Method for manufacturing solid electrolyte layer and solid electrolyte layer manufactured thereby

Abstract

Disclosed are a method of manufacturing a solid electrolyte layer and a solid electrolyte layer manufactured thereby. Specifically, a method for manufacturing a solid electrolyte layer using spark plasma sintering and a solid electrolyte layer manufactured thereby, in which an amorphous solid electrolyte is crystallized using spark plasma sintering. Therefore, a solid electrolyte layer having high density and excellent lithium ion conductivity can be prepared by rapid sintering only at a relatively low pressure.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a method of manufacturing a solid electrolyte layer using spark plasma sintering and a solid electrolyte layer manufactured by the method. In the process, amorphous solid electrolyte is crystallized using spark plasma sintering. Accordingly, a solid electrolyte layer having high density and excellent lithium ion conductivity can be prepared at a relatively low pressure by rapid sintering. BACKGROUND

[0002] Unlike a conventional lithium ion battery in which a separator is located between a positive electrode and a negative electrode and a liquid electrolyte is responsible for the movement of lithium ions to the positive electrode and the negative electrode, in an all-solid-state battery, a solid electrolyte layer simultaneously functions as a separator and a liquid electrolyte.

[0003] Materials for a solid electrolyte layer include sulfide-based solid electrolytes, oxide-based solid electrolytes, and halide-based solid electrolytes. Among them, sulfide-based solid electrolytes are emerging as the most suitable material for next-generation solid-state batteries due to low price, high ionic conductivity and low electronic conductivity, easy synthesis mechanism, and excellent performance

[0004] Despite these advantages, conventional sulfide-based solid electrolytes also have many limitations.

[0005] First, a conventional sulfide-based solid electrolyte is formed by subjecting a produced amorphous sulfide-based solid electrolyte to heat treatment at a high temperature for a long time in an Ar atmosphere to obtain a crystalline solid electrolyte, and then applying a high pressure to form a film. Here, in order to improve the crystallinity of the sulfide-based solid electrolyte, heat treatment is required, which makes it difficult to synthesize a uniform crystalline material due to the temperature gradient of the heat treatment furnace. The difference in the crystallinity of the resulting solid electrolyte causes non-uniform movement of lithium ions in the solid electrolyte layer, thereby causing a decrease in ionic conductivity, non-uniform current density, and thus short circuit at a high current density.

[0006] Second, depending on the composition / synthesis method, even the same sulfide-based solid electrolyte can exhibit a difference in electrolyte, which makes it challenging to easily produce a solid electrolyte layer at a high density. In addition, due to the nature of an all-solid-state battery, a high pressure must be applied to ensure contact between particles, which hinders the ability to increase the battery area.

[0007] Accordingly, even at a low pressure, a solid electrolyte layer must be able to exhibit a high density, thereby exhibiting excellent lithium ion conductivity.

[0008] The above information disclosed in this BACKGROUND section is only for enhancing the understanding of the background of the present disclosure, and therefore it can contain information that does not constitute prior art that is already known in this country to those ordinary skilled in the art. SUMMARY

[0009] The present disclosure is directed to solving the above problems associated with the prior art, and one object of the present disclosure is to provide a solid electrolyte layer by sintering for a short time at a relatively low pressure, as compared to a conventional method of manufacturing a solid electrolyte layer. Specifically, a solid electrolyte layer is manufactured by crystallizing an amorphous solid electrolyte using spark plasma sintering (SPS).

[0010] Another object of the present disclosure is to manufacture a solid electrolyte layer for a short time at a relatively low pressure using spark plasma sintering and to increase the area thereof.

[0011] The objects of the present disclosure are not limited to those described above. Other objects of the present disclosure will be clearly understood from the following description, and can be achieved by the means defined in the claims and combinations thereof

[0012] In one aspect, the present disclosure provides a method of crystallizing an amorphous solid electrolyte using spark plasma sintering (SPS) to manufacture a solid electrolyte layer including a crystalline solid electrolyte.

[0013] In an embodiment, preparing the amorphous solid electrolyte can include performing mechanical milling on a solid electrolyte raw material.

[0014] In an embodiment, the mechanical milling can include at least one selected from the group consisting of ball milling, air jet milling, bead milling, roll milling, planetary milling, hand milling, high-energy ball milling, planetary ball milling, stirred ball milling, vibration milling, mechanical fusion milling, jolting milling, planetary milling, sand mill type milling, disc milling, shaped milling, Nauta milling, Nobilta milling, high-speed mixing, and combinations thereof.

[0015] In an embodiment, crystallizing the amorphous solid electrolyte using SPS can include placing the amorphous solid electrolyte in a spark plasma sintering apparatus, vacuumizing the spark plasma sintering apparatus and applying a reaction pressure thereto, ramping a temperature of the spark plasma sintering apparatus to a reaction temperature while maintaining the reaction pressure thereon, and maintaining the reaction temperature for a predetermined reaction time to crystallize the amorphous solid electrolyte into a crystalline solid electrolyte.

[0016] In an embodiment, the reaction pressure can be about 10 MPa to 90 MPa.

[0017] In an embodiment, the reaction time can be about 5 to 10 minutes.

[0018] In an embodiment, the reaction temperature can be about 500 K to 700 K.

[0019] In an embodiment, the temperature increase rate to reach the reaction temperature can be about 30 K / min to 100 K / min.

[0020] In an embodiment, the method can further include cooling the crystalline solid electrolyte to room temperature after the crystallization.

[0021] In an embodiment, the crystalline solid electrolyte can include a sulfide-based solid electrolyte.

[0022] In an embodiment, the crystalline solid electrolyte can have a kesterite-type crystal structure.

[0023] In an embodiment, the crystalline solid electrolyte can be represented by the following formula:

[0024] [Formula]

[0025] Li 6+x-a-y A 1-x M x S 5-a X 1+a

[0026] wherein,

[0027] A is P or Sb;

[0028] M is Si, Ge, or Sn;

[0029] X includes any one selected from the group consisting of Cl, Br, I, and combinations thereof; and

[0030] x satisfies 0≤x≤0.5, y satisfies 0≤y≤0.2, and a satisfies 0≤a≤0.5, respectively.

[0031] In an embodiment, when A in the formula is P, the spark plasma sintering can be performed at a reaction temperature of about 523 K to 600 K.

[0032] In an embodiment, when A in the formula is Sb, the spark plasma sintering can be performed at a reaction temperature of about 573 K to 673 K.

[0033] In an embodiment, the solid electrolyte layer can have an ionic conductivity of about 1.30*10 -3 S / cm or more.

[0034] In an embodiment, the density of the solid electrolyte layer can be about 88% to 99% of the theoretical density.

[0035] In an embodiment, each element constituting the crystalline solid electrolyte is dispersed without being aggregated.

[0036] In one aspect, the present disclosure provides a solid electrolyte layer including a crystalline solid electrolyte crystallized using spark plasma sintering (SPS), wherein the crystalline solid electrolyte includes a sulfide-based solid electrolyte.

[0037] In an embodiment, the solid electrolyte layer can have an ionic conductivity of about 1.30*10 -3 S / cm or more.

[0038] In an embodiment, each element constituting the crystalline solid electrolyte is uniformly dispersed without aggregation.

[0039] Other aspects and preferred embodiments of the present disclosure are discussed below. BRIEF DESCRIPTION OF DRAWINGS

[0040] The above and other features of the present disclosure will now be described in detail with reference to certain exemplary embodiments thereof, which are illustrated in the accompanying drawings, wherein:

[0041] Figure 1 XRD results of a solid electrolyte layer manufactured according to the present disclosure and a solid electrolyte layer manufactured according to a conventional method are shown;

[0042] Figure 2 Measured impedance of a solid electrolyte layer according to Example 1 is shown;

[0043] Figure 3 Measured impedance of a solid electrolyte layer according to Comparative Example 1 is shown;

[0044] Figure 4 is a scanning electron microscope (SEM) image showing a solid electrolyte layer according to Example 1;

[0045] 5A to 5D Energy dispersive X-ray spectroscopy (EDS) images of sulfur (S), iodine (I), germanium (Ge), and antimony (Sb) in a solid electrolyte layer according to Example 1, respectively;

[0046] Figure 6 is a scanning electron microscope (SEM) image showing a solid electrolyte layer according to Comparative Example 1;

[0047] 7A to 7D Energy dispersive X-ray spectroscopy (EDS) images of sulfur (S), iodine (I), germanium (Ge), and antimony (Sb) in a solid electrolyte layer according to Comparative Example 1, respectively;

[0048] Figure 8 is a scanning electron microscope (SEM, x3,000) image showing a solid electrolyte layer according to Example 2;

[0049] Figures 9A to 9C are energy dispersive X-ray spectroscopy (EDS) images of sulfur (S), phosphorus (P), and chlorine (Cl) in the solid electrolyte layer according to Example 2, respectively;

[0050] Figure 10 is a scanning electron microscope (SEM, x3,000) image showing the solid electrolyte layer according to Comparative Example 3; and

[0051] Figures 11A to 11C are energy dispersive X-ray spectroscopy (EDS) images of sulfur (S), phosphorus (P), and chlorine (Cl) in the solid electrolyte layer according to Comparative Example 3, respectively. DETAILED DESCRIPTION

[0052] The above objects and other objects, features and advantages of the present disclosure will be more clearly understood from the following preferred embodiments taken in conjunction with the accompanying drawings, in which like reference characters refer to like elements throughout. The present disclosure, however, can be embodied in various forms, not just the preferred embodiments. The preferred embodiments are merely provided for full and complete understanding of the technical concept of the present disclosure, and fully convey the technical concept of the present disclosure to those skilled in the art.

[0053] Throughout the description and drawings, like reference numerals refer to like elements throughout. In the drawings, the size of the structures can be exaggerated for clarity and convenience. It will be understood that, although the terms "first", "second", etc. can be used herein to describe various elements, these elements should not be limited by these terms since such elements are commonly called by different names of first, second, etc. in the field of the present disclosure. For example, a "first" element can be called a "second" element, and similarly, a "second" element can be called a "first" element without departing from the scope of the present disclosure as defined by the appended claims. The singular forms are intended to include the plural forms unless the context clearly indicates otherwise.

[0054] It will be further understood that the terms "comprises" and / or "has," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof. Also, it will be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, it can be directly on the other element or intervening elements can also be present. In addition, it will be understood that when an element such as a layer, film, region, or substrate is referred to as being "under" another element, it can be directly under the other element, or intervening elements can also be present.

[0055] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Furthermore, the description herein of terms "unit", "-er", "-or" and "module" means a unit for processing at least one function and operation, and can be implemented by a hardware component or a software component and a combination thereof.

[0056] Although the exemplary embodiments are described as using a plurality of units to perform exemplary processes, it is understood that the exemplary processes can also be performed by one or more modules, and furthermore, it is understood that the term controller / control unit refers to a hardware device that includes a memory and a processor and is specifically programmed to perform the processes described herein. The memory is configured to store modules, and the processor is specifically configured to execute the modules to perform one or more processes described further below.

[0057] Furthermore, the control logic of the present disclosure can be embodied as non-transitory computer readable media on a computer readable medium that contains executable program instructions executed by a processor, controller, or the like. Embodiments of the computer readable medium include, but are not limited to, a ROM, a RAM, a compact disc (CD)-ROM, a magnetic tape, a floppy disk, a flash drive, a smart card, and an optical data storage device. The computer readable medium can also be distributed over network-coupled computer systems so that the computer readable medium is stored and executed in a distributed fashion, e.g., over a remote information processing server or controller area network (CAN).

[0058] Unless specifically stated or otherwise clear from context, as used herein, the term "about" is understood not to be to absolute precision, but rather to consist of the normal tolerances or margins of error for measurements of the art, e.g., within 2 standard deviations of the mean. "About" can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value, unless context clearly dictates otherwise. All numerical values provided herein are modified by the term "about", unless otherwise clearly indicated by context.

[0059] Unless otherwise indicated herein, all numbers, numerical expressions, and / or ranges expressed herein are approximate, which reflect the various uncertainties inherent in measuring, obtaining, and / or calculating such quantities, etc. For example, the term "about" should be understood to refer to a numerical value that is within 10% of the value being approximated. Also, when numerical ranges are disclosed, these ranges are inclusive of the minimum and maximum values, unless otherwise defined

[0060] It is to be understood that, in this specification, when a range is mentioned with respect to a parameter, the parameter encompasses all numbers within the range including the endpoints disclosed. For example, the range of "5 to 10" includes the numbers 5, 6, 7, 8, 9, and 10, as well as any sub-ranges, such as the ranges of 6 to 10, 7 to 10, 6 to 9, and 7 to 9, and any numbers in between the appropriate integers within the range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, and 6.5 to 9. Also, for example, the range of "10% to 30%" includes all integers, including the numbers such as 10%, 11%, 12%, and 13% and 30%, as well as any sub-ranges such as 10% to 15%, 12% to 18%, or 20% to 30%, and any numbers in between the appropriate integers within the range, such as 10.5%, 15.5%, and 25.5%.

[0061] The method of manufacturing a solid electrolyte layer according to an aspect of the present disclosure includes preparing an amorphous solid electrolyte, and crystallizing the amorphous solid electrolyte using spark plasma sintering (SPS) to form a solid electrolyte layer including a crystalline solid electrolyte

[0062] Hereinafter, each step will be described in more detail.

[0063] Preparation of amorphous solid electrolytes

[0064] Depending on the presence or absence of a crystal structure, a solid electrolyte can be classified into a crystalline and an amorphous (non-crystalline) electrolyte. Typical crystalline systems include a sulfur-LISICON, LGPS, and argyrodite crystal structure, while typical amorphous systems include a glass or glass-ceramic structure depending on the difference in heat treatment temperature.

[0065] The amorphous solid electrolyte prepared in this step can be prepared without particular limitation, as long as it can be converted into a crystalline solid electrolyte using spark plasma sintering. Also, for example, the amorphous solid electrolyte can be prepared as a powder.

[0066] In one embodiment, the amorphous solid electrolyte can be prepared by applying energy to a solid electrolyte raw material. Here, the solid electrolyte raw material is not particularly limited as long as it is required to synthesize the crystalline solid electrolyte according to the present disclosure. For example, the solid electrolyte raw material can include Li2S, Ge, Sb, S, LiI, P2S5, LiCl, or the like. Further, depending on the type of the crystalline solid electrolyte and the dopant element, the solid electrolyte raw material can be appropriately prepared.

[0067] The energy is mechanically applied and can include, for example, mechanical grinding. The mechanical grinding is not particularly limited as long as it can synthesize the amorphous solid electrolyte by pulverizing or mixing the solid electrolyte raw material, and can be any method commonly used in the related art.

[0068] The mechanical grinding can include, for example, at least one selected from the group consisting of a ball mill, air jet milling, bead milling, roll milling, planetary milling, hand milling, high-energy ball milling, planetary ball milling, stirred ball milling, vibration milling, mechanical fusion milling, jarring milling, planetary milling, sand mill type milling, disc milling, shaped milling, Nauta milling, Nobilta milling, high-speed mixing, and combinations thereof.

[0069] Further, depending on the type of the crystalline solid electrolyte synthesized according to the present disclosure, the amorphous solid electrolyte can be prepared by purchasing a known solid electrolyte.

[0070] Fabrication of solid electrolyte layers using spark plasma sintering

[0071] Then, the prepared amorphous solid electrolyte can be crystallized using spark plasma sintering. At this time, the amorphous solid electrolyte can be converted into the crystalline solid electrolyte.

[0072] The term "spark plasma sintering (SPS)" can refer to a method including applying pressure, low voltage, and high current to a material, and then rapidly sintering the material by generating plasma. Specifically, the spark plasma sintering refers to a method of allowing a desired material to be synthesized or sintered in a short time and effectively using high energy of a high-temperature plasma (discharge plasma) that is immediately generated when electric energy is directly applied as a pulse to a gap between particles of a pressurized powder by thermal diffusion, electric field action, or the like.

[0073] According to the present disclosure, using the spark plasma sintering can crystallize the amorphous solid electrolyte into the crystalline solid electrolyte in a short time. Compared to a conventional method requiring long-term heat treatment at a high temperature of more than 700 K, the crystallization can be achieved in a short time at a relatively low temperature, resulting in a more dense (i.e., high-density) crystalline solid electrolyte. Accordingly, the lithium ion conductivity of the solid electrolyte layer can be improved.

[0074] The spark plasma sintering used in the present disclosure can be performed using a spark plasma sintering apparatus. The spark plasma sintering apparatus can be used without particular limitation as long as it can crystallize an amorphous solid electrolyte into a crystalline solid electrolyte. For example, the spark plasma sintering apparatus includes a chamber having a predetermined internal space, a die configured to determine the size or shape of a solid electrolyte layer to be synthesized, and one or more punches configured to apply a pressure to a solid electrolyte introduced into the die.

[0075] In one embodiment, manufacturing a solid electrolyte layer can include adding an amorphous solid electrolyte to a spark plasma sintering apparatus.

[0076] Specifically, the die can be filled with the prepared amorphous solid electrolyte powder, and then can be installed in the chamber of the spark plasma sintering apparatus. In this case, boron nitride can be applied to the surface of the punch as a high-temperature release agent to prevent the solid electrolyte layer from adhering to the punch.

[0077] Then, the atmosphere of the spark plasma sintering apparatus can be evacuated to a vacuum or an equivalent state. Subsequently, the punch can be moved to apply a reaction pressure to the amorphous solid electrolyte filling the die.

[0078] In the case where the reaction pressure is applied, the spark plasma sintering apparatus can be heated to a predetermined reaction temperature. Then, the reaction pressure and the reaction temperature can be maintained for a predetermined reaction time. During this process, the amorphous solid electrolyte can be crystallized and converted into a crystalline solid electrolyte. At the same time, the pressure is applied to the amorphous or crystalline solid electrolyte in the die, so that a solid electrolyte layer corresponding to the shape and size of the die can be formed.

[0079] While the reaction pressure and the reaction temperature are maintained, the crystallization reaction can be performed for a predetermined reaction time. When the desired reaction time has elapsed, the reaction pressure can be released, and the temperature of the spark plasma sintering apparatus or the chamber can be cooled to room temperature. Then, the punch is removed using a cold stamping apparatus, and then the manufactured solid electrolyte layer or blank can be removed.

[0080] In one embodiment, the reaction pressure applied to the amorphous solid electrolyte can be 10 MPa to 90 MPa. In contrast, a conventional method of manufacturing a solid electrolyte layer by heat-treating an amorphous solid electrolyte for a long time and applying high pressure generally uses a pressure of about 370 MPa to about 550 MPa

[0081] Compared to a conventional method of performing crystallization and production of a solid electrolyte layer, the reaction pressure according to the present disclosure can be set at a relatively very low pressure. Thus, even when the size of the mold is increased, a proper reaction pressure can be applied to the amorphous solid electrolyte, which is advantageous in increasing the area of the mold.

[0082] When the reaction pressure applied to the amorphous solid electrolyte is less than 10 MPa, the crystallization reaction can not properly occur. In addition, when the reaction pressure is higher than 90 MPa, it can be disadvantageous to increase the area of the mold.

[0083] In one embodiment, the reaction temperature can be 500 K to 700 K. In addition, the reaction time for maintaining the reaction temperature can be 5 to 10 minutes. In a conventional method of manufacturing a solid electrolyte layer by long-time heat treatment of an amorphous solid electrolyte and application of high pressure, generally, a temperature of 723 K to 773 K is maintained for 1 to 5 hours to crystallize the amorphous solid electrolyte.

[0084] In the manufacturing method according to the present disclosure, crystallization and production of a solid electrolyte layer can be achieved by maintaining a relatively low reaction temperature for a much shorter time. Thus, the elements constituting the solid electrolyte can be uniformly dispersed without aggregation.

[0085] Spark plasma sintering according to the present disclosure does not require a high heat treatment temperature to be maintained for a long time as in a conventional method, thus reducing the size of a heat treatment furnace. Thus, quality deterioration of the crystalline solid electrolyte due to temperature imbalance in the heat treatment furnace can be suppressed. Here, quality deterioration can mean a decrease in crystallinity of the solid electrolyte, a decrease in density due to aggregation of the elements constituting the solid electrolyte, and thus a decrease in lithium ion conductivity.

[0086] Meanwhile, aggregation of the elements constituting the solid electrolyte can be confirmed by visually observing an image of the solid electrolyte layer analyzed by energy dispersive X-ray spectroscopy (EDS).

[0087] When the reaction temperature is lower than 500 K or the reaction time is less than 5 minutes, the crystallization reaction of the amorphous solid electrolyte can not properly occur. In addition, when the reaction temperature is higher than 700 K or the reaction time is longer than 10 minutes, the crystal structure can collapse due to excessive volatilization of a specific element (e.g., sulfur (S)) in the amorphous solid electrolyte.

[0088] In one embodiment, the temperature increase rate to reach the reaction temperature can be 30 K / minute to 100 K / minute. When the temperature increase rate to reach the reaction temperature is less than 30 K / minute and the amorphous solid electrolyte in the mold is heated too slowly, insufficient heat can be applied and the crystallization can not completely occur.

[0089] On the other hand, when the temperature increase rate at which the reaction temperature is reached is higher than 100 K / min, and the amorphous solid electrolyte in the mold is heated at an excessively high rate, too much heat is added in a short period of time, thus causing a risk that the crystal structure will collapse due to excessive volatilization of sulfur (S), a specific element in the amorphous solid electrolyte.

[0090] Therefore, crystallization of the amorphous solid electrolyte by spark plasma sintering can produce a crystalline solid electrolyte and a solid electrolyte layer containing the same.

[0091] The crystalline solid electrolyte is a material having high lithium ion conductivity, and oxide-based solid electrolytes and sulfide-based solid electrolytes are known. However, it is preferable to use a sulfide-based solid electrolyte that is inexpensive, has high lithium ion conductivity, and has low electronic conductivity

[0092] The sulfide-based solid electrolyte is not particularly limited, and can be Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, 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, (wherein m and n are positive numbers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (wherein x and y are positive numbers, and M is P, Si, Ge, B, Al, Ga, or In), Li 10 GeP2S 12 and the like.

[0093] Further, the crystalline solid electrolyte can have a argyrodite-type crystal structure. The argyrodite-type crystal structure is a solid electrolyte having lithium ion conductivity while having the same crystal structure as an argyrodite having a composition of Ag8GeS6. In an all-solid-state battery, Li7PS6 and Li6PS5X (X = Cl, Br, I) are representative electrolytes of Li-argyrodite structures having lithium ion (Li + ) conductivity.

[0094] In one embodiment, the crystalline solid electrolyte can be represented by the following formula.

[0095] [Formula]

[0096] Li6+x-a-y A 1-x M x S 5-a X 1+a

[0097] wherein A is P or Sb, M is Si, Ge, or Sn, X includes any one selected from the group consisting of Cl, Br, I, and combinations thereof, x satisfies 0≤x≤0.5, y satisfies 0≤y≤0.2, and a satisfies 0≤a≤0.5.

[0098] In the formula, when a is higher than 0, halogen is rich. Further, when y is higher than 0, lithium can be deficient. Further, although not shown in the formula, some of sulfur (S) can be replaced with selenium (Se).

[0099] In one embodiment, when A in the formula is phosphorus (P), the reaction temperature at which crystallization occurs by spark plasma sintering can be 523 K to 600 K. Further, when A in the above formula is antimony (Sb), the reaction temperature at which crystallization occurs by spark plasma sintering can be 573 K to 673 K.

[0100] When A in the formula is phosphorus (P), that is, when an amorphous solid electrolyte containing phosphorus (P) is crystallized using spark plasma sintering, crystallization can not properly occur at a reaction temperature lower than 523 K. Further, at a reaction temperature higher than 600 K, the crystal structure can collapse due to excessive volatilization of sulfur (S).

[0101] When A in the formula is antimony (Sb), that is, when an amorphous solid electrolyte containing antimony (Sb) is crystallized using spark plasma sintering, crystallization can not properly occur at a reaction temperature lower than 573 K. Further, at a reaction temperature higher than 673 K, the crystal structure can collapse due to excessive volatilization of sulfur (S).

[0102] The solid electrolyte layer containing a crystalline solid electrolyte according to the manufacturing method of the present disclosure exhibits higher density, improved lithium ion conductivity, and lower electronic conductivity compared to a solid electrolyte layer manufactured by a conventional method.

[0103] In one embodiment, the ionic conductivity of the solid electrolyte layer can be 1.30*10 -3 S / cm or more. Further, the density of the solid electrolyte layer can be 88% to 99% of the theoretical density. Further, the electronic conductivity of the solid electrolyte layer can be 1.09*10 -9 S / cm or less.

[0104] Hereinafter, the present disclosure will be described in more detail with reference to the following examples and comparative examples, etc. However, these examples and comparative examples should not be construed as limiting the scope of the present disclosure

[0105] Preparation 1 - Amorphous Li 6.25 Sb 0.75 Ge 0.25 S5I

[0106] To synthesize an amorphous solid electrolyte having a composition of Li 6.25 Sb 0.75 Ge 0.25 S5I, Li2S, Ge, Sb, S, and LiI were prepared as solid electrolyte raw materials. 70 g of zirconia balls having a diameter of 10 mm and a total of 3 g of the solid electrolyte raw materials prepared were added to a ball mill container to match stoichiometric calculations.

[0107] The ball mill container was operated at 350 rpm for 20 hours to synthesize an amorphous solid electrolyte having a composition of Li 6.25 Sb 0.75 Ge 0.25 S5I.

[0108] Preparation Example 2-Amorphous Li6PS5Cl

[0109] To synthesize an amorphous solid electrolyte having a composition of Li6PS5Cl, Li2S, P2S5, and LiCl were prepared as solid electrolyte raw materials. 70 g of zirconia balls having a diameter of 10 mm and a total of 3 g of the solid electrolyte raw materials prepared were added to a ball mill container to match stoichiometric calculations.

[0110] The ball mill container was operated at 350 rpm for 20 hours to synthesize an amorphous solid electrolyte having a composition of Li6PS5Cl.

[0111] Example 1 - Preparation Example 1 + Spark Plasma Sintering

[0112] A discharge plasma sintering apparatus (SPS Syntex Co., Ltd.; SPS-210LX) was prepared. The size of a punch installed on the spark plasma sintering apparatus was 13 mm, and a mold of an appropriate size for the punch was prepared. Boron nitride was sprayed to the punch to prevent the prepared solid electrolyte layer from adhering to the punch.

[0113] The amorphous solid electrolyte synthesized according to Preparation Example 1 in the form of a powder was injected into the mold, and then the punch was installed to press the powder in two directions.

[0114] The mold was installed in the chamber of the spark plasma sintering apparatus, and then the chamber was evacuated. Then, a reaction pressure of about 50 MPa was applied. The chamber temperature was increased at a rate of 50 K / min to reach a reaction temperature of 623 K while maintaining the reaction pressure. The reaction pressure and the reaction temperature were maintained for 8 minutes for the crystallization process. After 8 minutes, the reaction pressure was released, and the chamber was cooled to room temperature.

[0115] Then, the punch was removed using a cold press apparatus and the prepared solid electrolyte layer was collected.

[0116] Example 2 - Preparation Example 2 + Spark Plasma Sintering

[0117] A solid electrolyte layer was prepared using the same method as in Example 1, except that Preparation Example 2 was used as the amorphous solid electrolyte, and the reaction temperature and the reaction time were set to 523 K and 5 minutes, respectively.

[0118] Comparative Example 1-Preparation Example 1+Long-term heat treatment and high-pressure pressing

[0119] The amorphous solid electrolyte according to Preparation Example 1 was placed in a heat treatment furnace, a vacuum atmosphere was generated, and heat treatment was performed at about 723 K for 24 hours. A crystalline solid electrolyte was prepared by the heat treatment.

[0120] The crystalline solid electrolyte was injected into a pressurized mold, and a pressure of about 400 MPa was applied to prepare a solid electrolyte layer.

[0121] Comparative Example 2-Preparation Example 1

[0122] The amorphous solid electrolyte according to Preparation Example 1 was injected into a pressurized mold without performing a separate heat treatment, and then a pressure of about 400 MPa was applied thereto to prepare a solid electrolyte layer.

[0123] Comparative Example 3-Preparation Example 2+Long-term heat treatment and high-pressure pressing

[0124] A solid electrolyte layer was prepared in the same method as in Comparative Example 1, except that the amorphous solid electrolyte according to Preparation Example 2 was used.

[0125] Experimental Example 1 - Confirmation of the crystallinity of the solid electrolyte by XRD analysis

[0126] In order to determine whether the crystalline solid electrolyte was synthesized correctly, XRD (X-ray diffraction) analysis was performed on the solid electrolyte layers according to Example 1, Comparative Example 1, and Comparative Example 2. The results were compared with known Li6Sb S 5 I XRD peaks, as shown in Figure 1 In the graph, BM indicates ball milling, SPS indicates spark plasma sintering, and ANN indicates heat treatment (annealing).

[0127] From Figure 1 It can be seen that the solid electrolyte layer manufactured using long-term heat treatment and applying pressure using high-pressure pressing (Comparative Example 1; BM+ANN) and the solid electrolyte layer manufactured using spark plasma sintering in a short time of several minutes (Example 1; BM+SPS) are both manufactured using the same crystalline solid electrolyte. In terms of manufacturing time and process, according to the present disclosure, a crystalline solid electrolyte layer can be effectively manufactured while effectively suppressing the volatilization of sulfur in a short time.

[0128] Meanwhile, Comparative Example 2 (BM) which did not undergo a crystallization process such as long-term heat treatment or spark plasma sintering did not exhibit a peak, indicating that the solid electrolyte remained in an amorphous state.

[0129] Experimental Example 2-Measurement of physical properties of synthesized solid electrolytes

[0130] Impedance evaluation was performed to determine the ionic conductivity and electronic conductivity of the solid electrolyte layers according to Example 1 and Comparative Example 1. The results of the Nyquist impedance curve through impedance analysis are shown in Figure 2 and Figure 3 .

[0131] As can be seen from Figure 2 , the solid electrolyte layer manufactured using spark plasma sintering has a thickness of about 0.1 cm and a density of 2.6 g / cm 3 . In addition, the ionic conductivity and electronic conductivity measured or calculated by impedance evaluation are 1.34*10 -3 S / cm and 1.09*10 -9 S / cm, respectively.

[0132] As can be seen from Figure 3 , the conventional solid electrolyte layer prepared using long-term heat treatment and high-pressure pressing has a thickness of about 0.056 cm and a density of 1.87 g / cm 3 . In addition, the ionic conductivity and electronic conductivity measured or calculated by impedance evaluation are 4.72*10 -4 S / cm and 5.63*10 -9 S / cm, respectively.

[0133] Comparing Figure 2 and Figure 3 , spark plasma sintering increased the density of the solid electrolyte layer by about 40% and the ionic conductivity by about 3 times. At the same time, the electronic conductivity was reduced by about two times.

[0134] Experimental Example 3 - Solid electrolyte (Li 6.25 Sb 0.75 Ge 0.25 Image analysis of S5I

[0135] Image analysis was performed on the synthesized solid electrolyte layer to investigate the cause of the difference in the density, ionic conductivity, and electronic conductivity of the solid electrolyte layer measured in Experimental Example 2.

[0136] Figure 4 is a scanning electron microscope (SEM, x 3,000) image showing the solid electrolyte layer according to Experimental Example 1. 5A to 5D are energy dispersive X-ray spectroscopy (EDS) images of sulfur (S), iodine (I), germanium (Ge), and antimony (Sb), respectively, in the solid electrolyte layer according to Experimental Example 1.

[0137] As can be seen from Figure 4 It can be seen that, although voids are observed inside the solid electrolyte layer according to Experimental Example 1, the number thereof and the size thereof are smaller than those of Comparative Example 1, which will be described later. In addition, as can be seen from 5A to 5D It can be seen that each element constituting the crystalline solid electrolyte is uniformly dispersed and does not aggregate.

[0138] Figure 6 is a scanning electron microscope (SEM, x 3,000) image showing the solid electrolyte layer according to Comparative Example 1. 7A to 7D are energy dispersive X-ray spectroscopy (EDS) images of sulfur (S), iodine (I), germanium (Ge), and antimony (Sb), respectively, in the solid electrolyte layer according to Comparative Example 1.

[0139] As can be seen from Figure 6 It can be seen that, compared to Experimental Example 1, the solid electrolyte layer according to Comparative Example 1 has more voids. The pores act as resistance to prevent the conduction of lithium ions, and decrease the total density of the solid electrolyte layer, thereby decreasing the energy density of the battery.

[0140] In addition, as can be seen from 7A to 7D It can be seen that the element germanium (Ge) constituting the crystalline solid electrolyte appears brighter in the EDS phase, which means that it is not uniformly dispersed and does not uniformly aggregate. It is predicted that the uneven arrangement of the elements occurs due to the temperature gradient of the heat treatment furnace. The unevenness of these elements can hinder the uniform movement of lithium ions, thereby decreasing the battery performance.

[0141] Figures 4 to 7D The results of the image analysis of are numerically represented in Tables 1 and 2 below. Table 1 pertains to the solid electrolyte layer according to Experimental Example 1, and Table 2 pertains to the solid electrolyte layer according to Comparative Example 1.

[0142] [Table 1]

[0143] element Line Type Wt% Wt% σ Standard Labels atom% S K Series 29.93 0.13 FeS2 35 Ge L Series 7.92 0.09 Ge 4.0 Sb L Series 13.81 0.14 Sb 4.1 I L Series 29.02 0.17 I (v) 8.31

[0144] [Table 2]

[0145] element Line Type Wt% Wt% σ Standard Labels atom% S K Series 29.31 0.1 FeS2 32.9 Ge L Series 6.22 0.07 Ge 3.2 Sb L Series 14.67 0.11 Sb 4.5 I L Series 31.3 0.14 I (v) 9.1

[0146] As can be seen from Table 1 and Table 2, although the same amorphous solid electrolyte as in Preparation Example 1 was used, the contents of the elements were different. In particular, it can be seen that in Example 1 in which spark plasma sintering was used, the content of sulfur (S) was higher (35 atomic % compared to 32.9 atomic %). This is because the volatilization of sulfur was suppressed in Example 1 in which the crystallization time was short.

[0147] Experimental Example 4 - Image Analysis of Solid Electrolyte (Li6PS5Cl)

[0148] In order to determine whether the amorphous solid electrolyte (Li6PS5Cl) according to Preparation Example 2 exhibited high ionic conductivity, low electronic conductivity, improved dispersibility, and suppressed sulfur volatilization when spark plasma sintering was used, image analysis was performed on Example 2 and Comparative Example 3.

[0149] Figure 8 is a scanning electron microscope (SEM, x 3,000) image showing the solid electrolyte layer according to Example 2. Figures 9A to 9C are energy dispersive X-ray spectroscopy (EDS) images of sulfur (S), phosphorus (P), and chlorine (Cl), respectively, in the solid electrolyte layer according to Example 2.

[0150] As can be seen from Figure 8 It can be seen that although voids were observed inside the solid electrolyte layer according to Example 2, the number and size thereof were smaller than those of Comparative Example 3, which will be described later. In addition, as can be seen from Figures 9A to 9C It can be seen that each element constituting the crystalline solid electrolyte was uniformly dispersed and not aggregated.

[0151] Although not shown separately, the ionic conductivity of the solid electrolyte layer according to Example 2 was measured to be 1.83*10 -3 S / cm. This was more than twice as high as the ionic conductivity of the solid electrolyte layer according to Comparative Example 3, which will be described later.

[0152] Figure 10 is a scanning electron microscope (SEM, x 3,000) image showing the solid electrolyte layer according to Comparative Example 3. Figures 11A to 11C are energy dispersive X-ray spectroscopy (EDS) images of sulfur (S), phosphorus (P), and chlorine (Cl), respectively, in the solid electrolyte layer according to Comparative Example 3.

[0153] As can be seen from Figure 10 It can be seen that the solid electrolyte layer according to Comparative Example 1 had more voids than Example 2. These pores act as impedance, hindering the conduction of lithium ions and reducing the overall density of the solid electrolyte layer, thereby reducing the energy density of the battery.

[0154] In addition, as can be seen from Figures 11A to 11C As can be seen, the element chlorine (Cl) constituting the crystalline solid electrolyte appears brighter in the EDS phase, which indicates that it is not uniformly dispersed and is unevenly aggregated. It is predicted that the uneven arrangement of the elements occurs due to the temperature gradient of the heat treatment furnace. The unevenness of these elements can hinder the uniform movement of lithium ions and reduce battery performance.

[0155] Although not shown separately, the ionic conductivity of the solid electrolyte layer according to Comparative Example 3 was measured to be 8.9*10 -4 S / cm, which is more than twice lower than the ionic conductivity of the solid electrolyte layer according to Example 3.

[0156] Figures 8 to 11C The results of the image analysis of FIG. 1 are numerically expressed in Table 3 and Table 4 below. Table 3 relates to the solid electrolyte layer according to Example 2, and Table 4 relates to the solid electrolyte layer according to Comparative Example 3.

[0157] [Table 3]

[0158] element Line Type Wt% Wt% σ Standard Labels atom% P K Series 10.96 0.07 GaP 8.23 S K Series 46.32 0.23 FeS2 33.6 Cl K Series 10.93 0.08 NaCl 7.17

[0159] [Table 4]

[0160] element Line Type Wt% Wt% σ Standard Labels atom% P K Series 10.32 0.06 GaP 7.45 S K Series 43.18 0.2 FeS2 30.1 Cl K Series 10.67 0.07 NaCl 6.73

[0161] As can be seen from Table 3 and Table 4, although the same amorphous solid electrolyte as in Preparation Example 2 was used, there is a difference in the content of the elements. In particular, it can be seen that the content of sulfur (S) is higher (33.6 at% vs. 30.1 at%) in Example 2 in which the spark plasma sintering method was applied. This is because the volatilization of sulfur was suppressed in Example 2 in which the crystallization time was short

[0162] Accordingly, the solid electrolyte layer manufactured using the spark plasma sintering according to the present disclosure can effectively suppress the volatilization of elements such as sulfur because the crystallization and production of the solid electrolyte layer are achieved in a short time. In addition, the density of the manufactured solid electrolyte layer is about 88% to 99% of the theoretical density. This was confirmed by inputting the size of the unit cell for the solid electrolyte constituting the manufactured solid electrolyte layer and the type and amount of elements contained therein into an inorganic crystal structure database (ICSD).

[0163] Accordingly, compared to the conventional method using long-term heat treatment and high pressure, the solid electrolyte layer manufactured by the present disclosure can increase the density of the solid electrolyte layer by about 40%, improve the ionic conductivity by about 3 times, and reduce the electronic conductivity by about 2 times.

[0164] As is apparent from the foregoing, the present disclosure provides a manufacturing method of a solid electrolyte layer using spark plasma sintering, which allows the solid electrolyte layer to be manufactured in several minutes without a long heat treatment process.

[0165] Further, the present disclosure provides a method of manufacturing a solid electrolyte layer, which can provide a solid electrolyte layer having a higher density compared to a conventional manufacturing method involving a long heat treatment at high pressure. Accordingly, lithium ion conductivity of the solid electrolyte layer can be improved.

[0166] Effects of the present disclosure are not limited to those mentioned above. It should be understood that effects of the present disclosure include all effects that can be inferred from the description of the present disclosure

[0167] The present disclosure has been described in detail with reference to embodiments thereof. However, it will be appreciated by those skilled in the art that changes can be made to these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the appended claims and their equivalents.

Claims

1. A method for manufacturing a solid electrolyte layer, comprising: Preparation of amorphous solid electrolytes; as well as The amorphous solid electrolyte is crystallized using spark plasma sintering (SPS) to produce a solid electrolyte layer including a crystalline solid electrolyte.

2. The method according to claim 1, wherein The preparation of amorphous solid electrolytes involves mechanical grinding of solid electrolyte raw materials.

3. The method according to claim 2, wherein: The mechanical milling comprises at least one selected from the group consisting of air jet milling, bead milling, roller milling, planetary milling, hand milling, high energy ball milling, planetary ball milling, stirred ball milling, vibration milling, mechanical fusion milling, shaking milling, sand milling, disc milling, profile milling, Nauta milling, Nobilta milling, high speed mixing, and combinations thereof.

4. The method according to claim 1, wherein Crystallizing the amorphous solid electrolyte using spark plasma sintering comprises: placing the amorphous solid electrolyte in a spark plasma sintering apparatus; evacuating the spark plasma sintering equipment and applying reaction pressure thereto; ramping the temperature of the spark plasma sintering apparatus to a reaction temperature while maintaining the reaction pressure of the spark plasma sintering apparatus; and The reaction temperature is maintained for a predetermined reaction time to crystallize the amorphous solid electrolyte into the crystalline solid electrolyte.

5. The method according to claim 4, wherein The reaction pressure is 10 MPa to 90 MPa.

6. The method according to claim 4, wherein: The reaction time is 5 to 10 minutes.

7. The method according to claim 4, wherein: The reaction temperature is 500K to 700K.

8. The method according to claim 4, wherein The rate of temperature increase to reach the reaction temperature is 30 K / min to 100 K / min.

9. The method according to claim 4, further comprising: After crystallization, the crystalline solid electrolyte is cooled to room temperature.

10. The method according to claim 1, wherein The crystalline solid electrolyte includes a sulfide-based solid electrolyte.

11. The method according to claim 1, wherein The crystalline solid electrolyte includes an argyrodite-type crystal structure.

12. The method according to claim 1, wherein The crystalline solid electrolyte is represented by the following formula: Li 6+x-a-y A 1-x M x S 5-a X 1+a , in, A is P or Sb; M is Si, Ge or Sn; X comprises any one selected from Cl, Br, I and combinations thereof; and x satisfies 0≤x≤0.5, y satisfies 0≤y≤0.2, and a satisfies 0≤a≤0.

5.

13. The method according to claim 12, wherein: When A in the formula is P, spark plasma sintering is performed at a reaction temperature of 523K to 600K.

14. The method according to claim 12, wherein: When A in the formula is Sb, spark plasma sintering is performed at a reaction temperature of 573K to 673K.

15. The method according to claim 1, wherein The solid electrolyte layer has a thickness greater than or equal to 1.30*10 -3 S / cm ionic conductivity.

16. The method according to claim 1, wherein The density of the solid electrolyte layer is 88% to 99% of the theoretical density of the solid electrolyte.

17. The method according to claim 1, wherein Each element constituting the crystalline solid electrolyte is dispersed without agglomerating.

18. A solid electrolyte layer comprising a crystalline solid electrolyte crystallized using spark plasma sintering (SPS), in, The crystalline solid electrolyte includes a sulfide-based solid electrolyte.

19. The solid electrolyte layer according to claim 18, wherein The solid electrolyte layer has a thickness greater than or equal to 1.30*10 -3 S / cm ionic conductivity.

20. The solid electrolyte layer according to claim 18, wherein Each element constituting the crystalline solid electrolyte is dispersed without agglomerating.

Images