Composite positive electrode active material, method for preparing the same, positive electrode layer including the same, and all-solid-state secondary battery including the positive electrode layer

Abstract

The present invention relates to a composite cathode active material, a method for preparing the same, a cathode layer including the same, and an all-solid-state secondary battery including the cathode layer. The composite cathode active material includes cathode active material particles; and a coating layer on the surface of the cathode active material particles, wherein the coating layer includes acetate, and the acetate includes alkali metal acetate, alkaline earth metal acetate, transition metal acetate, or a combination or derivative thereof.

Description

[0001] Cross - reference to related applications

[0002] This application claims the priority and benefits of Japanese Patent Application No. 2020 - 027205 filed with the Japan Patent Office on February 20, 2020, and Korean Patent Application No. 10 - 2020 - 0052880 filed with the Korean Intellectual Property Office on April 29, 2020, and all benefits arising therefrom, and incorporates by reference in its entirety the content thereof herein. Technical field

[0003] The present disclosure relates to a composite positive electrode active material, a method for preparing the same, a positive electrode layer including the same, and a all - solid - state secondary battery including the positive electrode layer. Background art

[0004] In an all - solid - state secondary battery, when a reaction occurs at the interface between positive electrode active material particles and a solid electrolyte during charging, a resistive component (resistance component) is generated. In order to suppress the generation of the resistive component, a method of reducing the interface resistance by coating the surface of the positive electrode active material particles with another material has been proposed.

[0005] However, in such a method, there are the following problems: the improvement of battery characteristics is insufficient, and such a method can be complex or difficult. Therefore, there is a need for improved materials and improved methods for suppressing the increased resistance. Summary of the invention

[0006] Provided is a composite positive electrode active material capable of improving battery characteristics such as load characteristics and cycle characteristics of an all - solid - state secondary battery.

[0007] Provided is a method for preparing the composite positive electrode active material.

[0008] Provided is a positive electrode layer including the composite positive electrode active material.

[0009] Provided is an all - solid - state secondary battery including a positive electrode layer including the composite positive electrode active material.

[0010] Additional aspects will be set forth in part in the following description and will be apparent in part from the description.

[0011] According to one aspect, the composite positive electrode active material includes:

[0012] Positive electrode active material particles; and

[0013] A coating layer on the surface of the positive electrode active material particles, wherein the coating layer includes acetate or acetates.

[0014] According to one aspect, the positive electrode layer includes the composite positive electrode active material and a solid electrolyte on the surface of the composite positive electrode active material.

[0015] According to one aspect, a all-solid-state secondary battery includes:

[0016] a positive electrode layer including the composite positive electrode active material;

[0017] a negative electrode layer; and

[0018] a solid electrolyte layer between the positive electrode layer and the negative electrode layer.

[0019] According to one aspect, a method for preparing a composite positive electrode active material includes:

[0020] providing positive electrode active material particles;

[0021] setting lithium acetate and a C9-C20 trialkyl borate on the surface of the positive electrode active material particles to provide coated positive electrode active material particles; and

[0022] heat-treating the coated positive electrode active material particles at a temperature of about 200 °C to about 400 °C to prepare the composite positive electrode active material.

[0023] According to one aspect, the composite positive electrode active material includes:

[0024] positive electrode active material particles; and

[0025] a coating layer on the surface of the positive electrode active material particles,

[0026] wherein the coating layer includes Li, B, and acetate, and wherein the total content of the coating layer is between about 0.01 mol% and about 2 mol% based on 100 mol% of the positive electrode active material particles. Description of the Drawings

[0027] The above and other aspects, features, and advantages of some embodiments of the present disclosure will become more apparent from the following description when considered in conjunction with the accompanying drawings, wherein:

[0028] Figure 1 is a schematic diagram illustrating an embodiment of the structure of an all-solid-state secondary battery;

[0029] Figure 2 is a schematic diagram illustrating an embodiment of the structure of a composite positive electrode active material;

[0030] Figure 3 is a graph of intensity (in arbitrary units, a.u.) versus wavelength (cm -1 ) showing the results of the infrared spectra of the coating layers according to Example 13 and Comparative Example 4;

[0031] Figure 4 A graph of weight change (%) against temperature (°C), which illustrates the results of thermogravimetric analysis of the slurry for forming the coating layer according to Example 1;

[0032] Figures 5 - 7 A cross-sectional view of an embodiment of a all-solid-state secondary battery; and

[0033] Figure 8 A graph of weight change (%) against temperature (°C) for the thermogravimetric analysis of the composite positive electrode active material according to the embodiment. DETAILED DESCRIPTION

[0034] The embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings, wherein like reference numerals always refer to like elements. In this regard, the embodiments may have different forms and should not be construed as limited to the description set forth herein. Accordingly, the embodiments are described below only by way of example with reference to the accompanying drawings to illustrate aspects. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. The phrase "at least one (of)" when preceding or following a list of elements modifies the entire list of elements and not individual elements of the list.

[0035] It will be understood that although the terms "first", "second", "third", etc. may be used herein to describe various elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or part from another. Thus, without departing from the teachings herein, the "first element", "component", "region", "layer" or "part" discussed below may be referred to as a second element, component, region, layer or part.

[0036] The terms used herein are for the purpose of describing particular embodiments only and are not intended to be limiting. As used herein, the indefinite articles "a", "an", "the" and "at least one" do not denote a limitation of quantity and are intended to include both the singular and the plural, unless the context clearly dictates otherwise. For example, "(a) element" has the same meaning as "at least one element" unless the context clearly dictates otherwise. "At least one" should not be construed as limiting "a". "Or" means "and / or". It will be further understood that the terms "comprising" or "including" when used in this specification, specify the presence of the stated features, regions, wholes, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more additional features, regions, wholes, steps, operations, elements, components, and / or their groups.

[0037] In addition, relative terms such as "lower" or "bottom" and "upper" or "top" may be used herein to describe a relationship of one element to another element as illustrated in the figures. It will be understood that the relative terms are intended to cover different orientations of the device in addition to the orientation shown in the figures. For example, if the device in one of the figures is turned over, an element described as on the "lower" side of another element will then be oriented on the "upper" side of the other element. Thus, depending on the specific orientation of the figure, the term "lower" can encompass both the "lower" and "upper" orientations. Similarly, if the device in one of the figures is turned over, an element described as "beneath" or "under" another element will then be oriented "above" the other element. Thus, the terms "beneath" or "under" can encompass both above and beneath orientations.

[0038] As used herein, "about" or "approximately" includes the stated value and means within an acceptable deviation range for a particular value as determined by one of ordinary skill in the art in view of the measurements discussed and the error associated with the measurement of the particular quantity (i.e., the limitations of the measurement system). For example, "about" can mean within one or more standard deviations of the stated value, or within ±30%, 20%, 10%, or 5%.

[0039] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the present disclosure and the relevant art and will not be interpreted in an idealized or overly formal sense unless clearly so defined herein.

[0040] Embodiments are described herein with reference to cross-sectional views that are schematic illustrations of idealized embodiments. Thus, deviations from the shape of the figures as a result of, for example, manufacturing techniques and / or tolerances are to be expected. Accordingly, the embodiments described herein should not be construed as limited to the specific shapes of regions as illustrated herein, but include deviations in shapes that result, for example, from manufacturing. For example, regions illustrated or described as flat may typically have rough and / or non-linear features. Also, sharp corners illustrated may be rounded. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region and are not intended to limit the scope of the claims.

[0041] As used herein, "argyrodite-type" or "argyrodite structure" means that a compound has a structure isomorphic to argyrodite Ag8GeS6.

[0042] "Rock salt type structure" means that the compound has a structure isomorphic to NaFeO₂.

[0043] The C rate is the discharge rate of a unit cell and is obtained by dividing the total discharge capacity of the unit cell by the total discharge period of 1 hour. For example, the C rate of a battery with a discharge capacity of 1.6 ampere-hours will be 1.6 amperes.

[0044] Hereinafter, the composite cathode active material according to an embodiment, a method for preparing the same, a cathode layer including the composite cathode active material, and an all-solid-state secondary battery including the cathode layer will be described in detail with reference to the accompanying drawings.

[0045] According to one aspect, there is provided a composite cathode active material including: cathode active material particles; and a coating layer on the surface of the cathode active material particles, wherein the coating layer includes acetate or acetate salt.

[0046] In an all-solid-state secondary battery, a method of reducing the interfacial resistance has been attempted by manufacturing a coated cathode active material by forming a coating layer on the surface of the cathode active material particles. However, when the coated cathode active material is used, the characteristics of the all-solid-state secondary battery are not satisfactory.

[0047] Therefore, in order to solve these problems, the present inventors provide a composite cathode active material having a coating layer containing acetate salt on the surface of the cathode active material.

[0048] According to an embodiment, the composite cathode active material includes a coating layer including acetate salt on the surface of the cathode active material particles, which improves battery characteristics such as load characteristics and cycle characteristics of the all-solid-state secondary battery compared to those of the prior art all-solid-state secondary battery. In particular, when a charging voltage of 4 V or more is used, the increase in interfacial resistance can be reduced and the cycle characteristics can be improved compared to the cathode active material having other coating layers.

[0049] In addition, when the coating layer on the surface of the cathode active material particles includes only acetate salt, the composite cathode active material and the all-solid-state secondary battery can be manufactured more economically using suitable equipment even when dedicated manufacturing equipment is not provided.

[0050] According to an embodiment, based on the total content of the coating layer, the content of acetate in the coating layer is about 70 mole percent (mol%) - about 95 mole percent, about 75 mole percent (mol%) - about 90 mole percent, or about 80 mole percent (mol%) - about 85 mole percent. In one aspect, the content of the acetate can be measured by thermogravimetric analysis. Thermogravimetric analysis (TGA) is an analytical technique for determining the thermal stability of a material, and by monitoring the weight change that occurs as the sample is heated, the fraction of its volatile components can be determined. A constant rate of heating is mentioned.

[0051] In the thermogravimetric analysis of the sample, weight loss occurs between about 300 °C and about 500 °C, such as between about 350 °C and about 500 °C, and although not wishing to be bound by theory, the weight loss due to the acetate is understood to occur at about 400 °C. The content of the acetate can be determined from the weight loss.

[0052] According to an embodiment, Figure 8 the weight loss represented by A in the thermogravimetric analysis chart corresponds to the content of acetate. A represents the weight loss that occurs at 350 °C to 500 °C.

[0053] When the coating layer includes zirconia and / or boron oxide, and based on the total content of the coating layer, the total content of zirconia and boron oxide in the coating layer is about 2.5 mole percent - about 25 mole percent, about 5 mole percent - about 20 mole percent, or about 10 mole percent - about 15 mole percent, the battery characteristics such as load or rate characteristics and cycle characteristics of an all-solid-state secondary battery having a positive electrode layer including the composite positive electrode active material can be improved relative to when the coating layer is omitted.

[0054] Based on the total content of the coating layer, the total content of zirconia and / or boron oxide and lithium oxide in the coating layer is about 5 mole percent - about 30 mole percent, about 7 mole percent - about 25 mole percent, or about 9 mole percent - about 20 mole percent.

[0055] As described above, the composite positive electrode active material includes a coating layer: the coating layer contains a composite including acetate and zirconia and / or lithium oxide.

[0056] The positive electrode active material particles have an average secondary particle diameter of about 20 μm or less, about 10 μm or less, such as about 0.01 μm - about 20 μm, about 0.02 - about 15 μm, about 0.05 μm - about 10 μm, about 0.07 μm - about 7 μm, or about 0.1 μm - about 5 μm.

[0057] The positive electrode active material particles are materials capable of absorbing and desorbing lithium. The positive electrode active material particles may include a lithium transition metal oxide having a layered rock salt-type structure, and the lithium transition metal oxide may be LiNi x Co y Al z O2 (0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1) or LiNi x Co y Mn z O2 (0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1).

[0058] According to one aspect, a positive electrode layer including the composite positive electrode active material is provided.

[0059] According to one aspect, a all-solid-state secondary battery is provided, which includes: a positive electrode layer including the composite positive electrode active material; a negative electrode layer; and a solid electrolyte layer between the positive electrode layer and the negative electrode layer.

[0060] When the positive electrode layer includes a solid electrolyte and the solid electrolyte is a sulfur-containing solid electrolyte, the positive electrode layer exhibits improved performance.

[0061] The solid electrolyte in the positive electrode layer may be the same as or different from the solid electrolyte in the solid electrolyte layer.

[0062] In the all-solid-state secondary battery according to an embodiment, the solid electrolyte used in the positive electrode layer has a different particle diameter range from the solid electrolyte used in the solid electrolyte layer. The solid electrolyte used in the positive electrode layer has a smaller average particle diameter than, for example, the solid electrolyte used in the solid electrolyte layer.

[0063] The average particle diameter of the solid electrolyte used in the positive electrode layer is about 100 nm - about 10 μm, about 300 nm - about 8 μm, or about 500 nm - about 5 μm, and the average particle diameter of the solid electrolyte used in the solid electrolyte layer is about 500 nm - about 20 μm, about 700 nm - about 15 μm, or about 900 nm - about 10 μm.

[0064] Configuration of all-solid-state secondary battery

[0065] Figure 1 It is a schematic cross-sectional view for explaining an embodiment of the layer structure of the all-solid-state secondary battery 1. Figure 2 It is a schematic cross-sectional view for explaining an embodiment of the structure of the composite positive electrode active material 11. The all-solid-state secondary battery may be, for example, an all-solid-state lithium ion secondary battery.

[0066] As Figure 1As shown, the all-solid-state secondary battery 1 has a structure in which a solid electrolyte layer 30 is provided between a positive electrode layer 10 and a negative electrode layer 20. In one aspect, the solid electrolyte layer 30 is between the positive electrode layer 10 and the negative electrode layer 20, and the layers are stacked together.

[0067] Positive electrode layer

[0068] The positive electrode layer 10 includes a composite positive electrode active material 11 and a solid electrolyte 31 on the surface of the composite positive electrode active material 11. The positive electrode layer 10 may further include a conductive material to supplement the electron conductivity. The solid electrolyte 31 will be further described later together with the solid electrolyte layer 30.

[0069] As Figure 2 shown, the composite positive electrode active material 11 includes positive electrode active material particles 11A and a coating layer 11B on the surface of the positive electrode active material particles 11A. As the positive electrode active material particles 11A, the primary particles shown Figure 2 are mentioned. Moreover, secondary particles formed by aggregating a plurality of primary particles may be used, and the coating layer 11B may be provided on the surface of the primary particles, secondary particles, or both.

[0070] The positive electrode active material particles 11A can be used without limitation as long as they include a material capable of reversibly absorbing and desorbing lithium ions. The positive electrode active material particles 11A can be formed using a lithium-containing metal compound such as lithium cobalt oxide (hereinafter referred to as LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (hereinafter referred to as NCA), lithium nickel cobalt manganese oxide (hereinafter referred to as NCM), lithium manganate, or lithium iron phosphate, or a metal compound such as nickel sulfide, copper sulfide, lithium sulfide, sulfur, iron oxide, or vanadium oxide.

[0071] The materials of the positive electrode active material particles 11A can be used alone or in combination of two or more. As the positive electrode active material particles 11A, not only the primary particles shown Figure 2 can be used, but also secondary particles formed by aggregating a plurality of primary particles can be used. That is, the secondary particles can be an aggregate of two or more primary particles.

[0072] In addition, the positive electrode active material particles 11A may contain a lithium transition metal oxide having a layered rock salt-type structure. Here, the "layered rock salt-type structure" refers to a structure in which oxygen atom layers and metal atom layers are alternately and regularly arranged in the <111> direction of the cubic rock salt-type structure, and thus each of the atom layers forms a two-dimensional plane. In addition, the "cubic rock salt-type structure" refers to the sodium chloride (NaCl) type structure, which is a crystal structure, and more specifically, a face-centered cubic (FCC) unit cell formed by cations and anions, respectively, is offset by half of the ridge of the partial (offset) unit lattice.

[0073] As the lithium transition metal oxide having a layered rock salt structure, examples may be compounds represented by Formula 1.

[0074] Formula 1

[0075] Li a (Ni x Co y Mn z M k )O2

[0076] Wherein, in Formula 1,

[0077] M is at least one of the following: boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), or aluminum (Al), and

[0078] 0.95 ≤ a ≤ 1.3, 0 < x < 1, 0 < y < 1, 0 ≤ z < 1, 0 ≤ k < 1, and x + y + z + k = 1.

[0079] In Formula 1, 0.3 ≤ x < 1.

[0080] In Formula 1, the sum of the molar fractions of Ni, Co, Mn, and M may be 1.

[0081] In Formula 1, the content of nickel is, for example, about 30 mol% - about 95 mol%, about 50 mol% - about 95 mol%, about 50 mol% - about 90 mol%, or about 55 mol% - about 85 mol%, based on the total content of Ni, Co, Mn, and M in the compound of Formula 1.

[0082] In Formula 1, 0.5 ≤ x ≤ 0.95, 0 < y ≤ 0.5, 0 ≤ z ≤ 0.5, and 0 ≤ k ≤ 0.05. In Formula 1, a is 1 - 1.1, y is 0.1 - 0.3, and z is 0.05 - 0.3. According to an embodiment, in Formula 1, k is 0. According to an embodiment, in Formula 1, when 0 < k ≤ 0.05, M may be aluminum (Al).

[0083] Compounds of Formula 1 are, for example, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.8 Co 0.1 Mn 0.1O2, or LiNi 0.85 Co 0.1 Al 0.05 O2. Combinations including at least two of the foregoing may be used.

[0084] According to an embodiment, the lithium transition metal oxide having a layered rock salt structure may be, for example, a ternary lithium transition metal oxide such as Li a Ni x Co y Al z O2 (0.95 ≤ a ≤ 1.3, 0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1) or Li a Ni x Co y Mn z O2 (0.95 ≤ a ≤ 1.3, 0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1).

[0085] According to an embodiment, the lithium transition metal oxide having a layered rock salt structure may be, for example, a ternary lithium transition metal oxide such as LiNi x Co y Al z O2, where 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1; or LiNi x Co y Mn z O2, where 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1.

[0086] The positive electrode active material particles 11A have a shape such as a true sphere or an ellipse. The particle diameter of the positive electrode active material particles 11A is not particularly limited and may be within a range suitable for the all-solid-state secondary battery. In addition, the content of the positive electrode active material particles 11A in the positive electrode layer 10 is not particularly limited and may be within a range suitable for the positive electrode layer 10 of the all-solid-state secondary battery.

[0087] According to an embodiment, the positive electrode active material particles 11A have an average secondary particle diameter of 20 μm or less, or 10 μm or less. According to an embodiment, the positive electrode active material particles 11A have an average secondary particle diameter of about 1 μm - 20 μm or about 1 μm - about 10 μm. In this specification, the term "average secondary particle diameter" refers to the average particle diameter of the positive electrode active material secondary particles.

[0088] When the average secondary particle diameter of the positive electrode active material particles 11A is controlled to be about 1 μm to about 20 μm, the positive electrode active material 11 does not aggregate and is easily dispersed into the positive electrode layer 10, so that the reaction at the interface between the positive electrode active material 11 and the solid electrolyte 31 or between the positive electrode active material 11 and the conductive material can be promoted. In addition, when the average secondary particle diameter is controlled to be about 10 μm or less, the surface area of the positive electrode active material 11 increases, so that the reaction at the interface between the positive electrode active material 11 and the solid electrolyte 31 or between the positive electrode active material 11 and the conductive material can be further promoted.

[0089] The coating layer 11B includes, for example, lithium oxide (Li2O), boron oxide (B2O3), and acetate or its derivatives. The derivative of the acetate may be a product obtained by heating the acetate at about 200°C to about 500°C, about 250°C to about 450°C. For example, the heating may include heating in the presence of an oxide such as zinc oxide or boron oxide. The acetate may be an alkali metal acetate, an alkaline earth metal acetate, a transition metal acetate, a combination thereof, or a derivative thereof. The alkali metal acetate may be lithium acetate, sodium acetate, or potassium acetate. The alkaline earth metal acetate may be magnesium acetate, calcium acetate, or strontium acetate. The transition metal acetate may be an acetate of an element in Groups 3 to 12. Zinc acetate is mentioned. Combinations of at least two of the foregoing may be used.

[0090] The acetate or acetate salt is lithium acetate or a reaction product between lithium acetate and a trialkyl borate.

[0091] In one aspect, the acetate (ion) is derived from, for example, lithium acetate added as a starting material for the coating layer 11B.

[0092] Based on the total content of the coating layer 11B, the content of the acetate in the coating layer 11B is in the range of about 70 mol% to about 95 mol%. In addition to the acetate, the coating layer 11B may further include lithium oxide (Li2O), boron oxide (B2O3), or zirconium oxide (ZrO). Based on the total content of the coating layer 11B, the total content of the components other than the acetate is about 5 mol% to about 30 mol%, about 10 mol% to about 25 mol%, or about 15 mol% to about 20 mol%.

[0093] According to an embodiment, based on the total content of the coating layer 11B, the total content of zirconium oxide and / or boron oxide and lithium oxide is about 5 mol% to about 30 mol%, about 10 mol% to about 25 mol%, or about 15 mol% to about 20 mol%.

[0094] Regarding the ratio of lithium oxide (Li2O) and boron oxide (B2O3) contained in the coating layer 11B, the content of boron oxide (B2O3) can be greater than or equal to the content of lithium oxide (Li2O). That is, the content of boron oxide (B2O3) in the coating layer 11B is about 50 mol% or more, about 60 mol% or more, or about 62.5 mol% or more of the total content of lithium oxide (Li2O) and boron oxide (B2O3). Specific examples that satisfy the mixing ratio of lithium oxide and boron oxide in the coating layer 11B include Li3B 11 O 18 and so on.

[0095] When the coating layer 11B contains boron oxide and / or zirconium oxide, based on the total content of the coating layer, the total content of boron oxide and / or zirconium oxide is about 2.5 mol% - about 25 mol%, about 5 mol% - about 20 mol%, or about 10 mol% - about 15 mol%. When the total content of boron oxide and / or zirconium oxide is too low, the content ratio of lithium oxide in the coating layer 11B becomes high, and lithium oxide crystals are likely to precipitate in the coating layer 11B. When the crystals precipitate in this way, the lithium ion conductivity of the coating layer 11B can be reduced. On the contrary, when the total content of boron oxide and zirconium oxide is too high, the content ratio of lithium oxide in the coating layer 11B can be reduced, and the lithium ion conductivity in the coating layer 11B can be reduced.

[0096] When the total content of boron oxide and / or zirconium oxide is within the above range, a positive electrode active material with improved lithium ion conductivity in the coating layer 11B is thus obtained.

[0097] The content of the coating layer 11B relative to the positive electrode active material particles 11A is about 0.01 mol% - about 2 mol%, 0.05 mol% - about 1 mol%, or 0.1 mol% - about 0.5 mol%, based on 100 mol% of the uncoated positive electrode active material particles 11A. If the content of the positive electrode active material particles is 1 mol and the content of the coating layer is 0.02 mol, the content of the coating layer is 2 mol%. For example, 1 mol of positive electrode active material particles is when the content of the positive electrode active material particles is 100 g (the total molecular weight of the positive electrode active material particles is 100 g / mol).

[0098] The coating layer 11B has a thickness of about 0.5 nm - about 500 nm, or about 0.5 nm - about 100 nm. When the thickness of the coating layer 11B is within these ranges, the efficiency of the interfacial reaction between the positive electrode active material 11 and the solid electrolyte 31 can be improved, thereby improving the cycle characteristics of the all-solid-state secondary battery. In addition, when the thickness of the coating layer 11B is within these ranges, the resistance caused by the coating layer 11B can be low. The thickness of the coating layer 11B can be measured by a transmission electron microscope (TEM) using a cross-sectional image or the like.

[0099] The coating layer 11B can be a single layer or multiple layers of two or more layers. When the coating layer 11B includes multiple layers of two or more layers, the composition of each layer can be the same or different from each other. For example, the surface of the positive electrode active material particles 11A can be coated with a first coating layer including acetate, lithium oxide, and zirconium oxide, and the surface of the first coating layer can be coated with a second coating layer including acetate, lithium oxide, and boron oxide. In this case, the total content of zirconium oxide and boron oxide in the coating layer 11B refers to the sum of the content of zirconium oxide in the first coating layer and the content of boron oxide in the second coating layer.

[0100] According to an embodiment, each of the positive electrode active material particles 11A is coated with a coating layer 11B, but may have a structure in which the outer surface of the positive electrode active material formed in a plate shape is covered with the coating layer 11B.

[0101] The positive electrode active material according to an embodiment may include a first coating layer containing zirconium oxide and a second coating layer provided on the first coating layer and including boron oxide, lithium oxide, and acetate.

[0102] The positive electrode active material according to an embodiment may include a first coating layer containing acetate, lithium oxide, and zirconium oxide and a second coating layer containing acetate, lithium oxide, and boron oxide.

[0103] In the second coating layer, boron oxide, lithium oxide, and acetate may be in the form of an organic complex.

[0104] In addition to the above components, the positive electrode layer 10 may further include a conductive material, a binder, a filler, a dispersant, and an ion conductive material. Examples of the conductive material that can be blended in the positive electrode layer 10 may include graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and metal powder. Examples of the binder that can be blended in the positive electrode layer 10 may include styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. Suitable materials can be used as the filler, dispersant, binder, and ion conductive material for the electrode of the all-solid-state secondary battery.

[0105] Negative electrode layer

[0106] As Figure 1 shown, the negative electrode layer 20 includes a negative electrode active material 21 and a solid electrolyte 31. The solid electrolyte 31 will be described later together with the solid electrolyte layer 30.

[0107] The negative electrode active material 21 has a lower charge-discharge potential compared to the positive electrode active material included in the positive electrode active material particles 11A and can alloy with lithium or can reversibly absorb and desorb lithium.

[0108] For example, the negative electrode active material 21 may be at least one of a carbon-based negative electrode active material, a metal negative electrode active material, or a metalloid negative electrode active material.

[0109] Examples of the metal negative electrode active material or the metalloid negative electrode active material may include metals such as lithium (Li), indium (In), aluminum (Al), tin (Sn), silicon (Si), gold (Au), platinum (Pt), palladium (Pd), silver (Ag), bismuth (Bi), zinc (Zn), or alloys thereof. Any suitable metal negative electrode active material or any suitable metalloid negative electrode active material may be used as long as it forms an alloy or compound with lithium. For example, nickel (Ni) is not a metal negative electrode active material because it does not form an alloy with lithium.

[0110] Examples of the carbon-based negative electrode active material may include artificial graphite, graphite carbon fiber, resin-fired carbon, pyrolytically grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl resin-fired carbon, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite, or non-graphite carbon. The negative electrode active material 21 may be used alone, or may also be used in combination of two or more negative electrode active materials. The negative electrode active material 21 may include polyacene.

[0111] The negative electrode active material 21 may include a mixture of amorphous carbon and at least one of the following: gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), or zinc (Zn). The weight ratio of the mixture of amorphous carbon to, for example, gold (Au) is about 10:1 - about 1:2, about 5:1 - about 1:1, or about 4:1 - about 2:1, but is not limited thereto. The weight ratio is selected depending on the desired characteristics of the all-solid-state secondary battery. When the negative electrode active material has such a composition, the cycle characteristics of the all-solid-state secondary battery are improved.

[0112] The negative electrode active material includes a mixture of first particles and second particles, the first particles include amorphous carbon, and the second particles include a metal or a metalloid. Examples of the metal or the metalloid include gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), or zinc (Zn). The metalloid is additionally a semiconductor. Based on the total weight of the mixture, the content of the second particles is about 8 wt% - about 60 wt%, about 10 wt% - about 50 wt%, about 15 wt% - about 40 wt%, or about 20 wt% - about 30 wt%. When the content of the second particles is within the above range, for example, the cycle characteristics of the all-solid-state secondary battery 1 can be improved.

[0113] In addition, in the negative electrode layer 20, in addition to the negative electrode active material and the solid electrolyte 31, additives such as conductive materials, binders, fillers, dispersants, or ion conductive materials may be appropriately included.

[0114] The same additives as those to be blended into the positive electrode layer 10 can be used as those to be blended into the negative electrode layer 20.

[0115] Solid electrolyte layer

[0116] The solid electrolyte layer may be formed between the positive electrode layer 10 and the negative electrode layer 20 and may include the solid electrolyte 31.

[0117] The solid electrolyte 31 is in powder form and is composed of a sulfur-containing solid electrolyte material.

[0118] Examples of the solid electrolyte material may include Li2S-P2S5, Li2S-P2S5-LiX (X is a halogen atom, for example, at least one of I, Br, or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (m and n are each positive numbers, and Z is at least one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, and Li2S-SiS2-Li p MO q (p and q are each positive numbers, and M is at least one of P, Si, Ge, B, Al, Ga, or In). Here, the solid electrolyte material is prepared by treating starting materials (for example, Li2S, P2S5) by a melt quenching method or a mechanical grinding method. After the treatment, the solid electrolyte material can be heat-treated. The solid electrolyte 31 can be amorphous, crystalline, or a mixed state thereof.

[0119] The solid electrolyte 31 may include a solid electrolyte material containing sulfur (S), phosphorus (P), and lithium (Li). For example, the solid electrolyte material may include Li2S-P2S5.

[0120] Here, when forming the solid electrolyte 31 using a solid electrolyte material including Li2S-P2S5, the mixing molar ratio of Li2S and P2S5 can be selected, for example, within the range of about 50:50 - about 90:10 of Li2S:P2S5. The solid electrolyte layer 30 may include a binder. Examples of the binder in the solid electrolyte layer 30 may include styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene.

[0121] The solid electrolyte according to an embodiment may include at least one of the following: Li2S-P2S5, Li2S-P2S5-LiX (X is a halogen atom), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (m and n are each a positive number, and Z is one of Ge, Zn, and Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p and q are each a positive number, and M is one of P, Si, Ge, B, Al, Ga, and In), Li 7-x PS 6-x Cl x (0 ≤ x ≤ 2), Li 7-x PS 6-x Br x (0 ≤ x ≤ 2), or Li 7-x PS 6-x I x (0 ≤ x ≤ 2).

[0122] The solid electrolyte layer 30 may include a thiogermanate solid electrolyte.

[0123] The thiogermanate solid electrolyte may include at least one of the following: Li 7-x PS 6-x Cl x (0 ≤ x ≤ 2), Li 7-x PS 6-x Br x (0 ≤ x ≤ 2), or Li 7-x PS 6-x I x (0 ≤ x ≤ 2).

[0124] An example where the solid electrolyte 31 includes sulfur is given, but the solid electrolyte 31 used in the all-solid secondary battery 1 is not limited to containing sulfur, and any material can be used as long as it is suitable for the all-solid secondary battery 1.

[0125] The solid electrolyte may be, for example, an oxide-based solid electrolyte.

[0126] For example, the oxide-based solid electrolyte includes at least one of the following: Li 1+x+y Al x Ti 2-x Si y P 3- y O 12 (0 < x < 2 and 0 ≤ y < 3), BaTiO3, Pb(Zr a Ti 1-a )O3(0 ≤ a ≤ 1) (PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT)(0 ≤ x < 1 and 0 ≤ y < 1), Pb(Mg 1 / 3 Nb 2 / 3 )O3 - PbTiO3(PMN - PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, Li3PO4, Li x Ti y (PO4)3(0 < x < 2, 0 < y < 3), Li x Al y Ti z (PO4)3(0 < x < 2, 0 < y < 1, and 0 < z < 3), Li 1+x+y (Al a Ga 1-a ) x (Ti b Ge 1-b ) 2-x Si y P 3-y O 12 (0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ a ≤ 1, and 0 ≤ b ≤ 1), Li x La y TiO3(0 < x < 2 and 0 < y < 3), Li2O, LiOH, Li2CO3, LiAlO2, Li2O - Al2O3 - SiO2 - P2O5 - TiO2 - GeO2, and Li 3+x La3M2O 12(M is at least one of Te, Nb, or Zr and x is an integer from 1 to 10). The solid electrolyte is prepared by a sintering method or the like. For example, the oxide-based solid electrolyte may be a garnet-type solid electrolyte, which is Li7La3Zr2O 12 (LLZO) or Li 3+x La3Zr 2-a M a O 12 (e.g., M-doped LLZO, where M is at least one of Ga, W, Nb, Ta, or Al and x is an integer from 1 to 10).

[0127] Current collector

[0128] The all-solid-state secondary battery 1 may further include a positive electrode current collector that supplies current to the positive electrode layer 10. The positive electrode current collector is disposed outside the positive electrode layer 10. As the positive electrode current collector, a plate-like body or a foil-like body including indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof can be used.

[0129] The all-solid-state secondary battery 1 may include a negative electrode current collector that supplies current to the negative electrode layer 20. The negative electrode current collector is disposed outside the negative electrode layer 20. The negative electrode current collector may include a material that does not react with lithium, that is, a material that does not form both an alloy and a compound. Examples of the material of the negative electrode current collector may include copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), or nickel (Ni). The negative electrode current collector may be made of any one of these metals, or may be made of an alloy or a clad material of two or more of these metals.

[0130] Refer to Figure 5 , the all-solid-state secondary battery 1 includes: a negative electrode layer 20 including a negative electrode current collector 521 and a first negative electrode active material layer 22; a positive electrode layer 10 including a positive electrode current collector 511 and a positive electrode active material layer 12; and a solid electrolyte layer 30 between the negative electrode layer 20 and the positive electrode layer 10. The positive electrode layer 10 may include a sulfide-based solid electrolyte. For example, the positive electrode layer 10 may include a positive electrode active material, a sulfide-based solid electrolyte, and a conductive agent.

[0131] As Figure 6As shown in FIG. 0, the all-solid-state secondary battery 1 includes a thin film 24 provided on the negative electrode current collector 521 and including an element capable of forming an alloy with lithium. The thin film 24 is provided between the negative electrode current collector 521 and the first negative electrode active material layer 22. The thin film 24 includes an element capable of forming an alloy with lithium. Examples of the element capable of forming an alloy with lithium include, but are not limited to, gold, silver, zinc, tin, indium, silicon, aluminum, and bismuth. Any suitable element can be used as long as it is an element capable of forming an alloy with lithium. The thin film 24 is made of one of these metals or an alloy of several types of metals. When the thin film 24 is provided on the negative electrode current collector 521, for example, the second negative electrode active material layer (not shown) in the form of precipitation deposited between the thin film 24 and the first negative electrode active material layer 22 can be further flattened, and the cycle characteristics of the all-solid-state secondary battery 1 can be improved.

[0132] The thickness d24 of the thin film 24 is, for example, about 1 nm - about 800 nm, about 10 nm - about 700 nm, about 50 nm - about 600 nm, or about 100 nm - about 500 nm. When the thickness d24 of the thin film 24 is less than about 1 nm, the thin film 24 may not provide improved cycle characteristics of the all-solid-state secondary battery 1. When the thickness of the thin film 24 is too thick, the thin film 24 itself may absorb lithium to reduce the amount of lithium deposited in the negative electrode layer, thereby reducing the energy density of the all-solid-state secondary battery 1, and the cycle characteristics of the all-solid-state secondary battery 1 may deteriorate. The thin film 24 can be provided on the negative electrode current collector 521 by, for example, a vacuum deposition method, a sputtering method, a plating method, etc., but the present disclosure is not necessarily limited thereto. Any suitable method can be used as long as it can form the thin film 24.

[0133] Referring to Figure 7 , the all-solid-state secondary battery 1 further includes a second negative electrode active material layer 23 provided between the negative electrode current collector 521 and the solid electrolyte layer 30 by charging. The all-solid-state secondary battery 1 further includes a second negative electrode active material layer 23 provided between the negative electrode current collector 521 and the first negative electrode active material layer 22 by charging. Although not shown in the figure, the all-solid-state secondary battery 1 further includes a second negative electrode active material layer 23 provided between the solid electrolyte layer 30 and the first negative electrode active material layer 22 by charging. Although not shown in the figure, the all-solid-state secondary battery 1 further includes a second negative electrode active material layer 23 provided in the first negative electrode active material layer 22 by charging.

[0134] The second negative electrode active material layer 23 is a metal layer including lithium or a lithium alloy. The metal layer includes lithium or a lithium alloy. Therefore, since the second negative electrode active material layer 23 is a metal layer containing lithium, it serves as, for example, a lithium reservoir. Examples of the lithium alloy may include, but are not limited to, Li-Al alloy, Li-Sn alloy, Li-In alloy, Li-Ag alloy, Li-Au alloy, Li-Zn alloy, Li-Ge alloy, and Li-Si alloy. Any suitable lithium alloy can be used. The second negative electrode active material layer 23 can be made of one of these alloys or lithium, or made of multiple types of alloys.

[0135] The thickness d23 of the second negative electrode active material layer is not particularly limited, but can be, for example, about 1 μm - about 1000 μm, about 2 μm - about 500 μm, about 3 μm - about 200 μm, about 4 μm - about 150 μm, about 5 μm - about 100 μm, or about 6 μm - about 50 μm. When the thickness d23 of the second negative electrode active material layer is too thin, the second negative electrode active material layer 23 may not serve as a lithium reservoir. When the thickness d23 of the second negative electrode active material layer is too thick, the mass and volume of the all-solid-state secondary battery 1 increase, and there is a possibility of deterioration of the cycle characteristics. The second negative electrode active material layer 23 can be, for example, a metal foil having a thickness within this range.

[0136] In the all-solid-state secondary battery 1, the second negative electrode active material layer 23 is provided between the negative electrode current collector 521 and the first negative electrode active material layer 22 before assembling the all-solid-state secondary battery 1, or is deposited between the negative electrode current collector 521 and the first negative electrode active material layer 22 by charging after assembling the all-solid-state secondary battery 1.

[0137] When the second negative electrode active material layer 23 is provided between the negative electrode current collector 521 and the first negative electrode active material layer 22 before assembling the all-solid-state secondary battery 1, the second negative electrode active material layer 23 serves as a lithium reservoir because it is a metal layer containing lithium. The cycle characteristics of the all-solid-state secondary battery 1 including the second negative electrode active material layer 23 are improved. For example, a lithium foil is provided between the negative electrode current collector 521 and the first negative electrode active material layer 22 before assembling the all-solid-state secondary battery 1.

[0138] When the second negative electrode active material layer 23 is provided by charging after assembling the all-solid-state secondary battery 1, the energy density of the all-solid-state secondary battery 1 increases because the second negative electrode active material layer 23 is not included when assembling the all-solid-state secondary battery 1. For example, when the all-solid-state secondary battery 1 is charged, the all-solid-state secondary battery 1 is charged with a charge capacity exceeding that of the first negative electrode active material layer 22. That is, the first negative electrode active material layer 22 is overcharged. In the initial stage of charging, lithium is absorbed in the first negative electrode active material layer 22. That is, the negative electrode active material included in the first negative electrode active material layer 22 forms an alloy or a compound with the lithium ions transferred from the positive electrode layer 10. When the all-solid-state secondary battery 1 is charged with a charge capacity exceeding that of the first negative electrode active material layer 22, for example, lithium is deposited on the back surface of the first negative electrode active material layer 22, that is, between the negative electrode current collector 521 and the first negative electrode active material layer 22, and a metal layer corresponding to the second negative electrode active material layer 23 is formed by the deposited lithium. The second negative electrode active material layer 23 is a metal layer mainly including lithium (i.e., lithium metal). Such a result is obtained because the negative electrode active material included in the first negative electrode active material layer 22 is composed of a material that forms an alloy or a compound with lithium. During discharging, the lithium included in the first negative electrode active material layer 22 and the second negative electrode active material layer 23 is ionized and transferred toward the positive electrode layer 10. Therefore, lithium can be used as the negative electrode active material in the all-solid-state secondary battery 1. When the first negative electrode active material layer 22 covers the second negative electrode active material layer 23, the first negative electrode active material layer 22 serves as a protective layer for the second negative electrode active material layer 23 as a metal layer, and at the same time, suppresses the growth of lithium dendrite deposition. Therefore, the possibility of short circuit and the reduction of capacity of the all-solid-state secondary battery 1 are suppressed, and as a result, the cycle characteristics of the all-solid-state secondary battery 1 are improved. In addition, when the second negative electrode active material layer 23 is provided by charging after assembling the all-solid-state secondary battery 1, in the initial state or the discharging state of the all-solid-state secondary battery, the region between the negative electrode current collector 521 and the first negative electrode active material layer 22 is a Li-free region that does not include lithium (Li) metal or lithium (Li) alloy.

[0139] In the all-solid-state secondary battery according to the embodiment, the negative electrode active material layer may include a solid electrolyte. The solid electrolyte of the negative electrode active material layer may have a different particle diameter range from the solid electrolyte used in the solid electrolyte layer. The solid electrolyte used in the negative electrode active material layer may have a smaller average particle diameter than the solid electrolyte used in the solid electrolyte layer.

[0140] The average particle diameter of the solid electrolyte used in the negative electrode active material layer is about 100 nm to about 10 μm, about 300 nm to about 8 μm, or about 500 nm to about 5 μm, and the average particle diameter of the solid electrolyte used in the solid electrolyte layer is about 500 nm to about 20 μm, about 700 nm to about 15 μm, or about 900 nm to about 10 μm.

[0141] Method for manufacturing an all-solid-state secondary battery

[0142] In the foregoing, the configuration of the lithium-ion secondary battery 1 has been described in detail. Subsequently, a method for manufacturing the all-solid-state secondary battery 1 having the above configuration will be described. The all-solid-state secondary battery 1 can be manufactured by: preparing a positive electrode layer 10, a negative electrode layer 20, and a solid electrolyte layer 30, and then laminating these layers. Hereinafter, each process will be described in more detail.

[0143] Process for preparing the positive electrode layer

[0144] A method for preparing the positive electrode layer 10 will be described. The method for preparing the positive electrode layer 10 is not particularly limited, and for example, the positive electrode layer 10 can be prepared by the following process.

[0145] First, positive electrode active material particles 11A such as NCA (lithium nickel cobalt aluminum oxide) or NCM (lithium nickel cobalt manganese oxide) are prepared, and a coating layer 11B is formed on the surface of the positive electrode active material particles 11A.

[0146] The coating layer 11B is prepared using a coating slurry, which is a mixed solution obtained by: adding lithium acetate and a trialkyl borate having 9 to 20 carbon atoms to a solvent, and heating and dissolving the resulting product.

[0147] As the solvent, alcohols such as methanol and ethanol are used, and alcohols in an anhydrous state or a super dehydrated state can be used.

[0148] When the number of carbon atoms in the trialkyl borate is less than 9 or greater than 20, it is difficult to obtain a uniform coating layer composition. When using a non-uniform coating layer composition, the resistance of the positive electrode layer increases, which is not preferable. As a result, it is difficult to obtain positive electrode active materials having a coating layer containing acetate.

[0149] Examples of the trialkyl borate having 9 to 20 carbon atoms may include triisopropyl borate, tripropyl borate, tributyl borate, tripentyl borate, and trihexyl borate.

[0150] The mixing weight ratio of lithium acetate and trialkyl borate is about 1:5 - about 1:15, about 1:8 - about 1:13, or about 1:9 - about 1:11. When the mixing weight ratio of lithium acetate and trialkyl borate is within these ranges, the composition other than acetate in the coating layer 11B may include Li3B 11 O 18 .

[0151] Subsequently, the surface of the positive electrode active material particles 11A is coated with the coating slurry. In this case, after the coating layer 11B is formed on the positive electrode active material particles 11A, the coating amount of the coating layer 11B relative to the positive electrode active material particles 11A is adjusted to about 0.01 mol% - about 2.0 mol%, based on 100 mol% of the uncoated positive electrode active material particles.

[0152] When boric acid or triethyl borate is used instead of trialkyl borate to react with lithium acetate, it is difficult to obtain a uniform coating layer composition, and boric acid or triethyl borate thermally decomposes during the heat treatment step in the process of preparing the composite positive electrode active material with a coating layer. Therefore, it is difficult to obtain a composite positive electrode active material having a coating layer containing acetate.

[0153] Subsequently, for example, after applying the coating slurry to cover the entire surface of the positive electrode active material particles 11A, the solvent is removed by volatilization using an evaporator or the like, and then the slurry is heat-treated under the atmosphere to obtain the positive electrode active material 11. The heat treatment temperature is about 200°C - about 400°C, for example about 300°C - about 350°C.

[0154] When the heat treatment temperature is lower than about 200°C or higher than about 400°C, it is difficult to obtain a composite positive electrode active material having a coating layer containing acetate. In particular, when the heat treatment temperature is higher than about 400°C, acetates such as lithium acetate used as the starting material for the coating layer may be thermally decomposed.

[0155] The heat treatment time may vary depending on the heat treatment temperature and may be adjusted, for example, within the range of 0.5 - 3 hours, or 1 hour.

[0156] A slurry is prepared by adding the composite positive electrode active material 11, a binder, etc., which are materials for forming the positive electrode layer 10, to a non-polar solvent. The slurry may be in a paste state.

[0157] Subsequently, the obtained slurry is applied to the positive electrode current collector and dried. Subsequently, the obtained laminate is pressed to prepare the positive electrode layer 10.

[0158] The pressing may be, for example, pressing using isostatic pressure. The pressing process may be omitted. The material mixture constituting the positive electrode layer 10 may be compressed into a pellet shape, or may be spread in a sheet shape to prepare the positive electrode layer 10. When the positive electrode layer 10 is prepared in this manner, the positive electrode current collector may be omitted.

[0159] Process for preparing the solid electrolyte layer

[0160] The solid electrolyte layer 30 may be prepared from a solid electrolyte 31 formed of a sulfur-containing solid electrolyte material.

[0161] First, the starting materials are treated by a melt quenching method or a mechanical grinding method.

[0162] For example, when using the melt quenching method, the starting materials (e.g., Li2S, P2S5, etc.) are mixed in a predetermined amount to form a pellet, and the pellet is reacted in a vacuum at a predetermined reaction temperature and then quenched to prepare the solid electrolyte material. The reaction temperature of the mixture of Li2S and P2S5 is about 400°C - about 1000°C, for example about 800°C - about 900°C. The reaction time is about 0.1 hour - about 12 hours, or about 1 hour - about 12 hours. The quenching temperature of the reactants is 10°C or lower, for example 0°C or lower, and the quenching rate is about 1°C / second - about 10000°C / second, for example about 1°C / second - about 1000°C / second.

[0163] In addition, when using the mechanical grinding method, the starting materials (e.g., Li2S, P2S5, etc.) are reacted by stirring using a ball mill to prepare the solid electrolyte material. The stirring speed and stirring time in the mechanical grinding method are not particularly limited. The faster the stirring speed, the faster the production rate of the solid electrolyte material, and the longer the stirring time, the higher the conversion rate of the starting materials to the solid electrolyte material.

[0164] After that, the mixed starting materials obtained by the melt quenching method or the mechanical grinding method are heat-treated at a predetermined temperature and then pulverized to prepare the granular solid electrolyte 31. When the solid electrolyte 31 has a glass transition point, the solid electrolyte 31 can be changed from amorphous to crystalline by heat treatment.

[0165] Subsequently, the solid electrolyte 31 obtained by the above method is deposited using a known film-forming method such as an aerosol deposition method, a cold spray method, or a sputtering method to prepare the solid electrolyte layer 30. The solid electrolyte layer 30 may be prepared by pressing the particles of the solid electrolyte 31. The solid electrolyte layer 30 may also be prepared as follows: the solid electrolyte 31 is mixed with a solvent and a binder, the mixed solution is applied and dried, and then the resulting product is pressed.

[0166] Process for preparing the negative electrode layer

[0167] Next, a method for preparing the negative electrode layer 20 will be described. The method for preparing the negative electrode layer 20 is not particularly limited, and for example, the negative electrode layer 20 can be prepared by the following process.

[0168] When using a lithium-containing metal foil as the negative electrode active material 21, for example, the lithium-containing metal foil such as a lithium metal foil is stacked on the negative electrode current collector and pressed, thereby preparing the negative electrode layer 20.

[0169] When using a negative electrode active material 21 other than a lithium metal foil, for example, the materials constituting the negative electrode layer 20 (negative electrode active material particles 21, solid electrolyte 31, binder, etc.) are added to a polar solvent or a non-polar solvent to prepare a slurry. Subsequently, the obtained slurry is applied to the negative electrode current collector and dried. Subsequently, the obtained laminate is pressed (for example, pressing using isostatic pressure) to prepare the negative electrode layer 20. The pressing process can be omitted. The negative electrode layer 20 can be prepared by pressing a mixture of the materials constituting the negative electrode layer 20.

[0170] Lamination of layers

[0171] The positive electrode layer 10, the solid electrolyte layer 30, and the negative electrode layer 20 obtained as described above are laminated in this order and pressed to manufacture the all-solid-state secondary battery 1 according to the present embodiment.

[0172] Effects

[0173] According to the above method for preparing the composite positive electrode active material 11 and the above method for manufacturing the all-solid-state secondary battery 1, when the heat treatment temperature for forming the coating layer 11B is set to about 200°C - about 400°C, for example, about 350°C, the acetate such as lithium acetate used as the starting material for the coating layer 11B is not thermally decomposed and exists in the coating layer 11B in a content of about 70 mol% or more.

[0174] When the coating layer 11B includes acetate in an amount of about 70 mol% or more, the battery characteristics of the all-solid-state secondary battery 1 such as load characteristics and cycle characteristics can be significantly improved. In particular, when a high voltage of 4V or more is applied, compared with other coating layers, the increase in the interfacial resistance can be greatly reduced, and the cycle characteristics can be improved.

[0175] In addition, in the process of preparing the coating layer 11B for coating the positive electrode active material particles 11A, since the heat treatment temperature is lower than about 500°C, even when no dedicated manufacturing equipment is provided, the composite positive electrode active material 11 and the all-solid-state secondary battery 1 can be manufactured using appropriate equipment.

[0176] When the positive electrode active material particles 11A have a granular form and their entire surface is covered with a coating layer 11B, generation of a resistive component at the interface between the positive electrode active material particles 11A and the solid electrolyte 31 can be suppressed.

[0177] When the positive electrode active material particles 11A include the above-described ternary lithium transition metal oxide having a layered rock salt structure, the energy density and thermal stability of the all-solid-state secondary battery 1 can be improved.

[0178] When the positive electrode active material particles 11A are formed of a ternary lithium transition metal oxide such as NCA or NCM and include nickel (Ni), the capacity density of the all-solid-state secondary battery 1 can be increased, and elution of metal from the positive electrode active material particles 11A in a charged state can be reduced. Accordingly, the all-solid-state secondary battery 1 according to the present embodiment can improve long-term reliability and cycle characteristics.

[0179] The thermal weight loss of the composite positive electrode active material for the all-solid-state secondary battery obtained by thermogravimetric analysis from about 300 °C to about 500 °C, for example, from about 350 °C to about 500 °C, is about 70% - about 95%, about 70% - about 85%, or about 80%.

[0180] In the infrared spectroscopic analysis of the composite positive electrode active material, the C=O stretching vibration peak in the -COO group appears as a doublet at 1200 cm -1 -1700 cm -1 and the -OH peak appears at 3000 cm -1 .

[0181] Hereinafter, the present disclosure will be described in detail with reference to the following examples, but the scope of the present disclosure is not limited to these examples.

[0182] In the following examples, various types of positive electrode active materials were prepared, and all-solid-state secondary batteries were manufactured using these positive electrode active materials, and load characteristics evaluation and cycle life tests of the all-solid-state secondary batteries were performed.

[0183] Examples

[0184] Example 1

[0185] A coating layer was formed on the surface of the positive electrode active material particles

[0186] Using LiNi 0.5 Co 0.2 Mn 0.3O2 (NCM) particles are used as cathode active material particles. Lithium acetate and triisopropyl borate are dissolved in super-dehydrated ethanol solvent heated to 60 °C to obtain a mixed solution (coating slurry), and the cathode active material particles are coated using the mixed solution (coating slurry). In the mixed solution, lithium acetate (0.04 g) and triisopropyl borate (0.44 g) are added to 10 g of cathode active material particles at a weight ratio of lithium acetate to triisopropyl borate of 1:11, such that the composition other than acetate in the coating layer is finally Li3B 11 O 18 . Prepare the coating slurry such that the coating amount of Li2O-B2O3 (LBO) relative to NCM (i.e., the content of Li2O-B2O3 (LBO) and acetate relative to the uncoated cathode active material particles NCM) is 0.1 mol%, based on 100 mol% of the uncoated cathode active material particles NCM. The solvent is volatilized using an evaporator, and heat treatment is carried out in the atmosphere at 350 °C for 1 hour to obtain a composite cathode active material (also called the coated cathode active material) in which an LBO coating layer is formed on the surface of NCM.

[0187] Manufacture of all-solid-state secondary battery

[0188] First, weigh the reagents Li2S and P2S5 to obtain the target composition Li3PS4, and then perform mechanical grinding treatment using a planetary ball mill for 20 hours. The mechanical grinding treatment is carried out at room temperature in an argon atmosphere at a rotation speed of 380 rpm for 20 hours. After pulverizing the collected sample with an agate mortar, X-ray crystal diffraction is performed to confirm the absence of a residual crystal layer, and this material is used as a solid electrolyte. The cathode active material coated with LBO (composite cathode active material), the solid electrolyte (SE), and carbon nanofibers (CNF) as a conductive material are mixed at a weight ratio of 60:35:5 by weight% to prepare a cathode layer. In addition, graphite, Li3PS4 as a solid electrolyte, and vapor-grown carbon fibers (VGCF) as a conductive material are mixed at a weight ratio of 60:35:5 by weight% to prepare a negative electrode layer. The cathode layer (15 mg), the solid electrolyte (100 mg), and the negative electrode layer (15 mg) are sequentially laminated and pressed at a pressure of 3 tons / cm 2 to obtain a test unit cell (all-solid-state secondary battery).

[0189] Evaluation of load characteristics

[0190] The obtained test unit battery was charged at a constant current of 0.05C to an upper limit voltage of 4.3V at 25°C, and then discharged at a constant current of 0.05C to a lower limit voltage of 2.5V to measure the initial discharge capacity. Then, it was discharged at constant currents of 0.05C, 0.5C, and 1C to measure the characteristics for each rate. The ratio of the 1C discharge capacity to the initial discharge capacity was used as an index of the load characteristics. The higher this value, the smaller the internal resistance of the battery and the better the load characteristics of the battery. The results of the load characteristics evaluation test are shown in Table 1.

[0191] Cycle life test

[0192] The following charge-discharge cycle was repeated 50 times: The obtained test unit battery was charged at a constant current of 0.05C to an upper limit voltage of 4.3V at 25°C, and then discharged at a constant current of 0.05C to a discharge cut-off voltage of 2.5V. The ratio of the discharge capacity of 50 cycles to the discharge capacity of 1 cycle was defined as the discharge capacity retention rate. The discharge capacity retention rate is a parameter indicating the cycle characteristics, and the larger this value, the better the cycle characteristics. The results of the cycle life test are shown in Table 1.

[0193] Example 2

[0194] The composite positive electrode active material and the test unit battery were manufactured in the same manner as in Example 1, except that: the coating amount of Li2O-B2O3 (LBO) relative to NCM (i.e., the content of Li2O-B2O3 (LBO) and acetate relative to the uncoated positive electrode active material particles NCM) was 0.2 mol%, based on 100 mol% of the uncoated positive electrode active material particles NCM.

[0195] The load characteristics evaluation and the cycle life test were carried out on this test unit battery in the same order as in Example 1. The results of this test are shown in Table 1.

[0196] Example 3

[0197] The composite positive electrode active material and the test unit battery were manufactured in the same manner as in Example 1, except that: the coating amount of Li2O-B2O3 (LBO) relative to NCM (i.e., the content of Li2O-B2O3 (LBO) and acetate relative to the uncoated positive electrode active material particles NCM) was 0.3 mol%, based on 100 mol% of the uncoated positive electrode active material particles NCM. The load characteristics evaluation and the cycle life test were carried out on this test unit battery in the same order as in Example 1. The results of this test are shown in Table 1.

[0198] Example 4

[0199] The composite positive electrode active material and the test unit cell were fabricated in the same manner as in Example 1, except that the coating amount of Li2O-B2O3 (LBO) relative to NCM (i.e., the content of Li2O-B2O3 (LBO) and acetate relative to the uncoated positive electrode active material particles NCM) was 0.4 mol%, based on 100 mol% of the uncoated positive electrode active material particles NCM. The load characteristics evaluation and the cycle life test were performed on the test unit cell in the same order as in Example 1. The results of this test are shown in Table 1.

[0200] Example 5

[0201] The composite positive electrode active material and the test unit cell were fabricated in the same manner as in Example 1, except that the coating amount of Li2O-B2O3 (LBO) relative to NCM (i.e., the content of Li2O-B2O3 (LBO) and acetate relative to the uncoated positive electrode active material particles NCM) was 0.5 mol%, based on 100 mol% of the uncoated positive electrode active material particles NCM. The load characteristics evaluation and the cycle life test were performed on the test unit cell in the same order as in Example 1. The results of this test are shown in Table 1.

[0202] Example 6

[0203] The composite positive electrode active material and the test unit cell were fabricated in the same manner as in Example 1, except that the coating amount of Li2O-B2O3 (LBO) relative to NCM (i.e., the content of Li2O-B2O3 (LBO) and acetate relative to the uncoated positive electrode active material particles NCM) was 0.75 mol%, based on 100 mol% of the uncoated positive electrode active material particles NCM. The load characteristics evaluation and the cycle life test were performed on the test unit cell in the same order as in Example 1. The results of this test are shown in Table 1.

[0204] Example 7

[0205] The composite positive electrode active material and the test unit cell were fabricated in the same manner as in Example 1, except that the coating amount of Li2O-B2O3 (LBO) relative to NCM (i.e., the content of Li2O-B2O3 (LBO) and acetate relative to the uncoated positive electrode active material particles NCM) was 1.0 mol%, based on 100 mol% of the uncoated positive electrode active material particles NCM. The load characteristics evaluation and the cycle life test were performed on the test unit cell in the same order as in Example 1. The results of this test are shown in Table 1.

[0206] Comparative Example 1

[0207] The positive electrode active material and the test unit cell were fabricated in the same manner as in Example 1, except that: when preparing the positive electrode active material in which the surface of NCM was coated with LBO (referred to as the coated positive electrode active material), the heat treatment temperature was changed to 500 °C. The test unit cell was used to evaluate the load characteristics and perform the cycle life test in the same order as in Example 1. The results of this test are shown in Table 1.

[0208] Comparative Example 2

[0209] In Comparative Example 2, the test unit cell was fabricated in the same manner as in Example 1, except that: instead of the positive electrode active material, the positive electrode active material particles (NCM) without any coating treatment were used as they were. The test unit cell was used to evaluate the load characteristics and perform the cycle life test in the same order as in Example 1. The results of this test are shown in Table 1.

[0210] Table 1

[0211] Initial discharge capacity (mAh / g) Rate performance (1C / 0.05C) Cycling performance Example 1 143 22.8％ 65.1％ Example 2 150 55.5％ 63.6％ Example 3 146 47.7％ 83.7％ Example 4 156 53.9％ 83.2％ Example 5 154 54.6％ 85.8％ Example 6 153 52.8％ 84.0％ Example 7 156 51.1％ 83.9％ Comparative Example 1 101 1.4％ 59.2％ Comparative Example 2 122 19.5％ 65.3％

[0212] Example 8

[0213] A coating layer was formed on the surface of the positive electrode active material particles

[0214] Using LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM) particles as the positive electrode active material particles.

[0215] The slurry for coating was prepared in the same manner as in Example 1, except that: the coating amount of Li2O-B2O3 (LBO) relative to NCM (i.e., the total content of Li2O-B2O3 (LBO) and acetate relative to the uncoated positive electrode active material particles NCM) was 0.03 mol%, based on 100 mol% of the uncoated positive electrode active material particles NCM. The solvent was volatilized using an evaporator, and heat treatment was performed at 350 °C for 1 hour in an air atmosphere to obtain a positive electrode active material (composite positive electrode active material) having an LBO coating layer on its surface.

[0216] Preparation of the solid electrolyte

[0217] First, the reagents Li2S, P2S5, and LiCl, which are starting materials for the sulfur-containing electrolyte material, were weighed to obtain the target composition Li6PS5Cl. Subsequently, these reagents were mechanically milled using a planetary ball mill for 20 hours. The mechanical milling treatment was performed at room temperature (25 °C) in an argon atmosphere at a rotation speed of 380 rpm.

[0218] 800 mg of the powder sample of Li6PS5Cl obtained by the mechanical grinding treatment was pressed (pressure: 400 MPa / cm 2 ) to obtain a wafer having a diameter of 13 mm and a thickness of about 0.8 mm. The obtained wafer was covered with gold foil and placed in a carbon crucible to prepare a sample for heat treatment. The obtained sample for heat treatment was vacuum-sealed in a quartz glass tube. Subsequently, the sample for heat treatment was placed in an electric furnace, and the temperature in the electric furnace was raised from room temperature to 550 °C at a heating rate of 1.0 °C / minute. Subsequently, the sample for heat treatment was heat-treated at 550 °C for 6 hours. Subsequently, the sample for heat treatment was cooled to room temperature (25 °C) at a cooling rate of 1.0 °C / minute. The sample collected after the heat treatment was pulverized by an agate mortar. The pulverized sample was subjected to X-ray crystal diffraction, and it was confirmed that the target argyrodite-type crystal was formed.

[0219] Manufacture of All-Solid-State Secondary Battery

[0220] The positive electrode active material coated with LBO, the argyrodite-type solid electrolyte, and carbon nanofibers (CNF) as a conductive material were mixed at a weight ratio of 83:15:3 to prepare a positive electrode layer. As the negative electrode, a metal Li foil (thickness: 30 μm) was used. The positive electrode layer (10 mg), the solid electrolyte (150 mg), and the metal Li foil were sequentially laminated and pressed at a pressure of 3 tons / cm 2 to obtain a test cell battery.

[0221] Using this test cell battery, the load characteristic evaluation and the cycle life test were carried out in the same order as in Example 1. The results of this test are shown in Table 2.

[0222] Example 9

[0223] A composite positive electrode active material and a test cell battery were manufactured in the same manner as in Example 8, except that: the coating amount of Li2O-B2O3 (LBO) relative to NCM (i.e., the total content of Li2O-B2O3 (LBO) and acetate relative to the uncoated positive electrode active material particles NCM) was 0.07 mol%, based on 100 mol% of the uncoated positive electrode active material particles NCM. Using this test cell battery, the load characteristic evaluation and the cycle life test were carried out in the same order as in Example 1. The results of this test are shown in Table 2.

[0224] Example 10

[0225] The composite positive electrode active material and the test unit cell were fabricated in the same manner as in Example 8, except that: the coating amount of Li2O-B2O3 (LBO) relative to NCM (i.e., the total content of Li2O-B2O3 (LBO) and acetate relative to the uncoated positive electrode active material particles NCM) was 0.1 mol%, based on 100 mol% of the uncoated positive electrode active material particles NCM. The load characteristics evaluation and the cycle life test were performed on the test unit cell in the same order as in Example 1. The results of this test are shown in Table 2.

[0226] Example 11

[0227] LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM) particles (the same as those used in Example 8) were used as the positive electrode active material particles. The surface of the NCM particles was coated with a mixed solution of lithium methoxide, zirconium propoxide, and ethanol.

[0228] The mixed solution was adjusted so that the coating amount of Li2O-ZrO2 (LZO) relative to NCM (i.e., the total content of Li2O-ZrO2 (LZO) relative to the uncoated positive electrode active material particles NCM) was 0.25 mol%, based on 100 mol% of the uncoated positive electrode active material particles NCM. The mixed solution was prepared as follows: for 500 g of the positive electrode active material, 9.7 g of lithium methoxide and 6.1 g of zirconium propoxide were added to ethanol so that the composition in the coating layer was finally Li2ZrO3. The mixed solution was sprayed and dried to perform a surface coating treatment on the positive electrode active material. The surface coating treatment was carried out using an electric fluidized bed assembly and coater FD-MP-01E manufactured by Paurek Co., Ltd. The surface coating treatment was carried out under the following conditions to obtain a positive electrode active material with an LZO coating layer: the amount of positive electrode active material particles was 500 g, the air supply temperature was 90 °C, the air supply flow rate was 0.23 m 3 / h, the rotor speed was 400 rpm, the atomizing air flow rate was 50 NL / min, and the spraying rate was about 5 g / min.

[0229] An LBO coating layer is formed on the positive electrode active material having an LZO coating layer. In this case, the slurry for coating is prepared in the same manner as in Example 1, except that: the coating amount of Li2O-B2O3 (LBO) relative to NCM is changed to 0.03 mol%. In the same manner as in Example 1, heat treatment is carried out at 350 °C for 1 hour in an air atmosphere to obtain a positive electrode active material (composite positive electrode active material) having two coating layers, an LZO coating layer and an LBO coating layer. The test unit battery is manufactured in the same manner as in Example 8 using the positive electrode active material in which the surface of the positive electrode active material particles is covered with two coating layers. The load characteristics evaluation and cycle life test of this test unit battery are carried out in the same manner as in Example 1. The results of this test are shown in Table 2.

[0230] Example 12

[0231] Example 12 is carried out in the same manner as in Example 11, and the coating amount of Li2O-B2O3 (LBO) relative to NCM (that is, the content of Li2O-B2O3 (LBO) and acetate relative to the uncoated positive electrode active material particles NCM) is adjusted to 0.25 mol%, based on 100 mol% of the uncoated positive electrode active material particles NCM. The positive electrode active material that has undergone coating is heat-treated at 300 °C. Other procedures are carried out in the same manner as in Example 8 to prepare a composite positive electrode active material and a test unit battery. The load characteristics evaluation and cycle life test are carried out in the same order as in Example 8 using this test unit battery. The results of this test are shown in Table 2.

[0232] Comparative Example 3

[0233] In Comparative Example 3, a test unit battery is manufactured in the same manner as in Example 8, except that: instead of the positive electrode active material, the uncoated positive electrode active material particles (NCM) are used as they are. The load characteristics evaluation and cycle life test are carried out in the same order as in Example 8 using this test unit battery. The results of this test are shown in Table 2.

[0234] Table 2

[0235] Initial discharge capacity (mAh / g) Rate performance (1C / 0.05C) Cycling performance Example 8 222 84.2％ 86.3％ Example 9 221 83.9％ 83.1％ Example 10 228 83.5％ 82.0％ Example 11 218 86.4％ 93.4％ Example 12 216 84.5％ 83.8％ Comparative Example 3 206 73.0％ 76.8％

[0236] Example 13

[0237] To analyze the coating materials containing lithium (Li) and boron (B) in Examples 1-11, the coating materials were synthesized. Lithium acetate and triisopropyl borate were dissolved in a super-dehydrated ethanol solvent heated to 60 °C to have the same composition as in Example 1 to obtain a mixed solution, and the mixed solution was stirred for 3 hours. The stirred mixed solution was heat-treated at 350 °C for 1 hour using an electric furnace to remove the solvent, dried, and then analyzed using Fourier transform infrared absorption spectroscopy. In addition, the sample before heat treatment was analyzed using a thermogravimetric device. The analysis results are shown in Figure 3 and 4 .

[0238] Comparative Example 4

[0239] To analyze the coating materials containing lithium (Li) and boron (B) in Comparative Example 2, the coating materials were synthesized. Lithium acetate and triisopropyl borate were dissolved in a super-dehydrated ethanol solvent heated to 60 °C to have the same composition as in Example 1 to obtain a mixed solution, and the mixed solution was stirred for 3 hours. The stirred mixed solution was heat-treated at 500 °C for 1 hour using an electric furnace to remove the solvent, dried, and then IR analysis was performed using Fourier transform infrared absorption spectroscopy. The results are shown in Figure 3 .

[0240] From Figure 3 the results, in the infrared spectrum of Example 13, peaks belonging to acetate ions as organic substances were observed. More specifically, the C=O stretching vibration peak in the -COO group appeared as a doublet at 1200 cm -1 -1700 cm -1 and the -OH peak appeared at 3000 cm -1 .

[0241] In the infrared spectrum of Comparative Example 4, peaks belonging to carbonate ions as inorganic substances were observed.

[0242] From Figure 3 the results, in the case of Example 13 where the heat treatment temperature was 350 °C, acetate (radical) derived from lithium acetate was detected in the coating layer, but in the case of Comparative Example 4 where the heat treatment temperature was 500 °C, no acetate (radical) was detected. From the results, it was confirmed that the acetate (radical) in the coating layer decomposed at a heat treatment temperature between 350 °C and 500 °C. Taking Figure 4 the results of the thermogravimetric measurement together with Figure 3 the results of the IR analysis, it was predicted that Figure 4 the change in the value between 350 °C and 500 °C in Figure 4In this case, approximately 80% by weight of the coating layer varies between 350 °C and 500 °C, from which the content of acetate (radical) can be calculated.

[0243] The content of acetate (radical) can be changed by the addition amount or addition ratio of starting materials of the coating layer such as lithium acetate and triisopropyl borate. In Example 13, as in other examples, starting materials are added such that the composition of Li2O - B2O3 (LBO) in the coating layer is Li3B 11 O 18 . Therefore, when the composition of Li2O - B2O3 (LBO) in the coating layer is Li3B 11 O 18 , the composition of the LBO is changed by the heat treatment temperature, but the coating layer contains the same amount of acetate (radical) as in Example 13. In addition, as a result of Figure 4 , the content of acetate (radical) in the coating layer is even changed by the heat treatment temperature. For example, the acetate (radical) content is approximately 95 mol% at a heat treatment temperature of 300 °C and approximately 70 mol% at a heat treatment temperature of 400 °C.

[0244] As can be seen from the results of Table 1 and Table 2 above, compared with the characteristics of the all - solid secondary batteries of Comparative Examples 1 - 3, the battery characteristics of the positive electrode active materials using the coating material in Examples 1 - 12 are improved. In the all - solid secondary batteries of Examples 1 - 12, as can be seen from the results of Figure 3 , the presence of acetate (radical) (acetate ion) as an organic substance in the coating layer enables the construction of an all - solid secondary battery having improved battery characteristics compared with the comparative examples in which the coating layer does not contain an organic substance.

[0245] According to an embodiment, the composite positive electrode active material includes a coating layer covering the surface of the positive electrode active material particles and the coating layer includes acetate, which thus greatly improves battery characteristics such as load characteristics and cycle life characteristics of the all - solid secondary battery. In addition, since the coating layer only includes acetate, even when dedicated manufacturing equipment is not used, the composite positive electrode active material and the all - solid secondary battery can be easily manufactured using suitable equipment.

[0246] It should be understood that the embodiments described herein should be considered only in a descriptive sense and not for purposes of limitation. The description of features, aspects, or advantages in each embodiment should be considered applicable to other similar features, aspects, or advantages in other embodiments. Although one or more embodiments have been described with reference to the accompanying drawings, those of ordinary skill in the art will understand that various changes in form and detail can be made therein without departing from the spirit and scope as defined by the appended claims.

Claims

1. A composite cathode active material, comprising: Cathode active material particles; And A coating layer on the surface of the cathode active material particles, wherein the coating layer comprises acetate or acetate salt, Wherein the coating layer comprises a reaction product between lithium acetate and a C9-C20 trialkyl borate.

2. The composite cathode active material according to claim 1, wherein based on the total content of the coating layer, the content of acetate or acetate salt in the coating layer is 70 mol%-95 mol%.

3. The composite cathode active material according to claim 1, wherein the acetate or acetate salt comprises an alkali metal acetate, an alkaline earth metal acetate, a transition metal acetate, or a combination or derivative thereof.

4. The composite cathode active material according to claim 1, wherein the coating layer comprises lithium acetate.

5. The composite cathode active material according to claim 1, wherein The coating layer further comprises at least one of zirconia or boron oxide, and Based on the total content of the coating layer, the total content of at least one of zirconia or boron oxide in the coating layer is 2.5 mol%-25 mol%.

6. The composite cathode active material according to claim 5, wherein the coating layer further comprises lithium oxide.

7. The composite cathode active material according to claim 6, wherein based on the total content of the coating layer, the total content of at least one of zirconia or boron oxide and lithium oxide is 5 mol%-30 mol%.

8. The composite cathode active material according to claim 6, wherein the composite cathode active material comprises: A first coating layer comprising zirconia; and a second coating layer provided on the first coating layer and comprising acetate or acetate salt, boron oxide, and lithium oxide.

9. The composite cathode active material according to claim 6, wherein the composite cathode active material comprises: A first coating layer comprising acetate or acetate salt, lithium oxide, and zirconia; and a second coating layer comprising acetate or acetate salt, lithium oxide, and boron oxide.

10. The composite cathode active material according to claim 1, wherein the cathode active material particles are in the form of secondary particles, and the secondary particles have an average particle diameter of 20 μm or less.

11. The composite cathode active material according to claim 10, wherein the secondary particles have an average secondary particle diameter of 10 μm or less.

12. The composite cathode active material according to claim 1, wherein the coating layer has a thickness of 0.5 nm-500 nm.

13. The composite cathode active material according to claim 1, wherein the cathode active material particles comprise a lithium transition metal oxide having a layered rock salt structure.

14. The composite cathode active material according to claim 1, wherein the cathode active material particles comprise a compound represented by Formula 1: Formula 1 Li a (Ni x Co y Mn z M k )O2 Among them, In Formula 1, M is at least one of the following: boron, magnesium, calcium, strontium, barium, titanium, vanadium, chromium, iron, copper, zirconium, or aluminum, and 0.95 ≤ a ≤ 1.3, 0 < x < 1, 0 < y < 1, 0 ≤ z < 1, 0 ≤ k < 1, and x + y + z + k = 1.

15. The composite cathode active material according to claim 1, wherein the cathode active material particles comprise a lithium transition metal oxide represented by at least one of the following: LiNi x Co y Al z O2 or LiNi x Co y Mn z O2, where x, y, and z are each independently selected and 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1.

16. The composite cathode active material according to claim 1, wherein when measured by thermogravimetric analysis, the thermal weight loss of the composite cathode active material from 300°C to 500°C is 70%-95%.

17. The composite cathode active material according to claim 1, wherein when analyzed by infrared spectroscopy, the composite cathode active material has a C═O stretching vibration peak in the -COO group appearing in a bimodal form at 1200 cm -1 -1700 cm -1 , and an -OH peak at 2800 cm -1 -3550 cm -1 .

18. The composite positive electrode active material according to claim 1, wherein based on 100 mol% of the positive electrode active material particles, the content of the coating layer in the positive electrode active material particles is 0.01 mol% - 2 mol%.

19. A positive electrode layer, comprising: The composite positive electrode active material according to any one of claims 1 - 18.

20. An all - solid secondary battery, comprising: A positive electrode layer including the composite positive electrode active material according to any one of claims 1 - 18; A negative electrode layer; And A solid electrolyte layer between the positive electrode layer and the negative electrode layer.

21. The all - solid secondary battery according to claim 20, wherein The positive electrode layer further comprises a solid electrolyte, and The solid electrolyte contains sulfur.

22. The all - solid secondary battery according to claim 20, wherein The solid electrolyte layer includes a solid electrolyte, and The solid electrolyte includes at least one of the following: Li2S-P2S5; Li2S-P2S5-LiX, where X is a halogen atom; Li2S-P2S5-Li2O; Li2S-P2S5-Li2O-LiI; Li2S-SiS2; Li2S-SiS2-LiI; Li2S-SiS2-LiBr; Li2S-SiS2-LiCl; Li2S-SiS2-B2S3-LiI; Li2S-SiS2-P2S5-LiI; Li2S-B2S3; Li2S-P2S5-Z m S n , where m and n are each independently positive numbers, and Z is at least one of Ge, Zn, or Ga; Li2S-GeS2; Li2S-SiS2-Li3PO4; Li2S-SiS2-Li p MO q , where p and q are each independently positive numbers, and M is at least one of P, Si, Ge, B, Al, Ga, or In; Li 7-x PS 6- x Cl x , where 0 ≤ x ≤ 2; Li 7-x PS 6-x Br x , where 0 ≤ x ≤ 2; or Li 7-x PS 6-x I x , where 0 ≤ x ≤ 2.

23. The all - solid secondary battery according to claim 20, wherein The solid electrolyte layer includes a thio - silver - germanate - type solid electrolyte, and The argyrodite-type solid electrolyte includes at least one of the following: Li 7-x PS 6-x Cl x , where 0 ≤ x ≤ 2; Li 7- x PS 6-x Br x , where 0 ≤ x ≤ 2; or Li 7-x PS 6-x I x , where 0 ≤ x ≤ 2.

24. A method for preparing the composite positive electrode active material according to any one of claims 1 - 18, the method comprising: Providing positive electrode active material particles; Setting lithium acetate and a C9 - C20 trialkyl borate on the surface of the positive electrode active material particles to provide coated positive electrode active material particles; And Heat - treating the coated positive electrode active material particles at a temperature of 200°C - 400°C to prepare the composite positive electrode active material.

25. The method according to claim 24, wherein the C9 - C20 trialkyl borate is at least one of the following: tri - isopropyl borate, tri - propyl borate, tri - butyl borate, tri - pentyl borate, or tri - hexyl borate.

26. The method according to claim 24, wherein the heat - treatment includes heat - treating at a temperature of 300°C - 350°C.

27. The method according to claim 24, wherein the weight ratio of lithium acetate to the C9 - C20 trialkyl borate is 1:5 - 1:

15.

28. The method according to claim 24, wherein the content of lithium acetate and the C9 - C20 trialkyl borate in the coating layer on the positive electrode active material particles is 0.01 mol% - 2 mol%, based on 100 mol% of the positive electrode active material particles.

29. A composite positive electrode active material, comprising: Positive electrode active material particles; And A coating layer on the surface of the positive electrode active material particles, Wherein the coating layer includes a reaction product between lithium acetate and a C9 - C20 trialkyl borate, and Wherein based on 100 mol% of the positive electrode active material particles, the total content of the coating layer is between 0.01 mol% and 2 mol%.

Images