Sulfide-based solid electrolyte and all-solid-state battery including same

Abstract

The present invention relates to a sulfide-based solid electrolyte and an all-solid-state battery comprising the same, according to one aspect of the present invention, the sulfide-based solid electrolyte comprises at least one sulfide-based solid particle, the at least one sulfide-based solid particle having a scanning electron microscope (Scanning Electron Microscope), and an all-solid-state battery comprising the sulfide-based solid electrolyte. In the SEM image, a parameter value C defined by the following mathematical formula 1 is 0.8 or more. 'Mathematical formula 1' C = 4 [pi] A / P2, where A represents the area of a region defined along the outer profile of the at least one sulfide-based solid particle in the SEM image, and P represents the circumference 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 sulfide-based solid electrolyte, and more particularly, to a sulfide-based solid electrolyte with excellent ionic conductivity and an all-solid-state battery with high energy density. Background Art

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

[0003] One of the core goals of solid electrolyte development is to achieve high ionic conductivity at the level of liquid electrolytes at room temperature. 2- Compared to O 2- They have a larger ionic radius and polarizability, and thus have higher ionic conductivity than oxide-based solid electrolytes, and therefore have attracted much attention.

[0004] For all-solid-state batteries that include solid electrolytes, since the cathode, anode, and electrolyte are all solid, each electrode is formed as a mixture of active material and solid electrolyte to maximize energy density and ionic conductivity. However, due to the uneven particle size of sulfide-based solid electrolytes, it can be difficult to pack the solid electrolyte with the electrode active material at a high density in the electrode.

[0005] Sulfide-based solid electrolytes are prepared by a solid-phase method using grinding or a liquid-phase method using precipitation after dissolution in an organic solvent. It is known that techniques for preparing sulfide-based solid electrolytes with small particle sizes can be used to refine the particle size of the sulfide-based solid electrolyte by controlling the grinding time or dissolution conditions. However, the sulfide-based solid electrolyte particles prepared by these methods have irregular shapes and a wide particle size distribution, resulting in the difficulty of controlling the shape and particle size of the particles. On the other hand, when the solid electrolyte particles are uneven in shape and have a large particle size, many tiny pores may be formed, resulting in a problem of reduced ionic conductivity.

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

[0007] On the other hand, the above-mentioned background technology is the technical information that the inventor possesses in order to obtain the present invention or learned in the process of obtaining the present invention, and shall not be considered as the public knowledge disclosed to the public before the application of the present invention. Summary of the Invention

[0008] Technical issues

[0009] An object of one embodiment of the present invention is to provide a sulfide-based solid electrolyte with maximized ionic conductivity and an all-solid-state battery including the sulfide-based solid electrolyte.

[0010] Another object of the present invention is to provide a sulfide-based solid electrolyte having excellent energy density and an all-solid-state battery including the sulfide-based solid electrolyte.

[0011] Technical Solution

[0012] As a technical solution for solving the above-mentioned technical problems, according to one aspect of the present invention, a sulfide-based solid electrolyte includes at least one sulfide-based solid particle, and a parameter value C defined by the following [Mathematical Formula 1] in a scanning electron microscope (SEM) image of the at least one sulfide-based solid particle is greater than 0.8.

[0013]

Mathematical formula 1

[0014] C=4πA / P 2

[0015] Wherein, A represents the area of ​​a region defined along the outer contour of the at least one sulfide-based solid particle in the SEM image, and P represents the perimeter of the region.

[0016] According to another aspect of the present invention, the SEM image may be an image taken at a magnification of 5000 times or more.

[0017] According to another aspect of the present invention, there are a plurality of sulfide-based solid particles in the SEM image, and the number of the sulfide-based solid particles with the parameter value being greater than 0.8 may be greater than 28% of all particles in the SEM image.

[0018] According to yet another aspect of the present invention, the aspect ratio of the sulfide-based solid particles may be 0.7 to 1.5.

[0019] According to yet another aspect of the present invention, the average particle diameter of the sulfide-based solid particles may be 70 μm or less.

[0020] According to yet another aspect of the present invention, the ionic conductivity of the sulfide-based solid electrolyte may be greater than 3 mS / cm.

[0021] According to yet another aspect of the present invention, the sulfide-based solid particles may include sulfur (S), lithium (Li), and phosphorus (P).

[0022] According to yet another aspect of the present invention, the sulfide-based solid particles may have an argyrodite crystal structure.

[0023] As a technical solution for solving the above-mentioned technical problems, according to another aspect of the present invention, an all-solid-state battery includes: a cathode; an anode corresponding to the cathode; a sulfide-based solid electrolyte, arranged between the cathode and the anode, the sulfide-based solid electrolyte containing at least one sulfide-based solid particle, and the parameter value C defined by the following [Mathematical Formula 1] in the scanning electron microscope image of the sulfide-based solid particle is greater than 0.8.

[0024]

Mathematical formula 1

[0025] C=4πA / P 2

[0026] Wherein, A represents the area of ​​a region defined along the outer contour line in the SEM image of the sulfide-based solid particle, and P represents the perimeter of the region.

[0027] According to another aspect of the present invention, the SEM image may be an image taken at a magnification of 5000 times or more.

[0028] 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 greater in the SEM image may account for more than 28% in the SEM image.

[0029] According to yet another aspect of the present invention, the sulfide-based solid particles may include sulfur (S), lithium (Li), and phosphorus (P).

[0030] According to yet another aspect of the present invention, the sulfide-based solid particles may have an argyrodite crystal structure.

[0031] Technical Effects

[0032] According to any one of the technical solutions of the present invention described above, the sulfide-based solid electrolyte according to one embodiment of the present invention includes solid particles that meet specific parameters, and thus can have excellent electrochemical characteristics.

[0033] In addition, according to any one of the technical solutions of the present invention, the all-solid-state battery according to one embodiment of the present invention includes a sulfide-based solid electrolyte that meets specific parameters and can therefore be filled with high energy density, thereby maximizing the battery capacity.

[0034] The effects that can be obtained in the present invention are not limited to the effects described above, and those skilled in the art can clearly understand other effects not mentioned from the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a conceptual diagram schematically showing the structure of an all-solid-state battery;

[0036] Figure 2 It is schematically shown Figure 1 Cross-sectional view of the cathode microstructure;

[0037] Figure 3 It is a graph used to illustrate the changes in ionic conductivity and particle size of sulfide-based solid electrolytes at different milling times;

[0038] Figure 4 are 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;

[0039] Figures 5a to 5d are images showing SEM images and parameter values ​​of a sulfide-based solid electrolyte according to an embodiment of the present invention and a sulfide-based solid electrolyte according to a comparative example;

[0040] Figures 6a to 6d is a graph showing battery capacity measurement results of pressurized cells using the sulfide-based solid electrolyte according to an embodiment of the present invention and the sulfide-based solid electrolyte according to a comparative example. DETAILED DESCRIPTION

[0041] The following describes embodiments of the present invention in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in various forms and is not limited to the embodiments described herein. In addition, portions not relevant to the description are omitted from the drawings to clarify the present invention. Similar portions are denoted by similar reference numerals throughout the specification.

[0042] Throughout this specification, when a part is described as being "connected" to another part, this includes not only cases of "direct connection" but also cases of "indirect connection" with other parts or elements interposed therebetween. Furthermore, when a part is described as "including" a certain component, unless otherwise specified, this indicates that other components may be further included, not that other components are excluded.

[0043] The present invention will be described in detail below with reference to the accompanying drawings.

[0044] Figure 1 is a conceptual diagram schematically showing the structure of an all-solid-state battery.

[0045] Reference Figure 1 The all-solid-state battery 100 includes a cathode 110 , an anode 130 , and a solid electrolyte 120 between the cathode 110 and the anode 130 .

[0046] The cathode 110 , solid electrolyte 120 , and anode 130 of the all-solid-state battery are all composed in a solid state and can be composed to generate electricity based on the potential difference generated when metal ions of the cathode 110 pass through the solid electrolyte 110 and move to the anode 130 .

[0047] The cathode 110 is composed of a positive electrode active material rich in metal ions. The metal ions can be metal ions of the first or second group on the periodic table. The positive electrode active material can be composed of compounds that can embed / de-embed the first or second group metals. When lithium (Li) ions are used as metal ions, the positive electrode active material can be, for example, Li a A 1-b B' b D'2 (in the above formula, 0.90≤a≤1.8, and 0≤b≤0.5); Li a E 1-b B' b O 2-c D' c (In the above formula, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); LiE 2-b B' b O 4-c D' c (In the above formula, 0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b- c Co b B' c D' α (In the above formula, 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 (In the above formula, 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 (In the above formula, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); Li a Ni1-b-c Mn b B' c O 2-α F' α (In the above formula, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni b E c G d O2 (in the above formula, 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 (in the above formula, 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 (in the above formula, 0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2 (in the above formula, 0.90≤a≤1.8, 0.001≤b≤0.1); Li a MnG b O2 (in the above formula, 0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn2G b O4 (in the above formula, 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) A compound represented by any chemical formula of Fe2(PO4)3(0≤f≤2); LiFePO4.

[0048] In the 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; E is Co, Mn or a combination thereof, 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.

[0049] The anode 130 is composed of a negative active material and may be composed of a layer in which the above-mentioned metal ions (eg, Li ions) are not precipitated in the form of metal.

[0050] 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.

[0051] On the other hand, in order to maximize the conductivity of metal ions, the cathode 110 or the anode 130 may be composed of a mixture of an active material and a solid electrolyte 120. Figure 1 As shown, the cathode 110 is composed of a mixture of a positive electrode active material and a solid electrolyte 120 . The solid electrolyte 120 is composed so that metal ions generated from the positive electrode active material can easily move.

[0052] The solid electrolyte 120 can be composed of various types of materials such as sulfide-based, oxide-based, and polymer-based materials, but is preferably composed of sulfide-based materials. The following description will focus on the sulfide-based solid electrolyte 120.

[0053] The sulfide-based solid electrolyte 120 of the present invention is a solid electrolyte containing sulfide-based solid particles, and its technical characteristics lie in that the shape and particle size of the particles meet specific conditions.

[0054] 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 the first or Group 2. For example, the sulfide-based solid particles contain Li, S, and P, and may be conductive to Li ions.

[0055] 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, Li2S-P2S 5-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 etc. However, the types of the sulfide-based solid particles of the present invention are not limited to the above examples.

[0056] The sulfide-based solid particles are crystalline, and may have, for example, an argyrodite crystal structure.

[0057] The sulfide-based solid particles have an average particle diameter of 70 μm or less.

[0058] In addition, 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 [Mathematical Formula 1] of 0.8 or greater in an image captured by a scanning electron microscope (SEM).

[0059]

Mathematical formula 1

[0060] C=4πA / P 2

[0061] Wherein, A represents the area of ​​the region defined along the outer contour of the sulfide-based solid particle in the SEM image (i.e., the area of ​​the sulfide-based solid particle), and P represents the perimeter of the region defined along the outer contour of the sulfide-based solid particle in the SEM image (i.e., the perimeter of the sulfide-based solid particle).

[0062] The 4πA / P of the above-mentioned [Mathematical Formula 1] 2 The value is a parameter that quantitatively indicates how close a shape defined on a two-dimensional plane is to a circle, and is defined herein as a "parameter" for ease of explanation. The closer the parameter is to 1, the closer the shape defined on the two-dimensional plane is to a circle.

[0063] On the other hand, the SEM image may be an image taken at a magnification of 5000 times or more.

[0064] An image of the sulfide-based solid electrolyte 120 taken by SEM at a magnification of 5000 times or greater may contain a plurality of sulfide-based solid particles, and a plurality of sulfide-based solid particles having a parameter value of 0.8 or greater may exist. For example, the sulfide-based solid particles having a parameter value of 0.8 or greater may account for more than 28% of all particles, preferably more than 34%, and more preferably more than 50%.

[0065] 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 greater in a SEM image.

[0066] Preferably, in an SEM image of the sulfide-based solid electrolyte 120 at a magnification of 5000 times or more, particles with a parameter value of 0.7 or more may account for more than 61% of all particles, preferably, more than 63%, and more preferably, more than 79%.

[0067] On the other hand, the aspect ratio of the sulfide-based solid particles may be 0.7 to 1.5, wherein the aspect ratio refers to the aspect ratio of the sulfide-based solid particles on a SEM image at a magnification of 5000 times or more.

[0068] Reference Figure 2 The above-mentioned characteristics of the sulfide-based solid particles of the present invention will be described in more detail.

[0069] Figure 2 It is schematically shown Figure 1 Cross-sectional view of the cathode microstructure.

[0070] Specifically, Figure 2 (a) is a diagram showing an example of a SEM image of a cathode 210 composed of a mixture of a conventional sulfide-based solid electrolyte and a positive electrode active material, Figure 2 (b) is a diagram showing an example of a SEM image of the cathode 110 composed of a mixture of a sulfide-based solid electrolyte and a positive electrode active material according to one embodiment of the present invention.

[0071] Reference Figure 2(a), the existing sulfide-based solid electrolyte contains sulfide-based solid particles 212 with the parameter value being less than 0.8. In other words, the existing sulfide-based solid electrolyte has no or relatively few sulfide-based solid particles with the parameter value being 1 to 0.8.

[0072] Since the existing sulfide-based solid particles 212 are composed of the parameter value less than 0.8, Figure 2 As shown in (a), the two-dimensional SEM image has an uneven and rough shape.

[0073] Furthermore, the aspect ratio of the conventional sulfide-based solid particles 212 exceeds 1.5 or is less than 0.7. Therefore, the pattern defined along the outer contour of the conventional sulfide-based solid particles 212 in the SEM image has an uneven aspect ratio as a whole and has an elongated shape.

[0074] In addition, the average particle size of the existing sulfide-based solid particles 212 exceeds 70 μm. The existing sulfide-based solid particles 212 exist in the form of an uneven mixture of large particles and small particles, and the average particle size of all particles exceeds 70 μm.

[0075] In some embodiments, the existing sulfide-based solid particles 212 may contain particles having a parameter value of 0.8 or greater. However, a significant portion of the sulfide-based solid particles 212 in the cathode 210 may have a parameter value of less than 0.8. Specifically, the proportion of particles having a parameter value less than 0.8 among all particles present in the SEM image may be greater than 72%. Conversely, the proportion of sulfide-based solid particles 212 having a parameter value between 1 and 0.8 is less than 28%.

[0076] Conventional sulfide-based solid particles 212 have a large average particle size and a high aspect ratio, and the proportion of particles with a parameter value less than 0.8 is greater than 72%. In other words, the parameter is less than 0.8 for most particles. Therefore, in the cathode 210, large gaps G1 may exist between the sulfide-based solid particles 212, and the contact area between the conventional sulfide-based solid particles 212 and the positive electrode active material 211 may be small.

[0077] On the contrary, refer to Figure 2 (b) The sulfide-based solid electrolyte of the present invention comprises sulfide-based solid particles 112 having a composition such that the parameter value is 0.7 or greater. Preferably, the sulfide-based solid electrolyte comprises sulfide-based solid particles 112 having a composition such that the parameter value is 1 to 0.8.

[0078] Since the 4πA / P of particles with parameter values ​​of 1 to 0.8 2The value is close to 1, so its shape can be close to a circle in a two-dimensional SEM image. Therefore, in the cathode 110 comprising the sulfide-based solid electrolyte of the present invention, the sulfide-based solid particles 112 have a Figure 2 (b) shows a circle-like shape.

[0079] The aspect ratio of the sulfide-based solid particles 112 of the present invention is 0.7 to 1.5. Therefore, the figure defined along the outer contour of the sulfide-based solid particles 112 of the present invention in the SEM image has an aspect ratio close to 1 as a whole and has a circle-like shape.

[0080] The sulfide-based solid particles 112 of the present invention have an average particle size of 70 μm or less. Therefore, in the SEM image, most of the sulfide-based solid particles 112 can be densely present as fine nanoparticles.

[0081] The parameter value of some particles in the sulfide-based solid particles 112 of the present invention may be less than 0.8. However, as described above, the parameter value of most of the sulfide-based solid particles 112 of the present invention is between 1 and 0.8. For example, particles with parameter values ​​of 1 to 0.8 in the SEM image may account for at least 28% of all particles, and particles with parameter values ​​of 1 to 0.7 may account for at least 61% of all particles.

[0082] As described above, the sulfide-based solid electrolyte of the present invention not only has a small and uniform average particle size of 70 μm or less, but also has the characteristics of having a parameter value of 1 to 0.8 and an aspect ratio of 0.7 to 1.5. In particular, it is characterized in that particles having a parameter value of 1 to 0.8 account for at least 28% or more of all particles present in an SEM image measured at a magnification of 5000 times or more.

[0083] The inventors of the present invention have found that when the morphological characteristics of the sulfide-based solid electrolyte have the above characteristics, excellent Li ion conductivity can be achieved in the cathode 110 composed of a mixture of the sulfide-based solid electrolyte and the positive electrode active material 111, and the sulfide-based solid particles 112 and the positive electrode active material 111 can be packed at a high density. For a more detailed description of this, refer to Figure 3 .

[0084] Figure 3 It is a graph used to illustrate the changes in ionic conductivity and particle size of sulfide-based solid electrolytes at different milling times.

[0085] Conventional sulfide-based solid electrolytes are prepared by mixing electrolyte raw materials using an attrition mill or a ball mill, followed by high-temperature heat treatment and sintering.

[0086] From the perspective of energy density, it is necessary to fill as much solid electrolyte as possible in a limited volume, so it may be necessary to increase the grinding time to reduce the average particle size of the sulfide-based solid particles.

[0087] like Figure 3 As shown in Figure 2, as the grinding time increases, the average particle size d of the sulfide-based solid particles increases. SE becomes smaller, so the average particle size d of the positive electrode active material CAM The average particle size d of sulfide-based solid particles SE The ratio λ can be increased.

[0088] However, as the grinding time increases, the average particle size d of the sulfide-based solid particles increases. SE As the Li ion conductivity decreases, the Li ion conductivity will show a downward trend.

[0089] Therefore, the average particle size d of the sulfide-based solid particles can be reduced according to the grinding time. SE To fill more sulfide-based solid electrolyte in the cathode, but due to the decrease in ionic conductivity, Figure 3 As shown, the capacity of the cathode will have a certain critical value.

[0090] The inventors of the present invention discovered that simply reducing the average particle size of the sulfide-based solid electrolyte is not sufficient to increase the cathode capacity; the particle shape of the sulfide-based solid electrolyte must also be controlled. The inventors discovered that the closer the specific parameters of the two-dimensional sulfide-based solid particles in the SEM image of the sulfide-based solid electrolyte are to 1, the higher the density of the positive electrode active material and the sulfide-based solid electrolyte can be packed into the cathode without hindering Li ion conductivity, thereby increasing the battery capacity.

[0091] That is, when the average particle size of the sulfide-based solid electrolyte is controlled to be less than 70 μm and the sulfide-based solid electrolyte is photographed by SEM at a magnification of 5000 times or more, when the 4πA / P ratio of the sulfide-based solid particles in the obtained SEM image is 2 When the proportion of particles having a value of 0.8 or more (i.e., 1 to 0.8) is at least 28%, the decrease in Li ion conductivity can be minimized, and high-density filling of the positive electrode active material and the sulfide-based solid electrolyte can be achieved, thereby maximizing the battery capacity.

[0092] This is because as 4πA / P 2When the value reaches 0.8 or above, the shape of the sulfide-based solid particles is close to an ideal sphere. As the sulfide-based solid electrolyte has an average particle size of less than 70 μm, the size of the sulfide-based solid particles becomes smaller, and high-density filling can be achieved while fully maintaining the contact area between the sulfide-based solid particles and the positive electrode active material.

[0093] The sulfide-based solid electrolyte of the present invention can have an ion conductivity of 3 mS / cm or more.

[0094] Therefore, the sulfide-based solid electrolyte of the present invention can have excellent electrochemical characteristics and has the advantage of ensuring excellent charge capacity even when charge and discharge cycles are repeated.

[0095] The sulfide-based solid electrolyte of the present invention can be prepared by the following method.

[0096] The sulfide-based solid electrolyte is prepared by first generating droplets from a precursor solution containing a sulfide-based solid electrolyte precursor and spraying them into a reactor, heating the sprayed droplets to generate sulfide-based solid particles, and collecting the generated sulfide-based solid particles to obtain a sulfide-based solid electrolyte.

[0097] In this case, the sulfide-based solid electrolyte precursor may include lithium sulfide and a halogen compound.

[0098] The lithium sulfide may include one or more substances selected from Li2S, Li2S2, Li2S4 and Li2S6.

[0099] The halogen compound may include one or more substances selected from lithium bromide (LiBr), lithium chloride (LiCl), lithium iodide (LiI), and lithium fluoride (LiF).

[0100] The sulfide-based solid electrolyte precursor may further include a metal compound, which may include one or more substances selected from Al, Si, P, gallium (Ga), iodine (I), Sn, germanium (Ge), antimony (Sb), Zn, arsenic (As), tungsten (W), Se, V and calcium (Ca).

[0101] The precursor solution can be sprayed in various ways, for example, by generating droplets of the precursor solution using an ultrasonic vibrator.

[0102] There are many ways to heat the precursor droplets, and the method can be to heat the reaction space of the spray droplets by heating the reactor.

[0103] The collection of the sulfide-based solid electrolyte can be performed by various methods capable of collecting micro-nanoparticles, and is not particularly limited.

[0104] As described above, the sulfide-based solid electrolyte according to one embodiment of the present invention is performed in a manner of spraying a precursor solution, heat treating, and obtaining a powder, so that the sulfide-based solid electrolyte can be prepared in a simple manner, and since it consists of a simple process, it has the advantages of being easy to construct a mass production facility and being suitable for mass production.

[0105] Modes for Carrying Out the Invention

[0106] The excellent electrochemical characteristics of the sulfide-based solid electrolyte of the present invention are described below using experimental examples.

[0107] <Preparation Example 1, Preparation of Sulfide-Based Solid Electrolyte>

[0108] First, raw materials Li2S, P2S5, and LiCl were mixed in an inert gas atmosphere glove box to prepare a mixed powder, which was then dissolved in a mixed solvent of ethyl acetate and ethanol to prepare a precursor solution.

[0109] The precursor solution thus prepared was formed into droplets by ultrasonic spraying and flowed into a heated reactor using an inert carrier gas supplied at a flow rate of 10 liters / minute (10ℓ / min) to obtain a first powder.

[0110] The obtained powder was placed in an aluminum crucible, and heat treated at 550° C. for 4 hours while passing an inert gas, and then cooled to room temperature to prepare the sulfide-based solid electrolyte of Example 1.

[0111] The same precursor as above was used to form droplets, and the precursor was introduced into the reactor by supplying an inert carrier gas at a flow rate of 5 L / min to obtain a second powder, and the same heat treatment as above was performed to prepare the sulfide-based solid electrolyte of Example 2.

[0112] The same precursor as above was used to form droplets, and the precursor was introduced into the reactor by supplying an inert carrier gas at a flow rate of 15 L / min to obtain a third powder, and the same heat treatment as above was performed to prepare the sulfide-based solid electrolyte of Example 3.

[0113] The chemical formula of the sulfide-based solid electrolytes of Examples 1 to 3 is Li6PS5Cl.

[0114] On the other hand, as a comparative example, a Li6PS5Cl solid electrolyte was obtained and filtered through 325 mesh to prepare a sulfide-based solid electrolyte having an average particle diameter (D50) of 10 μm or less as the sulfide-based solid electrolyte of Comparative Example 1.

[0115] <Experimental Example 1, SEM Photography>

[0116] In order to compare the particles of the solid electrolyte according to the comparative example and the solid electrolyte according to Examples 1 to 3, the particles were photographed using a scanning electron microscope (SEM). The SEM images of each sample were taken at a magnification of 5000 times. The results are shown in FIG. Figure 4 shown.

[0117] Figure 4 are 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.

[0118] Reference Figure 4 It can be confirmed that the sulfide-based solid electrolytes of Examples 1 to 3 have rounder particles than the solid electrolyte according to the comparative example. In other words, the average particle size of the sulfide-based solid electrolyte particles of the comparative example is similar to that of Example 1, but it can be confirmed that the particle shape is uneven and the aspect ratio is also non-uniform.

[0119] On the other hand, it was confirmed that the particle size of the sulfide-based solid electrolyte of Example 3 was small, and most of the particles were round in shape.

[0120] <Experimental Example 2, Comparison of Particle Parameters>

[0121] The SEM images were analyzed to calculate the parameter value (4πA / P 2 ). The result is as follows Figures 5a to 5d shown.

[0122] Figures 5a to 5d are images showing SEM images and parameter values ​​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.

[0123] The parameter value of each particle is achieved by digitally analyzing the SEM image of each sample to generate a normalized image of the area defined along the outer contour of the sulfide-based solid particle, and then calculating the parameter value based on the area A value and the perimeter P value of the normalized image.

[0124] Reference Figure 5a , it can be seen that the parameter values ​​of most particles of 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 shown in the following [Table 1].

[0125]

Table 1

[0126]

[0127] As shown in Table 1, the sulfide-based solid electrolyte of the comparative example is confirmed to be composed of solid particles with a parameter value of less than 0.8. Specifically, the cumulative proportion of solid particles with a parameter value of less than 0.8 is 72.3%, while the proportion of solid particles with a parameter value between 1 and 0.8 is only 27.7%.

[0128] Reference Figures 5b to 5d It can be confirmed that the parameter values ​​of the majority of the sulfide-based solid particles in Examples 1 to 3 were 0.7 or higher, and the proportion of particles with values ​​of 0.8 or higher was 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.

[0129]

Table 2

[0130]

[0131]

Mathematical formula 2

[0132] σ = t / (a*R)

[0133] Here, σ represents ionic conductivity, t represents the thickness of the particle, R represents the bulk resistance value, and a represents the area of ​​the particle.

[0134] The evaluation results are shown in Table 3 below.

[0135]

Table 3

[0136]

[0137] As can be seen from Table 3, the sulfide-based solid electrolyte of the present invention has the same or better ion conductivity than the sulfide-based solid electrolyte of the comparative example.

[0138] <Preparation Example 2: Preparation of All-Solid-State Battery>

[0139] In order to evaluate the excellent electrochemical characteristics of the sulfide-based solid electrolyte of the present invention, pressurized cells were prepared using the sulfide-based solid electrolytes of the comparative example and Examples 1 to 3.

[0140] Specifically, the positive electrode active material NCM811 was mixed at 75, 80, and 85 wt%, and three all-solid-state pressurized cells were prepared for each sample. Meanwhile, a lithium metal electrode was used as the anode.

[0141] <Experimental Example 4, Measuring Battery Capacity>

[0142] The battery capacity of the pressurized battery cell prepared in Preparation Example 2 was measured at room temperature. Figures 6a to 6d shown.

[0143] Figures 6a to 6d is a graph showing battery capacity measurement results of pressurized cells using the sulfide-based solid electrolyte according to an embodiment of the present invention and the sulfide-based solid electrolyte according to a comparative example.

[0144] Specifically, Figure 6a This is a battery capacity measurement graph of a pressurized cell using a sulfide-based solid electrolyte of a comparative example. Figures 6b to 6d The graphs are battery capacity measurement graphs of pressurized cells using the sulfide-based solid electrolytes of Examples 1 to 3, respectively.

[0145] in addition, Figures 6a to 6d The battery capacity measurement results are shown in the following [Table 4].

[0146]

Table 4

[0147]

[0148] Refer to the [Table 4] and Figures 6a to 6d It can be seen that the lower the content of the positive electrode active material NCM811, the relatively greater the amount of the sulfide-based solid electrolyte, and thus the greater the battery capacity in a cell of the same volume.

[0149] On the other hand, the sulfide-based solid electrolyte of the comparative example and the sulfide-based solid electrolyte of Example 2 have about 350 similar particles in the SEM image at 5000 times, so it can be considered that the average particle size of the two samples is similar, but the sulfide-based solid electrolyte of Example 2 has a larger content of solid particles with the parameter value of 1 to 0.8 than the sulfide-based solid electrolyte of the comparative example (refer to Experimental Example 2). Therefore, by comparison Figure 6a and Figure 6c It can be seen that the sulfide-based solid electrolyte of Example 2 can provide superior battery capacity compared to the sulfide-based solid electrolyte of the comparative example. This is believed to be because most of the solid particles of Example 2 have nearly round properties, which maximizes the contact area with the positive electrode active material, thereby minimizing the reduction in Li ion conductivity.

[0150] In addition, by Figure 6b and Figure 6d It can be seen that when the average particle size of the sulfide-based solid electrolyte is small enough and the cumulative proportion of particles with parameter values ​​of 1 to 0.8 in SEM images of 5000 times or more is 50% or more, the battery capacity can be increased by about 10% or more compared with the sulfide-based solid electrolyte of the comparative example. It can be seen that the higher the proportion 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.

[0151] The above description of the present invention is intended to be illustrative only. Those skilled in the art will appreciate that the present invention can be readily modified into other specific forms without altering the technical principles or essential features of the present invention. Therefore, it should be understood that the embodiments described above are illustrative in all respects and are not intended to be limiting. For example, components described in a single form may be implemented separately, and components described in a separate form may also be implemented in a combined form.

[0152] The scope of the present invention is indicated by the appended claims rather than the detailed description above, and it should be interpreted that all changes or modifications derived from the meaning and scope of the claims and their equivalents are included in the scope of the present invention.

[0153] Industrial availability

[0154] The present invention can be applied to the secondary battery industry, for example, in secondary batteries for electric vehicles, secondary batteries for electronic devices such as laptop computers, tablet computers, and smartphones, and in the secondary battery industry for devices powered by battery energy.

Claims

1. A sulfide-based solid electrolyte comprising at least one sulfide-based solid particle, wherein a parameter value C defined by the following [Mathematical Formula 1] in a scanning electron microscope (SEM) image of the at least one sulfide-based solid particle is 0.8 or greater, 【Mathematical formula 1】 C=4πA / P 2 in, A represents the area of ​​a region defined along the outer contour of the at least one sulfide-based solid particle in a scanning electron microscope image, and P represents the perimeter of the region. 2 . The sulfide-based solid electrolyte according to claim 1 , wherein the scanning electron microscope image is an image taken at a magnification of 5000 times or more.

3. The sulfide-based solid electrolyte according to claim 2, wherein a plurality of sulfide-based solid particles are present in the scanning electron microscope image, and the number of the sulfide-based solid particles having a parameter value greater than 0.8 is greater than 28% of all particles in the scanning electron microscope image. 4 . 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 . The sulfide-based solid electrolyte according to claim 1 , wherein the average particle diameter of the sulfide-based solid particles is 70 μm or less. The sulfide-based solid electrolyte according to claim 1 , wherein the ion conductivity of the sulfide-based solid electrolyte is 3 mS / cm or higher. 7 . The sulfide-based solid electrolyte according to claim 1 , wherein the sulfide-based solid particles comprise 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. An all-solid-state battery, comprising: cathode (cathode); an anode corresponding to the cathode; a sulfide-based solid electrolyte disposed between the cathode and the anode, The sulfide-based solid electrolyte comprises at least one sulfide-based solid particle, The parameter value C defined by the following [Mathematical Formula 1] in the scanning electron microscope image of the sulfide-based solid particles is 0.8 or greater, 【Mathematical formula 1】 C=4πA / P 2 Wherein, A represents the area of ​​a region defined along the outer contour line in the scanning electron microscope image of the sulfide-based solid particle, and P represents the perimeter of the region. 10 . The all-solid-state battery according to claim 9 , wherein the scanning electron microscope image is an image captured at a magnification of 5000 times or more.

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 greater in the scanning electron microscope image accounts for more than 28% in the scanning electron microscope image. 12 . The all-solid-state battery according to claim 9 , wherein the sulfide-based solid particles comprise sulfur (S), lithium (Li) and phosphorus (P). 13 . The all-solid-state battery according to claim 9 , wherein the sulfide-based solid particles have an argyrodite crystal structure.

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