Patent Description:
Batteries having high energy density and high safety have been actively developed in accordance with industrial demand. For example, lithium-ion batteries are commercially available in the automotive field as well as in the fields of information-associated equipment and communication equipment. In the automotive field, the safety of lithium-ion batteries is particularly important.

A commercialized lithium-ion battery includes a liquid electrolyte including a flammable organic solvent, and thus there is a risk of overheating and fire when a short-circuit occurs. Accordingly, there is a need for an all-solid battery including a solid electrolyte instead of a liquid electrolyte.

<CIT> discloses an all-solid secondary battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer. The positive electrode layer includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector.

<CIT> discloses a nonaqueous electrolyte secondary battery, wherein a negative electrode mixture layer has a first layer and a second layer formed in that order from the side of a negative electrode current collector.

<CIT> discloses an all-solid-state lithium ion battery, including a solid electrolyte, a negative electrode, and a positive electrode. The solid electrolyte includes at least one selected from oxide-based and sulfide-based solid electrolytes.

Provided are an all-solid secondary battery which prevents a short-circuit during charging and discharging and has improved cycle characteristics and a method of manufacturing the same, as defined in the appended claims.

Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented aspects of the disclosure.

According to an aspect of the invention, an all-solid secondary battery is provided in accordance with claim <NUM>.

According to another aspect of the invention, a method of manufacturing an all-solid secondary battery is provided in accordance with claim <NUM>.

The above and other aspects, features, and advantages of certain aspects of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:.

Reference will now be made in detail to aspects, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the present aspects may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the aspects are merely described below, by referring to the figures, to explain aspects.

The terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. As used herein, "a," "an," "the," and "at least one" do not denote a limitation of quantity, and are intended to cover both the singular and plural, unless the context clearly indicates otherwise.

Furthermore, relative terms, such as "lower" or "bottom" and "upper" or "top," may be used herein to describe one element's relationship to another element's as illustrated in the Figures. The exemplary term "lower," can therefore, encompasses both an orientation of "lower" and "upper," depending on the particular orientation of the figure. The exemplary terms "below" or "beneath" can, therefore, encompass both an orientation of above and below.

For example, "about" can mean within one or more standard deviations, or within ± <NUM>%, <NUM>%, <NUM>%, <NUM>% of the stated value.

An all-solid battery does not include a flammable organic solvent, and thus has a reduced risk of fire or explosion even when a short-circuit occurs. Accordingly, the all-solid battery may have increased safety as compared with a lithium-ion battery using a liquid electrolyte.

In an all-solid secondary battery including a solid electrolyte, lithium is locally deposited in the interface between a solid electrolyte layer and an anode layer, and the deposited lithium may grow and consequentially pass through the solid electrolyte layer, causing a short-circuit in the battery. While not wanting to be bound by theory, it is understood that when the solid electrolyte layer and the anode layer are simply stacked, an effective interfacial area between the solid electrolyte layer and the anode layer is smaller than an actual contact area therebetween. Accordingly, the interfacial resistance at the interface between the solid electrolyte layer and the anode layer may be increased, causing an increase in internal resistance of the battery and consequentially deteriorating cycle characteristics of the battery.

In an aspect, an all-solid battery is provided in which a short-circuit is prevented during charge and discharge, and cycle characteristics of the battery are improved.

Hereinafter, example aspects of an all-solid secondary battery and a method of manufacturing an all-solid secondary battery will be described in greater detail.

As used herein, the term "metal" refers to a metal element selected from Groups <NUM> to <NUM> of the Periodic Table of Elements, including the lanthanide elements and the actinide elements.

A "metalloid" refers to B, Si, Ge, As, Sb, Te, or a combination thereof.

"Argyrodite," "argyrodite structure," or "argyrodite-type structure" as used herein means that the compound has a crystal structure that is isostructural with argyrodite, Ag<NUM>GeS<NUM>.

A garnet or "garnet-type" compound is a compound having the same or similar crystal structure (e.g., isostructure) with a compound of the formula X<NUM>Y<NUM>(SiO<NUM>)<NUM>, wherein X is a divalent cation, such as Ca<NUM>+, Mg<NUM>+, Fe<NUM>+, Mn<NUM>+, or a combination thereof, and Y is a trivalent cation, such as Al<NUM>+, Fe<NUM>+, Cr<NUM>+, or a combination thereof.

According to the invention, an all-solid secondary battery comprises: a cathode layer comprising a cathode active material layer; an anode layer; and a solid electrolyte layer comprising a solid electrolyte, wherein the solid electrolyte layer is disposed between the cathode layer and the anode layer, wherein the anode layer comprises an anode current collector, a first anode active material layer disposed on the anode current collector and in contact with the solid electrolyte layer; and a second anode active material layer disposed between the anode current collector and the first anode active material layer. The first anode active material layer comprises a first carbonaceous anode active material, the second anode active material layer includes a second carbonaceous anode active material, and a first intensity ratio (I<NUM>D/I<NUM>G) of an intensity of a D band peak to an intensity of a G band peak in a Raman spectrum of the first carbonaceous anode active material is less than a second intensity ratio (I<NUM>D/I<NUM>G) of an intensity of D band peak to an intensity of a G band peak of the second carbonaceous anode active material.

While not wanting to be bound by theory, it is understood that when the first intensity ratio (I<NUM>D/I<NUM>G) of the D band peak to the G band peak in the Raman spectrum of the first carbonaceous anode active material is less than the second intensity ratio (I<NUM>D/I<NUM>G) of the intensity of the D band peak to the intensity of the G band peak of the second carbonaceous anode active material, a content of defects in the first carbonaceous anode active material may be less than a content of defects in the second carbonaceous anode active material. Also, defects generated between the solid electrolyte layer and the first anode active material layer including the first carbonaceous anode active material may be reduced. Accordingly, localized lithium deposition in the interface between the solid electrolyte and the first anode active material layer may be suppressed. In addition, since the second anode active material layer is disposed on the first anode active material layer, and the second anode active material layer contains the second carbonaceous anode active material having more defects than the first carbonaceous anode active material, it is understood that the defects may serve as seeds for lithium deposition, thereby facilitating lithium deposition on the second anode active material layer, and lithium deposition (i.e., a formation of lithium layer) may be more uniform on the second anode active material layer. Due to the deposition of a uniform lithium layer between the solid electrolyte layer and the anode current collector, the all-solid secondary battery may be reversibly charged and discharged and have improved cycle characteristics.

Referring to <FIG>, an all-solid secondary battery <NUM> according to an aspect of the invention includes: a cathode layer <NUM> including a cathode active material layer <NUM> and a cathode current collector <NUM>; an anode layer <NUM>; and a solid electrolyte layer <NUM> including a solid electrolyte, disposed between the cathode layer <NUM> and the anode layer <NUM>. The anode layer <NUM> includes: an anode current collector <NUM>; a first anode active material layer <NUM> disposed on the anode current collector <NUM> and contacting the solid electrolyte layer <NUM>; and a second anode active material layer <NUM> disposed between the anode current collector <NUM> and the first anode active material layer <NUM>. The first anode active material layer <NUM> includes a first carbonaceous anode active material, and the second anode active material layer <NUM> includes a second carbonaceous anode active material. A first intensity ratio (I<NUM>D/I<NUM>G) of an intensity of a D band peak to an intensity of a G band peak in a Raman spectrum of first carbonaceous anode active material is less than a second intensity ratio (I<NUM>D/I<NUM>G) of an intensity of a D band peak to an intensity of a G band peak in a Raman spectrum of the second carbonaceous anode active material.

Referring to <FIG>, the first intensity ratio (I<NUM>D/I<NUM>G) of the intensity of the D band peak to the intensity of the G band peak in the Raman spectrum of the first carbonaceous anode active material included in the first anode active material layer <NUM> may be, for example, <NUM> or less, about <NUM> or less, about <NUM> or less, about <NUM> or less, or about <NUM> or less. The first intensity ratio (I<NUM>D/I<NUM>G) may be, for example, <NUM> to <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>. Since the first carbonaceous anode active material has an intensity ratio within these ranges, defects in the first anode active material layer may be reduced, and defects between the first anode active material layer and the solid electrolyte layer may also be reduced. As a result, the interfacial resistance between the first anode active material layer and the solid electrolyte layer may be reduced, and localized deposition of lithium may be suppressed. the second intensity ratio (I<NUM>D/I<NUM>G) of the intensity of the D band peak to the intensity of the G band peak in the Raman spectrum of the second carbonaceous anode active material included in the second anode active material layer <NUM> may be, for example, <NUM> or greater, about <NUM> or greater, or about <NUM> or greater. The second intensity ratio (I<NUM>D/I<NUM>G) of the intensity of the D band peak to the intensity of the G band peak in the Raman spectrum of the second carbonaceous anode active material included in the second anode active material layer <NUM> may be, for example, <NUM> to <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>. As the second carbonaceous anode active material has an intensity ratio within these ranges, defects in the second anode active material layer may be increased. As a result, lithium may be easily and uniformly deposited within the second anode active material layer and/or on a surface of the second anode active material layer.

The position of a D band peak center in the Raman spectrum of the first carbonaceous anode active material included in the first anode active material layer <NUM> may exhibit, for example, a blue shift of <NUM>-<NUM> or greater, about <NUM>-<NUM> or greater, about <NUM>-<NUM> or greater, or about <NUM>-<NUM> or greater with respect to the position of a D band peak center in the Raman spectrum of the second carbonaceous anode active material included in the second anode active material layer <NUM>. For example, the first carbonaceous anode active material may exhibit a blue shift of <NUM>-<NUM> to <NUM>-<NUM>, or about <NUM>-<NUM> to <NUM>-<NUM>, or about <NUM>-<NUM> to <NUM>-<NUM>. A blue shift means shifting to a position with higher energy, i.e., with a greater wave number. In an embodiment in which the first carbonaceous anode active material has such a D band peak center position, a short-circuit of the all-solid secondary battery may be suppressed, and cycle characteristics thereof may further be improved.

The position of a G band peak center in the Raman spectrum of the first carbonaceous anode active material included in the first anode active material layer <NUM> may exhibit a blue shift of <NUM>-<NUM> or greater, about <NUM>-<NUM> or greater, or about <NUM>-<NUM> or greater with respect to the position of a G band peak center in the Raman spectrum of the second carbonaceous anode active material included in the second anode active material layer <NUM>. For example, the first carbonaceous anode active material may exhibit a blue shift of <NUM>-<NUM> to <NUM>-<NUM>, or <NUM>-<NUM> to about <NUM>-<NUM>, or about <NUM>-<NUM> to about <NUM>-<NUM>. In an embodiment in which the first carbonaceous anode active material has such a G band center position, a short-circuit of the all-solid secondary battery may be suppressed, and cycle characteristics thereof may be further improved.

A width of the D band peak, e.g., a full width at half maximum (FWHM), of the first carbonaceous anode active material included in the first anode active material layer <NUM> may be <NUM>% or less, about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, or about <NUM>% or less of a width of the D band peak, e.g., a full width at half maximum (FWHM), of the second carbonaceous anode active material included in the second anode active material layer <NUM>. For example, the width of the D band peak of the first carbonaceous anode active material may be <NUM>% to <NUM> %, or <NUM>% to about <NUM>%, or <NUM>% to about <NUM>% of the width of the D band peak of the second carbonaceous anode active material. While not wanting to be bound by theory, it is understood that when the first carbonaceous anode active material has such a D band peak width, a short-circuit of the all-solid secondary battery may be suppressed, and cycle characteristics thereof may further be improved.

At least one of the first carbonaceous anode active material or the second carbonaceous anode active material may be, for example, in a particle form. The particles of the first carbonaceous anode active material and/or the particles of the second carbonaceous anode active material may have an average particle diameter of, for example, about <NUM> micrometers (µm) or less, about <NUM> or less, about <NUM> or less, about <NUM> or less, or about <NUM> nanometers (nm) or less. The particles of the first carbonaceous anode active material and/or the particles of the second carbonaceous anode active material may have an average particle diameter of, for example, <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, or <NUM> to <NUM>. As the first carbonaceous anode active material and/or the second carbonaceous anode active material have an average particle diameter within these ranges, reversible absorption and/or desorption of lithium during charge and discharge may be further facilitated. In other aspects, the average particle diameter of the first carbonaceous anode active material and/or the second carbonaceous anode active material may be an arithmetic mean of the particle sizes obtained from a scanning electron microscope (SEM) image. The term "size" of a particle as used herein refers to an average diameter of particles in the case of spherical particles or an average length of the major axes in the case of non-spherical particles. The average diameter of particles refers to a median diameter ("D50") of particles, and the median diameter is defined as a particle diameter corresponding to <NUM> vol% (i.e., volume percentage) of a cumulative diameter distribution and refers to a particle diameter of <NUM> % in samples. The median diameter ("D50") of particles may be measured using a particle size analyzer ("PSA").

At least one of the first carbonaceous anode active material included in the first anode active material layer <NUM> or the second carbonaceous anode active material included in the second anode active material layer <NUM> may include, for example, amorphous carbon. The amorphous carbon may be, for example, at least one of carbon black (CB), acetylene black (AB), furnace black (FB), ketjen black (KB), graphene, carbon nanotubes, or carbon nanofiber. However, aspects are not limited thereto. Any suitable amorphous carbon may be used.

At least one of the first anode active material layer <NUM> and the second anode active material layer <NUM> may consist of a carbonaceous material. For example, the first anode active material layer <NUM> may consist of the first carbonaceous anode active material, and/or the second anode active material layer <NUM> may consist of the second carbonaceous anode active material. When the first anode active material layer <NUM> and/or the second anode active material layer <NUM> consists of a carbonaceous material, the first anode active material layer <NUM> and/or the second anode active material layer <NUM> do not include a non-carbonaceous material, such as a metal, a metal oxide, or a ceram ic.

The first anode active material layer <NUM> may further include, in addition to the first carbonaceous anode active material, a metal or metalloid anode active material. The second anode active material layer <NUM> may further include, in addition to the second carbonaceous anode active material, a metal or metalloid anode active material. The metal or metalloid anode active material may comprise, for example, at least one of indium (In), silicon (Si), gallium (Ga), tin (Sn), aluminum (Al), titanium (Ti), zirconium (Zr), niobium (Nb), germanium (Ge), antimony (Sb), bismuth (Bi), gold (Au), platinum (Pt), palladium (Pd), magnesium (Mg), silver (Ag), or zinc (Zn). However, embodiments are not limited thereto. Any suitable metal anode active material or metalloid anode active material which forms an alloy or a compound with lithium may be used.

The first anode active material layer <NUM> may include, for example, a single anode active material, thus the first anode active material layer <NUM> may include, for example, the first carbonaceous anode active materials or a metal or a metalloid anode active material. Alternatively, the first anode active material layer <NUM> may include a composite of a plurality of different anode active materials. For example, the first anode active material layer <NUM> may include amorphous carbon alone, or in combination with at least one metal or metalloid of indium (In), silicon (Si), gallium (Ga), tin (Sn), aluminum (Al), titanium (Ti), zirconium (Zr), niobium (Nb), germanium (Ge), antimony (Sb), bismuth (Bi), gold (Au), platinum (Pt), palladium (Pd), magnesium (Mg), silver (Ag), or zinc (Zn). In other aspects, the first anode active material layer <NUM> may include a composite of amorphous carbon and at least one metal or metalloid anode active material of indium (In), silicon (Si), gallium (Ga), tin (Sn), aluminum (Al), titanium (Ti), zirconium (Zr), niobium (Nb), germanium (Ge), antimony (Sb), bismuth (Bi), gold (Au), platinum (Pt), palladium (Pd), magnesium (Mg), silver (Ag), or zinc (Zn). A weight ratio between the amorphous carbon and the metal or the metalloid in the composite may be, for example, about <NUM>:<NUM> to <NUM>:<NUM>, about <NUM>:<NUM> to <NUM>:<NUM>, or about <NUM>:<NUM> to <NUM>:<NUM>. For example, the metal in the composite may be silver. However, aspects are not limited to these ranges, and the weight ratio may be selected according to the desired characteristics of the all-solid secondary battery <NUM>. As the first anode active material layer <NUM> has a composition within these ratios, cycle characteristics of the all-solid secondary battery <NUM> may further be improved.

The second anode active material layer <NUM> may include, for example, a single anode active material from among the second carbonaceous active materials, or may be a composite of a plurality of different anode active materials. For example, the second anode active material layer <NUM> may include amorphous carbon alone, or in combination with at least one metal or metalloid of indium (In), silicon (Si), gallium (Ga), tin (Sn), aluminum (Al), titanium (Ti), zirconium (Zr), niobium (Nb), germanium (Ge), antimony (Sb), bismuth (Bi), gold (Au), platinum (Pt), palladium (Pd), magnesium (Mg), silver (Ag), or zinc (Zn). In other aspects, the second anode active material layer <NUM> may include a mixture of amorphous carbon and at least one metal or metalloid of indium (In), silicon (Si), gallium (Ga), tin (Sn), aluminum (Al), titanium (Ti), zirconium (Zr), niobium (Nb), germanium (Ge), antimony (Sb), bismuth (Bi), gold (Au), platinum (Pt), palladium (Pd), magnesium (Mg), silver (Ag), or zinc (Zn). A weight ratio of amorphous carbon and silver, or the like in the mixture may be, for example, about <NUM>:<NUM> to <NUM>:<NUM>, about <NUM>:<NUM> to <NUM>:<NUM>, or about <NUM>:<NUM> to <NUM>:<NUM>. However, aspects are not limited thereto. The weight ratio may be selected according to the desired characteristics of the all-solid secondary battery <NUM>. As the second anode active material layer <NUM> has such a composition as above, the all-solid secondary battery <NUM> may have further improved characteristics.

The first anode active material included in the first anode active material layer <NUM> may include, for example, a composite of first particles and second particles. The first particles may consist of amorphous carbon and the second particles may consist of a metal or a metalloid. As used herein, "composite" refers to a material formed by combining two or more materials having different physical and/or chemical properties, wherein the composite has properties different from each material constituting the composite, and wherein particles of each material are at least microscopically separated and distinguishable from each other in a finished structure of the composite. The composite may be a product obtained through thermochemical reaction by thermal treatment or through mechanochemical reaction by mechanical milling of a mixture. A composite may be distinguished from a mixture of the first particles and the second particles or a mixture of the first particles and the second particles bound together by a binder. The metal or metalloid in the composite may include, for example, at least one of indium (In), silicon (Si), gallium (Ga), tin (Sn), aluminum (Al), titanium (Ti), zirconium (Zr), niobium (Nb), germanium (Ge), antimony (Sb), bismuth (Bi), gold (Au), platinum (Pt), palladium (Pd), magnesium (Mg), silver (Ag), or zinc (Zn). In an aspect, the metalloid is a semiconductor. The amount of the second particles may be <NUM> weight percent (wt%) to <NUM> wt%, about <NUM> wt% to <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, or about <NUM> wt% to about <NUM> wt%, with respect to a total weight of the composite. As the amount of the second particles is within these ranges, the all-solid secondary battery <NUM> may have, for example, further improved cycle characteristics.

The anode active material included in the second anode active material layer <NUM> may include, for example, a mixture of first particles and second particles. The first particles may consist of amorphous carbon and the second particles may consist of a metal or a metalloid. The mixture may be a product formed by mixing the first particles and the second particles, or by physically binding the first particles and the second particles together with a binder. The metal or the metalloid may include, for example, at least one of indium (In), silicon (Si), gallium (Ga), tin (Sn), aluminum (Al), titanium (Ti), zirconium (Zr), niobium (Nb), germanium (Ge), antimony (Sb), bismuth (Bi), gold (Au), platinum (Pt), palladium (Pd), magnesium (Mg), silver (Ag), or zinc (Zn). In an aspect, the metalloid is a semiconductor. The amount of the second particles may be about <NUM> wt% to <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, or about <NUM> wt% to about <NUM> wt%, with respect to a total weight of the mixture. As the amount of the second particles is within these ranges, for example, the all-solid secondary battery <NUM> may have further improved cycle characteristics.

In the all-solid secondary battery <NUM>, for example, the amount of the metal or metalloid anode active material included in the second anode active material layer <NUM> and the amount of the metal or metalloid anode active material included in the first anode active material layer <NUM> may be different from each other. For example, the amount of the metal or metalloid anode active material included in the second anode active material layer <NUM> may be greater than the amount of the metal or metalloid anode active material included in the first anode active material layer <NUM>. As the amount of the metal or metalloid anode active material included in the second anode active material layer <NUM> is greater than the amount of the metal or metalloid anode active material included in the first anode active material layer <NUM>, lithium may be more easily deposited within and/or on the surface of the second anode active material layer <NUM>. A weight ratio of the amount of the metal or metalloid anode active material included in the second anode active material layer <NUM> and the amount of the metal or metalloid anode active material included in the first anode active material layer <NUM> may be, for example, about <NUM>:<NUM> to about <NUM>:<NUM>, about <NUM>:<NUM> to about <NUM>:<NUM>, or about <NUM>:<NUM> to about <NUM>:<NUM>.

The average particle diameter of the first particles consisting of amorphous carbon in the second anode active material layer <NUM> may be smaller than the average particle diameter of the first particles consisting of amorphous carbon in the first anode active material layer <NUM>. The average particle diameter of the first particles consisting of amorphous carbon in the second anode active material layer <NUM> may be, for example, <NUM>% or less, about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, or about <NUM>% or less of the average particle diameter of the first particles consisting of amorphous carbon in the first anode active material layer <NUM>.

The average particle diameter of the second particles consisting of the metal or metalloid in the second anode active material layer <NUM> may be smaller than the average particle diameter of the second particles consisting of metal or metalloid in the first anode active material layer <NUM>. The average particle diameter of the second particles consisting of the metal or metalloid in the second anode active material layer <NUM> may be, for example, <NUM>% or less, about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, or about <NUM>% or less of the average particle diameter of the second particles consisting of the metal or metalloid in the first anode active material layer <NUM>. Since the first particles and the second particles in the second anode active material layer <NUM> have reduced particle diameters relative to those in the first anode active material layer <NUM>, the second particles (e.g., metal or metalloid particles) may be more uniformly dispersed in the second anode active material layer <NUM>, and thus lithium may be more uniformly deposited inside of or on the surface of the second anode active material layer <NUM>.

The first carbonaceous anode active material included in the first anode active material layer may form, for example, at least one of a covalent bond or an ionic bond with the solid electrolyte included in the solid electrolyte layer <NUM>. The first carbonaceous anode active material included in the first anode active material layer may thus be bound to the solid electrolyte layer by at least one of a covalent bond or an ionic bond. For example, the formation of a covalent bond and/or an ionic bond may occur during the process of a thermally treating the precursors of the solid electrolyte layer <NUM> and the first anode active material layer <NUM>. Since the first anode active material layer <NUM> forms covalent bonds and/or ionic bonds with the solid electrolyte layer <NUM>, for example, the interfacial resistance between the first anode active material layer <NUM> and the solid electrolyte layer <NUM> may be reduced.

The first anode active material layer <NUM> may be, for example, an inorganic layer which does not include an organic material or organic compound. As used herein, an "organic compound" or "organic material" refers to a compound in which one or more atoms of carbon is covalently bound to hydrogen atom(s), and optionally another element. An organic compound or organic material does not include the carbonaceous materials disclosed herein. For example, the first anode active material layer <NUM> does not include an organic binder such as a polymer binder. In other words, the first anode active material layer <NUM> maybe an inorganic layer consisting of an inorganic material. Since the first anode active material layer <NUM> is an inorganic layer including an inorganic carbonaceous material and/or a metal or metalloid material, for example, side reactions during charge and discharge processes may be suppressed. For example, the first anode active material layer <NUM> may be an inorganic carbon layer consisting of amorphous carbon. For example, the first anode active material layer <NUM> may be an inorganic carbon-metal or metalloid composite layer consisting of amorphous carbon and a metal or metalloid.

The first carbonaceous anode active material included in the first anode active material layer <NUM> may be, for example, a sintered product of a carbonaceous precursor. That is, the first carbonaceous anode active material may be a product obtained by thermal treatment of a carbonaceous precursor. The carbonaceous precursor of the first carbonaceous anode active material may be, for example, the second carbonaceous anode active material. For example, the first carbonaceous anode active material may be obtained by thermal treatment of the second carbonaceous anode active material included in the second carbonaceous anode active material layer <NUM>. The first carbonaceous anode active material may be, for example, a thermal treatment product, i.e., a sintered product, of the second carbonaceous anode active material. Accordingly, for example, the first anode active material layer <NUM> may be sintered with the solid electrolyte layer <NUM> during a thermal treatment process to form a single body with the solid electrolyte layer <NUM>. Also, during the thermal treatment process, any organic material such as a binder included in the carbonaceous precursor, may be removed via carbonization or vaporization during the thermal decomposition process, and thus only the carbonaceous material and/or metal material remains.

A thickness of the first anode active material layer <NUM> may be <NUM>% or less, about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, or about <NUM>% or less of the total thickness of the cathode active material layer <NUM>. For example, the thickness of the first anode active material layer <NUM> may be about <NUM>% to <NUM>%, or about <NUM>% to about <NUM>%, or about <NUM>% to about <NUM>% of the total thickness of the cathode active material layer <NUM>. As the thickness of the first anode active material layer <NUM> decreases relative to the thickness of the cathode active material layer, the all-solid secondary battery may have improved energy density. The thickness of the first anode active material layer <NUM> may be, for example, <NUM> to <NUM>, about <NUM> to <NUM>, about <NUM> to <NUM>, about <NUM> to <NUM>, about <NUM> to <NUM>, about <NUM> to <NUM>, about <NUM> to <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>. When the first anode active material layer <NUM> has a thickness within these ranges, a short-circuit in the all-solid secondary battery may be suppressed, and cycle characteristics may be improved. When the thickness of the first anode active material layer <NUM> is too small, the first anode active material layer <NUM> may not effectively serve as an anode active material layer. When the thickness of the first anode active material layer <NUM> is too large, the all-solid secondary battery <NUM> may have reduced energy density and may have increased internal resistance due to the first anode active material layer <NUM>, and thus it may be difficult for the all-solid secondary battery <NUM> to have improved cycle characteristics.

The thickness of the second anode active material layer <NUM> may be, for example, <NUM>% or less, about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, or about <NUM>% or less of the total thickness of the cathode active material layer. For example, the thickness of the second anode active material layer <NUM> may be about <NUM>% to <NUM>%, or about <NUM>% to about <NUM>%, or about <NUM>% to about <NUM>% of the total thickness of the cathode active material layer <NUM>. As the thickness of the second anode active material layer <NUM> is less than the thickness of the cathode active material layer, the all-solid secondary battery may have improved energy density.

The thickness of the second anode active material layer <NUM> may be, for example, <NUM> to <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>. When the second anode active material layer <NUM> has a thickness within these ranges, a short-circuit in the all-solid secondary battery may be suppressed, and cycle characteristics may be improved. When the thickness of the second anode active material layer <NUM> is too small, lithium dendrites formed between the second anode active material layer <NUM> and the anode current collector <NUM> may collapse the second anode active material layer <NUM>, and thus it may be difficult for the all-solid secondary battery <NUM> to have improved cycle characteristics. When the thickness of the second anode active material layer <NUM> is excessively increased, the all-solid secondary battery <NUM> may have reduced energy density and may have increased internal resistance due to the second anode active material layer <NUM>, and thus it may be difficult for the all-solid secondary battery <NUM> to have improved cycle characteristics.

The thickness of the first anode active material layer <NUM> is less than the thickness of the second anode active material layer <NUM>. The thickness of the first anode active material layer <NUM> may be about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, or about <NUM>% or less of the thickness of the second anode active material layer <NUM>. For example, the thickness of the first anode active material layer <NUM> may be about <NUM>% to about <NUM>%, or about <NUM>% to about <NUM>%, or about <NUM>% to about <NUM>% of the thickness of the second anode active material layer <NUM>. When the first anode active material layer <NUM> has a thickness within these ranges, a short-circuit in the all-solid secondary battery may be suppressed, and cycle characteristics may be improved.

For example, the first anode active material layer <NUM> may be formed on the solid electrolyte layer <NUM> using a film formation method such as spin coating, drop coating, spray coating, pyrolysis, or solution filtration, and then a thermal treatment may be applied. However, aspects are not limited thereto. Any wet method suitable for forming the first anode active material layer <NUM> may be used. In other aspects, the first anode active material layer <NUM> may be disposed on the solid electrolyte layer <NUM> using vacuum deposition, sputtering, or plating. However, aspects are not limited to these methods. Any dry method suitable for forming the first anode active material layer <NUM> may be used.

At least one of the first anode active material layer <NUM> or the second anode active material layer <NUM> may further include, for example, a binder.

For example, the second anode active material layer <NUM> may include a binder. The binder may be, for example, at least one of a styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, a vinylidene fluoride/hexafluoropropylene copolymer, polyacrylonitrile, or polymethylmethacrylate. However, aspects are not limited thereto. Any suitable binder may be used. The binder may be a single binder or may include a plurality of different binders.

When the second anode active material layer <NUM> includes a binder, the second anode active material layer <NUM> may be stabilized on the anode current collector <NUM>. Also, despite a volume change and/or relative position change of the second anode active material layer <NUM> during a charge and discharge process, cracking of the second anode active material layer <NUM> may be suppressed. For example, when the second anode active material layer <NUM> does not include a binder, the second anode active material layer <NUM> may be easily separated from the anode current collector <NUM>. If a portion of the second anode active material layer <NUM> is separated from the anode current collector <NUM>, the anode current collector <NUM> may be exposed and may contact the solid electrolyte layer <NUM>, and thus a short circuit is more likely to occur. For example, the second anode active material layer <NUM> may be formed by coating a slurry on the anode current collector <NUM>, and drying the same. The slurry may include the ingredients for forming the second anode active material layer <NUM>. If a binder is included in the second anode active material layer <NUM>, the anode active material may be stably dispersed in the slurry. For example, when the slurry is coated on the anode current collector <NUM> using screen printing, clogging of a screen (for example, clogging by aggregates of the anode active material) can be suppressed.

For example, the anode current collector <NUM> may consist of a material which does not react with lithium to form an alloy or compound. The material of the anode current collector <NUM> may be, for example, at least one metal of copper (Cu), stainless steel (SUS), titanium (Ti), iron (Fe), cobalt (Co), or nickel (Ni). However, aspects are not limited thereto. Any material suitable as an anode current collector may be used. The anode current collector <NUM> may include one of the above-listed metals or may be an alloy or a compound of two or more of the above-listed metals. The anode current collector <NUM> may be, for example, in the form of a plate or a foil.

The second anode active material layer <NUM> of the all-solid secondary battery <NUM> may further include an additive(s), for example, at least one of a filler, a dispersing agent, or an ionic conducting agent.

In the all-solid secondary battery <NUM>, for example, the second anode active material layer <NUM> may include a second carbonaceous anode active material and a metal or metalloid anode active material, and the first anode active material layer <NUM> may consist of a first carbonaceous anode active material. That is, the first anode active material layer <NUM> does not include a metallic material, and specifically, does not include a metal or metalloid anode active material. As the all-solid secondary battery <NUM> has this structure, a short circuit of the all-solid secondary battery <NUM> may be suppressed, and cycle characteristics may be improved.

In other aspects, in the all-solid secondary battery <NUM>, the second anode active material layer <NUM> may consist of a second carbonaceous anode active material, and the first anode active material layer <NUM> may include a first carbonaceous anode active material and a metal or metalloid anode active material. That is, the second anode active material layer <NUM> does not include a metallic material and specifically, does not include a metal or metalloid active material. As the all-solid secondary battery <NUM> has this structure, a short-circuit in the all-solid secondary battery <NUM> may be suppressed, and cycle characteristics may be improved.

Referring to <FIG>, for example, the all-solid secondary battery <NUM> may further include, on the anode current collector <NUM>, a thin film <NUM> including an element alloyable with lithium. The thin film <NUM> may be disposed between the anode current collector <NUM> and the second anode active material layer <NUM>. For example, the thin film <NUM> may include an element alloyable with lithium. The element (metal) alloyable with lithium may be, for example, at least one of gold, silver, zinc, tin, indium, silicon, aluminum, or bismuth. However, aspects are not limited thereto, and any element alloyable with lithium may be used. The thin film <NUM> may consist of one of these metals or an alloy of two or more of the different metals. As the thin film <NUM> is disposed on the anode current collector <NUM>, for example, a third anode active material layer (not shown) deposited between the thin film <NUM> and the second anode active material layer <NUM> may have a more planar form, and the all-solid secondary battery <NUM> may have further improved cycle characteristics.

The thin film <NUM> may have a thickness of, for example, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>. When the thickness of the thin film <NUM> is less than <NUM>, it may be difficult for the thin film <NUM> to function properly. When the thickness of the thin film <NUM> is too great, the thin film <NUM> itself may absorb lithium so that a deposition amount of lithium on the anode may be reduced and the all-solid secondary battery may have reduced energy density, and thus have deteriorated cycle characteristics. The thin film <NUM> may be disposed on the anode current collector <NUM> using, for example, vacuum deposition, sputtering, or plating. However, aspects are not limited to these methods. Any suitable method may be used to form the thin film <NUM>.

Referring to <FIG> and <FIG>, an all-solid secondary battery <NUM> according to an aspect may further include a third anode active material layer <NUM>, between the anode current collector <NUM> and the second anode active material layer <NUM> (<FIG>) or between the first anode active material layer <NUM> and the second anode active material layer <NUM> (<FIG>). The third anode active material layer <NUM> may be deposited during charging of the all-solid secondary battery <NUM>. The third anode active material layer <NUM> may be a metal layer including lithium or a lithium alloy. Accordingly, the third anode active material layer <NUM>, as a metal layer including lithium or a lithium alloy, may function as a lithium reservoir. The lithium alloy may be, for example, at least one of 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, or a Li-Si alloy. However, aspects are not limited to these alloys, and any lithium alloy suitable for an all-solid secondary battery may be used. The third anode active material layer <NUM> may consist of lithium, a single lithium alloy, or a combination of various alloys.

The thickness of the third anode active material layer <NUM> is not specifically limited, and may be, for example, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>. When the thickness of the third anode active material layer <NUM> is too thin, the third anode active material layer <NUM> may not function as a lithium reservoir. When the thickness of the third anode active material layer <NUM> is too thick, the all-solid secondary battery <NUM> may be increased in mass and volume, and cycle characteristics may be degraded. The third anode active material layer <NUM> may be, for example, a metal foil having a thickness within the above-described ranges.

For example, the third anode active material layer <NUM> of the all-solid secondary battery <NUM> may be disposed, during assembly of the all-solid secondary battery <NUM>, between the anode current collector <NUM> and the second anode active material layer <NUM>, or between the first anode active material layer <NUM> and the second anode active material layer <NUM>. In another aspect, the third anode active material layer <NUM> of the all-solid secondary battery <NUM> may be precipitated after assembly and during charging of the all-solid secondary battery <NUM>, and may be disposed between the anode current collector <NUM> and the second anode active material layer <NUM>, or between the first anode active material layer <NUM> and the second anode active material layer <NUM>.

In the case where the third anode active material layer <NUM> is disposed during assembly of the all-solid secondary battery <NUM>, between the anode current collector <NUM> and the second anode active material layer <NUM>, or between the first anode active material layer <NUM> and the second anode active material layer <NUM>, the third anode active material layer <NUM> (which is a metal layer including lithium), may serve as a lithium reservoir. The all-solid secondary battery <NUM> including the third anode active material layer <NUM> may have further improved cycle characteristics. For example, during the assembly of the all-solid secondary battery <NUM>, a lithium foil as the third anode active material layer <NUM> may be disposed between the anode current collector <NUM> and the second anode active material layer <NUM>, or between the first anode active material layer <NUM> and the second anode active material layer <NUM>.

In the case where the third anode active material layer <NUM> is disposed after assembly by charging of the all-solid secondary battery <NUM>, the all-solid secondary battery <NUM> may have increased energy density since the third anode active material layer <NUM> is not present at a time of assembly. For example, the all-solid secondary battery <NUM> may be charged to exceed the charge capacity of at least one of the first anode active material layer <NUM> or the second anode active material layer <NUM>. That is, the first anode active material layer <NUM> and/or the second anode active material layer <NUM> may be overcharged. At an initial charging stage, lithium may be absorbed into at least one of the first anode active material layer <NUM> or the second anode active material layer <NUM>. That is, the anode active material in at least one of the first anode active material layer <NUM> or the second anode active material layer <NUM> may form an alloy or a compound with lithium ions as they move from the cathode layer <NUM> during charge of the all-solid secondary battery. When the all-solid secondary battery <NUM> is overcharged, i.e., charged greater than the capacity of the first anode active material layer <NUM> and/or the second anode active material layer <NUM>, for example, lithium may be precipitated on a rear surface of the second anode active material layer <NUM>, i.e., between the anode current collector <NUM> and the second anode active material layer <NUM>, thus forming a metal layer corresponding to the third anode active material layer <NUM>. In another aspect, when the all-solid secondary battery <NUM> is charged over the capacity of the second anode active material layer <NUM>, for example, lithium may be precipitated on a front surface of the second anode active material layer <NUM>, i.e., between the first anode active material layer <NUM> and the second anode active material layer <NUM>, thus forming a metal layer corresponding to the third anode active material layer <NUM>.

The third anode active material layer <NUM> may be a metal layer including lithium (i.e., metal lithium) as a major component. This may be attributed to, for example, the fact that the anode active material in the first anode active material layer <NUM> and the second anode active material layer <NUM> includes a material capable of forming an alloy or a compound with lithium. During discharge, lithium in at least one of the first anode active material layer <NUM>, the second anode active material layer <NUM>, or the third anode active material layer <NUM>, i.e., lithium metal layer, may be ionized and then move towards the cathode layer <NUM>. Accordingly, the all-solid secondary battery <NUM> may use lithium as the anode active material. Since at least one of the first anode active material layer <NUM> or the second anode active material layer <NUM> coat the third anode active material layer <NUM>, the at least one of the first anode active material layer <NUM> or the second anode active material layer <NUM> may function as a protective layer for the third anode active material layer <NUM>, i.e., metal layer, and at the same time suppress precipitation and growth of lithium dendrites. Accordingly, a short-circuit and reduction in capacity of the all-solid secondary battery <NUM> may be suppressed, and cycle characteristics of the all-solid secondary battery <NUM> may be improved. In the case where the third anode active material layer <NUM> is disposed through charging of the all-solid secondary battery <NUM> after assembly, the anode current collector <NUM>, the first anode active material layer <NUM>, the second anode active material layer <NUM>, and regions therebetween may be, for example, Li-free regions which do not include lithium (Li) in an initial state or a post-discharge state of the all-solid secondary battery.

Referring to <FIG>, the solid electrolyte layer <NUM> between the cathode layer <NUM> and the anode layer <NUM> may contain a solid electrolyte.

The solid electrolyte may be, for example, an oxide-containing solid electrolyte. The oxide-containing solid electrolyte may be at least one of Li<NUM>+x+yAlxTi<NUM>-xSiyP<NUM>-yO<NUM> (wherein <NUM><x<<NUM> and <NUM>≤y<<NUM>), BaTiO<NUM>, Pb(ZraTi<NUM>-a)O<NUM> (where <NUM>≤a≤<NUM>)(PZT), Pb<NUM>-xLaxZr<NUM>-y TiyO<NUM> (PLZT) (wherein <NUM>≤x<<NUM> and <NUM>≤y<<NUM>), Pb(Mg<NUM>/<NUM>Nb<NUM>/<NUM>)O<NUM>-PbTiO<NUM> (PMN-PT), HfO<NUM>, SrTiOs, SnO<NUM>, CeO<NUM>, Na<NUM>O, MgO, NiO, CaO, BaO, ZnO, ZrO<NUM>, Y<NUM>O<NUM>, Al<NUM>O<NUM>, TiO<NUM>, SiO<NUM>, Li<NUM>PO<NUM>, LixTiy(PO<NUM>)<NUM> (wherein <NUM><x<<NUM> and <NUM><y<<NUM>), LixAlyTiz(PO<NUM>)<NUM> (wherein <NUM><x<<NUM>, <NUM><y<<NUM>, and <NUM><z<<NUM>), Li<NUM>+x+y(Ala Ga<NUM>-a)x(TibGe<NUM>-b)<NUM>-xSiyP<NUM>-yO<NUM> (wherein <NUM>≤x≤<NUM>, <NUM>≤y≤<NUM>, <NUM>≤a≤<NUM>, and <NUM>≤b≤<NUM>), LixLayTiO<NUM> (wherein <NUM><x<<NUM> and <NUM><y<<NUM>), Li<NUM>O, LiOH, Li<NUM>CO<NUM>, LiAlO<NUM>, Li<NUM>O-Al<NUM>O<NUM>-SiO<NUM>-P<NUM>O<NUM>-TiO<NUM>-GeO<NUM>, and Li<NUM>+xLa<NUM>M<NUM>O<NUM> (wherein M is Te, Nb, or Zr, and x is <NUM>≤x≤<NUM>). The solid electrolyte may be prepared using, for example, sintering.

The oxide-containing solid electrolyte may be, for example, at least one Garnet-type solid electrolyte of Li<NUM>La<NUM>Zr<NUM>O<NUM> (LLZO) or Li<NUM>+xLa<NUM>Zr<NUM>-aMaO<NUM> (M-doped LLZO, wherein M is Ga, W, Nb, Ta, or Al, and <NUM>≤x≤<NUM>).

In another aspect, the solid electrolyte may be, for example, a sulfide-containing solid electrolyte. The sulfide-containing solid electrolyte may be, for example, at least one of Li<NUM>S-P<NUM>S<NUM>, Li<NUM>S-P<NUM>S<NUM>-LiX (wherein X is a halogen), Li<NUM>S-P<NUM>S<NUM>-Li<NUM>O, Li<NUM>S-P<NUM>S<NUM>-Li<NUM>O-LiI, Li<NUM>S-SiS<NUM>, Li<NUM>S-SiS<NUM>-LiI, Li<NUM>S-SiS<NUM>-LiBr, Li<NUM>S-SiS<NUM>-LiCl, Li<NUM>S-SiS<NUM>-B<NUM>S<NUM>-LiI, Li<NUM>S-SiS<NUM>-P<NUM>S<NUM>-LiI, Li<NUM>S-B<NUM>S<NUM>, Li<NUM>S-P<NUM>S<NUM>-ZmSn (wherein m and n are each independently a positive number, and Z is Ge, Zn, or Ga), Li<NUM>S-GeS<NUM>, Li<NUM>S-SiS<NUM>-Li<NUM>PO<NUM>, Li<NUM>S-SiS<NUM>-LipMOq (wherein p and q are each independently a positive number, and M is selected from P, Si, Ge, B, Al, Ga, and In), Li<NUM>-xPS<NUM>-xClx (wherein <NUM>≤x≤<NUM>), Li<NUM>-xPS<NUM>-xBrx (wherein <NUM>≤x≤<NUM>), or Li<NUM>-xPS<NUM>-xIx (wherein <NUM>≤x≤<NUM>). The sulfide-containing solid electrolyte may be prepared using a precursor source material, for example, at least one of Li<NUM>S or P<NUM>S<NUM>, and melt quenching or mechanical milling the precursor source material. After these treatments, a thermal treatment may further be performed. The sulfide-containing solid electrolyte may be amorphous, crystalline, or a mixed state thereof.

In addition, the sulfide-containing solid electrolyte may be, for example, any of the above-listed sulfide-containing solid electrolyte materials and including at least sulfur (S), phosphorous (P), and lithium (Li) as constituent elements. For example, the sulfide-containing solid electrolyte may be a material including Li<NUM>S-P<NUM>S<NUM>. When a sulfide-containing solid electrolyte including Li<NUM>S-P<NUM>S<NUM> is used, a mixed mole ratio of Li<NUM>S to P<NUM>S<NUM> (Li<NUM>S : P<NUM>S<NUM>) may be, for example, in a range of about <NUM> : <NUM> to about <NUM> : <NUM>, or about <NUM>:<NUM> to about <NUM>:<NUM>, or about <NUM>:<NUM> to about <NUM>:<NUM>.

The sulfide-containing solid electrolyte may include, for example, an argyrodite-type solid electrolyte represented by Formula <NUM>.

Formula <NUM>     Li+<NUM>-n-xAn+X<NUM>-<NUM>-xY-x.

In Formula <NUM>, A may be P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta, X may be S, Se, or Te, Y may be Cl, Br, I, F, CN, OCN, SCN, or N<NUM>, <NUM>≤n≤<NUM>, and <NUM>≤ x≤<NUM>.

The sulfide-containing solid electrolyte may be a compound having an argyrodite-type crystal structure. The compound having an argyrodite-type crystal structure may include, for example, at least one of Li<NUM>-xPS<NUM>-xClx (wherein <NUM>≤x≤<NUM>), Li<NUM>-xPS<NUM>-xBrx (wherein <NUM>≤x≤<NUM>), or Li<NUM>-xPS<NUM>-xIx (wherein <NUM>≤x≤<NUM>). In particular, the sulfide-containing solid electrolyte may be an argyrodite-type compound including at least one of Li<NUM>PS<NUM>Cl, Li<NUM>PS<NUM>Br, or Li<NUM>PS<NUM>I.

For example, the solid electrolyte layer <NUM> may further include a binder. The binder in the solid electrolyte layer <NUM> may be, for example, at least one of a styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or polyethylene. However, aspects are not limited thereto. Any suitable binder may be used. The binder of the solid electrolyte layer <NUM> may be the same as, or different from, the binders of the cathode active material layer <NUM> and the second anode active material layer <NUM>.

The cathode layer <NUM> may include a cathode current collector <NUM> and the cathode active material layer <NUM>.

The cathode current collector <NUM> may be a plate or foil including at least one of 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 cathode current collector <NUM> may be omitted.

The cathode active material layer <NUM> may include, for example, a cathode active material.

The cathode active material may be capable of intercalation and deintercalation of lithium ions. The cathode active material may be, for example, at least one of a lithium transition metal oxide, such as lithium cobalt oxide (LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium manganate, or lithium iron phosphate; a nickel sulfide; a copper sulfide; lithium sulfide; iron oxide; or vanadium oxide. However, aspects are not limited thereto. Any suitable cathode active material may be used. These cathode active materials may be used alone or in a combination of at least two cathode active materials.

The cathode active material may be, for example, a compound represented by the following formula: LiaA<NUM>-bB'bD<NUM> (wherein <NUM> ≤ a ≤ <NUM>, and <NUM> ≤ b ≤ <NUM>); LiaE<NUM>-bB'bO<NUM>-cDc (wherein <NUM> ≤ a ≤ <NUM>, <NUM> ≤ b ≤ <NUM>, and <NUM> ≤ c ≤ <NUM>); LiE<NUM>-bB'bO<NUM>-cDc (wherein <NUM> ≤ b ≤ <NUM>, and <NUM> ≤ c ≤ <NUM>); LiaNi<NUM>-b-cCobB'cDα (wherein <NUM> ≤ a ≤ <NUM>, <NUM> ≤ b ≤ <NUM>, <NUM> ≤ c ≤ <NUM>, and <NUM> < α ≤ <NUM>); LiaNi<NUM>-b-cCobB'cO<NUM>-αF'α (wherein <NUM> ≤ a ≤ <NUM>, <NUM> ≤ b ≤ <NUM>, <NUM> ≤ c ≤ <NUM>, and <NUM> < α < <NUM>); LiaNi<NUM>-b-cCobB'cO<NUM>-αF'<NUM> (wherein <NUM> ≤ a ≤ <NUM>, <NUM> ≤ b ≤ <NUM>, <NUM> ≤ c ≤ <NUM>, and <NUM> < α < <NUM>); LiaNi<NUM>-b-cMnbB'cDα (wherein <NUM> ≤ a ≤ <NUM>, <NUM> ≤ b ≤ <NUM>, <NUM> ≤ c ≤ <NUM>, and <NUM> < α ≤ <NUM>); LiaNi<NUM>-b-cMnbB'cO<NUM>-αF'α (wherein <NUM> ≤ a ≤ <NUM>, <NUM> ≤ b ≤ <NUM>, <NUM> ≤ c ≤ <NUM>, and <NUM> < α < <NUM>); LiaNi<NUM>-b-cMnbB'cO<NUM>-αF'<NUM> (wherein <NUM> ≤ a ≤ <NUM>, <NUM> ≤ b ≤ <NUM>, <NUM> ≤ c ≤ <NUM>, and <NUM> < α < <NUM>); LiaNibEcGdO<NUM> (wherein <NUM> ≤ a ≤ <NUM>, <NUM> ≤ b ≤ <NUM>, <NUM> ≤ c ≤ <NUM>, and <NUM> ≤ d ≤ <NUM>); LiaNibCocMndGeO<NUM> (wherein <NUM> ≤ a ≤ <NUM>, <NUM> ≤ b ≤ <NUM>, <NUM> ≤ c ≤ <NUM>, <NUM> ≤ d ≤<NUM>, and <NUM> ≤ e ≤ <NUM>); LiaNiGbO<NUM> (wherein <NUM> ≤ a ≤ <NUM>, and <NUM> ≤ b ≤ <NUM>); LiaCoGbO<NUM> (wherein <NUM> ≤ a ≤ <NUM>, and <NUM> ≤ b ≤ <NUM>); LiaMnGbO<NUM> (wherein <NUM> ≤ a ≤ <NUM>, and <NUM> ≤ b ≤ <NUM>); LiaMn<NUM>GbO<NUM> (wherein <NUM> ≤ a ≤ <NUM>, and <NUM> ≤ b ≤ <NUM>); QO<NUM>; QS<NUM>; LiQS<NUM>; V<NUM>O<NUM>; LiV<NUM>O<NUM>; LiI'O<NUM>; LiNiVO<NUM>; Li(<NUM>-f)J<NUM>(PO<NUM>)<NUM> (wherein <NUM> ≤ f ≤ <NUM>); Li(<NUM>-f)Fe<NUM>(PO<NUM>)<NUM> (wherein <NUM> ≤ f ≤ <NUM>); and LiFePO<NUM>. In the formulas above, A may be nickel (Ni), cobalt (Co), manganese (Mn), or a combination thereof; B' may be aluminum (Al), nickel (Ni), cobalt (Co), manganese (Mn), chromium (Cr), iron (Fe), magnesium (Mg), strontium (Sr), vanadium (V), a rare earth element, or a combination thereof; D may be oxygen (O), fluorine (F), sulfur (S), phosphorus (P), or a combination thereof; E may be cobalt (Co), manganese (Mn), or combination thereof; F' may be fluorine (F), sulfur (S), phosphorus (P), or a combination thereof; G may be aluminum (Al), chromium (Cr), manganese (Mn), iron (Fe), magnesium (Mg), lanthanum (La), cerium (Ce), strontium (Sr), vanadium (V), or a combination thereof; Q may be titanium (Ti), molybdenum (Mo), manganese (Mn), or a combination thereof; I' may be chromium (Cr), vanadium (V), iron (Fe), scandium (Sc), yttrium (Y), or a combination thereof; and J may be vanadium (V), chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), or a combination thereof.

The cathode active material may further include a surface coating layer (hereinafter, also referred to as "coating layer"). Alternatively, a mixture of a compound without a coating layer and a compound having a coating layer, the compounds being selected from the compounds listed above, may be used. In an aspect, the coating layer on the surface of such compounds may include at least one compound of a coating element selected from the group consisting of an oxide, a hydroxide, an oxyhydroxide, an oxycarbonate, or an hydroxycarbonate of the coating element. In an aspect, the compounds for the coating layer may be amorphous or crystalline. In an aspect, the coating element for the coating layer may be at least one of magnesium (Mg), aluminum (Al), cobalt (Co), potassium (K), sodium (Na), calcium (Ca), silicon (Si), titanium (Ti), vanadium (V), tin (Sn), germanium (Ge), gallium (Ga), boron (B), arsenic (As), or zirconium (Zr). In an aspect, the coating layer may be formed using any method that does not adversely affect the physical properties of the cathode active material. For example, the coating layer may be formed using a spray coating method, a dipping method, or the like. The above-mentioned coating methods are understood by one of ordinary skill in the art, and thus a detailed description thereof will be omitted.

The cathode active material may include, for example a lithium transition metal oxide having a layered rock salt-type structure among the above-listed lithium transition metal oxides. The term "layered rock salt-type structure" used herein refers to a structure in which oxygen atomic layers and metal atomic layers are alternately and regularly disposed in a (<NUM>) crystallographic direction, with each atomic layer forming a two-dimensional (2D) plane. A "cubic rock salt-type structure" refers to a sodium chloride (NaCl)-type crystal structure, and in particular, a structure in which face-centered cubic (fcc) lattices formed by respective cations and anions are disposed in a way that ridges of the unit lattices are shifted by <NUM>/<NUM>. The lithium transition metal oxide having such a layered rock salt-type structure may be, for example, a ternary lithium transition metal oxide such as LiNixCoyAlzO<NUM> (NCA) or LiNixCoyMnzO<NUM> (NCM) (wherein <NUM><x<<NUM>, <NUM><y<<NUM>, <NUM><z<<NUM>, and x+y+z = <NUM>). When the cathode active material includes such a ternary lithium transition metal oxide having a layered rock salt-type structure, the all-solid secondary battery <NUM> may have further improved energy density and thermal stability. For example, The lithium transition metal oxide having such a layered rock salt-type structure may be, for example, LiNixCoyMnzO<NUM> (<NUM>≤x≤<NUM>, <NUM><y≤<NUM>, <NUM><z≤<NUM>, and x+y+z=<NUM>), LiNixCoyAlzO<NUM>(<NUM>≤x≤<NUM>, <NUM><y≤<NUM>, <NUM><z≤<NUM>, and x+y+z=<NUM>), LiNixCoyAlvMnwO<NUM>(<NUM>≤x≤<NUM>, <NUM><y≤<NUM>, <NUM><v≤<NUM>, <NUM><w≤<NUM>, and x+y+v+w=<NUM>), LiNixCoyMnzO<NUM> (<NUM>≤x≤<NUM>, <NUM><y≤<NUM>, <NUM><z≤<NUM>, and x+y+z=<NUM>), LiNixCoyAlzO<NUM>(<NUM>≤x≤<NUM>, <NUM><y≤<NUM>, <NUM><z≤<NUM>, and x+y+z=<NUM>), LiNixCoyAlvMnwO<NUM>(<NUM>≤x≤<NUM>, <NUM><y≤<NUM>, <NUM><v≤<NUM>, <NUM><w≤<NUM>, and x+y+v+w=<NUM>), LiNixCoyMnzO<NUM> (<NUM>≤x≤<NUM>, <NUM><y≤<NUM>, <NUM><z≤<NUM>, and x+y+z=<NUM>), LiNixCoyAlzO2(<NUM>≤x≤<NUM>, <NUM><y≤<NUM>, <NUM><z≤<NUM>, and x+y+z=<NUM>), LiNixCoyAlvMnwO<NUM>(<NUM>≤x≤<NUM>, <NUM><y≤<NUM>, <NUM><v≤<NUM>, <NUM><w≤<NUM>, and x+y+v+w=<NUM>) or the like.

The cathode active material may include a coating layer as described above. The coating layer may be any suitable coating layer for a cathode active material of an all-solid secondary battery. The coating layer may include, for example, Li<NUM>O-ZrO<NUM>.

When the cathode active material includes, for example, a ternary lithium transition metal oxide including Ni, such as NCA or NCM, the all-solid secondary battery <NUM> may have an increased capacity density and elution of metal ions from the cathode active material may be reduced in a charged state. As a result, the all-solid secondary battery <NUM> may have improved cycle characteristics.

The cathode active material may be in the form of particles having, for example, a true-spherical shape or an oval-spherical shape. The particle diameter of the cathode active material is not particularly limited, and may be in a range applicable to a cathode active material of a commercially available lithium secondary battery. An amount of the cathode active material in the cathode layer <NUM> is not particularly limited, and may be in a range applicable to a cathode active material of a commercially available lithium secondary battery.

The cathode layer <NUM> may further include, in addition to a cathode active material as described above, at least one additive, for example, a conducting agent, a binder, a filler, a dispersing agent, an auxiliary ionic conducting agent, or a coating agent. The conducting agent may be, for example, at least one of graphite, carbon black, acetylene black, Ketjen black, carbon fibers, or a metal powder. The binder may be, for example, at least one of a styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, or polyethylene. The filler, the dispersing agent, the auxiliary ionic conducting agent, and the coating agent, which may be added to the cathode layer <NUM>, may be any material suitable for use in a cathode of an all-solid secondary battery.

The cathode layer <NUM> may further include a solid electrolyte. The solid electrolyte included in the cathode layer <NUM> may be similar to or different from the solid electrolyte included in the solid electrolyte layer <NUM>. As a detailed description of the solid electrolyte of the cathode layer <NUM>, the above-detailed description of the solid electrolyte layer <NUM> may be referred to.

The solid electrolyte included in the cathode layer <NUM> may be, for example, a sulfide-containing solid electrolyte. This sulfide-containing solid electrolyte may also be used in the solid electrolyte layer <NUM>.

In another aspect, the cathode layer <NUM> may include, for example, a liquid electrolyte. For example, the cathode layer may be soaked with the liquid electrolyte. The liquid electrolyte may include a lithium salt and at least one of an ionic liquid or a polymeric ionic liquid. The liquid electrolyte may be non-volatile. The ionic liquid may refer to a salt in a liquid state at room temperature or a fused salt at room temperature, each having a melting point equal to or below room temperature and consisting of ions. The ionic liquid may include at least one cation and at least one anion. The cation may be at least one of an ammonium cation, a pyrrolidinium cation, a pyridinium cation, a pyrimidinium cation, an imidazolium cation, a piperidinium cation, a pyrazolium cation, an oxazolium cation, a pyridazinium cation, a phosphonium cation, a sulfonium cation, or a triazolium cation, and the anion may be at least one of BF<NUM>-, PF<NUM>-, AsF<NUM>-, SbF<NUM>-, AlCl<NUM>-, HSO<NUM>-, ClO<NUM>-, CH<NUM>SO<NUM>-, CF<NUM>CO<NUM>-, Cl-, Br-, I-, SO<NUM><NUM>-, CF<NUM>SO<NUM>-, (FSO<NUM>)<NUM>N-, (C<NUM>F<NUM>SO<NUM>)<NUM>N-, (C<NUM>F<NUM>SO<NUM>)(CF<NUM>SO<NUM>)N-, or (CF<NUM>SO<NUM>)<NUM>N-. The ionic liquid may be, for example, at least one of N-methyl-N-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide, N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, or <NUM>-butyl-<NUM>-methylimidazolium bis(trifluoromethylsulfonyl)imide.

The polymeric ionic liquid (PIL) may include a repeating units including at least one cation and at least one anion. The cation may be at least one of an ammonium cation, a pyrrolidinium cation, a pyridinium cation, a pyrimidinium cation, an imidazolium cation, a piperidinium cation, a pyrazolium cation, an oxazolium cation, a pyridazinium cation, a phosphonium cation, a sulfonium cation, or a triazolium cation, and the anion may be at least one of BF<NUM>-, PF<NUM>-, AsF<NUM>-, SbF<NUM>-, AlCl<NUM>-, HSO<NUM>-, ClO<NUM>-, CH<NUM>SO<NUM>-, CF<NUM>CO<NUM>-, (CF<NUM>SO<NUM>)<NUM>N-, (FSO<NUM>)<NUM>N-, Cl-, Br-, I-, SO<NUM><NUM>-, CF<NUM>SO<NUM>-, (C<NUM>F<NUM>SO<NUM>)<NUM>N-, (C<NUM>F<NUM>SO<NUM>)(CF<NUM>SO<NUM>)N-, NO<NUM>-, Al<NUM>Cl<NUM>-, (CF<NUM>SO<NUM>)<NUM>C-, (CF<NUM>)<NUM>PF<NUM>-, (CF<NUM>)<NUM>PF<NUM>-, (CF<NUM>)<NUM>PF<NUM>-, (CF<NUM>)<NUM>PF-, (CF<NUM>)<NUM>P-, SF<NUM>CF<NUM>SO<NUM>-, SF<NUM>CHFCF<NUM>SO<NUM>-, CF<NUM>CF<NUM>(CF<NUM>)<NUM>CO-, (CF<NUM>SO<NUM>)<NUM>CH-, (SF<NUM>)<NUM>C-, or (O(CF<NUM>)<NUM>C<NUM>(CF<NUM>)<NUM>O)<NUM>PO-.

The lithium salt may be any lithium salt used in the art. For example, the lithium salt may be, for example, at least one of LiPF<NUM>, LiBF<NUM>, LiSbF<NUM>, LiAsF<NUM>, LiClO<NUM>, LiCF<NUM>SO<NUM>, Li(CF<NUM>SO<NUM>)<NUM>N, Li(FSO<NUM>)<NUM>N, LiC<NUM>F<NUM>SO<NUM>, LiAlO<NUM>, LiAlCl<NUM>, LiN(CxF2x+<NUM>SO<NUM>)(CyF2y+<NUM>SO<NUM>) (wherein x and y are each independently natural numbers), LiCl, or Lil. A concentration of the lithium salt in the liquid electrolyte may be about <NUM> molar (M) to about <NUM>. The amount of the liquid electrolyte soaked in the cathode layer <NUM> may be <NUM> to about <NUM> parts by weight, <NUM> to about <NUM> parts by weight, <NUM> to about <NUM> parts by weight, <NUM> to about <NUM> parts by weight, <NUM> to about <NUM> parts by weight, or <NUM> to about <NUM> parts by weight, with respect to <NUM> parts by weight of the cathode active material layer <NUM> excluding the liquid electrolyte.

According to another aspect, a method of manufacturing an all-solid secondary battery includes: providing a solid electrolyte layer; disposing a first anode active material composition on a first surface of the solid electrolyte layer <NUM>; thermally treating the first anode active material composition to dispose a first anode active material layer <NUM>; disposing a second anode active material layer on a surface of the first anode active material layer; and disposing a cathode active material layer <NUM> on a second surface of the solid electrolyte layer <NUM>. Due to the sequential arrangement of the first anode active material layer <NUM> and the second anode active material layer <NUM> on the solid electrolyte layer <NUM>, a short-circuit of the all-solid secondary battery <NUM> may be suppressed, and cycle characteristics of the all-solid secondary battery <NUM> may be improved.

For example, the all-solid secondary battery <NUM> according to an aspect may be manufactured by separately manufacturing the cathode layer and the solid electrolyte layer <NUM> on which the first anode active material layer <NUM> and the second anode active material layer <NUM> are sequentially disposed, and then stacking these layers upon one another.

The materials constituting the first anode active material layer <NUM>, for example, a first carbonaceous anode active material, optionally a metal or metalloid anode active material, and optionally at least one of a binder or an additive, may be added to a polar solvent or a non-polar solvent to prepare a slurry (first anode active material composition). The prepared slurry may be coated on a surface of the solid electrolyte layer <NUM> and dried to prepare a first laminate in which the first anode active material composition is disposed on a first surface of the solid electrolyte layer <NUM>. The first laminate may be thermally treated to prepare a second laminate in which the first anode active material layer <NUM>, which is a sintered product, is disposed on the solid electrolyte layer <NUM>. The thermal treatment temperature may be, for example, <NUM> to <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>. When the thermal treatment temperature is too low, an organic material such as a binder may remain, and the sintering of the solid electrolyte layer <NUM> and the first anode active material layer <NUM> may be insufficient. When the thermal treatment temperature is too high, the first carbonaceous anode active material and/or metal or metalloid anode active material may be deteriorated. The thermal treatment time may be <NUM> hour to <NUM> hours, about <NUM> hour to about <NUM> hours, about <NUM> hour to about <NUM> hours, about <NUM> hour to about <NUM> hours, or about <NUM> hour to about <NUM> hours. However, the thermal treatment temperature and time are not limited to these ranges, and may be adjusted as needed. The thermal treatment atmosphere may be an inert gas atmosphere. The inert gas may be argon or nitrogen, for example.

Subsequently, the materials constituting the second anode active material layer <NUM>, for example, a second carbonaceous anode active material, optionally a metal or metalloid anode active material, and optionally at least one of a binder or an additive, may be added to a polar solvent or a non-polar solvent to prepare a slurry (second anode active material composition). The prepared slurry may be coated on a surface of the first anode active material layer <NUM> and dried to prepare a third laminate in which the second anode active material layer <NUM> is disposed on a surface of the first anode active material layer <NUM>, and the first anode active material layer <NUM> is between the solid electrolyte layer <NUM> and the second anode active material layer <NUM>. The second anode active material composition may be the same as, or different from, the first anode active material composition.

Subsequently, the anode current collector <NUM> may be disposed on a surface of the dried third laminate and then pressed to thereby form a laminate of the solid electrolyte layer <NUM> and the anode layer <NUM>. The pressing may be carried out using, for example, roll pressing or flat pressing. However, aspects are not limited to these methods, and any pressing method used in the art may be used. A pressure applied in the pressing may be, for example, about <NUM> megapascals (MPa) to about <NUM> MPa, or about <NUM> MPa to about <NUM> MPa, or about <NUM> MPa to about <NUM> MPa. The pressing time for which a pressure is applied may be about <NUM> millisecond (ms) to about <NUM> minutes (min). The pressing may be carried out, for example, at a temperature from room temperature (<NUM>) to about <NUM>, or at a temperature from about <NUM> to about <NUM>. In another aspect, the pressing may be carried out at a temperature of about <NUM> or greater, for example, about <NUM> to about <NUM>, or about <NUM> to about <NUM>.

Before the second anode active material layer <NUM> is disposed on the first anode active material layer <NUM>, the surface of the first anode active material layer <NUM> may be washed with an acidic solution. Washing of the surface of the first anode active material layer <NUM> with an acidic solution, removes impurities from the surface of the first anode active material layer <NUM>, thereby reducing the interfacial resistance between the first anode active material layer <NUM> and the second anode active material layer <NUM>. The acidic solution may include an acid, for example, at least one of hydrochloric acid, nitric acid, or sulfuric acid, but the acid and acidic solution are not necessarily limited thereto, and any acid/acidic solution for use for removing surface impurities may be used. The acidic solution may have, for example, a pH of <NUM> to <NUM>, a pH of <NUM> to <NUM>, a pH of <NUM> to <NUM>, a pH of <NUM> to <NUM>, or a pH of <NUM> to <NUM>.

The materials of the cathode active material layer <NUM> (for example, the cathode active material, a binder), may be added to a non-polar solvent to prepare a slurry (cathode active material layer composition). The prepared slurry may be coated on the cathode current collector <NUM> and then dried to form a laminate. The obtained laminate may be pressed to thereby form the cathode layer <NUM>. The pressing may be performed using any suitable pressing method, and is not limited to a specific method. For example, the pressing can include roll pressing, flat pressing, or isotactic pressing. The pressing may be omitted. In other aspects, the cathode layer <NUM> may be formed by compaction-molding a mixture of the ingredients of the cathode active material layer <NUM> into pellets or extending the mixture into a sheet form. When these methods are used to form the cathode layer <NUM>, the cathode current collector <NUM> may be omitted. In another aspect, the cathode layer <NUM> may be impregnated with a liquid electrolyte before use.

For example, the solid electrolyte layer <NUM> including an oxide-containing solid electrolyte may be prepared by thermally treating precursors of an oxide-containing solid electrolyte material.

The oxide-containing solid electrolyte may be prepared by contacting the precursors in stoichiometric amounts to form a mixture and thermally treating the mixture. For example, the contacting may include milling, such as ball milling, or grinding. The mixture of the precursors combined in stoichiometric amounts may be subjected to a first thermal treatment under an oxidizing atmosphere to prepare a first thermal treatment product. The first thermal treatment may be carried out at a temperature of less than <NUM>,<NUM> for about <NUM> hour to about <NUM> hours. For example, the first thermal treatment may be performed at a temperature of about <NUM> to about <NUM>, or about <NUM> to about <NUM>. The first thermal treatment product may then be ground. The first thermal treatment product may be ground in a wet grinding or dry grinding manner. For example, the wet grinding may be carried out by mixing the first thermal treatment product with a solvent such as methanol and milling the mixture using, for example, a ball mill for about <NUM> hour to about <NUM> hours. Dry grinding may be performed using, for example, a ball mill without solvent. The ground first thermal treatment product may have a particle diameter of about <NUM> to about <NUM>, or about <NUM> to about <NUM>. The ground first thermal treatment product may be dried. The ground first thermal treatment product may be shaped in pellet form following mixing with a binder solution, or may be shaped in pellet form by simply being pressed at a pressure of about <NUM> to about <NUM> MPa, or about <NUM> MPa to about <NUM> MPa.

The shaped product in pellet form may be subjected to a second thermal treatment at a temperature of less than or equal to about <NUM>,<NUM> for about <NUM> hour to about <NUM> hours. Through the second thermal treatment, the solid electrolyte layer <NUM>, which is a sintered product, may be obtained. The second thermal treatment may be carried out, for example, at a temperature of about <NUM> to <NUM>,<NUM>, or about <NUM> to about <NUM>, or about <NUM> to about <NUM>. For example, the second thermal treatment time may be about <NUM> to about <NUM> hours. The second thermal treatment temperature for obtaining the sintered product may be greater than the first thermal treatment temperature. For example, the second thermal treatment temperature may be about <NUM> or greater, about <NUM> or greater, about <NUM> or greater, or about <NUM> or greater higher than the first thermal treatment temperature. The second thermal treatment of the shaped product may be carried out under at least one of an oxidizing atmosphere or a reducing atmosphere. The second thermal treatment may be carried out under a) an oxidizing atmosphere, b) a reducing atmosphere, or c) an oxidizing and reducing atmosphere.

For example, the solid electrolyte layer <NUM> including a sulfide-containing solid electrolyte may be prepared using a solid electrolyte including a sulfide-containing solid electrolyte material.

The sulfide-containing solid electrolyte may be prepared by treatment of a precursor (source) material with, for example, melt quenching or mechanical milling. However, aspects are not limited thereto. Any suitable method of preparing a sulfide-containing solid electrolyte may be used. For example, in the case of melt quenching, predetermined amounts of the source material, such as Li<NUM>S and P<NUM>S<NUM>, are mixed together, made into pellets, reacted at a predetermined reaction temperature under vacuum conditions, and then quenched to thereby prepare a sulfide-containing solid electrolyte. The reaction temperature of the mixture of Li<NUM>S and P<NUM>S<NUM> may be, for example, about <NUM> to about <NUM>, or about <NUM> to about <NUM>. The reaction time may be, for example, about <NUM> hour to about <NUM> hours, or about <NUM> hour to about <NUM> hours. The quenching temperature of the reaction product may be about <NUM> or less or about <NUM> or less, and the quenching rate may be about <NUM> per second (°C /sec) to about <NUM>,<NUM>/sec, or about <NUM>/sec to about <NUM>,<NUM>/sec. For example, in the case of using mechanical milling, the source materials such as Li<NUM>S and P<NUM>S<NUM> may be reacted while stirring using, for example, a ball mill, to thereby prepare a sulfide-containing solid electrolyte. The stirring rate and stirring time in the mechanical milling are not specifically limited. The higher the stirring rate, the greater the production rate of the sulfide-containing solid electrolyte. The longer the stirring time, the greater the rate of conversion of the source material into the sulfide-containing solid electrolyte. Then, the mixture of the source materials, obtained by melting quenching or mechanical milling, may be thermally treated at a predetermined temperature and then ground to thereby prepare a solid electrolyte in the form of particles. When the solid electrolyte has glass transition characteristics, the solid electrolyte may be converted from an amorphous form to a crystalline form by thermal treatment.

The solid electrolyte obtained through a method as described above may be deposited using a film formation method, for example, an aerosol deposition method, a cold spraying method, or a sputtering method, to thereby prepare the solid electrolyte layer <NUM>. In one or more aspects, the solid electrolyte layer <NUM> may be prepared by pressing the solid electrolyte particles. In another aspect, the solid electrolyte layer <NUM> may be formed by mixing a solid electrolyte, a solvent, and a binder together to obtain a mixture, and coating the mixture on a surface, drying, and then pressing the mixture.

The cathode layer <NUM>, and the laminate of the anode layer <NUM> and the solid electrolyte layer <NUM>, which are formed according to the above-described methods, may be stacked such that the solid electrolyte layer <NUM> is interposed between the cathode layer <NUM> and the anode layer <NUM>. The stacked layers are then pressed to manufacture the all-solid secondary battery <NUM>.

For example, the first laminate of the anode layer <NUM> and the solid electrolyte layer <NUM> may be disposed on the cathode layer <NUM> such that the solid electrolyte layer <NUM> contacts the cathode layer <NUM>, to thereby prepare a second laminate. The second laminate may then be pressed to thereby manufacture the all-solid secondary battery <NUM>. For example, the pressing may be performed using, for example, roll pressing, flat pressing, or isotactic pressing. However, aspects are not limited thereto, and any suitable pressing method may be used. A pressure applied in the pressing may be, for about <NUM> MPa to about <NUM> MPa, or about <NUM> MPa to about <NUM> MPa, or about <NUM> MPa to about <NUM> MPa. The pressing time for which a pressure is applied may be about <NUM> to about <NUM>. The pressing may be carried out, for example, at a temperature from room temperature (<NUM>) to about <NUM>, or at a temperature from <NUM> to about <NUM>. In another aspect, the pressing may be carried out at a temperature of <NUM> or greater, for example about <NUM> to about <NUM>, or about <NUM> to about <NUM>. Although the structures of the all-solid secondary battery <NUM> and the methods of manufacturing the all-solid secondary battery <NUM> are described above as aspects, the disclosure is not limited thereto, and the constituent members of the all-solid secondary battery and the manufacturing processes may be appropriately varied. The pressing may be omitted.

One or more aspects of the present disclosure will now be described in detail with reference to the following examples. However, these examples are only for illustrative purposes and are not intended to limit the scope of the one or more aspects of the present disclosure.

Carbon black (CB) having a primary particle diameter of about <NUM> and silver (Ag) particles having an average particle diameter of about <NUM> were prepared as anode active materials.

<NUM> grams (g) of the carbon black (CB) and <NUM> of the silver particles were put into a container. <NUM> of a polyvinyl alcohol-polyacrylic acid (PVA-PAA) binder solution (SUMITOMO SEIKA CHEMICALS CO. , LTD; AG binder) was mixed with <NUM> of distilled water, and then added into the container, and the contents were stirred at about <NUM>,000rpm for about <NUM> minutes to prepare a first slurry. <NUM> of zirconia balls and <NUM> of distilled water were added to the first slurry and stirred at about <NUM>,<NUM> rotations per minute (rpm) for about <NUM> minutes (secondary stirring) to prepare a second slurry. <NUM> of distilled water was added to the second slurry and stirred at <NUM>,<NUM> rpm for <NUM> minutes to prepare a third slurry.

Li<NUM>La<NUM>Zr<NUM>O<NUM> (LLZO) pellets having a thickness of about <NUM> were prepared as a solid electrolyte layer.

The third slurry was spin-coated onto a surface of the LLZO pellets, dried at room temperature for <NUM> hour, and then vacuum-dried for <NUM> hours to obtain a laminate of the solid electrolyte layer and a precursor layer. The obtained laminate was thermally treated at <NUM> for <NUM> hours to obtain a first anode active material layer, which was a sintered product. The surface of the first anode active material layer was washed with a hydrochloric acid solution to remove impurities from the surface of the first anode active material layer. The first anode active material layer had a thickness of about <NUM>.

The previously-prepared third slurry was spin-coated again on the first anode active material layer, dried at room temperature for <NUM> hour, and then vacuum-dried at <NUM> for <NUM> hours to obtain a second anode active material layer. The second anode active material layer had a thickness of about <NUM>. The second anode active material layer was prepared using the same composition and the same method as those applied to the precursor layer of the first anode active material layer, except for the thermal treatment.

An anode current collector consisting of a copper (Cu) foil having a thickness of <NUM> was disposed on the second anode active material layer and then pressed using cold isotactic pressing (CIP) at a pressure of <NUM> MPa and a temperature of about <NUM> to attach the anode current collector, thereby preparing a laminate of solid electrolyte layer/anode layer.

LiNi<NUM>Co<NUM>Mn<NUM>O<NUM> (NCM) was prepared as a cathode active material. In addition, a polytetrafluoroethylene (PTFE) binder (Teflon™ binder, available from DuPont) was prepared. Carbon nanofibers (CNF) were prepared as a conducting agent. Then, the cathode active material, the conducting agent, and the binder were mixed in a mass ratio of <NUM>:<NUM>:<NUM>. The mixture was stretched in the form of a sheet to prepare a cathode active material sheet. This cathode active material sheet was pressed onto a cathode current collector consisting of an aluminum foil having a thickness of <NUM> to form a cathode layer. A thickness of the cathode anode active material layer in the cathode layer was about <NUM>.

The cathode anode active material layer of the formed cathode layer was soaked with a liquid electrolyte including <NUM> lithium bis(fluorosulfonyl)imide (LiFSI) dissolved in the ionic liquid Pyr13FSI (N-propyl-N-methyl-pyrrolidinium bis(fluorosulfonyl)imide).

The cathode layer was disposed such that the cathode active material layer soaked with the ionic liquid electrolyte solution faced toward an upper end in an SUS cap. The laminate of the solid electrolyte layer/anode layer was disposed such that the solid electrolyte layer was placed on the surface of the cathode active material layer, and then sealed to manufacture an all-solid secondary battery. The cathode layer and the anode layer were insulated using an insulator. Part of each of the cathode current collector and the anode current collector protruded out of the sealed battery and used as a cathode terminal and an anode terminal, respectively.

An all-solid secondary battery was manufactured in the same manner as in Example <NUM>, except that the thermal treatment temperature was changed to <NUM> in the preparation of the first anode active material layer.

An all-solid secondary battery was manufactured in the same manner as in Example <NUM>, except that <NUM> of carbon black was used, instead of <NUM> of carbon black (CB) and <NUM> of the silver particles, in the preparation of the first anode active material layer.

An all-solid secondary battery was manufactured in the same manner as in Example <NUM>, except that <NUM> of carbon black was used, instead of <NUM> of carbon black (CB) and <NUM> of the silver particles, in the preparation of each of the first anode active material layer and the second anode active material layer.

An all-solid secondary battery was manufactured in the same manner as in Example <NUM>, except that, in preparation of the first anode active material layer, the thermal treatment temperature was varied to <NUM>.

An all-solid secondary battery was manufactured in the same manner as in Example <NUM>, except that, in preparation of the second anode active material layer, amounts of carbon black (CB) and silver particles in the first slurry were respectively varied to <NUM> grams (g) of the carbon black (CB) and <NUM> of the silver particles.

An all-solid secondary battery was manufactured in the same manner as in Example <NUM>, except that the step of forming the second anode active material layer was omitted, a thickness of the first layer was varied to <NUM>, and a laminate of the solid electrolyte /anode layer including only the first anode active material layer alone was prepared.

An all-solid secondary battery was manufactured in the same manner as in Example <NUM>, except that the step of forming the first anode active material layer was omitted, a thickness of the second layer was varied to <NUM>, and a laminate of the solid electrolyte/anode layer including only the second anode active material layer was prepared.

An all-solid secondary battery was manufactured in the same manner as in Example <NUM>, except that, in preparation of the first anode active material layer, only vacuum drying was performed at <NUM> for <NUM> hours, instead of the additional thermal treatment at <NUM>.

The scanning electron microscope (SEM) images of the surface of the precursor layer which was a product of drying performed before the thermal treatment at <NUM> in Example <NUM> and the surface of the first anode active material layer which was a product of sintering performed by the thermal treatment at <NUM> in Example <NUM> are shown in <FIG> and <FIG>, respectively.

As shown in <FIG> and <FIG>, the carbon black particles included in the first anode active material layer had a greater average particle diameter as compared with the average particle diameter of the carbon black particles included in the precursor layer.

Although not shown, the silver (Ag) particles included in the first anode active material layer had a greater average particle diameter as compared with the average particle diameter of the silver (Ag) particles included in the precursor layer.

The carbon black (CB) included in the precursor layer had an average particle diameter of about <NUM>, and the carbon black (CB) included in the first anode active material layer had an average particle diameter of about <NUM>.

The silver (Ag) particles included in the precursor layer had an average particle diameter of about <NUM>, and the silver (Ag) particles included in the first anode active material layer had an average particle diameter of about <NUM>.

The average particle diameters of the carbon black (CB) and silver (Ag) particles included in the first anode active material layer were determined by analyzing the SEM images thereof.

The first anode active material layer had a reduced thickness and increased density since the decomposition and removal of the binder through sintering, and the carbon black (CB) particles and the silver (Ag) particles had an increased particle size due to the sintering.

<FIG> is a SEM image of a cross-section of the laminate of the solid electrolyte layer/first anode active material layer prepared in Example <NUM>.

As shown in <FIG>, the first anode active material layer was found to be disposed on the surface of the solid electrolyte layer.

<FIG> is an energy-dispersive X-ray spectroscopy (EDX) carbon element mapping image of the cross-section of the laminate of the solid electrolyte layer/first anode active material layer prepared in Example <NUM>.

As shown in <FIG>, the first anode active material layer disposed on the surface of the solid electrolyte layer was found to include carbon.

A SEM image of the surface of the first anode active material layer obtained in Example <NUM>, which was a sintered product obtained through thermal treatment at <NUM>, is shown in <FIG>.

<FIG> and <FIG> are EDX silver (Ag) element mapping and carbon element mapping images, respectively, of the surface of the first anode active material layer prepared in Example <NUM>.

As shown in <FIG> and <FIG>, the first anode active material layer disposed on the surface of the solid electrolyte layer was found to include silver particles and carbon particles.

It was also found that because impurities such as Li<NUM>CO<NUM> remaining after the thermal treatment at <NUM> were removed through the treatment of the surface of the first anode active material layer with acid, the carbon was still exposed and present on the surface of the first anode active material layer after the acid treatment.

<FIG> is a SEM image of a cross-section of the laminate of solid electrolyte layer/anode layer prepared in Example <NUM>.

<FIG> is a partial enlarged view of an interfacial region (A) between the solid electrolyte layer and the first anode active material layer in <FIG>.

<FIG> is a partial enlarged view of an interfacial region (B) between the first anode active material layer (thermally treated layer) and a second anode active material layer (dried layer or a layer prepared by CIP).

<FIG> is a partial enlarged view of an inner region (C) of the second anode active material layer (dried layer or a layer prepared by CIP) in <FIG>.

<FIG> is an X-ray diffraction (XRD) pattern of the first anode active material layer (thermally treated layer) adjacent to the solid electrolyte layer in <FIG>.

<FIG> is an XRD pattern of the second anode active material layer (dried layer or a layer prepared by CIP) adjacent to the first anode active material layer (thermally treated layer) in <FIG>.

<FIG> is an XRD pattern of an inner region of the second anode active material layer (dried layer or a layer prepared by CIP) in <FIG>.

Referring to <FIG>, it is found that a diffraction pattern of crystallized carbon appeared partially in the first anode active material layer, whereas such a diffraction pattern did not appear in the second anode active material layer as shown in <FIG> and <FIG>.

Therefore, the carbon included in the first anode active material layer had greater degree of crystallinity than the carbon included in the second anode active material layer. It is also found that the first anode active material layer had a greater density than that of the second anode active material layer.

<FIG> is an EDX carbon element mapping image of a cross-section of the first anode active material layer (thermally treated layer) adjacent to the solid electrolyte layer in <FIG>.

<FIG> is an EDX carbon element mapping image of a cross-section of the second anode active material layer (dried layer or a layer prepared by CIP) adjacent to the first anode active material layer (thermally treated layer) in <FIG>.

<FIG> is an EDX carbon element mapping image of a cross-section of a certain region in the second anode active material layer (dried layer or a layer prepared by CIP) in <FIG>.

As shown in <FIG>, it is found that carbon was distributed in both of the first anode active material layer and the second anode active material layer.

The Raman spectrum images of the surface of the precursor layer of Example <NUM>, which was a product of drying before the thermal treatment at <NUM>, and the surface of the first anode active material layer which was a sintered product obtained through the thermal treatment at <NUM>, are shown in <FIG> and <FIG>, respectively. Data of the Raman spectra are represented in Table <NUM>. The precursor layer was prepared using the same method and with the same slurry as that for the second anode active material layer. Although not shown in the drawings, the Raman spectrum of the second anode active material layer was the same as the Raman spectrum of the precursor layer.

Overlapping Raman peaks in <FIG> were resolved, and an enlarged view of the intensity of each Raman peak is shown in <FIG> and <FIG>. In <FIG>, <FIG>, and <FIG>, the intensity (ID) of D band peak and the intensity (IG) of G band peak are the height of each peak from the base line to the highest peak point.

As shown in <FIG>, <FIG>, and <FIG>, in the Raman spectrum of the first anode active material layer, an intensity ratio (I<NUM>D/I<NUM>G) of a D band peak to a G band peak was <NUM>. Therefore, the intensity ratio (I<NUM>D/I<NUM>G) of a D band peak to a G band peak of the carbon black (CB) included in the first anode active material layer was <NUM>. As shown in <FIG>, <FIG>, and <FIG>, an intensity ratio (I<NUM>D/I<NUM>G) of a D band peak to a G band peak in the Raman spectrum of the precursor layer, i.e., the second anode active material layer, was <NUM>. Therefore, the intensity ratio (I<NUM>D/I<NUM>G) of a D band peak to a G band peak of the carbon black (CB) included in the second anode active material layer was <NUM>. It was confirmed that the carbon black (CB) included in the second anode active material layer had an increased intensity ratio (ID/IG) of a D band peak to a G band peak in the Raman spectrum thereof, as compared with that of the carbon black (CB) included in the first anode active material layer.

Therefore, it was confirmed that the carbon black (CB) included in the first anode active material layer had reduced defects and improved crystallinity, as compared with the carbon black (CB) included in the second anode active material layer.

As shown in Table <NUM>, the position of a D band peak center in the Raman spectrum of the first carbonaceous anode active material exhibited a blue shift of <NUM> units per centimeter (cm-<NUM>) with respect to the position of a D band peak center in the Raman spectrum of the second carbonaceous anode active material. Also, the position of a G band peak in the Raman spectrum of the first carbonaceous anode active material exhibited a blue shift of <NUM>-<NUM> with respect to the position of a G band peak center in the Raman spectrum of the second carbonaceous anode active material. Also, a D band peak width in the Raman spectrum of the first carbonaceous anode active material was about <NUM>% of a D band peak width in the Raman spectrum of the second carbonaceous anode active material.

The overall resistance of each all-solid secondary battery manufactured in Comparative Examples <NUM> and <NUM> was measured.

The impedance of each of the all-solid secondary batteries manufactured in Comparative Examples <NUM> and <NUM> was measured using an impedance analyzer (Solartron 1400A/1455A impedance analyzer) according to a <NUM>-probe method. The frequency range was <NUM> Hertz (Hz) to <NUM>, and the amplitude voltage was <NUM> millivolts (mV). The impedance measurement was carried out at <NUM> in ambient air atmosphere. Nyquist plots showing the results of the impedance measurement are shown in <FIG>.

As a result of fitting the Nyquist plot of <FIG> to an equivalent circuit, the all-solid secondary battery of Comparative Example <NUM> had an interfacial resistance of about <NUM>Ωcm<NUM>, and the all solid secondary battery of Comparative Example <NUM> had an interfacial resistance of about <NUM>Ωcm<NUM>.

Also, as shown in <FIG>, the all-solid secondary battery of Comparative Example <NUM> had a reduced ohmic resistance, as compared with that of the all-solid secondary battery of Comparative Example <NUM>.

Accordingly, it was confirmed that a total resistance of the interfacial resistance and the ohmic resistance of the all-solid secondary battery of Comparative Example <NUM> were reduced, as compared with that of the all-solid secondary battery of Comparative Example <NUM>.

Without being limited by theory, it is understood that the reduction in the total resistance of the all-solid secondary battery of Comparative Example <NUM> is attributed to sintering of the precursor layer along with the solid electrolyte layer during the thermal treatment of the precursor layer, and the formation of covalent bonds between the solid electrolyte layer and the first anode active material layer to thereby increase the active interfacial area, leading to an increased diffusion rate of lithium ions.

The charge and discharge characteristics of the all-solid secondary batteries manufactured in Examples <NUM> to <NUM> and Comparative Examples <NUM> and <NUM> were evaluated according to a charge-discharge test as follows. The charge-discharge test of the all-solid secondary batteries was carried out in a <NUM> thermostat.

In the <NUM>st cycle, charging was carried out with a constant current of <NUM> mA/cm<NUM> until a battery voltage of <NUM> V was reached, and subsequently, discharging was carried out with a constant current of <NUM> mA/cm<NUM> until a battery voltage of <NUM> V was reached.

In the <NUM>nd to <NUM>th cycles, charging was carried out with a constant current of <NUM> mA/cm<NUM> until a battery voltage of <NUM> V was reached, and subsequently, discharging was carried out with a constant current of <NUM> mA/cm<NUM> until a battery voltage of <NUM> V was reached.

In the <NUM>th to <NUM>th cycles, charging was carried out with a constant current of <NUM> mA/cm<NUM> until a battery voltage of <NUM> V was reached, and subsequently, discharging was carried out with a constant current of <NUM> mA/cm<NUM> until a battery voltage of <NUM> V was reached.

In the <NUM>th to <NUM>rd cycles, charging was carried out with a constant current of <NUM> mA/cm<NUM> until a battery voltage of <NUM>. 2V was reached, and subsequently, discharging was carried out with a constant current of <NUM> mA/cm<NUM> until a battery voltage of <NUM>. 8V was reached.

Some of the charge-discharge test results are shown in <FIG>, <FIG>, <FIG>, and <FIG>.

As shown in <FIG>, since the all-solid secondary battery of Example <NUM> simultaneously includes the first anode active material layer sintered with the solid electrolyte layer, and the second anode active material layer disposed on the first anode active material layer, the all-solid secondary battery of Example <NUM> could perform up to <NUM> cycles of charging and discharging and exhibited stable charge and discharge performance even at a high current density of <NUM> mA/cm<NUM>. Although not shown in the graph, the all-solid secondary battery of Example <NUM> exhibited a high charge and discharge efficiency of <NUM>% or higher even at the <NUM>th cycle. The charge and discharge efficiency at the <NUM>th cycle is a percentage of the discharge capacity at the <NUM>th cycle with respect to the charge capacity at the <NUM>th cycle. Accordingly, it was confirmed that the all-solid secondary battery of Example <NUM> maintained a stable interface during a charge and discharge process and induced uniform deposition of lithium.

As shown in <FIG>, in the all-solid secondary battery of Comparative Example <NUM> including the first anode active material layer alone, a short-circuit occurred during charging at the <NUM>st cycle.

As shown in <FIG>, in the all-solid secondary battery of Comparative Example <NUM> including the second anode active material layer alone, a short-circuit occurred during charging at the <NUM>st cycle.

Although not shown, in the all-solid secondary battery of Comparative Example <NUM>, in which a multilayer structure is formed and the first anode active material layer were not thermally treated, a short-circuit occurred during charging and discharging.

Although not shown, the all-solid secondary batteries of Examples <NUM>, <NUM>, <NUM>, and <NUM> also exhibited stable charge and discharge characteristics.

As shown in <FIG>, the all-solid secondary battery of Example <NUM> exhibited stable charge and discharge performance.

As described above, the all-solid secondary battery according to any of the above-described aspects may be applied to various portable devices or vehicles.

According to an aspect, the all-solid secondary battery may prevent a short-circuit and have excellent cycle characteristics.

Claim 1:
An all-solid secondary battery comprising:
a cathode layer comprising a cathode active material layer;
an anode layer; and
a solid electrolyte layer comprising a solid electrolyte, wherein the solid electrolyte layer is disposed between the cathode layer and the anode layer,
wherein the anode layer comprises
an anode current collector,
a first anode active material layer in contact with the solid electrolyte layer, and
a second anode active material layer disposed between the anode current collector and the first anode active material layer,
wherein the first anode active material layer comprises a first carbonaceous anode active material, and the second anode active material layer comprises a second carbonaceous anode active material, and
a first intensity ratio of an intensity of a D band peak to an intensity of a G band peak in a Raman spectrum of the first carbonaceous anode active material is less than a second intensity ratio of an intensity of a D band peak to an intensity of a G band peak in a Raman spectrum of the second carbonaceous anode active material,
wherein a thickness of the first anode active material layer is less than a thickness of the second anode active material layer.