Composite positive electrode active material, positive electrode comprising same, and all-solid-state secondary battery

Abstract

Disclosed are a composite positive electrode active material, a positive electrode comprising same, and an all-solid-state secondary battery, the composite positive electrode active material comprising a composite of Li2S, a lithium salt, and a carbon-based material, wherein the Li2S crystallite size obtained from an XRD spectrum of the composite is 9.5 nm or smaller, and the composite comprises a solid solution of the Li2S and the lithium salt, and has a pellet density of 1.65 g / cm3 or greater.

Description

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

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

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

[0003] Lithium 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 using 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 by using solid electrolytes instead of liquid electrolytes. All-solid-state batteries can also offer improved safety.

[0005] One aspect is to provide a composite cathode active material that provides improved specific capacity and cycle characteristics by having a reduced crystallite size and improved density.

[0006] Another aspect is to provide a positive electrode comprising the above composite positive electrode active material.

[0007] Another aspect is to provide an all-solid-state secondary battery including the above positive electrode.

[0008] According to the implementation example

[0009] It includes a composite of Li2S, lithium salt, and carbon-based material,

[0010] The size of Li2S crystallites obtained from the XRD spectrum of the above complex is 9.5 nm or less,

[0011] The above complex comprises a solid solution of Li2S and a lithium salt,

[0012] Pellet density is 1.65 g / cm 3 A composite bipolar active material is provided.

[0013] According to another implementation example,

[0014] A cathode current collector; and a cathode active material layer disposed on one or both sides of the cathode current collector,

[0015] A positive electrode is provided, wherein the positive electrode active material layer includes the composite positive electrode active material described above and a sulfide-based solid electrolyte.

[0016] According to another implementation example,

[0017] A positive electrode according to the above; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode,

[0018] An all-solid-state secondary battery is provided, 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.

[0019] According to another implementation example

[0020] A positive electrode according to the above; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode,

[0021] An all-solid-state secondary battery is provided, wherein the positive electrode comprises the composite positive electrode active material described above.

[0022] According to one aspect, it is possible to provide an all-solid-state secondary battery having increased specific capacity and improved cycle characteristics by having a composite cathode active material having a reduced crystallite size and improved density.

[0023] Figure 1 is an XRD spectrum of pulverized Li2S, the Li2S-LiI complex which is an intermediate product of Example 1, and the Li2S-LiI-CNF complex prepared in Example 1.

[0024] Figure 2a is a scanning electron microscope image of Li2S used in Example 1.

[0025] Figure 2b is a scanning electron microscope image of the Li2S-LiI-CNF composite manufactured in Example 1.

[0026] Figure 3 is a cross-sectional view of an all-solid-state secondary battery according to an exemplary embodiment.

[0027] Fig. 4 is a cross-sectional view of an all-solid-state secondary battery according to an exemplary embodiment.

[0028] Fig. 5 is a cross-sectional view of an all-solid-state secondary battery according to an exemplary embodiment.

[0029] Figure 6 is a cross-sectional view of an all-solid-state secondary battery according to an exemplary embodiment.

[0030] Fig. 7 is a cross-sectional view of an all-solid-state secondary battery according to an exemplary embodiment.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] "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.

[0039] In this disclosure, “particle diameter” refers to the average diameter when the particle is spherical, and refers to the average major axis length when the particle is non-spherical. The particle diameter 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, the median particle diameter.

[0040] D50 is the size of the particle corresponding to 50% of the cumulative volume, calculated from the particle side with a smaller particle size in the particle size distribution measured by laser diffraction.

[0041] D90 is the size of the particle corresponding to 90% of the cumulative volume, calculated from the particle side with a smaller particle size in the particle size distribution measured by laser diffraction.

[0042] D10 is the size of the particle corresponding to 10% of the cumulative volume, calculated from the particle side with a small particle size in the particle size distribution measured by laser diffraction.

[0043] In this disclosure, “metal” includes both metals and metalloids such as silicon and germanium, in their elemental or ionic states.

[0044] In this disclosure, “alloy” means a mixture of two or more metals.

[0045] In the present disclosure, “electrode active material” means an electrode material capable of undergoing lithiation and delithiation.

[0046] In the present disclosure, “positive electrode material” means a positive electrode material capable of undergoing lithiation and delithiation.

[0047] In the present disclosure, “negative electrode active material” means a negative electrode material capable of undergoing lithiation and delithiation.

[0048] In the present disclosure, “lithiation” and “lithiating” mean a process of adding lithium to an electrode active material.

[0049] In the present disclosure, “delithiation” and “delithiate” mean a process of removing lithium from an electrode active material.

[0050] In this disclosure, “charging” and “charging” mean a process of providing electrochemical energy to a battery.

[0051] In this disclosure, “discharging” and “discharging” mean the process of removing electrochemical energy from a battery.

[0052] In the present disclosure, “positive electrode” and “cathode” mean an electrode at which electrochemical reduction and lithiation occur during a discharge process.

[0053] In the present disclosure, “cathode” and “anode” mean electrodes where electrochemical oxidation and delithiation occur during a discharge process.

[0054] 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.

[0055]

[0056] Hereinafter, composite cathode active materials and cathodes and all-solid-state secondary batteries including the composite cathode active materials according to exemplary embodiments will be described in more detail.

[0057] [Composite cathode active material]

[0058] According to one embodiment, a composite cathode active material includes a composite of Li2S, a lithium salt, and a carbon-based material. The size of Li2S crystallites obtained from an XRD spectrum of the composite is 9.5 nm or less. The size of Li2S crystallites obtained from an XRD spectrum of the composite is, for example, 9.5 nm or less, 9.4 nm or less, 9.3 nm or less, 9.2 nm or less, 9.1 nm or less, or 9.0 nm or less. The composite includes a solid solution of Li2S and a lithium salt. The size of Li2S crystallites obtained from an XRD spectrum of the composite is, for example, 1 to 9.5 nm, 1 to 9.4 nm, 2 to 9.3 nm, 2 to 9.2 nm, 2 to 9.1 nm, or 3 to 9.0 nm. The complex contains a solid solution of Li2S and a lithium salt. The pellet density of the complex is 1.65 g / cm 3 This is ideal. The pellet density of the composite is, for example, 1.65 g / cm 3 Above, 1.66 g / cm 3 Above, 1.67 g / cm 3 Above, 1.68 g / cm 3 Above, 1.69 g / cm 3or more than 1.70 g / cm 3 That's all.

[0059] By forming a complex of Li2S with a lithium salt and a carbon-based material, the ionic conductivity and electronic conductivity of Li2S can be simultaneously improved. Since the complex includes a lithium salt, the ionic conductivity of the composite cathode active material can be improved, and the internal resistance of a cathode and a lithium battery including the composite cathode active material can be reduced. Since the complex includes a carbon-based material, the electronic conductivity of the composite cathode active material can be improved, and the internal resistance of a cathode and a lithium battery including the composite cathode active material can be reduced.

[0060] The composite includes Li2S crystallites, and as the size of the Li2S crystallites decreases, the volume change of the Li2S crystallites during charge and discharge can be alleviated. For example, as the size of the Li2S crystallites decreases, the volume change due to a single Li2S crystallite decreases, so the overall volume change of the composite during charge and discharge can be alleviated. For example, as the size of the Li2S crystallites decreases, the grain boundaries between a plurality of Li2S crystallites can more easily accommodate the volume change of the Li2S crystallites during charge and discharge, so the volume change of the composite during charge and discharge can be alleviated. The possibility of defects such as cracks occurring due to the volume change of the composite during charge and discharge can be reduced. When the composite cathode active material includes such a composite, the cycle characteristics of a secondary battery including the composite cathode active material can be improved. For example, the cycle characteristics of a lithium battery including such a composite cathode active material are improved.

[0061] The composite includes Li2S crystallites, and by reducing the size of the Li2S crystallites, the contact area between the Li2S crystallites and the lithium salt and / or the carbon-based material can be further increased. By increasing the contact area between the Li2S crystallites and the lithium salt and / or the carbon-based material, the ionic conductivity and / or battery conductivity of the composite can be further improved. By including such a composite in the composite cathode active material, the reversibility of the electrode reaction in a secondary battery including the composite cathode active material can be improved. As a result, the specific capacity of the composite cathode active material can be increased.

[0062] The ionic conductivity of the composite may increase when the composite includes a solid solution of Li2S and a lithium salt. For example, since the solid solution of Li2S and a lithium salt includes alkali metal 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. When the composite cathode active material includes such a composite, the cycle characteristics of a secondary battery including the composite cathode active material may be improved. For example, the high-rate characteristics of a secondary battery including such a composite cathode active material may be improved.

[0063] The pellet density of the composite is 1.65 g / cm 3 The energy density of an all-solid-state secondary battery including a composite can be improved by the above-mentioned method. The pellet density is 1.65 g / cm. 3 If it is less than this, the energy density of the all-solid-state secondary battery may decrease due to a decrease in the density of the positive electrode active material layer including the complex.

[0064] Li2S-lithium salt-carbon material composites are distinguished from simple mixtures of Li2S, lithium salt, and carbon-based materials. Simple mixtures of Li2S, lithium salt, and carbon-based materials fail to maintain a dense interface between the Li2S, lithium salt, and carbon-based materials, resulting in high interfacial resistance and consequently degrading the lifespan characteristics of secondary batteries.

[0065] The size of the composite cathode active material, i.e., the size of the composite, can be, for example, 1 to 10 μm, 2 to 10 μm, 3 to 10 μm, 3 to 9 μm, or 3 to 8 μm. By having a size in this range, the composite can simultaneously provide enhanced ionic and electronic conductivity. If the size of the composite is too small, it may be difficult to secure conductive paths between the composite cathode active material particles due to the micronization of the carbon-based material. If the size of the composite is too large, the degree of composite integration may be low. It may be difficult to secure electronic and ionic conductive paths within the composite. The size of the composite can be, for example, a D50 particle size. The size of the composite can be measured, for example, using a particle size analyzer (PSA) using a laser. The size of the composite can be calculated, for example, by software from a scanning electron microscope image of the composite powder.

[0066] The D10 particle size of the composite may be, for example, 1 ㎛ or more, 1.2 ㎛ or more, 1.5 ㎛ or more, or 2 ㎛ or more. When the D10 particle size of the composite is in this range, the fine particle content of the composite cathode active material may decrease. As the fine particle content of the composite cathode active material increases, the density of the cathode layer including the composite cathode active material may decrease, thereby lowering the energy density of the all-solid-state secondary battery including the cathode layer. As the fine particle content of the composite cathode active material increases, the interfacial resistance between the composite cathode active material particles may increase, and it may become difficult to form a conductive network. As a result, the cycle characteristics of the all-solid-state secondary battery including the composite cathode active material may deteriorate.

[0067] 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.

[0068] The size of the composite can be measured, for example, using laser diffraction, scanning electron microscopy, etc. The particle size of the composite can be measured, for example, using a scanning electron microscope image, which is an arithmetic mean of the particle sizes of multiple particles measured using software. The size of Li2S particles included in the composite can be measured, for example, using a scanning electron microscope.

[0069] For example, the electronic conductivity of the complex at 25°C and 1 atm may be 0.1 mS / cm or more, 0.5 mS / cm or more, 1.1 mS / cm or more, 1.2 mS / cm or more, 1.3 mS / cm or more, 1.5 mS / cm or more, 2.0 mS / cm or more, or 2.5 mS / cm or more. For example, the electronic conductivity of the composite at 25 ℃, 1 atm may be 0.1 mS / cm to 1 S / cm, 0.5 mS / cm to 1 S / cm, 1.1 mS / cm to 1 S / cm, 1.2 mS / cm to 0.9 S / cm, 1.3 mS / cm to 0.8 S / cm, 1.5 mS / cm to 0.7 S / cm, 2.0 mS / cm to 0.5 S / cm, or 2.5 mS / cm to 0.5 S / cm. The electronic conductivity can be measured using, for example, electrochemical impedance spectroscopy, a DC polarization method, etc. Since the composite has an electronic conductivity in this range, an increase in the internal resistance of the all-solid-state secondary battery can be suppressed. As a result, the cycle characteristics of the all-solid-state secondary battery can be improved.

[0070] For example, the ionic conductivity of the composite at 25°C, 1 atm may be 0.1 mS / cm or more, 0.3 mS / cm or more, 0.33 mS / cm or more, 0.36 mS / cm or more, 0.40 mS / cm or more, or 0.43 mS / cm or more. For example, the ionic conductivity of the composite at 25°C, 1 atm may be 0.1 mS / cm to 1 S / cm, 0.3 mS / cm to 1 S / cm, 0.33 mS / cm to 0.9 S / cm, 0.36 mS / cm to 0.8 S / cm, 0.40 mS / cm to 0.7 S / cm, or 0.43 mS / cm to 0.5 S / cm. Ionic conductivity can be measured using, for example, electrochemical impedance spectroscopy and direct current polarization methods. Since the composite possesses an ionic conductivity within this range, an increase in the internal resistance of an all-solid-state secondary battery can be suppressed. Consequently, the cycle characteristics of the all-solid-state secondary battery can be improved.

[0071] The composite includes Li2S. Since Li2S has a high theoretical capacity, a secondary battery having a high energy density can be provided. However, since Li2S has low ionic conductivity and / or electronic conductivity, a composite is formed with a lithium salt and a carbon-based material to overcome this drawback. The content of Li2S in the composite may be, for example, 10 to 80 wt%, 20 to 70 wt%, 30 to 60 wt%, or 40 to 60 wt% of the total weight of the composite. If the content of Li2S is excessively increased, it may not be easy to improve the ionic conductivity and / or electronic conductivity of Li2S. If the content of Li2S is excessively low, the energy density of the secondary battery may be reduced.

[0072] The complex comprises a lithium salt. 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 lithium salt binary compound may include, for example, LiI, LiBr, LiCl, LiF, LiH, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, Li3Al2, LiB3, or a combination thereof. The lithium salt ternary compound may 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 lithium salt in the composite, the ionic conductivity of the composite may be further improved. Such a lithium salt may more easily form a solid solution with Li2S in the composite, for example. The content of the lithium salt in the composite may be 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. If the content of the lithium salt increases excessively, the energy density of the secondary battery may decrease. If the lithium salt content is excessively low, the ionic conductivity of the composite may decrease, increasing the internal resistance of the composite cathode active material. Consequently, the cycle performance of the secondary battery may deteriorate.

[0073] 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 secondary battery including the composite cathode active material may be further improved. If the molar ratio of Li2S is excessively high, the ionic conductivity enhancement effect of lithium salts may be minimal. If the molar ratio of Li2S is excessively low, the energy density of secondary batteries containing composite cathode active materials may be reduced.

[0074] The composite comprises a carbon-based material. The carbon-based material may be any material containing carbon atoms that is used as a conductive material in the relevant technical field.

[0075] The carbon-based material may include, for example, amorphous carbon. By including amorphous carbon in the carbon-based material, side reactions between the carbon-based material and the solid electrolyte can be suppressed. Therefore, the cycle characteristics of an all-solid-state secondary battery including the composite can be further improved. 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.; graphite, activated carbon, or a combination thereof. The form of the carbon-based material may be, but is not limited to, particle form, sheet form, flake form, etc., and any form used as a carbon-based material in the relevant technical field may be used.

[0076] The carbon-based material may include, for example, a fibrous carbon-based material. By including the fibrous carbon-based material in the composite, the electronic conductivity of the composite may be further improved. By including the fibrous carbon-based material in the composite, electronic conduction may be more easily performed from the surface to the interior of the composite. The internal resistance of a composite cathode active material including the composite may be reduced, and the cycle characteristics of a secondary battery including the composite cathode active material may be further improved. The aspect ratio of the fibrous carbon-based material may 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 may 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 may be, for example, 2 to 30, 2 to 20, 2 to 10, 2 to 8, 2 to 5, or 2 to 4. When the fibrous carbon-based material has an aspect ratio in this range, the overall electronic conductivity of the composite is improved, and the imbalance of local electronic conductivity within the composite can be further alleviated. The fibrous carbon-based material may include, for example, a carbon nanostructure. The carbon nanostructure may include, for example, a carbon nanofiber (CNF), a carbon nanotube (CNT), a carbon nanobelt, a carbon nanorod, or a combination thereof. The carbon nanostructure may form a primary carbon nanostructure composed of a single carbon nanostructure, and a secondary carbon nanostructure in which a plurality of carbon nanostructures are aggregated.

[0077] 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.

[0078] Secondary carbon nanostructures are, for example, structures formed by assembling primary carbon nanostructures in whole or in part to form bundles or bundle-type structures. The secondary carbon nanostructures may include, for example, bundle-type carbon nanostructures, rope-type carbon nanostructures, or combinations thereof. The diameter of the secondary carbon nanostructures may be, for example, 2 nm to 200 nm, 3 nm to 150 nm, 5 nm to 100 nm, 5 nm to 50 nm, 5 nm to 30 nm, or 5 nm to 20 nm. The length of the secondary carbon nanotube structure can be, for example, 20 nm to 2 ㎛, 30 nm to 1.5 ㎛, 50 nm to 1 ㎛, 50 nm to 500 nm, 50 nm to 400 nm, 50 nm to 300 nm, 50 nm to 200 nm, or 50 nm to 100 nm or more. The diameter and length of the secondary carbon nanostructure can be measured from a scanning electron microscope (SEM) image or an optical microscope. Alternatively, the diameter and / or length of the secondary carbon nanostructure can be measured by laser diffraction. The secondary carbon nanostructure can be converted into the primary carbon nanostructure by, for example, dispersing it in a solvent or the like and then used in the preparation of a composite.

[0079] The content of the carbon-based material included in the composite 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 secondary battery may decrease. If the content of the carbon-based material decreases excessively, the electronic conductivity of the composite may decrease, which may increase the internal resistance of the composite cathode active material. As a result, the cycle characteristics of the secondary battery may deteriorate.

[0080] The composite may include, for example, 10 to 80 parts by weight of Li2S, 1 to 40 parts by weight of a lithium salt, and 1 to 20 parts by weight of a carbon-based material, relative to 100 parts by weight of the composite. The Li2S content included in the composite may be, for example, 10 to 80 parts by weight, 20 to 70 parts by weight, 30 to 60 parts by weight, or 40 to 60 parts by weight of Li2S, relative to 100 parts by weight of the composite. The lithium salt content included in the composite may be, for example, 10 to 40 parts by weight, 15 to 40 parts by weight, 20 to 40 parts by weight, or 25 to 35 parts by weight of the lithium salt, relative to 100 parts by weight of the composite. The carbon-based material content included in the composite may be, for example, 1 to 20 parts by weight, 5 to 20 parts by weight, or 5 to 15 parts by weight of the carbon-based material, relative to 100 parts by weight of the composite. Since the composite has a composition of Li2S, lithium salt, and carbon-based material in this range, a composite cathode active material including the composite can provide excellent ionic conductivity and / or electronic conductivity.

[0081] The Mohs hardness of the lithium salt and the carbon-based material may be greater than that of the Li2S. The Mohs hardness of Li2S is, for example, 0.6 or less. The Mohs hardness of Li2S is, for example, 0.6. 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 NaI is, for example, 2.1. 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 within this range, the pulverization of Li2S can be performed more easily during the milling process, and a Li2S-lithium salt-carbon-based material composite can be easily formed. The modal hardness of carbon nanofibers (CNF) is, for example, 1.5.

[0082] In the XRD spectrum of the composite, for example, a first lattice constant (d1) derived from a first peak corresponding to the (111) crystal plane of Li2S at a diffraction angle 2θ = 27° ± 2.0° may be larger than a second lattice constant (d2) derived from a second peak corresponding to the (111) crystal plane of Li2S at a diffraction angle 2θ = 27° ± 2.0° in the XRD spectrum of Li2S used in the preparation of the composite. Since the Li2S-lithium salt-carbon-based material composite has a larger lattice constant (d) than Li2S used in the preparation of the composite, alkali metal ions can be more easily transferred within the Li2S crystal structure of the composite. The ionic conductivity of a composite cathode active material including the composite can be further improved. The internal resistance of a secondary battery including the composite cathode active material can be reduced and the cycle characteristics can be improved. The difference between the first lattice constant (d1) and the second lattice constant (d2) may be 0.05 Å or more, 0.1 Å or more, 0.15 Å or more, 0.2 Å or more, or 0.25 Å or more. The size of the first lattice constant (d1) may be, for example, 5.78 Å or more, 5.80 Å or more, 5.82 Å or more, 5.85 Å or more, 5.90 Å or more, 5.95 Å or more, or 6.0 Å or more. Since the composite has such a size of the first lattice constant (d1), the ionic conductivity of the composite cathode active material including the composite may be further improved. The internal resistance of a secondary battery including the composite cathode active material may be reduced and the cycle characteristics may be improved.

[0083] In the XRD spectrum of the composite, for example, a first peak appearing at a diffraction angle 2θ = 27° ± 2.0° corresponding to the (111) crystal plane of Li2S has a first diffraction angle, and in the XRD spectrum of Li2S used in the preparation of the composite, a second peak appearing at a diffraction angle 2θ = 27° ± 2.0° corresponding to the (111) crystal plane of Li2S has a second diffraction angle, and the first diffraction angle may be smaller than the second diffraction angle. For example, the position of the first peak may shift to a low angle compared to the position of the second peak. Therefore, the Li2S-lithium salt-carbon-based material composite may have a reduced crystallite size compared to Li2S used in the preparation of the composite. Since the Li2S-lithium salt-carbon material composite has a reduced crystallite size, the volume change of the crystallites during charge and discharge is reduced, and thus the volume change of the composite containing multiple crystallites during charge and discharge can be alleviated. The occurrence of defects such as cracks during charge and discharge of the composite cathode active material containing such a composite can be suppressed. Consequently, the cycle characteristics of the secondary battery containing the composite cathode active material can be improved.

[0084] In the XRD spectrum of the composite, for example, a first peak appearing at a diffraction angle 2θ = 27° ± 2.0° corresponding to the (111) crystal plane of M2S has a first full width at half maximum (FWHM1), and in the XRD spectrum of Li2S used in the preparation of the composite, a second peak appearing at a diffraction angle 2θ = 27° ± 2.0° corresponding to the (111) crystal plane of Li2S has a second full width at half maximum (FWHM2), and the first full width at half maximum may be larger than the second full width. Accordingly, the Li2S-lithium salt-carbon-based material composite may have an increased lattice strain compared to the Li2S used in the preparation of the composite. For example, the Li2S-lithium salt-carbon-based material composite may have an increased lattice strain when Li2S and a lithium salt form a solid solution. Since the Li2S-lithium salt-carbon material composite has an increased full width at half maximum (FWHM) compared to the Li2S used in the composite preparation, the ionic conductivity of a composite cathode active material including the composite can be further improved. The internal resistance of a secondary battery including the composite cathode active material can be reduced and the cycle characteristics can be improved.

[0085] The first half-width (FWHM1) may be, for example, 1° or more, 1.05° or more, 1.10° or more, or 1.15° or more. When the composite has a first half-width (FWHM1) in this range, the ionic conductivity of the composite cathode active material including the composite can be further improved. The internal resistance of the secondary battery including the composite cathode active material can be reduced and the cycle characteristics can be improved.

[0086]

[0087] [anode]

[0088] [Cathode: Cathode active material]

[0089] According to one embodiment, a positive electrode includes a positive electrode current collector; and a positive electrode active material layer disposed on one or both surfaces of the positive electrode current collector. The positive electrode active material layer includes the composite positive electrode active material described above and a solid electrolyte. By including the composite positive electrode active material and the solid electrolyte, the positive electrode can have further reduced internal resistance. Accordingly, the cycle characteristics of a secondary battery including the positive electrode can be further improved.

[0090] Referring to FIGS. 3 to 7, the positive electrode (10) includes a positive electrode current collector (11); and a positive electrode active material layer (12) disposed on one or both sides of the positive electrode current collector (11). The positive electrode active material layer (12) includes the composite positive electrode active material and solid electrolyte described above.

[0091] The composite cathode active material may be included in an amount of 40 to 90 parts by weight, 40 to 80 parts by weight, 50 to 80 parts by weight, or 50 to 70 parts by weight, based on 100 parts by weight of the cathode active material layer (12). If the content of the composite cathode active material is excessively reduced, the energy density of the secondary battery is reduced. If the content of the composite cathode active material is excessively increased, the deterioration of the cathode may be accelerated due to the change in the volume of the cathode during charge and discharge. As a result, the cycle characteristics of the secondary battery (1) may be reduced.

[0092] The cathode active material layer (12) may additionally include other cathode active materials in addition to the composite cathode active material described above.

[0093] Other cathode active materials may include, for example, a Li2S-containing composite. The Li2S composite includes, for example, a composite of Li2S and a carbon-based material, a composite of Li2S and a carbon-based material and a solid electrolyte, a composite of Li2S and a solid electrolyte, a composite of Li2S and a lithium salt, a composite of Li2S and a metal carbide, a composite of Li2S and a carbon-based material and a metal carbide, a composite of Li2S and a metal nitride, a composite of Li2S and a carbon-based material and a metal nitride, or a combination thereof.

[0094] The composite of Li2S and a carbon-based material includes a carbon-based material. The carbon-based material refers to the carbon-based material of the composite cathode active material described above. The method for producing the composite of Li2S and a carbon-based material may be a dry method, a wet method, or a combination thereof, but is not limited thereto, and any method used in the art may be used. The method for producing the composite of Li2S and a carbon-based material includes, but is not limited to, milling, heat treatment, deposition, etc., and any method used in the art may be used.

[0095] A composite of Li2S, a carbon-based material, and a solid electrolyte includes a carbon-based material and a solid electrolyte. The carbon-based material refers to the composite of Li2S and a carbon-based material described above. The solid electrolyte can be, for example, any material used as an ion-conducting material in the relevant technical field. 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 includes, for example, Li, S, and P, and may optionally further include a halogen element. The sulfide-based solid electrolyte can be selected from among the sulfide-based solid electrolytes used in the electrolyte layer. The sulfide-based solid electrolyte has, for example, a molecular weight of 1×10 at room temperature. -5 It can have an ionic conductivity of S / cm or more. The oxide-based solid electrolyte contains, for example, Li, O, and transition metal elements, and may optionally contain other elements. The oxide-based solid electrolyte has an ionic conductivity of, 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 among oxide-based solid electrolytes used in the electrolyte layer.

[0096] The composite of Li2S and a solid electrolyte includes a solid electrolyte. The solid electrolyte refers to the composite of Li2S, a carbon-based material, and a solid electrolyte described above.

[0097] The composite of Li2S and a lithium salt comprises Li2S and a lithium salt. The lithium salt refers to the lithium salt of the composite cathode active material described above. The lithium salt is particularly one or more lithium halide compounds selected from LiF, LiCl, LiBr, and LiI. The composite of Li2S and a lithium salt may be, for example, a composite of Li2 and a lithium halide. The composite of Li2 and a lithium salt may provide improved ionic conductivity by including a lithium halide compound. The composite of Li2S and a lithium salt is distinguished from a simple mixture of Li2S, a carbon-based material, and a lithium salt. A simple mixture of Li2S and a lithium salt may provide high interfacial resistance by failing to maintain a dense interface between Li2S and a lithium salt, which may result in reduced cycle life characteristics of an all-solid-state secondary battery.

[0098] 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, 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 xor a combination thereof. The surface of the two-dimensional metal carbide is terminated with O, OH and / or F.

[0099] A composite of Li2S, a carbon-based material, and a metal carbide includes a carbon-based material and a metal carbide. The carbon-based material refers to the composite of Li2S and a carbon-based material described above. The metal carbide refers to the composite of Li2S and a metal carbide described above.

[0100] 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.

[0101] A composite of Li2S, a carbon-based material, and a metal nitride includes a carbon-based material and a metal nitride. The carbon-based material refers to the composite of Li2S and a carbon-based material described above. The metal carbide refers to the composite of Li2S and a metal nitride described above.

[0102] 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).

[0103] [Anode: Solid electrolyte]

[0104] The positive electrode active material layer (12) may include, for example, a solid electrolyte. The solid electrolyte may be, for example, a sulfide-based solid electrolyte. The solid electrolyte included in the positive electrode (10) may be the same as or different from the solid electrolyte included in the electrolyte layer (30). For more information on the solid electrolyte, refer to the electrolyte layer (30) section.

[0105] The solid electrolyte included in the positive electrode active material layer (12) may have a smaller average D50 particle diameter than the solid electrolyte included in the electrolyte layer (30). For example, the average D50 particle diameter of the solid electrolyte included in the positive electrode active material layer (12) 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 diameter of the solid electrolyte included in the electrolyte layer (30). The average D50 particle diameter is, for example, a 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 small particle size in a size distribution of particles measured by, for example, a laser diffraction method.

[0106] 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, based on 100 parts by weight of the positive electrode active material layer (12). If the content of the solid electrolyte is excessively reduced, the internal resistance of the positive electrode may increase, thereby deteriorating the cycle characteristics of the secondary battery. If the content of the sulfide-based solid electrolyte is excessively increased, the energy density of the secondary battery (1) may be reduced.

[0107] [Polar: Challenger]

[0108] 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).

[0109] The cathode active material layer (12) includes a carbon-based material, and the carbon-based material may be disposed only in the composite cathode active material. The cathode active material layer (12) may not additionally include a separate carbon-based material other than the composite cathode active material including the carbon-based material. Since the cathode active material layer does not include a separate carbon-based material, the energy density of the cathode and the secondary battery (1) can be improved and the manufacturing process can be simplified.

[0110] [Positive: Binder]

[0111] 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, 0.1 wt% to 10 wt%, 0.5 to 5 wt%, or 0.5 to 2 wt% of the total weight of the positive electrode active material layer (12). The binder may be omitted.

[0112] [Positive: Other additives]

[0113] 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.

[0114] 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.

[0115] [Anode: Anode current collector]

[0116] 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.

[0117] 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.

[0118] [Anode: Inert member]

[0119] Referring to FIGS. 6 and 7, the positive electrode (10) includes a positive electrode current collector (11) and a positive electrode active material layer (12) disposed on one side of the positive electrode current collector. An inactive member (40) is disposed on one side of the positive electrode (10). Referring to FIG. 6, 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. 7, the inactive member (40) is disposed on one side of the positive electrode active material layer (12) and between the electrolyte layer (30) and the positive electrode current collector (11) facing the electrolyte layer (30). The inactive member (40) is not disposed on one side of the positive electrode current collector (11). The electrolyte layer (30) may be, for example, a solid electrolyte layer.

[0120] 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.

[0121] 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.

[0122] The inert member (40) surrounds the side surface of the positive electrode (10) and is in contact with the electrolyte layer (30). By the inert member (40) surrounding the side surface of the positive electrode (10) and being 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 (20) 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.

[0123] Referring to FIGS. 6 and 7, the inert member (40) extends from one side of the positive electrode (30) 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 (30) to the end of the electrolyte layer (30).

[0124] Referring to FIGS. 6 and 7, 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.

[0125] 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.

[0126] 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).

[0127] 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.

[0128] 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).

[0129] 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).

[0130] 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%.

[0131] 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).

[0132] 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.

[0133] The inert member (40) has, for example, a single-layer structure. Alternatively, although not shown in the drawing, 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.

[0134] 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).

[0135] 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.

[0136] 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).

[0137] 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 (40) comprises, for example, a heat-pressure curable film and / or a cured product thereof. The heat-pressure curable polymer is, for example, TSA-66 from Toray.

[0138] 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).

[0139] 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).

[0140] 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.

[0141]

[0142] [All-solid-state secondary battery]

[0143] An all-solid-state secondary battery according to one embodiment includes the above-described positive electrode; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode. 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.

[0144] Referring to FIGS. 3 to 7, an all-solid-state secondary battery (1) includes a positive electrode (10); a negative electrode (20); and an electrolyte layer (30) disposed between the positive electrode (10) and the negative electrode (20). 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.

[0145] [anode]

[0146] See the above mentioned polarities.

[0147] [cathode]

[0148] [Cathode: Cathode active material]

[0149] Referring to FIGS. 3 to 7, the negative electrode (20) includes a first negative electrode active material layer (22). The first negative electrode active material layer (22) includes, for example, a negative electrode active material and a binder.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] Carbon-based negative electrode materials include, for example, amorphous carbon, crystalline carbon, porous carbon, or a combination thereof.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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 The y (0 <x≤1, 0<y≤1) 또는 이들의 조합을 포함할 수 있다. 금속과 금속산화물의 복합체는 예를 들어 Au와 Au x The y (0 <x≤2, 0<y≤3)의 복합체, Pt와 Pt x The y (0 <x≤1, 0<y≤2)의 복합체, Pd와 Pd x The y (0 <x≤1, 0<y≤1)의 복합체, Si와 Si x The y (0 <x≤1, 0<y≤2)의 복합체, Ag 와 Ag x The y (0 <x≤2, 0<y≤1)의 복합체, Al과 Al x The y (0 <x≤2, 0<y≤3)의 복합체, Bi와 Bi x The y (0 <x≤2, 0<y≤3)의 복합체, Sn과 Sn x The y (0 <x≤1, 0<y≤2)의 복합체, Te과 Te x The y (0 <x≤1, 0<y≤3), Zn과 Zn x The y (0 <x≤1, 0<y≤1)의 복합체, 또는 이들의 조합을 포함할 수 있다.

[0161] 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.

[0162] 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.

[0163] [Cathode: Binder]

[0164] 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.

[0165] 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).

[0166] [Cathode: Other additives]

[0167] 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.

[0168] [Cathode: Solid electrolyte]

[0169] 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.

[0170] 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).

[0171] [Cathode: First negative electrode active material layer]

[0172] 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 0.5 or 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) + It is determined by charging up to the maximum charging voltage. The initial charging capacity of the first negative electrode active material layer (22) is determined by the second open circuit voltage (2 nd Li / Li from open circuit voltage) +It is determined by charging up to 0.01 V.

[0173] 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 + can be 2.5 V for Li2S or Li2S complex. For example, the maximum charging voltage of Li / Li + It can be 3.0 V for. The ratio (B / A) of the initial charge capacity (B) of the first negative electrode active material layer (22) to the initial charge capacity (A) of the positive electrode active material layer is, for example, 0.01 to 0.5, 0.01 to 0.45, 0.01 to 0.4, 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 an all-solid-state half-cell using lithium metal as a counter electrode.

[0174] The initial charge capacity of each of the positive electrode active material layer (12) and the first negative electrode active material layer (22) is a constant current density, for example, 0.1 mA / cm 2 can be directly measured using an all-solid-state half-cell. For the positive electrode, the measurement is made from the first open circuit voltage (OCV) to the maximum charge voltage, for example, 3.0 V (vs. Li / Li + ) can be performed by charging to an operating voltage of up to 0.01 V for the negative electrode, for example, lithium metal, from a second open circuit voltage (OCV). For example, an all-solid-state half-cell having a positive electrode active material layer can be charged to an operating voltage of up to 0.1 mA / cm from a first open circuit voltage (OCV) to 3.0 V. 2 The all-solid-state 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 The all-solid-state half-cell having the positive electrode active material layer can be charged from the 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.

[0175] 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).

[0176] 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.

[0177] [Cathode: Second negative electrode active material layer]

[0178] Referring to FIG. 5, 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, but is not limited to, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, a Li-Si alloy, etc., and any lithium alloy used in the art may be used. The 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).

[0179] 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.

[0180] 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).

[0181] 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 disposed 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).

[0182] [Cathode: Negative current collector]

[0183] 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.

[0184] Referring to FIG. 4, 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 current collector (21). The thin film (23) is disposed between the negative electrode current 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.

[0185] 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 precipitated from the negative electrode, thereby lowering the energy density of the all-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.

[0186] 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, and consequently, improve the energy density of the negative electrode and lithium battery.

[0187]

[0188] [Electrolyte layer]

[0189] [Electrolyte layer: electrolyte]

[0190] Referring to FIGS. 3 to 7, the electrolyte layer (30) includes an electrolyte disposed between the positive electrode (10) and the negative electrode (20). The electrolyte may include, for example, a solid electrolyte, a gel electrolyte, or a combination thereof.

[0191] The solid electrolyte may include, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof.

[0192] The solid electrolyte is, for example, a sulfide-based solid electrolyte. The sulfide-based solid electrolyte is, for example, Li2S-P2S5, Li2S-P2S5-LiX, where X is a halogen element, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n , m, n are positive numbers, Z is one of Ge, Zn or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga In, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x, at least one selected from 0≤x≤2. The sulfide-based solid electrolyte is manufactured by treating starting materials such as Li2S and P2S5 by a melting rapid cooling method or a mechanical milling method. In addition, heat treatment may be performed after the treatment. The solid electrolyte may be amorphous, crystalline, or a mixture thereof. In addition, the solid electrolyte may be, for example, one containing sulfur (S), phosphorus (P), and lithium (Li) as at least constituent elements among the above-described sulfide-based solid electrolyte materials. For example, the solid electrolyte may be a material containing Li2S-P2S5. When using a sulfide-based solid electrolyte material containing Li2S-P2S5 to form a solid electrolyte, the mixing molar ratio of Li2S and P2S5 is, for example, in the range of Li2S:P2S5=20:80 to 90:10, 25:75 to 90:10, 30:70 to 70:30, 40:60 to 60:40.

[0193] The sulfide-based solid electrolyte may include, for example, an argyrodite type solid electrolyte represented by the following chemical formula 1:

[0194] <Chemical Formula 1>

[0195] Li + 12-n-x A n+ X 2- 6-x Y - x

[0196] 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-xPS 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.

[0197] 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 electrolyte layer by Li can be effectively suppressed.

[0198] Oxide solid electrolytes include, for example, Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 <x<2, 0≤y<3), BaTiO3, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT)(0≤x<1, 0≤y<1), PB(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, Li3PO4, Li x Ti y (PO4)3(0 <x<2, 0<y<3), Li x Al y Ti z (PO4)3(0 <x<2, 0<y<1, 0<z<3), Li1+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.

[0199] 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.

[0200] 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 (PVDF-HFP), polyethylene oxide (PEO), poly(styrene-b-ethylene oxide) block copolymer (PS-PEO), poly(styrene-butadiene), poly(styrene-isoprene-styrene), poly(styrene-b-divinylbenzene) block copolymer, poly(styrene-ethylene oxide-styrene) block copolymer, polystyrene sulfonate (PSS), polyvinyl fluoride (PVF), 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.

[0201] A gel electrolyte is, for example, a polymer gel electrolyte. A gel electrolyte can have a gel state without containing a polymer, for example.

[0202] 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-, BF4-, 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.

[0203] [Electrolyte layer: binder]

[0204] The electrolyte layer (30) may include, for example, a binder. The binder included in the electrolyte layer (30) is not limited to, but may include, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., and any binder used in the relevant technical field may be used. The binder of the electrolyte layer (30) may be the same as or different from the binder included in the positive electrode active material layer (12) and the negative electrode active material layer (22). The binder may be omitted.

[0205] The binder content included in the electrolyte layer (30) is 0.1 to 10 wt%, 0.1 to 5 wt%, 0.1 to 3 wt%, 0.1 to 1 wt%, 0 to 0.5 wt%, or 0 to 0.1 wt% with respect to the total weight of the electrolyte layer (30).

[0206] 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.

[0207] (Manufacturing of composite cathode active materials)

[0208] Example 1: Li2S-LiI-CNF, 2 steps, 10 hr + 6 hr, 600 rpm, 28G

[0209] (Stage 1)

[0210] Li2S and LiI were mixed in 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 for 10 h. The milling energy applied to the sample during milling was 28 G.

[0211] (Stage 2)

[0212] 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 prepare a Li2S-LiI-CNF composite. The milling conditions were 25°C, 600 rpm, and 6 h. The milling energy applied to the sample during milling was 28 G. The Li2S-LiI-CNF composite was used as a composite cathode active material.

[0213] The Mohs hardness of Li2S was 0.6, the Mohs hardness of LiI was 2.0, and the Mohs hardness of carbon nanofiber (CNF) was 1.5.

[0214] Example 2: Li2S-LiI-CNF, 2 steps, 10 hr + 3 hr, 600 rpm, 28G

[0215] A Li2S-LiI-CNF composite was prepared in the same manner as in Example 1, except that the milling time in the second step was changed to 3 hours.

[0216] Example 3: Li2S-LiI-CNF, 2 steps, 10 hr + 2 hr, 600 rpm, 28G

[0217] A Li2S-LiI-CNF composite was prepared in the same manner as in Example 1, except that the milling time in the second step was changed to 2 hours.

[0218] Example 4: Li2S-LiI-CNF, 2 steps, 10 hr + 8 hr, 600 rpm, 28G

[0219] A Li2S-LiI-CNF composite was prepared in the same manner as in Example 1, except that the milling time in the second step was changed to 8 hours.

[0220]

[0221] Comparative Example 1: Li2S-LiI-CNF, 2 steps, 10 hr + 1 hr, 600 rpm, 28G

[0222] A Li2S-LiI-CNF composite was prepared in the same manner as in Example 1, except that the milling time in the second step was changed to 1 hour.

[0223] Comparative Example 2: Li2S-LiI-CNF, 2 steps, 10 hr + 10 hr, 600 rpm, 28G

[0224] A Li2S-LiI-CNF composite was prepared in the same manner as in Example 1, except that the milling time in the second step was changed to 10 hours.

[0225] Comparative Example 3: Li2S-LiI-CNF, 2 steps, 10 hr + 10 hr, 510 rpm, 20G

[0226] (Stage 1)

[0227] A first mixture was prepared by mixing Li2S and LiI in a weight ratio of 30:20. The first mixture was mechanically milled using a ball mill to prepare a Li2S-LiI complex.

[0228] Milling conditions were 25 ℃, 510 rpm for 10 h. The milling energy applied to the sample during milling was 20 G.

[0229] (Stage 2)

[0230] A second mixture was prepared by mixing the Li2S-LiI complex and carbon nanofibers (CNF) at a weight ratio of 50:10. The second mixture was mechanically milled using a ball mill to produce a Li2S-LiI-CNF complex.

[0231] The milling conditions were 25°C, 510 rpm for 10 h. The milling energy applied to the sample during milling was 20 G. The Li2S-LiI-CNF composite was used as the composite cathode active material.

[0232] Comparative Example 4: Li2S-LiI-CNF, 2-step, 10 hr + 10 hr, 300 rpm, 7 G

[0233] A Li2S-LiI-CNF composite was manufactured in the same manner as in Example 1, except that the rotation speed was reduced to 300 rpm in the first and second steps and the milling energy was changed to 7 G.

[0234] Comparative Example 5: Li2S-LiI-CNF, 2-step, 10 hr + 10 hr, 700 rpm, 38 G

[0235] A Li2S-LiI-CNF composite was manufactured in the same manner as in Example 1, except that the rotation speed was increased to 700 rpm in the first and second steps and the milling energy was changed to 38 G.

[0236] Comparative Example 6: Simple mixture of Li2S and CNF

[0237] Li2S and carbon nanofibers (CNF) were mixed at a weight ratio of 30:30. The mixture was used as a cathode active material.

[0238] Comparative Example 7: Li2S-CNF, 1 step, 2 hr, 600 rpm, 28 G

[0239] Li2S and carbon nanofibers (CNF) were mixed at a weight ratio of 30:30. The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI composite. The milling conditions were 25°C, 600 rpm for 2 h. The milling energy applied to the sample during milling was 28 G. The Li2S-CNF composite was used as a composite cathode active material.

[0240] Comparative Example 8: Li2S-CNF-LiI, 2 stages, 10 hr + 10 hr, 600 rpm, 28G

[0241] (Stage 1)

[0242] Li2S and carbon nanofibers (CNF) were mixed at a weight ratio of 30:10. The mixture was mechanically milled using a ball mill to prepare a Li2S-CNF composite. The milling conditions were 25°C, 600 rpm, and 10 h. The milling energy applied to the sample during milling was 28 G.

[0243] (Stage 2)

[0244] Li2S-CNF composite and LiI were mixed at a weight ratio of 40:20. The mixture was mechanically milled using a ball mill to prepare a Li2S-CNF-LiI composite. The milling conditions were 25°C, 600 rpm for 10 h. The milling energy applied to the sample during milling was 28 G. The Li2S-LiI-CNF composite was used as a composite cathode active material.

[0245] Comparative Example 9: Li2S-SE-CNF, 2 steps, 10 hr + 10 hr, 600 rpm, 28G

[0246] (Stage 1)

[0247] Li2S and Li6PS5Cl solid electrolyte (SE) were mixed at a weight ratio of 30:20. The mixture was mechanically milled using a ball mill to prepare a Li2S-SE composite. The milling conditions were 25°C, 600 rpm, and 10 h. The milling energy applied to the sample during milling was 28 G.

[0248] (Stage 2)

[0249] Li2S-SE composite and CNF were mixed at a weight ratio of 50:10. The mixture was mechanically milled using a ball mill to prepare a Li2S-SE-CNF composite. The milling conditions were 25°C, 600 rpm, and 10 h. The milling energy applied to the sample during milling was 28 G. The Li2S-SE-CNF composite was used as a composite cathode active material.

[0250] Comparative Example 10: Li2S-LiI-CNF, 1 step, 2 hr, 600 rpm, 28 G

[0251] Li2S, LiI, and carbon nanofibers (CNF) were mixed in a weight ratio of 30:20:10. The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI-CNF composite. The milling conditions were 25°C, 600 rpm for 2 h. The milling energy applied to the sample during milling was 28 G. The Li2S-LiI-CNF composite was used as a composite cathode active material.

[0252]

[0253] (Manufacturing of positive and secondary batteries)

[0254] Example 5

[0255] (Polar electrode manufacturing)

[0256] The Li2S-LiI-CNF composite manufactured in Example 1 was prepared as a cathode active material. Li6PS5Cl (D50=3.0 μm, crystalline) in the form of an argyrodite crystal was prepared as a solid electrolyte. PTFE was prepared as a binder. These materials were mixed in a weight ratio of composite cathode active material: solid electrolyte: binder = 60:39:1 to prepare a cathode mixture. The cathode mixture was obtained by dry mixing using a ball mill.

[0257] The positive electrode was manufactured by placing the positive electrode active material mixture on one side of a positive electrode current collector made of aluminum foil coated on one side and plate pressing at a pressure of 200 MPa for 10 minutes. The thickness of the positive electrode was approximately 120 μm. The thickness of the positive electrode active material layer was approximately 100 μm, and the thickness of the carbon-coated aluminum foil was approximately 20 μm. The areas of the positive electrode active material layer and the positive electrode current collector were the same.

[0258] (Cathode manufacturing)

[0259] A 10 ㎛ thick SUS foil was prepared as a negative electrode 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.

[0260] 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.

[0261] (Manufacturing of solid electrolyte layer)

[0262] Li6PS5Cl solid electrolyte (D) in the form of argyrodite crystals 50=3.0 mm, 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 μm thick nonwoven fabric placed on a 75 μm thick PET substrate, and dried in air at 80°C for 10 minutes to prepare a laminate. The prepared laminate was vacuum-dried at 80°C for 2 hours to prepare a solid electrolyte layer.

[0263] (inert absence)

[0264] 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.

[0265] 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 ㎛.

[0266] 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.

[0267] (Manufacturing of all-solid-state secondary batteries)

[0268] Referring to Fig. 3, a solid electrolyte layer was placed on the negative electrode such that the first negative electrode active material layer was in contact with the solid electrolyte layer, and a positive electrode was placed on the solid electrolyte layer. A laminate was prepared by placing a gasket surrounding the positive electrode and in contact with the solid electrolyte layer. The thickness of the gasket was approximately 120 ㎛. The above-described 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 positive electrode and the solid electrolyte layer. The positive electrode was placed at the center of the solid electrolyte layer, and the gasket was placed so as to surround the positive electrode and extend to the end of the solid electrolyte layer. The area of ​​the positive electrode 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 positive electrode was not placed.

[0269] 85 prepared laminates o The 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 ㎛. 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.

[0270] 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.

[0271] Examples 6 to 8

[0272] A positive electrode and an all-solid-state secondary battery were manufactured in the same manner as in Example 5, except that the composite positive electrode active materials manufactured in Examples 2 to 4 were used.

[0273] Comparative examples 11 to 20

[0274] A positive electrode and an all-solid-state secondary battery were manufactured in the same manner as in Example 5, except that the composite positive electrode active materials manufactured in Comparative Examples 1 to 10 were used.

[0275]

[0276] Evaluation Example 1: XRD Analysis and Scanning Electron Microscopy Analysis

[0277] XRD spectra were measured using Cu Kα radiation for the raw material (bare) Li2S used in Example 1, the pulverized Li2S, the Li2S-LiI composite prepared in the first step in Example 1, and the Li2S-LiI-CNF composite prepared in Example 1.

[0278] 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 of 2θ = 27° ± 2.0° in the XRD spectrum.

[0279] 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.

[0280] The particle size (i.e., D50 particle diameter) of the composite was measured using a laser-based particle size analyzer (PSA) for the raw material Li2S used in Example 1, the pulverized Li2S, and the Li2S-LiI composite prepared in the first step in Example 1.

[0281] Scanning electron microscope images of the raw material Li2S used in Example 1 and the Li2S-LiI-CNF composite manufactured in Example 1 are shown in FIGS. 2a and 2b, respectively.

[0282] The Li2S particle size of the Li2S-LiI-CNF composite prepared in Example 1 was measured using a scanning electron microscope. The measurement results are shown in Table 1 and FIGS. 2a to 2b below.

[0283] Second peak position [°]Li2S crystallite size [nm]Li2S particle size [㎛]bare Li2S27.064.78First peak position [°]Li2S crystallite size [nm]Li2S particle size [㎛]crushed Li2S26.915.4-Li2S-LiI composite (first stage)26.68.81Less than Example 1 (Li2S-LiI-CNF composite)26.79.91Less than

[0284] As shown in Table 1, the position of the first peak for the (111) crystal plane appearing at a diffraction angle 2θ = 27° ± 2.0° of the Li2S-LiI-CNF composite of Example 1 was shifted to a low angle compared to the position of the second peak for the (111) crystal plane appearing at a diffraction angle 2θ = 27° ± 2.0° of bare Li2S.

[0285] 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 the crystallite size of bare Li2S.

[0286] As shown in Table 1 and Figure 1, the positions of the first peaks of the Li2S-LiI-CNF composite of Example 1 and the Li2S-LiI composite, which is an intermediate product of the first step of Example 1, were shifted to a low angle compared to the positions of the first peaks of the pulverized Li2S.

[0287] Although not shown in Table 1, the first lattice constant (d1) derived from the first peak for the (111) crystal plane appearing at a diffraction angle 2θ = 27° ± 2.0° of the Li2S-LiI-CNF composite of Example 1 was larger than the second lattice constant (d2) derived from the second peak for the (111) crystal plane appearing at a diffraction angle 2θ = 27° ± 2.0° of bare Li2S. The first lattice constant (d1) was 5.78 Å or more. It was determined that this was because LiI was dissolved in the Li2S crystal, increasing the lattice constant value. It was confirmed that the Li2S-LiI-CNF composite formed a solid solution.

[0288] Although not shown in Table 1, the first peak of the Li2S-LiI-CNF composite of Example 1 had a first full width at half maximum (FWHM1), and the second peak of bare Li2S had a second full width at half maximum (FWHM2), and the first full width was larger than the second full width. The first full width at half maximum (FWHM1) was 1° or greater.

[0289]

[0290] Evaluation Example 2: Composite Particle Size Analysis

[0291] The particle size (i.e., D50 particle size, D10 particle size) of the composites manufactured in Examples 1 to 4 and Comparative Examples 1 to 10 was measured using a particle size analyzer (PSA) using a laser.

[0292] The D50 particle size of the composites manufactured in Examples 1 to 4 was about 5 μm, and the D10 particle size was about 1 μm or more.

[0293] The D50 particle size of the composite manufactured in Comparative Example 1 was about 9 ㎛, and the D10 particle size was about 1 ㎛ or more.

[0294] The D50 particle size of the composite manufactured in Comparative Example 2 was less than 3 ㎛, and the D10 particle size was less than 1 ㎛.

[0295]

[0296] Evaluation Example 3: XRD Analysis and Scanning Electron Microscopy Analysis

[0297] XRD spectra were measured using Cu Kα radiation for the composite positive electrode active materials (ie, composites) manufactured in Examples 1 to 4 and Comparative Examples 1 to 10.

[0298] Some of the Li2S crystallite sizes calculated from the first peak for the (111) crystal plane appearing at a diffraction angle of 2θ = 27° ± 2.0° in the measured XRD spectrum are shown in Table 2 below. The crystallite sizes were calculated using the Sherrer Equation.

[0299] The Li2S particle sizes of the composite cathode active materials manufactured in Examples 1 to 4 and Comparative Examples 1 to 10 were measured using a scanning electron microscope. The Li2S particle size of the composite cathode active material is the arithmetic mean of the particle sizes of multiple Li2S particles measured using software from scanning electron microscope images. Some of the measurement results are shown in Table 2 below.

[0300] First stage millingSecond stage millingSolution formationLi2S crystallite size [nm]Li2S particle size [㎛]Example 1 (28 G, 6 hr) (Li2S-LiI-CNF composite)600 rpm, 28 G, 10 hr600 rpm, 28 G, 6 hr○8.91 or lessExample 2 (28 G, 3 hr) (Li2S-LiI-CNF composite)600 rpm, 28 G, 10 hr600 rpm, 28 G, 3 hr○9.11 or lessComparative example 1 (28 G, 1 hr) (Li2S-LiI-CNF composite)600 rpm, 28 G, 10 hr600 rpm, 28 G, 1 hr○9.61 or lessComparative example 2 (28 G, 10 hr) (Li2S-LiI-CNF Comparative Example 3 (Li2S-LiI-CNF composite) 600 rpm, 28 G, 10 hr 600 rpm, 28 G, 10 hr △9.81 Less than Comparative Example 3 (Li2S-LiI-CNF composite) 510 rpm, 20 G, 10 hr 510 rpm, 20 G, 10 hr ○9.91 Less than Comparative Example 4 (7 G, 10 hr) (Li2S-LiI-CNF composite) 300 rpm, 7 G, 10 hr 300 rpm, 7 G, 10 hr × 27.23 Comparative Example 5 (38 G, 10 hr) (Li2S-LiI-CNF composite) 700 rpm, 38 G, 10 hr 700 rpm, 38 G, 10 hr △15.62 Comparative Example 6 (0 G)(Li2S+ CNF Simple mixing)--×66.678 Comparative example 7 (28 G, 2 hr) (Li2S-CNF complex) 600 rpm, 28 G, 2 hr-×24.073 Comparative example 8 (28 G, 10 hr) (Li2S-CNF-LiI complex) 600 rpm, 28 G, 10 hr600 rpm, 28 G, 10 hr×15.22 Comparative example 9 (28 G, 10 hr) (Li2S-SE-CNF complex) 600 rpm, 28 G, 10 hr600 rpm, 28 G, 10 hr×8.91 Less than Comparative example 10 (28 G, 2 hr) (Li2S-LiI-CNF complex) 600 rpm, 28 G, 2 hr-○223

[0301] As shown in Table 2, the Li2S-LiI-CNF composites of Examples 1 to 2 included a Li2S-LiI solid solution, the size of the Li2S crystallites was 9.5 nm or less, and the Li2S particle size of the composite was 2 μm or less.

[0302] Although not shown in Table 2, the Li2S-LiI-CNF composites of Examples 3 to 4 also included a Li2S-LiI solid solution, the size of the Li2S crystallites was 9.5 nm or less, and the Li2S particle size of the composite was 2 μm or less.

[0303] The Li2S-LiI-CNF composite of Comparative Example 1 had a Li2S crystallite size of 9.5 nm or more due to the reduction in milling energy during manufacturing.

[0304] In the Li2S-LiI-CNF composite of Comparative Example 2, as the milling energy increased during manufacturing, LiI was phase separated into a separate phase, a solid solution was not formed, and the size of the Li2S crystallites also increased.

[0305] The Li2S-LiI-CNF composite of Comparative Example 4 failed to form a Li2S-LiI solid solution because the milling energy was excessively reduced during manufacturing.

[0306] In the Li2S-LiI-CNF composite of Comparative Example 5, a Li2S-LiI solid solution was not properly formed due to heat generation caused by increased milling energy during manufacturing.

[0307] The simple mixture of Li2S and CNF of Comparative Example 6, the Li2S-CNF complex of Comparative Example 7, and the Li2S-SE-LiI complex of Comparative Example 9 did not form a solid solution.

[0308] In the Li2S-CNF-LiI complex of Comparative Example 8, a Li2S-LiI solid solution was not properly formed because the Li2S-CNF complex was manufactured in the first step and then the Li2S-CNF-LiI complex was manufactured in the second step.

[0309] Since the Li2S-LiI-CNF composite of Comparative Example 10 was manufactured in the first step, it included a Li2S-LiI solid solution, but the Li2S crystallite size increased, and the Li2S particle size of the composite exceeded 2 μm.

[0310]

[0311] Evaluation Example 4: Measurement of ionic and electronic conductivity

[0312] Ionic conductivity and electronic conductivity were measured for the composites manufactured in Examples 1 to 4 and Comparative Examples 1 to 10. Pellets were prepared using the composites manufactured in Examples 1 to 4 and Comparative Examples 1 to 10.

[0313] A symmetrical cell was prepared by placing stainless steel current collectors on both sides of the pellet. The electronic conductivity was measured at 45°C and 1 atm using the DC polarization method.

[0314] After placing the solid electrolyte layer prepared in Example 5 on both sides of the pellet, a stainless steel current collector was placed on the solid electrolyte layer to prepare a symmetrical cell. The ionic conductivity at 45°C and 1 atm was measured using the DC polarization method. Some of the measurement results are shown in Table 3 below.

[0315] First stage millingSecond stage millingIonic conductivity [mS / cm]Electronic conductivity [mS / cm]Example 1 (28 G, 6 hr)(Li2S-LiI-CNF composite)600 rpm,28 G, 10 hr600 rpm,28 G, 6 hr0.431.38Example 2 (28 G, 3 hr)(Li2S-LiI-CNF composite)600 rpm,28 G, 10 hr600 rpm,28 G, 3 hr0.302.89Example 3 (28 G, 2 hr)(Li2S-LiI-CNF composite)600 rpm,28 G, 10 hr600 rpm,28 G, 2 hr0.292.01Example 4 (28 G, 8 hr)(Li2S-LiI-CNF complex)600 rpm, 28 G, 10 hr600 rpm, 28 G, 8 hr0.351.42Comparative example 1 (28 G, 1 hr)(Li2S-LiI-CNF complex)600 rpm, 28 G, 10 hr600 rpm, 28 G, 1 hr0.251.09Comparative example 2 (28 G, 10 hr)(Li2S-LiI-CNF complex)600 rpm, 28 G, 10 hr600 rpm, 28 G, 10 hr0.291.03Comparative example 3 (20 G, 10 hr)(Li2S-LiI-CNF complex)510 rpm, 20 G, 10 hr510 rpm, 20 G, 10 hr0.281.15

[0316] As shown in Table 3, the composites of Examples 1 to 4 had improved ionic conductivity and electronic conductivity compared to the composites of Comparative Examples 1 to 3.

[0317]

[0318] Evaluation Example 4: Pellet Density Measurement

[0319] The pellet density of the composite positive electrode active materials manufactured in Examples 1 to 4 and Comparative Examples 1 to 10 was measured using CARVER 4350L.

[0320] After measuring the initial height of the pressurized mold, a certain amount of the composite cathode active material samples manufactured in Examples 1 to 4 and Comparative Examples 1 to 10 was injected, and after maintaining the pressure at a certain level for 30 seconds, the height of the pressurized mold was measured.

[0321] The pellet density was calculated from the following mathematical formula 1. Some of the measurement results are shown in Table 4 below.

[0322] <Mathematical Formula 1>

[0323] Pellet density [g / cm 3 ] = composite cathode active material weight [g] / pellet volume [cm 3 ]

[0324]

[0325] Evaluation Example 5: Charge / Discharge Test

[0326] The charge / discharge characteristics of the all-solid-state secondary batteries of Examples 5 to 8 and Comparative Examples 11 to 20, which employed the composite positive electrode active materials manufactured in Examples 1 to 4 and Comparative Examples 1 to 10, were evaluated by the following charge / discharge test.

[0327] Charge and discharge tests were performed by placing the all-solid-state secondary battery in a constant temperature chamber at 45°C.

[0328] The first cycle involved charging for 12.5 hours at a constant current of 0.05 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 0.05 C until the battery voltage reached 0.3 V.

[0329] 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 1 below.

[0330] After the second cycle, charging and discharging were performed for up to 30 cycles under the same conditions as the first cycle. The measurement results are shown in Table 4 below. The initial efficiency is expressed by the following mathematical equation (2), and the capacity retention rate is expressed by the following mathematical equation (3).

[0331] <Mathematical Formula 2>

[0332] Initial efficiency [%] = [1st cycle discharge capacity / 1st cycle charge capacity] × 100

[0333] <Mathematical Formula 3>

[0334] Capacity retention rate [%] = [30th cycle discharge capacity / 1st cycle discharge capacity] × 100

[0335] 1st stage milling 2nd stage milling Pellet density [g / cm 3 ]Specific capacity [mAh / g]Initial efficiency [%]Capacity retention [%]Example 1 (28 G, 6 hr) (Li2S-LiI-CNF composite)600 rpm,28 G, 10 hr600 rpm,28 G, 6 hr1.6784182.584Example 2 (28 G, 3 hr) (Li2S-LiI-CNF composite)600 rpm,28 G, 10 hr600 rpm,28 G, 3 hr1.7084083.490Example 3 (28 G, 2 hr) (Li2S-LiI-CNF composite)600 rpm,28 G, 10 hr600 rpm,28 G, 2 hr1.6883281.381Example 4 (28 G, 8 hr) (Li2S-LiI-CNF complex)600 rpm, 28 G, 10 hr600 rpm, 28 G, 8 hr1.6682180.779Comparative Example 1 (28 G, 1 hr) (Li2S-LiI-CNF complex)600 rpm, 28 G, 10 hr600 rpm, 28 G, 1 hr1.6378077.453Comparative Example 2 (28 G, 10 hr) (Li2S-LiI-CNF complex)600 rpm, 28 G, 10 hr600 rpm, 28 G, 10 hr1.6180978.164Comparative Example 3 (20 G, 10 hr) (Li2S-LiI-CNF complex)510 rpm, 20 G, 10 hr510 rpm,20 G, 10 hr1.6381580.478

[0336] As shown in Table 4, the pellet density of the composite positive electrode active materials of Examples 1 to 4 is 1.65 g / cm3 That was it.

[0337] The lithium batteries of Examples 5 to 8 including the composite cathode active materials of Examples 1 to 4 had improved charge / discharge characteristics compared to the lithium batteries of Comparative Examples 11 to 13 including the composite cathode active materials of Comparative Examples 1 to 3.

[0338] It was determined that the composite cathode active material of Comparative Example 1 had poor charge / discharge characteristics of the lithium battery due to insufficient compositeness caused by excessive reduction in the second-stage milling time.

[0339] The composite cathode active material of Comparative Example 2 had a pellet density of 1.61 g / cm due to an excessive increase in the second-stage milling time and an increase in the content of fine particles with a particle size of less than 1 ㎛. 3 It decreased to .

[0340] In the composite cathode active material of Comparative Example 2, the second-stage milling time was excessively extended, resulting in the carbon-based material becoming micronized and difficulty in forming a conductive network between the composite particles. Consequently, it was determined that the internal resistance of the lithium battery containing the composite cathode active material of Comparative Example 2 increased, resulting in poor charge / discharge characteristics of the lithium battery.

[0341] Although not shown in the drawing, it was confirmed that a lithium metal layer was formed between the first negative electrode active material layer and the negative electrode current collector in the all-solid-state secondary batteries of Examples 5 to 8 after initial charging. This was confirmed through a cross-sectional scanning electron microscope image of the all-solid-state secondary battery.

[0342] [Explanation of symbols]

[0343] 1 All-solid-state secondary battery 10 Cathode

[0344] 11. Cathode current collector 12. Cathode active material layer

[0345] 20 Cathode 21 Cathode current collector

[0346] 22 First negative electrode active material layer 23 Thin film

[0347] 24 Second negative electrode active material layer 30 Electrolyte layer

[0348] 40 Inert elements

[0349] According to one aspect, it is possible to provide an all-solid-state secondary battery having increased specific capacity and improved cycle characteristics by having a composite cathode active material having a reduced crystallite size and improved density.

Claims

1. Contains a composite of Li2S, lithium salt, and carbon-based material, The size of Li2S crystallites obtained from the XRD spectrum of the above complex is 9.5 nm or less, The above complex comprises a solid solution of Li2S and a lithium salt, Pellet density is 1.65 g / cm 3 Ideal, composite bipolar active material.

2. A composite cathode active material according to claim 1, wherein the size of the composite is 1 to 10 ㎛.

3. A composite cathode active material in the first paragraph, wherein the D10 particle size of the composite is 1 ㎛ or more.

4. A composite cathode active material in the first paragraph, wherein the electronic conductivity of the composite at 25°C and 1 atm is 1.1 mS / cm or more.

5. A composite cathode active material in the first paragraph, wherein the ionic conductivity of the composite at 25°C and 1 atm is 0.3 mS / cm or more.

6. A composite cathode active material in the first paragraph, wherein the molar ratio of Li2S and lithium salt in the complex is 50:50 to 95:

5.

7. In the first paragraph, the carbon-based material is amorphous, 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 a carbon nanofiber, a carbon nanotube, a carbon nanobelt, a carbon nanorod, or a combination thereof. A composite cathode active material, wherein the content of the carbon-based material is 1 to 20 wt% of the total weight of the composite.

8. A composite cathode active material comprising 10 to 80 parts by weight of Li2S, 1 to 40 parts by weight of a lithium salt, and 1 to 20 parts by weight of a carbon-based material, based on 100 parts by weight of the composite in the first paragraph.

9. In the first paragraph, the Mohs hardness of the lithium salt and carbon-based material is greater than that of the Li2S, A composite cathode active material, wherein the Mohs hardness of the lithium salt and carbon-based material is each 0.7 or higher.

10. In the first paragraph, the first lattice constant (d1) derived from the first peak appearing at a diffraction angle 2θ = 27° ± 2.0° corresponding to the (111) crystal plane of Li2S in the XRD spectrum of the complex is greater than the second lattice constant (d2) derived from the second peak appearing at a diffraction angle 2θ = 27° ± 2.0° corresponding to the (111) crystal plane of Li2S in the XRD spectrum of Li2S used in the production of the complex. A composite cathode active material having a first lattice constant (d1) size of 5.78 Å or greater.

11. In the 10th paragraph, the first peak has a first diffraction angle, the second peak has a second diffraction angle, and the first diffraction angle is smaller than the second diffraction angle, or The first peak has a first half width (FWHM1) and the second peak has a second half width (FWHM2), and the first half width is larger than the second half width. A composite cathode active material having a first half-wave width of 1° or more.

12. A cathode current collector; and a cathode active material layer disposed on one or both sides of the cathode current collector, A cathode, wherein the cathode active material layer comprises a composite cathode active material according to any one of claims 1 to 11 and a solid electrolyte.

13. In the 12th paragraph, the positive electrode active material layer further includes a carbon-based conductive material, The above carbon-based conductive material comprises a fibrous carbon-based material, The above fibrous carbon material comprises fibrous carbon nanostructures, An anode, wherein the fibrous carbon nanostructure comprises carbon nanofibers, carbon nanotubes, carbon nanobelts, carbon nanorods or a combination thereof.

14. A positive electrode according to Article 12; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode, An all-solid-state secondary battery, wherein the negative electrode comprises a negative electrode current collector and a first negative electrode active material layer disposed on one surface of the negative electrode current collector.

15. In the 14th paragraph, the first negative electrode active material layer includes a negative electrode active material and a binder, An all-solid-state secondary battery, wherein the negative electrode active material has a particle form and the average particle diameter of the negative electrode active material is 4 ㎛ or less.

16. In the 15th 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. An all-solid-state 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.

17. In the 15th paragraph, the negative electrode active material comprises a mixture of first particles made of amorphous carbon and second particles made of a metal or a metalloid, An all-solid-state secondary battery, wherein the content of the second particles is 1 to 60 wt% based on the total weight of the mixture.

18. 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. An all-solid-state secondary battery, wherein the second negative electrode active material layer is a metal layer, and the metal layer contains lithium or a lithium alloy.

19. In the 14th paragraph, the electrolyte layer includes a solid electrolyte, a gel electrolyte or a combination thereof, The above solid electrolyte includes a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof. The above gel electrolyte comprises a polymer gel electrolyte, 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 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 , at least one selected from 0≤x≤2, The above sulfide-based solid electrolyte includes an argyrodite-type solid electrolyte, The above argyrodite-type solid electrolyte comprises at least one selected from Li6PS5Cl, Li6PS5Br and Li6PS5I, An all-solid-state secondary battery, wherein the density of the argyrodite-type solid electrolyte is 1.5 to 2.0 g / cc.

20. In the 14th paragraph, the positive electrode includes a positive 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. The above 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. An all-solid-state secondary battery further comprising an inert member disposed on one side of the positive electrode.

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