Method for predicting electrochemical properties of cathode active material for all-solid-state battery

Abstract

The present invention relates to a method for predicting electrochemical properties of a cathode active material for an all-solid-state battery, the method comprising: a first step of obtaining a scanning electron microscope (SEM) image of a cathode active material for an all-solid-state battery, which is in the form of secondary particles, each composed of the aggregation of a plurality of primary particles; a second step of deriving the average radius of primary particles and the average number of primary particles present in secondary particles from the SEM image; a third step of deriving the average active area from the derived average radius of primary particles and average number of primary particles present in secondary particles; and a fourth step of predicting rate characteristics of the all-solid-state battery from the derived average active area.

Description

Method for predicting electrochemical properties of positive electrode active materials for all-solid-state batteries

[0001] The present invention relates to a method for predicting electrochemical characteristics of a positive electrode active material for an all-solid-state battery, and more specifically, to a method for predicting the rate characteristics of an all-solid-state battery from visual information of a positive electrode active material for an all-solid-state battery.

[0002]

[0003] With research focusing on the safety issues and energy density of high-capacity batteries, all-solid-state batteries are gaining attention as next-generation batteries. By replacing liquid electrolytes, which can be prone to explosion, with solid electrolytes, all-solid-state batteries eliminate the use of flammable solvents, eliminating the risk of ignition or explosion caused by reactions like the decomposition of conventional electrolytes. This ensures battery safety. Furthermore, the ability to use lithium metal or lithium alloys as anode materials improves the energy density relative to the mass and volume of the battery.

[0004] All-solid-state batteries generally use inorganic solid electrolyte powder as the electrolyte, and unlike general lithium-ion batteries that use liquid electrolytes, their characteristics depend on the surface contact area between the positive electrode active material and the electrolyte, surface reaction characteristics, and whether physical surface contact is maintained after expansion / contraction during the charge / discharge process.

[0005] Thus, in all-solid-state batteries, the surface contact area between the positive electrode active material and the solid electrolyte (hereinafter referred to as the “active area” in this specification) is an important property that determines the electrochemical characteristics of the all-solid-state battery, but to date, a methodology capable of quantitatively analyzing the above property has not been established. In addition, after manufacturing positive electrode materials for all-solid-state batteries, a method of directly assembling cells and then evaluating the electrochemical characteristics was used in the past to select positive electrode materials of superior quality. However, in this case, cell assembly and electrochemical characteristic evaluation must be performed inevitably, which has problems in terms of time and cost.

[0006] In particular, solid electrolytes generally have the issue of lower ionic conductivity compared to liquid electrolytes, so research on the quantitative properties of positive electrode active materials for all-solid-state batteries that can maximize rate characteristics is necessary.

[0007]

[0008] Accordingly, one object of the present invention is to provide a method for predicting electrochemical characteristics of a cathode active material for an all-solid-state battery, which can quantitatively derive the active area between the cathode active material and the solid electrolyte from visual information of the cathode active material for an all-solid-state battery and predict the electrochemical characteristics (more specifically, rate characteristics) of the all-solid-state battery from this.

[0009]

[0010] One embodiment of the present invention provides a method for predicting electrochemical characteristics of a positive electrode active material for an all-solid-state battery, comprising: a first step of obtaining a SEM (scanning electron microscope) image of a positive electrode active material for an all-solid-state battery in the form of secondary particles formed by agglomeration of a plurality of primary particles; a second step of deriving an average radius of the primary particles and an average number of primary particles present in the secondary particles from the SEM image; a third step of deriving an average active area from the derived average radius of the primary particles and the average number of primary particles present in the secondary particles; and a fourth step of predicting a rate characteristic of the all-solid-state battery from the derived average active area.

[0011] In the second step, the average radius of the derived primary particles may be an area-based average radius calculated based on the area of ​​the primary particles or a circumference-based average radius calculated based on the circumference of the primary particles.

[0012] In the third step, the derived average active area may be a spherical average active area derived by assuming that the primary particle is a sphere, a cubic average active area derived by assuming that the primary particle is a cube, or an icosahedron average active area derived by assuming that the primary particle is an icosahedron.

[0013] The above 4th step is, the average active area derived above is 50 μm 2 If this is above the threshold value, it can be predicted that the rate characteristics of the all-solid-state battery are excellent.

[0014] When the average radius of the primary particles derived above is the average radius based on the area, and the average active area derived above is the average active area based on the sphere, the threshold value is 110 μm. 2 It could be.

[0015] When the average radius of the primary particles derived above is the average radius based on the area, and the average active area derived above is the average active area based on the cube, the threshold value is 104 μm. 2 It could be.

[0016] When the average radius of the primary particles derived above is the average radius based on the area, and the average active area derived above is the average active area based on the regular icosahedron, the threshold value is 127 μm. 2 It could be.

[0017] When the average radius of the primary particles derived above is the average radius based on the circumference, and the average active area derived above is the average active area based on a sphere, the threshold value is 103 μm. 2 It could be.

[0018] When the average radius of the primary particles derived above is the average radius based on the circumference, and the average active area derived above is the average active area based on a cube, the threshold value is 98 μm. 2 It could be.

[0019] When the average radius of the primary particles derived above is the average radius based on the circumference, and the average active area derived above is the average active area based on the regular icosahedron, the threshold value is 120 μm. 2 It could be.

[0020] The average particle diameter (D50) of the above secondary particles may be 5 μm or less.

[0021]

[0022] A method for predicting the electrochemical properties of a cathode active material for an all-solid-state battery according to one embodiment of the present invention derives an active area from a SEM image of the cathode active material, which is visual information, and can thereby predict the electrochemical properties (more specifically, rate characteristics) of the all-solid-state battery. Accordingly, in the process of selecting high-quality cathode materials, there is no need to directly evaluate electrochemical properties after cell assembly, as was done in the past, thereby reducing the time and cost of product selection.

[0023]

[0024] Figure 1 is an example of an SEM image of a positive electrode active material derived from the first step.

[0025] Figure 2 is an example of a software image showing the execution process of the second step.

[0026] Figure 3 is an image showing the process of obtaining the average active area based on a spherical reference in the third step.

[0027] Figure 4 is an image showing the process of obtaining the average active area based on a cube in the third step.

[0028] Figure 5 is an image showing the process of obtaining the average active area based on the icosahedron in the third step.

[0029]

[0030] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0031] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0032] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0033] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0034] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0035] In this specification, the term "combination(s) thereof" described in the expression in the Makushi format means one or more mixtures or combinations selected from the group consisting of the components described in the expression in the Makushi format, and means including any one or more selected from the group consisting of said components.

[0036] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0037]

[0038] All-solid-state batteries generally use inorganic solid electrolyte powder as the electrolyte, and unlike general lithium-ion batteries that use liquid electrolytes, their characteristics are largely determined by the surface contact area between the positive electrode active material and the electrolyte, surface reaction characteristics, and whether physical surface contact is maintained after expansion / contraction during the charge / discharge process.

[0039] Thus, in all-solid-state batteries, the surface contact area between the positive electrode active material and the solid electrolyte (hereinafter referred to as the “active area” in this specification) is an important property that determines the electrochemical characteristics of the all-solid-state battery, but to date, a methodology capable of quantitatively analyzing the above property has not been established. In addition, after manufacturing positive electrode materials for all-solid-state batteries, a method of directly assembling cells and then evaluating the electrochemical characteristics was used in the past to select positive electrode materials of superior quality. However, in this case, cell assembly and electrochemical characteristic evaluation must be performed inevitably, which has problems in terms of time and cost.

[0040] In particular, solid electrolytes generally have the issue of lower ionic conductivity compared to liquid electrolytes, so research on the quantitative properties of positive electrode active materials for all-solid-state batteries that can maximize rate characteristics is necessary.

[0041] Accordingly, the inventors of the present invention have conducted extensive research to establish criteria for selecting products with excellent electrochemical properties, particularly rate characteristics, of positive electrode active materials for all-solid-state batteries. As a result, they have obtained a method capable of deriving an active area from a SEM (scanning electron microscope) image, which is visual information of the positive electrode active material, and predicting the rate characteristics from the range of the derived active area, thereby completing the present invention. According to this, direct cell assembly and electrochemical characteristic evaluation are not required to select high-quality products as in the past, so the time and cost of product selection can be drastically reduced.

[0042]

[0043] Specifically, one embodiment of the present invention provides a method for predicting electrochemical characteristics of a positive electrode active material for an all-solid-state battery, including a first step of deriving a SEM (scanning electron microscope) image of a positive electrode active material for an all-solid-state battery in the form of secondary particles formed by agglomeration of a plurality of primary particles; a second step of deriving an average radius of the primary particles and an average number of primary particles present in the secondary particles from the SEM image; a third step of deriving an average active area from the derived average radius of the primary particles and the average number of primary particles present in the secondary particles; and a fourth step of predicting a rate characteristic of the all-solid-state battery from the derived average active area.

[0044] Hereinafter, a method for predicting electrochemical properties of a positive electrode active material for an all-solid-state battery according to one embodiment of the present invention will be described in detail step by step.

[0045]

[0046] Step 1

[0047] First, a SEM (scanning electron microscope) image of the positive electrode active material for an all-solid-state battery in the form of secondary particles formed by agglomeration of multiple primary particles is obtained.

[0048] Figure 1 is an example of an SEM image of a positive electrode active material derived from the first step.

[0049] Referring to FIG. 1, in the present specification, “secondary particle” means an aggregate, i.e., a secondary structure, formed by the physical or chemical bonding of tens to hundreds of primary particles without any intentional aggregation or assembly process for the primary particles. In addition, “primary particle” means the smallest particle unit that can be distinguished as a single lump when observing the cross-section of a positive electrode active material through a scanning electron microscope (SEM), and may be composed of a single crystal grain or multiple crystal grains. In addition, “crystal grain” means a distinct region in the form of a lattice structure in a certain direction of atoms within a primary particle.

[0050] Meanwhile, the positive electrode active material for the all-solid-state battery may include lithium metal oxide. At this time, the type of lithium metal oxide is not particularly limited. For example, the lithium metal oxide may be a typical nickel-based layered lithium metal oxide, a lithium-rich layered lithium metal oxide, an olivine-structured lithium iron phosphate oxide, a spinel-structured lithium manganese oxide, etc., but is not necessarily limited thereto.

[0051] Additionally, the specific composition of lithium metal oxide is not particularly limited.

[0052] Meanwhile, the average particle diameter (D50) of the secondary particles may be 2 to 7 μm, and more specifically, 3 to 5.5 μm. When the average particle diameter (D50) of the secondary particles satisfies the above range, the electrochemical characteristic prediction result of the positive electrode active material for an all-solid-state battery according to the present invention can be implemented more accurately. In the present specification, the average particle diameter (D50) can be defined as a particle diameter corresponding to 50% of the volume accumulation amount in the particle diameter distribution curve of the particles. The average particle diameter (D50) can be measured using, for example, a laser diffraction method.

[0053]

[0054] Step 2

[0055] Next, the average radius of the primary particles and the average number of primary particles present in the secondary particles are derived from the above SEM images.

[0056] Figure 2 is an example of a software image illustrating the execution process of the second step. Referring to Figure 2, the boundaries of individual primary particles within secondary particles are removed through image software, and then the outlines of individual primary particles are detected to derive an image segmented into individual primary particles. Through this software image, the average radius of the primary particles and the average number of primary particles present within the secondary particles can be derived.

[0057] At this time, the average radius of the primary particles derived above may be an area-based average radius calculated based on the area of ​​the primary particles or a circumference-based average radius calculated based on the circumference of the primary particles.

[0058] More specifically, the area-based average radius can be calculated by measuring the area (pixel) occupied by each primary particle within the secondary particle using image software from the SEM image derived from the first step, specifying the radius of a circle having the same area as the radius of each primary particle, and calculating the average value of the radius of each primary particle within the secondary particle.

[0059] In addition, the average radius based on the circumference can be calculated by measuring the circumference of each primary particle within the secondary particle using image software from the SEM image derived from the first step, specifying the radius of a circle with the same circumference as the radius of each primary particle, and calculating the average value of the radius of each primary particle within the secondary particle.

[0060] In addition, the average number of primary particles present in the secondary particles can be calculated using image software from the SEM image derived from the first step. Meanwhile, the number of primary particles at this time refers to the number of primary particles located on the surface of the positive electrode active material observed in the two-dimensional SEM image, and does not refer to the number of all primary particles present in the actual three-dimensional positive electrode active material.

[0061] Meanwhile, the average radius of the primary particles derived above and the average number of primary particles present in the secondary particles can be averaged by measuring the values ​​for 10 different secondary particles within the positive electrode active material sample. This can reduce measurement deviation and error.

[0062]

[0063] Step 3

[0064] Next, the average active area is derived from the average radius of the primary particles derived above and the average number of primary particles present in the secondary particles.

[0065] At this time, the average active area derived above may be a spherical average active area derived by assuming that the primary particle is a sphere, a cubic average active area derived by assuming that the primary particle is a cube, or an icosahedron average active area derived by assuming that the primary particle is an icosahedron.

[0066] More specifically, Fig. 3 is a conceptual diagram illustrating a process for deriving a spherical reference average active area by assuming that the primary particles are spherical. Referring to Fig. 3, the spherical reference average active area can be calculated using the following method. First, the average radius of the primary particles derived from the second step is assumed to be the radius of the spherical particles. Then, half of the total area of ​​the spherical particles is assumed to be the active area that is in direct contact with the solid electrolyte. Then, the average active area of ​​the positive electrode active material can be calculated by multiplying the active area of ​​each primary particle derived through this by the average number of primary particles present in the secondary particles.

[0067] In addition, Fig. 4 is a conceptual diagram showing the process of deriving the average active area based on a cube by assuming that the primary particles are cubes. Referring to Fig. 4, the average active area based on a cube can be calculated using the following method. First, the average radius of the primary particles derived from the second step is assumed to be the length of one edge of the cube. Then, half of the total area of ​​the cubic particles is assumed to be the active area that is in direct contact with the solid electrolyte. Then, the average active area of ​​the positive electrode active material can be calculated by multiplying the active area of ​​each primary particle derived through this by the average number of primary particles present in the secondary particle.

[0068] In addition, Fig. 5 is a conceptual diagram showing the process of deriving the average active area based on the icosahedron by assuming the primary particles to be regular icosahedrons. Referring to Fig. 5, the average active area based on the icosahedron can be calculated using the following method. First, the average radius of the primary particles derived from the second step is assumed to be the length of one edge of the icosahedron. Then, half of the total area of ​​the icosahedral particles is assumed to be the active area that is in direct contact with the solid electrolyte. Then, the average active area of ​​the positive electrode active material can be calculated by multiplying the active area of ​​each primary particle derived through this by the average number of primary particles present in the secondary particles.

[0069]

[0070] Step 4

[0071] Next, the rate characteristics of the all-solid-state battery are predicted from the average active area derived above.

[0072] More specifically, the fourth step is, the average active area derived above is 50 μm 2 If this is above the threshold value, it can be predicted that the rate characteristics of the all-solid-state battery are excellent.

[0073] In general, it is known that electrochemical characteristics such as capacity and rate characteristics are guaranteed when the active area, which is the contact area between the positive electrode active material and the solid electrolyte, has a value above a certain level. However, research on the upper limit threshold at which the electrochemical characteristics rather deteriorate is insufficient.

[0074] The present inventors derived the average active area for positive electrode active materials for all-solid-state batteries having a specific range of average particle diameters, and experimentally studied the correlation between these average active areas and the capacity or rate characteristics of all-solid-state batteries. As a result, they found that, in particular, controlling the average active area to a range below an upper threshold is important for maximizing the rate characteristics. The present inventors believe that this is because the surface area of ​​positive electrode active materials for all-solid-state batteries varies depending on the size of the primary particles and the average particle diameter of the secondary particles, and that if the surface area is too large, the electrochemical activity is reduced due to side reactions between the active material and the electrolyte. In particular, considering the issue of reduced rate characteristics of all-solid-state batteries due to low ionic conductivity of the solid electrolyte, the derivation of the upper threshold of the average active area is expected to play an important role as an indicator for selecting high-quality positive electrode materials for all-solid-state batteries.

[0075] In one embodiment, when the average radius of the derived primary particles is an area-based average radius and the derived average active area is a spherical-based average active area, the threshold value is 110 μm. 2 It could be.

[0076] In another implementation example, when the average radius of the derived primary particles is an area-based average radius and the derived average active area is a cube-based average active area, the threshold value is 104 μm. 2 It could be.

[0077] In another implementation example, when the average radius of the derived primary particles is the average radius based on the area, and the derived average active area is the average active area based on the regular icosahedron, the threshold value is 127 μm. 2 It could be.

[0078] In another implementation, when the average radius of the derived primary particles is the average radius based on the circumference, and the average active area derived is the average active area based on the sphere, the threshold value is 103 μm.2 It could be.

[0079] In another implementation example, when the average radius of the derived primary particles is the average radius based on the circumference, and the average active area derived is the average active area based on a cube, the threshold value is 98 μm. 2 It could be.

[0080] In another implementation example, when the average radius of the derived primary particles is the average radius based on the circumference, and the average active area derived is the average active area based on the icosahedron, the threshold value is 120 μm. 2 It could be.

[0081]

[0082] Hereinafter, embodiments of the present invention will be described in more detail through examples. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0083]

[0084] Manufacturing Example 1

[0085] (1) Preparation of positive electrode active material for all-solid-state batteries

[0086] (lithium metal oxide formation)

[0087] Ni 0.83 Co 0.12 Mn 0.05 (OH)2 transition metal hydroxide precursor and LiOH·H2O as lithium raw material were mixed at a molar ratio of 1:1.02 to form a mixture.

[0088] 1 kg of the above mixture was loaded into a tube and fired at a temperature of 730°C for 8 hours. During the firing, pure O2 was supplied so that the O2 concentration could be maintained at 99% or higher, so that LiNi 0.83 Co 0.12 Mn 0.05 O2 lithium metal oxide was formed.

[0089] (Preparing the coating solution)

[0090] Next, lithium was dissolved in dehydrated ethanol, and zirconium(IV) tetrapropoxide (70 wt. % in 1-propanol) was added and stirred to prepare a coating solution containing lithium ions and zirconium ions. At this time, the concentration of zirconium ions in the coating solution was set to 0.11 mol / L.

[0091] (Spraying coating solution)

[0092] The coating process was performed by spraying 420 mL of coating solution onto 1 kg of the lithium transition metal oxide formed above using a fluid coating device (MP-01, POWREX).

[0093] (Coating heat treatment)

[0094] Afterwards, the lithium transition metal oxide sprayed with the above coating solution was loaded into Saggar, and then heat treated at 300°C while supplying oxygen in a box-type electric furnace, thereby manufacturing a cathode active material in which an amorphous coating layer of Li2ZrO3 was formed on the surface of the lithium transition metal oxide.

[0095] (2) All-solid-state battery manufacturing

[0096] A mixture paste was prepared by mixing 75 wt% of the above-mentioned manufactured positive electrode active material, 22 wt% of argyrodite solid electrolyte (Li6PS5Cl), and 3 wt% of Super C65 as a conductive material with a solvent containing a small amount of binder dissolved therein. An electrode plate was manufactured using the mixture paste, and the plate was dried to prepare a composite electrode plate for the positive electrode.

[0097] First, 100 mg of argyrodite solid electrolyte (Li6PS5Cl) that functions as a separator was loaded into a jig for evaluating an all-solid-state battery, and pressurized at 300 MPa or more to a thickness of approximately 800 μm. Then, a positive electrode plate was placed on one side, and a second pressurization was performed to manufacture the positive electrode part.

[0098] Afterwards, a Li-In alloy was placed on the other side and appropriate pressure was applied to produce a battery for evaluating all-solid-state batteries.

[0099]

[0100] Manufacturing Examples 2 to 13

[0101] In the lithium metal oxide formation step, a cathode active material and an all-solid-state battery were manufactured in the same manner as in Example 1, except that the sintering temperature and sintering time were adjusted differently.

[0102]

[0103] Tables 1 to 3 below summarize the results of Experimental Examples 1 and 2 described below.

[0104] Secondary particle average particle size (D50, μm) Primary particle average radius (μm) Primary particle average number Area basis Circumference basis (units) Manufacturing example 14.180.240.24256 Manufacturing example 23.930.210.2348 Manufacturing example 33.860.230.22276 Manufacturing example 43.930.220.2305 Manufacturing example 53.930.220.22321 Manufacturing example 63.960.220.21358 Manufacturing example 73.90.230.23322 Manufacturing example 83.770.260.25306 Manufacturing example 94.180.260.25296 Manufacturing example 103.890.260.25310 Manufacturing example Manufacturing example 113.960.230.23367 Manufacturing example 123.770.260.25310 Manufacturing example 133.850.260.25300

[0105] Average active area r1 (area) - model 1 (sphere) r1 (area) - model 2 (cube) r1 (area) - model 3 (icosahedron) r2 (perimeter) - model 1 (sphere) r2 (perimeter) - model 2 (cube) r2 (perimeter) - model 3 (icosahedron) μm 2 μm 2 μm 2 μm 2 μm 2 μm 2Manufacturing Example 195.290.9110.994.690.3110.1 Manufacturing Example 210196.5117.78581.299 Manufacturing Example 391.387.1106.380.676.993.8 Manufacturing Example 490.486.3105.380.576.993.7 Manufacturing Example 596.291.911295.591.2111.2 Manufacturing Example 6107.7102.8125.4100.195.5116.5 Manufacturing Example 7111.1106.1129.4105.1100.4122.4 Manufacturing Example 8128.6122.8149.7124.7119.1145.3 Manufacturing example 9123.5117.9143.8116.3111135.4 Manufacturing example 10134.7128.6156.8117.4112.1136.7 Manufacturing example 11118.4113.1137.9126.6120.9147.4 Manufacturing example 12134.7128.6156.8117.4112.1136.7 Manufacturing example 13123.1117.5143.3121.7116.2141.7

[0106] Initial Capacity Rate Characteristics Charge Discharge Initial Efficiency 0.1C 0.5C 1.0C 0.5C / 0.1C 1.0C / 0.1C mAh / g mAh / g % mAh / g mAh / g mAh / g % % Manufacturing Example 1 226.3 212.6 94.00 % 212 196.9 181.39 2.98 5.5 Manufacturing Example 2 225.5 212.194.10 % 211.6 196.5 185.49 2.98 7.6 Manufacturing Example 3 226.2 213.294.20 % 212.4 197.1184.5 92.88 6.9 Manufacturing Example 4 2221.6 209.6 94.60 % 209.1193.9 1779 2.78 4.6 Manufacturing Example 5221.6209.694.60%209.1193.917792.784.6 Manufacturing example 6220.8208.194.20%207.3190.7177.59285.6 Manufacturing example 7224.5213.395.00%212.8195.1173.991.781.7 Manufacturing example 8216.8205.894.90%205.3188.2168.191.781.9 Manufacturing example 9215.520394.20%202.4184.616691.282 Manufacturing example 10220.920894.20%207.5188.2166.990.780.5 Manufacturing example 11218.6205.494.00%204.6184166.489.981.3 Manufacturing example 12222.9208.793.60%207.8185.6167.289.380.5 Manufacturing example 13218.5206.294.40%205.6183.5164.289.379.9

[0107]

[0108] Experimental Example 1: Analysis of the physical properties of the positive electrode active material

[0109] (1) Evaluation of secondary particle average diameter (D50)

[0110] For the active material powder, the particle size corresponding to 50% of the cumulative volume was measured using the laser diffraction method.

[0111] (2) Evaluation of the average radius of primary particles, evaluation of the average number of primary particles in secondary particles

[0112] SEM (scanning electron microscope) images were obtained from the positive electrode active material sample prepared in the above manufacturing example. The magnification of the SEM image was 15,000x.

[0113] Thereafter, the average radius of the primary particles and the average number of primary particles present in the secondary particles were derived from the SEM images. At this time, the average radius based on area and the average radius based on circumference were each calculated for each manufacturing example.

[0114] Specifically, the area-based average radius was calculated by measuring the area (pixel) occupied by each primary particle within the secondary particle using image software on the SEM image derived from the first step, specifying the radius of a circle with the same area as the radius of each primary particle, and calculating the average value of the radius of each primary particle within the secondary particle.

[0115] The average radius based on the circumference was calculated by measuring the circumference of each primary particle within the secondary particle using image software from the SEM image derived from the first step, specifying the radius of a circle with the same circumference as the radius of each primary particle, and calculating the average value of the radius of each primary particle within the secondary particle.

[0116] In addition, the number of primary particles present within the secondary particles was calculated from the SEM image using image software. In this case, the number of primary particles refers to the number of primary particles located on the surface of the positive electrode active material observed in the two-dimensional SEM image, and does not refer to the number of all primary particles present within the actual three-dimensional positive electrode active material.

[0117] Meanwhile, the average radius of the primary particles and the average number of primary particles present in the secondary particles were finally derived as the average values ​​of the values ​​measured for 10 different secondary particles in the positive electrode active material sample.

[0118] (3) Average active area evaluation

[0119] The average active area was derived from the average radius of the primary particles derived above and the average number of primary particles present in the secondary particles. At this time, the average active area based on a sphere, the average active area based on a cube, and the average active area based on an icosahedron were each calculated for the area-based average radius and the circumference-based average radius derived from the second step.

[0120] Referring to Fig. 3, the average active area based on a sphere can be calculated using the following method. First, the average radius of the primary particles derived from the second step is assumed to be the radius of the spherical particles. Then, half of the total area of ​​the spherical particles is assumed to be the active area in direct contact with the solid electrolyte. Then, the average active area of ​​the positive electrode active material can be calculated by multiplying the active area of ​​each primary particle derived through this by the average number of primary particles present in the secondary particles.

[0121] Referring to Fig. 4, the average active area based on a cube can be calculated using the following method. First, the average radius of the primary particles derived from the second step is assumed to be the length of one edge of the cube. Then, half of the total area of ​​the cubic particles is assumed to be the active area in direct contact with the solid electrolyte. Then, the average active area of ​​the positive electrode active material can be calculated by multiplying the active area of ​​each primary particle derived through this by the average number of primary particles present in the secondary particle.

[0122] Referring to Fig. 5, the average active area based on a regular icosahedron can be calculated using the following method. First, the average radius of the primary particles derived from the second step is assumed to be the length of one edge of the regular icosahedron. Then, half of the total area of ​​the regular icosahedron particles is assumed to be the active area in direct contact with the solid electrolyte. Then, the average active area of ​​the positive electrode active material can be calculated by multiplying the active area of ​​each primary particle derived through this by the average number of primary particles present in the secondary particle.

[0123]

[0124] Experimental Example 2: Evaluation of the electrochemical properties of an all-solid-state battery.

[0125] (1) Initial capacity and initial efficiency evaluation

[0126] After fabricating a lithium secondary battery half-cell, it was aged at 25°C for 12 hours and then subjected to a charge-discharge test at 30°C. To evaluate the initial capacity, the reference capacity was set to 210 mAh / g, and the battery was charged to 4.25 V at a constant current of 0.1 C. After switching to a constant voltage, the battery was charged until the end current reached 0.05 C. After a 10-minute rest time after charging, the battery was discharged to 2.5 V at a constant current of 0.1 C, using a reference capacity of 200 mAh / g.

[0127] (2) Rate characteristic evaluation

[0128] The output characteristics were evaluated by comparing the initial discharge capacity at 0.1C charge-0.1C discharge and the initial discharge capacity at 0.1C charge-1C / 5C / 10C discharge.

[0129]

[0130] Referring to Tables 1 to 3, it was confirmed that the average active area of ​​the derived positive electrode active material had a nearly linear correlation with the electrochemical characteristics of the all-solid-state battery, especially the rate characteristics, and that the correlation was very large.

[0131] Specifically, the average radius of the primary particles based on area - the average active area based on spherical shape is 110 μm 2 In the case of Manufacturing Examples 1 to 6 below, it was confirmed that the 1.0C discharge capacity was 175 mAh / g or more, the 0.5C / 0.1C rate characteristic was 92% or more, and the 1.0C / 0.1C rate characteristic was 84% ​​or more, which was very excellent. On the other hand, in the case of Manufacturing Examples 7 to 13 that were outside the above average active area value range, it was confirmed that the 1.0C discharge capacity, 0.5C / 0.1C rate characteristic, and 1.0C / 0.1C rate characteristic were inferior to those of Manufacturing Examples 1 to 6.

[0132] In addition, the average radius of the primary particles based on area - the average active area based on a cube is 104 μm 2 In the case of Manufacturing Examples 1 to 6 below, it was confirmed that the 1.0C discharge capacity was 175 mAh / g or more, the 0.5C / 0.1C rate characteristic was 92% or more, and the 1.0C / 0.1C rate characteristic was 84% ​​or more, which was very excellent. On the other hand, in the case of Manufacturing Examples 7 to 13 that were outside the above average active area value range, it was confirmed that the 1.0C discharge capacity, 0.5C / 0.1C rate characteristic, and 1.0C / 0.1C rate characteristic were inferior to those of Manufacturing Examples 1 to 6.

[0133] In addition, the average radius of the primary particles based on the area - the average active area based on the icosahedron is 127 μm 2 In the case of Manufacturing Examples 1 to 6 below, it was confirmed that the 1.0C discharge capacity was 175 mAh / g or more, the 0.5C / 0.1C rate characteristic was 92% or more, and the 1.0C / 0.1C rate characteristic was 84% ​​or more, which was very excellent. On the other hand, in the case of Manufacturing Examples 7 to 13 that were outside the above average active area value range, it was confirmed that the 1.0C discharge capacity, 0.5C / 0.1C rate characteristic, and 1.0C / 0.1C rate characteristic were inferior to those of Manufacturing Examples 1 to 6.

[0134] In addition, the average radius of the primary particles based on the circumference - the average active area based on the sphere is 103 μm 2 In the case of Manufacturing Examples 1 to 6 below, it was confirmed that the 1.0C discharge capacity was 175 mAh / g or more, the 0.5C / 0.1C rate characteristic was 92% or more, and the 1.0C / 0.1C rate characteristic was 84% ​​or more, which was very excellent. On the other hand, in the case of Manufacturing Examples 7 to 13 that were outside the above average active area value range, it was confirmed that the 1.0C discharge capacity, 0.5C / 0.1C rate characteristic, and 1.0C / 0.1C rate characteristic were inferior to those of Manufacturing Examples 1 to 6.

[0135] In addition, the average radius of the primary particles based on the circumference - the average active area based on the cube is 98 μm 2 In the case of Manufacturing Examples 1 to 6 below, it was confirmed that the 1.0C discharge capacity was 175 mAh / g or more, the 0.5C / 0.1C rate characteristic was 92% or more, and the 1.0C / 0.1C rate characteristic was 84% ​​or more, which was very excellent. On the other hand, in the case of Manufacturing Examples 7 to 13 that were outside the above average active area value range, it was confirmed that the 1.0C discharge capacity, 0.5C / 0.1C rate characteristic, and 1.0C / 0.1C rate characteristic were inferior to those of Manufacturing Examples 1 to 6.

[0136] In addition, the average radius of the primary particles based on the circumference - the average active area based on the icosahedron is 120 μm 2 In the case of Manufacturing Examples 1 to 6 below, it was confirmed that the 1.0C discharge capacity was 175 mAh / g or more, the 0.5C / 0.1C rate characteristic was 92% or more, and the 1.0C / 0.1C rate characteristic was 84% ​​or more, which was very excellent. On the other hand, in the case of Manufacturing Examples 7 to 13 that were outside the above average active area value range, it was confirmed that the 1.0C discharge capacity, 0.5C / 0.1C rate characteristic, and 1.0C / 0.1C rate characteristic were inferior to those of Manufacturing Examples 1 to 6.

[0137]

[0138] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the patent claims, the detailed description of the invention, and the attached drawings, and it is obvious that this also falls within the scope of the present invention.

[0139] Accordingly, the actual scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A first step of obtaining a SEM (scanning electron microscope) image of an all-solid-state battery positive electrode active material in the form of secondary particles formed by the agglomeration of multiple primary particles; A second step of deriving the average radius of primary particles and the average number of primary particles present in secondary particles from the above SEM images; A third step of deriving the average active area from the average radius of the primary particles derived above and the average number of primary particles existing in the secondary particles; and A fourth step of predicting the rate characteristics of the all-solid-state battery from the average active area derived above is included. Method for predicting electrochemical properties of positive electrode active materials for all-solid-state batteries.

2. In paragraph 1, A method for predicting electrochemical characteristics of a cathode active material for an all-solid-state battery, wherein in the second step, the average radius of the derived primary particles is an area-based average radius calculated based on the area of ​​the primary particles or a circumference-based average radius calculated based on the circumference of the primary particles.

3. In paragraph 2, In the third step, the derived average active area is a sphere-based average active area derived by assuming that the primary particles are spheres, a cubic-based average active area derived by assuming that the primary particles are hexahedrons, or an icosahedron-based average active area derived by assuming that the primary particles are icosahedrons. A method for predicting electrochemical characteristics of a cathode active material for an all-solid-state battery.

4. In paragraph 3, The above fourth step is, the average active area derived above is 50 μm 2 A method for predicting electrochemical characteristics of a cathode active material for an all-solid-state battery, wherein when the value is above a threshold value, the rate characteristics of the all-solid-state battery are predicted to be excellent.

5. In paragraph 4, When the average radius of the primary particles derived above is the average radius based on the area, and the average active area derived above is the average active area based on a sphere, the threshold value is 110 μm. 2 Method for predicting electrochemical properties of cathode active materials for all-solid-state batteries.

6. In paragraph 4, When the average radius of the primary particles derived above is the average radius based on the area, and the average active area derived above is the average active area based on a cube, the threshold value is 104 μm. 2 Method for predicting electrochemical properties of cathode active materials for all-solid-state batteries.

7. In paragraph 4, When the average radius of the above-derived primary particles is the average radius based on the area, and the average active area derived above is the average active area based on the icosahedron, the threshold value is 127 μm. 2 Method for predicting electrochemical properties of cathode active materials for all-solid-state batteries.

8. In paragraph 4, When the average radius of the primary particles derived above is the average radius based on the circumference, and the average active area derived above is the average active area based on a sphere, the threshold value is 103 μm. 2 Method for predicting electrochemical properties of cathode active materials for all-solid-state batteries.

9. In paragraph 4, When the average radius of the primary particles derived above is the average radius based on the circumference, and the average active area derived above is the average active area based on the cube, the threshold value is 98 μm. 2 Method for predicting electrochemical properties of cathode active materials for all-solid-state batteries.

10. In paragraph 4, When the average radius of the primary particles derived above is the average radius based on the circumference, and the average active area derived above is the average active area based on the icosahedron, the threshold value is 120 μm. 2 Method for predicting electrochemical properties of cathode active materials for all-solid-state batteries.

11. In paragraph 1, A method for predicting electrochemical characteristics of a cathode active material for an all-solid-state battery, wherein the average particle diameter (D50) of the above secondary particles is 2 to 7 μm.

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