Sulfide-based solid electrolyte and all-solid-state battery containing the same

Abstract

The present invention relates to a sulfide-based solid electrolyte and an all-solid-state battery including the same. According to one aspect of the present invention, the sulfide-based solid electrolyte includes at least one sulfide-based solid particle, and a scanning electron microscope (SEM) image of the at least one sulfide-based solid particle shows that a parameter value (C) defined by the following Equation 1 is 0.8 or more: <Formula 1> C=4πA / P 2 Here, A is the area of ​​a region defined along the outline of the at least one sulfide-based solid particle in an SEM image, and P is the perimeter of the region.

Description

[Technical Field]

[0001] The present invention relates to a sulfide-based solid electrolyte and an all-solid-state battery including the same, and more particularly to a sulfide-based solid electrolyte having excellent ionic conductivity and an all-solid-state battery with high energy density. [Background technology]

[0002] In recent years, the demand for high-energy, high-power-density lithium-ion batteries has been on the rise due to the increasing demand for electric vehicles. However, the use of flammable liquid electrolytes presents stability issues, including fire hazards, limiting their use as batteries for next-generation electric vehicles. To overcome these issues, research into solid electrolytes has been attracting attention. Solid electrolytes not only offer excellent stability, but can also be stacked in a bipolar structure, significantly improving energy density compared to conventional lithium-ion batteries.

[0003] One of the main goals in the development of solid electrolytes is to realize high ionic conductivity at room temperature, on the same level as that of liquid electrolytes. Among various inorganic solid electrolytes, sulfide-based solid electrolytes have 2- In contrast to S 2- Since the ionic radius and polarizability of these electrolytes are large, they have higher ionic conductivity than oxide-based solid electrolytes and are therefore considered the most promising.

[0004] In the case of an all-solid-state battery including a solid electrolyte, the cathode, anode, and electrolyte are all configured in a solid state, and therefore, each electrode is formed in a state in which the active material and the solid electrolyte are mixed to maximize energy density and ionic conductivity. However, since the particle size characteristics of sulfide-based solid electrolytes are not uniform, it may be difficult for the solid electrolyte to be densely packed with the electrode active material within the electrode.

[0005] Sulfide-based solid electrolytes are typically prepared by a solid-phase method using milling or a liquid-phase method in which the sulfide is dissolved in an organic solvent and then precipitated. To achieve finer particle size, techniques for producing sulfide-based solid electrolytes with small particle sizes have been introduced, such as controlling the milling time or dissolution conditions. However, sulfide-based solid electrolyte particles prepared by these methods have irregular morphologies and a broad particle size distribution, making it difficult to control the particle shape and particle size. Meanwhile, when solid electrolyte particles have an irregular shape and a large particle size, many fine pores can be formed, resulting in reduced ionic conductivity.

[0006] Therefore, it is necessary to develop a sulfide-based solid electrolyte that can realize excellent energy density by realizing high-density packing of the solid electrolyte and the electrode active material while minimizing the decrease in ionic conductivity of the sulfide-based solid electrolyte.

[0007] On the other hand, the above-mentioned background art is technical information that the inventor possessed for the purpose of deriving the present invention or that he acquired in the process of deriving the present invention, and is not necessarily publicly known art that was made public to the general public prior to the filing of the present invention. Summary of the Invention [Problem to be solved by the invention]

[0008] An object of one embodiment of the present invention is to provide a sulfide-based solid electrolyte having maximized ionic conductivity and an all-solid-state battery including the same.

[0009] Another embodiment of the present invention aims to provide a sulfide-based solid electrolyte having excellent energy density and an all-solid-state battery including the same. [Means for solving the problem]

[0010] As a technical means for achieving the above-mentioned technical object, according to one aspect of the present invention, a sulfide-based solid electrolyte includes at least one sulfide-based solid particle, and a scanning electron microscope (SEM) image of the at least one sulfide-based solid particle shows that a parameter value (C) defined by the following Equation 1 is 0.8 or more.

[0011] <Formula 1> C=4πA / P 2

[0012] Here, A is the area of ​​a region defined along the outline of the at least one sulfide-based solid particle in an SEM image, and P is the perimeter of the region.

[0013] According to another aspect of the present invention, the SEM image may be an image taken at a magnification of 5,000 times or more.

[0014] According to yet another aspect of the present invention, a plurality of sulfide-based solid particles may be present in the SEM image, and the number of the sulfide-based solid particles having the parameter value of 0.8 or more may account for 28% or more of all particles in the SEM image.

[0015] According to yet another embodiment of the present invention, the sulfide-based solid particles may have an aspect ratio of 0.7 to 1.5.

[0016] According to yet another aspect of the present invention, the sulfide-based solid particles may have an average particle size of 70 μm or less.

[0017] According to yet another aspect of the present invention, the sulfide-based solid electrolyte may have an ionic conductivity of 3 mS / cm or more.

[0018] According to yet another aspect of the present invention, the sulfide-based solid particles may contain sulfur (S), lithium (Li), and phosphorus (P).

[0019] According to yet another aspect of the present invention, the sulfide-based solid particles may have an argyrodite crystal structure.

[0020] As a technical means for achieving the above-mentioned technical object, according to another aspect of the present invention, an all-solid-state battery includes a cathode, an anode corresponding to the cathode, and a sulfide-based solid electrolyte disposed between the cathode and the anode, wherein the sulfide-based solid electrolyte includes at least one sulfide-based solid, and an SEM image of the sulfide-based solid particles has a parameter value (C) defined by the following <Equation 1> of 0.8 or more.

[0021] <Formula 1> C=4πA / P 2

[0022] Here, A is the area of ​​a region defined along the outline in an SEM image of a sulfide-based solid particle, and P is the perimeter of the region.

[0023] According to another aspect of the present invention, the SEM image may be an image taken at a magnification of 5,000 times or more.

[0024] According to yet another aspect of the present invention, the number of the sulfide-based solid particles having the parameter value of 0.8 or more present in the SEM image may be 28% or more in the SEM image.

[0025] According to yet another aspect of the present invention, the sulfide-based solid particles may contain sulfur (S), lithium (Li), and phosphorus (P).

[0026] According to yet another aspect of the present invention, the sulfide-based solid particles may have an argyrodite crystal structure. [Effects of the Invention]

[0027] According to any of the above-described means for solving the problems of the present invention, the sulfide-based solid electrolyte according to an embodiment of the present invention includes solid particles that satisfy specific parameters, and therefore can have excellent electrochemical properties.

[0028] Furthermore, according to any one of the means for solving the problems of the present invention, the all-solid-state battery according to an embodiment of the present invention includes a sulfide-based solid electrolyte that satisfies specific parameters, and therefore, packing with high energy density is possible, thereby maximizing battery capacity.

[0029] The effects obtained by the present invention are not limited to the effects mentioned above, and further effects not mentioned will be clearly understood by those having ordinary skill in the art to which the present invention pertains from the following description. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 1 is a conceptual diagram illustrating the structure of an all-solid-state battery. [Figure 2] 2A and 2B are cross-sectional views schematically illustrating the microstructure of the cathode of FIG. 1. [Figure 3] 1 is a graph illustrating changes in ionic conductivity and particle size of a sulfide-based solid electrolyte depending on milling time. [Figure 4] 1 shows SEM images of a sulfide-based solid electrolyte according to an example of the present invention and a sulfide-based solid electrolyte according to a comparative example. [Figure 5a] 1 is an image (1) showing SEM images and parameter values ​​of a sulfide-based solid electrolyte according to an embodiment of the present invention and a sulfide solid electrolyte according to a comparative example. [Figure 5b] 1 is an image (2) showing SEM images and parameter values ​​of a sulfide-based solid electrolyte according to an embodiment of the present invention and a sulfide solid electrolyte according to a comparative example. [Figure 5c] 10 is an image (3) showing SEM images and parameter values ​​of a sulfide-based solid electrolyte according to an embodiment of the present invention and a sulfide solid electrolyte according to a comparative example. [Figure 5d]10 is an image (4) showing SEM images and parameter values ​​of a sulfide-based solid electrolyte according to an embodiment of the present invention and a sulfide solid electrolyte according to a comparative example. [Figure 6a] 1 is a graph (1) showing the battery capacity measurement results of a pressurized cell using a sulfide-based solid electrolyte according to an embodiment of the present invention and a sulfide solid electrolyte according to a comparative example. [Figure 6b] 1 is a graph (2) showing the results of measuring the battery capacity of a pressurized cell using a sulfide-based solid electrolyte according to an embodiment of the present invention and a sulfide solid electrolyte according to a comparative example. [Figure 6c] 10 is a graph (3) showing the results of measuring the battery capacity of a pressurized cell using a sulfide-based solid electrolyte according to an embodiment of the present invention and a sulfide solid electrolyte according to a comparative example. [Figure 6d] 10 is a graph (4) showing the results of measuring the battery capacity of a pressurized cell using a sulfide-based solid electrolyte according to an embodiment of the present invention and a sulfide solid electrolyte according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0031] Hereinafter, with reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily understand the present invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein. Furthermore, in order to clearly explain the present invention in the drawings, parts that are not relevant to the description are omitted, and similar parts are designated by similar reference numerals throughout the specification.

[0032] Throughout the specification, when a part is described as being "connected" to another part, this includes not only "directly connected" but also "indirectly connected" via other members or elements therebetween. Furthermore, when a part is described as "comprising" a certain component, this does not mean that it excludes other components, but that it may further include other components, unless otherwise specified.

[0033] The present invention will now be described in detail with reference to the accompanying drawings.

[0034] FIG. 1 is a conceptual diagram that schematically illustrates the structure of an all-solid-state battery.

[0035] Referring to FIG. 1, the all-solid-state battery 100 includes a cathode 110, an anode 130, and a solid electrolyte 120 interposed between the cathode 110 and the anode 130.

[0036] In an all-solid-state battery, the cathode 110, the solid electrolyte 120, and the anode 130 are all constructed in a solid state, and may be configured to generate electricity based on the potential difference that occurs when metal ions in the cathode 110 pass through the solid electrolyte 110 and migrate to the anode 130.

[0037] The cathode 110 is composed of a metal ion-rich positive electrode active material, which may be a metal ion of Group 1 or Group 2 on the periodic table. The positive electrode active material may be composed of a compound capable of inserting / extracting the first or second group metal. When lithium (Li) ions are used as the metal ion, the positive electrode active material may be, for example, Li a A 1-b B' b D'2 (wherein 0.90≦a≦1.8 and 0≦b≦0.5); Li a E 1-b B' b O 2-c D' c (wherein 0.90≦a≦1.8, 0≦b≦0.5, and 0≦c≦0.05); LiE 2-b B' b O 4-c D' c (wherein 0≦b≦0.5 and 0≦c≦0.05); Li a Ni 1-b-c Co b B' c D' α (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, 0<α≦2); Li a Ni 1-b-c Co b B' c O 2-α F'α (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, 0<α<2); Li a Ni 1-b-c Mn b B' c D' α (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α≦2); Li a Ni 1-b-c Mn b B' c O 2-α F' α (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni b E c G d O2 (wherein 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0.001≦d≦0.1); Li a Ni b Co c Mn d G e O2 (wherein 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0.001≦e≦0.1); Li a NiG b O2 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li a CoG b O2 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li a MnG b O2 (wherein 0.90≦a≦1.8, 0.001≦b≦1); Li a Mn2G b O4 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiI'O2; LiNiVO4; Li (3-f) J2(PO4)3(0≦f≦2);Li (3-f) Compounds having any of the following chemical formulas may be used: Fe2(PO4)3(0≦f≦2); LiFePO4.

[0038] In the above chemical formula, A is nickel (Ni), cobalt (Co), manganese (Mn), or a combination thereof; B' is aluminum (Al), Ni, Co, Mn, chromium (Cr), iron (Fe), magnesium (Mg), strontium (Sr), vanadium (V), a rare earth element, or a combination thereof; D' is oxygen (O), fluorine (F), sulfur (S), phosphorus (P), or a combination thereof; and E is Co, Mn, or a combination thereof. wherein F' is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, lanthanum (La), cerium (Ce), Sr, V or a combination thereof; Q is titanium (Ti), molybdenum (Mo), Mn or a combination thereof; I' is Cr, V, Fe, scandium (Sc), yttrium (Y) or a combination thereof; and J is V, Cr, Mn, Co, Ni, copper (Cu) or a combination thereof.

[0039] The anode 130 may be made of a layer that is made of a negative electrode active material and in which the above-mentioned metal ions (for example, Li ions) are not deposited in a metallic form.

[0040] The negative electrode active material may include carbon (C), gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), Al, bismuth (Bi), tin (Sn), zinc (Zn), Li, or a combination thereof.

[0041] Meanwhile, in order to maximize the conductivity of metal ions, the cathode 110 or the anode 130 may be configured in a form in which the active material is mixed with the solid electrolyte 120. That is, as shown in Fig. 1, the cathode 110 is configured in a form in which the positive electrode active material is mixed with the solid electrolyte 120, and the solid electrolyte 120 is configured to facilitate the movement of metal ions generated from the positive electrode active material.

[0042] The solid electrolyte 120 may be made of various materials such as sulfide-based, oxide-based, and polymer-based materials, but is preferably made of a sulfide-based material. The following description will focus on the sulfide-based solid electrolyte 120.

[0043] The sulfide-based solid electrolyte 120 of the present invention is a solid-state electrolyte containing sulfide-based solid particles, and has a technical feature in that the shape and size of the particles satisfy specific conditions.

[0044] The sulfide-based solid particles contain S atoms and a metal belonging to Group 1 or Group 2 of the periodic table, and are conductive to metal ions of Group 1 or Group 2. The sulfide-based solid particles may contain, for example, Li, S, and P, and be conductive to Li ions.

[0045] Examples of sulfide-based solid particles include Li2S-P2S5, Li2S-P2S5-LiCl, Li2S-P2S5-H2S, Li2S-P2S5-H2S-LiCl, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SiS2-LiCl, Li2S-P2S5-SnS, and Li2S-P2S5 -Al2S3, Li2S-GeS2, Li2S-GeS2-ZnS, Li2S-Ga2S3, Li2S-GeS2-Ga2S3, Li2S-GeS2-P2S5, Li2S-GeS2-Sb2S5, Li2S-GeS2-Al2S3, Li2S-SiS 2, Li2S-Al2S3, Li2S-SiS2-Al2S3, Li2S-SiS2-P2S5, Li2S-SiS2-P2S5-LiI, Li2S-SiS2-LiI, Li2S-SiS2-Li4SiO4, Li2S-SiS2-Li3PO4, Li 10 GeP2S 12 However, the types of sulfide-based solid particles of the present invention are not limited to the above examples.

[0046] The sulfide-based solid particles described above have crystallinity and may have, for example, an argyrodite-type crystal structure.

[0047] The sulfide-based solid particles have an average particle size of 70 μm or less.

[0048] Furthermore, the sulfide-based solid electrolyte 120 of the present invention may include at least one sulfide-based solid particle having a parameter value (C) defined by the following Equation 1 of 0.8 or more in an image captured through a scanning electron microscope (SEM).

[0049] <Formula 1> C=4πA / P 2

[0050] Here, A means the size of the area defined along the outline of the sulfide-based solid particle in the SEM image (i.e., the size of the sulfide-based solid particle), and P means the perimeter of the area defined along the outline of the sulfide-based solid particle in the SEM image (i.e., the perimeter of the sulfide-based solid particle).

[0051] In the above <Equation 1>, 4πA / P 2 The value means a parameter that quantitatively indicates how close a figure defined on a two-dimensional plane is to a circle, and for convenience of explanation, this is defined as a "parameter" in this specification. The closer the parameter is to 1, the closer the figure defined on a two-dimensional plane is to a circle.

[0052] Meanwhile, the SEM image may refer to an image taken at a magnification of 5,000x or more. A large number of sulfide-based solid particles may be included in an image of the sulfide-based solid electrolyte 120 taken through an SEM at a magnification of 5,000x or more, and a large number of sulfide-based solid particles having the parameter value of 0.8 or more may be present. For example, the sulfide-based solid particles having the parameter value of 0.8 or more may account for 28% or more of all particles, preferably 34% or more, and more preferably 50% or more.

[0053] In some embodiments, the sulfide-based solid electrolyte 120 of the present invention may include at least one particle having a parameter value of 0.7 or more on an SEM image.

[0054] Preferably, particles having the parameter value of 0.7 or more in an SEM image of the sulfide-based solid electrolyte 120 at a magnification of 5,000 times or more may account for 61% or more of all particles, preferably 63% or more, and more preferably 79% or more.

[0055] On the other hand, the sulfide-based solid particles may have an aspect ratio of 0.7 to 1.5, where the aspect ratio refers to the aspect ratio of the sulfide-based solid particles on an SEM image at a magnification of 5,000 times or more.

[0056] For a more detailed explanation of the above-mentioned characteristics of the sulfide-based solid particles of the present invention, reference will also be made to FIG.

[0057] FIG. 2 is a cross-sectional view that schematically illustrates the microstructure of the cathode of FIG.

[0058] Specifically, FIG. 2(a) is a diagram illustrating an example of an SEM image of a cathode 210 made of a mixture of a conventional sulfide-based solid electrolyte and a positive electrode active material, and FIG. 2(b) is a diagram illustrating an example of an SEM image of a cathode 110 made of a mixture of a sulfide-based solid electrolyte and a positive electrode active material according to one embodiment of the present invention.

[0059] 2(a), the conventional sulfide-based solid electrolyte includes sulfide-based solid particles 212 having a parameter value of less than 0.8. In other words, the conventional sulfide-based solid electrolyte does not have or has relatively few sulfide-based solid particles having a parameter value of 1 to 0.8.

[0060] The conventional sulfide-based solid particles 212 are formed with the parameter value less than 0.8, and therefore have an uneven and rough morphology on a two-dimensional SEM image, as shown in FIG. 2(a).

[0061] Furthermore, the aspect ratio of the conventional sulfide-based solid particles 212 is greater than 1.5 or less than 0.7. Therefore, in an SEM image, the shape defined along the outline of the conventional sulfide-based solid particles 212 generally has a non-uniform aspect ratio and an elongated shape.

[0062] Furthermore, the average particle size of the conventional sulfide-based solid particles 212 exceeds 70 μm. Conventionally, the sulfide-based solid particles 212 exist in a form in which large particles and small particles are unevenly mixed, and the average particle size of all particles exceeds 70 μm.

[0063] In some embodiments, among the conventional sulfide-based solid particles 212, particles having the parameter value of 0.8 or more may exist. However, a large number of the sulfide-based solid particles 212 in the cathode 210 may be composed of particles having the parameter value of less than 0.8. Specifically, the proportion of particles having the parameter value of less than 0.8 to all particles present in the SEM image may be 72% or more. Meanwhile, the proportion of the sulfide-based solid particles 212 having the parameter value of 1 to 0.8 is less than 28%.

[0064] The conventional sulfide-based solid particles 212 have a large average particle size and a large aspect ratio, and the proportion of particles with the parameter value less than 0.8 is 72% or more. That is, most of the particles have a parameter value less than 0.8. This allows large gaps G1 to exist between the sulfide-based solid particles 212 in the cathode 210, and the contact area between the conventional sulfide-based solid particles 212 and the positive electrode active material 211 can be small.

[0065] 2(b), the sulfide-based solid electrolyte of the present invention includes sulfide-based solid particles 112 having the parameter value of 0.7 or more, and preferably includes sulfide-based solid particles 112 having the parameter value of 1 to 0.8.

[0066] The particles with the parameter value of 1 to 0.8 are 4πA / P 2This may be why the shape on the two-dimensional SEM image is close to a circle because the value is close to 1. As a result, in the cathode 110 containing the sulfide-based solid electrolyte of the present invention, the sulfide-based solid particles 112 have a shape similar to a circle, as shown in FIG. 2(b).

[0067] The aspect ratio of the sulfide-based solid particle 112 of the present invention is 0.7 to 1.5. As a result, the figure defined along the outline of the sulfide-based solid particle 112 of the present invention in an SEM image generally has an aspect ratio close to 1 and a shape similar to a circle.

[0068] The sulfide-based solid particles 112 of the present invention have an average particle size of 70 μm or less, which allows most of the sulfide-based solid particles 112 to be present densely as fine nanoparticles on an SEM image.

[0069] Some of the sulfide-based solid particles 112 of the present invention may have a parameter value of less than 0.8. However, as described above, most of the sulfide-based solid particles 112 of the present invention have a parameter value of 1 to 0.8. For example, in an SEM image, particles with a parameter value of 1 to 0.8 may account for at least 28% of all particles, and particles with a parameter value of 1 to 0.7 may account for at least 61% of all particles.

[0070] As described above, the sulfide-based solid electrolyte of the present invention not only has a small, uniform average particle size of 70 μm or less, but also has the above-mentioned parameter values ​​of 1 to 0.8 and an aspect ratio of 0.7 to 1.5. In particular, it is characterized in that particles with the parameter values ​​of 1 to 0.8 account for at least 28% of all particles present in an SEM image measured at a magnification of 5,000 times or more.

[0071] The present inventors have found that when the morphology of a sulfide-based solid electrolyte has the above-described characteristics, excellent Li-ion conductivity can be achieved in a cathode 110 formed by a mixture of a sulfide-based solid electrolyte and a positive electrode active material 111, and high-density packing of sulfide-based solid particles 112 and the positive electrode active material is possible. For a more detailed description of this, please also refer to FIG. 3.

[0072] FIG. 3 is a graph illustrating the change in ionic conductivity and particle size of a sulfide-based solid electrolyte depending on the milling time.

[0073] Conventional sulfide-based solid electrolytes are manufactured by mixing electrolyte raw materials using an attrition mill or ball mill, followed by sintering through high-temperature heat treatment. To achieve the required energy density, it is necessary to pack as much solid electrolyte as possible into a limited volume, which may require a longer milling time to reduce the average particle size of the sulfide-based solid particles.

[0074] As shown in Fig. 3, as the milling time increases, the average particle size of the sulfide-based solid particles (d SE ) becomes smaller, and as a result, the average particle size (d CAM ) to the average particle size of sulfide-based solid particles (d SE ) can be large.

[0075] However, the milling time increases and the average particle size (d SE ) becomes smaller, the Li ion conductivity tends to decrease.

[0076] This allows the average particle size of the sulfide solid particles (d SE By reducing the σ, the sulfide-based solid electrolyte can be packed more in the cathode, but the ionic conductivity decreases, so the capacity of the cathode has a certain threshold, as shown in Figure 3.

[0077] The inventors of the present invention have found that simply reducing the average particle size of the sulfide-based solid electrolyte is not enough to increase the capacity of the cathode; the particle shape of the sulfide-based solid electrolyte must also be controlled. The inventors of the present invention have found that the closer a specific parameter for two-dimensional sulfide-based solid particles present in an SEM image of the sulfide-based solid electrolyte is to 1, the higher the battery capacity can be by enabling high-density packing of the positive electrode active material and sulfide-based solid electrolyte in the cathode without impairing Li-ion conductivity.

[0078] That is, when the average particle size of the sulfide-based solid electrolyte is controlled to 70 μm or less and the sulfide-based solid electrolyte is photographed by SEM at a magnification of 5,000 times or more, the 4πA / P 2 When the ratio of particles with a value of 0.8 or more (i.e., 1 to 0.8) is at least 28% or more, the decrease in Li-ion conductivity can be minimized, and high-density packing of the positive electrode active material and sulfide-based solid electrolyte is possible, thereby maximizing battery capacity.

[0079] This is 4πA / P 2 This is thought to be because, when the value is 0.8 or more, the shape of the sulfide-based solid particles approaches an ideal sphere, and because the sulfide-based solid electrolyte has an average particle size of 70 μm or less, the size of the sulfide-based solid particles becomes small, allowing for high-density packing while maintaining a sufficient contact area between the sulfide-based solid particles and the positive electrode active material.

[0080] The sulfide-based solid electrolyte of the present invention may have an ionic conductivity of 3 mS / cm or more.

[0081] Therefore, the sulfide-based solid electrolyte of the present invention has excellent electrochemical properties and has the advantage of being able to ensure excellent charge capacity even after repeated charge-discharge cycles.

[0082] The sulfide-based solid electrolyte of the present invention may be produced by the following method.

[0083] First, droplets are generated from a precursor solution containing a sulfide-based solid electrolyte precursor and sprayed into a reactor, the sprayed droplets are heated to generate sulfide-based solid particles, and the generated sulfide-based solid particles are collected to obtain a sulfide-based solid electrolyte.

[0084] In this case, the sulfide-based solid electrolyte precursor may contain lithium sulfide and a halogen compound.

[0085] The lithium sulfide may include at least one material selected from the group consisting of Li2S, Li2S2, Li2S4, and Li2S6.

[0086] The halogen compound may include at least one substance selected from the group consisting of lithium bromide (LiBr), lithium chloride (LiCl), lithium iodide (LiI), and lithium fluoride (LiF).

[0087] The sulfide-based solid electrolyte precursor may further contain a metal compound, and the metal compound may contain at least one substance selected from the group consisting of Al, Si, P, gallium (Ga), iodine (I), Sn, germanium (Ge), antimony (Sb), Zn, arsenic (As), tungsten (W), Se, V, and calcium (Ca).

[0088] The precursor solution may be atomized in various ways, for example, by generating droplets of the precursor solution via an ultrasonic vibrator.

[0089] The method of applying heat to the precursor droplets may be selected from various methods, and may be carried out by applying heat to the reactor and thereby applying heat to the reaction space into which the droplets are sprayed.

[0090] The collection of the sulfide-based solid electrolyte may be carried out by various methods capable of collecting fine nanoparticles, and is not particularly limited.

[0091] As described above, the sulfide-based solid electrolyte according to an embodiment of the present invention can be manufactured in a simple manner by spraying a precursor solution, heat-treating, and obtaining a powder. Since the process is simple, it is easy to construct a mass-production facility, and therefore, it is suitable for mass production.

[0092] [Mode for carrying out the invention] The excellent electrochemical properties of the sulfide-based solid electrolyte of the present invention will be explained below through experimental examples.

[0093] <Production Example 1, Production of Sulfide-Based Solid Electrolyte> First, in a glove box under an inert gas atmosphere, raw materials Li2S, P2S5, and LiCl were mixed to prepare a mixed powder, which was then dissolved in a mixed solvent of ethyl acetate and ethanol to prepare a precursor solution.

[0094] The precursor solution was ultrasonically atomized to form droplets, which were then introduced into a heated reactor using an inert carrier gas at a flow rate of 10 L / min to obtain a first powder.

[0095] The obtained powder was placed in an aluminum crucible and heat-treated at 550° C. for 4 hours while flowing an inert gas, and then cooled to room temperature to produce the sulfide-based solid electrolyte of Example 1.

[0096] Droplets were formed using the same precursor as in the method described above, and an inert carrier gas was supplied at a flow rate of 5 L / min to cause the precursor to flow into a reactor, thereby obtaining a second powder. The second powder was then subjected to the same heat treatment as in the method described above, thereby producing the sulfide-based solid electrolyte of Example 2.

[0097] Droplets were formed using the same precursor as in the method described above, and an inert carrier gas was supplied at a flow rate of 15 L / min to cause the precursor to flow into a reactor, thereby obtaining a third powder. The sulfide-based solid electrolyte of Example 3 was produced by carrying out the same heat treatment as in the method described above.

[0098] The chemical formula of the sulfide-based solid electrolytes in Examples 1 to 3 was Li6PS5Cl.

[0099] On the other hand, as a comparative example, Li6PS5Cl solid electrolyte was obtained and filtered through a 325 mesh to produce a sulfide-based solid electrolyte having an average particle size (D50) of 10 μm or less, which was used as the sulfide-based solid electrolyte of Comparative Example 1.

[0100] <Experimental Example 1, SEM photography> To compare the particles of the solid electrolyte according to the comparative example with those of the solid electrolytes according to Examples 1 to 3, the particles were photographed using a scanning electron microscope (SEM). The SEM photographs of each sample were taken at a magnification of 5,000 times. The results are shown in Figure 4.

[0101] FIG. 4 shows SEM images of a sulfide-based solid electrolyte according to an example of the present invention and a sulfide-based solid electrolyte according to a comparative example.

[0102] 4, it can be seen that the sulfide-based solid electrolytes of Examples 1 to 3 have rounder particle shapes than the solid electrolyte of Comparative Example. That is, it can be seen that the sulfide-based solid electrolyte of Comparative Example has an average particle size similar to that of Example 1, but the particle shapes are uneven and the aspect ratios are not constant.

[0103] On the other hand, it can be seen that the sulfide-based solid electrolyte of Example 3 has very small particle sizes, and the particle shapes are almost round.

[0104] <Experimental Example 2, Comparison of particle parameters> The SEM images were analyzed to determine the parameter value (4πA / P 2 ) was calculated. The results are shown in Figures 5a to 5d.

[0105] 5a to 5d are SEM images and images showing parameter values ​​of a sulfide-based solid electrolyte according to an embodiment of the present invention and a sulfide solid electrolyte according to a comparative example.

[0106] The parameter values ​​of each particle were calculated by digitally analyzing the SEM image of each sample to generate a normalized image of a defined area along the outline of the sulfide-based solid particle, and then calculating the parameter values ​​based on the area A value and the circumference P value for the normalized image.

[0107] 5a, it can be seen that the parameter values ​​of most of the particles in the sulfide-based solid electrolyte of the comparative example are less than 0.8. The parameter values ​​and cumulative number of particles in the SEM image of the comparative example are as shown in Table 1 below.

[0108] [Table 1]

[0109] As shown in Table 1, it can be seen that the sulfide-based solid electrolyte of the comparative example is composed of solid particles having a parameter value of less than 0.8. That is, the cumulative ratio of solid particles having a parameter value of less than 0.8 is 72.3%, and the ratio of solid particles having a parameter value of 1 to 0.8 is only at the level of 27.7%.

[0110] 5b to 5d, it can be seen that the parameter values ​​of most of the sulfide-based solid particles of Examples 1 to 3 are 0.7 or more, and the proportion of particles with a value of 0.8 or more is also quite high. The parameter values ​​and cumulative number of particles in the SEM images of Examples 1 to 3 are shown in Table 2 below.

[0111] [Table 2]

[0112] <Formula 2> σ=t / (a*R)

[0113] Here, σ is the ionic conductivity, t is the thickness of the pellet, R is the bulk resistance, and a is the area of ​​the pellet.

[0114] The evaluation results are shown in Table 3 below.

[0115] [Table 3]

[0116] As can be seen from Table 3, the sulfide-based solid electrolyte of the present invention has ionic conductivity equivalent to or superior to that of the sulfide-based solid electrolyte of the comparative example.

[0117] <Production Example 2, Production of All-Solid-State Battery> In order to evaluate the excellent electrochemical properties of the sulfide-based solid electrolyte of the present invention, pressure cells were manufactured using the sulfide-based solid electrolytes of the Comparative Example and Examples 1 to 3.

[0118] Specifically, the positive electrode active material NCM811 was mixed at 75, 80, and 85 wt% to fabricate three types of all-solid-state pressure cells for each sample, while a Li metal electrode was used as the anode.

[0119] <Experimental Example 4, Measurement of Battery Capacity> The battery capacity at room temperature of the pressurized cell manufactured in Manufacturing Example 2 was measured, and the results are shown in Figures 6a to 6d.

[0120] 6a to 6d are graphs showing the results of measuring the battery capacity of pressurized cells using sulfide-based solid electrolytes according to examples of the present invention and sulfide solid electrolytes according to comparative examples.

[0121] Specifically, FIG. 6a is a graph showing the battery capacity measurement results of a pressurized cell using the sulfide-based solid electrolyte of the comparative example, and FIGS. 6b to 6d are graphs showing the battery capacity measurement results of pressurized cells using the sulfide-based solid electrolytes of Examples 1 to 3, respectively.

[0122] The battery capacity measurement results shown in FIGS. 6a to 6d are shown in Table 4 below.

[0123] [Table 4]

[0124] Referring to Table 4 and FIGS. 6a to 6d, it can be seen that as the content of the positive electrode active material NCM811 decreases, the amount of the sulfide-based solid electrolyte relatively increases, resulting in an increase in battery capacity within the same volume of the cell.

[0125] On the other hand, the sulfide-based solid electrolyte of the comparative example and the sulfide-based solid electrolyte of Example 2 have a similar particle count of approximately 350 in SEM images at 5,000x magnification, suggesting that the average particle size of the two samples is similar. However, the sulfide-based solid electrolyte of Example 2 contains more solid particles with parameter values ​​of 1 to 0.8 than the sulfide-based solid electrolyte of the comparative example (see Experimental Example 2 above). Therefore, as can be seen from a comparison of Figures 6a and 6c, the sulfide-based solid electrolyte of Example 2 provides superior battery capacity compared to the sulfide-based solid electrolyte of the comparative example. This is believed to be due to the fact that the solid particles of Example 2 have nearly circular properties, which maximizes the contact area with the positive electrode active material and minimizes the decrease in Li-ion conductivity.

[0126] Furthermore, as can be seen from FIGS. 6b and 6d, when the average particle size of the sulfide-based solid electrolyte is sufficiently small and the cumulative ratio of particles with parameter values ​​of 1 to 0.8 in an SEM image of 5,000x magnification or higher is 50% or more, the battery capacity can be improved by approximately 10% or more compared to the sulfide-based solid electrolyte of the comparative example. This indicates that the higher the ratio of solid particles with parameter values ​​of 1 to 0.8, the more the electrochemical properties of the sulfide-based solid electrolyte can be improved.

[0127] The above description of the present invention is for illustrative purposes only, and those skilled in the art will understand that the present invention can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and are not limiting. For example, each component described as a single component may be implemented in a distributed form, and similarly, components described as distributed may be implemented in a combined form.

[0128] The scope of the present invention is indicated by the claims that follow, rather than by the above detailed description, and all modifications and variations that come within the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention. [Industrial Applicability]

[0129] The present invention may be applied to the secondary battery industry, for example, secondary batteries for electric vehicles, secondary batteries for electronic devices such as notebooks, tablet PCs, and smartphones, and equipment that operates based on the energy source of the battery.

Claims

1. A sulfide-based solid electrolyte comprising at least one sulfide-based solid particle, wherein a scanning electron microscope (SEM) image of the at least one sulfide-based solid particle shows that a parameter value (C) defined by the following Equation 1 is 0.8 or more: <Formula 1> C=4πA / P ２ where A is the area of ​​a region defined along the outline of the at least one sulfide-based solid particle in the SEM image, P means the perimeter of the region.

2. The sulfide-based solid electrolyte according to claim 1, wherein the SEM image is an image taken at a magnification of 5,000 times or more.

3. 3. The sulfide-based solid electrolyte according to claim 2, wherein a plurality of sulfide-based solid particles are present in the SEM image, and the number of the sulfide-based solid particles having the parameter value of 0.8 or more is 28% or more of all particles in the SEM image.

4. 2. The sulfide-based solid electrolyte according to claim 1, wherein the aspect ratio of the sulfide-based solid particles is 0.7 to 1.

5.

5. 2. The sulfide-based solid electrolyte according to claim 1, wherein the sulfide-based solid particles have an average particle size of 70 μm or less.

6. 2. The sulfide-based solid electrolyte according to claim 1, wherein the sulfide-based solid electrolyte has an ionic conductivity of 3 mS / cm or more.

7. 2. The sulfide-based solid electrolyte according to claim 1, wherein the sulfide-based solid particles contain sulfur (S), lithium (Li), and phosphorus (P).

8. The sulfide-based solid electrolyte according to claim 1 , wherein the sulfide-based solid particles have an argyrodite crystal structure.

9. a cathode; and an anode corresponding to the cathode; A sulfide-based solid electrolyte disposed between the cathode and the anode, the sulfide-based solid electrolyte comprising: at least one sulfide-based solid; In the SEM image of the sulfide-based solid particles, a parameter value (C) defined by the following Equation 1 is 0.8 or more. <Formula 1> C=4πA / P ２ Here, A is the area of ​​a region defined along the outline in an SEM image of the sulfide-based solid particle, P means the perimeter of the region.

10. The all-solid-state battery according to claim 9 , wherein the SEM image is an image taken at a magnification of 5,000 times or more.

11. 11. The all-solid-state battery according to claim 10, wherein the number of the sulfide-based solid particles having the parameter value of 0.8 or more present in the SEM image is 28% or more in the SEM image.

12. 10. The all-solid-state battery according to claim 9, wherein the sulfide-based solid particles contain sulfur (S), lithium (Li), and phosphorus (P).

13. 10. The all-solid-state battery according to claim 9, wherein the sulfide-based solid particles have an argyrodite crystal structure.

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