KR20250147910A - All Solid Secondary Battery - Google Patents

Abstract

An all-solid-state secondary battery is provided, comprising: a positive electrode layer; a negative electrode layer; and a solid electrolyte layer between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer includes a positive electrode current collector and a positive electrode active material layer on one surface of the positive electrode current collector, the negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer on one surface of the negative electrode current collector, the first negative electrode active material layer includes a first negative electrode active material and a carbon-based material, and the first negative electrode active material includes an alloy phase.

Description

All-solid-state secondary battery

It's about all-solid-state secondary batteries.

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

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.

All-solid-state secondary batteries can reduce the risk of fire or explosion by using solid electrolytes instead of liquid ones. All-solid-state batteries can also offer improved safety.

One aspect is to provide an all-solid-state secondary battery having improved charge-discharge characteristics and suppressing volume change during charge-discharge, including a first negative electrode active material having an alloy phase in the negative electrode active material layer.

According to one embodiment, it comprises a positive electrode layer; a negative electrode layer; and a solid electrolyte layer between the positive electrode layer and the negative electrode layer,

The above positive electrode layer includes a positive electrode current collector and a positive electrode active material layer on one surface of the positive electrode current collector,

The above negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer on one surface of the negative electrode current collector,

The first negative electrode active material layer includes a first negative electrode active material and a carbon-based material,

An all-solid-state secondary battery is provided, wherein the first negative electrode active material includes an alloy phase.

According to one aspect, an all-solid-state secondary battery is provided in which a negative electrode active material layer includes a first negative electrode active material having an alloy phase, and a decrease in volume energy density is suppressed while a change in volume during charge and discharge is suppressed, and an improved lifespan and high-rate characteristics are achieved.

Figures 1 to 12 are cross-sectional views of an all-solid-state secondary battery according to an exemplary embodiment.

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.

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.

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.

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.

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.

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.

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.

"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.

In this disclosure, "particle diameter" or "size" refers to the average diameter when the particles are spherical, and refers to the average major axis length when the particles are non-spherical. The particle diameter or size can be measured using a particle size analyzer (PSA) or a scanning electron microscope. The "particle diameter" is, for example, the average particle diameter. The "average particle diameter" is, for example, the median particle diameter, D50.

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.

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.

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.

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

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

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

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

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

In the present disclosure, “thickness” means average thickness, and “length” means average length.

In this disclosure, “aspect ratio” means the ratio (L/D) of the length of the long axis (e.g., length L) to the length of the short axis (e.g., diameter D). In this disclosure, the aspect ratio, the length of the long axis, the length of the short axis, length, and diameter all represent average values.

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.

Hereinafter, an all-solid-state secondary battery according to exemplary implementation examples will be described in more detail.

[All-solid-state secondary battery]

An all-solid-state secondary battery according to one embodiment includes a positive electrode layer; a negative electrode layer; and a solid electrolyte layer between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer includes a positive electrode current collector and a positive electrode active material layer on one surface of the positive electrode current collector, the negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer on one surface of the negative electrode current collector, the first negative electrode active material layer includes a first negative electrode active material and a carbon-based material, and the first negative electrode active material includes an alloy phase.

The first negative electrode active material layer includes a first negative electrode active material having an alloy phase, thereby improving the initial charge/discharge efficiency of the all-solid-state secondary battery during charge/discharge. Since the all-solid-state secondary battery has improved initial charge/discharge efficiency, the irreversible capacity of the all-solid-state secondary battery can be reduced. Consequently, the specific capacity of the all-solid-state secondary battery can be increased, and the energy density of the all-solid-state secondary battery can be improved.

The volume change of the first negative electrode active material layer during charge and discharge of an all-solid-state secondary battery can be mitigated by including a first negative electrode active material having an alloy phase in the first negative electrode active material layer. Consequently, by mitigating the volume change of the negative electrode layer during charge and discharge of the all-solid-state secondary battery, the high-rate characteristics and/or life characteristics of the all-solid-state secondary battery can be improved. In addition, by mitigating the volume change of the negative electrode layer during charge and discharge of the all-solid-state secondary battery, the thickness of a buffer member for accommodating the volume change of the negative electrode layer can be reduced or the buffer member can be omitted. Consequently, the energy density of the all-solid-state secondary battery can be improved.

The first negative electrode active material layer comprises a carbon-based material, which provides a conductive path between the first negative electrode active material layers. Therefore, the carbon-based material can more easily suppress an increase in the internal resistance of the first negative electrode active material layer during charge/discharge of the all-solid-state secondary battery. Consequently, an increase in the internal resistance of the all-solid-state secondary battery can be suppressed.

The carbon-based material in the first negative electrode active material layer acts as a support/buffer between the first negative electrode active materials. Therefore, the carbon-based material can more easily mitigate the volume change of the first negative electrode active material layer during charge/discharge of the all-solid-state secondary battery. Consequently, the volume change during charge/discharge of the all-solid-state secondary battery can be reduced.

The content of the carbon-based material in the first negative electrode active material layer is 1 to 50 wt%, 1 to 40 wt%, 1 to 30 wt%, 1 to 20 wt%, or 1 to 10 wt% of the total weight of the first negative electrode active material and the carbon-based material. When the content of the carbon-based material is within the above range, the charge/discharge characteristics of the all-solid-state secondary battery can be improved.

Referring to FIGS. 1 to 12, an all-solid-state secondary battery (1) includes a positive electrode layer (10); a negative electrode layer (20); and a solid electrolyte layer (30) between the positive electrode layer (10) and the negative electrode layer (20). The positive electrode layer (10) includes a positive electrode current collector (11) and a positive electrode active material layer (12) on one surface of the positive electrode current collector (11). The negative electrode layer (20) includes a negative electrode current collector (21) and a first negative electrode active material layer (22) on one surface of the negative electrode current collector (21). The first negative electrode active material layer (22) includes a first negative electrode active material and a fibrous carbon-based material. The first negative electrode active material includes an alloy phase.

[Cathode layer]

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

Referring to FIGS. 1 to 12, the negative electrode layer (20) includes a first negative electrode active material layer (22). The first negative electrode active material layer (22) includes a first negative electrode active material.

The first negative electrode active material comprises an alloy phase. The first negative electrode active material is, for example, an alloy-based negative electrode active material. By including the alloy phase, the first negative electrode active material can provide increased initial charge/discharge efficiency and/or increased discharge capacity. The first negative electrode active material may comprise an alloy phase composed of a metal other than lithium, for example.

The first negative electrode active material may include, for example, silicon (Si), iron (Fe), and a first metal. The first negative electrode active material may include, for example, an alloy phase including two or more metals selected from silicon (Si), iron (Fe), and the first metal. The capacity of the first negative electrode active material may be improved by including silicon. One silicon atom may be bonded to 4.4 lithium atoms. The first negative electrode active material may include iron and/or the first metal to alleviate rapid volume changes of the first negative electrode active material, thereby improving the life characteristics of an all-solid-state secondary battery (1) including the first negative electrode active material. The first metal may include, for example, copper (Cu), aluminum (Al), titanium (Ti), chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), zirconium (Zr), niobium (Nb), molybdenum (Mo), tin (Sn), cerium (Ce), or a combination thereof.

The first negative electrode active material may include, for example, 60 to 90 at%, 65 to 90 at%, or 70 to 90 at% of silicon (Si) with respect to 100 at% of the total weight of the first negative electrode active material. When the first negative electrode active material includes silicon (Si) in this range, the first negative electrode active material may provide a high discharge capacity. The first negative electrode active material may include, for example, more than 0 to 30 at%, 1 to 25 at%, 1 to 20 at%, 1 to 15 at%, or 1 to 10 at% of iron (Fe) with respect to 100 at% of the total weight of the first negative electrode active material.

The first negative electrode active material may include, for example, 0 to 30 at%, 1 to 25 at%, 1 to 20 at%, 1 to 15 at%, or 1 to 10 at% of the first metal relative to 100 at% of the total first negative electrode active material.

The first negative electrode active material may include, for example, copper (Cu) in an amount of more than 0 to 20 at%, 1 to 15 at%, or 1 to 10 at% relative to 100 at% of the total first negative electrode active material.

The first negative electrode active material may include, for example, 0 to 10 at%, 0 to 7 at%, or 0 to 5 at% of aluminum (Al) relative to 100 at% of the total first negative electrode active material.

The first negative electrode active material can effectively suppress excessive volume change of the first negative electrode active material by including iron, the first metal, copper and/or aluminum in the content range described above.

The first negative electrode active material may include, for example, 60 to 90 at% of silicon (Si), more than 0 to 30 at% of iron (Fe), and more than 0 to 10 at% of the first metal. And the first negative electrode active material may include, for example, 60 to 90 at% of silicon (Si), more than 0 to 30 at% of iron (Fe), and more than 0 to 10 at% of copper (Cu).

The first negative electrode active material may include, for example, 60 to 90 at% of silicon (Si), more than 0 to 30 at% of iron (Fe), more than 0 to 10 at% of copper (Cu), and 0 to 10 at% of aluminum. Since the first negative electrode active material has the composition described above, the cycle characteristics of the all-solid-state secondary battery (1) including the first negative electrode active material can be further improved.

The first negative electrode active material may, for example, form an alloy with lithium or a compound with lithium. The first negative electrode active material may include, for example, a single phase of silicon, an alloy phase of silicon and iron, an alloy phase of silicon and a first metal, an alloy phase of iron and a first metal, an alloy phase of multiple first metals, or a combination thereof. The first negative electrode active material may further include, for example, a single phase of iron, a single phase of the first metal, or a combination thereof. The single phase of silicon may exhibit significant volume change, for example, by forming an alloy with lithium or a compound with lithium. The first negative electrode active material may include an alloy phase of silicon and iron, an alloy phase of silicon and a first metal, an alloy phase of iron and a first metal, an alloy phase of multiple first metals, or a combination thereof, and some or all of these alloy phases may, for example, form an alloy with lithium or a compound with lithium. Alternatively, at least one of the alloy phase of silicon and iron, the alloy phase of silicon and the first metal, the alloy phase of iron and the first metal, the iron single phase, the first metal single phase, and the plurality of first metal alloy phases can suppress the volume change of the first negative electrode active material by, for example, suppressing the volume change of the silicon single phase without combining with lithium. At least one of the alloy phase of silicon and iron, the alloy phase of silicon and the first metal, the alloy phase of iron and the first metal, the iron single phase, the first metal single phase, and the plurality of first metal alloy phases can surround, for example, part or all of the silicon single phase. For example, the silicon single phase can be uniformly and/or non-uniformly distributed within at least one of the alloy phase of silicon and iron, the alloy phase of silicon and the first metal, the alloy phase of iron and the first metal, and the plurality of first metal alloy phases. When the first negative electrode active material has such a structure, the volume change of the first negative electrode active material can be suppressed more effectively during charge and discharge. The alloy phase of silicon and iron can be represented, for example, by Fe _a Si _b (wherein a and b are each independently a natural number from 1 to 100). The alloy phase of silicon and the first metal can be represented, for example, by M1 _c Si _d (wherein c and d are each a natural number from 1 to 100). The alloy phase of iron and the first metal can be represented, for example, by Fe _e M1 _f (wherein e and f are each a natural number from 1 to 100). The alloy phase of a plurality of first metals can be represented, for example, by M1' _g M1" _h (wherein g and h are each a natural number from 1 to 100, and M1' and M1" are each a metal selected from M1). The alloy phase of silicon and iron can include, for example, FeSi ₂ , Fe ₂ Si ₅ , FeSi or a combination thereof. The alloy phase of the first metal can be, for example, an alloy phase of copper and aluminum.

The first negative electrode active material may further include, for example, boron (B), carbon (C), phosphorus (P), or a combination thereof. When the first negative electrode active material further includes boron (B), carbon (C), phosphorus (P), or a combination thereof, the volume change of the first negative electrode active material can be more effectively mitigated. Alternatively, the first negative electrode active material may not include, for example, boron (B), carbon (C), phosphorus (P), or a combination thereof. When the first negative electrode active material does not include boron (B), carbon (C), phosphorus (P), or a combination thereof, the first negative electrode active material can be manufactured more simply and easily.

The first negative electrode active material may be, for example, a lithiated negative electrode active material. A lithiated negative electrode active material is, for example, an alloy-based negative electrode active material having the above-described alloy phase, in which lithium is additionally substituted. A method for substituting lithium may include, but is not limited to, sputtering, electrochemical charging, milling, etc., and any method known in the art for substituting lithium in an alloy-based negative electrode active material may be used. The first negative electrode active material may include, for example, lithium (Li), silicon (Si), iron (Fe), and a first metal. The first negative electrode active material may include, for example, a lithium-silicon alloy phase. The first negative electrode active material includes, for example, lithium (Li), silicon (Si), iron (Fe), and a first metal, and may include a lithium-silicon alloy phase. Since the first negative electrode active material is a lithiated negative electrode active material, the initial charge/discharge efficiency of an all-solid-state secondary battery (1) including the first negative electrode active material can be further improved. As a result, the specific capacity of the all-solid-state secondary battery (1) can be increased and the energy density can be increased by reducing the irreversible capacity of the all-solid-state secondary battery (1).

The first negative electrode active material layer (22) includes a first negative electrode active material, and the first negative electrode active material has, for example, a particle form. The size of the first negative electrode active material having a particle form is, for example, 20 μm or less, 15 μm or less, 10 μm or less, or 7 μm or less. The size of the first negative electrode active material having a particle form is, for example, 0.1 to 20 μm, 0.5 to 20 μm, 1 to 20 μm, 1 to 15 μm, 1 to 10 μm or 3 to 7 μm. Since the first negative electrode active material has a size in this range, the first negative electrode active material can more easily perform reversible absorption and/or desorption of lithium during charge and discharge. The size of the first negative electrode active material is, for example, an average particle diameter of the first negative electrode active material. The average particle size of the first negative electrode active material is, for example, the median diameter (D50) measured using a laser particle size distribution analyzer. The size of the first negative electrode active material can be measured using, for example, a laser particle size distribution analyzer, a scanning electron microscope, etc.

The aspect ratio of the first negative electrode active material is, for example, 5 or less, 4 or less, 3 or less, or 2 or less. The aspect ratio of the first negative electrode active material is, for example, 1 to 5, 1 to 4, 1 to 3, or 1 to 2. Since the first negative electrode active material has an aspect ratio within this range, it can be more uniformly distributed within the first negative electrode active material layer (22). Consequently, the non-uniformity of the volume change during charge and discharge of the first negative electrode active material can be suppressed. The aspect ratio of the first negative electrode active material can be measured, for example, using a scanning electron microscope.

In the present disclosure, the average particle diameter is, for example, the median diameter (D50) measured using a laser particle size distribution meter. Alternatively, the average particle diameter can be determined automatically using software, for example, from electron microscope images, or manually by a manual method.

The first negative electrode active material layer (22) includes a first negative electrode active material. By having the first negative electrode active material having a weight ratio within this range, the cycle characteristics of the all-solid-state secondary battery (1) can be further improved.

[First negative electrode active material layer: carbon-based material]

The first negative electrode active material layer (22) includes a carbon-based material in addition to the first negative electrode active material. The carbon-based material may include, for example, a fibrous carbon-based material.

The first negative electrode active material layer (22) may include, for example, a mixture of a first negative electrode active material including an alloy phase and a fibrous carbon-based material. The first negative electrode active material layer (22) may include, for example, a mixture of a fibrous carbon-based material and one or more first negative electrode active materials selected from the group consisting of silicon (Si), gold (Au), platinum (Pt), palladium (Pd), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). The mixing ratio of the mixture containing the fibrous carbon-based material and the first negative electrode active material such as silicon is, for example, a weight ratio of 99:1 to 1:99, 10:1 to 1:10, 1:1 to 1:9, 1:1 to 1:8, 1:1 to 1:7, 1:1 to 1:6, 1:1 to 1:5, 1:1 to 1:4 or 1:1 to 1:3, but is not necessarily limited to this range and may be selected depending on the characteristics of the required all-solid-state secondary battery (1). When the fibrous carbon-based material and the negative electrode active material have this composition, the cycle characteristics of the all-solid-state secondary battery (1) can be further improved.

The first negative electrode active material layer (22) may include, for example, a mixture of first particles made of the first negative electrode active material and second particles made of a fibrous carbon-based material. The first particles may be particles including, for example, silicon (Si), iron (Fe), and a first metal, and an alloy phase of two or more elements selected from among these. The first metal may include, for example, copper (Cu), titanium (Ti), chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), zirconium (Zr), niobium (Nb), molybdenum (Mo), tin (Sn), cerium (Ce), or a combination thereof. The content of the second particles is, for example, 1 to 50 wt%, 1 to 40 wt%, 1 to 30 wt%, 1 to 25 wt%, 1 to 20 wt%, 1 to 15 wt%, or 1 to 10 wt% based on the total weight of the mixture. When the fibrous carbon-based material has a content within this range, the cycle characteristics of, for example, an all-solid-state secondary battery (1) can be further improved.

The fibrous carbon-based material may be, for example, a conductive carbon-based material. Since the fibrous carbon-based material has conductivity, it can provide a conductive path within the first negative electrode active material layer (22). The fibrous carbon-based material can more effectively reduce the internal resistance of the first negative electrode active material layer (22). As a result, the cycle characteristics of the all-solid-state secondary battery (1) are improved. The first negative electrode active material layer (22) may not additionally include any other carbon-based conductive material other than the fibrous carbon-based material. Since the first negative electrode active material layer (22) does not include any other carbon-based conductive material other than the fibrous carbon-based material, the energy density of the first negative electrode active material layer (22) can be further improved.

The aspect ratio of the fibrous carbon-based material can be, for example, 10 or more, 20 or more, 30 or more, or 50 or more. The aspect ratio of the fibrous carbon-based material can be, for example, 2000 or less, 1000 or less, 500 or less, 200 or less, or 100 or less. The aspect ratio of the fibrous carbon-based material can be, for example, 10 to 2000, 20 to 2000, 30 to 2000, or 50 to 2000. The aspect ratio of the fibrous carbon-based material can be, for example, 10 to 2000, 10 to 1000, 10 to 500, 10 to 200, 10 to 100, 10 to 50, or 10 to 20. The aspect ratio of the fibrous carbon-based material is, for example, the ratio of the length of the major axis of the fibrous carbon-based material, i.e., the length of the fibrous carbon-based material, to the length of the minor axis perpendicular to the major axis, i.e., the diameter of the fibrous carbon-based material. When the fibrous carbon-based material has an aspect ratio within this range, the fibrous carbon-based material can have a longer conducting path within the first negative electrode active material layer (22). The fibrous carbon-based material can form a three-dimensional conductive network within the first negative electrode active material layer (22), thereby more effectively reducing the internal resistance of the first negative electrode active material layer (22). As a result, the internal resistance of the all-solid-state secondary battery (1) is reduced. For example, the high-rate characteristics of the all-solid-state secondary battery (1) can be improved.

The fibrous carbon-based material may include, for example, an amorphous fibrous carbon-based material, a crystalline fibrous carbon-based material, or a combination thereof. When the fibrous carbon-based material includes an amorphous fibrous carbon-based material, side reactions between lithium and the fibrous carbon-based material can be more effectively suppressed. By improving the reversibility of the electrode reaction during charge and discharge of the all-solid-state secondary battery (1), the cycle characteristics of the all-solid-state secondary battery (1) can be improved.

The diameter of the fibrous carbon-based material may be, for example, 50 nm or less, 30 nm or less, 20 nm or less, or 10 nm or less. The diameter of the fibrous carbon-based material may be, for example, 1 nm to 50 nm, 1 nm to 30 nm, or 1 nm to 10 nm. Since the fibrous carbon-based material has a diameter in this range, the internal resistance of the first negative electrode active material layer (22) can be effectively reduced and the fibrous carbon-based material can be easily dispersed in a solvent and/or slurry during the manufacture of the first negative electrode active material layer (22).

The length of the fibrous carbon-based material can be, for example, 1000 μm or less, 100 μm or less, 50 μm or less, 10 μm or less, 5 μm or less, 2 μm or less, 1 μm or less, 500 nm or less, or 300 nm or less. The length of the fibrous carbon-based material can be, for example, 100 nm to 1000 μm, 100 nm to 500 μm, 100 nm to 100 μm, 100 nm to 50 μm, 100 nm to 10 μm, 100 nm to 5 μm, 100 nm to 2 μm, 100 nm to 1 μm, 100 nm to 500 nm, or 100 nm to 300 nm. The length of the fibrous carbon-based material may be, for example, 500 nm to 1000 μm, 500 nm to 500 μm, 500 nm to 100 μm, 500 nm to 50 μm, 500 nm to 10 μm, 1 μm to 10 μm, or 2 μm to 8 μm. As the length of the fibrous carbon-based material increases, the internal resistance of the electrode may decrease.

The fibrous carbon-based material may include, for example, fibrous carbon nanostructures. The fibrous carbon nanostructures may include, for example, carbon nanofibers, carbon nanotubes, carbon nanobelts, or combinations thereof.

The carbon nanotube may include, for example, a carbon nanotube primary structure, a carbon nanotube secondary structure formed by agglomeration of a plurality of carbon nanotube primary particles, or a combination thereof.

The primary structure of a carbon nanotube is a single carbon nanotube unit. A carbon nanotube unit has a graphite sheet in the shape of a cylinder with a nano-sized diameter and an sp2 bonding structure. Depending on the angle and structure of the graphite sheet, it can exhibit the properties of a conductor or a semiconductor. Carbon nanotube units can be classified into single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs) depending on the number of bonds forming the wall. The thinner the wall of a carbon nanotube unit, the lower the resistance.

The carbon nanotube primary structure may include, for example, a single-walled carbon nanotube (SWCNT), a double-walled carbon nanotube (DWCNT), a multi-walled carbon nanotube (MWCNT), or a combination thereof. The diameter of the carbon nanotube primary structure may be, for example, 1 nm or more or 2 nm or more. The diameter of the carbon nanotube primary structure may be, for example, 20 nm or less or 10 nm or less. The diameter of the carbon nanotube primary structure may be, for example, 1 nm to 20 nm, 1 nm to 15 nm, or 1 nm to 10 nm. The length of the carbon nanotube primary structure may be, for example, 100 nm or more or 200 nm or more. The length of the carbon nanotube primary structure can be, for example, 2 μm or less, 1 μm or less, 500 nm or less, or 300 nm or less. The length of the carbon nanotube primary structure can be, for example, 100 nm to 2 μm, 100 nm to 1 μm, 100 nm to 500 nm, 100 nm to 400 nm, 100 nm to 300 nm, or 200 nm to 300 nm. The diameter and length of the carbon nanotube primary structure can be measured from scanning electron microscope (SEM) or transmission electron microscope (TEM) images. Alternatively, the diameter and/or length of the carbon nanotube primary structure can be measured by laser diffraction.

A carbon nanotube secondary structure is a structure formed by assembling carbon nanotube primary structures, wholly or partially, into a bundle or bundle shape. The carbon nanotube secondary structure may include, for example, a bundle-type carbon nanotube, a rope-type carbon nanotube, or a combination thereof. The diameter of the carbon nanotube secondary structure may be, for example, 2 nm or more, or 3 nm or more. The diameter of the carbon nanotube secondary structure may be, for example, 50 nm or less, 30 nm or less, 20 nm or less, or 10 nm or less. The diameter of the carbon nanotube secondary structure may be, for example, 2 nm to 50 nm, 2 nm to 30 nm, or 2 nm to 20 nm. The length of the carbon nanotube secondary structure can be, for example, 500 nm or more, 700 nm or more, 1 μm or more, or 10 μm or more. The length of the carbon nanotube secondary structure can be, for example, 1000 μm or less, 500 μm or less, or 100 μm or less. The length of the carbon nanotube secondary structure can be, for example, 500 nm to 1000 μm, 500 nm to 500 μm, 500 nm to 200 μm, 500 nm to 100 μm, 500 nm to 50 μm, 500 nm to 10 μm, 1 μm to 10 μm, or 2 μm to 8 μm. The diameter and length of the carbon nanotube secondary structure can be measured from a scanning electron microscope (SEM) image or an optical microscope. Alternatively, the diameter and/or length of the carbon nanotube secondary structure can be measured by laser diffraction.

The carbon nanotube secondary structure can be converted into a carbon nanotube primary structure by dispersing it in a solvent, etc., and then used to manufacture the first negative electrode active material layer (22).

[First negative electrode active material layer: binder]

The first negative electrode active material layer (22) may further include a binder.

By binding the first negative electrode active material and the fibrous carbon-based material with the binder, the disconnection of the conductive path between the first negative electrode active material and the fibrous carbon-based material due to volume change of the first negative electrode active material during the precipitation and/or dissolution of lithium during charge and discharge can be more effectively suppressed. The non-uniformity of the electrode reaction of the all-solid-state secondary battery (1) can be suppressed.

The binder can improve the bonding strength between the first negative electrode active material layer (22) and the solid electrolyte layer (30) or between the first negative electrode active material layer (22) and the negative electrode current collector (21). For example, the binder can improve the wettability between the first negative electrode active material layer (22) and the solid electrolyte layer (30) or between the first negative electrode active material layer (22) and the negative electrode current collector (21). Therefore, the binder can more effectively reduce the increase in interfacial resistance due to the formation of pores between the first negative electrode active material layer (22) and the solid electrolyte layer (30) or between the first negative electrode active material layer (22) and the negative electrode current collector (21). The cycle characteristics of the all-solid-state secondary battery (1) can be improved.

If the first negative electrode active material layer does not include a binder, the surface of the solid electrolyte layer and/or the negative electrode current collector may be exposed due to the first negative electrode active material layer being detached from the solid electrolyte layer and/or the negative electrode current collector. For example, the exposed negative electrode current collector may cause a short circuit. The cycle characteristics of the all-solid-state secondary battery may deteriorate.

The binder is, for example, a polymer binder. The binder included in the first negative electrode active material layer (22) includes, 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. The binder may include, for example, a fluorinated binder.

The first negative electrode active material layer (22) includes a binder, so that 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, when 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 detached from the negative electrode current collector (21), the possibility of a short circuit occurring increases at the exposed portion of the negative electrode current collector (21) due to the negative electrode current collector (21) coming into contact with the solid electrolyte layer (30). 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 and the fibrous carbon-based 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).

The binder content may be 0.1 to 20 parts by weight, 0.1 to 15 parts by weight, 1 to 10 parts by weight, or 5 to 10 parts by weight, based on 100 parts by weight of the first negative electrode active material. By having a binder content within this range, the cycle characteristics of the all-solid-state secondary battery (1) can be further improved.

[First negative electrode active material layer: other additives]

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.

[Cathode layer: first cathode active material layer]

Referring to FIGS. 1 to 12, the positive electrode layer (10) includes a positive electrode active material layer (12) and the negative electrode layer (20) includes a first negative electrode active material layer (22).

The initial charge capacity (B) of the first negative electrode active material layer (22) is, for example, 75% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less of the initial charge capacity (A) of the positive electrode active material layer (12).

The ratio (B/A) of the initial charge capacity (B) of the first negative electrode active material layer (22) and the initial charge capacity (A) of the positive electrode active material layer (12) is, for example, 0.01 to 0.75, 0.01 to 0.7, 0.01 to 0.6, 0.01 to 0.5, 0.01 to 0.6, 0.01 to 0.5, 0.01 to 0.4, 0.01 to 0.3, 0.01 to 0.2, or 0.01 to 0.1. 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 (12) is, for example, 0.05 to 0.75, 0.1 to 0.7, 0.1 to 0.6, 0.2 to 0.6, 0.2 to 0.5, or 0.2 to 0.45. The initial charge capacity of the positive electrode active material layer (12) is determined by charging from the first open circuit voltage (1 ^st open circuit voltage) to the maximum charging voltage for Li/Li ⁺ . The initial charge capacity of the first negative electrode active material layer (22) is determined by charging from the second open circuit voltage (2 ^nd open circuit voltage) to 0.01 V for Li/Li ⁺ . The maximum charging voltage is determined depending on the type of positive electrode active material. The maximum charge 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 charge voltage of Li ₂ S or Li ₂ S complex can be determined between 2.5 and 3.0 V vs. Li/Li ⁺ . For example, the maximum charge voltage of lithium transition metal oxide can be determined between 3.0 and 4.5 V vs. Li/Li ⁺ .

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 multiple 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 multiple types of negative electrode active materials are used, the charge capacity density × 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. The initial charge capacity of each of the positive electrode active material layer (12) and the first negative electrode active material layer (22) can be directly measured using the all-solid-state half-cell at a constant current density, for example, 0.1 mA/cm ² . For the positive electrode, the measurement can be performed for an operating voltage from a first open circuit voltage (OCV) to a maximum charge voltage, for example, 3.0 V (vs. Li/Li ⁺ ). For the negative electrode, the measurement can be performed for an operating voltage from a second open circuit voltage (OCV) to 0.01 V for the negative electrode, for example, lithium metal. For example, the all-solid-state half-cell having the positive electrode active material layer can be charged from the first open circuit voltage to 3.0 V with a constant current of 0.1 mA/cm ² . The all-solid-state half-cell having the first negative electrode active material layer can be charged from the second open circuit voltage to 0.01 V with a constant current of 0.1 mA/cm ² . The current density during the constant current charging can be, 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, 4.0 V or 4.5 V. The maximum charging 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.

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/discharge processes may 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).

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 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%, or 1 to 10% 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 μm, 2 to 40 μm, 3 to 30 μm, 4 to 20 μm, or 5 μm to 20 μm. The thickness of the first negative electrode active material layer (22) is, for example, 5 to 50 ㎛, 10 to 50 ㎛, 15 to 50 ㎛, 20 to 50 ㎛, or 25 ㎛ to 50 ㎛. 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) may 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) is excessively increased, 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.

[Cathode layer: second cathode active material layer]

Referring to FIG. 3, the all-solid-state secondary battery (1) may further include, after being charged, a second negative electrode active material layer (24) disposed, for example, between the negative electrode current collector (21) and the first negative electrode active material layer (22). The second negative electrode active material layer (24) is a metal layer containing lithium or a lithium alloy. The metal layer contains lithium or a lithium alloy. Therefore, since the second negative electrode active material layer (24) is a metal layer containing lithium, it functions as, for example, a lithium reservoir. The lithium alloy is, for example, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, a Li-Si alloy, etc., but is not limited thereto, and any lithium alloy used in the art may be used. The second negative electrode active material layer (24) may be made of one of these alloys or lithium, or may be made of several types of alloys. The second negative electrode active material layer (24) is, for example, a plated layer. The second negative electrode active material layer (24) is deposited between the first negative electrode active material layer (22) and the negative electrode current collector (21), for example, during the charging process of an all-solid-state secondary battery (1).

The thickness of the second negative electrode active material layer (24) is not particularly limited, but is, for example, 1 to 200 μm, 1 to 150 μm, 1 to 100 μm, 1 to 50 μm, 1 to 30 μm, 1 to 22 μm, or 1 μm to 10 μm. 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.

The thickness of the second negative electrode active material layer (24) may be, for example, smaller than the thickness of the first negative electrode active material layer (22). The thickness of the second negative electrode active material layer (24) may be, for example, 70% or less, 60% or less, 50% or less, 40% or less, or 30% or less of the thickness of the first negative electrode active material layer (22). The thickness of the second negative electrode active material layer (24) may be, for example, 1 to 70%, 1 to 60%, 1 to 50%, 1 to 40%, or 1 to 30% of the thickness of the first negative electrode active material layer (22). Since the thickness of the second negative electrode active material layer (24) is smaller than the thickness of the first negative electrode active material layer (22), volume change during charge and discharge of the all-solid-state secondary battery may be suppressed. As a result, deterioration can be suppressed by volume change of the all-solid-state secondary battery.

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).

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, because the negative electrode active material included in the first negative electrode active material layer (22) includes 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 plays a role of suppressing the precipitation and growth of lithium dendrites. Therefore, it suppresses short circuit 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), the first negative electrode active material layer (22), and the region therebetween are Li-free regions that do not contain lithium (Li) in the initial state of the all-solid-state secondary battery (1) or in the state after complete discharge.

[Cathode layer: negative electrode collector]

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.

Referring to FIG. 2, the all-solid-state secondary battery (1) may further include a thin film (23) containing an element capable of forming an alloy with lithium on one surface of the negative electrode collector (21). The thin film (23) is disposed between the negative electrode collector (21) and the first negative electrode active material layer (22). The thin film (23) contains, for example, an element capable of forming an alloy with lithium. The element capable of forming an alloy with lithium includes, but is not limited to, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., and any element capable of forming an alloy with lithium in the art may be used. The thin film (23) is composed of one of these metals or an alloy of several types of metals. By placing the thin film (23) on one surface of the negative electrode current collector (21), for example, the deposition shape of the second negative electrode active material layer (24) deposited between the thin film (23) and the first negative electrode active material layer (22) becomes flatter, and the cycle characteristics of the all-solid-state secondary battery (1) can be further improved.

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.

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. If the base film includes an insulating thermoplastic polymer, the base film may soften or liquefy when a short circuit occurs, thereby blocking battery operation and suppressing a sudden 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 the all-solid-state secondary battery.

[Cathode layer: first inert member]

Referring to FIGS. 4 to 5 and 8 to 12, the all-solid-state secondary battery (1) may further include a first inactive member (40, 40a, 40b) disposed on at least one of the other surface of the negative electrode current collector (21) and the other surface of the positive electrode current collector (11).

The first inert member (40, 40a, 40b) may not include an electrode active material. The first inert member (40, 40a, 40b) may be, for example, an insulating member.

The first inert member (40, 40a, 40b) may additionally include a conductive material to have conductivity. The first inert member (40, 40a, 40b) may additionally include a flame retardant material to be, for example, a flame retardant inert member.

The first inert member (40, 40a, 40b) may be, for example, an elastic member. The first inert member (40, 40a, 40b) may be, for example, a porous elastic member. The first inert member (40, 40a, 40b) may be, for example, an elastic member having one or more of porosity, conductivity, and flame retardancy.

The first inert member (40, 40a, 40b) provides a buffering function to the all-solid-state secondary battery (1). The first inert member (40, 40a, 40b) provides, for example, stress relaxation and restoring force. The first inert member (40, 40a, 40b) can effectively accommodate changes in the volume of the all-solid-state secondary battery (1) and apply a constant pressure to the all-solid-state secondary battery (1).

The first inert member (40, 40a, 40b) may have a lower elastic modulus than, for example, the negative electrode current collector (21). Since the first inert member (40, 40a, 40b) has a lower elastic modulus than the negative electrode current collector (21), the volume change of the negative electrode layer (20) can be more effectively accommodated during charging and discharging of the all-solid-state secondary battery (1). The first inert member (50) can effectively alleviate internal stress due to volume change of the all-solid-state secondary battery (1) during charging and discharging of the all-solid-state secondary battery (1), thereby improving the cycle characteristics of the all-solid-state secondary battery (1).

The first inert member (40, 40a, 40b) may be disposed, for example, on the negative electrode layer (20) of the all-solid-state secondary battery (1). When the volume change of the negative electrode layer (20) is relatively large compared to the positive electrode layer (10) and the solid electrolyte layer (30) during charging and discharging of the all-solid-state secondary battery (1), the volume change of the negative electrode layer (20) can be accommodated more effectively by the first inert member (40, 40a, 40b) being disposed adjacent to the negative electrode layer (20). In addition, the first inert member (40, 40a, 40b) may induce, for example, uniform precipitation of lithium metal in the negative electrode layer (20) by applying a constant pressure to the negative electrode layer (20). Therefore, the generation of defects in the all-solid-state secondary battery (1) due to uneven precipitation of lithium metal can be more effectively prevented.

Alternatively, the first inert member (40, 40a, 40b) may be disposed, for example, on the positive electrode layer (10) of the all-solid-state secondary battery (1). Since the first inert member (40, 40a, 40b) is disposed adjacent to the positive electrode layer (10), the volume change of the all-solid-state secondary battery (1) can be accommodated more effectively. In addition, since the first inert member (40, 40a, 40b) applies a constant pressure to the all-solid-state secondary battery (1), uniform precipitation of lithium metal, for example, can be induced in the negative electrode layer (20). Therefore, the generation of defects in the all-solid-state secondary battery (1) due to uneven precipitation of lithium metal can be more effectively prevented.

The first inert member (40, 40a, 40b) may include a polymer material, a rubber material, or a combination thereof. The first inert member (40, 40a, 40b) may include a polymer material, a rubber material, or a combination thereof, so that the first inert member (40, 40a, 40b) may have stress relaxation and resilience. The polymer material may include, for example, a polyurethane-based polymer, a polyacrylic-based polymer, a polystyrene-based polymer, a polyester-based polymer, a polyamide-based polymer, a polyolefin-based polymer, or a combination thereof. The polymer material may be, for example, a polymer resin. The polymer material may be, for example, an adhesive resin. The rubber material may include, for example, natural rubber (NR), butadiene rubber (BR), nitrile rubber, silicone rubber, isoprene rubber (IR), styrene-butadiene rubber (SBR), isoprene-butadiene rubber, styrene-isoprene-butadiene rubber, acrylonitrile-butadiene rubber (NBR), ethylene-propylene-diene rubber, halogenated butyl rubber, chloroprene (CR), halogenated isoprene rubber, halogenated isobutylene copolymer, chloroprene rubber, butyl rubber (IIR), halogenated isobutylene-p-methylstyrene rubber, or combinations thereof. The polyurethane polymer may include, for example, polyester-based polyurethane, polyether-based polyurethane, or combinations thereof. The polyacrylic polymer may include, for example, polyacrylate, polymethyl acrylate, polymethacrylate, polymethyl methacrylate, or combinations thereof. The polystyrene polymer may include, for example, a styrene-ethylene-butylene copolymer (SEB), a styrene-butadiene-styrene copolymer (SBS), a hydrogenated form of SBS (styrene-ethylene-butylene-styrene copolymer (SEBS)), a styrene-isoprene-styrene copolymer (SIS), a hydrogenated form of SIS (styrene-ethylene-propylene-styrene copolymer (SEPS)), a styrene-isobutylene-styrene copolymer (SIBS), a styrene-butadiene-styrene-butadiene (SBSB), a styrene-butadiene-styrene-butadiene-styrene (SBSBS), polystyrene (PS), an acrylonitrile styrene copolymer (AS), an acrylonitrile butadiene styrene copolymer (ABS), or a combination thereof. Polyester polymers may include, for example, polyethylene terephthalate, polybutylene terephthalate, or combinations thereof. Polyamide polymers may include, for example, polyamide 6, polyamide 11, polyamide 12, polyamide 66, polyamide 610, or combinations thereof. Polyolefin polymers include, for example, polyethylene, polypropylene, ethylene propylene copolymer, propylene-1-hexene copolymer, propylene-4-methyl-1-pentene copolymer, propylene-1-butene copolymer, ethylene-1-hexene copolymer, ethylene-4-methyl-pentene copolymer, ethylene-1-butene copolymer, 1-butene-1-hexene copolymer, 1-butene-4-methyl-pentene, ethylene methacrylic acid copolymer, ethylene ethyl methacrylate copolymer, ethylene ethyl methacrylate copolymer, ethylene butyl methacrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-butylacrylate copolymer, propylene-methacrylic acid copolymer, propylene-methyl methacrylate copolymer, propylene-methacrylic acid It may include a polyolefin of ethyl copolymer, propylene-butyl methacrylate copolymer, propylene-methyl acrylate copolymer, propylene-ethyl acrylate copolymer, propylene-butylacrylate copolymer, ethylene-vinyl acetate copolymer (EVA), propylene-vinyl acetate copolymer, or a combination thereof.

The first inert member (40, 40a, 40b) may include, for example, a porous foam, a porous sponge, or a combination thereof. The first inert member (40, 40a, 40b) may include, for example, a porous foam sheet, a porous sponge sheet, or a combination thereof. By having this form, the first inert member (40, 40a, 40b) can provide both porosity and a cushioning function. The porous foam may include, for example, closed cells, open cells, or a combination thereof. The porous sponge may include, for example, closed cells, open cells, or a combination thereof. A closed cell means a cell or pore that is not connected to the surrounding atmosphere as a closed pore, for example. An open cell means a cell or pore that is connected to the surrounding atmosphere as an open pore, for example. The first inert member (40, 40a, 40b) may include, for example, a closed-cell porous foam, an open-cell porous foam, a closed-cell porous sponge, an open-cell porous sponge, or a combination thereof. The porous foam may, for example, contain both closed and open cells. The porous sponge may, for example, contain both closed and open cells.

The first inert member (40, 40a, 40b) may include, for example, a conductive material. The conductive material is, for example, graphite, carbon black, acetylene black, Ketjen black, Denka black, carbon fiber, carbon nanotube (CNT), graphene, metal fiber, metal powder, etc. The content of the conductive material included in the first inert member (40, 40a, 40b) is, for example, 1 to 30 parts by weight, 1 to 20 parts by weight, 1 to 15 parts by weight, 1 to 10 parts by weight, 5 to 40 parts by weight, 5 to 30 parts by weight, or 5 to 35 parts by weight, based on 100 parts by weight of the first inert member (40, 40a, 40b). Since the first inert member (50) is conductive, it can function as a negative electrode current collector (50).

The first inert member (40, 40a, 40b) 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. The matrix may have elasticity by including the fibrous substrate. The fibrous substrate includes, for example, one or more selected from pulp fibers, insulating polymer fibers, and ion-conducting polymer fibers. The strength of the matrix is improved by including the reinforcing material. The fibrous reinforcing material is, for example, glass fibers, metal oxide fibers, ceramic fibers, etc. The fibrous reinforcing material is, for example, a flame retardant material. The filler is, for example, a moisture getter and/or a flame retardant. The filler is, for example, a metal hydroxide having moisture absorbency. 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 thickness of the first inert member (40, 40a, 40b) is, for example, 1 ㎛ to 300 ㎛, 10 ㎛ to 200 ㎛, 10 ㎛ to 100 ㎛, or 10 ㎛ to 50 ㎛. If the thickness of the first inert member (40, 40a, 40b) is too thin, it may be difficult to provide the intended effect, and if the thickness of the first inert member (40, 40a, 40b) is too thick, the energy density of the all-solid-state secondary battery (1) may be reduced. The shape of the first inert member (40, 40a, 40b) is not particularly limited and may be selected according to the shape of the all-solid-state secondary battery (1). The first inert member (40, 40a, 40b) may be, for example, in the shape of a sheet, a rod, or a gasket. The first inactive member (40, 40a, 40b) may be omitted, for example.

[Anode layer]

[Cathode active material layer: Cathode active material]

Referring to FIGS. 1 to 12, the positive electrode layer (10) includes a positive electrode active material layer (12). The positive electrode active material layer (12) includes a positive electrode active material.

The cathode active material included in the cathode active material layer (12) is a cathode active material capable of reversibly absorbing and desorbing lithium ions. The cathode active material includes, for example, an oxide-based cathode active material, a sulfide-based cathode active material, or a combination thereof.

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

Sulfide-based cathode active materials include, for example, nickel sulfide, copper sulfide, Li ₂ S, Li ₂ S-containing complexes, or combinations thereof.

The oxide-based cathode active material may be, for example, at least one compound oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof. The lithium-containing oxide-based cathode active material may be, for example, Li _a A _1-b B' _b D ₂ (wherein 0.90 ≤ a ≤ 1, and 0 ≤ b ≤ 0.5); Li _a E _1-b B' _b O _2-c D _c (wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05); LiE _2-b B' _b O _4-c D _c (wherein 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05); Li _a Ni _1-bc Co _b B' _c D _α (in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Co _b B' _c O _2-α F' _α (in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Co _b B' _c O _2-α F' _α (in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b B' _c D _α (in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Mn _b B' _c O _2-α F' _α (in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b B' _c O _2-α F' _α (in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _b E _c G _d O ₂ (In the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li _a Ni _b Co _c Mn _d G _e O ₂ (In the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li _a NiG _b O ₂ (In the above formula, 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li _a CoG _b O ₂ (wherein 0.90 ≤ a ≤ 1 and 0.001 ≤ b ≤ 0.1); Li _a MnG _b O ₂ (wherein 0.90 ≤ a ≤ 1 and 0.001 ≤ b ≤ 0.1); Li _a Mn ₂ G _b O ₄ (wherein 0.90 ≤ a ≤ 1 and 0.001 ≤ b ≤ 0.1); LiV ₂ O ₅ ; LiI'O ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); LiFePO ₄ .

In the chemical formula representing the above-described compound, A is Ni, Co, Mn, or a combination thereof; B' is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F' is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I' is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof. It is also possible to use a compound having a coating layer added to the surface of the above-described compound, or it is also possible to use a mixture of the above-described compound and the compound having a coating layer added. The coating layer added to the surface of the above-mentioned compound includes a coating element compound of, for example, an oxide, a hydroxide, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, or a hydroxycarbonate of the coating element of the coating element. The compound forming the coating layer is amorphous or crystalline. The coating elements included in the coating layer are Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. The method for forming the coating layer is selected within a range that does not adversely affect the physical properties of the positive electrode active material. The coating method includes, for example, spray coating and dipping. Since the specific coating method is well understood by those working in the relevant field, a detailed description thereof will be omitted.

The oxide-based cathode active material may include, for example, a lithium transition metal oxide represented by the following chemical formulas 1 to 8:

<Chemical Formula 1>

Li _a Ni _x Co _y M _z O _2-b A _b

In the above chemical formula 1, 1.0≤a≤1.2, 0≤b≤0.2, 0.8≤x<1, 0≤y≤0.3, 0<z≤0.3, and x+y+z=1, M is manganese (Mn), niobium (Nb), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al), boron (B), or a combination thereof,

A is F, S, Cl, Br or a combination thereof,

<Chemical Formula 2>

LiNi _x Co _y Mn _z O ₂

<Chemical Formula 3>

LiNi _x Co _y Al _z O ₂

In the above chemical formulas 2 to 3, 0.8≤x≤0.95, 0≤y≤0.2, 0<z≤0.2 and x+y+z=1,

<Chemical Formula 4>

LiNi _x Co _y Mn _z Al _w O ₂

In the above chemical formula 4, 0.8≤x≤0.95, 0≤y≤0.2, 0<z≤0.2, 0<w≤0.2, and x+y+z+w=1,

<Chemical Formula 5>

Li _a Co _x M _y O _2-b A _b

In the above chemical formula 5,

1.0≤a≤1.2, 0≤b≤0.2, 0.9≤x≤1, 0≤y≤0.1, and x+y=1,

M is manganese (Mn), niobium (Nb), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al), boron (B), or a combination thereof,

A is F, S, Cl, Br or a combination thereof,

<Chemical Formula 6>

Li _a Ni _x Mn _y M' _z O _2-b A _b

In the above chemical formula 6,

1.0≤a≤1.2, 0≤b≤0.2, 0<x≤0.3, 0.5≤y<1, 0<z≤0.3, and x+y+z=1,

M' is cobalt (Co), niobium (Nb), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al), boron (B) or a combination thereof,

A is F, S, Cl, Br or a combination thereof,

<Chemical Formula 7>

Li _a M1 _x M2 _y PO _4-b X _b

In the above chemical formula 7, 0.90≤a≤1.1, 0≤x≤0.9, 0≤y≤0.5, 0.9<x+y<1.1, 0≤b≤2,

M1 is chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zirconium (Zr) or a combination thereof,

M2 is magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), zinc (Zn), boron (B), niobium (Nb), gallium (Ga), indium (In), molybdenum (Mo), tungsten (W), aluminum (Al), silicon (Si), chromium (Cr), vanadium (V), scandium (Sc), yttrium (Y) or a combination thereof, and X is O, F, S, P or a combination thereof.

<Chemical Formula 8>

Li _a M3 _z PO ₄

In the above chemical formula 8, 0.90≤a≤1.1, 0.9≤z≤1.1,

M3 is chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zirconium (Zr), or a combination thereof.

The oxide-based cathode active material may be covered by a covering layer. The covering layer may be any material known as a covering layer for cathode active materials of all-solid-state secondary batteries. Examples of the covering layer include Li ₂ O-ZrO ₂ (LZO).

The size of the oxide-based cathode active material may be, for example, 0.1 to 30 μm, 0.5 to 20 μm, or 1 to 15 μm. The oxide-based cathode active material may be, for example, a single-crystal particle or a polycrystalline particle.

The sulfide-based cathode active material may include, for example, a Li ₂ S-containing complex. The Li ₂ S-containing complex includes, for example, a complex of Li 2 S and carbon, a complex of Li 2 S, carbon, and a solid electrolyte, a complex of Li 2 S and a solid electrolyte, a complex of Li 2 S and a lithium salt, a complex of Li 2 S, a lithium salt, and carbon, a complex of Li 2 S and a metal carbide, a complex of Li 2 S, carbon, and a metal carbide, a complex of Li 2 S and a metal nitride, a complex of Li 2 S, carbon, and a metal nitride, or a combination thereof.

The composite of Li ₂ S and carbon comprises carbon. The carbon may be, for example, any material containing carbon atoms that is used as a conductive material in the art. The carbon may be, for example, crystalline carbon, amorphous carbon, or a combination thereof. The carbon may be, for example, a sintered product of a carbon precursor. The carbon may be, for example, a carbon nanostructure. The carbon nanostructure may be, for example, a one-dimensional carbon nanostructure, a two-dimensional carbon nanostructure, a three-dimensional carbon nanostructure, or a combination thereof. The carbon nanostructure may be, for example, a carbon nanotube, a carbon nanofiber, a carbon nanobelt, a carbon nanorod, graphene, graphene oxide (GO), reduced graphene oxide (rGO), graphene balls (GB), or a combination thereof. The carbon may be, for example, porous carbon or non-porous carbon. The porous carbon may include, for example, periodic and regular two-dimensional or three-dimensional pores. The porous carbon may be, for example, carbon black such as Ketjen black, acetylene black, Denka black, thermal black, channel black, etc.; graphite, activated carbon, or a combination thereof. The form of the carbon may be, for example, particle form, sheet form, fiber form, etc., but is not limited thereto, and any method used as carbon in the relevant technical field may be used. The method for preparing the composite of Li ₂ S and carbon may be, for example, a dry method, a wet method, or a combination thereof, but is not limited thereto, and the method for preparing the composite of Li ₂ S and carbon in the relevant technical field may be, for example, milling, heat treatment, deposition, etc., but is not necessarily limited thereto, and any method used in the relevant technical field may be used.

A composite of Li ₂ S and carbon and a solid electrolyte comprises carbon and a solid electrolyte. Carbon refers to the composite of Li ₂ S and carbon described above. The solid electrolyte may be any material used as an ion-conducting material in the art, for example, an amorphous solid electrolyte. The solid electrolyte is, for example, an inorganic solid electrolyte. The solid electrolyte is, for example, a crystalline solid electrolyte, an amorphous solid electrolyte, or a combination thereof. The solid electrolyte is, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a combination thereof. The sulfide-based solid electrolyte comprises, for example, Li, S, and P, and may optionally further comprise a halogen element. The sulfide-based solid electrolyte may be selected from among sulfide-based solid electrolytes used in the solid electrolyte layer. The sulfide-based solid electrolyte may have, for example, an ionic conductivity of 1×10 ^-5 S/cm or more at room temperature. Sulfide-based solid electrolytes include, for example, Li ₃ PO ₄ -Li ₂ SO ₄ , Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiX, where X is a halogen element, Li ₂ SP ₂ S ₅ -Li ₂ O, Li ₂ SP ₂ S ₅ -Li ₂ O-LiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS ₂ -LiI, Li ₂ S-SiS ₂ -LiBr, Li ₂ S-SiS ₂ -LiCl, Li ₂ S-SiS ₂ -B ₂ S ₃ -LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiI, Li ₂ SB ₂ S ₃ , Li ₂ SP ₂ S ₅ -Z _m S _n , m, n are positive numbers, Z is one of Ge, Zn or Ga, Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS ₂ -Li _p MO _q , p, q are positive numbers, M may include one of P, Si, Ge, B, Al, Ga In, and at least one selected from Li _7-x PS _6-x Cl _x , 0≤x≤2, Li _7-x PS _6-x Br _x , 0≤x≤2, and Li _7-x PS _6-x I _x , 0≤x≤2. The oxide-based solid electrolyte includes, for example, Li, O, and a transition metal element, and may optionally further include other elements. The oxide-based solid electrolyte may be, for example, a solid electrolyte having an ionic conductivity of 1×10 ^-5 S/cm or more at room temperature. The oxide-based solid electrolyte may be selected from oxide-based solid electrolytes used in the solid electrolyte layer. The solid electrolyte may be, for example, a mixture of a sulfide-based solid electrolyte and a lithium salt. For example, it may be a mixture of Li ₃ PO ₄ -Li ₂ SO ₄ and a binary lithium salt, or a mixture of Li ₃ PO ₄ -Li ₂ SO ₄ and a ternary lithium salt.

The complex of Li2S and a solid electrolyte includes a solid electrolyte. The solid electrolyte refers to the complex of _Li2S , carbon, and a solid electrolyte described above.

The complex of Li2S and a lithium salt comprises a lithium salt compound. The lithium salt compound does not contain, for example, a sulfur (S) atom. The lithium salt compound can be, for example, a binary compound composed of lithium and one element selected from Groups 13 to 17 of the Periodic Table of Elements. The binary compound can include, for example, one or more selected from LiF, LiCl, _LiBr , LiI, _LiH , _Li2S , _Li2O , _Li2Se , _Li2Te , Li3N, _Li3P , _Li3As , Li3Sb, _LiI3 , and _LiB3 . The lithium salt compound can be, for example, a ternary compound composed of lithium and two elements selected from Groups 13 to 17 of the Periodic Table of Elements. The ternary compound includes, for example, one or more selected from Li ₃ OCl, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiNO ₃ , Li ₂ CO ₃ , LiBH ₄ , Li ₂ SO ₄ , Li ₃ BO ₃ , Li ₃ PO ₄ , Li ₄ NCl, Li ₅ NCl ₂ and Li ₃ BN ₂ . The lithium salt compound is particularly one or more lithium halide compounds selected from LiF, LiCl, LiBr, and LiI. The complex of Li ₂ S and the solid electrolyte includes the solid electrolyte. The solid electrolyte refers to the solid electrolyte used in the complex of Li 2 S and carbon and the solid electrolyte described above. The complex of Li ₂ S and the solid electrolyte includes, for example, a complex of Li ₂ S and one or more lithium salts selected from LiF, LiCl, LiBr, _LiI , LiH, Li ₂ S, Li ₂ O, Li ₂ Se, Li ₂ Te, Li ₃ N, Li ₃ P, Li 3 As, Li ₃ Sb, LiI ₃ and LiB ₃ .

The complex of Li2S and a lithium salt and carbon includes a lithium salt compound and carbon. The lithium salt compound refers to the complex of _Li2S and a lithium salt described above. Carbon refers to the complex of _Li2S and carbon described above.

The composite of Li ₂ S and a metal carbide comprises a metal carbide. The metal carbide is, for example, a two-dimensional metal carbide. The two-dimensional metal carbide is, for example, MXene. The two-dimensional metal carbide is expressed as, 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). The two-dimensional metal carbide is, for example, Ti ₂ CT _x , (Ti _0.5 , Nb _0.5 ) ₂ CT _x , Nb ₂ CT _x , V ₂ CT _x , Ti ₃ C ₂ T _x , (V _0.5 , Cr _0.5 ) ₃ C ₂ T _x , Ti ₃ CNT _x , Ta ₄ C ₃ T _x , Nb ₄ C ₃ T _x or a combination thereof. The surface of the two-dimensional metal carbide is terminated with O, OH and/or F.

The complex of Li ₂ S and carbon and metal carbide includes carbon and metal carbide. Carbon refers to the complex of Li ₂ S and carbon described above. Metal carbide refers to the complex of Li ₂ S and metal carbide described above.

The complex of Li ₂ S and a metal nitride comprises a metal nitride. The metal nitride is, for example, a two-dimensional metal nitride. The two-dimensional metal nitride is expressed, for example, as 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). The surface of the two-dimensional metal nitride is terminated with O, OH, and/or F.

The complex of Li ₂ S with carbon and a metal nitride includes carbon and a metal nitride. Carbon refers to the complex of Li 2 S with carbon described above. Metal carbide refers to the complex of Li ₂ S with a metal nitride described above.

The Li2S-containing composite may further include, for example, a second fibrous sulfide-based solid electrolyte (not shown). The Li2S-containing composite may be a composite of Li2S and the second fibrous sulfide-based solid electrolyte, or a composite of Li2S and the second fibrous sulfide-based solid electrolyte and the above-described carbon, solid electrolyte, lithium salt, metal carbide, or metal nitride.

The Li2S-containing composite may further include a second fibrous sulfide-based solid electrolyte, so that the deterioration of the all-solid-state secondary battery can be further suppressed and the cycle characteristics of the all-solid-state secondary battery can be further improved. The size of the second fibrous sulfide-based solid electrolyte may be smaller than the size of the first fibrous sulfide-based solid electrolyte (100). The length and/or thickness of the second fibrous sulfide-based solid electrolyte may be 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less of the length and/or thickness of the first fibrous sulfide-based solid electrolyte (100), respectively. The length and/or thickness of the second fibrous sulfide-based solid electrolyte may be 0.1 to 50%, 0.5 to 40%, 1 to 30%, 1 to 20%, or 1 to 10% of the length and/or thickness of the first fibrous sulfide-based solid electrolyte (100), respectively. The second fibrous sulfide-based solid electrolyte may have, for example, the same shape as the first fibrous sulfide-based solid electrolyte (100) but a smaller size. The second fibrous sulfide-based solid electrolyte may be easily distributed in the Li2S-containing composite due to the reduced length and/or thickness. The second fibrous sulfide-based solid electrolyte may further suppress deterioration of the all-solid-state secondary battery and further improve cycle characteristics of the all-solid-state secondary battery due to the reduced length and/or thickness.

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

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

[Cathode active material layer: solid electrolyte]

The cathode active material layer (12) may further include, for example, a solid electrolyte. The solid electrolyte may be, for example, a sulfide-based solid electrolyte. The solid electrolyte included in the cathode layer (10) may be the same as or different from the solid electrolyte included in the solid electrolyte layer (30). For details on the solid electrolyte, refer to the section on the solid electrolyte layer (30).

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 solid 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 solid electrolyte layer (30). The average D50 particle diameter is, for example, a median particle diameter (D50). The median particle diameter (D50) is, for example, 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 laser diffraction.

The solid electrolyte content included in the positive electrode active material layer (12) may be, for example, 1 wt% to 40 wt%, 1 wt% to 30 wt%, 1 wt% to 20 wt%, or 1 wt% to 10 wt% of the total weight of the positive electrode active material layer (12).

[Cathode active material layer: conductive material]

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).

[Cathode active material layer: binder]

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

[Cathode active material layer: other additives]

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.

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

[Anode layer: Anode current collector]

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.

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. If the base film includes an insulating thermoplastic polymer, the base film may soften or liquefy when a short circuit occurs, thereby blocking battery operation and suppressing a sudden 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 all-solid-state secondary 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 melts, so that the metal layer can be electrically connected to the lead tab. To strengthen the welding between the metal layer and the lead tab, a metal chip can be added between the metal layer and the lead tab. The metal chip can 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, an aluminum foil, a copper foil, a 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 by welding the lead tab. 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 ㎛, 1.5 to 50 ㎛, 1.5 to 40 ㎛, or 1 to 30 ㎛. 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 current collector (11) can reduce the weight of the positive electrode and consequently improve the energy density of the positive electrode and the all-solid-state secondary battery.

[Anode layer: first inert member]

Referring to FIGS. 4 to 5 and 8 to 12, the all-solid-state secondary battery (1) may further include a first inactive member (40, 40a, 40b) disposed on at least one of the other surface of the negative electrode current collector (21) and the other surface of the positive electrode current collector (11).

For more specific details about the first inert member (40a, 40a, 40b), refer to the first inert member (40, 40a, 40b) of the cathode layer described above.

[Anode layer: second inert member]

Referring to FIGS. 6 to 12, the positive electrode layer (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 (11). A second inactive member (50) is disposed on one side of the positive electrode layer (10).

Referring to FIGS. 7, 9, and 11, the second inert member (50) is disposed on one side of the positive electrode active material layer (12) and between the solid electrolyte layer (30) and the positive electrode current collector (11) facing the solid electrolyte layer (30). The second inert member (50) is not disposed on one side of the positive electrode current collector (11). Referring to FIGS. 6, 8, 10, and 12, the second inert member (50) is disposed on one side of the positive electrode active material layer (12) and the positive electrode current collector (11). By including the second inert member (50), cracking of the solid electrolyte layer (30) is prevented during manufacturing and/or charging and discharging of the all-solid-state secondary battery (1), and as a result, the cycle characteristics of the all-solid-state secondary battery (1) are improved. In an all-solid-state secondary battery (1) that does not include a second inert member (50), when manufacturing the all-solid-state secondary battery (1) and/or charging and discharging, uneven pressure is applied to the solid electrolyte layer (30) in contact with the positive electrode layer (10), which increases the possibility of a short circuit occurring due to cracks occurring in the solid electrolyte layer (30) and growth of lithium metal through the cracks.

Referring to FIGS. 6 to 12, in the all-solid-state secondary battery (1), the thickness of the second inert member (50) is, for example, greater than the thickness of the first negative electrode active material layer (22). The thickness of the second inert member (50) is, for example, greater than the thickness of the solid electrolyte layer (30).

Referring to FIGS. 6 to 12, the second inert member (50) surrounds the side surface of the positive electrode layer (10) and is in contact with the solid electrolyte layer (30). Since the second inert member (50) surrounds the side surface of the positive electrode layer (10) and is in contact with the solid electrolyte layer (30), cracks in the solid electrolyte layer (30) that occur due to a pressure difference during the pressing process in the solid electrolyte layer (30) that is not in contact with the positive electrode layer (20) can be effectively suppressed. The second inert member (50) surrounds the side surface of the positive electrode layer (10) and is separated from the negative electrode layer (20), more specifically, the first negative electrode active material layer (22). The second inert member (50) surrounds the side surface of the positive electrode layer (10), is in contact with the solid electrolyte layer (30), and is separated from the negative electrode layer (20). Accordingly, the possibility of a short circuit occurring due to physical contact between the positive electrode layer (10) and the first negative electrode active material layer (22) or due to overcharging of lithium, etc., is suppressed. The possibility of a short circuit occurring due to contact between the positive electrode collector (11) and the negative electrode layer (20) is more effectively suppressed by simultaneously arranging the second inert member (50) on one side of the positive electrode active material layer (12) and the positive electrode current collector (11).

Referring to FIGS. 6 to 12, the second inert member (41, 41a, 41b) extends from one side of the positive electrode layer (30) to the end of the solid electrolyte layer (30). Since the second inert member (50) extends to the end of the solid electrolyte layer (30), cracks occurring at the end of the solid electrolyte layer (30) can be suppressed. The end of the solid electrolyte layer (30) is the outermost part that is in contact with the side of the solid electrolyte layer (30). The second inert member (50) extends to the outermost part that is in contact with the side of the solid electrolyte layer (30). The second inert member (50) is separated from the negative electrode layer (20), more specifically, from the first negative electrode active material layer (22). The second inert member (50) extends to the end of the solid electrolyte layer (30), but does not contact the negative electrode layer (20). The second inert member (50) fills a space extending from, for example, one side of the positive electrode layer (30) to the end of the solid electrolyte layer (30).

The area of the positive electrode active material layer (12) or the positive electrode layer (10) may be smaller than the area of the first negative electrode active material layer (22) or the negative electrode layer (20). The area of the positive electrode active material layer (12) or the positive electrode layer (10) may be smaller than the area of the solid electrolyte layer (30).

The second inert member (50) may be, for example, a gasket. By using a gasket as the second inert member (50), cracks in the solid electrolyte layer (30) caused by a pressure difference during the pressing process can be effectively suppressed.

The second inert member (50) may have, for example, a single-layer structure. Alternatively, although not shown in the drawing, the second inert member (50) may have a multi-layer structure. The multi-layer structure may have, for example, a two-layer, three-layer, or four-layer structure, and by having a multi-layer structure, the physical properties of the second inert member (50) can be more precisely controlled.

Although not shown in the drawing, part or all of the second inert member (50) may be disposed spaced apart from the side surface of the positive electrode active material layer (12). By disposing part or all of the second inert member (50) spaced apart from the side surface of the positive electrode active material layer (12), the manufacturing process of the all-solid-state secondary battery (1) may be facilitated and the manufacturing speed of the all-solid-state secondary battery (1) may be increased. By disposing part or all of the second inert member (50) spaced apart from the side surface of the positive electrode active material layer (12), the volume change in the side surface direction of the positive electrode active material layer (12) during charge and discharge may be more effectively accommodated, thereby further improving the life characteristics of the all-solid-state secondary battery (1). The distance between the side of the second inert member (50) and the positive electrode active material layer (12) is independently, for example, 0.1 µm to 10 mm, 1 µm to 1 mm, 1 µm to 500 µm, 1 µm to 100 µm, 1 µm to 50 µm or 1 µm to 10 µm.

Referring to FIGS. 6 to 12, the second inert member (50) may be selected from among the materials used in the first inert member (40, 40a, 40b) described above, for example. The second inert member (50) does not include, for example, an electrode active material. The second inert member (50) may be, for example, a flame-retardant inert member, an electronically insulating inert member, an ionically insulating inert member, or an elastic inert member.

[Solid electrolyte layer]

[Solid electrolyte layer: solid electrolyte]

Referring to FIGS. 1 to 12, the all-solid-state secondary battery (1) includes a solid electrolyte layer (30) disposed between a positive electrode layer (10) and a negative electrode layer (20). The solid electrolyte layer (30) includes, for example, a solid electrolyte or a combination of a solid electrolyte and a gel electrolyte.

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.

The solid electrolyte is, for example, a sulfide-based solid electrolyte. Sulfide-based solid electrolytes include, for example, Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiX, where X is a halogen element, Li ₂ SP ₂ S ₅ -Li ₂ O, Li ₂ SP ₂ S ₅ -Li ₂ O-LiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS ₂ -LiI, Li ₂ S-SiS ₂ -LiBr, Li ₂ S-SiS ₂ -LiCl, Li ₂ S-SiS ₂ -B ₂ S ₃ -LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiI, Li ₂ SB ₂ S ₃ , Li ₂ SP ₂ S ₅ -Z _m S _n , where m, n are positive numbers, and Z is one of Ge, Zn, or Ga, Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS ₂ -Li _p MO _q , p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga In, Li _7-x PS _6-x Cl _x , 0≤x≤2, Li _7-x PS _6-x Br _x , 0≤x≤2, and Li _7-x PS _6-x I _x , 0≤x≤2. The sulfide-based solid electrolyte is manufactured by treating starting materials such as Li ₂ S, P ₂ S ₅ by a melting rapid cooling method or a mechanical milling method. In addition, a 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 Li ₂ SP ₂ S ₅ . When using a sulfide-based solid electrolyte material containing Li ₂ SP ₂ S ₅ to form the solid electrolyte, the mixing molar ratio of Li ₂ S and P ₂ S ₅ is, for example, in the range of Li ₂ S : P ₂ S ₅ = 20 : 80 to 90 : 10, 25 : 75 to 90 : 10, 30 : 70 to 70 : 30, 40 : 60 to 60 : 40.

The sulfide-based solid electrolyte may include, for example, an argyrodite type solid electrolyte represented by the following chemical formula 9:

<Chemical Formula 9>

_Li ⁺ _12- ^nx _A ^{n +}

In chemical formula 9, 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 N ₃ , and 1 ≤ n ≤ 5, 0 ≤ x ≤ 2. The sulfide-based solid electrolyte may be, for example, an argyrodite-type compound including at least one selected from Li _{7-x PS 6-x Cl x} , 0 ≤ _x ≤ 2, Li _7-x PS _6-x Br _x , 0 ≤ x ≤ 2, and Li 7-x PS 6-x I x , 0 ≤ x ≤ 2. The sulfide-based solid electrolyte may be, for example, an argyrodite-type compound including at least one selected from Li ₆ PS ₅ Cl, Li ₆ PS ₅ Br, and Li ₆ PS ₅ I.

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

Oxide-based 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), BaTiO ₃ , Pb(Zr,Ti)O ₃ (PZT), Pb _1-x La _x Zr _1-y Ti _y O ₃ (PLZT)(0≤x<1, 0≤y<1), PB(Mg ₃ Nb _2/3 )O ₃ -PbTiO ₃ (PMN-PT), HfO ₂ , SrTiO ₃ , SnO ₂ , CeO ₂ , Na ₂ O, MgO, NiO, CaO, BaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , TiO ₂ , SiO ₂ , Li ₃ PO ₄ , Li _x Ti _y (PO ₄ ) ₃ (0<x<2, 0<y<3), Li _x Al _y Ti _z (PO ₄ ) ₃ (0<x<2, 0<y<1, 0<z<3), Li _1+x+y (Al, Ga) _x (Ti, Ge) _2-x Si _y P _3-y O ₁₂ (0≤x≤1 0≤y≤1), Li _x La _y TiO ₃ (0<x<2, 0<y<3), Li ₂ O, LiOH, Li ₂ CO ₃ , LiAlO ₂ , Li ₂ O-Al ₂ O ₃ -SiO ₂ -P ₂ O ₅ -TiO ₂ -GeO ₂ , Li _3+x La ₃ M ₂ O 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.

The oxide-based solid electrolyte is a garnet-type solid electrolyte selected from, for example, Li ₇ La ₃ Zr ₂ O ₁₂ (LLZO) and Li _3+x La ₃ Zr _2-a M _a O ₁₂ (M doped LLZO, M = Ga, W, Nb, Ta, or Al, 0<a<2, 0≤x≤10).

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 (DPASLi ⁺ ) or a combination thereof, but is not limited thereto, and any that can be used in polymer electrolytes in the relevant technical field is possible. The lithium salt may be any that can be used as a lithium salt in the relevant technical field. The lithium salt may be, for example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (x and y are each 1 to 20), LiCl, LiI or a mixture thereof. The polymer included in the polymer solid electrolyte is For example, it may be 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 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.

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

The polymer gel electrolyte may include, for example, a liquid electrolyte and a polymer, or may include 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 have a gel state, for example, 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 organic solvent is, for example, propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, or a mixture thereof. The lithium salt may be selected from lithium salts used in polymer solid electrolytes. Ionic liquids are salts that have a melting point below room temperature, are composed only of ions, and are liquid at room temperature or molten at room temperature. The ionic liquid may include, for example, one or more cations selected from among a) ammonium compounds, pyrrolidinium compounds, pyridinium compounds, pyrimidinium compounds, imidazolium compounds, piperidinium compounds, pyrazolium compounds, oxazolium compounds, pyridazinium compounds, phosphonium compounds, sulfonium compounds, triazolium compounds, and mixtures thereof, and b) one or more anions selected from among BF4-, PF6-, AsF6-, SbF6-, AlCl4-, HSO4-, ClO4-, CH3SO3-, CF3CO2-, Cl-, Br-, I-, SO4-, CF3SO3-, (FSO2)2N-, (C2F5SO2)2N-, (C2F5SO2)(CF3SO2)N-, and (CF3SO2)2N-. A polymer solid electrolyte can form a polymer gel electrolyte, for example, by being impregnated into a liquid electrolyte in a secondary battery. The polymer gel electrolyte can further include inorganic particles. The polymer included in the polymer gel electrolyte can 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 can 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.

[Solid electrolyte layer: binder]

The solid electrolyte layer (30) may include, for example, a binder. The binder included in the solid 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 solid 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.

The binder content included in the solid 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 solid electrolyte layer (30).

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.

(Manufacturing of sulfide-based composite cathode active materials)

Manufacturing Example 1: Li2S-LiI-CNF composite cathode active material

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

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, 510 rpm, and 10 h. The Li2S-LiI-CNF composite was used as a composite cathode active material.

(Manufacturing of all-solid-state secondary batteries)

Example 1: Elastic sheet (25 um)/positive electrode layer (112 um, NCA)/solid electrolyte layer (30 um)/negative electrode layer (37 um, Si alloy particles: CNT = 9:1 + binder)

(Anode layer manufacturing)

LiNi _0.8 Co _0.15 Al _0.05 O ₂ (NCA) coated with Li ₂ O-ZrO ₂ (LZO) was prepared as a cathode active material. The LZO coated cathode active material was prepared according to the method disclosed in Korean Patent Publication No. 10-2016-0064942A. Li ₆ PS ₅ Cl (D50 = 0.5 μm, crystalline) in the form of an argyrodite crystal was prepared as a solid electrolyte. Polytetrafluoroethylene (PTFE) binder was prepared as a binder. Carbon nanofibers (CNF) were prepared as a conductive agent. These materials were mixed with a xylene solvent in a weight ratio of cathode active material: solid electrolyte: conductive agent: binder = 84: 11: 3: 2, and the slurry was molded into a sheet shape, and then vacuum dried at 40°C for 8 hours to prepare a cathode sheet. The manufactured positive electrode sheet was placed on the carbon layer of a positive electrode current collector made of aluminum foil coated with a carbon layer on one side, and a positive electrode layer was manufactured by heated roll pressing at 85 ^o C. The total thickness of the positive electrode layer was approximately 112 ㎛. The thickness of the positive electrode active material layer was approximately 92 ㎛, and the thickness of the carbon-coated aluminum foil was approximately 20 ㎛.

The initial charge capacity of the positive electrode layer was measured using the half-cell described above. Using the half-cell, the initial charge capacity of the positive electrode active material layer was measured.

(Cathode layer manufacturing)

A 10 ㎛ thick SUS foil was prepared as a negative electrode current collector. As a first negative electrode active material, silicon-iron-copper-aluminum alloy (Si ₇₅ Fe _9.5 Cu _9.5 Al ₆ ) particles (MK Electronics Co., Ltd.) with a D50 particle size of 4 ㎛ were prepared. The silicon-iron-copper-aluminum alloy (Si-Fe-Cu-Al) particles included a silicon single phase, a silicon-iron alloy phase, a silicon-copper alloy phase, etc. In the silicon-iron-copper-aluminum alloy (Si-Fe-Cu-Al) particles, the silicon single phase had a structure in which the silicon was surrounded by a silicon-iron alloy phase, a silicon-copper alloy phase, etc.

Carbon nanotubes were prepared as fibrous carbon-based materials. The carbon nanotubes included a primary carbon nanotube structure and a secondary carbon nanotube structure. The primary carbon nanotube structure was composed of a single carbon nanotube unit. The length of the carbon nanotube unit was 200 nm to 300 nm, for example, 250 nm, and the diameter of the carbon nanotube unit was 5 nm to 10 nm, or 7.5 nm. The secondary carbon nanotube structure was formed by aggregation of multiple carbon nanotube units. The length of the secondary carbon nanotube structure was about 5 μm, and the diameter was about 40 nm.

A 4 g mixture of silicon-iron-copper-aluminum (Si-Fe-Cu-Al) particles and carbon nanotubes in a weight ratio of 9:1 was placed in a container, and 4 g of an NMP solution containing 7 wt% 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 substrate 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 27 μm.

The initial charge capacity of the negative electrode was measured using the half-cell described above. The initial charge capacity of the first negative electrode active material layer was measured using the half-cell.

The ratio (B/A) of the initial charge capacity (B) of the first negative electrode active material layer to the initial charge capacity (A) of the positive electrode active material layer was less than 0.5. The initial charge capacity of the positive electrode active material layer was determined from the ^first open circuit voltage to 4.25 V vs. Li/Li ⁺ . The initial charge capacity of the first negative electrode active material layer was determined from the ^second open circuit voltage to 0.01 V vs. Li/Li ⁺ . In Examples 2 to 3 and Comparative Example 1, the ratio (B/A) of the initial charge capacity (B) of the first negative electrode active material layer to the initial charge capacity (A) of the positive electrode active material layer, measured under the same conditions as in Example 1, was each less than 0.5.

(Manufacturing of solid electrolyte layer)

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, which is a Li ₆ PS ₅ Cl solid electrolyte (D ₅₀ = 3.0 (m, crystalline) in the form of argyrodite. Octyl acetate was added to the prepared mixture and stirred to prepare a slurry. The prepared slurry was applied onto a nonwoven fabric placed on a PET substrate using a bar coater and dried in the 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.

(Inert member: elastic sheet)

A porous polyurethane foam sheet with a thickness of 25 ㎛ was prepared as an elastic sheet.

(Manufacturing of all-solid-state secondary batteries)

A solid electrolyte layer was placed on the cathode so that the first cathode active material layer was in contact with the solid electrolyte layer, and an anode was placed on the solid electrolyte layer so that the cathode active material layer was in contact with the solid electrolyte layer, thereby preparing a laminate.

The prepared laminate was plate pressed at 85 ^o C and 500 MPa for 30 min. This pressurization sintered the solid electrolyte layer, thereby improving battery characteristics. The thickness of the sintered solid electrolyte layer was approximately 30 μm. The density of the Li ₆ PS ₅ Cl 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. An elastic sheet was additionally placed on the positive electrode collector of the pressed laminate.

A laminate including an elastic sheet was placed in a pouch and vacuum-sealed to manufacture an all-solid-state secondary battery. Parts of the positive and negative current collectors were extended outside the sealed battery to be used as positive and negative terminals.

Example 2: Elastic sheet (25 um)/positive electrode layer (112 um, NCA)/solid electrolyte layer (30 um)/negative electrode layer (37 um, lithiated Si alloy particles: CNT = 9:1 + binder)

An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that lithiated silicon-iron-copper-aluminum alloy (Si-Fe-Cu-Al) particles (MK Electronics Co., Ltd.) were used instead of silicon-iron-copper-aluminum (Si-Fe-Cu-Al) alloy particles (MK Electronics Co., Ltd.).

Comparative Example 1: Elastic sheet (100 um)/positive electrode layer (112 um, NCA)/solid electrolyte layer (30 um)/negative electrode layer (17 um, Ag-C + binder): (Ag-C = 4 weight ratio)

An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that instead of using a 9:1 weight ratio mixture of silicon-iron-copper-aluminum alloy particles and carbon nanotubes, 4 g of a 3:1 weight ratio mixture of carbon black (CB) and silver (Ag) was used, the thickness of the negative electrode active material layer was changed to 7 μm, and the thickness of the elastic sheet was changed to 100 μm. The thickness of the negative electrode layer is the total thickness of the negative electrode current collector and the negative electrode active material layer.

Example 3: Anode layer (113.8 um, Li2S-LiI-CNF)/solid electrolyte layer (30 um)/cathode layer (37 um, Si alloy particles:CNT=9:1+binder)

An all-solid-state secondary battery was manufactured in the same manner as Example 1, except that the positive electrode containing a sulfide-based positive electrode active material was used and the elastic sheet was omitted.

(Polar electrode manufacturing)

The Li2S-LiI-CNF composite manufactured in Manufacturing Example 1 was prepared as a cathode active material. _{Li6PS5Cl ,} an argyrodite-type crystal (D50=3.0 ㎛, crystalline), 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 = 60:40:1.2 to prepare a cathode mixture. The cathode mixture was obtained by mixing using a ball mill.

The positive electrode was manufactured by placing the positive electrode active material 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 total thickness of the positive electrode layer was approximately 113.8 μm. The thickness of the positive electrode active material layer was approximately 93.8 μm, and the thickness of the carbon-coated aluminum foil was approximately 20 μm.

The initial charge capacity of the positive electrode layer was measured using the half-cell described above. Using the half-cell, the initial charge capacity of the positive electrode active material layer was measured. The initial charge capacity of the negative electrode was measured in the same manner as in Example 1.

The ratio (B/A) of the initial charge capacity (B) of the first negative electrode active material layer and the initial charge capacity (A) of the positive electrode active material layer was less than 0.5. The initial charge capacity of the positive electrode active material layer was determined by charging from the ^first open circuit voltage to 2.8 V vs. Li/Li ⁺ .

Example 4: Anode layer (113.8 um, Li2S-LiI-CNF)/solid electrolyte layer (30 um)/cathode layer (37 um, lithiated Si alloy particles: CNT = 9:1 + binder)

An all-solid-state secondary battery was manufactured in the same manner as in Example 3, except that lithiated silicon-iron-copper-aluminum alloy (Si-Fe-Cu-Al) particles (MK Electronics Co., Ltd.) were used instead of silicon-iron-copper-aluminum alloy (Si-Fe-Cu-Al) particles (MK Electronics Co., Ltd.). The elastic sheet was omitted.

Comparative Example 2: Elastic sheet (50 um)/positive electrode layer (113.8 um, Li2S-LiI-CNF)/solid electrolyte layer (30 um)/negative electrode layer (17 um, Ag-C+binder): (Ag-C = 4 weight ratio)

An all-solid-state secondary battery was manufactured in the same manner as in Example 3, except that the positive electrode of Example 3 was used, 4 g of a 3:1 weight ratio mixture of carbon black (CB) and silver (Ag) was used instead of a 9:1 weight ratio mixture of silicon-iron-copper-aluminum alloy (Si-Fe-Cu-Al) particles and carbon nanotubes, the thickness of the negative electrode active material layer was changed to 7 μm, and the thickness of the elastic sheet was changed to 50 μm. The thickness of the negative electrode layer is the total thickness of the negative electrode current collector and the negative electrode active material layer.

Evaluation Example 3: Charge/Discharge Test

The charge/discharge characteristics of the all-solid-state secondary batteries manufactured in Examples 1-2 and Comparative Example 1 were evaluated by the following charge/discharge test. The charge/discharge test was performed by placing the all-solid-state secondary batteries in a constant temperature bath at 45°C.

The first cycle involved charging for 12.5 hours at a constant current of 0.5 mA/cm ² until the battery voltage reached 4.25 V. Subsequently, discharging was performed for 12.5 hours at a constant current of 0.5 mA/cm ² until the battery voltage reached 2.5 V.

Meanwhile, the charge/discharge characteristics of the all-solid-state secondary batteries manufactured in Examples 3 and 4 and Comparative Example 2 were evaluated by the following charge/discharge test. The charge/discharge test was performed by placing the all-solid-state secondary batteries in a constant temperature bath at 45°C.

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

The discharge capacity of the first cycle was taken as the standard capacity. After the first cycle, charging and discharging were performed up to 850 cycles under the same conditions as the first cycle. The measurement results are shown in Tables 1 and 2 below. Table 1 shows the results for Examples 1-2 and Comparative Example 1, and Table 2 shows the results for Examples 3-4 and Comparative Example 2.

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

The initial efficiency of each solid secondary battery is expressed by Equation 1 below, and the thickness change rate is expressed by Equation 2 below.

<Formula 1>

Initial efficiency (%) = [Discharge capacity of the first cycle / Charge capacity of the first cycle] × 100

<Formula 2>

Thickness change rate (%) = [(cell thickness after charging - initial cell thickness) / initial cell thickness] X 100

division Thickness change rate
(%) Initial efficiency [%] Cycle count [times] Example 1: Elastic sheet (25 um)/positive electrode layer (112 um, NCA)/solid electrolyte layer (30 um)/negative electrode layer (37 um, Si alloy particles: CNT = 9:1 + binder): 15 89 560 Example 2: Elastic sheet (25 um)/positive electrode layer (112 um, NCA)/solid electrolyte layer (30 um)/negative electrode layer (37 um, Lithiated Si alloy particles: CNT = 9:1 + binder): 8 99 740 Comparative Example 1: Elastic sheet (100 um)/positive electrode layer (112 um, NCA)/solid electrolyte layer (30 um)/negative electrode layer (17 um, Ag-C + binder): (Ag-C = 4 weight ratio) 21 85 400

As shown in Table 1, the all-solid-state secondary batteries of Examples 1 and 2 showed excellent initial efficiency and life characteristics by suppressing changes in thickness during charge and discharge and suppressing increases in internal resistance.

The all-solid-state secondary batteries of Examples 1 and 2 include a first negative electrode active material having an alloy phase, and thus have improved initial efficiency and lifespan characteristics compared to the all-solid-state secondary battery of Comparative Example 1.

division Thickness change rate
(%) Initial efficiency
[%] Cycle count [times] Example 3: Anode layer (113.8 um, Li2S-LiI-CNF)/solid electrolyte layer (30 um)/cathode layer (37 um, Si alloy particles:CNT=9:1+binder) 4.6 85 450 Example 4: Anode layer (113.8 um, Li2S-LiI-CNF)/solid electrolyte layer (30 um)/cathode layer (37 um, lithiated Si alloy particles: CNT = 9:1 + binder) 3.2 98 655 Comparative Example 2: Elastic sheet (50 um)/positive electrode layer (113.8 um, Li2S-LiI-CNF)/solid electrolyte layer (30 um)/negative electrode layer (17 um, Ag-C+binder): (Ag-C = 4 weight ratio) 9.2 81 300

As shown in Table 2, the all-solid-state secondary batteries of Examples 3 and 4 showed excellent initial efficiency and life characteristics by including a first negative electrode active material having an alloy phase, thereby suppressing thickness change during charge and discharge and suppressing increase in internal resistance.

Evaluation Example 4: High-Rate Characteristic Evaluation

The high-rate characteristics of the all-solid-state secondary batteries of Examples 1-2 and Comparative Example 1 were evaluated by the following charge-discharge test. The charge-discharge test was performed by placing the solid-state secondary batteries in a constant-temperature bath at 45°C.

The all-solid-state secondary batteries of Examples 1-2 and Comparative Example 1 were charged at a constant current of 0.1 C rate at 45°C until the voltage reached 3.9 V (vs. Li), and then cut-off at a current of 0.05 C rate while maintaining 3.9 V in constant voltage mode. Subsequently, they were discharged at a constant current of 0.1 C rate until the voltage reached 2.5 V (vs. Li) during discharge (formation cycle).

The solid-state secondary battery, which had undergone a Mars cycle, was charged at a constant current of 0.2 C rate at 45°C until the voltage reached 3.9 V (vs. Li). Subsequently, it was discharged at a constant current of 0.2 C rate until the voltage reached 2.5 V (vs. Li) (first cycle).

The solid-state secondary battery that had undergone the first cycle was charged at a constant current of 0.2 C rate at 45°C until the voltage reached 3.9 V (vs. Li). Subsequently, it was discharged at a constant current of 0.33 C rate until the voltage reached 2.5 V (vs. Li) (second cycle).

The solid-state secondary battery that had undergone the second cycle was charged at a constant current of 0.2 C rate at 45°C until the voltage reached 3.9 V (vs. Li). Subsequently, it was discharged at a constant current of 0.5 C rate until the voltage reached 2.5 V (vs. Li) (third cycle).

The solid-state secondary battery that had undergone the third cycle was charged at a constant current of 0.2 C rate at 45°C until the voltage reached 3.9 V (vs. Li). Subsequently, it was discharged at a constant current of 1.0 C rate until the voltage reached 2.5 V (vs. Li) (fourth cycle).

In every charge/discharge cycle, a 10-minute pause was provided after each charge/discharge cycle.

In addition, the high-rate characteristics of the all-solid-state secondary batteries of Examples 3-4 and Comparative Example 2 were evaluated by the following charge-discharge test. The charge-discharge test was performed by placing the solid-state secondary batteries in a constant-temperature bath at 45°C.

The all-solid-state secondary batteries of Examples 3-4 and Comparative Example 2 were charged at a constant current of 0.1 C rate at 45°C until the voltage reached 2.5 V (vs. Li), and then cut-off at a current of 0.05 C rate while maintaining 2.5 V in constant voltage mode. Subsequently, they were discharged at a constant current of 0.1 C rate until the voltage reached 0.3 V (vs. Li) during discharge (formation cycle).

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

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

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

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

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

<Formula 3>

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

division High rate characteristics (1C/0.1C) [%] Example 1: Elastic sheet (25 um)/positive electrode layer (112 um, NCA)/solid electrolyte layer (30 um)/negative electrode layer (37 um, Si alloy particles: CNT = 9:1 + binder) 94 Example 2: Elastic sheet (25 um)/positive electrode layer (112 um, NCA)/solid electrolyte layer (30 um)/negative electrode layer (37 um, lithiated Si alloy particles: CNT = 9:1 + binder) 95.3 Comparative Example 1: Elastic sheet (100 um)/positive electrode layer (112 um, NCA)/solid electrolyte layer (30 um)/negative electrode layer (17 um, Ag-C + binder): (Ag-C = 4 weight ratio) 90 Example 3: Anode layer (113.8 um, Li2S-LiI-CNF)/solid electrolyte layer (30 um)/cathode layer (37 um, Si alloy particles:CNT=9:1+binder) 87 Example 4: Anode layer (113.8 um, Li2S-LiI-CNF)/solid electrolyte layer (30 um)/cathode layer (37 um, lithiated Si alloy particles: CNT = 9:1 + binder) 89 Comparative Example 2: Elastic sheet (50 um)/positive electrode layer (113.8 um, Li2S-LiI-CNF)/solid electrolyte layer (30 um)/negative electrode layer (17 um, Ag-C+binder): (Ag-C = 4 weight ratio) 80

As shown in Table 3, the all-solid-state secondary batteries of Examples 1 and 2 had improved high-rate characteristics compared to the all-solid-state secondary battery of Comparative Example 1 due to the inclusion of the first negative electrode active material having an alloy phase.

In addition, the all-solid-state secondary batteries of Examples 3 and 4 included a first negative electrode active material having an alloy phase, and thus, as shown in Table 3, the high-rate characteristics were improved compared to the all-solid-state secondary battery of Comparative Example 2.

1 All-solid-state secondary battery 10 Cathode
11. Cathode current collector 12. Cathode active material layer
20 Cathode 21 Cathode current collector
22 First negative electrode active material layer 23 Thin film
24 Second negative electrode active material layer 30 Solid electrolyte layer
40. 40a, 40b First inert member 50 Second inert member

Claims (20)

It comprises an anode layer; a cathode layer; and a solid electrolyte layer between the anode layer and the cathode layer,
The above positive electrode layer includes a positive electrode current collector and a positive electrode active material layer on one surface of the positive electrode current collector,
The above negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer on one surface of the negative electrode current collector,
The first negative electrode active material layer includes a first negative electrode active material and a carbon-based material,
An all-solid-state secondary battery, wherein the first negative electrode active material comprises an alloy phase. In the first paragraph, the first negative electrode active material includes silicon (Si), iron (Fe) and a first metal,
An all-solid-state secondary battery, wherein the first metal comprises copper (Cu), aluminum (Al), titanium (Ti), chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), zirconium (Zr), niobium (Nb), molybdenum (Mo), tin (Sn), cerium (Ce), or a combination thereof. An all-solid-state secondary battery in claim 1, wherein the first negative electrode active material comprises 60 to 90 at% of silicon (Si) and more than 0 to 30 at% of iron (Fe) based on 100 at% of the total first negative electrode active material. In the first paragraph, the first negative electrode active material includes a single silicon phase, an alloy phase of silicon and iron, an alloy phase of silicon and a first metal, an alloy phase of iron and a first metal, an alloy phase of multiple first metals, or a combination thereof.
An all-solid-state secondary battery, wherein the alloy phase of silicon and iron includes FeSi ₂ , Fe ₂ Si ₅ , FeSi or a combination thereof. An all-solid-state secondary battery in claim 1, wherein the first negative electrode active material further comprises boron (B), carbon (C), phosphorus (P), or a combination thereof. An all-solid-state secondary battery in claim 1, wherein the first negative electrode active material is a lithium-substituted (lithiated) negative electrode active material. An all-solid-state secondary battery in claim 1, wherein the first negative electrode active material is in the form of particles, and the size of the first negative electrode active material is 0.1 to 20 μm. In the first paragraph, the carbon-based material includes a fibrous carbon-based material,
The aspect ratio of the above fibrous carbon material is 10 or more,
An all-solid-state secondary battery, wherein the fibrous carbon-based material comprises an amorphous fibrous carbon-based material, a crystalline fibrous carbon-based material, or a combination thereof. An all-solid-state secondary battery in claim 1, wherein the content of the carbon-based material is 1 to 50 wt% of the total weight of the first negative electrode active material and the carbon-based material. In the first paragraph, the carbon-based material includes a fibrous carbon nanostructure,
An all-solid-state secondary battery wherein the above fibrous carbon nanostructure comprises a carbon nanotube, a carbon nanofiber, a carbon nanobelt, a carbon nanorod, or a combination thereof. An all-solid-state secondary battery in claim 1, wherein the first negative electrode active material layer further comprises a binder. An all-solid-state secondary battery according to claim 11, wherein the binder comprises a polymer binder, and the binder comprises a fluorine-based binder. An all-solid-state secondary battery in claim 1, wherein the ratio (B/A) of the initial charge capacity (B) of the first negative electrode active material layer and the initial charge capacity (A) of the positive electrode active material layer is 0.01 to 0.75. In the first 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 includes lithium or a lithium alloy. In the first paragraph, the positive electrode active material layer includes a positive electrode active material,
The above cathode active material includes a sulfide cathode active material, an oxide cathode active material, or a combination thereof,
The above sulfide-based cathode active material includes nickel sulfide, copper sulfide, Li ₂ S, a Li ₂ S-containing complex, or a combination thereof,
An all-solid-state secondary battery, wherein the oxide-based cathode active material comprises a lithium transition metal oxide, a metal oxide, or a combination thereof, wherein the lithium transition metal oxide comprises lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium iron phosphate, or a combination thereof, and wherein the lithium oxide comprises iron oxide, vanadium oxide, or a combination thereof. In the first paragraph, the positive electrode active material layer further includes at least one selected from a solid electrolyte, a conductive material, and a binder,
An all-solid-state secondary battery, wherein the solid electrolyte comprises a sulfide-based solid electrolyte and the conductive material comprises a carbon-based conductive material. In the first paragraph, the solid electrolyte layer includes a solid electrolyte or a combination of a solid electrolyte and a gel electrolyte,
The above solid electrolyte includes a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof,
An all-solid-state secondary battery wherein the gel electrolyte comprises a polymer gel electrolyte. In claim 17, the sulfide-based solid electrolyte is Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiX, X is a halogen element, Li ₂ SP ₂ S ₅ -Li ₂ O, Li ₂ SP ₂ S ₅ -Li ₂ O-LiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS ₂ -LiI, Li ₂ S-SiS ₂ -LiBr, Li ₂ S-SiS ₂ -LiCl, Li ₂ S-SiS ₂ -B ₂ S ₃ -LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiI, Li ₂ SB ₂ S ₃ , Li ₂ SP ₂ S ₅ -Z _m S _n , m, n are positive numbers, Z is one of Ge, Zn or Ga, Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS ₂ -Li _p MO _q , p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga In, Li _7-x PS _6-x Cl _x , 0≤x≤2, Li _7-x PS _6-x Br _x , 0≤x≤2, and Li _7-x PS _6-x I _x , 0≤x≤2,
The above sulfide-based solid electrolyte includes an argyrodite-type solid electrolyte,
The above argyrodite-type solid electrolyte comprises at least one selected from Li ₆ PS ₅ Cl, Li ₆ PS ₅ Br and Li ₆ PS ₅ I,
An all-solid-state secondary battery, wherein the density of the above argyrodite-type solid electrolyte is 1.5 to 2.0 g/cc. In the first paragraph, at least one of the positive electrode collector and the negative electrode 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,
An all-solid-state secondary battery, wherein the metal layer comprises indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof. In the first paragraph, a first inactive member is further included that is arranged on at least one of the other surface of the positive electrode collector and the other surface of the negative electrode collector,
An all-solid-state secondary battery, wherein the first inert member is an elastic member.