Patent Description:
A solid secondary battery includes a cathode, a solid electrolyte, and an anode. For the solid electrolyte among these components, high ionic conductivity is desired.

Solid electrolytes include sulfide solid electrolytes and oxide-based solid electrolytes. To use these solid electrolytes in a solid secondary battery, it is desirable to reduce grain boundaries between crystal particles of the solid electrolyte.

In a case of manufacturing a solid secondary battery using a sulfide solid electrolyte as a solid electrolyte, the solid secondary battery may be manufactured by pressing the sulfide solid electrolyte. Also, the solid secondary battery employing the sulfide solid electrolyte may produce toxic sulfide gas when exposed to the air. Accordingly, a sulfide solid electrolyte for a solid secondary battery would desirably provide improved manufacturability and have improved good stability in air.

In a case of manufacturing a solid secondary battery using an oxide-based solid electrolyte as a solid electrolyte, due to the physical characteristics of the oxide-based solid electrolyte, improvement in the uniformity of the interfacial adhesion between the solid electrolyte and a cathode is desired.

<CIT> discloses solid-state lithium ion electrolytes of lithium fluoride based composites which contain an anionic framework capable of conducting lithium ions.

<NPL>, report a low-temperature ionic liquid method to synthesize nanostructured Li-rich fluoride solid electrolyte Li<NUM>GaF<NUM>, which is characterized by open-framework structured grains and ionic liquid decorated grain boundaries.

<CIT> discloses an open framework fluorine-based solid-state electrolyte material and a preparation method of the open framework fluorine-based solid-state electrolyte material.

<CIT> discloses compositions related to an electronically insulating amorphous or nanocrystalline mixed ionic conductor composition comprising a metal fluoride composite to which an electrical potential is applied to form <NUM>) a negative electrode, and <NUM>) a positive electrode, wherein the negative electrode and positive electrode are formed in situ.

Provided are a novel solid electrolyte and a method of preparing the same.

Provided is an electrochemical device including the solid electrolyte.

Provided is an electrochemical battery including the solid electrolyte.

According to an aspect of the invention, there is provided a solid electrolyte in accordance with claim <NUM>.

According to an embodiment, there is provided a protected cathode comprising:
a cathode; and a layer comprising the solid electrolyte of claim <NUM> on the cathode.

According to another embodiment, there is provided an electrochemical device including the solid electrolyte.

According to another embodiment, there is provided an electrochemical battery including: a cathode, an anode, and the solid electrolyte disposed between the cathode and the anode.

According to another aspect of the invention, there is provided a method of preparing the solid electrolyte in accordance with claim <NUM>.

It will be understood that, although the terms "first," "second," "third," etc. may be used herein to describe various elements, components, regions, layers, and/or sections, these elements, components, regions, layers, and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Thus, "a first element," "component," "region," "layer," or "section" discussed below could be termed a second element, component, region, layer, or section without departing from the teachings herein.

" 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.

Thus, the term "below" can encompass both an orientation of above and below.

Hereinafter, embodiments of a solid electrolyte, a method of preparing the same, and an electrochemical device and an electrochemical battery, each including the solid electrolyte, will be described in greater detail.

According to an aspect of the invention, there is provided a solid electrolyte including a compound represented by Formula <NUM> or <NUM>, wherein the compound represented by Formula <NUM> or <NUM> has a glass transition temperature of -<NUM> or lower and a glass or glass-ceramic structure.

Formula <NUM>     AQX-Ga<NUM>-zMz1(F<NUM>-kClk)<NUM>-3zZ3z1.

Formula <NUM>     AQX-aMz1Z3z1-bGa<NUM>-z(F<NUM>-kClk)<NUM>-3z.

The term "glass" used herein refers to an amorphous material exhibiting a glass transition phenomenon. The term "glass-ceramic" refers to a mixture of an amorphous material and at least one crystalline material. In the glass-ceramic, two components are observed, a glass phase (i.e., an amorphous phase) and a ceramic phase (i.e., a crystalline phase).

In Formula <NUM>, a and b are not both <NUM> at the same time, and <NUM><A<<NUM>.

The compound of Formula <NUM> or <NUM> and a solid electrolyte including the same may exhibit a glass transition phenomenon, and the solid electrolyte may have a glass transition temperature that is lower than the operation temperature of a battery. Accordingly, it may be easy to form the solid electrolyte as desired.

The above-described glass transition phenomenon is identified through differential scanning calorimetry (DSC) analysis. The compound of Formula <NUM> may have a glass transition temperature of about -<NUM> or lower, -<NUM> or lower, -<NUM> or lower, or for example, about -<NUM> to about -<NUM>, or about -<NUM> to about -<NUM>, about -<NUM> to about -<NUM>, or about -<NUM> to about -<NUM>.

To manufacture a solid secondary battery having improved safety, development of a solid secondary battery employing an oxide-based solid electrolyte that is stable in the air is desired. However, and while not wanting to be bound by theory, it is understood that due to the hard physical properties of the oxide-based solid electrolyte, contact between the solid electrolyte and a cathode is not uniform at the interface thereof. To provide more uniform contact between the cathode and the oxide-based solid electrolyte, there has been suggested a high-temperature sintering process of the cathode and the oxide-based solid electrolyte.

However, when high-temperature sintering is used, providing the battery structure through total solidification of a solid secondary battery while also satisfying general characteristics of the battery has been difficult. To resolve these problems, it has been suggested to introduce an ionic liquid electrolyte between the oxide-based solid electrolyte and the cathode to allow the oxide-based solid electrolyte and the cathode to contact each other more uniformly. However, introducing an ionic liquid electrolyte according to this method may cause corrosion of a current collector by the ionic liquid electrolyte and complicate processes in designing a stacked structure of the battery.

Therefore, to solve the above-described problems, the inventors disclose a solid electrolyte including the compound represented by Formula <NUM> and having a glass or glass-ceramic structure.

The solid electrolyte according to an embodiment is a halogen compound-based solid electrolyte having good formability, and can be provided without use of a high pressure, which is used to manufacture a solid secondary battery using a sulfide solid electrolyte. When manufacturing a battery using the disclosed solid electrolyte, interfacial characteristics having improved uniformity between the solid electrolyte and a cathode are provided.

The compound of Formula <NUM> comprises gallium (Ga), fluorine (F), and Cl, Br or I, and thus contain different halogens.

In one or more embodiments, the solid electrolyte may have a water content of <NUM> weight percent (wt%) or less, <NUM> wt%, or greater than <NUM> wt% and <NUM> wt% or less, based on a total weight of the solid electrolyte.

The solid electrolyte may have a water content of, for example, <NUM> wt%.

The term "water content" used herein refers to water present inside and/or on the surface of the solid electrolyte.

In a solid electrolyte which is sensitive to moisture, the absorbed moisture may decompose to produce a large amount of gas, and thus deteriorate the battery. Accordingly, it is common to reduce the content of moisture in the solid electrolyte.

However, in the solid electrolyte according to an embodiment, viscosity characteristics and conductivity may both be improved even when the water content is greater than <NUM> wt% and <NUM> wt% or less, unlike other solid electrolytes.

The solid electrolyte may have a water content of about <NUM> wt% to <NUM> wt%, <NUM> wt% to <NUM> wt%, about <NUM> wt% to about <NUM> wt%, for example, about <NUM> wt% to about <NUM> wt%, based on a total weight of the solid electrolyte.

The water content of the solid electrolyte may be determined using, for example, a thermogravimetric analysis method. In the thermogravimetric analysis, the water content of the solid electrolyte may be measured in air using a thermogravimetric analyzer, e.g., a TA Instruments SDT-Q600, over the temperature range from <NUM> to <NUM> at a heating/cooling rate of <NUM> per minute, and determined from a weight loss before and after, e.g., at <NUM>.

In one or more embodiments, the water content of the solid electrolyte may vary according to the water content of QX in a starting materials for forming the solid electrolyte including the compound of Formula <NUM> or Formula <NUM>, e.g., i) a mixture of QX and Ga<NUM>-z(F<NUM>-kClk)<NUM>-3z, ii)a mixture of QX, Mz1Z3z1, and Ga<NUM>-z(F<NUM>-kClk)<NUM>-3z, or iii)a mixture of QX and Ga<NUM>-zMz1(F<NUM>-kClk)<NUM>-3zZ3z1. Here, <NUM>≤z<<NUM>.

In Formula <NUM> or <NUM>, a and b are not both <NUM> at the same time, and <NUM><A<<NUM>.

The water content of QX may be about <NUM> wt% or less, about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, for example, about <NUM> to about <NUM> wt%.

To obtain QX having a water content of about <NUM> wt% or less, heat treatment may further be performed at about <NUM> to about <NUM>, about <NUM> to about <NUM>, for example, about <NUM> to about <NUM>. Through this heat treatment process, the water content in QX may be further reduced. The heat treatment time may be varied according to the heat treatment temperature, and may be, for example, within the range of about <NUM> to about <NUM> hours, about <NUM> to about <NUM> hours, or about <NUM> to about <NUM> hours.

In the solid electrolyte according to one or more embodiments, moisture may form a complex with the compound of Formula <NUM> constituting the solid electrolyte and thus have a hydrate form.

In the solid electrolyte according to one or more embodiments, moisture may be present in the form of being adsorbed on the surface of the solid electrolyte. In the solid electrolyte according to one or more embodiments, moisture may be adsorbed on the surface of the solid electrolyte and contained inside the solid electrolyte. In the solid electrolyte according to one or more embodiments, the water content may be highest on the surface of the solid electrolyte and may be gradually reduced towards the inside thereof.

In Formula <NUM>, when Q is a combination of Li and Na, K, or a combination thereof, a molar fraction of the Na and K may be about <NUM> to about <NUM>, about <NUM> to about <NUM>, for example, or about <NUM> to about <NUM>. A total molar fraction of Li and Na and K may be <NUM>.

In Formula <NUM>, Q may be Li or a combination of Li and Na.

In Formula <NUM>, <NUM>≤z<<NUM>, <NUM>≤z≤<NUM>, <NUM>≤z≤<NUM>, <NUM>≤z≤<NUM>, <NUM>≤z≤<NUM>, or <NUM>≤z≤<NUM>.

The compound of Formula <NUM> or <NUM> may be a compound represented by Formula <NUM>.

Formula <NUM>     ALiX-Ga<NUM>-zMz1(F<NUM>-kClk)<NUM>-3zZ3z1.

In Formula <NUM>, a and b are not both <NUM>. In Formula <NUM>, <NUM><A≤<NUM>, <NUM><A<<NUM>, <NUM>≤A≤<NUM>, or <NUM><A<<NUM>. In Formula <NUM>, <NUM>≤z≤<NUM>, <NUM>≤z≤<NUM>, <NUM>≤z≤<NUM>, <NUM>≤z≤<NUM>, or <NUM>≤z≤<NUM>.

In one or more embodiments, the compound of Formula <NUM> or <NUM> may be a compound represented by Formula <NUM>.

Formula <NUM>     ALiX-aMz1Z3z1-bGa<NUM>-z(F<NUM>-kClk)<NUM>-3z.

In one or more embodiments, the solid electrolyte may have an ionic conductivity at room temperature (<NUM>) of <NUM>/cm or greater, about <NUM>/cm or greater, about <NUM>/cm or greater, about <NUM>/cm or greater, or about <NUM>/cm or greater.

In one or more embodiments, the solid electrolyte may have an ionic conductivity at room temperature (<NUM>) of about <NUM>/cm to about <NUM>/cm, for example, about <NUM>/cm to about <NUM>/cm. Since the solid electrolyte has a high ionic conductivity, an electrochemical battery including the solid electrolyte may have further reduced internal resistance.

The solid electrolyte may have an activation energy at <NUM> of <NUM> meV to <NUM> meV.

For example, the compound of Formula <NUM> or <NUM> may be a compounds of Formulae <NUM> to <NUM>, or a combination thereof.

In Formula <NUM>, A may be <NUM>, <NUM>, or <NUM>.

Formula <NUM>     ALiCl-aMz1Z3z1-bGaF<NUM> wherein, in Formula <NUM>, A is <NUM> or <NUM>,.

<NUM><a<<NUM>, <NUM><b<<NUM>, <NUM><a+b, a+b=<NUM>-A, and <NUM>≤z1≤<NUM>.

In Formula <NUM>, <NUM>≤a≤<NUM>, and <NUM>≤b≤<NUM>.

For example, the compound of Formula <NUM> or <NUM> may be 2LiCl-GaF<NUM>, 3LiCl-GaF<NUM>, 4LiCl-GaF<NUM>, 3LiBr-GaF<NUM>, 2LiCl-LiOH-GaF<NUM>, 3LiCl-<NUM>. 1LaCl<NUM>-<NUM>. 9GaF<NUM>, 3LiCl-<NUM>. 1InCl<NUM>-<NUM>. 9GaF<NUM>, 3LiCl-<NUM>. 1ScCl<NUM>-<NUM>. 9GaF<NUM>, 3LiCl-<NUM>. 1AlCl<NUM>-<NUM>. 9GaF<NUM>, 3LiCl-<NUM>. 1TlCl<NUM>-<NUM>. 9GaF<NUM>, 3LiCl-<NUM>. 1YCl<NUM>-<NUM>. 9GaF<NUM>, 3LiCl-<NUM>. 1BCl<NUM>-<NUM>. 9GaF<NUM> , 2LiBr-GaF<NUM>, 4LiBr-GaF<NUM>, 2LiClO<NUM>-GaF<NUM>, 2LiClO<NUM>-LiOH-GaF<NUM>, 3LiCl-NaCl-GaF<NUM>, 3LiCl-<NUM>. 2LaCl<NUM>-<NUM>. 8GaF<NUM>, 3LiCl-<NUM>. 2lnCl<NUM>-<NUM>. 8GaF<NUM>, 3LiCl-<NUM>. 3LaCl<NUM>-<NUM>. 7GaF<NUM>, 3LiCl-<NUM>. 3lnCl<NUM>-<NUM>. 7GaF<NUM>, 3LiCl-<NUM>. 5LaCl<NUM>-<NUM>. 5GaF<NUM>, 3LiCl-<NUM>. 5lnCl<NUM>-<NUM>. 5GaF<NUM>, 3LiCl-<NUM>. 2ScCl<NUM>-<NUM>. 8GaF<NUM>, 3LiCl-<NUM>. 3ScCl<NUM>-<NUM>. 7GaF<NUM>, 3LiCI-<NUM>. 5ScCl<NUM>-<NUM>. 5GaF<NUM>, 3LiCl-<NUM>. 2AlCl<NUM>-<NUM>. 8GaF<NUM>, 3LiCl-<NUM>. 3AlCl<NUM>-<NUM>. 7GaF<NUM>, 3LiCl-<NUM>. 5AlCl<NUM>-<NUM>. 5GaF<NUM>, 3LiCl-<NUM>. 2BCl<NUM>-<NUM>. 8GaF<NUM>, 3LiCl-<NUM>. 3BCl<NUM>-<NUM>. 7GaF<NUM>, 3LiCl-<NUM>. 5BCl<NUM>-<NUM>. 5GaF<NUM>, 3LiCl-<NUM>. 2TlCl<NUM>-<NUM>. 8GaF<NUM>, 3LiCl-<NUM>. 3TlCl<NUM>-<NUM>. 7GaF<NUM>, 3LiCl-<NUM>. 5TlCl<NUM>-<NUM>. 5GaF<NUM>, 3LiCI-<NUM>. 2YCl<NUM>-<NUM>. 8GaF<NUM>, 3LiCl-<NUM>. 3YCl<NUM>-<NUM>. 7GaF<NUM>, 3LiCl-<NUM>. 5YCl<NUM>-<NUM>. 5GaF<NUM>, 2LiCl-GaF<NUM>Cl, 4LiCl-GaF<NUM>Cl, 3LiBr-GaF<NUM>Cl, 2LiCl-LiOH-GaF<NUM>Cl, 2LiCl-1NaCl-GaF<NUM>, 2LiCl-1KCI-GaF<NUM>, 3LiCl-GaF<NUM>Cl, 2LiCl-<NUM>. 1AlCl<NUM>-<NUM>. 9GaF<NUM>, 2LiCl-<NUM>. 1ScCl<NUM>-<NUM>. 9GaF<NUM>, 2LiCl-<NUM>. 1BCl<NUM>-<NUM>. 9GaF<NUM>, 2LiCl-<NUM>. 1YCl<NUM>-<NUM>. 9GaF<NUM>, 4LiCl-<NUM>. 1AlCl<NUM>-<NUM>. 9GaF<NUM>, 4LiCl-<NUM>. 1ScCl<NUM>-<NUM>. 9GaF<NUM>, 4LiCl-<NUM>. 1BCl<NUM>-<NUM>. 9GaF<NUM>, 4LiCl-<NUM>. 1YCl<NUM>-<NUM>. 9GaF<NUM>, or a combination thereof.

A CI 2p peak, obtained by X-ray photoelectron spectroscopy (XPS) analysis of the compound of Formula <NUM>, may appear at a binding energy of about <NUM> eV to about <NUM> eV. The Cl 2p peak, a peak associated with Ga-X, such as a Ga-CI bond, may be shifted towards a higher binding energy than a Cl 2p peak for a simple blend of LiX and GaF<NUM>.

In one or more embodiments, the compound of Formula <NUM> or <NUM>, when analyzed by XRD with Cu Kα radiation, may exhibit a main peak at a diffraction angle (2θ) of <NUM>° to <NUM>°, and a minor peak at diffraction angles (2θ) of <NUM>° to <NUM>°. The term "main peak" as used herein refers to a peak having the maximum intensity, and main and minor peaks are associated with crystalline characteristics like LiCI, and minor peaks have smaller intensity than the main peak.

In one or more embodiments, the compound of Formula <NUM> or <NUM>, as obtained by XRD with Cu Kα radiation, may exhibit peaks at diffraction angles (2θ) of <NUM>° to <NUM>°, <NUM>° to <NUM>°, and <NUM>° to <NUM>°.

In one or more embodiments, the compound of Formula <NUM> or <NUM>, as obtained by XRD with Cu Kα radiation, may exhibit peaks in a region of diffraction angles (2θ) of <NUM>° to <NUM>°, a region of diffraction angles (2θ) of <NUM>° to <NUM>°, a region of diffraction angles (2θ) of <NUM>° to <NUM>°, and a region of diffraction angles (2θ) of <NUM>° to <NUM>°.

Rheological characteristics of the solid electrolyte according to one or more embodiments will now be described.

The solid electrolyte may have a loss modulus of about Pa or greater, about <NUM>,<NUM> Pa or greater, about <NUM>,<NUM> Pa or greater, about <NUM>,<NUM> Pa or greater, for example, about <NUM>,<NUM> Pa to about <NUM>,<NUM>,<NUM> Pa, and the solid electrolyte may have a loss modulus of about <NUM> MPa or less, about <NUM> MPa or less, or about <NUM> MPa or less, where the upper and lower bounds are independently combinable. In one or more embodiments, the solid electrolyte may have a loss modulus of about <NUM> MPa to about <NUM> MPa, or about <NUM> MPa to about <NUM> MPa.

The loss modulus (G") and the storage modulus (G') is measured according to ASTM D4065, D4440, or D5279, and may be evaluated by measurement of the viscosity of the solid electrolyte using a rheometer while varying a shear rate. In more detail, the viscosity of the solid electrolyte may be measured using a cone and plate rheometer, e.g., a TA Instruments AR <NUM> analyzer.

After a solid electrolyte (sample) having a thickness of about <NUM> millimeter (mm) is disposed between a cone having a cone angle of <NUM>° and a plate having a diameter of <NUM>, the interval between the cone and the plate is adjusted, and then a stress is applied to the sample while the shear rate is varied, to perform a rheological evaluation.

The solid electrolyte may have flexible properties and be made into a thin film having a thickness of <NUM> micrometers (µm) or less. The solid electrolyte may have a thickness of, for example, about <NUM> to <NUM>, for example, about <NUM> to about <NUM>. Since the solid electrolyte has flexible properties, manufacture of a flexible solid secondary battery using the solid electrolyte may be facilitated.

The composition of the solid electrolyte may be determined through inductively coupled plasma (ICP) spectrometry.

In one or more embodiments, when the solid electrolyte has a water content of about <NUM> wt% to about <NUM> wt%, based on a total weight of the solid electrolyte, the solid electrolyte may have an ionic conductivity of <NUM>/cm or greater. The solid electrolyte may exhibit characteristics in which ionic conductivity rapidly increases when moisture is absorbed. As such, due to excellent sensitivity to moisture, the solid electrolyte may be used as an electrochemical-based sensor like a moisture sensor.

The temperature at which viscosity characteristics of the solid electrolyte are maintained may be about -<NUM> to about <NUM>.

When the compound of Formula <NUM> or <NUM> has a glass-ceramic structure, the amount of the ceramic may be about <NUM> wt% to <NUM> wt%, based on a total weight of the solid electrolyte. The amount of the ceramic may be varied according to the amount of QX, for example, LiCI, among the starting materials for forming the solid electrolyte including the compound of Formula <NUM>.

The compound of Formula <NUM> may be electrochemically stable at a voltage of about <NUM>. 0V to about <NUM>. 6V, for example, about <NUM>. 4V to about <NUM> V, with respect to lithium metal. The compound of Formula <NUM> may be present in the form of particles. The particles may have an average particle diameter of about <NUM> to about <NUM>, for example, about <NUM> to about <NUM>, for example, about <NUM> to about <NUM>, and have a specific surface area of about <NUM><NUM>/g to about <NUM><NUM>/g, for example, about <NUM><NUM>/g to about <NUM><NUM>/g.

A method of preparing the solid electrolyte according to one or more embodiments will be described.

First, i) a mixture of QX and Ga<NUM>-z(F<NUM>-kClk)<NUM>-3z, ii) a mixture of QX, Mz1Z3z1, and Ga<NUM>-z(F<NUM>-kClk)<NUM>-3z, or iii) a mixture of QX and Ga<NUM>-zMz1(F<NUM>-kClk)<NUM>-3zZ3z1 may be provided. A solid electrolyte may be obtained by subjecting the mixture to mechanical milling.

The amount of each component in the mixture may be stoichiometrically controlled so as to obtain the compound represented by Formula <NUM>. In the mixtures, i.e.,. , i) a mixture of QX and Ga<NUM>-z(F<NUM>-kClk)<NUM>-3z, ii) a mixture of QX, Mz1Z3z1, and Ga<NUM>-z(F<NUM>-kClk)<NUM>-3z, or iii) a mixture of QX and Ga<NUM>-zMz1(F<NUM>-kClk)<NUM>-3zZ3z1, Q, X, M, Z, and z are defined the same as Q, X, M, Z, and z in Formula <NUM> or <NUM>.

Mechanical milling applies the principle of generating surface energy from mechanical energy to coat interfaces having high surface energies by adhesion and/or fusion.

Mechanical milling may be implemented via mechanical friction of the components in a mixture, and for example, a compression stress may be applied mechanically via rotation at a rotation speed of about <NUM> rpm to about <NUM>,<NUM> rpm, about <NUM> rpm to about <NUM>,000rpm, or about <NUM> rpm to about <NUM> rpm.

Mechanical milling may be performed, for example, using a method of ball milling, air jet milling, bead milling, roll milling, planetary milling, hand milling, high-energy ball milling, stirring ball milling, vibrating milling, mechanofusion milling, shaker milling, attritor milling, disk milling, shape milling, NAUTA milling, NOBILTA milling, high-speed mixing, or a combination thereof, but is not limited thereto. Mechanical milling may be performed using, for example, ball milling, airjet milling, bead milling, roll milling, planetary milling, hand milling, or the like.

Mechanical milling may be performed, for example, under an inert gas atmosphere. The inert gas atmosphere may be created using an inert gas such as nitrogen, argon, helium, or the like.

The solid electrolyte preparation method may further include, after mechanical milling, a step of leaving to stand. Through the step of leaving to stand, the temperature of the product from the mechanical milling may be cooled down. Through the step of leaving to stand, for example, the temperature of the product from the mechanical milling may be controlled to be <NUM> or lower, for example, about <NUM> to <NUM>.

A separate heat treatment process can be omitted for the solid electrolyte according to one or more embodiments, unlike other methods of preparing a solid electrolyte. After the mechanical milling of the mixture for forming the solid electrolyte according to one or more embodiments, a separate heat treatment is not performed. If a thermal treatment process is further performed, it may be difficult to obtain the solid electrolyte according to one or more embodiments.

Through the mechanical milling of the mixture as described above, it may be possible to control the particle size of the product obtained from the mechanical milling. The particle size of the product obtained through the mechanical milling may be controlled to be about <NUM> or less, about <NUM> to about <NUM>, about <NUM> to about <NUM>, for example, about <NUM> to about <NUM>. When the particle size is controlled as above, the final solid electrolyte may have improved density. The term "particle size" as used herein may represent the diameter of particles when the particles are spherical, or the length of the major axis when the particles are non-spherical.

The mechanical milling may be, for example, high-energy milling. High-energy milling may be performed with, for example, Pulverisette <NUM> Premium line equipment at about <NUM> rpm to about <NUM> rpm, or about <NUM> rpm to about <NUM> rpm. Through such high-energy milling, the sizes of the components of the mixture may become fine and reaction there between occur more easily, and thus the solid electrolyte may be prepared within a shorter time.

After the step of leaving to stand is performed once, the mechanical milling step and the leaving to stand step may be repeatedly performed. One cycle of the steps of mechanical milling and leaving to stand may be repeatedly performed, for example, <NUM> to <NUM> cycles in total.

Although the mechanical milling time and the leaving to stand time may be variable, for example, the leaving to stand time may be controlled to be shorter than the mechanical milling time. The mechanical milling time may be, for example, about <NUM> minutes to about <NUM> hours, for example, about <NUM> hours to about <NUM> hours, and the standing time may be, for example, about <NUM> minute to about <NUM> minutes, about <NUM> minutes to about10 minutes, or about <NUM> minutes.

In the method according to one or more embodiments, QX may be LiX, or a mixture of LiX and NaX, KX, or a combination thereof. LiX may be LiCI, LiBr, LiOH, LiClO<NUM>, or a combination thereof.

The NaX, KX, or a combination thereof may be NaCl, NaBr, KCI, KBr, or a combination thereof.

In the method according to one or more embodiments, Mz1Z3z1 may be LaCl<NUM>, InCl<NUM>, AlCl<NUM>, YCl<NUM>, TlCl<NUM>, ScCl<NUM>, BCl<NUM>, or a combination thereof; Ga<NUM>-zF<NUM>-3z may be GaF<NUM>; and Ga<NUM>-zMz1(F<NUM>-kClk)<NUM>-3zZ3z may be LaCl<NUM>GaF<NUM>, InCl<NUM>GaF<NUM>, AlCl<NUM>GaF<NUM>, YCl<NUM>GaF<NUM>, TlCl<NUM>GaF<NUM>, ScCl<NUM>GaF<NUM>, BCl<NUM>GaF<NUM>, or a combination thereof.

According to another aspect, there is provided an electrochemical device including the solid electrolyte according to one or more embodiments.

The electrochemical device may be, for example, an electrochemical battery, an accumulator, a supercapacitor, a fuel cell, a sensor, or an electrochromic device. The sensor may be, for example, a moisture sensor.

According to another aspect, there is provided an electrochemical battery including the solid electrolyte according to one or more embodiments.

The electrochemical device may be a secondary battery including a cathode, an anode, and the solid electrolyte according to one or more embodiments interposed between the cathode and the anode.

The secondary battery may be a solid-electrolyte-containing secondary battery including: a cathode; an anode including lithium; and the solid electrolyte according to one or more embodiments interposed between the cathode and the anode. The secondary battery may be, for example, a lithium secondary battery, a lithium air battery, or a solid secondary battery. For example, the secondary battery may be a solid secondary battery.

The electrochemical battery may be used to provide a primary battery or a secondary battery. The shape of the electrochemical battery is not specifically limited and may be, for example, a coin, a button, a sheet, a stack, a cylinder, a plane, or a horn. The electrochemical battery according to one or more embodiments may be used in a medium- or large-sized battery for electric vehicles.

The electrochemical battery may be, for example, a solid secondary battery using a precipitation-type anode. The precipitation-type anode indicates an anode which has, at the time of assembly of an electrochemical battery, a coating layer including no anode active material, and the anode active material is formed through the precipitation of the anode active material, such as lithium metal, after charging of the electrochemical battery.

The solid electrolyte according to one or more embodiments may be a cathode electrolyte (catholyte), an electrolyte protective film, a cathode protective film, an anode protective film, or a combination thereof. A protected cathode comprises a cathode and layer comprising the solid electrolyte, i.e., a cathode protective film, thereon. A protected anode comprises an anode and a layer comprising the solid electrolyte, i.e., an anode protective film, thereon.

The solid electrolyte according to one or more embodiments may have a high oxidation stability potential of about <NUM> V or greater vs. Li/Li+, for example, <NUM> V to <NUM> V or greater vs. Li/Li+, and thus may be applicable as a catholyte, for example, a catholyte for an all-solid secondary lithium batteries.

The solid electrolyte according to one or more embodiments may replace an ionic liquid-containing electrolyte of a solid secondary battery using an existing oxide-based solid electrolyte.

The solid electrolyte according to one or more embodiments may be prepared using the compound of Formula <NUM>, and a sintering process may be avoided. The solid electrolyte according to one or more embodiments is flexible and has good formability, and thus may have a freeform. For example, the solid electrolyte according to one or more embodiments may be formed as an electrolyte having a thickness of about <NUM> or less through a roll-to-roll process.

The electrochemical battery may be a solid secondary battery. The solid secondary battery according to one or more embodiments may further include an oxide-based solid electrolyte which is stable in air.

The solid secondary battery may have a cathode/solid electrolyte/oxide-based solid electrolyte/lithium anode structure, where the solid secondary battery has layers as indicated and in the stated order.

The solid secondary battery may further include an ionic liquid-containing electrolyte and an oxide-based solid electrolyte to provide a cathode/ionic liquid-containing electrolyte/oxide-based solid electrolyte/solid electrolyte/oxide-based solid electrolyte/lithium anode structure, where the solid secondary battery has layers as indicated and in the stated order.

The lithium anode may be a lithium metal electrode or a lithium alloy electrode. When employing such a lithium anode, the solid secondary battery may have a high energy density per volume.

The oxide-based solid electrolyte may include a Garnet-based ceramic (Li<NUM>+xLa<NUM>M<NUM>O<NUM>) (wherein M may be Te, Nb, or Zr, and x may be an integer of <NUM> to <NUM>), lithium phosphorus oxynitride (LixPOyNz, wherein <NUM><x<<NUM>, <NUM><y<<NUM>, and <NUM><z<<NUM>) (LiPON), LixPyOzNk (wherein <NUM>≤x≤<NUM>, <NUM>≤y≤<NUM>, <NUM>≤z≤<NUM>, and <NUM>≤k≤<NUM>), LiwPOxNySz (wherein <NUM><w<<NUM>, <NUM><x<<NUM>, <NUM><y<<NUM>, and <NUM><z<<NUM>), Li<NUM>+x+yAlxTi<NUM>-xSiyP<NUM>-yO<NUM> (wherein <NUM><x<<NUM> and <NUM>≤y<<NUM>), BaTiO<NUM>, Pb(ZrxTi<NUM>-x)O<NUM> wherein <NUM>≤x≤<NUM>, Pb<NUM>-xLaxZr<NUM>-yTiyO<NUM> (PLZT) (wherein <NUM>≤x<<NUM> and <NUM>≤y<<NUM>), Pb(Mg<NUM>/<NUM>Nb<NUM>/<NUM>)O<NUM>-PbTiO<NUM> (PMN-PT), HfO<NUM>, SrTiO<NUM>, SnO<NUM>, CeO<NUM>, Na<NUM>O, MgO, NiO, CaO, BaO, ZnO, ZrO<NUM>, Y<NUM>O<NUM>, Al<NUM>O<NUM>, TiO<NUM>, SiO<NUM>, SiC, lithium phosphate (Li<NUM>PO<NUM>), lithium titanium phosphate (LixTiy(PO<NUM>)<NUM>) (wherein <NUM><x<<NUM> and <NUM><y<<NUM>), lithium aluminum titanium phosphate (LixAlyTiz(PO<NUM>)<NUM>) (wherein <NUM><x<<NUM>, <NUM><y<<NUM>, and <NUM><z<<NUM>), Li<NUM>+x+y(AlaGa<NUM>-a)x(TibGe<NUM>-b)<NUM>-xSiyP<NUM>-yO<NUM> (wherein <NUM>≤x≤<NUM>, <NUM>≤y≤<NUM>, <NUM>≤a≤<NUM> and <NUM>≤b≤<NUM>), lithium lanthanum titanate (LixLayTiO<NUM>, wherein <NUM><x<<NUM> and <NUM><y<<NUM>), lithium germanium thio phosphate (LixGeyPzSw) (wherein <NUM><x<<NUM>, <NUM><y<<NUM>, <NUM><z<<NUM>, and <NUM><w<<NUM>), lithium nitride-based glass (LixNy, wherein <NUM><x<<NUM> and <NUM><y<<NUM>), SiS<NUM>-based glass (LixSiySz, wherein <NUM><x<<NUM>, <NUM><y<<NUM>, and <NUM><z<<NUM>), P<NUM>S<NUM>-based glass (LixPySz, wherein <NUM><x<<NUM>, <NUM><y<<NUM>, and <NUM><z<<NUM>), Li<NUM>O, LiF, LiOH, Li<NUM>CO<NUM>, LiAlO<NUM>, a Li<NUM>O-Al<NUM>O<NUM>-SiO<NUM>-P<NUM>O<NUM>-TiO<NUM>-GeO<NUM>-based ceramic, or a combination thereof.

As the oxide-based solid electrolyte, for example, a Garnet-based oxide-based solid electrolyte having good reduction stability when in contact with a lithium anode may be used. For example, as the oxide-based solid electrolyte a Garnet-based ceramic (e.g., Li<NUM>+xLa<NUM>M<NUM>O<NUM>) (wherein M may be Te, Nb, or Zr, and x may be an integer of <NUM> to <NUM>), for example, LLZO (e.g., Li<NUM>La<NUM>Zr<NUM>Ta<NUM>O<NUM>), may be used.

The solid electrolyte according to one or more embodiments may be used as a cathode protective film in a solid secondary battery using an oxide-based solid electrolyte which is stable in air, to effectively reduce reaction between the oxide-based solid electrolyte and the cathode. The solid electrolyte according to one or more embodiments may be used as a cathode coating material to form a cathode protective film.

<FIG> is a schematic cross-sectional view illustrating a structure of a solid secondary battery according to an embodiment.

Referring to <FIG>, a first oxide-based solid electrolyte <NUM> and a solid electrolyte <NUM> according to an embodiment may be sequentially arranged on an anode <NUM>, and a cathode <NUM> is arranged adjacent to the solid electrolyte <NUM>. Thus, the solid electrolyte <NUM> is disposed between the first oxide-based solid electrolyte <NUM> and the cathode <NUM>, and the solid electrolyte <NUM> and the cathode <NUM> may uniformly contact each other without an ionic liquid-containing electrolyte. The solid electrolyte <NUM> may have good compatibility with the first oxide-based solid electrolyte <NUM>, and thus be used as a catholyte instead of an ionic liquid-containing electrolyte. The ionic liquid-containing electrolyte may be, for example, a liquid electrolyte containing an ionic liquid.

The ionic liquid may comprise, for example, N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidium bis(trifluoromethylsulfonyl)imide, <NUM>-butyl-<NUM>-methylimidazolium bis(trifluoromethylsulfonyl)imide, <NUM>-ethyl-<NUM>-methylimidazolium bis(trifluoromethylsulfonyl)imide, or a combination thereof.

<FIG> illustrates a structure of a solid secondary battery according to an embodiment.

Referring to <FIG>, an ionic liquid-containing electrolyte <NUM> may be arranged on a cathode <NUM>, and a second oxide-based solid electrolyte <NUM>', a solid electrolyte <NUM> according to an embodiment, and a first oxide-based solid electrolyte <NUM> may be sequentially arranged on the ionic liquid-containing electrolyte <NUM>. An anode <NUM> may be arranged adjacent to the first oxide-based solid electrolyte <NUM>. The anode <NUM> may be a lithium anode.

Due to the presence of the solid electrolyte <NUM> according to an embodiment, use of a high pressure for complete solidification may be avoided, and the cathode and the solid electrolyte may have improved uniformity at a contact interface therebetween.

A structure of a solid secondary battery <NUM> according to another embodiment will be described with reference to <FIG>.

As shown in <FIG>, the solid secondary battery <NUM> according to an embodiment may include a cathode <NUM>, an anode <NUM>, and a solid electrolyte <NUM> according to an embodiment.

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

For use as the cathode current collector <NUM>, for example, a plate structure or a foil structure, each made of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof, may be used. The cathode current collector <NUM> may be omitted.

The cathode active material layer <NUM> may include a cathode active material and a solid electrolyte. The solid electrolyte included in the cathode <NUM> may be similar to or different from the solid electrolyte <NUM>.

The cathode active material may be any cathode active material capable of reversible intercalation and deintercalation of lithium ions. For example, the cathode active material may be prepared using lithium cobalt oxide (LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium manganate, lithium iron phosphate, nickel sulfide, copper sulfide, lithium sulfide, iron oxide, or vanadium oxide. These cathode active materials may be used alone or in combination of two or more.

The cathode active material may be, for example, a lithium transition metal oxide such as LiNixCoyAlzO<NUM> (NCA) or LiNixCoyMnzO<NUM> (NCM) (wherein <NUM> < x < <NUM>, <NUM> < y < <NUM>, <NUM> < z < <NUM>, and x + y + z = <NUM>).

The cathode active material may be covered with a coating layer. In one or more embodiments, the coating layer may be any suitable coating layer of cathode active material for solid secondary batteries. An example of the coating layer may include, for example, Li<NUM>O-ZrO<NUM>.

When the cathode active material is formed of a lithium transition metal oxide such as NCA or NCM, and includes nickel (Ni), the capacity density of the solid secondary battery <NUM> may be increased, and the elution of metal from the cathode active material in a charged state may be reduced. Accordingly, long-term reliability and cycle characteristics of the solid secondary battery <NUM> according to an embodiment may be improved.

The cathode active material may be in the form of particles, for example, elliptical or spherical particles. The cathode active material may have a particle diameter, not specifically limited, within a range applied to cathode active materials of a solid secondary battery. In addition, the amount of the cathode active material of the cathode <NUM> is not specifically limited, and may be within a range applied to the cathode of a solid secondary battery. The particle size, shape, and amount of the cathode active material can be determined without undue experimentation.

In addition, the cathode <NUM> may include the cathode active material as described above and a solid electrolyte, and further additives, for example, a conducting agent, a binder, a filler, a dispersant, or an ion-conductive auxiliary agent, which may be appropriately mixed.

Examples of the conductive agent which can be mixed into the cathode <NUM> include graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and metal powder. Examples of the binder which can be mixed into the cathode <NUM> include styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidenefluoride, and polyethylene. The filler, the dispersant, and the ion-conductive auxiliary agent which can be mixed into the cathode <NUM> may be any suitable materials used for an electrode of a solid secondary battery.

The anode <NUM> may include an anode current collector <NUM> and a first anode active material layer <NUM>.

An anode active material included in the first anode active material layer <NUM> may be, for example, in the form of particles. The anode active material in the form of particles may have an average particle diameter of, for example, about <NUM> or less, <NUM> or less, about <NUM> or less, about <NUM> or less, or about <NUM> or less. The anode active material in the form of particles may have an average particle diameter of, for example, about <NUM> to about <NUM> or less, about <NUM> to about <NUM> or less, about <NUM> to about <NUM> or less, about <NUM> to about <NUM> or less, or about <NUM> to about <NUM> or less. As the anode active material has an average particle diameter within these ranges, this may further facilitate reversible absorption and/or desorption of lithium during charging and discharging. The average particle diameter of the anode active material is, for example, a median diameter (D50) measured using a laser particle size distribution analyzer.

The anode active material included in the first anode active material layer <NUM> may include, for example, a carbonaceous anode active material, a metal, or a metalloid anode active material, or combination thereof.

In particular, the carbonaceous anode active material may be amorphous carbon. The amorphous carbon may be, for example, carbon black (CB), acetylene black (AB), furnace black (FB), ketjen black (KB), graphene, or the like, but is not limited thereto. The amorphous carbon may be any suitable amorphous carbon material. The amorphous carbon may be a carbon having no or very low crystallinity and is distinguished from crystalline carbon or graphitic carbon.

The metal or metalloid anode active material includes gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or a combination thereof, but is not limited thereto. The metal or metalloid anode active material may be any suitable material used as a metal anode active material or metalloid anode active material that forms an alloy or compound with lithium in the art. For example, since nickel (Ni) does not form an alloy with lithium, nickel is not a metal anode active material.

The first anode active material layer <NUM> includes a single kind of anode active material or a mixture of a plurality of different anode active materials selected from these anode active materials. For example, the first anode active material layer <NUM> includes amorphous carbon alone, or gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or a combination thereof. In another example, the first anode active material layer <NUM> includes a mixture of amorphous carbon with gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or a combination thereof. A mixing ratio in a mixture of amorphous carbon and, for example, gold, may be, by weight, for example, <NUM>:<NUM> to <NUM>:<NUM>, <NUM>:<NUM> to <NUM>:<NUM>, or <NUM>:<NUM> to <NUM>:<NUM>, but is not limited thereto. The mixing ratio may be any suitable ratio selected according to desired characteristics of the solid secondary battery <NUM>. As the anode active material has such a composition, the solid secondary battery <NUM> has further improved cycle characteristics.

The anode active material included in the first anode active material layer <NUM> includes, for example, a mixture of amorphous carbon first particles and metal or metalloid second particles. The metal or metalloid includes, for example, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or the like. In other embodiments, the metalloid is a semiconductor. The amount of the second particles is about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, or about <NUM> wt% to <NUM> wt%, with respect to the total weight of the mixture. As the amount of the second particles is within these ranges, for example, the solid secondary battery <NUM> has further improved cycle characteristics.

The first anode active material layer <NUM> includes, for example, a binder. The binder may be, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene (PTEE), polyvinylidene fluoride (PVDF), polyethylene, a vinylidene fluoride/hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, or the like, but is not necessarily limited thereto. The binder may be any suitable material that is used as a binder in the art. The binder may consist of one binder alone or a plurality of different binders.

By the inclusion of a binder in the first anode active material layer <NUM>, the first anode active material layer <NUM> is stabilized on the anode current collector <NUM>. In addition, despite a change in volume and/or relative position of the first anode active material layer <NUM> during charging and discharging, cracking of the first anode active material layer <NUM> is suppressed. For example, in a case where the first anode active material layer <NUM> does not include a binder, the first anode active material layer <NUM> may be easily delaminated from the anode current collector <NUM>. A portion of the anode current collector <NUM> from which the first anode active material layer <NUM> is delaminated is exposed and contacts the solid electrolyte <NUM>, and thus, a short circuit is highly likely to occur. The first anode active material layer <NUM> is formed by, for example, coating, on the anode current collector <NUM>, a slurry in which materials constituting the first anode active material layer <NUM> are dispersed, and drying the slurry. By the inclusion of a binder in the first anode active material layer <NUM>, the anode active material may be stably dispersed in the slurry. For example, when the slurry is coated on the anode current collector <NUM> using a screen printing method, clogging of the screen (for example, clogging by aggregates of the anode active material) may be inhibited.

The thickness of the first anode active material layer <NUM> may be, for example, about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, or about <NUM>% or less of the thickness of a cathode active material layer. The thickness of the first anode active material layer may be, for example, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>. When the thickness (d22) of the first anode active material layer is too small, lithium dendrite formed between the first anode active material layer <NUM> and the anode current collector <NUM> collapses the first anode active material layer <NUM>, and thus, it is difficult to improve the cyclic characteristics of the solid secondary battery <NUM>. When the thickness of the firs anode active material layer <NUM> is excessively increased, the energy density of the solid secondary battery <NUM> is reduced, and the internal resistance of the solid secondary battery <NUM> caused by the first anode active material layer <NUM> is increased, and thus, it is difficult to improve the cyclic characteristics of the solid secondary battery <NUM>.

For example, the anode current collector <NUM> may comprise a material that does not react with lithium, that is, material that forms neither an alloy nor compound with lithium. Materials constituting the anode current collector <NUM> are, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), and the like, but are not limited thereto. Any suitable materials used for anode current collectors in the art may be used. The anode current collector <NUM> may consist of one of the above-listed metals, or may consist of an alloy or coating material of two or more metals thereof. The anode current collector <NUM> may be, for example, in the form of a plate or foil.

The first anode active material layer <NUM> may further include an additive used in existing solid secondary batteries, for example, a filler, a dispersant, an ion-conductive agent, or the like.

Referring to <FIG>, for example, the solid secondary battery <NUM> further includes, on the anode current collector <NUM>, a thin film <NUM> including an element capable of forming an alloy with lithium. The thin film <NUM> may be placed between the anode current collector <NUM> and the first anode active material layer <NUM>. The thin film <NUM> includes, for example, an element capable of forming an alloy with lithium. The element capable of forming an alloy with lithium is, for example, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, or the like, but is not limited thereto, and may be any suitable element known in the art, capable of forming an alloy with lithium. The thin film <NUM> consists of one of these metals, or an alloy of these different metals. As the thin film <NUM> is placed on the anode current collector <NUM>, for example, a second anode active material layer (not shown) deposited between the thin film <NUM> and the first anode active material layer <NUM> may have a more planarized form, and the solid secondary battery <NUM> may have further improved cyclic characteristics.

The thin film <NUM> may have a thickness of, for example, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>. When the thickness of the thin film <NUM> is less than <NUM>, it may be difficult that the function of the thin film <NUM> is exerted. When the thickness of the thin film <NUM> is too large, the thin film <NUM> itself absorb lithium so that the amount of deposition of lithium on the anode is reduced, thus lowering the energy density and cycle characteristics of the solid secondary battery <NUM>. The thin film <NUM> may be disposed on the anode current collector <NUM>, for example, by a vacuum deposition method, a sputtering method, a plating method, or the like. However, embodiments are not necessarily limited to these methods, and any method capable of forming the thin film <NUM> in the art may be used.

Referring to <FIG>, the solid secondary battery 1a further includes a second anode active material layer <NUM> that is formed, for example, between the anode current collector <NUM> and the solid electrolyte <NUM>, by charging. For example, the solid secondary battery 1a further includes the second anode active material layer <NUM> that is formed, for example, between the anode current collector <NUM> and the first anode active material layer <NUM>, by charging. Although not illustrated, the solid secondary battery <NUM> further includes the second anode active material layer <NUM> that is formed, for example, between the solid electrolyte <NUM> and the first anode active material layer <NUM>, by charging. Although not illustrated, the solid secondary battery <NUM> further includes the second anode active material layer <NUM> that is formed, for example, in the first anode active material layer <NUM> by charging.

The second anode active material layer <NUM> is a metal layer containing lithium or a lithium alloy. The metal layer includes lithium or a lithium alloy. Accordingly, since the second anode active material layer <NUM> is a metal layer containing lithium, the second anode active material layer <NUM> may act as, for example, a lithium reservoir. The lithium alloy is, for example, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, a Li-Si alloy, or the like, but is not limited thereto, and may be any suitable lithium alloy used in the art. The second anode active material layer <NUM> may consist of lithium or one of these alloys, or may consist of different alloys.

The second anode active material layer <NUM> has a thickness of, for example, but not specifically limited to, about <NUM> to about <NUM>,<NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>. When the thickness of the second anode active material layer <NUM> is too small, it may be difficult for the second anode active material layer <NUM> to serve as a lithium reservoir. When the thickness of the second anode active material layer <NUM> is too large, the mass and volume of the solid secondary battery <NUM> increase, and rather the cyclic characteristics thereof are likely to be deteriorated. The second anode active material layer <NUM> may be, for example, a metal foil having a thickness within these ranges.

In the solid secondary battery <NUM>, for example, the second anode active material layer <NUM> is disposed between the anode current collector <NUM> and the first anode active material layer <NUM> before assembly of the solid secondary battery, or the second anode active material layer <NUM> is deposited between the anode current collector <NUM> and the first anode active material layer <NUM> by charging after assembly of the solid secondary battery <NUM>.

In a case where the second anode active material layer <NUM> is disposed between the anode electrode current collector <NUM> and the first anode active material layer <NUM> before assembly of the solid secondary battery <NUM>, the second anode active material layer <NUM> is a metal layer including lithium and acts as a lithium reservoir. The solid secondary battery <NUM> including the second anode active material layer <NUM> has further improved cyclic characteristics. For example, before assembly of the solid secondary battery <NUM>, a lithium foil may be disposed between the anode current collector <NUM> and the first anode active material layer <NUM>.

In a case where the second anode active material layer <NUM> is deposited by charging after assembly of the solid secondary battery <NUM>, the energy density of the solid secondary battery <NUM> is increased since the second anode active material <NUM> is not present when the solid secondary battery <NUM> is assembled. For example, when charging the solid secondary battery <NUM>, the solid secondary battery <NUM> is charged to exceed the charge capacity of the first anode active material layer <NUM>. That is, the first anode active material layer <NUM> is overcharged. At the initial stage of charging, lithium is absorbed into the first anode active material layer <NUM>. That is, the anode active material included in the first anode active material layer <NUM> forms an alloy or compound with lithium ions migrated from the cathode <NUM>. When charging is performed to exceed the capacity of the first anode active material layer <NUM>, for example, lithium precipitates on the rear surface of the first anode active material layer <NUM>, that is, between the anode current collector <NUM> and the first anode active material layer <NUM>, and a metal layer, which corresponds to the second anode active material layer <NUM>, is formed by the precipitated lithium. The second anode active material layer <NUM> is a metal layer consisting mainly of lithium (that is, lithium metal). This result is obtained, for example, because the anode active material included in the first anode active material layer <NUM> consists of a material that forms an alloy or compound with lithium. During discharging, lithium in the first anode active material layer <NUM> and the metal layers, as the second anode active material layer <NUM>, is ionized and migrates toward the cathode <NUM>. Accordingly, in the solid secondary battery <NUM>, lithium may be used as an anode active material. In addition, since the first anode active material layer <NUM> covers the second anode active material layer <NUM>, the first anode active material layer <NUM> acts as a protective layer for the second anode active material layer <NUM>, that is, a metal layer, and at the same time inhibits the precipitation growth of lithium dendrites. Accordingly, a short circuit and capacity reduction in the solid secondary battery <NUM> are suppressed, and as a result, the solid secondary battery <NUM> has improved cyclic characteristics. In addition, in a case where the second anode active material layer <NUM> is deposited by charging after assembly of the solid secondary battery <NUM>, the anode current collector <NUM>, the first anode active material layer <NUM>, and a region therebetween are, for example, Li-free regions that do not contain lithium (Li) metal or a Li alloy in the initial state or after discharge of the solid secondary battery.

Referring to <FIG>, the solid secondary battery 1a according to an embodiment has a structure in which the second anode active material layer <NUM> is disposed on the anode current collector <NUM>, and the solid electrolyte <NUM> is directly disposed on the first anode active material layer <NUM>. The second anode active material layer <NUM> is, for example, a lithium metal layer or a lithium alloy layer. The solid electrolyte may be the solid electrolyte according to any of the embodiments or may further include a second solid electrolyte together with the solid electrolyte according to an embodiment.

The second solid electrolyte may include, for example, an oxide-based solid electrolyte, a sulfide electrolyte, or a combination thereof.

The sulfide solid electrolyte may include, for example, Li<NUM>S-P<NUM>S<NUM>, Li<NUM>S-P<NUM>S<NUM>-LiX (wherein X may be a halogen, for example, I, or CI), Li<NUM>S-P<NUM>S<NUM>-Li<NUM>O, Li<NUM>S-P<NUM>S<NUM>-Li<NUM>O-Lil, Li<NUM>S-SiS<NUM>, Li<NUM>S-SiS<NUM>-LiI, Li<NUM>S-SiS<NUM>-LiBr, Li<NUM>S-SiS<NUM>-LiCl, Li<NUM>S-SiS<NUM>-B<NUM>S<NUM>-LiI, Li<NUM>S-SiS<NUM>-P<NUM>S<NUM>-LiI, Li<NUM>S-B<NUM>S<NUM>, Li<NUM>S-P<NUM>S<NUM>-ZmSn (wherein m and n may each be a positive number, and Z may be one of Ge, Zn, and Ga), Li<NUM>S-GeS<NUM>, Li<NUM>S-SiS<NUM>-Li<NUM>PO<NUM>, Li<NUM>S-SiS<NUM>-LipMOq (wherein p and q may each be a positive number, and M may be one of P, Si, Ge, B, Al, Ga, and In). The sulfide solid electrolyte material may be prepared by treatment of a starting material (for example, Li<NUM>S or P<NUM>S<NUM>) using a melt quenching method or a mechanical milling method. In addition, after this treatment, heat treatment may be performed. The sulfide solid electrolyte may be amorphous, crystalline, or a mixture thereof.

The second solid electrolyte may use a sulfide solid electrolyte material as described above, including at least sulfur (S), phosphorous (P), and lithium (Li) as constituent elements, for example, a material including Li<NUM>S-P<NUM>S<NUM>. When the second solid electrolyte uses a sulfide solid electrolyte material including Li<NUM>S-P<NUM>S<NUM>, a mixed molar ratio of Li<NUM>S to P<NUM>S<NUM> (Li<NUM>S: P<NUM>S<NUM>) may be selected to be in a range of, for example, about <NUM>:<NUM> to about <NUM>:<NUM>.

The solid electrolyte <NUM> may further include a binder.

The binder included in the solid electrolyte <NUM> may be, for example, styrenebutadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, or polyethylene. The binder of the solid electrolyte <NUM> may be identical to or different from the binders of the cathode active material layer <NUM> and the first anode active material layer <NUM>.

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

LiCI (water content: <NUM>. 43wt%) and GaF<NUM> were mixed in a <NUM>:<NUM> molar ratio to obtain a mixture, and the mixture was subjected to high-energy milling for <NUM> minutes by ball milling using Pulverisette <NUM> Premium line equipment at <NUM> rpm. After the high-energy milling, the resulting product was cooled down by being left to stand for <NUM> minutes (one cycle). This cycle of the steps of high-energy milling and leaving to stand was repeatedly performed for <NUM> cycles in total, to thereby obtain a compound in clay form having the composition as in Table <NUM>.

Compounds in clay form having the compositions as in Table <NUM> were obtained according to the same method as in Example <NUM>, except that the mixed molar ratio of LiCI to GaF<NUM> was varied to <NUM>:<NUM> and <NUM>:<NUM>, respectively.

A compound in clay form having the composition as in Table <NUM> was obtained according to the same method as in Example <NUM>, except that LiBr was used instead of LiCl.

A compound in clay form having the composition as in Table <NUM> was obtained according to the same method as in Example <NUM>, except that LiCI, LiOH, and GaF<NUM> were used instead of LiCI and GaF<NUM>, and a mixed molar ratio of LiCI, LiOH, and GaF<NUM> was <NUM>:<NUM>:<NUM>.

A compound in clay form having the composition as in Table <NUM> was obtained according to the same method as in Example <NUM>, except that LiCI, LaCl<NUM>, and GaF<NUM> were used instead of LiCI and GaF<NUM>, and a mixed molar ratio of LiCI, LaCl<NUM>, and GaF<NUM> was <NUM>:<NUM>:<NUM>.

A compound in clay form having the composition as in Table <NUM> was obtained according to the same method as in Example <NUM>, except that LiCl, InCl<NUM>, and GaF<NUM> were used instead of LiCI and GaF<NUM>, and a mixed molar ratio of LiCl, InCl<NUM>, and GaF<NUM> was <NUM>:<NUM>:<NUM>.

LiCI (water content: <NUM> wt%) was dried in a <NUM> vacuum oven for <NUM> hours to obtain anhydrous LiCl.

A compound in clay form was obtained according to the same method as in Example <NUM>, except that the anhydrous LiCI was used instead of LiCI (water content: <NUM>. 43wt%) and the mixing molar ratio of LiCI and GaF<NUM> was changed to <NUM>:<NUM>.

Compounds in clay form having the compositions as in Table <NUM> were obtained according to the same method as in Example <NUM>, except that the compositions of the starting materials were changed to obtain the Compounds having the compositions as in Table <NUM>.

A compound in powder form having the composition as in Table <NUM> was obtained according to the same method as in Example <NUM>, except that LiOH was used instead of LiCI, and a mixed molar ratio of LiOH and GaF<NUM> was <NUM>:<NUM>.

A compound in powder form having the composition as in Table <NUM> was obtained according to the same method as in Example <NUM>, except that Li<NUM>O was used instead of LiCI, and a mixed molar ratio of Li<NUM>O and GaF<NUM> was <NUM>:<NUM>.

A compound in powder form having the composition as in Table <NUM> was obtained according to the same method as in Example <NUM>, except that LiCI and LaF<NUM> were used instead of LiCI and GaF<NUM>, and a mixed molar ratio of LiCI and LaF<NUM> was <NUM>:<NUM>.

A compound in powder form having the composition as in Table <NUM> was obtained according to the same method as in Example <NUM>, except that LiCI and InF<NUM> were used instead of LiCI and GaF<NUM>, and a mixed molar ratio of LiCI and InF<NUM> was <NUM>:<NUM>.

A compound in powder form having the composition as in Table <NUM> was obtained according to the same method as in Example <NUM>, except that LiCI and Ga<NUM>O<NUM> were used instead of LiCI and GaF<NUM>, and a mixed molar ratio of LiCI and Ga<NUM>O<NUM> was <NUM>:<NUM>.

LiCI and GaF<NUM> were mixed in a <NUM>:<NUM> molar ratio to obtain a mixture, and the mixture was subjected to high-energy milling for <NUM> minutes by ball milling using Pulverisette <NUM> Premium line equipment at <NUM> rpm.

After the high-energy milling, the resulting product was cooled down by being left to stand for <NUM> minutes (one cycle). After the cooling step, heat treatment was performed at <NUM> for <NUM> minutes.

In Comparative Example <NUM>, through the above-described processes, a compound exhibiting a glass transition phenomenon could not be obtained.

A compound in powder form having the composition as in Table <NUM> was obtained according to the same method as in Example <NUM>, except that LiCI and GaCh were used instead of LiCI and GaF<NUM>, and a mixed molar ratio of LiCI and GaCl<NUM> was <NUM>:<NUM>.

A compound in powder form having the composition as in Table <NUM> was obtained according to the same method as in Example <NUM>, except that LiCI and ScCl<NUM> were used instead of LiCI and GaF<NUM>, and a mixed molar ratio of LiCI and ScCl<NUM> was <NUM>:<NUM>.

LiCI and GaF<NUM> were mixed in a <NUM>:<NUM> molar ratio to obtain a mixture, and the mixture was subjected to high-energy milling for <NUM> minutes by ball milling using Pulverisette <NUM> Premium line equipment at <NUM> rpm. After the high-energy milling, the resulting product was cooled down by being left to stand for <NUM> minutes (one cycle). This cycle of the steps of high-energy milling and leaving to stand was repeatedly performed <NUM> cycles in total.

The resulting product was heat-treated at about <NUM> to obtain LiCl-GaF<NUM> in powder form.

LiGaCl<NUM> in powder form was obtained according to the same method as in Comparative Example <NUM>, except that LiCI and GaCl<NUM> were used instead of LiCI and GaF<NUM>.

LiCI and GaF<NUM> were mixed in a <NUM>:<NUM> molar ratio to prepare a blend of LiCI and GaF<NUM> in powder form.

NaCl and GaF<NUM> were mixed in a <NUM>:<NUM> molar ratio to obtain a mixture, and the mixture was subjected to high-energy milling for <NUM> minutes by ball milling using Pulverisette <NUM> Premium line equipment at <NUM> rpm. After the high-energy milling, the resulting product was cooled down by being left to stand for <NUM> minutes (one cycle). This cycle of the steps of high-energy milling and leaving to stand was repeatedly performed <NUM> cycles in total, to thereby obtain NaCl-GaF<NUM> in powder form.

As a result of differential scanning calorimetry (DSC) on NaCl-GaF<NUM> obtained in Comparative Example <NUM>, it was found that NaCl-GaF<NUM> did not exhibit a glass transition phenomenon and had a low ionic conductivity of <NUM>/cm.

First, a cathode was manufactured according to the following processes.

LiNi<NUM>Co<NUM>Mn<NUM>O<NUM> (NCM), a conductive agent (Super-P; Timcal Ltd. ), polyvinylidene fluoride (PVdF), and N-methylpyrrolidone were mixed to obtain a cathode active material layer formation composition. In the cathode active material layer formation composition, a mixed weight ratio of NCM, the conductive agent, and PVDF was <NUM>:<NUM>:<NUM>, wherein the amount of N-methylpyrrolidone was about <NUM> when the amount of NCM was <NUM>.

After the cathode active material layer formation composition was coated on an aluminum foil (having a thickness of about <NUM>) and dried at <NUM>, the dried product was dried in a vacuum at about <NUM> to thereby manufacture a cathode.

The cathode was impregnated with an ionic liquid-containing electrolyte. This ionic liquid-containing electrolyte was obtained by mixing N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR13TFSI) as an ionic liquid and lithium bistrifluoromethanesulfonimide (LiTFSI) as a lithium salt, and stirring the mixture at room temperature (<NUM>). A mixed weight ratio of the ionic liquid and the lithium salt was <NUM>:<NUM>.

A lithium metal anode (having a thickness of about <NUM>) was arranged on a current collector (copper foil), and a first oxide-based solid electrolyte, a solid electrolyte containing the compound of Example <NUM>, and a second oxide-based solid electrolyte were stacked on the lithium metal anode, and then bound together according to a cold isostatic pressing (CIP) method by applying about <NUM> MPa, to thereby manufacture a structure of lithium anode/first oxide-based solid electrolyte/solid electrolyte/second oxide-based solid electrolyte.

An LLZO (Li<NUM>La<NUM>Zr<NUM>Ta<NUM>O<NUM>) membrane and an LLZO (Li<NUM>La<NUM>Zr<NUM>Ta<NUM>O<NUM>) membrane were used as the first oxide-based solid electrolyte and the second oxide-based solid electrolyte, respectively. The solid electrolyte containing the compound of Example <NUM> was formed with a thickness of <NUM> by uniaxial pressing at a pressure of <NUM> MPa.

The cathode impregnated with the ionic liquid-containing electrolyte was attached to an upper surface of the structure of lithium anode/first oxide-based solid electrolyte/solid electrolyte/second oxide-based solid electrolyte, and heat-treated at about <NUM>, to thereby manufacture a sandwich-type secondary battery including the lithium anode/first oxide-based solid electrolyte/solid electrolyte/second oxide-based solid electrolyte /ionic liquid-containing liquid electrolyte/cathode.

LiNi<NUM>Co<NUM>Mn<NUM>O<NUM> (NCM), a conductive agent (Super-P; Timcal Ltd. ), polyvinylidene fluoride (PVdF), and N-methylpyrrolidone were mixed to obtain a cathode active material layer formation composition. In the cathode active material layer formation composition, a mixed weight ratio of NCM, the conductive agent, and PVDF was <NUM>:<NUM>:<NUM>, and the amount of N-methylpyrrolidone was about <NUM> when the amount of NCM was <NUM>.

A lithium metal anode (having a thickness of about <NUM>) was arranged on a current collector (copper foil), and an oxide-based solid electrolyte (LLZTO: Li<NUM>La<NUM>Zr<NUM>Ta<NUM>O<NUM>) was arranged on the lithium metal anode, and a solid electrolyte containing the compound of Example <NUM> was arranged on the oxide-based solid electrolyte. Subsequently, the cathode was arranged on the solid electrolyte and then pressed together according to a cold isostatic pressing (CIP) method by applying about <NUM> MPa for <NUM> minutes, to thereby manufacture a solid secondary battery including the lithium anode/LLZO membrane/ solid electrolyte containing the compound of Example <NUM>/cathode.

The solid electrolyte containing the compound of Example <NUM> was formed with a thickness of <NUM>µm by uniaxial pressing at a pressure of <NUM> MPa.

XRD spectra of the compounds obtained according to Examples <NUM> to <NUM> were measured, and the results are shown in <FIG>. For the XRD spectrum measurement, Cu Kα radiation was used, and the X-ray diffraction analysis was performed using a Bruker's D8 Advance.

Referring to <FIG>, it was observed that the compound of Example <NUM> (2LiCl-GaF<NUM>) exhibited main peaks at diffraction angles (2θ) of <NUM>° to <NUM>°, and a minor peak near at a diffraction angle (2θ) of <NUM>°. It was observed that the compound of Example <NUM> (3LiCl-GaF<NUM>) and the compound of Example <NUM> (4LiCl-GaF<NUM>) exhibited main peaks at diffraction angles (2θ) of <NUM>° to <NUM>°, and minor peaks at diffraction angles (2θ) of <NUM>°, <NUM>°, and <NUM>°.

Scanning electron microscopy (SEM) was performed on the compound of Example <NUM>. The SEM analysis was performed using a Hitachi SU <NUM> FE-SEM. The SEM analysis results are shown in <FIG>.

Referring to <FIG>, it was found that the compound of Example <NUM> had amorphous phase since grain boundaries were not formed.

Binding energies of the compound of Example <NUM> were measured using an X-ray photoelectron spectrometer (Thermo Fisher Scientific, Multilab- <NUM>), and the analysis results are shown in <FIG>.

The upper graphs in <FIG> represent results of XPS analysis of Li1s, Ga 2p3/<NUM>, F1s, and Cl2p, respectively, of the compound of Example <NUM>, and the lower graphs in <FIG> represent those of LiCI, GaF<NUM>, GaF<NUM>, and LiCI, respectively, for comparison with the upper graphs.

Referring to <FIG>, the Li1s peak of the compound of Example <NUM> appeared to be different from the LiCI peak.

Referring to <FIG>, the Ga 2p3/<NUM> and F1s peaks of the compound of Example <NUM> represented the same results as GaF<NUM> peak. In addition, as is known from <FIG>, the Cl 2p peak of the compound of Example <NUM>, which is attributed to Ga-Cl bonds, was observed in the binding energy region of <NUM> to 203eV.

From the results of <FIG>, it was found that the Cl 2p peak of the compound of Example <NUM> was shifted in the high binding energy direction, as compared with the Cl 2p peak of a simple blend of LiX and GaF<NUM>. From this result, it was found that the compound of Example <NUM> was a composite having Ga-CI bonds, unlike the blend of LiCI and GaF<NUM> obtained according to Comparative Example <NUM>.

The compounds in clay form (referred to also as clay compounds) of Examples <NUM> to <NUM> and Examples <NUM>-<NUM> to <NUM>-<NUM> and the compounds in powder form (referred to also as powder compounds) of Comparative Examples <NUM> to <NUM>, <NUM> and <NUM> were analyzed in terms of ionic conductivity and active energy as follows. About <NUM> of each of the clay compounds of Examples <NUM> to <NUM> and <NUM>-<NUM> to <NUM>-<NUM> was placed between SUS plates, each having a diameter of <NUM> and a thickness of <NUM>, in the form of SUS/compound/SUS, and a uniaxial pressure of <NUM> to <NUM> was applied thereto for <NUM> seconds to thereby form a circular SUS/compound/SUS structure. About <NUM> of each of the powder compounds of Comparative Examples <NUM> to <NUM>, <NUM>, and <NUM> was put into a pelletizer having a diameter of <NUM>, and a uniaxial pressure of <NUM> ton was applied for <NUM> minutes to thereby form pellets in circular disc form. SUS electrodes were placed on opposite sides of each pellet and a pressure was applied at a torque of <NUM> to thereby form a SUS/pellet/SUS structure.

A potentiostatic impedance measurement method was applied to measure the resistance of each SUS/pellet/SUS structure in a range of -<NUM> to <NUM> at open circuit voltage while the <NUM> mV alternating current was varied from <NUM> to <NUM> for impedance evaluation, and the results are shown in <FIG>.

The total resistance (Rtotal) was obtained from the impedance results, and conductivity values were calculated from this value via calibration of electrode's area and pellet's thickness. From the results of the electrochemical impedance spectroscopy (EIS) measured while changing the temperature of a chamber into which each sample was loaded, a value of activation energy (Ea) for lithium (Li) ion conduction was calculated. The values of conductivity measured with respect to temperature in the range of <NUM> to <NUM> were converted into the Arrhenius plot (Ln (σT) vs. <NUM>/T) of Equation <NUM>, and the values of activation energy (Ea) were calculated from the slope of the Arrhenius plot.

In Equation <NUM>, Ea is the activation energy, T represents absolute temperature, A represents the pre-exponential factor, R is the gas constant, and σ represents the conductivity.

The values of activation energy obtained according to the above procedure are shown in Table <NUM>, and the ionic conductivity of each compound is shown in <FIG>.

As shown in <FIG>, the compounds of Examples <NUM> to <NUM> were found to have excellent ionic conductivity in the range of various temperatures. In particular, the compound of Example <NUM> exhibited, as shown in <FIG>, an ionic conductivity of <NUM>/cm at room temperature (<NUM>). Referring to Table <NUM>, it was also found that the compounds of Examples <NUM> to <NUM> had greatly improved conductivity, as compared with the compounds of Comparative Examples <NUM> to <NUM>, <NUM> to <NUM>, <NUM>, and <NUM>. The ionic conductivity of the compound of Comparative Example <NUM> was not measured as it was beyond the measurable range.

The compounds of Examples <NUM>, <NUM>-<NUM>, <NUM>, <NUM>, <NUM> to <NUM> exhibited lower activation energies of less than <NUM>. 37eV/atom, as compared with those of the compounds of Comparative Examples <NUM> to <NUM>. Thus, when the activation energies of the compounds are reduced, the compounds exhibit improved ionic conductivities at low temperature.

In addition, the compounds of Examples <NUM>-<NUM> to <NUM>-<NUM> exhibited equivalent levels of ionic conductivity as that of the compound of Example <NUM>. The compounds of Examples <NUM>-<NUM> and <NUM>-<NUM> also exhibited excellent conductivities, and the compounds of Examples <NUM>-<NUM> and Example <NUM>-<NUM> exhibited similar conductivities to that of the compound of Example <NUM>.

The ionic conductivity of the compound in clay form obtained according to Example <NUM> was evaluated in the same manner as applied to the compound in clay form of Example <NUM>, and the evaluation results are shown in <FIG> and Table <NUM>.

<FIG> illustrates impedance characteristics of the compound in clay form obtained according to Example <NUM>.

Referring to <FIG> and Table <NUM>, it was found that the compound of Example <NUM> had excellent ionic conductivity.

After attaching Li on one surface of Li<NUM>La<NUM>Zr<NUM>Ta<NUM>O<NUM> (LLZTO, Toshima Manufacturing Co. ) pellet by cold isostatic pressing (CIP) at <NUM> MPa for <NUM> minutes, the compound in clay form of Example <NUM>, as an electrolyte, was disposed on the other surface of the LLZTO pellet by uniaxial pressing at <NUM> to thereby form a Li/LLZTO/electrolyte structure.

The Li/LLZTO/electrolyte structure was analyzed by cyclic voltammetry (a scan rate of <NUM> mV/s and a voltage of <NUM> V to <NUM>. The cyclic voltammetry analysis results are shown in <FIG>.

Referring to <FIG>, it was found that the compound of Example <NUM> was stable at up to <NUM>.

Differential scanning calorimetry (DSC) was performed on the compounds Examples <NUM> to <NUM> and the compound of Comparative Example <NUM>. The DSC was performed using a TA Instruments Discovery DSC at a starting temperature of -<NUM>, a termination temperature of <NUM>, and a temperature increase rate of <NUM>/minute under a nitrogen atmosphere.

The DSC analysis results are shown in <FIG>. In <FIG>, 2LiCl-GaF<NUM>, 3LiCl-GaF<NUM> and 4LiCl-GaF<NUM> represent the compounds of Examples <NUM> to <NUM>, respectively, and 3LiCl-ScCl<NUM> represents the compound of Comparative Example <NUM>.

The compounds of Examples <NUM> to <NUM> exhibited a glass transition phenomenon as shown in <FIG>. A glass transition phenomenon at <NUM> or higher refers to a phenomenon in which viscosity and rubber-like properties are exhibited at a certain temperature or higher, and exhibits characteristics in which the slope of heat flow with respect to temperature in a DSC plot changes at a certain temperature and is the same above and below the certain temperature.

The compound of Example <NUM> had a glass transition temperature of -<NUM>, indicating that the compound of Example <NUM> had glass characteristics in the range of battery operation temperatures from -<NUM> to <NUM>.

The compound of Example <NUM> had a glass transition temperature of -<NUM>, and the compound of Example <NUM> had a glass transition temperature of -<NUM>.

DSC analysis was performed on the compounds of Comparative Examples <NUM> to <NUM> under the same conditions as the DSC analysis conditions of the compound of Example <NUM>.

As a result of the DSC analysis, the compounds of Comparative Examples <NUM> to <NUM> did not exhibit a glass transition phenomenon in the temperature range of -<NUM> to -<NUM>, unlike the compounds of Examples <NUM> to <NUM>.

Viscosity was measured using rheology measurement equipment, i.e., a cone- and-plate rheometer (TA Instruments AR <NUM>). Each of the electrolyte samples using the compounds of Examples <NUM> to <NUM>, respectively, was placed between a cone having a cone angle of <NUM>° and a plate having a diameter of <NUM>, and then the interval between the cone and the plate was adjusted. Here, each electrolyte sample was prepared with a thickness of about <NUM> by applying <NUM> MPa of pressure to a compound in clay form with a uniaxial press.

After obtaining a cone/electrolyte/plate structure through the above processes, the cone was rotated repeatedly, and rheological evaluation was performed at room temperature (<NUM>) at a <NUM>% strain while varying the shear rate. The shear rate was in the range of <NUM> rad/s to <NUM> rad/s.

The storage modulus and loss modulus of each sample were measured while varying the angular frequency value.

The measurement results are shown in <FIG>. The storage modulus and loss modulus of each sample at an angular frequency of <NUM> rad/s are shown in Table <NUM>.

The compounds of Example <NUM> to <NUM> exhibited loss modulus and storage modulus characteristics as shown in Table <NUM>.

Rheology characteristics of the compounds of Comparative Examples <NUM> to <NUM> were evaluated using the same rheology characteristic evaluation method as applied to the compounds of Examples <NUM> to <NUM>.

As a result of the evaluation, the compounds of Examples <NUM> to <NUM> exhibited the rheology characteristics. The rheology characteristics as exhibited in the compounds of Comparative Examples <NUM> to <NUM> were not observed, unlike the compounds of Examples <NUM> to <NUM>.

SEM-EDS analysis was performed on the solid secondary battery of Manufacture Example <NUM> to investigate the interfacial states of the cathode, the solid electrolyte (SE), and the LLZTO solid electrolyte and the distribution state of the solid electrolyte in the cathode. The SEM-EDS analysis was performed using a Hitachi SU <NUM> FE-SEM.

<FIG> are SEM images showing the interfacial state of the cathode and the solid electrolyte (SE) and the interfacial state of the solid electrolyte (SE) and the LLZTO solid electrolyte, respectively. <FIG> are images showing EDS analysis results, in which <FIG> are to be compared with <FIG>, and <FIG> are to be compared with <FIG>.

It was found that, as shown in <FIG>, the binding of the cathode and the solid electrolyte (SE) was well implemented, and the interface state and binding state of the solid electrolyte (SE) and the LLZTO solid electrolyte were good. Referring to <FIG>, it was found that Ga, F, and Cl, which are components of the compound of Example <NUM>, were uniformly distributed, and in particular were found to permeate into the porous cathode.

The solid secondary battery of Manufacture Example <NUM> was charged and discharged at a current rate of <NUM> mA/cm<NUM> at <NUM> in the voltage range of <NUM>-<NUM> V. The solid secondary battery was charged with a constant current of <NUM>. 067C for <NUM> hours until the battery voltage reached <NUM>. 2V, and then discharged with a constant current of <NUM>. 067C for <NUM> hours until the battery voltage reached <NUM>. A C rate is a measure of the rate a battery is charged or discharged relative to its maximum capacity. A 1C rate means a current which will discharge the entire capacity in one hour.

A voltage profile after the charging and discharging is shown in <FIG> illustrates impedance characteristics of the solid secondary battery at <NUM>.

Referring to <FIG>, it was found that the solid electrolyte including the compound of Example <NUM> had excellent compatibility with a Garnet-based solid electrolyte. It was also found that the solid secondary battery of Manufacture Example <NUM> reversibly exhibited a capacity of about <NUM> mAh/cm<NUM> near a designed capacity of <NUM> mAh/cm<NUM>.

Charge and discharge profiles of the batteries of Comparative Manufacture Examples <NUM> to <NUM> were evaluated in the same manner as the method of evaluating the Charge and discharge profiles of the solid secondary battery of Manufacture Example <NUM>.

As a result of the evaluation, the batteries of Comparative Manufacture Examples <NUM> to <NUM> were found to have poor characteristics, as compared with the secondary solid battery of Manufacture Example <NUM>.

The solid secondary battery of Manufacture Example <NUM> and the solid secondary batteries of Comparative Manufacture Examples <NUM> to <NUM> were charged and discharged under the same conditions as those in Evaluation Example <NUM> at <NUM>, a voltage range of <NUM>- <NUM> V, and a current rate of <NUM> mA/cm<NUM>, and cycle characteristics of the solid secondary batteries were evaluated in a <NUM> thermostat.

After charging with a constant current of <NUM>. 1C for <NUM> hours until the battery voltage reached <NUM>. 2V, discharging was performed with a constant current of <NUM>. 1C for <NUM> hours until the battery voltage reached <NUM>. 85V (<NUM>st cycle).

A voltage profile and cycle characteristics after the <NUM>st cycle of charging and discharging are shown in <FIG>, respectively.

Referring to <FIG>, it was found that the solid secondary battery of Manufacture Example <NUM> had excellent compatibility with LLZO Garnet, and the solid electrolyte of the solid secondary battery of Manufacture Example <NUM> can be used as a solid electrolyte in a secondary battery.

Referring to <FIG>, it was found that the solid secondary battery of Manufacture Example <NUM> could operate when the solid electrolyte is used as the solid electrolyte for a cathode.

Referring to <FIG>, it was found that the solid secondary battery of Manufacture Example <NUM> exhibited good cycle characteristics.

Change in ionic conductivity according to the introduction of moisture in the compound of Example <NUM> was observed. Changes in ionic conductivity when the compound was mixed with water in an amount of 10wt%, <NUM> wt%, or 30wt% were investigated. The results are shown in <FIG>.

Referring to <FIG>, when exposed to air, gellation through moisture absorption was observed. It was observed that the ionic conductivity of the solid electrolyte was increased when the water content was <NUM> wt%, <NUM> wt%, or <NUM> wt%.

The compound in clay form of Example <NUM> was evaluated for formability.

As shown in <FIG>, it was possible to freely shape the compound of Example <NUM> as desired, like rubber or clay.

The compounds in powder form of Comparative Examples <NUM> to <NUM> were evaluated for formability.

As a result of the formability evaluation, the compounds of Comparative Examples <NUM> to <NUM> did not exhibit flexible properties, and it was difficult to shape the compounds as desired.

Water contents of the compound (3LiCl-GaF<NUM>) in clay form prepared in Example <NUM> and LiCl used as a starting material were measured by thermogravimetric analysis. The thermogravimetric analysis was performed using a TA instruments SDT-Q600 thermogravimetric analyzer (U. A) in air over a temperature range of <NUM> to <NUM> at a heating/cooling rate of <NUM> per minute.

The results of the thermogravimetric analysis of the starting material LiCI are shown in <FIG>.

As a result of the thermogravimetric analysis, the starting material LiCI had a water content of about <NUM> wt% as shown in <FIG>, and the compound (3LiCl-GaF<NUM>) of Example <NUM> had a water content of about <NUM>.

As described above, according to the one or more embodiments, a solid electrolyte may exhibit improved ionic conductivity at room temperature. The solid electrolyte may also have flexible and clay characteristics, and thus excellent formability, and thus may be useful in manufacturing flexible solid secondary batteries. The solid electrolyte may be used as a lithium ion conductor, and may be utilized as a cathode electrolyte due to having improved lithium stability and high oxidation potential.

Claim 1:
A solid electrolyte comprising:
a compound represented by Formula <NUM> or Formula <NUM>,
wherein the compound represented by Formula <NUM> or Formula <NUM> has a glass transition temperature of -<NUM> or less, and a glass or glass-ceramic structure

        Formula <NUM>     AQX-Ga<NUM>-zMz1(F<NUM>-kClk)<NUM>-3zZ3z1

wherein, in Formula <NUM>,
Q is Li or a combination of Li and Na, K, or a combination thereof,
M is In, Sc, Al, TI, Y, B, La, or a combination thereof,
X is Cl, Br, I, OH, or a combination thereof,
Z is Cl, Br, I, SCN, OCN, CN, OH, N<NUM>, or a combination thereof,
<NUM><A<<NUM>, <NUM>≤z<<NUM>, <NUM>≤z1≤<NUM>. and <NUM>≤k<<NUM>,

        Formula <NUM>     AQX-aMz1Z3z1-bGa<NUM>-z(F<NUM>-kClk)<NUM>-3z

wherein, in Formula <NUM>,
Q is Li or a combination of Li and Na, K, or a combination thereof;
M is In, Sc, Al, Tl, Y, B, La, or a combination thereof,
X is Cl, Br, I, OH, or a combination thereof,
Z is Cl, Br, I, SCN, OCN, CN, OH, N<NUM>, or a combination thereof,
<NUM><a≤<NUM>, <NUM><b≤<NUM>, <NUM><a+b, a+b=<NUM>-A, <NUM><A<<NUM>, <NUM>≤z<<NUM>, <NUM>≤z1≤<NUM>, and <NUM>≤k<<NUM>;
wherein the glass transition temperature is determined by differential scanning calorimetry (DSC) at a starting temperature of -<NUM>, a termination temperature of <NUM>, and a temperature increase rate of <NUM>/minute under a nitrogen atmosphere.