ALL-SOLID SECONDARY BATTERY AND METHOD OF PREPARING THE SAME

An all-solid secondary battery, including: 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 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.

BACKGROUND

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.

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.

DETAILED DESCRIPTION

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.

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.1is a cross-sectional view illustrating an all-solid secondary battery1according to an embodiment, andFIG.2is a cross-sectional view illustrating an anode20inFIG.1.FIGS.3and4are views illustrating the effect of charge and discharge on the anode20of the all-solid secondary battery1.

Referring toFIGS.1and2, the all-solid secondary battery1according to an embodiment is a secondary battery that includes a solid electrolyte as an electrolyte. For example, the all-solid secondary battery1may be an all-solid lithium ion secondary battery, in which lithium ions migrate between a cathode10and the anode20.

The all-solid secondary battery1includes the cathode10(also referred to herein as the cathode), a solid electrolyte30, and the anode20(also referred to herein as the anode).

Cathode

The cathode10may include a cathode current collector11and a cathode active material layer12.

For example, the cathode current collector11may 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 collector11may be omitted.

For example, the cathode active material layer12may 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:

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 <111> 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 LiNixCoyAlzO2(NCA) or LiNixCoyMnzO2(NCM) (where 0<x<1, 0<y<1, 0<z<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 battery1may 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, Li2O—ZrO2.

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 battery1increases, and thus metal elution from the cathode active material in a charged state may be reduced. As a result, the all-solid secondary battery1according 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 cathode10is 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 cathode10, 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 cathode10, and may be any material that suitable for use in an electrode of an all-solid secondary battery.

The cathode10may further include a solid electrolyte. The solid electrolyte in the cathode10may be similar to or different from the solid electrolyte in the solid electrolyte30. Details of the solid electrolyte in the cathode are the same those described with reference to the solid electrolyte30.

The solid electrolyte in the cathode10may 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 electrolyte30.

In some embodiments, the cathode10may 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 BF4−, PF6−, AsF6−, SbF6−, AlCl4−, HSO4−, CIO4−, CH3SO3−, CF3CO2−, Cl−, Br−, I−, BF4−, SO4−, CF3SO3−, (FSO2)2N−, (C2F5SO2)2N−, (C2F5SO2)(CF3SO2)N−, (CF3SO2)2N−, 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 BF4−, PF6−, AsF6−, SbF6−, AlCl4−, HSO4−, ClO4−, CH3SO3−, CF3CO2−, (CF3SO2)2N−, (FSO2)2N−, Cl−, Br−, I−, SO4−, CF3SO3−, (C2F5SO2)2N−, (C2F5SO2)(CF3SO2)N−, NO3−, Al2Cl−, (CF3SO2)3C−, (CF3)2PF4−, (CF3)3PF3−, (CF3)4PF2−, (CF3)5PF−, (CF3)6P−, SF5CF2SO3−, SF5CHFCF2SO3−, CF3CF2(CF3)2CO−, CF3SO2)2CH−, (SF5)3C−, (O(CF3)2C2(CF3)2O)2PO−, or a combination thereof. The lithium salt is not limited and may be any suitable lithium salt. The lithium salt may be, for example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, Li(FSO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(CxF2x+1SO2)(CyF2y+1SO2) (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 cathode10may 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 layer12not including the liquid electrolyte.

Solid Electrolyte

The solid electrolyte30may be disposed between the cathode10and the anode20. The solid electrolyte30includes a solid electrolyte. In an aspect, the solid electrolyte30may be a solid electrolyte layer.

The oxide-based solid electrolyte may be, for example, a garnet-type solid electrolyte selected from Li7La3Zr2O12(LLZO) and Li3+xLa3Zr2−aMaO12(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, Li2S—P2S5, Li2S—P2S5—LiX (where X is a halogen), Li2S—P2S5—Li2O, Li2S—P2S5—Li2O—LiI, Li2S—SiS2, Li2S—SiS2—LiI, Li2S—SiS2—LiBr, Li2S—SiS2—LiCl, Li2S—SiS2—B2S3—LiI, Li2S—SiS2—P2S5—LiI, Li2S—B2S3, Li2S—P2S5—ZmSn(where m and n are positive integers, and Z is Ge, Zn, or Ga), Li2S—GeS2, Li2S—SiS2—Li3PO4, Li2S—SiS2—LipMOq(where p and q are positive integers, and M is P, Si, Ge, B, Al, Ga, In, or a combination thereof), Li7-xPS6-xClx(where 0≤x≤2), Li7−xPS6−xBrx(where 0≤x≤2), and Li7−xPS6−xIx(where 0≤x≤2). The sulfide-based solid electrolyte material is prepared by melting and quenching the starting materials (e.g., Li2S or P2S5), 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 Li2S—P2S5. When the material including Li2S—P2S5is used as a sulfide-based solid electrolyte, a mixing molar ratio of Li2S and P2S5(Li2S:P2S5) 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 Li7−xPS6−xClx(where 0≤x≤2), Li7−xPS6−xBrx(where 0≤x≤2), Li7−xPS6−xIx(where 0≤x≤2), or a combination thereof. In particular, the sulfide-based solid electrolyte may be an argyrodite-type compound including Li6PS5Cl, Li6PS5Br, Li6PS5I, or a combination thereof.

For example, the solid electrolyte30may further include a binder. Examples of the binder in the solid electrolyte30include 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 electrolyte30may be the same as or different from a binder of the cathode and/or the anode.

Anode

Referring toFIGS.1and2, the anode20includes an anode current collector21, an anode active material layer22, and a contact layer23.

During a process of charging the all-solid secondary battery1, a volume of the anode20may increase as shown inFIG.3. During a process of discharging the all-solid secondary battery1, a volume of the anode20may decrease as shown inFIG.4.

For example, the anode current collector21may 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 collector21may 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 collector21may include any one metal alone, an alloy of at least two different metals, or a coating material. The anode current collector21may be, for example, in the form of a plate or a foil.

The anode active material layer22may include a first anode active material layer221and a second anode active material layer222.

The first anode active material layer221may be disposed on the anode current collector21and may include a first metal. The first anode active material layer221may thus be a first metal layer. The first metal may include lithium metal or a lithium alloy. Accordingly, since the first anode active material layer221is a metal layer including lithium or a lithium alloy, for example, the first anode active material layer221may 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 layer221may include one of the lithium alloys or lithium metal, or may include a combination of various alloys selected therefrom.

A thickness t1of the first anode active material layer221may be about 10 μm or greater. For example, the thickness t1of the first anode active material layer221may 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 t1of the first anode active material layer221is too thin, the first anode active material layer221may not function as a lithium reservoir. When the thickness t1of the first anode active material layer221is too thick, a weight and a volume of the all-solid secondary battery1increases, and cycle characteristics of the all-solid secondary battery1may be deteriorated.

The first anode active material layer221may be disposed between the anode current collector21and the second anode active material layer222. When the all-solid secondary battery1is charged, lithium is deposited in the first anode active material layer221, and a volume or a thickness of the first anode active material layer221may increase due to the deposited lithium.

A volume of the first anode active material layer221after charge may be about 150% to about 5,000% of a volume of the first anode active material layer221after discharge. A thickness of the first anode active material layer221after charge may be about 150 to about 5,000% of a thickness of the first anode active material layer221after 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 layer221may be greater than a volume change rate of the contact layer23. In the charging/discharging process, a volume change rate of the first anode active material layer221may be greater than a volume change rate of the second anode active material layer222. In the charging/discharging process, a thickness change rate of the first anode active material layer221may be greater than a thickness change rate of the contact layer23. In the charging/discharging process, a thickness change rate of the first anode active material layer221may be greater than a thickness change rate of the second anode active material layer222.

The second anode active material layer222may be disposed between the first anode active material layer221and the solid electrolyte30and 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 layer222may 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 layer222may 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 layer222may 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 material222may 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 battery1. When the second anode active material layer222has this composition, cycle characteristics of the all-solid secondary battery1may improve.

The anode active material in the second anode active material layer222may 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 battery1may improve.

A thickness t2of the second anode active material layer222may 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 layer222is within these ranges, a short-circuit in the all-solid secondary battery1may be suppressed, and cycle characteristics of the all-solid secondary battery1may improve.

The thickness t2of the second anode active material layer222may be less than the thickness t1of the first anode active material layer221. The thickness t2of the second anode active material layer222may be less than ½ of the thickness t1of the first anode active material layer221. The thickness t2of the second anode active material layer222may be less than 20% of the thickness t1of the first anode active material layer221. In an aspect, the thickness t2may be about 50% to about 1%, about 40% to about 2%, or about 30% to about 4% of the thickness t1.

When the second anode active material layer222includes a carbon-based active material, the volume of the second anode active material layer222may change according to a volume change of the first anode active material layer221. For example, when the first anode active material layer221expands during a charging process, the second anode active material layer222may absorb and alleviate the volume expansion of the first anode active material.

The second anode active material layer222includes a carbon-based active material and thus may include a void (pore) therein. The second anode active material layer222after discharge may include a void generated therein. During a charging process, lithium fills the void of the second anode active material layer222, and in this regard, the volume expansion of the first anode active material layer221may be alleviated. As the volume expansion of the first anode active material layer221is alleviated, a pressure applied by the anode20on the solid electrolyte30is reduced, and thus a short-circuit of the solid electrolyte30may be delayed.

A volume of the second anode active material layer222after charging may be greater than a volume of the second anode active material layer222after discharging. The volume of the second anode active material layer222after charging may be about 2 times or less the volume of the second anode active material layer222after discharging. A thickness t21of the second anode active material layer222after charging may be greater than a thickness t22of the second anode active material layer222after discharging. The thickness t21of the second anode active material layer222after charging may be about 2 times or less than the thickness t22of the second anode active material layer222after 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 layer222includes a carbon-based active material as described above, volume expansion of the first anode active material layer221may be alleviated, whereas an interface adhesive strength with the solid electrolyte may be deteriorated. Accordingly, when the second anode active material layer222is disposed such that the second anode active material layer222directly contacts the solid electrolyte30, an interfacial resistance between the anode20and the solid electrolyte30may increase.

In this regard, the anode20of the all-solid secondary battery1according to an embodiment includes the contact layer23disposed between the second anode active material layer222and the solid electrolyte30.

At least a portion of the contact layer23is disposed between the second anode active material layer222and the solid electrolyte30and directly contacts the solid electrolyte30. As the contact layer23directly contacts the solid electrolyte30, the second anode active material layer222may be prevented from directly contacting the solid electrolyte30. 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 layer23may improve an interface adhesive strength between the anode20and the solid electrolyte30.

An interfacial resistance between the contact layer23and the solid electrolyte30may be a prescribed level or less. For example, an interfacial resistance between the contact layer23and the solid electrolyte30may be about 500 ohm cm2or less, or about 400 ohm cm2or less, or about 300 ohm cm2or less. For example, an interfacial resistance between the contact layer23and the solid electrolyte30may be about 200 ohm cm2or less.

An interfacial resistance between the contact layer23and the solid electrolyte30may be lower than an interfacial resistance between the second anode active material layer222and the solid electrolyte30. For example, an interfacial resistance between the contact layer23and the solid electrolyte30may be less than 10% ( 1/10) of an interfacial resistance between the second anode active material layer222and the solid electrolyte30. For example, when an interfacial resistance between the second anode active material layer222and the solid electrolyte30directly contacting each other is greater than about 2,000 ohm cm2, an interfacial resistance between the contact layer23and the solid electrolyte30directly contacting each other may be about 200 ohm cm2or less.

For example, the contact layer23may 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.

When in a charged state, the contact layer23may include lithium metal or lithium alloy. When in a discharged state, the contact layer23may include lithium metal or lithium alloy. As another example, when in a discharged state, the contact layer23may include metal alloyable with lithium and may not include lithium metal or lithium alloy. Before being charged for the first time, the contact layer23may 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 layer23may not include a carbon-based material. For example, the contact layer23may 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 layer23may not include an organic material such as a binder. The contact layer23may include, for example, a metal layer formed of a metal, a metalloid, an alloy thereof, or a combination thereof. Since the contact layer23is 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 layer23includes the second metal layer and does not include a carbon-based material, the contact layer23may form an interface having an excellent adhesive strength to the solid electrolyte30compared to that of the second anode active material layer222including a carbon-based active material.

Since the contact layer23includes the second metal, the contact layer23induces fast dispersion of the lithium ions input through the solid electrolyte30in the charging process. Accordingly, a surface of the solid electrolyte30is 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 anode20by using a fast diffusion phenomenon via the contact layer23.

In the charging process, the contact layer23may 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 layer221.

A thickness t3of the contact layer23may be a predetermined thickness or less. For example, the thickness t3of the contact layer23may be about 1 μm or less. For example, the thickness t3of the contact layer23may be about 700 nm or less. For example, the thickness t3of the contact layer23may be about 500 nm or less. For example, the thickness t3of the contact layer23may be about 300 nm or less. For example, the thickness t3of the contact layer23may be about 200 nm or less. For example, the thickness t3of the contact layer23may be about 100 nm or less. For example, the thickness t3of the contact layer23may be about 70 nm or less. For example, the thickness t3of the contact layer23may be about 50 nm or less.

However, when the thickness t3of the contact layer23is too thin, the original purpose for the second anode active material layer222to directly contact the solid electrolyte30may not be achieved, and thus the thickness t3of the contact layer23may be about 1 nm or greater. For example, the thickness t3of the contact layer23may be 30 nm or greater. In an aspect, the thickness t3of the contact layer23may 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 t3of the contact layer23is not uniform, the thickness t3of the contact layer23is defined as an average thickness of the contact layer23.

The thickness t3of the contact layer23is less than the thickness t1of the first anode active material layer221. For example, the thickness t32of the contact layer23after discharge may be less than the thickness t12of the first anode active material layer221after discharge. For example, when the thickness t12of the first anode active material layer221after discharge is greater than about 10 μm, a thickness t32of the contact layer23after discharging may be about 1 μm or less. For example, the thickness t32of the contact layer23after discharge may be about 700 nm or less. For example, the thickness t32of the contact layer23after discharge may be about 500 nm or less. For example, the thickness t32of the contact layer23after discharge may be about 300 nm or less. For example, the thickness t32of the contact layer23after discharge may be about 200 nm or less. For example, the thickness t32of the contact layer23after discharge may be about 100 nm or less. For example, the thickness t32of the contact layer23after discharge may be about 70 nm or less. For example, the thickness t32of the contact layer23after discharge may be about 50 nm or less. However, for example, the thickness t32of the contact layer23after discharge may be about 30 nm or greater. For example, the thickness t32of the contact layer23may 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 t3of the contact layer23may be about 20% (⅕) or less of the thickness t1of the first anode active material layer221. The thickness t3of the contact layer23may be about 10% ( 1/10) or less of the thickness t1of the first anode active material layer221. The thickness t3of the contact layer23may be about 5% ( 1/20) or less of the thickness t1of the first anode active material layer221. The thickness t3of the contact layer23may be about 3.33% ( 1/30) or less of the thickness t1of the first anode active material layer221. The thickness t3of the contact layer23may be about 2.5% ( 1/40) or less of the thickness t1of the first anode active material layer221. The thickness t3of the contact layer23may be about 2% ( 1/50) or less of the thickness t1of the first anode active material layer221. The thickness t3of the contact layer23may be about 1% ( 1/100) or less of the thickness t1of the first anode active material layer221. The thickness t3of the contact layer23may be about 0.5% ( 1/200) or less of the thickness t1of the first anode active material layer221. The thickness t3of the contact layer23may be about 0.1% ( 1/1000) or greater of the thickness t1of the first anode active material layer221. For example, the thickness t3of the contact layer23may 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 t1of the first anode active material layer221.

The thickness t32of the contact layer23after discharge may be about 20% (⅕) or less of the thickness t12of the first anode active material layer221after discharge. The thickness t32of the contact layer23after discharge may be about 10% ( 1/10) or less of the thickness t12of the first anode active material layer221after discharge. The thickness t32of the contact layer23after discharging may be about 5% ( 1/20) or less of the thickness t12of the first anode active material layer221after discharging. The thickness t32of the contact layer23after discharging may be about 3.33% ( 1/30) or less of the thickness t12of the first anode active material layer221after discharging. The thickness t32of the contact layer23after discharging may be about 2.5% ( 1/40) or less of the thickness t12of the first anode active material layer221after discharging. The thickness t32of the contact layer23after discharging may be about 2% ( 1/50) or less of the thickness t12of the first anode active material layer221after discharging. The thickness t32of the contact layer23after discharging may be about 1% ( 1/100) or less of the thickness t12of the first anode active material layer221after discharging. The thickness t32of the contact layer23after discharging may be about 0.5% ( 1/200) or less of the thickness t12of the first anode active material layer221after discharging. The thickness t32of the contact layer23after discharging may be about 0.1% ( 1/1000) or greater of the thickness t12of the first anode active material layer221after discharging. For example, the thickness t32of the contact layer23after 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 t12of the first anode active material layer221after discharge.

The thickness t31of the contact layer23after charge may be about 10% ( 1/10) or less of the thickness t11of the first anode active material layer221after charge. The thickness t31of the contact layer23after charge may be about 5% ( 1/20) or less of the thickness t11of the first anode active material layer221after charge. The thickness t31of the contact layer23after charge may be about 2.5% ( 1/40) or less of the thickness t11of the first anode active material layer221after charge. The thickness t31of the contact layer23after charging may be about 1.66% ( 1/60) or less of the thickness t11of the first anode active material layer221after charging. The thickness t31of the contact layer23after charging may be about 1.25% ( 1/80) or less of the thickness t11of the first anode active material layer221after charging. The thickness t31of the contact layer23after charging may be about 1% ( 1/100) or less of the thickness t11of the first anode active material layer221after charging. The thickness t31of the contact layer23after charging may be about 0.5% ( 1/200) or less of the thickness t11of the first anode active material layer221after charging. The thickness t31of the contact layer23after charging may be about 0.25% ( 1/400) or less of the thickness t11of the first anode active material layer221after charging. The thickness t31of the contact layer23after charging may be about 0.05% ( 1/2000) or greater of the thickness t11of the first anode active material layer221after charging. For example, the thickness t31of the contact layer23after 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 t11of the first anode active material layer221after charge.

Accordingly, by designing the thickness t3of the contact layer23to be a predetermined thickness (or less) and the thickness t1of the first anode active material layer221to be greater than the thickness of the contact layer23, an amount of the metal deposited as the contact layer23during charge of the all-solid secondary battery1may be decreased, and the metal may be induced to be deposited in the first anode active material layer221.

When the thickness t3of the contact layer23is greater than the predetermined thickness, an amount of the lithium metal locally deposited as the contact layer23during the charging process may increase. This may generate cracks in the solid electrolyte30.

In particular, when the solid electrolyte30includes an oxide-based solid electrolyte, which has a greater hardness than a sulfide-based solid electrolyte, cracks may be generated in the solid electrolyte30due to the localized deposition of the lithium metal in the contact layer23, and the lithium metal may penetrate the solid electrolyte30through 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 battery1.

Also, due to the lithium metal locally deposited as the contact layer23, in the repeated charge/discharge process, a void may be formed between the contact layer23and the solid electrolyte30, and a contact area between the contact layer23and the solid electrolyte30may be reduced, which may lead to overvoltage of the all-solid secondary battery1.

However, in the all-solid secondary battery1according to an embodiment, the metal is also deposited in the first anode active material layer221, and thus an amount of the lithium metal deposited in the contact layer23may be reduced. In this regard, the short circuiting and overcharge of the all-solid secondary battery1may be prevented.

When an amount of lithium deposited in the contact layer23in the charging process is reduced, a volume change rate of the contact layer23in the charge/discharge process may be small.

For example, a volume of the contact layer23after charge may be about 150% or less of a volume of the contact layer23after discharge. A volume of the contact layer23after charge may be about 140% or less of a volume of the contact layer23after discharge. A volume of the contact layer23after charge may be about 130% or less of a volume of the contact layer23after discharge.

For example, in the charge/discharge process, a volume change rate of the contact layer23may be less than a volume change rate of the first anode active material layer221. In the charge/discharge process, a volume change rate of the contact layer23may be about 70% or less of a volume change rate of the first anode active material layer221. In the charge/discharge process, a volume change rate of the contact layer23may be about 60% or less of a volume change rate of the first anode active material layer221. 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 layer23may be the same as the first metal of the first anode active material layer221. 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.5A and5Bare, 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 anode20.FIGS.6A and6Bare, respectively, an enlarged cross-section SEM image of the periphery of the contact layer23and the second anode active material layer222inFIG.5Aand an enlarged cross-section SEM image of the periphery of the contact layer23and the second anode active material layer222inFIG.5B.

Referring toFIGS.5A and5B, a thickness t11of the first anode active material layer221after charge is in a range of about 32 μm to about 34 μm, and a thickness t12of the first anode active material layer221after discharge is in a range of about 17 μm to about 18 μm.

On the other hand, referring toFIGS.6A and6B, a thickness t21of the second anode active material layer222after charge is in a range of about 5 μm to about 6 μm, and a thickness t22of the second anode active material layer222after discharge is also in a range of about 5 μm to about 6 μm. Also, a thickness t31of the contact layer23after charge is in a range of about 0.5 μm to about 1.5 μm, and a thickness t32of the contact layer23after 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 anode20according to an embodiment, a thickness change rate of the contact layer23and a thickness change rate of the second anode active material layer222are each less than a thickness change rate of the first anode active material layer221.

A method of preparing the all-solid secondary battery1according to an embodiment includes providing an anode20; disposing the anode20on a surface of a solid electrolyte30; and disposing a cathode10on another surface of the solid electrolyte30.

FIGS.7A to7Dare illustrations of an exemplary embodiment of a method of preparing the anode20.

Referring toFIG.7A, a first layer321is formed on a first substrate100.

The first layer321may 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 layer321may 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 layer321may 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 substrate100may 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 substrate100may 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 substrate100may 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 substrate100may be, for example, in the form of a plate or a foil. The first substrate100may be an anode current collector21.

A second layer322is disposed on a second substrate.

The second layer322may 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 layer322may 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 layer322, the metal alloyable with lithium may be omitted.

In terms of forming the second layer322on 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 substrate200. The second layer322may function as a precursor of the second anode active material layer222.

The second substrate200may 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 substrate200may include a material having a predetermined hardness of about 100 megapascals or greater. An example of the material of the second substrate200may include stainless steel, but the material of the second substrate200is 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 substrate200may be, for example, in the form of a plate or a foil.

Referring toFIG.7B, the first layer321and the second layer322are disposed to face each other, and the first substrate100and the second substrate200may be pressed together at a predetermined pressure.

For example, the first substrate100and the second substrate200may be pressed using pressing plates1001and1002. The pressing plates1001and1002may be formed of a material having a predetermined hardness to facilitate the pressing of the first and second substrates100and200at a predetermined pressure. For example, a material of the pressing plates1001and1002may be stainless steel, but the material of the pressing plates1001and1002is not limited thereto.

As a result of the pressing, the first layer321and the second layer322move 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 toFIG.7C, while the first layer321and the second layer322are pressed at a predetermined pressure, the contact layer23, which is a third layer including the same metal as the metal in the first layer321, is formed between the second substrate200and the second layer322. Without being limited by theory, it is understood that the formation of the contact layer23occurs as a result of a portion of the first layer321moving through the second layer322.

When the first layer321includes lithium metal and the second layer322includes a metal alloyable with lithium, the metal included in the second layer322may form an alloy layer during the pressing by reacting with lithium in the first layer321and the contact layer23. Accordingly, the first layer321may be the first anode active material layer221including a lithium alloy, and the contact layer23may be a contact layer23including a lithium alloy.

When the metal alloyable with lithium is not included in the second layer322, the first layer321may be the first anode active material layer221including lithium metal, and the contact layer23may be a contact layer23including lithium metal.

In the pressing of the first layer321and the second layer322with a predetermined pressure, a portion of the lithium in the first layer321may be injected into the second layer322. Thus, the second layer322may be the second anode active material layer222including a carbon-based active material and lithium.

Referring toFIG.7D, by removing the second substrate200, the anode20is provided in which the first anode active material layer221, the second anode active material layer222, and the contact layer23are sequentially stacked on the first substrate100in this stated order by removing the second substrate200.

FIG.8is an image that shows the anode20according to an embodiment. Referring toFIG.8, after the pressing of the first layer321and the second layer322at a predetermined pressure and the removal of the second substrate200, it may be confirmed that a surface color of the anode20appears to be not black, which is the color of the second anode active material layer222including a carbon-based active material. In this regard, it may be confirmed that the contact layer23having a relatively bright color is formed on the second anode active material layer222.

In the preparing of the anode20, when the second substrate200is removed after pressing the first layer321and the second layer322, for example, with a predetermined pressure of about 150 MPa or less, the anode20has a structure in which the first layer321and the second layer322are attached to each other, as shown inFIG.9. Accordingly, it may be confirmed that a surface color of the anode20appears to be black, as shown inFIG.10, which is the color of the second anode active material layer222including a carbon-based active material.

FIGS.11to13are cross-section SEM images of the anode20prepared by using the above-described exemplary method.FIG.12is an enlarged view of a portion ofFIG.11, andFIG.13is an enlarged view of a portion ofFIG.12.

Referring toFIGS.11to13, it may be confirmed that the contact layer23having a thickness less than that of the first anode active material layer221is formed on the second anode active material layer222by undergoing the preparation method described above.

FIGS.14A to14Fare illustrations of an exemplary embodiment of a method of manufacturing the anode20.

Referring toFIGS.14A to14C, the method of manufacturing an anode according to the embodiment may include providing (e.g., preparing) a first stack LF1in which a first layer321and a second layer322are stacked on a first substrate100.

Referring toFIG.14A, in the preparing the first stack LF1, the first layer321disposed on the first substrate100and the second layer322disposed on the second substrate200are prepared.

The first layer321may include a metal. The metal may include lithium metal.

A material of the first layer321is not limited thereto and may include a lithium alloy. The first layer321may 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 layer321may comprise one of these alloys or lithium metal, or may comprise various alloys.

A thickness of the first layer321may 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 substrate100may 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 substrate100may 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 substrate100may comprise any metal selected therefrom alone or may comprise an alloy of at least two different metals or a coating material. The first substrate100may be, for example, in a form of a plate or a foil. The first substrate100may be an anode current collector21.

The second layer322may 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 layer322may 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 layer322, the metal alloyable with lithium may be omitted.

In terms of forming the second layer322on 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 substrate200, and the coated second substrate may be dried. The second layer322may function as a precursor electrode of the second anode active material layer222.

The second substrate200may 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 substrate200may include a material having a predetermined firmness. Examples of the material of the second substrate200may include stainless steel, but the material of the second substrate200is 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 substrate200may be, for example, in a form of a plate or a foil.

Since the preparation processes of the first layer321and the second layer322are the same as described in connection withFIG.7A, a detailed description thereof will be omitted.

Referring toFIG.14B, after the first layer321and the second layer322are disposed to face each other, the first substrate100and the second substrate200may be pressed such that the first substrate100and the second substrate200move closer to each other. Although not shown, the first substrate100and the second substrate200may 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 substrate100and the second substrate200may 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 layer321and the second layer322may be assembled while being in a close contact with each other. As the first layer321and the second layer322are pressed with less than a certain level of pressure, the first layer321may be attached to the second layer322without forming a separate contact layer23between the second substrate200and the second layer322.

Referring toFIG.14C, the second substrate200may be removed from the second layer322. By removing the second substrate200, the first stack LF1in which the first layer321and the second layer322are stacked on the first substrate100may be manufactured.

Referring toFIG.14D, the method of manufacturing the anode according to the embodiment, may include preparing a second stack LF2including a third layer323disposed on the solid electrolyte30, apart from the first stack LF1.

The third layer323may be deposited on the solid electrolyte30. For example, the third layer323which is deposited on the solid electrolyte may be thinner than the first layer321. The thickness t3of the third layer323deposited on the solid electrolyte30may be less than or equal to a predetermined thickness. For example, the thickness t3of the third layer323may be about 1 μm or less. For example, the thickness t3of the third layer323may be about 0.5 μm or less. For example, the thickness t3of the third layer323may be about 0.1 μm or less. The thickness of the third layer323may 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 layer323may be in the range of about 10° C. to about 90° C. The deposition temperature of the third layer323may be in the range of about 15° C. to about 50° C. The deposition temperature of the third layer323may be in the range of about 20° C. to about 35° C.

The third layer323may 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 LF2is performed separately from the preparation of the first stack LF1, the preparation of the second stack LF2may be performed simultaneously with the preparation of the first stack LF1, or before the preparation of the first stack LF1, or after the preparation of the first stack LF1.

Referring toFIG.14E, the second layer322and the third layer323may be disposed to face each other, and pressing may be performed such that the first stack LF1and the second stack LF2move closer to each other. Although not shown, the first substrate100of the first stack LF1and the solid electrolyte30of the second stack LF2may be pressed by a pressing plate (not shown).

A pressure applied to the first substrate100of the first stack LF1and the solid electrolyte30of second stack LF2may 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 substrate100of the first stack LF1and the solid electrolyte30of the second stack LF2is 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 toFIG.14F, by pressing, the third layer323and the second layer322may be assembled to be in close contact with each other.

When the third layer323and the second layer322are pressed with a certain level of pressure, or greater, for example, the pressure of 250 MPa or greater, a portion of the first layer321, for example, lithium, may move through the second layer322. In this case, the third layer323may be converted into a layer containing lithium alloy.

Since the certain level of pressure is applied to the first stack LF1and the second stack LF2, the third layer323and the second layer322may be attached to each other. Accordingly, an anode in which the contact layer23, the second anode active material layer222, the first anode active material layer221, and the anode current collector21may be sequentially stacked on the solid electrolyte30, can be manufactured.

FIGS.15A to15Fare illustrations of an exemplary embodiment of aa method of manufacturing an anode20.

Referring toFIG.15A, the method of manufacturing an anode according to an embodiment may include preparing a first stack LF1A including the first layer321disposed on the first substrate100.

The first layer321may include a metal. The metal may include lithium metal.

A material of the first layer321is not limited thereto and may include a lithium alloy. The first layer321may 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 layer321may comprise one of these alloys, lithium metal, or may comprise various alloys.

A thickness of the first layer321may 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 substrate100may 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 substrate100may 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 substrate100may comprise any metal selected therefrom alone or may comprise an alloy of at least two different metals or a coating material. The first substrate100may be, for example, in a form of a plate or a foil. The first substrate100may be an anode current collector21.

Referring toFIGS.15B to15D, the method of manufacturing the anode according to the embodiment may include preparing a second stack LF2A in which the third layer323and the second layer322are sequentially stacked the solid electrolyte30, apart from the preparation step of the first stack LF1A.

Referring toFIG.15B, preparing the second stack LF2A may include preparing a third layer323formed on the solid electrolyte30. For example, the third layer323may be formed on the solid electrolyte30by deposition.

The third layer323may 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 layer323which is deposited on the solid electrolyte may be thinner than the first layer321. A thickness t3of the third layer323may be a predetermined thickness or less. For example, the thickness t3of the third layer323may be about 1 μm or less. For example, the thickness t3of the third layer323may be about 0.5 μm or less. For example, the thickness t3of the third layer323may be about 0.1 μm or less. The thickness of the third layer323may 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 LF2A may include preparing the second layer322formed on the second substrate200.

The second layer322may 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 layer322may 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 layer322, the metal alloyable with lithium may be omitted.

In terms of forming the second layer322on 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 substrate200, and the coated second substrate may be dried. The second layer322may function as a precursor electrode of the second anode active material layer222.

The second substrate200may 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 substrate200may include a material having a predetermined firmness. Examples of the material of the second substrate200may include stainless steel, but the material of the second substrate200is 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 substrate200may be, for example, in a form of a plate or a foil.

Referring toFIG.15C, the third layer323and the second layer322may be disposed to face each other, and pressing may be performed such that the solid electrolyte30and the second substrate200move closer to each other.

The pressure applied to the solid electrolyte30and the second substrate200may 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 layer323and the second layer322may be assembled while being in a close contact with each other.

Referring toFIG.15D, the second substrate200may be removed from the second layer322. By removing the second substrate200, a second stack LF2A in which the third layer323and the second layer322are sequentially stacked on the solid electrolyte30may be manufactured.

Referring toFIGS.15E and15F, pressing may be applied such that, while the second layer322and the first layer321face each other, the second stack LF2A and the first stack LF1A come close to each other. The first layer321and the second layer322may be attached by pressing.

The pressure applied to the first stack LF1A and the second stack LF2A 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 LF1A and the second stack LF2A, a portion of the first layer321may pass through the second layer322and react with the third layer323. For example, lithium in the first layer321moves through the second layer322, so that the third layer323may include a lithium alloy.

Since the first stack LF1A and the second stack LF2A are pressed, the third layer323and the second layer322may be attached to each other. Accordingly, an anode in which the contact layer23, the second anode active material layer222, the first anode active material layer221, and the anode current collector21may be sequentially stacked on the solid electrolyte30, 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 layer12such 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 collector11. The obtained stack is pressed to prepare a cathode10. 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 layer12is compressed into the form of a pellet or stretched (molded) in the form of sheet to prepare the cathode10. When the cathode10is prepared in this manner, the cathode current collector11may be omitted. In some embodiments, the cathode10may be used by being impregnated with an electrolyte solution.

Preparation of Solid Electrolyte

A solid electrolyte30including 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 electrolyte30is 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 electrolyte30including 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., Li2S and P2S5, 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 Li2S and P2S5may 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., Li2S and P2S5, 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 electrolyte30. In some embodiments, the solid electrolyte30may be prepared by pressing a plurality of the solid electrolyte particles. In some embodiments, the solid electrolyte30may 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 anode20which is prepared by the anode manufacturing method 1 described above, the cathode10, and the solid electrolyte30prepared as described above are stacked in such a way that the cathode10and the anode20have the solid electrolyte30disposed therebetween to prepare a stack, and the stack is pressed to prepare an all-solid secondary battery1.

For example, the contact layer23of the anode20is disposed to face a surface of the solid electrolyte30, and the anode20and the solid electrolyte30are pressed at a predetermined pressure to attach the anode20to the surface of the solid electrolyte30.

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 anode20prepared by the anode manufacturing methods 2 and 3 is attached to the solid electrolyte30, the attaching of the anode20to one side of the solid electrolyte30may be omitted.

Next, the cathode10is disposed on a surface of the solid electrolyte30which is different from (e.g., opposite to) the surface on which the anode20is disposed, and the resultant is pressed with a predetermined pressure to attach the cathode10to the other surface of the solid electrolyte30.

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

(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 Li6.5La3Zr1.5Ta0.5O12(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 Li6.5La3Zr1.5Ta0.5O12(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 Li6.5La3Zr1.5Ta0.5O12(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 Li6.5La3Zr1.5Ta0.5O12(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 Li6.5La3Zr1.5Ta0.5O12(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 Li6.5La3Zr1.5Ta0.5O12(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

A Li6.5La3Zr1.5Ta0.5O12(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.

LiNi0.8Co0.15Mn0.05O2(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).

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

A Li6.5La3Zr1.5Ta0.5O12(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

A Li6.5La3Zr1.5Ta0.5O12(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

A Li6.5La3Zr1.5Ta0.5O12(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

A solid electrolyte having a Li6.5La3Zr1.5Ta0.5O12(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 inFIGS.16and17.

Referring toFIGS.16and17, 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·cm2, 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·cm2.

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/cm2) 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/cm2) 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/cm2) cathode were used.

As shown inFIG.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/cm2, and, as shown inFIG.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/cm2. As shown inFIG.20, even though the contact layer and the first anode active material layer were included, a short circuit occurred at 0.7 mA/cm2in the structure having an anode that does not include a carbon layer (Comparative Example 4).

On the other hand, as shown inFIG.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/cm2.

Meanwhile, as shown inFIG.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/cm2, the discharge capacity was 2 mAh/cm2or less.

On the other hand, as shown inFIG.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/cm2, and the difference in the discharge capacity according to the current density was small. For example, at 2.0 mA/cm2, the discharge capacity was 4 mAh/cm2or greater. As shown inFIG.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/cm2, and the difference in the discharge capacity according to the current density was small. For example, at 2.0 mA/cm2, the discharge capacity was 4 mAh/cm2or greater. As shown inFIG.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/cm2, and the difference in the discharge capacity according to the current density was small. For example, at 2.0 mA/cm2, the discharge capacity was 4 mAh/cm2or greater. As shown inFIG.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/cm2, and the difference in the discharge capacity according to the current density was small. For example, at 1.6 mA/cm2, the discharge capacity was 2.4 mAh/cm2or 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.