Solid electrolyte, all-solid-state battery, and method for manufacturing solid electrolyte

Abstract

The present invention has been made to solve the problems of the prior art, and aims at providing a solid electrolyte having improved ionic conductivity. The solid electrolyte of the present invention comprises Al and has an argyrodite-type crystal structure. The solid electrolyte of the present invention is represented by chemical formula Li7-x-3yAlyPS6-xHax. In chemical formula, Ha is at least one element selected from halogen elements, 0 < x < 2.5, and 0 < y < 0.1. In the solid electrolyte of the present invention, a peak intensity ratio I2 / I1 of I2, which is a maximum peak intensity at 30.15°≤2θ≤30.25°, to I1, which is a maximum peak intensity at 29.9°≤2θ≤30.1°, as measured by X-ray diffraction, is 0.15 or less.

Description

Solid electrolyte, all-solid-state battery and method for manufacturing solid electrolyte

[0001] The present invention relates to a solid electrolyte, an all-solid-state battery, and a method for manufacturing a solid electrolyte.

[0002] This application claims priority based on Japanese application No. 2024-232653 filed on December 27, 2024, and all contents disclosed in the specification of said application are incorporated into this application.

[0003] To achieve higher energy density and improved stability, the development of all-solid-state batteries is underway, in which the organic electrolyte of conventional lithium-ion batteries is replaced with a solid electrolyte. While solid electrolytes include oxides, sulfides, and chlorides, sulfide solid electrolytes with excellent moldability and electrochemical properties, such as argyrodite-based and Li₂O₃, are being utilized. 10 GeP2S 12 Systems and others are attracting attention as materials for all-solid-state batteries.

[0004] In addition, the development of Li metal anodes with a theoretical capacity approximately 10 times higher than conventional graphite and all-solid-state Li batteries utilizing them is attracting attention. However, many sulfide solid electrolytes have low electrochemical stability with respect to Li metal anodes. Since Li metal has a low potential, it undergoes a reduction reaction when in contact with a solid electrolyte, causing the solid electrolyte to decompose. This decomposition reaction promotes the growth of lithium dendrites, which leads to a short circuit in the battery.

[0005] Recently, research has been conducted on using Al as a material to improve the electrochemical stability of Li metal anodes. Patent document 1 discloses an all-solid-state battery in which dendrite growth is suppressed by adding Al metal particles to a solid electrolyte layer. Non-patent document 1 discloses a Li-Al alloy and an all-solid-state battery that prevent the reduction reaction of a sulfide solid electrolyte.

[0006] [Prior Art Literature]

[0007] [Patent Literature]

[0008] Patent Document 1: Japanese Patent Publication No. 2022-529975

[0009] [Non-patent literature]

[0010] Non-patent Document 1: Hui Pan et al., “Carbon-free and binder-free Li-Al alloy anode enabling an all-solid-state Li-S battery with high energy and stability”, Sci. Adv. 8, ebn4372 (2022). DOI: 10.1126 / sciadv. abn4372

[0011] However, the Al metal particles used in Patent Literature 1 have a maximum diameter of 1 μm, which hinders the Li ion conduction of the solid electrolyte. In addition, in Non-Patent Literature 1, pre-lithiation such as electrodeposition is required to obtain a Li-Al alloy, which increases the cost of mass production. Therefore, in order to improve the electrochemical stability of all-solid-state batteries and reduce mass production costs, it is necessary to develop a solid electrolyte that has high ion conductivity and excellent electrochemical stability for the Li metal anode.

[0012] The present invention is made to solve the problems of the prior art as described above, and has one objective of improving the electrochemical stability of a Li metal anode using only a solid electrolyte.

[0013] In addition, another objective of the present invention is to provide a solid electrolyte with improved ion conductivity.

[0014] As a result of carefully examining the above problem, the inventors discovered that in the case of a solid electrolyte having a specific composition and a specific XRD peak area ratio, the electrochemical properties and ionic conductivity of the Li metal cathode are improved, and thus reached the completion of the present invention.

[0015] To solve the above problem, the present invention includes the following configuration.

[0016] The solid electrolyte according to the present embodiment is,

[0017] It has an azyrodite-type crystal structure,

[0018] The above sulfide-based solid electrolyte has the chemical formula Li 7-x-3y Al y PS 6-x Ha x It is displayed as,

[0019] In the above chemical formula,

[0020] The above Ha is one or more elements selected from halogen elements, and

[0021] Satisfying 0 < x < 2.5 and 0 < y < 0.1,

[0022] The ratio of the peak intensity of the maximum peak intensity I2 at 30.15° ≤ 2θ ≤ 30.25° to the maximum peak intensity I1 at 29.9° ≤ 2θ ≤ 30.1° measured by X-ray diffraction, I2 / I1, is 0.15 or less.

[0023] In one embodiment, Al may be present at the 48h site of an azirodite-type crystal structure.

[0024] In one embodiment, in the above formula, Ha may include Cl and Br.

[0025] In one embodiment, when the D50 of the solid electrolyte is 5 μm or more and 50 μm or less, the solid electrolyte may have an ionic conductivity of 12 mS / cm or more.

[0026] In one embodiment, when the D50 of the solid electrolyte is 0.1 μm or more and less than 5 μm, the solid electrolyte may have an ionic conductivity of 7 mS / cm or more.

[0027] In one embodiment, the solid electrolyte may have a critical current density of 1.8 mA / cm² or more.

[0028] In one embodiment, the rate of change of the resistance value at the interface between the solid electrolyte and the Li metal may be 25% or less.

[0029] The present invention is a method for producing a sulfide-based solid electrolyte as described in any one of the aforementioned embodiments, wherein

[0030] A step of mixing a lithium source, an aluminum source, phosphorus, a sulfur source, and a halogen source to obtain a mixture, and

[0031] A method is provided that includes the step of calcining the above mixture at a temperature of 450°C or lower.

[0032] The present invention relates to an all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, wherein

[0033] The present invention provides an all-solid-state battery in which the solid electrolyte layer comprises a solid electrolyte described in any one of the embodiments described above.

[0034] In one embodiment, the cathode may be a Li metal cathode.

[0035] In one embodiment, the all-solid-state battery may include a compound containing Al between the solid electrolyte layer and the negative electrode.

[0036] In one embodiment, the compound containing Al may further contain Li.

[0037] In one aspect, according to the present invention, a solid electrolyte having electrochemical stability for a Li metal cathode can be provided.

[0038] In addition, in another aspect, the present invention can provide a solid electrolyte with improved ionic conductivity.

[0039] Figure 1 is a diagram showing DTA curves obtained from thermogravimetric analysis (TG-DTA) measurements of Example 2, Comparative Example 1, and Comparative Example 4.

[0040] Figure 2 is a diagram showing the X-ray diffraction (XRD) patterns of Example 2 and Comparative Example 1.

[0041] Figure 3 is a figure showing the ratio I2 / I1 of the peak intensity of the maximum peak intensity I2 of 30.15°≤2θ≤30.25° to the maximum peak intensity I1 of 29.9°≤2θ≤30.1° measured by XRD of Comparative Example 1.

[0042] Figure 4 is a diagram showing the XRD peak shift of the azirodite phase of Comparative Example 1.

[0043] FIG. 5a is a diagram showing the XRD patterns of Examples 1 to 3, Comparative Example 2, and Comparative Example 4.

[0044] FIG. 5b is an enlarged view of the area near the maximum peak of 29.9°≤2θ≤30.1° of the XRD patterns of Examples 1 to 3, Comparative Example 2, and Comparative Example 4.

[0045] FIG. 6 is a schematic diagram of a Li metal symmetric cell containing a sulfide solid electrolyte layer with added Group 3 element (Al).

[0046] FIG. 7 is a schematic diagram of a Li metal symmetric cell containing a sulfide solid electrolyte layer without the addition of a group 3 element (Al).

[0047] Figure 8a is a graph showing the polarization voltage and current density by the CCD (Critical Current Density) test of Example 4.

[0048] FIG. 8b is a graph showing the polarization voltage and current density by the CCD (Critical Current Density) test of Example 5.

[0049] FIG. 8c is a graph showing the polarization voltage and current density by the CCD (Critical Current Density) test of Example 6.

[0050] Figure 8d is a graph showing the polarization voltage and current density obtained by the CCD (Critical Current Density) test of Comparative Example 3.

[0051] Figure 9a is a graph showing the impedance measurement results of Example 4 during critical current density measurement.

[0052] Figure 9b is a graph showing the impedance measurement results of Example 5 during critical current density measurement.

[0053] Figure 9c is a graph showing the impedance measurement results of Example 6 during critical current density measurement.

[0054] Figure 9d is a graph showing the impedance measurement results of Comparative Example 3 during critical current density measurement.

[0055] The present invention will be described in more detail below.

[0056] Terms and words used in this specification and claims shall not be interpreted as being limited to their ordinary or dictionary meanings, and shall be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe their invention.

[0057] In the drawings, parts unrelated to the description have been omitted to clearly explain the invention, and similar parts throughout the specification have been given similar reference numerals. Additionally, the sizes and relative sizes of the components shown in the drawings are not related to the actual scale and may be reduced or exaggerated for clarity of explanation.

[0058] In this specification, 'Dn' represents a particle size distribution and refers to the particle size at the n% point of the cumulative distribution of the number of particles by particle size. That is, D50 is the particle size (center particle size, average particle size) at the 50% point of the cumulative distribution of the number of particles by particle size, D90 is the particle size at the 90% point of the cumulative distribution of the number of particles by particle size, and D10 is the particle size at the 10% point of the cumulative distribution of the number of particles by particle size. The particle size distribution can be measured using a laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500), and the difference in the diffraction pattern by particle size is measured when the particle passes through the laser beam to calculate the particle size distribution.

[0059] [Solid Electrolyte for All-Solid State Batteries]

[0060] The solid electrolyte for an all-solid-state battery according to the present invention comprises a sulfide solid electrolyte. In addition to sulfides, the electrolyte for an all-solid-state battery according to the present invention may also comprise oxide-based solid electrolytes and polymer-based solid electrolytes. Preferably, the electrolyte for an all-solid-state battery according to the present invention is a sulfide-based solid electrolyte. The solid electrolyte for an all-solid-state battery may be mixed into an anode composite and used as an anode material, mixed into a cathode composite and used as a cathode material, or used as a separator. Depending on the application, the solid electrolyte for an all-solid-state battery may further include additives such as lithium salts, conductive materials, and binder resins.

[0061] <Sulphide-based solid electrolytes>

[0062] Sulfide-based solid electrolytes can have a crystalline structure. Sulfide-based solid electrolytes having a crystalline structure promote the conduction of lithium ions, thereby enabling high lithium ion conductivity.

[0063] Sulfide-based solid electrolytes can generally have crystal structures of the azirodite, NASICON, perovskite, garnet, or LGPS type. Preferably, the sulfide-based solid electrolyte according to the present invention has an azirodite crystal structure. Since the sulfide-based solid electrolyte having an azirodite crystal structure has high stability with respect to lithium metal, it enables the use of lithium metal with a high mass energy density as a negative electrode material.

[0064] Sulfide-based solid electrolytes can be in the form of amorphous, glass, or glass ceramics.

[0065] Sulfide-based solid electrolytes are those having the ionic conductivity of metals belonging to Group 1 or Group 2 of the periodic table, and may include Li-PS-based glass or Li-PS-based glass ceramics. Non-limiting examples of such sulfide-based solid electrolytes include Li2S-P2S5, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, Li2S-GeS2-ZnS, etc., and may include one or more of these. However, they are not particularly limited to these.

[0066] Sulfide-based solid electrolytes may include crystalline and amorphous phases. Sulfide-based solid electrolytes may include a crystalline phase (also referred to herein as the azirodite phase) having an azirodite-type crystal structure and other phases (also referred to herein as impurity phases). The azirodite-type crystal structure is preferably cubic. The other phases may be crystalline or amorphous. Regardless of whether they are crystalline or amorphous, the other phases may include Li2S phase, P2S5 phase, LiCl phase, LiBr phase, Li3PS4 phase, Al2S3 phase, Ga2S3 phase, and In2S3 phase, etc. Preferably, the sulfide-based solid electrolyte does not include, or substantially does not include, an impurity phase other than the azirodite phase. That is, preferably, the sulfide-based solid electrolyte may consist only of the azirodite phase. When a sulfide-based solid electrolyte does not contain or substantially does not contain an impurity phase, lithium ion conduction is not easily inhibited, so the sulfide-based solid electrolyte can have a high lithium ion conductivity.

[0067] A sulfide-based solid electrolyte according to one embodiment of the present invention is, with the chemical formula Li 7-x-3y M y PS 6-x Ha x It is represented as follows. In the above chemical formula, M is one or more elements selected from Group 13 elements, Ha is one or more elements selected from halogen elements, and satisfies 0 < x < 2.5 and 0 < y < 0.1. Such a sulfide-based solid electrolyte can have high lithium ion conductivity. As an example, the composition of the solid electrolyte according to the present invention, that is, the values ​​of x and y in the above chemical formula, can be determined by ICP measurement. However, it is not limited to the aforementioned determination method, and a method for determining composition generally used in the art may be used.

[0068] The sulfide-based solid electrolyte of the present invention is Li 7-x PS6-x Ha x Some of the lithium in may be substituted with a Group 13 element (M) that can become a trivalent cation. The Group 13 element (M) substituting the lithium may be one or more selected from the group consisting of aluminum (Al), gallium (Ga), and indium (In). Aluminum (Al), gallium (Ga), and indium (In) may be used alone or in combination. The ionic radius (4-coordinate) of lithium (Li) is 59 pm, and the ionic radii (4-coordinate) of aluminum (Al), gallium (Ga), and indium (In) are 39 pm, 47 pm, and 62 pm, respectively. Based on the valence of the elements, three lithiums may be substituted with one Group 13 element (M). By substituting lithium sites with the Group 13 element (M), lithium site vacancies are created, and lithium ion conductivity may be improved. In addition, the lattice constant and lattice volume of the sulfide-based solid electrolyte change due to the substitution of lithium sites by a Group 13 element (M), so that it can have a crystal structure suitable for lithium ion conduction.

[0069] In addition, sulfide-based solid electrolytes have a Group 13 element (M) that can become a trivalent cation, Li 7-x PS 6-x Ha x It may be an element that has intervened into the crystal lattice. The Group 13 element (M) intervening into the crystal lattice may be one or more selected from the group consisting of aluminum (Al), gallium (Ga), and indium (In). Aluminum (Al), gallium (Ga), and indium (In) may be used alone or in combination. Li 7-x PS 6-x Ha x The lattice constant and lattice volume of the sulfide-based solid electrolyte change due to the intrusion of a group 13 element (M) into the crystal lattice, and the crystal structure suitable for lithium ion conduction can be obtained.

[0070] Preferably, the Group 13 element (M) is aluminum (Al). When the Group 13 element (M) is aluminum (Al), the sulfide-based solid electrolyte can have a high degree of crystallinity, and as a result, the sulfide-based solid electrolyte can have a high ionic conductivity. This is thought to be because the ionic radius of lithium (Li) is 59 pm and the ionic radius of aluminum (Al) is 39 pm, so the azirodite-type crystal structure is easily maintained even after substitution by the Group 13 element (M).

[0071] The above chemical formula Li 7-x-3y M y PS 6-x Ha x The amount y of the Group 13 element (M) added in satisfies 0 < y < 0.2. When the Group 13 element (M) is aluminum (Al), preferably y satisfies 0 < y < 0.1, more preferably 0.01 ≤ y ≤ 0.08, even more preferably 0.02 ≤ y ≤ 0.07, and most preferably 0.03 ≤ y ≤ 0.06. The lower limit of the range of y may be greater than 0, greater than or equal to 0.01, greater than or equal to 0.02, greater than or equal to 0.03, or greater than or equal to 0.04, and the upper limit of the range of y may be less than 0.1, less than or equal to 0.08, less than or equal to 0.07, or less than or equal to 0.06. When y satisfies the above range, the sulfide-based solid electrolyte may have a high ionic conductivity. When y is 0, the change in crystal structure due to the substitution of a group 13 element (M) is not obtained, so the ionic conductivity may be low. When y is 0.2 or higher, the azyrodite-type crystal structure of the sulfide-based solid electrolyte may not be maintained, and additionally, the impurity phase that inhibits lithium ion conduction in the sulfide-based solid electrolyte increases, so the ionic conductivity may be low.

[0072] When the Group 13 element (M) is aluminum (Al), the azirodite-type crystal structure of the sulfide-based solid electrolyte can be maintained even when the amount of addition y is large. When the Group 13 element (M) is gallium (Ga) or indium (In), the azirodite-type crystal structure of the sulfide-based solid electrolyte can be maintained at a relatively small amount of addition y. Although not bound by theory, it is thought that the difference in properties between aluminum (Al), gallium (Ga), and indium (In) is the reason. For example, when gallium (Ga) is used as a component of an alloy, it has the property of promoting alloying with other metal elements because it is easy to diffuse the grain boundaries of the alloy. This property can be observed in indium (In), which has electrons in the d orbital, just like gallium (Ga). Due to these characteristics, it is thought that gallium (Ga) or indium (In) can maintain the azirodite-type crystal structure of sulfide-based solid electrolytes at a relatively smaller amount of addition y than aluminum (Al).

[0073] Preferably, a Group 13 element (M) (preferably Al) exists at the 48h site of an azirodite-type crystal structure. More preferably, a Group 13 element (M) exists only at the 48h site of an azirodite-type crystal structure. A site is represented by a combination of a number and an English notation, where the number indicates the number of positions where an element can be placed within the crystal structure, and the English notation indicates the crystallographic symmetry of the site, assigned in order of increasing crystallinity as a, b, c, d... The azirodite-type crystal structure may be cubic, hexagonal, tetragonal, rotagonal, monoclinic, triclinic, etc. When the argyrodite-type crystal structure is cubic (space group F-43m), a Group 13 element (M) can exist at the 48h site in the crystal structure. The existence of a Group 13 element (M) at the 48h site in the crystal structure can be determined by neutron crystal structure analysis. Although not bound by theory, it is thought that if Al exists at the 48h site, which is the conduction path for Li ions, Al can also be conducted via the Li ion conduction path.

[0074] The above chemical formula Li 7-x-3y M y PS 6-x Ha xThe halogen (Ha) in the structure is one or more elements selected from halogen elements. It is preferable that the halogen (Ha) include bromine (Br). More preferably, the halogen (Ha) includes chlorine (Cl) and bromine (Br). Although not bound by theory, sulfur (S) is a divalent anion and exists in isolated sites of PS4 tetrahedra and 4a sites in an azyrodite-type crystal structure. By including monovalent anions such as chlorine (Cl) and bromine (Br), the occupancy of sulfur (S) in isolated sites is lowered, and the occupancy of halogens is increased. Considering the charge balance of the entire structure, the substitution of some of the divalent sulfur (S) with monovalent halogen elements lowers the occupancy of lithium accordingly. Consequently, voids are created in the lithium sites, which can increase the mobility of lithium ions. As a result, it is believed that the lithium ion conductivity can be improved. Furthermore, although not bound by theory, bromine (Br) can combine with Li in sulfide-based solid electrolytes to form lithium bromide (LiBr), an absorbent material. It is believed that lithium bromide (LiBr) can improve the lithium ion conductivity of sulfide-based solid electrolytes by adsorbing moisture, which can lower lithium ion conductivity.

[0075] The above chemical formula Li 7-x-3y M y PS 6-x Ha x The ratio x of the halogen (Ha) in the above range satisfies 0 < x < 2.5, preferably 1.0 ≤ x ≤ 2.3, more preferably 1.3 ≤ x ≤ 2.0, and even more preferably 1.3 ≤ x ≤ 1.8. When x satisfies the above range, the azirodite-type crystal structure is stabilized, and the sulfide-based solid electrolyte can have a high ionic conductivity.

[0076] The ionic conductivity of a sulfide-based solid electrolyte can be influenced by the degree of crystallization of the sulfide-based solid electrolyte. The degree of crystallization can be evaluated from the XRD pattern. In the XRD pattern, if phases other than the argyrodite crystalline phase (crystalline or amorphous phases such as Li2S phase, P2S5 phase, LiCl phase, LiBr phase, Li3PS4 phase, Al2S3 phase, Ga2S3 phase, and In2S3 phase) are not observed or are hardly observed, the sulfide-based solid electrolyte can have high ionic conductivity. Furthermore, even among the argyrodite crystalline phase, the design composition (e.g., Li 7-x-3y M y PS 6-x Ha x In cases where a composition deviating from ) (e.g., a halogen-excess system) is not observed or is hardly observed, sulfide-based solid electrolytes can have high ionic conductivity.

[0077] The proportion of the crystalline phase contained in a sulfide-based solid electrolyte can be evaluated quantitatively or semi-quantitatively from the XRD pattern. As one method, the proportion of the crystalline phase can be evaluated by comparing the peak intensities (height or area) of the XRD pattern.

[0078] In addition, the proportion of impurity phases other than the azirodite phase of the design composition in the solid electrolyte according to the present invention can be evaluated by the ratio I2 / I1 of the peak intensity of the maximum peak intensity I2 of 30.15°≤2θ≤30.25° to the maximum peak intensity I1 of 29.9°≤2θ≤30.1° measured by XRD. The maximum peak of 29.9°≤2θ≤30.1° is the peak of the azirodite-type crystalline phase having the design composition according to the present invention, and the maximum peak of 30.15°≤2θ≤30.25° is the peak of the azirodite-type crystalline phase having a composition deviating from the design composition. When the ratio I2 / I1, which is the peak intensity of the maximum peak intensity I2 for 30.15° ≤ 2θ ≤ 30.25° relative to the maximum peak intensity I1 for 29.9° ≤ 2θ ≤ 30.1°, is small, it means that in the solid electrolyte, the ratio of an azirodite-type crystalline phase having a composition deviating from the design composition to an azirodite-type crystalline phase having the design composition is small. I2 / I1 may be 0.15 or less, preferably 0.12 or less, 0.10 or less, more preferably 0.08 or less, 0.05 or less, 0.03 or less, and most preferably 0.01 or less. Additionally, I2 / I1 may be 0 or greater. I2 / I1 = 0 indicates that there is no azirodite-type crystalline phase having a composition deviating from the design composition. When I2 / I1 has a value of 0.15 or less, the proportion of a azirodite-type crystal phase having the design composition is high, and the ionic conductivity of the solid electrolyte can be improved.

[0079] The average particle size of solid electrolytes can be controlled depending on the application.

[0080] The average particle size (D50) of the solid electrolyte can be controlled by changing conditions such as whether or not grinding is performed after calcination, or the rotation speed and time of the ball mill device during grinding. Accordingly, it is possible to manufacture a solid electrolyte coarse powder with a relatively large average particle size and a solid electrolyte fine powder with a relatively small average particle size. In addition, as an example, D50 can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500), and the difference in diffraction patterns due to particle size when the particles pass through the laser beam is measured to calculate the particle size distribution and measure D50. In addition, when the solid electrolyte is in an all-solid-state battery, the D50 of the solid electrolyte can be determined by confirming the particle size distribution, for example, through SEM observation.

[0081] The average particle size of the solid electrolyte coarse particles may be larger than the average particle size of the solid electrolyte fine particles. The average particle size of the solid electrolyte coarse particles is 5 μm or more and 50 μm or less, preferably 8 μm or more and 30 μm or less, and more preferably 10 μm or more and 20 μm or less. The average particle size of the solid electrolyte fine particles is 0.1 μm or more and less than 5 μm, preferably 0.5 μm or more and less than 5 μm, and more preferably 1 μm or more and 3 μm or less.

[0082] The average particle size of the sulfide-based solid electrolyte included in the solid electrolyte layer may be larger than the average particle size of the sulfide-based solid electrolyte included in the positive electrode active material layer. Since coarse solid electrolyte particles have a large average particle size and fewer grain boundaries per unit volume, they can exhibit high ionic conductivity when used in the solid electrolyte layer. Therefore, by making the average particle size of the sulfide-based solid electrolyte included in the solid electrolyte layer larger than that of the sulfide-based solid electrolyte included in the positive electrode active material layer, the discharge capacity and cycle characteristics of the all-solid-state battery can be improved. On the other hand, since fine solid electrolyte particles have a small average particle size and many grain boundaries per unit volume, they tend to have lower ionic conductivity compared to coarse solid electrolyte particles; however, when used in the positive electrode active material layer, they can enter the gaps between positive electrode active material particles, providing a lithium ion conduction pathway to the positive electrode active material, which is an advantage. In addition, when using solid electrolyte fine powder together with a lithium metal electrode, the average particle size is small and the gaps between solid electrolyte layers are small, so compared to solid electrolyte coarse powder, it has the advantage of suppressing the dendrite growth of lithium metal and preventing short circuits.

[0083] The ionic conductivity of a sulfide-based solid electrolyte (also referred to as "lithium ionic conductivity" in this specification) refers to the ionic conductivity at room temperature (25°C, 298K) and atmospheric pressure (1 atm), unless otherwise specifically stated. When a sulfide-based solid electrolyte is used in an all-solid-state battery, it is practical to have an ionic conductivity of 4 mS / cm or higher. The ionic conductivity of a sulfide-based solid electrolyte according to one embodiment of the present invention may be 10 mS / cm or higher in the case of a solid electrolyte coarse powder, preferably 12 mS / cm or higher, more preferably 13 mS / cm or higher. The ionic conductivity of a sulfide-based solid electrolyte according to one embodiment of the present invention may be 4 mS / cm or higher in the case of a solid electrolyte fine powder, preferably 6 mS / cm or higher, more preferably 7 mS / cm or higher, and most preferably 7.5 mS / cm or higher.

[0084] The electrochemical stability of a sulfide-based solid electrolyte can be evaluated, for example, by fabricating a Li metal symmetric cell using the sulfide-based solid electrolyte and conducting a Critical Current Density (CCD) test. A current density is applied to the Li metal symmetric cell to precipitate and dissolve Li on both sides of the solid electrolyte. As the current density is gradually increased, decomposition and short circuits of the solid electrolyte occur due to the precipitation and dissolution of Li. The maximum current density at which such decomposition and short circuits occur is called the CCD or critical current density. It can be said that the electrochemical stability with respect to Li metal is higher the larger the CCD. In the case of the sulfide-based solid electrolyte according to the present invention, the critical current density may be 1.5 mA / cm² or higher, preferably 1.8 mA / cm² or higher, more preferably 2.0 mA / cm² or higher, and most preferably 2.2 mA / cm² or higher.

[0085] In addition, AC impedance measurement can be performed simultaneously with the above CCD test to measure the interfacial resistance of the interface between the sulfide-based solid electrolyte and the Li metal. In the case of the sulfide-based solid electrolyte according to the present invention, the rate of increase in resistance at each current density calculated by Equation 1 below may be 25% or less at a current density of 1.5 mA / cm², preferably 20% or less, more preferably 10% or less, even more preferably 5% or less, and most preferably 1% or less. When the rate of increase in resistance at a current density of 1.5 mA / cm² is 25% or less, the solid electrolyte according to the present invention may have improved electrochemical stability with respect to the Li metal electrode.

[0086] [Equation 1]

[0087] (Rate of increase in resistance (%)) = 100 × {(Interfacial resistance at each current density (Ω)) - (Interfacial resistance at 0 mA / cm² (Ω))} / (Interfacial resistance at 0 mA / cm² (Ω))

[0088] A sulfide-based solid electrolyte according to one embodiment of the present invention can be obtained by a manufacturing method comprising the steps of: mixing a lithium source, a Group 13 element source, a phosphorus source, a sulfur source, and a halogen source to obtain a mixture; and calcining the mixture at a temperature of 450°C or lower under an inert atmosphere such as argon gas and nitrogen gas.

[0089] The lithium source, the Group 13 element source, the phosphorus source, the sulfur source, and the halogen source may be compounds such as sulfides, oxides, and nitrides. Lithium sulfide (Li2S) may be used as the lithium source, phosphorus pentasulfide (P2S5) as the phosphorus source, and lithium halides (LiHa), such as lithium chloride (LiCl) and lithium bromide (LiBr), may be used as the halogen source. For example, sulfides may be used as the Group 13 element source. Alternatively, sulfur may be supplied from other element sources. That is, one or more of the lithium source, the Group 13 element source, the phosphorus source, and the halogen source may serve as the sulfur source.

[0090] For sulfide-based solid electrolytes having an azirodite-type crystal structure, the calcination temperature is generally around 400°C to 550°C. However, since decomposition reactions from the azirodite phase of the designed composition may occur at temperatures above a certain level, it is more desirable to calcin at a temperature below that decomposition reaction temperature. For the solid electrolyte according to the present invention, the calcination temperature is preferably 450°C or lower, more preferably 400°C to 450°C, and even more preferably 410°C to 440°C. When the calcination temperature satisfies the above range, the formation of the azirodite-type crystal structure is promoted, preventing decomposition reactions, and the sulfide-based solid electrolyte can have a high degree of crystallinity and a low impurity phase ratio. Accordingly, a sulfide-based solid electrolyte having high ionic conductivity can be obtained.

[0091] [All-solid-state battery]

[0092] The electrolyte for an all-solid-state battery according to the present invention can be used in an all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer. The solid electrolyte for an all-solid-state battery can be used together with an active material in the electrode active material layer at the positive and negative electrodes. The solid electrolyte for an all-solid-state battery can be used as a material for the solid electrolyte layer. The average particle size of the electrolyte for an all-solid-state battery can be controlled according to the application. By controlling the average particle size of the electrolyte for an all-solid-state battery, the ion conductivity can be improved.

[0093] <Solid Electrolyte Layer>

[0094] The solid electrolyte layer is located between the anode and the cathode. In the present invention, the thickness of the solid electrolyte layer may be about 50 μm or less, preferably about 15 μm or more and 50 μm or less. Within the aforementioned range, a suitable thickness may be taken into consideration ion conductivity, physical strength, and the energy density of the applied battery. For example, in terms of ion conductivity or energy density, the thickness may be 10 μm or more, 20 μm or more, or 30 μm or more. On the other hand, in terms of physical strength, the thickness may be 50 μm or less, 45 μm or less, or 40 μm or less. In addition, the solid electrolyte layer may have a thickness range and simultaneously possess a tensile strength of 100 kgf / cm² or more and about 2,000 kgf / cm² or less. Furthermore, the solid electrolyte layer may have a porosity of 15 vol% or less, or about 10 vol% or less. Thus, the solid electrolyte layer according to the present invention can possess high mechanical strength despite being a thin film.

[0095] <Anode and Cathode>

[0096] In the present invention, the anode and the cathode comprise a current collector and an electrode active material layer formed on at least one surface of the current collector, and the electrode active material layer comprises a plurality of electrode active material particles and a solid electrolyte. Additionally, the electrode may further comprise one or more of a conductive material and a binder resin as needed. Furthermore, the electrode may further comprise various additives for the purpose of supplementing or improving the physicochemical properties of the electrode.

[0097] In the present invention, any material capable of being used as a negative electrode active material for a lithium-ion secondary battery may be used as the negative electrode active material. For example, the negative electrode active material may be carbon such as non-graphitizable carbon, graphitic carbon, etc.; Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me y O zOne or more selected from metal composite oxides such as (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of Group 1, Group 2, and Group 3 of the periodic table, halogens; 0<x≤1; 1≤y≤3; 1≤z≤8); lithium metal; lithium alloy; silicon metal; silicon-based alloy; indium metal; indium alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; titanium oxide; lithium titanium oxide, etc. may be used. In a specific embodiment, the negative electrode active material may include a carbon-based material and / or Si.

[0098] In the present invention, a Li metal cathode may preferably be used as the cathode. Although not bound by theory, Al in the solid electrolyte is conducted via the Li ion conduction path, and a compound (precipitate) containing Al is formed at the interface with the Li metal cathode in contact with the solid electrolyte, thereby improving the electrochemical stability of the Li metal cathode and thus improving the cycle characteristics of the battery. It is preferable that the compound (precipitate) containing Al also contains Li.

[0099] In the case of the positive electrode, the electrode active material may be used without restriction as long as it is suitable for use as a positive electrode active material for a lithium-ion secondary battery. For example, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-xLithium manganese oxides such as O4 (x is 0–0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-x A x Ni-site type lithium nickel oxide represented by O2 (A=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, x=0.01–0.3); chemical formula LiMn 2-x A x Lithium manganese composite oxide represented as O2 (A=Co, Ni, Fe, Cr, Zn or Ta, x=0.01–0.1) or Li2Mn3AO8 (A=Fe, Co, Ni, Cu or Zn); LiNi x Mn 2-x Lithium manganese complex oxide with a spinel structure denoted by O4; Li(Ni a Co b Mn c It may include, but is not limited to, NCM-based complex oxides represented by )O2 (where a, b, and c are atomic fractions of independent elements, 0 < a < 1, 0 < b < 1, 0 < c < 1, a+b+c=1); LiMn2O4 in which part of the Li of the chemical formula is substituted with alkaline earth metal ions; disulfide compounds; Fe2(MoO4)3, etc.

[0100] In the present invention, the current collector may be a current collector known in the field of secondary batteries having electrical conductivity, such as a metal plate, and may be appropriately used according to the polarity of the electrode.

[0101] In the present invention, the conductive material is typically added in an amount of 1% to 30% by weight based on the total weight of the mixture containing the electrode active material. Such a conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and may include, for example, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or a mixture of two or more types selected from conductive materials such as polyphenylene derivatives.

[0102] In the present invention, the binder resin is not particularly limited as long as it is a component that assists in the bonding of the active material and the conductive material, and the bonding to the current collector, and examples include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, and various copolymers. The binder resin may typically be included in a range of 1 to 30 weight% or 1 to 10 weight% with respect to 100 weight% of the electrode active material layer.

[0103] In the present invention, the electrode active material layer may include one or more additives such as an oxidation stabilizing additive, a reduction stabilizing additive, a flame retardant, a heat stabilizer, and an antifogging agent, as needed.

[0104] The present invention provides a secondary battery having the structure described above. In addition, the present invention provides a battery module including the secondary battery as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. Specific examples of the device include, but are not limited to, a power tool driven by receiving power from an electric motor; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), etc.; an electric two-wheeled vehicle including an electric bicycle (E-bike) or an electric scooter (E-scooter); an electric golf cart; and a power system.

[0105] Example

[0106] The present invention will be explained in more detail below using examples and comparative examples. However, the scope of the present invention is not limited to the examples.

[0107] <1. Preparation of Solid Electrolytes>

[0108] (Example 1)

[0109] Lithium sulfide (Li2S, Mitsuwa Chemical), phosphorus pentasulfide (P2S5, Aldrich), aluminum sulfide (Al2S3, Japan Pure Chemical), lithium chloride (LiCl, Aldrich), and lithium bromide (LiBr, Aldrich) were used as raw materials. These raw materials, with a composition of Li 5.4-3y Al y PS 4.4 Cl 1.0 Br 0.6A mixed powder was obtained by weighing and mortar-and-mortar mixing in an Ar gas glove box so that (y=0.025). This mixed powder was placed into a zirconia port along with zirconia (ZrO2) balls and sealed to obtain a sealed port. This sealed port was installed in a planetary ball mill and ball milled at 380 rpm for 20 hours. Afterward, the port was opened in an Ar gas glove box to recover the precursor powder. This precursor powder was placed in a carbon crucible and sealed, then calcined at 430°C for 8 hours while flowing Ar gas. The calcined powder was ground in a mortar for 5 minutes to obtain 5g of crude solid electrolyte powder.

[0110] (Example 2)

[0111] Jo Seong-i Li 5.4-3y Al y PS 4.4 Cl 1.0 Br 0.6 It was manufactured in the same manner as Example 1, except that the raw material was weighed to (y=0.05).

[0112] (Example 3)

[0113] Jo Seong-i Li 5.4-3y Al y PS 4.4 Cl 1.0 Br 0.6 It was manufactured in the same manner as Example 1, except that the raw material was weighed to (y=0.075).

[0114] (Examples 4 to 6: Micronized solid electrolyte)

[0115] The solid electrolyte crude powder obtained in Examples 1 to 3 was introduced into a zirconia pot, and wet grinding was performed at 250 rpm for 1 hour using zirconia balls and anisole solvent to obtain fine solid electrolyte powder for use as an anode composite material, except that the solid electrolyte fine powder was prepared in the same manner as in Examples 1 to 3.

[0116] (Comparative Example 1)

[0117] A solid electrolyte crude powder was obtained in the same manner as in Example 2, except that the calcination temperature was set to 460℃.

[0118] (Comparative Example 2)

[0119] A solid electrolyte crude powder not containing Al was obtained in the same manner as in Example 2, except that aluminum sulfide was not used among the raw materials. The composition of the solid electrolyte obtained in Comparative Example 2 was Li 5.4 PS 4.4 Cl 1.0 Br 0.6 It was.

[0120] (Comparative Example 3)

[0121] The Al-free solid electrolyte crude powder obtained in Comparative Example 2 was introduced into a zirconia pot and finely ground by wet grinding at 250 rpm for 1 hour using zirconia balls and anisole solvent, except that it was prepared in the same manner as Comparative Example 2.

[0122] (Comparative Example 4)

[0123] Jo Seong-i Li 5.4-3y Al y PS 4.4 Cl 1.0 Br 0.6 It was manufactured in the same manner as Example 1, except that the raw material was weighed to (y=0.1).

[0124] <2. Evaluation Methods for Solid Electrolytes>

[0125] (1) TG-DTA measurement

[0126] To optimize the synthesis temperature, TG-DTA measurements were performed. Approximately 10 mg of the precursor powder obtained in Example 2, Comparative Example 1, and Comparative Example 4 was placed in an aluminum oxide (Al2O3) pan, and the phase transition temperature was measured using a TG-DTA device installed in an Ar gas glove box. The measurement temperature range was set from room temperature (approx. 25°C) to 600°C, and the Ar flow rate was set to 450 mL / min.

[0127] (2) XRD measurement

[0128] A predetermined amount (about 30 mg) of the solid electrolyte powders of Examples 1 to 3, Comparative Example 1, Comparative Example 2, and Comparative Example 4 was placed in a sealed holder inside an Ar gas glove box, and XRD measurements were performed. Using the SmartLab XRD device of the CuKα1 vacuum tube, measurements were performed in a measurement range of 2θ = 10° or higher and 60° or lower.

[0129] (3) Particle size distribution measurement

[0130] The solid electrolyte powders of Examples 1 to 6 and Comparative Examples 1 to 4 were added to a heptane solvent, and a solid electrolyte dispersion solution was prepared using Span80 as a dispersant. Using this dispersion solution, the particle size distribution was measured by a particle size distribution measuring device Mastersizer 3000. The refractive index of the solid electrolyte used for data analysis was set to 2.16.

[0131] (4) Ionic conductivity measurement

[0132] After weighing a predetermined amount (approximately 50 mg) of the solid electrolyte powder of Examples 1 to 7 and Comparative Examples 1 to 4, a pellet forming jig (lower press pin) and a MACOR with a diameter of 5 mm ® A pipe was assembled, and a weighed solid electrolyte powder was introduced into the Mako pipe. Subsequently, combined with a pellet forming jig (upper press pin), it was press-formed at approximately 370 MPa using a single-axis press. After placing a predetermined amount (about 20 mg) of gold powder on both sides of the obtained pellet, it was press-formed at approximately 554 MPa using a single-axis press. The fabricated Mako pipe cell was installed in an electrochemical measurement jig cell, and an ion conductivity measurement cell was obtained by applying pressure up to 80 MPa using a torque wrench. This measurement cell was connected to an impedance measuring device, and the resistance value of the solid electrolyte pellet was measured to derive the ion conductivity.

[0133] (5) Crystal structure analysis

[0134] Obtained Example 2 (Li 5.25 Al 0.05 PS 4.4 Cl 1.0 Br 0.6 ) and Comparative Example 2 (Li 5.4 PS 4.4 Cl 1.0 Br 0.6 Neutron diffraction measurements were performed using the solid electrolyte powder of ). Using the obtained data, crystal structure analysis was performed using the Z-Rietveld program.

[0135] (6) CCD test

[0136] (6-1) Fabrication of Li metal symmetric cells

[0137] To evaluate the electrochemical stability of Li metal, a Li metal symmetric cell was fabricated. 150 mg of the solid electrolyte fine powder obtained in Examples 4 to 6 and Comparative Example 3 was weighed, placed in a molding jig, and pressurized at 550 MPa for 1 minute to obtain a solid electrolyte layer pellet. Subsequently, Li foil was placed on both sides of the solid electrolyte pellet, and a SUS plate was placed on top of the Li foil. Then, it was pressurized at 18 MPa for 2 seconds. After placing this in a jig cell, a restraining pressure of approximately 8 MPa was applied to obtain a Li metal symmetric cell.

[0138] Representative schematic diagrams of the Li metal symmetric cell of the example and comparative example are shown in FIGS. 6 and 7. As shown in FIGS. 6 and 7, a sulfide solid electrolyte layer (3) with a group 3 element (Al) added or a sulfide solid electrolyte layer (4) without a group 3 element (Al) added is in direct contact with a Li foil (2). By precipitating and dissolving Li on both sides of the solid electrolyte layer of this Li metal symmetric cell, the electrochemical stability of the Li metal can be evaluated.

[0139] (6-2) CCD test of a Li metal symmetric cell

[0140] Using the Li metal symmetry cell obtained in (6-1), a Critical Current Density (CCD) test was performed at 25°C. The current density was set to a range of 0 mA / cm² or higher and 3 mA / cm² or lower, the deposition and dissolution time was 1 hour, and the increase in current density was 0.1 mA / cm².

[0141] (7) Impedance measurement

[0142] Using the Li metal symmetric cell obtained in (6-1), AC impedance measurements were performed simultaneously with CCD testing to observe changes in the interfacial resistance between the solid electrolyte and the Li metal. Impedance measurements were taken in the range of 7 MHz to 100 mHz immediately after the cell was fabricated, at every 0.5 mA / cm² increase in current density. In addition, using the measured interfacial resistance values, the rate of increase in resistance at each current density was calculated based on Equation 1 below.

[0143] [Equation 1]

[0144] (Rate of increase in resistance (%)) = 100 × {(Interfacial resistance at each current density (Ω)) - (Interfacial resistance at 0 mA / cm² (Ω))} / (Interfacial resistance at 0 mA / cm² (Ω))

[0145] <3. Evaluation Results of Solid Electrolytes>

[0146] (1) TG-DTA measurement

[0147] The evaluation results of the phase transition temperature by TG-DTA measurement are shown in Table 1. Additionally, the obtained DTA curves are shown in Figure 1. For all measured compositions, an endothermic peak appeared around 460°C, indicating that some reaction was occurring. Furthermore, as the amount of Al added increased, the endothermic peak temperature tended to decrease to around 456°C.

[0148] [Table 1]

[0149]

[0150] (2) XRD measurement

[0151] (2-1) Optimization of firing temperature

[0152] XRD measurements were performed on samples of Example 2 and Comparative Example 1 to identify the products around the endothermic peak at 456°C to 460°C, the presence of which was confirmed by TG-DTA measurement. The obtained XRD patterns are shown in Fig. 2. As shown in Fig. 2, an impurity phase appeared in Comparative Example 1, which was calcined at 460°C, whereas there was no impurity phase in Example 1.

[0153] More specifically, to compare the amount of the impurity phase, the ratio I2 / I1 of the peak intensity of the maximum peak intensity I2 at 30.15° ≤ 2θ ≤ 30.25° to the maximum peak intensity I1 at 29.9° ≤ 2θ ≤ 30.1° measured by XRD was calculated. The results of Comparative Example 1 are shown in Fig. 3. When the maximum peak I1 appearing around 30° is normalized to 1, the maximum peak I2 of the impurity phase originating from the chlorinated Li6PS5Cl appearing at 30.2° becomes 0.16, and thus the value of I2 / I1 was calculated to be 0.16. On the other hand, when the same analysis was performed, the value of I2 / I1 in Example 2 was 0.

[0154] Figure 2 also shows the results of identifying the impurity phases around 29°–32° confirmed in the XRD pattern of Comparative Example 1. As a result of identifying the impurity phases, all impurities correspond to a azirodite-type solid electrolyte, including brominated Li6PS5Br, chlorinated Li6PS5Cl, and chlorine-excessive Li 5.5 PS 4.5 Cl 1.5...was detected. When comparing the ionic radii of the anions within the phase, Br (1.96 Å) > S (1.84 Å) ≈ Cl (1.81 Å). As the ionic radius increases, the lattice constant also increases; therefore, based on the area around 30°, the bromine-based phase appears at 29.8° on the low-angle side and the chlorine-based phase appears at 30.2° on the high-angle side. Additionally, a chlorine-excess phase, in which lithium is further reduced and chlorine is increased, appears at 30.4°. Considering the measurement results of the aforementioned TG-DTA, the endothermic peak at around 456° to 460° is thought to be a reaction in which the phase of the design composition containing Al decomposes into each azirodite phase corresponding to the impurity phase.

[0155] In addition, Figure 4 shows the peak shift of the azirodite phase of Comparative Example 1 (calcined at 460°C) relative to Example 2 (calcined at 430°C). No peak splitting was observed in any of the samples, and they remained as single peaks. In Comparative Example 1, compared to Example 2, it was confirmed that both peaks around 30° and 31.4° were shifted slightly (about 0.01°) toward a higher angle. A shift toward a higher angle implies a decrease in the lattice constant, that is, a reduction in the lattice. A reduction in the lattice makes it difficult for Li ions to conduct. Meanwhile, an expansion of the full width at half maximum was not observed visually in the XRD pattern. Accordingly, it is thought that there is not a plurality of main phases, but only one main phase, and that the stoichiometric composition is slightly misaligned due to the presence of the aforementioned impurity phase, resulting in a reduction in the lattice.

[0156] From the above results, it was determined that when manufacturing a solid electrolyte having an azirodite-type crystal structure, a calcination temperature of 450°C or lower is preferable. Therefore, in the example, the calcination temperature was set to 430°C.

[0157] (2-2) Confirmation of crystallization

[0158] The evaluation results of the crystal phases identified from the XRD patterns obtained by XRD measurement are shown in Table 2. Additionally, the XRD patterns are shown in Figures 5a and 5b. As shown in Table 2 and Figure 5a, in the solid electrolyte powders of Examples 1 to 3 (y=0.025–0.075) and Comparative Example 2 (y=0), almost only peaks of the azirodite phase appeared, and no peaks of the impurity phase appeared. However, in Comparative Example 4 (y=0.1), an impurity phase peak appeared near 2θ=29°. In addition, as shown in FIG. 5b, in Examples 1 to 3, Comparative Example 2, and Comparative Example 4, a peak at 29.9° ≤ 2θ ≤ 30.1° (a peak of an azirodite-type crystal phase having a design composition) appeared, but no peak at 30.15° ≤ 2θ ≤ 30.25° (a peak of an azirodite-type crystal phase having a composition deviating from the design composition) appeared. Therefore, for Examples 1 to 3, Comparative Example 2, and Comparative Example 4, the ratio I2 / I1 of the peak intensity of the maximum peak intensity I2 at 30.15° ≤ 2θ ≤ 30.25° to the maximum peak intensity I1 at 29.9° ≤ 2θ ≤ 30.1° measured by XRD was calculated to be 0.

[0159] [Table 2]

[0160]

[0161] (3) Particle size distribution measurement

[0162] The results of the particle size distribution measurement are shown in Table 3. The D50 of the solid electrolyte coarse powder of Examples 1 to 3 and the solid electrolyte fine powder of Examples 4 to 6 were 11.1 μm to 15.0 μm and 2.04 μm to 2.29 μm, respectively. In addition, the D50 of the solid electrolyte coarse powder of Comparative Example 2 (y=0) and the solid electrolyte fine powder of Comparative Example 3 were 15.7 μm and 2.20 μm, respectively. From these results, it was confirmed that the solid electrolyte can be finely pulverized by the solid electrolyte pulverization process.

[0163] [Table 3]

[0164]

[0165] (4) Ionic conductivity measurement

[0166] The measurement results of ionic conductivity are shown in Table 2. As shown in Table 2, the ionic conductivity was 13.1 mS / cm or higher for the coarse solid electrolytes of Examples 1 to 3, and 6.46 mS / cm or higher for the fine solid electrolytes of Examples 4 to 6. In addition, it was 11.5 mS / cm for the coarse solid electrolyte of Comparative Example 2 and 6.98 mS / cm for the fine solid electrolyte of Comparative Example 3. In the examples and comparative examples, it was confirmed that the ionic conductivity decreased due to pulverization.

[0167] Furthermore, Comparative Example 1, calcined at 460°C, exhibited an ionic conductivity of 5.9 mS / cm, which is significantly lower than that of Example 2, which had the same composition and was calcined at 430°C. This is due to the brominated Li6PS5Br, chlorinated Li6PS5Cl, and chlorine-excessive Li confirmed in the XRD pattern of Comparative Example 1. 5.5 PS 4.5 Cl 1.5 It is believed that this is because the ionic conductivity of the impurity phase is low, approximately 5 mS / cm, 3 mS / cm, and 8 mS / cm, respectively. In addition, in Comparative Example 1, as previously mentioned, compared to Example 2, the peak of the azirodite phase shifted toward a higher angle, confirming that the lattice was reduced. From these results, it is possible to consider two causes for the lower ionic conductivity in Comparative Example 1, which was calcined at 460°C: (a) the formation of the impurity phase, and (b) the contraction of the ion conduction path due to the shrinkage of the lattice.

[0168] (5) Crystal structure analysis

[0169] The results of the neutron crystal structure analysis of the solid electrolyte coarse powder obtained in Example 2 (y=0.05) and Comparative Example 2 (y=0) are shown in Tables 4 and 5, respectively. In the tables, g represents the occupancy rate of each site. Additionally, x, y, and z are parameters determined by the site and represent the ratio of the lattice constants in the x, y, and z directions to the location of the element. Biso is an atomic displacement parameter and represents the distribution of displacement due to thermal vibration of atoms. In the neutron crystal structure analysis, Li (-1.90) and Al (3.449) can be distinguished by the difference in atomic scattering factors, allowing for verification of whether Al acts as a carrier ion or a framework-forming element. Compared to Comparative Example 2, it can be seen that in the solid electrolyte coarse powder obtained in Example 2, Al is present at the 48h site, which corresponds to the Li ion conduction path in the crystal structure. The ionic radii of Al and Li are 0.39 Å and 0.59 Å, respectively, and the ionic radius of Al is smaller than that of Li. Because of this, Al and Li can coexist at the 48h site. Therefore, it is thought that Al also conducts via the Li ion conduction pathway as a carrier ion, albeit in small amounts. The lattice constants of Example 2 and Comparative Example 2 obtained from crystal structure analysis are 9.869164 (7) Å and 9.868944 (6) Å, respectively, and are slightly larger in Example 2, which has Al added. It is thought that this increase in lattice constant widens the Li ion conduction pathway, contributing to the improvement of ion conductivity.

[0170] Analysis result of the neutron crystal structure of the solid electrolyte powder of Example 2

[0171] [Table 4]

[0172]

[0173] Analysis result of the neutron crystal structure of the solid electrolyte powder of Comparative Example 2

[0174] [Table 5]

[0175]

[0176] (6) CCD test

[0177] Figures 8a to 8d show the polarization voltage and current density obtained by the Critical Current Density (CCD) test. As the current density increases, the accompanying polarization voltage also increases symmetrically. However, if one side of the solid electrolyte interface decomposes, the shape of the polarization voltage becomes asymmetric, leading to further short circuits. The maximum current density at which this asymmetry occurs is the critical current density (CCD). The electrochemical stability of the Li metal cathode can be evaluated using this CCD value. As shown in Figures 8a to 8d, for Example 4 (y=0.025), Example 5 (y=0.05), and Example 6 (y=0.075), the CCD values ​​were 2.4 mA / cm², 2.1 mA / cm², and 1.5 mA / cm², respectively. In the case of Comparative Example 3, the CCD was 1.5 mA / cm², which was lower than that of Examples 4 and 5. In other words, it was confirmed that the CCD was improved by the addition of Al. Although not bound by theory, it is believed that the electrochemical stability was improved because Al in the solid electrolyte is conducted via the Li ion conduction pathway, and precipitates containing Al are formed at the interface of the Li metal in contact with the solid electrolyte.

[0178] (7) Impedance measurement

[0179] FIGS. 9a to 9d show the impedance measurement results of Examples 4 to 6 and Comparative Example 3 during critical current density measurement. Resistance of the solid electrolyte-Li metal interface corresponding to 1 MHz to 1 kHz, and charge transfer resistance of the Li metal corresponding to 1 kHz or less are observed. Tables 6a and 6b show the resistance values ​​(Table 6a) and the rate of increase (Table 6b) of the solid electrolyte-Li metal interface of Examples 4 to 6 and Comparative Example 3. As the current density increases, the resistance value in Comparative Example 3 increases significantly, whereas it does not increase to the same extent in Examples 4 to 6. Specifically, the rate of increase of the resistance value of the solid electrolyte-Li metal interface at a current density of 1.5 mA / cm² was a maximum of 21.3% for Examples 4 to 6, whereas it was 53.8% for Comparative Example 3. In particular, Example 4 showed a small increase rate of less than 1%. From these results, it was confirmed that the increase in interfacial resistance at the interface between the solid electrolyte and the Li metal was suppressed by the addition of Al. Thus, when Al is added to the solid electrolyte, reductive decomposition caused by contact between the solid electrolyte and the Li metal anode is suppressed, thereby improving the increase in interfacial resistance and interfacial non-uniformity caused by decomposition products. Therefore, it is believed that Li dendrite growth caused by interfacial non-uniformity can be suppressed. As described above, the improvement in electrochemical stability of the Li metal anode by the addition of Al is suggested, and applications in all-solid-state batteries are expected.

[0180] [Table 6a]

[0181]

[0182] [Table 6b]

[0183]

[0184] [Explanation of the symbol]

[0185] 1: The whole house

[0186] 2: Li Park

[0187] 3: Solid electrolyte layer (Al added)

[0188] 4: Solid electrolyte layer (no Al added)

Claims

1. Having an azyrodite-type crystal structure, Chemical formula Li 7-x-3y Al y PS 6-x Ha x It is displayed as, In the above chemical formula, The above Ha is one or more elements selected from halogen elements, and Satisfying 0 < x < 2.5 and 0 < y < 0.1, A solid electrolyte in which the ratio of the peak intensity of the maximum peak intensity I2 at 30.15° ≤ 2θ ≤ 30.25° to the maximum peak intensity I1 at 29.9° ≤ 2θ ≤ 30.1° measured by X-ray diffraction, I2 / I1, is 0.15 or less.

2. In Paragraph 1, A solid electrolyte in which Al is present at the 48h site of an azirodite-type crystal structure.

3. In Paragraph 1, A solid electrolyte in which, in the above chemical formula, Ha comprises Cl and Br.

4. In Paragraph 1, A solid electrolyte having an ionic conductivity of 12 mS / cm or more, when the D50 of the solid electrolyte is 5 μm or more and 50 μm or less.

5. In Paragraph 1, A solid electrolyte having an ionic conductivity of 7 mS / cm or more when the D50 of the solid electrolyte is 0.1 μm or more and less than 5 μm.

6. In Paragraph 1, A solid electrolyte having a critical current density of 1.8 mA / cm² or more.

7. In Paragraph 1, The above solid electrolyte is a solid electrolyte in which the rate of change of resistance value at the interface between the solid electrolyte and Li metal is 25% or less.

8. A method for manufacturing a solid electrolyte as described in any one of claims 1 to 7, wherein A step of mixing a lithium source, an aluminum source, a phosphorus source, a sulfur source, and a halogen source to obtain a mixture, and A method for manufacturing a solid electrolyte, comprising the step of calcining the above mixture at a temperature of 450°C or lower.

9. having an anode, a cathode, and a solid electrolyte layer interposed between the anode and the cathode, An all-solid-state battery in which the above-mentioned solid electrolyte layer comprises a solid electrolyte described in any one of claims 1 to 7.

10. In Paragraph 9, All-solid-state battery in which the above-mentioned negative electrode is a Li metal negative electrode.

11. In Paragraph 9, An all-solid-state battery comprising a compound containing Al between the solid electrolyte layer and the cathode.

12. In Paragraph 11, The above compound is an all-solid-state battery further comprising Li.

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