ratio can be evaluated using a scanning electron microscope (SEM).

[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] Below, a cathode and a lithium secondary battery having the cathode according to exemplary embodiments are described in more detail.

[0038] Lithium sulfide is an insulator with virtually no electrical conductivity. Therefore, its use as a cathode active material requires a complexation with a highly conductive carbon material to address its low electrical conductivity. Furthermore, all-solid-state secondary batteries contain virtually no solvent in the solid electrolyte, cathode, and anode composite layers, resulting in low electronic and lithium ion conductivity, making it difficult to secure sufficient capacity during charge and discharge. Therefore, it is crucial to design an interface between the cathode active material and the solid electrolyte to facilitate active electrochemical reactions.

[0039] To address the low electrical conductivity of lithium sulfide, methods include forming lithium sulfide-carbon nanocomposites or coating the particle surface with conductive materials to increase electrochemical activity. Other attempts include introducing protective layers to the electrode surface and reducing the size of lithium sulfide particles.

[0040] To solve the above-described problems, the cathode according to one embodiment contains a cathode active material and a gamma sulfur-fibrous carbon-based material composite, thereby improving the specific capacity and capacity retention rate through improved electronic / ionic conductivity. Here, the cathode active material is Li2S, a Li2S composite, or a combination thereof.

[0041] The gamma sulfur-fibrous carbon-based material composite has a structure in which monoclinic gamma phase sulfur (S) is arranged on carbon nanofibers (CNF), which are fibrous carbon-based materials.

[0042] Sulfur includes, for example, α sulfur (orthorhombic), β sulfur (monoclinic), γ sulfur (monoclinic), and amorphous sulfur. Among them, alpha sulfur is the most stable at room temperature, and beta sulfur can be obtained by heating alpha sulfur to a temperature exceeding 94.4℃, and beta sulfur is quickly converted to alpha sulfur below 94℃.

[0043] Alpha-sulfur undergoes a reaction in which the sulfur intermediate product, lithium polysulfide, is formed, as shown in the following reaction scheme 1, and this material is converted into lithium sulfide. However, lithium polysulfide easily dissolves in the electrolyte, resulting in a loss of battery capacity and lifespan, and thus requires improvement.

[0044] <Reaction Scheme 1>

[0045] α-S ↔ LPS(Li2S6, Li2S8) ↔ Li2S

[0046] Gamma sulfur has a melting point of approximately 106.8°C and converts to alpha sulfur at room temperature. However, gamma sulfur-fibrous carbon composites obtained by depositing gamma sulfur on carbon nanofibers are stable at room temperature. Furthermore, unlike alpha sulfur, gamma sulfur is directly converted to Li2S, enabling a redox reaction without lithium polysulfides when using a liquid electrolyte containing a carbonate-based organic solvent.

[0047] Gamma-sulfur-fibrous carbon composites can simultaneously function as cathode active materials and conductive agents. Using a cathode containing such a gamma-sulfur-fibrous carbon composite as a thick-film electrode can improve ion / electron networks, resulting in enhanced high-rate characteristics, minimized cathode overvoltage, minimized formation of sulfur intermediates Li2S6 and Li2S8, and improved capacity retention and high-rate charge / discharge characteristics due to direct conversion of Li2S and S8. This allows the manufacture of lithium secondary batteries.

[0048] Lithium secondary batteries are, for example, all-solid-state secondary batteries.

[0049] In the gamma sulfur-fibrous carbon-based material composite, the fibrous carbon-based material is defined by a length and a diameter, wherein an aspect ratio of the length and diameter is 2 or greater, and the fibrous carbon-based material has a length of 1 to 50 μm, 2 to 45 μm, 3 to 30 μm, or 5 to 30 μm and a diameter of 10 nm to 10 μm. Here, the length and diameter represent average values.

[0050] The above fibrous carbon-based material includes carbon nanofibers, carbon nanotubes or a combination thereof, and includes, for example, carbon nanofibers.

[0051] The fibrous carbon-based material has the length and diameter ranges described above, facilitating the formation of a conductive network within the anode. The cross-section of the fibrous carbon-based material may include polygonal shapes such as circles, triangles, and squares.

[0052] 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.

[0053] Furthermore, utilizing the aforementioned composite can secure a more extended ion conduction path in the cathode active material layer. Therefore, during charging and discharging of a lithium secondary battery, the interruption of the ion conduction path due to volume changes in the cathode active material layer can be more effectively prevented. Consequently, the initial efficiency, discharge capacity, high-rate characteristics, and / or cycle life characteristics of the lithium secondary battery can be improved.

[0054] The carbon nanofibers described above can be controlled to increase conductivity and reduce side reactions between the positive electrode active material and the sulfide-based solid electrolyte by nitrogen and fluorine doping.

[0055] By using a composite containing the above-described fibrous carbon-based material, it is possible to manufacture a cathode capable of thick film formation by complementing the brittle nature of the cathode, thereby producing a solid-state secondary battery with increased energy density. In addition, since the inclusion of the fibrous carbon-based material allows the volume change of the cathode active material during charge and discharge to be accommodated by dispersing it along the entire length, the volume change of the cathode active material can be accommodated more effectively than, for example, a carbon-based material in the form of spherical particles. Consequently, the disconnection between the cathode active material and the solid electrolyte due to the volume change of the cathode active material within the cathode active material layer can be suppressed, and the uniformity of the components within the cathode active material layer can be improved. Consequently, the cycle characteristics of the all-solid-state secondary battery can be improved.

[0056] The gamma sulfur-fibrous carbon-based material composite has excellent ionic and electronic conductivity, and by improving the ion / electron network, an all-solid-state secondary battery can be manufactured with superior energy density, initial efficiency, and improved lifespan characteristics compared to a case where the positive electrode active material layer is manufactured without using the gamma sulfur-fibrous carbon-based material composite when manufacturing the positive electrode active material layer. The content of the sulfide-based solid electrolyte when manufacturing the positive electrode active material layer is 5 to 40 parts by weight, or 7 to 35 parts by weight, based on 100 parts by weight of the total weight of the positive electrode active material layer. And the content of the positive electrode active material is 30 to 65 parts by weight, or 30 to 60 parts by weight, based on 100 parts by weight of the total weight of the positive electrode active material layer. The gamma sulfur-fibrous carbon-based material composite according to one embodiment is, for example, a gamma sulfur-carbon nanofiber composite.

[0057] The content of the gamma sulfur-fibrous carbon-based material composite is 1 to 30 parts by weight, 1 to 20 parts by weight, or 1 to 10 parts by weight based on 100 parts by weight of the total weight of the positive electrode active material layer. When the content of the gamma sulfur-fibrous carbon-based material composite is within the above range, a lithium secondary battery can be manufactured with improved rate characteristics and improved capacity retention and energy density due to improved ion and electron networks.

[0058] The Brunauer-Emmett-Teller (BET) surface area of ​​the above gamma sulfur-fibrous carbon material composite is 10 m 2 / g or less, and the cross-section of the fibrous carbon material contains a polygonal shape such as a circle, triangle, or square, and is further doped with at least one selected from nitrogen (N) and fluorine (F).

[0059] As shown in Fig. 6, the XRD spectrum for the above gamma sulfur-carbon nanofiber composite shows a first peak at a diffraction angle 2θ = 11° ± 2.0° corresponding to the (111) crystal plane, a second peak at a diffraction angle 2θ of 18 to 32° corresponding to the (122) crystal plane, and a third peak at a diffraction angle 2θ of 27 to 28° corresponding to the (222) crystal plane.

[0060] The Li2S complex is a complex of the above Li2S and a lithium salt, which is Li2S-Li a X b (1≤a≤5, 1≤b≤5), and X is I, Br, Cl, F, H, O, Se, Te, N, P, As, Sb, Al, B, OCl, PF6, BF4, SbF6, AsF6, ClO4, AlO2, AlCl4, NO3, CO3, BH4, SO4, BO3, PO4, NCl, NCl2, BN2, or a combination thereof.

[0061] A complex of Li2S and a lithium salt is, for example, the result of mechanical milling of Li2S and a lithium salt. A complex of Li2S and a lithium salt is, for example, the result of a mechanochemical reaction of Li2S and a lithium salt, and is therefore distinct from a simple mixture of Li2S and a lithium salt. A simple mixture of Li2S and a lithium salt does not maintain a dense interface between Li2S and a lithium salt, and thus the positive electrode has a high interfacial resistance. The Li2S-Li a X bIn , a is, for example, 1, 2, 3, 4, or 5. b is, for example, 1, 2, 3, 4, or 5. A lithium salt is, for example, a compound that does not contain sulfur (S). The lithium salt may be, for example, a binary compound or a ternary compound. The lithium salt may be, for example, a binary compound composed of lithium and one element selected from groups 13 to 17 of the periodic table of elements. The lithium salt may be, for example, a ternary compound composed of lithium and two elements selected from groups 13 to 17 of the periodic table of elements. The binary compound may include, for example, LiI, LiBr, LiCl, LiF, LiH, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, Li3Al2, LiB3, or a combination thereof. By including such a binary compound in the composite, the ionic conductivity of the composite can be further improved. By including such a complex in the positive electrode, the internal resistance of the positive electrode can be further reduced. As a result, the cycle characteristics of an all-solid-state secondary battery including such a positive electrode can be further improved. The ternary compound can include, for example, Li3OCl, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiNO3, Li2CO3, LiBH4, Li2SO4, Li3BO3, Li3PO4, Li4NCl, Li5NCl2, Li3BN2, or a combination thereof. By including such a ternary compound in the composite, the ionic conductivity of the composite can be further improved. By including such a complex in the positive electrode, the internal resistance of the positive electrode can be further reduced. As a result, the cycle characteristics of an all-solid-state secondary battery including such a solid electrolyte separator can be further improved.

[0062] The above complex may further include a carbon-based material.

[0063] The carbon-based material may be any material containing carbon atoms that is used as a conductive material in the relevant technical field. The carbon-based material may be, for example, crystalline carbon, amorphous carbon, or a combination thereof. The carbon-based material may be, for example, a sintered product of a carbon precursor. The carbon-based material may be, for example, a carbon nanostructure. The carbon nanostructure may be, 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 be, for example, a carbon nanotube, a carbon nanofiber, a carbon nanobelt, a carbon nanorod, graphene, or a combination thereof. The carbon-based material may be, for example, a porous carbon-based material or a non-porous carbon-based material. The porous carbon-based material may include, for example, periodic and regular two-dimensional or three-dimensional pores. The porous carbon-based material may be, for example, carbon black such as Ketjen Black, acetylene black, Denka Black, thermal black, channel black, etc.; It may be graphite, activated carbon, or a combination thereof. The form of the carbon-based material may be, for example, particle-shaped, sheet-shaped, or flake-shaped, but is not limited thereto. Any carbon-based material used in the relevant technical field may be used.

[0064] The complex is a complex of Li2S, a lithium salt, and a carbon-based material.

[0065] The content of the carbon-based material included in the composite of Li2S, lithium salt, and carbon-based material may be, for example, 1 to 20 wt%, 5 to 20 wt%, or 10 to 20 wt% of the total weight of the composite. If the content of the carbon-based material increases excessively, the energy density of the dry positive electrode film and the all-solid-state secondary battery may decrease. If the content of the carbon-based material decreases excessively, the electronic conductivity of the composite of Li2S, lithium salt, and carbon-based material may decrease, which may increase the internal resistance of the dry positive electrode film. As a result, the cycle characteristics of the all-solid-state secondary battery may deteriorate.

[0066] The Mohs hardness of the lithium salt and the carbon-based material may be greater than that of Li2S. The Mohs hardness of Li2S is, for example, 0.6 or less. The Mohs hardness of the lithium salt may be 0.7 or more, 0.8 or more, 0.9 or more, 1.0 or more, 1.5 or more, or 2.0 or more. When the lithium salt has a Mohs hardness in this range, the pulverization of Li2S can be performed more easily during the milling process, and a solid solution of Li2S and the lithium salt can be formed more easily. The Mohs hardness of LiI is, for example, 2.0. The Mohs hardness of the carbon-based material may be 0.7 or more, 0.8 or more, 0.9 or more, 1.0 or more, 1.2 or more, or 1.5 or more, respectively. Since the carbon-based material has a Mohs hardness in this range, the grinding of Li2S can be performed more easily during the milling process, and a composite of Li2S, a lithium salt, and a carbon-based material can be formed more easily. The modal hardness of carbon nanofibers (CNF) is, for example, 1.5.

[0067] The carbon-based material may include, for example, a fibrous carbon-based material. By including the fibrous carbon-based material in the composite of Li2S, a lithium salt, and a carbon-based material, the electronic conductivity of the composite of Li2S, a lithium salt, and a carbon-based material can be further improved. By including the fibrous carbon-based material in the composite of Li2S, a lithium salt, and a carbon-based material, electronic conduction can be more easily performed from the surface to the inside of the composite of Li2S, a lithium salt, and a carbon-based material. The internal resistance of a dry cathode film including a composite of Li2S, a lithium salt, and a carbon-based material can be reduced, and the cycle characteristics of an all-solid-state secondary battery including a dry cathode film can be further improved.

[0068] The aspect ratio of the fibrous carbon-based material of the composite of Li2S, lithium salt, and carbon-based material is identical to the aspect ratio of the fibrous carbon-based material of the gamma-sulfur-fibrous carbon-based material composite. Since the fibrous carbon-based material of the composite of Li2S, lithium salt, and carbon-based material has an aspect ratio within this range, the overall electronic conductivity of the composite of Li2S, lithium salt, and carbon-based material is improved, and the local electronic conductivity imbalance within the composite of Li2S, lithium salt, and carbon-based material can be further alleviated.

[0069] The fibrous carbon-based material may include, for example, carbon nanostructures. The carbon nanostructures may include, for example, carbon nanofibers (CNFs), carbon nanotubes (CNTs), carbon nanobelts, carbon nanorods, or combinations thereof.

[0070] The carbon nanostructure can form a primary carbon nanostructure composed of a single carbon nanostructure and a secondary carbon nanostructure composed of a plurality of carbon nanostructures aggregated together.

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

[0072] A secondary carbon nanostructure is, for example, a structure formed by assembling primary carbon nanostructures to form a bundle-type or rope-type carbon nanostructure, in whole or in part. The secondary carbon nanostructure may include, for example, a bundle-type carbon nanostructure, a rope-type carbon nanostructure, or a combination thereof. The diameter of the secondary carbon nanostructure may be, for example, 2 nm to 200 nm, 3 nm to 150 nm, 5 nm to 100 nm, 5 nm to 50 nm, 5 nm to 30 nm, or 5 nm to 20 nm. The length of the secondary carbon nanostructures can be, for example, 20 nm to 2 ㎛, 30 nm to 1.5 ㎛, 50 nm to 1 ㎛, 50 nm to 500 nm, 50 nm to 400 nm, 50 nm to 300 nm, 50 nm to 200 nm, or 50 nm to 100 nm or more. The diameter and length of the secondary carbon nanostructures can be measured from a scanning electron microscope (SEM) image or an optical microscope. Alternatively, the diameter and / or length of the secondary carbon nanostructures can be measured by laser diffraction. The secondary carbon nanostructures can be converted into primary carbon nanostructures, for example, by dispersing them in a solvent or the like, and then used to prepare a composite of Li2S, a lithium salt, and a carbon-based material.

[0073] A composite of Li2S and a lithium salt or a composite of Li2S, a lithium salt, and a carbon-based material may include, for example, a solid solution of Li2S and a lithium salt. The ionic conductivity of the composite may increase by including the solid solution of Li2S and a lithium salt. For example, since the solid solution of Li2S and a lithium salt includes lithium ions arranged within Li2S crystallites, the ionic conductivity of the solid solution of Li2S and a lithium salt may be improved compared to the ionic conductivity of Li2S. Consequently, the ionic conductivity of the composite may be improved and the internal resistance of the composite may be reduced. By including such a composite in the positive electrode, the internal resistance of the positive electrode may be further reduced. Consequently, the cycle characteristics of an all-solid-state secondary battery including such a positive electrode may be further improved.

[0074] The size of Li2S crystallites obtained from the XRD spectrum of a complex of Li2S and a lithium salt or a complex of Li2S, a lithium salt and a carbon-based material may be, for example, 20 nm or less, 15 nm or less, or 10 nm or less. The size of Li2S crystallites obtained from the XRD spectrum of the complex may be, for example, 1 to 20 nm, 1 to 15 nm, or 3 to 10 nm. As the size of Li2S crystallites decreases, the contact area between Li2S and a lithium salt may further increase. As the contact area between Li2S and a lithium salt further increases, the ionic conductivity of the complex of Li2S and a lithium salt may further increase. The internal resistance of the positive electrode may further decrease when the positive electrode includes such a complex. As a result, the cycle characteristics of a solid-state secondary battery including such a positive electrode may further improve.

[0075] Since Li2S has low ionic conductivity, a complex with a lithium salt is formed to overcome this drawback. A complex of Li2S and a lithium salt or a composite of Li2S and a lithium salt and a carbon-based material can provide improved ionic conductivity compared to Li2S alone. The content of Li2S in the complex may be 50 to 95 wt%, 50 to 90 wt%, 50 to 80 wt%, or 50 to 70 wt% of the total weight of the complex of Li2S and a lithium salt. By having the complex with a Li2S content in this range, a cathode with improved ionic conductivity and durability can be manufactured. The content of the lithium salt in the complex of Li2S and a lithium salt may be 5 to 50 wt%, 10 to 50 wt%, 20 to 50 wt%, or 30 to 50 wt% of the total weight of the complex of Li2S and a lithium salt.

[0076] The molar ratio of Li2S and lithium salt in the composite may be, for example, 50:50 to 95:5, 60:40 to 95:5, 60:40 to 90:10, 65:35 to 90:10, 65:35 to 85:15, or 70:30 to 85:15. The molar ratio of Li2S and lithium salt in the composite may be, for example, 50:50 to 95:5, 50:50 to 90:10, 50:50 to 85:15, 50:50 to 80:20, 50:50 to 75:25, or 50:50 to 70:30. By having Li2S and lithium salt in this range of molar ratio, the cycle characteristics of a lithium battery including the composite cathode active material can be further improved. If the molar ratio of Li2S is excessively high, the improvement in ionic conductivity by lithium salts may be minimal. If the molar ratio of Li2S is excessively high, the energy density of lithium batteries containing composite cathode active materials may decrease.

[0077] In the composite of Li2S, a lithium salt, and a carbon-based material, the content of the lithium salt may be, for example, 1 to 40 wt%, 5 to 35 wt%, 10 to 35 wt%, 15 to 35 wt%, 20 to 35 wt%, or 25 to 35 wt% of the total weight of the composite of Li2S, a lithium salt, and a carbon-based material. If the content of the lithium salt is excessively increased, the energy density of the all-solid-state secondary battery may decrease. If the content of the lithium salt is excessively low, the ionic conductivity of the composite of Li2S, a lithium salt, and a carbon-based material may decrease, which may increase the internal resistance of the dry positive electrode film. As a result, the cycle characteristics of the all-solid-state secondary battery including the dry positive electrode film may deteriorate.

[0078] In the composite of Li2S, a lithium salt, and a carbon-based material, the molar ratio of Li2S and a lithium salt may be, for example, 50:50 to 95:5, 60:40 to 95:5, 60:40 to 90:10, 65:35 to 90:10, 65:35 to 85:15, or 70:30 to 85:15. In the composite of Li2S, a lithium salt, and a carbon-based material, the molar ratio of Li2S and a lithium salt may be, for example, 50:50 to 95:5, 50:50 to 90:10, 50:50 to 85:15, 50:50 to 80:20, 50:50 to 75:25, or 50:50 to 70:30. By maintaining the molar ratio of Li2S and lithium salt within this range, the cycle characteristics of an all-solid-state lithium battery including a dry cathode film can be further improved. If the molar ratio of Li2S is excessively high, the ionic conductivity enhancement effect of the lithium salt may be minimal. If the molar ratio of Li2S is excessively high, the energy density of a lithium battery including a composite cathode active material may be reduced.

[0079] The ionic conductivity of a complex of Li2S and a lithium salt or a complex of Li2S, a lithium salt and a carbon-based material is, for example, 1×10 at 25°C. -5 S / cm or more, 2×10 -5 S / cm or more, 4×10 -5S / cm or more, 6×10 -5 S / cm or more, 8×10 -5 S / cm or more or 1×10 -4 It can be S / cm or more. The ionic conductivity can be measured using, for example, electrochemical impedance spectroscopy, direct current polarization method, etc. Since the complex of Li2S and lithium salt has an ionic conductivity in this range, the internal resistance of the positive electrode including the complex of Li2S and lithium salt can be further reduced. The cycle characteristics of an all-solid-state secondary battery including the positive electrode can be improved.

[0080] The Li2S-containing composite may further comprise a solid electrolyte. The solid electrolyte may further comprise a sulfide-based solid electrolyte.

[0081] The content of the complex of Li2S and a lithium salt can be, for example, 0.1 to 20 wt%, 0.5 to 20 wt%, 0.5 to 15 wt%, 0.5 to 10 wt% or 1 to 5 wt% of the total weight of the complex of Li2S and a lithium salt and the sulfide-based solid electrolyte. The content of the complex of Li2S and a lithium salt can be, for example, 0.1 to 20 wt%, 0.5 to 20 wt%, 0.5 to 15 wt%, 0.5 to 10 wt% or 1 to 5 wt% of the total weight of the positive electrode. When the positive electrode has the content of the complex of Li2S and a lithium salt in this range, the durability of the positive electrode can be further improved and the internal resistance can be further reduced.

[0082] The cathode active material layer may include, for example, composite particles of Li2S and a lithium salt and sulfide-based solid electrolyte particles. The size of the composite particles of Li2S and a lithium salt may be smaller than, for example, the size of the sulfide-based solid electrolyte particles. The size of the composite particles of Li2S and a lithium salt may be, for example, 90% or less, 80% or less, 60% or less, 40% or less, 20% or less, or 10% or less of the size of the sulfide-based solid electrolyte particles. The composite particles of Li2S and a lithium salt may be arranged in pores between a plurality of sulfide-based solid electrolytes, for example. By arranging the composite particles of Li2S and a lithium salt in the pores between a plurality of sulfide-based solid electrolytes, pinhole formation within the cathode can be suppressed, and the internal resistance of the cathode can be reduced. As a result, the durability of the cathode can be improved.

[0083] The size of the sulfide-based solid electrolyte particles may be, for example, 1 to 10 μm, 1 to 8 μm, 1 to 6 μm, 1 to 5 μm, or 1 to 3 μm. When the sulfide-based solid electrolyte particles have a size in this range, the durability of the positive electrode can be further improved. The size of the sulfide-based solid electrolyte particles can be measured using, for example, laser diffraction, scanning electron microscopy, etc. The size of the sulfide-based solid electrolyte particles is, for example, an arithmetic mean of the particle sizes of multiple particles measured using software from a scanning electron microscope image.

[0084] The size of the composite particles of Li2S and a lithium salt may be, for example, 10 μm or less, 8 μm or less, 5 μm or less, 2 μm or less, 1.5 μm or less, or 1 μm or less. The size of the composite particles may be, for example, 1 to 10 μm, 2 to 10 μm, 2 to 8 μm, or 3 to 8 μm. The size of the composite particles may be, for example, 0.1 to 10 μm, 0.1 to 8 μm, 0.1 to 5 μm, 0.1 to 2 μm, 0.1 to 1.5 μm, or 0.1 to 1 μm or less. When the composite particles of Li2S and a lithium salt have a size in this range, they can be more easily arranged in the gaps between the plurality of sulfide-based solid electrolytes, pinhole formation within the positive electrode can be suppressed, and the internal resistance of the positive electrode can be reduced. As a result, the durability of the positive electrode can be improved. The size of the composite particles of Li2S and lithium salt can be measured using, for example, laser diffraction, scanning electron microscopy, etc. The size of the composite particles of Li2S and lithium salt is, for example, the arithmetic mean of the particle sizes of multiple particles measured using software from scanning electron microscopy images.

[0085] The size of the Li2S particles included in the composite cathode active material, i.e., the size of the Li2S particles included in the composite, may be, for example, 2 ㎛ or less, 1.5 ㎛ or less, or 1 ㎛ or less. The size of the Li2S particles may be, for example, 0.1 to 2 ㎛, 0.1 to 1.5 ㎛, or 0.1 to 1 ㎛ or less. Since the Li2S particles have a size in this range, the volume change during charge and discharge is suppressed, and thus the deterioration of the composite cathode active material including the composite during charge and discharge can be suppressed. If the size of the Li2S particles increases excessively, the volume change of the composite during charge and discharge may increase, which may accelerate the deterioration of the composite cathode active material including the composite. As a result, the cycle characteristics of a secondary battery including such a composite cathode active material may deteriorate.

[0086] The ratio of the size of the sulfide-based solid electrolyte particles to the size of the composite particles of Li2S and lithium salt may be, for example, 2:1 to 200:1, 2:1 to 100:1, or 2:1 to 50:1. When the ratio of the size of the sulfide-based solid electrolyte particles to the size of the composite particles of Li2S and lithium salt is within this range, defect formation in the positive electrode is suppressed, thereby further improving the durability of the positive electrode. If the ratio of the size of the sulfide-based solid electrolyte particles to the size of the composite particles of Li2S and lithium salt is excessively small, the porosity of the positive electrode may increase excessively, thereby reducing the durability of the positive electrode. If the ratio of the size of the sulfide-based solid electrolyte particles to the size of the composite particles of Li2S and lithium salt is excessively large, uniform dispersion of the composite particles of Li2S and lithium salt within the positive electrode may be difficult.

[0087] By using a positive electrode containing the above-described composite, a lithium metal negative electrode can be eliminated, enabling the use of an all-solid-state secondary battery without an anode, thereby providing an all-solid-state secondary battery with improved energy density. Furthermore, by including such a composite positive electrode active material in the positive electrode, the cycle characteristics of the all-solid-state secondary battery containing the composite positive electrode active material can be improved. For example, the high-rate characteristics of the secondary battery containing such a composite positive electrode active material can be improved.

[0088] In the positive electrode active material layer, the solid electrolyte may be, for example, a sulfide-based solid electrolyte. The solid electrolyte included in the positive electrode may be the same as or different from the solid electrolyte included in the electrolyte layer. The solid electrolyte included in the positive electrode active material layer may have a smaller average D50 particle size than the solid electrolyte included in the electrolyte layer. For example, the average D50 particle size of the solid electrolyte included in the positive electrode active material layer may be 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, or 20% or less of the average D50 particle size of the solid electrolyte included in the electrolyte layer. The average D50 particle size is, for example, the median particle diameter (D50). The median particle diameter (D50) is the size of particles corresponding to 50% of the cumulative volume, calculated from the side of particles having a smaller particle size in a size distribution of particles measured by, for example, laser diffraction.

[0089] The solid electrolyte may be included in an amount of 10 to 60 parts by weight, 10 to 50 parts by weight, 20 to 50 parts by weight, or 30 to 50 parts by weight, per 100 parts by weight of the cathode active material layer.

[0090] [All-solid-state secondary battery]

[0091] An all-solid-state secondary battery according to one embodiment includes a positive electrode; a negative electrode; and a solid electrolyte layer disposed between the positive electrode and the negative electrode, wherein the positive electrode includes the positive electrode according to one embodiment.

[0092] Referring to FIGS. 1 to 5, an all-solid-state secondary battery (1) includes a positive electrode (10); a negative electrode (20); and a solid electrolyte layer (30) disposed between the positive electrode (10) and the negative electrode (20).

[0093] [anode]

[0094] [Cathode: Cathode active material]

[0095] Referring to FIGS. 1 to 5, the positive electrode (10) includes a positive electrode current collector (11); and a positive electrode active material layer (12) disposed on one or both surfaces of the positive electrode current collector (11). The positive electrode active material layer (12) includes Li2S, a Li2S complex, or a combination thereof as a positive electrode active material.

[0096] The cathode active material layer (12) may additionally include other cathode active materials in addition to the cathode active materials described above.

[0097] Other cathode active materials may include, for example, a Li2S-containing composite. The Li2S-containing composite includes, for example, a composite of Li2S and carbon, a composite of Li2S and carbon and a solid electrolyte, a composite of Li2S and a solid electrolyte, a composite of Li2S and a lithium salt and carbon, a composite of Li2S and a metal carbide, a composite of Li2S and carbon and a metal carbide, a composite of Li2S and a metal nitride, a composite of Li2S and carbon and a metal nitride, or a combination thereof.

[0098] The Li2S and carbon complex comprises carbon. The carbon may be any material containing carbon atoms that is used as a conductive material in the art. The carbon may be, for example, crystalline carbon, amorphous carbon, or a combination thereof. The carbon may be, for example, a sintered product of a carbon precursor. The carbon may be, for example, a carbon nanostructure. The carbon nanostructure may be, 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 be, for example, a carbon nanotube, a carbon nanofiber, a carbon nanobelt, a carbon nanorod, graphene, graphene oxide (GO), reduced graphene oxide (rGO), graphene balls (GB), or a combination thereof. The carbon may be, for example, porous carbon or non-porous carbon. The porous carbon may include, for example, periodic and regular two-dimensional or three-dimensional pores. The porous carbon may be, for example, carbon black such as Ketjen black, acetylene black, Denka black, thermal black, channel black, etc.; graphite, activated carbon, or a combination thereof. The form of the carbon may be, for example, particle form, sheet form, flake form, etc., but is not limited thereto, and any method used as carbon in the art may be used. The method for preparing the composite of Li2S and carbon may be, for example, a dry method, a wet method, or a combination thereof, but is not limited thereto, and the method for preparing the composite of Li2S and carbon in the art may be, for example, milling, heat treatment, deposition, etc., but is not necessarily limited thereto, and any method used in the art may be used.

[0099] The composite of Li2S, carbon, and a solid electrolyte comprises carbon and a solid electrolyte. Carbon refers to the composite of Li2S and carbon described above. The solid electrolyte may be any ion-conducting material used in the relevant technical field, for example, an amorphous solid electrolyte. The solid electrolyte is, for example, an inorganic solid electrolyte. The solid electrolyte is, for example, a crystalline solid electrolyte, an amorphous solid electrolyte, or a combination thereof. The solid electrolyte is, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a combination thereof. The sulfide-based solid electrolyte comprises, for example, Li, S, and P, and may optionally further comprise a halogen element. The sulfide-based solid electrolyte may be selected from among the sulfide-based solid electrolytes used in the solid electrolyte layer. The sulfide-based solid electrolyte may have, for example, a 1×10 -5 It can have an ionic conductivity of S / cm or more. Sulfide-based solid electrolytes include, for example, Li3PO4-Li2SO4, Li2S-P2S5, Li2S-P2S5-LiX, where X is a halogen element, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z. m S n , m, n are positive numbers, Z is one of Ge, Zn or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga In, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x, may include one or more selected from 0≤x≤2. The oxide-based solid electrolyte includes, for example, Li, O, and transition metal elements, and may optionally further include other elements. The oxide-based solid electrolyte may include, for example, 1×10 at room temperature. -5 It may be a solid electrolyte having an ionic conductivity of S / cm or more. The oxide-based solid electrolyte may be selected from oxide-based solid electrolytes used in the solid electrolyte layer. The solid electrolyte may be, for example, a mixture of a sulfide-based solid electrolyte and a lithium salt. For example, it may be a mixture of Li3PO4-Li2SO4 and a binary lithium salt, or a mixture of Li3PO4-Li2SO4 and a ternary lithium salt.

[0100] The composite of Li2S and a solid electrolyte includes a solid electrolyte. The solid electrolyte refers to the composite of Li2S, carbon, and a solid electrolyte described above.

[0101] A complex of Li2S and a lithium salt and carbon comprises a lithium salt compound and carbon. The lithium salt compound does not contain, for example, a sulfur (S) atom. The lithium salt compound can be, for example, a binary compound composed of lithium and one element selected from Groups 13 to 17 of the Periodic Table of Elements. The binary compound can include, for example, one or more selected from LiF, LiCl, LiBr, LiI, LiH, Li2S, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, LiI3, and LiB3. The lithium salt compound can be, for example, a ternary compound composed of lithium and two elements selected from Groups 13 to 17 of the Periodic Table of Elements. The ternary compound includes, for example, one or more selected from Li3OCl, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiNO3, Li2CO3, LiBH4, Li2SO4, Li3BO3, Li3PO4, Li4NCl, Li5NCl2, and Li3BN2. The lithium salt compound is particularly one or more lithium halide compounds selected from LiF, LiCl, LiBr, and LiI. Carbon refers to the complex of Li2S and carbon described above.

[0102] The composite of Li2S and metal carbide includes metal carbide. The metal carbide is, for example, a two-dimensional metal carbide. The two-dimensional metal carbide is, for example, MXene. The two-dimensional metal carbide is, for example, M n+1 C n T x (M is a transition metal, T is a terminal group, T is O, OH and / or F, n=1, 2, or 3, and x is the number of terminal groups) is expressed as 2D metal carbides, for example, Ti2CT x , (Ti 0.5 , Nb 0.5 )2CT x , Nb2CT x , V2CT x, Ti3C2T x , (V 0.5 , Cr 0.5 )3C2T x , Ti3CNT x , Ta4C3T x , Nb4C3T x or a combination thereof. The surface of the two-dimensional metal carbide is terminated with O, OH and / or F.

[0103] The complex of Li2S, carbon, and metal carbide includes carbon and metal carbide. Carbon refers to the complex of Li2S and carbon described above. Metal carbide refers to the complex of Li2S and metal carbide described above.

[0104] The complex of Li2S and metal nitride includes a metal nitride. The metal nitride is, for example, a two-dimensional metal nitride. The two-dimensional metal nitride is, for example, M n+1 N n T x (M is a transition metal, T is a terminal group, T is O, OH and / or F, n=1, 2, or 3, and x is the number of terminal groups) is expressed as The surface of the two-dimensional metal nitride is terminated with O, OH and / or F.

[0105] A complex of Li2S, carbon, and a metal nitride includes carbon and a metal nitride. Carbon refers to the complex of Li2S and carbon described above. Metal carbide refers to the complex of Li2S and a metal nitride described above.

[0106] The size of the cathode active material can be, for example, 0.1 to 50 μm, 0.5 to 30 μm, 0.5 to 20 μm, or 1 to 10 μm. The size of Li2S can be, for example, 1 nm to 10 μm, 10 nm to 5 μm, 10 nm to 3 μm, or 10 nm to 1 μm. The size of the Li2S-containing composite can be, for example, 0.1 to 50 μm, 0.5 to 30 μm, 0.5 to 20 μm, or 1 to 10 μm.

[0107] The cathode active material layer (12) may additionally include, for example, a sulfide-based compound that is distinct from the cathode active material described above. The sulfide-based compound may be, for example, a compound containing a metal element other than Li and the element sulfur. The sulfide-based compound may be, for example, a compound containing a metal element belonging to Groups 1 to 14 of the Periodic Table of Elements having an atomic weight of 10 or more and the element sulfur. The sulfide-based compound may be, for example, FeS2, VS2, NaS, MnS, FeS, NiS, CuS, or a combination thereof. By the cathode active material layer additionally including a sulfide-based compound, the cycle characteristics of the all-solid-state secondary battery may be further improved. The content of the sulfide-based compound included in the cathode active material layer (12) may be 10 wt% or less, 5 wt% or less, 3 wt% or less, or 1 wt% or less of the total weight of the cathode active material layer (12).

[0108] The shape of the positive electrode active material is, for example, a particle shape such as a sphere or an ellipse. The particle size of the positive electrode active material is not particularly limited and is within a range applicable to positive electrode active materials of a conventional all-solid-state secondary battery. The content of the positive electrode active material of the positive electrode layer (10) is also not particularly limited and is within a range applicable to positive electrode layers of a conventional all-solid-state secondary battery. The content of the positive electrode active material included in the positive electrode active material layer (12) may be, for example, 30 wt% to 99 wt%, 30 wt% to 90 wt%, 30 wt% to 80 wt%, 30 wt% to 70 wt%, or 30 wt% to 50 wt% of the total weight of the positive electrode active material layer (12).

[0109] [Polar: Challenger]

[0110] The cathode active material layer (12) may further include a conductive material. The conductive material may be, for example, a carbon-based conductive material, a metal-based conductive material, or a combination thereof. The carbon-based conductive material may be, for example, graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or a combination thereof, but is not limited thereto, and any material used as a carbon-based conductive material in the art may be used. The metal-based conductive material may be, for example, metal powder, metal fiber, or a combination thereof, but is not limited thereto, and any material used as a metal-based conductive material in the art may be used. The content of the conductive material included in the cathode active material layer (12) may be, for example, 1 wt% to 30 wt%, 1 wt% to 20 wt%, or 1 wt% to 10 wt% of the total weight of the cathode active material layer (12).

[0111] [Positive: Binder]

[0112] The positive electrode active material layer (12) may further include a binder. The binder may be, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., but is not limited thereto, and any binder used in the relevant technical field may be used. The binder content included in the positive electrode active material layer (12) may be, for example, 1 wt% to 10 wt% of the total weight of the positive electrode active material layer (12). The binder may be omitted.

[0113] [Positive: Other additives]

[0114] The cathode active material layer (12) may further include additives such as fillers, coating agents, dispersants, and ion conductive aids in addition to the cathode active material, solid electrolyte, binder, and conductive agent described above.

[0115] As fillers, coating agents, dispersants, ion conductivity aids, etc. that the positive electrode active material layer (12) may include, known materials generally used in electrodes of all-solid-state secondary batteries may be used.

[0116] [Anode: Anode current collector]

[0117] The positive electrode collector (11) uses a plate or foil made of, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof. The positive electrode collector (11) may be omitted. The thickness of the positive electrode collector (11) is, for example, 1 µm to 100 µm, 1 µm to 50 µm, 5 µm to 25 µm, or 10 µm to 20 µm.

[0118] The cathode current collector (11) 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. The base film may be, for example, an insulator. Since the base film includes an insulating thermoplastic polymer, when a short circuit occurs, the base film softens or liquefies, thereby blocking battery operation and suppressing a rapid increase in current. The metal layer may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), or an alloy thereof. The metal layer can act as an electrochemical fuse and be cut off in case of overcurrent to prevent a short circuit. The limit current and the maximum current can be controlled by adjusting the thickness of the metal layer. The metal layer can be plated or deposited on the base film. As the thickness of the metal layer decreases, the limit current and / or the maximum current of the positive electrode current collector (11) decreases, thereby improving the stability of the lithium battery in case of a short circuit. A lead tab can be added on the metal layer for connection to the outside. The lead tab can 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 the metal layer melt, so that the metal layer can be electrically connected to the lead tab. In order to strengthen the welding of the metal layer and the lead tab, a metal chip can be added between the metal layer and the lead tab.The metal piece may be a thin piece of the same material as the metal of the metal layer. The metal piece may be, for example, a metal foil, a metal mesh, etc. The metal piece may be, for example, aluminum foil, copper foil, SUS foil, etc. After the metal piece is placed on the metal layer, the lead tab may be welded to the metal piece / metal layer laminate or the metal piece / metal layer / base film laminate. During welding, the base film, the metal layer, and / or the metal piece may melt, so that the metal layer or the metal layer / metal piece laminate may be electrically connected to the lead tab. A metal chip and / or a lead tab may be added to a portion of the metal layer. The base film may have a thickness of, for example, 1 to 50 μm, 1.5 to 50 μm, 1.5 to 40 μm, or 1 to 30 μm. When the base film has a thickness in this range, the weight of the electrode assembly can be more effectively reduced. The melting point of the base film may be, for example, 100 to 300°C, 100 to 250°C or less, or 100 to 200°C. Since the base film has a melting point within this range, the base film can be melted and easily bonded to the lead tab during the welding process of the lead tab. To improve the adhesion between the base film and the metal layer, a surface treatment such as corona treatment may be performed on the base film. 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. Since the metal layer has a thickness within this range, conductivity can be maintained while ensuring the stability of the electrode assembly. The thickness of the metal piece may be, for example, 2 to 10 μm, 2 to 7 μm, or 4 to 6 μm. Since the metal piece has a thickness within this range, the connection between the metal layer and the lead tab can be performed more easily. By having this structure, the positive electrode collector (11) can reduce the weight of the positive electrode and consequently improve the energy density of the positive electrode and lithium battery.

[0119] [Anode: Inert member]

[0120] Referring to FIGS. 4 and 5, the positive electrode (10) may include a positive electrode current collector (11), and a carbon coating layer (not shown) may be disposed on one surface of the positive electrode current collector. The positive electrode active material layer (12) may be positioned on the carbon coating layer. An intermediate layer may be further disposed between the carbon coating layer and the positive electrode active material layer (12).

[0121] An inactive member (40) is disposed on one side of the positive electrode (10). Referring to FIG. 4, the inactive member (40) is disposed on one side of the positive electrode active material layer (12) and the positive electrode current collector (11). Referring to FIG. 5, the inactive member (40) is disposed on one side of the positive electrode active material layer (12) and between the solid electrolyte layer (30) and the positive electrode current collector (11) facing the solid electrolyte layer (30). The inactive member (40) is not disposed on one side of the positive electrode current collector (11).

[0122] By including an inert member (40), cracking of the electrolyte layer (30) is prevented during the manufacture and / or charging / discharging of the all-solid-state secondary battery (1), and as a result, the cycle characteristics of the all-solid-state secondary battery (2) are improved. In an all-solid-state secondary battery (1) that does not include an inert member (40), when the manufacture and / or charging / discharging of the all-solid-state secondary battery (1) is performed, uneven pressure is applied to the electrolyte layer (30) in contact with the positive electrode (10), which increases the possibility of cracking in the electrolyte layer (30), and thus, a short circuit may occur due to the growth of lithium metal through the crack.

[0123] In the all-solid-state secondary battery (1), the thickness of the inert member (40) is greater than or equal to the thickness of the positive electrode active material layer (12). Alternatively, in the all-solid-state secondary battery (1), the thickness of the inert member (40) is substantially equal to the thickness of the positive electrode (10). Since the thickness of the inert member (40) is equal to the thickness of the positive electrode (10), a uniform pressure is applied between the positive electrode (10) and the electrolyte layer (30), and the positive electrode (10) and the electrolyte layer (30) are sufficiently adhered to each other, so that the interfacial resistance between the positive electrode (10) and the electrolyte layer (30) can be reduced. In addition, since the electrolyte layer (30) is sufficiently sintered during the pressurized manufacturing process of the all-solid-state secondary battery (1), the internal resistance of the electrolyte layer (30) and the all-solid-state secondary battery (1) including the same is reduced.

[0124] The inert member (40) surrounds the side surface of the positive electrode (10) and is in contact with the electrolyte layer (30). Since the inert member (40) surrounds the side surface of the positive electrode (10) and is in contact with the electrolyte layer (30), cracks in the electrolyte layer (30) that occur due to a pressure difference during the pressing process in the electrolyte layer (30) that does not come into contact with the positive electrode (10) can be effectively suppressed. The inert member (40) surrounds the side surface of the positive electrode (10) and is separated from the negative electrode (20), more specifically, the first negative electrode active material layer (22). The inert member (40) surrounds the side surface of the positive electrode (10), is in contact with the electrolyte layer (30), and is separated from the negative electrode (20). Therefore, the possibility of a short circuit occurring due to physical contact between the positive electrode (10) and the first negative electrode active material layer (22) or a short circuit occurring due to overcharging of lithium, etc., is suppressed. For example, by placing an inert member (40) on one side of the positive electrode active material layer (12) and simultaneously on one side of the positive electrode current collector (11), the possibility of a short circuit occurring due to contact between the positive electrode current collector (11) and the negative electrode (20) is more effectively suppressed.

[0125] Referring to FIGS. 4 and 5, the inert member (40) extends from one side of the positive electrode (10) to the end of the electrolyte layer (30). By extending the inert member (40) to the end of the electrolyte layer (30), cracks occurring at the end of the electrolyte layer (30) can be suppressed. The end of the electrolyte layer (30) is the outermost part that is in contact with the side of the electrolyte layer (30). The inert member (40) extends to the outermost part that is in contact with the side of the electrolyte layer (30). The inert member (40) is separated from the negative electrode (20), more specifically, from the first negative electrode active material layer (22). The inert member (40) extends to the end of the electrolyte layer (30), but does not contact the negative electrode (20). The inert member (40) fills a space extending from, for example, one side of the anode (10) to the end of the electrolyte layer (30).

[0126] Referring to FIGS. 4 and 5, the width of the inert member (40) extending from one side of the positive electrode (10) to the end of the electrolyte layer (30) is, for example, 1 to 30%, 1 to 25%, 1 to 20%, 1 to 15%, 1 to 10%, or 1 to 5% of the width between one side of the positive electrode (10) and the other side opposite to the one side. If the width of the inert member (40) is excessively large, the energy density of the all-solid-state secondary battery (1) is reduced. If the width of the inert member (40) is excessively small, the effect of arranging the inert member (40) is minimal.

[0127] The area of ​​the anode (10) is smaller than the area of ​​the electrolyte layer (30) in contact with the anode (10). An inert member (40) is arranged to surround the side of the anode (10) to compensate for the area difference between the anode (10) and the electrolyte layer (30). By compensating for the difference between the area of ​​the anode (10) and the area of ​​the electrolyte layer (30), cracks in the electrolyte layer (30) caused by the pressure difference during the pressing process are effectively suppressed. For example, the sum of the area of ​​the anode (10) and the area of ​​the inert member (40) is equal to the area of ​​the electrolyte layer (30). The electrolyte layer (30) may be, for example, a solid electrolyte layer.

[0128] The area of ​​the anode (10) is, for example, less than 100%, 99% or less, 98% or less, 97% or less, 96% or less, or 95% or less of the area of ​​the electrolyte layer (30). The area of ​​the anode (10) is, for example, 50% to less than 100%, 50% to 99%, 55% to 98%, 60% to 97%, 70% to 96%, 80% to 95%, or 85% to 95% of the area of ​​the electrolyte layer (30).

[0129] If the area of ​​the positive electrode (10) is equal to or larger than the area of ​​the electrolyte layer (30), the possibility of a short circuit occurring due to physical contact between the positive electrode (10) and the first negative electrode active material layer (22) or overcharging of lithium increases. The area of ​​the positive electrode (10) is, for example, equal to the area of ​​the positive electrode active material layer (12). The area of ​​the positive electrode (10) is, for example, equal to the area (11) of the positive electrode current collector.

[0130] The area of ​​the inert member (40) is, for example, 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less of the area of ​​the anode (10). The area of ​​the inert member (40) is, for example, 1% to 50%, 5% to 40%, 5% to 30%, 5% to 20%, or 5% to 15% of the area of ​​the anode (10).

[0131] The area (S1) of the positive electrode (10) is smaller than the area (S4) of the negative electrode current collector (21). The area (S1) of the positive electrode (10) is, for example, less than 100%, 99% or less, 98% or less, 97% or less, 96% or less, or 95% or less of the area (S4) of the negative electrode current collector (21). The area (S1) of the positive electrode (10) is, for example, 50% to less than 100%, 50% to 99%, 55% to 98%, 60% to 97%, 70% to 96%, 80% to 95%, or 85% to 95% of the area (S4) of the negative electrode current collector (21). The area (S4) of the negative electrode current collector (21) is, for example, the same as the area of ​​the negative electrode (20). The area (S4) of the negative electrode current collector (21) is, for example, the same as the area of ​​the first negative electrode active material layer (22).

[0132] As used herein, “same” area, length, width, thickness, and / or shape includes all instances of having “substantially the same” area, length, width, thickness, and / or shape, except where the area, length, width, thickness, and / or shape are intentionally different from each other. “Same” area, length, width, and / or thickness includes a range where the unintentional difference in the area, length, width, and / or thickness of the compared objects is, for example, less than 3%, less than 2%, less than 1%, less than 0.5%, or less than 0.1%.

[0133] The thickness of the inert member (40) is, for example, greater than the thickness of the first negative electrode active material layer (22). The thickness of the first negative electrode active material layer (22) is, for example, 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less of the thickness of the inert member (40). The thickness of the first negative electrode active material layer (22) is, for example, 1% to 50%, 1% to 40%, 1% to 30%, 1% to 20%, or 1% to 10% of the thickness of the inert member (40).

[0134] The inert member (40) may be a gasket. By using a gasket as the inert member (40), cracks in the electrolyte layer (30) caused by a pressure difference during the pressing process can be effectively suppressed.

[0135] The inert member (40) has, for example, a single-layer structure. Alternatively, the inert member (40) may have a multi-layer structure. In the inert member (40) having a multi-layer structure, each layer may have a different composition. The inert member 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. The inert member (40) having a multi-layer structure may include, for example, one or more adhesive layers and one or more support layers. The adhesive layer effectively prevents, for example, a separation between the positive electrode (10) and the electrolyte layer (30) due to a change in the volume of the positive electrode (10) that occurs during the charge / discharge process of the all-solid-state secondary battery (10), and improves the film strength of the inert member (40) by providing a bonding force between the support layer and other layers. The support layer provides support to the inert member (40), prevents unevenness of pressure applied to the electrolyte layer (30) during the pressurization process or the charge / discharge process, and prevents deformation of the all-solid-state secondary battery (1) being manufactured.

[0136] The inert member (40) is, for example, a flame-retardant inert member. The flame-retardant inert member prevents thermal runaway and ignition of the all-solid-state secondary battery (1) by providing flame retardancy. Consequently, the safety of the all-solid-state secondary battery (1) is further improved. The flame-retardant inert member prevents deterioration of the all-solid-state secondary battery (1) by absorbing residual moisture within the all-solid-state secondary battery (1), thereby improving the lifespan characteristics of the all-solid-state secondary battery (1).

[0137] The flame-retardant inert member includes, for example, a matrix and a filler. The matrix includes, for example, a substrate and a reinforcing material. The matrix includes, for example, a fibrous substrate and a fibrous reinforcing material. Since the matrix includes the substrate, the matrix can have elasticity. Therefore, the matrix can effectively accommodate volume changes during charge and discharge of the all-solid-state secondary battery (1) and can be arranged at various positions. The substrate included in the matrix includes, for example, a first fibrous material. Since the substrate includes the first fibrous material, the volume changes of the positive electrode (30) occurring during charge and discharge of the all-solid-state secondary battery (1) can be effectively accommodated and deformation of the inert member (40) due to the volume changes of the positive electrode (30) can be effectively suppressed. The first fibrous material is, for example, a material having an aspect ratio of 5 or more, 20 or more, or 50 or more. The first fibrous material is, for example, a material having an aspect ratio of 5 to 1000, 20 to 1000, or 50 to 1000. The first fibrous material is, for example, an insulating material. Since the first fibrous material is an insulating material, a short circuit between the positive electrode (30) and the negative electrode (20) caused by lithium dendrites, etc., generated during the charge and discharge process of the all-solid-state secondary battery (1) can be effectively prevented. The first fibrous material includes, for example, at least one selected from pulp fibers, insulating polymer fibers, and ion-conductive polymer fibers. The strength of the matrix is ​​improved by the inclusion of a reinforcing material in the matrix. Therefore, the matrix can prevent excessive volume change during charge and discharge of the all-solid-state secondary battery (1) and deformation of the all-solid-state secondary battery. The reinforcing material included in the matrix includes, for example, a second fibrous material. Since the reinforcing material includes the second fibrous material, the strength of the matrix can be increased more uniformly. The second fibrous material is, for example, a material having an aspect ratio of 3 or more, 5 or more, or 10 or more.The first fibrous material is, for example, a material having an aspect ratio of 3 to 100, 5 to 100, or 10 to 100. The second fibrous material is, for example, a flame-retardant material. Since the second fibrous material is a flame-retardant material, ignition due to thermal runaway occurring during the charge / discharge process of the all-solid-state secondary battery (1) or due to external impact can be effectively suppressed. The second fibrous material is, for example, glass fiber, metal oxide fiber, ceramic fiber, etc.

[0138] The flame-retardant inert member includes a filler in addition to a matrix. The filler may be disposed within the matrix, on the surface of the matrix, or on both the interior and the surface. The filler is, for example, an inorganic material. The filler included in the flame-retardant inert member is, for example, a moisture getter. The filler removes moisture remaining in the all-solid-state secondary battery (1) by adsorbing moisture, for example, at a temperature below 100°C, thereby preventing deterioration of the all-solid-state secondary battery (1). In addition, when the temperature of the all-solid-state secondary battery (1) increases to 150°C or higher due to thermal runaway occurring during the charge / discharge process of the all-solid-state secondary battery (1) or an external impact, the filler releases the adsorbed moisture, thereby effectively suppressing ignition of the all-solid-state secondary battery (1). That is, the filler is, for example, a flame retardant. The filler is, for example, a metal hydroxide having moisture adsorption properties. The metal hydroxide contained in the filler is, for example, Mg(OH)2, Fe(OH)3, Sb(OH)3, Sn(OH)4, TI(OH)3, Zr(OH)4, Al(OH)3, or a combination thereof. The content of the filler contained in the flame-retardant inert member is, for example, 10 to 80 parts by weight, 20 to 80 parts by weight, 30 to 80 parts by weight, 40 to 80 parts by weight, 50 to 80 parts by weight, 60 to 80 parts by weight, or 65 to 80 parts by weight, based on 100 parts by weight of the flame-retardant inert member (4).

[0139] The flame-retardant inert member may further comprise, for example, a binder. The binder may comprise, for example, a curable polymer or a non-curable polymer. A curable polymer is a polymer that cures by heat and / or pressure. A curable polymer is, for example, a solid at room temperature. The flame-retardant inert member may comprise, for example, a thermo-pressure curable film and / or a cured product thereof. An example of a thermo-pressure curable polymer is TSA-66 from Toray.

[0140] The flame-retardant inert member may additionally include other materials in addition to the above-described substrate, reinforcing material, filler, and binder. The flame-retardant inert member may further include one or more selected from among paper, an insulating polymer, an ion-conducting polymer, an insulating inorganic material, an oxide-based solid electrolyte, and a sulfide-based solid electrolyte. The insulating polymer may be, for example, an olefin-based polymer such as polypropylene (PP) or polyethylene (PE).

[0141] The density of the substrate or the density of the reinforcing material included in the flame-retardant inert member may be, for example, 10% to 300%, 10% to 150%, 10% to 140%, 10% to 130%, or 10% to 120% of the density of the positive electrode active material included in the positive electrode active material layer (12).

[0142] The inert member (40) is a member that does not contain an electrochemically active material, for example, an electrode active material. The electrode active material is a material that absorbs / releases lithium. The inert member (40) is a member made of a material other than the electrode active material and used in the relevant technical field.

[0143] [cathode]

[0144] [Cathode: Cathode active material]

[0145] Referring to FIGS. 1 to 5, the negative electrode (20) includes a negative electrode current collector (21) and a first negative electrode active material layer (22) disposed on one surface of the negative electrode current collector (21).

[0146] The first negative electrode active material layer (22) is, for example, a metal layer, and the metal layer may include lithium or a lithium alloy.

[0147] Alternatively, the first negative electrode active material layer (22) may include, for example, a negative electrode active material and a binder.

[0148] The negative electrode active material included in the first negative electrode active material layer (22) is, for example, a negative electrode material that can form an alloy or compound with lithium.

[0149] The negative electrode active material included in the first negative electrode active material layer (22) has, for example, a particle form. The average particle diameter of the negative electrode active material having a particle form is, for example, 4 ㎛ or less, 3 ㎛ or less, 2 ㎛ or less, 1 ㎛ or less, 500 nm or less, 300 nm or less, or 100 nm or less. The average particle diameter of the negative electrode active material having a particle form is, for example, 10 nm to 4 ㎛, 10 nm to 3 ㎛, 10 nm to 2 ㎛, 10 nm to 1 ㎛, 10 nm to 500 nm, 10 nm to 300 nm, or 10 nm to 100 nm. When the negative electrode active material has an average particle diameter in this range, reversible absorption and / or desorption of lithium can be facilitated during charge and discharge. The average particle size of the negative electrode active material is, for example, the median diameter (D50) measured using a laser particle size distribution meter.

[0150] The negative electrode active material included in the first negative electrode active material layer (22) includes, for example, at least one selected from among a carbon-based negative electrode active material and a metal or semi-metal negative electrode active material.

[0151] Carbon-based negative electrode materials include, for example, amorphous carbon, crystalline carbon, porous carbon, or a combination thereof.

[0152] The carbon-based negative electrode material is, in particular, amorphous carbon. Amorphous carbon includes, but is not limited to, carbon black (CB), acetylene black (AB), furnace black (FB), ketjen black (KB), and graphene, and any material classified as amorphous carbon in the relevant technical field is acceptable. Amorphous carbon is carbon that has no crystallinity or very low crystallinity, and is distinguished from crystalline carbon or graphite-based carbon.

[0153] The carbon-based negative electrode active material may be, for example, porous carbon. The porous carbon has a pore volume of, for example, 0.1 cc / g to 10.0 cc / g, 0.5 cc / g to 5 cc / g, or 0.1 cc / g to 1 cc / g. The porous carbon has an average pore diameter of, for example, 1 nm to 50 nm, 1 nm to 30 nm, or 1 nm to 10 nm. The porous carbon has a BET surface area of, for example, 100 m 2 / g to 3000 m 2 / g is.

[0154] The metal or metalloid negative electrode active material includes, but is not limited to, one or more 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), and any metal or metalloid negative electrode active material that forms an alloy or compound with lithium in the relevant technical field may be used. For example, nickel (Ni) does not form an alloy with lithium and therefore is not a metal negative electrode active material.

[0155] The first negative electrode active material layer (22) includes a type of negative electrode active material among these negative electrode active materials, or includes a mixture of a plurality of different negative electrode active materials. For example, the first negative electrode active material layer (22) includes only amorphous carbon, or includes at least one 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). Alternatively, the first negative electrode active material layer (22) includes a mixture of amorphous carbon and at least one 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 mixing ratio of the mixture of amorphous carbon and gold, etc., is a weight ratio, for example, 99:1 to 1:99, 10:1 to 1:2, 5:1 to 1:1, or 4:1 to 2:1, but is not necessarily limited to this range and is selected according to the required characteristics of the all-solid-state secondary battery (1). When the negative electrode active material has this composition, the cycle characteristics of the all-solid-state secondary battery (1) are further improved.

[0156] The negative electrode active material included in the first negative electrode active material layer (22) includes, for example, a mixture of first particles made of amorphous carbon and second particles made of a metal or a metalloid. The metal or metalloid includes, for example, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). Alternatively, the metalloid is a semiconductor. The content of the second particles is 1 to 99 wt%, 1 to 60 wt%, 8 to 60 wt%, 10 to 50 wt%, 15 to 40 wt%, or 20 to 30 wt% based on the total weight of the mixture. When the second particles have a content in this range, the cycle characteristics of, for example, an all-solid-state secondary battery (1) are further improved.

[0157] Alternatively, the first negative electrode active material layer (22) includes a composite negative electrode active material. The composite negative electrode active material may include, for example, a carbon-based support and a metal-based negative electrode active material supported on the carbon-based support. Since the composite negative electrode active material has such a structure, the metal-based negative electrode active material can be prevented from being localized within the first negative electrode active material layer and a uniform distribution can be achieved. As a result, the cycle characteristics of the all-solid-state secondary battery (1) including the first negative electrode active material layer (22) are further improved.

[0158] The metal-based negative electrode active material supported on the carbon-based support includes, for example, a metal, a metal oxide, a composite of a metal and a metal oxide, or a combination thereof. The metal includes, for example, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), tellurium (Te), and zinc (Zn). The metal oxide includes, for example, gold (Au) oxide, platinum (Pt) oxide, palladium (Pd) oxide, silicon (Si) oxide, silver (Ag) oxide, aluminum (Al) oxide, bismuth (Bi) oxide, tin (Sn) oxide, tellurium (Te) oxide, and zinc (Zn) oxide. The metal oxide includes, for example, Au x O y (0 <x≤2, 0<y≤3), Pt x O y (0 <x≤1, 0<y≤2), Pd x O y (0 <x≤1, 0<y≤1), Si x O y (0 <x≤1, 0<y≤2), Ag x O y (0 <x≤2, 0<y≤1), Al x O y (0 <x≤2, 0<y≤3), Bi x O y (0 <x≤2, 0<y≤3), Sn x O y (0 <x≤1, 0<y≤2), Te x O y (0 <x≤1, 0<y≤3), Zn x O y (0 <x≤1, 0<y≤1) 또는 이들의 조합을 포함할 수 있다. 금속과 금속산화물의 복합체는 예를 들어 Au와 Au x O y (0 <x≤2, 0<y≤3)의 복합체, Pt와 Pt x O y (0 <x≤1, 0<y≤2)의 복합체, Pd와 Pd x O y(0 <x≤1, 0<y≤1)의 복합체, Si와 Si x O y (0 <x≤1, 0<y≤2)의 복합체, Ag 와 Ag x O y (0 <x≤2, 0<y≤1)의 복합체, Al과 Al x O y (0 <x≤2, 0<y≤3)의 복합체, Bi와 Bi x O y (0 <x≤2, 0<y≤3)의 복합체, Sn과 Sn x O y (0 <x≤1, 0<y≤2)의 복합체, Te과 Te x O y (0 <x≤1, 0<y≤3), Zn과 Zn x O y (0 <x≤1, 0<y≤1)의 복합체, 또는 이들의 조합을 포함할 수 있다.

[0159] The carbonaceous support is, for example, amorphous carbon. Amorphous carbon includes, but is not limited to, carbon black (CB), acetylene black (AB), furnace black (FB), ketjen black (KB), graphene, activated carbon, carbon nanofibers (CNF), carbon nanotubes (CNT), etc., and any material classified as amorphous carbon in the relevant technical field is possible. Amorphous carbon is carbon that has no crystallinity or very low crystallinity, and is distinguished from crystalline carbon or graphite carbon. Carbonaceous materials are, for example, carbonaceous negative electrode active materials.

[0160] The composite negative electrode active material may have, for example, a particle form. The particle size of the composite negative electrode active material having a particle form is, for example, 10 nm to 4 ㎛, 10 nm to 1 ㎛, 10 nm to 500 nm, 10 nm to 200 nm, or 10 nm to 100 nm. When the composite negative electrode active material has a particle size in this range, reversible absorption and / or desorption of lithium may be facilitated during charge and discharge. The metal-based negative electrode active material supported on the support may have, for example, a particle form. The particle size of the metal-based negative electrode active material may be, for example, 1 nm to 200 nm, 1 nm to 150 nm, 5 nm to 100 nm, or 10 nm to 50 nm. The carbon-based support may have, for example, a particle form. The particle size of the carbon-based support may be, for example, 10 nm to 2 ㎛, 10 nm to 1 ㎛, 10 nm to 500 nm, 10 nm to 200 nm, or 10 nm to 100 nm. By having a particle size in this range, the carbon-based support can be more uniformly arranged within the first negative electrode active material layer. The carbon-based support may be, for example, nanoparticles having a particle size of 500 nm or less. The particle sizes of the composite negative electrode active material, the particle sizes of the metal-based negative electrode active material, and the particle sizes of the carbon-based support are, for example, average particle sizes. The average particle size is, for example, the median diameter (D50) measured using a laser particle size distribution analyzer. Alternatively, the average particle size may be determined automatically using software, for example, from an electron microscope image, or manually by a manual method.

[0161] [Cathode: Binder]

[0162] The binder included in the first negative electrode active material layer (22) is, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, etc., but is not necessarily limited thereto and any binder used in the relevant technical field may be used. The binder may be composed of a single binder or a plurality of different binders.

[0163] Since the first negative electrode active material layer (22) includes a binder, the first negative electrode active material layer (22) is stabilized on the negative electrode current collector (21). In addition, cracking of the first negative electrode active material layer (22) is suppressed despite changes in the volume and / or relative position of the first negative electrode active material layer (22) during the charge and discharge process. For example, if the first negative electrode active material layer (22) does not include a binder, the first negative electrode active material layer (22) can be easily separated from the negative electrode current collector (21). As the first negative electrode active material layer (22) is separated from the negative electrode current collector (21), the possibility of a short circuit occurring increases as the negative electrode current collector (21) comes into contact with the electrolyte layer (30) at the exposed portion of the negative electrode current collector (21). The first negative electrode active material layer (22) is manufactured by, for example, applying a slurry in which the material constituting the first negative electrode active material layer (22) is dispersed onto the negative electrode current collector (21) and drying the slurry. By including a binder in the first negative electrode active material layer (22), stable dispersion of the negative electrode active material in the slurry is possible. For example, when applying the slurry onto the negative electrode current collector (21) by screen printing, it is possible to suppress clogging of the screen (for example, clogging by aggregates of the negative electrode active material).

[0164] [Cathode: Other additives]

[0165] The first negative electrode active material layer (22) may further include additives used in a conventional all-solid-state secondary battery (1), such as fillers, coating agents, dispersants, and ion conductive aids.

[0166] [Cathode: Solid electrolyte]

[0167] The first negative electrode active material layer (22) may further include a solid electrolyte. The solid electrolyte may be, for example, a material selected from among the solid electrolytes included in the electrolyte layer (30). The solid electrolyte included in the first negative electrode active material layer (22) may act as a reaction site where lithium metal formation begins within the first negative electrode active material layer (22), a space where the formed lithium metal is stored, or a path for transferring lithium ions. The solid electrolyte may be omitted.

[0168] In the first negative electrode active material layer (22), the content of the solid electrolyte may be high, for example, in an area adjacent to the electrolyte layer (30), and low, for example, in an area adjacent to the negative electrode current collector (21). In the first negative electrode active material layer (22), the solid electrolyte may have a concentration gradient in which the concentration decreases, for example, from an area adjacent to the electrolyte layer (30) to an area adjacent to the negative electrode current collector (21).

[0169] [Cathode: First negative electrode active material layer]

[0170] The ratio (B / A) of the initial charge capacity (B) of the first negative electrode active material layer (22) and the initial charge capacity (A) of the positive electrode active material layer is 0.005 to 0.45. The initial charge capacity of the positive electrode active material layer (12) is the first open circuit voltage (1 st Li / Li from open circuit voltage) + The initial charge capacity of the first negative electrode active material layer (22) is determined at the maximum charging voltage. The initial charge capacity of the first negative electrode active material layer (22) is determined at the second open circuit voltage (2 nd Li / Li from open circuit voltage) + It is determined at 0.01 V.

[0171] The maximum charging voltage is determined by the type of cathode active material. The maximum charging voltage can be, for example, 1.5 V, 2.0 V, 2.5 V, 3.0 V, 3.5 V, 4.0 V, 4.2 V, or 4.3 V. For example, the maximum charging voltage of Li2S or Li2S composite is Li / Li + It can be 2.5 V or 3.0 V. The ratio (B / A) of the initial charge capacity (B) of the first negative electrode active material layer (22) and the initial charge capacity (A) of the positive electrode active material layer (12) is, for example, 0.01 to 0.3, 0.01 to 0.2, or 0.05 to 0.1. The initial charge capacity (mAh) of the positive electrode active material layer (12) is obtained by multiplying the charge capacity density (charge specific capacity) (mAh / g) of the positive electrode active material by the mass (g) of the positive electrode active material in the positive electrode active material layer (12). When several types of positive electrode active materials are used, the charge capacity density × mass value is calculated for each positive electrode active material, and the sum of these values ​​is the initial charge capacity of the positive electrode active material layer (12). The initial charge capacity of the first negative electrode active material layer (22) is also calculated in the same way. The initial charge capacity of the first negative electrode active material layer (22) is obtained by multiplying the charge capacity density (mAh / g) of the negative electrode active material by the mass of the negative electrode active material in the first negative electrode active material layer (22). When several types of negative electrode active materials are used, the charge capacity density Х mass value is calculated for each negative electrode active material, and the sum of these values ​​is the initial charge capacity of the first negative electrode active material layer (22). The charge capacity density of each of the positive electrode active material and the negative electrode active material can be measured using a solid half-cell using lithium metal as a counter electrode. The initial charge capacity of each of the positive electrode active material layer (12) and the first negative electrode active material layer (22) is obtained by multiplying the charge capacity density (mAh / g) of the negative electrode active material by the mass value of the negative electrode active material in the first negative electrode active material layer (22). 2can be directly measured using a solid-state half-cell. For the positive electrode, the measurement is made from the first open circuit voltage (OCV) to the maximum charge voltage, e.g., 3.0 V (vs. Li / Li + ) can be performed for an operating voltage of up to 0.01 V for the cathode, for example, lithium metal, from the second open circuit voltage (OCV). For example, a solid-state half-cell having a cathode active material layer (12) can be measured for an operating voltage of up to 0.1 mA / cm from the first open circuit voltage to 3.0 V. 2 The solid half-cell having the first negative active material layer is charged with a constant current of 0.1 mA / cm from the second open circuit voltage to 0.01 V. 2 It can be charged with a constant current. The current density during constant current charging is, for example, 0.2 mA / cm 2 , or 0.5 mA / cm 2 A solid-state battery having a positive electrode active material layer (12) can be charged from a first open circuit voltage to, for example, 2.5 V, 2.0 V, 3.5 V, or 4.0 V. The maximum charge voltage of the positive electrode active material layer can be determined by the maximum voltage of the battery that satisfies the safety conditions according to JISC8712:2015 of the Japanese Standards Association.

[0172] If the initial charge capacity of the first negative electrode active material layer (22) is too small, the thickness of the first negative electrode active material layer (22) becomes very thin, so that lithium dendrites formed between the first negative electrode active material layer (22) and the negative electrode current collector (21) during repeated charge and discharge processes collapse the first negative electrode active material layer (22), making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1). If the charge capacity of the first negative electrode active material layer (22) increases excessively, the energy density of the all-solid-state secondary battery (1) decreases and the internal resistance of the all-solid-state secondary battery (1) due to the first negative electrode active material layer (22) increases, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1).

[0173] The thickness of the first negative electrode active material layer (22) is, 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 (12). The thickness of the first negative electrode active material layer (22) is, for example, 1 to 50%, 1 to 40%, 1 to 30%, 1 to 20%, 1 to 10%, or 1 to 5% of the thickness of the positive electrode active material layer (12). The thickness of the first negative electrode active material layer (22) is, for example, 1 µm to 20 µm, 2 µm to 15 µm, or 3 µm to 10 µm. If the thickness of the first negative electrode active material layer (22) is too thin, lithium dendrites formed between the first negative electrode active material layer (22) and the negative electrode current collector (21) collapse the first negative electrode active material layer (22), making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1). If the thickness of the first negative electrode active material layer (22) increases excessively, the energy density of the all-solid-state secondary battery (1) decreases and the internal resistance of the all-solid-state secondary battery (1) due to the first negative electrode active material layer (22) increases, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1). If the thickness of the first negative electrode active material layer (22) decreases, for example, the initial charge capacity of the first negative electrode active material layer (22) also decreases.

[0174] [Cathode: Second negative electrode active material layer]

[0175] Referring to FIG. 4, the all-solid-state secondary battery (1) further includes, after being charged, a second negative electrode active material layer (24) disposed, for example, between the negative electrode current collector (21) and the first negative electrode active material layer (22). The second negative electrode active material layer (24) is a metal layer containing lithium or a lithium alloy. The metal layer contains lithium or a lithium alloy. Therefore, since the second negative electrode active material layer (24) is a metal layer containing lithium, it functions as, for example, a lithium reservoir. The lithium alloy is, 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, etc., but is not limited thereto, and any lithium alloy used in the art may be used. The second negative electrode active material layer (24) may be made of one of these alloys or lithium, or may be made of several types of alloys. The second negative electrode active material layer (24) is, for example, a plated layer. The second negative electrode active material layer (24) is deposited between the first negative electrode active material layer (22) and the negative electrode current collector (21), for example, during the charging process of an all-solid-state secondary battery (1).

[0176] The thickness of the second negative electrode active material layer (24) is not particularly limited, but is, for example, 1 ㎛ to 500 ㎛, 1 ㎛ to 200 ㎛, 1 ㎛ to 150 ㎛, 1 ㎛ to 100 ㎛, or 1 ㎛ to 50 ㎛. If the thickness of the second negative electrode active material layer (24) is too thin, it is difficult for the second negative electrode active material layer (24) to perform the role of a lithium reservoir. If the thickness of the second negative electrode active material layer (24) is too thick, the mass and volume of the all-solid-state secondary battery (1) may increase, and the cycle characteristics of the all-solid-state secondary battery (1) may rather deteriorate.

[0177] Alternatively, in the all-solid-state secondary battery (1), the second negative electrode active material layer (24) may be disposed between the negative electrode current collector (21) and the first negative electrode active material layer (22), for example, before assembling the all-solid-state secondary battery (1). When the second negative electrode active material layer (24) is disposed between the negative electrode current collector (21) and the first negative electrode active material layer (22) before assembling the all-solid-state secondary battery (1), the second negative electrode active material layer (24) 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 (21) and the first negative electrode active material layer (22) before assembling the all-solid-state secondary battery (1).

[0178] When the second negative electrode active material layer (24) is precipitated by charging after assembling the all-solid-state secondary battery (1), the energy density of the all-solid-state secondary battery (1) increases because the second negative electrode active material layer (24) is not included when assembling the all-solid-state secondary battery (1). When charging the all-solid-state secondary battery (1), the charging is performed in excess of the charging capacity of the first negative electrode active material layer (22). That is, the first negative electrode active material layer (22) is overcharged. At the initial stage of charging, lithium is absorbed into the first negative electrode active material layer (22). The negative electrode active material included in the first negative electrode active material layer (22) forms an alloy or compound with the lithium ions that have moved from the positive electrode (10). When charging exceeds the capacity of the first negative electrode active material layer (22), for example, lithium is deposited on the back surface of the first negative electrode active material layer (22), that is, between the negative electrode current collector (21) and the first negative electrode active material layer (22), and a metal layer corresponding to the second negative electrode active material layer (24) is formed by the deposited lithium. The second negative electrode active material layer (24) is a metal layer mainly composed of lithium (i.e., metallic lithium). This result is obtained, for example, by the negative electrode active material included in the first negative electrode active material layer (22) including a material that forms an alloy or compound with lithium. During discharge, lithium in the first negative electrode active material layer (22) and the second negative electrode active material layer (24), that is, the metal layer, is ionized and moves toward the positive electrode (10). Therefore, it is possible to use lithium as the negative electrode active material in an all-solid-state secondary battery (1). In addition, since the first negative electrode active material layer (22) covers the second negative electrode active material layer (24), it acts as a protective layer for the second negative electrode active material layer (24), i.e., the metal layer, and at the same time, it suppresses the precipitation and growth of lithium dendrites. Accordingly, it suppresses short circuits and capacity reduction of the all-solid-state secondary battery (1), and consequently improves the cycle characteristics of the all-solid-state secondary battery (1).In addition, when the second negative electrode active material layer (24) is placed by charging after assembling the all-solid-state secondary battery (1), the negative electrode (20), i.e., the negative electrode current collector (21) and the first negative electrode active material layer (22) and the region between them are Li-free regions that do not contain lithium (Li) in the initial state or the state after complete discharge of the all-solid-state secondary battery (1).

[0179] [Cathode: Negative current collector]

[0180] The negative electrode current collector (21) is composed of, for example, a material that does not react with lithium, i.e., does not form an alloy or a compound. The material constituting the negative electrode current collector (21) is, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni), but is not necessarily limited thereto, and any material that can be used as an electrode current collector in the relevant technical field can be used. The negative electrode current collector (21) may be composed of one type of the above-described metal, or may be composed of an alloy or a coating material of two or more types of metals. The negative electrode current collector (21) is, for example, in the form of a plate or foil.

[0181] Referring to FIG. 3, the all-solid-state secondary battery (1) may further include a thin film (23) containing an element capable of forming an alloy with lithium on one surface of the negative electrode collector (21). The thin film (23) is disposed between the negative electrode collector (21) and the first negative electrode active material layer (22). The thin film (23) contains, 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 (23) is composed of one of these metals or an alloy of several types of metals. By placing the thin film (23) on one surface of the negative electrode current collector (21), for example, the deposition shape of the second negative electrode active material layer (24) deposited between the thin film (23) and the first negative electrode active material layer (22) becomes flatter, and the cycle characteristics of the all-solid-state secondary battery (1) can be further improved.

[0182] The thickness of the thin film (23) is, 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 (23) is less than 1 nm, it may be difficult for the function of the thin film (23) to be exerted. If the thickness of the thin film (23) is excessively thick, the thin film (23) itself absorbs lithium, which reduces the amount of lithium precipitation from the negative electrode (20), thereby lowering the energy density of the solid-state battery and deteriorating the cycle characteristics of the all-solid-state secondary battery (1). The thin film (23) may be disposed on the negative electrode current collector (21) by, for example, a vacuum deposition method, a sputtering method, a plating method, or the like, but is not necessarily limited to these methods, and any method capable of forming the thin film (23) in the relevant technical field may be used.

[0183] Although not shown in the drawing, the negative electrode current collector (21) 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. The polymer may be an insulating polymer. Since the base film includes an insulating thermoplastic polymer, when a short circuit occurs, the base film may soften or liquefy, thereby blocking battery operation and suppressing a rapid increase in current. The metal layer may include, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), or an alloy thereof. The negative electrode current collector (21) may additionally include a metal piece and / or a lead tab. For more specific details regarding the base film, metal layer, metal chip, and lead tab of the negative electrode collector (21), refer to the positive electrode collector (11) described above. By having this structure, the negative electrode collector (21) can reduce the weight of the negative electrode (20), and consequently, improve the energy density of the negative electrode and lithium battery.

[0184] [Solid electrolyte layer]

[0185] [Solid electrolyte layer: electrolyte]

[0186] Referring to FIGS. 1 to 5, a solid electrolyte layer (30) is disposed between the positive electrode (10) and the negative electrode (20). The solid electrolyte layer (30) may further include, for example, a solid electrolyte, a gel electrolyte, or a combination thereof.

[0187] The solid electrolyte contained in the solid electrolyte layer (30) is a sulfide-based solid electrolyte.

[0188] The above sulfide-based solid electrolyte is 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 and 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 , 0≤x≤2, is at least one selected from. And the sulfide-based solid electrolyte includes an argyrodite-type solid electrolyte, and the argyrodite-type solid electrolyte includes at least one selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I. And the density of the argyrodite-type solid electrolyte is 1.5 to 2.0 g / cc, and the sulfide-based solid electrolyte is in the form of particles, and the average particle diameter (D50) of the particles is 0.1 ㎛ to 1.9 ㎛.

[0189] The sulfide-based solid electrolyte may include, for example, an argyrodite type solid electrolyte represented by the following chemical formula 1:

[0190] <Chemical Formula 1>

[0191] Li+ 12-n-x A n+ X 2- 6-x Y - x

[0192] In the above formula, A is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb or Ta, X is S, Se or Te, Y is Cl, Br, I, F, CN, OCN, SCN or N3, and 1≤n≤5, 0≤x≤2. The sulfide-based solid electrolyte is, for example, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x , may be an argyrodite-type compound including at least one selected from 0≤x≤2. The sulfide-based solid electrolyte may be, for example, an argyrodite-type compound including at least one selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0193] The density of the argyrodite-type solid electrolyte may be 1.5 to 2.0 g / cc. Since the argyrodite-type solid electrolyte has a density of 1.5 g / cc or more, the internal resistance of the all-solid-state secondary battery is reduced, and penetration of the solid electrolyte layer by Li can be effectively suppressed.

[0194] The solid electrolyte additionally included in the solid electrolyte layer (30) may include, for example, an oxide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof.

[0195] Oxide solid electrolytes include, for example, Li 1+x+y Al xTi 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), or a combination thereof. The oxide-based solid electrolyte is manufactured, for example, by a sintering method.

[0196] Oxide-based solid electrolytes include, for example, 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) 고체전해질이다.

[0197] The polymer solid electrolyte may, for example, comprise a mixture of a lithium salt and a polymer, or a polymer having ion-conducting functional groups. The polymer solid electrolyte may, for example, be a polymer electrolyte that is solid at 25°C and 1 atm. The polymer solid electrolyte may, for example, not comprise a liquid.The polymer solid electrolyte comprises a polymer, and the polymer is, for example, polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), 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), polymethyl methacrylate (PMMA, poly(methylmethacrylate), 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), poly(styrene sulfonate) (PSS), lithium 9,10-Diphenylanthracene-2-sulfonate (lithium 9,10-diphenylanthracene-2-sulfonate, DPASLi. +) or a combination thereof, but is not limited thereto, and any lithium salt that can be used in polymer electrolytes in the relevant technical field is possible. The lithium salt can be any lithium salt that can be used in the relevant technical field. The lithium salt is, for example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are each 1 to 20), LiCl, LiI or a mixture thereof, etc. The polymer included in the polymer solid electrolyte may be, for example, a compound including 10 or more, 20 or more, 50 or more, or 100 or more repeating units. The weight average molecular weight of the polymer included in the polymer solid electrolyte may be, for example, 1000 Dalton or more, 10,000 Dalton or more, 100,000 Dalton or more, or 1,000,000 Dalton or more. In the present disclosure, the weight average molecular weight may be measured by gel permeation chromatography.

[0198] According to one embodiment, the electrolyte layer further includes a liquid electrolyte, a solid electrolyte, a gel electrolyte, or a combination thereof. The gel electrolyte is, for example, a polymer gel electrolyte. The gel electrolyte may, for example, be in a gel state without including a polymer.

[0199] A polymer gel electrolyte may include, for example, a liquid electrolyte and a polymer, or an organic solvent and a polymer having an ion-conducting functional group. The polymer gel electrolyte may be, for example, a polymer electrolyte that is in a gel state at 25°C and 1 atm. The polymer gel electrolyte may, for example, have a gel state without containing a liquid. The liquid electrolyte used in the polymer gel electrolyte may be, for example, an ionic liquid, a mixture of a lithium salt and an organic solvent; a mixture of a lithium salt and an organic solvent; a mixture of an ionic liquid and an organic solvent; or a mixture of a lithium salt, an ionic liquid, and an organic solvent. The polymer used in the polymer gel electrolyte may be selected from among the polymers used in solid polymer electrolytes. The organic solvent may be selected from among the organic solvents used in liquid electrolytes. The lithium salt may be selected from among the lithium salts used in solid polymer electrolytes. An ionic liquid refers to a salt that has a melting point below room temperature, is composed solely of ions, and is liquid at room temperature or a molten salt at room temperature. The ionic liquid may include, for example, one or more cations selected from among a) ammonium compounds, pyrrolidinium compounds, pyridinium compounds, pyrimidinium compounds, imidazolium compounds, piperidinium compounds, pyrazolium compounds, oxazolium compounds, pyridazinium compounds, phosphonium compounds, sulfonium compounds, triazolium compounds, and mixtures thereof, and b) one or more anions selected from among BF4-, PF6-, AsF6-, SbF6-, AlCl4-, HSO4-, ClO4-, CH3SO3-, CF3CO2-, Cl-, Br-, I-, SO4-, CF3SO3-, (FSO2)2N-, (C2F5SO2)2N-, (C2F5SO2)(CF3SO2)N-, and (CF3SO2)2N-. A polymer solid electrolyte can form a polymer gel electrolyte, for example, by being impregnated into a liquid electrolyte in a secondary battery. The polymer gel electrolyte may further include inorganic particles. The polymer included in the polymer gel 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 of the polymer included in the polymer gel electrolyte may be, for example, 500 Dalton or more, 1000 Dalton or more, 10,000 Dalton or more, 100,000 Dalton or more, or 1,000,000 Dalton or more.

[0200] [Method for manufacturing an all-solid-state secondary battery]

[0201] A method for manufacturing an all-solid-state secondary battery according to an embodiment of the present invention includes the steps of providing Li2S or a composite thereof; providing a sulfide-based solid electrolyte; preparing a mixture by mixing the Li2S composite, a gamma sulfur-carbon nanofiber composite, and the sulfide-based solid electrolyte; and preparing a positive electrode by coating and drying the mixture on a positive electrode current collector.

[0202] The gamma-sulfur-carbon nanofiber composite is obtained according to the manufacturing method disclosed in U.S. Patent Publication No. 2020 / 0313188. For example, stable monoclinic gamma-sulfur is deposited on a porous material substrate via vapor deposition in a sealed deposition device at a temperature sufficient to vaporize sulfur and for a time sufficient to provide monoclinic gamma-sulfur (γ-S), and then cooled to a temperature of 0 to 50°C.

[0203] The Li2S complex provides a complex of Li2S and a lithium salt or a complex of Li2S, a lithium salt, and a carbon-based material. The complex of Li2S and a lithium salt can be prepared, for example, by mechanically milling Li2S and a lithium salt. The milling conditions are not particularly limited, and any conditions that can form a complex of Li2S and a lithium salt can be used. The complex of Li2S and a lithium salt can be prepared by placing Li2S particles and a lithium salt in a ball mill and stirring at a speed of 100 to 1000 rpm for 1 to 20 hours. The stirring can be performed more than once.

[0204] As lithium salts, for example, LiI, LiBr, LiCl, LiF, LiH, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, Li3Al2, LiB3, Li3OCl, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiNO3, Li2CO3, LiBH4, Li2SO4, Li3BO3, Li3PO4, Li4NCl, Li5NCl2, Li3BN2 or combinations thereof can be used.

[0205] A composite of Li2S, a lithium salt, and a carbon-based material can be manufactured, for example, through a step of mechanically milling Li2S and a lithium salt; a step of adding a carbon-based material to the milled product, and milling the same.

[0206] A sulfide-based solid electrolyte is provided. A mixture is prepared by mixing a Li2S-lithium salt complex and the sulfide-based solid electrolyte.

[0207] The mixing ratio of the Li2S complex and the sulfide-based solid electrolyte may be, for example, a weight ratio of 50:50 to 95:5, 50:50 to 90:10, 50:50 to 80:20, or 50:50 to 70:30.

[0208] The mixture may additionally include a process solvent. By additionally including a process solvent, the mixture may take the form of a slurry. The solvent may be, for example, octyl acetate, but is not limited thereto, and any solvent used in the art may be used. Alternatively, the mixture may be prepared dry without including a process solvent.

[0209] Mechanical milling can be used in the above milling. A ball mill, etc. can be used in the mechanical milling.

[0210] After the step of placing a solid electrolyte layer between the positive and negative electrodes, a step of obtaining a battery assembly and pressurizing it may be performed.

[0211] Pressurization is not limited to a roll press, a flat press, etc., but any pressurization method used in the relevant technical field may be used. The pressurization step may be omitted.

[0212] Pressurization is performed at a temperature of, for example, room temperature (20°C to 25°C) to 90°C. Alternatively, pressurization is performed at a high temperature of 100°C or higher. The pressurization time is, for example, 30 minutes or less, 20 minutes or less, 15 minutes or less, or 10 minutes or less. The pressurization time is 1 ms to 30 minutes, 1 ms to 20 minutes, 1 ms to 15 minutes, or 1 ms to 10 minutes. The pressurization method is, for example, isotactic press, roll press, flat press, etc., but is not necessarily limited to these methods and any pressurization method used in the art is possible. The pressure applied during pressurization is, for example, 500 MPa or less, for example, 400 MPa or less, 300 MPa or less, 200 MPa or less, or 100 MPa or less. The pressure applied during pressurization is, for example, 50 MPa to 500 MPa, 50 MPa to 400 MPa, 50 MPa to 300 MPa, 50 MPa to 200 MPa, 50 MPa to or 100 MPa. By this pressurization, for example, the solid electrolyte powder is sintered to form one solid electrolyte.

[0213] The pressurizing step is for example 40 to 100°C, for example 85 o Plate press treatment is performed at a pressure of 500 MPa for 30 min at C. This pressurization treatment sinteres the solid electrolyte layer, thereby improving battery characteristics.

[0214] According to another embodiment, the pressurization process described above may be omitted.

[0215] The present invention is explained in more detail through the following examples and comparative examples. However, the examples are intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0216] (Manufacture of a complex of Li2S and lithium salt)

[0217] Manufacturing Example 1: Li2S-LiI complex

[0218] Li2S and LiI were mixed at a weight ratio of 30:20. The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI composite. The milling conditions were 25°C, 600 rpm, and 10 h.

[0219] The size of the Li2S-LiI complex was less than 1 μm. The size of the Li2S-LiI complex was calculated by software from scanning electron microscope images of the Li2S-LiI complex powder. The size of the Li2S-LiI complex is the average particle diameter of D50.

[0220] The Mohs hardness of Li2S was 0.6, and that of LiI was 2.0. The Mohs hardness of the Li2S-LiI composite was less than 2.

[0221] Comparative Manufacturing Example 1: Simple mixture of Li2S and LiI

[0222] A mixture of Li2S and LiI with a weight ratio of 30:20 was used as is.

[0223] (Manufacture of Li2S-LiI-CNF cathode active material)

[0224] Manufacturing Example 2: Li2S-LiI-CNF

[0225] Li2S and LiI were mixed at a weight ratio of 30:20. The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI composite. The milling conditions were 25°C, 510 rpm, and 10 h.

[0226] Li2S-LiI composite and carbon nanofiber (CNF) were mixed at a weight ratio of 50:10. The mixture was mechanically milled using a ball mill to produce a Li2S-LiI-CNF composite. The milling conditions were 25°C, 510 rpm, and 10 h.

[0227] A Li2S-LiI-CNF composite was used as a composite cathode active material.

[0228] Manufacturing Example 3: Manufacturing of a gamma-sulfur-carbon nanofiber (γ-S-CNFs) composite

[0229] A gamma sulfur-CNF composite in which monofilament gamma sulfur is arranged on carbon nanofibers (CNF) was manufactured in a freestanding carbon nanofiber state according to the manufacturing method disclosed in U.S. Patent Publication No. 2020 / 0313188.

[0230] Punching of freestanding CNF mat using stainless steel die (ø = 11 mm)

[0231] The CNF disks were weighed and placed in an autoclave (stainless steel 316) developed in-house, and dried in an oven at 180°C for 24 hours. The autoclave consisted of a sulfur reservoir at the bottom and a perforated disk at the top for placing the electrodes. After 24 hours, the autoclave was slowly cooled to room temperature (25°C) over a period of 6 to 8 hours. The electrodes obtained through this process were weighed and transferred to an argon-filled glove box for battery manufacturing after being vacuum-dried at room temperature overnight in a waiting room.

[0232] (Manufacturing of positive and secondary batteries)

[0233] Example 1: (Li2S-LiI-CNF composite)+γ-S-CNFs+solid electrolyte+binder (60:20:19:1.0)

[0234] (Polar electrode manufacturing)

[0235] As a cathode active material, the Li2S-LiI-CNF composite manufactured in Manufacturing Example 2 was prepared. As a solid electrolyte, Li6PS5Cl (D50=3.0 μm, crystalline) which is an argyrodite type crystal was prepared. PVDF-HFP was prepared as a binder, and γ-S-CNFs obtained according to Manufacturing Example 3 were used when preparing the cathode composite. These materials were mixed in a weight ratio of cathode active material: γ-S-CNFs: solid electrolyte: binder = 60:20:19:1.0, and octyl acetate was added thereto to prepare a composition.

[0236] The above composition was coated on one side of a cathode current collector made of aluminum foil coated with carbon on one side, and dried at 80°C for 10 minutes to manufacture a cathode.

[0237] The thickness of the positive electrode was approximately 120 μm, and the loading level of the positive electrode mixture was approximately 8 mg / cm2. 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 the same.

[0238] (Cathode manufacturing)

[0239] A 10 ㎛ thick SUS foil was prepared as a negative electrode current collector. Carbon black (CB) with a primary particle diameter of approximately 30 nm and silver (Ag) particles with an average particle diameter of approximately 60 nm were prepared as negative electrode active materials.

[0240] 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 first negative electrode active material layer / negative electrode current collector structure. The thickness of the first negative electrode active material layer was approximately 15 μm. The areas of the first negative electrode active material layer and the negative electrode current collector were the same.

[0241] (Manufacturing of solid electrolyte layer)

[0242] Li6PS5Cl solid electrolyte in the form of argyrodite crystals (D 50 =3.0 um, crystalline), a mixture was prepared by adding 1.5 parts by weight of an acrylic binder to 98.5 parts by weight of the solid electrolyte. 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 ㎛ thick nonwoven fabric placed on a 75 ㎛ thick PET substrate, and dried in air at 80 ℃ for 10 minutes to prepare a laminate. The prepared laminate was vacuum-dried at 80 ℃ for 2 hours to prepare a solid electrolyte layer.

[0243] (inert absence)

[0244] A flame-retardant inert member was manufactured by forming a slurry containing pulp fiber (cellulose fiber), glass fiber, aluminum hydroxide (Al(OH)3), an acrylic binder, and a solvent into a gasket shape and then removing the solvent.

[0245] The weight ratio of pulp fiber (cellulose fiber), glass fiber, aluminum hydroxide (Al(OH)3), and acrylic binder was 20:8:70:2. The thickness of the inert material was 120 ㎛.

[0246] Before placing the manufactured flame-retardant inert material on the solid electrolyte layer, moisture, etc. of the flame-retardant inert material was removed by vacuum heat treatment at 80°C for 5 hours.

[0247] (Manufacturing of all-solid-state secondary batteries)

[0248] A solid electrolyte layer was placed on the cathode, and an anode was placed on the solid electrolyte layer. A laminate was prepared by placing a gasket surrounding the anode and in contact with the solid electrolyte layer. The thickness of the gasket was approximately 120 ㎛. The above-mentioned flame-retardant inert material was used as the gasket. The gasket was placed so as to be in contact with the side surface of the anode and the solid electrolyte layer. The anode was placed at the center of the solid electrolyte layer, and the gasket was placed so as to surround the anode and extend to the end of the solid electrolyte layer. The area of ​​the anode was approximately 90% of the area of ​​the solid electrolyte layer, and the gasket was placed over the entire remaining 10% of the area of ​​the solid electrolyte layer where the anode was not placed.

[0249] 85 prepared laminates oThe solid electrolyte layer was plate-pressed at 500 MPa for 30 min at C. This pressurization process sintered the solid electrolyte layer, thereby improving battery characteristics. The thickness of the sintered solid electrolyte layer was approximately 45 μm. The density of the Li6PS5Cl solid electrolyte, which was 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.

[0250] The pressurized laminate was placed in a pouch and vacuum-sealed to manufacture an all-solid-state secondary battery. Portions of the positive and negative current collectors were extended outside the sealed battery to serve as positive and negative terminals.

[0251] Example 2: (Li2S-LiI-CNF composite)+γ-S-CNFs+solid electrolyte+binder (60:10:29:1)

[0252] When preparing the positive electrode composite (Li2S-LiI-CNF composite), the mixing weight ratio of γ-S-CNFs, solid electrolyte, and binder was changed to 60:10:29:1.0, and the positive electrode and all-solid-state secondary battery were manufactured in the same manner as in Example 1.

[0253] Example 3: (Li2S-LiI-CNF composite)+γ-S-CNFs+solid electrolyte+binder (60:5:34:1)

[0254] When preparing the positive electrode composite (Li2S-LiI-CNF composite), the mixing weight ratio of γ-S-CNFs, solid electrolyte, and binder was changed to 60:5:34:1, and the positive electrode and all-solid-state secondary battery were manufactured in the same manner as in Example 1.

[0255] Example 4: (Li2S-LiI-CNF composite)+γ-S-CNFs+solid electrolyte+binder (60:30:9:1)

[0256] (Polar electrode manufacturing)

[0257] The Li2S-LiI-CNF composite manufactured in Manufacturing Example 2 was prepared as a cathode active material. Li6PS5Cl, an argyrodite-type crystal (D50=3.0 μm, crystalline), was prepared as a solid electrolyte. PTFE was prepared as a binder, and the γ-S-CNFs obtained according to Manufacturing Example 3 were used in the preparation of the cathode mixture. These materials were physically mixed in a mortar at a weight ratio of cathode active material: γ-S-CNFs: solid electrolyte: binder = 60:30:9:1.0 to prepare a cathode mixture. The cathode mixture was obtained by dry mixing using a ball mill.

[0258] The positive electrode mixture was placed on one side of a positive electrode current collector made of aluminum foil coated on one side and plate pressed at a pressure of 200 MPa for 10 minutes to produce a positive electrode in the form of a sheet. The thickness of the positive electrode was approximately 120 μm and the loading level of the positive electrode mixture was approximately 8 mg / cm2. 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.

[0259] Comparative Example 1: (Li2S-LiI-CNF composite) + solid electrolyte + binder (60:39:1)

[0260] A positive electrode and an all-solid-state secondary battery were manufactured in the same manner as in Example 1, except that γ-S-CNFs were not used in the manufacture of the positive electrode composite and the mixing weight ratio of the Li2S-LiI-CNF composite, solid electrolyte, and binder was changed to 60:39:1.

[0261] Comparative Example 2: (Li2S-LiI-CNF composite)+γ-S-CNFs+solid electrolyte+binder (60:20:19:1): manufactured by milling.

[0262] A positive electrode and an all-solid-state secondary battery were manufactured in the same manner as in Example 1, except that the positive electrode was manufactured according to the following process.

[0263] As a cathode active material, the Li2S-LiI-CNF composite manufactured in Manufacturing Example 2 was prepared. Li6PS5Cl, an argyrodite-type crystal (D50=3.0 μm, crystalline), was prepared as a solid electrolyte. PTFE was prepared as a binder, and the γ-S-CNF composite obtained according to Manufacturing Example 3 was used when preparing the cathode mixture. These materials were physically mixed in a mortar at a weight ratio of cathode active material: γ-S-CNFs: solid electrolyte: binder = 60:20:19:1 to prepare a cathode mixture. The cathode mixture was obtained by dry mixing using a ball mill.

[0264] When the γ-S-CNF composite was manufactured according to Comparative Example 2, the γ-S-CNF composite became unstable due to the heat generated during milling.

[0265] Comparative Example 3: (Li2S-LiI-CNF composite)+(γ-S)+CNF+solid electrolyte+binder (60:10:29:1): manufactured by milling.

[0266] A positive electrode and a lithium-sulfur battery were manufactured in the same manner as in Example 1, except that the positive electrode was manufactured according to the following process.

[0267] A positive electrode mixture was prepared by physically mixing in a mortar and pestle the Li2S-LiI-CNF composite manufactured in Manufacturing Example 2 as a positive electrode active material, gamma sulfur, CNF, Li6PS5Cl (D50=3.0 um, crystalline) as an argyrodite-type crystal as a solid electrolyte, and PTFE as a binder at a weight ratio of 60:10:29:1. The positive electrode mixture was obtained by dry mixing using a ball mill.

[0268] Reference Example 1: (Li2S-LiI-CNF composite)+CNF+solid electrolyte+binder (60:10:29:1)

[0269] A cathode and an all-solid-state secondary battery were manufactured using the same method as Example 1, except that carbon nanofibers (CNFs) were used instead of γ-S-CNFs in the manufacture of the cathode composite.

[0270] Evaluation Example 1: XRD Analysis and Scanning Electron Microscopy Analysis

[0271] XRD spectra were measured using Cu Kα radiation for the raw material (bare) Li2S used in Manufacturing Example 1, the pulverized Li2S, the Li2S-LiI composite manufactured in the first step of Manufacturing Example 2, and the Li2S-LiI-CNF composite manufactured in Manufacturing Example 2. The measurement results are shown in Table 1 and Fig. 1 below. The Li2S crystallite size and lattice constant were derived from the first peak for the (111) crystal plane appearing at a diffraction angle 2θ = 27° ± 2.0° in the XRD spectrum.

[0272] The crushed Li2S was prepared by milling under the same conditions as in the first step of Example 1, except that the 30:20 weight ratio mixture of Li2S and LiI was changed to 50 parts by weight of Li2S. The second step was not performed.

[0273] The particle size (i.e., D50 particle diameter) of the composites was measured using a laser-assisted particle size analyzer (PSA) and a scanning electron microscope for the raw Li2S, pulverized Li2S, the Li2S-LiI composite prepared in the first step, and the Li2S-LiI-CNF composite, and the Li2S particle size of the composites was measured using a scanning electron microscope. The measurement results are shown in Table 1 and FIGS. 2a and 2b below.

[0274] Distinction 2nd peak position [°]Li2S crystallite size [nm]Li2S particle size [㎛]bare Li2S27.0211658 1st peak position [°]Li2S crystallite size [nm]Li2S particle size [㎛]crushed Li2S26.927015-Li2S-LiI composite (first stage)26.60748.81 Less than Production example 2 (Li2S-LiI-CNF composite)26.70209.91 Less than

[0275] As shown in Table 1, the position of the first peak for the (111) crystal plane at a diffraction angle 2θ = 27° ± 2.0° of the Li2S-LiI-CNF composite of Preparation Example 2 shifted to a lower angle compared to the position of the second peak for the (111) crystal plane at a diffraction angle 2θ = 27° ± 2.0° of bare Li2S. The first diffraction angle of the first peak of the Li2S-LiI-CNF composite of Example 1 was smaller than the second diffraction angle of the second peak of bare Li2S. Therefore, the crystallite size of the Li2S-LiI-CNF composite of Example 1 was significantly reduced compared to that of bare Li2S.

[0276] As shown in Table 1, the positions of the first peaks of the Li2S-LiI-CNF composite and the Li2S-LiI composite shifted to a low angle compared to the position of the first peak of the crushed Li2S. And although not shown in Table 1, the first peak of the Li2S-LiI-CNF composite had a first full width at half maximum (FWHM1), and the second peak of the bare Li2S had a second full width at half maximum (FWHM2), and the size of the first full width at half maximum was larger than the size of the second full width at half maximum. The first full width at half maximum (FWHM1) was 1° or more.

[0277] As shown in Table 1, the particle size and crystallite size of the Li2S-LiI composite were significantly reduced compared to Li2S. Although not shown in Table 1, the lattice constant of the Li2S-LiI composite was larger than that of bare Li2S. The increase in the lattice constant of the Li2S-LiI composite compared to that of bare Li2S was thought to be due to the dissolution of LiI within the Li2S crystal. Therefore, it was confirmed that the Li2S-LiI composite formed a solid solution.

[0278] Although not shown in Table 1, the particle size of the composite of Example 1 was approximately 5 μm.

[0279] Evaluation Example 2: Charge / Discharge Test

[0280] The charge / discharge characteristics of the all-solid-state secondary batteries manufactured in Examples 1 to 4 and Comparative Examples 1 and 2 were evaluated by the following charge / discharge test.

[0281] Charge and discharge tests were performed by placing the all-solid-state secondary battery in a constant temperature chamber at 45°C.

[0282] The first cycle involved charging for 12.5 hours at a constant current of 0.1 C until the battery voltage reached 2.5 V to 2.8 V. Subsequently, discharging was performed for 12.5 hours at a constant current of 0.1 C until the battery voltage reached 0.3 V.

[0283] The discharge capacity of the first cycle was taken as the standard capacity. The standard capacity is expressed as the specific capacity of Li2S in Table 2 below.

[0284] After the second cycle, charging and discharging were performed for up to 150 cycles under the same conditions as the first cycle. The measurement results are shown in Table 2 below. The initial efficiency is expressed by Equation 1 below.

[0285] <Formula 1>

[0286] Initial efficiency [%] = [1st cycle discharge capacity / 1st cycle charge capacity] × 100

[0287] The cycle count is the number of cycles required for the discharge capacity to decrease to 80% of the standard capacity after the second cycle. A higher cycle count is considered to indicate better life characteristics.

[0288] ClassificationAnode Energy Density (mAh / g)Initial Efficiency [%]Cycle Number (Times)Example 1 (Li2S-LiI-CNF composite)+γ-S-CNFs+Solid Electrolyte+Binder (60:20:19:1) 89085320Example 2 (Li2S-LiI-CNF composite)+γ-S-CNFs+Solid Electrolyte+Binder (60:10:29:1) 93087400Example 3 (Li2S-LiI-CNF composite)+γ-S-CNFs+Solid Electrolyte+Binder (60:5:34:1) 93588.5380Example 4 (Li2S-LiI-C NF complex) + γ-S-CNFs + solid electrolyte + binder (60:30:9:1) 80085280 Reference Example 1 (Li2S-LiI-CNF complex) + CNF + solid electrolyte + binder (60:10:29:1) 90087210 Comparative Example 1 (Li2S-LiI-CNF complex) + solid electrolyte + binder (60:39:1) 95089250 Comparative Example 2 (Li2S-LiI-C NF complex) + γ-S-CNFs + solid electrolyte + binder (60:10:29:1): manufactured by milling 3506580 Comparative Example 3 Li2S-LiI-CNF complex) + (γ-S) + CNF + solid electrolyte + binder (60:10:29:1): manufactured by milling Manufacturing 2005530

[0289] As shown in Table 2, the all-solid-state secondary batteries of Examples 1 to 4 showed improved life characteristics compared to Reference Example 1 and Comparative Examples 1 to 3. Among the all-solid-state secondary batteries of Examples 1 to 4, the all-solid-state secondary battery manufactured according to Example 2 in particular showed the best life characteristics due to the formation of the γ-S-CNFs macro electron / ion network. The all-solid-state secondary battery of Example 2 showed slightly decreased initial efficiency and capacity characteristics compared to the all-solid-state secondary battery of Comparative Example 1 due to the initial loss of γ-S-CNFs.

[0290] According to Comparative Example 1, the initial efficiency was excellent, but the life characteristics were deteriorated compared to Examples 1 to 4.

[0291] The γ-S-CNF composite of Comparative Example 2 was manufactured by milling and became unstable due to the heat generated during milling compared to the γ-S-CNF composite of Example 2. As a result, the energy density, initial efficiency, and life characteristics were reduced.

[0292] According to Comparative Example 3, a simple blend of gamma sulfur and CNF was used and manufactured by milling, and the solid electrolyte may have its performance deteriorated by milling, resulting in a decrease in initial efficiency and life characteristics.

[0293] Evaluation Example 3: High-rate characteristics (rate performance)

[0294] The high-rate characteristics of the all-solid-state secondary batteries manufactured in Examples 1 to 4, Reference Example 1, and Comparative Examples 1-3 were evaluated by the following charge-discharge test. The charge-discharge test was performed by placing the all-solid-state secondary batteries in a constant-temperature bath at 45°C.

[0295] Each solid-state secondary battery was charged at a constant current of 0.1 C rate at 45°C until the voltage reached 2.5 V (vs. Li), and then cut-off at a current of 0.05 C rate while maintaining 2.5 V in constant voltage mode. Subsequently, the battery was discharged at a constant current of 0.05 C rate until the voltage reached 0.3 V (vs. Li) during discharge (formation cycle).

[0296] Each solid-state secondary battery was charged at a constant current of 0.1 C rate at 45°C until the voltage reached 2.5 V (vs. Li), and then cut-off at a current of 0.05 C rate while maintaining 2.5 V in constant voltage mode. Subsequently, the battery was discharged at a constant current of 0.1 C rate until the voltage reached 0.3 V (vs. Li) (first cycle).

[0297] The solid-state secondary battery that had undergone the Mars cycle was charged at a constant current of 0.2 C rate at 45°C until the voltage reached 2.5 V (vs. Li). Subsequently, it was discharged at a constant current of 0.2 C rate until the voltage reached 0.3 V (vs. Li) (second cycle).

[0298] The solid-state secondary battery that had undergone the first cycle was charged at a constant current of 0.2 C rate at 45°C until the voltage reached 2.5 V (vs. Li). Subsequently, it was discharged at a constant current of 0.33 C rate until the voltage reached 0.3 V (vs. Li) (second cycle).

[0299] The solid-state secondary battery that had undergone the second cycle was charged at a constant current of 0.2 C rate at 45°C until the voltage reached 2.5 V (vs. Li). Subsequently, it was discharged at a constant current of 0.5 C rate until the voltage reached 0.3 V (vs. Li) (third cycle).

[0300] The lithium battery that had undergone the third cycle was charged at a constant current of 0.2 C rate at 45°C until the voltage reached 2.5 V (vs. Li). Subsequently, it was discharged at a constant current of 1.0 C rate until the voltage reached 0.3 V (vs. Li) (4th cycle).

[0301] In all charge / discharge cycles, a 10-minute pause was observed after each charge / discharge cycle. Some of the results of the room-temperature charge / discharge experiments are shown in Table 3 below. The high-rate characteristics are defined by Equation 2 below.

[0302] <Formula 2>

[0303] High-rate characteristic [%] = [Discharge capacity in the 4th cycle / Discharge capacity in the 1st cycle] × 100

[0304] Distinctive Anode High Rate Characteristics (1C / 0.1C) [%] Example 1 (Li2S-LiI-CNF composite) + γ-S-CNFs + Solid electrolyte + Binder (60:20:19:1) 83 Example 2 (Li2S-LiI-CNF composite) + γ-S-CNFs + Solid electrolyte + Binder (60:10:29:1) 87 Example 3 (Li2S-LiI-CNF composite) + γ-S-CNFs + Solid electrolyte + Binder (60:5:34:1) 85 Example 4 (Li2S-LiI-CNF composite) + γ-S-CNFs + Solid electrolyte + Binder (60:30:9:1) 80 Reference Example 1 (Li2S-LiI-CNF composite) + CNF + Solid electrolyte + binder (60:10:29:1) 75 Comparative Example 1 (Li2S-LiI-CNF composite) + solid electrolyte + binder (60:39:1) 71 Comparative Example 2 (Li2S-LiI-CNF composite) + γ-S-CNFs + solid electrolyte + binder (60:10:29:1): manufactured by milling 55 Comparative Example 3 (Li2S-LiI-CNF composite) + (γ-S) + CNF + solid electrolyte + binder (60:10:29:1): manufactured by milling 45

[0305] As shown in Table 3, the all-solid-state secondary batteries of Examples 1 to 4 had improved high-rate characteristics compared to the all-solid-state secondary batteries of Comparative Examples 1 to 3 and Reference Example 1.

Claims

1. A positive electrode current collector; and a positive electrode active material layer disposed on one or both sides of the positive electrode current collector and containing a positive electrode active material, a gamma sulfur-fibrous carbon-based material composite, and a sulfide-based solid electrolyte. The above cathode active material includes Li2S, a Li2S complex or a combination thereof, A gamma sulfur-fibrous carbon-based material composite is an anode having a structure in which monoclinic gamma phase sulfur (S) is arranged on a fibrous carbon-based material.

2. In the first paragraph, the content of the gamma sulfur-fibrous carbon-based material composite is 1 to 30 parts by weight based on 100 parts by weight of the total weight of the positive electrode active material layer.

3. In the first paragraph, in the gamma sulfur-fibrous carbon-based material composite, the fibrous carbon-based material has an aspect ratio of 2 or more, An anode wherein the fibrous carbon-based material has a length of 1 to 50 μm and a diameter of 10 nm to 10 μm, and wherein the fibrous carbon-based material comprises carbon nanofibers, carbon nanotubes, or a combination thereof.

4. In the first paragraph, the BET specific surface area of ​​the gamma sulfur-fibrous carbon-based material composite is 10 m 2 / g or less, and the cross-section of the fibrous carbon material contains a polygonal shape, and is further doped with at least one selected from nitrogen (N) and fluorine (F).

5. In the first paragraph, an anode in which, in the XRD spectrum for the gamma sulfur-fibrous carbon-based material composite, a first peak appears at a diffraction angle 2θ = 11° ± 2.0° corresponding to the (111) crystal plane, a second peak appears at a diffraction angle 2θ of 18 to 32° corresponding to the (122) crystal plane, and a third peak appears at a diffraction angle 2θ of 27 to 28° corresponding to the (222) crystal plane.

6. In the first paragraph, the Li2S complex is a cathode including a complex of Li2S and a carbon-based material, a complex of Li2S and a carbon-based material and a solid electrolyte, a complex of Li2S and a solid electrolyte, a complex of Li2S and a lithium salt, a complex of Li2S and a metal carbide, a complex of Li2S and a carbon-based material and a metal carbide, a complex of Li2S and a metal nitride, a complex of Li2S and a carbon-based material and a metal nitride, or a combination thereof.

7. In the 6th paragraph, the carbon-based material is an anode including graphene, graphene oxide, reduced graphene oxide, carbon nanofibers, carbon nanotubes, carbon nanobelts, carbon nanorods, or a combination thereof.

8. In the first paragraph, the Li2S complex includes a composite of Li2S and a lithium salt, and the composite of Li2S and a lithium salt is Li2S-Li a X b (1≤a≤5, 1≤b≤5), wherein X is I, Br, Cl, F, H, O, Se, Te, N, P, As, Sb, Al, B, OCl, PF6, BF4, SbF6, AsF6, ClO4, AlO2, AlCl4, NO3, CO3, BH4, SO4, BO3, PO4, NCl, NCl2, BN2 or a combination thereof, the anode.

9. In the 8th paragraph, the Li2S complex further includes a carbon-based material, The above carbon-based material includes a fibrous carbon-based material. The above fibrous carbon material includes a carbon nanostructure, and the carbon nanostructure includes carbon nanofibers, carbon nanotubes, carbon nanobelts, carbon nanorods, or a combination thereof. An anode, wherein the content of the carbon-based material is 1 to 20 wt% of the total weight of the composite.

10. In the first paragraph, the Li2S complex comprises a solid solution of Li2S and a lithium salt, A cathode having a Li2S crystallite size of 20 nm or less obtained from the XRD spectrum of the above complex.

11. A positive electrode according to claim 1, wherein the Li2S complex is a complex of Li2S, LiI, and a carbon-based material, the size of Li2S crystallites obtained from the XRD spectrum of the complex is less than 9.9 nm, and the complex includes a solid solution of Li2S and LiI.

12. In the first paragraph, the gamma sulfur-fibrous carbon-based material composite is a product in which gamma sulfur is formed by vapor deposition on carbon nanofibers, and includes monoclinic sulfur that is stable at a temperature below 80°C.

13. In paragraph 8, the lithium salt is a binary compound or a ternary compound, The above binary compound comprises LiI, LiBr, LiCl, LiF, LiH, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, Li3Al2, LiB3 or a combination thereof, A cathode, wherein the ternary compound comprises Li3OCl, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiNO3, Li2CO3, LiBH4, Li2SO4, Li3BO3, Li3PO4, Li4NCl, Li5NCl2, Li3BN2 or a combination thereof.

14. A positive electrode; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode, The above negative electrode includes a negative electrode current collector and a first negative electrode active material layer disposed on one surface of the negative electrode current collector, A lithium secondary battery, wherein the positive electrode is the positive electrode of any one of claims 1 to 13.

15. In the 14th paragraph, the electrolyte layer further includes a liquid electrolyte, a solid electrolyte, a gel electrolyte, or a combination thereof, The above liquid electrolyte contains a lithium salt and an organic solvent, The above solid electrolyte includes a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof, A lithium secondary battery, wherein the gel electrolyte comprises a polymer gel electrolyte.

16. In the 15th paragraph, the solid electrolyte is a sulfide-based solid electrolyte, and the sulfide-based solid electrolyte is 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 and 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 , at least one selected from 0≤x≤2, A lithium secondary battery, wherein the sulfide-based solid electrolyte comprises an argyrodite-type solid electrolyte, and the argyrodite-type solid electrolyte comprises at least one selected from among Li6PS5Cl, Li6PS5Br, and Li6PS5I.

17. In the 14th paragraph, the first negative electrode active material layer is a metal layer, and the metal layer contains lithium or a lithium alloy, or A lithium secondary battery, wherein the first negative electrode active material layer includes a negative electrode active material and a binder, the negative electrode active material has a particle form, and the average particle diameter of the negative electrode active material is 4 ㎛ or less.

18. In the 17th paragraph, the negative electrode active material includes at least one selected from a carbon-based negative electrode active material and a metal or metalloid negative electrode active material, The above carbon-based negative electrode active material includes amorphous carbon, crystalline carbon, porous carbon, or a combination thereof. A lithium secondary battery wherein the metal or metalloid negative electrode active material includes gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or a combination thereof.

19. In the 14th paragraph, a second negative electrode active material layer is further included, which is disposed between the negative electrode current collector and the first negative electrode active material layer and between the negative electrode current collector and the electrolyte layer. A lithium secondary battery, wherein the second negative electrode active material layer is a metal layer, and the metal layer includes lithium or a lithium alloy.

20. In the 14th paragraph, the negative electrode includes a negative electrode collector, At least one of the positive electrode current collector and the negative electrode current collector includes a base film and a metal layer disposed on one or both sides of the base film, The above base film comprises a polymer, and the polymer comprises polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI) or a combination thereof, A lithium secondary battery, wherein the metal layer comprises 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.

Images