Patent Publication Number: US-2023163279-A1

Title: All-solid secondary battery and method of preparing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Continuation-In-Part of U.S. patent application Ser. No. 17/093,989, filed on Nov. 10, 2020, in the U.S. Patent and Trademark Office, and claims priority to and the benefit of Korean Patent Application No. 10-2020-0029166, filed on Mar. 9, 2020, in the Korean Intellectual Property Office, and all the benefits accruing therefrom under 35 U.S.C. § 119, the contents of both which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     1. Field 
     The present disclosure relates to an all-solid secondary battery and a method of preparing the all-solid secondary battery. 
     2. Description of the Related Art 
     Recently, in accordance with industrial demand, batteries having high energy density and high safety have been developed. For example, lithium-ion batteries have been put to practical use in the automotive field as well as in information-related equipment and communication equipment. In the field of automobiles, lithium-ion battery safety is particularly important. 
     Currently available lithium-ion batteries include an electrolyte solution including a flammable organic solvent, and thus when short-circuit occurs, there is a potential for overheating of the organic solvent and the occurrence of a fire. In this regard, an all-solid secondary battery including a solid electrolyte instead of an electrolytic solution has been proposed. 
     In an all-solid secondary battery, a flammable organic solvent is not used, and thus the potential for a fire to occur, or an explosion, even when short-circuit occurs, may be reduced. Therefore, an all-solid secondary battery may have greatly increased safety as compared to a lithium-ion battery using an electrolyte. 
     To increase the energy density of such an all-solid secondary battery, lithium may be used as an anode active material. For example, the specific capacity (capacity per unit mass) of lithium is about 10 times greater than the specific capacity of graphite (often used as an anode active material). Thus, when lithium is used as an anode active material, an all-solid secondary battery may be manufactured in the form of a thin film and may have an increased output. 
     However, there remains a need for improved all-solid secondary batteries in which a short circuit is less likely to occur. 
     SUMMARY 
     Provided is an all-solid secondary battery and a method of preparing the all-solid secondary battery, wherein the formation of cracks in a solid electrolyte may be prevented and an interfacial resistance between an anode and the solid electrolyte may be reduced in the all-solid secondary battery. 
     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 embodiments of the disclosure. 
     According to an aspect of an embodiment, an all-solid secondary battery includes a cathode, an anode, and a solid electrolyte disposed between the cathode and the anode, wherein the anode includes an anode current collector, a first anode active material layer in contact with the anode current collector and including a first metal; a second anode active material layer disposed between the first anode active material layer and the solid electrolyte and including a carbon-containing active material; and a contact layer disposed between the second anode active material layer and the solid electrolyte, the contact layer including a second metal, and having a thickness less than a thickness of the first anode active material layer, wherein the second metal comprises at least one of lithium metal, a lithium alloy, and a metal alloyable with lithium, or a combination thereof. 
     The first metal may include lithium metal or a lithium alloy, and the second metal may include lithium metal or a lithium alloy. 
     The first metal and the second metal may be the same. 
     The thickness of the contact layer may be about 20% or less of the thickness of the first anode active material layer. 
     The thickness of the contact layer may be about 0.5% ( 1/200) or less of the thickness of the first anode active material layer. 
     The thickness of the contact layer may be about 0.1% ( 1/1000) or greater of a thickness of the first anode active material layer. 
     The thickness of the contact layer may be about 0.1% to about 20% of the thickness of the first anode active material layer. 
     The thickness of the contact layer may be about 1 micrometer (μm) or less. 
     The thickness of the contact layer may be 30 nanometers (nm) or greater. 
     The thickness of the contact layer may be about 30 nanometers to about 1 micrometer. 
     The thickness of the contact layer may be less than a thickness of the second anode active material layer. 
     During a charge/discharge cycle, a volume change of the first anode active material layer may be greater than a volume change of the contact layer. 
     During a charge/discharge cycle, a volume change of the second anode active material layer may be greater than a volume change of the contact layer. 
     A volume of the contact layer after charge may be about 1.5 times to about 20 times a volume of the contact layer after discharge. 
     A volume of the first anode active material layer after charge may be about 1.5 times to about 500 times a volume of the first anode active material layer after discharge. 
     A volume of the second anode active material layer after charge may be greater than a volume of the second anode active material layer after discharge and the volume of the second anode active material layer after charge may be about 2 times or less the volume of the second anode active material layer after discharge. 
     The solid electrolyte may include an oxide-containing solid electrolyte. 
     According to an aspect of another embodiment, a method of preparing an all-solid secondary battery may include providing a cathode; providing an anode; providing a solid electrolyte; attaching the anode to a surface of the solid electrolyte; and attaching the cathode to another surface of the solid electrolyte, wherein the providing of the anode includes: disposing a first layer including lithium metal or a lithium alloy on a first substrate; disposing a second layer including a carbon-containing active material on a second substrate; disposing the first layer and the second layer to face each other; and pressing the first substrate and the second substrate such that the first substrate and the second substrate move closer to each other, wherein in the process of pressing the first substrate and the second substrate, a third layer including lithium metal or a lithium alloy may be formed between the second substrate and the second layer, and the third layer has a thickness less than a thickness of the first layer. 
     The second layer may include a metal alloyable with lithium, and in the pressing of the first substrate and the second substrate the metal alloyable with lithium may form an alloy with lithium in the first layer and in the third layer. 
     The providing of the anode may further include removing the second substrate after the forming of the third layer. 
     A pressure applied in the pressing of the first substrate and the second substrate may be about 150 megapascals (MPa) to about 1,000 megapascals. 
     According to an aspect of another embodiment, a method of preparing an anode of an all-solid secondary battery may include preparing a first layer including lithium metal or a lithium alloy disposed on a first substrate and a second layer including a carbon-containing active material disposed on a second substrate; disposing the first layer and the second layer to face each other; and pressing the first substrate and the second substrate such that the first substrate and the second substrate to be close to each other, wherein in the pressing of the first substrate and the second substrate, a third layer including lithium metal or a lithium alloy and having a thickness less than that of the first layer may be formed between the second substrate and the second layer. 
     The second layer may include a metal alloyable with lithium, and the metal may form alloy with lithium in the first layer and the third layer in the pressing of the first substrate and the second substrate. 
     In the preparing of the anode, the second substrate may be removed after the forming of the third layer. 
     A pressure applied in the pressing of the first substrate and the second substrate may be about 150 MPa or higher. 
     According to an aspect of an embodiment, a method of manufacturing an all-solid secondary battery the method including providing a first stack including a first layer including lithium metal or a lithium alloy on a first substrate, and a second layer including a carbon-containing active material on the first layer; providing a second stack including a third layer disposed on a solid electrolyte, wherein the third layer includes lithium metal, a lithium alloy, a metal alloyable with lithium, or a combination thereof; disposing the first stack on the second stack such that the second layer and the third layer face each other, and pressing the first stack and the second stack such that the first stack and the second stack move closer to each other to attach the second layer to the third layer, and providing a cathode on the solid electrolyte opposite the third layer to manufacture the all-solid secondary battery, wherein the third layer is disposed between the second layer and the solid electrolyte, and a thickness of the third layer is be less than a thickness of the first layer. 
     The providing the first stack may include providing the first layer disposed on the first substrate and the second layer disposed on a second substrate, and disposing the first layer and the second layer to face each other, and pressing the first substrate and the second substrate such that the first layer and the second layer move closer to each other. 
     In the preparing the first stack, the second substrate may be removed from the second layer, and the first substrate may be an anode current collector. 
     According to an aspect of an embodiment, a method of manufacturing an all-solid secondary battery the method including providing a first stack including a first layer including lithium metal or a lithium alloy on a first substrate; providing a second stack including a second layer including a carbon-containing active material, and a third layer disposed on a solid electrolyte, wherein the third layer includes lithium metal, a lithium alloy, a metal alloyable with lithium, or a combination thereof; disposing the first stack and the second stack such that the first layer and the second layer face each other; pressing the first stack and the second stack such that the first stack and the second stack move closer to each other to attach the first layer to the second layer; and providing a cathode on the solid electrolyte opposite the third layer to manufacture the all-solid secondary battery, wherein the third layer is thinner than the first layer. 
     The providing the second stack may include providing the third layer disposed on the solid electrolyte and the second layer disposed on a second substrate, and disposing the third layer and the second layer to face each other, and pressing the second substrate and the solid electrolyte such that the third layer and the second layer move closer to each other. 
     In the providing the second stack, the second substrate may be removed from the second layer, and the first substrate may be an anode current collector. 
     According to an aspect, a solid electrolyte/anode stack subassembly for an all-solid secondary battery, the solid electrolyte/anode stack subassembly includes: an anode current collector; a first anode active material layer in contact with the anode current collector and including a first metal; a second anode active material layer disposed between the first anode active material layer and a solid electrolyte, and including a carbon-containing active material; and a contact layer between the second anode active material layer and the solid electrolyte, the contact layer including a second metal, and having a thickness less than a thickness of the first anode active material layer, wherein the second metal includes lithium metal, a lithium alloy, a metal alloyable with lithium, or a combination thereof. 
     According to an aspect, a method of manufacturing the solid electrolyte/anode stack subassembly, the method may include providing a first stack including a first layer including lithium metal or a lithium alloy on a first substrate, and a second layer including a carbon-containing active material on the first layer; providing a second stack including a third layer disposed on a solid electrolyte, wherein the third layer includes lithium metal, a lithium alloy, a metal alloyable with lithium, or a combination thereof; and disposing the first stack on the second stack such that the second layer and the third layer face each other, and pressing the first stack and the second stack such that the first stack and the second stack move closer to each other to attach the second layer to the third layer, wherein the third layer is disposed between the second layer and the solid electrolyte, and a thickness of the third layer is less than a thickness of the first layer. 
     According to an aspect, a method of manufacturing the solid electrolyte/anode stack subassembly, the method may include providing a first stack including a first layer including lithium metal or a lithium alloy on a first substrate; providing a second stack including a second layer including a carbon-containing active material, and a third layer disposed on a solid electrolyte, wherein the third layer includes lithium metal, a lithium alloy, a metal alloyable with lithium, or a combination thereof; disposing the first stack and the second stack such that the first layer and the second layer face each other; and pressing the first stack and the second stack such that the first stack and the second stack move closer to each other to attach the first layer to the second layer, wherein the third layer is thinner than the first layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG.  1    is a cross-sectional view that illustrates an exemplary embodiment of an all-solid secondary battery; 
         FIG.  2    is a cross-sectional view that illustrates the anode in  FIG.  1   ; 
         FIG.  3    is a cross-sectional view of an exemplary embodiment of an anode of an all-solid secondary battery after charge; 
         FIG.  4    is cross-sectional view of the anode of the all-solid secondary battery after discharge; 
         FIG.  5 A  is a scanning electron microscope (SEM) image of a cross-section of an exemplary embodiment of an anode after charge; 
         FIG.  5 B  is an SEM image of a cross-section of an exemplary embodiment of the anode after discharge; 
         FIG.  6 A  is an enlarged view of the SEM image of  FIG.  5 A , showing the periphery of the contact layer and the second anode active material layer; 
         FIG.  6 B  is an enlarged view the SEM image of  FIG.  5 B , showing the periphery of the contact layer and the second anode active material layer; 
         FIGS.  7 A to  7 D  are views illustrating an exemplary embodiment of a method of preparing an anode; 
         FIG.  8    is an image of an exemplary embodiment of an anode; 
         FIG.  9    is a cross-sectional view of an anode of the Comparative Examples; 
         FIG.  10    is an image of the anode of the Comparative Examples; 
         FIG.  11    is a SEM image of a cross-section of an exemplary embodiment of an anode; 
         FIG.  12    is an enlarged view of a portion of  FIG.  11   ; 
         FIG.  13    is an enlarged view of a portion of  FIG.  12   ; 
         FIGS.  14 A to  14 F  are views illustrating an exemplary embodiment of a method of manufacturing an anode; 
         FIGS.  15 A to  15 F  are views illustrating an exemplary embodiment of a method of manufacturing an anode; 
         FIG.  16    is a Nyquist plot of imaginary impedance (Z″, ohms per square centimeter, ohm/cm 2 ) versus real impedance (Z′, ohm/cm 2 ) showing the impedance measurement results of Comparative Examples 1 and 2 and Example 1; 
         FIG.  17    is an enlarged view of a portion of  FIG.  16   ; and 
         FIGS.  18  to  26    are each a graph of potential (volts versus Li/Li + ) versus areal capacity (milliampere hours per square centimeter, mAh/cm 2 ), showing the charge/discharge curves of all-solid secondary batteries including the anodes prepared in accordance with Comparative Examples 1 to 5 and Examples 1 to 6. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain aspects. 
     It will be understood that when an element is referred to as being “on” another element, it can be directly on the other element or intervening elements may be present therebetween. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. 
     It will be understood that, although the terms “first,” “second,” “third” etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, “a first element,” “component,” “region,” “layer,” or “section” discussed below could be termed a second element, component, region, layer or section without departing from the teachings herein. 
     The terminology used herein is for the purpose of describing particular embodiments 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. For example, “an element” has the same meaning as “at least one element,” unless the context clearly indicates otherwise. “Or” means “and/or.” As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     “About” or “approximately” as used herein is inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (i.e., the limitations of the measurement system). For example, “about” can mean within one or more standard deviations, or within ±30%, 20%, 10%, or 5% of the stated value. End points in ranges may be independently combined. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Exemplary embodiments are described herein with reference to cross section illustrations that are schematic illustrations of idealized embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments described herein should not be construed as limited to the particular shapes of regions as illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, a region illustrated or described as flat may, typically, have rough and/or nonlinear features. Moreover, sharp angles that are illustrated may be rounded. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region and are not intended to limit the scope of the present claims. 
     Hereinafter, an all-solid secondary battery according to an embodiment, an anode used in the all-solid secondary battery, and a method of preparing the all-solid secondary battery will be described in detail with reference to the accompanying drawings. Like reference numerals in the drawings denote like elements. Sizes of components in the drawings may be exaggerated for convenience of explanation. Hereinafter, one or more embodiments described below are merely illustrative, and various modifications are possible from these embodiments. 
     In an all-solid secondary battery including a solid electrolyte as an electrolyte and lithium as an anode active material, lithium metal may be irregularly deposited on a surface of the solid electrolyte during a charging process, and this may cause cracks in the solid electrolyte. The cracks of the solid electrolyte may result in a short-circuit of the all-solid secondary battery. The present disclosure provides an all-solid secondary battery including a thin contact layer including a metal between an anode active material layer and the solid electrolyte to minimize generation of cracks and the occurrence of a short-circuit. 
       FIG.  1    is a cross-sectional view illustrating an all-solid secondary battery  1  according to an embodiment, and  FIG.  2    is a cross-sectional view illustrating an anode  20  in  FIG.  1   .  FIGS.  3  and  4    are views illustrating the effect of charge and discharge on the anode  20  of the all-solid secondary battery  1 . 
     Referring to  FIGS.  1  and  2   , the all-solid secondary battery  1  according to an embodiment is a secondary battery that includes a solid electrolyte as an electrolyte. For example, the all-solid secondary battery  1  may be an all-solid lithium ion secondary battery, in which lithium ions migrate between a cathode  10  and the anode  20 . 
     The all-solid secondary battery  1  includes the cathode  10  (also referred to herein as the cathode), a solid electrolyte  30 , and the anode  20  (also referred to herein as the anode). 
     Cathode 
     The cathode  10  may include a cathode current collector  11  and a cathode active material layer  12 . 
     For example, the cathode current collector  11  may be a plate or a foil including indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), an alloy thereof, or a combination thereof. The cathode current collector  11  may be omitted. 
     For example, the cathode active material layer  12  may include a cathode active material. 
     The cathode active material may be a cathode active material capable of reversibly absorbing and desorbing lithium ions. Examples of the cathode active material may include a lithium transition metal oxide, such as a lithium cobalt oxide (LCO), a lithium nickel oxide, a lithium nickel cobalt oxide, a lithium nickel cobalt aluminum oxide (NCA), a lithium nickel cobalt manganese oxide (NCM), a lithium manganate, a lithium iron phosphate, or a combination thereof; a nickel sulfide; a copper sulfide; a lithium sulfide; an iron oxide; a vanadium oxide; or a combination thereof, but embodiments are not limited thereto, and any material suitable for use a cathode active material may be used. The foregoing examples of the cathode active material may be used alone or in combination, for example, a mixture of at least two selected therefrom. 
     The lithium transition metal oxide may be, for example, a compound represented by one of the following formulae: 
     Li a A 1-b B′ b D 2  (where 0.9≤a≤1 and 0≤b≤0.5); Li a E 1-b B′ b O 2-c D c  (where 0.9≤a≤1, 0≤b≤0.5, and 0≤c≤0.05); LiE 2-b B′ b O 4-c D c  (where 0≤b≤0.5 and 0≤c≤0.05); Li a Ni 1-b-c Co b B′ c D α  (where 0.9≤a≤1, 0≤b≤0.5, 0≤c≤0.05, and 0&lt;α≤2); Li a Ni 1-b-c Co b B′ c O 2-α F′ α  (where 0.9≤a≤1, 0≤b≤0.5, 0≤c≤0.05, and 0&lt;α&lt;2); Li a Ni 1-b-c Co b B′ c O 2-α F′ 2  (where 0.9≤a≤1, 0≤b≤0.5, 0≤c≤0.05, and 0&lt;α&lt;2); Li a Ni 1-b-c Mn b B′ c D α  (where 0.9≤a≤1, 0≤b≤0.5, 0≤c≤0.05, and 0&lt;α≤2); Li a Ni 1-b-c Mn b B′ c O 2-α F′ α  (where 0.9≤a≤1, 0≤b≤0.5, 0≤c≤0.05, and 0&lt;α&lt;2); Li a Ni 1-b-c Mn b B′ c O 2-α F′ 2  (where 0.9≤a≤1, 0≤b≤0.5, 0≤c≤0.05, and 0&lt;α&lt;2); Li a Ni b E c G d O 2  (where 0.9≤a≤1, 0≤b≤0.9, 0≤c≤0.5, and 0.001≤d≤0.1); Li a Ni b Co c Mn d GeO 2  (where 0.9≤a≤1, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, and 0.001≤e≤0.1); Li a NiG b O 2  (where 0.9≤a≤1 and 0.001≤b≤0.1); Li a CoG b O 2  (where 0.9≤a≤1 and 0.001≤b≤0.1); Li a MnG b O 2  (where 0.9≤a≤1 and 0.001≤b≤0.1); Li a Mn 2 G b O 4  (where 0.9≤a≤1 and 0.001≤b≤0.1); QO 2 ; QS 2 ; LiQS 2 ; V 2 O 5 ; LiV 2 O 5 ; LiI′O 2 ; LiNiVO 4 ; Li (3-f) J 2 (PO 4 ) 3  (where 0≤f≤2); Li (3-f) Fe 2 (PO 4 ) 3  (where 0≤f≤2); or LiFePO 4 . In the above compounds, 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 a combination thereof; F′ may be fluorine (F), sulfur (S), phosphorus (P), or a combination thereof; G may be (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 above compounds may have 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 may be used, where the compounds are selected from the compounds listed above. In some embodiments, the coating layer may include at least one of an oxide, a hydroxide, an oxyhydroxide, an oxycarbonate, or a hydroxycarbonate of the coating element. In some embodiments, the compounds for the coating layer may be amorphous or crystalline. In some embodiments, the coating element for the coating layer may be 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), zirconium (Zr), or a combination thereof. In some embodiments, the coating layer may be formed using any method that does not adversely affect the physical properties of the cathode active material when a compound of the coating element is used. For example, the coating layer may be formed using a spray coating method or a dipping method. The coating methods are well understood by one of ordinary skill in the art, and thus a detailed description thereof is omitted herein. 
     The cathode active material may include, for example, a lithium transition metal oxide including a lithium salt of a transition metal oxide that has a layered rock-salt type structure. For example, the term “layered rock-salt type structure” refers to a structure in which an oxygen atom layer and a metal atom layer are alternately and regularly arranged in a &lt;111&gt; direction in a cubic rock-salt type structure, and where each of the atom layers forms a two-dimensional flat plane. The term “cubic rock-salt type structure” refers to a sodium chloride (NaCl) type structure, which is one of the known crystalline structures, in which face-centered cubic (fcc) lattices respectively formed of anions and cations are shifted by only a half of the ridge of each unit lattice. Examples of the lithium transition metal oxide having a layered rock-salt type structure may include a ternary lithium transition metal oxide such as LiNi x Co y Al z O 2 (NCA) or LiNi x Co y Mn z O 2  (NCM) (where 0&lt;x&lt;1, 0&lt;y&lt;1, 0&lt;z&lt;1, and x+y+z=1). When the cathode active material includes a ternary transition metal oxide having the layered rock-salt type structure, an energy density and thermal stability of the all-solid secondary battery  1  may improve. 
     The cathode active material may include a coating layer as described above. The coating layer is not limited and may be any suitable material for use as a coating layer of a cathode active material of an all-solid secondary battery. The coating layer may be, for example, Li 2 O—ZrO 2 . 
     When the cathode active material includes nickel (Ni) as a ternary lithium transition metal oxide such as NCA or NCM, a capacity density of the all-solid secondary battery  1  increases, and thus metal elution from the cathode active material in a charged state may be reduced. As a result, the all-solid secondary battery  1  according to an embodiment may have improved cycle characteristics in a charged state. 
     The cathode active material may have, for example, a particle shape such as a true spherical shape, an elliptical shape, or a semi-spherical shape. A particle diameter of the cathode active material is not particularly limited, but may be in a range suitable for a cathode active material of an all-solid secondary battery. An amount of the cathode active material in the cathode  10  is not particularly limited and may be in a range suitable for a cathode of an all-solid secondary battery. 
     Additives such as a conducting agent, a binder, a filler, a dispersant, and an ion conducting agent may be included in the cathode  10 , in addition to the cathode active material. Examples of the conducting agent may include graphite, carbon black, acetylene black, ketjen black, carbon fiber, a metal powder, or a combination thereof. Examples of the binder may include styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, or a combination thereof. The coating agent, the dispersant, and the ion conducting agent may be appropriately added to the cathode  10 , and may be any material that suitable for use in an electrode of an all-solid secondary battery. 
     The cathode  10  may further include a solid electrolyte. The solid electrolyte in the cathode  10  may be similar to or different from the solid electrolyte in the solid electrolyte  30 . Details of the solid electrolyte in the cathode are the same those described with reference to the solid electrolyte  30 . 
     The solid electrolyte in the cathode  10  may be, for example, a sulfide-based (e.g., sulfide-containing) solid electrolyte. The sulfide-based solid electrolyte may also be used as a sulfide-based solid electrolyte in the solid electrolyte  30 . 
     In some embodiments, the cathode  10  may be, for example, impregnated in a liquid electrolyte. The liquid electrolyte may include a lithium salt and at least one of an ionic liquid or a polymer ionic liquid. The liquid electrolyte may be non-volatile. The ionic liquid refers to a salt in a liquid state at room temperature or a room temperature molten salt that has a melting point of room temperature or lower and is only formed of ions. The ionic liquid may be a compound including: a) a cation of an ammonium-based cation, a pyrrolidinium-based cation, a pyridinium-based cation, a pyrimidinium-based cation, an imidazolium-based cation, a piperidinium-based cation, a pyrazolium-based cation, an oxazolium-based cation, a pyridazinium-based cation, a phosphonium-based cation, a sulfonium-based cation, a triazolium-based cation, or a combination thereof, and b) an anion of BF 4   − , PF 6   − , AsF 6   − , SbF 6   − , AlCl 4   − , HSO 4   − , CIO 4   − , CH 3 SO 3   − , CF 3 CO 2   − , Cl − , Br − , I − , BF 4   − , SO 4   − , CF 3 SO 3   − , (FSO 2 ) 2 N − , (C 2 F 5 SO 2 ) 2 N − , (C 2 F 5 SO 2 )(CF 3 SO 2 )N − , (CF 3 SO 2 ) 2 N − , or a combination thereof. The ionic liquid may be, for example, N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidinium bis(3-trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, or a combination thereof. 
     The polymer ionic liquid may have a repeating unit including: a) a cation of an ammonium-based cation, a pyrrolidinium-based cation, a pyridinium-based cation, a pyrimidinium-based cation, an imidazolium-based cation, a piperidinium-based cation, a pyrazolium-based cation, an oxazolium-based cation, a pyridazinium-based cation, a phosphonium-based cation, a sulfonium-based cation, a triazolium-based cation, or a combination thereof; and b) an anion of BF 4   − , PF 6   − , AsF 6   − , SbF 6   − , AlCl 4   − , HSO 4   − , ClO 4   − , CH 3 SO 3   − , CF 3 CO 2   − , (CF 3 SO 2 ) 2 N − , (FSO 2 ) 2 N − , Cl − , Br − , I − , SO 4   − , CF 3 SO 3   − , (C 2 F 5 SO 2 ) 2 N − , (C 2 F 5 SO 2 )(CF 3 SO 2 )N − , NO 3   − , Al 2 Cl − , (CF 3 SO 2 ) 3 C − , (CF 3 ) 2 PF 4   − , (CF 3 ) 3 PF 3   − , (CF 3 ) 4 PF 2   − , (CF 3 ) 5 PF − , (CF 3 ) 6 P − , SF 5 CF 2 SO 3   − , SF 5 CHFCF 2 SO 3   − , CF 3 CF 2 (CF 3 ) 2 CO − , CF 3 SO 2 ) 2 CH − , (SF 5 ) 3 C − , (O(CF 3 ) 2 C 2 (CF 3 ) 2 O) 2 PO − , or a combination thereof. The lithium salt is not limited and may be any suitable lithium salt. The lithium salt may be, for example, LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiClO 4 , LiCF 3 SO 3 , Li(CF 3 SO 2 ) 2 N, Li(FSO 2 ) 2 N, LiC 4 F 9 SO 3 , LiAlO 2 , LiAlCl 4 , LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2 ) (where x and y are each a natural number), LiCl, LiI, or a combination thereof. A concentration of the lithium salt in the liquid electrolyte may be, for example, in a range of about 0.1 molar (M) to about 5 M, or about 0.05 M to about 4.0 M, or about 0.1 M to about 3.0 M, or about 0.5 M to about 2.0 M, or about 0.5 M to about 1.5 M. An amount of the liquid electrolyte in the cathode  10  may be, for example, in a range of 0 part to about 100 parts by weight, 0 part to about 50 parts by weight, 0 part to about 30 parts by weight, 0 part to about 20 parts by weight, 0 part to about 10 parts by weight, or 0 part to about 50 parts by weight, based on 100 parts by weight of the cathode active material layer  12  not including the liquid electrolyte. 
     Solid Electrolyte 
     The solid electrolyte  30  may be disposed between the cathode  10  and the anode  20 . The solid electrolyte  30  includes a solid electrolyte. In an aspect, the solid electrolyte  30  may be a solid electrolyte layer. 
     The solid electrolyte may be, for example, an oxide-based (e.g. oxide-containing) inorganic solid electrolyte. The oxide-based solid electrolyte may include Li 1+x+y Al x Ti 2−x Si y P 3−y O 12  (where 0&lt;x&lt;2 and 0≤y&lt;3), BaTiO 3 , Pb(Zr p Ti 1−p )O 3  (PZT, where 0≤p≤1), Pb 1−x La x Zr 1−y Ti y O 3  (PLZT) (where 0≤x&lt;1 and 0≤y&lt;1), Pb(Mg 1/3 Nb 2/3 )O 3 —PbTiO 3  (PMN-PT), HfO 2 , SrTiO 3 , SnO 2 , CeO 2 , Na 2 O, MgO, NiO, CaO, BaO, ZnO, ZrO 2 , Y 2 O 3 , Al 2 O 3 , TiO 2 , SiO 2 , Li 3 PO 4 , Li x Ti y (PO 4 ) 3  (where 0&lt;x&lt;2 and 0&lt;y&lt;3), Li x Al y Ti z (PO 4 ) 3  (where 0&lt;x&lt;2, 0&lt;y&lt;1, and 0&lt;z&lt;3), Li 1+x+y (Al p Ga 1−p ) x (Ti q Ge 1−q ) 2−x Si y P 3−y O 12  (where 0≤x≤1, 0≤y≤1, 0≤p≤1, and 0≤q≤1), Li x La y TiO 3  (where 0&lt;x&lt;2 and 0&lt;y&lt;3), Li 2 O, LiOH, Li 2 CO 3 , LiAlO 2 , Li 2 O—Al 2 O 3 —SiO 2 —P 2 O 5 —TiO 2 —GeO 2 , Li 3+x La 3 M 2 O 12  (where M is Te, Nb, or Zr, and x is an integer of 1 to 10), or a combination thereof. The solid electrolyte may be prepared using a sintering method. 
     The oxide-based solid electrolyte may be, for example, a garnet-type solid electrolyte selected from Li 7 La 3 Zr 2 O 12  (LLZO) and Li 3+x La 3 Zr 2−a M a O 12  (M-doped LLZO, where M is Ga, W, Nb, Ta, or Al, and x is an integer of 1 to 10). 
     In some embodiments, the solid electrolyte may be, for example, a sulfide-based solid electrolyte. The sulfide-based solid electrolyte may include, for example, Li 2 S—P 2 S 5 , Li 2 S—P 2 S 5 —LiX (where X is a halogen), Li 2 S—P 2 S 5 —Li 2 O, Li 2 S—P 2 S 5 —Li 2 O—LiI, Li 2 S—SiS 2 , Li 2 S—SiS 2 —LiI, Li 2 S—SiS 2 —LiBr, Li 2 S—SiS 2 —LiCl, Li 2 S—SiS 2 —B 2 S 3 —LiI, Li 2 S—SiS 2 —P 2 S 5 —LiI, Li 2 S—B 2 S 3 , Li 2 S—P 2 S 5 —Z m S n  (where m and n are positive integers, and Z is Ge, Zn, or Ga), Li 2 S—GeS 2 , Li 2 S—SiS 2 —Li 3 PO 4 , Li 2 S—SiS 2 —Li p MO q  (where p and q are positive integers, and M is P, Si, Ge, B, Al, Ga, In, or a combination thereof), Li 7 -xPS 6 -xCl x (where 0≤x≤2), Li 7−x PS 6−x Br x  (where 0≤x≤2), and Li 7−x PS 6−x I x  (where 0≤x≤2). The sulfide-based solid electrolyte material is prepared by melting and quenching the starting materials (e.g., Li 2 S or P 2 S 5 ), or by mechanical milling of the starting materials. Subsequently, the resultant may be heat-treated. The sulfide-based solid electrolyte may be amorphous, or crystalline, or a mixed form thereof. 
     The sulfide-based solid electrolyte may include sulfur (S), phosphorus (P), and lithium (Li), as component elements. For example, the sulfide-based solid electrolyte may be a material including Li 2 S—P 2 S 5 . When the material including Li 2 S—P 2 S 5  is used as a sulfide-based solid electrolyte, a mixing molar ratio of Li 2 S and P 2 S 5 (Li 2 S:P 2 S 5 ) may be, for example, in a range of about 50:50 to about 90:10. 
     The sulfide-based solid electrolyte may be an argyrodite-type compound including Li 7−x PS 6−x Cl x  (where 0≤x≤2), Li 7−x PS 6−x Br x  (where 0≤x≤2), Li 7−x PS 6−x I x  (where 0≤x≤2), or a combination thereof. In particular, the sulfide-based solid electrolyte may be an argyrodite-type compound including Li 6 PS 5 Cl, Li 6 PS 5 Br, Li 6 PS 5 I, or a combination thereof. 
     For example, the solid electrolyte  30  may further include a binder. Examples of the binder in the solid electrolyte  30  include styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, or a combination thereof, but is not limited thereto, and any material suitable for use as a binder may be used. The binder of the solid electrolyte  30  may be the same as or different from a binder of the cathode and/or the anode. 
     Anode 
     Referring to  FIGS.  1  and  2   , the anode  20  includes an anode current collector  21 , an anode active material layer  22 , and a contact layer  23 . 
     During a process of charging the all-solid secondary battery  1 , a volume of the anode  20  may increase as shown in  FIG.  3   . During a process of discharging the all-solid secondary battery  1 , a volume of the anode  20  may decrease as shown in  FIG.  4   . 
     For example, the anode current collector  21  may be formed of a material that does not react with lithium, that is, a material neither forming an alloy with lithium nor a compound with lithium. Examples of material forming the anode current collector  21  may include copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), or a combination thereof, but embodiments are not limited thereto, and any material available suitable for use as an electrode (anode) current collector in the art may be used. The anode current collector  21  may include any one metal alone, an alloy of at least two different metals, or a coating material. The anode current collector  21  may be, for example, in the form of a plate or a foil. 
     The anode active material layer  22  may include a first anode active material layer  221  and a second anode active material layer  222 . 
     The first anode active material layer  221  may be disposed on the anode current collector  21  and may include a first metal. The first anode active material layer  221  may thus be a first metal layer. The first metal may include lithium metal or a lithium alloy. Accordingly, since the first anode active material layer  221  is a metal layer including lithium or a lithium alloy, for example, the first anode active material layer  221  may function as a lithium reservoir. 
     The lithium metal refers to metallic lithium and thus consists of lithium (Li), and does not include a metal alloyable with lithium. The lithium alloy includes lithium and a metal alloyable with lithium. Examples of the lithium alloy may include a Li—Ag alloy, a Li—Au alloy, a Li—Al alloy, a Li—Sn alloy, a Li—In alloy, a Li—Zn alloy, a Li—Ge alloy, a Li—Si alloy, or a combination thereof, but embodiments are not limited thereto, and any material suitable as a lithium alloy may be used. The first anode active material layer  221  may include one of the lithium alloys or lithium metal, or may include a combination of various alloys selected therefrom. 
     A thickness t 1  of the first anode active material layer  221  may be about 10 μm or greater. For example, the thickness t 1  of the first anode active material layer  221  may be in a range of about 10 μm to about 1,000 μm, about 10 μm to about 500 μm, about 10 μm to about 200 μm, about 10 μm to about 150 μm, about 10 μm to about 100 μm, or about 10 μm to about 50 μm. When the thickness t 1  of the first anode active material layer  221  is too thin, the first anode active material layer  221  may not function as a lithium reservoir. When the thickness t 1  of the first anode active material layer  221  is too thick, a weight and a volume of the all-solid secondary battery  1  increases, and cycle characteristics of the all-solid secondary battery  1  may be deteriorated. 
     The first anode active material layer  221  may be disposed between the anode current collector  21  and the second anode active material layer  222 . When the all-solid secondary battery  1  is charged, lithium is deposited in the first anode active material layer  221 , and a volume or a thickness of the first anode active material layer  221  may increase due to the deposited lithium. 
     A volume of the first anode active material layer  221  after charge may be about 150% to about 5,000% of a volume of the first anode active material layer  221  after discharge. A thickness of the first anode active material layer  221  after charge may be about 150 to about 5,000% of a thickness of the first anode active material layer  221  after discharge. 
     In a charging/discharging process (e.g., a charge/discharge cycle), a volume change rate (e.g., a percent volume change) of the first anode active material layer  221  may be greater than a volume change rate of the contact layer  23 . In the charging/discharging process, a volume change rate of the first anode active material layer  221  may be greater than a volume change rate of the second anode active material layer  222 . In the charging/discharging process, a thickness change rate of the first anode active material layer  221  may be greater than a thickness change rate of the contact layer  23 . In the charging/discharging process, a thickness change rate of the first anode active material layer  221  may be greater than a thickness change rate of the second anode active material layer  222 . 
     The second anode active material layer  222  may be disposed between the first anode active material layer  221  and the solid electrolyte  30  and may include a carbon-based (e.g., carbon-containing) active material. 
     The carbon-based active material may include amorphous carbon. Examples of the amorphous carbon may include carbon black (CB), acetylene black (AB), furnace black (FB), furnace black (FB), ketjen black (KB), graphene, carbon nanotubes, carbon nanofibers, or a combination thereof, but is not limited thereto, and any material classified as an amorphous carbon may be used. 
     The second anode active material layer  222  may include a metal or a metalloid as an anode active material. As used herein, “metalloid” means B, Si, Ge, As, Sb, Te, or a combination thereof. 
     The metal or metalloid anode active material may include 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), zinc (Zn), or a combination thereof, but is not limited thereto, and any metal anode active material or metalloid anode active material capable of forming an alloy or a compound with lithium may be used. 
     The second anode active material layer  222  may include an anode active material including a carbon-based active material, a metal or a metalloid anode active material, or a combination of the carbon-based active material and the metal or metalloid active material. For example, the second anode active material layer  222  may include only amorphous carbon, or the second anode active material layer may include 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), zinc (Zn), or a combination thereof. In some embodiments, the second anode active material  222  may include a composite of amorphous carbon and a metal or a metalloid including 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), zinc (Zn), or a combination thereof. A composite ratio of a composite of amorphous carbon and a metal (e.g., silver) or metalloid is a weight ratio, which may be, for example, in a range of about 10:1 to about 1:2, about 5:1 to about 1:1, or about 4:1 to about 2:1, but embodiments are not limited thereto, and the composite ratio may be determined by the person of skill in the art according to the desired characteristics of the all-solid secondary battery  1 . When the second anode active material layer  222  has this composition, cycle characteristics of the all-solid secondary battery  1  may improve. 
     The anode active material in the second anode active material layer  222  may include, for example, a mixture of first particles of an amorphous carbon and second particles of a metal or a metalloid. The mixture may comprise, consist of, or consist essentially of a dispersion of the first particle and the second particle. Alternatively, the mixture may further include a binder and the first particle and the second particles may be physically bound together by the binder. For example, the metal or metalloid may include 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), zinc (Zn), or a combination thereof. In some embodiments, the metal or metalloid may be a semiconductor. An amount of the second particles may be in a range of about 8 weight % (wt %) to about 60 wt %, about 10 wt % to about 50 wt %, about 15 wt % to about 40 wt %, or about 20 wt % to about 30 wt %, based on the total weight of the mixture. When the amount of the second particles is within these ranges, for example, cycle characteristics of the all-solid secondary battery  1  may improve. 
     A thickness t 2  of the second anode active material layer  222  may be, for example, in a range of about 10 nm to about 10 μm, about 100 nm to about 10 μm, about 200 nm to about 10 μm, about 300 nm to about 10 μm, about 400 nm to about 10 μm, about 500 nm to about 10 μm, about 1 μm to about 10 μm, about 1 μm to about 8 μm, about 2 μm to about 7 μm, or about 3 μm to about 7 μm. When the thickness of the second anode active material layer  222  is within these ranges, a short-circuit in the all-solid secondary battery  1  may be suppressed, and cycle characteristics of the all-solid secondary battery  1  may improve. 
     The thickness t 2  of the second anode active material layer  222  may be less than the thickness t 1  of the first anode active material layer  221 . The thickness t 2  of the second anode active material layer  222  may be less than ½ of the thickness t 1  of the first anode active material layer  221 . The thickness t 2  of the second anode active material layer  222  may be less than 20% of the thickness t 1  of the first anode active material layer  221 . In an aspect, the thickness t 2  may be about 50% to about 1%, about 40% to about 2%, or about 30% to about 4% of the thickness t 1 . 
     When the second anode active material layer  222  includes a carbon-based active material, the volume of the second anode active material layer  222  may change according to a volume change of the first anode active material layer  221 . For example, when the first anode active material layer  221  expands during a charging process, the second anode active material layer  222  may absorb and alleviate the volume expansion of the first anode active material. 
     The second anode active material layer  222  includes a carbon-based active material and thus may include a void (pore) therein. The second anode active material layer  222  after discharge may include a void generated therein. During a charging process, lithium fills the void of the second anode active material layer  222 , and in this regard, the volume expansion of the first anode active material layer  221  may be alleviated. As the volume expansion of the first anode active material layer  221  is alleviated, a pressure applied by the anode  20  on the solid electrolyte  30  is reduced, and thus a short-circuit of the solid electrolyte  30  may be delayed. 
     A volume of the second anode active material layer  222  after charging may be greater than a volume of the second anode active material layer  222  after discharging. The volume of the second anode active material layer  222  after charging may be about 2 times or less the volume of the second anode active material layer  222  after discharging. A thickness t 21  of the second anode active material layer  222  after charging may be greater than a thickness t 22  of the second anode active material layer  222  after discharging. The thickness t 21  of the second anode active material layer  222  after charging may be about 2 times or less than the thickness t 22  of the second anode active material layer  222  after discharging. In other words, the volume and/or thickness of the second anode active material layer after charge does not increase more than 2 fold relative to the volume and/or thickness of the second anode active material layer during discharge. 
     When the second anode active material layer  222  includes a carbon-based active material as described above, volume expansion of the first anode active material layer  221  may be alleviated, whereas an interface adhesive strength with the solid electrolyte may be deteriorated. Accordingly, when the second anode active material layer  222  is disposed such that the second anode active material layer  222  directly contacts the solid electrolyte  30 , an interfacial resistance between the anode  20  and the solid electrolyte  30  may increase. 
     In this regard, the anode  20  of the all-solid secondary battery  1  according to an embodiment includes the contact layer  23  disposed between the second anode active material layer  222  and the solid electrolyte  30 . 
     At least a portion of the contact layer  23  is disposed between the second anode active material layer  222  and the solid electrolyte  30  and directly contacts the solid electrolyte  30 . As the contact layer  23  directly contacts the solid electrolyte  30 , the second anode active material layer  222  may be prevented from directly contacting the solid electrolyte  30 . Thus the contact layer is between the second anode active material layer and the solid electrolyte, and is disposed such that the contact layer prevents contact between the second anode active material layer and the solid electrolyte. Accordingly, the contact layer  23  may improve an interface adhesive strength between the anode  20  and the solid electrolyte  30 . 
     An interfacial resistance between the contact layer  23  and the solid electrolyte  30  may be a prescribed level or less. For example, an interfacial resistance between the contact layer  23  and the solid electrolyte  30  may be about 500 ohm cm 2  or less, or about 400 ohm cm 2  or less, or about 300 ohm cm 2  or less. For example, an interfacial resistance between the contact layer  23  and the solid electrolyte  30  may be about 200 ohm cm 2  or less. 
     An interfacial resistance between the contact layer  23  and the solid electrolyte  30  may be lower than an interfacial resistance between the second anode active material layer  222  and the solid electrolyte  30 . For example, an interfacial resistance between the contact layer  23  and the solid electrolyte  30  may be less than 10% ( 1/10) of an interfacial resistance between the second anode active material layer  222  and the solid electrolyte  30 . For example, when an interfacial resistance between the second anode active material layer  222  and the solid electrolyte  30  directly contacting each other is greater than about 2,000 ohm cm 2 , an interfacial resistance between the contact layer  23  and the solid electrolyte  30  directly contacting each other may be about 200 ohm cm 2  or less. 
     For example, the contact layer  23  may include a second metal. The contact layer may be a second metal layer. The second metal may include lithium metal, a lithium alloy, a metal alloyable with lithium, or a combination thereof. 
     The second metal may include lithium metal. 
     Examples of the lithium alloy may include a Li—Al alloy, a Li—Sn alloy, a Li—In alloy, a Li—Ag alloy, a Li—Au alloy, a Li—Zn alloy, a Li—Ge alloy, a Li—Si alloy, or a combination thereof, but embodiments are not limited thereto, and any material suitable as a lithium alloy may be used. 
     The metal alloyable with lithium may be, for example, aluminum (Al), tin (Sn), indium (In), silver (Ag), gold (Au), zinc (Zn), germanium (Ge), or silicon (Si), and is not limited thereto, and may be any suitable metal alloyable with lithium that is used in the art. 
     The contact layer  23  may include the lithium alloy, lithium metal, or a combination thereof. The contact layer  23  may include lithium metal, Li—Al alloy, Li—Sn alloy, Li—In alloy, Li—Ag alloy, Li—Au alloy, Li—Zn alloy, Li—Ge alloy, Li—Si alloy, aluminum (Al), tin (Sn), indium (In), silver (Ag), gold (Au), zinc (Zn), germanium (Ge), silicon (Si), or a combination thereof. 
     When in a charged state, the contact layer  23  may include lithium metal or lithium alloy. When in a discharged state, the contact layer  23  may include lithium metal or lithium alloy. As another example, when in a discharged state, the contact layer  23  may include metal alloyable with lithium and may not include lithium metal or lithium alloy. Before being charged for the first time, the contact layer  23  may include metal alloyable with lithium and may not include lithium metal or lithium alloy. The second metal may be the same material as the first metal. However, a material of the second metal is not limited thereto, and may be different from a material of the first metal. 
     For example, the contact layer  23  may not include a carbon-based material. For example, the contact layer  23  may not include a carbon-based material such as a carbon-based active material, e.g., graphite or carbon black, or a carbon-based conducting material, e.g., carbon nanofibers. The contact layer  23  may not include an organic material such as a binder. The contact layer  23  may include, for example, a metal layer formed of a metal, a metalloid, an alloy thereof, or a combination thereof. Since the contact layer  23  is a metal layer and does not include a carbon-based material, a side reaction between a carbon-based material and/or an organic material in a charge/discharge process (cycle) may be prevented. 
     Also, since the contact layer  23  includes the second metal layer and does not include a carbon-based material, the contact layer  23  may form an interface having an excellent adhesive strength to the solid electrolyte  30  compared to that of the second anode active material layer  222  including a carbon-based active material. 
     Since the contact layer  23  includes the second metal, the contact layer  23  induces fast dispersion of the lithium ions input through the solid electrolyte  30  in the charging process. Accordingly, a surface of the solid electrolyte  30  is irregular, and thus even when the lithium ions are input to solid electrolyte while being locally focused by the contact layer, the lithium ions may be evenly dispersed throughout the whole anode  20  by using a fast diffusion phenomenon via the contact layer  23 . 
     In the charging process, the contact layer  23  may be configured such that an amount of the metal, e.g., lithium metal or a lithium alloy, deposited during formation of the contact layer is less than an amount of the first metal in the first anode active material layer  221 . 
     A thickness t 3  of the contact layer  23  may be a predetermined thickness or less. For example, the thickness t 3  of the contact layer  23  may be about 1 μm or less. For example, the thickness t 3  of the contact layer  23  may be about 700 nm or less. For example, the thickness t 3  of the contact layer  23  may be about 500 nm or less. For example, the thickness t 3  of the contact layer  23  may be about 300 nm or less. For example, the thickness t 3  of the contact layer  23  may be about 200 nm or less. For example, the thickness t 3  of the contact layer  23  may be about 100 nm or less. For example, the thickness t 3  of the contact layer  23  may be about 70 nm or less. For example, the thickness t 3  of the contact layer  23  may be about 50 nm or less. 
     However, when the thickness t 3  of the contact layer  23  is too thin, the original purpose for the second anode active material layer  222  to directly contact the solid electrolyte  30  may not be achieved, and thus the thickness t 3  of the contact layer  23  may be about 1 nm or greater. For example, the thickness t 3  of the contact layer  23  may be 30 nm or greater. In an aspect, the thickness t 3  of the contact layer  23  may be about 1 nm or greater, about 5 nm or greater, about 10 nm or greater, about 20 nm or greater, or about 30 nm or greater. The thickness of the contact layer may thus be about 1 nm to about 1 μm, about 1 nm to about 700 nm, about 1 nm to about 500 nm, about 1 nm to about 300 nm, about 1 nm to about 200 nm, about 1 nm to about 100 nm, about 1 nm to about 70 nm, or about 1 nm to about 50 nm. The thickness of the contact layer may be uniform or may not be uniform. Here, when the thickness t 3  of the contact layer  23  is not uniform, the thickness t 3  of the contact layer  23  is defined as an average thickness of the contact layer  23 . 
     The thickness t 3  of the contact layer  23  is less than the thickness t 1  of the first anode active material layer  221 . For example, the thickness t 32  of the contact layer  23  after discharge may be less than the thickness t 12  of the first anode active material layer  221  after discharge. For example, when the thickness t 12  of the first anode active material layer  221  after discharge is greater than about 10 μm, a thickness t 32  of the contact layer  23  after discharging may be about 1 μm or less. For example, the thickness t 32  of the contact layer  23  after discharge may be about 700 nm or less. For example, the thickness t 32  of the contact layer  23  after discharge may be about 500 nm or less. For example, the thickness t 32  of the contact layer  23  after discharge may be about 300 nm or less. For example, the thickness t 32  of the contact layer  23  after discharge may be about 200 nm or less. For example, the thickness t 32  of the contact layer  23  after discharge may be about 100 nm or less. For example, the thickness t 32  of the contact layer  23  after discharge may be about 70 nm or less. For example, the thickness t 32  of the contact layer  23  after discharge may be about 50 nm or less. However, for example, the thickness t 32  of the contact layer  23  after discharge may be about 30 nm or greater. For example, the thickness t 32  of the contact layer  23  may be about 30 nm to about 1 μm, about 30 nm to about 700 nm, about 30 nm to 500 nm, about 30 nm to about 300 nm, about 30 nm to about 200 nm, about 30 nm to 100 nm, about 30 nm to about 70 nm, or about 30 nm to about 50 nm. 
     The thickness t 3  of the contact layer  23  may be about 20% (⅕) or less of the thickness t 1  of the first anode active material layer  221 . The thickness t 3  of the contact layer  23  may be about 10% ( 1/10) or less of the thickness t 1  of the first anode active material layer  221 . The thickness t 3  of the contact layer  23  may be about 5% ( 1/20) or less of the thickness t 1  of the first anode active material layer  221 . The thickness t 3  of the contact layer  23  may be about 3.33% ( 1/30) or less of the thickness t 1  of the first anode active material layer  221 . The thickness t 3  of the contact layer  23  may be about 2.5% ( 1/40) or less of the thickness t 1  of the first anode active material layer  221 . The thickness t 3  of the contact layer  23  may be about 2% ( 1/50) or less of the thickness t 1  of the first anode active material layer  221 . The thickness t 3  of the contact layer  23  may be about 1% ( 1/100) or less of the thickness t 1  of the first anode active material layer  221 . The thickness t 3  of the contact layer  23  may be about 0.5% ( 1/200) or less of the thickness t 1  of the first anode active material layer  221 . The thickness t 3  of the contact layer  23  may be about 0.1% ( 1/1000) or greater of the thickness t 1  of the first anode active material layer  221 . For example, the thickness t 3  of the contact layer  23  may be about 0.1% to about 10%, about 0.1% to about 5%, about 0.1% to about 3.33%, about 0.1% to about 2.5%, about 0.1% to about 2%, about 0.1% to about 1%, or about 0.1% to about 0.5%, of the thickness t 1  of the first anode active material layer  221 . 
     The thickness t 32  of the contact layer  23  after discharge may be about 20% (⅕) or less of the thickness t 12  of the first anode active material layer  221  after discharge. The thickness t 32  of the contact layer  23  after discharge may be about 10% ( 1/10) or less of the thickness t 12  of the first anode active material layer  221  after discharge. The thickness t 32  of the contact layer  23  after discharging may be about 5% ( 1/20) or less of the thickness t 12  of the first anode active material layer  221  after discharging. The thickness t 32  of the contact layer  23  after discharging may be about 3.33% ( 1/30) or less of the thickness t 12  of the first anode active material layer  221  after discharging. The thickness t 32  of the contact layer  23  after discharging may be about 2.5% ( 1/40) or less of the thickness t 12  of the first anode active material layer  221  after discharging. The thickness t 32  of the contact layer  23  after discharging may be about 2% ( 1/50) or less of the thickness t 12  of the first anode active material layer  221  after discharging. The thickness t 32  of the contact layer  23  after discharging may be about 1% ( 1/100) or less of the thickness t 12  of the first anode active material layer  221  after discharging. The thickness t 32  of the contact layer  23  after discharging may be about 0.5% ( 1/200) or less of the thickness t 12  of the first anode active material layer  221  after discharging. The thickness t 32  of the contact layer  23  after discharging may be about 0.1% ( 1/1000) or greater of the thickness t 12  of the first anode active material layer  221  after discharging. For example, the thickness t 32  of the contact layer  23  after discharge may be about 0.1% to about 20%, about 0.1% to about 10%, about 0.1% to about 5%, about 0.1% to about 3.33%, about 0.1% to about 2.5%, about 0.1% to about 2%, about 0.1% to about 1%, or about 0.1% to about 0.5%, of the thickness t 12  of the first anode active material layer  221  after discharge. 
     The thickness t 31  of the contact layer  23  after charge may be about 10% ( 1/10) or less of the thickness t 11  of the first anode active material layer  221  after charge. The thickness t 31  of the contact layer  23  after charge may be about 5% ( 1/20) or less of the thickness t 11  of the first anode active material layer  221  after charge. The thickness t 31  of the contact layer  23  after charge may be about 2.5% ( 1/40) or less of the thickness t 11  of the first anode active material layer  221  after charge. The thickness t 31  of the contact layer  23  after charging may be about 1.66% ( 1/60) or less of the thickness t 11  of the first anode active material layer  221  after charging. The thickness t 31  of the contact layer  23  after charging may be about 1.25% ( 1/80) or less of the thickness t 11  of the first anode active material layer  221  after charging. The thickness t 31  of the contact layer  23  after charging may be about 1% ( 1/100) or less of the thickness t 11  of the first anode active material layer  221  after charging. The thickness t 31  of the contact layer  23  after charging may be about 0.5% ( 1/200) or less of the thickness t 11  of the first anode active material layer  221  after charging. The thickness t 31  of the contact layer  23  after charging may be about 0.25% ( 1/400) or less of the thickness t 11  of the first anode active material layer  221  after charging. The thickness t 31  of the contact layer  23  after charging may be about 0.05% ( 1/2000) or greater of the thickness t 11  of the first anode active material layer  221  after charging. For example, the thickness t 31  of the contact layer  23  after charge may be about 0.05% to about 10%, about 0.05% to about 5%, about 0.05% to about 2.5%, about 0.05% to about 1.66%, about 0.05% to about 1.25%, about 0.05% to about 1%, about 0.05% to about 0.5%, or about 0.05% to about 0.25%, of the thickness t 11  of the first anode active material layer  221  after charge. 
     Accordingly, by designing the thickness t 3  of the contact layer  23  to be a predetermined thickness (or less) and the thickness t 1  of the first anode active material layer  221  to be greater than the thickness of the contact layer  23 , an amount of the metal deposited as the contact layer  23  during charge of the all-solid secondary battery  1  may be decreased, and the metal may be induced to be deposited in the first anode active material layer  221 . 
     When the thickness t 3  of the contact layer  23  is greater than the predetermined thickness, an amount of the lithium metal locally deposited as the contact layer  23  during the charging process may increase. This may generate cracks in the solid electrolyte  30 . 
     In particular, when the solid electrolyte  30  includes an oxide-based solid electrolyte, which has a greater hardness than a sulfide-based solid electrolyte, cracks may be generated in the solid electrolyte  30  due to the localized deposition of the lithium metal in the contact layer  23 , and the lithium metal may penetrate the solid electrolyte  30  through the cracks. The penetration of the lithium metal into the solid electrolyte may cause a short circuit which may deteriorate stability of the all-solid secondary battery  1 . 
     Also, due to the lithium metal locally deposited as the contact layer  23 , in the repeated charge/discharge process, a void may be formed between the contact layer  23  and the solid electrolyte  30 , and a contact area between the contact layer  23  and the solid electrolyte  30  may be reduced, which may lead to overvoltage of the all-solid secondary battery  1 . 
     However, in the all-solid secondary battery  1  according to an embodiment, the metal is also deposited in the first anode active material layer  221 , and thus an amount of the lithium metal deposited in the contact layer  23  may be reduced. In this regard, the short circuiting and overcharge of the all-solid secondary battery  1  may be prevented. 
     When an amount of lithium deposited in the contact layer  23  in the charging process is reduced, a volume change rate of the contact layer  23  in the charge/discharge process may be small. 
     For example, a volume of the contact layer  23  after charge may be about 150% or less of a volume of the contact layer  23  after discharge. A volume of the contact layer  23  after charge may be about 140% or less of a volume of the contact layer  23  after discharge. A volume of the contact layer  23  after charge may be about 130% or less of a volume of the contact layer  23  after discharge. 
     For example, in the charge/discharge process, a volume change rate of the contact layer  23  may be less than a volume change rate of the first anode active material layer  221 . In the charge/discharge process, a volume change rate of the contact layer  23  may be about 70% or less of a volume change rate of the first anode active material layer  221 . In the charge/discharge process, a volume change rate of the contact layer  23  may be about 60% or less of a volume change rate of the first anode active material layer  221 . A volume change rate of the contact layer may be about 5% to about 70% of a volume change rate of the first anode active material layer, or a volume change rate of the contact layer may be about 10% to about 60% of a volume change rate of the first anode active material layer, or a volume change rate of the contact layer may be about 10% to about 50% of a volume change rate of the first anode active material layer. The second metal of the contact layer  23  may be the same as the first metal of the first anode active material layer  221 . For example, the second metal and the first metal may both be lithium metal. For example, the second metal and the first metal may both be a lithium alloy, and the metal forming an alloy with lithium may be the same. 
     However, the second metal is not necessarily the same as the first metal layer, and the material may vary according to the preparation method or desired used. 
       FIGS.  5 A and  5 B  are, respectively, a cross-section scanning electron microscope (SEM) image after charge and a cross-section SEM image after discharge of an exemplary embodiment of the anode  20 .  FIGS.  6 A and  6 B  are, respectively, an enlarged cross-section SEM image of the periphery of the contact layer  23  and the second anode active material layer  222  in  FIG.  5 A  and an enlarged cross-section SEM image of the periphery of the contact layer  23  and the second anode active material layer  222  in  FIG.  5 B . 
     Referring to  FIGS.  5 A and  5 B , a thickness t 11  of the first anode active material layer  221  after charge is in a range of about 32 μm to about 34 μm, and a thickness t 12  of the first anode active material layer  221  after discharge is in a range of about 17 μm to about 18 μm. 
     On the other hand, referring to  FIGS.  6 A and  6 B , a thickness t 21  of the second anode active material layer  222  after charge is in a range of about 5 μm to about 6 μm, and a thickness t 22  of the second anode active material layer  222  after discharge is also in a range of about 5 μm to about 6 μm. Also, a thickness t 31  of the contact layer  23  after charge is in a range of about 0.5 μm to about 1.5 μm, and a thickness t 32  of the contact layer  23  after discharge is also in a range of about 0.5 μm to about 1.5 μm. 
     In this regard, it may be confirmed that for the anode  20  according to an embodiment, a thickness change rate of the contact layer  23  and a thickness change rate of the second anode active material layer  222  are each less than a thickness change rate of the first anode active material layer  221 . 
     A method of preparing the all-solid secondary battery  1  according to an embodiment includes providing an anode  20 ; disposing the anode  20  on a surface of a solid electrolyte  30 ; and disposing a cathode  10  on another surface of the solid electrolyte  30 . 
     (Anode Manufacturing Method 1) 
       FIGS.  7 A to  7 D  are illustrations of an exemplary embodiment of a method of preparing the anode  20 . 
     Referring to  FIG.  7 A , a first layer  321  is formed on a first substrate  100 . 
     The first layer  321  may include a metal layer. The metal layer may include lithium metal, a lithium alloy, or a combination thereof. 
     The lithium alloy may include a Li—Ag alloy, a Li—Au alloy, a Li—Al alloy, a Li—Sn alloy, a Li—In alloy, a Li—Zn alloy, a Li—Ge alloy, a Li—Si alloy, or a combination thereof, but embodiments are not limited thereto, and any suitable lithium alloy may be used. 
     The first layer  321  may be formed of a lithium alloy, the lithium metal, or may be formed of a combination of the lithium alloys. 
     A thickness of the first layer  321  may be in a range of about 1 μm to about 1,000 μm, about 1 μm to about 500 μm, about 1 μm to about 200 μm, about 1 μm to about 150 μm, about 1 μm to about 100 μm, or about 1 μm to about 50 μm. 
     The first substrate  100  may be formed of a material that does not react with lithium, that is, a material neither forming an alloy with lithium nor a compound with lithium. Examples of the material forming the first substrate  100  may include copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), an alloy thereof, or a combination thereof, but embodiments are not limited thereto, and any material capable of functioning as an electrode current collector may be used. The first substrate  100  may be formed of a single metal selected therefrom alone, or may be formed of an alloy of at least two different metals or a coating material. The first substrate  100  may be, for example, in the form of a plate or a foil. The first substrate  100  may be an anode current collector  21 . 
     A second layer  322  is disposed on a second substrate. 
     The second layer  322  may include a carbon-based active material. The carbon-based active material may include an amorphous carbon. Examples of the amorphous carbon may include carbon black (CB), acetylene black (AB), furnace black (FB), furnace black (FB), ketjen black (KB), graphene, carbon nanotubes, carbon nanofibers, or a combination thereof but embodiments are not limited thereto, and any material classified as amorphous carbon may be used. 
     The second layer  322  may further include a metal alloyable with lithium. Examples of the metal alloyable with lithium may include silver (Ag), gold (Au), aluminum (Al), tin (Sn), indium (In), zinc (Zn), germanium (Ge), silicon (Si), or a combination thereof, but embodiments are not limited thereto, and any metal alloyable with lithium may be used. In the second layer  322 , the metal alloyable with lithium may be omitted. 
     In terms of forming the second layer  322  on the second substrate, a carbon-based active material, a metal alloyable with lithium, and a binder are mixed to prepare a slurry, and the slurry may be evenly coated and dried on the second substrate  200 . The second layer  322  may function as a precursor of the second anode active material layer  222 . 
     The second substrate  200  may be, for example, formed of a material that does not react with lithium, that is, a material neither forming an alloy with lithium nor a compound with lithium. The second substrate  200  may include a material having a predetermined hardness of about 100 megapascals or greater. An example of the material of the second substrate  200  may include stainless steel, but the material of the second substrate  200  is not limited thereto, and a material which does not react with lithium, e.g., copper (Cu), titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), or combination thereof, may be used. The second substrate  200  may be, for example, in the form of a plate or a foil. 
     Referring to  FIG.  7 B , the first layer  321  and the second layer  322  are disposed to face each other, and the first substrate  100  and the second substrate  200  may be pressed together at a predetermined pressure. 
     For example, the first substrate  100  and the second substrate  200  may be pressed using pressing plates  1001  and  1002 . The pressing plates  1001  and  1002  may be formed of a material having a predetermined hardness to facilitate the pressing of the first and second substrates  100  and  200  at a predetermined pressure. For example, a material of the pressing plates  1001  and  1002  may be stainless steel, but the material of the pressing plates  1001  and  1002  is not limited thereto. 
     As a result of the pressing, the first layer  321  and the second layer  322  move closer to each other and are closely contacted. 
     Examples of the pressing may include roll pressing, uni-axial pressing, flat pressing, warm isotactic pressing (WIP), or cold isotactic pressing (CIP), but embodiments are not limited thereto, and any suitable pressing method may be used. 
     A pressure applied during the pressing may be, for example, about 150 MPa or greater. A pressure applied during the pressing may be, for example, about 250 MPa or greater, or about 500 MPa or greater. A pressure applied during the pressing may be, for example, about 1,000 MPa or less. For example, the pressure applied during the pressing may be about 150 MPa to about 1,000 MPa, or about 250 MPa to about 1,000 MPa, or about 250 MPa to about 750 MPa. 
     A time for the pressing may be about 10 minutes or less, or about 8 minutes or less, or about 5 minutes or less, or about 1 minute or less, or about 30 seconds or less. For example, a time for the pressing may be in a range of about 5 milliseconds (ms) to about 10 minutes (min), or about 1 second to about 7 minutes, or about 30 seconds to about 7 minutes. For example, a time for the pressing may be in a range of about 2 min to about 7 min. 
     For example, the pressing may be performed at room temperature. For example, the pressing may be performed at a temperature in a range of about 15° C. to about 25° C., but the pressing temperature is not limited thereto, and may be in a range of about 25° C. to about 90° C., or a high temperature of about 100° C. or higher. 
     Referring to  FIG.  7 C , while the first layer  321  and the second layer  322  are pressed at a predetermined pressure, the contact layer  23 , which is a third layer including the same metal as the metal in the first layer  321 , is formed between the second substrate  200  and the second layer  322 . Without being limited by theory, it is understood that the formation of the contact layer  23  occurs as a result of a portion of the first layer  321  moving through the second layer  322 . 
     When the first layer  321  includes lithium metal and the second layer  322  includes a metal alloyable with lithium, the metal included in the second layer  322  may form an alloy layer during the pressing by reacting with lithium in the first layer  321  and the contact layer  23 . Accordingly, the first layer  321  may be the first anode active material layer  221  including a lithium alloy, and the contact layer  23  may be a contact layer  23  including a lithium alloy. 
     When the metal alloyable with lithium is not included in the second layer  322 , the first layer  321  may be the first anode active material layer  221  including lithium metal, and the contact layer  23  may be a contact layer  23  including lithium metal. 
     In the pressing of the first layer  321  and the second layer  322  with a predetermined pressure, a portion of the lithium in the first layer  321  may be injected into the second layer  322 . Thus, the second layer  322  may be the second anode active material layer  222  including a carbon-based active material and lithium. 
     Referring to  FIG.  7 D , by removing the second substrate  200 , the anode  20  is provided in which the first anode active material layer  221 , the second anode active material layer  222 , and the contact layer  23  are sequentially stacked on the first substrate  100  in this stated order by removing the second substrate  200 . 
       FIG.  8    is an image that shows the anode  20  according to an embodiment. Referring to  FIG.  8   , after the pressing of the first layer  321  and the second layer  322  at a predetermined pressure and the removal of the second substrate  200 , it may be confirmed that a surface color of the anode  20  appears to be not black, which is the color of the second anode active material layer  222  including a carbon-based active material. In this regard, it may be confirmed that the contact layer  23  having a relatively bright color is formed on the second anode active material layer  222 . 
     In the preparing of the anode  20 , when the second substrate  200  is removed after pressing the first layer  321  and the second layer  322 , for example, with a predetermined pressure of about 150 MPa or less, the anode  20  has a structure in which the first layer  321  and the second layer  322  are attached to each other, as shown in  FIG.  9   . Accordingly, it may be confirmed that a surface color of the anode  20  appears to be black, as shown in  FIG.  10   , which is the color of the second anode active material layer  222  including a carbon-based active material. 
       FIGS.  11  to  13    are cross-section SEM images of the anode  20  prepared by using the above-described exemplary method.  FIG.  12    is an enlarged view of a portion of  FIG.  11   , and  FIG.  13    is an enlarged view of a portion of  FIG.  12   . 
     Referring to  FIGS.  11  to  13   , it may be confirmed that the contact layer  23  having a thickness less than that of the first anode active material layer  221  is formed on the second anode active material layer  222  by undergoing the preparation method described above. 
     (Anode Manufacturing Method 2) 
       FIGS.  14 A to  14 F  are illustrations of an exemplary embodiment of a method of manufacturing the anode  20 . 
     Referring to  FIGS.  14 A to  14 C , the method of manufacturing an anode according to the embodiment may include providing (e.g., preparing) a first stack LF 1  in which a first layer  321  and a second layer  322  are stacked on a first substrate  100 . 
     Referring to  FIG.  14 A , in the preparing the first stack LF 1 , the first layer  321  disposed on the first substrate  100  and the second layer  322  disposed on the second substrate  200  are prepared. 
     The first layer  321  may include a metal. The metal may include lithium metal. 
     A material of the first layer  321  is not limited thereto and may include a lithium alloy. The first layer  321  may include lithium metal or the lithium alloy. Examples of the lithium alloy may include a Li—Ag alloy, a Li—Au alloy, a Li—Al alloy, a Li—Sn alloy, a Li—In alloy, a Li—Zn alloy, a Li—Ge alloy, or a Li—Si alloy, but embodiments are not limited thereto, and any suitable material available as a lithium alloy in the art may be used. 
     The first layer  321  may comprise one of these alloys or lithium metal, or may comprise various alloys. 
     A thickness of the first layer  321  may be in a range of about 1 μm to about 1000 μm, about 1 μm to about 500 μm, about 1 μm to about 200 μm, about 1 μm to about 150 μm, about 1 μm to about 100 μm, or about 1 μm to about 50 μm. 
     The first substrate  100  may comprise a material that does not react with lithium, that is, neither forming an alloy nor a compound with lithium. Examples of the material forming the first substrate  100  may include copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), or nickel (Ni), but embodiments are not limited thereto, and any suitable material available as an electrode current collector may be used. The first substrate  100  may comprise any metal selected therefrom alone or may comprise an alloy of at least two different metals or a coating material. The first substrate  100  may be, for example, in a form of a plate or a foil. The first substrate  100  may be an anode current collector  21 . 
     The second layer  322  may include a carbon-based active material. Examples of the carbon-based active material may include amorphous carbon. Examples of the amorphous carbon may include carbon black (CB), acetylene black (AB), furnace black (FB), furnace black (FB), ketjen black (KB), graphene, carbon nanotubes, or carbon nanofibers, but embodiment are not limited thereto, and any suitable material classified as amorphous carbon in the art may be used. 
     The second layer  322  may further include a metal alloyable with lithium. Examples of the metal alloyable with lithium may include silver (Ag), gold (Au), aluminum (Al), tin (Sn), indium (In), zinc (Zn), germanium (Ge), or silicon (Si), but embodiments are not limited thereto, and any suitable material available as a metal alloyable with lithium in the art may be used. In the second layer  322 , the metal alloyable with lithium may be omitted. 
     In terms of forming the second layer  322  on the second substrate, a carbon-based active material, a metal alloyable with lithium, and a binder are mixed to prepare a slurry, the slurry may be evenly coated on the second substrate  200 , and the coated second substrate may be dried. The second layer  322  may function as a precursor electrode of the second anode active material layer  222 . 
     The second substrate  200  may be, for example, comprising a material that does not react with lithium, that is, neither forming an alloy nor a compound with lithium. The second substrate  200  may include a material having a predetermined firmness. Examples of the material of the second substrate  200  may include stainless steel, but the material of the second substrate  200  is not limited thereto, and a material not reacting with lithium, e.g., copper (Cu), titanium (Ti), iron (Fe), cobalt (Co), or nickel (Ni) may be used. The second substrate  200  may be, for example, in a form of a plate or a foil. 
     Since the preparation processes of the first layer  321  and the second layer  322  are the same as described in connection with  FIG.  7 A , a detailed description thereof will be omitted. 
     Referring to  FIG.  14 B , after the first layer  321  and the second layer  322  are disposed to face each other, the first substrate  100  and the second substrate  200  may be pressed such that the first substrate  100  and the second substrate  200  move closer to each other. Although not shown, the first substrate  100  and the second substrate  200  may be pressed by a pressuring plate. 
     Examples of the pressing may include roll pressing, uni-axial pressing, flat pressing, warm isotactic pressing (WIP), or cold isotactic pressing (CIP), but embodiments are not limited thereto, and any suitable pressing method available in the art may be used. 
     A pressure applied to the first substrate  100  and the second substrate  200  may be less than a certain level. For example, the pressure applied during pressurization may be less than about 150 MPa. For example, the pressure applied during pressurization may be less than about 100 MPa. For example, the pressure applied during pressurization may be less than about 50 MPa. For example, the pressure applied during pressurization may be less than about 20 MPa. In an aspect, the pressure applied during pressurization may be about 1 MPa to about 150 MPa, about 1 MPa to about 100 MPa, about 1 MPa to about 50 MPa, or about 1 MPa to about 20 MPa. 
     For example, the pressing may be performed at room temperature. For example, the pressing may be performed at a temperature in a range of about 15° C. to about 25° C., but the pressing temperature is not limited thereto, and may be in a range of about 25° C. to about 90° C., or a high temperature of about 100° C. or higher, for example, about 100° C. to about 200° C., about 100° C. to about 300° C., or about 100° C. to about 400° C. 
     Due to the pressing, the first layer  321  and the second layer  322  may be assembled while being in a close contact with each other. As the first layer  321  and the second layer  322  are pressed with less than a certain level of pressure, the first layer  321  may be attached to the second layer  322  without forming a separate contact layer  23  between the second substrate  200  and the second layer  322 . 
     Referring to  FIG.  14 C , the second substrate  200  may be removed from the second layer  322 . By removing the second substrate  200 , the first stack LF 1  in which the first layer  321  and the second layer  322  are stacked on the first substrate  100  may be manufactured. 
     Referring to  FIG.  14 D , the method of manufacturing the anode according to the embodiment, may include preparing a second stack LF 2  including a third layer  323  disposed on the solid electrolyte  30 , apart from the first stack LF 1 . 
     The third layer  323  may be deposited on the solid electrolyte  30 . For example, the third layer  323  which is deposited on the solid electrolyte may be thinner than the first layer  321 . The thickness t 3  of the third layer  323  deposited on the solid electrolyte  30  may be less than or equal to a predetermined thickness. For example, the thickness t 3  of the third layer  323  may be about 1 μm or less. For example, the thickness t 3  of the third layer  323  may be about 0.5 μm or less. For example, the thickness t 3  of the third layer  323  may be about 0.1 μm or less. The thickness of the third layer  323  may be in the range of about 30 nm to about 100 nm, about 30 nm to about 500 nm, or about 30 nm to about 1 μm. 
     The deposition temperature of the third layer  323  may be in the range of about 10° C. to about 90° C. The deposition temperature of the third layer  323  may be in the range of about 15° C. to about 50° C. The deposition temperature of the third layer  323  may be in the range of about 20° C. to about 35° C. 
     The third layer  323  may include a second metal. The second metal may include lithium metal, a lithium alloy, a metal alloyable with lithium, or a combination thereof. The second metal may include lithium metal. 
     Examples of the lithium alloy may include 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, but embodiments are not limited thereto, and any suitable material available as a lithium alloy in the art may be used. 
     The metal alloyable with lithium may be, for example, aluminum (Al), tin (Sn), indium (In), silver (Ag), gold (Au), zinc (Zn), germanium (Ge), or silicon (Si), and is not limited thereto, and may be any suitable metal alloyable with lithium that is used in the art. 
     Since the preparation of the second stack LF 2  is performed separately from the preparation of the first stack LF 1 , the preparation of the second stack LF 2  may be performed simultaneously with the preparation of the first stack LF 1 , or before the preparation of the first stack LF 1 , or after the preparation of the first stack LF 1 . 
     Referring to  FIG.  14 E , the second layer  322  and the third layer  323  may be disposed to face each other, and pressing may be performed such that the first stack LF 1  and the second stack LF 2  move closer to each other. Although not shown, the first substrate  100  of the first stack LF 1  and the solid electrolyte  30  of the second stack LF 2  may be pressed by a pressing plate (not shown). 
     A pressure applied to the first substrate  100  of the first stack LF 1  and the solid electrolyte  30  of second stack LF 2  may be equal to or greater than a certain level. For example, the pressure applied during pressing may be 150 MPa or greater. For example, the pressure applied during pressing may be 250 MPa or greater. 
     The pressure applied to the first substrate  100  of the first stack LF 1  and the solid electrolyte  30  of the second stack LF 2  is not limited thereto, and may be less than a certain level. For example, the pressure applied during pressing may be less than 250 MPa. For example, the pressure applied during pressing may be less than 150 MPa. 
     Examples of the pressing may include roll pressing, uni-axial pressing, flat pressing, warm isotactic pressing (WIP), and cold isotactic pressing (CIP), but embodiments are not limited thereto, and any suitable pressing method available in the art may be used. 
     For example, the pressing may be performed at room temperature. For example, the pressing may be performed at a temperature in a range of about 15° C. to about 25° C., but the pressing temperature is not limited thereto, and may be in a range of about 25° C. to about 90° C., or a high temperature of about 100° C. or greater, for example, about 100° C. to about 300° C., about 100° C. to about 500° C., or about 100° C. to about 700° C. 
     Referring to  FIG.  14 F , by pressing, the third layer  323  and the second layer  322  may be assembled to be in close contact with each other. 
     When the third layer  323  and the second layer  322  are pressed with a certain level of pressure, or greater, for example, the pressure of 250 MPa or greater, a portion of the first layer  321 , for example, lithium, may move through the second layer  322 . In this case, the third layer  323  may be converted into a layer containing lithium alloy. 
     Since the certain level of pressure is applied to the first stack LF 1  and the second stack LF 2 , the third layer  323  and the second layer  322  may be attached to each other. Accordingly, an anode in which the contact layer  23 , the second anode active material layer  222 , the first anode active material layer  221 , and the anode current collector  21  may be sequentially stacked on the solid electrolyte  30 , can be manufactured. 
     (Anode Manufacturing Method 3) 
       FIGS.  15 A to  15 F  are illustrations of an exemplary embodiment of aa method of manufacturing an anode  20 . 
     Referring to  FIG.  15 A , the method of manufacturing an anode according to an embodiment may include preparing a first stack LF 1 A including the first layer  321  disposed on the first substrate  100 . 
     The first layer  321  may include a metal. The metal may include lithium metal. 
     A material of the first layer  321  is not limited thereto and may include a lithium alloy. The first layer  321  may include lithium metal or the lithium alloy. Examples of the lithium alloy may include a Li—Ag alloy, a Li—Au alloy, a Li—Al alloy, a Li—Sn alloy, a Li—In alloy, a Li—Zn alloy, a Li—Ge alloy, or a Li—Si alloy, but embodiments are not limited thereto, and any suitable material available as a lithium alloy in the art may be used. 
     The first layer  321  may comprise one of these alloys, lithium metal, or may comprise various alloys. 
     A thickness of the first layer  321  may be in a range of about 1 μm to about 1000 μm, about 1 μm to about 500 μm, about 1 μm to about 200 μm, about 1 μm to about 150 μm, about 1 μm to about 100 μm, or about 1 μm to about 50 μm. 
     The first substrate  100  may comprise a material that does not react with lithium, that is, neither forming an alloy nor a compound with lithium. Examples of the material forming the first substrate  100  may include copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), or nickel (Ni), but embodiments are not limited thereto, and any suitable material available as an electrode current collector may be used. The first substrate  100  may comprise any metal selected therefrom alone or may comprise an alloy of at least two different metals or a coating material. The first substrate  100  may be, for example, in a form of a plate or a foil. The first substrate  100  may be an anode current collector  21 . 
     Referring to  FIGS.  15 B to  15 D , the method of manufacturing the anode according to the embodiment may include preparing a second stack LF 2 A in which the third layer  323  and the second layer  322  are sequentially stacked the solid electrolyte  30 , apart from the preparation step of the first stack LF 1 A. 
     Referring to  FIG.  15 B , preparing the second stack LF 2 A may include preparing a third layer  323  formed on the solid electrolyte  30 . For example, the third layer  323  may be formed on the solid electrolyte  30  by deposition. 
     The third layer  323  may include a second metal. The second metal may include lithium metal, a lithium alloy, a metal alloyable with lithium, or a combination thereof. In an aspect, the second metal is lithium metal. 
     Examples of the lithium alloy may include 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, but embodiments are not limited thereto, and any suitable material available as a lithium alloy in the art may be used. 
     The metal alloyable with lithium may be, for example, aluminum (Al), tin (Sn), indium (In), silver (Ag), gold (Au), zinc (Zn), germanium (Ge), or silicon (Si), and is not limited thereto, and may be any suitable metal alloyable with lithium that is used in the art. 
     The third layer  323  may comprise a lithium alloy lithium metal, or a combination thereof. The third layer  323  may include lithium metal, Li—Al alloy, Li—Sn alloy, Li—In alloy, Li—Ag alloy, Li—Au alloy, Li—Zn alloy, Li—Ge alloy, Li—Si alloy, aluminum (Al), tin (Sn), indium (In), silver (Ag), gold (Au), zinc (Zn), germanium (Ge), silicon (Si), or a combination thereof. 
     The third layer  323  which is deposited on the solid electrolyte may be thinner than the first layer  321 . A thickness t 3  of the third layer  323  may be a predetermined thickness or less. For example, the thickness t 3  of the third layer  323  may be about 1 μm or less. For example, the thickness t 3  of the third layer  323  may be about 0.5 μm or less. For example, the thickness t 3  of the third layer  323  may be about 0.1 μm or less. The thickness of the third layer  323  may be in the range of about 30 nm to about 100 nm, about 30 nm to about 500 nm, or about 30 nm to about 1 μm. 
     The preparing of the second stack LF 2 A may include preparing the second layer  322  formed on the second substrate  200 . 
     The second layer  322  may include a carbon-based active material. Examples of the carbon-based active material may include amorphous carbon. Examples of the amorphous carbon may include carbon black (CB), acetylene black (AB), furnace black (FB), furnace black (FB), ketjen black (KB), graphene, carbon nanotubes, or carbon nanofibers, but embodiment are not limited thereto, and any suitable material classified as amorphous carbon in the art may be used. 
     The second layer  322  may further include a metal alloyable with lithium. Examples of the metal alloyable with lithium may include silver (Ag), gold (Au), aluminum (Al), tin (Sn), indium (In), zinc (Zn), germanium (Ge), or silicon (Si), but embodiments are not limited thereto, and any suitable material available as a metal alloyable with lithium in the art may be used. In the second layer  322 , the metal alloyable with lithium may be omitted. 
     In terms of forming the second layer  322  on the second substrate, a carbon-based active material, a metal alloyable with lithium, and a binder are mixed to prepare a slurry, the slurry may be evenly coated on the second substrate  200 , and the coated second substrate may be dried. The second layer  322  may function as a precursor electrode of the second anode active material layer  222 . 
     The second substrate  200  may be, for example, comprising a material that does not react with lithium, that is, neither forming an alloy nor a compound with lithium. The second substrate  200  may include a material having a predetermined firmness. Examples of the material of the second substrate  200  may include stainless steel, but the material of the second substrate  200  is not limited thereto, and a material not reacting with lithium, e.g., copper (Cu), titanium (Ti), iron (Fe), cobalt (Co), or nickel (Ni) may be used. The second substrate  200  may be, for example, in a form of a plate or a foil. 
     Referring to  FIG.  15 C , the third layer  323  and the second layer  322  may be disposed to face each other, and pressing may be performed such that the solid electrolyte  30  and the second substrate  200  move closer to each other. 
     The pressure applied to the solid electrolyte  30  and the second substrate  200  may be a certain level or greater. For example, the pressure applied during pressing may be about 150 MPa or greater. For example, the pressure applied during pressing may be about 250 MPa or greater. In an aspect, the pressure applied during pressing may be about 150 MPa to about 750 MPa, about 250 MPa to about 650 MPa, or about 350 MPa to about 550 MPa. 
     For example, the pressing may be performed at room temperature. For example, the pressing may be performed at a temperature in a range of about 15° C. to about 25° C., but the pressing temperature is not limited thereto, and may be in a range of about 25° C. to about 90° C., or a high temperature of about 100° C. or greater. For example, about 100° C. to about 300° C., about 100° C. to about 500° C., or about 100° C. to about 700° C. 
     Due to the pressing, the third layer  323  and the second layer  322  may be assembled while being in a close contact with each other. 
     Referring to  FIG.  15 D , the second substrate  200  may be removed from the second layer  322 . By removing the second substrate  200 , a second stack LF 2 A in which the third layer  323  and the second layer  322  are sequentially stacked on the solid electrolyte  30  may be manufactured. 
     Referring to  FIGS.  15 E and  15 F , pressing may be applied such that, while the second layer  322  and the first layer  321  face each other, the second stack LF 2 A and the first stack LF 1 A come close to each other. The first layer  321  and the second layer  322  may be attached by pressing. 
     The pressure applied to the first stack LF 1 A and the second stack LF 2 A may have equal to or greater than a predetermined level of intensity. For example, the pressure applied during pressing may be 150 MPa or greater. 
     Since the certain level or greater of pressure is applied to the first stack LF 1 A and the second stack LF 2 A, a portion of the first layer  321  may pass through the second layer  322  and react with the third layer  323 . For example, lithium in the first layer  321  moves through the second layer  322 , so that the third layer  323  may include a lithium alloy. 
     Since the first stack LF 1 A and the second stack LF 2 A are pressed, the third layer  323  and the second layer  322  may be attached to each other. Accordingly, an anode in which the contact layer  23 , the second anode active material layer  222 , the first anode active material layer  221 , and the anode current collector  21  may be sequentially stacked on the solid electrolyte  30 , can be manufactured. 
     In an aspect, a solid electrolyte/anode stack subassembly for an all-solid secondary battery, the solid electrolyte/anode stack subassembly comprises: an anode current collector; a first anode active material layer in contact with the anode current collector and comprising a first metal; a second anode active material layer disposed between the first anode active material layer and a solid electrolyte, and comprising a carbon-containing active material; and a contact layer between the second anode active material layer and the solid electrolyte, the contact layer comprising a second metal, and having a thickness less than a thickness of the first anode active material layer, wherein the second metal comprises lithium metal, a lithium alloy, a metal alloyable with lithium, or a combination thereof. 
     In an aspect, a method of manufacturing the solid electrolyte/anode stack subassembly, the method may comprise providing a first stack comprising a first layer comprising lithium metal or a lithium alloy on a first substrate, and a second layer comprising a carbon-containing active material on the first layer; providing a second stack comprising a third layer disposed on a solid electrolyte, wherein the third layer comprises lithium metal, a lithium alloy, a metal alloyable with lithium, or a combination thereof; and disposing the first stack on the second stack such that the second layer and the third layer face each other, and pressing the first stack and the second stack such that the first stack and the second stack move closer to each other to attach the second layer to the third layer, wherein the third layer is disposed between the second layer and the solid electrolyte, and a thickness of the third layer is less than a thickness of the first layer. 
     In an aspect, a method of manufacturing the solid electrolyte/anode stack subassembly, the method may comprise providing a first stack comprising a first layer comprising lithium metal or a lithium alloy on a first substrate; providing a second stack comprising a second layer comprising a carbon-containing active material, and a third layer disposed on a solid electrolyte, wherein the third layer comprises lithium metal, a lithium alloy, a metal alloyable with lithium, or a combination thereof; disposing the first stack and the second stack such that the first layer and the second layer face each other; and pressing the first stack and the second stack such that the first stack and the second stack move closer to each other to attach the first layer to the second layer, wherein the third layer is thinner than the first layer. 
     Preparation of Cathode 
     The materials constituting a cathode active material layer  12  such as a cathode active material and a binder are added to a non-polar solvent to prepare a slurry. The slurry is coated and dried on a cathode current collector  11 . The obtained stack is pressed to prepare a cathode  10 . The pressing of the stack may be performed by, for example, roll pressing, flat pressing, or isotactic pressing, but embodiments are not limited thereto, and any pressing method may be used. The pressing of the stack may be omitted. A mixture of the materials constituting the cathode active material layer  12  is compressed into the form of a pellet or stretched (molded) in the form of sheet to prepare the cathode  10 . When the cathode  10  is prepared in this manner, the cathode current collector  11  may be omitted. In some embodiments, the cathode  10  may be used by being impregnated with an electrolyte solution. 
     Preparation of Solid Electrolyte 
     A solid electrolyte  30  including an oxide-based solid electrolyte may be prepared by heat-treating precursors of the oxide-based solid electrolyte. 
     The oxide-based solid electrolyte may be prepared by contacting the precursors in stoichiometric amounts, forming a mixture, and then heat-treating the mixture. The contacting may be, for example, performed by milling such as ball milling or pulverization. The mixture of the precursors, mixed in stoichiometric amounts, is primarily heat-treated in an oxidative atmosphere to prepare a primary heat-treatment resultant. The primary heat-treatment may be performed at a temperature less than about 1,000° C. for about 1 hour to about 36 hours. The primary heat-treatment resultant may be pulverized. The pulverizing of the primary heat-treatment may be dry pulverizing or wet pulverizing. For example, the wet pulverizing may be performed by mixing a solvent such as methanol with the primary heat-treatment resultant, and milling the mixture using a ball mill for about 0.5 hours to about 10 hours. The dry pulverizing may be performed by milling the primary heat-treatment resultant using a ball mill without a solvent. A particle diameter of the primary heat-treatment resultant may be in a range of about 0.1 μm to about 10 μm or about 0.1 μm to about 5 μm. The pulverized primary heat-treatment resultant may be dried. The pulverized primary heat-treatment resultant is mixed with a binder solution and molded in the form of a pellet or may be simply pressed at a pressure of about 1 ton to about 10 tons to form a pellet. 
     The pellet may be subjected to a secondary heat-treatment at a temperature less than about 1,000° C. for about 1 hour to about 36 hours. From the secondary heat-treatment, a solid electrolyte  30  is obtained as a sintered resultant. The secondary heat-treatment may be performed at a temperature, for example, in a range of about 550° C. to about 1,000° C. The secondary heat-treatment may be performed for about 1 hour to about 36 hours. A temperature of the secondary heat-treatment is greater than the temperature of the primary heat-treatment to obtain the sintered resultant. For example, the temperature of the secondary heat-treatment is about 10° C. or greater, about 20° C. or greater, about 30° C. or greater, or about 50° C. or greater than the temperature of the primary heat-treatment. The pellet may be subjected to the secondary heat-treatment in an oxidative atmosphere, a reductive atmosphere, or a combination thereof. The secondary heat-treatment may be performed in a) an oxidative atmosphere, b) a reductive atmosphere, or c) an oxidative atmosphere and a reductive atmosphere. 
     For example, the solid electrolyte  30  including a sulfide-based solid electrolyte may be prepared by using a solid electrolyte formed of sulfide-based solid electrolyte materials. 
     The sulfide-based solid electrolyte may be prepared by treating starting materials with a melt quenching method or a mechanical milling method, but embodiments are not limited thereto, and any method of preparing a sulfide-based solid electrolyte available may be used. For example, when the sulfide-based solid electrolyte is prepared by using a melt quenching method, predetermined amounts of the starting materials, e.g., Li 2 S and P 2 S 5 , are mixed into a pellet phase, reacted at a predetermined reaction temperature in a vacuum, and quenched to obtain a sulfide-based solid electrolyte. The reaction temperature of the mixture of Li 2 S and P 2 S 5  may be, for example, in a range of about 400° C. to about 1000° C. or about 800° C. to about 900° C. A period of time for the reaction may be in a range of about 0.1 hours to about 12 hours, or, for example, about 1 hour to about 12 hours. A temperature of the quenching may be, for example, about 10° C. or less, or, for example, about 0° C. or less, and a rate of the quenching may be in a range of, for example, 1° C. per second (° C./sec) to about 10,000° C./sec, or, for example, about 1° C./sec to about 1,000° C./sec. For example, when the sulfide-based solid electrolyte is prepared by using a mechanical milling method, predetermined amounts of the starting materials, e.g., Li 2 S and P 2 S 5 , are mixed and reacted by using a ball mill to obtain a sulfide-based solid electrolyte. A rate and a period of time of stirring for the mechanical milling method are not particularly limited, but, when the rate of stirring is high, a production rate of the solid electrolyte increases, and, when the period of time of stirring increases, a conversion ratio from the starting materials to the solid electrolyte also increases. Subsequently, the mixture obtained from the melt quenching method or the mechanical milling method is heat-treated at a predetermined temperature, and then the resultant is pulverized to prepare a solid electrolyte in the form of particles. When the solid electrolyte has glass transition characteristics, the solid electrolyte may be changed from amorphous to crystalline by the heat-treatment. 
     Thus obtained solid electrolyte may be deposited by using a method known to those of skill in the art, for example, an aerosol deposition method, a cold spray method, or a sputtering method, to prepare a solid electrolyte  30 . In some embodiments, the solid electrolyte  30  may be prepared by pressing a plurality of the solid electrolyte particles. In some embodiments, the solid electrolyte  30  may be prepared by mixing a solid electrolyte, a solvent, and a binder to prepare a mixture and then coating, drying, and pressing the mixture. 
     Preparation of all-Solid Secondary Battery 
     The anode  20  which is prepared by the anode manufacturing method 1 described above, the cathode  10 , and the solid electrolyte  30  prepared as described above are stacked in such a way that the cathode  10  and the anode  20  have the solid electrolyte  30  disposed therebetween to prepare a stack, and the stack is pressed to prepare an all-solid secondary battery  1 . 
     For example, the contact layer  23  of the anode  20  is disposed to face a surface of the solid electrolyte  30 , and the anode  20  and the solid electrolyte  30  are pressed at a predetermined pressure to attach the anode  20  to the surface of the solid electrolyte  30 . 
     The pressing may be performed by, for example, roll pressing, uni-axial pressing, flat pressing, warm isotactic pressing (WIP), or cold isotactic pressing (CIP), but embodiments are not limited thereto, and any pressure application method may be used. The pressure applied in the pressing may be in a range of about 50 MPa to about 750 MPa, or about 100 MPa to about 700 MPa. A time for the pressing may be in a range of about 5 seconds to about 5 min. The pressing may be performed at a temperature, for example, in a range of room temperature to about 90° C. or about 20° C. to about 90° C. In some embodiments, the pressing is performed at a high temperature of about 100° C. or greater. 
     Since the anode  20  prepared by the anode manufacturing methods 2 and 3 is attached to the solid electrolyte  30 , the attaching of the anode  20  to one side of the solid electrolyte  30  may be omitted. 
     Next, the cathode  10  is disposed on a surface of the solid electrolyte  30  which is different from (e.g., opposite to) the surface on which the anode  20  is disposed, and the resultant is pressed with a predetermined pressure to attach the cathode  10  to the other surface of the solid electrolyte  30 . 
     The pressing may be performed by, for example, roll pressing, uni-axial pressing, flat pressing, warm isotactic pressing (WIP), or cold isotactic pressing (CIP), but embodiments are not limited thereto, and any pressure available in the art may be used. The pressure applied in the pressing may be in a range of about 50 MPa to about 750 MPa, or about 100 MPa to about 700 MPa. A time for the pressing may be in a range of about 5 seconds to about 5 min. The pressing may be performed at a temperature, for example, in a range of room temperature to about 90° C., or about 20° C. to about 90° C. In some embodiments, the pressing is performed at a high temperature of about 100° C. or greater. 
     In an aspect, a method of manufacturing an all-solid secondary battery, the method comprises providing a first stack comprising a first layer comprising lithium metal or a lithium alloy on a first substrate, and a second layer comprising a carbon-containing active material on the first layer; providing a second stack comprising a third layer disposed on a solid electrolyte, wherein the third layer comprises lithium metal, a lithium alloy, a metal alloyable with lithium, or a combination thereof; disposing the first stack on the second stack such that the second layer and the third layer face each other, and pressing the first stack and the second stack such that the first stack and the second stack move closer to each other to attach the second layer to the third layer, and providing a cathode on the solid electrolyte opposite the third layer to manufacture the all-solid secondary battery, wherein the third layer is disposed between the second layer and the solid electrolyte, and a thickness of the third layer is be less than a thickness of the first layer. 
     The providing the first stack may comprise providing the first layer disposed on the first substrate and the second layer disposed on a second substrate, and disposing the first layer and the second layer to face each other, and pressing the first substrate and the second substrate such that the first layer and the second layer move closer to each other. 
     In the preparing the first stack, the second substrate may be removed from the second layer, and the first substrate may be an anode current collector. 
     In an aspect, a method of manufacturing an all-solid secondary battery, the method comprises providing a first stack comprising a first layer comprising lithium metal or a lithium alloy on a first substrate; providing a second stack comprising a second layer comprising a carbon-containing active material, and a third layer disposed on a solid electrolyte, wherein the third layer comprises lithium metal, a lithium alloy, a metal alloyable with lithium, or a combination thereof; disposing the first stack and the second stack such that the first layer and the second layer face each other; pressing the first stack and the second stack such that the first stack and the second stack move closer to each other to attach the first layer to the second layer; and providing a cathode on the solid electrolyte opposite the third layer to manufacture the all-solid secondary battery, wherein the third layer is thinner than the first layer. 
     The providing the second stack may comprise providing the third layer disposed on the solid electrolyte and the second layer disposed on a second substrate, and disposing the third layer and the second layer to face each other, and pressing the second substrate and the solid electrolyte such that the third layer and the second layer move closer to each other. 
     In the providing the second stack, the second substrate may be removed from the second layer, and the first substrate may be an anode current collector. 
     A composition and a preparation method of the all-solid secondary battery are examples of embodiments, where elements of the composition and processes of the preparation method may be appropriately modified. The pressing may be omitted. 
     An embodiment will now be described in more detail with reference to the following examples. However, these examples are not intended to limit the scope of the disclosed embodiment. 
     EXAMPLES 
     Example 1 (Anode Comprising a Silver-Lithium Alloy Layer, Silver-Carbon Layer, and Silver-Lithium Alloy Layer 
     (Manufacture of Solid Electrolyte/Anode Stack Subassembly Using Manufacturing Method 1) 
     Carbon black, as a conducting material and an anode active material, and silver (Ag) nanoparticles alloyable with lithium were mixed with a binder to prepare a slurry, the slurry was evenly coated on a stainless steel foil (a second substrate), and the coated stainless steel foil was dried. As a result, a second precursor electrode (second layer) of the second anode active material layer was manufactured. Separately, a first precursor electrode (lithium metal, first layer) of a first anode active material layer disposed on an anode current collector (first substrate) was prepared. 
     After placing the second precursor electrode and the first precursor electrode face each other, a pressure of 150 megapascals (MPa) at a temperature of 25° C. was applied to the resultant by cold isotactic pressing (CIP) to attach the precursor electrode to the lithium metal electrode. 
     In the attaching process, a Li—Ag alloy layer (a contact layer) was formed between the second precursor electrode and the stainless steel foil, and the first precursor electrode reacted with silver (Ag) and was thus changed to a Li—Ag alloy layer (a first anode active material layer). 
     Then, the stainless steel foil was removed to prepare an anode in which the lithium-silver (Li—Ag) alloy layer having a thickness of about 20 μm, the silver-carbon layer having a thickness of about 5.5 μm, and the lithium-silver (Li—Ag) alloy layer having a thickness of about 0.5 μm were sequentially stacked in this stated order on an anode current collector. 
     A Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12  (LLZO) pellet having a thickness of about 350 μm was prepared. 
     The anode was disposed on a surface of the LLZO pellet to face the Li—Ag alloy layer having the thickness of about 0.5 μm, and CIP was applied thereto with a pressure of 250 MPa at 25° C. to attach the anode to the LLZO pellet to prepare a solid electrolyte/anode stack subassembly. 
     (Preparation of Cathode and all-Solid Secondary Battery) 
     A cathode and an all-solid secondary battery were prepared in the same manner as in Example 1, except that the solid electrolyte/anode prepared as described above was used. 
     Example 2 (Anode Comprising a Lithium Layer, Carbon Layer, and Lithium Layer 
     (Manufacture of Solid Electrolyte/Anode Stack Subassembly Using Manufacturing Method 1) 
     After preparing a slurry by mixing carbon black used as a conductive material and an anode active material with a binder, the slurry was uniformly coated on a stainless steel foil (second substrate), and the coated stainless steel foil was dried. In this manner, a precursor electrode (a second layer) of an anode was prepared. Separately, a lithium metal electrode (a first layer) disposed on an anode current collector (a first substrate) was prepared. 
     After placing thus prepared precursor electrode and the lithium metal electrode face each other, a pressure of 150 MPa at a temperature of 25° C. was applied to the resultant by cold isotactic pressing (CIP) to attach the precursor electrode to the lithium metal electrode. 
     In the attaching process, a Li layer (contact layer) was formed between the precursor electrode and the stainless steel foil. Also, the precursor electrode was changed to a carbon layer (a second anode active material layer) including a carbon-based active material and lithium. 
     Then, the stainless steel was removed to prepare an anode in which the Li layer having a thickness of about 20 μm, the carbon layer having a thickness of about 5.5 μm, and a Li layer having the thickness of about 0.5 μm were sequentially stacked in this stated order on an anode current collector. 
     A Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12  (LLZO) pellet having a thickness of about 350 μm was prepared. 
     The anode was disposed on a surface of the LLZO pellet to face the Li layer having the thickness of about 0.5 μm, and CIP was applied thereto with a pressure of 250 MPa at 25° C. to attach the anode to the LLZO pellet (solid electrolyte). 
     (Preparation of Cathode and all-Solid Secondary Battery) 
     A cathode and an all-solid secondary battery were prepared in the same manner as in Example 1, except that the solid electrolyte/anode prepared as described above was used. 
     Example 3 (Anode Comprising a Lithium Layer, Carbon Layer, and Silver (Ag) Layer 
     (Manufacture of Solid Electrolyte/Anode Stack Subassembly Using Manufacturing Method 2) 
     A Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12  (LLZO) pellet having a thickness of about 350 μm was prepared. 
     A second stack, a solid electrolyte/contact layer (third layer) assembly, was prepared by depositing silver (Ag) on the solid electrolyte at 25° C. to form a silver (Ag) layer having a thickness of about 30 nm. 
     Meanwhile, prepared was a stack of a first anode active material layer (first layer)/anode current collector in which a lithium (Li) metal having a thickness of 20 μm was coated on a copper (Cu) foil, which is an anode current collector, having a thickness of 10 μm. 
     Separately, after preparing a slurry by mixing carbon black, which is used as a conductive material and an anode active material, with a binder, the slurry was uniformly coated on a stainless steel foil having 10 μm (second substrate), and the coated stainless steel foil was dried. As a result, a precursor electrode (second layer) of the second anode active material layer was manufactured. 
     The second anode active material layer (C)/stainless steel substrate and the first anode active material layer (Li metal)/anode current collector layer were arranged such that the second anode active material layer and the first anode active material layer were in contact with each other, and uni-axial press was applied with a pressure of 10 MPa thereto at 25° C., to prepare a stainless steel substrate/second anode active material layer (carbon)/first anode active material layer (lithium)/current collector stack. Then, the stainless steel substrate attached to the second anode active material layer was removed therefrom, thereby preparing a first stack in which the first anode active material layer (lithium) and the second anode active material layer (carbon) were sequentially stacked on the anode current collector. 
     The first stack was placed on the second stack such that the contact layer and the second anode active material layer were in contact with each other, and cold isotactic pressing (CIP) was applied thereon with a pressure of 250 MPa at 25° C. to prepare an anode on a solid electrolyte, the anode in which a contact layer (Ag) having a thickness of 30 nm, a second anode active material layer (C) having a thickness of 5 μm, a first anode active material layer (Li) having a thickness of 20 μm, and an anode current collector (Cu) were sequentially stacked. 
     (Preparation of Cathode and all-Solid Secondary Battery) 
     A cathode and an all-solid secondary battery were prepared in the same manner as in Example 1, except that the solid electrolyte/anode prepared as described above was used. 
     Example 4 (Anode Comprising a Lithium Layer, Carbon Layer, and Tin (Sn) Layer 
     (Manufacture of Solid Electrolyte/Anode Stack Subassembly Using Manufacturing Method 3) 
     A Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12  (LLZO) pellet having a thickness of about 350 μm was prepared. 
     A solid electrolyte/contact layer assembly was prepared by depositing tin (Sn) on the solid electrolyte at 25° C. to form a Sn layer having a thickness of about 30 nm to about 100 nm. 
     Separately, after preparing a slurry by mixing carbon black, which is used as a conductive material and an anode active material, with a binder, the slurry was uniformly coated on a stainless steel substrate having 10 μm (second substrate), and the coated stainless steel substrate was dried. As a result, a precursor electrode (carbon layer) of the second anode active material layer was manufactured. 
     The precursor electrode/stainless steel substrate stack was arranged on the solid electrolyte/contact layer assembly such that the contact layer and the carbon layer come into contact, and then was subjected to CIP with a pressure of 250 MPa at 25° C. Then, the stainless steel substrate attached to the precursor electrode was removed therefrom to prepare a second stack in which a contact layer and a precursor electrode were stacked on a solid electrolyte. 
     Separately, a first stack in which a lithium metal electrode (first layer) was disposed on an anode current collector (first substrate, Cu) was prepared. While the precursor electrode (carbon layer) of the previously prepared second stack and the lithium (Li) metal electrode (first layer) of the first stack were arranged to face each other, CIP was performed thereon with a pressure of 150 MPa at 25° C. to attach the precursor electrode to the lithium metal electrode. As a result, prepared was, on the solid electrolyte, an anode in which a contact layer (Sn) having a thickness of 30 nm, a second anode active material layer (C) having a thickness of 5 μm, and a first anode active material layer (Li) having a thickness of 20 μm, and an anode current collector (Cu) were sequentially stacked. 
     (Preparation of Cathode and all-Solid Secondary Battery) 
     A cathode and an all-solid secondary battery were prepared in the same manner as in Example 1, except that the solid electrolyte/anode prepared as described above was used. 
     Example 5 (Anode Comprising a Lithium Layer, a Carbon Layer, and a Zinc (Zn) Layer 
     (Manufacture of Solid Electrolyte/Anode Stack Subassembly Using Manufacturing Method 3) 
     A Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12  (LLZO) pellet having a thickness of about 350 μm was prepared. 
     A solid electrolyte/contact layer assembly was prepared by depositing zinc (Zn) on the solid electrolyte at 25° C. to form a zinc layer having a thickness of about 30 nm to about 100 nm. 
     The preparation of the anode in which the contact layer (Zn), second anode active material layer (C), first anode active material layer (Li), and the anode current collector (Cu) were sequentially stacked, and the preparation of the cathode and the secondary battery, were performed in the same manner as in Example 4, except that the solid electrolyte/contact layer (Zn) assembly manufactured as described above was used. 
     (Preparation of Cathode and all-Solid Secondary Battery) 
     A cathode and an all-solid secondary battery were prepared in the same manner as in Example 1, except that the solid electrolyte/anode prepared as described above was used. 
     Example 6 (Anode Comprising a Silver-Lithium Ally Layer, Carbon Layer, and Silver (Ag) Layer 
     (Manufacture of Solid Electrolyte/Anode Stack Subassembly Using Manufacturing Method 3) 
     A Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12  (LLZO) pellet having a thickness of about 350 μm was prepared. 
     A solid electrolyte/contact layer stack was prepared by depositing silver (Ag) on the solid electrolyte at 25° C. to form a silver (Ag) layer having a thickness of about 200 nm. 
     Separately, carbon black, as a conducting material and an anode active material, and silver (Ag) nanoparticles alloyable with lithium were mixed with a binder to prepare a slurry, the slurry was evenly coated on a stainless steel substrate having a thickness of 10 μm (a second substrate), and the coated stainless steel substrate was dried. As a result, a precursor electrode (silver-carbon layer) of the second anode active material layer was manufactured. 
     The precursor electrode of the second anode active material layer was attached to the solid electrolyte/contact layer stack such that the contact layer contacts the silver-carbon (AgC) layer, and CIP was applied thereon with a pressure of 250 MPa at 25° C. Then, the stainless steel substrate attached to the precursor electrode of the second anode active material layer was removed therefrom to prepare a second stack in which a contact layer (Ag) and a second anode active material layer (AgC) were stacked on a solid electrolyte. 
     Separately, a first stack was prepared in which the precursor electrode (lithium metal) of the first anode active material layer was disposed on the anode current collector (first substrate, Cu). While the carbon surface of the second stack, which is the previously prepared solid electrolyte/contact layer (Ag)/second anode active material layer (AgC) stack, was arranged to face the precursor electrode (lithium metal, first layer) of the first stack, CIP was applied thereto with a pressure of 250 MPa at 25° C. to attach the second anode active material layer (AgC) of the second stack to the precursor electrode of the first anode active material layer. At this time, the precursor electrode (lithium metal) of the first anode active material layer reacts with Ag in the second anode active material layer to form a lithium-silver alloy layer (first anode active material layer). Accordingly, a stack comprising a solid electrolyte/contact layer (Ag)/second anode active material layer (AgC)/first anode active material layer (AgLi)/anode current collector (Cu) was prepared. As a result, on the solid electrolyte, prepared was an anode in which a contact layer (Ag) having a thickness of 200 nm, a second anode active material layer (AgC) having a thickness of 5 μm, a first anode active material layer (AgLi) having a thickness of 20 μm, and an anode current collector (Cu) were sequentially stacked. 
     (Preparation of Cathode and all-Solid Secondary Battery) 
     A cathode and an all-solid secondary battery were prepared in the same manner as in Example 1, except that the solid electrolyte/anode prepared as described above was used. 
     Comparative Example 1: Anode Comprising a Single Lithium Metal Layer 
     (Preparation of Solid Electrolyte/Anode Stack Subassembly) 
     A Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12  (LLZO) pellet having a thickness of about 350 μm was prepared. An anode prepared by coating a copper (Cu) foil having a thickness of about 10 μm with a lithium (Li) metal at a thickness of about 20 μm, disposing the coated copper foil on a surface of the LLZO pellet, and applying a pressure of 250 MPa at a temperature of 25° C. to the resultant by cold isotactic pressing (CIP) to prepare a solid electrolyte/anode stack subassembly. 
     (Preparation of Cathode) 
     LiNi 0.8 Co 0.15 Mn 0.05 O 2 (NCM) was used as a cathode active material. Also, polytetrafluoroethylene (Teflon®; available from DuPont) was used as a binder. Also, carbon nanofibers (CNFs) were used as a conducting material. Next, the cathode active material, the conducting material, and the binder were mixed at a weight ratio of 100:2:1 to prepare a mixture. The mixture was stretched in the form of sheet to prepare a cathode active material sheet. Also, the cathode active material sheet was pressed on a cathode current collector formed of an aluminum foil having a thickness of about 18 μm to prepare a cathode. 
     The cathode active material sheet of the cathode was impregnated with an electrolyte solution prepared by dissolving 2.0 M of LiFSI in an ionic liquid, N-propyl-N-methyl-pyrrolidinium bis(fluorosulfonyl)imide (Pyr13FSI). 
     (Preparation of all-Solid Secondary Battery) 
     The cathode was disposed in a SUS (stainless steel) cap such that the cathode active material layer impregnated in the ionic liquid electrolyte solution faced upward. The solid electrolyte/anode stack subassembly was disposed such that the solid electrolyte was on the cathode active material layer, and the resultant was sealed to prepare an all-solid secondary battery. 
     The cathode and the anode were insulated with an insulator. Portions of the cathode current collector and the anode current collector were exposed to the outside of the sealed battery and used as a cathode terminal and an anode terminal. 
     Comparative Example 2 (Anode Comprising a Lithium-Alloy Layer and Carbon-Metal Composite Layer 
     (Preparation of Solid Electrolyte/Anode Stack Subassembly) 
     A Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12  (LLZO) pellet having a thickness of about 350 μm was prepared. Meanwhile, a first stack in which a lithium (Li) metal having a thickness of 20 μm was coated on a copper (Cu) foil, which is an anode current collector having a thickness of 10 μm, was prepared. 
     Separately, prepared was a second stack in which a second anode active material layer having a composite (AgC) was disposed on a stainless steel substrate having a thickness of 10 μm. Herein, the composite (AgC) includes a carbon active material and silver (Ag) and has a thickness of 10 μm. 
     The second anode active material layer was prepared by mixing carbon black (CB) having a particle size of about 38 nm, which is a carbon-based material, and silver (Ag) nanoparticle powder, and a mixture obtained by mixing 2.692 g of a PVDF binder solution (Solvay, Solef5130) with 7 g of methylpyrrolidone (N-methylpyrrolidone, N-Methyl-2-pyrrolidone, NMP) was added thereto. The resultant was stirred at 1000 rotations per minute (rpm) for 30 minutes to prepare a slurry, which was then bar-coated on a stainless steel substrate. The coated stainless steel substrate was dried at room temperature (25° C.) for 1 hour and then vacuum dried for 12 hours to prepare a metal-containing second stack of a second anode active material layer (AgC)/stainless steel substrate. 
     The second stack of the second anode active material layer (AgC)/stainless steel substrate and the first stack of the first anode active material layer (Li metal)/anode current collector, the second anode active material layer (AgC) and the first anode active material layer (Li metal) were arranged to be in contact with each other, and a pressure of 10 MPa was applied thereto using an uni-axial press at a temperature of 25° C. to prepare a stainless steel substrate/second anode active material layer/first anode active material layer/anode current collector stack. Then, the stainless steel substrate attached to the second anode active material layer was removed therefrom, thereby preparing a first stack in which the first anode active material layer and the second anode active material layer were sequentially stacked on the anode current collector. 
     The first stack was placed on a solid electrolyte such that the second anode active material layer (AgC) faces one surface of the solid electrolyte (LLZO pellet), and CIP was applied thereto with the intensity of 10 MPa at 25° C. to obtain such a structure that the second anode active material layer, the first anode active material layer, and the anode current collector, which constitute an anode, were sequentially stacked on the solid electrolyte. 
     (Preparation of Cathode and all-Solid Secondary Battery) 
     A cathode and an all-solid secondary battery were prepared in the same manner as in Comparative Example 1, except that the solid electrolyte/anode prepared as described above was used. 
     Comparative Example 3: Anode Comprising a Contact Layer and Second Anode Active 
     Material Layer (Carbon Layer) 
     (Preparation of Solid Electrolyte/Anode Stack Subassembly) 
     A Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12  (LLZO) pellet having a thickness of about 350 μm was prepared. Prepared was, on a surface of LLZO pellet, a second stack in which a contact layer was stacked on a solid electrolyte by stacking silver (Ag) at 25° C. to form an Ag layer having a thickness of about 100 nm. 
     Separately, carbon black, which is used as an anode active material and a conductive material, was mixed with a binder to prepare a slurry, and then, the slurry was uniformly coated on a copper (Cu) foil (anode current collector) having a thickness of 10 μm, and the coated Cu foil was dried. For the carbon layer, a mixture obtained by adding 2.692 g of a PVDF binder solution (Solvay, Solef5130) to 7 g of methylpyrrolidone (N-methylpyrrolidone, N-Methyl-2-pyrrolidone, NMP) was added to carbon black (CB) having a particle size of about 38 nm, and the resultant was first stirred at 1000 rpm for 30 minutes to prepare a slurry, which was then bar-coated on a copper foil (anode current collector). The coated copper foil was dried at room temperature (25° C.) for 1 hour, and then vacuum dried for 12 hours to obtain a first stack in which the carbon layer was stacked on the anode current collector. 
     The first stack in which the carbon layer is stacked on the anode current collector was arranged with respect to the second stack in which the contact layer is stacked on the solid electrolyte while the contact layer was in contact with the carbon layer, and CIP was applied thereto with a pressure of 10 MPa at 25° C. to prepare a solid electrolyte/anode stack subassembly in which the contact layer, the carbon layer, and the anode current collector were sequentially stacked. 
     (Preparation of Cathode and all-Solid Secondary Battery) 
     A cathode and an all-solid secondary battery were prepared in the same manner as in Comparative Example 1, except that the solid electrolyte/anode prepared as described above was used. 
     Comparative Example 4: Anode Comprising a Contact Layer and First Anode Active Material Layer (Indium Layer 
     (Preparation of Solid Electrolyte/Anode Stack Subassembly) 
     A Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12  (LLZO) pellet having a thickness of about 350 μm was prepared. Prepared was, on a surface of LLZO pellet, a second stack in which a contact layer was stacked on a solid electrolyte by stacking silver (Ag) at 25° C. to form a silver (Ag) layer having a thickness of about 100 nm. 
     Separately, a first stack of an anode current collector/indium metal layer in which indium (In) metal having a thickness of 50 μm was pressed on a copper (Cu) foil having a thickness of 10 μm, which is an anode current collector, was prepared. 
     The first stack was arranged on the second stack such that the indium (In) metal layer faces the silver (Ag) contact layer, and then, CIP was applied thereto with a pressure of 10 MPa at 25° C., and the contact layer (Ag) on the solid electrolyte to prepare such a structure in which the contact layer (Ag), the indium metal layer, and the anode current collector, which constitute the anode, were sequentially stacked on the solid electrolyte. 
     (Preparation of Cathode and all-Solid Secondary Battery) 
     A cathode and an all-solid secondary battery were prepared in the same manner as in Comparative Example 1, except that the solid electrolyte/anode prepared as described above was used. 
     Comparative Example 5 (Anode Comprising a Lithium Layer and Carbon Layer without Contact Layer 
     (Preparation of Solid Electrolyte/Anode Stack Subassembly) 
     A solid electrolyte having a Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12  (LLZO) pellet having a thickness of about 350 μm was prepared. 
     Meanwhile, a stack of a first anode active material layer/anode current collector in which a lithium (Li) metal having a thickness of 20 μm was coated on a copper (Cu) foil having a thickness of 10 μm, which is an anode current collector, was prepared. 
     Separately, a second anode active material layer/stainless steel substrate stack was prepared in which a second anode active material layer containing a carbon-based active material and having a thickness of 10 μm was placed on a stainless steel substrate having a thickness of 10 μm. The second anode active material layer/stainless steel substrate stack was prepared by mixing carbon black (CB) having a particle size of about 38 nm, which is a carbon-based material, with a mixture obtained by mixing 2.692 g of a PVDF binder solution (Solvay, Solef5130) with 7 g of methylpyrrolidone (N-methylpyrrolidone, N-Methyl-2-pyrrolidone, NMP). The resultant was first stirred at 1000 rpm for 30 minutes to prepare a slurry, which was then bar-coated on a stainless steel substrate. The coated stainless steel substrate was dried at room temperature (25° C.) for 1 hour, and then vacuum dried for 12 hours to obtain a second stack of a second anode active material layer (carbon)/stainless steel substrate. 
     The second stack of the second anode active material layer (carbon)/stainless steel substrate and the first stack of the first anode active material layer (Li metal)/anode current collector were arranged such that the second anode active material layer is in contact with the first anode active material layer, and a pressure of 10 MPa was applied thereto using an uni-axial press at a temperature of 25° C. to prepare a stainless steel substrate/second anode active material layer (carbon)/first anode active material layer (lithium)/anode current collector stack. Then, the stainless steel substrate attached to the second anode active material layer was removed to prepare a stack (first stack) of second anode active material layer (carbon)/first anode active material layer (lithium)/anode current collector. 
     The first stack was placed on a solid electrolyte such that the second anode active material layer (carbon) faces a surface of the solid electrolyte (LLZO), and then, CIP was applied thereto with a pressure of 10 MPa at 25° C. to obtain such a structure that the second anode active material layer (carbon), the first anode active material layer (lithium), and the anode current collector, of an anode, were sequentially stacked on the solid electrolyte. 
     (Preparation of Cathode and all-Solid Secondary Battery) 
     A cathode and an all-solid secondary battery were prepared in the same manner as in Comparative Example 1, except that the solid electrolyte/anode prepared as described above was used. 
     Evaluation Example 1: Evaluation of Interfacial Resistance 
     Interfacial resistance of the full-cells prepared in Comparative Examples 1 and 2 and Example 1 were each measured. 
     Impedance of the pellets was measured by a 2-probe method using an impedance analyzer (Solartron 1400A/1455A impedance analyzer) with respect to the full-cells prepared in Comparative Examples 1 and 2 and Example 1. A frequency range was in a range of about 0.1 Hertz (Hz) to about 1 MHz, and an amplitude voltage was about 10 millivolts (mV). 
     The measurement was performed in the air atmosphere at a temperature of about 25° C. The Nyquist plots of the impedance measurement results are shown in  FIGS.  16  and  17   . 
     Referring to  FIGS.  16  and  17   , an interfacial resistance of a structure having an anode in which a carbon layer is in direct contact with a solid electrolyte (Comparative Example 2) was greater than about 2,000 Ohm·cm 2 , but an interfacial resistance of a structure having an anode in which a lithium metal layer or lithium alloy layer is in contact with a solid electrolyte (Comparative Example 1 and Example 1) was less than about 2,000 Ohm·cm 2 . 
     Evaluation Example 2: Charging/Discharging Test 
     Charge/discharge characteristics of the all-solid secondary batteries prepared in Comparative Examples 1, 2, 4 and 5 and Examples 1, 3, 4, 5, and 6 were evaluated by the following charge/discharge test. The charge/discharge test of the all-solid secondary battery according to Comparative Examples 1, 2, 4 and Example 1 were performed by charging and discharging of the batteries while changing a current density under a temperature condition of about 60° C. to confirm driving characteristics of the all-solid secondary batteries in a high current density state, wherein a 70 μm thick LLZO solid electrolyte and NCM622 (4.4 mAh/cm 2 ) cathode were used. The charge/discharge test of the all-solid secondary battery according to Comparative Example 5 and Examples 3, 4, and 5 were performed by charging and discharging of the batteries while changing a current density under a temperature condition of about 25° C. to confirm driving characteristics of the all-solid secondary batteries in a high current density state, wherein a 500 μm thick LLZO solid electrolyte and NCA (5.1 mAh/cm 2 ) cathode were used. The charge/discharge test of the all-solid secondary battery according to Example 6 was performed by charging and discharging of the batteries while changing a current density under a temperature condition of about 25° C. to confirm driving characteristics of the all-solid secondary batteries in a high current density state, wherein a 100 μm thick LLZO solid electrolyte and NCM (3.2 mAh/cm 2 ) cathode were used. 
     As shown in  FIG.  18   , a structure having an anode formed of a single lithium metal layer (Comparative Example 1) had short-circuits occur at about 1.0 mA/cm 2 , and, as shown in  FIG.  19   , a structure having an anode in which a carbon layer directly contacting a solid electrolyte (Comparative Example 2) had short-circuits occurred at about 0.9 mA/cm 2 . As shown in  FIG.  20   , even though the contact layer and the first anode active material layer were included, a short circuit occurred at 0.7 mA/cm 2  in the structure having an anode that does not include a carbon layer (Comparative Example 4). 
     On the other hand, as shown in  FIG.  21   , in a structure having a multilayer structure in which a thin Li—Ag alloy layer is in contact with a solid electrolyte (Example 1), stable operation was possible without short-circuit occurrence until 1.8 mA/cm 2 . 
     Meanwhile, as shown in  FIG.  22   , in the case of the structure having an anode formed of a first anode active material layer and a second anode active material layer in which a contact layer is not present (Comparative Example 5), the discharge capacity varied depending on the current density. For example, at 2.0 mA/cm 2 , the discharge capacity was 2 mAh/cm 2  or less. 
     On the other hand, as shown in  FIG.  23   , in the case of a structure having a multilayer structure in which a thin Ag metal layer is in contact with a solid electrolyte (Example 3), the driving was stably performed without short circuits until 2.5 mA/cm 2 , and the difference in the discharge capacity according to the current density was small. For example, at 2.0 mA/cm 2 , the discharge capacity was 4 mAh/cm 2  or greater. As shown in  FIG.  24   , in the case of a structure having a multilayer structure in which a thin Sn metal layer is in contact with a solid electrolyte (Example 4), the driving was stably performed without short circuits until 2.0 mA/cm 2 , and the difference in the discharge capacity according to the current density was small. For example, at 2.0 mA/cm 2 , the discharge capacity was 4 mAh/cm 2  or greater. As shown in  FIG.  25   , in the case of a structure having a multilayer structure in which a thin Zn metal layer is in contact with a solid electrolyte (Example 5), the driving was stably performed without short circuits until 2.0 mA/cm 2 , and the difference in the discharge capacity according to the current density was small. For example, at 2.0 mA/cm 2 , the discharge capacity was 4 mAh/cm 2  or greater. As shown in  FIG.  26   , in the case of a structure having a multilayer structure in which a thin Ag metal layer is in contact with a solid electrolyte (Example 6), the driving was stably performed without short circuits until 1.6 mA/cm 2 , and the difference in the discharge capacity according to the current density was small. For example, at 1.6 mA/cm 2 , the discharge capacity was 2.4 mAh/cm 2  or greater. 
     From this result, it may be evaluated as that an anode having a multi-layered structure in which a thin metal layer is in contact with a solid electrolyte may have a reduced volume change occurring during the charging/discharging, and that short-circuits of an all-solid secondary battery including the anode may be prevented by reducing a current being topically focused at a high current density. 
     As described above, according to one or more embodiments, an all-solid secondary battery and a method of preparing the all-solid secondary battery may prevent cracks of a solid electrolyte and may reduce an interfacial resistance between an anode and the solid electrolyte. 
     It should be understood that embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should be considered as available for other similar features or aspects in other embodiments. While one or more embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims.